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GIFT OF
MICHAEL REESE

A SYSTEMATIC HANDBOOK

VOLUMETRIC ANALYSIS.

SYSTEMATIC HANDBOOK

VOLUMETRIC ANALYSIS;

OR,

THE QUANTITATIVE ESTIMATION

OF CHEMICAL SUBSTANCES BY MEASURE, APPLIED TO
LIQUIDS, SOLIDS, AND GASES,

ADAPTED TO THE REQUIREMENTS OF PURE CHEMICAL RESEARCH,
PATHOLOGICAL CHEMISTRY, PHARMACY. METALLURGY, MANUFACTURING

CHEMISTRY, PHOTOGRAPHY, ETC., AND FOR THE VALUATION
OF SUBSTANCES USED IN COMMERCE, AGRICULTURE, AND THE ARTS.

FRANCIS SUTTON, F.I.C., F.C.S.,

PUBLIC ANALYST FOR THE COUNTY OF NORFOLK:

LATE ^lEMBER OF OtTUNCIL OF THE SOCIETY OF PUBLIC ANALYSTS ;

LATE MEMBER OF COUNCIL OF THE PHARMACEUTICAL SOCIETY OF GREAT BRITAIN;

CO I! RESPONDING MEMBER OF THE IMPERIAL PHARMACEUTICAL SOC. OF ST. PETERSBURG!! ;

CORRESPONDING MEMBER OF THE AUSTRIAN APOTHEKER VEREIN, VIENNA;

CONSULTING CHEMIST TO THE NORFOLK CHAMBER OF AGRICULTURE;

ETC., ETC.

OF THE

DIVERSITY

SEVENTH EDITION, ENLARGED AND IMPROVED.

LONDON:

J. & A. CHURCHILL, 7 GREAT MARLBOROUGH STREET

(Removed from 11 Neiv Burlington Street),
1896.

[All rights reserrej,']

OWING to the large edition of this work issued at the end of
1890, a rather longer period than usual has occurred
between successive issues. The book, however, has been
out of print for nearly a year owing to pressure of other
matters, and the time required for investigation of new
processes or modifications of old ones.

It will be seen that considerable alterations and additions
have been made in various sections, so as to bring the
work up to date as closely as possible.

The sections thus altered, "<aiict> 'pthers entirely new,
comprise chiefly the articles on Calibration of Instruments,
the Kjeldahl process, Boric Acid, Hydrofluoric Acid and
Fluorides, Arsenic, Chromium, Copper, Cyanogen and
Cyanides, Iron, Lead, Manganese, Mercury, Nickel,
Phosphoric Acid, Sugar, Sulphur and its compounds,

Tannin, Zinc, Oils and Fats, and Urine.

-
As respects the volumetric method as applied to many

organic substances, and the action of modern indicators
in such work, nothing has been attempted, partly because
the results hitherto obtained have not been altogether
satisfactory, but mainly because this subject comes
specially within the scope of my friend A. H. Allen's
well-known work on Organic Analysis, and it cannot in
my opinion be left in better hands.

My thanks are especially due to Mr. W. B. Giles, F.I.C.,
for his original article on the estimation of Hydrofluoric
Acid, and for the benefit of his long practical experience
in the examination of Sulphur Compounds and Phosphoric

Acid.

VI PREFACE.

Mr. J. W. Westmoreland has also rendered great
service in the articles on Copper, Iron, and Manganese.

Dr. James Edmunds has also favoured me with
suggestions on Urinary analysis, which I believe to be of
considerable practical value.

I have availed myself in some instances of the excellent
abstracts of original papers now being published in the
Analyst, which reflect great credit upon the present
management in this department.

My son, W. L. Sutton, A.I.C., has rendered me help in
the general revision of the book and the correction of
proof sheets.

This labour has hitherto been taken, in the five previous
editions, by my friend W. Thorp, B.Sc., who would
willingly have continued his kind services, but the delay
in preparation of the book has necessitated extra rapidity
in printing and revision.

The nomenclature of chemical substances is mainly the
same as in previous editions, and inasmuch as the book is
largely used by many persons who are practical workers, and
not advanced theoretical chemists, I have continued the
use of such terms as sodic bicarbonate in place of sodium
hydrogen carbonate, and similar modern terms.

The aim throughout the whole series of editions has
been to make the book a guide to practical workers, and to
condense the descriptions of processes as much as is
possible, without the sacrifice of accuracy or clearness.
Notwithstanding, the present edition will be enlarged by
more than thirty pages.

FEANCIS SUTTON.

NORWICH,
August, 1896.

CONTENTS

PART I.

Sect. Page

1. GENERAL PRINCIPLES . . . . .1

2. The Balance ..... 5

3. Volumetric Analysis without "Weights . . .5

4. Volumetric Analysis without Burettes ... 6

5. The Burette . . . . . .7

6. The Pipette ... 15

7. The Measuring Flasks . . . . .15

8. The Correct Reading of Graduated Instruments . . 17

9. Calibration of Graduated Apparatus . . .19

10. The Weights and Measures to be adopted in Volumetric Analysis 23

11. Preparation of Normal Solutions in General . . 27

12. Direct and Indirect Processes of Analysis . . .31

PAET II.

13. ALKALIMETRY ..... 33

14. Indicators used in Saturation Analyses . . .33

15. Normal Alkaline and Acid Solutions ... 44

16. Correction of Abnormal Solutions . . . .51
Table for the Systematic Analysis of Acids, Alkalies, and Alkaline

Earths ..... 54

17. Titration of Alkaline Salts . . . .55

18. Titration of Alkaline Earths .... 69

19. Ammonia . . . . . .72

20. ACIDIMETEY ..... 88

21. Acetic Acid . . . . . .89

22. Boric Acid and Borates .... 92

23. Carbonic Acid . . . . . .93

24. Citric Acid ..... 103

25. Formic Acid ...... 104

26. Hydrofluoric Acid ..... 105

27. Oxalic Acid . . . . . .109

28. Phosphoric Acid . . . . .109

29. Sulphuric Anhydride ..... Ill

30. Tartaric Acid . . . . .112

31. Estimation of Combined Acids in Neutral Salts . .114

32. Extension of Alkalimetric Methods 117

Vlll CONTENTS.

PART III.

Sect. Page

33. ANALYSIS BY OXIDATION OR REDUCTION . . . 120

34. Permanganic Acid and Ferrous Oxide . . . 121

35. Titration of Ferric Salts by Permanganate . vC . 124

36. Calculation of Permanganate Analyses . . . 125

37. Chromic Acid and Ferrous Oxide . . ... . 126

38. Iodine and Thiosulphate . . . .128

39. Analysis of Substances by Distillation with Hydrochloric Acid . 132

40. Arsenious Acid and Iodine - . 136

PART IV.

41. ANALYSIS BY PRECIPITATION . . , . 138

42. Indirect Analyses by Silver and Potassic Chromate . . 140

43. Silver and Thiocyanic Acid .... ... 142

44. Precision in Colour Reactions 143

PART V.

45. Alumina ...... 145

46. Antimony . . . . . 147

47. Arsenic . . . . . . 149

48. Barium . . . . . .154

49. Bismuth ...... 154

50. Bromine . . . . . .156

51. Cadmium ...... 159

52. Calcium . . . . . .160

53. Cerium ...... 162

54. Chlorine . . . . . .162

55. Chlorine Gas and Bleach .... 164
Chlorates, lodates, and Bromates .... 166

56. Chromium ...... 167

57. Cobalt . . . . . .173

58. Copper . ... 175

59. Cyanogen . . . . . . 189

60. Ferro- and Ferri-C3ranides .... 195
Thiocyanates or Sulphocyanides .... 197

61. Gold . 198

62. Iodine ...... 199

63. Ferrous Iron ..... 206

64. Ferric Iron ...... 210

65. Iron Ores . . , . . .214

66. Lead ..... . . 222

67. Manganese. ..... 226

68. Mercury . . . . . .238

69. Nickel 243

CONTENTS. IX

Sect.

70. Nitrogen as Nitrates and Nitrites. . . . 245

71. Oxygen and Hydrogen Peroxide . 269

72. Phosphoric Acid and Phosphates . . . 284

73. Silver ..... 297

74. Sugar .... -305

75. Sulphur, Sulphides, and Sulphites

76. Sulphuric Acids and Sulphates . . • 325

77. Sulphuretted Hydrogen .... 329

78. Tannic Acid . . . . . - 331

79. Tin . . . 339

80. Uranium

81. Vanadium .... 341

82. Zinc . ... 342

83. Oils and Pats

84. Glycerin . -363

85. Phenol (Carbolic Acid) . . 366

86. Carbon Bisulphide . • 367

APPENDIX TO PART V.

Arsenic and Arsenic Acid

Boric Acid in Milk

Mixtures of Chlorides, Hypochlorites, and Chlorates 372

Chloric and Nitric Acids . . • 373

PART VI.

87. Analysis of Urine ..... 377

88. Analysis of Potable Waters and Sewage . . . 398

89. Analytical Processes for Water . . 405

90. Interpretation of Results of Water Analysis . . 444

91. Water Analysis without Gas Apparatus . . 455

92. Reagents and Processes employed .... 463

93. Oxygen Dissolved in Water .... 474
Table for Calculations and Logarithms . . . 476

PART VII.

94. Volumetric Analysis of Gases and Construction of Apparatus 480

95. Gases Estimated Directly and Indirectly . . . 494

96. H}rdrochloric, Hydrobromic, and Hydriodic Acids . 494

97. Analysis of Air, Carbonic Anhydride, SH2, and SO2 . . 496

98. Indirect Determinations .... 502

99. Improvements in Gas Apparatus .... 517

100. Simpler Methods of Gas Analysis . . .. 547

101. The Nitrometer, Gasvolumeter, and Gravivolumeter . 557—568

Names of Elementary Substances occurring- in Volumetric
Methods, with their Symbols and Atomic Weights.

Name.

Symbol.

Exact Atomic
Weight
as found by
the latest
researches.

Atomic Weight
adopted in
this Edition.

Aluminium

27-3

Antimony
Arsenic

119-6
74-9

120-0
75-0

Barium

136-8

Bismuth .

208-0

Bromine

79-75

80-0

Cadmium .

111-6

Calcium

39-9

40-0

Carbon

11-97

12-0

Cerium

141-2

141'2

Chlorine .

35-37

Chromium

52-4

Cobalt

58-6

59-0

Copper
Gold

Cu
Au

63-18
196-2

63-0
196-5

Hydrogen
Iodine

1-0
126-86

1-0
127-0

Iron .

55-88

56-0

Lead

206-4

Magnesium
Manganese
Mercury
Molybdenum
Nickel

Mg
Mn
Hg
Mo

23-94
55-0
199-8
95-8
58-6

24-0
55-0
200-0
95-8
59-0

Nitrogen .
Oxygen
Phosphorus
Platinum

N
0
P
Pt

14-01
15-96
30-96
194-3

14-0
16-0
31-0
194-3

Potassium

39-04

39-0

Silver .
Sodium

107-66
22-99

107-66
23-0

Strontium

87-2

Sulphur .
Tin .

S
Sn

31-98
117-8

32-0
118-0

Tungsten .
Uranium

184-0
239-8

184-0
240-0

Vanadium

51-2

Zinc .

64-9

65-0

[XI]

Abbreviations and Explanations.

The formulae are constructed on the basis H=l. 0 = 16
H20 = 18.

The normal temperature for the preparation and use of standard
solutions is 16° C., or about 60° Fahr.

c.c. denotes cubic centimeter.

gm. „ gram = 15-43235 grains English.

grn. „ grain.

dm. „ decem= 10 fluid grains at 16° C.

1 liter=1000 c.c. at 16° C.

1 c.c. = 1 gm. distilled water at 16° C.

1 dm. = 10 grn. „ „

Distilled water is to be used in all the processes, unless other-
wise expressed.

Normal Solutions are those which contain one gram atom of
reagent (taken as monobasic), or an equivalent in some active
constituent (e.r/. oxygen) in the liter (see page 28).

Decinormal Solutions are one-tenth of that strength = T^-.
Centinormal, one hundredth = —-$.

Empirical Standard Solutions are those which contain no
exact atomic proportion of reagent, but are constructed generally so
that 1 c.c. = 0'01 gm. (one centigram) of the substance sought.

A Titrated Solution (from the French word titre, title or
power) denotes a solution whose strength or chemical power has
been accurately found by experiment.

When a chemical substance or solution is directed to be titrated,
the meaning is, that it is to be quantitatively tested for the amount
of pure substance it contains by the help of standard or titrated
solutions. The term is used in preference to tested or analyzed,
because these expressions may relate equally to qualitative and
quantitative examinations, whereas titrations can only apply to
quantitative examination.

J. C. S. denotes Journal of the Chemical Society (Transactions
only).

/. S. C. I. „ Journal of the Society of Chemical Industry.
Z. a. (7. „ Zeitschrift fiir Analytische Chemie.
C. N. „ Chemical News.

Other book-references are given in full.

EREATA AND ADDENDA.

Page 25. Line 15 from top, read 760 in.m. in place of 0'76 m.m.

Page 139. Line 3 from bottom, read " nitrates " in place of " hydrates."

Page 149. Line 3 from bottom, omit the words " arsenic obtained as
sulphide/' and substitute " arsenical material."

OF THE ,

P"KIVERSITY

VOLUMETRIC ANALYSIS

LIQUIDS AND SOLIDS,

PART I.

GENERAL PRINCIPLES.

§ 1. QUANTITATIVE analysis by weight, or gravimetric analysis,
consists in separating out the constituents of any compound, either
in a pure state or in the form of some new substance of known
composition, and accurately weighing the products. Such opera-
tions are frequently very complicated, and occupy a long time,
besides requiring in many cases elaborate apparatus, and the exercise
of much care and experimental knowledge. Volumetric processes
on the other hand, are, as a rule, quickly performed ; in most cases
are susceptible of extreme accuracy, and need much simpler
apparatus. The leading principle of the method consists in sub-
mitting the substance to be estimated to certain characteristic
reactions, employing for such reactions solutions of known
strength, and from the volume of solution necessary for the pro-
duction of such reaction, determining the weight of the substance
to be estimated by aid of the known laws of chemical equivalence.

Volumetric analysis, or quantitative chemical analysis by measure,
in the case of liquids and solids, consequently depends upon the
following conditions for its successful practice : —

1. A solution of the reagent or test, the chemical power of
which is accurately known, called the " standard solution."

2. A graduated vessel from which portions of it may be
accurately delivered, called the " burette."

3. The decomposition produced by the test solution with any
given substance must either in itself or by an indicator be such,
that its termination is unmistakable to the eye, and thereby the
quantity of the substance with which it has combined accurately
calculated.

VOLUMETRIC ANALYSIS. § 1.

Suppose, for instance, that it is desirable to know the quantity of
pure silver contained in a shilling. The coin is first dissolved in
nitric acid, by which means a bluish solution, containing silver,
copper, and probably other metals, is obtained. It is a known fact
that chlorine combines with silver in the presence of other metals
to form silver chloride, which is insoluble in nitric acid. The pro-
portions in which the combination takes place are 35*37 of chlorine
to every 107*66 of silver; consequently, if a standard solution of
pure sodic chloride is prepared by dissolving in water such a weight
of the salt as will be equivalent to 35*37 grains of chlorine ( = 58 -37
grains XaCl) and diluting to the measure of 1000 grains; every
single grain measure of this solution will combine with 0*10766 grain
of pure silver to form silver chloride, which is precipitated to the
bottom of the vessel in which the mixture is made. In the process
of adding the salt solution to the silver, drop by drop, a point is at
last reached when the precipitate ceases to form. Here the process
must stop. On looking carefully at the graduated vessel from
which the standard solution has been used, the operator sees at
once the number of grain measures which has been necessary to
produce the complete decomposition. For example, suppose the
quantity used was 520 grain measures ; all that is necessary to be
done is to multiply 520 by the coefficient for each grain measure,
viz. 0*10766, which shows the amount of pure silver present to be
55*98 grains.

This method of determining the quantity of silver in any given
solution occupies scarcely a quarter of an hour, whereas the estimation
by weighing could not be done in half a day, and even then not so
accurately as by the volumetric method. It must be understood
that there are certain necessary precautions in conducting the above
process which have not been described; those will be found in their
proper place; but from this example it will at once be seen that the
saving of time and trouble, as compared with the older methods of
analysis, is immense ; besides which, in the majority of instances
in which it can be applied, it is equally accurate, and in many cases
much more so.

The only conditions on which the volumetric system of analysis
are to be carried on successfully are, that great care is taken with
respect to the graduation of the measuring instruments, and their
agreement with each other, the strength and purity of the standard
solutions, and the absence of other matters which would interfere
with the accurate estimation of the particular substance sought.

The fundamental distinction between gravimetric and volumetric
analysis is, that in the former method, the substance to be
estimated must be completely isolated in the purest possible state
or combination, necessitating in many instances very patient and
discriminating labour ; whereas, in volumetric processes, such com-
plete separation is very seldom required, the processes being so
contrived as to admit of the presence of half a dozen or more

$ 1. GENERAL PRINCIPLES. 3

other substances which have no effect upon the particular chemical
reaction required.

The process just described for instance, the estimation of silver
in coin, is a case in point. The alloy consists of silver and copper,
with small proportions of lead, antimony-, tin, gold, etc. None of
these things affect the amount of salt solution which is chemically
required to precipitate the silver, whereas, if the metal had to be
•determined by weight it would be necessary to first filter the nitric
acid solution to free it from insoluble tin, gold, etc. ; then
precipitate with a slight excess of sodic chloride; then to bring the
precipitate upon a filter, and wash repeatedly with pure water until
•every trace of copper, sodic chloride, etc., is removed. The pure
silver chloride is then carefully dried, ignited separately from the
filter, and weighed ; the filter burnt, residue as reduced metallic
silver and filter ash allowed for, and thus finally the amount of
silver is found by the balance with ordinary weights.

On the other hand the volumetric process has been purely
chemical, the burette or measuring instrument has taken the place
of the balance, and theoretical or atomic weights have supplanted
ordinary weights.

The end of the operation in this method of analysis is in all
•cases made apparent to the eye. In alkalimetry it is the change
of colour produced in litmus, turmeric, or other sensitive colouring
matter. The formation of a permanent precipitate, as in the
•estimation of cyanogen. A precipitate ceasing to form, as in
•chlorine and silver determination. The appearance of a distinct
colour, as in iron analysis by permanganate solution, and so on.

I have adopted the classification of methods used by Mohr and
others, namely :

1. Where the determination of the substance is effected by
saturation with another substance of opposite properties — generally,
understood to include acids and alkalies, or alkaline earths.

2. Where the determination of a substance is effected by a
reducing or oxidizing agent of known power, including most
metals, with their oxides and salts ; the principal oxidizing agents
being potassic permanganate, potassic bichromate, and iodine; and
the corresponding reducing agents, ferrous and stannous compounds,
:and sodic thiosulphate.

3. Where the determination of a substance is effected by
precipitating it in some insoluble and definite combination, an
•example of which occurs in the estimation of silver described
above.

This classification does not rigidly include all the volumetric
processes that may be used, but it divides them into convenient
sections for describing the peculiarity of the reagents used, and
their preparation. If strictly followed out, it would in some cases
necessitate the registration of the body to be estimated under two
or three heads. Copper, for instance, can be determined residually

B 2

4 VOLUMETRIC ANALYSIS. § 1.

by potassic permanganate ; it can also be determined by precipitation
with sodic sulphide. The estimation of the same metal by potassic
cyanide, on the other hand, would not come under any of the
heads. •

It will be found, therefore, that liberties have been taken with
the arrangement ; and for convenient reference all analytical pro-
cesses applicable to a given body are included under its name.

It may be a matter of surprise to some that several distinct
volumetric methods for one and the same substance are given;
but a little consideration will show that in many instances greater
convenience, and also accuracy, may be gained in this way. The
operator may not have one particular reagent at command, or he
may have to deal with such a mixture of substance as to preclude
the use of some one method; whereas another may be quite
free from such objection. The choice in such cases of course
requires judgment, and it is of the greatest importance that the
operator shall be acquainted with the qualitative composition of the
matters with which he is dealing, and that he should ask himself
at every step why such and such a thing is done.

It will be apparent from the foregoing description of the
volumetric system, that it may be successfully used in many
instances by those who have never been thoroughly trained as
analytical chemists ; but we can never look for the scientific
development of the system in such hands as these.

In the preparation of this work an endeavour has been made to
describe all the operations and chemical reactions as simply as
possible, purposely avoiding abstruse mathematical expressions,,
which, though they may be more consonant with the modern study
of chemical science, are hardly adapted to the technical operator.

NIVERSIT

§ 2. INSTRUMENTS.

THE IKSTBUMENTS AND APPAKATUS.

THE BALANCE.

§ 2. STRICTLY speaking, it is necessary to have two balances in
order to carry out the volumetric system completely ; one to carry
•about a kilogram in each pan, and turn when loaded with
about five milligrams. This instrument is used for graduating
flasks, or for testing them, and for weighing large amounts of pure
reagents for standard solutions. The second balance should be
light and delicate, and to carry about fifty grams, and turn easily
and quickly when loaded with one or two-tenths of a milligram.
This instrument serves for weighing small quantities of substances
to be tested, many of which are hygroscopic, and need to be
weighed quickly and with great accuracy ; it also serves for testing
the accuracy of pipettes and burettes.

For all technical purposes, however, a moderate-sized balance
of medium delicacy is quite sufficient, especially if rather large
quantities of substances are weighed and brought into solution-
then further subdivided by means of measuring flasks and pipettes.

The operator also requires, besides the balance and the graduated
instruments a few beakers, porcelain basins, flasks, funnels, stirring
rods, etc., as in gravimetric analysis ; above all he must be
practically familiar with proper methods of filtration, washing of
precipitates, and the application of heat.

VOLUMETRIC ANALYSIS WITHOUT WEIGHTS.

§ 3. THIS is more a matter of curiosity than of value; but,
nevertheless, one can imagine circumstances in which it might be
useful. In carrying it out, it is necessary only to have (1) a
correct balance, (2) a pure specimen of substance to use as a weight,
(3) an accurate burette filled with the appropriate solution. It is
not necessary that the strength of this should be known ; but the
state of concentration should be such as to permit the necessary
reaction to occur under the most favourable circumstances.

If a perfectly pure specimen of substance, say calcic carbonate,
be put into one scale of the balance, and be counterpoised with an
impure specimen of the same substance, and both titrated with the
same, acid, and the number of c.c. used for the pure substance be
called 100, the number of c.c. used for the impure substance wrill
correspond to the percentage of pure calcic carbonate in the specimen
examined.

The application of the process is, of course, limited to the use of
such substances as are to be had pure, and whose weight is not
variable by exposure; but where even a pure substance of one kind
cannot be had as a weight, one of another kind may be used as a
substitute, and the required result obtained by calculation. For

6 VOLUMETRIC ANALYSIS. § 4.

instance, it is required to ascertain the purity of a specimen of sodic
carbonate, and only pure calcic carbonate is at hand to use as a
weight; equal weights of the two are taken, and the impure
specimen titrated with acid. To arrive at the required answer, it
is necessary to find a coefficient or factor by which to convert the
number of c.c. required by the sodic carbonate, weighed on the
calcic, into that which should be required if weighed on the sodic,
basis. A consideration of the relative molecular weights of the
two bodies will give the factor thus —

Calcic carbonate 100

=— TTf ; , .w. =

bodic carbonate lOb

If, therefore, the c.c. used are multiplied by this number, the
percentage of pure sodic carbonate will be obtained. The method
may be extended to a number of substances, 011 this principle, with
the exercise of a little ingenuity.

L. de Koningh has communicated to me a similar method
devised by himself and Peacock, in which the same end is
attained without the aid of a pure substance as standard, thus :
Say a specimen of impure common salt is to be examined, a
moderate portion is put on the balance and counterpoised with
silver nitrate; the latter is then dissolved up to 100 c.c. and placed
in a burette. The salt is dissolved in water, a few drops of
chromate added and titrated with the silver solution, of which
10 c.c. is required; the salt is therefore equal to 10 per cent,
of its weight of silver nitrate, then —

16-96 : 58-37 : : 10 = 344 % XaCl

Or, in the case of an impure soda ash, an equal weight of oxalic-
acid is taken and made up to 100 c.c. ; the soda requires, say,
50 c.c. for saturation, or 50 per cent., then —

126 : 106 : : 50 = 42 % Na2CO:{

It may happen that, in some cases, more than one portion of the
reagent is required to decompose the substance tested, and to
provide against this two or more lots should be weighed in the
first instance.

VOLUMETRIC ANALYSIS WITHOUT BURETTES OR
OTHER GRADUATED INSTRUMENTS.

§ 4. THIS operation consists in weighing the standard solutions
on the balance instead of measuring them. The influence of
variation in temperature is, of course, here of no consequence. The
chief requisite is a delicate flask, fitted with a tube and blowing-
ball, as in the burette fig. 7, or an instrument known as
Schuster's alkalimeter may be used. A special burette has been
devised for this purpose by Casamajor (C. N. xxxv. 98). The

§ 5.

INSTRUMENTS.

method is capable of very accurate results, if care be taken in
preparing the standard solutions and avoiding any loss in pouring
the liquid from the vessel in which it is weighed. It occupies
much more time than the usual processes of volumetric analysis,
but at great extremes of temperature it is far more accurate.

THE BURETTE.

§ 5. THIS instrument is used for the delivery of an accurately
measured quantity of any particular standard solution. It invari-
ably consists of a long glass tube of even bore, throughout the

Fig. l. Pig. 2.

length of which are engraved, by means of hydrofluoric acid,
certain divisions corresponding to a known volume of fluid.

VOLUMETRIC ANALYSIS.

It may be obtained in a great many forms, under the names of their
respective inventors, such as Mohr, Gay Lussac, Links, etc.,
but as some of these possess a decided superiority over others, it is
not quite a matter of indifference which is used, and therefore a
slight description of them may not be out of place here. The
burette, with india-rubber tube and clip, contrived by Mohr, is
shown in figs. 1 and 2, and with stop-cock in fig. 3. "This latter
form of instrument is now made and sold at such a moderate price
that it has largely displaced the original.

Fig. 3.

Fig. 4.

The advantages possessed by Mohr's burette are, that its fixed
upright position enables the operator at once to read off the volume
of solution used for any analysis. The quantity of fluid to be
delivered can be regulated to the greatest nicety ; and the instru-
ment not being held in the hand, there is no chance of increasing
the bulk of the fluid by the heat of the body, and thus leading to
incorrect measurement, as is the case with Bin ks' or Gay Lussac's

§ 5.

INSTRUMENTS.

burette.. The principal disadvantage, however, of these two latter
forms is, that a correct reading can only be obtained by placing
them in an upright position, and allowing the fluid to find its perfect
level. The preference should, therefore, unhesitatingly be given
to Mohr's burette. The tap burette may be used not only for
solutions affected by the rubber tube, but for all other solutions,
and may also be arranged so as to deliver the liquid in drops,
leaving both the hands of the operator disengaged. A new

Pig. 5.

arrangement is shown in fig. 4, the tap being placed obliquely
through the spit, so as to avoid its dropping out of place ; the
floats shown are very small thermometers. Owing to the action of
caustic alkalies upon glass, tap burettes do not answer well for
strong solutions of potash or soda, unless emptied and washed
immediately after use. Two convenient forms of stand for Mohr's
burettes are shown in figs. 5 and 6 ; in the latter, the arms carrying

VOLUMETRIC ANALYSIS.

the burettes revolve. A very good modification of this burette, as
usually made, is to have the top funnel-shaped, which not only
admits of easier filling, but the burette may be slung in a stand by
the funnel without other support, so as to be tilted from the
vertical when titrating hot solutions. When not in use the dust
may be kept out by a greased glass plate.

Special care should always be taken with Molir's form of
burette to fill the delivery point of the instrument and the
intervening rubber tube with the liquid, before commencing a
titration. This is easily done by filling the burette well above the
0 mark, then rapidly opening the clip wide to expel the air
bubbles — when this is done the excess of liquid may be quietly
run out to the mark. In the tap burette the air space is smaller
than with the rubber tube, but the same method should be
invariably adopted.

We are indebted to Mohr for another form of instrument to
avoid the contact of permanganate and india-rubber, viz., the foot
burette, with elastic ball, shown in fig. 7.

The flow of liquid from the
exit tube ca^n be regulated to
a great nicety by pressure
upon the ball, which should
be large, and have two open-
ings,— one cemented to the
tube with marine glue, and
the other at the side, over
which the thumb is placed
when pressed, and on the
removal of which it refills
itself with air.

G a v L u s s a c ' s burette ,
supported in a wooden foot,
may be used instead of the
above form, by inserting a
good fitting cork into the
open end, through which a
small tube bent at right
angles is passed. If the
burette is held in the right
hand, slightly inclined to-
wards the beaker or flask
into which the fluid is to be
measured, and the mouth
applied to the tube, any
portion of the solution may
be emptied out by the pressure
of the breath, and the disadvantage of holding the instrument in
a horizontal position, to the great danger of spilling the contents,

INSTRUMENTS.

is avoided ; at the same time the beaker or flask can be held
in the left hand and shaken so as to mix the fluids, and by
this means the end of the operation be more accurately determined
(see fig. 8).

There is an arrangement of Mohr's burette which is extremely
serviceable, when a series of titrations of the same character have
to be made, such as in alkali works, assay offices, etc. It consists
in having a ~J~ piece of glass tube inserted between the lower
end of the burette and the spring clip, communicating with

Fi-. 9. Pig. 10.

a reservoir of the standard solution, placed above so that the
burette may be filled by a syphon, as often as emptied, and in so
gradual a manner that no air bubbles occur, as in the case of filling
it with a funnel, or pouring in liquid from a bottle ; beside which,
this plan prevents evaporation or dust in the standard solution
either in the burette or reservoir.

Figs. 9 and 11 show this arrangement in detail. Connections

VOLUMETRIC ANALYSIS.

§ 5.

of this kind may now be had with glass stop-cocks, either of the
simple form or the patent two-way cock, made by Greiner and
Fried richs, and supplied by most apparatus dealers (fig. 10).

It sometimes happens that a solution requires titration at a hot or
even boiling temperature, such as the estimation of sugar by copper

-Fig. 11.

rig. 12.

solution: here the ordinary arrangement of Mohr's burette will
not be available, since the steam rising from the liquid heats the
burette and alters the volume of fluid. This may be avoided either
by using a special burette, in which the lower end is extended at a
right angle with a stop-cock, or by attaching to an ordinary burette

§ 5. INSTRUMENTS. 13

a much longer piece of india-rubber tube, so that the burette
stands at the side of the capsule or beaker being heated, and the
elastic tube is brought over its edge ; the pinch-cock is fixed
midway ; no heat can then reach the body of fluid in the burette,,
since there can be no conduction past the pinch-cock, or a burette-
with funnel neck described on p. 10 may be used.

Gay Lussac's burette is shown in figs. 8 and 12. By using it
in the following manner, its natural disadvantages may be overcome
to a great extent. Having fixed the burette into the foot securely,,
and filled it, take it up by the foot, and resting the uppeu end upon
the edge of the beaker containing the solution to be titrated, drop
the test fluid from the burette, meanwhile stirring the contents,
of the beaker with a glass rod ; by a slight elevation or depression,
the flow of test liquid is regulated until the end of the operation is
secured, thus avoiding the annoyances which arise from alternately
placing the instrument in an upright and horizontal position.

Pig. 13.

B inks' burette is well known, and need not be described; it
is the least recommendable of all forms, except for very rough
estimations.

It is convenient to have burettes graduated to contain from
30 to 50 c.c. in y1^ c.c., and 100 or 110 c.c. in 4 or -J c.c.

The pinch-cock generally used in Mohr's burette is shown in
fig. 1. These are made of brass and are now generally nickel-plated
to prevent corrosion ; another form is made of one piece of steel
wire, as devised by Hart; the wire is softened by heating and
coiled round, as shown in fig. 13. When the proper shape has
been attained, the clip is hardened and tempered so as to convert it.
into a spring. .

VOLUMETRIC ANALYSIS.

Another pinch-cock is shown in fig. 13. It may be made of
hard wood, horn, or preferably, of flat glass rod. The levers
should be long. A small piece of cork, of the same thickness
as the elastic tube of the burette when pressed close, should be
fastened at the angles of the levers as shown in the engraving.

50 CC

10CC

Pig. 14.

Pig. 15.

The use of any kind of pinch-cock may be avoided, and a very
ilelicate action obtained, by simply inserting a not too tightly fitting
piece of solid glass rod into the elastic tube^ between the end of the
burette and the spit ; a firm squeeze being given by the finger and
thumb to the elastic tube surrounding the rod, a small canal is
opened, and thus the liquid escapes, and of course can be controlled
by the operator at will (see fig. 14).

§ 6. INSTRUMENTS.

THE PIPETTE.

§ 6. THE pipettes used in volumetric work are of two kinds,
viz., those which deliver one certain quantity only, and those which
are graduated on the stem, so as to deliver various quantities at the
discretion of the analyst. In the former kind, or whole pipette,
the graduation should be that in which the fluid runs out by its
own weight, but the last few drops empty themselves slowly ;
if, however, the lower end of the pipette be touched against the
moistened edge of the beaker or the surface of the fluid into
which it is emptied, the flow is hastened considerably, and in
graduating the pipette, it is preferable to adopt this plan.

In both the whole and graduated pipettes, the upper end is
narrowed to about -J inch, so that the pressure of the finger is
sufficient to arrest the flow at any point.

Pipettes are invariably filled by sucking the upper end with the
mouth, unless the liquid is volatile or highly poisonous, in which
case it is best to use some other kind of measurement. Beginners
invariably find a difficulty in quickly filling the pipette
above the mark, and stopping the fluid at the exact
point. Practice with pure water is the only method of
overcoming this.

Fig. 15 shows two whole pipettes, one of small and the
other of large capacity, and also a graduated pipette of
medium size. It must be borne in mind that the pipette
graduated throughout the stem is not a reliable in-
strument for accurate titration, owing to the difficulty of
stopping the flow of liquid at any given point, and
reading off the exact measurement. Its chief use is in
the approximate estimation of the strength of any
standard solution in the course of preparation.

Fig. 16 shows a very useful form of pipette for
measuring strong acids or alkalies, etc., the bulb prevent-
ing the entrance of any liquid into the mouth. Pig. 16.

THE MEASURING- FLASKS.

§ 7. THESE indispensable instruments are made of various
capacities ; they serve to mix up standard solutions to a given
volume, and also for the subdivision of the substance to be
tested by means of the pipettes. They should be as narrow
in the neck as is compatible with pouring in and out, and the
graduation line should fall just below the middle of the neck,
so to allow room for shaking up the fluid. Convenient sizes
are 100, 200, 250, 300, 500, and 1000 c.c., all graduated to
contain the respective quantities. If required to deliver these
volumes they must have a second higher mark in the neck,
obtained by weighing into the wetted and drained flasks the

VOLUMETRIC ANALYSIS.

respective number of grams of distilled water at 16° C.
flask is shown in fig;. 17.

A liter

Pig. 17.

Fisr. 18.

W. B. Giles lias described a modified flask (C. N. Ixix. 99)
shown in fig. 18. It is handy in making up standard solutions
where the reagent cannot be weighed in an absolutely pure state,
for instance, sulphuric acid, ammonic thiocyanate, or uranic salts.
Such a quantity, hoAvever, is taken as will give a solution about
a ninth or tenth too strong, and the measure is made up to 1100 c.c.
The real strength is then taken by two titrations on 25 or 30 c.c.
with a known standard, so that its exact working strength is
known ; the remainder of the 100 c.c. is then removed down to the
1000 c.c. mark, and a slight calculation will show how much water
has to be added to the 1000 c.c. to make a correct solution. If
only a liter is made up, an unknown volume is left in the flask,
and it must be transferred to a measuring cylinder, where, owing
to the large diameter of the vessel, the graduation can never be so
accurate as in the narrow neck of . the flask. Should the solution
prove to be only about a tenth too strong, the necessary dilution
may be made in the flask itself; but if stronger than this, the
flask must be emptied into the store bottle and rinsed out with the
measured quantity of water required, which is then drained into
the store bottle, and the whole carefully mixed.

INSTRUMENTS.

Besides the measuring flasks
it is necessary to have graduated
vessels of cylindrical form,
for the purpose of preparing
standard solutions, etc.

Fig. 19 shows a stoppered
cylinder for this purpose,
generally called a test mixer.
Wide-mouthed open cylinders,
with spouts, are also used of
various sizes and graduated
like fig. 19.

ON THE CORRECT

READING- OF GRADUATED

INSTRUMENTS.

§ 8. THE surface of liquids
contained in narrow tubes is
always curved, in consequence
of the capillary attraction
exerted by the sides of the
tube, and consequently there
is a difficulty in obtaining a
distinct level in the fluid to
be measured. If, however,
the lowest point of the curve
is made to coincide with the
graduation mark, a correct
proportional reading is always
obtained, hence this method of
reading is the most satisfac-
tory (see fig. 20).

The eye may be assisted
materially in reading the
divisions on a graduated
tube by using a piece of
white paper or opal glass
held at an angle of 30 or
40° from the burette and
near the surface of the
liquid, or a small card, the
lower half of which is
blackened, the upper re-
maining white. If the line
of division between the
black and white be held
about an eighth of an inch below the surface of the liquid,

Fig. 20.

VOLUMETRIC ANALYSIS.

and the eye brought on a level with it, the meniscus then can be
seen by transmitted light, bounded below by a sharply defined
black line. A card of this kind, sliding up and down a support,,
is of great use in verifying the graduation of the burettes or
pipettes with a cathetometer. Another good method
is to use a piece of mirror, upon which are gummed
two strips of black paper, half an inch apart ; apply it
in contact with the burette so that the eye can be
reflected in the open space. The operator may consult
with advantage the directions for calibration on the
opposite page, and details of graduating and verifying*
measuring instruments for the analysis of gases as-
described in Part 7. In taking the readings of
burettes, pipettes, and flasks, the graduation mark
should coincide as nearly as possible with the level of
the operator's eye.

Pig. 21.

Erdmann's Float. — This useful little instrument
to accompany Mohr's burette, gives the most accurate
reading that can be obtained j one of its forms is
shown in fig. 21, another, containing a thermometer,
is shown in fig. 4. The latest form is shown in fig. 22,
where the ring-mark is made within the bulb, as indeed
it is best to be in all -cases. A special form for use with
dark-coloured solutions like iodine, permanganate, &c., is
to have two bulbs with the ring-mark in the upper bulb,
and the instrument is so weighted that the upper bulb
stands out of the liquid, and of course may then be read
off as easily as if the liquid were transparent. The
instrument consists essentially of an elongated glass tube,
K rather smaller in diameter than the burette itself, and
Pio- 22 weighted at the lower end with a globule of mercury.
The actual height of the liquid in the burette is not-
regarded, because if the operator begins with the line on
the float, opposite the 0 graduation mark on the burette,
the same proportional division is always maintained.

It is essential that the float should move up and down
in the burette without wavering, and the line upon it

should always be parallel to the
burette.

graduations of the

Filter for ascertaining: the end re-action in certain pro-
cesses.— This is shown in fig. 23, and the instrument is
known as Be ale's filter. It serves well for taking a few
drops of clear solution from any liquid in which a pre- ^f*
cipitate will not settle readily. To use it, a piece of filter
paper is tied over the lower end, arid over that a piece of fine muslin,
to keep the paper from being broken. When dipped into a muddy

§ 9. INSTRUMENTS. 19

mixture, the clear fluid rises and may be poured out of the little
spout for testing. If the process in hand is not completed, the
contents are washed hack to the bulk, and -the operation repeated
as often as may be required.

THE CALIBRATION OF GRADUATED APPARATUS.

§ 9. IT is obvious that in the practice of volumetric analysis
the absolute correctness of the graduations of the vessels used to
a given standard is not necessary, so long as they agree with one
another. In the present day there* are many makers of in-
struments, some using the liter of 1000 grams of distilled water
at 4° C., others at 15'5° C., and again at 17'5° C. Under these
circumstances it is conceivable that operators may purchase, from
time to time, a mixture of instruments of a heterogeneous
character. The German Imperial Standard Commission have,
I believe, now made it legal only to use for official purposes the
liter and its divisions, containing 1000 grams of pure water at
4° C. (p. 23). These instruments for use in that country are all
stamped in the same way as commercial measures are stamped by
law in this country. If, then, instruments are sent abroad, they
Avill not agree with the bulk of those hitherto used. On this
account, as well as for general accuracy, it is necessary to calibrate
or measure the divisions upon the various instruments by
actual experiment, carried on in a room kept at the temperature
of 16° C.

Flasks. — The shortest way to get at the true contents of a liter
flask, or to correct it for a given temperature by making a fresh
mark, is to weigh the contents by substitution, which is done as
follows : —

The flask is cleaned and dried, by first rinsing with alcohol, then
ether, and the latter blown out with a bellows or driven off by
warming, when cool it is placed on a sufficiently large and
sensitive balance, together with a kilogram weight, side by side —
a shallow metal tray is placed on the other pan, and sufficient shot
added to exactly balance the flask and weight ; both the latter are
then removed, leaving the shot on the other pan. The flask is
then placed level, and distilled water at 16° C. poured in up to
the mark ; the moisture in the neck is removed after a few
minutes by filter paper and the flask placed on the empty pan, if
the two pans are in equilibrium the mark is correct, if not, water
must be added or removed, with a small pipette, and the mark
altered. Smaller flasks are calibrated in the same way.

To calibrate a flask for delivering an exact liter or less, some
water is poured into the empty flask, which is drained for half
a minute, and weighed with its stopper ; it is then filled to the
neck with pure water, and closed by the glass or rubber stopper,

c 2

20 VOLUMETRIC ANALYSIS. § 9.

to prevent evaporation, and water added or removed as before.
A nick is then made with a diamond, or sharp file, opposite the
lowest part of the meniscus, which may be extended to a proper
mark after the flask is emptied. Such a flask, when correctly
marked, will deliver the volume required at the given temperature,
after the contents have been poured out and drained for half
a minute.

Burettes. — After firmly fixing in its stand, filling with pure
water at 16° C., and getting rid of the air bubbles in the tap or
spit, the exact level at the 0 mark is made preferably with aij
ErdmaAn float; successive quantities of 5 or 10 c.c. are then run
into a small dry tared beaker and rapidly weighed. If great
accuracy is required a closed vessel ought to be employed, but this
necessitates the drying after each weighing ; a very small beaker
can be easily wiped dry, and rapid weighings made without any
sensible loss of accuracy. If the weighings have shown reasonable
accuracy, say within a milligram or so for each c.c., it will be
sufficiently correct ; if otherwise, a table must be constructed,
showing the correct contents at any given point.

An excellent method of calibrating tap burettes is described by
Carnegie (C. N. Ixiv. 42), which saves the labour involved in
the separate weighings just described, but does not give the weight
contents. A small column of CS2, saturated with water, and
tinted with iodine, is used to measure the spaces between the
graduation marks of the instrument. The burette is connected by
rubber tube with a reservoir of water like that used for mercury
in gas apparatus, and by the pressure of the water in this reservoir
5 c.c. or so of the CS2 may be moved from the bottom upwards,
throughout the whole length of the instrument, so as to compare
portions of the scale throughout. It is essential that the measure-
ment takes place from the bottom, which is done by allowing
water to flow in up to the lower mark of the burette, then gently
running in the portion of CS2 from a long fine pipette ; when
settled, and the meniscus observed, a cautious opening of the tap
will allow of the movement of the column, through the various
divisions, up to the top.

Pipettes. — With the instrument made to deliver one quantity
only it is generally sufficient to fill it by suction above the mark,
then gently release the pressure of the finger, until the exact mark
is reached. The contents are then run into a dry tared beaker,
drained for half a minute in contact with the sides of the beaker,
and the beaker quickly weighed. If not fairly correct, trials must
be made by placing a thin strip of gummed paper on the stem,
and marking the height of each trial until the correct weight is
found, when a permanent mark may be made.

Graduated pipettes are best calibrated by filling them above the

§ 9.

PRESERVATION OF SOLUTIONS.

mark, fixing them in a stand like a burette, closing the top with
a stout piece of rubber tube, clamped with a strong clip, then,
after adjusting the level, drawing off in quantities of 5 c.c. or so,
and weighing in the same way as directed for burettes.

Cylinders. — The only method of calibrating these vessels is to
measure into them repeatedly various volumes of water, from
delivery pipettes of proved accuracy, taking precautions as to level,
meniscus, and the proper drainage of the pipette after each
delivery.

Preservation of Solutions. — There are test solutions which, in
consequence of their proneness to decomposition, cannot be kept
at any particular strength for a length of time ; consequently they
must be titrated on every occasion before being used. Stannous
chloride and sulphurous acids are examples of such solutions.
Special vessels have been devised for keeping solutions liable to
alter in strength by access of air, as shown in figs. 24 and 25.

Pig. 25.

VOLUMETRIC ANALYSIS.

§ 9.

Fig. 24 is especially applicable to caustic alkaline solutions, the
tube passing through the caoutchouc stopper being filled with dry
soda-lime, resting on cotton wool.

Fig. 25, designed by Mohr, is a considerable improvement
upon this, since it allows of the burette being filled with the
solution from the store bottle quietly, and without any access of
air whatever. The vessel can be used for caustic alkalies, baryta,
stannous chloride, permanganate, and sulphurous acids, or any other
liquid liable to undergo change by absorbing oxygen. The corks
are dried and soaked in melted paraffins ; or, still better, may be
substituted by caoutchouc stoppers ; and a thin layer of rectified
paraffin oil is poured on the top of the solution, where, of course,
owing to its low specific gravity, it always floats, placing an
impermeable division between the air and the solution ; and as
this body (which should always be as pure as possible) is not
affected by these reagents in their diluted state, this form offers
great advantages. Solutions not affected chemically by contact
with air should nevertheless be kept in bottles, the corks or stoppers
of which are perfectly closed, and tied over with india-rubber or
bladder to prevent evaporation, and should further be always
shaken before use, in case they are not quite full. The influence
of bright light upon some solutions is very detrimental to their
chemical stability ; hence it is advisable to preserve some solutions
not in immediate use in the dark, and
at a temperature not exceeding 15 or
16° C.

The apparatus devised by J. C.
Chorley, and shown in fig 26, will be
found useful for preserving and delivering
known volumes of such solutions as
alcoholic potash, which are liable to
contamination by exposure to air. The
wash bottle inserted in the cork of the
large store bottle contains a solution of
caustic soda, and serves to wash all air
entering the large bottle. By means of
the three-way stop-cock at the bottom of
the apparatus the solution is allowed to
fill the pipette and overflow into its upper
chamber, the excess being caught in the
small side bulb and reservoir ; this solution
serves to wash all air entering the pipette
when the stop-cock is turned to deliver
the solution, which is run off to a mark
just above the tap. When full, the side
reservoir may be emptied by withdrawing
the small ground stopper. Fig. 26.

§ 10. WEIGHTS AND MEASURES. 2o

ON THE SYSTEM OF WEIGHTS AND MEASURES
TO BE ADOPTED IN VOLUMETRIC ANALYSIS.

§ 10. IT is mucli to be regretted that the decimal system of
weights and measures used on the Continent is not universally
adopted, for scientific and general purposes, throughout the civilized
world. Its great advantage is its uniformity throughout. The
unit of weight is the gram ( = 15-43235 grains troy), and a gram
of distilled water at 4° C., or 39° Fahr., measures exactly a cubic
centimeter. The kilogram contains 1000 grams, the liter 1000
cubic centimeters.

It may not be out of place here to give a short description of the
origin of the French decimal system, now used exclusively for
scientific purposes in that country, and also in Prussia, Austria,
Holland, Sweden, Denmark, Belgium, and Spain.

The commission appointed in France for the purpose of instituting
a decimal system of weights and measures, founded their standard
on the length of the meridian arc between the pole and equator,
the ten-millionth part of which' was called the metre ( = 39*3710
English inches), although the accuracy of this measurement has
been disputed. It would have been preferable, as since proposed,
that the length of a pendulum vibrating exactly 86,400 times in
twenty-four hours, or one second for each vibration, equivalent to
39 '1372 English inches, should have been taken as the standard
•juttrvj in which case it would have been much easier to verify the
standard in case it should be damaged or destroyed. However, the
actual mid-re in use is equal to 39 '371 inches, and from this standard
its multiples and subdivisions all proceed decimally ; its one-tenth
part being the decimetre, one-hundredth the centimetre, and one-
thousandth the millimetre.

In accordance with tins, a cube of distilled water at its greatest
density, viz., 4° C., or 39° Fahr., whose side measures one decimeter,
has exactly the weight of one kilogram, or 1000 grams, and occupies
the volume of one liter, or 1000 cubic centimeters.

This simple relationship between liquids and solids is of great
value in a system of volumetric analysis, and even for ordinary
analysis by weight ; for technical purposes it is equally as applicable
as the grain system, the results being invariably tabulated in
percentages.

With these brief explanations, therefore, I have only to state
that the French decimal system will be mainly used throughout
this treatise ; but at the same time, those who may desire to adhere
to the ordinary grain weights, can do so without interfering with
the accuracy of the processes described.

As has been before stated, the true cubic centimeter contains
one gram of distilled water at its greatest density, viz., 4° C.,
or 39° Fahr. ; but as this is a degree of temperature at which it
is impossible to work for more than a month or two in the year, it
is better to take the temperature of 16° C., or about 60° Fahr., as

24 VOLUMETRIC ANALYSIS. § W.

the standard ; because in winter most laboratories or rooms have
furnaces or other means of warmth, and in summer the same
localities ought not, under ordinary circumstances, to have a much
higher degree of heat than 16° C. In order, therefore, that the
graduation of instruments on the metrical system may be as-
uniform as possible with our own fluid measures, the cubic-
centimeter should contain one gram of distilled water at 16° C,
The true c.c. (i.e. = 1 gm. at 4° C., or 39° Fahr.) contains only
0-999 gm. (strictly 0-998981) at that temperature; but for con-
venience of working, and for uniformity with our own standards-
of volume, it is better to make the c.c. contain one gram at 16° C.
The real difference is one-thousandth part. The operator, there-
fore, supposing he desires to graduate his own measuring flasks,
must weigh into them 250, 500, or 1000 grams of distilled water
at 16° C., or 60° Fahr.

Fresenius and others have advocated the use of the strict liter
by the graduation of instruments, so that they shall contain
999 gm. at 16° C. Mohr, on the contrary, uses a 1000 gm., at
the temperature of 17 '5°, the real difference being T2 c.c. in the
liter, or about one eight-hundredth part.

It will be seen above that I have advocated a middle course on
two grounds: (1) That in testing instruments it is much easier
to verify them by means of round numbers, such as 5 or 10 gm.
(2) That there are many thousands of instruments already in use-
varying between the two extremes ; and as these cannot well be
annihilated, the adoption of a mean will -give a less probable amount
of error between the respective instruments ; and, moreover, the
difference between the liter at 4° and 16° being one-thousandth
part, it is easy to correct the measurement for the exact liter.

It matters not which plan is followed, if all the instruments in
a particular set coincide with each other ; but it would be
manifestly wrong to use one of Mohr's burettes with one of
Fresenius' measuring flasks. Operators can, however, without
much difficulty re-mark their measuring flasks to agree with their
smaller graduated instruments, if they are found to differ to any
material extent.

Variations of Temperature. — In the preparation of standard
solutions, one thing must especially be borne in mind ; namely,
f that saline substances on being dissolved in water have a consider-
able effect upon the volume of the resulting liquid. The same is
also the case in mixing solutions of various salts or acids with each
other (see Gerlach, " Specifische Gewichte der Salzosungen ; "
also Gerlach, " Sp. Gewichte von wasserigen Losungen," Z. a C.
viii. 245).

In the case of strong solutions, the condensation in volume is as
a rule considerable : and, therefore, in preparing such solutions for
volumetric analysis, or in diluting such solutions to a given volume

10.

INFLUENCE OF TEMPERATURE.

for the purpose of removing aliquot portions subsequently for
examination, sufficient time must be given for liquids to assume
their constant volume at the standard temperature. If the strength
of a standard solution i-s known for one temperature, the strength
corresponding to another temperature can only be calculated if the
rate of expansion by heat of the liquid is known. The variation
cannot be estimated by the known rule of expansion in distilled
water; for Gerlacli has shown that even weak solutions of acids
and salts expand far more than water for certain increments of
temperature. The rate of expansion for pure water is known,
and may be used for the purpose of verifying the graduation of
instruments, where extreme accuracy is required. The following
short table furnishes the data for correction.

The weight of 1000 c.c. of water at t° C., when determined by
means of brass weights in air of t° C., and at 0'76 m.ni. pressure,
is equal to 1000 — x gm.

Slight variations of atmospheric pressure may be entirely
disregarded.

15 16

1-34

1-43 1-52

1'63

176

1-89 2-04

2'2

2-37

2-55

t°

25 26

274

2-95

3-17

3-39

3'63

3-88 4-13

4-39

4-67

4-94

5-24

x is the quantity to be subtracted from 1000 to obtain the
weight of 1000 c.c. of water at the temperature i°. Thus at 20°
2-74 must be deducted from 1000 = 997*26.

Bearing the foregoing remarks in mind, therefore, the safest plan
in the operations of volumetric analysis, so far as measurement is \
concerned, is to use solutions as dilute as possible. Absolute!
accuracy in estimating the strength of standard solutions can only
be secured by weight, the ratio of the weight of the solution to the
weight of active substance in it being independent of temperature.

Casamajor (C. N. xxxv. 160) has made use of the
data given by Matthiessen in his researches on the expansion
of glass, water, and mercury, to construct a table of corrections to
be used in case of using any weak standard solution at a different
temperature to that at which it was originally standardized.

The expansion of water is different at different temperatures ;
the expansion of glass is known to be constant for all temperatures
up to 100°. The correction of volume, therefore, in glass burettes,
must be the known expansion of each c.c. of water for every 1° C.,
less the known expansion of glass for the same temperature.

It is not necessary here to reproduce the entire paper of
Casamaj or, but the results are shortly given in the following table.

•*

UNIVERSITY

26 VOLUMETRIC ANALYSIS. § 10.

The normal temperature is 15° C. ; and the figures given are the
relative contractions below, and expansions above, 15° C.

DC?. C. Deg. C.

7 _ -Q00612 24 + '001686

8 _ -000590 25 + '001919

9 _ -000550 26 + '002159
10 _ -000492 ' 27 + '002405

1 1 — -000420

12 — '000334

28 4- '002657

29 + -002913

13 — '000236 30 + "003179

14 — '000124 31 + '003453

15 Normal 32 + "003739

16 + '000147 33 + -004035

17 + -000305 34 + -004342

18 + -000473 35 + '004660

19 + '000652 36 + '0049S7

20 + -000841 37 + "005323

21 + -001039 38 + -005667

22 + -001246 39 + '006040

23 + '001462 40 + '000382

By means of these numbers it is easy to calculate the volume of
liquid at 15° C. corresponding to any volume observed at any
temperature. If 35 c.c. of solution has been used at 37° C., the
table shows that 1 c.c. of water in passing from 15° to 37° is
increased to 1 -005323 c.c. ; therefore, by dividing 35 c.c. by 1 "005323
is obtained the quotient 34'819 c.c., which represents the volume
at 15° corresponding to 35 c.c. at 37° ; or the operation can be
simplified by obtaining the factor, thus :

1^5323 = 0-991705

A table can thus be easily constructed which would show the
factor for each degree of temperature.

These corrections are useless for concentrated solutions, such as
normal alkalies or acids ; with great variations of temperature
these solutions should be used by weight.

Instruments graduated on the Grain System. — Burettes, pipettes,
and flasks may also be graduated in grains, in which case it is best
to take 10,000 grains as the standard of measurement. In order
to lessen the number of figures used in the grain system, so far
as liquid measures are concerned, I propose that ten fluid grains be
called a decem, or for shortness dm. ; this term corresponds to the
cubic centimeter, bearing the same proportion to the 10,000 grain
measure as the cubic centimeter does to the liter, namely, the
one-thousandth part. The use of a term like this will serve to
prevent the number of figures, which are unavoidably introduced
by the use of a small unit like the grain.

Its utility is principally apparent in the analysis for percentages,
particulars of which will be found hereafter.

§ 11. NORMAL SOLUTIONS. 27

The 1000 grain burette or pipette will therefore contain 100
tlecems, the 10,000 gr. measure 1000 dm., and so on.

The capacities of the various instruments graduated on the grain
system may be as follows : —

Flasks : 10,000, 5000, 2500, and 1000 grs. = 1000, 500, 250, and
100 dm. Burettes : 300 grs. in 1-gr. divisions, for very delicate
purposes = 30 dm. in y^j-GOO grs. in 2-gr. divisions, or i dm.;
1100 grs. in 5-gr. divisions, or J dm. ; 1100 grs. in 10-gr. divisions,
or 1 dm. The burettes are graduated above the 500 or 1000 grs.
in order to allow of analysis for percentages by the residual method.
Whole pipettes to deliver 10, 20, 50, 100, 200, 500, and 1000 grs.,
graduated ditto, 100 grs. in y1^ dm. ; 500 grs. in ?, dm. ; 1000 grs.
in 1 dm.

Those who may desire to use the decimal systems constructed on
the gallon measure = 70,000 grains, will bear in mind that the
"septem"of Griffin, or the "decimillem" of Acland are each
equal to 7 grs. ; and therefore bear the same relation to the
pound = 7000 grs., as the cubic centimeter does to the liter, or the
decem to the 10,000 grs. An entirely different set of tables for
calculations, etc., is required for these systems ; but the analyst
may readily construct them when once the principles contained in
this treatise are understood.

VOLUMETRIC ANALYSIS BASED ON THE SYSTEM OF
CHEMICAL EQUIVALENCE AND THE PREPARATION
OF NORMAL TITRATED SOLUTIONS.

§11. WHEX analysis by measure first came into use, the test
solutions were generally prepared so that each substance to be tested
had its own special reagent ; and the strength of the standard
solution was so calculated as to give the result in percentages.
Consequently, in alkalimetry, a distinct standard acid was used for
soda, another for potash, a third for ammonia, and so on, necessi-
tating a great variety of standard solutions.

Griffin and Ure appear to have been the first to suggest the use
of standard test solutions based on the atomic system; and folio wing-
in their steps Mohr has worked out and verified many methods of
analysis, which arc of great value to all who concern themselves
with scientific and especially technical chemistry. .Not only has
Mohr done this, but in addition to it, he has enriched his
processes with so many original investigations, and improved the
necessary apparatus to such an extent, that he may with justice
be called the father of the volumetric system.

Normal Solutions. — It is of great importance that no misconcep-
tion should exist as to what is meant by a normal solution ; but it
does unfortunately occur, as may be seen by reference to the
chemical journals, also to Muir's translations, of Fleischer's
book (see Allen, C. N. xl. 239, also Analyst, xiii. 181).

VOLUMETRIC ANALYSIS. § 11.

Normal solutions as originally devised are prepared so that one
liter at 16° C. shall contain the hydrogen equivalent of the active
reagent weighed in grams (H=l). Seminormal, quintinormal,
clecinormal, and centinormal solutions are also required, and may
be shortly designated as J f- -~~ and y^ solutions.*

In the case of univalent substances, such as silver, iodine,
hydrochloric acid, sodium, etc., the equivalent and the atomic
(or in the case of salts, molecular) weights are identical ; thus, a
normal solution of hydrochloric acid must contain 36*37 grams of
the acid in a liter of fluid, and sodic hydrate 40 grams. In the
case of bivalent substances, such as lead, calcium, oxalic acid,
sulphurous acid, carbonates, etc., the equivalent is one half of the
atomic (or in the case of salts, molecular) weight ; thus, a normal
solution of oxalic acid would be made by dissolving 63 grams of
the crystallized acid in distilled water, and diluting the liquid to
the measure of one liter.

Further, in the case of trivalent substances, such as phosphoric
acid, a normal solution of sodic phosphate would be made by
weighing -f-= 119*3 grams of the salt, dissolving in distilled
water, and diluting to the measure of one liter.

One important point, however, must not be forgotten, namely,
that in preparing solutions for volumetric analysis the value of a
reagent as expressed by its equivalent hydrogen-weight must not
always be regarded, but rather its particular reaction in any given
analysis ; for instance, tin is a quadrivalent metal, but when
using stannous chloride as a reducing agent in the analysis of

* It is much to be regretted that the word "normal," originally based on the
equivalent system, should now be appropriated by those who advocate the use of
solutions based on molecular weights, because it not only leads to confusion between
the two systems, but to utter confusion between the advocates of the change them-
selves. In Fleischer's German edition of his Maasanalyse the molecular system
is advocated, but, as the old atomic weights are used, the solutions are really, in the
main, of the same strength as those based on the equivalent system. Pattiusoii
Muir, however, in his translation, has thought proper to use modern atomic weights,
and the curious result is that one is directed to prepare a normal solution of caustic
potash, with 39 '1 grams K to the liter, while a normal potassic carbonate is to contain
138'2 grams K-COa, or 78'2 grams K, in the same volume of solutions. Again, Muter,
in his Manual of Analytical Chemistry, defines a normal solution as having one molecular
weight of the reagent in grams per liter; then follows the glaring inconsistency,
among others, of directing that a decinormal solution of iodine should contain 12 '7
grams of I per liter, whereas, if it was strictly made according to the original definition,
it shotild contain 25'4 grams in the liter. Menschutkin's Analytical Chemistry,
translated by Locke, recently published by Macmillan & Co., unfortunately adopts
the molecular system.

If the unit H be adopted as the basis or standard, everything is simplified, and
actual normal solutions may be made and used; but, on the molecular system, this
is, in many cases, not only unadvisable but impossible, besides leading to ridiculous
inconsistencies. As Allen points out in the reference above, it is, to say the least
of it, highly inconvenient that the nomenclature of a standard solution should be
capable of two interpretations. I have given the term systematic to this handbook,
and I maintain that the equivalent system used is the only systematic and consistent
one ; it was adopted originally by M o h r , followed by Freseuius, and continued
by Classen in the new edition of Mohr's Titrirmethode. Allen himself has
unhesitatingly preferred to tise it in his Organic Analysis, and these, together with
this treatise, being all text-books having a wide circulation, ought to settle definitely
the meaning of the term normal as applied to systematic standard solutions. Anyhow,
it is to be hoped that those who communicate processes to* the chemical journals, or
abstractors of foreign articles for publication, will take care to distinguish between
the conflicting systems.

§ 11. NORMAL SOLUTIONS. 29

iron, the half, and not the fourth, of its molecular weight is
required, as is shown by the equation Fe2 Cl° + Sn C12 = 2 Fe Cl2
+ Sn Cl4.

In the same manner with a solution of potassie permanganate
Mn KO4 when used as an oxidizing agent, it is the available oxygen
which has to be taken into account, and hence in constructing a
normal solution one-fifth of its molecular weight =J^ = 31*6 grams
must be contained in the liter.

Other instances of a like kind occur, the details of which will
be given in the proper place.

A further illustration may be given in order to show the method
of calculating the results of this kind of analysis.

Each c.c. of ^ silver solution will contain Yy-Jo-Q- of the atomic
weight of silver = 0*010766 gin., and will exactly precipitate
T_i__ of the atomic weight of chlorine = 0 '003537 gm. from any
solution of a chloride.

In the case of normal oxalic acid each c.c. will contain ^Vo of
the molecular weight of the acid = 0*063 gm., and will neutralize
__!__ of the molecular weight of sodic monocarbonate = 0*053 gm.,
or will combine with o-^Vo °f the atomic weight of a dyad metal
such as lead = 0;1032 gm., or will exactly saturate ToVo- °f the
molecular weight of sodic hydrate = 0*040 gm., arid so on.

Where the 1000 grain measure is used as the standard in place
of the liter, 63 grains of oxalic acid would be used for the normal
.solution;- but as 1000 grains is too small a quantity to make, it is
better to weigh 630 grains, and make up the solution to 10,000
grain measures = 1000 dm. The solution would then have exactly
the same strength as if prepared on the liter system, as it is pro-
portionately the same in chemical power ; and either solution may
be used indiscriminately for instruments graduated on either scale,
bearing in mind that the substance to be tested with a c.c. burette"
must be weighed on the gram system, and vice versa, unless it be
desired to calculate one system of weights into the other.

The great convenience of this equivalent system is, that the
numbers used as coefficients for calculation in any analysis are
familiar, and the solutions agree with each other, volume for
volume. We have hitherto, however, looked only at one side of
its advantages. For technical purposes the plan allows the use of
all solutions of systematic strength, and simply varies the amount
.of substance tested according to its equivalent weight.

Thus, the normal solutions say, are-
Crystallized oxalic acid =63 gm. per liter
Sulphuric acid =49 gm.
Hydrochloric acid -=36.37. gm.
Nitric acid =63 gm.
Anhydrous sodic carbonate =53 gm.
Sodic hydrate =40 gm.
Ammonia = 17 gm.

30 VOLUMETRIC ANALYSIS. § 11.

100 c.c of any one of these normal acids should exactly neutralize
100 c.c. of any of the normal alkalies, or the corresponding amount
of pure substance which the 100 c.c. contain. In commerce we
continually meet with substances used in manufactures which, are
not pure, and it is necessary to know how much pure substance
they contain.

Let us take, for instance, refined soda ash (sodic carbonate). If
it were absolutely pure, 5 '3 gm. of it should require exactly 100 c.c.
of any normal acid to saturate it. If we therefore weigh that
quantity, dissolve it in water, and deliver into the mixture the
normal acid from a burette, the number of c.c. required to saturate
it will show the percentage of pure sodic carbonate in the sample.
Suppose 90 c.c. are required— 90 %.

Again — a manufacturer buys common oil of vitriol, and requires
to know the exact percentage of pure hydrated acid in it; 4'9 grams
are weighed, diluted with water, and normal alkali delivered in
from a burette till saturated; the number of c.c. used will be the
percentage of real acid. Suppose 58'5 c.c. are required = 58'5 %.

On the grain system, in the same way, 53 grains of the sample of
soda ash would require 90 dm. of normal- acid, also equal to 90 %.

Or, suppose the analyst desires to know the equivalent percentage
of dry caustic soda, free and combined, contained in the above
sample of soda ush, without calculating it from the carbonate found
as above, 3'1 gm. is treated as before, and the number of c.c.
required is the percentage of sodic oxide. In the same sample
52'6 c.c. would be required = 52*6 per cent, of sodic oxide, or 90
per cent, of sodic carbonate.

Method for percentag-e of Purity in Commercial Substances. — The
rules, therefore, for obtaining the percentage of pure substance in
any commercial article, such as alkalies, acids, and various salts,
by means of systematic normal solutions such as have been
described are these—

1. With normal solutions ^ or — (according to its atomicity)
of the molecular weight in grams of the substance to be analyzed
is to be weighed for titration, and the number of c.c. required to
produce the desired reaction is the percentage of the substance
whose atomic weight has been used.

With decinormal solutions —-$ or TT— of the molecular weight
in grams is taken, and the number of c.c. required will, in like
manner, give the percentage.

Where the grain system is used it will be necessary, in the case
of titrating with a normal solution, to weigh the whole or half the
molecular weight of the substance in grains, and the number of
decems required will be the percentage.

With decinormal solutions, y1^- or J^- of the molecular weight in
grains is taken, and the number of decems will be the percentage.

It now only remains to say, with respect to the system of weights-

§ 12. VOLUMETRIC PROCESSES. 31

and measures to be used, that the analyst is at liberty to choose his
own plan. Both systems are susceptible of equal accuracy, and he
must study his own convenience as to which he Avill adopt. The
normal solutions prepared on the gram system are equally applicable
for that of the grain, and vice versa, so that there is no necessity
for having distinct solutions for each system.

Factors, or Coefficients, for the Calculation of Analyses. — It
frequently occurs that from the nature of the substance, or from
its being in solution, this percentage method cannot be conveniently
followed. For instance, suppose the operator has a solution con-
taining an unknown quantity of caustic potash, the strength of
which he desires to know ; a weighed or measured quantity of it
is brought under the acid burette and exactly saturated, 32 c.c.
being required. The calculation is as follows : —

The molecular Aveight of potassic hydrate being 56 : 100 c.c. of
normal acid will saturate 5*6 gm. ; therefore, as 100 c.c. are to 5*6 srni.*

so are 32 c.c. to #,'— JQQ~~= 1*792 gm. KH.O.

The simplest way, therefore, to proceed, is to multiply the
number of c.c. of test solution required in any analysis, by the
TTTO (T (or T<TO o- ^ bivalent) of tli3 molecular weight of the substance
sought, which gives at once the amount of substance present.

An example may be given — 1 gm. of marble or limestone 'is
taken for the estimation of pure calcic carbonate, and exactly
saturated with standard nitric or hydrochloric acid — (sulphuric or
oxalic acid are, of course, not admissible) 17 '5 c.c. are required,
therefore 17 -5 x 0*050 (the o-oVir °f the molecular weight of
CaCO3) gives 0'875 gm., and as 1 gm. of substance only was

taken = 87 "5% of calcic carbonate.

ON THE DIRECT AND INDIRECT PROCESSES OF
ANALYSIS AND THEIR TERMINATION.

§ 12. THE direct method includes all those analyses where the
substance under examination is decomposed by simple contact with
a known quantity or equivalent proportion of some other body
capable of combining with it, and where the end of the decomposition
is manifested in the solution itself.

It also properly includes those analyses in which the substance
reacts upon another body to the expulsion of a representative
equivalent of the latter, which is then estimated as a substitute
for .the thing required.

Examples of this method are readily found in the process for
the determination of iron by permanganate, where the beautiful
rose colour of the permanganate asserts itself as the end of the
reaction.

The testing of acids and alkalies comes, also, under this class, the

32 VOLUMETRIC ANALYSIS. § 12.

great sensitiveness of litmus, or other indicators, allowing the
most trifling excess of acid or alkali to alter their colour.

The indirect method is exemplified in the analysis of manganese
ores, and also other peroxides and oxygen acids, by boiling with
hydrochloric acid. The chlorine evolved is estimated as the
equivalent of the quantity of oxygen which has displaced it. We
are indebted to Bun sen for a most accurate and valuable series of
processes based on this principle.

The residual method is such that the substance to be analyzed is
not estimated itself, but the excess of some other body added for
the purpose of combining with it or of decomposing it ; and the
quantity or strength of the body added being known, and the con-
ditions under which it enters into combination being also known,
by deducting the remainder or excess (which exists free) from the
original quantity, it gives at once the proportional quantity of the
substance sought.

An example will make the principle obvious : — Suppose that a
sample of native calcic or baric carbonate is to be tested. It is not
possible to estimate it with standard nitric or hydrochloric acid in
the exact quantity it requires for decomposition. There must be
an excess of acid and heat applied also to get it into solution ; if,
therefore, a known excessive quantity of standard acid be first
added and solution obtained, and the liquid then titrated backward
with an indicator and standard alkali, the quantity of free acid can
be exactly determined, and consequently that which is combined
also.

In some analyses it is necessary to add a substance which shall
be an indicator of the end of the process j such, for instance, is
litmus or the azo colours in alkalimetry, potassic chromate in silver
and chlorine, and starch in iodine estimations.

There are other processes, the end of which can only be
determined by an indicator separate from the solution ; such is
the case in the estimation of iron by potassic bichromate, where
a drop of the liquid is brought into contact with another drop of
solution of red potassic prussiate on a white slab or plate ; when
.a blue colour ceases to form by contact of the two liquids, -the end
of the process is reached.

INDICATORS.

PAET II.

ANALYSIS BY SATURATION.

ALKALIMETRY.

§ 13. GAY LUSSAC based his system of alkalimetry upon a
standard solution of sodic carbonate, with a corresponding solution
of sulphuric acid. It possesses the recommendation, that a pure
standard solution of sodic carbonate can be more readily obtained
than any other form of alkali. Mohr introduced the use of
caustic alkali instead of a carbonate, the strength of which is
established by a standard solution of oxalic or sulphuric acid.
The advantage in the latter system is, that in titrating acids with
a caustic alkali, the well-known interference produced in litmus
by carbonic acid is avoided ; this difficulty is now overcome
wherever it is desired by the new indicators to be described.

INDICATORS USED IN ALKALIMETRY.

§ 14. 1. Litmus Solution. — It has
been the custom since the introduction
of the azo indicator, to regard litmus as
old fashioned and of very doubtful
sensitiveness. This is a mistake, for if
properly prepared, it is, in the absence
of carbonic acid, one of the most
sensitive of the indicators used for
alkalies. The difficulty which occurs
when carbonates are titrated may be
overcome by boiling off the gas, but
this is tedious, and like most of the
indicators in use, it is less sensitive in hot
than in cold liquids, nevertheless it has
excellent qualities, arid will hold its
position against many more modern
indicators. The litmus of commerce
differs considerably in purity and colour,
but a careful examination will at once
detect a good specimen by the absence
of a greyish muddy colour, due to
inert matters, both of vegetable and mineral nature.

A simple solution may be made by treating the cubes with
repeated small quantities of hot water; mixing all the extracts,
and allowing the liquid to stand in a covered beaker for a day or
night. The clear blue liquid is then poured off and placed in the
stock bottle, together with two or three drops of chloroform, this

34 VOLUMETRIC ANALYSIS. §14.

latter agent prevents the development of bacteria, and if the
bottle is simply covered with a piece of paper, through which the
pipette is passed, the solution will keep for a long period. If the
colour is a deep blue it must be modified by a few drops of diluted
hydrochloric acid, until it is a faint purple. In course of time it
may lose its colour, but this may be restored by simple exposure
in a basin. Another method of preparing an extract of litmus in
a concentrated form for dilution whenever required is as follows :
extract all soluble matters from the solid litmus by repeated
quantities of hot wrater ; evaporate the mixed extracts to a moderate
bulk, and add acetic acid in slight excess to decompose carbonates;
evaporate to a thick extract, transfer this to a beaker, and add a large
proportion of hot 85 per-cent. alcohol or methylated spirit ; by this
treatment the blue colour is precipitated, and the alkaline acetates,
together with some red colouring matter, remain dissolved; the
fluid with precipitate is thrown on a filter, washed with hot spirit,
and the pure colouring matter finally evaporated to a paste, which
is placed in a wide-mouthed bottle, together with a few drops of
chloroform ; this extract will keep for years unchanged.

Another recent method gives the best results of any. The
crushed litmus is extracted with warm distilled water, as before
described, and the several extracts mixed, then allowed to stand
in a beaker till quite clear — this clear extract is poured off,
freely acidified with hydrochloric acid, and put into a dialyser,
which is surrounded by running water and kept so for about
a week. The colouring matter of litmus being a colloid, all the
calcium and other salts are removed, and a pure soluble colour in
hot distilled water remains, which may be preserved in the
manner previously described, or evaporated to a pasty condition
and kept for use at any time when required.

Free carbonic acid interferes considerably with the production of
the blue colour, and its interference in titrating acid solutions with
alkaline carbonates can only be got rid of by boiling the liquid
during the operation, in order to displace the gas from the solution.
If this is not done, it is easy to overstep the exact point of neutrality
in endeavouring to produce the blue colour. The same difficulty is
also found in obtaining the pink-red when acids are used for
titrating alkaline carbonates, hence the great value of the caustic
alkaline solutions free from carbonic acid when this indicator is used.

It sometimes occurs that titration by litmus is required at night.
Ordinary gas or lamp light is not adapted for showing the reaction
in a satisfactory manner ; but a very sharp line of demarcation
between red and blue may be found by using a monochromatic
light. With the yellow sodium flame the red colour appears
perfectly colourless, while the blue or violet appears like a mixture
of black ink and water. The transition is very sudden, and even
sharper than the change by daylight.

The operation should be conducted in a perfectly dark room ;

§ 14 INDICATORS. 35

and the flame may be best obtained by heating a piece of platinum
coil sprinkled with salt, or a piece of pumice saturated with a
concentrated solution of salt, in the Bunsen flame.

2. Litmus Paper. — Is simply made by dipping strips of
calendered unsized paper in the solution and drying them ; the
solution used being rendered blue, red, or violet as may be
required.

3. Cochineal Solution. — This indicator possesses the advantage
over litmus, that it is not so much modified in colour by the presence
of carbonic acid, and may be used by gas-light. It may also be used
with the best effect with solutions of the alkaline earths, such as
lime and baryta water ; the colour with pure alkalies and earths is
especially sharp and brilliant. The solution is made by digesting
1 part of crushed cochineal with 10 parts of 25 per-cent. alcohol.
Its natural colour is yellowish-red, which is turned to violet by
alkalies ; mineral acids restore the original colour ; it is not so
easily affected by weak organic acids as litmus, and therefore for
these acids the latter is preferable. It cannot be used in the
presence of even traces of iron or alumina compounds or acetates,
which fact limits its use.

4. Turmeric Paper. — Pettenkof er, in his estimation of car-
bonic acid by baryta water, prefers turmeric paper as an indicator.
For this purpose it is best prepared by digesting pieces of the root,
first in repeated small quantities of water to remove a portion of
objectionable colouring matter, then in alcohol, and dipping strips
of calendered unsized paper into the alcoholic solution, drying and
preserving them in the dark.

Thomson in continuance of his valuable studies on various
indicators, found that turmeric paper is of very little use for
ammonia, or the alkaline carbonates, or sulphides and sulphites,
but he prepared a special paper of a light red-brown colour, by
dipping it into the alcoholic tincture of turmeric rendered slightly
alkaline by caustic soda. If this paper is wetted with water the
colour is intensified to a dark red-brown ; when partly immersed in
a very dilute solution of an acid, the wetted portion becomes bright
yellow, while immediately above this a moistened dark red-brown
band is formed, and the upper dry portion retains its original
colour. This appearance only occurs in the titration of a com-
paratively large proportion of an acid, when the latter is nearly all
neutralized, and thus serves to indicate the near approach to the
end-reaction. When neutral or alkaline, the colour of the immersed
portion of paper is simply intensified as already described. This
intensification is quite as decided as a change of tint. This red-
brown paper is equally as sensitive as phenolphthalein for the
titration of citric, acetic, tartaric, oxalic and other organic acids by
•standard soda or potash, and may be used for highly coloured

D 2

36 VOLUMETRIC ANALYSIS. § 14.

solutions. It is also available, like phenolphthalein, for the
estimation of small quantities of acid in strong alcohol.

Indicators derived from the Azo Colours, etc.

A great stride has been taken in the application of these
modern indicators, and the best thanks of all chemists are due to
R. T. Thomson for his valuable researches on them, read before
the Chemical Section of the Philosophical Society of Glasgow, and
published in their Transactions ; also reprinted (C. A7", xlvii. 123,
185; xlix. 32, 119; J. &. C. I. vi. 195). The experiments
recorded in these papers are most carefully carried out, and the
truthfulness of their results has been verified by Lunge and other
practical men as well as by myself.

Space will only permit here of a record of the results, fuller
details being given in the publications to which reference has been
made.

Much discussion has arisen as to the comparative sensitiveness
of litmus and methyl orange, but there can be no doubt that in
the absence of CO2 litmus bears the palm, especially with very
dilute solutions. In the titration of alkaline carbonates litmus
may safely be used, if a considerable excess of standard acid is
first added, the CO2 completely boiled off, the liquid rapidly
cooled, then titrated back with standard alkali free from CO'2.
Where very great delicacy is required, not only must the standard
solutions be free from CO2 but the distilled water used for dilution
should have been recently boiled.

5. Methyl Orang-e, or para-dimethylaniline-azo-benzone-sulphonic
acid is prepared by the action of diazotized sulphanilic acid upon
dimethylaniline, the commercial product being either an ammonium
or sodium salt of the sulphonic acid thus produced. If carefully
prepared from the purest materials it possesses a bright orange
colour, perfectly soluble in water ; but the commercial product is
often of a dull colour, due to slight impurities in the substances
from which it is produced, and often not completely soluble in
water. These impurities may generally IDC removed by
recrystallizatiori from hot alcoholic solution. Complaints have
been made by some operators that the commercial article is some-
times unreliable as an indicator ; it may be so, but although I have
examined many specimens, I have not yet found any in which the-
impurities sensibly affected its delicate action when used in the
proper manner. The common error is the use of too much of it ;
again, there is the personal error of observation, some eyes being-
much more sensitive to the change of tint than others. The
great value of this indicator is that, unlike litmus and some other
agents, it is comparatively unaffected by carbonic acid, sulphuretted
hydrogen, hydrocyanic, silicic, boric, arsenious, oleic, stearic,.
palmitic, and carbolic acids, etc. It must not be used for the-

§ 1-1. INDICATORS. 37

organic acids, such as oxalic, acetic, citric, tartaric, etc., since
the end-reaction is indefinite ; nor can it be used in the presence
of nitrous acid or nitrites, which decompose it. It may safely be
used for the estimation of free mineral acids in alum, ferrous
sulphate or chloride, zinc sulphate, cupric sulphate or chloride. The
acid radical (and consequently -its equivalent metal) in cupric
sulphate and similar salts may be estimated with accuracy by pre-
cipitating the solution with sulphuretted hydrogen, filtering, and
titrating the filtrate at once with normal alkali and methyl orange.

Methyl orange is especially useful for the accurate standardizing
of any of the mineral acids by means of pure sodic carbonate in the
cold, the liberated carbonic acid having practically no effect, as is the
case with many indicators. Its effect is also excellent with ammonia
or its salts. A convenient strength for the indicator is 1 gram of
the powder in a liter of distilled water ; a single small drop of the
liquid is sufficient for 100 c.c. or more of any colourless solution —
the colour being faint yellow if alkaline, and pink if acid ; if too
much is used the end-reaction is slower and much less definite.
All titrations with methyl orange should be carried on at ordinary
temperatures if the utmost accuracy is desired. •

There are two other azo-compounds in use, more especially by
continental chemists, which possess the same properties and give
much the same effect as methyl orange, namely Fischer's
dimethylamido-azobenzene and tropoeolin 00. My experience is
that these preparations are less sensitive than methyl orange, and
wherever they are recommended for any process of titration the
latter may be substituted with advantage.

6. Phenacetolin. — This substance is prepared by boiling together
for several hours equal molecular proportions of phenol, acetic
anhydride, and sulphuric acid. The product is well washed with
water to remove excess of acid and dried for use ; it is soluble
only in alcohol, and a convenient strength is 2 gm. per liter. The
solution is dark brown, which gives a scarcely perceptible yellow
with caustic soda or potash, when a few drops are used with the
ordinary volumes of liquid. With ammonia and the normal
alkaline carbonates it gives a dark pink, with bicarbonate a much
more intense pink, and with mineral acids a golden yellow. This
indicator may be used to estimate the amount of caustic potash
or soda in the presence of their normal carbonates if the proportion
of the former is not very small, or of caustic lime in the presence
of carbonate.

Practice however is required with solutions of known composition,
so as to acquire knowledge of the exact shades of colour.

7. Phenolphthalein. — This substance is obtained by heating
together at 120° C., for ten or twelve hours, five parts of phthalic
anhydride, ten of phenol, and four of sulphuric acid j the product

38 VOLUMETRIC ANALYSIS. § 14

is boiled with water, and the residue dissolved in dilute soda and
filtered. The nitrate contains the phenolphthalein, which may
be precipitated by neutralizing with acetic and hydrochloric acids,
and purified by solution in alcohol, boiling with animal charcoal
and re-precipitating with boiling water ; it is of a resinous nature,
but quite soluble in 50 per-cent. alcohol. A convenient strength
is 10 gm. per liter.

A few drops of the indicator show no colour in the ordinary
volumes of neutral or acid liquids ; the faintest excess of caustic
alkalies, on the other hand, gives a sudden change to purple-red.

This indicator is useless for the titration of free ammonia, or its
compounds, or for the fixed alkalies when salts of ammonia are-
present, except with alcoholic solutions, in which case caustic soda
or potash displace the ammonia in equivalent quantities at ordinary
temperatures, and the indicator forms no compound with the
ammonia.

It may, however, be used like phenacetoKn for estimating the
proportions of hydrate and carbonate of soda or potash in the
same sample where the proportion of hydrate is not too small.
Unlike methyl orange, this indicator is especially useful in titrating
all" varieties of organic acids ; viz., oxalic, acetic, citric, tartaric,
etc.

One great advantage possessed by phenolphthalein is, that it
may be used in alcoholic solutions, or mixtures of alcohol and
ether,* and therefore many organic acids insoluble in water may
be accurately titrated by its help ; in addition to this it may be
used to estimate the acid combined with many organic bases,
such as morphia, quinia, brucia, etc., the base having no effect
on the indicator.

8. Kosolic Acid is soluble in 50 per-cent. alcohol, and a con-
venient strength is 2 gm. per liter. Its colour is pale yellow,
unaffected by acids, but turning to violet-red with alkalies. It
possesses the advantage over litmus and the other indicators, that
it can be relied upon for the neutralization of sulphurous acid
with ammonia to normal sulphite (Thomson). Its delicacy-
is sensibly affected by salts of ammonia and by carbonic acid.
It is excellent for all the mineral, but useless for the organic acids^
excepting oxalic,

9. Lacmoid. — This indicator is a product of resorcin, and is-
therefore somewhat allied to litmus ; nevertheless, it differs from it
in many respects, and has a pronounced and valuable character of
its own, especially when used in the form of paper. It may be

* H. 1ST. and. C. Draper (C. N. Iv. 143) have shown that this indicator is rapidly
decomposed by atmospheric carbonic acid, which is more readily absorbed, by alcohol
than by water. Fortunately this is less the case with hot solutions than with cold ;
titrations of this kind should therefore be quickly done, and with not too small
a quantity of the indicator.

§ 14. INDICATORS.

prepared by heating gradually to 110° C. a mixture of 100 parts
of resorcin, five parts of sodic nitrite, and five parts of water;
after the violent reaction moderates, it is heated to 120° C. until
evolution of ammonia ceases. The residue is dissolved in warm
water, and the lacmoid precipitated therefrom by hydrochloric
acid ; it is well washed from free acid and dried for use. Lacmoid
is soluble in dilute alcohol, and the indicator is best made by
dissolving 2 gm. to the liter.

10. Lacmoid Paper. — This is prepared by dipping slips of
calendered unsized paper into the blue or red solution, and drying
them.

Thomson states that, in nearly every particular, lacmoid paper,
either blue or red, is an excellent substitute for methyl orange,
and may be employed in titrating coloured solutions where the
latter would be useless. Solution of lacmoid, on the other hand,
is not so valuable as the paper, inasmuch as it is more easily affected
by weak acids such as carbonic, boric, etc.

There are a host of other indicators belonging to the same category
as those mentioned above, such as Congo red, Porrier's blue,
fluorescin, etc. ; but as they have no special advantages over them,
and indeed are practically inferior in delicacy, no description of
them will be given here.

Two or more indicators are sometimes useful in one and the
same solution, and will be described as occasion requires.

Special indicators for certain purposes, such as potassic chromate
for silver, ferric sulphate for sulphocyanides, etc., will be described
in their proper place.

Extra Sensitive Indicators. — Mylins and Fb'rster (Bericlite,
xxiv. 1482 ; also C. N. Ixiv. 228, et seq.) describe a series of
experiments on the estimation of minute traces of alkali and the
recognition of the neutrality of water by means of an etheieal
solution of iodeosin or erythrosin. This body is a derivative of
fluorescin, and occurs plentifully in commerce as a dye for fabrics
and paper. The commercial material is purified by solution in
aqueous ether, and the filtered solution is shaken with dilute
caustic soda which removes the colour; the latter is then precipitated
with stronger alkali. The salt is then filtered off, washed with
spirit . and finally recrystallized from hot alcohol. The indicator
used by the operators was made by dissolving 1 decigram
of the dry powder in a liter of aqueous pure ether. The
ether of commerce is purified and rendered neutral by washing
with weak alkali, afterwards with pure water, and keeping
the ether over pure water. The indicator so prepared is quite
useless for the ordinary titration of acids and alkalies ; its
chief use is for the detection and measurement of very minute
proportions of alkali such as would occur in water kept in glass

40 VOLUMETRIC ANALYSIS. § 14.

vessels, or the solubility of calcium or other earthy carbonates in
water free from carbonic acid, or in the use of millinormal solutions
of alkalies and acids, also the neutrality of so-called pure salts
or water. The method of using the indicator is that of shaking
up say 20 c.c. of the indicator with 100 c.c. of the liquid to
be examined, when, if alkali is present, a rose colour will be
communicated to the layer of ether which rises to the top. The
indicator may be used in conjunction with millinormal standard
solutions, or colorimetrically, like the well-known Xessler test.
Further details of its use are described in the contributions
mentioned. Another similar indicator is mentioned by Ru hem ami
(J. C. S. Trans. Ixi. 285), the imide of dicinnamylphenylazimide.
This material gives a violet rose colour with the most minute traces
of alkali, such, for instance, as would occur from merely heating
alcohol in a test tube, — the faint trace of alkali thus derived from
the glass being sufficient to cause a rapid development of colour.

SHORT SUMMARY OF THOMSON'S RESULTS WITH
INDICATORS AND PURE SALTS OF THE ALKALIES
AND ALKALINE EARTHS,

The whole of the base or acid in the following list of substances
may be estimated with delicacy and precision unless otherwise
mentioned.

Litmus Cold. — Hydrates of soda, potash, ammonia, lime, baryta,
etc. ; arsenites of soda and potash, and silicates of the same bases ;
nitric, sulphuric, hydrochloric, and oxalic acids.

Litmus Boiling. — The neutral and acid carbonates of potash,
soda, lime, baryta, and magnesia, the sulphides of sodium and
potassium, and silicates of the same bases.

Methyl Orange Cold. — The hydrates, carbonates, bicarbonates,
sulphides, arsenites, silicates, and borates of soda, potash, ammonia,
lime, magnesia, baryta, etc., all the mineral acids, sulphites, half the
base in the alkaline and earthy alkaline phosphates and arseniates.

Rosolic Acid Cold.— The whole of the base or acid may be
estimated in the hydrates of potash, soda, ammonia, and arsenites
of the same ; the mineral and oxalic acids.

Rosolic Acid Boiling. — The alkaline and earthy hydrates and
carbonates, bicarbonates, sulphides, arsenites, and silicates.

Phenacetolin Cold. — The hydrates, arsenites, and silicates of the
alkalies ; the mineral acids.

Phenacetolin Boiling. — The alkaline and earthy hydrates, car-
bonates, bicarbonates, sulphides, arsenites, and silicates.

§ 14. INDICATORS. 41

Phenolphthalein Cold. — -The alkaline hydrates, except ammonia;
the mineral acids, oxalic, citric, tartaric, acetic, and other organic
acids.

Phenolphthalein Boiling. — The alkaline and earthy hydrates,
carbonates, bicarbonates, and sulphides, always excepting ammonia
and its salts.

Lacmoid Cold. — The alkaline and earthy hydrates, arsenites and
borates, and the mineral acids. Many salts of the metals which are
more or less acid to litmus are neutral to lacmoid, such as the
sulphates and chlorides of iron, copper, and zinc ; therefore this
indicator serves for estimating free acids in such solutions.

Lacmoid Boiling. — The hydrates, carbonates, and bicarbonates of
potash, soda, and alkaline earths.

Lacmoid Paper — The alkaline and earthy hydrates, carbonates,
bicarbonates, sulphides, arsenites, silicates, and borates ; the mineral
acids ; half of the base in sulphites, phosphates, arseniates.

This indicator reacts alkaline with the chromates of potash or
soda, but neutral with the bichromates, so that a mixture of the
two, or of bichromates with free chromic acid, may be titrated by
its aid, which could also be done with methyl orange were it not
for the colour of the solutions.

The following substances can be determined by standard
alcoholic potash, with phenolphthalein as indicator. One c.c.
normal caustic potash (1 c.c. = '056 gm. KHO) is equal to —
(Hehner and Allen)

•088 gm. butyric acid. '1007 gm. tributyrin

•282 ,, oleic acid. '2947 ,, triolein.

•256 ,, palmitic acid '2687 „ tripalmitin.

•284 ,, stearic acid '2967 ,, tristearin.

•410 ,, cerotic acid. '6760 ,, myricin.

•329 ,, resin acids (ordinary colophony, chiefly sylvic acid).

General Characteristics of the Foregoing Indicators.

It is interesting to notice the different degrees of sensitiveness
shown by indicators used in testing acids and alkalies. This is well
illustrated by Thomson's experiments, where he used solutions
of the indicator containing a known weight of the solid material,
and so adjusted as to give, as near as could be judged, the same
intensity of colour in the reaction.

It was found that lacmoid, rosolic acid, phenacetolin, and
phenolphthalein were capable of showing the change of colour
with one-fifth of the quantity of acid or alkali which was required
in the case of methyl orange or litmus ; that is to say, in 100 c.c.
of liquid, where the latter took 0*5 c.c., the same effect with the
former was gained by O'l c.c.

42 VOLUMETRIC ANALYSIS. §' 14

Another important distinction is shown in their respective
behaviour with mineral and organic acids.

It is true the whole of them are alike serviceable for the
mineral acids and fixed alkalies ; but they differ considerably in
the case of the organic acids and ammonia. Methyl orange
and lacmoid appear to be most sensitive to alkalies, while
phenolphthalein is most sensitive to acids ; the others appear to^
occupy a position between these extremes, each showing, however,
special peculiarities. The distinction, however, is so marked, that,
as Thomson says, it is possible to have a liquid which may be
acid to phenolphthalein and alkaline to lacmoid.

The presence of certain neutral salts has, too, a definite effect
on the sensitiveness of certain indicators. Sulphates, nitrates,
chlorides, etc., retard the action of methyl orange slightly, while in
the case of phenacetolin and phenolphthalein they have no effect.
On the other hand, neutral salts of ammonia have such a disturbing
influence on the latter as to render it useless, unless with special
precautions.

Nitrous acid alters the composition of methyl orange ; so also
do nitrites when existing in any quantity. Forbes Carpenter
has noted this effect in testing the exit gases of vitriol chambers
(J. S. C. I. v. 287).

Sulphites of the fixed alkalies and alkaline earths are practically
neutral to phenolphthalein, but alkaline to litmus, methyl orange,
and phenacetolin.

Sulphides, again, can be accurately titrated with methyl orange
in the cold, and on boiling off the H2S a tolerably accurate result can
be obtained with litmus and phenacetolin, but with phenolphthalein
the neutral point occurs when half the alkali is saturated. The
phosphates of the alkalies, arseniates, and arsenites, also vary in
their effects on the various indicators.

Again, boric acid and the borates can be very accurately titrated
by help of methyl orange or lacmoid paper, but the other indicators
are practically useless, except with the modification on page 44.

Thomson classifies the usual neutrality indicators into three
groups. The methyl orange group, comprising that substance,
together with lacmoid, dimethylamidobenzene, cochineal and Congo
red ; the phenolphthalein group, consisting of itself and turmeric ; the
litmus group, including litmus, rosolic acid, and phenacetolin. The
methyl orange group are most susceptible to alkalies, the phen-
olphthalein to acids, and the litmus somewhat between the two.
This classification has nothing to do with delicacy of reaction, but
with the special behaviour of the indicator under the same circum-
stances ; for instance, saliva, which is generally neutral to litmus
paper, is always strongly alkaline to lacmoid or Congo red, and acid
to turmeric paper. Fresh milk reacts very much in the same way.
No absolutely hard and fast line can however be drawn.

Thomson gives the following table as an epitome of the results

INDICATORS.

obtained with indicators, and 011 which several processes have beert
based. The figures refer to the number of atoms of hydrogen
displaced by the monatomic metals, sodium or potassium, in the
form of hydrates. Where a blank is left it is meant that the end-
reaction is obscure. The figures apply also to ammonia, except
where phenolphthalein is concerned, and when boiling solutions are
used. Calcic and baric hydrates also give similar results, -.except
where insoluble compounds are produced. Lacmoid paper acts in
every respect like methyl orange, except that it is not affected by
nitrous acid or its compounds. Turmeric paper behaves exactly
like phenolphthalein with the mineral acids and also with thio-
sulphuric and organic acids.

Acids.

Methyl Orange. 'Phenolphthalein.

Litmus.

Name.

Formula.

Cold.

Boiling.

Cold.

Boiling.

Sulphuric . .

H2SO4

Hydrochloric .

HC1

Nitric . . .

HNO3

Thiosulpliuric .

H-'S203

Carbonic . .

H2C03

1 dilute! 0

• — -

Sulphurous

H2SO:?

—

Hydrosulphuric

H2S

1 dilute

o —

Phosphoric

HAPO4

• — ;

—

Arsenic . . .

H3AsO4

—

Arsenious . .

IFAsO3

—

Nitrous . . .

HNO2

indicator destroyed •*•

—

Silicic . . .

H4Si04

—

Borio . . .

H3B03

—

Chromic . .

H2Cr04

—

Oxalic . . .

H2C204

Acetic . . .

HC2H302

— 1

—

1 nearly

—

Butyric . . .

HC4H7O2

—

1 nearly

—

Succiuic . . .

H2C4H4O4

—

2 nearly

—

Lactic . . .

HC3H503

—

Tartaric . . .

H2C4H40(

— .

—

Citric . . .

H3C6H50'

—

Allen (Pliarm. Jour., May llth, 1889) clearly points out that
the acid which enters into the composition of an indicator must be
weaker than the acid which it is required to estimate by its means.
The acid of which methyl orange is a salt is a tolerably strong one,
since.it is only completely displaced by the mineral acids; the
organic acids are not strong enough to overpower it completely,
hence the uncertainty of the end-reaction. The still weaker acids,
such as carbonic, hydrocyanic, boric, oleic, etc., do not decompose
the indicator at all, hence their salts may be titrated by it, just as
if the bases only were present. On the other hand the acid of
phenolphthalein is extremely weak, hence its salts are easily
decomposed by the organic and carbonic acids. A combination of
the two indicators is frequently of service ; say, for instance, in a

44 VOLUMETRIC ANALYSIS. § 15.

mixture of normal and acid sodic carbonate, if first titrated with
plienolphthalein and standard mineral acid, the rose colour dis-
appears exactly at the point when the normal carbonate is saturated,
the bicarbonate can then be found by continuing the operation
with methyl orange. The study of these new indicators is still
imperfect, and requires further elucidation ; more especially if we
take into consideration some new aspects of the question mentioned
in a paper by K. T. Thomson (/. S. C. I. xii. 432). The
experiments there recorded and which are too voluminous to
produce here, are of a very interesting character and point to the
supposition that molecular condition, viscosity of the liquid or
some such influence was at work, so as to modify very considerably
the action of the indicator. The irregularities occurring in the cases
mentioned are no doubt exceptional, and need not disturb the faith
hitherto reposed in well-known and much-used methods of titration.

The particular indicator whose erratic action was under
discussion was phenolphthalein and it was demonstrated, that in
using this indicator in the titration of boric acid with £ soda, no
satisfactory end-reaction could be got in a merely aqueous solution,
but that by the addition of not less than 30 per cent, of glycerine
to the mixture, a perfectly correct determination could be made.
Other substances such as starch, glucose, and cane sugar had
a similar effect, but not to the same extent as glycerine.

The result of these investigations, is to give a satisfactory
method of estimating volumetrically the boric acid existing in its
natural compounds, which has hitherto been a much desired thing.

PREPARATION OF THE NORMAL ACID AND ALKALINE

SOLUTIONS.

§ 15. IT is quite possible to carry out the titration of acids
and alkalies with only one standard liquid of each kind; but it
frequently happens that standard acids or alkalies are required
in other processes of titration beside mere saturation, and it is
therefore advisable to have a variety.

Above all things it is absolutely necessary to have, at least, one
standard acid and alkali prepared with the most scrupulous
accuracy to use as foundations for all others.

I prefer sulphuric acid for the normal acid solution, inasmuch as
there is no difficulty in getting the purest acid in commerce. The
normal acid made with it is totally unaffected by boiling, even
when of full strength, which cannot be said of either nitric or
hydrochloric acid. Hydrochloric acid is however generally pre-
ferred by alkali makers, owing to its giving soluble compounds
with lime and similar bases. Nitric and oxalic acids are also
sometimes convenient.

Sodic carbonate, on the other hand, is to be preferred for the
standard alkali, because it may readily be prepared in a pure

§ 15. NORMAL SOLUTIONS. 45

state, or may be easily made from pure- bicarbonate as
described further on. Differences of opinion exist among
chemists as to the best material to be used as a standard, in
preparing the various solutions used in alkalimetry and acidimetry.
Some give the preference to borax with methyl orange as indicator
for alkalies. Others to potassic quadroxalate for acids with
phenolphthalein as indicator. My experience satisfies me, that
although many of these modifications may serve very well as
controls, there is no more reliable standard than pure sodie
carbonate.

The chief difficulty with sodic carbonate is, that with litmus as
indicator, the titration must be carried on at a boiling heat in
order to get rid of carbonic acid, which hinders the pure blue
colour of the indicator, notwithstanding the alkali may be in
great excess. This difficulty is now set aside by the use of methyl
orange. In case the operator has not this indicator at hand, litmus-
gives perfectly accurate results, if the saturation is first conducted
by rapidly boiling the liquid in a thin flask for a minute after each
addition of acid until the point is reached when one drop of acid
in excess gives a pink-red colour, which is not altered by further
boiling. This is used as a preliminary test, but as titrations are
usually conducted at ordinary temperatures, the final adjustment
should be made by adding in the second trial a moderate excess of
the acid, then boiling to get thoroughly rid of the CO2, rapidly
cooling the liquid in a closed flask, and titrating back with an
accurate standard alkali. A slight calculation will then give the
figures for adjustment.

As has been previously said, these two standards must be pre-
pared with the utmost care, since upon their correct preparation and
preservation depends the verification of other standard solutions.

It may, however, be remarked, that in place of a standard solution
of sodic carbonate, which is of limited use for general purposes,
the pure anhydrous salt may be used for the rigid adjustment of
normal acid. In this case about 3 grams of pure ^N"a2C03 or 4 gm.
of pure XaHCO3 are heated to dull redness for ten minutes in a
weighed platinum crucible, cooled under an exsiccator, the exact
weight quickly taken, then transferred to a flask by means of a
funnel, through which it is washed and dissolved - with distilled
water, methyl orange added, and the operation completed by
running the acid of unknown strength from a burette divided into-
-±j c.c. into the soda solution in small quantities until exact
saturation occurs.

A second trial should now be made, but preferably with
a different weight of the salt. The saturation is carried out
precisely as at first. The data for ascertaining the exact strength
of the acid solution by calculation are now in hand.

A strictly normal acid should at 16° C. exactly saturate sodic-.
carbonate in the proportion of 100 c.c. to 5 -3 gm.

46 VOLUMETRIC ANALYSIS. § 15.

Suppose that 2'46 gm. sodic carbonate required 41 '5 c.c. of tlie
acid in the first experiment, then

2-46 : 5-3 : : 41'5 : x = 89'4 c.c.

Again: 2*153 gm. sodic carbonate required 36*32 c.c. of acid,
then

2-153 : 5-3 : : 36'32 : x = S9'4 c.c.

The acid may now be adjusted by measuring 890 c.c. into the
graduated liter cylinder, adding 4 c.c. from the burette, or
with a small pipette, and filling to the liter mark with distilled
water.

Finally, the strength of the acid so prepared must be proved by
taking a fresh quantity of sodic carbonate, or by titratioii with a
•strictly normal sodic carbonate solution previously made, and using
not less than 50 c.c. for the tit-ration, so as to avoid as much
as possible the personal errors of measurement in small quantities.
If the measuring instruments all agree, and the operations are
.all conducted with due care, a drop or two in excess of either
acid or alkali in 50 c.c. should suffice to reverse the colour of
the indicator.

In all alkalimetric titrations it must not be forgotten that some
glass vessels yield a notable quantity of alkali to boiling water,.
and even more to hot alkaline solutions. The use of vessels made
•of Jena glass is therefore preferable.

1. Normal Sodic Carbonate.
53 gm. !STa2C03 per liter..

This solution is made by quickly weighing and dissolving
•53 gm. of pure sodic monocarboiiate, previously gently ignited and
cooled under the exsiccator in hot distilled water, and when cooled
diluting to 1 liter at 16° C. Absolutely pure sodic carbonate is
-difficult to find in commerce, and even if otherwise pure, is
generally contaminated with insoluble dust contracted in the
process of drying ; very pure bicarbonate is not difficult to find,
but its purity must be proved, the usual impurities are traces of
chlorides, sulphates, and occasionally thiosulphate or sulphite.

To obtain a salt which shall be suitable for a standard, the best
white bicarbonate should be selected, and 20 or 30 grams
dissolved in about half a liter of hot water. If the solution is
free from any sediment or floating particles, a portion is acidified
with pure nitric acid in a small beaker and tested with silver
nitrate for chlorine, another portion for sulphate with baric
chloride ; if either of these are found the salt is freed from them
by packing, say half a pound, into a clean funnel, the neck of
which is stopped with a plug of cotton wool. Cold distilled water
free from any trace of chloride or sulphate is then poured on the
.salt in repeated small quantities, and allowed to filter through
until the testing shows the absence of these impurities. Of

§ 15. NORMAL SOLUTIONS. 47

course this means a waste of some bicarbonate, but as the salt is
not very soluble in cold water it is of no consequence. When
the impurities are found to be removed, the funnel is allowed to
drain completely, the contents spread out on a clean flat dish or
plate, tied over loosely with porous paper, and placed on the water
bath or in some other warm position to dry, finally put into
a stoppered bottle for conversion into monocarbonate as required.

If on the other hand the sample has not dissolved quite clear,
another method must be adopted by making a saturated solution
of the salt in boiling distilled water, filtering at once through
paper in a heated funnel into a clean porcelain dish and keeping
the solution stirred until quite cold ; by this means a pure salt
deposits in a granular state which, after pouring off the superfluous
liquid, may be dried and kept for "use as before described. In
using this salt for the standard the procedure is as follows : —

About 85 gm. is heated to dull redness (not to fusion) in a
platinum crucible, for fully ten minutes, stirring it occasionally
with a platinum wire, then placed under an exsiccator to cool ;
when placed upon the balance it will be found that very little
more than 53 gm. remains. The excess is removed as quickly as
possible, and the contents of the crucible washed into a beaker
with hot distilled water; when the salt is dissolved the solution is
cooled to a proper temperature, decanted into a liter flask and
filled up to the mark with distilled water at 16° C. If cold
water is used a hard cake is produced which dissolves very slowly.

2. Normal Potassic Carbonate.

69 gm. K2C03 per liter.

This solution is sometimes, though rarely, preferable to the soda
salt, and is of service for the estimation of combined acids in certain
cases, where, by boiling the compound with this agent, an inter-
change of acid and base occurs.

It cannot be prepared by direct weighing of the potassic carbonate,
and is therefore best established by titrating a solution of unknown
strength with strictly normal acid.

3. Normal Sulphuric Acid.
49 grn. H2S04 per liter.

About 30 c.c. of pure sulphuric acid of sp. gr. 1'840, or there-
abouts, are mixed with three or four times the volume of distilled
water and allowed to cool, then put into the graduated cylinder and
diluted up to the liter at the proper temperature. The solution
may now be titrated by strictly normal alkali, or with sodic
carbonate.

25 c.c. of the solution, diluted to 250 c.c., may be con-
trolled by precipitation with baric chloride at a boiling heat,
in which case 100 c.c. should produce as much baric sulphate as is
•equal to 49 gm. per liter.

48 VOLUMETRIC ANALYSIS. § 15.

In using this control it is best to make two determinations, and
preferably with different quantities of the acid, the mean is then
taken for basis of calculation.

4. Normal Oxalic Acid.
63 gm. C204H2,2H20, or 45 gm. C204H2 per liter.

This solution cannot very well be established by direct weighing,
owing to uncertain hydration ; hence it must be titrated by normal
alkali of known accuracy.

The solution is apt to deposit some of the acid at low tempera-
tures, but keeps well if preserved from direct sunlight, and will
bear heating without volatilizing the acid. Very dilute solutions
of oxalic acid are very unstable ; therefore, if a decinormal or
centinorrnal solution is at any time required, it should be made
when wanted.

5. Normal Hydrochloric Acid.

36-37 gm. HC1 per liter.

It has been shown by Roscoe and Dittmar (J. C. S. xii. 128,
1860) that a solution of hydrochloric acid containing 20'2 per cent,
of the gas when boiled at about 760 m.m. pressure, loses acid and
water in the same proportion, and the residue will therefore
have the constant composition of 20 "2 per cent., or a specific
gravity of 1-10. About 181 gm. of acid of this gravity, diluted
to one liter, serves very well to form an approximate normal
acid.

The actual strength may be determined by precipitation with
"silver nitrate, or by titration with an exactly weighed quantity of
pure sodic monocarbonate. Hydrochloric acid is useful on account
of its forming soluble compounds with the alkaline earths, but it has
the disadvantage of volatilizing at a boiling heat. Dittmar says
that this may be prevented by adding a few grains of sodic sulphate.
In many cases this would be inadmissible, for the same reason that
sulphuric acid cannot be used. The hydrochloric acid from which
standard solutions are made must be free from chlorine gas or
metallic chlorides, and should leave no residue when evaporated in
a platinum vessel.

6. Normal Nitric Acid.
63 gm. H2xT03 per liter.

A rigidly exact normal acid should be established by sodic
carbonate, as in the case of normal sulphuric and hydrochloric acids.

The nitric acid used should be colourless, free from chlorine
and nitrous acid, sp. gr. about T3. If coloured from the
presence of nitrous or hyponitrous acids, it should be mixed with
two volumes of water, and boiled until white. When cold it may
be diluted and titrated as previously described for sulphuric acid.

§15. NORMAL SOLUTIONS. 49

7. Normal Caustic Soda or Potash.
40 gin. NallO or 56 gm. KHO per liter.

Pure caustic soda made from metallic sodium may now be readily
obtained in commerce, and hence it is easy to prepare a standard
solution of exceeding purity, by simply dissolving the substance in
distilled water till of about 1*05 sp. gr., or about 50 gm. to the
liter, roughly estimating its strength by normal acid and methyl
orange or litmus, then finally adjusting the exact strength by
titrating 50 c.c. with normal acid.

However pure caustic soda or potash may otherwise be, they are
both in danger of absorbing carbonic acid, and hence in using
litmus the titration must be conducted with boiling. Methyl
orange permits the use of these solutions at ordinary temperature
notwithstanding the presence of CO2.

Soda and potash may both be obtained in commerce sufficiently
pure for all ordinary titration purposes, but in case they are not at
hand the requisite solutions may be prepared as follows : —

Two parts of pure sodic or potassic carbonate are to be dissolved
in twenty parts of distilled water, and boiled in a clean iron pot ;
during the boiling, one part of fresh quick-lime, made into a cream
with water, is to be added little by little, and the whole boiled until
all the carbonic acid is removed, which may be known by the clear
solution producing no effervescence on the addition of dilute acid ;
the vessel is covered closely and set aside to cool and settle ; when
cold, the clear supernatant liquid should be poured or drawn off
and titrated by normal acid, and made of the proper strength
as directed for sulphuric acid.

Soda or potash solutions may be freed from traces of chlorine,
.sulphuric, silicic, and carbonic acids, by shaking with Mi lion's
base, trimercur-ammonium (C. N. xlii. 8). Carbonic acid may be
removed by the cautious addition of baric hydrate in solution,
shaking well, and then after settling clear ascertaining the exact
strength with correct standard acid.

In preparing these alkaline solutions, they should be exposed as
little as possible to the air, and when the strength is finally settled,
should be preserved in the bottle shown in fig. 24, or in full bottles
having their glass stoppers slightly greased with vaseline.

8. Semi-normal Ammonia.
8-5 gm. NH:3 per liter.

For some years past I have used this strength of standard
ammonia for saturation analyses, and have been fully satisfied with
its behaviour ; it is cleanly, does not readily absorb carbonic acid,
holds its strength well for two or three months when kept in a cool
place and well stoppered ; and can at any time be prepared in a few

50 VOLUMETKIC ANALYSIS. § 15.

minutes, by simply diluting strong solution of ammonia with fresh
distilled water.

A normal solution cannot be used with safety, owing to evapora-
tion of the gas at ordinary temperatures.

It is necessary to add that, even in the case of ~ strength,
the solution should be titrated from time to time against correct
normal acid. —^ ammonia keeps its strength for a long time
in well-closed bottles.

9. Decinormal Caustic Baryta.

The solution of caustic baryta is best made from the crystallized
hydrate, approximately of ~ strength. This is best done by
shaking up in a stoppered bottle powdered crystals of baric
hydrate with distilled water, and allowing it to stand a day or
two until quite clear ; there should be an excess of the hydrate,
in which case the clear solution, when poured off into a stock
bottle fitted with CO2 tube, will be nearly twice the required
strength. It is better to dilute still further (after taking its
approximate titre with £§ HC1 and phenolphthalein) with freshly
boiled and cooled distilled water ; the actual working strength
may be checked by evaporating 20 or 25 c.c. to dryness with
a slight excess of sulphuric acid, then igniting over a Bun sen
flame and weighing the BaSO4. The corresponding acid may be
either ^ oxalic, nitric, or hydrochloric, and the proper indicator
is phenolphthalein. Oxalic acid is recommended byPettenkofer
for carbonic acid estimation, because it has no effect upon the
baric carbonate suspended in weak solutions; but there is the
serious drawback in oxalic acid, that in dilute solution it is liable
to rapid decomposition ; and as in my experience ~ hydrochloric
acid in very dilute mixtures has no effect upon the suspended
baric carbonate, it is preferable to use this acid.

The baryta solution is subject to constant change by absorption
of carbonic acid, but this may be prevented to a great extent by
preserving it in the bottle shown in fig. 24. A thin layer of light
petroleum oil on the surface of the liquid preserves the baryta at
one strength for a long period in the bottle shown in fig. 25.

The reaction between baryta and yellow turmeric paper is very
delicate, so that the merest trace of baryta in excess gives a decided
brown tinge to the edge of the spot made by a glass rod on the
turmeric paper. If the substance to be titrated is not too highly
coloured, phenolphthalein should invariably be used.

10. Normal Ammonio-Cupric Solution for Acetic Acid and free
Acids and Bases in Earthy and Metallic Solutions.

This acidimetric solution is prepared by dissolving pure cupric
sulphate in warm water, and adding to the clear solution liquid
ammonia, until the bluish-green precipitate which first appears is-

§ 16. NORMAL SOLUTIONS. 51

nearly dissolved ; the solution is then filtered into the graduated
cylinder, and titrated by allowing it to flow from a pipette graduated
in i or y1^- c.c. into 10 or 20 c.c. of normal sulphuric or nitric acid
(not oxalic). While the acid remains in excess, the bluish-green
precipitate which occurs as the drop falls into the acid rapidly
disappears ; but so soon as the exact point of saturation occurs, the
previously clear solution is rendered turbid by the precipitate
remaining insoluble in the neutral liquid.

The process is especially serviceable for the estimation of the free
acid existing in certain metallic solutions, i.e. mother-liquors, etc.,
where the neutral compounds of such metals have an acid reaction
on litmus — such as the oxides of zinc, copper, and magnesia, and
the protoxides of iron, manganese, cobalt, and nickel; it is also
applicable to acetic and the mineral acids.

If cupric nitrate be used for preparing the solution instead of
sulphate, the presence of barium, or strontium, or metals precipitable
by sulphuric acid is of no consequence. The solution is stand-
ardized by normal nitric or sulphuric acid ; and as it slightly alters
by keeping, a coefficient must be found from time to time by
titrating with normal acid, by which to calculate the results
systematically. Oxides or carbonates of magnesia, zinc, or other
admissible metals, are dissolved in excess of normal nitric acid,
and titrated residually with the copper solution.

Example : 1 gra. of pure zinc oxide was dissolved in 27 c.c. of normal
acid, and 2'3 c.c. of normal copper solution required to produce the
precipitate ==24*7 c.c. of acid; this multiplied by 0'0405, the coefficient
i'or zinc oxide, - I'OOO gm. '

ESTIMATION OF THE CORRECT STRENGTH OF STANDARD
SOLUTIONS NOT STRICTLY NORMAL OR SYSTEMATIC.

§ 16. IN discussing the preparation of the foregoing standard
solutions, it has been assumed that they shall be strictly and
absolutely correct; that is to say, if the same measure be filled
first with any alkaline solution, then with an acid solution, and the
two mixed together, a perfectly neutral solution shall result, so that
a drop or two either way will upset the equilibrium.

Where it is possible to weigh directly a pure dry substance, this
approximation may be very closely reached. Sodic monocarbonate,
for instance, admits of being thus accurately weighed. On the
other hand, the caustic alkalies cannot be so weighed, nor can
the liquid acids.- An approximate quantity, therefore, of these
substances must be taken, and the exact power of the solution
found by experiment. »

In titrating such solutions it is exceedingly difficult to make them
so exact in strength, that the precise quantity, to a drop or two,
shall neutralize each other. In technical matters a near approxima-
tion may be sufficient, but in scientific investigations it is of the
greatest importance that the utmost accuracy should be obtained ;

E 2

52 VOLUMETRIC ANALYSIS. § 16.

it is therefore advisable to ascertain the actual difference, and to
mark it upon the vessels in which the solutions are kept, so that
a slight calculation will give the exact result.

Suppose, for instance, that a standard sulphuric acid is prepared,
which does not rigidly agree with the normal sodic carbonate (not
at all an uncommon occurrence, as it is exceedingly difficult to hit
the precise point) ; in order to find out the exact difference it must
be carefully titrated as in § 15. Suppose the weight of sodic
carbonate to be 1*9 gm., it is then dissolved and titrated with the
standard acid, of which 36*1 c.c, are required to reach the exact
neutral point.

If the acid were rigidly exact it should require 35 '85 c.c. ; in
order, therefore, to find the factor necessary to bring the quantity
of acid used in the analysis to an equivalent quantity of normal
strength, the number of c.c. actually used must be taken as the
denominator, and the number which should have been used, had
the acid been strictly normal, as the numerator, thus —

35'8-5-0-99V
36-1 '

Q'993 is therefore the factor by which it is necessary to multiply
the number of c.c. of that particular acid used in any analysis
in order to reduce it to normal strength, and should be marked
upon the bottle in which it is kept.

On the other hand, suppose that the acid is too strong, and that
35 '2 c.c. were required instead of 35*85,

1-0184 is therefore the factor by which it is necessary to multiply
the number of c.c. of that particular acid in order to bring it to
the normal strength., This plan is much better than dodging about
with additions of water or acid.

Under all circumstances it is safer to prove the strength of any
standard solution by experiment, even though its constituent has
been accurately weighed in the dry and pure state.

Further, let us suppose that a solution of caustic soda is to be.
made by means of lime as described previously. After pouring off
the clear liquid, water is added to the sediment to extract more
alkaline solution ; by this means we may obtain two solutions, one
of which is stronger than necessary, and the other weaker. Instead,
of mixing them in various proportions and repeatedly trying the
strength, we may find, by two experiments and a calculation,
the proportions of each necessary to give a normal solution, thus : —

The exact actual strength of each solution is first found, by
separately running into 10 c.c. of normal acid as much of each
alkaline solution as will exactly neutralize it. We have, then, in
the case of the stronger solution, a number of c.c. required less
than 10. Let us call this number V.

§ 16. NORMAL SOLUTIONS. 53

In the weaker solution the number of c.c. is greater than 10,
represented by v. A volume of the stronger solution — x will
saturate 10 c.c. of normal acid as often as V is contained in x.

A volume of the weaker solution = y will, in like manner, saturate

10 y 10 x 10 ?/,

— - — c.c. ot normal acid; both together saturate y -\ -- — •

and the volume of the saturated acid is precisely that of the two
liquids, thus- 1() x 1Q

-I

mence

= x

1Q>* + 10 Vy = ¥*.* + Vp y

v x (10 - Y) = V y (v - 10).

And lastly, ,r / , m

x_ _ V (v + 10)

~y ~ v (10 - V)"

An example will render this clear. A solution of caustic soda
was taken, of which 5*8 c.c. were required to saturate 10 c.c. normal
acid; of another solution, 12*7 c.c. were required. The volumes of
each necessary to form a normal solution were found as follows : —

5-8 (12-7 -10) = 15-66
12-7 (10 -5-8) = 53-34

Therefore, if the solutions are mixed in the proportion of 15'66
c.c. of the stronger with 53 '34 c.c. of the weaker, a correct solution
ought to result. The same principle of adjustment is, of course,
applicable to standard solutions of every class.

Again: suppose that a standard solution of sulphuric acid has
been made, approximating as nearly as possible to the normal
strength, and its exact value found by precipitation with baric
chloride, or a standard hydrochloric acid with silver nitrate, and
such a solution has been calculated to require the coefficient 0*995
to convert it to normal strength, — by the help of this solution,
though not strictly normal, we may titrate an approximately normal
alkaline solution thus : — Two trials of the acid and alkaline solu-
tions show that 50 c.c. alkali =48'5 c.c. acid, having a coefficient
of 0'995 = 48'25 c.c. normal ; then, according to the equation,
x 50 := 48'25 is the required coefficient for the alkali.

= 0-965.

And here, in the case of the alkaline solution being sodic carbonate,
we can bring it to exact normal strength by a calculation based on
the equivalent weight of the salt, thus —

1 : 0-965 : : 53 : 5M45.

The difference between the two latter numbers is 1'855 gm., and
this weight of pure sodic carbonate, added to one liter of the
solution, will bring it to normal strength.

VOLUMETRIC ANALYSIS.

TABLE FOR THE SYSTEMATIC ANALYSIS OF ALKALIES,
ALKALINE EARTHS AND ACIDS.

Substance.

Formula.

Atomic
Weight. -

Quantity to be
weighed so that 1
c.c. Normal Solu-
tion=l per cent,
of substance.

Normal
Factor.*

Soda

Na2O

3'1 gm.

0-031

Sodic H}Tdrate . .

NaHO

4-0 gm.

0-040

Sodic Carbonate . .

Na2C03

106

5'3 gm.

0-053

Sodic Bicarbonate

NaHCO3

8'4 gm.

0-084

Potash

K2O

4' 7 gm.

0-047

Potassic Hydrate . .

KHO

5'6 gm.

0-056

Potassic Carbonate .

K-CO3

138

6'9 gm.

0-069

Potassic Bicarbonate

KHCO3

100

lO'O gm.

O'lOO

Ammonia ....

NH3

1:7 gm.

0-017

Ainmonic Carbonate

(NH4)2CO3

4'8 gm.

0-048

Lime (Calcic Oxide) .

CaO

2-8 gm.

0-028

Calcic Hydrate . .

CaH202

3'7 gm.

0-037

Calcic Carbonate . .

CaCO3

100

5'0 gm.

O'OoO

Baric Hvdrate . .

BaH2O2

171

8'55 gm.

0'0855

Do. (Crystals) . .

BaO2H2(H20)s

315

1575 gm.

0-1575

Baric Carbonate . .

BaCO3

197

9-85 gm.

0-0985

Strontia

SrO

103'5

5*175 gm.

0-05175

Strontic Carbonate .

SrCO3

147'5

7-375 gm.

0-07375 '

Magnesia ....

MgO

2'00 gm.

0-020

Magnesic Carbonate.

MgCO3

4'20 gm.

0-042

Nitric Acid. . . .

HNO3

6'3 gm.

0-063

Hydrochloric Acid .

HC1

36-37

3'637 gm.

0-03637

Sulphuric Acid . .

H2SO4

4'9 gm.

0-049

Oxalic Acid . . .

C2O4H2(H2O)2

126

6'3 gm.

0-063

Acetic Acid . . - .

C2O2H4

6'0 gm.

0-060

Tartaric Acid . . .

C40GHr,

150

7-5 gin.

0075

Citric Acid ....

C°0'HS + H20

210

7-0 gm.

0-070

Carbonic Acid . . .

CO2

0'022

* This is the coefficient by which the number of c.c. of normal solution used in
any analysis is to be multiplied, in order to obtain the amount of pure substance
present in the material examined.

If grain weights are used instead of grams, the decimal point must be moved
one place to the right to give the necessary weight for examination; thus sodic
carbonate, instead of 5'3 gm., would be 53 grains, the normal factor in this case would
also be altered to 0'53.

§ 17. ALKALINE SALTS. 55

THE TITRATION OF ALKALINE SALTS.
1. Total Alkali in Caustic Soda or Potash, or their Carbonates.

§ 17. THE necessary quantity of substance being weighed or
measured, as the case may be, and mixed with distilled water to a
proper state of dilution (say about one per cent, of solid material),
an appropriate indicator is added, and the solution is ready for the
burette. Xormal acid is then cautiously added from a burette
till the change of colour occur. In the case of caustic alkalies
free from CO2, the end-reaction is very sharp with any of the
indicators ; but if CO'2 is present, the only available indicators in
the cold are methyl orange or lacmoid paper. If the other indica-
tors are used, the CO2 must be boiled off after each addition of acid.

In examining carbonates of potash or soda, or mixtures of caustic
and carbonate, where it is only necessary to ascertain the total
alkalinity, the same method applies.

In the examinations of samples of commercial refined soda or
potash salts, it is advisable to proceed as follows : —

Powder and mix the sample thoroughly, weigh 10 gm. in a platinum or
porcelain crucible, and ignite gently over a spirit or gas lamp, and allow the
crucible -to cool under the exsiccator. Weigh again, the loss of weight gives
the moisture ; wash the contents of the crucible into a beaker, dissolve and
filter if necessary, and dilute to the exact measure of 500 c.c. with distilled
water in a half-liter flask ; after mixing it thoroughly take out 50 c.c. — 1 gm.
of alkali with a pipette, and empty it into a small flask, bring the flask under
a burette containing normal acid and graduated to i or TV c.c., allow the acid
to flow cautiously as before directed, until the neutral point is reached : the
process may then be repeated several times if necessary, in order to be certain
of the correctness of the analysis.

Residual Titration : As the presence of carbonic acid with litmus and the
other indicators, except methyl orange, always tends to confuse the exact end
of the process, the difficulty is best overcome, in the case of not using methyl
orange, by allowing an excess of acid to flow into the alkali, boiling to expel
the CO2, and then cautiously adding normal caustic alkali, drop by drop,
until the liquid suddenly changes colour; by deducting the quantity of
caustic alkali from the quantity of acid originally used, the exact volume of
acid necessary to saturate the 1 gm. of alkali is ascertained.

This method of re-titration gives a very sharp end-reaction, as
there is 110 carbonic acid present to interfere with the delicacy of
the indicator. It is a procedure sometimes necessary in other cases,
owing to the interference of impurities dissipated by boiling, e.g.
sulphuretted hydrogen, which would otherwise bleach the indicator,
except in the case of methyl orange and lacmoid paper, either of
which are indifferent to H2S in the cold. An example will make
the plan clear : — -

Example : 50 c.c. of the solution of alkali prepared as directed, equal to
1 gm. of the sample, is put into a flask, and 20 c.c. of normal acid allowed to
flow into it ; it is then boiled and shaken till all CO2 is expelled, and normal
caustic alkali added till the neutral point is reached ; the quantity required
is 3'4 c.cv which deducted from 20 c.c, of acid leaves 16'6 c.c. The following

56 VOLUMETKIC ANALYSIS. § IT.

calculation, therefore, gives the percentage of real alkali, supposing it to
be soda : — 31 is the half molecular weight of anhydrous soda (Na-O) and 1 c.c.
of the acid is equal to 0'031 gm., therefore 16'6 c.c. is multiplied by 0'031,
which gives 0 5146 ; and as 1 gm. was taken, the decimal point is moved
two places to the right, which gives 5T46 per cent, of real alkali ; if calculated
as carbonate, the 16'6 would be multiplied by 0'053, which gives 0'8798 gm.
= 87'98 per cent.

2. Mixed Caustic and Carbonated Alkaline Salts.

The alkaline salts of commerce, and also alkaline lyes used in
soap, paper, starch, and other manufactories, consist often of a
mixture of caustic and carbonated alkali. If it be desired to
ascertain the proportion in which these mixtures occur, the total
alkaline power of a weighed or measured quantity of substance (not
exceeding 1 or 2 gm.) is ascertained by normal acid and noted; a
like quantity is then dissolved in about 150 c.c. of water in a
200 c.c. flask, and exactly enough solution of baric chloride added
to remove all carbonic acid from the soda or potash.

Watson Smith has shown (J. S. C. I. i. 85) that whenever an
excess of baric chloride is used in this precipitation so as to form
baric hydrate, there is an invariable loss of soda : exact precipita-
tion is the only way to secure accuracy.

The flask is now filled up to the 200 c.c. mark with distilled
water, securely stoppered, and put aside to settle. When the
supernatant liquid is clear, take out 50 c.c. with a pipette, and
titrate with normal hydrochloric acid to the neutral point. The
number of c.c. multiplied by 4 will be the quantity of acid required
for the caustic alkali in the original weight of substance, because
only one-fourth was taken for analysis. The difference is calculated
as carbonate, or the precipitated baric carbonate may be thrown
upon a dry filter, washed well and quickly with boiling water, and
titrated with normal acid, instead of the original analysis for the
total alkalinity ; or both plans may be adopted as a check upon
each other.

^--iThe principle of this method is, that when baric chloride is added
to a mixture of caustic and carbonated alkali, the carbonic acid of
the latter is precipitated as an equivalent of baric carbonate, while
the equivalent proportion of caustic alkali remains in solution as
baric hydrate. By multiplying the number of c.c. of acid required
to saturate this free alkali with the y^Vo atomic weight of caustic
potash or soda, according to the alkali present, the quantity of
substance originally present in this state will be ascertained.

As caustic baryta absorbs CO2 very readily when exposed to the
atmosphere, it is preferable to allow the precipitate of baric
carbonate to settle in the flask as here described, rather than to
filter the solution as recommended by some operators, especially
also as the filter obstinately retains some baric hydrate.

A very slight error, however, occurs in all such cases, in

§ 17. ALKALINE SALTS. 57

consequence of the volume of the precipitate being included in
the measured liquid.

K. Williams (/. S. C. I. vi. 346) estimates the caustic soda in.
soda ash by digesting a weighed quantity in strong alcohol in a
tightly stoppered flask with frequent shaking and finally allowing
to stand overnight ; the undissolved carbonate is filtered off,
washed with alcohol until a drop gives no alkaline reaction —
the nitrate and washings are then titrated with normal acid and
phenolphthalein.

Peter Hart recommends the following technical method of
ascertaining the relative proportions of caustic and carbonated
soda in sola ash : — 50 grains of the sample are dissolved in
10 ounces of water, phenolphthalein added, and the standard
acid (1 dm. - 0'5 grn. Na20) slowly run in until the colour-
disappears. At this point all the caustic soda and one-naif the
carbonate has been neutralized, say 30 dm. has been used. To
the same solution (in which the soda now exists as bicarbonate)
methyl orange is added, and the titration continued until pink ;
the burette now reads 50 dm. Then 50 - 30 = 20 as NaHCO",
but as this originally existed in the sample as Na2CO:), this figure
must be doubled = 40, which deducted from 50 leaves 10 dm. as
representing the caustic soda in the sample.

3. Estimation of Hydrates of Soda or PotasB. with small
proportions of Carbonate.

This may be accomplished by means of phenacetolin (Lunge,
/. & C. I. i. 56). The alkaline solution is coloured a scarcely
perceptible yellow with a few drops of the indicator. The standard
acid is then run in until the yellow gives place to a pale rose
tint; at this point all the caustic alkali is saturated, and the
volume of acid used is noted. Further addition of acid now
intensifies this red colour until the carbonate is decomposed, when
a clear golden yellow results. The neutralization of the NaHO or
the KHO is indicated by a rose tint permanent on standing ; that
of Xa2C03 or K2C03 by the sudden passage from red to yellow.

Practice is required with solutions of known composition to
accustom the eye to the changes of colour. Phenolphthalein may
also be employed for the same purpose as follows : —

Add normal acid to the cold alkaline solution till the red colour
is discharged, taking care to use a very dilute solution, and keeping
the spit of the burette in the liquid so that no CO2 escapes. The
point at which the colour is discharged occurs when all the hydrate
is neutralized and the carbonate converted into bicarbonate ; the
volume of acid is noted, and the solution heated to boiling, with
small additions of acid, till the red colour produced by the decom-
position of the bicarbonate is finally destroyed.

In both these methods it is preferable, after the first stage, to

E8E LIB,

OF THE

UNIVERSITY,

. m OF

58 VOLUMETRIC ANALYSIS. § 17.

add excess of acid, boil off the CO2, and titrate back with normal
alkali. The results are quite as accurate as the method of precipi-
tation with barium.

4. Estimation of Alkaline Bicarbonates in presence of
Normal Carbonates (Lring-e, J. S. C. I. i. 57).

To a weighed quantity of the solid bicarbonate, or a measured
quantity of a solution, there is added an excess of J ammonia,
followed by an excess of solution of baric chloride. The mixture
is made in a measuring flask, and the whole diluted with hot
distilled water to the mark.

A portion of the clear settled liquid, or filtered through a dry
filter, is then titrated with normal acid : the alkaline strength due
to the excess of ammonia, above that required to convert the bicar-
bonate into normal carbonate, deducted from the total ammonia
added, gives the equivalent of the bicarbonate present.

Example (Lunge) : 20 gm. sodic bicarbonate in the course of manufac-
ture were dissolved to a liter. 50 c.c. of this solution required 12' 1 c.c.
normal acid=0'3751 gm. Na2O ; 50 c.c. were then mixed with 50 c.c. of
standard ammonia (50 ' c.c. =24'3 normal acid) and the whole treated with
excess of baric chloride. One half of the clear liquid required 6'25 c.c.
of normal acid, 24'3 — (6'25 x 2) = 11'8 c.c. : this is, therefore, the equivalent
of the CO2 as bicarbonate.

' XaHCO3 : 11-8 x -084= '9912 gm.
Xa-CO3 : (12-1— 11-8) x "053= "0159.

A simpler plan than the above has been devised by Thomson,
which gives good results when carefully carried out.

To the cold solution of the sample, an excess of normal caustic
soda, free from CO2, is added, the CO2 is then precipitated with
neutral solution of baric chloride, and the excess of sodic hydrate
found by standard acid, using phenolphthalein as indicator. The
precipitate of baric carbonate has no effect on the indicator in the
cold. The calculation is the same as before.

5. Estimation of small quantities of Sodic or Potassic
Hydrates in presence of Carbonates.

This method, by Thomson, has just been alluded to, and
consists in precipitating the carbonates by neutral solution of baric
chloride in the cold : the baric carbonate being neutral to phenol-
phthalein, this indicator can be used for the process. When the
barium solution is added, a double decomposition occurs, resulting
in an equivalent quantity of sodic or potassic chloride, while the
baric carbonate is precipitated, and the alkaline hydrate remains in
solution.

Example (Thomson): 2 gm. of pure sodic carbonate were mixed in
solution with '02 gm. of sodic hydrate; excess of baric chloride was then

§17. ALKALINE SALTS.

which in three trials an average of 5 c.c. was required ; therefore,
5 x '004 = '02 gm. exactly the quantity used.

In this process the presence of chlorides, sulphates, and sulphites
does not interfere ; neither do phosphates, as baric phosphate is
neutral to the indicator. With sulphides, half of the base will be
estimated ; but if hydrogen peroxide be added, and the mixture
allowed to rest for a time, the sulphides are oxidized to sulphates,
Avhich have no effect. If silicates or aluminates of alkali are
present, the base will of course be recorded as hydrate.

Thomson further says : —

"The foregoing method can also be applied to the determination
of hydrate of sodium or potassium in various other compounds,
which give precipitates with baric chloride neutral to phenolph-
thalein, such as the normal sulphites and phosphates of the alkali
metals. An illustration of the use to which the facts I have
stated in this and former papers may be put will be found in the
analysis of sulphite of sodium. Of course sulphate, thiosulphate,
and chloride are determined as usual, but to estimate sulphite,
carbonate and hydrate, or bicarbonate of sodium by methods in
ordinary use is rather a tedious operation. To find the proportion
of hydrate, all that is necessary is to precipitate with baric chloride
and titrate with standard acid, as above described. Then, by
simple titration of another portion of the sample in the cold, using
phenolphthalein as indicator, the hydrate and half of the carbonate
can be found, and finally, by employment of methyl orange as
indicator, and further addition of acid, the other half of the
carbonate and half of the sulphite can- be estimated. By simple
calculations, the respective proportions of these three compounds
can be obtained, a result which can be accomplished in a few
minutes. It must be borne in mind that if a large quantity of
sodic carbonate is in the sample the proportion of that compound
found will only be an approximation to the truth, as the
end-reaction is only delicate with small proportions of sodic
carbonate. If there is no hydrate found, bicarbonate of sodium
can be tested for, and determined by Lunge's method described
above" (§ 17.4).

6. Estimation of Alkalies in the presence of Sulphites.

It is not possible to estimate the alkaline compounds in the
presence of sulphites by titration with acids, as a certain' quantity
of acid is taken up by the sulphite, SO2 being evolved. This
difficulty may be completely overcome by the aid of hydrogen
peroxide, which speedily converts the sulphites into sulphates
(Grant and Cohen, J. & C. I. ix. 19). These operators proved
that neither caustic or carbonate alkali were affected by H202, nor
had the latter any prejudicial effect on methyl orange in the cold.

60 VOLUMETRIC ANALYSIS. § 17.

The quantity of H202 required in any given analysis must depend
on the amount of sulphite present ; for instance, the caustic
salts of commerce contain about 50 % of sulphite, and it suffices
to take 10 o.c. of ordinary 10 vol. H202 for every O'l gm. of the
salts in solution. In the case of mixtures containing less or more
sulphite the quantity may be varied.

The Analysis : A measured volume of the peroxide is run into a beaker,
and three or four drops of methyl orange added. As the H-O- is invariably
faintly acid, the acidity is carefully corrected by adding- drop by drop from a
pipette T£T caustic soda. The required quantity of salt to be analyzed is
then added in solution, and the mixture gently boiled, during the boiling the
methyl orange will be bleached. The liquid is then cooled, a drop or two
more of methyl orange added, and the titration for the proportion of alkali
carried out with normal acid in the usual way. The results are very
satisfactory.

7. Estimation of Caustic Soda, or Potach by standard
Bichromate of Potash.

This process was devised by Richter, or rather the inverse of
it, for estimating bichromate with caustic alkali by the aid of
phenolphthalein. Exact results may be obtained by it in titrating
soda or potash as hydrates, but not ammonia as recommended
by Richter.

For the process there are required a decinormal solution of bichromate con-
taining 1474 gm. per liter, and ^ soda or potash solution titrated against
sulphuric acid. A comparison liquid containing about 1 gm. of monochro-
mate of potash in 150 — 200 c.c. water is advisable for ascertaining the exact
end of the reaction ; 50 c.c. of the alkali being diluted with the same volume
of water, is coloured with phenolphthalein, and the bichromate run in from
a burette ; the fine red tint changes to reddish yellow, which remains till
the neutral point is nearly reached, when the yellow colour of the mono-
chromate is produced; the change is not instantaneous as with mineral acids,
so that a little time must be allowed for the true colour to declare itself.

8. Estimation of Potash in Neutral Salts free from Soda.

Stolba precipitates the potash from a tolerably concentrated solution of
the substances with hydrofluosilicic acid and strong alcohol. The method is
also applicable to the estimation of potash in potassic platinum chloride. To
ensure complete decomposition, it is well to warm the mixture for a little
time before adding the alcohol, which must be of about the same volume as
the liquid itself. After some hours, when the precipitate has settled, the
solution is filtered off, the beaker and precipitate well washed with equal
mixtures of alcohol and water, the whole transferred to a white porcelain
basin, water rather freely added, and heated to boiling, a few drops of
litmus added, and normal or semi-normal alkali run in until exact
saturation occurs ; or a known excess of alkali may be added, and the amount
found by residual titration with normal acid. The results are generally
about 1°'0 too low, owing to the difficulty of fully decomposing the pre-
cipitate.

2 eq. alkali = 1 eq. potash.

The process is very limited in its use, and is not applicable when

§17. ALKALINE SALTS. 61

sulphates are present, nor in the presence of any great amount of
free acid. Sulphuric acid may be previously removed by calcic
acetate and alcohol ; other acids by moderate ignition previous to
precipitation. Large proportions of ammonia salts must also be
removed ; and, of course, all other matters precipitable by hydro-
fluosilicic acid, especially soda.

9. Direct estimation of Potash in tb.e presence of Soda.

Fleischer recommends the following method; and my own
experiments confirm his statements, so far at least as the pure salts
are concerned.

The solution must contain no other bases except the alkalies, nor any acids
except nitric, hydrochloric, or acetic. This can almost invariably be easily
accomplished. Earthy alkalies are removed by ammonic carbonate or
phosphate ; sulphuric, chromic, phosphoric, and arsenic acids by baric
chloride, followed by ammonic carbonate.

The solution should be tolerably concentrated, and the volume about 25 or
30 c.c. ; 10—15 c.c. of neutral solution of ammonic acetate of sp. gr.
T035 are added ; followed by finely powdered pure tartaric acid in sufficient
quantity to convert the potash into acid tartrate, with an excess to form some
ammonic tartrate, but not enough to decompose the whole. This is the weak
part of the method ; however, as a guide, it is not advisable to add more
than 5 gm. tartaric acid for 10 c.c. of ammonic acetate. If the quantity of
potash is approximately known, it is best to add about one-third more than
is sufficient to convert the whole into acid tartrate.

After adding the tartaric acid the mixture must be well stirred for five or
ten minutes, without rubbing the sides of the beaker; a like volume of 95
per-cent. alcohol is added, and again well stirred. The precipitate contains
the whole of the potash as tartrate, and a portion of ammonium tartrate.
After standing half an hour with occasional stirring, the precipitate is
collected on a porous filter, and repeatedly washed with alcohol and water in
equal parts until clean.

When the washing is finished the precipitate will be entirely free from
soda ; filter and precipitate are transferred to a porcelain basin, treated with
sufficient hot water to dissolve the tartrates, then exactly neutralized with
normal alkali and litmus, and the volume so used noted. A like volume, or
preferably, a larger known volume of normal alkali is now added, and the
mixture boiled to expel all ammonia ; the end may be known by holding
litmus paper in the steam. The excess of normal alkali is now found by
titration with normal acid ; the amount so found must be deducted from that
which was added in excess after the exact titration of the tartrate : the
difference equals the ammonia volatilized. By deducting this difference
from the volume of normal alkali originally required, the volume corre-
sponding to potash is found.

Example : 29'4 c.c. of normal alkali were required in the first instance to
neutralize a given precipitate ; 40 c.c. of the same alkali were then added,
the boiling accomplished, and 22'5 c.c. normal acid used for the excess ; then
40— 22-5 = 17-5 c.c., and again 29'4— I7'5 = ir9, which multiplied by the
factor for KHO = 0'056 gives 0'6664 gm.

The soda in the nitrate may be obtained by evaporation with
hydrochloric acid as sodic chloride, and estimated as in § 42.

62 VOLUMETRIC ANALYSIS. § 17.

10. Mixed Caustic Soda and Potash.

This process depends upon the fact, that potassic bitartrate is
almost insoluble in a solution of sodic bitartrate.

Add to the solution containing1 the mixed salts a standard solution of
tartaric acid till neutral or faintl}7" acid — this produces neutral tartrates
of the alkalies — now add the same volume of standard tartaric acid as before —
they are now acid tartrates, and the potassio bitartrate separates almost
completely, filter off the sodic bitartrate and titrate the filtrate with normal
caustic soda ; the quantity required equals the soda originally in the
mixture— the quantity of tartaric acid required to form bitartrate with the
soda subtracted from the total quantity added to the mixture of the two
alkalies, gives the quantity required to form potassic bitartrate, and thus
the quantity of potash is found.

This process is only applicable for technical purposes.

Mixtures of potash and soda in the form of neutral chlorides are
estimated by J. T. White as follows (C. N. Ivii. 214) :— 20 c.c. of the
solution containing about 0'2 gm. of the mixed salts are placed into
a 100 c.c. flask, and 5 c.c. of a hot saturated solution of ammoiiic bicarbonate
added ; the mixture is cooled, and alcohol added in small quantities, with
shaking, until the measure is made up to 100 c.c. After three or four hours,
10 c.c. of the clear liquid are removed with a pipette, evaporated and ignited,
the residue is moistened with a few drops of ammonic chloride solution
and again ignited; the sodic chloride so obtained is then titrated
with standard silver solution, 1 c.c. of which represents '001 gm. Cl ; this is
calculated to iSaCl and the KC1 found by difference.

11. Potash as Platino-chloride:

111 cases where potash exists in combination as a neutral salt,
such as kainit or kieserit, etc., or as a constituent of minerals,
it has to be first separated as double chloride of potassium and
platinum. The method usually adopted is that of collecting the
double salt upon a tared filter, when the weight of the dry double
salt is obtained, the wreight of potash is ascertained by calculation.

It may, however, be arrived at by volumetric means as follows : —

The potash having been converted into double chloride in the usual way
is dried, collected, and mixed with about double its weight of pure sodic
oxalate, and gently smelted in a platinum crucible ; this operation results in
the production of metallic platinum, chlorides of sodium and potassium,,
with some carbonate of soda. The quantity of potash present is, however,,
solely measured by the chlorine ; in order to arrive at this, the fused mass is
lixiviated with water, filtered, nearly neutralized with acetic acid, and the
chlorine estimated with -£$ silver and chromate, the number of c.c. of silver
required is multiplied by the factor 0'00157, which gives at once the weight
of potash. This factor is used because 1 molecule of double chloride contains
3 atoms chlorine, hence the quantity of ^V silver used is three times as much
as in the case of sodic or potassic chloride.

L. de Koninck (Chem. Zeit. xix. 301) has improved this process
materially by the use of formic; acid as a reducing agent. The
chloroplatinate is filtered and washed in the usual way, dissolved in boiling
water and decomposed by calcic formate free from Cl. The liquid is heated
until the platinum is fully separated and the solution colourless; it is
neutralized with a small quantity of pure calcic carbonate, filtered, washed,
and the chlorine determined by titratiou with •& silver solution and
chromate.

§ 17. ALKALINE COMPOUNDS. 63

12. Separation of the Potash as Bitartrate.

The mixed salts being rendered as nearly neutral as possible, a saturated
solution of sodic bitartrate is added in excess, and the whole evaporated to
dryness in the water bath. The dry mass is then deprived of the excess of
sodic bitartrate by washing it on a filter with a saturated solution of potassic
bitartrate ; when all the soda salt has been removed, the potash salt is
dissolved in hot water, and titrated with normal alkali, of which 1 c.c.
represents 0'039 gm. K. In cases where potash is to be separated as
bitartrate, the operator should consult § 26, 2 and 3.

TECHNICAL EXAMINATION OF SOME ALKALINE

COMPOUNDS FOUND IN COMMERCE OH OCCURRING IN

COURSE OF MANUFACTURE.

There is now considerable unanimity among English and foreign
manufacturers of alkaline compounds, as to methods of analysis to
be adopted either for guidance in manufacture or commercial
valuation. Lunge has contributed important papers on the
subject (/. S. C. I. i. 12, 16, 55, 92), also in conjunction with
Hurter in the Alkali Makers' Pocket Book* which contains
valuable tables and processes of analysis. So far as volumetric-
methods are concerned, the same processes will be given here with
others.

13. Soda Ash, Black Ash, Mother-liquors, etc.

Soda Ash or Refined Alkali.— 5 or 10 gm. are dissolved in about 150 c.c.
of warm distilled water, and any insoluble matter filtered off (German,
chemists do not filter), and the volume diluted to \ or 1 liter.

The total quantity of alkali is determined in 50 c.c. by normal sulphuric,
nitric, or hydrochloric acid, as in § 17. l.f

The quantity of caustic alkali present in any sample is determined as
in § 17. 2 or 5.

The presence of sulphides is ascertained by the smell of sulphuretted
hydrogen when the alkali is saturated with an acid, or by dipping paper,
steeped in sodic nitro-prusside into the solution : if the paper turns blue or
violet, sulphide is present.

The quantity of sulphide and sulphite may be determined by saturating
a dilute solution of the alkali with a slight excess of acetic acid, adding starch
and titrating with /^ iodine solution till the blue colour appears. The
quantity of iodine required is the measure of the sulphuretted hydrogen
and sulphurous acid present.

The proportion of sulphide is estimated as follows : — 13'820 gm. of pure
silver are dissolved in dilute nitric acid, and the solution, together with an
excess of liquid ammonia, made up to a liter. Each c.c.— 0'005 gm. Na2S.

The Analysis : 100 c.c. of the alkali liquor is heated to boiling, some
ammonia added, and the silver solution dropped in from a burette until no
further precipitate of Ag-S is produced. Towards the end filtration will be
necessary, in order to ascertain the exact point, to which end the Be ales
filter is serviceable (fig. 23). The amount of Na2S so found is deducted
from the total sulphide and sulphite found by iodine.

Sodic chloride (common salt) may be determined by carefully neutralizing
1 gin. of the alkali with nitric acid, and titrating 'with deciuormal silver

* Bell & Sons, York Street, Covent Garden.

f This gives a alight error, owing- to traces of aluminat3 of £o;li ani lime, which
consume acid.

<64= VOLUMETRIC ANALYSIS. § 17.

solution and potassic chromate. Each c.o. represents 0'005837 gm. of
common salt. Since the quantity of acid necessary to neutralize the alkali
has already been found, the proper measure of T^ nitric acid may at once
,be added.

Sodic sulphate is determined, either directly or indirectl}% as in § 76.
Each cc. of normal baric chloride is equal to 0*071 gm. of dry sodic
sulphate.

Examination of Crude Soda Lyes and Red Liquors. — K aim aim
andSpiiller (Dingl. polyf. */., 264, 456— 459) recommend a process based
on the insolubility of baric sulphite and the solubility of baric thiosulphate
in alkaline solutions. The estimation is performed in the following
manner: — 1. — The total alkalinity is determined in a measured volume of
'the liquor under examination by titration with normal acid, methyl orange
being used as indicator. The acid consumed equals sodic carbonate 4- sodio
sulphide, + sodic hydroxide, + one-half sodic sulphite (Na2SO3 is alkaline
•and NaHSO3 neutral to methyl orange). 2. — An equal volume of the
liquor is titrated with T\ solution of iodine, the volume consumed corres-
ponding with the sodic sulphide + the sodic sulphite, + the sodic
thiosulphate. 3.— Twice the volume of liquor as that used in (1) and (2)
is precipitated with an alkaline zinc solution, and the mixture made up to
a certain measure, one-half of which is filtered, acidified, and titrated with
yV iodine. The iodine consumed equals sodic sulphite + sodic thiosulphate.
4. — Three or four times the volume of liquor used in (1) and (2) is treated
with an excess of a solution of baric chloride, the mixture made up to
a known volume with water, and filtered, (a) One-third or one-fourth
(as the case may be) of the filtrate is titrated with normal acid, the amount
used corresponding with the sodic hydroxide + the sodic sulphite.
(b) A new third or fourth of the filtrate is acidified and titrated with -^
iodine, the iodine consumed being equal to sodic sulphite + sodic thio-
.sulphate. The calculation is made as follows :—

2 — 4i —A c.c. ^ iodine corresponding to ... Na2SO3

2 — 3 = B c.c. yV iodine corresponding to Na2S

46 — (2 — 3) ... = C c.c. £$ iodine corresponding to Na2S2O3

4a — rVB = D c.c. normal acid corresponding to ... NaOH

1 — (4a +TV A) =E c.c. normal acid corresponding to ... Na'2CO3

Black Ash.— Digest 50 gm. with warm water in a half-liter flask, fill up to
mark, and allow to settle clear.

(1) Total Alkali existing as carbonate, hydrate, and sulphide, is found
by titrating 10 c.c. = l gm. of ash with standard acid and metlryl orange in
Ihe cold.

(2) Caustic Soda. — 20 c.c. of the liquid are put into a 100 c.c. flask with
10 c.c. of solution of baric chloride of 10 per cent, strength, filled up with
hot water, well shaken, and corked after settling a few minutes. The clarified
liquid is filtered, and 50 c.c. = 1 gm. ash, titrated with standard acid and
metlryl orange ; or it may be titrated without filtration if standard oxalic
acid and phenolphthalein are used, this acid having no effect on the baric
carbonate. Each c.c. normal acid = 0'031 Na20. This includes sulphides.

(3) Sodic Sulphide. — Put 10 c.c. of liquor into a flask, acidulate with
acetic acid, dilute to about 200 c.c. and titrate with T^ iodine and starch.
Each c.c. = 0-0039 Na2S, or 0'0031 Na2O.

(4) Sodic Chloride. — 10 c.c. are neutralized exactly with normal nitric
acid, and boiled till all H-S is evaporated. Any sulphur which may have
been precipitated is filtered off, and the filtrate titrated with TN¥ silver and
chromate. Each c.c. =0'00 5837 gm. NaCl.

(5) Sodic Sulphate. — This is best estimated by precipitation as baric
.sulphate, and weighing, the quantity being small. If, however, volumetric
estimation is desired, it may be done as in § 76, taking 50 c.c. of liquor.

§17. ALKALINE COMPOUNDS. 65

For other methods of examining the various solid and liquid
alkali wastes used for soda and sulphur recovery, etc., the reader is
referred to the Alkali Makers' Pocket Book already mentioned.

14. Salt Cake.

Is the impure sodic sulphate used in alkali manufacture or left in
the retorts in preparing hydrochloric acid from sulphuric acid and
salt, or nitric acid from sodic nitrate. It generally contains free
sulphuric acid existing as sodic bisulphate, the quantity of which
may be ascertained by direct titration with normal alkali.

The common salt present is estimated by decinormal silver solution and
chromate ; having first saturated the free acid with pure sodic carbonate,
1 c.c. silver solution is equal to 0'005837 gm. of salt.

Sulphuric acid, combined with soda, is estimated either directly or
indirectly as in § 76 ; 1 c.c. of normal barium solution is equal to 0'07l gm.
or 0'71 grn. of dry sodic sulphate.

Iron is precipitated from a filtered solution of the salt cake with amtaonia
in excess, the precipitate of ferric, oxide re-dissolved in sulphuric acid,
reduced to the ferrous state with zinc and titrated with permanganate.

Grossman adopts a method suggested by Bohlig (see § 32),
and has worked out the process in the case of salt cake in careful
detail (C. N. xli. 114) as follows :—

The neutral solution of salt cake (3'55 gm.) is put into a 500 c.c.
flask, 250 c.c. of a cold saturated solution of baric hydrate added,
the flask filled with water, and shaken up. Of the filtered clear liquid
250 c.c. are put in an ordinary flask, carbonic acid passed through
for about ten minutes, and then the contents of the flask boiled so
as to decompose any baric bicarbonate which may be in solution. After
cooling, the contents of the flask are again transferred to the 500 c.c.
flask, the latter filled up with water to the mark, shaken up, and filtered.
250 c.c. of the filtrate — i.e., one-fourth of the original quantity used — are
then titrated with one-fourth normal sulphuric acid. The number of c.c. of
one-fourth normal acid used multiplied by two will give the percentage of
sodic sulphate.

There are, however, sources of error in the experimental working of this
method which make certain corrections necessary. They arise — •

(1) From the impurities of the caustic baryta.

(2) Prom the precipitate formed in the measured liquid.

(3) Prom certain constant losses.

The commercial caustic baryta always contains baric nitrate, and sometimes
baric chloride. It is evident that on adding a solution of baric hydrata
which contains baric nitrate to a solution of sodic sulphate, a quantity of the
latter, equivalent to the quantity of the baric nitrate present, will be
converted into sodic nitrate, and thus escape the alkalimetric test, as will be
seen by the following equations : —

Ba(N O3)2 + Na2SO4=BaSO4 + 2NaNO3.
Ba(NO3)2+2NaOH + CO2=BaCO3+2NaN03+H2O.

It is therefore necessary to measure approximately the quantity of baryta
solution used, so as to know the amount of baric nitrate introduced into the
process. The latter can be easily ascertained by passing carbonic acid in
excess through the cold saturated solution of baric hydrate, boiling, filtering,
and precipitating tke baryta left in solution by sulphuric acid as usual.

66 VOLUMETRIC ANALYSIS. § 17.

250 c.c. of a baryta solution used for experiment yielded 0*0280 gin. of BaSO4,
which corresponds to Q'0171 gni. of Na2S04, or 0*96 c.c. of one-fourth normal
acid ; and it follows that for every 250 c.c. of this baryta solution was found
0-0171 gm. of Na2SO4 too little ; or, that there must be added 0'24 c.c. of
one-fourth normal acid to the result of the final titration (of one-fourth of
the original quantity). If the baryta contain caustic alkali, a corresponding
quantity of baric nitrate will be found less by the test ; but it is easily
understood, that the calculations will not be influenced as long as the baric
nitrate is in excess of the caustic alkali, which is always the case in good
commercial baryta.

The second error arises from the precipitates of baric sulphate and carbonate
taking up some space in the 500 c.c. flask, the final results thus being found
too high. If it is assumed that a cold saturated solution of baryta contains
about 23 gm. of BaO per liter, it will be near enough for all practical purposes
if in the experiment, working with 3'55 gm. of Na-SO4 and 250 c.c, of baryta
solution, 0'4 per cent, is subtracted from the final results for this error.

Three experiments made with 3' 55 gm. of pure ignited sodic sulphate gave
the following results :—

• Used one-fourth normal acid ... 49'37 c.c.
Add for Ba (NO3)2 0'24 c.c.

49*61 c.c.
=99-22 per cent. Na2SO4.

II.

Used one-fourth normal acid ... 49'21 c.c.
Add for Ba(NO3)2 0'24 c.c.

49-45 c.c.
=98*90 per cent. Na2SO4.

III.

Used one-fourth normal acid ... 49'37 c.c.
Add for Ba(NO3)2 0'24 c.c.

49-61 c.c.
=99'22 per cent. Na2SO4.

The average of these three experiments gives 99'1 per cent. ; and if 0"4
per cent, be subtracted for the precipitate, the result is 98'7 per cent, instead
of 100.

Grossman states that this loss of 1'3 per cent, in working with 3'55 gm.
of sulphate in the given dilution is a constant, and by dividing all results by
0'987 correct results are obtained.

It now remains to show the applicability of this method to the assay of
salt cake and like substances. The following is a complete analysis of a
sample of salt cake made in the usual way : —

Moisture 0'49

Insoluble ... 0'29

Free sulphuric hydrate 0*38

Aluminium sulphate 0*23

Ferric sulphate 0'42

Calcic sulphate 1'17

Sodic chloride 2'00

Sodic sulphate (by difference) 95'02

lOO'OO

§ 17. ALKALINE COMPOUNDS. 67

In order to make a good analysis of salt cake by weight it is necessary to
estimate seven constituents, to find by difference the quantity of actual sodic
sulphate, which is the only constituent wanted.

When baric hydrate is added to a solution of salt cake the free acid is
precipitated, so are alumina and iron, and the sulphuric acid combined with
them and with lime. The lime is partly thrown down as such, and what is
left as lime in solution is precipitated as carbonate in the second operation.
Thus, whatever other sulphates be present, only the sodic sulphate is given;
and by one simple test we are thus able to get a result which formerly could
onhr be attained by a tedious complete analysis.

The salt cake, of which a complete analysis is given above, was tested by
the alkalimetric method. 3"55 gm. required —

One-fourth normal acid 46'95 c.c.

Add for Ba(NO3)2 0'24 c.c.

47'19 c.c.
=94-38 per cent. Na2SO4.

(94-38— 0-40)=93'98.

93-98 : 0-987=95-2 per cent. 1SVSO4.

Thus, by the alkalimetric test, 95*2 per cent, of JS"a2S04 occurs,
whereas the analysis gives 95 '02 per cent. If it be considered how
difficult it is to wash soda salts completely from precipitates, it is
not surprising to find the result too low in the complete analysis,
as in five precipitates a very minute quantity will make up 0*2
per cent.

It is hardly necessary to point out that none of the figures for
the correction of the errors enumerated above can be used by any
one else working by this method, but that they must be ascertained
in every individual case. It is absolutely necessary to ascertain
after the first operation that there is no sulphate, and after the
second (before titrating) that there is no baryta in solution.

15. Raw Salt, Brine, etc.

Lime may be estimated by precipitation with ammonic oxalate, and the
precipitate titrated with permanganate, as in § 52.

Sulphuric acid as in § 76.

Magnesia is precipitated as ammoniacal phosphate, by a solution of sodic
phosphate containing ammonia, first removing the lime by ammonic oxalate,
the precipitate of double phosphate of magnesia and ammonia is brought on
a filter, washed with cold water containing ammonia, then dissolved in acetic
acid, and titrated with standard uranium solution, or by the process for
P-05 (§ 24).

The quantity of real salt in the sample may be ascertained by treating a
weighed quantity in solution with caustic baryta, boiling, setting aside that
the excess of baryta may precipitate itself as carbonate, or more quickly by
udding ammonic carbonate, filtering, evaporating the solution to dryness, and
gently igniting— the residue is pure salt. The loss of weight between this
and the original specimen taken for analysis, will show the percentage of
impurities.

16. Silicates of Soda and Potash.

A weighed quantity of the substance is gently ignited, until no aqueous
vapours are given off, and the residue weighed — thus the respective per-
centages of water and anhydrous material are obtained.

F 2

68 VOLUMETRIC ANALYSIS. § 17.

Another portion of the substance is dissolved in hot water, and titrated
with litmus and normal acid boiling, or with methyl orange after cooling. The
volume of acid is calculated to soda or potash. Solid alkaline silicates require
to be finely powdered previous to solution in hot water.

17. Soap.

The methods here given are a combination of those published
by A. R. Leeds (C. N. xlviii. 166) and C. R. A. Wright (Journ.
Soc. Arts, 1885, 1117, also J. S. C. I. iv. 631), and others.

(1) Moisture and Volatile Matters. — 15 gin. are dried to a constant
weight, first at 100°, then at 110° C.

(2) Free Fats. — Residue of (1) is exhausted in a S o x h 1 e t tube, with light
petroleum ether, and the extract, after evaporation of the ether, weighed.

(3) Fatty Acids, Chlorides, Sulphates, G-lycerine, etc. — The residue
from (2), wrhich has been treated with ether, represents 15 gm. soap ; it is
weighed, and two-thirds of it are dissolved in water, and normal nitric acid
added in excess to separate the fatty acids. These are collected on a tared
filter, dried, and weighed. The acid filtrate is now titrated with normal soda
or potash (free from chlorides or sulphates), with phenolphthalein as indicator ;
the difference between the volumes of acid and alkali used gives roughly the
total alkali. The residual neutral liquid is divided into two equal parts, in
one of which chlorine is estimated with TN^ silver and chromate, and in the
other sulphuric acid by normal baric chloride. If glycerine is present,
it may be estimated by Muter's copper test in the absence of sugar.
Sugar is, however, often largely used in transparent soaps in place of
glycerine; when both are present, the separate estimation is difficult, but
"Wright suggests the method of Fehliug for the sugar, first inverting
with acid ; the copper retained in solution by the glycerine being estimated
colorimetrically, using for comparison a liquid containing both sugar and
glycerine to known extents, treated side by side with the sample tested.

(4) Free and Total Alkali. — These are obtained by Wright's alcohol test.
Two or three grams of the soap are boiled with 95 per cent, alcohol, the extract
filtered off and residue washed with alcohol. The solution so obtained may
be either positively alkaline with caustic alkali, or negatively alkaline from
the presence of fatty acids or a diacid soap, according to the kind of soap
used. Phenolphthalein is added, which shows at once whether free alkali is
present, and in accordance with this either standard alcoholic acid or alkali is
used for titration. The residue on the filter is then dissolved in water, and
titrated Avith normal or decinormal acid ; the alkali so found may include
carbonate, silicate, borate, or aluminate of soda or potash, and also any
soluble lime. The sum of the two titrations will be the total alkalinity in
case both showed an alkaline reaction ; if otherwise, the alkali used to
produce a colour in the alcoholic extract is deducted from the volume of acid
used in the water extract. This method of taking the alkalinity of a soap
is very fairly exact; the error ought never to exceed _+ 0'5 per cent.
J. A. Wilson (C. N. lix. 280) states that the estimation of free caustic
alkali in high class soaps, containing no free glycerides, by the alcoholic
method is correct, but in the case of common commercial soaps it is
entirely misleading.

(5) Combined A IJcali— Wilson (C. N. Ixiv. 205) proceeds as follows : —
1. The alkali, in all forms, is determined by titration with standard acid in the
usual manner. 2. Another weighed quantity of the soap is decomposed in an
Erlenmeyer flask with a slight excess of dilute H2SO4, and the flask kept
on the water-bath till the fatty acids separate quite clear. The flask is then
placed in ice-water to cool, and then filtered. The fatty acids are washed three
times successively Avith 250 c.c. of boiling water and allowed to cool each time

§ 18. ALKALINE EARTHS. 69

uiid filtered. The united filtrates are diluted to 1 liter, and 500 c.c. placed
in a clear white beaker and tinted with methyl orange ; T^ alkali is then
dropped in till the liquid acquires the usual colour, after which a little
phenolphthalein is added, and the addition of standard alkali continued till
a permanent pink is established. The number of c.c. used in the latter
titration are due to the soluble acids, and are calculated to caprylic acid.
The fatty acids in the flask, and any little on the filter are dried and
weighed, and then dissolved in alcohol, and titrated with | alcoholic alkali.
The alkali so used, together with that required for neutralization of the
soluble acids, and deducted from the total alkali, gives the alkali existing
In other forms than as soap. Of course, if desired, the soap may be
decomposed with standard H2SO4, and the alkali required to neutralize the
methyl orange noted, which, deducted from the total acid used, would give
the acid equivalent to the alkali existing in all forms.

The method of C. Hope is undoubtedly the quickest and best for the
examination of the alcoholic solution of soap. Two grams of soap are dissolved
in hot absolute alcohol, a drop of phenolphthalein indicator added, and some
bubbles of CO2 passed through till the colour disappears. The liquid is
filtered ; the residue, consisting of total impurities, is washed with hot alcohol,
weighed and titrated with r\ acid and methyl orange, which gives the alkali
not existing as soap. The alcoholic solution is evaporated to dryness at
100° C. and the dry soap weighed. It is then gently ignited, dissolved in
water, and titrated with T^- acid and methyl orange to find the alkali existing
as soap. The difference between this and the soap residue, before ignition,
gives the fatty anhydrides, which multiplied by 1*03 gives the fatty acids.
The water is found by deducting the weights of the impurities arid dry soap
from 100. Fuller information on this subject may be found in Allen's
Organic Analysis and in Lant Carpenter's treatise on Soap and Candles.

TITRATION OF AL.KALINE EARTHS.

§ 18. STANDARD hydrochloric or nitric acid must in all cases be
used for the titration of the caustic or carbonated alkaline earths, as
these are the only acids yielding soluble compounds, except in the
case of magnesia. The hydrates, such as caustic lime, baryta,
strontia, or magnesia, may all be estimated by any of the indicators,
using the residual method, i.e., adding a known excess of standard
acid, boiling to expel any trace of CO2, and re-titrating with
standard alkali.

The carbonates of the same bases may of course also be
estimated in the same way, bearing in mind, that when methyl
orange is used, the liquid is best cooled before re-titration. All
heating may be avoided when using methyl orange in titrating
mixtures of hydrates and carbonates, or the latter only, unless it is
impossible to dissolve the substance in the cold. A good excess
of acid is generally sufficient.

The total amount of base in mixtures of caustic and carbonated
alkaline earths is also estimated in the same way.

(1) Estimation of Mixed Hydrates and Carbonates. — This may
be done either by phenacetolin or phenolphthalein as indicator.
The former has been recommended byDegener and Lunge : the
method, however, requires practice in order to mark the
change of colour.

70 VOLUMETRIC ANALYSIS. § 18.

The liquid containing the compound in a fine state of division is tinted
with the indicator so as to be of a faint 3Tellow; standard acid is then
cautiously added until a permanent pink occurs (at this stage all the hydrate
is saturated), more acid is now cautiously added until the colour becomes deep
yellow, the volume of acid so used represents the carbonate.

The method is especially adapted to mixtures of calcic hydrate
and carbonate. It is also applicable to barium, but not to
magnesium, owing to the great insolubility of magnesic hydrate in
dilute acid. If phenolphtlialein is used as indicator, the method
is as follows : —

Heat the liquid to boiling, and cautiously add standard acid until the red
colour is just discharged. The carbonates of lime and baryta, rendered
dense by boiling, are both quite neutral to the indicator. To obtain the
whole of the base, excess of standard acid is used, and the mixture re-titrated
with standard alkali.

Magnesia in solution as bicarbonate may be accurately estimated
in the cold with methyl orange as indicator.

(2) Estimation of Calcium, Barium, Magnesium, and Strontium
in Neutral Soluble Salts.— The amount of base in the chlorides and
nitrates of the alkaline earths may be readily estimated as
follows : —

The weighed salt is dissolved in water, cautiously neutralized if acid or
alkaline, phenolphtlialein added, heated to boiling, and standard sodic
carbonate delivered in from time to time with boiling until the red colour
is permanent.

Magnesium salts cannot however be estimated in this way,
or even mixtures of lime and magnesia, as magnesic carbonate
affects the indicator in a different manner to the other carbonates.

(3) Precipitation of the Alkaline Earths from their Central Salts as
Carbonates. — Soluble salts of lime, bar}Tta, and stroutia, such as chlorides,
nitrates, etc., are dissolved in water, and the base precipitated as carbonate,
with excess of ammonic carbonate and some free ammonia. The mixture is
heated to about 60° C. for a few7 minutes. The precipitated carbonate is then
to be filtered, well washed with hot water till all soluble matters, especially
ammonia, are removed, and the precipitate with filter titrated with normal
acid, as already described.

Magnesia salts require caustic soda or potash instead of ammonic carbonate ;
but the process gives results slightly too low, owing to the slight solubility of
magnesic hydrate in the alkaline liquid.

(4) Lime and Magnesia Carbonates in Waters. — The amount of calcic
or calcic and magnesic carbonates, dissolved in ordinary non- alkaline waters
may be very readily, and with accuracy, found by taking 200 or 300 c.c.
of the water, heating to near boiling, adding phenacetolin or lacmoid, and
titrating cautiously with T^- nitric or sulphuric acid. An equally accurate
result may be obtained by methyl orange in the cold liquid.

(5) Magnesia. — The magnesia existing in the commercial Stassfurt salts
used for manures, etc., and other soluble magnesia salts, may very readily
be determined with accuracy by Stolba's method, as given for P2O5 in
§ 24.2, or in all cases where separation can be made as ammonio-magnesic

ALKALINE EAKTHS. 71

phosphate. The precipitation ma}7 be hastened considerably by precipitating
with microcosmic salt, in the presence of a tolerably large proportion of
ammonic chloride, accompanied with vigorous stirring. Half an hour quite
suffices to bring down the whole of the double phosphate, and its adherence
to the sides of the beaker is of no consequence, if the titration is made in
the same beaker, and with the same glass rod, using an excess of standard
acid, and titrating back with weak standard ammonia and methyl orange.

The precipitate may also be titrated with standard uranium (§ 72).
Precht (Z. a, C. 1879, 438) adopts the following method for soluble
magnesia salts in kaiuit, kieserit, etc., depending upon the insolubility of
magnesic hydrate in weak caustic potash : —

10 gm. of the substance are dissolved, filtered, and mixed with 25 c.c. of
normal caustic potash, if it contains less than 50 per cent, of magnesic
sulphate ; or 50 c.c. if it contains more than 50 per cent. The mixture is
warmed somewhat, transferred to a 500 c.c. flask, and the volume made up
with water. After standing at rest for half an hour, 50 c.c. of the clear
liquid are withdrawn, and the excess of normal alkali estimated in the usual
way with normal acid. Ammonium and metallic salts must be absent.

1 c.c. normal potash— 0'02 gm. MgO.

(6) Hardness of Water estimated without Soap Solution. — As is
generally known, the soap-destroying power of a water is ascertained
in Clark's process by a standard solution of soap in weak alcohol,
titrated against a standard solution of calcic chloride. The
valuation is in so-called degrees, each degree being equal to I grain
of calcic carbonate, or its equivalent, in the imperial gallon. The
process is an old and familiar one, but open to many objections
from a scientific point of view. The scale of degrees is arbitrary,
and is seriously interfered with by the presence of varying
proportions of magnesia..

We are indebted, primarily to Mohr, and subsequently to
Hehner, for an ingenious method of determining both the
temporary and permanent hardness of a water without the use
of soap solution.

The standard solutions required are -^ sodic carbonate and
-£$ sulphuric acid. Each c.c. of standard acid exactly neutralizes
1 m.gm. of CaCO3, and each c.c. of the alkali precipitates the like
amount of CaCO3, or its equivalent in magnesia, in any given
water.

Process : 100 c.c. of the water are tinted with an indicator of suitable
character, heated to near boiling, and standard acid cautiously added until
the proper change of colour occurs. Hehner recommends phenacetolin ;
but my own experiments give the preference to lacmoid, which is also
commended by Thomson. Draper (C. N. li. 206) points out the value
of lacmoid and carminic acid for such a process, and I fully endorse his
opinion with respect to both indicators. Practice is desirable in order
to recognize the precise end-reaction. The number of c.c. of acid used
represents the number of Clark's degrees of temporary hardness per 100,000.
To obtain degrees per gallon, multiply the number of c.c. by 0'7. The
permanent hardness is ascertained by taking 100 c.c. of the water and adding
to it a rather large known excess of the standard sodic carbonate. The
quantity must of course be regulated by the amount of sulphates, chlorides,
or nitrates of lime and magnesia present in the water ; as a rule, a volume

72 VOLUMETRIC ANALYSIS. § 19.

equal to the water will more than suffice. Evaporate in a platinum dish to
dryness (glass or porcelain will not do, as they affect the hardness), then
extract the soluble portion with small quantities of distilled water, through
a very small filter, and titrate the filtrate with the standard acid for the
excess of sodic carbonate : the difference represents the permanent hardness.

Some waters contain alkaline carbonates, in which case there is
of course no permanent hardness, because the salts to which this is
clue are decomposed by the alkaline carbonate. In examining a
water of this kind, the temporary hardness will be shown to be
greater than it really is, owing to the alkaline carbonate ; and the
estimation for permanent hardness will show more sodic carbonate
than was actually added. If the difference so found is deducted
from the temporary hardness, as first noted, the remainder will be
the true temporary hardness.

AMMONIA.

§ 19. IN estimating the strength of solutions of free ammonia
by the alkalimetric method, it is better to avoid the tedious process
of weighing any exact quantity, and to substitute for it the following
plan, which is applicable to most liquids for the purpose of
ascertaining both their absolute and specific weights.

Let a small and accurately tared flask, beaker, or other convenient vessel
be placed upon the balance, and into it 10 c.c. of the ammoniacal solution
delivered from a very accurately graduated 10 c.c. pipette. The weight
found is, of course, the absolute weight of the liquid in grams ; suppose it to
be 9'65 gm., move the decimal point one place to the left, and the specific
weight or gravity is at once given (water being 1), which in this case is 0'965.

It must be borne in mind that this system can only be used properly with
tolerably delicate balances and ver}r accurate pipettes. The latter should
invariably be tested by weighing distilled water at 16° C.

The 10 c.c. weighing 9'65 gm., are now mixed with water and titrated with
nesmal acid of which 49 c.c. are required, therefore 49 x 0'017=0'833 gm. NH3
=8'64 per cent, of real ammonia; according to Otto's table 0'965 sp. gr. is
equal to 8'50 per cent. Ammonic carbonate, and a mixture of the same with
bicarbonate, as it most commonly occurs in commerce, may be titrated direct
with normal acid for the percentage of real ammonia, using methyl orange
as indicator. The carbonic acid can be determined by precipitating the
solution while hot with baric chloride, and when the precipitate is well
washed, dissolving it with an excess of normal acid and titrating backward
with normal alkali; the number of c.c. of acid used multiplied by 0'022
(the i mol. wt. of CO2) will give the weight of carbonic acid present in
the sample.

1. Estimation of Combined Ammonia "by distillation with Alkalies
or Alkaline Earths.

This method allows of the expulsion of ammonia from all its
salts. Caustic soda, potash, or lime, may any of them be used
where no organic nitrogenous compound exists in the substance ;

§19. AMMONIA. 73

but should such be the case, it is preferable to use freshly ignited
magnesia.

The distilling apparatus may conveniently be arranged by con-
necting an ordinary well-stoppered small retort to a small Liebig
condenser, and leading the distilled gas into a vessel containing an
excess of normal acid. After the operation is ended, the excess
of acid is ascertained by residual titration with normal alkali or
§ ammonia, and thus the amount of displaced ammonia is found.

The retort must be so supported that its neck inclines well
upwards, in order that any alkali mechanically carried into it by
the spray which occurs during ebullition shall not reach the
condenser. An angle of about 30° suffices ; and in order that a
convenient connection may be made with the condenser, the end of
the retort is bent downward, and the connection securely made with
india-rubber tubing. In like manner, the end of the condenser is
elongated by a glass tube and india-rubber joint, so that the tube
dips into a two-necked bottle or bulb, containing the measured
normal acid ; the end of this tube should be cut obliquely, and
reach nearly, but not quite, to the surface of the acid. The outlet
of the receiver is fitted with a tube containing glass wool, broken
glass, or fibrous asbestos, wetted with a portion of the normal
acid, so that any traces of ammonia which may possibly escape
condensation in the bulk of the acid may be retained.

The retort containing the ammoniacal compound in solution
being securely fixed, and all the apparatus tightly connected, the
stopper of the retort is removed, and a strong solution of caustic
alkali, or, in case of compounds in which ammonia is quickly
released, pieces of solid alkali are rapidly introduced, the stopper
inserted, and the distillation forthwith commenced. Lime or
magnesia, suspended in water, must be added through a small
funnel ; the distillation is continued until the steam has washed all
traces of ammonia out of the condenser tube into the normal acid.
Cold water is of course run continuously through the condenser as
usual. Finally, the tubes connected with the receiver are well
washed out into the bulk of normal acid, methyl orange added, and
the titration completed with normal alkali or J ammonia.

Each c.c. of normal acid neutralized by the displaced ammonia
represents O'OIT gm. NH3.

The apparatus shown in fig. 28 is of great value in determining
accurately all the forms of ammonia which can be displaced by
soda, potash, or lime, and the gas so evolved collected in a known
volume in excess of normal acid, the excess of acid being after-
wards found by residual titration with normal alkali or § ammonia.

Many modifications of this apparatus have been suggested, such
as the introduction of a condenser between the two flasks to cool
the distillate; another is the use of a (J tube containing some
standard acid in place of c. I do not find that any of these
modifications are required to secure accuracy, if the apparatus

VOLUMETRIC ANALYSIS.

is tightly fitted. It is necessary that a bulb should exist in
the distilling tube, just above the cork of the distilling flask,
otherwise the spray from the boiling liquid is occasionally projected
into the tube, and is blown over with the condensed steam.

Fig. 28.

Another precaution is advisable where dilute liquids are boiled,
and much steam generated, that is, to immerse the condenser flask
in cold water.

The little flask, holding about 200 c.c. and placed upon the wire
gauze, contains the ammoniacal substance. The tube d is filled with strong
solution of caustic potash or soda. The large flask holds about half a liter,
and contains a measured quantity of normal acid, part being contained in
the tube c, which is filled with glass wool or broken glass, and through which
the normal acid has been poured. The stoppers of the flasks should be
caoutchouc, failing which, good corks soaked in > melted paraffin may be
used.

The substance to be examined is weighed or measured, and put into the
distilling flask with a little water, the apparatus then being made tight at
every part; some of the caustic alkali is allowed to flow in by opening the
clip, and the gas or spirit lamp is lighted under it.

§ 19. AMMONIA. 75

The contents are brought to gentle boiling, taking care that the froth, if
any, does not enter the distilling tube. It is well to use a movable gas
burner or common spirit lamp held under the flask in the hand ; in case
there is any tendency to boil over, the heat can be removed immediately, and
the flask blown upon by the breath, which reduces the pressure in a moment.
In examining guano and other substances containing ammouiacal salts and
organic matter by this means, the tendency to frothing is considerable; and
unless the above precautions are taken, the accuracy of the results will be
interfered with. A small piece of bee's wax or solid paraffin is very
serviceable in allaying the froth.

The distilling tube has both ends cut obliquely ; and the lower end nearlv,
but not quite, reaches to the surface of the acid, to which a little methyl
orange may be added. The quantity of normal acid used must, of course, be
more than sufficient to combine with the ammonia produced ; the excess is
afterwards ascertained by titration with normal alkali or ^ ammonia.

It is advisable to continue the boiling for say ten or fifteen minutes,
waiting a minute or two to allow all the ammonia to be absorbed ; then opening
the clip, blow through the pipette so as to force all the remaining gas into
the acid flask. The tube c must be thoroughly washed out into the flask
with distilled water, so as to carry down the acid with any combined gas which
may have reached it. The titration then proceeds as usual. This process
is particularly serviceable for testing commercial ammouiacal salts, gas
liquor, etc. (see below). The results are extremely accurate.

2. Indirect Method.

In the case of tolerably pure ammoniacal salts or liquids, free
from acid, or in which the free acid is previously estimated,
a simple indirect method can be used, as follows : —

If the ammoniacal salt be boiled in an open vessel with normal caustic
alkali, the ammonia is entirely set free, leaving its acid combined with the
fixed alkali. If, therefore, the quantity of alkaline solution is known, the
excess beyond that, necessary to supplant the ammonia, may be found by
titration with standard acid. The boiling of the mixture must be continued
till a piece of red litmus paper, held in the steam from the flask, is no longer
turned blue.

Example : 1*5 gm. of purest sublimed ammonic chloride was placed in a
wide-mouthed flask with 40 c.c. of normal soda, and boiled till all ammonia
was expelled, then titrated back with normal sulphuric acid, of which
11'9 c.c. were required; 28'1 c.c. of normal alkali had therefore been
neutralized, which multiplied by 0'05337, the factor for ammonic chloride,
gave T499 gm., instead of 1'5 gm. originally taken.

3. Technical Analysis of Gras Liquor, Sulphate of Ammonia, Sal
Ammoniac, etc., arranged for the use of Manufacturers.

This process depends upon the fact, that when ammoniacal salts
are heated with caustic soda, potash, or lime, the whole of the
ammonia is expelled in a free state, and may by a suitable apparatus
(fig. 29) be estimated with extreme accuracy (see § 19. 1).

The set of apparatus here described consists of a distilling flask
B, and condensing flask F, fitted together in such a manner, that no
loss of free ammonia can occur ; the whole of the ammonia being
liberated from the distilling flask into a measured quantity of free

76 VOLUMETRIC ANALYSIS. § 19.

acid contained in the condensing flask, where its amount is after-
wards found by the method hereinafter described.

Analysis of Gas Liquor. — This liquid consists of a solution of
carbonates, sulphates, hyposulphites, sulphides, cyanides, and other
salts of ammonia. The object of the ammonia manufacturer is to
get all these out of his liquor into the form of sulphate or chloride
as economically as possible. The whole of the ammonia existing
as free or carbonate in the liquor, can be distilled off at a steam
heat ; the fixed salts, however, require to be heated with soda,
potash, or lime (the latter is generally used on a large scale as most
economical), in order to liberate the ammonia contained in them.

The valuation of gas liquor is almost universally made in Great
Britain by Twaddle's hydrometer, every degree of which is taken
to represent what is technically called "two-ounce strength;" that is
to say, a gallon of such liquor should neutralize exactly two ounces by
weight of concentrated oil of vitriol — thus 5 degrees, Twaddle, is
called " ten-ounce " liquor — but experiment has clearly proved, that
although the hydrometer may be generally a very convenient
indicator of the commercial value of gas liquor, it is not accurate
enough for the manufacturer who desires to work with the utmost
economy. Sometimes the liquor contains a good deal of free
ammonia, and in such case the hydrometer would show it to be
weaker than it really is ; on the other hand, sometimes, from
accidental causes, other solid matters than ammonia salts occur in
the liquor, and the hydrometer shows it to be stronger than it really
is. The method of saturation, by mixing standard acid with the
liquor, is perhaps more correct than the hydrometer; but this
system is entirely at fault in the presence of much fixed ammonia,
and is, moreover, a very offensive and poisonous operation.

The apparatus here described is exactly the same on a small
scale as is necessary in the actual manufacture of sulphate of
ammonia in quantities ; and its use enables any manufacturer to
tell to a fraction how much sulphate of ammonia he ought to
obtain from any given quantity of gas liquor. It also enables him
to tell exactly how much ammonia can be distilled off with heat
alone, and how much exists in a fixed condition requiring lime.

The measures used in this process are on the metrical system ;
the use of these may, perhaps, at first sight appear strange to
English manufacturers ; but as the only object of the process is to
obtain the percentage of ammonia in any given substance, it is
a matter of no importance which system of measures or weights is
used, as when once the percentage is obtained, the tables will at
once show the result in English terms of weight or measure.

a is a small pipette, holding 10 cubic centimeters to the mark in neck :
this is the invariable quantity of liquor used for the analysis, whatever the
strength may be. This measure is filled to the mark by suction and
transferred, without spilling a drop, to flask B— the fittings being previously

78 VOLUMETRIC ANALYSIS. § 19.

removed— the tube C is then filled in the same manner, with strong
caustic soda solution from a clean cup or other vessel, in order to do
which, the clip at the top must be opened : the cork is then replaced, and
the flask B is then securely imbedded in perfectly dry sand, in the sand-
bath D. The graduated pipette E is then filled in the same manner to
the O mark, with standard acid, and 20, 30, 40, or 50 c.c. (according
to the estimated strength of the liquor) allowed to flow into the flask P,
through the cup G, which is filled with broken glass placed on a layer of
glass wool or fibrous asbestos. The broken glass should be completely
wetted with the acid, so that any vapours of ammonia which may escape
the acid in the flask shall become absorbed by the acid. The quantity
of standard acid to be used is regulated by the approximately known
strength of the liquor, which of course can be told by Twaddle's
hydrometer: thus, for a liquor of 3C Twaddle=6-oz. liquor, 20 c.c. —
8-oz., 25 c.c. — 10-oz., 30 c.c. of acid will be sufficient — but there must
always be an excess. The required quantity can always be approx-
imately known, since every 10 c.c. of acid represents 1 per cent, of
ammonia. The standard acid having been carefully passed through G,
the apparatus is fitted together at H by the elastic tube, and the india-rubber
stoppers securely inserted in both flasks; this being done, the lamp is
lighted under the sand-bath, and at the same time the spring-clip on C is
pressed, so as to allow about two-thirds of the caustic soda to flow into B ;
the rest will gradually empty itself during the boiling. The heat is continued
to boiling, and allowed to go on till the greater bulk of the liquid in B
is boiled away into P. A quarter of an hour is generally sufficient for this
purpose, but if the boiling is continued till the liquid in B just covers the
bottom of the flask, all the ammonia will have gone over to P; during
the whole operation the distilling tube must never dip into the acid in P.
In order to get rid of the last traces of ammonia vapour out of B, the lamp
is removed, and the mouth being applied to the tube over the spring-clip,
the latter is opened, and a good blast of air immediately blown through.
The apparatus may then be detached at H ; distilled or good boiled drinking
water is then poured repeatedly through G in small quantities, till all traces of
acid are removed into flask P. This latter now contains all the ammonia out of
the sample of liquor, with an excess of acid, and it is necessar}r now to find out
the quantity of acid in excess. This is done by means of the burette I, and
the standard solution of soda, w:hich soda is of exactly the same strength as
the standard acid. In order to find out how much of the standard acid has been
neutralized by the ammonia in the liquor distilled, the burette I is filled to 0
with standard soda, and one drop of methyl orange, or a sufficiency of any
other indicator, other than phenolphthalein, being added to the cooled contents
of flask P, the soda is slowly dropped into it from the burette, with constant
shaking, until the indicator changes colour. The number of c.c. of soda so
used, deducted from the number of c.c. of standard acid used, will show
the number neutralized by the ammonia in the liquor distilled ; therefore, if
the number of c.c. of soda used to destroy the pink colour be deducted
from the number of c.c. of standard acid originally used, it will show the
number of c.c. of standard acid neutralized by the ammonia, which has been
distilled out of the liquor, and the strength of the solutions is so arranged
that this is shown without any calculation. The following examples will
suffice to show this :— Suppose that a liquor is to be examined which marks
5° Twiddle, equal to 10-ounce liquor ; 10 c.c. of it are distilled into 30 c.c.
of the standard acid, and it has afterwards required 6 c.c. of standard
soda to neutralize it ; this leaves 24 c.c. as the volume of acid saturated
by the distilled ammonia, and this represents 2'4 per cent. ; and on referring
to the table it is found that this number corresponds to a trifle more than
11 ounces, the actual figures being 2*384 per cent, for 11 ounce strength.

The strength of the standard soda and acid solutions is so

§19. AMMONIA. 79

arranged, that when 10 c.c. of liquor are distilled, every 10 c.c. of
acid solution represents 1 per cent, of ammonia in the liquor. In.
like manner 13 c.c. of acid will represent 1'3 per cent, of ammonia
corresponding to 6-ounce liquor.

The burette is divided into tenths of a cubic centimeter, and
those who are familiar with decimal calculations can work out the
results to the utmost point of accuracy ; the calculation being, that
every 1 per cent, of ammonia requires 4 '61 ounces of concentrated
oil of vitriol (sp. gr. 1 *S45) per gallon, to convert it into sulphate :
thus, suppose that 10 c.c. of any given liquor have been distilled,
and the quantity of acid required amounts to 18 '6 c.c., this is
1*86 per cent., and the ounce strength is shown in ounces and
decimal parts as follows : —

4-61
1-86

2766
3688
461

8 '5746 ounces of oil of vitriol.

The liquor is therefore a trifle over 8|-ounce strength.

Spent Liquors. — It is frequently necessary to ascertain the
percentage of ammonia in spent liquors, to see if the workmen
have extracted all the available ammonia. In this case the same
measure, 10 c.c. of the spent liquor, is taken, and the operation
conducted precisely as in the case of a gas liquor.

Example : 10 c.c. of a spent liquor were distilled, and found to neutralize
3 c.c. of acid : this represents three-tenths of a per-cent. equal to 1-oz. and
four-tenths of an ounce, or nearly 1£ oz. Such a liquor is too valuable to
throw away, and should be worked longer to extract more ammonia.

Process for Sulphate of Ammonia or Sal Ammoniac : An average
sample of the salt being drawn, ten grams are weighed, transferred without
loss to a beaker or a flask having a 100 c.c. mark upon it, distilled or boiled
drinking water poured on it, and well stirred till dissolved, and finally
water added exactly to the mark. The 10 c.c. measure is then filled with
the solution, and emptied into the distilling flask B ; 30 c.c. of standard
acid are put into flask E and the distillation carried on precisely as in
the case of a gas liquor. The number of c.c. of standard acid required
shows directly the percentage of ammonia ; thus, if 24*6 c.c. are used in
the case of sulphate, it contains 24'6 per cent, of ammonia.

The liquors when tested must be measured at ordinary tempera-
tures, say as near to 60° F. as possible. The standard solutions
must be kept closely stoppered and in a cool place.

The following table is given to avoid calculations ; of course, it
will be understood that the figures given are on the assumption
that the whole of the ammonia contained in the liquor is extracted

VQLUMETKIC ANALYSIS.

19.

in the manufacture as closely as it is in the experiment. With the
most perfect arrangement of plant, however, this does not as a rule
take place ; but it ought to be very near the mark with proper
apparatus, and care on the part of workmen.

Approxi-
mate
measure of
Standard
Acid in c.c.

Percentage
of Ammonia
NH3

Ounce
strength
pei-
gallon.

Weight of Sulphuric Acid in pounds
and decimal parts required for each
gallon of liquor.

Yield of
Sulphate
per gallon in
Ibs. and
decimal

C. O. V.

T> n \r Chamber
• U< V- AnirJ

and tenths.

169° Tw.

144,° Tw ACIO.
Iw- 120= Tw.

parts.

2-2

•2168

•0625 '0781

•0893

•0841

4'3

•4336

•1250

•1562

•1786

•1682

6-5

•6504

•1875

•2343

•2679

•2523

87 '8672

•2500

•3124

•3572

•3364

lO'l 1-0840

•3125

•3905

•4465

•4205

13'0 1-3000

•3750

•4686

'5358

•5046

15-2 1-5176

•4375

•5467

•6251

•5887

17-3

17344

•5000

•6248

•7144

•6728

19-5

1-9512 ; 9

•5625

•7029

•8037

•7569

21-7

2-1680

•6260

•7810

•8930

•8410

23-8

2-3840

•6875

•8591

•9823

•9251

26-0

2-6016

•7600

•9372

1-0716

1-0092

28-2

2-8184

•8125

1-0153

1-1609

1-0933

30-4

3-0350

•8750

1-0934

1-2502

1-1774

32-5

3-2520

•9375

1-1715 i 1-3395

1-2615

34-7

3-4688

16 I'OOOO

1-2496 1-4288

1-3456

36-9

3-6856

17 1-0625

1-3277

1-5181

1-4297

39-0

3-9024

18 1-1250

1-4058

1-6074

T5138

41-2

4-1192

T1875

1-4839

1-6967

1-5979

43'3

4-3360

1-2500

1-5620 ! 1-7860

1-6820

The weight of sulphuric acid being given in decimals renders it
very easy to arrive at the weight necessary for every thousand
gallons of liquor, by simply moving the decimal point ; thus 8-oz.
liquor would require 500 Ibs. of concentrated oil of vitriol, 625 Ibs.
of brown oil of vitriol, or 714J Ibs. chamber acid for every 1000
gallons, and should yield in all cases 672*8 (say 673) Ibs. of
sulphate.

4. Combined Nitrog-en in Organic Substances.

The old-fashioned process consists in heating the dried substance
in a combustion tube with soda lime, by which the nitrogen is con-
verted into ammonia; and this latter being led into a measured
volume of normal acid contained in a suitable bulb apparatus,
combines with its equivalent quantity ; the solution is then
titrated resiclually with standard alkali for the excess of acid,
and thus the quantity of ammonia found.

As the combustion tube with its arrangements for organic
analysis is well known, and described in any of the standard books
on general analysis, it is not necessary to give a description here.

§ 19. AMMONIA.

5. Kjeldahl's Method.

This has met with considerable acceptance in lieu of the
combustion method, on account of its easy management and
accurate results. Unlike the combustion method, the ammonia is
obtained free from organic matters or colour, and moreover salts of
ammonia and nitrates may be estimated with extreme accuracy.
It was first described by Kjeldahl (Z. a. C. xxii. 366), and has
since been commented upon by many operators, among whom are
Warington (G. N. lii. 162), Pfeiffer and Lehmann (Z. a. C.
xxiv. 388), Marcker and others (Z. a. C. xxiii. 553; xxiv.
199,393; xxv. 149, 155; xxvi. 92; xxvii. 222, 398); Gunning
(idem xxviii. 188); Arnold and Wedermeyer (idem xxxi. 525);
and recently by Bernard Dyer (J. C. S. Ixvii.-viii. 811).

The original process consisted in heating the nitrogenous substance
in a flask, with concentrated sulphuric acid, to its boiling point,
and when the oxidation through the agency of the acid is nearly
completed, adding finely powdered permanganate of potash in small
quantities till a green or pink colour remains constant ; the whole
of the nitrogen is thus converted into ammonic sulphate. The
flask is then cooled, diluted with water somewhat, excess of
caustic soda added, the ammonia distilled off' into standard acid,
and the amount found by titration in the usual way.

Some practical difficulties occurred in the process as originally
devised; and, moreover, with some organic substances a very
long time was required to destroy the carbon set free by the
strong acid.

Another difficulty was, that if nitrates were present in the
compound analyzed their reduction to ammonia was not certain nor
regular, and unless this difficulty could be overcome the value of
the process was limited.

The experience of many hundreds of operators since this
method was first introduced has resulted in rendering it as perfect
as need be, and the results of this experience in all essential
particulars will -now be described, omitting the details as to some
of the special forms of apparatus, and which are not absolutely
essential. The method requires the following re-agents and
apparatus : —

1 . Standard acid, which may be either sulphuric or hydrochloric ;
a convenient strength is semi-normal.

2. Standard alkali, either ammonia, soda, or potash, of corres-
ponding strength to the acid.

3. Concentrated sulphuric acid free from nitrates and ammonic
sulphate.*

* Commercial oil of vitriol frequently contains ammonia, owing to the fact that
makers sometimes add ammonic sulphate during concentration in order to get rid of
nitrous compounds. Meldola and Moritz state that any traces of ammonia may be
destroyed by digesting the acid for two or three hours at a temperature below boiling

82 VOLUMETRIC ANALYSIS. § J 9.

4. Mercuric oxide prepared in the wet way or metallic
mercury.

5. Powdered potassic sulphate.

6. Granulated zinc.

7. Solution of potassic sulphide in water, 40 gm. in the
liter.

8. A saturated solution of caustic soda free from nitrates or
nitrites.

9. An indicator — litmus, methyl orange, or cochineal are
suitable, but any other except phenolphthalein may be used.

10. Digestion flasks with long neck and round bottom, holding
about 200 — 250 c.c. These flasks should be well annealed and
not too thick, preferably made of Jena glass — the neck about
-f inch wide, and 3| — 4 inches long.

1 1 . Distillation flasks of hard Bohemian glass and Erlenmeyer
pattern, 550 — 600 c.c. capacity, fitted with a rubber stopper and
a bulb above with curved delivery tube, to prevent the spray of
the boiling alkaline liquid from being carried over into the
condenser tubes. Copper distilling bottles or flasks are used by
some operators for technical purposes with good results, but in this
case it is advisable to put the soda into the vessel first then add
the acid liquid.

12. The condenser. Owing to the undoubted solubility of
glass in fresh distilled water containing ammonia, it is advisable to
have the condenser tube made of block tin. This should be about
three-eighths of an inch wide externally, and is connected with the
bulb tube of the distilling flask with stout pure rubber tube. It is
surrounded by either a metal or glass casing, through which
cold water is passing in the usual manner. It is very easy to
fit up such an arrangement with the condenser tubes made
entirely of glass sold by the dealers in chemical apparatus. The
end of the condenser tube may be simply inserted into the neck
of a flask in an oblique position, containing the standard acid,
or it may have a delivery tube connected by rubber leading
into a beaker. There is no necessity for dipping the delivery
tube into the acid unless the temperature of the place is
very high.

In places where it is difficult to arrange for a flow of water to
keep the distilling tube cool the simple apparatus shown in fig. 30
may be serviceable, and unless the temperature of the place is
exceedingly high there is no loss of ammonia, This arrangement
is used by Stutzer, whose results with it compare well

with sodic or potassic nitrite in the proportion of 0'5 gm. of the salt to 100 c.c. of
acid. Lunge objected to this treatment, because of the probable formation of nitro-
sulphuric acid. Experiments have since been made by Mori tz which prove that the
objection is groundless, provided the digestion is carried on for a period sufficient to
expel the nitrous acid (J. S. C. I. ix. 443). The purification of the acid may of course
be obviated by ascertaining once for all the amount of ammonia in any given stock of
acid, by making a blank experiment with pure sugar and allowing in all cases for the
amount of NH-i so found.

§19. AMMONIA.. 83

with others made in condensers surrounded by flowing

water ; and equally
accurate figures
have been got in
comparison with
the ordinary con-
denser, using the
same quantity of
substance for
digestion. The
explanation of this
is, no doubt, the
very strong affinity
of ammonia for
Tig. 30. water, and when

in very minute

quantity it is held very tenaciously, even at a tolerably high
temperature. The tube should be not less than 3 feet long.
Where a large number of estimations are being carried on it is
convenient to have a special condenser, which will allow of six
or more distillations being worked at the same time. Several
forms of such arrangements have been devised, and are obtainable
of the apparatus dealers.

For use in my own laboratory where a large number of agricul-
tural samples are examined, the form shown in fig. 31 has been
adopted, and has been found to answer well. The body of the
condenser consists of an ordinary 10-gallon iron drum filled AA7ith
water; the block tin distilling tubes run through this at equal
distances from each other, and emerge at the bottom of sufficient
length to dip into the vessels containing the standard acid. With
this arrangement there is no necessity for running water, and six
distillations may be carried on simultaneously without fear of
losing ammonia ; the body of water is so great that the lower
portion is quite cool after the distillations are finished. In case
of extremely hot weather or in a very hot laboratory, the cover
may be removed and a lump of ice placed in the water, if a large
number of distillations are required.

The distilling flasks are closed with rubber stoppers, and fitted
with ball top arrangement shown more plainly in fig. 30.* These
are connected with the tin tubes by rubber joints, and supported on
an iron frame over which is laid a strip of wire gauze. The Bunsen
burners are of Fletcher's make, with nickel gauze tops which
give a smokeless flame of any desired size. So well does this
arrangement work, that during many hundreds of distillations not
one breakage has occurred, due to the heating or the distillation.
The tin condensing tubes do not in this case dip into the standard
acid, as various experiments have proved it unnecessary.

*These may be had of Gerhard t, Bonn, and probably of other apparatus dealers.

G 2

VOLUMETRIC ANALYSIS.

19.

Dyer uses a block tin condensing tube rising 15 — 18 inches
vertically from the distilling flask with no condenser, but bent

Pig. 31.

downwards and fitting into a pear-shaped adapter (with large
expansion to allow of varied pressure), whose narrowed end dips
actually into the acid.

13. " A convenient stand for
holding the digestion flasks is shown
in fig. 32, and they rest in an
oblique position. Heat is supplied
by small Buns en burners. With
a little care the naked flame can be
applied directly to the flask with-
out danger. Some operators prefer
to close the digestion flasks with
a loosely fitting glass stopper
elongated to a point, and having
a balloon-shaped top. This aids in the condensation of any acid

rig. 32.

§ 19. AMMONIA. 85

which may distil, but if the flasks are tolerably long in the neck,
there is practically no loss of acid except as SO2 which occurs in
any case. It is almost needless to say that the digestion should be
done in a fume closet with good draught.

The Kjeldahl-Grunning Process : From 05 to 5 gm. of the substance
according to its nature is brought into a digestion flask with approximately
O'o gm. of mercuric oxide or a small globule of metal and 20 c.c. of
sulphuric acid (in case of bulky vegetable substances 30 c.c. or more may
be necessary). The flask is placed on wire gauze over a small Bun sen
burner in an upright position, or in the frame above described in an inclined
position, and heated below the boiling-point of the acid for from five to
fifteen minutes, or until frothing has ceased. The heat is then raised till
the acid boils briskly, this is continued for about fifteen minutes, when
about 10 grams of potassic sulphate are added, and the boiling continued.
No further attention is required till the contents of the flask have become
a clear liquid, which is colourless, or at least has only a very pale straw
colour. The flask is then removed from the frame, and after cooling, the
contents are transferred to the distilling flask with repeated quantities of
water amounting in all to about 250 c.c., and to this 25 c.c. of potassic
sulphide solution are added, 50 c.c. of the soda solution*, or sufficient to
make the reaction strongly alkaline, and a few pieces of granulated zinc.
The flask is at once connected with the condenser, and the contents are
distilled till all ammonia has passed over into the standard acid, and the con-
centrated solution can no longer be safely boiled. This operation usually
requires from twenty to thirty minutes. The distillate is then titrated with
standard alkali.

The use of mercury or its oxide in this operation greatly shortens the
time necessary for digestion, which is rarely over an hour, and in the case
of substances most difficult to oxidize, is more commonly less than an
hour. Potassic sulphide removes all mercury from solution, and so prevents
the formation of mercuro-ammonium compounds which are not completely
decomposed by soda solution. The addition of zinc gives rise to an evolution
of hydrogen, and prevents violent bumping. Previous to use the stock of
reagents should always be tested by a blank experiment; in many cases
if potassic sulphate is used there is no necessity for mercury, and therefore
no sulphide is required.

The following modifications must be used for the determination
of nitrogen in substances which contain nitrates.

Estimation of Nitrog-en, including- Nitrates, by the Kjeldahl-
Grunning1- Jodlbauer Process.

The requisite quantity of substance to be analyzed is put into the digesting
flask together with 1 or 2 gm. of zinc dust. From 20 to 30 c.c. of
sulphuric acid containing 2 gm. of salicylic acid are then quickly poured over
the mixture so as to cover it at once. The whole is then gently heated till
frothing is over, and the process finished with or without the potassic sulphate
as before described.

The following observations by Bernard Dyer are of consider-
able importance in connexion with the modified process : —
" When nitrates are present in addition to organic or ammoniacal

*Some operators prefer to close the distilling flask with, a caoutchouc stopper,
through which in addition to the distilling tube, a funnel with tap is fixed for running
in the alkali, this is to guard against possible loss of ammonia.

86 VOLUMETRIC ANALYSIS. § 19.

nitrogen, Jodlbauer's modification (Cliem. Centr. iii., xvii., 433)
suffices to determine accurately the total nitrogen. This process
consists in previously adding to the sulphuric acid used for
oxidation, either phenol or, preferably, salicylic acid — generally
about 2 grams for a determination. While the contents of the
flask are still cold, from 1 to 2 grams of zinc dust are added (as
well as a drop of mercury or some oxide) and allowed to dissolve
before the flask is heated. The process is then continued exactly
as previously described, when the whole of the nitrogen is
obtained as ammonia. There is no difficulty whatever in
determining the nitrogen in potassium or sodium nitrate in
this manner ; but I find that when ammonia salts are present as
well as potassium or sodium nitrate, the results are invariably too
low, unless the sulphuric acid containing the salicylic acid is
poured quickly into the flask out of a beaker, so that the nitrate
shall be completely covered by the acid before the lapse of an
appreciable interval of time ; this prevents the formation of the
lower oxides of nitrogen, and consequent loss. When even
ammonium nitrate is treated in this way, the whole of the nitrogen
is retained in solution. I allude to this detail, because I have
nowhere seen attention drawn to it, and because I think there is
a probability of large errors occurring in the analysis of compound
fertilisers, including mixtures of ammonia salts and alkali nitrates,
if the acid is allowed to flow on to the sample from a pipette in
the usual way." The experiments carried on by this chemist, and
recorded in the paper already mentioned are extremely valuable.
They show that the Kjeldahl process either with the modifications
of Gunning and Arnold, or with that of the same and
Jodlbauer is capable of accurately estimating the nitrogen in
a very large variety of complex substances, and with the
expenditure of very little time as compared with older
methods.

As respects the substances available for the accurate estimation
of their nitrogen by the Kjeldahl method, Dyer finds that if
zinc alone (without the use of phenol or salicylic acid) be used
with aromatic nitro-compounds there is loss of nitrogen, as though
it were necessary that more carbon should be present.

The Kjeldahl-Gunning method fails to furnish the calculated
quantity of nitrogen in azobenzene or amido-azobenzene. Mere
reduction by zinc suffices with amido-azobenzene, but in the case of
azobenzene the complete Jodlbauer modification is necessary.
With amido-azotoluene the correct amount was obtained by the
Kjeldahl-Gunning process supplemented by reduction with
zinc and with carbazol by the Kjeldahl-Gunning method
alone.

Hydroxylamine hydrochloride, which contains 20-21 per cent,
of nitrogen, yielded only 3 per cent, by the Kjeldahl-Gunning
method; by reduction with zinc about 10 per cent, was obtained ;

§ 19. AMMONIA. 87

by the Kjeldahl-Gunning-Jodlbauer method about 19 per
cent, j by reduction with sugar and zinc less than 19 per cent.
The Kjeldahl-Gunning-Jodlbauer method with the addition
of sugar as well as zinc, however, gave the calculated quantity in
each of three separate determinations. Acetaldoxime, by the
K j eld a hl-Gu lining method, gave somewhat low results, but with
the addition of sugar and zinc furnished correct results.
jXaphthoquinone-oxinie yields its full percentage by the Kjeldahl-
Guniiing method.

Potassium cyanide and ethyl cyanide both give nearly correct
results by the K j e 1 d a h 1 - G u n n i n g method ; no trace of
hydrocyanic acid is evolved if the sulphuric acid used be strong.
Potassium ferrocyanide also yields accurate results. Potassium
ferricyanide, however, only gives sufficiently accurate results when
reduced by the addition of sodium thiosulphate. Sodium
nitroprusside failed with any modification of the method to yield
all its nitrogen.

Phenylhydrazine derivatives cannot by any modification of the
method tried be made to give correct results ; there is invariably
loss of nitrogen, presumably liberated in the free state.

H. C. Sherman (Jour. Amer. Chem. Soc. xvii. 567) states
that no known modification will give accurate results, where large
proportions of both chlorides and nitrates exist in the substance
digested.

The Stock Method. — A method based on the same principle as
that of Kjeldahl has been devised by W. F. K. Stock (Analyst
xvii. 109, idem xviii. 58), but the oxidation in this case depends
not on the sulphuric acid but on manganic oxide. From 0'5 to
1 '0 gm. of the substance is digested at a temperature below boiling,
with 10 c.c. of strong sulphuric acid and 5 gm. of finely ground
MnO2 until the black carbonaceous matters are destroyed and
a greenish liquid results ; this is distilled in a special apparatus,
arranged by the author of the method much in the same way as
in Kje Id a hl's process, with excess of soda and titrated in the
same way.

The results obtained by me with organic substances have almost
invariably been low in comparison with the Kjeldahl method
described above, and this is probably due to the same cause as that
existing in the original Kjeldahl method where a lower
temperature was used, and the oxidizing influence of permanganate
was relied on for completing the decomposition.

All modern authorities appear to agree in discarding the use of
permanganate in the Kjeldahl method as not only useless but
even harmful.

It is only fair to say that very good results have been obtained
in the case of certain nitrogen compounds by the Stock method,
and further research may result in its being improved.

88 VOLUMETRIC ANALYSIS. § 20.

ACIDIMETRY OB- THE TITRATION OF ACIDS.

§ 20. THIS operation is simply the reverse of all that has been
said of alkalies, and depends upon the same principles as have
been explained in alkalimetry.

With free liquid acids, such as hydrochloric, sulphuric, or nitric,
the strength is generally taken by means of the hydrometer or
specific-gravity bottle, and the amount of real acid in the sample
ascertained by reference to the tables constructed by Otto,
Bine an, or lire. The specific gravity may very easily be taken
with the pipette, as recommended with ammonia, and of course the
real acid may be quickly estimated by normal caustic alkali and an
appropriate indicator.

In the case of titrating concentrated acids of any kind it is
preferable in all cases to weigh accurately a small quantity, dilute
to a definite volume, and take an aliquot portion for titration.

Delicate End-reaction in Acidimetry.

If an alkaline iodate or bromate be added to a solution of an
alkaline iodide in the presence of a mineral acid, iodine is set free
and remains dissolved in the excess of alkaline iodide, giving the
solution the well-known colour of iodine. This reaction has been
long observed, and is capable of being used with excellent effect as
an indicator for the delicate titration of acids, and therefore of
alkalies, by the residual method. Kjeldahl, for instance, uses it
in his ammonia process, where the distillate contains necessarily an
excess of standard acid. The reaction is definite in character, and
may be used in various ways in volumetric processes. For instance,
potassic bromate liberates iodine in exact proportion to its contained
oxygen in the presence of excess of dilute mineral acid, and the
iodine so liberated may be accurately titrated writh sodic thiosulphate.
In acidimetry, however, the method is simply used for its exceeding
delicacy as an end-reaction, one drop of T^ sulphuric, nitric, or
hydrochloric acid being quite sufficient to cause a deep blue colour
in the presence of starch.

The adjustment of the standard liquids is made as follows : —
2 or 3 c.c. of — - acid are run into a flask, diluted somewhat with
water, and a crystal or two of potassic iodide thrown in ; 1 or 2 c.c.
of a 5 per cent, solution of potassic iodate are then added, which
at once produces a brown colour, due to free iodine. A solution
of sodic thiosulphate is added from a burette, with constant
shaking, until the colour is nearly discharged ; a few drops of clear
freshly prepared starch solution are now poured in, and the blue
colour removed by the very cautious addition of thiosulphate..
The quantity of thiosulphate used represents the comparative
strengths of it and the standard acid, and is used as the basis
of calculation in other titrations. The first discharge of the blue-
colour must be taken in all cases as the correct ending, because OH

§ 21. ACIDIMETRY. 89

standing a few minutes the blue colour returns, due to some
obscure reaction from the thiosulphate. This has been probably
regarded as one of the drawbacks of the process, and another is the
instability of the thiosulphate solution ; but these by no means
invalidate its accuracy, and it moreover possesses the advantage of
being applicable to excessively dilute solutions, and may be used
by artificial light. The organic acids cannot be estimated by this
method, the action not being regular. Neutral alkaline and
alkaline earthy salts have no interference, but salts of the organic
acids and borates must be absent.

ACETIC ACID.

C2H402 =» 60.

§ 21. IN consequence of the anomaly existing between the sp. gr.
of strong acetic acid and its actual strength, the hydrometer is not
reliable, but the volumetric estimation is now rendered extremely
accurate by using phenolphthaleiii as indicator, acetates of the
alkalies and alkaline earths having a perfectly neutral behaviour to
this indicator. Even coloured vinegars may be titrated when
highly diluted. Where, however, the colour is too much for this
method to succeed Pettenkofer's plan is the best, and this opinion
is endorsed by A. K. Leeds (Jour. Am. Chem. Soc. xvii. 741).
The latter takes 50 c.c. of the vinegar and 50 c.c. of water with
a drop of phenolphthalein, adds -£§ baryta to slight excess which
causes the organic colouring matters to separate either in the cold
or on warming, the excess of baryta is then found by titration
with -^ acid and turmeric paper.

Several processes have at various times been suggested for the
accurate and ready estimation of acetic acid, among which is that
of Greville Williams, by means of a standard solution of lime
syrup. The results obtained were very satisfactory.

C. Mohr's process consists in adding to the acid a known
excessive quantity of precipitated neutral and somewhat moist
calcic carbonate. When the decomposition is as nearly as possible
complete in the cold, the mixture must be heated to expel the CO2,
and to complete the saturation ; the residual carbonate is then
brought upon a filter, washed with boiling water, and titrated with
excess of normal acid and back with alkali.

In testing the impure brown pyroligneous acid of commerce,
this method has given fairly accurate results.*

The titration of acetic acid or vinegar may also be performed by
the ammonio-cupric solution described in § 15.10.

*A. E. Leeds (loo. cit.) has not found this method to answer, which I think must
be due to using dried calcic carbonate. I have only used it for commercial wood acid,
and the figures obtained by me were the highest among several other methods ; but an
error has been committed in not mentioning that the CaCQ3 should not be thoroughly
dried, and the alkalinity of which is known.

90 VOLUMETRIC ANALYSIS. § 21.

1. Free Mineral Acids in Vineg-ar. — Hehlier has devised ail
•excellent method for this purpose (Analyst i. 105).

Acetates of the alkalies are always present in commercial vinegar ;
and when such vinegar is evaporated to dryness, and the ash ignited,
the alkalies are converted into carbonates having a distinct alkaline
reaction on litmus; if, however, the ash has a neutral or acid
reaction, some free mineral acid must have been present. The
alkalinity of the ash is diminished in exact proportion to the
amount of mineral acid. added to the vinegar as an adulteration.
Hence the following process :

50 c.c. of the vinegar are mixed with 25 c.c. of -£$ soda or potash,
evaporated to dryness, and ignited at a low red heat to convert the acetate?
into carbonates ; when cooled, 25 c.c. of ^r acid are added ; the mixture
heated to expel CO', and filtered ; after washing the residue/the filtrate and
washings are exactly titrated with ^ alkali ; the volume so used equals the
amount of mineral acid present in the 50 c.c. of vinegar.

1 c.c. /„ alkali=0'0049 gra. H2SO4 or 0'003037 gm.liCl.

If the vinegar contains more than 0'2 per cent, of mineral acid,
more than 25 c.c. of ~ alkali must be used to the 50 c.c, vinegar
before evaporating and igniting.

2. Acetates of the Alkalies and Earths. — These salts are
converted by ignition into carbonates, and can be then residually
titrated with normal acid ; no other organic acids must be present,
nor must nitrates, or similar compounds decomposable by heat.
1 c.c. normal acid^O'06 gm. acetic acid.

3. Metallic Acetates. — Neutral solutions of lead and iron acetates
may be precipitated by an excess of normal sodic or potassic carbonate, the
precipitate well boiled, filtered, and washed with hot water, the filtrate and
washings made up to a definite volume, and an aliquot portion titrated with
N or ^ acid ; the difference between the quantity so used and calculated for
the original volume of alkali will represent the acetic acid.

If such solutions contain free acetic or mineral acids, they must
be exactly neutralized previous to treatment.

If other salts than acetates are present, the process must be
modified as follows : —

Precipitate with alkaline carbonate in excess, exactly neutralize with
hydrochloric acid, evaporate the whole or part to dryuess, ignite to convert
the acetates into carbonates, then titrate residually with normal acid. Any
other organic acid than acetic will, of course, record itself in terms of acetic
acid.

4. Commercial Acetate of Lime. — The methods just described
are often valueless in the case of this substance, owing to tarry
matters, which readily produce an excess of carbonates.

Presenius (Z. a. c. xiii. 153) adopts the following process for tolerabl}r
pure samples : — 5 gm. are weighed and transferred to a 250 c.c. flask,
dissolved in about 150 c.c. of water, and 70 c.c. of normal oxalic acid added ;
the flask is then well shaken, and filled to the mark, 2 c.c. of water are added

§ 21. ACETIC ACID. • 91

to allow for the volume occupied by the precipitate, the whole is again well
shaken, and left to settle. The solution is then filtered through a dry filter
into a dry flask : the volume so filtered must exceed 200 c.c.

100 c.c. are first titrated with normal alkali and litmus ; or, if highly
coloured, by help of litmus or turmeric paper ; the volume used multiplied
by 2' 5 will give the volume for 5 gm.

Another 100 c.c. are precipitated with solution of pure calcic acetate in
slight excess, warmed gently, the precipitate allowed to settle somewhat,
then filtered, well washed, dried, and strongly ignited, in order to convert
the oxalate into calcic carbonate or oxide, or a mixture of both. The
residue so obtained is then decomposed with excess of normal acid, and
titrated residually with normal alkali. By deducting the volume of acid
used to neutralize the precipitate from that of the alkali used in the first
100 c.c., and multiplying by 2'5, is obtained the volume of alkali expressing
the weight of acetic acid in the 5 gm. of acetate.

In the case of very impure and highly coloured samples of
acetate, it is only possible to estimate the acetic acid by repeated
distillations with phosphoric acid and water to incipient dryness,
and then titrating the acid direct with ~ alkali, each c.c. of which
represents 0'006 gm. acetic acid.

The distillation is best arranged as suggested by Still well and
Gladding, or later by Harcourt Phillips (C. N. liii. 181).

A 100 to 120 c.c. retort, the tubulure of which carries a small funnel
fitted in with a caoutchouc stopper, and the neck of the funnel stopped
tightly with a glass rod shod with elastic tube, is supported upon a stand in
such a way that its neck inclines upwards at about forty-five degrees : the
end of the neck is drawn out, and bent so as to fit into the condenser by
help of an elastic tube. The greater part of the retort neck is coated with
flannel, so as to prevent too much condensation.

1 gm. of the sample being placed in the retort, 10 c.c. of a 40 per cent,
solution of P2O5 are added, together with as much water as will make about
50 c.c. A small naked flame is used, and if carefully manipulated, the
distillation may be carried on to near dryness without endangering the
retort. After the first operation the retort is allowed to cool somewhat, then
50 c.c. of hot water added through the funnel, another distillation made as
before, and the same repeated a third time, Avhich will suffice to carry
over all the acetic acid. The distillate is then titrated with alkali and
phenolphthalein.

By this arrangement the frothing and spirting is of no con-
sequence, and the whole process can be completed in less than
an hour. The results are excellent for technical purposes.

Weber (Z, a. C. xxiv. 614) has devised a ready and fairly
accurate method of estimating the real acetic acid in samples of
acetate of lime, based on the fact that acetate of silver is insoluble
in alcohol.

Process : 10 gm. of the sample in powder are placed in a 250 c.c. flask,
a little water added, and heated till all soluble matters are extracted, cooled,
and made up to the measure : 25 c.c. are then filtered through a dry filter,
put into a beaker, 50 c.c. of absolute alcohol added, and the acetic acid at
once precipitated with an alcoholic solution of silver nitrate. The silver
acetate, together with any chloride, sulphate, etc., separates free from
colour. The precipitate is brought on a filter, well washed with 60 per cent,
alcohol till the free silver is removed ; precipitate is then dissolved in weak

92 • VOLUMETRIC ANALYSIS. § 22.

nitric acid, and titrated with ^ salt solution. Each c.c. represents O'OOG gm.
acetic acid.

Several trials made in comparison with the distillation method
with phosphoric acid gave practically the same results.

A good technical process has been devised by Grim aha w
(Allen's Organic Analysis i. 397). 10 gm. of the sample are treated
with water and an excess of sodic bisulphate (ISfaHSO4), the
mixture diluted to a definite volume, filtered, and a measured
portion of the filtrate titrated with standard alkali ; a similar
portipn meanwhile is evaporated to dryness with repeated
moistening with water, to drive off all free acetic acid. The
residue is dissolved and titrated with standard alkali, when the
difference between the volume now required and that used in the
original solution will correspond to the acetic acid in the sample.
Litmus paper is the proper indicator.

BORIC ACID AND EQUATES.

Boric anhydride B203 =70.

§ 22. THE soda in borax may, according to Thomson, be
very accurately estimated by titrating the salt with standard H2S04
and methyl orange or lacmoid paper. Litmus and phenacetolin
give very doubtful end-reactions : phenolphthaleiii is utterly useless.

Example : T683 gm. sodic pyroborate in 50 c.c. of water required in one
case 16'7 c.c. normal acid, and in a second 16'65 c.c. The mean of the two
represents 0'517 gm. Na2O. Theory requires 0'516 gm.

The estimation of boric acid as such has up to the present time
presented great difficulties, and no volumetric method of any
value has been available.

R. T. Thomson has now removed this difficulty by finding
a method easy of execution, and • of considerable accuracy
(J. S.C.I, xii. 432), see also page 44 in this book.

Process : To determine boric acid in articles of commerce it is
necessary to use methyl orange, to which indicator boric acid is perfectly
neutral. In the case of boric acid in borax 1 gm. is dissolved in water,
metlryl orange added, and then dilute sulphuric acid till the pink colour just
appears. Boil for a short time to expel carbonic acid, cool, and add normal
or fifth-normal soda till the pink colour of the methyl orange (a little more
of which should be added if necessary) just assumes a pure yellow tinge.
At this stage all the boric acid will exist in the free state. Add glycerine in
such proportion that the total solution after titration will contain 30 per
cent, at least, then add a little phenolphthaleiii, and lastly normal or fifth-
normal soda from a burette until a permanent pink colour is produced.
More glycerine may be added during the estimation if it is found necessary.
The proportion of boric acid present is calculated from the number of c.c. of
soda consumed.

1 c.c. normal NaOH=0'0620 gm. H3BO3

1 c.c. „ „ =0-0505 gm. Na2B407

1 c.c. „ „ =0-0955 gm. Na2B4O7+10H-O

§ 23. CARBONIC ACID. 93

In the case of boric acid of commerce, which generally contains salts of
ammonium, 1 gin. may be dissolved in hot water, a slight excess of sodic
carbonate added, and the solution boiled down to about half its bulk to expel
ammonia. Any precipitate which appears may then be filtered off, and the
filtrate titrated as already described.

The method may also be applied to boracite or borate of lime by dissolving
1 gm. of either of these minerals in dilute hydrochloric acid with the aid of
heat, nearly neutralizing with caustic soda, boiling to expel carbonic
acid, cooling, exactly neutralizing to rnetlryl orange, and continuing the
determination as in borax. If much iron is present, however, it may be
removed by a preliminary treatment with sodic carbonate, and removal of
oxide of iron as well as the carbonates of calcium and magnesium ~by
nitration.

Thomson has also attempted to apply the process to the
estimation of boric . acid in milk and other foodstuffs. This of
course necessitates the removal of phosphoric acid from the ash of
the milk, for which purpose a barium salt was found to be
a successful precipitant, and if the solution be sufficiently dilute
will leave the boric acid in solution. The experiments have not
as yet been completely successful.

CARBONIC ACID AND CARBONATES.

§ 23. ALL carbonates are decomposed by strong acids ; the
carbonic acid which is liberated splits up into water and carbonic
anhydride (CO2), which latter escapes in the gaseous form.

It will be readily seen from what has been said previously as
to the estimation of the alkaline earths, that carbonic acid in
combination can be estimated volumetrically with a very high
degree of accuracy (see § 18).

The carbonic acid to be estimated may be brought into
combination with either calcium or barium, these bases admitting
of the firmest combination as neutral carbonates.

If the carbonic acid exist in a soluble form as an alkaline mono-
carbonate, the decomposition is effected by the addition of baric or
calcic chloride as before directed ; if as bicarbonate, or a compound
between the two, ammonia must be added with either of the
chlorides.

As solution of ammonia frequently contains carbonic acid, this
must be removed by the aid of baric or calcic chloride, previous
to use.

1. Carbonates Soluble in Water.

It is necessary to remember, that when calcic chloride is used as
the precipitant in the cold, amorphous calcic carbonate is first
formed ; and as this compound is sensibly soluble in water, it is
necessary to convert it into the crystalline form. In the absence of
free ammonia this can be accomplished by boiling. When ammonia
is present, the same end is obtained by allowing the mixture to

94 VOLUMETRIC ANALYSIS. § 23.

stand for eight or ten hours in the cold, or by heating for an hour
or two to 70 — 80° C. "With barium the precipitation is regular.

Another fact is, that when ammonia is present, and the precipi-
tation occurs at ordinary temperatures, ammonic carbamate is
formed, and the baric or calcic carbonate is only partially precipi-
tated. This is overcome by heating the mixture to near boiling for
a couple of hours, and is best done by passing the neck of the
flask through a retort ring, and immersing the flask in boiling
water.

When caustic alkali is present in the substance to be examined,
it is advisable to use barium as the precipitant ; otherwise, for all
volumetric estimations of CO2 calcium is to be preferred, because
the precipitate is much more quickly and perfectly washed than
the barium compound.

Example : 1 gra. of pure anhydrous sodic carbonate was dissolved in
water, precipitated while hot with baric chloride, the precipitate allowed to
settle well, the clear liquid decanted through a moist filter, more hot water
containing a few drops of ammonia poured over the precipitate, which was
repeatedly done so that the bulk of the precipitate remained in the flask,
being washed by decantation through the filter ; when the washings showed
no trace of chlorine, the filter was transferred to the flask containing the
bulk of the precipitate, and 20 c.c. of normal nitric acid added, then titrated
with normal alkali, of which 1/2 c.c. was required=18'8 c.c. of acid ; this
multiplied by 0'022, the coefficient for carbonic acid, gave O4136 gin. CO-=
41'36 per cent., or multiplied by 0 053, the coefficient for sodic carbonate,
gave 0*9964 gm. instead of 1 gm.

2. Carbonates Soluble in Acids.

It sometimes occurs that substances have to be examined for
carbonic acid, which do not admit of being treated as above
described ; such, for instance, as the carbonates of the metallic
oxides (white lead, calamine, etc.), carbonates of magnesia, iron,
and copper, the estimation of carbonic acid in cements, mortar, and
many other substances. In these cases the carbonic acid must be
evolved from the combination by means of a stronger acid, and
conducted into an absorption apparatus containing ammonia, then
precipitated with calcic chloride, and titrated as before described.

The following form of apparatus (fig. 33) affords satisfactory
results.

The weighed substance from which the carbonic acid is to be evolved is
placed in b with a little water; the tube d contains strong hydrochloric
acid, and c broken glass wetted with ammonia free from carbonic acid.
The flask « is about one-eighth filled with the same ammonia : the bent tube
must not enter the liquid. When all is ready and the corks tight, warm the
flask a gently so as to fill it with vapour of ammonia, then open the clip and
allow the acid to flow circumspectly upon the material, which may be heated
until all carbonic acid is apparently driven off ; then by boiling and shaking
the last traces can be evolved, and the operation ended. When cool, the
apparatus may be opened, the end of the bent tube washed into a, and also
a good quantity of boiled distilled water passed through c, so as to carry

§ 23.

CARBONIC ACID.

95>

down any ammonic carbonate that may have formed. Then add solution of
calcic chloride, boil, filter, and titrate the precipitate as before described.

-During- the filtration, and while ammonia is present, there is a great
avidity for carbonic acid, therefore boiling water should be used for washin°-
and the funnel kept covered with a small glass plate.

In many instances CO2 may be estimated by its equivalent in
chlorine with -—- silver and potassic chromate, as in § 39.

Fig. 33.
3. Carbonic Acid. G-as in

etc.

Waters,

The carbonic acid existing in waters as neutral carbonates of the
alkalies or alkaline earths may very elegantly and readily be titrated
directly by ^ acid (see-§ 18).

"Well or spring water, and also mineral waters, containing free
carbonic acid gas, can be examined by collecting measured quantities
of them at their source, in bottles containing a mixture of calcic
and ammonic chloride, afterwards heating the mixture in boiling
water for one or two hours, and titrating the precipitate as before
described.

Pettenkofer's method with caustic baryta or lime is decidedly
preferable to any other. Lime water may be used instead of'

96 VOLUMETRIC ANALYSIS. § 23.

baryta with equally good results, but care must be taken that the
precipitate is crystalline.

The principle of the method is that of removing all the carbonic
acid from a solution, or from a water, by excess of baryta or lime
water of a known strength ; and, after absorption, finding the
excess of baryta or lime by titration with -^ acid and turmeric
paper.

The following is the best method to be pursued for ordinary
drinking waters not containing large quantities of carbonic acid : —

100 c.c. of the water are put into a flask with 3 c.c. of strong solution of
calcic or baric chloride, and 2 c.c. of saturated solution of ammonic chloride ;
45 c.c. of baryta or lime water, the strength of which is previously ascertained
by means of decinormal acid, are then added, the flask well corked and put
aside to settle ; when the precipitate is f ully subsided, take out 50 c.c. of the
clear liquid with a pipette, and let this be titrated with decinormal acid.
The quantity required must be multiplied by 3 for the total baryta or lime
solution, there being 50 c.c. only taken ; the number of c.c. so found must be
deducted from the original quantity required for the baryta solution added ;
the remainder multiplied by 0'0022 will give the weight of carbonic acid
existing free and as bicarbonate in the 100 c.c.

The addition of the baric or calcic chloride and ammonic chloride is made
to prevent any irregularity which might arise from alkaline carbonates or
sulphates, or from magnesia.

If it be desirable to ascertain the volume of carbonic acid from
the weight, 1000 c.c. of gas, at 0° and 0*76 m.m., weigh
1 '96663 gm. 100 cubic inches weigh 47'26 grains.

4. Carbonic Acid in Aerated Beverages, etc.

For ascertaining the quantity of carbonic acid in bottled aerated
•waters, such as soda, seltzer, potass, and others, the following
.apparatus is useful.

Fig. 34 is a brass tube made like a cork -borer, about five inches long, having
four small holes, two on each side, and about two inches from its cutting end ;
the upper end is securely connected with the bent tube from the absorption
flask (tig. 35) by means of a vulcanized tube ; the flask contains a tolerable
quantity of pure ammonia, into which the delivery tube dips ; the tube
a contains broken glass moistened with ammonia.

Everything being ready the brass tube is greased, and the bottle being
-held in the right hand, the tube is screwed a little aslant through the cork
by turning the bottle round, until the holes appear below the cork and the
gas escapes into the flask. When all visible action has ceased, after the
bottle has been well shaken two or three times to evolve all the gas that can
ibe possibly eliminated, the vessels are quietly disconnected, the tube a washed
out into the flask, and the contents of the bottle added also ; the whole is
then precipitated with calcic chloride and boiled, and the precipitate titrated
as usual. This gives the total carbonic acid free and combined.

To find the quantity of the latter, another bottle of the same manufacture
must be evaporated to dryness, and the residue gently ignited, then titrated
with normal acid and alkali ; the amount of carbonic acid in the mono-
-carbonate deducted from the total, will give the weight of free gas originally
present.

CARBONIC ACID.

The volume may be found as follows : — 1000 c.c. of carbonic acid at 0°,
and 76 m.m., weigh T96663 gm. Suppose, therefore, that the total weight
of carbonic acid found in a bottle of ordinary soda water was 2'8 gm., and
the weight combined with alkali 0'42 gm., this leaves 2'38 gm. CO2 in
a free state —

1-96663 : 2'38

1000 : x = 1210

If the number of c.c. of carbonic acid found is divided by the
number of c.c. of soda water contained in the bottle examined, the
quotient will be the volume of gas compared with that of the soda
water. The volume of the contents of the bottle is ascertained by
marking the height of the fluid previous to making the experiment ;
the bottle is afterwards filled to the same mark with water, emptied
into a graduated cylinder and measured ; say the volume was
292 c.c., therefore

4-14 vols. CO2.

rig. si.

5. Carbonic Acid in Air.

A dry glass globe or bottle capable of being securely closed by
a rubber stopper, and holding 4 to 6 liters, is filled with the air
to be tested by means of a bellows aspirator ; baryta water is then
introduced in. convenient quantity and of known strength as
compared with T~ acid.'" The vessel is securely closed, and the
liquid allowed to flow round the sides at intervals during half an
hour or more. When absorption is judged to be complete, the

* Clowes and C o 1 e m a n prefer to use saturated lime water in place of baryta, and
have obtained good results : see their Quantitative Analysis, 2nd. edit. p. 416.

98 VOLUMETRIC ANALYSIS. § 23.

baryta is emptied out quickly into a stoppered bottle, and the
excess of baryta at once ascertained in a measured portion by T^y-
hydrochloric acid and turmeric paper as described in § 15.9. The
final calculation is of course made on the total baryta originally
used, and upon the exact measurement of the air-collecting vessel.
It is above all things necessary to prevent the absorption of CO2
from extraneous sources during the experiment. The error may be
reduced to a minimum by carrying on the titration in the vessel
itself, which is done by fixing an accurately graduated pipette
through the cork or caoutchouc stopper of the air vessel, to the
upper end of which is attached a stout piece of elastic tube, closed
with a pinch-cock ; and this being filled to the 0 mark with dilute
standard acid acts as a burette. The baryta solution tinted with
phenolphthaleiii is placed in the air bottle which must be of
colourless glass, and after absorption of all CO2, the excess of
baryta is found by running in the acid until the colour disappears.
The cork or stopper must have a second opening to act as
ventilator ; a small piece of glass tube does very well.

If a freshly made solution of oxalic acid is used containing
0*2863 gm. per liter, each c.c. represents 1 mgm. CO2. The liquid
holds its strength correctly for a day, and can be made as required
from a strong solution, say 28*636 gm. per liter.

Another method of calculation is, to convert the volume of
baryta solution decomposed into its equivalent volume in ~ acid,
1 c.c. of which = 0*0022 gm. CO2 or by measurement at 0° C. and
760 m.m. pressure represents 1*119 c.c. The method above
described is a combination of those of Pettenkofer and Dal ton,
and though much used, is liable to considerable error from various
causes.

A. H. Gill in a report from the Sanitary and Gas Analysis
Laboratory of the Technical Institute at Boston, U.S.A.
(Analyst xvii. 184), gives a somewhat modified arrangement of the
Pettenkofer method. Ordinary green glass bottles of one or
two gallon capacity are measured with water, and the contents in
c.c. ascertained preferably by weighing on a good balance.

The bottles are dried before being used, this may easily be done
by rinsing first with alcohol or methylated spirit, draining, then
rinsing with ether and after again draining, the bottle is quickly
dried by blowing air through it witli the ordinary laboratory bellows.
If this plan is not used they must be dried after draining well, in
a warm closet. A special form of bellows for filling the bottle
with air is used by Gill, but the usual aspirator made on the
accordion pattern suffices, or a small fan blower, the driving parts
of which are connected by rubber bands to render it noiseless, may
be used.

The bottle is fitted with a rubber stopper carrying a glass tube,
closed by a plug of solid rubber.

The air to be tested is drawn into the bottle by repeated use of

§ 23. CAKBONIC ACID. 99

the aspirator so as to collect a representative sample, and if the
test is made in a room everything should be quiet, and care must
be taken to avoid draughts or the proximity of a number of
persons.

Process : 50 c.c. of the standard barium hydrate are run into the
bottle rapidly from a burette (the tip passing entirely through the tube in
the stopper), the nipple replaced, and the solution spread completely over the
sides of the bottle while waiting three minutes for the draining of the
burette, before reading, unless it be graduated to deliver 50 c.c. The bottle
is now placed upon its side, and shaken at intervals for forty to sixty
minutes, taking care that the whole surface of the bottle is moistened with
the solution each time. The absorption of the last traces of carbon dioxide
is very slow indeed, half an hour in many cases being insufficient.

At the time at which the barium solution is added, the temperature and
pressure should be noted. At the end of the above period, shake well to
insure homogeneity of the solution, remove the cap from the tube, and
invert the large bottle quickly over a 60 or 70 c.c. glass stoppered bottle, so
that the solution shall come in contact with the air as little as possible. With-
out waiting for the bottle to drain, withdraw a portion of 15 or 25 c.c. with
a narrow-stemmed spherical-bulbed pipette and titrate with sulphuric acid*
(1 c.c.=l mgm. CO2), using rosolic acid as an indicator. The difference
between the number of c.c. of standard acid required to neutralize the
amount of barium hydrate (e.g., 50 c.c.) before and after absorption, gives
the number of milligrams of carbon dioxide present in the bottle.

This is expressed in cubic centimeters under standard conditions, and
divided by the capacity of the bottle under standard conditions, and the
results reported in parts per 10,000. To reduce the air in the bottle to standard
•conditions, a hygrometric measurement of the air in the room from which
the sample was taken, is necessary. This in ordinary cases is usually
omitted, as the object of the investigation is comparative results, as regards
the efficiency of ventilation, and the rooms in the same building Avould not
vary appreciably in the amount of moisture in the atmosphere. This
correction may make a difference of about 0'15 parts per 10,000.

Another method on the same principle is to attacli a bulb
apparatus, containing a measured quantity of baryta or lime
water, to an aspirator bottle filled with water; the tap of the
"bottle is opened to such an extent as to allow the air to bubble
through the test solution at a moderate rate. The process of
titration is the same as above. This method takes longer time,
and the volume of air, which should not be less than five or six
liters, is ascertained by measuring the volume of water allowed to
run out of the aspirator, and the rate of flow being regulated so
that from two to three hours is required to pass the above volume
•of air. If a flask, fitted with tubes, is used in place of, the bulb
apparatus, the titration may be done without transferring the test
solution.

* Sulphuric acid, in distinction to oxalic acid, enables one to estimate the excess of
"barium hydrate in presence of the suspended barium carbonate, and also of caustic
alkali, which is a frequent impurity of commercial barium hydrate. Professor
Johnson, in the American edition of Fresenius' Quantitative Analysis, calls
attention to the fact that the normal alkaline oxalates decompose the alkaline earthy
carbonates, so that the reaction continues alkaline if the least trace of soda or potash
be present. The sulphuric acid may be prepared by diluting 46*51 c.c. normal sulphuric
acid to a liter.

H 2

100 VOLUMETRIC ANALYSIS. § 23,

6. Sckeibler's Apparatus for the estimation of Carbonic Acid

by "Volume.

This apparatus is adapted for the estimation of the CO2 contained
in native carbonates, as well as in artificial products, and has been
specially contrived for the purpose of readily estimating the CO2
in the bone-black used in sugar refining. The principle upon,
which the apparatus is founded is simply this : — That the quantity
of CO2 contained in calcic carbonate can be used as a measure
of the quantity of that salt itself ; and instead of determining, as
has usually been the case, the quantity of gas by weight, this
apparatus admits of its. estimation by volume ; and it is by this
means possible to perform, in a few minutes, operations which
would otherwise take hours to accomplish, while, moreover, the
operator need scarcely possess any knowledge of chemistry. The
results obtained by this apparatus are correct enough for technical
purposes.

The apparatus is shown in fig. 36, and consists of the following
parts : — The glass vessel, A, serves for the decomposition of the
material to be tested for CO2, which for that purpose is treated
with dilute HC1 ; this acid is contained, previous to the experiment,.
in the gutta-percha vessel s. The glass stopper of A is perforated,
and through it firmly passes a glass tube, to which is fastened the
india-rubber tube r, by means of which communication is opened
with B, a bottle having three openings in its neck. The central
opening of this bottle contains a glass tube (r) firmly fixed, which
is in communication, on the one hand, with A, by means of the
flexible india-rubber tube already alluded to, and, on the other
hand, inside of B, with a very thin india-rubber bladder, K.
The neck (</) of the vessel B is shut off during the experiment by
means of a piece of india-rubber tubing, kept firmly closed with
a spring clamp. The only use of this opening of the bottle B,,
arranged as described, is to give access of atmospheric air to the
interior of the bottle, if required. The other opening is in
communication with the measuring apparatus C, a very accurate
cylindrical glass tube of 150 c.c. capacity, divided into 0*5 c.c. ;
the lower portion of this tube C is in communication with the
tube D, serving the purpose of controlling the pressure of the gas.
The lower part of this tube D ends in a glass tube of smaller
diameter, to which is fastened the india-rubber tube p, leading
to E, but the communication between these parts of the apparatus
is closed, as seen at p, by means of a spring clamp. E is a water
reservoir, and on removal of the clamp at p, the water contained
in C and D runs off towards E ; when it is desired to force the
water contained in E into C and I), this can be readily done
by blowing with the mouth into V, and opening the clamp
at p.

The main portion of the apparatus above described, with the
exception, however, of the vessel A, is fixed by means of brass

23.

CARBONIC ACID.

101

fittings to a wooden board ; a thermometer is also attached. The
filling of the apparatus with water is very readily effected by
pouring it through a suitable funnel placed in the open end of the
tube D, care being taken to remove, or at least to unfasten, the
.spring clamp at p ; in this manner the water runs into E, which

should be almost entirely filled. Distilled water is preferable for
this purpose, especially as the filling only requires to be done once,
because the water always remains in E as long as the apparatus is
intended to be kept ready for use. When it is required to fill the
tubes C and I) with water, so as to reach the zero of the scale

102 VOLUMETRIC ANALYSIS. § 2S.

of the instrument, it is best to remove the glass stopper from A.
The spring clamp at p is next unfastened, and air is then blown by
means of the mouth into the tube V, which communicates with E ;
by this operation the water rises up into the tubes C and D,
which thus become filled with that liquid to the same height.
Care should be taken not to force the water up above the zero*
of the scale at C, and especial care should be taken against forcing
so much of the fluid up that it would run over into the tube ?/,.
and thence find its way to B, whereby a total disconnection of
all the parts of the apparatus would become necessary. If by any
accident the water should have been forced up above the zero at C,,
before the operator had closed the spring clamp at p, this is easily
remedied by gently opening that clamp, whereby room is given for
the water to run off to E in such quantity as may be required to-
adjust the level of that fluid in C precisely with the zero of the scale.
The filling of the tube C with water has the effect of forcing the
air previously contained in that tube into E, where it causes the
compression of the very thin india-rubber ball placed within B.
If it should happen that this india-rubber ball has not become
sufficiently compressed and flattened, it is necessary to unfasten the
spring clamp at q, and to cautiously blow air into B, through
the tube q, by which operation the complete exhaustion of the-
india-rubber bladder placed within B is readily performed. This-
operation is also required only once, because during the subsequent
experiments the india-rubber bladder K is emptied spontaneously.
It may happen, however, that while the filling of the tubes I) and C
with water is being proceeded with, the india-rubber bladder K
has become fully exhausted of air before the water in C reaches
the zero of the scale. In that case the level of the water in the
tubes D and C will not be the same, but will be higher in D :
it is evident, however, that this slight defect can be at once
remedied by momentarily unfastening the spring clamp at q.

The apparatus should be placed so as to be out of reach of direct
sunlight, and should also be protected against the heat of the
operator's body by intervention of a glass screen, and is best placed
near a north window, so as to afford sufficient light for reading off
the height of the water in the tubes.

In testing carbonates the method is as follows : —

Put the very finely powdered portion of carbonate into the perfectly dry
decomposing glass A, fill the gutta-percha tube with 10 c.c. hydrochloric
acid of 1'12 sp. gr., place the tube cautiously in the decomposing glass, and
then close the bottle with the well-tallowed stopper. Here the water will
sink a little in C and rise in D ; open q for a moment, and the equilibrium
Avill be restored. Now note the thermometer and barometer, grasp the bottle
with the right hand round the neck to avoid warming, raise it, incline it
slightly so that the hydrochloric acid may mix with the substance gradually,
and at the same time with the left hand regulate p, so that the water in the
two tubes may be kept at exactly the same height ; continue these operations
without intermission, till the level of the water in C does not change for
a few seconds. Now bring the columns in C and D to exactly the same height,

§ 24. CITRIC ACID. 103

read off the height of the water, and note whether the temperature has
remained constant. If it has, the number of c.c. read off indicates the
liberated CO'2, but as a small quantity has been dissolved by the hydrochloric
acid, it is necessary to make a correction. Scheibler has determined the
small amount of carbonic acid which remains dissolved in the 10 c.c.
hydrochloric acid at the mean temperature, and he directs to add 0'8 c.c. to
the volume of the carbonic acid read off. Warington (C. N. xxxi. 253)
states that this is not a constant quantity, but is dependent upon the volume
of gas evolved, and this ratio he fixes at 7 per cent, of the gas measured.
Lastly, the volume being reduced to 0°, 760 m.m., and the dry condition, the
weight is found.

Under no circumstances can the method be considered actually accurate,
but for technical purposes it is convenient, as the operation is performed in
a very short time, and is specially suitable for comparative examinations
of various specimens of the same material.

If it is desired to dispense with all corrections, each set of
experiments may be begun by establishing the relation between
the CO2 obtained in the process (i.e. the CO2 actually yielded
+ 0*8 c.c.) and pure calcic carbonate. This relation is, of course,
dependent on the temperature and pressure prevailing on the
particular day. For example, from 0'2737 gm. calcic carbonate
containing 0*1204 gm. CO2, 63*8 c.c. were obtained, including
the 0*8 c.c. ; and in an analysis of dolomite under the same
circumstances from 0'2371 gm. substance, 57*3 c.c. were obtained,
including the 0*8 c.c.

Therefore 63*8 : 57*3 : : 0*1204 : x, or £ = 0*1082, consequently
the dolomite contains 45*62 per cent, of CO2.

For the special procedure in testing bone-black, used in sugar
refining, the reader is referred to the printed instructions supplied
with the apparatus.*

"Wigner (Analyst i. 158) has obtained exceedingly good results
in the analysis of lead carbonates, etc., with Me Leod's gas
apparatus. The nitrometer has also been turned to good account
for the same purpose.

CITRIC ACID.

C607H8xH20 = 210.

§ 24. THIS acid in the free state may readily be titrated
with pure normal soda and phenolphthalein. 1 c.c. normal alkali
= 0*07.gm. crystallized citric acid.

1. Citrates of the Alkalies and Earths.— These citrates may be
treated with neutral solution of lead nitrate or acetate, in the absence of
other acids precipitable by lead. The lead citrate is washed with a mixture
of equal parts alcohol and water, the precipitate suspended in water, and
H2S passed into it till all the lead is converted into sulphide; the clear
liquid is then boiled to remove IPS, and titrated with normal alkali.

* It is perhaps almost needless to say that the modern apparatus designed by
Hemp el, Lunge, and others, for technical gas analysis, practically supersedes that
of Scheibler. The methods are all, however, open to the objection that an uncertain
portion of CO- is lost by aqueous absorption.

104 VOLUMETRIC ANALYSIS. § 25.

2. Fruit Juices, etc. — If tartaric is present, together with free
citric acid, the former is first separated as potassic bitartrate,
which can very well be done in the presence of citric acid, as
follows : —

A cold saturated proof spirit solution of potassic acetate is added to a
somewhat strong solution of the mixed acids in proof spirit, in sufficient
quantity to separate all the tartaric acid as bitartrate, which after stirring
well is allowed to stand some hours ; the precipitate is then transferred to a
filter, and first washed with proof spirit, then rinsed off the filter with a cold
saturated solution of potassic bitartrate, and allowed to stand some hours,
with occasional stirring; this treatment removes any adhering citrate. The
bitartrate is again brought on to a filter, washed once with proof spirit, then
dissolved in hot water, and titrated with normal alkali, 1 c.c. of which —
0'15 gni. tartaric acid.

The first filtrate may be titrated for the free citric acid present after
evaporating the bulk of the alcohol.

3. Lime and Lemon Juices. — The citric acid contained in lemon,
lime, and similar juices, may be very fairly estimated by
Warington's method (J. C. S. 1875, 934).

15 or 20 c.c. of ordinary juice, or 3—4 c.c. of concentrated juice, are first
exactly neutralized with pure normal soda, made up, if necessary, to about
50 c.c., heated to boiling in a salt bath, and so much solution of calcic
chloride added as to be slightly in excess of the organic acids present. The
mixture is kept at the boiling point for about half-an-hour, the precipitate
collected on a filter and washed with hot water, filtrate and washings concen-
trated to about 15 c.c., and a drop of ammonia added ; this will produce a
further precipitate, which is collected separately on a very small filter by
help of the previous filtrate, then washed with a small quantity of hot water.
Both filters, with their precipitates, are then dried, ignited at a low red heat,
and the ash titrated with normal_or ^ acid, each c.c. of which represents
respectively O'OY or O'OOT gm H3 Ci + H2O.

FORMIC ACID.

HCOOH = 4G.

§ 25. H. C. JONES (Amer. Cliem, Jour. xvii. 539— 541) has
worked out a method which though not acidimetric may be
quoted here. It is based on a' process originally devised by
Peau de Saint-Gilles, by titration with potassic permanganate
in the presence of an alkaline carbonate. Lieben confirmed
this, using a more elaborate process. The method is on the same
principle, but the procedure differs from that of Lieben.

Process : The solution containing the formic acid is made alkaline with
Na2CO3, warmed and an excess of standard permanganate added. All the
formic acid is thus oxidized, and a precipitate of manganese hydroxide
thrown down. The solution is acidified with H-'SO4, and a measured volume
of oxalic acid run in until all the precipitate has dissolved and the
permanganate disappeared. The excess of oxalic acid is then titrated with
standard permanganate. A volume of oxalic acid equal to that taken is also
titrated with the permanganate solution, and the difference between the result
<md the total permanganate used gives the quantity of permanganate required
fco oxidize the formic acid. The experimental results agree well among
themselves and with those obtained by other methods.

§ 26. HYDROFLUOKIC ACID. 105

The author further shows that Saint- Gilles' statement that
oxalic acid can be titrated in acid solution in the presence of
formic acid is unreliable, since formic acid is also oxidized to some
extent by the permanganate under these conditions.

F. Freyer (Chem, Zeit. xix. 1184), having occasion to determine
the formate in a mixture of calcium acetate and formate, has
devised the following method.

Process : The mixed calcium salts are distilled with dilute sulphuric acid
in a current of steam until the distillate is no longer acid ; an aliquot portion
of the distillate is titrated with alkali to determine the total acid, wiiilst
another portion is evaporated, if necessary, with excess of caustic soda to
concentrate it, and is treated as follows : 10 to 20 c.c , containing about
0'5 gm. of formic acid, are heated for half an hour to an hour with 50 c.c.
of a 6 per cent, solution of potassic bichromate and 10 c.c. of concentrated
sulphuric acid in a flask provided with an inverted condenser. The liquid is
now made up to 200 c.c., and the unaltered chromic acid determined in
10 c.c. of it. For this purpose, 1 to 2 gm. of pure potassic iodide, 10 c.c.
of a 25 per cent, solution of phosphoric acid, and some water are added ; and
after five minutes the solution is diluted to about 100 c.c. with boiled water,
and titrated with T^- thiosulphate solution in the usual manner: The
phosphoric acid is added according to Meineke's recommendation, and is
for the purpose of rendering the change from the blue colour of the iodide
of starch to the green of the chromium salt more visible ; the commercial
glacial acid may be dissolved in water, oxidized by potassium permanganate
until it has a faint rose colour, and filtered before being used.

The bichromate solution used for the oxidation is titrated in the same
way. One mol. potassic bichromate is equivalent to three mols. formic acid.

The results quoted by the author show that the method is fairly
accurate, both in the absence and in presence of acetic acid.

HYDROFLUORIC ACID, SILICOFLUORIC ACID,
AND FLUORIDES.

1 c.c. of ^ alkali = 0-02 gm. of HF = 0'024 gm. of H2SiF«.

§ 26. COMMERCIAL hydrofluoric acid, which is now a not
inconsiderable article of commerce, is as a rule far from pure. It
generally contains in addition to hydrofluoric acid, silicofluoric acid,
sulphuric acid, sulphurous acid, and frequently traces of iron and
lead. Two analyses of commercial acid gave the following
figures : —

1. 2.

Hydrofluoric acid 4S'00 45'80

Silicofluoric acid 13'05 9'49

Sulphuric acid 4'07 3'23

Sulphurous acid 0*49 ...... 1'06

Left on evaporation 0'16

Water by difference 34-23 4-0*42

100-00 100-00

106 VOLUMETRIC ANALYSIS. § 26.

If it is desired to prepare pure acid, the best way is to add to the
commercial acid peroxide of hydrogen till it ceases to bleach
iodine, and then potassic hydric fluoride sufficient to fix all the
silicofluoric and sulphuric acids. Re-distillation in a lead retort
with a platinum condenser will then give perfectly pure acid.

The total amount of free acid may be estimated with normal
alkali (preferably potash), using •phenolphthalein or litmus, the
former is best. Methyl orange and lacmoid do not give
good results. In the case of pure acid, each c.c. of ~ alkali
indicates 0*02 gm. of HF, and the reaction when phenolphthalein is
employed is very sharp, When, however, commercial acid is thus
titrated a difference is observed ; the pink colour obtained on
adding the alkali only endures for a second or so and then fades
away, and this may be repeated for some time till at last
a permanent pink is produced. The cause of this is the presence
of silicofluoric acid. The first appearance of pink ensues when
the reaction H2SiF6 + K20 = K-'SiF6 + H20 occurs. Then another
reaction sets in

K2SiF6 + 2K20 = (KF)6 + SiO2,

but from the slight solubility of the potassium silicofluoricle some
time elapses before it is complete.

The sulphuric and sulphurous acid must also be estimated if the
real amount of HF is required.

Estimation of Sulphuric Acid in Presence of Hydrofluoric Acid
(W. B. Giles). Long experience has convinced the author of this new
process, that all methods depending upon the supposed solubility of barium
fluoride, and the corresponding insolubility of the sulphate in either hot or
cold diluted hydrochloric acid give most erroneous results. For instance,
a sample of hydrofluoric acid known to contain 4°/0 of H2SO4was treated in
the way described by Fresenius, using a large volume of hot dilute
hydrochloric acid, and' the precipitate was copiously washed with the same
weak acid. The barium precipitate obtained was equal to 6'08 °/0 of SO3 or
over 50 °/0 more than was present, and it was found that on repeatedly
moistening the precipitate with dilute H-SO4, and re-igniting, that the
weight increased materially, showing co-precipitation of barium fluoride.
The author therefore devised the following process for the estimation of the
SO3 which gives accurate results. Its basis is — -

1. The conversion of HF into H-'SiF°, which is easily accomplished.

2. The precipitation of the SO3 from this solution by means of lead silico-
fluoride.

3. The total insolubility of PbSO4 in a solution containing an excess of
the said lead salt.

Process : A convenient weight of the hydrofluoric acid is placed in
a platinum dish, about half its volume of water is added, and then
precipitated silica in evident excess, and the whole is allowed to stand with
occasional stirring for a few hours. It is then filtered, using an ebonite
funnel, into another suitable platinum basin, and the excess of silica
thoroughly washed, the filtrate and washings are then evaporated to
a convenient bulk, and solution of lead silicofluoride is added in excess. If
the least trace of sulphuric acid was contained in the acid originally, an
almost immediate precipitate of PbSO4 Avill form, as it is exceedingly

§ 26. HYDROFLUORIC ACID. 107

insoluble in the presence of the lead silicofluoride. The solution is allowed!
to stand an hour or two, and the PbSO4 separated by nitration, when it can
of course be treated in any convenient volumetric way for the estimation of
the lead, or it may be weighed direct.

Lead silicofluoride is easily prepared by saturating commercial HF with
coarsely powdered flint in a lead basin, and then agitating with powdered
litharge. Its solubility is very great, and the specific gravity of the
solution may reach 2'000 or more.

Example : To 37'89 gm. of chemically pure HF of 1250 sp. gr., there
was added 25 c.c. of normal acid=ro gm. SO3. The mixture was then
treated as described above, and gave PbSO4 3'782 gm.=l'0002 gm. of SO3.

Estimation of the Silicofluoric Acid.— To a convenient quantity of the
acid contained in a platinum dish, a solution of potassic acetate in strong
methylated spirit is added in excess, and then more spirit is added, so that
there may be about equal volumes of liquid and spirit. Allow to stand for
several hours, and then filter and wash with a mixture of half spirit and
half water. The resulting potassium silicofluoride may then be titrated
with normal alkali according to the equation :

or if the filter was a weighed one, it may be dried at 100° C. and weighed
direct.

Example : 2 gm. of chemically pure precipitated silica were dissolved in
a large excess of pure diluted HF. Treated as above described, it yielded
7'35 gm. of K2SiF° which equals 2'004 gm. of silica; 2 gm. of some
powdered flint treated in the same way with 50 gm. of pure HF (of 40 °/ )
gave 7-168 gm. of K2SiF6=l'958 gm. of silica.

Sulphurous Acid.— This is easily estimated by taking the solution which
results from the total acidity determination and titrating with decinormal
iodine. Commercial hydrofluoric acid generally contains from 0'5 to 2'0 %•

The amount of each of the impurities being thus known, the
percentage of real HF is easily calculated; e.g., 10 gm. of an
acid was found to neutralize 276'0 c.c. of normal alkali. It was
found to give the following results : —

c c. normal alkali 8'0 = 3 -2 3 SO3

„ 39-0= 9-36H2SiF°
276 -4:7 = 229 c.c. x 0'02 = 45-80 % HF.

41-61% H20 by difference

100-00
In this instance the amount of SO2 was not allowed for.

Bifluorides. — -These salts have lately been used to some extent
on the Continent by distillers. They may be titrated in the same
way as the acid with phenolphthalein. They generally contain
some silicofluoride.*

The estimation of fluorine in soluble fluorides has been done

* The whole of this section, to this point, is kindly contributed by W. B. Giles,
F.I.C., who has had large practical experience on the subjects treated.

108 VOLUMETRIC ANALYSIS. § 26.

volumetrically by Knob loch (Pliarm. Zeitslirift xxxix. 558).
The process is based on the following facts : —

"When a solution of ferric chloride is mixed with its equivalent
quantity of potassic fluoride the decomposition is complete, and
the resulting ferric fluoride solution is colourless. In this state
the iron is not detectable by such tests as thiocyanate, salicylic
acid, etc. Still more interesting is the fact that ferric fluoride
does not liberate iodine from iodides.

The following standard solutions, &c., are required : —

-A potassic fluoride ; 5 '809 gm. of the pure ignited salt in
a liter of water.

^j- solution of ferric chloride, which the author prepared by
diluting 19 gm. of the officinal ferric chloride of the Prussian
pharmacopoeia to a liter.

~Q sodic thiosulphate solution.

Zinc iodide solution, made by mixing 10 gm. of iodine, 5 gm.
of zinc powder, and 25 c.c. of water in a flask, and warming till
the violent action is over and the solution colourless, then diluting
to 40 c.c. and filtering.

Process: The liquid containing the fluorides in solution is mixed with
a known excess of ferric chloride solution, then with excess of zinc iodide,
and allowed to remain in a closed vessel at 35 — 40° C. for half an hour ; the
liberated iodine is then titrated with thiosulphate. The volume of the
latter used is deducted from that of the ferric chloride — the difference is the
measure of the fluorine, 1 c.c. thiosulphate = 0'0019 gm. P.

The author states that calcium and strontium in their soluble
salts may also be estimated by the same method by acidifying
their solutions with hydrochloric acid, adding equal volumes, first
of potassic fluoride and then ferric chloride solutions in excess,
excess of zinc iodide is then added, and digested at 35 — 40° C.
and the liberated iodine ascertained as before, 1 c.c. of thiosulphate
-0-002 Ca.

None of these reactions have been verified by me, but the
method as given here is novel, and probably capable of being
developed by experience.

A very interesting paper on the acidimetry of hydrofluoric acid
is contributed by Hag a and Osaka (J. C. S. xvii. xviii. 251), being
the results of independent experiments made by them in the
laboratory of the Imperial University, Japan.

The authors examined the behaviour of the usual indicators in
the neutralization of hydrofluoric acid. That its alkali salts blue
litmus, and that its avidity number places it among the vegetable
acids rather than with the strong mineral acids, appear to be the
only two facts yet recorded bearing upon its acidimetry. ' •

To get uniform indications it was found necessary to have not
only the acid pure, but the titrating solutions also ; a little silica,
alumina, or carbon dioxide affecting the titration more than it
would in the case of the ordinary mineral acids.

§ 28. PHOSPHORIC ACID.

Phenolphthalein is the best indicator, and leaves nothing to be
desired when potash or soda is used for the titration. Rosolic acid
is almost equal to it, and can be used besides with ammonia.
"With both indicators the change of colour has the advantage of
being very evident in platinum vessels. Methyl orange is useless.
Litmus, lacinoid and phenacetolin are all capable of being made to
yield accurate results in the hands of an experienced operator.

The fact that accurate results can only be obtained with very-
pure acid and reagents, militates against the value of any
acidimetric process, and therefore the indirect method by Giles,
described above, is of greater technical value.

OXALIC ACID.

C2H2042H20-126.

§ 27. THE free acid can be accurately titrated with normal
alkali and phenolphthalein.

In combination with alkalies, the acid can be precipitated with calcic
chloride as calcic oxalate, where no other matters occur precipitable by
calcium; if acetic acid is present in slight excess it is of no consequence, as
it prevents the precipitation of small quantities of sulphates. The precipi-
tate is well washed^dried, ignited, and titrated with normal acid, 1 c.c. of
which = 0-063 gm. O~.

Acid oxalates are titrated direct for the amount of free acicL
The reaction continues to be acid until alkali is added in such
proportion that 1 molecule acid = 2 atoms alkali metal.

The combined acid may be found by igniting the salt, and
titrating the residual alkaline carbonate as above.

PHOSPHORIC ACID.

§ 28. FREE tribasic phosphoric acid cannot be titrated directly
with normal alkali in the same manner as most free acids, owing ta
the fact, that when an alkaline base (soda, for instance) is added to»
the acid, a combination occurs in which at one and the same time
red litmus paper is turned blue and blue red. This fact has been
repeatedly noticed in the case of some specimens of urine, also in
milk. In order, therefore, to estimate phosphoric acid, or alkaline
phosphates, alkalimetrically, it is necessary to prevent the formation
of soluble phosphate of alkali, and to bring the acid into a definite
compound with an alkaline earth. Such a method gives tolerably
good results when carried out as follows : —

The solution of free acid, or its acid or neutral combination with alkali in
a somewhat dilute state, is placed in a flask, and a known volume of normal
alkali in excess added, in order to convert the whole of the acid into a basic
salt; a drop or two of rosolic acid is added, then sufficient neutral baric

110 VOLUMET1MC ANALYSIS. § 28.

chloride poured in to combine with all the phosphoric acid, the mixture is
heated nearly to boiling; and, while hot, the excess of alkali is titrated with
normal acid. The suspended baric phosphate, together Avith the liquid,
possesses a rose-red colour until the last drop or two of acid, after continuous
heating, and agitation, gives a permanent Avhite or slightly yellowish, milky
appearance, when the process is ended.

The volume of normal alkali, less the volume of acid, represents the
amount of alkali required to convert the phosphoric acid into a chemically
neutral salt, e.g. trisodic phosphate. 1 c.c. alkali = 0'02366 gm. P2O5. In
dealing with small quantities of material, it is better to use f or ^ standard
solutions.

Thomson has shown in his researches on the indicators, that
phosphoric acid, either in the free state, or in combination with
soda or potash, may with very fair accuracy be estimated by the
help of methyl orange and phenolphthalein. If, for instance,
normal potash be added to a solution of phosphoric acid" until the
pink colour of methyl orange is discharged, KH2P04 is formed
(112 KHO-142 P205). If now phenolphthalein is added, and
the addition of potash continued until a red colour occurs, K2HP04
is formed. (Again 112 KHO = 142 P205.) On adding standard
hydrochloric or sulphuric acid, until the pink colour of methyl
orange reappears, the titration with standard potash may be
repeated.

Many attempts have been made to utilize these reactions for the
accurate estimation of P205 in manures, etc., but, so far as my
own experience goes, without adequate success.

Titration as Ammonio-magnesian Phosphate- — Stolba (Cliem.
Gent, 1866, 727, 728) adopts an alkalimetric method, which
depends upon the fact, that one molecule of the double salt
requires two molecules of a mineral acid for saturation.

The precipitation is made with magnesia mixture, the precipitate well
washed with ammonia, and the latter completely removed by Avashing with
alcohol of 50 or 60 per cent. The precipitate is then dissolved in a measured
excess of ^ acid, methyl orange added, and the amount of acid required found
by titration with ^ alkali. Care must be taken that all free ammonia is
removed from the filter and precipitate, and that the whole of the double
salt is decomposed by the acid before titration, which may always be insured
by using a rather large excess and warming. The titration is carried on cold.

This method has given me very good results in comparison with
the gravimetric method. The same process is applicable to the
estimation of arsenic acid, and also of magnesia,

1 c.c. of T^ acid -0-00355 gm. P2O
= 0-00575 gm. As203
= 0-002 gm. MgO

= -

The reaction in the case of phosphoric acid may be expressed as
follows : —

Mg (NEP) PO4 + 2HC1 - (NH4) H2P04 + MgCl2.

§ 29. SULPHURIC ANHYDRIDE. Ill

Method for the Determination of Phosphoric Acid in its Pure
Solutions — E. Segalle (Z.A.C. xxxiv. 33—39) has investigated various
methods for the above purpose with the following result: —

By far the most accurate results are obtained by Glucksinann's method.
In this, the phosphoric acid is precipitated by an excess of " magnesia
mixture " of known strength in free ammonia, the precipitate filtered off,
and the free ammonia left in solution is titrated by standard acid. From
the equation —

H3P04 + MgSO4 + 3 NIP - MgNH4P04 + (NH4)2SO4

it will be seen that H3PO4=3NH3.

The following modification is recommended as being more convenient and
simple. To the phosphoric acid solution, contained in a graduated flask, an
excess of standard ammonia (preferably normal) is added, followed by an
excess of a saturated neutral solution of magnesium sulphate. The liquid
is then diluted to the mark, well shaken, and filtered, and the residual
ammonia titrated in an aliquot part of the filtrate.

On account of its simplicity, the modified method is well adapted for
ascertaining the strength of the solutions of phosphoric acid employed in
pharmacy.

SULPHURIC ANHYDRIDE.

SO3 = 80.

§ 29. NORDHAUSEX or fuming sulphuric acid consists of a
mixture of SO3 and H2SO. When it is rich in SO3 it occurs in
a solid form, and being very hygroscopic cannot be weighed in the
ordinary manner. Its strength is therefore best taken in the way
recommended by Mess el as follows : — A very thin, bulb tube with
capillary ends is inserted into a bottle of the melted acid. The
ends are bent like the letter /, the bulb being in the middle. The
bottle should be of such size, that one end of the tube projects out
of its mouth. As soon as the bulb is filled, the upper capillary
end is sealed, the tube lifted out, wiped, inverted, and the other
end sealed ; the tube is then carefully wiped with blotting paper
till dry and clean, then weighed. A stoppered bottle, just large
enough to allow the tube being placed loosely inside it, is then
about one-third filled with water, the tube gently inserted, the
stopper replaced, held firmly in by the hand, and a vigorous shake
.given so as to break the tube. A sudden vibration occurs from
contact of the acid with the water, but no danger is incurred.
A white cloud is seen on the sides of the bottle, which disappears
on shaking for a few minutes. After the bottle is cooled the
contents are emptied into a measuring flask. An aliquot portion
is then taken out and titrated with — iodine for SO2, which is
always present in small quantity : another portion is titrated with
standard alkali and methyl orange for sulphuric acid. No other
indicator is available, and as Lunge has pointed out (Zeii, Angew.
Cliem. 1895, 221), neutrality is reached when the acid sulphite is
formed, and not when the whole of the SO2 is neutralized.

112 VOLUMETRIC ANALYSIS. § 30.

TARTARIC ACID.

C4H60G=150.

§ 30. THE free acid may be readily titrated with normal alkali
and phenolphthalein.

1 c.c. alkali = 0*075 gm. tartaric acid.

The amount of tartaric acid existing in tartaric acid liquors is
best estimated by precipitation as potassic bitartrate ; the same is
also the case with crude argols, lees, etc. Manufacturers are highly
indebted to War in gt on and Grosjean for most exhaustive
papers on this subject, to which reference should be made by all
who desire to study the nature and analysis of all commercial
compounds of citric and tartaric acids (Warington, J. C. S. 1875r
925—994; Grosjean, J. C. S. 1879, 341—356).

Without entering into the copious details and explanations given
by these authorities, the methods may be summarized as follows : —

1. Commercial Tartrates.

In the case of good clean tartars, even though they may contain sulphates
and carbonates, very accurate results may he obtained by indirect methods.

(a] The very finely powdered sample is first titrated with normal alkali,
and thus the amount of tartaric acid existing as bitartrate is found; another
portion of the sample is then calcined at a moderate heat, and the ash
titrated. By deducting from the volume of acid so used the volume used
for bitartrate, the amount of base corresponding to neutral tart rates is
obtained.

(b) The whole of the tartaric acid is exactly neutralized with caustic
soda, evaporated to dryness, calcined, and the ash titrated with normal acid ;
the total tartaric acid is then calculated from the volume of standard acid
used ; any other organic acid present Avill naturally be included in this
amount. In the case of fairly pure tartars, etc., this probable error may he-
disregarded.

Warington's description of the first process is as follows :—

5 gni. of the finely powdered tartar are heated with a little water to
dissolve any carbonates that may be present. If it is wished to guard against
crystalline carbonates, 5 c.c. of standard HC1 are added in the first instance1,
and the heating is conducted in a covered beaker. Standard alkali is next
added to the extent of about three-fourths of the amount required by a good
tartar of the kind examined, plus that equivalent to the acid used, and the
whole is brought to boiling; when nearly cold, the titration is finished.
From the amount of alkali consumed, minus that required by the HC1, the
tartaric acid present as acid tartrate is calculated.

2 gm. of the powdered tartar are next weighed into a platinum crucible
with a well-fitting lid ; the crucible is placed over an argand burner ; heat is
first applied very gently to dry the tartar, and then more strongly till
inflammable gas ceases to be evolved. The heat should not rise above very
low redness. The black ash is next removed with water to a beaker. If the
tartar is known to be a good one, 20 c.c. of standard H2SO4 are now run
from a pipette into the beaker, a portion of the acid being used to rinse the
crucible. The contents of the beaker are now brought to boiling, filtered,
and the free acid determined with standard alkali. As the charcoal on the
filter under some circumstances retains a little acid, even when well washed,.

§ .30. TARTARIC ACID. 113

it is advisable when the titration is completed to transfer the iilter and its
contents to the neutralized fluid, and add a further amount of alkali if
necessar}r. From the neutralizing power of a gram of burnt tartar is
subtracted the acidity of a gram of unburnt tartar, both expressed in c.c. of
standard alkali, the difference in the neutralizing power of the bases existing
as neutral tartrates, and is then calculated into tartaric acid on this
assumption.*

If the tartar is of low quality, 5 c.c. of solution of hydrogen peroxide
(1 volume — 10 volumes O) are added to the black ash and water, and
immediately afterwards, the standard acid ; the rest of the analysis proceeds
.as already described ; the small acidity usually belonging to the peroxide
.-solution must, however, be known and allowed for in the calculation. By
the use of hydrogen peroxide the sulphides formed during ignition are
reconverted into sulphates, and the error of excess which their presence
would occasion is avoided.

The above method does not give the separate amounts of acid
and neutral tartrates in the presence of carbonates, but it gives the
correct amount of tartaric acid ; it is also correct in cases where
free tartaric acid exists, so long as the final results show that some
acid existed as neutral salt. Whenever this method shows that
the acidity of the original substance is greater than the neutralizing
power of the ash, it will be necessary to use the method b, which
is the only one capable of giving good results when the sample
contains much free tartaric acid.

Instead of the alkalimetric estimation in both the above methods,
equally good results may be got by a carbonic acid determination
in the asli with S c he i bier's apparatus (§ 23.6), or any of the
usual methods.

2. Tartaric Acid Liquors.

Old factory liquors contain a great variety of substances gradually
accumulated, from which the actual tartaric acid can only be
separated as bitartrate by the following process : —

(c) A quantity of liquor containing 2—4 gm. of tartaric acid, and of
30 — 40 c.c. volume, is treated Avith a saturated solution of neutral potassic
citrate, added drop by drop with constant stirring. If free sulphuric acid is
present no precipitate is at first produced ; but as soon as the acid is satisfied,
the bitartrate begins to appear in streaks on the sides of the vessel. When
this is seen, the remainder of the citrate is measured in to avoid an undue
excess : 4 c.c. of a saturated solution of potassic citrate will be found
sufficient to precipitate the maximum of 4 grams of tartaric acid supposed to
be present. If the liquor contain a great deal of sulphuric acid, a fine
precipitate of potassic sulphate will precede the formation of bitartrate, but
is easily distinguished from it. With liquors rich in sulphuric acid, it is
advisable to stir the mixture vigorously at intervals for half an hour, then
proceed as in 3 d.

Grosjean modifies this process by precipitating the liquor with an excess
of calcic carbonate, then boiling the mixture with excess of potassic oxalate.

* It is obvious that the neutralizing power of the ash of an acid tartrate is exactly
the same as the acidity of the same tartrate before burning-. In making the calcula-
tions, it nmst be remembered that the value of the alkali in tartaric acid is twice as
great in the calculation made from the acidity of the unburnt tartar, as in the
. calculation of the acid existing as neutral tartrates.

114 VOLUMETRIC ANALYSIS. § 31.

By this means the alumina, iron, phosphoric and sulphuric acids are thrown
down with the calcic oxalate, and the precipitate allows of ready nitration.
The separation as bitartrate then follows, as in d.

3. Very impure Lees and Argrols.

Grosjean (/. C. S. 1879, 341) gives a succinct method for
the treatment of these substances, based on War ing ton's original
oxalate process, the principle of which is as follows : —

The finely ground sample ( — about 2 gm. tartaric acid) is first moistened
with a little water, heated to 100° C., then digested for 15 minutes or so with
an excess of neutral potassic oxalate (the excess must not be less than
1'5 gm.), and nearly neutralized with potash. After repeated stirring, the
mixture is transferred to a vacuum filter, and the residue washed; the
liquid so obtained contains all the tartaric acid as neutral potassic tartrate ;
excess of citric acid is added, which precipitates the whole of the tartaric
acid as bitartrate, and the amount is found by titration with standard alkali
in the usual way.

One of the chief difficulties in treating low qualities of material is the
filtration of the nearly neutral mixture above mentioned. Grosjean adopts-
the principle of Casamajor's filter (C. N. xxxii. 45), using an ordinary
funnel with either platinum, lead, or pumice disc ; but whether this, or
Bun sen's, or other form of filter is used, the resulting filtrate and washings-
(which for 2 gm. tartaric acid should not much exceed 50 c.c.) are ready for
the separation of the bitartrate in the following improved way : —

(d) To the 50 c.c. or so of cold solution 5 gm. of powdered potassic-
chloride are added, and stirred till dissolved : this renders the subsequent
precipitation of bitartrate very complete. A 50 per-cent. solution of citric
acid is then mixed with the liquid in such proportion, that for every 2 gm.
of tartaric acid an equal, or slightly greater amount of citric acid is present.
By continuously stirring, the whole of the bitartrate comes down in ten
minutes (Grosjean) ; if the temperature is much above 16°, it is preferable
to wait half an hour or so before filtering. This operation is best done on
the vacuum filter, and the washing is made with a 5 per-cent. solution of
potassic chloride, saturated at ordinary temperature with potassic bitartrate ;
if great accurac}7 is required, the exact* acidity of the solution should be
found by ^5- alkali, and the washing continued until the washings show no-
greater acidity, thus proving the absence of citric acid. Finally, the washed
precipitate is gently pressed into a cake to free it from excess of liquid,,
transferred to a beaker Avith the filter, hot \vater added, and titrated with
standard alkali.

The troublesome filtration can be avoided in many cases by taking*
30 — 40 gm. of substance, and after decomposition by oxalate, and neutralizing-
with potash, making up the volume to 150 or 200 c.c., adding water in
corresponding proportion to the bulk of the residue, then taking an aliquot
portion for precipitation. A blank experiment made by Grosjean in this
way, gave a volume of 3'75 c.c. for the residue in 10 gm. lees. Other things,
being equal, therefore, 30 or 40 gm. may respectively be made up to 161 and
215 c.c., then 50 c.c. taken for precipitation. >

ESTIMATION OF COMBINED ACIDS AND BASES IN
NEUTRAL SALTS.

§ 31. THIS comprehensive method of determining the quantity
of acid in neutral compounds (but not the nature of the acid), is
applicable only in those cases where the base is perfectly precipitated

§ 31. COMBINED ACIDS AND BASES. 115

by an excess of caustic alkali or its carbonate. The number of
bodies capable of being so precipitated is very large, as has been
proved by the researches of Langer and "VVawnikiewicz (Ann.
Chem. u. Phar. 1861, 239), who seem to have worked out the
method very carefully. These gentlemen attribute its origin to
Bunsen ; but it does not seem certain who devised it. The best
method of procedure is as follows : — •

The substance is weighed, dissolved in water in a 300-c.c. flask, heated to
boiling or not, as may be desirable ; normal alkali or its carbonate, according
to the nature of the base, is then added from a burette, until the whole is
decidedly alkaline. It is then diluted to 300 c.c. and put aside to settle, and
100 c.c. are taken out and titrated for the excess of alkali ; the remainder
multiplied by 3, gives the measure of the acid combined with the original
salt, i.e. supposing the precipitation is complete.

Example : 2 gm. crystals of baric chloride were dissolved in water, heated
•to boiling, and 20 c.c. normal sodic carbonate added, diluted to 300 c.c. and
100 c.c. of the clear liquid titrated with normal nitric acid, of which 1*2 c.c.
was required ; altogether, therefore, the 2 gm. required 16'4 c.c. normal
alkali ; this multiplied by 0'122 gave 2'0008 gm. Bad2 2H2O instead of
2 gm. ; multiplied by the factor for chlorine 0'03537, it yielded 0'58007 gm.
Theory requires 0'5809 gm. chlorine.

The following substances have been submitted to this mode of
examination with satisfactory results : —

Salts of the alkaline earths precipitated with an alkaline
carbonate while boiling hot.

Salts of magnesia, with pure or carbonated alkali.

Alum, with carbonate of alkali.

Zinc salts, boiling hot, with the same.

Copper salts, boiling hot, with pure potash.

Silver salts, with same.

Bismuth salts, half an hour's boiling, with sodic carbonate.

Nickel and cobalt salts, with the same.

Lead salts, with the same.

Iron salts, boiling hot, with pure or carbonated alkali.

Mercury salts, with pure alkali.

Protosalts of manganese, boiling hot, with sodic carbonate.

Chromium persalts, boiling hot, with pure potash.

Where the compound under examination contains but one base
precipitable by alkali, the determination of the acid gives, of
course, the quantity of base also.

Wolcott Gibbs (C. N. 1868, i. 151) has enunciated a new
acidimetric principle applicable in cases where a base is precipitable
at a boiling temperature by hydric sulphide, and the acid set free
so as to be estimated with standard alkali. Of course the method
can only be used where complete separation can be obtained, and
where the salt to be analyzed contains a fixed acid which has no
effect upon hydric sulphide. A weighed portion is dissolved in

i 2

116 VOLUMETRIC ANALYSIS. § 31.

water, brought to boiling, and the gas passed in until the metal is
completely precipitated ; which is known by testing a drop of the
clear liquid upon a porcelain tile with sulphuretted hydrogen
water, or any other appropriate agent adapted to the metallic salt
under examination.

The liquid is filtered from the precipitate, and the latter well
washed, and the solution made up to a definite measure. An
aliquot portion is then titrated with normal alkali as usual, Avith
one of the phenol indicators.

In the case of nitrates or chlorides, where nitric or hydrochloric
acid would interfere with the hydric sulphide, it was found that the
addition in tolerable quantity of a neutral salt containing an organic
acid (e.g. sodic or potassic tartrate, or the double salt) obviated all
difficulty.

The results obtained by Gibbs in the case of copper, lead,,
bismuth, and mercury, as sulphate, nitrate, and chloride, agreed
very closely with theory.

Though not strictly belonging to the domain of acidimetry,
a method worked out by Neumann (Z. A. C. xxxiv. 454) may here
be mentioned for the technical estimation of some of the heavy
metals precipitable by sodic sulphide. The strength of the sulphide
solution is ascertained by boiling it with a measured excess of
standard acid till all the H2S is dissipated ; the excess of acid is
then found by titration with standard alkali, using phenolphthalein
as indicator. Having established the working strength of the
sulphide solution, the neutral solution of the metal to be estimated
is first precipitated with a known excess of standard sulphide,
and the solution containing the suspended sulphide or hydroxide
is rendered clear, if necessary, by the addition of strong sodium
chloride solution, and diluted to a definite volume at 16° C.
An aliquot part of the solution is then filtered off, or removed
by means of a pipette, and the excess of sulphide indirectly
determined in it. This indirect process is necessary, because the
alkaline sulphide destroys the colour of litmus or of phenolphthalein.
The estimation of the amounts of metal in the following salts by
this method gave excellent results : — alum, chrome alum, silver
sulphate, copper sulphate, cobalt sulphate, cadmium sulphate, lead
nitrate, manganese sulphate, nickel sulphate, ferrous sulphate,
ferrous ammonium sulphate, ferric chloride. This method, of course,
is not applicable if the solutions contain any free acid. Solutions
of chlorides containing free hydrochloric are first evaporated on
the water-bath, the residue moistened with alcohol, and again
evaporated to dryness. Sulphates are first converted into chlorides
by treatment with barium chloride and hydrochloric acid, and
the solutions so obtained are treated as before described for the
removal of the free HC1. .Nitrates are twice evaporated to dryness
with concentrated HC1, excess of the latter being finally removed
in the above-mentioned manner.

§ 32, ALKALIMETBIC METHODS. 117

EXTENSION OF ALKALIMETBIC METHODS.

§ 32. BOHLIG (Z. a. C. 1870, 310) has described a method
for the estimation of sulphuric acid, baryta, chlorine, iodine, and
bromine, which appears worthy of some consideration, since the
only standard solutions required are an acid and an alkaliv

Alkaline sulphates are known to be partially decomposed, in
contact with baric carbonate, into alkaline, carbonates and baric
sulphate. The decomposition is complete in the presence of free
carbonic anhydride ; acid carbonates of the alkali-metals are left in
solution, together with some acid baric carbonate, which can be
removed by boiling. The solution is filtered, and the alkaline
carbonate determined by means of a standard acid solution, and
the amount of sulphuric acid or alkaline sulphate calculated
from the amount of normal acid required. This process has been
satisfactorily used by Hanbst for sulphates in waters (C. N.
xxxvi. 227), and by Grossmann for salt cake (C. N. xli. 114).
See also § 17.14.

Neutral chlorides, bromides, and iodides, more especially of the
alkali-metals, are most readily decomposed by pure silver oxide
into insoluble silver salts, leaving the alkali-metal in solution as
hydrate (ammonia salts always excepted), which can then be
determined as usual by standard acid.

The author treats solutions containing sulphates of the heavy
metals, of the earths or alkaline earths, and free from acids whose
presence would influence the method, viz., phosphoric, arsenic,
oxalic, etc., with a solution of potassic carbonate so as to precipitate
the bases and leave about double or treble the amount of alkaline
carbonate in solution. From 1 to 1J gm. of substance is operated
upon in a flask. The solution is made up to 500 c.c., well shaken,
and the precipitate allowed to subside. 50 c.c, are then filtered,
and titrated with standard acid and methyl orange. Another 100 c.c.
are filtered in like manner into a strong quarter-liter flask, and
diluted with about 100 c.c. of hot water; the requisite quantity of
normal acid is then run in at once from a burette ; the solution
diluted to 250 c.c. ; and about a gram of dry baric carbonate
(free from alkali) added. The flask is next closed, and the liquid
well agitated. The decomposition of the alkaline sulphate is
complete in a few minutes. The flask should be opene.d now and
then to allow the carbonic anhydride to escape. Finally, about
J gm. of pulverized baric hydrate is added, the whole well shaken,
and a portion of the rapidly clearing liquid tested qualitatively for
barium and sulphuric acid. The result should be a negative one.
50 c.c., corresponding to 20 c.c. of the original solution, are then
filtered and titrated with normal acid, and the quantity of sulphuric
acid (sulphate) calculated as usual.

The source of carbonic anhydride is thus placed in the liquid
itself, provided the quantity of potassic carbonate be not -too small.

118 VOLUMETIIIC ANALYSIS. § 32.

Equivalent quantities of K2S04 + 2K2C03 + 2HC1 + BaCO3 when
mixed with sufficient water change into BaSO4 + 2KHC03 + 2KC1,
and it is therefore more than sufficient to add twice the quantity
of potassic carbonate compared with the alkaline sulphate operated
upon.

Baric hydrate is added with a view of removing any carbonic
anhydride left in the liquid after boiling, which would otherwise
dissolve some of the excess of baric carbonate contained in the
precipitate.

Any baric hydrate not required to remove CO2 is acted upon by
the acid potassic carbonate, but does not influence the final result.

Phosphoric and oxalic acids the author proposes to remove by
means of calcic chloride ; chromic acid by deoxidizing agents,
such as alcohol and hydrochloric acid. Bohlig recommends this
method for estimating sulphuric acid in ashes, crude soda, Stassfurth
salts, etc,

Solutions containing baryta are estimated in like manner by
precipitation as carbonate, and decomposition with potassic sulphate
in a solution containing free carbonic acid. Chlorine is determined
in solutions by first precipitating any metallic chloride with potassic
carbonate added in moderate excess. The filtrate is made up to
250 c.c., and the excess of potassic carbonate determined in 50 c.c.
by means of a normal solution of HC1. 125 c.c. of the solution
are next treated with excess of silver oxide and made up to 250 c.c.,
well shaken (out of contact with the light) and filtered. 100 c.c.
of the nitrate are titrated with normal hydrochloric acid. The
difference between the quantity of acid required in the last and
that of the first experiment, multiplied by 5, gives the amount
of chlorine contained in the original solution. A portion of the
filtrate should be tested for chlorine by means of mercurous nitrate.

The filtrate is obtained perfectly clear only in the presence of
some potassic or sodic carbonate, and by employing argentic oxide
free from argentous oxide. A few drops of pure potassic per-
manganate added to the argentic oxide preserved in water prevent
formation of the latter. The oxide to be employed for each
experiment is filtered when required, and thoroughly washed.

Bromine and iodine are determined in like manner, The author
has not been able, however, to estimate the mixtures of the halogen
salts ; but Jie has made the interesting observation that potassic
iodide, when boiled with potassic permanganate, is completely
oxidized into iodate. This facilitates the detection of small
quantities of chlorine and bromine, in the presence of much
iodide. The greater part of iodate may be separated also by
precipitation with baric nitrate before determining chlorine. The
standard acid solutions which Bohlig employed contained not more
than one-third of the equivalent of HC1 or SO3 per liter.

For further particulars the reader is referred to the original
paper (Arch. Pharm. 3 cxlv. 113).

§ 32. ALKALIMETRIC METHODS. 119

Siebold (Year Bool- of Pharmacy, 1878, 518) describes a very-
ingenious process, devised by himself, for the titration of caustic
and carbonated alkalies by means of prussic acid, the principle of
which is explained in § 59. The process is useful in the case of
carbonates, since CO2 is no hindrance.

0'5 to 1 gm. of the alkali or alkaline carbonate is dissolved in about 100 c.c.
of water, and an excess of hydrocyanic acid (say 10 or 20 c.c.) of 5 per cent,
solution added; then ~ silver solution cautiously added with constant
stirring until a faint permanent turbidity occurs. Each c.c. of T^j- silver
= 0-0138 gm. K2CO3, or 0'0106 gm. Na2CO3.

In the case of chlorides being present, their quantity may be
determined by boiling down the mixture to about half its volume
to expel all free prussic acid, adding a drop or two of potassic
•chromate as indicator, then titrating with ~$ silver. Any excess
.above that required in the first titration will be due to chlorine,
and may be calculated accordingly.

120 VjOLUMETKIC ANALYSIS. § 33.

PART III.
ANALYSIS BY OXIDATION OR REDUCTION.

§ 33. THE series of analyses which occur under this system are
very extensive in number, and not a few of them possess extreme
accuracy, such in fact, as is not possible in any analysis by weight.
The completion of the various processes is generally shown by
a distinct change of colour ; such, for instance, as the occurrence
of the beautiful rose-red permanganate, or the blue iodide of
starch ; and as the smallest quantity of these substances will
colour distinctly large masses of liquid, the slightest excess of the
oxidizing agent is sufficient to produce a distinct effect.

The principle involved in the process is extremely simple.
Substances which will take up oxygen are brought into solution,
and titrated with a substance of known oxidizing power ; as, for
instance, in the determination of ferrous salts by permanganic-
acid. The iron is ready and willing to receive the oxygen,
the permanganate is equally willing to part with it ; while the iron
is absorbing the oxygen, the permanganate loses its colour almost
as soon as it is added, and the whole mixture is colourless ; but
immediately the iron is satisfied, the rose colour no longer disappears,
there being no more oxidizable iron present. In the case of potassic
permanganate the reaction is: lOFeO + 2MnK04 = 5Fe20:! +
2MnO + K-'O. Oxalic acid occupies the same position as the
ferrous salts ; its composition is C204H2 + 2H-O = 126. If perman-
ganate is added to it in acid solution, the oxalic acid is oxidized to
carbonic acid, and the manganic reduced to manganous oxide, thus
Mn207 + 5C20*H2 + 2H2S04 = 10C02 + 2MnS04 + 7H2O. When
the oxalic acid is all decomposed, the colour of the permanganate
no longer disappears. On the other hand, substances which will
give up oxygen are deoxidized by a known excessive quantity of
reducing agent, the amount of which excess is afterwards ascertained
by residual titration with a standard oxidizing solution; the strength
of the reducing solution being known, the quantity required is
a measure of the substance which has been reduced by it.

The oxidizing agents best available are — potassic permanganate,
iodine, potassic bichromate, and red potassic prussiate.

The reducing agents are — sulphurous acid, sodic hyposulphite,'""
sodic thiosulphate, oxalic acid, ferrous oxide, arsenious anhydride,
stannous chloride, yellow potassic prussiate, and zinc or magnesium.

With this variety of materials a great many combinations may be
arranged so as to make this system of analysis very comprehensive;
but the following are given as sufficient for almost all purposes,

:;: S c li il t z e 11 b e r g e r ' s preparation is here meant.

*r |

UNIVERSITY

§ 34. STANDARD PERMANGAN

and as being susceptible of the greatest amount of purity and
stability of material, with exceedingly accurate results:—

1. Permanganate and ferrous salts (with the rose colour as
indicator) ; permanganate and oxalic acid (with the rose colour
as indicator).

2. Potassic bichromate and ferrous salts (with cessation of blue
colour when brought in contact with red potassic prussiate, as
indicator).

3. Iodine and sodic thiosulphate (with starch as indicator) ;
iodine and sodic arsenite (with starch as indicator).

PREPARATION OF STANDARD SOLUTIONS.

PERMANGANIC ACID AND FERROUS OXIDE.

1. Potassic Permang-anate.
Mn2K208 = 315'6. Decinormal Solution = 3 '156 gm. per liter.

§ 34. THE solution of this salt is best prepared for analysis by
dissolving the pure crystals in fresh distilled water, and should be
of such a strength that 17*85 c.c. will oxidize 1 decigram of iron.
The solution is then decinormal. If the salt can be had perfectly
pure and dry, 3'156 gm. dissolved in a liter of water at 16° C., will
give an exactly decinormal solution ; but, nevertheless, it is always
well to verify it as described below.* If kept in the light in
ordinary bottles it will retain its strength for several months, if in
bottles covered with black paper much longer, nevertheless, it
should from time to time be verified by titratioii in one of the
following ways : —

2. Titration of Permanganate.

(a) With. Metallic Iron. — The purest iron to be obtained is
thin annealed binding-wire free from rust, generally known as
flower wire.f Its actual percentage of pure iron may be taken
as 99-6

* Very fairly pure permanganate, in large crystals, may now be obtained in commerce,
and if this salt is recrystallized twice from hot distilled water and dried thoroughly at
1')JJ C., it will be found practically pure.

t Miss C. F. Roberts (Amer. Jour. Sci. 1894, 286, 290) advocates the use of pure
iron, prepared by electrolysis, as follows : About 10 gin. -of ferrous-ammonium sulphate
are dissolved in 150 c.c. of water. 5 c.c. of a saturated solution of potassic oxalate
added, and then heated with a sufficiency of solution of animonic oxalate until clear.
A weighed piece of platinum foil, shaped so as to be easily placed into a rather large
weighing bottle, is then pvit into a beaker containing the iron solution, and the latter
decomposed with a current of about two amperes between two platinum electrodes. In
about two hours enough iron will be deposited for a tit-ration. The deposited metal is
of course well washed, dried, and weighed in the weighing bottle, then dissolved in
dilute acid, precisely as in the case of iron wire.

122 VOLUMETRIC ANALYSIS. § 34.

Process : Fit a tight cork or rubber stopper, with bent delivery tube, into
a flask holding about 300 c.c., and clamp it in a retort stand in an inclined
position, the tube so bent as to dip into a small beaker containing pure
water. Pill the flask one-third with dilute pure sulphuric acid, and add
a few grains of sodic carbonate in crystals ; the CO2 so produced will drive
out the air. While this is being done weigh about O'l gram of the wire;
put it quickly into the flask when the soda is dissolved, and apply «a gentle
heat till the iron is completely in solution, a few black specks of carbon are
of no 'consequence. The flask is then rapidly cooled under a stream of cold
water, diluted if necessary with some recently boiled and cooled water, and
the permanganate run in cautiously from a TV c.c. tap burette, Avith constant
shaking, until a faint rose-colour is permanent. Instead of this arrange-
ment for dissolving the iron the apparatus shown in the section on iron
analysis ma}^ be used, § 63.

The decomposition which ensues from titrating ferrous oxide by
permanganic acid may be represented as follows : —

lOFeO and Mn207- 2MnO and 5Fe20:).

The weight of wire taken, multiplied by 0*996, will give the
actual weight of pure iron upon which to calculate the strength of
the permanganate.

Example: Exactly O'l gm. of wire was dissolved and titrated with
a permanganate solution, of which the quantity required was 17*6 c.c.
The equation O'l : 0'0996 : : 17'85=^ gives 17'45, the permanganate is
therefore a trifle too strong, but correct enough for all practical purposes.

(b) "With Ferrous-ammonium Sulphate. — In order to ascertain
the strength of the permanganate, it may be titrated with
a weighed quantity of this substance instead of metallic iron.

This salt is a convenient one for titrating the permanganate, as it saves the
time and trouble of dissolving the iron, and Avhen perfectly pure, it can be
depended on without risk. To prepare it, 139 parts of the purest crystals of
ferrous sulphate, and 66 parts of pure crystallized ammonic sulphate are
separately dissolved in the least possible quantity of distilled water of about
40° C. (if the solutions are not perfectly clear they must be filtered) ; mix
them at the same temperature in a porcelain dish, adding a few drops of
pure sulphuric acid, and stir till cold. During the stirring the double salt
will fall in a finely granulated form. Set aside for a few hours, then pour
off the supernatant liquid, and empty the salt into a clean funnel with a little
cotton wool stuffed into the neck, so that the mother-liquor may drain away ;
the salt may then be quickly and repeatedly pressed between fresh sheets of
clean filtering paper. Lastly, place in a current of air to dry thoroughly,
so that the small grains adhere no longer to each other, or to the paper in
which they are contained, then preserve in a stoppered bottle for use.

The formula of the salt is— Fe (XH4)'2 (SO4)2, 6H20 = 392.
Consequently it contains exactly one-seventh of its weight of iron ;
therefore 0*7 gm. represents O'l gm. Fe, and this is a convenient
quantity to weigh for the purpose of titrating the permanganate.

Process : 0'7 gm. being brought into "dilute cold solution in a flask or
beaker, and 20 c.c. of dilute sulphuric acid (1 to 5) added (the titration of
permanganate, or any other substance by it, should always take place in the
presence of free acid, and preferably sulphuric), the permanganate is delivered

§ 34 STANDARD PERMANGANATE. 123

from a burette with glass tap divided in TV c.c., as before described, until
a point occurs when the rose colour no longer disappears on shaking.

(<?) With Oxalic Acid. — This is a very quick method of titrating
permanganate, if the exact acidimetric value of the solution of pure oxalic
acid is known. 10 c.c. of normal solution are brought into a flask with dilute
sulphuric acid, as in the case of the iron salt, and considerably diluted with
water, then warmed to about 60° C., and the permanganate added from the
burette. The colour disappears slowly at first, but afterwards more rarpidly,
becoming first brown, then yellow, and so on to colourless. More care must
be exercised in this case than in the titration with iron, as the action is not
momentary. 100 c.c. should be required to be strictly decinormal. The
chemical change which occurs is explained on page 120.

(d) With Lead Oxalate.— Stolba prefers this salt to oxalic acid, for
the reasons that it contains no water, is not liable to absorb an}' from
exposure, and has a high molecular weight, 1 part of the salt representing
0'42799 of oxalic acid, or 63 oxalic acid=147'2 lead oxalate.

The method of titration is similar to that with oxalic acid, using dilute
sulphuric acid, and warming the mixture to ensure the complete decomposi-
tion of the salt into lead sulphate and free oxalic acid. Sodic oxalate is
also anhydrous and equally serviceable.

The lead oxalate is prepared by precipitating pure lead acetate with oxalic
acid in excess, and washing the precipitate by decantation with warm water
till all free acid is removed; the precipitate is then dried at 120° C., and
preserved for use. Some operators prefer to use ammonic oxalate in place of
oxalic acid or lead oxalate, as being a substance of definite hydration, and
easily obtained in a pure state. Its formula is (NH4)2 C2O4, H26 - 142=2Fe.
The titration is carried on precisely as in the case of oxalic acid.

0) With Hydrogen Peroxide in the Nitrometer. — In a paper on
this subject by Lunge ('/. S. C. I. ix. 21) it is shown by very carefully
conducted experiments with purest materials and verified apparatus that
-exceedingly accurate results may be obtained by the modified nitrometer
with patent tap (illustrated at the end of Part VII.). Lunge's experiments
were made on a semi-normal solution of permanganate (1 c.a=0'004 gin. O),
but whether equally exact results would be obtained with T\ permanganate
I cannot say, not having tried it ; but of course an approximately semi-normal
solution may be made and reduced to either -| or T^ strength, if desired,
by dilution with fresh distilled water. The exact method of using this
instrument will be described under the head of Nitrometer in Part VII. ;
but so far as permanganate is concerned it was found that convenient
quantities of substances to use were 10 c.c. of £ permanganate, 15 c.c.
of ordinary 10 volume H202, and 30 c.c. of sulphuric acid 1 : 5. The
nitrometer having been charged with water, the mixture was shaken up
and allowed to stand ten minutes, shaken again and read off after five
minutes. The volume of oxygen so obtained was corrected for temperature
and pressure, then calculated into weight. The results of three experiments
using the quantities mentioned above were as follows : —

1. Corrected volume of O 55'92 c.c.=0'0040C7 gm.

2. „ „ „ 55-82 c.c.=0-004000 „

3. „ „ „ 55'82 c.c.=0'004000 „
Average 0'004002 gm. of oxygen per c.c. of solution.

Three experiments with the same permanganate solution gave, when iron
wire was used, an average of 0*00399 gm., and with oxalic acid 0'OU3997 gm.
•of oxygen respectively per c.c.

Lunge says : *' Wo cannot but infer that standardizing a solution

124 VOLUMETRIC ANALYSIS. § 35.

of permanganate with hydrogen peroxide in the nitrometer when
observing the prescribed precautions is one of the most accurate
known methods for this purpose, and withal possesses the great
advantage that it is carried out within an extremely short time,
without requiring a fundamental substance of accurately known
composition."

Many other substances have been proposed for standardizing
permanganate, such as potassic ferrocyanate, thiocyanate, vanadic
oxide, etc., but they are all inferior in value to those above named.

3. Precautions in Titrating with Permanganate.

Tt must be borne in mind that free acid is always necessary in
titrating a substance with permanganate, in order to keep the
resulting mangaiious oxide in solution. Sulphuric acid, in a dilute
form, has no prejudicial effect on the pure permanganate, even at
a high temperature. With hydrochloric acid the solution to be
titrated must be very dilute and of low temperature, otherwise
chlorine will be liberated and the analysis spoiled. This acid acts
as a reducing agent on permanganate in concentrated solution,
thus —

Mn207 + 14HC1 = 7H20 + 10C1 + 2MnCK

The irregularities due to this reaction may be entirely obviated
by the addition of a few grams of manganous or magnesic sulphate
before titration.

Organic matter of any kind decomposes the permanganate, and
the solution therefore cannot be filtered through paper, nor can it
be used in Mohr's burette, because it is decomposed by the
india-rubber tube. It may, however, be filtered through gun
cotton or glass wool.

TITRATION OF FERRIC SALTS BY PERMANGANATE.

§ 35. ALL ferric compounds requiring to be estimated by
permanganate must, of course, be reduced to the ferrous state.
This is best accomplished by metallic zinc or magnesium in
sulphuric acid solution. Hydrochloric may also be used with the
precautions mentioned.

The reduction occurs on simply adding to the warm diluted
solution small pieces of zinc (free from iron, or at least with
a known quantity present) or coarsely powdered magnesium until
colourless ; or until a drop of the solution brought in contact with
a drop of potassic thiocyanate produces no red colour. All the
zinc or magnesium must be dissolved previous to the titration.

The reduction may be hastened considerably as shown in § 61.3.

When the reduction is complete, no time should be lost in
titrating the solution.

§ 36. STANDARD PERMANGANATE. 125

CALCULATION OF ANALYSES MADE WITH
PERMANGANATE SOLUTION.

§ 36. THE calculation of analyses with permanganate, if the
solution is not strictly decinormal, can be made by ascertaining its
coefficient, reducing the number of c.c. used for it to decinormal
strength, and multiplying the number of c.c. thus found by -^3^-$
of the equivalent weight of the substance sought ; for instance —

Suppose that 15 c.c. of permanganate solution have been found
to equal Ol gm. iron; it is required to reduce the 15 c.c.
to decinormal strength, which would require 1000 c.c. of per-
manganate to every 5'6 gm. iron, therefore 5*6 : 1000 : : O'l : x =
17-85 c.c. ; 17-85 x 0-0056 = 0-09996 gm. iron, which is as near to
O'l gm. as can be required. Or the coefficient necessary to reduce
the number of c.c. used maybe found as follows: — O-'l : 15 : :

5'6 : .«= 84 c.c,, therefore -o-p=-- 1 '19. Consequently 1-19 is the

coefficient by which to reduce the number of c.c, of that special
permanganate used in any analysis to the decinormal strength, from
whence the weight of substance sought may be found in the
usual way.

Another plan is to find the quantity of iron or oxalic acid repre-
sented by the permanganate used in any given analysis, and this being
done the following simple equation gives the required result : —

Fe (56) eq. weight of the weight the weight of

or : the substance : : of Fe or : substance

O (63) sought O found sought

In other words, if the equivalent weight of the substance analyzed
be divided by 56 or 63 (the respective equivalent weights of iron or
oxalic acid), a coefficient is obtained by which to multiply the
weight of iron or oxalic acid, equal to the permanganate used,
and the product i§ the weight of the substance titrated.

For example : sulphuretted hydrogen is the substance sought,
the eq. weight of H'2S corresponding to 2 eq. Fe is 17; let this

17
number therefore be divided by 56, -^ = 0-3036, therefore, if the

quantity of iron represented by the permanganate used in an
estimation of H2S be multiplied by 0'3036, the product will be
the weight of the sulphuretted hydrogen sought.

Again : in the case of manganic peroxide whose equivalent
weight is 43*4.

5=0.775

The weight of iron therefore found by permanganate in any analysis
multiplied by the coefficient 0*775 will give the amount of manganic
peroxide, MnO2. Again: if m gm. iron = k c.c. permanganate,

then 1 c.c permanganate = -r gm. metallic iron.

126 VOLUMETRIC ANALYSIS. § 37.

The equivalents here given are on the hydrogen scale, in
accordance with the normal system of solutions adopted ; and thus
it is seen that two equivalents of iron are converted from the
ferrous to the ferric state by the same quantity of oxygen as
suffices to oxidize one equivalent of oxalic acid, sulphuretted
hydrogen, or manganic peroxide.

1 c.c. decinormal permanganate is equivalent to
0'0056 gm. Fe estimated in the ferrous state

0-0072

FeO

„

0-008

Fe2O3

0-003733

from' PeS

0-0059

„ SnCl2

0-00295

« SnS2

0-00315

„ CuS

0-00274

„ MnS

0-00315

„ Cu+Fe2CF

0-0063

„ CuO+Fe

0-0017

H2S

55 35

0-0008

0-0063

0-002

Ca from

CaC2O4

0-0120

Ur „

UrO, etc., etc.

When possible the necessary coefficients will be given in the
tables preceding any leading substance.

•

CHROMIC ACID AND FERROUS OXIDE.

§ 37. POTASSIC bichromate, which appears to have been first
proposed by Penny, possesses the advantage over permanganate,
that it is absolutely permanent in solution, may easily be obtained
in a pure state, and its solution may be used in Mohr's burette
without undergoing the change peculiar to permanganate : on the
other hand, the end of the reaction in the estimation of iron can
only be known by an external indicator ; that is to say, a drop of
the mixture is brought in contact with a drop of solution of red
potassic prussiate (freshly prepared) upon a white slab or plate.
While the ferrous oxide is in tolerable excess, a rich blue colour
occurs at the point of contact between the drops • but as this
excess continues to lessen by the addition of the bichromate, the
blue becomes somewhat turbid, having first a green, then a grey,
and lastly a brown shade. When the greenish-blue tint has all
disappeared, the process is finished. This series of changes in the
colour admits of tolerably sure reading of the burette, after some
little practice is obtained.

The .Reaction between chromic acid and ferrous oxide may be
represented by the formula :

2Cr08 + 6FeO - CrW + 3Fe203.
The decomposition takes place immediately, and at ordinary

STANDARD BICHROMATE.

temperatures, in the presence of free sulphuric or hydrochloric acid.
Xitric acid is of course inadmissible.

The reduction of ferric compounds to the ferrous state may be
accomplished by zinc,""" magnesium, sodic sulphite, ammonic
bisulphite, or sulphurous acid; or, instead of these, stannous
chloride may be used, which acts very rapidly as a reducing agent
upon ferric oxide, the yellow colour of the solution disappearing
almost immediately.

In the analysis of iron ores, reduction by the latter is very rapid
and serviceable ; the greatest care, however, is necessary that the
stannous chloride is not present in excess, as this would consume
the bichromate solution equally with the ferrous oxide, and so
lead to false results.

The discharge of the yellow colour of the iron solution may with
care be made a very sure indicator of the exact point of reduction.
But in order to obviate the inaccuracy which would be produced
by an excess of tin in the state of protosalt, an aqueous solution of
mercuric chloride should be added to the mixture in slight excess ;
the stannous chloride is then all converted into stannic chloride,
and the titration with bichromate may proceed fas usual ;
a precipitate of Hg2Cl2 does not interfere. The concentrated
hydrochloric solution of iron is heated to gentle boiling, and the
moderately dilute tin solution added with a pipette, waiting
a moment for each addition till the last traces -of colour have
disappeared ; the solution is then poured into a beaker, diluted
with boiled and cooled water, mercuric solution added, and titrated
with the bichromate as above described. See also § 64.

It is absolutely necessary that the solution of potassic ferri-
cyanide used as the indicator with bichromate should be free from
f errocyanide ; and as a solution when exposed to air for a short
time becomes in some measure converted into the latter, it is
necessary to use a freshly prepared liquid.

1. Preparation of the Decinormal Solution of Bichromate.
4 '9 13 gm. per liter.

The reaction which takes place between potassic bichromate and
ferrous oxide is,

6FeO + Cr2K20" - 3Fe203 + Cr203 + K20

It is therefore necessary that J eq. in grams should be used for the
liter as a normal solution and ^ for the decinormal ; and as it is
preferable on many accounts to use a dilute solution, the latter is
the more convenient for general purposes.

Taking the equivalent number of chromium as 52 '4, that of
potassic bichromate is 294'S ; if, therefore, /^ of this latter number

* When zinc is used, the zinc ferricyanide somewhat obscures the critical point in.
testing with the indicator.

128 VOLUMETRIC ANALYSIS. § 38.

= 4'913 gm. of the pure \vell dried salt be dissolved in a liter of
water, the decinormal solution is obtained.

1 c.c. of this solution is capable of yielding up y^^ eq. in
grams of oxygen, and is therefore equivalent to the yo^jo^ eq. of
any substance which takes up 1 equivalent of oxygen.

2. Solution of Stannous Chloride.

About 10 gm. of pure tin in thin pieces are put into a large
platinum capsule, about 200 c.c. strong pure hydrochloric acid
poured over it, and heated till it is dissolved ; or it may be
dissolved in a porcelain capsule or glass flask, adding pieces of
platinum foil to excite a galvanic current. The solution so
obtained is diluted to about a liter with distilled water, and pre-
served in the bottle (fig. 24) to which the air can only gain access
through a strongly alkaline solution of pyrogallic acid. When
kept in this manner, the strength will not alter materially in
a month. If not so preserved, the solution varies considerably
from day to day, and therefore should always be titrated before
use as described in § 64 if required for quantitative analysis.

Examples of Iron Tit ration : 0'7 gm. of pure and dry ammonio-ferrous
sulphate=0'l gm. iron, was dissolved in water, and titrated with decinormal
bichromate, of which 17'85 c.c. were required; this multiplied by 0'03913
gave 0'699 gm. instead of 0'7 gm.

0'56 gm. of iron wire required 99'8 c.c. =0*5588 gm. ; as it is impossible
to obtain iron wire perfectly pure, the. loss is undoubtedly owing to the
impurities.

IODINE AND SODIC THIOSULPHATE.

§ 38. THE principle of this now beautiful and exact method of
analysis was first discovered by Dupasquier, who used a solution
of sulphurous acid instead of sodic thiosulphate. Bun sen im-
proved his method considerably by ascertaining the sources of
failure to which it was liable, which consisted in the use of a too
concentrated solution of sulphurous acid. The reaction between
iodine and very dilute sulphurous acid may be represented by the
formula —

SO2 + 12 + 2H20 = 2HI + H2SO.

If the Sulphurous acid is more concentrated, i.e. above 0404 per
cent., in a short time the action is reversed, the irregularity of
decomposition varying with the quantity of water present, and the
rapidity with which the iodine is added.'""

Sulphurous acid, however, very rapidly changes by keeping even
in the most careful manner, and cannot therefore be used for
a standard solution. The substitution of sodic thiosulphate is
a great advantage, inasmuch as the salt is easily obtained in

* Tliis irregularity is now obviated by tie' method of Giles and Shearer (§ 75.5),
in which solutions of SO2 or sulphites of any strength may be accurately titrated
with iodine, by adding the latter to the former in excess, and when the reaction is
complete titrating the excess of iodine with tMosulphate.

§ 38. IODOMETRY. 129

a pure state, and may be directly weighed for the standard solution.
The reaction is as follows : —

2Na2S203 + 2I = 2]S

the result being that thiosulphuric acid takes oxygen from the
water, with the production of tetrathionic and hydriodic acids in
combination with soda.

In order to ascertain the end of the reaction in analysis by this
method an indicator is necessary, and the most delicate and sensitive
for the purpose is starch, which produces with the slightest trace of
free iodine in cold solution the well-known blue iodide of starch.
Hydriodic or mineral acids and iodides have no influence upon the
colour. Caustic alkalies destroy it.

The principle of this method, namely, the use of iodine as an
indirect oxidizing body by its action upon the elements of water,
forming hydriodic acid with the hydrogen, and liberating the oxygen
in an active state, can be applied to the determination of a great
variety of substances with extreme accuracy.

Bodies which take up oxygen, and decolorize the iodine solution,
such as sulphurous acid, sulphites, sulphuretted hydrogen, alkaline
thiosulphites and arsenites, stannous chloride, etc., are brought
into dilute solution, starch added, and the iodine delivered in
with constant shaking or stirring until a point occurs at which
a final drop of iodine colours the whole blue — a sign that the
substance can take up no more iodine, and that the drop in excess
has shown its characteristic effect upon the starch.

Free chlorine, or its active compounds, cannot, however, be
titrated with thiosulphate directly, owing to the fact that, instead
•of tetrathionic acid being produced as with iodine, sulphuric acid
occurs, as may be readily seen by testing with baric chloride.
In such cases, therefore, the chlorine • must be evolved from its
compound and passed into an excess of solution of pure potassic
iodide, where it at once liberates its equivalent- of iodine, which
can then, of course, be estimated with thiosulphate.

All bodies which contain available oxygen, and which evolve
chlorine when boiled with strong hydrochloric acid, such as the
chromates, manganates, and all metallic peroxides, can be readily
and most accurately estimated by this method.

1. Preparation of the Decinormal Solution of Iodine.

I = 127 ; 12 '7 gm. per liter.

Chemically pure iodine may be obtained by intimately mixing
dry commercial iodine with about one-fourth of its weight of
potassic iodide, and gently heating the mixture between two large
watch-glasses or porcelain capsules ; the lower one being placed
upon a heated iron plate, the iodine sublimes in brilliant plates,
•which, with the exception of a trace of moisture, are pure.

130 VOLUMETRIC ANALYSIS. § 38.

The watch-glass or capsule containing the iodine is placed under
the exsiccator to cool, and also to deprive it of any traces of watery
vapour; then 12*7 gm. are accurately weighed, and together with
about 18 gm. of pure potassic iodide (free from iodate)""' dissolved,
in ahout 250 c.c. of water, and diluted to a liter. The flask must
not be heated in order to promote solution, and care must be taken
that iodine vapours are not lost in the operation.

The solution is best preserved in stoppered bottles, kept in the
dark, and which should be completely filled ; but under any
circumstances it does not hold its strength well for any length
of time, and consequently should be titrated before use in
analysis.

The verification of the iodine solution may be done in many
ways. Pure sodic thiosulphate prepared as described below, or
a strictly -f$ solution of it, or again pure arsenious acid or its ^
solution, with the addition of a little sodic bicarbonate, or baric-
thiosulphate as proposed by Plimpton and Chorley, may be
used; this latter salt possesses a high molecular weight, 267 parts
being equivalent to 127 of iodine, but being sparingly soluble in
water the titration must be carefully done, inasmuch as the
crystalline powder has to be gradually decomposed by the iodine,,
and the end-point may easily be overstepped. A weighed quantity
of the salt is put into a stoppered bottle with water, and the
iodine run in from a burette with continuous shaking, until the
salt is nearly dissolved; starch indicator is then added, and the
iodine continued with shaking until the blue colour is faintly
permanent.

Pure baric thiosulphate is easily prepared by mixing together
a warm solution of 50 gm. of sodic thiosulphate in 300 c.c. of
water, and 40 gm. of baric chloride in a like volume of warm
wrater ; after stirring well, the salt soon separates in fine powdery
crystals. These are collected in a funnel stopped with glass or
cotton wool, repeatedly washed with cold water till all chlorine
is removed, then dried at below 30° C. on a glass or porcelain
plate until all extraneous moisture is removed ; or the crystals may
be treated, after thorough washing with alcohol and ether, as.
described below for sodic thiosulphate.

2. Decinormal Sodic Thiosulphate.
]STa2S203, 5H20 = 248-27 = 24*827 gm. per liter.

It is not difficult either to manufacture or procure pure sodic •
thiosulphate, but there may be uncertainty as to extraneous water

* Morse and Burton (Amer. Chem. Jour,, 1888) state that potassic iodide may be
completely freed from iodate by boiling a solution of it with zinc amalgam, prepared
by shaking zinc dust in good proportion with mercury in presence of tartaric acid, and
washing with water. The iodate is completely reduced with formation of zinc hydroxide.
The pure solution of iodide is filtered for use through a paper filter saturated with hot
water.

§ 38. IODOMETEY. 131

held within the crystals. In order to avoid this, Me in eke
(Gli em. Zeit. xviii. 33) recommends that the otherwise pure crystals
be broken to coarse powder, washed first with pure alcohol, then
with ether, and lastly dried in a current of dry air at ordinary
temperature. The salt so prepared may be weighed directly, and
dissolved in a liter of distilled water, and then titrated with the
iodine solution and starch indicator ; or it may be checked with
— j bichromate as recommended by Mohr, by digesting a measured
volume of the bichromate with an excess of potassic iodide, and
hydrochloric acid, in a well-stoppered flask at moderate heat.
When the mixture has cooled, the liberated iodine is measured by
the thiosulphate, and the working power of the latter ascertained.
It is advisable to preserve the solution in the dark. After a time
all solutions of thiosulphate undergo a slight amount of oxidation,
and sulphur deposits upon the bottle ; it is therefore always
advisable to titrate it previous to use.

Beside the clecinornial iodine and thiosulphate, it is convenient
in some cases to use centinormal solutions, which can readily be
prepared by diluting the decinormal solution when required.

In using the iodine solution Mohr's burette may be employed,
but care must be taken that the solution is not left in it for
any length of time, as decomposition slowly takes place, and the
tube becomes hard ; the tap burette is on this account preferable.

3. Starch. Indicator;

One part of clean potato starch, or arrowroot, is first mixed
smoothly with cold water into a thin paste, then gradually poured
into about 150 or 200 times its weight of boiling water, the boiling
continued for a few minutes, then allowed to stand and settle
thoroughly ; the clear solution only is to be used as the indicator,
of which a few drops only are necessary/'5' The solution may
be preserved for some long time by adding to it a few drops of
chloroform, and shaking well in a stoppered bottle.

Lintnar's soluble starch acts well as an indicator, as it gives at
once a clear solution in boiling water. It is prepared by steeping
potato starch, at ordinary temperature, for a week in dilute hydro-
chloric acid, washing out the acid with repeated quantities of cold
water,, and drying the starch at a moderate temperature. The
colour which occurs with this form of starch is not quite so pure
a blue as fresh ordinary starch, owing to the presence of some
dextrine produced unavoidably in the preparation, but it is no
hindrance to the end-point in practice.

Concentrated Solution of Starch. — This will keep any length of
time. Made by rubbing about 5 gm. starch to a smooth emulsion,

* In iodometric analyses it is always advisable in titrating- the free iodine with thio-
sulphate or arsenious solution to delay adding the starch until the iodine colour is nearly-
removed j a much more delicate ending may be obtained and with very little starch.

K 2

132 VOLUMETRIC ANALYSIS. § 39.

with about 50 c.c. water. Then add 25 c.c. of strong solution of
caustic potash and shake well, dilute with half a liter of water,
boil, and allow to settle. This indicator answers very well in
cases where the alkali is of no consequence, but is not available
for the delicate acidimetric method by iodic acid unless the alkali
is exactly corrected. It answers well, however, with the addition
of 2 gm. of potassic iodide as a reagent for nitrites, and keeps
perfectly though exposed to light.

ANALYSIS OF SUBSTANCES BY DISTILLATION WITH
HYDROCHLORIC ACID.

§ 39. THERE are a great variety of substances containing oxygen,
which when boiled with hydrochloric acid yield chlorine, equivalent

to the whole or a part only of the oxygen they contain according to
circumstances. Upon this fact are based the variety of analyses
which may be accomplished by means of iodine and sodic thio-
sulphate, or arsenite ; the chlorine so evolved, however, is not itself
estimated, but is conveyed by means of a suitable apparatus into
a solution of potassic iodide, thereby liberating an equivalent
quantity of iodine. This latter body is then estimated by thio-
sulphate ; the quantity so found is, therefore, a measure of the
oxygen existing in the original substance, and consequently
a measure of the substance itself. Analyses of this class may be
made the most exact in the whole range of volumetric analysis,
far outstripping any process by weight.

39.

IODOMETRY.

The apparatus used for distilling the substances, and conveying
the liberated chlorine into the alkaline iodide, may possess a variety
of forms, the most serviceable, however, being the three kinds
devised respectively by Bun sen, Fresenius, and Mohr.

Bunsen's arrangement consists of an inverted retort, into the
neck of which the tube from the small distilling flask is passed.

Owing to the great solubility of HC1 in the form of gas, the
apparatus must be so constructed that when all Cl is liberated and
HC1 begins to distil, the liquid may not rush back to the flask
owing to condensation.

Fig. 38.

The best preventive of this regurgitation is, however, suggested
by Fresenius, and applicable to each kind of apparatus; namely,
the addition of a few pieces of pure magnesite. This substance
dissolves but slowly in the hydrochloric acid, and so keeps up
a constant flow of CO2, the pressure of which is sufficient to
prevent the return of the liquid.

The apparatus contrived by Fresenius is shown in fig. 37, and
is exceedingly useful as an absorption apparatus for general
purposes.

VOLUMETRIC ANALYSIS. § 39.

Mo hr's apparatus is shown in fig. 38 and is, on account of its
simplicity of construction, very easy to use.

The distilling flask is of about 2 oz. capacity, and is fitted with
a cork soaked to saturation in melted paraffin ; through the cork
the delivery tube containing one bulb passes, and is again passed
through a common cork, fitted loosely in a stout tube about 12 or
13 inches long and 1 inch wide, closed at one end like a test tube.
This tube, containing the alkaline iodide, is placed in an hydrometer
glass, about 12 inches high, and surrounded by cold water ; the
delivery tube is drawn out to a fine point, and reaches nearly to
the bottom of the condenser. No support or clamp is necessary,
as the hydrometer glass keeps everything in position. The
substance to be distilled is put into the flask and covered with
strong hydrochloric acid, the magnesite added, the condenser
supplied with a sufficient quantity of iodide solution, and the
apparatus put together tightly. Either an argand or common
spirit lamp, or gas, may be used for heating the flask, but the
flame must be manageable, so that the boiling can be regulated at
will. In the case of the common spirit lamp it may be held in the
hand, and applied or withdrawn according to the necessities of the
case : the argand spirit or gas lamp can, of course, be regulated by
the usual arrangements for the purpose. If the iodine liberated
by the chlorine evolved should be more than will remain in
solution, the cork of the condensing tube must be lifted, and more
solution added. "When the operation is judged to be at an end,
the apparatus is disconnected, and the delivery tube washed out
into the iodide solution, which is then emptied into a beaker or
flask and preserved for titration, a little fresh iodide solution is
put into the condenser, the apparatus again put together, and
a second distillation commenced, and continued for a minute or so,
to collect every trace of free chlorine present. This second
operation is only necessary as a safeguard in case the first should
not have been complete.

The solutions are then mixed together and titrated in the
manner previously described. In all cases the solution must be
cooled before adding the thiosulphate, otherwise sulphuric acid
might be formed.

Instead of the large test tube, some operators use a (J tube to
contain the potassic iodide, having a bulb in each limb, but the
latter is not necessary if magnesite is used.

The solution of potassic iodide may conveniently be made of
such a strength that T2^- eq. or 33 '2 gin. are contained in the liter.
1 c.c. will then be sufficient to absorb the quantity of free iodine,
representing 1 per cent, of oxygen in the substance analyzed,
supposing it to be weighed in the metric system. In examining
peroxide of manganese, for instance, 0'436 gm. or 4*36 grn. would
be used, and supposing the percentage of peroxide to be about
sixty, 60 c.c. or dm. of iodide solution would be sufficient to absorb

IODOMETRY.

135

the chlorine and keep in solution the iodine liberated by the
process ; it is advisable, however, to have an excess of iodide, and,
therefore, in this case, about 70 c.c. or dm. should be used.
A solution of indefinite strength will answer as well, so long as
enough is used to absorb all the iodine. It may sometimes happen
that not enough iodide is present to keep all the liberated iodine in
solution, in which case it will separate out in the solid form ; more
iodide, however, may be added to dissolve the iodine, and the
titration can then be made as usual.

The process of distillation above described may be avoided in
many cases. There are a great number of substances which, by
mere digestion with hydrochloric acid and potassic iodide at an
elevated temperature, undergo decomposi- |
tion quite as completely as by distillation, sjjf
For this purpose a strong bottle with
a very accurately ground stopper is neces-
sary ; and as the ordinary stoppered bottles
of commerce are not sufficiently tight, it is
better to re-grind the stopper with a little
very fine emery and water. It must then
be tested by tying the stopper tightly
down and immersing in hot water ; if any
bubbles of air find their way through the
stopper the bottle is useless. The capa-
city may vary from 30 to 150 c.c., accord-
ing to the necessities of the case.

The stopper may be secured by fine copper binding-wire, or
a kind of clamp contrived by Mohr may be used, as shown in
fig. 39 ; by means of the thumb-screws the pressure upon the
stopper may be increased to almost any extent.

The substance to be examined, if in powder, is put into the
bottle with pure flint pebbles or small garnets, so as to divide it
better, and a sufficient quantity of saturated solution of potassic
iodide and pure hydrochloric acid added ; the stopper is then
inserted, fastened down, and the bottle suspended in a water
bath, and the water is gradually heated to boiling by a gas
name or hot plate as may be most convenient. When the
decomposition is complete the bottle is removed, allowed to cool
someAvhat, then placed in cold water, and, after being shaken,
emptied into a beaker, and the liquid diluted by the washings
for titration.

The salts of chloric, iodic, bromic, and chromic acids, together
with many other compounds, may be as effectually decomposed by
digestion as by distillation ; many of them even at ordinary tem-
peratures. Recently precipitated oxides, or the natural oxides,
when reduced to fine powder are readily dissolved and de-
composed by very weak acid in the presence of potassic iodide
(Pickering).

136 VOLUMETRIC ANALYSIS. § 40.

The potassic iodide used in the various analyses must be abso-
lutely free from potassic iodate and free iodine, or if otherwise, the
effect of the impurity must be known by blank experiment.

ARSENIOTJS ACID AND IODINE.

§ 40. THE principle upon which this method of analysis is
based is the fact, that when arsenious acid is brought in contact
with iodine in the presence of water and free alkali, it is converted
into arsenic acid, the reaction being —

AS203 + 41 + 2K'20 = As205 + 4KI.

The alkali must be in sufficient quantity to combine with the
hydriodic acid set free, and it is necessary that it should exist in
the state of bicarbonate, as caustic or monocarbonated alkalies
interfere with the colour of the blue iodide of starch used as indicator.

If, therefore, a solution of arsenious acid containing starch is
titrated with a solution of iodine in the presence of an alkaline
bicarbonate, the blue colour does not occur until all the arsenious
acid is oxidized into arsenic acid. In like manner, a standard
solution of arsenious acid may be used for the estimation of iodine
or other bodies which possess the power of oxidizing it.

The chief value, however, of this method is found in the
estimation of free chlorine existing in the so-called chloride of
lime, chlorine water, hypochlorites of lime, soda, etc., in solution;
generally included under the term of chlorimetry.

Preparation of the ^ Solution of Alkaline Arsenite.
As203= 198 ; 4-95 gm. per liter.

The iodine solution is the same as described in § 38.

The corresponding solution of alkaline arsenite is prepared by
dissolving 4'95 gm. of the purest sublimed arsenious oxide in
about 250 c.c. of distilled water in a flask, with about 20 gm. of
pure sodic carbonate.'"" It is necessary that the acid should be in
powder, and the mixture needs warming and -shaking for some
time in order to complete the solution ; when this is accomplished
the mixture is diluted somewhat, cooled, then made up to the
liter.

In order to test this solution, 20 c.c. are put into a beaker with
a little starch indicator, and the iodine solution allowed to flow in
from a burette, graduated in -^ c.c. until the blue colour appears.
If exactly 20 c.c. are required, the solution is strictly decinormal ;
if otherwise, the necessary factor must be found for converting it
to that strength.

* In the previous edition of this book, the arsenkms solution was recommended to
be made with alkaline bicarbonate, but this has, after keeping, been found to give
defective results with bleach analyses from some cause not yet understood.

§ 40. . IODOMETRY. 137

Iodized Starch-paper. —Starch solution cannot be used for the
direct estimation of free chlorine, consequently resort must be had
to an external indicator ; and this is very conveniently found in
starch-iodide paper, which is best prepared by mixing a portion of
starch solution with a few drops of solution of potassic iodide on
a plate, and soaking strips of pure filtering paper therein. The
paper so prepared is used in the damp state, and is far more
sensitive than when dried.

Example of Titration : 50 c.c. of chlorine water were mixed with solution
of sodic carbonate, and brought under the arsenic burette, and 20 c.c. of
solution added ; on touching the prepared paper with the mixture no colour
was produced, consequently the quantity used was too great; starch was
therefore added, and decinorinal iodine, of which 3"2 c.c. were required to
produce the blue colour. This gave 16'8 c.c. of arsenious solution, which
multiplied by 0'003537, gave 0*05942 gm. of Cl in the 50 c.c. A second
operation with the same water required 16'8 c.c. of arseuious solution direct,
before the end of the reaction with iodized starch-paper was reached.

138 VOLUMETRIC ANALYSIS. § 41.

PART IV.
ANALYSIS BY PRECIPITATION.

§ 41. THE general principle of this method of determining the
quantity of any given substance is alluded to in § 1, and in all
instances is such that the body to be estimated forms an insoluble
precipitate with a titrated reagent. The end of the reaction is,
however, determined in three ways.

1. By adding the reagent until no further precipitate occurs,
as in the determination of chlorine by silver.

2. By adding the reagent in the presence of an indicator con-
tained either in the liquid itself, or brought externally in contact
with it, so that the slightest excess of the reagent shall produce
a characteristic reaction with the indicator ; as in the estimation
of silver with sodic chloride by the aid of potassic chromate, or
with thiocyanate and ferric sulphate, or that of phosphoric acid
with uranium by yellow potassic prussiate.

3. By adding the reagent to a clear solution, until a precipitate
occurs, as in the estimation of cyanogen by silver.

The first of these endings can only be applied with great accuracy
to silver and chlorine estimations. Very few precipitates have the
peculiar quality of chloride of silver ; namely, almost perfect
insolubility, and the tendency to curdle closely by shaking, so as to
leave the menstruum clear. Some of the most insoluble precipitates,
such as baric sulphate and calcic oxalate, are unfortunately excluded
from this class, because their finely divided or powdery nature
prevents their ready and perfect subsidence.

In all these cases, therefore, it is necessary to find an indicator,
which brings them into class 2.

The third class comprises only two processes; viz., the deter-
mination of cyanogen by silver, and that of chlorine by mercuric
nitrate.

Since the estimation of chlorine by precipitation with silver,
and that of silver by thiocyanic acid, can be used in many cases
for the indirect estimation of many other substances with great
exactness, the preparation of the necessary standard solutions will
now be described.

SILVER AND CHLORINE.
I. Decinormal Solution of Silver.

10-766 gm. Ag or 16-^66 gm. AgXO:! per liter.

10 '7 6 6 gm. of pure silver are dissolved in pure dilute nitric acid
with gentle heat in a flask, into the neck of which a small funnel
is dropped to prevent loss of liquid by spirting. T\rhen solution
is complete, the funnel must be washed inside and out with

§ 41. PKECIPITATIOX ANALYSES. 139

distilled water into the flask, and the liquid diluted to a liter ; but
if it be desired to use potassic chromate as indicator in any analysis,
the solution must be neutral ; in which case the solution of silver
in nitric acid is evaporated to dryness, and the residue dissolved in
a liter; or, what is preferable, 16-966 gm. of pure silver nitrate,
previously heated to 120° C. for ten minutes, are dissolved in
a liter of distilled water.

2. Decinormal Solution of Salt. s

5-837 gm. 2sraCl per liter.

5-837 gm. of pure sodic chloride are dissolved in distilled water,
and the solution made up to a liter.

There are two methods by which the analysis may be ended :

(a) By adding silver cautiously, and well shaking after each
addition till no further precipitate is produced. For details
see § 73.

(/;) By using a few drops of solution of pure potassic rnono-
chromate as indicator, as devised by Mohr. If the pure salt is
not at hand, some silver nitrate should be added to the solution of
the ordinary salt, to remove chlorine, and the clear liquid used.

The method I is exceedingly serviceable, on the score of saving
both time and trouble. The solutions must be neutral, and cold.
When, therefore, acid is present in any solution to be examined, it
should be neutralized with pure sodic or calcic carbonate in very
slight excess.*

Process : To the neutral or faintly alkaline solution, two or three
drops of a cold saturated solution of chromate are added, and the silver
solution delivered from the burette until the last drop or two produce
a faint blood-red tinge, an evidence that all the chlorine has combined with
the silver, and the slight excess has formed a precipitate of silver chromate ;
the reaction is very delicate and easily distinguished. The colour reaction
is even more easily seen by gas-light than by daylight. It may be rendered
more delicate by adopting the plan suggested by I) up re (Analyst v. 123).
A glass cell, about 1 centimeter in depth, is filled with water tinted with
chromate to the same colour as the solution to be titrated. The operation is
performed in a white porcelain basin. The faintest appearance of the red
change is at once detected on looking through the coloured cell. Tor the
analysis of waters weak in chlorine this method is very serviceable,
but contrary to what has been generally accepted, the accuracy of the
results are seriously interfered with by great dilution or high temperature
(W. G. Young, Analyst xviii. 125). As is the case with most volumetric
processes, it is therefore necessary in order to secure a high degree of
accuracy to titrate under the same conditions under which the standard was
fixed.

Example: 1 gm. of pure sodic chloride was dissolved in 100 c.c. of water,
a few drops of chromate added, and titrated with ^V silver, of which 17'1 c.c.
were required to produce the red colour ; multiplied by the T*V factor for
sodic chloride = 0'005837 the result was 0'998 gm. NaCl, instead of 1 gm.

* Silver chromate is sensibly soluble in the presence of alkaline or earthy nitrates,
especially at a high temperature ; sodic and calcic hydrates have the least effect ;
arninonic, potassic, and inagnesic nitrates the greatest. See also Forbes Carpenter
(J. S. C. I. v. 286).

140 VOLUMETRIC ANALYSIS. § 42.

INDIRECT ESTIMATION OF AMMONIA, SODA., POTASH,
LIME, AND OTHER ALKALIES AND ALKALIN * EAxtTH •?,
WITH THEIR CARBONATES, NITRATES, AND CHLO-
RATES, ALSO NITROGEN, BY MEANS OF DECINORMAL
SILVER SOLUTION, AND POTASSIC CHROMATE, AS
INDICATOR.

1 CiC. _*_ silver solution = Tolyo^ ^. eq. of each substance.

§ 42. MOHR, with, his characteristic ingenuity has made use
of the delicate reaction between chlorine and silver, with potassic
chromate as indicator, for the determination of the bodies men-
tioned above. All compounds capable of being converted into.
neutral chlorides by evaporation to dryness with hydrochloric acid
may be determined with great accuracy. The chlorine in a com-
bined state is, of course, the only substance actually determined ;
but as the laws of chemical combination are exact and well known,
the measure of chlorine is also the measure of the base with which
it is combined.

In most cases it is only necessary to slightly supersaturate the
alkali, or its carbonate, with pure hydrochloric acid ; evaporate on
the water bath to dryness, and heat for a time to 120° C. in the air
bath, then dissolve to a given measure, and take a portion for
titration ; too great dilution must be avoided.

Alkalies and Alkaline Earths with organic acids are ignited to
convert them into carbonates, then treated with hydrochloric acid,
and evaporated as before described.

Carbonic Acid in combination may be determined by precipita-
tion with baric chloride, as in § 23. The washed precipitate is
dissolved on the filter with hydrochloric acid (covering it with
a watch-glass to prevent loss), and then evaporated to dryness
repeatedly till all HC1 is driven off. In order to titrate with
accuracy by the help of potassic chromate, the baryta must
be precipitated by means of a solution of pure sodic or potassic
sulphate, in slight excess ; the precipitated baric sulphate does
not interfere with the delicacy of the reaction. If this precaution
Avere not taken, the yellow baric chromate would mislead.

Free Carbonic Acid is collected by means of ammonia and baric
chloride (as in § 23), and the estimation completed as in the case of
combined CO2.

Chlorates are converted into chlorides by ignition before titration.

Nitrates are evaporated with concentrated hydrochloric acid, and
the resulting chlorides titrated, as in the previous case.

Nitrogen. — The ammonia evolved from guano, manures, oilcakes,

§ 42. PRECIPITATION ANALYSES. 141

and sundry other substances, when burned with soda lime or
obtained by the Kj el da hi method, is conducted through dilute
hydrochloric acid; the liquid is carefully evaporated to dryness
before titration.

In all cases the operator will, of course, take care that no chlorine
from extraneous sources other than the hydrochloric acid is present;
or if it exists in the bodies themselves as an impurity, its quantity
must be first determined.

Example : 0'25 gm. pure sodic carbonate was dissolved in water, and
hydrochloric acid added till in excess ; it was then dried on the water bath
till no further vapours of acid were evolved; the resulting white mass was
heated for a few minutes to about 150° C., dissolved and made up to 3»0 c.c.
100 c.c. required 15'7 c.c. T^ silver, this multiplied by 3 gave 47'1 c.c., which
multiplied by the T^ factor for sodic carbonate— 0'0053, gave 0'24963 gm.
instead of 0*25 gm.

Indirect Estimation of Potash and Soda existing as Mixed
Chlorides.— It is a problem of frequent occurrence to determine the
relative quantities of potash and soda existing in mixtures of the
two alkalies, such as occur, for instance, in urine, manures, soils,
waters, etc. The actual separation of potash from soda by means
of platinum is tedious, and not always satisfactory.

The following method of calculation is frequently convenient,
since a careful estimation of the chlorine present in the mixture is
the only labour required ; and this can most readily be accom-
plished by ~Q silver and chromate, as previously described.

(1) The weight of the mixed pure chlorides is accurately found and noted.

(2) The chlorides are then dissolved in water, and very carefully titrated
with /„ silver and chromate for the amount of chlorine present, which is
also recorded ; the calculation is then as follows : —

The weight of chlorine is multiplied by the factor 2'103 ; from the product
so obtained is deducted the weight of the mixed salts found in 1. The
remainder multiplied by 3'6288 will give the weight of sodic chloride
present in the mixture.

The weight of sodic chloride deducted from the total as found in 1 will
give the weight of potassic chloride.

Sodic chloride x 0'5302=Soda (NaeO).
Potassic chloride x 0'63l7=Potash (K2O).

The principle of the calculation, which is based on the atomic constitution
of the individual chlorides, is explained in most of the standard works on
general analysis. Indirect methods like this can only give useful results
when the atomic weights of the two substances differ considerably, and when
the proportions are approximately equal.

Another method of calculation in the case of mixed potassic and
sodic chlorides is as follows : —

The weight of the mixture is first ascertained and noted ; the chlorine is
then found by titration with T^ silver, and calculated to NaCl : the weight
so obtained is deducted from the original weight of the mixture, and the
remainder multiplied by 2'42857 will give the potassium.

142 VOLUMETRIC ANALYSIS. § 43.

SILVER AND THIOCYANIC ACID.

§ 43. THIS excellent and most accurate method has been devised
"by Volhard and is fully described by the author (Lielig's Ann. cL
CJiem. cxc. 1), and has been favourably noticed by Falck (Z. a. C.
xiv. 227), Briigelman (Z. a. C. xvi. 7), and Drechsel (Z. a. C.
xvi. 351), and many other well known chemists. It differs from
Mohr's chromate method in that the silver solutions may contain
free nitric acid, which renders it of great service in indirect
analyses.

This method is based on the fact that when solutions of silver
and an alkaline thiocyanate are mixed in the presence of a ferric
salt, so long as silver is in excess, the thiocyanate of that metal
is precipitated, and any brown ferric thiocyanate which may
form is at once decomposed. When, however, the thiocyanate is
added in the slightest excess, brown ferric thiocyanate is formed,
and asserts its colour even in the presence of much free acid.
The method may of course be used for the estimation of silver,
and by the residual process, for the estimation of substances which
are completely precipitated by silver.'""

It may be used for the estimation of silver in the presence of
copper up to 70 per cent. ; also in presence of antimony, arsenic,
iron, zinc, manganese, lead, cadmium, bismuth, and also cobalt and
nickel, unless the proportion of these latter metals is such as to
interfere by intensity of colour.

It may further be used for the indirect estimation of chlorine,
bromine, and iodine, in presence of each other, existing either in
minerals or inorganic compounds, and for copper, manganese, and
zinc ; these will be noticed under their respective heads.

1, Decinormal Ammonic or Potassic Thiocyanate.

This solution cannot be prepared by weighing the thiocyanate
direct, owing to the deliquescent nature of the salts; therefore
about 8 gm. of the ammonium, or 10 gm. of the potassium salt
may be dissolved in about a liter of water as a basis for getting an
exact solution, which must be finally adjusted by a correct
decinormal silver solution.

The standard solution so prepared remains of the- same strength
for a very long period if preserved from evaporation.

2. Decinormal Silver Solution.

This is the same as described in a preceding section (§ 41), and
may contain free nitric acid if made direct from metallic silver.

* In cases where chlorine is precipitated by excess of silver, and the excess has to be
found by thiocyanate, experience has proved that it is absolutely necessary to filter off
the chloi'ide and titrate the filtrate and washings. If this be not done the solvent
effect of the thiocyanate upon the AgCl will give inaccurate results. This fact seems
to have been overlooked at the time the method was first introduced.

§ 44. COLOUR REACTIONS. 143

3. Ferric Indicator.

This may consist simply of a saturated solution of iron alum ;
or may be made by oxidizing ferrous sulphate with nitric acid,
evaporating with excess of sulphuric acid to dissipate nitrous
fumes, and dissolving the residue in water so that the strength
is about 10 per cent.

5 c.c. of either of these solutions are used for each titration,
which must always take place at ordinary temperatures.

4. Pure Nitric Acid.

This must be free from the lower oxides of nitrogen, secured by
diluting the usual pure acid with about a fourth part of water,
and boiling till perfectly colourless. It should then be preserved
in the 'dark.

The quantity of nitric acid used in the titration may vary
within wide limits, and seems to. have no effect upon the precision
of the method.

The Process for Silver : 50 c.c. of •& silver solution are placed into
a flask, diluted somewhat with water, and 5 c.c. of ferric indicator added,
together with about 10 c.c. of nitric acid. If the iron solution should
cause a yellow colour, the nitric acid will remove it. The thiocyauate is
then delivered in from a burette; at first a white precipitate is produced
rendering the fluid of a milky appearance, and as each drop of thiooyanate
falls in, it produces a reddish-brown cloud which quickly disappears on
shaking. As the point of saturation approaches, the precipitate becomes
flocculent and settles easily ; finally, a drop or two of thiocyanate produces
a faint brown colour which no longer disappears on shaking. If the
solutions are correctly balanced, exactly 50 c.c. of thiocyanate should be
required to produce this effect.

The colour is best seen ~by holding the flask so as to catch the reflected
light of a white Avail or a suspended sheet of white paper.

PRECISION IN COLOUR REACTIONS:

§ 44. DUPRE adopts the following ingenious method for colour
titrations (Analyst v. 123) : — As is well known, the change from
pale yellow to red, in the titration of chlorides by means of silver
nitrate with neutral chromate as indicator, is more distinctly
perceived by gas-light than by daylight ; and in the case of potable
waters, containing from one to two grains of chlorine per gallon,
it is absolutely necessary to concentrate by evaporation previous
to titration, or else to perform the titration by gas-light. The
adoption of the following simple plan enables the operator to
perceive the change of colour as sharply, and with as great
a certainty, by daylight as by gas-light. Nevertheless, as has
been before mentioned, it is impossible to get accurate results
with very weak solutions of chlorine unless the silver solution
is standardized upon similar solutions.

The water is placed into a white porcelain dish (100 c.c. are
a useful quantity), a moderate amount of neutral chromate is added

144 VOLUMETRIC ANALYSIS. § 4-i.

(sufficient to impart a marked yellow colour to the water), but
instead of looking at the water directly, a flat glass cell containing
some of the neutral chromate solution is interposed between the
eye and the dish. The effect of this is to neutralize the yellow
tint of the water ; or, in other words, if the concentration of the
solution in the cell is even moderately fairly adjusted to the depth
of tint imparted to the water, the appearance of the latter, looked
at through the cell, is the same as if the dish were filled with pure
water. If now the standard silver solution is run in, still looking
through the cell, the first faint appearance of a reel coloration
becomes strikingly manifest; and what is more, when once the
correct point has been reached the eye is never left in doubt, how-
ever long we may be looking at the water. A check experiment
in which the water, with just a slight deficiency of silver, or excess
of chloride, is used for comparison is therefore unnecessary.

A similar plan will be found useful in other titrations. Thus,
in the case of turmeric, the change from yellow to brown is per-
ceived more sharply and with greater certainty when looking
through a flat cell containing tincture of turmeric of suitable
concentration than with the naked eye. The liquid to be titrated
should, as in the former case, be placed into a white porcelain dish.
Again, in estimating the amount of carbonate of lime in a water
by means of decinormal acid and cochineal, the exact point of
neutrality can be more sharply fixed by looking through the
cell filled with a cochineal solution. In this case the following
plan is found to answer best. The water to be tested — about
250 c.c. — is placed into a flat porcelain evaporating dish, part of
which -is covered over with a white porcelain plate. The water is
now tinted with cochineal as usual, and the sulphuric acid run in,
the operator looking at the dish through the cell containing the
neutral cochineal solution. At first the tint of the water and the
tint in which the porcelain plate is seen are widely different ; as,
however, the carbonate becomes gradually neutralized, the two
tints approach each other more and more, and when neutrality is
reached they appear identical ; assuming that the strength of the
cochineal solution in the cell, and the amount of this solution
added to the water, have been fairly well matched. Working in
this manner it is not difficult (taking |- liter of water) to come
within 0*1 c.c. of decinormal acid in two successive experiments,
and the difference need never exceed 0'2 c.c. In the cell employed
the two glass plates are a little less than half an inch apart.

A somewhat similar plan may be found useful in other titrations,
or, in fact, in many operations depending on the perceptions of
.colour change.

§ 45. ALUMINIUM. 145

PAET V.

APPLICATION OF THE FOREGOING PRINCIPLES OF
ANALYSIS TO SPECIAL SUBSTANCES.

AL.TJMINITJM.

Al = 27-3.

§ 45. ALUMINIUM salts (the alums and aluminium sulphates
used in dyeing and paper-making) may be titrated for alumina
in the absence of iron (except in mere traces) by mixing the acid
solutions with a tolerable quantity of sodic acetate, then a known
volume in excess of y^ phosphate solution (2O9 gm. of ammonio-
sodic phosphate per liter), heating to boiling, without filtration; the
excess of phosphate is found at once by titration with standard
uranium. If iron in any quantity is present, it may be estimated
in a separate portion of the substance, and its amount deducted
before calculating the alumina. The latter is precipitated as
A1P04, and any iron in like manner as FePO4. Each c.c. of ~
phosphate = 0*005 13 gm. A12O3. Only available for rough purposes.

Baeyer's Method. — As originally proposed, this process for
estimating alumina in alums and aluminic sulphates was carried
out by two titrations, a measured portion of the solution being first
treated with an excess of normal soda in sufficient quantity to
dissolve the precipitate of hydrate of alumina first formed. It was
then diluted to a definite volume, half being titrated with normal
acid and litmus, other half with tropoeolin 00, the difference being
calculated to alumina. «

A considerable improvement however has been made by using
phenolphthalein as the indicator, one titration only being necessary.
The method is based on the fact that, if to a solution of alumina,
containing the indicator, normal soda is added in excess, or until
the red colour is produced, normal acid be then added until the
colour disappears, the volume of acid so required is less than the
soda originally added in proportion to the quantity of alumina
present.

The volume of acid which so disappears is in reality the quantity
necessary to combine with the alumina set free by the alkali ; and
if this deficient measure of acid be multiplied by the factor
0-01716 (J mol. wt. of A1203), the weight of alumina will be
obtained. This factor is given on the assumption that the normal
sulphate APS SO4 is formed.

The titration must take place in the cold and in dilute solutions.
Very fair technical results have been obtained by me with

146 VOLUMETRIC ANALYSIS. § 45.

potash and ammonia alums and the commercial sulphates of
alumina.

Alumina existing as aluminate of alkali in caustic soda, for
instance, may be very well estimated by taking advantage of the
fact, that such alumina is quite indifferent to methyl orange, but
reacts acid with phenolphthalein. This fact has been recorded by
Thomson and others, but the priority of discovery appears to be
due to Baeyer (Z. a. C. xxiv. 542), who, however, used litmus in
the place of phenolphthalein and tropceolin 00 instead of methyl
orange.

Cross and Be van (J. S. C. I. viii. 252) in their examination of
caustic soda for alumina, found by experiment, that the mean of
the differences between the titration with methyl orange and
phenolphthalein required the factor O0205 per c.c. of normal acid
for the alumina, pointing to the salt as 2AP03 : 5S03.

The estimation of the alumina in caustic soda has given rise to
much discussion between even very experienced operators, notably
MM. Cross and Bevan and Lunge, but the former chemists
have proved, as far as possible, by various methods, the accuracy
of their views that the above-named equation is correct. The
method adopted by them consists in boiling the weighed sample
with a slight excess of standard acid, allowing to cool and titrating
back with standard soda and phenolphthalein. The acid so con-
sumed represents the total alkali present. To a similar portion
a slight excess of acid is added and titrated back with soda and
methyl orange.

Estimation of free Acid. — Alum cakes or aluminic sulphates of
various kinds often contain free H2S04, and many methods have
been proposed for its estimation. Baeyer titrates a 10 per cent,
solution of the substance in water with normal soda, and tropceolin
00 or methyl orange.

R. Williams (C. N. Ivi. 194) adopts the -alcohol method by
digesting the substance for at least twelve hours with strong
alcohol, filtering off and washing with the same agent, and titrating
the solution without dilution or evaporation with •£-$ acid and
phenolphthalein.

Beilsteiii and Grosset (Bull, de I'Academie Imp. des Sciences
de St. Petersburg, xiii. 41) have examined with great care all the
proposed methods for this purpose, and have devised one which
gives very good technical results.

Process : 1 to 2 gin. of substance is dissolved in 5 c.c. of water, 5 c.c.
of a cold saturated neutral solution of ammonic sulphate added, and stirred
for a quarter of an hour. 50 c.c. of 95 per cent, alcohol are then added, the
mixture thrown on a small filter, and washed with 50 c.c. of the same
alcohol. The nitrate is evaporated on the water bath, the residue dissolved
in water, and titrated with ^ alkali and litmus. The whole of the neutral
aluminic sulphate is precipitated as ammonia alum, the alcohol contains all
the free acid.

§ 46. ANTIMONY. 147

ANTIMONY.

Sb = 120.

1. Conversion of Antimonious Acid in Alkaline Solution into
Antimonic Acid by Iodine (Mohr).

§ 46. ANTIMONIOUS oxide, or any of its compounds, is brought
into solution as tartrate by tartaric acid and water ; the excess of
acid neutralized by sodic carbonate ; then a cold saturated solution
of sodic bicarbonate added, in the proportion of 10 c.c. to about
O'l gm. Sb203 ; to the clear solution starch is added and —
iodine until the blue colour occurs. No delay must occur in the
titration when the bicarbonate is added, otherwise a portion of the
metal is precipitated as antimonious hydrate, upon which the iodine
fas little effect.*

For the estimation of antimonic acid and its salts, G.vonKnorre
(Zeit. Angeic. Chem., 1888, 155) gives the following method as
accurate : —

The solution of the salt, strongly acidified with hydrochloric acid, is treated
in a roomy flask with strong solution of sodic sulphide, added gradually in
small portions. It is then vigorously boiled until all SO2 is expelled, a drop
of phenolphthalein is added, then caustic potash until red ; this is in turn
removed by a small excess of tartaric acid. Sodic bicarbonate is then added,
and the titration with iodine carried out in the usual way.

The colour disappears after a little time, therefore the first
appearance of a permanent blue is accepted as the true measure
of iodine required.

1 c.c. T^ iodine = 0-0060 gm. Sb.

Estimation of Antimony in presence of Tin (Type and Britannia
metal, etc.). — The finely divided alloy is dissolved in strong hydro-
chloric acid by heat, adding frequently small quantities of potassic
chlorate. The liquid is boiled to remove free chlorine, cooled,
a slight excess of strong solution of potassic iodide added, and
the liberated iodine estimated by standard thiosulphate. Some
operators prefer to collect the liberated iodine in carbon bisulphide
previous to titration.

120 Sb liberate 253 I, and the weight of I found multiplied
by 0-47 5 = Sb.

If iron or other metal capable of liberating iodine be present,
treat the alloy with nitric acid, and evaporate to obtain the oxides
of antimony and tin — wash, boil in hydrochloric acid, and proceed
as before described. The rationale is, that antimonic chloride is
reduced to antimonious chloride, while stannic chloride is not affected.

H. Oxidation by Potassic Bichromate or Permanganate (Kessler),
Bichromate or permanganate added to a solution of antimonious

*Dunstaii and Boole (Pharm. Jour., Nov., 1888) have proved that the accurate
•estimation of the antimony in tartar emetic may be secured by this method, using the
precautions above mentioned.

L 2

148 VOLUMETRIC ANALYSIS. § 46.

chloride, containing not less than J of its volume of hydrochloric
acid (sp. gr. 1*12), converts it into antimonic chloride.

The reaction is uniform only when the minimum quantity of acid
indicated above is present, but it ought not to exceed i the volume,
and the precautions before given as to the action of hydrochloric
acid on permanganate must be taken into account, hence it is
preferable to use bichromate.

Kessler (Poggend. Annal. cxviii. 17) has carefully experimented
upon this method and adopts the following processes.

A standard solution of arsenious acid is prepared containing
5 gm. of the pure acid, dissolved by the aid of sodic hydrate,
neutralized with hydrochloric acid, 100 c.c. concentrated hydro-
chloric acid added, then diluted with water to 1 liter ; each c.c. of
this solution contains 0'005 gm. As203, and represents exactly
0-007253 gm. Sb'203.

Solutions of potassic bichromate and ferrous sulphate of known
strength in relation to each other, are prepared in the usual way ;
and a freshly prepared solution of potassic ferricyanide used as
indicator.

The relation between the bichromate and arsenious solution is
found by measuring 10 c.c. of the latter into a beaker, 20 c.c.
hydrochloric acid of sp. gr. 1*12, and from 80 to 100 c.c. of water
(to insure uniformity of action the volume of HC1 must never be
less than J or more than J) ; the bichromate solution is then added
in excess, the mixture allowed to react for a few minutes, and the
ferrous solution added until the indicator shows the blue colour.
To find the exact point more closely, J or 1 c.c. bichromate solution
may be added, and again iron, until the precise ending is obtained.

Process : The material, free from organic matter, organic acids, or heavy
metals, is dissolved in the proper proportion of HC1, and titrated precisely
as just described for the arsenious solution ; the strength of the bichromate
solution having been found in relation to As2O3 the calculation as respects
Sb2O3 presents no difficulty. Where direct titration is not possible the same
course may be adopted as with arsenic (§ 47) ; namely precipitation with
H2S and digestion with mercuric chloride.

In the case of using permanganate it is equally necessary to have
the same proportion of HC1 present in the mixture, and the
standard solution must be added till the rose colour is permanent.
The permanganate may be safely used with J the volume of HC1,
with the addition of some magnesic sulphate, and as the double
tartrate of antimony and potassium can readily be obtained pure,
and the organic acid exercises no disturbing effect in the titration,
it is a convenient material upon which to standardize the solution.

3. Distillation of Antimonious or Antimonic Sulphide -with.
Hydrochloric Acid, and Titration of the evolved Sulphuretted
Hydrogen (Schneider).

When either of the sulphides of antimony is heated with
hydrochloric acid in Bunsen's, Fresenius', or Mohr's distilling

§ 47. AKSENIC. 149

apparatus (§ 39), for every 1 eq. of antimony present as sulphide,
3 eq. of HAS are liberated. If, therefore, the latter be estimated,
the quantity of antimony is ascertained.

Process : The antimony to be determined is brought into the form of ter-
or penta -sulphide (if precipitated from a hydrochloric solution, tartaric acid
•must be previously added to prevent the precipitate being contaminated with
chloride), which, together with the filter containing it, is put into the distilling
flask with a tolerable quantity of hydrochloric acid not too concentrated.
The absorption tube contains a mixture of caustic soda or potash, with a
definite quantity of ^V arsenious acid solution in sufficient excess to retain all
the sulphuretted hydrogen evolved. The flask is then heated to boiling, and
the operation continued till all evolution of sulphuretted hydrogen has ceased ;
the mixture is then poured into a beaker, and acidified with hydrochloric
acid, to precipitate all the arseuious sulphide. The whole is then diluted to,
say 300 c.c., and 100 c.c. taken with a pipette, neutralized with sodic
carbonate, some bicarbonate added, and the titration for excess of arsenious
acid performed with ^ iodine and starch, as directed in § 40. The separa-
tion of antimony may generally be insured by precipitation as sulphide. If
arsenic is precipitated at the same time, it may be removed by treatment
with ammonic carbonate.-

ARSENIC.

As = 75. As203 = 198. As205^230.
1. Oxidation by Iodine (Mo hr).

§ 47. THE principle upon which the determination of arsenious
acid by iodine is based is explained in § 40.

Experience has shown, that in the 'estimation of arsenious
compounds by the method there described, 'it is necessary to use
sodic bicarbonate for rendering the solution alkaline as in the case
of antimony.

Process : To a neutral aqueous solution, add about 20 c.c. of saturated
solution of sodic bicarbonate to every O'l gm. or so of As2O3, and then titrate
with 3^ iodine and starch. When the solution is acid, the excess may be
removed by neutral sodic carbonate, then the necessary quantity of bicar-
bonate added, and the titration completed as before.

Process for Arsenic Acid: This is best done by dissolving the acid in water,
and boiling with potassic iodide in the presence of hydrochloric acid in large
excess until all iodine vapours are dissipated. The'AsHO4 is completely
reduced to AsHO3. The liquid is then cooled, sodic carbonate added to
neutrality, then some bicarbonate, and the arsenious acid titrated with
iodine in the usual way. Younger (J. 8. C. I. ix. 158) has verified this
method and proved that the reduction is complete : he also states that when
the boiled solution cools, the liberation of a slight amount of iodine occurs,
which may be prevented by using a few c.c. of glycerine. Of course the
arsenic acid must contain no nitric acid, nitrates, or similar interfering
bodies.

1 c.c. T\ iodine - 0-00495 gm. As203, or 0*00575 gm. As205.

Arsenic in Copper, Iron, Pyrites, etc. — The method generally
adopted is the distillation of the arsenic obtained as sulphide,
with ferric chloride, and titration of the distillate with iodine as
above described, but F. Flatten (J. S. C. I. xvii. 324) has made

150 VOLUMETRIC ANALYSIS. § 47.

use of the discovery, that if As2S3 is simply boiled with pure
water for a period of from 1 to 3 hours or until the liquid is
quite colourless and all H2S dissipated, the whole of the arsenic
will exist as As203, and may be titrated with Tf y- iodine direct.
The results obtained by this method are as exact as any other, and
saves an immense amount of work.

Titration of Alkaline Arseniates. — In a previous edition of this
book it was recommended, on the authority of Barnes, to estimate
the arsenic acid in commercial arseniates of soda, etc., by reduction
with sulphurous acid (passing the gas through the liquid), boiling
off the excess of SO'2, neutralizing with sodic bicarbonate, and
titrating with iodine as described above. This method has not
given me satisfactory results. The mere passing the gaseous SO2
through the liquid does not, in all cases, insure the complete
reduction to arsenious acid.

Holthof (Z. a. C. xxii. 378) and McKay (0. N. liii. 221—243)
have experimented largely on this method of estimating arsenic,
which was really originally suggested by Mohr, but never widely
adopted, owing to the defect already mentioned. Holthof proved
that various forms of arsenic, on being converted into arsenic acid,
would bear evaporation to dryness with HC1 without loss, and that
arsenic sulphide could be oxidized by strong nitric acid, or with
HC1 and KC103 to arsenic acid, and reduced to the lower state of
oxidation by copious treatment with SO2, the method being to add
300 or 400 c.c. of strong solution of SO2, digest on the water bath
for two hours, then boil down to one-half, and when cool add
sodic bicarbonate, and titrate with iodine and starch.

McKay shortens the method considerably by placing the
mixture in a well-stoppered bottle, tying down the stopper, and
digesting in boiling water for one hour. At the end of that time
the bottle is removed and allowed to cool somewhat, then emptied
into a boiling flask, diluted with about double its volume of water,
and boiled down by help of a platinum spiral to one-half. The
liquid is cooled, diluted, and either the whole or an aliquot portion
titrated in the usual way.

For quantities of material representing about 0*1 gm. As, 30 c.c.
of saturated solution of SO2 will suffice, and the reduction may
therefore be made in a bottle holding 50 or 60 c.c. (fig. 39). The
results are very satisfactory. In the case of titrating commercial
alkaline arseniates, which often contain small quantities of
arsenious acid, this must be estimated first, and the amount
deducted from the total obtained after reduction.

2. Oxidation by Potassic Bichromate (Kessler).

This method is exact!}' the same as is fully described in § 46 for antimony.

The arsenious compound is mixed with T\ bichromate in excess in presence
of hydrochloric acid and water, in such proportion that at least ^ of the total
volume consists of hydrochloric acid (sp. gr. 1'12).

§ 47. ARSENIC. 151

The excess of bichromate is found by a standard solution of pure iron, or
of double iron salt, with potassic ferricyanide as indicator ; the quantity of
bichromate reduced is, of course, the measure of the quantity of arsenious
converted into arsenic acid.

1 c.c. T\ bichromate -0-00495 gm. As203.

In cases where the direct titration of the hydrochloric acid solution cannot
be accomplished, the arsenious acid is precipitated with H'2S (with arsenates
at 70°C.)5 the precipitate well washed, the filter and the precipitate placed in
a stoppered flask, together with a saturated solution of mercuric chloride in
hydrochloric acid of 1/12 sp. gr., and digested at a gentle heat until the
precipitate is white, then water "added in such proportion that not less than ^
of the volume of liquid consists of concentrated HC1 ; ^V bichromate is then
added, and the titration with standard ferrous solution completed as usual.

3. Indirect Estimation by Distilling- with Chromic and
Hydrochloric Acids (B u n s e n) .

The principle of this very exact method depends upon the fact,
that when potassic bichromate is boiled with concentrated hydro-
chloric acid, chlorine is liberated in the proportion of 3 eq. to 1 eq.
chromic acid.

If, however, arsenious acid is present, but not in excess, the
chlorine evolved is not in the proportion mentioned above, but so
much less as is necessary to convert the arsenious into arsenic acid.

AS2Q3 + 4C1 + 2H20 - As205 + 4HC1.

Therefore every 4 eq. of chlorine, short of the quantity yielded
when bichromate and hydrochloric acid are distilled alone, represent
1 eq. arsenious acid. The operation is conducted in the apparatus
fig. 37 or 38.

4. By Precipitation as TJranic Arsenate (Bodeker).

The arsenic must exist in the state of arsenic acid (As-O5), and the process
is in all respects the same as for the estimation of phosphoric acid, devised
by N e u b a u e r , P i n c u s , and myself ( § 72) . The strength of the uranium
solution may be ascertained and fixed by pure sodic or potassic arseuate, or
by means of a weighed quantity of pure arsenious acid converted into arsenic
acid by evaporation with strong nitric acid, and neutralizing with alkali, then
dissolved in acetic acid. The method of testing is precisely the same as with
phosphoric acid ; the solution of uranium should be titrated upon a weighed
amount of arsenical compound, bearing in mind here, as in the case of P'O0,
that the titration must take place under precisely similar conditions as to
quantity of liquid, the amount of sodic acetate and acetic acid added, and
the depth of colour obtained by contact of the fluid under titration with the
yellow prussiate solution.

Bo am ((7. N. Ixi. 219), who has had large experience in the
examination of arsenical ores, recommends this method as being
rapid and accurate, and carries it out as follows : —

1 to 1-5 gm. of dried and powdered ore is boiled to dryness with 20—25
c.c. of strong nitric acid ; when cool about 30 c.c. of 30 % caustic soda
solution is added and boiled for a few minutes ; then diluted, filtered and

152 VOLUMETRIC ANALYSIS. § 47.

made up to 250 c.c. 25 c.c. of the liquid are acidified with a solution
containing 10 per cent, of sodic acetate in 50 per cent, acetic acid, and
heated to near boiling, then titrated with the standard uranium as usual. For
this latter, the same authority recommends what he terms a fourth normal
solution of uranium, containing 17'1 gm. uranic acetate, and 15 c.c. glacial
acetic acid made up to 2 liters with water, 1 c.c. being equal to T25 m.gm.
As. But if the method has to be considered accurate, this suggestion can
scarcely be adopted, since the uranic acetate of commerce is of indefinite
hydration; and moreover, to insure exactitude, it is necessary that the
titration should be carried out with the same proportions of saline matters,
acetic acid, etc., as existed in originally standardizing the uranium. I there-
fore unhesitatingly recommend that the uranium should be standardized
with a known weight of pure arsenic or arsenate in the presence of the same
proportions of sodic hydrate and acetate, acetic acid, etc., as will actually
be used in the analysis of an ore. The method may be used for all ores
which can be attacked by nitric acid. It is also available for iron pyrites
containing tolerable quantities of arsenic ; the ferric arsenate being readily
decomposed by excess of NaHO, thus allowing the ferric hydrate to be
filtered off free from As.

The solution of arsenic acid must of course be free from
metals liable to give a colour with the indicator and from
phosphates. Alkalies, alkaline earths, and zinc are of no con-
sequence, but it is advisable to add nearly the required volume of
uranium to the liquid before heating. The arsenic acid must be
separated from all bases which would yield compounds insoluble
in weak acetic acid.

The AsH3 evolved from Marsh's apparatus may be passed into
fuming HNO3, evaporated to dryness, the arsenic acid dissolved in
water (antimony if present is insoluble), then titrated cautiously
with uranium in presence of free acetic acid and sodic acetate as
above described.

5. By Standard Silver as Arsenate.

The principle of this method has been adopted by Pearca
of the Colorado Smelting Company, and also by McCay (G, N.
xlviii. 7). The authors, however, differ in the details of the
process. The former prefers to separate the arsenic as silver
arsenate, and, estimating the silver so combined, thence calculate
the arsenic. The latter nses a known excess of standard silver,
and estimates the combined silver residually.

P e a r c e ' s Process. — The finely-powdered substance for analysis is mixed
in a large porcelain crucible with from six to ten times its weight of
a mixture of equal parts of sodic carbonate and potassic nitrate. The mass
is then heated with a gradually increasing temperature to fusion for a few
minutes, allowed to cool, and the soluble portion extracted by warming with
water in the crucible, and filtering from the insoluble residue. The arsenic
is in the filtrate as alkaline arsenate. The solution is acidified with nitric
acid and boiled to expel CO"2 and nitrous fumes. It is then cooled to the
ordinary temperature, and almost exactly neutralized as follows : — Place
a small piece of litmus paper in the liquid: it should show tin acid reaction.
Now gradually add strong ammonia till the litmus turns blue, avoiding
a great excess. Again make slightly acid with a drop or two of strong nitric

§ 47- ARSENIC. 153

acid ; and then, by means of very dilute ammonia and nitric acid, added drop
by drop, bring the solution to such a condition that the litmus paper, after
having previously been reddened, will, in the course of half a minute,
begin to show signs of alkalinity. The litmus paper may now be removed
and washed, and the solution, if tolerably clear, is ready for the addition of
silver nitrate. If the neutralization has caused much of a precipitate
(alumina, etc.), it is best to filter it off at once, to render the subsequent
filtration and washing of the arsenate of silver easier.

A solution of silver nitrate (neutral) is now added in slight excess ; and
after stirring a moment, to partially coagulate the precipitated arsenate,
which is of a brick-red colour, the liquid is filtered, and the precipitate
washed with cold water. The filtrate is then tested with silver and dilute
ammonia, to see that the precipitation is complete.

The object is now to determine the amount of silver in the precipitate,
and from this to calculate the arsenic. The arsenate of silver is dissolved on
the filter with dilute nitric acid (which leaves undissolved any chloride
of silver), and the filtrate titrated, after the addition of ferric sulphate, with
ammonic thiocyanate (§ 43).

From the formula 3Ag2O.As205, 648 parts Ag-150 parts As,
or Ag: As =108: 25. ,
i

McCay's Process. — The preliminary fusion is the same as in the
former method, but after acidulating with nitric acid and boiling
off CO2, the liquid is evaporated to drynessand heated till no more
acid fumes are given off. The residue is taken up with wa-ter,
filtered, made up to a definite volume, and the arsenic determined
in the following manner : —

The solution of arsenic acid or arsenate is heated to boiling, and excess of
standard silver nitrate run in ; the liquid is then stirred briskly until the
precipitate begins to settle and the liquid becomes clear, when the beaker is
to be removed from the flame and left to cool to about 37 °. Dilute ammonia
is now carefully added until a cloudiness ceases to form. The solution
should be well stirred before each successive addition, so as to obtain a clear
liquid in order to observe the cloud formation more distinctly. The silver
arsenate is finally filtered off and well washed ; the filtrate is acidulated with
nitric acid ; ferric sulphate added ; and the silver titrated with ammonic
thiocyanate (§ 43). The amount of silver thus found deducted from the
quantity taken gives the amount combined with the arsenic ; and from this
datum the quantity of arsenic present is calculated.

Of these two methods the preference must be given to the first
on the score of accuracy, there being less probability of error from
contaminating substances; both, however, are available for technical
purposes.

Owing to the large amount of arsenate of silver formed from
a small quantity of arsenic (nearly six times by weight), it is
not at all necessary or even desirable to work with large amounts
of substance. 0'5 gm. is usually sufficient for the determination of
the smallest quantity of arsenic ; and where the percentage is high,
as little as O'l gm. may be taken with advantage. The method
has been used with very satisfactory results on the sulphide of
arsenic obtained in the ordinary course of analysis.

Substances such as molybdic and phosphoric acids, which may

154 VOLUMETRIC ANALYSIS. § 49.

behave similarly to arsenic under this treatment, interfere, of course,
with the method. Antimony, by forming antimoniate of sodium,
remains practically insoluble and without effect.

The method has been used by Me Cay for the estimation of
arsenic in the presence of alkaline earths, as occurring in some
minerals, with success.

BARIUM.
Ba = 136-8.

§ 48. IN a great number of instances the estimation of barium
is simply the Converse of the process for sulphuric acid (§ 76),
using either a standard solution of sulphuric acid or a neutral
sulphate in a known excess, and finding the amount by residual
titration.

When barium can be separated as carbonate, the estimation
is made as in § 18.2.

Precipitation as Baric Clare-mate. — A clecinormal Solution of
bichromate for precipitation purposes must differ from that used
for oxidation purposes. In the present case the solution is made
by dissolving 7 '37 gm. of pure potassic bichromate in water, and
diluting to 1 liter.

The barium compound, which may contain alkalies, magnesia, strontia,
and lime, is dissolved in a good quantity of water, ammonia free from
carbonate added, heated to 60° or 70° C., and the standard bichromate added
cautiously, with shaking, so long as the yellow precipitate of baric chromate
is formed, and until the clear supernatant liquid possesses a faint yellow
colour. 1 c.c. y^ solution = 0'00684< gm. Ba.

Titration of the Precipitate with Permanganate. — In this case the
precipitate of baric chromate is well washed, transferred to a flask, and mixed
with an excess of double iron salt ; the amount of iron oxidized by the
chromic acid is then estimated by titration with permanganate ; the quantity
of iron changed to the ferric state multiplied by the factor 0'8187 = Ba.

BISMUTH.

Bi = 208.

§ 49. THE estimation of this metal or its compounds volume t-
rically has occupied the attention of Pa tt ins on Muir, to whom
we are indebted for several methods of gaining this end. Two of
the best are given here, namely, (1) precipitation of the metal as
basic oxalate, and titration with permanganate ; (2) precipitation
as phosphate with excess of standard sodic phosphate, and titration
of that excess by standard uranic acetate.

1. Titration as Oxalate.

Normal bismuth oxalate, produced by adding excess of oxalic
acid to a nitric solution of the metal when separated by filtration,

§ 49. BISMUTH. 155

and boiled with successive quantities of water for three or four
times, is transformed into basic oxalate. The method of titratioii
is as follows : —

The solution containing bismuth must be free fr0om hydrochloric acid, as
the basic oxalate is readily soluble in that acid. A large excess of nitric
acid must also be avoided. Oxalic acid must be added in considerable
excess. If the precipitate be thoroughly shaken up with the liquid, and the
vessel be then set aside, the precipitate quickly settles, and the supernatant
liquid may be poured off through a filter in a very short time. If the
precipitate be boiled for five or "ten minutes with successive quantities of
about 50 c.c. of water, it is quickly transformed into the basic salt. So soon
as the supernatant liquid ceases to show an acid reaction, the transformation
is complete. It is well to employ a solution of permanganate so dilute, that
at least 50 c.c. are required for the titration (^ strength suffices). The basic
oxalate may be dissolved in dilute sulphuric acid in place of hydrochloric ;
it is more soluble, however, in the latter acid. If the solution contains but
little hydrochloric acid, there is no danger of chlorine being evolved during
the process of titration.

In applying this process to the estimation of bismuth in a solution
containing other metals, it is necessary, if the solution contain substances
capable of acting upon, or of being acted on b}7 permanganate, to separate
the bismuth from the other metals present. This is easily done by
precipitating in a partially neutralized solution with much warm water and
a little ammonic chloride. The precipitate must be dissolved in nitric acid,
and the liquid boiled down once or twice with addition of the same acid in
order to expel all hydrochloric acid, before precipitating as oxalate. The
liquid should contain just sufficient nitric acid to prevent precipitation of
the basic nitrate before oxalic acid is added. 1 molecule oxalic acid corresponds
to 1 atom bismuth, or 126 = 203.

A shorter method, based on the same reactions, has been arranged
by Muir and Robbs (J. C. S. I. xli. 1). In this case, however,
the double oxalate of potassium and bismuth is the compound
obtained, the excess of oxalate of potash being determined
residually. Reis (Bericlite, xiv. 1172) has shown that when
normal potassic oxalate is added to a solution of bismuth nearly
free from mineral acid, but containing acetic acid, a double salt of
the formula Bi'2 (C204)a, K2C204 is precipitated. In applying this
process for the estimation of bismuth in mixtures, it is necessary
to separate the metal as oxychloride, and that it should be obtained
in solution as nitrate with a small excess of nitric acid. This is
done by evaporating off the greater part of the free acid, allowing
just sufficient to remain that the bismuth may remain in solution
while hot. A large excess of acetic acid is then added, it is made
up to a definite measure, and an aliquot portion taken for titration.

The solution of normal potassic oxalate standardized by perman-
ganate must not be added in great excess. It is well, therefore,
to deliver it into the bismuth liquid from a burette until the
precipitation is apparently complete, then add a few extra c.c., and
allow to remain for some time with shaking. It is then filtered
through a dry filter, a measured portion taken, and the residual
oxalic acid found by permanganate.

156 VOLUMETBIC ANALYSIS. § 50.

2. Precipitation as Phosphate.

The necessary standard solutions are —

(a) Standard sodic phosphate containing 35*8 gin. per liter.
1 c.c. -0-0071 gm. P205.

(b) Standard uramc acetate, corresponding volume for volume
with the above, when titrated with an approximately equal amount
of sodic acetate and free acetic acid.

Success depends very much upon identity of conditions, as is
explained in § 72.

The bismuth to be estimated must be dissolved in nitric acid ; bases other
than the alkalies and alkaline earths must be absent. The absence of those
acids which interfere with the determination of phosphoric acid by the
uranium process (non-volatile, and reducing organic acids, sulphuretted
hydrogen, hydriodic acid, etc.) must be assured. As bismuth is readily
separated from other metals, with the exception of antimony and tin, by
addition of much warm water and a little ammonic chloride to feebly acid
solutions, a separation of the bismuth from those other metals which are
present should precede the process of estimation. If alkalies or alkaline
earths be alone present, the separation may be dispensed with. The pre-
cipitated bismuth salt is to be washed, dissolved in a little strong nitric acid.
and the solution boiled down twice with addition of a little more nitric acid,
in order to remove the whole of the hydrochloric acid present.

Such a quantity of a tolerably concentrated solution of sodic acetate is
added as shall insure the neutralization of the nitric acid, and therefore the
presence in the liquid of free acetic acid. If a precipitate form, a further
addition of sodic acetate must be made. The liquid is heated to boiling ;
a measured volume .of the sodic phosphate solution is run in ; the boiling
is continued for a few minutes ; the liquid is passed through a ribbed filter.
the precipitate being washed repeatedl}" with hot water ; and the excess of
phosphoric acid is determined in the filtrate by titration with uranium.
If the filtered liquid be received in a measuring flask, which is subsequently
filled to the mark with water, and if the inverted uranium method be then
employed, the results are exceedingly accurate. This method is especially to
be recommended in the estimation of somewhat large quantities of bismuth,
since it is possible that in such cases a large amount of sodic acetate will
have been used, which, as is well known, has a considerable disturbing effect
on the reaction of the indicator.

If the bismuth solution contain a large excess of nitric acid, it is better to
neutralize nearly with sodic carbonate before adding sodic acetate and titrating.

Fuller details of both the above processes are contained in J. C. S.
1877 (p. 674) and 1878 (p. 70).

BROMINE.

Br-80.

§ 50. THIS element, or its unoxidized compounds, can be
estimated precisely in the same way as chlorine by -~ silver solution
(§ 42), or alkalimetrically as in § 32, or by thiocyanate (§ 43),
but these methods are seldom of any avail, since the absence of
chlorine or its combinations is a necessary condition of accuracy.

Bromine in aqueous solution, or as gas, may be estimated by

§ 50. BROMINE. 157

absorption with solution of potassic iodide, in many cases by mere
digestion, and in other cases by distillation, in any of the forms of
apparatus given in § 39, and the operation is carried out precisely
as for chlorine (§ 54). 1 eq. I = 1 eq. Br. or I found x O63 = Br.

A process for the estimation of bromine in presence of chlorine
is still much wanted in the case of examining kelp liquors, etc.
Heine (Journ. f. pract. Cliem. xxxvi. 184) uses a colour method
in which the bromine is liberated by free chlorine, absorbed by
ether, and the colour compared with an ethereal solution of bromine
of known strength. Fehling states that with care the process
gives fairly accurate results. It is of course necessary to have an
approximate knowledge of the amount of bromine present in any
given solution.

Reimann (Annal. d. CJiem. u. Pkarm. cxv. 140) adopts the
following method, which gives tolerably accurate results, but
requires skill and practice.

The neutral bromine solution is placed in a stoppered vessel,
together with a globule of chloroform about the size of a hazel nut.
Chlorine water of known strength is then added cautiously from
a burette, protected from bright light, in such a way as to insure
first the liberation of the bromine, which colours the chloroform
orange yellow ; then more chlorine water, until the yellowish white
colour of chloride of bromine occurs (KBr + 2C1 = KC1 + BrCl).

The operation may be assisted by making a wreak solution of
potassic chromate, of the same colour as a solution of chloride of
bromine in chloroform, to serve as a standard of comparison.

The strength of the chlorine water is ascertained by potassic
iodide and -^ thiosulphate. 2 eq. Cl.=l eq. Br.

In examining mother-liquors containing organic matter, they
must be evaporated to dryness in presence of free alkali, ignited,
extracted with water ; then neutralized with hydrochloric acid
before titrating as above.

Cavazzi (Gazz. Chim. Hal. xiii. 174) gives a method which
answers well for estimating bromine in small quantity, when mixed
with large proportions of alkaline chlorides. It is based on the
fact that, when such a mixture is heated to 100° C. with baric
peroxide and sulphuric acid, the whole of the bromine is liberated
with a mere trace of chlorine ; the bromine so evolved is absorbed
in any convenient apparatus, such as fig. 37. The distillation
is made in a 350 c.c. flask with double-bored stopper; one bore
contains an open tube reaching to the bottom of the flask, the
other carries the delivery tube which is connected with the (J tubes.
The first U tu^e ig empty; the second contains 20 c.c. of
a standard solution of arsenious acid in hydrochloric acid, con-
taining 0-005 gm. As203 in each c.c., and is connected with an
aspirator. The apparatus is arranged so that the flask and empty
(J tube are immersed in boiling water, the vapours of H202 are
thus decomposed, and the stream regulated by the aspirator.

158 VOLUMETRIC ANALYSIS. § 50.

The requisites used by the author are —

Baric peroxide, containing 63 % BaO2.

Dilute sulphuric acid 1:2.

Arsenious acid dissolved in dilute hydrochloric acid, 5 gm. of
pure As203 per liter.

Standard permanganate, 3 '55 gm. per liter.

It was found that the relative strengths of the arsenic and
permanganate solutions, when titrated together, diluted, and boiling,
were, 18*2 c.c. of the latter to 20 c.c. of the former. Therefore
1 c.c. of permanganate by calculation = 0*00888 gm. Br.

The author found that treating 2 gm. of KC1 in the apparatus,
without bromine, always gave a faint trace of Cl, so that only
18 c.c. of permanganate were required for the 20 c.c. of arsenic,
instead of 18 '2 c.c. ; and this he regards as a constant for that
quantity of material. The examples of analysis with from
O'Oo to 0*2 gm. KBr, and all with the correction of 0*2 c.c., are
satisfactory.

Norman McCulloch (C. N. Ix. 259) has described a method,
devised by himself, for the rapid and accurate estimation of bromine,
in presence of iodine or chlorine, in any of the ordinary commercial
forms or chemical combinations, free from oxidizing and reducing
agents and metals forming bromides, insoluble in hydrochloric
acid. The author's explanation of the principles upon which
the method is based is complicated and voluminous, for which the
reader is referred to the original article. I have not been able to
verify the method, but as the author is . known to have practical
experience, as well as theoretical knowledge, a short summary is
given here.

The requisites described by the author are —

Standard permanganate, 31 '9 grains of the salt in 10,000 grains
of water (or 3*19 gm. per liter).

Standard potassic iodide, 82 '78 grains of KI in 10,000 grains of
water" (or 8 '2 7 8 gm. per liter.)

The solutions should agree volume for volume, but it is pre-
ferable to verify them by dissolving 3-5 grains of iodine in
•caustic soda, in a 5-oz. stoppered bottle, adding HC1 in good excess,
cooling, then adding the permanganate from a burette, until nearly
colourless. A little chloroform as indicator is then added, and the
permanganate cautiously run in, with shaking until the violet
colour of the iodine is discharged, owing to production of IC1,
due to the reaction of Cl liberated by the permanganate from
HC1.

The iodine equivalent of the permanganate is calculated to
bromine by the coefficient x 0'6713 and each decem of permanganate
should represent about 0*04 grain Br (or each c.c 0*004 gm
Br).

The other reagents are purified chloroform, made by adding
some permanganate, then HC1 till colour is discharged, then a little

§ 51. CADMIUM. 159

KI and the I so liberated again discharged with permanganate,
finally the chloroform is washed free from all acid.

A three per cent, solution of hydrocyanic acid, made by decom-
posing a solution of pure potassic cyanide, with excess of HC1, and
adding permanganate till a faint pink colour remains. 600 grains
of KC1ST in 13 J ounces of water (or 40 gm. in 400 c.c.) with
2J- ounces of HC1 (or 70 c.c.) will give such a solution. Owing to
its poisonous nature great caution must be used in making this
solution, and to avoid as much as possible the evolution of prussic
acid the temperature must be kept down by ice, or a freezing
mixture of nitre and sal ammoniac. If the cyanide contains, as is
often the case, some alkaline carbonate, this should be removed
previously by Bad, as otherwise CO2 will be liberated and a loss
of HCX occur, finally the cool solution is rendered faintly pink
with some permanganate.

Solution of manganous chloride, made by dissolving half a pound
of MnCl2 + 4H20 in 4 oz. of warm water (or 500 gm. in 250 c.c.),
This solution is used to prevent the liberation of free chlorine
from the HC1 in the analysis.

Process : The weighed bromide, containing from 1 to 3 grains of Br
(0'05 to 0'15 gm.), is dissolved in half an ounce (15 c.c.) of water in a 5 oz.
stoppered bottle, and about an ounce (30 c.c.) of the manganese sohition
added ; permanganate is then run in excess of the required quantity, and the
bottle cooled rapidly to 50° P. (10° C.) by ice or a freezing mixture. When
cooled, the bottle is shaken by a rotary motion, and about half an ounce
(15 c.c.) of moderately strong HC1 slowly added, with motion of the bottle
to dissolve the manganic hydroxide, 3 to 6 dm. (2 — 4 c.c.) 0f hydro-
cyanic solution are then delivered in, the bottle closed and returned to the
cooling mixture for about half an hour. The liquid is then titrated with
the standard potassic iodide, until nearly decolorized from the decomposition
of the manganic chloride, and then slightly coloured from liberation of
free I. Lastly, the slight excess of iodide is estimated by adding a little
chloroform, and the titration finished with permanganate. The bromine is
calculated by taking the difference between the amounts of bromine,
represented by total permanganate and iodide used. If iodine is present it
is of course recorded as bromine, and its amount, if required, must be
ascertained by some other method capable of its estimation in the presence
of bromine.

The author gives several very good results with pure sodic
bromide, an example of which may be given. Each measure of
permanganate=0-0392 Br. T032 grain Br was taken, and 40 '6
measures of permanganate with 14*3 measures of iodide used, then
40-6 -14-3=26-3 which multiplied by 0-0392=1-031 Br.

CADMIUM.

Cd=lll-6.

§ 51. THIS metal may be estimated, as is the case with many
others, by precipitation as sulphide, and decomposing the sulphide
with a ferric salt, the iron being reduced to the ferrous state in
proportion to the amount of sulphide present.

160 VOLUMETRIC ANALYSIS. § 52.

Follenius has found that when cadmium is precipitated as
sulphide in acid liquids, the precipitate is apt to be contaminated
with salts other than sulphide to a small extent. The separation
as sulphide is hest made by passing H2S into the hot liquid which
contains the cadmium, and which should be acidified with 10 per-
cent, of concentrated sulphuric acid by volume. . From hydrochloric
acid solutions the metal is only completely separated by H2S when
the hot solution contains not more than 5 per cent, of acid of
sp. gr. I'll, or 14 per cent, if the liquid is cold.

Ferric chloride is to be preferred for the decomposition of the
cadmium sulphide, and the titration is carried out precisely as in
the case of zinc (§ 81).

P. von Berg (Z. a. C. xxvi. 23) gives a good technical process
for the estimation of either cadmium or zinc as sulphides, by
means of iodine, as follows : — -

The washed sulphide of zinc or cadmium is allowed to drain upon the
filter, and then transferred, together with the filter, to a stoppered flask
containing 800 c.c. of water deprived of air by boiling and the passage of
carbonic acid gas. The whole is well shaken to break up the precipitate and
bring it intfl the most finely divided condition possible, so that the sulphide
may not be protected from the action of the iodine by separated sulphur.
A moderate quantity of hydrochloric acid is added, there being no necessity
to entirely dissolve the sulphide, and then an excess of iodine solution of
known strength. The residual free iodine is then titrated with thiosulphate
without loss of time. The whole operation, from the transference of the
sulphide to the flask to the final titration, occupies about five minutes, and
gives results varying between 98'8 and 100'2 per cent. The reaction proceeds
according to the equation, ZnS+2HCl+2l = ZnCl2+2HI + S.

Cadmium may also be estimated, when existing as sulphate or
nitrate, by precipitation as oxalate, and titration of the washed
precipitate by permanganate. The details are carried out precisely
as in the case of estimating zinc as oxalate (§ 81).

CALCIUM.

Ca—40.

1 c.c. y^ permanganate = 0'002S gm. CaO

- 0-0050 gm. CaCO3
= 0-0086 gm. CaS04 +
,, normal oxalic acid— 0-0280 gm. CaO

Cryst. oxalic acid x 0-444 = CaO

Double iron salt x 0-07143 = CaO

§ 52. THE estimation of calcium alkalimetrically has already
been given (§ 18), but that method is of limited application, unless
calcic oxalate, in which form Ca is generally separated from other
bases, be converted into carbonate or oxide by ignition, and thus
determined with normal nitric acid and alkali. This and the
following method by Hemp el are as exact in their results as the

§ 52. CALCIUM. 161

determination by weight ; and where a series of estimations have
to be made, the method is very convenient.

Titration with. Permanganate. — The readiness with which calcium
can be separated as oxalate facilitates the use of this method, so
that it can be applied successfully in a great variety of instances.
It is not necessary here to enter into detail as to the method
of precipitation ; except to say, that it may occur in either
ammoniacal or weak acetic acid solution ; and that it is absolutely
necessary to remove all excess of ammonic oxalate from the
precipitate by washing with warm water previous to titration.

Process : When the clean precipitate is obtained, a hole is made in the
filter, and the bulk of the precipitate is washed through the funnel into
a flask ; the filter is then treated with small quantities of hot dilute sulphuric
acid, and again washed into the flask. Hydrochloric acid in moderate
quantity may be safely used for the solution of the oxalate, since there is
not the danger of liberating free chlorine Avhich exists in the case of iron
(Fleischer, Titrirmethode, p. 76), but the sulphuric is better.

When the precipitate is completely dissolved, the solution is freely diluted
with water, and further acidified with sulphuric acid, warmed to 60° or 70°,
and the standard permanganate cautiously delivered into the liquid with
constant agitation until a faint permanent pink tinge occurs, precisely as in
the case of standardizing permanganate with oxalic acid (§ 34.2c).

Process for Lime in Blast Furnace Slags : Place about 1 gm. of the very
finely-ground slag into a beaker, cover with water, and boil gently, then
add gradually strong HC1 until the whole is dissolved, including SiO'2.
Dilute the liquid, nearly neutralize with ammonia, and add a solution of
ammonic acetate. The silica and alumina form a flocculent precipitate
which is easily washed on a filter. The filtrate and washings are concen-
trated somewhat, and the CaO precipitated with oxalate of ammonia and
free ammonia ; the precipitate is dissolved as before described in hot dilute
sulphuric acid, and titrated with permanganate. If much manganese is
present, the calcic oxalate must be re-dissolved and re-precipitated before
the titration is made.

In all cases where a clean oxalate precipitate can be obtained,
such as mineral waters, manures, etc., very exact results are obtain-
able ; in fact, quite a,s accurate as by the gravimetric method.
Ample testimony on this point is given by Fresenius, Mohr,
Hempel, and others. •

Tucker (Iron, ^"ov. 16, 1878) has given the results of many
experiments made by him upon mixtures of Ca.with abnormal
proportions of iron, magnesia, alumina, etc. ; and even here the
numbers obtained did not vary more than 2 to 3 per cent, from the
truth. In the case of large proportions of these substances it will
be preferable to re-precipitate the oxalate, so as to free it from
adhering contaminations previous to titration.

Indirect Titration. — In the case of calcic salts soluble in water and
of tolerably pure nature, the estimation by permanganate can be
made by adding to the solution a measured excess of normal oxalic
acid, neutralizing with ammonia in slight excess, and heating to

162 VOLUMETRIC ANALYSIS. § 54

boiling, so as to rapidly separate the precipitate. The mixture is
then cooled, diluted to a measured volume, filtered through a dry
filter, and an aliquot portion titrated with permanganate after
acidifying with sulphuric acid as usual. A great variety of calcium
salts may be converted into oxalic by a short or long treatment
with oxalic acid or ammonic oxalate, including calcic sulphate,
phosphate, tartrate, citrate, etc.

CERIUM.

Ce- 141-2.

§ 53. THE most exact method of estimating this metal is by
precipitating as cerotis oxalate, then drying the precipitate, and
strongly igniting in an open crucible, so as to convert it into eerie
oxide.

Stolba (Z. a. C. xix. 194) states that the moist oxalate may be
titrated precisely as in the case of calcic oxalate with permanganate,
and with accurate results. ~No examples or details, however, are
given.

CHLORINE.

01=35-37.

1 c.c. ~ silver solution^O'00^537 gm. Cl.
=0-005837 sin.

§ 54. THE powerful affinity existing between chlorine and silver
in solution, and the ready precipitation of the resulting chloride,
seem to have led to the earliest important volumetric process in
existence, viz., the assay of silver by the wret method of Gay
Lussac. The details of the process are more particularly described
under the article relating to the assay of silver (§ 73) ; the deter-
mination of chlorine is just the converse of the process there
described, and the same precautions, and to a certain extent the
same apparatus, are required.

The solutions required, however, are systematic, and for exactness
and convenient dilution are of decinormal* strength as described in
§ 41. In many cases it is advisable to possess also centinormal
solutions, made by diluting 100 c.c. of ~ solution to 1 liter.

1. Direct Precipitation -with ^Q Silver.

Very weak solutions of chlorides, such as drinking waters, are not easily
examined for chlorine by direct precipitation, unless they are considerably
concentrated by evaporation previous to treatment, owing to the fact that,
unless a tolerable quantity of chloride can be formed, it Avill not collect
together and separate so as to leave the liquid clear enough to tell on the
addition of fresh silver whether a distinct formation of chloride occurs.
The best effects are produced when the mixture contains chlorine equal to
from H to 2 gm. of salt per 100 c.c. Should the proportion be much less

§ 54. . CHLORINE. 163

than this, the difficulty of precipitation may be overcome by adding a
quantity of freshly precipitated chloride, made by mixing1 equal volumes of
-j^r salt and silver solution, shaking vigorously, pouring off the clear liquid,
and adding the chloride to the mixture under titration. The best vessel to
use for the trial is a well-stoppered round white bottle, holding 100 to 150
c.c., and fitting into a paper case, so as to prevent access of strong light
during the titration. Supposing, for instance, a neutral solution of potassic
chloride requires titration, 20 or 30 c.c. are measured into the shaking
bottle, a few drops of strong nitric acid added (free acid must always be
present in direct precipitation), and a round number of c.c. of silver solution
added from the burette. The bottle is placed in its case, or may be enveloped
in a dark cloth and vigorous!}7 shaken for half a minute, then uncovered,
and gently tapped upon a table or book, so as to start the chloride downward
from the surface of the liquid \vhere it often swims. A quick clarification
indicates excess of silver. The nearer the point of exact counterbalance the
more difficult to obtain a clear solution by shaking, but a little practice soon
accustoms the eye to distinguish the faintest precipitate.

In case of overstepping the balance in any trial, it is only
necessary to add to the liquid under titration a definite volume of
~ salt solution, and finish the titration in the same liquid,
deducting, of course, the same number of c.c. of silver as has been
added of salt solution. .

Fuller details and precautions are given in § 73.

2. Precipitation by Silver in Neutral Solution with Chromate
Indicator (see § 41, 2 t>).

3. Titration with ^ Silver and ' Thiocyanate (see § 43).

This method gives very accurate results if, after the chlorine is
precipitated with excess of — silver, the silver chloride is filtered
off, washed well, and the filtrate and washings titrated with —
thiocyanate for the excess of silver. .

Process : The material to be titrated, such as water residues, beer ash, or
other substances in which the chlorine is to be estimated being brought into
clear solution, a known volume of ^ silver in excess is added, having previously
acidified the mixture with nitric acid ; the mixture is well stirred, and the
supernatant liquid filtered off through a small filter, the chloride well
washed, and to the filtrate and washings 5 c.c. of ferric indicator (§ 43.3)
and the same volume of nitric acid (§ 43.4) are added. The flask is then
brought under the thiocyanate burette, and the solution delivered in with
a constant gentle movement of the liquid until a permanent light-brown
colour appears. If the silver chloride is not- removed from the liquid
previous to titration a serious error may occur, owing to the read}^ solubility
of the chloride in the thiocj-auate solution.

4. By Distillation and Titration with Thiosulphate or Arsenite.

In cases where chlorine is evolved direct in the gaseous form or
as the representative of some other body (see § 39), a very useful
absorption apparatus is shown in fig. 37. The little flask a is used
as a distilling vessel, connected with the bulb tubes by an india-

M 2

164 VOLUMETRIC ANALYSIS.

rubber joint ;* the stoppers for the tubes are also of the same
material, the whole of which should be cleansed from sulphur by
boiling in weak alkali. A fragment of solid magnesite may with
advantage be added to the acid liquid in the distilling flask ; in
all other respects the process is conducted exactly as is described
in § 39.

This apparatus is equally well adapted to the absorption of
ammonia or other gases, and possesses the great recommendation
that there is scarcely a possibility of regurgitation.

Mohr's apparatus (fig. 38) is also serviceable for this method.

CHLORINE G-AS AND BLEACHING- COMPOUNDS.

1 c.c. yjj- arsenious or thiosulphate solution=0*003537 gm. CI.
1 liter of chlorine at 0° C., and 760 m.m., weighs 3'167 gm.

§ 55. CHLORINE water may be titrated with thiosulphate by
adding a measured quantity of it to a solution of potassic iodide,
then delivering the thiosulphate from a burette till the colour of
the free iodine has disappeared; or by using an excess of the
reducing agent, then starch, and titrating residually with —• iodine.
When arsenious solution is used for titration, the chlorine water is
delivered into a solution of sodic carbonate, excess of arsenious
solution added, then starch and — iodine till the colour appears,
or iodized starch-paper may be used.

Bleaching- Powder. — The chief substance of importance among
the compounds of hypochlorous acid is the so-called chloride of
lime. The estimation of the free chlorine contained in it presents
no difficulty when arsenious solution is used for titration.

Commercial bleaching powder consists of a mixture in variable
proportions of calcic hypochlorite (the true bleaching agent), calcic
chloride, and hydrate; and in some cases the preparation contains
considerable quantities of chlorate, due to imperfect manufacture or
age. It is generally valued and sold in this country by its
percentage of chlorine. In France it is sold by degrees calculated
from the volume of gaseous chlorine: 100° Erench=31<78 per
cent. English.

1. Titration by Arsenious Solution (Penot).

The first thing to be done in determining the value of a sample
of bleaching powder is to bring it into solution, which is best
managed as follows : —

The sample is well and quickly mixed, and 7'17 gm. weighed, put into
a mortar, a little water added, and the mixture rubbed to a smooth cream ;
more water is then stirred in with the pestle, allowed to settle a little while,
then poured off into a liter flask; the sediment again rubbed with water,

* India-rubber and specially vulcanized rubber is open to some objection in these
analyses, and apparatus is now readily to be had with glass connections.

§ 55. BLEACHING POWDER. 165

poured off, and so on repeatedly, until the whole of the chloride has been
conveyed into the flask without loss, and the mortar washed quite clean.
The flask is then filled to the mark with water, well shaken, and 50 c.c. of
the milky liquid taken out with a pipette, emptied into a beaker, and the •&•
arsenious solution delivered in from a burette until a drop of the mixture
taken out with a glass rod, and brought hi contact with the prepared starch-
paper (§ 40) gives no blue stain.

The starch-paper may be dispensed with by adding arsenious solution in
excess, then starch, and titrating residually with & iodine till the blue
colour appears. The number of c.c. of arsenic used shows direct percentage
of available chlorine.

A more rapid technical method can be adopted in cases where a series of
samples has to be tested, as follows :— 4'95 gm. of pure arsenious acid are
finely powdered and dissolved by the aid of a gentle heat in about 15 c.c.
of glycerine, then diluted with water to 1 liter ; 25 c.c. are measured into
a flask, and 1 c.c. of indigo solution added. The turbid solution of bleaching
powder is poured into a suitable burette, and before it has time to settle is
•delivered with constant shaking into the blue arsenious solution until the
colour is just discharged : the percentage of chlorine is then found by a slight
•calculation.

2. Bunsen's Method.

10 or 20 c.c. of the chloride of lime solution, prepared as above, are
measured into a beaker, and an excess of solution of potassic iodide added ;
the mixture is then diluted somewhat, acidified with acetic acid, and the
liberated iodine titrated with T^ thiosulphate and starch; 1 eq. iodine so
found represents 1 eq. chlorine.

The presence of chlorate does not affect the result when acetic
acid is used. If it be desired to estimate the amount of chlorate
in bleach, the following method has been devised by R. Fresenius.
It depends on the fact that hypochlorites are decomposed by lead
acetate with formation of lead peroxide, whilst the chlorate which
may be present is unaffected.

Process ; 20 gm. of bleaching powder are ground up with water in
repeated quantities and made up to a liter; after settling, 50 c.c. — 1 gm. of
bleach are filtered off through a dry filter, put into a flask, and mixed with
a solution of lead acetate in some excess. There is formed at first a white
precipitate of lead chloride and lead hydroxide, these being acted on by the
hypochlorite become first yellow, then brown, with liberation of chlorine and
passing into lead peroxide. After the precipitate has settled, more lead
solution is added, to be sure that the conversion is complete. The mixture
is allowed to stand in the open flask, with frequent shaking, till all smell of
chlorine has disappeared, which occurs in from eight to ten hours. The
precipitate is then filtered off and washed till the wash-water is free from
acid. ' The washings are evaporated somewhat, added to the filtrate, and the
whole mixed with sodic carbonate in slight excess, to precipitate the lead and
lime as carbonates— these are well Avashed, the filtrate and wrashings
•evaporated nearly to dryness, then transferred to either a P r e s e n i u s or
Mohr apparatus (fig. 37 or 38) and distilled with HC1 as directed in § 39.
1 cq. :I-1 eq. Cl-O5.

3. Gasometric Process.

This method has been devised by Lunge (Bericlde xix. 868,
also J. S. C. I. ix. 22) and is both accurate and rapid. The
instrument used for the analysis is preferably the improve^

166 VOLUMETRIC ANALYSIS.

nitrometer, with patent tap and bulb (see Part VII.), winch permits
the use of a larger weight of the sample than the ordinary 50 c.c.
nitrometer. In both instruments for this class of analysis ordinary
tap water may be used, instead of mercury, with equally accurate
results.

The reagent used for the decomposition of the bleach is
hydrogen peroxide, and the reaction is CaOCl2 + H202=CaCl2 +
H20 + O2. Lunge's directions are as follows : —

It is not necessary to know the exact composition of the hydrogen peroxide,
but as it is desirable not to employ too large an excess of it in this case, it is
best to estimate its percentage by a preliminary test occupying but a few
minutes, in which a certain yolume of H-O- is decomposed by an excess of
bleach solution (the inverse of the titration of the latter). This need be
done only quite roughly. For the ana-lysis of chloride of lime the hydrogen
peroxide must be diluted before use so as not to give out more than 7 c.c. of
oxygen per c.c., and it must be made alkaline by means of caustic soda
solution up to the point where a flocculent precipitate appears. The alkaline
reaction ought to be quite distinct, but any fjreat excess of alkali should be
avoided. It is not necessary to shake much, and the reading ought to be
made quickly, say five minutes after mixing the liquids, otherwise the results
will be too high owing to the gradual evolution of more oxygen from the
alkaline liquid. It might be thought that muddy solutions, such as arc
regularly employed in testing commercial bleaching powder, would yield less
reliable results, the solid matter favouring the evolution of oxygen from
II-O- otherwise than through the action of CaOCl2; but this is not so;
muddy solutions can be tested by the nitrometer just as well as clear bleach
liquors, provided the time of five minutes is not exceeded. As the reaction
does not produce a sensible change of temperature, that time will quite
suffice, provided that the operator has avoided raising the temperature of the
flask in manipulating it, which he can do by handling it always by the neck
with his thumb and forefinger only.

In order to find the percentage of available chlorine by weight, that is,
the English chlorometrical degrees, it should be borne in mind that every
c.c, of gas evolved, reduced to 0° and 760 m.m., represents 0'003167 gin. of
chlorine. Hence, if the quantity of bleach employed is = 1 gin. (for
instance, by dissolving 20 gm. in 500 c.c. of water, and employing 25 c.c.
of the solution for each test), each c.c. of gas is = 0 3167 per cent, of
available chlorine in the bleach. This involves the use of a bulb nitrometer
holding 140 c.c. If only a 50 c.c. instrument is at hand, it will be necessary
to take, say, 5 c.c. of the first-mentioned bleach solution, in which case every
c.c. of gas represents 5xO'3167 = l'58 per cent, of chlorine. The most con-
venient way is to dissolve 7'917 gm. of bleach in 250 c.c. of water, and
emploj'ing 10 c.c. of the solution for each test, when each c.c. of oxygen
evolved will directly indicate 1 per cent, of available chlorine, and a 50 c.c.
nitrometer should be used.

The general method of manipulating the nitrometer is described
in Part VII.

CHLORATES, IODATES, AND BROMATES.

Chloric anhydride, C1205=150'74. lodic anhydride, I205=333.
Bromic anhydride, Br205=239'5.

The compounds of chloric, iodic, and bromic anhydrides may
all be determined by distillation or digestion with excess of

§ 56. CHROMIUM. 167

hydrochloric acid ; with chlorates the quantity of acid must be
considerably in excess.

In. each case 1 eq. of the respective anhydrides taken as
monobasic or their compounds, liberates 6 eq. of chlorine, and
consequently 6 eq. of iodine when decomposed in the digestion
flask. In the case of distillation, however, iodic and bromic acids
only set free 4 eq. iodine, while iodous and bromous chlorides
remain in the retort. In both these cases digestion is preferable
to distillation.

Example : 0'2043 gm. pure potassic chlorate, equal to the sixth part of
r"TJJinr eq. was decomposed by digestion with potassic iodide and strong
hydrochloric acid in the bottle shown in fig. 39. After the reaction was
complete, and the bottle cold, the stopper was removed, and the contents
washed out into a beaker, starch added, and 103 c.c. T^ thiosulphate delivered
in from the burette ; then again 23'2 c.c. of ^ iodine solution, to reproduce
the blue colour ; this latter was therefore equal to 2'32 c.c. T^- iodine, which
deducted from the 103 c.c. thiosulphate gave 100'68 c.c., which multiplied by
the factor 0'002043, gave 0'2056 gm., instead of 0'2043 gm.

CHROMIUM.

Cr=52-4.
1. Ueduction by Iron.

§ 56. THE estimation of chromates is very simply arid success-
fully performed by the aid of ferrous sulphate, being the converse
of the process devised by Penny for the estimation of iron
(see § 37).

Process : A very small beaker or other convenient vessel is partly or
wholly filled, as may be requisite, with perfectly dry and granular double
sulphate of iron and ammonia ; the exact weight then taken and noted.
The chromium compound is brought into solution, not too dilute, acidified
with sulphuric acid, and small quantities of the iron salt added from time to
time with a dry spoon, taking care that none is spilled, and stirring with
a glass rod, until the mixture becomes green, and the iron is in excess, best
known by a small drop being brought in contact with a drop of red'prussiate
of potash on a white plate; if a blue colour appears at the point of contact,
the iron is in excess. It is necessary to estimate this excess, which is most
conveniently done by ^ bichromate being added until the blue colour
produced by contact with the red prussiate disappears. The vessel containing
the iron salt is again weighed, the loss noted; the quantity of the salt
represented by the ^ bichromate deducted from it, and the remainder
multiplied by the factor required by the substance sought. A freshly made
standard -solution of iron salt, well acidified with sulphuric acid, may be used
in place of the dry salt.

Example : 0'5 gm. pure potassic bichromate was taken for analysis, and to
its acid solution 4'15 gm. double iron salt added. 33 c.c. of /¥ bichromate
Avere required to oxidize the excess of iron salt ; it was found that 0'7 gm. of
the salt= 17'85 c.c. bichromate, consequently 3'3 c.c. of the latter were equal
to 0'12985 gm. iron salt; this deducted from the quantity originally used
left 4-02015 gm., which multiplied by 01255 gave 0'504 gm. instead of
0'5 gm.

168 VOLUMETRIC ANALYSIS. § 56.

In the case of lead chromate being estimated in this way, it is
best to mix both the chromate and the iron salt together in
a mortar, rubbing them to powder, adding hydrochloric acid,
stirring well together, then diluting with water and titrating as
before. ...Where 'pure double iron salt is not at hand, a solution of
iron wire in sulphuric acid, freshly made, and of ascertained
strength, may be used.

2. Estimation of Chromates by Distillation with Hydrochloric Acid.

When chromates are boiled with an excess of strong hydrochloric
acid in one of the apparatus (fig. 37 or 38), every 1 eq. of chromic
acid liberates 3 eq. chlorine. For instance, with potassic bichromate
the reaction may be expressed as follows —

K2O2Or + 14HC1=2KC1 + Cr2Cl6 + 7H20 + 6C1.

If the liberated chlorine is conducted into a solution of potassic
iodide, 3 eq. of iodine are set free, and can be estimated by —
arsenite or thiosulphate. 3 eq. of iodine so obtained=379'5
represent 1 eq. chromic acid— 100 '40. The same decomposition
takes place by mere digestion, as described in § 39.

3. Chrome Iron Ore, Ste'el, etc.

The ore varies in quality, some samples being very rich, while
others are very poor, in chromium. In all cases the sample is to
be first of all brought into extremely fine powder. About a gram is
rubbed tolerably fine in a steel mortar, then finished fractionally
in an agate mortar.

Christomanos recommends that the coarse powder should be
ignited for a short time on platinum previous to powdering with
the agate mortar ; after that it should be sifted through the finest
material that can be used, and the coarser particles returned to the
mortar for regrinding.

Previous to analysis it should be again ignited, and the analysis
made on the dry sample.

O'Neill's Process.— The very finely powdered ore is fused with
ten times its weight of potassic bisulphate for twenty minutes, taking care
that it does not rise over the edge of the platinum crucible ; when the fusion
is complete, the molten mass is caused to flow over the sides of the crucible,
so as to prevent the formation of a solid lump, and the crucible set aside to
cool. The mass is transferred to a porcelain dish, and lixiviated with warm
water until entirely dissolved (no black residue must occur, otherwise the
ore is not completely decomposed) ; sodic carbonate is then added to the
liquid until it is stro'ngly alkaline ; it is then brought on a filter, washed
slightly, and the filter dried. When perfectly dry, the precipitate is
detached from the filter as much as possible ; the filter burned separately ;
the ashes and precipitate mixed with about twelve times the weight of the
original ore, of a mixture of two parts potassic chlorate and three parts
sodic carbonate, and fused in a platinum crucible for twenty minutes or so ;
the resulting mass is then treated with boiling water, filtered, and the filtrate
titrated for chromic acid as in 5 56.1.

§ 56.

CHROMIUM. 169

The ferric oxide remaining on the filter is titrated, if required,
by any of the methods described in §§63 and 64.

Britton's Process.— Reduce the mineral to the finest state of
division possible in an agate mortar. Weigh off 0'5 gm., and add to it
4 gm. of flux, previously prepared, composed of one part potassic chlorate
and three parts soda-lime ; thoroughly mix the mass by triturating in a
porcelain mortar, and then ignite in a covered platinum crucible at a bright-
red heat for an hour and a half or more. 20 minutes is sufficient with 'the
gas blowpipe. The mass will not fuse, but when cold can be turned out of
the crucible by a few gentle taps, leaving the interior of the vessel clean
and bright. Triturate in the mortar again and turn the powder into a tall
4-oz. beaker, and add about 20 c.c. of hot water, and boil for two or three
minutes ; when cold add 15 c.c. of HC1, and stir with a glass rod, till
the solid matter, with the exception probably of a little silica in flakes,'
becomes dissolved. Both the iron and chromium will then be in the highest
state of oxidation — Ee2O3 and Cr'2O3. Pour the fluid into a white porcelain
dish of about 20-oz. capacity, and dilute with washings of the beaker to
about 3 oz. Immediately after, also, add cautiously 1 gm. of metallic iron
of known purity, or an equivalent quantity of double iron salt, previously
dissolved in dilute sulphuric acid, and further dilute with cold water to
about 5-oz., to make up the volume in the dish to about 8 oz., then titrate
with £j permanganate the amount of. ferrous oxide remaining. The
difference between the amount of iron found and of the iron weighed will
be the amount oxidized to sesquioxide by the chromic acid. Every one part
so oxidized will represent 0'320 of Cr"or 0'4663 of sesquioxide, Cr2O3, in
which last condition the substance usually exists in the ore.

If the amount of iron only in the ore is to be determined, the process is
still shorter. After the fluxed mineral has been ignited and reduced to
powder, as already directed, dissolve it by adding first, 10 c.c. of hot water
and applying a gentle heat, and then 15 c.c. of HC1, continuing the heat to
incipient boiling till complete decomposition has been effected; cool by
immersing the tube in a bath of cold water, add pieces of pure metallic zinc
sufficient to bring the iron to the condition of protoxide and the chromium
to sesquioxide, and apply heat till small bubbles of hydrogen cease, and the
zinc has become quite dissolved; then nearly fill the tube with cold water,
acidulated with one-tenth of sulphuric acid, and pour the contents into the
porcelain dish, add cold water to make up the volume to about 8 oz., and
complete the operation with standard permanganate or bichromate.

Sell's Process. — This method is described in J. C. S. 1879
(p. 292), and is carried out by first. fusing the finely ground ore
with a mixture of sodic bisulphate and fluoride in the proportion
of I mol. bisulphate, and 2 mol. fluoride, and subsequent titration
of the chromic acid by standard thiosulphate and iodine.

Prom O'l to 0'5 gm. of the ore is placed on the top of ten times its weight
of the above-mentioned mixture in a large platinum crucible, and ignited for
fifteen minutes ; an equal weight of sodic bisulphate is then added and well
incorporated by fusion, and stirring with a platinum wire; then a further
like quantity of bisulphate added in the same way. When complete
decomposition has occurred, the mass is boiled with water acidulated with
sulphuric acid, and the solution diluted to a definite volume according to the
quantity of ore originally taken.

To insure the oxidation of all the chromium and iron previous to titration,
a portion, or the whole, of the solution is heated to boiling, and permanganate
added until a permanent red colour occurs. Sodic carbonate is then added
in slight excess, and sufficient alcohol to destroy the excess of permanganate ;

170 VOLUMETRIC ANALYSIS. § 56.

the manganese precipitate is then filtered off, and the clear solution titrated
with T^j- thiosulphate and iodine.

The author states that the analysis of an ore by this method
may be accomplished in one hour and a half.

For the oxidation of salts of chromium, the same authority
recommends boiling with potash or sodic carbonate (to which
a small quantity of hydrogen peroxide is added) for 1 5 minutes.

For the preliminary fusion and oxidation of chrome iron ore,
Dittmar recommends a mixture of two parts borax glass, and one
and a half part each of sodic and potassic carbonate. These are
fused together in a platinum crucible until all effervescence ceases,
•then poured out into a large platinum basin or upon a clean iron
plate to cool, broken up, and preserved for use.

Ten parts of this mixture is used for one part of chrome ore,
and the fusion made in a platinum crucible, closed for the first five
minutes, then opened for about forty minutes, frequently stirring
with a platinum wire, and using a powerful Bunsen name. The
gas blowpipe hastens this method considerably.

The above described methods of treating the ores of chromium,
so as to obtain complete decomposition, are apparently now super-
seded to a great extent by the use of sodic peroxide, but the action
of this agent is so energetic upon platinum, gold, silver, nickel, or
porcelain that its use requires great care. Many well known
authorities on the analysis of chrome ores use a basic mixture
such as was first suggested by Clark, but modified by Stead, i.e.,
magnesia or lime four parts, potassic and sodic carbonates of each
one part. Clark's original mixture of magnesia and caustic soda
acts on platinum, but Stead's mixture does not.

The fusion is made by mixing the very finely ground sample with ten
times its weight of the basic mixture in a platinum crucible, and heating to
bright redness at the back of a gas muffle for about an hour. When the
crucible is removed and cool the mass is found sintered together. It is
removed to a beaker, and the crucible washed out with water and dilute
sulphuric acid. The decomposition i.« generally complete, but if any black
specks are found they must be separated by filtration, dried, and again fused
with some of the basic mixture ; finally the whole is mixed with excess of
ferrous salt, and the unoxidized iron titrated with bichromate as before
described.

Hi deal and Rosenblum (J. S. C. 1. xiv. 1017) give a series
of experiments on the estimation of chromium in ores, steels, etc.,
and on the use of sodic peroxide, which latter they find has a
most destructive effect 011 all kinds of vessels in which the
decomposition is made — nickel seems the best material if not
exposed to too high a temperature, but they found also that a good
deal of nickel was dissolved from the crucibles by the sulphuric
acid used to dissolve the melt, and they therefore attach great
importance to the filtration of the aqueous solution of the melt, se-
as to remove nickel and iron oxides, which otherwise interfere with
the titration by masking the colour of the indicator.

§ 56. CHROMIUM.

Ferroclirome, Ciirommm Steel, etc. — S puller and Ivalman
(Chein. Zeit. xvii. 880 and 1207) describe a method which gives
good results, but is unfortunately tedious in working.

Process for Ferroclirome. — 0'35 gm. of the finely-powdered sample first
sifted through linen and then rubbed down in an agate mortar, is mixed
with 4 gm. of sodium peroxide and 8 gm. of caustic soda, and heated in
a silver dish over a slightly smoky flame. The temperature is gradually
raised so that at the end of five minutes the edge of the mixture begins
to fuse, and after a further period of ten minutes the whole mass has
become liquid. The heating is continued for half an hour over the slightly
smoky flame until the bottom of the dish is covered with soot. During the
last quarter of an hour the melt is stirred with a silver spatula. The attack
of the ferro-chromium is then complete if the heating has been conducted
as described, and the sample has been powdered sufficiently fine. The basin
Avith its contents is allowed to cool to 40° — 50° C., freed from soot, and
digested, in a large hemispherical porcelain dish, with hot water. The dish
is then removed and rinsed into the basin. The loss in weight of a silver
dish Aveighing about 38 gm. may be as much as 0'04 — 0'05 gm. for a single
fusion. The aqueous extract of the melt contains sodium manganate and
ferrate as well as chromate. Only traces of sodium peroxide remain, as the
bulk is decomposed during solution. Sodium manganate and ferrate are
removed by the addition of successive small quantities of sodium peroxide,
which reduces these salts, itself undergoing simultaneous reduction. A
quantity of 0'3— 0'6 gm. is usually requisite, and any excess that may be
added is got rid of either by allowing the solution to stand while being
kept warm for some hours, or preferably by passing CO2 into the solution
for an hour and heating it for fifteen minutes on a water or sand bath.
By the latter treatment hydrogen peroxide is liberated from the sodium
peroxide, and being unstable in alkaline solution is decomposed on heating.
Sodium chromate is not affected by excess of the peroxide in alkaline
solution. Clark and E/ideal both find that mere boiling for ten minutes,
is sufficient to decompose the excess of peroxide.

The aqueous solution of the melt is made up to 500 c.c., the contents
of the flask allowed to stand and an aliquot portion (?.g. 100 c.c.) filtered
from ferric oxide, etc., and the chromium in it determined by a permanganate
solution of which 1 c.c. equals about O'OOS gm. of iron, and a solution of
ferrous ammonium sulphate containing 7 gm. of the salt in 500 c.c. The
chromium solution is diluted with 1 liter of cold Avater which has been
previously boiled and acidified with 20 c.c. of sulphuric acid (1 : 5 by volume);
100 c.c. of ferrous ammonium sulphate are added, and the mixture titrated
back with permanganate. The strength of the ferrous solution is determined
by a blank experiment under similar conditions.

Process for Chromium Steel : The material is dissolved in dilute sulphuric
acid, evaporated to dry ness and fused Avith caustic soda and sodium peroxide,,
as above described. The mass is digested with Avater, and after removal of
any alkaline manganate or ferrate with peroxide and decomposing excess of
the latter by CO12 or by simple boiling,. the' solution is diluted to a definite
volume, and aliquot portions titrated as before mentioned.

Rideal and llosenbluni have obtained excellent results with
ferrochrome, by fusion with sodic peroxide alone. The manner of
procedure was as follows : —

About 0'5 gm. of a very finely poAvdered ferrochrome was mixed with
3 gm. of sodic peroxide and heated very gently in a nickel crucible, until

172 VOLUMETRIC ANALYSIS. § 56.

•the mass began to melt, and then to glow by itself. The heating was then
•continued for ten minutes, and after the mass was partially cooled 1 gm. of
sodic peroxide was added and the heating continued for another five minutes.

The crucible, when still moderately warm, was placed in a suitable
porcelain basin, which was then half filled with hot water and covered with
a clock glass. The melt easily dissolved in the hot water, the solution
obtained being of a deep purple colour, due to sodic ferrate, which is
abundantly formed during the fusion. The solution also contained sodic
manganate, resulting from the oxidation of the manganese which is present
in ferrochrome.

To decompose both these salts a small quantity of sodic peroxide was
ndded, on which the solution immediately lost its purple colour. The
•solution was then boiled for ten minutes to decompose the excess of sodic
peroxide and the insoluble residue of iron, nickel, and manganese oxide was
filtered off. An excess of sulphuric acid wras then added to the solution and
after cooling it was titrated in the usual manner.

Galbraith's method, modified somewhat by Stead (Jour. Iron
and Steel Institute, 1893, 153), is considered the most rapid method
for the estimation of chromium in irons and steels.

The sample is dissolved in dilute sulphuric acid, filtered, the solution
diluted to about 300 c.c., and heated to boiling. Strong solution of potassic
permanganate is now" added until the red colour is permanent for ten
minutes, then 80 c.c. of 10 per cent, hydrochloric acid, and the liquid
heated until decolorized ; 150 c.c. of water are added, about 100 c.c. boiled
•off to expel the chlorine; and the chromium is then titrated. The residue
insoluble in dilute sulphuric acid is mixed with 0'5 gm. of the basic mixture
•previously mentioned, and heated to intense redness for half an hour ; the
chromium is afterwards titrated in hydrochloric acid solution with ferrous
•sulphate and bichromate.

Another process consists in dissolving 2 gm. of the sample in hydrochloric
•acid ; without filtering, the liquid is nearly neutralized with a 2 per cent,
solution of caustic soda, and after diluting to 300 c.c., 10 c.c. of a 5 per cent.
-solution of sodic phosphate and 30 gm. of sodic thiosulphate are added. After
boiling to expel the SO2, 20 c.c. of a saturated solution of sodic acetate
•are added, and the boiling continued for five minutes ; the precipitated
chromium phosphate is then washed with a 2 per cent, solution of ammonium
nitrate, dried, calcined, and fused with the basic mixture. The melt,
dissolved in 30 c.c. of hydrochloric acid and 150 c.c. of water, is boiled
for ten minutes and titrated. The process may be used in presence of
vanadium. In this case, the chromium must be titrated by means of ferrous
•sulphate and permanganate in presence of sulphuric acid.

E ideal and Rosenbl urn's experiments appear to show that
.•sodic peroxide, if certain conditions be observed in its use, is
.a very valuable agent for the analysis of chrome ore, ferro-
• chrome, and chrome steel, as it removes the two main defects
of former methods, viz., the necessity of repeated fusion to effect
complete decomposition and the inconvenient slowness of these
processes. The conditions which should be observed are sum-
marized by them as follows : —

(1) Great care should be taken to reduce the chrome ore or the ferro-
chrome to an almost impalpable powder. This can be done without much
difficulty if the ore or the alloy be crushed in a steel mortar until a powder
is obtained which will pass through a linen bag. This powder is then

§ 57. COBALT.

ground in an agate mortar to the required degree of fineness, a little water
feeing added to facilitate the grinding.

(2) The water solution of the melt, before acidulation, must be freed,
from an excess of sodic peroxide. Whenever sodium ferrate or sodium
manganate is formed during the fusion it must be decomposed in the water
solution of the melt.

(3) As the result of the analysis depends to a large extent upon the
titration, and especially upon a clear perception of its final point, it is
important that the solution in which the chrome is to be determined should
be as free as possible from other metallic salts, as for instance, iron,
manganese, and nickel salts. We have also observed that the ferricyanide
solution which is used as an indicator is most satisfactory when it contains
no more than 1 per cent, of ferricyanide.

COBALT.

Co=59.
Estimation "by Mercuric Oxide and Permanganate (W inkier).

§ 57. IF an aqueous solution of cobaltous chloride or sulphate be-
treated with moist finely divided mercuric oxide, no decomposition-
ensues, but on the addition of permanganate to the mixturej
hydrated cobaltic and manganic oxides are precipitated. It is
probable that no definite formula can be given for the reaction,
and therefore practically the working effect of the permanganate
is best established by a standard solution of c'obalt of known
strength, say metallic cobalt dissolved as chloride, or neutral
cobaltous sulphate.

Process : The solution, free from any great excess of acid, is placed in
a flask, diluted to about 200 c.c., and a tolerable quantity of moist mercuric
oxide (precipitated from the nitrate or perchloride by alkali and washed)'
added. Permanganate from a burette is then slowTly added to the cold solution-
with constant shaking until the rose colour appears in the clear liquid above
the bulky brownish precipitate.

The appearance of the mixture is somewhat puzzling at the
beginning, but as more permanganate is added the precipitate
settles more freely, and the end as. it approaches is very easily
distinguished. The final ending is when the rose colour is
persistent for a minute or two; subsequent bleaching must not
be regarded.

The actual decomposition as between cobaltous sulphate and
permanganate may be formulated thus —

GCoSO4 + 5H20 + 2MnK04 = K2S04 + 5H2S04 + 3Co203 + 2Mn02
but as this exact decomposition cannot be depended upon in all the
mixtures occurring, it is not possible to accept systematic .numbers-
calculated from normal solutions.

Solutions containing manganese, phosphorus, arsenic, active
chlorine or oxygen compounds, or organic matter, cannot be used
in this estimation ; moderate quantities of nickel are of no
consequence.

174 VOLTJMET1UC ANALYSIS. § 57.

Norman McCulloch (C. N. lix. 51) has proved that cobaltic
oxide, as cobalticyanide, is a stable compound, and makes use of
this fact to establish a process which gives very good results, by
conversion of cobaltocyanide to the higher state of oxidation, the
estimation of the oxygen being the measure of the cobalt itself.
The method is exact in the presence of nickel, manganese, lead,
arsenic, zinc, antimony, uranium, etc., but not in that of iron or
copper.

The standard solutions required are the ordinary ~ potassic
bichromate, 1 c.c. of which represents O0059 gm. of Co, and an
acid solution of ammonio-ferrous sulphate, whose strength is known
by titration with the bichromate. There is also required a 5 per
cent, solution of pure potassic cyanide, and a solution of nickel
sulphate.

The apparatus required may be simply a 12-oz. flask, fitted with
two-hole stopper, one for a thistle funnel and the other as an
•escape for vapour. The mouth of the funnel should be somewhat
•constricted, and the lower end must dip beneath the surface of the
liquid in the flask.

Process : The standard bichromate and cyanide solutions are conveyed in
their proper quantities to the flask above described, a few drops of ammonia
added for subsequent neutralization of any free acid in solution to be tested,
and the whole diluted, if necessary, to a convenient bulk with Avater.

The amount of bichromate taken need not greatly exceed the theoretical
requirement for the greatest probable quantity of cobalt to be estimated, but,
with the cyanide, an allowance is made also for the conversion to soluble
double c}ranides of such other metals as may be present.

The cork and thistle-funnel are now placed in position, and the.solution
boiled to expel air from the flask. Tho hot solution to be tested, of con-
venient bulk and not too acid, and free, of course, from oxidizing or reducing
constituents, is now added, and the ensuing reaction is instantaneously
•complete.

After this stage the continued use of the cork and thistle-funnel is
necessary only in presence of manganese.

The contents of the flask are now cautiously treated with excess of
a moderately warm concentrated solution of ammonic chloride, and the
ebullition sustained for about ten minutes longer to expel volatile cyanide
.(an operation conducted in a fume chamber or in a draught of air to carry
off poisonous fumes).

It now remains, preceding the estimation of non-reduced chromic acid
with ferrous salt, to throw down soluble cobaltocyanide and decompose
potassium-nickel cyanide by the addition of nickel sulphate. This is to
prevent the subsequent formation of ferrous cobaltocyanide and double
cyanide of iron and nickel respectively — compounds difficultly soluble in
•dilute acid — and, consequently, low results. To effect the above precipitation,
a weight of nickel is required at least equal to that of the nickel and cobalt
'existing in the contents of the flask, but if such acids as arsenic and phosphoric
are present more is needed, as their precipitation is involved. Simply, the
solution of nickel is added until no further precipitate is formed, or until the
•precipitate settles in a peculiar manner, to be known by experience ; great
-excess of nickel is thus avoided, which would tend to interfere with the
!erric3'anide reaction in the subsequent operation.

The contents of the flask are now poured into excess of a hot aqueous

§ oS. COPPER. 175

solution of standard ferrous salt contained in a basin, acidified with a few
drops of hydrochloric acid, and titrated with bichromate in usual way.

The cobalt is calculated by multiplying the difference between the number
of c.c. of bichromate taken at the outset of the estimation and that found
at the completion, by 0*0059, and correcting- this by a slight allowance for
reducing action of the potassic cyanide and its impurities on the chromate.
In the author's case this correction was taken from experiment, and it was
deemed sufficiently near to accept the reducing action of the cyanide as
simp]}' proportionate to the quantity of this reagent used in the estimation,
although it is not altogether independent of the proportion and amount
of the bichromate, the degree of dilution, length of time of boiling, etc.
The result showed that 100 c.c. of the bichromate boiled for a few minutes
with its own bulk of the cyanide, and then for about ten minutes more with
addition of excess of ammonic chloride, lost in value to the extent of about
one c.c., which was deducted from the amount of bichromate reduced by the
cobaltocyanide in such estimations, using the above bulk of cyanide, a fifth
of this for 25 or 30 c.c., and so on. It is, of course, advisable, where the
highest accuracy is desired,. to determine the necessary correction by a blank
experiment, and duplicating also the approximate quantity of cobalt.

It is best to separate iron as well as copper, and in the case of a cobalt ore
the author would dissolve the sample in aqua-regia, and evaporate to dryness.
The nitric acid would then be destroyed by two or three evaporations to
dryness with hydrochloric acid, and the copper precipitated from the solution
of the residue by sulphuretted hydrogen. In the filtrate from sulphide
the iron would be separated by the acetate of soda method, and the iron
precipitate re-dissolved and re-precipitated in a similar way to separate any
small portion of cobalt. The combined filtrates from the acetate precipitates
would be evaporated to convenient bulk, and the excess of acid neutralized
by sodic hydrate or carbonate. The solution so obtained would then be added
to suitable amounts of bichromate and cyanide, as described above.

Examples : 0*114 gm. Co taken and 25*4 c.c. respectively of bichromate
and cyanide used. The volume of bichromate reduced, allowing for the
correction, was 19 2 c.c.=l*113 gm. Co. Again, 0*114 gm. Co and 0*228 gm.
Ni taken, 25 c.c. of bichromate and 50 c.c. of cyanide used, the volume of
the former reduced was 19'1 c.c.=0*112 gm. Co. Equally good results were
obtained with mixtures of manganese, lead, arsenic, etc.

COPPER.

Cu=63.

1 c.c. ~ soliitioii=0*0063 gm. Cu.
Iron x 1-125 =Cu.

Double Iron Salt x O1607=Cu.

1. Reduction by Grape Sugar and subsequent titration with Ferric
Chloride and Permanganate (Schwarz).

§ 58. THIS process is based upon the fact that grape sugar
precipitates cuprous oxide from an alkaline solution of the metal
containing tartaric acid ; the oxide so obtained is collected and
mixed with ferric chloride and hydrochloric acid. The result is
the following decomposition : —

Cu20 + Fe2Cl6 + 2HCl=:2CuCl2 + 2FeCl2 + H20.
Each equivalent of copper reduces one equivalent of ferric to ferrous

176 VOLUMETRIC ANALYSIS. § 58.

chloride, which is estimated by permanganate with due precaution.
The iron so obtained is calculated into copper by the requisite factor.

Process : The weighed substance is brought into solution by nitric or
sulphuric acid or water, in a porcelain dish or glass flask, and most of the
acid in excess saturated with sodic carbonate ; neutral potassic tartrate is then
added in not too large quantity, and the precipitate so produced dissolved to
a clear blue liquid by adding caustic potash or soda in excess ; the vessel is
next heated cautiously to about. 50° C. in the water bath, and sufficient
grape sugar added to precipitate the copper present ; the heating is continued
until the precipitate is of a bright red colour, and the upper liquid is
brownish at the edges from the action of the alkali on the sugar : the heat
must never exceed 90° C. When the mixture has somewhat cleared, the
upper fluid is poured through a moistened filter, and afterwards the precipitate
brought on the same, and washed with hot water till thoroughly clean ; the
precipitate which may adhere to the dish or flask is well washed, and the
filter containing the bulk of the protoxide put with it, and an excess of
solution of ferric chloride (free from nitric acid or free chlorine) added,
together with a little sulphuric acid ; the whole is then warmed and stirred
until the cuprous chloride is all dissolved. It is then filtered into a good-
sized flask, the old and new filters being both well washed with hot water, to
which at first a little free sulphuric acid should be added, in order to be
certain of dissolving all the oxide in the folds of the paper. The entire
solution is then titrated with permanganate in the usual way. Bichromate
ma}7' also be used, but the end of the reaction is not so distinct as usual, from
the turbidity produced by the presence of copper.

2. Reduction by Zinc and subsequent titration with Ferric Chloride
and Permang-anate (Fleitmann).

The metallic solution, free from nitric acid, bismuth, or lead, is
precipitated with clean sticks of pure zinc ; the copper collected,
washed, and dissolved in a mixture of ferric chloride and hydro-
chloric acid : a little sodic carbonate may be added to expel the
atmospheric air. The reaction is —

Cu + Fe2Cl6=:CuCl2 + 2FeCP.

When the copper is all dissolved, the solution is diluted and
titrated with permanganate; 56 Fe=31'5 Cu.

If the original solution contains nitric acid, bismuth, or lead,
the decomposition by zinc must take place in an ammoniacal
solution, from which the precipitates of either of the above metals
have been removed by filtration ; the zinc must in this case be
finely divided and the mixture warmed. The copper is all
precipitated when the colour of the solution has disappeared. It
is washed first with hot water, then with weak HC1 and water to
remove the zinc, again with water, and then dissolved in the acid,
and ferric chloride as before.

3. Estimation as Cuprous Iodide (E. O. Brown).

This excellent method is based on the fact that when potassic
iodide is mixed with a salt of copper in acid solution, cuprous
iodide is precipitated as a dirty white powder, and iodine set free..

§ 58. COPPER.

If the latter is then immediately titrated with thiosulphate and
starch, the corresponding quantity of copper is found.

The solution of the metal, if it contain nitric acid, is evaporated
with sulphuric acid till the former is expelled, or the nitric acid is
neutralized with sodic carhonate, and acetic acid added ; the
sulphate solution must be neutral, or only faintly acid ; excess of
acetic acid is of no consequence, and therefore it is always
necessary to get rid of all free mineral acids and work only Avith
free acetic acid.

J. W. Westmoreland (/. S. C. I. v. 51), who has had very large
experience in examining a variety of copper products, strongly
recommends this process for the estimation of copper in its various
ores, etc. The metal may very conveniently be separated from a hot
sulphuric acid solution by sodic thiosulphate : this gives a flocculent
precipitate of subsulphide mixed with sulphur, which filters readily,
and can be washed with hot water. Arsenic and antimony, if
present, are also precipitated ; tin, zinc, iron, nickel, cobalt, and
manganese are not precipitated. On igniting the precipitate most
of the arsenic and the excess of sulphur is expelled, an impure
subsulphide of copper being left. Sulphuretted hydrogen may of
course be used instead of the thiosulphate, but its use is objection-
able to many operators, beside which, under some circumstances,
a small amount of copper remains in the solution, and moreover
iron in small quantity is also precipitated with the copper, and
cannot be entirely removed by washing. If HAS is used it should
be passed for some time, and the precipitate allowed to stand a few
hours to settle — after nitration and washing the CuS should be
redissolved in HXO3 and reprecipitated with -the gas, it is then quite
free from iron.

Standardizing- the Thiosulphate Solution. — This may be done on
pure electrotype copper, but this is not always pure, and the safest
standard is high conductivity wire, dissolved first in nitric acid,
boiling to expel nitrous fumes, diluting, neutralizing with sodic
carbonate till a precipitate occurs, then adding acetic acid till clear.
The liquid is then made up to a definite volume, and a quantity
equal to about 0'5 gm. Cu taken in a flask or beaker, about ten
times the copper weight of potassic iodide added, and when
dissolved the thiosulphate is run in from a burette until the free
iodine is nearly removed, add then some starch, and finish the
titration in the usual way. The thiosulphate will of course need
to be checked occasionally.

If strictly -— thiosulphate is used, each c.c. =0*0063 gm. Cu.

Process : For estimating the copper in iron pyrites or burnt ore 5 gm. of
the substance should be taken, 2 gm. for 30 — 40 °/0 mattes or 1 gin. for
60 °/'o mattes, and with precipitates it is best to dissolve say 5 gm. and dilute
to a definite volume, and take as much as would represent from 0'5 to 07 gm.
of Cu for titration. The solution is made with nitric acid, to which hydrochloric
is also added later on, and then evaporated to dryness with excess of sulphuric

178 VOLUMETRIC ANALYSIS. § 58.

acid to convert the bases into sulphates ; the residue is treated with warm
water and any insoluble PbSO4, £c., filtered off. The filtrate is heated to
boiling and precipitated with sodic thiosulphate, this precipitate is filtered
off, washed with hot water, dried, and roasted, the resulting copper oxide is
then dissolved in nitric acid, and after the excess of acid is chiefly removed
by evaporation sodic carbonate is added, so as to precipitate part of the
copper and ensure freedom from mineral acid, acetic acid is added till
a clear solution is obtained ; about ten parts of potassic iodide to one of
copper, supposed to be present, are then added, and the titration carried out in
the usual way.

A modification of this process is adopted in tlie United States
(Peters, Eng. and Min. Journ. lix. 124) as follows : —

In the treatment of ores 1 gin. is heated with hot, strong nitric acid, to
which is then added strong hydrochloric acid. After boiling, strong-
sulphuric acid is added, and the volatile acids evaporated off. After
diluting, the PbSO4, &c., is filtered off, and the solution, which should not
exceed 75 c.c., is run into a beaker, at the bottom of which is a strip of
aluminium 3 in. long, 1^ in. wide, and turned up at the ends so that the
body of the strip can lie flat. The copper is all precipitated after boiling for
six or seven minutes. The liquid is filtered off, and the loose and adherent
copper is all dissolved in a little nitric acid. To this is added half a gram
of chlorate of potash, to fulty oxidize any arsenic present, and the solution
boiled down to small bulk, but not sufficiently low to produce a basic salt
of copper. The solution is then neutralized with ammonia, acidified with
acetic acid, and titrated in the usual manner.

This treatment removes all interfering impurities or renders them inert.
Zinc is not such a good precipitant for the copper as aluminium, as some
iron is also carried down even from strongly acid solutions. When aluminium
is used, the precipitation may be effected without boiling by adding a little
hydrochloric acid to the solution, but this is not so desirable as the method
described. For the success of the titration it is essential that no free nitric
acid or nitrate of copper be present. Cold ammonia in excess does not,
apparently, entirely decompose the latter, hence the necessity for boiling.
Care must be taken that the aluminium contains no copper, or if it does
its quantity must be known.

By either of the above methods there is no interference from
arsenic or bismuth, so long as no free mineral acid is present.

4. Estimation by Potassic Cyanide (P;'arkes and C. Itlohr).

This well-known and much-used, process for estimating copper
depends upon the decoloration of an ammoniacal solution of copper
by potassic cyanide. • The reaction (which is not absolutely uniform
with variable quantities of ammonia) is such that a double cyanide
of copper and ammonia is formed; cyanogen is also liberated, which
reacts on the free ammonia, producing urea, oxalate of urea,
ammonic cyanide and formate (Liebig). Owing to the influence
exercised by variable quantities of ammonia, or its neutral salts,
upon the decoloration of a copper solution by the cyanide, it has
been suggested by Beringer to substitute some other alkali for
neutralizing the free acid in the copper solution other than
ammonia. The suggestion has been adopted by Da vies (C. N.
Iviii. 131) and by Eessenden (C. N. Ixi. 131), who both

COPPER. ] 79

recommend sodic carbonate. My own experiments completely
confirm their statement that none of the irregularity common to
variable quantities of ammonia or its salts occurs with soda or
potash. Suppose for example that copper has been separated as
sulphide, and brought into solution by nitric acid, the free nitro-
sulphuric acid is neutralized with JXra2C03, and an excess of it
added to redissolve tlie precipitate. The cyanide solution is then
cautiously ran into the light blue solution until the colour is just
discharged. My own experience is, that it is impossible to
redissolve the whole of the precipitate without using a very large
excess of soda ; but there is no need to add such an excess, as
the precipitate easily dissolves when the cyanide is added.
I have used a modification of this method, which gives excellent
results, viz., to neutralize the acid copper solution either with
Na'2CO:J or NaHO, add a trifling excess, and then 1 c.c. of
ammonia 0'960 sp. gr. ; a deep b^ue clear solution is at once given,
which permits of very sharp end-reaction with the cyanide.

J. J. and C. Beringer (C. N. xlix. iii.) have already adopted
the method of neutralizing the acid copper solution with soda,
then adding ammonia, but the proportion they recommend is larger
than necessary.

In standardizing the cyanide, it is advisable to arrange so that
copper is precipitated with soda exactly as in the titration of
a copper ore ; that is to say, free nitric or mtro-sulphuric acid
should be added, then neutralized with slight excess of soda,
cleared with 1 c.c. of ammonia, then titrated with cyanide. Large
quantities of nitrate or sulphate of soda or potash, however, make
very little difference in the quantity of cyanide used.

It lias generally feeen thought that where copper and iron occur together,
it is necessary to separate the latter before using the cyanide. P. Field,
however, has stated that this is not necessary (C. N. i. 25) ; and I can fully
eadorse his statement that the presence of the suspended ferric oxide is no
hindrance to the estimation of the copper ; in fact, it is rather an advantage,
as it acts as an indicator to the end of the process.

While the copper is in excess, the oxide possesses a purplish-brown colour,
but as this excess lessens, the colour becomes gradually lighter, until it is
orange brown. If it be now allowed to settle, which it does very rapidly, the
clear liquid above will be found nearly colourless. A little practice is of
course necessary to enable the operator to hit the exact point.

It is. impossible to separate the ferric oxide by filtration without
leaving some copper in it, and no amount of washing will remove
it. For example, 10 c.c. of a copper solution with 10 c.c. of ferric
solution were directly titrated with cyanide after treatment with
]NraHO in slight excess and 1 c.c. of ammonia: The cyanide
required was 12 c.c. Another 10 c.c. of the same copper and iron
solutions were then precipitated with soda and ammonia in same
proportions. This gave a complete solution of the copper with the
ferric oxide suspended in it. The solution was filtered and the
ferric oxide well washed with hot water, then the filtrate cooled and

N 2

180 VOLUMETRIC ANALYSIS. § 58.

titrated with cyanide, 9*5 c.c. only being required. On treating the
ferric oxide on the filter with nitric acid, neutralizing with XaHO
and NH8 in proper proportions exactly, 2 '5 c.c. of cyanide were
required, showing that the ferric oxide had retained 20 per cent,
of the copper.

I strongly recommend that operators who have to deal with
copper determination upon samples containing much iron, should
practise the use of the cyanide method in the presence of the iron,
and accustom their eyes to the exact colour which the ferric oxide
takes when the titration is finished, always, however, with this
proviso, that the cyanide solution is standardized upon a known
weight of copper in the presence of a moderate amount of iron.

The solution of potassic cyanide should he titrated afresh at
intervals of a few days. Further details of this process are given
in § 58.8.

Dulin (Jour. Amer. Cliem. Soc.^vii. 346) advocates the cyanide
process for copper ores as follows : —

Process : The ore is treated in the way described in § 58.3 to obtain a solution
of the copper practically free from silver and lead. The copper is then pre-
cipitated upon aluminium foil as there mentioned. Should cadmium be
present it is also precipitated to some extent, but only after the copper
is thrown down. If care be taken to stop the boiling immediately after
the copper is precipitated, which a practised eye will readily detect, the
amount of cadmium precipitated is so small as to cause no sensible error.
The liquid being decanted from the copper and foil, the latter are washed
well with hot water, taking care to lose no metal ; when quite clean, dilute
nitric acid is added and boiled till the copper is dissolved, the liquid then
neutralized with excess of ammonia, and titrated with cyanide in the
usual way.

5. Estimation as Sulphide (Pelouze).

It is first necessary to have a solution of pure copper of known
strength, which is best made by dissolving 39*523 gm. of pure
cupric sulphate in 1 liter of water ; each c.c. will contain
0-01 gm. Cu.

Precipitation in Alkaline Solution. — This process is based on the
fact that if an ammoniacal solution of copper is heated to from
40° to 80° C., and a solution of sodic sulphide added, the whole
of the copper is precipitated as oxysulphide, leaving the liquid
colourless. The loss of colour indicates, therefore, the end of the
process, and this is its weak point. Special practice, however, will
enable the operator to hit the exact point closely.

Example : A measured quantity (say 50 c.c.) of standard solution of copper
is freely supersaturated with ammonia, and heated till it begins to boil.
The temperature will not be higher than 80° C. in consequence of the
presence of the ammonia ; it is always well, however, to use a thermometer.
The sodic sulphide is delivered cautiously from a Molar's burette, until the
last traces of blue colour have disappeared from the clear liquid above the
precipitate. The experiment is repeated, and if the same result is obtained,
the number of c.c. required to precipitate the amount of copper contained

§ 58. COPPER. 181

in 50 c.c.— 0'5 gin., is marked upon the alkaline sulphide bottle. As the
strength of the solution gradually deteriorates, it must be titrated afresh every
day or two. Special regard must be had to the temperature of the precipi-
tation, otherwise the accuracy of the process is seriously interfered with.

Casamajor (0. N. xlv. 167) uses instead of ammonia the alkaline
tartrate solution same as for Fehling, adding a slight excess so as
to make a clear blue solution. The addition of the sulphide gives
an intense black brown precipitate, which is stirred vigorously till
clear. The copper sulphide agglomerates into curds, and the
reagent is added until no further action occurs with a drop of
the sodic sulphide. This modification can also be used for lead.
PbSO4 is easily soluble in the tartrate solution, and can be estimated
by the sodic sulphide in the same way as copper.

The colour of the solution is not regarded, but the clotty
precipitate of sulphide, which is easily cleared by vigorous stirring.
Very good results may be gained by this modification.

Copper can also be first separated by glucose, or as thiocyanate
(Rivot), then dissolved in HXO3, and treated with the tartrate.

Precipitation in Acid Solution. — The copper solution is placed
in a tall stoppered flask of tolerable size (400 or 500 c.c.), freely
acidified with hydrochloric acid, then diluted with about 200 c.c.
of hot water.

The alkaline sulphide is then delivered in from a burette,
the stopper replaced, and the mixture well shaken ; the precipitate
of copper sulphide settles readily, leaving the supernatant liquid
clear ; fresh sulphide solution is then at intervals added until no
more precipitate occurs. The calculation is the same as in the case
of alkaline precipitation, but the copper is precipitated as pure
sulphide instead of oxysulphide.

6. Estimation by Staniious Chloride (Weil).

This process is based on the fact, that a solution of a cupric salt
in large excess of hydrochloric acid at a boiling heat shows, even
when the smallest trace is present, a greenish-yellow colour. If to
such a solution stannous chloride is added in minute excess, a
colourless cuprous chloride is produced, and the loss of colour
indicates the end of the process.

2CuCl2 + SnCl2==Cu2Cl2 + SnCl4.

The change is easily distinguishable to the eye, but should any
doubt exist as to whether stannous chloride is in excess, a small
portion of the solution may be tested with mercuric chloride. Any
precipitate of calomel indicates the presence of stannous chloride.

The tin solution is prepared as described in § 37.2.

A standard copper solution is made by dissolving pure cupric
sulphate in distilled water, in the proportion of 39 '523 gm. per
liter=10 gm, of Cu.

182 VOLUMETRIC ANALYSIS. § 58.

Process for Copper alone. — 10 c.c. of the copper solution— O'l gm. of
Cu are put into a Avhite-glass flask, 25 c.c. of pure strong hydrochloric acid
added, placed on a sand-bath and brought to boiling heat ; the tin solution is
then quickly delivered in from a burette until the colour is nearly destroyed,
finally a drop at a time till the liquid is as colourless as distilled water. No
oxidation will take place during the boiling, owing to the flask being filled
with acid vapours.

A sample of copper ore is prepared in the usual way by treatment Avith
nitric acid, which is afterwards removed by evaporating with sulphuric acid.
Silica, lead, tin, silver, or arsenic, are of no consequence, as when the solution
is diluted with water to a definite volume, the precipitates of these substances
settle to the bottom of the measuring flask, and the clear liquid may
be taken out for titration. In case antimonic acid is present it will be
reduced with the copper, but on exposing the liquid for a night in an open
basin, the copper will be completely re-oxidized but not the antimony ;
a second titration will then show the amount of copper.

Process for Ores containing1 Copper and Iron. — In the case of copper
ores where iron is also present, the quantity of tin solution required will of
course represent both the iron and the copper. In this case a second titration
of the original solution is made with zinc and permanganate, and the quantity
so found is deducted from the total quantity; the amount of tin solution
corresponding to copper is thus found.

Example : A solution was prepared from 10 gm. of ore and diluted to
250 c.c. : 10 c.c. required 26'75 c.c. of tin solution whose strength was
16'2 c.c. for O'l gm. of Cu.

10 c.c. of ore solution were diluted, warmed, zinc and platinum added till
reduction Avas complete, and the solution titrated with permanganate Avhose
quantity=0-0809 gm.-of Fe.

The relative strength of the tin solution to iron is 18'34 c.c.=0'l gm.
of Fe : thus :

63 : 56 =0-1 : 0'0888.

therefore O'l gm. of Cu=0'0888 gm. of Fe=16'2 c.c. of SnCP
whence 0'0888 : 0'1=16'2 :" 18'34
thus 0*0809 Fe (found above)=14'837 c.c. of SnCl2
O'l : 0 0809=18-34 : 14'837 hence

Iron and copper = 26'750 c.c. SnCl2

Subtract for iron = 14'837

Leaving for copper 1T913

10 c.c. of ore solution therefore contained 16'2 : O'l : : 11-913=0'0735 gm.
of Cu, and as 10 gm. of ore=250 c.c. contained T837 gm. of Cu=18'37 per
cent. Aiiatysis by weight as a control gave 18'34 per cent. Cu.
Fe voluinetrically 20'25 per cent., by Aveight 20' iO per cent.

The method is specially adapted for the technical analysis of
fahl-ores.

Process for Ores containing Nickel or Cobalt. — The ore is dissolved
in nitric or nitre-hydrochloric acid, then nearly neutralized with sodic
carbonate, diluted Avith cold water, and freshly precipitated baric carbonate
and some ammouic chloride added ; the whole is Avell mixed together,
producing a precipitate containing all the copper and iron, AAiiile the nickel
or cobalt remains in solution ; the precipitate is first washed by decantation,
collected on a filter, well washed, then dissolved in hydrochloric add, and
titrated with stannous chloride as before described.

COPPEK. 183

Method for Copper, Iron, and Antimony. — The necessary solutions
arc: — (I) Standard copper. 19'667 gm. of copper sulphate are dissolved
in water to 500 c.c. (2) A similar solution containing 7'867 gin. of copper
sulphate. (3) Standard tin solution. 4'5 to 5 gm. of stannous chloride,
and 230 gm. of HC1, are made up to 500 c.c. with water. This solution is
standardized with No. 1, 10 c.c. of which solution should be mixed with
25 c.c. hydrochloric acid, boiled, and the tin solution to be standardized run
in until the green colour disappears.

Estimation of Copper. — 5 gm. of substance are dissolved in HC1 or
IT2S04, and made up to 250 c.c. 10 c.c. of this solution are taken, 25 c.c.
HC1 added, and then titrated as above.

Estimation of Iron. — When there are 2£ vols. of free HCl to 1 vol. of
the ferric solution no indicator is necessary, and the standard tin solution is
run in until the iron solution is colourless ; in this way the quantity of iron
is obtained in terms of copper. Of solutions containing 2 gm. of the sample
in 250 c.c., 10 c.c. are evaporated in a porcelain capsule, with 10 c.c. of the
copper solution (No. 2) ; to the concentrated mixed solution large excess
(about 75 c.c.) of HC1 is added, and this is titrated with the tin solution as
before. Of course the tin required for the copper used must be deducted.
The copper is used as an indicator, and is not required with substances
containing more than 2 per cent, of iron.

Estimation of Iron and. Copper. — 5 gm. of ore in 250 c.c. Titrate as
before directed. In another 10 c.c. of solution, precipitate the copper with
zinc, filter, reconvert the ferrous into ferric salt by means of permanganate,
and titrate the iron again.

Estimation of Antimony.— In making up the 250 c.c. in this case, it is
necessary to use aqueous solution of tartaric acid to prevent precipitation of
antimony. The solution of antimonic chloride is mixed with No. 1 copper
solution and a large excess of HCl, then titrated; the c.c. of standard tin
solution used indicates the sum of the Cu and Sb. If the mixed solution of
cuprous and antimonious chloride is allowed to remain some hours the Cu
becomes re-oxidized, but the Sb does not, therefore a second titration gives
the quantity of Cu only; this is scarcely required when the strength and
volume of copper solution added is known.

Antimony, Copper, and Iron, when together in same sample, are thus
determined. 5 gm. substance are dissolved in nitric acid, evaporated down,
and filtered. The filtrate contains iron and copper, which are determined as
above directed. The precipitate contains all the antimony ; it is dissolved in
HCl, treated with permanganate, and the antimonic chloride determined as
directed.

This process depends on the reducing action of stannous chloride. It is
therefore necessary to get rid of extraneous oxidizing influences, such as
free chlorine, nitric acid, or excess of permanganate, etc., before titration ;
this is effected by evaporating to dryness, taking up with hydrochloric acid,
and repeating, until the solution or vapour evolved on boiling ceases to turn
iodized starch-paper blue.

All the above described Weil methods must only be taken as
approximately accurate, but sufficiently so for technical use.

7. Volhard's method.

The necessary standard solutions are described in § 43, Each c.c,
of ~Q thiocyanate represents 0*0063 gm. Cu,

184 VOLUMETRIC ANALYSIS. § 58.

Process : The copper in sulphuric or nitric acid solution is evaporated to
remove excess of acid, or if the acid is small in quantity neutralized with
sodic carbonate, washed into a 300 c.c. flask, and enough aqueous solution of
SO2 added to dissolve the traces of basic carbonate and leave a distinct smell
of SO2. Heat to boiling, and run in from a burette the thiocyanate until the
addition produces no change of colour, add 3 or 4 c.c., and note the entire
quantit}7", allow to cool, fill to mark, and shake well. 100 c.c. are then filtered
through a dry filter, 10 c.c. of ferric indicator with some nitric acid added,
then titrated with T^ silver till colourless : then again thiocyanate till the
reddish colour occurs. The volume of silver solution, less the final correction
with thiocyanate, deducted from the original thiocyanate, will give the
volume of the latter required to precipitate the copper"

The process is not accurate in presence of Fe, Ag, Hg, Cl, I or Br.

8. Technical Examination of Copper Ores (Steinbeck's
Process):

In 1867 the Directors of the Mansfield Copper Mines offered
a premium for the best method of examining these ores, the chief
conditions being tolerable accuracy, simplicity of working, and the
possibility of one operator making at least eighteen assays in the day.

The fortunate competitor was Dr. Steinbeck, whose process
satisfied completely the requirements. The whole report is con-
tained in Z. a. C. viii. 1, and is also translated in C. JV. xix. 181.
The following is a condensed ri'sunu'. of the process, the final
titration of the copper being accomplished by potassic cyanide as
in § 58.4. A very convenient arrangement for filling the burette
with standard solution where a series of analyses has to be made,
and the burette continually emptied, is shown in fig. 40 ; it may
be refilled by simply blowing upon the surface of the liquid.

(a) The extraction of the Copper from the Ore. — 5 gm. of pulverized
ore are put into a flask with from 40 to 50 c.c. of hydrochloric acid (specific
gravity 1*16), whereb}r all carbonates are converted into chlorides, while
carbonic acid is expelled. After a while there is added to the fluid in
the flask 6 c.c. of a special nitric acid, prepared by mixing equal bulks of
water and pure nitric acid of 1'2 sp. gr. As regards certain ores, however,
specially met with in the district of Mansfield, some, having a very high
percentage of sulphur and bitumen, have to be roasted previous to being
subjected to this process; and others, again, require only 1 c.c. of nitric acid
instead of 6. The flask containing the assay is digested on a sand-bath for
half an hour, and the contents boiled for about fifteen minutes; after which
the whole of the copper occurring in the ore, and all other metals, are in
solution as chlorides. The blackish residue, consisting of sand and schist,
has been proved by numerous experiments to be either entirely free from
copper, or to contain at the most only O'Ol to 0'03 per cent.

(b) Separation of the Copper. — The solution of metallic and earthy
chlorides, and some free HC1, obtained as just described, is separated by
filtration from the insoluble residue, and the fluid run into a covered beaker
of about 400 c.c. capacity. In this beaker a rod of metallic zinc, weighing
about 50 gm., has been previously placed, fastened to a piece of stout
platinum foil. The zinc to be used for this purpose should be as much as
possible free from lead, and at any rate should not contain more than from
O'l to 0'3 per cent, of the latter metal. The precipitation of the copper in

COPPER.

185

the metallic state sets in already during the nitration of the warm and
concentrated fluid, and is, owing especially also to the entire absence of
nitric acid, completely finished in from half to three-quarters of an hour after
the beginning of the filtration. If the fluid be tested with SH2, no trace
of copper can or should be detected; the spongy metal partly covers the
platinum foil, partly floats about in the liquid, and in case either the ore
itself or the zinc applied in the experiment contained lead, small quantities
of that metal will accompany the precipitated copper. After the excess of
zinc (for an excess must always be employed) has been removed, the metal is
repeatedly and carefully washed by decantation with fresh water, and care
taken to collect together every particle of the spongy mass.

Pig. 40.

(c) Estimation of the precipitated Copper.— To the spongy metallic-
mass in the beaker glass, wherein the platinum foil is left, since some of the
metal adheres to it, 8 c.c. of the special nitric acid are added, and the copper
dissolved by the aid of moderate heat in the form of cupric nitrate, which,,
in the event of any small quantity of lead being present, will of course be
contaminated with lead.

"VYhen copper ores are dealt with containing above 6 per cent, of copper,
which may be approximately estimated from the bulk of the spongy mass off

186 VOLUMETRIC ANALYSIS. § 58.

precipitated metal, 16 c.c. of nitric acid, instead of 8, are applied for
dissolving the metal. The solution thus obtained is left to cool, and next
mixed, immediately before titration with potassic cyanide, with ]() c.c. of
special solution of liquid ammonia, prepared by diluting 1 volume of liquid
ammonia (sp. gr. 0'93) with 2 volumes of distilled water.

The titration with cyanide is conducted as described in § 58.4.

In the case of such ores as }rield over 6 per cent, of copper, and when a
double quantity of nitric acid has consequent!}' been used, the solution i.?
diluted with water, and made to occupy a bulk of .100 c.c.; this bulk is then
exactly divided into two portions of 50 c.c. each, and each of these separately
mixed with 10 c.c. of ammonia, and the copper therein volumetrically
determined. The deep blue coloured solution only contains, in addition to
the copper compound, ammouic nitrate ; any lead which might have been
dissolved having been precipitated as hydrated oxide, which does not interfere
with the titration with cyanide. The solution of the last-named salt is so
arranged, that 1 c.c. thereof exactly indicates 0'005 gin. of copper (about
21 gm. of the pure salt per liter). Since, for every assay, 5 gin. of ore have
been taken, 1 c.c. of the titration fluid is equal to 0*1 per cent, of copper,
it hence follows that, by multiplying the number of c.c. of cyanide solution
used to make the blue colour of the copper solution disappear by O'l, the
percentage of copper contained in the ore is immediately ascertained.

Steinbeck tested tins method specially, in order to see what
influence is exercised thereupon by (1) ammonic nitrate, (2) caustic
ammonia, (3) lead. The copper used for the experiments for this
purpose was pure metal, obtained by galvanic action, and was
ignited to destroy any organic matter which might accidentally
adhere to it, and next cleaned by placing it in dilute nitric acid.
5 gm. of this metal were placed in a liter flask, and dissolved in
266*6 c.c. of special nitric acid, the flask gently heated, and, after
cooling, the contents diluted with water, and thus brought to a
bulk of 1000 c.c. 30 c.c. of this solution were always applied to
titrate one and the same solution of cyanide under all circumstances.
When 5 gm. of ore, containing on an average 3 per cent, of copper,
are taken for assay, that quantity of copper is exactly equal to
0*150 gm. of the chemically pure copper. The quantity of nitric
acid taken to dissolve 5 gm. of pure copper (266*6 c.c.) was
purposely taken, so as to correspond with the quantity of 8 c.c. of
special nitric acid which is applied in^ the assay of the copper
obtained from the ore, and this quantity of acid is exactly met
Avith in 30 c.c. of the solution of pure copper.

The influence of double quantities of ammonic nitrate and free
caustic ammonia (the quantity of copper remaining the same) is
shown as follows : —

(a) 30 c.c. of the normal solution of copper, containing exactlj' O'lSO gm.
of copper, were rendered alkaline with 10 c.c. of special ammonia, and were
found to require, for entire decoloration, 29'8 c.c. of cyanide. A second
experiment, again with 30 c.c. of copper solution, and otherwise under
identically the same conditions, required 29 9 c.c. of cyanide. The average
is 29'85 c.c.

(6) When to 30 c.c. of the copper solution, first 8 c.c. of special nitric
acid are added, and then 20 c.c. of special ammonia instead of only 8, whereby

COPPER. 187

the quantity of free ammonia and of amraonic nitrate is double what it was
in the case of «, there is required of the same cyanide 30*0 c.c. to produce
decoloration. A repetition of. the experiment,' exactly under the same
conditions, gave 30'4 c.c. of the cyanide ; the average is, therefore, 30'35 c.c.
The difference amounts to only 0'05 per cent, of copper, which may be
allowed for in the final calculation.

When, however, larger quantities of ammoniacal salts are present
in the fluid to be assayed for copper, by means of cyanide, and
especially when •ammonic carbonate, sulphate, and worse still,
chloride are simultaneously present, these salts exert a very dis-
turbing influence.* The presence of lead in the copper solution
to be assayed has the effect of producing, on the addition of 10 c.c.
of normal ammonia, a milkiness with the blue tint ; but this does
not at all interfere with the estimation of the copper by means
of the cyanide, provided the lead be not in great excess ; and a
slight milkiness of the solution even promotes the visibility of the
approaching end of the operation.

Steinbeck purposely made some experiments to test this point,
and his results show that a moderate quantity of lead has no
influence.

Experiments were also carefully made to ascertain the influence
of zinc, the result of which showed that up to 5 per cent, of the
copper present, the zinc had no disturbing action; but a considerable
variation occurred as the percentage increased above that proportion.
Care must therefore always be taken in washing the spongy copper
precipitated from the ore solution by means of zinc.

The titration must always take place at ordinary temperatures,
since heating the ammoniacal solution while under titration to 40°
or 45° C. considerably reduces the quantity of cyanide required.

9. Estimation of Copper by Colour Titration.

This method can be adopted with very accurate results, as in the
case of iron, and is available for slags, poor cupreous pyrites,
waters, etc. (see Carnelly, C. N. xxxii. 308).

The reagent used is the same as in the case of iron, viz., potassic
ferrocyanide, which gives, a purple-brown colour with very dilute
solutions of copper. This reaction, however, is not so delicate as
it is with iron, for 1 part of the latter in 13,000,000 parts of water
can be detected by means of potassic ferrocyanide ; while 1 part
of copper in a neutral solution, containing ammonic nitrate, can
only be detected in 2,500,000 parts of water. Of the coloured
reactions which copper gives with different reagents, those with
sulphuretted hydrogen and potassic ferrocyanide are by far the
most delicate, both showing their respective colours in 2,500,000
parts of water.

* I have retained this technical process in its original form, notwithstanding the use
of ammonia, because it is systematic, and the results obtained by it are all comparable
among themselves. Of course soda or potash may be used in place of ammonia, if the
cyanide is standardized with them.

188 VOLUMETRIC ANALYSIS. § 58.

Of the two reagents sulphuretted hydrogen is the more delicate ;
but potassic ferrocyanide has a decided advantage over sulphuretted
hydrogen in the fact that lead, when not present in too large
quantity, does not interfere with the depth of colour obtained,
whereas to sulphuretted hydrogen it is, as is well known, very
sensitive.'"'

And though iron if present would, without special precaution
being taken, prevent the determination of copper by means of
ferrocyanide ; yet, by the method as described below, the amounts
of these metals contained together in a solution can be estimated
by this reagent.

Ammonic nitrate renders the reaction much more delicate ; other
salts, as ammonic chloride and potassic nitrate, have likewise the
same effect.

The method of analysis consists in the comparison of the
purple-brown colours produced by adding to a solution of potassic
ferrocyanide — first, a solution of copper of known strength ; and,
secondly, the solution in which the copper is to be determined.

The solutions and materials required are as follows : — -

(1) Standard Copper solution. — Prepared by dissolvingO'395gm.
of pure CuSO4, 5H20 in one liter of water. 1 c.c. = O'l m.gm. Cu.

(2) Solution of Ammonic nitrate. — Made by dissolving 100 gm.
of the salt in one liter of water.

(3) Potassic ferrocyanide solution. — 1 : 25.

(4) Two glass cylinders holding rather more than 150 c.c. each,
the point equivalent to that volume being marked on the glass.
They must both be of the same tint, and as colourless as possible.

A burette, graduated to y1^ c.c. for the copper solution; a 5 c.c.
pipette for the ammonic nitrate ; and a small tube to deliver the
ferrocyanide in drops.

Process : Five drops of the potassic ferrocyanide are placed in each
cylinder, and then a measured quantity of the neutral solution in which
the copper is to be determined is placed into one of them, and both filled
up to the mark with distilled water, 5 c.c. of the ammonic nitrate solution
added to each, and then the standard copper solution ran gradually into
the other till the colours in both cylinders are of the same depth, the
liquid being well stirred after each addition. The number of c.c. used are
then read off. Each c.c. corresponds to O'l m.gm. of copper, from which
the amount of copper in the solution in question can be calculated.

The solution in which the copper is to be estimated must be
neutral ; for if it contain free acid the latter lessens the depth of
colour, and changes it from a purple-brown to an earthy brown.
If it should be acid, it is rendered slightly alkaline with ammonia,
and the excess of the latter got rid of by boiling. The solution
must not be alkaline, as the brown coloration is soluble in ammonia

* In colour titrations of this character it is essential that the comparisons be made
under the same circumstances as to temperature, dilution, and admixture of foreign
substances, otherwise serious errors will arise.

§ 58. CYANOGEN. 189

and decomposed by potash or soda ; if it be alkaline from ammonia,
this is remedied as before by boiling it off; while free potash or
soda, should they be present, are, neutralized by an acid, and the
latter by ammonia,

Lead, when present in not too large quantity, has little or no
effect on the accuracy of the method. The precipitate obtained on
adding potassic ferrocyanide to a lead salt is white ; and this, except
when present in comparatively large quantity with respect to the
copper, does not interfere with the comparison of the colours.

When copper is to be estimated in a solution containing iron,
the following method is adopted : —

A few drops of nitric acid are added to the solution in order to oxidize the
iron, the liquid evaporated to a small bulk, and the iron precipitated by
ammonia. Even when very small quantities of iron are present, this can be
done easily and completely if there be only a very small quantity of fluid.
The precipitate of ferric oxide is then filtered off, washed once, dissolved in
nitric acid, and re-precipitated by ammonia, filtered and washed. The iron
precipitate is now free from copper, and in it the iron can be estimated by
dissolving in nitric acid, making the solution nearly neutral with .ammonia,
and determining the iron by the method in § 64.4. The filtrate from the
iron precipitate is boiled till the ammonia is completely driven off, and the
copper estimated in the solution so obtained as already described.

When the solution containing copper is too dilute to give any
coloration directly with ferrocyanide, a measured quantity of it
must be evaporated to a small bulk, and filtered if necessary;
.and if it contain iron, also treated as already described.

In the determination of copper and iron in water, for which the
method is specially applicable, a measured quantity is evaporated
to dryness with a few drops of nitric acid, ignited to get rid of any
organic matter that might colour the liquid, dissolved in a little
boiling water and a drop or two of nitric acid ; if it is not all
soluble it does not matter. Ammonia is next added to precipitate
the iron, the latter filtered off, washed, re-dissolved in nitric acid,
and again precipitated by ammonia, filtered off, and washed. The
filtrate is added to the one previously obtained, the iron estimated
in the precipitate, and the copper in the united filtrates.

CYANOGEN.

CIST-=26.

1 c.c. T^ silver solution=0'0052 gin.

Cyanogen.
=0-0054 gm.

Hydrocyanic acid.
=0;01302 gm.

Potassic cyanide.
„ yjj iodine solution=0'003255 gm.

Potassic cyanide.

190 VOLUMETRIC ANALYSIS.

1. By Standard Silver Solution (Lie big).

§ 59. THIS ready and accurate method of estimating cyanogen
in prnssic acid, alkaline cyanides,1 etc., was discovered by Liebig,
and is fully described in Ann. der Ghem. und Pliarm. Ixxvii. 102.
It is based on the fact, that when a solution of silver nitrate is
added to an alkaline solution containing cyanogen, with constant
stirring, no permanent precipitate of silver cyanide occurs until all
the cyanogen has combined with the alkali and the silver, to form
a soluble double salt (in the presence of potash, for example,
KCy, AgCy). If the slightest excess of silver, over and above the
quantity required to form this combination, be added, a permanent
precipitate of silver cyanide occurs, the double compound being
destroyed. If, therefore, the silver solution be of known strength,
the quantity of cyanogen present is easily found ; 1 eq. of silver
in this case being equal to 2 eq. cyanogen.

So fast is this double combination, that, when sodic chloride is
present, no permanent precipitate of silver chloride occurs, until
the quantity of silver necessary to form the compound is slightly
overstepped.

Siebold, however, has pointed out that this process, in the case
of free hydrocyanic acid, is liable to serious errors unless the
following precautions are observed : —

(«) The solution of sodic or potassic hydrate should be placed in the
beaker first, and the hydrocyanic acid added to it from a burette dipping
into the alkali. If, instead of this, the acid is placed in the beaker first,
and the alkaline hydrate added afterwards, there mny be a slight loss by
evaporation, which becomes appreciable whenever there is any delay in the
addition of the alkali.

(5) The mixture of hydrocyanic acid and alkali should be largely diluted
with water before the silver nitrate is added. The most suitable proportion
of water is from ten to twenty times the volume of the officinal or of
Scheele's acid. With such a degree of dilution, the final point of the-
reaction can be observed with greater precision.

(c) The amount of alkali used should be as exactly as possible that
required for the conversion of the hydrocyanic acid into alkaline cyanide.,
as an insufficiency or an excess both affect the accuracy of the result. It is
advisable to make first a rough estimation with excess of soda as a guide,
then finish with a solution as neutral as possible.

Caution. — In using the pipette for measuring hydrocyanic acid,
it is advisable to insert a plug of cotton wool, slightly moistened
with silver nitrate, into the upper end, so as to avoid the danger
of inhaling any of the acid ; otherwise it is decidedly preferable
to weigh it.

Example ivith Commercial Potassic Cyanide : The quantity of this sub-
stance necessary to be taken for analysis, so that each c.c. or dm. shall be
equal to 1 per cent, of the pure C3*auide. is 1'30 gm. or 13'0 grn. 13 grains,
therefore, of the commercial article were dissolved in water, no further alkali
being necessaiy, and 54 dm. yV silver required to produce the permanent
turbidity. The sample therefore contained 54 per cent, of real cyanide.

§ 59. CYANOGEN. 191

2. By Standard Mercuric Chloride (Hannay).

This convenient method is fully described by the author (/. C. S.
1878, 245), and is well adapted for the technical examination of
commercial cyanides, etc., giving good results in the presence of
cyanates, sulphocyanates, alkaline salts, and compounds of ammonia
and silver.

The standard solution of mercury is made by dissolving 13 '537
gm. HgCl2 in water, and diluting to a liter. Each c.c.=:0'00651 gm.
of potassic cyanide or 0*0026 gm. Cy.

Process : The cyanide is dissolved in water, and the beaker placed upon
black paper or velvet ; ammonia is then added in moderate quantity, and
the mercuric solution cautiously added with constant stirring until a bluish-
white opalescence is permanently produced. With pure substances the
reaction is very delicate, but not so accurate with impure mixtures occurring
in commerce.

3. By Iodine (Fordos and Gelis).

This process, which is principally applicable to alkaline cyanides,
depends on the fact, that when a solution of iodine is added to one
of potassic cyanide, the iodine loses its colour so long as any
imdecomposed cyanide remains. The reaction may be expressed
by the following formula : — -

Therefore, 2 eq. iodine represent 1 eq. cyanogen in combination; so
that 1 c.c. of -^ iodine expresses the half of To-Jo-o eq. cyanogen
or its compounds. The end of the reaction is known by the
yellow colour of the iodine solution becoming permanent.

Commercial cyanides are, however, generally contaminated with
caustic or monocarbonate alkalies, which would equally destroy
the colour of the iodine as the cyanide ; consequently these must
be converted into bicarbonates, best done by adding carbonic acid
water (ordinary soda water).

Example : 5 gm. of potassio cyanide were weighed and dissolved in 500 c.c.
water; then 10 c.c. (=0'1 gni. cyanide) taken with a pipette, diluted with
about i liter of water, 100 c.c. of soda water added, then T^ iodine delivered
from the burette until the solution possessed a slight but permanent yellow
colour; 25'5 c.c. were required, which multiplied by 0'003255 gave 0'08300
gm. instead of O'l gm., or 83 per cent, real cyanide. Sulphides must of
course be absent.

4. By ]-0 Silver and Chromate Indicator.

Yielhaber (Arch. PJtarm. [3] xiii. 408) has shown that weak
solutions of prussic acid, such as bitter-almond water, etc., may be
readily titrated by adding magnesic hydrate suspended in water
until alkaline, adding a drop or two of cliromate indicator, and
delivering in —$ silver until the red colour appears, as in

192 VOLUMETRIC ANALYSIS. § 59.

the case of titrating chlorides. 1 c.c. silver solution=0'0027
gm. HCy.

This method may be found serviceable in the examination of
opaque solutions of hydrocyanic acid, such as solutions of bitter-
almond oil, etc. ; but of course the absence of chlorine must be
insured, or, if present, the amount must be allowed for.

It is preferable to add the HCy solution to a mixture of
magnesia and chromate, then immediately titrate with silver.

5. Cyanides used in Gold Extraction.

All interesting series of papers on this subject have been
contributed by Glenn ell (G. N. Ixxvii. 227, and Eettel, idem
286, 298). The experiments carried out by these chemists are
far too voluminous to be reproduced here, but a short summary
of the results may be acceptable for the technical examination of
the original solutions and their nature, after partial decomposition
and admixture with zinc and other impurities which naturally
occur in the processes of gold extraction. The results of both
•chemists point to the fact that the estimation of cyanide in the
weak solutions used in the MacArthur-Forrest process is much
hampered by zinc double cyanide, by thiocyanates, also by ferro and
ferricyanides, together with organic matters which occur in the
liquors after leaching the ores. According to Glenn ell the presence
of ferrocyanides gives too high a result when the silver process of
Liebig is used, but is not of much consequence unless the cyanide
is relatively small as compared with the ferrocyanide ; with the
iodine process the interference of ferrocyanide is much less, and
•very fair technical results may be obtained in the presence of both
ferro and ferri salts by this process. The silver process appears to
be fairly serviceable where the quantity of ferrocyanide is not too
large ; the reddish precipitate which forms at first from the ferri salt
is soluble in the presence of excess of cyanide, and a definite end-
•reaction can be obtained. Thiocyanates render the silver process
useless, but do not interfere with the iodine process. Ammonic
carbonate interferes with the silver process unless potassic iodide is
added so as to produce silver iodide, which is insoluble in the
ammonia salt. Ferrocyanides, in the absence of other reducing
.agents, may be accurately estimated, as in § 60. 1 ; the presence of
•cyanides and ferricyanides does not seriously interfere. Ferri-
cyanides may be estimated as in § 60.2; ferrocyanides do not
seriously interfere, but cyanides render the results somewhat low.
These remarks apply to solutions not complicated by admixture of
zinc or other matters which naturally occur in the cyanide liquors
after they have been in contact with the ore. For the actual
methods which have been found useful in examining the usual
cyanide liquors the following processes, devised by Bettel, are
given, not as being absolutely correct, but sufficiently so for
technical purposes, and occupying little time in the working : —

§59. CYANOGEN. 193

It is necessary to state at the outset that the following remarks have
reference to the MacArthur-Forrest working solutions containing zinc,
an element which complicates the analysis in a truly surprising manner.
Before dealing with the analysis proper, attention is drawn to the peculiarities
of a solution of the double c}ranide of zinc and potassium, usually written
K2ZnCy4. As is stated in works on chemistry, this cyanide is alkaline to
indicators. Now here lies the peculiarity. To phenolphthalein the alkalinity,
as tested by T^ acid, is equal to 19' 5 parts of cyanide of potassium out of
a possible 130'2 parts. "With methyl orange as indicator, the whole of the
metallic cyanide may be decomposed by T\ acid, as under : —

K2ZnCy4+4HCl=ZnCl2+2KCl+4HCy.

On titration with silver nitrate solution the end-reaction is painfully indefinite.
If caustic alkali in excess (a few c.c. normal soda) be added to a known
quantity of potassic zinc cyanide solution together with a few drops of
potassic iodide, and standard silver solution added to opalescence, the reaction
will indicate sharply the total cyanogen present in the double cyanide even
in presence of ferrocyanides. If to a solution of potassic zinc cyanide
be added a small quantity of ferrocyanide of potassium, and the silver
solution added, the flocculent precipitate of what is supposed to be normal
zinc ferrocyanide (Zn2FeCy6) appears, the end-reaction is fairly sharp, and
indicates 19' 5 parts of potassic cyanide out of the actual molecular contents
of 130'2 KCy. If, however, an excess of ferrocyanide be present, the
flocculeut precipitate does not appear, but in its place one gets an opalescence
which speedily turns to a finely granular (sometimes slimy) precipitate of
potassic zinc ferrocyanide, K2Zn3Fe2Cy12. This introduces a personal equation
into the analysis of such a solution, for if the silver solution be added
rapidly the results are higher than if added drop by drop, as this ferro-
cyanide of zinc and potassium separates out slowly in dilute solutions
alkaline or neutral to litmus paper.

For the estimation of free hydrocyanic acid use is made of Sieb old's
ingenious method for estimating alkalies in carbonates and bicarbonates, by
reversing the process, adding bicarbonate of soda, free from carbonate, to
the solution to be titrated for hydrocyanic acid and free cyanide. This is
the one instance where hydrocyanic acid turns carbonic acid out of its
combinations, and as such is interesting.

2KHC03+AgN03+2HCy=KAgCy2+KN03+2C02+2H20.

The methods of analysis are as follows :—

1. Free Cyanide. — 50 c.c. of solution are taken and titrated with silver
nitrate to faint opalescence or first indication of a flocculeut precipitate.
This will indicate (if sufficient ferrocyanide be present to form a flocculent
precipitate of zinc ferrocyanide) the free cyanide, and cyanide equal to 7'9
per cent, of the potassic zinc cyanide present.

2. Hydrocyanic Acid.— To 50 c.c. of the solution add a solution of
alkaline bicarbonate, free from carbonate or excess of carbonic acid. Titrate
as for free cyanide. Deduct the first from the second result

=HCy 1 c.c. AgN03==:0-00829 °/0 HCy.

3. Double Cyanides: — Add excess of normal caustic soda to 50 c.c. of
solution and a few drops of a 10 per cent, solution of KI, titrate to opalescence
with AgNO3. This gives 1, 2, and 3. Deduct 1 and 2=K2ZnCy4 as KCy
less 7'9 per cent.

A correction is here introduced. The KCy found in 3 is calculated to
K2ZnCy4. Factor : KCy (as K2ZnCy4) x 0'9493=K?ZnCy4. Add to this
7'9 per cent, of total, or for every 92'1 parts of K2ZnCy4 add 7'9 parts.

194 VOLUMETRIC ANALYSIS. § 59.

If this fraction, calculated back to KCj, be deducted from 1, the true free
cyanide (calculated to KCy) is obtained.

4. Ferro cyanides and Thiocyanates. — In absence of organic matters
it is found that an acidified solution of a simple cyanide, such as KCy, or
a double cyanide (as K'-ZnCy4), i.e., solution of HCy, is not affected by
dilute permanganate. On the other hand, acidified solutions of femxryanides
and sulphocyanides are rapidly oxidized—the one to ferrocyanide, the other
to H2SO4+ilCy.

If, now, the ferroc}ranogen be removed as Prussian blue, by ferric chloride
in an acid solution, the filtrate will contain ferric and hydric thiocyanate,
both of which are oxidized by permanganate as if iron were not present ;
by deducting the smaller from the larger result, we get the permanganate
consumed in oxidizing ferrocyanide, the remainder equals the permanganate
consumed in oxidizing thiocyanate.

The method of titratiou is as follows (in presence of zinc) : — A burette
is filled with the c}ranide solution for analysis, and run into 10 or 20 c.c.
rjfo K2Mn2O8 strongly acidified with H2SO4 until colour is just discharged.
Result noted (a).

A solution of ferric sulphate or chloride is acidified with H2SO4 and
50 c.c. of the cyanide solution poured in. After shaking for about half
a minute, the Prussian blue is separated from the liquid by filtration, and
the precipitate and filter paper washed. The filtrate is next titrated Avith
T^T K2Mn208 (b).

Let c — c.c. permanganate required to oxidize ferrocyanide.

Then a—b = c.

(*) 1 c.c. y^- K2Mn2O8=0'0001618 gm. KCNS.

5. Oxidizable Org-anic Matter in Solution.— In treating spruit tail-
ings, or material containing decaying vegetable matter., the following method
is used for testing coloured solutions : —

Prepare a solution of a thiocyanate, so that 1 C.C.—T^ K2Mn2O8.

To 50 c.c. solution add sulphuric acid in excess, and then a large
excess of permanganate, y^. Keep at 60—70° C. for an hour. Then cool
and titrate back with the KCNS solution.

Result O consumed in oxidizing organic matter.
„ O „ „ K'FeCy6.

„ O „ „ KCNS.

After estimating KCNS and K4FeCy6, a simple calculation gives the
oxygen to oxidize organic matter. This result multiplied by 9 will give
approximately the amount of organic matter present.

In order to clarify such organically charged solutions, they are shaken
up with powdered quicklime and filtered ; the solution is then of a faint
straw colour, and is in a proper condition for analysis. In such clarified
solution the oxidizable organic matter is no longer present, and the
estimations are readily performed.

6. Alkalinity. — Potassic cyanide acts as caustic alkali, when neutralized
by an acid; the end-reaction, however, is influenced to some extent by
the hydrocyanic acid present, and is therefore not sharp. It is possible,
however, to estimate —

With phenolphtMeinas indicator.

}^™^1-™'*"- '"•
Ey T^- acid the K2O in ZnK2O2 ... With phenolphthalein as indicator.

§ 59. FERRO- AND FERRI-CYANIDES. 195

It will be necessary to point out the decompositions which result from
adding alkali, or a carbonate of an alkali, to a working solution containing
;zinc.

K2ZnCy4 + 4KHO=ZnK2O2 + 4KCy .
K2ZnCy4 + 4Na2CO3 + 2H2O=2KCy + 2NaCy + ZnNa2O2 + 4NaHCO3.

Bicarbonates have no action upon potassic or sodic zinc cyanide.
Potassic or sodic zinc oxide (in solution as hydrate) acts as an alkali
towards phenolphthalein and methyl orange.

ZnK2O2 + 4HC1 = 2KC1 + ZnCl2 + 2H2O .

Calcic and magnesic hydrates decompose the double salt of K2ZuCy4 to
some extent, but not completely, so that it is possible to find in one and the
same solution a considerable proportion of alkalinity towards phenolphthalein,
•due to calcic hydrate in presence of K2ZnCy4.

The total alkalinity as determined by T^ acid with methyl orange as
indicator gives, in addition to those before mentioned, the bicarbonates.
If to a solution containing sodic bicarbonate and potassic zinc cyanide be
added lime or lime and magnesia, the percentage of C3ranide will increase,
the zinc remaining in solution as zinc sodic oxide.

Clennell (C. N. Ixxi. 93) gives a method for the approximate estimation
of alkaline hydrates and carbonates in the presence of alkaline cyanides,
as follows : —

(1) Estimation of the cyanide by direct titration with silver.

(2) Estimation of the hydrate and half the carbonate of alkali on adding
phenolphthalein to the previous solution (after titration with silver) by
•^ hydrochloric acid.

(3) Estimation of the total alkali by direct titration, in another portion
of the solution, with T^ hydrochloric acid and methyl orange.

7. Ferricyanide Estimation. — This is effected by allowing sodium
amalgam to act for fifteen minutes on the solution in a narrow cylinder,
then estimating the ferrocyanide formed by permanganate in an acid
solution. Deduct from the results obtained the ferrocyauide and thiocyanate
previously found, 1 c.c. ^ permanganate^O'003293 gm. K6Fe2Cy12.

8. Sulphides. — It rarely happens that sulphides are present in a cyanide
solution ; if present, however, shake up with precipitated carbonate of lead,
filter, and titrate with T£-0- permanganate. The loss over the previous
estimation (of 'K4FeCy6KCNS, &c.) is due to elimination of sulphides.

1 c.c.'T£¥ K2Mn2O8=0'OOOl7 gm. H2S, or 0'00055 gm. K2S.

The hydrogen alone being oxidized by dilute permanganate in acid solution
where the permanganate is not first of all in excess.

9. Ammonia. — If sufficient silver nitrate be added to a solution (say
10 c.c.) to wholly precipitate the cyanogen compounds and a drop or two of
f HC1 be added, the Avhole made up to 100 c.c., and filtered ; then 10 c.c.
distilled with about 150 c.c. of ammonia free water and Nesslerized in the
usual way, the amount of ammonia may be ascertained.

FERRO- AND FERRI-CYANIDES.

Potassic Ferrocyanide.

Metallic iron 7 -541= Crystallized Potassic ferrocyanide.

Double iron salt x 1*077= „ „ „

o 2

196 VOLUMETRIC ANALYSIS. § 60.

1. Oxidation to Ferricyanide by Permanganate (De Ha en).

§ 60. THIS substance may be estimated by potassic permanga-
nate, which acts by converting it into red prussiate. The process
is easy of application, and the results accurate. A standard
solution of pure ferrocyanide should be used as the basis upon
which to work, but may, however, be dispensed with, if the operator
chooses to calculate the strength of his permanganate upon iron or its
compounds. If the permanganate is decinormal, there is of course
very little need for calculation (1 eq.=422 must be used as the
systematic number, and therefore 1 c.c. of ^5- permanganate is
equal to OO422 gm. of yellow prussiate). The standard solution
of pure ferrocyanide contains 20 gm. in the liter : each c.c. will
therefore contain 0'02 gm.

Process : 10 c.c. of the standard prussiate solution are put into a white
porcelain dish or beaker standing on white paper, and 250 c.c. or so of water
added; it is then acidified pretty strongly with sulphuric acid, and the
permanganate delivered from the burette until a pure uranium yellow colour
appears ; it is then cautiously added until the faintest pink tinge occurs.

Ferrocyanides in Alkali waste. — Acidulate the solution with
HC1, and add strong bleaching powder solution with agitation until
a drop of the liquid gives no blue colour with ferric indicator. The
liquid is then titrated with a solution of cupric sulphate, standardized
on pure potassic ferrocyanide, using dilute ferrous sulphate as
indicator; as soon as no more blue or grey colour occurs, but
a faint reddening, the process is ended.

Ferrocyanides in G-as Liquor. — 250 c.c. are evaporated to dryness^.
dissolved in water, the solution filtered, and the ferrocyanides
precipitated as Prussian blue by ferric chloride. The blue is
filtered off, wTashed, and decomposed with caustic soda. The ferric
hydroxide so obtained is, after filtering, washing, and dissolving in
dilute H2S04 reduced with zinc, and titrated with permanganate..
Fe x 5-07-=(NH4)4FeCy6.

POTASSIC FERRICYANIDE.

K6Cy12Fe2=658.

Metallic iron x 5 '88 = Potassic ferricyanide.

Double iron salt x 1*68 = ,, „

TNo- Thiosulphate x 0-0329 „ „

2. By Iodine and Thiosulphate.

This salt can be estimated either by reduction to ferrocyanide
and titratioii with permanganate or bichromate as above, or by
Lenssen's method, which is based upon the fact, that when
potassic iodide and ferricyanide are mixed with tolerably concen-
trated hydrochloric acid, iodine is set free.

§ 60. THIOCYANATES. 197

K6jVCy12 + 2KI=2K*Cy6Fe + 12

the quantity of which can be estimated by -^ thiosulphate and
starch. This method does not, however, give the most satis-
factory results, owing to the variation produced by working
with dilute or concentrated solutions. C. Mohr's modification
(see Zinc, § 81) is, however, more accurate, and is as follows : —
The ferricyanide is dissolved in a convenient quantity of water,
potassic iodide in crystals added, together with hydrochloric acid
in tolerable quantity, then a solution of pure zinc sulphate in
excess ; after standing a few minutes to allow the decomposition
to perfect itself, the excess of acid is neutralized by sodic carbonate,
.so that the latter slightly predominates.

At this stage all the zinc ferricyanide first formed is converted
into the ferrocyanide of that metal, and an equivalent quantity of
iodine set free, which can at once be titrated with T^ thiosulphate
and starch, and with very great exactness. 1 c.c. ~ thiosalphate
= 0'0329 gm. potassic ferricyanide.

The mean of five determinations made by Mohr gave 10O21
instead of 100.

Another method consists in boiling with excess of potash, then
cooling, and adding H202 till the colour is yellow. The excess of
the peroxide is then boiled off, H2S04 added, and titrated with
permanganate.

3. Reduction of Ferri- to Ferro-cyanide.

This process is, of course, necessary when the determination by
permanganate has to be made, and is best .effected by boiling the
weighed ferricyanide with an excess of potash or soda, and adding
small quantities of concentrated solution of ferrous sulphate until
the precipitate which occurs possesses a blackish colour (signifying
that the magnetic oxide is formed). The solution is then diluted
to a convenient quantity, say 300 c.c., well mixed and filtered
through a dry filter; 50 or 100 c.c. may then be taken, sulphuric
acid added, and titrated with permanganate as before described.

Kassner suggests the use of sodic peroxide for the reduction
of ferri- to ferrocyanide (Arch. Pharm. ccxxxii. 226) as being
rapid and complete. About 0'5 gm. in 100 c.c. water requires
about. 0*06 gm. -of the peroxide ; the mixture is heated till all
effervescence is over, acidified with sulphuric acid, cooled, and
titrated with permanganate in the usual way.

THIOCYANATES.

For the estimation of thiocyanic acid in combination with the
alkaline or earthy bases, Barnes and Liddle (/. S. C. I. ii. 122)
have devised a method which is easy of application, and gives good
technical results. It is not, however, available for gas liquors.

198 VOLUMETRIC ANALYSIS. § 61.

The method depends upon the fact that when a solution of
a cupric salt is added to a solution of a thiocyanate in presence
of a reducing agent, as sodic bisulphite, the insoluble cuprous salt
of thiocyanic acid is precipitated, the end of the reaction being
ascertained by a drop of the solution in the flask giving a brown
colouration when brought in contact with a drop of ferrocyanide,.
The following reactions take place : —

2CuS04 + 2KSCX + Xa2S03 + H20 =

and

2CuS04 + Ba(SC^sT)2 + !STa2S03 + H20 =
Cu2S2C2JST2 + BaSO4 + 2

The following solutions are required : —

1. A standard solution of Cupric sulphate containing 6 '2375
gm. per liter, 1 c.c. of which is equivalent to 0 '00 145 gm. SC^N".

2. A solution of Sodic bisulphite of specific gravity 1*3.

3. A solution of Potassic ferrocyanide (1 : 20).

Process: About 3 gm. of the sample are weighed from a stoppered
tube into a liter flask, dissolved in water, and made up to the mark. After
well mixing, 25 c.c. are measured into a flask, about 3 c.c. of the bisulphite
added, and the whole boiled. Whilst this is heating a burette is filled with
the copper solution, and a white porcelain slab is dotted over with the
ferrocyanide. When the liquid in the flask has reached the boiling point,
20 c.c. of the copper solution are run in, well shaken, the precipitate allowed
to settle for about a minute, a drop is taken out by means of a glass rod, and
brought in contact with a drop of ferrocyanide, and should no brown
colouration appear, more of the copper solution is run in, say 1 c.c. at
a time, and again tested. This is continued until a drop gives an immediate
colour. By this means an approximation to the truth is obtained. It will
be observed, during a titration, that the mixed drops, after standing for
a minute, or even less, produce a brown tint. It is of the utmost importance
that the colouration be immediate.

A second 25 c.c. of the thiocyanate solution are run into a clean flask,
the bisulphite added, and boiled as before.

Suppose that in the first experiment, after an addition of 27 c.c. of copper
solution, no colour was formed with ferrocyanide, but that 28 c.c. gave an
immediate colour ; then in the second experiment 27 c.c. are run in at once,
and the liquid is again tested, when no colour should appear. The copper
solution is then run in drop by drop until there is a slight excess of copper,
as proved by the delicate reaction with the ferrocyanide. The second
experiment is thus rendered more exact by the experience gained in the first.

GOLD.

Au- 196-5.
1 c.c. or 1 dm. normal oxalic acid=0'0655 gm. or 0'655 grn. Gold.

§ 61. THE technical assay of gold for coining purposes is
invariably performed by cupellation. Terchloride of gold is,
however, largely used in photography and electro-gilding, and

§ 62. IODINE. 199

therefore it may be necessary sometimes to ascertain the strength
of a solution of the chloride, or its value as it occurs in commerce.

If to a solution of gold in the form of chloride (free from nitric
acid) an excess of oxalic acid be added, in the course of from
eighteen to twenty-four hours all the gold will be precipitated in
the metallic form, while the corresponding quantity of oxalic acid
has been dissipated in the form of carbonic acid ; if, therefore, the
quantity of oxalic acid originally added be known, and the excess,
after complete precipitation of the gold, be found by permanganate,
the amount of gold will be obtained.

Example : A 15-grain tube of the chloride of gold of commerce was
dissolved in water, and the solution made up to 300 decems. 20 dm. of
normal oxalic acid were then added, and the flask set aside for twenty-four
hours in a warm, dark place ; at the end of that time the gold had settled,
and the supernatant liquid was clear and colourless. 100 dm. were taken
out with a pipette, and titrated with T^ permanganate, of which 25 dm. were
required ; this multiplied by 3 gives 75 dm.=7'5 dm. normal oxalic acid,
which deducted from the 20 dm. originally added, left 12'5 dm. ; this
multiplied by ^ the equivalent of gold (1 eq. of gold chloride decomposing
3 eq. oxalic acid)=0'655 gave 8'195 grn. metallic gold, or multiplied by 101
(=1 eq. AuCl3) gave 12'625 grn. ; the result was 84 per cent, of chloride of
gold instead of 100. A more rapid method consists in boiling the gold
solution with an excess of standard solution of potassic oxalate containing
8'3 gm. of the pure salt per liter, and titrating back with a permanganate
solution which has the same working strength as the oxalate. Each c.c.
of oxalate solution decomposed represents 0'00855 gm. Au.

IODINE.

1=127-0.
1. By Distillation.

in potassic iodide, and titration with starch and -—- thiosulphate,
as described in § 38.*

Combined iodine in haloid salts, such as the alkaline iodides,
must be subjected to distillation with hydrochloric acid, and some
other substance capable of assisting in the liberation of free iodine,
which is received into a solution of potassic iodide, and then
titrated with ~ thiosulphate in the ordinary way. Such a
substance presents itself best in the form of ferric oxide, or some
of its combinations ; if, therefore, hydriodic acid, or what amounts
to the same thing, an alkaline iodide, be mixed with an excess of

62. FREE iodine is of course very readily estimated by solution

* I would here again impress upon the operator's notice that it is of great importance
to ascertain the exact strength of the standard solutions of iodine and thiosulphate as
compared with each other. Both solutions constantly undergo an amount of change
depending upon the temperature at which they are kept, their exposure to light, etc.,
and therefore it is absolutely necessary, to ensure exactness in the multifarious analyses
which can be made by the aid of these two reagents, to verify their agreement by
weighing a small portion of pure dry iodine at intervals, and titrating it with the
standard thiosulphate, or checking the iodine with baric or sodic thiosulphate of
known purity.

OF THE

UNIVERSITY

CAI icrikBNliA*

200 VOLUMETRIC ANALYSIS. § 62.

ferric oxide or chloride, and distilled in the apparatus shown in
fig. 37 or 38, the following reaction occurs : —

Fe203 + 2IH=2FeO + H20 + 12.

The best form in which to use the ferric oxide is iron alum.

The iodide and iron alum being brought into the little flask (fig. 38),
sulphuric acid of about 1 '3 sp. gr. is added, and the cork carrying
the still tube inserted. This tube is not carried into the solution
of potassic iodide in this special case, but within a short distance
of it ; and the end must not be drawn out to a fine point, as there
represented, but cut off straight. The reason for this arrangement
is, that it is not a chlorine distillation for the purpose of setting
iodine free from the iodide solution, as is usually the case, but an
actual distillation of iodine, which would speedily choke up the
narrow point of the tube, and so prevent the further progress
of the operation,

As the distillation goes on, the steam washes the condensed
iodine out of the tube into the solution of iodide, which must be
present in sufficient quantity to absorb it all. When no more
violet vapours are to be seen in the flask, the operation is ended ;
but to make sure, it is well to empty the solution of iodine out
of the condensing tube into a beaker, and put a little fresh iodide
solution with starch in, then heat the flask again ; the slightest
traces of iodine may then be discovered by the occurrence of the
blue colour when cooled. In case this occurs the distillation is
continued a little while, then both liquids mixed, and titrated
with j~ thiosulphate as usual.

It has been previously stated that the rubber joints to the
special apparatus of Fresenius, Bunsen, or Mohr for iodine
distillations are objectionable. Topf avoids this by fitting his
apparatus together, so that although rubber is used, the reagents
do not come in contact with it (Z. a. C. xxvi. 293).

Another form of apparatus designed by Stortenbeker (Z. a. C.
xxix. 273) is shown in fig. 41, in which rubber joints are entirely
dispensed with, and glass connections used. The connection
between the distilling tube and the absorbing apparatus is a water
joint, the tube resting in a socket kept wet with water, the
chloride of calcium tube is filled with glass pearls, moistened
with concentrated solution of potassic iodide, and the connection
with the absorbing apparatus is ground in like an ordinary stopper.
The absorbing bulbs are immersed in water to the middle of the
bulbs, and the iodide solution filled to the lower end of them.

Ferric chloride may be used instead of the iron alum, but it
must be free from nitric acid or active chlorine (best prepared
from dry Fe203 and HC1).

The iodides of silver, mercury, and copper cannot be accurately
analyzed in this way, but must be specially treated. They should
be dissolved in the least possible quantity of sodic thiosulphate

§ 62. IODINE. 201

solution, and precipitated boiling with sodic sulphide, then filtered ;
the nitrate contains the whole of the iodine free from metal. The
nitrate is evaporated to dryness and ignited, then dissolved in
water, and distilled with a good excess of ferric salt (Mensel
Z. a. C. xii. 137).

2. Mixtures of Iodides, Bromides, and Chlorides.

Don a th (Z. a. C. xix. 19) has shown that iodine may be
accurately estimated by distillation in the presence of other halogen
salts, by means of a solution containing about 2 to 3 per cent, of
chromic acid, free from sulphuric acid.

In the case of iodides and chlorides together the action is
perfectly regular, and the whole of the iodine may be received into
potassic iodide without any interference from the chlorine.

Fig. 41.

In the case of bromides being present, the chromic solution must
be rather more dilute, and the distillation must not be continued
more than two or three minutes after ebullition has commenced,
otherwise a small amount of bromide is decomposed.

The reaction in the case of potassic iodide may be expressed
thus :

6KI + 8Cr03 = I6 + Cr203 + 3K2OW.

The distillation may be made in Mohr's appnratus (fig. 38),
using about 50 c.c. of chromic solution for about 0'3 gm. I.

The titration is made with thiosulphate in the usual way.

A much less troublesome method of estimating iodine in the
presence of bromides or chlorides has been worked out by Cook
(/. C. S. 1885, 471), and depends on the fact that hydrogen
peroxide liberates iodine completely from an alkaline base in the

202 VOLUMETRIC ANALYSIS. § 62.

presence of excess of acetic acid, while neither bromine nor
chlorine are affected.

Hydrogen peroxide alone will only partially liberate iodine from
potassic iodide, but with excess of a weak organic acid to combine
with the alkaline hydroxide, the liberation is complete. Strong
mineral acids must not be used, or bromine and chlorine, if present,
would also be set free.

Process : The solution is strongly acidified with acetic acid, and sufficient
hydrogen peroxide added to liberate the .iodine (5 c.c. will suffice for 1 gm.
KI). The mixture is allowed to stand from half an hour to an hour; the
whole of the iodine separates, some being in the solid state if the quantity
is considerable. Chloroform is now added in sufficient volume to dissolve
the iodine, the solution syphoned off, and the globule repeatedly washed
with small quantities of water to remove excess of peroxide, then titrated
with thiosulphate, with or without starch, in the usual way. If the
peroxide is not completely removed by washing, it will decompose the sodic
iodide produced in the titration, and so liberate traces of iodine.

The results obtained by Cook in mixtures of bromides, iodides,
and chlorides, were about 99 per cent, of the iodine present.

Gooch and Browning (Ainer. Jour. Science xxxix. March,
1890, also C. N. Ixi. 279) publish a method of estimating iodine
in halogen salts of the alkalies which gives excellent results, and
which is based on the fact that arsenic acid in strongly acid solution
liberates iodine, becoming itself reduced to arsenious acid, according
to the equation

IPAsO4 + 2HI = HMsO3 + H20 + 21.

A very careful series of experiments are detailed in the original
paper, the outcome of the whole- being summarized in the following
process : — •

Process : The substance (which should not contain of chloride more
than an amount corresponding to 0'5 gm. of sodic chloride, nor of bromide
more than corresponds to 0'5 gm. of potassic bromide, nor of iodide much
more than the equivalent of 0'5 gm. of potassic iodide) is dissolved in water
in an Erlenmeyer beaker of 300 c.c. capacity, and to the solution are
added 2 gm. of potassic binarseniate dissolved in water, and 20 c.c. of a
mixture of sulphuric acid and water in equal volumes, and enough water to
increase the total volume to 100 c.c. or a little more. A platinum spiral is
introduced, a trap made of a straight two-bulb drying tube, cut off short, is
hung with the larger end downward in the neck of the flask, and the liquid
is boiled until the level reaches a mark put upon the flask to indicate a
volume of 35 c.c. Great care should be taken not to press the concentration
be}*ond this point on account of the double danger of losing arsenious
chloride and setting up reduction of the arseniate by the bromide. On the
other hand, though 35 c.c. is the ideal volume to be attained, failure to-
concentrate below 40 c.c. introduces no appreciable error. The liquid
remaining is cooled and nearly neutralized by sodic hydrate (ammonia is not
equally good), neutralization is completed by potassic bicarbonate, an excess
of 20 c.c. of the saturated solution of the latter is added, and the arsenious
oxide in solution is titrated by standard iodine in the presence of starch.

With ordinary care the method is rapid, reliable, and easily

§ 62. IODINE. 203

executed, and the error is small. In analyses requiring extreme
accuracy, all but accidental errors may be eliminated from the
results by applying the corrections indicated.

The indicated corrections are based on a long series of ex-
periments, which cannot well be given here, but the results may
be stated shortly as follows : —

When no chloride or bromide is present the iodine may be
estimated with a mean error of 0*2 m.gm. in 0*5 gm. or so of the
alkaline iodide. When sodic chloride is present there is a slight
deficiency in iodine, which is proportional to the amount of iodide
decomposed. For about 0*56 gm. of potassic iodide and 0*5 gm.
of sodic chloride the deficiency in iodine amounted to 0*0011 gm.
When the iodide is decreased, say to one-tenth or less, the deficiency
falls to 0*0002 gm. The presence of potassic bromide liberates
traces of bromine, and consequently increases the AsO3, and gives
apparent excess of iodine, the mean error being 0*0008 gm. for
0*5 gm. of bromide.

The simultaneous action of the chloride and bromide tends of
course to neutralize the error due to each. Thus, in a mixture
weighing about 1*5 gm. and consisting of sodic chloride, potassic
bromide, and potassic iodide in equal parts, the mean error amounts
to -0*0003 gm. The largest error in the series is +0*0016 gm.,
when the bromide was at its maximum, and no chloride was
present; and the next largest was - 0*0013 gm., when the chloride
was at its maximum and no bromide was present.

From a series of experiments detailed in the original paper, it
was deduced that the amount of iodine to be added, in each case,
may be obtained by multiplying the product of the weights in
grams of sodic chloride and potassic iodide by the constant 0*004 ;
and the amount to be subtracted, by multiplying the weight in
grams of potassic bromide by 0*0016; but in order to make use
of these corrections, the approximate amounts of these salts must
be known.

3. Titration with -j^ Silver and Thiocyanate.

The thiocyanate and silver solutions are described in § 43.

The iodide is dissolved in 300 or 400 times its weight of water
in a well-stoppered flask, and y^r silver delivered in from the burette
with constant shaking until the precipitate coagulates, showing
that silver is in excess. Ferric indicator and nitric acid are then
added in proper proportion, and the excess of silver estimated
by thiocyanate as described in § 43.

4. Oxidation of combined Iodine toy Chlorine (Golfier Besseyre
and D u p r e) .

This wonderfully sharp method of estimating iodine depend3
upon its conversion into iodic acid by free chlorine. When a

204 VOLUMETRIC ANALYSIS. § 62.

solution of potassic iodide is treated with successive quantities of
chlorine water, first iodine is liberated, then chloride of iodine
(IC1) formed. If starch, chloroform, benzole, or -bisulphide of
carbon be added, the first will be turned blue, while any of the
others will be coloured intense violet. A further addition of chlorine,
in sufficient quantity, produces pentachloride of iodine (IC15), or
rather, as water is present, iodic acid (I03H). No colouration of
the above substances is produced by these compounds, and the
accuracy with which the reaction takes place has been made use of
byGolfier Besseyre and Dupre, independently of each other,
for the purpose of estimating iodine. The former suggested the use
of starch, the latter chloroform or benzole, with very dilute chlorine
water. Dupre 's method is preferable on many accounts.

Example : 30 c.c. of weak chlorine water were put into a beaker with
potassic iodide and starch, and then titrated with ^ thiosulphate, of which
17 c.c. were required.

10 c.c. of solution of potassic iodide containing O'OIO gm. of iodine were
put into a stoppered bottle, chloroform added, and the same chlorine water as
above delivered in from the burette, with constant shaking, until the red
colour of the chloroform had disappeared ; the quantity used was 85'8 c.c.
The excess of chlorine was then ascertained by adding sodic bicarbonate,
potassic iodide, and starch. A slight blue colour occurred ; this was removed
by T£g- thiosulphate, of which 1*2 c.c. was used. Now, as 30 c.c. of the
chlorine solution required 17 c.c., the 85'8 c.c. required 48'62 c.c. of thio-
sulphate. From this, however, must be deducted the 1*2 c.c. in excess,
leaving 47'42 c.c. T£77=4'742 c.c. of r^ solution, which multiplied by 0'00211,
the one-sixth of Twinr eQ- (\ e(l- °f iodic acid liberating 6 eq. iodine), gave
0'010056 gin. iodine instead of O'Ol gm.

Mohr suggests a modification of this method, which dispenses
with the use of chloroform, or other similar agent.

The weighed iodine compound is brought into a stoppered flask, and
chlorine water delivered from a large burette until all yellow colour has
disappeared. A drop of the mixture brought in contact with a drop of
starch must produce no blue colour ; sodic bicarbonate is then added till
the mixture is neutral or slightly alkaline, together with potassic iodide
and starch ; the blue colour is then removed by f^ thiosulphate. The
strength of the chlorine water being known, the calculation presents no
difficulty.

Mohr obtained by this means 0*010108 gm. iodine, instead of
1-01 gm.

5. Oxidation by Permanganate (Reinig-e).

This process for estimating iodine in presence of bromides and
chlorides gives satisfactory results.

When potassic iodide and permanganate are mixed, the rose
colour of the latter disappears, a brown precipitate of manganic
peroxide results, and free potash with potassic iodide remains in.
solution. 1 eq. I=l27 reacts on 1 eq. K2Mn2Os==316, thus—

KI + K2Mn208==KIO:5 + K20 + 2Mn02.

§ 62. IODINE. 205

Heat accelerates the reaction, and it is advisable, especially with
weak solutions, to add a small quantity of potassic carbonate to
increase the alkalinity. Xo organic matter must be present.

The permanganate and thiosulphate solutions required in the
process may conveniently be of T^- strength, but their reaction upon
each other must be definitely fixed by experiment as follows : —
2 c.c. of permanganate solution are freely diluted with water, a few
drops of sodic carbonate added, and the thiosulphate added in very
small portions until the rose colour is just discharged. The slight
turbidity produced by .the precipitation of hydrated manganic
oxide need not interfere with the observation of the exact point.

Process : The iodine compound being dissolved in water, and always
existing only in combination with alkaline or earthy bases, is heated to
gentle boiling, rendered alkaline with sodic or potassic carbonate, and
permanganate added till in distinct excess, best known by removing the
liquid from the fire for a minute, when the precipitate will subside, leaving-
the upper liquid rose-coloured; the whole may then be poured into a 500-c.c.
flask, cooled, diluted to the mark, and 100 c.c. taken out for titration with
thiosulphate. The amount so used, being multiplied by 5, will give the
proportion required for the whole liquid, whence can be calculated the
amount of iodine. To prove the accuracy of the process in a mixture of
iodides, bromides, and chlorides, with excess of alkali, the following experi-
ment was made. 7 gm. commercial potassic bromide, the same of sodic
chloride, with 1 gm. each of potassic hydrate and carbonate, were dissolved
in a convenient quantity of water, and heated to boiling ; permanganate was
then added cautiously to destroy the traces of iodine and other impurities
affecting the permanganate so long as decolouration took place; the slightest
excess showed a green colour (manganate). To the mixture was then added
0'1246 gm. pure iodine, and the titration continued as described : the result
was 0'125 gm. I.

With systematic solutions of permanganate and thiosulphate-

the calculation is as follows : —

1 c.c. solution=0-0127 m. I.

6. By Nitrous Acid and Carbon Bisulphide (Fresenius).
This process requires the following standard solutions : —

(a) Potassic iodide, about 5 gm. per liter.

(b) Sodic thiosulphate, ^V normal, 12;4 gm. per liter, or there-
about.

(d) Pure Carbon bisulphide.

(e) Solution of Sodic bicarbonate, made by dissolving 5 gm. of
the salt in 1 liter of water, and adding 1 c.c. of hydrochloric acid.

The strength of the sodic thiosulphate in relation to iodine is
first ascertained by placing 50 c.c. of the iodide solution into
a 500 c.c. stoppered flask, then about 150 c.c. water, 20 c.c.

206 VOLUMETRIC ANALYSIS. § 63.

carbon bisulphide, then dilute sulphuric acid, and lastly, 10 drops
of the nitrous solution. The stopper is then replaced, and the
whole well shaken, set aside to allow the carbon liquid to settle,
and the supernatant liquid poured into another clean flask. The
carbon bisulphide is then treated three or four times successively
with water in the same way till the free acid is mostly removed,
the washings being all mixed in one flask ; 10 c.c. of bisulphide
are then added to the washings, well shaken, and if at all coloured,
the same process of washing is carried on. Finally, the two
quantities of bisulphide are brought upon a moistened filter,
washed till free from acid, a hole made in the filter, and the
bisulphide which now contains all the iodine in solution allowed
to run into a clean small flask, 30 c.c, of the sodic bicarbonate
solution added, then brought under the thiosulphate burette, and
the solution allowed to flow into the mixture while shaking until
the violet colour is entirely discharged. The quantity so used
represents the weight of iodine contained in 50 c.c. of the standard
potassic iodide, and may be used on that basis to ascertain any
unknown weight contained in a similar solution.

When very small quantities of iodine are to be titrated, weaker
solutions and smaller vessels may be used.

7. By ^5- Silver Solution and Starch Iodide (Pisani).

The details of this process are given under the head of silver
assay (§ 73.2), and are of course simply a reversal of the method
there given. This method is exceedingly serviceable for estimating
small quantities of combined .iodine in the presence of chlorides
and bromides, inasmuch as the silver solution does not react upon
these bodies until the blue colour is destroyed.

IRON.

Fe = 56.
Factors.

1 c.c. ~ permanganate, bichromate,

or thiosulphate = 0-0056 Fe

= 0-0072 FeO
= 0-0080 FeW

ESTIMATION IN THE FERROUS STATE.

1. Verification of the standard solutions of Permanganate or

Bichromate.

§ 63. THE estimation of iron in the ferrous state has already
been incidentally described in §§ 34, 35, and 37. The present
and following sections are an amplification of the methods there
given, as applied more distinctly to ores and products of iron
manufacture ; but before applying the permanganate or bichromate

§ 63. IRON. 207

process to these substances, and since many operators prefer, with
reason, to standardize such solutions upon metallic iron, especially
for use in iron analysis, the following method is given as the
Lest : —

A piece of soft iron wire, known as flower wire, is well cleaned with
scouring paper, and about 1 gram accurately weighed ; this is placed into
a, 250 c.c. boiling flask a, and 100 c.c. of dilute pure sulphuric acid (1 part
concentrated acid to 5 of water) poured over it; about a gram of sodic
carbonate in crystals is then added, and the apparatus fixed together as
in fig. 42, the pinch-cock remaining open. The flask a is closed by a tight-
fitting india-rubber stopper, through which is passed the bent tube. The
flask c contains 20 or 30 c.c. of pure distilled water; the flask a being
supported over a lamp is gently heated to boiling, and kept at this
temperature until all the iron is dissolved; meanwhile about 300 c.c. of
distilled water are boiled in a separate vessel to remove all air, and allowed to
cool. As soon as the iron is dissolved, the lamp is removed, and the pinch-
cock closed ; when cooled somewhat, the pinch-cock is opened, and the wash
water suffered to flow back together with the boiled water, which is added
to it until the flask is filled nearly to the mark. The apparatus is then
disconnected, and the flask a securely corked with a solid rubber cork, and
suffered to cool to the temperature of the room. Finally, the flask is filled
exactly to the mark with the boiled water, and the whole well shaken and
mixed. When the small portion of uudissolved carbon has subsided,
SO c.c., equal to i the weight of iron taken, may be removed with the pipette
for titration with the permanganate or bichromate.

In the case of permanganate the 50 c.c. are freely diluted with freshly
boiled and cooled distilled water, and the standard solution cautiously added
from a tap burette, divided into TV c.c., until the rose colour is faintly
perceived.

In the case of bichromate the solution should be less diluted, and the
titration conducted precisely as in § 37.

The amount of pure iron contained in the portion weighed for titration is
found by the co-efficient 0'996, and from this is calculated the wrorking
.strength of the oxidizing solution (see p. 122.)

Pig. 42.

Instead of the two flasks, many operators use a single flask, fitted
^vith caoutchouc stopper, through which a straight glass tube is
passed, fitted with an india-rubber slit valve (known as Bunsen's
valve), which allows gas or vapour to pass out, but closes by
atmospheric pressure when the evolution ceases. Another
arrangement is described on p. 122.

208 VOLUMETRIC ANALYSIS. § 6£

A large number of technical operators do not trouble themselves
to arrange any apparatus of the kind described, but simply dissolve
a weighed quantity of wire of known ferrous contents in a conical
beaker covered with a clock glass. If kept from draughts of cold
air while dissolving so as to avoid convection, it is said that
practically no oxidation takes place.

The double iron salt (p. 122) is a most convenient material for
adjusting standard solutions, but it must be most carefully made
from pure materials, dried perfectly in the granular form, and kept
from the light in small dry bottles, well closed. In this state it
will keep for years unchanged, and only needs immediate solution
in dilute H2S04 for use. Even in the case of the salt not being
strictly free from ferric oxide, due to faulty preparation, if it be
once thoroughly dried, and kept as above described, its actual
ferrous strength may be found by comparison with metallic iron,
and a factor found for weighing it in system.

It should be borne in mind that ferrous compounds are much
more stable in sulphuric than in hydrochloric acid solution, and
whenever possible, sulphuric acid should be used as the solvent.
When hydrochloric acid must be used, manganous or magnesia
sulphate should be added unless the solution is very dilute.

2. Reduction of Ferric Compounds to the Ferrous State.

This may be accomplished by metallic zinc OP magnesium, for use with
permanganate, or by stannous chloride or an alkaline sulphite for bichromate
solution. The magnesium method is elegant and rapid but costty. In the
case of zinc being used, the metal must either be free from iron, or if it
contain any, the exact quantity must be known and allowed for ; and further,
the pieces of zinc used must be entirely dissolved before the solution is-
titrated.* The solution to be reduced by zinc should not contain more than
0'15 gm. Fe. per 250 c.c., and for this quantity about 10 gin. of Zn. and
25 c.c. H2SO4 are advisable ; when the zinc is all dissolved, the whole
should be boiled with exclusion of air, then cooled rapidly before titration
with the permanganate. In the case of stannous chloride the solution must
be clear, and is best made to contain 10 to 15 gm. per liter, as directed
in § 37.2. The point of exact reduction in the boiling hot and somewhat
concentrated acid liquid may be known very closely by the discharge of
colour in the ferric solution : but may be made sure by the use of a saturated
aqueous solution of mercuric chloride as mentioned p. 127. Some operators
use a few drops of solution of platinic chloride in addition to the mercury.

It is exceedingly difficult to hit the exact point of reduction so-
that there shall be neither excess of tin nor unreduced iron, and

* Many operators now use amalgamated zinc in conjunction with platinum foil for
the reduction, but a practical difficulty occurs from the platinum becoming also
amalgamated through contact with the zinc and stopping the action. Beebe
(C. N. liii. 269) suggests the following convenient arrangement : — A strip of thin
platinum foil, 1 in. square, is perforated with pin holes all over, then bent into
a U form, and the ends connected with platinum wire so as to form a basket. In this
is placed a piece of amalgamated zinc, and the whole suspended by a stout platinum
wire in the reducing flask. When lowered into the solution, another strip of platinum
foil, 2 in. square, is dropped in and leaned against the wire carrying the basket : a very
free evolution of hydrogen is then obtained from the foil. When the reduction-
is complete, the basket is lifted out and well washed into the beaker containing the
liquid to be titrated.

§ 63. IRON. 209

technical iron analysts now almost universally use mercuric chloride
as a precaution against excess of tin solution. The general method
of procedure is to dissolve the material in diluted hydrochloric acid
(1 acid 2 water) in a conical beaker moderately heated over a rose
burner; when solution is complete the sides of the vessel are
washed down with hot water, the liquid brought to gentle boiling,
and strong tin solution added from a dropping bottle until the
colour of the iron solution is nearly discharged, a dilute tin
solution is then dropped in until all colour has disappeared, and
there is a decided slight excess of tin. Cold air-free water is then
washed over the sides of the beaker, the vessel covered with
a clock-glass placed in a bowl of cold water and allowed to cool,
an excess of the mercuric solution is then added, and the
titratioii with bichromate is at once completed in the usual way.

Some technical operators prefer to use sodic sulphite or ammonic
bisulphite for the reduction. In the case of using the sodic
sulphite the solution of iron must not be too acid and should
be dilute, say a volume of half a liter for J gm. of Fe, the
sulphite is added and the flask gently heated till the liquid
is colourless. It is then boiled briskly till all SO2 is dissipated,
when cooled it is ready for titration with bichromate. In the case
of ores containing titanium it is preferable to avoid the use of zinc
for reduction, as it reduces also more or less the titanium ; alkaline
sulphite does not.

The ammonic bisulphite is used as follows : — (Atkinson C. N. xlvi. 217).
To the acid solution of the ore or metal, diluted and filtered, ammonia
is added until a faint precipitate of ferric oxide occurs. This is re-dissolved
with a few drops of IIC1, and some strong solution of bisulphite added, in
the proportion of about 1 c.c. for each O'l gm. of ore, or 0'05 gm. Fe. The
mixture is well stirred, boiling water added, then acidified with dilute
sulphuric acid, and boiled for half an hour : it is then ready for titration.

I). J. Carnegie (J. C. 8. liii. 468) points out the value of zinc dust for
the rapid reduction of ferric solutions, and suggests the following method
of carrying it out.

The bottom of a dry and narrow beaker is covered with zinc dust sifted
through muslin. A known volume of ferric solution, previously nearly
neutralized with ammonia, is placed in the beaker and shaken with the zinc
dust ; then a known volume of dilute sulphuric acid is added and shaken for
a few moments. The reduction is much more rapid in neutral than in acid
solutions, but of course acid in this case must be present in excess to keep
the iron in solution. Carnegie withdraws a portion of the reduced
solution from the undissolved zinc by help of a filter, such as is described on
p. 18, and as measured volumes have been used, an aliquot part taken with
a pipette may be at once titrated, and the amount of iron found.*

* Commercial zinc dust is probably a by-product in zinc manufacture, and cannot
therefore be obtained pure. Samples examined by myself, and apparently others also,
do not, however, contain much iron, but a good deal of zinc oxide with traces of
cadmium and lead. Carnegie states that the oxide maybe removed by repeatedly
digesting- with weak acid, and still better, by treatment with ammonic chloride and
ammonia, the well-washed dust being 'finally dried on porous tiles in a vacuum.
I find that by washing once with strong alcohol after the water, and finally with ether,
the dust may be rapidly dried in good condition, and when a quantity of such purified
dust is obtained, its amount of iron may easily be estimated once for all, and allowed
for in titration. Good zinc dust is undoubtedly a valuable reagent in a laboratory for
other purposes beside iron titrations.

210 VOLUMETRIC ANALYSIS. § 64.

Clemens Jones in a paper read before the American Institute of
Mining Engineers, and which is reproduced in C. N. Ix. 93, adopts the plan
suggested by Carnegie, and has designed a special apparatus for filtering
the ferric solution through a column of zinc dust. This arrangement gives
complete reduction in a very short period of time, and is serviceable where
a large number of titrations have to be carried on.

ESTIMATION OF IRON IN THE FERRIC STATE.
1. Direct Titration of Iron by Stannous Chloride.

§ 64. THE reduction of iron from the ferric to the ferrous state
by this reagent has been previously referred to ; and it will be
readily seen that the principle involved in the reaction can be made
available for a direct estimation of iron, being, in fact, simply
a reversion of the ordinary process by permanganate and
bichromate.

Fresenius has recorded a series of experiments made on the
weak points of this process, and gives it as his opinion that, with
proper care, the results are quite accurate. The summary of his
process is as follows : —

(a) A solution of ferric oxide of known strength is first prepared by
dissolving 10*04 gm. of soft iron wire (=10 gm. of pure iron) in pure hydro-
chloric acid, adding potassic chlorate to complete oxidation, boiling till the
excess of chlorine is removed, and diluting the solution to 1 liter.*

(6) A clear solution of stannous chloride, of such strength that about one
volume of it and two of the iron solution are required for the complete
reaction (see § 37.2).

(<?) A solution of iodine in potassic iodide, containing about O'OIO gm.
of iodine in 1 c.c. (if the operator has the ordinary decinormal iodine solution
at hand, it is equally applicable). The operations are as follows : —

(1) 1 or 2 c.c. of the tin solution are put into a beaker with a little starch,
and the iodine solution added from a burette till the blue colour occurs ;
the quantity is recorded.

(2) 50 c.c. of the iron solution (-=0'5 gm. of iron) are put into a small
flask with a little hydrochloric acid, and heated to gentle boiling (preferably
on a hot plate) ; the tin solution is then allowed to flow in from a burette
until the yellow colour of the solution is nearly destroyed ; it is then added
drop by drop, waiting after each addition until the colour is completely
gone, and the reduction ended. If this is carefully managed, there need be
no more tin solution added than is actually required; however, to guard
against any error in this respect, the solution is cooled, a little starch
added, and the iodine solution added by drops until a permanent blue colour
is obtained. As the strength of the iodine solution compared with the tin
has been found in 1, the excess of tin solution corresponding to the iodine
used is deducted from the original quantity, so that by this means the volume
of tin solution corresponding to 0'5 gm. of iron is found.

The operator is therefore now in a position to estimate any

* A ferric standard may also be made, as suggested by French (C. N. Ix. 271), by
dissolving a weighed amount of double iron salt in dilute sulphuric acid, adding- an
•excess of hydrogen peroxide, warming up, and finally boiling to dissipate the excess of
the peroxide.

§ 64 IRON. 211

unknown quantity of iron which may exist in a given solution, in
the ferric state, by means of the solution of tin.*

If the iron should exist partly or wholly in the state of ferrous
oxide, it must be oxidized by the addition of potassic chlorate, and
boiling to dissipate the excess of chlorine, as described in a, or
with hydrogen peroxide.

Example : 50 c.c. of iron solution, containing 0*5 gm. of iron, required
25 c.c. of tin solution.

A solution containing an unknown quantity of iron was then taken for
analysis, which required 20 c.c., consequently a rule-of-three sum gave the
proportion of iron as follows : —

25 : 0'50 gm. : : 20 : 0'40 gm.

It must be remembered that the solution of tin is not permanent, conse-
quently it must be tested every day afresh. Two conditions are necessary in
order to ensure accurate results.

(1) The iron solution must be tolerably concentrated, since the end of
the reduction by loss of colour is more distinct ; and further, the dilution of
the liquid to any extent interferes with the quantity of tin solution necessary
to effect the reduction. Fresenius found that by diluting the 10 c.c. of
iron solution with 30 c.c. of distilled water, O'l c.c. more was required than
in the concentrated state. This is, however, always the case with stannous
chloride in acid solution, and constitutes the weak point in Streng's method
of analysis by its means.

(2) The addition of the tin solution to the iron must be so regulated, that
only a very small quantity of iodine is necessary to estimate the excess ; if
this is not done another source of error steps in, namely, the influence which
dilution, on the one hand, or the presence of great or small quantities of
hydrochloric acid on the other, are known to exercise over this reaction.
Practically, it was found that where the addition of tin to the somewhat
concentrated iron solution was cautiously made, so that the colour was just
discharged, the mixture then rapidly cooled, starch added, and then iodine
till it became blue, the estimation was extremely accurate.

2. Titration by Sodic Thiosulphate.

Scherer first suggested the direct titration of iron by thio-
sulphate, which latter was added to a solution of ferric chloride
until no further violet colour was produced. This was found by
many to be inexact, but Kremer ( Journ. f. Pract. Chem. Ixxxiv.
339) has made a series of practical experiments, the result of which
is that the following modified method can be recommended.

The reaction which takes place is such as to produce ferrous
chloride, sodic tetrathionate, and sodic chloride. 2S203Na2 +
Fe2Cl6 + 2HC1 = S406H2 + 4ffaCl + 2FeCl2. The thiosulphate,
which may conveniently be of T^- strength, is added in excess,
and the excess determined by iodine and starch.

* F. H.. Morgan (Journ. Anal. Chem. ii. 169) points out a very simple and useful
method of finding the end-point in titrating iron solutions with stannous chloride
without resorting to an indicator. It consists in using a round bottom white glass
flask containing the boiling liquid under titration, fixed over a small bluish-coloured
B u n s e n flame at a distance of 13 m.m. in a darkened room or a dark corner. So long
as the slightest trace of unreduced iron exists, a distinct green colour appears when
looking at the faint blue flame through the solution. It is stated that one part of iron
as oxide may be recognized in 1,500,000 parts of solution by this means.

p 2

212 VOLUMETKIC ANALYSIS. § 64V

Process : The iron solution, containing not more than 1 per cent, of metal,
which must exist in the ferric state without any excess of oxidizing material
(best obtained by adding excess of hydrogen peroxide, then boiling till the
excess is expelled), is moderately acidified with hydrochloric acid, sodic
acetate added till the mixture is red, then dilute hydrochloric acid until the
red colour disappears ; then diluted till the iron amounts to i or i per cent.,
and T^5- thiosulphate added in excess, best known by throwing in a particle of
potassic sulphocyanide after the violet colour produced has disappeared ; if
any red colour occurs, more thiosulphate must be added. Starch and ^
iodine are then used to ascertain the excess. A mean of several experiments
gave 100-06 Fe, instead of 100.

Oudemanns' Method. — A simpler process for the direct titra-
tion of iron by thiosulphate has been devised by Oudemanns
(Z. a. C. vi. 129 and ix. 342), which gives very good results.

Process: To the dilute ferric solution, which should not contain more
than O'l to 0'2 gm. Fe in 100 c.c. nor much free HC1, 3 c.c. of 1 per cent,
solution of cupric sulphate are added, 2 c.c. of concentrated hydrochloric
acid, and to about every 100 c.c. of fluid, 1 c.c. of a 1 per cent, solution
of potassic thiocyanate.

The mixture may with advantage be very slightly warmed, and the
thiosulphate delivered in from the burette at first pretty freely. The red
colour produced by the indicator gradually fades away; as this occurs, the
thiosulphate must be added in smaller quantities, constantly agitating the
liquid until it becomes as colourless as pure water. If any doubt exists as
to the exact ending, a slight excess of thiosulphate may be added, and the-
quantity found by T^- iodine and starch. Greater accuracy will always be
insured by this latter method.

The accuracy of the process is not interfered with by the1
presence of salts of the alkalies, strontia, lime, magnesia, alumina,,
or manganous oxide ; neither do salts of nickel, cobalt, or copper,,
unless their -quantity is such as to give colour to the solution.

The process is a rapid one, and with care gives very satisfactory
results.

3. Estimation by Iodine and Sodic Thiosulphate.

When ferric chloride is digested with potassic iodide in excess,,
iodine is liberated, which dissolves in the free potassic iodide —

Fed3 + KI - Fed2 + KC1 + L

Process : The hydrochloric acid solution, which must contain no free-
chlorine or nitric acid, and all the iron in the ferric state, is nearhr
neutralized with caustic potash or soda, transferred to a well-stoppered flask,
and an excess of strong solution of potassic iodide added ; it is then heated
to 50° or 60° C. on the water bath, closely stoppered, for about twenty
minutes ; the flask is then cooled, starch added, and titrated with thiosulphate
till the blue colour disappears. This process gives very satisfactory results
in the absence of all substances liable to affect the potassic iodide, such as
free chlorine or nitric acid, and is particularly serviceable for estimating.
small quantities of iron.

'§ 64 IRON. 213

4. Estimation of Iron by Colour Titration.

These methods, which approach in delicacy the Nessler test
for ammonia, are applicable for very minute quantities of iron,
such as may occur in the ash of bread when testing for alum, water
residues, alloys, and similar cases.

It is first necessary to have a standard solution of iron in the ferric state,
which can be made by dissolving 1*004 gm. of iron wire in nitro-hydrochloric
acid, precipitating with ammonia, washing and re-dissolving the ferric oxide
in a little hydrochloric acid, then diluting to 1 liter. 1 c.c. of this solution
•contains 1 milligram of pure iron in the form of ferric chloride. It may be
further diluted, when required, so as to contain ^ milligram in a c.c./and
this is the best standard to use.* The solution for striking the colour is
•either potassic ferrocyanide or thiocyanate dissolved in water (1 : 20).

Example with Ferrocyanide : The material containing a minute unknown
quantity of iron, say a wrater residue, is dissolved in hydrochloric acid, and
diluted to 100 c.c., or any other convenient measure. 10 c.c. are placed
into a white glass cylinder marked at 100 c.c., 1 c.c. of concentrated nitric
acid added (the presence of free acid is always necessary in this process), then
diluted to the mark with distilled water, and well stirred.

1 c.c. of ferrocyanide solution is then added, well mixed, and allowed to
stand at rest a few minutes to develop the colour.

A similar cylinder is then filled with a mixture of, say 1 c.c. of standard
iron solution, 1 c.c. nitric acid and distilled water, and 1 c.c. ferrocyanide
added ; if this does not approach the colour of the first mixture, other
•quantities of iron are tried until an exact similarity of colour occurs. The
exact strength of , the iron solution being known, it is easy to arrive at the
quantity of pure iron present in the substance examined, and to convert
it into its state of combination by calculation.

Carter Bell (J. S. C. I. viii. 175) adopts the following plan in
the case of waters : — 70 c.c. of the water are evaporated to
dryrjess in a platinum dish, and gently ignited to burn off organic
matters. 1 c.c. of dilute nitric acid, 50 c.c. of strong acid in
a liter, is then poured over the residue from a pipette, and
evaporated to dryness in the water bath ; the residue is then
dissolved in 1 c.c. of a 10 per cent, hydrochloric acid, 5 or 10 c.c.
of distilled water added, and the solution filtered and washed
through a small filter, and made up to 50 c.c. in a Messier glass;
and finally tested with 1 c.c. each of ferrocyanide solution and
nitric acid.

With Thiocyanate. — Thomson (J. C. S. 1885, 493) recom-
mends this method as being specially available in the presence of
other ordinary metals and organic matters, silver, copper, and
cobalt being the only interfering substances. The delicacy is said
to be such, that 1 part of iron can be recognized in 50 million parts
of water. The presence of free mineral acids greatly adds to the

* A solution of this strength can also be made by weighing 0'7 gin. of pure ammonio-
ferrous sulphate (§ 34.2b), dissolving in water, acidifying- with sulphuric acid, adding
sufficient permanganate solution to convert the iron exactly into ferric salt, then
diluting to 1 liter. Hydrogen peroxide may also be used in place of permanganate,
taking care to dissipate the excess by boiling.

214 VOLUMETRIC ANALYSIS. § 65.

sensitiveness. The standard ferric solution may be the same as for
ferrocyanide ; and in preparing the material for titration, the
weighed quantity is dissolved in an. appropriate acid, evaporated
nearly to dryness, taken up with water, converted into the ferric
state by cautious addition of permanganate, then diluted with water
to a measured volume, and an aliquot portion taken for titration.

The standard iron used by Thomson — y1^ m.gm. per c.c.
(0*7 gm. double iron salt [oxidized] per liter).

Example : Into two colourless glass cylinders marked at 100 c.c. pour
5 c.c. of nitric or hydrochloric acid (1 : 5), together with 15 c.c. of
thiocyanate, and to one glass a measured volume of the solution to be tested :
fill up both glasses to the mark with pure water. If iron be present, a blood
red colour more or less intense will be produced. Standard iron is then
cautiously added from a burette to the other glass till the colour agrees.
The quantity of Pe taken should not require more than 2 or 3 c.c. of the:
standard to equal it, or the colour will be too deep for comparison.

If other metals are present which form two sets of salts, they
must be in the higher state of oxidation, or the colour is destroyed.
Oxalic acid also destroys it. Examples in the presence of a great
variety of metals show very good results.

IRON ORES.

§ 65. THE great desideratum in the analysis of iron ores is
to get them into the finest possible state of division, and ten
minutes' hard work with the agate mortar will often save hours
of treatment of the material with acids. The operator of
experience can generally tell if the ore to be examined will dissolve-
in acids. Some clay iron stones and brown haematites contain
organic matters, and they are best first roasted in an open platinum
crucible, gradually raising the heat to redness; this course is
advisable also when an ore contains pyrites ; this latter is easily
converted to Fe203 by roasting. The proportion in iron ores is
generally under half a per cent. Some ores give a residue in any
case by treatment with HC1, this should be separated by nitration and
fused with sodic carbonate which will render all the iron in a soluble
state. In the analysis of iron ores it is very often necessary to.
determine not only the total amount of iron, but also the state in
which it exists; for instance, magnetic iron ore consists of
a mixture of the two oxides in tolerably definite proportions, and
it is sometimes advisable to know the quantities of each.

In order to prevent, therefore, in such cases, the further oxidation
of the ferrous oxide, the little flask apparatus (fig. 43) adopted by
Mohr is recommended, or fig. 42 is equally serviceable.

The left-hand flask contains the weighed ore in a finely powdered state, to
which, tolerably strong hydrochloric acid is added ; the other flask contains-
distilled water only, the tube from the first flask entering to the bottom of the
second. When the ore is ready in the flask and the tubes fitted, hydrochloric
acid is poured in, and a few grains of sodic bicarbonate added to produce

IRON ORES.

215

a flow of CO'2. The air of the flask is thus dispelled, and as the acid dissolves
the ore, the gases evolved drive out in turn the CO-, which is partly absorbed
by the water in the second flask. When the ore is all dissolved and the
lamp removed, the water immediately rushes out of the second flask into the
first, diluting and cooling the solution of ore, so that, in the majority
of cases, it is ready for immediate titration. If not sufficiently cool or
dilute, a sufficient quantity of boiled and cooled distilled water is added.

When the total amount of iron present in any sample of ore has
to be determined, it is necessary to reduce any peroxide present to-
the state of protoxide previous to titration.

Reduction to the Ferrous state may be done by sodic sulphite
in dilute solution, but not so with stannous chloride, the latter
must be used in a boiling and concentrated solution strongly
acidified with hydrochloric acid. Most technical operators now
use the tin method, which, by the help of mercuric chloride as
described § 63.2, is rendered both rapid and trustworthy. Both
with the sulphite and tin method bichromate is the invariable
titrating solution. When permanganate is to be used for titration
the reduction is always best made with zinc or magnesium in
sulphuric or very weak hydrochloric acid solution. With bichro-
mate, the best agent is either pure sodic sulphite, ammonic
bisulphite, or stannous chloride.

1. Bed and Brown Haematites. — Red haematite consists generally
of ferric oxide accompanied with matters insoluble in acids.
Sometimes, however, it contains phosphoric acid, manganese, and
earthy carbonates.

Brown haematite contains hydrated ferric oxide, often accompanied

216 VOLUMETRIC ANALYSIS. § 65.

"by small quantities of ferrous oxide, manganese, and alumina ;
sometimes traces of copper, zinc, nickel, cobalt, with lime, magnesia
and silica ; occasionally also organic matters.

In cases where the total iron only has to be estimated, it is
advisable to ignite gently to destroy organic matters, then treat
with strong hydrochloric acid at near boiling heat till all iron is
dissolved, and in case ferrous oxide is present add small quantities
of potassic chlorate, afterwards evaporating to dryness to dissipate
free chlorine ; then dissolve the iron with hot dilute hydrochloric
acid, filter, and make up to a given measure for reduction and
titration.

In some instances the insoluble residue persistently retains some
iron in an insoluble form; when this occurs, resort must be had to
fluxing the residue with sodic carbonate, followed by solution in
hydrochloric acid.

2. Magnetic Iron Ore. — The ferrous oxide is determined first by
means of the apparatus fig. 42 or 43. The ore is put into the
vessel in a state of very fine powder, strong hydrochloric acid
added, together with a few grains of sodic bicarbonate, and heat
applied gently with the lamp until the ore is dissolved, then
diluted if necessary, and titrated with bichromate or permanganate.
Technical operators generally use only a covered beaker.

Example : 0"5 gm. of ore was treated as above, and required 19"5 c.c. of
xo- bichromate, which multiplied by 00)56 gave 0-1032 gin. of iron = Q-14D4
gm. of ferrous oxide = 28"08 per cent. FeO.

The ferric oxide was now found by reducing 0'5 gm. of the same ore, and
estimating the total iron present: the quantity of bichromate required was —
59 c.c. T^=0-3304 gm. total Fe
Deduct 0-1092 gm. Fe as FeO

Leaving 0'2212 gm. Fe as Fe-O3

The result of the analysis is therefore —

Ferrous oxide 28'08 per cent.

Ferric oxide 63'20

Difference (Gangue, etc.) ... 872 „

100-00

3. Spathose Iron Ore. — The total amount of ferrous oxide in
this carbonate is ascertained directly by solution in hydrochloric
acid ; as the carbonic acid evolved is generally sufficient to expel
all air, the tube dipping under water may be dispensed with. If
the ore contains pyrites it should be first roasted, but this of course
converts the ferrous carbonate into Fe203.

As the ore contains, in most cases, the carbonates of manganese,
lime, and magnesia, these may all be determined, together with the
iron, as follows : —

A weighed portion of ore is brought into solution in hydrochloric acid,
after ignition if pyrite is present, and filtered, if necessary, to separate
insoluble silicious matter.

§ Go. IRON ORES. 217

The solution is then boiled, Avith a few drops of nitric acid to peroxidize
the iron, diluted, nearly neutralized with ammonia, and a solution of
ummonic acetate added, then boiled for two minutes and allowed to settle.
The precipitate is collected on a filter and washed with boiling water,
•containing a little ammonic acetate. It is then dissolved off the filter in
HC1 which also dissolves any A12O3 or P2O5 which may be present. The
liquid is then evaporated, reduced, and titrated as usual. "

The filtrate from the above is concentrated by evaporation, cooled, 3 or
4 c.c. of bromine added, and well mixed by shaking; when most of the
bromine is dissolved the liquid is rendered alkaline by ammonia, and gently
warmed till the Mn separates in large flocks as hydrated oxide, which is
collected and titrated by one of the methods in § 67.

The filtrate from the last is mixed with ammonic oxalate to precipitate the
lime, which is estimated by permanganate, as in § 52.

The filtrate from the lime contains the magnesia, which may be precipitated
with sodic phosphate and ammonia, and the precipitate weighed as usual, or
titrated with uranium solution.

4. Estimation of Iron in Silicates. — Wilbur and Wllittlesey
(C. N. xxii. 5) give a series of determinations of iron existing in
various silicates, either as mixtures of ferric and ferrous salts or of
either separately, which appear very satisfactory.

The very finely powdered silicate is mixed with rather more than its own
weight of powdered fluor-spar or cryolite (free from iron) in a platinum
crucible, covered with hydrochloric acid, and heated on the water-bath until
the silicate is all dissolved. During the digestion either carbonic acid gas or
coal gas free from H2S is supplied over the surface of the liquid so as to
prevent access of air. When decomposition is complete (the time varying
with the nature of the material), the mixture is diluted and titrated with
permanganate in the usual way for ferrous oxide ; the ferric oxide can then
be reduced by zinc and its proportion found.

By Hydrofluoric Acid. — 2 gm. of the finely powdered silicate are placed
in a deep platinum crucible, and 4O c.c. of hydrofluoric acid (containing
about 20 per cent. HF) added. The mixture is heated to near the boiling
point and occasionally stirred with a platinum wire until the decomposition
of the silicate is complete, which occupies usually about ten minutes. 10 c.c.
of pure H2SO4 diluted with an equal quantity of water are then added, and
the heat continued for a few minutes. The crucible and its contents are
then quickly cooled, diluted with fresh boiled water, and the ferrous salt
estimated with permanganate or bichromate as usual.

Leeds (Z. a. C. xvi. 323) recommends that the finely powdered
silicate be mixed with a suitable quantity of dilute sulphuric
acid, and air excluded by CO2 during the action of the hydrofluoric
acid. The titration may then at once be proceeded with when the
decomposition is complete.

If the hydrofluoric acid has been prepared in leaden vessels, it
invariably contains SO2 ; in such cases it is necessary to add to it,
previous to use, some hydrogen peroxide (avoiding excess) so as to
oxidize the SO2.

The process is a rapid and satisfactory one, yielding much more
accurate results than the method of fusion with alkaline carbonates
or acid potassic sulphate.

218 VOLUMETRIC ANALYSIS. § 65.

5. Colorimetric estimation of Carbon in Steel and Iron. — The
method devised by Eggertz, and largely adopted by chemists, for
estimation of combined carbon, is well known, but is open to the
objection that minute quantities of carbon cannot be discriminated
by it, owing to the colour of the ferric nitrate present. Stead
(G. N. xlvii. 285) in order to overcome this difficulty has devised
a method described as follows : —

In some careful investigations on the nature of the colouring
matter which is produced by the action of dilute nitric acid upon
white iron and steel, it was found it had the property of being
soluble in potash and soda solutions, and that the alkaline solution
had about two and a half times the depth of colour possessed by
the acid solution. This being so, it was clear that the colouring
matter might readily be separated from the iron, and be obtained
in an alkaline solution, by simply adding an excess of sodic
hydrate to the nitric acid solution of iron, and that. the coloured
solution thus obtained might be used as a means of determining
the amount of carbon present. Upon trial this was found to
be the case, and that as small a quantity as OO3 per cent, of
carbon could be readily determined.

The solutions required are : —

Standard solution of Nitric acid, 1 '20 sp. gr.

Standard solution of Sodic hydrate, 1'27 sp. gr.

Process : One gram of the steel or iron to be tested is weighed off and
placed in a 200 c.c. beaker, and after covering with a watch-glass, 12 c.c.
of standard nitric acid are added. The beaker and contents are then placed
on a warm plate, heated to about 90° to 100° C., and there allowed to remain
until dissolved, which does not usually take more than ten minutes. At the
same time a standard iron containing a known quantity of carbon is treated
in exactly the same way, and when both are dissolved 30 c.c. of hot water
are added to each, and 13 c.c. soda solution.

The contents are now to be well shaken, and then poured into a glass
measuring-jar and diluted till they occupy a bulk of 60 c.c. After again
well mixing and allowing to stand for ten minutes in a warm place, they are
filtered through dry filters, and the filtrates, only a portion of which is usedr
are compared. This may be done by pouring the two liquids into two
separate measuring tubes in such quantity or proportion that upon looking
down the tubes the colours appear to be equal.

Thus if 50 measures of the standard solution are poured into one tube, and if
the steel to be tested contains say half as much as the standard, there will be
100 measures of its colour solution required to give the same tint. The carbon
is therefore inversely proportional to the bulk compared with the standard,
and in the above assumed case, if the standard steel contained 0'05 per cent,
carbon,, the following simple equation would give the carbon in the sample
tested :—

0'05 x 50

— ,,-.,-. — = 0'02o per cent.

J-Ul/

The proportions here given must be strictly adhered to in order to insure
exactness. The colours from low carbon irons differ in tint from those in
high carbon steels, and therefore a low standard specimen must be used for
comparison. It is evident that the safest plan to insure absolute comparison

§ 65. IRON. 219

is to weigh and dissolve a known standard steel or iron for each batch
of tests.

Stead has devised a special colorimeter for the process, but it is
evident that any of the usual instruments may be used.

Arnold (Steel Works Analysts, p. 46) gives the following
conditions as necessary for the accurate working of the Eggertz
test.

(a) The standard steel should have been made by the same process as the
sample.

(b) The standard should be in the same physical condition, as far as this
can be secured by mechanical means.

(d) The solution of the standard and the samples should be made at the
same time, and under identical conditions, and the comparisons should be
made without delay.

(e) Above all, the standard should be above suspicion, its carbon contents*
having been settled on the mean of several concordant combustions made on
different weights of steel from a homogeneous bar.

6. Estimation of Arsenic in Iron Ores, Steel, and Pig- Iron
(J. E. Stead). — The best method of separating arsenic from iron
solutions is undoubtedly that of distilling with hydrochloric acid
and ferrous chloride.

Stead found after many trials and experiments, that if the
distillation is conducted in a special manner, the whole of the
arsenic may be obtained in the distillate, unaccompanied with any
traces of chloride of iron, and that if the hydrochloric acid is
nearly neutralized with ammonia, and finally completely neutralized
with bicarbonate of soda, the arsenic can be determined
volumetrically with a standard solution of iodine.

The standard solutions required are : —

Arsenious oxide. O66 gin. (0'5 gm. metallic arsenic) of pure
arsenious acid in fine powder is weighed and placed into a flask,
with '2 gm. of sodic carbonate and 100 c.c. of boiling distilled
water, and the liquid boiled till all the arsenious oxide has
dissolved. When cool, 2 gm. of sodic bicarbonate are added
and diluted to one liter : 1 c.c. = 0'0005 gm. As.

Iodine solution. 1*275 gm. of pure iodine is dissolved in 2 gm.
of potassic iodide and water, the solution diluted to one liter, then
standardized by titrating 20 c.c. of the arsenious solution. If the
iodine. has been pure, 20 c.c. of the solution should be required to
just produce a permanent blue with starch indicator.

These solutions keep fairly well without alteration for several
months. It is advisable, however, to periodically ascertain the
value of the iodine by titrating 20 or 30 c.c. of the arsenic
solution.

Process for Steel: Prom 1 to 50 gm. of the steel in drillings are
introduced into a 30-ounce flask, and a sufficient quantity of equal parts of
strong hydrochloric acid and water is added to dissolve it. The mouth of the
flask is closed with a rubber cork carrying a safety tube, and a tube to

220 VOLUMETRIC ANALYSIS. § 65.

convey the gas evolved into the Winkler's spiral absorption tubes,
•containing a strong saturated solution of bromine in water.

The tube is filled to one-third of its length with the solution, and about
i c.c. of free bromine is run in to replace the bromine which is consumed or
carried out with the passing gas.

The contents of the flask are now gently heated to such a degree that
•a steady but not rapid current of gas passes through the bromine solution.

In about one hour the whole of the steel will be dissolved, and when no
more evolution of hydrogen can be observed, the liquid in the flask is wrell
boiled, so as to completely drive all the gas into and through the bromine
solution.

The absorption tube is now disconnected, and the bromine solution
containing that part of the arsenic which has passed off as gas is rinsed out
into a small 100 c.c. beaker, and the excess of bromine is gently boiled off,
and the clear colourless solution is poured into the flask. About 0'5 gm. of
.zinc sulphide is now dropped into the iron solution and the contents are
violently shaken for about three minutes, by which time the whole of the
arsenic will be in the insoluble state, partly as sulphide and partly as a black
precipitate of possibly free arsenic and arsenide of iron.

It has been found that violent agitation for a few minutes is quite as
efficacious in effecting the complete separation of arsenic sulphide as by the
method of passing a current of CO2 through the solution to remove the
excess of hydric sulphide, or by allowing it to stand ten or twenty hours to
settle out.

The insoluble precipitate is now rapidly filtered through a smooth filter-
paper, and the flask is rinsed with cold distilled water. The precipitate
usually does not adhere to the filter, and in such cases the paper is spread
out flat upon a porcelain slab, and the arsenic compounds are rinsed off with
a fine jet of hot water into a small beaker. The precipitate is now dissolved
in bromine water, and a drop or two of HC1.

The bromine solution now containing all the arsenic is gently boiled to
expel the bromine, and it is then poured into a 10-ounce retort and is
distilled with ferrous chloride and hydrochloric acid.

The apparatus used consists of an ordinary Liebig's condenser, but the
retort has its neck bent to an angle of about 150°, and this is attached to the
condenser, so that any iron mechanically carried over may run back. By
this device, the distillate wrill never contain more than the very slightest
trace of iron.

The solution containing the arsenic having been run into the retort, the
beaker is washed out and the washings are also poured in. If the solution
is much above 20 c.c. in bulk, it is advisable to add a strong solution of
ferrous chloride containing about 0'5 gm. of iron in the ferrous state, and
for this purpose nothing answers so well as a portion of the steel solution
remaining after separating the arsenic, which is first well boiled to free it
from hydric sulphide, and should contain about 10 per cent, of soluble iron
as ferrous chloride. 5 c.c. of this solution will contain the necessary amount
of iron to add to the retort. After adding the chloride, it is best to boil
down the solution to about 20 c.c. before adding any HC1, taking care, of
course, to collect what liquid distils over. When the necessary concentration
has been effected, 20 c.c. strong HC1 is run in, and the distillation is
continued till all excepting about 10 c.c. has passed over. A further
quantity of 20 c.c. mixed with 5 c.c. of water is run in, and this is all
distilled over. At this point, as a rule, all the arsenic will have passed into
the distillate, but it is advisable to make quite certain, and to add a third portion
of acid and wrater, and to distil it over. If the distillation has not been
forced, the distillate will be quite colourless. The arsenic in the distillate
will exist as arseaious chloride, accompanied with a large excess of
hydrochloric acid. A drop of litmus is put into this solution, and strong

§ 65.

IRON. 221

ammonia is run in until alkaline. It is now made slightly acid with a few
drops of HC1, and a slight excess of solid bicarbonate of soda is dropped in.
The contents of the flask are now cooled by a stream of water, and, after
adding a clear solution of starch, the standard iodine is run in from a burette
till a deep permanent blue colouration is produced.

If the steel or iron contains much arsenic, a smaller quantity, say, one or
two gm., may be dissolved in nitric acid of T20 specific gravity and the
solution evaporated to dryness, the residue being dissolved in hydrochloric
acid, and the solution transferred to the retort, and distilled directly with
ferrous chloride and hydrochloric acid, care being taken that the distillation
is not forced, so as to avoid any of the iron solution passing over into the
distillate.

Process for Pig Iron : In testing pig irons, they may be dissolved in
nitric acid and evaporated to dryness, or be treated in a flask with HC1
exactly in the manner described above, but it is advisable, if the latter
method is adopted, after treating the voluminous mass of silica and
graphite, &c., with bromine and hydrochloric acid, to filter off the insoluble
matter and distil the clear solution.

Process for Iron Ores : In testing ores, it is only necessary to place the
powdered ore directly into the retort, and distil at once with HC1 and
ferrous chloride, taking care to place a few pieces of fire-brick also in the-
vessel, to avoid bumping.

If the ore contains much manganese, it is advisable to dissolve it in
a separate vessel to liberate and expel the chlorine, and then to transfer it
into the retort.

The time taken to test iron or steel need not exceed two hours, and for
iron or other ores not much more than half an hour.

It is quite possible to accurately determine as small a quantity as 0'002
per cent, of arsenic by this method.

When dissolving steels in dilute HC1, if there is no rust on the sample or
ferric chloride present in the acid, and the presence of air is carefully
avoided, as a rule only about one-tenth of the total arsenic present passes off
with the gas.

Platten's method, alluded to on page 149, depends on the fact
that when sulphide of arsenic (obtained by treating the arsenical
distillate with H2S) is boiled with pure water, the gas escapes, and
arsenious oxide remains in solution. This solution is then titrated
with iodine in the usual way.

Both methods have been proved to give identical results, when
carried out by separate skilled operators on the same samples of
material.

7. Estimation of Phosphorus in Iron and Steel. Dudley and
Pease (/. Anal. Cliem. vii. 108) adopt the following method: —

1 gm. of the sample is dissolved in an Erlenmeyer flask, in 75 c.c. of
nitric acid of sp. gr. T15 ; when dissolved, it is boiled for a minute and
mixed with 10 c.c. of a solution of potassic permanganate, and then again
boiled until manganese dioxide begins to separate. The liquid is now
cleared by the cautious addition of pure ferrous sulphate, heated to 85° C.,
and mixed with 75 c.c. of ammonium molybdate solution at 27° C. After
shaking for five minutes in a whirling apparatus, the precipitate is washed
with solution of ammonic sulphate until the washings give no colouration
with ammonic sulphide, and then dissolved in a mixture of 5 c.c. of
ammonia and 25 c.c. of water. The solution is now mixed with 10 c.c. of

222 VOLUMETKIC ANALYSIS. § 66.

strong sulphuric acid, diluted to 200 c.c., and reduced with zinc. The
solution is then titrated with permanganate. The volume of the latter
which represents 1 gm. of Pe equals 0'0172444 gm. of P.

8. Estimation of Sulphur in Iron and Steel. — The necessary
solutions for this method are —

Standard iodine, 1 c.c. of which equals 1 m.gm. of S, made by
dissolving 7 '9 gm. of pure iodine with 16 gm. of potassic iodide
in a liter of water.

Standard sodic thiosulphate of corresponding strength — this
solution should also contain about 20 gm. of sodic bicarbonate in
the liter. The two solutions are adjusted by titration with starch.

Solution of caustic soda — 280 gm. of good commercial hydrate
are dissolved in a liter of water, and as the soda generally contains
some substances capable of liberating iodine, a titration must be
made for each lot of solution to find the constant for that
particular solution.

Process : 5 gm. of drillings are put into a 20 oz. flask, to which is fitted
a rubber stopper with two holes, through one of which is a safety funnel
and the other a blank pipette, the upper end of which is bent twice at right
angles, and attached by a small rubber stopper to a f-in. bulb \J tube.
Into this latter is put 7 c.c. of the caustic soda solution and the apparatus
put together. 75 c.c. of dilute HC1 (2 acid 1 water) are poured through the
funnel, and the flask placed over a burner and heated moderately until the
steel is dissolved. The tube containing the soda solution is disconnected,
poured and washed into a beaker containing 15 c.c. of dilute H-SO4 (1 : 4)
mixed with as much iodine solution as will be in excess of the sulphur
expected. The mixture is diluted to about 200 c.c. and at once titrated
with thiosulphate and starch. The number of c.c. of iodine required, plus
•the caustic soda constant, multiplied by 20 will give the percentage of
sulphur.

LEAD.

Pb = 206-4.

1 c.c. -3^- permanganate =0*01032 gin. Lead.
1 c.c. normal oxalic acid = 0'1032 gm. ,,
Metallic iron x 1'846= „

Double iron salt x 0'263 = „

§ 66. THE accurate estimation of lead is in most cases better
effected by weight than by measure ; th^re are, however, instances
in which, the latter may be used with advantage.

1. As Oxalate (Hem pel). The acetic lead solution, which must contain
no other body precipitable by oxalic acid, is put into a 300 c.c. flask, and
a measured quantity of normal oxalic acid added in excess, the flask filled to
the mark with water, shaken, and put aside to settle ; 100 c.c. of the clear
liquid may then be taken, acidified with sulphuric acid, and titrated with

rmanganate for the excess of oxalic acid. The amount so found multiplied
3, and deducted from that originally added, will give the quantity
combined with the lead.

Where the nature of the filtrate is such that permanganate cannot be used

§ 66. LEAD. 223

for titration, the precipitate must be collected, well washed, dissolved in
dilute nitric acid, with a considerable quantity of sodic acetate, sulphuric
acid added, and titrated with permanganate.

In neither case are the results absolutely accurate, owing to the slight
solubility of the precipitate, but with careful manipulation the error need
not exceed 1 per cent. The error is much increased in the presence of
ammoniacal salts.

The technical analysis of red lead is best made as follows : —

2*064 gm. (7V eq. of Pb) are placed in a 300 c.c. porcelain basin, and 20 or
30 c.c. nitric acid sp. gr. 1'2 poured over it, then warmed gently with stirring.
In a few minutes the lead oxide is dissolved and the peroxide left insoluble.
50 c.c. of £ oxalic acid are added and the mixture boiled : this decomposes
and dissolves the peroxide, leaving undissolved uny adulterant such as baryta,
lead sulphate, oxide of iron, gypsum, or sand. While still hot f permanganate
is added in moderate portions until the colour is permanent for a few seconds.
The volume of permanganate deducted from 50 gives direct the percentage
of lead existing as peroxide.

The total lead may be found in the same solution b}' removing the excess
of permanganate with a drop or two of oxalic acid, neutralizing with ammonia,
adding a good excess of ammonic or sodic acetate, and titrating with bichro-
mate as described in this section.

Lead acetates in crystals or in solution may readily and with
tolerable accuracy be titrated direct with normal oxalic acid. The
best effects are obtained however by adding the lead solution
(diluted and rendered clear by a little acetic acid) from a burette
into the oxalic acid contained in a flask or beaker, warmed by
a water-bath. The addition of the lead solution is continued with
shaking and warming until no further precipitation takes place.

Another method for acetates is to precipitate the lead with
a slight excess of normal sulphuric acid in a 300 c.c. flask, fill
to the mark, estimate the excess of H2S04 in 100 c.c. by weight,
then calculate the combined acid into lead ; then by titrating
another portion for acidity with phenolphthalein, the proportion
of acetic acid can be obtained by deducting the free H2S04 from
the total acid found.

2. As Chromate (Schwarz). The lead is precipitated as chromate,
<well washed, and digested with a weighed excess of double iron salt and
hydrochloric acid; the resulting solution contains ferric and chromic
chlorides, together with lead chloride, and undecomposed iron salt. The
quantity of the last is found by permanganate, and deducted from the
original weight; the remainder, multiplied by the factor 0'263, will give the
weight. of lead.

The difficulty with this method is the end-point, owing to the
confusion produced by the yellow chromate. Diehl (Z. a. C. 1880,
-306) modified the process by precipitating the lead with excess
of bichromate and estimating the excess by thiosulphate, but this
again is open to the objection of an indistinct end-point.

Cushman and Hayes Campbell (Journ. Amer. Chem. Sac.
xvii. 901) have, however, modified the process so as to be
workable. Their method consists in titrating the solution after

224 VOLUMETRIC ANALYSIS. § 66,

filtering off the precipitated lead chromate, with a standard
solution of ammonio-ferrous sulphate, using ferricyanide as an
outside indicator, under exactly the same conditions observed in
standardizing bichromate solutions. The bichromate solution is
made up of convenient empirical strength, and standardized
against a weighed amount of pure ammonio-ferrous sulphate.
Slightly more than the equivalent weight of the latter salt is then
weighed out and dissolved in a liter of water, with the addition
of a few drops of sulphuric acid. The solution is transferred to-
a stock bottle into which is immediately poured a sufficient
quantity of some light paraffin oil to form a layer over the solution r
thus protecting it from oxidation. The stock bottle is fitted with
a syphon tube and pinch-cock, so that the solution can be drawn
out when needed. With this arrangement change in strength
of the ammonio-ferrous sulphate solution takes place very slowly,,
while, as a few moments only are required to titrate it against the
standard bichromate, its exact strength can be easily determined
from day to day.

Process : About 1 gm. of finely pulverized ore is digested in a casserole or
evaporating dish with 15 c.c. of a mixture of two parts of nitric acid and
one part sulphuric acid, until decomposition is complete. 10 c.c. more
of sulphuric acid are now added, and the liquid evaporated until it fumes
freely. Cool, dilute with 10 c.c. of dilute sulphuric acid (1 — 10), and then
add gradually 40 c.c. of water. Heat to boiling, filter, and wash by
decantation with dilute sulphuric acid (1 — 10), getting as little of the lead
sulphate on the filter as possible. To the residue in the dish add 20 c.c.
of strong ammonia, then make slightly acid with acetic acid. Boil until the
lead sulphate is dissolved, then pour the liquid through the filter, having first
moistened the paper with ammonia. Wash the filter with water containing
ammonic acetate in solution, and finally once or twice with hot water.
Cool the filtrate, and run in from a burette an excess of standard bichromate
solution, stirring until the precipitate settles rapidly and the supernatant
liquid has a yellow colour. Allow to settle for a few minutes, then filter,
under pressure if possible ; wash a few times, and titrate the filtrate against
the standard ammonio-ferrous sulphate.

After a little practice the method can be carried out as above detailed
in about thirty minutes. In case the ore is known to be free from bismuth
and antimony, the method can be materially shortened. Instead of bringing
the ore into solution with a mixture of nitric and sulphuric acids, nitric acid
alone is used. After solution the acid is neutralized with an excess of
ammonia, and "then made acid with acetic acid : this dissolves any lead
sulphate that has been formed. This solution is then immediately titrated
with the bichromate and ammonio-ferrous sulphate solutions exactly as
described above. In general it may be said that the results are a trifle low.
The mean of the amount of lead recovered in twenty determinations. was
99'6 per cent, of that taken.

3. Alkalimetric Method (M o h r) . — The lead is precipitated as carbonate
by means of a slight excess of ammonic carbonate, together with free
ammonia : the precipitate well washed, and dissolved in a measured excess
of normal nitric acid; neutral solution of sodic sulphate is then added
to precipitate the lead as sulphate. "Without filtering, the excess of nitric
acid is then estimated by normal alkali, each c.c. combined being equal to
0'1032 gm. of lead.

66. LEAD. 225

4. As Sulphide (Casamaj or). — The lead, if not in a state convenient
for titration, is separated as sulphate, well washed, and while still moist is
dissolved in alkaline tartrate solution exactly as in the case of copper (see
§ 58.5) ; the precipitated sulphide separates very freely, and if the operation
is performed in a white basin the end-point is easy of detection.

The chief drawback to the method is the instability of the sulphide
solution, which necessitates a fresh standardizing with known quantities of
metal every day.

5. Estimation of Lead in presence of Tin. — For technical purposes
this may be readily done as follows : —

The alloy is treated with nitric acid, by which means the lead is dissolved,
and the tin rendered insoluble as stannic acid. The excess of nitric acid is
removed by a very faint excess of sodic hydrate, then slightly acidified with
acetic acid. The solution is diluted, so that it contains not less than half
a per cent, of lead. It is then titrated with a standard solution of potassic
ferrocyanide containing 10'2 gm. per liter, Avhich has been standardized
against a lead nitrate solution containing 15'987 gm. per liter, using drops
of ferric chloride solution on a white plate as indicator.

6. Colorimetric estimation. — Where there is no other metal
than lead present, simple addition of freshly made sulphuretted
hydrogen water in the presence of weak acetic acid as suggested
by Miller gives good results, comparison being made with
a standard solution of lead acetate containing 0*1831 gm. per liter.
Each c.c. = O'OOOl gm. lead. The estimation is made in colourless
glass cylinders in the same way as described for copper or iron
§§ 58, 64, taking care that the comparative tests are made under
precisely the same conditions.

7. Leadin Citric and Tartaric Acids, etc. — Warington has worked
out the best method of ascertaining the proportions of lead in
these commercial acids, and shows that ammonium sulphydrate
is to be preferred to sulphuretted hydrogen for the process,
inasmuch as the tint produced is much more uniform throughout
a long scale, and very free from turbidity. Warington's
description of the method is as follows : — • •

The depth of tint produced for the same quantity of lead present is far
greater in an ammouiacal tartrate or citrate solution than in the same
volume of water ; it is quite essential, therefore, if equality of tint is to be
interpreted as equality of lead, that all comparisons should be between two
citrate and tartrate solutions, and not between one of these and water.

To carry out the method it is necessary to have solutions of lead-free
tartaric and citric acid supersaturated with pure ammonia ; these solutions
should develop no colour when treated with ammonium sulphydrate.
A convenient strength is 100 gm. of acid in 300 c.c. of final solution.*

Of the tartaric or citric acid to be examined, 40 gm. are taken and dissolved
in a little water ; warm water is most convenient for crystal and cold for
powder ; the solution is best prepared in a flask. To the cold solution pure
strong ammonia is gradually added till it is in slight excess ; the final point
is indicated in the case of tartaric acid by the solution of the acid ammonium

* Tlie standard lead solutions are made by dissolving T6 gin. of crystallized lead
nitrate dried over sulphuric acid in a liter of water, each c.c. =0'001 gm. Pb. A weaker
solution is also made by diluting 100 c.c. of this to a liter.

226 VOLUMETRIC ANALYSIS. § 67.

tart rate first formed ; in the case of citric acid it is conveniently shown by
a fragment of turmeric paper floating in the liquid. When an excess
of ammonia is reached the liquid is cooled, diluted to 120 c.c., and filtered.

As a preliminary experiment 10 c.c. are taken, diluted to 50 c.c. in the
measuring cylinder, and placed in a Nesslerizing glass, one drop of ammonium
sulphydrate solution added, and the whole well stirred ; the colour developed
indicates what volume of solution should be taken for the determination, this
volume may range from 5 c.c. to 50 c.c. If less than 50 c.c. are taken the
volume is brought to 50 c.c. with water, and one drop of ammonium
sulphydrate is then added.

The tint thus adopted has now to be matched with the pure solutions.
A volume of the pure ammoniacal tartrate or citrate, identical with that
taken of the acid under examination, receives a measured quantity of lead
solution from the burette, the -volume is brought to 50 c.c., it is placed
in a Nesslerizing glass, and receives one drop of ammonium sulplrydrate ;
the experiment is repeated till a match is obtained. As in the previous
method, the best comparison of tints is obtained by making finally three
simultaneous experiments, one with the acid under examination, the other
two with pure acid containing slightly varying amounts of lead, the aim
being that the tint given by the acid to bo analyzed shall lie within this
narrow scale. In following this method, considerable use has to be made of
the weaker of the two lead solutions alread}r mentioned.

The whole time required for a determination of lead by this method now
given is about 1| hour; this time will be somewhat shortened as the
operator becomes familiar with the tints produced by varying proportions
of lead. If traces of copper or iron are present, any interference on their
part may be removed by adding to the alkaline solution a few drops of
potassic cyanide solution.

MANGANESE.

Mn=55, MnO = 71, Mn02=S7.
Factors.

Metallic iron x 0'63393=MnO.

x 0-491 =Mn.

x 0-7768 =Mn02.

Double iron salt 0-0911 =.MnO.

Cryst. oxalic acid x 0-6916 =Mn02.

Double iron salt x 0 • 1 1 1 = MnO2.

1 c.c. T^ solutioii=0-00355 gm. MiiO or=0'00435 gm. MnO2.

§ 67. ALL the oxides of manganese, with the exception of the
first or protoxide, when boiled with hydrochloric acid, yield
chlorine in the following ratios : —

Mn203=l eq. 0= 2 eq. Cl.
Mn3O=r.l eq. 0=2 eq. Cl.
Mn 02=1 eq. 0= 2 eq. Cl.
Mn 03=2 eq. 0= 4 eq. Cl.
Mn207=5 eq. 0 = 10 eq. Cl.

The chlorine so produced can be allowed to react upon a known
weight of ferrous salt; and when the reaction is completed, the

§67. M.VXGAXESE. 227

unchanged amount of iron salt is found by permanganate or
bichromate.

Or, the chlorine may be led by a suitable arrangement into
a solution of potassic iodide, there setting free an equivalent
quantity of iodine, which is found by the aid of sodic thio-
sulphate.

Or, in the case of manganese ores, the reaction may take place
with oxalic acid, resulting in the production of carbonic acid,
which can be weighed as in Fresenius' and Wills' method,
or the amount of unchanged acid remaining after the action can
l)e found by permanganate.""'

The largely increased use of manganese in the manufacture of
steel has now rendered it imperative that some rapid and trust-
worthy method of estimation should be devised, and happily this
has been done simultaneously by two chemists, Pattinson and
Kessler; both have succeeded in finding a method of separating
manganese as dioxide, of perfectly definite composition. Pattinson
found that the regular precipitation was secured by ferric chloride,
and Kessler by zinc chloride. Wright and Menke have
experimented on both processes with equally satisfactory results,
but give a slight preference to zinc. Pattinson titrates the
resulting MnO- with standard bichromate, and Kessler with
permanganate.

Pat tins on's method has been fully described (/. C. S. 1879,
-365), and again with slight modifications in J. S. C. I. x. 337.

1. Precipitation as MnO? and Titration with Bichromate
(Pattinson).

The author's own description of the method is as follows : —

This method depends upon the whole of the manganese being
precipitated as hydrated dioxide by calcium carbonate, when
chlorine or bromine is added to a solution of manganous salt
containing also a persalt of iron or a salt of zinc, and under
certain conditions of temperature, &c. We have reason to believe
that this method is now adopted by many chemists both in private
laboratories and in the laboratories of steel works; and we therefore
think that the following description of it in its slightly modified
form, as we now use it for determining manganese in manganiferous
iron ores, manganese ores, spiegeleisen, ferromanganese, &c., will
not be out of -place.

* The literature of manganese compounds and their estimation has now become very
-voluminous. The principal contributions to the subject are as follows : —
Wright and Menke J. C. JS. 1880, 22-48.

Morawski and S t i n g 1 Jour. /. pract. Chem. xviii. 96.
Volhard Anna! en, cxcviii. 318.

Guyard Bull. Soc. Chim. [2] i. 88.

Kessler Z. a. C. 1879, 1-14.

Pattinson J. C. S. 1879, 365.

Pattinson J. S. C. I. x. 337.

228 VOLUMETRIC ANALYSIS. § 67.

Process: A quantity of the sample to be analyzed, containing not more
than about 4 grains (0'25 gm.) of manganese, is dissolved in hydrochloric
acid. In the case of spiegeleisen and ferromanganese, about 50 grains
(3 — 4 c.c.) of nitric acid are afterwards added to oxidize the iron. In the
case of manganese ores, ferromanganese, and manganese slags, which do not
contain about as much iron as manganese, we add to the solution as much
iron, in the form of ferric chloride, as will make the quantities of iron and
manganese in the solution about equal. An excess of iron is no draw-
back, except that a larger precipitate has afterwards to be filtered and
washed.

The excess of acid in the solution is then neutralized by the addition
of calcium carbonate, which is added until a slight reddening of the solution
is produced. The solution is then rendered very slightly acid by dropping
into it just enough hydrochloric acid to remove the red colour.

We then add in all cases 1 oz. (30 c.c.) of a solution of zinc chloride
containing 7 grains (0'5 gm.) of metallic zinc per ounce. The liquid is then
brought to the boiling point, and diluted with boiling water to about 10 oz.
(300 c.c.).

Two oz. (60 c.c.) of a solution of calcium hypochlorite, made by dissolving
1500 grains of 35 per cent, bleaching powder in 100 oz. of water (about 33 gm.
of bleaching powder per liter) and filtering, are then poured into the
manganese solution; but we add to the hypochlorite solution, before pouring
it into the manganese solution, just enough hydrochloric acid to give it
a faint permanent greenish-fellow colour after gentle agitation.

The object of this addition of acid is to prevent a precipitate forming
when the hypochlorite is added, due to the alkalinity of this solution.
When hydrochloric acid is added in this way to the solution of calcium
hypochlorite, the manganese solution remains clear on the addition of the
calcium hypochlorite, and any possible local precipitation of manganese in
a lower state of oxidation than MnO'2 is obviated.

Finally, Ave add to the manganese solution about 45 grains (3 gm.) of
calcium carbonate diffused in about half an ounce (15 c.c.) of boiling water.
After the first evolution of carbonic acid has ceased, during which time the
cover is kept on the beaker, the precipitate is stirred to make it collect
together, and half a dram (2 c.c.) of methylated spirits of wine is added
and it is again stirred.

The precipitate is then thrown upon a large filter of English filtering paper
and washed, at first with cold water until the greater part of the chlorine is
removed, and afterwards, to make the washing more rapid, with warm \vater
at about 150° P. (65° C.). It is washed until, after draining, a drop shaken
down straight from the precipitate, by gently jolting the funnel, shows
no indication of chlorine when tested with a strip of iodized starch-paper.
As a matter of practice we always give two or three washings after there has
ceased to be any indication of chlorine.

By carrying out the process in the manner here described, the temperature
of the liquid, immediately after the precipitation is complete, is about
1703 1\ (77° C.), and we find that the best and most constant results are
obtained when the temperature after precipitation is near this point.

1000 grains of an acidified solution of ferrous sulphate, containing about
10 grains of iron 'per 1000 grains of the solution, and made by dissolving
crystallized ferrous sulphate in a mixture of one part of monohydrated
sulphuric acid and three parts of water, are then accurately measured off by
a pipette and run into the beaker in which the precipitation was made. The
precipitate, together with the filter paper, are then removed from the funnel
and placed in the solution of ferrous sulphate in the beaker. The precipitate
readily dissolves even in the cold (sometimes it may be necessary to add
a little more acid to dissolve the ferric hydrate completely), the manganese
dioxide converting its equivalent of ferrous sulphate into ferric sulphate.

§ 67. MANGANESE. 229

A sufficient quantity of cold water is now added, and the ferrous sulphate
still remaining is titrated with a standard solution of potassium dichromate.

The exact amount of ferrous sulphate in 1000 grains of the ferrous
sulphate solution is determined hy measuring off into a clean beaker another
portion of 1000 grains, and titrating with standard dichromate solution.
The difference between the amounts of dichromate solution required gives
the quantity of ferrous sulphate oxidized by the manganese dioxide, and
from this the percentage of manganese in the sample can be calculated.

The ferrous sulphate solution should be standardized from day to day, as it
undergoes slow oxidation on exposure to air.

A solution of bromine in water may of course be used instead of the
hypochlorite solution, in which case no acid is added to the bromine solution.
"When using bromine a solution containing about 10 grains of bromine
per ounce (about 22 gm. per liter) should be used, and 3 oz. of this solution
(90 c.c.) used for precipitating about 4 grains of manganese.

The unpleasantness of working with bromine may be mitigated, to some
extent, by adding to the bromine solution before pouring it into the liquid
containing the manganese, a few drops of a solution of sodium hydrate until
nearly all, but not quite all, the bromine is taken up. If an excess of
sodium hydrate were added to the bromine it would produce a precipitate on
pouring it into the manganese solution, and this is to be avoided.

We prefer to have both zinc and iron in solution with the manganese.
When working with either of these alone we obtain all the manganese in
the form of dioxide, but with iron alone there is a greater tendency to
the formation of permanganate, than when zinc is also present. This point
was also noticed by Wright arid Menke (J. C. S. Trans. 1880, 43).
When zinc alone is present we have found that the precipitation of the
dioxide does not take place so rapidly as when iron is also present. When
both iron and zinc are used, there is very seldom any permanganate formed,
if care is taken not to use an t unnecessarily large excess of chlorine or
bromine, but occasionally there is a small quantity formed, especially if the
precipitate is left to stand some considerable time before filtering. We have
found that the addition of a very small quantity of alcohol immediately
after the precipitation of the manganese is complete, entirely prevents the
formation of. permanganate even when a large excess of chlorine has been
used, and for this reason we make a practice of adding it.

We find that when filtering paper has been wetted with the solution
containing free chlorine or bromine and afterwards washed clean, it has no
reducing action either upon potassium dichromate or upon ferric sulphate.
The addition of the filter together with the precipitate to the solution
'of ferrous sulphate therefore does not influence the result.

We must point out that the presence of lead, copper, nickel, cobalt, and
•chromium in the substances under examination interferes with the accuracy
of this method of testing manganese.

It was found that so large a proportion as 1 per cent, of lead, copper, and
nickel does not greatly interfere with the test, but the interference of cobalt
and, especially of chromium, is serious. All these substances, except
chromium, form, under the conditions of the test, higher oxides insoluble in
water, which are precipitated with the manganese dioxide, and which
oxidize ferrous sulphate to ferric sulphate ; whilst chromium forms some
insoluble chromate which goes down with the manganese dioxide.

Fortunately these metals rarely, if ever, occur in the ores of manganese
or in spiegeleisen and ferromanganese in sufficient quantity to affect the
practical accuracy of this test.

This volumetric method cannot, however, be applied to the determination
•of manganese in alloys of these metals, such as ferrochrome or in ores
containing these metals, without previously separating them from the
solution containing the manganese.

230 VOLUMETRIC ANALYSIS. § G7.

The method as above described is undoubtedly one of the best
volumetric ones known for the estimation of manganese in various
compounds and ores; but Saniter in criticising the method gives
it credit for slightly low results, and advocates the standardizing
of the bichromate, not upon iron, but upon a manganese oxide of
known composition (/. S. C. I. xiii. 112).

Atkinson ( J, S. C. I. v. 365) gives the following short descrip-
tion of the method as practically in daily use in a large steel works.

Weigh out 0'5 gm. or 0'6 gm. of an ore containing about 20 per cent,
manganese, dissolve in 7 or 8 c.c. of strong HC1, and when dissolved, wash
the whole, without filtering, into a large narrow-sided beaker. When cold
it is neutralized with precipitated calcic carbonate, until the liquid assumes
a reddish hue. 40 or 50 c.c. of saturated bromine water are added, and the
mixture allowed to stand in the cold for half-an-hour. At the expiration of
that time the beaker is nearly filled up with boiling water, and precipitated
calcic carbonate added until there is no further effervescence, and part of the
carbonate is evidently unacted upon. A small quantity of spirits of wine is
then added, the whole well stirred, and the precipitate allowed to settle. The
clear liquid is filtered off and fresh boiling water added to the residue in the
beaker, a little spirits of wine being used to reduce any permanganate which
is formed. The filtration and washing are repeated until the nitrate when
cooled no longer turns iodized starch-paper blue. During the washing about
1'9 to 2' 5 gm. of pure granular ferrous-ammonium sulphate are weighed
out, washed into the beaker in which the precipitation took place, and about
30 to 50 c.c. of dilute sulphuric acid added. The filter containing the pre-
cipitated MnO2 is then placed in the beaker, and the latter is quickty dissolved
by the oxidation of a portion of the ferrous salt into ferric sulphate. The
remaining ferrous iron is then titrated with potassic bichromate in the usual
way. The difference in the number of c.c. of bichromate used from the
number which the original weight of the ferrous-ammonium sulphate would
have required if directly titrated, is a measure of the quantity of MnO-
present. For rapidity and simplicity this volumetric process leaves nothing
to be desired ; duplicate experiments agree within very narrow limits ; and
if the assumption is accepted that the presence of ferric chloride enables the
complete oxidation of the manganese to the state of peroxide, no other
process can compete with it.

Pattinson prefers to use bleach solution to bromine, because
the formation of permanganate is more easily seen. In any case
not more than a trace of permanganate should be formed, and if
the first experiment shows this to be the case, another trial must
be commenced with less oxidizing material.

J. "W. Westmoreland, in a communication to me, describes
a modified method which is designed to overcome some objections
raised against the above processes.

With ferro-manganese and ores containing about 50 to 60 c 0 of Mn about
0*4 gm. is taken ; ores with 40 % °'5 gm- '•> manganiferous iron ores, with
say about 20 % each of Fe and Mn, 0'75 gm.; spiegeleisen and silicospiegels,
with about 25 % Mn, the same.

The material having been brought into solution by any of the methods
described, is concentrated to a small bulk in a large conical beaker.
A solution of ferric chloride, containing about the same amount of iron as
there is approximately of Mn, is added, together with a solution of zinc

§ 67. MANGANESE. 231

chloride, containing about 0'5 gm. of Zn. The excess of acid is then
neutralized with caustic potash, so that the bulk of liquid is about 80 c.c.,
to this is added about 60 c c. of saturated bromine water, more for
ferro-manganese, less for manganiferous iron ores, and zinc oxide emulsion *
is graduall}' dropped in with shaking, until the Pe and Mn are pre-
cipitated, care must be taken to avoid a large excess of zinc oxide, the
beaker is then filled up with boiling tap-water, and the clear liquid poured
through a filter, previously adding a few drops of alcohol. The beaker is
then filled with boiling water five times in succession, the precipitate being
stirred up with the hot water each time of washing and allowed to settle.
It is then brought on the filter, and again freely washed with boiling
distilled water. The filter and contents are then transferred to the beaker,
an excess of acid solution of ferrous sulphate added, and when the precipitate
is dissolved the liquid is diluted with cold distilled water, and the excess of
ferrous iron estimated at once with permanganate. The value of the iron
solution in metallic iron is found by titrating the same volume of iron
solution as has actually been used for dissolving the Mn precipitate, and the
Fe oxidized multiplied by 0'491 = Mn.

It is absolutely necessary, in order to get accurate results, to
wash the precipitate as thoroughly as mentioned.

2. By Precipitation with Potassic Permanganate (G-uyard).

If a dilute neutral or faintly acid solution of manganese salt be
heated to 80° C. and permanganate added, hydrated MnO2 is pre-
cipitated, and the end of the reaction is known by the occurrence of
the usual rose colour of permanganate in excess. The reaction is
exact in neutral solutions. Any large excess of either HC1 or H'2S04
causes irregularity, as also do ferric or chromic salts; nickel, cobalt,
zinc, alumina, or lime, in moderate quantity are of no consequence.

This method is of easy execution, and gives good results in cases
where it can be properly applied, but such instances are few.

Process : 1 or 2 gm. of the manganese compound are dissolved in aqua
refjia, boiled a few minutes, the excess of acid neutralized with alkali, then
diluted largely with boiling water (1 or 2 liters), kept at a temperature
of 80° C., arid standard permanganate added so long as a brownish precipitate
forms, and until the clear supernatant liquid shows a distinct rose colour.
2 eq. of permanganate = 3 eq. of manganese, therefore 1 c.c. of T^ solution =
0-0016542 gm. of Mn.

Volhard's method.— This is now largely used by Continental
chemists, the details of the original process being as follows : —

A quantity of material is taken so as to contain from 0'3 to 0'5 gm. Mn,
dissolved in hydrochloric or nitric acid, evaporated in porcelain to dryness,
first adding a little ammonia nitrate, then heated over the flame to destroy
organic matter. The residue is digested with HC1, adding a little strong
H-SO4, and again evaporated to dryness, first on the water-bath, then with
greater heat till vapours of SO3 occur. It is then washed into a liter flask
and neutralized with sodic hydrate or carbonate : sufficient pure zinc oxide,
made into a cream, is added to precipitate all the iron. The flask is filled to

* The emulsion of zinc oxide may, of course, be readily made by rubbing down pure
zinc oxide in water so as to be about the consistence of cream. Emmertpn (Trans.
Antcr. Inst. Min. Eng. x. 201) suggests the following method of preparing this reagent.
Dissolve ordinary zinc white in HC1, add the powder until there remains some

232 VOLUMETRIC ANALYSIS. § 67.

the mark, shaken, and 200 c.c. filtered off into a boiling flask, acidified with
2 drops of nitric acid, sp. gr. 1'2, heated to boiling, and titrated with
T^j- permanganate whilst still hot.

Blair (Chem. Anal. Iron, 2nd edit.) for practical working recommends
dissolving the material in HC1 and H2S04, evaporate to dryness until fumes
of the latter escape; allow to cool, add water, and heat till sulphates are
dissolved. Wash into a 300 c.c. flask, add solution of Na2CO3 until the
precipitate, which at first forms, dissolves only with difficulty. Then add
slowly the zinc oxide emulsion, shaking well after each addition, till the iron
precipitate curdles ; after the precipitate has settled, there is left a slightly
milky upper liquid. Fill the flask to the mark with water, and agitate well
by pouring the contents of the flask back and forward into a dry beaker.
Finally filter off 200 c.c. and titrate Avith permanganate as before described,
first adding 2 drops of HNO3. The permanganate should be added slowly
from the burette, shaking after each addition to facilitate the collection
of the precipitate and avoid an excess of permanganate. If the solution
during the process should cool too much, it should be heated up to near
boiling again.

Saniter recommends that any iron or chromium should be first separated
by ammonia and ammonic acetate, and the manganese precipitated with
bromine and ammonia. This precipitate is, after ignition, dissolved in
hydrochloric acid, and neutralized with zinc oxide suspended in water, any
excess of the latter being dissolved by adding nitric acid drop by drop.

Another variation of this method is given (Jour. Ainer. Chem.
Soc. xviii. 228) by G. E. Stone, in some criticisms on a previous
paper by M. Auchy.

The material taken should contain 0'05 to 0'15 Mn. If an alloy, dissolve
in HNO3 (sp.'gr. ri) ; if an ore or cinder, in HC1, and boil with a little
KC1O3 ; use but small excess of acid. Cool and wash into a 500 c.c. flask
with cold water, then add zinc emulsion until precipitate curdles ; the
change is sharp and distinct. Dilute to mark, shake well and pour into
a beaker ; allow to settle ; measure 100 c.c. into a 4-inch casserole, dilute
to about 200 c.c., heat nearly to boiling, and titrate with permanganate,
1 c.c. of which=0 001 gin. Mn (1'99 gin. K-MnO4 per liter). The greater part
of the permanganate should be added at once with vigorous stirring. The
Mn in spiegels is easily obtained in half an hour ; ores somewhat longer,
as more difficult to dissolve.

There are many other volumetric methods in use for estimating
manganese either as binoxide or metal, among which may be
mentioned that of Chalmers Harvey (C. N. xlvii. 2) by
stannous chloride, and that of Williams (Trans. Amer. Inst. of
Mining Engineers, x. 100), which consists in separating MnO2
from a nitric solution by potassic chlorate, dissolving in excess of
standard oxalic acid, and estimating the excess by permanganate.

A critical paper on this process, accompanied with the results of
experiment, is contributed by Macintosh (C. N. 1. 75). Also
another by Hintz (Z. a. C. xxiv. 421 — 438) reviewing a large
number of volumetric methods for manganese, but as none of them

undissolved, then add a little bromine water; heat the mixture, filter and precipitate
the zinc oxide from the filter with the slightest possible excess of ammonia. Wash
thoroughly by decantation, and finally wash into an appropriate bottle with enough
water to give a proper consistence. By this method a very finely divided oxide is
obtained, owing to its not being dried.

§ 67. MANGANESE. 233

are more accurate or convenient than the methods here given, the
details are omitted.

3. Estimation of Manganese in small quantities (Chatard).

This method depends upon the production of permanganic acid
by the action of nitric acid and lead peroxide, originally used by
Crum as a qualitative test. The accuracy of the process as
a quantitative one can, however, only be depended on when the
quantity of manganese is very small, such as exists in some
minerals, soils, etc.

The material to be examined is dissolved in nitric acid and
boiled with lead peroxide, by which means any manganese present
is converted to permanganate ; the quantity so produced is then
ascertained by a weak freshly made standard solution of oxalic
acid or ammonic oxalate.

The process gives good results in determining manganese in
dolomites and limestones, where the proportions amount to from
yy to 2 per cent. In larger quantities the total conversion of the
manganese cannot be depended on.

Thorpe and Hambly ( J. C. S. liii. 182) found that the final
point in the titration with ammonic oxalate was apt to be obscured
by the precipitation of lead carbonate, and they suggest a modifi-
cation which consists in using some dilute sulphuric acid with
the lead peroxide and nitric acid during the oxidation of the
manganese ; no lead then passes into solution, and the filtered
liquid remains perfectly clear on titration. These operators found
the method quite trustworthy for quantities of manganese below
O'Ol gm., and carried out as follows : —

Process : To the manganese solution, which must be free from chlorine
and not too dilute, say about 25 c.c., add 5 c.c. of nitric acid (sp. gr. 1'4),
2 — 3 gm. of lead peroxide, and 10—20 c.c. of dilute sulphuric acid (1 : 2).
Boil gently for about four minutes, wash down the sides of the flask with
hot water, and continue the boiling for half a minute. Allow the lead
sulphate and peroxide to subside and filter at once (best with filter pump
through asbestos, previously ignited and washed with dilute H2SO4). Wash
the residue in fl-ask with boiling water by decantation, heat the clear filtrate
to 60° C., and titrate with T^ ammonic oxalate.

Peters avails himself of this method for estimating manganese
in pig iron or steel, by weighing O'l gm. of the sample and boiling
in 3 or 4 c.c. of nitric acid until solution of the metal is complete,
adding O2 or 0'3 gm. PbO2, and again boiling for two or three
minutes, without filtering off the insoluble graphite, if such should
be present. The solution is then cooled, filtered through asbestos
into a suitable graduated tube, and the colour compared with
a standard solution of permanganate contained in a similar tube.

The standard permanganate is best made by diluting 1 c.c. of
Y^ solution with 109 c.c. of water; each c.c. will then represent
0 '00001 gm. Mn. It has been previously mentioned that accurate

234 VOLUMETRIC ANALYSIS. § 67.

results by this method can only be obtained by using very small
quantities of material. Peters finds this to be the case, and hence
recommends, that for irons containing from O10 to 0'35 per cent,
of Mn Ol gm. should be operated upon ; when from 0~8 to 1
per cent, is present, 0*1 gm. of the sample is weighed and one-
fourth of the solution only treated with PbO'2 ; in still richer
samples proportionate quantities must be taken. As a guide, it is
well to assume, that when the amount of iron taken yields a colour
equal to 25 — 35 c.c. of the standard, the whole of the Mn is
oxidized. The actual amount of manganese in any test should not
exceed half a milligram (G. N. xxxiii. 35).

4. Teslinical EXE mination of Manganese Ores used for Bleaching-
Purposes, etc.

The ore, when powdered and dried for analysis, rapidly absorbs
moisture on exposing it to the air, and consequently has to be
weighed quickly ; it is better to keep the powdered and dried
sample in a small light stoppered bottle, the weight of which,,
with its contents and stopper, is accurately known. About 1 or 2
gm., or any other quantity within a trifle, can be emptied into-
the proper vessel for analysis, and the exact quantity found by
reweighing the bottle.

A hardened steel or agate mortar must be used to reduce the-
mineral to the finest possible powder, so as to insure its complete
and rapid decomposition by the hydrochloric acid.

Considerable discussion has occurred as to the best processes-
for estimating the available oxygen in manganese ores, arising from
the fact that many of the ores now occurring in the market contain
iron in the ferrous state ; and if such ores be analyzed by the usual
iron method with hydrochloric acid, a portion of the chlorine
produced is employed in oxidizing the iron contained in the original
ore. Such ores, if examined by Fresenius and Wills' method,,
show therefore a higher percentage than by the iron method, since-
no such consumption of chlorine occurs in the former process.
Manufacturers have therefore refused to accept certificates of
analysis of such ores when based on Fresenius and "Wills'
method. This renders the volumetric processes of more importance,,
and hence various experiments have been made to ascertain their
possible sources of error.

The results show that the three following methods give very
satisfactory results (see Scherer and Eumpf, C. N. xx. 302;
also Pattinson, Hid. xxi. 266; and Paul, xxi. 16).

5. Direct Analysis by Distillation with Hydrochloric Acid.

This is the quickest and most accurate method of finding the
quantity of available oxygen present in any of the ores of manganese
or mixtures of them. It also possesses the recommendation that the

§ 67. MANGANESE. 235

quantity of chlorine which they liberate is directly expressed in the
analysis itself ; and, further, gives an estimate of the quantity of
hydrochloric acid required for the decomposition of any particular
sample of ore, which is a matter of some moment to the manu-
facturer of bleaching powder.

The apparatus for the operation may be those shown in figs.
37 and 38. For precautions in conducting the distillation
see § 39.

Process : In order that the percentage of dioxide shall be directly
expressed by the number of c.c. of r^ thiosulphate solution used, 0'436 2:111.
of the properly dried and powdered sample is weighed and put into the little
flask ; solution of potassic iodide in sufficient quantity to absorb all the
iodine set free is put into the large tube (if the solution containing T27 eq. or
33'2 gin. in the liter be used, about 70 or 80 c.c. Will in ordinary cases be
sufficient) ; very strong hydrochloric acid is then poured into the distilling
flask, and the operation conducted as in § 39. Each equivalent of iodine
liberated represents 1 eq. Cl, also 1 eq. MnO2.

Instead of using a definite weight, it is well to do as before
proposed, namely, to pour about the quantity required out of the
weighed sample-bottle into the flask, and find the exact weight
afterwards.

Barlow (0. N. liii. 41) records a good method. of separating
Mn from the metals of its own group as well as from alkalies and
alkaline earths.

For the quantitative estimation of Fe and Mn in the same
solution as chlorides (other metals except Cr and Al may be present,
but best absent), solution of iSrH4Cl is first added, then strong
NH4HO in excess, boil, then hydrogen peroxide so long as a
precipitate falls, boil for a few minutes, filter, wash with hot water,
ignite, and weigh the mixed oxides together as Fe203 + Mn304.

The oxides are then distilled with HC1, and the amount of
iodine found by thiosulphate.

The weight of mixed oxides, minus the Mn304, gives the weight
of Fe203.

Pickering (/. 0. S. 1880, 128) has pointed out that pure
manganese oxides, freshly prepared, or the dry oxides in very
fine powder, may be rapidly estimated without distillation by
merely adding them to a large excess of potassic iodide solution
in a beaker, running in 2 or 3 c.c. of hydrochloric acid, when
the oxides are immediately attacked and decomposed; the liberated
iodine is then at once titrated with thiosulphate. Impure oxides,
containing especially ferric oxide, cannot however be estimated in
this way, since the iron would have the same effect as manganic
oxide ; hence distillation must be resorted to in the case of all
such ores, and it is imperative that the strongest hydrochloric acid
should be used.

Pickering's modified process is well adapted to the examination
of the Weldon mud, for its available amount of manganese dioxide.

236 VOLUMETRIC ANALYSIS. § 67.

6. Estimation by Oxalic Acid.

The very finely powdered ore is mixed with a known volume of
normal oxalic acid solution, sulphuric acid added, and the mixture
heated and well shaken, to bring the materials into intimate contact
and liberate the CO2. When the whole of the ore is decomposed,
which may be known by the absence of brown or black sediment,
the contents of the vessel are made up to a definite volume, say
300 c.c., and 100 c.c. of the dirty milky fluid well acidified,
diluted, and titrated for the excess of oxalic acid by permanganate.
If, in consequence of the impurities of the ore, the mixture be
brown or reddish coloured, this would of course interfere with the
indication of the permanganate, and consequently the mixture in
this case must be filtered ; the 300 c.c, are therefore well shaken
and poured upon a large filter. When about 100 c.c. have passed
through, that quantity can be taken by the pipette and titrated as
in the former case.

If the solution be not dilute and freely acid, it will be found
that the permanganate produces a dirty brown colour instead of its
well-known bright rose-red ; if the first few drops of permanganate
produce the proper colour immediately they are added, the solution
is sufficiently acid and dilute.

If 4-357 gm. of the ore be weighed for analysis, the number of
c.c. of normal oxalic acid will give the percentage of dioxide ; but
as that is rather a large quantity, and takes some time to dissolve
and decompose, half the quantity may be taken, when the per-
centage is obtained by doubling the volume of oxalic acid.

Example : The permanganate was titrated with normal oxalic acid, and it
was found that 1 c.c.=0'25 c.c. of normal oxalic acid. 2'1T8 gm. of a rich
sample of commercial manganese (pyrolusite) were treated with 50 c.c. of
normal oxalic, together with 5 c.c. of concentrated sulphuric acid, until the
decomposition was complete. The resulting solution was milky, but con-
tained nothing to obscure the colour of the permanganate, and therefore
needed no filtration. It was diluted to 300 c.c., and 100 c.c. taken for titra-
tion, which required 6'2 c.c. of permanganate. A second 100 c.c. required
G'3, mean 6'25, which multiplied by 3 gave 18'75 c.c.; this multiplied by
the factor 0'25 to convert it into oxalic acid gave 4'68 c.c. normal oxalic,
and this being deducted from the original 50 c.c. used, left 45'32 c.c.=90'64
per cent, of pure manganic dioxide.

This process possesses an advantage over the following, inasmuch
as there is no fear of false results occurring from the presence of
air. The analysis may be broken off at any stage, and resumed
at the operator's, convenience.

7. Estimation by Iron.

The most satisfactory form of iron is soft " flower " wire, which
is readily soluble in sulphuric acid. If a perfectly dry and un-
oxidized double iron salt be at hand, its use saves time. 1 mol.
-of this salt = 392, representing 43 '5 of MnO2, consequently, 1 gm. of

§67. MANGANESE. 2S7

the latter requires 9 gm. of the double salt ; or in order that the
percentage shall be obtained without calculation,, I'lll gm. of ore
may be weighed and digested in the presence of free sulphuric acid,
with 10 gm. of double iron salt, the whole of which would be
required supposing the sample were pure dioxide. The. undecom-
posed iron salt remaining at the end of the reaction is estimated by
permanganate or bichromate ; the quantity so found is deducted
from the original 10 gm., and if the remainder be multiplied by 10
the percentage of dioxide is gained.

Instead of this plan, which necessitates exact weighing, any
convenient quantity may be taken from the tared bottle, as before
described, and digested with an excess of double salt, the weight
of which is known. After the undecomposed quantity is found by
permanganate or bichromate, the remainder is multiplied by the
factor O'lll, which gives the proportion of dioxide present,
whence the percentage may be calculated.

The decomposition of the ore may be made in any of the
apparatus used for titrating ferrous iron. The ore is first put
into the decomposing flask, then the iron salt and \vater, so as to
dissolve the salt to some extent before the sulphuric acid is added.
Sulphuric acid should be used in considerable excess, arid the
flask heated by the spirit lamp till all the ore is decomposed ;
the solution is then cooled, diluted, and the whole or part titrated
with permanganate or bichromate.

Example : 1 gin. of double iron salt was titrated with permanganate
solution of which 21'4 c.c. were required.

I'll I gm. of the sample of manganese was accurately weighed and digested
with 8 gin. of iron salt, and sulphuric acid. After the decomposition, 8'8 c.c.
of permanganate were required to peroxidize the undecomposed iron salt
(=0'42 gm.), which deducted from the 8 gm. originally used left 7*58 gin. ;
or placing the decimal point one place to the right, 75'8 per cent, of pure
dioxide.

In the case of using -^ bichromate for the titration, the following-
plan is convenient : — 100 c.c. of —^ bichromate = 3 '92 gm. of double
iron salt (supposing it to be perfectly pure), therefore if 0'436 gm.
of the sample of ore be boiled with 3 '92 gm. of the double salt
and excess of acid, the number of c.c. of bichromate required
deducted from 100 will leave the number corresponding to the
percentage.

Example : 0'436 gm. of the same sample as examined before was boiled
with 3'92 gm. of double salt, and afterwards required 24 c.c. 'of T^ bichro-
mate, which deducted from 100 leaves 76 per cent, of dioxide, agreeing very
closely with the previous examination.

When using metallic iron for the titration (which in most cases is preferred)
Pattinson proceeds as follows:— 30 grn. of clean iron wire are placed in
a suitable apparatus, with 3 oz. of dilute sulphuric acid, made by adding
3 parts of water to one of concentrated acid. When the iron is quite dissolved,
30 grn. of the finely powdered and dried sample of manganese ore to be
tested are put into the flask, the cork replaced, and the contents again made

238 VOLUMETRIC ANALYSIS. § 68.

to boil gently over a gas flame until it is seen that the whole of the black
part of the manganese is dissolved. The Avater in the small flask is then
allowed to recede through the bent tube into the larger flask, more distilled
Avater is added to rinse out the small flask or beaker and bent tube, the cork
well rinsed, and the contents of the flask made up to about 8 or 10 oz. with
distilled water. The amount of iron remaining unoxidized in the solution
is then ascertained by means of a standard solution of potassic bichromate.
The amount indicated by the bichromate deducted from the total amount of
iron used, gives the amount of iron which has been oxidized by the manga-
nese ore, and from which the percentage of manganic dioxide contained in
the ore can be calculated. Thus, supposing it were found that 4 grn. of
iron remained unoxidized, then 30—4—26 grn. of iron which have been
oxidized by the 30 grn. of ore. Then, as

5G : 43'5 : : 26 : 20'2

the amount of dioxide in the 30 gru. of ore. The percentage is therefore
67'33. Thus—

30 : 20-2 : : 100 : 67'33

Grain weights are given in this example, but those who use the
.gram system will have no difficulty in arranging the details
.accordingly.

MERCURY.

Hg = 200.

1 c.c. T\ solution = 0-0200 gm. Hg.
-0-0208 gm. Hg20
= 0-0271 gm. HgCl2

Double iron salt x 0*5104 = Hg.

„ x 0-6914 = HgCl2

1. Precipitation as Mercurous Chloride.

§ 68. THE solution to be titrated must not be warmed, and
must contain the metal only in the form of protosalt. ~ sodic
•chloride is added in slight excess, the precipitate washed with the
least possible quantity of water to ensure the removal of all the
sodic chloride • to the nitrate a few drops of chromate indicator are
added, then pure sodic carbonate till the liquid is of a clear yellow
colour, y1^- silver is then delivered in till the red colour occurs.
The quantity of sodic chloride so found is deducted from that
originally used, and the difference calculated in the usual way.

2. By Ferrous Oxide and Permanganate (Mohr).

This process is based on the fact that when mercuric chloride
(corrosive sublimate) is brought in contact with an alkaline solution
of ferrous oxide in excess, the latter is converted into ferric oxide,
while the mercury is reduced to mercurous chloride (calomel).
The excess of ferrous oxide is then found by permanganate or
^bichromate —

2HgCl2 + 2FeCl2 = Hg2Cl2 + Fe2Cl6.

§ 68. MERCURY. 239

It is therefore advisable in all cases to convert tlie mercury to be
estimated into the form of sublimate, by evaporating it to dryness
with nitro-liydrochloric acid ; this must take place, however, below
boiling heat, as vapours of chloride escape with steam at 100° C.
(Fresenius).

Citric acid or free chlorine must be altogether absent during
the decomposition with the iron protosalt, otherwise the residual
titration will be inexact, and the quantity of the iron salt must be
more than sufficient to absorb half the chlorine in the sublimate.

Example : 1 gm. of pure sublimate was dissolved in warm water, and
3 gm. of double iron salt added, then solution of caustic soda till freely
ulkaline. The mixture became muddy and dark in colour, and was well
shaken for a few minutes, then sodic chloride and sulphuric acid added, con-
tinuing the shaking till the colour disappeared and the precipitate of ferric
oxide dissolved, leaving the calomel white ; it Avas then diluted to 300 c.c.
filtered through a dry filter, and 10D c.c. titrated with ^ permanganate, of
which 13'2 c.c. were required — 13'2 x 3=39'6, which deducted from 76'5 c.c.
(the quantity required .for 3 gm. double iron salt), left 36'9 c.c.=r447 gm.
of undecomposed iron salt, which multiplied by the factor 0'6914, gave
1-0005 gm. of sublimate, instead of 1 gm., or the 36'9 c.c. may be multiplied
by the ^ factor for mercuric chloride, which will give 1 gm. exactly.

3. By Iodine and Thiosulphate (Hem pel).

If the mercury exist as a protosalt it is precipitated by sodic
chloride, the precipitate well washed and together with its filter
pushed through the funnel into a stoppered flask, a sufficient
quantity of potassic iodide added, together with —^ iodine solution
(to 1 gm. of calomel about 2 '5 gm. of iodide, and 100 c.c. of ~
iodine), the flask closed, and shaken till the precipitate has
dissolved —

Hg2Cl2 + 6KI + 21 = 2HgK2P + 2KC1.

The brown solution is then titrated with ^ thiosulphate till
colourless, diluted to a definite volume, and a measured portion
titrated with ~ iodine and starch for the excess of thiosulphate.
1 c.c. T^- iodine = 0'02 gm. Hg.

Where the mercurial solution contains nitric acid, or the metal
exists as peroxide, it may be converted into protochloride by the
reducing action of ferrous sulphate, as in Mohr's method. The
solution must contain hydrochloric acid or common salt in sufficient
quantity to transform all the mercury into calomel. At least three
times the weight of mercury present of ferrous sulphate in solution
is to be added, then caustic soda in excess, the muddy liquid well
shaken for a few minutes, then dilute sulphuric acid added in
excess, and the mixture stirred till the dark-coloured precipitate
lias become perfectly white. The calomel so obtained is collected
on a filter, well washed, and titrated with T^- iodine and thiosulphate
as above. '

240 VOLUMETRIC ANALYSIS. § 68.

4. Direct Titration -with Sodic Thiosulphate (Scherer).

The standard thiosulphate is made by dissolving -^ eq. = 12'4
gm. of the salt in 1 liter of water.

The reaction which takes place with thiosulphate in the case of
mercurous nitrate is —

- Hg2S + Na2SO* + N*05.
With mercuric nitrate —

3Hg(N03)2 + 2Na2S203 - 2HgS.Hg(N03)2 + 2Xa2804 + 23S'205.
"With mercuric chloride —

SHgCl2 + 2Na2S203 + 2H20 - 2HgS.HGl2 + 2Xa2SO* + 4HC1.

(a) Mercurous Salts. — The solution containing the metal as a pro to-
salt only is diluted, gently heated, and the thiosulphate delivered in from the
burette at intervals, meanwhile well shaking until the last drop produces no
brown colour. The sulphide settles freely, and allows the end of the reaction
to be easily seen. 1 c.c. of thiosulphate— 0'020 gm. Hg, or 0'0208 gm.
Hg20.

(b) Mercuric Nitrate.— The solution is considerably diluted, put into
a stoppered flask, nitric acid added, and the thiosulphate cautiously delivered
from the burette, vigorously shaken meanwhile, until the last drop produces
no further }rellow precipitate. Scherer recommends that when the greater
part of the metal is precipitated, the mixture should be diluted to a definite
volume, the precipitate allowed to settle, and a measured quantity of the
clear liquid taken for titration ; the analysis may then be checked by a second
titration of the clear liquid, if needful. 1 c.c. thiosulphate=0'015 gin. Hg,
or 0-0162 gm. HgO.

(c) Mercuric Chloride. — With mercuric chloride (sublimate) the end of
the process is not so easily seen. The procedure is as follows : — The very
dilute solution is acidified with hydrochloric acid, heated nearly to boiling,
and the thiosulphate cautiously added so long as a white precipitate is seen
to form ; any great excess of the precipitant produces a dirty -looking colour.
Filtration is necessary to distinguish the exact ending of the reaction, for
which purpose Beale's filter (fig. 23) is useful.

Liebig's method is the reverse of that used for determining
chlorides in urine, sodic phosphate being used as indicator in the
estimation of mercury, instead of the urea occurring naturally in
urine The method is capable of very slight application.

5. As Mercuric Iodide (Personne), Compt. Rend. Ivi. 63.

This process is founded on the fact that if a solution of mercuric
chloride be added to one of potassic iodide, in the proportion of
1 equivalent of the former to 4 of the latter, red mercuric iodide is
formed, which dissolves to a colourless solution until the balance is
overstepped, when the brilliant red colour of the iodide appears as
a precipitate, which, even in the smallest quantity, communicates-
its tint to the liquid. The mercuric solution must always be added

§ 68. MEUCUKY. 241

to the potassic iodide ; a reversal of the process, though giving
eventually the same quantitative reaction, is nevertheless much less
speedy and trustworthy. The mercurial compounds to be estimated
by this process must invariably be brought into the form of neutral
mercuric chloride.

The standard solutions required are decinormal, made as follows : —

Solution of Potassic iodide. — 33*2 gm. of pure salt to 1 liter.
1 c.c.=0-01 gin. Hg. or 0-01355 gm. HgCR

Solution of Mercuric chloride — 13 '537 gm. of the salt, with
about 30 gm. of pure sodic chloride (to assist solution), are dissolved
to 1 liter. 1 c.c. =0*1 gm. Hg.

The conversion of various forms of mercury into mercuric chloride
is, according to Personne, best effected by heating with caustic
soda or potash, and passing chlorine gas into the mixture, which
is afterwards boiled to expel excess of chlorine (the mercuric
chloride is not volatile at boiling temperature when associated with
alkaline chloride). The solution is then cooled and diluted to
a given volume, placed in a burette, and delivered into a measured
volume of the decinormal potassic iodide until the characteristic
colour occurs. It is preferable to dilute the mercuric solution con-
siderably, and make up to a given measure, say 300 or 500 c.c. ;
and as a preliminary trial take 20 c.c. or so of iodide solution,
and titrate it with the mercuric solution approximately with
a graduated pipette ; the exact strength may then be found by
using a burette of sufficient size.

6. By Potassic Cyanide (Hannay).

This process is exceedingly valuable for the estimation of almost
all the salts of mercury when they occur, or can be separated, in
a tolerably pure state. Organic compounds are of no consequence
unless they affect the colour of the solution.

The method depends on the fact that free ammonia produces
a precipitate, or (when the quantity of mercury is very small) an
opalescence in mercurial solutions, which is removed by a definite
amount of potassic cyanide.

The delicacy of the reaction is interfered with by excessive
quantities of ammoniacal salts, or by caustic soda or potash ; but
this difficulty is lessened by the modification suggested by Tuson
and Xeison (J. C. S. 1877, 679).

Chapman Jones (/. C. S. Ixi. 364) has further modified the
process so as to make it easier to detect the end-point, and says of
the method as worked by Tuson and Xeison: "Their general
method consists in dissolving the mercury compound in acid, as
may be convenient, adding a little ammonium chloride, and then
potassic carbonate, until an opalescent precipitate appears. The

242 VOLUMETKIC ANALYSIS. § G8.

cyanide solution is then added. They give experiments showing
the trustworthiness of the process as applied to the nitrate,
sulphate, acetate, oxalate, sebate, and citrate of mercury ; and
state that the presence of nitrates, sulphates, chlorides, acetates,
oxalates, citrates, and butyrates of potassium, sodium, calcium,
and magnesium, and organic matter as far as tested, does not
interfere with the accuracy of the method.

From my experience, I cannot affirm that these methods of
working are satisfactory. There is considerable uncertainty as to
the end of the reaction, because less potassic cyanide will effect
a clearance if longer time is allowed.

These difficulties and uncertainties can, I find, be entirely
eliminated, and the process reduced to a series of operations which
are comparatively simple and rapid, by performing the titration in
an entirely different manner from either variation suggested by
the authors referred to. I employ a solution of mercuric chloride
containing O'Ol gm. of metal per c.c., and a solution of crystallized
potassic cyanide made by dissolving 7 gm. to the liter, the exact
value of which is found by titrating it against the mercury solution.
Strong ammonia diluted to ten times its bulk, and some diluted to
fifty or a hundred times its bulk, are convenient.

Process : If the mercury solution is not fit for titration, the metal is
precipitated as sulphide, which, after washing, is washed off the filter and
allowed to subside ; the clear water is then decanted off, and aqua regia
added to the moist residue. The precipitate, with the paper it is on, might
doubtless be treated direct with aqua regia, as Tuson and Neison found
that organic matter, so far as ihey tried it, does not influence the result.
To avoid the possibility of volatilizing the mercury salt, the aqua regia is
allowed to act in the cold. In a few hours, sometimes in far less time, the
residue is of a pure ^yellow colour, and the solution may be diluted and
filtered. The solution, or an aliquot part of it, is then coloured distinctly
with litmus, treated with successive small quantities of powdered potassic
carbonate until alkaline, warming but slightly, and then rendered just acid
with dilute hydrochloric acid, with subsequent boiling to remove the carbonic-
anhydride. The mercury is not precipitated at all, unless the carbonic
anhydride is boiled out before acidification. After cooling, the dilutest
ammonia mentioned above is added, a drop at a time, until the litmus in the
solution shows that the excess of acid is very slight, or in just insufficient
quantity to produce a permanent precipitate. A quantity of cyanide
solution, which is known to be in excess of that required, is added, and, as
a guide for the first titration, the ammonia may be added until a slight
precipitate is produced, and cyanide until the solution is cleared. Two or
three drops (not more) of the 1 in 10 ammonia are introduced, and then
more of the mercury solution is added until the permanent turbidity
produced matches that obtained by adding O'l c.c. of the mercury solution
to about the same bulk of water as the test, and containing approximately
the same amounts of litmus and free ammonia. Each drop of the mercury
solution added produces its maximum turbidity in a few seconds, and it can
be seen at a glance, if the flasks are properly placed, whether this turbidity
is equal to or less than the standard. In a few seconds more it is quite
obvious whether the turbidity is permanent or is growing less. Too much
free ammonia causes the precipitate to clot together, and so vitiates the
result. The presence of the litmus tends, in my experience, to lessen the

§ G9. NICKEL. 243

error due to the variation in the state of aggregation of the precipitate
when too much ammonia has been added. The turbidities so obtained will
remain apparently unchanged for many hours. The (VI c.c. excess of
mercury solution is of course allowed for in the calculation."

NICKEL.

§ 69. THE estimation of this metal volumetrically has now
become satisfactory, and we are indebted to T. Moore (C. N. Ixxii.
92) for a much more perfect process than was given by him in the
previous edition. The modified process consists in discarding the
use of cupric ferrocyanide as the indicator, and substituting silver
iodide in its place. Moore's own description of the method is as
follows : —

"If to an ammoniacal solution of nickel containing Agl in
suspension (silver iodide being almost insoluble in weak ammonia)
there is added potassic cyanide, the solution will remain turbid so
long as all the nickel is not converted into the double cyanide of
nickel and potassium, the slightest excess of cyanide being indicated
by the clearing up of the liquid, and, furthermore, this excess
may be exactly determined by adding a solution of silver until the
turbidity is reproduced. It is a fortunate circumstance that the
complicated side-reactions existing in Parke's copper assay do not
appear to take place with nickel solutions, at least not when the
temperature is kept below 20° C. This is fully borne out by the
fact that the potassic cyanide may be standardized on either silver
or nickel solutions with equal exactness. In practice it has been
found best to proceed in the following manner : —

Standard solution of Silver nitrate, containing about 3 gm. of
silver per liter. The strength of this solution must be accurately
known.

Potassic iodide, 10 per cent, solution.

Potassic cyanide, 22 to 25 gm. per liter. This solution must be
tested every few days, owing to its liability to change.

Standardizing- the Cyanide Solution. — This may be accomplished in
two ways: (a) on a solution of nickel of known metallic contents, or (6) on
the silver solution.

(a) First accurately establish the relation of the cyanide to the silver
solution, by running into a beaker 3 or 4 c.c. of the former; dilute this with
about 150 c.c. of water, render slightly alkaline with ammonia, and then add
a few drops of the potassic iodide. Now carefully run in the silver solution
until a faint permanent opalescence is produced, which is finally caused to
disappear b\~ the further addition of a mere trace of cyanide. The
respective volumes of the silver and cyanide solutions are then read off, and
the equivalent in cyanide of 1 c.c. silver solution calculated. A solution
containing a known quantity of nickel is now required. This must have
sufficient free acid present to prevent the formation of any precipitate, on
the subsequent addition of ammonia to alkaline reaction ; if this is not so,
a little anmionic chloride may be added. A carefully measured quantity of
the solution is then taken, containing about O'l gm. of nickel, and rendered
distinctly alkaline with ammonia, a few drops of potassic iodide added, and

R 2

244 VOLUMETEIG ANALYSIS. § 69.

the liquid diluted to 150 or 200 c.c. A few drops of the silver solution are
now run in, and the solution stirred to produce a uniform turbidity. The
solution is now ready to be titrated with the potassic cyanide, which is
added slowly and with constant stirring until the precipitate wholly
disappears; a few extra drops are added, after which the beaker is placed under
the silver nitrate burette, and this solution gently dropped in until a faint
permanent turbidity is again visible ; this is now finally caused to dissolve
by the mere fraction of a drop of the cyanide. A correction must now be
applied for the excess of the cyanide added, by noting the amount of silver
emplo^yed, and working out its value in cyanide from the data already
found; this excess must then be deducted, the corrected number of c.c.
being then noted as equivalent to the amount of nickel employed.

(b) Having determined the relative value of the cyanide to the silver
solution, and knowing accurately the metallic contents of the latter, then
Ag x G'27196 gives the nickel equivalent. This method is quite as accurate
as the direct titration.

A modification of the above process, wherein one burette only
is necessary, has been found very convenient, and lias given most
excellent results. It is as follows : —

When a solution of potassic cyanide, containing a small quantity of
silver cyanide dissolved in it, is added to an ammoniacal solution of nickel
containing potassic iodide, it is seen that silver iodide is precipitated, and
the turbidity thus caused in the solution continues to increase up to the
point where the formation of the nickelo-potassic c}ranide is complete ; any
further addition after this stage is reached will produce a clearing up of the
liquid, until, at last, the addition of a single drop causes the precipitate to
vanish. This final disappearance is most distinct, and leaves no room for
doubt. Such a solution may be prepared by dissolving 20 to 25 gm. of
potassic cyanide in a liter of water, adding to this about 0'25 gm. silver
nitrate previously dissolved in a little water. For large quantities of nickel
the quantity of silver may advantageously be diminished, and vice versa.
The value of the cyanide is best ascertained in the manner already
described, on a nickel solution.

Small quantities of cobalt do not seriously affect the results, but
It must be remembered that it will be estimated with the nickel ;
its presence is at once detected by the darkening of the solution.
Manganese or copper render the process valueless, so also does
zinc ; the latter, however, in alkaline pyrophosphate solution
exercises no influence. In the presence of alumina, magnesia, or
ferric oxide, citric acid, tartaric acid, or pyrophosphate of soda
may be employed to keep them in solution. The action of iron is
somewhat deceptive, as the solution, once cleared up, often
becomes troubled again on standing for a minute ; should this
occur, a further addition of cyanide must be given until the liquid
is rendered perfectly limpid. The temperature of the solution
should never exceed 20° C. : above this the results become
irregular. The amount of free ammonia has also a disturbing
influence ; a large excess hinders or entirely prevents the reaction ;
the liquid should, therefore, be only slightly but very distinctly
alkaline. A word of caution must be given regarding the potassic
cyanide, as many of the reputed pure samples are very far from

§ 70. NITRATES. 245

being so. The most hurtful impurity is, however, sulphur, as it
gives rise to a darkening of the solution, owing to the formation of
the less readily soluble silver sulphide ; to get rid of the sulphur
impurity it is necessary to thoroughly agitate the cyanide liquor
with oxide of lead, or, what is far preferable, oxide of bismuth.

As regards the exactness of the methods, it may be said, that,
after a prolonged experience, extending over many thousands of
estimations, they have been found to be more accurate and reliable
than either the electrolytic or gravimetric methods, and when time
is a consideration the superiority is still more pronounced. The
employment of organic acids or sodic pyrophosphate in the case
when iron, zinc, etc., are present, allows the operator to dispense
with the tedious separation which their presence otherwise entails-;
and this is a matter of considerable importance in the assay of
nickel mattes or German silver."

NITROGEN AS NITRATES AND NITRITES.

Nitric Anhydride.

:NT205=108.

Nitrous Anhydride.

Normal acid x 0-0540 = ]ST205

Ditto x 0-1011 =KNT03

Metallic iron x 0-3750 = HNO3

Ditto x 0-601 8 = KN03

Ditto x 0-3214 = N205

§ 70. THE accurate estimation of nitric acid in combination.
presents great difficulties, and can only be secured by indirect
means ; the methods here given are sufficient for most purposes.
Very few of them can be said to be simple, but it is to be feared
that no simple process can ever be obtained for the determination
of nitric acid in many of its combinations.

1. Gay L.US sac's Method modified by Abel (applicable only
to Alkaline Nitrates).

This process depends upon the conversion of potassic or sodic
nitrates into carbonates by ignition with carbon, and the titration
of the carbonate so obtained by normal acid. The number of c.c.
of normal acid required multiplied by O'lOl will give the weight
of pure potassic nitrate in grams ; by 0'085, the weight of sodic
nitrate in grams.

The best method of procedure is as follows : —

The sample is finely powdered and dried in an air bath, and 1 gm., or- an
equivalent quantity in grains, weighed, introduced into a platinum crucible.

246 VOLUMETRIC ANALYSIS.

and mixed with a fourth of its weight of pure graphite (prepared by
Erodie's process), and four times its weight of pure ignited sodic chloride.
The crucible is then covered and heated moderately for twenty minutes over
a B un sen's burner, or for eight or ten minutes in a muffle (the heat must
not be so great as to volatilize the chloride of sodium to any extent). If
sulphates are present they will be reduced to sulphides ; and as these would
consume the normal acid, and so lead to false results, it is necessary to
sprinkle the fused mass with a little powdered potassic chlorate, and heat
again moderately till all effervescence has ceased. The crucible is then set
aside to cool, warm water added, the contents brought upon a filter, and
washed with hot water till the washings are no longer alkaline. The filtrate
is then titrated with normal acid in the ordinary way.

2. Estimation of Nitrates by Distillation with Sulphuric Acid.

This method is of very general application, but particularly so
with the impure alkaline nitrates of commerce. The process needs
careful manipulation, but yields accurate results.

There are two methods of procedure.

(a) To bring the weighed nitrate into a small tubulated retort with
a cooled mixture of water and strong sulphuric acid, in the proportion of 10
c.c. of water and 5 c.c. of sulphuric acid for 1 gin. of nitrate. The neck of
the retort is drawn out to a point and bent downward, entering a potash or
other convenient bulb apparatus containing normal caustic alkali. The
retort is then buried to its neck in the sand-bath, and heated to 170° C.
(338° Fahr.) so long as any liquid distils over ; the heat must never exceed
175° C. (347° Fahr.), otherwise traces of sulphuric acid will come1 over with
the nitric acid. The quantity of acid distilled over is found by titrating the
fluid in the receiver with normal acid as usual.

(b) Distillation in a Partial Vacuum (Finkener).- — By this
arrangement there is no danger of contaminating the distillate with
sulphuric acid, inasmuch as the operation is conducted in a water
bath, and when once set going needs no superintendence.

The retort is the same as before described, but the neck is not drawn out
or bent; the stopper of the tubulure must be well ground. The receiver is
a 200-c.c. flask with narrow neck, containing the requisite quantity of normal
alkali diluted to about 30 c.c. The receiver is bound, air-tight, to the neck
of the retort (which should reach nearly to the middle of the flask) by
means of a vulcanized tube; the proportions of acid and water before
mentioned are introduced into the retort with a tube funnel. The stopper
of the retort is then removed, and the contents, both of the receiver and
retort, heated by spirit or gas lamp to boiling, so as to drive out the air ; the
weighed nitrate contained in a small tube is then dropped into the retort,
the stopper inserted, the lamps removed, and the retort brought into the
water bath, while the receiver is kept cool with wet tow, or placed in cold
water. The distillate is titrated as before. 1 or 2 gm. of saltpetre require
about four hours for the completion of the process.

Finkener obtained very accurate results by this method.
"When chlorides are present in the nitrate, a small quantity of
moist oxide of silver is added to the mixture before distillation.

§ 70.

NITRATES.

247

3. Estimation by conversion into Ammonia (Schxilze and
Vernon Harcourt).

The principle of this method is based on the fact that when
a nitrate is heated with a strong alkaline solution, and zinc added,

Fig. 44.

ammonia is evolved ; when zinc alone is used, however, the
quantity of ammonia liberated is not a constant measure of the
nitric acid present. Vernon Ha r court and Sie we rt appear to
have arrived independently at the result that by using a mixture
of zinc and iron the reaction was perfect (/. C. S. 1862, 381 ; An.
diem. u. Phar. cxxv. 293).

A convenient form of apparatus is shown in fig. 44.

The distilling flask holds about 200 c.c., and is closely connected by a bent
tube Avith another smaller flask, in such a manner that both may be placed
obliquely upon a sand-bath, the bulb of the smaller flask coming just under
the neck of the larger. The oblique direction prevents the spirting of the
boiling liquids from entering the exit tubes, but as a further precaution,
these latter are in both flasks turned into the form of a hook ; from the second
flask, which must be somewhat wide in the mouth, a long tube passes through
aLiebig's condenser (which may be made of wide glass tube) into an
ordinary tubulated receiver, containing normal sulphuric acid coloured with
an indicator. The end of the distilling tube reaches to about the middle of
the receiver, through the tubulure of which Harcourt passes a bulb
apparatus of peculiar form, containing also coloured normal acid ; instead of
this latter, however, a chloride of calcium tube, filled with broken glass, and
moistened with acid, will answer the purpose. The distilling tube should be
cut at about two inches from the cork of the second flask, and connected by
means of a well-fitting vulcanized tube ; by this means water may be passed
through the tube when the distillation is over so as to remove any traces of
ammonia which may be retained on its sides. All the corks of the apparatus
should be soaked in hot paraffine, so as to fill up the pores.

All being ready, about 50 gm. of finely granulated zinc (best made by
pouring molten zinc into a warm iron mortar while the pestle is rapidly
being rubbed round) are put into the larger flask with about half the
quantity of clean iron filings which have been ignited in a covered crucible
(fresh iron and zinc should be used for each analysis) ; the weighed nitrate
is then introduced, either in solution, or with water in sufficient quantity to

2-iS VOLUMETRIC ANALYSIS. § 70.

dissolve it, strong solution of caustic potash added, and the flask immediately
connected with the apparatus, and placed on a small sand-bath, which can
be heated by a gas-burner, a little water being previously put into the
second flask. Convenient proportions of material are i gm. nitre, and
about 25 c.c. each of water, and solution of potash of spec, grav. .1/3.
The mixture should be allowed to remain at ordinary temperature for about
an hour (Eder).

Heat is now applied to that part of the sand-bath immediately beneath
the larger flask, and the mixture is gradually raised to the boiling point.
"When distillation has actually commenced, the water in the second flask is
made to boil gently ; by this arrangement the fluid is twice distilled, and any
traces of fixed alkali which may escape the first are sure to be retained in the
second flask. The distillation with the quantities above named will occupy
about an hour and a half, and is completed when hydrogen is pretty freely
liberated as the potash becomes concentrated. The lamp is then removed,
and the whole allowed to cool, the distilling tube rinsed into the receiver,
also the tube containing broken glass ; the contents of the receiver are then,
titrated with ^ caustic potash or soda as usual.

Eder recommends that an ordinary retort, with its beak set upwards,
should be used instead of the flask for holding the nitrate, and that an
aspirator should be attached to the exit tube, so that a current of air may be
drawn through during and after the distillation.

Chlorides and sulphates do not interfere with the accuracy
of the results. Harcourt, Eder, and many others, including
myself, have obtained very satisfactory results by this method.

Siewert has suggested a modification of this process. The dis-
tilling apparatus is a 300 — 350 c.c. flask with tube leading to two
small flasks connected together as wash bottles, and containing
standard acid. For 1 gm. of nitre, 4 gm. of iron, and 10 gm.
of zinc filings, with 16 gm, of caustic potash, and 100 c.c. of
alcohol of sp. gr. 0*825 are necessary. After digesting for half an
hour in the cold or in slight warmth, a stronger heat may be
applied to drive out all the ammonia into the acid flasks. Finally.
10 — 15 c.c. of fresh alcohol are admitted to the distilling flask,
and distilled off to drive over the last traces of ammonia, and the
acid solution then titrated residually as usual. The alcohol is
used to prevent bumping, but this is also avoided in the original
process by adopting the current of air recommended by Eder.

The copper-zinc couple devised by Gladstone and Tribe has
been used by Thorp for the reduction of nitrates and nitrites
occurring in water residues, etc. (/. C. S. 1873, 545). The
resulting ammonia is distilled into weak hydrochloric acid, and an
aliquot portion then JSTesslerized in the usual way.

M. W. Williams (J, C. S. 1881, 100) has shown that this
reduction, in the case of small quantities of nitric or nitrous acids,
may be carried on by mere digestion with a properly arranged
couple at ordinary temperatures, and may safely be hastened by
increasing the temperature to about 25° C. in the presence of
certain saline or acid substances ; alkaline substances, on tho
contrary, retard the action. The details are further described ii\
Part VI,

§ TO. NITRATES. 249

4. By Oxidation of Ferrous Salts (Pelouze). Not available in the
presence of Organic Matter.

The principle upon which this well-known process is based
is as follows : —

(a) When a nitrate is brought into contact with a solution of
ferrous oxide, mixed with free hydrochloric acid, and heatedj part
of the oxygen contained in the nitric acid passes over to the iron,
forming a persalt, while the base combines with hydrochloric acid,
and nitric oxide (NO2) is set free. 3 eq. iron= 168 are oxidized
by 1 eq. nitric acid— 63. If, therefore, a weighed quantity of the
nitrate be mixed with an acid solution of ferrous chloride or
sulphate of known strength, in excess, and the solution boiled, to
expel the liberated nitric oxide, then the amount of unoxidized
iron remaining in the mixture found by a suitable method of
titration, the quantity of iron converted from ferrous into ferric
oxide will be the measure of the original nitric acid in the propor-
tion of 168 to 63 ; or by dividing 63 by 168, the factor 0'375 is
obtained, so that if the amount of iron changed as described be
multiplied by this factor, the product will be the amount of nitric
acid present.

This method, though theoretically perfect, is in practice liable to
serious errors, owing to the readiness with which a solution of
ferrous oxide absorbs oxygen from the atmosphere. On tins-
account accurate results are only obtained by conducting hydrogen
or carbonic acid gas through the apparatus while the boiling is-
carried on. This modification has been adopted by Fresenius
with very satisfactory results.

The boiling vessel may consist of a small tubulated retort, supported
in such a manner that its neck inclines upward : a cork is fitted into the
tubulure, and through it is passed a small tube connected with a vessel for
generating either carbonic acid or hydrogen. If a weighed quantity of pure
metallic iron is used for preparing the solution, the washed carbonic acid or
hydrogen should be passed through the apparatus while it is being dissolved ;
the solution so obtained, or one of double sulphate of iron and ammonia of
known strength, being already in the retort, the nitrate is carefully introduced,
and the mixture heated gently by a small lamp, or by the water bath, for ten
minutes or so, then boiled until the dark-red colour of the liquid disappears,,
and gives place to the brownish-yellow of ferric compounds. The retort is
then suffered to cool, the current of carbonic acid or hydrogen still being
kept up, then the liquid diluted freely, and titrated with & permanganate.

Owing to the irregularities attending the use of permanganate
with hydrochloric acid, it is preferable, in case this acid has been
used, to dilute the solution less, and titrate with bichromate. Two
grams of pure iron, or its equivalent in double iron salt, 0'5 gm.
of saltpetre, and about 60 c.c. of strong hydrochloric acid, are
convenient proportions for the analysis.

Eder (Z. a. C. xvi. 267) has modified Fresenius' improve-
ments as follows : —

250 VOLUMETRIC ANALYSIS.

1*5 gm. of very thin iron wire is dissolved in 30 to 40 c.c. of pure fuming
hydrochloric acid, placed in a retort of about 200 c.c. capacity ; the beak of
the retort points upwards, at a moderately acute angle, and is connected with
ti U-tube, which contains water. Solution of the iron is hastened ~by appty-
ing a small flame to the retort. Throughout the entire process a stream of
CO2 is passed through the apparatus. When the iron is all dissolved the
solution is allowed to cool, the stream of CO2 being maintained ; the weighed
quantity of nitrate contained in a small glass tube (equal to about 0'2 gm.
HNO3) is then quickly passed into the retort through the neck ; the heating
is continued under the same conditions as before, until the liquid assumes
the colour of ferric chloride. The whole is allowed to cool in a stream of
CO2 ; water is added in quantity, and the unoxidized iron is determined l>y
titration with permanganate. The results are exceedingly good.

If the CO2 be generated in a flask, with a tube passing down-
wards for the reception of the acid, air always finds its way into the
retort, and the results are unsatisfactory. Eder recommends the
use of Kipp's CO2 apparatus. By carrying out the operation
exactly as is now to be described, he has obtained very good results
with ferrous sulphate in place of chloride.

The same apparatus is employed ; the tube through which CO2 enters the
retort passes to the bottom of the liquid therein, and the lower extremity of
this tube is drawn out to a fine point. The bubbles of CO2 are thus reduced
in size, and the whole of the nitric acid is removed from the liquid by the
passage of these bubbles. The iron wire is dissolved in excess of dilute
sulphuric acid (strength 1 : 3 or 1 : 4). When the liquid in the retort has
become cold, a small tube containing the nitrate is quickly passed, by means
of a piece of platinum wire attached to it, through the tubulus of the retort,
and the cork is replaced before the tube has touched the liquid ; CO2 is again
passed through the apparatus for some time, after which, by slightly loosening
the cork, the tube containing the nitrate is allowed to fall into the liquid.
The Avhole is allowed to remain at the ordinary temperature for about an
hour — this is essential— after which time the contents of the retort are heated
to boiling, CO2 being passed continuously into the retort, and the boiling
continued till the liquid assumes the light yellow colour of ferric sulphate.
After cooling, water is added (this maybe omitted with bichromate), and the
unoxidized iron is determined by permanganate.

Eder also describes a slight modification of this process, allowing
of the use of a flask in place of the retort, and of ammonio-ferrous
sulphate in place of iron wire. Although the titration with per-
manganate is more trustworthy when sulphuric acid is employed
than when hydrochloric acid is used, he nevertheless thinks that the
use of ferrous chloride is generally to be recommended in preference
to that of ferrous sulphate. When the chloride is employed, no
special concentration of acid is necessary ; the nitric oxide is more
readily expelled from the liquid, and the process is finished in
a shorter time.

The final point in the titration with permanganate, when the
sulphate is employed, is rendered more easy of determination by
adding a little potassic sulphate to the liquid.

& Direct titration of the resulting- Ferric salt by Stanncms

§ 70. NITRATES. 251

Chloride. — Fresenius has adopted the use of stannous chloride for
titrating the ferric salt with very good results.

The following plan of procedure is recommended by the same
authority.

A solution of ferrous sulphate is prepared by 'dissolving 100 gm. of the
crystals in 500 c.c. of hydrochloric acid of spec. grav. 1*10 ; when used for
the analysis, the small proportion of ferric oxide invariably present in it
is found by titrating with stanuous chloride. The nitrate being Aveighed
or measured, is brought together with 50 c.c. (more or less, according to the
quantity of nitrate) of the iron solution into a long-necked flask, through
the cork of which two glass tubes are passed, one connected with a CO'2
apparatus, and reaching to the middle of the flask, the other simply an outlet
for the passage of the gas. When the gas has driven out all the air, the flask
is at iirst gently heated, and eventually boiled, to dispel all the nitric oxide.
The CO2 tube is then rinsed into the flask, and the liquid, while still boiling
hot, titrated for ferric chloride, as in § 64.1.

The liquid must, however, be suffered to cool before titrating
with iodine for the excess of stannous chloride. While cooling,
the stream of CO2 should still be continued. The quantity of iron
changed into peroxide, multiplied by the factor O375, will give the
amount of nitric acid.

Example : (1) A solution of stannous chloride was used for titrating
10 c.c. of solution of pure ferric chloride containing 0*215075 gm. Fe.
25'65 c.c. of tin solution were required, therefore that quantity was equal
to 0*0807 gm. of HNO3, or 0*069131 gm. of N2O5-

(2) 50 c.c. of acid ferrous sulphata were titrated with tin solution for
ferric oxide, and 0*24 c.c. was required.

(3) 1 c.c. tin solution=3*3 c.c. iodine solution.

(4) 0*2177 gm. of pure nitre was boiled, as described, with 50 c.c. of the
acid ferrous sulphate, and required 45*03 c.c. tin solution, and 4*7 c.c. iodine —

4*7 c.c. iodine solution =1*42 c.c. SnCl'2

The peroxide in the protosulphate solution=0*24 c.c.

f66

45-03 — 1-66=43-37, therefore 25'65 : 0'069131=43'37 : ^,=0*1169 N2O5
instead of 0'1163, or 53*69 per cent, instead of 53*41. A mean of this, with
three other estimations, using variable proportions of tin and iron solutions,
gave exactly 53*41 per cent. The process is therefore entirely satisfactory in
the case of pure materials.

The above process is slightly modified by Eder. About 10 gm.
of ammonio-ferrous sulphate are dissolved in a flask, in about 50 c.c.
of hydrochloric acid (sp. gr. 1 -07) in a stream of CO2. The tube
through which the CO2 enters is drawn to a point ; an exit-tube,
somewhat trumpet-shaped, to admit of any liquid that may spirt
rinding its way back into the flask passes downwards into water.
After solution of the double salt, the nitrate is dropped in with
the precautions already detailed, and the liquid is boiled until the
nitric oxide is all expelled. The hot liquid is diluted with twice
its own volume of water, excess of standard stannous chloride
solution is run in, the whole is allowed to cool in a stream of CO2,
and the excess of tin is determined by means of standard iodine.

^JtS

f OF THE

(UNIVERSITY
V r^,.

9n9

VOLUMETEIC ANALYSIS.

(c) Holland's Modification of the
Pelouze Process. — The arrangement of
apparatus shown in fig. 45 obviates the
use of an atmosphere of H or CO2. A is
a long-necked assay flask drawn off at B, so
as to form a shoulder, over which is passed
a piece of stout pure india-rubber tube, D,
about 6 centimeters long, the other end
terminating in a glass tube, F, drawn off
so as to leave only a small orifice. On
the elastic connector D is placed a screw
clamp. At c, a distance of 3 centimeters
Fig. 45. from the shoulder, is cemented with

a blow-pipe a piece of glass tube about

2 centimeters long, surmounted by one of stout elastic tube rather
more than twice that length. The elastic tubes must be securely
attached to the glass by binding with wire. After binding, it is as
well to turn the end of the conductor back, and smear the inner
surface with fused caoutchouc, and then replace it to render the
joint air-tight.

Process : A small funnel is inserted into the elastic tube at c, the clamp
at D being for the time open ; after the introduction of the solution,
followed by a little Avater which washes all into the flask, the funnel is
removed, and the flask supported by means of the wooden clamp, in the
inclined position it occupies in the figure. The contents are now made to
boil so as to expel all air and reduce the volume of the fluid to about 4 or
5 c.c. When this point is reached a piece of glass rod is inserted into the
elastic tube at c, which causes the water vapour to escape through F.

Into the small beaker is put about 50 c.c. of a previously boiled solution of
ferrous sulphate in hydrochloric acid (the amount of iron already existing
as persalt must be known).

The boiling is still continued for a moment to ensure perfect expulsion of
air from F, the lamp is then removed, and the caoutchouc connector slightly
compressed with the first finger and thumb of the left hand. As the flask
cools the solution of iron is drawn into it ; when the whole has nearly receded
the elastic tube is tightly compressed with the fingers, whilst the sides of the
beaker are washed with a jet of boiled water, which is also allowed to pass
into the flask. The washing may be repeated, taking care not to dilute more
than is necessary or admit air. Whilst F is still full of water, the elastic-
connector previously compressed with the fingers is now securely closed with
the clamp, the screw of which is worked with the right hand. Provided
the clamp is a good one, F will remain full of water during the subsequent
digestion of the flask.

After heating in a water bath at 100° for half an hour, the flask is removed
from the water bath and cautiously heated with a small flame, the fingers at
the same time resting on the elastic connector at the point nearest the
shoulder ; as soon as the tube is felt to expand, owing to the pressure from
within, the lamp is removed and the screw clamp released, the fingers main-
taining a secure hold of the tube, the gas-flame is again replaced, and when
the pressure on the tube is again felt, this latter is released altogether, thus
admitting of the escape of the nitric oxide through F, -which should be
below the surface of water in the beaker whilst these manipulations are
performed. The contents of the flask are now boiled until the nitric oxide

NITRATES.

253

is entirely expelled, and the solution of iron shows only the brown colour of
the perchloride. At the completion of the operation the beaker is first
removed, and then the lamp.

It now only remains to transfer the ferric solution to a suitable vessel, and
determine the perchloride with staunous chloride as in b.

A mean of six experiments for the percentage determination of
X-05 in pure nitre gave 53'53 per cent, instead of 53*41. The
process is easy of execution, and gives satisfactory results. The
point chiefly requiring attention is that the apparatus should be
air-tight, which is secured by the use of good elastic tubes and
clamp.

5. S chlos in g-'s Method (available in the presence of Organic

Matter).

The solution of nitrate is boiled in a flask till all air is expelled,
then an acid solution of ferrous chloride drawn in, the mixture
boiled, and the nitric oxide gas collected over mercury in a balloon
filled with mercury and milk of lime ; the gas is then brought,
without loss, in contact with oxygen and water, so as to convert it

again into nitric acid, then titrated with -f^ alkali as usual.

This method was devised by Schlosing for the estimation of
nitric acid in tobacco, and is especially suitable for that and similar
purposes, where the presence of organic matter would interfere with

254 VOLUMETttlC ANALYSIS.

the direct titration of the iron solution. "Where the quantity of
nitric acid is not below O15 gin. the process is fairly accurate, but
needs a special and rather complicated arrangement of apparatus,
the description of which may be found in the original paper in
Annal. de Chim. [3] xl. 479, or in Fresenius' Quant. AnaL, sixth
edition.

An arrangement of apparatus, dispensing with the use of mercury,
has been devised by Wildt and Scheibe (Z. a. C. xxiii. 151),
which simplifies the analysis and gives accurate results with not
less than 0*25 gin. N205. With smaller quantities the results are
too low. Fig. 46 shows the apparatus used.

A is an Erlenmeyer's flask of 250 c.c. capacity, containing
the solution to be analyzed. B is a round-bottomed flask of
250 — 300 c.c. capacity, half filled with caustic soda, to absorb any
HC1 which might be carried over from A. C is an Erlenmeyer's
flask of 750 c.c. capacity, containing a little water to absorb the
nitric acid. D is a tube, containing water to collect any nitric
acid not absorbed by the water in C. The tube d is bent, as shown
in the diagram, and drawn out to a point, to diminish the size of
the bubbles. The tube e is wide, and cut obliquely to prevent
water collecting and passing into C.

Process : The clip b is closed and c opened, and the tube e disconnected
from f. The solutions in A and B are then boiled for 20 minutes to remove
all oxygen. The tubes e and /are again connected, the clip c is closed, the
flame under B increased to prevent the liquid in C from being drawn
back, and the clip b is opened. As soon as steam issues from the tube a, it
is dipped into a conical glass containing 50 c.c. of ferrous chloride prepared
according to Schldsing's directions, and the flume under A is removed.
when the ferrous chloride enters the flask. The clip b is regulated with the
finger and thumb, so as to prevent the entry of air into the flask. The
conical vessel is rinsed two or three times with water, and this is allowed
to enter the flask, and the clip b is then closed, and the vessel A heated.
The liquid in A turns brown in a short time, and nitric acid is evolved.
The clip c is opened slightly from time to time until the pressure is high
enough, when it is opened entirely. The flames must be regulated so that
a slow current of gas bubbles through the water in C. The hydrochloric
acid is removed by the caustic soda in B, and the nitric oxide on coming
in contact with the air in C. is oxidized, and the nitric acid absorbed by
the water. In case the current of gas is too rapid, the escaping nitric
acid is absorbed in I). After an hour the tubes e and / are disconnected,
while the solutions in A and B are still boiling, and the nitric acid is
titrated with dilute caustic soda (about i normal). The vessel C must
be well cooled during the whole experiment, which occupies about an
hour and a half.

Good results were obtained with nitrates of potash and soda,
both alone and mixed with ammonium sulphate, superphosphate,
and amido compounds. With superphosphate the solution should
be made slightly alkaline, to prevent the liberation of nitric acid.

AVarington (J. C. S. 1880, 468) has made a series of experi-
ments on the original Schlosing process, for the purpose of
testing its accuracy, when small quantities of nitric acid have to be

70.

NITRATES.

determined in the presence of organic substances, such for instance
as in soils, the sap of beet-root, etc. ; but instead of converting the
nitric oxide back into nitric acid as in the original method, he
collected the gas either over caustic soda as recommended by
Reich ardt, or over mercury, and ascertained its amount by
measurement in Frankland's gas apparatus. The results obtained
by AVarington plainly showed that even on the most favourable
circumstances the method as usually worked in Germany, either by
the alkalimetric titration or by measurement of the gas, invariably
gave results much too low, especially if the quantity of nitrate
operated on was small, say 5 or 6 centigrams of nitre ; moreover,,

Fig. 47.

when sugar or similar organic substance was present the resulting
gas was very impure, and the distillates were highly coloured from
the presence of some volatile products.. The nitric oxide also
suffered considerable diminution of volume, when left for any time
in contact with the distillate, especially when over caustic soda.
This being the case, the following modification originally recom-
mended by Schlosing was adopted, in which CO2 was employed,
both to assist in expelling the air from the apparatus, and to chase
out the nitric oxide produced.

The form of apparatus adopted by Warington is shown in
fig. 47. The vessel in which the reaction takes place is a small

256 VOLUMETRIC ANALYSIS. § 70.

tubulated receiver, the tubulure of which has been bent near its
extremity to make a convenient junction with the delivery tube,
which dips into a trough of mercury on the left. The long supply
tube attached to the receiver is of small bore, and is easily filled by
a J c.c. of liquid. The short tube to the right is also of small bore,
and is connected by a caoutchouc tube and clamp with an apparatus
for the continuous production of carbonic acid.

In using this apparatus the supply tube is first filled with
strong HC1, and CO2 is passed through the apparatus till a portion
of the gas collected in a jar over mercury is found to be entirely
absorbed by caustic potash. The current of gas is then stopped
by closing the clamp to the right. A chloride of calcium bath at
140° is next brought under the receiver, which is immersed one-
half or more in the hot fluid ; the temperature of the bath is
maintained throughout the operation by a gas burner placed beneath
it. By allowing a few drops of HC1 to enter the hot receiver, the
CO2 it contains is almost entirely expelled. A jar filled with
mercury is then placed over the end of the delivery tube, and all
is ready for the commencement of a determination.

The nitrate, which should be in the form of a dry residue in
a small beaker or basin, is dissolved in about 2 c.c.* of strong
ferrous chloride solution, 1 c.c. of strong HC1 is added, and the
whole is then introduced into the receiver through the supply tube,
being followed by successive rinsings with HC1, each rinsing not
•exceeding a J c.c., as the object is to introduce as small a bulk of
liquid as possible. The contents of the receiver are in a few
minutes boiled to dryness ; a little CO2 is admitted before dryness
is reached, and again afterwards to drive over all remains, of nitric
oxide. If the gas will not be analyzed till next day, it is advisable
to use more CO2, so as to leave the nitric oxide diluted with several
times its volume of that gas. As soon as one operation is concluded
the apparatus is ready for another charge.

This mode of working presents the following advantages : —

(1) The volume of liquid introduced into the apparatus is much
diminished, and with this of course the amount of dissolved air
contributed from this source.

(2) By evaporation to dryness a complete reaction of the nitrate
.and ferrous chloride, and a perfect expulsion of the nitric oxide
formed, is as far as possible attained.

(3) The nitric oxide in the collecting jar is left in contact with
.a much smaller volume of acid distillate, and its liability to
absorption is greatly diminished by its dilution with CO-.

The results obtained with this apparatus by Warington on
small quantities of nitre alone, and mixed with variable quantities

* Supposing the ferrous chloride to contain 2 gm. of iron per 10 c.c., then 1 c.c. of
the solution will be nearly equivalent to 0'12 gm. of nitre, or 0'0166 gin. of nitrogen.
A considerable excess of iron should, however, always be used.

§ 70. NITRATES. 257

of ammonic salts and organic substances including sugar, showed
a marked improvement upon the method as usually carried out.

A further improvement has been made in this method by
Warington (/. C. S. 1882, 345), and described by him as
follows : —

The apparatus now employed is quite similar to that shown in fig. 47, with
the only difference that the bulb retort in which the reaction takes place is
now only 1£ inch in diameter, thus more exactly resembling the. form
employed by Sch losing. A bulb of this size is sufficient for the analysis
of soil extracts ; for determinations of nitrates in vegetable extracts a larger
bulb is required.

The chief improvement consists in the use of CO2 as free as possible from
oxygen. The generator is formed of two vessels. The lower one consists of
a bottle with a tubulurc in the side near the bottom; this bottle is supported
in an inverted position, and contains the marble from which the gas is
generated. The upper vessel consists of a similar bottle standing upright ;
this contains the HC1 required to act on the marble. The two vessels are
connected by a glass tube passing from the side tubulure of the upper vessel
to the inverted mouth of the lower vessel ; the acid from the upper vessel
thus enters below the marble. CO2 is generated and removed at pleasure by
opening a stop-cock attached to the side tubulure of the lower vessel, thus
allowing HC1 to descend and come in contact with the marble. The
fragments of marble used have been previously boiled in water. The boiling
is conducted in a strong flask. After boiling has proceeded some time,
a caoutchouc stopper is fixed in the neck of the flask, and the flame removed ;
boiling will then continue for some time in a partial vacuum. The lower
reservoir is nearly filled with the boiled marble thus prepared. The HC1
has been also well boiled, and before it is introduced into the upper reservoir
it has dissolved in it a moderate quantity of cuprous chloride. As soon as
the acid has been placed in the upper reservoir it is covered by a layer of
oil. The apparatus being thus charged is at once set in active work by
opening the stop-cock of the marble reservoir ; the acid descends, enters the
marble reservoir, and the CO2 produced drives out the air which is necessarily
present at starting. As the acid reservoir is kept on a higher level than the
marble reservoir, the latter is always under internal pressure, and leakage of
air from without cannot occur.

The presence of the cuprous chloride in the hydrochloric acid not only
ensures the removal of dissolved oxygen, but affords an indication to the eye
of the maintenance of this condition. So long as the acid remains of
an olive tint, oxygen will be absent ; but should the acid become of a clear
blue-green, it is no longer certainly free from oxygen, and more cuprous
chloride must be added.

A further slight improvement adopted consists in the use of freshly-boiled
reagents, which are employed in as small a quantity as possible. When
boiling the hydrochloric acid it is well to add a few drops of ferrous chloride,
in order more certainly to remove any dissolved oxygen.

The mode of operation is as follows : — The apparatus is fitted together, the
long funnel tube attached to the bulb retort being filled with water.
Connection is made with the glass stop- cock of the CO2 generator by means
of a short stout caoutchouc tube, provided with a pinch-cock. The pinch-
cock being opened, the stop-cock is turned till a moderate stream of bubbles
rises in the mercury trough ; the stop-cock is left in this position, and the
admission of gas is afterwards controlled by the pinch-cock, pressure on
which allows a few bubbles to pass at a time. The heated chloride of calcium
bath is next raised, so that the bulb retort is almost submerged; the
temperature, shown by a thermometer which forms part of the apparatus,

258 VOLUMETRIC ANALYSIS. § 70.

should be 130 — 140°. By boiling small quantities of water or hydrochloric
acid in the bulb retort in a stream of CO2 the air present is expelled; the
supply of gas must be stopped before the boiling has ceased, so as to leave
little in the retort. Previous to very delicate experiments it is advisable to
introduce through the funnel tube a small quantity of nitre, ferrous chloride,
and hydrochloric acid, rinsing the tube Avith the latter reagent ; any trace of
oxygen remaining in the apparatus is then consumed by the nitric oxide
formed, and after boiling to d^ness, and driving out the nitric oxide with
CO2, the apparatus is in a perfect condition for a quantitative experiment.

Soil extracts may be used without other preparation than concentration.
Vegetable juices, which coagulate when heated, require to be boiled and
filtered, or else evaporated to a thin syrup, treated with alcohol and filtered.
A clear solution being thus obtained, it is concentrated over a water-bath to
the smallest volume, in a beaker of smallest size. As soon as cool, it is mixed
with 1 c.c. of a cold saturated solution of ferrous chloride and 1 c.c. HC1,
both reagents having been boiled and cooled immediately before use. In
mixing with the reagents care must be taken that bubbles of air are not
entangled; this is especial^ apt to occur with viscid extracts. The quantity
of ferrous chloride mentioned is amply sufficient for most soil extracts, but
it is well perhaps to use 2 c.c. in the first experiment of a series; the
presence of a considerable excess of ferrous chloride in the retort is thus
ensured. With bulky vegetable extracts more ferrous chloride should be
employed ; to the syrup from 20 gm. of mangel sap should be added 5 c.c.
of ferrous chloride, and 2 c.c. of hydrochloric acid.

The mixture of the extract with ferrous chloride and HC1 is introduced
through the funnel tube, and rinsed in with three or four successive ^ c.c.
of HC1. The contents of the retort are then boiled to dry ness, a little CO-
being from time to time admitted, and a more considerable quantity used at
the end to expel any remaining nitric oxide. The most convenient tem-
perature is 140°, but in the case of vegetable extracts it is well to commence
at 130°, as there is some risk of the contents of the retort frothing over.
The gas is collected in a small jar over mercury. As soon as one operation
is completed, the jar is replaced by another full of mercury, and the
apparatus is ready to receive a fresh extract. A series of five determinations,
with all the accompanying gas analyses, may be readity performed in one
day. The bulb retort becomes encrusted with charcoal when extracts rich
in organic matter are the subject of analysis ; it is best cleaned first with
water, and then by heating oil of vitriol in it.

Mercury, contrary to the statement in most text-books, is gradually
attacked by hj'drochloric acid in the presence of air ; the mercury in the
trough is thus apt to become covered with a grey chloride, and it is quite
necessary to keep the store of mercury in contact with sulphuric acid to
preserve its mobile condition.

The gas analysis is of a simple character; the gas is measured after
absorption of the CO2 by potash, and again after absorption of the nitric
oxide, the difference giving the amount of this gas. For the absorption of
nitric oxide, a saturated solution of ferrous chloride was for some time
employed. This method is not, however, perfectly satisfactory when the
highest accuracy is required, the nitric oxide being generally rather under-
estimated, except the process of absorption is repeated with a fresh portion
of ferrous chloride. The error is greater in proportion to the quantity of
unabsorbed gas present. ThuSj with a mixture of nitrogen and nitric oxide
containing little of the former, absorption of the nitric oxide by successive
treatment with oxygen and pyrogallol over potash showed 97' 8 per cent, of
nitric oxide ; while the same gas, analyzed by a single absorption with ferrous
chloride (after potash), showed 97' 5 per cent, of nitric oxide. With a mixture
containing more nitrogen, the oxygen method showed 65'9 per cent, of nitric
oxide ; while one absorption with ferrous chloride gave 64'2 per cent., and

§ 70. NITRATES. 259

a second absorption, in which the ferrous chloride was plainly discoloured,
66'2 per cent. The use of ferrous chloride as an absorbent for nitric oxide
has now been given up, and the oxygen method substituted. All the
measurements of the gas are now made without shifting the laboratory
vessel ; the conditions are thus favourable to extreme accuracy^

The chief source of error attending the oxygen process lies in the
small quantity of carbonic oxide produced during the absorption with
pyrogallol ; this error becomes negligible if the oxygen is only used
in small excess. The difficulty of using the oxygen in nicely
regulated quantity may be removed by the use of Bischof's gas
delivery- tube. This may be made of a test-tube, having a small
perforation half an inch from the mouth. The tube is partly
filled with oxygen over mercury, and its mouth is then closed by
a finely-perforated stopper, made from a piece of wide tube, and
fitted tightly into the test-tube by means of a covering of
caoutchouc. When this tube is inclined, the side perforation
being downwards, the oxygen is discharged in small bubbles from
the perforated stopper, while mercury enters through the side
opening. Using this tube, the supply of oxygen is perfectly
under control, and can be stopped as soon as a fresh bubble ceases
to produce a red tinge in the laboratory vessel. The trials made
with this apparatus have been very satisfactory. If nitrites are to
be estimated by this method, it is necessary first to convert them
into nitrates, with excess of hydrogen peroxide, which is entirely
destroyed by the subsequent evaporation to dryness.

Technical method for Alkaline Nitrates and Nitrated Manures.

Wagner uses a simple arrangement of apparatus, which gives
fairly good results, and permits of rapid working.

A 200 c.c. flask is fitted with a two-hole rubber stopper. One hole carries
an ordinary gas delivery tube, and the other a thistle funnel, having a stop-
cock below the funnel. The end of this tube is narrowed, and does not
quite reach the liquid in the flask.

A solution of 200 gm. of iron wire in hydrochloric acid is made and
diluted to 1 liter. 40 c.c. of this solution are placed in the flask, and the air
expelled by boiling. 10 c.c. of a standard solution of sodic nitrate, con-
taining 33 gm. per liter, are then placed in the funnel, and allowed gradually
to drop into the boiling solution of iron. A gas tube graduated to 100 c.c.
is filled with boiled and cooled distilled water, and the nitric oxide collected
in the usual way. When the nitre solution is nearly all dropped in, the
funnel is filled with 20 per cent. HC1, and run down ; this is repeated, the
liquid being still kept gently boiling. 10 c.c. of the solution to be tested
are now put into the funnel, taking care that not more than 100 c.c. of gas
will result. The gas is collected as before in a fresh tube precisely as in the
case of the pure nitrate. In this manner five or six estimations can be
made with the one and the same ferrous solution. Finally, a fresh test is
made with standard nitre solution ; the readings of the tubes are taken, and
as they will all be of same temperature and pressure no correction is
necessary, all being allowed to cool to the same point.

s 2

260 VOLUMETRIC ANALYSIS.

The calculation is easy. Suppose that the pure nitre gave 90c.c.
of gas, this volume = 6-33 gm, of XaXO8, or 1 c.c. = 0*00366
gin. = 0-000604 gm. X.

Technical use of the Pelouze Process for Manures. — Vincent
Edwards adopts the following method for manures containing
nitrates together with ammonia and other matters (C. N. Ixxi. 307).
The solutions required are : —

Standard Potassic bichromate, 14*742 gm. per liter. 1 c.c. =
0-0085 gm. XaXO3 or 0-0101 gm. KXO3.

Ferrous Sulphate. 100 gm. of crystallized salt with 100 c.c. of
concentrated H2S04 per liter.

The exact working strength of these two solutions in practice, is
found by boiling 50 c.c, of the iron solution till it becomes thick
in a stout well annealed glass flask, preferably of Jena glass, which
is fitted with a Buns en valve, made by cutting the rubber tube
with a sharp razor, the glass tube to which it is fitted passing-
through a light fitting rubber stopper ; after boiling the flask is set
aside to cool, then 100 c.c. or so of water are added, and the
titration made with bichromate in the usual way with fresh
solution of ferricyanide as indicator.

Process : 10—20 gm. of the nitrated manure, according to its richness, are
exhausted with water and the liquid made up to 200 c.c.

20 c.c. of this solution are placed in the boiling flask together with 50 c.c.
of the iron solution, the stopper with valve is then inserted, and the mixture
boiled until it becomes thick, and semi-solid drops are splashed against the
sides of the flask ; the flask is then enveloped in a cloth, and removed
to cool ; when this has occurred, 100 c.c. or so of water are run into the flask,
well shaken, then titrated with the bichromate as in the case of the blank
experiment.

Example : The blank titration showed that £0 c.c. of iron solution
required 54 c.c. of bichromate. 20 c.c. of the manure solution = 1 gm.
manure were treated as above described, and required 31 c.c. of bichromate,
therefore 54—31 = 23 c.c. which multiplied by 0'0085 = 0'1955 or 19'55 %
of XaXO3 in the manure. The manure was known to be a mixture of
20°/0 of nitrate of soda, of 95'5% strength, with 80 per cent, of an
ammouiacal guano.

This technical process is, of course, chiefly valuable where the
nitrate is required to be estimated apart from the ammonia,

6. By the Kj eldahl Process.

By the modified method described on page 85, it is now quite
possible to estimate the nitrogen in commercial nitrates with great
accuracy and very little personal attention.

7. lodometric Estimation of Nitrates.

F. A. Goocli and H. Gruener (Amer. J. Sci. xliv. 117)
recommend distilling the nitrate (about 0'2 gm.) with 20 c.c. of

§ 70. NITRATES. 261

a saturated solution of crystallized manganous chloride in strong
hydrochloric acid, in a current of CO'2. The products of the
distillation are passed into a solution of potassic iodide, and the
liberated iodine is afterwards titrated by means of sodic thiosulphate.
3 mols. of iodine correspond with 2 mols. of nitric acid

Process : The apparatus employed consists of a bent pipette, serving
instead of a retort, which is connected with a Kipp's apparatus evolving
CO2. The other goose-neck-like end is sealed to a Will and Varrentrap
nitrogen bulb, the exit tube of which is drawn out, so that it may be pushed
well within the inlet tube of a Will and Varrentrap absorption flask.
A third receiver simply acts as a trap to exclude air from the absorption
apparatus proper. The titration should be completed immediately after the
distillation, during which the nitrogen bulbs should be immersed in cold
wrater; otherwise, traces of dissolved nitric oxide might get oxidized and
liberate more iodine.

Another method worked out by H. Gruener consists in
distilling the nitrate with potassic iodide and phosphoric acid
(Amer. J. Sd. xlvi., July, 1883.)

Process : The nitrate, not to exceed in amount 0'05 gm. of potassio nitrate,
is introduced into a retort, together with ten times its weight of potassic
iodide, and 17 to 20 c.c. of phosphoric acid, of specific gravity 1'43. All
water used should be recently boiled. CO2 is passed from a proper apparatus.
The neck of the retort passes into a receiver containing a known amount
of TV arsenious oxide, alkaline with a good excess of sodic' bicarbonate, and
diluted to a convenient bulk. To this flask is attached for additional safety
a simple trap containing water. The solution in the retort is boiled until it
is clear that no more iodine remains, when the receiver, after proper washing
and addition of the liquid in the trap, is titrated with iodine to find the
amount of arsenious oxide still left. This gives the measure of the iodine
evolved and consequently of the nitrate present.

These processes are simply mentioned here, as perhaps being
available under particular circumstances, but the author has had
no experience of them. The test examples given by the operators
are fairly satisfactory, especially the first.

8. G-asometric estimation as Nitric Oxide.

This method of estimating nitrogen existing as nitric and nitrous
acids, either separately or together, is an exceedingly delicate one,
and capable of great accuracy under proper manipulation.

It is now best known as the Crum-Frankland method, the
original idea emanating from Crum, and afterwards improved in
detail of manipulation by Frankland and Armstrong, in their
well-known method of water analysis.

So far as the use of the method for water analysis is concerned,
the process is given in Part VI., where the shaking tube which is
used for the decomposition of the nitrogen compounds by mercury
and sulphuric acid is figured, and the details of the process as
applied to waters fully described.

262 VOLUMETRIC ANALYSIS. § 70.

The method there given, however, requires the use of a gas
apparatus. This method obviates that necessity, and though the
results cannot be said to be absolutely as exact, they are very
satisfactory for some purposes, such as the examination of nitrous
vitriol, raw commercial nitrates, manures, etc.

The apparatus used is Lunge's nitrometer, a figure of which is
given in the section on technical gas analysis, accompanied with
a description of the method of using it. The 'application of the
instrument to the estimation of nitrous and nitric acids in vitriol
and other substances is explained in the same section.

The volume of the nitric oxide obtained can be read off to -^ c.c. ;
it is reduced by Buns en's tables to 0° and 760 m.m., and the
percentage of the acid calculated from it. Each c.c. of XO,
measured at 0° and 760 m.m., corresponds to 1*343 m.gm. XO, or
1-701 m.gm. K20:}, or 2-417 m.gm. X205, or 4-521 KXCF, or
3-805 m.gm. K"aN03. By this process, of course, nitric and nitrons
acids cannot be distinguished, but are always estimated together.

The principle of the reaction is explained in the section on Water
Analysis (Estimation of titrates and Nitrites), and the satisfactory
nature of the method for vitriol-testing has been amply demonstrated
by Watts, by Davis (C. N. xxxvii. 45), and many others. The
instrument itself has been made in several modified ways, but the
principle of its construction is the same.

Allen (Analyst v. 181) recommends the use of this instrument
for the estimation of nitrates and nitrites in water residues ; and
to obviate the difficulty in reading the volume Avhich sometimes
arises from the mercurial froth, he uses two nitrometers side by
side, in one of which is worked a pure standard nitrate solution,
and in the other the material for analysis under precisely the same
conditions of temperature, pressure, etc. If the apparatus
containing the comparative test is free from leakage, it may be
retained for a long period for the purpose of comparison.

9. Colorimetric Methods.

Phenol Method (Spr eng-el).— Both this and the carbazol method
are applicable chiefly to waters where only small proportions of
nitric acid are to be estimated. The solutions required are —

Standard Potassic nitrate. — 0-7215 gm. of IvXO3 is dissolved
in a liter of water. 1 c.c. of this solution = -f^ m.gm. of X, or one
part X in 100,000. 100 c.c. of it should be diluted to a liter for
use in the actual analysis, and 10 c.c. taken, to avoid the possible
error resulting from measuring only 1 c.c.

Phenol Sulphomc acid. — 80 c.c. of liquefied pure phenol are
poured into 200 c.c. of pure concentrated sulphuric acid in
a flask, and kept on a boiling water bath for eight hours. The
mixture is cooled, and 140 c.c. of pure hydrochloric acid with
420 c.c. of water added. The solution is then ready for use.

§ 70. NITRATES. 263

Process : 10 c.c. of the water under examination and 10 c.c. of the
standard potassic nitrate are pipetted into two small beakers and placed near
the edge of a hot plate. When nearly evaporated they are removed to the
top of the water-oven and left there till they are evaporated to complete
dryness. As this operation usually takes about an hour and a half, it is
better, when time is an object, to evaporate to dryness in a platinum dish
over steam. The residue in each case is then treated with 1 c.c. of the
phenolsulphuric acid, and the beakers are placed on the top of the water-
oven. If the water under examination contain a large quantity of nitrates
the liquid speedily assumes a red colour, which, in a good water, will not
appear for about ten minutes. After standing for fifteen minutes the beakers
are removed, the contents of each washed out successively into a 100 c.c.
measuring glass, a slight excess (about 20 c.c. of 0'96) of ammonia added,
the 100 c.c. made up by the addition of water, and the yellow liquid
transferred to a Nessler glass. The more strongly coloured liquid is then
partly transferred to the measuring glass again and the tints compared
a second time. In this way the tints are adjusted, and when, as far as
possible, matched, the liquid that has been partially removed is made up to
the 100 c.c. mark with water, and, after well mixing, finally compared, If
not exactly the same, a new liquid can at once be made up, probably of
exactly the same tint, as the first experiment gives very nearly the number
of c.c. of the one equivalent to the 100 c.c. of the other. A. E. Johnson
in his very useful Analyst's Laboratory Companion (p. 50) has given
a table for obtaining the nitrogen in parts per 100,000, and also in grains
per gallon, by this method.

In the case of very good waters, 20, 50, or more c.c. should be evaporated
to a small bulk, rinsed into a small beaker, and evaporated to dryness and
treated as above — only 5 c.c. of the standard potassic nitrate ( = 0'5 N in
100,000) being taken. In the case of very bad waters, 10 c.c. should be
pipetted into a 100 c.c. measuring flask and made up to the mark with
distilled water, then 10 c.c. of the well mixed liquid (=1 c.c. original water)
withdrawn and treated as above.

A. II. Gill (Tech. Quarterly vii., 1894, 55—62) has studied
this method, and says : — The phenolsulphonic acid used should be
the pure disulphonic acid (C6H3 (OH) S03H2), which, with nitric
acid, gives picric acid even in the cold (Kekule, Lehrbucli iii. 236.)
To prepare it, 3 gm. of pure phenol and 37 gm. (20 '1 c.c.) of pure
sulphuric acid of 1 '84 sp. gr. are mixed in a flask and heated for
six hours to 100° in a water bath. The acid, as thus prepared,
may crystallize out on standing, but may be brought into solution
again by reheating for a short time.

Process : The author takes 1 or 2 c.c. of the water (diluted if necessary),
containing about 0-0007 m.gm. of nitrogen as nitrate, and rapidly evaporates
over a steam bath, in a 2£ inch porcelain dish, the dish being removed as
soon as dry, or, preferably, when just a drop remains. With "ground
waters/' 10 c.c. of a portion which has been decolourized by alumina in the
cold are evaporated. The residue is treated in the dish with enough of the
acid to cover it, 10 drops (=0'7 c.c.) being usually sufficient, and by stirring
with a glass rod every part of the residue is moistened. Seven c.c. of water
are added and stirred, and then ammonia in excess, and the solution again
stirred. The colour is compared with the standard, either in a similar dish,
or both are poured into tubes If inch deep and f inch internal diameter.

The standard solution of potassic nitrate is made by dissolving
0'720 gm. KNO:s in water, diluting to 1 liter, evaporating 10 c.c. in vacua

264 VOLUMETRIC ANALYSIS. § 70.

over sulphuric acid, treating the residue -with phenolsulphonic acid, as above,
and diluting to 1 liter. One c.c. of this solution contains O'OOL m.gm.
nitrogen. A measured volume of it is made alkaline with ammonia as
required.

The author concludes from his experiments that : —

1. The pure disulphonic acid gives the best results.

2. No advantage is gained by treating the water residue with the acid at
100°, as Sprengel directs; equally good results are obtained in the cold ;
but if the temperature be as low as 0°, decidedly low results are obtained.

3. The amount of acid used makes very little difference so long as there is
enough used.

4. There is a loss of nitrogen during evaporation, which is least if the
evaporation take place in vacua over sulphuric acid, or rapidly in an open
dish at 100° ; slower evaporation, at 65°, caused more loss, and the dry
residues, if further heated, lose nitrogen. The addition of sodium carbonate
does not prevent the loss.

5. Chlorine does not interfere if less than two parts per 100.000 be
present ; if more be present, evaporation should be conducted in vacua ;
but if the chlorine exceed seven parts per 100,000 it should be removed
by pure silver sulphate before evaporation.

6. In comparing the colours the most accurate estimations are made
when the intensity of the colour does not exceed that produced by 1 c.c. of
a water containing about 0'05 part nitrogen per 100,000. The colour
produced by O'lO part per 100,000 is very difficult to match accurately.

7. The process does not estimate the nitrogen as liitrite, as the action of
nitrous acid results in the formation of nitrosophenol C°H4 (NO) (OH),
which is colourless in dilute solutions.

The Carbazol Method. — The standard potassic nitrate and pure
sulphuric acid, as above, are required as well as the following
special reagents : —

(a) Silver sulphate solution containing 4 '3945 gm. per liter;
1 c.c. will precipitate one part of chlorine per 100,000 from
100 c.c. of water.

(b) Aluminium sulphate solution free from chlorides and iron,
5 gm. per liter.

(c) Carbazol Solution. — 0'6 gm. carbazol is dissolved in glacial
acetic acid, and the solution made up to 100 c.c. with the glacial
acid. For use, 1 c.c. of this solution is withdrawn by a pipette
and mixed writh 15 c.c. of pure re-distilled sulphuric acid.

It is advisable to prepare a series of solutions containing 0-03,
0'05, 0'07, etc., parts of nitrogen per 100,000 from the standard
nitrate solution by diluting with water.

Process : To 100 c.c. of the water, the amount of chlorides in which has
first been ascertained, sufficient of the silver sulphate solution is added from
a burette to precipitate all the chlorides. To this solution, containing the
silver chloride in suspension, 2 c.c. of the aluminium sulphate solution are
added, and the whole made up to a convenient bulk, 110 c.c. in the case of
waters containing 1 to 6 parts of chlorine per 100,000. The solution is then
filtered, and 2 c.c. of this filtrate are then taken for the nitrate estimation,
and, of course, the amount found must be calculated from the diluted bulk
of the solution. To the 2 c.c. of the filtered water contained in a test-tube,
4 c.c. concentrated sulphuric acid are added, and the mixture well cooled,

70.

NITRITES.

265

1 c.c. of the carbazol solution in sulphuric acid as above described is then
added, and a bright green colour appears in a few moments if nitrates are
present. The amount of nitrate is roughly gauged from the colour
produced, and 2 c.c. of the standard nitrate solution, considered to be equal
to it, are placed in a second test-tube, and the operation repeated with it and
a fresh 2 c.c. of the water under examination at the same time. If the
tints are not similar a fresh comparison must be made, and in every case it is
necessary to repeat the operation with a fresh quantity of the water, so that
the colours may be developed as nearly as possible simultaneously.

The author states that 0*0008 m.gm.of nitrogen as nitrate maybe detected
by the carbazol method. The removal of chlorides is necessary for accurate
results, but the nitration does not take much time when aluminium sulphate
solution is added as described.

Other special methods for the estimation of nitrates in water
will be given in the section on Water Analysis.

Fig. 48.

NITRITES.
1, lodometric method.

Dunstan and Dymond (Pliarm. Journ.
[3] xix. 741) have devised a method for the
estimation of N203 in organic and inorganic
combination which is both simple in operation
and accurate in results. The authors point
out that although the inorganic nitrites may
be accurately analyzed by gasometric methods,
or by permanganate1, it is impossible to use
such methods for the organic compounds or
their alcoholic solutions. The reaction upon
wThich the method depends is not new, being
based on the following equation —

2HI + 2ffisT02 m 2H20 + 2NO + 12.

The liberated iodine is titrated with -— thio-
sulphate in the usual way. The chief merit
in the process is the simple form of apparatus
used, and which is shewn in fig. 48.

A stout glass flask, having a capacity of
about 100 c.c., is closed by a tightly fitting
rubber stopper, through which passes a piece of
rather wide glass tubing (C), one end of which
(that within the flask) is cut. off obliquely, so
that liquid may flow freely through it. The
other end of the tube is connected by means
of a piece of thick rubber tubing with
a large glass tube, which forms a lipped funnel
(A). A steel screw clamp (B) regulates com-
munication between the funnel and the tube,
and the short interval of rubber which is not
occupied by glass tubing forms a hinge upon

2G6 VOLUMETRIC ANALYSIS. § 70.

which the flask may be moved into a position at right angles to-
the funnel, in order to mix by agitation the liquids which are
introduced into the apparatus. The absence of any leak in the
apparatus is ascertained by boiling about 50 c.c. of water in the
flask until steam has continuously issued from the funnel for some
few minutes, when the screw clip is quickly closed and simul-
taneously the source of heat is removed. A little water is now-
placed in the funnel and the flask is cooled by immersion in water.
On sharply inverting the flask the " click " of the water against
the airless flask should be quite distinct. ]NTo water should be
drawn from the funnel or from any of the joints into the flask,
and no diminution in the intensity of the " click " should be
observed after the apparatus has been standing, neither when the
flask is inverted and the funnel empty should any bubbles of air
pass through into the liquid. Having thus proved the absence
of any leak in the apparatus, it is ready for use. The flask is now
free from all but mere traces of oxygen. A conclusive proof of
this is obtained by boiling in the flask a solution of potassic
iodide, acidified with diluted sulphuric acid, and then, after the
closed flask has been cooled, the funnel removed and its place
taken by a smaller glass tube filled with air-free water, the
apparatus is connected with a reservoir of pure nitric oxide.
When the clamp is unscrewed nitric oxide is drawn into the flask,,
and should any oxygen be present nitrous acid will be produced,
and consequently iodine will be set free. This experiment has
often been made by the authors, who have failed to observe any
but an insignificant trace of liberated iodine.

Process : 5 c.c. of a 10 per cent, solution of potassic iodide, 5 c.e. of
a 10 per cent, solution of sulphuric acid, and 40 c.c. of water are introduced
into the flask, which is securely fitted with the cork carrying the funnel and
tube. The screw clip being open, and a free passage left for the escape of
steam, the liquid is boiled. After a few minutes, when a,r\y iodine which
may have been liberated has been expelled, and the upper part of the flask is
completely filled with steam, which is also freely issuing from the funnel, the
clip is tightly closed, and at the same moment the source of heat is removed.
A little water is now put into the funnel, and also on the rim of the flask, as
a safeguard against a possible minute leakage, and the vessel is cooled, by
immersion in water. A solution containing a known weight of the nitrite
(equivalent to about O'l gm. of nitrous acid) is placed in the funnel, and
slowly drawn into the flask by cautiously unscrewing the clip. The liquid
which adheres to the funnel is washed into the flask with recently boiled and
air-free water, care being taken that during this operation no air is admitted
into the flask. When experiments are being made with organic nitrites
which are insoluble in water, they are dissolved in alcohol, and alcohol is also
used to wash the funnel. When the nitrite is very volatile, a little cold
alcohol should be put in the funnel, and the point of the pipette containing
the nitrite should be held at the bottom of the funnel beneath the alcohol,
and the liquid quickly drawn from the pipette into the flask. The nitrate
having been introduced, the flask is well shaken and the liberated iodine is
titrated with a standard solution of sodic thiosulphate, small quantities of
which are delivered from a burette into the funnel and gradually drawn into-

NITRITES. 267

the flask ; the screw clip renders it quite easy to admit minute quantities of
the solution. As soon as the iodine is decolorized any standard solution
remaining in the funnel is returned to the burette. Or the funnel may,
before the titration is commenced, be replaced by the burette itself, and the
standard solution delivered direct into the flask. Starch may be used as an
indicator, but it is usually quite easy to observe the complete disappearance of
the yellow colour of the dissolved iodine. From the volume of the standard
solution used, the amount of nitrous acid is calculated from the equation
before given.

It is obvious that the apparatus might be improved in several
respects, as, for example, by constructing it entirely of glass, with
a ground stopper and tap, as well as by the use of a graduated
funnel to deliver the standard solution, and also in other ways.

The authors quote numerous experiments, comparing the method
with careful estimations of sodic and ethyl nitrites, gasometrieally
shelving excellent results.

As a further test of the accuracy of the process, experiments
were made with various organic nitrites of known purity. In
each instance a solution of the nitrite was made by weight, and
a weighed quantity was used for the estimation. To prevent any
loss of these volatile nitrites the experiments were conducted in
the following manner : — A well-stoppered bottle half filled with
the alcohol corresponding to the nitrite'"' to be estimated was
weighed. Sufficient of the nitrite was now introduced by means
of a pipette to constitute approximately a 2 per cent, solution, and
the liquid again weighed. The exact strength of the solution
having been thus determined, the contents of the bottle were well
mixed, and the neck and stopper of the bottle dried. The bottle
was now re-weighed, and about 2 c.c. of the solution removed by
a pipette, care being taken not to wet the neck of the bottle. The
liquid having been introduced into the flask without exposure to
air, in the manner which has been previously described, the bottle
containing the solution was again weighed. The results obtained
with ethyl nitrite were : —

Taken. Found.

O'OSS gin. 0'089 gm.

0-176 „ 0-179 „

0-113 . 0-115 ,

2. Analysis of Alkaline Nitrites by Permanganate.

Kinnicutt and Xef have experimented on the following
method, and obtained very fair results.

The sample of nitrite is dissolved in cold water in the proportion of about
1 to 300 : to this liquid T^ permanganate is added drop by drop, till it has

* The corresponding alcohol was employed to prevent loss consequent on the occurrence
of a reverse chemical change, which takes place when a lower homologous alcohol is
mixed with the nitrite corresponding to a higher homologous alcohol ; for example,
a solution of ainyl nitrite in ethyl alcohol soon becomes a solution of ethyl nitrite in
amyl alcohol, from which the ethyl nitrite rapidly volatilizes.

268 VOLUMETRIC ANALYSIS. § 70.

a permanent red colour ; then 2 or 3 drops of dilute H-SO4, and immediately
afterwards a known excess of the permanganate. The liquid, which should
now be of a dark red colour, is strongly acidified with pure H-SO4, heated
to boiling, and the excess of permanganate determined by means of freshly
prepared T^ oxalic acid. 1 c.c. permanganate-=0'0345 gm. ]STaNO'2, or
0-0425 gm. KNO2.

Of course there must be no other reducing substance than the
nitrite present in the material examined, and, to ensure accuracy,
a blank experiment should be made with the like proportions of
H2S04 and oxalic acid.

3. Gasometric method.

Percy Frankland («/". C. S. liii. 364) adopts this method for
the estimation of nitrous acid in small quantity, but too large for
colorimetric estimation, and where also ammonia, organic matters,
and nitrates may co-exist. It is based on the fact that when
nitrous acid, together with excess of urea, is mixed with sulphuric
acid in the cold, the reaction is

2CO(JSTH2)2 + X 20:5 - CO(jSTETO)2 + CO2 + 2X2.

The decomposition is made in the Cr urn-Frank land shaking tube,
described and figured in Part VI., and the evolved nitrogen gas
measured in the usual gas apparatus. The ordinary nitrometer may
also be used for larger quantities of XO2 by the same method.

In the case of an ordinary alkali nitrite, the dry substance, or
its solution evaporated to dryness, is mixed with excess of
crystallized urea, and dissolved in about 2 c.c. of boiling water in
a beaker, then transferred, with the rinsings, to the cup of the
apparatus, and passed into the tube. A few c.c. of dilute
sulphuric acid (1:5) are then passed in. A vigorous evolution of
gas takes place, and continues for some five minutes ; the gas is
a mixture of nitrogen and carbonic anhydride. The decomposition
is complete in fifteen minutes. A solution of pure sodic hydrate
(1 : 3) is now added through the cup, and the mixture violently
shaken, until the CO2 is absorbed. The gas and liquid are then
transferred, by means of another mercury trough, to the laboratory
vessel, and the gas, which is double the volume of the X existing
as ]S203, measured in a gas ajiparatus, and its weight calculated in
the usual way.

Example : A solution of sodic nitrite was made and standardized with
permanganate, the result being that 10 c.c.=0'001346 gm. N. 10 c.c. of the
same solution were evaporated to dryness in a small beaker, about 0'2 gm. of
urea added, the whole dissolved in 2 c.c. of hot water, which, with the
rinsings, were transferred through the cup into the tube, treated with
sulphuric acid and caustic soda, then transferred to the gas apparatus with
the following results: — Volume of N, 13'79 c.c.; mercurial pressure, 127'5
m.m. ; temperature, 17'7° C. The weight of N thus found, after the
necessary corrections, was 0'0013645 gm.

§ 71. OXYGEN. 269

The Crum -Frank land mercury method, described in the
section on Water Analysis, and in which the same shaking tube is
used, does not distinguish between nitric and nitrous nitrogen ;
but Percy Frank land required a method for the estimation of
nitrous acid in a mixture of nitrates, peptones, sugar, and various
salts occurring in a solution used for cultivation of micro-organisms,
and the experiments carried out by him showed that when such
a mixture was evaporated to dryness the loss of HNO2 was consider-
able, and the results came out much too low. Further experiment,
however, showed that the addition of a slight excess of caustic
potash during evaporation prevented the loss of any HNO2; and
on the other hand the addition of a slight excess of ammonic chloride
entirely destroyed it. Therefore by a combination of the mercury
and the urea methods, the estimation of nitric and nitrous acids
may be satisfactorily accomplished, the destruction of the HXO2
on the one hand being effected by excess of NH4C1, whilst on the
other hand all loss of HJSTO2 may be avoided by evaporation with
caustic alkali. The mode of procedure has the advantage over all
differential methods, in that each acid is determined individually
and independently of the other.

4. Mixtures of Alkaline Sulphites, Thiosulphates, and Nitrites.

Lunge and Smith (J. S. C. I. ii. 465) have shown that the only
satisfactory method of completely oxidizing sulphites and thio-
sulphates by permanganate is to add to the solution a large excess
of permanganate, more than sufficient for complete oxidation, and
Avith formation of MnO2. Excess of FeSO4 is then added, and
again permanganate till pink. When such a mixture contains
nitrites, they will of course be oxidized to nitrates.

To find the amount of nitrites present, therefore, the following
method is adopted : —

The solution of the substance in not too large quantity is
exactly oxidized as described, a known volume of standard ferrous
sulphate is added, together with a large excess of strong H2SO4.
The mixture is boiled nearly to dryness in a flask with slit valve,
diluted, and, when cool, titrated with permanganate. The difference
between the volume then required and that required by the original
Fe2SQ4, represents the nitric acid which has been reduced and
escaped as NO.

The exceedingly delicate colorimetric method of estimating
nitrites originally devised by Griess, and improved by others, will
be described in the section on Water Analysis.

OXYGEN.

0=16.

§ 71. THE volumetric determination of the dissolved oxygen in
water, .is an operation of some importance in water analysis. It is.

270 VOLUMETRIC ANALYSIS. § 71.

well known that organic and bacterial contamination generally
•exist side by side ; the organic matter offering a suitable nidus for
the growth of bacterial life. Water thus contaminated is
•de-oxygenated by the living organisms, which consume oxygen
during their growth ; hence the importance of the estimation of
•dissolved oxygen in water, as a means of ascertaining the
•co-existence of the two kinds of impurity.

In brewing also a knowledge of the state of aeration of the wort
is sometimes of importance, especially at the fermentation stage of
the process.

Several methods have been proposed for carrying out the
•estimation. Mo hr's method, depending on the oxidation of ferrous
compounds, with subsequent titration by permanganate, has not
•come greatly into use. Winkler (Bericlite, 1888, 2851) has quite
recently proposed to take advantage of the oxidation of manganous
hydroxide* by dissolved oxygen, the higher oxide formed being
•decomposed by sulphuric acid and potassic iodide with liberation
of iodine, which is estimated by titration with sodic thiosulphate.
This method is disturbed by the presence of nitrites, which also
liberate iodine from acidified potassic iodide ; great organic con-
tamination also interferes, inasmuch as the impurities present take
up a portion of the liberated iodine.

Schiitzenberger's method,! fully described in the last edition
of this book, has received great attention from many operators,
some of whom have reported favourably, whilst others find the
process unreliable. The reason for the anomalies apparent in the
reports of the various experimenters is shown in the results of an
interesting critical investigation of the process carried out by
Koscoe and Lunt (/. C. S. 1889, 552). They show that an
important disturbing influence had been overlooked, and explain
many previously ill-understood points in the process.

Schiitzenberger's original process depends on the reducing
action of sodic hyposulphite Na2S02, prepared by the action of
zinc dust on a saturated solution of sodic bisulphite, containing
an excess of sulphurous acid. The estimation was originally
carried out in a large "Woullf 's bottle, of about two liters capacity,
filled with pure hydrogen. About 20 — 30 c.c. of water were
introduced, and slightly coloured blue by indigo-carmine solution.
The blue colour was then cautiously discharged by the careful
dropping in of hyposulphite solution. To the yellow reduced
liquid thus produced, the water to be examined was added from
.a pear-shaped vessel holding about 250 c.c. The dissolved oxygen
restored the blue colour by oxidation, and the amount of hypo-
. sulphite required to again decolorize the liquid was noted.

Schiitzenberger showed that when a small amount of indigo

* Obtained by mixing solutions of a manganous salt and caustic alkali.

t See Fermentation by P. S c h il t z e u b e r g e r (International Scientific Scries).

§ 71. OXYGEN. 271

was employed in the estimation, the' yellow colour produced when
the titration was completed quickly returned to blue, and this
when decolorized again turned blue, and so on for some time, until
double the first amount of hyposulphite had been used. He
showed also that by using a much larger amount of indigo the
•double portion of hyposulphite was required at once.

By titrating an ammoniacal solution of copper sulphate with the
hyposulphite used he arrived at a value (though an erroneous one)
for the hyposulphite employed in his experiments, and concluded
that, at the first yellow colour produced in a titration where
a small amount of indigo was used, only half the oxygen actually
present had been obtained. The other half he accounted for by
saying that the reaction between hyposulphite and dissolved oxygen
is such, that one-half the oxygen becomes latent as hydrogen
peroxide, which slowly gives up half its oxygen. He thus accounted
for the return of the blue colour, as well as his observation that
only half the oxygen was at once obtained. To explain the
observation, that when a large amount of indigo was employed
the wliole, of the dissolved oxygen was found, he assumed that
a different reaction takes place, one between dissolved oxygen
and reduced indigo, in which the peroxide of hydrogen is not
formed.

Ramsay and Williams (/. C. S. 1886, 751), whilst agreeing
with Schiitzenberger and with Dupre,* that the process gives
reliable results, throw a doubt on the chemical explanation given
•of the above experiments.

Instead of the ratio 1 : 2, they find 3 : 5 to be the ratio
between the first and total quantity of hyposulphite required when
-a small amount of indigo is employed, but give it only as the mean
expression of the varying ratios they obtain, and add, " but it is
difficult to devise an equation which will in a rational manner
account for this partition of oxygen" into two stages of the
process. Eoscoe and Lunt's investigation (J". C. S. 1889, 552)
lias thrown a new light on these experiments. They show (1) that
•a series of fifteen estimations carried out with every care in
improved apparatus, and under apparently identical conditions,
gave discordant results, varying between 4 '55 and 6*50 c.c. of
hyposulphite for the same volume of water, showing a difference
of 0'35 per cent, of the moan value. (2) The rapidity of titration
has a great influence on the result. The mean of a series of ten
estimations carried out drop by drop was 5 '47, whilst ten
experiments with the same sample of water gave a mean of 7 '12
when the titration was performed quickly. (3) Not only is
a low result obtained by a slow titration and a high result by
a quick one, but by varying the time of titration still more, extreme
variations in the result are obtained; any value between 1 and 100

* Analyst x. 156.

272

VOLUMETRIC ANALYSIS.

71.

per cent, of the total oxygen- present being shown to be possible.
(4) The ratio between the first reading and the total quantity
of hyposulphite required is not a constant one, and is shown to
be capable of an infinite range of variation.

Fig. 49.

The key to the explanation of these remarkable results is given
by the authors as follows: — "The conclusion" from their experi-
ments "was, that when aerated water is introduced into an
atmosphere of pure hydrogen, it immediately begins to lose oxygen

§71. OXYGEN. 273

by diffusion into the hydrogen until an equilibrium is established."
By the recognition of this disturbing influence, the previous
anomalies are easily explainable on the following data.

(1) Discordant results are obtained from the same water,
because the several titrations are not performed in exactly the same
time, therefore, varying amounts of oxygen diffuse, and leave
a vary ing 'residue for titration.

(2) The high results of a quick titration are accounted for by
the fact that a large amount of oxygen is titrated and fixed before
it has had time to diffuse, whilst the slow titration gives a low
result, because a large amount of oxygen has already diffused
from the liquid before the titration is completed. JS'o greater
proof of the rapidity with which the water under examination lost
oxygen by the old process need be given than the fact, that
Schiitzenberger's results show that half the oxygen had left the
liquid by diffusion before the estimation could be completed.

(3) The return of the blue colour is due to the re-absorption
of the diffused oxygen by the sensitive yellow liquid, oxidation by
gaseous oxygen producing the blue colour, which is thus not due
to a reaction -within the liquid.

(4) The whole of the oxygen is obtained when a large amount
of indigo is used, because when reduced it is capable of at once
fixing the whole of the dissolved oxygen and thus prevents
diffusion. The use of so large a quantity of indigo, necessary to
effect this result, however, so disturbs the end-reaction that " it is
difficult to fix the point at which the last trace of blue has been
discharged with any degree of accuracy" (Dupre loc. cit.). Hence
a new method must be resorted to in which diffusion is eliminated,
and Roscoe and Lunt have devised the following method to
satisfy the conditions of the case. The apparatus employed by
them is shown in fig. 49.

It consists essentially (1) of an apparatus for the continuous
generation and purification of hydrogen, by the action of dilute
sulphuric acid on zinc ; (2) a 200 c.c. wide-mouthed bottle, fitted
with three burettes with glass taps, inlet and outlet tubes for
a current of hydrogen, and an outlet tube for the titrated liquid ;
(3) Winchester stock bottles of hyposulphite, indigo (not shown),
and water (sample), communicating with their respective burettes
by glass* syphons. The hydrogen generated in A passes through
two wash-bottles containing caustic potash, thence through two
E miner ling's tubes filled with glass beads, moistened with an
alkaline solution of potassic pyrogallate, an arrangement being
made whereby the beads may be re-moistened with fresh pyrogallate
from the bottles beneath, the liquid being forced up by hydrogen
pressure. Pure hydrogen is supplied continuously (1) to the

* India-rubber tubing must not be used for the conveyance of the hyposulphite
solution (or the water under examination), as atmospheric oxygen rapidly diffuses
through the india-mbber and affects the strength of the solution.

274 VOLUMETKIG ANALYSIS. § 71.

stock bottle of hyposulphite, (2) to the hyposulphite burette, and
(3) to the titration bottle.

Preparation of the Reagents. — The reagents required arc—
Hyposulphite solution.
Indigo-carmine solution.
Standard aerated distilled water.

The Hyposulphite solution is prepared by dissolving 125 gm. of
sodic bisulphite in 250 c.c. of water, and passing a current of SO2
through the solution until saturation is effected. The solution is
poured into a stoppered bottle of about 500 c.c. capacity, containing
50 gm. of zinc dust, the bottle is almost filled up with water, and
the mixture well shaken for five minutes, after which the bottle is
placed beneath a running tap to cool. The mixture is again
agitated after a quarter of an hour and left to deposit the excess of
zinc. The clear liquid is poured off from the sediment into
a Winchester quart bottle half full of water. Milk of lime is
added in excess, and the solution made up to fill the bottle almost
completely. The mixture is now thoroughly shaken and allowed
to stand (best overnight) until clear.

The solution thus obtained is much too strong for use. 200 c.c.
of this may be poured into a "Winchester quart bottle of water
(never into a bottle filled with air) and well shaken with as little
air as possible. The approximate strength of this dilute solution
must now be found by titrating good tap water in the apparatus
already described. The strength should be such that 100 c.c. of
water require about 5 c.c. of hyposulphite, and the solution should
be made up approximately to this value. It slowly loses strength
on keeping, even in hydrogen, and its value should be determined
daily as required to be used.

The Indigo-carmine solution is prepared by shaking up 200 gm.
of indigo-carmine in a Winchester quart bottle of water, and
filtering the blue solution, which must be diluted to such a strength
that 20 c.c. require about 5 c.c. of the above hyposulphite solution
for decolorization.

Standard Aerated Distilled "Water. — Two Winchester quart bottles
half filled with freshly distilled water are vigorously agitated for
five minutes, and the air renewed several times by filling up one
bottle with the contents of the other, and again dividing into two
portions, which are repeatedly shaken with fresh air. Finally, one
bottle being filled, the temperature of the water is taken, and also
the barometric pressure, after which the bottle is allowed to stand
stoppered for half an hour, to get rid of minute air-bubbles. The
following table, due to Eoscoe and Lunt, gives the volume of
oxygen contained in this standard aerated water, and the results
show that Buns en's co-efficients, previously used, are inaccurate.

OXYGEN. 275

Oxyg-en Dissolved by Distilled Water. 5—30° C.

| .

Temp.
C.

c.c. Oxygen
N.T.P.
per liter Aq.

Diff. for ' Temp.
0'5° C. C.

c.c. Oxygen
N.T.P.
per liter Aq.

Diif. for
0-5° C.

5-0°

8-68

18'0°

6-54

0-07

5-5

8-58

o-io

18'5

6-47

0-07

6-0

8-49

0'09 19'0

6-40

006

6-5

8'40

0'09

19-5

6'34

0-06

7-0

8'31

0-09 20-0

6-28

0-06

7'5

8-22

0-09

20-5

6-22

0-06

8'0

8-13

0-09 21-0

6-16

0-06

8'5

8-04

0'09 21-5

6-10

0-06

9-0

7-95

0-09 22-0

6*04

0-05

9-5

7-86

0'09

22-5

5-99

0-05

10-0

777

0-09

23-0

5'94

0'05

10-5

7-68

0-08 23-5 5-89

0-05

ll'O

7-60

0-08 24-0 5-84

O'Ol

11-5

7'52

0-08

24-5

5-80

0-04

12-0

744

0-08

25'0

5-76

0-04

12'5

7'36

0-08

25'5 5-72

0-04

13-0

7'28

0'08

28-0 5'68

0-04

13-5

7-20

0'08

26'5 5'64

0'04

14-0

7-12

0'08

27'0 • 5'60

0'03

14-5

7-04

0-08

27'5 5'57

0'03

15'0

6-96

0-08

28-0 5-54

0-03

15-5

6-89

0-07 28'5 5-51

0-03

16-0

6-82

0-07 29-0 5-48

0-03

16-5

675

0'07 29'5 5-45

0-02

17'0

668

0'07 30'0 5-43

17'5

6-61

0'07

In this table the results are calculated for aeration at an observed
barometric pressure of 760 m.m. When the observed pressure is below
760 m.m. TVth the value must be subtracted for every 10 m.m. diff. The
same^value must be added when the pressure is above 760 m.m.

The Estimation : The burettes having been filled, and a preliminary trial
made —

(1) 20 c.c. of the water are introduced into the small bottle and about
3 c.c. of indigo solution added.

(2) A moderite current of hydrogen is passed through the blue liquid by
a very fine jet for three minutes to free both water and supernatant gas
from free oxygen.

(3) Hyposulphite is now carefully added, during the flow of hydrogen,
until the change from blue to yellow occurs, taking care not to overstep this
point.

(4) A further measured quantity of hyposulphite is now added (say 10 c.c.)
sufficient to combine with all the dissolved oxygen in the volume of water
(50 — 100 c.c.) proposed to be used in the estimation.

(5) The important point is, that the water is now quickly run in from
a burette by a capillary tube passing beneath the surface of the liquid to the
bottom of the vessel. The water is thus introduced into a liquid which will
at once fix the free oxygen and thus prevent its diffusion on coming in
contact with the hydrogen, the reduced indigo acting as an indicator for the
complete oxidation of the hyposulphite. The liquid is kept in constant
motion during the addition of the water, which is shut off the moment
a permanent blue colour appears.

T 2

276 VOLUMETRIC ANALYSIS. § 71.

(6) The blue is decolorized by a further slight addition of hyposulphite.
The volume of water used and the total hyposulphite, minus the first
addition, are noted and the estimation repeated for confirmation.

When the water contains very little oxygen the second addition
of hyposulphite may be omitted, the reduced indigo-carmine being
-sufficient to take up all the dissolved oxygen. In this case, care
must be taken that the oxygen added should require not more
than half the hyposulphite first added to decolorize the indigo-
carmine.

Standardizing: the Hyposulphite. — In order to complete the
estimation it is necessary to know the strength of the hyposulphite
solution employed, and for this purpose the bottle of standard
aerated distilled water is titrated. This method has the great
advantage that it is a titration carried out under almost the same
conditions as the examination of the sample. The result of an
estimation is easily obtained by the following formula —

d x hs x Od

— r~y — = # c.c. O per liter of water
8 x lid

where d and s = the volumes of distilled water and sample
respectively used, lid and hs — the hyposulphite required for the
distilled water and sample respectively, arid Od the volume of
dissolved oxygen contained in one liter of the standard water.

Standardizing- the Indigo. — When once the hyposulphite has
been carefully standardized by distilled water, the rather trouble-
some aeration may be avoided by finding the oxygen-value of the
indigo-carmine solution. This solution remaining constant may be
used for the subsequent standardizing of the hyposulphite.

It is only necessary to take a suitable quantity of indigo solution,
diluted with water if necessary, free it from all dissolved oxygen
by a current of pure hydrogen continued for five minutes, then
carefully decolorize with hyposulphite, the value of which has
been found by using aerated distilled water.

The authors show that Schutzenberger's method of standard-
ization, depending on the decolorization of ammoniacal copper
sulphate, gives inaccurate results.

Free acids or alkalies greatly disturb the process. Bicarbonates
have no effect. Of course when other substances than oxygen,
which decompose hyposulphite, are present, the accuracy of the
method is proportionately disturbed. The authors have applied the
process to waters of very varied character, and containing widely
different amounts of oxygen, and show that the method is capable
of giving good results, compared with the actual volume of oxygen
found by extracting the gases by boiling in vacua.

The delicacy of the reaction is such that one part of oxygen in
two million parts of water is easily detected.

§ 71.

OXYGEN.

277

The following numbers were obtained from five different samples
of London tap- water collected on five different days.

(1)

(2)

(3)

(4)

(5)

Nitrogen

c.c.
13*22
5-15

7'98

c.c.
13-95
5-91
9-29

c.c.
13-36
5-38
6-70

c.c.
13-43
6-31
7-35

c.c.
13-49
5-80
8-11

Oxygen

Carbonic acid
Total o-as . .

26-35

29-15

25-44

27-09

27-40

Oxygen by the new
volumetric method . . .
Gas obtained

5-52
5-15

6-13
5-91

5-64
5-38

6-41
6'31

6-24
5-80

Difference .

0-37

0-22

0-26

o-io

0-44

Mean difference 0'28 c.c. oxygen per liter of water.

The oxygen values obtained by the two methods show close
agreement, considering the possible experimental error in so
complex a comparison.

M. A. Adams describes and figures a very convenient arrange-
ment for carrying out this process (J. C. S. Ixi. 310), which is
well adapted for technical work, and less cumbrous than the
apparatus here described.

lodometric Method.

A simpler method than the foregoing has been proposed by
Thresh (/. C. S. Ivii. 185), which by comparison with Roscoe
and Lunt's method appears to give satisfactory results when
aerated distilled water was under titration, the differences occurring
only in the second decimal place. The author was led to
investigate the method by observing the. large amount of iodine
which a very minute quantity of a nitrite caused to be liberated,
when potassic iodide and dilute sulphuric acid were added to water
containing it. The amount of iodine liberated varies with the
length of exposure to air. If air is excluded no increase of free
iodine occurs after the first few minutes, and if the water is
previously boiled and cooled in an air-free space still less iodine is
liberated. In this latter case the action is represented by the
equation —

2HI + 2HX02 = I2 + 2H20 + 2X0.

When oxygen has access to the solution, the nitric oxide acts as
a carrier, and more hydrogen iodide is decomposed, the nitric oxid«

2/8 VOLUMETRIC ANALYSIS. § 71.

apparently remaining unaffected, and capable of causing the
decomposition of an unlimited quantity of the iodide.

This reaction is the one utilized in the process devised by
Thresh for estimating the oxygen dissolved in water. As 16 parts
by weight of oxygen will liberate 254 parts of iodine, thus —

and as the latter element admits of being accurately estimated,
theoretically the oxygen should be capable of very precise
determination. Practically such is the case ; the oxygen dissolved
in drinking waters admits of being estimated both rapidly and
with precision. It is only necessary to add to a known volume of
the water a known quantity, of sodic nitrite, together with excess
of potassic iodide and acid, avoiding access of air, and then to
determine volumetrically the amount of iodine liberated. After
deducting the proportion due to the nitrite used, the remainder
represents the oxygen which was dissolved in the water and in the
volumetric solution used.

The following are the reagents required : —

(1) Solution of sodic nitrite and potassic iodide : —

Sodic nitrite 0'5 gm.

Potassic iodide 20'0 gm.

Distilled water 100 c.c.

(2) Dilute sulphuric acid : —

Pure sulphuric acid 1 part.

Distilled water 3 parts.

(3) A clear fresh solution of starch.

(4) A volumetric solution of sodic thiosulphate : —

Pure crystals of thiosulphate, 7 '7 5 gm.

Distilled water to 1 liter.

1 c.c. corresponds to 0'25 milligram of oxygen.

The apparatus required is very simple, and can readily be fitted
up. It consists of a wide-mouthed white glass bottle (A, fig. 50)
of about 500 c.c. capacity, closed with a caoutchouc stopper having
four perforations. Through one passes the tube B, drawn out at
its lower extremity to a rather fine point, and connected at the
upper end, by means of a few inches of rubber tubing, with the
burette C, containing the thiosulphate. Through another opening
passes the nozzle of a separatory tube D, having a stopper and
stopcock. The capacity of this tube when full to the stopper
must be accurately determined. Through the third opening passes
a tube E, which can be attached to an ordinary gas supply. Through
the last aperture is passed another tube, for the gas exit, and to
tin's is attached a sufficient length of rubber tubing to enable the

§ 71.

OXYGEN.

279

cork G at its end to be placed in the neck of the tube D when the
stopper is removed. A small piece of glass tube projects through
the cork, to allow of the escaping gas being ignited.

The apparatus is used in the following manner : — The bottle A
being cleaned and dry, the perforated bung is inserted, the burette
charged, and the tube B fixed in its place. E is connected with
the gas supply. The tube D is filled to the level of the stopper
with the water to be examined, 1 c.c. of the solution of sodic
nitrite and potassic iodide added from a I c.c. pipette, then 1 c.c.
of the dilute acid, and the stopper instantly fixed in its place,
displacing a little of the water, and including no air. If the
pipette be held in a vertical position with its tip just under the
surface of the water, botli the saline solution and the acid, being
much denser than the water, flow in a sharply defined column to
the lower part of the tube, so that an infinitesimally small quantity

(if any) is lost in the water which overflows when the stopper is
inserted. The tube is next turned upside down for a few seconds
for uniform admixture to take place, and then the nozzle is pushed
through the bung of the bottle, and the whole allowed to remain
at rest for 15 minutes, to enable the reaction to become complete.
A rapid current of coal gas is now passed through the bottle A,
until all the air is displaced and the gas burns at G with a full

280 VOLUM ETHIC ANALYSIS. § 71.

luminous flame ; the flame is now extinguished, the stopper of D
removed, and the cork G rapidly inserted. On turning the stop-
cock, the water flows into the bottle A. The stopcock is turned
off, the cork G removed, and the supply of gas regulated so that
a small flame only is produced when this gas is ignited at G.
Thiosulphate is now run in slowly until the colour of the iodine is
nearly discharged. A little solution of starch is then poured into
D, and about 1 c.c. allowed to flow into the bottle by turning the
stopcock. The titration with thiosulphate is then completed.
After the discharge of the blue colour, the latter returns faintly in
the course of a few seconds, due to the oxygen dissolved in the
volumetric solution ; after standing about two minutes, from 0*05
to O'l c.c. of thiosulphate must be added to effect the final
discharge. The amount of volumetric solution used must now be
noted. This will represent a, the oxygen dissolved in the water
examined, + &, the nitrite in the 1 c.c. of solution used, and the
oxygen in the acid and starch solution + c, a portion of the dissolved
oxygen in the volumetric solution. To find the value of a, it is
obvious that I and c must be ascertained. This can be effected in
many ways, and once known does not require re-determination
unless the conditions are changed.

To Find the Value of 1>. — Probably the best plan is to complete
a determination as above described, and then, by means of the
stoppered tube, introduce into the bottle in succession 5 c.c. of
nitrite solution, dilute acid, and starch solution. After standing
a few minutes, titrate. One-fifth of the thiosulphate used will be
the value required.

To Find the Value of c. — This correction is a comparatively
small one, and admits of determination with sufficient accuracy if
it is assumed that the thiosulphate solution normally contains as
much dissolved oxygen as distilled water saturated at the same
temperature. Complete a determination as above described, then
remove the stoppered tube, and insert a tube similar to that
attached to the burette, and drop in from it 10 or 20 c.c. of
saturated distilled water exactly as the thiosulphate is dropped in.
Allow to stand a few minutes and titrate. One-tenth or one-
twentieth of the volumetric solution used, according to the
number of c.c. of water added, will represent the correction for
each c.c. of volumetric solution used. Call this value d.

Let e be the number of c.c. of thiosulphate used in an actual
determination of the amount of oxygen in a sample of water ;

/= the capacity in c.c. of the tube employed -2 c.c., the volume
of reagents added ;

17 = the amount of oxygen in milligrams dissolved in 1 liter of
the water ;

1000, 7 ,,
then • V = -. . (e-l- e<?)

71. OXYGEN.

With a tube made to hold exactly 250 c.c., the most convenient

quantity to use, — — becomes unity, and

In the author's experiments two nitrite solutions were used;
in the first l = 2'l c.c., in the second 3'1 c.c. A number of
determinations of d were made, at temperatures varying from
40° to 60° F. The value of d was found to vary between 0'03
and 0*031 5. In all the author's recent experiments d was taken
as 0-031.

When e = 3 c.c. the reaction seems to be complete in five
minutes, but, to be on the safe side, it is better to fix the minimum
at fifteen minutes.

The use of coal-gas is recommended by the author without
passing it over alkaline pyrogallol or otherwise treating it before
allowing it to pass through the apparatus.

The results obtained, however, can be made to vary, the extreme
limit being less than 0'5 milligram of oxygen per liter of water,
using 250 c.c. for the estimation. To quote an extreme case. In
one experiment (1), after the air had been wholly expelled from
the bottle A, no more gas was passed through, and the titration
was effected in the closed apparatus, the volumetric solution being
run in as rapidly as possible. The end-reaction was not well
defined. In the second experiment (2), the volumetric solution
was run in very slowly drop by drop, and a brisk current of gas
was kept passing through the apparatus. End-reaction well
defined.

Volume of water. Thiosulphate. Oxygen per liter.

(1) ...... 322 c.c. 15-35 c.c. ' 9 '14 milligrams.

(2) ...... 322 „ 14-9 „ 8-80

The difference is probably due to nearly all the oxygen dissolved
in thiosulphate being used up in the first case, and being lost by
diffusion in the second.

In the examination of waters from various sources, and making
the experiments in pairs, using tubes of different sizes, the author
found that exceedingly concordant results could easily be
obtained.

In estimating the oxygen in distilled water saturated with air,.
the author found that the results at 25° and 30° C. were higher
than those obtained by Roscoe and Lunt, whilst at the lower
temperatures they were almost identical, and it occurred to him that
the difference was probably due to the mode of saturation. The
agitation in a couple of Winchesters was done as directed by
them, but the water used had been previously saturated at the
lower temperatures, and probably was slightly super-saturated.
A further series of experiments were then made with freshly-

282 VOLUMETRIC ANALYSIS. § 71.

distilled water, which was not agitated with air until it had
attained the desired temperature. The results proved that this
surmise was correct. Probably some such explanation accounts for
the uniformly higher results obtained by Dittmar.

No doubt there will be exceptional cases in which the process
cannot be used, and others in which some modification may be
required. A water containing nitrites will require the amount of
the nitrous acid to be determined if the utmost accuracy is
required. (A water containing 1 part of HNO2 in 1,000,000, will
affect the results + 0 '17 milligram of oxygen per liter, 94 parts
of the acid corresponding to 16 of oxygen). Where nitrites are
present in sufficient quantity to interfere, the amount may be
determined by any of the ordinary processes, but the author
prefers the following method : —

To 250 c.c. of the water to be examined, rendered faintly
alkaline if not already so, add a few drops of strong solution of
potassic iodide, and boil vigorously for a few minutes. Then
transfer to the bottle A used in the oxygen determination, and
allow to get quite cold in a slow current of coal gas. Then add
a few drops of dilute sulphuric acid and solution of starch, and
titrate with the thiosulphate. The correction to be made in the
oxygen determination is thus ascertained. One or two experi-
mental results may be quoted.

Quantity Thiosulphate p™.,^ ar-\ Milligrams of
of water. used. CoiiectecL oxygen per liter.

Tap water 232T> 13'2 9'7 10'43

Tap water + 5 milli- ^

grams commercial C 232' 5 15'95 9' 55 10'27

sodic nitrite )

Tap water + 10 milli- ) 000. K i n-i Q

1 • -j •• "* <_•>_ O Jo O «7 ~rO J-V J-«/

grams sodic nitrite )

In number 2, the thiosulphate used by 250 c.c. of the boiled

water was 2*8 c.c.

In number 3, the thiosulphate used by 250 c.c. of the boiled
water was 5 '45 c.c.

The results are fairly satisfactory, even with such large pro-
portions of nitrite, proportions far larger than are likely to be met
with in practice.

Nitrates do not interfere, even when present in large quantities ;
but fresh urine, when present to the extent of 1 per cent., has
a small but very appreciable effect.

The following is an example of the method at ordinary
temperature : —

§ 71. HYDROGEN PEROXIDE. 283

Temperature 15° C.

Quantity of Thiosulphate | , _ fe _ ,d \ Milligrams of Difference

water taken. used. ' Oxygen per liter, from mean.

1...

2...

322-0 15-45 12-87 9'99 — 0'04

322-0 15-55 12-97 10'07 + 0'04

3... 232-5 11-90 9-43 10'14 +0'11

4... 232-5 11-70 9-23 9'92 — O'll

Mean... - 10'03

Barometer reading 30 in.
10-03 milligrams=7'02 c.c. at N.P.T.
Eoscoe and Lun't found 6'96 „ Difference + 0'06.

Hydrog-en Peroxide.
IPO2 =34.

This substance is now largely used in commerce, and is sold
as containing 5, 10, or 20 volumes of oxygen in solution. This
should mean that the specified number of volumes can be obtained
from the solution itself, but preparations are sent into the market
under false pretences. A so-called 10 volume solution gives, it is
true, 10 volumes of 0 when decomposed gasometrically with
permanganate, but 5 volumes of the 0 comes from the per-
manganate itself, and therefore such a solution is really only 5
volume. A true 10 volume solution should yield from itself, when
fully decomposed, ten times its volume of O, and contain by weight
3 '04 per cent, of H202 or 1'43 per cent, by weight of 0.

Kingzett (J. C. S. 1880, 792) has clearly shown that the best
•and most rapid estimation of the hydrogen peroxide, contained in
.any given solution of it, is made by iodine and thiosulphate in the
presence of a tolerably large excess of sulphuric acid, the reaction
being —

The function performed by the sulphuric acid is difficult of ex-
planation, but the want of uniformity in the reaction experienced
by many operators no doubt has arisen from the use of insufficient
•acid.

Process : Kingzett's consists in mixing 10 c.c. of the peroxide solution
to be examined with about 30 c.c. of dilute sulphuric acid (1 : 2) in a beaker,
adding crystals of potassic iodide in sufficient quantity, and after standing
five minutes titrating the liberated iodine with ^ thiosulphate and starch.
The peroxide solution should not exceed the strength of 2 volumes; if
stronger, it must be diluted proportionately before the analysis.

In the case of a very weak solution it will be advisable to titrate with
x-iju- thiosulphate.

1 c.c. & thiosulphate = 0'0017 gm. H-O2 or 0*0016 gm. O.

The estimation of this substance may also be readily made in the

284 VOLUMETRIC ANALYSIS. § 72.

absence of organic or other reducing matters by weak standard per-
manganate in the presence of free sulphuric acid, the permanganate
being added until a faint rose colour occurs : the reaction is —

2KMn04 + 5H202 + 3IPS04 = K2S04 + 2MnS04 + 8H20 + 502.

Process : To about 500 c.c. of water in a white porcelain dish there is
added 5 c.c. of dilute H-SO4, and then sufficient permanganate to give
a faint persistent pink colour. 5 c.c. of the peroxide solution are then
pipetted into the mixture, and standard permanganate containing 2'625 gm.
per liter run in until the colour no longer disappears. The number of c.c.
used, divided by ten, gives the volume of oxygen liberated by each c.c. of
the hydrogen peroxide.

Carpenter and Nicholson (Analyst ix. 36) report a series
of experiments on the analysis of hydrogen peroxide, both by the
iodine and permanganate methods.

The conclusion they arrive at is, that the process of Kingzett
is accurate, but in their hands somewhat tedious, owing to slow
decomposition towards the end. Kingzett however states that if
a volume of strong sulphuric acid equal to the peroxide taken be
used, and especially if the dilute solution be slightly wanned, the
reaction is complete in a few minutes, and this is my own
experience.

Soclic Peroxide.

L. Archbutt (Analyst xx. 5) gives the results of some
experiments on the estimation of the oxygen contained in this
substance, and found that a near approximation to the truth could
be obtained by simple titration with permanganate, the peroxide
(one or two decigrams) being added to cold water acidified with
H2S04 contained in a white dish, and — j permanganate dropped in
with stirring, until the colour became permanent ; but a more
exact method would be to add a known weight of the peroxide to
an excess of ~ permanganate, previously mixed with dilute
H2S04, and titrate for the excess of permanganate with -f^ oxalic
acid. Archbutt, however, prefers to use the nitrometer, and
recommends the following procedure : about 0*25 gm. of the
substance is placed in the dry tube of the nitrometer flask, and in
the flask itself about 5 c.c. of pure water, containing in suspension
a few milligrams of precipitated cobalt sesqui-oxide, this latter
reagent brings about a rapid and complete decomposition of the
peroxide, the volume of oxygen evolved being the available oxygen
in the sample.

PHOSPHORIC ACID AND PHOSPHATES.

§ 72. THE estimation of phosphoric acid volu metrically may
be done with more or less accuracy by a variety of processes, among

§ 72. PHOSPHORIC ACID. 285

which may be mentioned that of Mohr as lead phosphate, the
indirect method as silver phosphate (the excess of silver being found
by thiocyanate), by standard uranium nitrate or acetate, by
P ember ton's method as phospho-molybdate, or when existing
only as monocalcic phosphate, by standard alkali, as recommended
by Mo 11 end a or Emm er ling. These processes are mainly useful
•in the case of manures, or the raw phosphates from which manures
are manufactured, and for P205 in urine, etc. For the purpose
mentioned, that is to say, when in combination with alkaline or
•earthy alkaline bases and moderate quantities of iron or alumina,
phosphoric acid may be estimated volumetrically with very fair
accuracy, and with much greater rapidity than by gravimetric
means as usually carried out. This remark, however, can only be
applied to uranium or molybdenum methods ; therefore only these
will be described.

1. Precipitation as Uranic Phosphate in Acetic Acid Solution.

This method is based on the fact that when uranic acetate or
nitrate is added to a neutral solution of tribasic phosphoric acid,
such, for instance, as sodic orthophosphate, the whole of the
phosphoric acid is thrown down as yellow uranic phosphate Ur203,
P205 + Aq. Should the solution, however, contain free mineral
acid, it must be neutralized with an alkali, and an alkaline acetate
added, together with excess of free acetic acid. In case of using
ammonia and ammonic acetate, the whole of the phosphoric acid
is thrown down as double phosphate of uranium and ammonia,
having a light lemon colour, and the composition Ur20:j
2(XH40), P205 + Aq. When this precipitate is washed with hot
water, dried and burned, the ammonia is entirely dissipated leaving
uranic phosphate, which possesses the formula Ur203, P205, and
contains in 100 parts 80 '09 of uranic oxide and 19*91 of phosphoric
acid. In the presence of fixed alkalies, instead of ammonia, the
precipitate consists simply of uranic phosphate. By this method
phosphoric acid may be completely removed from all the alkalies
and alkaline earths ; also, with a slight modification, from iron ;
not, however, satisfactorily from alumina when present in any
quantity.

The details of the gravimetric process were fully described by
me (C. N. i. 97 — 122), and immediately after the publication of
that article, while employed in further investigation of the subject,
I devised the volumetric method now to be described. Since that
time it has come to my knowledge that jS'eubauer* and Pincusf
had independently of each other and myself arrived at the same
process. This is not to be wondered at, if it be considered how
easy the step is from the ordinary determination by weight to that

* Archiv. f&r wissenschuftliclie Heillcunde, iv. 228.
f Journal fur Prald. Chem. Ixxvi. 104.

286 VOLUMETRIC ANALYSIS. § 7 '2.

by measure, when the delicate reaction between uranium and
potassic ferrocyanide is known. Moreover, the great want of a
really good volumetric process for phosphoric acid in place of those
hitherto used has been felt by all who have anything to do with it,
and consequently the most would be made of any new method
possessing so great a claim to accuracy as the gravimetric estimation
of phosphoric acid by uranium undoubtedly does.

Conditions under -which, accxiracy may be insured. — Objections
have been urged, not without reason, that this process is inaccurate,
because varying amounts of saline substances have an influence
upon the production of colour with the indicator. Again, that
very different shades of colour occur with lapse of time. This
is all true, and the analysis is unfortunately one of that class which
requires uniform conditions; but when the source of irregularity is
known, it is not difficult to obviate them. Therefore it is absolutely
essential that the standardizing of the uranium solution should be
done under the same conditions as the analysis. For instance, a
different volume of uranium will be required to give the colour in
the presence of salts of ammonia to that which would be necessary
with the salts of the fixed alkalies or alkaline earths. But if the
standard solution is purposely adjusted with ammonia salts in about
the same proportion, the difficulties all vanish. Fortunately this
can be easily done, and as the chief substances requiring analysis
are more or less ammoniacal in their composition, such as urine,
manures, etc., no practical difficulty need occur.

Excessive quantities of alkaline or earthy salts modify the colour,
but especially is it so with acetate or citrate of ammonia. For this
reason it is necessary to ensure the complete washing of the citro-
magnesian precipitate, where that method of separating P205 is
adopted previous to titration.

2. Estimation of Phosphoric Acid in combination with Alkaline
Bases, or in presence of small quantities of Alkaline Earths.

The necessary materials are —

(a) A standard solution of Uranium, 1 c.c. — 0*005 gm. P205.

(&) A standard solution of tribasic Phosphoric acid.

(c) A solution of Sodic acetate in dilute acetic acid, made by
dissolving 100 gm. of sodic acetate in water, adding 50 c.c. of
glacial acetic acid, and diluting to 1 liter. Exact quantities are
not necessary.

(d) A freshly prepared solution of Potassic ferrocyanide, or
some finely powdered pure crystals of the same salt.

Standard Solution of Uranium. — This solution may consist
either of uranic nitrate or acetate. An approximate solution is
obtained by using about 35 gm. of either salt to the liter.
In using uranic nitrate it is imperative that the sodic acetate

§ 72. PHOSPHORIC ACID. 287

should be added in order to avoid the possible occurrence of free
nitric acid in the solution. With acetate, however, it may be
omitted at the discretion of the operator, but it is important
that the method used in standardizing the uranium be invariably
adhered to in the actual analysis. The solution should be perfectly
clear and free from basic salt. Whether made from acetate or
nitrate, it is advisable to include about 50 c.c. of pure glacial acetic,
or a corresponding quantity of weaker acid to each liter of
solution ; exposure to light has then less reducing action.

My own practice is to use in all cases acetate solution, and
dispense entirely with the addition of sodic acetate.

3. Titration of the Uranium Solution.

Standard Phosphoric Acid. — When the uranium solution is not
required for phosphate of lime, it may be titrated upon ammonio-
sodic phosphate (microcosmic salt) as follows : — 5'886 gm. of the
crystallized, non-effloresced salt (previously powdered and pressed
between bibulous paper to remove any adhering moisture) are
weighed, dissolved in water, and diluted to 1 liter. 50 c.c. of this
solution will represent O'l gm. of P-05.*

Process : 50 c.c. of this solution are measured into a small beaker, 5 c.c. sodic
acetate solution added if uranic nitrate is to be used, and the mixture heated to
90° or 100° C. The uranium solution is then delivered in from a burette,
divided into TV c.c., until a test taken shall show the slight predominance of
uranium. This is done by spreading a drop .or two of the hot mixture upon
a clean white level plate, and bringing in contact with the middle of the drop
a small glass rod moistened with the freshly made solution of f errocyanide,
or a dust of the powdered salt. The occurrence of a faint brown tinge shows
an excess of uranium, the slightest amount of which produces a brown
precipitate of uranic f errocyanide.

A second or third titration is then made in the same way, so as
to arrive exactly at the strength of the uranium solution, which
is then diluted and re-titrated, until exactly 20 c.c. are required to
produce the necessary reaction with 50 c.c. of phosphate.

Suppose 18*7 c.c. of the uranium solution have been required to
produce the colour with 50 c.c. of phosphate solution, then every
18 '7 c.c. will have to be diluted to 20 c.c. in order to be of the
proper strength, or 935 to 1000. After dilution, two or three
fresh trials must be made to insure accuracy.

It is of considerable importance that the actual experiment for
estimating phosphoric acid by means of the uranium solution
should take place with about the same bulk of fluid that has
been used in standardizing the solution, and with as nearly as

* "W. B. Giles, who has had great experience in the determination of phosphoric acid
in various forms, has called my attention to dihydric potassic phosphate, KH-'PO4, as an
excellent form of salt for a standard solution. The sample sent to nie was in beautifully
formed crystals which do not alter on exposure to the air, and makes a solution which
keeps clear. Every one knows how unsatisfactory sodic phosphate is, both as to its
state of hydration and its keeping qualities in solution : the microcosmic salt is better,
but is open to objection on the score of indefinite hydration. If the potassium salt ia
used, a standard solution of the proper strength is made by dissolving 3'83 gm. in a liter.

288 VOLUMETRIC ANALYSIS. § 72.

possible the same relative amount of sodic acetate, and the
production of the same depth of colour in testing. Hence the
proportions here recommended have been chosen, so that 50 c.c. of
liquid shall contain O'l gm. P205.

Standard Phosphoric Acid corresponding- volume for volume with
Standard TJianium. — This solution is obtained by dissolving
14 '7 15 gm. of microcosmic salt in a liter, and is two and a half
times the strength of the solution before described ; it is used for
residual titration in case the required volume of uranium is over-
stepped in any given analysis.

A little practice enables the operator to tell very quickly the
precise point ; but it must be remembered that when the two drops
are brought together for the production of the chocolate colour,
however faint it seems at first, owing to the retarding action of the
sodic acetate and acetic acid upon the formation of uranic
ferrocyanide, if left for some little time the colour increases con-
siderably ; but this has no effect upon the accuracy of the process,
since the original standard of the solution has been based on an
experiment conducted in precisely the same way.

Process : In estimating unknown quantities of P205, it is necessary to have
an approximate knowledge of the amount in any given material, so as to
fulfil as nearly as possible the conditions laid down above ; that is to say,
50 c.c. of solution shall contain about O'l gm. P2O5, or whatever other pro-
portion may have been used in standardizing the uranium.

The compound containing the P205 to be estimated is dissolved in water ;
if no ammonia is present, 1 c.c. of 10 per cent, solution is dropped in and
neutralized with the least possible quantity of acetic acid (also 5 c.c. of sodic
acetate if uranic nitrate has to be used), and the volume made up to about
50 c.c., then heated to about 90° C. on the water bath, and the uranium
solution delivered in cautiously, with frequent testing as above described,
until the faint brown tinge appears.

The first trial will give roughly the amount of solution required, and
taking that as a guide, the operator can vary the amount of liquid and sodic
acetate for the final titration, should the proportions be fonnd widely
differing from those under Avhich the strength of the uranium was
originally fixed.

Each c.c. of uranium solution=0'005 gm. P2O5.

£. Estimation of Phosphoric Acid in combination with Lime and
Magnesia (Bones, Bone Ash, Soluble Phosphates, and other
Phosphatic Materials, free from Iron and Alumina).

The procedure in these cases differs from the foregoing in two
Tespects only ; that is to say, the uranium solution is preferably
•standardized by tribasic calcic phosphate ; and in the process of
titration it is necessary to add nearly the full amount of uranium
required before heating the mixture, so as to prevent the precipita-
tion of calcic phosphate, which is apt to occur in acetic acid
solution when heated; or the modification adopted by Fresenius,
Xeubauer, and Luck, may be used, which consists in reversing
"the process by taking a measured volume of uranium, and delivering

§ 72. PHOSPHORIC ACID. 289

into it the solution of phosphate until a drop of the mixture ceases
to give a brown colour with ferrocyanide. This plan gives, how-
ever, much more trouble, and possesses no advantage on the score
of accuracy, because in any case at least two titrations must occur,
and the first being made somewhat roughly, in the ordinary way,
shows within 1 or 2 c.c. the volume of standard urani am required ;
and in the final trial it is only necessary to add at once nearly the
quantity, then heat the mixture, and finish the titration by adding
a drop or two of uranium at a time until the required colour is
obtained.

This reversed process is strongly advocated by many operators,
but except in rare instances I fail to see its superiority to the direct
method for general use. The best modification to adopt in the
reverse process is to use invariably an excess of uranium, and to
titrate back with standard phosphate solution till the colour
disappears ; this avoids all the trouble of preparing and cleaning
a burette for the solution to be analyzed, and if a standard phosphate
is made to correspond volume for volume with the uranium, an
analysis may always be brought into order at any stage.

Standard Calcic Phosphate. — It is not safe to defend upon the
usual preparations of tricalcic phosphate by weighing any given
quantity direct, owing to uncertainty as to the state in which the
phosphoric acid may exist ; therefore, in order to titrate the
uranium solution with calcic phosphate, it is only necessary to
take rather more than 5 gin. of precipitated pure tricalcic phosphate
such as occurs in commerce, dissolve it in a slight excess of dilute
hydrochloric acid, precipitate again with a slight excess of ammonia,
re-dissolve in a moderate excess of acetic acid, then dilute to
a liter ; by this means is obtained a solution of acid monocalcic
phosphate, existing under the same conditions as occur in the
actual analysis. In order to ascertain the exact amount of tribasic
phosphoric acid present in a given measure of this solution, two
portions of 50 c.c. each are placed in two beakers, each holding
about half a liter. A slight excess of solution of uranic acetate
or nitrate is then added to each, together with about 10 c.c. of the
acetic solution of sodic acetate ; they are then heated to actual
boiling on a hot-plate or sand-bath, the beakers filled up with
boiling distilled water, and then set aside to settle, which occurs
very speedily. The supernatant fluid should be faintly yellow
from excess of uranium. When perfectly settled, the clear liquid
is withdrawn by a syphon or poured off as closely as possible with-
out disturbing the precipitate, and the beakers again filled up with
boiling water. The same should be done a third time, when the
precipitates may be brought on two filters, and need very little
further washing.

"When the filtration is complete, the filters are dried and ignited
separate from the precipitate, taking care to burn off all carbon.

290 VOLUMETRIC ANALYSIS. § 72.

Before being weighed, however, the uranic-phosphate must be
moistened with strong nitric acid, dried perfectly in the water bath
or oven, and again ignited ; at first, very gently, then strongly, so
as to leave a residue when cold of a pure light lemon colour. This
is uranic phosphate Ur203, P205, the percentage composition of
which is 80 '09 of uranic oxide, and 19 '91 of phosphoric acid.

The two precipitates are accurately weighed, and should agree to
within a trifle. If they differ, the mean is taken to represent the
amount of P20.5 in the given quantity of tricalcic phosphate, from
which may be calculated the strength of the solution to be used as
a standard. Of course any other accurate method of determining
the P205 may be used in place of this.

The actual standard required is 5 gm. of pure tricalcic phosphate
per liter ; and it should be adjusted to this strength by dilution,
after the actual strength has been found. In this way is obtained
a standard which agrees exactly with the analysis of a super-
phosphate or other similar manure.

Standard Uranium Solution. — This is best adjusted to such
strength that 25 c.c. are required to give the faint chocolate colour
with ferrocyaiiide, when 50 c.c. of the standard acetic solution of
calcic phosphate are taken for titration. Working in this manner
each c.c. of uranium solution represents 1 per cent, of soluble
tricalcic phosphate, when 1 gm. of manure is taken for analysis,
because 50 c.c. of the calcic phosphate will contain monocalcic
phosphate equal to 0'25 gm. of Ca:jP208 and will require 25 c.c.
of uranium solution to balance it.

These standards are given as convenient for manures, but they
may be modified to suit any particular purpose.

Process in case of Superphosphate free from Fe and Al, except
in mere traces : — 10 gm. of the substance are weighed, placed in a small glass
mortar and gently broken down by the pestle, coid water being used to bring
it to a smooth cream. The material should not be ground or rubbed hard,
which might cause the solution of some insoluble phosphate in the
concentrated mixture. The creamy substance is washed gradually without
loss into a measuring flask marked at 503'5 c.c., the 3'5 c.c. being the space
occupied by the insoluble matters in an ordinary 25 to 30 per cent,
superphosphate. The flask is filled to the mark with cold water, and shaken
every few minutes during about half-an-honr. A portion is then filtered
through a dry filter into a dry beaker, and 50 c.c.==i gm. of manure
measured into a beaker holding about 100 c.c. Sufficient 10 per cent, ammonia
is then added to precipitate the monocalcic phosphate in the form of
Ca3P2O8 (in all ordinary superphosphates there is enough Ca present as
sulphate to ensure this, and four or five drops of ammonia generally suffice
to effect the precipitation). Acetic acid is then added in just sufficient
quantity to render the liquid clear. Should traces of gelatinous A1PO4 or
FePO4 occur at this stage, the liquid will be slightly opalescent ; but this
may be disregarded if only slight, as the subsequent heating will enable the
uranium to decompose it. If more than traces occur, the method will not
be accurate, and recourse must be had to separation by the citro-magnesic
solution.

While the liquid is still cold, a measured volume of the standard uranium

§ 72. PHOSPHORIC ACID. 291

is run in with stirring, and occasional drops are taken out with a glass rod,
and put in contact with some ferrocyanide indicator sprinkled on a white
plate until a faint colour occurs. The beaker is then placed in the water-
bath for a few minutes, and again the mixture tested with the indicator :
ufter heating in this way the testing ought to show no colour. More
uranium is then added with stirring, and drop by drop till the proper reaction
occurs. This titration is only a guide for a second, which maybe made more
accurate by running in at once very nearhr the requisite volume of uranium.

This operation may be reversed, if so desired, by making the
clear solution of phosphate up to a definite volume (say 60 c.c.),
and running it into a measured volume of uranium until a test
taken shows no colour.

5. Estimation of Phosphoric Acid in Minerals or other substances
containing- Iron, Alumina, or other disturbing- matters.

In order to make use of any volumetric process for this purpose,
the phosphoric acid must be separated. As has been already
described, this may be ^lone either by the molybdic precipitation
followed by solution in !N"H3, again precipitated with ordinary
magnesia mixture, or direct separation by the citro-magnesia
mixture described below. In either case the ammonio-magnesic
salt is dissolved in the least possible quantity of nitric or
hydrochloric acid, neutralized with ammonia, acidified with acetic
acid, and the titration with uranium carried out as before described.

6. Joulie's Method.

This differs somewhat from the foregoing, and may be summarized
as follows (Munro, C.N. Hi. 85).

Joulie applies the citro-magnesia method to all phosphates,
whether containing iron and alumina or not, and prefers nitrate to
acetate of uranium.

1 to 10 gm. of the sample are dissolved in HC1. Some chemists use
nitric acid with a view of leaving as much ferric oxide as possible undissolved.
This course is condemned by the author, because the presence of ferric salts
in no way interferes with the process, and because HC1 is a much better
solvent of mineral phosphates than nitric acid, and leaves a residue free from
iron, by the whiteness of which one may judge of the completeness of the
attack. In the case of phosphates containing a little pyrites, nitric acid
should be used in conjunction with hydrochloric. The removal of silica by
evaporation to dry ness is necessary only in those cases where the sample
contains silicates decomposable by HC1, with separation of gelatinous silica.
The sample is boiled with the acid in a measuring flask until the residue is
perfectly white, the contents are cooled, made up to the mark with cold
water, mixed, filtered through a dry filter, and such a fraction of the filtrate
withdrawn by a pipette as contains about 50 m.gm. of P-05. The sample
being delivered from the pipette into a small beaker, 10 c.c. of citro-magnesic
solution are added, and then a large excess of ammonia. If this quantity
of citro-magnesic solution is sufficient, no precipitate will form until the lapse
of a few moments ; should an immediate precipitate form, it is iron or
aluminium phosphate. In this case a fresh sample must be pipetted off, and
20 c.c. of citro-rnagnesic solution are added ; it is of no use adding another 10 c.c.

u 2

292 VOLUMETRIC ANALYSIS. § 72.

of the citric solution to the original sample, as the precipitated phosphates
of iron and aluminium do not readily redissolve when once formed.

Citro-Magnesic Solution. — 27 gm. of pure maguesic carbonate are added
by degrees to a solution of 270 gm. of citric acid in 350 c.c. of warm water ;
when all effervescence is over and the liquid cool, about 400 c.c. of solution
of ammonia are added, containing 10 per cent, of NH3 (about 0'96 sp. gr.),
or if other strength is used, enough to ensure decided excess of NH3 :" the
whole is then diluted to a liter, and preserved in a well-stoppered bottle.

The old plan of adding first citric acid and then " magnesia mixture " to
the solution under analysis frequently leads to incomplete precipitation of
the phosphoric acid, because . the ammonio-magnesic phosphate is slightly
soluble in ammonic citrate unless a sufficient excess of magnesium salt is
present, and therefore the quantity of magnesium salt should be increased
pari passu with the citric acid required, which is best done when they are in
solution together. The liquid after precipitation is allowed to stand from 2
to 12 hours (covered to prevent evaporation of ammonia), and then decanted
through a small filter. The precipitate remaining in the beaker is washed
Avith weak ammonia by decantation, and then on the filter until the filtrate
gives no precipitate with sodic phosphate. Dilute nitric acid is next poured
into the beaker to dissolve the precipitate adhering to the glass, thence on to
the precipitate on the filter. The nitric solution is received in a beaker
holding about 150 c.c. and marked at 77 c.c. After two or three washings
with acidulated water the filter itself is detached from the funnel and added
to the contents of the beaker, as the paper is found to retain traces of P-O5
even after many washings. Dilute ammonia is next added until a slight
turbidity is produced, which is removed by the addition of one or two drops
of dilute nitric acid, the liquid is heated to boiling, 5 c.c. of the sodic acetate
solution added (§ 72.2c.), and the titration Avith uranic nitrate immediately
proceeded with.

The Standard Uranic Nitrate is made by dissolving about 40 gm. of the
pure crj^stals in 800 c.c. water, adding a few drops of ammonia to produce
a slight turbidity, then acetic acid until cleared, and diluting to 1 liter.
Acetate of uranium should not be used, as it impairs the sensibility of the
end-reaction. The uranium solution is titrated with 10 c.c. of a standard
solution of acid ammonic phosphate containing 8'10 gm. of the pure dry salt
per liter (1 c.c.=0'005 gm. P-O5). The ammonic phosphate solution is-
verified by evaporating a measured quantity (say 50 c.c.) of it to dryness
with a measured quantity of a solution of pure ferric nitrate containing an
excess of ferric oxide, and calcining the residue. The difference in weight
between this calcined residue and that from an equal volume of ferric nitrate
solution evaporated alone, is the weight of phosphoric anhydride contained
in the 50 c.c. of ammonic phosphate solution. The actual verification of the
uranic nitrate is performed by measuring accurately 10 c.c. of the ammonic
phosphate into a beaker marked at 75 c.c., adding 5 c.c. of the sodic-
acetate, making up with water to about 30 c.c., and heating to boiling.
9 c.c. uranium are then run in from a burette, and the liquid tested in the
usual way with ferrocyanide. From, this point the uranium is added two or
three drops at a time, until the end-reaction just appears, the burette being
read off at each testing. As soon as the faintest colouration appears,
the beaker is immediately filled to the mark with boiling distilled Avater,
and another test made. If the operation has been properly conducted no
brown colour will be detected, owing to the dilution of the liquid, and one
or two drops more of the uranium solution must be added before the colour
becomes evident, and the burette is finally read off. A constant correction is
subtracted from all readings obtained in this way : it is the quantity of
uranium "found necessary to give the end-reaction Avith 5 c.c. of the sodic
acetate solution alone, diluted to 75 c.c. Avith boiling Avater as above described.
The end-point must always be verified by adding three or four drops o£

8 72. PHOSPHORIC ACID. 293

uranium in excess, and testing again, when a strongly marked colour should
be produced. The standard uranium is made of the same strength as the
standard ammonic phosphate, in order to eliminate the error caused by
changes in the temperature of the laboratory. The actual analysis is made
in the same way as the titration of the standard uranium, except that
a slight error is introduced by the number of tests that have to be made
abstracting a small fraction of the assay. To correct this, a second estimation
should always be made, and nearly the whole of the uranium • found
necessary in the first trial should be added at once. Tests are then made at
intervals of two or three drops, and the final and correct result should
slightly exceed that obtained in the first trial.

7. Pemberton's Original Molybdic Method.

This process, with all the steps that led to its adoption, and the
difficulties involved, is described in a paper read before the chemical
section of the Franklin Institute in 1882 (C. N. xlvi. 4).

The process is based on the fact that, if a standard aqueous
solution of ammonic molybdate be added to one of phosphoric
acid, in the presence of a large proportion of ammonic nitrate,
accompanied with a small excess of nitric acid, and heat applied to
the mixture, the whole of the P205 is immediately and completely
•carried down as phospho-molybdate quite free from MoO3. A small
•excess of the precipitant renders the supernatant liquid clear and
colourless, and the ratio of molybdic trioxide to phosphoric
anhydride is always the same.

The weak part of the method is the difficulty in finding the
exact point at which the precipitation is ended, because the
yellow precipitate does not settle in clots like silver chloride,
and hence filtration is necessary, in order to obtain a portion of
clear liquid for testing with a drop of the molybdate. Very good
results may be obtained with some little patience and practice by
using the Bcale filter (fig. 23). When the precipitation is thought
to be nearly complete, the filter is dipped into the hot liquid, so
as to obtain 2 c.c. or so in a clear condition : this is transferred
to a clean test tube or small short beaker, and a drop or two
of the precipitant added, then heated in the bath to see if a yellow
colour occurs ; if it does, the filter and beaker are washed again
into the bulk with hot water in very small quantities from a small
wash-bottle. A second titration ought to result in "a very near
approximation, and a third will be exact. A convenient small
suction asbestos filter is figured and described by Professor
C a Id well as well adapted to this process (C. N. xlviii. 61).
As each titration can be made in a very short time, the process
may be made valuable for technical purposes in the absence of
either iron or alumina except in mere traces. ,

It is, however, imperative here, as it is in the usual molybdic
process, to avoid the presence of soluble silica, organic matter, and
organic acids, also iron and alumina. Chlorides in moderate
quantity do not interfere.

294 VOLUMETRIC ANALYSIS. § 72.

The necessary solutions and reagents are —

Standard Ammonic molybdate. 89'543 gin. of the pure crystallized
salt are dissolved in about 900 c.c. of water ; if not quite clear,
a very few drops of ammonia may be added to ensure perfect
solution ; the flask is then filled to the liter mark. The weight of
salt used is based on the proportion of 24 MoO:J to 1 of P205, and
each c.c. precipitates 3 m.gm. P205. If any doubt exists as to the
purity of the molybdate, the solution should be standardized with
a solution of P205 of known strength. In any case this is to be
recommended.

Ammonic nitrate in granular form and neutral.

Nitric acid, sp. gr. not less than 1'4; or if of less strength,
a proportionate increase must be used in the titration.

Process : The phosphate to be titrated is taken in quantity containing not
over O'l gm. P205 or 0'15 gm. at the utmost. If silica is present, the
solution is evaporated to dryness. In presence of organic matter ignite
gently and evaporate to dryness twice with HNO3. There is no advantage
in filtering off the SiO'2. The solution is transferred to a beaker of 100 to
125 c.c., using as little water as possible to prevent unnecessary dilution
and is just neutralized with NH4HO, i.e., until a slight precipitate is
formed.

If much iron is present the ammonia is added until the yellow colour
begins to change to a darker shade. 2 c.c. of nitric acid are added. Care
must be taken that the sp. gr. of the acid is not less than T4, otherwise more
must be added. 10 gm. of granular nitrate of ammonia are now added.
After a little experience the quantity can be judged with sufficient accuracy
by the eye without the trouble of weighing. The solution is now heated to
140° P. or over and the molybdate solution run in (most conveniently from
a Gay Lussac burette), meanwhile stirring the liquid. The beaker is now
left undisturbed for about a minute on the water-bath or hot plate until the
precipitate settles, leaving the supernatant liquid not clear but containing
widely disseminated particles, in which the yellow cloud can easily be seen
on the further addition of the molybdate. This addition is continued as
long as the precipitate is thick and of a deep colour. But as soon as it
becomes rather faint and thin, a little of the solution, about 2 to 3 c.c., after
settling of the precipitate, is filtered into a very small beuker, and this is
heated on a hot plate and 4 or 5 drops of the molybdate added. If
a precipitate is produced, the whole is poured back into the large beaker, and
a further addition of the molybdate (1, 2, or 3 c.c.) added, according to the
quantity of the precipitate in the small beaker. After stirring and settling,
another small quantity is filtered and again tested. If the mark has been
overstepped and too much molybdate added, a measured quantity of P-O"
solution of known strength is added, and the corresponding amount of
P2O5 deducted. The results may be checked by adding 1 c.c. of standard
P2O5 solution, and then again testing. This can be repeated as often as
desired. The portion that finally produces a cloud is the end-point ; from
this is deducted 0'5 c.c. (for neutralizing the solvent action of the nitric
acid), the remainder multiplied by 3 gives the weight of P205 in milligrams.
O'l gm. of P205 gives about 275 gm. of the yellow precipitate, and the
accuracy of the method is largely due to the low percentage of P2O5.

8. P ember ton's new Molybiic Method.

This method, a full description of which is given in Jour.
jimer. Cliem. Soc. 1894, 278, is one which requires great delicacy

§ 72. PHOSPHOEIC ACID. 295

of manipulation, but gives excellent results with all the alkaline
or earthy phosphates, but unfortunately is practically useless with
the phosphates of iron or alumina, or with materials containing
more than mere traces of these substances. For superphosphates
it is available, unless the amount of iron or alumina or both exist
in more than ordinary proportion, and also for the raw phosphates
from which they are made. One great recommendation of the
method is that it occupies little time, the whole operation may be
performed in less than an hour in the case of a raw phosphate of
lime. With superphosphates there has of course to be the extraction
of the soluble phosphate, but once this is done the determination
of the soluble P205 may readily be done in half-an-hour, and
moreover two or three determinations may be carried on simul-
taneously with the expenditure of very little extra time.

The method is based on the fact, which has been proved by
numerous experiments, that if a pure yellow phospho-molybdate
be titrated with alkali and a proper indicator, so much of it as
contains one molecule of P205 will exactly represent 23 molecules
of XjiHO. Of course it is of the greatest importance that in the
method a pure phosphomolybdate should be obtained, and hence
the difficulty where such bases as iron or alumina are present, as it
seems impossible to prevent their being carried down with the
yellow precipitate even in presence of much nitric acid. As
has been already said, the process is one of great delicacy of
treatment, and cannot be satisfactorily used by inexperienced
operators. The most suitable alkali for the standard is caustic
potash which should be free from CO2, and the most delicate
indicator is phenolphthalein. Further, the quantity of material
taken for the titration must be very small, preferably containing not
more than Ol gin. of P205. It will readily be seen that if an
error is made it becomes a serious matter, when results are
calculated into percentages.

The solutions required are : —

Ammonic molybdate. 1 c.c. of which will precipitate 3 m.gm.
of P205. This is made by dissolving 90 gm. of the pure salt in
about 700 c.c. of water, and allowing to stand a few hours, if
then quite clear it may be diluted at once to a liter, but if a slight
precipitate of molybdic acid occurs the clear liquid is decanted,
the precipitate dissolved in a few drops of ammonia, and the
whole made up to the liter. The strength of this solution need
not be absolutely exact.

Standard Caustic Potash. Made by diluting 323 '7 c.c. of
strictly normal solution (free from CO2) to a liter.

Standard Sulphuric Acid. Made to correspond exactly with
the standard alkali, using phenolphthalein as the indicator in the
cold. The phenolphthalein solution is the same as described on
page 37, and not less than 0'5 c.c. should be used for each titration.

296 VOLUMETRIC ANALYSIS. § 72.

There are also required a saturated aqueous solution of ammonic
nitrate and nitric acid of about 1*4 sp. gr.

Process for raw Phosphates of Lime : 1 gm. of the phosphate is dissolved
in nitric acid, an excess of which can be used with impunity, and the
solution filtered into a 250 c.c. flask and made up to the mark. The solution
can even be poured into the flask without filtering, since the presence of
a little insoluble matter does not interfere in the least with the titration.
Moreover, since most phosphate rocks seldom contain over 10 per cent,
of insoluble matter, and as this has the specific gravity of, at least, 2, it
occupies a volume of about 0'05 c.c., an amount so small that it may be
neglected.

After the clear solution has been poured off, it is well to treat the
sand, etc., at the bottom of the beaker, with a c.c. or so of HC1, in the
warmth, to insure complete solution.

It is not necessary to evaporate to dryness. Isbert and Stutzer have
shown (Z. A. C. xxvi. 584), that when the yellow precipitate is washed with
water, the soluble silica is removed, and that evaporation (to render the
silica insoluble) is superfluous. In the event of its being desirable to
remove silica by evaporation for any purpose, the evaporation should be
performed over a water-bath, or, if on an iron plate, with great care, since,
otherwise, meta- or pyrophosphates are formed, with results that are
correspondingly low.

25 c.c. of the solution (equal to O'l gm.) are now measured out and
delivered into a beaker holding not more than 100 to 125 c.c. A large
beaker requires unnecessary washing to remove the free acid in washing the
yelloAV precipitate. The solution is neutralized with ammonia— until
a precipitate just begins to form — and 5 c.c. of nitric acid of sp. gr. 1*4
added ; 10 c.c. of the ammonic nitrate solution are poured in, and the entire
bulk of the mixture made up to 60 or 70 c.c. by adding water.

Heat is now applied, and the solution brought to a full boil. It is then
removed from the lamp, no more heat being applied, and treated at once
with. 5 c.c. of the aqueous solution of ammonium molybdate, which is run into
it slowly from a 5 c.c. pipette, the solution being stirred as the precipitate is
added. The beaker is now allowed to rest quietly for about one minute,
during which time the precipitate settles almost completely. The 5 c.c.
pipette is filled with the molybdate solution, and a part of its contents
allowed to drop in, holding the beaker up to the light. If a formation of
a yellow cloud takes place — it is at once perceptible — in which case the
remainder of the pipetteful is run in, the solution stirred and allowed to
settle. A third pipetteful is now added as before. Should it cause no
further cloud, only about one-half of its contents are added.

It is seldom that more than 15 c.c. of the molybdate have to be added.
Since each c.c. precipitates 3 m.gm. of P2O5, 15 c.c. will precipitate 45 m.gm.
of P2O5. This is equivalent to 45 per cent, on the O'l gm. taken for
analysis, and it is not often that any material to be examined contains over
this percentage. This is not strictly true, for the reason that a small
quantity (something over 1 c.c.) of the molybdate is required to neutralize
the solvent action of the nitric acid. Therefore, in very high grade
phosphates a fourth 5 c.c. pipetteful may be required. In this process the
point at Avhich sufficient of the precipitant has been added is easily seen.
No molybdic acid separates, because, in the first place, no great excess of
molybdate is added; and because, in the second place, the solution is
filtered immediately, or as soon as it has settled, which requires only
a minute or two. The time required from the first addition of the molybdate
to the beginning of the filtration is never over ten minutes, and is generally
less. The filtrate and washings from the precipitate when treated with
additional molybdate solution, give, on standing on a hot plate for an hour

§ 72. SILVER. 297

or so, a snow-white precipitate of molybdic acid, showing that all of the
phosphoric acid has been precipitated.

The yellow precipitate is now filtered through a filter 7 c.m. in diameter,
decanting the clear solution only. This is repeated three or four times,
washing down the sides of the beaker, stirring up the precipitate, and
washing the filter and sides of the funnel above the filter each time. The
precipitate is then transferred to the filter and washed there. When the
precipitate is large it cannot be churned up by the wash water, and cannot
be washed down to the apex of the filter. This is generally the case when
there is over 10 to 15 per cent, of phosphoric acid present in the substance
analyzed. In such an event, the precipitate is washed back into the beaker,
and the funnel tilled with water above the level of the filter, this being done
two or three times, then the precipitate washed back into the filter. It is
not necessary to transfer to the filter the precipitate adhering to the sides of
the beaker.

During the washing no ammonia must be present in the atmosphere of
the laboratory. Inasmuch as the beaker, funnel, filter and precipitate are
small, the washing does not take long to perform. It requires, in fact, from
ten to fifteen minutes, even when large precipitates (=30 to 40 per cent.
P-O5) are handled. The precipitate and filter are now transferred together
to the beaker. The standard alkali is run in until the precipitate has
dissolved, phenolphthalein then added, and the acid run in without delay
until the pearly colour disappears and the solution is colourless. The
presence of the filter paper does not interfere in the least. The reaction of
the indicator is not so sharp as when only acid and alkali are used, but it is
easy to tell with certainty the difference caused by one drop of either acid
or alkali. After deducting the volume of acid used from that of the alkali,
the remainder gives the percentage of P-O5 directly, each c.c. being equal to
1 per cent. P2O5. Thus, if there are 28'3 c.c. of alkali consumed, the
material contains 28'3 per cent. P2O5 when one decigram is taken for
analysis. From the time the 25 c.c. are measured out until the result is
obtained, from thirty to forty minutes are required.

Process for soluble P205 in Superphosphates : A measured portion of the
clear aqueous solution of the material according to its grade, and representing
not more than 0'05 gm. P2O5, are pipetted into a small beaker and treated
exactly as described above.

B. W. Kilgore (Jour. Amer. Cliem. Soc. 1894, 765) states that
good results in general were obtained by him in using this method,
but that occasionally too high figures for P205 were obtained.
This is also stated by other operators. The variations in this
direction are generally caused by the deposition of molybdic acid,
but .they may, of course, be also caused by imperfect washing of
the precipitate. Kilgore prefers to use the ordinary official acid
molybdic solution, and to precipitate at 50° or 60° C. instead of 100°
C. The official molybdic solution is made by dissolving 100 gm.
of molybdic acid in 417 c.c. of ammonia, sp. gr. 0*96, and
pouring this into 1250 c.c. of nitric acid, sp. gr. 1*2, then filtering
before use.

SILVER.

Ag=: 107-66.

1 c.c. or 1 dm. -— sodic chloride- 0'010766 gm. or 0'10766 grn.
Silver; also 0*016966 gm. or 0*16966 grn. Silver nitiate.

298 VOLUMETRIC ANALYSIS. § 73.

3. Precipitation with ^ Sodic Chloride.

§ 73. THE determination of silver is precisely the converse of
tl;e operations described under chlorine (§ 54, 1 and 2), and the
process may either be concluded by adding the sodic chloride till
no further precipitate is produced, or potassic chromate may be
used as an indicator. In the latter case, however, it is advisable
to add the salt solution in excess, then a drop or two of chromate,
and titrate residually with — silver, till the red colour is produced,
for the excess of sodic chloride.

2. By Ammonic Sulphocyanate (Thiocyanate) .

The principle of this method is fully described in § 43, and
need not further he alluded to here. The author of the method
(Volhard) states, that comparative tests made by this method
and that of Gay Lussac gave equally exact results, both being
controlled by cupellation, but claims for this process that the end
of the reaction is more easily distinguished, and that there is no
labour of shaking, or danger of decomposition by light, as in the
case of chloride. My own experience fully confirms this.

3. Estimation of Silver, in Ores and Alloys, by Starch Iodide
(Method of Pisani and P. Field).

If a solution of blue starch-iodide be added to a neutral solution
of silver nitrate, while any of the latter is in excess, the blue colour
disappears, the iodine entering into combination with the silver ;
as soon as all the silver is thus saturated, the blue colour remains-
permanent, and marks the end of the process. The reaction is
very delicate, and the process is more especially applicable to the
analysis of ores and alloys of silver containing lead and copper, but
not mercury, tin, iron, manganese, antimony, arsenic, or gold in
solution.

The solution of starch iodide, devised by Pisani, is made by
rubbing together in a mortar 2 gm. of iodine with 15 gm. of starch
and about 6 or 8 drops of water, putting the moist mixture into
a stoppered flask, and digesting in a water bath for about an hour, or
until it has assumed a dark bluish-grey colour ; water is then added
till all is dissolved. The strength of the solution is then ascertained
by titrating it with 10 c.c. of a solution of silver containing 1 gm.
in the liter, to which a portion of pure precipitated calcic carbonate
is added; the addition. of this latter removes all excess of acid, and
at the same time enables the operator to distinguish the end of the
reaction more accurately. The starch iodide solution should be of
such a strength that about 50 c.c. are required for 10 c.c. of the
silver solution ( = O'Ol gm. silver).

F. Field (C. N. ii. 17), who discovered the principle of this
method simultaneously with Pisani, uses a solution of iodine in
potassic iodide with starch. Those who desire to make use of

§ 73. SILVER. 299

this plan can use the T^ and Tgy solutions of iodine described
in § 38.

In the analysis of silver containing copper, the solution must be
considerably diluted in order to weaken the colour of the copper ;
a small measured portion is then taken, calcic carbonate added, and
starch iodide till the colour is permanent. It is best to operate
with about from 60 to 100 c.c., containing not more than 0'02 gni.
silver; when the quantity is much greater than this, it is preferable
to precipitate the greater portion with — sodic chloride, and to
complete with starch iodide after filtering off the chloride. When
lead is present with silver in the nitric acid solution, add sulphuric
acid, and filter off the lead sulphate, then add calcic carbonate to
neutralize excess of acid, filter again if necessary, then add fresh
carbonate and titrate as described above.

4. Assay of Commercial Silver (Plate, Bullion, Coin, etc.). Gray
Lussac's Method modified by J. G-. Mulder.

For more than thirty years Gay Lussac's method of estimating
silver in its alloys has been practised intact, at all the European
mints, under the name of the " humid method," in place of the old
system of cupellation. During that time it has been regarded as one
of the most exact methods of quantitative analysis. The researches
of Mulder, however, into the innermost details of the process
have shown that it is capable of even greater accuracy than has
hitherto been gained by it.

The principle of the process is the same as described in § 41,
depending on the affinity which chlorine has for silver in preference
to all other substances, and resulting in the formation of chloride
of silver, a compound insoluble in dilute acids, and which readily
separates itself from the liquid in which it is suspended.

The plan originally devised by the illustrious inventor of the
process for assaying silver, and which is still followed, is to consider
the weight of alloy taken for examination to consist of 1000 parts,
and the question is to find how many of these parts are pure silver.
This empirical system was arranged for the convenience of commerce,
and being now thoroughly established, it is the best plan of
procedure. If, therefore, a standard solution of salt be made of
such strength that 100 c.c. will exactly precipitate 1 gm. of silver,
it is manifest that each yy c.c, will precipitate 1 in.gm. or y^cr
part of the gram taken ; and consequently in the analysis of
1 gm. of any alloy containing silver, the number of y1^ c.c.
required to precipitate all the silver out of it would be the number
of thousandths of pure silver contained in the specimen.

In practice, however, it would not do to follow this plan precisely,
inasmuch as neither the measurement of the standard solution nor
the ending of the process would be gained in the most exact
manner ; consequently, a decimal solution of salt, one-tenth the
strength of the standard solution, is prepared, so that. 1000 c.c.

SOO VOLUMETRIC ANALYSIS. § 73.

will exactly precipitate 1 gm. of silver, and, therefore, 1 c.c.
1 m.gm.

The silver alloy to be examined (the composition of which must
be approximately known) is weighed so that about 1 gm. of pure
silver is present ; it is then dissolved in pure nitric acid by the aid
of a gentle heat, and 100 c.c. of standard solution of salt added
from a pipette in order to precipitate exactly 1 gm. of silver ; the
bottle containing the mixture is then well shaken until the chloride
of silver has curdled, leaA^ing the liquid clear.

The question is now : Which is in excess, salt or silver ? A drop
of decimal salt solution is added, and if a precipitate be produced
1 c.c. is delivered in, and after clearing, another, and so on as long
as a precipitate is produced. If on the other hand the one drop of
salt produced no precipitate, showing that the pure silver present
was less than 1 gm., a decimal solution of silver is used, prepared
by dissolving 1 gm. pure silver in pure nitric acid and diluting to
1 liter. This solution is added after the same manner as the salt
•solution just described, until no further precipitate occurs; in either
•case the quantity of decimal solution used is noted, and the results
calculated in thousandths for 1 gm. of the alloy.

The process thus shortly described is that originally devised by
Gay Lussac, and it was taken for granted that when equivalent
€hemical proportions of silver and sodic chloride were brought thus
in contact, that every trace of the metal was precipitated from the
solution, leaving sodic nitrate and free nitric acid only in solution.
The researches of Mulder, however, go to prove that this is not
strictly the case, but that when the most exact chemical proportions
of silver and salt are made to react on each other, and the chloride
has subsided, a few drops more of either salt or silver solution will
produce a further precipitate, indicating the presence of both silver
nitrate and sodic chloride in a state of equilibrium, which is upset
on the addition of either salt or silver. Mulder decides, and no
doubt rightly, that this peculiarity is owing to the presence of sodic
nitrate, and varies somewhat with the temperature and state of
dilution of the liquid.

It therefore follows that when a silver solution is carefully
precipitated, first by concentrated and then by dilute salt solution,
until no further precipitate appears, the clear liquid will at this
point give a precipitate with dilute silver solution ; and if it be
added till no further cloudiness is produced, it will again be
precipitable by dilute salt solution.

Example : Suppose that in a given silver analysis the decimal salt solution
has been added so long as a precipitate is produced, and that 1 c.c. (=20 drops
of Mulder's dropping apparatus) of decimal silver is in turn required to
precipitate the apparent excess, it would be found that when this had been
done, 1 c.c. more of salt solution would be wanted to reach the point at which
110 further cloudiness is produced by it, and so the changes might be rung
time after time ; if, however, instead of the last 1 c.c. (=20 drops) of salt,
half the quantity be added, that is to say 10 drops (=| c.c.), Mulder's

§ 73. SILVEB. 301

so-called neutral point is reached ; namely, that i n which, if the liquid be
divided in half, both salt and silver will produce the same amount of
precipitate. At this stage the solution contains silver chloride dissolved
in sodic nitrate, and the addition of either salt or silver expels it from*
solution.

A silver analysis may therefore be concluded in three ways —

(1) By adding decimal salt solution until it just ceases 1x>
produce a cloudiness.

(2) By adding a slight excess of salt, and then decimal silver;
till no more precipitate occurs.

(3) By finding the neutral point.

According to Mulder the latter is the only correct method, and
preserves its accuracy at all temperatures up to 56° C. ( = 133°
Fahr.), while the difference between 1 and 3 amounts to | a m.gm.,
and that between 1 and 2 to 1 m.gm. on 1 gm. of silver at,
16° C. (= 60° Fahr.), and is seriously increased by variation of
temperature.

It will readily be seen that much more trouble and care is
required by Mulder's method than by that of Gay Lussac, but,,
as a compensation, much greater accuracy is obtained.

On the whole it appears to me preferable to weigh the alloy so,
that slightly more than 1 gm. of silver is present, and to choose the-
ending No. 1, adding drop by drop the decimal salt solution until
just a trace of the precipitate is seen, and which, after some practice,
is known by the operator to be final. It will be found that the-
quantity of salt solution used will slightly exceed that required by
chemical computation; say lOO'l c.c. are found equal to 1 gm. of
silver, the operator has only to calculate that quantity of the salt
solution in question for every 1 gm. of silver he assays in the form
of alloy, and the error produced by the solubility of silver chloride
in sodic nitrate is removed.

If the decimal solution has been cautiously added, and the
temperature not higher than 17° C. (62° Fahr.), this method of
conclusion is as reliable as No. 3, and free from the possible errors^
of experiment ; for it requires a great expenditure of time and
patience to reverse an assay two or three times, each time
cautiously adding the solutions drop by drop, then shaking and'
waiting for the liquid to clear, besides the risk of discolouring the
chloride of silver, which would at once vitiate the results.

The decimal silver solution, according to this arrangement, would,
seldom be required ; if the salt has been incautiously added, or the
quantity of alloy too little to contain 1 gm. pure silver, then it is
best to add once for all 2, 3, or 5 c.c., according to circumstances,
and finish with decimal salt as iNo. 1, deducting the silver added.

The Standard Solutions and Apparatus.

(«) Standard Salt Solution. — Pure sodic chloride is prepared by treating;-
a concentrated solution of the whitest table-salt first with a solution of

VOLUMETRIC ANALYSIS, § 73.

caustic baryta to remove sulphuric acid and magnesia, then with a slight
excess of bodic carbonate to remove baryta and lime, warming and allowing
the precipitates to subside, then evaporating to a small bulk that crystals
may form ; these are separated by a filter, and slightly washed with cold
distilled water, dried, removed from the filter, and heated to dull redness,
and when cold preserved in a well-closed bottle for use. The mother-liquor
is thrown away, or used for other purposes. Of the salt so prepared, or of
chemically pure rock-salt (Steinsalz, a substance to be obtained freely in
Germany), 5'4145 gui. are to be weighed and dissolved in 1 liter of distilled
water at 16° C. 100 c.c. of this solution will precipitate exactly 1 gm. of
silver. It is preserved in a well-stoppered bottle, and shaken before use.

(b) Decimal Salt Solution. — 100 c.c. of the above solution are diluted to
exactly 1 liter with distilled water at 16° C. 1 c.c. will precipitate O'OOl gm.
of silver.

(c) Decimal Silver Solution; — Pure metallic silver is best prepared by
galvanic action from pure chloride ; and as clean and seeure a method as any
is to wrap a lump of clean zinc, into which a silver wire is melted, with
a piece of wetted bladder or calico, so as to keep any particles of impurity
contained in the zinc from the silver. The chloride is placed at the bottom
of a porcelain dish, covered with dilute sulphuric acid, and the zinc laid in
the middle ; the silver wire is bent over so as to be immersed in the chloride.
As soon as the acid begins to act upon the zinc the reduction commences in
the chloride, and grows gradually all over the mass ; the resulting finely-
divided silver is well washed, first with dilute acid, then with hot water, till
all acid and soluble zinc are removed.

The moist metal is then mixed with a little sodic carbonate, saltpetre,
and borax, say about an eighth part of each, dried perfectly, then melted.
Mulder recommends that the melting should be done in a porcelain crucible
immersed in sand contained in a common earthen crucible; borax is sprinkled
over the surface of the sand so that it may be somewhat vitrified, that in
pouring out the silver when nielted no particles of dirt or sand may fall into
it. If the quantity of metal be small it may be melted in a porcelain crucible
over a gas blowpipe.

The molten metal obtained in either case can be poured into cold water
and so granulated, or upon a slab of pipe-clay, into which a glass plate has
been pressed when soft so as to form a shallow mould. The metal is then
washed well with boiling water to remove accidental surface impurities, and
rolled into thin strips by a goldsmith's mill, in order that it may be readily
cut for weighing. The granulated metal is, of course, ready for use at once
without any rolling.

1 gm. of this silver is dissolved in pure dilute nitric acid, and
diluted to 1 liter; each c.c. contains O'OOl gm. of silver. It should
be kept from the light.

(<i) Dropping- Apparatus for Concluding- the Assay.- — Mulder
constructs a special affair for this purpose, consisting of a pear-
shaped vessel fixed in a stand, with special arrangements for
preventing any continued flow of liquid. The delivery tube has an
opening of such size that 20 drops measure exactly 1 c.c. The
vessel itself is not graduated. As this arrangement is of more
service to assay than to general laboratories, it need not be further
described here. A small burette divided in -^ c.c. with a conve-
nient dropping tube, will answer every purpose, and possesses the
further advantage of recording the actual volume of fluid delivered.

§ 73. SILVEE. 303

The 100-c.c. pipette, for delivering the concentrated salt solution,
must be accurately graduated, and should deliver exactly 100 gm.
of distilled water at 16° C.

The test bottles, holding about 200 c.c., should have their
stoppers well ground and brought to a point, and should be fitted
into japanned tin tubes reaching as high as the neck, so as to pre-
serve the precipitated chloride from the action of light, and, when
shaken, a piece of black cloth should be covered over the stopper.

(e) Titration of the Standard Salt Solution. — From what has
been said previously as to the principle of this method, it will be
seen that it is not possible to rely absolutely upon a standard
solution of salt containing 5 '4 145 gm. per liter, although this is
chemically correct in its strength. The real working power must
be found by experiment. From 1*002 to 1*004 gm. of absolutely
pure silver is weighed on the assay balance, put into a test bottle
with about 5 c.c. of pure nitric acid, of about 1'2 sp. gr., and gently
heated in the water or sand bath till it is all dissolved, The
nitrous vapours are then blown from the bottle, and it is set aside
to cool down to about 16° C. or 60° Fahr.

The 100 c.c. pipette, which should be securely fixed in a support,
is then carefully filled with the salt solution, and delivered into
the test bottle contained in its case, the moistened stopper inserted,
covered over with the black velvet or cloth, and shaken con-
tinuously till the chloride has clotted, and the liquid becomes clear ;
the stopper is then slightly lifted, and its point touched against the
neck of the bottle to remove excess of liquid, again inserted, and
any particles of chloride washed down from the top of the bottle
by carefully shaking the clear liquid over them. The bottle is
then brought under the decimal salt burette, and J c.c. added, the
mixture shaken, cleared, another | c.c. put in, and the bottle lifted
partly out of its case to see if the precipitate is considerable *
lastly, 2 or 3 drops only of the solution are added at a time until
no further opacity is produced by the final drop. Suppose, for
instance, that in titrating the salt solution it is found that 1 *003 gm.
of silver require 100 c.c. concentrated, and 4 c.c. decimal solution,
altogether equal to 100 '4 c.c. concentrated, then —

.1-003 silver : 100*4 salt : : 1*000 : x. £=100*0999.

The result is within -jo-J^yo" °^ 100*1, which is near enough for the
purpose, and may be more conveniently used. The operator
therefore knows that 100*1 c.c. of the concentrated salt solution
at 16° C. will exactly precipitate 1 gm. silver, and calculates
accordingly in his examination of alloys.

In the assay of coin and plate of the English standard, namely,
11*1 silver and 0*9 copper, the weight corresponding to 1 gm. of
silver is 1*081 gm., therefore in examining this alloy 1*085 gm.
may be weighed.

304 \7OLUMET11IC ANALYSIS. § 73.

When the quantity of silver is not approximately known,
a preliminary analysis is necessary, which is best made by
dissolving J or 1 gm. of the alloy in nitric acid, and precipitating
very carefully with the concentrated salt solution from a ^ c.c.
burette. Suppose that in this manner 1 gm. of alloy required
45 c.c. salt solution,

100-1 salt : 1-000 silver : : 45 : x. « = 0-4495.
Again 0-4495 : 1 : : 1-003 : x = 2'23l.

2'231 gm. of this particular alloy are therefore taken for the
assay.

Where alloys of silver contain sulphur or gold, with small
quantities of tin, lead, or antimony, they are first treated with
a small quantity of nitric acid so long as red vapours are disengaged.,
then boiled with concentrated sulphuric acid till the gold has
become compact, set aside to cool, diluted with water, and titrated
as above.

Assaying- on the Grain System.

It will be readily seen that the process just described may quite
as conveniently be arranged on the grain system by substituting 10
grains of silver as the unit in place of the gram ; each decem of
concentrated salt solution would then be equal to ~ of a grain
of silver, and each decem of decimal solution to —-$ of a grain.

5. Analysis of the Silver Solutions used in Photography.

The silver bath solutions for sensitizing collodion and paper
frequently require examination, as their strength is constantly
lessening. To save calculation, it is better to use an empirical
solution of salt than the systematic one described above.

This is best prepared by dissolving 43 grains of pure sodic
chloride in 10,000 grains of distilled water. Each decem ( = 10 grn.)
of this solution will precipitate 0-125 grn. (i.e, \ grn.) of pure
silver nitrate ; therefore, if one fluid drachm of any silver solution
be taken for examination, the number of decems of salt solution
required to precipitate all the silver Avill be the number of grains
of silver nitrate in each ounce of the solution.

Example : One fluid drachm of an old nitrate bath was carefully measured
into a stoppered bottle, 10 or 15 drops of pure nitric acid and a little
distilled water added ; the salt solution was then cautiously added, shaking-
well after each addition until no further precipitate was produced. The
quantity required was 26'5 dm. — 26| grains of silver nitrate in each ounce
of solution.

Crystals of silver nitrate may also be examined in the same way,
by dissolving say 30 or 40 grn. in an ounce of water, taking one
drachm of the fluid and titrating as above.

§ 74 SUGAR. 305

In consequence of the rapidity and accuracy with which silver
may be determined, when potassic chromate is used as indicator,
some may prefer to use that method. It is then necessary to have
a standard solution of silver, of the same chemical power as the
salt solution : this is made by dissolving 125 grains of pure and
dry neutral silver nitrate in 1000 dm. of distilled water; both
solutions will then be equal, volume for volume.

Suppose, therefore, it is necessary to examine a silver solution
used for sensitizing paper. One drachm is measured, and
if any free acid be present, cautiously neutralized with a weak
solution- of sodic carbonate ; 100 dm. of salt solution are then
added with a pipette. If the solution is under 100 grn. to
the ounce, the quantity will be sufficient. 3 or 4 drops of
chromate solution are then added, and the silver solution delivered
from the burette until the red colour of silver chromate is just
visible. If 25'5 dm. have been required, that number is deducted
from the 100 dm. of salt solution, which leaves 74'5 dm., or
74J- grains to the ounce.

This method is- much more likely to give exact results in the
hands of persons not expert in analysis than the ordinary plan by
precipitation, inasmuch as, with collodion baths, containing as they
always do silver iodide, it is almost impossible to get the supernatant
liquid clear enough to distinguish the exact end of the analysis.

SUGAR.

§ 74. SUGARS belong to the large class of organic bodies known
as " carbo-hydrates," of which there are three main classes, viz. : —

(1) The Glucoses, C6H120°, the principal members of which
are — glucose, dextrose, or grape sugar, occurring in the urine in
Diabetes mellitus, and with levulose in most sweet fruits and in
honey ; levulose or fruit sugar ; galactose.

(2) The Di-saccharides, C12H22On, the chief members of which
are — cane sugar or sucrose, occurring in the juice of the sugar
cane, beet root, and maple ; milk sugar or lactose, occurring in the
milk of mammals and in various pathological secretions ; malt
sugar or maltose, formed by the action of malt diastase upon
starch.

(3) The Poly-saccharides, or starches and gums (C6H1005X of
which the most important members are starch, glycogen (found in
the liver), dextrine, and cellulose or wood-fibre.

The di- and poly-saccharides are "inverted" or " hydrolyzed "
by being boiled with dilute acids, or by the action of unorganized
ferments like diastase and pepsin, and those contained in yeast
and saliva ; i.e., they become converted into glucoses. Cane sugar
on inversion yields equal parts of dextrose and levulose (invert
sugar), milk sugar yields dextrose and galactose, maltose yields

306 VOLUMETRIC ANALYSIS. § 74

dextrose ; starch, glycogen, dextrose, and cellulose all yield dextrose
as the final product.

The methods in general use for the quantitative estimation of
the various kinds of sugar are — the fermentation method,
estimating the final density of the saccharine solution, and
the amount of CO2 evolved; the optical method, by the polarimeter ;
gravimetrically, by the reduction of an alkaline copper solution ;
volumetrically, by reduction of copper or mercury solutions.

All the glucoses reduce the alkaline copper solution, known as
Fehling's, more or less readily; maltose and lactose reduce it in
a less degree ; starch, cane sugar, dextrine, and cellulose rrot at all.
Other substances besides sugars reduce Fell ling's solution, e.g.,
chloroform, salicylic and uric acids, creatinine and phenyl-
hyclrazine.

The volumetric method of estimating glucose by Fehl ing's
copper solution has for a long time been thought open to question
on the score of accuracy, and the extensive and elaborate experi-
ments of Soxhlet have clearly shown, that only under identical
conditions of dilution, etc., can concordant results be obtained.
The high official position of this chemist, together with the evident
care shown in his methods, leave no doubt as to the general
accuracy of his conclusions. His rather sweeping statement, how-
ever, that the accurate gravimetric estimation of glucose by
Fehling's solution is impossible, is strongly controverted by
Brown and Heron, whose large experience leads them to
a different conclusion. It is probable, however, that both
authorities are right from their own points of view, and that
Brown and Heron do obtain concordant results when working in
precisely the same way; whereas Soxhlet is equally correct in
stating that the gravimetric estimation, as usually performed under
varying conditions, is open to serious errors.

Kjeldahl maintains that Fehling's solution, however pure its
constituents, always undergoes a slight reduction on prolonged
heating, especially in strong solution, and he fixes the limit of
time for which the liquid should be exposed to the temperature of
boiling water at twenty minutes.

The Solution of Sugar. — For all the processes of titration this
must be so diluted as to contain J or at most 1 per cent, of sugar :
if on trial it is found to be stronger than this, it must be further
diluted with a measured quantity of distilled water.

If the sugar solution to be examined is of dark colour, or likely
to contain extractive matters which might interfere with the
distinct ending of the reaction, it is advisable to heat a measured
quantity to boiling, and add a few drops of milk of lime, allow the
precipitate to settle, then filter through purified animal charcoal,
and dilute with the washings to a definite volume. In some
instances cream of alumina or basic lead acetate may be used to

§ 74. SUGAR. 307

clarify highly coloured or impure solution, Imt no lead must be
left in the solution.'*

From thick mucilaginous liquids, or those which contain a large
proportion of albuminous or extractive matters, the sugar is best
extracted by Graham's dialyser.

The Fell ling method may be applied directly to fresh diabetic
urine (see Analysis of Urine), as also to brewer's wort or distiller's
mash. Dextrine does not interfere, unless the boiling of the
liquid under titration is long continued.

]. Inversion of Various Sugars into Glucose.

Ordinary cane sugar is best inverted by heating to about 70° C.
a dilute solution (in no case should the concentration exceed 25 per
cent.) of the sugar with 10 per cent, of fuming hydrochloric acid
for 15 minutes. Dilute sulphuric acid is preferred by some
operators. If the mixture is boiled, the inversion occurs in from
5 to 10 minutes. The inversion of milk sugar takes longer time
than cane sugar.

Maltose or malt sugar takes a much longer time than milk
sugar, but may be done by the addition of 3 c.c. of concentrated
sulphuric acid to 100 c.c. of wort, and heating for 3 hours in
a boiling water bath ; if dextrine is present, it is also inverted at
the same time.

The inversion of the slowly changing sugars may be hastened
considerably by heating at increased atmospheric pressure, although
some authorities condemn the process. 0' Sullivan however
states that a good result with maltose or dextrine is obtained by
heating 30 gm. of the substance in 100 c.c. of water containing
1 c.c. of H2S04 for 20 minutes, at a pressure of one additional
atmosphere (Allen's Organic Analysis i. 217).

Allen also gives a handy means of carrying out this method,
which consists in using a soda water bottle with rubber stopper
through which passes a long glass tube bent at right angles, and
immersed to a depth of 30 inches in mercury contained in
a vertical tube of glass or metal. The rubber stopper must be
secured by wire, and the bottle heated to boiling in a saturated
solution of sodic nitrate, which gives a temperature corresponding
to an extra atmosphere. Of course in all cases where acid has
been used for the inversion of sugar, it must be neutralized before
the copper titration takes place ; this may be done either with
sodic or potassic hydrates or carbonates, or calcic carbonate may be
used.

* Although traces of lead are of no great consequence when clarifying sugars for the
polariscope, it is of great importance to remove all lead in the volumetric method. In
order to do this it is best to treat a measured quantity of the sugar solution which has
been clarified by lead with a strong solution of sulphurous acid until no further
precipitate occurs, then add a few drops of alumina hydrate suspended in water,
dilute to a definite volume and filter. In many cases concentrated solution of sodic
carbonate will suffice to remove all lead. These methods of clarification are highly
necessary in the case of albuminous or gelatinous liquids, as otherwise the copper oxide
will not settle readily, and it becomes difficult to tell when the end-reaction occurs.

x 2

308 VOLUMETEIC ANALYSIS. § 74.

Starch from various sources may be inverted in the same way
as the sugars, but it needs a prolonged heating with acid. For
approximate purposes 1 gm. of starch should be mixed to a smooth
cream writh about 30 c.c. of cold water, then 1 c.c. of strong
hydrochloric acid added, and the mixture kept at a boiling
temperature in an obliquely fixed flask for 8 or 10 hours, replacing
the evaporated water from time to time to avoid charring the
sugar, and testing with iodine to ascertain when the inversion is
complete. The product is glucose.

For the estimation of the starch itself a number of processes
were tried by Ost (Cliem. Zeit. 1895, xix. 1501), the one which
was found to answer best being that of Sachsse (Cliem. CentralM.
viii. 732), slightly modified. In this modification 3 gm. of the
starch are heated with 200 c.c. of water and 20 c.c. of hydrochloric
acid, specific gravity 1'125 ( - 5*600 gm. of HC1), for two to three
hours in a boiling water bath, using the factor 0*925 to calculate
the glucose found in the starch. Longer heating gives results too
low, and two hours on the water bath are not sufficient. Slightly
higher yields of glucose (89*8 instead of 89*5 per cent.) can be
obtained by heating for a much longer period with less starch and
acid, but there is no advantage to be gained by the alteration.
Oxalic acid gives no better results. Dextrine may be determined
in the same manner • also maltose, if 1 gm. of the latter be heated
for five hours with 100 c.c, of 1 to 2 per cent, hydrochloric acid
as before.

100 parts of grape sugar, found by Fehling's process, represent
90 parts of starch or dextrine. When dextrine is present with
grape sugar, care must be taken not to boil the mixture too long
with the alkaline copper solution, as it has been found that a small
portion of the copper is precipitated by the dextrine (Rumpf and
Heintzerling, Z. a. C. ix. 358).

An inversion of starch may be produced more rapidly, and at
lower temperature, by using some form of diastase in place of
acid. An infusion of malt is best suited to the purpose, but the
temperature must not exceed 71° C. (160° Fahr.). The digestion
may vary from fifteen minutes to as many hours. The presence of
unchanged starch may be found by occasionally testing with iodine.
If the digestion is carried beyond half an hour, a like quantity of
the same malt solution must be digested alone, at the same
temperature, and for the same time, then titrated for its amount of
sugar, which is deducted from the total quantity found in the
mixture. O'Sullivan (J. C. S. 1872, 579) has, however, clearly
shown that the effect of the so-called diastase is to produce maltose,
which has only the power of reducing the copper solution to the
extent of about three-fifths that of dextrose or true grape sugar,
the rest being probably various grades of dextrine. Brown and
Heron's experiments clearly demonstrate that no dextrose is
produced from starch by even prolonged treatment with malt

§ 74 SUGAR. 309

extract ; the only product is maltose. Sulphuric or other similar
acids cause complete inversion.

For the exact estimation of starch in grain of various kinds
O'Sullivan gives very elaborate directions, involving the treat-
ment of the substance with alcohol and ether, to remove fatty and
other constituents previous to digestion with diastase. The same
authority also gives special directions for the preparation of the
proper kind of diastase, all of which may be found in J. C. S.
xlv. 1.

2. Estimation of Glucose by Fehling's Solution.

Preparation of the Standard Solutions. — Fehling's Standard
Copper Solution. — Crystals of pure cupric sulphate are powdered
and pressed between unsized paper to remove adhering moisture ;
69 '28 gm. are weighed, dissolved in water, about 1 c.c. of pure
sulphuric acid added, and the solution diluted to 1 liter.

Alkaline Tartrate Solution.- — 350 gm. of Rochelle salt (sodio-
potassic tartrate) are dissolved in about 700 c.c. of water, and the
solution filtered, if not already clear ; there is then added to it
a clear solution of 100 gm. of caustic soda (prepared by alcohol)
in about 200 c.c. of water. The volume is made up to 1 liter.

These solutions are prepared separately, and when mixed in
exactly equal proportions form the original Fell ling solution,
each c.c. of which should contain 0*03464 gm. of cupric sulphate,
and represents 0*005 gm. of pure anhydrous grape sugar, if the
conditions of titration laid down below are adhered to.'" The
method is based on the fact that although Fehling's solution
may be heated to boiling without change, the introduction into it
of the smallest quantity of grape sugar, at a boiling temperature,
at once produces a precipitate of cuprous oxide, the ratio of
reduction being uniform if the conditions of experiment are
always the same.

The Titration of Glucose with Fehling's Solution. — 5 c.c. each of
standard copper and alkaline tartrate solutions are accurately measured into
a thin white porcelain basin, 40 c.c. of water added, and the basin quickly
heated to boiling on a sand-bath or by a small flame. No reduction or
change of colour should occur; it' it does, the alkaline tartrate solution
is probably defective from age. This may probably be remedied by the
addition of a little fresh caustic alkali on second trial, but it is advisable to
use a new solution. The % or 1 per cent, sugar solution is then delivered in
from a burettef in small quantities at a time, with subsequent boiling, unti

* If pure cupric sulphate has been used, and the solutions mixed only at the time of •
titration, there need be very little fear of inaccuracy ; nevertheless it is advisable to
verify the mixed solutions from time to time. This may be done by weighing and
dissolving 0'95 gm. of pure cane sugar in about 500 c.c. of water, adding 2 c.c. of.
hydrochloric acid, and heating to 70° C. for ten minutes. The acid is then neutralized
with sodic carbonate and diluted to a liter. 50 c.c. of this liquid should exactly
reduce the copper in 10 c.c. of Fell ling's solution. A standard solution of inverted
sugar, which will keep good for many months, may be made in the foregoing manner :
it should be of aboiit 20 per cent, strength, and rendered strongly alkaline with soda or
potash.

t The instrument should be arranged as described on page 12.

310 VOLUMETRIC ANALYSIS. § 74.

the blue colour of the copper solution is just discharged, a point which is
readily detected by inclining the basin, so that the colour of the clear
supernatant fluid may be observed against the white sides of the basin.
Some operators use a small thin boiling flask instead of the basin.

It is almost impossible to hit the exact point of reduction in the
first tit ration, but it affords a very good guide for a more rapid and
exact addition of the sugar solution in a second trial, when the
sugar may be added with more boldness, and the time of exposure
of the copper solution to the air lessened, which is a matter of
great importance, since prolonged boiling has undoubtedly a
prejudicial effect on the accuracy of the process.'"'

When the exact point of reduction is obtained, it is assumed
that the volume of sugar solution used represents O05 gm. of
grape sugar or glucose, for 10 c.c. Feh ling's solution contain
O'll gm. cupric oxide, and 5 molecules CuO (396) are reduced
to cuprous oxide by 1 molecule of glucose (180), therefore
396 : 180 = 0*11 : 0'05, i.e. 0*05 gm. glucose exactly reduces
10 c.c. Feh ling's solution.

With this assumption, however, Soxhlet does not agree, but
maintains from the results of his experiments on carefully prepared
standard sugars, that the accuracy of the reaction is interfered
with by varying concentration of the solutions, duration of the
experiment, and the character of the sugar.

For example, he found that the reducing power of glucose,
invert sugar, and galactose was in each case lowered by dilution of
the Fehling's solution, whilst that of maltose was raised, and that
of milk sugar was not affected.

The remarks which Soxhlet appends to his experiments are
thus classified : —

(1) The reducing power of inverted sugar, for alkaline copper solution, is
importantly influenced by the concentration of the solutions : a smaller
quantity of sugar being required to decompose Fehling's solution in the
undiluted state than when it is diluted Avith 1, 2, 3, or 4 volumes of water.
It is immaterial whether the sugar solution be added to the cold or boiling
copper reagent.

(2) If inverted sugar acts on a larger quantity of copper solution than it
is just able to reduce, its reducing power will be increased, the increment
var}dng according to the amount of copper in excess and the concentration
of the cupric liquid ; in the previous experiments the equivalents varied
from 1 : 97 to 1 : 12*6, these numbers being by no means the limit of
possible variation.

(3) In a volumetric estimation of inverted sugar by means of Fehling's
solution, the amount of copper reduced by each successive addition of sugar
solution is a decreasing quantity ; the results obtained are therefore perfectly
empirical, and are only true of that particular set of conditions.

(4) The statement that 1 equivalent of inverted sugar reduces 10

* It has been proposed to use an excess of copper, and to estimate the excess
iodometrically or with cyanide (§ 58) in view of the alleged uncertain ending in the
ordinary Fehling process. My experiments with these methods show that the
errors are g reater than the one they are siipposed to cure. Moreover, in practised
hands the true ending presents no difficulty.

§ 74. SUGAR. 311

equivalents of cupric oxide is not true, the hypothesis that 0'5 gm. inverted
sugar reduces 100 c.c. of Fehling's solution being shown to be incorrect;
the real amount under the conditions laid down by Fehling (1 volume of
alkaline copper solution. 4 volumes of water, sugar solution fc— 1 per cent.)
being 97 c.c., the results obtained under this hypothesis are, therefore, 3 per
cent, too low. Where, however, the above conditions have been fulfilled, the
results, although not absolutely, are relatively correct; not so, however, those
obtained by gravimetric processes, since the interference of concentration
and excess has not been previously recognized.

These facts, however, do not vitiate the process as carried out
under the well recognized conditions insisted on in the directions
for titration that were given above. If these are adhered to it is
found the sugars have the following reducing powers —

10 c.c. Feh ling solution are completely reduced by
O05 gm. glucose, levulose, galactose
0'0475 gm. cane sugar (after inversion)
O067S gm. milk sugar
0*0807. gm. maltose
0'045 gm. starch (after inversion).

Lowe, and more recently Haines, have advocated the sub-
stitution of an alkaline solution of glycerine for the alkaline tartrate
in F,e hi ing's solution. This solution is said to keep indefinitely,
but it is riot so delicate a test as Fehling's.

3. Estimation of Glucose by Mercury.

Knapp's Standard Mercuric cyanide. — 10 gm. of pure dry
mercuric cyanide are dissolved in about 600 c.c. of water ; 100 c.c.
of caustic soda solution (sp. gr. 1'145) are added, and the liquid
diluted to 1 liter.

Sachsse's Standard Mercuric iodide. — 18 gm. of pure dry
mercuric iodide and 25 gm. of potassic iodide are dissolved in
water, and to the liquid is added a solution of 80 gm. of caustic
potash ; the mixture is finally diluted to 1 liter.

These solutions, if well preserved, will hold their strength
unaltered for a long period.

These solutions are very nearly, but not quite, the same in
mercurial strength, Knapp's containing 7'9365 gm. Hg in the
liter, Sachsse's 7 '92 95 gm. 100 c.c. of the former are equal to
100-1 c.c. of the latter.

Indicators for the Mercurial Solutions. — In the case of Fehling's
solution, the absence of blue colour acts as a sufficient indicator,
but with mercury solutions the end of reaction must be found by
an external indicator. In the case of Knapp's solution the end
of the reaction is found by placing a drop of the clear yellowish
liquid above the precipitate on pure white Swedish filter paper,
then holding it first over a bottle of fuming HC1, then over strong
sulphuretted hydrogen water ; the slightest trace of free mercury
shows a light brown or yellowish-brown stain. The indicator best

312 VOLUMETEIC ANALYSIS. § 74

adapted for Sachsse's solution is a strongly alkaline solution of
stannous chloride spotted on a porcelain tile. An excess of
mercury gives a brown colour.

The Titration : 40 c.c. of either solution are placed in a porcelain basin
or a flask, diluted with an equal bulk of water, and heated to boiling. The
solution of sugar of i per cent, strength is then delivered in until all the
mercur}7- is precipitated, the theory being in either case that 40 c.c. should
be reduced by O'l gm. of dextrose.

The results of Soxhlet's experiments show that this estimate
is entirely wrong""" ; nevertheless, it does not follow that these
mercurial solutions are uselessi It is found that, using them l>y
comparison with Feh ling's solution, it is possible to define to
some extent the nature of mixed sugars, on the principle of indirect
analysis.

Knapp's solution is strongly recommended by good authorities
for the estimation of diabetic sugar in urine. The method of using
it is described in the section on Urinary Analysis.

The behaviour of the sugars with alkaline mercury solutions was tested
by Soxhlet both with Knapp's solution and Sachsse's solution.

He found that different results are obtained from Knapp's solutions,
according as the sugar solution is added gradually, or all at once ; when
gradually added more sugar being required; with Sachsse's, however, the
reverse is the case.

To get comparable results the sugar must be added all at once, the solution
boiled for two or three minutes, and the liquid tested for mercury, always
using the same indicator ; in using the alkaline tin solution as indicator,
0'200 — 0'202 gm. of grape sugar was always required for 100 c.c. Knapp,
in a large number of experiments. It is remarkable that these two solutions,
although containing almost exactly the same amount of mercury, require
very different quantities of sugar to reduce equal volumes of 'them. This is
shown to be due, to a great extent, to the different amounts of alkali present
in them.

The various sugars have different reducing powers for the
alkaline mercury solutions, and there is no definite relation between
the amount of Knapp's and Sachsse's solutions required by
them; the amount of Sachsse's solution, to which 100 c.c.
Knapp's correspond, varying from 54*7 c.c. in the case of galactose,
to 7 4 '8 c.c. in the case of invert sugar.

The two mercury methods have no advantage in point of
accuracy or convenience over Fehlin g's method, the latter having
the preference on account of the great certainty of the point at
which the reduction is finished.

The mercury methods are, however, of great importance, both
for the identification of a sugar and for the estimation of two
sugars in presence of each other, as proposed by Sachsse.
For instance, in the estimation of grape and invert sugars in
presence of each other, there are the two equations: ax + by = ~F,,
ex + dy = S.

* Careful experiment shows that 40 c.c. of Sachsse's solution is redrc3d by 0'1342.
gin. dextrose or 0'1072 gm. invert sugar.

§ 74.

SUGAR.

313

Where —
a — number of 1 c.c. Fehling, reduced by 1 gm. grape sugar.

„
Saclisse

invert sugar.

,, „ grape sugar.

d — ,, „ ,, ,, invert sugar.

F — ,, Fehling, used for 1 vol. sugar solution.

S = „ Saclisse „ „ „

x — amount of grape sugar in gms. in 1 vol. of the solution.
y= „ invert sugar

It need hardly be mentioned that the above, like all other indirect
methods, leaves room for increased accuracy ; but nevertheless the
combination of a mercury method with a copper method in the
determination of a sugar whose nature is not exactly known, gives
a more serviceable result than the hitherto adopted plan, by which
a solution that reduced 10 c.c. .Fehling was said to contain
0-05 gm. of sugar (J. C. S. Abstracts, 1880, 758).

Taking the reducing power of grape- sugar =100, the reducing
powers of the other sugars are : —

Fehling (undiluted). Knapp. Sachsse.

Grape sugar ............. , ..... 100 100 100

Invert sugar .................. 96'2 99'0 124-5

Levulose (calculated) ......... 92*4 102*2 148-6

Milk sugar ..................... 70-3 64-9 70'9

Galactose ..................... 93'2 83*0 74'8

Inverted milk sugar ... ...... 96'2 90'0 85*5

Maltose .. 61 -0 63'8 65-0

4. Sidersky's Method.

•

This process has found great favour among French sugar experts,
and is based on the use of Soldaini's cupric solution, which was
devised to remedy the faults common to Fehling and other
copper solutions containing tartrated and caustic or carbonated
alkalies.

This liquid is prepared, according to Degener, in the following
manner : — 40 gm. of cupric sulphate are dissolved in water, and, in
another vessel, 40 gm. of sodic carbonate are also dissolved in water.
The two solutions are mixed, and the copper precipitated in the
state of hydrobasic carbonate. The precipitate is washed with
cold water and dried. This precipitate is added to a very con-
centrated and boiling solution of bicarbonate of potash (about
415 gm.) and agitated until the whole is completely or nearly
dissolved, water is added to form a volume of 1400 c.c., and the
whole mass heated for two hours upon a water-bath. The insoluble
matter is filtered, and the filtrate, after cooling, is of a deep blue
colour. The sensibility of this liquid is so great that it gives

3J4 VOLUMETRIC ANALYSIS. § 74.

a decided reaction with 0*0014 gm. of invert sugar. The presence
of sucrose in the solution increases this sensibility still more.

Sidersky has recently offered a new volumetric method, based
upon the use of Soldaini's solution. With .sugars the same
method as is now in use with Fehling's solution can easily be
followed, watching the disappearance of the blue colour, and
testing the end with ferrocyanide and acetic acid. This process
offers no serious objections common to Fehling's solution, but is
inapplicable to coloured sugar solutions, such as molasses, etc. For
the last the following is recommended : — 25 gm. of molasses are
dissolved in 100 c.c. of water and sub-acetate of lead added in
sufficient quantities to precipitate the impurities, and the volume
raised to 200 c.c. and filtered. To 100 c.c. of the filtrate are
added 25 c.c. of concentrated solution of carbonate of soda,
agitated, and filtered again. 100 c.c. of the second filtrate with
excess of lead removed are taken for analysis. On the other hand,
100 c.c. of Soldaini's solution are placed in a flask and heated five
minutes over an open flame. The sugar solution is now added
little by little, and the heating continued for five minutes. Finally,
the heat is withdrawn and cooled by turning in 100 c.c. of cold
water, and filtered through a Swedish filter, washed with hot
water, letting each washing run off before another addition. Three
or four washings will generally remove completely the alkaline
reaction. The precipitate is then washed through a hole in the
filter into a flask, removing the last trace of copper. 25 c.c. of
normal sulphuric acid are added with two or three crystals of
chlorate of potash, and the whole gently heated to dissolve com-
pletely the oxide of copper, which is transformed into copper
sulphate. The excess of sulphuric acid is determined by a
standard ammonia solution (semi-normal), of which the best
indicator is the sulphate of copper itself. When the deep blue
colour gives place to a greenish tinge the titration is completed.
The method of titration is performed as follows : — Having cooled
the contents of the flask, a quantity of ammonia equivalent to
25 c.c. of normal sulphuric acid is added. From a burette
graduated into one-tenth c.c. standard sulphuric acid is dropped
in drop by drop, agitating after each addition. The blue colour
disappears with each addition to reappear after shaking. When
the last trace of ammonia is saturated the titration is complete,
which is known by a very feeble greenish tinge. The number of
€.c. is read from the burette, which is equivalent to the copper
precipitated. The equivalent of copper being taken at 31 '7, the
normal acid equivalent is 0'0317 of copper. Multiplying the
topper found by 3546 the invert sugar is found. A blank titration
is needed to accurately determine the slight excess which gives
the pale green tinge.'"

* Report of Proceedings of Fifth Animal Co-.ivcn'iou of the Ameiicui Association
of Official Agricultural Che nists (188S).

§ 74 SUGAR. 315

5. Pavy's modified Fehling; Process.

This method consists in adding ammonia to the ordinary
Fehling solution, by which means the precipitation of cuprous
oxide is entirely prevented, the end of the reaction being shown by
the disappearance of the blue colour in a perfectly clear solution
(C. N. xL 77).

The solution recommended by Pavy is made by mixing 120 c.c.
ordinary Fehling solution* (see p. 309) with 300 c.c. of strong
ammonia (sp. gr. 0*880), adding 100 c.c. of a 10 per cent, caustic
soda solution or of a 14 per cent, solution of potash, and diluting
to a liter. If Fehling's solution is not available, Pavy's solution
may be made directly by adding a cooled solution of 21 '6 gm.
Eochelle salt and 1S!4 gm. of soda (or 25 '8 gm. of potash) to
a solution of 4'157 gm. pure cupric sulphate, adding 300 c.c.
of strong ammonia, and making up to a liter. 100 c.c.
Pavy's solution =10 c.c. Fehling's solution = 0*05 gm. of
glucose.

As ammoniacal cuprous solutions are readily oxidized, it is
important to exclude air from the liquid during titration. The
titratioii should be made in a small boiling flask, through the
cork of which the elongated end of the burette is passed. A small
escape tube, preferably with a valve, also passes through the same
cork, and leads into a vessel containing water or weak acid, to
condense the ammonia. Allen has found a layer of paraffin over
the liquid an effective means of excluding air.

In carrying out the titration (100 c.c. of the Pavy's solution is
a convenient quantity to take) a few pieces of pumice or pipe-
stem are added, the liquid brought to boiling, and kept boiling
whilst the sugar solution is gradually run in. The end-point is
very sharp. Whilst rapid manipulation is desirable, the solution
must not be run in too quickly, because reduction takes place
more slowly than with Fehling's solution.

The method is well adapted for the examination of diabetic
urine and milk, also mixtures of milk and cane sugars, and
certainly has the advantage over the ordinary Fehling method
by its definite end-point.

Z. Peska gives the following method for the volumetric
estimation of sugar by means of ammoniacal copper solution
(Chem. Zeit. Rep. 1895, 257). In order to avoid the oxidation of
the copper oxide in solution, a layer of vaseline is used instead of
the usual current of hydrogen. Two solutions are prepared :
6 -927 gin. of the purest crystallized copper sulphate are dissolved
in water, 160 c.c. of 25 per cent, ammonia added, and the whole
made up to 500 c.c. ; 3 4 '5 gm. of Rochelle salt and 10 gm. of
caustic soda are also dissolved and diluted to 500 c.c.

* In ammoniacal solution only 5 molecules CuO are reduced by 1 molecule glucose
instead of 6 CuO, as in Fehling's solution, hence 120 c.c. of the latter are used in
making Pavy's solution, and not 100 c.c.

316

VOLUMETRIC ANALYSIS.

§ 74

Process : A mixture of 50 c.c. of each liquid is heated in a beaker under
a layer of vaseline oil 5 m.m. thick, to a temperature of 80° C. ' The sugar
solution is run in 1 c.c. at a time for the first test, but on a repetition the
whole amount may be added at once. Towards the end of the titration, the
temperature must be raised to 85°, and the heating continued for two minutes
when working on either glucose or invert sugar, four minutes for maltose,
and six minutes for milk sugar. Dextrine increases the reducing power of
the sugar in this solution less than in the one prepared with potash, and as
the ammonia has no injurious action, the whole process is both exact and
convenient. When saccharose is present, 1 gm. of it has a reducing action
equivalent to 0'026 gm. of invert sugar. In the determination of lactose in
milk the albuminoids should be precipitated with lead acetate and the excess,
of lead removed by sodium sulphate. The following table gives directly the
number of milligrams of each sugar in 100 c.c. of solution.

c.c.'s Glucose.

Invert

Milk

Maltose. c.c.

's Glucose.

Invert

Milk

Maltose.

used.

sugar.

used.

sugar.

997-8

1049-2

— 50

163-0

173-2

318-1

360-0

889-4

935-1

—

159-8

169-8

311-9

353-0

802'3

844-6

—

156-8

166-5

306-0

346-3

730-7

770-0

—

153-9

163-4

300-3

339-9

670-8

707-6

—

— _

151-1

160-4

294-8

333-8

620*0

654-5

—

148'4

157-5

289-4

327-9

576-3

608-7

. .

145-7

154-7

284-2

322-2

538-4

568-9

1033*9

—

143-1

152-0

279-3

316-7

505-2

534-2

971-4

— 58

140-6

149-4

274-5

311-4

475-8

503-3

916*0

1023-0 59

138-2

146-9

269-9

306-3

449-7

475-7

866-5

968-8 60

135-9

144-5

265-4

301-3

426-3

451-2

822-3

920-3 61

133-7

142-2

261-1

296-4

405-2

429-0

782-4

876-3 62

131-5

139-9

256-9

291-6

386-0

408-8

746-0

836-4 63

129-4

137-7

252-9

287-0

368-7

390-6

713-0

800-0 64

127-4

135-5

249-0

282-6

352-8

373-8

682-7

766-5 65

125-4

133-4

245-2

278-3

338-2

358-4

654-8

735-8 66

123-5

131-4

241-5

274-1

324-8

344-3

629-2

707-5 67

121-7

129-5

237'9

270'0

312-4

331-2

605-5

681-3 68

119-9

127-6

234-4

266-1

300-9

319-3

583-5

656-8 69

118-2

125-7

231-0

262-3

290-3

307-8

563-1

634-1 70

116-5

123-9

227-7

258-6

280-3

297-3

544-1

613-0 71

114-9

122-2

224-6

255-0

271-1

287*5

526-2

593-2 i 72

113-3

120-5

221-5

251-5

262-4

278-2

509-5

574-5 73

111-8

118-9

218-5

248-1

254-2

269-6

493-8

557'1

110*3

117-3

215-6

244-8

246-6

261-6

479-1

540-8

108-8

115-8

212-8

241-6

239-3

253-9

465-3

525-3

107-4

114-3

210-0

238-4

232-6

246-7

452-2

510-7

106-0

112-8

207-3

235-3

226-1

240-0

439-8

496-8

104-6

111-4

204-7

232-3

220-0

233-5

428-1

483-7

103-3

110-0

202-1

229-4

214-3

227-4

417*0

471-3

102-0

108-6

199-6

226-6

208-8

221-7

406-5

459*5

100-8

107-2

—

223-9

203-6

216-2

396-5

448*3

99-6

105-9

—

221-2

198-7

211-0

387-0

437-6

—

104-6

—

218-6

194-1

206-0

377-8

427-4

— ,

103-4

• —

216-0'

189-7

201-3

369-2

417-7

—

102-2

—

213-5

185-4

198-7

360-9

408*4

—

101-1

—

211-1

181-2

192-3

353-0

399-5

—

208-7

177-3

188-1

345-4

391-0

—

206-4

173-5

184-1

338-1

382-8

—

204-1

169-9

180-3

331-2

374' 9 90

—

201-9

166-4

176-7

324-5

367-3 ; 91

—

199-7

§ 74. SUGAB. 317

6. Gerrard's Cyano-cupric Process.

This process (Year Book Pharm. 1892, 400), as improved by
Gerrard and A. H. Allen, promises to prove a valuable addition
to the processes of titration based on the reducing power of glucose. .
It has the advantage over Pavy's method in causing no evolution
•of ammonia ; moreover, the reduced solution is reoxidized so slowly
that titration may even be conducted in an open dish with reason-
able expedition. The process is based on the following facts : — -
When a solution of potassium cyanide is added to a solution of
•copper sulphate a colourless stable double cyanide of copper and
potassium is formed, thus : —

CuSO* + 4KCy = CuCy 2,2KCy + K2SO*.

This salt is not decomposed by alkalies, hydrogen sulphide, or
ammonium sulphide. If potassium cyanide be added to Feh ling's
solution the latter is decolourized, the above double salt being
formed at the same time, and if the colourless solution be boiled
with glucose no cuprous oxide is precipitated. If there be present
-excess of Feh ling's solution over the amount capable of being
decolourized by the potassium cyanide, the mixture is blue, and when
it is boiled with a reducing sugar the extra portion is reduced, but
no cuprous oxide is precipitated, the progress of the reduction
being marked by the gradual and final disappearance of the colour
of the solution, just as in Pavy's process.

Process of Titration. — 10 c.c. of fresh Pehling's solution, or 5 c.c. of
each of the constituent solutions are diluted with 40 c.c. of water in
a porcelain dish and heated to boiling. An approximately 5 per cent,
solution of potassium cyanide is added very cautiously from a "burette or
pipette to the still boiling and "well agitated blue liquid, till the colour is
just about to disappear. Excess of cyanide must be carefully avoided.*

10 c.c. of Fehling solution are now accurately measured into the dish,
and the sugar solution (of about \ per cent, strength glucose) run in slowly
from a burette with constant stirring and ebullition, till the blue colour
disappears. Only the second measure of Fehling's solution suffers
reduction. The volume of sugar solution run in contains 0'05 gin. of
glucose.

Some technical applications of these Solutions to mixtures of
various Sugars.

It cannot be claimed for these estimations that they are
absolutely exact ; but with care and practice, accompanied with
uniform conditions, they are probably capable of the best possible
results whatever methods may be used.

Cane Sugar, Grape Sugar, and Dextrine (Biard and Pellet,
Z. a. C. xxiv. 275). The solution containing these three forms is first
titrated with the usual Fehling solution for grape sugar. A second portion

* As the double cyanide solution keeps for some time, a stock may be made up, so
that 59 c.c. contain 10 c.c. of Fehling' s solution, and that volume taken for each
titration, instead of going through the process of exact decolonization every time.

318 VOLUMET1UC ANALYSIS. § 75.

is boiled with acetic acid (which only inverts cane sugar) and titrated.
Finally, a third portion is completely inverted with sulphuric acid and
titrated. The difference of the first and second titrations gives the cane
sugar, and that of the second and third the dextrine.

Milk and Cane Sug-ar. — If the estimation of milk sugar is alone re-
quired, and by the usual Fehling solution, the casein and albumen must
be first removed. Acidify the liquid with a few drops of acetic acid, warm
until coagulation is effected, and filter. Boil the filtrate to coagulate the
albumen. Filter again, and neutralize with soda previous to treatment for
sugar by the copper test. The number of c.c. of Fehling's solution
required, multiplied by 0'0067S6, will give the weight of milk sugar in
grams. Direct estimation by Pa vy-F eh ling is preferable to this method.
Cane sugar in presence of milk sugar may be estimated as follows : — Dilute
the milk to ten times its bulk, having previously coagulated it with a little
citric acid, filter, and make up to a definite volume, titrate a portion with
Pavy-Fehling solution, and note the result. Then take 100 c.c. of the
filtrate, add 2 gm. of citric acid, and boil for 10 minutes, cool, neutralize,
make up to 200 c.c., and titrate with copper solution as before. The difference
between the reducing powers of the solutions before and after conversion is
due to the cane sugar, the milk sugar not being affected ~by citric acid.

Stokes and Bodmer (Analyst x. 62) have experimented largely on this
method, and with satisfactory results. The plan adopted by them is to use
40 c.c. of Pavy-Fehling liquid ( = 0'02 gm. glucose), and to dilute the
sugar solution (without previous coagulation), so that from 6 to 12 c.c. are
required for reduction. By using a screw-clamp on the rubber burette tube,
the sugar solution is allowed to drop into the boiling liquid at a moderate
rate. If Cu2O should be precipitated before the colour disappears, a fresh
trial must be made, adding the bulk of the sugar at once, then finishing by
drops. If, on the other hand, the sugar has been run in to excess, which
owing to the rather slow reaction is easily done, fresh trial must be again
made until the proper point is reached : this gives the milk sugar. Mean-
while a portion of the mixed sugar solution is boiled with 2 per cent, of
citric acid, neutralized with NH3, made up to double its original volume,
and titrated as before.

These operators have determined the reducing action of milk,
cane, and grape sugar on the Pavy-Fehling liquid, the result
being that 100 lactose represents respectively 52 glucose, or 49 '4
sucrose.

The Pavy-Fehling liquid is admirably adapted for the esti-
mation of lactose in milk direct after dilution, no coagulation being
necessary.

SULPHUR.

Estimation in Pyrites, Ores, Residues, etc.
1. Alkalimetric Method (Pelouze).

§ 75. THIS process, designed for the rapid estimation of sulphur
in iron and copper pyrites, has hitherto been thought tolerably
accurate, but experience lias shown that it cannot be relied upon
except for rough, technical purposes.

§ 75. SULPHUR, 319

The process is based on tlie fact, that when a sulphide is ignited
with potassic chlorate and sodic carbonate, the sulphur is converted
entirely into sulphuric acid, which expels its equivalent proportion
of carbonic acid from the soda, forming neutral sodic sulphate ; if
therefore, an accurately weighed quantity of the substance be
fused with a known weight of pure sodic carbonate in excess, and
the resulting mass titrated with normal acid, to find the quantity
of unaltered carbonate, the proportion of sulphur is readily
calculated from the difference between the volume of normal acid
required to saturate the original carbonate, and that actually
required after the ignition.

It is advisable to take 1 gm. of the finely levigated pyrites, and
5 '3 gm. of pure sodic carbonate for each assay; and as 5*3 gm. of
sodic carbonate represent 100 c.c. of normal sulphuric acid, it is
only necessary to subtract the number of c.c. used after the ignition
from 100, and multiply the remainder by 0'016, in order to arrive
at the weight of sulphur in the 1 gm. of pyrites, and by moving
the decimal point two places to the right, the percentage is obtained.

Example : 1 gm. of finely ground FeS3 was mixed intimately with 5'3 gm.
sodic carbonate, and about 7 gm. each of potassic chlorate, and decrepitated
sodic chloride, in powder ; then introduced into a platinum crucible, and
gradually exposed to a dull red heat for ten minutes ; the crucible suffered
to cool, and warm water added ; the solution so obtained was brought on
a moistened filter, the residue emptied into a beaker and boiled with a large
quantity of water, brought on the filter, and washed with boiling water till
all soluble matter was removed ; the filtrate coloured with methyl orange^
and titrated. 67 c.c. of normal acid were required, which deducted from 100,
left 33 c.c. ; this multiplied by 0*016 gave 0'528 gm. or 52*8 per cent. S.

Burnt Pyrites. — The only satisfactory volumetric method of
estimating the sulphur in the residual ores of pyrites, is that
described by Watson (J. S. C. I. yii. 305), and which is in daily
use in large alkali works. In order to avoid calculation, Watson
adepts the following method : —

Standard Hydrochloric Acid. — 1 c.c. =0*02 gm. ^Na2O.

Sodic bicarbonate. — This may be the ordinary commercial salt,
but its exact alkalinity must be ascertained by the standard acid.
Where a number of analyses are being made, a good quantity of
the salt should be well mixed, and kept in a stoppered bottle. Its
exact alkalinity having been once determined it will not alter,
though daily opened.

Process: 2 gm. of bicarbonate is placed in a crucible which may be
either of platinum, porcelain, or nickel, and to it is added 5'16 gm. of the
finely powdered ore, then intimately mixed with a flattened glass rod.
Heat gently over a Bunsen burner for 5 or 10 minutes, and break up the
mass with a stout copper wire. After stirring, the heat is increased and
continued for 10 or 15 minutes. The crucible is then washed out with hot
water into a beaker. The mixture is boiled for 15 minutes, filtered into
a flask, the residue washed repeatedly with hot water, then cooled and
titrated with the standard acid, using methyl orange as indicator.

320 VOLUMETRIC ANALYSIS. § 75.

Example : 2 gm. of the bicarbonate originally required 37' 5 c.c. of acid.
After ignition with the ore, 28 c.c. were required = 9'5 c.c., this divided by
5 will give 1'9, which is the percentage of total sulphur in the ore.

This total sulphur includes that which exists as soluble sulphide,
and which is not available for acid making. In order to find
the amount of this soluble sulphur, Watson boils 5*16 gm. of the
ore with 5 c.c. of standard sodic carbonate (1 c.c. = 0*05 gm. ]N"a20)
diluted with water, for 15 minutes. After filtering and washing,
the filtrate is titrated with the standard hydrochloric acid, and the
difference between the volume used and that which was originally
required for 5 c.c. of the soda solution is divided by 5, as in the
€ase of the former process, which gives at once the percentage of
•sulphur existing in the ore in a soluble form. The results are not
absolutely exact, but quite near enough to guide a manufacturer in
the working of the furnaces.

This method is not available for unburnt pyrites.

2. Estimation of Sulphur in Coal Gas.

A most convenient and accurate process for this estimation is
that of Wildenstein (§ 76.2). The liquid produced by burning
the measured gas in a Lethe by or Tern on Ha re our t apparatus
is well mixed, and brought to a definite volume ; a portion repre-
senting a known number of cubic feet of gas is then poured into
a glass, porcelain, or platinum basin, acidified slightly with HC1,
heated to boiling, and a measured excess of standard baric chloride
added ; the excess of acid is then cautiously neutralized with
rammonia (free from carbonate), and the excess of barium ascer-
tained by standard potassic chromate exactly as described in
§ 76.2.

The usual method of stating results is in grains of sulphur per
100 cubic feet of gas. This may be done very readily by using
semi-normal solutions of baric chloride and potassic chromate on
the metric system, and multiplying the number of c.c. of baric
solution required with the factor 0*1234, which at once gives the
.amount of sulphur in grains.

3. Estimation of Sulphur in Sulphides decomposable by
Hydrochloric or Sulphuric Acids (Weil).

This process, communicated to me by M. Weil, is based on the
fact that, in the case of sulphides where the whole of the sulphur
is given off as H2S by heating with HC1 or H2S04, the IPS may
"be evolved into an excess of a standard alkaline copper solution.
After the action is complete, the amount of Cu left unreduced is
•estimated by standard .stannous chloride. The method is available
for the sulphides of lead, antimony, zinc, iron, etc. Operators

§ 75. SULPHUR. 321

should consult and practise the methods described in § 58.6, in
order to become accustomed to the special reaction involved.

Process : Prom 1 to 10 gm. of material (according to its richness in
sulphur) in the finest state of division, are put into a long-necked flask of
about 200 c.c. capacity, to which is fitted a bent delivery tube, so arranged as
to dip to the bottom of a tall cylinder, containing 50 or 100 c.c. of standard
copper solution made by dissolving 39'523 gm. of cupric sulphate, 200 gm.
of Eochelle salt and 125 gm. of pure caustic soda in water, and diluting to
1 liter (10 c.c. = O'l gm. Cu). When this is ready, a fewr pieces of granulated
zinc are added to the sulphide. 75 c.c. of strong HC1 are then poured over
them, the cork with delivery tube immediately inserted, connected with the
copper solution, and the flask heated on a sand-bath until all evolution of
H2S is ended. The blue solution and black precipitate are then brought on
a filter, filtrate and washings collected in a 200 or 250 c.c. flask, and diluted
to the mark ; 20 c.c. of the clear blue liquid are then measured into a boiling
flask, and evaporated to 10 or 15 c.c. 25 to 50 c.c. of strong HC1 are then
added, and the standard tin solution dropped in while boiling, until the blue
gives place to a clear pure yellow.

Each c.c. of standard copper solution represents 0*50393 gm.
of sulphur. The addition of the granulated zinc facilitates the
liberation of the H2S, and sweeps it out of the flask ; moreover,
in the case of dealing with lead sulphide, which forms insoluble
lead chloride, it materially assists the decomposition. Alkaline
tartrate solution of copper may be used in place of ammoniacal
solution if so desired.

Examples (Weil) : 1 gm. of galena was taken, and the gas delivered into
50 c.c. of standard copper solution (=0'5 gm. Cu). After complete pre-
cipitation the blue liquid was diluted to 200 c.c. 20 c.c. of this required
12'5 c.c. of stannous chloride, the titre of which was 16'5 c.c. for 0'04 gm.
Cu. Therefore lf/5 : 0'04 : : 12'5 : 0'0303. Thus 200 c.c. (= 1 gm. galena)
represent 0'303 gm. Cu. Then 0'5 gm. Cu, less 0'303 = 0'197 gm. for 1 gm.
galena or 197 for 100 gm. Consequently 197 x 0'50393 = 9'92 per cent. S.
Estimation by weight gave 9'85 per cent. Again, 1 gm. zinc sulphide was
taken with 100 c.c. copper solution and made up to 250 c.c., 25 c.c. of which
required 14'3 c.c. of same stannous chloride, or 143 c.c. for the 1 gm.
sulphide. This represents 0'347 gm. Cu. Thus 1— 0'347 — 0'653 gm. Cu
(precipitated as CuS) or 65'3 per 100. Consequently 65'3 x 0'50393 = 32'9
per cent. S. Control estimation by weight gave 33 per cent.

The process has given me good technical results with Sb2S3, but
the proportion of sulphur to copper is too great to expect strict
accuracy.

4. Estimation of Alkaline Sulphides by Standard Zinc Solution.

This method, which is simply a counterpart of § 82.3, is
-especially applicable for the technical determination of alkaline
rsulphides in impure alkalies, mother-liquors, etc.

If the zinc solution be made by dissolving 3 '253 gm. of pure
metallic zinc in hydrochloric acid, supersaturating with ammonia,
.and diluting to 1 liter, 1 c.c. will respectively indicate —

322 VOLUMETRIC ANALYSIS. § 75.

0-0016 gin. Sulphur
0-0039 „ Sodic sulphide
0-00551 „ Potassic sulphide
0*0034 „ Ammonic sulphide.

The zinc solution is added from a burette until no dark colour is
shown when a drop is brought in contact with solution of nickel
sulphate spread in drops on a white porcelain tile.

5. Sulphurous Acid and Sulphites:

The difficulties formerly presented in the iodometric analyses of
these substances are now fortunately quite overcome by the
modification devised by Giles and Shearer (J. S. C. I. iii. 197
and iv. 303). A valuable series of experiments on the estimation
of SO2, either free or combined, are detailed in these papers. The
modification is both simple and exact, and consists in adding the
weighed SO2 or the sulphite in powder to a measured excess
of J^. iodine without dilution with water, and when the decomposi-
tion is complete, titrating back with —^ thiosulphate. Yery con-
centrated solutions of SO2 are cooled by a freezing mixture, and
enclosed in thin bulbs, which can be broken under the iodine-
solution : this is, however, not required with the ordinary pre-
parations. Sulphites and bisulphites of the alkalies and alkaline
earths, also zinc and aluminium, may all be titrated in this way
with accuracy ; the less soluble salts, of course, requiring more
time and agitation to ensure their decomposition. A preliminary
titration is first made with a considerable excess of iodine, and
a second with a more moderate excess as indicated by the first
trial. 1 c.c. T^ iodine = 0-0032 gm. SO2.

The authors found that when perfectly pure iodine and neutral
potassic iodide were used for the standard solution, its strength
remained intact for a long period ; and the same with the
thiosulphate, if the addition of about 2 gm. of potassic bicarbonate
to the liter was made, and the stock solution kept in the dark.

From a large number of experiments, they also deduced the
simple law of the ratio between any given percentage of SO2
in aqueous solution at 15-4° and 760 m.m., and its specific gravity ;.
namely, the percentage found by titration multiplied by OO05'
and added to unity gives the sp. gr.

In cases where the iodine method may not be suitable, W. B.
Giles recommends the use of a standard ammoniacal silver nitrate.
This process is applicable alike to SO2, sulphites and bisulphites.
The silver solution may conveniently be of ~ strength, but before
use ammonia is added in sufficient quantity, first to produce
a precipitate of silver oxide, then to dissolve it to a clear solution.
A known excess of this solution is digested in a closed bottle.
with the substance, in a water-bath for some hours, the result of

§ 75. SULPHUR. 323

which is the reduction of the silver as a bright mirror on the
sides of the vessel. The filtered liquid and washings may then
be titrated by thiocyanate for the excess of silver, or the mirror
together with any collected on the filter after washing and burning
to ash may be dissolved in nitric acid and estimated by the same
process (§ 43). 1 c.c. T^ silver=0'0032 gm. of SO2.

Example : 0'1974 gm. of chemically pure potassium metasulphite was
weighed out and treated as above described, the mirror of silver and a little
on the filter estimated gave 0'1918 gm. of metallic silver, which multiplied
by the factor T028 gives 0'19717 of metasulphite or 99'9 %.

This method is very useful in determining the percentage of the
SO2 in liquefied sulphurous acid, which is now found in large
quantities in commerce. By cooling down this substance to
a point where it has no tension, small bulbs can be filled with
facility and sealed up. After weighing they are introduced into
a -we/Z-stoppered bottle containing an excess of the ammoniacal
silver, and the stopper firmly secured by a clamp. By shaking the
bottle vigorously the bulb is broken, and the estimation is then
conducted as above described.

A«2ON205 + SO2 + xNH3 = As2 + SO3 + WO5 + xNH3.

6. Estimation of Mixtures of Alkaline Sulphides, Sulphites,
Thiosulphates, and Sulphates.

No method up to the present has apparently been successfully
devised for the estimation of the above-mentioned substances
when existing together in any given solution. Richardson and
Aykroyd (J. S. C. 1. xv. 171) have, however, now published
a method which seems to give fairly accurate results.

The estimation of the SO3 in such a mixture cannot be done
volumetrically, but by the addition of about 5 gm. of tartaric acid to
such a quantity of solution of mixed thiosulphate, sulphate, and
sulphite as would be usually taken for analysis, the SO3 may
readily be precipitated with baric chloride in the cold. The
precipitate of BaSO4 contains some baric sulphite, but this is
easily removed by hot dilute HC1 and boiling water. The
thiosulphate produces no SO3 whatever under these circumstances,
whereas in the presence of a mineral acid sulphate is always
produced.

The sulphides are estimated by standard ammoniacal zinc
solution, which may conveniently be of such strength that
1 c.c. = 0'0016 of S, using nickel sulphate solution as an external
indicator.

The zinc solution is easily made from pure metallic zinc
dissolved in HC1, and the precipitate which is formed by adding
ammonia, is brought into clear solution by a moderate excess of
the same re-agent.

Y 2

324 VOLUMETRIC ANALYSIS. § 75.

This zinc solution is also used for removing sulphides from
a mixture of these with thiosulphates, sulphites, and sulphates
prior to the estimation of the latter bodies. In this case it is
only necessary to add a slight excess of the zinc solution, and
filter off the precipitated sulphide.

The authors of this method after pointing out the value of
Giles and Shearer's method of estimating sulphites by iodine,
described in this section (par. 5), mention a method devised by
themselves, which they believe enables them to estimate not only
sulphites but free SO2, not only in a pure state but in mixtures
with sulphates, thiosulphates, and sulphides. They avail them-
selves of the well-known reaction, that when iodine is added to
a neutral sulphite, neutral sulphate and an equivalent amount of
hydriodic acid are formed

H20 - Na2S04 + 2HI,

and the acidity of the solution may be accurately measured by
standard alkali and methyl orange.

The authors proceed to state that the best plan is to convert all
sulphites to bisulphites, i.e., to the hydrogen sulphite of the base :
this is necessary because a sulphite may be alkaline, or it may be
exclusively acid. Sodic bisulphite is quite neutral to methyl
orange, and by titrating the solution of a neutral sulphite with
decinormal sulphuric acid, using methyl orange, we arrive exactly
at a point when all the sulphite is converted into the acid sulphite.
The reason for this is patent when the reaction which takes place
when an acid sulphite acts upon iodine is considered —

KaH.S08 + OH2 + 12 - NaH.SO* + 2HL

Here is a new factor, inasmuch as the titration with alkali and
with methyl orange as indicator is concerned ; although the acid
sulphite of soda is neutral to methyl orange, the acid sulphate of
soda is acid to the full and exact extent of its combining power.

Thus one molecule of sodic bisulphite, on titration with —- iodine,
liberates acid equivalent to three molecules of sodic or potassic
hydrate.

A solution containing 1'62 per cent, of Na2SO3.7Aq was titrated. Iodine
solution equivalent to 9'5 c.c. T\ I ; 29'9 c.c. were required; the mixture
required 14'6 c.c. of ^ NaHO. Now 9'5 c.c. T\ I and 14'6 c.c. T^ NaHO
are in the ratio of 2 : 3 almost exactly; by using 0'0126 as the factor for
the c.c. of T\ I and 0'084 for the ^ NaHO, both results give T64 per cent.
of Na2SO3.7Aq. (Of course the sulphite solution had been previously
titrated with ^T H2SO4 in the presence of methyl orange.)

As the details of calculation may be somewhat obscure to those who have
not experimented in this direction, the working out of an actual analysis
may be of interest. A solution containing 1 per cent, of pure sodic
tine-sulphate, and 0'78 per cent, of sodic sulphite, was titrated upon 20 c.c.
of iodine ; 19'3 c c. were required to decolorize ; to neutralize with methyl
orange as indicator 17*9 c.c. of £5- soda were required ; therefore ICO c.c. of

§ 76. SULPHURIC ACID. 325

the mixture required 103'6 c.c. iodine and 92-7 c.c. of T\ soda respectively ;
the c.c. of soda x 0'0084 give 0'7787 as the percentage of Na2SO3.7Aq, and
this figure-:- 0*0126 (the factor for 1 c.c. iodine in Na2SO3.7Aq) gives 61'8 c.c.,
and this subtracted from 103'6 c.c. of total iodine required gives 41'8 c.c.,
and this x 0'0248 gives T036 instead of 1 per cent, of Na2S2O3.5Aq.

The immense advantage of this method is better seen in the
case of a complex mixture, where one must remove sulphides or
other bodies by the addition of an alkaline solution of zinc or
other precipitating agent. The alkaline filtrate is speedily brought
into a suitable condition for iodimetric and alkalimetric titration
'by the method proposed.

Example : A solution of known amounts of sodic thiosulphate and
sulphite was treated with 10 c.c. of a strongly ammoniacal zinc-chloride
solution, and the mixture was titrated with it until it gave a neutral
reaction with methyl orange; it was now made to 1000 c.c., and was titrated
upon a known volume of f$ iodine, using starch to find the end-reaction
(which is otherwise somewhat obscured by the methyl orange). The
disappearance of the blue colour and the appearance of the pinkish-purple
of the acidified methyl orange is both interesting and striking. Titration
with /TJ- NaHO was now easily accomplished. The results were exact in the
case of thiosulphate, and very slightly in excess in the case of sulphite.

After the sulphite and thiosulphate solution has been titrated
upon a known volume of y^- iodine, the sulphate formed is
estimated by barium at a boiling heat in the presence of a little
dilute HC1. Any sulphate in the original solution is, of course,
estimated by the tartaric acid method and deducted from the
result. Ammonic tartrate must be avoided in the process, owing
to its solvent action on barium sulphate.

SULPHURIC ACID AND SULPHATES.
Monohydrated Sulphuric Acid.

H2S04 = 98.

Sulphuric Anhydride.

SO3 = 80.

I. Mohr's Method.

§ 76. THE indirect process devised by C. Mohr (Ann. der
Chem. u. Pharm. xc. 165) consists in adding a known volume of
baric solution to the compound, more than sufficient to precipitate
the SO3. The excess of barium is converted into carbonate, and
titrated with normal acid and alkali.

formal Baric chloride is made by dissolving 12177 gm. of
pure crystals of baric chloride in the liter ; this solution likewise
suffices for the determination of SO3 by the direct method.

Process : If the substance contains a considerable quantity of free acid,
it must be brought near to neutrality by pure sodic carbonate ; if alkaline,

326 VOLUMETRIC ANALYSIS. § 76.

slightly acidified with hydrochloric acid ; a round number of c.c. of baric
solution in excess is then added, and the whole digested in a warm place for
some minutes; the excess of barium is precipitated by a mixture of
carbonate and caustic ammonia in slight excess ; if a piece of litmus paper
be thrown into the mixture, a great excess may readily be avoided. The
precipitate containing both sulphate and carbonate is now to be collected on
a filter, thoroughly washed with boiling water, and titrated.

The difference between the number of c.c. of baric solution
added, and that of normal acid required for the carbonate, will be
the measure of the sulphuric acid present ; each c.c. of baric
solution is equal to 0*040 gm. SO3.

Example : 2 gm. of pure and dry baric nitrate, and 1 gm. of pure potassic
sulphate were dissolved, mixed, and precipitated hot with carbonate and
caustic ammonia ; the precipitate, after being thoroughly washed, gave
T002 gm. potassic sulphate, instead of 1 gm.

For technical purposes this process may be considerably shortened
by the following modification, which dispenses with the washing of
the precipitate.

The solution containing the sulphates or sulphuric acid is first rendered
neutral ; normal baric chloride is then added in excess, then normal sodic
carbonate in excess of the baric chloride, and the volume of both solutions
noted ; the liquid is then made up to 200 or 300 c.c. in a flask, and an aliquot
portion filtered off and titrated with normal acid. The difference between
the baric chloride and sodic carbonate gives the sulphuric acid.

The solution must of course contain no substance precipitable by
sodic carbonate except barium (or if so, it must be previously
removed) ; nor must it contain any substance precipitable by
barium, such as phosphoric or oxalic acid, etc.

2. Titration by Baric Chloride and Potassic Chroxnate
(Wildenstein).

To the hot solution containing the SO3 to be estimated (which
must be neutral, or if acid, neutralized with caustic ammonia, free
from carbonate), a standard solution of baric chloride is added in
slight excess, then a solution of potassic chromate of known
strength is cautiously added to precipitate the excess of barium.
So long as any barium remains in excess, the supernatant liquid is
colourless ; when it is all precipitated the liquid is yellow, from the
free chromate ; a few drops only of the chromate solution are
necessary to produce a distinct colour.

Wildenstein uses a baric solution, of which 1 c.c. = 0*015
gm. of SO3, and chromate 1 c.c. = 0*010 gm. of SO3. I prefer
to use I- solutions, so that 1 c.c. of each is equal to 0*02 gm.
of SO3. If the chromate solution is made equal to the baric
chloride, the operator has simply to deduct the one from the other,
in order to obtain the quantity of baric solution really required to
precipitate all the SO3.

§ 76. SULPHURIC ACID. 327

Process : The substance or solution containing SO3 is brought into a small
flask, diluted to about 50 c.c., acidified if necessary with HC1, heated to
boiling, and precipitated with a slight excess of standard baric chloride
delivered from the burette. As the precipitate rapidly settles from a boiling
solution, it is easy to avoid any great excess of barium, which would prevent
the liquid from clearing so speedily. The mixture is then cautiously
neutralized with ammonia free from carbonic acid (to be certain of this, it is
well to add to it two or three drops of calcic chloride or acetate solution).

The flask is then heated to boiling, and the chromate solution added
in i c.c. or so, each time removing the flask from the heat and allowing to
settle, until the liquid is of a light yellow colour ; the quantity of chromate
is then deducted from the barium solution, and the remainder calculated
for SO3.

Or the mixture with barium in excess may be diluted to 100 or 150 c.c.
the precipitate allowed to settle thoroughly, and 25 or 50 c.c. of the clear
liquid heated to boiling, after neutralizing, and precipitated with chromate
until all the barium is carried down as baric chromate, leaving the liquid of
a light yellow colour; the analysis should be checked by a second titration.
The process has yielded me very satisfactor}7 results in comparison with the
barium method by weight ; it is peculiarly adapted for estimating sulphur in
gas when burnt hi the Letheby sulphur apparatus, details of which will be
found on page 320.

The presence of alkaline and earthy salts is of no consequence —
Zn and Cd do not interfere— Xi, Co, and Cu give coloured
solutions which prevent the yellow chromate being seen, but this
difficulty can be overcome by the use of an external indicator for
the excess of chromate. This indicator is an ammoniacal lead
solution, made b^ mixing together, at the time required, one
volume of pure ammonia and four volumes of lead acetate solution
(1 : 20). The liquid has an opalescent appearance. To use the
indicator, a large drop is spread upon a white porcelain plate, and
one or two drops of the liquid under titration added; if the
reddish-yellow colour of lead chromate is produced, there is an
excess of chromate, which can be cautiously reduced by adding
more barium until the exact balance occurs.

3. Direct Precipitation -with. Normal Baric Chloride.

Yery good results may be obtained by this method when
carefully performed.

Process : The substance in solution is to be acidified with hydrochloric
acid, heated to boiling, and the baric solution allowed to flow cautiously in
from the burette until no further precipitation occurs. The end of the
process can only be determined by filtering a portion of the liquid, and
testing with a drop of the baric solution. Beale's filter (shown in fig. 23)
is a good aid in this case. A few drops of clear liquid are poured into a test
tube and a drop of baric solution added from the burette ; if a cloudiness
•occurs, the contents of the tubes must be emptied back again, washed out
into the liquid, and more baric solution added until all the SO3 is precipitated.
It is advisable to use r\ solution towards the end of the process.

Instead of the test tube for finding whether barium or sulphuric
acid is in excess, a plate of black glass may be used, on which a drop

328 VOLUMETRIC ANALYSIS. § 76.

of the clear solution is placed and tested by either a drop of baric
chloride or sodic sulphate, — these testing solutions are preferably
kept in two small bottles with elongated stoppers. A still better
plan is to spot the liquids on a small mirror, as suggested by
Haddock (C. N. xxxix. 156); the faintest reaction can then be
seen, although the liquid may be highly coloured.

Wildenstein "has arranged another method for
direct precipitation, especially useful where a con-
stant series of estimations have to be made. The
apparatus is shown in fig. 51. A is a bottle of
900 or 1000 c.c. capacity, with the bottom removed,
and made of well-annealed glass so as to stand
heating ; B a thistle funnel bent round, as in the
figure, and this syphon filter is put into action by
opening the pinch-cock below the cork. The mouth
of the funnel is first tied over with a piece of fine
cotton cloth, then two thicknesses of Swedish filter
_, paper, and again with a piece of cotton cloth, the

whole being securely tied with waxed thread.
In precipitating SO3 by baric chloride, there occurs a point
similar to the so-called neutral point in silver assay, when in one
and the same solution both barium and sulphuric acid after a
minute or two produce a cloudiness. Owing to this circumstance,
the barium solution must not be reckoned exactly by its amount
of Bad2, but by its working effect; that is to say, the process
must be considered ended when the addition of a drop or two of
barium solution gives no cloudiness after the lapse of two minutes.

Process : The solution containing the SO3 being prepared, and preferably
in HC1, the vessel A is filled with warm distilled water, and the pinch-cock
opened so as to fill the filter to the bend C ; the cock is then opened and
shut a few times so as to bring the water further down into the tube, but
not to fill it entirely ; the water is then emptied out of A, and about 400 c.c.
of boiled distilled water poured in together with the SO3 solution, then, if
necessary, a small quantity of HC1 added, and the baric chloride added in
moderate quantity from a burette. After mixing well, and waiting a few
minutes, a portion is drawn off into a small beaker, and poured back without
loss into A ; a small quantit}7 is then drawn off into a test tube, and two
drops of baric chloride added. So long as a precipitate occurs, the liquid is
returned to A, and more barium added until a test is taken which shows no
distinct cloudiness; the few drops added to produce this effect are deducted.
If a distinct excess has been used, the analysis must be corrected with
a solution of SO3 corresponding in strength to the barium solution.

A simpler and even more serviceable arrangement of apparatus
on the above plan may be made, by using as the boiling and
precipitating vessel an ordinary beaker standing on wire gauze or
a hot plate. The filter is made by taking a small thistle funnel, tied
over as described, with about two inches of its tube, over which is
tightly slipped about four or five inches of elastic tubing, terminating
with a short piece of glass tube drawn out to a small orifice like

§77. SULPHURETTED HYDROGEN. 329

a pipette ; a small pinch-cock is placed across the elastic tube just
above the pipette end, so that when hung over the edge of the
beaker with the funnel below the surface of the liquid, the
apparatus will act as a syphon. It may readily be filled with warm
distilled water by gentle suction, then transferred to the liquid
under titration. By its means much smaller and more concentrated
liquids may be used for the analysis, and consequently a more
distinct evidence of the reaction obtained.

SULPHURETTED HYDROGEN.
IPS = 34.

1 c.c. -fjj arsenious solution = O00255 gm. IPS.
1. By Arsenious Acid (Mohr).

§ 77. THIS residual process is far preferable to the direct titration
of sulphuretted hydrogen by iodine. The principle is based on the
fact, that when H2S is brought into contact with an excess of
arsenious acid in hydrochloric acid solution, arsenic sulphide is-
formed ; 1 eq. of arsenious acid and 3 eq. of sulphuretted hydrogen
produce 1 cq. of arsenic sulphide and 3 eq. of water,

As203 + 3H2S = As2S3 + 3H20.

The excess of arsenious acid used is found by — iodine and starchy
as in § 40. In estimating the strength of sulphuretted hydrogen
water, the following plan may be pursued.

Process : A measured quantity, say 10 c.c. of ^ arsenious solution, is put
into a 300 c.c. flask, and 20 c.c. of sulphuretted hydrogen water added, well
mixed, and sufficient HC1 added to produce a distinct acid reaction ; this-
produces a precipitate of arsenic sulphide, and the liquid itself is colourless.
The whole is then diluted to 300 c c., filtered through a dry filter into a dry
vessel, 100 c.c. of the filtrate taken out and neutralized with sodic-
bicarbonate, then titrated with T^ iodine and starch. The quantity of
arsenious acid so found is deducted from the original 10 c.c., and the
remainder multiplied by the requisite factor for H2S.

The estimation of IPS contained in coal gas, may by this
method be made very accurately by leading the gas very slowly
through the arsenious solution, or still better, through a dilute
solution of caustic alkali, then adding arsenious solution, and
titrating as before described. The apparatus devised by Mohr for
this purpose is arranged as follows : —

The gas from a common burner is led by means of a vulcanized tube into-
two successive small wash-bottles, containing the Alkaline solution; from the
last of these it is led into a large Woulf f's bottle filled with water. The
bottle has two necks, and a tap at the bottom ; one of the necks contains
the cork through which the tube carrying the gas is passed; the other,
a cork through which a good-sized funnel with a tube reaching to the bottom

"330 VOLUMETRIC ANALYSIS. § 77.

of the bottle is passed. When the gas begins to bubble through the flask,
the tap is opened so as to allow the water to drop rapidly ; if the pressure of
gas is strong, the funnel tube acts as a safety valve, and allows the water to
rise up into the cup of the funnel. "When a sufficient quantit}' of gas has
passed into the bottle, say six or eight pints, the water which has issued from
the tap into some convenient vessel is measured into cubic inches or liters,
and gives the quantity of gas which has displaced it. In order to insure
accurate measurement, all parts of the apparatus must be tight.

The flasks are then separated, and into the second 5 c.c. of arsenious
solution placed, and. acidified slightly with HC1. If any traces of a
precipitate occur it is set aside for titration with the contents of the first
flask, into which 10 c.c. or so of arsenious solution are put, acidified as
before, both mixed together, diluted to a given measure, filtered, and a
measured quantity titrated as before described.

This method does not answer for very crude gas containing large
•quantities of H2S unless the absorbing surface is largely increased.

2. By Permang-anate (Moh.r).

If a solution of H2S is added to a dilute solution of ferric
.•sulphate, the ferric salt is reduced to the ferrous state, and free
sulphur separates. The ferrous salt so produced may be measured
accurately by permanganate without removing the separated
.sulphur. Ferric sulphate, free from ferrous compounds, in
sulphuric acid solution, is placed in a stoppered flask, and the
solution of H2S added to it with a pipette ; the mixture is allowed
to stand half an hour or so, then diluted considerably, and per-
manganate added until the rose colour appears.

56 Fe=17 H2S

•or each c.c. of -^ permanganate represents O0017 gm. of IPS.
The process is considerably hastened by placing the stoppered llask
containing the acid ferric liquid into hot water previous to the
addition of H2S, and excluding air as much as possible.

3. By Iodine.

Sulphuretted hydrogen in mineral waters may be accurately
estimated by iodine in the following manner : —

Process : 10 c.c or any other necessary volume of T£V iodine solution are
measured into a 500 c.c. flask, and the water to be examined added until the
colour disappears. 5 c.c. of starch indicator are then added, and T£y iodine
until the blue colour appears ; the flask is then filled to the mark with pure
distilled water. The respective volumes of iodine and starch solution,
together with the added water, deducted from the 500 c.c., will show the
volume of water actually titrated by the iodine. A correction should be
made for the excess of iodine necessary to produce the blue colour.

Fresenius examined the sulphur water of the Grindbrunnen,
in Frankfurt a. M. (Z. a. C. xiv. 321), both volume trically and

•§ 78. TANNIC ACID. 331

by weight for H2S with very concordant results. 361*44 gm. of
water (correction for blue colour being allowed) required 20*14 c.c.
•of iodine, 20*52 c.c. of which contained 0 '02 527 of free iodine
= H2S 0*009194 gm. per million. 444'65 gm. of the same water
required, under the same conditions, 25 '05 c.c. of the same iodine
solution = H2S 0-009244 gm. per million. By weight the H2S
was found to be 0*009377 gm. per million.

TANNIC ACID.

§ 78. THE estimation of tannin in the materials used for
tanning is by no means of the most satisfactory character. Many
methods have been proposed, and given up as practically useless.
In the previous editions of this book LowenthaPs method
as then perfected was given • but it is still somewhat deficient
in accuracy or constancy of results, although much ingenuity and
intelligence have been expended on it.

One difficulty is still urisurmounted, and i^hat is, the preparation
•of a pure tannic acid to serve as standard. The various tannins in
existence are still very imperfectly understood,* but so far as the
comparative analysis of tanning materials among themselves is
•concerned, the method in question is theoretically the best.

The principle of the method depends on the oxidation of the
tannic acid, together with other glucosides and easily oxidizable
substances by permanganate, regulated by the presence of soluble
indigo-carmine, which also acts as an indicator to the end of the
reaction. The total amount of such substances being found and
•expressed by a known volume of permanganate, the actual available
tannin is then removed by gelatine, arid the second titration is
made upon the solution so obtained in order to find the amount of
oxidizable matters other than tannin.

The volume of permanganate so used, deducted from the volume
used originally, shows the amount of tannin actually available for
tanning purposes expressed in terms of permanganate.

It will be at once seen that this method is essentially a practical
one, because it is only the particular tannin capable of combining
with organic tissue which is estimated. It has been critically
examined with approbation by good authorities, among whom may
be mentioned, Procter (C. N. xxxvi. 59 ; ibid, xxxvii. 256),
Kathreiner (Z. a. C. xviii. 112), (Diiigler's Polyt. Jour.
•cxxvii. 481), and Hewitt (Tanner's Jour., May, 1877, 93). My

*Von Schroder, whose suggestions have been adopted by the German Association
of Tanners, selects a commercial pure tannic acid for use as a standard by dissolving
2 gm. in a liter of water. 10 c.c. of this is titrated with permanganate as described.
50 c.c. are then digested twenty hours with 3 gm. moistened hide powder. 10 c.c. of
the filtrate from this is then titrated, and if the permanganate consumed amounts to
less than 10 per cent, of the total consumed by the tannin, it is suitable for a standard.
1000 parts being considered equivalent in reducing power to 1048 parts of tannin pre-
cipitable by hide, according to Hammer's experiments, therefore Von Schroder,
after titrating as described, calculates the dry matter, and multiplies by the round
number 1 '05 to obtain the value in actual tannin precipitable by hide.

332 VOLUMETRIC ANALYSIS. § 78.

own experiments have shown that for all materials containing,
tannin, even catechu, it is the best process yet discovered, but
requires patient practice to ensure concordant results. Lowenthal's-
description of the method is given in Z. a. C. xvi. 33.

The extraction of the tannic acid from the raw material is best
performed by boiling it in a large flask with about a liter of
distilled water for half an hour, then straining, and diluting when
cold to 1 liter. Portions are filtered if necessary. Concentrated
extracts are dissolved before titration by adding them to boiling
water, then cooling and diluting to the measure. In the case of
strong materials such as sumach or valonia 10 gm., or oak-bark
20 gm., are used.

The quantity of these extracts to be used for titration must be
regulated to some extent by the amount of permanganate required
to oxidize the tannic and gallic acids present. Practice and
experience will enable the operator to judge of the proper propor-
tions to use in dealing with the various materials, bearing in mind
that volumetric processes are largely dependent upon identity of
conditions for securing concordant results.

Procter, who is probably one of the best authorities on this
•.subject, has modified to some extent the details of this process
(/. S. C. I. iii. 82, and ibid. v. 79), and these modifications are
embodied here.

Standard Solutions and Re-agents.

Standard Potassic permanganate. — Kathreiner recommends
that this solution should contain not more than 1*333 gm. of
the pure salt per liter (better only about 1 gm.) ; therefore, if
the operator is accustomed to use the decinormal solution, a very
convenient strength is made by diluting one volume of it with
two of water, thus obtaining a solution of -£$ strength ( = 1 '052 gm.
per liter).

This standard is the more advisable because it enables the
operator to calculate its value into oxalic acid, and so arrive at the
theoretical standards adopted by Neubauer and Oser; namely,
that 0*063 gm. of oxalic acid represents 0'04157 gm. of gallo-tannic
acid (gall-nut tannin), or 0*062355 gm. of querci-tannic acid (oak
bark tannin). These coefficients for calculation are now largely
adopted, and are certainly preferable to standardizing the perman-
ganate upon any specimen of so-called pure tannin.

30 c.c. of -jf^j- permanganate will therefore represent 0'063 gm.
of oxalic acid or the weights of tannin above mentioned.

Solution of Indigo Carmine. — This should be a clear solution of
about 5 gm. to the liter with about 50 c.c. of pure H2S04.

Solution of Gelatine. — This solution is used to precipitate the
available tannin in any given solution after its total oxidizable
matters have been determined by the indigo and permanganate. It

§ 78. TANNIC ACID. 333

should be made fresh for each series of titrations, by dissolving
2 gm. of Nelson's gelatine in 100 c.c. of water and filtering.
Dilute Sulphuric Acid.— MO.

Processes of Tit-ration : The first thing to be done is to ascertain the
relationship between the permanganate and indigo solutions (it is assumed
that the permanganate is correct as regards its relation to oxalic acid), and
therefore 10 or 20 c.c. of the indigo are measured into a white porcelain basin,
and diluted to f of a liter with distilled wrater, or good ordinary water free
from organic matter or other substances capable of reducing permanganate.
10 c.c. of the dilute acid are measured in, and the permanganate delivered
in with a hand-pipette in drops, with constant stirring, until the colour is
just discharged, leaving a clear faint yellow tint, with just a shade of pink
at the rim.

This experiment will act as a guide to the final adjustment of the indigo
with an accurate 30 c.c. burette in •£$, which should be of such dilution that
about 20 c.c. correspond to about 15 c.c. of permanganate.

Titration of the Tanning Material : It is very important, in order to
avoid uncertainty in the end-point of the reaction,' that only so much
material shall be used as shall consume about 7 or 8 c.c. of permanganate of
-5^5- strength above that point which is required for the indigo.

Procter and Kathreiner both insist upon these proportions, and the
general method adopted by them is to add 20 c.c. of indigo with 10 c.c. of
dilute acid to about i of a liter of water, in a porcelain dish, followed by 5 c.c.
of tannin solution. The permanganate is then delivered in very slowly, with
constant stirring, until a faint rose colour appears round the edges of the
liquid. The time allowed for the titration is also very important. "

Von Schroder, representing the Association of German Tanners,
prefers to add the permanganate 1 c.c. at a time with vigorous
stirring, until the colour of the liquid indicates that a few drops
only are required to end the titration. Procter, on the other
hand, prefers the rapid drop method for the commencement, and
until near the end. He also finds that the method of stirring
influences the result in no very slight degree. Whatever plan the
operator adopts, it is advisable to keep consistently to it in order
that the results may be comparatively the same.

It must be remembered that neither by this nor any other
method is it possible to accurately estimate the tannin, but only as
a means of comparing two samples of the same material.

Precipitation of the Tannin, and subsequent Titration of Substances
other than Tannin. — Procter's procedure is to take 50 c.c. of the tannin
infusion (5 c.c. of which has been titrated), and add to it 28'6 c.c. of gelatine
solution in a flask holding about 150 c c. The mixture is well shaken, then
saturated with clean table salt, and 10 c.c. of the dilute acid added, together
with a teaspoonful of kaolin : the whole is vigorously shaken, then filtered,
and made up to exactly 100 c.c. 10 c.c. of this liquid, representing 5 c.c. of
the tannin decoction, are then titrated in precisely the same manner as before.
The calculation of percentage is then made as follows : Let the first titration
(two of which should be made for security) be called a ; the second, also in
duplicate, b. If further, c be the quantity of permanganate required to
•oxidize 10 c.c. of ^V oxalic acid, and 10 gm. of substance have been employed
for 1 liter of decoction, then c : (a — b) : : 6'3 : x, where x is the percentage
•of tannin expressed in terms of oxalic acid.

334 VOLUMETRIC ANALYSIS. § 78.

Hunt, who is also an undoubted authority on tannin estimation,
differs from Procter on the question of saturating the liquid for
final titration with salt (J. C. S. I. iv. 263), on the ground that, in
the case of material containing much gallic acid, some of it is
precipitated with the tannin, thus leading to higher results. This
he has proved by experiment, and therefore prefers to act as-
follows : —

50 c.c. of the tannin solution are run into a small dry flask, to this 25 c.c.
of the fresh filtered gelatine solution are added, and the flask shaken. 25 c.c.
of a saturated solution of salt, containing 50 c.c. of strong H'2SO4 per liter,
are now added, and about a teaspoonful of kaolin, or baric sulphate. The
flask is thoroughly shaken for a feAV minutes, after which a clear bright
filtrate may be obtained.

For materials containing over 45 per cent, tannin, it is advisable
to take 25 c.c. instead of 50, and to use 50 c.c. of salt, the amount
of gelatine solution. being the same. The same authority also states
that, for gambler and its allies, the method of titration as above
described does not give accurate results, inasmuch as the gelatine
and salt do not remove all the substances of tanning value from the
liquid. In such case it is necessary to digest the liquid for at least
twelve hours with pure hide powder. The mixture is then filtered
and titrated in the usual way.

It is impossible to give here the opinions held by various
authorities on this subject, therefore the reader who desires fuller
information should consult the papers to which reference has been
made.

The table on next page by Hunt is appended, as the result of
careful working, and as a guide to the nature of various tanning
materials : —

The " total extract " in the table was determined by evaporating
a portion of the tannin solution to dryness in a small porcelain
basin and drying the residue at 110° C. The "insoluble matter"
was also dried at 110° C.

The hide powder process for tannin not being a volumetric one
is not described here.

Tannin in Tea. — The extract in this substance is made upon
10 gm. of the tea, by boiling it with repeated quantities of distilled
water, filtering and diluting the liquid when cool to a liter. The
percentage varies from about 12 in black tea to 18 or 20 in green.

78.

TANNIC ACID.

335>

Total
matters

NAME or MATERIAL. ^g^.
g-auate, as
i Oxalic Ac.

Tannin, as
Oxalic Ac,
(Procter)

Tannin, as
Oxalic Ac.
(H u n t)

Total
Extract.

Insoluble.

per cent.

English Oak Bark ... 1570

13-54

11-97

18-38

66-15

CanadianHemlockBark 9'03

7-46

7-08

13-96

75-25

Larch Bark

8-20

7-17

6-15

20-64

60'80

Mangrove Bark

31-35

29-71

28-48

26-60

49-70

Alder Bark

8'27

6-15

5-73

19-36

68-00

Blue Gum Bark

10-18

8-91

11-76

74-65

Valonia

37-41

35-24

30-50

38-50

46-05

Myrabolans

48-23

38-43

38-00

42-80

—

Sumach

42-53

34-30

31-46

44-10

47-77

BetelNut

15-91

13-87

13-79

17-94

67-00

Turkish Blue Galls ...

73-38

65-83

59-96

48*40

36-35

Aleppo Galls

98-85

87-82

83-05

68-80

1432

Wild Galls

26-21

18-75

16-56

31-70

54-17

Divi-Divi

66-98

62-62

61-22

54-38

29-90

Balsamocarpon (poor

and old sample) ...

50-49

37-76

32-88

57-14

28-25

Pomegranate Rind . . .

27-58

21-18

23-12

41-00

49-50

Tormentil Root

22-27

20-98

20-68

1970

67-95

Rhatany Root

22-27

20-15

19-30

18-80

66-00

Pure Indian Tea

23-06

18-65

17-40

34-46

53-40

Pure China Tea

1 8-03

14-21

14-09

24-50

62'6'0

Cutch

57"65

51-95

44-24

61-60

4-75

Gum Kino

66-39

59-55

51-55

7930

i-oo

Hemlock Extract ...

35-16

33-17

30*98

48-78

i—

Oak wood Extract ...

33-49

26-90

23*86

37-78

—

Chestnut Extract ...

39-77

32-63

28'88

50-28

—

Quebracho Extract ...

48-22

44-45

40-84

49-00

—

"Pure Tannin"

135-76

122-44

121-93

—

— .

TanLiquor,sp. gr.1'030

4-84

3-14

2-10

6-01

—

Spent Tan Liquor, sp.

gr. 1'0165

1-40

0-37

0-25

3-10

—

Absorbed

by Dry

Pure Skin.

Gambier, Cube

70-12

51-07

74-40

5-31

„ Sarawak . . .

63-13

—

47-09

70-70

3-67

Bale

56-00

—

43-70

63'54

1'40

Tannin in Wine, Cider, etc. — The method now generally adopted
for this estimation is that of treating a known volume of the
wine, etc., with catgut (violin strings which have not been oiled,
and which have been purified by washing in dilute alcohol acid
and water, until they have no reducing action on permanganate in
the cold). The digestion is carried on at ordinary temperature for
a week, in a closely stoppered bottle. The original substance, and
that from which the tannin has been removed, are then titrated
with permanganate, and the difference calculated to tannin.

Another method consists in mixing equal parts of an eight per

.336 VOLUMETRIC ANALYSIS. § 78.

•cent, solution of alum and the wine, collecting the precipitate on
.a filter, washing slightly with cold water, transferring the precipitate
*by a stream of water from a wash-bottle to a beaker, then acidifying
•with H2S04 and titrating with indigo and permanganate as usual.

Dreaper's Copper Process for Tannic and Gallic Acids. — This
as described in a paper contributed to /. C. S. I. xii. 412, from
which the following abstract is taken.

The methods hitherto proposed for the estimation of tannin may
IDC divided into two classes, viz. :—

(1) Those which act by precipitating the tannic acid as an
insoluble compound.

(2) Those which act by oxidation.

To the former class belongs the well-known hide powder process,
.and to the latter Lowenthal's permanganate method, which has
been modified by Procter and others. These fairly represent the
two classes, and are the only ones in general use at the present
-day.

Dreaper, however, has adopted a modified form of Darton's
method, the novelty of which consists in precipitating the tannic
.acid by means of an ammonio-copper sulphate solution, after
a preliminary treatment with sulphuric acid to remove the ellagic
acid, and then a treatment with ammonia, filtering after each
treatment. Procter states that this preliminary treatment is
unnecessary in the case of some extracts, but Dreaper has never
found any precipitation to take place in the case of the so-called
pure tannic acids, probably owing to the removal of the impurities
during the process of purification. The original solution and the
(filtrate are titrated with permanganate as in Lowenthal's method,
the difference in the two results being due to the tannic acid
present. The copper compound may be dried at 110° C. and
weighed, or else ignited and weighed as copper oxide. Fleck
states that the tannic acid can be calculated from this by multi-
plying by the factor 1 "034.

The standard copper solution used by the author contained
."30 gm. of pure crystallized copper sulphate in a liter of water.
Baric carbonate is also required, which should be free from calcic
.-salts.

The process is based on the direct precipitation of the gallic and tannic
acids by means of a copper salt, using as outside indicator potassic ferro-
cyanide. If a standard solution of copper sulphate be run into a solution
of the mixed acids, a certain amount of copper tannate and gallate will be
precipitated, depending on the dilution of the solution and the amount of
acid set free from the copper sulphate. The precipitate is, under these
circumstances, of a bulky nature and ill adapted to any separation by quick
filtration, so necessary in a process of this description. It was found that
when a solution of copper sulphate was added to a solution of the mixed
acids in the presence of baric carbonate, the precipitation proceeds with the
utmost regularity. The carbonate immediately forms insoluble sulphate
-with the free acid, and also helps to consolidate the precipitated copper salts,

§ 78.

TANNIC ACID.

so that towards the end of the reaction they fall rapidly to the bottom of
the vessel, leaving the supernatant liquid clear. This separation is a good
indication that the end of the titration is near, and is supplemented hy the
ferrocyanide test.

A modified method of testing for the excess of copper in the solution
is as follows : Pieces of stout Swedish filter-paper one inch square are folded
across the middle, and a drop of the liquid to be tested taken up on a glass
rod and gently dropped on to the top surface. The liquid will percolate
through to the under fold, leaving the precipitate on the upper one. It
is then only necessary to unfold the sheet and apply a drop of ferrocyanide
to the under surface. If the reaction is complete a faint pink colouration
will take place, which is perhaps more easily recognized by transmitted light.

The results obtained by duplicate experiments tend to show that the copper
salts are perfectly constant in composition when precipitated in this manner,
and the results equal in accuracy any obtained with other processes.

About 1 gin. of baric carbonate was added in each case and the solution
heated up to 90° C. before titration. The temperature at the end of the
titration should not be less than 30° C.

The precipitation by copper is done say on 25 c.c. of the solution of the
sample, and the results noted. 50 c.c. of the same sample are then mixed
with the usual proportions of gelatine, salt, acid, and baric sulphate ; diluted
to 100 c.c., then filtered through a dry filter and 50 c.c. ( = 25 c.c. of the
original liquid) titrated with copper solution as before, the difference being
calculated to available tannin.

The experiments show that the separation of the tannic acid by means of
an acid solution of gelatine and salt will not affect the general results
obtained, and this method for want of a better was used in the experiments,
Procter's modification being considered the most accurate, and therefore
adopted.

The following table was prepared from experiments, showing the error
due to the indicator in c.c. of standard solution added to different quantities
of water:—

c.c. of Water.

c.c. of Standard Solution
required.

0-3

0-4

100

1-0

150

1-5

The above correction should be made in all cases.

A sample of so-called pure tannic acid gave the following results

Weight taken.

c.c. required.

Gni.

O'o

25-0

0-5

25-2

0-5

25-2

Slightly lower results were obtained when the operation was conducted in
the cold, probably owing to the slower action of the carbonate on the free

338

VOLUMETEIC ANALYSIS.

§ 78.

acid ; but the rate of running in of the solution had no appreciable effect
on the quantity required.

A sample of the purest gallic acid that could be obtained gave the
following figures :—

Weight taken.

c.c. required.

GUI.

0-5

45'0

0-5

448

Allowing that the acid was of 90 per cent, purity, these results would give
a value for each c.c. of O'Olll gm. This figure must of course only be
taken as approximate. It will be seen that more solution is required to
precipitate the gallic than the tannic acid. This is also noticed in
Lowenthal's method.

The chief advantages claimed by the author of this method over
Lowenthal's are as follows : —

(1) Both the tannic and gallic acids are estimated.

(2) Rapidity of estimation where a simple assay is sufficient.

(3) The results are expressed in terms of the copper oxide
precipitated.

(4) The standard solution keeps well, and there is no correction
necessary for indigo-carmine solution or gelatine.

(5) Larger quantities of the solution can be titrated, thus
reducing the working error.

It seems to be possible to use this method for substances other
than tannic or gallic acids, e.g. Fustic.

The following results were obtained with a sample of pure
Fustic extract 51° Tw.

0*5 gin. taken required 11 '5 c.c. of standard solution.

0'5 gm. taken required 11*6 c.c. of standard solution.

The end of the reaction was sharp when the titration was
carried on at the boiling-point and the precipitate settled well.

Other Methods of Estimating- Tannin.

Direct Precipitation by Gelatine. — The difficulty existing with
this method is that of getting the precipitate to settle, so that it
may be clearly seen when enough gelatine has been added.

Tolerably good results may sometimes be obtained by using
a strong solution of sal ammoniac or chrome alum as an adjunct.
The best aid is probably barium sulphate, 2 or 3 gm. of which
should be added to each portion of liquid used for titration.

The Standard Solution of Gelatine should contain 1*33 gm. of
dry gelatine per liter, in which is also mixed a few drops of
chloroform or a small quantity of thymol to preserve it. 45 c.c.
= 0'05 gm. tannin (Carles). This method is adapted only for
rough technical purposes, as also the following.

'§ 79. TIN.

Direct Precipitation by Antimony. — This method is still in
favour with some operators ; but, like the gelatine process, is beset
with the difficulty of getting the precipitate to settle.

The Standard Antimony solution is made by dissolving 2*611
.gm. of crystals of emetic tartar dried at 100° C. in a liter. I c.c. =
'0*005 gm. tannin. This liquid may also be kept from decomposition
by a few grains of thymol. 50 c.c. of the tannin solution may be
taken for titration, to which is added 1 or 2 gm. of sal ammoniac,
:and the antimonial solution run in until no further cloudiness is
produced.

In both the above methods the final tests must either be made
by repeatedly filtering small portions to ascertain whether the
precipitation is complete, or by bringing drops of each liquid
together on black glass or a small mirror.

TIN.

Sn = 118.

Metallic iron 1*0536 =Tin.

Double iron salt 0*1505= „

Factor for T^- iodine

or permanganate

solution 0*0059

§ 79. THE method, originally devised by Streng, for the
direct estimation of tin by potassic bichromate, or other oxidizing
agents in acid solution, has been found most unsatisfactory, from
the fact that variable quantities of water or acid seriously interfere
with the accuracy of the results. The cause is not fully under-
stood, but that it is owing partly to the oxygen mechanically
contained in the water reacting on the very sensitive stannous
chloride there can be very little doubt, as the variations are
considerably lessened by the use of water recently boiled and
cooled in closed vessels. These difficulties are set aside by the
processes of Lenssen, Lowenthal, Stromeyer, and others, now
to be described, and which are found fairly satisfactory.

1. Direct Titration by Iodine in Alkaline Solution (Lenssen).

Metallic tin or its protosalt, if not already in solution, is
dissolved in hydrochloric acid, and a tolerable quantity of Rochelle
salt added, together with sodic bicarbonate in excess. If
enough tartrate be present, the solution will be clear ; starch is
then added, and the mixture titrated with ~ iodine. Metallic tin
is best dissolved in HC1 by placing a platinum crucible or cover in
contact with it, so as to form a galvanic circuit.

Benas (Cliem. Gentr-blatt. li. 957) points out that the chief
•error in the estimation as above arises from oxygen dissolved in

z 2

340 VOLUMETRIC ANALYSIS. § 79.

the liquid, or absorbed during the operation. In order to obtain
constant results, it is necessary to dissolve the tin compound
in HC1, dilute with oxygen-free water, and add at once excess of
standard iodine, which excess is found by residual titration with
standard thiosulphate.

2. Indirect Titration by Ferric Chloride and Permanganate
(Lbwenthal, Stromeyer, etc.).

This method owes its value to the fact, that when stannous
chloride is brought into contact with ferric or cupric chloride, it
acts as a reducing agent, in the most exact manner, upon these
compounds, stannic chloride being formed, together with a pro-
portionate quantity of ferrous or cuprous salt, as the case may be.
If either of the latter be then titrated with permanganate, the
original quantity of tin may be found, the reaction being, in the
case of iron, —

SnCl2 + Fe2Cl6=SnCl4 + 2FeCl2.

56 iron=59 tin. If decinormal permanganate, or the factor
necessary to convert it to that strength, be used, the calculation by
means of iron is not necessary.

Process: The solution of stannous chloride, or other protosalt of tin in
HC1, or the granulated metal, is mixed with pure ferric chloride, which,
if tolerably concentrated, dissolves metallic tin readily, and Avithout evolution
of hydrogen, then diluted with distilled water, and titrated with perman-
ganate as usual. To obtain the most exact results, it is necessary to make an
experiment with the same permanganate upon a like quantity of water,
to which ferric chloride is added; the quantity required to produce the
same rose colour is deducted from the total permanganate, and the remainder
calculated as tin.

Stannic salts, also tin compounds 'containing iron, are dissolved in water,
HC1 added, and a plate of clean zinc introduced for ten or twelve hours ;
the tin so precipitated is carefully collected and washed, then dissolved
in HC1, and titrated as ahove; or the finely divided metal may at once
be mixed with an excess of ferric chloride, a little HC1 added, and when
solution is complete, titrated with permanganate. 4 eq. of Iron ( = 224)
occurring in the form of ferrous chloride represent 1 eq. ( = 118) of tin.

Tin may also be precipitated from slightly acid peroxide solution
as sulphide by H2S, the sulphide well washed, and mixed with
ferric chloride, the mixture gently warmed, the sulphur filtered
off, and the filtrate then titrated with permanganate as above.
4 eq. of iron=l eq. of tin.

Tin Ore. — In the case of analysis of cassiterite, Arnold (C. N.
xxxvi. 238) recommends that 1 gm. of the very finely powdered
mineral be heated to low redness for two hours in a porcelain boat
in a glass tube with a brisk current of dry and pure hydrogen gas,
by which means the metal is reduced to the metallic state. It is
then dissolved in acid ferric chloride, and titrated with perman-
ganate or bichromate in the usual way.

§ 80. VANADIUM. 341

URANIUM.

Ur = 240.

§ 80. THE estimation of uranium may be conducted with great
accuracy by permanganate, in precisely the same way as ferrous
salts (§ 63). The metal must be in solution either as acetate,
sulphate, or chloride, but not nitrate. In the latter case it is
necessary to evaporate to dryness with excess of sulphuric or
hydrochloric acid, or to precipitate with alkali, wash and redissolve
in acetic acid.

The reduction to the ura nous state is made with zinc, but as the
end of reduction cannot, like iron, be known by the colour, it is
necessary to continue the action for a certain time ; in the case of
small quantities a quarter, larger half an hour, at a temperature of
50° to 60° C., and in the presence of excess of sulphuric acid;
all the zinc must be dissolved before titration. The solution is
then freely diluted with boiled water, sulphuric acid added if
necessary, and then permanganate until the rose colour is faintly
permanent. The ending is distinct if the solution be well diluted,
and the reaction is precisely the same as in the case of ferrous
salts ; namely, 2 eq. of uranium existing in the uranous state
require 1 eq. of oxygen to convert them to the uranic state ; hence
56 Fe = 120 Ur, consequently the strength of any permanganate
solution in relation to iron being known, it is easy to find the
amount of uranium.

VANADIUM.

'§ 81. VANADIUM salts, or the oxides of this element, may be
very satisfactorily titrated by reduction with a standard ferrous
solution ; thus —

2FeO + VO3 = Fe203 + VO.

1 gm. of Fe represents 1 "630357 gm. of vanadic pentoxide.

Lindemann (Z. a. C. xviii. 99) recommends the use of a
solution of ferrous ammonio-sulphate (double iron salt) standardized
by y1^ potassic bichromate.

Of course it is necessary that the vanadium compound should be
in the highest state of oxidation, preferably in pure sulphuric acid
solution. The blue colour of the tetroxide in the dilute liquid has
no misleading effect in testing with ferridcyanide.

With hydrochloric acid great care must be taken to insure
absence of free Cl or other impurities. The end-point in the case
-of this acid is different from that with sulphuric acid, owing to the
colour of the ferric chloride, the mixture becoming clear green.

The accuracy of the reaction is not interfered with by ferric or
chromic salts, alumina, fixed alkalies, or salts of ammonia.

342 VOLUMETRIC ANALYSIS. § 82.

Vanadic solutions being exceedingly sensitive to the action of

reducing agents, great care must be exercised to exclude dust
or other carbonaceous matters, alcohol, etc.

ZINC.
Zn = 65.

1 c.c. T^ solution =0-003 2 5 gm. Zinc.
Metallic iron x 0*5809 = Zinc.

,, x 0-724 = Zinc oxide.

Double iron salt x 0-08298 = Zinc.

„ x 0-1034 = Zinc oxide.

1. Indirect Method (Mann).

§ 82. THIS process gives exceedingly good results, and consists
in precipitating the zinc as hydrated sulphide, decomposing the
sulphide with moist silver chloride, then estimating the zinc
chloride so formed with ammonic thiocyanate as in Volhard's
method (§ 43).

The requisite materials are —

Silver chloride. — Well washed and preserved from the light-
under water.

Standard Silver nitrate. — 33'18 gm. of pure silver, dissolved in
nitric acid and made up to 1 liter, or 52'3 gm. silver nitrate per
liter. If made direct from silver, the solution must be well boiled
to dissipate nitrous acid. 1 c.c. = 0*01 gm. of zinc.

Ammonic thiocyanate. — Of such strength that exactly 3 c.c..
suffice to precipitate 1 c.c. of the silver solution.

Ferric Indicator and Pure Citric Acid (see § 43.3 and 4).

Process: 0'5 to 1 gm. of the zinc ore is dissolved in nitric acid. Heavy
metals are removed by H2S, iron and alumina by double precipitation
with ammonia. The united filtrates are acidified with acetic acid, and H2S
passed into the liquid until all zinc is precipitated as sulphide. Excess of
H'-S is removed by rapid boiling, so that a drop or two of the filtered liquid
gives no further stain on lead paper. The precipitate is then allowed to settle,
decanted while hot, the precipitate brought on a filter with a little hot water,
and without further washing, the filter with its contents is transferred to
a small beaker, 30 — 50 c.c. of hot water added, well stirred, and so much
moist silver chloride added as is judged necessary to decompose the sulphide,
leaving an excess of silver. The mixture is now boiled till it shows signs of
settling clear ; 5 or 6 drops of dilute sulphuric acid (1 : 5) are added to the
hot mixture, and in a few minutes the whole of the zinc sulphide will be
converted into zinc chloride. The free sulphur and excess of silver chloride
are now filtered off, washed, and the chloride in the mixed filtrate and
washings estimated as follows :—

To the cool liquid, measuring 200 or 300 c.c., are added o c.c. of ferric
indicator, and so much pure nitric acid as is necessary to remove the yellow
colour of the iron. A measured excess of the standard silver solution is then

§ 82. ZINC. 343

delivered in with the pipette, and without filtering off the silver chloride, or
much agitation, so as to clot the precipitate, the thiocyanate is cautiously
added, with a gentle movement after each addition, until a permanent light
brown colour appears.

The volume of silver solution represented by the thiocyanate
being deducted from that originally used, will give the volume to
be calculated to zinc, each c.c. being equal to 0*01 gm. Zn.

2. Precipitation as Sulphide and subsequent titration with. Ferric
Salts and Permang-anate (Schwarz).

The principle of this method is based on the fact, that when zinc
sulphide is mixed with ferric chloride and hydrochloric acid, or
better still, with ferric sulphate and sulphuric acid, ferrous or zinc
chloride, or sulphates respectively, and free sulphur are produced.
If the ferrous salt so produced is estimated with permanganate or
bichromate, the proportional quantity of zinc present is ascertained.
2 eq. Fe represent 1 eq. Zn.

Preparation of the Ammpniacal Zinc Solution. — In the case of rich
ores 1 gm., and poorer qualities 2 gm., of the finely powdered material are
placed into a small wide-mouthed flask, and treated with HC1, to which
a little nitric acid is added, the mixture is warmed to promote solution, and
when this has occurred the excess of acid is evaporated by continued heat.
If lead is present, a few drops of concentrated sulphuric acid are added
previous to complete dryness, in order to render the lead insoluble ; the
residue is then extracted 'with water and filtered. Should metals of the fifth
or sixth group be present, they must be removed by H2S previous to the
following treatment. The solution will contain iron, and in some cases
manganese. If the iron is not already fully oxidized, the solution must be
boiled with nitric acid ; if only traces of manganese are present, a few drops
of bromized HC1 should be added. When cold, the solution may be further
diluted if necessary, and then super-saturated with ammonia to precipitate
the iron ; if the proportion of this metal is small, it will suffice to filter off
and wash the oxide with ammoniacal warm water, till the washings give no
precipitate of zinc on adding ammonic sulphide. Owing to the fact that
this iron precipitate tenaciously holds about a fifth of its weight of zinc, it
will be necessary when the proportion is large to redissolve the partly washed
precipitate in HC1, and reprecipitate (best as basic acetate) ; the filtrate from
this second precipitate is added to the original zinc filtrate, and the whole
made up to a liter.

Process : The ammouiacal zinc solution (prepared as described above) is
heated, and the zinc precipitated in a tall beaker, with a slight excess of
sodic or ammonic sulphide, then covered closely with a glass plate, and set
aside in a warm place for a few hours. The clear liquid is removed by
a syphon, and hot water containing some ammonia again poured over the
precipitate, allowed to settle, and again removed, and the washing by
decantation repeated three or four times ; finally, the precipitate is brought
upon a tolerably large and porous filter, and well washed with warm water
containing ammonia, till the washings no longer discolour an alkaline lead
solution. The filter pump may be used here with great advantage.

The filter with its contents is then pushed through the funnel into a large
flask containing a sufficient quantity of ferric sulphate mixed with sulphuric
acid, immediately well stopped or corked, gently shaken, and put into a warm
place ; after some time it should be again well shaken, and set aside quietly

344 VOLUMETRIC ANALYSIS. § 82.

for about ten minutes. After the action is all over the mixture should
possess a yellow colour from the presence of undecomposed ferric salt ; when
the cork or stopper is lifted there should be no odour of H2S. The flask is
then nearly filled with cold distilled water, if necessarj- some dilute
sulphuric acid added, and the contents of the flask titrated with permanganate
or bichromate as usual.

The free sulphur and filter will have no reducing effect
upon the permanganate if the solution be cool and very dilute.

3. Precipitation by Standard Sodic Sulphide, with Alkaline Lead
Solution as Indicator (applicable to most Zinc Ores and Products).

The Ammoniacal Solution of Zinc is prepared just as previously
described in Schwarz's method.

Standard Sodic sulphide. — A portion of caustic soda solution is
saturated with H2S, sufficient soda added to remove the odour of
the free gas, and the whole diluted to a convenient strength for
titrating.

Standard Zinc Solution. — 44*12 gin. of pure zinc sulphate are
dissolved to the liter. 1 c.c. will then contain 0*01 gm. of
metallic zinc, and upon this solution, or one prepared from pure
metallic zinc of the same strength, the sulphide solution must be
titrated.

Alkaline Lead Indicator. — Is made by heating together lead
acetate, tartaric acid, and caustic soda solution in excess, until
a clear solution is produced. It is preferable to mix the tartaric
acid and soda solution first, so as to produce sodic tartrate ; or if
the latter salt is at hand, it may be used instead of tartaric acid.
Some operators use sodic nitroprusside instead of lead.

Process: 50 c.c. of zinc solution (=0*5 gm. Zn) are put into a beaker,
a mixture of solutions of ammonia and ammonic carbonate (3 of the former
to about 1 of the latter) added in sufficient quantity to redissolve the
precipitate which first forms. A few drops of the lead solution are then, by
means of a glass rod, placed at some distance from each other, on filtering
paper, laid upon a slab or plate.

The solution of sodic sulphide contained in an ordinary Mohr' s burette
is then suffered to flow into the zinc solution until, on bringing a drop from
the mixture and placing it upon the filtering paper, so that it may expand
and run into the drop of lead solution, a black line occurs at the point of
contact ; the reaction is very delicate. At first it will be difficult, probably,
to hit the exact point, but a second trial with 25 or 50 c.c. of zinc solution
will enable the operator to be certain of the corresponding strength of the
sulphide solution. As this latter is always undergoing a slight change, it is
necessary to titrate occasionally.

Direct titration with pure zinc solution gave 99'6 and 100'2, instead of 100.

Groll recommends the use of nickel protochloride as indicator,
instead of sodic nitroprusside or lead. The drops are allowed to
now together on a porcelain plate ; while the point of contact shows
a blue or green colour the zinc is not all precipitated by the sodic
sulphide, therefore the latter must be added until a greyish black
colour appears at contact.

§82. ZINC. 345

4. Precipitation as Sulphide with Ferric Indicator (Schaffner) .

Schaffner's modification of this process, and which is used
constantly at the laboratory of the Vieille Montagne and the
Rhenish Zinc Works, is conducted as follows : — For ores containing
over 35 per cent, zinc, 0*5 gm. is taken ; for poorer ones, 1 gm. to
2 gm. Silicates, carbonates, or oxides, are treated with hydro-
chloric acid, adding a small proportion of nitric acid at boiling heat
to peroxidize the iron. Sulphur ores are treated with aqua regia,
evaporated to dryness, and the zinc afterwards extracted by hydro-
chloric acid ; the final ammoniacal solution is then prepared as
described on page 343.

Process : The titration is made with a solution of sodio sulphide, 1 c.c. of
which should equal about O'Ol gm. Zn. The Vieille Montagne laboratory
uses ferric chloride as an indicator, according to Schaffner's method.
For this purpose a single drop or some few drops of this chloride are let fall
into the ammoniacal solution of zinc. The iron which has been added is at
once converted into red flakes of hydrated ferric oxide, which float at the
bottom of the flask. If sodic sulphide be dropped from a burette into the
solution of zinc, a white precipitate of zinc sulphide is at once thrown down,
and the change in the colour of the flakes of iron from red to black shows
the moment when all the zinc is sulphuretted, and the titration is ended. It
is advisable to keep the solution for titration at from 40 to 60° C. Titration
carried out under exactly equal conditions, with a known and carefully
weighed proportion of zinc, gives comparative data for calculation, and thus
for the determination of the contents of any zinc solution by means of
a simple equation. If, for example, 30'45 c.c. of sodic sulphide have been
used to precipitate 0'25 gm. of zinc, 1 c.c. of it will precipitate 8'21 m.gm.
of zinc (30'45 : 0'25 -1 : x, and therefore #=0-00821).

The following method is adopted in the laboratory of a well-
known copper works in Wales : —

Reduce the sample to fine powder, and dry at a temperature of about
105° C. Dissolve 0'5 gm. of the sample thus prepared in aqua regia,
evaporate nearly to dryness, take up with hot water, add 20 c.c. of
ammonia and 10 c.c. of a solution of ammonic carbonate (1 to 10), then
a few drops of solution of permanganate to precipitate lead and manganese.
Now heat nearly to boiling-point and filter into a larger flask, wash the
precipitate well with hot water containing ammonia until a drop of the
washings shows no reaction with sodic sulphide. The volume of the filtrate
and washings should be about 250 c.c., and the temperature about 50° C. Now
titrate with a standard solution of sodic sulphide. The most convenient
strength is 70 c.c. = 0'5 gm. of pure zinc, heat the sample liquid almost to
boiling-point, and add not quite enough sulphide solution to precipitate the
whole of the zinc. Now take a drop of a dilute solution of ferric chloride,
and let it fall into a small beaker containing a few drops of dilute ammonia,
wash the whole contents of the beaker into the assay, and continue titrating
slowly and cautiously, at last adding the sulphide solution by O'l c.c. at
a time, while continually agitating the flask until the ferric oxide at the
bottom of the flask begins to turn black, when the assay is finished.

The number of c.c. of sulphide solution used is noted. In order to
determine the strength of the sulphide solution, weigh 0'5 gm. pure zinc,
place this in a flask, dissolve in 10 c.c. of HC1, and add some hot water, 20
c.c. of ammonia, and 10 c.c. of ammonic carbonate as above, and fill up with
hot water to about 250 c.c. Then titrate with the sulphide solution

346 VOLUMETRIC ANALYSIS. § 82.

as described. From the number of c.c. used for the O'o gm. pure zinc
(standard), and the number used for the sample, the zinc contents of the
latter can be easily calculated.

The copper present in blendes and calamines does not usually exceed 0'5
per cent. It may be estimated colori metrically, and the amount deducted
from the total produced.

If any considerable amount of copper or other impurities be present,,
they must be separated by the ordinary well-known methods. In order to
obtain greater accuracy a correction is made by measuring the volume of
the liquid after the assay is finished, and deducting 0'6 c.c. from the
sulphide solution used for every 100 c.c. of the volume of the assay : this
correction is equally applied to the standard. Experiments have shown that
oxide of iron prepared as described above placed in 100 c.c. of distilled
water containing ammonia, requires 0'6 c.c. of a sulphide solution of the
above strength to turn distinctly black.

The essential point in this volumetric process practised at the
Vieille Montagne is the perfect uniformity of working adopted in
the assays with reference to the volume of the solutions and
reagents used and the colour of the indicator. In titrating,.
the same quantities of ferric chloride, hydrochloric acid and
ammonia are steadily used. Work is done always at one tem-
perature and in the same time, particularly at the end of the
operation, when the iron begins to take on that characteristic
colour which the flakes take at the edges — points which should
not he overlooked. As a further precaution, the titrating
apparatus is provided in duplicate, two assays being always made.
It permits the execution of several titrations without the necessity
of a too frequent renewal of sodic sulphide, which is stored in
a yellow flask of large capacity supplying two Mohr's burettes,
under which the beakers can be placed and warmed. A mirror
shows by reflection the iron flakes which settle down after shaking
the liquid.

Too much stress cannot be laid upon the necessity of standard-
izing the sodic sulphide under the same conditions as to volume of
fluid, proportions of NHy and HC1, and colour of the indicator, as
will actually occur in the analysis.

5. Estimation as Ferrocyanide.

In Acetic Acid Solution (Galetti). — When ores containing zinc
and iron are dissolved in acid, and the iron precipitated with
ammonia, the ferric oxide invariably carries down with it
a portion of zinc, and it is only by repeated precipitation that the
complete separation can be made. In this process the zinc is
converted into soluble acetate, and titrated by a standard solution
of potassic ferrocyanide in the presence of insoluble ferric acetate.

The Standard Solution of Potassic ferrocyanide, as used by
Galetti, contains 41 '250 gm. per liter. 1 c.c. = O'Ol gm. Zn, but
its actual working power must be fixed by experiment.

Standard Zinc Solution, 10 gm. of pure metallic zinc per liter
dissolved in hydrochloric acid.

§ 82. ZINC. 347

The process is available in the presence of moderate quantities of
iron and lead, but copper, manganese, nickel, and cobalt must be
absent.

The adjustment of the ferrocyanide solution (which should be
freshly prepared at short intervals) must be made in precisely the
same way, and with the same volume of liquid as the actual
analysis of ores, and is best done as follows : — -

25 c.c. of zinc solution are measured into a beaker, 15 c.c. of liquid
ammonia of sp. gr. 0'900 added to render the solution alkaline, then very
cautiously acidified with acetic acid, and 50 c.c. of acid ammonic acetate
(made by adding together 20 c.c. of ammonia of sp. gr. 0'900, 15 c.c. of
concentrated acetic acid and 65 c.c. of distilled water), which is poured into
the mixture, then dilated to 250 c.c., and warmed to about 50° C. The
titration is then made with the ferrocyanide solution by adding it from
a burette until- the whole of the zinc is precipitated. Galetti judges the
ending of the process from the first change of colour from white to ash greyy
which occurs when the ferrocyanide is in excess ; but it is best to ascertain
the ending by taking drops from the solution, and bringing them in contact
with solution of uranic acetate on a wiiite plate until a faint brown colour
appears. The ferroc}ranide solution should be of such strength that
measure for measure it agrees with the standard zinc solution. In the
present case 25 c.c. would be required.

In examining ores of zinc, such as calamine and blende, Galetti takes
0'5 gm. for the analysis, and makes the solution up to 500 c.c. Calamine
is at once treated with HOI in sufficient quantity to bring it into solution.
Blende is treated with aqua regia, and evaporated with excess of HC1 to-
remove nitric acid. The solutions of zinc so obtained invariably contain
iron, which together with the zinc is kept in solution by the HC1, but to
insure the peroxidation of the iron, it is always advisable to add a little
potassic chlorate at a boiling heat during the extraction of the ore. The
hydrochloric solution is then diluted to about 100 c.c., 30 c.c. of ammonia
added, heated to boiling, exactly neutralized with acetic acid, 100 c.c. of the
acid ammonic acetate poured in, and diluted to about 500 c.c. The mixture
as prepared will contain all the zinc in solution, and the iron will be
precipitated as acetate. The titration may at once be proceeded with at
a temperature of about 50° to 60° C. by adding the ferrocyanide until the
necessary reaction with uranium is obtained. As before mentioned,
Galetti takes the change of colour as the ending of the process, and when
iron is present this is quite distinguishable, but it requires considerable
practice, to rely upon, and it is therefore safer to use the uranium indicator.
When using the uranium, however, it is better to dilute the zinc solution less,
both in the adjustment of the standard ferrocyanide and the analysis of
ores. The dilution is necessaiy with Galetti's method of ending the
process, but half the volume of liquid, or even less, is better with the
external indicator.

in Hydrochloric Acid Solution (Fahlberg and Maxwell Ly te).
This method is not available in the presence of iron, copper, nickel,
cobalt, or manganese.

The Standard Solution of Ferrocyanide. — 1 c.c. = 0*01 gm. of
zinc. Lyte finds that this is obtained by dissolving 43 '2 gm. of
pure potassic ferrocyanide and diluting to 1 liter. This corresponds
volume for volume with a solution of 10 gm. of pure zinc in excess
of hydrochloric acid diluted to 1 liter. My experiments confirm

348 VOLUMETllIC ANALYSIS. § 82.

this, but each operator is advised to adjust his solutions by
experiment, always using the same quantities of reagents and
volume of liquid. The end of the reaction between the zinc and
ferrocyanide is found by uranium.

Process : If a solution of zinc freely acidified with HCl is heated to nearly
boiling-point, two or three drops of uranic acetate or nitrate solution added,
and the ferrocyanide delivered into the mixture from a burette, white zinc
ferrocyanide immediately precipitates, and as the drops of ferrocyanide fall
into the mixture, a brown spot of uranic ferrocyanide appears, but dis-
appears again on stirring so long as free zinc exists in solution. The
moment all the zinc is converted into ferrocyanide, the addition of test
solution tinges the whole liquid brown. This addition of uranium to the
liquid may be used as a guide to the final testing on a porcelain plate, since
as the precipitation approaches completion, the tinge of brown disappears
more slowly. The actual ending, however, is always ascertained by spreading
a drop or two of the liquid upon the plate, bringing into contact with it
a glass rod moistened with uranic solution ; when the same shade of colour
is produced as occurred in the original titration of the ferrocyanide
solution, the process is ended.

Ly te gives the following method of treating a blende containing
lead, copper, and iron (C. N. xxi. 222) : —

2 gm. of finely powdered ore were boiled with strong HCl and a little
KC1O3, the insoluble matter again treated in like manner, the solutions
mixed and evaporated somewhat, washed into a beaker, cooled, and moist
baric carbonate added to precipitate iron, allowed to stand a few hours, then
filtered into a 200 c.c. flask containing 10 c.c. of strong HCl, and washed
until the exact measure was obtained. 20 c.c. ( = 0'2 gm.) of blende were
measured into a small beaker, diluted with the same quantity of water,
3 drops of uranic solution added, and the ferrocyanide delivered in from
a burette. When 70 c.c. were added the brown tinge disappeared slowly ;
the testing on a white plate was then resorted to, and the ferrocyanide
added drop by drop, until the proper effect occurred at 73 c.c. As a slight
excess of ferrocyanide was necessary to produce the brown colour, 0'2 c.c.
was deducted, leaving 72'8 c.c. as the quantity necessary to precipitate all
the zinc. The 0'2 gm. of blende therefore contained 0'0728 gm. of Zn or
36'4 per cent.

The sample in question contained about 2*7 per cent, of copper,
but this was precipitated with the iron by the baric carbonate ; had
it contained a larger quantity, the process would not have been
available unless the copper was removed by other means.

Mahon (Amer. Chem. Journ. iv. 53) uses the ferrocyanide
method much in the same way as above described, but finds that
Mn must be absent to ensure good results. In the presence of
Mil he separates the Zn from a strong acetic solution with H2S.
The sulphide is then dissolved in HCl and titrated as before.

A modification of the ferrocyanide method so as to be available
for the estimation of both zinc and manganese in the presence of
each other has been devised by G. C. Stone (Jour. Amer. Cliem.
Soc. xvii. 437).

The standard solutions required are : —

§ 82. ZINC. 349

Potassic ferrocyanide, about 30 gm. per liter. Its actual working
strength is found by titrating it upon a known weight of either
zinc or manganese in slightly acid solution, using a very dilute
solution of cobalt nitrate as outside indicator. A correction is
made in all cases for the amount of ferrocyanide required to give
the reaction with the indicator, and may be taken as 0*5 c.c. for
every 100 c.c. of the solution titrated.

Potassic permanganate, 1*99 gm. of the pure salt per liter, 1 c.c.
= 1 m.gm. of Mn.

The end-point of reaction with the indicator is found by placing
drops of the cobalt solution on a white tile, and bringing a drop of
the liquid under titration in contact with it, but not actually
mixing. The occurrence of an immediate faint green line at the
junction of the drops is accepted as the correct reading.

Process : The ore is dissolved in HC1 with the addition of KC1O3 as an
oxidizer, and care must be taken to have sufficient acid to keep all the
manganese in solution.

Lead alone need not be separated ; copper can be precipitated by lead ; or
lead and copper can both be precipitated by aluminium. Cadmium should
be precipitated by H2S, and the nitrate oxidized. Iron and aluminium are
best separated by baric carbonate, but the latter must be free from alkaline
carbonates and hydroxides, baric hydroxide and ammonium salts. A salt
sufficiently pure for the purpose may be obtained by suspending the ordinary
pure carbonate (first proved free from ammonium salts) in warm water for
several hours with 2 or 3 per cent, of its weight of baric chloride.

The well oxidized solution of the ore is put into a 500 c.c. flask, and baric
carbonate suspended in water added until the precipitate coagulates. The
Avhole is then poured into a beaker, well mixed, allowed to settle, and the
clear liquid decanted through a dry filter, and diluted to 500 c.c. Portions
of 50, 100, or 200 c.c. of the filtrate are used for each titration. One portion,
which should contain between O'Ol and 0'04 gm. of manganese, is diluted to
200 c.c., heated nearly to boiling in a porcelain dish, and titrated rapidly
with permanganate with vigorous stirring.

A second portion is made slightly acid with hydrochloric acid, the
zinc and manganese are titrated together in the cold with ferroc}7anide ; the
dark colour of the precipitate suddenly changes to light yellowish green
shortly before the end of the reaction. It is not necessary to test with the
cobalt solution until 1 or 2 c.c. of the ferrocyanide have been added after
the lightening of the precipitate.

Example : 1 c.c. of the ferrocyanide solution equalled 0'00606 gm. of
zinc, or 0'00384 of manganese; 1 c.c. of the permanganate equalled O'OOl
gm. of manganese. 2^ gm. of the ore were dissolved, and the iron
precipitated and filtered out. 50 c.c. of the solution were diluted, heated,
and titrated with permanganate, requiring 18'45 c.c. = 7'38 per cent, of
manganese. 100 c.c. titrated with ferrocyanide required 27'85 c.c., of which
9'6l c.c. would be used by the manganese present. Deducting this, 18'24
c.c. was left for the zinc, equal to 0'11053 gm., or 22'11 per cent. The
amounts of zinc and manganese as determined gravimetrically were 22 05
and 7' 58 per cent, respectively.

Von Schulz and Low's Method (Eng. and Min. Jour. 1892, 178).—
Prepare a solution of potassic ferroc}ranide by dissolving 44 gm. of the pure
salt in distilled water and diluting to 1 liter. Then prepare a standard
solution as follows : Dissolve 200 m.gm. of pure zinc oxide in 10 c.c. of pure-,

350 VOLUMETRIC ANALYSIS. § 82.

strong hydrochloric acid. Add 7 gm. of chemically pure ammonic chloride
(free from copper) and about 100 c.c. of boiling water. Titrate the clear
liquid with the ferrocyanide solution until a drop tested on a porcelain plate
with a drop of a strong aqueous solution of uranic acetate shows a brown
tinge. About 16 c.c. of ferrocyanide solution are required. When the brown
tinge is obtained, see if any of the previous tests subsequently develop
a similar colour, and, if so, correct the burette reading accordingly. Usually
the correction for two previous drops has to be made. One c.c. of this
solution equals about O'Ol gm. of zinc.

In the test take exactly 1 gm. of ore and treat it in a 3^-in. porcelain
crucible with 25 c.c. of a saturated solution of chlorate of potash in nitric
acid. Do not cover the vessel at first, but warm gently until any violent
action is over and greenish vapours have ceased to come off. Then cover
with a Avatch-glass and boil rapidly to complete dryness, but avoid over-
heating and baking. A drop of nitric acid adhering to the cover does no
harm. Cool sufficiently and add 7 gm. of ammonic chloride, 15 c.c. of
strong ammonia, and 25 c.c. of hot water. Cover and boil for one minute,
and thea, with a rubber-tipped glass rod, see that all solid matter on the
cover, sides, and bottom of the crucible is either dissolved or disintegrated.
Filter into a beaker and wash several times with hot ammonic chloride
solution (10 gm. to the liter). A blue-coloured filtrate indicates the
presence of copper. In that case add 25 c.c. of strong pure hydrochloric
acid and about 40 gm. of granulated test lead. Stir the lead about in the
beaker until the liquid has become perfectly colourless, and continue the
stirring for a short time, to make sure that the copper is all precipitated.
The solution, which should still be quite hot, is now read}' for filtration.
In the absence of copper the lead is omitted and only the acid added.

About one-third of the solution is now set aside, and the main portion is
titrated rapidly with the ferrocyanide until the end-point is passed, using
the uranium indicator as in the standardization. The greater part of
the reserved portion is now added, and the titration continued with more
caution until the end-point is again passed. Then add the remainder of
the reserved portion and finish the titration carefully, by additions of
two drops of ferrocyanide at a time. Make corrections for the final reading
of the burette as in the standardization. In this process cadmium behaves
like zinc, and must be separated, if necessary, by some other method.

Technical process for Ores containing- Iron. — Voigt (Zeit. ang. Chem.
1889, 307, 308).— The solution of the substance in hydrochloric acid is
oxidized with nitric acid and diluted to about 100 c.c. Sufficient potassic
tartrate to keep the iron in solution is added, and then ammonia to feeble
alkalinity, and the liquid is further diluted to about 250 c.c. Standard
solution of potassic ferrocyanide is then run in, until a drop of the mixture
brought in contact with strong acetic acid develops a permanent blue. The
ferrocyanide is of suitable strength if 1 c.c. is equal to O'Ol gm. of zinc.
About 46 gm. of the salt are dissolved to a liter, and the solution is standard-
ized against one of zinc made by dissolving 12'461 gm. of zinc oxide in
hydrochloric acid and diluting to a liter; 10 c.c. of this solution are mixed
with 5 gin. of potassic tartrate, a few drops of ferric chloride, ammonia, and
water to 250 c.c., and should require 10 c.c. of the ferrocyanide. An essential
condition is that the excess of ammonia should be as small as possible.
Incorrect results are obtained when much manganese is present ; lead is not
injurious.

6. Estimation of Zinc as Oxalate.

This method is based on the fact that all the metals of the
magnesia group are precipitated in the absence of alkaline salts by

§ 82. ZINC. 351

oxalic acid, with the addition of alcohol. The cases are very few
in which such a method can be made available, but the process as
described by W. G. Leison (Silliman's Journ. Sept. 1870)
is here given.

The zinc compound is obtained, preferably as sulphate, in neutral solution,
and strong solution of oxalic acid and a tolerable quantity of strong alcohol
are added. Zinc oxalate quickly separates in a fine crystalline powder, which
when washed by alcohol from excess of oxalic acid and dried, can be dissolved
in hot dilate sulphuric acid, and titrated with permanganate ; the amount
of zinc is calculated from the weight of oxalic acid so found. If the zinc
•oxalate be washed on a paper filter, it cannot be separated from the paper
without contamination with fibres of that material, which would of course
affect to some extent the permanganate solution. Hence it is advisable to
filter through very clean sand, best done by a special funnel ground conical
at the throat ; into this is dropped a pear-shaped stopper with a long stem,
the pear-shaped stopper fitting the funnel throat tightly enough to prevent
sand but not liquids from passing; a layer of sand being placed upon the
globular end of the stopper and packed closely, the liquid containing the
oxalate is brought upon it and so washed ; finally the stopper is lifted, the
sand and oxalate washed through with dilute acid into a clean flask, and the
titratiou completed.

7. Zinc Dust.

The value of this substance depends upon the amount of metallic
.zinc contained in it ; but as it generally contains a large proportion
of zinc oxide, the foregoing methods are not available for its
valuation. The volume of hydrogen yielded by it on treatment
with acids appears to be the most accurate, as suggested by
Presenius or by Barnes (•«/". S. C. I. v. 145). This may very
well be done in the nitrometer with decomposing flask, and
comparing the volume of gas yielded by pure zinc and the sample
of dust under examination.

"Weil decomposes a known volume of standard solution of
copper by digesting 0'4 gm. of the zinc dust in a platinum capsule,
with 50 c.c. of copper solution containing 0*5 gm. Cu. The zinc-
precipitates metallic copper equivalent for equivalent. After
removing the zinc refuse and metallic copper by filtration and
washing, an aliquot portion of the filtrate is titrated with standard
tin solution for the excess of copper as described in § 58.6. The
amount, of Cu precipitated, when multiplied by the factor 1'0236,
will give the Zn in the 0'4 gm. of dust.

Many other methods have been proposed for the valuation of
this substance. The best is that of Klemp (Z. a. C. xxix. 253),
which consists in treating the dust with an excess of caustic
potash and potassic iodate ; the latter is reduced in definite pro-
portion by the metallic zinc to potassic iodide, and the latter
estimated by distillation in the iodometric apparatus, figs. 37 or
38. The solutions of potash and iodate must be somewhat con-
centrated, and the mixture with the zinc dust must be intimate,
which may be best secured by shaking the whole together in

352 VOLUMETEIC ANALYSIS. § 83.

a well-stoppered 200 c c. flask with glass beads. A 5 per cent,
solution of iodate should be used, and the potash solution should
be about 40 per cent. For 1 gin. of the dust, 30 c.c. of the iodate
and so much of the potash solution should be used as to measure
130 c.c. The weighed substance, together with the beads, being
already in the flask, the solutions are added, the stopper greased
with vaseline, tied down and shaken for five minutes, then heated
on the water bath, with occasional shaking, for one hour.
(Digestion without heat gives practically the same results.) The
flask is then cooled and the contents diluted to 250 or 500 c.c., and
50 or 100 c.c. placed in the distilling flask, acidified with sulphuric
acid, and the iodine so set free distilled into solution of potassic
iodide, and titrated with thiosulphate in the usual way. Each
0*2 gm. of iodine so found = 0*25644 gm. Zn or 1 part of Zn should
theoretically liberate 07799 part of I.

8. Zinc Oxide and Carbonate.

Benedikt and Cantor (Zeit. angew. CJiem. 1888, 236, 237)
shew that zinc oxide and carbonate can be accurately titrated with
standard acid and alkali, using methyl orange as indicator, and
other zinc salts, using phenolphthalein. The oxide or carbonate is
dissolved in excess of acid, and the excess titrated back by soda
solution. Zinc salts are dissolved in water (50 c.c. to O'l gm. ZnO),
phenolphthalein is added, and then standard soda solution to intense
red colour. A few more c.c. of soda are then added, the mixture
is boiled for some minutes, and the excess of soda titrated, If
either free acid or zinc oxide is present in the zinc salt, it is
neutralized in presence of methyl orange by alkali or acid, as the
case may be.

OILS AND FATS.

§ 83. THE examination of fatty matters by titration of their
soluble or volatile and total fatty acids has of late assumed very
considerable importance, in view of furnishing results which aid
in determining the amount of adulteration to which they are
subject. It has been found especially serviceable in the case of
butter, and two methods are in vogue, both of which give good
results. The same methods are more or less available for the
examination of fats other than butter ; and further experiments
by various operators have rendered the methods of value for
differentiating various fatty bodies. The titration methods, more
especially for butter, were originated by Koettstorf er (Z. a. C.
xix. 199) and Keichert (Z. a. (7. xviii. 68): this latter method
has been considerably improved by the suggestions of Wollny,
based on a long series of experiments (Bied. Centr. 699, also
Analyst xii. 203), and is now known commonly as the Reichert-
Wollny method.

§ 83. OILS AND FATS. 353

Another interesting method of examining the nature and
composition of various fats, is by the power they possess of
absorbing bromine or iodine. This method, as regards bromine,
has been worked out with considerable diligence and ability by
Mills and Snod grass (J. S. C. /, ii. 435 and ibid iii. 366), also
by Allen (ibid v. 68, and also in his well-known treatise on
Organic Analysis). The iodine method of Hubl is described in
/. $. G. I. iii. 641. These various methods have been most
voluminously discussed in their chemical and practical aspects, so
that it must suffice here to give shortly the methods of analysis.
It is only perhaps necessary to say that Hubl's iodine method is
now generally adopted in preference to the absorption by bromine
except in the case of Hehner's gravimetric bromine method.
The literature on this subject is extremely voluminous and cannot
be quoted here. An excellent digest of the Various methods and
opinions is given in Allen's Organic Analysis, also by Droop
Kichmond (Analyst xvii. 171).

Butter.

Bei chert's Method. — This method is based on the fact, that
butter fat in a genuine state never contains less than 4 per cent,
of volatile fatty acids, whereas other fats contain either none at all
or very much less than butter. The process consists in saponifying
the fat to be examined by an alkali, separating the fixed acids by
neutralizing the alkali, and distilling off the volatile acids (chiefly
butyric and caproic) for titration with standard acid. In this and
Koettstorfer's method, where also alcoholic solution of caustic
alkali is used, it is essential to avoid absorption of CO2 by long
exposure.

The necessary solutions are : —

1. Standard Baric hydrate. -~ strength is most convenient,
but any solution approximating to that strength may be used, and
a factor found to convert it to that strength in calculating the
results of titration. It must be carefully preserved from CO2 by
any of the usual arrangements, and where a constant series of
titrations are carried on, it is best to have a store bottle and
burette fitted, as shown p. 12, fig. 11.

2. Phenol phthalein, see p. 37.

3. Alcohol of about 95 per cent, strength, recently distilled from
caustic soda.

4. Solution of caustic soda. Made by dissolving 100 gm. of good
sodic hydrate in 100 c.c. of distilled water which has been recently
well boiled and cooled ; this solution will not be contaminated with
CO2 to any extent, since any JSTa2C03 which might be formed is
quite insoluble in the strong solution ; it must be allowed to
stand until quite clear, then poured off and well preserved.

Leffmann and Beam advocate the use of alkali-glycerol in

A A

VOLUMETRIC ANALYSIS.

83.

place of alcoholic alkali in saponifying the fat, and the
re-agent is made by mixing 25 c.c. of the 50 per cent,
caustic soda described above with 125 c.c. of pure glycerine.
10 c.c. of this solution will perfectly saponify 5 gm. of
butter fat when the two are heated carefully over a Buns en flame
in a small flask for five minutes with shaking. The operation of
evaporating off the alcohol together with the risks of absorption
of CO2 is thus obviated. After complete saponification, the soap is
dissolved in about 100 c.c. of water added, at first, drop by drop,
and the distillation carried on as usual.

5. Dilute sulphuric acid for separating the fatty acids, is made
by diluting 25 c.c. of strongest H2S04 to a liter.

6. The apparatus for digestion and distillation are shown in
fig. 52, the same Erlenmeyer flask being used for the digestion
and for the distillation. The distilled liquid drops into a small

Tig. 52.

funnel containing a small porous filter for separating any scum
which may pass over with the distillate ; the receiver holding the
funnel is marked at 50 c.c. and 100 c.c., so as to be available for
either 2 '5 gm. or 5 gm. of butter fat.

The following method of manipulation as drawn up by the
Association of Official Agricultural Chemists, U.S.A., is recom-
mended as being all that is required to ensure accuracy, and
applies to the treatment of approximately 5 gm. of fat for each
operation. Many operators prefer to take about half that
quantity, which saves time, and need not be any the less accurate.

Process, Weighing the Fat : The butter or fat to be examined should be
melted and kept in a dry warm place at about 60° C. for two or three hours
until the moisture and curd have entirely settled out. The clean supernatant
fat is poured off and filtered through a dry filter paper in a jacketed filter
containing boiling water, to remove all foreign matter and any traces of

§ 83. OILS AND FATS. 355

moisture. Should the filtered fat in a fused state not be perfectly clear the
treatment above mentioned must be repeated.

The sapoiiific-ition flasks are prepared by having them thoroughly washed
with water, alcohol, and ether, wiped perfectly dry on the outside, and
heated for one hour to 100° C. The flasks should then be placed in a tray
by the side of the balance and covered with a silk handkerchief until they
are perfectly cool. They must not be wiped with a silk handkerchief within
fifteen or twenty minutes of the time they are weighed. The weight of
each flask is determined accurately, using a flask for a counterbalance or not,
as may be convenient. The weight of the flasks having been accurately
determined they are charged with the melted fat in the following way: —

A pipette with a long stem marked to deliver 5'75 c.c. is warmed to
a temperature of about 50° C. The fat having been poured back and forth
once or twice into a dry beaker in order to thoroughly mix it, it is taken up
in the pipette, the nozzle of the pipette carried to near the bottom of the
flask, it having been previously wiped to remove any adhering fat. The
5'75 c.c. of fat are allowed to flow into the flask and the pipette is removed.
After the flasks have been charged in this way they should be re-covered
with the silk handkerchief and allowed to stand fifteen or twenty minutes,
when they are again weighed to ascertain the exact amount of fat.

The Saponificati.on : 10 c.c. of 95 per cent, alcohol re-distilled from caustic
soda are added to the fat in the flask, 2 c.c. of the concentrated soda solution are
udded, a soft cork stopper inserted in the flask, and tied down with a piece of
twine. The saponification is then completed by placing the flasks upon the
water or steam bath. The flasks during the saponification, which should last
for one hour, should be gently rotated from time to time, being careful not
to project the soap for an}r distance up the sides of the flask. At the end of
an hour the flasks, after having been cooled to near the room temperature,
are opened.

Removal of the Alcohol : The stoppers having been laid loosely in the
mouth of the flasks the alcohol is removed by dipping the flasks
into a steam bath. The steam should cover the whole of the
flask except the neck. After the alcohol is nearly removed, frothing
nriy be noticed in the soap, and to avoid any loss from this cause, or any
creeping of the soap up the sides of the flask, it should be taken from the
bath and shaken to and fro until the frothing disappears. The last traces
of alcohol vapour may be removed from the flask by waving it briskly,
mouth down, to and fro. Complete removal of the alcohol with the pre-
cautions above noted should take about forty-five minutes.

Dissolving the Soap : After the removal of the alcohol the soap should
be dissolved by adding 100 c.c. of recently boiled distilled water, and warmed on
the steam bath with occasional shaking until the soap is completely dissolved.

Setting Free the Fatty Acids : When the soap solution has cooled to
about 60° or 70° C., the fatty acids are separated by adding 40 c.c. of the
dilute sulphuric acid mentioned above.

MMing the Fatty Acids: The flasks should now be re-stoppered as in the
first instance, and the fatty acids melted by replacing the flasks on the steam
bath. According to the nature of the fat examined the time required for
the fusion of the fatty acids may vary from a few minutes to hours.

The Distillation : After the fatty acids are completely melted, which can
be determined by their forming a transparent oily layer on the surface of
the water, the flasks are cooled to room temperature and a few pieces of
pumice stone added. The pumice stone is prepared by throwing it, at white
heat, into distilled water, and keeping it under water until used. The flask
is now connected with the condenser, slowly heated with a naked flame until
ebullition begins, and then the distillation continued by regulating the flame
in such a way as to collect 100 c.c. of the distillate in as nearly as possible
thirty minutes.

A A 2

356 VOLUMETRIC ANALYSIS. § 83.

Titration of the Volatile Acids: The 100 c.c. of the filtered distillate are
poured into a beaker holding from 200 — 250 c.c., 0'5 c.c. of phenolphthalein
solution added, and decinormal baric hydrate run in until a red colour is
produced. The contents of the beaker are then returned to the measuring-
flask to remove any acid remaining therein, poured again into the beaker,
and the titration continued until the red colour produced remains
apparently unchanged for two or three minutes.

It must be borne in mind that this method is not one of strict
chemical accuracy, but the experience of the author and a host of
other very competent operators, clearly show that the distillate
from 5 gm. of genuine normal butter fat when carried out as
described, should require not less than 25 c.c. of ~j alkali to
neutralize the volatile acids present. It is true that butters known
to be genuine have occasionally been found to give lower figures
from some unexplained causes, one of which seems to be due to
milk taken from cows towards the end of their period of lactation.
The figure may also rise to 32 or 33 c.c. of alkali. This is often
the case with butters produced in warmer climates than Great
Britain. The general average for butters taken from the mixed
milk of a number of cows will be between 27 and 28 c.c., whereas
margarine will rarely require more than 0'5 c.c., beef fat and
lard about the same, while cocoa-nut fat, which gives the highest
figures, requires about 7 c.c.

It may therefore be concluded that any sample of butter fat,
which requires less than 25 c.c. of ~ alkali must be looked upon
with suspicion.

Koettstorfer's Method. — This operation estimates the saponi-
fying equivalent of any fatty substance, but is allowed on all
hands to be less satisfactory in discriminating mixtures of other
fats with butter, although extremely useful. In this method the
whole of the acids existing in the fat are estimated. The solutions
required are the following : —

Standard Hydrochloric Acid. — Semi-normal strength, i.e., 18*185
gm. per liter.

Standard Solution of Caustic Potash in Alcohol. — Methylated
spirit, previously digested with permanganate, dehydrated with dry
potassic carbonate, then distilled, rejecting the first portions, may
be used in place of pure alcohol. In any case the strength should
not be less than 90 per cent., and the solution should be freshly
made to avoid any deep colouration likely to interfere with the
indicator. As it rapidly changes in strength, it is not possible to
rely upon its being semi-normal, but it should be roughly adjusted
at about that strength with absolutely accurate hydrochloric acid,
and a blank experiment made side by side with each titration of
fat. The excess of potash used in the fat titration is thus expressed
in terms of £ acid, and to arrive at the percentage of potash each
c.c. is multiplied by 0'02805. The saponification equivalent of
the fat or oil is found by dividing the weight in milligrams of the

83.

OILS AND FATS.

357

sample by the number of c.c. of normal (not ^) acid corresponding
to the alkali neutralized by the oil. If the percentage of potash
is known, the saponifying equivalent may be found l}y dividing
this percentage into 5610, or if j^aHO is the alkali used,
into 4000.

Process : From 2 to 2'5 gm. of the fat, previously purified by melting and
filtration, are carefully weighed into a flask fitted with vertical tube. 25 c.c.
of standard potash are then added, the mixture heated on the water bath to
gentle boiling, with occasional agitation, until a. perfectly clear solution is
obtained. Koettstorfer recommends heating for fifteen minutes ; but in
the case of butters this is generally more than sufficient ; with other
fats twenty minutes to half an hour may be required. At the end of the
saponification the flasks are removed from the bath, a definite and not too
small a quantity of phenolphthalein added, and the titration carried out with
as little exposure to the air as is possible.

The method of calculation adopted by Koettstorfer is to
ascertain the number of milligrams of KHO required to saturate
the acids contained in 1 gm. of fat, or, in other words, parts
per 1000. He found that, operating in this way, pure butters
required from 221*5 to 232 '4 m.gm. of KHO for 1 gm., whereas
the fats usually mixed with butter, such as beef, mutton, and pork
fat, required a maximum of 197 m.gm. for 1 gm., and other oils
and fats much less.

Practically this means that the amount of KHO required for
genuine butters ranges from 23*24 to 22'15 per cent., the latter
being the inferior limit. If caustic soda is used instead of potash,
other numbers must of course be used.

My experience, and, I believe, also that of others, shows that
the method cannot be depended upon in the case of old re-melted
butters, although perfectly genuine.

The following list shows the parts of KHO required per 1000
of fat ; the first four being calculated from their known equivalents,
the rest obtained experimentally by Koettstorfer, Allen,
Stoddart, or Archbutt: —

Tripalinitin 208'8 Linseed - 189 — 195

Tristearin - - - 189 1 Cotton Seed - - 191—196

Trioleiii - - - 190'4 Whale - - - 190—191

Tributyr-in - - - 557'3 Seal - 191—196

Cocoamit Oil - - 270-0 Colza and Rape - - 175—179

Dripping - - - 197'0 Cod Oil 182—187

Lard - 195'6 Pilchard - - - 186—187

Horse Fat - - - 199'4 Castor - - - 176—178

Lard Oil - - - 191—196 Sperm - - - 130—134

Olive Oil - - - 191—196 Shark 84'5

Niger Oil - - - 189—191

A further application of this method may be made in estimating
separately the amounts of alkali required for saturating the free
fatty acids and saponifying the neutral glycerides or other ethers
of any given sample of fat, oil, or wax (see Allen^ Organic
Analysis ii. 45, 76),

358 VOLUMETRIC ANALYSIS. § 83.

Titration of Miscellaneous Oils and Fats with Bromine or Iodine.

The best method of carrying out this examination as regards
bromine, appears to be that of Mills and Snodgrass, to which
reference has previously been made. The idea of using bromine
is by no means new. Cailletet in 1857 adopted such a method ;
but the difficulty then, and up to the time when the task was
undertaken by the operators mentioned, was the accurate measure-
ment of the excess of bromine used, and the adaptation of such
a solvent for both the fats and the bromine as would exclude the
presence of water, and the tendency to form substitution products
of variable and unknown character in preference to merely additive
products.

Our knowledge of the exact composition of the great family of
fats and oils is at present limited, and it is not possible to make
this reaction possess any strict chemical valency ; but experiment
has shown that there are certain well-defined fats which absorb
within a very narrow limit the same amount of the halogen under
the same conditions, and hence the method may be made highly
suggestive as to mixtures of various fats whose absorption powers
have been observed.

In the first instance the common solvent used for the fat
and the bromine was carbon disulphide ; but although very good
results were obtained, compared with solvents previously tried by
other operators, there were the drawbacks of its offensive smell,
and .the solutions of bromine in it did not possess much stability.
Finally, Dr. Mills adopted carbon tetrachloride as. the medium
with the happiest effects ; and it was found that the bromide
solution could be preserved for at least three months without
diminution of standard. On the other hand, by using this
medium, there is the necessity of working with greater delicacy,
since the presence of the merest trace of water has more effect in
producing substitution compounds than in the case of the disulphide.
The accurate estimation of the excess of bromine, after the absorp-
tion is complete, is necessarily a matter of great importance ; and
this can be done either by comparison of colour with bromine solu-
tion of known strength (the least effective method) ; or by titration
with thiosulphate, using starch and potassic iodide as the indicator,
which is better. But, best of all, the operators after long research
found that by using j3 naphthol (a substance which is readily and
cheaply obtainable, and which forms in the presence of carbon
tetrachloride a mono-bromo derivative) they could construct
a solution of corresponding strength to the standard bromine, and
thus titrate back in the same way as is commonly practised in
alkalimetry. Very fair results were obtained colorimetrically by
adopting the device of interposing a stratum of pctassic chromate
solution, so as to neutralize the yellow colour produced with
some of the fish oils, and which tended to mask the red colour of

83.

OILS AND FATS.

359

the bromine. Experiments showed that, using a bromine solution
having a mean standard of 0*00644 grn. per c.c., the average
probable error per cent, in a single result, when adopting the colour
method or the thiosulphate and iodine was 0*62, whereas with
/3 naphthol it was reduced to 0*46. But it is hardly necessary to
say that, using such a small portion of material as is absolutely
necessary in order to avoid secondary results, considerable care
and practice are required. The sample of oil or fat must be dried
as completely as possible, by heating and subsequent filtering
through dry scraps of bibulous paper, or through dry double filters,
before being weighed.

Process: O'l to 0'2 gm. of the fat is dissolved in 50 c.c. of the tetra-
chloride and standard bromine added, until at the end of 15 minutes there
is a permanent red colour. If the colorimetric method is used 50 c.c. of
tetrachloride is tinted with standard bromine to correspond. If the iodine
re-action, the solution of brominated material is added to potassic iodide and
starch, and T^ sodic thiosulphate delivered in from a burette till the colour is.
discharged. If, on the other hand, the standard naphthol solution is used,
it is also cautiously added from a burette until the colour is removed. It is
imperative that the operations in all cases be carried on out of direct sunlight.
If the operator is unable to use carbon tetrachloride, the disulphide may be
used; but the solution of bromine in this medium is less stable, and must
be checked more frequently. Somewhat larger portions of oil or fat may
however be used for the analysis.

It may be of service to give some few of the results obtained
by Mills and Snodgrass.

Absorption per cent. —

OILS.

FATS.

WAXES.

Almond (from Beef

35-01

Beeswax -

o-oo

bitter fruit) 26'27

Butter (fresh) -

27-93

Carnauba

33-50

Do. (from sweet) 53'74

Do. (commercial)

25-0

Japan (1)

2-33

Cod - - - 83-00

Butterine Scotch

36-32

Do. (2)

1-53

Nut - - - 30-24

Do. (French) -

39-71

Myrtle -

6-34

Ling Liver - 82'44

Cocoanut -

570

Mustard - - 46' 15

Vaseline -

5-55

Neatsfoot - - 38'33

Stearic Acid

o-oo

Olive - - 60-61

Lard

37-29

Palm - - 35-00

O 1 *' *T.O 4

Seal - - - o7 34
Whale - - 30-92

NIV°ERSITY)

Linseed - - 76'09
Mineral Oil - 30'31

Shale Oil )

according to > 22 to 12

sp. gr. )
Aniline - - 169'8

Turpentine (dry) 236'0

360 VOLUMETRIC ANALYSIS. § 83.'

The same operators determined the percentage absorption by
pure anhydrous turpentine, aniline and olive oil purified by
filtration after long standing at low temperature. The calculated
values are based on the known ratios —

CioHi6 . Bl4 C6H7^ : Br2 and (C3H5) (C18H8302)3 : Br«.

The mean of three estimations each in turpentine and aniline were
236*0 and 169*8 per cent., five estimations in olive oil (triolein)
54 per cent. The percentage by calculation is respectively 235'3,
172, and 54-3.

The Iodine Method. — This has been worked out by Hubl
and others, but is not nearly so expeditious as the method just
described; though, as before stated, it has to a large extent replaced
it, owing mainly to the fact that less trouble is required, and the
reactions involved are less delicate while equally accurate.
• The Standard Iodine Solution. — This is made by dissolving
respectively 5 gm. of iodine and 6 gm. of mercuric chloride in
separate portions of strongest alcohol, of 100 c.c. each, then mixing
the two liquids, and allowing to stand for 12 hours before taking
the standard with thiosulphate and starch. This solution must
always be standardized before use, and it is advisable not to mix
a large quantity unless, it can be consumed at once.

Process : 0'2 to 0'5 gm. of the fat or oil is dissolved in 10 c.c. of purest
chloroform in a well-stoppered wide-mouthed bottle, and 20 c.c. of the iodine
solution added. After not less than two hours' digestion the mixture
should possess a dark brown tint ; under any circumstances it is necessary
to have a considerable excess of iodine (at least double the amount
absorbed ought to be present), and the digestion should be from six
to eight hours. At tli3 end of that time the liquid is transferred to
a beaker, the bottle rinsed out with some solution of potassic iodide, the
rinsings added to the beaker, then more of the iodide solution added until all
free iodine is dissolved, the whole is then diluted with 150 c.c. of water,
and y^- thiosulphate delivered in till the colour is nearly discharged.
Starch is then added, and the titration finished in the usual way.

If after standing, say two hours, the amount of iodine is insufficient, it is
"best to make a fresh experiment with either less fat or more iodine.

The numbers obtained by Hubl are given in /. S. C. /. iii. 642.

A blank experiment should in every case be made side by side
with the sample, using the same proportions of chloroform and
iodine solution.

Example with pure Lard (E. TT. T. Jones): About 20 drops of the
melted lard were dropped into a carefully weighed dry bottle, the weight of
fat taken, the bottle then placed on the water bath so as to melt the fat, and
then before quite cold the 10 c.c. of chloroform added and mixed. "When
quite cold 20 c.c. of the iodine mixture were measured in and the whole
allowed to stand the required time. The thiosulphate was not of strict f^-
strength, but a careful titration showed that each c.c. =0'0127678 gm. 1.
The amount of fat taken was 0'5C6 gm., and after digestion with 20 c.c. of
the Hubl solution required 9'4 c.c. of thiosulphate. The 20 c.c. of Hubl

§ 83. OILS AND FATS. 361

originally required 35'6 c.c. of thiosulphate, hence 35'6 — 9'4 — 26*2 x

-I ,\r\

O'O 127678 x ~- ^ = 59'1 % of iodine.
O'obb

Allen states that, in both the bromine and iodine methods of
titration, the amount of halogen taken up may be considered as
a measure of the unsaturated fatty acids (or their glycerides)
present. Thus, the acids of the acetic or stearic series exhibit no
tendency to combine with bromine or iodine under the conditions
of the experiments, while the acids of the acrylic or oleic series
assimilate two, and the acids of the linoleic series four atoms of
the halogen.

We are indebted to K. T. Thompson and H. Ballantyne
(/. S. C. I. ix. 588) for a very careful revision of the constants
required in the analysis of Oils and Fats, the results of which are
given in the following table.""" The lards operated upon were
rendered by themselves and are therefore genuine. The fact is
brought out that for each O'l increase in specific gravity, there is
an increase of 1 '3 per cent, of iodine absorption, and beef fat seems
to follow the same rule. Cotton seed oil shows only about half
that proportion.

In using the iodine absorption method these operators found
that some oils required fully eight hours for complete absorption,
and they recommend, as a rule, to start the digestion in the evening
and titrate the solutions on the following morning.

* Since the figures in the following table were published, the authors have revised
them by further experiments (.T. £>. o'. JT. x. 233), and compared them with results
obtained by other chemists. The conclusion is that in the case of Olive oils, the
figures may vary for iodine absorption from 79 % in Gioja to 88'9 in Mogadore oil;
slight variations also occur in the potash neutralizing power, the numbers being
generally too low.

362 VOLUMETRIC ANALYSIS. § S3.

Table of Constants in the Analysis of Oils.

Nature of Oil or Fat.

Sp. Gr.
at 15-5° C.

Sp. Gr.
at 99J C.

Iodine
Absorptn.

KOH

Neutrlizd.

Free Acid.

per cent.

Olive (Gioja)

915-6

—

79-0

19-07

9-42

Olive (Gioja) after re-

moval of free acid ...

915-2

—

79-0

19-07

None.

Olive

914-8

_'_

83-2

18-93

3-86

'Olive

9147

80-0

23-78

Olive

916'8

___

83'1

19-00

5'19

Olive

916-0

81-6

19-83

Olive (for dyeing)

915-4

—

78-9

19-00

9-67

Olive

914-5

—

86-4

18-90

11-28

Olive (for cooking)

915-1

—

83-1

19-20

4-15

Olive (for cooking)

916-2

—

81-2

1921

Not done

Lard (from omentum) ...

—

859-8

52-1

—

Lard (from leg)

—

860-5

61-3

—

Lard (from ribs)

—

860-6

62-5

—

Beef fat (from suet) ...

—

857-2

34-0

—

Beef fat (oleomargarine)

—

858-2

462

—

Pat from marrow of ox...

—

858'5

45-1

19-70

—

Fat from bone of ox ...

859-2

47'0

19-77

—

Cotton seed

923-6

8C8-4

110-1

—

Cotton seed

922-5

. .

106-8

19-35

027

Linseed (Baltic)

934-5

—

187-7

19-28

—

Linseed (East India) ...

931-5

—

178-8

19-28

—

Linseed (Eiver Plate) ...

932-5

—

175*5

19-07

—

Linseed

932-5

173-5

19-00

0'76

Linseed

931-2

168-0

19-00

Rape

916-8

105-6

17-53

243

Rape

913-1

100'7

17-33

. .

Rape

914"5

104'1

17-06

2-53

Rape

915-0

104-5

17-19

3-10

Rape

914-1

—

100-5

17-39

—

Castor (commercial)

967-9

—

83-6

18-02

2-16

Castor (commercial)

965-3

—

17*86

—

Castor (medicinal)

963-7

—

17-71

—

Arachis (commercial) ...

920-9

—

987

1921

6-20

Arachis (French refined)

917-1

—

98-4

IS'93

0-62

Lard oil (prime)

917-0

—

76-2

—

Southern sperm

880-8

—

81-3

13-25

— •

Arctic sperm (bottle-nose)

879-9

— .

82-1

13-04

—

Whale (crude Norwegian)

920-8

—

109-2

—

Whale (pale)

919-3

—

110-1

—

Seal (Norwegian)

925-8

—

152-1

—

Seal (cold drawn, pale) . . .

926-1

—

145-8

19-28

—

Seal (steamed, pale)

924-4

—

142-2

18-93

—

Seal (tinged)

925-7

—

152-4

—

Seal (boiled)

923-7

—

142-8

—

Menhaden

931-1

160-0

18-93

—

Newfoundland cod

924-9

1600

—

Scotch cod

925-0

—

158-7

—

Cod liver (medicinal) . . .

926-5

—

166-6

18-51

0-36

Mineral ,.

873-6

—

12-8

- — •

—

Mineral

886-0

—

26-1

—

Rosin

986-0

—

67-9

—

§ 8-4. GLYCERIN. 365

GLYCERIN (GL.YCEROL,).

C:JH803 = 92.

§ 84. UP to a very recent time no satisfactory method of
determining glycerin had been devised, but the problem has now
been solved in a tolerably satisfactory manner. The permanganate
method appears to have been originally suggested by Wanklyn,
improved by him and Fox, and further elaborated by Eenedikt
and Zsigmondy (CJiem. Zeit. ix. 975). It depends on the
saponification of the fat, and oxidation of the resultant glycerin
by permanganate in alkaline solution, with formation of oxalic
acid, carbon dioxide, and water, thus —

C3H808 + 302 = C2H204 + CO2 + 3H20.

Aqueous solutions of glycerin may of course be submitted to
the method very easily.

The excess of permanganate is destroyed by a sulphite, the
liquid filtered from the manganese precipitate, the oxalic acid then
precipitated by a soluble calcium salt in acetic solution, and the
precipitated calcic oxalate, after ignition to convert it into carbonate,
titrated with standard acid in the usual way, or the oxalic
precipitate titrated with permanganate. The oxalic solution may be
titrated direct after addition of H'2S04 with permanganate ; but
Allen and Belcher have found this method faulty, probably
from the formation of a dithionate, due to the sulphite. On the
other hand, they have obtained very satisfactory results by the
alkalimetric or the permanganate titration, on known weights of
pure oxalic acid and glycerin.

These operators have also shown that, in the case of dealing with
fats, where it has been recommended by Wanklyn and Fox to
use ordinary alcohol as the solvent, and by Benedikt methyl
alcohol, both these media, especially ethylic alcohol, produce in
themselves a variable quantity of oxalic acid when treated with
alkaline permanganate, and hence vitiate the process. Again, if it
be attempted to avoid this by boiling off the alcohols, there is
a danger of losing glycerin.*

Allen's method with oils and fats is as follows : —

10 gm. of the fat or oil are placed in a strong small bottle, together with
4 gm. of pure KH.O dissolved in 25 c.c¥. of water. A solid rubber stopper is
then used to close the bottle, and tied down firmly with wire. It is then
placed in boiling water, or in a water oven, and heated, with occasional
shaking, from 6 to 10 hours, or until the contents are homogeneous, and all
oil}" globules have disappeared. "When saponification is complete, the bottle
is emptied into a beaker and diluted with hot water which should give a clear
solution, the fatty acids are then separated by dilute acid, filtered, and the
filtrate made up to a given volume.

* In dealing- with waxes or similar bodies including1 sperm oil, potash dissolved in
methyl alcohol must be used for the saponitication, as it is almost impossible to do it
with aqueous potash.

364 VOLUMETRIC ANALYSIS. § 84.

This solution, which will usually contain from 0'2 to 0'5 of glycerol,
according to its origin, is transferred to a porcelain basin and diluted with
cold water to about 400 c c. From 10 to 12 gm. of caustic potash should
next be added, and then a saturated aqueous solution of potassic permanganate
until the liquid' is no longer green but blue or blackish. An excess does no
harm. The liquid is then heated and boiled for about an hour, when a strong
solution of sodic sulphite should be added to the boiling liquid until all
violet or green colour is destroyed. The liquid containing the precipitated
oxide of manganese is then poured into a 500 c.c. flask, and hot water
added to 15 c.c. above the mark, the excess being an allowance for the
volume of the precipitate and for the increased measure of the hot liquid.
The solution is then passed through a dry filter, and, when cool, 400 c.c. of
the filtrate should be measured off, acidified with acetic acid, and precipitated
with calcic chloride. The solution is kept warm for three hours, or until
the deposition of the calcic oxalate is complete, and is then filtered, the
precipitate being washed with hot water. The precipitate consists mainly of
calcic oxalate, but is liable to be contaminated more or less with calcic;
sulphate, silicate, and other impurities, and hence should not be directly
weighed. It may be ignited, and the amount of oxalate previously present
deduced from the volume of normal acid neutralized by the residual calcic,
carbonate, but a preferable plan is to titrate the oxalate by standard
permanganate. For this purpose, the filter should be pierced and the
precipitate rinsed into a porcelain basin. The neck of the funnel is then
plugged, and the filter filled with dilute sulphuric acid. After standing
for five or ten minutes this is allowed to run into the basin and the filter
washed with water. Acid is added to the contents of the basin in quantity
sufficient to bring the total amount used to 10 c.c. of concentrated acid, the
liquid diluted to about 200 c.c., brought to a temperature of about 60° C.,
and decinormal permanganate added gradually till a distinct pink colouration
remains after stirring. Each c.c. of permanganate used corresponds to
O'0045 gm. of anhydrous oxalic acid, or to 0'004y gm. of gl.ycerin. Operating
in the way described, the volume of permanganate solution required will
generally range between 70 and 100 c.c.

C. Mangold '(Zeit. f. angew. Chem. 1891, p. 400) advocates
the reduction of the excess of permanganate by hydrogen peroxide
in preference to sodic sulphite as used by Allen. The author
simplifies the method by carrying out the oxidation in the cold.

Process : 0'2 to 0'4 gm. of glycerin is dissolved in about 300 c.c. of water,
10 gm. potassic hydrate and so much 5 per cent, solution of permanganate
is added, that for each part of glycerin about seven parts of permanganate
are present. The mixture is allowed to stand at ordinary temperature for
half an hour. Hydrogen peroxide is then added until the liquid is
colourless, well shaken, filled up to one liter, 500 c.c. are filtered off through
a dry filter, boiled for half an hour to destro}r the excess of peroxide,
allowed to cool to about 80° C., and after acidulation with dilute sulphuric
acid, the oxalic acid titrated with standard permanganate.

Otto Hehner has experimented largely on the estimation of
glycerol in soap leys and crude glycerins, the results of which are
given in /. S. C. I. viii. 4. The volumetric methods recommended
in preference to the permanganate are the oxidation Avith potassic
bichromate or the conversion of the glycerol into triacetin.

The Bichromate Method.: — One part of glycerol is completely

§ 84 GLYCERIN. 365

converted into carbonic acid by 7 '486 parts of bichromate in the
presence of sulphuric acid. The solutions required are : —

Standard Potassic bichromate. — 74*86 gm. of pure potassic
bichromate is dissolved in water. 1 50 c.c. of concentrated sulphuric
acid added, and when cold diluted to a liter. 1 c.c. =0'01 gm.
glycerol.

A weaker solution is also made by diluting 100 c.c. of the strong
solution to a liter.

These solutions should be controlled by a ferrous solution
of known strength, if there is any doubt about the purity of the
bichromate.

Solution of double Iron salt. — 240 gm. of ferrous ammonium
sulphate is dissolved with 50 c.c. of concentrated sulphuric acid to
a liter, and its relation to the standard bichromate must be
accurately found from time to time by titration with the latter,
using the ferricyanide indicator (§ 37, p. 127).

Process : With concentrated or tolerably pure samples of glycerin it is
only necessary to take a small weighed portion, say 0'2 gm. or so, dilute
moderately, add 10 or 15 c.c. of concentrated sulphuric acid and 30 or 40 c.c.
of the stronger bichromate, place the beaker covered with a watch glass in
a water bath and digest for two hours; the excess of bichromate is then
found by titration with the standard iron solution. The weaker bichromate
is useful in completing the titration where accuracy is required. As the
stronger bichromate and the iron solution are both concentrated, they must
be used at a- temperature as near 16° C. as possible. In the case of crude
glycerin it must be purified from chlorine or aldehyde compounds as
follows: — About 1"5 gm. of the diluted sample is placed in a 100 c.c. flask,
some moist silver oxide added, and allowed to stand 10 minutes. Basic lead
acetate i's then added in slight excess, the measure made up to 100 c.c.,
filtered through a dry filter, and 25 c.c. or so digested with excess of
bichromate, and titrated as before described.

The Acetin Method. — This method is due to Benedikt and
Cantor (Monatsheft ix. 521), and recommends itself by its
simplicity and rapidity as compared with other methods. Hehner
lias pointed out the precautions necessary to insure accuracy as
follows : —

Procfss : About 1'5 gm. of the crude glycerin is placed in a round-
bottomed flask, together with 7 gm. of acetic anhydride and 3 gm. of
perfectly anhydrous sodic acetate; an upright condenser is attached to the
flask, and the contents are heated to gentle boiling for one hour and a half.
After cooling, 50 c.c. of water are added, and the mixture heated until all
triacetin has dissolved. The solution is then filtered into a large flask, the
residue or filter well washed, the liquid cooled, some phenolphthalein added,
and the acidity exactly neutralized by a dilute solution of caustic soda. The
triacetin is then saponified by adding 25 c.c. of an approximately 10 per
cent, solution of pure caustic soda standardized on normal sulphuric or
hydrochloric acid, and boiling for 10 minutes, taking care to attach a reflux
condenser to the flask. The excess of alkali is then titrated back with
normal acid, each c.c. of which represents 0'03067 gm. of glycerin.

It is essential that the processes of analysis should be rapid and
continuous, and especially that the free acetic acid in the first process be,-

-"366 VOLUMETRIC ANALYSIS. § 85.

.neutralized very cautiously, and with constant agitation to avoid the local
action of alkali.

Weak soap lyes should be concentrated to 50 per cent, of
glycerin if estimated by the acetin method ; if not the bichromate
method must be used.

For fats and soaps about 3 gm. should be saponified with
alcoholic potash, diluted with 200 c.c. of water, the fatty acids
.-separated and filtered off. The filtrate and washings are then
.rapidly boiled to one-half and titrated with bichromate.

PHENOL, (CARBOLIC ACID).

C6H5OH=94.

§ 85. THE only method claiming accuracy for the estimation of
rthis substance volumetrically was originated' by Ivoppeschaar
(Z. a. C. xvi. 233), and consists in precipitating the phenol from
dts aqueous or dilute alcoholic solution with bromine water in the
form of tribromphenol.

The strength of the bromine water was established by
IKoppeschaar, by titratioii with thiosulphate and potassic iodide
with starch.

Allen modifies the process as follows : —

A certain weight of the sample is dissolved in water: as much as
corresponds to O'l gm. of phenol is taken out and put into a stoppered bottle

^holding 250 c.c. Further, to 7 c.c. of normal soda solution ( = 0'04 gm.
TsaOH per c.c.) bromine is gradually added till a yellow colour appears and

•remains ; the liquid is then boiled till it has become colourless again. It
now contains 5 molecules of sodic bromide and 1 of sodic bromate. When
completely cooled, it is put into the phenol solution, after which 5 c.c. con-
centrated hydrochloric acid are at once added, and the bottle stoppered and

•shaken for some time. The reactions are : —

II. CliH(iO + 6Br - C6H3Br3O + 3HBr.

The bromine set free in the first, and not fixed by phenol in the second
reaction, must be still free, and is estimated by adding potassic iodide and
titrating the iodine liberated, by -*$ thiosulphate : —

III. 2KI + Br2 = 2KBr+2L

IV. F+2Na2S203 = Na2S406+2NaI.

For this purpose the bottle is allowed to stand for 15 or 20 minutes ;

: a solution of about 1'25 gm. potassic iodide (free from iodate) is added, the
bottle is stoppered, shaken up, and allowed to rest. Its contents are now
poured into a beaker ; the bottle is rinsed out, a little starch solution is added,

- and thiosulphate is run in from a burette till the blue colour is gone. (It
will be best not to add the starch till the colour of the liquid has diminished
to light yellow.) The calculation is made as follows : — 7 c.c. of normal soda
solution neutralize 0'56 gm. of bromine, all of which is liberated by HC1.
O'l gm. phenol would require 0'4068 and leave a surplus of 0'1532 gm. ; the
latter would liberate enough iodine to saturate 19'5 c.c. of ^ thiosulphate.
Every c.c. of thiosulphate used over and above this indicates 0'00197 gm.

:, impurities in O'l gm. of the sample— that is, T27 per cent.

§ 86. CARBON BISULPHIDE. 367

If a number of estimations liave to be made at one time, it
would seem decidedly preferable to adopt Koppeschaar's original
method, rather than to prepare special bromine solution as above.
For the estimation of phenol in raw products, Toth (Z. a. C.
xxv. 160) modifies the bromine process as follows : —

20 c.c. of the impure carbolic acid are placed in a beaker with 20 c.c. of
caustic potash solution of 1/3 sp. gr., well shaken, and allowed to stand for
half an hour, then diluted to about i liter with water. By this treatment
the foreign impurities are set free, and may mostly be removed by filtration ;
the filter is washed with warm water, until all alkali is removed. The
filtrate and washings are acidulated slightly with HC1, and diluted to 3 liters.
50 c.c. are then mixed with 150 c.c. of standard bromine solution, and then
5 c.c. concentrated HC1. After twenty minutes, with frequent shaking,
10 c.c. of iodide solution are added, mixed, and allowed to rest three to five
minutes, then starch, and the titration with thiosulphate carried out as usual.

Example : 20 c.c. raw carbolic oil were treated as above described. 50 c.c.
of the solution, with 150 c.c. bromine solution (made by dissolving 2'04 gin.
sodic bromate and 6'959 gm. sodic bromide to the liter), then 5 c.c. of HC1,
required 17'8 c.c. of thiosulphate for titration. The 150 c.c. bromide
= 0'237 gm. Br. The 17'8 c.c. thiosulphate required for residual titration
= 0'052 gm. Br, leaving 0'185 gm. Br for combination with the phenol.
According to the equation —

2^ 3HBr+CGH2OHBrl

One mol. phenol = 3 mol. Br, hence the percentage of phenol was 10'86.

Ivle inert (Zt. a. C. xxxiii. 1) suggests, and his experiments
appear to prove, that in titrating acid creosote oil by Koppeschaar's
method for phenol, a serious error occurs in virtue of such oil
containing substances of higher boiling-point than phenol, which
are soluble in water, and behave with bromine in the same manner
as true phenol.

Meissinger and Wortmann (Pharm. Z&it. f. Russland
xxix. 759) describe a method of estimating phenol based on the
fact, that iodine combines with phenol in alkaline solution, in
the proportion of 6 atoms I to 1 mol. phenol.

Process : 2 to 3 gm. phenol are dissolved in caustic soda solution (3 eq.
NaHO to 1 eq. phenol) and made up to 500 c.c. with water; 10 c.c. of t,his
are placed in a flask, warmed to 60° C., and /^ iodine added until the solution
is faintly yellow, with formation of a red precipitate. When cold, the
solution is acidified with dilute H2SO4, made up to 500 c.o. and filtered. In
100 c.c. of the filtrate, the excess of I is titrated with ^ thiosulphate ; this
amount, deducted from the total I used, gives the amount absorbed by
phenol, which, when multiplied by 0'123518, gives amount of phenol in the
sample.

CARBON DISU-LPHIDE AND THIOCABBONATES.

CS2=76.

§ 86. FOR the purpose of estimating carbon disulphide in
the air of soils, gases, or in thiocarbonates, Gas tine has devised
the following process (Oompt. Rend, xcviii. 1588) : —

368 VOLUMETRIC ANALYSIS. § 86.

The gas or vapour to be tested is carefully dried, and then passed through
a concentrated solution of recently fused potassic hydroxide in absolute
alcohol. The presence of even traces of water seriously diminishes the
delicacy of the reaction. The alcoholic solution is afterwards neutralized
with acetic acid, diluted with water, and tested for xanthic acid by adding
copper sulphate.

In order to determine the distribution of carbon bisulphide introduced
into the soil, 250 c.c. of the air in the soil is drawn by means of an aspirator
through sulphuric acid, and then through bulbs containing the alcoholic
potash. For quantitative determinations, a larger quantity of air must be
used, and the xanthic acid formed is estimated by means of the reaction
2C3HGOS2+I2 = 2C3H5OS2 + 2HI. The alkaline solution is slightly acidified
with acetic acid, mixed with excess of sodic bicarbonate, and titrated in the
usual way with a solution of iodine containing T68 gm. per liter, 1 c.c. of
which is equivalent to 1 m.gm. of carbon bisulphide.

To apply this method to thiocarbonates, about 1 gm. of the substance,
together with about 10 c.c. of water, is introduced into a small flask and
decomposed by a solution of zinc or copper sulphate, the flask being heated
on a water bath, and the evolved carbon bisulphide passed, first through
sulphuric acid, and then into alcoholic potash. In the case of gaseous
mixtures of carbon bisulphide, nitrogen, hydrogen sulphide, carbonic
anhydride, carbonic oxide, and water-vapour, the gas is passed through
a strong aqueous solution of potash, then into sulphuric acid, and finally into
alcoholic potash. The thiocarbonate formed in the first flask is decomposed
by treatment with copper or zinc sulphate as above, and the xanthic acid
obtained is added to that formed in the third flask, and the whole titrated
with iodine.

Another method available for technical purposes, such as the
comparative estimation of CS2 in coal gas, or in comparing
samples of thiocarbonates, is as follows : —

The liquid or other substance containing the disulphido is added to
strong alcoholic potash, or gas containing the CS2 is passed slowly through
the alkaline absorbent. The disulphide unites with the potassic ethylate to
form potassic xanthate. The liquid is neutralized with acetic acid and the
xanthate is then estimated by titrating with a standard solution of cupric
sulphate (12'47 gm. per liter), until an excess of copper is found by potassic
ferroc3ranide used as an external indicator. Each c.c. of copper solution
represents 0'0076 gm. CS2.

BORIC AND ARSENIC ACIDS. 309

APPENDIX TO PART V.

Addition to § 22.

Boric Acid in Milk. — R. T. Thomson (Glasgow City Anal. Soc.
Repts., 1895, p. 3). One to two gm. of sodic hydrate are added to
100 c.c. of milk, and the whole evaporated to dryness in a platinum
dish. The residue is thoroughly charred, heated with 20 c.c. of
water, and hydrochloric acid added drop by drop until all but the
carbon is dissolved. The whole is transferred to a 100 c.c. flask,
the bulk not being allowed to get above 50 or 60 c.c., and 0'5 gm.
dry calcium chloride added. To this mixture a few drops of
phenolphthalein solution are added, then a 10 per cent, solution of
caustic soda, till a permanent slight pink colour is perceptible, and
finally 25 c.c. of lime-water. In this way all the P205 is
precipitated as calcic phosphate. The mixture is made up to 100
c.c., thoroughly mixed and filtered through a dry filter. To 50 c.c.
of the nitrate (equal to 50 gm. of the milk) normal sulphuric acid
is added till the pink colour is gone, then methyl orange, and the
addition of the acid continued until the yellow is just changed to
pink. £ caustic soda is now added till the liquid assumes the
yellow tinge, excess of soda being avoided. At this stage all acids
likely to be present exist as salts neutral to phenolphthalein, except
boric acid (which, being neutral to methyl orange, exists in the
free condition), and a little carbonic acid, which is expelled by
boiling for a few minutes. The solution is cooled, a little
phenolphthalein added, and as much glycerin as will give at least
30 per cent, of that substance in the solution, and titrated with -J
caustic soda till a distinct permanent pink colour is produced ; each
c.c. of the soda is equal to 0*0124 gm. crystallized boric acid.
A series of experiments with this process showed that no boric
acid was precipitated along with the phosphate of lime so long as
the solution operated upon did not contain more than 0'2 per cent,
of crystallized boric acid, but when stronger solutions were tested,
irregular results were obtained. The charring of the milk is apt
to drive off boric acid, but by carefully carrying the incineration
only so far as is necessary to secure a residue which will yield
.a colourless solution, no appreciable loss occurs.

Addition to § 47.

The Estimation of Arsenic Acid in Arsenates. — A. Williamson
•(Journal of the Society of Dyers and Colourists, May, 1896) has
devised the following ready method as being applicable to
•commercial arsenates, and has made use of the reaction which
takes place between arsenic and hydriodic acids in strong acid

B B

370 VOLUMETRIC ANALYSIS.

solution. Under these circumstances arsenic acid is quantitatively
reduced with liberation of iodine. The reaction is

As205 + 4HI = As208 + 2H20 + 41.

It was found that the reduction is only complete in strongly acid
solution, and if such a solution be diluted the reverse reaction
takes place to a certain extent, a portion of the arsenious becoming
oxidized to arsenic acid. The iodine may, however, be estimated
before dilution, by means of thiosulphate, and in the absence of
other bodies capable of liberating iodine it may be taken as
a measure of the arsenic acid. The acid solution may then be
neutralized, and the arsenite titrated with iodine. This serves as
a check on the thiosulphate titration.

The reduction may be effected either in hydrochloric or sulphuric
acid solution, but in either case a considerable excess of acid must
be present, otherwise the reduction is incomplete.

Example: A. standard solution of arsenate of soda was prepared by
oxidizing 4'95 gm. of arsenious oxide with nitric acid, evaporating to dryness
on the water bath, neutralizing with sodic carbonate, and diluting to one
liter. 25 c.c. of this standard were then treated with 3 gra. potassic iodide
and 25 c.c. of hydrochloric acid, sp. gr. 1*16, and the liberated iodine titrated
with thiosulphate.*

The decolorized solution was then neutralized with sodic carbonate, and
after the addition of bicarbonate, was titrated with iodine. The arsenic
acid calculated from the thiosulphate was 99'6, and from the iodine 100'2,
instead of 100. To ensure complete reduction in the cold, the solution must
contain one-half its volume of hydrochloric acid and the quantity of potassic
iodide- mentioned. With less quantities than these, there is a danger of the
reduction not being immediately complete. The amount of thiosulphate
consumed agrees very well with the arsenite found in the neutralized
solution by titration with iodine.

As commercial sodic arsenate usually contains some nitrate,
experiments were made to ascertain whether the presence of this
salt interferes with the accuracy of the thiosulphate titration.
A pure solution of arsenate was prepared as before, and 1 gm. of
sodic nitrate added. 25 c.c. of this solution were then treated
with potassic iodide and hydrochloric acid, and the iodine titrated
with thiosulphate, as before. The arsenic acid calculated from the
thiosulphate consumed was 100*3, instead of 100. It is evident
that the presence of nitrate causes little or no liberation of iodine
in the cold, but if the arsenate is digested with hydrochloric acid
and potassic iodide in a closed bottle immersed in boiling water,
the iodine liberated is considerably in excess of that corresponding

* A brown precipitate falls on adding this quantity of acid, but it dissolves as the
solution becomes diluted by titration with thiosulphate. The amount of thiosulphate
required to decolorize the small quantity of iodine liberated by mixing the same weight
of potassium iodide and hydrochloric acid under the same conditions was subtracted.
It is advisable not to have the solution of arsenate stronger than decinormal, or the
dilution consequent on titrating with thiosulphate may cause the reverse reaction to
take place to a slight extent, and the result would come out too low. The solution
should be quite cold before titrating the iodine.

AKSENATES. 371

to the arsenic acid. In this case, the quantity of thiosulphate
consumed is of no value. The arsenic can, however, be accurately
estimated by titrating the arsenite after the iodine has been
decolorized.

Instead of hydrochloric acid, 15 c.c. of a mixture of sulphuric
acid and water, in equal volumes, may be used. Since the
addition of sulphuric acid causes the solution to become slightly
heated, it is cooled before titrating the iodine. The results are
practically the same as with hydrochloric acid.

Xot less than 3 gm. potassic iodide should be added, or complete
reduction is not immediately effected. The presence of small
quantities of nitrate does not interfere with the accuracy of the
thiosulphate titration. Complete reduction can be brought about
with 2 gm. potassic iodide and 10 c.c. of sulphuric acid, if the
solution is heated for five minutes on the steam bath. A portion
of the iodine volatilizes, but no arsenic is lost. The iodine is
exactly decolorized with thiosulphate, the solution neutralized and
titrated with iodine in the ordinary manner.

Process with Commercial Arsenate of Soda : 10 gm. are dissolved to 1
liter, and the arsenic acid in 25 c.c. estimated by one of the methods given
above. The thiosulphate titration only records the arsenic previously
existing as arsenic acid. The small proportion of As2O3 which usually exists
is ascertained by direct titration. When this is calculated to arsenic acid, and
added to that found by thiosulphate, the results approximate very closely to
those found by titrating the arsenite.

Estimation of Arsenic in presence of Tin. — If both these elements
are present in the lower state of oxidation, the tin may be oxidized
with iodine in strong acid solution, the arsenic being unaffected.
Rochelle salt is then added, the solution neutralized, and the
arsenite titrated with iodine.

Example: 25 c.c. of -*-$ sodic arsenite were mixed with 25 c.c. of hydro-
chloric acid, and 3 gm. stannous chloride added. The tin was then exactly
oxidized with standard iodine, and the arsenic titrated in the alkaline
solution, 24'9 c.c. of T^- iodine were required.

If they are present in the highest state of oxidation, the arsenic
may be reduced by one of the methods given under the estimation
of arsenic acid. The stannic salt is not affected.

It is thus possible to estimate the arsenic in a mixture of
arsenate and stannate of soda. In presence of a considerable
quantity of tin, however, the complete reduction of the arsenic
acid is not effected quite as readily as when tin is absent. The
following method has given good results : — •

4 or 5 gm. of the mixture are dissolved in as small a quantity of HC1 as
possible, an equal weight of tartaric acid is dissolved in the solution, which
is then diluted to 250 c.c. (If the tartaric acid is not added a precipitate
forms on dilution which contains both tin and arsenic). 25 c.c. of this
solution are then mixed with 3 gm. potassic iodide and 25 c.c. HC1, sp. gr.

B B 2

372 VOLUMETFJC ANALYSIS.

1'16, and the solution heated on the steam bath for two or three minutes to
ensure the complete reduction of the arsenic acid. The liberated iodine is
exactly decolorized with thiosulphate, and the arsenic estimated by titration
with iodine in the neutralized solution. A mixture of arsenate and stannate
in equal quantities and containing a known percentage of arsenic gave
28'57 instead of 28'75 per cent, of arsenic acid.

Addition to §§ 54, 55.

Mixtures of Chlorides, Hypochlorites, and Chlorates. — It is
known that chlorine acting upon alkaline and alkaline-earthy
hydrates gives rise to chlorides, and at the same time to chlorates,
or to hypochlorites, according as the temperature and the con-
centration are higher or lower. In average conditions the three
kinds of salts are formed simultaneously.

A mixture of the same salts is produced if solutions of sodic
chloride are submitted to electrolysis, according to the processes
recently tried for the manufacture of free chlorine and of caustic
soda, or of chlorates or hypochlorites.

In these various cases it is of great industrial importance to
determine easily the proportion of each of the salts present.

For the analysis of such a mixture of salts, the subjoined
method is recommended as at once expeditious and accurate. All
the determinations are performed successively upon one and the
same specimen of the saline solution (A. Garnet, Compt. Rend.
cxxii. 449).

Process: 1. The mixture of hypochlorite, chlorate, and chloride taken
from the solution of electrolyzed sodic chloride, or from the liquid obtained
on lixiviating chloride of lime, is poured into a test-glass. There is then run
into it from a burette a standard solution of alkaline arsenite, prepared as
usual, until the bypochlorite is completely reduced. To find the exact
moment when the reduction is completed, a drop of the liquid is placed
upon a porcelain plate in contact with a drop of solution of potassic iodide
and starch.

On the mixture of the two drops there appears a blue colour as long as
there remains any hypochlorite not reduced. As soon as the mixture ceases
to become coloured, the volume of the arsenite liquid is noted, and the
proportion of hypochlorite or hypochlorous acid wrhich has transformed it
into arsenic acid is obtained ; or, consequently, that of the corresponding
chlorine.

As2O3+ CaCl-O2 = As2O5 + CaCl2,
or

As2O3+2NaC10 = As205+2NaCl.

2. The liquid (which now contains merely chlorate and chloride) is
slightly acidified with sulphuric acid, and a quantity of ammonium-ferrous
sulphate added, at least twenty times of that of the supposed chlorates.
Heat to about 100°, adding in small successive quantities 5 c.c. of
sulphuric acid diluted with 15 c.c. of water. It is best to use
a tap-funnel, letting the acid fall in drop by drop. After having stoppered
the vessel, to avoid contact of air, it is allowed to cool for a short time, and
the excess of ferrous salt is then titrated with permanganate. As the
quantity of ferrous salt which was introduced, is known, by difference the

CHLORIDES, HYPOCHLORITES, CHLORATES, NITRATES. 373

quantity which has been peroxidized at the expense of the chlorate reduced
to the state of chloride is found.

NaC103+GFeO = NaCl+Pe-O3.

It is thus easy to calculate the proportion of chlorate or of chloric acid,
or the corresponding quantity of chlorine.

3. The total chlorine, which is now entirely present in the state of
chloride, is determined as follows : — The rose tint produced by the
permanganate is removed by adding a trace of ferrous sulphate, crystallized
or in solution. Then add a measured volume of silver nitrate, more than
enough to precipitate all the chlorine, and determine the excess of the
silver salt by means of standard thiocyanate (§ 43). The ferric salt
previously formed by the peroxidation of the ferrous salt serves as an
indicator, by producing a permanent red colouration as soon as there is no
more silver salt to precipitate. The arsenic acid produced in the first
operation does not interfere in the least.

In order to avoid the use of too large a quantity of silver nitrate, which
would be necessary on account of the large proportion of chlorine to be
precipitated, an aliquot part of the solution may be taken.

The chlorine found in the state of a chloride in the original liquid is
easily calculated by deducting from the total chlorine just determined the
two quantities already found in the state of hypochlorite and of chlorate.

The three operations succeed each other without interruption, and with-
out separate preparation, and are completed in a short time.

In a number of experiments with mixtures, the discrepancies found
between the experimental results and the calculated numbers rarely reached
1 m.gm. when operating upon from 250 to 500 m.gm.

Additions to §§ 54 and 70.

The lodometric Estimation, of Chloric and Nitric Acids. — The
following methods by McGowan (/. G. S. Ixix. 530, and /. C. S.
Ixi. 87) depend on the principle that, when a fairly concentrated
solution of a nitrate or chlorate is warmed with an excess of pure,
strong hydrochloric acid, a nitrate is completely decomposed, and
the production of nitrosyl chloride and chlorine is quantitative,
the reaction being

HXO3 + 3HC1=XOC1 + Cl2 + 2IPO.

If the operation is conducted in an atmosphere of carbonic acid,
and the escaping gases are passed through a solution of potassic
iodide, an amount of iodine is liberated exactly equivalent to the
whole of the chlorine present (free and combined), nitric oxide
escaping. 1 mol. of nitric acid thus yields 3 atoms of chlorine
or iodine. The iodine can then be titrated in the usual manner
with thiosulphate. With chlorates only chlorine is evolved.
De Koninck and Nihoul (Zeit. fiir ancjew. Chem. August 15,
1890) give details of a process depending upon the same principle.

Process for Nitrates. — It is, of course, absolutely essential that air should
be completely excluded from the apparatus, as, if any were present, the
escaping nitric oxide would be re-oxidized to nitrogen trioxide or tetroxide,
and this wrould in its turn liberate a further quantity of iodine from the
iodide solution.

374

VOLUMETRIC ANALYSIS.

The apparatus required is very simple, and can readily be made by any
one moderately expert at glass-blowing. The main point to be attended to
is to have no corks or rubber stoppers, &c., for the escaping chlorine to act
upon. Fig. 53 is a sketch of the apparatus ; the condensing arrangement
for the chlorine does its work perfectly, and may therefore be used Avith
advantage, not only for this, but also for other similar methods in Avhich
iodine is set free. The measurements given are those of the apparatus as
used by the author.

A is a small, round-bottomed flask, into the neck of which a glass stopper,
x, is accurately ground (with fine emery and oil). The capacity of the
bulb is about 46 c.c., and the length of the neck, from x to y, 90 m.in.
The first condenser is a simple tube, slightly enlarged at the foot into two

small bulbs. The length from a to I is 300 m.m., from b to c 180 m.m., and
from e to f 30 m.m. The capacity of the bulb J? is 25 c.c., and the total
capacity of the two bulbs and tube, up to the top of C, 41 c.c. This
condenser is immersed, up to the le\rel of c, in a beaker of Avater. D is
a Geissler bulb apparatus, and E a chloride of calcium tube, filled with
broken glass, Avhich acts as a tower, g is a small funnel, attached by rubber
and clip to the branch tube li. Between the tube i and the Avash-bottle
for the carbonic acid is placed a short piece of glass tubing, *. containing
a strip of filter paper, slightly moistened with iodide of starch solution.
This tube s is really hardly necessary, as no chlorine escapes backAvards
if a moderate current of carbonic acid is kept passing, but it serves as
a check. The joints p and q are of narroAV rubber tubing. The joint o
is made by grinding one tube into the other, k is the outlet tuba.

The operation is performed in the following manner: — The evolution
flask is Avashed and thoroughly dried, and the nitrate (say about 0'25 gin.
of potassic nitrate) is tapped into it from the weighing tube. 1 to 2 c.c.

NITRATES AND CHLORATES. 375

of water are now added, and the bulb is gently warmed, so as to bring the
nitrate into solution, after which the stopper of the flask is firmly inserted
into it. About 15 c.c., or so, of a solution of potassic iodide (1 in 4) are
run into the first condensing tube, any iodide adhering to the upper portion
of the tube being washed down with a little water, and 5 c.c. of the same
solution, mixed with 8 to 10 c.c. of water, are sucked into the Geissler
bulbs, whilst the glass in tower E is also thoroughly moistened with the
iodide. The Geissler bulbs should be so arranged that gas only bubbles
through the last of them, the liquid in the others remaining quiescent.

All the joints having been made tight, the CO2 is turned on briskly, and
passed through the apparatus until a small tubeful collected at I, over caustic
potash solution, shows that no appreciable amount of air is left in it. The
small outlet tube I is now replaced by a chloride of calcium tube, filled with
broken glass which has been moistened with the above iodide solution, and
closed by a cork through which an outlet tube passes, the object of this
"trap" tube being to prevent any air getting back into the apparatus;
and the brisk current of CO- is continued for a minute or two longer, so
as to practically expel all the air from this last tube. The stream of gas is
now stopped for an instant, and about 15 c.c. of pure concentrated hydro-
chloric acid, free from chlorine, run into A through the funnel g (into the
tube of which it is well to have run a few drops of water before beginning to
expel the air from the apparatus), and A is shaken so as to mix its contents
thorouglil}'. A slow current of CO- is now again turned on (1 to 2 bubbles
through the wash-bottle per second), and A is gently warmed over a burner.
It is a distinct advantage that the reaction does not begin until the mixed
solutions are warmed, when the liquid becomes orange-coloured, the colour
again disappearing after the nitrosyl chloride and chlorine have been expelled.
The warming should be very gentle at first, in order to make sure of the
conversion of all the nitric acid, and also because the first escaping vapours
are relatively very rich in chlorine ; afterwards the liquid in A is briskly
boiled. A very little practice enables the operator to judge as to the proper
rate of warming. When the volume of liquid in A has been reduced to
about 7 c.c., or so (by which time it is again colourless), the stream of CO2
is slightly quickened, and the apparatus allowed to cool down a little. The
burner is now set aside for a few minutes, and 2 c.c., or so, more of hydro-
chloric acid, previously warmed in a test-tube, run in gently through <j ;
there is no fear either of the iodide solution running back, or of any bubbles
of air escaping through y, if this is done carefully. This is a precautionary
measure, in case a trace of the liberated chlorine might have lodged in the
comparatively cool liquid in tube li. The CO2 is once more turned on
slowly, and the liquid in A is boiled again until it is reduced to about 5 c.c.
It is now only necessary to allow the apparatus to cool down, passing CO2
all the time, after which the contents of the condensers are transferred to
a flask and titrated with thiosulphate. At the end of a properly conducted
experiment, the glass in the upper part of tower E should be quite colourless,
and there should only be a mere trace of iodine showing in the lower part
of the tower, while the liquid in the last bulb of the Geissler apparatus
ought to be only pale yellow. During the operation, the stopper of A and
the various joints can be tested for tightness from time to time by means
of a piece of iodide of starch paper, and, before disjointing, it is well to
test the escaping gas (say, at m) in the same wa}*, to make sure that all
nitric oxide has been thoroughly expelled.

Example: 0'2627 gm. of pure KNO3 was taken. The liberated iodine
required 38'56 c.c. of thiosulphate (of which 1 c.c. =0*003805 gm. KNO3)
for conversion. This gave 0'2624 gm. nitrate found, or 99'89 per cent.

Process for Chlorates. — The apparatus employed is the same as for nitrates,
but since it is unnecessary in this estimation to previously expel the air

376 VOLUMETRIC ANALYSTS.

present by a current of CO2, those tubes which come after the tower E are
dispensed with. The details of the operation are also practically the same
as in the case of a nitrate, only simpler. Comparatively dilute hydrochloric
acid may be employed, and the CO' is required merely to ensure a regular
passage of the vapours through the iodine solution, and to prevent any
chlorine escaping backwards. This is tested, as before, by the small piece
of iodide of starch paper in tube s, which should be so placed as never to
get warm.

The chlorate is weighed out into the dry evolution flask A, then dissolved
in 8 to 10 c.c. of w\ater, and, after all the necessary connections have been
made, 8 to 10 c.c. of pure concentrated hydrochloric acid are run in through
the funnel g. Since the reaction begins in the cold, the CO'2 must be
turned on immediately, and kept passing at the rate of about four bubbles
per second. Care should be taken to heat very gently at first, until the
bulk of the chlorine has come over, after which the lamp flame may be
gradually turned up and the liquid boiled, exactly as in the case of the
nitrate ; this ensures that no chlorine escapes backwards. And, as before,
after all the chlorine has been apparently driven out, and the solution has
become colourless, a second quantity of warm hydrochloric acid (1 in 2)
is run in, and the boiling repeated for a few minutes.

§ 87. URIXF, 377

PART VI.

SPECIAL APPLICATIONS OF THE VOLUMETRIC

SYSTEM TO THE ANALYSIS OF URINE, POTABLE

WATERS, SEWAGE, ETC.

ANALYSIS OF URINE.

§ 87. THE complete and accurate determination of the normal
and abnormal constituents of urine presents mere than ordinary
difficulty to even experienced chemists, and is a hopeless task in
the hands of any other than such. Fortunately, however, the
most important matters, such as urea, sugar, phosphates, sulphates,
and chlorides, can all be determined volumetrically with accuracy
by ordinary operators, or by medical men who cannot devote
much time to practical chemistry. The researches of Liebig,
Neubauer, Bence Jones, Vogel, Beale, Hassall, Pavy,
and others, during the last few years, have resulted in a truer
knowledge of this important secretion ; and to the two first
mentioned chemists we are mainly indebted for the simplest
and most accurate methods of estimating its constituents. With
the relation which the proportion of these constituents bear
to health or disease the present treatise has nothing to do, its
aim being simply to point out the readiest and most useful
methods of determining them quantitatively. Their pathological
importance is very fully treated by some of the authorities just
mentioned, among the works of which Neubauer and Vogel's
Anal i i se des Hams, Be ale's Urine, Urinary Deposits, and Calculi,
and M elm's Traite de Cliiinie Medicale, are most prominent and
exhaustive ; and we now have the collected experience of all
the best authorities in the world in The Pathological Handbook
of Drs. Lander Brunton, Klein, Foster, and Burdon
Sanderson (Churchill), and in Allen's Chemistry of Urine
(Churchill).

The gram system of weights and measures will be adopted
throughout this section, while those who desire to use the grain
system will have no difficulty in working, when once the simple
relation between them is understood* (see § 10 p. 26). The question
of weights and measures is, however, of very little consequence, if
the analyst considers that he is dealing with relative parts or pro-
portions only ; and as urine is generally described as containing so

* In a word, whenever c.c. occurs, dm. may be substituted ; and in case of using1
grains for grains, move the decimal point one place to the right ; thus 7*0 grams would
be changed to 70 grains. Of course it is understood that where grains are taken c.c.
must be measured, and with grains dm., the standard solution being the same for both
systems.

378 VOLUMETRIC ANALYSIS. § 87.

many parts of urea, chlorides, or phosphates, per 1000, the absolute
weight may be left out of the question. The grain system is more
readily calculated into English ounces and pints, and therefore is
generally more familiar to the medical profession of this country.

One thing, however, is necessary as a preliminary to the exami-
nation of urine, and which has not generally been sufficiently
considered ; that is to say, the relation between the quantity of
secretion passed in a given time, and the amount of solid matters
found in it by analysis. In a medical point of view it is a mere
waste of time, generally speaking, to estimate the constituents in
half-a-pint or so of urine passed at any particular hour of the day
or night, without ascertaining the relation which that quantity,
with its constituents, bears to the whole quantity passed during,
say, 24 hours ; and this is the more necessary, as the amount of
fluid secreted varies very considerably in healthy persons ; besides
this, the analyst should register the colour, peculiarity of smell (if
any), consistence, presence or absence of a deposit (if the former,
it should be collected for separate analysis, filtered urine only
being used in such cases for examination), and lastly its reaction to
litmus should be observed.

1. Specific Gravity.

This maybe taken by measuring 10 c.c. with an accurate pipette
into a tared beaker or flask. The observed weight say is 10*265
gm. ; therefore 1026*5 will be the specific gravity, water being 1000.
Where an accurate balance, pipette, or weights are not at hand,
a good uririometer may be used. These instruments are now to be
had with enclosed thermometer and of accurate graduation.

2. Estimation of Chlorides (calculated as Sodic Chloride).

This may be done in several ways, and I have placed the
methods in the order in which I consider they ought to be ranked
as regards accuracy. Liebig's method is by far the simplest, but
the end-point is generally so obscure that the liability to error is
very great. Mohr's method I have modified by the use of
ammonic in place of potassic nitrate, owing to 'the solvent effect
which the latter has been found to produce on silver chroinate.
By ignition the ammonia salt is destroyed.

(a) By Silver Nitrate (Mohr). — 10 c.c. of the urine are
measured into a thin porcelain capsule, and 1 gm. of pure ammonic
nitrate in ponder added ; the whole is then evaporated to dryness,
and gradually heated over a small spirit lamp to low redness till
all vapours are dissipated and the residue becomes white'" ; it is

*Dr. Edmunds has called my attention to the fact, that there is great danger of
losing chlorine if the ignition is made at a high temperature, and there is no doubt he
is right. He prefers to char the urinary residue thoroughly over a spirit lamp, and
wash out the chlorides with hot water, the filtered liquid is then available for direct
estimation v/ith silver and chroinate or by the V o 1 h ar d method.

§ 87. URINE. 379

then dissolved in a small quantity of water, and the carbonates
produced by the combustion of the organic matter neutralized by
dilute acetic acid ; a few grains of pure calcic carbonate to remove
all free acid are then added, and one or two drops of solution of
potassic chromate.

The mixture is then titrated with ~ silver, as in § 41.2 (/;).

Each c.c. of silver solution represents 0*005837 gm. of salt,
consequently if 12 '5 c.c. have been used, the weight of salt in the
10 c.c. of urine is 0*07296 gm., and as 10 c.c. only were taken,
the weight multiplied by 10, or what amounts to the same thing,
the decimal point moved two places to the right, gives 7*296 gm.
of salt for 1000 c.c. of urine.

If 5'9 c.c. of the urine are taken for titration, the number of c.c. of TV
silver used will represent the number of parts of salt in 1000 parts of urine.

(1) By Volhard's Method. — This is a direct estimation of
Cl by excess of silver and the excess found by ammonic or potassic
thiocyanate (§ 43), which gives very good results in the absence of
much organic matter, and is carried out as follows : —

10 c.c. of urine are placed in a 100 c.c. flask and diluted to about 60 c.c.
2 c.c. of pure nitric acid and 15 c.c. of standard silver solution (1 c.c. =0*01
gm. NaCJ) are then added ; the closed flasked is well shaken, and the measure
made up to 100 c c. with distilled water.

The mixture is then passed through a dry filter, and about 70 or 80 c.c. of
the clear fluid titrated with standard thiocyanate for the excess of silver,
using the ferric indicator described on page 143. The relative strength of
the silver and thiocyanate being known, the measure of the former required
to combine with the chlorine in the 7 or 8 c.c. of urine is found and
calculated into NaCl.

Arnold (Pflilger'1 s Arcldv. xxxv. 541) carries out this process
as follows : —

10 c.c. of urine are mixed with 10 to 20 drops of nitric acid sp. gr. 1*2,
2 c.c. of ferric indicator, and 10 to 15 drops of solution of permanganate to
oxidize organic matter. The liquid is then filtered and titrated as described
above.

Dr. James Edmunds, of Dover Street, Piccadilly, who is not
only a prominent London physician but also an excellent chemist,
has kindly contributed his special way of carrying out the estimation
of chlorides in urine by this process.

" In determining the chlorides of urine, and other organic liquids, by
desiccation and ignition, I find the results generally too low. It seems
impracticable to prevent the fume of charring from mechanically carrying
off chlorides, and the heat of ignition from volatilizing a further portion.
By careful charring at a low temperature, breaking up the char, and
washing out the soluble salts, the loss of chlorides is minimized. On the
other hand, I know of no measurement which is more entirely satisfactory
than the determination of chlorides by the beautiful process devised by
Volhard. The organic matters of urine open up the way to two fallacies.

880 VOLUMETRIC ANALYSIS. § 87.

1. The reduction of nitric acid and the production of a red shade due to
the lower oxides of nitrogen. But this never amounts to the full red which
is given, in cases of doubt, by running in a further portion of the
thiocyanate, and then titrating back with the silver until the red is about to
fade out. In that way the true end-point of the reaction is made sharp
and unequivocal. 2. The second possible fallac}r is the reduction of the
ferric indicator to the ferrous condition. But this does not prevent the
end-point from showing, unless the whole of the ferric has been reduced to
ferrous oxide, and, if a full measure of a good ferric indicator is used, this
cannot happen. In case of any uncertainty the addition of a fresh c.c. of
the ferric indicator, at the moment when the titration seems to be
complete, is decisive as to the true end-point. In some cases it may be
necessary to get rid of oxalic acid, or other active reducers by previous
treatment with potassic permanganate free from chlorine, until a slight rose
tint persists, and this may be perfectly removed by passing the liquid
through a filter paper.

" The indicator which I use is a very simple and convenient one. It is
made by dissolving 2'8 gm. of clean soft iron wire in nitric acid of about
1250 sp. gr., boiling off the red fumes, and then making up to 100 c.c.
with pure nitric acid and water— so that the solution has a sp. gr. of about
1 385, and is well below the fuming point at ordinary temperatures. To
remove the last traces of the nitrogen oxides, I then put the solution into
a tall jar, and blow air through it by means of a glass tube attached to
a rubber-ball bellows. The solution which is thus obtained is a pale
greenish yellow ; it is a pure ferric nitrate in slightly diluted nitric acid ;
and it keeps well. This gives, at one addition, the ferric indicator and the
nitric acid which is needed for the process. It cannot be sucked up into
a pipette without serious risk of causing pneumonia, and it should be
poured out into a 10 c.c. tubular measure. For ordinary liquid, where no
organic matter is present, this solution may be reduced to ten times its
volume with additional pure nitric acid and water, and, if its colour goes
wrong, air must again be blown through it, or it must be heated until,
when cold, it is a pale greenish yellow.

" In the analysis, I dilute the urine to 10 volumes with distilled water
which reduces its colour and dilutes its organic matter, and I use
solutions of thiocyanate and of silver, which are the chlorine-reciprocals
of normal solutions ; i.e., normal solutions diluted to 35'37 volumes, and of
which 1 c.c. is equal each to O'OOl Cl. These solutions may be marked
K Ij7~~ or 35^jT They are very convenient and eliminate all calculation.
In fact, this method of calculating and marking various standard solutions
is very useful. Placing 10 c.c. of the diluted urine into a beaker on white
paper, I add 10 c.c. of the ferric indicator, and at once run in 1 c.c. of the
thiocyanate, so as to get a sharp red colour, and stir thoroughly. I then run
in the silver with continuous stirring until the red colour begins to
distinctly fade. From this point onwards continuous stirring, and the slow
addition of the last drops of silver gives a sharp and unquestionable end-
point. If overdone by accident, I add another c.c. of thioc}ranate, and
repeat the silver more cautiously as the end-point approaches, stirring very
actively. The titration should commence Avith the burettes at 0, and then
a simple reading of the burettes at the end of the operation gives both
quantities used, however often the titration backwards and forwards may
have been done. The silver c.c., minus the thiocyauate c.c., give the milligrams
of chlorine in 1 c.c. of urine. It is necessary to use a small very accurately
graduated burette, say 20 c.c. in TV : it' the tube is narrow it is possible to
have very distinct readings.

" It cannot be possible to get an easier, quicker, or more precise
determination of chlorides in urines, milk serums, and other organic liquids
than this."

§ 87. URINE. 381

(/•) By Mercuric Nitrate (LieMg). — The principle of this
method is as follows : — If a solution of mercuric nitrate, free from
any excess of acid, is added to a solution of urea, a white gelatinous
precipitate is produced, containing urea and mercuric oxide in the
proportions of 1 eq. of the former to 4 eq. of the latter (4HgO +
Ur). When sodic chloride, however, is present in the solution,
this precipitate does not occur until all the sodic chloride is
converted by double decomposition into mercuric chloride (sub-
limate) and sodic nitrate, the solution remaining clear ; if the
exact point be overstepped, the excess of mercury immediately
produces the precipitate above described, so that the urea present
acts as an indicator of the end of the process. It is therefore
possible to ascertain the proportion of chlorides in any given
sample of urine by this method, if the strength of the mercurial
solution is known, since 1 eq. of mercuric oxide converts 1 eq. of
sodic chloride into 1 eq. each of corrosive sublimate and sodic
nitrate.

Standard Solution of Mercuric nitrate. — It is of great im-
portance that the solution be pure, for if the mercury from which
it is made be contaminated with traces of other metals, such as
bismuth, silver, or lead, they will produce a cloudiness in the
liquid while under titration, which may possibly obscure the exact
ending of the reaction ; therefore 18 '42 gm. of the purest precipi-
tated mercuric oxide are put into a beaker, with a sufficiency of
pure nitric acid of about 1'20 spec. grav. to dissolve it by the
aid of a gentle heat ; the clear solution so obtained is evaporated
on the water bath to remove any excess of free acid. When the
liquid is dense and sirupy in consistence, it may be transferred to
the graduated cylinder or flask and diluted to a liter. 1 c.c. of the
solution so prepared is equal to 0*01 gm. of sodic chloride, or
0-006059 gm. of chlorine.

If pure mercuric oxide is not at hand, the solution is best made ~by
weighing 25 gm. of mercuric chloride, which is dissolved in about a liter of
water and the oxide precipitated with a slight excess of caustic potash or
soda. The precipitate of yellow oxide is allowed to settle clear and the
liquid decanted. It is repeatedly washed in this manner Avith warm
distilled water until the washings show no amount of alkali or alkaline
chloride ; the precipitate is then dissolved in the smallest quantit}^ of pure
nitric acid, and diluted to about 950 c.c. If any great excess of nitric acid is
present, it may be cautiously neutralized by pure sodic hydrate or carbonate.

Verification of the Mercuric Solution. — This is carried out by
the help of the following solutions : —

Pure Sodic chloride. — 20 gm. per liter.

Solution of Urea. — 4 gm. of pure urea in 100 c.c.

Solution of pure Sodic sulphate. — Saturated at ordinary tem-
peratures. This is used to regulate the action of the free acid
which is liberated in the reaction. In the case of natural urine it
is not necessary.

382 VOLUMETRIC ANALYSIS. § 87.

Process of Tilration : 10 c.c. of the standard sodic chloride ( = 0'2 gm.
NaCl) are placed iu a small beaker, together with 3 c.c. of the urea solution,
and 5 c.c. of sodic sulphate. The mercuric solution is then delivered in from
the burette, with constant stirring, until a decided permanent white pre-
cipitate is seen to form. A mere opalescence may occur even at the beginning,
arising from slight impurities in the mercury, but this may be disregarded.
If the mercuric solution has been made from weighed pure oxide, exactly 20
c.c. should be required ; if, on the contrary, it has been made from the fresh
umveighed oxide, somewhat less than 20 c.c. should be required. Say that
18' 5 c.c. have been found to give the necessary reaction, then the solution
must be diluted with distilled water in the proportion of 1'5 c.c. to every
18'5, or 925 c.c. made up to a liter.

(d) Baryta Solution for removing- Phosphoric and Sulphuric
Acids. — Before urine can be submitted to titration by the mercurial
solution, it is necessary to remove the phosphoric acid, and the
proper agent for this purpose is a mixture composed of 1 vol. of
cold saturated solution of baric nitrate and 2 vols. of saturated
baric hydrate ; the same agent is used previous to the estimation
of urea, and may be simply designated Baryta solution.

Process : 40 c.c. of the clear urine are mixed with 20 c.c. of baryta
solution, and the thick mixture poured upon a small dry filter; when
sufficient clear liquid has passed through, 15 c.c. ( = 10 c.c. of urine) are
taken with a pipette and just neutralized, if necessary, with a drop or two of
nitric acid. If not alkaline, the probability is that sufficient baryta solution
has not been added to precipitate all the phosphoric and sulphuric acids.
This may be known by adding a drop or so of the baryta solution to the
filtrate ; if any precipitate is produced, it will be necessary to mix a fresh
quantity of urine with three-fourths or an equal quantity of baryta, in which
case I7i or 20 c.c. must be taken to represent 10 c.c. of urine ; the excess in
either case of baryta must be cautiously neutralized with nitric acid.

The vessel containing the fluid is then brought under a Mo hr's burette
containing the mercurial solution, and small portions delivered in with
stirring, until a distinct permanent precipitate is produced. The volume of
solution used is then read off and calculated for 1000 parts of urine.

'Example : 15 c.c. of the liquid prepared with a sample of urine, as
described above ( = 10 c.c. of urine), required 6'2 c.c. of mercurial solution :
the quantity of salt present was therefore 0'062 gm., or 6'2 parts in 1000
parts of urine.

3. Estimation of Urea (Lie big).

The combination between urea and mercuric oxide in neutral or
alkaline solutions has been alluded to in the foregoing article on
chlorides ; it will therefore probably be only necessary to say that
the determination of urea in nrine is based on that reaction ; and
as the precipitate so produced is insoluble in water or Aveak alkaline
solutions, it is only necessary to prepare a standard solution of
mercury of convenient strength, and to find an indicator by which
to detect the point when all the urea has entered into combination
with the mercury, and the latter slightly predominates. This
indicator is sodic carbonate. Liebig's instructions are, that when
in the course of adding the mercurial solution from the burette to

§ 87. URINE. 38l>

the urine, a drop of the mixture is taken from time to time and
brought in contact with a few drops of solution of sodic carbonate
on a glass plate or in a watch-glass, no change of colour is
produced at the point of contact until the free urea is all removed ;
when this is the case, and the mercury is slightly in excess,,
a yellow colour is produced, owing to the formation of hydrated
mercuric oxide.

The compound of urea and mercury consists, according to
Liebig's analysis, of 1 eq. of the former to 4 eq. of the latter;
that is to say, if the nitric acid set free by the mixture is
neutralized from time to time with sodic carbonate or other
suitable alkali. If this be not done, the precipitate first formed
alters in character, and eventually consists only of 3 eq. of mercury
with 1 of urea. In order to produce the yellow colour with
sodic carbonate, there must be an excess of mercurial solution.
Theoretically, 100 parts of urea should require 720 parts of
mercuric oxide ; but practically, 772 parts of the latter are-
necessary to remove all the urea, and at the same time" show
the yellow colour with alkali ; consequently the solution of
mercuric nitrate must be of empirical strength, in order to give-
accurate results.

Preparation of the Mercuric Solution. — 77 '2 gin. of red mercuric-
oxide, or 71 '5 gm. of the metal itself, are treated with nitric acid,,
as described in the previous article on chlorides, and in either case
diluted to 1 liter : 1 c.c. of the solution is then equal to O'Ol gm.
of urea. (The extreme care required to remove traces of foreign
metals from the mercury is not so necessary here as in the foregoing
instance, but no large amount of free acid, must be present.)
Dragendorff prefers to use mercuric chloride in the preparation
of the standard solution, by weighing 96*855 gm. of the pure salt,,
which is dissolved in water, then precipitated with dilute caustic
soda, the precipitate well washed by decantation until free from
chlorine, then dissolved in a slight excess of nitric acid, and the
solution diluted to 1 liter.

Process : Two volumes of the urine are mixed with one of baryta solution
as before described in the case of chlorides (reserving the precipitate for the
determination of phosphoric acid, if necessarj7), and 15 c.c. (=10 c.c. of
urine) taken in a small beaker for titration ; it is brought under the burette
containing the mercurial solution (without neutralizing the excess of baryta,,
as in the case of chlorides), and the solution added in small quantities so
long as a distinct precipitate is seen to form. A plate of glass laid over
dark paper is previously sprinkled with a few drops of solution of sodic
carbonate, and a drop of the mixture must be brought from time to time, by
means of a small glass rod, in contact with the soda. So long as the colour
remains white, free urea is present in the mixture ; when the yellow colour
is distinctly apparent, the addition of mercury is discontinued, and the
quantity used calculated for the amount of urea. It is always advisable to
repeat the analysis, taking the first titration as a guide for a more accurate
estimation by the second.

384 VOLUMETRIC ANALYSIS. § 87.

Example : 15 c.c. of urine deprived of phosphates ( = 10 c.c. of the original
urine) were titrated as described, and required 17'6 c.c. of mercurial solution :
consequently there was 0'176 gm. of urea present in the 10 c.c., or 17'6 parts
in the 1000 of urine.

The experiments of Rautenberg (Ann. d. Chem. u. Pit arm.
cxxxiii. 55) and Pfliiger (Z. a. C. xix. 375) show, however, that
the method, as devised byLiebig, is open to serious errors, due to
the uncertainty in the point of neutralization.

Pfliiger's researches are very complete, and lead to the follow-
ing modification of the process.

A solution of pure urea is prepared containing 2 gm. in 100 c.c.
10 c.c. of this solution is placed in a beaker, and 20 c.c. of the
mercury solution ran into it in a continuous stream ; the mixture is
then immediately brought under a burette containing normal sodic
carbonate, and this solution is added with constant agitation until
a permanent yellow colour appears. The volume of soda solution
so used is noted as that which is necessary to neutralize the acidity
produced by 20 c.c. of the mercury solution in the presence of urea.
Pfliiger found that by titrating 10 c.c. of the urea solution by
small additions of the mercury, and occasional neutralization, the
end of the reaction occurred generally at from 17 '2 to 17 '8 c.c. of
mercury ; but wrhen he ran in boldly 19 '7 c.c. of mercury, followed
immediately by normal sodic carbonate to near neutrality, then
alternately a drop or two of first mercury, then soda, the exact
point was reached at 20 c.c. of mercury ; and when 10 c.c. of the
mercury solution wrhich gave this reaction were analyzed as
sulphide by weight, a mean of several determinations gave '0 '7726
gm. of HgO, which agrees very closely with Liebig's number.

In the case of titrating urine, the following method is adopted : —

A plate of colourless glass is laid upon black cloth, and some drops of
a thick mixture of sodic bicarbonate (free from carbonate) and water placed
upon it at convenient distances. The mercury solution is added to the urine
in such volume as is judged appropriate, and from time to time a drop of the
white mixture is placed" beside the bicarbonate so as to touch, but not mix
completely. At first the urine mixture remains snow-white, but with
further additions of mercury a point at last occurs when the white gives
place to yellow. "When the colour has developed itself, both drops are rubbed
quickly together with a glass rod : the colour should disappear. Further
addition of mercury is made cautiously until a faint yellow is permanent.
Now is the time to neutralize by the addition of the normal soda to near the
volume which has been found necessary to completely neutralize a given
volume of mercury solution. If the time has not been too long in reaching
this point, it will be found that a few tenths of a c.c. will suffice to complete
the reaction. If, however, much time has been consumed, it may occur that,
notwithstanding the mixture is distinctly acid, the addition of soda produces
a more or less yellow colour : in this case, nothing is left but to go over the
analysis again, taking the first trial as a guide for the quantities of mercury
and soda solutions, Vhich should be delivered in one after the other as
speedily as possible until the exact end is reached.

It is absolutely necessary, with this modified process, to render

OF THE

UNIVERSITY

335

tlie urine perfectly neutral, after it is freed from phosphates and
sulphates by baryta solution.

Corrections and Modifications (Liebig). — In certain cases the results
obtained by the above methods are not strictly correct, owing to the variable
state of dilution of the liquid, or the presence of matters which affect the
mercury solution. The errors are, however, generally so slight as not to
need correction. Without entering into a full description of their origin,
I shall simply record the facts, and give the modifications necessary to be
made where thought desirable.

The Urine contains more than 2 per cent, of Urea, i.e., more
than 20 parts per 1000. This quantity of urea would necessitate 20 c.c.
of mercurial solution for 10 c.c. of urine. All that is necessary to .be done
when the first titration has shown that over 2 per cent, is present, is to add
half as much water to the urine in the second titration as has been needed of
the mercurial solution above 20 c.c. Suppose that 28 c.c. have been used at
first, the excess is 8 c.c., therefore 4 c.c. of water are added to the fluid before
the second experiment is made.

The Urine contains less than 2 per cent, of Urea. In this case,
for every 4 c.c. of mercurial solution less than 20, O'l c.c. must be deducted,
before calculating the quantity of urea ; so that if 16 c.c. have been required
to produce the yellow colour with 10 c.c. urine, 15'9 is to be considered the
correct quantity.

The Urine contains more than 1 per cent, of Sodic Chloride,
i.e., more than 10 parts per 1000. In this case 2 c.c. must be deducted from
the quantity of mercurial solution actually required to produce the yellow
colour with 10 c.c. of urine.

The Urine contains Albumen. In this case 50 c.c. of the urine are
boiled with 2 drops of strong acetic acid to coagulate the albumen, the
precipitate allowed to settle thoroughly, and 30 c.c. of the clear liquid mixed
with 15 c.c. of baryta solution, filtered, and titrated for both chlorides and
urea, as previously described.

The Urine contains Ammonic Carbonate. The presence of this
substance is brought about by the decomposition of urea, and it may
sometimes be of interest to know the quantity thus produced, so as to
calculate it into urea.

As its presence interferes with the correct estimation of urea direct, by
mercurial solution, a portion of the urine is precipitated with baryta as
usual, and a quantity, representing 10 c.c. of urine, evaporated to dryuess in
the water bath to expel the ammonia, the residue then dissolved in a little
water, arid the urea estimated in the ordinary way. On the other hand,
50 or 100 c.c. of the urine, not precipitated with baryta, are titrated with
normal sulphuric acid and litmus paper, each c.c. of acid representing
0'017 gm. of ammonia, or 0*03 gm. of urea.

Pfl tiger's correction for concentration of the urea differs from
Liebig's, his rule being as follows : —

Given the volume of urea solution + the volume of NaCO3 required + the
volume of any other fluid free from urea which may be added, and call this
V1 ; the volume of mercury solution is V2 ; the correction, C, is then

C= — (V1— Y2)x0'08.

This formula holds good for cases where the total mixture is less than three
times the volume of mercury used.

With more concentrated solutions this formula gives results too high.

C C

386 VOLUMETRIC ANALYSIS. § 87.

Pfeiffer (Zeit. f. Biol. xx. 540) has made a careful comparison
of Liebig's (as modified by Pfliiger)and Rautenberg's methods
of estimating urea. The essential difference of Rautenberg's
method consists in maintaining the urea solution neutral throughout
by successive additions of calcic carbonate ; under these conditions,
the composition of the precipitate differs from that formed when
the titration is made according to Pfliiger's process, a fact which,
accounts for the diminished consumption of mercuric nitrate in the
former method. The general conclusions from his observations
may be summarized as follows : — (1) In estimating the correction
for sodic chloride, the amount of free acid should be as small as
possible, and O'l c.c. should be subtracted from every c.c. of
mercuric nitrate used, but in human urine it is preferable to
precipitate the chlorine with silver nitrate, as a slight excess of the
latter does not influence the result. (2) The coefficient for
dilution should be determined afresh for every new standard
solution.

4. Estimation of Urea by its conversion into Nitrogen Gas.

If a solution of urea is mingled with an alkaline solution of
hypochlorite or hypobromite, the urea is rapidly decomposed and
nitrogen evolved, which can be collected and measured in any of
the usual forms of gas apparatus described in the section on
analysis of gases.

Test experiments with pure urea have shown, that the whole of
the nitrogen contained in it is eliminated in this process, with the
exception of a constant deficit of 8 per cent. In the case of urine
there are other nitrogenous constituents present, such as uric acid,
hippuric acid, and creatinine, which render up a small proportion
of their nitrogen in the process, but the quantity so obtained is
insignificant, and may be disregarded. Consequently, for all
medical purposes, this method of estimating urea in urine is
sufficiently exact.

In the case of diabetic urines, 'however, Menu and others have
pointed out that this deficiency is diminished, and if, in addition
to the glucose present, cane sugar be also added, it will almost
entirely disappear. Mehu therefore recommends that in the
analysis of saccharine urines cane sugar be added to ten times the
amount of urea present, when the difference between the actual
and theoretical yield of nitrogen will not exceed 1 per cent. (Bull.
Soc. Chim. [2] xxxiii. 410).

Russell and West (/. C. S, [2] xii. 749) have described a
very convenient apparatus for working the process, and which gives
very good results in a short space of time. This method has given
rise to endless forms of apparatus devised by various operators,
including Mehu, Yvon, Dupre, Apjohn, Maxwell Simpson,
Dor emus, O'Keefe, etc., etc. ; the principles of construction are

§ 87.

URINE.

387

all, however, the same. Those who may wish to construct simple
forms of apparatus from ordinary laboratory appliances, will do
well to refer to the arrangements of Dupre (J. C. S. 1877, 534)
or Maxw'ell Simpson (ibid. 538). The nitrometer, with side
flask, and using mercury, is perhaps the best of all for the
gasometric estimation of urea. Each c.c. of X produced, after
correction for temperature, pressure, and moisture, being equal to
0'002952 gm. of urea on the assumption that 92 % is evolved.

The apparatus devised by Russell and West is shown in
fig. 54, and may be described as follows : —

The tube for decomposing the urine
is about 9 inches long, and about half
an inch inside diameter. At 2 inches
from its closed end it is narrowed, and
an elongated bulb is blown, leaving the
orifice at its neck f of an inch in
diameter; the bulb should hold about
12 c.c. The mouth of this tube is
fixed into the bottom of a tin tray
abouir If inch deep, which acts as a
pneumatic trough ; the tray is supported
on legs long enough to allow of a
small spirit lamp being held under the
bulb tube. The measuring tube for
collecting the nitrogen is graduated into
cubic centimeters, and of such size as
to fit over the mouth of the decom-
posing tube ; one holding about 40 c.c.
is a convenient size. Russell and West
have fixed by experiment the propor-
tions, so as to obviate the necessity for
•correction of pressure and temperature, namely, 37'1 c.c. = Ol gm.
-of urea, since they found that 5 c.c. of a 2 per cent, solution of
urea constantly gave 37*1 c.c. of nitrogen at ordinary temperatures
.and pressures. The entire apparatus can be purchased of most
•operative chemists for a moderate sum.

Hypobromite Solution. — This is best prepared by dissolving
100 gm. of caustic soda in 250 c.c. of water and at the time
required 25 c.c. of the solution are mixed with 2*5 c.c. of bromine ;
this mixture gives a rapid and complete decomposition of the
urea. Strong solution of sodic or calcic hypochlorite answers
•equally well.

Process : 5 c.c. of the urine are measured into the bulb-tube, fixed in
its proper position, and the sides of the tube washed down with distilled
water so that the bulb is filled up to its constriction. A glass rod, having
.a thin band of india-rubber on its end, is then passed down into the tube so
as to plug up the narrow opening of the bulb. The hypobromite solution is
then poured into the upper part of the tube until it is full, and the trough
is afterwards half filled with water.

C C 2

Fig. 54.

388 VOLUMETRIC ANALYSIS. § 87.

The graduated tube is filled with water, the thumb placed on the opeiu
end, and the tube is inverted in the trough. The glass rod is then pulled
out, and the graduated tube slipped over the mouth of the bulb-tube.

The reaction commences immediately, and a torrent of gas rises into the-
measuring tube. To prevent any of the gas being forced out by the reaction,,
the upper part of the bulb-tube is slightly narrowed, so that the gas is directed
to the centre of the graduated tube. With the strength of Irypobromite-
solution above described, the reaction is complete in the cold in about ten or
fifteen minutes ; but in order to expedite it, the bulb is slightly warmed.
This causes the mixing to take place more rapidly, and the reaction is then
complete in five minutes. The reaction will be rapid and complete only
when there is considerable excess of the hypobromite present. After the
reaction the liquid should still have the characteristic colour of the-
hypobromite solution.

The amount of constriction in the tube is by no means a matter
of indifference, as the rapidity with which the reaction takes place
depends upon it. If the liquids mix too quickly, the evolution of
the gas is so rapid that loss may occur. On the other hand, if the
tube is too much constricted, the reaction takes place too slowly.

The simplest means of supporting the measuring tube is to have
the bulb-tube corked into a well, wfcich projects from the bottom of
the trough about one inch downwards. The graduated tube stands-
over the bulb-tube, and rests upon the cork in the bottom of the
well. It is convenient to have, at the other end ctf ihe trough,
another well, which will form a support for the measuring tube-
when not in use.

To avoid all calculations, the measuring tube is graduated so that
the amount of gas read off expresses at once what may be called
the percentage amount of urea in the urine experimented upon ::
i.e. the number of grams in 100 c.c., 5 c.c. being the quantity of
urine taken in each case. The gas collected is nitrogen saturated
with aqueous vapour, and the bulk will obviously be more or less-
affected by temperature and pressure. Alterations of the barometer
produce so small an alteration in the volume of the gas, that it
may be generally neglected ; e.g. if there are 30 c.c. of nitrogen,,
the quantity preferred, an alteration of one inch in the height of
barometer would* produce an error in the amount of urea of about
0*003 ; but for more exact experiments, the correction for pressure
should be introduced.

In the wards of hospitals, and in rooms where the experiments
are most likely to be made, the temperature will not vary much
from 65° F., and a fortunate compensation of errors occurs with
this form of apparatus under these -circumstances. The tension of
the aqueous vapour, together with the expansion of the gas at this
temperature, almost exactly counterbalances the loss of nitrogen
in the reaction.

The authors found from experience that 5 c.c. of urine is the
most advantageous quantity to employ, as it usually evolves a con-
venient bulk of gas to experiment with, i.e. about 30 c.c. They

.§ 87. URINE. 389

have shown that 5 c.c. of a standard solution containing 2 per cent,
of urea evolve 37'1 c.c. of nitrogen, and have consequently taken
this as the basis of the ^raduation of the measuring tube. This
bulk of gas is read off at once as 2 per cent, of urea, and in the
same way the other graduations on the tube represent percentage
amounts of urea.

If the urine experimented with is very rich in urea, so that the
5 c.c. evolve a much larger volume of gas tMIn 30 c.c., then it is
best at once to dilute tllfe urine with its own bulk of water ; take
5 c.c. of this diluted urine, and multiply the volume of gas obtained
by two.

If the urine contains much albumen, this interferes with the,
process so far that it takes a long ^me for the bubbles of gas to
subside, before the volume of gas obtained can be accurately read
off. It is therefore better in such cases to remove as much as
possible of the albumen by heating the urine with two or three
•drops of acetic acid, filtering, and then using the nitrate in the
usual manner.

Hamburger (Zeit.f. JBioL xx. 286) describes a method founded
on Quinquand's (Monit. Scien. 1882, 2), in which the decom-
position of urea»by hypobromite is supposed to take place thus :—

CO(XH2)2 + 3XaBrO=3NaBr + 2H20 + CO2 + N*.

This reaction requires the proportion of bromine, sodic hydrate, and
water to be exactly balanced or incorrect results will be obtained.
The author claims for his method that it will yield correct results,
no matter in what proportions these reagents are present. It
consists essentially in adding an excess of an alkaline solution
of sodic hypobromite (of known strength in relation to standard
alkaline arsenite) to the liquid containing urea, then destroying
the excess oiWiypobromite with an excess of standard arsenite
( — 19 '8 gin. As203 per liter), and finally determining the amount
of arsenite remaining unoxidized, by titration with standard iodine,
the amount of urea then being readily calculated from the amount
of arsenite remaining unoxidized. The author's experiments as to
the accuracy of the method, show that a certain quantity of urea
always requires the same amount of hypobromite, and that the
dilution of the solution of urea has no ^effect on the quantity of
hypobromite employed.

To decide on the applicability of the method to natural urine,
great pains were taken, the urea being determined as described, the
effect of its dilution with water studied, pure urea added, and the
whole estimated, and lastly sodic hypobromite of various degrees of
concentration, employed; the results of "the experiments are given
very fully and tabulated. On the whole, they are very satisfactory,
the differences falling well within the limits of errors of observa-
tion and manipulation ; the method may therefore be considered
applicable to the determination of urea in urine.

390 VOLUMETRIC ANALYSIS. § 87.

5. Estimation of Phosphoric Acid (see also § 72).

The principle of this method is fully described at page 285.
The following solutions are required :—

(1) Standard Uranic acetate or nitrate. 1 c.c. =0*005 gm.
P205 (see p. 286).

(2) Standard Phosphoric acid (see p. 287).

(3) Solution of Sodic acetate (see p. 286).

(4) Solution of Potassic ferrocyanide. — About 1 part to 20
of water, freshly prepared.

Process : 50 c.c. of the clear urine are measured into a small beakerr
together w^th 5 c.c. of the solution of sodic acetate (if uranic nitrate is used).
The mixture is then warm^ in the water bath, or otherwise, and the uranium
solution delivered in from the burette, with constant stirring, as long as a
precipitate is seen to occur. A small portion of the mixture is then removed
with a glass rod and tested as described (p. 286) ; so long as no brown colour
is produced, the addition of uranium may be continued ; when the faintest-
indication of this reaction is seen, the process must be stopped, and the
amount of colour observed. If it coincides with the original testing of the
uranium solution with a similar quantity of fluid, the result is satisfactory.,
and the quantity of solution used may be calculated for the total phosphoric
afrid contained in the 50 c.c. of urine ^ if the uranium has been used
accidentally in too great quantity, 10 or 20 c.c. of the same urine may be
added, and the testing concluded more cautiously. Suppose, for example,
that the solution has been added in the right proportion, and 19'2 c.c. used,
the 50 c.c. will have contained 0'096 gm. phosphoric acid (=1/92 per 100).
With care and some little practice the results are very satisfactor}'.

Earthy Phosphates. — The above determination gives the total amount
of phosphoric acid, but it may sometimes be of interest to know how much of
i^is combined with lime and magnesia. To this end 100 or 200 c.c. of the
urine are measured into a b«aker, and rendered freely alkaline with ammonia ;
the vessel is then set aside for ten or twelve hours, for the precipitate of
earthy phosphates to settle : the clear fluid is then decanted through a filter,
the precipitate brought upon it and washed with ammoniacal water ; a hole
is then made in the filter and the precipitate washed through ; the paper
moistened with a little acetic acid, and washed into the vessel containing
the precipitate, which latter is dissolved in acetic acid, some sodic acetate
added, and the mixture diluted to about 50 c.c. and titrated as before
described ; the quantity of phosphoric acid so found is deducted from the
total previously estimated, and the remainder gives the quantity existing in

combination with alkalies.

•

6. Estimation of Sulphuric Acid.

Standard Baric chloride. — A quantity of crystallized baric
chloride is to be powdered, and dried between folds of blotting-
paper. Of this, 30*5 gm. are dissolved in distilled water, and the
liquid made up to a liter. 1 c.c. =0*01 gm. of SO3.

Solution of Sodic sulphate. — 1 part to 10 of water.

Process : 100 c.c. of the urine are poured into a beaker, a little hydro-
chloric acid added, and the whole placed on a small sand bath, to which heat

§ 87. URINE. 391

is applied. When the solution boils, the baric chloride is allowed to flow
in very gradually as long as the precipitate is seen distinctly to increase.
The heat is removed, and the vessel allowed to stand still, so that the
precipitate may subside. Another drop or two is then added, and so on,
until the whole of the SO3 is precipitated. Much time, however, is saved
by using Be ale's filter, represented in fig. 23. A little of the fluid is thus
filtered clear, poured into a test-tube, and tested with a drop from the
burette; this is afterwards returned to the beaker, and more of the test
solution added, if necessary. The operation is repeated until the precipita-
tion is complete. In order to be sure that too much of the baryta solution
has not been added, a drop of the clear fluid is added to the solution of sodic
sulphate placed in a test-tube or upon a small mirror (see p. 328). If no
precipitate occurs, more baryta must be added ; if a slight cloudiness takes
place, the analysis is finished ; but if much precipitate is produced, too large.
a quantity of the test has been used, and the analysis must be repeated.

For instance, suppose that 18'5 c.c. have been added, and there
is still a slight cloudiness produced which no longer increases after
the addition of another J c.c., we know that between 18^ and
19 c.c. of solution have been required to precipitate the whole of
the sulphuric acid present, and that accordingly the 100 c.c. of
urine contain between 0*185 and 0*19 gm. of SO3.

7. Estimation of Sugar.

Feh ling's original method is precisely the same as described
in § 74, but the most suitable methods for urine are Gerrard's
(p. 317) or the Pavy-Fehling (p. 315).

Process for the Ct/ano-cupric Solution .- 10 c.c. of the clear urine are diluted
by means of a measuring flask to 200 c.c. with water, and a large burette
filled with the fluid. To 10 c.c. of the copper solution prepared as directed
(p. 317) are then measured another 10 c.c. of copper and the liquid, the
vessel brought to boiling ; the diluted urine is then delivered in cautiously
from the burette while still boiling, and with constant stirring, until the
bluish colour has nearly disappeared. The addition of the urine must then
be continued more carefully, until the colour is all removed, the burette
is then read off, and the quantity of sugar in the urine calculated as
follows : —

Suppose that 40 c.c. of the diluted urine have been required to reduce
the 10 c.c, of copper solution, that quantity will have contained 0'05 gm. of
sugar; but, the urine being diluted 20 times, the 40 c.c. represent only 2 c.c.
of the original urine; therefore 2 c.c. of it contain 0'05 gm. of sugar, or
25 parts per 1000.

If the Pavy-Fehling solution is used it is prepared as described
in § 74 (p. 315).

Process : 10 c.c. of clear urine are diluted as just described, and delivered
cautiously from the burette into 50 or 100 c.c. of the Pavy-Fehling
liquid (previously heated to boiling) until the colour is discharged. The
calculation is the same as before. 100 c.c. of Pavy-Fehling solution
=0'05 gm. glucose.

The ammoniacal fumes are best absorbed by leading an elastic tube
from the reduction flask into a beaker of water ; the end of the tube should
be plugged with a piece of solid glass rod, and a transverse slit made in the

392 VOLUMETRIC ANALYSIS. § 87.

elastic tube just above the plug. This valve allows the vapours to escape,
but prevents the return of the liquid in case of a vacuum.

Dr. Edmunds communicates the following colorimetric method
for Sugar in Urine.

A ready preliminary test for sugar in urine is essential for medical
practitioners at the bedside or in the consulting room. An excellent and
handy test is that of picric acid, as recommended by Sir George Johnson,
but which has not come into general use because of the complexity of the
process ; the two solutions and the urine being added together in different
portions. I simplify the proceeding by substituting soda for potash, which
gives a soluble salt ; and then making the solution up so that it and the
, imne are always added together in equal volumes : on boiling the depth of
colour at once displays the presence of sugar, unless only questionable traces
are present, a question to decide which the ordinary laboratory processes
must be resortod to.

For the ready test I take a solution containing 0'5 % of pure picric acid
and 1 % of pure caustic soda, made up with freshly boiled distilled water to
volume. Any convenient quantity of the urine is poured into a test tube,
and to it is added about an equal volume of the picrate solution. On boiling
the mixture for one minute the presence of an opaque red-brown colour at
once appears if there be as much as 1 % of sugar in the urine. Normal
urine gives a full transparent blood-red colour, as can be seen at once by
testing any normal urine. This red colour is due to the kreatinine in the
urine, which, reduces the picric to picramic acid, precisely as is done by
glucose. The standard of colour can also be precisely realized by using
a 0'2 °/0 solution of pure dextrose in distilled water.

It is most convenient to pour 10 c.c. of this solution of dextrose into an
ordinary 25 c.c. hand-measure, and then to fill up to 20 c.c. with the sodium
picrate solution. On boiling this mixture in a test -tube for one minute,
a deep transparent blood-red solution is obtained which represents the
reducing power of the kreatinine in normal urine. If, on testing a urine,
an opaque red-brown liquid be obtained, the urine should then be diluted
with distilled water to ten times its volume, and the test reapplied to the
diluted urine in equal volumes as at first. If this gives still an opaque-red,
the urine must be further diluted, and again used in equal measured volumes
with the test solution. On the other hand, if the resulting mixture is too
pale the dilution must be less, and the dilution factor multiplied with 0'2 °/0
gives the percentage of glucose in the urine. For precise colorimetric work
the mixture should be poured into standard tubes of equal diameter as
recommended by Allen, and then viewed side by side with the decoction
obtained by using a 0'2 °/0 solution of pure dextrose in distilled water.

The solution above described keeps perfectly, and the process is as handy
as that of estimating albumen in urine by boiling and acidulating with
normal acetic acid.

8. Estimation of Uric Acid.

A method for the accurate estimation of this constituent of
urine has, up to the present, not been found. The difficulty is
caused by the complicated character of the urine itself, and how-
ever accurate the process may be with the acid in a separate pure
state, it becomes far less reliable when such method is applied to
normal or abnormal urine. The precipitation of the acid in
combination with some metal, such as silver or copper, carries

§ 87. UIUXE. 393

with it also the so-called alloxuric bases, and the separation by
hydrochloric acid contaminates the precipitate with colouring and
other matters which militate against its accurate estimation with
permanganate. I am, however, of the opinion that the latter
method is even now the best for a rapid comparative estimation
of this constituent.

Process : 200 c.c. of the urine are put into an evaporating basin with
a few drops of concentrated hydrochloric acid, and evaporated on the water
bath to about half the volume ; it is then transferred to a closely-stoppered
flask, together with any slight precipitate which may have formed. 5 c.c.
of concentrated hydrochloric acid are then added, and the mixture violently
shaken for a few minutes. It is then allowed to settle for half an hour and
the liquid passed through a small filter of smooth, hard texture, taking care
to pass as little as possible of the sediment to the filter. About 20 c.c. of
cold water are then added to the precipitate in the flask, which is in turn
passed through the filter. The filter is then also washed with about the
same quantity of water; a hole is then made at its apex, and the small
quantity of adhering precipitate washed into the original flask. Finally
about 10 c.c. of concentrated solution of caustic potash (1 : 10) are added
to the contents of the flask and slightly warmed until a clear solution is
obtained. The mixture is then diluted with about 100 c.c. of cold water,
20 c.c. of dilute sulphuric acid added (1 : 5), and the titration with T^
permanganate carried out in the usual manner.

Xo absolute weight of uric acid can be calculated from the
results, but Mohr assumes that each c.c. of ~ permanganate
= 0'0075 gm. of uric acid;'"" the process may, however, be made
available for pathological purposes by comparing the results from
time to time with the urine from the same person.

The following recent method has, in my opinion, a better claim
to accuracy as respects the actual amount of uric acid present in
any given specimen of urine than any other. It is based on the
fact that an alkaline solution of uric acid reduces Fehling
solution in the same way as glucose. The method is worked
out by E. Eiegler (Z. a. C. 1896, 31), who found that an average
of many experiments gave 0*8 gin. of reduced copper for 1 gm.
of uric acid. The acid is first separated from the urine under
examination as ammonic urate in the following manner : —

Process : 200 c.c. of urine are mixed with 10 c.c. of a saturated solution
of sodic carbonate, allowed to stand for half an hour, and filtered from the
precipitated phosphates. The precipitate is washed with 50 c.c. of hot
water, and to the filtrate and wash-water 20 c.c. of a saturated solution of
ammonic chloride added. The liquid is well stirred, and after five hours
filtered, preferably through a Schleicher and S chilli filter, No. 597,
11 c.m. The precipitate is washed with 50 c.c. of water, and then introduced
by means of a jet from a washing-bottle into a 300 c.c. beaker. Several
drops of potash are added to clear the liquid, then 60 c.c. of Fell ling's
solution, and the whole well stirred. The beaker is then heated on a wire
gauze until the liquid boils, the boiling being continued for five minutes.

* This figaire has been verified by F. G. Hopkins (Allen's Chemistry of Urine,
]?. 171).

394 VOLUMETRIC ANALYSIS. § 87.

AVhen the precipitate has subsided, the liquid is filtered through a small
tough filter (Schleicher and S chilli, No. 590, 9 c.m.), the precipitate
well washed, and dissolved in 20 c.c. of nitric acid (sp. gr. I'l), the filter
being washed with 60 c.c. of water.

To this solution dry powdered sodic carbonate is added little by little
until there is a permanent turbidity. The liquid is then cleared by the
cautious addition of dilute sulphuric acid, and made up to 100 c.c. 25 c.c.
of this are placed in a 100 c.c. flask, 1 gm. of potassic iodide in 10 c.c. of
water added, allowed to stand for ten minutes, then titrated with standard
thiosulphate solution (1 c.c. = 0'002 gm. uric acid), using starch as the
indicator. To the total amount of uric acid found in the 200 c.c. of urine,
an additional 0'030 gm. should be added to allow for the solubility of the
ammonic urate in urine.

The standard thiosulphate solution is made by diluting 126 c.c.
of y^- solution to 500 c.c. The reaction is : — •

2Cu(ST03)2 + 4KI =Cu2!2 + 4KN03 + 12.

The reduced cuprous oxide may also be weighed directly or reduced
to metallic copper, as in the estimation of sugar. In the latter
case the amount of copper, multiplied by the factor 1*25, gives
the corresponding amount of uric acid.

Dr. Edmunds sends me the following pertinent remarks as to
the estimation of Uric Acid.

1. Chemical uric acid differs entirely in its habitudes from urinary uric
acid. Its crystalline form is always uniform as chemical uric acid— colour-
less— and quite different from urinary uric acid, which, as got from urine, is
always coloured yellow-brown, and is protean in its crystalline forms.

2. The problem of titrating chemical uric acid — or pure uric acid — is
not quite the same as that of titrating the uric acid in urine. I am not
yet able to say in what the difference consists, and I have often crystallized
pure uric acid out of iron and other solutions, but have never been able to
colour uric acid, nor to get it to crystallize again like urinary uric acid.
The only way in which I have succeeded is to add an alkaline solution of
chemical urate of potash to a urine out of which I had precipitated all its-
uric acid with HC1. In that way I found that the uric acid took up from
the urine something which gave it the colouration and the protean crystalline
form of urinary uric acid. I have thought that urinary uric acid is really
a combination of chemical uric acid with some animal base or colourant
of urine.

3. To purify urinary uric acid it should be dissolved (and thrown out by
dilution) in H2SO4 three successive times. In titrating this with per-
manganate I am not prepared to give you the reaction, but the practical
point is that, as the permanganate goes in by drops, it is instantly decolour-
ized as long as there is any uric acid present, and the end-point is marked
quite distinctly (if you are on the look out for it) by a certain hang or
hesitation in the decolonization of the permanganate.

4. Fokker's process, as modified by Hopkins, is, I think, the best.
The saturation with absolutely pure NH4C1 of an acid urine (which should
be freshly passed and filtered at 120°) throws out all the uric acid as ammonic
urate. This is well set out in Allen's Chemistry of Urine, p. 168, et seq.
But much of the work does not say whether the processes have been worked
out on the chemical uric acid or on the real "uric acid," as we call it,

§ 87. uniXE. 395

freshly obtained from urine. "What we have to deal with in medicine is that
coloured protean crystalline . substance which comes out constantly from
urines on adding pure strong HC1 and setting aside for forty-eight hours.
That is what we get in the uric acid diathesis, in gout, and in calculi.

For the estimation of uric acid I set aside 100 c.c. of fresh urine, filtered
at about 120° F., and acidify it with 5 °/0 of pure strong hydrochloric acid.
At the end of forty-eight hours a deposit of uric acid will be seen at the
bottom of the tube, and from this a very good idea is gained of the uric
acid in the urine. If closer quantification be wanted, the uric acid is
collected on a small fine filter paper, washed with a few centimeters of ice-
cold distilled water, then dried and weighed, with deduction for the filter
paper, and with addition for the uric acid dissolved in the 105 c.c. of acid
urinar}'" mother-liquor. The amount of uric acid contained in the 105 c.c,
of liquid would depend upon the temperature before and at the time of
filtration. At 33° F. it would contain only some 2 m.gm., at 68° F. it would
contain 6 m.gm., at 212° F. it would contain 62'5 m.gm.

9. Estimation of Lime and Mag-nesia.

Process: 100 c.c. of the urine are precipitated with ammonia, the
precipitate re-dissolved in acetic acid, and sufficient ammonic oxalate added
to precipitate all the lime present as oxalate. The precipitate is allowed to
settle in a warm place, then the clear liquid passed through a small filter,
the precipitate brought upon it, washed with hot water, the filtrate and
washings set aside, then the precipitate, together with the filter, pushed
through the funnel into a flask, some sulphuric acid added, the liquid freely
diluted, and titrated with permanganate, precisely as in § 52; each c.c. of
jV permanganate required represents 0'0028 gin. of CaO.

Or the following method may be adopted : —

The precipitate of calcic oxalate, after being washed, is dried and, together
with the filter, ignited in a platinum or porcelain crucible, by which means
it is converted into a mixture of calcic oxide and carbonate. It is then
transferred to a flask by the aid of the washing-bottle, and an excess of •£$
nitric acid delivered in with a pipette. The amount of acid, over and above
what is required to saturate the lime, is found by T\ caustic alkali, each c.c.
of acid being equal to 0'0028 gm. of CaO.

In examining urinary sediment or calculi for calcic oxalate, it is
first treated with caustic potash to remove uric acid and organic
matter, then dissolved in sulphuric acid, freely diluted, and titrated
with permanganate ; each c.c. of ~ solution represents 0'0054 gm.
of calcic oxalate.

Mag-nesia. — The filtrate and washings from the precipitate of
calcic oxalate are evaporated on the water bath to a small bulk,
then made alkaline writh ammonia, sodic phosphate added, and set
aside for 8 or 10 hours in a cool place, that the magnesia may
separate as ammonio-magnesic phosphate. The supernatant liquid
is then passed through a small filter, the precipitate brought upon
it, washed with ammoniacal water in the cold, and dissolved in
acetic acid, then titrated with uranium solution, as in § 72 ; each
c.c. of solution required represents 0*002815 gm. of magnesia.

396 VOLUMETRIC ANALYSIS. § 87.

10. Ammonia.

The only method hitherto applied to the determination of
.ammonia in urine is that of 8 ch losing, which consists in placing
a measured quantity of the urine, to which milk of lime is
previously added, under an air-tight hell-glass, together with an
•open vessel containing a measured quantity of titrated acid. In
the course of from 24 to 36 hours all the ammonia will have
passed out of the urine into the acid, which is then titrated with
standard alkali to find the amount of ammonia absorbed.

One great objection to this method is the length of time required,
.since no heating must be allowed, urea being decomposed into free
ammonia, when heated with alkali. There is also the uncertainty
as to the completion of the process ; and if the vessel be opened
before the absorption is perfect, the analysis is spoiled. The
following plan is recommended as in most cases suitable : — When
a solution containing salts of ammonia is mixed with a measured
quantity of free fixed alkali of known strength, and boiled until
ammoniacal gas ceases to be evolved, it is found that the resulting
liquid has lost so much of the free alkali as corresponds to the
ammonia evolved (§ 19) ; that is to say, the acid which existed in
combination with the ammonia in the original liquid has simply
changed places, taking so much of the fixed alkali (potash or soda)
as is equivalent to the ammonia it has left to go free. In the case
of urine being treated in this way, the urea will also be decomposed
into free ammonia, but happily in such a way as not to interfere
with the estimation of the original amount of ammoniacal salts.
The decomposition is such that, while free ammonia is evolved from
the splitting up of the urea, carbonate of fixed alkali (say potash)
is formed in the boiling liquid, arid as this reacts equally as alkaline
as though it were free potash, it does not interfere in the slightest
degree with the estimation of the original ammonia.

Process : 100 c.c. of the urine are exactly neutralized with ^ soda or
potash, as for the estimation of free acid ; it is then put into a flask capable
of holding five or six times the quantity, 10 c.c. of normal alkali added, and
the whole brought to boiling, taking care that the bladders of froth which
at first form do not boil over. After a few minutes these subside, and the
boiling proceeds quietly. When all ammoniacal fames are dissipated, the
lamp is removed, and the flask allowed to cool slightly ; the contents then
emptied into a beaker, and normal nitric acid delivered in from the burette
with constant stirring, until a fine glass rod or small feather dipped in the
mixture and brought in contact with violet-coloured litmus paper produces
neither a blue nor a red spot. The number of c.c. of normal acid are
deducted from the 10 c.c. of alkali, and the rest calculated as ammonia.
1 c.c. of alkali = 0'017 gm. of ammonia.

Example : 100 c.c. of urine were taken, and required 7 c.c. of -^f alkali
to saturate its free acid ; 10 c.c. of normal alkali were then added, and the
mixture boiled until a piece of moistened red litmus paper was not turned
blue when held in the steam ; 4'5 c.c. of normal acid were afterwards required
to saturate the free alkali ; the quantity of ammonia was therefore equal to
5'5 c.c., which, multiplied by O'OIT, gave 0'0935 gm. in 1000 of urine.

§ 87. UIUXE. 397

It must be borne in mind, that the plan just described is not applicable to
urine which has already suffered decomposition by age or other circumstances
so as to contain carbonate of ammonia ; in this case it would be preferable to
adopt Schl 6 sing's method; or where no other free alkali is present, direct
titratiou with normal acid may be adopted.

11. Estimation of Free Acid.

The acidity of urine is doubtless owing to variable substances,,
among the most prominent of which appear to be acid sodic phos-
phate and lactic acid. Other free organic acids are probably in
many cases present. Under these circumstances, the degree of
acidity cannot be placed to the account of any particular body ;.
nevertheless, it is frequently desirable to ascertain its amount,
which is best done as follows : —

100 c.c. of urine are measured into a beaker, and ^ alkali delivered in
from a small burette, until a thin glass rod or feather, moistened with the-
mixture and streaked across some well-prepared violet litmus paper, produces
no change of colour ; the degree of acidity is then registered as being equal
to the quantity of ^V alkali used.

12. Estimation of Albumen.

Bodeker has worked out a method of titration which gives
approximate results when the quantity of albumen is not too
small, say not less than 2 per cent. The principle is based on the
fact that, potassic ferrocyanide completely precipitates albumen
from an acetic acid solution in the atomic proportions of 211
ferrocyanide to 1612 albumen.

Standard Solution of Ferrocyanide. — 1*309 gm. of the pure-
salt in a liter of distilled water. 1 c.c. of the solution precipitates
O01 gm. of albumen. It must be freshly prepared.

Process : 50 c.c. of the clear filtered urine are mixed with 50 c.c. of
ordinary commercial acetic acid, and the fluid put into a burette. Pive or
six small niters are then chosen, of close texture, and put into as many
funnels, then moistened with a few drops of acetic acid, and filled up with
boiling water ; by this means the subsequent clear filtration of the mixture
is considerably facilitated. 10 c.c. of the ferrocyanide solution are then
measured into a beaker, and 10 c.c. of the urinary fluid from the burette
added, well shaken, and poured upon filter No. 1. If the fluid which
passes through is bright and clear with yellowish colour, the ferrocyanide
will be in excess, and a drop of the urine added to it will produce a cloudiness.
On the other hand, if not enough ferrocyanide has been added, the filtrate
will be turbid, and pass through very slowl}r ; in this case, frequently both
the ferrocyanide and the urine will produce a turbidity when added. In
testing the filtrate for excess of ferrocyanide, care must be taken not to add
too much of the urine, lest the precipitate of hydroferrocyanide of albumen
should dissolve in the excess of albumen.

According to the results obtained from the first filter, a second trial is
made, increasing the quantity of urine or ferrocyanide half or as much
again, and so until it is found that the solution first shown to be in excess is
reversed. A trial of the mean between this quantity and the previous one
will bring the estimation closer, so that a final test may be decisive.

398 VOLUMETRIC ANALYSIS. § 88.

Example: 50 c.c. of urine passed by a patient suffering from B right's
disease were mixed with the like quantity of acetic acid, and tested as
follows: —

In filtrate

Urine. Ferrocyanide. Urine Ferrocyanide

gave

1. 10 c.c. ' 10 c.c. 0 prec.

2. 10 „ 20 „ prec. 0

3. 10 „ 15 „ 0 prec.

4. 10 „ 17-5 ., 0 faint prec.

5. 10 „ 18 „ 0 0

Therefore the 10 c.c. of diluted urine ( = 5 c.c. of the original
secretion) contained 0P18 gm. albumen, or 36 parts per 1000.

13. Estimation of Soda and Potash..

50 c.c. of urine are mixed with the same quantity of baryta solution,
allowed to stand a short time, and filtered ; then 80 c.c. ( = 40 c.c. urine)
measured into a platinum dish and evaporated to dryness in the water bath ;
the residue is then ignited to destroy all organic matter, and when cold
dissolved in a small quantity of hot water, ammonic carbonate added so long
as a precipitate, occurs, filtered through a small filter, the precipitate washed,
the filtrate acidified with hydrochloric acid and evaporated to dr}mess, then
cautiously heated to expel all ammoniacal salts. The residue is then treated
with a little water and a few drops each of ammonia and ammonic carbonate,
filtered, the filter thoroughly washed, the filtrate and washings received into
a tared platinum dish, then evaporated to dryness, ignited, cooled, and
weighed.

By this means the total amount of mixed sodic and potassic
chlorides is obtained. The proportion of each is found by titrating
for the chlorine as in § 41, and calculating as directed on page 141.

14. Estimation of Total Nitrogen.

This can now be easily accomplished by Kjeldahl's method
(§ 19.5) and is especially serviceable, since it has been found that
the results of the titration method for urea by Lie big's process,
either in its original way or by subsequent modifications, cannot
give the true data for calculating the nitrogen in any given specimen
of urine.

Process : 5 c.c. of urine of average concentration are measured into
a flask holding about 300 c.c., together with 20 c.c. of sulphuric acid, then
heated to boiling, and the heat continued until all vapour and gases are
given off and the fluid possesses a clear yellow tint. 25 to 30 minutes
generally suffices. The flask is then suffered to cool, the liquid diluted, and
distilled with caustic soda and zinc as described on page 85.

ANALYSIS OF NATURAL WATERS AND SEWAGE.

§ 88. THE analysis of natural waters and sewage has for a long
period received the attention of chemists, but until lately no methods
of examination have been produced which could be said to satisfy
the demands of those who have been interested in the subject

§ 88. WATER ANALYSIS. 399

from various points of view. The researches of Frank land, and
Armstrong, Miller, "Wanklyn, Tidy, Bischof, Warington,
and others, have, however, now brought the whole subject into
a more satisfactory form, so that it may fairly be said that, as regards
accuracy of chemical processes, or interpretation of results from
a chemical and sanitary point of view, very little addition is
required. Considerable space will be devoted to the matter here ;
and as most of the processes are now volumetric, and admit of
ready and accurate results, the general subject naturally falls with-
in the scope of this work. Care has been taken to render the
treatment of the matter practical and trustworthy.

The following processes mainly originated by Frankland and
Armstrong necessitate the use of peculiar materials and
apparatus : the preparation and arrangement of these will be
described at some length previous to the introduction of the
general subject.

THE PREPARATION OF REAGENTS.

A. Reagents required for the Estimation of Nitrogen present as

Ammonia.

(a) Xessler's Solution. — Dissolve 62*5 gm. of potassic iodide
in about 250 c.c. of distilled water, set aside a few c.c,, and add
gradually to the larger part a cold saturated solution of corrosive
sublimate until the mercuric iodide precipitated ceases to be
redissolved on stirring. When a permanent precipitate is obtained,
restore the reserved potassic iodide so as to redissolve it, and
continue adding corrosive sublimate very gradually until a slight
precipitate remains undissolved. (The small quantity of potassic
iodide is set aside merely to enable the mixture to be made rapidly
without danger of adding an excess of corrosive sublimate.)

^N"ext dissolve 150 gm. of solid potassic hydrate (that usually
sold in sticks or cakes) in 150 c.c. of distilled water, allow the
solution to cool, add it gradually to the above solution, and make
up with distilled water to one liter.

On standing, a brown precipitate is deposited, and the solution
becomes clear, and of a pale greenish-yellow colour. It is ready
for use as soon as it is perfectly clear, and should be decanted into
a smaller bottle as required.

(/3) Standard Solution of Ammonic chloride. — Dissolve 1'9107
gm. of pure dry ammonic chloride in a liter of distilled water ; of
this take 100 c.c., and make up to a liter with distilled water.
The latter solution will contain ammonic chloride corresponding to
0'00005 gm. of nitrogen in each c.c. In use it should be measured
from a narrow burette of 10 c.c. capacity divided into tenths.

[If it is desired to estimate " ammonia " rather than " nitrogen as
ammonia," take T5735 gm. of ammonic chloride instead of 1'9107 gm.
1 c.c. will then correspond to O'OOOOS gm. of ammonia (NH3).]

400 VOLUMETRIC ANALYSIS. § 88.

(y) Sodic carbonate. — Heat anhydrous sodic carbonate to
redness in a platinum crucible for about an hour, taking care not
to fuse it. While still warm rub it in a clean mortar so as to
break any lumps which may have been formed, and transfer to
a clean dry wide-mouthed stoppered bottle.

(3) Water free from Ammonia. — If, when 1 c.c. of !N"essler's
solution (A. a) is added to 100 c.c. of distilled water in a glass
cylinder, standing on a white surface (see Estimation of Ammonia),
no trace of a yellow tint is visible after five minutes, the water is
sufficiently pure for use. As, however, this is rarely the case, the
following process must usually be adopted. Distil from a large
glass retort (or better, from a copper or tin vessel holding 15 — 20
liters) ordinary distilled water which has been rendered distinctly
alkaline by addition of sodic carbonate. A glass Liebig's
condenser, or a clean tin worm should be used to condense the
vapour ; it should be connected to the still by a short india-rubber
joint. Test the distillate from time to time with jSTessler's
solution, as above described, and when free from ammonia collect
the remainder for use. The distillation must not be carried to
dryness. Ordinary water may be used instead of distilled water,
but it occasionally continues for some time to give off traces of
ammonia by the slow decomposition of the organic matter present
in it.

B. Reagents required for the Estimation of Organic Carbon and

Nitrogen.

(a) Water free from Ammonia and Organic Matter. — Distilled
water, to which 1 gm. of potassic hydrate and 0'2 gm. of potassic
permanganate per liter have been added, is boiled gently for about
twenty-four hours in a similar vessel to that used in preparing
water free from ammonia (A. £), an inverted condenser being so
arranged as to return the condensed water. At the end of that
time the condenser is adjusted in the usual way, and the water
carefully distilled, the distillate being tested at intervals for
ammonia, as in. preparing A. 3. When ammonia is no longer
found the remainder of the distillate may be collected, taking care
to stop short of dryness. The neck of the retort or still should
point slightly upwards, so that the joint which connects it with
the condenser is the highest point. Any particles carried up
mechanically will then run back to the still, and not contaminate
the distillate. The wate"r thus obtained should then be rendered
slightly acid with sulphuric acid, and re-distilled from a clean
vessel for use, again stopping short of dryness.

(/3) Solution of Sulphurous acid. — Sulphurous anhydride is
prepared by the action of pure sulphuric acid upon cuttings of
clean metallic copper which have been digested in the cold with

§88. WATER ANALYSIS. 401

concentrated sulphuric acid for twenty-four hours, and then washed
with water. The gas is made to bubble through water to remove
mechanical impurities, and then conducted into water free from
ammonia and organic matter (B. a) until a saturated solution is
•obtained.

(y) Solution of Hydric sodic sulphite. — Sulphurous anhydride,
prepared and washed as above, is passed into a solution of sodic
carbonate made by dissolving ignited sodic carbonate (A. y) in
water free from ammonia and organic matter (B. a). The gas is
passed until carbonic anhydride ceases to be evolved.

(o) Solution of Ferrous chloride. — Pure crystallized ferrous
•sulphate is dissolved in water, precipitated by sodic hydrate, the
precipitate well washed (using pure water B. a for the last
washings), and dissolved in the smallest possible quantity of pure
hydrochloric acid. Two or three drops must not contain an
appreciable quantity of ammonia. It is convenient to keep the
solution in a bottle with a ground glass cap instead of a stopper,
so that a small dropping tube may be kept in it always ready
for use.

(e) Cupric oxide. — Prepared by heating to redness with free
access of air, on the hearth of a reverberatory furnace, or in
•a muffle, copper wire cut into short pieces, or copper sheets cut into
strips. That which has been made by calcining the nitrate cannot
be used, as it appears to be impossible to expel the last traces of
nitrogen. After use, the oxide should be extracted by breaking
the combustion tube, rejecting the portion which was mixed with
the substance examined. As soon as a sufficient quantity has been
recovered, it should be recalcined. This is most conveniently
•done in an iron tube about 30 m.m. in internal diameter, and about
the same length as the combustion furnace. One end should be
•closed with a cork, the cupric oxide poured in, the tube placed in
the combustion furnace (which is tilted at an angle of about 15°,
so as to produce a current of air), the cork removed, and the tube
Icept at a red heat for about two hours. In a Hofmann's gas
furnace, with five rows of burners, two such tubes may be heated
at the same time if long clay burners are placed in the outer rows,
and short ones in the three inner rows. If the furnace has but
three rows of burners, a rather smaller iron tube must be used.
"When cold, the oxide can easily be extracted, if the heat has not
"been excessive, by means of a stout iron wire, and should be kept
in a clean dry stoppered bottle. Each parcel thus calcined should
invariably be assayed by filling with it a combustion tube of the
usual size, and treating it in every respect as an ordinary combustion.
It should yield only a very minute bubble of gas, which should be
almost wholly absorbed by potassic hydrate. (The quantity of
•CO2 found should not correspond to more than 0-00005 gm. of C,

D D

402 VOLUMETRIC ANALYSIS. § 88.

otherwise the oxide must be recalcined). The finer portions of the
oxide should, after calcining, he sifted out by means of a sieve of
clean copper gauze, and reserved for use as described hereafter.

New cupric oxide as obtained from the reverberatory furnace
should be assayed, and if not sufficiently pure, as is most likely the
case, calcined as above described, and assayed again.

(£) Metallic Copper. — Fine copper gauze is cut into strips
about 80 m.m. wide, and rolled up as tightly as possible on
a copper wire so as to form a compact cylinder 80 m.m. long. This
is next covered with a tight case of moderately thin sheet copper,
the edges of which meet without overlapping. The length of the
strip of gauze, and the consequent diameter of the cylinder, must
be regulated so that it will fit easily, but not too loosely in the
combustion tubes. A sufficient number of these cylinders being-
prepared, a piece of combustion tube is filled with them, and they
are heated to redness in the furnace, a current of atmospheric air
being passed through them for a few minutes in order to burn off
organic impurity, and coat the copper gauze superficially with
oxide. A current of hydrogen, dried by passing through strong
sulphuric acid, is then substituted for the air, and a red heat
maintained until hydrogen issues freely from the end of the tube.
It is then allowed to cool, the current of hydrogen being continued,
and when cold the copper cylinders are removed, and kept in
a stoppered bottle. After being used several times they must be
heated in a stream of hydrogen as before, and are then again ready
for use. The heating in air need not be repeated.

(rj) Solution of Potassic bichromate. — This is used as a test
for and to absorb sulphurous anhydride which may be present in
the gas obtained by combustion of the water residue. It should
be saturated, and does not require any special attention. The
yellow neutral chromate may also be used, but must be rendered
slightly acid, lest it should absorb carbonic as well as sulphurous
anhydride,

(6) Solution of Potassic hydrate. — A cold saturated solution,
made by dissolving solid potassic hydrate in distilled water.

(t) Solution of Pyrogallic acid. — A cold saturated solution,
made by dissolving in distilled water solid pyrogallic acid obtained
by sublimation.

(K) Solution of Cuprous chloride. — A saturated solution of
cupric chloride is rendered strongly acid with hydrochloric acid,
a quantity of metallic copper introduced in the form of wire or
turnings, and the whole allowed to stand in a closely stoppered
bottle until the solution becomes colourless.

(X) Oxygen. — Blow a bulb of about 30 c.c. capacity at the end
of a piece of combustion tube, and draw out the tube so that its
internal diameter for a length of about 30 m.m. is about 3 m.m.

§ 88. WATER ANALYSIS. 403

This is done in order that the capacity of the apparatus apart from
the bulb may be as small as possible. Cut the tube at the wide
part about 10 m.m. from the point at which the narrow tube
commences, thus leaving a small funnel-shaped mouth. Then
introduce, a little at a time, dried, coarsely powdered, potassic
chlorate until the bulb is full. Cut off the funnel, and, at
a distance of 100 m.m. from the bulb, bend the tube at an angle
of 45°, and at 10 m.m. from the end bend it at right angles in the
opposite direction. It then forms a retort and delivery tube in
one piece, and must be adjusted in a mercury trough in the usual
manner, taking care that the end does not dip deeper than about
20 m.m. below the surface, as otherwise the pressure of so great
a column of mercury might destroy the bulb when softened by
heat. On gently heating, the potassic chlorate fuses and evolves
oxygen. The escaping gas is collected in test tubes about 150 m.m.
long and 20 m.m. in diameter, rejecting the first 60 or 80 c.c.,
which contain the nitrogen of the air originally in the bulb retort,
l^ive or more of these tubes, according to the quantity of oxygen
required, are collected and removed from the mercury trough, in
very small beakers, the mercury in which should be about 10 m.m.
above the end of the test tube. Oxygen may be kept in this way
for any desired length of time, care being taken, if the temperature
falls considerably, that there is sufficient mercury in the beaker to
keep the mouth of the test tube covered. About 10 c.c. of
the gas in the first tube collected is transferred by decantation in
a mercury trough to another tube, and treated with potassic hydrate
and pyrogallic acid, when, if after a few minutes it is absorbed,
with the exception of a very small bubble, the gas in that and the
remaining tubes may be considered pure. If not, the first tube is
rejected, and the second tested in the same way, and so on.

(n) Hydric metaphosphate. — The glacial hydric metaphosphato,
usually sold in sticks, is generally free from ammonia, or very
nearly so. A solution should be made containing about 100 gm.
in a liter. It should be so far free from ammonia as that 10 c.c.
do not contain an appreciable quantity.

(v) Calcic phosphate. — Prepared by precipitating common
disodic phosphate with calcic chloride, washing the precipitate
with water by decantation, drying, and heating to redness for
an hour.

C. Reagents required for the Estimation of Nitrogen present as
Nitrates and Nitrites (drum's process).

(a) Concentrated Sulphuric acid. — This must be free from
nitrates and nitrites.

(/3) Potassic permanganate. — Dissolve about 10 gm. of crys-
tallized potassic permanganate in a liter of distilled water.

D D 2

404 VOLUMETRIC ANALYSIS. § 88.

(y) Sodic carbonate. — Dissolve about 10 gm. of dry, or an
equivalent quantity of crystallized sodic carbonate free from

nitrates, in a liter of distilled water.

For the Estimation of Nitrogen as Nitrates and Nitrites in Waters
containing1 a very large quantity of Soluble Matter, but little
Organic Nitrogen.

(f) Solution of Sodic hydrate. — Dissolve 100 gm. of solid
sodic hydrate in a liter of distilled water ; when cold, put it in
a tall glass cylinder, and introduce about 100 sq. cm. of aluminium
foil, which must be kept at the bottom of the solution by means of
a glass rod. When the aluminium is dissolved, boil the solution
briskly in a porcelain basin until about one-third of its volume has
been evaporated, allow to cool, and make up to its original volume
with water free from ammonia. The absence of nitrates is thus
ensured.

(£) Broken Pumice. — Clean pumice is broken in pieces of the
size of small peas, sifted free from dust, heated to redness for
about an hour, and kept in a closely stoppered bottle.

(rj) Hydrochloric acid free from Ammonia. — If the ordinary
pure acid is not free from ammonia, it should be rectified from
sulphuric acid. As only two or three drops are used in each
experiment, it will be sufficient if that quantity does not contain
an appreciable proportion of ammonia.

For the Estimation of Nitrites by G-riess's Process.

(6} Meta-phenylene-diamine. — A half per cent, solution of the
base in very dilute sulphuric or hydrochloric acid. The base alone
is not permanent. If too highly coloured, it may be bleached by
pure animal charcoal.

(i) Dilute Sulphuric acid. — One volume of acid to two of
water.

(K) Standard Potassic or Sodic nitrite. — Dissolve 0*406 gm.
of pure silver nitrite in boiling distilled water, and add pure
potassic or sodic chloride till no further precipitate of silver
chloride occurs. Make up to a liter ; let the silver chloride settle,
and dilute 100 c.c. of the clear liquid to a liter. It should be kept
in small stoppered bottles completely filled, and in the dark.

1 c.c. -O'Ol m.gm. X20:!.

The colour produced by the reaction of nitrous acid on meta-
phenylene-diamine is triamidoazo-benzene, or " Bismarck brown."

§ 89. WATER ANALYSIS. 405

D. Reag-ents required for the Estimation of Chlorine present as

Chloride.

(a) Standard Solution of Silver nitrate. — Dissolve 2 '3944
gni. of pure recrystallized silver nitrate in distilled water, and
make up to a liter. In use it is convenient to measure it from
a burette which holds 10 c.c. and is divided into tenths.

((3) Solution of Potassic chromate. — A strong solution of pure
neutral potassic chromate free from chlorine. It is most con-
veniently kept in a bottle similar to that used for the solution of
ferrous chloride (B. <)).

E. Reagents required for determination of Hardness.

(a) Standard Solution of Calcic chloride. — Dissolve in dilute
hydric chloride, in a platinum dish, 0'2 gin. of pure crystallized
calcite, adding the acid gradually, and having the dish covered
with a glass plate, to prevent loss by spirting. When all is
dissolved, evaporate to dryness on a water bath, add a little distilled
water, and again evaporate to dryness. Repeat the evaporation
several times to ensure complete expulsion of hydric chloride.
Lastly, dissolve the calcic chloride in distilled water, and make up
to one liter.

(/3) Standard Solution of Potassic soap. — Rub together in
a mortar 150 parts of lead plaster (Emplast. Plumbi of the
druggists) and 40 parts of dry potassic carbonate. ' When they are
fairly mixed, add a little methylated spirit, and continue triturating
until an uniform creamy mixture is obtained. Allow to stand for
some hours, then throw on to a filter, and wash several times with
methylated spirit. The strong solution of soap thus obtained
must be diluted with a mixture of one volume of distilled water
and two volumes of methylated spirit (considering the soap solution
as spirit), until exactly 14'25 c.c. are required to form a permanent
lather with 50 c.c. of the standard calcic chloride (E. a), the
experiment being performed precisely as in determining the hardness
of a water. A preliminary assay should be made with a small
quantity of the strong soap solution to ascertain its strength.
After making the solution approximately of the right strength,
allow it to stand twenty-four hours ; and then, if necessary, filter
it, and afterwards adjust its strength accurately. It is better to
make the solution a little too strong at first, and dilute it to the
exact strength required, as it is easier to add alcohol accurately
than strong soap solution.

THE ANALYTICAL PROCESSES.

§ 89. To form, for sanitary purposes, an opinion of the character
of a natural water or sewage, it will in most cases suffice to
determine the nitrogen as ammonia, organic carbon, organic nitrogen,

406 VOLUMETRIC ANALYSIS. § 89.

total solid matter, nitrogen as nitrates and nitrites, suspended
matter, chlorine, and hardness ; and in the following pages the
estimation of these will be considered in detail, and then, more
briefly, that of other impurities.

The method of estimating nitrogen as ammonia is substantially
that described by the late W. A. Miller (/. C. S. [2] iii. 125),
and that for estimating organic carbon and nitrogen was devised
by Frank land and Armstrong, and described by them in the
same journal ([2] vi. 77 et seq.).

1. Collection of Samples. — The points to be considered under
this head are, the vessel to be used, the quantity of water required,
and the method of ensuring a truly representative sample.

Stoneware bottles should be avoided, as they are apt to affect the
hardness of the water, and are more difficult to clean than glass.
Stoppered glass bottles should be used if possible ; those known
as " Winchester Quarts," which hold about two and a half liters
each, are very convenient and easy to procure. One of these will
contain sufficient for the general analysis of sewage and largely
polluted rivers, two for well waters and ordinary rivers and streams,
and three for lakes, and mountain springs. If a more detailed
analysis is required, of course a larger quantity must be taken.

If corks must be used, they should be neic, and well washed
with the water at the time of collection.

In collecting from a well, river, or tank, plunge the bottle itself,
if possible, below the surface ; but if an intermediate vessel must
be used, see that it is thoroughly clean and well rinsed with the
water. Avoid the surface water and also any deposit at the
bottom.

If the sample is taken from a pump or tap, take care to let the
water which has been standing in the pump or pipe run off before
collecting, then allow the stream to flow directly into the bottle.
If it is to represent a town water-supply, take it from the service
pipe communicating directly with the street main, and not from
a cistern.

In every case, first fill the bottle completely with the water thus
expelling all gases and vapours, empty it again, rinse once or twice
carefully with the water, and then fill it nearly to the stopper, and
tie down tightly.

At the time of collection note the source of the sample, whether
from a deep or shallow well, a river or spring, and also its local
name so that it may be clearly identified.

If it is from a well, ascertain the nature of the soil, subsoil, and
water-bearing stratum ; the depth and diameter of the well, its
distance from neighbouring cesspools, drains, or other sources
of pollution ; whether it passes through an impervious stratum
before entering the water-bearing stratum, and if so, whether the
sides of the well above this are, or are not, water-tight.

§ 89. WATER ANALYSIS. 407

If the sample is from a river, ascertain the distance from the
source to the point of collection ; whether any pollution takes
place above that point, and the geological nature of the district
through which it flows.

If it is from a spring, take note of the stratum from which it
issues.

2. Preliminary Observations. — In order to ensure uniformity,
the bottle should invariably be well shaken before taking out
a portion of the sample for any purpose. The colour should be
observed as seen in a tall, narrow cylinder standing upon a white
surface. It is well to compare it Avith distilled water in a similar
vessel. The taste and odour are most easily detected when the
water is heated to 30°— 35° C.

Before commencing the quantitative analysis, it is necessary to
decide whether the water shall be filtered or not before analysis.
This must depend on the purpose for which the examination is
undertaken. As a general rule, if the suspended matter is to be
determined, the water should be filtered before the estimation of
organic carbon and nitrogen, nitrogen as ammonia, and total solid
residue ; if otherwise, it should merely be shaken up. If the
suspended matter is not determined, the appearance of the water,
as wrhether it is clear or turbid, should be noted. This is
conveniently done when measuring out the quantity to be used for
the estimation of organic carbon and nitrogen. If the measuring
flask be held between the eye and a good source of light, but with
an opaque object, such as a window bar, in the line drawn from
the eye through the centre of the flask, any suspended particles
will be seen well illuminated on a dark ground.

Water derived from a newly sunk well, or which has been
rendered turbid by the introduction of innocuous mineral matter
from some temporary and exceptional cause should be filtered, but
the suspended matter in most such cases need not be determined.
The introduction of organic matter of any kind Avould almost
always render the sample useless.

3. Estimation of Nitrogen as Ammonia. — Place about 50 C.C. of
the water in a glass cylinder about 150 m.m. high, and of about
70 c.c. capacity, standing upon a white glazed tile or white paper.
Add about 1 c.c. of ^sessler's solution (A. a), stir with a clean
glass rod, and allow to stand for a minute or so. If the colour
then seen does not exceed in intensity that produced when O'l c.c.
of the standard ammonic chloride (A. /5) is added to 50 c.c. of
water free from ammonia (A. £), and treated in the same way,
half a liter of the water should be used for the estimation. If
the colour be darker, a proportionately smaller quantity should be
taken ; but it is not convenient to use less than 20 or 25 c.c.

If it has been decided that the water should be filtered before
analysis, care must be taken, should it contain only a small quantity.

408 VOLUMETRIC ANALYSIS. § 89.

of ammonia, that the filter paper is free from ammonia. If it is
not, it must be steeped in water free from ammonia for a day or so,
and when used, the first portion of the filtrate rejected. Wasliimj
with water, even if many times repeated, is generally ineffectual.
When a large quantity of ammonia is present, as in highly polluted
water and sewage, any ammonia in the filter paper may be' neglected.
A moderate quantity of suspended matter may also generally be
neglected with safety, even if the water is to be filtered in
estimating organic carbon and nitrogen and total solid matter.

The water, filtered or unfiltered as the case may be, should be
carefully measured and introduced into a capacious retort, connected
by an india-rubber joint with a Liebig's condenser, the volume
being if necessary, made up to about 400 c.c. with water free from
ammonia. Add about 1 gni. of sodic carbonate (A. y), and distil
rapidly, applying the lamp flame directly to the retort, and collect
the distillate in a small glass cylinder, such as is described above.
When about 50 c.c. have distilled into the first cylinder, put it aside
and collect a second 50 c.c., and as soon as that is over remove the
lamp, and add to the second distillate about 1 c.c. of Messier 's
solution, stir with a clean glass rod, and allow to stand on a white
tile or sheet of paper for five minutes. To estimate the ammonia
present, measure into a similar cylinder as much of the standard
ammonic chloride solution as you judge by the colour to be present
in the distillate ; make it up with water free from ammonia to the
same volume, and treat with I^essler's solution in precisely the
same way. If, on standing, the intensity of colour in the two
cylinders is equal, the quantity of ammonia is also equal, and this
is known in the trial cylinder. If it is not equal, another trial
must be made with a greater or less quantity of ammonic chloride.
The ammonic chloride must not be added after the JSTessler's
solution, or a turbidity will be produced which entirely prevents
accurate comparison. If the ammonia in the second distillate does
not exceed that in 0*2 c.c. of the standard ammonic chloride, the
distillation need not be proceeded with any further, but if otherwise,
successive quantities must be distilled and tested until ammonia
ceases to be found. If the ammonia in the second distillate
corresponds to 0*4 c.c. or less of the ammonic chloride, that in the
first may be estimated in the same way ; but if the second contains
a greater quantity of ammonia, the first must be measured, and an
aliquot part taken and diluted to about 50 c.c. with water free from
ammonia, as it is likely to contain so much ammonia as to give
a colour too intense to admit of easy comparison. A colour produced
by more than 2 c.c. of ammonic chloride cannot be conveniently
employed.'"" When, as in the case of sewage, a large quantity of

* In order to insure absolute accuracy in Nesslerizing it is necessary that the distillate
should be of the same temperature as the standard liquid made by mixing the ammonic
chloride with distilled water. Hazen and Clark (Amer. Cliem. Jour. xii. 425) found
that the water Nesslerized from a metal condenser, immediately after collection, gave
a, lower figure than when the two liquids were allowed to assume the same temperature.

§ 89. WATER ANALYSIS. 409

ammonia is known to be present, it saves trouble to distil about
100 c.c. at first, and at once take an aliquot part of that, as above
described. If the liquid spirts in distilling, arrange the retort so
that the joint between the retort and condenser is the highest point;
the distillation will proceed rather more slowly, but anything
carried up mechanically will be returned to the retort. When the
ammonia has been estimated in all the distillates, add together the
corresponding volumes of ammonic chloride solution ; then, if 500
c.c. have been employed for the experiment, the number of c.c. of
ammonic chloride used divided by 100 will give the quantity of
nitrogen as ammonia in 100,000 parts of the water; if less than
that, say y c.c. have been used, multiply the volume of ammonic
chloride by 5 and divide by y.

Eefore commencing this operation, ascertain that the retort and
condenser are free from ammonia by distilling a little common
water or distilled water with sodic carbonate until the distillate is
free from ammonia. Remove the residue then, and after each
estimation, by means of a glass syphon, without disconnecting the
retort. If a small quantity of water is to be distilled, the residue
or part of it from a previous experiment may be left in the retort,
instead of adding water free from ammonia, care being taken that
the previous distillation was continued until ammonia ceased to be
evolved.

When urea is present the evolution of ammonia is long continued,
owing to the decomposition of the urea. In such cases, collect tbe
distillate in similar quantities, and as soon as the first rapid
diminution in the amount of ammonia has ceased, neglect the
remainder, as this would be due almost wholly to decomposition of
the urea.

4. Estimation of Org-anic Carbon and Nitrogen. — This should be
commenced as soon as the nitrogen as ammonia has been determined.
If that is less than 0'05 part per 100,000, a liter should be used ;
if more than 0'05, and less than 0'2, half a liter; if more than
0'2 and less than I'O, a quarter of a liter; if more than 1*0,
a hundred c.c. or less. These quantities are given as a guide in
dealing with ordinary waters and sewage, but subject to variation
in exceptional cases. A quantity which is too large should be
avoided as entailing needless trouble in evaporation, and an
inconveniently bulky residue and resulting gas. If it is to be
filtered before analysis, the same precaution as to filter paper must
be taken as for estimation of nitrogen as ammonia, the same filter
being generally used.

Having measured the quantity to be used, add to it in a capacious
flask 15 c.c. of the solution of sulphurous acid (B. /3), and boil
briskly for a few seconds, in order to decompose the carbonates
present. Evaporate to dryness in a hemispherical glass dish, about
a decimeter in diameter, and preferably without a lip, supported in

410 VOLUMETRIC ANALYSIS. § 89.

a copper dish with a flange (fig. 56 d e). The flange has a diameter
of about 14 centimeters, is sloped slightly towards the centre, and
has a rim of about 5 m.m. turned up on its edge, except at one
point, where a small lip is provided. The concave portion is made
to fit the contour of the outside of the glass dishes, and is of such
a depth as to allow the edge of the dish to rise about 15 m.m.
above the flange. The diameter of the concavity at / is about
90 m.m., and the depth at fj about 30 m.m. A thin glass shade,
such as is used to protect statuettes, about 30 centimeters high,
stands on the flange of the copper dish, its diameter being such as
to fit without difficulty on the flange, and leave a sufficient space
between its interior surface and the edge of the glass dish. The
copper dish is supported on a steam or water bath, and the water
as it evaporates is condensed on the interior of the glass shade, runs
down into the copper dish, filling the space between it and the
glass dish, and then passes off by the lip at the edge of the flange,
a piece of tape held by the edge of the glass shade, and hanging
over the lip, guiding it into a vessel placed to receive it.

We are indebted to Bischof for an improved apparatus for
evaporation, which by keeping the dish always full by a self-acting
contrivance, permits the operation to proceed without attention
during the night, and thus greatly reduces the time required.
This form of apparatus is shown in fig. 56. The glass dish d is
supported by a copper dish e as described above, and resting on
the latter is a stout copper ring Jt which is slightly conical, being
115 m.m. in diameter at the top and 130 at the bottom. At the top
is a narrow flange of about 10 m.m. with a vertical rim of about
5 m.m. The diameter across this flange is the same as the diameter
of the dish e, so that the glass shade i will fit securely either on k
or e. The height of the conical ring is about 80 m.m.

The automatic supply is accomplished on the well-known prin-
ciple of the bird fountain, by means of a delivery tube I, the upper
end of which is enlarged to receive the neck of the flask a con-
taining the water to be evaporated, the joint being carefully ground
so as to be water-tight. The upper vertical part of />, including
this enlargement, is about 80 m.m. in length, and the sloping part
about 260 m.m. with a diameter of 13 m.m. The lower end
which goes into the dish is again vertical for about 85 m.m., and
carries a side tube c of about 3 m.m. internal diameter, by which
air enters the delivery tube whenever the level of the water in the
dish falls below the point at which the side tube joins the delivery
tube. The distance from this point to the end of the tube which
rests on the bottom of the dish at g, and is there somewhat con-
tricted, is about 30 m.m. The side tube c should not be attached
on the side next the flask, as if so the inclined part of I passes
over its mouth and renders it very difficult to clean. Mills
prevents circulation of liquid in the sloping part of the tube by
bending it into a slightly undulating form, so that permanent

89.

WATER ANALYSIS.

411

bubbles of air are caught and detained at two points in it. The
flask a should hold about 1200 c.c. and have a rather narrow neck
— about 20 m.m. — and a flat bottom. A small slot is cut in the
upper edge of the copper ring li to accommodate the delivery tube,
as shown in fig. 55. Its size and shape should be such that the
tube does not touch the edge of the glass shade i, lest water
running down the inner surface of the shade should find its way
down the outside of the delivery tube into the dish. This being

Fig. 55.

Pig. 56.

avoided, the opening should be as closely adjusted to the size of the
delivery tube as can be. The copper dish e should rest on a steam
or water bath, so that only the spherical part is exposed to the
heat.

After the addition of the 15 c.c. of sulphuric acid, the water
may either be boiled in the flask a, or in another more capacious
one, and then transferred to a. It should be allowed to cool
before the delivery tube is adjusted, otherwise the joint between
the two is liable to become loose by expansion of the cold socket

412 VOLUMETRIC ANALYSIS. § 89.

of the delivery tube, after being placed over the hot neck of
the flask.

The glass dish having been placed on the copper dish e, the
conical ring It is fitted on, and the flask with the delivery tube
attached inverted, as shown in fig. 56, a b. This should not be
done too hurriedly, and with a little care ther? is no risk of loss.
The flask is supported either by a large wooden filtering stand, the
ring of which has had a slot cut in it to allow the neck of the flask
to pass, or by a clamp applied to the upper end of the delivery
tube where the neck of the flask fits in. The delivery tube having-
been placed in the slot made to receive it, the glass shade is fitted
on, and the evaporation allowed to proceed. When all the water
has passed from the flask into the dish, the flask and delivery tube,,
and the conical ring h may be removed, and the glass shade placed
directly on the dish e until the evaporation is complete. If the
water is expected to contain a large quantity of nitrates, two or
three drops of chloride of iron (B. £) should be added to the first
dishful ; and if it contains little or no carbonate, one or two c.c.
of hydric sodic sulphide (B. 7). The former facilitates the destruc-
tion of nitrates and nitrites, and the latter furnishes base for the
sulphuric acid produced by oxidation of the sulphurous acid, and
which would, if free, decompose the organic matter when concen-
trated by evaporation. An estimate of the quantity of carbonate
present, sufficiently accurate for this purpose, may generally be
made by observing the quantity of precipitate thrown down 011
addition of sodic carbonate in the determination of nitrogen as-
ammonia.

With sewages and very impure waters (containing upwards of Ol
part of nitrogen as ammonia per 100,000 for example) such great
precaution is hardly necessary, and the quantity to evaporate being
small, the evaporation may be conducted in a glass dish placed
directly over a steam bath, and covered with a drum or disc of filter
paper made by stretching the paper by means of two hoops of light
split cane, one^ thrust into the other, the paper being between them,
in the way often employed in making dialysers. This protects the
contents of the dish from dust, and also to a great extent, from
ammonia which may be in the atmosphere, and which would impair
the accuracy of the results. As a glass dish would be in some danger
of breaking by the introduction of cold water, the flask containing
the water being evaporated in this or in the first described manner,
must be kept on a hot plate or sand bath at a temperature of about
60° or 70° C., and should be covered with a watch-glass. This
precaution is not necessary when Bischof's apparatus is used.
If, at any time, the water in the flask ceases to smell strongly of
sulphurous acid, more should be added. The preliminary boiling
may be omitted when less than 250 c.c. is used. When the
nitrogen as nitrates and nitrites exceeds 0'5 part, the dish, after
the evaporation has been carried to dryness, should be filled with

§ 89. WATER ANALYSIS.

distilled water containing ten per cent, of saturated sulphurous
acid solution, and the evaporation again carried to dryness. If it
exceeds I'O part, a quarter of a liter of this solution should be
evaporated on the residue ; if 2'0 parts, half a liter ; and if 5 parts,
a liter. If less than a liter has been evaporated, a proportionally
smaller volume of this solution may be used. The estimation of
nitrogen as nitrates and nitrites will usually be accomplished before
this stage of the evaporation is reached.

M. W. Williams proposes to avoid the use of sulphurous acid,
with its acknowledged disadvantages and defects, by removing
the nitric and nitrous acids with the zinc-copper couple and
converting them into ammonia. If the amount is large, it is best
distilled from a retort into weak acid ; if small, into an empty
Messier tube. The amount so found is calculated into nitrogen
as nitrates and nitrites, if the latter are found in the water. The
residue, when free from ammonia is further concentrated, the
separated carbonates re-dissolved in phosphoric or sulphurous
acid, in just, sufficient quantity, then transferred to a glass
basin for evaporation to dryness as usual ready for combustion
(J. 0. S. 1881, 144).

In the case of sewage, however, it is advisable to employ hydric
metaphosphate in the pJace of sulphurous acid, as the ammonic
phosphate is even less volatile than the sulphite. This can only
be employed for sewage and similar liquids, which are free from
nitrates and nitrites. To the measured quantity of liquid to be
evaporated add, in the glass dish, 10 c.c. of the hydric metaphos-
phate (B. fj.), and, in order to render the residue more convenient
to detach from the dish, about half a gram of calcic phosphate
(B. v), and proceed as usual. No chloride of iron, sulphurous
acid, or sodic sulphite is required ; nor is it necessary to boil
before commencing the evaporation.

The next operation is the combustion of the residue. The
combustion tube should be of hard, difficultly fusible glass, with
an internal diameter of about 10 m.m. Cut it in lengths of about
430 m.m., and heat one end of each in the blowpipe flame to round
the edge. Wash well with water, brushing the interior carefully
Avith a tube brush introduced at the end whose edge has been
rounded, rinse with distilled water, and dry in an oven. When
dry, draw off and close, at the blowpipe, the end whose edge has
been left sharp. The tube is then ready for use.

Pour on to the perfectly dry residue in the glass dish, standing
on a sheet of white glazed paper, a little of the fine cupric oxide
(B. e), and with the aid of a small elastic . steel spatula (about 100
m.m. long and 15 m.m. wide) .carefully detach the residue from the
glass and rub it down with the cupric oxide. The spatula readily
accommodates itself to the curvature of the dish, and effectually
scrapes its surface. When the contents of the dish are fairly
mixed, fill about 30 m.m. of the length of the combustion tube

414

VOLUMETEIC ANALYSIS.

§ 89.

with granulated cupric oxide (B. e), and transfer the mixture in the
dish to the tube. This is done in the usual way by a scooping
motion of the end of the tube in the dish, the last portions being

Fig. 57.

transferred by the help of a bent card or a piece of clean and smooth
platinum foil. Kinse the dish twice with a little fine cupric oxide,
rubbing it well round each time with the spatula, and transfer to

§ 89. WATER ANALYSIS. 415

the tube as before. Any particles scattered on the paper are also
to be put in. Fill up to a distance of 270 m.m. from the closed
end with granular cupric oxide, put in a cylinder of metallic copper
(B. £), and then again 20 m.rn. of granular cupric oxide. This last
is to oxidize any traces of carbonic oxide which might be formed
from carbonic anhydride by the reducing action of iron or other
impurity in the metallic copper. 2sow draw out the end of the
tube so as to form a neck about 100 m.m. long and 4 m.m. in
diameter, fuse the end of this to avoid injury to the india-rubber
connector, and bend it at right angles. It is now ready to be
placed in the combustion furnace and attached to the Sprengel
pump.

The most convenient form of this instrument for the purpose is
shown in fig. 57. The glass funnel a is kept supplied with mercury,
and is connected by a caoutchouc joint with a long narrow glass
tube which passes down nearly to the bottom of a wider tube d,
900 m.m. long, and 10 m.m. in internal diameter. The upper end
of d is cemented into the throat of a glass funnel c from which
the neck has been removed. A screw clamp b regulates the flow of
mercury down the narrow tube. A piece of ordinary glass tube / g,
about 6 m.m. in diameter and 600 m.m. in length, is attached at g
to a tube g h /»•, about 6 m.m. in diameter, 1500 m.m. long, with
a bore of 1 m.m. This is bent sharply on itself at h, the part h k
being 1300 m.m. long, and the two limbs are firmly lashed together
with copper wire at two points, the tubes being preserved from
injury by short sheaths of caoutchouc tube. The end 7»: is recurved
for the delivery of gas. At the top of the bend at h, a piece of
ordinary tube k I, about 120 m.m. long, and 5 m.m. in diameter, is
sealed on. The whole I Jc is kept in a vertical position by a loose
support or guide, near its upper part, the whole of its weight resting
on the end A; so that it is comparatively free to move. It is
connected at / with the lower end of d, by means of a piece of caout-
chouc tube covered with tape, and furnished with a screw clamp e.
At I it is connected with the combustion tube o, by the connecting
tube I m n, which is made of tube similar to that used for 7* 7r. A
cork slides on h I, which is fitted into the lower end of a short
piece of tube of a width sufficient to pass easily over the caoutchouc
joint connecting the tubes at I. After the joint has been arranged
(the ends of the tubes just touching) and bound with wire, the
cork and wide tube are pushed over it and filled with glycerine.
The joint at n is of exactly the same kind, but as it has to be fre-
quently disconnected, water is used instead of glycerine, and the
caoutchouc is not bound on to the combustion tube with wire. It
will be seen that the joint at I is introduced chiefly to give flexi-
bility to the apparatus. At m is a small bulb blown on the tube
for the purpose of receiving water produced in the combustion.
This is immersed in a small water trough x. The tube h k stands in
a mercury trough p, which is shown in plan on a larger scale at B.

416 VOLUMETRIC ANALYSIS. § 89.

This trough should be cut out of a solid piece of mahogany, as it
is extremely difficult to make joints to resist the pressure of such
.a depth of mercury. It is 200 m.m. long, 155 m.m. wide, and
100 m.m. deep, outside measurement. The edge r r is 13 m.m.
wide, and the shelf s 65 m.m. wide, 174 m.m. long, and 50 m.m.
deep from the top of the trough. The channel t is 25 m.m. wide,
and 75 m.m. deep, having at one end a circular well w, 42 m.m. in
diameter, and 90 m.m. deep. The recesses u u are to receive the
ends of two Sprengel pumps. They are each 40 m.m. long,
25 m.m. wide, and of the same depth as the channel t. A short-
iron wire v, turning on a small staple, and resting at the other end
against an iron pin, stretches across each of these, and serves as
:a kind of gate to support the test tube, in which the gas delivered
by the pump is collected. The trough stands upon four legs, 75
m.m. high, and is provided at the side with a tube and screw
clamp q, by which the mercury may be drawn off to the level of
the shelf s.

The combustion tube being placed in the furnace, protected from
the direct action of the flame by a sheet-iron trough lined with
asbestos, and the water joint at n adjusted, the gas is lighted at
the front part of furnace so as to heat the whole of the metallic
copper and part of the cupric oxide. A small screen of sheet
iron is adjusted astride of the combustion tube to protect the
part beyond the point up to which the gas is burning from the
heat.

At the same time a stream of mercury is allowed to flow from the
funnel «, which fills the tubes d and/' until it reaches h, when it
falls in a series of pellets down the narrow tube li /', each carrying
before it a quantity of air drawn from the combustion tube. The
flow of mercury must be controlled by means of the clamps I) and e,
so as not to be too rapid to admit of the formation of these separate
pistons, and especially, care should be taken not to permit it to go
so fast as to mount into the connecting tube I m n, as it cannot be
removed thence except by disconnecting the tube. During the
exhaustion, the trough x is filled with hot water to expel from the
bulb in any water condensed from a previous operation. In about
ten minutes the mercury will fall in the tube li It with a loud, sharp,
clicking sound, showing that the vacuum is complete. As soon as
this occurs, the pump may be stopped, a test tube filled with mercury
inverted over the delivery end of the tube A', cold water substituted
for hot in the trough x, the iron screen- removed, and combustion
proceeded with in the usual way. This will take from fifty to sixty
minutes. As soon as the whole of the tube is heated to redness,
the gas is turned off, and the tube immediately exhausted, the
gases produced being transferred to the tube placed to receive them.
When the exhaustion is complete, the test tube of gas may be
removed in a small beaker, and transferred to the gas analysis
apparatus.

§ 89.

WATER ANALYSIS.

This gas collected consists of carbonic anhydride, nitric oxide,
nitrogen, and (very rarely) carbonic oxide, which can readily be
separated and estimated by the ordinary methods of gas analysis.

Pig. 58.

This is rapidly accomplished with the apparatus, shown in the
accompanying diagram, which, whilst it does not permit of analysis
by explosion, leaves nothing to be desired for this particular

E E

OF THE

418 VOLUMETRIC ANALYSIS. § 89.

operation. It is essentially that described by Frankland (J. O. S.
[2] vi. 109), but is slightly modified in arrangement. In the
diagram, a c d is a measuring tube, of which the cylindrical
portion a is 370 m.m. long, and 18 m.m. in internal diameter, the
part c 40 m.m. long, and 7 m.m. in diameter, and the part d 175
m.m. long, and 2*5 m.m. in diameter. To the upper end of d
a tube, with a capillary bore and stop-cock /, is attached, and bent
at right angles. Allowing 20 m.m. for each of the conical portions
at the joints between a and c, and c and d, and 25 m.m. for the
vertical part of the capillary tube, the vertical measurement of
the entire tube is 650 m.m. It is graduated carefully from below
upward, at intervals of 10 m.m., the zero being about 100 m.m.
from the end, as about that length of it is hidden by its support,
and therefore unavailable. The topmost 10 m.m. of d should be
divided into single millimeters. At the free end of the capillary
tube a small steel cap, shown in fig. 59, B, is cemented gas-tight.

Pig. 59.

The lower end of a is drawn out to a diameter of 5 m.m. The
tube I) is about 1*2 meter long, and 6 m.m. internal diameter, is
drawn out like a at the lower end, and graduated in millimeters
from below upward, the zero being about 100 m.m. from the end.""'
The tubes a c d and b pass through a caoutchouc stopper 0, which
fits into the lower end of a glass cylinder n n, intended to contain
water to give a definite temperature to the gas in measuring. The
zeros of the graduations should be about 10 m.m. above this
stopper. Immediately below this the tubes are firmly clasped by
the wooden clamp p (shown in end elevation and plan at fig. 58,
B, C), the two parts of which are drawn together by screws, the
tubes being protected from injury by a piece of caoutchouc tube
fitted over each. The clamp is supported on an upright piece of
wood, screwed firmly to the base A. If the stopper o is carefully
fitted, and the tubes tightly clamped, no other support than p will
be necessary. The tubes below the clamp are connected by joints
of caoutchouc covered with tape, and strongly bound with wire, to
the vertical legs of the union piece q, to the horizontal leg of
which is attached a long caoutchouc tube of about 2 m.m. internal
diameter, which passes to the glass reservoir t. This tube must
be covered with strong tape, or (less conveniently) have a lining of
canvas between two layers of caoutchouc, as it will be exposed to

* The graduation is not shown in the diagram.

§ 89. WATER ANALYSIS. 419

considerable pressure. In its course it passes through the double
screw steel pinch-cock r, the lower bar of which is fixed to the side
of the clamp p. It is essential that the screws of the pinch-cock
should have smooth collars like that shown in fig. 59 A, and that
the upper surface of the upper bar of the pinch-cock should be
quite flat, the surfaces between which the tube is passed being
cylindrical.

Franklaiid has introduced a form of joint by which the steel
caps and clamp are dispensed with. The capillary tube at the
upper end of a c d is expanded into a small cup or funnel, and the
capillary tube of the laboratory vessel bent twice at right
angles, the end being drawn out in a conical form to fit into the
neck of the above-named cup. The opposed surfaces are fitted
by grinding or by covering the conical end of the laboratory
vessel with thin sheet caoutchouc. The joint is kept tight by
an elastic band attached at one end to the stand, and at the other
to a hook on the horizontal tube of the laboratory vessel, and the
cup is filled with mercury.

In the base A is fixed a stout iron rod, 1'4 meter long, with

Fig. 60. Fig. 61.

a short horizontal arm at its upper end, containing two grooved
pulleys. The reservoir t is suspended by a cord passing over these
pulleys, and attached to an eye u in the iron rod, the length of the
cord being such that, when at full stretch, the bottom of the
reservoir is level with the bottom of the clamp p. A loop is made
on the cord, which can be secured by a hook v on the rod, so that
when thus suspended, the bottom of t is about 100 m.m. above the
stop-cock /. A stout elastic band fitted round t at its largest
diameter acts usefully as a fender to protect it from an accidental
blow against the iron rod. A thermometer <?, suspended by a wire
hook from the edge of the cylinder n n, gives the temperature of
'the contained water, the uniformity of which may be insured
.(though it is scarcely necessary) by passing a slow succession of
bubbles of air through it, or by moving up and down in it a wire
with its end bent into the form of a ring. The jar k is called the
laboratory vessel, arid is 100 m.m. high, and 38 m.m. in internal
diameter, having a capillary tube, glass stop-cock, and steel cap c/ h
exactly like / y. The mercury trough I is shown in figs. 60 and
•61. It is of solid mahogany, 265 m.m. long, 80 m.m. broad, and
90 m.m. deep, outside measurement. The rim a a a a is 8 m.m.
Inroad, and 15 m.m. deep. The excavation l> is 230 m.m. long,

E E 2

420 VOLUMETKIC ANALYSIS. § 89.

26 m.m. broad, and 65 m.m. deep, with a circular cavity to receive
the laboratory vessel sunk at one end, 45 m.m. in diameter, and
20 m.m. in depth below the top of the excavation. Two small
lateral indentations c c (fig. 61) near the other end accommodate
a capsule for transferring to the trough tubes containing gas. This
trough rests upon a telescope table, which can be fixed at any
height by means of a screw, and is supported on three feet. It
must be arranged, so that when the laboratory vessel is in its place
in the trough, the two steel caps exactly correspond face to face.

The difference of level of the mercury in the tubes b and a c d,
caused by capillary action, when both are freely open to the air,
must be ascertained by taking several careful observations. This
will be different for each of the portions a c and d, and must be
added to or deducted from the observed pressure, as the mercury
when thus freely exposed in both tubes to the atmospheric pressure
stands in a c or d above or below that in &. This correction will
include also any that may be necessary for difference of level of
the zeros of the graduations of the two tubes, and, if the relative
positions of these be altered, it must be redetermined. A small
telescope, sliding on a vertical rod, should be used in these and all
other readings of the level of mercury.

The capacity of the measuring tube a c d at each graduation
must now be determined. This is readily done by first filling the
whole apparatus with mercury, so that it drips from the cap g.
The stop-cock / is then closed, a piece of caoutchouc tube slipped
over the cap, and attached to a funnel supplied with distilled
water. The reservoir t being lowered, the clamp r and the stop-
cock / are opened, so that the mercury returns to the reservoir,
water entering through the capillary tube. As soon as it is below
the zero of the graduation, the stop-cock / is closed, the funnel and
caoutchouc tube removed from the cap, and the face of the last
slightly greased in order that water may pass over it without
adhering. Now raise the reservoir, open the stop-cock /, and allow
the water -to flow gently out until the top of the convex surface of
the mercury in a just coincides with the zero of the graduation.
The mercury should be controlled by the clamp i; so that the water
issues under very slight pressure, l^ote the temperature of the
water in the water-jacket, and proceed with the expulsion of the
water, collecting it as it drops from the steel cap in a small carefully
weighed glass flask. When the mercury has risen through 100 m.m.
stop the flow of water, and weigh the flask. The weight of water
which was contained between the graduations 0 and 100 on the
tube is then known, and if the temperature be 4° C., the weight in
grams will express the capacity of that part of the tube in cubic
centimeters. If the temperature be other than 4° C., the volume
must be calculated by the aid of the co-efficient of expansion of
water by heat. In a similar way the capacity of the tube at
successive graduations about 100 m.m. apart is ascertained, the

§ 89. WATER ANALYSIS. 421

last determination in a being at the highest, and the first in c at
the lowest graduation on the cylindrical part of each tube ; the
tube between these points and similar points on c and d being so
distorted by the glass blower that observations could not well
be made. The capacity at a sufficient number of points being
ascertained, that at each of the intermediate graduations may be
calculated, and a table arranged with the capacity marked against
each graduation. As the calculations in the analysis are made by
the aid of logarithms, it is convenient to enter on this table the
logarithms of the capacities instead of the natural numbers.

In using the apparatus, the stop-cocks on the measuring tube
and laboratory vessel should be slightly greased with a mixture of
resin cerate and oil, or vaseline, the Avhole apparatus carefully filled
with mercury, and the stop-cock/ closed ; next place the laboratory
vessel in position in the mercury trough, and suck out the air.
This is readily and rapidly done by the aid of a short piece of
caoutchouc tube, placed in the vessel just before it is put into the
mercury trough, and drawn away as soon as the air is removed.
Suck out any small bubbles of air still left through the capillary
tube, and as soon as the vessel is entirely free from air close the
stop-cock. Slightly grease the face of both caps with resin cerate
(to which a little oil should be added if very stiff), and clamp them
tightly together. On opening both stop-cocks mercury should now
freely through the capillary communication thus formed, and the
whole should be quite free from air. To ascertain if the joints are
all in good order, close the stop-cock It, and lower the reservoir t to
its lowest position ; the joints and stop-cocks will thus be subjected
to a pressure of nearly half an atmosphere, and any leakage would
speedily be detected. If all be right, restore the reservoir to its
upper position.

Transfer the tube containing the gas to be analyzed to an
ordinary porcelain mercury trough ; exchange the beaker in which
it has been standing for a small porcelain capsule, and transfer it
to the mercury trough I, the capsule finding ample room where the
trough is widened by the recess D.

Carefully decant the gas to the laboratory vessel, and add a drop
or two of potassic bichromate solution (B. 77) from a small pipette
with a bent capillary delivery tube, to ascertain if the gas contains
any sulphurous anhydride. If so, the yellow solution will
immediately become green from the formation of a chromic salt,
and the gas must be allowed to stand over the chromate for four or
five minutes, a little more of the solution being added if necessary.
The absorption may be greatly accelerated by gently shaking from
time to time the stand on which the mercury trough rests, so as to
cause the solution to wet the sides of the vessel. With care this
may be done without danger to the apparatus. Mercury should be
allowed to pass slowly into the laboratory vessel during the whole
time, as the drops falling tend to maintain a circulation both in

422 VOLUMETRIC ANALYSIS.

the gas and in the absorbing liquid. The absence of sulphurous
anhydride being ascertained, both stop-cocks are set fully open, the
reservoir t lowered, and the gas transferred to the measuring tube.
The stop-cock h should be closed as soon as the liquid from the
laboratory vessel is within about 10 m.m. of it. The bore of the
capillary tube is so fine, that the quantity of gas contained in it is
too small to affect the result. ]Srext bring the top of the meniscus
of mercury seen through the telescope exactly to coincide with one
of the graduations on the measuring tube, the passage of mercury
to or from the reservoir being readily controlled by the pinch-cock r.
jSbte the position of the mercury in the measuring tube and in the
pressure tube ?>, the temperature of the water-jacket, and the height
of the barometer, the level of the mercury in the pressure tube and
barometer being read to the tenth of a m.m. and the thermometer
to 0*1° C. This done, introduce into the laboratory vessel from
a pipette with a bent point, a few drops of potassic hydrate solution
(B. 6), and return the gas to the laboratory vessel. The absorption
of carbonic anhydride will be complete in about three to five
minutes, and if the volume of the gas is large, may be much
accelerated by gently shaking the stand from time to time, so as to
throw up the liquid on the sides of the vessel. If the small
pipettes used to introduce the various solutions are removed from
the mercury trough gently, they will always contain a little mercury
in the bend, which will suffice to keep the solution from flowing
out, and they maybe kept in readiness for use standing upright in
glass cylinders or other convenient supports. At the end of five
minutes the gas, which now consists of nitrogen and nitric oxide,
is again transferred to the measuring tube, and the operation of
measuring repeated ; the barometer, however, need not be observed,
under ordinary circumstances, more than once for each analysis,
as the atmospheric pressure wrill not materially vary during the
twenty-five to thirty minutes required. JSText pass into the
laboratory vessel a few drops of saturated solution of pyrogallic
acid (B. t), and return the gas upon it. The object of adding the
pyrogallic acid at this stage is to ascertain if oxygen is present, as
sometimes happens when the total quantity of gas is very small,
and the vacuum during the combustion but slightly impaired.
Under such circumstances, traces of oxygen are given off by the
cupric oxide, and pass so rapidly over the metallic copper, as to
escape absorption. This necessarily involves the loss of any nitric
oxide which also escapes the copper, but this is such a very small
proportion of an already small quantity that its loss will not
appreciably affect the result. If oxygen be present, allow the gas
to remain exposed to the action of the pyrogallate until the liquid
when thrown up the sides of the laboratory vessel runs off without
leaving a dark red stain. If oxygen be not present, a few bubbles
of that gas (B. X) are introduced to oxidize the nitric oxide to
pernitric oxide, which is absorbed by the potassic hydrate. The

89.

WATER ANALYSIS.

423

oxygen may be very conveniently added from the gas pipette shown

in fig. 62, where a b are glass
bulbs of about 50 m.m. dia-
meter, connected by a glass
tube, the bore of which is
constricted at c, so as to allow
mercury to pass but slowly
from one bull) to the other,
and thus control the passage
Q2 °f gas through the narrow

delivery tube d. The other
end e is provided with a short piece of caoutchouc tube, by blowing
through which any desired quantity of gas may be readily delivered.
Care must be taken after use that the delivery tube is not removed
from the trough till the angle d is filled with mercury.

To replenish the pipette with oxygen, fill the bulb b and the
tubes c and d with mercury ; introduce the point of d into a tube
of oxygen standing in the mercury trough, and draw air from the
tube e. The gas in b is confined between the mercury in c and
that in d.

When the excess of oxygen has been absorbed a"s above described,
the residual gas, which consists of nitrogen, is measured, and the
analysis is complete.*

There are thus obtained, three sets of observations, from which,
by the usual methods, we may calculate A the total volume, B the
volume of nitric oxide and nitrogen, and C the volume of nitrogen,
all reduced to 0° C. and 760 m.m. pressure ; from these may be
obtained —

A - B = vol. of CO2,

and hence the weight of carbon and nitrogen can be readily
found.

It is much less trouble, however, to assume that the gas in all
three stages consists wholly of nitrogen ; then, if A be the weight
of the total gas, B its weight after treatment with potassic hydrate,
and C after treatment with pyrogallate, the weight of carbon will

be (A - B) i. and the weight of nitrogen — ^— • for the weights
of carbon and nitrogen in equal volumes of carbonic anhydride and

*When the quantity of carbon is very large indeed, traces of carbonic oxide are-
occasionally present in the gas, and will remain with the nitrogen after treatment with
alkaline pyrogallate. When such excessive quantities of carbon are found, the stop-
cock / should be closed when the last measurement is made, the laboratory vessel
detached, washed, and replaced filled with mercury. Introduce then a little solution
of cuprous chloride (B. K), and return the gas upon it. Any carbonic oxide will be
absorbed, and after about five minutes the remaining nitrogen may be measured. In
more than twenty consecutive analyses of waters of very varying kinds, not a trace of
carbonic oxide was found in any of the gases obtained on combustion.

424

VOLUMETRIC ANALYSIS.

nitrogen, at the same temperature and pressure, are as 6 : 14 ; and
the weights of nitrogen in equal volumes of nitrogen and nitric
oxide are as 2 : 1.

The weight of 1 c.c. of nitrogen at 0° C. and 760 m.m. is 0-0012562

, ,, , • * iv - T- 'i *- • 0-001 2562 x y x p

£mi.. and the formula tor the calculation is u- = -^. — A AAO^^\ ^/»n>

(1 + 0m006bit) i bO

in which w — the weight of nitrogen, v the volume, p the pressure
corrected for tension of aqueous vapour, and t the temperature in
degrees centigrade. To facilitate this calculation, there is given in

0-0012562
Table 2 the logarithmic value of the expression ,, j-O-OOSfP/^ ^60

for each tenth of a degree from 0° to 29 '9° C., and in Table 1 the
tension of aqueous vapour in millimeters of mercury. As the
measuring tube is always kept moist with water, the gas when
measured is always saturated with aqueous vapour.

The following example will show the precise mode of calcu-
lation : —

Volume of gas ....

A B

m 4. i After absorption
Total. Qf C02i

4-4888 c.c. 0-26227 c.c.
13-5° 13-6°
m.m. m.m.
310 0 480-0
193-5 343-5

C
Nitrogen.

0-26227 c.c.
13-7°
m.m.
480-0
328-2

Height of mercury in a, c, d
,, „ ,, b

Difference
Plus tension of aqueous vapour .

Deduct correction for capillarity.

Deduct this from height of bar .
Tension of dry gas

Logarithm of volume of gas
0-0012562

116-5
11-5

136-5
11-6

151-8
11-7

128-0
0-9

Add for 7 0.2
capillarity ) " ^

2-2

127-1

769-8
127-1

150-3

769-8
150-3

165-7

769-8
165-7

642-7
0-65213

619-5
1-41875

604-1
T41875

(l+0'00367t)760
,, ,, tension of dry gas .

Logarithm of weight of gas calcu-
lated as N

6-19724

2-80801

6-19709
2-79204

6-19694
2-78111

3-65738
0-0045434

440788
0-0002558

4-3968G
0-0002494 gm.

From these weights, those of carbon and of nitrogen are obtained
by the use of the formulae above mentioned. Thus —

A- B = 0-0042876 B + C = 0-0005052

x 3 ^2

-f- 7)0-0128628 Weight of nitrogen, Q-Q002526
Weight of carbon, Q-Q01837

When carbonic oxide is found, the corresponding weight of
nitrogen may be found in a similar manner, and should be added
to that corresponding to the carbonic anhydride before multiplying

§ 89. WATER ANALYSIS. 425

by ^, and must be deducted from the weight corresponding to the

volume after absorption of carbonic anhydride.

As it is impossible to attain to absolute perfection of manipulation
and materials, each analyst should make several blank experiments
by evaporating a liter of pure distilled water (B. a) with the usual
quantities of sulphurous acid and ferrous chloride, and, in addition,
O'l gin. of freshly ignited sodic chloride (in order to furnish
a tangible residue). The residue should be burnt and the resulting
gas analyzed in the usual way, and the average amounts of carbon
and nitrogen thus obtained deducted from the results of all
analyses. This correction, which may be about O'OOOl gm. of C,
and 0*00005 gm. of X, includes the errors due to the imperfection
of the vacuum produced by the 8pr.en.gel pump, nitrogen retained
in the cupric oxide, ammonia absorbed from the atmosphere during
evaporation, etc.

When the quantity of nitrogen as ammonia exceeds O'OOT part
per 100,000, there is a certain amount of loss of nitrogen during
the evaporation by dissipation of ammonia. This appears to be
very constant, and is given in Table 3, which is calculated from
Table 5, which has been kindly furnished by Dr. Frankland.
The number in this table corresponding to the quantity of nitrogen
as ammonia present in the water analyzed should be added to the
amount of nitrogen found by combustion. The number thus
obtained includes the nitrogen as ammonia, and this must be
deducted to ascertain the organic nitrogen. If "ammonia" is
determined instead of " nitrogen as ammonia," Table 5 may be used.

When, in operating upon sewage, hydric metaphosphate has
been employed, Tables 4 or 6 should be used.

Rules for Converting- Parts per 100,000 into Grains per Gallon,
or the reverse.

To convert parts per 100,000 into grains per gallon, multiply
by 0-7.

To convert grains per gallon into parts per 100,000, divide
by 07. .

To convert grams per liter into grains per gallon, multiply
by 70.

426 VOLUMETRIC ANALYSIS. § 89.

TABLE 1.

Elasticity of Aqueous "Vapour for each jLth degree centigrade
from 0° to 30° C. (Reg-nault).

all?

•s!*?

.2 1&

*16

•Ss£

Temp.

Ill

Temp.

Tom p.

o? I

Temp.

|||

'ia^

las

'i^^

aSa

°°2 5 iS

|j|£

l|<s

H|<«

£, .,_, F-4

£p|2

0°

4-6

6-0°

7'0

12-0°

10-5

18-0°

15-4

24-0°

22-2

•1

4-6

•1

7-0

10-5

15-5

22-3

4'7

•2

10-6

•2

15-6

•2

22-5

•3

7-1

•3

107

•3

157

•3

22-6

•4

7-2

•4

107

•4

157

•4

227

4-8

7-2

•5

10-8

15-8

•5

22'9

•6

4'8

•6

7-3

•6

10-9

•6

15-9

•6

23'0

4-8

•7

7'3

10-9

16-0

231

•8

4-9

•8

7'4

•8

11-0

•8

161

•8

23-3

•9

4'9

•9

7-4

•9

111

•9

1G-2

•9

23'4

1-0

4'9

7'0

7'5

13-0

11-2

19-0

16-3

25-0

23-5

•1

5-0

7*5

11-2

16-4

237

5-0

•2

7-0

•2

11*3

•2

16-6

23-8

5-0

•3

11-4

•3

167

•3

24-0

•4

5-1

•4

11-5

•4

16-8

•4

241

•5

7-8

•5

11-5

•5

IG'9

24-3

•6

5-2

•6

7'8

•6

11-6

17-0

•6

24-4

•7

5'2

•7

7-9

117

171

24'6

•8

5 '2

•8

7'9

•8

11-8

•8

17-2

•8

247

•9

5-3

•9

8-0

•9

11-8

•9

17-3

•9

24-8

2-0

5'3

8-0

14-0

11-9

20-0

17-4

26-0

25'0

5'3

12-0

17-5

251

•2

5'4

•2

12-1

17-6

253

•3

5*4

•3

8-2

•3

121

•3

177

•3

25-4

•4

5-5

•4

8-2

•4

12-2

•4

17-8

•4

25-6

•5

5-5

•5

8-3

•5

12-3

•5

17'9

•5

257

•6

5-5

8'3

•6

12-4

•6

18-0

•6

25-9

•7

5-6

8'4

12-5

18'2

26-0

•8

5'6

•8

8-5

•8

12-5

•8

18-3

•8

26'2

•9

5-6

•9

8-5

•9

12-6

•9

18'4 -9

26-4

3-0

9-0

8-6

15-0

12-7

21-0

1S'5

27-0

26'5

•1

8-6

12-8

18-6

267

•2

5'8

•2

12-9

187

26'8

•3

5-8

•3

12-9

•3

18-8

•3

27'0

•4

5-8

•4

8'8

•4

13-0

•4

19'0

•4

271

•5

5-9

8'9

•5

131

•5

191

•5

27-3

•6

5-9

•6

8-9

•6

13-2

•6

19'2

•6

27-5

•7

G-0

9-0

13-3

19-3

27'G

•8

6-0

•8

9-0

•8

13-4

•8

19-4

•8

27-8

•9

6-1

•9

13-5

•9

19-5

•9

27-9

4-0

6-1

10-0

9'2

16-0

13-5

22-0

197

28-0

281

•1

6-1

9-2

13-6

•1

19-8

28-3

•2

6-2

•2

9-3

•2

137

19-9

•2

28-4

•3

6-2

•3

9-3

•3

13-8

•3

20-0

•3

28'6

•4

6-3

•4

9-4

•4

13-9

•4

201

•4

28-8

•5

6-3

•5

9-5

•5

14-0

20-3

28-9

•6

6-4

•6

9-5

•6

141

•6

20-4

•G

291

•7

6-4

9-6

14-2

20'5

29'3

•8

6-4

•8

14-2

•8

20 -6

•8

09-4

•9

6-5

•9

14-3

•9

20-8

•9

29-6

5-0

6-5

11-0

9-8

17-0

14-4

23-0

20'9

29-0

29-8

6-6

•1

9-9

•1

14-5

21-0

30-0

•2

G-6

9-9

•2

14-6

211

•2

301 !

•3

6-7

•3

10-0

•3

147

•3

21'3

•3

30-3

•4

6-7

•4

101

•4

14-8

•4

21-4

•4

30-5 1

6-8

101

•5

14-9

•5

21'5

•5

307

•6

6-8

•6

10-2

•6

15-0

•6

217

•6

30-8 1

•7

6-9

10-3

151

21-8

31-0

•8

6-9

•8

10-3

•8

15-2

•8

21-9

•8

31-2 1

•9

7-0

•9

10-4

•9

15-3

•9

221

•9

31-4

§ 89.

WATER ANALYSIS.

427

TABLE 2.

Baduction of Cubic Centimeters of Nitrogen to Grams.

A'AAI OXf!»>

Lo.

0-00367)760

from °° to 30°

t.c.

o-o

O'l

0-2

0-3

0-4

0-5

0-6

0-7

0-8

0-9

0°

"6-21824

808

793

777

761

745

729

713

697

681

665

649

633

617

601

586

570

554

538

522

507

491

475

459

443

427

412

396

380

364

349

333

318

302

286

270

255

239

223

208

192

177

161

145

130

114

098

083

067

051

035

020

004

*989

*973

*957

*942

-926

*911

*895

6-20S79

864

848

833

817

801

786

770

755

739

723

708

692

676

661

645

629

614

598

583

567

552

536

521

505

490

474

459

443

428

413

397

382

366

351

335

320

304

289

274

259

244

228

213

198

182

167

151

136

121

106

090

075

060

015

029

014

*999

*984

*969

619953

93S

923

907

892

877

862

846

831

816

800

785

770

755

740

724

709

694

679

664

648

633

618

603

588

573

558

543

528

513

497

482

467

452

437

422

407

392

377

362

346

331

316

301

286

271

256

241

226

211

196

181

166

151

136

121

106

091

076

061

046

031

016

001

*986

*971

*956

*941

*926

*911

6-18897

882

887

852

837

822

807

792

777

762

748

733

718

703

688

673

659

644

629

614

600

585

570

555

540

526

511

496

481

466

452

437

422

408

393

378

363

349

334

319

. 305

290

275

261

246

231

216

202

187

172

158

143

128

114

099

084

070

055

041

026

012

*997

*982

*968

*953

*938

*924

*909

*895

*8SO

"6-17866

851

837

822

808

793

779

764

750

735

721

706

692

677

663

648

634

619

605

590

576

561

547

532

518

503

489

475

460

446

432

417

403

388

374

360

345

331

316

302

428

VOLUMETRIC ANALYSIS.

89.

TABLE 3.

Loss of Nitrogen by Evaporation of NH3.
With Sulphurous Acid.

Parts per 100,000.

Nas

Loss

Nas

Loss

Nag

Loss

Nas

Loss

Nas

Loss

Nas

Loss

NH3.

of N.

NH3.

of N.

NH3.

of N.

NH3.

of N.

NH3.

of N.

NH3.

of N.

5-0

1-741

3'9

1-425

2-8

•898

•370

•6

•145

•04

•009

4-9

1-717

3'8

1-378

•850

1-6

•338

•5

•109

•03

•007

4'8

1-693

3-7

1-330

2-6

•802

1-5

•324

•4

•075

•02

•005

1-669

3-6

1-282

2-5

•754

1-4

•309

•3

•057

•01

•003

4'6

1-645

3-5

1-234

2-4

•706

1-3

•295

•2

•038

•008

•002

4-5

1-621

3-4

1-186

2-3

•658

1-2

•280

•1

•020

•007

•001

4'4

1-598

3-3

1-138

2-2

•610

1-1

•266

•09

•018

4-3

1-574

3-2

1-090

2-1

•562

i-o

•252

•08

•017

4-2

1-550

3-1

1-042

2-0

•514

•9

•237

•07

•015

4-1

1-521

3-0

•994

1-9

•466

•8

•217

•06

•013

4-0

1-473

2-9

•946

1-8

•418

•7

•181

•05

•on

TABLE 4.

Loss of Nitrogen by Evaporation of NIP.
With Hydric Metaphosphate.

Parts per 100,000.

°3

•1

•i

co"

3 g

°o

§ C3

*o ^

'o ^

C/l

'o ^

*o S,

100 c.c.

8'2

•482

100 c.c.

5-9

•385

100 c.c.

3'6

•28 L

100 c.c.

1-3

•142

8-1

•477

5-8

•381

3-5

•277

1'2

•136

8-0

•473

5-7

•377

3-4

•272

1-1

•129

7-9

•469

5-6

•373

3-3

•267

i-o

123

7-8

•465

5'5

•368

3-2

•261

•9

117

7'7

•461

5'4

•364

•255

•8

•111

7'6

•456

5'3

•360

•249

250 c.c.

•088

•452

5-2

•356

2-9

•242

•6

•073

7'4

•448

5-1

•352

2-8

•236

•061

7'3

•444

5-0

•347

•230

SOOc.c.

•4

•049

7-2

•440

4'9

•343

2-6

•223

•3

•036

7-1

•435

4'S

•338

2-5

•217

1000 c.c.

•024

7-0

•431

4-7

•334

2-4

•211

•012

6-9

•427

4-G

•329

2-3

•205

•09

•on

•423

4-5

•324

2-2

•198

•08

•010

6'7

•419

4-4

•319

192

•07

•008

6-6

•414

4'3

'315

2-0

•186

•05

•007

6-5

•410

4'2

•310

1-9

•180

•05

•006

6-4

•403

...

4-1

•305

1-8

•173

•04

•005

6-3

•402

4-0

•301

•167

•03

•004

•398

...

3-9

•296

1-6

161

•02

•002

6-1

•394

3'8

•291

1-5

154

•01

•001

••

6-0

•389

3-7

•286

1-4

•118

89. WATER ANALYSIS.

TABLE 5.

Loss of Nitrogen l>y Evaporation
With Sulplmrous Acid.

Parts per 100,000.

429

NH3.

Loss
of N.

NH3.

Loss
of N.

NH3.

Loss
of N.

NH3.

Loss
of N.

NH3.

Loss
of N.

NH3.

Loss
of N.

6-0

1727

4-8

1-451

3-6

•977

2 "4

•503

1-2

•250

•09

•014

5-9

1707

1-411

3-5

•937

2-3

•463

1-1

•238

•08

•013

5-8

1-688

4-6

1-372

3-4

•898

2-2

•424

i-o

•226

•07

•012

1-668

4-5

1-332

3-3

•858

2'JL

•38 1

•9

•196

•05

•010

5-6

1-648

4'4

1-293

•819

2-0

•345

•8

•166

•05

•009

5-5

1-628

4-3

1-253

779

1-9

•333

•136

•04

•007

5-4

1-609

4-2

1-214

740

1-8

•321

•6

•106

•03

•006

5'3

1-589

4-1

1-174

2-9

700

1-7

•309

•5

•077

•02

•004

1-569

4-0

1-135

2-8

•661

1-6

•297

•4

•062

•01

•ors

5-1

1-549

3-9

1-095

2-7

•621

1-5

•285

•3

•04-7

•009

•001

5-0

1-530

3-8

1-056

2-G

•582

1-4

•274

•2

•032

4-9

1-490

1-016

2-5

•542

1-3

•262

•1

•017

TABLE 6.

Loas of Nitrogen by Evaporation of NHX
With Hydric Metaphosphate.

Parts per ICO, COO.

2*2

ft'

8*8

I~H

§"£

'o 2

eg,

>«
o

0
Hi

100 c.c.

10-0

•483

100 c.c.

7-2

•386

100 c.c.

4-4

•283

100 c.c.

1-6

•143

9'9

•480

7-1

•383

4'3

•279

1-5

•137

9-8

•476

7'0

•379

4'2

•275

1-4

•132

•473

6'9

•375

4-1

•271

1-3

•127

9-6

•469

6'8

•372

4'0

•267

1-2

•122

9'5

•466

•368

3-9

•262

1-1

•117

9'4

•462

6'6

•365

3-8

•257

i-o

•112

9'3

•459

6'5

•361

•252

253 c.c.

•9

•096

9'2

•455

6'4

•358

•247

•8

•080

9.1

•452

6'3

•354

...

3-5

•242

•070

9'0

•448

6'2

•351

3'4

•236

•6

•060

8-9

•445

6-1

•348

3*3

•231

500 c.c.

•5

•050

8'8

•441

6"0

•345

3'2

•226

•4

•040

•438

5'9

•341

3-1

•221

•3

•030

8'6

•434

5-8

•337

3-0

•216

1000 c.c.

•2

•020

8'5

•431

•333

•211

•1

•010

8-4

•428

5-6

•330

•205

•09

•009

8-3

•424

•326

2-7

•200

•08

•008

8-2

•421

5-4

•322

2-6

•195

•07

•007

8-1

•417

•318

2-5

•190

•06

•006

8'0

•414

•314

2'4

•184

•05

•005

7'9

•410

5'1

•310

2'3

•179

•04

•004

7'8

•407

5-0

•306

2'2

•174

•03

•003

7-7

•403

4-9

•302

2-1

•169

•02

•002

7-6

•400

4'8

•298

2'0

•164

•01

•001

7'5

•396

4-7

•204

1-9

•158

7'4

•393

•291

1-8

•153

7-3

•389

4-5

•287

1-7

•148

430 VQLUMETHIC ANALYSIS. § 89.

5. Estimation of Total Solid Matter. — Evaporate over a steam
or water bath half a liter or a less quantity of the water in a platinum
dish which has been heated to redness and carefully weighed.
The water should be filtered or unfiltered, according to the decision
made in that respect at the commencement of the analysis. The
quantity to be taken is regulated chiefly by the amount of nitrate
present, as the residue from this operation is, with certain exceptions,
employed for the determination of the nitrogen as nitrates and
nitrites. As a general rule, for water supplies and river water
half a liter should be used ; for shallow well waters, a quarter
of a liter. Of sewages, 100 c.c., and of waters containing more
than 0'08 part of nitrogen as ammonia per 100,000, a quarter of
a liter will generally be convenient, as in these cases the residue
will not be used for the estimation of nitrogen as nitrates and
nitrites ; and the only point to lie considered is to have a quantity
of residue suitable to weigh. It is desirable to support the platinum
dish during evaporation in a glass ring with a flange, shaped like
the top of a beaker,- the cylindrical part being about 20 m.m. deep.
This is dropped into the metal ring on the water bath, and thus
lines the metal with glass, and keeps the dish clean. A glass
disc with a hole in it to receive the dish is not satisfactory, as
drops of water conveying solid matter find their way across the
under surface from the metal vessel to the dish, and thus soil
it. As soon as the evaporation is complete, the dish with the
residue -is removed, its outer side wiped dry with a cloth, and
it is dried in a water or steam oven for about three hours. It
is then removed to a desiccator, allowed to cool, weighed as rapidly
as possible, returned to the oven, and weighed at intervals of an
hour, until between two successive weighings it has lost less than
0-001 gm.

6. Estimation of Nitrogen as Nitrates and Nitrites. — The residue
obtained in the preceding operation may be used for this estimation.
Treat it with about 30 c.c. of hot distilled w^ater, taking care to
submit the whole of the residue to its action. To ensure this it
is advisable to rub the dish gently with the finger, so as to detach
the solid matter as far as possible, and facilitate the solution of
the soluble matters. The finger may be covered by a caoutchouc
finger-stall. Then filter through a very small filter of Swedish
paper, washing the dish several times with small quantities of hot
distilled water.

The filtrate must be evaporated in a very small beaker, over
a steam bath, until reduced to about 1 c.c,, or even to clryness.
This concentrated solution is introduced into the glass tube shown
in fig. 63, standing in the porcelain mercury trough, rilled up to
the stop-cock with mercury. (If the nitrometer of Lunge is
used in place of Cr urn's tul3e, the use of the laboratory tube and
gas apparatus is avoided.) The tube is 210 m.m. in total length,

89. WATER ANALYSIS. 431

and 15 m.m. in internal diameter. By pouring the liquid
into the cup at the top, and then cautiously opening the
stop-cock, it may he run into the tuhe without admitting
any air. The beaker is rinsed once with a very little hot
distilled water, and then two or three times with strong
sulphuric acid (c. a.), the volume of acid being to that of
the aqueous solution about as 3 : 2. The total volume of
acid and water should be about 6 c.c. Should any air by
chance be admitted at this stage, it may readily be removed
by suction, the lips being applied to the cup. With care
there is but little danger of getting acid into the mouth.

In a few cases carbonic anhydride is given off on
addition of sulphuric acid, and must be sucked out before
proceeding.

Now grasp the tube firmly in the hand, closing the open
end by the thumb, which should be first moistened ;
withdraw it from the trough, incline it at an angle of about
45°, the cup pointing from you, and shake it briskly with
a rapid motion in the direction of its length, so as to
throw the mercury up towards the stop-cock. After
Fig. 63. a very little practice there is no danger of the acid finding-
its way down to the thumb, the mixture of acid and.
mercury being confined to a comparatively small portion of the
tube. In a few seconds some of the mercury becomes very finely
divided \ and if nitrates be present, in about a minute" or less
nitric oxide is evolved, exerting a strong pressure on the thumb.
Mercury is allowed to escape as the reaction proceeds, by partially,
but not wholly, relaxing the pressure of the thumb. A slight
excess of pressure should be maintained within the tube to prevent
entrance of air during the agitation, which must be continued
until no more gas is evolved.

"When the quantity of nitrate is very large, the mercury, on
shaking, breaks up into irregular masses, which adhere to one
another as if alloyed with lead or tin, and the whole forms a stiff
dark-coloured paste, which it is sometimes very difficult to shake ;
but nitric oxide is not evolved for a considerable time, then comes
off slo\yly, and afterwards with very great rapidity. To have room
for the gas evolved, the operator should endeavour to shake the
tube so as to employ as little as possible of the contained mercury
in the reaction. At the close of the operation the finely divided
mercury will consist for the most part of minute spheres, the alloyed
appearance being entirely gone. An experiment with a large
quantity of nitrate may often be saved from loss by firmly resisting
the escape of mercury, shaking until it is judged by the appearance
of the contents of the tube that the reaction is complete, and then
on restoring the tube to the mercury trough, allowing the finely-
divided mercury also to escape in part. If the gas evolved be not
more than the tube will hold, and there be no odour of pernitric

432 VOLUMETPJC ANALYSIS. § 89.

oxide from the escaped finely-divided mercury, the operation may
be considered successful. If the amount of nitrate be too large,
a smaller quantity of the water must be evaporated and the operation
repeated. When no nitrate is present, the mercury usually
manifests very little tendency to become divided, that which does
so remains bright, and the acid liquid does not become so turbid as
it does in other cases.

The reaction completed, the tube is taken up closed by the
thumb, and the gas is decanted into the laboratory vessel, and
measured in the usual way in the gas apparatus. The nitric acid
tube is of such a length, that when the cup is in contact with the
end of the mercury trough, the open end is just under the centre
of the laboratory vessel. If any acid has been expelled from the
tube at the close of the shaking operation, the end of the tube and
the thumb should be washed with water before introducing into
the mercury trough of the gas apparatus, so as to remove any acid
which may be adhering, which would destroy the wood of the
trough. Before passing the gas into the measuring tube of the gas
apparatus, a little mercury should be allowed to run over into the
laboratory vessel to remove the acid from the entrance to the
capillary tube,

As nitric, oxide contains half its volume of nitrogen, if half
a liter of water has been employed, the volume of nitric oxide
obtained will be equal to the volume of nitrogen present as nitrates
and nitrites in one liter of the water, and the weight of the
nitrogen may be calculated as directed in the paragraph on the
estimation of organic carbon and nitrogen.

When more than O'OS part of nitrogen as ammonia is present in
100,000 parts of liquid, there is danger of loss of -nitrogen by
decomposition of ammonic nitrite on evaporation ; and therefore
the residue from the estimation of total solid matter cannot be
used. In such cases acidify a fresh quantity of the liquid with
dilute hydric sulphate, add solution of potassic permanganate,
a little at a time, until the pink colour remains for about a minute,
and render the liquid just alkaline to litmus paper with sodic
carbonate. The nitrites present will then be converted into
nitrates and may be evaporated without fear of loss. Use as little
of each reagent as possible. Sewage may be examined in this
way ; but it is hardly necessary to attempt the determination,
as sewage is almost invariably free from nitrates and nitrites.
Out of several hundred specimens, the writer only found two
or three which contained any, and even then only in very
small quantity.

7. Estimation of Nitrogen as Nitrates and Nitrites in Waters
containing- a very large quantity of Soluble Matter, with but little
Ammonia or Organic Nitrogen. — When the quantity of soluble
matter is excessive, as, for example, in sea-water, the preceding
method is inapplicable, as the solution to be employed cannot be

§ 89. WATER ANALYSIS. 433

reduced to a sufficiently small bulk to go into the shaking tube.
If the quantity of organic nitrogen be less than (H part in 100,000,
the nitrogen as nitrates and nitrites may generally l>e determined
by the following modification of Schulze's method devised by
E. T. Chapman. To 200 c.c. of the'water add 10 c.c. of sodic
hydrate solution (c. e), and boil briskly in an open porcelain dish
until it is reduced to about 70 c.c. When cold pour the residue
into a tall glass cylinder of about 120 c.c. capacity, and rinse the
dish with water free from ammonia. Add a piece of aluminium
foil of about 15 sq. centim. area, loading it with a piece of clean
glass rod to keep it from floating. Close the mouth of the cylinder
with a cork, bearing a small tube filled with pumice (C. £), moistened
with hydric chloride free from ammonia (C. 77).

Hydrogen will speedily be given off from the surface of the
aluminium, and in five or six hours the whole of the nitrogen as
nitrates and nitrites will be converted into ammonia. Transfer to
a small retort the contents of the cylinder, together with the
pumice, washing the whole apparatus with a little water free from
ammonia. Distil, and estimate ammonia in the usual way with
lSTessler solution. It appears impossible wholly to exclude ammonia
from the reagents and apparatus, and therefore some blank experi-
ments should be made to ascertain the correction to be applied for
this. This correction is very small, and appears to be nearly constant.

8. Estimation of Nitrogen as Nitrates and Nitrites "by the Indig-o
Process. — This method will be described further on.

9. Estimation of Nitrates as Ammonia by the Copper-zinc
Couple. — It is well known that when zinc is immersed in copper
sulphate solution it becomes covered with a spongy deposit of
precipitated copper. If the solution of copper sulphate be
sufficiently dilute, this deposit of copper is black in colour and
firmly adherent to the zinc. It is, however, not so generally
known that the zinc upon which copper has thus been deposited
possesses the power of decomposing pure distilled water at the
ordinary temperature, and that it is capable of effecting many
other decompositions which zinc alone cannot. Among these is
the decomposition of nitrates, and the transformation of the nitric
acid into ammonia, Gladstone and Tribe have shown that
the action of the " copper-zinc couple " (as they call the conjoined
metals) upon a nitre solution consists in the electrolysis of the
nitre, resulting in the liberation of hydrogen and the formation
of zinc oxide. This hydrogen is liberated upon and occluded
by the spongy copper, and when thus occluded, it is capable of
reducing the nitre solution in its vicinity. The nitrate is first
reduced to nitrite, and the nitrous acid is subsequently trans-
formed into ammonia by the further action of the hydrogen.
M. W. Williams has shown (J. C. S. 1881, 100) that even in
very dilute solutions of nitre the nitric acid can be completely

F F

434 VOLUMETRIC ANALYSIS.

converted into ammonia in tins manner with considerable rapidity ;
and further, that the reaction may be greatly hastened by taking-
advantage of the influence of temperature, acids, and certain
neutral salts, which increase the electrolytic action of the couple.
His experiments prove that carbonic acid — feeble acid as it is —
suffices to treble the speed of the reaction, and that traces of sodic
chloride (0*1 per cent.) accelerated it nearly as much as carbonic
acid. A rise of a few degrees in temperature was also found to
hasten the reaction in a very marked degree. The presence of
alkalies, alkaline earths, and salts having an alkaline reaction, was
found to retard the speed of the reduction.

Williams has, upon those experiments, founded a simple and
expeditious process for estimating the nitric and nitrous acid in
water analysis, which, when used with skill, may be applied to by
far the greater number of waters with which the analyst is usually
called upon to deal (Analyst, 1881, 36). The requisite copper-zinc
couple is prepared in the following manner : — The zinc employed
should be clean, and for the sake of convenience should be in the
form of foil or very thin sheet, It should be introduced into
a flask or bottle, and covered with a solution of copper sulphate,
containing about 3 per cent, of the crystallized salt, which should
be allowed to remain upon it until a copious, firmly adherent coating,
of black copper has been deposited. This deposition should not
be pushed too far, or the copper will be so easily detached that the
couple cannot be washed without impairing its activity. When
sufficient copper has been deposited the solution should be poured
off, and the conjoined metals washed with distilled water. The
wet couple is then ready for use.

To use it for the estimation of nitrates it should be made in
a wide-mouthed stoppered bottle. After washing, it is soaked with
distilled water ; to displace this, it is first washed with some of the-
water to be analyzed, and the bottle filled up with a further
quantity of the water. The stopper is then inserted, and the bottle-
allowed to digest in a warm place for a few hours. If the bottle
be well filled and stoppered, the temperature may be- raised to-
30° C., or even higher, without any fear of losing ammonia. The-
reaction will then proceed very rapidly ; but if it be desired to>
hasten the reaction still more, a little salt should be added (about
O'l gm. to every 100 c.c.), or if there be any objection to this, the
water may have carbonic acid passed throtigh it for a few minutes
before it is poured upon the couple. In the case of calcareous
waters, the same hastening effect may be obtained, and the lime
may at the same time be removed by adding a very little pure
oxalic- acid to the water before digesting it upon the couple.
Williams has shown that nitrous acid always remained in the
solution until the reaction was finished. By testing for nitrous
acid the completeness of the reaction may be ascertained with
certainty, and perhaps the- most delicate test that can, be applied for

§ 89. WATER ANALYSIS. 435

this purpose is that of Gricss, in which metaphenylene-diamine
is the reagent employed. When a solution of this substance is
added to a portion of the fluid, and acidified with sulphuric
acid, a yellow colouration is produced in about half an hour if
the least trace of a nitrite be present. The reaction easily detects
one part of nitrous acid in ten millions of water. When no
nitrous acid is found, the water is poured off the couple into
a stoppered bottle, and, if turbid, allowed to subside. A portion
of the clear fluid, more or less according to the concentration of
the nitrates in the water, is put into a Kessler glass, diluted if
necessary, and titrated with Xessler's reagent in the ordinary way.

This process may be used for the majority of ordinary waters —
for those that are coloured, and those that contain magnesium or
other substances sufficient to interfere with the JSTessler reagent,
a portion of the fluid poured off the couple should be put into
a small retort, and distilled with a little pure lime or sodic
carbonate, and the titration of the ammonia performed upon the
distillates.

About one square decimeter of zinc should be used for every
200 c.c. of a water containing five parts or less of nitric acid in
100,000. A large proportion should be used with waters richer
in nitrates. The couple, after washing, may be used for two or
three waters more. When either carbonic or oxalic or any other
acid has been added to the water, a larger proportion of Messier
reagent should be employed in titrating it than it is usual to add.
3 c.c. to 100 of the water are sufficient in almost all cases.

Blunt (Analyst vi. 202) points out that the above process may
be used without distillation, and with accuracy, in the case of any
water, by adding oxalic acid to a double quantity of the sample,
dividing, and using one portion (clarified completely by subsidence
in a closely stoppered bottle) as a comparison liquid for testing
against the other, which has been treated with the copper-zinc
couple. When dilution is used it must be done in both portions
equally. This plan possesses the advantages that an equal turbidity
is produced by Messier in both portions, and any traces of
ammonia contained in the oxalic acid will have the error due to it
corrected.

In calculating the amount of nitric acid contained in a water
from the amount of ammonia obtained in this process, deductions
must of course be' made for any ammonia pre-existing in the water,
as well as for that derived from any nitrous acid present.

10. Estimation of Nitrites toy Griess's Method. — 100 c.c. of
the water are placed in a J^essler glass, and 1 c.c. each of
metaphenylene-diamine and dilute acid (p. 404) added. If colour
is rapidly produced the water must be diluted with distilled water
free from 2xT203, and other trials made. The dilution is sufficient
when colour is plainly seen at the end of one minute. The weak

F F 2

436 VOLUMETRIC ANALYSIS. § 89.

point of the process is that the colour is progressively developed ;
however, this is of little consequence if the comparison with
standard nitrite is made under the same conditions of temperature,
dilution, and duration of experiment. Twenty minutes is a
sufficient time for allowing the colours to develop before final
comparison.

M. AV. Williams obviates the uncertainty of the comparison
tests by using colourless Xessler tubes, 30 m.m. wide and
200 m.m. long, graduated into millimeters. They are used as
follows : — The comparison of the water to be examined with the
standard nitrite is roughly ascertained ; the glasses are then filled
to the same height, and the test added, and allowed to stand a few
minutes. Usually one will be somewhat deeper than the? other.
The height of the deeper-coloured liquid is read off on the scale,
and a portion removed with a pipette, until the colours correspond.
The amount of N203 in the shortened column is taken as equal to
the other, when a simple calculation will show the amount sought.

11. Estimation of Nitrites by Naphthylamine. — "Waringtoii
(J. C. S. 1881, 231) has drawn attention to this test, originally
devised by Griess, and which is of such extreme delicacy, that
by its means it is possible to detect one part of X203 in a thousand
millions of water.

Ilosvay has improved this test by using acetic acid instead of
a mineral acid. The colour is more intense and more rapidly
developed. He dissolves (1) 0'5 gm. of sulphanilic acid in 150
c.c. of dilute acetic acid, (2) boils O'l gm. of a-naphthylamine
with 20 c.c. of water, pours off the colourless solution, and mixes
it with 150 c.c. of dilute acetic acid. These two solutions are
mixed, thus gaining the advantage of having a single reagent
instead of two, and one which indicates by its colour whether it
has become contaminated by nitrous acid derived from the air. The
mixture is not affected by light, but should be protected from the
air. Should it, however, become coloured by absorption of nitrous
acid, it may be shaken with zinc-dust and filtered.

This test is almost too delicate to be used quantitatively, but is
evidently very serviceable as a quantitative test for very minute
quantities of nitrous acid. By its means "Warington has detected
nitrous acid in the atmosphere of various places by exposing water
containing a few drops of the requisite solutions to the air in a basin
for a few hours ; the like mixture kept in a closed flask or cylinder
at the same time undergoing no change of colour.

12. Estimation of Nitrites by Potassic Iodide and Starch. — Ekin
has pointed out (Pharm. Trans. 1881, 286) that this well-known
test will give the blue colour with nitrous acid in a few minutes,
when the proportion is one part in ten millions ; in twelve hours
when one part in a hundred millions ; and in forty-eight hours
when one in a thousand millions. Experience has proved that

§ 89. WATER ANALYSIS. 437

waters charged with much organic matter must be clarified by the
addition of a little pure alum, then well agitated and filtered
before testing.

Ekin used acetic acid for acidifying the water to be tested, and
blank experiments with pure water were simultaneously carried on.
Sulphuric or hydrochloric acid will, no doubt, give a sharper
reaction, but both these acids are more liable to contain impurities
affecting the reaction than is the case with pure acetic acid. Owing
to the instability of alkaline iodides, zinc iodide, however, is not
open to this objection, and is now generally used.

13. Estimation of Suspended Matter. — Filters of Swedish paper,
about 110 m.m. in diameter, are packed one inside another, about
15 or 20 together, so that water will pass through the whole group,
moistened with dilute hydrochloric acid, washed with hot distilled
water until the washings cease to contain chlorine, and dried. The
ash of the paper is thus reduced by about 60 per cent., and must
be determined for each parcel of filter paper by incinerating 10
filters, and weighing the ash. For use in estimating suspended
matter, these washed filters must be dried for several hours at
120 — 130° C., and each one then weighed at intervals of an hour
until the weight ceases to diminish, or at least until the loss of
weight between two consecutive weighings does not exceed 0*0003
(fm. It is most convenient to enclose the filter during weighing in
two short tubes, fitting closely one into the other. The closed ends
of test tubes, 50 m.m. long, cut off by leading a crack round with
the aid of a pastille or very small gas jet, the sharp edges being
afterwards fused at the blow-pipe, answer perfectly. Each pair of
tubes should have a distinctive number, which is marked with
a diamond on both tubes. In the air bath they should rest in.
grooves formed by a folded sheet of paper, the tubes being drawn
apart, and the filter almost, but not quite, out of the smaller tube.
They can then be shut up whilst hot by gently pushing the tubes
together, being guided by the grooved paper. They require to
remain about twenty minutes in a desiccator to cool before weighing.
Filtration will be much accelerated if the filters be ribbed before
drying. As a general rule, it will be sufficient to filter a quarter
of a liter of a sewage, half a liter of a highly polluted river, arid
a liter of a less polluted water ; but this must be frequently varied
to suit individual cases. Filtration is hastened, and trouble
diminished, by putting the liquid to be filtered into a narrow-
necked flask, which is inverted into the filter, being supported by
a funnel-stand, the ring of which has a slot cut through it to allow
the neck of the flask to pass. With practice the inversion may
be accomplished without loss, and without previously closing the
mouth of the flask. When all has passed through, the flask should
be rinsed out with distilled water, and the rinsings added to the
filter. Thus any particles of solid matter left in the flask are

4£8 VOLUMETRIC ANALYSIS. § 89.

secured, and the liquid adhering to the suspended matter and filter
is displaced. The filtrate from the washings should not be added
to the previous filtrate, which may be employed for determination
of total solid matter, chlorine, hardness, etc.

Thus washed, the filter with the matter upon it is dried at
100° C., then transferred from the funnel to the same pair of tubes
in which it was previously weighed, and the operation of drying at
120° - 130° C. and weighed until constant repeated. The weight
thus obtained, minus the weight of the empty filter and tubes,
gives the weight of the total suspended matter dried at 120° — 130° C.

To ascertain the quantity of mineral matter in this, the filter
with its contents is incinerated in a platinum crucible, and the
total ash thus determined, minus the ash of the filter alone, gives
the weight of the mineral suspended matter.

14. Estimation of Chlorine present as Chloride. — -To 50 c.c. of
the water add two or three drops of solution of potassic eliminate
(D. /3), so as to give it a faint tinge of yellow, and add gradually
from a burette standard solution of silver nitrate (D. a), until the
red silver chromate which forms after each addition of the
nitrate ceases to disappear on shaking. The number of c.c. of
silver solution employed will express the chlorine present as
chloride in parts in 100,000. If this amount be much more than
10, it is advisable to take' a smaller quantity of water.

If extreme accuracy be necessary, after completing a determination,
destroy the slight red tint by an excess of a soluble chloride, and
repeat the estimation on a fresh quantity of the water in a similar
flask placed by the side of the former. By comparing the contents
of the flasks, the first tinge of red in the second flask may be
detected with great accuracy. It is absolutely necessary that the
liquid examined should not be acid, unless with carbonic acid, nor
more than very slightly alkaline. It must also be colourless, or
nearly so. These conditions are generally found in waters, but, if
not, they may be brought about in most cases by rendering the
liquid just alkaline with lime water (free from chlorine), passing-
carbonic anhydride to saturation, boiling, and filtering. The calcic
carbonate has a powerful clarifying action, and the excess of alkali
is exactly neutralized by the carbonic anhydride. If this is not
successful, the water must be rendered alkaline, evaporated to
dryness, and the residue gently heated to destroy organic matter.
The chlorine may then be extracted with water, and estimated in
the ordinary way, either gravimetrically or volumetrically.

15. Estimation of Hardness. — The following method, devised by
tile late Dr. Thomas Clark, of Aberdeen, is in general use ; and
from its ease and rapidity is of some value, though it can hardly
be called accurate. (For estimating the hardness of waters
without soap solution see page 71.)

Uniformity in conducting it is of great importance ; especially

§ 89. HARDNESS OF WATERS. 439

the titration of the soap solution, and the estimation of the hardness
of waters, should be performed in precisely similar ways.

Measure 50 c.c. of the water into a well-stoppered bottle of about
250 c.c. capacity, shake briskly for a few seconds, and suck the
air from the bottle by means of a glass tube, in order to remove
any carbonic anhydride which may have been liberated from the
water. Add standard soap solution (E. j3) from a burette, one c.c.
at a time at first, and smaller quantities towards the end of the
operation, shaking well after each addition, until a soft lather is
obtained, which, if the bottle is placed at rest on its side, remains
continuous over the whole surface for five minutes. The soap
should not be added in larger quantities at a time, even when the
volume required is approximately known. This is very important.

When more than 16 c.c. of soap solution are required by 50 c.c.
of the water, a less quantity (as 25 or 10 c.c.) of the latter should
be taken, and made up to 50 c.c. with recently boiled and cooled
distilled water, so that less than 16 c.c. of soap solution will suffice,
and the number expressing the hardness of the diluted water
multiplied by 2 or 5, as the case may be.

When the water contains much magnesium, which may be
known by the lather having a peculiar curdy appearance, it should
be diluted, if necessary, with distilled water, until less than 7 c.c.
are required by 50 c.c.

The volume of standard soap solution required for 50 c.c. of the
water being known, the weight of calcic carbonate (CaCO3) corres-
ponding to this may be ascertained from the following Table 7* : —

* The table is calculated from that originally constructed by Dr. Clark, which is
ilS follows : —

Degree of Hardness. Measures of Differences for the

Soap Solution. next 1° of hardness.

0° (Distilled water) ... 1'4 ... 1'8

1 ... ... 3-2 ... 2-2

5-4 2-2

7-6 ... ... 2-0

9-6 ... 2-0

11-6 2-0

13-6 ... 2-0

15-6 ... ... 1-9

17-5 1-9

19-4
21-3
23-1

1-9

1-8
1-8
1-8

24-9

13 26-7 1-8

14 ... ... 23-5 ... . . 1-8

15 30-3 1-7

16 32-0

Each "measure" being 10 grains, the volume of water employed 1000 grains, and each
" degree " 1 grain of calcic carbonate in a gallon.

If the old weights and measures, grains and gallons, be preferred, this table may be
used, the process being exactly as above described, but 1000 grains of water taken
instead of 50 c.c., and the soap solution measured in 10-graiu measures instead of cubic
centimeters. If the volume of soap solution used be found exactly in the second column
of the table, the hardness will, of course, be that shown on the same line in the first
column. But if it be not, deduct from it the next lower number in the second column,
when the corresponding degree of hardness in the first column will give the integral
part of the resiilt ; divide the remainder by the difference on the same line in the third
column, and the quotient will give the fractional part. For example, if 1000 grains of
water require 16 " measures " of soap, the calculation will be as follows : —

440

VOLUMETRIC ANALYSIS.

89>.

TABLE 7.

Table of Hardness, Parts in 100,000.

16-0
—15-6 (=7° hardness).

Ill

„!"

*o ^
2 cu 3

Jl^

§ ^-2
2 JS

« 8

8S~

loj

= 11

ft O

o o
> m

°S

£ A

> CQ

°s>

c.c.

c.o.

C.C.

4-0

4-57

8-0

10-30

12-0

16-43

•71

•45

•59

•86

•60

•75

5-00

•75

•90

•14

•90

17'06

•29

11-05

•22

•43

•20

•38

0-7

•oo

•57

•35

•54

0-8

•16

•71

•50

•70

0-9

•32

•86

•65

•86

i-o

•48

5-0

6-00

9-0

•80

13-0

18-02

•63

•14

•95

•17

•79

•29

12-11

•33

•95

•43

•26

•49

I'll

•57

•41

•65

•27

•71

•56

•81

•43

•85

•71

•97

•56

7-00

•86

19-13

•69

•14

13-01

•29

•82

•29

•16

•44

1 2-0

•95

6-0

•43

10-0

•31

14-0

•60

2-08

•57

•46

•76

•21

•71

•61

•92

•34

•86

•76

20-08

•47

8-00

•91

•24

•60

•14

14-06

•40

•73

•29

•21

•56

•86

•43

•37

•71

•99

•57

•52

•87

3-12

•71

•68

21-03

3-0

•25

7-0

•86

! 11-0

•84

15-0

•19

•38

9-00

15-00

•35

•51

•14

•16

•51

•64

•29

•32

•68

•77

•43

•48

•85

•90

•57

•63

22-02

4-03

•71

•79

•18

•16

•g->

•95

•35

•29

10-00

16-11

•52

3-9

•43

7-9

•15

i 11-9

•27

•69

16-0

•86

(Difference =) (l'9)/4

•21

therefore the hardness is 7'21 grains of CaCO3 per gallon. The water must be diluted
with distilled water if necessary, so that the quantity of soap required does not exceed.
32 measures in ordinary waters, and 14 measures in water containing much magnesia..

§ 89. MINERALS AND METALS IN WATERS. 441

When water containing calcic and magnesic carbonates, held
in solution by carbonic acid, is boiled, carbonic anhydride is
expelled, and the carbonates precipitated. The hardness due to
these is said to be temporary, whilst that due to sulphates,,
chlorides, etc., and to the amount of carbonates soluble in pure
water (the last-named being about three parts per 100,000) is
called permanent.

To estimate permanent hardness, a known quantity of the water
is boiled gently for half an hour in a flask, the mouth of which
is freely open. At the end of the boiling, the water should be
allowed to cool, and the original weight made up by adding
recently boiled distilled water.

Milch trouble may be avoided by using flasks of about the same
weight, and taking so much water in each as will make up the
same uniform weight. Thus if all the flasks employed weigh
less than 50 gm. each, let each flask with its contents be made to
weigh 200 gm.

After boiling and making up to the original weight, filter the
water, and determine the hardness in the usual way. The hardness
thus found, deducted from that of the unboiled water, will give
the temporary hardness.

16. Mineral Constituents and Metals. — The quantities of the
following substances which may be present in a sample of water
are subject to such great variations, that no definite directions can
be given as to the volume of water to be used. The analyst must
judge in each case from a preliminary experiment what will be
a convenient quantity to take.

Sulphuric Acid. — Acidify a liter or less of the water with
hydrochloric acid, concentrated on the water bath to about 100c.c.r
and while still hot add a slight excess of baric chloride. Filter,
wash, ignite, and weigh as baric sulphate, or estimate volumetricallyy
as in § 76.

Sulphuretted Hydrogen. — Titrate with a standard solution of
iodine, as in § 77.3.

Phosphoric Acid. — This substance may be determined in the
solid residue obtained by evaporation, by moistening it with nitric
acid, and again drying to render silica insoluble ; the residue is
again treated with dilute nitric acid, filtered, molybdic solution
(p. 297) added, and set aside for twelve hours in a warm place ;
filter, dissolve the precipitate in ammonia, precipitate with magnesia
mixture, and weigh as magnesic pyrophosphate, or estimate volu-
metrically as in § 72.

Another method is to add to 500 c.c. of the sample about 10 c.c.
of solution of alum, then a few drops of ammonia, lastly acidify
slightly with acetic acid, and set aside to allow the precipitated
A1P204 to settle. The clear liquid may then be poured off, the-

442 VOLUMETRIC ANALYSIS. §89.

precipitate dissolved in nitric acid and estimated with molybdic
solution.

These estimations are only available in cases where the P-05
is very large. In most waters it is simply necessary to record
whether the molybdic precipitate is in heavy or minute traces.

Silicic Acid. — Acidify a liter or more of the water with
hydrochloric acid, evaporate, and dry the residue thoroughly.
Then moisten with hydrochloric acid, dilute with hot water, and
filter off, wash, ignite, and weigh the separated silica.

Iron. — To the nitrate from the estimation of silicic acid add a few
drops of nitric acid, dilute to about 100 c.c., and estimate by colour
titration, as in § 64.4 ; or where the amount is large, add excess of
ammonia, and heat gently for a short time. Filter off the precipitate
and estimate the iron in the washed precipitate colorimetrically,
as in § 64.

Calcium. — To the filtrate from the iron estimation add excess of
ammonic oxalate, filter off the calcic oxalate, ignite and weigh
as calcic carbonate, or estimate volumetrically with permanganate,
as in § 52.

Magnesium. — To the concentrated filtrate from the calcium
estimation add sodic phosphate (or, if alkalies are to be determined
in the filtrate, ammonic phosphate), and allow to stand for twelve
hours in a warm place. Filter, ignite the precipitate, and weigh
as magnesic pyrophosphate, or, without ignition, titrate with
uranium.

Barium. — Is best detected in a water by acidifying with
hydrochloric acid, filtering perfectly clear if necessary, then
add a clear solution of calcic sulphate, and set aside in a warm
place. Any white precipitate which forms is due to barium.

Potassium and Sodium. — These are generally determined jointly,
and for this purpose the filtrate from the magnesium estimation
may be used. Evaporate to dryness, and heat gently to expel
ammonium salts, remove phosphoric acid with plumbic acetate, and
the excess of lead in the hot solution by ammonia and ammonic
carbonate. Filter, evaporate to dryness, heat to expel ammonium
salts, and weigh the alkalies as chlorides.

It is, however, generally less trouble to employ a separate
portion of water. Add to a liter or less of the water enough pure
baric chloride to precipitate the sulphuric acid, boil with pure milk
of lime, filter, concentrate, and remove the excess of lime with
ammonic carbonate and a little oxalate. Filter, evaporate, and
weigh the alkaline chlorides in the filtrate. If the water contains
but little sulphate, the baric chloride may be omitted, and a little
ammonic chloride added to the solution of alkaline chlorides.

§ 89. MINERALS AND METALS IN WATERS. 443

If potassium and sodium must each be estimated, separate them
by means of platinic chloride ; or, after weighing the mixed
chlorides, determine the chlorine present in them, and calculate the
amounts of potassium and sodium by the following formula : —
Calculate all the chlorine present as potassic chloride ; deduct this
from the weight of the mixed chlorides, and call the difference d.
Then as 16'1 : 58'37 : : d : XaCl present. (See also § 42.)

Lead. — May be estimated by the method proposed by Miller.
Acidulate the water with two or three drops of acetic acid, and
add -i- of its bulk of saturated aqueous solution of sulphuretted
hydrogen. Compare the colour thus produced in the colorimeter
or a convenient cylinder, with that obtained with a known quantity
of a standard solution of a lead salt, in a manner similar to that
described for the estimation of iron (§ 64.4). The lead solution
should contain 0'1831 gin. of normal crystallized plumbic acetate in
a liter of distilled water, and therefore each c.c. contains 0*0001 gm.
of metallic lead.

It is obvious that in the presence of copper or other heavy metals
the colour produced by the above method will all be ascribed
to lead ; it is preferable, therefore, to adopt the method of Harvey
(Analyst vi. 146), in which the lead is precipitated as chromate.
The results, however, are not absolute as to quantity, except so
far as the eye may be able to measure the amount of precipitate.

The standard lead solution is the same as in the previous
method. The precipitating agent is pure potassic bichromate,
in fine crystals or powder.

250 c.c. or so of the water is placed in a Phillips' jar with
a drop or two of acetic acid, and a few grains of the reagent added,
and agitated by shaking. One part of lead in a million parts of
water will show a distinct turbidity in five minutes or less. In six
or eight hours the precipitate will have completely settled, and the
yellow clear liquid may be poured off without disturbing the
sediment, which may then be shaken up with a little distilled
water, and its quantity judged by comparison with a similar
experiment made with the standard lead solution.

Copper. — Estimate by colour titration, as in § 58.9.

Arsenic. — Add to half a liter or more of the water enough
sodic hydrate, free from arsenic, to render it slightly alkaline,
evaporate to dryness, and extract with a little concentrated
hydrochloric acid. Introduce this solution into the generating
flask of a small Marsh's apparatus, and pass the evolved hydrogen,
first through a U-tube filled with pumice, moistened with plumbic
acetate, and then through a piece of hard glass tube about 150 m.m.
in length, and 3 m.m. in diameter (made by drawing out combustion
tube). At about its middle, this tube is heated to redness for
a length of about 20 m.m. by the flame of a small Bun sen burner,

444 VOLUMETRIC ANALYSIS. § 90.

and here the arsenetted hydrogen is decomposed, arsenic "being
deposited as a mirror on the cold part of the tube. The mirror
obtained after the gas has passed slowly for an hour is compared
with a series of standard mirrors obtained in a similar way from
known quantities of arsenic. Care must be taken to ascertain in
each experiment that the hydrochloric acid, zinc, and whole apparatus
are free from arsenic, by passing the hydrogen slowly through the
heated tube before introducing the solution to be tested.

Zinc. — This metal exists in waters as bicarbonate, and on
exposure of such waters in open vessels a film of zinc carbonate
forms on the surface ; this is collected on a platinum knife or foil
and ignited. The residue is of a yellow colour when hot, and
turns white on cooling. The reaction is exceedingly delicate.

THE INTERPRETATION OF THE RESULTS OF ANALYSIS.

§ 90. THE primary form of natural water is rain, the chief impurities in
which are traces of organic matter, ammonia, and ammouic nitrate derived
from the atmosphere. On reaching the ground it becomes more or less
charged with the soluble constituents of the soil, such as calcic and magnesic
carbonates, potassic and sodic chlorides, and other salts, Avhich are dissolved,
some by a simple solvent action, others by the agency of carbonic acid in
solution. Draining off from the land, it will speedily find its way to a stream
which, in the earlier part of its course, will probably be free from pollution by
animal matter, except that derived from any manure which may have been
applied to the land on which the rain fell. Thus comparatively pure, it will
furnish to the inhabitants on its banks a supply of water which, after use,
will be returned to the stream in the form of sewage charged with impurity
derived from animal excreta, soap, household refuse, etc., the pollution being
perhaps lessened by submitting the sewage to some purifying process, such as
irrigation of land, filtration, or clarification. The stream in its subsequent
course to the sea will be in some measure purified by slow oxidation of the
organic matter, and by the absorbent action of vegetation. Some of the
rain will not, however, go directly to a stream, but sink through the soil to
a well. If this be shallow, it may be considered as merely a pit for the
accumulation of drainage from the immediately surrounding soil, which, as
the well is in most cases close to a dwelling, will be almost inevitably
charged with excretal and other refuse ; so that the water when it reaches
the well will be contaminated with soluble impurities thence derived, and
with nitrites and nitrates resulting from their oxidation. After use the
Avater from the well will, like the river water, form sewage, and find its
wray to a river, or again to the soil, according to circumstance-.

In the case of a deep well, from which the surface water is excluded, the
conditions are different. The shaft will usually pass through an impervious
stratum, so that the water entering it will not be derived from the rain
wrhich falls on the area immediately surrounding its mouth, but from that
which falls on the outcrop of the pervious stratum below the impervious one
just mentioned; and if this outcrop be in a district which is uninhabited
and uncultivated, the water of the well will probably be entirely free from
organic impurity or products of decomposition. But even if the water be
polluted at its source, still it must pass through a very extensive filter before
it reaches the well, and its organic matter will probably be in great measure
converted by oxidation into bodies in themselves innocuous.

This is very briefly the general history of natural waters, and the problem
presented to the analyst is to ascertain, as far. as possible, from the nature

§ 90. INTERPRETATION OF RESULTS. 445

and quantity of the impurities present, the previous history of the water,
and its present condition and fitness for the purpose for which it is to
be used.

It is impossible to give any fixed rule by which the results obtained by the
foregoing method of analysis should be interpreted. The analyst must form
an independent opinion for each sample from a consideration of all the results
he has obtained. Nevertheless, the following remarks, illustrated by reference
to the examples given in the accompanying table, which may be considered
as fairly typical, will probably be of service. (See Table 8.)

Total Solid Matter.

Waters which leave a large residue on evaporation are, as a rule, less suited
for general domestic purposes than those which contain less matter in solution,
and are unfit for many manufacturing purposes. The amount of residue is
also of primary importance as regards the use of the water for steam boilers,
as the quantity of incrustation produced will chiefly depend upon it. It may
vary cousiderabhr, apart from any unnatural pollution of the water, as it
depends principally on the nature of the soil through or over which the
water passes. River water, when but slightly polluted, contains generally
from 10 to 40 parts. Shallow well water varies greatly, containing from 30
to 150 parts, or even more, as in examples X. and XIII., the proportion
here depending less on the nature of the soil than on the original pollution
of the water. Deep well water also varies considerably; it usually contains
from 20 to 70 parts, but this range is frequently overstepped, the quantity
depending largely upon the nature of the strata from which the wrater is
obtained. Example XV. being in the New E-ed Sandstone, has a small pro-
portion but XVII. and XVIII. in the Chalk have a much larger quantity.
Spring waters closely resemble those from deep wells. Sewage contains
generally from 50 to 100 parts, but occasionally less, and frequently much
more, as in example XXXIV. The total solid matter, as a rule, exceeds the
sum of the constituents determined ; the nitrogen, as nitrates and nitrites,
being calculated as potassic nitrate, and the chlorine as sodic chloride ; but
occasionally this is not the case, owing, it is likely, to the presence of some
of the calcium as calcic nitrate or chloride.

Organic Carbon or Nitrogen.

The existing condition of the sample, as far as organic contamination is
concerned, must be inferred from the amount of these two constituents. In
a good water, suitable for domestic supply, the former should not, under
ordinary circumstances, exceed 0'2 and the latter 0'02 part.

Waters from districts containing much peat are often coloured more or
less brown, and contain an unusual quantity of organic carbon, but this
peaty matter is probably innocuous unless the quantity be extreme. The
large proportion of organic carbon and nitrogen given in the average for
unpolluted upland surface water in Table- 8 (XXVIII.) is chiefly due to the
fact that upland gathering grounds are very frequently peaty. The examples
given (I. to V.) may be taken as fairly representative of the character of
upland surface waters free from any large amount of peaty matter. In
surface waters from cultivated areas the quantity of organic carbon and
nitrogen is greater, owing to increased density of population, the use of
organic manures, etc., the proportion being about 0'25 to 0'3 part of organic
carbon, and 0'04 to 0'05 part of organic nitrogen. The water from shallow
wells varies so widely in its character that it islmpossible to give any useful
average. In many cases, as for example in XIII. and XIV., the amount is
comparatively small, although the original pollution, as shoAvn by the total
inorganic nitrogen and the chlorides, was very large ; the organic matter in

446

TABLE 8.

VOLUMETRIC ANALYSIS. § 90.

Results of Analysis expressed

Sample.

DESCRIPTION.

REMARKS.

II.

III.

IV.

VI.
VII.

VIII.

IX.

XI.

XII.
XIII.
XIV.

XV.
XVI.

XVII.
XVIII.

XXI.

XXII.

XXIII.

XXIV.

XXV.

XXVI.

Upland Surface Waters.

The Dee above Balmoral, March 9th, 1872
Glasgow Water supply from Loch Katrine— average of ")
monthly analyses during five years, 1876 — 81 >

Liverpool Watersupply from RivingtonPike,June4th,1869
Manchester Water supply, May 9th, 1874
Cardiff Water supply, Oct. 18th, 1872

Surface Water from Cultivated Land.
Dundee Water supply, March 12th, 1872
Norwich Water supply, June 18th, 1872

Shallow Wells.

Cirencester, Market Plnce, Nov. 4th, 1870
Marlborough, College Yard, Aug. 22nd, 1873 ...
Birmingham, Hurst Street, Sept. 18th, 1873 ...

Sheffield, Well near, Sept. 27th, 1870

London, Aldgate Pump, June 5th, 1872
London, Wellclose Square, June 5th, 1872
Leigh, Essex, Churchyard Well, Nov. 28th, 1871

Deep Wells.

Birmingham, Short Heath Well, May 16th, 1873
Caterham, Water Works Well, Feb. 14th, 1873
Ditto, Softened (Water supply) ..."

London, Albert Hall, May, 1872
Gravesend, Kail way Station, Jan. 17th, 1873 ...

Spring-s.

Dartmouth Water supply, Jan. 8th, 1873
Grantham Water supply, July llth, 1873

Clear

Clear; very pale 1

Clear ... '

Turbid

Clear

Turbid ; brownish 3
Slightly turbid...

Slightly turbid...

Clear

Clear; strong saline

C Very turbid & off
sive. Swarm

(. with bacteria,
Clear ...
Slightly turbid; salii
Slightly turbid...

Clear

Slightly turbid...
Clear

Turbid
Clear

London Water supply— average monthly analyses dur ing 21 years, 1869

From the Thames ...

From the Lea

From Deep Chalk Wells (Kent Company)

Ditto (Colne Valley Co.) softened— thirteen years, 1877—89

Ditto (Tottenham)— thirteen years, 1877— 89... ... I

Birmingham Water supply— average monthly analyses, 1875—1880.

Average Composition of Unpolluted
Bain Water
Upland Surface Water

Deep Well Water

Spring Water
Sea Water

Water.

39 samples

195

157

198

Sewage.

Average from 15 "Midden" Towns, 37 analyses
Average from 16 "Water Closet" Towns, 50 analyses ..
Salford, Wooden Street Sewer, March 15th, 1869
Merthyr Tydfil, average 10 a.m. to 5 p.m., Oct. 20th, 1871

(after treatment with lime)
Ditto, Effluent Water ...

EXAMPLES OF WATER AND SEWAGE ANALYSES. 447

in parts per 100, CCO.

TABLE 8.

i
i

Organic
Carbon.

Organic
Nitro-
gen.

Nitro-
gen !IS
Am-
monia.

Nitrogen
as
Nitrates
and
Nitrites.

Total
Inorganic
Nitrogen

Total
Combined

Nitrogen

L Chlorine.

Hardness.

Tem-
porary.

Perma-
nent.

Total.

•132

•014

9-4

•014

•50

1-5

ii.

•148

•016

9-2

•005

•022

•64

—

•9

;•;

•210

•029

7'2

•002

•C31

1-53

•3

3-7

4-0

•132

•031

•002

•033

•90

2-7

•212

•031

6-8

•034

•065

1-40

7-1

129

20'0

•418

•059

7-1

•001

•081

•082

•141

1-75

6-0

•432

•080

5-4

•012

•036

•048

•128

3-10

21-3

5-3

26-6

•041

•008

5-1

•362

• -370

1-GO

18-4

4-6

23-0

8 -049

•015

3-3

•613

•628 1-90

15-6

101

25-7

0 -340

•105

3'2

•511

14-717

15-228

15'33o

36-50

27-5

99-6

127-1

0 j 1-200

•126

9-5

•091

•217

2'20

2-0

1-4

0 1 '144

•141

i-o

•181

6-851

7-032

7-173

12-85

37-1

40-0

77-1

0 -278

•087

3'2

25-8:10

25-840

25-927

34-60

26'7

164-3

191-0

•210

•065

5-047

5-112

13;75

14-3

45-7

60-0

•C09

•004

2-2

•447

•451

1-30

4-6

5-1

9-7

•028

•009

3-1

•021

•030

1-55

15-2

6-0

21-2

•015

•003

5-0

—

. —

—

. —

—

4-4

•168

•042

4-0

•007

•066

•073

•115

15-10

3-4

5-6

>L)

•127

•029

4'4

•063

2-937

3-000

3-029

5-40

27-9

14-5

42-4

•060

•016

•330

•346

2-45

1-6

10-0

11-G

•048

•018

•2-7

•833

•851

2-05

17-1

6-5

23-6

•191

•033

5-8

•210

•243

1'68

20-1

• -134

•025

5'4

•226

•226 -251 1-76

20-9

•049

•on

4'5

•446

•458 2-47

— .

—

28-5

•059

•014

4'2

•003

•367

•370

•384 1 1-70 —

—

6-0

•068

•016

4'2

•054

•143

•196

2-85

—

23-3

•245

•054

4-6

•002

•231

•233

•287

1-73

7'7

8-8

16'5

'•070

•015

4-7

•024

•003

•027

•042

•22

•3

•322

•032

10-1

•002

•009

•on

•043

1-13

1-5

4-3

5-4

•061

•018

3-4

•010

•495

•505

•523

5-11

15-8

9-2

25-0

•056

•013

4-3

•001

•383

•381-

•397

2'49

11-0

7-5

18-5

•278

•165

1'7

•005

•033

•038

•203

1975-6

48-9

748-0

796-9

Suspended Matter.

Mineral. Organic. Total.

4-181

1-975

2-1

4-476

6-451

11-54

17-81

21-30

39-11

4-696

2-205

2-1

.5-520

•003

5-523

7-728

10-66

24-18

20-51

44-69

11-012

7-634

5-468

13-102

20-50

18-88

26-44

45-32

1-282

•952

1-3

1-054

•052

1-106

2-058

5-25

7-88

6-56

14-44

•123

•031

4-0

•048

•300

•348

•379

2-60

Trace.

448 VOLUMETEIC ANALYSIS.

-these cases having heen almost entirely destroyed hy powerful oxidation. In
VIII. and IX. the original pollution was slight ; and oxidation being active,
the organic carhon and nitrogen have been reduced to extremely small
quantities. On the other hand, in XI. the proportion of organic matter is
enormous, the oxidizing action of the surrounding soil being utterly
insufficient to deal with the pollution. The danger attending the use of
shallow well waters, which contain when anatyzed very small quantities of
organic matter, arises chiefly from the liability of the conditions to variation.
Change of weather and many other circumstances may at any time prevent
the purification of .the water, which at the time of the analysis appeared to
be efficient. Moreover, it is by no means certain, that an oxidizing action
which would be sufficient to reduce the organic matter in a water to a very
small proportion, would be equally competent to remove the specific poison
of disease. Hence the greater the impurity of the source of a water the
greater the risk attending its use.

In deep well waters the quantity of organic carbon and nitrogen also
extends through a wide range, but is generally low, the average being
•about 0 06 part carbon and 0'02 part nitrogen (XXIX). Here the conditions
are usually very constant, and if surface drainage be excluded, the source of
the water is of less importance. Springs in this, as in most other respects,
resemble deep wells ; the water from them being generally, however, some-
what purer. In sewage great variations are met with. On the average it
contains about four parts of organic carbon and two parts of organic nitrogen
-(XXXII. and XXXIII.), but the range is very great. In the table, XXXIV.
is a very strong sample, and XXXV. a weak one. The effluent Avater from
land irrigated with sewage is usually analogous to waters from shallow wells,
and its quality varies greatly according to the character of the sewage and
,the conditions of the irrigation.

Ratio of Organic Carbon to Organic Nitrogen.

The ratio of the organic carbon to the organic nitrogen given in the
.seventh column of the table (which shows the fourth term of the proportion
— organic nitrogen : organic carbon : : 1 x), is of great importance as
furnishing a valuable indication of the nature of the organic matter present.
When this is of vegetable origin, the ratio is very high, and when of animal
-origin venr low. This statement must, however, be qualified, on account of
the different effect of oxidation on animal and vegetable substances. It is
found that when organic matter of vegetable origin, with a high ratio of
carbon to nitrogen, is oxidized, it loses carbon more rapidly than nitrogen,
so that the ratio is reduced. Thus unoxidized peaty waters exhibit a ratio^
varying from about 8 to 20 or even more, the average being about 12 ;
whereas, the ratio in spring water originally containing peaty matter, varies
from about 2 to 5, the average being about 3'2. When the organic matter
is of animal origin the action is reversed, the ratio being increased by
.oxidation. In unpolluted upland surface waters the ratio varies from about
6 to 12, but in peaty waters it may amount to 20 or more. In surface \\ater
from cultivated land it ranges from about 4 to 10, averaging about 6. In
water from shallow wells it varies from about 2 to 8, with an average of
about 4, but instances beyond this range in both directions are very frequent.
In water from deep wells and springs, the ratio varies from about 2 to 6,
with an average of 4, being low on account, probably, of the prolonged
oxidation to which it has been subjected, which, as has been stated above,
removes carbon more rapidly than nitrogen. In sea water this action
reaches a maximum, the time being indefinitely prolonged, and the ratio is
on the average about 1'7. This is probably complicated by. the presence, in
some cases, of multitudes of minute living organisms.. In sewage the ratio
/ranges from about 1 to 3, with an average of about 2.

§ 90. INTERPRETATION OF RESULTS^- 44.9

_ When, in the case of a water containing much nitrogen as nitrates and
nitrites, this ratio is unusually low, incomplete destruction of nitrates during
the evaporation may be suspected, and the estimation should be repeated.
To provide for this contingency, if a water contain any considerable quantity
of ammonia, it is well, when commencing the evaporation in the first
instance, to set aside a quantity sufficient for this repetition, adding to it the
usual proportion of sulphurous acid.

Nitrogen as Ammonia.

The ammonia in natural waters is derived almost exclusively from animal
contamination, and its quantity varies between very wide limits. In upland
surface waters it seldom exceeds O'OOS part, the average being about 0'002
part. In water from cultivated land the average is about 0'005, and the
range is greater, being from nil to 0'025 part, or even more. In water from
shallow wells the variation is so great that it would be useless to attempt to
state an average, all proportions from nil to as much as 2*5 parts having
been observed. In waters from deep wells a very considerable proportion is
often found, amounting to O'l part or even more, the average being O'Ol
part, and the variations considerable. In spring water it is seldom that
more than O'Ol part of nitrogen as ammonia occurs, the average being only
O'OOl part. Sewage usually contains from 2 to 6 parts, but occasionally as
much as 9 or 10 parts, the average being about five. Ammonia is readily
oxidized to nitrates and nitrites, and hence its presence, in considerable
quantity, usually indicates the absence of oxidation, and is generally
coincident with the presence of organic matter. That sometimes found in
waters from very deep wells is, however, probably due to subsequent
decomposition of nitrates.

Nitrogen as Nitrates and Nitrites.

Nitrates and nitrites are produced by the oxidation of nitrogenous
organic matter, and almost always from animal matter. In upland surface
waters the proportion varies from nil to 0'05 part or very rarely more, but
the majority of samples contain none or mere traces (I. to V.), the average
being about 0'009 part. In surface waters from cultivated land the quantity
is much greater, varying from nil, which seldom occurs, to 1 part, the
average being about 0'25 part. The proportion in shallow wells is usually
much greater still, ranging from nil, which very rarely occurs, to as much
as 25 parts. It would be probably useless to attempt to state an average,
but quantities of from 2 to 5 parts occur most frequently. In water from
deep wells the range is from nil to about 3 parts, and occasionally more, the
average being about 0'5 part. In spring water the range is about the same
as in deep well water, but the average is somewhat lower.

It sometimes happens that, when the supply of atmospheric oxygen is
deficient, the organic matter in water is oxidized at the expense of the
nitrates present ; and occasionally, if the quantities happen to be suitably
proportioned, they are mutually destroyed, leaving no evidence of pollution.
This reduction of nitrates often occurs in deep well water, as for example,
in that from wells in the Chalk beneath London Clay, where the nitrates are
often totally destroyed. In sewages, putrefaction speedily sets in, and
during this condition the nitrates are rapidly destroyed, arid so completely
and uniformly that it is probably needless to attempt their estimation,
except in sewages which are very weak, or for other special reasons
abnormal. Out of a large number of samples, only a very few have been
found which contained any nitrates, and those only very small quantities.

Nitrites occurring in deep springs or wells no doubt arise from the
deoxidation of nitrates by ferrous oxide, or certain forms of organic matter

G G

450 VOLUMETRIC ANALYSIS.

of a harmless nature ; but whenever they occur in shallow wells or river
water, they may be of much greater significance. Their presence in such
cases is most probably due to recent sewage contamination, and such waters
must be looked upon with great suspicion.

Total Inorganic Nitrogen.

When organic matter is oxidized it is ultimately resolved into inorganic
substances. Its carbon appears as carbonic acid, its hydrogen as water, and
its nitrogen as ammonia, nitrous acid, or nitric acid; the last two combining
with the bases always present in water to form nitrites and nitrates. The
carbon and hydrogen are thus clearly beyond the reach of the analyst ; but
the nitrogen compounds, as has been shown, can be accurately determined,
and furnish us with a means of estimating the amount of organic matter
which was formerly present in the water, but wrhich has already undergone
decomposition.

The sum of the amounts of nitrogen found in these three forms con-
stitutes then a distinct and valuable term in the analysis, the organic
nitrogen relating to the present, and the total inorganic nitrogen to the
past condition of the water. Since ammonia, nitrites and nitrates are quite
innocuous, the total inorganic nitrogen does not indicate actual evil like
the organic nitrogen, but potential evil, as it is evident that the innocuous
character of a water which contains much nitrogen in these forms depends
wholly on the permanence of the conditions of temperature, aeration,
nitration through soil, etc., which have broken up the original organic
matter; if these should at any time fail, the past contamination would
become present, the nitrogen appearing in the organic form, the water being
loaded in all likelihood with putrescent and contagious matter.

In upland surface waters which have not been contaminated to any
extent by animal pollution the total inorganic nitrogen rarely exceeds 0'03
part. In water from cultivated districts the amount is greater, ranging as
high as 1 part, the average of a large number of samples being about 0'22 part.
It is useless to attempt any generalization for shallow wells, as the pro-
portion depends upon local circumstances. The amount is usually large and
may reach, as seen in Examples XIII., the enormous quantity of twenty-five
parts per 100,000. Waters containing from one to five parts are very commonly
met with. In water from deep wells and springs, quantities ranging up to
3' 5 parts have been observed, the average on a large series of analyses being
0'5 part for deep wells and about 0'4 part for springs. It must be re-
membered that the conditions attending deep wells and springs are
remarkably permanent, and the amount of filtration which the water under-
goes before reaching the well itself, or issuing from the spring is enormous.
Meteorological changes here have either no effect, or one so small and slow
as not to interfere with any purifying actions which ma}'- be taking place.
All other sources of water, and especially shallow wells,' are on the other
hand subject to considerable changes. A sudden storm after drought will
wash large quantities of polluting matter into the water-course ; or dissolve
the filth which has been concentrating in the pores of the soil during the
dry season, and carry it into the well. Small indications therefore of a
polluted origin are very serious in surface waters and shallow well waters,
but are of less moment in water from deep wells and springs; the present
character of these being of chief importance, since whatever degree of
purification may be observed, may usually be trusted as permanent. The
term "total inorganic nitrogen" has been chosen chiefly because it is
based on actual results of analysis without the introduction of any theory
whatever. It will be seen that it corresponds very nearly with the term
"previous sewage or animal contamination," which was introduced by Dr.
Prankland, and which was employed in the second edition of this work.

§ 90. INTERPRETATION OF RESULTS. 451

Perhaps few terms have been more wonderfully misunderstood and mis-
represented than that phrase, and it is hoped that the new term will be less
liable to misconception. It will be remembered that the "previous sewage
•contamination " of a water was calculated by multiplying the sum of the
quantities of nitrogen present as ammonia, nitrates, aiid nitrites, by 10,000
•and deducting 320 from the product, the number thus obtained representing
the previous animal contamination of the water in terms of average filtered
London sewage. It was purely conventional, for the proportion of organic
nitrogen present in such sewage was assumed to be 10 parts per 100,000,
whereas in the year 1857 it was actually 8'4 parts, and in 1869 only 7 parts.
The deduction of 320 was made to correct for the average amount of
inorganic nitrogen in rain water, and this is omitted in calculating "total
inorganic nitrogen " for the following reasons : — The quantity is small,
and the variations in composition of rain water at different times and under
different circumstances very considerable, and it appears to obscure the
significance of the results of analysis of very pure waters to deduct from
all the same fixed amount. As, too, the average amount of total inorganic
nitrogen in unpolluted surface waters is only O'Oll part (XXVIII.), it
cannot be desirable to apply a correction amounting to nearly three times
that average, and so place a water which contains 0'032 part of total
inorganic nitrogen on the same level as one which contains no trace of any
previous pollution.

Chlorine.

This is usually present as sodic chloride, but occasional!}^ as has been
mentioned before, it is most likely as a calcic salt. It is derived, in some
cases, from the soil, but more usually from animal excreta (human urine
contains about 500 parts per 100,000), and is therefore of considerable
importance in forming a judgment as to the character of a water. Un-
polluted river and spring waters usually contain less than one part; average
town sewage about eleven parts. Shallow well water may contain any
quantity from a mere trace up to fifty parts or even more. Its amount is
scarcely affected by any degree of filtration through soil : thus, the effluent
water from land irrigated with sewage contains the same proportion of
chlorine as the .sewage, unless it has been diluted by subsoil water or con-
centrated by evaporation. Of course, attention should be given to the
geological nature of the district from which the water comes, the distance
from the sea or other source of chlorine, etc., in order to decide on the
•origin of the chlorine. Under ordinary circumstance, a water containing
more than three or four parts of chlorine should be regarded with suspicion.

Hardness.

This is chiefly of importance as regards the use of the water for cleansing
and manufacturing purposes, and for steam boilers. It is still a moot point
as to whether hard or soft water is better as an article of food. The
temporary hardness is often said to be that due to carbonates held in solution
by carbonic acid, but this is not quite correct; for even after prolonged
boiling, water will still retain about three parts of carbonate in solution,
and therefore when the total hardness, exceeds three parts, that amount
should be deducted from the permanent hardness and added to the temporary,
in order to get the quantity of carbonate in solution. But the term
"temporary" hardness properly applies to the amount of hardness which
may be removed by boiling, and hence, if the total hardness be less than
three parts, there is usually no temporary. As the hardness depends
•chiefly on the nature of the soil through and over which the water passes,
the variations in it are very great; that from igneous strata has least
liardness, followed in approximate order by that from Metamorphic,

G G 2

452 VOLUMETRIC ANALYSIS. § 90.

Cambrian, Silurian and Devonian rocks, Millstone Grit, London Clay,
Bagshot Beds, New Eed Sandstone, Coal Measures, Mountain Limestone,
Oolite, Chalk, Lias, and Dolomite, the average in the case of the first
being 2'4 parts, and of the last 41 parts. As animal excreta contain u
considerable quantity of lime, highly polluted waters are usually extremely
hard. Water from shallow wells contains varying proportions up to nearly
200 parts of total hardness (XIII.). No generalization can be made as to
the proportion of permanent to temporary hardness.

Suspended Matter.

This is of a less degree of importance than the matters hitherto considered.
Prom a sanitary point of view it is of minor interest, because it may be in
most cases readily and completely removed by filtration. Mineral suspended
matter is, however, of considerable mechanical importance as regards the
formation of impediments in the river bed by its gradual deposition, and
as regards the choking of the sand filters in water-Avorks ; and organic-
suspended matter is at times positively injurious, and always favours the
growth of minute organisms.

From the determinations which have been described, it is believed that
a sound judgment as to the character of a water may be made, and the
analyst should hardly be content with a less complete examination. If,
however, from lack of time or other cause, so much cannot be done,
a tolerably safe opinion may be formed, omitting the determination of total
solid matter, and organic carbon and nitrogen. But it must not be forgotten
that by so doing the inquiry is limited as regards organic impurity, to. the
determination of that which was formerly present, but has already been
converted into inorganic substances. If still less must suffice, the estimation
of nitrogen as nitrates and nitrites may be omitted, its place being to>
a certain extent supplied by that of chlorine, but especial care must then be
taken to ascertain the source of the latter by examination of the district.
If it be in any degree of mineral origin, no opinion can be formed from it
as to the likelihood of organic pollution. At best, so slight an examination
must be of but little value, and considering the rapidity with which the
nitrogen as nitrates can be determined b^y the indigo process (§ 92), the saving;
of time would be very small.

General Considerations.

In judging of the character of a sample of water, due attention must
of course be paid to the purpose for which it is proposed to be used. The
analyst frequently has only to decide broadly whether the water is good or
bad ; as, for example, in cases of the domestic supply to isolated houses or of
existing town supplies. "Water which would be fairly well suited for the
former might be very objectionable for the latter, where it would be
required to a certain extent for manufacturing purposes. Water which
would be dangerous for drinking or cooking may be used for certain kinds-
of cleansing operations; but it must not be forgotten, that unless great care
and watchfulness are exercised there is considerable danger of this restriction
being neglected, and especially if the objectionable water is nearer at hand
than the purer supply. There would for this reason, probably, be some
danger attending a double supply on a large scale in a town, even if the
cost of a double service of mains, etc., were not prohibitive.

It is often required to decide between several proposed sources of supply,
and here great care is necessary, especially if the differences between the
samples are not great. If possible, samples should be examined at various
seasons of the year ; and care should be taken that the samples of the several
waters are collected as nearly as possible simultaneously and in a normal
condition. The general character of a water is most satisfactorily shown by

§ 90. GENERAL CONSIDERATIONS. 453

the average of a systematic series of analyses ; and for this reason the average
analysis of the water supplies of London, taken from the Reports of Dr.
Frankland to the Registrar General, of Glasgow by Dr. Mills, and of
Birmingham by Dr. Hill, are included in the table. River waters should,
as a rule, not be examined immediately after a heavy rain when they are in
flood. A sudden rainfall after a dry season wrill often foul a river more
than a much heavier and more prolonged downfall after average Aveather.
Similarly the sewage discharged from a town at the beginning of a heavy
rainstorm is usually extremely foul, the solid matter which has been
accumulating on the sides of the sewers, and in corners and recesses, being
rapidly washed out by the increased stream.

The possibility of improvement in quality must also be considered. A
turbid water may generally be rendered clear by filtration, and this will
often also effect some slight reduction in the quantity of organic matter;
but while somewhat rapid filtration through sand or similar material will
usually remove all solid suspended matter, it is generally necessary to pass
the water very slowly through a more efficient material to destroy any large
proportion of the organic matter in solution. Very fine sand, animal
charcoal, and spongy iron are all in use for this purpose. The quantity
of available oxygen must not be neglected in considering the question of
filtration. If the water contains only a small quantity of organic matter
and is well aerated, the quantity of oxygen in solution may be sufficient,
and the filtration may then be continuous; but in many instances this
is not the case, and it is then necessary that the filtration should be
intermittent, the water being allowed at intervals to drain off from the
filtering material in order that the latter may be well aerated, after which
it is again fit for work.

Softening water by Clark's process generally removes a large quantity
of organic matter (see Table 8, XVI.) from solution, it being carried down
with the calcic carbonate precipitate.

It is evident that no very definite distinction can be drawn between deep
and shallow wells. In the foregoing pages, deep wells generally mean such
as are more than 100 feet deep, but there are many considerations which
qualify this definition. A deep well may be considered essentially as one
the water in which has filtered through a considerable thickness of porous
material, and whether the shaft of such a well is deep or shallow will depend
on circumstances. If the shaft passes through a bed of clay or other
impervious stratum, and the surface water above that is rigidly excluded, the
well should be classed as " deep," even if the shaft is only a few feet in
depth, because the water in it must have passed for a considerable distance
below the clay. On the other hand, however deep the shaft of a well, it
must be considered as "shallow" if water can enter the shaft near the
surface, or if large cracks or fissures give free passage for surface water
through the soil in which the well is sunk. With these principles in view,
the water from wells may often be improved. Every care should be taken
to exclude surface water from deep wells; that is to say, all water from
strata within about 100 feet from the surface or above the first impervious
bed. In very deep wells which pass through several such beds, it is desirable
to examine the water from each group of pervious strata, as this often varies
in quality, and if the supply is sufficient, exclude all but the best.

In shallow wells much may occasionally be accomplished in a similar
manner by making the upper part of the shaft water-tight. It is also
desirable that the surface for some distance round the well should be puddled
with clay, concreted, or otherwise rendered impervious, so as to increase the
thickness of -the soil through which the water has to pass. Drains passing
near the well should be, if possible, diverted ; and of course cesspools should
t>e either abolished, or, if that is impracticable, removed to as great
a distance from the well as is possible, and in addition made perfectly

454 VOLUMETRIC ANALYSIS. § 90.

water-tight. Changes such as these tend to diminish the uncertainty of the
conditions attending a shallow well, but in most cases such a source of
supply should, if possible, be abandoned as dangerous at best.

Clark's Process for Softening- Hard Water.

The patent right of this process having expired, the public are free to use it.

This method of softening consists in adding lime to the hard water. It is
only applicable to water which owes its hardness entirely, or chiefly, to the
calcic and magnesic carbonates held in solution by carbonic acid (temporary
hardness). Water which owes its hardness to calcic or magnesic sulphate
(permanent hardness} cannot be thus softened ; but an}" water which softens
on boiling for half an hour will be softened to an equal extent by Clark's
process. The hard water derived from chalk, limestone, or oolite districts,
is generally well adapted for this operation.

To soften 700 gallons of water, about one ounce of quicklime is required
for each part of temporary hardness in 100,000 parts of water. The quantity
of quicklime required is thoroughly slaked in a pailful of water. Stir up
the milk of lime thus obtained, and pour it immediately into the cistern
containing at least 50 gallons of the water to be softened, taking care to-
leave in the pail any heavy sediment that may have settled to the bottom in
the few seconds that intervened between the stirring and pouring. Pill the
pail again with water, and stir and pour as before. The remainder of the
700 gallons of water must then be added, or allowed to run into the cistern
from the supply pipe. If the rush of the water does not thoroughly mix
the contents of the cistern, this must be accomplished lay stirring with
a suitable wooden paddle. The water will now appear very milky, owing to-
the precipitation of the chalk which it previously contained in solution
together with an equal quantity of chalk which is formed from the quick-
lime added.

After standing for three hours the water will be sufficiently clear to use
for washing ; but to render it clear enough for drinking, at least twelve
hours' settlement is required. This process not only softens water, but it
removes to a great extent objectionable organic matter present.

The proportion of lime to water may be more accurately adjusted during
the running in of the hard water, by taking a little water from the cistern
at intervals in a small white cup, and adding to it a drop or two of solution
of nitrate of silver, which will produce a yellow or brownish colouration as
long as there is lime present in excess. As soon as this becomes very faint,
and just about to disappear, the flow of water must be stopped. The
carbonate may be removed b}r filtration in a very short time after the addition
of lime, and on the large scale this may be done with great rapiditjr by
means of a filter press, as in Porter's process. This latter method of
rapidly softening and purifying water is the invention of the late
J. Henderson Porter, C.E., Queen Victoria Street, London, Avhose
apparatus is largely in use for public water supplies, and for softening waters
used in manufacturing processes, and the prevention of boiler incrustations,
etc. The chief objections to the original Clark process are, the large space
required for mixing and settling tanks, and the time required for subsidence
of the precipitate. On the contrary, in Porter's process, the space
occupied is small, and the clarification immediate. The results are
admirable, and are achieved at a very moderate cost.

Another apparatus devised by M.M. Gaillet and Hiiet, of Lille, consists-
of a lofty tank containing a series of sloping troughs. The water after
mixing with the due proportion of lime water passes slowly downwards-
through the tank and deposits all the carbonate precipitate in^the troughs,
from which it can be run off as mud. The process is thus continuous and
very convenient in dealing with large volumes of water.

§ 91. WATER ANALYSIS. 455

METHODS OF ESTIMATING- THE ORGANIC IMPURITIES IN
WATER WITHOUT GAS APPARATUS.

§ 91. THE foregoing methods of estimating the organic
impurities in potable waters, though very comprehensive and
trustworthy, yet possess the disadvantage of occupying a good deal
of time, and necessitate the use of a complicated and expensive set
of apparatus, which may not always be within the reach of the
operator.

ISTo information of a strictly reliable character as to the nature of the
organic matter or its quantity can be gained from the use of standard
permanganate solution as originally devised by Forschammer,
and the same remark applies to the loss on ignition of the residue,
both of which have been in past time largely used.

The For sc hammer or oxygen process, however, as improved by
Letheby, and further elaborated by Tidy, may be considered as
worthy of considerable confidence in determining the amount of
organic substances contained in a water.

The Oxygren Process.

This process depends upon the estimation of the amount of
oxygen required to oxidize the organic and other oxidizable matters
in a known volume of water, slightly acidified with pure sulphuric
acid. For this purpose, a standard solution of potassic permanganate
is employed in excess. The amount of unchanged permanganate,
after a given time, is ascertained by means of a solution of sodic
thiosulphate, by the help of the iodine and starch reaction.

Tidy and Frank land in all cases make a blank experiment
with pure distilled water, side by side with the sample.

As regards the time during which the sample of water should be
exposed to the action of the permanganate, authorities somewhat
differ. It is manifest that, if the water contains certain reducing
agents such as nitrites, ferrous salts, or sulphuretted hydrogen, an
immediate reduction of the reagent will occur, and Tidy is
disposed to register the reduction which occurs in three minutes, in
the known absence of iron and sulphuretted hydrogen, as due to
nitrites. The same authority adopts the plan of making two
observations, one at the end of one hour and another at the end of
three hours, at the ordinary temperature of the laboratory (say 60°
Fahr. or 16°C.).

Frankland admits this process to be the best volumetric
method in existence for the estimation of organic matters, but is
content with one experiment lasting three hours (also at ordinary
temperature).

The Water Committee of the Society of Public Analysts of
Great Britain and Ireland have adopted the periods of fifteen

456 VOLUMETEIC ANALYSIS. § 91.

minutes and four hours for the duration of the experiment, at the
fixed temperature of 80° Fahr. or 27° C.*

Dupre has carried out experiments (Analyst vii. 1), the
Jesuits of which are in favour of the modifications adopted by the
Committee. The chief conclusions arrived at are : —

(1) That, practically, no decomposition of permanganate takes
place during four hours when digested in a closed vessel at 80°
with perfectly pure water and the usual proportion of pure
sulphuric acid.

By adopting the closed vessel, all dust or reducing atmospheric
influence is avoided.

(2) The standardizing of the thiosulphate and permanganate,
originally and from time to time, must be made in a closed vessel
in the same manner as the analysis of a water, since it has been
found that when the titration is made slowly in an open beaker
less thiosulphate is required than in a stoppered bottle. This is
probably due to a trifling loss of iodine by evaporation.

(3) That with very pure waters no practical difference is
produced by a rise or fall of temperature, the same results being
obtained at 32° F. as at 80° F. On the other hand, with polluted
waters, the greater the organic pollution, the greater the difference
in the amount of oxygen absorbed according to temperature.

(4) As to time, it appears that very little difference occurs in
good waters between three and four hours' digestion; but with bad
waters there is often a very considerable increase in the extra hour ;
and thus Dupre doubts whether even four hours' digestion suffices
for very impure waters.

The necessary standard solutions for working the process will be
described further on.

*Dupre in further comment on the temperature at which it is advisable to carry
out this method ( Analyst x. 118), and also as to the reactions involved, points out one
feature which has in all probability impressed itself upon other operators, that is to
say, the effect of chlorides when present in any quantity. It is evident that if in this
case the permanganate is used at a high temperature and in open vessels, chlorine will
be liberated ; part escaping into the air, and the rest nullifying the reducing effect of
any organic matter present on the permanganate. If, however, the experiment be
conducted at high temperature in a closed vessel, the probable error is eliminated,
because the chlorine is retained, and subsequently, when cool and the potassic iodide
added, the free Cl liberates exactly the same amount of iodine as would have been set
free by the permanganate from which it was produced. It thus becomes possible to
estimate the amount of oxidizable organic matter, even in sea water. In order, how-
ever, to reduce the probable error from the presence of chlorides, Dupre prefers to
carry on the experiment at a very low temperature, in fact, as near 0° C. or 32° F. as
possible, and uses phosphoric acid in place of sulphuric (250 gm. glacial acid to the
liter; 10 c.c. of which is used for each ouarter or half liter of water). The sample is
cooled, the reagent added in a stoppered bottle, and kept in an ordinary refrigerator
for twenty-four hours. The same operator very rightly condemns the pi-actice adopted
by some chemists, especially those of Germany, of boiling a water with permanganate
arid sulphuric acid. The presence of chlorides in varying proportions must in such
case totally vitiate the results.

§ 91.

OXYGEN PROCESS FOR WATER.

457

Comparison of the Results of this Process -with the Combustion
Method. — I cannot do better than quote Dr. Frank land's remarks
on this subject, as contained in his treatise on Water Analysis: —

" The objections to the oxygen process are first, that its indications are
only comparative, and not absolute ; and, second, that its comparisons are
only true when the organic matter compared is substantially identical in
composition.

" For many years, indeed, after this process was first introduced, the action
of the permanganate was tacitly assumed to extend to the complete oxidation
of the organic matter in the water, and, therefore, the result of the
experiment was generally stated as ' the amount of oxygen required to
oxidize the organic matter ; ' whilst some chemists even employed the number
so obtained to calculate the actual weight of organic matter in the water on
the assumption that equal weights of all kinds of organic matter required
the same weight of oxygen for their complete oxidation.

"Both these assumptions have been conclusively proved to be entirely
fallacious, for it has been experimentally demonstrated by operating upon
known quantities of organic substances dissolved in water, that there is no
relation either between the absolute or relative weight of different organic,
matters and the oxygen which such matters abstract from permanganate.

"Nevertheless, in the periodical examination of waters from the same
source, I have noticed a remarkable parallelism between the proportions of
organic carbon and of oxygen abstracted from permanganate. Thus, for
many years past, I have seen in the monthly examination of the waters of
the Thames and Lea supplied to London such a parallelism between the
numbers given by Dr. Tidy, expressing 'oxygen consumed,' and those
obtained by myself in the determination of ' organic carbon.'

" This remarkable agreement of the two processes, extending as it did to
1,418 out of 1,686 samples, encouraged me to hope that a constant multiplier
might be found, by which the 'oxygen consumed' of the For sc hammer
process could be translated into the 'organic carbon' of the combustion
method of analysis. To test the possibility of such a conversion, my pupil,
Mr. Woodland Toms made, at my suggestion, the comparative experi-
ments recorded in the following tables : —

I.— River Water.

Sovirce of Sample.

Oxygen C Organic
consumed, X „ ; £*%&

Chelsea Company's supply ...

G'098 x 2'6 = 0-256

West Middlesex Co.'s „

0-116 x 2-5 =

0-291

Lambeth Co.'s ,,

0-119 x 2-43 =

0-282

Southwark Co/s „

0-121 x 222 =

0-269

New River Co.'s „

0076 x 2-4 =

0183

Chelsea Co.'s second sample ...

0-070 x 2-69 =

0-188

Lambeth Co.'s „

0-119 x 1-99 =

0-234

New River Co.'s „

0-107 x 2-25 =

0-221

"As the result of these experiments the average multiplier is 2'38, and
the maximum errors incurred by its use would be — 0'02L part of organic
•carbon in the case of the second sample of the Chelsea Company's water,
and +0*049 part in that of the second sample of the Lambeth Company's
water. These errors would practically have little or no influence upon the

458

VOLUMETRIC ANALYSIS.

§ 91.

analyst's opinion of the quality of the water. It is desirable that this
comparison should be extended to the water of other moderately polluted
rivers.

II.— Deep "Well Water.

Source of Sample.

Oxygen
consumed.

c
o

Organic
carbon by
combustion.

Kent Company's supply

0-015

5'1 ==

0-077

Colne Valley Co.'s „

0-0133

6-9 ==

0-094

Hodgson's Brewer}r well ... ... 1 0*03

5-3 =

0-158

" The relation between ' oxygen consumed ' and ' organic carbon ' in the
case of deep well waters is thus very different from that Avhich obtains in the
case of river waters, and the average multiplier deduced from the foregoing
examples is 5' 8, with maximum errors of +0'01 of organic carbon in the case
of the Kent Company's water, and — 0 015 in that of the Colne Valley
water. Such slight errors are quite unimportant.

"Similar comparative experiments made with shallow well and upland
surface waters showed amongst themselves a wider divergence, but pointed
to an average multiplier of 2'28 for shallow well water, approximately the
same as that found for moderately polluted river water, and 1'8 for upland
surface water.

" In the interpretation of the results obtained, either by the P o r s c h a m m e r
or combustion process, the adoption of a scale of organic purity is often useful
to the analyst, although a classification according to such a scale may require
to be modified by considerations derived from the other analytical data. It
is indeed necessary to have a separate and more liberal scale for upland surface
water, the organic matter of which is usually of a very innocent nature, and
derived from sources precluding its infection by zymotic poisons.

"Subject to modification by the other analytical data, the following scale of
classification has been suggested by Dr. Tidy and myself: —

Section I.— Upland Surface Water.

" Class I. Water of great organic purity, absorbing from permanganate
not more than O'l part of oxygen per 100,000 parts of water, or 0'07 grain
per gallon.

"Class II. Water of medium purity, absorbing from O'l to 0'3 part of
oxygen per 100,000 parts of water, or 0*07 to 0'21 grain per gallon.

"Class III. Water of doubtful purity, absorbing from 0'3 to 0'4 part
per 100,000, or 0'21 to 0'28 grain per gallon.

"Class IV. Impure water, absorbing more than 0:4 part per 100,000,,
or 0'28 grain per gallon.

Section II.— Water other than Upland Surface.

" Class I. Water of great organic purity, absorbing from permanganate
not more than 0'05 part of oxygen per 100,000 parts of water, or 0'035 grain
per gallon.

§ 91. OXYGEN PROCESS FOR WATER. 459

"Class II. Water of medium purity, absorbing from 0*05 to 0'15 part
of oxygen per 100,000, or 0*035 to O'l grain per gallon.

"Class III. Water of doubtful purity., absorbing from 0'15 to 0'2 part
of oxygen per 100,000, or O'l to 0'15 grain per gallon.

"Class IV. Impure water, absorbing more than 0'2 part of oxygen
per 100,000, or 0'15 grain per gallon."

Dr. James Edmunds, Public Analyst for St. James's, London,
in a communication to the author, writes as follows : —

Medical practitioners who wish to use permanganate as a ready indicator
for organic matter in drinking waters, may be glad of some farther detail as
to the significance of the decolourization which permanganate undergoes
when in contact with organic, and other reducing matters.

Two molecules of potassic permanganate (2KMnO4 = 316) contain five atoms
of separable nascent oxygen. Five atoms of oxygen are equivalent to ten
atoms of hydrogen, arid, the hydrogen-equivalent being the base of
volumetric analysis, it follows that 31'6 gm. KMnO4 with distilled
water to 1000 c.c. will constitute the normal solution, while 3*16 per 1000
c.c. will constitute the decinormal solution. Of tbis *-$ permanganate, each
c.c. yields O'OOOS of nascent oxygen, and, under proper conditions, will
oxidize O'OOOl of hydrogen. So long as the separable nascent oxygen only
is regarded, the above solutions constitute the true £ and *-$ permanganate.
But, under certain conditions, other reactions intervene ; and, in view of
these, we require also to consider the hydrogen-equivalent of the
permanganate as regards its potassium, and as regards its manganese. On
reckoning out these latter equivalences, it will be seen that the decinormal
permanganate, while ^ as to its separable oxygen, is ^/TT a$ to its potash,
and ^THT as to its manganese. It therefore follows that, to precisely
neutralize the potash of the permanganate, and also to dissolve its manganese
as a manganous salt, there would be required -£-£$ H'2SO4 equal in volume
to the /F permanganate used.

It must be recollected that the decolouration which permanganate under-
goes, is in no sense a measure of the organic, or other reducing matter. It
is a measure only of the oxygen-absorbing power of the particular reducing
matters — under a particular set of conditions. This fact is fundamental in
studying the action of permanganate. With a given quantity of the same kind
of organic or other reducing matter, the decolourization of permanganate is,
doubtless, a perfectly constant quantity — so long as the conditions of the
reaction are identical. But if the conditions are not identical, new factors
come in and vary the results. The practical point therefore is to secure
identical conditions for each operation, so as to make the results comparable
and reliable as a measure of the oxygen-absorbing power of a particular
water.

Now 3' 160 gm. KMnO4 breaks up into

K-O 0-940)
MnO T420 £ =3-160
Separable as nascent O 0*800 )

Each c.c. of the -^ permanganate will therefore contain ^Vrr of the above
quantities. But O'OOOS of nascent oxygen from each c.c. of this
permanganate is obtainable only under properly adjusted conditions.
Under other conditions the Mn2O7 is not reduced to 2MnO, but only to
2MnO2. In the latter case, each c.c. yields only 0'00048 of nascent oxygen

460 VOLUMETRIC ANALYSIS. § 91.

instead of O'OOOSO, and the significance of the decolonization varies
accordingly. If either of the above conditions, or a definite combination of
the two sets of conditions, could be uniformly secured ; or. if the amount of
MnO2 which comes out could afterwards be conveniently determined, there
would be no difficulty in calculating the significance of the decolourization.
The problem therefore, is, to secure a definite basis for calculation, when
we use the decolourization as marking our end-point.

In order that all the separable oxygen may come out in the nascent
condition, so as to combine with the reducing matters whose ox}rgeu-
absorbing powers are to be measured, wre must have the following
conditions : —

1. The titrate (i.e., the solution about to be titrated by the permanganate)
must contain H2SO4 in such excess as will neutralize the potash, and also
will instantly seize and draw into solution the MnO which has to be
separated from the available ox3rgen. It has already been seen that, as
regards the aggregated potash and manganese, the permanganate is really
a y^\ solution, although yV as regards its separable oxygen. Therefore,
6 c.c. of T^j- H2SO4 would, in the end, neutralize the potash, and take up the
manganese, of 1 c.c. of the ^ permanganate. In practice, however, a very
large excess of H2SO4 must be on hand in the solution in order to secure
the complete reduction of the manganese to the mauganous condition, and
the withdrawal of this into solution in the form of MnSO4. Otherwise, the
nascent moment of part of the oxygen is lost, the hydrated peroxide of
manganese comes out, and we get a muddy brown liquid whose turbidity
and colour obscure the end-point. Practically the MnO2 which thus
conies out cannot be got back again into solution, nor can it be easily
quantified. Any precipitation of black oxide consequently spoils the
titration.

2. The titrate should in each case be made up to the same volume, and
its dilution should bear a reasonable relation to the volume of permanganate
\vhich it may require.

3. The temperature at which the reaction is conducted must be the same
for the Avhole series of titrations, and the time during which the action
proceeds must be the same. Otherwise, the reaction must be so prolonged
as to reduce the maximum possible volume of the permanganate, and yield
a water-white or clear pink solution.

4. The dropping in of the permanganate should closely follow up the
disappearance of the colour, and as the decolourizatiou halts, the dropping
in of the permanganate should be checked.

5. If the permanganate be crowded in, under conditions where the
chemical potential is on the balance, it becomes easier to reduce a surplus of
Mn2O7 one stage to 2MnO2, than to reduce the minimum quantity of Mn2O7
two stages down to 2MnO. In this case crowding the permanganate in will
bring out the hydrated peroxide and spoil the titration.

6. The operations should be conducted in glass-stoppered white bottles.
8-oz. bottles are convenient. In routine titrations the white basin is
preferable.

It must be recollected that, under similar conditions, different substances
have a very different chemical potential in their reducing action upon
permanganate. In some the chemical potential is so great that they are
adequately active at all temperatures, while others cannot be titrated with
permanganate unless at an elevated temperature. Thus an acid solution of
a ferrous salt reduces permanganate instantly at all temperatures.
Oxalic acid at 0° C., or even at the ordinary temperature of the laboratory,
reduces permanganate so slowly that it cannot be conveniently titrated. Yet

§ 91. ACTION OF PERMANGANATE. 461

the oxalic acid titrate when heated to 60° C reduces the permanganate
rapidly, and, if not overcrowded, gives a beautifully sharp end-point.
Matters not really in solution — such as bacterial organisms in water,
epithelium and other organic debris in urine — react slowl)r and variously
with permanganate, and cannot be accurately titrated. On the other hand,
fresh normal urine, filtered warm, makes a useful titrate. By its means the
decolourization of permanganate with organic matter, under various per-
centages of acidity and at various temperatures, may be studied conveniently.
The filtered urine should be diluted to ten times its volume with pure distilled
water. Of this diluted urine 10 c.c. are taken for each titrate, and made up
to 100 c.c. with various percentages of f H2SO4 and distilled water. Each
such titrate contains 1 c.c. of filtered urine. The experiments may be made
in glass-stoppered white 8-oz. bottles, at the ordinary temperature of the
laboratory, and the bottles should be open only while the permanganate is
dropped in.

In working the permanganate into the titrate, several elemental results
come out — often more or less mixed. Those results may be summarized as
follows : —

1. Bleaching continuously out to water-white without turbidity, without
brown film in bottle, and without brown precipitate. Here the Mn2O7 is
reduced to 2MnO, and a perfectly sharp pink colour is obtained as the end-
point. A transient yellowing sometimes occurs. Five atoms of nascent
oxygen are set free.

2. As the oxygen-absorbing power of the titrate is exhausted there
comes a halt, and the decolourization is no longer instantaneous. In some
titratious, as that for uric acid, this first halt in the decolourization should
be taken as the end-point. In other cases the halt marks the exhaustion
only of the most active reducers in a complex titrate, and should be noted
as a useful datum. In that case, further additions of permanganate require
a longer time, or a higher temperature in order to raise the potential and
quicken the reduction. So soon as the titration is completed, one drop of
permanganate in excess gives a clear permanent faint pink colour.

3. Sometimes the permanganate forms a ruby-red compound, the tint of
which is quite distinct from the purple-pink. On standing, this ruby-red
generally yellows or browns out to a turbid liquid, ultimately depositing
a brown precipitate of hydrated peroxide of manganese, and leaving a water-
white supernatant liquid.

4. A distinct smokiness, or a yellowing or browning out of the purple
sometimes occurs. On standing, MnO2 comes out. This may appear as
a brown film which, on tilting the bottle, contrasts well with the water-
white liquid; as a brown sediment ; or as a fine smoky turbidity which takes
hours, or even days, to come out as a deposit of MnO"2.

If titrates be made up— (A) of 100 c.c. of pure distilled water; (B) of
100 c.c. of £ H2SO4; (C) of 1 gm. of MnSO4 in 100 c.c. of distilled water ;
(D) of 1 gm. of MnSO4 in 100 c.c. of £ H2SO4— a series of control titrates
are obtained. On adding 1 c.c. of permanganate to each titrate, A and B
will remain for many days a full colour practically unchanged, though
A will at once assume the rub}^-red colouration ; while B will retain the tint
of the purple permanganate. On the other hand, the titrates C and D,
containing the manganous sulphate, will instantly reduce the permanganate and
throw out a brown precipitate which subsides much more rapidly in C than in
D. This shows that, apart altogether from the presence of organic or other
reducing matters, the accumulation of manganous sulphate in the titrate
upsets the balance of the subsequently added permanganate, and throws out
hydrated peroxide.

Another series of titrates may each contain 1 c.c. of filtered urine, with

462 VOLUMETRIC ANALYSIS. § 91.

H2SO4 Y in a series of proportions, and in each case made up with H2O to
100 c.c. Ten such titrates containing of £ sulphuric acid 90, 80, 70, 60, 50, 40,
30, 20, 10, and 0 °/0, will show that, on adding to each of the series 1 c.c.
TV permanganate, and repeating the addition from time to time till 5 c.c.
permanganate have been added, the titrates break up into characteristic
groups according to the percentage of sulphuric acid present, and that the
groupings will again vary according to the temperatures at which the
reactions are conducted, or according to the times for which the titrates are
allowed to stand over in their bottles. A comparison of the results shown
in ten such titrates— 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10, with the results seen
in the control titrates A B C 1), will illustrate the complexity of the considera-
tions which are involved in measuring the oxygen-absorbing power of
organic and other reducing matters, by means of permanganate. As has
already been indicated, the action of the permanganate does not quantify
the organic or other reducing matters which may be in the titrate ; it merely
indicates the oxygen-absorbing powers of those titrates under specific
conditions.

The Albuminoid Ammonia Process.

Wanklyn, Chapman, and Smith are the authors of this well-
known method of estimating the quantity of nitrogenous organic
matter in water, which depends upon the conversion of the nitrogen
in such organic matter into ammonia, when distilled with an alkaline
solution of potassic permanganate (/. C. S. 1867, 591).

The authors have given the term "Albuminoid ammonia" to
the NH3 produced from nitrogenous matter by the action of the
permanganate, doubtless because the first experiments made in
the process were made with albuminous substances ; but the authors
also proved that ammonia may be obtained in a similar way from,
a great variety of nitrogenous organic substances, such as hippuric
acid, narcotine, strychnine, morphine, creatine, gelatine, casein, etc.
Unfortunately, however, although the proportion of nitrogen
yielded by any one substance when treated with boiling alkaline
permanganate appears to be definite, yet different substances give
different proportions of their nitrogen. Thus hippuric acid and
narcotine yield the whole, but strychnine and morphine only one-
half of their known proportion of nitrogen. Hence the value of the
numerical results thus obtained depends entirely on the assumption
that the nitrogenous organic matter in water is uniform in its
nature, and the authors say that in a river polluted mainly by
sewage "the disintegrating animal refuse would be pretty fairly
measured by ten times the albuminoid ammonia which it yields."

It is stated by the authors that the albuminoid ammonia from a
really good drinking water should not exceed O'OOS part in 100,000.
The average of fifteen samples of Thames water supplied to London
by the various Water Companies in 1867 was 0'0089, and in five
samples supplied by the JSVsv River Company 0*0068 part per
100,000.

The necessary standard solutions and directions for working the
process will be described further on (page 465).

§ 92. WATER ANALYSIS WITHOUT GAS APPARATUS. 463

PREPARATION OF THE REAGENTS FOR THE SANITARY
ANALYSIS OF WATERS WITHOUT GAS APPARATUS.

§ 92. THE Water Committee of the Society of Public Analysts
•of Great Britain and Ireland have drawn up some very concise
directions for the practice of water analysis for sanitary purposes,
based upon well-known processes, the essential parts of which
.are given below. There are some slight modifications, such as the
use of the decem or 10-grain measure instead of the grain, etc.
The insertion here of these directions in full, or nearly so, necessarily
repeats some processes which have been already described in §§ 88
and 89, but it avoids cross-references and at the same time gives
some slight practical modifications which, to some operators,
may seem desirable." The Committee recommend the results to be
recorded in grains per imperial gallon ; but whatever system of
weights and measures the individual "analyst may use, a slight
calculation will enable him to state the results in any required way.

Reagents for the Estimation of Chlorine.

Standard Solution of Silver nitrate.— -Dissolve 4 '7887 parts of
pure recrystallized silver nitrate in distilled water, and make the
solution up to 1000 parts. The solution is to be standardized
against the standard solution of sodic chloride, and adjusted if
necessary. 1 c.c. — O'OOl gm. of chlorine, or 1 dm. = O'Ol grn. of
chlorine.

Standard Solution of Sodic chloride. — Dissolve 1'648 part of
pure dry sodic chloride in distilled water, and make the solution
up to 1000 parts. 1 c.c. contains O'OOl gm. chlorine, or 1 dm. =
O'Ol grn. of chlorine.

Potassic monochromate. — 50 parts of potassic monochromate
are dissolved in 1000 parts of distilled water. A solution of
silver nitrate is added, until a permanent red precipitate is
produced, which is allowed to settle. This removes any accidental
chlorine in the salt.

Reagent for the Estimation of Phosphoric Acid.

Molybdic Solution. — One part pure molybdic acid is dissolved
in 4 parts of ammonia, sp. gr. 0-960. This solution, after nitration,
is poured with constant stirring into 15 parts of nitric acid of T20
sp. gr. It should be kept in the dark, and carefully decanted
from any precipitate which may form.

Reagents for the Estimation of Nitrogen in Nitrates.
Concentrated Sulphuric acid. — In order to ensure freedom from

464 VOLUMETRIC ANALYSIS. § 92.

oxides of nitrogen, this should be kept in a bottle containing
mercury, and agitated from time to time, which will ensure their
absence.

Metallic Aluminium. — As thin foil.

Solution of Sodic hydrate. — Dissolve 100 parts of solid sodic
hydrate in 1000 parts of distilled water. When cold, introduce
a strip of about 100 square c.m., say fifteen square inches, of
aluminium foil, previously heated just short of redness, wrapped
round a glass rod. When the aluminium is dissolved, boil the
solution briskly in a porcelain basin until about one-third of its
volume has been evaporated, allow it to cool, and make it up to
its original volume with water free from ammonia. The solution
must be tested by a blank experiment to prove the absence of
nitrates.

Broken Pumice. — Clean pumice, broken into pieces of the size
of small peas, sifted free from dust, heated to redness, and kept
in a closely stoppered bottle.

Hydrochloric acid free from Ammonia. — If the ordinary pure
acid is not free from ammonia, it should be distilled. As only two
or three drops are used in each experiment, it will be sufficient
if that quantity does not contain an appreciable proportion of
ammonia.

Copper sulphate Solution. — Dissolve 30 parts of pure copper
sulphate in 1000 parts of distilled water.

Metallic Zinc. — As thin foil. This should be kept in a dry
atmosphere, so as to be preserved as far as possible from oxidation.

Standard Solution of Ammonic chloride (see below),
^essler's Solution (see below).

Standard Potassic nitrate of y^y- strength, made by dissolving
O'lOll gm. KNO3 in a liter of water free from nitrates or nitrites.

Indigo Carmine. — A good quality of this substance (sodic
sulphindylate) should be selected, such as will not give a very
dark brown when oxidized with nitric acid, and about a gram
dissolved in half a liter of dilute pure sulphuric acid (1 to 20).
This solution keeps in the dark for months without diminution of
strength.

Pure Sulphuric Acid.— This must be free from nitric or nitrous
compounds, and of not less sp. gr. than 1*843.

§ 92. WATER ANALYSES WITHOUT GAS APPARATUS. 465

Reagents for the Estimation of Nitrogen as Ammonia and
Albuminoid Ammonia.

•Concentrated Standard Solution of Ammonic chloride. — Dissolve
3 '15 parts of pure ammonic chloride in 1000 parts of distilled water
free from ammonia.

Standard Solution of Ammonic chloride. — Dilute the above
with pure distilled water to 100 times its bulk. This solution is
used for comparison in Xesslerizing, and contains one part of
ammonia (NH;5) in 100,000, or ~^ m.gm. in each c.c.

Xessler Solution. — Dissolve 35 parts of potassic iodide in
100 parts of water. Dissolve 17 parts of mercuric chloride in
300 parts of water. The liquids may be heated to aid solution,
but if so must be cooled. Add the latter solution to the former
until a permanent precipitate is produced. Then dilute with
a 20 per cent, solution of sodic or potassic hydrate to 1000 parts ;
add mercuric chloride solution until a permanent precipitate again
forms ; allow to stand till settled, and decant off the clear solution.
The bulk should be kept in an accurately stoppered bottle, and
a quantity transferred from time to time to a small bottle for use.
The solution improves by keeping. It will be noticed that this
solution is only about half the strength of the one given on page
399 ; of course a larger volume has to be used in testing.

Sodic carbonate. — A 20 per cent, solution of recently ignited
pure sodic carbonate.

Alkaline Permanganate Solution. — Dissolve 200 parts of potassic
hydrate and eight parts of pure potassic permanganate in 1100 parts
of distilled water, and boil the solution rapidly till concentrated to
1000 parts.

Distilled Water free from Ammonia (see page 400).

Reagents for the Estimation of Oxygen absorbed.

Standard Solution of Potassic permanganate. — Dissolve 0*395
part of pure potassic permanganate in 1000 of water. Each c.c.
•contains O'OOOl gm. of available oxygen, and each dm. contains
0-001 grn.

Potassic iodide Solution. — One part of the pure salt dissolved
in ten parts of distilled water.

Dilute Sulphuric acid. — One part by volume of pure sulphuric
.acid is mixed with three parts by volume of distilled water, and
solution of potassic permanganate dropped in until the whole
retains a very faint pink tint, after warming to 80° F. for four
iiours.

H H

466 VOLUMETRIC ANALYSIS. § 92.

Sodic thiosulphate. — One part of the pure crystallized salt
dissolved in 1000 parts of water.

Starch Indicator. — The best form in which to use this is the
alkaline solution, page 131.

Reag-ents for the Estimation of Hardness.

Concentrated Standard Solution of Calcic chloride. — Dissolve
1*144 gm. of pure crystallized calc-spar in dilute hydrochloric acid
(with the precautions given on page 405), then dissolve in water,
and make up to a liter. On the grain system, a solution of the same-
strength is made by dissolving 11*44 grn. of calc-spar in 1000 dm.

Standard Water of 8° Hardness. — This is made by diluting the
foregoing concentrated solution to ten times its volume with
freshly boiled and cooled distilled water.

Standard Soap Solution (is made precisely as directed on page
405). — It should be of such strength as just to form a permanent
lather, when 18 c.c. or dm. measures are shaken with 100 c.c. or
dm. of water of 8° hardness. The following table will then give
the degrees of hardness corresponding to the number of c.c. or dm.
measures employed.

c.c. or dm. c.c. or dm.

Hardness. Measures. Hardness. Measures.

0° 0-9 . 5° 12-0

1° 2-9 6° 14-0

2° 5-4 7° 16-0

3° 7-7 8° 18-0

4° 9-9

After which one degree = 2 c.c. or dm. measures. This is the
last solution recommended by Dr. Clark, and differs slightly
from the scale given on page 439 ; the variation, however, is very
insignificant, except in the first two stages of the table.

The Analytical Processes.
Collection of Samples. — The same as directed on page 406.

Appearance in Two-foot Tube. — The colour or tint of the water must
be ascertained, by examination, in a tube two feet long and two inches in
diameter. This tube should be made of glass as nearly colourless as may be,
and should be covered at each end with a disc of perfectly colourless glass,
cemented on, an opening being left for filling and emptying the tube. This
opening may be made, either by cutting a half-segment off' the glass disc at
one end, or by cutting a small segmental section out of the tube itself, before
the disc is cemented on. These tubes are most conveniently kept on hooks
in a horizontal position to prevent the entrance of dust.

The tube must be about half-filled with the water to be examined, brought

§ 92. ANALYTICAL PROCESSES FOR WATEU. 467

into a horizontal position level with the eye, and directed towards a well-
illuminated white surface. The comparison of tint has to be made between
the lower half of the tube containing the water under examination, and the
upper half containing atmospheric air only.

Smell. — Put not less than three or four ounces of the water into a clean
eight-ounce wide-mouthed stoppered glass bottle, which has been previously
rinsed with the same water. Insert the stopper, and warm the water in a
water bath to 100° F. (38° C.). Remove the bottle from the water bath, rinse
it outside with good water perfectly free from odour, and shake it rapidly
for a few seconds ; remove the stopper, and immediately observe if the water
has any smell. Insert the stopper again, and repeat this test.

"When the water has a distinct odour of any known or recognized polluting
matter, such as peat or sewage, it should be so described ; when this is not
the case, the smell must be reported simply as none, very slight, slight, or
marked, as the case may be.

Chlorine. — Titrate at least 100 c.c. or dm. of the water with the standard
silver nitrate solution, either in a white porcelain basin or in a glass vessel
standing on a porcelain slab, using potassic chromate as an indicator. The
titration is conducted as follows : — The sample of water is measured into the
basin or beaker, and 1 c.c. or 1 dm. of potassic chromate solution added.
The standard silver nitrate solution is then run in cautiously from a burette,
until the red colour of the precipitated silver chromate, which is always
observed at the point where the silver solution drops in, is no longer entirely
discharged on stirring. The burette is then read off. It is best to repeat
the experiment, as follows : — Add a few drops of dilute sodic chloride solution
to the water last titrated, which will discharge the red colour. Measure out
a fresh portion of the wrater to be titrated into another basin, and repeat the
titration, keeping the first sample, the colour of which has been discharged,
side by side with the second, so as to observe the first permanent indication
of difference of colour. If the quantity of chlorine be so small that still
greater accuracy is necessary, the titration may be conducted in the same way
as last described, but instead of the operator looking directly at the water
containing the chromate solution, he may place between the basin containing
the water and his eye, a flat glass cell containing some water tinted with the
chromate solution to the same tint as the water which is being tested, or may
look through a glass coated with a gelatine film coloured with the same salt
(see § 44) . Care must always be taken that the water is as nearly neutral
as possible before titration. If originally acid, it should be neutralized with
precipitated carbonate of lime. If the proportion of chlorine be less than
0*5 grain per gallon, it is desirable to take a larger quantity of the water, say
250 c.c. or 350 dm., for the estimation, and to concentrate this quantity on
the water bath before titrating it, so as to bring it to about 100 c.c. or
150 dm. This titration may be performed by gas-light.

Phosphoric Acid. — The ignited total residue, obtained as hereafter
directed, is to be treated with a few drops of nitric acid, and the silica
rendered insoluble by evaporation to dryness. The residue is then taken
up with a few drops of dilute nitric acid, some water is added, and the
solution is filtered through a filter previously washed with dilute nitric
acid. The filtrate, which should measure 3 c.c. (or 5 dm.) is mixed with
3 c.c. of inolybdic solution, gently warmed, and set aside for fifteen minutes,
at a temperature of 80° F. The result is reported as "traces," "heavy
traces," or " very heavy traces," when a colour, turbidity, or definite
precipitate, are respectively produced, after standing for fifteen minutes.
Another method is given on page 441.

H H 2

468 VOLUMETRIC ANALYSIS. § 92.

Nitrogen in Nitrates. — This may be determined by one of the following
processes: viz., Crum, Copper-zinc, Aluminium, or Indigo. Analysts should
report which process is employed.

Crum Process. — This is described on page 430, or it may be carried out in
a Lunge's nitrometer as follows: — 250 c.c. or dm. of the water must be
concentrated in a basin to 2 c.c. or. 3 dm. measure. A Lunge's nitrometer
is charged with mercury, and the three-way stop-cock closed, both to measuring
tube and waste pipe. The concentrated filtrate is poured into the cup at the
top of the measuring tube, and the vessel which contained it rinsed with 1 c.c.
of water, and the contents added. The stop-cock is opened to the measuring
tube, and, by lowering the pressure tube, the liquid is drawn out of the cup
into the tube. The basin is again rinsed with 5 c.c. of pure strong sulphuric
acid, and this is also transferred to the cup and drawn into the measuring
tube. The stop-cock is once more closed, and 12 c.c. more sulphuric acid put
into the cup, and the stop-cock opened to the measuring tube until 10 c.c. of
acid have passed in. The excess of acid is discharged, and the cup and waste
pipe rinsed with wrater. Any gas which has collected in the measuring tube
is expelled by opening the stop-cock and raising the pressure tube, taking
care no liquid escapes. The stop-cock is closed, the measuring tube taken
from its clamp and shaken by bringing it slowly to a nearly horizontal
position, and then suddenly raising it to a vertical one. This shaking is
continued until no more gas is given off, the operation being, as a rule,
complete in fifteen minutes. Now prepare a mixture of one part of water
with five parts of sulphuric acid, and let it stand to cool. After an hour,
pour enough of this mixture into the pressure tube to equal the length
of the column of acidulated water in the working tube, bring the two tubes
side by side, raise or lower the pressure tube until the mercury is of the same
level in both tubes, and read off the volume of nitric oxide (for calculation
of nitrogen see page 262). This volume, expressed in c.c.'s and corrected to
normal temperature and pressure, gives, when multiplied by 0'175, the
nitrogen in nitrates, in grains per gallon, if 250 c.c. of the water have
been used.

Copper-zinc Process (already described on page 433).

Aluminium Process.— This is carried out as follows: — 50 c.c. or 100 dm.
of the water are introduced into a retort, and 50 c.c. or 100 dm. of a 10 per
cent, solution of caustic soda, free from nitrates, added. If necessary, the
contents of the retort should be distilled until the sample is free from
ammonia. The retort is then cooled, and a piece of aluminium foil
introduced into it. The neck of the retort is inclined upwards, and its
mouth closed with a perforated cork, through which passes the narrow end
of a small chloride of calcium tube filled with powdered pumice or glass
beads wetted with very dilute hydrochloric acid free from ammonia. This
tube is connected with a second tube containing pumice stone moistened
with strong sulphuric acid, which serves to prevent any ammonia from the
air entering the apparatus, which is allowed to stand in this way for a few
hours or overnight. The contents of the first absorption tube— that next
the retort— are washed into the retort with a little distilled water free from
ammonia, and the retort adapted to a condenser. The contents of the retort
are distilled to about half their original volume. The distillate is collected,
and an aliquot part Nesslerized; and, if necessary, the rest of the distillate
is diluted, and an aliquot part again Nesslerized as hereafter directed.

Indigo Process. — An elaborate series of experiments made by "War in gt on
upon this method were described in a former edition of this book; but
experience has shown that the only method by which it can be made
serviceable in the case of waters is to have a solution of indigo carmine of

§ 92. ANALYTICAL PROCESSES FOE WATER. 469

good quality, which is standardized upon a very weak solution of potassic
nitrate. A definite volume of indigo must be used invariably, and the
water to be examined varied in quantity according to its contents of N2O5.
In this manner very excellent results may be obtained, but it must always
be remembered that the process is only accurate with moderate proportions
of nitrates, because any error is enormously multiplied when calculated
upon a liter or a gallon of water.

The process now to be described was in constant use in the laboratory of
the late Dr. Meymott Tidy, and Mr. J. E. Skelton, F.I.C., his chief
assistant for some years, has kindly given me several details of the process
as worked by him under Dr. Tidy's direction. I have also found this
modification very serviceable for the rapid estimation of nitrates in ordinary
potable Avaters.

Standardizing the Indigo. — 10 c.c. of the standard nitrate (p. 464) are run
into a thin flask holding about 150 c.c., then 10 c.c. of indigo. 20 c.c. of
sulphuric acid are then quickly added from a graduated measure, and a rotary
motion given to the flask to mix the liquids — the flask is then quickly held
over a spirit lamp or small rose gas burner to maintain the heat.

If the indigo is at once decolorized, more is run in with constant heating,
until, after heating for about thirty seconds, a persistent greenish colour is
noted. From the number of c.c. of indigo decolorized the necessary degree
of dilution is calculated, and must always be made with the five per cent,
sulphuric acid, and not with plain water. Fresh trials are made in the same
manner until the strength of the indigo is accurately determined.

Process for Nitrates in water. — A trial titration is first made by taking
10 c.c. of the water, adding indigo, then strong sulphuric acid in volume
equal to the united volumes of indigo and water, and heating exactly as in
standardizing the indigo. This first titration will show how much the water
under examination must be diluted, so that it may contain nitric acid
approximately equal to the roW potassic nitrate. After the water has been
diluted with distilled water free from nitrates or nitrites, fresh titrations are
made as before described until the exact number of c.c. of indigo decolorized
by 10 c.c. of the diluted water is known. In all cases it is important to
work to the same shade of greenish colour, after heating for thirty seconds,
as was obtained in the original standardizing of the indigo. The colour of
the oxidized indigo by itself should be a clear yellow.

Ammonia, Free and Saline. — The estimation of ammonia present in
the water in a free or saline form, and of that }delded by the nitrogenous
matter present in the water (commonly called albuminoid ammonia), is to be
made on the same portion of the sample to be analyzed.

Take not less than 500 c.c. or 700 dm. (one deci-gallon) of the water for
these determinations, and distil in a 40-oz. stoppered retort, which is large
enough to prevent the probability of portions of the water being spirted
over into the condenser. The neck of the retort should be small enough to
pass three or four inches into the internal glass tube of a Liebig's
condenser. If the fit between the retort and the inside tube of the
condenser is good, the joint may be made by wrapping a small piece of
washed tinfoil round the retort tube so as to pass just inside the mouth of
the condenser tube. Many analysts prefer, however, to work with a retort
fitting loosely into the condenser ; and, in such cases, the joint between the
two may be made in one of the two following ways:— (1) Either by an
ordinary india-rubber ring— such as those used for the top of umbrellas—
which has been previously soaked in a dilute solution of soda or potash —
being stretched over the retort tube in such a position, that when the retort
tube is inserted in the condenser it shall fit fairly tightly within the mouth

470 VOLUMETRIC ANALYSIS. § 92.

of the tube, about half-an-inch from the end : (2) Preferably, when the
shape of the large end of the condenser admits of it, by a short length, say
not more than two inches, of large size india-rubber tubing, which has been
previously soaked in a dilute solution of soda or potash, being stretched
outside both retort tube and condenser tube, so as to couple them together,
so that the tube of the retort still projects some inches into that of the
condenser. It is very desirable to have a constant stream of water round
the condenser, whenever it can be obtained. Before distillation, a portion
of the water must be tested with cochineal, in order to ascertain if it shows
an alkaline reaction. The portion so tested must, of course, be rejected,
and not put into the retort. If the water does not show an alkaline
reaction, a sufficient quantity of ignited sodic carbonate, to render the water
distinctly alkaline, must be added. The distillation should then be com-
menced, and not less than 100 c.c. or 150 dm. distilled over. The receiver
should fit closely, but not air-tight, on the condenser. The distillation
should be conducted as rapidly as is compatible with a certainty that no
spirting takes place. After 100 c.c. or 150 dm. have been distilled over, the
receiver should be changed, that containing the distillate being stoppered to
preserve it from access of ammoniacal fumes. 100 c.c. measuring flasks
make convenient receivers. The distillation must be continued until 50 c.c.,
or say 75 dm. more, are distilled over ; and this second portion of the
distillate must be tested with Nessler's reagent, to ascertain if it contains
any ammonia. If it does not, the distillation for free or saline ammonia
may be discontinued, and this last distillate rejected ; but if it does contain
any, the distillation must be continued still longer, until a portion of 50 c.c.,
or 75 dm., when collected, shows no colouration with the Nessler test.
The whole of the distillates must be Nesslerized as follows : — The standard
solution of ammonia for comparison is that given on page 465. The
distillate is transferred to a clean Nessler glass, and one-twentieth of its
volume of Nessler solution added. No turbidity must ensue on the
addition of the Nessler solution to the water, as such turbidity Avould
be a proof that the distillate was contaminated by reason of spirting, and
must, therefore, be rejected, and the determination repeated.

After thoroughly mixing the water and Nessler solution in the glass, an
approximate estimate can be formed of the amount of ammonia present, by
the amount of colouration produced in the solution. It will now be neces-
sary to mix one or more standard solutions with which to compare the tint
thus obtained. These solutions must be made by mixing the standard
solution of ammonic chloride with distilled water absolutely free from
ammonia, and subsequently adding some of the same Nessler solution as
was previously added to the distillate. This precaution is essential, because
the tint given by different samples of Nessler solution varies.

Albuminoid Ammonia.— As soon as the distillation of the free ammonia
has been started, the alkaline solution of permanganate should be measured
out into a flask, ready for addition to the water under examination, for the
distillation of the albuminoid ammonia. The volume of the alkaline
permanganate solution to be taken must be at least one-tenth of that of the
water which is being distilled ; and should not exceed that proportion unless
the water is of very bad quality, and the solution must be made in
accordance with the directions contained in these instructions. This
solution must be diluted with four times its own volume of water, and must
be placed in a flask and boiled during the whole time that the distillation
of the sample for free ammonia is being carried on, care being taken that
the concentration does not proceed to too great an extent. There must be
enough of this boiled and diluted alkaline permanganate solution to make
up the residue in the retort to about 500 c.c. or 700 dm. When the
distillation of the sample of water for free and saline ammonia is completed,

§ 92. ANALYTICAL PROCESSES FOR WATER. 471

the alkaline permanganate solution, which has been thus diluted and
boiled, will be ready for use, and the distillation for albuminoid ammonia
may be proceeded with, as follows : —

To the residue left in the retort from which the free ammonia has been
distilled, add the alkaline permanganate solution to make it up again to
a volume of at least 500 c.c., or say 700 dm., and the lamp being replaced,
the distillation must be continued, and successive portions of the distillate
again collected in precisely the same way as during the process of distillation
for free ammonia.

After 200 c.c. or 300 dm., say two-fifths of the volume contained in the
retort, have been distilled over, the receiver should be changed, and further
portions of 50 c.c. or 75 dm. collected separately, until the distillate is
practically free from ammonia. The distillate must then be mixed, and
Nesslerized in the same way as previously directed for free ammonia. The
result so obtained must be calculated to ammonia in grams per liter or
grains per gallon, and returned as albuminoid ammonia.

Special care must be taken that the atmosphere of the room in which,
these distillations are performed is kept free from ammoniacal vapours, and
that the receivers fit close, but not air-tight, to the end of the Liebig's
condenser. It is also specially necessary to observe that the colour of the
distillate deepens gradually after the addition of the Nessler reagent, and
that it is not possible to read off the amount of colour correctly until the
Nesslerized liquor has stood for at least three minutes, and been intimately
mixed with the Nessler solution (see also note, page 408).

Special care must be taken that the retort, condensers, receivers, funnels,
Nessler glasses, etc., used are all rendered perfectly free from ammonia
before use'. Where the water in use in the laboratory is good, this ma}r be
used to thoroughly rinse the apparatus two or three times, draining out the
adhering water ; otherwise pure distilled water must be used. These
ammonia and albuminoid ammonia determinations should be made as soon
as possible after the water has been received for analysis.

Oxygen Absorbed. — Two separate determinations have to be made, viz.,
the amount of oxygen absorbed during fifteen minutes, and that absorbed
during four hours. Both are to be made at a temperature of 80° E. (27° C.).
It is most convenient to make these determinations in 12-oz. stoppered flasks,
which have been rinsed with sulphuric acid and then with water. Put
250 c.c. or dm. into each flask, which must be stoppered and immersed in
a water bath or suitable air bath until the temperature rises to 80° P. Now
add to each flask 10 c.c. or 10 dm. of the dilute sulphuric acid, and then
10 c.c. or 10 dm. of the standard permanganate solution. Fifteen minutes
after the addition of the permanganate, one of the flasks must be removed
from the bath and two or three drops of the solution of potassic iodide added
to remove the pink colour. After thorough admixture, run from a burette
the standard solution of thiosulphate, until the yellow colour is nearly
destroyed, then add a few drops of starch indicator, and continue the
addition of the thiosulphate until the blue colour is just discharged. If the
titration has been properly conducted, the addition of one drop of
permanganate will restore the blue colour. At the end of four hours
remove the other flask, add potassic iodide, and titrate with thiosulphate, as
just described. Should the pink colour of the water in the flask diminish
rapidly during the four hours, further measured quantities of the standard
solution of permanganate must be added from time to time so as to keep it
markedly pink.

The thiosulphate solution must be standardized, not only at first, but
(since it is liable to change) from time to time in the following way :— To
250 c.c. or dm. of pure redistilled water add two or three drops of the solution
of potassic iodide, and then 10 c.c. or dm. of the standardized solution of

472 VOLUMETRIC ANALYSIS. § 92.

permanganate. Titrate with the thiosulphate solution as above described.
The quantity used will be the amount of thiosulphate solution corresponding
to 10 c.c. or 10 dm., as may be, of the standardized permanganate, and the
factor so found must be used in calculating the results of the thiosulphate
titrations to show the amount of the standard permanganate solution usedy
and thence the amount of oxygen absorbed.

Great care should be taken that absolutely pure and fresh distilled water
is used in standardizing the solution, which should also be kept in the dark
and cool. It suffices to compare the solution, if kept in this way, once in
three or four days.

The amount of thiosulphate solution thus found to be required to combine
with the iodine liberated by the permanganate left undecomposed in th&
water is noted down, and the calculation made as follows : — Let A = amount
of thiosulphate used in distilled water, and B = that used for water under
examination. Then A expresses the amount of permanganate added to the water
under examination, and B the amount of permanganate in excess of that which
the organic matter in the water has destroyed. Therefore A — B is the amount
actually consumed. If the amount of available oxygen in the quantity of
permanganate originally added be a, the oxygen required to oxidize the

organic matter in the water operated on would be -£-*—. "^ut a (ava^a^e

oxygen in the 10 c.c. of standard permanganate used) =0'001. Therefore,
A— B x 0 001 A — B x 0-4

— T — — = oxygen for 250 c.c.; or, r = parts of oxygen

required for 100,000 parts of water. Or, in other words, the difference
between the quantity of thiosulphate used in the blank experiment and
that used in the titration of the samples of water multiplied by the amount
of available oxygen contained in the permanganate added, and the product
divided by the volume of thiosulphate corresponding to the latter, is equal
to the amount of oxygen absorbed by the water.

Hardness before and after Boiling-. — Place 100 c.c. or 100 dm. of the-
water in an accurately stoppered 8-oz. flask. Run in the soap solution from
a burette in small quantities at a time. If the water be soft, not more than
^ c.c. or dm. at a time ; if hard, in quantities of 1 c.c. at first. After each
addition, shake the flask vigorously for about a quarter of a minute. As
soon as a lather is produced, lay the flask on its side after each addition, and
observe if the lather remains permanent for five minutes. To ascertain this,
at the end of five minutes roll the flask half-wa}r round ; if the lather breaks,
instead of covering the whole surface of the water, it is not permanent ; if
it still covers the whole surface it is permanent ; now read the burette.

Repeat the experiment, adding gradually the quantity of soap solution
employed in the first experiment, less about 2 c.c. or 2 dm. ; shake as before,
add soap solution very gradually till the permanent lather is formed : read
the burette, and take out the corresponding hardness from the table. If
magnesian salts are present in the water the character of the lather will be
very much modified, and a kind of scum (simulating a lather) will be seen
in the water before the reaction is completed. The character of this scum
must be carefully watched, and the soap test added more carefully, with an
increased amount of shaking between each addition. With this precaution
it will be comparatively easy to distinguish the point when the false lather
due to the magnesian salts ceases, and the true persistent lather is produced-

If the water is of more than 16° of hardness, mix 50 c.c. or dm. of the
sample with an equal volume of recently boiled distilled water which has-
been cooled in a closed vessel, and make the determination on this mixture
of the sample and distilled water. In this case it will, of course, be-
necessary to multiply the figures obtained from the table by 2.

To determine the hardness after boiling, boil a measured quantity of tk*

§ 92. REPORTING RESULTS OF WATER ANALYSIS. 473

water in a flask briskly for half an hour, adding distilled water from time to
time to make up for loss by evaporation. It is not desirable to boil the water
under a vertical condenser, as the dissolved carbonic acid is not so freely
liberated. At the end of half an hour, allow the water to cool, the mouth
of the flask being closed ; make the water up to its original volume with
recently boiled distilled water, and, if possible, decant the quantity necessary
for testing. If this cannot be done quite clear, it must be filtered. Conduct
the test in the same manner as described above.

The hardness is to be returned in each case to the nearest half-degree.

Total Solid Matters. — Evaporate 250 c.c. or ^th of a gallon, in
a weighed platinum dish on a water bath ; dry the residue at 220° I\
(104° C.), and cool under a desiccator. Weigh the dish containing the
residue accurately, and note its colour and appearance, and especially
whether it rapidly increases in weight. Return to the water bath for
half an hour and re-weigh until it ceases to lose weight, then graduallj'
heat it to redness, and note the changes which take place during this
ignition. Especially among these changes should be observed the smell,.
scintillation, change of colour, separation of more or less carbon, and partial
fusion, if any. The ignited residue is to be used for the estimation of
phosphoric acid, as before directed.

Microscopical Examination of Deposit — The most convenient plan
of collecting the deposit is to place a circular microscopical covering glass at
the bottom of a large conical glass holding about 20 oz. The glass should
have no spout, and should be ground smooth on the top. After shaking up
the sample, this vessel is filled with the water, covered with a plate of ground
glass, and set aside to settle. After settling, the supernatant water is drawn
off by a fine syphon, and the glass bearing the deposit lifted out, either by
means of a platinum wire (which should have been previously passed under
it), or in some other convenient way, and inverted on to an ordinary
microscopical slide for examination. It is desirable to examine the deposit
first by a |th and then bya^th objective. The examination should be made
as soon as the water has stood overnight. If the water be allowed to stand
longer, organisms peculiar to stagnant water may be developed and mislead
the observer. Particular notice should be taken of bacteria, infusoria, ciliata
or flagellata, disintegrated fibres of cotton, or linen, or epithelial debris.

It is particularly desirable to report clearly on this microscopical
examination ; not merely giving the general fact that organisms were
present, but stating as specifically as possible the names or classes of the
organisms, so that more data may be obtained for the application of the
examination of this deposit to the characters of potable waters.

It is also desirable to examine the residue left on a glass slide by the
evaporation of a single drop of the water. This residue is generally most
conveniently examined without a covering glass. The special appearances
to be noticed are the presence or absence of particles of organic matter, or
organized structure, contained in the crystallized forms which may be seen ;
and also whether any part of the residue left, especially at the edges, is
tinted more or less with green, brown, or yellow.

Reporting: the Results of Water Analysis.— The Report of the
Committee appointed by the British Association to confer with the Committee
of the American Association with a view of forming a uniform system of
recording results of Water Anatysis, B. A. Meeting, 1889 (Chem. News.
60, 203—204) is as follows: — The committee recommend a system of
statement for a complete analysis of which the following is an epitome.
Results to be expressed in parts per 10(),COO. In a potable water, the numbers-
to be given in the following order : Total solid matters (a) in suspension,.
(b) in solution ; organic carbon ; organic nitrogen ; oxygen consumed, as-

474 VOLUMETRIC ANALYSIS. § 93.

indicated by decoloration of permanganate ; ammonia expelled on boiling
with sodic carbonate; ammonia expelled on boiling with alkaline perman-
ganate ; nitrogen as nitrates and nitrites ; chlorine ; hardness- temporary,
permanent, total. In a mineral Avater — carbonate of lime; carbonate of
magnesia ; carbonate of soda (calculated from residual alkalinity after
boiling and filtering off precipitated CaCO3 and MgCO3) ; total of each
of the following elements— calcium, magnesium, potassium, sodium, iron
(ferrous), iron (ferric), and each of the following radicles — sulphuric (SO4),
nitric (NO3), nitrous (NO2), phosphoric (PO4), silicic (SiO3) ; then each of
the elements — chlorine, bromine, and iodine, and of sulphur as sulphide.
Dissolved gases : c.c. at 0° C. and 760 m.m. in 1 liter of water. Carbonic
anhydride (CO2) ; oxygen ; nitrogen ; sulphuretted hydrogen.

They consider that this uniform method should be adopted in all cases
where communications come before learned bodies and Avhenever possible in
professional practice ; that the decimal numerical notation is to be preferred ;
that the different scales for potable and mineral waters suggested by the
American Committee are undesirable ; that all results obtained by calculation
should be sharply distinguished from those obtained by direct determination ;
that a statement of mineral constituents combined as salts is not to be
approved of unless the analytical data upon which it is based are clearly
stated ; that the American Committee's suggestion of recording the proportion
of each element of binary compounds, and recording all the oxygen in
oxy-compounds in combination with the negative element, as indicated
above, is the most convenient for all purposes of calculation, although the
want of a name for these negative groups and the custom of quoting
metallic elements as bases are objections to this system ; finall}r, that volumes
of dissolved gases may be given as above, or in volumes of gas per 100
volumes of water.

OXYGEN DISSOLVED IN WATERS.

§ 93. The necessary apparatus and standard solutions for
carrying out this estimation are described in § 71 (page 269),
together with the methods of manipulation.

The interpretation of the results as regards polluted waters, as
given by Dupre, may be summarized as follows : —

The method depends on the fact that, if a perfectly pure water is
once fully aerated, and then kept in a bottle so that it could neither
lose nor gain oxygen, it would remain fully aerated for any length
of time ; but, on the other hand, if the water contained living
organic matters capable of absorbing oxygen, such water would after
a period of time contain less oxygen, the loss so found being taken
as the measure of impurity. The method is really another form of
ascertaining the presence of germs and their amount in contrast to
the method of cultivation by gelatine and microscopic analysis.

The practical results from various experiments made by Dupre,
and reported by him to the Medical Department of the Local
Government Board, 1884, are as follows : —

(1) A water which does not diminish in its degree of aeration during
a given period of time, may or may not contain organic matter, but
presumably does not contain growing organisms. Such organic matter
therefore as it may be found to contain by chemical analysis (permanganate
or otherwise) need~ not be considered as dangerous impurity.

(2) A water which by itself, or after the addition of gelatine or other

§ 93. OXYGEN IN WATEKS. 475

appropriate cultivating matter, consumes oxygen from the dissolved air at
lower temperatures, but does not consume any after heating for say three
hours at 60° C., may be regarded as having contained living organisms, but
none of a kind able to survive exposure to that temperature.

(3) A water which by itself, or after addition of gelatine or the like,
continues to absorb oxygen from its contained air after heating to 60° C.,may
be taken as containing spores or germs able to survive that temperature.

The exact nature of organisms differing in this way is of course
not revealed by the method. D up re's conclusion is, that in the
vast majority of cases the consumption of oxygen from the dissolved
air of a natural water is due to growing organisms, and that in the
complete absence of such . organisms little or no oxygen would
be then consumed.

The paper is accompanied by tables of results of analysis by this
and other methods, which are too voluminous to insert here.

Principle of the method. — Dupre states that a water, fully aerated,
contains at 20° C. and 760 m.m. pressure 0'594 grain of oxygen per gallon,
•or 0'04158 gm. per liter.* The proportion varies with the temperature and
pressure. The formula given by Bunsen is adopted in this method —

a=2'0225 j8 ; and j8=0;020346 - 0'00052887^+p-000011156^ ;
•\vhere a is the co-efficient of absorption of oxygen in cubic centimeters,
,/3 the co-efficient for absorption of nitrogen, and t the temperature.

The variation due to atmospheric pressure is so slight that it
may practically be disregarded. The composition of air is taken as
2 1 volumes oxygen and 7 9 nitrogen. Dupre adopts the temperature
of 20° C. for all waters under experiment; and as a rule the
samples were all placed in an appropriate bottle, and kept at
a constant temperature of 20° C. for ten days previous to the
estimation of the oxygen.

The maximum degree of oxygen which a pure water should
contain at this temperature is called 100, and any less degree found
on analysis is recorded as a percentage of this maximum.

Process: The sample of water is placed in an ordinary bottle, and
vigorously shaken to ensure full aeration ; after standing the requisite time
it is poured into the experimental bottle, and the estimation of oxygen
•carried out as described in § 71.

* R o s c o e and L u n t , and also D i 1 1 in a r , show by their experiments that these
figures are too low.

476 VOLUMETRIC ANALYSIS. § 93.

Calculation of the Results of Water Analysis.

Substance estimated.

Measure of water
taken.

Volume or weight
obtained or used.

Factor for grains per
gallon.

100 c.c. or dm. .

f c.c. or dm. stan- )
( dard AgNO3 )

x 0-7 =C1

„ ...

140 dm. (-^-gal.)

dm. „ „ „

x 0-5 =C1

N as HNO3 (
(Crum) J

250 c.c. .
250 dm. .

c.c. of NO

55 J5

55 5>

x 0-175 =N
x 0'27 =N
x 0-193 =N

100 c.c.' w ° '.

grams of NH3

x 576-45 =N

NH3 copper-zinc N

50 c.c. .

yy 39

x 1152-9 =N

or aluminium 1

150 dm. .

grains of NH3

x 38-43 =N

100 dm. .

55 55

x 57-64 =N

Free or Alb. NH3

500 c.c. .

f c.c. standard ")
I NH4C1 )

x 00014=NH3

55 }> 55

700 dm. .

dm. „ „

x OO'l =NH3

O absorbed .

250 c c. .

C 10, 15, or 20 c.c. )
( permanganate )

( x 0'28(lorl-5or
) 2-£#' -0

350 dm.

f 10, 15, or 20 dm. }

C x 0'02 (lor 1-5 or

55 5> 55

^ permanganate )

/ 2 — — *) = O

Total solids .

250 c.c. .

grams

x 280-0

„

350 dm. .

grains

x 20-0

Coefficients and Logarithms for Volumetric Analysis.

Coefficients.

Logarithms.

Normal H-SO4 1 c.c.=0'049 gm. H2S04

... 2-6901961

„ =0-048 „ SO4

... 2-6812412

„ —0-040 „ SO3

... 2-6020600

Normal HC1 1 c.c.=0'0365 „ HC1

... 2-5622929

„ =0-0355 „ Cl

... 2-5502284

Normal HNO3 1 c.c.=0'063 „ HNO3

... 2-7993405

„ =0-062 „ NO5

... 5-7923917

„ =-0-054 „ N2O5

... 2-7323938

Normal H2C204 1 c.c.=0'063 „ H2C2O4, 20H2

... 2-7993405

„ —0-045 , H2C2O4

... 2-6532125

Normal Acid 1 c.c.=0'0l7

, NH3

... 2-2304489

=0-035

, NH4HO ..

... 2-5440680

=0-J91

, Na2B2O'10H-O

... 1-2810334

=0-037 ,

, Oa2HO

... 2-5682017

=0-028

, CaO

... 2-4471580

=0-05

, CaCO3

... 2-6989700

=0-0855

, BaH-02 ...

... 2-9319661

=0-1575

, BaH2O28H2O

... 1-1972806

=0-0985

, BaCO3

... 2-9934362

=0-02

, MgO

... 2-3010300

=0-042

, MgCO3

... 2-6232493

'„ =0-056

, KHO

... 2-748188O

„ =0-069

, K2CO3

... 2-8388491

„ =0-188

, KHC4H4Ofi...

... 1-2741578

* A— c.c. or dm. of tniosulphate solution corresponding to 10 c.c. or dm. of perman-
ganute. B=c.c. or dm. of thiosulpbate solution used after the time of reaction is
complete.

§ 93.

COEFFICIENTS.

Normal Acid

Normal NaHO
Normal KHO
Normal Na2C03

Normal Alkali

Silver

i^j- Iodine

Bichromate

i o

Thiosulphate

gm.

KC2H302 ...

KNaC4H4O6

NaHO

Na2C03

Na2C0310H2O

NaHCO3 ...

NaHO

Na2O

KHO

K20

Na2CO3

CO3

CO2

IIC2H3O2 ...

H3C6H5O7H2O

HC1

HB2 ......

HNO3

H2S04

Coefficients.
1 c.c.=0-102

M =0-098

„ =0-141

„ =0-04

„ =0-053

„ -0-143

„ =0-084
1 c.c.=0'040

„ =0-031
1 c.c.=0'056

„ =0-047
1 c.c.=0'053

„ =0-030

„ =0-022
1 c.c.=0-06

„ =0-07

„ =0-0365

}} =0-0808

„ =0-0128

„ =0-063

„ =0-049

„ =0-075
1 c.c.=0'0108

„ =0-017

„ =0-00355

„ =0-00535

„ =0-00745

„ =0-0119

„ =0-0103

„ =0-0064
1 c.c.=0'0032

„ =0-0041

„ =0-00495

„ =0-0248

„ =0-0126

„ =0-0097
1 c.c.=0'0456

„ =0-051

„ =0-0849

„ =0-0348

„ =0-0696

„ =0-0216
1 c.c.=0'0248

„ =0-0127

„ =0-00355

„ =0-0080
CALCIUM (Ca=40)

1 c.c. yV permanganate=0'0028 gm. CaO

=0-0050 gm. CaCO3 ...
=0-0086 gm. CaSO4, 2OH2
„ normal oxalic acid=0'0280 gm. CaO ...

Cryst. oxalic acid x G'444 =CaO

Double iron salt xO'07143=CaO

Ag ......

AgNO3

Cl ......

NH4C1

KC1 ......

KBr ......

NaBr

Na2HAs04 ...
SO2 ......

H2S03

As203

Na2S2O35H2O

Na2S037H20

K2S032H20

FeSO4

Fc2S04H20...

FeSO47H2O...

FeCO3

Fe304

FeO ......

Sodic thiosulphate

Cl
Br

477

Logarithms.
1-0086002
2-9912261
1-1492191
2-6020600
2-7242759
1-1553660
2-9242793
2-6020600
2-4913617
27481880
2-6720979
2-7242759
2-4771213
2-3424227
2-7781513
2-8450980
2-5622929
2-9074114
1-1072100
2-7993405
2-6901961
2-8750613
2-0334238
2-2304489
3-5502284
3-7283538
3-8721563
2-0755470
2-0128372
3-8061800
3-5051500
3-6127839
3-6946052
2-3944517
2-1003705
3-9867717
2-6589648
2-7075702
2-9289077
2-5415792
2-8426092
2-3344538
2-3944517
2-1038037
3-5502284
3-9030900

3-4471580
3-6989700
3-9344985
2-4471580
1-6473830
2-8538807

CHLOEINE (Cl=35'37)

1 c.c. T^ silver solution=0'003537 gm. Cl

=0-005837 gm. NaCl

„ arsenious or thiosulphate solutiou=0'003537 gm. Cl.

3-5486351
3-7661897
3-5486351

478

VOLUMETRIC ANALYSIS.

93.

CHROMIUM (Cr=52'4) Logarithms.

Metallic iron x 0'3123 =Cr 1-4945720

„ xO'5981=CrO3 1*7767738

„ x 0'8784=K2Cr2O7 1'9436923

x 1-926 =PbCrO4 0-2846563

Double iron salt x 0'0446=Cr 2'6493349

„ xO'0854=CrO3 2'9314579

x 0-1255=K2Cr2O" 1-0986437

x 0-275 =PbCrO4 1'4393327

1 c.c. tV solution=0'003349 gm. CrO3 S'5249151

=0-00492 gm. K-Cr207 3'6919651

COPPER (Cu=63)

1 c.c. T\ solution=0'0063 gm. Cu 3"'7993405

Ironx T125=copper 0'0511525

Double iron salt xO'1607=copper 1-2060159

CYANOGEN (CN=26)

1 c.c. TN7 silver solution=0'0052 gm. CN

=0-0054 gm. HCN

=0-01302 gm. KCN

„ i^ iodine =0'003255 gm. KCN

POTASSIC FERROCYANIDE (K4FeCy6, 30H2=422)

Metallic iron x 7'541=cryst. potassic ferroc}rauide ...
Double iron salt x 1-077= „ „ „

POTASSIC FERBICYANIDE (K6Fe2Cy12=658)

Metallic iron x 5'88 =potassic ferricyanide

Double iron salt x 1*68 = „ „

:nj- thiosulphate xO'0329= „ „

GOLD (Au=196-5)

1 c.c. normal oxalic acid=0"0655 gm. gold

IODINE (1=127)

1 c.c. *f thiosulphate=0-0127 gm. iodine

IRON (Fe=56)

1 c.c. T^ permanganate, bichromate,, or thiosulphate

=0-0056 Fe

,, „ „ =0-0072 FeO

„ =0-0080 Fe20a

LEAD (Pb=206'4)

1 c.c. YT5- permanganate =0'01032 gm. lead
1 c.c. normal oxalic acid=0'1032 gm. lead

Metallic iron x l'842=lead

Double iron salt x 0'263=lead

3-7160033
3-7323938
2-1146110
3-5125510

0-8774289
0-0322157

0-7693773
0-2253093
2-5171959

2-8162413
2-1020905

3-7481880
3-8573325
3-9030900

2-0136797
1-0136797
0-2652896
1-4199557

MANGANESE (Mn=55)

MnO=7l. Mn02=87.

Metallic iron x 0-491 =Mn 1*6910815

xO'63393=MnO 1-8020413

x 0-7768 =MnO2 1-8903092

Double iron salt x 0-09 11 =MnO 2-9595184

x O'lll =MnO2 1-0453230

Cryst, oxalic acid x 0'6916=MnO2 1-8398550

1 c.c. ^5- solution=0'00355 gm. MnO 3-5502284-

=0-00435 gm. MiiO- 3'6384893

§ 93. COEFFICIENTS. 479

MERCURY (Hg=200) Logarithms.

Double iron salt xO'5104=Hg 17079107

x 0'6914=HgCl2 1-8397294

1 c.c. & solution=0-0200 gm. Hg 2-3010300-

=0-0208 gm. Hg2O 2-3180633-

=0-0271 gm. HgCl2 2-4329693

NITROGEN AS NITRATES AND NITRITES (N2O5=108. N2O3=76)

Normal acidxO'0540=N2O5 2'7323938

xO'1011=KNO3 1-0047512

Metallic iron xO-3750=HNO3 1-5740313

xO-6018=KNO3 1-7794522

„ xO'3214=N2O5 1-5070459

SILVER (Ag=107-66)

1 c.c. TN¥ NaCl=0'010766 gm. Ag 2*0320544

=0-016966 gm. AgNO3 , 2'2295795-

SULPHURETTED HYDROGEN (H2S=34)

1 c.c. ^3- arsenious solution=0'00255 gm. H2S S'4065402

TIN (Sn=118)

Metallic iron x r0536=tin 0'0226758-

Double iron salt xO'1505=tin T1775365

Pactor for T^ iodine or permanganate solution 0'0059... ... 3-7708520-

ZINC (Zn=65)

Metallic iron x 0'5809=Zn 1-7641014

x 0*724 =ZnO ... 1-8597386

Double iron salt x 0'08298=Zn 2'9189734

x 0-1034 =ZnO T0145205

1 c.c. TN^ solution=0'00325 gni. Zn 3'511883-i

480 VOLUMETRIC ANALYSIS. 8 94

PART VII.
VOLUMETRIC ANALYSIS OF GASES.

Description of the necessary Apparatus, with Instructions for
Preparing-, Etching-, Graduating-, etc.

§ 94. THIS branch of chemical analysis, on account of its
•extreme accuracy, and in consequence of the possibility of its
application to the analysis of carbonates, and of many other bodies
from which gases may be obtained, deserves more attention than
it has generally received, in this country at least. It will therefore
be advisable to devote some considerable space to the consideration
..of the subject.

Eor an historical sketch of the progress of gas analysis, the
reader is referred to Dr. Frank land's article in the
Hand'wdrterlmch der CJiemie, and more complete details
of the process than it will be necessary to give here will
be found in that article; also in Bun sen's Gasometry
and in Dr. Russell's contributions to Watt's Chemical
Dictionary.

The apparatus employed by Bun sen, who was the first
successfully to work out the processes of gas analysis, is
very simple. Two tubes, the absorption tube and the
eudiometer, are used, in which the measurement and
analysis of the gases are performed. The first of these
tubes is about 250 m.m. long and 20 m.m. in diameter,
closed at one end, and with a lip at one side of the open
extremity, to facilitate the transference of the gas from the
absorption tube (fig. 64) to the eudiometer (fig. 65). The
eudiometer has a length of from 500 to 800 m.m., and
a diameter of 20 m.m. Into the closed end two platinum
wires are sealed, so as to enable the operator to pass an
electric spark through any gas which the tube may contain.
The mode of sealing in the platinum wires is as follows: —
^ken *ne en(* °^ ^ie tu^e ig cl°sed, an(l while still hot,
' ' a finely pointed blowpipe flame is directed against the
side of the tube at the base of the hemispherical end.
When the glass is soft, a piece of white-hot platinum wire is
pressed against it and rapidly drawn away. By this means
a small conical tube is produced. This operation is then repeated
on the opposite side (fig. 66). One of the conical tubes is next
cut off near to the eudiometer, so as to leave a small orifice (fig. 67),

§ 94 APPARATUS FOR ANALYSIS OF GASES. 481

through which a piece of the moderately thin platinum wire, reaching
about two-thirds across the tube, is passed. The fine blow-pipe
flame is now brought to play on the wire at the point where it enters
the tube ; the glass rapidly fuses round the wire, making a perfectly
gas-tight joint. If it should be observed that the tube
has any tendency to collapse during the heating, it will
be necessary to blow gently into the open end of the tube.
This may be conveniently done by means of a long piece
of caoutchouc connector, attached to the eudiometer,
which enables the operator to watch the effect of the
blowing more easily than if the mouth were applied
directly to the tube. When a perfect fusion of the glass
round the wire has been effected, the point on the opposite
side is cut off, and a second wire sealed in in the same
manner (fig. 68). The end of the tube must be allowed
to cool very slowly ; if proper attention is not paid to
this, fracture is very liable to ensue. When perfectly
cold, a piece of wood with a rounded end is passed
up the eudiometer, and the two wires carefully pressed
against the end of the tube, so as to lie in contact with
the glass, with a space of 1 or 2 m.m. between their
points (fig. 69). It is for this purpose that the wires,
when sealed in, are made to reach so far across the tube.
The ends of the wires projecting outside the tube are
then bent into loops. These loops must be carefully
treated, for if frequently bent they are very apt to break
off close to the glass ; besides this, the bending of the
wire sometimes causes a minute crack in the glass, which
may spread and endanger the safety of the tube. These
difficulties may be overcome by cutting off the wire close
to the glass, and carefully smoothing the ends by rubbing
them with a piece of ground glass until they are level
with the surface of the tube (fig. 70). In order to make
contact with the induction coil, a wooden American paper-
clip, lined with platinum foil, is made to grasp the tube;
the foil is connected with two strong loops of platinum
wires, and to these the wires from the coil are attached
(fig. 71). In this way no strain is put on the eudiometer
wires by the weight of the wires from the coil, and
perfect contact is ensured between the foil and platinum
wires. It is also easy to clean the outside of the
eudiometer without fear of injuring the instrument.

It will now be necessary to examine if the glass is perfectly
fused to the wires. For this purpose the eudiometer is Fig. 65.
filled with mercury, and inverted in the trough. If the
tube has 800 m.m. divisions, a vacuous space will be formed in the
upper end. Note the height of the mercury, and if this remains
constant for a while the wires are properly sealed. Should the

i i

482

VOLUMETRIC ANALYSIS.

§ 94

eudiometer be short, hold it in the hands, and bring it down with
a quick movement upon the edge of the india-rubber cushion at
the bottom of the trough, taking care that the force of impact is
slight, else the mercury may fracture the sealed end of the tube.
By jerking the eudiometer thus, a momentary vacuum is formed,
and 'if there is any leakage, small bubbles of air will arise from the
junction of the wires with the glass.

Fig. 66.

Tig. 67.

Kg. 68.

Tig. 69.

Pig. 70.

The tubes are graduated by the following processes : — A cork
is fitted into the end of the tube, and a piece of stick, a file, or
anything that will make a convenient handle, is thrust into the
cork. The tube is heated over a charcoal fire or combustion furnace,
and coated with melted wax by means of a earners-hair brush.
Sometimes a few drops of turpentine are mixed with the wax to

APPARATUS FOR ANALYSIS OF GASES.

483

1 11! |

render it less brittle, but this is not always necessary.

cooling it should be found that

the layer of wax is not uniform,

the tube may be placed in

a perpendicular position before

n fire and slowly rotated so as

to heat it evenly. The wax will

then be evenly distributed on

the surface of the glass, the

excess flowing off. The tube

must not be raised to too high

a temperature, or the wax may

become too thin ; but all thick

masses should be avoided, as

they may prove troublesome in

the subsequent operation.

The best and most accurate
mode of marking the millimeter
divisions on the wax is by
a graduating machine; but the
more usual process is to copy
the graduations from another
tube in ihe following manner.
A hard glass tube, on which
millimeter divisions have al- 1
ready been deeply etched, is
fixed in a groove in the gra- P
duating table, a straight-edge
of brass being screwed down
on the tube and covering the
ends of the lines. The standard
tube is shown in the figure at
the right-hand end of the
apparatus (fig. 72). The
waxed tube is secured at the
other end of the same groove,
and above it are fixed two
brass plates, one with a straight-
edge, and the other with
notches at intervals of 5 m.m.,
the alternate notches being
longer than the intermediate
ones (fig. 73). A stout rod of
wood provided with a sharp
steel point near one end, and
a penknife blade at the other
(fig. 74), is held so that the
•steel point rests in one of the

i i 2

If,

484 VOLUMETRIC ANALYSIS. § 94.

divisions of the graduated tube, being gently pressed at the same
time against the edge of the brass plate ; the point of the knife-
blade is then moved by the operator's right hand across the portion
of the waxed tube which lies exposed between the two 'brass plates.
When the line has been scratched on the wax, the point is moved
along the tube until it falls into the next division ; another line is
now scratched on the wax, and so on. At every fifth division the
knife-blade will enter the notches in the brass plate, making
a longer line on the tube. After a little practice it will be found
easy to do fifty or sixty divisions in a minute, and with perfect
regularity. Before the tube is removed from the apparatus, it must
be carefully examined to see if any mistake has been made. It
may have happened that during the graduation the steel point
slipped out of one of the divisions in the standard tube ; if
this has taken place, it will be found that the distance between
the line made at that time and those on each side of it will
not be equal, or a crooked or double line may have been produced.
This is easily obliterated by touching the wax with a piece of heated
platinum wire, after which another line is marked. The tube is
now taken out of the table, and once more examined. If any
portions of wax have been scraped off by the edges of the apparatus,

Fig. 75.

or by the screws, the coating must be repaired with the hot
platinum wire. Numbers have next to be marked opposite each
tenth division, beginning from the closed end of the tube, the
first division, which should be about 10 m.m. from the end, being
marked 10 (see fig. 69). The figures may be well made with
a steel pen. This has the .advantage of producing a double line
when the nib is pressed against the tube in making a down-stroke.
The date, the name of the maker of the tube, or its number,
may now be written on the tube.

The etching by gaseous hydrofluoric acid is performed by
supporting the tube by two pieces of wire over a long narrow
leaden trough containing sulphuric acid and powdered fluor-spar
fig. 75), and the whole covered with a cloth or sheet of paper,
f course it is necessary to leave the cork in the end of the tube
to prevent the access of hydrofluoric acid to the interior, which
might cause the tube to lose its transparency to a considerable
extent. The time required for the action of the gas varies with
the kind of glass employed. With ordinary flint glass from ten
minutes to half an hour is quite sufficient ; if the leaden trough is
heated, the action may take place even still more rapidly. The

APPARATUS FOR ANALYSIS OF GASES.

485

tube is removed from time to time, and a small portion of the
wax scraped off from a part of one of the lines ; and if the division
can be felt with the finger-nail or the point of a knife, the
operation is finished ; if not, the wax must be replaced, and the
tube restored to the trough. When sufficiently etched, the tube
is washed with water, heated before a fire, and the wax wiped
off with a warm cloth.

The etching may also be effected with liquid hydrofluoric acid,
by applying it to the divisions on the waxed tube with a brush,
or by placing the eudiometer in a gutta-percha tube closed at one
end, and containing some of the liquid.

Pig. 76.

Fig. 77.

As all glass tubes are liable to certain irregularities of diameter,
it follows that equal lengths of a graduated glass tube will not
contain exactly equal volumes ; hence it is, of course, impossible
to obtain by measurement of length the capacity of the closed end
of the tube.

In order to provide for this, the tube must be carefully calibrated.
For this purpose it is supported vertically (fig. 76), and successive
quantities of mercury poured in from a measure. This measure
should contain about as much mercury as ten or twenty divisions
of the eudiometer, and is made of a piece of thick glass tube,
closed at one end, and with the edges of the open end ground
perfectly flat. The tube is fixed into a piece of wood in order to

486

VOLUMETRIC ANALYSIS.

avoid heating its contents during the manipulation. The measure
may be filled with mercury from a vessel closed with a stop-cock
terminating in a narrow vertical tube, which is passed to the bottom
of the measure (fig. 77). On carefully opening the stop cock the
mercury flows into the measure without leaving any air-bubbles
adhering to the sides. A glass plate is now pressed on the ground
edges of the tube, which expels the excess of mercury and leaves
the measure entirely filled. The mercury may be introduced into
the measure in a manner which is simpler and as effectual, though
perhaps not quite so convenient, by first closing it with a glass
plate, and depressing it in the mercurial trough, removing the plate
from the tube, and again replacing it before raising the measure
above the surface of the mercury. After pouring each measured
quantity of mercury into the eudiometer, the air-bubbles are
carefully detached from the sides by means of a thin wooden rod
or piece of wrhalebone, and the level of the mercury at the highest
part of the curved surface carefully observed.

In all measurements
in gas analysis it is, of
course, essential that the
eye should be exactly on
a level with the surface
of the mercury, for the
parallax ensuing if this
were not the case would
produce grave errors
in the readings. The
placing of the eye in the
proper position may be
ensured in two ways. A
small piece of looking-
glass (the back of which
is painted, or covered
with paper to prevent the
accidental soiling of the
mercury in the trough) is
placed behind, and in contact with the eudiometer. The head is
now placed in such a position that the reflection of the pupil of
the eye is precisely on a level with the surface of the mercury in
the tube, and the measurement made. As this process necessitates
the hand of the operator being placed near the eudiometer, which,
might cause the warming of the tube, it is preferable to read off
with a telescope placed at a distance of from two to six feet from
the eudiometer. The telescope is fixed on a stand in a horizontal
position, and the support is made to slide on a vertical rod. The-
image of the surface of the mercury is brought to the centre of
the field of the telescope, indicated by the cross. wires in the eye-
piece, and the reading taken. The telescope has the advantage of

CALIBRATION OF INSTRUMENTS.

487

magnifying the graduations, and thus facilitating the estimation
by the eye of tenths of the divisions. Fig. 78 represents the
appearance of the tube and mercury as seen by an inverting
telescope.

By this method the capacity of the tube at different parts of its
length is determined. If the tube were of uniform bore, each
measure of mercury would occupy the same length in the tube ;
but as this is never the case, the value of the divisions at all parts
of the tube will not be found to be the same.

From the data obtained by measuring the space in the tube
which is occupied by equal volumes of mercury, a table is con-
structed by which the comparative values of each millimeter of the
tube can be found. The following results were obtained in the
calibration of a short absorption eudiometer :

On the introduction of the 3rd volume of mercury, the reading was 12'8 m.m.
4th 18-4

Thus, he standard

5th
6th
7th

8th

24-0

35-2
41-0

volumes occupied 5'6 ni.in., hetween 12'8 and 18'4

5-6

5-8

5'8

18'4 „ 24'Q

24-0 „ 29-8

29-8 „ 35-2

35-2 „ 41-0

If we assume the measure of mercury to contain 5 '8 volumes
(the greatest difference between two consecutive readings on the
tube), the volume at the six points above given will be as follows : —

At 12-8 it will be 174 or 5-8 x 3

184
24-0
29-8
35-2
41-0

23-2
29-0
34-8
40-6
464

5-8x4
5-8x5
5-8x6
5-8x7

5-8x8

Between the first and second readings these 5*8 volumes are con-
tained in 5'6 divisions, consequently each millimeter corresponds to

v-» = 1 -0357 vol. This is also the value of the divisions between the

O'O

second and third readings. Between the third and fourth 1 m.m.
contains 1 vol. ; between the fourth and fifth, 1 m.m. contains

— =1-0741 vol. ; and between the fifth and sixth m.m. = l vol.

D -±

From these data the value of each millimeter on the tube can
readily be calculated. Thus 13 will contain the value of 12 '8 +
the value of 0*2 of a division at this part of the tube, or 174 +
(1-0357 x 0'2) = 17-60714. There is, however, no need to go
beyond the second place of decimals, and, for all practical purposes,
the first place is sufficient. Thus, by adding or subtracting the
necessary volumes from the experimental numbers, we find the

488

VOLUMETRIC ANALYSIS.

§ 94.

values of the divisions nearest to the six points at which the
readings were taken to be —

13=17-61 or 17-6
18=22-79 „ 22-8
24=29-00 „ 29-0
30=35-00 „ 35-0
35=40-38 „ 40-4
41=46-40 „ 46-4

In a precisely similar manner the values of the intermediate
divisions are calculated, and we thus obtain the following table : — •

Values.

Values. i ;§

Values.

1 W

14-50

14-5

25-89

25-9

37-15

37-1

15-54

15-5

22 26-93

26-9

38-22

38-2

16-57

16-6

27-96

28-0

39-30

39-3

17-61

17-6

29-00

29-0

40-38

40-4

18-65

18-6

30-00

30-0

41-40

41-4

19-68

19-7

31-00

31-0

42-40

42-4

20-71

20-7

32-00

32-0

43-40

43-4

21-75

21-8

33-00

33-0

44-40

44-4

22-79

22-8

34-00

34-0

45-40

45-4

23-82

23-8

35-00

35-0

46-40

46-4

24-86

24-9

36-07

36-1

&c.

If it be desired to obtain the capacity of the tube in cubic
centimeters, it is only necessary to determine the weight of the
quantity of mercury the measure delivers, and the temperature at
which the calibration was made, and to calculate the contents by
the following formula : —

0x (1+0-0001815*)
13-596V

in which g represents the weight of the mercury contained in the
measure, t the temperature at which the calibration is made,
0-0001815 being the coefficient of expansion of mercury for each
degree centigrade, V the volume read off in the eudiometer, and C
the number of cubic centimeters required.

A correction has to be made to every number in the table on
account of the surface of the mercury assuming a convex form in
the tube. During the calibration, the convexity of the mercury is
turned towards the open end of the tube (fig. 79), whilst in the

CALIBRATION OF INSTRUMENTS.

489

measurement of a gas the convexity will be in tne opposite direction
(fig. 80). It is obvious that the quantity of mercury measured
during the calibration, while the eudiometer is inverted, will be
less than a volume of gas contained in the tube when the mercury
stands at the same division, while the eudiometer is erect. The
necessary amount of correction is determined by observing the
position of the top of the meniscus, and then introducing a faw
drops of a solution of corrosive sublimate, which will immediately
cause the surface of the mercury to become horizontal (fig. 81), and
again measuring.

It will be observed that in fig. 79 the top of the meniscus was
at the division 39, whereas in fig. 81, after the addition of corrosive
sublimate, the horizontal surface of the mercury stands at 38*7,
giving a depression of 0*3 m.m. If the tube were now placed
erect, and gas introduced so that the top of the meniscus was at 39,

*Eig. 79.

*Fig. 80.

Fig. 81.

and if it were now possible to overcome the capillarity, the horizontal
surface would stand at 39 '3. The small cylinder of gas between
38-7 and 39'3, or 0'6 division, would thus escape measurement.
This number 0'6 is therefore called the error of meniscus, and must
be added to all readings of gas in the eudiometer. The difference,
therefore, between the two readings is multiplied by two, and the
volume represented by the product obtained — the error of meniscus
— is added to the measurements before finding the corresponding
capacities by the table. In the case of the tube, of which the
calibration is given above, the difference between the two readings
was 0'4 m.m., making the error of meniscus 0'8.

All experiments on gas analysis, with the apparatus described,

* In these the mercury shovll just torch

CFTHE

UNIVERSITY

490

VOLUMETRIC ANALYSIS.

§ 94

should be conducted in a room set apart for the purpose, with the
window facing the north, so that the sun's rays cannot penetrate
into it, and carefully protected from flues or any source of heat
which might cause a change of temperature of the atmosphere.
The mercury employed should be purified, as far as possible, from
lead and tin, which may be done
by leaving it in contact with dilute
nitric acid in a shallow vessel for
some time, or by keeping it when
out of use under concentrated
sulphuric acid, to which some mer-
curous sulphate has been added.
This mercury reservoir may con-
veniently be made of a glass globe
with a neck at the top and a
stop-cock at the bottom (fig. 82),
and which is not filled more than
one-half, so as to maintain as large
a surface as possible in contact
with the sulphuric acid. Any
foreign metals (with the exception
of silver, gold, and platinum)
which may be present are removed
by the mercurous sulphate, an
equivalent quantity of mercury
being precipitated. This process,
which wras originated by M.
Deville, has been in use for
many years with very satisfactory
results, the mercury being always
clean and dry when drawn from
the stop-cock at the bottom of the
globe. The mouth of the globe
should be kept close to prevent
the absorption of water by the
sulphuric acid.

In all cases, where practicable,
gases should be measured when
completely saturated with aqueous
vapour : to ensure this, the top
of the eudiometer and absorption
tubes should be moistened before
the introduction of the mercury.
This may be done by dipping the end of a piece of iron wire
into wrater, and touching the interior of the closed extremity of
the tube with the point of the wire.

In filling the eudiometer, the greatest care must of course be-
taken to exclude all air-bubbles from the tubes. This may be

Fig. 82.

THE EUDIOMETER.

491

effected in several ways : the eudiometer may be held in an inverted
or inclined position, and the mercury introduced through a narrow
glass tube which passes to the end of the eudiometer and com-
municates, with the intervention of a stop-cock, with a reservoir
of mercury (fig. 83). On carefully opening the stop-cock, the
mercury slowly flows into the eudiometer, entirely displacing the air.
The same result may be obtained by placing the eudiometer nearly
in a horizontal position, and carefully introducing the mercury
from a test-tube without a rim (fig. 84). Any minute bubbles
adhering to the side may generally be removed by closing the
mouth of the tube with the thumb, and allowing a small air-bubble
to rise in the tube, and thus to wash it out. After filling the
eudiometer entirely with mercury, and inverting it over the trough,
it will generally be found that the air-bubbles have been removed.

For the introduction of the gases, the eudiometer should be
placed in a slightly inclined position, being held by a support
attached to the mercurial trough (fig. 85), and the gas transferred

rig. S3.

from the tube in which it has been collected. The eudiometer is
now put in an absolutely vertical position, determined by a
plumb-line placed near it, and a thermometer suspended in close
proximity. It must then be left for at least half an hour, no one
being allowed to enter the room in the meantime. After the
expiration of this period, the operator enters the room, and, by
means of the telescope placed several feet from the mercury table,
carefully observes the height of the mercury in the tube, estimating
the tenths of a division with the eye, which can readily be done
after a' little practice. He next reads the thermometer with the
telescope, and finally the height of the mercury in the trough is read
off on the tube, for which purpose the trough must have glass sides.
The difference between these two numbers is- the length of the
column of mercury in the eudiometer, and has to be subtracted
from the reading of the barometer. It only remains to take the
height of the barometer. The most convenient form of instrument
for gas analysis is the syphon barometer, with the divisions etched

492

VOLUMETRIC ANALYSIS.

§ 94.

on the tube. This is placed on the mercury table, so that it may
be read by the telescope immediately after the measurements
in the eudiometer. There are two methods of numbering the
divisions on the barometer : in one the zero point is at or
near the bend of the tube, in which case the height of the
lower column must be subtracted
from that of the higher; in the other
the zero is placed near the middle of
the tube, so that the numbers have to
be added to obtain the actual height.
In cases of extreme accuracy, a correction
must be made for the temperature of the
barometer, which is determined by a ther-
mometer suspended in the open limb of the
instrument, and passing through a plug of
cotton wool. Just before observing the
height of the barometer, the bulb of the
thermometer is depressed for a moment
into the mercury in the open limb, thus
causing a movement of the mercurial
column, which overcomes any tendency
that it may have to adhere to the glass.

In every case the volume observed must
be reduced to the normal temperature and
pressure, in order to render the results
comparable. If the absolute volume is
required, the normal pressure of 760 in.m.
must be employed : but when comparative
volumes only are desired, the pressure of
1000 m.m. is generally adopted, as it
somewhat simplifies the calculation. In
the following formula for correction of the
volume of gases —

V1 = the correct volume.

V = the volume found in the table, and
corresponding to the observed height of
the mercury in the eudiometer, the error
of meniscus being, of course, included.

B = the height of the barometer (cor-
rected for temperature, if necessary) at
the time of measurement.

b = the difference between the height of the mercury in the
trough and in the eudiometer.

t = the temperature in centigrade degrees.

T = the tension of aqueous vapour in millimeters of mercury
at t°. This number is, of course, only employed when the gas is
saturated with moisture at the time of measurement.

§ 94. CORRECTIONS FOR TEMPERATURE AND PRESSURE. 493

Then

vl= Yx(E-ft-T)
760 x (1 + 0-003665^)'

when the pressure of 760 m.m. is considered the normal one ; or,

yi= Yx(B-fr-T)

1000x(l+0-003665f)'

when the normal pressure of 1 meter is adopted.

In cases where the temperature at measurement is below 0°
(which rarely happens), the factor 1 - 0'003665£ must be used.

Tables have been constructed containing the values of T; of
1000 x (1+0-0036650, and of 760 y (1+0-003665^), which
very much facilitate the numerous calculations required in this
branch of analysis* These will be found at the end of the book.

iiiiipiiipiiiiii'.

We shall now be in a position to examine the methods employed
in gas analysis. Some gases may be estimated directly ; that is,
they may be absorbed by certain reagents, the diminution of the
volume indicating the quantity of the gas present. Some are
determined indirectly; that is, by exploding them with other
gases, and measuring the quantities of the products. Some gases
may be estimated either directly or indirectly, according to the
circumstances under which they are found.

* Mr. Sutton will forward a copy of these Tables, printed separately for laboratory
use, to any one desiring them, on receipt of the necessary address.

494 VOLUMETRIC ANALYSIS. • § 96.

§95.

1. G-ASES ESTIMATED DIRECTLY.

A. Gases Absorbed by Crystallized Sodic Phosphate and Potassic

Hydrate :—

Hydrochloric acid,
Hydrobromic acid,
Hydriodic acid.

B. Gases Absorbed by Potassic Hydrate, and not by Crystallized

Sodic Phosphate:—

Carbonic anhydride,
Sulphurous anhydride,
Hydrosulphuric acid.

C. Gases Absorbed by neither Crystallized Sodic Phosphate nor

Potassic Hydrate:—

Oxygen,
Xitric oxide,
Carbonic oxide,

Hydrocarbons of the composition Cn H2n,
Hydrocarbons of the formula (Cn H2n+l)2,
Hydrocarbons of the formula Cn H2n-i-2,
except Marsh gas.

2. GASES ESTIMATED INDIRECTLY.

Hydrogen,
Carbonic oxide,
Marsh gas,
Methyl,

Ethylic hydride,
Ethyl,

Propylic hydride,
Butylic hydride,
Nitrogen.

DIRECT ESTIMATIONS.

Group A, containing- Hydrochloric, Hydrobromic, and
Hydriodic Acids.

§ 96. IN Bun sen's method the reagents for absorption are
generally used in the solid form, in the shape of bullets. To make
the bullets of sodic phosphate, the end of a piece of platinum wire,
of about one foot in length, is coiled up and fixed in the centre of
a, pistol-bullet mould. It is well to bend the handles of the mould,

§ 96. DIRECT ESTIMATIONS. 495

so that when it is closed the handles are in contact, and may be
fastened together by a piece of copper wire (tig. 86). The usual
practice is to place the platinum wire in the hole through which the
mould is filled ; but it is more convenient to file a small notch in
one of the faces of the open mould, and place the wire in the notch
before the mould is closed. In this manner the wire is not in the
way during the casting, and it is subsequently more easy to trim
the bullet. Some ordinary crystallized sodic phosphate is fused in
a platinum crucible (or better, in a small piece of wide glass tube,
closed at one end, and with a spout at the other, and held by
a copper-wire handle), and poured into the bullet mould (fig. 87).
When quite cold, the mould is first gently warmed in a gas-flame,
opened, and the bullet removed. If the warming of the mould is
omitted, the bullet is frequently broken in consequence of its
adhering to the metal. Some chemists recommend the use of sodic
sulphate instead of phosphate, which may be made into balls by
dipping the coiled end of a piece of platinum wire into the salt

ig. 86. Fig. 87.

fused in its water of crystallization. On removing the wire,
a small quantity of the salt will remain attached to the wire.
When this has solidified, it is again introduced for a moment
and a larger quantity will collect ; and this is repeated until the
ball is sufficiently large. The balls must be quite smooth, in
order to prevent the introduction of any air into the eudiometer.
When the bullets are made in a mould, it is necessary to remove
the short cylinder which is produced by the orifice through which
the fused salt has been poured.

In the estimation of these gases, it is necessary 'that they should
be perfectly dry. This may be attained by introducing a bullet of
fused calcic chloride. After the lapse of about an hour, the bullet
may be removed, the absorption tube placed in a vertical position,
with thermometer, etc., arranged for the reading, and left for
half an hour to assume the temperature of the air. When the
reading has been taken, one of the bullets of sodic phosphate or
sodic sulphate is depressed in the trough, wiped with the fingers

496

VOLUMETPJC ANALYSIS.

§ 97.

while under the mercury in order to remove any air that it might
have carried down with it, and introduced into the absorption tube,
which for this purpose is inclined and held in one hand, while
the bullet is passed into the tube with the other. Care must be
taken that the whole of the platinum wire is covered with mercury
while the bullet remains in the gas, otherwise there is a risk of
air entering the tube between the mercury and the wire (fig. 88).

After standing for an hour, the bullet is withdrawn from the
absorption tube. This must be done with some precaution, so as
to prevent any gas being removed from the tube. It is best done
by drawing down the bullet by a brisk movement of the wire, the
gas being detached from the bullet during the rapid descent of the
latter into the mercury. The bullet may then be more slowly
removed from the tube. As sodic phosphate and sodic sulphate
contain water of crystallization, and a corresponding proportion
of this is liberated for every equivalent of sodic chloride formed,
care must be taken that the
bullets are not too small, else
the water set free will soil the
sides of the eudiometer, especially
if there is a large volume of gas
to be absorbed. As a further
precaution, drive off some of the
water of crystallization before
casting the bullet. When the
bullet has been removed, the gas
must be dried as before with
calcic chloride and again measured.
If two or more of the gases are
present in the mixture to be
analyzed, the sodic phosphate ball
must be dissolved in water, and
the chlorine, bromine, and iodine
determined by the ordinary ana-
lytical methods. If this has to
be done, care must be taken
that the sodic phosphate employed is free from chlorine.

88.

Group B. Gases absorbed by Potassic Hydrate, but not by
Sodic Phosphate.

Carbonic anhydride, sulphuretted hydrogen, and
sulphurous anhydride.

§ 97. IF the gases occur singly, they are determined by means
of a bullet of caustic potash made in the same manner as the sodic
phosphate balls. The caustic potash employed should contain
sufficient water to render the bullets so soft that they may be

POTASH ABSORPTIONS. 497

marked with the nail when cold. Before use the balls must be
slightly moistened with water ; and if large quantities of gas have
to be absorbed, the bullet must be removed after some hours,
washed with water, and returned to the absorption tube. The
absorption may extend over twelve or eighteen hours. In order to
ascertain if it is completed, the potash ball is removed, washed,
again introduced, arid allowed to remain in contact with the gas
for about an hour. If no diminution of volume is observed the
operation is finished.

The following analysis of a mixture of air and carbonic anhydride
will serve to show the mode of recording the observations and the
methods of calculation required.

Analysis of a Mixture of Air and Carbonic Anhydride.

1. Gas Saturated with Moisture.

Height of mercury in trough . 171*8 m.m.

Height of mercury in absorption eudio-
meter . . . 89*0 m.m.

Column of mercury in tube, to be sub-

tracted from the height of barometer = b = 82-8 m.m.

Height of mercury in eudiometer 89 '0 m.m.

Correction for error of meniscus 0'8 m.m.

" 89*8m.m.

"Volume in table corresponding to 89 -8

m.m. . . . = V = 96-4

Temperature at which the reading was

made . . . = t = 12*2°

Height of barometer at time of obser-
vation . . . =B = 765-25 m.m.
Tension of aqueous vapour at 12 -2° = T = 10'6 m.m.

Vx(B-fr-T)
1000x(l + 0-003665/()
96-4 x (765-25 -82-8 -10-6) =
1000 x [1 + (0 003665 x 12*2)] ~

96-4x671-85
1000 x 1-044713"

log. 96-4 -1-98408
log. 671-85 = 2-82727

4-81135

log. (1000 x 1-044713) = 3-01900

1-79235 = log. 61-994 = V1
Corrected volume of aTF~and CO2 = V1 = 61*994.

K K

498 VOLUMETRIC ANALYSIS. § 97.

After absorption of carbonic anhydride by bullet of
potassic hydrate.

Gas Dry.

Height of mercury in trough . 172'0 m.m.

Height of mercury in absorption eudio-
meter . . . — 6 2 -5 m.m.

Column of mercury in eudiometer = I = 109 '5 m.m.

Height of mercury in eudiometer 62 '5 m.m.

Correction for error of meniscus 0*8 m.m.

63-3 m.m.

Volume in table corresponding to 6 3 '3

m.m. . . = V - 69-35

Temperature . . . = t = 10 '8°

Barometer . . . = B = 766*0 m.m.

yl= Vx(B-J)

1000 x (1+0-003665^)

69-35 x (766-0- 109-5)
1000 x [1 + (0-003665 x 10-8)]

69-35x656-5

1000x1-039582

log. 69-35 = 1-84105
log. 656-5 -2-81723

4-65828
log. (1000 x 1-039582) = 3-01686

1-64142= log. 43-795 = V1

Corrected volume of air = 43'795
Air + CO2 = 61 -994
Air =43-795

C02 = 18-199

61-994 : 18-199 : : 100 : x = percentage of CO2

_ 18-199 x 100 _
61-995

Percentage of CO2 in mixture of air and gas = 29 -355.

97. POTASH ABSOEPTIONS. 499

Gas Moist.

Height of mercury in trough . 174*0 m.m.

Height of mercury in eudiometer 98*0 m.rn.

Column of mercury in tube . = b= 76*0 m.m.

Height of mercury in eudiometer 98 '0 m.m.

Correction for error of meniscus 0*8 m.m.

98-8 m.m.

Volume in table, corresponding to 98 '8

m.m. . . . =V= 105-6

Temperature . . . = t = 12 '5°

Barometer . . . = B = 738*0 m.m,

Tension of aqueous vapour at 12 '5° = T = 10 '8 m.m.
Corrected volume of air and carbonic

anhydride . . . 65 '754

After absorption of CO2.
Gas Dry,

Height of mercury in trough . 173*0 m.rn.

Height of mercury in absorption eudio-
meter ... 70-3 m.m.

Column of mercury in tube . =1= 102*7 m.m.

Height of mercury in eudiometer 70*3 m.m.

Correction for error of meniscus 0*8 m.m.,

71*1 m.m.

Volume in table corresponding to 71*1

m.m. . . . =V= 77*4

Temperature . . . =£=14*1°

Barometer . . . =B = 733*5 m.m.

Corrected volume of air = 46*425

Air + CO2 = 65*754

Air = 46-425

CO2 = 19*329
65*754 : 19*329 :: 100 : 22*396.

i. n.

Percentage of CO2 in mixture of air and gas 29*335 25'396

If either sulphurous anhydride or sulphuretted hydrogen occurs
together with carbonic anhydride, one or two modes of operation
may be followed. Sulphuretted hydrogen and sulphurous anhydride
are absorbed by manganic peroxide and by ferric oxide, which
may be formed into bullets in the following manner. The oxides

K K 2

500 VOLUMETRIC ANALYSIS. § 97.

are made into a paste with water, and introduced into a bullet
mould, the interior of which has been oiled, and containing the
coiled end of a piece of platinum wire ; the mould is then placed
on a sand bath till the ball is dry. The oxides will now be left in
a porous condition, which would be inadmissible for the purpose
to which they are to be applied ; the balls are therefore moistened
several times with a sirupy solution of phosphoric acid, care being
taken that they do not become too soft, so as to render it difficult
to introduce them into the eudiometer. After the sulphuretted
hydrogen or sulphurous anhydride has been removed, the gas
should be dried by means of calcic chloride. 'the carbonic
anhydride can now be determined by means of the bullet of
potassic hydrate.

The second method is to absorb the two gases by means of
a ball of potassic hydrate containing water, but not moistened on
the exterior, then to dissolve the bullet in dilute acetic acid which
has been previously boiled and allowed to cool without access of
air, and to determine the amount of sulphuretted hydrogen or
sulphurous anhydride by means of a standard solution of iodine.
This process is especially applicable when rather small quantities of
sulphuretted hydrogen have to be estimated.

Group C. This group contains the gases not absorbed by Potassic
Hydrate or Sodic Phosphate, and consists of Oxygen, Nitric
Oxide, Carbonic Oxide*, Hydrocarbons of the formulae CnH?n
(Cn2H-n+l)2, and CnH'2n+', except Marsh gas.

Oxygen was formerly determined by means of a ball of
phosphorus, but it is difficult subsequently to free the gas from
the phosphorous acid produced, and which exerts some tension, and
so vitiates the results ; besides which, the presence of some gases
interferes with the absorption of oxygen by phosphorus ; and if
any potassic hydrate remains on the side of the tube, from the
previous absorption of carbonic anhydride, there is a possibility of
the formation of phosphoretted hydrogen, which would, of course,
vitiate the analysis. A more convenient reagent is a freshly
prepared alkaline solution of potassic pyrogallate introduced into
the gas in a bullet of papier-mache. The balls of papier-mache
are made by macerating filter-paper in water, and forcing as much
of it as possible into a bullet mould into which the end of a piece
of platinum wire has been introduced. In order to keep the mould
from opening while it is being filled, it is well to tie the handles
together with a piece of string or wire, and when charged it is
placed on a sand bath. After the mass is dry the mould may be
Opened, when a large absorbent bullet will have been produced.
The absorption of oxygen by the alkaline pyrogallate is not very
rapid, and it may be necessary to remove the ball once or twice
during the operation, and to charge it freshly.

§97. OXYGEN ABSORPTION. 501

Nitric oxide cannot be readily absorbed in an ordinary
absorption tube ; it may, however, be converted into nitrous
anhydride and nitric peroxide by addition of excess of oxygen,
absorbing the oxygen compounds with potassic hydrate, and the
excess of oxygen by potassic pyrogallate. The diminution of the
volume will give the quantity of nitric oxide. This process is
quite successful when the nitric oxide is mixed with olefiant gas
and ethylic hydride, but it is possible that other hydrocarbons
might be acted on by the nitrous compounds.

Carbonic oxide may be absorbed by two reagents. If carbonic
anhydride and oxygen be present they must be absorbed in the
usual manner, and afterwards a papier-mache ball saturated with
a concentrated solution of cuprous chloride in dilute hydrochloric
acid introduced. A ball of caustic potash is subsequently employed
to remove the hydrochloric acid given off by the previous reagent,
and to dry the ' gas. Carbonic oxide may also be absorbed by
introducing a ball of potassic hydrate, placing the absorption tube
in a beaker of mercury, and heating the whole in a water bath to
100° for 60 hours. The carbonic oxide is thus converted into
potassic formate and entirely absorbed.

Olefiant Gas and other Hydrocarbons of the formula
CnH2n are absorbed by Nordhausen sulphuric acid, to which an
additional quantity of sulphuric anhydride has been added. Such
an acid may be obtained by heating some Nordhausen acid in
a retort connected with a receiver containing a small quantity of
the same acid. This liquid is introduced into the gas by means of
a dry coke bullet. These bullets are made by filling the mould,
into which the usual platinum wire has been placed, with a mixture
of equal weights of finely powdered coke and bituminous coal.
The mould is then heated as rapidly as possible to a bright red
heat, and opened after cooling ; a hard porous ball will have been
produced, which may be employed for many different reagents.
It is sometimes difficult to obtain the proper mixture of coal and
coke, but when once prepared, the bullets may be made with the
greatest ease and rapidity. The olefiant gas will be absorbed by the
sulphuric acid in about an hour, though they may be left in contact
for about two hours with advantage. If, on removing the bullet,
it still fumes strongly in the air, it may be assumed that the
absorption is complete. The gas now contains sulphurous, sulphuric,
and perhaps carbonic anhydrides ; these may be removed by
a manganic peroxide ball, followed by one of potassic hydrate, or
the former may be omitted, the caustic potash alone being used.
The various members of the CnH2n group cannot be separated
directly, but by the indirect method of analysis their relative
quantities in a mixture may be determined.

The hydrocarbons (CnH2n + 1)2 and CnH2n + 2 may be absorbed
by absolute alcohol, some of which is introduced into the
absorption tube, and agitated for a short time with the gas.

502 VOLUMETRIC ANALYSIS. § 98.

Correction lias then to be made for the weight of the column of
alcohol on the surface of the mercury, and for the tension of the
alcohol vapour. This method only gives approximate results, and
can only be employed in the presence of gases very slightly soluble
in alcohol.

The time required in the different processes of absorption just
described is considerable ; perhaps it might be shortened by
surrounding the absorption eudiometer with a wider tube, similar
to the external tube of a Liebig's condenser, and through which
a current of water is maintained. By means of a thermometer in
the space between the tubes the temperature of the gas would be
known, and the readings might be taken two or three minutes
after the withdrawal of the reagents. Besides this advantage, the
great precaution necessary for maintaining a constant temperature
in the room might be dispensed with. A few -experiments made
some years ago in this direction gave satisfactory results.

INDIRECT DETERMINATIONS.

§ 98. GASES which are not absorbed by any reagents that are
applicable in eudiometers over mercury, must be determined in an
indirect manner, by exploding them with other gases, and noting
either the change of volume or the quantity of their products
of decomposition; or lastly, as is most frequently the case, by
a combination of these two methods. Thus, for example, oxygen
may be determined by exploding with excess of hydrogen, and
observing the contraction ; hydrogen may be estimated by exploding
with excess of oxygen, and measuring the contraction ; and marsh
gas by exploding with oxygen, measuring the contraction, and also
the quantity of carbonic anhydride generated.

The operation is conducted in the following manner : — -The long
eudiometer furnished with explosive wires is filled with mercury
(after a drop of water has been placed at the top of the tube by
means of an iron wire, as before described), and some of the gas to
be analyzed is introduced from the absorption eudiometer. This
gas is then measured with the usual precautions, and an excess of
oxygen or hydrogen (as the case may be) introduced. These gases
may be passed into the eudiometer directly from the apparatus in
which they are prepared ; or they may be previously collected in
lipped tubes of the form of absorption tubes, so as to be always
ready for use.

For the preparation of the oxygen a bulb is used, which is blown
at the closed end of a piece of combustion tube. The bulb is about
half filled with dry powdered potassic chlorate, the neck drawn out,
and bent to form a delivery tube. The chlorate is fused, and the
gas allowed to escape for some time to ensure the expulsion of the
atmospheric air; the end of the delivery tube is then brought
under the orifice of the eudiometer, and the necessary quantity of

§ 98.

INDIRECT DETERMINATIONS.

503

gas admitted. When it is desired to prepare the oxygen beforehand,
it may be collected directly from the bulb ; or, another method to
obtain the gas free from air may be adopted by those who are
provided with the necessary appliances. This is, to connect a bulb
containing potassic chlorate with a Sprengel's mercurial air-pump,
and, after heating the chlorate to fusion, to produce a vacuum in
the apparatus. The chlorate may be again heated until oxygen
begins to pass through the mercury at the end of the Sprengel, the
heat then withdrawn, and a vacuum again obtained. The chlorate
is once more heated, and the oxygen collected at the bottom of
the Sprengel. Of course the usual precautions for obtaning an
air-tight joint between the bulb and the Sprengel must be taken,
such as surrounding the caoutchouc connector with a tube filled
with mercury.

The hydrogen for these
experiments must be pre-
pared by electrolysis, since
that from other sources is
liable to contamination with
impurities which would
vitiate the analysis. The
apparatus employed by
Bunsen for this purpose
(fig. 89) consists of a glass
tube, closed at the lower
end, and with a funnel at
the other, into which a de-
livery tube is ground, the
funnel acting as a water-
joint. A platinum wire is
sealed into the lower part of
the tube ; and near the
upper end another wire,
with a platinum plate at-
tached, is fused into the
glass. Some amalgam of
zinc is placed into the tube
so as to cover the lower
platinum wire, and the ap-
paratus filled nearly to the neck with water, acidulated with
sulphuric acid. On connecting the platinum wires with a battery
of two or three cells, the upper wire being made the negative
electrode, pure hydrogen is evolved from the platinum plate, and,
after the expulsion of the air, may be at once passed into the
eudiometer, or, if preferred, collected in tubes for future use,
Unfortunately, in this form of apparatus, the zinc amalgam soon
becomes covered with a saturated solution of zinc sulphate, which
puts a stop to the electrolysis. In order to remove this layer,

Fig. 89.

504

VOLUMETRIC ANALYSIS.

§ 93.

Bunsen has a tube fused into the apparatus at the surface of the
amalgam ; this is bent upwards parallel to the larger tube, and
curved downwards just below the level of the funnel. The end
of the tube is closed with a caoutchouc stopper. On removing the
stopper, and pouring fresh acid into the funnel, the saturated liquid
is expelled.

Another form of apparatus for preparing electrolytic hydrogen
may readily be constructed. A six-ounce wide-mouth bottle is
fitted with a good cork, or better, with a caoutchouc stopper. In
the stopper four tubes are fitted (fig. 90). The first is a delivery
tube, provided with a U-tube, containing broken glass and sulphuric
acid, to conduct the hydrogen to the mercurial trough. The second
tube, about 5 centimeters long, and filled with mercury, has fused
into its lower end a piece of platinum wire carrying a strip of

foil, or the wire may be
simply flattened. The third
tube passes nearly to the
bottom of the bottle, the
portion above the cork is
bent twice at right angles,
and cut off, so that the
open end is a little above
the level of the shoulder
of the bottle ; a piece of
caoutchouc tube, closed by
a compression cock, is fitted
to the end of the tube.
The fourth tube is a piece
of combustion tube about
30 centimeters in length,
and which may with ad-
vantage be formed into a
funnel at the top. This
tube reaches about one-third
down the bottle, and inside
it is placed a narrower glass
tube, attached at its lower
end by a piece of caoutchouc
connector to a rod of amalgamated zinc. The tube is filled with
mercury to enable the operator readily to connect the zinc with
the battery ; some zinc amalgam is placed at the bottom of the
bottle ; and dilute sulphuric acid is poured in through the wide-
tube until the bottle is nearly filled with liquid. To use the
apparatus, the delivery tube is dipped into mercury, the wire from
the positive pole of the battery placed into the mercury in the
tube to which the zinc is attached, and the negative pole connected
by means of mercury with the platinum plate. The current,
instead of passing between the amalgam at the bottom of the

fig. 90.

98.

EXPLOSION OF GASES.

505

vessel and the platinum plate, as in Bun sen's apparatus, travels
from the rod of amalgamated zinc to the platinum, consequently
the current continues to pass until nearly the whole of the liquid
in the bottle has become saturated with zinc sulphate. As soon as
the hydrogen is evolved, of course a column of acid is raised in
the funnel until the pressure is sufficient to force the gas through
the mercury in which the delivery tube is placed. Care must be
taken that the quantity of acid in the bottle is sufficient to prevent
escape of gas through the funnel tube, and also that the delivery
tube does not pass too deeply into the mercury so as to cause the
overflow of the acid. When the acid is exhausted, the compression
cock on the bent tube is opened and fresh acid poured into the
funnel ; the dense zinc sulphate solution is thus replaced by the
lighter liquid, and the apparatus is again ready for use.

A very convenient apparatus for transferring oxygen and
hydrogen into eudiometers is a gas pipette, figured and described
(fig. 62, page 423).

It is necessary in all cases to add an excess of the oxygen
or hydrogen before exploding, and it is well to be able to measure
approximately the amount added without going through the whole
of the calculations. This may be conveniently done by making
a rough calibration of the eudiometer in the following manner : —
The tube is filled with mercury, a volume of air introduced into
it from a small tube, and the amount of the depression of the
mercury noted; a second volume is now passed up, a further
depression will be produced, but less in extent than the previous
one, in consequence of the shorter column of mercury in the tube.
This is repeated until the eudiometer is filled, and by means of a
table constructed from these observations, but without taking any
notice of the variations of thermometer or barometer, the operator
can introduce the requisite quantity of gas. It may be convenient
to make this calibration when the eudiometer is inclined in the
support, and also when placed perpendicularly, so that the gas
may be introduced when the tube is in either position. A table
like the following is thus obtained : —

Measures.
1

2
3
4
5

7
&c.

DIVISIONS.

Tube
Inclined.

88
100
109
&c.

Tube
Perpendicular.

87
102
116

128
138
&c.

In explosions of hydrocarbons with oxygen, it is necessary to

506 VOLUMETRIC ANALYSIS. § 98.

have a considerable excess of the latter gas in order to moderate
the violence of the explosion. The same object may be attained
by diluting the gas with atmospheric air, but it is found that
sufficient oxygen serves equally well. If the gas contains nitrogen,
it is necessary subsequently to explode the residual gas with
hydrogen ; and if oxygen only has been used for diluting the
gas, a very large quantity of hydrogen must be added, which
may augment the volume in the eudiometer to an inconvenient
extent. When atmospheric air has been employed, this incon-
venience is avoided. After the introduction of the oxygen, the
eudiometer is restored to its vertical position, allowed to stand
for an hour, and the volume read off.

The determination of the quantity of oxygen which must be
added to combustible gases so as to prevent the explosion from being
too violent, and at the same time to ensure complete combustion,
has been made the subject of experiment. When the gases
before explosion are under a pressure equal to about half that
of the atmosphere, the following proportions of the gases must
be employed : —

Volume of Volume of

Combustible Gas. Oxygen.

Hydrogen .... 1 T5

Carbonic oxide ... 1 1-5

Marsh gas .... 1 5

Gases containing two atoms of

carbon in the molecule, as

Methyl, C2H6 ... 1 10

Gases containing three atoms of

carbon in the molecule, as

Propylic hydride, C3H8 .1 18

Gases containing four atoms of

carbon in the molecule, as

Ethyl, OH10 ... 1 25

In cases of mixtures of two or more combustible gases,
proportionate quantities of oxygen must be introduced.

At the time of the explosion, it is necessary that the
eudiometer should be carefully closed to prevent the loss
of gas by the sudden expansion. For this purpose a
thick plate of caoutchouc, three or four centimeters wide, is
cemented on a piece of cork by means of marine glue, or some
similar substance, and the lower surface of the cork cut so as to lie
firmly at the bottom of the mercurial trough (fig. 91). It is, how-
ever, preferable to have the caoutchouc firmly fixed in the trough.
As the mercury does not adhere to the caoutchouc, there is
some risk of air entering the eudiometer after the explosion ;
this is obviated by rubbing the plate with some solution of
corrosive sublimate before introducing it into the mercury, which

§ 98.

EXPLOSION OF GASES.

507

causes the metal to wet the caoutchouc and removes all air from
its surface. When the caoutchouc is not fixed in the trough, the
treatment with the corrosive sublimate has to be repeated before
every experiment, and this soils the surface of the mercury to an
inconvenient extent. The cushion is next depressed to the bottom
of the trough, and the eudiometer placed on it and firmly held
down (fig. 92). If this is done with the hands, the tube must
be held by that portion containing the mercury, for it is found
that when eudiometers burst (which, however, only happens when
some precaution has been neglected)
they invariably give way just at the
level of the mercury within the tube,
•and serious accidents might occur if
the hands were at this point. The
cause of the fracture at this point is
the following : — Though the gas is at
a pressure below that of the atmosphere
before the explosion, yet at the instant
of the passage of the spark, the ex-
pansion of the gas at the top of the
tube condenses the layer just below it ;
this 011 exploding increases the density
of the gas further down the tube, and
by the time the ignition is communicated
to the lowest quantity of gas, it may
be at a pressure far above that of the
atmosphere. It may be thought that
the explosion is so instantaneous that
this explanation is merely theoretical ;
but on exploding along column of gas, the
time required for the complete ignition
is quite perceptible, and sometimes the
flash may be observed to be more
brilliant at the surface of the mercury.
Some experimenters prefer to fix the
•eudiometer by means of an arm from
a vertical stand, the arm being hollowed
out on the under side, and the cavity
lined with cork.

If. a large quantity of incombustible
gas is present, the inflammability of

the mixture may be so much reduced that either the explosion
does not take place at all, or, what may be worse, only a partial
combustion ensues. To obviate this, some explosive mixture of
oxygen and hydrogen, obtained by the electrolysis of water,
must be introduced. The apparatus used by Bun sen for this
purpose is shown in fig. 93. The tube in which the electrolysis
takes place is surrounded by a cylinder containing alcohol, in order

Fig. 92.

508

VOLUMETRIC ANALYSIS.

98.

to prevent the heating of the liquid. A convenient apparatus-
for the preparation of this gas is made by blowing a bulb of
about four centimeters in diameter on the end of a piece of narrow
glass tube, sealing two pieces of flattened platinum wire into
opposite sides of the globe, and bending the tube so as to form
a delivery tube. Dilute sulphuric acid, containing about one volume-
of acid to twenty of water, is introduced into the globe, either
before bending the tube, by means of a funnel with a fine long;
stem, or, after the bending, by warming the apparatus, and

plunging the tube into-
the acid. Care must be
taken that the acid is-
dilute, and that the
battery is not too strong,
in order to avoid the
formation of ozone, which
would attack the mer-
cury, causing the sides
of the eudiometer to be
soiled, at the same time
producing a gas too rich
in hydrogen.

The spark necessary
to effect the explosion
may be obtained from
several sources. An ordi-
nary electrical machine
or electrophorus may be
used, but these are liable
to get out of order by
damp. Bunsen uses a
porcelain tube, which is
rubbed with a silk rub-
ber, coated with electrical
amalgam ; by means of
Fig. 93. this a small Leyden jar-

is charged. A still more

convenient apparatus is an induction coil large enough to produce
a spark of half an inch in length.

After the explosion, the eudiometer is slightly raised from the
caoutchouc plate to allow the entrance of mercury. When no more
mercury rushes in, the tube is removed from the caoutchouc plate,
placed in a perpendicular position, and allowed to remain for at
least an hour before reading. After measuring the contraction, it is-
generally necessary to absorb the carbonic anhydride formed by the
combustion by means of a potash ball, in the way previously
described. In some rare instances the amount of water produced
in the explosion with oxygen must be measured. If this has to be

METHODS OF CALCULATION.

509

done, the eudiometer, the mercury, the original gas, and the oxygen
must all be carefully dried. After the explosion, the eudiometer
is transferred to a circular glass vessel containing mercury, and
attached to an iron-wire support, by which the entire arrangement
can be suspended in a glass tube adapted to the top of an iron
boiler, from which a rapid current of steam may be passed through
the glass tube, so as to heat the eudiometer and mercury to an
uniform temperature of 100°. From the measurements obtained at
this temperature the amount of water produced may be calculated.
If three combustible gases are present, the only data required for
calculation are, the original volume of the gas, the contraction on
explosion, and the amount of carbonic anhydride generated. When
the original gas contains nitrogen, the residue after explosion with
excess of oxygen consists of a mixture of oxygen and nitrogen. To
this an excess of hydrogen is added, and the mixture exploded ; the
contraction thus produced divided by 3 gives the amount of oxygen
in the residual gas, and the nitrogen is found by difference.

It is obvious that, by subtracting the quantity of residual oxygen,
thus determined by explosion with hydrogen, from the amount
added, in the first instance, to the combustible gas, the volume of
oxygen consumed in the explosion may be obtained. Some chemists
prefer to employ this number instead of the contraction as one of
the data for the calculation.

We must now glance at the mode of calculation to be employed
for obtaining the percentage composition of a gas from the numbers
arrived at by the experimental observations.

The following table shows the relations existing between the
volume of the more important combustible gases and the products
of the explosion : — -

Name of Gas.

Volume of
Combustible
Gas.

Volume of
Oxygen
Consumed.

Contraction
after
Explosion.

"o S'St*

ill!

2<31&

Hydrogen, H

0-5

1-5

Carbonic Oxide, CO

0-5

Methylic Hydride, CH3H .

Acetylene, C2H2 .

2-5

1-5

Olefiant Gas, C2H4 . ' .

Methyl, CH3, CH3

3-5

2-5

Ethylic Hydride, C2rf5H

3-5

2-5

Propylene, C3H6 .

4-5

2-5

Propylic Hydride, C3H7H .

Butylene, C4H8 .

Ethyl, C2H5, C2H5

6-5

3-5

Butylic Hydride, C4H9H

6-5

3-5

510 VOLUMETRIC ANALYSIS. § 98.

As an example, we may take a mixture of hydrogen, carbonic
oxide, and marsh gas, which gases may be designated by x, y, and z
respectively. The original volume of gas may be represented by A,
the contraction by C, and the amount of carbonic anhydride by D.

A will, of course, be made up of the three components, or

A = x + y + z.

C will be composed as follows : — When a mixture of hydrogen and
oxygen is exploded, the gas entirely disappears. One volume of
hydrogen combining with half a volume of oxygen, the contraction
will be 1J times the quantity "of hydrogen present, or 1 J.r. In the
case of carbonic oxide, 1 volume of this gas uniting with half its
volume of oxygen produces 1 volume of carbonic anhydride, so
the contraction due to the carbonic oxide will be half its volume,
or Jv/. Lastly, 1 volume of marsh gas combining with 2 volumes of
oxygen generates 1 volume of carbonic anhydride, so the contraction
in this case will be twice its volume, or 2z. Thus we have —

Since carbonic oxide on combustion forms its own volume of
carbonic anhydride, the amount produced by the quantity present
in the mixture will be y. Marsh gas also generates its own volume
of carbonic anhydride, so the quantity corresponding to the marsh
gas in the mixture will be z. Therefore

i>=y+z.

It now remains to calculate the values of x, y, and z from the
experimental numbers A, C, and D, which is done by the help
of the following equations : —

To find x—

x+y+z= A ,.

x = A - P .

For y we have— ^ + 4, == 4I) ?

= 3 A - 3D ,

3A-2C + D '

y = -

The value of z is thus found —

• 3A-2C + D

~3 ' °r

2C-3A + 2D m

§ 98. METHODS OF CALCULATION. 511

By replacing the letters A, C, and D by the numbers obtained
by experiment, the quantities of the three constituents in the
volume A may easily be calculated by the three formulae —

x = A — D = hydrogen ,

3A-2C + D

2/= - • — o — •*" = carbonic oxide ,

2C-3A + 2D
z— — — o — — = marsh gas .

The percentage composition is, of course, obtained by the simple
proportions —

A : x : : 100 : per-cent. of hydrogen ,

A : y : : 100 : per-cent. of carbonic oxide,

A : z : : 100 : per-cent. of marsh gas .

If the gas had contained nitrogen, it would have been determined
by exploding the residual gas, after the removal of the carbonic
anhydride, with excess of hydrogen. The contraction observedr
divided by 3, would give the volume of oxygen in the residue, and
this deducted from the residue, would give the amount of nitrogen.
If A again represents the original gas, and n the amount of nitrogen
it contains, the expression A — n would have to be substituted for
A in the above equations.

It may be as well to develop the formula for obtaining the same
results by observing the volume of oxygen consumed instead of the
contraction. If B represent the quantity of oxygen, we shall have

the values of A and D remaining as before, x = A - D.
z is thus found —

3z = 2B - A , or

x + y + z =

2B-A

For y —

? _3D-2B + A

512 VOLUMETEIC ANALYSIS. § 98.

Thus we have —

x = A-D

3D-2B + A

y= 3

2B-A

Having thus shown the mode of calculation of the formulae, it
will be well to give some examples of the formulae employed in
some of the cases which most frequently present themselves in gas
analysis. In all cases —

A = original mixture ,

C =sz contraction ,

D = carbonic anhydride produced.

1. Hydrogen and Nitrogen.

Excess of oxygen is added, and the contraction on explosion
-observed : —

_2C
= 3 '

3A-2C

y = - - , or A - x .

2. Carbonic Oxide and Nitrogen.

The gas is exploded with excess of oxygen, and the amount of
.carbonic anhydride produced is estimated : —

3. Hydrogen, Carbonic Oxide, and Nitrogen.

In this case the contraction and the quantity of carbonic
.anhydride are measured : —

2C-D

3A-2C-2D

98. METHODS OF CALCULATION. 513

4. Hydrogen, Marsh Gas, and Nitrogen.

2C-4D
--

3A-2C + D

-- ~

Carbonic Oxide, Marsh Gas, and Nitrogen,
4D-2C

3
2C-D •

C. Hydrogen, Methyl (or Ethylic Hydride), and
Xitrogen.

H = ar; C2H6 = y ; N-=&
4C-5D

3A-2C + D
3

7. Carbonic Oxide, Methyl (or Ethylic Hydride),
and Nitrogen.

5D - 4C

2C-D

3A - 4D + 2G
3

L L

514 VOLUMETRIC ANALYSIS. § 98.

8. Hydrogen, Carbonic Oxide, and Marsh Gas.

3A-2C + D

2C-3A + 2D

9. Hydrogen, Carbonic Oxide, and Ethylic Hydride
(or Methyl).

3A + 2C-4D

~~6~
3A-2C + D

10. Carbonic Oxide, Marsh Gas, and Ethylic Hydride
(or Methyl).

C0=ar; CH4 = // ; C2H6 = ::.

3A-2C + D
x=- -5-

3A + 2C-4D

11. Hydrogen, Marsh Gas, and Acetylene.
H = x • CH4 = y ; C2H2 = ::.

5A-2C -D

a?= - g - '

?/ = 2C-3A,
D-2C + 3A
2 '

12. Hydrogen, Marsh Gas, and Ethylic Hydride

(or Methyl).
H = x • CH4 = y ; C2HG = z.

This mixture cannot be analyzed by indirect determination, since
a mixture of two volumes of hydrogen with two volumes of ethylic

§98. METHODS OF CALCULATION. 515

hydride (or methyl) has the same composition as four volumes of
marsh as —

and, consequently, would give rise to the same products on
combustion with oxygen as pure marsh gas —

C2H° + H2 + 0s = 2C02 + 40H2 ;

In this case it is necessary to estimate by direct determination the
ethylic hydride (or methyl) in a separate portion of the gas by
absorption with alcohol, another quantity of the mixture being
exploded with oxygen, and the amount of carbonic anhydride pro-
duced and measured. If the quantity absorbed by alcohol =E, then

x = A - 1) + E ,

13. Hydrogen, Carbonic Oxide, Propylic Hydride,

3A + 4C-5D
— 9 —

3A-2C + D

?/= —3 >

2C-3A + 2D

~9~ ~-

14. Carbonic Oxide, Marsh Gas, and Propylic Hydride,

3A-2C + D
3A + 4C-5D
_Dj-A

15. Carbonic Oxide, Ethylic Hydride (or Methyl),

and Propylic Hydride.
CO = x ; C2H6 = y ; C3HS = z.
3A-2C + D

x= ~ 3 '

3A + 4C-5D

y«- -3 '

4D-3A - 2C

L L 2

516 VOLUMETRIC ANALYSIS. § 98.

16. Marsh Gas, Ethylic Hydride (or Methyl), and
Propylic Hydride.

= x ; C2H° = y ; C3H8 = z.

As a mixture of two volumes of marsh gas and two of propylic
hydride has the same composition as four of ethylic hydride (or
methyl) —

CH4 + C3H8 = 2C2H6,

the volume absorbed by alcohol, and which consists of ethylic
hydride (or methyl) and propylic hydride, must be determined,
and another portion of the gas exploded, and the contraction
measured. If E represents the volume absorbed —

a; = A-E,

y = 4A - 2C + 2E ,
&W2C-4A-E.

17. Hydrogen, Carbonic Oxide, and Ethyl (or Butylic

Hydride).

A + 2C-2D

-v -'

3A-2C+D

y= -y- -,

2C + 2D-3A

18. Nitrogen, Hydrogen, Carbonic Oxide, Ethylic
Hydride (or Methyl), and Butylic Hy-dride (or Ethyl).

N = »; !! = «;; C0=>; C2H5 = // ; C4H10 = •:.

In one portion of the gas the ethylic hydride (or methyl) and
the butylic hydride (or ethyl) are absorbed by alcohol ; the amount
absorbed = E.

A second portion of the original gas is mixed with oxygen and
exploded, the amount of contraction and of carbonic anhydride
being measured.

The residue nowr contains the nitrogen and the excess of oxygen;
to this an excess of hydrogen is added, the mixture exploded, and
the contraction measured. From this the quantity of nitrogen is
thus obtained. *Let —

G = excess of oxygen and nitrogen,
v = excess of oxygen,
u -— nitrogen,
C' = contraction on explosion with hydrogen.

99. IMPROVED GAS APPARATUS. 517

Then—

G = v + n ,

3G-C'

3 "'

From these data the composition of the mixture can be
determined —

2C - D - 3E

W = — —

3
_3A-2C-2D + 12E-3n

_ 2C - 3A + '2P-6E + 3K
6

MODIFICATIONS AND IMPROVEMENTS UPON THE
FOREGOING^ PROCESSES.

§ 99. IN the method of gas analysis that we have been consider-
ing, the calculations of results are somewhat lengthy, as will be
seen by a reference to the example given of the analysis of a
mixture of air and carbonic anhydride (page 497). Besides this, the
operations must be conducted in a room of uniform temperature,
and considerable time allowed to elapse between the manipulation
and the readings in order to allow the eudiometers to acquire the
temperature of the surrounding air ; and, lastly, the absorption of
gases by solid reagents is slow. These disadvantages are to a
great extent counterbalanced by the simplicity of the apparatus,
and of the manipulation.

From time to time various chemists have proposed methods by
which the operations are much hastened and facilitated, and the
calculations shortened. It will be necessary to mention a few of
these processes, which, however, require special forms of apparatus.

Williamson and Russell have described (Proceeding* of the
Royal Society, ix. 218) an apparatus, by means of which the
gases in the eudiometers are measured under a constant pressure,,,
the correction for temperature being eliminated by varying the
column of mercury in the tube so as to compensate for the alteration
of volume observed in a tube containing a standard volume of moist
air. In this case solid reagents were employed in the eudiometers.

518 VOLUMETRIC ANALYSIS. § 99.

In 1864 they published (/. C. S. xvii. 238) a further develop-
ment of this method, in which the absorptions were conducted in
a separate laboratory vessel, by which means the reagents could be
employed in a pasty condition and extended over a large surface.

And in 1868 Russell improved the apparatus, so that liquid
reagents could be used in the eudiometers, and the analysis rapidly
executed. A description of this last form of instrument may be
found in /. 0. S. xxi. 128.

The gutta-percha mercury trough employed is provided with
a deep well, into which the eudiometer can be depressed to any
required extent, and on the surface of the mercury a wide glass
cylinder, open at both ends and filled with water, is placed. The
eudiometer containing the gas to be examined is suspended within
the cylinder of water by means of a steel rod passing through
a socket attached to a stout standard firmly fixed to the table. In
a similar manner, a tube containing moist air is placed by the side
ef the eudiometer. The clamp supporting this latter tube is
provided with two horizontal plates of steel, at which the column
of the mercury is read off. When a volume of gas has to be
measured, the pressure tube containing the moist air is raised or
lowered, by means of an ingeniously .contrived fine adjustment,
until the mercury stands very nearly at the level of one of the
horizontal steel plates. The eudiometer is next raised or lowered
until the column of mercury within it is at the same level. The
final adjustment to bring the top of the meniscus exactly to the
lower edge of the steel bar is effected by sliding a closed wide glass
tube into the mercury trough. Thus we have two volumes of gas
under the same pressure and temperature, and both saturated with
moisture. If the temperature of the water in the cylinder increased,
there would be a depression of the columns in both tubes ; but by
lowering the tubes, and thus increasing the pressure until the
volume of air in the pressure tube was the same as before, it would
be found that the gas in the eudiometer Avas restored to the original
volume. Again, if the barometric pressure increased, the volumes
of the gases would be diminished ; but, by raising the tubes to the
necessary extent, the previous volumes would be obtained. There-
fore, in an analysis, it is only necessary to measure the gas at
a pressure equal to that which is required to maintain the volume
of moist air in the pressure tube constant. The reagents are
introduced into the eudiometer in the liquid state by means of
a small syringe made of a piece of glass tube about one-eighth of
an inch in diameter. For this purpose the eudiometer is raised
until its open end is just below the surface of the mercury, and
the syringe, which is curved upwards at the point, is depressed in
the trough, passed below the edge of the water-cylinder, and the
extremity of the syringe introduced into the eudiometer. When
a sufficient quantity of the liquid has been injected, the eudiometer
is lowered and again raised, so as to moisten the sides of the tube

with the liquid, and thus hasten the absorption. Ten minutes was
found to be a sufficient time for the absorption of carlxmic
anhydride when mixed with air.

To remove the liquid reagent, a ball of moistened cotton wool is
employed. The ball is made in the following manner : — A piece
of steel wire is bent into a loop at one end, and some cotton wool
tightly wrapped round it. It is then dipped in water and squeezed
with the hand under the liquid until the air is removed. The end
of the steel wire is next passed through a piece of glass tube,
curved near one end, and the cotton ball drawn against the curved
extremity of the tube. The ball, saturated with water, is now
depressed in the mercury trough, and, after as much of the water
as possible has been squeezed out of it, it is passed below the
eudiometer, and, by pushing the wire, the ball is brought to the
surface of the mercury in the eudiometer and rapidly absorbs all
the liquid reagent, leaving the meniscus clean. The ball is removed
with a slight jerk, and gas is thus prevented from adhering to it.
It is found that this mode of removing the liquid can be used
without fear of altering the volume of the gas in the eudiometer.

Carbonic anhydride may be absorbed by a solution of potassic
hydrate, and oxygen by mfans of potassic hydrate and pyrogallic
acid. The determination of ethylene is best effected by means of
fuming sulphuric acid on a coke ball, water and dilute potassic
hydrate being subsequently introduced and removed by the ball of
cotton wool.

Doubtless this mode of using the liquid reagents might be
employed with advantage in the ordinary process of analysis to
diminish the time necessary for the absorption of the gases. By
this process of Russell's the calculations are much shortened
and facilitated, the volumes read off being comparable among
themselves ; this will be seen by an example, taken from the
original memoir, of the determination of oxygen in air —

Volume in Table

corresponding

to reading.

Volume of air taken . . . ISO'S 132 '15

Volume after absorption of oxygenl

by potassic hydrate and pyro- - 103-5 104*46
gallic acid . . . . j
132-15
104-46

'2 1 -6 9 volumes of oxygen in 132 '15 of air.
132*15 : 27'69 : : 100 : 20 '953 percentage of oxygen in air.

Russell has also employed his apparatus for the analysis of
carbonates (/. C. S. [x.s.] vi. 310). For this purpose he adapted
a graduated tube, open at both ends, to a glass flask by means of
a thick piece of caoutchouc tube. Into the flask a weighed
quantity of a carbonate was placed, together with a vessel

520

VOLUMETRIC ANALYSIS.

§ 20.

containing dilute acid. The position of the mercury in the
graduated tube was first read off, after which the flask was shaken
so as to bring the acid and carbonate in contact, and the increase in
volume was due to the carbonic anhydride evolved. The results
thus obtained are extremely concordant.

In eight experiments with sodic carbonate the percentage of
carbonic anhydride found varied from 41*484 to 41 -GOT, theory
requiring 41 '509.

Thirteen experiments with calc-spar gave from 43 '520 to 43*858,
the theoretical percentage being 44*0; and in nine other analyses
from 43-581 to 43*901 were obtained.

Two experiments were
made with manganic per-
oxide, oxalic acid and sul-
phuric acid, and gave 58*156
and 58*101 per cent, of
carbonic anhydride.

Some determinations of
the purity of magnesium
were also performed by dis-
solving the metal in hydro-
chloric acid and measuring
the resulting hydrogen.
Four operations gave num-
bers varying between 8*255
and 8*282. The metal
should yield 8*333.

Russell has also em-
ployed this process for the
determination of the com-
bining proportions of nickel
and cobalt (/. C. S. [N.S.]
vii. 294).

Eegnault and Reiset
described (Jinn. Cldm. PJn/s.
[3] xxvi. 333) an appara-
tus by which absorptions
could be rapidly conducted
by means of liquid reagents
brought in contact with the
gases in a laboratory tube.

The measurements are made

Pig. P4.

in a graduated tube, which can be placed in communication with
the laboratory tube by means of fine capillary tubes provided with
stop-cocks, the lower end of the measuring tube being connected by
an iron socket and stop-cock with another graduated tube in which
the pressure to which the gas is subjected is measured. The
measuring and pressure tubes are surrounded by a cylinder of water.

FIIANKLAND AND WATID'S APPARATUS. 521

An apparatus similar in principle to this lias recently been
constructed by Frank land, and is fully described in the section
on Water Analysis (§ 89, page 417).

Frankland and Ward (/. C. S. vi. 197) made several
important improvements in the apparatus of Regnault and
Keiset. They introduced a third tube (fig. 94), closed at the top
with a stopper, and which is made to act as a barometer, to indicate
the tension of the gas in the measuring tube, thus rendering the
operation entirely independent of variations of atmospheric pressure.
The correction for aqueous vapour is also eliminated, by introducing
a drop of water into the barometer as well as into the measuring
tube, the pressures produced by the aqueous vapour in the two
tubes thus counterbalancing one another, so that the difference of
level of the mercury gives at once the tension of the dry gas. The
measuring tube is divided into ten equal divisions (which, for some
purposes, require to be calibrated), and in one analysis it is
convenient to make all the measurements at the same division, or
to calculate the tension which would be exerted by the gas if
measured at the tenth division. Frankland and Ward also
adapted an iron tube more than 760 m.m. long at the bottom of
the apparatus, which enables the operator to expand the gas to any
required extent, and thus diminish the violence of the explosions
which are performed in the measuring tube. During the operation
a constant stream of water is kept flowing through the cylinder,
which maintains an uniform temperature.

By the use of this form of apparatus the calculations of analyses
are much simplified. . An example of an analysis of atmospheric
air will indicate the method of using the instrument.

Volume of Air used. Determined at 5th Division on
the Measuring Tube.

m.m.

Observed height of mercury in barometer . 673*0

Height of 5 th division . . . . 383-Q

Tension 01 gas

Corrected tension of gas at 10th division

Volume after Admission of Hydrogen. Determined
at 6th Division.

m.m.

Observed height of mercury in barometer . 772'3

Height of 6th division . . 304-Q

TeLsion of gas . 468'3
0-6
Corrected tension at 10th division . 280 98

522 VOLUMETRIC ANALYSIS. § 99.

Volume after Explosion. Determined at 5th Division.

m.m.

Observed height of mercury in barometer . 763*3

Height of 5th division .... 383*0

Tension of gas . 3 80 '3
0-5

Corrected tension at 10th division . . 190*15

Tension of air with hydrogen . . .280*98

Tension of gas after explosion . . .190*15

Contraction on explosion . . . 90*83
of which one-third is oxygen.

90*83

— 0—^ = 30*276 = volumes of oxygen in 145*0 volumes of air

145*0 : 30*276 : : 100 : x

30*276x100 _Q
.x= j~jV7A = 20 *8b = percentage ot oxygen in air.

If all the measurements had been made at the same division, no
correction to the tenth division would have been necessary, as the
numbers would have been comparable among themselves.

Another modification of Frank land and "Ward's, or
Kegnault's apparatus has been designed by McLeod (/. C. >SY.
[N.S.] vii. 313), in which the original pressure tube of Regnault's
apparatus, or the filling tube of Frank land and Ward, is
dispensed with, the mercury being admitted to the apparatus
through the stop-cocks at the bottom.

The measuring tube A (fig. 95) is 900 m.m. in length, and about
20 m.m. in internal diameter. It is marked with ten divisions, the
first at 25 m.m. from the top, the second at 50, the third at 100,
and the remaining ones at intervals of 100 m.m. In the upper
part of the tube, platinum wires are sealed, and it is terminated by
a capillary tube and fine glass stop-cock, a, the capillary tube being
bent at right angles at 50 m.m. above the junction. At the bottom
of the tube, a wide glass stop-cock b is sealed, which communicates,
by means of a caoutchouc joint surrounded with tape and well
wired to the tubes, with a branch from the barometer tube B.
This latter tube is 5 m.m. in width, and about 1200 m.m. long,
and is graduated in millimeters from bottom to top. At the upper
extremity a glass stop-cock d is joined, the lower end being curved
and connected by caoutchouc with a stop-cock and tube C,
descending through the table to a distance of 900 m.m. below the
joint. It is advisable to place washers of leather at the end of the
plugs of the stop-cocks c and &, as the pressure of the mercury
which is afterwards to be introduced has a tendency to force them
out • if this should happen, the washers prevent any great escape
of mercury.

§ 99.

C LEOD S APPARATUS.

523

lig. 95.

524 VOLUMETRIC ANALYSIS. § 99.

The two tubes are firmly held by a clamp D, on which rests
a wide cylinder E, about 55 m.m. in diameter, surrounding the
tubes, and adapted to them by a water-tight caoutchouc cork F.
The cylinder is maintained in an upright position by a support at
its upper end G, sliding on the same rod as the clamp. Around
the upper part of the barometer tube a syphon H is fixed by means
of a perforated cork, through which the stop-cock d passes. A small
bulb-tube e, containing some mercury, is also fitted in this cork, so
as to allow of the air being entirely removed from the syphon. The
syphon descends about 100 m.m. within the cylinder, and has
a branch at the top communicating by caoutchouc with a bent tube
contained in a wider one J affixed to the support. A constant
current of water is supplied to the cylinder through a glass tube,
which passes to the bottom, and escapes through the syphon and
tubes to the drain.

To the end of the narrow tube C is fastened a long piece of
caoutchouc tube K, covered with tape, by which a communication
is established with the mercurial reservoir L, suspended by a cord
so that by means of the winch M, it may be raised above the level
of the top of the barometer tube. As the mercury frequently forces
its way through the pores of the caoutchouc tube, it is advisable
to surround the lower part with a piece of wide flexible tube ; this
prevents the scattering of the mercury, which collects in a tray
placed on the floor. Into the bottom of the tray a screw must be
put, to which the end of the glass tube is firmly attached by wire.
The capillary stop-cock a is provided with a steel cap, by means of
which it may be adapted to a short and wide laboratory tube
capable of holding about 150 c.c., and identical in form with,
the one described in the section on Water Analysis (§ 89). The
mercurial trough for the laboratory tube is provided with a stand
with rings, for the purpose of holding two tubes containing gases
that may be required.

The apparatus is used in the same way as Frank land and
Ward's, except that the mercury is raised and lowered in the tubes
by the movement in the reservoir L, instead of by pouring it into
the centre supply-tube.

To arrange the apparatus for use, the reservoir L is lowered to the
ground, and mercury poured into it. The laboratory tube being
removed, the stop-cocks are all opened, and the reservoir gradually
raised. When the tube A is filled, the stop-cock a is closed, and
the reservoir eleA'ated until mercury flows through the stop-cock d at
the top of the barometer. It is convenient to have the end of
the tube above the stop-cock so bent that a vessel can be placed
below to receive the mercury. This bend must, of course, be so
short that, when the plug of the stop-cock is removed, the syphon
will pass readily over. When the air is expelled from the barometer
tube, the stop-cock is closed. A few drops of water must next be
introduced into the barometer : this is accomplished by lowering

§ 99. MC LEOD'S GAS APPARATUS. 525

the reservoir to a short distance below the top of the barometer, and
gently opening the stop-cock d, while a small pipette, from which
water is dropping, is held against the orifice, the stop-cock being
closed when a sufficient amount of water has penetrated into the
tube. In the same manner, a small quantity of water is passed into
the measuring tube. In order to get rid of any bubbles of air which
may still linger in the tubes, the reservoir is lowered to the ground
so as to produce a vacuum in the apparatus ; in this manner the
interior surfaces of the tubes become moistened. The reservoir is
now gently raised, thus refilling the tubes with mercury. Great
care must be taken that the mercury does not rush suddenly against
the tops of the measuring and barometer tubes, which might cause
their destruction. This may be avoided by regulating the flow of
mercury by means of the stop-cock c, which may be conveniently
turned by a long key of wood, resting against the upper table of
the sliding stand of the mercurial trough. When the reservoir
has again been elevated abcve the top of the barometer, the
stop-cocks of the measuring and barometer tubes are opened, and
the air and water which have collected allowed to escape.

The heights of the mercurial columns in the barometer, corre-
sponding to the different divisions of the measuring tube, have now
to be determined. This is done by running out all the mercury
from the tub?-s, and slowly readmitting it until the meniscus of the
mercury just touches the lowest division in the measuring tube.
This may be very conveniently managed by observing the division
through a small telescope of short focus, and sufficiently close to the
apparatus to permit of the key of the stop-cock c being turned, while
the eye is still at the telescope. When a reading is taken, the
black screen 0 behind the apparatus must be moved by means of
the winch P, until its lower edge is about a millimeter above the
division. The telescope is now directed to the barometer tube, and
the position of the mercury carefully noted. As the tubes only
contain aqueous vapour, and are both of the same temperature, the
columns in the two tubes are those which exactly counterbalance
one another, and any difference of level that may be noticed is due
to capillarity.

The same operation is now repeated at each division of the tube.
The measuring tube next requires calibration, an operation performed
in a manner perfectly similar to that described in. § 89 (page 420),
namely, by filling the measuring tube with water, and weighing the
quantities contained between every two divisions. The eudiometer
being filled with water, and the stop-cock b closed, the reservoir is
raised and the mercury allowed to rise to the top of the barometer.
The capillary stop-cock a having been opened, the cock b is gently
turned, and the water allowed to flow out until the mercury reaches
the lowest division of the tube. A carefully weighed flask is now
supported just below the steel cap, the stop-cock b again opened,
until the next division is reached, and the quantity of water is

526 VOLUMETRIC ANALYSIS. § 99.

-weighed, the temperature of the water in the wide cylinder being
observed. The same operation is repeated at each division, and by
calculation the exact contents of the tube in cubic centimeters may
be found.

In this manner, a table, such as the following, is obtained : —

Division
on
measuring
tube.

Height of Mercury in
Barometer tube
corresponding to

division.

Contents.
Cubic Centimeters.

Log.

756-9

8-6892

9389S14

706-7

18-1621

2591664

606-8

36-9307

5673880

506-5

55-7344

7461232

406-8

74-4299

1-8717477

306-8

93-3306

9700244

206-9

112-4165

0508303

107-0

131-6335

•1193666

7-1

151-1623

•1794435

AVhen a gas is to be analyzed, the laboratory tube is filled with
mercury, either by sucking the air out through the capillary
stop-cock, while the open end of the tube stands in the trough, or
much more conveniently, by exhausting the air through a piece of
flexible tube passed under the mercury to the top of the laboratory
tube, the small quantity of air remaining in the stop-cock and at
the top of the wide tube being afterwards very readily withdrawn.
The face of one of the steel pieces is greased with a small miantity
of resin cerate, and, the measuring apparatus being full of mercury,
the clamp is adjusted.

Before the introduction of the gas, it is advisable to ascertain if
the capillary tubes are clear, as a stoppage may arise from the
admission of a small quantity of grease into one of them. For
this purpose the globe L is raised above the level of the top of the
measuring tube, and the capillary stop-cocks opened ; if a free
passage exists, the mercury will be seen to flow through the tubes.
The stop-cock of the laboratory tube is now closed. When all is
properly arranged, the gas is transferred into the laboratory tube,
and the stop-cock opened, admitting a stream of mercury. The
cock c is gently turned, so as just to arrest the flow of mercury
through the apparatus, and the reservoir lowered to about the level
of the table, which is usually sufficient. By carefully opening the
cock c, the gas is drawn over into the measuring tube, and when
the mercury has reached a point in the capillary tube of the
laboratory tube, about midway between the bend and the stop-cock,
the latter is quickly closed. It is necessary that this stop-cock
should 1)0 very perfect. This is attained by grinding the plug into

§ 99. MC LEOD'B GAS APPARATUS. 527

the socket with fine levigated rouge and solution of sodic or potassic
hydrate. By this means the plug and socket may be polished so
that a very small quantity of resin cerate and a drop of oil renders
it perfectly gas-tight. In grinding, care must be taken that the
operation is not carried on too long, otherwise the hole in the plug
may not coincide with the tubes. If this stop-cock is in sufficiently
good order, it is unnecessary to close the stop-cock a during an analysis.

The mercury is allowed to flow out of the apparatus until its
surface is a short distance below the division at which the measure-
ments are to be made. The selection of the division depends on
the quantity of gas and the kind of experiment to be performed
with it. A saving of calculation is effected if all the measurements
in one analysis are carried on at the same division. When the
mercury has descended below the division, the cock c is closed, the
reservoir raised, and the black screen moved until its lower edge is
about a millimeter above the division, and the telescope placed so-
that the image of the division coincides with the cross-wires in the
eye-piece. The stop-cock c is now gently opened until the meniscus
just touches the division ; the cock is closed and the height of the-
mercury in the barometer is measured by means of the telescope.
The difference between the reading of the barometer, and the
number in the table corresponding to the division at which the
measurement is taken, gives in millimeters the tension of the gas.
The volume of the gas is found in the same table, and with the
temperature which is read off at the same time as the pressure, all
the data required for the calculation of the volume of the gas at
0Q and 760 m.m. are obtained. ISfo correction is required for
tension of aqueous vapour ; the measuring tube and barometer tube
being both moist, the tensions in the tubes are counterbalanced.
Absorptions are performed with liquid reagents by introducing a few
drops of the liquid into the laboratory tube, transferring the gas
into it, and allowing the mercury to drop slowly through the gas for
about five minutes. The gas is then passed over into the measuring
tube, and the difference of tension observed corresponds to the
amount of gas absorbed. It is scarcely necessary to add, that the
greatest care must be taken to prevent any trace of the reagent
passing the stop-cock. If such an accident should occur, the
measuring tube must be washed out several times with distilled
water at the conclusion of the analysis. If the reagent is a solution
of potassic hydrate it may be got rid of by introducing into the tube
some . distilled water, to which a drop of sulphuric acid has been
added. If this liquid is found to be acid on removing it from the
tube, it may be presumed that all the alkali has been neutralized.

"When explosions are to be performed in the apparatus, the
gas is first measured and then returned to the laboratory tube.
A quantity of oxygen or hydrogen, as the case may be, which is
judged to be the proper volume, is transferred into the laboratory
tube, and some mercury is allowed to stream through the gases so-

o2S VOLUMETRIC ANALYSIS. § 99.

as to mix them thoroughly. The mixture is next passed into the
eudiometer and measured. If a sufficient quantity of the second
gas has not been added, more can readily be introduced. After
the measurement, it may be advisable to expand the mixture, in
order to diminish the force of the explosion. This is done by
allowing mercury to flow out from the tube into the reservoir.
When the proper amount of expansion has been reached, the
stop-cocks a and b are closed. To enable the electric spark to pass
between the wires, it is necessary to lower the level of the water in
the cylinder. For this purpose, the bent glass tube at the extremity
of the syphon is made to slide easily through the cork which closes
the top of the wide tube J. Ly depressing the bent tube, the
water flows out more rapidly than before, and the level consequently
falls. When the surface is below the eudiometer wires, a spark
from an induction-coil is passed, exploding the gas. The syphon
;tube is immediately raised, and, when the water in the cylinder has
reached its original level, the gas is cool enough for measurement.
900 c.c. of mercury are amply sufficient for the whole apparatus;
and as there is no cement used to fasten the wide tubes into iron
sockets, a great difficulty in the original apparatus is avoided.

The following details of an analysis, in which absorptions only
Avere performed, will show the method employed. The gas was
.a mixture of nitrogen, oxygen, and carbonic anhydride, and the
measurements were all made at division Xo. 1 on the eudiometer,
which has been found to contain 8 '6892 c.c.

Original Gas.

m.m.

'Temperature of water in cylinder, 15'4°.

Height of mercury in barometer tube .... 980 '5

,, ,, corresponding to Division Xo. 1 (see
Table) 756'9

Pressure of the gas ........ 223'6

After absorption of the carbonic anhydride by solution

of potassic hydrate —
Height of mercury in barometer tube

,, ,, corresponding to Division Xo. 1

Pressure of the gas after removal of carbonic anhydride

Pressure of original gas ......

,, gas after removal of carbonic anhydride .

Tension of carbonic anhydride .....

After absorption of the oxygen by potassic pyrogallate —
Height of mercury in barometer tube .... 8854
„ ,, corresponding to Division Xo. 1 . 756 •!)

Pressure of nitrogen ....... 128'5

CALCULATIONS,

529

Pressure of oxygen and nitrogen
„ nitrogen .

Pressure of nitrogen

. 184-8
. 128-5

„ oxygen 56*3

These measurements, therefore, give us the following numbers : —

m.m.

128-5

56-3

38-8

oxygen .

carbonic anhydride .

original gas

223-6

If the percentage composition of the gas is required, it is readily
obtained by a simple proportion, the temperature having remained
constant during the experiment : —

m.m. m.m. m.m.

223-6 : 128-5 : : 100
223-6 : 56-3 : : 100

38-8 : : 100

223-6

57-469 per cent. N
25-179 per cent. 0
17-352 per cent. CO2
100,000

If, however, it is necessary to calculate the number of cubic
centimeters of the gases at 0° and 760 m.m., it is done by the
following formulae : —

8-6892 x 128-5

7~60 x [1 +(0-003665 x 15'4)~
8-6892 x 56-3

= 1'3906 c.c. of nitrogen.

= 0-6093 c.c. of oxygen.

760 x[l + (0-003665 x 15'4)J

8-6892x38-8 , , .

— — — n — nAO£/?K IK A\-\ = 0'4199 c.c. of carbonic anhydride
760 x [1 + (0-00366o x 15'4)J

8-6892x223-6 „ ,, . . ,

7607rr+^QQ3665x 15-4)] = 8 *'«' °f the °ri*mal ^

If many of the calculations are to be done, they may be very
much simplified by constructing a table containing the logarithms
of the quotients obtained by dividing the contents, of each division
of the tube by 760 x (1 +0'003665^). The following is a very
short extract from such a table : —

T°.

Division No. 1.

Lc~ 8'6892

Division No. 2.
T™ 18-1621

°"760x(l + 5t).

8 760x(l+8t).

15-0

2-03492

2-35511

•1

2-03477

2-35496

•2

2-03462

2-35481

•3

2-03447

2-35466

•4

2-03432

2"-34451

M M

530

VOLUMETRIC ANALYSIS.

§ 99.

By adding the logarithms of the tensions of the gases to those
in the above table, the logarithms of the quantities of gases are
obtained ; thus : —

Log. corresponding to Division Xo. 1,
and 15-4° .....

Log. 128*5 = pressure of nitrogen .

Log. of quantity of nitrogen .
Volume of nitrogen at 0° and
760 m.m.

Log. 56 '3 = pressure of oxygen

Log. of quantity of oxygen

Volume of oxygen at 0° and
760 m.m.

Log. 38 -8 = pressure of carbonic anhy-
dride ......

Log. of quantity of carbonic anhy-
dride ......

Volume of carbonic anhydride at
0° and 760 m.m.

Log. 2 23 '6 = pressure of original gas
Log. of quantity of original gas
Volume of original gas at 0° and
760 m.m.

2-03432
200890

0714322 = log. 1-3906

1-3906 c.c.

2-03432

1-75051

T-78483 = log. 0-6093

0-6093 c.c.
2-03432

T-58883

1-62315 = log. 0-4199

0-4199 c.c.

2-03432
2-34947

0-38379 = log. 2-4198

2-4198 c.c.

Nitrogen
Oxygen

Carbonic anhydride
Total

1-3906
0-6093
0-4199

or
or
or
or

1-391 c.c.
0-609 c.c.
0-420 c.c.
2-420 c.c.

The following example of an analysis of coal gas will show the
mode of working with this apparatus, and the various operations to
be performed in order to determine the carbonic anhydride, oxygen,
hydrocarbons absorbed by Xordhauseii sulphuric acid, hydrogen,
marsh gas, carbonic oxide, and nitrogen.

The measuring tube and laboratory tube were first filled with
mercury, some of the gas introduced into the laboratory tube, and
passed into the apparatus.

The gas was measured at the second division.

Height of mercury in the barometer tube . 989 '0

„ „ „ measuring tube . 706 -8

Pressure of the gas at 16 -6° 282'2

§ 99. MEASUREMENT OF GASES. 531

Two or three drops of a solution of potassic hydrate were
now placed in the laboratory tube, and the gas passed from the
measuring tube, the mercury being allowed to drop through the
gas for ten minutes. On measuring again —

Height of mercury in barometer . . . 984*0

Some saturated solution of pyrogallic acid was introduced into
the laboratory tube, and the gas left in contact with the liquid for
ten minutes. On measuring —

Height of mercury in barometer
Height of mercury when measuring original gas .
,, ,, after absorption of CO2

Pressure of CO2

„ ,, after absorption of CO2

,, ,, after absorption of 0 .

Pressure of 0 0'4

» The volume of the. gases being proportional to their pressures, it
is simple to obtain the percentages of carbonic anhydride and
oxygen in the original gas.

Original s;as. CO-

282-2 : 5-0 :: 100 : 1*772 per cent. CO2

Original gas. O

282*2 : 0-4 : : 100 : 0*142 per cent. 0

By subtracting 1'914 from 100, we obtain the remainder,
98'086, consisting of the hydrocarbons absorbed by Xordhausen
sulphuric acid, hydrogen, carbonic oxide, marsh gas, and nitrogen ;

thus : —

Original gas . . . . . . . lOO'OOO

0 and CO2 1*914

CnH%. H. CO. CH4. X. . . . 98-086

While the gas remains in the measuring tube, the laboratory tube
is removed, washed, dried, filled with mercury, and again attached
to the apparatus. Much time is saved by replacing the laboratory
tube by a second, which was previously ready. As a minute
quantity of gas is lost in this operation, in .consequence of the
amount between the stop-cocks being replaced by mercury, it is
advisable to pass the gas into the laboratory tube, then transfer it
to the eudiometer, and measure again.

On remeasuring, the mercury in the barometer

stood at t 983*3

The mercury in the measuring tube . . . 706 -8

Pressure of CnH-n. H. CO. CH4. X. "276^

M M 2

532 VOLUMETRIC ANALYSIS. § 99.

The gas is again passed into the laboratory tube, and a coke ball,
soaked in faming sulphuric acid, left in contact with the gas for
an hour ; the bullet is then withdrawn, and some potassic hydrate
introduced and left in the tube for ten minutes, in order to remover
the vapours of sulphuric anhydride, and the sulphurous and
carbonic anhydrides formed during the action of the Xordhausen
acid on the gas. The gas is now measured again.

Height of mercury in barometer tube . . 969 '3
,, ,, ,, before absorbing

CnH2n 983-3

after . . 969'3

Pressure of CnH2n 14-Q

The percentage of these hydrocarbons is thus found : —
Gas containing CnH2n. H. CO. CH4. K

CnH^n.

276-5 : 14-0 :: 98-086 : 4-966 per cent. CnH-n

It now remains to determine the hydrogen, carbonic oxide, marsh
gas, and nitrogen in a portion of the residual gas. The laboratory
tube is therefore removed, some of the gas allowed to escape, and
another laboratory tube adapted to the apparatus. The portion of
gas remaining is expanded to a lower ring (in this special case to
the third division), and the tension measured: —

Height of mercury in the barometer tube . . 042 "2

„ ,, measuring tube . . 606*7

Pressure of residue 35-5

An excess of oxygen has now to be added. For this purpose
the gas is passed into the laboratory tube, and about five times its
volume of oxygen introduced from a test tube or gas pipette. The
necessary quantity of oxygen is conveniently estimated by the aid
of rough graduations on the laboratory tube, which are made by
introducing successive quantities of air from a small tube in the
manner previously described for the calibration of the eudiometers.

After the introduction of the oxygen, the mixed gases are passed
into the eudiometer and measured.

Height of mercury in the eudiometer after

addition of 0 789-5

The mixture has now to be exploded, and when the pressure is
considerable, it is advisable to expand the gas so as to moderate the
violence of the explosion. When sufficiently dilated, the stop-cock
at the bottom of the eudiometer is closed, the level of the water
lowered beneath the platinum; wires by depressing the syphon, and
the spark passed. The- explosion should be so powerful that it
should be audible, and the flash visible in not too bright daylight.

§ 99. MEASUREMENT OF GASES. 533

The stop-cock at the bottom of the eudiometer is now opened,
and the gas measured.

Height of mercury in barometer after explosion . 732 '5

The difference between this reading and tlrj previous one gives
the contraction produced by the explosion :

Height of mercury in barometer before explosion 789 '5

after „ 7 32 -5

Contraction =C 57 '0

It is now necessary to estimate the amount of carbonic anhydride
formed. This is done by absorbing with potassic hydrate as before
described.

Height of mercury in barometer tube after

absorbing CO'2 715*8

This number deducted from the last reading gives the carbonic
anhydride.

Height of mercury in barometer after exploding 732 '5

„ ,, ,, after absorbing CO2 715*8

Carbonic anhydride =D 16'7

It now remains to determine the quantity of oxygen which was
riot consumed in the explosion, and which excess now exists mingled
with the nitrogen. For this purpose, a volume of hydrogen about
three times as great as that of the residual gas is added, in the same
way as the oxygen was. previously introduced, and the pressure of
the mixture determined.

Height of mercury in barometer after adding H 1031 '3

This mixture is exploded and another reading taken.

Height of mercury in barometer after exploding

with H 706-7

This number subtracted from the former, and the difference
divided by 3, gives the excess of oxygen.

Height of mercury in barometer before exploding

withH 1031-3

Height of mercury in barometer after exploding

with H 706-7

3; 324-6
Excess of oxygen 108 '2

In order to obtain the quantity of nitrogen in the gas analyzed,
this number has to be deducted from the volume of gas remaining
after the explosion with oxygen and the removal of the carbonic
anhydride.

534 VOLUMETRIC ANALYSIS. § 99.

Height of mercury in barometer after absorbing

CO' . . ...... 715-8

,, „ in eudiometer at division ]S"o. 3 606 '7

Xitrogen and excess of oxygen . . . 109*1

Excess of oxygen . . . . . 108 '2

Nitrogen 0*9

TTe have now all the data necessary for the calculation of the
composition of the coal gas. It is first requisite to calculate the
proportion of the combustible gas present in the coal gas, which is
done by deducting the sum of the percentages of gas determined
by absorption from 100.

Percentage of carbonic anhydride . . . 1*772

„ oxygen ..... 0'142

CnH2n ..... 4-966

CO2. 0. CnH'-'n ~ 6-880

Original gas ....... 100-000

CO2. 0. CnH2ii ...... 6-880

H. CO. CH4. X 93-120

The formulae for the calculation of the analysis of a mixture of
hydrogen, carbonic oxide, and marsh gas, are (see page 510) —

Hydrogen — .>: = A — D

3A-2C + D

Carbonic oxide =//= - o —

2C-3A + 2D

Marsh gas =::=•. Q

A=35-5 - 0-9 = 34-6
C=57-0
D = 16-7
A=n 34-6
L>= J.6-7

1 7 -9 = a-= Hydrogen in 35 -5 of the gas exploded

with oxygen.

A== 34-6 C= 57-0

3 _2

3A= 103-8 2C= '114-0

D= 16-7
= 120-5

3) 6-5=3A + D-2C

o \ , ~i\ _^ 9p __

— o — ' •= 2-167=v/=Carbonic oxide in 35'5 of the gas.

§99. ESTIMATION OF HYDROCARBONS. 535

D= 167

2D — 33-4

2C = 114-0

2.D + 2C = 1474

3A = LOS

2D + 2C-3A

= 14*533 = 2 = Marsh gas in 35*5 of the gas.

These numbers are readily transformed into percentages, thus : —

35-5 : 17-9 : : 93*12 : 46*952 per cent, of Hydrogen.

35-5 : 2-167 : : 93-12 : 5*684 per cent, of Carbonic oxide.

35-5 : 14-533 : : 93-12 : 38*122 per cent, of Marsh gas.

35-5 : 0*9 : : 93*12 : 2*361 per cent, of Xitrogen.

This completes the calculations, the results of which are as
follows : —

Hydrogen . . . .46*952

Marsh gas . . . .38*122
CnH2n .... 4*966

Carbonic oxide . . . 5*684

Carbonic anhydride . . 1772

Oxygen . ' . . . 0*142

o-en 2*361

99*999

It is obvious that this analysis is not quite complete, since it
does not give any notion of the composition of the hydrocarbons
absorbed by the Nordhausen acid. To determine this, some of
the original gas, after the removal of carbonic anhydride and oxygen,
is exploded with oxygen, and the contraction and carbonic anhy-
dride produced are measured. The foregoing experiments have
shown the effect due to the hydrogen, carbonic oxide, and marsh
gas, the excess obtained in the last explosion being obviously caused
by the hydrocarbons dissolved by the sulphuric acid, and from
these data the composition of the gas may be calculated.

It may be remarked that analyses of this kind were performed
with the apparatus at the rate of two a day when working for
seven hours.

It may be useful to show how this analysis appears in the
laboratory note-book :

5S6

VOLUMETRIC ANALYSIS.

99.

Analysis of Coal Gas.

989-0^
706-8 I

original

282-2 j §as

934-0 Aft. absorb. CO2

983-6 Aft. absorb. 0
983-3 Remeasured

969-3 Aft. Absorb. CnH2i

642 -2 N

606-7 (portion of

~i^j Residue

789-5 with 0

732-5 Aft. expl.
715-8 Aft. absorb. CO2

1031-3 withH
706-7 Aft. expl.

CO = y =•

' 2C

9890
984-0

984-0
983-6

0-4 = <

282-2 :5-0 : : 100 : 1772 CO2
282-2 : 0-4 : : 100 : 0-142 0

1-914

100-000

1-914 CO2. O

93-086 CnH2n. H. CO. CH*. N

983-3

706-8

983-3
969-3

276-5 140 CnH2n

276-5 : 14-0 : : 9S'OS6 : 4-966 CnH2n

35-5 = H. CO. OH*. N
0-9= N

J34-6 = 11. CO. CH-i=A

789-5
732-5

= 0-142

6-880

32-5

15-8

57-0 = contraction = C 167 = CO2 = D

1031-3

7067

3) 324-6
108r2 = 0

= 17-9

715-8
606-7

109-1 =
108j2=0
0-9 = N

CH4 = z -

2C - 3A +2D

34-600

34-6 =
16-7 =

A
D

x = H
C

34-6
3

= A

=-3A
= D

= 3A H
= 2C

-6

17-9 =

57-0 =
2

103-8
167

120-5
114-0

16-7 - D

33-4 = 2D

114-0 =2C

147-4 =2C + 2D
103-8 = 3 A

114-0 = 20

3) 6-5 =3A + D-2C

3) 43-6 =2D + 2C-3A

100-000
6-880 CO. 0. CnH'-'n

93-120 H. CO. CH-*. N

35 5 : 17-9 : : 93-12

35-5 : 2-167 : : 93-12

35-5 : 14-533 : : 93-12

35-5 : 0-9 : : 93'12

46-952 H
5-684 CO

38 -122 CH<
2-361 N

THOMAS'S GAS APPARATUS. 537

H = 46-952

CH4 - 38-] 22

CnH-n = 4-966

CO = 5684

CO^ = 1-772

0 = 0-142

N = 2-361

"99-999

It is assumed in the above example, that the temperature of the
water in the cylinder remained constant throughout the period
occupied in performing the analysis. As this very rarely happens,
the temperature should be carefully read off after every measure-
ment of the gas and noted, in order that due correction be made for
any increase or decrease of volume which may result in consequence.

THOMAS'S IMPROVED GAS APPARATUS.

In the Chemical Societies Journal for May, 1879, Thomas
described an apparatus for gas analysis (fig. 96) which has the
closed pressure tube of Frankland and "Ward, and is supplied
with mercury by means of the flexible caoutchouc tube arrangement
of Me Leod. The manner in which this apparatus is filled with
mercury and got into order for working is so similar to that already
described, that no further reference need be made thereto.

The eudiometer is only 450 m.m. long from .shoulder to shoulder,
and the laboratory tube and mercury trough are under the command
of the operator from the floor level. The eudiometer has divisions
20 m.m. apart, excepting the uppermost, which is placed as close
beneath the platinum wires as is convenient to obtain a reading.
The method explained in sequel of exploding combustible gases
under reduced pressure, without adding excess of gas to modify the
force of the explosion, permits the shortening of the eudiometer as
above, and enables the apparatus to be so erected, that a long
column of the barometer tube shall stand above the summit of the
eudiometer. By means of such an arrangement a volume of gas
may be measured under nearly atmospheric pressure, and as this
pressure is equal to more than 700 m.m., plus aqueous tension, the
sensitiveness of the apparatus is considerably augmented. The
barometer tube is 1000 m.m. in length, having about 700 m.m.
lines above Division 2 on the eudiometer. The steel clamp and
facets forming the connections between the eudiometer and detach-
able laboratory tube of the apparatus previously described are
dispensed with, as in this form the eudiometer and laboratory
vessels are united by a continuous capillary tube, 12 m.m. (outside)
diameter, and one three-way glass tap is employed in lieu of the
two stop-cocks. The arrangement is simple, The glass tap is
hollow in the centre, and through this hollow a communication is
made with the capillary, by means of which either the laboratory

538 VOLUMETRIC ANALYSIS. § 99.

tube or the eudiometer can be washed out. As the laboratory
vessel is not disconnected for the removal of the reagent used in
an absorption, it is supported by a clamp, as shown in the drawing ;
and when it requires washing out the mercury trough is turned
aside, in order that an enema syringe may be used for injecting a
stream -of water. A few drops of water are let fall into the hollow
of the tap, and blown through the capillary tube three times in
succession, so as to get rid of the absorbent remaining in the
capillary, then the syringe is brought into play once more, the
excess of water removed by wiping, and the trough turned back
into position. The laboratory tube may be refilled with mercury
as described on page 526 : but it will be found much more serviceable
if a double-acting syringe, connected to a bulb appaiatus (to catch
any mercury that may come over), and then to the orifice of the
hollow in the tap by a ground perforated stopper, be used, as this
will obviate the destructive effect of heavy suction upon the gums
and teeth. The mercury trough is supported upon a guide which
travels over the upright U, and is turned aside for the purpose of
washing out the laboratory vessel in the following manner : — The
spiral spring is depressed by means of the tension rods until the
sloe is brought below the stud fixed in the upright U ; and the top
ferrule holding the guide rods being movable, the trough can lie
turned round out of the way, but is prevented from coming in
contact with the glass water-cylinder by an arrangement in the top
of the guide, which comes against the stud in the upright. The
height of the trough can be accurately adjusted by the screw in the
top of the lever guide. When the trough is in position, the clamp
holding the laboratory vessel may be loosed when necessary.

The eudiometer and barometer tubes pass through an india-
rubber cork, as in Me Leod's apparatus, but are not supported by
the clamp C, which here simply bears the water-cylinder. Xo
glass stop-cocks are used, or glass-work of any kind employed in
the construction of the lower portion of the apparatus. The lower-
end of the eudiometer has a neck of the same outside diameter as
the barometer tube (9*5 m.m.), and both tubes are fixed into the
steel block X, without rigidity, by the usual steam cylinder-gland
arrangement, small india-rubber rings being used to form the
packing. The steel block is fixed to the table by a nut screwed
upon the f-inch hydraulic iron tube, which runs to the bottom of
the table. The tap in the steel block is so devised that it first cuts
off connection with the barometer tube, in order that the gas may
he drawn over from the laboratory vessel into the eudiometer with-
out risking the fracture of the upper end of the barometer tube by
any sudden action of the mercury. This precaution is necessary, as
during the transferring of the gas the mercury in the barometer
tube is on the point of lowering, to leave a vacuous space in the
summit of the tube. By moving the handle a little further on
the quadrant a communication is made with both tubes and the

THOMAS S GAS APPARATUS.

539

reservoir for the purpose of bringing the gas interposition, so as to
take a reading; then the handle is drawn a little further to cut off

Fig. 90.

the reservoir supply, whilst there is a way still left between the
eudiometer and barometer tubes, and if the handle be drawn

540 VOLUMETRIC ANALYSIS. § 99.

forward a little more, all communication is cut off for the purpose
of exploding.

The windlass B, for raising and lowering the mercury reservoir L,
is placed beneath the table, in order that it may be under command
from a position opposite the laboratory vessel, and it is furnished
with a spring ratchet motion, so as to be worked by one hand. The
water-cylinder should be four inches in diameter, and the casing tube
of the barometer as wide as practicable, so that the temperature of
the apparatus may be maintained as constant as possible. To attain
an accurate result it is as essential to keep the barometer tube
of uniform temperature as the eudiometer, since the tension of
aqueous vapour varies proportionally. The stream of water from
the service main is run into the casing tube at the upper end of
the barometer, and, whilst the water-cylinder is filling, the tap at
the bottom is opened slightly, so that water may run out very
slowly. When the water-cylinder is full, the upright tube G acts
as a syphon, and sucks out the excess of water from the top of the
cylinder, thus keeping up the circulation at the point where it is
most required. For a further detailed description of the apparatus
see /. C. S., May, 1879.

There are only twro working taps upon this apparatus — the
three-way glass tap between the eudiometer and laboratory tube,
and the steel tap at the lower ends of the barometer and eudiometer.
The steel tap is greased with a little beef-tallow (made from clean
baef-suet), or with real Russian tallow ; it will last for twelve
months without further attention. A moderately thick washer of
india-rubber, placed between the steel washer and the nut at the
end of the steel tap, adds greatly to the steady working of the
needle on the quadrant. Moderately soft resin cerate is best for
the glass tap.

When filling the laboratory vessel with mercury, suction is
maintained until the mercury has reached some height in the
hollow of the three-way tap. The remainder of the hollow space
is replenished by pouring the mercury from a small crucible ; any
water that may be present is then removed, and the small stopper
inserted. When the laboratory vessel has to be washed out after
an absorption, the gas is transferred to the eudiometer until the
absorbent gets within a quarter of an inch of the stop-cock. The
mechanical arrangement should be so manageable that this nicety
of adjustment can be accomplished with ease. Much depends, of
course, upon the care bestowed in cerating the tap, so that the
capillary is not carelessly blocked up. As soon as the gas has
passed over to the extent required, turn the three-way tap until the
through-way is at right angles to the capillary, and the way to the
hollow of the tap is in communication with the laboratory vessel,
then take out the little stopper from the hollow, so that the mercury
shall flow out, and allow the laboratory vessel to become emptied
whilst the reading of the volume of the gas is being taken. The

99.

THOMAS 8 GAS APPARATUS.

541

best arrangement for washing out the laboratory tube is a " syphon
enema" (Dr. Higginson's principle, which maybe obtained of
any druggist), adapting in the place of the usual nozzle a bent glass-
tube. This syringe is constant in its action, as it fills itself when
the pressure is released, if the tube at the lower end is placed in
a vessel of water. The laboratory vessel can be washed out and
refilled in a very little time, as it is already connected, and for all
ordinary absorptions it is sufficient to wipe the vessel out once by
passing up a fine towel twisted on a round stick. When CnH2ii
gases are to be absorbed by fuming sulphuric acid, the water should
be carefully blown out of the capillary tube into the laboratory
vessel, which must be repeatedly dried. A few drops of strong,
sulphuric acid were at first run into the hollow of the tap and then
through the capillary whilst the labora-
tory vessel was full of mercury, in order
to remove any moisture remaining, but
it has since been found unnecessary, as
the drying can be performed thoroughly
without.

To calibrate the eudiometer with
water, introduce the quantity required
through the hollow in the stopper, then
remove the latter, and collect the water
in a light flask from the bottom of the
tap-socket.

In the same paper (J. C. S., May,
1879), Thomas pointed out that it was
not essential to add excess of either
oxygen or hydrogen for the purpose of
modifying the force of the explosion
when combustible gases were under
analysis, and it is necessary to take
advantage of this when working with so
short an eudiometer. The method is
however, applicable to all gas apparatus
having a reasonable length of barometer
column above the eudiometer ; in fact,
the exploding pressures were first worked

out and employed in an apparatus onMcLeod's model. AVhen the
percentage of oxygen in a sample of air has to be determined by
explosion, only one-half its volume of hydrogen is required, and the-
pressure need not be reduced below 400 m.m. If much more than
one-half volume of hydrogen has been added by accident, explode
under atmospheric pressure. When the excess of oxygen used in an-
analysis has to be determined, add 2 '5 times its volume of hydrogen,
and reduce the pressure to 180 m.m. of mercury before exploding.
After adding the hydrogen and the reading has been taken, the gas
is expanded by lowering the mercurial reservoir until a column of

Tig. 97.

•542

VOLUMETRIC ANALYSIS.

mercury, measuring

the number of m.m.'s in length just referred to

and in the following table, stands above the meniscus of the mercury
in the eudiometer. This column can be read off quite near enough by
the eye, as there is no risk of breaking the apparatus by the force of
the explosion if the pressure is 20 m.m. greater than that given ;
but if the gas under analysis is all combustible, it is better to
explode at a slightly less pressure than to exceed that recommended.

•si

e*-j °

° o bii

01 '-« •

Q •

gggj

Name of Gas.

§IJ

1 §|

g ^ o 'd

"o 3

"o t^

§8 IF

i ^6

^ 0

Hydrogen -

200 m.m.

Carbonic Oxide -

200 m.m.

Marsh Gas

2-5

170 m.m.

Acetylene -

150 m.m.

Olefiant Gas 1

3-5

145 m.m.

Methyl and Hydride of Ethyl 1

140 m.m.

Propyl

135 m.m.

Hydride of Propyl

5-5

130 m.m.

Butyl

125 m.m.

Ethyl and Hydride of Butyl

120 m.m.

It follows, naturally, that the exploding pressure will depend upon
the proportion of combustible gas introduced ; and experience
alone can enable one to determine with any degree of exactness
what that pressure must be, as no general law can be laid down.
For instance, if more than three volumes of hydrogen were added
to one of oxygen, the exploding pressure should exceed 200 m.m. ;
and if much nitrogen or other gas were present that did not take
.a part in the reaction, the pressure should be still more increased.
As a consequence, the same experience is necessary when dealing
with explosive gases by the other method, because the addition
•of too much inert gas, with a view to modify the force of the
explosion, may lead to imperfect combustion, inasmuch as the
cooling effect of the tube and gas can reduce the temperature
below that required. In all instances, when the approximate com-
position of the gas is known, it is not difficult to determine the
quantity of oxygen or hydrogen, as the case may be, which is
required for explosion, or the pressure under which the gas should
be exploded. In order to do this systematically, it is always well
to remember certain points observed during the stages of the
-analysis. The gas in the laboratory vessel, before being transferred
to the eudiometer, occupies a certain volume in a position between
(or otherwise) the calibration divisions. After transferring and
reading off, bear in mind the number of m.ni.'s which the volume

§ 99. REISER'S GAS APPARATUS. 543

represents ; and calculate, as the gas is being re-transferred to the
laboratory vessel to be mixed with that employed in the explosion,
the height at which the mercury should stand in the barometer
tube when measuring the mixed gases, and how much of the
laboratory vessel was occupied on a previous occasion when a similar
reading was obtained. If this is done, one can realize at once, after
reading off the volume of the mixed gases, the proportion of com-
bustible gas added, and the pressure under which the gas has been
measured. Another glance at the volume which the gas occupies in
the eudiometer, with a comparison of the pressure recorded upon
the barometer tube, enables one, after a little practice, to at once
expand the mixture to the point at which it will explode with
satisf actor v results. It is not expedient to place too much reliance
upon the marks showing equal volumes upon the laboratory vessel,
especially when dealing with small quantities of gas ; and
a comparison of the volumes obtained in reading before and after the
addition of oxygen or hydrogen is always prudent, in order to see
that sufficient gas has been added, as well as to enable one to judge
the pressure under which the gas should be exploded.

NOTE. — Meyer and Seubert (Z. a. C. xxiy. 414) have designed a gas apparatiis
similar in many respects to that of McLeod and Thomas, but of simpler con-
struction, and especially adapted for explosions under diminished pressure.

K e i s e r ' s Portable Gas Apparatus.

This apparatus is based on the principle of determining the
volume of a gas from the weight of mercury which it may be made
to displace at a known temperature and pressure. It dispenses
entirely with the long graduated tubes and other vessels common to
the apparatus previously described, without any sacrifice of accuracy.

The following description occurs in the Amer. Chem. Journ., 1886
(but is reproduced here from The Analyst, xi. 106) : —

Fig. 98 shows the construction of the measuring apparatus arid
the absorption pipette. A is the measuring apparatus, B is the
absorption pipette; a and l> are glass bulbs of about 150 c.c.
capacity. They are connected at the bottom by a glass tube of
1 m. m. bore, carrying the three-way stop-cock d. The construction
of the key of the stop-cock is shown in the margin. One hole is
drilled straight through the key, and by means of this the vessels
a and b may be made to communicate. Another opening is drilled at
right angles to the first, which communicates with an opening
extending through the handle, but does not communicate with the
first opening. By means of this, mercury contained in either a or b
may be allowed to flow out through the handle d into a cup placed
beneath. The bulb b is contracted at the top to an opening 20 m.m.
in diameter. This is closed by a rubber stopper carrying a bent
glass tube, to which is attached the rubber pump e. To a second
glass tube passing through the stopper, a short piece of rubber

544

VOLUMETRIC ANALYSIS.

99.

tubing with a pinch-cock is attached. By means of the pump e air
may be forced into or withdrawn from /;, as one or the other end of
the pump is attached to the glass tube. The bulb a terminates at
the top in a narrow glass tube, to which is fused the three-way stop-
cock c. The construc-
tion of the key of this
stop-cock is also shown
in the cut. By means
of it the vessel a may
be allowed to com-
municate with the
outside air, or with
the tube passing to
the absorption pipette,
or with the gauge y.
The gauge rj is a glass
tube having a bore
1 m.m. in diameter
and bent, as shown in
the figure. By pouring
a few drops of water

into the open end of
Fig. 98. ., . , , l •, _c

this tube a column 01

water several centimeters high in both limbs of the tube is obtained.
This serves as a manometer, and enables the operator to know when
the pressure of the gas equals the atmospheric pressure. To secure
a uniform temperature, the bulbs a and b are surrounded by water
contained in a glass vessel! This vessel for holding water is merely
an inverted bottle of clear glass from which the bottom has been
removed. The handle of the stop-cock d passes through a rubber
stopper in the neck of the bottle. A thermometer graduated to i°
is placed in the water near the bulb a. The whole apparatus is
supported upon a vertical wooden stand.

The absorption pipette B consists of two nearly spherical glass
bulbs of about 300 c.c. capacity. They communicate at the bottom
by means of a glass tube, 3 m.m. inside diameter, c is a two-way
stop-cock. The holes in the key are drilled at right angles, so that
the tube which connects with the measuring apparatus may be put
in communication either with the funnel or with the absorption
bulb. The funnel is of service in removing air from the tube which
connects the measuring apparatus with the absorption pipette. By
pouring mercury or water into the funnel and turning the stop-
cocks c and c in the proper directions all the air is readily removed.
/ is a rubber pump used in transferring gas from B to A. The
lower part of the pipette contains mercury, which protects the
reagent from the action of the air.

To measure the volume of a gas, the vessel a is filled completely
with pure mercury. This is easily accomplished by pouring the

§ 99. REISER'S GAS APPARATUS. 545

mercury into b, and then, after turning c until a communicates with
the outside air, forcing it into a by means of the pump e. Any
excess of mercury in b is then allowed to flow out through the stop-
cock d. When a and b are now placed into communication the
mercury will flow from a to &, and gas will be drawn in through the
stop-cock c. The volume of mercury which flows into It is equal to
the volume of gas drawn into a. When the mercury no longer
rises in b, and it is desired to draw in still more gas into a, then it
is only necessary to exhaust the air in b by means of the pump e.
After the desired quantity of gas has been drawn into a the stop-
cock c is closed. After standing a few minutes the temperature of
the gas becomes the same as that of the water surrounding a.
The pressure of the gas is then made approximately equal to atmos-
pheric pressure by allowing the mercury to flow out of b into a
weighed beaker placed beneath the stop-cock d until it stands at
nearly the same level in both a and b. Communication is now
established between a and //, and by means of the pump e the
pressure can be adjusted with the utmost delicacy until it is exactly
equal to atmospheric pressure. The stop-cock d is then closed, and
the remainder of the mercury in b is allowed to flow out into the
beaker. The weight of the mercury displaced by the gas divided
by the specific gravity of mercury at the observed temperature gives
the volume of the gas in cubic centimeters.

If it is desired to remove any constituent of the gas by absorption,
a pipette B, containing the appropriate reagent, is attached to the
measuring apparatus. All the air in the connecting tube is expelled
by pouring mercury into the funnel and turning the stop-cocks
<•' and c so that the mercury flows out through c. A little more
than enough mercury to expel the gas in the vessel a is poured into b.
The small quantity of air which is confined in the tube connecting b
with the stop-cock is removed by allowing a few drops of mercury
to run out through b. Then a and b are placed in communication.
The stop-cocks c and e are turned so that the gas may pass into the
pipette, the mercury which filled the connecting tube passes into the
absorbing reagent and unites with that which is already at the
bottom of the pipette. The transfer is facilitated by the pump e.
After absorption the residual volume is measured in the same way
that the original volume was measured, a is completely filled with
mercury from the upper to the lower stop-cock, and all the mercury
in b is allowed to run out ; the gas is then drawn back into the
measuring apparatus, the last portion remaining in the connecting
tube being displaced, by means of mercury from the funnel. The
volume is then determined as before.

The calculation of the results of an analysis is very simple. If
the temperature and pressure remain the same during an analysis, as
is frequently the case, then the weights of mercury obtained are in
direct proportion to the gas volumes, and the percentage composition
is at once obtained by a simple proportion.

N N

546 VOLUMETRIC ANALYSIS. § 99.

If the temperature and pressure are different when, the
measurements are made, it is necessary to reduce the volumes to
0° and 760 m.m. The following formula is then used : —

-
~

D (1+ 0-00367 x^) 760'
in which

W — weight of mercury obtained (in grams),
D = specific gravity of mercury at t°,

t == temperature at which the gas is measured,
H= height of the barometer,
h = tension of aqueous vapour,
T'' = reduced gas volume (in cubic centimeters).
In all the measurements made with the apparatus the gas is
saturated with aqueous vapour, because it comes in contact with
the water in the manometer //.

The following experiments were made to test the accuracy of the
instrument. A quantity of air was drawn into the measuring bulb
and its volume determined. The air was then transferred to an
absorption pipette which contained only mercury and no reagent.
It was then brought back again into the measuring apparatus and
its volume redetermined. The following results were obtained : —

Volume at 0°— 763 in. in.
Volume of air taken ... ... ... 57'55S c.c.

„ after first transfer ... ... 57'567

„ „ second transfer ... ... 57'570

II..

At 0°— 760 m.m.
Volume taken ... ... ... ... 93'216 c.c.

after transferring 93'229

III.

At 0°— 760 m.m.

Volume taken ... ... ... ... 133-473 c.c.

after transferring ... 133'490

IV.

At 0°— 760 m.m.
Volume taken ... ... ... ... 92'275 c.c.

„ after transferring ... ... 92'260

At 0°— 760 in. in.
Volume taken ... ... ... 109'025 c.c.

„ after transferring ... ... 109'020

VI.

At 0s — 750 m.m.
Volume taken ... ... ... ... 103'970 c.c.

after first transfer ... ... 103'955

„ „ second transfer ... ... 103*980

The apparatus was also tested by making analyses of atmospheric
air. It has been shown both by Winkler and Hempel that the
composition of the air varies from day to day. This variation is

§ 100.

SIMPLER METHODS OF GAS ANALYSIS.

547

sometimes as much as 0*5 per cent. The causes which produce
these fluctuations in the composition of the atmosphere are at
present but imperfectly understood. It is therefore desirable to
have some simple instrument by means of which the composition
of the air may be determined rapidly and yet with great accuracy.
The following analyses show that the apparatus here described
is well adapted to this purpose. The reagent used to absorb the
oxygen and carbon dioxide was an alkaline solution of pyrogallol,
prepared by mixing one volume of a 25 per cent, solution of
pyrogallol with six volumes of a GO per cent, solution of potassic
hydrate.

Analysis of Air taTcen from the Laboratory.

Air taken 1738'53

Vol. of nitrogen 1377'62

1376-40

743-37
74337
743-55

15-8
15-8
15-75

Per cent, of O aud CO'2, 20'765.

"Per cent.
V 0+CO,'.

116-435 c.c.
92-264. 20-760
92-255 20-771

Vol. of air 170S'01

nitrogen 1356'04

II.

748-08
74733

15-0
15-2

Per cent.

v o+co-'.

11 5-545 C.C.
91-564 20-755

Per cent, of O and CO2 found, 20755.

The following analyses were made with a sample of atmospheric air
collected on a subsequent day : —

Vol. of air 1704'81

„ nitrogen 1348'33

1344-71

H
754-92

754-78
755-92

12'2
12-08
11-7

Per cent.
V 0+CO,'.

117:814 c.c.
93-216 20-877
93-229 20-868

Per cent, of O and CO-, 20'872.

Vol. of air 1669*39

„ nitrogen 1323'24

1322-38

II.

756-30
755-49
755-30

10-15
10-05

10-00

Per cent, of O and CO2, 20'86G.

Per cent.

V O+CO-1.

116-584 C.C.
92-260 20-863
92-252 20*870

The apparatus described in the preceding pages was made for the author,
ost excellent manner, by Mr. Emil Griener, 79, Nassau Street, New York.

in most exc

SIMPLER METHODS OF GAS ANALYSIS.

§ 100. ALL the sets of apparatus previously described are adapted
to secure the greatest amount of accuracy, regardless of speed or the
time occupied in carrying out the various intricate processes involved.

For industrial and technical purposes the demand for something
requiring less time and care, even at the sacrifice of some accuracy,
has been met by a large number of designs for apparatus of a
simpler class, among which may be mentioned those of Orsat,

XTNIVERSITT

548 VOLUMETRIC ANALYSIS. § 100.

Bunte, Wink el, Hempel, Stead, Lunge, etc. Many of these
are arranged to suit the convenience of special industries, and will
not be described here.

The most useful apparatus for general purposes is either that of
Hempel or Lunge, both of which will be shortly described.
Fuller details as to these and other special kinds of apparatus are
contained in Winkler's Handbook of Technical Gas Analysis,
translated by Lunge.'""

The general principles upon which these various sets of apparatus
are based, and the calculation of results, are the same as have been
described in preceding pages ; and of course due regard must be
had to tolerable equality of temperature and pressure, and the effects
of cold or warm draughts of air upon the apparatus whilst the
manipulations are carried on. If the operator is not already
familiar with methods of gas analysis, a study of the foregoing
sections will be of great assistance in manipulating the apparatus
now to be described.

Simple Titration of Gases. — Many instances occur in which an
absorbable gas can be passed through a solution of known standard
in excess, and the measure of the gas being known either by
emptying an aspirator of water containing a known volume, or by
the use of a gas-meter. The amount of gas absorbed may be found
by titration of the standard absorbent residually. Such instances
occur in the exit gases of vitriol and chlorine chambers. In the case
of vitriol exits the gases are drawn through a standard solution of
soda or other alkali contained in T odd's absorption tubes or some
similar arrangement, to which is attached a vessel containing
a known volume, say exactly TV of a cubic foot of water. A tap
is fixed at the bottom of this vessel, so that when all is tightly
fitted and the tap partially opened, a small flow of water is
induced, which draws the gases through the absorbent. When the
aspirator is empty the flow of gases ceases, and of course the volume
of water so run out represents that of the gases passed.

Another way of measuring the gases is to use an india-rubber
vessel, which can be compressed by the hand, known as a finger-
pump. The volume contents being known by measurement with
water or air, the aspirations made by it may be calculated ; the
aspirated gases are then drawn slowly through the absorbent liquid.
In the case of chlorine exits the gases are passed through a solution
of potassic iodide in excess, and the amount of liberated iodine
subsequently found by titration with standard sodic arsenite. A
most convenient vessel is the revolving double glass aspirator,
known as Dancer's or Muencke's.

The standard solutions used in these cases are generally so
arranged as to avoid calculations, and the result found for legal
purposes in England is given in grains per cubic foot, in order to

* Van Voorst, 1885.

§ TOO. NORMAL SOLUTIONS FOR GAS ANALYSIS. 549

comply '\vith the conditions of the Noxious Vapours Act, which
enjoins that not more than 4 grains of SO3, or 2^ grains of Cl, in
one cubic foot shall be allowed to pass into the atmosphere.

Sometimes a gas may be estimated by the reaction which takes
place when brought in contact with a chemical absorbent, such as
the formation of a precipitate, or the change of colour AArhich it
produces in an indicator. The gas in this case can be measured
by a graduated aspirator, the flow of which is stopped when the
peculiar reaction ceases or is manifested.

Normal Solutions for Gas Analysis. — In the titration of gases by
these methods, particularly on the Continent, the custom is to use
special normal solutions, 1 c.c. of which represents 1 c.c. of the
absorbable gas in a dry condition, and at 760 m.m. pressure and
0°C. temperature. These solutions must not be confounded with
the usual normal solutions used in volumetric analysis of liquids or
solids. For instance, a normal gas solution for chlorine Avould be
made by dissolving 4*4288 gm. of As203, with a feAv grams of sodic
carbonate to the liter, and a corresponding solution of iodine
containing 11 '3396 gm. per liter, in order that 1 c.c. of either
should correspond to 1 c.c. of chlorine gas. 1 c.c. of the same
iodine solution would also represent 1 c.c. of dry SO2, and so on.

A very convenient bottle for the titration of certain gases is
adopted by Hesse. It is made in a conical form, like an
Erlenmeyer's flask, and has a mark in the short neck, down to
which is exactly fitted a caoutchouc stopper having two holes,
which will either admit the spit of a burette or pipette, or may be
securely closed by solid glass rods. The exact contents of the vessel
up to the stopper is ascertained, and a conATenient size is about 500
or 600 c.c. The exact volume is marked upon the vessel.

In the case of gases not affected by Avater, the bottle is filled Avith
that liquid and a portion displaced by the gas, and the stopper Avith
its closed holes inserted. If water cannot be used, the gas is dra\vn
into the empty bottle by means of tubes Avith an elastic pump.
The absorbable constituent of the gas is then estimated Avith an
excess of the standard solution run in from a pipette or burette.
During this a volume of the gas escapes equal to the volume of
standard solution added, Avhich must of course be deducted from
the contents of the absorbing vessel. The gas and liquid are left to
react w.itli gentle shaking until complete. The excess of standard
solution is then found residually by another corresponding standard
solution; and in the case of using gas normal solutions, the difference
found corresponds to the volume of the absorbed constituent of the
gas in c.c. ; and from this, and from the total volume of gas employed,
may be calculated the percentage, alloAving for the correction men-
tioned. This arrangement may be used for CO2 in air, using normal
gas baric hydrate and a corresponding normal gas oxalic acid with
phenolphthalein. The normal oxalic acid should contain 5*6314 gm.

550

VOLUMETRIC ANALYSIS.

§ 100.

per liter, in order that 1 c,e. may represent 1 c.c. of CO2. The baryta
solution must correspond, or its relation thereto found by blank
experiment at the time. The arrangement is also available for HC1
in gases, using a normal gas silver solution containing 4*8233 gm.
Ag per liter, as absorbent, with a corresponding solution of
thiocyanate (§ 43) and ferric indicator ; or the HC1 may be absorbed
"by potash, then acidified with HXO3,
and the titration carried out by the

same process ; or again,

an alkaline

earbonate may be used, and the titration
made with a normal gas silver solution
using the chromate indicator (§41, 2&).

Hem pel's Gas Burette.— This consists
ef two tubes of glass on feet, one of which
is graduated to 100 c.c. in i c.c. (the
burette proper), and the other plain (the
level tube). They are connected at the
feet by an elastic tube, much in the
same way as Lunge's nitrometer. The
arrangement is shown in fig. 99.

The illustration shows the burette with
three-way stop-cock at bottom, which is
necessary in the case of gases soluble in
water, or where any of the constituents
are affected thereby. If this is not the
case, a burette without such stop-cock
is substituted (fig. 100). The elastic tube
should not be in one piece, but con-
nected in the middle by a shoit length
of glass tube to admit of ready dis-
connection.

Fig. 100 will illustrate not only the original He m pel burette
with level tube, but also the method of connection with the gas
pipette, and also the way in which the elastic tube is joined by the
intervening glass tube.*

Hempel, with great ingenuity, has devised special pipettes to
Be used in connection with the burette, and which render the
instrument very serviceable for general gas analysis. The pipette
shown in fig. 100 is known as the simple absorption pipette, and
serves for submitting the gas originally in the burette to the action
of some special absorbent. With a series of these pipettes the gas

* Tlie same chemist has since designed a gas burette which has the advantage of
being unaffected by the fluctuating temperature and pressure of the atmosphere. This
fs effected by connecting the measuring apparatus with a space free from air, but
saturated with aqueous vapour. A figure showing the arrangement is given in
C. N. Ivi. 264. These simpler forms of gas apparatus in great variety, including variovis
forms of the nitrometer, are kept in stock by Messrs. Townson and Mercer, 89 Bishops-
g-ate Street Within, London, E.G., and probably by most of the dealers in apparatus in
the kingdom.

100.

HEMPEL'S BURETTE AND PIPETTES.

551

is submitted to the action of special absorbents, one after another,
until the entire composition is ascertained. The connections must
in all cases be made of best stout rubber, and bound with wire.

Fig. 100.

Collection and measurement of the Gas over Water. — Both tubes
are filled completely with water (preferably already saturated
mechanically with the gas), care being taken that all air is driven
out of the elastic tube. The clip is then closed at the top of the
burette, and the bulk of the water poured out of the level tube, the
elastic tube being pinched meanwhile with the finger and thumb to
prevent air entering the burette. The latter is then connected by
a smal] glass tube with the source of the gas to be examined, when,

552

VOLUMETRIC ANALYSIS.

100.

by lowering the level tube, the gas flows in and displaces the water
from the burette into the level tube. The pressure is then regulated
by raising or lowering either of the tubes until both are level, when
the volume of gas is read off. It is convenient of course to take
exactly 100 c.c. of gas to save calculation.

Collection and measurement of the Gas without Water. — In this
case the three-way tap burette (fig. 99) is dried thoroughly by first
washing with alcohol, then ether, and drawing air through it. The
three-way tap is then closed, the upper tube connected with the gas
supply, and the burette filled either by the pressure of the gas, or
by using a small pump attached to the three-way cock to draw out
the air and fill the burette with the gas. When full the taps are-
turned off, and connection made with the level tube, which is then
filled with water, the tap opened so that the water may flow into
the burette and absorb the soluble gases present. As the burette
holds exactly 100 c.c. between the three-way tap and the upper clip,,
the percentage of soluble gas is shown directly on the graduation.

The method of Absorption. — In the case of the simple pipette
fig. 100, a is filled with the absorbing liquid, which reaches into the
syphon bend of the capillary tube ; the bulb b remains nearly
empty. In order to fill the instrument, the liquid is poured into /^
and the air sucked out of a by the capillary tube. It is convenient
to keep a number of these pipettes filled with various absorbents,,
well corked, and labelled.

Another pipette of similar char-
acter is shown in fig. 101, and i&
adapted for solid reagents, such as
stick phosphorus in water. The
instrument has an opening at the
bottom, which can be closed with
a caoutchouc stopper. This pipette
is also used for absorbing CO2 by
filling it with plugs of wire gauze
and caustic potash solution, so as
to expose a large active surface
when the liquid is displaced by
the gas.

To make an absorption, the
capillary U-tube is connected with
the burette containing the mea-
sured gas by a small capillary

Fig. 101.

tube (fig. 101), the pinchcock of course being open, then by raisin
the level tube, the gas is driven over into the cylindrical bulb,,
where it displaces a portion of the liquid into the globular bulb.
When the whole of the gas is transferred, the pinchcock is closed f
and the absorption promoted by shaking the gas with the reagent.
When the action is ended, communication with the burette is

§ 100. HEMPEL'S PIPETTES 553

restored, and the gas syphoned back with the level tube into the
burette to be measured.

The double absorption Pipette shown in fig. 102 is of great utility
in preserving absorbents which would be acted on by the air, such
for instance as alkaline pyrogallol, cuprous chloride, etc. The bulb
next the syphon tube is filled with the absorbent, the next is empty,
the third contains water, and the fourth is empty. When the gas
is passed in, the intermediate water passes on to the last bulb
to make room for the gas, thus shutting off all contact with the
atmosphere, except the small amount in the second bulb. An
arrangement is also made for the use of solid reagents, by sub-
stituting for the globe next the U capillary tube a cylindrical bulb
as in fig. 101.

Hydrogen Pipette. — The hydrogen gas necessary for explosions
or combustions is produced from a hollow rod of zinc fixed over
a glass rod passed through the rubber stopper (fig. 101). The bulb
being filled with dilute acid, gas is generated, and as it accumulates
the acid is driven into the next bulb and the action ceases.

Explosion Pipette. — Another arrangement provides for explosions
by the introduction into a thicker bulb, measured volumes of the
gas, of air, and of hydrogen. The bulb being shut off with
a stop-cock, a spark is passed through wires sealed into the upper
portion of the bulb.

Pipette with Capillary Combustion Tube. — This simple arrange-
ment consists of a short glass capillary tube bent at each end in
a right angle, into which an asbestos fibre impregnated with finely
divided palladium is placed, so as to allow of the passage of the gas.'"'
The gas being mixed with a definite volume of air in the burette,
and the measure ascertained (not more. than 25 c.c. of gas 'and 60
or 70 c.c. of air), the asbestos tube is heated gently with a small gas
flame or spirit lamp, and the pinchcocks being opened, the mixture
is slowly passed through the asbestos and back again, the operation
being repeated so long as any combustible gas remains. Xo

* To prepare palladium asbestos, dissolve about 1 gin. palladium in aqua regia,
evaporate to dryness on water bath to expel all acid. Dissolve in a very small quantity
of water, and add 5 or 6 c.c. of saturated solution of sodic formate, then sodic carbonate
until strongly alkaline. Introduce into the liquid about 1 gin. soft, long-fibred asbestos,
which should absorb the whole liquid. The fibre is then dried at a gentle heat, and
finally in the water bath till perfectly dry • it is then soaked in a little warm water, put
into a glass funnel, and all adhering salts washed out carefully without disturbing the
palladium deposit. The asbestos so prepared contains about 50 per cent. Pd, and in
a perfectly dry state is capable of causing the combination of H and O at ordinary
temperature, but when used in the capillary tube it is preferable to use heat as mentioned.
The capillary combustion tubes are about 1 m.m. bore and 5 m.m. outside diameter,
with a length of abotit 15 c.m. The fibre is placed into them before bending the angles
as follows : — Lay a few loose fibres, about 4 c.m. long, side by side on smooth filter

Eaper, moisten with a drop or two of water, then by sliding the finger over them twisted
ito a kind of thread about the thickness cf darning cotton. The thread is taken
carefully up with pincers and dropped into the tube held vertically, then by aid of
water and gentle shaking moved into position in the middle of the tube. The tube is
then dried in a warm place, and finally the ends bent at right angle for a length of 3| to
4 c.m. Platinum asbestos may be prepared in the same way, using, however, only from
half to one-fourth the qiiantity of metal.

554

VOLUMETKIC ANALYSIS.

100.

explosion need be feared. The residue of gas ultimately obtained
is then measured, and the contraction found ; from this the volume
of gas burned is ascertained either directly, or by the previous
removal of CO2 formed by the combustion with the potash pipette.
H is very easily burned, CO less easily. Ethylene, benzine, and
acetylene require a greater heat and longer time. CH4 is not
affected by the method, even though mixed with a large excess of
combustible gases.

Fig. 102.

In order to illustrate the working of the whole set of apparatus, the
analysis of a mixture containing most or all of the gases likely to be met
with in actual testing is given from a paper contributed by Dr. W. Bott
(J. S. C. I. iv. 163). The mixture of gases consists of CO-, O, CO, C-H4,
CH4, H and N. A sample of this gas— say 100 c.c.— is collected and
measured in the gas burette. The CO"2 is next absorbed by passing the gas
into a pipette (fig. 100) containing a solution of 1 part of KHO in
2 parts of water. To ensure a more rapid absorption, the bulb shown
in fig. 101 containing the caustic potash may be partly filled with plugs
of wire gauze. The absorption of the CO- is almost instantaneous. It is
only necessary to pass the gas into the apparatus and syphon it back again
to be measured. The contraction produced gives directly the percentage
of CO'-, since 100 c.c. were used at starting. The remaining gas contains
O, CO, H, C2H4, CH4, N. The oxygen is next absorbed. This may be
effected in two ways — by means of moist phosphorus or by an alkaline
solution of pyrogallic acid. The former method is by far the more elegant of
the two, but not universally applicable. The absorption is done in a pipette
(fig. 101), the corked bulb of which is filled with thin sticks of yellow phosphorus
surrounded by water. The gas to be tested is introduced in the usual manner,
and by displacing the water comes into contact with the moist surface of the
phosphorus, which speedily absorbs all the oxygen from it. The absorption
proceeds best at about 15—20° C., and is complete in ten minutes. The small
quantity of P2O3 formed by the absorption dissolves in the water present, and
thus the surface of the phosphorus always remains bright and active. This
neat and accurate method is not however universally applicable ; the following
are the conditions under which it can be used : — The oxygen in the gas must

§ 100. HEMPEL'S METHODS OF GAS ANALYSIS. 555

not be more tluiu 50 per cent., and the gas must be free from ammonia, C-II4
and other hydrocarbons, vapour of alcohol, ether and essential oils. In the
instance chosen, the phosphorus method would hence not be applicable, as the
mixture contains C'2H4 ; therefore pyrogallic acid must be used. The absorption
is carried out in the compound absorption pipette (fig. 102), the bulb of which
is completely filled with an alkaline solution of pyrogallol made by dissolving
1 part (by volume) of a 25 per cent, pyrogallic acid solution in 6 parts of
a 60 per cent, solution of caustic potash. The absorption is complete in about
live minutes, but mavr be hastened by shaking. The remainder of the gas
now contains C-H4, CO, CH4, H, N, arid the next step is to absorb the C-H4 by
means of fuming SO3, the CH4 being subsequently determined by explosion.
In choosing the latter method a portion, say half, of the residual gas is taken
for the estimation of hydrogen. The absorption of the hydrogen is based on
the fact that palladium black is capable of completely burning hydrogen
when mixed with excess of air, and slowly passed over the metal at the
ordinarjr temperature. About 1 £ gm. of palladium black are placed in a small
U-tube plunged into a small beaker of cold water, and the gas, mixed with an
excess of air (which, of course, must be accurately measured), is passed slowly
through the tube two or three times,* the tube at the time being connected
with an ordinary absorption pipette filled with water or else with the KOH
pipette, which in this case, of course, simply serves as a kind of receiver.
.Finally the gas is syphoned back into the burette and measured — two-thirds
of the contraction correspond to the amount of H originally present in the
mixture of gas and air. The CH4 is not attacked by ordinary '30 per cent. SO3
Xordhausen acid during the absorption of the C'2H4. The acid is contained
in an absorption pipette (fig. 101), the bulb of which is filled with pieces of
broken glass so as to offer a larger absorbing surface to the gas. The
absorption is complete in a few minutes, but the remaining gas previous to
measuring should be passed into the KOH pipette and back again, so as to
free it from fumes of SO3. Residual gas : CO, CH4, H, N. The CO is next
absorbed by means of an ammoniacal solution of cuprous chloride in a com-
pound absorption pipette. The gas has to be shaken with the absorbent for
about three minutes. It must be borne in mind that Cu2Cl2 solution also
absorbs oxygen, and, according to Hempel, considerable quantities of C'2H4,
hence these gases must be removed previously. Residue : CH.4, H, N. Both
CH4 and II may now be estimated either by exploding with an excess of air
in the explosion pipette and measuring (1) the contraction produced, and (2)
the amount of CO" formed (by means of the KOH pipette) ; or, according to
Hempel, absorb the hydrogen first of all as described above — provided the
U-tube be kept well cooled with water, inasmuch as that at about 200° C.
a mixture of air and CH4 is also acted upon by palladium. The presence of
CO, vapours of alcohol, benzine and hydrochloric acid also interfere with
the absorption by palladium.

The palladium may be used for many consecutive experiments, but must
be kept as dry as possible. After it has been used for several absorptions it
may be regenerated by plunging the tube into hot water and passing
a current of dry air through it.

Having estimated the hydrogen, the CH4 in the remaining portion of the
gas has to be determined. This contains CH4, N and H, the amount of the
latter being kno vvn from the previous experiment. The gas is mixed with the
requisite quantity of air and hydrogen, introduced into the explosion pipette
and fired by means of a spark. The water resulting from the combustion
Condenses in the bulb of the pipette, whilst the CO'2 formed is absorbed by the
KOH solution present. Hence the total contraction produced corresponds to:

a. The hydrogen present in the original gas + i its vol. of O (the quantity
requisite for complete combustion).

*Instead of this the H may le binned in the tube containing the palladium asbestos
fib.-e previously described.

556

VOLUMETRIC ANALYSIS.

§ 100.

I. The known quantity of hydrogen added + i its vol. of O.
c. The CEL4 present + 2 vols. of O requisite for its combustion.
CH4 + O4 = (CO2 + 2H2O)

2 4 disappears.

Since a and b are known, or can be readily calculated from the previous datar
by subtracting (a + k) from the total contraction it is possible to obtain C—
(a + b) = c contraction due to CH4 alone, and one-third of this is equal to the
volume of CH4 present, as will be readily seen from the above equation.
The remaining nitrogen is estimated by difference.

storing- and
an arrange-

In work-
gas to E,

Improved arrangement of Hempel's Pipettes for
using- absorbents. — P. P. Beds on has designed
ment of pipettes which he uses in connection with a Dittmar's
measuring apparatus, hut which may of course be used with
other forms of gas apparatus, by suitable connections. The
pipettes are shown in fig. 103, and their use may be described
as follows : — A capillary tube with a three-way cock A is soldered

to the Hem pel pipette— the
capillary is drawn out and bent
so as to pass into the mercury
trough. The tap A can be
/D placed in connection with C, to
which is attached a movable
mercury reservoir D.
ing, e.s/., transferring
the absorbent fills E and the
capillary of tap A. By raising
D the vessel C and capillary B
are entirely filled with mercury.
B, of course, is immersed in
the mercury trough. Having
filled B with mercury, the test
tube containing the gas to be
examined is brought over the
end of B and some gas drawn
into C by depressing D. The
tap is then turned to put the
tube in connection with E, and
the gas forced into E by
By raising and lowering the tube

the gas can be brought into intimate contact with the absorbent
and absorption thus promoted. To bring all the gas into E, D is
again used and the remainder of gas drawn into C by depressing D ;
then by turning the tap round the gas from C can be forced
into E ; the tap is then turned so as to put the capillary and
E in connection, and the gas flows into E with a small portion
in capillary B, retained by the column cf mercury filling the
bent limb.

103.

depressing the tube in trough.

§101. . THE NITROMETER. 557

The gas may be left thus for some hours ; and to transfer it to
the tube, C and E are placed in connection by suitably turning the
tap ; then by depressing 1) some gas is drawn into C and the tap
turned so as to put C and the tube in connection.

By carefully raising D the mercury is washed out of B and some
of the gas passes into the tube. With B clear of mercury and
filled with gas, the tube and E are placed in connection and the
gas flows out of E into the tube. When the liquid from E has
risen so as to fill the vessel up to the tap (the capillary of the tap
being also filled), the tap is turned to put C and B in connection ;
then by raising D all gas is washed out of C and capillary into the
tube used for its collection and transferred to the measuring tube.

Professor Beds on also attaches to the measuring apparatus
a vessel containing a known volume of air at known temperature
and pressure, as recommended by Lunge, so as to dispense with
the otherwise necessary corrections. Further details as to the
various uses to which II em pel's gas pipettes and other simple
forms of gas apparatus may be adapted, will be found in Hem pel's
Gas Analysis (Macmillan, 1892).

THE NITROMETER.

§ 101. THIS instrument has been incidentally alluded to in § 70
(page 262) as being useful for the estimation of nitric acid 'in the
form of nitric oxide. It was indeed for this purpose that the
instrument was originally contrived, more especially for ascertaining
the proportion of nitrogen acids in vitriol.

The instrument has been found extremely useful also for general
technical gas analysis, and for the rapid testing of such substances
as manganese peroxide, hydrogen peroxide, bleaching powder, urea,
etc. The apparatus in its simplest form is shown in fig. 104, and
consists of a graduated measuring tube fitted at the top with
a three-way stop-cock, and a glass cup or funnel ; the graduation
extends from the tap downwards to 50 c.c. usually, and is divided
into -~ c.c. The plain tube, known as the pressure or level tube,
is about the same size as the burette, and is connected with the
latter by means of stout elastic tubing bound securely with wire.
Both tubes are held in clamps on a stand, and it is advisable to fix
the burette itself into a strong spring clamp, so that it may be
removed and replaced quickly.

One great advantage over many other kinds of technical gas
apparatus which pertains to this instrument is, that it is adapted
for the use of mercury, thus insuring more accurate measurements,
and enabling gases soluble in water, etc., to be examined.

Another form of the same instrument is designed by Lunge
for the estimation of the nitric acid in saltpetre and nitrate of
soda, where a larger volume of nitric oxide is dealt with than
occurs in many other cases. In this instrument a bulb is blown
on. the burette just below the tap, and the volume contents of this

558

VOLUMETRIC ANALYSIS.

§ 101.

bulb being found, the graduation showing its contents begins on the
tube at the point where the bulb ends, and thence to the bottom ;
the level tube also has a bulb at bottom to contain the mercury
displaced from the burette. Illustrations of this form of nitrometer
will be found further on.

The following description of the
manipulation required for the estima-
tion of nitrogen acids in vitriol applies
to the ordinary nitrometer, and applies
equally to the estimation of nitrates
in water residues and the like (see
page 468) : —

The burette a is filled with mercury in
such quantity that, on raising b and keeping
the tap open to the burette, the mercury
stands quite in the tuphole, and about tuo
inches up the tube I. The tap is now closed
completely, and from O'o to 5 c.c. of the
nitrous vitriol (according to strength) poured
into the cup. b is then lowered and the tap
cautiously opened to the burette, and shut
quickly when all the acid except a mere
drop has run in, carefully avoiding the
passage of any air. 3 c.c. of strong pure
H-SO4 are then placed in the cup and drawn
in as before, then a further 2 or 3 c.c. of
acid to rinse all traces of the sample out of
the cup. a is then taken out of its clamp,
and the evolution of gas started by inclining
itseveral times almost toahorizontal position
and suddenly righting it again, so that the
mercury and acid are well mixed and shaken
for a minute or two, until no further gas is
evolved. The tubes are so placed that the
mercury in b is as much higher than that in
a as is required to balance the acid in a ;
this takes about one measure of mercury fur
65 measures of acid. "When the gas has
assumed the temperature of the room, and
all froth subsided, the volume is read off,
and also the temperature and pressure from
a thermometer and barometer near the place
of operation. The level should be checked
by opening the tap, when the mercury level
ought not to change. If it rises, too much
pressure has been given, and the reading
must be increased a trifle. If it sinks, thy
reversa. A good plan is to put a little acid
into the cup before opening the tap : this
will be drawn in if pressure is too low, or
blown up if too high. These indications Avill cerve for a correct repetition
of the experiment.

To empty the apparatus ready for another trial, lower a and open the tap,
then raise b so as to force both gas and acid into the cup ; by opening the tap
then outwards, the bulk of the acid can be collected in a beaker, the last

10.1.

THE NITROMETER.

5591

drops being wiped out with blotting-paper. It is hardly necessary to say that
the tap must be thoroughly tight, and kept so by the use of a little vaseline,
taking care that none gets into the bore-hole.

The calculations for nitrogen are given on page 262.

It is evident that the nitrometer can be made to replace Hempel's
burette if so required, by attaching to the side opening of the three-
way tap the various pipettes previously described, or smaller pipettes
of the same kind to be used with mercury, as described by Lunge-
(Bericlite, xiv. 14, 92),

The instrument may also be very well employed for collecting,
measuring, and analyzing the gases dissolved in water or other
liquids. An illustration of this method is given by Lunge and
Schmidt (Z. a. C. xxv. 309) in the examination of a sample of
water from the hot spring at Leuk in Switzerland.

Pig. 306.

The determination of the dissolved gases was made in the nitre-
meter, arranged as shown in figs. 105 and 106 : —

The flask A is complete!}' filled with the water ; an indiarubber plug with
a capillary tube («) passing through it is then inserted in the flask, and the
tube is thereby completely filled with water. The whole is then weighed,
and the difference between this and the weight of the empty flask and tube
gives the amount of water taken. The end of the capillary tube is then
connected to the side tube of the nitrometer by the tube b. The nitrometer
is then completely filled with mercury, and when the tubes are quiet, the flask
and measuring tube of the nitrometer are quickly placed in connection, with-
out the introduction of the slightest trace of air. The water in the flask is-

560

VOLUMETRIC ANALYSIS.

101.

then slowly heated to boiling. Some water as well as the dissolved gases
collect in the measuring tube of the nitrometer. The tube N of the nitro-
meter should be lowered in order that the boiling may take place under
reduced pressure. After boiling for five to ten minutes, the stop-cock is
quickly turned through 180°, so that the flask is placed in combination with
the cup B containing mercury, and the flame removed. Since the mercury

Tig. 107.

Fig. 109.

stands lower in N than in M, it is not possible for any loss of gas to take
place at the moment of turning the tap. It is also impossible for any gas or
steam to escape through the mercury cup, since the pressure is inward.
A small bubble of gas always remains under the stopper; this is brought into
M by lowering the tube N as much as possible, and then turning the stop-

§ 101. LUNGE'S IMPROVED NITROMETER. 561

cock so that the flask and measuring tube are again placed in connection, and
when the bubble has passed over, quickly reversing the tap again.

When the whole of the gas is collected in the nitrometer, it is connected
with a second instrument 0 P, quite full of mercury. The gas is then
transferred by placing the tap in such a position that it is closed in all
directions, and the tube M is heated by passing steam through the tube B.
When it is quite hot the tube N is lowered, causing the water in M to boil,
in order to expel every trace of dissolved gas. The taps are then placed in
connection and the gas passes over. It can then be cooled, measured, and
submitted to analysis. Two experiments gave 505 grn. water taken, gas
evolved 5'OG c.c.,= 10'02 per 1000 gm. ; 502 gm. water taken, gas evolved
4'94 c.c.,^9'84 per 1000 gm.

Lunge's Improved Nitrometer for the Gas-Volumetric Analyses
of Permanganate, Chloride of Lime, Manganese, Peroxide, etc.—

Lunge in describing this instrument (/. C. S. I. ix. 21) says: —

" In a paper published in the ChemiscJie Industrie, 1885, 161, I described
the manifold uses to which the nitrometer can be put as an apparatus for
gas analysis proper, as an absorptiometer, and especially for gas-volumetric
analyses. To fit it for the last-mentioned object, I added to it a flask,
provided with an inner tube fused on to its bottom, and suspended from
the side tube of the nitrometer, as shown in fig. 107, which at the same
time exhibits the Greiner and Priedrich's patent tap. This shows
how any ordinary nitrometer, such as are now found in most chemical
laboratories, can be applied to the before-mentioned uses. Where, however,
the methods concerned are to be employed not merely occasionally, but
regularly, it will be preferable to get a nitrometer specially adapted to this
use, of which figs. 108 and 109 show various forms. They liave no cup at the
top, which is quite unnecessary for this purpose, but merely a short outlet
tube for air. Fig. 108 shows an instrument provided with one of the new
patent taps, which are certainty very handy, and cause a much smaller
number of spoiled tests than the ordinary three-way tap, as shown in fig. 109,
which at the same time exhibits the form of nitrometer intended for large
quantities of gas, the upper part being widened into a bulb, below which the
graduation begins with either 60 or 100 c.c., ending at 100 or 140 c.c.
respectively. There are also various shapes of flasks shown in these
instruments, but it is unnecessary to say that these, as well as the bulb
arrangements, can be applied to any other form of the instrument. The
nitrometers used for gas-volumetric analyses are best graduated in such
manner that the zero point is about a centimeter below the tap, whilst
ordinary nitrometers have their zero point at the tap itself. I will say at
once that for all estimations of oxygen in permanganate, bleach or manganese
(see pages 123, 105), it is quite unnecessary to employ mercury for filling the
instruments, since identical results are obtained with ordinary tap water;
but it is decidedly advisable to place this instrument, like any ordinary
nitrometer or any other apparatus in which gases are to be measured, in
a room where there are as few changes of temperature by cold draughts or
gas-burners and so forth as possible.

" It may be as well to give here a general description of the mode of
procedure for manipulating gas-volumetric analysis with the nitrometer,
common to all analyses according to this method. Pill the nitrometer with
water or mercury by raising the level tube till the level of the liquid in the
graduated tube is at zero (in the case of instruments bearing the zero-mark
a little below the tap, as in figs. 108 and 109), or at TO c.c. (in the case of
ordinary nitrometers beginning their graduation at the tap itself). It is
unnecessary to say that in the latter case all readings must be diminished by
1 c.c. Close the glass tap. Put the substance to be tested into the outer
space of the flask, together with any other reagent apart from the H2O2 (in the

O o

562 VOLUMETRIC ANALYSIS. § 101.

case of bleaching-powder nothing but the bleach liquor, in that of perman-
ganate the 30 c.c. of sulphuric acid, etc.). Now put the H-O2 into the inner
tube of the flask, after having, in the case of testing for chlorine, made it
alkaline in the previously described way. Put the india-rubber cork, still
hanging from the tap, on to the flask, without warming the latter as above
described. As this produces a compression of the air within the flask,
remove this by taking out the key of the tap in figs. ]07, 108, or 109,
turning it for a moment so as to communicate with the short outlet tube.
Now turn the tap back, mix the liquids by inclining the flask, shake up and
alloAv the action to proceed. As the gas passes over into the graduated tube,
lower the level tube, so as to produce no undue pressure ; at last bring the
liquid in both tubes to an exact level and read off.

" In the case of bleach analysis all the oxygen of the chloride of lime is
given off, together with exactly as much oxygen of the H-O-. The total is
just equal to the volume of chlorine gas which would be given off by the
chloride of lime, and thus immediately represents the French or Gay-Lussac
ehlorometric degrees, of course after reducing the volume to 0° and 700 m.m.
pressure. (The reading of the barometer must be corrected by deducting
the tension, of aqueous vapour for the temperature observed as well as the
expansion of mercury, according to the tables found everywhere.) These
reductions can easily be performed by the tables contained in the " Alkali-
Makers' Pocket-book" (pages 28 to 39), which I had calculated a number of
years ago, just in order to facilitate the use of the nitrometer."

Lunge's Gasvolumeter is an apparatus for dispensing with
seduction calculations in measuring gas volumes (described by
Lunge in Zeitsclirift /. angeic. Chem. 1890, 139 — 144, and here
quoted from J. S. C. I. ix. 547).

In technical gas analysis a considerable amount of time is taken
up by calculations for reducing gas volumes to standard temperature
and pressure, In pure gas analysis the inconvenience is not so
great ; for technical purposes the initial and end temperature and
pressure may be taken as the same, owing to the short duration of
the experiment, and for more accurate purpose " compensators "
have been devised. Where, however, the gas to be measured is
evolved from a weighed quantity of a liquid or solid (so that
volume and weight have finally to be connected) the matter is
different, and readings of thermometer and barometer have' to be
made, and then the necessary calculations are to be gone through.
Tables of reduction have certainly been compiled for reduction of
gases at various temperatures and pressures, but still readings of
thermometer and barometer have to be made, and part of the time
only is saved. To further reduce the time occupied and to render
the technical chemist in this department to a great extent
independent of temperature and atmospheric pressure the present
apparatus has been constructed.

By means of a T-tube, D (fig. 110), and thick-walled rubber tubing,
are connected the three tubes A, B, C. A is for measuring the gas ; it
.nay be any form of nitrometer, a Bunte's burette or other convenient
ourette. B is the " reduction tube," which has at its upper end a spherical
or cylindrical bulb. The volume to the first mark is 100 c.c , the remaining
narrow portion of the tube being calibrated up to 130—140 c.c. in divisions
representing 1^- c.c. This '•' reduction tube " is set once for all at the

101.

LUXGE S GASVOLUMETEE.

beginning of work by observing tliermometer and barometer, calculating the
volume which 100 c.c. of perfectly dry air, measured at 0° C. and 760 m.m.,
would occupy under the existing conditions. This quantity of air is then
introduced, and the tube closed by means of the stop-cock shown, or by
fusing up the inlet (having in place of the inlet tube shown in the figure
a tube of capillary bore) . If it be necessary to measure the gas moist a drop
of water is introduced into this tube, and of course in the calculation
necessary the barometric pressure must be reduced by the vapour tension of
water ; if the gases are to be measured perfectly dry (as, for instance, when
using the nitrometer with sulphuric acid), a drop of sulphuric acid takes the
place of the water.

C is the pressure or levelling tube.
If necessary for the purpose of

regulating the temperature A and B
may be surrounded with water-jackets.
A, B, and C are supported by spring
clamps. It is easily seen that when by

raising C the level of the mercury in

B has been forced up to the mark

100, exactly the amount of pressure is

exerted by C as will compress the gas

in B to its volume under standard

conditions.

In taking a reading A and B must be

levelled andthemercurylevelin B must

have been brought up to 100. The

volume shown on A is then the volume

reduced to standard temperature and

pressure. In cases where the gas is

generated in A itself, or where the gas

Is transferred to A, this is all that

need be done. If, however, the gas is

generated in a side apparatus, as shown

in fig. 110, A and C must first be

levelled and the stop-cock of A then

•closed so that the gas in A is collected

•at atmospheric pressure. After this

reduction may be effected as already

explained.

In nitrogen determinations by

Dumas' method, A contains caustic

potash as well as mercury; this is

compensated by "having on the reduc-
tion tube, B, a mark at a distance

below the 100 mark equal to one-tenth

of the height of the caustic potash

column (sp. gr. of the caustic potash

equals one-tenth sp. gr. of mercury) ;

when taking a reading the mercury in

B must be at 100, and that in A must

be on a level with this new lower mark

of B. Similar allowance may be made

in nitrometric determinations, but the

case is here more difficult, owing to

the variations in the quality and specific

gravity of the sulphuric acid used. It

is better in such cases to liberate the gas in a separate vessel and transfer

subsequently to the burette for reduction and measurement. Pig. Ill

Pig. 110.

O O 2

564

VOLUMETKIC ANALYSIS.

101.

shows a convenient form of apparatus. Of course the working part E, F
need not be graduated. Before beginning the operation the mercury is
made to fill E with the side tube a, which side tube is then capped with
a caoutchouc stopper to prevent escape of the mercury during subsequent
shaking. A, with its side tube e, is also completely filled with mercury.
The substance under examination, and subsequently the acid, are added
through C as usual. To transfer the gas from E to A, the cap b is removed
and a is fitted to e by means of the rubber connection d. F is then raised
and C lowered, the taps are carefully opened, and transference effected until,
the acid in E just fills e.

Fig. 111.

A further saving of time may be effected in works, where the
instrument is to be used for always one and the same object, by
marking on the gas burette or nitrometer the weight in milligrams
corresponding to certain volumes ; this may be done either instead

§ 101.

JAPP S GRAVIYOLUMETER.

565

of or alongside the c.c. divisions; or by using a fixed quantity of
substance, percentages may be marked off directly. For nitrogen
determinations by Dumas' method 1 c.c. of nitrogen under normal
conditions weighs 1/254 m.gm. In the case of azotometric deter-
minations of ammoniacal nitrogen (by sodic hypobromite) the
graduations may be made to represent ammonia. Correction must
he made in graduating, however, for the incompleteness of the
reaction. Tables giving the corrections have been introduced, but
the author has shown (Chem. Ind. 1885, 165) that these may be
•dispensed with, and that it is sufficient to make a correction of 2 '5
per cent. For urea, however, the correction is 9 per cent.

The following table shows substances for which gasometric
methods are used : —

Substance.

Basis to which
Percentages are
Calculated.

Method
Employed.

Gas
Evolved.

1 c.c. of Gas
=m.gm. of Basis,
(Col. II.)

Organic substances

Nitrogen

Dumas'

1-254

Ammonia salts ...

Hypobrmte.

1-285*

?? ?J

Ammonia

1-561*

Urine

Urea

2'952*

; Bone-charcoal, etc.

Carbon dioxide

Decomposed
with HC1

CO2

1-966

Calcic carbonate

CO2

4-468

Pyrolusite
Bleaching powder

Manganese dioxide
Chlorine

By H202

3-882
1-5835

Potassic perman-
ganate . . .

Oxygen

„

G'715

Chili saltpetre ...

Sodic nitrate

Nitrometer

3805

Nitrous bodies ..

N2O3

}»

1-701

HNO3

2-820

Nitric acid 36° B.

5330

•',

Sodic nitrate

3805

Nitroglycerol, dy-
namite, etc

Trinit rogly cerol

3-387

•)

Nitrogen

0-6267

Nitrocellulose, py-
rox}'lin

06267

* The corrections above referred to have here already been made.

Professor Japp (J. C. S. lix. 894) describes a modification of
Lunge's gasvolumeter, by means of which with accurately
graduated ordinary 50 c.c. gas burettes any required single gas
may, without observation of temperature or pressure, and without
calculation, be measured under such conditions that each c.c.
represents a milligram of the gas. The name "gravi volumeter"
is appropriately given to this instrument, and it undoubtedly
possesses this advantage over Lunge's instrument, that it obviates
the necessity of having a number of different gasvolumeters for
different substances, and moreover its manufacture involves no

566

VOLUMETRIC ANALYSIS.

101.

large amount of skill, as the ordinary graduation in c.c. in y1^- or ~
is all that is required.

The apparatus is represented in fig. 112. • It consists of two gas burettes,
of 50 c.c. capacity each, both furnished with obliquely bored taps. One of
these burettes, A, wrhich has a three-way tap, is the gas measuring
tube; the other, B, \vhich need only have a single tap, performs
the function of the regulator in Lunge's gasvolumeter, and may
be termed the "regulator tube." As in Lunge's instrument, both
tubes are moistened internally with a drop of water, in order that the gases
they contain may be saturated with aqueous vapour, and both are connected,
by means of stout, flexible tubing and a "["-piece, with the same movable

Pig. 112.

reservoir of mercury, C. And since, in certain determinations, the level of
the mercury reservoir is considerably below the lower end of the two
burettes, and an inward leakage of air might thus occur at the junctions of
the burettes with the india-rubber tubing, these junctions are surrounded
with pieces of wider india-rubber tubing, D, D, tied round the bottom and
open at the top, and filled with water, so as to form a wrater joint.

The 25 c.c. division of the regulator tube is taken as the starting point in
calculating what may be termed the " gravivolumetric values " of the
different gases to be measured. Thus in the case of nitrogen it is necessary

§ 101. JAPP'S GRAVIVOLUMETEE. 567

to calculate to what volume 25 c.c. of standard dry nitrogen must be
brought in order that 1 c.c. may correspond with 1 m.gm. of the gas ; that
is to say, 25 c.c. of standard dry nitrogen weigh 0'001256 x 25=0'0314 gm. ;
and, therefore, these 31'4 m.gm. must be brought to the volume of 31'4 c.c.
The division 31*4 on the regulator tube is marked N2. Corresponding points
are in like manner determined for the various other gases which it is desired
to measure, and these points are marked O2, CO2, &c., as the case may be, on
the regulator tube. Finally, the thermometer and barometer are read
(a process onl}' necessary once for all in setting the regulator), the volume
which 25 c.c. of standard dry air would occupy if measured moist at the
observed temperature and pressure is calculated, and this calculated volume
of air is admitted at atmospheric temperature and pressure into the regulator
tube and the tap closed. The instrument is now ready for use.

Suppose it is desired to ascertain the weight of a quantit}r of nitrogen
contained in the measuring tube. The mercury reservoir is raised or
lowered until the mercur}r in the regulator tube stand at the nitrogen mark,
31'4, at the same time adjusting the regulator tube itself by raising or
lowering it bodily, so that the mercury level in the measuring tube and the
regulator tube may be the same. Under these circumstances each cubic
centimeter of gas in the measuring tube represents 1 m.gm. of nitrogen. For
since in the regulator tube 25 c.c. of standard dry air have been made to
occupy the volume of 31'4 c.c., and since the gases in the two tubes are
under the same conditions as regards temperature, pressure, and saturation
with aqueous vapour, therefore, in tlie measuring tube, every 25 c.c. of
standard dry nitrogen have also been made to occupy the volume of 31:4 c.c.
But 25 c.c. of standard dry nitrogen weigh, as we have seen, 31*4 m.gm. ; so
that the problem is solved, and the cubic centimeters and tenths of cubic
centimeters give directly the weight of the gas in milligrams and tenths of
milligrams.

The various other single (i.e., unmixed) gases may be weighed in like
manner by bringing the me re my in the regulator tube to the " gravi-
volumetric mark" of the gas in question, and adjusting the levels as before.
An exception would be made in the case of hydrogen, which would be
brought to such a volume that the cubic centimeter would contain a tenth
of a milligram.

Mixtures of gases may also be weighed, provided that the density of the
mixture is known.

Lastly, if the mercury in the regulator tube be brought to the mark 25
and the levels adjusted, a gas or mixture of gases in the measuring tube
will have the volume which it would occupy in the standard dry state. In
this form the instrument is merely a gasvolumeter, as described by Lunge,
and may be used for ordinary gas analysis.

The experiments made by Japp with the view of ascertaining
the degree of accuracy of which the apparatus is capable were
very satisfactory, details being given in the paper mentioned. The
substances experimented on were Methane, with a gravivolumetric
value- of 17'9; Nitrogen, 31-4; Air, 32'35; and Carbon dioxide,
49-3.

The measuring tube and regulator tube were held by a double clamp, the
arms of which could be moved horizontally, so as to admit of bringing the
tubes close together when necessary. The two tubes were so arranged that,
after adjusting the levels and ascertaining that the mercury in the regulator
tube was at the gravivolumetric mark, it was possible to read both levels
without moving the position of the eye. The object of this was that any
possible error of parallax might occur equally and in the same direction in

568 VOLUMETRIC ANALYSIS. § 101.

both tubes, in which case the two errors would tend to neutralize one another
in the final result.* The mercury reservoir was held by a clamp attached to
a separate stand, so that in the case of extreme differences of pressure the
entire stand could be placed on a different level from the rest of the
apparatus.

Assuming the graduation of a gravivolumeter to be correct, or the defects
of graduation to be eliminated by calibration, the sources of error in such
an instrument are, broadly speaking, four in number, and are to be found in
imperfections (1) in filling the regulator, (2) in adjusting the levels, (3) in
reading the regulator, and (4) in reading the measuring tube. The first of
these operations, that of filling the regulator, is performed once for all with
very great care, and may, for all practical purposes, be disregarded as a source
of error. Again, in adjusting the levels, the two tubes can be brought, by
means of the double clamp, within such a short distance of one another that
the adjustment is also practical!}' accurate. The real sources of error lie in the
two last operations. The burettes are divided into tenths of cubic centi-
meters, and can be read with the eye alone accurately to -^V c.c. Calculating
this error on 25 c.c. as the average volume of gas contained in the regulator
tube and measuring tube respectively, we have l/(20x 25)=-^ as the error
for each tube. But as the error in the regulator repeats itself in exact
proportion in the altered volume of gas in the measuring tube, we must add
the error of the regulator to the independent error of the measuring tube,
in order to ascertain the maximum error, which would thus be ^ ; and
this, calculated as assumed, upon 25 c.c. of gas, would be equal to an error
of reading O'l c.c. in the final result. An inspection of the foregoing
experimental results, however, discloses the fact that the maximum error is
only half this amount, or 0'05 c.c. ; and this the author attributes to the
fact that, owing to the method of reading employed, the errors of reading
in the regulator and measuring tube are not, as assumed in the foregoing
calculation, independent, but tend to neutralize one another.

This error of 0'05 c.c. is, however, the error of reading of any gas burette
•which is read with the eye alone ; and the gravivolumeter ma}r, therefore,
claim to possess the same degree of accuracy as instruments of this class
generally.

* Suppose the eye in reading to be too high, the mercury in the regulator would stand
below the gravivolumetric mark, and the gas in the ineasiiring tube would consequently
be expanded beyond its proper volume. But owing to the eye being too high, this too
great volume in the measuring tube would be read off as smaller than it actually is.
In the case of equal volumes of gas in regulator and measuring tube, there would thus
be a total correction of the error committed (since the two tubes are of equal bore) .,
and in every case a diminution.

§ 101.

VOLUMETRIC ANALYSIS.

569

TABLE for Correction of Volumes of Gases for Temperature,
according to the Formula

760 x (1 + 5 1)
5 t from 0° to 30°. 5 = 0'003665.

t 1 + 5t

Log. (1 + 51)

1 + St Log. (1 + 5 1)

1 + 5t

Log. (1 + 5 i)

O'O I'OOOOOOO

•1 1-0003665

O'OOO 0000
1591

5-0 1-0183250J 0-007 88G4
•11-0186915 0-008 0427

16-0

•]

1-0366500
T0370165

0-015 6321

7857

•2 1-0007330

3182

•21-0190580

1989

T0373830

9391

•3 1-0010095

4772

•3I1-0194245

4551

•3

1-0377495

0-016 0925

•41-0014660

G362

•41-0197910

5112

•4

L'0381160

2459

0-r> 1-0018325

7951

5-51.-0201575

6672

10-5

1-0384825

3992

•6 1-0021990

9540

•61-0205240

8232

•6

T038S490

5524

7 1-00:2 30 5 5

0-001 1128

•71-0208905

9791

•7

1-0392155

7056

•81-0029320

2715

•81-0212570

0-009 1350

•8

1-0395820

8588

•91-0032985

4302

5-91-0216235

2909

10-9

1-0399485

0-017 0118

] -01-0036650

O'OOl 5888

G-0 1-0219900

0-009 4466

11-0

T0403150

0-017 1648

•1 1-0040315

7473

•1

1-0223565

6024

•1

1-0406815

3178

•21-0043980

9058

•2 1-0227230

7580

•2

1-0410480

4708

•3 1-0047645

0-002 0643

•31-02308^5

9136

•3

L'0414145

6236

•41-0051310

2227

•4 1-0234560

0-010 0692

•4

1-0417810

7764

1-51-0054975

3810

C-5 1-0238225

2247

11-5

1-0421475) 9292

•61-0058640

5393

•Gjl'0241890

3801

•6

1-0425140' 0-018 0819

71-0062305

6974

•7lr0245555

5355

1-0428805 2346

•8 1-0065970

8556

•81-0249220

6908

•8

1-0432470 3871

1-91-0069635

0-003 0137

6-9

1-0252885

8461

11-9

1-0436135 5397

2-01-0073300

0-003 1718

7-0

1-0256550

0-011 0013

12-0

1-0439800 0-018 0922

•ill -0076965

3298

•1

1-0260215

1565

•]

T0443465

8446

•21*0080680

4877

•2

1-0263880

3116

•2

1-0447130

9970

•31-0084295

6455

•3

1-0267545

4G6G

•3

1-0450795

0-019 1493

•4J1-0087960

8033

1-0271210

6216

•41-0454460

3016

2-5 1-0091625

9611

7-5

1-0274875

7765

12-5

L-0458125

4538

•6 1-0095290

Q'004 1188

•6

1-0278540

9314

•6

1-0461790

6060

•7 1-0098955

2764

•7

1-0282205

0-012 0863

1'0465455

7581

•81-0102620

4340

•8

1-0285870

2410

•8

1-0469120

9102

2-91-0106285

5916

7-9

1-0289535

3957

12-9

L'0472785

0-020 0622

3-01-0109950

0-004 7490

8-0

1-0293200

0'012 5504

13'0

T0476450

0-020 2141

•11-0113615

9064

•1

1-0296865

7050

•1

1-0480115

3660

•2J1-0117280

0-005 0638

1-03C 0330

8596

•2

1-0483780

5179

•31-0120945

2211

•3

1-0304195

0-013 0141

•3

1-0187445

6697

•4 1-0124610

3783

•41-0307860

1685

•4

1-0491110

8214

3-51-0128275
•61-0131940
•71-0135605

5355

6926

8497

8-51-0311525
•G 1-0315190
•71-0318855

3229
4772
6315

13-5

•6

1-0494775 9731
1-04984400-021 1248
L'0502105 2764

•8J1-0139270

0-OOG 0037

•81-0322520

7857

•8

1-0505770 4279

3-91-0142935

1636

8-91-0326185

9399

13-9

1-0509435 5794

4-01-0146600

0-OOG 3205

9'0'r0329850

0-014 0940

14-0

1-0513100 0-021 7308

•11-0150265

4774

•11-0333515

2-181

•1

L'0516765

8822

•21-0153930

6342

•21-0337180

4021

•2

1-0520430

0-022 0335

•3 1-0157595

7909

•3!r0340S45

5560

•3

1-0524095

1848

•4 1-0161260

9476

•41-0344510

7099

•4

1-0527760

3360

4'5 1-0164925

0-007 1042

9'5 L'0348175

8638

14-5

1-0531425

4871

•6 1-0168590

2607

•6J1-0351840

0-015 0175

•6

1-0535090

6382

•7 1-0172255

4172

'71-0355505

1713

1-0538755

7893

• '81-0175920 5737

•81-0359170

3250

•8

1-0542420 9403

4-91-01795851 7301

9-9,1-0362835

4786

14'9

1-0546085 0-023 0193

570 TABLES. § 101.

TABLE for Correction of Volumes of Gases— continued.

l+St

Log. a + 5 o

1 +8t

Log. (1 + 5 t)

1 + 5t

Log. (1+5 1)

15'0 r0549750 0'023 24-22

20'0r0730000

0-030 7211

25-0 1*0916250

0-038 0734

•lil'0553415

3930

•1!1-0736665

8694

•11-0919915

2192

•21-0557080

5438

•21-0740330

0'C31 0176

•2U-0923580

3650

•3 1-0560745

6946

•31-0743995

1658

•31-0927245

5107

•41-0564410

8452

•4

r074766i

3139

•4:1-0930910 6563

15-5

1-0568075

9959

20-5

1-0751325

4620

25-51-0934575 8020

•6

1-0571740

0-024 1465

•6

1-0754990

eioo

•6 1-0938240 9474

•7

1-0575405

2970

1-0758655

7580

•7 1-0941905

U'039 0929

•81-0579070

4475

•8

1-0762320

9059

•8 1-0945570

2384

15-91-0582735

5979

20-9

1-0765985

0*032 0538

•91-0949235

3838

16-01-0586400

0-024 7483

21-0

1-0769650

0-032 2016

26-01-0952900

0-039 5291

•11-0590065

8986

•1

1-0773315

3493

•11-0956565

6745

•2J1-0593730

0-025 0489

•2

1-0776980

4971

•2|l-096023U

8197

'31-0597395

1991

•3

1-0780645

6447

1-0903395

9649

•41-0601060

3493

•4

1-0781310

7924

•4

1-0967560

0'040 1101

16-5

1-0604725

4994

21-5

1-0787975

9399

26'5

1-0971225

2551

•6 1-0608390

6495

•6

1-0791640

0-033 0874

•6

1-0974890

4002 l

•7

1-0612055

7995

•7

1-0795305

2349

1-0978555

5452 i

•81-0615720

9495

•8

1-0798970

3823

•8

1-0982220

6901

16-9jl-0619385

0-026 0994

21-9

1-0802635

5298

•9

1*0985885

8351

17-0

1-0623050

0-026 2492

22'0

1-0806300

0-033 6771

27-0

1-0989550

0-040 9800 i

•1

1-0626715

3990

•1

1-0809965

8243

•1

1-099321 5

0-041 1247

•21-0630380

5488

•2

1-0813630

9715

1-0996880

2695

•3!l'0634045

6935

•3

1-0817295

0-034 1186

•3

1-1000545

4143

•4

1-0637710

8482

•41-0820960

2658

•4

1-1004210

5589

17-5

1-0641375

9978

22-5

1-0824625

4129

27-5

1-1007875

7036

•6

1-0645040

0*027 1473

•6

1-0828290

5598

•6

T1011540

8481

•7

1-0648705

2968

1-0831955

7069

•-

T1015205

9926

•8

1-0652370

4462

•8

1-0835620

8538

1-1018870

0-042 1371

17-9

1-0656035

5956

22-9

1-0839285

0-035 0006

•9

1-1022535

2815

18-0

1-0659700

0-027 7450

23-0

1-0842950

0'035 1475

28-0

1-1026200

0-042 4259

•1

1-0663365 8943

•1

1-0846615

2942

•1

1-1029865

5703

•2

1-0667030

0-028 0435

•2

1-0850280

4409

•2

1-1033530

7145

•3

1-0670695

1927

•3

1-0853945

5876

•3

1-1037195

8587

•4

1-0674360

3418

•4

1-0857610

7342

•41-1040860

0-043 0029

18.5

1-0678025

4909

23-51-0861275

8808

28-5 T1044525

1471

•6

1.0681690

6400

•61-0864940

0-036 0273

•6

1-1048190

2911

•71-0685355

7889

•71-0868605

1738

•71-1051855

4352

•81-0689020

9379

•810872270

3202

•81-1055520

5792

18-91-0692685 0'029 0868

23-91-0875935

4666

•91-1059185

7231

19-01-0696350 0'029 2356

24-01-0879600

0-036 6129

29-01-1062850

0-043 8671

•11-0700015 3844

•H'0883265

7592

•11-1066515

0-044 0109

•2l'0703680l 5331

•21-0886930

9054

•2;1-1070180

1546

•3 1-0707345] 6818

•3 1-0800595

0-037 0517

•31-1073845 2985

•41-0711010- 8304

•41-0894260

1978

•4 1-10775 101 4422

19-51-0714675

9790

24'5! 1-0897925

3438

29-51-1081175 5858

•6

1-0718340

O'CSO 1275

•61-0901590

4899

•611-1084840 7295

1-0722005

2760

•71-0905255

6359

•7 1-1088505 8730

•81-0725670

4244

•81-0908920

7817

•8 1-1092170 0-045 0165

19-91-0729335

5728

•91-0912585

9277

•9,1-1095835 1600

30'0 1-1099500 G'045 3035

101.

VOLUMETPJC ANALYSIS.

571

TABLE for Correction of Volumes of Gases for
Temperature, giving the Divisor for the Formula

V x

76O x (1 -f

760 x
(! + *}.

Log. [760 x
(l + St)].

760 x
(1 + 5;).

Log. [760 x
(1-f 8t)].

760 x
(!+*>.

Log. [760 x
(1 + »01.

O'O 760*0000

2-880 8136

4-0

771-1 1162-887 1341

8-0782-28322-893 3640

•1

760-2785 9727

• I 771-4201

2910

•1 7*2-56171 5186

•2 760-5571 2-831] 319

•2 771-6987

4478

•2782-8403 6732

•3760-8356 2908

•:; 771-9772

6044

•3783-1188 8276

•4761-1142 4498

•4772-2558

7611

•4783-3974 9821

0-5

761-3927

6087

4'5 772'53 43

9178

s-5 7*3-6759 2-894 1365

•0761-6712

7676'

•6 772-8128

2-888 0743

•6J783-9544

2908

•7 761-9498

9264

•7773-0914

2309

•7 784-2330

4452

•8
•9

762-2283:2-882 0851
762-5061' 2437

•S 773-3699
•'.' 773-6485

3872
5437

•> 784 5115
•9784-7901

5994
7536

1-0 762-7854 2-882 4024.

5-C 773-9270

2*888 7000

9-0785-0686

2-894 9076

•i

763-0639! 5610

•1774-2055

8563

•1785-3471

2-895 0617

•2 703-34251 7194

•2774-4841

2-8890125

•2 785-6257

2157

•3 763-6210 8779

•3 774-7626

1686

•3 785-9042

3696

•4 763-89968-883 0362

•4775-0412

3248

•4786-1828

5235

1-5

764-1781

1017

5" 5

775-3197

4808

9-5786-4613

6774

' '764-4566

3528

•6

775*5982

6368

'6786-7398

8311

•7764-7352

5111

•7

775-8768

7927

•7 787-0184

9849

W65*0137

6692

•s

776-1553

9487

•8787*2969

2-896 1385

•9765-2923

8273

•9

776-4339

2-890 1044

•9787-5755

2923

2T> 765-570S 2-883 9854

6-0

776*7124

2'890 2602

10-0787-8540

2*896 4457

-1 765-84932-8841433

•1

776-9909

4159

•1788-1325

5993

..»

766-1279

3013

•2 777-2695

5716

*2 788-4111

7528

•3 766-40:; 4

4591

•3777*5480

7272

•3788-6896

9061

•4766-6850

6170

•4

777-8266

8828

•4788-9682

2-8970595

2*5

766-9635

7747

6'5

778-1051

2-891 C383

10-5789-2467

2128

767-2420

9323

•6

778-3836

1937

•6789-5252

3660

• ~

767*5206

2-885 0900

778-6622

3491

'7789-8038

5192

•8f767'7991

2476

778-9407

5044

•8790-0823

6724

•1) 768-0777

4052

779-2193

6597

•9 790-3609

8255

:ru 768-3562 2-885 5626

7 •'> 7 79-4978

2-891 8149

H-0790'6394

2-897 9785

•1768-fi347i 7200

•1 7797763

9701

•1790-9179

2-898 1315

•2768-9133J 8772
•:J769-1918'2-8860347

•2780-05492-892 1251
•3 780-3334 2802

•2791-1965
•3791-4750

2844
4373

•4769-4704 1919

•4780-6120 4352

•4791-7536

5901

3-5769-7489

3491

7 •:> 780-8905 5901

H-5792'0321

7428

•6770-0274

5061

•0781-1690

7450

•6792-31061 8954

770-3060

6633

'7781-4476

8998

•779258922-8990482

•8770-5845

8203

•8781-7261

2'S93 0547

•8792-8677 2008

•9770-8631; 9773

".'782*0047

2094

•9793-1463I 3534

TABLES.

101,

TABLE for Correction of Volumes of Gases— continued.

760 x
(l+5t).

Log. [760 x
(l+8t)].

760 x
(1 + 5t).

Log. [760 x
(1+ 5t)].

760 x

a + sy.

Log. [760 x

(i + Sty].

12-0793-42482 899 5057

16-5

805-9591

2-90G 3131

21-0

818-4934

2-9130152

•1793-7033

6583

•6

806-2376

4630

•1818-7719

1629

•2793-9819

8106

806-5162

6131

•218 19-0505

3107

•3 794-2604

9629

806-7947

7631

•3819-3290

4584

•4794-5390

2-900 1153

•9

807-0733

9130

•4819-6076

6059

12-5794-8175
•0795-0960

2674
4196

807-3518
807-6303

2-907 0627
2126

21-5|819-8S61

•6820-1646

7535

9010

•71795-3746

5717

- -21807-9089

3624

•71820-4432

2-914 0485

•8795-6531

7238

808-1874

5121

•8820-7217

1959

•9J795-9317

8758

808-4660

6617

21-9 821-01)03

3434

13-0796-2102

2-901 0277

17-5

808-7445

8114

22-0

821-2788

2-9144906

•l'796-4SS7

1796

•6809-0230

9609

•1

821-5573

6379

•2:796-7673

3316

'7 809'30] 6

2-9081103

•2

821-8359

7852

•3797-0458

4833

•8809-5801

2599

•3

822-1141

9322

•4:797-3244

6351

•9

309-8587

4092

•4

822-3930

2-9150794

13-5797-6029

7867

18-0

SlO'13722-9085586

22'5

822-0715

2265

•6J797-S814

9383

•1|810-4157

. 7079

822-9500

3734

•7798-16002-9020900

•2810-6943

8572

823-2286

5204

•8798-4385 2415

•3,810-9728

2-909 0063

•8823-5071

0074

•9798-71711 3931

•4

811-2514

1554

•9823-7857

8143

14-0 798-9956 2-902 5444

18'5

811-5299

3046

23-0824-0642

2-9159610

•] 709-2741

6958

•GJ811-80S4

4535

•1824-3427

2-916 1078

•2:799-5527

8471

•7:812-0870

6026

•2824-0213

2546

•3799-8312
•4800-1098

9983
2-903 1496

"8
•9

812-3655
812-6441

7515

9004

•3,824-8998
•4825-1784

4012

5478

14-5800-3883
•6800-6668

3008
4518

190,812-9226
•l!813-2011

2-910 0492
1980

23-5
•6

825-4569
825-7354

6944
8409

•7J800-9454 6029
•8801-2239 7539

•2813-4797
•3J813-7582

3468
4953

•7:826-0140
•8826-2925

9874

2-917 1339

•9801-5025 9049

•4814-0368

6440

•9826-5711

2802

15-0 SOl'7810 2-904 0557
•1 802-0595! 2067

19-5814-3153

•6;814-5938

7927
9411

24-0826-8496
•1827-1281

2-917 4265

5728

•2802-338l| 3574

•7814-87242-9110896

•2:827-4067

7191

•3 802-6166 5081

•8;815-1500 2380

•3!827'6852

8652

•4802 8952

6589

815-4295

3865

•4'S27'9638

2-918 0114

15-5803-1737

8095

20-0815-7080

2-911 5347

24-5j828'2423

1574

•6J803-4522 9601

•1815-9865

6830

•6828-5208

3034

•7803-7308

2-905 1106

•2816-2651

8313

•7828-7994

4495

•81804-0093

2612

•3816-5436

9794

•8829-0779

5953

•9804-2879

4116

•4816-8222

2-912 1276

249829-3565

7413

16-0804-5664

2-905 5618

20-5817-1007

2756

25-OJ829-6350

2*918 8871

•1 804-8449

7122

•6817-3792

4236

•1829-9135

2-919 0329

•2^805-1235

8625

817-6578

5716

•2:830-1921

1786

•3805-4020

2-206 0127

•8817-93(13

7195

•3830-4706

3242

•4805-6806

1629

SIS'2149

8674

•4830-7492

4699

§ 101. VOLUMETRIC ANALYSIS. 573

TABLE for Correction of Volumes of Gases— continued.

760 x
(1 + 5f).

Log. [760 X

(l + St)].

760 x
(1 + SO

Log. [760 X
(1 + St].

760 x
(1+50-

Log. [760 x
(! + &)].

25-5831-027712-919 6155

27-0

835-20582-921 7935

28'5 839-3839 2-923 9607

•6831-3062! 7610

•1

835-4843

9384

•6839-66242-9241047

•7:831-58481 9065

•2835-76292-9220831

•7!839'9410| 2488

•8
25'9

831-86332-9200520
8321419 1974

•3

•4

836-0414 2279
836-3200 3725

•8840-2195
28 9 840-4981

3928

5368

26'0

832-4204 2-920 3427

27-5

836-5985

5172

29-0840-7766

2-924 6806

•1

832-6939 4880

•6 836-8770

6616

•1841-0551 8245

•2

832-9775 6333

•7837-1556

8062

•2:841-3337 9683

•3

833-25601 7784

•8837-4341

9507

•3 841-6122^-925 1120

•4

833-534^

9236

27-9

8377127

2-923 0951

•4

841-8908

2558

26-5

833-8131

2-921 0688

28-0

837-9912

2*923 2394

29'5!842-1693

3995

•6

834-0916

2137

-L

838-2697

3838

•6)842-4478 5431

•7

834-3702! 3588

•2838-5483

5281

'7812-7264 6836

•8

834-6487

5038

•3838-8268

6723

•8843-0049 8301

26-9

834-9273

6487

•4

839-1054

8165

29'9|843'2835

9737

30-0843-56202-926 1170

TABLES.

§ 101.

Pressure of Aqueous Vapour in Millimeters of Mercury,
from-9'9° to + 35° C.

111 .in.

in. in.

in. m.

m.m.

HI .ni.

in. in.

-9-0

2-096

-5'4

3-034

-6-9

4-299

3-5 5-889

8'0 8-017

12'5 LO'804

•8

•114

•3

•058

•8

•331

•6

•930

•1

•072

•c| '875

•132

•082

•364

•972

•2

•126

•71 '947

•150

•1

•106

•397

G'014

•3 '181

•811-019

•168

-5-0

•131

•430

3-9

'055

•4 '236

12'9

•090

-9-4

•186

-4'9

3-156

-0-4

•463

4-0

6-097

8-5 '291

13-0

Ll-162

•3

•204

•181

•497

•1

•140

•(j '347

•1

•23a

•2

•223

•7

•206

•531

•2

•183

•7i '404

•2

•309

•1

•242

•231

•3

•565

•3

•226

•8' '461

•3

•383

-9-0

•261

•5

•257

-o-o

4'600

•4

•270

8-9

•517

•4

•456

-8-9

2'280

-44

•283

+ O'f

4-600

4.5

•313

9-0

8-574

13-5

•530

•299

•3

•309

•1

•633

'357

•1

•632

'605

•318

•335

•667

•7

'401

•690

•681

•6

•337

•361

•3

•700

•8

•445

•3

•748

•8

•757

•356

-4-0

•387

•4

•733

4-9

•490

•4

•807

1 °'Q

•832

- 8-4

•376

-3'P

3-414

0-5

•767

5-0

6-534

9-5

•865

14'0

11-908

•3

•396

•441

•801

•1

•580

•6

•925

•1

•986

•2

•416

•468

•836

•2

•625

•985

12-064

•1

•436

'495

•8

•871

•3

•671

•8

9-045

•142

-8-0

•456

•522

0'9

•905

•4

717

9'9

•105

•4

•220

-7-9

2-477

-3-4

•550

i-o

4-940

5-5

•763

10-0

9-165

14'5

•298

•8

•498

•3

'578

•1 -975

•6

•810

•1

•227

•6

•378

•7

•519

•9

'606

•2 5*011

•857

•9

•288

•458

•6

•540

•1

•634

•3 1 '047

•8

•904

•3

•350

•8

•538

•5

•561

-3'U

• '662

•4 '082

5-9

•951

•4

•412

14-9

•619

-7'4

•582

-2-9

3-691

1-5

•118

6-0

6-998

10-5

•474

15'0

12-699

•3

•603

•8

•720

•f

•155

•1

7-047

•6

•537

•1

•781

•2

•624

" i

•749

' i

•191

•2

•095

•601

•2

•864

•1

•645

778

•228

•3

•144

•8

•665

•3

•947

-7-o

•666

•807

1-9

•265

•4

•193

10-9

•728

•4

13-029

-6-9

2-688

-2-4

•836

2-0

5-302

6-5

•242

ll'O

9-792

15'5

•112

710

•3

•865

•340

•6

•292

•1

'857

•6

•197

•7

•732

•9

•895

•378

•342

•923

•7

•281

•6

•754

•1

•925

•3

•416

•8

•392

•3

•989

•8

•366

'776

-2-0

•955

•454

6-9

•442

•4

10-054

15-9

•451

- 6-4

•798

-1-9

3-985

2-5

•491

7-0

7'492

11-5

•120

16'0

13'536

•3

•821

•8

4-016

•6

•530

•1

•544

•6

•187

•1

•623

•9

•844

•7

•047

'569

•2

•595

' /

'255

•'2

•710

•1

•867

•6

•078

•8

•608

•3

•647

•8

•322

•3

•797

-6-0

•&90

•109

2.9

•647

•4

•699

11-9

•389

•4

•885

-5-9

2-914

-1-4

•140

3-0

5'687

7'5

•751

12-0

10-457

16-5

•972

•8

•938

•3

•171

•1

•727

•6

•804

•1

•526

•6

14-062

•962

•9

•203

•767

•857

•596

•151

•6

•986

•1

•235

•3

•807

•3

•910

•3

•665

•3

•241

3-010

i-o

•267

•4

•848

7-9

•964

•734

16-9

•331

§ 101.

VOLUMETIUC ANALYSIS.

0/0

Pressure of Aqueous Vapour — continued.

in. in.

ni.ru.

m.m.

17-0

14-421

20-0

17-391

23-0 20-888

26-0

24-988

29-0

29-782

32-0

35-359

•I

•513

•1

•500

•J

21'OIG

•1

25-138

•1

•956

•1

•559

•2

•605

•2

•008

•9

•144

•2

•288

•2

30-131

•760

•3

•697

•3

•717

•3

•272

•3

•438

•3

•305

•3

•962

•790

•4

•826

•4

•400

•4

•588

•4

•479

•4

36-165

17-5

•882

20-5

•935

23-5

•528

26-5

•738

29-5

•654

32-5

•370

•6

•977

•6

18-047

•6

•659

•6

•891

•6

•833

•6

•576

•7

15-072

•159

•790

' /

20-045

31-011

•783

•8

•167

•8

•271

•8

•921

•8

•198

•8

•190

•8

'991

17'9

•202

20-9

•383

23-9

22-053

26-9

•351

29'9

•369

32'9

37-200

IS'O

15-357

21-0

18-495

24'C

22-184

27-0

26-505

30-0

31/548

33'0

37*410

•1

•454

•1

•610

•1

•319

•1

•663

•J

•729

•1

•621

•552

•2

•724

•2

•453

•820

•2| '911

•2

•832

•3

•650

•3

•839

•3

•588

•978

•3

32-094

• 0
O

38-045

•4

•747

•4

•954

•4

•723

•4

27-136

•4

•278

•4

•258

18-5

•845

21-5

19-069

24-5

'858

27-5

•294

30-5

•463

33'5

•473

•945

•6

•187

•e

•996

•6

•455

•6

•650

•6

•689

IC'045

•305

•7

23-135

•7

•617

•837

•906

•8

•145

•423

•8

•273

• '8

•778

•8

33-026

•8

39124

18-9

•246

21-9

•541

24'9

•411

27-9

•939

30-9

•215

33-9

•344

19-0

16-346

22'0

.19-659

250

23-550

28-0

28-101

31-0

33*405

34-0

39*565

•1

•449

•1

•780

•1

•692

•1

•267

•1

•596

•1

•786

•552

•901

•834

•433

•2

•787

40-007

•3

•655

•3

20-022

•3

•976

•3

•599

•3

•980

•230

•4

•758

•4

•143

•4

24119

•4

•765

•4

34-174

•4

•455

19'5

•861

22-5

•265

25-5

•261

28'5

•931

31-5

•368

34-5

•680

•6

•967

•389

•6

•406

•6

29-101

•6

•564

•6

•907

•7

17-073

•514

•7

•552

•7

•271

•761

•7

41-135

•8

•179

•8

•639

•8

•697

•8

•441

•8

•959

•364

19-9

•285

22-9

•763

25-9

•842

28'9

•612

31-9

35-159

34-9

•595

35-0

827

INDEX.

Absorption apparatus, Mohr's, 133
Absorption apparatus, Fresenius',

132
Absorption equivalents shown by oils

and fats for bromine, 359
Acetates, alkaline and earthy, titration

of, 90

Acetate of lime, analysis of, 90
Acetates, metallic, 90
Acidimetry, 88
Acidimetry, delicate end-reaction for,

Acid, acetic, titration of, 89
Acid, arsenic, titration of, 151, 152, 153
Acid, carbolic, titration of, 366
Acid, carbonic, estimation of, 93
Acid, chromic, titration of iron with,

126

Acid, citric, estimation of lead in, 225
Acid, citric, titration of, 103
Acid, formic estimation of, 104
Acid liquors, tartaric, 113
Acid, nitric, pure for titrations, 48
Acid, oxalic, titration of, 109
Acid, phosphoric, titration of, 109, 284
Acid, tannic, titration of, 331
Acid, tartaric, estimation of lead in,

225

Acid, tartaric, titration of, 112
Acid, uric, estimation of, 392
Acids and bases combined in neutral

salts, 114

Acids, mineral, in vinegar, 90
Acids, titration of, 88
Acids, titration of by iodine and thio-

sulphate, 88
A e'rated distilled water, preparation of,

274
Air and carbonic anhydride gas, analysis

of, 497

Air, carbonic acid in, titration of, 97
Albumen in urine, estimation of, 397
Albuminoid ammonia process for water,

Alkalies, caustic and carbonated, titra-
tion of, 56

Alkalies, caustic, titration of, by potas-
sic bichromate, 60

Alkalies, indirect estimation of; 140

Alkalies in presence of sulphites, titra-

of, 59

Alkalimeter, Schuster's, 6
Alkalimetric estimation of various me-
tallic salts, 117

Alkalimetric methods, extension of, 117
Alkalimetry, 33, 55
Alkalimetry, GayLussac's, 33
Alkaline carbonates, titration of, 55
Alkaline compounds, commercial, 63
Alkaline earths, indirect estimation of,

140

Alkaline earths, titration of, 69
Alkaline earths, titration of mixed

hydrates and carbonates, 69
Alkaline tartrate solution, for sugar

estimation, 309

Alkaline permanganate, for water ana-
lysis, 465

Alkaline salts, titration of, 55
Alkaline silicates, titration of, 67
Alkaline sulphides, titration of, 64, 321
Alloys of silver, assay of, 298
Alumina, estimation of, 145
Alumina in caustic soda, etc., estima-
tion of, 146
Aluminic sulphates, estimation of free

acid in, 146
Ammonia, albuminoid process, for

water, 462

Ammonia, combined, estimation of, 72
Ammonia, estimation of, 72
Ammonia, indirect titration of, 75
Ammonia in urine, estimation of, 396
Ammonia in water, estimation of, 407
Ammonia., semi-normal, 49
Ammonia, sulphate and chloride of,

estimation of, 79

Ammonia, technical estimation of, 75
Ammoniacal liquor, table showing tho
amount of sulphate obtainable
from, 80

A mmonic molybdate, standard, 294, 295
Ammonio-cupric solution, normal, 50
Analyses, saturation, 33
Analysis by oxidation or reduction, 120
Analysis by precipitation, 138
Analysis, factors for calculation, 54
Analysis, gas, simple methods of, 547

578

INDEX.

Analysis of substances by distillation
with hydrochloric acid, 132

Analysis, volumetric and gravimetric,
distinction between, 2

Analysis, volumetric and gravimetric,
fundamental distinction between, 2

Analysis, volumetric, general princi-
ples, 1

Analysis, volumetric, methods of classi-
fication, 3

Analysis, volumetric, systematic, 27

Analysis, volumetric, without burettes, 6

Analysis, volumetric, without weights, 5

Analysis, water, reagents for 399, 463

Antimony, estimation of, as sulphide,
148

Antimony, estimation of, by bichro-
mate, 147

Antimony ^ estimation of, by iodine, 147

Antimony, estimation of, by perman-
ganate, 147

Aiatimony in presence of tin, estimation
of, 147

Antimony, titration of, by stannous
chloride, 183

Apparatus, absorption, Fresenius',
132

Apparatus, absorption, Mohr's, 133

Apparatus, Bischof's, for evapora-
tion, 411

Apparatus for iodine distillation,
Stortenbek&r's, 201

Apparatus for chlorine distillation,
132, 133

Apparatus for CO2, Scheibler's,
101

Apparatus for gas analysis (Bunsen's
method), 480

Argol, titration of, 114

Arseniates, estimation of, by iodine,
149, 370

Arseniates, estimation of, by silver, 152

Arseniates, estimation of, by uranium,
151

Arsenic acid, titration of, 150, 151, 369

Arsenic, estimation of, by bichromate,
150

Arsenic, estimation of, by distillation,
151

Arsenic, estimation of, by iodine, 149,
370

Arsenic, estimation of, by silver, 152

Arsenic, estimation of, by uranium,
151

Arsenic, estimation of, in presence of
tin, 371

Arsenical ores, analysis of, 149, 151

Arsenious acid and iodine analyses, 136

Asbestos, palladium, 553

Ash, black, titration of, 64

Backward or residual titration, 32, 55
Balance, the, 5

Baric chloride, preparation of normal,
325

Baric thiosulphate as standard, 130

Barium in neutral salts, 70

Barium, estimation of, as chromate, 154

Barium, titration of, by permanganate,
154

Baryta solution for removing phos-
phates and sulphates from urine,
382

Baryta solution, standard, 50

Base, M i 1 1 o n ' s , use of, 49

Beal's filter, 18

Beverages, carbonic acid in, 96

Bicarbonates in presence of carbonates,
titration of, 58

Bichromate, standard solution of, 127

Bifluorides, titration of. 107

Bischof's apparatus for evaporation,
411

Bismuth, estimation of, as oxalate, 154

Bismuth, estimation of, as phosphate,
156

Bleaching compounds, titration of, 164

Bleaching powder, gasometric estima-
tion of, 165

Bleaching powder, titration of, by
arsenious solution, 164

Bleaching powder, titration of, by
iodine, 165

Boric acid and borates, titration of, 92

Boric acid in milk, estimation of, 369

Bottle for digestion in iodine estima-
tions, 135

Bromates, titration of, by iodine, 166

Bromine, absorption of, by oils and
fats, 358

Bromine, colour method of estimation,
157

Bromine, estimation of, by digestion,
157

Bromine, estimation of, by distillation,
156

Bromine, estimation of, by Cavazzi's
method, 157

Bromine, estimation of, by McCul-
loch's method, 158

Bromine, iodine, and chlorine together,
201

Bullets for gas analysis, how made, 467

Burette, B inks', 13

Burette clips, 13

Burette for hot titrations, 12

Burette, Gay Lussac's, 12

Burette, Mohr's, 8

Burette, Mohr's, advantages of, 8

Burette, the, 7

Burette, the blowing, 10

Burette, the foot, 10

Burette, the tap, 8, 11

Burette, without pinchcock, 14

Burette with enclosed thermometer
float, figure of, 8

Burette, with reservoir, 12

Burette, with oblique tap, 8

Burettes and pipettes, calibration of, 19

Butter, titration of, 353

INDEX.

579

Butter, Reichert's method for, 353
Butter, Koettstorfer's method,

356
Butylic hydride gas, estimation of, 466

Cadmium, estimation of, as oxalate,
160

Cadmium, estimation of, as sulphate,
160.

Calcium, estimation of, as oxalate, 160

Calcium, estimation of, as perman-
ganate, 161

Calcium, estimation of, in slags and
mixtures, 161

Calcium, in neutral salts, 70

Calibration of gas apparatus for water
analysis. 420

Carbolic acid, titration of, 366

Carbon disulphide, titration of, 367

Carbon in iron and steel, estimation
of, 218

Carbon tetrachloride, use of, for titra-

ti^'of fats, 358
Carbonates, Pet

'ettenkofer's method

for, 95

Carbonates, alkaline, titration of, 55
Carbonates, analysis of, 93
Carbonates, indirect estimation of, 95
Carbonates soluble in acids, 94
Carbonates soluble in water, 93
Carbonates, titration of, in presence

of bicarbonates, 58
Carbonic acid in air, titration of, 97
Carbonic acid in beverages, 96
Carbonic acid in waters, 95
Carbonic anhydride gas, estimation of,

in gas apparatus, 497
Carbonic acid gas, estimation of, 95
Cathetometer, the, 18
Caustic alkalies, titration of, by potassic

bichromates, 60

Caustic and carbonated alkalies, titra-
tion of, 56

Caustic soda or potash, titration of, 56
Centimeter, cubic, the, 23
Cerium, estimation of, 162
Chlorates, indirect estimation of, 140
Chlorates, titration of, by iodine, 167,

373
Chlorates, chlorides, and hypochlorites,

mixtures of, 372
Chloric and nitric acids, estimation of,

373

Chloride of lime, titration of, 164
Chlorine and silver analyses, 138
Chlorine, bromine, and iodine together,

estimation of, 201
Chlorine, direct precipitation with

silver, 162
Chlorine, estimation of, by distillation.

163

Chlorine estimations, indirect, 140
Chlorine, estimation of, by silver and

chromate indicator, 139
Chlorine gas, titration of, 164

Chlorine, indirect estimation of, by

silver and thiocyanate, 163
Chlorine in waters, estimation of, 162

Chlorine water, titration of, 164
Chorley's apparatus for preserving
solutions, 22

Chromate indicator for silver, 139

Chromates, estimation of by distilla-
tion, 168

Chrome iron ore, analysis of, 168

Chromic acid in iron titration, 126,
206

Chromium, titration of by iron, 167

Chromium steel, titration of, 171

Citrates, titration of, 103

Citro-magnesic solution for phosphates.
292

Clark's process for softening water,
454

Clips for burettes, 13

Coal gas, analysis of, 536

Coal gas, estimation of sulphuretted
hydrogen in, 329

Coal gas, estimation of sulphur in, 320

Cobalt, estimation of, by permanganate,
173

Cobalt, estimation of, as cyanide, 174

Cochineal indicator, 35

Colour reactions, device for seeing,
139, 143

Colour reactions, precision in, 143

Commercial alkaline compounds, tech-
nical analysis of, 63

Condenser for Kjeldahl method, 82,
83

Constants used in the analysis of oils
and fats, 362

Copper and iron, titration of, in same
liquid, 182, 183

Copper, iron, and^ntimony, estimation
of, in same liquid, 183

Copper, extraction from ores, 177, 184

Copper, estimation of, as iodide, 176

Copper, estimation of, as sulphide, 180

Copper, estimation of, by colour titra-
tion, 187

Copper, indirect estimation of, by
silver, 184

Copper ores, technical analysis of, 184

Copper, separation of, by electrolysis,
176

Copper in presence of iron, titration
of, 182

Copper solution for sugar, F e h 1 i n g ' s ,
309

Copper solution, Pavy's, for sugar,
315

Copper, titration of, by cyanide, 178,
184

Copper, titration of, by permanganate,
176

Copper, titration of, by stannous
chloride, 181

Correct reading of graduated instru-
ments, 17

p p 2

580

INDEX.

Corrections for temperature of solu-
tions, 25

Cubic centimeter, the, 23
Cupric oxide for combustions, 401
Cuprous chloride for water analysis, 402
Cyanides, alkaline, titration of, by

silver, 190
Cyanides used in gold extraction,

estimation of, 192

Cyanogen, titration of, by iodine, 191
Cyanogen, titration of, by mercury,

191

Cyanogen, titration of, by silver, 191
Cylinders, graduated, calibration of, 21

Decem, the, 26

Decimal system, origin of, 23

Decimillem, the, 27

Decinormal bichromate solution, 127

Decinormal iodine, preparation of, 129

Decinormal permanganate solution, 121

Decinormal salt solution, 139

Decinormal silver solution, 138

Decinormal sodic arsenite, 136

Decinormal sodic chloride, 139

Decinormal thiocyanate, 142

Dextrine, inversion of, 308

Dextrose, 305

Digesting bottle for iodine estimation.

135

Direct and indirect processes, 31
Disaccharides, nature of, 305
Dissolved oxygen in waters, 269, 474
Dropping appai*atus for silver assay, 302

Earths, alkaline, titration of, 69
Erdmann's float, 18
Erdmann's float, newest form, 18
Estimations, indirect, by means of

silver and chromate, 140
Ethyl gas, estimation of, 513
Ethylic hydride gas, estimation of, 513
Eudiometer, B u 11 s e n ' s, calibration

of, 482

Explosion of gases, 502, 527
Extension of alkalimetric methods, 117

Factors for calculation of analyses, 31
Fats and oilp, titration equivalents of,

with potash, 352
Fats and oils, titration of, with bromine

or iodine, 358

F e h 1 i n g ' s copper solution, 309
Ferric compounds, reduction of, 208
Ferric indicator for analyses by thio-
cyanate, 143
Ferric iron, titration of, by stannous

chloride, 210

Ferric standard, to prepare, 210
Ferri cyanides, titration of, 196
Ferrochrome titration of, 171
Ferrocyanides in alkali waste, 196
Ferrocyanides in gas liquor, 196
Ferrocyanides in gold extraction, 194
Ferrocyanides, titration of, 195

Ferro-Manganese, estimation of man-
ganese in, 227, 229, 230
Ferrous iron, how obtained for titration,

215

Filter, Beale's. 18
Filter, Porter-Clark, 454
Filter for baric sulphate, Wilden-

stein's, 328
Flasks, measuring, 16
1 Flasks, verification of, 19
Float, Erdmann's, 18
Float, with thermometer, 8
Fluoric acid, estimation of, 105
Fluorides, estimation of, 105
Fluorescin, 39

; Foraiic acid, estimation of, 104
| Frankland's and Ward's gas

apparatus, 520
: F r a n k 1 a n d ' s j oint for gas apparatu s,

419

Free acid in urine, estimation of, 397
Free ammonia in water, 407
F r e s e n i u s ' absorption apparatus, 132
Fruit juices, titration of, 104

, Galactose, 305, 313

i Gas analysis, B u n s e n ' s apparatus

for, 480

i Gas analysis, calculations for, 508, 517
Gas analysis, normal solutions for, 549
j Gas analysis, simple methods of, 547
Gas apparatus, etching of, 480
Gas apparatus, Frankland's, for

water analysis, 417

! Gas apparatus, K e i s e r ' s portable, 54 4
; Gas burette, H e m p e 1 ' s , 550

Gas liquor, analysis of, 75
1 Gas liquor, spent, analysis of, 79
Gas liquor, table showing the amount
of sulphate of ammonia to be
obtained from, 80 .

Gas pipettes, B e d s o n ' s modified, 556
Gas pipettes, II e m p e 1' s , 552
Gasvolumeter, Lunge's, 563
Gases, analysis of, 480
Gases, explosion of, 502, 507
Gases, indirect estimation of, 502
Gases, simple titration of, 547
Gases soluble in water, estimation of,

by the nitrometer, 559
Glucose or grape sugar, 305, 307
Glucose, constitution of, 305
i Glycerin, titration of, 363
Glycerin, estimation of, by per-
manganate, 363
Glycerin, estimation of, by bichromate,

364
j Glycerin, estimation of, by the acetin

method, 365
Gold, estimation of, 198
Graduated instruments, correct reading

of, 17

Grain measures, 26
Grains, fluid, 26
Gravi volumeter, J a p p ' s , 566

INDEX.

581

Haematites, analysis of, 215

Hardness of water estimated without

soap solution, 71
Hardness of water, soap solution for,

405

Hardness in waters, estimation of, 438
Hardness in waters, tables of, 439—466
Hardness in waters, Frankland's

table for, 439

H e m;p el's gas burette, 550
II e m p e 1 ' s gas pipettes, 552
Hot titration s, burette for, 12
Hydrobromic acid gas, estimation of,

494

Hydrocarbon gases, estimation of, 501
Hydrochloric acid, analysis of sub-
stances by distillation with, 132
Hydrochloric acid, normal, 48
Hydrocyanic acid, titration of, by

silver, 190

Hydriodic acid gas, estimation of, 494
Hydrochloric acid gas, estimatipn of,

494

Hydrofluoric acid, estimation of, 105
Hydrofluoric acid, cammercial composi-
tion of, 105
Hydrofluoric acid, H a g a and 0 s a k e 's

experiments on, 108
Hydrosulphuric acid gas, estimation

of, 494

Hydrogen apparatus, B u n s e n ' s 503
Hydrogen peroxide, titration of, 283
Hydrogen sulphuretted, titration of,

329

Hypobromite solution for urea, 387
Hyposulphite of soda, Schutzen-
berger's solution of, 274

Improved gas apparatus, 517
Indicator, ferric, for analyses by

thiocyanate, 143

Indicator, starch, preparation of, 131
Indicator, chromate, for silver, 139 .
Indicator for mercuric solutions in

sugar analysis, 311
Indicators, 33

Indicators, extra sensitive, 39
Indicators, azo, 36
Indicators, combination of, 43
Indicators, external and internal, 32
Indicators, various effects of heat and

cold on, 40
Indicators, Thompson's results

with, 40
Indicators, general characteristics of.

Indicators, table of results with, 43
Indigo solution, standard, 464, 469
Instruments graduated, correct reading

of, 17
Instruments graduated, verification of,

19
Todate, how to remove from alkaline

iodides, 130
lodates, titratFon of, 166

I lodeosin, a new indicator, 39
Iodine, absorption of, by oils and fats,

358-360
I Iodine, estimation of, by distillation,

199
Iodine, estimation of, byGrooch and

Browning's method, 202
Iodine, bromine, and chloi-ine, mixed,

estimation of, 201

Iodine, estimation of, by chlorine, 203
I Iodine, estimation of, by nitrous acid

and carbon bisulphide, 205
Iodine, estimation of, by permanganate

and thiosulphate, 204
Iodine solution, decinormal, verifica-
tion of, 130
Iodine, titration of, by thiocyanate and

silver, 203
Iodine, titration of, by silver and

starch iodide, 206

i Iodine solution, decinormal, prepara-
tion of, 129
j Iodine and thiosulphate, titrations by,

128

i Iodine and arsenious acid analyses, 136
j Iodized starch-paper, 137
{ Iron compounds, reduction of, for

titration, 208
1 Iron, estimation of, with bichromate,

206
Iron, estimation of, with permanganate,

206
Iron, estimation of, by colour titration,

213

Iron, estimation of, in ferric state, 210
: Iron, estimation of, in ferrous state, 206
Jron ore, magnetic, analysis of, 216
Iron ore, spathose, analysis of, 216
Iron ores, analysis of, 214
Iron ores, to render soluble, 214
Iron in silicates, estimation of, 217
Iron, titration of, by thiosulphate, 212
Iron, titration in ferrous state, 206
Iron and steel, estimation of, arsenic

in, 219
Iron and steel, estimation of, carbon

in, 218

Iron and steel, estimation of phos-
phorus in, 221

Iron and steel, estimation of, sulphur
in, 222

Reiser's gas apparatus, 544

Kjeldahl's method for nitrogen , 81

E j e I da hi' s method, new condenser
for, 84

Kjeldahl method, substances in
which their nitrogen may be
estimated by, 86

Kjeldahl method, modification of
for nitrates, 85

Kjeldahl method, Dyer's experi-
ments on, 85

Kjeldahl method, apparatus and
solutions for, 81, 82

582

INDEX.

Knapp's standard mercuric cyanide
for sugar, 311

Lacmoid paper, 39

Lacmoid, preparation of, 38

Lacmoid solution, 39

Lead acetates, titration of, 223

Lead, as carbonate, estimation of, 224

Lead in citric and tartaric acids, 225

Lead, as sulphide, estimation of, 225

Lead, estimated as oxalate, 222

Lead in presence of tin. estimation of,

225

Lead, estimation of, as chromate, 223
Lead, red, titration of, 223
Lees, tartaric, titration of, 114
Lemon juice, titration of, 104
Levulose, 305, 311
Lime acetate, analysis of, 90
Lime and magnesia in urine, 395
Lime and magnesia in waters, 70
Lime, chloride of, gasometric estima-
tion, 165

Lime, estimation of (see Calcium), 160
Lime juice, titration of, 104
Liquors, red, examination of, 64
Litmus indicator, 33
Litmus, interference in, by carbonic

acid, 33

Litmus paper, 35
Litnms, pure extract of, 34
Litmus, preparation of, 33
Litmus, preservation of, 34
Litmus, xise of, by artificial light, 34
Logarithms for use in volumetric

analysis, 476

L u n g e ' s nitrometer, 123, 262, 468
Lyes, soda, examination of, 64

Magnesia and lime in urine, 395

Magnesia and lime in waters, 70

Magnesia, estimation of, 70

Magnesia, titration of, 70

Magnesic-citrate solution for phos-
phates, 292

Magnesite, use of, for preventing re-
gurgitation in distilling chlorine,
133

Magnetic iron ore, analysis of, 216

Magnesium as reducing agent for ferric
salts, 208

Maltose or malt sugar, 305, 307, 308,
311

Manganese, estimation of, by distilla-
tion with hydrochloric acid, 234

Manganese, estimation of, by iron,
236

Manganese, estimation of, by oxalic
acid, 236

Manganese, Westmoreland's
process for, 230

Manganese, Volhard's process for,
231

Manganese, estimation by Pattin son's
method, 227

Manganese in small quantities, estima-
tion of, 233
Manganese ores, analysis of, 227, 230,

Manganese ores, moisture in, 234
Manganese oxides, nature of, 226
Manganese, precipitation as dioxide,

227

Manganese, precipitation of, by per-
manganate, 231

Manganese, technical method of esti-
mating, 230

Marsh gas, estimation of, 466
M c L e o d ' s gas apparatus, 523
Measuring flasks, 16
Mercurial trough, 416
Mercuric cyanide, standard for sugar,

311

Mercuric iodide for sugar, 311
Mercury, estimation, as chloride, 238'
Mercury, estimation of, as iodide, 240
Mercury, estimation of, by cyanogen,

241

Mercury, preservation of, for gas appa-
ratus, 462

Mercury solution for urea, 383
Mercury, titration of, by thiosulphate,

240
Metallic salts of all kinds, alkalimetric

titration of, 117
Metals, heavy titration of, 116
Metals and minerals in waters, estima-
tion of, 441

Method for percentages, 30
Methyl gas, estimation of, 466
Methyl orange, 36

Methyl orange, the proper use of, 36
M ethyl orange, commercial, the defects

of, 36

Mill on 's base, use of, 49
Milk sugar, inversion of, 307
Mineral acids in vinegar, 90
Mirror for detecting precipitates, 328
Mixer, test, 17

Mixtures of sugars, titration of, 317
Mohr Dr. F., father of the volumetric

system, 27

M o h r ' s burette, advantages of, 8
Molybdenum solution for precipitating

phosphoric acid, 297
Molybdenum solution, Pern be r ton's
standard, 294, 225

Napthol /J, for titrating bromine, 358
Nessler's solution, preparation of,

399, 465

Nickel, estimation of, 243
Nitrate baths for photography, assay

of, 304
Nitrates, colorimetric estimation of,

262
Nitrates, estimation of, by ferrous salts,

249—258, 260
Nitrates, estimation of, by nitrometer

262

INDEX.

583

Nitrates, indirect estimation of, 140
Nitrates in water, aluminium process

for, 433, 468
Nitrates in water, estimation of, in

nitrometer, 468

Nitrates by K j eldahl method, 85
Nitrates in manures, technical method

of titration 259, 260
Nitric acid, estimation of, by distilla-
tion, 246
Nitric and chloric acids, estimation of,

373
Nitric acid, estimation of, by indigo,

469
Nitric acid, estimation of, by

Schlo's ing's method, 253
Nitric acid, estimation of, Pelouze

method, 249, 260
Nitric acid, estimation of, in absence

of organic matter, 249
Nitric acid, estimation of, in presence

of organic matter, 253
Nitric acid, normal, 48
Nitric acid, pure, for titrations, 143
Nitric oxide gas, estimation of, 494, 501
Nitrite, standard solution of, for water

analysis, 404

Nitrites alkaline, titration of, 267
Nitrites, colorimetric titration of, 248
Nitrites, estimation by iodometric

method, 265

Nitrites, estimated gasometrically, 268
Nitrites, sulphites and thiosulphates,

analysis of mixtures thereof, 269
Nitrogen as nitrates and nitrites,

factors for, 245
Nitrogen as nitrate, estimation of, by

copper-zinc couple, 248, 430
Nitrogen combined in organic sub-
stances, 80
Nitrogen, estimation of, as nitric oxide,

2tfl

Nitrogen gas, estimation of, 466
Nitrogen in alkaline nitrates, 245, 259
Nitrogen, indirect estimation of, 140
Nitrogen, Kjeldahl's method for,

81
Nitrogen, total in urine, estimation of,

398

Nitrometer, general uses of, 533
Nitrometer, Lunge's, 529—537
Normal acid and alkaline solutions,

preparation of, 44
Normal acid solutions, verification of,

Normal ammonio-cupric solution, 50
Normal baric chloride, preparation of,

325

Normal hydrochloric acid, 48
Normal nitric acid, 48
Normal oxalic acid, 48
Normal potash solution, 49
Normal potassic carbonate, 47
Normal soda solution, 49
Normal sodi$ carbonate, 46

Normal solutions, 27

Normal solutions, definition of, 28

Normal solutions, based on molecular

weights, 28

Normal solution for gases, 521
Normal sulphuric acid, 47

Oils and fats, titration equivalents of,

with potash, 357
Oils and fats, titration of, with bromine

or iodine, 358
Oils and fats, titration of, by iodine,

360

Olefiant gas, estimation of, 473
Orange, methyl, the proper use of, 36
Orange, methyl, 36
Ore, tin, titration of, 340
Ores, arsenical, analysis of, 151, 152
Ores, copper, technical analysis of,

184

Ores, iron, analysis of, 214
Ores, iron, to render soluble, 214
Organic carbon and nitrogen in waters,

409 _
Organic impurities in water, estimation

of, without gas apparatus, 445
Organic nitrogen and carbon in waters,

409, 445

Oxalates, titration of, 109
Oxalic acid, normal, 48
Oxidation and reduction analyses, 120
Oxidizing agents, 120
Oxygen dissolved in waters, 269, 474
Oxygen dissolved in water at various

temperatures, 275
Oxygen gas, estimation of, 500
Oxygen in water, estimation of, 269,

474

Oxygen in water, Adam's method, 277
Oxygen in waters, Mohr's method of

estimating, 270
Oxygen in waters, W i n k 1 e r ' s method

of estimating, 270
Oxygen in waters.Schiitzenberger's

method of estimating, 270
Oxygen in waters, Koscoe and

Lunt's method of estimating,

270, 271
Oxygen in waters, iodometric method

of estimating, 277
Oxygen process for water, comparison

with combustion methods, 457
Oxygen process for water, 455, 471

Palladium asbestos for gases, 553

Paper, iodized starch, 137

Paper, lacmoid, 39

Paper, litmus, 35

Paper, turmeric, 35

Paper, turmeric, alkaline, 35

Pavy's copper solution for sugars,

315

Percentages, method for, 30
Permanganate, alkaline, for water

analysis, 465

584

INDEX.

Permanganate analyses, calculation of,

125
Permanganate for oxygen process in

water analysis, 465
Permanganate of potash, gasometric

titration of, 123
Permanganate, precautions in using,

124

Permanganate, preparation of stan-
dard solution, 121
Permanganate, titration with double

iron salt, 122

Permanganate, titration with iron, 121
Permanganate, titration of ferric salts

by, 124
Permanganate, titration of, with lead

oxalate, 123
Permanganate, titration of, with oxalic

acid, 123
Permanganate, titration of, with

hydrogen peroxide, 123
Permanganate, verification of standard

solution, 121
Permanganate, verification of standard

solution by hydrogen peroxide, 123
Phenacetolin, 37
Phenacetolin, preparation of, 37
Phenol, titration of, 366
Phenolphthalein, 37
Phenolphthalein, preparation of, 37
Phenolphthalein, disadvantages in

using, 38

Phosphates, earthy, in urine, 390
Phosphates of alkalies in urine, 390
Phosphates of lime, titration of, 288
Phosphoric acid, alkalimetric titration

of, 110
Phosphoric acid in combination with

alkaline bases, estimation of, 286
Phosphoric acid in minerals, estimation

of, 291
Phosphoric acid, Pemberton's

methods for, 293, 294
Phosphoric acid, titration of by molyb-

date, 293, 294.
Phosphoric acid, uranium method for,

285

Pinchcocks for burettes, 13
Pipette, the, 15
Pipette the, calibration of, 19
Plate, silver, assay of, 299
Poly-soccharides, nature of, 305
Porter-Clark process for softening

water, 454
Potash and soda, caustic, titration of,

55
Potash and soda, indirect estimation

of, 140

Potash and soda, mixed, 56
Potash and soda in urine, 398
Potash, estimation of, 60, 61
Potash, estimation of in neutral salts,

free from soda, 60
Potash, estimation of in presence of

soda, 61

! Potash solution, normal, 49
Potash in waters, estimation of, 442
Potassic carbonate, normal, 47
Potassic ferri cyanide as indicator, 127
Potassic iodide, how to free from

iodate, 130
Potassic permanganate, preparation of

standard solution, 121
Potassic permanganate, titration of

standard solution, 121
Preservation of solutions, 21
Preservation of solutions, Chorley's

apparatus for, 22
Pressure and temperature in gas

analysis, 492

Processes, direct and indirect, 31
Processes, titration, termination of,

32
Propylic hydride gas, estimation of,

Pump, S p r e n g e 1 , for water analysis,

414

Pyrites, burnt, analysis of, 319
Pyrites, estimation of sulphur in, 318

Red liquors, examination of, 64
Reduction and oxidation analyses, 120
Reduction agents. 120
Regnault and R e i s e t ' s gas appara-
tus, 520

Residual titration, 55
Residues, water, combustion of, 413
Rosolic acid or corallin, 38

Sachsse's mercuric iodide for sugar,

311

Sal ammoniac, analysis of, 79
Salt cake, 65
Salt raw, analysis of, 67
Salt solution, decinormal, 139
Salt, standard, for silver assay, 301
Salts, alkaline, titration of, 55
Salts, metallic, various, titration of,

alkalimetrically, 115
Samples of water, collection of, 406
Scheibler's apparatus for CO2, 101
Schiitzenberger's method of estima-
ting oxygen in waters, 270
Septem, the, 27

Silicates, iron estimated in, 217
Silicates of potash and soda, titration

of, 67

Silico-fluoric acid, estimation of, 105
Silver and chlorine analyses, 138
Silver and thiocyanic acid, 142
Silver assay, Mulder's improved

method, 300
Silver, assay of, by Gay Lussac's

method, 299

Silver, alloys, assay of, 298, 299
Silver chromate, solubility of, 139
Silver, estimation of, by standard sodic

chloride, 298, 299
Silver plate, assay of, 299
Silver solution, decinormal, 138

INDEX.

585

Silver solutions used in photography,

assay of, 304
Silver, titration of, by starch iodide,

298
Silver, titration of, by thiocyanate, 142,

298

Slags, manganese in. 228
Soap, analysis of, 68
Soap solution for water hardness, 405,

466
Soda and potash, indirect estimation

of, 141

Soda and potash in urine, 398
Soda and potash, mixed, estimation

of, G2
Soda and potash solutions, purification

of, 49

Soda ash, titration of, 63
Soda lyes, examination of, 64
Soda solution, normal, 49
Sodic carbonate, normal, 46
Sodic chloride, decinormal, 139
Sodic hyposulphite, Schittzenber-

ger's, 120, 270
Sodic peroxide, titration of, 284
Sodic peroxide, use of, as flux, 170
Sodic sulphide, titration of, 64
Sodic thiosulphate solution, decinormal,

preparation of, 130
S ol d a i n i ' s copper solution for sugar,

314
Solids, total in water, estimation of,

430

Solutions, alkaline and acid, prepara-
tion of, 44
Solutions, correction of volume for

temperature, 25, 26
Solutions, metallic acid, titration of, by

copper, 51

Solutions, normal, 27, 44
Solutions, normal, definition of, 28
Solutions, normal, based on molecular

weights, 29

Solutions, preservation of, 21
Solutions, standard, correction of, 51
Solutions, standard, factors for, 52,

54
Solutions, standard, used by weight,

6,21
Soxhlet's critical experiments on

sugar titration, 310
Spiegeleisen, estimation of manganese

in, 227—232
S p r e n g e 1 pump for water analysis,

Standard alkaline nitrite for water

analysis, 404

Standard ammonic molybdate, 294, 295
Standard ammonic phosphate, 288
Standard baryta solution, 50
Standard calcic phosphate, 289
Standard copper solution for sugar,

Fehling's, 309
Standard copper solution for sugar,

Pavy's,315

Standard copper solution for sugar,

Gerrard's, 317
Standard indigo solution, 464, 469
Standard potassic phosphate, 287
Standard salt solution for silver assay,

301
Standard silver solution for water, 405,

463
Standard soap solution for hardness,

405, 466

Standard solutions, correction of, 51
Standard solutions, factors for, 31, 54
Standard solutions used by weight, 6,

21
Standard water for hardness (Clark's),

405, 466
Stannous chloride solution, preparation

of, 128
Starch and potassic iodide, permanent

solution of, 132

Starch, concentrated solution of, 131
Starch indicator, preparation of, 131
Starch, inversion of, 308
Starch solution, preparation of, 131
i Starch paper iodized, 137
Steel, estimation of manganese in,

227—232

! Stock method for organic nitrogen, 87
Strontium in neutral salts, 70
Sugar, grape or glucose, 305 — 317
i Sugar in urine, estimation of, 391
Sugar in urine, colorimetric method

for, 392

Sugar, malt or maltose, 307
Sugar, modifications of, 307, 308
Sugar of milk, inversion of, 307
Sugar solutions, classification of, for

analysis, 305
Sugars, titration of, by S id er sky's

method, 313
Sugar, titration of, by Gerrard's

process, 317

Sugar, titration of, by Pe ska's pro-
cess, 315

Sugar, varieties of, 305
Sugars, critical experiments on the

analysis of, 3]0

Sugars, inverted by acid, 305, 307
Sugars, mixed, titration of, 317
Sugars, various ratios of reduction,

with Fehling's solution, 313, 316
Sugars, various, inversion into glucose,

307

Sulphates in urine, 390
Sulphides, alkaline, titration of, 64,

320, 323

Sulphides in alkali, detection of, 63
Sulphides, sulphites, and thiosulphates

in same solution, estimation of, 323
Sulphides, estimation of sulphur in,

'320

Sulphites, alkaline titration of, 64, 322
Sulphites in presence of alkalies,

destruction of, 59
Sulphites, titration of, 32^

586

INDEX.

Sulphocarbonates, titration of, 368
Sulphur in coal gas, estimation of, 320
Sulphur in pyrites, estimation of, 318
Sulphur in sulphides, estimation of, 320
Sulphuric acid, normal, 47
Sulphuric acid, combined, titration of,

325

Sulphuric acid in presence of hydro-
fluoric acid, estimation of, 100
Sulphuric anhydride, titration of, HI
Sulphurous acid, ratio of, in solution,

to specific gravity, 322
Sulphurous acid, titration of, 107, 322
Sulphurous acid in 'hydrofluoric acid,

estimation of, 107
Sulphurous anhydride gas, estimation

of, 466
Sulphuretted hydrogen in coal gas,

estimation of, 329

Sulphuretted hydrogen in water, esti-
mation of, 330
Sulphuretted hydrogen, titration of,

329

Superphosphates, titration of, 290
Syringe for cleaning gas apparatus, 541
System, decimal, origin of, 23
System of weights and measures for
volumetry, 23

Tannic acid, titration of, 331

Tannin, estimation of, by antimony,

339
Tannin, estimation of, by gelatine,

338
Tannin, titration of, Lowenthal's

process, 331

Tannin, titration of, Dreaper's pro-
cess, 336
Tanning materials, percentage of tannin

in, 335
Tanning materials, preparation of for

titration, 332

Tartar emetic, titration of, 147
Tartrate solution, alkaline, for sugar,

309

Tartrates, titration of, 112
Temperature and pressure in gas

analysis, 492
Temperature, variations, influence of

on solutions, 24, 25
Test mixer, 17

Thiocarbonates, titration of, 368
Thiocyanate, clecinormal, 142
Thiocyanates, estimation of, 197
Thiocyanic acid and silver, 142
Thiosulphate and iodine, titration by,

128
Thiosulphate solution, preparation of,

130
Thiosulphates, sulphides, and sulphites,

mixtures of, 323
Thomas's gas apparatus, 537
Tin, titration of, 339
Tin ore, titration of, 340
Titrated solutions, preservation of, 21

Titration, backward, 32, 55
Titration, residual, 32, 55
Turmeric paper, alkaline, 35
Turmeric paper, 35

Two-foot tube for water examination,
466

Uranium method for phosphoric acid,

285

Uranium method, Joulie's, 291
Uranium, standard solution of, 290
Uranium, titration of, 341
Urea, titration of, by hypobromite and

sodic arsenite, 386, 389
Urea estimation, apparatus for, 387
Urea estimation, corrections for, 385
Urea, estimation of, by hypobromite,

386

Urea, estimation of, by mercury, 382
Urea estimations, experiments on, 384
Urea, Liebig's method of titration.

382

Uric acid, estimation of, 392
Urine, albumen in, estimation of, 397
Urine, analysis of, 377
Urine, baryta solution, for removing

phosphates and sulphates from,

382
Urine, estimation of chlorides in,

378—382

Urine, free acid in, 397
Urine, potash and soda in, 398
Urine, estimation of total nitrogen in,

Vanadium, titration of, 341
Variations of temperature, influence

of, on solutions, 24
Vinegar, estimation of mineral acids

in, 90
Vinegar, titration of, by copper

solution, 51, 89

Volumetric analysis, general prin-
ciples, 1
Volumetric and gravimetric analysis,

distinction between, 2
Volumetric analysis without weights,

5,6

Volumetric methods, classification of, 3
Volumetric methods, various, reasons

for, 4

Water analysis, calculation of results,
476

Water analysis, interpretation of results
of, 444

Water analysis, reagents for, 399, 463

Water free from ammonia, preparation
of, 400

Water free from ammonia and organic
matter, 400

Water, hardness of, estimated without
soap solution, 71

Water deposits, microscopical examina-
tion of, 473

INDEX.

587

Water residues, combustion of, 413
Water, softening by Clark's process,

454
Water, esitmation of, total solids in,

430, 473

Waters, carbonic acid in, 95
Waters potable, analysis of, 398, 463
Weighing standard solutions instead of

measuring, 6
Weights and measures, systematic, for

volumetry, 23
Wildenstein's filter,' 328
Williamson and Russell's gas

apparatus, 489

Zinc, ammoniacal solution, preparation
of, 343

Zinc containing iron, analysis of, 347,
350

Zinc dust, analysis of, 351

Zinc dust for reducing ferric com-
pounds, 209

Zinc dust, purification of, for reducing
purposes, 209

Zinc dust, titration of, 351

Zinc, as ferrocyanide, estimation of,
346

Zinc ores, analysis of by Vieille
Montagne method, 345

Zinc, as oxalate, estimation of, 350

Zinc, as sulphide, titration of, 344, 345

Zinc oxide and carbonate, analysis of,
352

Zinc, titration of, 342—352

OF THE

UNIVERSITY

C.XIVERSITY OF CALIFORNIA LIBRARY

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

FEB 17 1916

30m-6,'14

YC 2189!

UNIVERSITY OF CALIFORNIA LIBRARY

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Full text of "A systematic handbook of volumetric analysis; or, The quantitative estimation of chemical substances by measure, applied to liquids, solids and gases .."

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