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A TEXT-BOOK OF
QUANTITATIVE CHEMICAL ANALYSIS



A TEXT-BOOK

OF

Quantitative Chemical
| Analysis



BY

ALEXANDER CHARLES GUMMING, D.Sc.

ii

Lecturer in Chemistry r , University of Edinburgh
AND

SYDNEY ALEXANDER KAY, D.Sc.

Assistant in Chemistry, University of Edinburgh



\ \ V * V <

NEW YORK

JOHN WILEY & SONS, INC.,
432 FOURTH AVENUE

1913



\ V \ /V



i... .-...-.



PREFACE

/

THIS book is intended primarily for University and College
students, and in planning it we have not overlooked the
fact that those who study Chemistry as a subsidiary subject
usually devote so short a time to it that it is impossible for
them to cover any comprehensive course, and that, even
when Chemistry is one of the main subjects of study, the
student, as a rule, has a strictly limited time for laboratory
work.

We have endeavoured, therefore, to arrange the book in
such a manner that some knowledge of the principles of
Quantitative Analysis may be acquired by a practical study
of the subjects included in Parts I., II., and III., and that the
further requirements of those who are making a special study
of Chemistry should be met by the later portions of the book.

Volumetric Analysis is dealt with in Part II. before Gravi-
metric Analysis, partly because the manipulation is easier,
and partly because the exercises in Volumetric Analysis
present a greater variety than those in simple Gravimetric
Analysis. The educative value of volumetric methods is
probably greater than that of any other branch of analysis,
and we are of opinion that a student should receive a
thorough training in Volumetric Analysis^ even if the time
remaining at his disposal permits of little or no gravimetric
work.

Most of the typical exercises in Parts II. and III. may
be performed with pure substances, but it is desirable that
the student should be accustomed from the commencement
of his course to the analysis of substances of " unknown "
composition. The serious student finds that this enhances



vi PREFACE

the value of the exercise, whilst the occasional student who
" only wants to know the method " has his attention directed
to the real purpose of Quantitative Analysis. A list of
solutions suitable for analysis is given in the Appendix. In
describing typical exercises, care has been taken to give the
practical details of manipulation as fully as possible, and
where full details are not given, reference is invariably made
to the pages where they may be found.

In Part V., all the common elements and radicals are
considered, together with the methods for their separation
and determination. As the arrangement is alphabetical
and copious references to other parts of the book are given,
it is hoped that this section will prove a useful index to
quantitative methods in general.

Water analysis is included because it always appears to
interest students, and because it affords useful exercises in
the determination of substances present only in traces.

In order to avoid constant repetition of particulars in
regard to the concentration of reagents, it has been assumed
throughout the book that, unless the contrary is stated, the
concentration of a reagent is that specified in the Appendix.
The concentrations usually recommended for indicator solu-
tions are such that even " a few drops " is often more than
ought to be used. The concentrations recommended in the
Appendix are so chosen that I c.c. of the indicator is the
normal amount required, and throughout the book it is
assumed that these dilute indicator solutions are used.

All the diagrams have been specially drawn for the book
in a large number of cases from original photographs of
the apparatus.

We desire heartily to acknowledge our indebtedness to
Dr Leonard Dobbin, whose helpful counsel has been at our
disposal during the preparation of the manuscript.

CHEMISTRY DEPARTMENT,

UNIVERSITY OF EDINBURGH,
October, 1913.



CONTENTS



PART L GENERAL PRINCIPLES.



Introductory

Volumetric and Gravimetric

Methods .

The Balance and Weighing .
Calibration of Weights .
Notes on General Apparatus .



PAGE

I

2

4

10

14



Preparation of the Substance for

Analysis . . . .16
Solution of the Substance . . 20

Evaporation 21

Precipitation ..... 22
Filtration 23



PART II. VOLUMETRIC ANALYSIS.



28



Introductory .....
The Measurement of Volumes of

Liquids 30

Standardisation of Instruments . 32
General Notes on the Preparation

of Standard Solutions . . 41



ACIDIMETRY AND ALKALIMETRY.

Introductory 44

The Use of Indicators . . .44
Standard Hydrochloric Acid. . 47
Standard Sulphuric Acid . . 52
Standard Sodium Hydroxide . 52
Analyses involving the Use of
Standard Acid and Alkali
Acetic Acid in Vinegar . . 55

Borax 55

Solubility of Lime in Water . 56

Mercury 56

Oxide and Carbonate in Quick-
lime 57

Acidic Radical in Salts of

Heavy Metals . .58

Ammonia (Indirect Method) . 58
Ammonia (Direct Method) . 59

Nitrate 60

Persulphate . . . .61
Standard Baryta Solution . . 61
Standard Lime-Water . . .63
vii



67
67
68



STANDARD POTASSIUM PERMAN-
GANATE AND DICHROMATE.
Decinormal Potassium Perman-
ganate . . . . (
Analyses involving the Use of

Standard Permanganate
Oxalic Acid and Oxalates .
Peroxides ....
Nitrite ....
Calcium . . . . .69

Nitrate 70

Decinormal Potassium Dichromate 71
Analyses involving the Use of
Standard Permanganate or
Dichromate Solutions
Iron in Iron Wire . . -74
Iron in Ferrous and Ferric

Compounds . . .76
Total Iron in a Mineral . . 80
Separate Determination of Fer-
rous and Ferric Iron in a
Mineral ....
Iron in Black Ink
Iron and Chromium in Chrome
Iron Ore ,



82
83



STANDARD IODINE AND STANDARD
SODIUM THIOSULPHATE.

Decinormal Sodium Thiosulphate 85
Decinormal Iodine . . ,88



viii



CONTENTS



PART II. VOLUMETRIC ANALYSIS continued.



Analyses involving the Use of
Standard Iodine and Standard
Sodium Thiosulphate

Copper 89

Sulphurous Acid and Sulphites . 91
Hydrogen Sulphide . .91

Peroxides, Chromates, Chlorates 92
Available Chlorine in Bleaching

Powder . . . -94
Tin in an Alloy . . .95
Tin in an Ore . . . . 9 6

STANDARD SILVER NITRATE AND
POTASSIUM THIOCYANATE.

Decinormal Silver Nitrate . . 98
Analyses involving the Use of

Standard Silver Nitrate

Chloride and Bromide . . 99

Chloride in Barium Chloride . 99

Cyanide 99



PAGE
100



Hydrocyanic Acid

Decinormal Silver Nitrate and

Decinormal Potassium Thio-

cyanate 101

Analyses involving the Use of
Standard Silver Nitrate and
Standard Thiocyanate
Chloride, Bromide, and Iodide . 103

Chlorate 104

Silver 104

Mercury 104

Total Chlorine in Bleaching

Powder .... 105

VARIOUS VOLUMETRIC PROCESSES.

Available Chlorine in Bleaching
Powder by means of Standard
Sodium Arsenite Solution . 107

Zinc by means of Standard Sodium

Sulphide Solution . . . 108



PART III. GRAVIMETRIC ANALYSIS.



Introductory .... 109

Notes on Apparatus . . . no

The Gooch Crucible . . .112

The Rose Crucible . . .115

The Ignition and Weighing of

Precipitates . . . .116

TYPICAL GRAVIMETRIC EXERCISES.

Water in Magnesium Sulphate

Heptahydrate . . .123

Water in Barium Chloride Crystals 124

Anhydrous Disodium Hydrogen
Phosphate in the Crystalline
Salt 124

Iron in Iron Ammonium Alum by

Ignition . . . .125

Other Examples of Analysis by

Ignition . . . .126



Iron as Ferric Oxide . . .127

Aluminium as Oxide . . .130

Sulphate as Barium Sulphate . 131

Chloride as Silver Chloride . .133

Magnesium as Pyrophosphate . 135

Zinc as Oxide . . . .137

Copper as Cupric Oxide . . 139

Copper as Cuprous Sulphide . 141

Calcium as Oxalate . . . 143

ELECTROLYTIC METHODS.

General 145

Copper (with Stationary Elec-
trodes) 148

Cadmium ..... 149

Copper (with a Rotating Cathode) 150

Nickel 153

Lead as Dioxide . . . .153



PART IV. COLORIMETRIC METHODS.



Introductory
Iron
Copper .



155
156
158



Ammonia . . . . .159

Lead . . . . . .161

Manganese . . t i2



CONTENTS



ix



PART V. SYSTEMATIC QUANTITATIVE ANALYSIS.



Aluminium 165

Ammonium ..... 167

Antimony 167

Arsenic ..... 168

Barium 169

Bismuth 170

Bromide 173

Cadmium 174

Calcium 175

Carbonate 175



Chlorate

Chloride

Chromium .

Chromate and Bichromate

Copper ....

Iron ....



181
181
182
182
183
185



PAGE

Lead . . . ... .187

Magnesium 188

Manganese . . . . .189
Mercury ..... 192

Nickel 195

Phosphate 196

Potassium and Sodium . . . 199
Silica and Silicates . . . 206

Silver 211

Sodium . . . . .211
Sulphate . . . . .211

Sulphide 212

Tin ... . . . 212

Water 213

Zinc 216



PART VI. THE ANALYSIS OF SIMPLE ORES AND
ALLOYS.



Silver Coin .
German Nickel Coin
Solder .

Bronze . . ,
Fusible Alloy
Limestone or Dolomite
Insoluble Silicate .



220
221
223
224
226
228
232



Glass 236

Iron Pyrites 239

Copper Pyrites . . . .241

Galena 244

Zinc Blende 245

Pyrolusite or Manganite . . 248
Superphosphate Manure . . 249



PART VII. GA^ ANALYSIS.



Introductory 253

Collection of a Sample of Gas for

Analysis 254

GAS ANALYSIS WITH THE HEMPEL
APPARATUS.

The Gas-Burette . . . .256
Absorption Pipettes . . . 259
Reagents used in Absorption

Pipettes . . . . 261
Manipulation of Apparatus . . 264
Analysis of a Gaseous Mixture . 266



GAS ANALYSIS WITH THE ORSAT
APPARATUS.

The Orsat Apparatus . . . 269
Collection of the Sample . .271
Analysis of the Gas . . .271
Determination of Hydiogen l.y
Combustion in Contact with
Palladium .... 272

ANALYSES INVOLVING THE USE OF A
LUNGE NITROMETER.

The Lunge Nitrometer . -275
Nitrogen in a Nitrate or Nitrite . 275



CONTENTS



PART VII. GAS ANALYSIS continued.



Hydrogen Peroxide
Zinc Dust



PAGE
, 277
, 278



DETERMINATION OF GASES PRESENT

ONLY IN TRACES.
General . , . . . 279



Sulphur in Coal Gas .. .
Atmospheric Carbon Dioxide
Hydrogen Sulphide in Coal Gas
Hydrocyanic Acid in Coal Gas
Sulphur Dioxide in Flue Gases



PAOK

. 280
, 282

,285
, 285
, 285



PART VIII. WATER ANALYSIS.



Introductory



. 286



PHYSICAL AND CHEMICAL METHODS
OF EXAMINATION AND ANALYSIS.

Collection of Samples of Water . 289
Physical Examination . . . 290
Chemical Examination

Total Solids . . . .292
Free and Albumenoid Ammonia 293
Reducing Power . . . 296
Chloride 298



Nitrite . . . . . 299
Nitrate . . . . . 300
Phosphate . . . . . 302

Hardness 302

Relative Acidity and Alkalinity 307

Lead 311

Action of Water on Lead . .312
Iron . . . . . 313

Zinc and Copper . . .313
Saline Constituents . . .313
Significance of the Results of

Analysis of a Potable Water 315



PART IX.- QUANTITATIVE ANALYSIS OF ORGANIC
SUBSTANCES.



Combustion Apparatus . . .318

Preparation of the Combustion

Tube 322

Combustion of a Solid Substance
containing Carbon and
Hydrogen . . * . 324

Combustion of a Liquid . . 327



Modification if Nitrogen is Present 328
Modification if Sulphur or a

Halogen is Present . . 329
Nitrogen by Dumas' Method . 329
Nitrogen by Kjeldahl's Method . 334
Chlorine, Bromine, and Iodine . 335
Sulphur 336



PART X. THE DETERMINATION OF MOLECULAR

WEIGHTS.



Victor Meyer's (Constant Pres-
sure) Method . . -339

Lumsden's (Constant Volume)

Method 342

The Freezing-Point Method . . 345



Beckmann's Boiling-Point Method 353
Modification with Electrical

Heating . ^ , . 355
Landsberger's Boiling - Point

Method. . . 356



CONTENTS



APPENDIX.



List of Common Reagents .

Special Reagents .

Indicator Solutions

Standard Solutions for Analysis

Typical Analyses .

Density and Concentration

Various Acids
Density and Concentration

Various Alkalis



PAGE PAGE

, 361 Density and Concentration of
, 363 Aqueous Alcohol . . . 370

, 364 Weight of i litre of Various Dry
. 364 Gases ....

. 366 Vapour Pressure of Water .

of Vapour Pressure of Potassium
. 368 Hydroxide Solutions . .371

of Table of Logarithms . . -372

. 370 Atomic Weights .... 374



371

371



INDEX OF SEPARATIONS



37S



INDEX



377



QUANTITATIVE CHEMICAL
y ANALYSIS

/

PART I

GENERAL PRINCIPLES

WHEN the examination of any substance is undertaken
for the purpose of determining the respective amounts of any
of its constituents, the investigation is known as quantitative
analysis. The problem may be a simple or a complex one,
depending on the nature of the substance, and on whether
a complete or only a partial analysis is required. For many
purposes, it is not necessary to ascertain the amounts of all
the constituents of a substance ; it may be of importance
to determine the amount of only one of them. It is
comparatively simple to determine, for example, the amount
of iron in an ore, the amount of carbon dioxide in a sample
of air, or the amount of chloride in a water supply. On the
other hand, it may be necessary to make a complete analysis
of a complex ore or rock, containing as many as ten or
twenty constituents, or to carry out a detailed investigation
of a sample of water. The complexity of an analysis depends,'
however, as much on the nature of the constituents as on
their number, and the determination of the amount of even
a single constituent may involve a lengthy and refined
investigation, demanding the highest skill on the part of
the chemist.

There are usually several distinct methods for the
determination of one and the same substance, all of which
may not be applicable, however, to the particular case. The

A



$ : tastfEfcAL PRINCIPLES

procedure adopted is sometimes a matter of convenience,
but the choice of the best method more often requires
careful consideration.

The gravimetric method of analysis in most cases involves

(1) the separation of the constituents of the substance in
the form of insoluble compounds of known composition ;

(2) the determination of the weight of the compounds so
obtained.

The volumetric method of analysis, on the other hand, is
based on the use of a reagent of known concentration and on
the measurement of the volume of this reagent required to
complete the chemical change involved.

A fundamental distinction between the two methods is,
that in gravimetric analysis the constituent which is to be
determined must first be separated from all the other con-
stituents of the substance ; whereas, in volumetric analysis^
the complete isolation of the constituent is very frequently
unnecessary, and one of the constituents of a substance can
often be rapidly and accurately determined in presence
of all the others, thus enormously simplifying the analytical
process.

Most substances can be determined either gravimetrically
or volumetrically. In the systematic treatment of the
subject, it is convenient to consider gravimetric and volu-
metric methods separately ; but in practice the two methods
of procedure are frequently combined, in order that the
analysis may be completed as rapidly and as accurately as
possible. When a complete analysis of a complex substance
has to be made, the constituents must, as a rule, be separated
from one another before the amount of each can be
ascertained, and in such a case gravimetric methods are
usually employed ; whereas, if only a partial analysis is
required, involving, it may be, only one of the constituents,
volumetric methods are often applicable. The latter are
almost invariably more expeditious than gravimetric methods,
and, in analysis for technical purposes, where economy of
time is often imperative, volumetric methods not necessarily
less accurate than gravimetric are used as far as possible.

As an example in illustration of some of the foregoing
principles, two methods of determining the respective



GENERAL PRINCIPLES 3

amounts of iron and aluminium in a solution containing
ferric and aluminium chlorides may be briefly outlined.

(1) In order to accomplish this by gravimetric methods
alone, the iron and aluminium must be separated by adding
an excess of sodium hydroxide to a weighed or measured
portion of the solution. The precipitate, which consists of
ferric hydroxide, is filtered; the filtrate contains the
aluminium as sodium aluminate.

The precipitate, which is contaminated with alkali
hydroxide, is dissolved in nitric acid, and ammonia is
added in order to reprecipitate the ferric hydroxide. The
latter, after filtration, is converted into ferric oxide which
is weighed.

The filtrate, containing the sodium aluminate, is acidified
with hydrochloric acid, and the aluminium is precipitated as
aluminium hydroxide by adding ammonia. The precipitate
is filtered and, by heating to a high temperature, is converted
into alumina which is weighed.

From the weights of ferric oxide and alumina, the
respective amounts of iron and aluminium in the solution
can then be calculated.

(2) By a combination of gravimetric and volumetric
methods, which in this case is much to be preferred, no
separation of the iron and aluminium is necessary; the
procedure is accordingly simpler and more expeditious, and
accurate results are more readily obtained.

The iron and aluminium are precipitated together as
hydroxides by adding ammonium chloride and ammonia to
a weighed or measured portion of the solution, and the
precipitate, by heating strongly, is converted into a mixture
of ferric oxide and alumina, which is weighed, The mixture
of ferric oxide and alumina is then dissolved (or another
measured portion of the original solution is taken), and the
iron in the solution is determined volumetrically. The
volumetric process consists, briefly, in reducing the ferric
salt to the ferrous state by means of hydrogen sulphide or
other suitable reducing agent, and in then determining the
amount of iron present by means of a solution of potassium
permanganate of known concentration. The aluminium does
not interfere with the volumetric determination of the iron.



4 GENERAL PRINCIPLES

It is then easy to calculate how much ferric oxide is
present in the mixture of ferric oxide and alumina, and the
difference between the total weight of the mixed oxides
(which has already been determined gravimetrically) and the
weight of the ferric oxide, is the weight of the alumina. The
respective amounts of iron and aluminium in the original
solution can then be calculated.

The Balance.

For accurate analytical work a suitable balance, capable
of supporting a maximum load of 100 to 200 grams in each
pan, is indispensable. It is important that the maximum
load, whatever it may be, should not be exceeded. With a
good balance, properly adjusted and used, very accurate
measurements can be made. For example, it is possible to
distinguish between two masses of about 10 grams each
when they differ in weight by only 01 milligram,*'.*?, by i
part in 100,000. A balance is, therefore, a delicate instru-
ment of precision, and the greatest possible care must be
taken in using it. The rules regarding the use of the balance
must be carefully read, and thereafter strictly adhered to.

When weighing in a comparatively rough fashion, it is
generally assumed that equipoise is established when the
excursions of the pointer towards either side of the mid-point
of the scale are of equal amplitude. There are reasons,
however, why this method is not adopted in accurate
work.

(1) The resting-point, or zero-point, of the unloaded

balance, i.e. the position which the pointer would
apparently take up if the oscillating beam were
allowed to come to rest, seldom coincides exactly
with the mid-point of the scale.

(2) Since the oscillating beam, if left to itself, ultimately

comes to rest, the amplitude of each oscillation, even
when equipoise is established, is less than that of
the preceding one. It follows that, if an excursion
of the pointer to the left is equal to the preceding
one to the right, the weight on the right is greater
than that on the left (assuming the zero-point to
coincide with the mid-point of the scale).



USE OF THE BALANCE 5

Routine Method of Weighing.

In making a weighing, accurate to o-i milligram (o-oooi
gram), the following method should be used :

(i) Find the zero-point of the unloaded balance.

Release the beam gently, and if necessary set it oscillat-
ing (by wafting air down upon one of the pans) so that the
pointer moves through about five scale divisions on either
side of the middle point. Close the balance-case, and,
neglecting the first complete oscillation (two excursions of
the pointer), carefully observe and note down the next three
extreme positions of the pointer, two observations being
made on one side and one on the other side of the mid-point
of the scale. Assume the scale to be numbered from the
extreme left towards the right, i.e. from o to 20, the mid-
point being 10, and estimate tenths of the scale divisions.

If, for example, the observations were

Left. Right.

(i) 5-0

(2) 15-8

(3) 5-4

the turning-point on the left, corresponding with the point
15-8 on the right, is the mean of 5-0 and 5-4, i.e. 5-2, and the
resting-point is therefore



Repeat the observations several times. The results should
not differ by more than one or two tenths of a scale division,
and the mean is taken as the zero-point of the balance. As
the zero-point is frequently subject to slight fluctuations, it
should be determined before each set of weighings is
commenced.

(2) Place the vessel to be weighed on the left pan of the
balance and proceed to counterpoise it. It is best to begin
with a weight that will probably prove too heavy, as this
may save time in the end. For example, if the weight of the



6 GENERAL PRINCIPLES

vessel is thought to lie between 15 and 20 grams, the latter
weight is placed on the right scale-pan. If, on releasing the
beam, the 2o-gram weight is seen to be too much, it is
replaced by a lo-gram weight, and the necessary smaller
weights are added in regular succession until finally it is
found that, for example, 16-46 grams is too little, whilst 16-47
grams is too much.

In place of the inconveniently small milligram weights, it
is preferable, at this stage, to use a rider, which weighs o-oi
gram, whilst its effective weight depends on its position on
the divided beam. After some experience, it will be found
possible approximately to estimate, by observing the extent
and rapidity of the oscillation, what additional weight is
required to establish equilibrium. If, for instance, it is found
that with 16-46 grams on the pan the pointer is deflected
slowly to the right whilst with 16-47 grams it is deflected
much more rapidly and to a greater extent to the left, the
weight of the vessel is nearer 16-46 than 16-47 grams.

Place the rider, then, on the beam, in such a position that
'equipoise is nearly established for example, at division 3.
Close the balance-case and determine the resting-point.
Suppose it is found to be 9-6.

(3) Find the " sensitiveness " of the balance, i.e. the dis-
placement of the resting-point produced by an alteration of
I milligram : Alter the position of the rider by an amount
corresponding to i milligram in such a direction that the
resting-point is shifted to the other side of the zero-point
and again determine the resting-point. Suppose it to be
1 1- 1 when the rider is at division 2. The sensitiveness is
then equal to

11-1-9-6=1-5 scale divisions.

(4) Now calculate, as follows, the alteration of the weight
necessary to counterpoise the vessel exactly :

The zero-point using the figures assumed in the fore-
going is 10-5, and the resting-point with a load of 16-462
grams is u-i. The vessel weighs, therefore, more than
16-462 grams, the additional amount being equal to that
necessary to displace the resting-point from n-i to 10-5, or
0-6 of a scale division. Since, however, 1-5 scale divisions cor-



USE OF THE BALANCE 7

responds with I milligram, 0-6 scale division is equivalent to

06

= 0-4 milligram.

The weight of the vessel is therefore 16-4624 grams.

The complete weighing thus involves the determination
of three resting-points the first, that observed with the
empty balance; the second, after approximately counterpois-
ing; the third, after making an alteration of I milligram.
All the observations made in the above example are shown
below :

Resting-points.



Mean
Resting-points



(1)

Unloaded
balance.


(2)

With load of
16-463 grams.


(3)
With load of
16-462 grams.


5-0


4-4


6-7


15-8
5'4


14-7

4-6


15-3
7-0

6-9 15-3

IM


5-2 15-8
10-5


4-5 147
9-6


iveness
ion


= IM 9-6
= IM-IO-5


= 1-5 scale divisions

= ' 6





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