Full text of "Practical methods of electro-chemistry"

Google

This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project

to make the world's books discoverable online.

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject

to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books

are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other maiginalia present in the original volume will appear in this file - a reminder of this book's long journey from the

publisher to a library and finally to you.

Usage guidelines

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing tliis resource, we liave taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.
We also ask that you:

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.

+ Refrain fivm automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.

+ Maintain attributionTht GoogXt "watermark" you see on each file is essential for in forming people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liabili^ can be quite severe.

About Google Book Search

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web

at |http: //books .google .com/I

PRACTICAL METHODS OF

ELECTRO-CHEMISTRY

BY THE SAME AUTHOR

QUALITATIVE CHEMICAL ANALYSIS
(Organic and Inorganic)

With 9 Illustrations and Spectrum Plate

8vo, y, 6d,

LONGMANS, GREEN, AND CO.

LONDON, NEW YORK, AND BOMBAY

PRACTICAL METHODS

E LECT RO-CH E M I ST R\'

F. MOLLWO PERKIN. PU.D.

tfaCM. ANt> SIXTY-FOUR ILLOSTHATtt^tt
fX TffF TFXT

Longmans, green, and C'

39 PATERNOSTER ROW. LONDON
NEW YORK AND IIUMBAY

PRACTICAL METHODS

ELECTRO-CHEMISTRY

j F. MOLLWO PERKIN. Ph.D.

WITH FRONTISPIECE, AMD SIXTY-FOUR ILLUSTRATIONS
IN THE TEXT

LONGMANS. GREEN, AND CO.

39 PATERNOSTER ROW, LONDON
NEW YORK AND BOMBAY

All rigkli rutmJ

th;-; : . ■ ..k
PUBL.: ■ ..ARY

706450

TIlD. r. f v. -.^.a; iONS

• »-■ w-

• I

•• • ••

• • ••

• •••

• •<

• _•

• •

• •• '

'• • •
• • •

(• • •

• • • •

,•• •

: .•:.".••

DEDICATED TO
SIR JOSEPH SWAN, D.Sc. F.R.S.

FIRST PRESIDENT OF THE FARADAY SOCIETY

t • >

• » * t » ■

: .:■ • • .. :\ •

PRACTICAL METHODS OF

ELECTRO-CHEMISTRY

X Hints to Students.

and variations in these conditions will also cause variations in
the time factor, and in the E.M.F.

Absolute cleanliness is essential to correct results; the least
trace of grease upon the electrodes may be sufficient to ruin
an experiment. Platinum is largely employed in electro-
chemistry, but the average student, and some very much above
the average, look upon platinum as being imperishable. This
is a very grave error; platinum requires the most careful usage,
and should be handled as if it were — as it is — ^a precious
substance.

In all cases in this book, except where otherwise specially
stated, the Current Density, CD., refers to the square
decimeter of surface. The flag electrodes preferred by the
author usually have a surface of \ square decimeter; therefore,
if a CD. of I ampere is stated as being required, then only \
ampere of current must be employed; a registered current of
I ampere would represent a CD. of 2 amperes.

The student is advised, after having made a few analytical
determinations, to carry out the analytical and preparative work
conjointly.

CONTENTS

PART I.
GENERAL.

CHAPTER PAGE

I. Electrolysis 3

II. Measurement of Current 12

III. Instruments for Measuring Intensity of Current . 22

IV. Energy 27

V. Sources of Current 34

VI. Regulation of Current 69

VII. Apparatus for Electrolysis 76

PART II.
ELECTRO-CHEMICAL ANALYSIS.

VIII. Electro-Chemical Analysis 8$

IX. Metals deposited as Oxides at the Anode . . . 136

X. Separation of Metals 151

PART III.
PREPARATIONS BY ELECTROLYTIC MEANS.

XI. Preparations 195

XII. Preparation of Inorganic Products 200

XIII. Organic Electrolysis 225

XIV. Reduction of Organic Compounds 235

XV. Oxidation of Organic Compounds 261

Preparation of Reagents 282

Some Useful Data . 285

The Use of Logarithms 291

Five-figure Logarithms 297

Index i\>\

LITERATURE ABBREVIATIONS

Amer, Chem, Journ,

Amer. Chern, Soc

Amer,Journ, of Science and Arts
Amer, Phil, Soc

Annalen . . . .
Ann. Chern. Pharm.
Ber.

Berg, und Hiltten Zeit.
British Assoc. Report
Bull. Soc. Chim. .
Chetn. Central Blatt
Chern. News .
Chern. Soc.

Chern, ZHtung . ,
Compt. Rendus .
D.R.P, . . .

Elictro-chcm. and Met.
Electrochem. Zeit,

E. P.

Jahrbuch

Journ, Amer, Electro-chetn.

Journ. Anal, Chem.

Journ. f. prakt. Chem.

Monatsheft

Phil, Mag. . . .

Phil. 'Jrans. , , ,

Proc. Royal Soc. . .
Soc. Chem. Ind. .
Trans. Faraday Society
U. S.P..,,.

Zeit,/, Anal, Chem.
Zeit./, Angew, Chem.
Zeit,/. Elektrochem, .
Zeit./, Phys, Chem, .

American Chemical JoamaL
Journal of the American Chemical Sodet}
American Journal of Science and Arts.
Proceedings of the American PhiW*^^'

Society.
Liebig's Annalen d<
Annalen der Chemi^
Berichte der Dent

lachaft.
Berg, und Hiitteni
Report of British At
Bulletin de la Soci^j
Chemisches Central]
Chemical News.
Journal of the Chei
Chemiker-Zeitung.
Comptes Rendus.
German Patent.
Electro-chemist an<
Electrochemische 7a
English Patent.
Jahrbuch der Eleclrj
Journal of the Am|

Society.
Journal of Analytica^E. ^«aci

Journal fiir praktiscl
Monatsheft fur Chei
Philosophical Magazine.
Philosophical Transactions of the Ro)

Society.
Proceedings of the Ro3ral Society.
Journal of the Society of Chemical Industi
Transactions of the Faraday Society.
American Patent.

Zeitschrift fiir Analytische Chemie.
Zeitschrift fiir Angewandte Chemie.
Zeitschrift fiir Elektrochemie.
Zeitschrift fiir Physikalische Chemie.

CHAPTER I.

ELECTROL VSI.S.

While electro-chemistry may be said to date back to the dis-
covery of the galvanic element by Voltain 1800, a discovery which
led to the isolation of the alkali metals by Davy in t8o6, we have
to thank Faraday before all others for placing tlie subject upon a
firm and scientific foundation. Not only did Faraday, by formu-
lating the laws governing the passage of the electric current through
electrolytesj in 1853, lay the foundation stone of theoretical and
practical electro-chemistry; but in 1831 he had already shown
that a temporary current is induced in a closed circuit by the
movement of a magnet in its neighbourhood — an observation, the
application of which in future years was destined to revolutionise
many phases of chemical industry, and to found a new branch
of engineering, the development of which seems to have no
bounds.

Electrolysis.

That some substances, such as metals, conduct electricity
readily, and that other substances, such as glass and porcelain,
will not allow its passage has been known for a great number of
years. Since the time of Volta, it has been recognised that
certain liquids may also be classed among conductors of the
electrical current.

Faraday called metals and similar substances conductors of
the first class ; liquids he called conductors of the second
class. We shall not here concern ourselves with the manner in
which the electric current passes through a metallic conductor : a

4 Practical Electro-Chefmstry.

frw years nj;o ihcrr was vi*ry little controversy as to how this took
|)lart— t()-<lay there are several theories. It is, however, necessary
to iiav<- soiiK- conception of the way in which liquids may be
siH)|)()S(mI to he al)l<' to conduct electricity.

All li«iuids are not conductors; pure water itself is not a
roiiductor. Aqueous solutions of salts^ acids, and bases permit
llir passa^^c of the current; on the other hand, solutions of some
suhstano's, such as sugar, j^um, etc., do not possess this property,
ll is therefore ohvious that salts, acids, and bases behave differently
in solution from other classes of substances.

According to our present conceptions, it is presumed that salts,
acids, and l)ases, when in solution, arc not there exclusively in 1
the form of complete molecules, but that the molecules are, in
solution, dissociated to a greater or less extent into ions. For
example, common sail, XaCi, when dissolved in water is supposed
lo he sjjjit up into the positive ion Na, and the negative ion CL
In the sol ill condition sodium chloride is electrically neutral,
having neither a positive nor a negative charge, or, what comes
to the same thing, it has opposed charges in equal proportion.
In solution, however, some at least of the molecules break up
into the ion Na carrying a heavy positive electrical charge, and
ilie ion CI with an equal charge of negative electricity. In a
similar manner, ])otassium hydroxide in solution is split up into
th(^ positive ion K, and the negative ion OH, known as the
hydroxyl ion.^

W^hen two pieces of platinum, connected with the opposite
poles of an electric battery (these pieces of platinum when so con-
nected are called electrodes), are placed in a solution of scidium
chloride, a current of electricity passes through the solution,
and it is found that chlorine gas is evolved at the piece of platinum
connected to the positive pole of the battery, while hydrogen gas
is given off at the piece in connection with the negative pole.
It lias already been stated that pure water will not conduct
electricity ; how is it, then, that the electric current readily passes

^ The valency of the cation is represented by a (*) ; thus in Ag* and in
I3a". The valency of the anion is represented thus ('), e.g. CT and SO/'.

Electrolysis. 5

h rough a solution of soiiiani chloride? It is a wtll-known law
electrical science, that like attracts unlike, and like rcpi-ls like,
\^. negatively charged bodies attract positively electrified bodies,
tnd repel negatively electrified bodies. Now, in a solution of
rodium chloride there are present CI ions carrying a negative
iectric charge, and Na ions charged with an equal quantity of
Wsitive electricity. It follows that the negative ions will be
Lttracted to the positive pole, and the positive ions to the negative
Xile. In other words, the electric current wiU be conveyed across
%s solution from one pole to the other by the ions. The CI, or
legative, ions will convey the negative electricity to the positive
Slectrode, where they will become neutralised by the positive
dectricity at that electrode. The Na, or positive, ions will
convey the positive electricity to the negative electrode, where
^y will become neutralised by the poiBiUve electricity al that
pole.

It was Faraday who first called the particle which conveys the
iuirent in solutions an ion, — from the Greek word meaning
'anderer or traveller. He called the ion which conveyed the
ositive electricity, and therefore appears at the negative pole,
le cation, and the negarive pole the cathode. The ion which
xrnveys the negative electricity was designated the anion, and
positive pole at which it is neutralised the anode.
The ion CI is not molecular chlorine as we know it — a yellow
[as of unpleasant odour. Neither is the ion Na molecular sodium
-a readily oxidisiable metal, which decomposes wafer. The
lolecules are electrically neutral ; the ions, on the other hand,
tossess an electric charge— the anion being negatively charged,
cation having an equal positive chaise. The moment the
are liberated at the electrode, i.e. have their charges neu-
talised by an equal quantity of the opposite charge, they become
jms which, uniting together, become molecules of the substances
the free state as we know them. Thus, as soon as the electric
sses through the solution, a smell of chlorine gas is
irceptible at the anode, and hydrogen is evolved at the cathode ;
e solution in the neighbourhood of the cathode becoming

Practical Blectro-Cheniistry.

Ikaline, owing to the metallic sodium at the
tion reacting with the water thus —

Na + H,0 = NaOH -

The production of hydrogen in this example is thus due to a.
secondary action. An example might, however, be taken i
which both the anion and cation, on neutralisation, give rise t«
the corresponding molecular forms. For instance, in a solution
of copper chloride we have the cation Cu"' and the two i
CI, the two anions together bearing the same amount of electricityi
but of opposite sign, as the Cu" cation. On electro) ysing this
solution gaseous chlorine makes its appearance at the anode, and
metallic copper is plated on to the cathode.

According to Le Blanc, leaving out of account metallic sa^
solutions and salts of the halogens, the electrolysis of water inttf
be looked upon as being a primary decomposition. In water we
have H and OH ions. Now, the electrical conductivity of a.
solution is brought about by all the ions in the solution,
electrolysing a solution of potassium sulphate, what we notice tsl
the separation of hydrogen at the cathode, and oxygen at the
anode. When therefore the current is not too strong, it is nol
necessary to assume the separation of potassium at the cathode
and the SOj radical at the anode, although this assumption i
usually made. There will always be H and OH ions preSenl
since these will be immediately generated by the undissociata
water. At the electrode, the action which will take place ^
naturally that which proceeds the most readily; tiiat is, in thi
case, the separation of the H and OH radicals. As a mattei q
fact, in ordinary electrolysis, when currents of considerable i
sity are being used, we may presiune that we have both a primai;
and secondary reaction proceeding simultaneously.

Faraday, in Iris researches into the phenomena of electrolysis

found by careful measurement that the quantity of substanc

deposited at the electrodes always corresjxjnded to the a

of electricity which bad been pabsed through the solution.

I further found that amount of substance deposited at the cathod

Electrolysis. 7

always bore the same ratio to the quantity given up at the anode;
further, that the quantity of different elements yielded up at tht
electrodes by a given current bore a simple ratio to their com-
bining weights. The laws of Faraday, deduced from these facts,
are usually formulated as follows : —

I. The amount of a substance liberated b^ the eUciric current is
proportional to the total quantity of electridty passed through the

2. By the same quantity of current equivalent proportions of
different electrolytes are decomposed. And the amount of different
substances deposited is in the ratio of their equivalent weights.

The first law states that the amount of substance liberated
depends upon the quantity of current passed. It does not matter
whether the current has been passed slowly or rapidly. For
example, in i hour a current of i ampere will deposit i'i8s8 grm.
of copper at the cathode, a current of i amperes would liberate
this quantity in half an hour, and one of half an ampere would
require to be passed for 3 hours to deposit the same quantity.

When a current of i ampere is passed through a circuit for
I second, the quantity of electricity which passes is called a
coulomb ; that is, a coulomb is i ampere second, A current of
t ampere passing for 96,540 seconds will deposit the gram equivalent
of an element ; in other words, 96,540 coulombs of electricity
are required to deposit the gram equivalent of an element. This
quantity of electricity is sometimes called a Faraday. Lehfeldt '
suggests that the name might be brought into more common use ;
we win, tlierefore, in this book employ the term faraday to denote
the quantity of electricity 96,540 coulombs. One coulomb will
deposit o'ooiiiS grm, of silver from a solution of a silver salt
If this quantity is divided into the atomic weight of silver, we
obtain^

-;- - ig = 96,538 coulombs.

Again, i coulomb of electricity will deposit o'ooo3294 grm. of

copper from a solution of a cupric salt, and if this number is

' " Eleclio-chemisliy," ]it. 1. p. 3,

8 Practical Electro-Oiemistry,

divided into 31*8, the hydrogen equivalent of copper, compared
to oxygen as 16, we obtain —

31-8

. = 96,530 coulombs.

o 0003294 ^ ^^"^^

But when i coulomb is passed through a solution of a cuprous
salt 0*0006588 grm. of copper is deposited. The equivalent
in this case is 63*6, the cuprous ion being monovalent,

/: Qo = 96,539 coulombs.

0*0006588 ^ ^^^^

The last two examples prove Faraday's second law, that the
same quantity of current will liberate equivalent proportions of
the different elements. The quantity of electricity necessary to
liberate 1*008 grm. of hydrogen will liberate io7'93 grm. of
silver, 31*8 grm. of copper from cupric salts, and 63*6 grm.
of copper from cuprous salts. These examples all refer to sub-
stances liberated at the cathode, but the same quantity of current,
will likewise liberate at the anode 8 grm. of oxygen, 35*45 grm.
of chlorine, 1 26*85 g^"^- of iodine, etc.

Only the elements most likely to be required in general electro-
chemical work have been included in the following table. There is,
however, no difficulty in calculating the electro-chemical equivalent
of an element. If the atomic weight and the valency are known,
then the electro-chemical equivalent is found by, first dividing
the atomic weight by the valency number and the number so
obtained by 96,540. For example, the atomic weight of boron is

II (O = 16) and its valency is 3. We therefore get — = 3*6666.

The number 3*6666 is the oxygen equivalent of boron, and from
this we obtain —

3*666
^^^ = o-<>3797 mg.

That is, 0*03797 mg. of boron would be deposited in i second by
a current of i ampere passing through its solutions.

■

Eieetrolysis. ^^^^^B

TABLE 1.

-ATOMIC AND EQUIVALENT WEIGHTS AND H

ELECTRO-CHEMICAL EQUIVALENTS OF THE ELEMENTS. H

Calculated Ftora the table of atomic weights drawn up by the Intemalional ^|

Committee for 1903. ^H

Ei™«it.

Formula
apd

Per

™!swT.

„=.

= .6 H = .

1 perMK.

Alaminium

Al-

96-90

27-10 : S-966

9-033 1 0-09357

0-3368

AntimDay

Sb-

119-30

12O-20 39-766

40-067 1 0-41504

1-4941

Aisenlc

As-

74-40

75-00 24-800

0-9323

Buinm

Ba-

136-40

.3?-40' 68-200

68-700:0-71160

2-5619

Bismuth

Bi"

10690

20850 68 966

69-50010-7(991

25917

BromiiM:

Br-

79-36

7996 79-360

79-960 0-81830

2-9818

Cadminm

ed-

iii'6o

112-40 55-800

56-200 ; 0-58220

2-0957

-■Caloiiun

Ca-

39 So

40-10 19-900

10-050 020769

0-7477

Chlorine

CI'

35-18

35-45 35-180

35-450 0-36721

1-3220

Chromium

51-70

5i-io 25850

26-050 1 0-26984

0-9714

Cr-

51-70

Sa-ro 17-233

0-6476

.Cobalt

Co"

SS-S6

59-00 29-2i,0

ereS'o-lsli

Copper

Cu-

63- 'O

63-60 63-100

2-3717

Cu"

63-'o

63-60 3.-550

31-800 0-32940

1-1858

Gold

Au-

19570

197-20 65-233

65-733

0-68090

2-4513

HydrofiH.

1-008 I -000

1-008

0-01044

0-03759

lodiDc

US 90

126 -85 125-900

126-850

1-31400

47303

Iron

Fe"

55-50

55-90 27-750

27-950

0-28952

1-0423

Fe-

55-50

55-90 iS-500

18633

0- 19301

0-6949

I-^

Pb"

205-35

103-450' 1-07165

3-8580

Li-

6-98

7-03 6-9S0

7-030

0-07282

0-26215

Me"

24-18

24-36 i2-ogo

12180

0-12626

0-454S

Manganese

Mn-

54-60

55-00 27-300

27-500

0-28486

I -0255 J

Mn-

54-60

55-00' 13-200

18330

018991

0-6837

Hg-

198-50

200-00 198-500

2-07170

7-4580

He-

193-50

aoo-Qo 99250

I -03590

3-7291

Mo--

96-00. 47-650

48-000

0-49721

1-7900

Nfckel

Ni-

5S-70 29-150

''^

0-30402

1-0945

Sitngen

N'"

lis

1404 4-643

0-048478

0-17452
0-29833

.n^™

16-00 7-940

S'ooo

0-08287

Pt-

■Ii:s

194-80 48-325

48-70010-50446

i-8i65

'potasgiulQ

K-

39-15 38-860

39-150 0-40550
10-793 i-iiSoo

1-4598

mYBt
Sodiam

Ag-

107-12

107-93' 107-120

4-0248

Na-

32-SS

23-05! 22-8S0

23-050 0-23876

0-8596

.Stionfian)

Sr-

86-94

87-80 43-470

43-900 0-4S371

'■6333

jTb.

Sn"-

iia-io

ttg-oo 59-050

59-500 0-61630

2-2188

B^BngEten

Sn—

ii8-[o
iS2-6o

119-00 39-520
1S4-00 91-300

29-750 0-30817
92-000 0-95300

Zn"

64-90

65-40 32-450

32-700 0-33873

1-2194

Zr—

89-90; 90-60 M-475

22-650 0-23460

0-8445

L J

ID Practical Electro-Chemistry.

Experimental Proof of Faraday's Laws.

Take four beakers and place in them respectively a lo per
cent, solution of copper sulphate slightly acidified with sulphuric
acid, a solution of cuprous chloride in hydrochloric acid, a lo
per cent, solution of nickel sulphate, and a solution of cadmium
sulphate, with a few drops of sulphuric acid {see p. aSa),

Place the beakers in a row close together, and connect t
together in the manner shown in Fig, i. The electrodes markfia
with the — sign are to be carefully weighed; for the rest, the
arrangement of the apparatus explains itself. The anodes and
cathodes may be made of sheet metal or of metal rods to which
pieces of copper wire have been soldered, in order to connect them
together. Electrolj^ic cells arranged as here shown are said to
be cormected up in scries. Also place in series irith the cells an
ammeter, so that the intensity of the
current may be noted, the strength
of the current can be regulated by
means of a resistance. Fig. 2 shows
diagram matically the arrangement
of the battery, etc. b is the battery
or source of current, A the ammeter,
^i"- "■ c the cells, and R the resistance.

In carrying out the experiment, carefully weigh the cathodes,
then regulate the current by means of the resistance to, say, o'5
ampere, and note the time. After allowing the current to pass
hour, taking care that its intensity remains constant, it is
switched off. The cathodes are taken out, washed with distilled
and alcohol, dried in the steam oven and weighed. If the

Electrolysis.

experiment has bec-n carefully performed, it wi!l lit found that the
metals have increased in weight in the ratio of their hydrogen
equivalents. The current passed should not exceed i ampere per
square decimeter of cathode surface, otherwise unsatisfactory and
badly adhering deposits may be obtained, which are difficult to
weigh. It is not by any means an easy matter to obtain satis-
factory results from cuprous solutions, as there is a tendency for
the deposit to be powdery and not to adhere well. Of course,
solutions of other metallic salts may be used instead of those here
described.

From what has been already stated, it follows that there is a
definite relationship between the valency of an element and the
electric charge which the ions carry. Thus the quantity of
electricity necessary to deposit 63-6 grm, of copper from a
cuprous solution is 96'54o coulombs, but double that quantity is
required to deposit the same weight of the divalent copper from a
cupric solution. Aluminium, which is trivalent, must have three
times the above quantity of current in order to deposit 27 grm.
of the metal. 96,540 coulombs of electricity will deposit 200
grm. of mercury from a solution of a mercurous salt, but it
requires twice that quantity of electricity to deposit »oo grm. of
mercury from a mercuric salt The same rule applies to the
substances liberated at the anode— the current which will liberate
1 grm. of hydrogen will liberate 8 grm. of oxygen, and so on.
It must be clearly understood that 96,540 coulombs of electricity
deposit \h.e gramequivaUrtlwelghtjan^ not the gram atomic weight.
For example, the gram atomic weight of oxygen is 16, but as
oxygen is divalent, the graiff equivalent weight is 8. On the
other hand, the gram atomic weight of silver is io7'93, but as
silver is monovalent, the gram equivalent weight is also io7'93.

CHAPTER II.
MEASUREMENT OF CURRENT.

There are instruments for measuring the intensity or rate of
flow of current in a circuit at any given time, and instruments to
measure the quantity of current which has passed. Apparatus for
measuring quantity of current will first be described. These
generally depend upon the amount of gas which is evolved when
an aqueous acid or alkaline solution is electrolysed for a given
time, or upon the quantity of metal which is deposited from a
given metallic solution. By Faraday's Law, we know that a given
current will deposit a given weight of copper in a given interval
of time, and that, during the same time, the same current will
liberate an equivalent quantity of oxygen and of hydrogen from
an acidified solution of water.

The apparatus employed for thus determining the quantity of
current which has passed in a given time is generally called a
voltameter. Seeing, however, that we have also instruments
called voltmeters for measuring electrical potential, and bearing
in mind that the instrument called a voltameter has absolutely
nothing to do with volts, but registers the number of coulombs of
electricity which have flowed through a circuit, entirely independent
of the potential, we propose to call the instrument a coulom-
meter. The term voltameter was originally employed to honour
Volta, but as his name is perpetuated in the volt, it will be doing
no dishonour to him to drop the term voltameter — which is often,
especially with beginners, confused with the voltmeter — and
substitute the more correct term coulommeter.

Measurement of Current.

The Coulom meter.

3as Coulommeter. —There are many forms of coulom-
T employed for measuring the quantity of electricily which has
sd through a circuit in a given time. One of the oldest aiid
known is the oxygen and hydrogen coulommeter, in which
r^ume of oxygen and hydrogen liberated in a given time is

sured. There art two forms of this instrument — the detouat-
gas apparatus, in whii,h the two gases are colkcttd together ;
tiie one in which thty are collected separate!) Fig. 3 shows
ttonating gas coulommeter. It consists of two cylindera of
it nickel, placud the one within the other, in a glass cylinder, the

14 Practical Electro-Chemistry.

distance between the sheets being about i cm. The glass cylinder I
is closed with a rubber stopper, through which passes a short tube
to lead off the liberated gas. A piece of stout nickel wire is
riveted on to each of the nickel sheets ; these wires are connected
to a terminal fastened on the outside of the rubber stopper. The
cylinder is nearly filled with a 15 per cent, solution of causlic

soda, which should be free from chlorides. There is also a t
funnel passing through the cork, which is used for filling in <f
tilled water, as it is decomposed by electrolysis. A piece i
stout rubber tube is fastened over the outlet tube, by 1
of which the issuing gas can be collected in a burette or
measuring vessel. When in use the two terminals are connected

Measurement of Current

with the opposite poles of the source of current. A current of
I ampere passed for 1 minute liberates 10-45 '^•'^- ^^ explosive
gas, measured at 0° and 760 mm. pressure. In Fig. 4 a similar
coulommeter for collecting the oxygen and hydrogen separately is
shown. In it the nickel anode is separated from the cathode
by means of a porous cell. The electrolyte, as in the previous
case, is 15 per cent, caustic soda.

As arranged in Figs. 3 and 4, the quantity of gas which can
be collected is limited by the size of the burette or measuring
cylinder-j and therefore the current can only be passed for a short
time. The following arrangement, Fig. 5, may be employed

r when it is desired to pass the current for some considerable
length of time. The tube conducting the gas from the electro-
lysing cell is connected to a tube, a, passing through a rubber
L stopper into a large bottle, e^. a Winchester quart. The rubber
\ stopper has a second hole, through which passes a tube, b, bent at
right angles, and to which is connected a piece of rubber tubing
which can be closed by means of a clip, c. This tube passes to
the bottom of the bottle and acts as a siphon. Before commencing
I experiment, the bottle is filled with water, the siphon being

vtstry,

also filled, but prevented from running by the clip c. The outaB
end of the siphon is placed in an empty cylinder,
the electrolysis is started the clip is opened, when some ■
will siphon over ; but if the apparatus be air-tight it will at (
cease running. This water should not be thrown away;
adjusting the levels of the water at the end of the experim

it will flow back to the gas reservoir. If, however, the wi
timies to flow, this will be due to the apparatus not being air-light;*
and this must be remedied before proceeding with the experiment.
The electrolysis is now started. From the construction of the
apparatus it follows that for every cubic centimeter of gas evolved

Measurement of Cnrremf. i?

1 c.c. of water will pass over into the cylinder. At the end of the
Operation the levels are adjusted, the clip closed, and the water
poured into a measuring vessel. The volume of the gas is then
reduced to normal temperature and pressure. In i hour 626'4 c.c.
of miaed hydrogen and oxyi^en is evolved at N.'l'.l'., when a
current of i ampere passes through the coulommcter, or aoS'S c.c.
of oxygen and 41 7'6 c.c. of hydrogen. By employing two siphons
the oxygen and hydrogen can be collected separately, the coulom-
meter shown in Fig. 4 being then employed.

Coulomnieters with platinum electrodes containing as electro-
lyte sulphuric or phosphoric acid are sometimes used. Generally
speaking, they have a higher resistance, and the quantity of gas
given off is slightly less than should theoretically be obtained,
owing to the fact that part of the oxygen is given off as oitone.
Neumann's explosion gas coulommcter is shown in Fig, 6.

^Veight Coulommeter.— For very exact measurements the
Silver coulommcter is generally employed, because there are very
few possibilities of complication occurring in the deposition of
silver from its solutions. But this coulommcter can only be
employed when extremely small currents arc being used, because
the silver has a tendency to be deposited in a feathery and non-
adherent form. Even with low Ijij

crystalline deposit from slightly
acid or neutral solutions of silver
nitrate, such solutions being

generally employed in the silver —

coulommcter. The usual form

of apparatus employed is shown J|_^_^

1 \

mw^

in Fig, 7- It consists of a p^^ — =^::::^

^ 1

weighed platinum or silver basin i'"^- ?■ ■
which serves as cathode and is partially filled with a 7 per cent. 1
solution of silver nitrate. The anode of stout silver rod hangs in 1
the upper portion of the solution, and is wrapped in a piece of thin H
calico to prevent the silver — which always becomes more or less ^|

Practical Electro-Chemistry.

disintegrated— from falling into the platinum basin. The calico
should be carefully washed in hot water and then rinsed out in
distilled water before being used. If it is desired to use a silver
coulommeter when high currents are being employed, the coulom-
meter must be used on a shunt circuit (p. 24), through which only,
say, 1 00th or 1 000th of the current is allowed to pass. Or else it
should only be kept in the circuit for a very short time, otherwise
the amount of silver dissolved from the anode is considerable.

Copper Coulommeter. — For general work the copper
coulommeter is the most satisfactory. It is not quite so accurate

-^CT^Or

Fig. 8.

as the silver instrument, but is generally quite exact enough for ordi-
nary work, where it is not, as a rule, necessary to know to more than

aljout o'25 of an ampere hour how much current has passed. Say,
for example, that an operation required the passagt; of 20 ampere
hours, a quarter of an ampere one way or the other would not be
of any material importance. Fig, 8 shows a copper coulumraeter.
The cathode hangs in the centre of two anodes, so that an even
current density is obtained on either side ; in the diagram only
one electrode is seen. For preparation of solution see p. 282.
In order to obtain a good deposit, and one which adheres firmly,
it is not admissible to allow more than I'as amperes per square
decimeter to pass through the apparatus. Where fairly high
currents are being employed, a coulommeter of several cells may

f, i'^ff--M

be employed. Fig. 9 shows one consisting of three cells, the
anodes and cathodes being connected up in parallel (p. 49) ;
by this means three times the anode and cathode surface caji
be obtained, and therefore three times the current strength be
employed as with a single cell of similar she. If a rapid current

Practical EUctro-Chemistry.

of air or carbonic acid gas is passed through the coulom meter,
or if the cathode is cylindrical and is rotated, then a very much
higher current density can be employed per unit of surface.

The coulommeter, although often indispensable, is at best a
tiresome instrument to use, because it is necessary to dry and
weigh the cathode plates. This is especially unpleasant when
a more or less irregular current is passing, because, in order to
know exactly the quantity of current which has passed, it is
constantly necessary to stop the current, take out the coulom-
meter cathodes, dry and weigh ttiem. In order to avoid this
difficulty, the Reason Manufacturing
Company of Brighton ' manufacture
a mercury coulommeter (Wright's
electrolytic metre) in which the
mercury, as it is deposited on the
cathode, falls into a graduated glass
lube. Each gradation in most of
the instruments made (the coulom-
nieiers are generally made for electric
light purposes) represents i Board
of 'Irade unit {p. 29), but they can
also be made to read in ampere
hours. It is not possible to pass a
heavy current through a solution of
a mercury salt (in this apparatus
mercurous nitrate) without the sur-
face of the mercury becoming coated
with crystals of mercurous salt.
' ■ '"' Therefore these instruments are fitted

with a shunt, so that only a definite fraction of the current passes
through the mercury solution.

Fig. 10 illustrates the construction and working of the meter.
The current enters at the terminal d, and the greater part
of it passes round the low resistance r to the terminal e. The
shunt current, which works the coulommeter, and which is always
1 Piix. lint. ELi

901,31.

'53-

Measurement of Current. 21

an exact fraction of the total current, passes from d througli the
fine wire resistance p to the mercury anode a.
Thence it goes through the electrolyte to the cathode (j \f

C, and finally to the terminal e. The relations of /__\*
p and B are calculated in the first instance, but ' \x^)^^
the exact final adjustment is made hy sliding the
two wires l and m up or down in two holes drilled
in E and d, thus varying the value of r.

When 3» current is passing through the meter,
metallic mercury is deposited on the cathode,
whence it falls in minute globules into the first
graduated tube c, which reads (Fig. 11) direct in
units. This is made in the form of a siphon, so
that when it is filled by a quantity of mercury equal
to 100 units, it automatically empties itself into the
lower tube, which is provided with a scale, s, each ^'°' "'
division of which is equal to 100 units. The mercury as it is
dissolved from the anode is simultaneously replaced by fresh

metal drawn from the anode feeder f. This

ingenious arrangement acts in the same manner
as the well-known " bird-fountain " in keeping
the level of the mercury constant.

After the number of units for which the
coulommeter was designed have been regis-
tered, the meter must be reset to zero. This
is done by the simple operation of tilting the
whole tube about the hinged supporting
brackets, so that all the mercury is returned
to the anode feeder.

rig. 12 shows a complete coulommeter
designed to read up to 250 Board of Trade
units ; this has not the lower scale depicted
in Fig. II. For electro-chemical purposes it
is more convenient to have the instrument
graduated to read in ampere hours; and,
for convenience of moving about, it may be fixed on to a stand.

CHAPTER III.

INSTRUMENTS FOR MEASURING INTENSITY AND

POTENTIAL OF CURRENT.

Am meters.

When a current passes through a wire spiral, a magnetic field
is produced, which has the power of attracting a bar of soft iron.
Measuring instruments called ammeters are made, based upon
this property. (A spiral of wire through which the current passes
is called a solenoid.) It is not within the scope of this book
to describe the mechanism of the ammeter ; suffice it to say, the
ammeter is an instrument which depends upon the property erf" a
spiral of wire to become magnetic when the electric current flows
through it. The intensity of the magnetic field is proportional
to the amount of current which passes.

Ammeters are arbitrarily graduated, the best instruments bebg
extremely accurate. Fig. 13 illustrates an ammeter made by
Messrs. Nalder Brothers & Thompson of London, reading from
o to 50 amperes. These instruments can also be obtained
having a range of 2 amperes, graduated in hundredths of an
ampere ; and by means of a shunt, the range can be made
to extend from o to 20 amperes in tenths. For analytical
purposes it is very rarely that currents above 2 amperes are
required, therefore the lower range of readings can be employed
for this purpose, so that instruments made on this shunt system
are especially useful for reading very low currents. Such an
ammeter must be connected with a two-way switch, the higher
or lower reading being obtained by simply changing the direction
of the switch.

Instruments for measuring Intensity of Cvrrent. 23

The Weston instruments arc also extremely good, and are
very largely used. The r.ase uf the MaldiT inslnimint is of brass ;

the Weston ammeter has usually at
against outside magnetic influences

iron case, which guards it
Nalder instnimcnts can,

however, be obtained with iron cases. Fig. 14 shows a Weston

standard portable mil

hammettr, nhich is of

extreme accurary and

IS often employed for

calibrating other lustru

menti. In many m

struments, such as the

Weston -ind Nilder am

meters, the whole of

the mam current dot

not pass through the

instrument, hut each

instrument is provided with a resistance called a shunt ; in other

words, the ammeter is placed in a shunt circuit (p. 24). The

amount of current which passes through the instniment thus

Practical Elgctro-Clumistry.

depends upon the difference of potential lietnecn the two ends
of the shunt. When the instruments are for taking small cuirenls,
the shunt is generally fitted inside the case of ihe ammeter, but
on large station ammeters the shunt is fixed outside the instrument.

INSTRUMENTS FOR MEASURING POTENTIAL.

Voltmeters.

An ammeter is .in instrument of very low internal resistance;
it can therefore he placed in the main circuit, its resistance being
so low that it may, for most purposes, be neglected, A voltmeter
is practically an ammeter, the coil of M'hich is wound with a large
number of turns of very thin wire, and has therefore a very high
resistance of several hundreds or thousands of ohms. A volt-
meter is therefore always used on a shunt circuit ; since, if it were
placed in the main circuit, it would oppose so much resistance
to the passage of the current, that practically no current would
pass, and the instrument would probably be burnt out.

Shunt Circuit. — If part of a circuit branches, as shown in
Fig. ij, the current has a choice of two paths, a and b. When
» ...A the two wires are of equal resist-

ance, then \ of the current flows
along each wire. But suppose
the resistance of a to be i

and that of b to be lo ohms., then only ^ of the current -will
along I!, the remaining ^ passing through a.

Now, a voltmeter is of such high resistance that the amount
of current which passes through it is inappre-
ciable; in fact, the higher the resistance of
the instrument the better, otherwise an appre-
ciable quantity of the current would take this
path. Fig, r6 shows the method in which a
voltmeter is connected up. The bulk of the
along the main conductors, and only a minute
t passes through the Bhunt circuit. If th(

ir\

current passes ;
fraction of the c

Instruments for measuring Potential.

.total resistance of the main
of the voltmeter looo ohms,
then j^ of the current will
pass through the shunt cir-
cuit.

'* An ammeter is often

' kept in the circuit during
the whole time the current

■ is passing ; it is not so usual
to keep the voltmeter in cir-
cuit, because there is a ten-

I dency for the instrument to

I heat, and tiiis, of course,
affects its accuracy. Fig, 17
shows a voltmeter; the in-

^ strument has a double read-
ing, on the low side reading from

j the high reading from o

to 3
iiU volts.

Employment of Voltmeter to Measure
Current.

I Voltmeters can be used to measure current intensity as well
jtue to measure electrical potential. According to Ohm's Law
f jp, 71), if we know the resistance R and the potential E of a
I arcuit, we can calculate the current flowing through it by the
I equation —

.All that it is necessary to do is to shunt into the main circuit
Jl known resistance. If, for example, a resistance of -^ ohm is
jAiunted into the circuit, then every volt registered on the instru-
ttnent represents a reading of 10 amperes, and a reading of ^ of a
Tolt represents i ampere.

26 Practical Electro-Chemistry.

With a resistance of yJo ^^ ^" ohm, a reading of i volt represents
loo amperes. Whereas if the resistance employed is i ohm,
every volt represents i ampere. The employment of a voltmeter
for reading current in this way is often very useful in measuring
heavy currents. The arrangement of the circuit is represented in
Fig. 18. v is the voltmeter, which is connected on either side of

* » >

<v>

■mmMm-

-««

Fig. 18.

the known resistance. Of course, in this method a resistance is
placed in the main circuit, but as only very low resistances are
employed, this is a matter of very little importance. This method
is simply the principle adopted in the Weston and other ammeters,
only in these instruments the resistance is usually enclosed in the
case of the instrument.

CHAPTER IV.

ENERG v.

So far we have dealt only with the measurements of quantity
of electricity, and of electrical potential separately, But the
energy given out by a dynamo or battery, or used up in an
-electrolytic process, is not shown by merely reading the current
on an ammeter, or the volts registered on a voltmeter^ electrical
energy is the product of the current and potential.

An ampere may be defined as t}u rate of flow of eketrieity through
any cross section of a condneter when then is a difference of potential
in the circuit of i volt, and the resistance is i ohm. Or, more
generally, an ampere is the rate of flow of electricity through a con-
ductor when the ratio betweeti the potential and the resistance is one.

A coulomb, as has been already st-ited (p. 7), is the quantity
of electricity which passes through a circuit in i second, when the
current intensity is r ampere. The" unit of electrical energy taken
is therefore the volt-coulomb.

There is a tendency, on the part of beginners, to look upon
the ampere as being a quantity of electricity : this is a mistake j
the coulomb is a quantity, and is the amount of electricity which
passes through a circuit in 1 second, when the current intensity or
rate of the flow of the current is i ampere. An ampere is no
more a quantity than rate of flow of water is a quantity. We may
say that if water continue to flow through a pipe of certain cross
section at the speed of r metre per second in a given time, 10
Htres (which is a quantity) of water will have passed a certain
point If the pressure, which governs the rate of flow of the
water, is increased, as registered on a pressure gauge, then the

a given time may also
but increasing the

Practical EUetrO'Ckemistry.

rate of flow of the water will be increased, and iherefore a
volume will pass in a given time. In a similar manner,
voltage of a current is increased, the current will flow
rapidly, and therefore the ammeter measuring rate of flow
show a higher reading. The voltmeter may therefore be compared
to a pressure gauge, and the ammeter to an instrument for n
ing speed of flow of a liquid.

The quantity of water which will flow
be increased by keeping the pressure
cross section of the pipe through which it is flowing, i.e. decreas-
ing the resistance. In a similar way we can increase the flow
of electricity through a circuit by decreasing the resistance, the
voltage remaining constant.

It has been found experimentally, by careful measurement in
a calorimeter, that, when a coulomb of electricity passes through
a circuit in which the drop in potential is i volt, 0*2394 calorie is
generated.' This number we may call the electrical eqniva-
lent of heat, and it follows that 4"i75 volt-coulombs will generate
1 cal. It has also been proved experimentally, that when i grra.
falls through a space of 42,350 centimeters, it may be made by
friction to generate the calorie of heat, i.e. to generate enough heat
to raise i grm. of water from 0° to 1° C. This iiumber is called
the mechanical equivalent of heat. From the above numbers
we find that i volt-coulomb expressed in terms of the mechanical
equivalent of heat = 10144 grm. cm, (gravitation units).

In referring to work done, or to the energy capacity of a
dynamo or other electrical machine, the electrical
is the volt-ampere-second ; this unit is called the watt. This
equivalent to saying that i coulomb passes in 1 second at'
pressure of 1 volt. The watt itself is not often employed, becai
it is such an extremely small quantity of electricity. The
watt, which is rooo watts, is the unit most generally ado]
From the kilowatt the horse-power can be calculated. In Englist

' In round numbers, this maj be taken as 0*24 cal. In other words, when
0'2394 calorie is converted into electrical energy r coulomb of electricily is
generaletl.

Energy. 29

weights a horse-power is defined as thi; amount of work necessary
to raise 33,000 lbs. through the space of i foot in i niinutc.
Expressed in mttric units, a horbe-power is the amount of work
expended in raising 75 kilograms through the space of i meter in
1 second. Now, a watt is equal to second-kilogrammeters,

therefore 1 kilowatt is one thousand times this, or —
1000 X -70" = ioi'93 kilogram meters

But as 1 horse-power is 75 kilograiiiLiieters, it follows that 1
kilowatt is equal to I'jO horse-power.

' ""• ' '^T ' ''2* "■'"■

Board of Trade Unit. — The electrical unit for power and

lighting purposes used in this country is called the Board of Trade
itnit, and is the kilowatt hour, which is equal to 1000 volt-ampere
hours. Thus if a current of 10 amperes be maintained at a
potential difference of 50 volts, in a circuit for a hours, then i
kilowatt of energy will have been used up.

Calculation of Decomposition Voltage from
Thermo'^chemical Data.

When two elements combine together, the energy involved
in the change makes itself evident in the form of heat. Now,
according to the law of the conservation of energy, if a given
amount of energy is required to bring about a chemical change,
the chemical reaction can only be reversed by application of the
same amount of energy again. In order to bring about a reversal
of the change, it is not, however, necessary for the energy to be-
applied in the same form as that originally used. Thus, for
example, most chemical changes take place through the addition
or absorption of heat; these changes can be reversed by the
application of an equivalent addition of electrical energy. If,
therefore, we know the heat of combination of a substance, it

30 Practical Electro-Clietnistry.

is easy to calculate the voltage which is necessary to decompose
or electrolyse the substance. For example, the heat of combina-
tion of sodium and chlorine is 97,300 calories. On p. 28 we
found that one volt-coulomb of electricity generates 0*24 calorie,
therefore the number of volt-coulombs which corresponds to
97,300 calories is —

97,300

-.—- = 405,417 volt-coulombs
o 24

Now, according to " Faraday's Law " (p. 7), 96,540 coulombs
of electricity, i,e, one faraday, is necessary to decompose the gram-
molecule of a substance. If, therefore, we divide this into the
number just obtained, we obtain the decomposition voltage of
sodium chloride as —

96,540 ^
Or take the case of i)otassium bromide —

K + Br = KBr + 95,300 cals.

From this we obtain the number of volt-coulombs corresponding
to the calories, as —

05,300 „ , , ,

= 397»oo3 volt-coulombs

and the decomposition voltage as —

397,083 ,

,— - = 3 193 volts
96,540 ^ ^^

As a further example, zinc chloride may be taken; the thermo-
chemical equation is —

Zn + 2CI = ZnCla + 97,200 cals
The volt-coulombs requisite are, therefore —

97,200

— : = 4o5iOoo volt-coulombs

o 24 ^ ^'

and the decomposition voltage —

405,000

_ 4«oog volts

96,540 ^ ^^

• _

Energy. 31

The deconnxjsilion voltages Jiere given must be employed iii order
to decompose the several substances. But it nill generally be
found necessary in actual practice to employ slightly higher
voltages, owing to the resistance of the bath, the distance of the
electrodes apart, and other mechanical causes which invariably
arise.

The electrolysis of aqueous solutions is slightly different. Here
we are dealing with substances which are ionised, and these ions
cany the current; the mere fact of the passage of the current,
therefore, takes place without expenditure of enei^y. Work is
only done at the electrode when the electrical charge is neu-
tralised, and the work done is in neutralising the polarisation
current, which exerts an electro-motive force in the reverse
direction to the primary current which is being passed. Le
Blanc' found that with platinum electrodes the electromotive
force of polarisation is independent of the nature of the electro-
lyte, when the substance which separates at the electrode is the
same. Thus the values for E with all oxygen acids and bases
is the same, viz. about i'70 volts.

Certain differences, however, are noticed with acids in Which
the products of electrolysis are not the same. For example, with
the halogen acids the tensions obtained for normal solutions are —

The reason that these acids show a lower value for E is traceable
to the simultaneous separation of hydrogen and oxygen at the
electrodes, along with the halogen. As the dilution of hydrochloric
acid increases, more and more oxygen is liberated in comparison
with the halogen, and consequently the polarisation tension, i.e. the

value of E, rises, so that at — solution the value for E is I'fig.

Appended is a table of some of the best-known acids and
bases with the values for E, which have been experimentally
found.

■ Z^. Pkys. Cliem., iBgc, B. p, 299 ; iSga, 13. p. 333.

Sulphuiic add [Bj

Nitric ncid 1-69

HydtochloHC acid 1 -fig

Phosphoric acid 1*70

Munochloioncetic add 1*72

Dichlotoacelic ncid r66

Malonic add i'69

Perdilor

Sodiuni hydiale 1-69

Potassium hydrate 1*67

Ammtiniani hydnLe 1-74

Mcthylamino? 175

Diethylamine - r68

The decomposition values of the salts of various metals are
different foe each metal. But the values for sulphates and nitrates
of the same metal are very nearly equal. The decomposition
values for the salts of the strongly ionised acids have nearly the
same value — viz. about a'zo volts.

TABLK

III.

Sodium nitrate .
Polassjiun niltaie .

With

Calcium niltaie

Barium nitrate

Sodium sulphate

Potassium sulphate

the halogen acids the numbers are

slightly

lower

TAULE

IV.

Sodium chloride .
Potassium chloride
Lithium chloride .
Calcium chloride
Strontium chloride
Sodium bromide .
Potassium bromide
Sodium iodide
Potassium iodide .

■ ■

; \

Energy. 33

The next table shows the decomposition voltage of a few
substances in which the metal is deposited at the cathode.

TABLE V.

Volts.
Zinc sulphate 2*35

Zinc bromide i 'So

Nickel sulphate 2*09

Nickel chloride 1*85

Lead nitrate 1*52

Silver nitrate 0*70

Cadmium sulphate 2*03

Cadmium nitrate 1*98

Cadmium chloride i'88

Cobalt sulphate i '92

Cobalt chloride 178

It will be noticed that salts of the same metal with different
acids give slightly different decomposition voltages. This fact
may be made use of in separating the metals from each other by
gradation of potential, although its application is very limited.
For further information on the subject the student should study
the original literature or text-books upon the physical side of
electro-chemistry. For example, that of Le Blanc, Arrhenius,
Lehfeldt, H. Jones, or the works of Ostwald.

CHAPTER V.

SOURCES OF CURRENT.

Thp:re are practically only two sources from which current is
obtained for electro-chemical work, the dynamo and secondaiy
batteries or accumulators. The use of primary cells, except in
cases where only a small and intermittent current is required, has
been almost discontinued, partly because of the trouble required
to charge and recharge them, and also because of their incon-
stancy. Considering the inconvenience of primary cells, one is
really astonished at the amount of important pioneering work in
connection with electro-chemistry which Davy, Bunsen, and otheis
carried out with their aid. As, however, a knowledge of the
theory of the primary battery is of great use in understanding the
mechanism of the secondary battery, and because for certain pur-
poses they are still of great practical importance, a. few of the
principal cells will be described here.

Introduction.

If a piece of zinc is placed into a solution of copper sulphate,
the zinc gradually goes into solution as zinc sulphate, and copper
is deposited out. We have here a chemical change taking place,
and the progress of the change is accompanied by the evolution
of heat.

Now, suppose that a rod of zinc is placed in a porous cell filled
with zinc sulphate solution, and this porous cell is put into a
beaker containing a solution of copper sulphate in which is also
placed a rod of copper. It is obvious that neither the zinc nor

Sources of Current. 35

the copper will pass into solution. But connect the iinc to the
copper by means of a piece of wire, and it is found that the zmc
commences to dissolve, and that for every equivalent of i:inc
which passes into solution an equivalent of copper is plated out
upon the copper rod. But this is not all ; if now a galvanometer
is brought near to the wire which connects tbf zinc to the copper,
the needle of the galvanometer becomes deflected — showing that
there is an electric current flowing through the wire.

Here we have chemical energy being transformed into
electrical energy, In the first example, in which zinc was placed
into a solution of copper sulphate, the chemical energy made itself
manifest in the form of heat. In the second case the chemical
enei^ is transformed into electrical energy.

Now, because the zinc passes into solution and the copper
becomes deposited out, we say that the current passes in the outer
circuit, i. e, through the connecting wire, from the copper to the zinc,
and through the solution from the zinc to the copper. The zinc is
therefore called tlie negative pole and the copper the poBitive
pole, but the /.inc is said to be electro-positive to the copper. The
plate which goes into solution and is electro-positive to the other
metal forms the negative pole in the external circuit. Thus one
often refers to the zinc or negative pole, because the zinc is
electro-positive to the other metals.

Positive and Negative, Relative Terms,

It must, however, be distinctly understood that the terms
positive and negative are purely relative. By changing the con-
ditions we can cause the metal which before was negative to
become positive. A very good example of this is found in a
cell in which the opposite plates are copper and aluminium, both
metals being in the same electrolyte,

I, In the first place, caustic soda is employed as the electro-
lyte, the aluminium will go into solution, but the copper will
■ not : the aluminium is therefore electro-positive to the copper,
and the current passes in the external circuit from the copper

mutry.

to ihc aluminium, in ihe solution from the alaminium to the
copper.

2. Secondly, use nitric add as the electrolyte j the copper
will now go into solution, but the nitric add has practically no
action upon the aluminium, therefore now the aluminium is electro-
negative 10 the copper, and the current passes in the external
circuit from the aluminium to the copper, and through the
electrolyte from the copper to the aluminium.

3. Finally, an example might be given of a cell in which ihe
poles are of the same metal, yet one is negative and the other
positive. Such a cell can be made with two aluminium plates,
separated from each other by means of a porous diaphrj^n. The
one plate immersed in strong nitric acid, and the other in a
solution of caustic potash. Under these conditions, the aluminium
plate in contact with the causlic potash will pass into solution,
but that immersed in the nitric acid will be unacted upon. We
therefore have the aluminium plate, which is standing in caustic
potash, electro-positive to the plate surrounded with the nitric acid,
Consequently the current passes in the outer circuit from the
aluminium immersed in nitric acid to the rod standing in ihe
caustic soda.

From these examples it is obvious that the terms negative and
positive are relative, and that when we say one metal is electro-
negative to another, it must be remembered that under certain
conditions the order of sign may be reversed. In fact, it is simply
a question of chemical action taking place. If we have two
metals, A and B, and a given solution, the question whether A is
electro-negative or electro-positive will depend whether A or B is
acted upon by the solution. If, for example, A is dissolved by
the solution, but B is unacted upon by it, then A will be electro-
positive to be B, and vice versa. Platinum and carbon are electro-
negative to other metals because they are not acted upon by
solvents.

In the following table the metals are arranged in their order
of sign when placed in various solutions, the most electro-positive
being placed at the head of the column. It will be noticed

Sources of Current.

in all the solutions zinc is electro -positive lo all l!ie other metals;
from this it follows that zinc will replace all other melals, itsi:lf
going into solution and the other metals bemg prccipilated out.
The other metals, however, arc not always in the same order.
Lead, for example, would replace tin from nitric acid solutions,
but from solutions ui sulphuric acid tin would replace lead. In a
solution acidified with sulphuric acid, nickel would replace copper,
but from alkaline solutions copper would replace nickel.

TAliLE VI.

MJutemliic

uid.

diknideMluliOD.

Sodium Ghhuidt

PoUBiuni

-fZinc

+Zirc

+Zinc

Lead

Tin

AntimoQT

Lead

Nickel

liismulh

Antimony

Binnulh

Bismaih

Nickel

Antimonj'

Copper

\tcrcnry

— Platintitn

Potential and Polarisation.

The electro- motive force (E.M.F.) or potential of a cell is
dependent upon the heat of solution of the electro-positive metal
in the solvent which forms the electrolyte. Theoretically, there-
fore, the potential of the cell should remain consL-int until the
whole of the metal has gone into solution.

Practically, for several reasons, this is not the case. In the
first place, the concentration of the electrolyte is continually
varying. As the metal passes into solution, tiie strengtli of the
electrolyte decreases ; therefore solution of the metal is retarded,
and, as a consequence, the number of calories given out in a
given time is less, and the KM.F. therefore falls— the cell becomes
polarised. In the second place, in a great many cells gas is given

3* Practical Electro-Ckemistry.

off at the poles vhen ihcy arc in use, and this gas produces gaseouB-
polarisation. An example will serve to make this clearer.

When a plate of zinc and a plate of copper are immersed
together in a beaker of dilute sulphuric acid, and are con-
nected together by means of a piece of copper wire, an electric
current passes through the wire from the copper to the ?.inc. But
after a short time it is found that the current becomes weaker and
weaker, and finally may be hardly perceptible. This weakening
of the current is due to polarisation. In order that a complete
cycle may be made by the current, it must not only pass along
the wire from the copper to the zinc, but must also pass through
the solution from the zinc to the copper. Now, when the electric
current passes through the electrolyte, decomposition of the water
takes place, and oxygen and hydrogen are liberated. In the
under consideration, the oxygen being liberated at the surface of
the zine, oxidises it to zinc oxide, but this immediately dissolves
the dilute sulphuric acid wiih formation of zinc sulphate, therefore
the surface of the zinc always has a clean metallic appearance.
At the same time the hydrogen is yielded up on the surface of the
copper ; this element, however, is unable to form a compound with
the copper, but produces a thin coating of gas upon the surface of
the metal. The dilute sulphuric acid is now no longer able to come
in direct contact with the copper, and a resistance is thus opposed
to the passage of the current ; furthermore, we may suppose that
there is a tendency for the hydrogen, as it is liberated, to reduce
the zinc sulphate with reformation of zinc and sulphuric add.

ZnSO.Aq + 2H = Zn + H^O.Aq - Z485K'
This reaction is contrary to the primary reaction which is the
solution of the zinc in the sulphuric acid. In other words,
the electric current is proportional to the heat produced by the
exothermic reaction —

Zn + H,SOjAq = ZnSO.Aq + zH + 2485K

syinbol \\. tuptesenls OstHiild's caloric, which is one hundred
limes greater tlian ttic small calorie (cal.), and ten limes less than the krge
;*LJ. We have IhuB—

I limes greater

that is, the heat of solution of ihe zinc in sulphuric add, bul by
the reduction of the zinc sulphatt: to nine and sulphuric acid we
have an endothermic reaction ; therefore the one will neutralise
the other.

The polarisation effects are said to produce a back electro-
motive force. The back E.M.F,, acting in a reverse direction to
the primary E.M.F., neutralises part of ihe primary potential, and
thus the voltage of the cell falls. If, for example, the potential of
a cell when it is first made up is fj volts, and after a short time,
owing to polarisation, a back E.M.F of i volt is set up, then the
potential of the cell falls to o'3 volt, and the current, of course,
falls at the same time.

In al! primary cells which are in any way satisfactory, depo-
larisers are used to prevent, or, at any rate, retard, polarisation.
Either an oxidising agent is used as a depolariser, its function
being to oxidise the hydrogen with formation of water; or the
positive pole may be placed in a solution from which there is
plated out the metal of which the positive pole consists ; in this
case there is no formation of gas, and the depolariser may be said
to be metallic

Even although depolarisers are employed to keep the cells as
constant as possible, no primary cell can be termed constant;
therefore they cannot be used as standards of potential.

Standard Cell.

The cell which is generally used for a standard was devised by
Latimer Clark in 1872.' It consists of an amalgam of pure zinc
and pure mercury, covered with mercurous sulphate and a saturated
solution of zinc sulphate.

- (Zn - ZnSO, - Hg.SO, - Hg) +

The form of cell devised by Lord Rayleigh- is shown in

= Phil. Trans. Roy. Soc.

Practical Electro-CkemUtry.

Fig. 19 i this cell, known as I,urd Rayluigh's H form,
as follows ; —

One of the legs is filled lo about onc-fiflh of its height with
■ an amalgam of zinc, a, formed by [(lacing pure zinc into pure
mercury which has previously been distilled in vacuum ; the odier
leg with pure mercury, b, and is covered with a layer of mercurous
sulphate, c ; the whole is then fiUed up above the level of the

■L-.^ <r- Zinc Mil
*j - lino BHialga

cross tube with a pure saturated solution of zinc sulphate. Do,
crystals of zinc sulphate being added to ensure the solution always
being saturated. The two tubes are then closed by paraffined
corks in order to prevent evaporation. Electrical contact is made
by means of the two platinum wires fused through the two leg
the H tube.

Fig. 20 shows the Board of Trade form of Clark's cell.

The chemical unergy of the Clark cell is represented by
following equation.

Zn + •A%^Q,—J±Zv&0, + aHg.

When read from left to right, the equation represents the
discharge of the cell ; when read in the opposite direction the
charging of the cell.

s of

The E.M.F. of the Clark c

'5"

IS 1-4328 volt.

The constancy of the Clark element is due to having alwayaj

Sources of Cnrrent. 41

saturated solution of the electrolyte present; there is no possi-
bilily of gassing, because the electro-positive metal goes into
solution, and the electro-negative metal is deposited out.

There is, however, one source of inconstancy in the Clark cell,
and that is the variation of potential produced by changes in
temperature. Thus —

At rs" the E.M.F. is 1-4328 volt.

T. 20' „ „ „ i'4367 „

„ 30° « .. » i"4i34 n

The temperature co-efEcient for each degree above 15° is o'ooii

volt.

Weston Cadmium Cell.

The Weston cell in which we have

- {Cd - CdSO. - Hg.SO, - Hk) +
is made on the same system as the Clark cell, but it !ias one great
advantage over it in having an estrcmely low temperature coefficient.
Fig. 21 shows the cell diagram mat ically, as described by Dr.
Henderson, without the need of further explanation.

The formula representing the chemical energy of the Weston
' cell is shown in the following equation : —

Cd -f- Hg,S0j^^CdSO. -I- 2Hg

The E.M.F. of the Weston cell is 1-019 volts, and this is practically

I the same for all temperatures. The Weston cell is now largely

superseding the Clark cell as a standard for measuring potential.

Practical Electro-Chemistry.

It must be remembered that neither the Clark nor the Weston
cell can be employed for obtaining current, the amount of current
generated being infinitesimal.

PRIMARY CELLS,

The Daniell Cell.

One of the most simple and at the same time efficient of
primary batteries is the Daniell celL Fig. 22 shows the cell
diagrammatically in its simplest form. It consists of an amalga-
mated zinc rod in dilute sulphuric acid or a solution of zinc sulphate,

and a copper rod in a saturated
solution of copper sulphate. The
two solutions are separated from
each other by means of a porous
partition.

The zinc rod is the n^ative
pole, and the copper rod the posi-
tive pole. On connecting the two
poles together by means of a piece
of wire a current flows through
the wire from the copper to the
zinc plate, and through the solu-
tion from the zinc to the copper
plate. When the current passes,
owing to the zinc having a greater
tendency than the copper to pass
into solution and form a compound with the electrolyte, the zinc
dissolves and the copper becomes plated out from the copper
sulphate solution upon the copper rod or plate. The action
may be represented by the following equation : —

Zn + 2H- S0"4 = Zn'- S0"4 + 2H'

The hydrogen is not liberated as gas, but while in the ionic state
passes with the current to the copper sulphate solution, where it

V///M//////A

Fig. 22.

Sources of Cur ret I.

interchanges with ihe Cu of Uii; CuSOj wiih
sulphuric acid and deposition of non-ionised coppei.

2H- + Cu- S0,"= aH' SO". + Cu

It is obvious that after the current has passed for sonie time
all the copper will become plated out, when of course the cell will
cease to work. In order to avoid this, in the modern forms of
the cell, provision is made for keeping the concentration of the
copper sulphate constant. Fig. 33 shows in section the form of
■ cell now generally employed. It
consists of a cylindrical copper
vessel, A, which acts as the -f-
pole ; this is filled with the soli
of copper sulphate, and has stand-
ing in it a porous earthenware
cylinder, b, which contains the
dilute sulphuric acid and the zinc
rod. Running round the top of
the inside of the copper vessel
there is a perforated tray of
copper; this ts kept filled with
crystallised copper sulphate, which
goes into solution as the copper is
deposited from the coppej sul- f,g, 33.

jdiate.

In this cell we really have the non-ionised zinc exchanging
with the ionised CuSOj. That is, the zinc takes on an electric
charge, and the copper becomes electrically neutral. The chemical
action thus resolves itself into an exchange of ions, and the
equation might therefore be written —

Zn + CuSO, = ZnSO, -i- Cu.

The depolariser in the Danicll cell is a metallic one. In
the first place, the zinc cannot polarise, because it goes into solution.
There is no polarisation at the copper, because the hydrogen never
assumes the non-ionised state, but simply changes place with the

f 44 Practical Ekctro-Chemistry.

' coi'per of the cupper sulphate, which becomes plated upon ihe
copper of the -f- pole.

'I'he E.M.F, of the Daiiiell cell varies from I'ljS volts, wheD
I part by volume of sulphuric aeid lo 12 parts by volume of water
is employed, to Vq-j when a concentrated solution of zinc sulphate
is used.

Bunsen Cell.

The Bunsen cell, as shown in Fig, 24, consists of a glass vessel
nearly filled with dilute sulphuric acid (i vol. acid, 2 vols, water),
and containing a zinc plate, a, which
is amalgamated mth mercury to
minimise the local action of the sul-
phuric acid. The zinc piate is beni
in the form of a cylinder, and sur-
rounds a porous cell containing
concentrated nitric acid ; the porous
cell c contains the positive pole e,
which is made of gas carbon or of
graphite.

Ill preparing this cell, the carbon
should be heated, and should then
have about an inch of one end
"^' "" dipped in melted paraffin ; because

if this is not done, after being used for some time, the nitric
acid gradually creeps up the carbon and corrodes the brass
binding-screws. The zinc should be well amalgamated by rubbing
it with dilute sulphuric acid and mercury ; this can be done by
means of a stick with a piece of cloth tied on the end. Finally,
the porous cell should be soaked for about twenty minutes nfj
dilute sulphuric acid before being used.

In this battery tlie depolariser is the nitric acid which

the hydrogen. Hence, the longer the cell remains in operatii

the weaker the nitric acid becomes, from the reducing actii

of the hydrogen. Therefore its efficiency becomes less, and

Lithe battery has been in use for some time, the current becomt

Sources of Current.

mucli weaker. The fuming of the nitric acid owing to the
formation of nitrogen peroxide is another great objection to this
form of the Bunsen cell. The following equations represent tlie
reactions which take place.

Zn + H^O^ = ZnSO. + zH

2H + aHNO, = jNOo + aH,0
2H + HNO' = HNO, + H.O

The E.M.F. of the Bunsen cell, when
s from 1-8 to r86 volts.

1 good working order

Chromic Acid Cell.

The phromic acid cell is really a modification of the Bunsen cell ;
it contains a solution of sulphuric acid with sodium or potassium
dlchromate as depolariser. The negative pole is of amalgamated
zinc, and the positive pole of retort carbon. The solution emjiloyed
is the same for both poles, therefore there is no necessity for
separating them by means of a porous cell, consequently the
internal resistance of the cell is less
than that of the one just described.
The solution employed may consist of
aoo grm. sodium dichromate dissolved
in I litre of water, to which is then
added 150 ex. of concentrated sulphuric
acid. Or, if potassium dichromate is
employed, dissolve 105 grms, in i litre
of water and add 1 10 c.c. of concentrated
sulphuric acid.

The most convenient form of this
battery is illustrated in Fig. 25. It con-
sists of a thick glass flask containing the
solution ; two carbon plates which serve
as the positive pole dip into the solu- ' '''°*'5-

tion ; the negative pole, consisting of an amalgamated zinc plate,
is placed between the carbons. When not in use, the zinc plate

Practical El&:trO' Chemistry.

can be drawn up, and this prevents its being corroded away. The
reaction which takes place may be represented by the following
equations : —

3Zn + 3HSO, = jZnSO, + 6H
I. Na,Cr,0, + H^O, + H^O = aH.CrO, + Na^SO

II. aHjCrO, + 6H + sH^SO, = Cr, {SO,);, + 8H,0

III. Cr5(S0,):, + Na3S04 + 24H,0 = 2[NaCr(SOj3, isHsO]

When sodium dichromate is used as shown in the above equations,
very little of the sodium chrome alum crystallises out, owing to
its solubility, but when potassium dichromate is employed the
crystals of potassium chrome alum often cause the carbon plates to
disintegrate, when the battery is left out of use for some time. It
is also better to use the sodium dichromate for another reason, viz.
because weight for weight the sodium salt yields a lai^er amount
Of CrO^. J

Leclanche Cell.

The Leclanch^ cell is very largely used in telegraphy, and for
other purposes, such as electric bells, where the current is only
required intermittently. It consists of a negative zinc pole and a
positive carbon pole ; the electrolyte is ammonium chloride, and
the depolariser manganese dioxide.

The carbon pole a, which is made of gas carbon, is placed in
a porous cell and surrounded with a mixture of granular manganese
dioxide and broken gas carbon. The top of the cell is generally
closed in with a coating of pitch, through which passes a glass tube
to allow ingress of air and egress of gases. The outer cylinder,
which contains the negative pole^a zinc rod, b — is of glass, and
contains a concentrated solution of ammonium chloride.

A very usual form of the cell is shown in Fig. 36. The
chemical reactions which take place in the cell are perhaps rather
complicated, but the equations below probably give a fair idea of
wliat occurs.

Sources of Current.

(i.) Zn + iH,0 = Zn (OH), + aH

(a.) 2H + aMoO. = MiijO, + H,0

(3.) Zn (OH), 4- aNH^CI = ZnCl,, aNH, + aH,0

When the cell is working there is always a smell of ammonia

produced, so that probably the following reaction also lakes

place —

(r.) Zn + iNH.Cl = ZnCI, + 2NH.
(2.) aNH, + 2Mn0i= Mn,0, + aNH, + H,0

Probably only a very small portion of the ammonia shown in

the last equation will be evolved in iho free stale, ihe major

portion combining with the zinc

chloride to produce the double

salt(ZnCl„2NH,).

The E.M.F. of the Leclanche

cell lies between i'4 and 1 6 volt*;

and is generally, after being in us

for some time, about Vi% to 1

volts. The internal resistance nl

different cells varies widely, m

some cases being as low as o 4 of

an ohm, while in others it may be

several ohms. When the cell is

in constant use, it rapidly loses

strength through the reduction of

the manganese dioxide and consequent polarisation. But if left

for some time unused, it gradually returns to its original condition,

owing to the oxidation of the manganese sesquioxide back to

manganese dioxide again.

Mn,0, + O = aMnO,

mangane

Cupron Element.

The cupron element, or Lalande cell, consists of a positive
made of a plate of compressed cupric oxide, a, which hangs
between two amalgamated zinc plates, b, b, in a solution of caustic

pole J

angs I

ustic \

Praclical Eleclro-Chemistry.

potash or soda, as shown in Figs. 27, 38. The cupric oxide acts
as the depolariser, and as soon as this becomes reduced, the cell
ceases to act properly. The cupric oxide, being of a porous
structure, is readily regenerated. This is done hy Caking the

=. R-* n

_% \ I. \

i" f

- — — -

- -

!HUh,

positive plate out of the solution, washing it with water, and then
exposing it to the air for from ao to 30 hours. If, however, it is
heated to 100 or 180" the oxidation is complete in 30 to 40 minutes.
The chemical changes which take place are very simple, and may
he expressed as follows : — ■

Zn 4- 2KOH = K;ZnO., + zH H

CuO + 2H = Cu -f H,0 H

When the battery has been in use for some time the electrolyte
requires renewing, and the zinc plates, which become coated with
a greyish deposit of hydrated sodium zincate, should be scraped and
reamalgamated.

One advantage of the cell is its very low internal resistance.
The E.M.F., however, is rather low, being at the commencement
i'2 volts. This rapidly falls to o-8z of a volt, at which point it
remains constant until the electrolyte becomes almost exhausted
or the copper oxide reduced.

Sources </ Cntrenl.
Grouping: of Cells.

For obtainiug a liigh E.M.l*'., cells should bf

series, for producing a iow internal
iws three Bimseu cells connected

led iti
parallel. Fig. 19
series, the opposite poles

of neighbouring cells being connected up together ; the zincs, it

will be seen, are joined to the carbons. The E.M.F. of such a

. systemislhree times that of a single cell ; ('.cif we takethe E.M.F.

a Bunsen cell as i'8 we get i^S X 3 = 5^4 volts.

Connecting the cells up in series, although it increases the

E.M.F., also increases the internal resistance of the system.

Fig' 30 represents three Bunsen cells connected in parallel,

the zincs to the iincs and the carbons with the carbons. This
arrangement decreases the internal resistance of the cell: the

so Practical Electro- Cfiefnistry.

internal resistance of two cells connected in parallel is only half
the resistance of one alone, and of three cells only one-third.
The effect of joining up in parallel is really to increase the size of
the plates : if a plate has a surface of loo sq. centimeters, then,
connecting it in parallel with another cell of equal size is
equivalent to having a plate of 200 sq. centimeters surface.

When the external resistance is high, cells should be connected in
series ; but w/ien the external resistance is low, they should he
connected in parallel

This will be best shown by means of a few examples. Ohm's
Law says : " The current strength in a circuit is equal to the electro-
motive force divided by the resistatice of the circuit, i.e. the internal
resistance plus the external resistance."

If, then, b is the internal resistance of the system, r the
external resistance, and E the electromotive force, then the current
strength C will be represented by the formula —

c= E

b->rr

It follows from this formula that C may be increased either by
increasing the electromotive force, E, or by decreasing the internal
resistance, b.

Example I.

The E.M.F. of a cell is i*i volts. The internal resistance is
o*8 ohm. The external resistance is 15 ohms. With various
groupings we can obtain —

A. Connecting in Series.

1 cell C = - .g-r — = o'ooQ amp.

O o -]- 15
2 X I-I

2 cells m series C = ^ v o'8 + m ~ ^'^^^ ^™P-

6 X I'l
6 cells in series C = ^r— = 0*333 amp.

6 X 0-8 + 15

Sources of Current, 51

B. Connecting in Parallel.

1*1
2 cells in parallel C = .g = 0071 amp.

I'l
6 cells in parallel C = -rg = 0*072 amp.

-6-+ ^5

Example II.
With an external resistance of 0*15 ohm.
A. Connecting in Series.

T'l

I cell C = -

2 cells in series C =

o"^8 + o-r5 = '''5 amps.

2 X I'l
2 X 0-8 +~5-i5 = ^'^5 amps.

/: 11 • n 6 X ri

6 cells m series C = 5^-0:3 -4.-. j^ = ^'ZZ amps.
B Connecting in Parallel.

2 cells C =

6 cells C =

I'l

0-8
2

I'l

— 20 amps.

0-8
6"

+ o'

— 4 ^ ^ amps

In order to decrease the internal resistance of a battery, and
yet maintain a fairly high E.M.F., it is often useful to connect up
the cells partly in series and partly in parallel. Fig. 31 represents
diagrammatically a set of twelve cells connected in three sets of
four cells each; Such a battery will give an electromotive force
equal to four cells, but the resistance of the system will be one-
third of that which would be exerted by three cells.

Practical Electro-Clieinistry,

From the examples given, the student will have no difficulty

after a little experience in de-
termining which, for diflferent
work, is the best grouping of
his cells, in order to obtain the
maximum efficiency from his
battery. The rule for group-
ing is to connect up in such a
manner that the internal and
external resistance are as nearly
as possible the same. Under
such conditions, the greatest
Fig. 31. efficiency is obtained.

@-@-@-^

Accumulators.

It has already been shown that in a Daniell cell (p. 42) the
electric current passes through the solution from the zinc to the
copper, and, in the outer circuit, from the copper to the zinc
— the zinc going into solution, and the copper being deposited
out. If now a current from a dynamo or other source of elec-
trical energy is caused to pass in the opposite direction — from the
zinc to the copper in the outer circuit, and through the solution
from the copper to the zinc — the copper will go into solution,
and the zinc will be deposited upon the zinc electrode. The
battery will thus be regenerated, and if the same amount of
current is passed in this, the reverse direction, as was originally
taken out of the battery, the cell will have obtained its original
condition. In the first place, chemical energy was converted into
electrical energy ; and in the second, electrical energy has been
converted into chemical energy. That is, electrical energy has
been stored up in the form of chemical energy, from which it can
be again obtained ; this is the principle of the accumulator
or storage cell. The storage cell is a reversible cell, and is an
apparatus for storing up electrical energy in the form of chemical
energy. By a reversal of the action this chemical energy can

Sources of Current. 53

again be converted into electrical energy. For many reasons
the Daniel! cell does not make a satisfactory accumulator, and it
is never so used in practice.

The Lead Accumulator.

The lead accumulator consists of a positive pole of lead
peroxide (PbOj), and a negative pole of spongy lead. The first
lead accumulator made was that of Plants in i860. Plant^ pre-
pared his cell by passing the electric current through sulphuric
acid, in which both the negative and the positive pole were of
lead. When the current was passed, the positive lead plate
became covered with a brown coating of lead peroxide, while the
surface of the negative plate became more or less spongy. On
stopping the current and connecting the positive and negative
plates together, an electric current was produced. Plante' found
that this process of charge and discharge could be repeated as
often as he liked, and that the more often it was repealed the
greater became the capacity of the cell. It is not in the scope
of this book to go into details of the various methods of making
accumulators, or of the rival merits of the different kinds. It
must suffice to say that accumulators at the present day are rarely
made by this costly method of charge and discharge, but the
active material is generally made in the form of a paste which is
caused to adhere to n lead grid.

Chemical Process.

The plates having been properly formed, consist, then, of the
positive lead peroxide plate and the negative plate of spongy
lead. On discharge, the negative plate becomes converted into
lead sulphate —

PIj + H^Oj = PbSOj + 2H-
The hydrogen ions convey the positive electricity to the peroxide
plates, and there give up their charge. At the moment the

Practical Eleciro-Chemistry.

hydrogen yields up its diarge it reacts with Ihc lead peroxide,
and reduces it lo lead monoxide —

PbOa + jH = PbO + H„0

This lead monoxide then reacts with the sulphuric acid, and ia
converted into lead sulphate —

PbO + H,SO< = PbSO, + H,0

The positive current flows from the lead piate (Fig. 32) through
the sulphuric add to the lead peroxide plate, and from the lead
peroxide plate through the external circuit to the lead plate ; that
is, from the electro-positive lead piate to the electro-negative lead
peroxide plate. This passage of current, and
the chemical actions above set out, continue
until the spongy lead and the lead peroxide
are converted into lead sulphate. The solu-
tion at Che end of the discharge, therefore,
contains less sulphuric acid than at the com-
mencement, because during discharge both
plates use up sulphuric acid. Hence the
specific gravity of the electrolyte in a dis-
^'"^ 3'- charged cell is always lower than in a fully

charged one. When an electric current is caused to pass in the
opposite direction by connecting the -f plate with the positive
pole, and the — plate with the negative pole of a dynamo or
other source of current, an opposite reaction lakes place. The
electrolyte for conveying the current consists, of course,
sulphuric acid.

H2S04=2H'-f SO4"

The negatively charged SO"j ions have their chai'ge neutralised at
the -f plate, but as SO^ is incapable of existence in the molecular
condition, it reacts with the lead sulphate on the plate, and
oxidises it to lead peroxide, with regeneration of sulphuric acid,

-. PhO, ■

2H,S0,

Sources of Current.

The hydrogen ions give up their charge at the negative plate, and
there reduce the lead sulphate to spongy lead, and reform
sulphuric acid —

PbSO, + aH = Pb + H^SOj
This chemical action — the conversion of lead sulphate into lead
peroxide at the positive plate, and the formation of metallic lead
at the negative plate — goes on until the whole of the lead sulphate
is converted respectively into lead peroxide and spongy lead.
Further passage of the current now
only causes electrolysis of the water
to take place, with a consequent
disengagement of oxygen gas at thu
positive plate, and hydrogen gas at
the negative plate. Fig. 33 shows
a cell manufactured hy the Electrical
Power Storage Company (E.l'.S.
cell), in which there are three positive
plates and four negative plates. Ac-
cumulators always contain an odd
number of plates, thus one of throe
plates would contain two negative
plates and one positive plate, the
positive plate being placed between the two negative plates. A
cell with seven plates would have four n^ative plates, and three
positive plates. The greater the number of plates in a cell-
thai is, the greater the active suiface— the higher the ampere-hour
capacity of the cell. The E.M.F. is, of course, the same, whether
there are three plates or twenty-one plates.

Charging and Discharging Accumulators.

The sulphuric acid employed must be as pure as possible,
and may on no account contain arsenic or chlorides, as these
impurities are very detrimental to the cell. The acid must be
diluted to the required specific gravity (I'lS to I'l;} before being
placed in the cells. Charging should be commenced directly the

i_l

S6 Practical Eleetre-Ckemistry.

acid has been placed in the cells, and should, if possible, be
conlinued unintemipledly for about twenty hours. When it is not
possible to charge in one run, the first charge should be at least
for eight hours. In charging, a resistance should always be
placed in series with the dynamo. When the cells are being
charged for the first time, it is generally necessary, at the
commencement, to shunt in a considerable resistance, because
the cells themselves at the outset oppose very little resistance.
As the cells become charged, and their E.M.F. rises, their
resistance increases, and, in order to keep the charging cunent
constant, it is necessary to take out some of the external resist-
ance. The increased resistance of the cells as they become
charged, is due to the back E.M.F. ivhich they exert. The back
E.M.F. for the first few minutes is, of course, practically nothing,
but it gradually reaches i'8 volts, and finally, when fully charged,
is about 2 '4 volts. During the first few hours of charging, the
gravity of the acid sinks : but then it increases, until, when the
cells are fully charged, it is about V2 to I'aa : the final gravity,
however, depends, to a certain extent, upon the form of
cells used and the gravity of the acid employed at the
commencement.'

When the cells are nearly charged, gas commences to bo
given off at the plates — oxygen at the positive, and hydrogen
at the negative. When fully charged, the cells gas freely, and
the liquid becomes milky and opaque from the quantity of gas
bubbles which it contains; the cells are then said to boil. This
boiling is due to the electrolysis of the electrolyte, and although
it does not hurt the plates, it should not be carried on for too
long a. period, because it wastes the electrolyte by spurting, and,
if the current is excessive, may disintegrate the positive plates. It
is advisable to coat all metallic connections, which might become
injured by the add spray, with vaseline, which can readily be
painted on with a brush,

' The numberF- here given refer lo llie Eleclric Power Slorage Co. cells.
Starling with n gravily of 1*17, llic acid will, when Ihe cells are fully charged,
have reached n grin'il)' of I'z.

Sources of Current. 57

After the cells have been completely charged, the pressurt: at
the terminais is generally a'a to 2'4 volts; it, however, soon falls to
z volts, at which point it remains for some time, and then gradually
falls as the cell is discharged. When it falls to i'8o volts, the
cells should be recharged, because they get out of condition if the
voltage is allowed to fall too low. Even when the cells are not in
use the E.M.F. slowly falls. It is not advisable to allow cells to
remain without charging for a longer period than from four to six
weeks, even when they are not in use, An accumulator should
not be too rapidly discharged, otherwise the plates are very lilteJy
to buckle and get out of shape. This may cause a short circuit,
which would ruin the cell. Neither should they be charged with
a very high current density. When a very high density is
employed, there is always a large amount of current wasted simply
in electrolysing the electrolyte.

When currents of sufficiently high voltage can be obtained,
it is best to charge the cells connected up in series. The negative
pole of the .source of current is connected with the negative pole
of the accumulator — i.e. with the lead pole— and tlie positive pole
with the positive or lead peroxide plate. The E.M.F. of the
charging current must be sufficiently high to overcome the back
E.M.F. of the accumulator; this may be put as a^s, therefore to
charge one cell a potential of at least 3 volts must he employed.
If six cells are connected up in series, the total b.ack E.M.F.
would be 2"s X 6 = rg volts. (It is only towards the end of
charging that the potential of a cell is as high as z^s volts.) A
potential sufficient to overcome this back E.M.F. of 15 volts
would require to he used in order to charge the six cells connected
up in series.

By connecting the cells up in parallel, the internal resistance
of the system is lowered, being very little more than that of only
one cell. Now, the E.M.F., as has already been stated, of one
cell is rather over z volts ; therefore, in charging the cells con-
nected in parallel) it is only necessary to use a voltage sufficient
to overcome the back E.M.F. of, say, z'5 volts. A potential of
about 4 volts would therefore be amply sufficient to charge with.

S8 Practical Electro-Chemistry.

Charging in parallel generally takes much longer than
charging in series, because the available current is divided
between all the cells, which are being chained. Thus, if six cells
connected in series are being charged with a current of la
amperes, then each individual cell is being charged at the rate
of 12 amperes. But if the cells are connected in parallel, the
12 amperes is divided among the six cells, and each individual
cell is being charged at the rate of a amperes per hour. In
order to completely charge the cells in parallel, the current
would therefore require to be passed six times as long as if
they were connected in series. The total energy put into the
cells would be the same, but in the one case it would be delivered
more rapidly than in the other.

To a certain extent the condition of the cell can be told
by noting the specific gravity of the electrolyte. As the cell
discharges, the specific gravity of the electrolyte falls ; this is
because some of the sulphuric acid is used up to form lead
sulphate. When the cell is in norma! condition, the specific
gravity rises again on recharging. If the cells have not been
long in use, taking the specific gravity gives an excellent criterion
as to their condition ; but with cells which have been in use a long
time without the acid being changed, too much reliance should
not be placed upon the gravity alone. In any case, if the gravity
is below j*2 after the cell has been charged, probably something
is the matter. The infallible proof of the condition of the cell is
the E.M.F, After the cell has been charged and boiling has
taken place, if the potential is below 2 volts, then the cell is
out of order. As the charging of a cell becomes completed there
is always a certain amount of gassing ; this means that a certain
amount of the electrolyte is being carried away by spraying.
Therefore, after some time of use, partly from this reason, and
partly from evaporation, the electrolyte requires replenishing.
Generally the addition of f>ure distilled water is all that is neces-
sary, because the main portion of the loss is through evaporation,
but a certain quantity of acid is invariably lost through spraying.

The constant addition of water without adding fresh acid may

be the cause of the gravity being low ; at the same time the
voltage may be quite correct. If this is the case, a small quantity
of strong pure sulphuric acid is added to bring the eleclrolyt* up
to the required specific gravity. The acid may be added to the
cells in sittt, but it is better to siphon off the electrolyte, bring up
to the required gravity, and then retum to the cell. Before
interfering with the electrolyte, however, care should be taken to
ascertain that the specific gravity really is low. If water has
recently been added thorough mixing may not have taken place,
and, after one or two charges, the gravity may be found to be
quite correct. If both the gravity and the E.M.F. of the cell are
low, even after a long charge, then the cell is said to be sick ;
probably in this case the positive plates will be of a reddish
chocolate colour, instead of a dark brown, and the negative plates
will very likely be a dirty whitish grey or may have lai^e white
patches of lead sulphate on them : the cause of the cell being out
of order is due to snlphating. Generally speaking, charging
alone will not put this right, and, if this is found to be the case,
the cell should be taken down, the electrolyte siphoned ofT, and
the negative plates scrubbed with a hard bristle brush under
running water. Great care must be taken not to allow the least
trace of grease to get upon the plates when they are being washed.
The positive plates must not be allowed to dry, but should be
well washed in running water; they must not, however, be
scrubbed, because this would probably detach some of the lead
peroxide. The cleaning of lead accumulators is not by any
means an easy operation, and must be carried out with great care,
otherwise the plates may be completely rained.

The lead negative plates usually have a longer life than the
positive peroxide plates. If the positive plates become damaged,
it does not follow that the negative plates are also out of order,
and the cell can be put in working order again by renewing
the positives.

Practical Electrfi-Chermhtry.

Edison Storage Battery.

In the Edison sloragu battery the negative pole consists of
iron ; the positive pole is oxide of nickel, which is supposed to
be nickel peroxide, NiOj. The electrolyte is a ao per cent
solution of caustic potash. Compared with the lead accumu-
lator the voltage of this cell is comparatively low, being after
recent charging i'5 volt, but the normal discharge voltage is
not much above vi or fs volt

The reactions which take place may probably be represented
by the following equations r —

aNiOa + Fe = Ni,0, + FeOl

NijO,+ Fe = aNiO + reOj

NiO + FeO = Fe 4- NiO^ 1

Ni.O, + FeO = aNiOa + Fe J

On discharging.

On charging.

The last two equations are brought about by the passage of
the current through the electrolyte, hydrogen being liberated at
the negative pole, which reduces the oxide of iron to the metallic
state. Likewise oxygen is liberated at the positive plate, and
oxidises the reduced nickel oxide back to nickel peroxide again— 'j
2K0H=2K'+ HjO +0
aK + 2Hi,0 = 2K0H + iH

At first sight it might be thought that, owing to its low E.M.F.,
the Edison cell could not compete with the lead storage cell.
But it has certain advantages which go a long way towards com-
pensating for its lower voltage. These are claimed to be^

(i) Stability of the cell, absence of deterioration by work ;

(a) Large storage capacity per unit of mass ;

(3) Capacity for being rapidly charged and dischai^ed, without
buckling ;

(4) Capability of withstanding rough treatment ;

The cell is coming into very considerable use for automobile
work, especially in America ; hut so far, at any rate in England,

Sources of Current. 6i

il has nol been employed for laboratory purposes, II is VLTy
doubtful whether, at any rale for a long time lo come, the alkaline
accumulator will take the place of the lead battery. Although the
cell may possess the above-mentioned advantages, the question
as to its walt-liour capacity and as to the economy of charging
are also important factors, and these have not yet been proved
Lo be higher than those of the lead accumulator.

Electrolytic Rectification of Alternating
Currents.

It is found that wben a plale of aluminium is made the anode
in an electrolytic cell, at the moment of completing the circuit,
the current flows as usual, but it rapidly becomes less and less,
and b the course of a few seconds, if the E.M.I*", is not more
than ao to 25 volts, the current ceases to pass. Obviously this
connot be due to polarisation, because the back electromotive
force due to gaseous polarisalion would not be much above
I volt.

It is a well-known fact that aluminium readily becomes super-
ficially coated with a film of oxide, and that this film exerts a
protective action, preventing further osidation from taking place.
It is this superficial oxidation of aluminium which makes it so
diffictdt to weld the metal or to plate other metals upon its
surface. When aluminium is made the anode in dilute sulphuric
acid, or in a sodium -phosphate solution, there is a tendency, on
completing the circuit, for the aluminium to pass into solution.
The moment, however, it commences to dissolve, the surface
becomes coated with a film of hydrate or basic sulphate or
phosphate, and this prevents actual contact between the solution
and the aluminium. This film is a dielectric, so we get a
dielectric polarisalion, and the film acts as a condenser between
the metal and the electrolyte. The dielectric polarisation almost
absolutely prevents the passage of the current with potentials
below 30 volts, but with higher voltages it partially breaks down,
and a certain amount of current will pass. The resisting action

Practkal Electro-Chemistry.

is also better at low temperatures, and is to a certain exti
dependent upon the nature of the electrolyte. Grata
first to point out that this peculiar behaviour of aluniiniuni
might be employed to rectify alternating currents. In an alter-
nating current there is a pulsation first in the one direction,
and then in the other, or, in other words, the electrodes in a
cell through which an alternating current is being passed are
one moment negative, and the next moment positive. It is,
therefore, not possible to conduct ordinary electrolysis with an
alternating current. Although an aluminium plate cannot be
employed as anode in electrolysis, for the reasons already ex-
plained, it can be used as a cathode, because in this case any
protective coaling, if it is produced, is removed by tlie reducing
action of the hydrogen. As the alternating current consists of
impulses first in one direction and then in the other, it should
follow that, if an aluminium plate opposed to one of lead or carbon
is placed in an electrolytic cell and connected with the alternating
current, the positive phase will be unable to pass, but the
negative will have no such
difficulty. This is actually
found to be the case, pro-
vided the E.M.F. is not
too high ; but, of course,
with a single cell 50 per
cent, of the current would
be losL The best method
of connecting up in order to
obtain the maximum recti-
fication and efficiency is
shown in Fig. 34.
M, M are the terminals from the alternating mains, and
and A, a' are four electrolytic cells. The long lines repres
the aluminium plates, and the short lines lead or carbon. Now,
when the current tries to travel through the cell b the negative
impulse will pass without difficulty, but the positive will be
prevented from passing by the aluminium plate ; it will therefc

^sei^l

Sources of Current. 63

be thrown back, but will be able to pass through the cell a. The
same applies to the current endeavouring to pass through b' ; the
positive will be thrown back, but will pass through a'. The
negative currents from b and b' are united in the conductor gg,
and the positive currents unite in the conductor ee. We have
therefore, at the two terminals C and c, a continuous current,
the terminal carrying the current from the aluminium plates being
positive, and the terminal taking the current from the lead plates
negative. The number of plates in the cells u, b' and a, a'
depends upon the E.M.F. of the alternating current. As a matter
of fact, it is not a question of the number of plates, but of the
number of cells. Thus, as shown in the diagram, there are two
long and two short lines in the cells ; tliis really represents two
cells connected together in series. One cell at ordinary tem-

I peratures will only rectify successfully if the E.M.F. of the alter-
nating current does not exceed about 25 volls; at o'' the E.M.F.
may be as high as 45 to 50 volts without the cell breaking down.

I In some districts the alternating current ia used for lighting ;

I the current cannot therefore be emjiloyed for electrolytic pur-
poses, or for charging accumulators. The current rectified as
above explained will, however, be found quite satisfactory for
charging accumulators. Absolute rectification, except perhaps at
very low voltages, probably never takes place, there being always a
greater or less amount of leakage. This leakage is due to a partial
breaking down of the dielectric; at high temperatures the pro-
tective film seems to get more or less crystalline in structure, and
then the leakage becomes very considerable. Presumably, when
the negative impulse strikes the plate, sufficient breaking down,
due to reduction of the film, does take place to allow the passage
of the negative current, otherwise no current would pass in either
direction. There is a certain voltage above which all dielectrics
will break down; and under ordinary circumstances and at ordi-
nary temperatures, with the film produced on the aluminium plate
this is about 25 volts.

A very interesting phenomenon is noticed when an alternating
current is passed through an electrolyte where one of the plates

Practical ElKtro-Chemistry.

is alumiiiium. The alutninium plate is noticed to phospliare^cc,
and its whole surface scintillates in a very beautiful maimer. The
electrode opposed to the alumiuium
does not show this peculiarity.
Aluminium is not the only metal
which prevents the passage of the
positive electric current ; ma^e-
siutn, chromium, and indeed most
metals have this property to some
extent.

One difficulty in using electro-
lytic rectifiers is the great heating
of the solution which takes place.
Fig. 35 shows a sectional elevation
and Fig. 36 the plan of one of the
cells which have been successfully
employed for chaining accumulators
at the Borough Polytechnic. The
ct^Il consists of a sheet of stout
aluminium shaped into a cylinder;
this is surrounded by a coil of Itad or composition pipe, through
which water circulates. The aluminium is made the one pole,
and the lead pipe the other
pole. The electrolyte con-
sists of a cold saturated
solution of ammonium phos-
phate, (NHJaHPOj.

Mor recently better re-

ul 1 ve been obtained by

u ng a closed aluminium

J 1 de and circulating cold

bo h through this

c} Imd and through the lead

pipe. (The form of the apparatus s th s. me tb shown in Figs.

35 and 36, except that tlie alummmm Lyhnder closed and has a

tube for ingress and egress of the cold water.) The efficiency of

Scitrces cf Current. 65

the rectifier is very much greater at low than at high temperatures.
Further, the aluminium plates last very much longer ; it has teen
found that if the temperature k allowed to rise from 30° lo 40",
the plates corrode away in the course of a few weeks. Whereas,
when the electrolyte is maintained at a temperature below zo°,
the plates appear to be very little att-icked.

There is always considerable loss of energy in using these
cells, unless the plates and solution are kept well cooled. I)y
cooling the aluminium plates as above explained, over 90 per
cent, rectification is readily obtained, i.e. the current efficiency is
over go per cent., as shown by the amount of copper deposited
from a copper coulommeter. Even if considerable loss does take
place, the conversion of an alternating into a continuous current
by this means is a very great convenience.

LITER A TURE.
L. Griitz, Zeit. f. EUktrochan. (1897), 4, 67: K. Norden, Z«V./.
Ekklrochem. (1S99), 6, 159 and 188 ; Livingston, Morgan and DufT,
Joum. Amer. Ghent. Sec, 22, 331 : W, L. Hildburgh, Journ. Amer.
Chem, Soc, 28, 300 ; C. Hambiichen, Journ. Amer. EU(tro-c)um.
Soc. (1903), 4, 105 ; Journ. Ame?: Electro-difm. Soc. (1904), 6.

Distribution of Current,

Fig. 37 represents diagrammatically an arrangement designed
by the author which may be employed for distributing the current
from storage cells. The arrangement here adopted is to avoid
the multiplication of measuring instruments. The switch-board is
designed to supply three circuits on three sides of a room. Each
circuit may have any number of terminals to suit the desired
number of students ; but, of course, all the students working on
the same circuit have to use the same number of cells. But by
means of resistances the strength of the current which it is desired
to employ can be regulated. The switch-board shown is connected
with three circuits.

Each circuit is provided with an ammeter and voltmeter. Every
working place is fitted with a separate set of terminals and a fixed
resistance of about 20 ohms ; heavier resistances caii of course be

Sources of Current. 67

employed if required. The resistances are mounted, together
with switches for the ammeter and voltmeter, on an enamelled
slate base, and are fixed on the wall just above the benches. By
means of one switch the student is enabled to take the ammeter
reading, and having done so, to switch off and continue the
electrolysis without keeping the instrument continually in the
circuit — the resistance of the ammeter, being very low, is
leglected. A second switch for the voltmeter is arranged in a
similar manner. Thus, several students can use the same instru-
ments without interfering with each oiher's work, and multipli-
cation of these expensive pieces of apparatus is avoided.

The Distributing Board is arranged so that the cells may
be connected up either in series or in parallel, or part in series and
part in parallel. Further, although in the diagram there are only
twelve cells, the whole number may be switched on to one
circuit, ten on to another, and eight on to the third, and all
circuits may be in use at the same time. Of course a smaller
number of cells can be employed on any of the circuits when
it is found desirable. The diagram shows the arrangement of the
plug-board, and the manner in which it is connected with the
- accumulators, also the way in which the current is distributed to
the several circuits.

From the diagram, which explains itself, it will be seen that a
fuse is inserted in each of the leading wires from the battery, which
protects the apparatus from damage in the event of an accidental
short circuit taking place. Each cell is also separately fused.

It is not very often that it is necessary to have cells con-
nected up in parallel, and in installations in which it may not
be desired to have this arrangement, the distributing-board could
be very much simplified by having only one row of plug holes.
This would, at the same time, make the hoard very much cheaper.
In the diagram, two cells are shown connected in series on to
Circuit No. II. When the ammeter switch is moved on to the
stud marked " On," the current passes through the decomposition
cell which is in connection with the two terminals, but would

fould H

68 Practical Electro- Chemistry.

not be passing through the ammeter. On switching i
" Ammeter reading," the current passes through the ammeter and
work. As soon as the student has taken his reading, he switches
back to "On," and continues the work with the instrument
thrown out. The voltmeter, which is of course on a shunt
circuit, is so arranged that besides taking the P.D. of the work,
the terminal E.M.F. of the circuit can also be taken.

The Resistances.— These are made from insulated " pla-
tinoid " wire, wound on asbestos-covered brass tubes. The
advantage of winding on tubes is that a current of air passes
through them and serves to keep the resistance cool. The
contact is a double sliding one, and connection is made with
the resistance wire by removing the insulation from the upper
and lower surfaces of the coil. Each instrument has a re-
sistance of about 3o ohms, and will carry a current of about
4 amperes without unduly heating. An ideal resistance at a
moderate cost is a very difficult thing to obtain. With a re-
sistance such as is here described, there is not much difficulty
in cutting down by very small fractions of an ampere ; but if it
be required to carry a current of considerable density, and at the
same time to reduce or increase the current by small fractions of
an ampere, the best method is to employ a liquid resistance such
as that shown in Fig. 41, p. 75. The method of distributing the
current here described is simply given as an example of one which
has been found in actual work to be very satisfactory. The method
tote adopted in any laboratory will require to be modified to suit
the special requirements of the work which it is intended to carry out.
Pole Papers. — It is sometimes necessary to test whether
a wire is connected with the positive or negative pole. For this
purpose turmeric paper moistened with a solution of sodium
sulphate may be used ; on placing the wires near together on the
moist paper, a brown mark is produced where the negative wire
touches it, due to the liberation of sodium. Tole papers often
have phenolphthalein and sodium sulphate on them, and then the
negatii'e wire produces a pink mark.

In all electro-cbeniical operations it is a matter of great im-
portance to be able to control the quantity of current which is
to pass through the electrolytic bath in a given time. Flow of
water from a pipe is regulated by means of a tap, the amount
of water which will flow depending upon how far the tap is
turned on. The flow of the electric current is regulated by
means of resistances ; the greater the resistance switched into
the circuit, the less the quantity of current that will flow.

la order to be able to compare diiferent resistances, it is
necessary to have a standard or unit of resistance. The unit of
resistance is called the ohm. The ohm is defined as being the
resistatia offered by a column of pure mercury io6'3 cettlimcters in
kngth, having a uniform section of i square millimeter, al a
* temperature of o° C The weight of this column of mercury is
14-4521 grm.

In practical working it would not be convenient (.0 employ
columns of mercury as resistances. Use is therefore made of
the &ct that different metals oppose different resistances to the
passage of the electric current. Iron wire, for example, offers
a very much greater resistance to the passage of the current
than does copper wire. Resistances are often therefore made of
.iron wire. But for laboratory purposes it is more general to employ
resistances made from certain alloys, such as platinoid or
tnanganin.

The resistance of a wire is proportional to its length
and inversely proportional to its cross section. The

Practical Electro-chemistry,

specific resistance of a material is the resistance between two
opposed faces of a cube of the substance, each edge of which is
I cm. in length. The appended table gives the specific resistances
of a number of substances, measured in microhms (a microhm is
the millionth of an ohm, i,e, lo-* ohm). The measurements
given have been taken at o°.

TABLE VII.

Substance.

Silver, hard drawn
Gold, annealed
Copper, annealed

,, hard drawn
Aluminium, annealed
Iron, annealed
Platinum, annealed
German silver
Manganin
Platinoid

S^cific
Resistance.

1-468
2-053
1*560
1*629
2*905

9693

9*035
20-886

46*700
41731

Resistance of

z metre of z S(q. mm.

cross section.

0*01468
002053
0*01560
0*01629
0*02905
0*09693
009035
0*20886
0*46700

0-41731

Temperature Coefficient. — When the current passes
through a wire, the wire becomes hot; but a hot wire offers a
greater resistance to the passage of the current than a cold wire,
therefore the resistance is more or less variable, the variation
depending upon the temperature co-efficient of the metal or
alloy. The great advantage of an alloy such as platinoid is,
that it has a very low temperature coefficient. For instance,
the conducting power of pure iron falls by 39*2 per cent, when
it is heated from 0° to 100°; whereas, through the same range
of temperature, platinoid only falls by 2*09 per cent. The
temperature coefficient, therefore, per degree is respectively 0*392
and 0*0209. The appended table gives the temperature coefficient
per cent, of certain metals and alloys.

Regulation of Current. yi

TABLE VIII.

Metal.

1 Increased resistance per cent.

1 a . a .

o- lO loo- c.

Silver, annealed

•

40*0

„ hard drawn

40-0

Copper, annealed

42-8

„ hard drawn

38-8

Iron, pure

39*2

„ annealed

625

Aluminium

390

Platinum

367

Gun metal

392

German silver

4'4

Platinoid

2*09

Ohm's Law.

Ohm^s Law states " that the current strength varies directly as
the electromotive force and inversely as the resistance ; " or we may
say — the ratio between the electromotive force and the current
shows the resistance. Thus, if E represents the electromotive
force, C the current, and R the resistance, then we have —

Therefore knowing the electromotive force and the resistance,
we can find the current strength of a circuit.

C = ^

I. For example, suppose the electromotive force of the
batteries in a circuit is 12 volts, and the resistance is 9 ohms,
what current will pass through the circuit ?

_ 12

C = - = 1*33 amperes

II. Similarly, if the current and the resistance are known,
we can calculate the electromotive force. If the resistance of a

72 Practical Electro- Chemistry,

circuit is 15 ohms, and the current 1*5 amperes, what is the
E.M.F.?

E = 1*5 X 15 = 22*5 volts

III. And the resistance R can be calculated when we know
the E.M.F. and the current. If the E.M.F. is 16 volts, and the
current 0*5 ampere, what is the resistance?

R = ~ ^ = 32 ohms.

As a rule, the calculations are not quite so simple as the
above, because in any circuit the total resistance is made up of
a number of smaller resistances. There are the leads which
convey the current; these represent a certain resistance. The
various connections, especially if the junctions are not well
cleaned, are sure to cause a greater or less resistance. Then
there is the known resistance for regulating the current. Finally,
there is the unknown resistance of the electrolytic cell, which
may be continually varying, either owing to polarisation or to
changes in the concentration of the electrolyte and to heating
effects.

Resistance of the Electrolytic Cell. — It is sometimes
useful to know the resistance of the electrolytic cell. This we
are able to calculate from Ohm's Law. What we require to
know is the current which is passing, and the drop in potential
between the electrodes.

For example, in an electrolytic cell in which the electrolyte
consisted of a 15 per cent, solution of copper sulphate and the
electrodes were both of copper, a current of 2*5 amperes was
found to be passing. The drop in potential between the
electrodes was 3*2 volts, therefore the resistances of the cell
was —

3*2

R = — = 1*28 ohms.
2*5

The above example was purposely taken, because in such a
cell, where both the electrodes are of the same metal, and the

RegttfatioH of Current. 73

eieclrolytc is a salt of the metal, there art- no [wlarisatiuii effects.
Generally, however, tliere is a greater or less back E.M.F. pro-
duced by polarisation.

Cell Polarisation and Back E.M.F.— I'olarisation always
produces a back electromotive force, and in ordi:r to calculate
correctly the resistance we must measure the back E.M.F. of the
cell. This may be done by connecting a voltmeter across the
two electrodes. The voltmeter will show the apparent drop in
potential between the electrodes. Now switch off the current, the
voltmeter will recede back until it stops for a short lime at a
point somewhere above zero, and then gradually fall back until
it conies to zero. The position to which il fell iii the first
instance is the polarisation voltage. An example will make
this clear. In a cell which contained a solution of sodium
sulphate both the anode and cathode were of lead. After
the current had been passing for some time the voltmeter was
shimted across the electrodes, and was found to read 4'8 volts ;
the ammeter at the same time showed a reading of 3 amperes.
The ciurent was then cut off; the voltmeter fell to a volts,
where it remained for a short time, and then gradually fell to
zero. The back E.M.F. was therefore 2 volts, which was opposed
to the passage of the current. Thus the resistance of the cell
due to the back E.M.F. was—

R =

4-8-^

= 0-93 olinis.

Some Forms of Resistance.

A simple form of resistance is shown in Fig. 38. It consists
of coiled lengths of wire fastened on to a frame. By moving the
switch on to different studs, various amounts of resistance can be
thrown in. Each length of wire generally represents a known
resistance : for example, each wire may represent a resistance of
1 ohm ; therefore, when the switch is on the fifth stud, there will be
. resistance of 5 ohms thrown in. When heavy currents are

74 Practical Electro-Chemistry.

employed, the resistance wire may become very hot, and the ivire is
then generally mounted on an iron frame fixed upon a siate bast.

Fig, 39 shows another form of adjustable resistance,
made of insulated platinoid wire wound upon an ashes to s-coveredfl
brass tube. Contact is made by sliding the brass rubber A
the bar n — connection being made with the resistance wire bjfT
removing a portion of the irisitl.ilion from its upper surface.

■n

^^o+

Fig. 40 illustrates another form of adjustable resistance which; J
can be made for carrying still heavier currents.

When it is necessary to cut a heavy current down, and tal
regulate by small fractions, it is best to pass the current through aJ
liquid resistance. Fig. 41. This may be simply a glass or, better, ■

Regitlation of Current. 75

an earthenware trough, containing dilute auipliuric acid or caustic
soda (the concentration of the electrolyte depending upon the
resistance required), and
having two lead plates
as electrodes, when sul-
phuric acid is used, or
nickel plates when caustic
soda is the electrolyte.
The resistance is regu-
lated by moving the two
plates A A either nearer
together, to increase the ■ . ■ .

current ; or further apart, to di'cri.'asc the current.

The only objection to this form of resistance is that, if the
current is very heavy, the solution becomes hot and evaporates
away. If, however, one of the electrodes consists of a coil of

lead pipe, through which cold water is allowed to flow, the heating
of the solution is very much reduced. Many other forms of
resistance might be described, but for general laboratory work
the ones here described should be quite suflScient. The class of
resistance employed will depend upon the kind of work for which
it is required, and to a great extent upon the personal experience
and likes of the experiment is t.

CHAPTER Vll.

APPARATUS FOR ELECTROLYSIS.

In almost all eleclrolylic depositions it is necessary to employ
platinum anodes and cathodes. The cathodes are either in the
form of basins, cylinders, cones, or flags. Basins have perhaps
been more largely used than any other form of electrode, but
they are extremely expensive, and have really no advantage over
a gauze cylinder or flag electrode.

When a basin is employed, it should be of sufficient capacity
to hold from 150 to 180 c.c. of solution. The
best form of anode is of platinum wire coiled
concentrically, as illustrated in Fig. 42. In
using the basin a stand of the following con-
struction will be found very convenient (Fig. 43).
The base of the stand is of slate or marble,
and the brass rod which conveys the — current
is hollow ; through this brass rod an insulated
wire for carrying the + current passes, and is
^ connected at the lop of the rod to an insulated
g binding-screw, and at the bottom with the
binding-screw fixed on to the slate base. The
arm for holding the anode is insulated from
the upright brass rod by means of a piece of ebonite. The
ring which supports the basin has three little platinum points
at equal intervals on its circumference ; on these the basin rests,
thus ensuring good contact. The -|- pole of the source of cuiren^.]
is connected with the binding-screw fixed in the slate base, andi
the negative pole with the binding-screw marked — .

'•J

Apparatus for El^tfelysis.

During the course of electrolysis — especially whtn hot solutions
i used— it often happens that tlie volume of the solution falls
below the edge of the deposited metal, which may then become
oxidised and lead to incorrect results. In Fig. 44 is shown an
arrangement for getting over ihis difficulty. A small beaker is held
in a ring which is placed upon the upper part of the rod of the

stand ; the beaker is filled with distilled water, and has hanging
over its side a piece of lampwick. One end of (he wick is in the
water, and the other end is twisted round the anode ; the water
slowly siphons over from the beaker, and by arranging the number
of threads in the wick and the height of the beaker from the basin,
the water can be made to flow into the basin as rapidly as it is
evaporated or electrolysed away. If it is desired to keep the
solution acid, as, for example, in the analysis of zinc by the oxalate
method (p. 119), then the beaker is filled with dilute oxalic acid.

Practical Electro- Chcnistry.

Heating Platinum Basins during
Electrolysis.

Special precautions are necessary for heating platinum basins.
The flame of the burner may on no account come in contact with
the basin, as this causes the platinum to become dull, probably
from formation of carbide. Another drawback to direct heating
is, that the heating may become too local, and this may cause the
deposit to scale off; the deposits are almost certain to scale if the
solution is boiled. In order to give a diffused heat, a piece of
sheet asbestos may be placed upon a ring under the basin, or
a very small flame may be placed some
4 cm. below the basin. Perhaps the best
method is to use a water-bath of the form
depicted in Fig. 44. The batfi really acts
as an air-batb, as it is so arranged that the
basin shall not come in contact with the
water, the only openings to the bath being
the two small funnels A, A. Three small
pieces of platinum wire are soldered into
the copi>er cavity, and on these the basin
rests. There is an air space of about 2 cm.
all round the basin.

It will be found that if the bath be
filled with a mixture of equal parts of water
and glycerin, that this mixture can be
healed to a temperature of about 130°
without boiling, and that then ihe tempera-
ture of the solution in the platinum basin
will be between 50 and 60°.

Fig- 45 shows a cylindrical gauze elec-
1""= <5. trode with its anode. Cylindrical electrodes

other than gauze cannot be recommended, because of the great
unevenness of current density, the metal being mainly deposited
upon'the inside of the cylinder, and only to a limited extent upon
the otitside.

Perhaps the hest form of tlertrode is the flag form shown in
Fig. 46; the cathode is m the form of a flag and is made of
platinum gauze, which should be
sufificiently stout to permit of heuiy;
sand-hlasted it is held ngid h) i
means of a platino-iridium frami^
(10 per cent, iridium); the frame^
which is roughened by means of
the sand-blast, has a stout piece
of iridio-platinum wire welded on
to it. The wire is for holding
the electrode in position during
analysis. The loop near the top
of the wire is for hanging the elec-
trode on the balance. The anode
is made of platinum wire, and is hent upon itself ii
that when it is placed into
position for electrolysis,
as illustrated in Fig. 47,
an even current density is
obtained on all parts of Ihf
cathode. The distance be-
tween the two sides of tlie
anode is 2-5 cm., therefore
when in position it is 12^
cm. distant from each side
of the cathode.

The cathode is 6 cm.
high and 4"3 cm. wide, and
the length of the supporting
wire is 7-5 cm., the loop
being 2'5 cm. from the end.
As the anode is opposed
to both sides of the cathode ^'°' "'

during electrolysis, it follows from the above measurements that
the total cathode surface is 5o'4 sq. cm,, that is, practically

— #

half a square decimeter, which, as the current density (CD.) for
analytical purposes is generally calculated per scjuare decimeter of
surface, is a very convenient size. It is not essential for the
cathode to be made of gauze-^in many cases sheet platinum is
quite as useful ; but for metallic deposits which are inclined to
exfoliate, such as bismuth and antimony, the gauze is more
satisfactory ; it is also very useful for mercury and for jjeroxide
deposits. The gauze should not be too fine ; the finest thai
I have found satisfactory is about 80 to 90 meshes to the
square centimeter. When it is too fine there is a tendency for
hydrogen to collect upon the surface and thus cause polarisation.

The weight of the cathode, when made of platinum sheet,
is about i4'5 grm, If thinner platinum is employed, the weight
can be reduced to 8 grm., but it is found better not to make theni;;
of very thin platinum, because then they are loo fragile, and theTe<
is a tendency for the deposits not to adhere well at the edge
The weight of the gauze electrode is about 15 grm.

Current Density (CD,), as already stated, is the intenal
of current per unit of surface. Thus, if the surface is i squai
decimeter, and the current is 2 amperes, we say that the CD. ii
z amperes. If, however, the electrode was only o'z5 of a squan
decimeter, then, if the current was 2 amperes, the CD. would b
8 amperes. The current densities given in Ibis book always
represent the CD. per square decimeter.

Rotating Electrodes.

The rate of deposition of a metal from its solutions is veij
much accelerated, and a higher CD. cau be employed, when th4
cathode is kept in rapid rotation. In Fig. 48 is shown a rotating
cathode, and the arrangement employed for rotating it The
support for the cathode consists of a gun-metal arm, the end
of which is drilled to allow a spindle to pass. This spindle
carries a small chuck (such as is used for Ji.xing small drills)
which is used for holding the rotator. The grooved pulley,
which is fastened on to the upper end of the spindle, bears or

Apparatus for Eleclrel^0s, 8i

top of Ihe anil, which is ground smootli. 'i'lie wiiole artangenieiil
is driven by means of a belt from a water-turbine or ek-clric
motor. This arrangument is found to give very |H:rfcct contact
and lo work with very httlt friction. The parts should only
be slightly lubricated,
the best lubricant being
a mixtik'e of graphite
and oil.

The cathode, as is
seen from the figure, is
a small sand - blasted
cylinder, of platinum
gauze, which lift a com-
bined surface of about
35 cm. The anode is
in the form of a double
circle of stout platinucn
wire, and has four little
baffles placed a1 inter-
vals round it, to prevent
the liquid from rotating
with the cathode. A double coil of stout platinum wire serves
equally well. Of course for peroxide deposits the rotating elec-
trode would be the anode. A cylinder of sheet platinum also
gives very good results, but in this case very little metal is deposited
upon the inner surface. I,oiigitudiiial slits, however, partially
get over this difficulty, but with gauze as shown in the figure
the deposition is practically equal inside and outside. Not only

■ are the metals deposited more rapidly by the use of a rotating
cathode, but the deposits are generally exceedingly bright and
have a magnificent burnished appearance ; this is especially the
case when cobalt is deposited from a solution containing

I ammonium tartrate. When the cathode is of gauze the brilliancy
of the deposit is not so marked as when a smooth cathode, such
as that described bj^ Gooch, which consists of a platinum crucible,
is employed.

Practical Eleetro-Chanistry.

Preparation of Electrodes.

In all forms of analysis, cleanliness of apparatus is a matter of
importance ; if possible, it is even more important when electro-
chemical methods are employed. The slightest trace of grease or
dirt upon the cathode must be avoided, otherwise the deposit will
be patchy, and often non-adherent. In order to clean the electrodes
they should first be healed in nitric or hydrochloric acid, or warmed
with a mixture of sulphuric acid and potassium dichromate. They
should then be thoroughly washed under the tap, and afterwards
with distilled water. If tliey still appear greasy, they may be
washed with caustic allcali, well rinsed, and finally healed to
redness in the bunsen fiame or by means of the blowpipe. It is
not necessary to cool them in a desiccator before weighing. It is,
however, generally speaking, better— as far as possible^to allow
the electrodes to cool for the same length of time before weighing,
say twenty minutes or half an hour. After ignition the cathode
surface must on no account be touched with the fingers, because
the grease of the fingers might be sufficient to spoil the metallic
deposit.

Before igniting platinum, great care must be taken that every
l«irticle of the metallic deposit has been removed; otherwise, on'
heating, an alloy may be formed which will spoil the apparatus.
On no account may platinum be heated in a smoky flame, as this
dulls the surface and forms a carbide. From time to time, if the
platinum becomes dull, it may be necessary to polish it with
a little very fine sand or pumice powder; when this is carefully
done, the weight of the platinum is not appreciably altered.

PART II

ELECTRO-CHEMICAL ANALYSIS

CHAPTER VIII.

ELECTRO-CHEMICAL ANALYSIS.

Although so far back as 1801 Cniikshank suggested the employ-
ment of the electrical current for analytical purposes, and in i8iz
Fischer recommended it for the detection of small quantities of
arsenic, the careful and successful study of electro-chemical methods
is of comparatively recent date. Yet while many processes of
great importance and usefulness have heen discovered, it must not
be supposed that it is possible to carry out analysis solely and
entirely by electrical methods. In a great many cases pure salts
of the metals may be very readily and conveniently analysed
electrically, yet it often happens that it is much more convenient
to employ methods of separation which are purely chemical. For
example, although silver and copper can comparatively readily be
separated from each other by variations of electrical potential,
still, generally speaking, it is better to first separate chemically and
then to electrolyse the two separately. Theoretically speaking, it
should be possible to separate practically all the metals by care-
fully regulating the electromotive force, because, as Magnus
stated in 1856, " in every mixed electrolyte there is a certain limit
of intensity, at which only one of the components will be de-
composed." But it is usually found in mixtures, unless the limit
at which the various constituents are decomposed lies compara-
tively far apart, that the one metal upon being deposited brings
down a certain quantity of the other metal, and that therefore
a complete separation does not take place.

In studying electro-chemica! methods of analysis, it is usual
and advisable, in the first place, to investigate the behaviour of

Practical Eledrp-Chemistry.

solutions of pure salts, before endeavouring to separate n
of the metals.

The metals may be roughly grouped according as to whether i
they are deposited in acid, alkaline, or neutral solutions or as to
whether they can be obtained as cathode or anode deposits. In
any case, however, the grouping is only very relative, because as a
rule metais which can be deposited from acid solutions may also
be deposited from solutions which are alkaline or neutral. No
special attempt will therefore be made to follow out any particular
line of grouping, but as far as possible those metals will be placed
first which are the most easy to deal with.

Copper.

Copper may readily be deposited from solutions which con-
tain considerable quantities of nitric or sulphuric acid. But good
deposits can also be obtained from cyanide solutions, ajid it is
possible to employ solutions containing an excess of ammonia.

Nitric Acid. — Dissolve about i grm. of copper sulphate
or other copper salt in about 140 c.c, of water, and add 5 to
10 c.c. of nitric acid (sp. gr. r'42) to the solution, that is, from
8 to 10 per cent, of the acid. If the Bag electrode (p. 79) is
employed, usually about lao c.c. of water is sufficient, in which
case proportionately less nitric acid must be used. The solution
may either be electrolysed at ordinary atmospheric temperature,
or heated from 45-50° C. ; in the latter casSj the time required
for the complete deposition of the metal is considerably lessened.
The best CD. to employ is from o'S to i'2 amperes, with an
E.M.F. of from z to f% volts. A bright red film will be seen to
flash across the cathode almost immediately the circuit is com-
pleted. In cold solutiot\s, from 2} to 3 hours will be required
to completely deposit the metal ; with hot solutions the rate of
deposition is considerably accelerated.

End Reaction. — In order to ascertain whether all the
metal has been deposited out, the level of the solution may

Electro-Chemical Analysis. S7

be raised — ir a basin is being used — a few millimelres by
pouring in distilled water; if, after about 10 minutes, no copptr
is deposited upon tbe ciean platinum surface thus covered, the
electrolysis may be considered as finished. In other cases, where
a flag or cylindrical electrode Is employed, withdraw about i c.c.
of the solution by means of a pipette, transfer to a test tube,
make alkaline with ammonia, then acid with acetic acid, and add
a few drops of potassium ferrocyanide ; the formation of a brown
precipitate or colouration shows that there is still some copper
left in the solution, in which case, of course, it is necessary to
continue the electrolysis until, on further testing with the reagent,
no colouration is produced.

Washing the Deposit. — As the electrolyte contains an
excess of nitric acid in which the copper deposit is readily soluble,
it is recommended by some writers to siphon off the solution and,
at the same time, to run in distilled water ; by others, to add excess
of sodium or ammonium acetate to fix the free nitric acid.

CH3 . COONa + HNO, = CH, . COOH + NaNO^
These precautions, however, are not necessary, provided the
operator is a fairly quick manipulator. 'I'he author ])refers to have
a basin of water ready at hand, and an empty beaker or basin ;
then, as soon as the circuit is broken, to pour the solution into the
empty vessel and at once rinse out in the basiii of water, after
which to rinse out twice with distilled water, and, finally, with
about 10 c.c. of absolute alcohol, ; ' then, to drj' in the steam oven
for about ten minutes — or the dish may be dried by carefully
holding above the flame of a bunsen burner. When a flag or
cylindrical electrode is used, it should, on breaking the circuit,

' The alcohol used should be of good qualily, and must leave no re^tidilc
on evaporation. Instead of using absolole alcohol, methylated spirit, which
\ must contain no mineral nil, can be employed. It should, however, be tirst
purified by allowing it to stand over caustic soda for iwcniy-four hours and
then distilling. Quicklime is now added to ihe distillate, and, after standing
for nnolher twentyfoar bunrs, the methylated spirit slioulit again be distilled
directly from Ihe quicklime, without first filtering. Alcohol treated ia this
way is almost absolute.

88 Practical EFeetro- Chemistry.

be dipped into water, rinsed with distilled water, and finally v
alcohol ; this is best done with a wash bottle, the electrode being' J
held over a beaker in order that the alcohol may not be lost: I
Or it may be dipped in a beaker of alcohol.

The deposit obtained from nitric acid is bright red, and
generally has a more or less crystalline appearance. If the CD,
has lM2en too high the deposit will very likely be "burnt" and
have a brownish appearance, and may be of a powdery nature and
non-adherent. When it is desired to electrolyse over-nighl, and
this is often found very convenient, a CD. of from 0-2 to o'j of
an ampere is used. It is generally advisable in this case to add
more nitric acid, Ijecause owing to the reducing action of the
hydrogen liberated at the cathode, the nitric acid becomes
converted into ammonia. This formation of ammonia causes
the deposit to be spongy and of a bad colour, when it is difficult
to wash and weigh. For running over night about 2 c.c. extra of J
nitric acid should be added for every 100 c.c. of solution.

In commercial copper analysis, it often happens that there c
small quantities of arsenic or antimony present in the metal to befl
analysed. When they ate present there is a tendency for trace
of these elements to be deposited along with the copper. If any |
considerable quantities of antimony or arsenic have been deposited
their presence can generally be noticed by the deposit not being
so bright and having a dark appearance {the darkness due to the
deposition of antimony and arsenic is not the same as the " burnt "
amorphous appearance produced by employment of excessive
current densities). In order to eliminate this source of error, the
electrode with the copper deposit is heated to duJI redness for a
short time, by which means the copper is converted into oxide,
and the antimony and arsenic are volatilised. The copper oxide
is then dissolved in nitric acid, and again electrolysed. Holiard
and Bertiaux find that the addition of a small quantity of ferric
sulphate prevents the deposition of the arsenic. The addition of
quantities of a lead salt prevents the deposition of the
antimony. Where there are very lat^e quantities of antimony
: present, it is better to separate them by i

)y chemical J

Elsctro-Chemual Analysis, Sg

means before e lee iroly sing. Tin, bismuth, mercury, and especially
silver, also have a tendency to come down in small quantities, but
they are much less likely to do so if a considerable excess of nitric
acid is employed.

Sulphuric Acid. — The deposit obtained when sulphuric acid
is employed as the electrolyte is not nearly so brilliant as when
nitric acid is used, but is generally of a dull red appearance and
has no crystalline surface. The analytical results, also, are
hardly as good and reliable as in the preceding case : this method
is very often employed for commercial analysis.

The amount of sulphuric acid used should be from 7 to ro per
cent., and should not exceed the latter quantity. When concen-
trated sulphuric acid is employed, from 4 to 5*5 c.c. would
represent the above quantities. About l grra. of the copper
salt is sufficient. With a current of o'8 ampere at atmospheric
temperature the separation is completed in the course of two or
two and a half hours. At temperatures of from 50 to 60" the
separation is considerably accelerated. The E.M.F. required is
from 2's to 3'2 volts. The CD. should not be allowed to exceed
o'5 to o'S ampere, otherwise the deposit is spongy and dark and
non-adherent. In any case, owing to the tendency to formation of
spongy copper, this method is not so satisfactory as the preceding.

If a small quantity of hydroxylamine sulphate is added to the
solution, the deposit is much brighter, and less inclined to be
pulverent. When it is desired to carry out the deposition over-
night by use of a CD. of from o'l to o'a, the addition of 0^5 grm.
of hydroxylamine sulphate is sufficient, and it is not necessary
to add more than 3 c.c. of concentrated sulphuric acid; but
for ordinary work, when currents of from i to f2 amperes are
employed, about i grm. of hydroxylamine sulphate and about 5 to
6 c.c. of sulphuric acid should be used. Classen also recommends
the employment of small quantities of urea to prevent ihe forma-
tion of a spongy deposit. Although it undoubtedly has this effect,
its use is not to be recommended, because small quantities of
carbon and traces of platinum, from the anode, always contaminate

Practical Eleclro-Ckemistry.

the copper deposit, and thus the results obtained have a tendency
to be loo higli. The exact action of these substances is not clearly
understood. It is also as well to take similar precautions as those
already described in breaking the circuit and washing the deposit.

Potassium Cyanide— Of all the copper deixjsits, the most
beautiful is that obtained from solutions containing potassium
cyanide. The colour of the deposited metal is pinkish red and
beautifully smooth. But from other points of view the deposition
from cyanide solutions has no advantage over the deposits
obtained from acid solutions. In carrying out this process, the
copper salt is dissolved in about 30 or 40 c.c. of distilled water,
and then a freshly prepared solution of potassium cyanide added.
A greenish yellow precipitate is at first produced, but, on adding
more of the solution of potassium cyanide, it dissolves, a coloui-
less or straw-coloured solution being produced. Slightly more
potassium cyanide than is necessary to dissolve the precipitate
should be used, but any considerable excess must be avoided.
Generally speaking, from i to i"5 grams of potassium cyanide 1
should be used for every gram of copper salt taken.

The CD. employed should be from o'8 to V2 amperes. TheJ
E.M.F, required in cold solutions will be found to be about 5 to fil
volts j in warm solutions, from 4 to 5 volts. The whole of the J
copper is deposited in 2 to 3\ hours.

LITERA TURE.
Gibbs, Zeit. f. Anal. Chem., III. 334; lioisbaiidraii, Bull. Soc.
Chim., 1867,468; Merrick, Atiur. Chmi., II. 136; Vitrpia, Zeit.f.
Anal. Chem., XV. 335 ; Wrightson, Zeii. f. Anal. Chem., XV. 299 ;
Classen, Ber., XIV. 1632 and 1627 ; Classen and von Reiss, Zeit.f.
Anal. Chem., XIV. 246 ; Hampe, Berg, und Hiilten Zeit., XXI. 22cv,
and XXV. 113; Richd, Zeit.f. Anal. Chem., XXI. 116 j Rudorfl^",
Ber., XXI. 3050 ; Luckow, Zeil./. Anal. Chem., VIII. 23 ; Warwid^'j
Zeit.f. Anorg. Chem., I. 28s; Smith, Amer. Chem. Soc., XI!. '329 J"
Croasdale, Journ. Anal. Chem., V. 133 ; Foote, Amer. Chem. Journ.
VI. 333 i Meeker, Journ. Anal. Chan., VI. 267 ; Classen, Ber.,
XXVII. 2060; Heidenreich, ^«-., XXIX. 1585; Regelsberger, Z«/.
//f«f«c C//<-»7., 1891, XVI. 473; Oettel, CA^w. ZwVw/^, 1894,879 ;
'. .Fcmberger and .Smith, Avnr. Chem. Soc, XXI. 1001 ; Wagner,

{

Eieetro-Chemical Analysis. gi

Zeit. f. Ehklrochem., II, 613 ; Foerster and Seiiiel, Zeil. /. Amrg.
Chem., XIV. 106 ; Revay, Zeil. f. Elektrochem., IV. 313 i Hollard,
Compt. Reiidux, 138, 1003 ; KoUock, Anur. Ourn. Soc, XXI. 923 ;
Richards and Bisbee, Amer. Chens. Soc, 1904, 36, 530 ; Hollard and
Bertiaux, Bull. Sac. C/n'm., 1904 [iii.], 81, 900.

Hittorf's Explanation of Electrolysis of
Complex Cyanides.

When excess of a solution of potassium cyanide is added to a
solution of a copper salt the reaction lakes place in two stages ; in
the first place, a greenish yellow precipitate of copper cyanide is

ERRATA

On p. 91 the first equation would he more correctly written in
two stages, because cupnc cyanide is very unstable, being split
up immediately on formation into cuprous cyanide, thus—

2Cu(CN)., = iCuCN + (CN),,
The second ef|ua(ion would then read—

CuCNf + KCN = KCu(CN),
This correction does not alter the theoretical considerations, it
IS only a question of siihstimtiug the one formula for the other.

according to the equation —

2K + K,Cu (CN),=4KCN + Cu-
The copper thus liberated travels in the ionic state to the cathod!S7
where it is deposited, and the regenerated potassium cyanide dis-
solves the Cu(CN)a which has been deposited upon the anode
regenerating the salt K5Cu(CN)^. As, beside the fact of this
liberated potassium cyanide, there is always excess of cyanide
present, and as in any case the interactions are momentary, there
is never a deposit of cupricyanide perceptible at the anode.

Practical Rleclrff-Chemistry.

Many other methods for the quantitative deposition of copper
have been devised. Thus, for example, electrolysis of soUitions
containing excess of ammonium hydrate, together with ammonium
sulphate or, better, nitrate, but the depositions in this case are not
nearly so satisfactory as those already given, neither is there any-
thing to be gained by using Classen's oxalate method. The
ammonia method, as improved by Oettel, may sometimes be
found useful in separation of copper from other metals, and when
chlorides are present.'

Nickel.

Nicke! is a metal which it is impossible to deposit from
solutions containing free mineral acids or excess of organic acids.
Although a great number of methods have been suggested for
the electrolytic deposition of nickel, only a very few of these are
really of practical importance. Probably the most useful method
is that of Fresenius and Bergmann, in which the double sulphates
of ammonium or potassium and nickel, together with excess of
ammonia, are used. The nickel salt is dissolved in water, and then,
about 4 or 5 grams of ammonium sulphate, also dissolved in
water, added, and about 30 to 35 c.c. of ammonium hydrate
(sp. gr. 880) ; the solution is then made up to the required bulk.
If more than about i grm. of nicke! salt is used, the amount of
ammonium hydrate must be increased. As, however, the use of
large quantities of ammonium hydrate contaminates the atmo-:
sphere of the laboratory, it is better to employ smaller quanlities
of the salt rather than to increase the volume of ammonia ; on the
other hand, if loo Httle ammonia is used, the nickel deposit has
often a dark brownish appearance, and there is a tendency for,
nickel oxide to be deposited at the anode. Nitrates should not
he present, as their presence very considerably retards the rate of
deposition of the nicke!. When nitrates are present, the nickel
salt should be evaporated down to dryness with a little sulphuric:
acid, in order to expel the nitric acid, before being electrolysed."

Electro-Chemical Analysis. 93

The solution niay be electrolysed al normal temperature with
curreats from 1 to i'5 amperes; the E.M.F. will he from 2'8 to
3"5 volts. Under these conditions the electrolysis will be com-
plete in about two and a half hours. When the solution is warmed
to from 45° to so\ one and a half to two hours will he required.
The appearance of the deposit varies from a silver grey to that of
burnished platinum; sometimes it is difficult to tell where the
nickel deposit leaves off and the platinum begins.

End Reaction. — When the solution has become colourless,
withdraw about i c.c. by means of a pipette, and add a few drops
of sulphuretted hydrogen water ; if a brown coloration is pro-
duced, all the nickel has not been deposited. The electrolysis
is then carried on until, on further testing, no coloration is
produced. Yellow ammonium sulphide should not he used in
this test, because the yellow colour often masks the brown colour
of the nickel sulphide. Neither should only a single drop of
the electrolyte on the end of a glass rod be taken, as is often
recommended, in testing for the end reaction, because it is
often the case that no brown appearance is shown by a single
drop, yet on taking 1 c.c. of the electrolyte and treating it with
sulphuretted hydrogen, distinct traces of nickel can be found in
the solution.

As soon as all the nickel has been deposited, wash the cathode
several times with distilled water, then with a little alcohol, and
dry in the steam oven or over the bunsen flame^this, however,
must be done cautiously.

Removal of Deposit. — Nickel, when electrolylically
deposited, has a great tendency to become " passive ; " it is for this
reason, as a rule, very difficult to dissolve. Warm nitric or sul-
phuric acid may be used for dissolving it. Great care must be
taken that the whole of the nickel has been dissolved off the
cathode before it is again ignited, preparatory to further use.
The nickel deposit is at times so bright tliat it is not easy to tell
for certain whether the whole of the deposit has been dissolved or

PracHcai Electro-Chemistry.

is very harmful to the platinum electrode to ignite it while
r-there is still a trace of the deposit upon it, as it will be found that
I black marks are formed upon it which are only removed with great
^ 'difliculty.

Satisfactory deposits cannot readily be obtained from neutral
solutions of nickel containing neutral inorganic salts. Thus,
when a solution of a neutral salt of nickel containing sodium or
potassium sulphate is subjected to electrolysis, it is only by using
a high E.M.I'', that it is possible to deposit the nickel; but since,
owing to the ready conduct! bility of a solution of such a salt, a
high E.M.E, can only be obtained by employing a relatively high
current, or by having the electrodes placed a great distance apart —
this solution is not convenient to employ. Neither is a satisfactory
deposit obtained when tlie double cyanide of nickel and potassium
is used.

Organic Salts. — Very good deposits of nickel can be
obtained by using ammonium oxalate or tartrate, but when these
organic salts are used there is a tendency for the deposit to be
more or less contaminated with carbon ; if, however, the CD.
employed is not too high the results are usually quite satisfactory.

Double Oxalate.— The solution may be prepared by dis-
solving the nickel salt in water, and then dissolving 4 to 5 grams
of ammonium oxalate in water and adding this solution to that of
the nickel salt. It is best to electrolyse at a temperature of from
45° to 50°. With a current of i ampere the separation will be com- *
plete in from four to five hours ; the E.M.F. will be from 3 to y^
volts. When the deposition is conducted at ordinary temperatures, '
the time required is from 55 Lo 65 hours. The deposit may have |
a brilliant pobshed appearance or may be matt and greyish. \

Double Tartrate. — The deposit obtained when a solution
containing the double tartrate of ammonia and nickel is electrolysed
is generally very brilliant, and the results are quite as trustworthy
as when the oxalate is employed. About 3 grams of ammonium
; is sufficient, and the CD. should not exceed o-g ampere,

Ebctre-Ckemieal Analysis. 95

and is better to be 0-4 to o'6. With a temperature of about 40'
the deposition of the metal is complete in four to live hours ; the
E.M.F. is from 3-8 to 5^5 volts, Exceedingly brilliant deposits
are obtained when .1 current of o'lo to o'2o ampere is employed,
and the electrolysis conducted over tiijjht. Specks of carbon are
often noticed when the deposit obtained from organic salts is dis-
solved in acid, owing to carbon being deposited along with the
metal.

Ammonium Hydrate and Ammonium Borate. — This
solution is made up by dissolving the nickel salt in about 30 c.c.
water and then adding about 70 c.c. of a solution consisting of 50
grams of ammonium borate dissolved in 700 c.c, water and 300
C.C. of ammonium hydrate (sp. gr. o'88). Use a current of o's to
I ampere, and electrolyse at about 30°. Or the solution may be
electrolysed cold with a current of o'2 to o'4 of an ampere, and
run overnight. Sometimes there is a tendency for a slight anode
deposit to be formed ; if this is noticed, the addition of a few cubic
centimeters of strong ammonia will cause its disappearance. The
time required is from three to four hours. This method has been
found by the author to be very accurate, but the apjicarance of
the deposit is not so fine as when the other methods arc employed,
being usually of a dead silver-white colour, which at times has a
distinct brownish or smoky tinge.

Although a solution containing sodium phosphate and phos-
phoric acid gives such very good results in the case of cobalt
(p. 98), it is not so satisfactory when employed with nickel,
the results being rather low.

LITER A TURK.

Merrick, Amer. Client., II. 136; Gibbs, Ziil. f. Anal. Chcm.,
III. 336 ; Ibid., XI. 10 ; Ibid., XXII. 558 ; Wrightson, Ztit. f. Anal.
Chem., XV. 300 and 333 ; Cheney and Richards, Atner. Jour, of
Science and Arls,XlY. 178; OW, Zeit. f. Anal. CAem.,XVlU. 523;
Luckow,Z«V./. Anal. Chcm., XIX. 314 ; Rich^, ZHt.J. Anal. Chem.,
XXI. ; Classen and Von Reiss, Ber., XIV. 1622 and 2771 ; Classen,
Ber., XXVII. 2061 ; Vortmann, Zeit. f. Ekktrochem., I., 1894, 141 ;
Sucbt, Zeit. f. Anal. Chem., XXI. 493; Kohn and Woodgate, 5oi:.

Praetieal Electro-C/iemistry.

Ckem. hid., VIII. 256; Marshall, British Assoc. Report, 1886;
Riidorff, Zeit.f. Angcw. Chem., 1892, 6 j Braad, Zeit.f. Anal. Clicm.,
XXVIII. 588; Vortmann, Monatske/l., XIV. 536; Campbell and
Andrews, Ainer. Cheiii. Soc, XVII. 125 ; Oetiel, Zei/./. JHnktrockem.,
I. 192; Fresenius and Bergniann, Zeit.f. Anal. Ckem., XIX. 320;
Cohen and Glaser, Zeil. f. Anal. Clum., 38, 9 ; Taggart, Tr. Amer.
CAem. Soc, 35, 1039 ; Perkin and Prebble, Trans. Faraday Society,
1804.

Cobalt.

Nickel and cubalt art: ciiemically and physically very much
alike in character, and for this reason all chemical methods of
separating these metals are beset by considerable difficulties;
electrolytically the same difficulties exist. Cobalt is a mucli
more difficult metal to separate from its solutions in the pure
state than nickel. Not only are the results almost invariably
slightly loo high, but generally the appearance of the deposit
leaves very much to be desired, being often of a brown to black
appearance, and it is only rarely that it can be obtained as a
really brilliant deposit.

But, strange as it may appear, it often happens that the de-
posits which are marked by their unsightly appearance give just
as good— if not better — results analytically than those which are
bright. The author has made a very careful study of the best
electrolytes and conditions for obtaining accurate analytical
results and, at the same time, satisfactory deposits of cobalt.

Extremely brilliant deposits may be obtained when sodium
hypophosphite is added to the electrolyte, but as a rule the
results are about 5 per cent, too high, owing to the deposition, not
of pure cobalt, but of a phosphide of cobalt. Fairly correct
analytical numbers can be obtained by using ammonium sulphate
and ammonia, but the deposit is almost invariably of a dark-brown
coloiu". Of organic salts, ammonium tartrate gives the best
deposit, but the results ate usually slightly too high. The reason
that the electrolytic deposition of cobalt is generally slightly too
high is probably due to the fact diat cobalt is more readily oxi-
disable than nickel ; and yet this seems strange, because a good J

Ekctro-Chemkal Analysis. 97

deposit of cobalt retains its brightness in moist air equally as
well, if not better than nickel. The tnost satisfactory results, both
analytically and from point of view of the appearance, are obtained
with sodium phosphate (NaHaPO,) and phosphoric acid.

Ammonium Sulphate and Ammonia. — Make up the
solution as described under nickel, except that it is better to add
a rather larger quantity of ammonia, from 35 to 40 cc. (sp.
gr. o'88). In order to obtain the best deposits it is advisable to
commence electrolysing with a low current of from o'3 to 0-4
ampere, and the temperature of the solution should be from 30'^ to
40°. After the electrolysis has proceeded for about an hour,
the CD, may be increased to i ampere. The removal of the last
traces of cobalt takes considerably longer than is the case with
nickel, the deposition often requiring niore than four or five hours,
and there is therefore a tendency to obtain rather low numbers,
unless the current is passed for a considerable time.

End Reaction. — This is found by the same method as that
used for nickel, i.e. with sulphuretted hydrogen. Or take a few
drops of the electrolyte, place in a test tube, make just acid with
acetic acid, and add about 2 cc. of ammonia thiocyanate ; then
add 2 cc, amy! alcohol and i cc. ether. On shaking up, if any
cobalt remains in solution an intense blue colour is produced
in the ether and amyl alcohol layer. This latter lest is extremely
delicate.

Removal of Deposit. — Contrary to the experience with
nickel, cobalt deposits arc extremely readily removed on the
addition of moderately strong nitric add. The cobalt shows no
tendency to assume the passive state.

Ammonium Tartrate, — The cobalt is dissolved in a little
water and a solution of about 3 grams of ammonium tartrate
added to it, after which the mixture is made up to the required
volume with distiOed water. The pink solution thus obtained is
subjected to electrolysis with a commencing current of o'z to 04
ampere, which is raised after an hour to i ampere, or, in cases

Practical Electro-Ckemistry.

where the electrolysis is conducted overnight, the lower current is
employed throughout. With the higher current the time required
is about four oc five hours. The results obtained are usually
slightly high, owing to small quantities of carbon being deposited
along with the cobalt. The deposited cobalt often has a brilliant
burnished appearance, more especially when the electrolysis is
carried out with low currents. It may, however, have a smoky
and brown surface.

Ammonium Oxalate.— The solution is made up in a
similar manner to that described for nickel (p. 94). The CD.
should be low at the commencement of the operation, but may be
raised to i'4 ampere after the first fifty minutes. Generally speak-
ing, the deposit has a very poor appearance, hut sometimes it is
quite bright, as if it had been burnished. The time necessary for
the operation varies from 5 to 6i hours. When a low current is
employed and the electrolysis is conducted overnight, it is usually
advisable, in order to remove the last traces of cobalt, to raise the
current to i or I'j amperes for half an hour before disconnecting
the electrodes. As with the tartrates, so with oxalates, small
traces of carbon are usually deposited along with the metal, and
the results are thus slightly high.

Ammonia and Ammonium Borate. — The cobalt J
deposits obtained by electrolysing solutions containing borates are
not generally very sightly, and the results are usually rather high,
but are more accurate than by any of the previous methods
described. The solution and the conditions are the same as those
described under nickel (p. 95). I

Sodium Phosphate and Phosphoric Acid.— The solu-
tion from which the most exact results can be obtained is one
containing sodium di-hydrogen phosphate and a little free
phosphoric acid. The solution is made up by adding 2 c.c. of a
5 per cent solution of phosphoric acid to the cobalt salt, dissolved
in 70 to So c.c. of water ; and then 20 to 25 c.c. of a 10 per cent,
solution of di-hydrogen sodium phosphate is run in from a burette, |

The solution should be stirred with a glass rod during the addition
of the sodium phosphate, to prevetil thi: formation of the double
^ll of cobalt aiid sodium phosphate. The solution is then made
up to the required bulk, and electrolysed.

It is important to use di-Aydregai sodium phosphate or the
corresponding ammonium or potassium sail, because if Ni.HPO,
or Na^.PO^ arc employed, the double salt of sodium and cobalt
phosphate precipitates out as an almost insoluble purple powder,
and it requires the addition of large quantities of phosphoric acid
to bring it into solution again. It might be supposed that equally
satisfactory results would be obtained by adding a large quantity of
phosphoric acid in the first case, but as it is very difficult to gauge
ihe right quantity of phosphoric acid which it is necessary to add,
this is not to be recommended.

The electrolysis should be commenced cold with a low CD.
of o'B to o'3 ampere; after about an hour the current may be
raised to o^S to vs ampere, and the solution warmed to from 50°
to 60°. It often happens that when the electrolysis has jiro-
ceeded for some thirty or forty minutes a brown anode deposit is
obtained ; this is especially the case when the electrolysis is
commenced hot, the deposit being in this case sometimes quite
black. It will be found that the addition of o'l to oa grm. of
hydroxylamine sulphate or chloride causes the almost immediate
disappearance of the anode deposit. If, after being -removed,
the deposit returns again, a further addition of the hydroxylamine
salt may be made. Formaldehyde can also be used to remove
the anode deposit, but it acts very much more slowly. The
following conditions will be found to give satisfactory results —

CU o-J increasing lo ll a[ni>«re.

E.M.F. , , . 2-0 10 35 volls.

Temp. . . cold at commencemeiil, bul may be inisal

to 50 or 60° after about an hour.
Time . , . . 4 to 6 hours.

The deposit is almost invariably brilliant, being very rarely
marred by burning. It is an advantage, after the solution has
become colourless, to add a few drops of very dilute ammonia to

'VU^i^^'^

loo Practical EUctro-Ckemistry.

neutralise the excess of acid which has been formed during the
electrolysis. The neutralisation of the acid causes the last tr
of cobalt— which are always rather difficult to precipitate — to be.
deposited much more rapidly.

This method gives a better deposit and more accurate results
than any other process at present in use,

LITERA TURE.

Gibbs, X(n.f.Anal.Ckem.,\\\.^ib\ /6i,/.,Xl. lo j /6ii/.,XXU.
S48 i Wrightson, Zeii. /. Anal. Chem., XV. 300 and 333 ; Schweder,
Zeil.f. Anal. Chem.,X.\l. 344; Ohy, Zeit. /. Anal. Chem.,KVin.
523; Luckow, ir<//. / Anal. CAem.,KlX. 3H; JlSchi, Zeil. /. Anai.,
CAent.,ii6i Schachi, Zei/./. Anal. CAem., XXI. ^g'i; Brand, ifeiV.jC
Anal. CAem., X.XVIII. 588 ; Cheney and Richards, A»Kr. Jourii. <^
Science and Arls, XIV. (3), 178 ; Classen and Von Reiss, Ber., XIV.
1632 and 3771; Classen, 5«f., XXVII. 2061 ; heKoy, Compt.Rnnius,
CXII. 722 ; Vorlmann, MoHatskift., XIV. 536; Kohn and Woodgate,,
Joiirn. Sec. C/um. Ind., VIII. 256 ; Marshall, Brithk Assoc. Report,
1898, 300; Oettel, ZeU. f. EUktrochem., I. 195; Fresenius and
Bergmannj Zeit. J. Anal. Chem., XIX. 329; I'crkin and Prebble,
Trans. Faraday Sof., 1904.

Iron.

Owing to the fact that, on electrolysing neutral solutions of
iron salts of inorganic acids, ferric hydrate is always precipitated
at the anode, and that it is not possible to deposit iron quanti-
tatively from solutions acidified with mineral acids, it is only
possible to obtain deposits of iron, which are satisfactory from an
analytical point of view, by using salts of organic acids
electrolyte. It is a well-known fact that the presence of most'
organic acids prevents the precipitation of iron from its salts
hydrate by means of anunonia, atid this fact is sometimes made
use of in ordinary qualitative analysis to separate the iron from
Hucb metals as cerium, for example. But among organic acids or
salts of organic acids, there are very few which can satisfactorily be
employed as electrolytes in the electrolytic analysis of iron ; the
reason being tliat, with organic acids of higher molecular weight,

Electro-Chemical Analysis.

the iron deposit invariably contains traces of carbon, which at
times are so considerable as to cause really serious errors.
Furthermore, practically only salts of ammonia may be employed ;
salts of sodium or potassium cannot be used because, as the
organic acid is decomposed, carbonates of these metals are
produced, and this causes precipitation of hydrated carbonate of
iron. But whatever organic acid is employed, even with oxalates
and tartrates, carbon is invariably deposed to a more or less
extent with iron. Further, the higher the current density, the
greater the tendency for deposition of carbon to take place. As
a matter of fact, the small traces of carbon deposited along with
the iron, when the ammonium salts of oxalic and tartaric acid
are employed, do not seriously interfere with the value of the
process, because it is extremely difficult, if not impossible, to
throw out the last traces of iron which remain in the solution, and
it is found that the slight error due to the deposition of carbon,
along with the iron, is practically counterbalanced by the small
traces of iron which remain in the solution. There is, however,
some diversity of opinion upon this subject; Classen, for
example, considers that if the current is kept below r ampere,
carbon is not deposited ; other authorities, however, are unable
to agree with Classen upon this point.

Ammonium Oxalate.— This method, which was first
suggested by Classen, is the one generally recommended for
analysis of iron. The iron solution, which should he free
from chlorides or nitrates, must be poured into the solution of
ammonium oxalate, if it is in the ferrous condition ; otherwise, if
the solution of ammonium o.xalale is added to the solution of the
ferrous salt, a precipitate of ferrous oxalate is produced, which can
only be dissolved again with considerable difficulty, if, indeed, it
is possible to dissolve it at all. With ferric salts, it does not
matter whether the oxalate is added to the iron salt or the iron
salt to the oxalate.

Dissolve 5 to 7 grm. of ammonium oxalate or acid ammonium
oxalate in a small quantity of hot water, and add the iron salt —

Practical Ekctro-Chemistry.

ferrous ammonium sulphate— also dissolved in a little water, and
make the solutiou up to about 150 c.c As the electrolysis
proceeds it will sometimes be noticed that a small quantity of
ferric hydrate separates out in the form of a flaky precipitate ; if
this takes place it is necessary to add small quantities of oxalie
acid to dissolve the precipitate. The formation of this precipitate,
which is due to the solution becoming alkaline as the electrolysis
proceeds, is the chief objection to the oxalate method, because
more attention is required than in the case of the tartrate, in
which this does not occur. According to Smith and Muir,' the
addition of 5 c.c. of a saturated solution of borax is an advantage,
extremely good results being obtained when this substance is
present.

CONDITIONS. '

CD. .
E.M.F. .

Temp. .

> to I '2 amper«. | CD. .

o 4-3 volts. E.M.F.

rmal. Temp. .

o 5 hours. Time .

II.

2'5 to 3'5 hours.

End Reaction. — Withdraw at least i c.c. of the solution
from the electrolyte, acidify with hydrochloric acid, and add at
least two or three cubic centimeters of a solution of potassium
thiocyanate. As long as a red coloration is produced it is
necessary to continue the electrolysis.

The deposited iron has generally the appearance of polished
steel, but at times it has a rather foggy look, or may have
brownish streaks. As soon as the electrolysis is finished, the
deposit is washed, as rapidly as possible, with distilled water, and
then with absolute alcohol, and dried either in the steam
by carefully holding above the Bunsen flame. If it is not dried
fairly rapidly, the results may be too high, owing to slight super-
ficial rusting. Dilute sulphuric acid is the best solvent. When
the deposit is dissolved, minute specks of carbon may be noticed
in the solution, and the hydrogen given off usually has that

Ckem. Sot.

18. fi54.

Electro-Chemical Analysis. 103

peculiar snteil which is produced when metals conlaiiiing carbon
are dissolved in acids.

Ammonium Tartrate— Dissolve 3 to 4 grm. nf ammonium
tartrate in water, and add the iron salt to the solution ; or ihe
solution of ammonium tartrate may be added to the iron solution.
The yellow solution thus obtained is electrolysed with a CD. of
r to I-3 amperes, the E.M.F, being about 4'7 to 6 vdts. One
advantage in using the tartrate solution is that there is never
precipitation of ferric hydrate, as is often the case when
areimonium oxalate is employed ; therefore the process requires
less attention. It will be found, as in the case of oxalates, that
the metallic deposit always contains traces of carbon ; therefore
the tendency is for the results to be fractionally too high. But
according to a long series of experiments carried out by the
author, if the CD. is not allowed to rise too high, this is
negligible. With currents of from o'S to I'l ampere, the time
required for complete deposition is from aj to 4 hours. When
the electrolysis is carried out overnight, a current of 0-25 to
0-4 ampere is sufficient.

It will he found that the iron from ferric salts takes an
appreciably longer time to deposit than the iron from ferrous salts.

Electrolysis of Iron Salts containing an
Organic Radical.

Many pharmaceutical preparations of iron contain the iron
united with an oiganic acid. Since the presence of the organic
radical prevents the precipitation of the iron on the addition of
ammonium hydrate, the analysis of these substances by ordinary
chemical methods is rather troublesome. These iron salts can
often be directly analysed elect rolytically by dissolving them in
water and adding 4 or 5 grm. of ammonium tartrate, making up
to the required bulk and electrolysing.

Generally si>eaking, the deposition is rather more protracted
than when iron salts with an inorganic radical are analysed, but

PraeHad Electro-Chemistry.

\ ttie excess of time is not very great except with iron salts of
citric acid, in which case it is often very tedious.

LITERATURE.

Wrightson, Ztil. J. Anal. CItem., XV. 305 ; Luckow, Zeti.f. Anal.
Chem., XIX. 18 ; Classen and Von Reiss, Ber., XIV. 1622 ; Classen,
Zeit.f. EUklTochem., 1. 288; Smith, Amer. Chtm. Journ., X. 330;
Moore, Cktm-News, LIII. 209; Brand, Z«/./ Anal. Chem., XXVill.
581 ; RiidorfT, Z«/./. Angirai. Ckem., XV. 19S ; Vortmann, yt/"u«a/-
skeft., XIV. 542 ; Heidenreich, Ber., XXIX. 1585 ; Kohn, British
Assoc. Report, 1896; Avery and Dales, Ber., 33, 64; Verwer and
GoU, Ber.. 32, S06 ; Averj- and Dales, Ber., 32, 2233.

Mercury.

Ordinary chemical methods of analysing mercury are rather tire-
some, hut it is very readily separated from its solutions by means.
of the electric current. Further, it adheres tenaciously to platinum,
especially if it has heen sand-blasted, and is therefore readily
weighed. A gauze flag electrode is hest suited for determinations
of mercury, hecause very considerahle quantities of mercury will
adhere to it, without falling off". The author has also obtained
very satisfactory results with a gold cathode containing 5 per cent,
of plalinum to stiffen it. The mercury adheres very firmly, pro-
ducing an amalgam. It is, however, readily removed by heating
the electrode in the Bunsen flame. See Note, p. 284.

The solutions from wliich the metal may be deposited are
those containing nitric or sulphuric acid; hydrochloric acid can
also be employed, and very satisfactory results may be obtained
from solutions in sodium sulphide or in potassium cyanide.

Sulphuric Acid. — The mercury salt is dissolved in water,
and from 1 to 2 c.c. of concentrated sulphuric acid added ft«
every 100 c.c. of solution. The electrolysis is conducted with H
CD. of from o'3 to o'8 ampere; towards the end of the opera*
tion the current may be increased to i ampere. The potentiid
difference is from 3"3 to 3*6 volts. The operation can be cai
it at ordinary temperatures, but it is more rapid when a temperatur^

Electro-Chemical Analysis.

of from 50° to 60° is employed. During the electrolysis merciirous
salts are often produced owing to cathodic reduction, and are
precipitated. As a rule, however, this causes no trouble, as they
gradually pass into solution, and are then deposited out as metallic
mercury. The addition of a few drops of hydrochloric acid causes
their more rapid disappearance. As a matter of fact, mercurous
salts can be directly employed; in this case they are suspended in
water with the requisite quantity of sulphuric acid {see above),
a few drops of hydrochloric acid added, and the current passed.
Even such insoluble compounds as cinnabar can be analysed in
this way. The most satisfactory method of getting rid of the
mercurous salts is to add a small quantity of ammonium or
potassium persulphate. The persulphate gradually oxidises the
mercurous salt to the mercuric condition, It is not advisable
to add large quantities of the persulphate at one time; about
0.1 grm. should be added from time to time. The formation of
the mercurous salt can be entirely prevented by adding the
persulphate at the commencement of the electrolysis.

End Reaction. — In order to ascertain whether all the
mercury has been deposited, about l c.c. of the solution is drawn
off, and a little sulphuretted hydrogen water added ; if the solution
becomes brownish, this shows that all the mercury has not been
deposited. Or a small piece of thin copper wire may be hung
over the cathode, so that it just dips in the liquid; if, after
ten minutes, there is no deposit of mercury on the copper wire,
the electrolysis may be considered at an end.

Washing the Deposit.— The mercury adheres firmly to
the cathode in the form of minute globules. As soon as the
process is finished, the cathode is washed several times with water
and dried in a desiccator. The use of alcohol is not permissible,
as it loosens the globules and also coats the mercury with a thin,
greyish pellicle. When, however, a gold cathode is employed,
there is no objection to washing with water, and then with
alcohol, because the mercury is amalgamated with the surface of
the cathode- As drying in a desiccator takes some hours, it is

I06 Practical Electro-Chemistry.

therefore recommended to use a goid flag electrode, made of sheet
gold : because, after washing with absolute alcohol, the electrode
can be dried in a few minutes by means of an air blast. It should,
however, after the alcohol has been driven off, be placed in a
desiccator for half an hour before weighing. The mercury is
readily removed from the gold electrode, by heating it to low
redness in the flame of a Bunsen burner.

Nitric Acid. — Add from z to 3 c.c. of concentrated nitric
acid to every 100 c.c. of solution, and electrolyse at a temperature
of about 50". The time required for about o'S grm. of mercuric
chloride is from 4 to 5 hours.

CONniTIONS.

CD 01 to 0'2 ampere.

E.M.F 3toa'3 volLs.

Owing to the presence of nitric acid the end reaction in this case
is best ascertained by neutralising with ammonium, and adding
a few drops of hydrochloric acid and then sulphuretted hydrogen.

Hydrochloric Acid. — When hydrochloric acid is employed
as the electrolyte, only a small quantity should be used, not more
than I c.c. to the too c.c. of solution. The current conditions
are the same as those described for sulphuric acid. Several other
methods have been suggested for the electrolysis of mercury
solutions, Classen, for example, uses ammonium oxalate ; Edgar
F. Smith obtains good results from a solution containing potassium
cyanide, and also from solutions containing sodium sulphide.

Sodium Sulphide. — From 20 to 25 c.c. of sodium sulphide,
prepared as described on p. 281, is added to the mercury solution,
which is then made up to 125 to 150 c.c, and electrolysed under
the following conditions : —

CD OTI 100-15 ampere.

E.M.F 2-5 to 27 volts.

Temp es^tpyo"

Time 4 lo S hours.

If the mercury salt is contained in an acid solution, the m
can be precipitated as sulphide by passing hydrogen sulphid

Electro-Chemical Analysis. 107

it, which, after filtering off and washing, may he dissolved in
20 to ag c.c. of sodium sulphide solution.

The deposit of mercury obtained is bright and adherent.
E. Smith has employed this method for the direct analysis of
cinnabar. The finely powdered cinnabar is placed upon the
bottom of a weighed platinum basin, which is made the anode,
and the mercury deposited upon a platinum spiral, which should, for
this purpose, be sand-blasted. The estimation, according lo Smith,
employing the conditions set out above, does not exceed 3 hours.
Potassium Cyanide.— From i to i'5 grm. potassium
cyanide is used for every o'l to o'a grm. of metallic mercury.
CONDITIONS.

CD o'ol to o'lo ampere.

E.M.F i'6 103-4 volts.

Temp 65°

Time 3 'o 4 hours.

The metal when deposited from this solution coats the electrode
evenly, and has a greyish appearance.

Estimation of Mercury in Pharmaceutical
Preparations.

It sometimes happens that the estimation of mercury in

pharmaceutical preparations, especially substances containing an
oi^anic radical, is a matter of considerable difRculty ; electro-
lyticaliy, however, there is no difficulty in the estimation.

It will depend upon circumstances which of the methods
described will be found the most convenient to employ. Mercury
tannate, for example, dissolves readily in sodium sulphide ; it can,
therefore, be readily deposited from this solution. Lister's cyanide
may be estimated from cyanide solutions. Mercury salicylate, and
other organic substances which do not readily dissolve in either
of these solvents, are best determined from solutions containing
nitric or sulphuric acid.

When nitric acid is employed, the substance should be covered
with a little fuming nitric acid, and heated until most of the organic
material lias been oxidised. The product is then diluted with

Practical Electro-Chemistry.

water, and electrolysed as usual. When sulphuric acid is used,
the substance is covered with concentrated sulphuric acid, about
I grm. of ammonium or potassium persulphate, and the mixture
heated until the, at first, black mass becomes nearly colourless ; it
is then diluted with water, filtered if necessary, and electrolysed
as described on p, 104.

Note. — When a basin electrode is used as cathode for the
analysis of mercury, there is a tendency for the results to be too
low, more especially when the temperature of the bath rises
above 50' — the electrolysis is often conducted at 70°; — Bind-
schedler has shown that this is due to the evaporation of the solu-
tion, and the consequent exposure of the already deposited metal
to the atmosphere. With the flag electrode, which dips completely
below the surface of the solution, this difficulty does not arise.

LITER A TURK.
Classen and Ludwig, Ber., 18, 323 ; Hoskinson, Amcr. Ckem.
Journ., 8, 209 ; Smith and Kerr, Anier. Cliem. Joum-, 8, 206 ; Smith
and Vra.n\ic\, Afner. Chcm.Jaurii.,W, 264 ; Vortmann, 5«'.,24,3749;
Brandt, ZeiL/. Anorg. Chem., 1891, 202 ; RiidorfF, ZiU.f.Anorg. Ckem.,
188S, S ; Schmucker, Journ. Amer. Ckem. Soc, 15, 204 ; Rising and
Lenher, S^r^. und Hiilten Zeit., 65, 175 ; Wallace and Smith, yoKrn.
Amer. Ckitn. Soc, 18, 169 i Femberger and Smith, Journ. Amer.
Chein. Soc, 21, 1006 ; KoUoek, Journ. Amer. Ckem. Soc., 21, 911 ;
Bindschedler ; Zeit. f. Eleklrochem., 8, 329; Medicus and Mebold,
Zeit./. Ehktroclum., 8, 690.

Antimony.

One of the most important properties of antimony is its power
to form complex anions. It forms, in fact, two monovalent anions,
antimonious (SbOj) and antimonic (ShOa ). It further has the power
of forming thio-salts, in which the oxygen is replaced by sulphur ;
we have thus thio-antimonious anions (SbS.j) and thio-antimonic
anions (SbSj), From the point of electro-chemical analysis the salts
of these of anions are of the greatest importance, because it is from
them that we obtain the most satisfactory deposits of antimony. As
a matter of fact, rJnlimony can be precipitated from acid solutions '

ElectrO'Cltemical Analysis. Tog

and from solutions containing potassium oxalate, but the deposits
do not adhere firtDly or satisfactorily to the cathode. Tartrates
may also be employed, and satisfactory quantitative results can be
obtained from neutral tartrate solutions, which are electrolysed at
high temperatures,

Ammonium sulphide or sodium sulphide may be employed,
preferably the latter, because, when ammonium sulphide is used,
especially if it contains poly sulphides, there is usually a certain
quantity of sulphur deposited upon the precipitated metal. It is
a rather difficult matter to remove this sulphur, which generally
forms a thin and homogeneous skin over the metallic deposit.
But after washing with alcohol, the sulphur can be removed by
carefully rubbing with a piece of rubber-tubing fastened on to the
end of a piece of glass rod. Of course another objection to the use
of ammonium sulphide is its unpleasant smell, and its action upon
the metallic instruments in the laboratory. Sodium sulphide,
which was first suggested by Classen, is not ojKin to the above
objections, and gives very good results ; it has the additional
advantage that, when present in excess, it prevents the deposition
of tin. The sodium sulphide (NajS) used must be pure; the
method of preparation will be found on p. 281. A. Fischer and
also A. Hollard recommend the addition of potassium cyanide to
the sodium sulphide solutions, as this prevents the formation of
poly sulphides, and consequently the deposition of sulphur. The
action of the potassium cyanide upon the polysulphides is to form
potassium thio-cyanate thus —

Na-jSi + 3KCN = 3KCNS + Na^
The sodium sulphide * may be added in excess to the solution of
the antimony salt, so long as this is not acid ; but it is preferable
to acidify with dilute hydrochloric acid, and saturate the solution
with sulphuretted hydrogen. The precipitated antimony sulphide
is then filtered and washed with hot water, and can be directly
dissolved off the filter-paper by pouring on sodium sulphide.

' Potassium sulphide \i not permissible, because complete; deposiliuo does
not take place from il5 solution.

Gauze or roughened electrodes should be used for anlimony
deposits, because the metal does not adhere well to polished
surfaces, and therefore such surfaces can only be used when the
amount of antimony is very small.

70 to 80 c^, of the solution of sodium monosulphide, pre-
pared as described 011 p. z8i, is used for dissolving the sulphide,
or is added to the antimony solution. It is best to electrolyse at
a temperature of 50° to 60°, with a current of from o'8 to i
ampere; the E.M.F, is between i'3 to 2-5 volts. Under these
conditions the time required is from 2^ to 3^ hours. When a cold
solution is electrolysed with a current of from 02 to 0^4 ampere,
the time required for complete deposition is from 17 to 18 hours.

The reaction may be represented as one of reduction of the
anion SbS."'.

3Na-SbS.;" + 3H = 3Na-HS' + 3Sh
When antimony is obtained in solution with poly sulphides, as, for
example, in analysis, the excess of sulphur which is then present
would make the solution unsuitable for electrolytic determinations.
Classen recommends heating the solution with an excess of
ammoniacal hydrogen peroxide until it becomes colourless. It
may happen, if too large an excess of the peroxide has been
added, that, owing to the decomposition of the alkali sulphide,
antimony sulphide is precipitated. As soon as the solution is
colourless, or if sulphide of antimony has been precipitated, about
70 c.c. of the solution of sodium sulphide is added. Or, instead
of using hydrogen peroxide, a solution of potassium cyanide may
be added until the yellow solution becomes colourless.

End Reaction. — The end of the electrolysis can be told by j
hanging a small piece of platinum wire over the cathode for about I
ten minutes; if there is no deposit, this shows that all the
antimony has been thrown out. Or i c.c. of the solution may be I
withdrawn, and acidified with hydrochloric acid. An orange |
precipitate or coloration shows that the process must be |
continued.

If ammonium sulphide is used instead of sodium sulphidt^itl

Eleciro-Chemical Analysis.

is best to employ Ibe hydros ulphide NH^HS, as there is less
lilcelibood of sulphur being deposited at the cathode, although
as a rule a certain amount is deposited on the anode.

Removal of the Deposit— The antimony can be dissolved
off the cathode by means of a mixture of nitric and tartaric acids.
When tartaric acid is not used, antimony oxide is formed, and this
s rather difficult to

Deposition from Sulphide Solutions containing
Potassium Cyanide.— The antimony sah or sulphide is treated
with 60 or 80 CO. of sodium sulphide, as already described, and
from zo to 30 cc. of a freshly prepared solution of potassium
cyanide run into the solution ; if this quantity is not sufficient
to cause the solution to become colourless, more must be added
tmttl the solution is no longer coloured.
CONDITIONS.

I CD 0*3 lo o-S ampere.

I E.M.F 17 lo 1-9 volts.

Temp 20° to 30°

Time 5 lo 6 hours.

With currents of o'l to o'2 ampere and in a cold solution, the
time required is about 18 hours.

From Tartrate Solutions. — As is well known, antimony
compounds readily dissolve in tartaric acid or tartrates. The
deposition of antimony from solutions in free tartaric acid is very
slow, and the E.M.F. required is high owing to the small amount
of ionisation of tartaric acid. On the other hand, the whole
of the antimony can be deposited in 2), to 3 hours, when a neutral
solution of ammonium tartrate is employed. When deposited
from cold solutions, the metal is rather amorphous in character,
but with care it may be washed and dried. When deposited
with low currents and at high temperatures, the metal adheres
very firmly and is often quite brilliant. The solution is prepared
by dissolving the antimony salt in water, and adding 8 to to grm.
of ammonium tartrate; or it is dissolved in tartaric acid, and the
solution then neutralised with an

Pructicnl Electro-Chemistry.

CONDITIONS.

11.

K.M.F.

, CD. . . o-a ampere.

I K.M.F. . 2-5 volts.

I Temp. . ordinary temperature

I Time . . all nifhl.

LITERA TURE.

farodi and 'iA-A.^aa£\m,Zeit.f. Anal. CAew^XVIII. 588 ; LuckowJ
Zcit.f. Anal. Chcm., XIX. 13 ; Classen and Von ReJss, Bir., XIV. 1
Jill/., XIV. 1622 ; IMd., XVII. 3467; /6uf., XVIII. 1104; Brand^l
CkiM. 2a/., 1886. i2ig; Vortmann,5«r.,XXIV. 2762 ; Kohn, Brt/tik
Assoc. Rgfior/, 1896, 251 ; Riidorff, Zei/.f. Angew. diem., i8q2, 199 ;
Classen, Ber., XXVII. 2060 ; Fischer, Ber., S6, 2348 ; Hollard, Bull.
Sec. dim., 29, 262.

Tin. *

Tin, like antimony and arsenic, forms oxides which have an
acidic character, and, like these elements also, has the power of
forming thio-salts. The capacity for giving thio-salts is linked with
the capacity of these metals to form acid oxides. Just as these
oxides dissolve in alkalis, so the sulphides dissolve in alkaline
sulphides. As is the case with antimony, so one of the most
satisfactory methods for depositing tin is from the thio-salts ; in
this case, however, not, as with antimony, from the sodium salt,
but from its ammonium salt. In weak solutions of sodium
sulphide, tin is only partly precipitated, while in strong solutions
it is not thrown out at all. Hence we have here a method for
the separation of tin and antimony. See p. 181,

Deposition from Ammonium Sulphide. — Sufficient
yellow ammonium sulphide to dissolve the precipitate first formed
is added to the solution of the tin salt. If the solution is acid it
must first be neutralised with ammonia ; and if in doing this a
slight precipitate is caused, it may be neglected, because the
of the ammonium sulphide will dissolve it. The solution
is then made up to the required volume with distilled water, and
electrolysed at a temperature of 50' to 60". The current density

a/ysis. 113

may be from i to I'S amperes, and the E.M.F. will be from 3'5
to 4'5 volts. With these conditions the time required is from 35
to 4^ hours. If sulphur is deposited upon ihe cathode it can,
after washing with alcohol, he removed by gentle rubbing with a
piece of rubber fixed on the end of a glass rod.

When, as is sometimes the case in analysis, the tin is already
in solution with sodium sulphide, it is necessary to convert it into
the ammonium salt before electrolysing it. To do this, Classen
recommends the addition of from 20 to 25 grm. of /wrc ammonium
sulphate to the solution, which is then gently warmed until no
more sulphuretted hydrogen is evolved ; it is then kept gently
boiling for another 10 or 15 minutes. When the conversion into
ammonium sulphide is complete, the solution becomes greenish
yellow. If the mixture is heated too long, tin sulphate or hydrate
may separate out, in which case it is dissolved in ammonium
sulphide. If, after cooling, any sodium sulphate should crystallise
out, it is dissolved by the addition of water.

End Reaction. — Withdraw about i c.c, of the solution,
acidify with dilute sulphuric acid, and gently warm. If the solu-
tion deposits brown or yellow stannous or stannic sulphide, the
electrolysis must be continued. A small quantity of sulphur will,
of course, be precipitated, because of the decomposition of the
ammonium sulphide.

Double Oxalate. — According to Classen, satisfactory
deposits of tin can be obtained by electrolysing a solution con-
taining ammonium oxalate and oxalic acid. But unless oxalic
acid is present in excess, flakes of tin hydroxide are precipitated,
owing to the solution becoming alkaline from the decomposition
of the ammonium oxalate. In preparing the oxalate solution, 4
grm. ammonium oxalate should be employed for every 0-3 grm.
of tin present, and 9 to 10 grm. of oxalic acid. The solution is
electrolysed at a temperature of from 50° to 60°, with a current of
I to I'S amperes, The electrolyte may be kept acid with acetic
instead of with oxalic acid. When acetic acid is used, the appearance
of the deposit is usually better than when oxalic acid is employed ;

I
J

Practical Electro-Chemistry.

it is also to be recommended because it is not decomposed by
the electric current, wtiereas oxalic acid is.

Removal of the Deposit. — Tin adheres very firmly to the
electrodes, and does not readily dissolve in acids ; it is therefore
sometimes recommended to first coat the electrodes with copper
or silver. Iti order to remove the deposit, the electrode must he
boiled with strong hydrochloric acid, but even then it is only very
slowly dissolved. Nitric acid can also be employed, but the
surface becomes coated nith oxide, which requires to be removed
in order that the acid may attack fresh surfaces. Another method
is to cover the tin deposit with dilute sulphuric acid and
make the electrode the anode, a piece of copper wire serving as
cathode.

For purposes of electrolysis, half a gram of tin can be dis-
solved in hypochloric acid ; but this is rather a tedious operation.
It is better to use tin ammonium chloride, SnCl,, iNH,Cl.

LITERA TURK.

Classen iintl Von Reiss, Ber., XIV. 1622 ; Luckow, Zeit.f. Anal.
Chem., XIX. 13; Classen, Ber., XVII. 246?; and XVIH. 1104;
Bongartz and Classen, .fffr., XXI. 2900; Gibbs, CA«». iVirwJ, XL. agi ;
RaAoiS, Zeil./. Angew.Chem.,\ii)2, 196; Classen, .ffifr., XXVII. 2074 ;
Engels, Zeit. f. EUktrochem., II. 417 ; Freudenberg, Zeit. f. Pkys.
Chan., XH., 121 i Kohn, Bril. Assoc. Report, 1896; Campbell and
Champion, Joiirn. Artier. Chan. Soc, 20, 687.

Cadmium.

Cadmium cannot be deposited from solutions which contain
much free mineral acid, although the presence of a very small 1
quantity is advantageous, as it prevents the deposited metal I
coming down in the spongy condition. Good deposits can rarely J
be obtained from neutral or alkaline solutions, the cadmium ]
generally coming down spongy, and is consequently non-adherent,
In order to obtain satisfactory deposits of cadmium, it is important I

Electro-Chemical Analysis.

that the CD. should he equal at all parts of the electrode.
There are three methods which may be used for the electrolysis ;
(i) cyanide, (2) feebly acid solutions, {3) oxalate or tartrate.

Cyanide Solution. — About 0-5 grm. of the cadmium salt,
preferably the sulphate or acetate, is dissolved in water, and a
solution of potassium cyanide added until the precipitate first
formed is redissolved ; a fair excess of cyanide is an advantage,
and causes the deposit to be firmer. The solution is then made
up to the required bulk, ajid electrolysed.

COND1TION.S.

CD. .
E.M.F.

Time

o'So to 075 ampere.

CD. .

E.M.F.

o' I to o'3 ampete.
33 "> 45 volli.

SO°lo6cf'
5 to 6 hours.

End Reaction.— Add a little sulphuretted hydrogen water
to a portion of the solution. If no yellow precipitate or coloration
is produced, then the whole of the metal has been deposited.

Acid Solutions. — Occasionally very good adherent deposits
can be obtained from solutions containing a little free sulphuric
acid. The cadmium salt and about 3 grm. of ammonium
sulphate is dissolved in water, and from 1 to 2 c.c. of lo-per-cent.
sulphuric acid added.

CONDITIONS.

C.D o'l to o"3 ampere.

E.M.F ZS voils.

Tenip 60° lo 70°

Time 3 lo 4 liours.

The deposited metal, when not spongy, is of a brilliant silver-
white colour. Instead of using sulphuric acid, the solution may
be acidified with acetic or formic acids, in which case the salt of
cid employed is used, instead of ammonium sulphate.
Oxalate and Tartrate.— To the solution of the cadmium

[

ii6 Practical Electro-Chemistry.

sail add a solution of from 8 to lo grtn. of ammonium oxalate.
The electrolysis may either be conducted at ordinary or at higher
temperatures. It will be found advantageous to add a little oxalic
acid from time to time, in order to keep the solution feebly acid.
The deposit is then denser and more adherent,

CONDITION'S.

1. n.

C.D. . . O'S lo 0-75 ampere. 1 C U. . . O'S lo ro ampere.

E.M.F. . 1*5 to 3'S volls. E.M.F. . . I'5 lo 4'o volts.

Temp. . , so" lo 60° Temp. . . nonnal.

Time . . 3'5 to 4 hours. 1 Time , . 4 in 5 hours.

When tartrates are employed, about 5 grm. of ammonium tartrate
and a few drops of tartaric acid are added to the solution. The
■electrolysis is best conducted at a temperature of from 50° to 60".

LITERA TURK.

Smith, Amer. Pkil. Soc, 1878 ; Clarke, Zeil. f. Anal. Chem.,

XVIII. 104; Beilstcin and Jawein, Ber., XII. 759; Smith, Amir.
Cfum. Jourrt., II. 43; Luckow, Zeit. f. Anal. Chem., XIX. 16;
Wrightson, Zeit. /. Anal. Chem., XV. 303 ; Classen and Von Reiss,
Ber., XIV. 1628 ; Warwick, Zeit. f. Aiiorg. Chem., I, 258 j Moore,
Chem. News, LIII. 209; Smith, Amer. Chem. Joiirn., XII. 329;
Vortmann, Btr., XXIV. 2749; Classen, Ber., XXVII. 2060;
Heidenreich, Bc^.,XXIX. 1586 ; Avery and Dales, Amer. Chem.Soe.,

XIX. 380 ; Wallace and Smith, Amer. Chem. Sffc., XIX. 870, and

XX. 279 i Balachowsky, Compt. Rendus, 131, 384 ; Miller and Pa^^e,
Zeit. f. Anorg. Chem., XXVIII. 333; KoUock, Amer. Chem. Soc,
XX!. 911 ; Hollard, Electro^hemisl, 1904, III, 409,

Bismuth.

]

Bismuth is one of the more difficult metals to deposit, electro-
lytically. In fact, it is a very difficult matter to obtain satisfactor)'
results at all. From a great many solutions the bismuth deposits
partly as oxide at the anode, and partly as metal on the cathode.
Even when no oxide is deposited, the bismuth is often powdery
and spongy, and consequently non-adherent.

Electro-Chemical Analysis. 117

Umitry-Balachowsky ' gives the following conditions for de-
positing bismuth : —

(i) Weakly acid solution.

(2) Only small traces of the halogens should be present.
{3) Low current density.
(4) Roughened electrode.
(5} Addition of urea or aldehyde.
When the CD. is too high, oxidation of the deposit takes place.

Balachowsky uses a solution containing free nitric acid : from
o'6 to I'l grra. Bi(SO.)j is dissolved in water with 5 to 7 c.c. nitric
acid, and 3 to 5 grm. urea. The CD. employed is from 0^04
to o'o6 ampere per square decimeter. E.M.F., 1-7 to 2 volts.
Temperature of solution, 60" to 70°. Time, eight to ten hours.
Instead of using urea, formaldehyde may be equally well employed.
Wimmenaneur ■' recommends for the solution of the bismuth
nitrate a mixture of two parts water and one part glycerol. He
also advises the use of a rotatbg anode, as this prevents the forma-
tion of peroxide. The solution is acidified with nitric acid. C.D.
OT at the commencement, which is later on reduced to o'oj. The
temperature should not be above 50°.

Dr. Kohn^ found the results irregular when free- nitric acid
only is present, and obtained better results with sulphuric acid.
He states that the best results are obtained when raetaphosphoric
or citric acid arc used. When citric acid is employed the bismuth
can be deposited in ammoniacal solutions. The quantity of
bismuth present should not exceed o^z grm. The commencing
CD. should be o'o8, finishing at o'l ampere, the quantity of
citric acid taken being 2 to 3'S grm. The deposition required from
eighteen to twenty hours. It is best to precipitate the bismuth as
hydroxide, dissolve in sufficient nitric acid, add the citric acid, and
then electrolyse.

Although by taking great care good deposits of bismuth can
be obtained, generally speaking the results are anything but
satisfactory.

' Cempt. Riiidus, 131, 179-182. ' y.^i.f. Awrg. Clam., 27, 1-21,

' ~ h AsstK. Report, 1900, p. 173.

Practical EUclro-Chemisfry.

Zinc.

Like cadmium, zinc cannot be deposited from solutions which
contain more than the merest trace of free mineral acid. Zinc is
also very prone io be deposited in a spongy and non-adherent form ;
this is especially the case with solutions which are quite neutral.

Deposition of the Metal. — Electro-deposited zinc, being
very pure, is only removed from the electrodes upon which it
has been deposited with considerable difficulty. If platinum
electrodes are employed, it is advisable to first coat them with a
thin layer of copper; because, when zinc is directly deposited
upon platinum, as a rule a black powdery coating is left, after
the zinc has heen dissolved off. This deposit can only be got
rid of by rubbing the electrode with fine sand, a proceeding not
to be recommended. Vortmann considers that this black deposit
consists of finely divided platinum. Instead of using coated
platinum electrodes, nickel electrodes can be employed. When
nickel is used, it is understood, of course, that the zinc deposit
must not be dissolved off with an acid, because acids also act
upon nickel. Zinc electrolytically deposited, however, dissolves-
fairly readily in caustic soda, but it is best to employ a moderately
strong warm solution.

Colour of Deposit.^Zinc is rather apt to be deposited
dark and spongy or speckly. As a rule, good quantitative results
can only he obtained when the deposit is quite dense, and of a
bluish grey appearance. During the coarse of the electrolysis, the
gas given off often causes the solution to have a milky appearance,
but this milkiness usually disappears when the bulk of the zinc
has been deposited.

Cyanide Solution.^ Very good deposits of ?inc can be
obtained from solutions containing potassium cyanide, but the
analytical results are rather uncertain. The zinc salt is dissolved
■n water, and potassium cyanide solution added in small portions

eetro-Ckemual Analysis.

at a lime, until the zinc cyanide, which is at first formed, com-
pletely dissolves in the excess of the cyanide. The clear solution
so obtained is diluted to the required volume, and electrolysed.

CONDITIONS.

CD, .
E.M.F. .

tZI' :

. 0-5 ii. ro ampere. ! CD. .
. 47S"o6-o volts. F.M.F. .
. normal. Temp, .
, 8 lo 16 hours. 1 Time

tl.
. o-5lfirlampere

. 4*5 lo 6'o volt!,.
. so" to 60=.
. 6 to 7 hours.

End Reaction.^In order to test whether all the zinc has
been deposited, a small portion of the solution may be wanned
with dilute hydrochloric acid to decompose the cyanide, and
treated with a little potassium ferro- or ferricyanide. The electro-
lysis must be continued until no further precipitate is produced.

Oxalate Method.— Deposits of very fine appearance are
obtained from solutions containing ammonium oxalate : it is
necessary, however, in order to obtain adherent deposits, to keep
the electrolyte feebly acid with oxalic acid, or better, tartaric acid.
If this precaution is neglected the deposits are usually spongy in
character.

The solution is prepared by dissolving about 1 grm. of zinc
sulphate in water and adding it to a hot solution of from 4 lo 5
grm, of ammonium or potassium oxalate. Zinc oxalate is at first
precipitated, but dissolves in the excess of the alkali oxalate. The
solution so obtained is electrolysed with a current of 0*5 to o'6
amperes; the E.M.F. is 3' 7 t04-3volts. As soon as the electrolysis
has commenced, about 3 c.c. of a 5-per-cent. solution of oxalic
or tartaric acid is added ; further small quantities of the acid are
added during the electrolysis, should the solution become neutral
or alkaline. The best way to keep the solution acid is to employ
the siphon arrangement described on p. 77, Fig. 44. The beaker
is filled with a dilute {5 per cent.) solution of oxalic or tartaric
acid. The time required is from three to four hours. The draw-
back to this method is that traces of carbon are often deposited
ivith the

lao Practical Electro-Cketnisiry

The end of the electrolysis may be tested by making alkaline
with ammonia, an^ adding a few drops of ammonium sulphide
to a portion of the solution.

Acetic Acid and Ammonium Acetate. — To the solution
of the zinc salt about 3 grm. of ammonium or sodium acetate is
added. The solution is made up to the required volume, and the
dectrolysis commenced. After a few minutes about i c.c. of
glacial ascetic acid is added, and the electrolysis continued.
CD. o"S to o'8 ampere, E.M.F. 5 to 7 volts. The rate of deposi-
tion is accelerated by healing tlie solution to 35° to 65°. After
the electrolysis has proceeded for about an hour, a few drops of
ammonia are added, in order to neutralise the excess of acid
which has been produced by the decomposition of the zinc sul-
phate. Time, two to two and a half hours.

Rochelle Salt and Caustic Alkah.^Heinrick Faweck'
has recently suggested a solution containing rochelle salt and
caustic soda or potash. To the zinc sulphate solution is added
7 grm. of rochelle salt and 5 grm. of caustic soda. The solution
after being made up to the required volume is electrolysed with a
CD. of from o'l to 0-5 of an ampere, the E.M.F. being a'g to 3'i
volts. The metal is completely deposited in about three or four
hours at ordinary temperatures.

Sulphuric Acid and Sodium Sulphate. — The solution
in this case is made up by dissolving 8 to 10 grm. of sodium
sulphate in water, and adding it to the solution of the zinc salt ;
the electrolysis is then commenced, and, as soon as a thin coating
of zinc has been obtained on the electrode, 3 drops (not more)
of concentrated sulphuric acid added. When the electrolysis
has been in progress from thirty to forty minutes, a few drops of
very dilute ammonia are added to neutralise the escess of sulphuric
acid. The addition of ammonia is repeated every thirty
or so. If this precaution is not taken the zinc may go into

rCy minutes J

ito solution 9

ilectro-Q

alysts.

again, owing to the excessive quantity of sulphuric acid which the
solution contains. The zinc is deposited as a smooth grey coaling
of very fine appearance, and is completely deposited in from
three to four hours. This method gives one of the finest deposits
of zinc, but it requires care.

CONDITIONS.

CD.

E.M.F.

Temp.

o'4 to 0*6 ampeie.

! CD. .
1 E.M.F.

Temp.

Time .

. o'6 ampere.
. 3-5 to 3-0 volts.
. 50° to 60".

LITERA rURE.
Wrightson, ZHt. f. Anal. Chun., X\'. 303 ; Parodi and Mas-
caKini, Ber., X. 1098; Rieh^ Zcil. f. Anal. Chun., XVII. 216;
Beilstein and Jawein, Bir., XII. 446 ; Richd, Zeti. f. Anal. Ckem.,

XXI. 1 19 ; Reinhardt and thle, fouru. f. Prakf. Chim., XX[V. 193 ;
Classen and Von Reiss, Bsr., XIV. 1622 j Gibbs, Zeit.f. Anal. Chem.,

XXII. 558 ; Luckow, Zdf. /. Anal. Client., XXV. 113 ; Brand, Zeil.
f. Anal. Chem., 28, 581 ; Warwick, Zeit. /. Anorg. Chem., I. 258 ;
Vortmann, Ber., 24, 2753 ; Riidorff, Zeit. f. Anorg. Chem., 1883,
197 ; Vortmann, Monalshe/i, XIV. j;?^ ; Jordis, Zeit./, Elektrochem.,
II. 138, 565, and 655; Classen, Zeil. f. Elektrochem., II. 589;
Nissenson, IKd., 590; Wagner, Ibid., 614; Millot, Bui. Soe. Chim.,
87, 339 ; Nicholson and Avery, Amer. Chem. Soc, 18, 659 ; Paweck,
Berg. wndHiitten Zeil., 46, 570 ; Williams, British Assoc. Report, 1888,
295 ; Smith, Amer. Chem. Soc, 24, 1073; Amberg, 5cr., 36, 2489;
Hollard, Bull. Soc. Chim., 1903, 29, 266 ; HoUard and Bertiaux,
Compi. Rendiis, 1903, 136, 1266.

Silver.

Silver is a metal which can bt; deposited, either from acid,
alkaline, or neutral solutions, and from solutions of its double
cyanide. At the same time, there is really only one process which
is satisfactory, and that is the cyanide method.

When silver is deposited from solutions containing free
acid, the metal generally separates in a crystalline and feathery
form, and therefore does not adhere well to the cathode,
further difficulty is that very often a portion of the silver

lery M

122 Practical Electro-Chemistry.

deposited at the anode in the fonn of the peroxide. The addition
of small quantities of certain organic acids, such as tartaric or
lactic acids, prevents the separation of peroxide, but even when
this is done it is only possible to obtain an adherent cathode
deposit by the employment of extremely feeble currents. The
metal is sometimes deposited at the cathode in a powdery form,
and may have a brownish or greyish appearance. This appears
to be due to the CD. being too high.

All silver salts dissolve in ammonia, and attempts have been
made to deposit the metal from solutions containing free ammonia.
The results, however, are rarely satisfactory ; generally speaking
the metal is deposited as a brown powder, which does not
adhere to the electrode. Neutral solutions also give unsatis-
fectory results.

From Potassium Cyanide Solution. — About i grni. of
the silver salt is dissolved in water, and a freshly prepared solution
of potassium cyanide added. A precipitate is at first formed, but
on the further addition of the cyanide solution it dissolves with
production of a clear solution, oiving to the formation of the so-
called double salt of potassiuna and silver cyanide (see p. 91).

KCN + AgNO, = AgCN -(- KNO.
AgCN + KCN = KAg(CN),

It is very important that the purest obtainable potassium cyanidd;,
be employed. That made by passing hydrocyanic acid into
alcoholic potassium hydroxide is the best. The deposited metal,
when impure cyanide is used, is often brownish in appearance,
and is liable to adhere badly. In order to obtain complete solu-
tion of the silver salt, it is generally necessary to use from 3 to 4
grm. of potassium cyanide. The conditions necessary are : —

EUctro-Ckemical Analysis. 123

For rimiiiiig all right a CD. of from q-oS to o'ao aiiii>ercs may
be employed, the E.M.F. being 3"z to 3'4 volts.

The deposited metal is of a dull silver-white appearance, and
adheres firmly to the cathode.

Sometimes the metal appears quite " matt," at other times
it possesses a crystalline structure. At times, especially if the
current conditions have not been attended to, brown spots make
their appearance on the deposited metal ; these do not necessarily
cause the results to be incorrect, but it is as well to avoid them as
far as possible. Gauze or roughed electrodes are the most suitable
for silver depositions. Breaking the circuit and washing should
be carried out as rapidly as possible, because metallic silver is
acted upon by solutions of potassium cyanide.

End Reaction.— Treat a small portion of the solution with
dilute nitric acid, and boil off the liberated hydrocyanic acid, then
add a drop of hydrochloric acid. If no white precipitate or
turbidity is produced the electrolysis is completed.

Insoluble silver salts should be warmed with potassium cyanide
solution until they are dissolved, and then subjected to elec-
trolysis.

LITERA TURE.

Fresenius and Bergman n, Zi'f/.^^ Anal. Ckem., XIX. 324 ; Krutwig,
Ber., XV. 1267 ; 5chucht, Zeit.f. Anal. Ckem., 22, 417 ; Amer. Ckem.
Soc, IV. 22 ; Riidorff, Zeil.f. Angiw. Ckem., 1893, 5 ; Smith, Amer.
Ckem. Journ.^ XII. 335 ; Fulweiler and Smith, Amer. Ckem. Soc,
23, 583.

Gold.

The noble metal gold can be deposited from almost any of its
solutions by the passage of the electric current. But satisfactory
deposits from acid or alkaline solutions are rarely obtained, the
gold usually coming down in the form of a brown non-adherent
amorphous precipitate. Indeed, when deposited from acid or
alkaline solutions, the colour of the solution may at times become
greenish or purplish, owing to the suspension of finely divided
particles of gold.

>4 Practical Ela:tro- Chemistry.

Tractically there are three solutions which t

employed for depositin;
thiosalls, and solutions h

On adding a solution of
the gold salt— which, of cou
whitish precipitate is prodi

:an be successfully
These are the auricyanides,
thiocyanate.
alkali cyanide to the solution of
must not be strongly acid — a
d. This precipitate, however,
readily dissolves when an excess of the cyanide is added, with
formation, in the case of potassium cyanide, of potasaimn
auricyanide —

Au 4- 3CN = Au(CN)3
Au(CN), + KCN = KAu(CN).
Now, as tlic ions of potassium auricyanide are K' and Au(CN)'i,
the electrolytic separation of gold from such a solution is really a
secondary reaction. The explanation given on p. 91 for deposi-
tion of copper from cyanide solutions applies also for solutions of
gold cyanide.

Deposition from Cyanide Solutions. — To the gold solu-
tion, from I to 2'5 grm. of pure potassium cyanide is added ; the
colourless soludon so obtained is made up to the required volume
with distilled water. If the gold solution is strongly acid, it should
be partially neutralised with potassium hydratCj or, what is better
still, evaporated nearly to dryness, and then taken up with distilled
water. The solution of the auricyanide may either be electrolysed
at ordinary temperatures or at a temperature of from 50^ to 60°. A

CONDITIONS.

„

CD. .

E.M.F.

. □■I51oo-4ampere. CD.
. 3 10 3-25 volts. E.M.F. .

. 06 lo 08 amper
. 3 to 3'2 volls.

Temp. .
Time ,

atmospheric. ' Temp. .
, 10 to 12 hours. 1 Time ,

. 50° to 60=
. 2 to 3 hours.

Deposition from Solutions of Alkali Sulphides, — On

adding a solution of an alkali sulphide to a solution of a gold salt,
a brownish precipitate is at first formed, but this immediately dis-
solves in excess of the reagent with formation of a gold thiosalt—

Au.jS, -

sNa^S = zNa,AuSj

Ehctro-Ckemica! Analysis.

Smith and Wallace have shown that the ammonium thiosalt does
not give quantitative results. But satisfactory and quantitative
deposits can he obtained by employing potassium or sodium
sulphide.

Course of Reaction. — The reaction which leads lo the
deposition of the gold al ihe cathode is rather involved, hut it may
perhaps be looked upon as behig one of reduction. We have in
solution the complex molecule NajAuSj' or rather the ions of
this complex ; the reduction would then take place as follows :^

zNa^AuSj + 6H = zAu + 6NaHS

The sodium hydrogen sulphide being then funher oxidised at the

6NaHS +30 = 3Na^, + sH.^O

The reaction might, however, be explained on similar lines to
those which Hittor employs in the case of the complex cyanides.
The sodium auiisulphide is ionised into the cations 3Na' and the
complex anion AuSs'". The cation travels to the cathode, and
there becomes neutralised, and the liberated sodium then reacts
with the water, forming sodium hydrate. The anion migrates to
the anode, and is there deposited. The sodium on Uheration
at the cathode now reacts with some of the unchanged NajAuSj,
and liberates gold ions, which in their turn travel to the cathode
" where they are deposited.

I. 3Na + Na,AuSs = Au + 3Na,S
The reformed sodium sulphide dissolves the gold sulphide
which has been deposited at the anode, and reforms sodium
aurisulphide, and liberates sulphur, which combines with other
molecules of sodium sulphide to form poly sulphides.

' It is nol certain that tlie salt NajAuSj is produced when gold sulphide is
dissolved in sodium sulphide ; it may be NsjAu.Sj. la fact, this latter salt has
been isolated by dissolving AujS, in NiUS and pouting the solution into
alcohol. But the presence of polysulphides would probably lead to the
fortnatiun of the first-mentioned sait,

I
I

126 Practical Electro-Chemistfy.

II. 2 AuS7 + 3Na,S = zNa.AuS, + 3S '
It is, of course, not necessary to assume that the same molecules
of sodium sulphide liberated in reaction I. take part in reaction
II., because in actual practice there is always a considerable
excess of sodium sulphide. Sulphur and oxygen are always
liberated to a certain extent at the anode and hydrogen al the
cathode, so that at the cathode part of the sodium, sulphide mli
be reduced to sodium hydrogen sulphide, which may, again, at
the anode be partially oxidised back to the monosulphide. At
the same time the liberated sulphur will produce polysulphides.

The solution for electrolysis is prepared by adding about
30 c.c, saturated or nearly saturated solution of the alkali sulphide
to the gold solution ; a precipitate is at first formed, but this
redissolves, and a clear solution is obtained. The mixture is then
diluted to the requisite volume, and electrolysed at the ordinary
temperature.

CONDITIONS.

CD . o'l to o'25 ampere.

E.M.F 2 volts.

Time 5 to 6 hours.

Both with cyanide and sulphide solutions, brilliant yellow |
firmly adhering deposits of gold can be obtained. |

Thiocyanate. — Dissolve 5 to 7 grm. ammonium thiocyanale
in 70 to 80 c.c. water, and warm to 50° or 60" ; then run in the gold
solution with constant stirring. If the solution is cold, a precipitate
of gold thiocyanate may be produced, and this is only dissolved
on heating the mixture. The solution usually has a red colora-
tion at first, but gradually becomes colourless. Make the solution
up to the required bulk with distilled water, and electrolyse.

' We might assume Ibat tlie anion AuS,'" when liheraled al the anoile
gives up an atom of sulphur, and becomes AuS„ this sulphide being known,
whereas AuS, has not been Isolated. The equation would then be —
lAu.S, + 3Na,S = 2Na,AiiS, 4- S

^0-Chemical Analysis.

40° to 50°.
.•5 to z hours.

The deposit is very often quite as brilliant as that obtained
with cyanide or sulphide solutions, but at times it may have a
rather smoky appearance; this does not, however, affea the
accuracy of the resdls. Very often during the electrolysis a small
quantity of a yellow precipitate separates out. This is canarine
{see p. 271), and is due to the oxidising action of anodic oxygen
on the thiocyatiate ; it does not interfere with the deposition of
the gold. Potassium thiocyanate, although it gives accurate results,
generally gives a deposit of poor appearance.

End Reaction.— The small portion of the solution should
be boiled with a few drops of concentrated sulphuric acid, to
decompose the double salt, and a few drops of stannous chloride
added ; a purple or violet colour, due to formation of Purple of
Cassius, shows that the electrolysis is not yet finished.

Removal of Deposit. — The best method to remove the
deposit is to cover the electrode with a solution of potassium
cyanide, to which has been added 3 or 4 c.c. of hydrogen peroxide,
or 2 grm. of sodium peroxide or ammonium persulphate. The
deposit is in this way removed in a minute or two. If the solution
is warm, the gold goes into solution in a few seconds. When
hydrogen peroxide is used the reaction may be expressed thus : —
aAu + 4KCN 4- HA = 2KAu{CN)o + zKOH

LITERATURE.

Luckow, Zeit. f. Anal. Chem., IB, 14 ; Brugnatelli, Pkil. Mag.,
31, 187 ; Smith, Amer. Chem. Journ., XIII. 206 ; Smith and Muir,
Amer. Chem. Journ., XIII. 417; Smith and Wallace, Ber., 26,
779 ; Person, Ann. Chem. Pharm., 66, 164 ; Rudorff, Zeii.f. Ange^.
Chem., 1892, 69; ; Perkin and Prebble, Eleciro-chem. ajui Mel.,

Hi. 490.

xtro- CAettttsiry.

Platinum.

Platinum, like gold, can be deposited from solutions containing
free mineral acids ; but unlike gold, which from these solutions is
deposited in a non-adherent form, it may, if a very feeble current
is employed, be deposited in a dense reguline condition. With
high currents a deposit of platinum black is invariably produced.
Solutions of platinum chloride, containing a few drops of concen-
trated hydrochloric or sulphuric acid, may be employed.

CONDITIONS.

CD O'OI to 0'04 ampere.

E.M.F 1-8 volts.

Temp yP to 60°.

Time 4*5 to 6 hours.

When a solution containing free phosphoric acid and sodium
phosphate is employed, a somewhat heavier current (o'oy to o-io
amp.) can be used, but in this case a rather longer time is necessary
to completely deposit the metal. The platinum electrodes should
be coated with copper before being used for the deposition
of platinum.

The electrolytic deposition of platinum may be indirectly em-
ployed to estimate ammonium and potassium. Both ammonium
and potassium are precipitated by means of hydroplatinic acid
as the respective platinichlo rides. But as they are both distinctly
soluble in water, alcohol is always added to complete the precipi-
tation. If the precipitated and washed plaiinichloride be dis-
solved in excess of water, and hydrochloric acid added, then the
platinum may be elect roiytically deposited, and from the a
of platinum obtained the original quantity of potassii
ammonium is readily determined.

LITER A TURE.

Luckow, Zeit.f. Ano)-g. Chem., 19, t3 ; Classen, Ber., 17, 2467;
Smith, Amer. Chetn. Journ., 13, 206 ; Riidorff, Zeit. AHorg;. Chem.
1808, 696.

Electro-Chemical Analysis.

Palladium

May be deposited from acid solutions in much the sai
as platinuiB, a low current density and a low E.M.F.
necessary. ,' By employing a current of less than o'l of an ampere
the palladiiirii can be deposited in a bright and reguline condition.
Cowper-Coles ' suggests a solution of paladium-amnionium chloride
[Pd^NH, CIX] and ammonium chloride, at a temperature of 25°.
This solution does not, however, appear to have been employed
by him for analytical purposes, But Smith *■" has obtained good
quantitative results by using this solution.

The deposition can be carried out by dissolving the salt in
ammonium hydrate; after solution about 30 c.c. more of the
ammonium hydrate is added (sp. gr. o'93s) and 100 c.c. of water.
The palladium can be deposited overnight by passing a current
of o'oj — o"i ampere. The deposited metal has the appearance
of rolled palladium. The platinum electrodes which are employed
as cathodes should be first coated with silver or copper.

Amberg" finds that by using an anode rotating at about 600
revolutions per minute, he is able to deposit palladium from
solutions containing hydrochloric acid. The temperature should
be 60" to 65°, and the E.M.F. must not be allowed to exceed
I -as volts. The rotating anode prevents the formation of
peronide.

Rhodium.

Smith has shown that rhodium can be rapidly and accurately
deposited from solutions containing sodium phosphate and
phosphoric acid. The CD. may conveniently be o'i8. The
solution, which at the commencement has a fine purple colour,
gradually becomes colourless. As a rule, the deposited metal
has a black colour, but is reguline and firm in character.

^ Jharbuch, 1899, VI, icp, 3.nA Eng. and Mm. foum,^, \i. 5.
- EltclTOchemical Analysit, 3rd edit. 1802, p. 106.
' Zeii.f. ElfkhBthfm., 1904, X. 385.

129 ■

le way ^|

being ^|

130 Practical EUctro-Chemistry.

The electrodes upon which the metal is deposited must be
coaled either with copper or silver,

LITERA TURE.

Smilh, Amei: Chem, Soc, B, 201 ; Joly and Leidi^, Compt. Retidus
112, 793.

Tellurium.

Giovanni Pellini' deposits tellurium from a solution of tellurium
anhydride in hydrochloric acid to which ammonium tartrate has
been added. The solution is made up by dissolving o'l to
o'a grm. of the anhydride in 5 c.c. of concentrated hydrochloric
acid, to which is then added 100 to 120 ex. of a cold saturated
solution of acid ammonium tartrate. With the following con-
ditions, about 9 hours is required to deposit the tellurium : CD.
o"oi, E.M.F. I'Ss to 2'2 volts, and temperature 55" to 60°.

The tellurium is deposited in a smooth reguline condition, and
is at the end of the operation washed with water and alcohol, and
dried at 100°. As the tellurium is rather easily oxidised, water
which has previously been boiled should bo used for washing
purposes.

End Reaction. — A small portion of the solution is with-
drawn, and warmed with stannous chloride and hydrochloric acid :
if no brown coloration due to precipitated tellurium is produced,
then the electrolysis is completed.

H,TeO, + aSnCli + 4HCI = Te + aSnClj + jH.O.

This reaction is very delicate, and is said to show the presence of
□"oooi grm. of tellurium in a solution.

A better method ^ is to dissolve the finely powdered tellurium
in a few cubic centimeters of hot concentrated sulphuric acid ; a
beautiful pink coloration is first produced. When all the tellurium

' Alii. R. Accad. dei. Lined. Roma fS], IZ, II. 31a.

' G. Gallo, Atti. R. AuaJ. Lincei, 1904 [v,], 13, i. 713.

wmtcalAnafysis.

131

has dissolved, the solution is heated until the pink colour vanishes.
The white anhydride thus obtained is washed with a little freshly
boiled water into a beaker, and then from 80 to too c.c. of a 10-
per-cenl. solution of pyro phosphoric acid or sodium pyrophosphate,
freshly boiled, added. The mixture is then electrolysed with a
CD, of o'l ampere, the RM.F. being about i-5 volts. The
solution is hot to commence with, but is allowed to cool as the
electrolysis proceeds. Time, 4 to 5 hours.

Removal of Deposit. — The deposited tellurium readily
dissolves in moderately strong nitric acid.

Thallium.

Electrolytically, thallium strongly resembles lead, in that it
can both be deposited as metal at the cathode or as oxide on
the anode. It further resembles lead in the behaviour of the
deposited metal, which cannot be washed and dried without
undergoing superficial oxidation ; it is, therefore, not possible to
determine thallium quantitatively as a cathodic deposit. For
the determination as oxide, see p. 140. G. Neumann,' however,
describes a method for analysing thallium which depends upon
depositing it as metal from solutions containing ammonium
oxalate : the metallic deposit is not weighed, but is treated with
hydrochloric acid, and the volume of hydrogen which is evolved
is determined. This volume, calculated at N.T.P., is equivalent
to the weight of thallium which has been deposited from a weighed
quantity of the thallium salt. About 5 to 6 grm. of ammonium
oxalate is added to the solution of the thallium salt, and the
mixture electrolysed with a current density of about i ampere.

End Reaction. — The electrolysis is finished when the
addition of ammonium sulphide to a small portion of the solution
produces no orange precipitate or coloration of thallium sulphide.

The apparatus employed by Neumann is depicted in Fig. 49.
I Bir., XXI. 356.

PractUal Electro-Chemistry.

It consists of a small flask, k, into which two electrodes are hised ;
the surface of each electrode Is about 9 cm. The flask is not
fastened on to the gas-measur-
ing apparatus until after the
electrolysis has been com-
pleted. Before connecting to
the measuring apparatus, the
solution cotitainitig ammonium
oxalate and carbonate — the
latter produced by the electro-
lytic decomposition of the am-
monium oxalate — is washed
out by means of a siphon
arrangement, the electrolytic
circuit not being broken until
the washing is completed. It
is then connected up as shown
in Fig. 49, and hydrochloric acid added to dissolve the thallium
salt The method even at best is tiresome, and would only be
employed if a large number of determinations were required.

Amalgams.

It has already been noticed that certain metals are very
difficult to deposit in a smooth reguline condition, being either
deposited in a spongy form, or else they are brittle and show
a great tendency to exfoliate. Cadmium, for example, has a
a marked tendency to be deposited in a spongy and non-adherent
form ; and it is almost impossible to deposit bismuth b a weighable
condition, because the metal either peels oH" owing to the brittle
character of the deposit, or else it is obtained, like cadmium,
in a powdery or spongy form. Vortmarm and Luckow and
others have shown that most metals can be deposited as amalgams
if a mercury salt is added to the solution to be electrolysed. The
method of procedure is much the same as that adopted for
electrolysing mercury solutions ; it stands to reason, of course, that .

irse, that ij

EUclro-Cheniical Analysis.

only such solutions as can be employed for depositing nicrtury
may be used. This method can be employed for the deposition
a laige variety of metals, but it is only In a few cases that there
is any advantage in using it A few examples will give an idea
of how the method may be worked, the student will then be in
a position to adopt it in any given case that may appear desirable.

Cadmium Amalgam.

The cadmium salt is dissolved as usual in about 150 ex. of
distilled water, and then the mercury salt and i cc. of concen-
trated sulphuric acid added. Mercuric chloride is the most
convenient salt of mercury to add, because it is readily obtained
pure. For every part of cadmium salt taken (calculated as
metallic cadmium), from four to five parts of mercuric chloride
{calculated as metallic mercury) should he used. The amalgam
then obtained is solid, but when larger quantities of mercury
are used, it is fluid or semi-fluid. Thus for 0-5 grm. of cad-
mium sulphate which contains about o'a grm, of metallic
cadmium, about I'S of mercuric chloride containing I'l grm. of
metallic mercury would be necessary. When the mercury and
cadmium salts have been dissolved, from z to 3 cc. of 20-per-
cent, sulphuric acid is added, and the solution made up to 125 to
130 cc.

CONDITIONS.

CD 0-3 to 0-5 ampere.

E.M.F i-gloi'j vollE.

Temp 60° lo 70°.

Time S lo 6 houis.

If during the electrolysis some of the mercury salt is reduced to
the mercurous condition, and becomes precipitated, the addition
of small quantities of ammonium or potassium persulphate from
time to time will cause this to go into solution.

End Reaction. — I, This is determined as usual by the addi-
tion of a small quantity of sulphuretted hydrogen water to a few
cubic centimeters of the solution which is withdrawn for the purpose.

134

Practical Electro-Chemistry.

When all the metal has been deposited, the electrode is removed
and rapidly washed with distilled water and alcohol, and dried in
a desiccator. The drying operation is much more rapid if, after
washing with alcohol, the electrode is played upon with the air-hlast
from the blowpipe for a few minutes. It can then be heated to
70° for a few minutes without harm.

II. Ammonium tartrate and free tartaric acid also gives very
good results. In this case the cadmium and mercury salt are
dissolved up as already described, then 2 grm. of ammonium
tartrate and about 3 gnn. of tartaric acid added, and the
electrolysis conducted under practically the same conditions as
those described for the acid solutions.

Bismuth Amalgam.

Owing to the great difficulty in obtaining satisfactory deposits
of bismuth, the amalgam method is to be recommended above all
others for the electrolytic determination of this metal. The pro-
portions of mercury salt employed to the bismuth salt should be
about the same as that recommended for cadmium, namely from
four to five times as much mercury as bismuth.

Solution containing Free Nitric Acid.— The mercury
salt is first dissolved in water, then the bismuth salt added and
sufficient nitric acid to cause the bismuth oxysalt first produced
to enter into solution. It is not advantageous to add a large
excess of nitric acid, otherwise there is a tendency to obtain an
anode deposit of hydrated bismuth oxide. If, however, 1 grm. of
tartaric acid is added to the electrolyte, this formation of oxide at
the anode is prevented. 'I'he tartaric acid should be added before
commencing to electrolyse, because when the anode deposit has
once formed, it is very difficult to remove.

CONDITIONS.

C.D 07 to I'l ampere. '

E.M.K 3'5t0 4volls.

Temp Normal or 5o°-6q°,

Time 6 to ij hours.

ectro-L.

alysts.

"35

Su1|^uric acid can be employed instead of nitric acid, bui, us
the results with nitric acid are very satisfactory, there is no advantage
to be obtained by its employment.

If the quantity of mercury salt used is too small, the bismuth
is often obtained partially as an amalgam and partially as a
blackish powder, which covers the surface of the amalgam. The
amalgam may be dissolved off with moderately strong nitric add.

Lead Amalgam.

This metal readily forms an amalgam, and may be deposited
as such from solutions containing the lead salt and mercuric
chloride, to which is added 5 grni. of ammonium acetate, 3 or
4 c.c. of acetic acid, and a little potassium or sodium nitrite. If
the nitrite is not added, a [lortion at least of the lead will be
deposited as peroxide on the anode. The lead amalgam when
dry only oxidises very slowly in tlie air, but when wet the oxida-
tion is somewhat rapid. It should be therefore rapidly washed
in water, and then in alcohol, and dried in a desiccator, or at a
temperature of 5o°, but it should not be left long in the air-bath.

Antimony, tin, zinc, lead, and several other metals can be
deposited as amalgams, but since the ordinary methods of
electrolysis give good results, the amalgamation method is not
often employed. Zinc, as has already been pointed out {p. 118),
has a tendency to act upon the platinum electrode, and is only
completely removed with considerable trouble; the same difficulty
L is met with in ;^inc amalgams.

CHAPTER IX.
METALS DEPOSITED AS OXIDES AT THE A.\'ODE.

Lead.

Certain mttals, owing to their great tendency to become
oxidised, or to their decomposing water, either cannot, under the
conditions usually prevailing in electrolytic analysis, be deposited
as metals on the cathode, or, if they are deposited, do not give
satisfactory analytical results. For example, it is a by no means
difficult matter to deposit lead in the metallic state from weakly
acid, neutral, or alkaline solutions. But the lead is very apt to be
precipitated in a feathery and non-adherent form. There is also
a great tendency for the lead to separate at the anode in the form
of lead peroxide simultaneously with its deposition at the cathode
as metal. Furthermore, although the whole of the lead may,
under certain conditions, be deposited in a smooth reguline con-
dition, yet, during the process of washing and drying, a certain
amount of superficial oxidation invariably occurs. Thus the
results are too high, and are therefore useless for analysis. In
depositing lead for analytical purposes, therefore, conditions are
employed which prevent the lead from being deposited at the
cathode, but cause it to be wholly deposited as peroxide at the
anode. The most satisfactory conditions are to employ a solu-
tion containing a considerable excess of nitric acid.

Procedure. — Dissolve about i grm. of lead nitrate in about
30 c.c. of distilled water, then add to the solution about 25 to 35
c.c. concentrated nitric acid, and dilute to the required bulk, which

Metals deposited as Oxides at t/ie Anode. 137

should not be more than about 175 c.c. The best ekctrode to
employ as anode is the gau^e flag electrode, wliich should bt
roughened by the sand-blast or a similarly roughened basin, As a
mle, the peroxide does not adhere very well upon a polished surface.
If during the electrolysis a separation of metallic lead should be
noticed at the cathode, a few cubic centimeters more concentrated
nitric acid must be added. The electrolysis may either be conducted
at ordinary temperature or at from 50° to 55 '. It is not advisable
to employ much higher temperatures, because there is then a
tendency for the peroxide to scale off.

CONDITIONS,

CD. .

E.M.F.
Temp.
Time .

o'S loi-S ampere,
z lo 2'5 volts.
Normal.
2 lo 3 hoHr^.

CD. .
E.M.F. .

Time

At the commencement of the electrolysis a yellowish deposit
s obtained, which becomes orange or red, and finally dark brown
)r black.

End Reaction.^Take a few drops of the solution and make
alkaline with ammonia, then add a few drops of sulphuretted
hydrogen water or ammonium sulphide. A black or brown
coloration or precipitate indicates that some lead still remains in
the solution. Or make just alkaline with ammonia, then acidify
with acetic acid, and add a little potassium chromate or dichro-
L mate. If no cloudiness or precipitate of lead chromate is pro-
duced, then the electrolysis is finished.

As soon as the deposition is complete, the electrode is
removed, rapidly washed with water and alcohol, and heated in
an air-bath to 180° or aio'"' until the weight becomes constant. It
is absolutely necessary to beat to this high temperature, because
the peroxide is deposited in a more or less hydrated condition.

Removal of Deposit.— The deposit of lead peroxidi
cannot be removed by simply heating with acids. It can, however,

138 Practical Eleetro-Chemistry^

be readily and rapidly dissolved off by warming it with a mixlure
of nitric acid and glucose. The best mixture is equal volumes of
concentrated nitric acid and water, to which is added 4 or 5 gnn.
of glucose; on gently warming, the deposit quickly dissolves.

The method usually recommended is to place a piece of zinc
or copper foil in contact with the electrode, and then immerse in
dilute nitric acid, whereby a galvanic couple is formed. This
method is quite satisfactory, but the first method described is
simpler.

LITERATURE.

Kiliani,^^^. undHmten Zeit., 1888, 253 ; Luckow.Zj^y./. Anal.
Chem., XIX. 215; Richd, Zeii f. Anal. Chem., XXI. 117 ; Hampe,
Zeii/. Anal. Chem., XIU. 183 ; Classen, Zeil./. Anal. Chem., XXI.
2S7 ; Parodi and Mascazzini, Ber., X. 1098 ; Rich^, Ztil. /. Anal.
Chem., XVn. 219 ; Schucht, Zeii.f. Anal. Chem., XXI. 4B8 ; Tenny,
Anur. Chem. yourn., 5, 413 ; Vortmann, Ber., S4, 2749 ; Von Giese,
Zeit. f. Elektrochem., II. 586 and 598; Riidorff, Zeit. f. Angew.
Chem., 1882, 198 ; Warwick, Zeit./. Anorg. Chem., I. 258 ; Classen,
Ber., 37, 163 ; Kreichgauer, Ber., 27, 31; ; Classen, Ber., 27, 2060;
Medicus, Ber., 26, 2490 ; Neumann, Chem. Zeilung, 1886, 381 ;
Hollard, Bull. Soc. Chim., IB, 91 1 ; Linn, Amer. Chem. Soc., 24, 435 ;
Marie, Chem. Zeitung, 24, 341 and 480 ; Nissenson and Neumann,
Chem. Zeitnng, 18, n43 ; Hollard, Compt. Rendus, 1808, 138. 229.

Mans:anese.

It is not possible to deposit manganese from its solutions in
the metallic condition, because pure manganese decomposes water.
The metal can, however, be deposited at the anode in the form of
its peroxide. But it is much more difficult to obtain satisfactory
results with manganese than with lead. With lead a large excess
of nitric acid can be employed, but with manganese only very
small quantities of free acid are permissible. With large amounts
permanganic acid is produced, and no deposit of oxide is
obtained at the anode.

A very large amount of work has been done upon the electro-
lytic deposition of manganese, but of the many solutions suggested
only a comparatively few give satisfactory results. The main

Metals deposited as Oxides at the A node. 1 39

difficulty in dealing with manganese is to obtain an adherent
deposit. The deposit is generally of a more or less friable nature,
and crumbles ofT on washing or drying. It is absolutely essential
to employ roughened electrodes. Engels ' finds that the addition
of small quantities of chrome alum causes the deposit to be much
more dense and adherent.

Ammoniuni Acetate. — Dissolve the manganese salt,
MnSO.(NH,)jS04,6HuO, which is rt-adily obtained pure, in about
40 or 50 c.c. warm water, then add S to 10 grm. of ammonium
acetate and i'5 to 3 grm. of chrome alum. The solution is then
made up to the required volume, and electrolysed at a temperature
of 75° to 80''.

CONDITIONS.

CD o'e 10 O'g nnipete.

E.M.F 2-8lo4'zyo!l5.

Temp 75° lo 80°.

Time li to I hours.

Small quantities of acetic acid or mineral acids may be added, but
this has no advantage except in cases where separations are being
carried out. Chlorides should not be present, because they cause
the deposit to be less adherent.

End Reaction.— Take a few drops of the solution in a test
tube, add about 3 cc. of concentrated nitric acid, about i grm.
of red lead. Now boil for a minute or two and dilute with
water. If any manganese is present the supernatant liquid will
be coloured pink or red owing to the formation of permanganic
acid. This reaction is extremely delicate.

When all the manganese has been deposited the electrode is
washed with water and alcohol, and then ignited strongly in the
blowpipe flame ; the ignition must be continued until the whole
of the black dcjKisit becomes a dull orange red, owing to the
formation of trimanganese tetroxide, MujOj ; it is then cooled and
weighed. The weight of the deposit multiplied by 072 gives
the weight of metallic manganese.

■ Zdl./. Ekklnchim., II„ 413.

140 Practical Eleclro-Chemistry.

Removal of Deposit. — The Crimanganese tetroxidt; can be
readily removed by placing the electrode in wairo moderately
strong hydrochloric acid.

Treatment of Permanganates. — The permanganate is
treated with acetic acid, and sufficient hydrogen peroxide to cause
the solution to become colourless. The mixture is then boiled with
a few cubic centimeters of a solution of a chromate, in order to
decompose any excess of hydrogen peroxide. If the hydrogen per-
oxide is not completely decomposed the deposited manganese oxide
does not adhere satisfactorily to the electrode.

In order to cause the adherence of the manganese oxide to
the electrode, alcohol may be used instead of chrome alum, but
ill' this case only about i grm. of the manganese salt, giving
about o'ai grm. of MdsOj should be used, whereas with chrome
alum 3 grm. can be safely employed. Acetone has been sug-
gested, but no substance is so satisfactory as chrome alum.

LITERATURE.

Luckow, Zeit.f. Anal. Ckem., 19, 17 j Schucht, Zeit.f. Anal. Ckem.,
28. 493 i Classen and Von Reiss, Btr., 14, 1622 ; Moore, Chem. Nevis,
53, 209 ; Smith and Frankel, Journ. Anal. Chem., 3, 385, and CAem.
News, eo, 262 ; Brand, Zeii./. Anal. Ckem., 28, 581 ; RiidorfT, Zeil./.
Angew. Ckem., 15, 6 ; Classen, Ber., 37, 2060 ; Engels, Zeit. f.
Elektrochem., 2, 413, and 8, 286 ; Groeger, Zeii. J. Angew. Chem.,
1B8B, aS3i Kaeppel, Zeit.f. Anorf;. Chem., 18, 268; Hollard and
Bertiaux, Compt. Rendus, 136, 1366 ; Koster, Zeit.f. Elclitrochem., X.
[1904], 533'

Thallium.

Heiberg ' employs the following method for depositing thallium I
as oxide. About o"5 grm. of the thallium salt is dissolved in
about 100 c.c, of water. Then from z to 6 c.c. normal sulphuric
acid and 5 to ro c.c. of acetone added to the solution. After
heating to 50° or 55" it is electrolysed, the E.M.F. being kept
between 17 and 2'-^ volts, but towards the end of the operation
it may be allowed to rise to z'l-, voits.

I Zdt.f. Anora. Chem., 1903, 3S, 347.

Metals deposited as Oxides at the Anode,

In order to prevent metallic thallium Ijeing deposited at the
cathode and to avoid the formation of hydroxide, the solution
must be kept acid, but an excess must be avoided because the
oxide is somewhat soluble in this acid. The electrode must be
roughened, otherwise the deposit may scale off. When the
electrolysis is completed, the electrode is waslied with water and
alcohol, and heated in an air oven lo 160'' or i65Tor about twenty
minutes.

Uranium,

According to L. G. KoUock and E. Smith ' and E. F.
Kom,^ uranium can be deposited from solutions containing small
quantities of acetic acid and sodium acetate. If the solution is
alkaline to commence with, it is not necessary to add the
sodium acetate. For every 100 c.c. of solution about a'5 grm.
ammonium or sodium acetate is employed, and then t c.c. of 50-
per-cent. acetic acid added for every 100 c.c. of solution.

CONDITIONS.

CD *04 lo '05 aoipfre.

E.M.F eioSvolis.

Temp 65° to 70".

Time 5 lo 8 hours.

At the commencement of the electrolysis the uranium is deposited
as yellow oxide, then as the black protoxide (U:,O4,3H,j0). At
the end of the operation the electrode is heated to redness,
whereby the hydrated oxides are converted lo Ui,Oa. The
electrode should be cooled in a desiccator. Chromium salts
prevent the deposition. When large quantities of uranium are
deposited, the oxide is liable to adhere badly to the electrode.
This method leaves a good deal to be desired, because there is a
great tendency for the uranium to come down on the cathode in
the metallic condition and then to be oxidised. When this
happens the anode deposit is, of course, unsatisfactory.

' /. Amer. Chcm. Sot., 28, 60;.
^ Ibid., 23, 685.

Practical Electro-Chemistry.

End Reaction. ^Add to a few drops of the electrolyte a
solution of potassium ferrocyanide ; a reddish brown precipitate
or a hlood-red colorarion shows the presence of undeposited

Molybdenum.

Lily G. Kollock and E. Smith ' state that when a neutral solu
tion of sodium molybdate is electrolysed, no deposition takes
place, but on the addition of a trace of sulphuric acid the solution
darkens, and a black anode deposit of sesquiojcide is immediately
obtained. The molybdenum salt is dissolved in water, made up to
izS c.c, and oi to o? c.c. of concentrated sulphuric acid added,
and the solution electrolysed. It is advisable to add 3 or 4 grm.
of ammoniun sulphate to the solution, in order to increase the
conductivity.

CONDITIONS.

CD o'oz lo o'oj ampere.

E.M.F 2'oto2'25 volfc:.

Temp 70° to 85°.

Time 2'7S to 4'75 hours.

As soon as the electrolysis is finished the deposit is washed with
water, treated with nitric acid, and evaporated to dryness ; by this
means a white powder of molybdenum trioxidc MoO.i is produced.
If, as is sometimes the case, there are blue specks noticeable in
the white trioxide, it must again be evaporated to dryness with

End Reaction. ^Acidify a small portion of the solution with
hydrochloric acid, add a few cubic centimeters of a solution of
ammonium thiocyanate and then a small piece of zinc. If a
blood-red coloration is produced, then the electrolysis is not com-
plete. Phosphoric acid does not destroy this coloration, but it
destroys the red coloration of ferric thiocyanate.

' Jmrn. Amer. Chem, Six., 83. 669.

I M

Metah deposited ns Oxides at the Anode. 143

Vanadium.

p. Truchot' has succeeded in estimating vanadium as its oxide
V3O.V A small quantity of ammonia is added to the solution of
the vandanate, and the mixture subjected to electrolysis.

CONDITIONS.

CD 0'4 ampere.

E.M.F I to as volts.

Temp 85° lo 90°.

Time 8 to lo hours.

The solution should not contain more than o'JS grm. of V9O0
to the litre. During the electrolysis the water lost by evaporation
should be made up, by employing the siphon arrangement
recommended on p. 77. The hydrated oxide is deposited on the
anode as an adherent brown coating. At the end of the reaction
it Is washed with water and alcohol, and heated until it melts ; when
sufBciently heated it is completely converted into the pentoxide,
which is of an orange-red colour. If after ignition the deposit has
a greenish or bluish colour, it must be remelted until it becomes
homogeneously orange-red.

Considering the extremely dilute solutions which require to be
employed, this method can hardly be considered of any great
importance.

The Halogfens.

Vortmann has shown that if a .solution of a halogen salt is
electrolysed, using a silver anode, the halogen unites with the
silver. The increa.se in weight, therefore, of the anode shows the
amount of halogen which has been deposited. It is further
possible, by carefully regulating the voltage, to separate a mixture
of the halogens, iodine being first deposited out at a lower voltage,
and then, by increasing the E.M.F. and changing the electrode,
the bromine is precipitated out, and may in turn be weighed.

' Jiihrbuch, 1B02. IX. 374.

^eciro-Chemistty.

The chloride which remains in solution can be determined by
titration with normal or decinonnal silver nitrate.

Method. —The silver anode should be made of wire coiled
into a flat spiral, as shown in the case of platinum, Fig. 42, p. 76.
The cathode may be either of copper, nickel, or platinum. The
solution to be electrolysed is made alkaline, and an alkali tartrate
added. It is not necessary to notice the CD., but in hot solutions
the E.M.F. should not rise above i'3 volts. In cold solutions it
must not exceed 2 volts. The end of the process can be deter-
mined by acidifying a portion of the solution, adding a little
starch paste and a few drops of chlorine water. If there is any
iodine left in the solution, its presence is shown by the formation
of a blue colour of iodide of starch.

When the operation is completed, the anode is well washed in
distilled water and dried in an air-bath ; the temperature should
be nearly sufBcient to melt the silver iodide.

Should there be bromine in the solution, the E.M.F. is
increased and the bromine deposited upon a clean silver anode.

E. MuUer recommends for the quantitative estimation of
iodine in presence of bromine and chlorine the addition of small
quantities of a soluble chromate to the electrolyte, because he
finds that with an E.M.F. too low to discharge the Br' and CI' ions
the whole of the iodide is oxidised to iodate. A freshly platinised
platinum electrode is employed; the E.M.F, will be about 16
volts and the CD, o'lo to o^oi ampere. The time required to
completely oxidise about oTo of a grm. of iodide to iodate is
about twenty hours.

In order to carry out the electrolysis Miiller recommends tlie
preparation of the following reagents : —

I. Potassium dicbromate, i c.c
solution.

II. Normal potassium hydrate.

III. Potassium iodide, i c,c, =
solution.

0-6 c.c. — thiosulpbate

M&ais deposited as Oxides at the Anode.

As an exercise to determine ihe iodine alone, other halogens
not beii^ present, lalce i c.c. of solution I,, i c.c. of solution II.,
and lo c.c. of solution III., then dilute with 90 c.c. water. At
the end of the electrolysis, excess of potassium iodide is added,
and the solution acidulated with sulphuric acid, iodine being
thereby liberated —

HIO, + sHI = 3H,0 + 3l,

the liberated iodine is then titrated with — sodium thiosulphate

as usual, the number of cubic centimeters used up by the
chromate being subtracted from the total number of cubic centi-
meters employed.

aNa-AO, + 1^= Na.jSA + "Nal
aCrO, + 6HI = 3I, + Cr,0, + 3H3O.

In presence of chlorine : take 1 c.c. solution I., i c.c.
solution II., and i c.c. solution III., then add 100 c.c. of a
saturated solution of sodium chloride. Time required for electro-
lysis, twenty hours.

In presence of bromine : 2 cc. solution 1., t c,c. solution
II., and I c.c. solution III., then 100 c.c. of a solution of normal
potassium bromide. Time, twt:nty-two hours.

It is most important to keep the anode completely covered ;
the E.M.F. must not be allowed to rise above i'6i or i'6z,
otherwise the chloride and bromide will take part in the electro-
lysis. Metals of the alkaline earths must be removed before
commencing the electrolysis.

LITERATURE.

Whitfield, Amur. Ckcm. Jourit., 8, 421 ; Vorlmann, Ehktro-
technhche Zeit., I. 137, and II. 169 ; Muller, iVr., 35, 950.

Determination of Nitric Acid and Nitrates.

If a solution of a nitrate or nitric acid is acidified with
sulphuric acid and then electrolysed, the nitrate is not reduced

14^ Practical Electro-Chetnislry.

lo ammonia. Hut Luckow has shown ihat when an acidified
solution, wliich also contains a metallic salt such as copper
sulphate, is electrolysed, the metal is de]xjsited at the cathode,
and at the same time the nitric acid is reduced to ammonia.

Method. — About equal quantities of copper sulphate and
of the nitrate to be analysed are taken; the solution is then
acidified with sulphuric acid and electrolysed. The end of the
reduction may be shown by adding a drop of the solution lo
a trace of brucine on a watch-glass, and then adding a drop of
concentrated sulphtiric acid ; if no pink coloration is produced
then the reduction is completed. W. H. Easton ' reconmiends a
CD. of I ampere and the addition of about 30 c.c. of dilute
sulphuric acid (sp. gr. 1062).

As soon as the reduction is finished the solution is transferred
to a flask, made alkaline with caustic alkali, and the ammonia

distilled over into a known volume of sulphuric acid. On

titrating the excess of acid with - caustic soda, the amount

of ammonia produced by the reduction of the nitrate is readily
determined.

Preparation of Standard Sulphuric Acid,

\Vhen a solution of pure copper sulphate is electrolysed, the
copper is deposited out, and an equivalent quantity of sulphuric
acid remains in tlie solution —

CuSO, + H.,0 = Cu + H..S04+0.

In order to know the exact quantity of the sulphuric acid in the
solution, it is therefore only necessary to weigh the amount of
copper which has been deposited, because 49 parts of sulphuric
acid will invariably be produced from 3i'8 parts of copfjer, which
was originally present as copper sulphate. This method is hardly
C'lem. Sac., 26, 1039.

Metals deposited as Oxides at the Anode. iA7

one which could be employed for preparing standard sulphuric
acid in quantity, but it could very usefully be adopted for
standardising alkaline solutions.

When it is desired to prepare a given quantity of an exact
normal or decinormal solution, it is then necessary to exactly
weigh out the pure crystallised copper sulphate before electro-
lysing. The amount of copper deposited then serves as a check
on the original weighing. Thus, for example, i'249 grm. of pure
crystallised copper sulphate {CuSOj, 5 H^O) would yield on electro-
lysis o'49 grm. of sulphuric acid, which on dilution to 100 c.c.
would be exactly decinormal.

Dr. C. Kohn' recommends the employment of a U.D. of o'2
to o"4 ampere. If a high current density is used, there is a
tendency for the copper to become spongy ; it is then difficult
to weigh, and it might fall off and contaminate the solution.

Arsenic.

It is not possible to deposit arsenic (juantitatively in the metal-
loid condition, neither can it be precipitated at the anode as
oxide. Arsenic is a substance which is very readily converted by
nascent hydrogen to arseniuretted hydrogen, its gaseous hydride
AsHjj for this reason the- electrolytic methods of analysis are
not employed for analysing arsenic compounds. It is, however,
possible to estimate very small quantities of arsenic contained in
food, etc., by electrolysis. The process consists of evolving
electrolytic hydrogen in presence of the arsenic whereby the
arsenic is converted into arseniuretted hydrogen. The gaseous
hydride is then passed through a glass tube, heated with a small
bimsen burner. This decomposes the hydride, and the arsenic
is deposited upon the tube in the form of a mirror. In order
now to estimate the amount of the arsenic the mirror is compared
with the mirror on a number of tubes which have been prepared
from known quantities of arsenic.

In iSis Fischer- suggested the employment of the electric
' So€. Chrm. hid., ISOO, 962. ' GiWerfs Ann., 42, 91.

148 Practical Electro-Chemistry.

current to detect the presence of very small quantities of arsenic.
It was again suggested by Bloxam' in iS6r, but the apparatus
as then suggested had several disadvantages, and never came
into practical use. Since then various modifications have been
suggested by different authors, and, in 1903, Dr. T. E. Thorpe*
published a new form of the apparatus, which has been success-
fully employed for the analysis of traces of arsenic in food, beer,

and other substances. The apparatus consists of a platinum
cathode, a, hung in a glass cylindrical vessel, B, which is open
at the end and fits into a Pukal porous cell, d. The porous
cell is surrounded by the anode, and stands in an outer vessel, e.
The upper portion of the cylinder b is open, and has a ground
neck for the insertion of the drying-tube c, which is filled with
anhydrous calcium chloride and also carries tlie funnel, which
is fitted with a tap, through which the solution to be tested can
be run in. A capillary tube, g, is connected on to the end of the
calcium chloride tube c. The middle of the capillary tube is

Metals d€pMited as Oxides at the Anode. 149

heated by means of Che small liunsen burner w, and is siirrouiidtc)
where the flanie heats it vfitli a piece nf platinum or iron wire
gauze, to prevent the lube being fused. The whole apparatus is
placed in a vessel, f, containing cold water, to prevent undue
heating during electrolysis.

Method of Working. — The apparatus is carefully washetl
with distilled water. The outer cell e is filled with dilute sulphuric
acid, 30 per cent Then the dilute sulphuric acid is run into the
porous cell by means of the funnel. (The porous cell should
be soaked in dilute sulphuric acid for about half an hour before
being used.) As soon as all the connections are made, the bunsen
burner is placed in position, but not lighted, and the current is
passed. A current of about 5 amperes should be used, because
then the escaping hydrogen issues at sufficient speed to produce a
flame of about 3 mm. in size. As soon as all the air has been
driven out, which usually occupies about ten minutes, the issuing
hydrogen is ignited and the bunsen burner lighted. If after
about fifteen minutes no brown ring makes its appearance, then
the reagents may be considered free from arsenic. About 2 c.c,
of amyl alcohol {to prevent frothing) may be run in,^ and then the
solution to be tested. At the end of thirty minutes the capillary
tube is sealed off and the open end also fused together. The
mirror is then compared with the standard mirrors obtained from
various quantities of arsenic.

Preparation of Standard Deposit.— Pure resublimed
arscnious oxide is ground up in an agate mortar and dried at roo°.
Then \fr\ s d efully weighed and washed into a r-litre flask,
the flask th be n^ fill d to the mark with distilled water. Every
1 c.c. of th s olu on therefore contains o-oooi grm. of arsenious
oxide. Now take 00 c.c, of this solution, and dilute to i litre.
This seconl solut on contains o-oooor grm. of arsenious acid
to each I c.c. or o'oi nig. Standard tubes containing o'oo4,
o-oo6, o'ooS, o-oio, etc., mg. can then be prepared.

' The addilion of nmyl alcohol rather diminishes llie delicacy of tin
method ; therefore, unless (here is considerable frothing, it is not to In
recommended.

150 Practical Ehctro-Chemistry.

When foot! stuffs are being examined for arsenic, Dr. Thorpe
considers it best, in order to prepare a standard mirror, to take
a portion of the food stuff — arsenic free — and add the known
quantity of arsenic to this before proceeding to electrolyse it.
Then when the suspected food is examined, the conditions are
the same as when the standard tube was prepared. For general
work, however, this precaution is not necessary.

S. R. Trotman' recommends the adoption of a parchment
membrane in place of the porous Pukal cell, as he considers this
decreases the resistance and thus makes the apparatus more
sensitive.

Dr. Sand and J. E. Hackford ^ use the p.irchment membrane,
but they also employ a heavy lead cathode and a lead anode.
This causes their apparatus to be much cheaper than that of
Dr. Thorpe, and they claim equal accuracy — in fact, it is stated
the apparatus is more delicate, because the hydrogen is given
off from the surface of the lead electrode at a higher voltage
than from one of platinum. When platinum is employed as
cathode, the hydrogen evolved has not sufficient energy to reduce
arsenates (o arsenites and then to AsHj, therefore it is necessary
when dealing with arsenates to first reduce with sulphurous acid
before electrolysing. But with lead electrodes, owing to the
higher tension at which the hydrogen is liberated, this preliminary
treatment is not necessary. Full particulars of the apparatus of
Sand and Hackford can be found in the original paper.

CHAPTER X.

SEPARATION OF THE METALS.

The electrolytic separation of the metals may be brought about in
several ways. NVTien various metals occur together, we do not
generally make a complete separation by electro-chemical methods
only, without bringing to our aid separations which are purely
chemical in character. But by a judicious employment of electro-
chemical and chemical means, separations of the most complex
mixtures can be brought about, which by the employment of only
electro-chemical or only of chemical methods might be matters of
considerable difficulty. The purely electro-chemical methods of
separation may be classed under five heads : —

I. Separation by means of Variable Potential.— As the
decomposition values of the various salts of metals vary, it is
possible to separate the metals by keeping a constant E.M.F.,
which is high enough to decompose the metal whose salt has the
lower decomposition value, but too low to deposit the metal of
higher decomposition value. This method is only applicable when
the decomposition values do not lie too close together.

il. Separation by depositing one Metal on the Cathode
and the other on the Anode as Oxide.— It has already been
found that certain metals can bo deposited on the anode as oxides,
while other metals in the same solution are deposited in the
metallic condition on the cathode. For example, iii a solution
acidified with nitric acid, copper is deposited at the cathode in
the metallic form, but lead is precipitated on the anode as lead
peroxide.

III. Separation by choice of Electrolyte. — Some metals

lUClUl^i _

Practical Electro-Ckemistry.

art; deposited from acid solutions, other metals can only be pre-
cipitated from solutions which are neutral or alkaline; certain
metals are deposited from strongly add solutions, but others can
only be deposited from dilute acid solutions.

IV. Artificial alteration of Decomposition Value. —
This can be effected by the formation of complex salts, such as
the so-called double cyanides and the thiosulphides, or by altering
the state of oxidation of the salt.

V. HoUard's Methods. — The first method of Hollard, which
we will call A, really comes under the heading IV. It depends
upon the reduction of the resistance of the bath by suppressing
the gas formation at the anode. This is carried out by the
addition of rcducing-agents, such as sulphurous acid, to the bath.

Although, as shown under I., metals can be separated from each
other by varying the potential, only metals whose polarisation
potentials are lower than that of hydrogen can be satisfactorily
separated in this manner. Owing to the necessity of maintaining a
low potential, the current to deposit the metal is always weak, but
when the polarisation potential is higher than that of hydrogen,
then there is a greater tendency for hydrogen to separate than for
the metal, so that the deposition of the metal is never complete.
The metal may be fairly readily deposited at first, but when
towards the end of the electrolysis the concentration of the
metallic ions becomes low, then the liberation of hydrogen com-
^TTB!, pletely prevents any further deposition,

fi \ '^^ hydrogen ions alone conveying the

|Z p n current.

B. Secondly, Hollard finds, that when

a soluble anode is employed, the oxygen

liberation is suppressed. The method is

shown diagram ma ticaily in Fig, 51 : a is a

zinc anode which is connected to the

■ '"' platinum cathode n by the wire zn. The

anode and cathode are separated by means of a parchment

membrane or porous diaphragm, p.

Suppose, now, that it is desired ii

n solution to separate J

Separation of t/w Metah.

nicktjl from zinc. This solution is placed in the cl-U containing the
cathode, a solution of an indifferent substance, such as magnesium
sulphate, being placed in the anode compartment. By this means
a reversible cell of two liquids of thu Daniell type is made. The
current passes through the external circuit from the platinum to the
zinc, and through the liquid from the zinc to the platinum. Nickel
thus becomes deposited out, and the zinc remains in solution.

C. Influence of the Nature of the Cathode.— Uy taking
a cathode made of the same metal as that to be deposited the
polarisation potential of hydrogen is raised above the polarisation
potential of the metal to be deposited. By this means it is
possible to precipitate such metals as lead, tin, and cadmium from
solutions which are strongly acid. Cadmium and zinc can, for
example, be separated by employing a platinum electrode on
which a coating of cadmium has been already deposited. The
cadmium is then deposited, but the sine remains in .solution.

It is not intended to set forth all the possible separations of
the difTerent metals ; only those of the most importance will be
given. But the student who has carefully worked through the
depositions of the metals from pure salt solutions should be in a
position, after a little experience, to work out methods of separa-
tion for himself. When the separation is one in which several
metals are to be dealt with, it is almost invariably necessary to
combine electro-chemical and chemical methods. The separations
will be found under the heading of the individual metals. The best
form of electrode to use for the separation of the metals is generally
the flag electrode (p. 79), because, when the flag electrode is
removed from a solution, only a very small quantity of the solution
which contains the other metal or metals adheres to the electrode,
and this can generally Ije quite easily washed off into the beaker
with the wash bottle.

Generally the current density and E.M.F. will not be stated,
except when it is different from that required in depositing from
pure solutions ; in all other cases the reference to the method will
be given.

Practical Electro-Chemistry .

COPPER.

Copper is one of the most readily deposited of metals, because
it can be thrown out from strongly acid solutions, alkaline solutions,
or solutions containing potassium cyanide.

Copper from Iron.

For practice in carrying out the separation of copper and iron,
prepare a solution containing about i grm. each of copper
sulphate and ferrous ammonium sulphate or of iron alum. Acidify
this solution with z'5 to 3 c.c. of concentrated sulphuric acid, and
dilute to 130 or 150 c.c. Electrolyse with a current density of
about 1 ampere at ordinary temperatures. The time required to
deposit all the copper will be between three and four hours ; with
warm solutions the copper can he completely deposited under
three hours. The end reaction is found in the usual way by
lowering the cathode slightly into the solution j if after ten minutes
no deposit has taken place on the freshly immersed cathode
surface, the deposition is complete. When all the copper is
deposited the electrode is removed, and washed and dried as
usual. (See p. 87-)

The solution, which now only contains the iron, has about
4 grm. of ammonium oxalate or tartrate added to it, and is then
neutralised with ammonia. If too much ammonia is accidentally
added, the solution may be neutralised back with oxalic or tartaric
acid. The mixture is now electrolysed at a temperature of 40" to
50°, with a CD. of o'S to i ampere. (See p. loi.)

The only drawback to employing sulphuric acid in the separa-
tion is, that the copper is very often deposited in a spongy and
non-adherent form. If, instead of using sulphuric acid, 4 to 5 c.c.
of nitric acid is taken, then the copper is deposited in a dense and
firm condition (p. 86). But when nitric acid is used, and there-
fore, on neutralising, nitrates are present, the iron is often partially
precipitated as ferric hydrate. For this reason, in this case, it is
best to add excess of ammonia, and precipitate the iron as ferric

Separation of ike Melals.

hydrate. The precipitate is filtered off, waslied with hot water,
and then dissolved in a little warm solution of tartaric or oxalic
acid. The solution is then neutralised with ammonia and
electrolysed as usual. Or the solution may be evaporated nearly
to dryness, with a little sulphuric acid, in order to expel the
nitric add. The salts are then dissolved in water, 3 or 4 grm. of
tartaric or oxalic acid added, and the solution neutralised with
ammonia.

Copper from Cobalt or Nickel.

fater, V

in the separation from iron, from
ric or with nitric acid. The same
character of the deposited copper

acid has a tendency to cause a
food deposit is invariably obtained

The copper is deposited a
solutions acidified with sulphi
remarks with reference to the
apply in this case. Sulpburii
poorly adhering deposit, but a
when nitric acid is used.

If sulphuric acid is taken as the electrolyte, and the other
iDCtal is nickel, it is only necessary to make the solution strongly
alkaline with ammonia, after the copper has been deposited, and
then to deposit the nickel directly from this solution (p. 92).

If the other metal is cobalt, then, after depositing out the
copper, the solution is made slightly alkaline with ammonia, and
then just acid with phosphoric acid ; after which 3 grm. ammonium
dihydrogen phosphate is added, and the cobalt deposited as
usual from an acid phosphate solution (p. 98).

Both cobalt and nickel are deposited with difficulty from
solutions containing nitrates ; therefore, if nitric acid has been
employed for depositing the copper, the solution should be
evaporated down nearly to dryness with a little sulphuric acid
to drive off the nitric acid. It is then diluted with water, and
treated as above described. Only in this case the borate method
may be used for depositing the nickel (p. 95).

Practical Electro-Oiefnistry.

Copper from Cadmium.

In separating copper from cadmium, either nitric acid or
sulphuric acid can be employed, but the former gives the better
results.

Smith and Wallace' recommend the'addition of a c.c. nitric
acid to every loo c.c. of solution, the solution to be electrolysed
at a temperature of 50°, and with an E.M.F. of 2'5 volts, the
current imder these conditions will be ot ampere.

Heidenreich' states that good results are obtained when 15 c.c.
sulphuric acid (I'og sp. gr.) is added to the solution, and the
electrolysis conducted at an E.M.F. not exceeding i"85 volts.

When the whole of the copper has been deposited, the
solution is made just alkaline with sodium hydrate, and sufficient
potassium cyanide added to dissolve the precipitate of cadmium
cyanide first formed. The solution is then electrolysed as
described on p. 115.

Smith also recommends separation by employment of a solu-
tion containing hydrogen disodium phosphate and free phosphoric
acid. He takes 20 c.c. of a solution of hydrogen disodium phos-
phate (sp. gr. i'o35) and 10 c.c. of a solution of phosphoric acid
(sp. gr. i'347); temperature, 60°, with a current of 0-07 to o'oS
ampere, and a potential of 2'5 volts. The time required to
deposit the copper is about three hours.

The cadmium can be deposited first, the copper remaining
in solution if excess of potassium cyanide is added to the solution
of the mixed salts. It has already been noticed under copper,
p. 90, that when excess of potassium cyanide is present the
deposition of the copper is prevented ; this, however, is not the
case with cadmium.

In order to carry out this operation, sufficient potassium
cyanide is added to the mixed solution to dissolve the first-
formed precipitate of copper and cadmium cyanides, and then
3 to 4 grm. more potassium cyanide added. The E.M.F. should
1. S(v., 19, 870 ; A«,t.: Chem. /mirn., 12, 329,

Separation of the Metals,

not be allowed to exceed 2-6 or 27 volts, otherwise a portion
of the copper may be precipitated as an alloy with the cadmium.
The cyanide method for depositing cadmium is certainly the most
sure, but it generally requires from six to eight hours.

Copper from Zinc.

Acid solutions can he employed in this separation, provided
that the acid is not too dilute. Nitric acid, although it yields the
best results for topper, has the disadvantage — already frequently
noted with other metals — of preventing a satisfactory subsequent
deposition of the zinc. When, therefore, nitric acid is employed,
the solution must, after the copper has been deposited, be
evaporated down almost to dryness with a little sulphuric acid,
in order to drive off the nitric acid. The zinc salt remaining
is then dissolved in water, and the excess of sulphuric acid
neutralised with ammonia. Solutions containing a trace of sul-
phuric acid give very good deposits of zinc (p. 120}; the pre-
caution of adding a little ammonia to neutralise the acid freed
as the zinc is deposited must not be omitted, otherwise the
deposit may commence to dissolve again.

The deposition of zinc from cyanide solutions is not satis-
factory, but Classen's oxalate method gives very good results.
This method, with the necessary precautions, is set out on p. 119.

Copper from Silver.

In the separation of copper from silver the method usually
employed depends upon variation of potential. Several solutions
may be tised ; for example, solutions acidified with nitric acid
or the double cyanide can be employed. As a low E.M.F. is
of necessity employed in the operation, it follows that the current
is also low, and therefore the separation requires some little time.
When a solution containing nitric acid is employed the potential
should not exceed r-3 to i"4 volts, otherwise copper will be
deposited along with the silver. The chief objection to using

img J

Practical Eleciro-Ckemistry.

a solution acidified with nitric acid is tbe form in which the
silver comes down, it being very often of a crystalline nature,
and the crystals are apt to become detached when the deposit
is being washed.

The regulation of the E.M.F. is of very great importance;
the source from which the current is obtained should not liave
a potential much above that which is required in the experiment.
One difficulty is, that when most of the silver has been deposited
and the electrolyte becomes attenuated in silver ions, the E.M.F,
rises, and unless the experiment is being carefully watched, it will
be found that towards the end of the operation an alloy of copper
and silver instead of pure silver has been obtained.

Method for regulating the Potential.— When a long
bath of copper sulphate has two electrodes placed at either end,
the central space being free, a considerable E.M.F. is necessary
in order to cause a current of any intensity to pass through
the bath. Now, when in between the two electrodes plates of
copper are hung in such a manner that they make no electrical
contact, it is found that these plates become di-polar— the one
side becoming anode and

|||]|| ^ the other side cathode.

The drop in potential be-
tween the plates is accord-
ing to their distance apart.
The drop in potential in
a lo-per-cent, copper sul-
phate solution is about o'3
of a volt, when the plates
are fixed about a centi-
meter apart, and a current
of I ampere is passing
through the cell. Such a
cell is shown diagrammatically in Fig. 52.

In the figure there are seven plates hung independently ; two
electrolysing cells are shown, which are connected respectively

Separation of the Metals. 1 59

between the ~ pole and plate No. 4, and between plate No. 2 and
the -f- pole. If, now, the drop in potential is o"3 volt between
each plate, it follows that by taking five plates a shunted current
will be obtained, having an E.M.F. of i^s volts. Therefore the
highest potential the bath could possibly show would be I'S volls.
\Vhen higher potentials are required, the distance between the two
end electrodes is increased, with 3 consequent rise in E.M.F.

It is not, of course, necessary to have so many plates in
between, but by having a number of plates ihe current can be
shunted off for a number of experiments. The main portion
of the current passes, of course, directly through the copper bath,
and any slight variation in the shunt circuit will have no practical
effect upon the voltage. By increasing the current in the copper
bath, and therefore the E.M.F., the potential of the shunt circuit
will also be raised. It is advisable to reverse the current at the
terminals of the copper bath every twenty-four hours or so, in
order to keep the copper plates in condition.

Such an arrangement as this can, of course, only be employed
where low currents are required.

Another good method for obtaining low voltages, but which
does not admit of such delicate graduation as the one just
described, is to use cupron elements (p. 48), the RM.F. of each
cell being about o'8 volt. Therefore s cells coupled in series
give a potential of i'6, and 3 cells 3'4 volts. A thermopile can
also he used with advantage.

Copper from Silver in Cyanide Solution. — Both copper
and silver can be readily deposited from solutions containing
potassium cyanide in which they both form complex anions. But
ihe silver is deposited at a lower potential than is required to
precipitate the copper. In order that silver only may be de-
posited, the potential must not be allowed to rise above about
i"6 to i'7 volts. It is also advisable to have a considerable
quantity of potassium cyanide present, because the E.M.F. neces-
sary to deposit copper is higher when the concentration of the
cyanide is fairly high. The solution is made up by c

i6o Practical Electro-Chemistry.

the copper and silver salts in water, and adding sufficitint of a
solution of potassium cyanide to dissolve the precipitate first
formed, then about another 3 or 4 grm. of potassium cyanide
is added to the solution. After all the silver has been deposited,
which can be ascertained by boiling a few cubic centimeters of
the solution with a drop or two of hydrochloric acid — this portion
withdrawn must be returned again, — the copper can be deposited
by raising the E.M.F. Since, however, the cyanide solution
is rather strong for the satisfactory deposition of copper, a little
sulphuric acid is added to it in order to decompose the excess
of potassium cyanidc^f-iw must, of course, be done in the draught
cupboard.

Separation in Nitric Acid Solutions.' — In solutions
containing nitric acid the silver is deposited without the copper
if the potential is not allowed to rise abovei"3 to i'4 volts. As
soon as all the silver is deposited, the E.M.F. is increased, and
this causes the copper to be deposited.

The separation of silver by either of these methods may take
a considerable time if there is any quantity of the silver salt
present, from ten to fifteen hours often being required to remove
less than 0-5 grm. of silver. Therefore these separations are best
conducted overnight.

Copper from Mercury.

These metals may be separated by means of solution in
potassium cyanide, the mercury being deposited out at a lower
potential than the copper. Smith and Spencer* recommend to
electrolyse at a temperature of 55° to 70°, with a CD. of o'o6 to
o"o8 ampere; the E.M.F. must not exceed a'5 volts. About o'l
grm, mercury can thus be deposited in from three to four hours.
For this quantity of mercury, and an equal quantity of copper,

' Kiliani, Berg, iind Hiilten Zeil., I8B3, 375 ; Freudenbiug, Ztit.f. Phys.
Ckt-m., 18, 197.

' Anur. Chim.Soc., 1894,

Sifaralion of tite Metals. i6i

to 2 grm. of potassiuiu cyanide is sufficient. When all
! mercury is deposited out, the current is increased, and tlie
»pper is in turn precipitated.

Copper from Lead.

By usiny solutions containing a considerable quantity of nitric
there is no difficulty in deirasiting copper and lead siniui-
[janeously. A sand-blasted flag electrode or roughened basiii is
le the anode, the cathode being of the usual wire form generally
iployed as the anode.
To every loo c.c. of solution about 7 to 8 grm, of con-
.centrated nitric acid is added, and the solution electrolysed at a
[(temperature of 55" to 60°. The CD. may be from i to 175
'amperes, and the E.M,r. will be about 1-4 to I'S volts.

The lead is all deposited in about an hour and a half, but
the copper takes considerably longer to deposit. If the amount
of copper is large, it is better to stop the electrolysis when the
whole of tlie lead has been thrown out, and remove the electrode
on which the peroxide has been deposited. A fresh cathode of
larger surface is then placed in the solution, and the electrolysis
of the copper recommenced, the original cathode being now the
anode. This change of electrode is rather tiresome when a basin
anode has been employed, but it entails no trouble with a flag
electrode. The deposition of the copper is carried out according
to the usual method of operation in solutions containing nitric
acid (p. 86). It is sometimes advisable to partially neutralise the
excess of nitric acid after the lead has been deposited, because
copper is only slowly thrown out from solutions containing very
large quantities of nitric acid.

Copper from Manganese.

Copper and manganese can be separated in much the same
manner as copper and lead, only if nitric acid is employed its
amount must not exceed 3 or 4 per cent., because with stronger

Practical Electro- Chemistry.

162

solutions of nitric acid permanganic acid is produced and no
anode deposit is formed. It will be remembered that considerable
difficulty is experienced in obtaining a satisfactory and adherent
anode deposit of manganese oxide; in fact, the only really
satisfactory rnethod is the one described on p. 139. There it is
mentioned that in cases of separation small quantities of a mineral
acid may be added.

The solution is therefore made up by dissolving the manganese
and copper salt in water, adding about a to 3 grm, of chrome
alum, about 8 grm. of ammonium acetate, and z c.c. of sulphuric
acid. This mixture is then electrolysed with a CD. of o'6 to i
ampere, at a temperature of 75° to 80°, The copper will probably
be deposited in a badly adheriiig form, and it may be advisable to
redissolve it in nitric acid and re-deposit it.

With care the copper and manganese can he separated from
solutions containing about 2 to 3 per cent, of nitric acid ; but
the manganese deposit is rarely satisfactory, although the copper
is generally quite good. But as the manganese deposit is not
very readily dissolved up again, this method is not of much
value, owing to the difficulty of obtaining a solution of the
manganese if it is desired to re-deposit the metal.

Separation of Copper from Antimony. See p.
Separation of Copper from Gold. Seep. 186.

IRON.

Iron from Copper.

This separation will be found on p. 154.

Iron from Silver.

Since silver can be deposited from solutions containing e
of nitric acid, we have here a method of separation of iron from
silver. As, however, the deposit of silver is not always satisfactory J

S^areaien of tke Metals. 163

from solutions containing nitric acid, and as the presence of nitrates
is harmful when depositing iron, this method is hardly to be
recommended. Silver is likewise readily deposited from solutions
which contam potassium cyanide, but iron is not ; seeing Ukewisc
that the cyanides can be afterwards decomposed by boiling with
dilute sulphuric acid, the cyanide method is fairly satisfactory.

The solution containing the salts of iron and silver has about
2 or 3 grm. of potassium cyanide added to il, and the clear
solution is electrolysed at a temperature of from 50' to do , an
E.M.F. of about a a to 2-e, volts being employed. The electrolytic
separation of iron and silver is not of any importance.

Iron from Mercury.

The separation of iron from mercury is readily carried out iii
solutions acidified with nitric acid (see Mercury, p. 105). Here
Bgain, however, it is necessary to remove the nitric acid or nitrates
before adding ammonium oxalate or ammonium tartrate. In order
to effect the removal of the nitric acid, a few cubic centimeters
of sulphuric acid are added, and the solution evaporated nearly to
dryness. It is then taken up with water, the excess of ammonia
added, and the alkaline solution then neutralised with oxalic or
tartaric acid.

Iron and mercury can likewise be satisfactorily separated in
solutions acidulated with sulphuric acid. Add 1 c.c. of strong
sulphuric acid to the solution, and dilute to 130 c.c. Electrolyse
at a temperature of 60°, with a current of o'4 to 06 ampere. In
about an hour and a half the whole of the mercury will be
deposited.

Mercury can be readily deposited from solutions containing
excess of sodium sulphide (p. 106), whereas iron does not go into
solution, but is precipitated as sulphide. This method may be made
use of to separate the two metals. Excess of sodium sulphide is
added to a hot neutral solution of the two metals, and the mixture
is boiled for a few minutes, and then filtered. The iron sulphide is
washed with a little hot water, the washings being added to the

164

Practical Eleciro-Chemistry.

solution of the mercury sulphide. The mercury is thcd electrolysed
in the usual manner, care being taken that there is a sufficient
excess of sodium sulphide present. The iron sulphide is dissolved
in a little dilute sulphuric acid, and the solution boiled to drive off
the sulphuretted hydrogen. It is then made alkaline with ammonia,
and neutralised with oxalic or tartaric acid, and electrolysed as
usual.

Iron from Zinc.

Iron is not deposited from solutions containing free sulphuric
acid, whereas zinc can he precipitated from such solutions, pro-
vided there is not a large excess of sulphuric acid present. It
might therefore be supposed that there would be no difficulty in
thus effecting a separation ; this, however, is not the case. When
a mixed solution of an iron and zinc salt containing a small
quantity of sulphuric acid is electrolysed, an alloy of zinc and
iron is obtained. Although this might appear to entirely invalidate
the method, this is not the case, because the whole of the iron
and zinc can be deposited as an alloy, and the alloy, after being
weighed, is dissolved in dilute sulphuric acid. The iron goes into
solution in the ferrous state, and can then be titrated with standard
permanganate. The difference in the quantity of iron found and
of the total weight of the alloy represents the weight of the zinc.

There are several solutions from which the alloy of zinc and
iron may be deposited, Classen uses the double oxalate method.

I, The neutral solution of zinc and iron is poured into a hot
solution of 8 to 10 grm. of ammonium oxalate. Duritig the
electrolysis the mixture is kept just acid by addition of small
quantities of oxalic acid. The solution may be electrolysed warm
with a CD. of from o'5 to r ampere.

When the electrolysis is finished, the electrode is removed,
and washed and dried as usual ; it is then weighed. The electrode
is now placed in about 30 per cent, sulphuric acid, and the solution
gently warmed, when the deposit slowly dissolves. As soon as
the whole of the deposited metal has dissolved, the solution

Se/iaration of the Metals.

diluted with water, and titrated with standard potassium per-
manganate, the amount of iron being thus estimated.

If the amount of zinc in the original alloy is too great, there is
a tendency for it to go into solution again towards the end of the
reaction, and, at the same lime, for hydrated oxide of iron to be
precipitated.

II. The separation can also be very satisfactorily carried out
from solutions containing sodium sulphate, and traces of free
sulphuric acid. Here, again, if there is a lai^e excess of zinc
present, it shows a tendency to go into solution towards the end
of the operation, if the precaution of adding small quantities of
ammonia from time to time is omitted (p. 120), A CD. of o'4 to
o"8 ampere may be used, and the solution electrolysed cold.

III. Vortmann recommends the use of Rochelle salt and
caustic soda : 3 or 4 grm, of Rochelle salt is added to the solution,
and then an excess of 10 to 20 per cent, caustic soda solution.
The mixture is then electrolysed with a low CD. of 0*07 to o'l
ampere. Toward the end of the electrolysis the temperature is
advantageously increased to 50° or 60°. The whole of the iron is
deposited in three or four hours, while the zinc remains in solution.

Hollard and Bertiaux ' find, by first adding sulphurous acid to
the solution of the sulphates of iron and zinc, then after nearly
neutralising with sodium hydrate adding potassium cyanide, which
produces potassium ferrocyanide, that only zinc is deposited.

Note. — In the deposition of zincj it must be borne in mind that
platinum electrodes should not be used for the reasons set out on
p. izo. When an alloy is produced, and the solution has afterwards
to be titrated with permanganate, the platinum should first be
coated with silver, because the presence of copper would interfere
with the end reaction.

Iron from Nickel and Cobalt.

The most satisfactory way of estimating iron in presence of
nickel or cobalt is again the method of alloy. Classen uses

' Compt. Rfndus, 136, iaG6.

1 66

Practical Electro-Chemistry.

his double oxalate method, and deposits the nickel and iron
together as an alloy. The alloy is then weighed, and afterwards
dissolved in sulphuric or hydrochloric acid, and the solution
titrated ivith potassium permanganate in order to estimate ihe
iron.

The mixed iron and nickel salt is poured into a solution of
about 6 to 8 grm. of ammonium oxalate, and the mixture electro-
lysed at a temperature of 60" to 70°, with a CD. of o^s to i'5
ampere, the whole of the metals being deposited in the form of
an alloy in from two and a half to three hours.

The alloy of iron and nickel is extremely difficult to dissolve
in either dilute sulphuric or hydrochloric acids, although either
acid will dissolve it if given sufficient time. Fairly concentrated
warm hydrochloric acid is the best solvent, but the iron must then

be titrated with — potassium dichromate.

Ammonium tartrate may be used for this separation quite as
satisfactorily as ammonium oxalate, in fact the deposit often has a
better appearance from this solution than from the oxalate solution,

A mixture of iron and cobalt is treated in exactly the same
manner as for nickel and iron. The only difficulty is due to the
red colour of the solution when titrating the iron. Tliis red colour
can, however, be neutralised by addition of small quantities of
nickel sulphate to the solution, a solution of the green nickel salt
and the red cobalt salt producing an almost colourless liquid.

Iron from Chromium.

When a mixed solution containing iron and diromiure
electrolysed after addition of ammonium oxalate or tartrate, the
iron is deposited at the cathode as usual, and the whole of the ,
chromium salt is converted into the form of a chromate. When {
the deposition of the iron is completed, the electrode is removed,
and washed and dried as usual.

The solution now contains the chromium compound as
chromate, which may be estimated by acidifying the solutions '

with dilute sulphuric acid and titrating with ferrous ;
sulphate. This estimation can be carried out either by an addition
of an excess of a weighed quantity of ferrous ammonium sulphate
and titrating back with potassium permanganate— the end reaction,
however, is rather difficult to see; or by titrating with a standard
solution of ferrous amraontum sulphate, using potassium fern-
cyanide as an indicator.

Another method is to acidify the solution with sulphuric acid
and reduce the chromate with sulphurous acid ; or reduce by
acidifying with hydrochloric acid and boiling with alcohol. The
chromium in the reduced solution is then precipitated as hydroxide
by addition of ammonia, and the hydroxide is filtered off, washed,
dried, and ignited, the chromium being estimated as CrjOj.

Iron from Aluminium.

A method somewhat similar to that employed in separating
iron from chromium may be employed for separating iron and
aluminium. Excess of ammonium oxalate or tartrate, about 8 to
lo grm., is added to the neutral solution of the mixed metals, and
the solution electrolysed as usual.

At the commencement of the electrolysis only iron is deposited,
but as the quantity of iron decreases, and ammonium carbonate is
produced by the decomposition of the ammonium oxalate, small
quantities of aluminium hydroxide may be deposited as white
gelatinous flakes. If the quantity of aluminium hydroxide thus
deposited is only small, it can be neglected. But when a con-
siderable amount is thrown out, it has a tendency to adhere to
the negative electrode, and is then rather difficult to remove ; this
causes the weight of iron to appear too high, and that of the
aluminium too low. In this case it is best to add a slight excess
of oxalic acid, in order to bring the hydroxide into solution again ;
on further electrolysing, the whole of the iron is thrown out. The
aliuninium in the solution is estimated by addition of excess of
ammonium hydrate, whereby the aluminium is precipitated
hydroxide, and is.then estimated in the usual manner as ALO3.

Practical Eleciro-Ckemistry.

\Vheii ammonium tartrate is used as electrolyte, the aluminium
hydroxide is not precipitated, therefore it is to be recommended
rather than the oxalate. In this latter case, the CD. should not
exceed i ampere, but is better to be kept at o'8 of an ampere.

According to HoUard and Bertiaux,' the addition of sulphtjrous
acid to the electrolyte prevents the deposition of aluminium
hydroxide, when oxalate solutions of aluminium and iron are
electrolysed.

Iron and Manganese.

As iron and manganese are constantly met occurring together,
and as the ordinary methods of separation of these two metals are
not very satisfactory, a good electrolytic method would he of
great importance. Owing to these causes a great many attempts
to obtain a satisfactory separation have been made, but it is only
quite recently that a successful process has been devised. It
might be supposed, seeing that manganese can readily be deposited
at the anode, but that iron is always precipitated on the cathode,
that there should be no difficulty in devising a separation. But
unfortunately there is a great tendency on the part of the iron to
be deposited in greater or less quantities as hydrated oxide along
with the manganese oxide.

Classen has recommended his oxalate method for separating
iron and manganese, but there is here always a tendency for a
mixture of ferric hydrate to be deposited along with the manganese r
hydrate at the anode.

A, HoUard and Bertiaux ^ find that the addition of sulphurous '
acid prevents the precipitation of the iron oxide. The electrolyte
consists of a mixture of ammonium citrate and ammonium,
sulphate, about 3 to 4 grm. of each. The solution is electrolysed '
with a CD. of r ampere, and at a temperature of 48°. It is found \
that the iron is deposited more rapidly than the manganese, there-
fore the larger electrode, e^. the basin or flag, is made the cathode.

tft. Rfndu!, 1903, 130, 1366.
903, 136, 1366.

Separation of tke Mttals. 169

As soon as all the iron has been deposited, the cathode is removed,
the iron dissoivcd in dilute sulphuric acid, and titrated with
potassium permanganate, A certain amount of the cathode
deposit may consist of iron sulphide, and when this is dissolved,
sulphuretted hydrogen is evolved. It is necessary, of course, to
make sure this has all been driven off before titrating with per-
manganate.

The larger electrode is now made the anode, the smaller
previous anode coated with some of the peroxide being now the
cathode. This coating of peroxide passes into solution, and,
together with the manganese remaining in the original solution,
is deposited upon the anode. The temperature employed for this
latter electrolysis is go" to 95°. The amount of ihe deposited
manganese is determined by ascertaining how much iodine is
liberated by it from an acid solution of potassium iodide.
MnO, + aHI + H,SO, = MnSO, + 2H,0 + I^

When a solution containing iron and manganese, to which has
been added an excess of ammonium oxalate, is electrolysed, the
iron commences to come down before the manganese, and it is
only after some little time that the manganese peroxide commences
to separate. As soon as the manganese begins to separate, J.
Kuster' finds that the addition of small quantities of phosphorous
acid, added from time to time during the first two hours of the
electrolysis, prevents the deposition of ferric hydrate, and likewise
prevents the precipitation of manganese peroxide.

The solution is electrolysed with a CD. of i'5 to 2 amperes
at ordinary temperatures, and as soon as the manganese com-
mences to be deposited at the anode, i or 2 c.c. of a lo-per-cent.
solution of phosphorous acid is added. The manganese deposit
immediately vanishes, and the solution becomes reddish. As
more manganese is thrown out, a furdier quantity of phosphorous
acid is added. After about 2 hours, when the main portion of
iron has been deposited, it is no longer necessary to add any more
phosphorous acid. The addition of about 15 c.c of phosphorous
' Bcr., 1903, 36, 2716.

I70

Practical Electro-Chemistry.

acid at the commencement of the operation entirely prevents the
deposition of manganese peroxide. Too much phosphorous acid
should not be added, because this causes the iron lo be pre-
cipitated very slowly. The whole of the iron is deposited in from
five to ten hours, depending upon the amount of phosphorous acid
added. Toward the end of the reaction the solution becomes
dark brown in colour, and may be opaque from the presence of
more or less precipitated hydrated oxide of manganese. On
dilution with water the hydroxide is thrown out.

Iron from Lead.

Iron can readily be separated from lead by electrolysing in a
solution containing excess of nitric acid. The lead is deposited
at the anode as peroxide, and the iron remains in solution.
Before depositing the iron, it is necessary to get rid of the nitric
acid. The best way is to precipitate the iron as ferric hydrate by
the addition of excess of ammonia ; the precipitate is then well
washed with hot water and dissolved in oxalic acid, and the
oxalic acid solution neutralised with ammonia. Or the ferric
hydrate may be dissolved in tartaric acid, the solution exactly
neutralised with ammonia, and the iron deposited as usual.

^k the metal

COBALT AND NICKEL.

Many attempts have been made to separate cobalt and nickel
electrolytically, but none of the methods so far published can be
said to give very satisfactory results. The only method which can
be at all recommended is that of A. Coehn and M. Glaser,' and
even this cannot be termed absolutely quantitative, but probably
with a little alteration it might be improved.

The process depends upon the simultaneous deposition of the
two metals — nickel at the catliode and cobalt at the anode.
In order to deposit cotalt quantitatively at the anode, naturally
the metal must, by some means or other, be prevented from being

' Zal.f. Anorg. Chcm., 33. g.

Separation of the Metals.

precipilated on ihe cathode. Now, as hydrogen i? only deposited
0-22 volts higher than cobalt, too high an E.M.F. must not be
employed, or else oni; must employ some method in which the
deposition takes place at a lower potential than that at which
the H ions are discharged, e^. the addition of a chromate to the
solution. The method employed by Coehn and Glaser is as
follows ; —

To the neutral solution, which should not contain more than
oT grm, of cobalt, o'r to o'a grm. K-jCrjOj is added, and 3 to
4 grm. potassium sulphate. The solution which is made up to
Sooc.c. iselectrolysed withanE.M.F. of 3'3 to 2-4 volts, the current
being about o"io to 0M5 ami>erc. In about ten hours the whole
of the cobalt is deposited as peroxide, and the nickel as metat on
the cathode. The cobalt oxide deposit is afterwards dissolved in
acid, and after neutralisation deposited in the usual manner in the
metallic form on the cathode.

Cobalt and Nickel from Iron. — See p. 1C5.

Cobalt and Nickel from Copper.

The solution containing the cobalt and copper salts or a
mixture of all these is electrolysed in a solution containing an
excess of nitric acid. Copper only is deposited on the cathode,
the nickel and cobalt remaining in solution.

As both nickel and cobalt are only deposited with difficulty"
from solutions containing nitric acid or nitrates, the solution
remaining after the copper has been deposited must lie evaporated
to small bulk with sulphuric acid in order to drive off the nitric
acid. The cobalt or nickel are then analysed in the usual n

Cobalt and Nickel from Silver.

Two methods may be used to effect the separation of nickel
or cobalt from silver. Either a solution acidified with nitric acid
can be employed, or a solution containing the double cyanides

Practical Electro-Chemistry.

of these metals. Solutions of the double cyanide are preferable.
The E.M.F. is kept as low as possible, a current of o'l ampere
being employed, but however much care is taken, there is always
a tendency for the silver and nickel to be deposited together.
Seeing with what great ease silver can be separated from cobalt
and nickel by ordinary chemical means, it is obvious that there
is no advantage to be obtained by employing the somewhat
doubtful electrolytic method.

Cobalt and Nickel from Zinc.

The mixed salts are dissolved in water, and then poured into
a solution of from 5 to 6 grm. of rochelle salt (potassium sodium
tartrate) and then excess of sodium hydrate added, after which
the solution is made up to the required bulk. A current of from
o'3 to o'6 ampere may be used. The zinc is deposited, but the
nickel and cobalt remain in solution, the whole of the zinc is
deposited in from three to four hours. With cobalt salts there is
a tendency for part of the cobalt to be deposited at the anode as
oxide ; if this should be noticed, the addition of small quantities
of hydroxylamin sulphate or chloride from time to time will cause
it to dissolve off, or a small quantity of potassium iodide may
be added. There is a marked tendency for the zinc to be
deposited in a spongy form, and to be very burnt in appearance.

Cobalt and Nickel from Lead.

This separation is readily carried out in solutions containingj
excess of nitric acid. The cobalt and nickel are not deposited!!
but the lead is precipitated as peroxide on the anode. A current 1
of 1 to I's amperes may be employed, and the solution is best ]
electrolysed at 60° to 70°. If it is afterwards desired to deposit
the nickel or cobalt, the nitric acid must first be got rid of,
because in presence of nitrates the metals are thrown out exceed- '
!, although the deposits are often extremely good

Cobalt and Nickel from Manganese.

The separation of nickel or cobalt from manganese may be
carried out in a similar manner to that described for separating
iron and manganese. The method can, however, hardly be
recommended as being one of any great degree of accuracy

(see p. i6S).

Nickel and Cobalt from Mercury.

This separation can be carried out in solutiona containing free
nitric or sulphuric acid. Owing to the fact that nickel and cobalt
are only slowly deposited from solutions containing nitrates, it
is better in this case to use solutions containing about 3 per
cent, of sulphuric acid. The electrolysis may either he conducted
at ordinary temperatures or at a temperature of 55° to 70°; the
ordinary precautions adopted in depositing mercury must be
observed (see p. 104).

Beside employing acid solutions, solutions containing potas-
sium cyanide may be used ; from the latter solution, nickel and
cobalt are only deposited with currents of a considerable E.M.F.,
whereas mercury can be depositi^d readily with currents of low
potential, from about i'5 volts. It is best to electrolyse at .a
temperature of from 55° to 70° ; the presence of cobalt causes the
mercury to be deposited more slowly. Generally speaking, about
o'3 grra. of mercury can be deposited in about three hours, but it
may require from four to five hours. The E.M.F. should not rise
above I'g volts.

MERCURY.

The separation of mercury from the other metals can be carried
out on much the same lines as the methods adopted for separating
silver from other metals.

Separation of Mercury from Copper.— See p. 160.
Separation of Mercury from Iron. — See p, ifi^.

174 Practical Electro-Ckemistry.

Separation of Mercury from Cobalt and Nickel.—
See p. 173.

Mercury from Lead.^

It might be supposed that mercury and lead could be very
readily separated by electro lytical methods, in solutions contain-
ing nitric acid, the mercury being deposited on the cathode, and
the lead as peroxide at the anode. To a considerable extent this
does take place; but if less than 15 per cent, of nitric acid be
present, the lead is only partially deposited at the anode, a portion
coming down as metal at the cathode and forming an amalgam
with the mercury. If low currents arc employed, this combined
deposition at the cathode can be almost completely prevented.
The CD. should not be above o"2 ampere, and dierc should be
from 25 to 30 c.c. of nitric acid (sp. gr. i"3) added for every r5o
cc. of solution.

Mercury from Manganese.

From solutions containing free sulphuric acid and a small
quantity of chrome alum, mercury and manganese can be separated,
the manganese being deposited on the anode as oxide, and the
mercury on the cathode. The smaller electrode must he used
as cathode ; for the rest, it is only necessary to use the conditions I
and precautions necessary for depositing manganese, in order to I
obtain a complete separadon (see p, 13S).

Mercury from Silver and Gold.

It is not possible to directly separate mercury from silver and
gold by electrolytic means, as the decomposition values of the
salts of these three metals lie too closely together. But mercury '
and silver or mercury and gold can readily be obtained as
amalgams, either from solutions containing free nitric acid tx
from cyanide solutions.

' Smith and Moyer, Zal. f. Anorg. Chem., 4, 267. Hddenreicb, Btr^,
29, ,585.

Separation of the Metals.

The CD. may vary from o'l to 07 amperes. When the
mercury and silver or mercury and gold have been deposited, the
amalgam is weighed, and then the mercury driven off by heating ;
on cooling and again weighing, the loss of weight represents the
amount of mercury which had been deposited. Care must be
taken not to heat the amalgam to too high a temperature, or
there will be a danger of causing the silver or gold to alloy
with the platinum electrode. In order to make quite sure that
the whole of the mercury has been driven off, the electrode
should be again heated, and, if any loss in weight is noticed,
it must be heated until a constant weight is obtained.

Mercury from Antimony.

When a solution containing a mixture of mercury and
antimony salts is electrolysed with a current of from 0-015 ^°
o'og ampere and an E.M.F. of a'o to 3'6 volts, tlie whole of
the mercury is deposited, while the antimony remains in solution.
About s grm. of tartaric acid and 15 to 20 c.c. of lo-per-cent.
ammonia is added to the solution to be electrolysed, which, after
heating to 50° or 60°, is electrolysed with the currents above
stated; the antimony must be present in the higher state of oxida-
tion. The deposition requires about six or seven hours. After
all the mercury has been deposited, the antimony can either be
deposited from the same solution by rendering it quite neutral, and
passing a current of from 0-5 to o'S ampere — the electrolysis is
best conducted at ordinary temperatures ; or the antimony can
be precipitated widi sulphuretted hydrogen, dissolved in excess
of sodium sulphide, and electrolysed as described on p. io8.

Mercury from Arsenic.

Mercury can readily be separated from arsenic, from solutions
containing free nitric acid ; about i to 3 per cent, is sufficient.
The E.M.F, should not exceed 18 volts; the mercury is de-
posited, and the arsenic remains in solution. When high currents
are employed, the deposited mercury is contaminated with arsenic.

176

Practical Ekclro^Chemistry.

Mercury from Tin.

Mercury can be separated from tin in an exactly similar
naanner to that employed in separating it from antimony, namely,
from solutions containing tartaric acid and ammonium tartrate.
The mercury salt should first be added to the tartaric acid, and
then the ammonia mixed with it, after which the tin salt may be
added, and the mixture electrolysed at a temperature of 55^, the
potential not being allowed to exceed i"7 volts.

Mercury can also be separated from tin by taking advantage
of die fact that, although mercury can be deposited from solutions
containing a large excess of sodium sulphide, tin is not precipi-
tated from such solutions by the electric current. About 20 to 30
c.c. of a concentrated solution of sodium sulphide is added to
the mixture of mercury and tin, and the solution diluted to 125
or 130 c.c.

This mixture is tlien electrolysed with a current of from o*i
to o'i5 ampere, the temperature being about 7o°j under these
conditions the E.M.F, will he about 2 "5 volta. In about five or
six hours the whole of the mercury will have been deposited.

SILVER.

Separation of Silver from Copper. — See p. 157.
Separation of Silver from Iron. — See p. i5a.
Separation of Silver from Nickel and Cobalt. —

Separation of Silver from Mercury, ^See p. 174.

Silver from Cadmium.

From Cyanide Solution. — About 2 grm. of potassium
cyanide — which must be pure, otherwise the silver deposit may
be brown in colour — -is added to the solution containing the 1
cadmium and silver salts, and the solution diluted to ahout 130 c.c.
With low currents of o'oa to 003 ampere, and at a temperature of \

Separation of the Metals.

60' to 80°, the whole of the silver will be deposited, while the
cadmium will remain in solution. The E.M.F. will be about
2-1 volts; from five to six hours will be required to deposit
o'l to o-z grm. of silver.

The cadmium can either be deposited from the cyanide solu-
tion by increasing the current to o'S or o'S ampere, or the cyanide
can be decomposed, and one of the other methods described
under Cadmium {p. 114) may be employed for its deposition.

From Nitric Acid Solution. — To the solution of the
mixed salts add 10 to iz c.c, of nitric acid (sp. gr. r'4), and make
up to 130 or 140 c.c. Heat to 60" or 65°, and electrolyse with
a low current, so that the E.M.F. shall not exceed z'o to 2-&
volts. The silver may in this case be deposited in a more or
less crystallme form, and probably will not adhere very well to the
electrode.

The cadmium remains in solution, and can be deposited by
adding excess of sodium or ammonium acetate to neutralise the
nitric acid, and then electrolysing with a current of o*i to o^i
ampere.

Silver from Lead.

Add 8 c.c. concentrated nitric acid to the solution containing
the mixture of lead and silver salts, and then make up to about
150 c.c. Electrolyse at a temperature of 80°, with a current of
o"i8 to o'2 ampere. The silver and lead are deposited simut-
taneously— the silver on the cathode, the lead on the anode as
peroxide. The usual precautions as to washing and drying the
deposits, necessary for silver and lead, are adopted.

For the estimation of small quantities of silver in presence of
large amounts uf lead, see p. 189.

Silver from Tin.

The separation of silver from tin is best carried out by a

ind electrolytical methods, and may

combination of chemical
be done as follows : —

Practical Electro-Chemtstry.

Pass sulphuretted hydrogen into tho acid solution containing
the tin and silver salts. Filter off the mixed sulphides, well wash
with water, and then treat with successive small quantities of
ammonium sulphide.

The tin sulphide dissolves, and the solution so obtained, after
dilution to the requisite volume, is electrolysed hot, with a current
of o-g to I ampere, the usual precautions necessary to electro-
lysing tin being followed. (See p. iiz.)

The silver sulphide is washed with water and dissolved in a
solution of potassium cyanide, or dissolved in warm nitric acid,
evaporated to small bulk to drive off excess of nitric acid,
neutralised with ammonia and treated with potassium cyanide
It is then electrolysed as described on p,

Silver from Antimony.

The separation of silver from antimony is similar to that
employed for separating it from tin. The mixed sulphides are
treated with ammonium sulphide, or better with sodium sulphide,
and the antimony solution so obtained electrolysed as usual ; the
silver, after treatment with potassium cyanide, electrolysed/^ se.

Silver and antimony can also be separated by purely electro-
lytical methods, and these are extremely exact when carried out
with care. According to A. Fischer,' the metals can be separated
from a solution in nitric acid in the following manner ; —

I. To a solution of the antimony and silver salt, the total
volume of which is i6o c.c, 5 grm. of tartaric acid and 2 c.c. of
nitric acid (sp. gr. 1-4) are added. This solution is electrolysed in
the cold with an E.M.F, of i'3 to i '5 volt, the current varying from
o"oi to o'os ampere. Under these conditions the time required
is about eighteen hours. But at a temperature of 50'' to 60'', with
the same E.M.F., the current is o'oa to o'la ampere, and the
whole of the silver is deposited in eight to nine hours.

When the whole of the silver has been deposited
solution is evaporated to small bulk, made alkaline with
' Ber., 38, 3345-

ited out, the ^H
with Eodtum^l

Separation of tke Metais. 179

hydrate, and about 80 cc of sodium sulphide added. If the
solution is yellow, potassium cyanide may be added until it
becomes colourless. The antimony is then deposited from this
solution in the usual manner (p. loS).

II. The separation can also be carried out from solutions con-
taining potassium cyanide and tartaric acid ; the addition of tartaric
acid is necessary to cause the solution of the antimony salt. The
electrolysis can either be conducted at the ordinary temperature,
when eighteen hours are required to deposit all the silver, or at
30" to 50°, when eight hours are sufficient.

Procedure, — Add to the solution a solution of from 3 to
S grm. potassium cyanide and o'j to i grm. of tartaric acid : the
mixture is then made up to 150 to 160 c.c, and electrolysed with
an E.M.F. of 20 to 24 volts. The antimony, when in the pentad
condition, is not deposited unless the E.M.F. rises above 26
volts; but when it is in the lower state of oxidation it begins
to be reduced at 2'o to I'l volts ; therefore, in order to separate
the two metals in potassium cyanide solution, the antimony must
be in the pentad condition.

It is important that the potassium cyanide employed should
be of the purest, otherwise the solution becomes brown, and
polymerisation products of hydrocyanic acid may be deposited
upon the silver, and lead to incorrect results.

When the whole of the silver has been deposited, the solution
is evaporated to small bulk, and 70 to 80 c.c. of sodium sulphide
added ; the antimony is then deposited as usual.

Silver from Zinc.

Both zinc and silver can be deposited from cyanide solutions,
but the silver can be deposited at a much lower potential than
the zinc. If, therefore, a low current density is employed, the
E.M.F, obtained is not sufficient to deposit the zinc; while it is
quite high enough to decompose the silver solution. With a
current density of o-ozs to o'o35, the E.M.F. is about 2-6s to
75 volts; in about three or four hours the whole of the silver
will be deposited.

I will be d

Practical Electro-Chemistry.

Since the deposition of zinc from cyanide solutions is extremely
slow and rather uncertain, it is best to decompose the cyanide
by warming with small quantities of sulphuric acid, and, after
nearly neutralising the excess of sulphuric acid with ammonium
hydrate, electrolysing with a CD. of o'o^ to o'o6 ampere. The
whole of the zinc will be deposited in about two or three hours.
For the precautions necessary when depositing zinc from sulphuric
acid solutions, see p. 120.

LEAD.

Separation of Lead from Copper.^ — See p. 161.
Separation of Lead from Iron. — See p. 170.
Separation of Lead from Cobalt and Nickel. — See
p. 172.

Separation of Lead from Mercury. ^See p, 174.
Separation of Lead from Silver. — See p. 177.

Separation of Lead from Antimony.

Antimony and lead are often found together in alloys, there-
fore a good method of separating these metals would be extremely
useful. Neumann and Nissenson ' recommend dissolving the
alloy (z"5 grm.) in a warm mixture of 10 grm, of tartaric acid, 15
c.c. water, and 4 c.c. nitric add (sp. gr. i-4). A clear solution
can thus be obtained, and to this is added 4 c.c. of concentrated
sulphuric acid; on coohng, the solution is made up to 250 c.c
The precipitated lead sulphate is then filtered off, and, in order
to determine the antimony, 50 c.c. of the filtrate is made strongly
alkaline with caustic soda, and 50 c.c, of a strong solution of
sodium sulphide added. The mixture is then warmed, and, if
necessary, it is filtered, and the clear solution electrolysed for
antimony as usual with a current density of i'5 to 175 amperes,
(See p. 108.)

' Neumann and Nissensun., C/iem. Zn'l., 1895, 49.

Separation of the Metals.

If it is desired to estimate the lead, the lt;ad sulphate is
digested with a little concentrated ammonium hydrate for a few
minutes. The lead sulphate is therehy converted into hydrate,
then it is cautiously washed into a solution of lo c.c. nitric
acid. After making up to the required bulk, thu solution is
electrolysed as usual (p. 137).

ANTIMONY.

Separation of Antimony from Silver. — See p. 1
Separation of Antimony from Mercury. — Sec [

Antimony from Copper.

Copper may be separated from antimony in solutions con-
taining tartrates, the copper being deposited, the antimony
remaining in solution.' To a solution containing about o'l grm.
of the two metals add 8 grm. of tartaric acid and 25 c.c. of strong
ammonia. It is necessary for the antimony to be present in the
pentad condition. Heat the mixture to 50°, and electrolyse with
a current density of o'o8 to o'lo ampere ; the E.M.F will be about
I "8 to 2'o volts. The whole of the copper is deposited in from
five to six hours. The antimony can then be deposited, by making
the solution exactly neutral with tartaric acid, and electrolysing the
hot solution with a current of o'a to 0-5 ampere. (Sec p. 1:1.)

Antimony from Tin.^

While tin can be quantitatively deposited from solutions con-
taining excess of ammonium sulphide, it cannot be obtained
quantitatively from solutions to which has been added sodium
sulphide; in fact, if sufficient excess of sodium sulphide is pre-
sent, the precipitation of the tin by the electric current is entirely
prevented.

'n. Amer. Chem. Soc., 15, i()5, and ZeU./. Aiwrs. Chem., 4, i^^.
• .Sn-., XVII. 2345; X.VII1. uioand 2060.

Practical Efectro-Ckemistry.

'I'he sodium sulphide should be as pure as possible ; for this
reason it is best to etnploy the solution prepared as described
on p. 282. When the article of commerce is employed^ which
always contains free caustic alkali and other impurities — a con-
centrated solution should be prepared and saturated with sul-
phuretted hydrogen gas. The solution is then boiled and filtered,
and finally evaporated until, when cold, it commences to crystallise.

In order to carry out the separation, 70 to 80 c.c, of the
concentrated solution of sodium sulphide is added to the sulphides
of the two metals. The tin, if not already in the stannic con-
dition, must be converted into the higher state of oxidation by
the addition of hydrogen peroxide before adding the sodium
sulphide. If the metals are obtained in acid solution, sufficient
sodium hydrate is added to make the mixture just alkaline
^a precipitation of the hydrates of tin or antimony does not
matter— and the sodium sulphide is added. In any case, after
the addition of the sodium sulphide i to z grm. of sodium
hydrate is added; this must be of sufficient purity not to give
a precipitate with sulphuretted hydrogen.

The solution may either be electrolysed at ordinary tempe-
ratures or at a temperature of 50° to 60°.

CONDITIONS.

CD 0-2 10 0-9 ampere.

E.M.F. . . . 0-9 tQ ri volts.

Time . . . z to 15 hours, tlepcnding apun the temperature

and CD. AHemperaluiestifSo" to6o''and
with o'5 ampeie CD. Lelween 2 and 3 houis
are required.

At the commencement of the reaction die solution often
becomes opaque from the gassing which takes place, but toward
the end of the process the solution becomes quite clear. When
the whole of the antimony has been deposited, the electrodes are
removed, and the cathode is rapidly washed and dried.

The tin cannot be de^xisited from solutions containing sodium
sulphide ; it is therefore necessary to convert the sodium sulphide
into ammonium sulphide. This can be done by adding about
zs grra. of ammonium sulphate and warming until the evol

Separation of tfie Metals.

of hydtogun sulphide ceases, after which boii for ten to fifteen
minutes. Cool, and, if any sodium sulphate separates out, add
sufficient water to dissolve this. The tin can now be deposited
by electrolysing with a CD. of 0-3 to 0*5 ampere, either at the
nonnal temperature or at 30".

Another method is to precipitate the sulphide of tin by acidi-
fying with dilute hydrochloric acid ; this can then he filtered off,
and, after washing, he dissolved in ammonium sulphide.- As,
however, stannic sulphide is rather difficult to filter, it is better to
employ the first method.

Classen prefers to convert the thioatannate into the oxalate,
and, as tin deposits very well from solutions of the double
oxalate, the method may be recommended. In order to do this,
the thiosalts are partly decomposed with sulphuric acid — the solu-
tion must not be made acid. On warming, the major portion of
the thiosalts are decomposed, and hydrogen sulphide is driven off.
Hydrogen peroxide is now added until the metastannic acid
precipitated becomes quite white. The mixture is now acidulated
with sulphuric acid, neutralised with ammonia, a further quantity
of hydrogen pero.tide added, and the mixture boiled until all the
peroxide is decomposed, as shown by effervescence ceasing.

The stannic acid is then filtered off and dissolved in oxalic
acid ; then, after addition of 3 or 4 grms, of ammonium oxalate,
the solution is electrolysed with a CD, of o"2 to 0*3 ampere.
The time required will he about eight or nine hours.

Tartaric acid and ammonium tartrate may be substituted for
the oxalic acid and ammonium oxalate.

A. Fischer' and also A. Hollard' find that the separation of
tin and antimony can be carried out when small quantities of
potassium cyanide are present. The sulphides of the two metals
are dissolved as usual in sodium sulphide, and potassium cyanide
solution is added drop by drop until the solution is quite colour-
less; it is then electrolysed with an E.M.F., which must not
exceed I'l volt, and at a temperature of 30°. The tin which
remains in solution is then worked up as usual.

' Bir., 36, 234S. = Bull. SfC. Chim., 29, 262.

Practical Ekctro-Chemistry.

ARSENIC.

In separating arsenic from solutions containing other metals, 1
it is never attempted to deposit out the arsenic ; but conditions are ]
sought which will allow the deposition of the other metal, while 1
the arsenic remains in solution and can afterwards be estimated I
by chemical means. Generally speaking, when arsenic is preseatj,!
it is necessary to employ a lower CD. in depositing the other 1
metal than is otherwise the case.

Copper from Arsenic.

I. From Solutions containing Potassium Cyanide. '
— To the solution containing arsenic and copper .add potassium
cyanide until the precipitate first formed is just dissolved, E!ec-
trolyse at a temperature of 6o° with a CD. of from o'2o to o'2S ]
ampere ; the E.M.F. will be 3'3 to 3-6 volts. The whole of the \
copper can usually be deposited in from 3 to 3'5 hours.

II. Nitric Acid Solution. — Add about 5 c.c. of c
trated nitric acid to every 100 c.c. of solutiooj and electrolyse aCfl
a temperature of 50° to 60°, taking care not to allow the E.M.i

to exceed I'g volts. Or the deposition may be carried out in the I
cold overnight. According to HoUard and Bertiaux, the additionj
of small quantities of ferric sulphate prevents the depositio
the arsenic, the arsenic thereby being kept in the higher stale o
oxidation.*

Antimony from Arsenic.

Treat the alloy or compound (about i grm.) containing arsenic 1
and antimony with aqua rcgia, and evaporate to dryness. Add a
few cubic centimeters of water to the residue, and from 2 to
3 grm. of sodium hydrate ; then add 70 or 80 c.c. of a concen-
trated solution of sodium hydrate and i grm. of potassium cyanide,
dilute to the required volume, and electrolyse at a temperature of

CONDITIONS.

Ii: the end lo r5 volts.

t. Sdc. Chim., 1904, [hi.] 31, 900.

Separation of the Metals.

In about 6 or 7 hours the whole of the antimony will have
been deposited. The arsenic remains in solution, and may be
estimated by ordinary chemical means.

If metals of the copper group are present, they must be sepa-
rated chemically before the antimony is deposited, in which case
the antimony and arsenic will be obtained in the form of their
sulphides, and can Uien be directly dissolved in 70 c.c. of sodium
sulphide.

ANALYSIS OF ALLOYS.

Sterling Silver.

SterUng silver is an alloy consisting of silver and copper.

The Brilibh silver coin contains silvei gz'S per cent.

The United Stales silver coin contains silver 90 per cent.

The German „ „ „ go ,,

The French „ „ ,, 83-5 to 90 per cent.

The analysis of this alloy is comparatively simple, but it re-
quires care when conducted upon purely elect rolytical lines. The
simplest method is to dissolve the coin in nitric acid, and pre-
cipitate the silver as chloride. The silver can then be weighed
as chloride or dissolved in potassium cyanide and electrolysed.
The solution containing the copper must then be evaporated
nearly to dryness, in order to expel the excess of hydrochloric
acid, then taken up with water and nitric acid, and the electro-
lysis conducted as usual (see p. 86). If the separation is to be
carried out entirely with the electric current, then the two metals
can be separated either from solutions containing free nitric acid
(see p. i6d), or, better, from solutions containing potassium
cyanide (see p. 159}.

Bronze — Copper Coinage.

From o'2 to 0*4 grni. of the alloy in the form of turnings or
filings is dissolved in nitric acid. It is best to first cover the
alloy with strong nitric acid {sp. gr. i"5), and then add water drop
by drop until a vigorous reaction sets in. When the whole of the

r86 Practical Electro-Ckemistry.

alloy has dissolved, the solution is diluted with water and boiled,
and the precipitated oxide of tin filtered off and thoroughly washed,
the washings being returned to the origiiial solution.

The simplest procedure with reference to the tin is to weigh
it directly as oxide, or it can be boiled up with ammonium sulphide
solution, and analysed electrolytically from this solution, (See

p. 1.2.)

The filtrate containing the copper and zinc and excess of free
nitric acid is electrolysed directly. The copper is deposited on
the cathode, the zinc remaining in solution, (See p. 86.)

Before proceeding to estimate the zinc, the nitric acid should
be removed, after which the zinc may be estimated from an
oxalate (p. 119) or acetate (p. lao) solution. Bronze coinage in
Great Britain contains :—

Copper 9S par's.

Tin 4 pirls.

Bell metEl> contains 3 parts copper and i part tin ; Bpeon*
lum metal i part tin and 2 parts copper ; but these alloys
vary to some extent. Qon metal contains about 90 parts
copper and 10 parts tin.

Bronzes sometimes contain small quantities of lead, in which
case the lead is deposited on tlie anode as peroxide when electro-
lysing the solution for copper. They also frequently contain
traces of iron.

Copper and Gold— Sterling Gold.

SterUng gold used in making the British coinage contains I
9I-66 per cent, gold, the rest being copper. The alloy employed J
for making the German gold coinage contains 90 per cent, of J
gold aud 10 per cent, of copper. Pure gold is said to be 24 carats.
Sterling gold is 22 carats. Gold of 18 carats contains i3 parts of \
gold and 6 parts of copper or some other metal alloyed with it ;
and 15 carat gold consists of 15 parts of gold and 9 parts of some j
other metal, usually copper or silver.

Separation of the Metals.

Ill order to analyse an alloy of gold and silver, the material
is dissolved in aqua rtgia, and evaporated to dryness. The
residue is then taken up with a little dilute hydrochloric acid,
a slight excess of sodium hydrate is added, and about 4 gtm.
of potassium cyanide. The solution is then electrolysed with a
CD. o'o5 Co o'oS ampere; the potential should not be allowed
to exceed 2 volts. The solution should be electrolysed at a
temperature of 60° to 65°. The whole of the gold can at this
tein|>erature be deposited in about three hours.

The copper can he deposited from tlie cyanide solution by
decomposing a portion of the cyanide with dilute nitric acid,
and electrolysing with a current density of 0-5 to i amjwre.

Alloys of Copper and Nickel —
Nickel Coinage.

The alloy is dissolved in nitric acid, which should be fairly
dilute. The solution is then made up to the required volume,
and about 3 or 4 c.c. of concentrated nitric acid added. It is
now electrolysed for copper as usual.

After all the copper has been removed, the solution is evapo-
rated nearly to dryness with a little sulphuric acid, in order to
drive off tlie excess of nitric acid, diluted with water, and 3 grm.
of ammonium borate and 30 c.c. of strong ammonia added. The
solution is electrolysed as usual for nickel. (See p. 95.)

It generally happens that small quantities of iron are present
in the alloy ; the iron, if any, is precipitated as hydrate when the
ammonia is added. It should be filtered off before proceeding
to determine the nickel.

The ferric hydrate can be dissolved in oxalic acid or tartaric
acid, and, after neutralisation with ammonia, estimated electro-
lyCically as usual. (See p. loi.)

The German nickel coin consists of copper 75 per cent., and
nickel 25 per cent. The nickel coin used in the United States
contains the same quantities of nickel and copper as the German

^ emo.

Practical Electro-Clietnistry.

Copper, Zinc, and Nickel— German Silver.

The metal is dissolved in nitric acid, and the copper deposited
out as in the separation of copper from nickel.

The solution, which now contains the zinc and nickel, is
evaporated to small bulk with sulphuric acid, in order to expel
the excess of nitric acid. From this solution either the nickel
can be deposited first — the zinc remaining in solution — or the
zinc can first be thrown out, leaving behind the nickel.

Deposition of the Zinc. — Five to six grm. of RochcUe
salt, sodium potassium tartrate, is added to the solution, and then
a considerable excess of caustic soda. A current of o'3 to 0-5
ampere is then passed through the solution, which is kept at
ordinary temperatures. In from three to four hours, the whole
of the zinc will have been deposited. If there is a tendency for
nickel oxide to separate at the anode, about o'z to o'5 grm. of
hydroxylamine hydrochloride maybe added; this causes the oxide
to pass into solution again.

As soon as the whole of the zinc has been deposited, which
may be determined by hanging a piece of copper wire over the
cathode, the solution is, after the removal of the cathode, acidified
with sulphuric acid, then made strongly alkaline with ammonia,
and the nickel determined as usual. (See p. 92.)

Deposition of the Nickel. — Von Foregger finds that it
is possible to deposit tlie whole of the nickel first, while the zinc
remains in solution. To the solution which remains, after the
copper has been deposited, and from which the excess of nitric
acid has been driven off, 10 grm. of ammonium carbonate and 10
c.c, ammonium hydrate (sp. gr. O'88o) are added. The solutioa
is then diluted to 150 c.c, and electrolysed with a CD. of o"3
to o"5 a pe h h to a d h end s ncreased to i ampere. .
The tempe a ure of he electrolj s n an aiued at 55° to 60°.

When he whole of h n ckel has b en deposited, which can
be ascerta ed by 1 e add on of an mon um sulphide to a small

veighed. H

Separation of the Metals.

quantity of the solution, the cathode is removed and weighed.
The zinc which remains in solution can be deposited by making
the solution slightly acid with oxalic acid, and electrolysing as
usual when determining zinc in oxalate solutions (p. 119).

Commercial Lead for Traces of Silver.

Arth and Nicholas' have determined the most favourable
conditions for estimating small quantities of silver in presence
of large amounts of lead.

In solutions containing sufficient acid, lead is not deposited
on the cathode in the metallic form, and only at the anode as
peroxide, when a large amount of free acid is present. In order
to deposit metallic lead, the E.M.F. required is fairly high, and
the amount of free acid employed must be considerable.

Silver only requires moderately acid solutions, and a low
E.M.F. ; but, as already mentioned, silver is very apt to be de-
posited in a crystalline or spongy non-adherent form from acid
solutions. Kuster and Steinwehr have shown that this difficulty
can be surmounted by using an E.M.F. which does not exceed
I "38 volts. Bearing these facts in mind, the authors found with
i'2 volts that a spongy deposit of lead began to form along
with the silver. With i*i volt this was not the case.

In order not to exceed a pressure of i^i volt, they find it best
to employ a source of current which on the open circuit does
not exceed r'l volt. The minimum concentration of acid is i
per cent, by volume; 5 c.c. of alcohol is also added. With a ^k

lai^er quantity of acid, lead may be deposited. At ordinary H

temperatures the deposition of silver is incomplete, and adheres H

badly ; therefore the electrolysis must be carried out at a tempe- H

rature of 60°. H

This method has been employed for the detection and estima- ^

tion of silver in ordinary sheet lead. For example, in one case
in 100 grm. of lead, 0-0042 grm. silver was obtained, or i part
■ ' Bull. Set. CMm., XXIX. 13. ■

PractUal Electro-Chemistry.

: part i

3 parts of lead wag

190

in 33,809 ; in another case,
found and estimated.

In dealing with such large quantities of lead, the bulk of'
solution will have to be very considerable, and the solution should
be kept agitated, if not continuously, at any rate, from time to

Antimony, Arsenic, and Tin— Britannia
Metal.

The metal is brought into solution by treatment with aqua
regia, and, after evaporating just to dryness on the water bath,
the residue is treated with a little caustic soda, and then with
sufficient sodium sulphide to bring it completely Into solution-
generally from 60 to 70 c.c. is sufficient. The antimony is de-
posited from this solution as described on p. 109.

The solution now contains arsenic and tin ; it is acidified with
dilute hydrochloric acid, whereby the arsenic and tin sulphides
are precipitated. The mixed sulphides are filtered off and washed)
and then washed through the filter paper, and digested with
ammonium carbonate. The sulphide of arsenic passes into solu-
tion, and sulphide of tin is left behind; this is dissolved in
ammonium sulphide, and the tin determined as described on
p. 112.

The arsenic may be determined gravimetrically as sulphide^r
the solution in ammonium carbonate being acidified, a little sul-
phuretted hydrogen water being added to cause complete precipi-
tation as sulphide ; or the solution may be made up to a litre
with distilled water, and from this litre 1 c.c. taken and diluted
down again to i litre, and, if necessary, i c.c. again taken and
diluted to I litre. Finally, i c.c. of this attenuated solution is
placed in a Thorpe (p. 148) or Sand and Hackford (p. 150)
arsenic apparatus, and the amount of arsenic determined by
comparison with a standard arsenic mirror.

Small quantities of copper, and occasionally bismuth, may be

Separation of tJte Metals.

present in Britannia metal. If a qualitative analysis shows these
metals to be present, must be separated by the usual chemical
methods.

Zinc Residues from Qalvanising Bath.

(Contained Zinc, Iron, Copper and I-ead.)
A very hard alloy is obtained from the zinc residues left in the
galvanising baths, the hardness and infusibility being due to the
presence of iron in the 7.inc, In order to analyse such an alloy, it
is dissolved in warm moderately dilute citric acid. The solution
is made up to the required volume, and about lo c.c. concentrated
nitric acid added. It is now electrolysed, using a large anode and
a small cathode surface at a temperature of 60° or 70° and a CD.
of i'5 amperes. In about two hours the whole of the lead will
have been deposited on the anode as peroxide. Probably a
portion of the copper — if there is any — will have been deposited
upon the cathode, but on removing the anode, this immediately
dissolves in the strong nitric acid. A fresh flag cathode is placed
in the solution, which is then partially neutralised with ammonia
and the copper deposited with a current of about 0-5 ampere.
As soon as all the copper has been deposited, the solution is
neutralised with ammonia; ammonium oxalate, and sufficient
oxalic acid to make the solution just add, added, and the zinc
and iron deposited together.

The deposit, after weighing, is dissolved in dilute sulphuric acid,
and the quantity of iron determined by titration with standard
potassium permanganate. Or the iron and zinc can be determined
separately by adding excess of ammonia, after the copper has been
precipitated. The ferric hydrate thus precipitated is dissolved
in oxalic or tartaric acid, neutralised with ammonia and deter-
mined as usual (see p. 100). The solution containing the zinc
is neutralised with oxalic acid and deposited as described on

The constitution, as would naturally be expected, of this

his alloy ■

192 Practical Electro- Chemistry,

varies considerably. The analysis of a sample was made in the
above manner and checked by chemical means —

Zinc 9375

Iron 3-65

Copper 0*09

Lead 1*53

The Other constituents consisted of carbon and oxygen. Many
samples examined contained no copper.

PART III

PREPARATIONS BY ELECTROLYTIC

MEANS

CHAPTER XI.

FREPARA TIONS.

In canriiiE out tiiu preparations set out in the following chapters,
it will often be necessary to separate the anode from the caliiode
by means of a porous membrane. The most usual form of
diaphragm, or membrane, for this purpose is a cell of ungla/ed
earthenware, such as is used in many forms of primary battery.

Before using these cells, they should be filled with water in
order to ascertain whether they have actual holes through defects
in manufacture. When filled with water, the outside of the cell
should become moist within fifteen to thirty minutes, but the water
should not actually trickle out. The porous cells can be obtained
ill a variety of forms ; it is desirable to have them fairly thin in
order that they may cause as little resistance to the passage of
the current as possible. After having once been used, the cells
should be kept in a basin and covered with cold water, otherwise
they are very apt to disintegrate from the substances of the
electrolyte crystallising in the pores-
One of the chief drawbacks to the employment of iwrous
pots is, that as a rule they cannot be used for different experiments,
owing to the difficulty of thoroughly cleaning them, i'or example,
if a cell had been used in the preparation of iodoform, it could not
satisfactorily be used afterwards in preparing — say azobenzene —
because it would cause this second preparation to have the
smell of the iodoform. Again, after a short time, especially in
alkaline solution, the cells begin to disintegrate and break down,
portions of the walls of the cell often falling off in flakes, or as a

fine powder.

Practical Electro-Cfiemistry.

A Torm of cell illustrated in Fig. 53 gels over this difficulty.
It is made cither of Wedgwood ware or of a glaned material. The
actual cell consists of two portions, one fitting within the other.
Thus, in the figure, where two cells are shown, a fits into b, and C
fits into D, Each complete cell consists of two perforated cells,
the perforations being large enough for an ordinary pin to pass

through, the inner or smaller of which fits loosely into the larger
one. When put together, a liquid can pass readily through the
complete ceil, and of course it does not act as a diaphragm. In
order to use the cell as a diaphragm, the inner cell is wrapped
tightly with ashestos paper, until it can just be passed down
into the outer cell. The asbestos should be wrapped in such a
manner that there is considerable overlapping at the bottom end.
This is then folded over so as to practically make a bag, and, when
pushed home, the inner cell rests tightly upon the asbestos.
Generally, about three folds of thin asbestos jiaper is sufficient to
cause the one cell to fit tightly into the other. The cell prepared
in this manner is soaked in water or the electrolyte, such, e^., as
sulphuric acid or a salt solution, and is ready for use. When
carefully packed, this makes a very efficient membrane, because
since the two portions of the cell are, owing to the perforations,
to all intents and purposes open to the passage of the current,
the diaphragm employed, so far as resistance is concerned, is
practically one of asbestos paper.

Preparations. 197

For most purposes, for sulphuric acid, M'hicii is not stronger
than ag to 30 per cent., or for moderate strengths of caustic
alkali, and of course for neutral solutions, it is not necessary
to employ asbestos, ordinary filter paper making an exceedingly
effective diaphragm. As is well known, filter paper — blotting-
paper — can be bought in sheets at a low cost, and the diaphragm
is prepared by wrapping it several times round the inner cell in the
manner described for asbestos. Parchment can also be em-
ployed, or a pulp of asbestos poured into the annular space
between the two cells ; a pulp of blotting paper has also been
found to act very well, indeed ordinary brown paper has been
used, and found quite satisfactory. Finally, coarse sand or
coarsely powdered glass may be filled in between the pots, and
makes an exceedingly good diaphragm, and will of course stand
the action of the strongest acids and alkalis. It is sometimes a
little difficult to obtain sand or powdered glass of quite the
requisite degree of coarseness to prevent it passing through the
holes, ordinary sand requiring first to be sifted through a sieve-
Asbestos or a pulp of well-washed nitrated cotton wool can be
very well used, even with strong acids and alkalis.

After the cells have been used, all that is necessary in order to
clean them is to remove the inner cell from the outer one, throw
away the substance which has been used as diaphragm, and the
cells can then be readily cleaned, after which they are ready for
further use.

It is sometimes found necessary in electrolysis to keep a small
bag, containing the substance which is in solution and is bemg
electrolysed, hanging in the solution in order to keep the con-
centration of the electrolyte constant. Now, a linen or muslin
hag often gets acted upon, and more or less disintegrated by
the electrolyte. One of the cells, above described, without a
diaphragm will be found extremely useful for this purpose,
because it allows free ingress and egress of the electrolyte. Of
course, the substance used must not he so finely powdered that it
passes through the perforations of the cell.

Practical Electro-Chemist ry.

>efl

Agitation of Solution,— In the preparations to be describt
it will often be recommended to agitate the electrolyte. This can
be done by means of paddles or fans, either of metal or of glass,
wood or ebonite. Generally, it is an advantage to connect the
, stirrer with one of the poles of the

j^ pll circuit. Thus, when oxidi.sing an

C I ' organic substance, a stirrer of platinum

^^^■(^B Ifc*^ ^^ ^^^^ ^^^ ^^ satisfactorily employed,
^ 1" and is connected with the positive

pole. Fig. 54 shows such a stirrer
made of platinum ; the method of
making contact has already been de-
scribed on p. 8i, Fig. 48.

The lead stirrer may be made as

follows : — Thin lead pipe, to which

the vanes for mixing the liquid are

" burned " or soldered, is drawn over

a steel rod of the same diameter as

the bore of the pipe. The steel rod

protrudes about 5 to 10 cm. above

the top of the pipe, in order that it

may be fastened in the chuck. The

|iipc is burned or soldered at the

bottom and top to prevent the solution

' " ^'* from running in between it and the

steel core. If a central core of steel is not used, lead electrodes

are not sufficiently rigid to be used for rotating purposes. For,

diagram of glass stirrer, see p. 272.

Electrodes — The electrodes emplojed in this section of th(
bo k -ire usually of pi un lain ckel or graphite.
1 lat nun s u ed ts w re fo 1 or gau e platinum is joined tal
plat n n ilmost var ibly b) Id ng which is an easy process
to carry out b p] ose for example t s desired to weld a piece
of w re to 1 sheet of flat num The heet platinum is laid upon
1 flat I cc of s 00 h ro OS I an anvil, the wire is

Preparations, 199

held against the sheet with a pair of pliers, and the flame of
a blowpipe caused to play upon the sheet and wire. When
the platinum has reached a bright red heat, the wire is struck
a sharp blow with a hammer, the flame of the blowpipe is kept
on the point to be hammered, and the hammering continued
until a good welded joint has been produced.

Every electro-chemist should be able to make his own
electrodes, and must therefore be able to use a soldering iron.
The form or shape of an electrode employed will be modified by
circumstances and by the ingenuity of the operator. The best
form of graphite to use for carbon electrodes is the "Acheson"
artificial graphite, made at the Niagara Falls. It is an excellent
conductor, and has the enormous advantage over other forms of
carbon electrodes, that it can be easily cut and machined.

CHAPTER XII.
PREPARATION OF INORGANIC PRODUCTS.

Persulphuric Acid.

H2S2O8

One of the first substances to be prepared by electrolytic
methods, and which had not previously been obtained by purely
chemical means, was persulphuric acid. Sulphur heptoxide S2O7,
the anhydride of persulphuric acid, was discovered in 1878 by
Berthelot, who obtained it by the action of the silent electric
discharge on a well- cooled mixture of oxygen and sulphur dioxide.
He also showed that when a moderately concentrated solution of
sulphuric acid is electrolysed, the acid in the neighbourhood of
the anode, after the passage of the current, possesses oxidising
properties. Further, that on addition of barium chloride to
the sulphuric acid solution, and filtering off the precipitate of
barium sulphate, and then boiling the filtrate, another quantity
of barium sulphate was produced, the soluble barium salt of
persulphuric acid having been decomposed on boiling into barium
sulphate, sulphuric acid, and oxygen.

BaS^Os + H2O = BaS04 + H2SO4 + O

I. Preparation of Persulphuric Acid.

Persulphuric acid can be produced both with and without a
diaphragm. In the latter case, when the electrolysis is conducted
in such a manner that the anode is placed considerably below

Preparation of Inorganic Products.

the cathode, practically no intermingling of the upper and lower
layers of sulphuric acid takes place, and persulphuric acid is
formed round the anode.

Dilute sulphuric acid is supposed to contain the ions zH- and
SOj", and, on electrolysis, hydrogen is yielded up at the cathode,
and the SOj" has its electrical charge neutralised at the anode ;
but since SOi is incapable' of existence in the molecular con-
dition, it reacts with a molecule of water, and oxygen gas is given
up at the anode.

2SO. + jH,0 = zH,S04 + Oa

But when a fairly concentrated solution of sulphuric acid (50
to 60 per cent.) is electrolysed and the solution kept cool, it is
noticed that, although hydrogen is given off as vigorously as
usual at the cathode, very little oxygen is evolved at the anode.
In strong sulphuric acid we assume that the ions, instead of being
aH- and SO/, are mainly H' and HSOj'. Now, on electrolysing
such a solution, hydrogen is yielded up at the cathode ; but at
the anode the ions HSO,', at the moment of having their electrical
charge neutralised, unite together to produce a molecule of per-
sulphuric acid thus : —

,0H HO, ^OHHO

so/ - sSOj = SO ' ■;S0, + Ha

^OiH HO ^O- — 0'

Similarly, a strong solution of an acid sulphate, e^. potassium
hydrogen sulphate, is ionised into the ions H' and KSO/, and on
electrolysis a persulphate is produced.

OK KO OK KO
SO SO = SO SO + H

OH HO O O

The conditions necessary are a high anode current density
and a cold solution , the temperature of the solution should not
be allowLd to rise above +5°

A very convenient apparatus for demonstrating the frrmation
of persulphuric ac d and persulphates is bhonn in Fig 55

a large bo 1 ng tul e wh ch is nearly filkd with a solution *

202 Practical Electro-Chemistry,

of 50 10 60 per cent, sulfjiuric acid, or .1 saturated solutio
acid potassium sulphate. The tube b, which is open at both ends, I
is supported in a liy means of a piece of copper wire or by a J
perforated cork, notched at theJ
edges to allow the escape of .1
gases. C is a narrow glass tube, I
at the lower end of which a J
small spiral of platinuiu wire ia 1
fused. It is filled with mercury^ ,V
and connected with the + pole 'I
of the current supply. D is
cathode of stout platinum wire. J
The whole apparatus is placed '
in a heakcr filled with cold water.
On imssing the current, about
I ampere, hydrogen is evolved '
^'°' *^' at the cathode, and, as this is J

close to the surface of the solution, the hydrogen passes into theJ
air without mixing with the solution round the anode. Any!
oxygen which is given off at the anode passes up the tube i
After the current has been passing for a short time, a small portioa J
of the solution may be withdrawn from the neighbourhood of the I
anode by means of a pipette. On adding a solution of polassium. |
iodide to it, iodine is liberated, thus showing the presence of |
persulphuric acid. The conditions necessary are a high current-{
density at the anode, and a cold solution. Although the actual
current registered on the ammeter is only about i ampere, yel^ .
owing to the very small surface of the anode, the current density
win be from 60 to 80 or more amperes per square decimeter.

For studying the course of the reaction, by titration with I
ferrous ammonium sulphate (see p. 205), it is better to employ I
the apparatus depicted in Fig. 56. The solution should be
well mixed, and then 10 c.c. withdrawTi by means of a pipette,
and the solution titrated, the o])eration being repeated every 45
minutes, and continued until the maximum amount of persulphuric
acid is obtained : the current efficiency may then be calculated.

Preparation of Inorganic Products. 203

When potassium hydrogen sulphate is electrolysed under the
same conditions, after the current has heen passing for some ten
or twenty minutes, a cloud of potassium persulphate begins to
separate round the anode. In making the solution of acid
potassium sulphate, a saturated solution should be made at normal
temperature, and then cooled down before being placed in the
apparatus, otherwise crystals of acid potassium sulphate may
separate out during the electrolysis, and will interfere with the

II. Preparation of Potassium Persulphate,
using a Diaphras:ni.

A porous pot, A (Fig. 56), is made the cathode compartment,
the cathode being a coil of lead or copper tube, e, through
which cold water is circulated, so that the solution may be kept
quite cool. In order to make electrical connection, a piece of
copper wire is soldered on to the coiied pipe, and connected with

Practical Electro- Chemistry.

204

the negative pole of the current supply. The cathode solution {
consists of 50-per-cent. sulphuric acid.

The anode is a coil of thin platinum wire, d, wound about t
three times round the outside of the cathode compartment;
should be of such a, surface that, with a registered current of g
or 6 amperes, a current density of 50 or 60 amperes is obtained.
The porous pot and the anode are then placed into a beaker, c, of I
about 600 to 700 c.c. capacity, the whole apparatus being placed (
in a glass basin, and surrounded with ice or a mixture of ice and
salt. The anode solution is a saturated solution of acid potassium
sulphate, containing a few cubic centimeters of dilute sulphuric
acid. For most experiments, when only small quantities of the
persulphate are required, a porous cell with a capacity of roo to
12Q c.c. may be used. This is placed in a beaker or glass jar
of such capacity that only about 200 to 350 c.c. of the saturated
solution of potassium bisulphate is required to practically fill it.

As the electrolysis proceeds, and the potassium persulphate
separates out, the concentration of the acid potassium sulphate
decreases. In order to keep the solution constantly saturated,
a small perforated cylinder, such as is described on p. ig6, Fig. 53,
filled wth crystals of potassium hydrogen sulphate, is supported
in the upper portion of the anode compartment, where it is held
in position by means of a clamp.

Miiller finds that the yield of persulphates is increased by the
addition of small quantities of hydrofluoric acid. When this acid
is added, the electrolysis must be conducted without a diaphragm,
and the glass vessel must be coated with paraiBn to prevent the
HF acting upon the glass; probably a celluloid vessel could be
satisfactorily employed.

Ill, Ammonium Persulphate.

The same appar.itus and conditions as are employed for the
preparation of potassium persulphate are used for preparing the
ammonium salt. The anode solution consists of a concentrated
solution of ammonium sulphate in a solutionof5-per-cent. sulphuric

Preparation of Inorganic Products.

acid. The preparation of ammonmm persulphate is more
factory than that of the potassium salt, because the acid
sulphate is more soluble in water. The perforated cylinder for
keeping the concentration constant is in this case filled with
crystals of ammonium sulphate. Persulphuric acid and the per-
sulphates are derivatives of hydrogen peroxide, as is shown by
the structural formula. When a solution of persulphuric acid or
a persulphate is heated, oxygen gas is evolved.
OK KO
O^ /SOa + H^O = 2KHS0i +

o — o

The persulphates are therefore very powerful oxidismg agents :
the action is not very rapid, but it is very thorough ; this is
probably due to the fact that they are fairly stable, and are not
rapidly decomposed. A mixture of a persulphate and sulphuric
acid is known as Caros acid, and is often employed in organic
chemistry, owing to its extremely powerful oxidising action.

The barium salt of persulphuric acid is soluble in water; we
have therefore here a means of separating this acid from sulphuric
acid. In order to do this, excess of barium hydrate is added to
the mixed solution, when barium sulphate is precipitated, and may
be filtered off. The solution now contains a mixture of barium
hydrate and barium persulphate ; by careful addition of sulphuric
acid, until no further precipitate is produced, a solution con-
taining persulphuric acid is obtained.

BaSjOa -I- H,S04 = BaSO, -)- H.SaO,

Estimation of Persulphuric Acid. — The quantity of
persulphuric acid in a solution can be estimated by means of
ferrous ammonium sulphate, which is oxidised to the ferric con-
dition. The operation may be carried out by adding an excess
of a solution of ferrous ammonium sulphate of known stregglh
and titrating back with potassium permanganate.

H.jSaO„ + aFeSO, = Fe,(S04)j + HjSO,

In carrybg out the operation, a known volume of the acid
solution, or a weighed quantity of a persulphate (dissolved in

2o6 Practical Eieclro-C/temistry.

water) is taken, and a considerable excess of a solution of ferrous
ammonium sulphate, of known strength, added, and also dilute
sulphuric, about 5 c.c. to every 10 cc. of solution; then about
roo c.c. of boiling ivaiur is piiured into the mixture, which is
immediately titrated back with potassium permanjjanate,' If the hot
water is not added, the reaction between the ferrous salt and the
persulphate is slow, only being completed after some considerable
time. It is not necessary to add sulphuric acid when a solution
containing persulphuric acid and sulphuric acid is to be titrated. I
Potassium or sodium persulphate can be determined by simjdv'
heating a weighed portion of the salt,

KAOa = K.jSO^ + SO, + O
The loss in weight shows the amount of persulphate which w
present in the sample taken.

LITER A TURE.

Bcrthelot, CoiHpt. Rewtus, 86, 20, 277 ; H. Marshall, Joura. Chem, 1
Soc.^ 1881, 771 ; Berthclol, Comp. Rmdus, 114, 876 ; K. Elbs aiid O. ^
'^€D&\i\,^XT^Zeit.f.EUktrockem.,\Z'^,l.!^\T. Y..}L\\i^,JoHrn.f.prakt. '
Ckem., 1893, 48, 158 ; Zeit. EUklroehem., 1895, 2, 245 ; A. R. Foster
and E. F. Smith, Anur. Ckem. Sac, 1899, 21, 934 ; H. Marshall,
CA^m. NcTvs, 88, 76; Le Ulanc and Eckardt, Zeit. f. Eleklrackem..
V. 355 ; Mijller, Zdt.f. Eleklrockcm., X. 776 (1904).

IV. Sodium Hypochlorite.

When a strong solution of sodium chloride is electrolysed il
' tiie cold, without a diaphragm, the main product produced i
sodium hypochlorite. The reaction in its simplest form may^
be -represented by the following equations :—

I. NaCr=Na- + Cl'

II. Na + HaO = NaOH + H

III. 2NaOH + zCl = NaCl + NaOCl + H,0
It would therefore appear that, if the electrolysis is continued 1
for a sufficiently long time, a large proportion of the chloride wiQ 1
' Li: Ulanc and EcUardl, Zdt.f. EUktrochcia , V. 355.

Preparation of Inorganic Products.

become converted to hypochlorite. This, however, for several
reasons, is not the case. In the first place the hydrogen, at the
moment of its liberation at the cathode, exerts a reducing action
upon the hypochlorite, regenerating sodium chloride.

NaOCl + 2H = NaCI + H,0
In order to obtain the minimum of reduction, the cathode
should be smaller than the anode ; that is to say, a high current
density at the cathode should be employed. Under these con-
ditions the reducing action of the hydrogen is localised, and there
is more chance for the hydrogen atoms to unite to form molecules
without first acting upon the hypochlorite. On the other hand,
the CD. at the anode need not be quite so high as that at the
cathode, but neither must it be very low. When the current
density is low, very little oxygen is given off at the anode ; this,
of course, prevents oxidation of the hypochlorite to chlorate, but
the amount of hypochlorite produced is not so great, because,
after a certain quantity of hypochlorite has been produced there
are present Na' and OCl' ions. The OCl' ions help to carry the
current, and, being discharged at the anode, cause oxygen to be
liberated and hypochlorous and chloric acids to be formed.

I. 2OCI' + H,0 = bHOCI -f O
H. 60Cr -f 3HiO = 2CIO; +4CI' + 6H- + 3O'

Now, since the OCl' anions are relatively more readily dis-
charged at the anode than the CI' ions, i.e. less energy is re-
quired for their discharge, the tendency is for a considerable amount
of the electrical energy to be wasted in these secondary changes.
To prevent this as far as possible, a high anode C.D. and good
circulation of the electrolyte are desirable, but in order to prevent
cathodic reduction, the cathode is kept smaller than the anode.
For example, with an anode of one square decimeter the cathode
might have an area of 075 sq. dcm.

But there are also other methods for preventing cathodic
reduction. It is found that if the sodium chloride used contains
a small quantity of a calcium salt, that a thin pellicle of calcium

rent

Practical Electro-Chemistry. ^^^^

hydrate is produced on the cathode. This pellicle scales off, but
is immediately reformed. Now, since there is a high current
density at the anode, anytliing which will momentarily hinder
gas on its liberation from coming in contact with the electrolj
will tend to cause union of the atoms to molecular hydrogen.
When the hydrogen has once assumed the form of molecules,
then its reducing power is at an end. This very unstable
membrane or diaphragm of calcium hydroxide is able to
the union of the atoms to a very large extent. Foerster has ft
that a small quantity of an alkali chromate gives even bctt
results than a calcium salt. The quantity of cliromate required!
is extremely small (o"5 to i per cent.), and yet it is remarkably
effective. The temperature should not be allowed to rise abovB
20", because the higher the tera[x;rature the greater the inclinatioa
to form chlorates.

Process. — A glass battery-jar of about 500 to 700 c.C^J
capacity is nearly filled with a saturated solution of common salt.
If the solution is not clear, it should first of all be filtered,
best to use both anode and cathode of platinum, but the cathode
may be of nickel or graphite, and graphite can also be substituted
for the platinum anode. The cathode should be in the form of a
spiral of stout wire, in order that as high a C. D. as possible may be,
employed. The anode may either be of sheet platinum or c
platinum wire, but the most satisfactory results, oil a small scale^j
are obtained when a rotating anode is used, such, c^':, as that!
described on p. 19S.

CONDITIONS.

Anode CD 12 lo 16 amiierea.

Cathode CD 20 10 30 amperes.

E.M.F 3"5 m 4'S volts.

Temp 18° 10 20°

If the anode is not rotated, it should be fixed at the opposite side 1
of the electrolysing vessel to the cathode, and should be kept
near the upper portion of the solution. Agitation of some form
or other is to be recommended. As the CD. employed is very
high, the platinum wire carrying the current should be stout i

Preparation of Inorganic Prodttcts. 209

order to prevent heating. To carry this current without undue
heating, the wire should be from i'5 to 2 mm. in diameter.

In order to study the course of the electrolysis, 10 c.c.
of the solution is withdrawn every half-hour, and titrated. To
this quantity of solution is qdded excess of a solution of potassium
iodide, and the mixture is then acidified with dilute hydrochloric

(-/) HCIO + HCl = Cls + H,0
(h) CI, + 2HI = 2HCI + L

The amount of the liberated iodine is then determined by

N
means of — thiosulphate, in the usual way.

2Na5S,0, + I, = Na^SA + 2Nar
It is very instructive to follow the course of the electrolysis by
analysing the gases evolved at stated intervals. To do this, a gas
coulommeter should be placed in series with the hypochlorite cell.
The electrolysing cell must be closed with a rubber stopper through
which a delivery tube passes. The amount of current which is
being passed in during, say, ten minutes is easily measured by the
coulommeter, and this can be compared with the quantity of gas
which escapes from the electrolysing cell. The gases will con-
sist of oxygen and hydrogen, with a trace of chlorine ; this latter
can, however, be neglected. The gases are collected in a
Hempel's burette, and the quantity of oxygen estimated by
absorption with alkaline pyrogallol. The loss of hydrt^en shows
the quantity of the gas which is being used up in reducing the
hypochlorite.

Titration and gas analytical experiments should be tried with
plain sodium chloride solutions, and with solutions containing a
small quantity of potassium chromate. Curves showing the
current efficiency and yield of hypochlorite in a given time should
then be plotted.

LITERA TURE.
F. Oettel, Zeit. Eleklrocktm., 1894, I. 69 and 356 ; Cketn. Zeitvng,
iS94,18,6g; H.Bischoffand F. ¥QerS.eT,Zeit.f. EUkirockem., 1897,4,
46t i A. Sieverts, Eleklrorlum., 1 899, 6, 364 and 374 ; F. Oettel, Zeil.f.

Elektroehem., 1900, 7, 31 5 and 449 ; Viktor Engelhardt, Zeit.f. £
chem., 1900, 7, 390, and Viktor Enfe'dhardi, Hypochlorite w. EleklT'
Bkhlu {SN\\hs\m Knapp, 1903).

CHLORATES.

In the second equation, on p. 207, it has already been shoi
that when hypochlorite anions take part in the electrolyi
they are on discharge converted into chloric ions.

60C1* 4- sHjO = 3CIO3' -f- 4CI' + 6H- + 3O"
Now, the conditions of electrolysis of chlorides can be ;
altered that the final product will be a chlorate. But the reaction
just referred to is not the only one which occurs when chlorates
are produced.

In-all probability the production of hypochlorites is always 1J
first stage in the reaction, and that then, partially through t
hypochlorite taking part in the electrolytic process and bd:
oxidised at the anode, we may get :

aClO' + OH' = HCIO, + CI'

This primary oxidation probably takes place in a slightly alkaluj

solution in which there are free OH ions. But in an acid solutid]

(solution containing a bicarbonate) we probably get —

(«) 3HC10 + Cl' = CiO; + 3H- + 3Cl'

{b) cio' + zHcio = cio; + 2H- + zcr

In an alkaline solution direct oxidation of the chlorine ions n
also take place.

CI + 3O = ClOs'

The equations just given may all take place in the cold, but \
order to obtain the best results in the preparation of chlorates, a"
hot solution is always employed, and therefore the following
equation also takes place, and is probably the main reaction : —

3KCIO = KCIO, + 2KCI
When the electrolysis is conducted at high temperatures, per-
chlorate is not produced, but it is formed in cold solutions. In the

Preparation of Inorganic Products.

electrolytic preparation of chlorates, a certain quantity of oxygen
is invariably given off, which is probably due to the hypochlorite
ions taking part in conveying the current.

zClO' + HjO = 2HOCI +

In preparing hypochlorites it has already been found that the
reducing action of the hydrogen can, to a very large extent, be
prevented by the addition of small quantities of calcium salts or
of chromates. In preparing chlorates, the addition of a small
quantity of potassium chromate is even more advantageous.

In the preparation of chlorates [he following points are of
importance :' —

I. Prevention of cathodic reduction, e.g. by addition of calcium
salts or potassium chromate.

II. Slight acidity of the solution in order to aid the formation
of free hypochlorous acid. This can be brought about by passing
a stream of carbonic acid gas through the solution.

III. The employment of sufficient volume of solution in pro-
portion to the CD., and good agitation of the electrolyte, to allow
the secondary reactions to laVe place as completely as possible.

IV. The temi)erature to be at least 40° in order to prevent the
formation of perchlorates, and also to lower the resistance and
therefore the E.M.F.

V. Preparation of Potassium Clilorate.

Make a saturated solution of potassium chloride at 40° or 50°,
and to every 100 grm, of potassium chloride add r grm. of
potassium carbonate and i grm. of potassium dichromate. The
solution is then poured into a beaker of about 400 c.c. capacity,
which is placed on a sand bath, so that the temperature can readily
be maintained at from 45° to Go°. The anode must I)e platinum ;
the rotating anode is the most satisfactory to employ, but a piece
of sheet phtinum, or, better, platinum gauze, may be used. The

' Jahi-hnch, 18&8, VI. 207,

cathode should also be of platinum — -preferably stout wire — bul

a graphite rod or a spiral of thick nickel wire may be employed,

CONDITIONS.

C.D l8 to 2D amperes at anode.

E.M.F 47 to S7 volts.

Temp 45° to 60°

A slow stream of carbonic acid gas is also conducted through'
the electrolyte; this is in order to convert the potassium carbonate
into potassium bicarbonate. If a platinum stirrer is not at hand
to use as anode, it is advisable to agitate the solution with a stirrer
of glass. When preparing sodium hypochlorite, it will be remem-
bered that the electrodes were placed a considerable distance from
each other. In the preparation of chlorates, however, they should,
not be more than i cm. apart.

Afier the current has passed for some time, crystals of potassiui
chlorate sometimes commence to fall out, and, on cooling,
allowing the current to pass for some three hours, large quantitlf
of the salt crystallise out. These crystals, after filtering and wash-'
ing with cold water, will be found to be almost free from chloride
and after one crystallisation they are obtained quite pure. By
evaporating down the mother liquor, a further quantity of crystals
is obtained, but they are not quite so pure as the first crop.

If it is desired to obtain a large quantity of potassium chlorate,
a perforated cell (Fig. 53, p. 196) filled with potassium chloride
may be suspended in the electrolyte ; by this means the solution
will be always saturated with potassium chloride, and the process
made continuous. The current yield is fairly good, generally
being between 65 and 70 per cent.

Sodium Chlorate can be prepared in the same mannerf'
but, owing to the relative solubility of sodium chlorate to sodium
chloride, it is not so easy to obtain a complete separation of the
two substances.

VI. Potassium Bromate.

Dissolve 70 grm. of potassium bromide
and add 0-5 grm. potassium dichromate.

200 C.C. of ■
; electrodes

■ater, 1
used!

Preparation of Inorganic Products.
for [Mtassium chlorate can be employed for the electrolysis of
bromide solutions. The temperature of the bath should be kept
at about 40°, otherwise the conditions are practically the same as
those employed in the preparation of chlorates.

CONDITIONS.

CD II to iz amperes at anude.

E.M.F 4-310 s-o Tolls.

As a rule, the potassium bromate does not commence to
crystallise out until the solution is cooled. The quantities given
above require the passage of about 75 ampere hours of current.

Sodium Brotnate can be prepared in a similar manner ;
but it is even more diiBcult to separate from sodium bromide, than
sodium chlorate From sodium chloride.

The theoretical considerations given for the electrolytic pro-
duction of chlorates apply also Co the preparation of bromates.
But it is found that bromates are much more readily reduced in
an alkaline solution than are chlorates.

VII. Potassium lodate.

Dissolve 50 grm. potassium iodide in 300 c.c, water, add
I grm. potassium carbonate and 0^5 grm. potassium dichromate.

CONDITIONS.

CD 11 to 12 amperes at anode,

E.M.F 4'3 to 5-3 vqIIs.

Temp 40°

After passing about fifty ampere hours of current, the elec-
trolysis is stopped, the solution evaporated to about half its bulk,
and allowed to stand overnight in a cool place to crystallise.
The current efficiency is very good.

LITERATUl^E.
There is a yreat deal of literature upon the electrolysis of chlorides,
and the preparation of chlorates, etc. The easiest way to study thi;
subject is to read the risiim^ in the Jahrbudi for 1888, p. 186 ;
1889, p. 198 ; also 1902, p. 357.

Pr delicti! Electro- Cliem is try.

VIII. Potassium Perchlorate.

Chlorates can be further oxidised by the electric current t
perchlorates. In fact, both chlorates and perchlorates, i
the former, are manufactured on a large scale by the electrolysi
of chlorides. Indeed, nearly all the chlorates at present i
factured are made by the electrolytic process.

Method. — I'reiiare a cold saturated solution of potassiuiB
chlorate, and, in order that the solution may remain s
a perforated cell filled with potassium chlorate is suspended i
the solution.

Electrodes of sheet platinum or platinum gauite should be \
used, and the electrolyte must not he agitated— at any rate, not
con nuou ag ta d — a hough an occasional stir is an advantage.
Th "c o y n u no b allowed to become alkahne ; in order
to p en h s be e o add a few drops of diiute sulphuric

acid o ake he o u on just acid — the acidity may, however,
only be e y )^

CONDITIONS.

CD 9 to 12 amperes at the anode.

E.M.K S'S to i6voUs.

Temp Not above 20° or 24°

As the current density employed is fairly high, there
tendency for the electrolyte to become heated. It is therefore
best to stand the electrolytic cell in a basin of cold water, which
is continually filled by water running in, and at the same time
siphoning out.

When the current has passed for from thirty to forty minutes,
the potassium perchlorate begins to rain down from the neigh-
bourhood of the anode in the form of brilliant crystal plates,
the C.U. rises too high, it is rather difficult to keep the solution
sufficiently cool.

When the solution is kept cold, and is not alkaline, the re-
action which takes place may be represented by the following
equation : —

H,0 + 2CIO; = HClOj + HCiO,

Preparation of Inorganic Products. 1 1 5

The appearance of any quantity of oxygen gas at the anode
points to the reaction going mostly in the following manner : —
2CIO; + H,0 = 2HCIO, + O

There is always a small quantity of oxygen given off at the
anode; hut it will be noticed that this increases very rapidly if
the temperature is allowed to rise much over ao".

Potassium perbromate is readily prepared in the same
manner as the perchlorate, but the preparation of the periodate is
attended with considerable difficulties, and it is necessary to keep
the solution alkaline. MUller and Friedberger have succeeded in
obtaiuing the free periodic acid by electrolysing iodic acid in the
anode compartment.

LITERA TURE.

Foerster, Zeit.f, Elektrockem., 4, 386 ; Winteler, Zeit. f, EUktro-
chem., 6, 49, and 217 ; Miiller, Zeit.f. Elektrockem., 7, 509 ; Miiller and.
Friedlierger, Ber., 35 (3), 2652.

IX. Lead Peroxide.

Litharge (lead monoxide) can be elect rolytically oxidised to
its higher oxide lead peroxide. The operation is carried out by
electrolysing a solution of sodium or other alkali chloride in which
litharge is suspended.

Process. — Twenty grm. of litharge is susijended in a 2o-per-
cent. solution of sodium chloride, contained in a battery jar of
about 500 to 700 c,c. capacity. The cathode is hung at one side
of the jar, the anode at the other ; the cathode may be of lead or
graphite, but it should be wrapped in a piece of parchment, or
surrounded with a piece of asbestos paper, and placed in one of
the smaller perforated cells described on p. 196, Fig. 53. The
anode can be either of platinum or graphite. The mixture must
he very vigorously agitated, either by rotating the anode, or by
having a separate arrangement for agitating the mixture.
CONDITIONS.

E.M.F 3'sio4vuhs.

Temp Normal.

ba&-_

As the electrolysis proceeds, the oitide gradually becomes lighi
brown, and, finally, dark brown, showing that all the PbO ba&'
been changed to PbOj. At the end of the reaction, the lead
oxide is filtered off, washed with water to free it from adherii
chloride, and warmed with moderately dilute nitric acid, in order
to dissolve out any unchanged lead monoxide. During the
electrolysis no chlorine will be liberated, because sodium hypo-
chlorite is produced. The formation of the lead peroxide is,
indeed, due to the action of the hypochlorite upon the lead
monoxide, a small portion of which becomes dissolved
plumbite.

Pb:

ONa

+ NaOCt + H,0 = Pb( + aNaOH + NaCl

^ONa

And also to a certa.in extent to the direct action of chlorine

n the sodium plumbite.

Pb;

^■ONa

It is important that the litharge should be well ground, oth
wise it is inclined to be only superficially oxidised. This pro(
is of commercial importance, lead peroxide among other useU
being largely employed in the match industry.

LITERA TORE.
Elbs and Forssell, Zeil. f. Eleklrochem., 8, 760, D.k
I24S12.

X. White Lead.

There are several electrolytic methods for preparing whifs
lead; most of them, however, are indirect. The method 1
Luckow is direct, the lead necessary for the production of th*
white lead being obtained from a lead anode, which goes i
solution as the current is passed. The chief drawback is
extremely dilute solutions which are employed. The manufactur

Preparation of Inorganic Products. 317

of white lead by this process was carried on for some time at
Cologne.

Process. — 12 grm. of sodium or potassium chlorate and 3
grm. of sodium carbonate are dissolved in 1 litre of wator. Both
the anode and cathode consist of sheet lead, which is hung about
2 cm. from the bottom of the electrolysing cell.
CONDITION y.

CD o'^l to o'6 ampeie.

K.M.F r8 to 2 volts, electrodes 1 cm, aparl.

Temp Normal.

During the electrolysis a slow stream of carbonic acid gas is
passed into the solution, behind the cathode ; it should be passed
in such a manner that the fluid is as little disturbed as possible,
so that the white lead produced may sink to the bottom of the
cell.

Almost as soon as the electrolysis commences, a thin white
pellicle forms on the anode, which continually peels off during the
time the current is passing. The electrode at the end of the
reaction has a bright metallic appearance, as if it had been freshly
cleaned.

The sodium chlorate causes the lead anode to go into solu-
tion as lead chlorate; this is then acted upon by the sodium
carbonate, which with the water forms hydrated lead carbonate.
The carbonic acid is passed into the solution to prevent formation
of sodium hydrate ; at the same time, it should not be passed in
sufficiently rapidly to produce sodium bicarbonate.

An extremely interesting indirect process is that patented by
Browne and Chaplin. In this process a solution of sodium nitrate
is electrolysed in a divided cell, with a lead anode and a copper
cathode. In the cathode compartment sodium hydrate is pro-
duced, in the anode cell nitric acid ; this causes the lead anode
to dissolve with formation of lead nitrate. After the electrolysis
is finished, the solutions are mixed, when lead hydrate and sodium
nitrate are produced.

rb(NOa). + aNaOH = ?b(OHX + zNaNO,

The lead hydrate is then converted into white lead by addition

of sodium carbonate, and the regenerated sodium nitrate can then
be again employed for production of a further quantity of lead
nitrate and caustic soda.

XI. Chrome Yellow.

Luckow's mt-thoti for pr(;paring white lead can also be
employed for producing other mineral colouring matters, such, f^f.,
as chrome ytUow ; in this case, sodium or potassium chromate is
employed instead of sodium carbonate. The current conditions
are the same as in the preparations of white lead. At the com-
mencement of the electrolysis the chrome yellow which falls off
from the anode has a fine fiery appearance. But after a short time
it becomes reddish and smeary looking, consequently it is ng
possible to obtain good quality chrome yellow in quantity by tl
method.

LITER A TURE.

liorschers, Zeit. f. Ekktrodiem., 3, 4S2 ; Luckow, D.K.F., <^\y*
and 105143; Browne and Chaplin, d/.^.A, 1885, 551361, and 188
555,332 ; Le Blanc and Bindschcdler, Zeil. f. Ekktrochem., 8, 255
A. Isenburg, 9, 275.

XII. Potassium Permanganate.

Prepare a strong solution of potassium carbonate, about 4
per cent, such a solution has a sp. gr. of about i'42. The obj'e*
of employing a solution as strong as this is that the permanganaK
is much less soluble in a concentrated solution of potassiuQ
carboiute than in weaker solutions. This solution of potassiu
carbonate can be used both for anode and cathode.

The anode consists of a piece of ferromanganese or ■
metallic manganese. Ferro-manganese can be obtained witii \
very high percentage of manganese, but pure manganes
absolutely free from iron, is not so readily obtained. 11
presence of iron in the ferro-manganese does not, however, ex«
any harmful effect, the iron being simply precipitated as hydralea
carbonate.

Preparation of Inorganic Products. 219

The ferro-mangaiiese is, when not obtainable in rods, wound
round with platinum or iron wire, which is connected with the
positive pole of the current supply. The cathode of iron or other
metal is placed in a porous cell, which stands in a beaker con-
taining the potassium carbonate. The best fomi of porous cell to
use, when the solution is so strongly alkaline, is the perforated cell
described on p. 196, with a diaphragm of asbestos, or belter sand.

As soon as the current— the strength of which may vary within
wide limits — is passed, permanganate begins to form, and flows
off the anode in purple streams ; in a short time the whole anode
solution becomes deep purple.

The course of the electrolysis, and the current efficiency, can
be followed by titrating with oxalic acid.
sKMnO. + sC.H.,04 + 3H,S04

= loCO., + K,^Oj + 2MnSO, + SR.O
It is possible to prepare potassium permanganate without sepa-
rating the anode from the cathode. In this case the cathode
is made of the positive plate of an accumulator or of the copper
oxide plate of a cupron cell.

Any ferric hydrate which is produced during the reaction is
precipitated to the bottom of the anode cell. When the current
is passed for a sufficient length of time, crystals of potassium
permanganate separate out.

XIII. Potassium Chromate.

If instead of using an anode of ferro- manganese, one of ferro-
chrome is employed in a solution of potassium hydrate, then a
solution of potassium chromate is produced. As is the case in
the preparation of potassium permanganate, ferric hydrate is pro-
duced from the iron in the ferro-cbrome ; this is, of course, pre-
cipitated, and can be filtered off. The course of the electrolysis
should be followed by titration from time to time ivith ferrous

monium sulphate.
aKjCrO^ + 6FeS0, + 8H.,S0,

= 3Fc,(SO^):, + Cr,{SO.J, + aK.^0. + 8H,0

XIV. Metallic Hydroxides.'

When a metal is made the anode in a solution of an alkali
chloride, nitrate or sulphate with an insoluble cathode such
graphite or platinum or a strip of the same metal employed as
anode, the metal at Che anode is dissolved, and a metallic
hydroxide produced. The formation of the hydroxide is due to
the metallic salt produced at the anode coming into contact
the alkali hydroxide liberated at the cathode.

{a) NaCl=Na-+a'

Na+H,,O = Na0H + H

(6) 2Cl + M = MCla

MCL+2NaOH = M(OH),-H2NaCl

(M is a divalent metal.)

Since, when a metal is made the anode and goes into solution,
partial disintegration invariably takes place, and particles of the
metal fall to the bottom of the electrolysing eel!, thus contaminating
the electrolyte, the anode should be wrapped in a piece of cloth
or, better, parchment, to prevent this happening.

In the preparation of these hydroxides, it is advantageous
keep the solution well agitated. One of the easiest ways of doing
this is to cause the anode or the cathode to rotate. This U.
readily done by soldering a piece of stout wire to the electrode^
and fixing it in the chuck of the rotating arrangement described
on p. 80.

One great advantage in this method of preparing hydroxides
is, that the solution always remains neutral. For this reason there
is no possibility of dissolving hydroxides which have an acidic
character; further, the amount of alkali salt in the solution never
increases beyond the quantity which was originally present, and
thus washing of the precipitate is easy.

The material of the electrolyte exerts considerable influenc6'
upon the nature of the hydroxide produced; thus in lo-per-cenL

' Loiuiu, Zeit.f. Anorg, Chem., 12, 396 and 436,

Preparation of Inorganic Products. 221

solutions of sodium chioi'tde, potassium nitrate and sodium

sulpiiate, the following compounds are formed, with various
anodes.

^iu„c.,oKd..

Sodium .ulpbMt.

Cadmium ....

CdlOH),

Cd(OH),

Cii(OH),

Ct.(OH},

CujO at 100°

CuO al 100=

CnO at 100°

PbO,

Irpn

FeO

Mercury ....

Hg,0

Sd(OH),

Sii(OH),

Sn(On),

Except in the case of copper, where the anhydride of the oxide is
produced at high temperatures, it is better to work at a temperature
of from -^o" to 80" or higher, because, when the hydroxide is formed
at high temperatures, it is more readily filtered and washed.

XV. Metallic Sulphides.

Cadmium Sulphide (Cadmium Yellow).
Metallic sulphides can be obtained in an analogous manner to
that in which metallic hydroxides are prepared. Copper sulphide
is made the cathode in a solution of an alkali chloride, nitrate, or
sulphate, and the metal the sulphide of which it is desired to
prepare the anode. Copper sulphide is practically the only
sulphide which can be employed as cathode because it conducts
the current readily, whereas most sulphides do not conduct the
current at all, or conduct it very poorly. When the copper
sulphide can be obtained in the form of a rod, there is no
difficulty in forming the cathode; it must, however, be wrapped
in cloth or parchment to prevent particles falUng to the bottom
and contaminating the product. Generally copper sulphide is
obtained in the form of a coarse powder ; when in this form, the
only way to make the cathode is to pack the sulphide closely
round a piece of copper wire in a porous pot or in a stout

t should then be electrolysed for a short time with an

222 Practical Electro-Chemistry.

insoluble anode, that the outer portions of the cell may become
saturated with the alkali sulphide.

In order now to prepare cadmium sulphide, an 'anode made
from a rod of cadmium is placed in the bath, containing a lo-per-
cent. solution of sodium chloride, nitrate, or sulphate. The anode
should he wrapijed round with a piece of calico to prevent dis-
integrated portions falling into the electrolyte. The solution must
also be agitated, and the simplest method is to cause the anode
rotate {see p. iia).

CONDITIONS.

CD I to 2 amperes.

E.M.F 3 lo 4 volts.

Temp 6c^ to 70"

Almost as soon as the circuit is closed, a yellow precipitate
cadmium sulphide commences to fall down. Generally a small
amount of cadmium hydroxide contaminates the sulphide, owing
to the cathode reaction being a little slow ; therefore, after filtering
the cadmium sulphide, it should be washed with a little sulphuretted
hydrogen water, or the sulphuretted hydrogen water added before
filtering.

The mechanism of the reaction is practically the same as in
the case of hydroKide formation. When the current is passed
NOa', CI', or SO," ions, as the case may be, are liberated at the
anode, and oxidise it, causing the metal to pass into solution.
At the cathode the reducing action of the hydrogen produces
sulphuretted hydrogen, which unites with the salt to produce
cadmium sulphide.

By replacing the cadmium anode by one of other metals, the
sulphides of the various metals can be produced.

1st

XVI. Hydroxy lam ine Hydrochloride.

NH,OH . HCl.
When nitric acid is reduced in presence of a metallic salt, such
as copper sulphate, ammonia is produced, and this reduction may
be used as a method for estimating nitrates fp. 145). When, how-
ever, the reduction takes place in presence of dilute sulphuric acid

Preparation of Inorganic Products.

and with a cathode of amalgamated lead, then the nitric acid
cau be almost quantitatively reduced to hydro xylamine. The
nitric acid is probably first of all reduced to nitrous acid,
hydroxylamine being the next stage, and the final stage is
ammonia. Tafel considers that the ready formation of ammonia,
by the reduction of nitric acid in presence of a copper salt
(see p. 146), is not due to the formation of NH^OH and its
further reduction, but that the copper exerts a specific influence
which prevents the formation of hydro xylamine. Spongy copper
or copper sulphate have no action on hydroxyl amine, it is there-
fore probably a question of the effect of the cathode material
upon the potential at which the hydrogen is liberated.

H0.NO,-S-H0.NO-S-HO.NHa-*NH;,

The reduction is carried out in an amalgamated circular lead
vessel, which acts as cathode. A glass plate is laid on the bottom
of the vessel, and on this a porous cell is placed. The anode
should consist of a coiled lead tube through which cold water can
be circulated. The whole apparatus is-then stood in a freezing
mixture. The diameter of the cathode should be about 10 centi-
meters {about 4"), the diameter of the anode cell from yo to 7"5
centimeters (275 to 3 inches).

Amalgamation.— In order to amalgamate the cathode it
must be first carefully cleaned with sand and caustic soda. After
this it is washed out with dilute nitric acid, and then thoroughly
amalgamated by rubbing it with mercury by means of a rod of
wood with a piece of cloth tied on the end.

A ring-shaped stirrer made from a piece of lead pipe passes
round the outside of the anode cell.

The anode cell is filled about three quartets full with so-per-
cent, sulphuric acid. About 170 to 200 c,c, of acid of the same
strength is placed in the cathode compartment. The whole appa-
ratus is now cooled and the circuit closed, a current of about 24
amperes being passed. Twenty grams of nitric acid (30 c.c,
50-per-cent. HNO;)) is then slowly run into the cathode solution

224 Practical Electro-Chemistry.

from a dropping funnel : ihe operation of running in should take
about two hours. After all the nitric acid has beea run in, the
solution is electrolysed for another forty or fifty minutes, until the
solution on testing shows only traces of nitric acid.

During the electrolysis the cathode solution should be stirred
every few rninutes. It is, indeed, better if the stirrer can be fixed
on to a rising and falling beam or a slow-moving eccentric, so
that the stirring may be continuous.

As soon as the electrolysis is finished the cathode solution is
transferred to a beaker, and a warm concentrated solution of
barium chloride run in, care being taken, however, that the
temperature does not rise above 30" or at most 40°. The barium
chloride neutralises the sulphuric acid, and then converts the
hydroxylamine sulphate into hydroxylamine chloride.

(NH5.0H);H^0, + BaCl.j = zNH.-OH, HCl -f- BaSO.

Care must be taken not to add an excess of barium chloride.
The solution is then freed from barium sulphate by filtration,
and the clear solution evaporated to dryness on the water bath.
If possible, the evaporation should be done in a vacuum, the only
difficulty being due to the rather vigorous bumping which often takes
place. There is no great difficulty in distilling off the water in
a vacuum, provided a good condenser is employed. The residue
consists of NHj.OH, HCl with about 8 per cent, of ammonium
chloride. The ammonium chloride can be separated by dissolving
the mixture in about half its volume of hot water, when the hydro-
xylamine salt crystallises out almost pure. The yield of hydro-
xylamine is from 75 to So per cent, of the nitric acid taken.

LITERA TURE.
J. Tafel, Zrit. Anorg. Chem. (1902), 31, 289.

CHAPTER XIII.

ORGANIC ELECTROLYSIS.

Electrolysis of Organic Acids.

Owing to the very feeble conductivity of organic acids, i.e. to
the slight amount of lonisation which they undergo, the acids
per se can only be electrolysed with difficulty, and by the expen-
diture of a large amount of electrical energy — that is to say, with
currents of high potential. On tlie other hand, the alkaline salts
of the acids are fairly good electrolytes, and, therefore, by em-
ploying salts of the organic acids, we are able to obtain anionic
reactions, the cathodic reactions being of very little importance.
The electrodes employed in the electrolysis of the organic acids
must be of some material which is unacted upon by the decom-
position products or by the oxygen evolved at the anode. Platinum
is usually the most satisfactory, although at times graphite or
peroxidised lead can be used.

Concentration of the electrolyte, the intensity of current
density, and the temperature determine, to a great extent, in what
manner the electrolytic decomposition will proceed.

I, In dilute aqueous solution the action is mainly the pro-
duction of oxygen at the anode and hydrogen at the cathode.
The cathode reaction is always the same, and is simply the
secondary reaction due to the discharge of the alkali ions; as,
for example—

I. Na -H HaO = NaOH -|- H
The anode reaction with a dilute aqueous solution of, say, sodium

acetate, is merely a question of oxygen being given up and the
acid reformed.

+ a.o = 2CH,

^OH

This is the primary reaction which ensues, but secondary reactions
may be produced by the oxygen when it is discharged at the
anode oxidising the acid itself,

II. With concentrated aqueous solutions the reactions may
be much more compHcated, and may take place in several ways.
One of the most well-known reactions is the preparation of
ethane from sodium acetate, in which the carboxyl of the anion
is split off, and then two hydrocarbon rests unite together to form
ethane.

III. 2CH,-C:^ = CH,

-CH, -

At the same time small quantities of ethylene arc also formed
This must be looked upon as being produced by the decoDI
position of some of the anions as shown above, and of otha
as set out below.

IV.

CHj . COO' OH'
CH3 . COO' ■*■ OH'

= II ■
CHa

According to the above reaction, it is presumed that, at tl
moment the CHj . COO' ion is liberated at the anode, it splits i:
into the radical CH3 and CO,, and that, before the CH3 has tin:
to unite with another CH3 radical, two such radicals are attache
by hydroxyl groups, which have been simultaneously liberate!
with formation of water and ethylene, thus ; —

CH^.H' OH'

+
CH, . H' OH'

CH,
II ■
CHs

H,0
H..0

Now, in the case of acetates this reaction only takes place „
a very small extent, the main product being ethane produced b]

I the union of

Organic Eleetrolysis. 227

n of two CHj radicals as in III. With alkali propionates,
on the other hand, the main reaction is the formation of ethylene,
only a small portion of the CHj.CH;, — radicals uniting to
produce butane.

CH,.CHa.COO' OH'

CH,

+ ~

3 II

CHs.CH,.COO' OH'

CH,

A further reaction may also take place in which one anion splits
off COfl, and the alkyl rest so obtained unites with another anion
to produce an ester. For example —

. aCH,

C, =CH,

c'<

OCH

A very good example of this class of reaction is illustrated
by the formation of the trichlor-methyl ester of trichloracetic acid
when trichloracetic acid is electrolysed.

yO ,0

2cci,.cr =cci3.c/ +coa

■'0 ^OCCJ,

A. Crum Brown and J. Walker, by electrolysing the acid
esters of dicarboxylic acids, were able to produce additive com-
pounds, the production of which is made clear by an examination
of equation IH. As an example, may be given the formation
of diethyl succinate when sodium ethyl malonatc is electrolysed.
Only one of the carboxyl groups is able to take part in the
reaction, because the other one is masked by the alkyl group,
which prevents it being ionised.

^COOCH,
,COOQH, CH,
VII. bCH/ = I + zCO..

^COO CH„

"^COOCH.-,

Finally, H. Hofer and M. Moest find that when an organic acid
is electrolysed in presence of an alkali sulphate, carbonate, or —

jot/ Effctro-C/temislry.

better— perchlorate, that an alcohol is produced. The i
depends upon the discharge of hydroxyl ions thus—

VIII. CH,.C00 + 0H = CHj.0H+CO2
The hydroxyl anion may either be discliarged as such, or may
be produced by the discharge of the inorganic acid anion, as, for
eJtample, with perchloric ions —

IX. C10,-f-H0H = HC10. + 0H
We may therefore formulate the production of methyl alcohol
by the electrolysis of sodium acetate in presence of sodium
perchlorate, as —
X. CH,. COO + ClOj + H2O = CHa . OH + HaO^ + COj
The fact that, when an acid is electrolysed in presence of
sodium carbonate, an alcohol is produced, explains why it is
that on electrolysing a concentrated solution of sodium acetate
without a diaphragm, the yield of ethane, which at first is almost
quantitative, rapidly falls off. This, therefore, is due to the presence
of an alkali carbonate which is produced during the course of
the electrolysis, and that, as soon as it is produced, the reaction
proceeds according to equation VIII. With dibasic acids, only
one of the carboxyl groups is attacked ; thus, from succiruc..j
acid /3-oxy propionic acid is produced.

CH..COO OH CH^.OH

J + = I +CO

CH..COOH CH5.COOH

XVII. Preparation of Ethane.

A porous cell is fitted tightly with a rubber cork, throuj
" which passes a delivery-tube and a piece of stout platmum w
bent in the form of a spiral, and which is intended to fund
as anode ; a piece of sheet platinum may be used instead
spiral. The porous cell is then filled two-thirds full with \
cold saturated solution of sodium acetate, to which is added i c
2 per cent, of glacial acetic acid.

Organic Electrolysis. 229

Tht anode cell, round which is coiled a piece of nickel wire
to serve as cathode, is placed in a beaker^ which is iheji nearly
filled with a similar solution
of sodium acetate to that
employed for the anode
compartmeat. The whole
apparatus is then placed in
a vessel of cold water. This
form of apparatus can only
he employed when it is
desired to collect the anode
gas alone \ if, as is often
desirable, it is intended also
to collect the cathode gas, the cell must be placed in a wide-
mouthed bottle or a cylindrical glass vessel, and must be fixed
air-tight by means of a rubber ring or stopper. The apparatus
depicted in Fig. 58 is perhaps the best to employ, when both

gases are to be collected. The two Woolf bottles are employed
in order to equalise the pressure on the anode and cathode, the
gases being collected from the tubes a and b. Elbs employs
a somewhat similar arrangement, in which, however, he
tube opening to a bell-shaped end, instead of the porous coll.

230

Practical Electro-Chemistry.

A currL-m density of from Oo to So amperes should 1
ployud; this is easily obiained, because ilie anode surface used
is small. Tiie temi>erature sliould not be allowed to rise above
20", because the higher the temperature the lower the yield of
ethane. The two wash vessels contain a strong solution of
caustic soda to absorb the CO, which is produced at the anode,
as shown in the equation —

,,0 CHa
2CH,Cf = i +C0,

CH,

XVllI. Preparation of Ethylene.

The apparatus and electrodes employed in the preparation
of ethylene may be the same as those used in preparirig ethane.
If, however, the presence of hydrogen with the ethylene is not
a disadvantage — as, for example, in the preparation of ethylene
dihromide, when the gas is passed through a mixture of bromine
and water, ^then there is no necessity to separate the anode from
the cathode, and the electrolysis can be conducted in a wide-
mouthed bottle. The anode is placed in the centre and surrounded
with a cyhnder of nickel, which acts as cathode. This arrange-
ment has the advantage of decreasing the resistance and of
making it easier to keep the apparatus cool. The solution to
be electrolysed is prepared by dissolving 40 to 50 grms. of
sodium propionate in 100 c.c. of water, and then adding 25 to
30 grms. of propionic acid. When the anode and cathode are
separated, a solution of sodium carbonate may be used for
cathode compartment,

The CD, must, as in the preparation of ethane, be high-
it should not be less than 70 amperes, and may rise to 100,
provided the temperature of the solution does not rise above
35° or 40°. The yield of the ethylene is between 35 and 50 pei
cent, of the theoretical amount.

are

CH, . CH, . COO'
CH,.CH„.COO'

OH'

CH,

+ 3CO, + aH.O

Organic Electrolysis.

XIX. Preparation of Diethyl Succinate.

The electrolyte consists of a nearly saturated solution of acid
potassium or sodium malonate, which is contained in a beaker
standing in cold water. As the hydrogen evolved during the
reaction has no action upon the products of electrolysis, it is
not necessary to separate the anode from the cathode by means
of a diaphragm. The anode should be a spiral of stout platinum
wire, and should be sufficiently thick not to become hot when
the current is passed. The cathode may conveniently be made
of sheet platinum.

CONDITION.
CD 50 to 70 ajnperes.

As the solution is very strong, the electrolyte is rather viscid;
and this, and the high current employed, cause very considerable
frothmg to take place. Therefore the beaker in which the
electrolysis is conducted must not be more than half filled with
the electrolyte.

After a little while the diethylsuccinate b^ms to separate out
as a mobile oil, which floats upon the surface of the solution.
\Vhen rather more than the theoretical amount of current has
been passed the electrolysis is stoppedj the mixture transferred
to a separating funnel, diluted with water, and extracted twice
with ether. After drying over calcium chloride, the ether is
distilled off and the ethyl succinate fractionated; b.p. 2r6°.
,^COOC,H,
,COOC,H, CH,
2CH,( = I + aCO,

NCOO CH.,

■^ COOC^Hj

For the preparation of potassium ethyl -malonate, see p. 283.

XX. Preparation of Diethyl Adipic Acid.

The method of preparation of diethyl adipic acid is similar
to that adopted for the preparation of diethyl succinate. A nearly
saturated solution of potassium ethyl succinate is electrolysed in a

232 Ptaetieal EUctro-Chemistry.

[all buaker, which, as in the case of the previous experiment,
must not be more than half full, owing to the frothing which
takes place.

CONDITION.
C.U 50 lo 75 amperes.

At the end of the reaction — 70 c.c. of solution will require
the passage of about 20 ampere hours — the mixture with the
adipic ester floating upon its surface is diluted with water and
extracted twice with ether, and the ethereal solution dried over
calcium chloride. After driving off the ether, the oil which
remains has a pleasant fruity odour, due to the presence of
small quantities of ethyl acrilate, CHa : CH . COOQHs. In order
to free it from this and obtain it quite pure, the ester should be
heated to izo" for about half an hour, and then fractionated, b.p.
at normal pressure 254°; but it is more satisfactory to distil
under diminished pressure. The yield of ethyl adipic acid is from
30 to 35 per cent When potassium methyl succinate is electro-
lysed under the same conditions, dimethyl adipic acid is produced.
CH,.COOC..H,

CH,.COOC,H, CH.,
2 1' =1 + 2CO.

CH,, - COO CH,

I
CH, . COOCjH^

For method of preparing potassum ethyl or methyl succinate,

see p. 283.

XXI. Preparation of Methyl Alcohol.

Make up a solution containing 225 grm. potassium acetate,
52 grm. potassium carbonate, and 55 grm. potassium bicarbonate
to the litre. In order to prepare methyl alcohol, this solution
may either be electrolysed in an undivided cell, or it can be
electrolysed in the anode compartment of a partitioned cell.
CONDITIONS.

CD 20-25 amperes.

E.M.F 7-S volts.

Temp 250-30°

Organic Electrolysis.

The anode sliould be of platinum, and it is an advantage to
have it slowly rotating. As the current density is rather high, the
solution is apt to become very hot, and this causes evaporation
and loss of the methyl alcohol. For this reason the electrolytic
cell should be placed in a basin of cold water, and as a further
precaution the cathode should be made from a coil of thin lead
pipmg, on to which is soldered a piece of copper wire to convey
the current. Water is caused to flow through the lead pipe, and
the coil is placed round the anode compartment, or when the cell
is not divided, the lead coil is run close to the outer wall of the
electrolysing vessel, the anode being in the centre.

As the electrolysis proceeds, acetic acid is allowed to slowly
drop in from a dropping funnel, to take the place of the decom-
posed acetic ions,

CHa . COO + OH' = CH, . OH + CO,
The acetic acid must on no account be run in sufficiently quickly
to cause the solution to become acid, otherwise methyl alcohol
will not be produced.

When about 50-60 ampere hours of current have been passed,
the electrolysis is stopped. The solution containing the methyl
alcohol is transferred to a flask, and about one-fifth of it distilled
off on a sand bath. The distillate contains the methyl alcohol
and traces of formaldehyde. In order to obtain the pure methyl
alcohol, small pieces of caustic lime or an excess of anhydrous
potassium carbonate isi added to the solution, and, after standing
for about 24 hours, the flask containing the methyl alcohol and
lime is placed on a water bath, and the alcohol distilled off. The
yield of methyl alcohol is from 50-60 per cent. There is really
no advantage in employing a divided cell, because methyl alcohol
is not reduced by the cathodic hydrogen. The weight of the
alcohol can be ascertained by multiplying die number of c.c.
obtained by o'ySg, the s[>ecific gravity of methyl alcohol.

LITERA rURE.
Kolbe, Antialeii, 69, 261 ; Kekule, Annalen, 181, 79 ; Brazier and
Gosleth, Aimakn, 76, 265 ; Murray, Ber., 26, 492 ; Hamonei,

234 Practical Electro-Cliefuistry.

Compt, Rendusy 128, 252 ; Lob, Zeit, /. Elektrochem,^ 3, 42 ; Schall,
Zeit.f. Elektrochem,^ 3, 83, and 6, 102 ; Rohland, Zeit. f, Elektro-
chem.^ 4, 120 ; Schall and Klien, ZeU, f. Elektrochem,, 5, 256 ; Elbs,
Journ, f. prakL Chem., 47, 104 ; Elbs and Kratz, Journ, f, prakt
Chem.y 55, 502 ; Troeger and Ewers, Journ, f, prakL Ghent. ^ 68,
121, and 59, 464; Aarland, Journ. f, prakt, Chem., 6, 256; Crum,
Brown and Walker, Annalen^ 261, 107, and 274, 41 ; Walker and
Cormack, Chem, Central Blatt^ 71, I. 770, and Proc, Chem. Soc.^
16, 58 (1900) ; Von Miller and Hofer, Ber.^ 27, 461, and 28, 2427 ; also
Zeit,f. Elektrochem.^ 4, 56 ; Hofer, Ber.y 33, 650 ; Hofer and Moest,
Annaleriy 328, 304 (1902) ; Moest, DM.P.f 138,442 (1903) ; Foerster
and Piquet, Zeit. f, Elektrochem.^ X. 729 (1904) ; Hofer and Moest,
Zeit.f. Elektrochem,, 10, 833 (1904).

CHAPTER XIV.

REDUCTION OF ORGANIC COMPOUNDS.

The electrolytic reduction of organic compounds has been very
fully studied, and the results obtained have heen of great import-
ance. Compared with methods of electrolytic oxidation those
of reduction are comparatively easy. Very different results can
be obtained by varying the conditions of reduction. Thus, for
example, different reduction products are obtained from the same
substance by reducing in strong acid or dilute acid solutions, in
alkaline or neutral solutions. The material of the electrode also
has a considerable influence upon the manner of the reduction.
This is not due to the difference of the metal, but to ihe fact
that with certain metals the hydrogen is yielded up at a higher
potential. In fact, the chief influence in the reduction is the
potential at which the hydrogen ions are discharged. W. Lob
and R. W, Moore' find that nitrobenzene can be reduced in
alkaline solution with a cathode of platinum, copper, tin, zinc, lead,
or nickel, or with a platinum cathode and the hydroxide of tin,

In general chemistry it is well known that when nitrobenzene
is reduced in acid solutions aniline is produced, but reduction
in alkaline solution leads to the formation of azoxybenzene,
azobenzene and hydrazobenzene. The electrolytic reduction
of nitrobenzene and of substituted compounds of nitro-
benzene has been very thoroughly studied, and it is found
j that it is possible to bring about by electrical means the same
j changes as those produced by purely chemical methods, and ver}-

■ ' ZrtV./. Phy!. CItiDi. (1904), 47, S18.

Practical EUctro-Ckeinhtry.

oflcii witli vtry mucii greater readiness. Some of ihe reactions
are due to primary electrolytic ruduclion, but others must be
classed as being brought about by secondary changes. F. Haber'
has drawn up a scheme in order to show this in a clear manjiei.
In the scheme, here given, the vertical arrows show the primary
changes, and the oblique indicate secondary reaction.

REDUCTION IN ACID SOLUTION.

The primary reaction from nitrobenzene to nitrosobenzene,
phenylhydroxylamine, and aniline takes place in moderately dilute
acid soiution. When strong acid is employed, the main product
is p-amido phenol. In strong sulphuric acid phenylhydroxylamine
undergoes intramolecular change, the OH group exclianging place
with a hydrogen atom in the para-position thus : —

Cf,Hj . NH . OH ^ HO . CeHj . NH, J

XXII. Preparation of Aniline.

25 gnu. of nitrobenxene is dissolved in 100 c.c. of alcohtd,
and added to zoo c.c. of sulphuric acid (35 to 30 jwr cent.). This
mixture is placed in a porous cell which acts as cathode chamber.
The cathode is made of a sheet of lead bent into the form of a

' Zdt.f. Eliklrachem. {189M), 4, 506.

Reduction of Organic Compounds.

cylinder, and having narrow slots cut into it at intervals. A small
lead paddle, also connected with the negative pole of the source
of current, is placed in the centre of the cell, and rapidly rotated
during the time the electrolysis is being conducted. If the
mixture is not agitated, sufficient alcohol should be employed to
keep the nitrobenzene almost completely in solution, and the
cathode solution is placed in a high beaker, the porous pot
containing the anode.

The anode may be a cylinder or sheet of lead, the anode-
solution sulphuric acid of the same strength as that employed for
the cathode solution.

CONDITIONS.

CD 4 to S amperes.

E.M.F 3-7 1Q4-0 volts.

Temp 65° to So"

The electrolysis is commenced at normal temperature, but the
passage of the current rapidly raises the temperature to the boiling
point of alcohol. The object of the high beaker is to condense
as far as possible the alcohol which is vaporised by the high
temperature. From the equation it is seen that 123 grm. of
nitrobenzene require the passage of six faradays or 6 x 96540

C,H,NO., + 6H = CjH.NHa + aH^O

coulombs of electricity in order to reduce it to aniline. Therefore
25 grm. require about 33 amjicre hours. As toward the end of
the reaction a certain quantity of hydrogen is invariably lost, the
current should be passed for about 35 ampere hours.

The alcohol is now distilled off, the solution made alkaline
with caustic soda, and steam distilled. If there is a trace of
nitrobenzene left, this can be separated by a preliminary steam
distillation before making alkaline. The aqueous distillate is
extracted with ether, and the aniline recovered as usual. Yield
about So per cent, or higher. Crystals of aniline sulphate can
be obtained by evaporating the acid solution to small bulk, but
there is no advantage in this.

238 Practical EtcctrO'Ckemistry.

Toluidines.

Ortho- meta- and para-nitrotoluene are readily reduced b a
similar manner to nitrobenzene with a formation of the coire-
sponding toluidines. The yields of toluidines are very satisfactory,
hut the o- and ni-nitrotoluenes give rather higher yields of the
corresponding toluidines than the p-nitro- toluene.

XXllI. Preparation of p-AmJdophenol.'

I wee n
■at^S

As has already been stated (p. 236), [vamidophenol is obtained
when nitrobenzene is reduced in strong solutions of sulphuric
acid. The strong acid causing an intra molecular change between
the OH group of the hydroxylamine and the hydrogen
situated in the |)ara-position.

Owing to the strong suljihuric used, and the high tempera!
at which the reaction is conducted, platinum electrodes must
be employed. The anode and cathode are separated; either
an ordinary porous cell may be used, or one of the double
perforated cells (p. 196), in which the inner portion is wrapped
round with asbestos, can be employed.

30 grm. of nitrobenzene is mixed with 200 c.c. of strong
sulphuric acid, and about 4 to 6 c.c. of water added. This
solution is placed in a beaker which constitutes the cathode space ;
the anode compartment, which has first been soaked in strong
sulphuric acid, is placed in the middle of the beaker. A spiral of
thick platinum wire, which forms the cathode, is wound loosely
round the anode cell, or a cylinder of platinum may be used
instead of wire. The anode may either be a cylinder of pladnum
foil or, better, a stout coil of platinum wire,

I CONDITIONS.

Reduction of Organic Compounds. 239

No heating is required, but during the reaction the temperature
rises to 75"^ or 80°. It must not be allowed to exceed 85", otherwise
sulphonation takes place, and p-amidophenol sulphonate is
produced; even at this lower temperature a. certain amount of
sulphonation does ensue. As the electrolysis proceeds, the
solution becomes of a dark -blue colour. After about 30 ampere
hours of current have passed the reduction is stopped, and the

OH
CsHjNO., + 4H = CjH, + H.,0

NH,
anode cell removed. On allowing to stand for some time in
a cool place or by placing the beaker in a freezing mixture the
p-amidophenol crystallises out, the whole mass becoming a thin
porridge of crystals. The crystals are filtered off on the filter
pump, glass wool or asbestos being used to filter through. After
filtration, the crystals are spread on a piece of porous plate to
remove as much of the sulphuric acid as possible, and recrystalUsed
from alcohol. The yield is generally about 20 to 30 per cent.,
but if the temperature has been allowed to rise too high, it may
be very much lower. There is always a certain quantity of the
sulphonic acid formed, and varying quantities of higher reduc-
tion products. When 80-per-cent. sulphuric acid is used, less
sulphonation takes place, but in this case the cathode must be
rapidly rotated.

REDUCTION IN ALKALINE SOLUTION.

In alkaline solution the reactions are mostly secondary ;
according to Haber's scheme (p. 236), it is seen that azoxy
and azo compounds are produced. The formation of the azoxy
compounds may be written as : —

■ O.
2C,H,NO, -!- 6H = C„H,N - N . C^H, + 3H,0

It probably is also produced as a secondary reaction between
phenylhydroxylamine and nitrosobenzene.

-O
CHjNH .OH -I- QHjNO = QH^N - NQH^ + H.O

240 Practical Electro-Chemistry,

The nitrobenzene is first reduced to nitrosobenzene, a portion
of which is then further reduced to phenylhydroxylamine, and the
iDteraction of these two substances causes the formation of the
azoxybeiuene.

XXIV. Preparation of Azoxybenzene.'

As cathode compartment use a fairly wide porous cell about
8 or 9 cm. in diameter, and place it in a cylindrical lead
vessel, which Is to serve as anode. The anode solution is a
15-per-ceut. solution of sodium sulphate slightly acidified with
sulphuric acid.

Mix 30 grm, of nitrobenzene with 300 to 400 c.c. of 3-per-cent.
solution of sodium hydrate, and place the mixture in the cathode
cell. The cathode may consist of a nickel gauze cylinder or a
close coil of stout nickel wire, wound so as to fit closely against
the walls of the cathode cell. A nickel stirrer is then placed in
the centre of the cell, and the mixture is vigorously agitated so as
to produce a thorough emulsion, the nickel stirrer being also con-
nected with the negative source of current. ^^B
CONDITIONS. ^1

No external heat is applied, but during the electrolysis the
temperature of the solution rises considerably.

According to the equation already given, two molecules
of nitrobenzene are seen to require about 33 ampere hours
of current, therefore 30 grm. theoretically should need i6"S
ampere hours. It will be found advisable to give the experiment
about 22 ampere hours. Shortly after the current has been
passed the solution becomes bright red, but towards the end
of the reaction the solution often appears rather muddy and of a
brownish red colour.

After the electrolysis is finished, the mixture is transferred to a
flask and steam distilled to remove unchanged nitrobenzene and
' CItem. Zat., 17, 210,

Reduction of Organic Compounds. 241

ly aniline which may have heen formed. As the azoxybeniene
is also to a certain extent volatile with steam, the distillation
must be stopped when the distillate only smells faintly of nitro-
benzene — that is, after 30 or 40 minutes' distillation. The bulk of
water is poured off the oi! which remains at the bottom of the
distillation flask, and the oil poured into a beaker. On standing
for some litde time in a cool place the oil solidifies. The crude
azoxybenzene is purified by recrystallisation from petroleum ether
or from ligroin. It is obtained as crystalline plates or needles of
a light yellow colour ; m.p. 36°. The yield varies considerably,
but is not usually above 40 per cent.

Very little work appears to have been done upon the nitro-
toluenes, but p-azoxy toluene has been prepared by electrolytic
reduction of p-nitrotoluene with a CD. of i to z amperes. It is
a red sandy substance which on crystallisation from alcohol
forms orange-red needles, m.p, 75",

XXV. Preparation of Azobenzene.'

When the reduction is carried a stage further than is necessary
for the formation of azoxybenzene, azobenzene is produced.

zG,HsNO, -H 8H = QH,N = NC„H, + 4H,0
Dissolve 30 grm. of nitrobenzene in aoo c.c. of 70-per-cent. alcohol,
and add 8 grm. of sodium acetate ; this solution forms the cathode
mixture. Place it in a narrow beaker, and as anode compartment
use a porous cell. The anode solution consists of a cold
saturated solution of sodium carbonate. The anode may be
of platinum foil or wire, or a graphite rod can be employed. The
cathode should be a nickel gauze cylinder, placed between the
anode cell and the beaker.

CONDITIONS.

but as the electrolysis proceeds the mixture rapidly reaches
the boiling-point of the alcohol. The object of having a taJI
narrow beaker is to condense, as far as possible, the volatilised
alcohol ; it may, however, be necessary to add fresh quantities
of alcohol from time lo time. Toward the end of the reaction
the CD. is reduced to a amperes, and the current passed for
about i^ hours at this density. About 30 ampere hours are
required to complete the reduction — that is, the passage of
slightly more than the theoretical amount of current. As a high
CD. is being used, and because during the electrolysis the anode
solution tends to become depleted of cations, the anode cell
should not be too small, as otherwise, owing to resistance being
set up, a high E.M.F. is required to drive the current through,
and the heating of the solution becomes excessive.

As soon as the process is finished, the mixture is transferred
to a flask, and air is aspirated or blown through it for about
half an hour. The object of passing air through the raijiture is to
decompose any hydrazobenzene which may have been produced,
as it is found that a small quantity of this product is invariably
formed. Traces of azoxybenzene may also be present. The
bulk of the alcohol is distilled off, excess of water added, and
the precipitated azobenzeue filtered off and washed. If the
reduction has not been carried far enough, the unchanged
nitrobenzene remaining makes it very difficult to get the azoben-
zene to crystallise. The only thing to do in this case is either to
further reduce the product or to steam distil it, but this latter
method always results in loss, because some of the azobenzene
passes over with the steam. It is then recrystallised from alcohol
or light petroleum spirit, when it is obtained in beautiful red
plates ; ni.p. 58°. Yield about 70 to 75 per cent.

XXVI. Preparation of Hydrazobenzene/

From the equation for the formation of hydrazobenzene, it is
seen that two more hydrogen atoms are required to produce it
than are necessary for the preparation of azobenzene.
' K. Elbs and O. Kopp, Zei/./. £Uklroch^iii.t B

Reduction of Organic Compounds. 243

zCH^NOa + loH = CeHoNH - NHQH, + 4H;0
In preparing hydrazobezene, the conditions of the experiment,
solution, electrodes, etc., is the same as in the previous case.
For 30 grm. of nitrobenzene theoretically about 32 ampere hours
are required, but to ensure complete reduction the current should
be passed for about 35 ampere hours. After sufficient current to pro-
duce azobenzene has been passed, the CD. should be dropped to
2 or 3 amperes— say, e.g., after the passage of 25 ampere hours.
As the reduction becomes completed, crystals of hydra iobenzene
commence to fall out ; when the process is completed, the beaker
containing the product is placed in a basin of cold water, and
a low current of o's to 075 ampere passed while the substance
is cooling, say for three-quarters of an hour. The bulk of the
bydrazobenzene thus crystallises out, and, on rapidly filtering on
the pump and washing, first with dilute acetic acid, and then
with alcohol, the bydrazobenzene is found to be practically pure.
Another crop of crystals can be obtained from the mother liquors
by addition of water containing a little ammonium sulphidc^to
prevent oxidation. This last portion can be obtained quite
pure by recrystalUsation from alcohol. Hydrazobenzene forms
colourless tablets ; m.p. 131° ; yield over 80 per cent.

XXVII. Preparation of Benzidine.'

When hydrazobenzene is acted upon by strong sulphuric acid
it is converted by intramolecular change into benzidene, as shown
by the following scheme ; —

H<^^ ^N - N<^^~^H->H,N<;^^^-

>NHa

This preparation can hardly be called an electrolytic one, but
as it is very readily produced from hydrazobenzene, it is in-
cluded here. In order to prepare it, the cathodic mixture is
after electrolysis, without cooling, poured into moderately strong
hot sulphuric acid (aoo c.c. H„SO„ 400 c.c. 11,0).' This must
' \V. Lob, Z~-il. f. Eliklro^hctn., 7, 320 am.1 333, also 597.

Practical Bteetro-Chemistry.
be done with caution, because the solution conta.ining the
hydrazobentene is strongly alkaline, and when it is poured into
the hot acid, unless care i>s taken, the reaction becomes too
violent In order to prevent reduction of the hydrazobenjene
it is advisable to add a few crystals of sodium sulphite to the
cathode solution before pouring it into the sulphuric acid. The
benzidine sulphate separates out as a crystalline powder, and,
after cooling, this is separated off- In order to remove any azo-
benzene which may be present, owing to oxidation, it is washed with
warm alcohol. About 65 per cent, of the theoretical amount of
benzidine sulphate is produced. The free base is obtained by
grinding up the benzidine sulphate in a mortar with excess d(
ammonia. The base is then filtered off and washed with a little
cold water to remove the ammonium sulphate, and the benzidine
crystallised from boiling water. As it is not very soluble in
water, a considerable quantity is required to dissolve it. On
cooling, large colourless plates or leaflets are obtained, which are
filtered off and washed with a little water and dried, m.p. 122°.

The azo- and hydrazo-compounds of other nitro-conapounds
are readily prepared by the same methods as those used for
preparing these compounds from nitrobenzene. Thus the
azoxy compounds obtained from p-nitro-anisol and from the
nitroxylenes are really easier to prepare than ordinary azoxy
and a^oben^ene, because they meit at much higher temperatures
and are therefore more readily crystallised. Other substituted
azoxy and azobenzenes can be produced by employing substi-
tuted nitrobenzenes. For example, the three chloronitrobenzenes
yield the corresponding cliloroazoxy benzenes, etc.

XXVIII. Preparation of p-Phenylenedia-
mine."

By reduction of the ortho-and para-nitraniHne the correspond-
ing diamines are readily obtained ; e.g. with p-nitraniline —

' Commercially hyJrochloric acid is generally employed instead of
sulphuric add.

" A. Noycs and J. J. Dorrance, Bcr., 28, 2350.

Reduction of Organic Compounds. 245 V

NO„{p) NH.. 1

CsH, + 6H = Z^^i + 2H,0

Take 20 grm. p-nitraniline and dissolve in about 150 to 200 c.c.
of alcohol; now dissolve S lo 7 grm. sodium acetate in 100 c.c.
of hot water, and mix the two solutions. This mixture is then
placed in a beaker, which acts as the cathode cell. The cathode
is of nickel gauze, as also is the anode. The anode cell is filled
with a 2o-per-cent. solution of sodium carbonate.

CONDITION.^.

C.D 14 lo 18 amperes.

E.M.F 7to8voIls.

Temp , ... 7;° to 80=

The mixture is made warm to start with; the high current used
keeps it at the boiling-point of the alcohol. The evaporated
alcohol may be replaced from time to time.

After the passage of 24 ampere hours the current is stopped.
The first 18 or 20 ampere hours of electricity are passed at a
high current density, then the current is gradually cut down lo 2
amperes.

At the end of the reaction the still hot cathode fluid is poured
into a mixture of 50 c.c. sulphuric acid and idd c.c. water.
The mixture is allowed to stand for an hour or two, filtered
on the pump, and then spread on a porous plate. By this means
colourless plates of p-phenylenediamine sulphate are obtained.
The yield is about 75 per cent, of the theoretical quantity
obtainable.

It should be noticed that whereas o-nitraniline upon re-
duction in the above manner yields o-phenylenedi amine,
m-nitraniline yields, when reduced under similar conditions,
m-diamidoazobenzene. This peculiarity is due to the tendency
of the ortho- and [lara-compounds to form quinones, a tendency
which is not exhibited by the raeta compounds.

246 Practical Electro-Chemistry.

REDUCTION OF A MIXTURE OF
NITROBENZENE AND BENZALDEHYDE,

XXIX. Preparation of Benzylidenephenyl-
hydroxylamine.'

The preparation of ben/ylidenephenyihydroxylamine by the
reduction of nitrobenzene in presence of benzaldehyde is of
considerable theoretical importance, because it proves that
phenylhydroxylamine is a product of the reduction of nitro-
benzene, and that aniline is produced by its further reduction.
The reactions which take place in the preparation of benzyl
denephenylhydroxylamine may be written in two stages.
I. C,H.NO. + 4H = C„H,NH . OH + H,0

,0H O-

II. C„HjN;f + 7C . QH, = C„H,N— CH . QH, -f H,o;

H '

The cathode mixture consists of t8 gnn. nitrobenzene and 20
gim. benzaldehyde dissolved in 40 grm. of glacial acetic acid, to
this solution 40 grm, (about 22 c.c. of concentrated sulphuric
acid) is added. The mixture is poured into a beaker, which acts
as cathode compartment.

The anode solution is made up of 3 parts concentrated
sulphuric acid and i part water, and is placed in a porous cell which
stands in the beaker.

Both anode and cathode must be made of platinum. Stout
platinum wire is the most satisfactory form to employ for the anode.
The cathode may either consist of platinum wire coiled loosely
roimd the anode cell, or, better, a cylinder of platinum— for
example, a cylinder such as is employed in electrolytic analysis.
CONDITIONS.

' Gatlennann, Bsr., 1

Reduction of Organic Compounds.

The whole apparatus is placed in a vessel of cold water to prevent
the temperature rising above about 20°.

The amount of current necessary to reduce 18 grm. of nitro-
benzene to phenyl hydroxylamine is 1 5 '5 ampere hours, but in order
to obtain a good yield of benzylideneplienylhydroxylamine it is
found necessary to pass the current for more than double this
time, about 35 ampere hours.

When the requisite amount of current has been passed, the
electrolysis is interrupted, and the contents of the cathode vessel
poured upon ice or into ice-cold water. The crystalline product
so obtained has usually a brownish or reddish-broi n pp n e
and often contains small quantities of oil, due to und on pos d
nitrobenzene or benzaldehyde. The substance s fi t a he 1
with water, then with dilute alcohol, and finally cry tall sed f om
alcohol, by which means colourless needle-shaped crystals a e
obtained ; ni.p. ro8' to 109°. Yield about 60 per cent.

XXX. Preparation of Ortho- and Para-
chloroaniline.

On p. 238 it has been found that when nitrobenzene is
electrolysed in a strong solution of sulphuric acid that the
phenyl hydroxy la mine which is produced in the second stage of the
reduction is converted by intramolecular change into p-amido-
phenol. On electrolysing a mixture of nitrobenzene and strong
hydrochloric acid, intramolecular change also takes place, but
with production of chloroanilines, the change which takes place
may best be shown as follows : —

UH.NOa -i- 4H = CflIT,NH.OH -f- H=0

In presence of strong hydrochloric acid the phenylhydroxylamine
is converted into phenylchloramine, which then undei^oes intra-
molecular change, a portion of the chlorine changing places with
the hydrogen atom in the ortho position, and a part with the
hydrogen atom in the para position, thus : —

lectrc-Chemistry, J

(i) C„H,NH,OH -i- HC1= C„H„NH.CI + H,0 I
(a) QH,NHCI-*C1.C„H4.HN, ^

Process. — A small porous pot, capable of holding aoo to 250

C.C., which should not be less than from 5 to 6 cm. in diameter, is
employed as cathode compartment. The cathode may either be
a cylinder of platinum or a fairly dose coil of platinum wire,
wound so as to come against the sides of the porous cell.
In the centre of the cell there should be placed a small
stirrer of stout platinum wire to which has been welded a
piece of thick platinum foil, to act as a paddle. The cathode
solution is made by suspending 35 grm. of nitrobenzene in 175
to 200 cm. of the strongest hydrochloric acid. The cell is then
placed in a beaker filled with dilute sulphuric acid (20 per cent).
Platinum foil or wire may be used for the anode. Before com-
mencing the reduction, the stirrer, which should be rotated
sufficiently rapidly to create a good emulsion, is started, and the,
current then switched on.

CONDITIONS.

1-5 U

S><

It is necessary to pass the current for considerably longer time than
is theoretically required, 45 to 50 ampere hours being used instead
of 30 ampere hours, the theoretical amount. If, however, the smell
of nitrobenzene is no longer noticed, the electrolysis can be stopped
when less current than above mentioned has been passed. The
solution in the porous pot has a greenish colour, and it will be
found on pouring it into a beaker that a small quantity of greenish
precipilate is suspended in it ; filter this off. Now evaporate the
solution nearly to dryness on the water bath ; on cooling, crystals
separate out. Add sufficient water to dissolve these crystals and
then excess of caustic soda ; at first a precipitate forms, but this
rapidly changes into a violet-coloured oil. This mixture is then
steam-distilled, an almost colourless oil being obtained in the
receiver (a certain quantity of a violet-coloured oil remains in the
distilling flask). The distillate is e.-itracted with ether, dried over

he C

Reduction of Organic Compounds. 249

calcium chloride, and the ether distiiled off. The oily substance
which remains after this treatment is a mixture of ovtho- and
p-chloroaniline.

Separation of Ortho- and Para-chloroaniline.— The

oily mixture is boiled witli acetic anhydride, whereby the acetyl
compounds are obtained. The anilides are then washed free
from excess of acetic anhydride, dried and boiled for some time
with a considerable excess of benzene in a fla.sk fitted with a
reflux condenser. The o-chloroaniline dissolves, and a small
portion of the para-conipound. The benzene solution is filtered
off, and, on cooling, crystals separate out ; these consist of the
dissolved para-compound. After separating these crystals the
benzene solution is distilled off, an oil being obtained which
rapidly solidifies ; this is the ortho-compound : m.p. 87". The
acetyl -p-chloroaniline melts at 172" to 173°.

If desired to prepare the pure bases from ihe acetyl com-
pounds, this can be done by heating in a closed tube with
hydrochloric acid to a temperature of i3o°. The solution so
' obtained is then made alkaline and steam-distilled. The boiling-
point of the ortho-compound is 206°, while the p-chloroanilinc
melts at 71° and boils at 231°.
' The reaction does not go completely in the manner set out

I in the equations, because there is always zo per cent, or more

iof the nitrobenzene converted into a violet-coloured oil. This
oil, the constitution of which has not yet been determined, is
left behind in the flask when the ortho- and p-chloroaniline are
steam-distilled.

i REDUCTION OF SUBSTANCES CON-

TAINING THE KETO GROUP.

In the reduction of substances containing the carbonyl group
>C0, the nature of the cathode is, as Tafel ' has shown, of very
I great importance. With platinum electrodes, generally speaking,
L ' Bev., 33, 220?.

Practical EUctro-Chemistry.

very lilllc reduction takes place, the most powerful effects being
produced when lead cathodes are employed. When lead is
used as cathode the hydrogen ions are discharged at a higher
potential than when other metals are employed. In fact, the
presence of only very small quantities of foreign metals seems to
considerably lower this over-potential. From his experiments,
Tjfel draws the following conclusion :^" That substanas wfuch
are difficult to reduce can only be reduced in sulphuric acid solution
when such cathodes are employed which give a particularly high
over-potential at tlte ealhede."

Furthermore, the concentration of the acid is of importance :
but the best results are obtained with solutions of a concentration
between 30 and 60 per cent. With very strong sulphuric acid,
the acid itself becomes reduced, and sulphur is thrown out.

Anotiier point of importance is the current density — generally
speaking, the lower the current density the more rapid and complete
the reduction. This, of course, means the employment of a large
cathode surface.

During the reduction, it is often advantageous to add small
quantities of lead acetate solution (about 0-5 c.c. of a normal
solution of lead acetate) ; this is to counteract the influence of
small quantities of metallic impurities which may be present.

Preparation of Lead Electrodes.

The lead should be as pure as possible, but it is not abi

lutoly essential that it should be chemically pure. No soldered

joints may come near to the

electrolysing cell. The best

way to cut the lead is shown

in Fig. 59; by cutting in

this manner, two electrodes

can be obtained from each

^"'- 59- piece of sheet lead. The

electrode b has a long narrow piece of metal, at the end of

which a piece of copper wire can be soldered. The electrode a

ISO'S

Redricfion of Organic Compounds.

has a similar extension on which the copper connection may
be fixed. The electrodes can then be bent into any desired

In order to prepare the surface of the electrode, it is well
nibbed with sand and water, washed with caustic soda, and again
rinsed with water. It is then placed in a vessel of 2o-per-cent.
sulphuric acid, in which it is made the anode, and a current of
2 amperes per square decimeter passed for about half an hour.
The surface of the electrode is now covered with a coating of
lead peroxide. It is then washed under the tap, and placed into
boiling water for a. few minutes, and finally it is dipped into alcohol
and then dried by means of a blast of air. The electrode is now
ready for use.

The first action of the current, when this electrode is made
the cathode, is to reduce the peroxide coating and to cover the
surface of the electrode with a thin membrane of spongy lead.
Even if the lead in the first case was not quite pure, this treat-
ment goes a long way towards improving its purity, and further
hydrogen given off on the surface of spongy lead appears to be
given up at a higher over-voltage than from a polished lead
surface.

It is advisable to oxidise the electrode each time before
employing it in a new experiment.

Preparation of Porous Cell.

The porous cells often contain more or less metallic im-
purities ; they must also be carefully purified. This is done by
first soaking them in a warm dilute solution of caustic soda for
a few hours, and then placing them in boiling distilled water for
another few hours ; after which they are soaked in dilute hydro-
chloric acid over-nighl — Tafel recommends for several days;
finally soaked for a day or two in distilled water, which should be
changed every now and then.

REDUCTION OF SUBSTANCES

CONTAININQ THE KETONE (CARBONVL

GROUP).

When a substance containing the carbonyl group is reduced,
there are three possible changes which may take place. In the
first place, a secondary alcohol may be produced —

C0 + 2H =

^CH.OH

Or two molecules may condense together with formation of a
pinakone,

R R, OH OH R

II. 2 ~^co + 2H= \c-c.;'

Or, thirdly, the oxygen atom may be eliminated with formation
of water, the place of tlie oxygen being taken by two atoms of
hydrogen.

R'^ R'^

Wlien acetone is reduced with a mercury cathode, the electrolyte
being dilute sulphuric acid, then reaction I. takes place, and
isopropyl alcohol is produced. When, however, it is electrolysed
with lead or other insoluble electrodes, the electrolyte being the
same, the reaction goes partially according to I. and partiaUy'.
according to 11., so that a mixture of isopropyl alcohol and
pinacone is obtained.

XXXI. Preparation of Isopropyl Alcohol.^

The cathode solution is prepared by dissolving 20 grm. acetcuie
in TOO r.c. of 4o-per-cent. sulphuric acid. The anode solution.

Tafel, Z,-i/./. Eliklroclum. (1902), E

Reduction of Organic Compounds.

lb 10 in,r-cent sulphuric acid, and the anode may be a pie^e of
Lomiio pipe to which a copper wirt. is soldered The apparatus
(.miiloyed is depicted in Fig 60 It consists of a glass cell, tho
bottom of which is covered with a layer of mercurj, 4, about
I to 2 cm deep b is a piece of stout platinum wire which
passes through a glass tube to the bottom of the vessel, and
makes electrical connection with the mercury 1 he porous, cell
L IS clamped in such a way that
It IS about s c m above the sur
face of the mercury In order
to keep the mixture cool dunng
electrolysis, the whole apparatus is

placed in a vessel of cold water. Tafel recommends the appa-
ratus shown in Fig. 61, The advantage of Tafel's apparatus is
that it allows the collection of the cathode gases, so that one is
able to follow the course of the reduction, and it is easy to find
. out how much of the hydrogen is used for reduction and how
much is unused.

In order to ascertain the CD., it is, of course, necessary to
know the surface of the mercury j this is readily found by
measuring the diameter of the electrolysing cell.

If a current of 4 amperes is passed, the electrolysis will be
complete in about 10 hours. When much higher currents than
this are employed, it is sometimes rather diiBcult to keep the
solution sufficiently cool.

Pnutkal Electro- Chemistry.

As soon as the reduction is completed tlie clear cathode solution
is neutralised with solid caustic potash, care being taken not to
allow the temperature to rise above 25° or 30°. As soon as the
mixture is slightly alkaline, excess of anhydrous potassium car-
bonate is added, the mixture transferred to a flask and distilled
from the water bath. The isopropyl alcohol which passes over is
dried with a little anhydrous potassium carbonate and fractionated,
when almost the whole of it passes over between 80" and 8i°j
The yield is about 18 to 19 grm.

XXXIl. Preparation of Isopropyl Alcohol
and Pinacone.'

In order to prepare isopropyl alcohol and pinacone at thS"
same time, the only difference from the last experiment is in the
material of the electrode, which is lead. The best form of
apparatus is a small lead vessel, which is used as cathode ; the
anode may be also of lead, and is placed as before in a porous
cell. A current density of 4 amperes per square decimeter is
employed, and the solution is kept cool by placing the lead
vessel into a basin through which cold water is circulated. The
following equations both take place concurrently : —

I. CH,.CO.CH, + 2H = CH,.CH(OH).CH3 dl
II. aCH^.CO.CH, + 2H = CH,.C(OH).CH;, ^|

CH,.C(OH).CH,
As soon as the reaction is completed, which can be told from
the vigorous evolution of hydrogen, the clear solution obtained
is treated with caustic potash until slightly alkaline, and then
with excess of anhydrous potassium carbonate; the mixture is,
however, not directly subjected to distillation, as in the last
experiment. The addition of the excess of potassium carbonate
causes the formation of two layers, the lower one being a con-
centrated aqueous solution of potassium carbonate. This is
separated from the upper layer, which consists of a mixture of
' E. Merck, D.R.P., 113,719 (:Sa3).

CH,-

-CH

CH.-C— CH

CH,-

1
CH,

Camphor.

Reduction of Organic Conipoimds.

isopropyl alcohol and pinacone. The two substances arc now
readily separated by fractionation. The boiling -point of isopropyl
alcohol is 80° to 81°, that of pinacone 171° to 172°. With water
pinacone forms a crystalline hydrate (CHa);,C(OH) . C(OH) (CHJ
+ fiH^O; tn.p. 42°. The Tin hydrous pinacone melts at 33^^.

XXXIil. Preparation of Borneol/

Camphor also contains the koto group, and on reduction yields
ihe secondary alcohol borneol.

CH, CH CH,

-- CH,— C— CH,

CH,. C CH . OH

I
CH,

Borneol.

The cathode may be a lead vessel, all the joints of which must
be burnt and not soldered. This vessel is prepared in the manner
already described for lead electrodes (p. 351). The anode should
be a piece of pure sheet lead, and is placed in a porous cell,
which stands upon a piece of glass placed on the bottom of the
cathode cell. Or it may be held about 5 cm. from the bottom of
the vessel by means of a clamp. The cathode solution is prepared
by dissolving 10 grm. of camphor in 100 to izo c.c. alcohol,
and then addmg 60 to 100 c.c. of js-per-cent. sulphuric acid.
If the camphor is precipitated out, a further quantity of alcohoi
must be added. The anode solution raay be 70-per-cent.
sulphuric acid. In order to prevent the mixture becoming hot
during the electrolysis, the lead cell is placed in a vessel through
which cold water is circulated.

With a current of 3 amperes the reduction is finished in ten
hours. The CD. may be from 10 to 12 amperes, so that if the
cathode surface is i square decimeter, then a current of 6 amperes

' J. Tafel and K. Schmitz, 7-HtJ. Eliklrochem. (1902). 8, 2SB.

Practical Electro-Chemistry.

may be employed, provided the temperature does not rise above 20°
to 24°, and in this case the reduction would be finished in five
hours. The electrolyte does not conduct the current very well,
therefore the E.M.F. will be found to be from 10 to 15 volts,
altliough it may fall considerably toward the end of the reaction.

When the electrolysis is finished the cathode mixture is poured
into a beaker, when it will be found to separate into two layers.
Excess of water is now added, and a semi-crystalline mass
obtained; this is extracted with ether; the ethereal solution is
washed and dried and the ether distilled off. The crystalline
mass so obtained is then purified by recrystallisation from ligrijin.
The m.p. of the pure product is 304° to 205°, and the yield from
42 to 4S per cent.

The third form of reduction (p. 852), where the keto group is
converted into the CH.j group, takes place, as has been shown by
Tafel, when caffeine is electrolytically reduced, desoxycaflfeine
being produced ; thus :^

CH,.N— CO

CH,.N— CH,
^.CH-, II ,CH,

CO C — N + 4H= CO C — N<'

I II >CH I 1 >CH

.N— C— N CH,.N-C — N

This form of reduction also takes place when uric acid is reduced,
purone being formed : — _

1 NH-6 CO

I I

2 CO S C — 7 NH.

I II )

3 NH— 4C— 9NH-^

Uric Acid.

NH— CHs

I I

= CO— CH -

NH— CH — NH^

PURONE.

The reduction here, however, is not confined to the replacement
of the oxygen of the 6 carbonyl group, but goes a step further,
and also reduces the double-bonded carbon atoms 4 and 5. It is
an interesting fact that until Tafel succeeded in electrolytically
reducing uric acid, all attempts at its reduction had failed.

Reduction of Organic Compounds.

Tafel finds the above reaction, in which the carboiiyl group is
reduced to the CH^ group, to be general; alkyl xynthines and
alky] derivatives of uric acid are also reduced in a similar manner.

The preparation and purification of purone presents consider-
able difficulties, whereas the reduction of caffeine is comparatively
easy; the preparation of desoxycaffeine is therefore given as an
example of this class of reduction,

XXXIV. Preparation of Desoxycaffeine/

Fifteen grm. of caffeine is dissolved in a mixture of 22 c.c.
concentrated sulphuric acid and 40 c.c. water. This solution is
placed in a beaker, inside wliich tiiere is a small porous cell which
has previously been soaked in 50-per-cent. sulphuric acid, the
anode solution consisting of sulphuric acid of this strength. The
anode is a piece of lead sheet, or of lead pipe. The cathode is
made of lead sheet, which has previously been prepared as described
on p. 251, and is bent in the form of a cylinder, so as to surround
the anode cell. The whole apparatus is placed in a bath of cold
water. A carefully prepared lead vessel may be used instead of
the beaker for holding the cathode solution ; in this case, of course,
the lead vessel acts as cathode. Or the cathode solution may be
placed in the porous cell, and Che lead vessel made the anode.

CONDITIONS.

CD 3 to 5 amperes.

E.M.F 5 to 7 volts.

Temp should not rise above 20°

According to the equation, 15 grm, of caffeine requires the passage
of 8'4 ampere hours of current.

CHijN^Oa + 4H = QHi,N,0 + H,0
It is better to give it slightly more than this in order to ensure
complete reduction, say lo ampere hours.

Ab soon as the reduction is complete, the cathode fluid
diluted with an equal volume of water, and neutralised with slaked
. Baillie and J. Tafel, B^r., 33, 68.

lid is M

ilaked H

358

Practical Electro-Chemistry.

1 sulphate filtered off and washed

.ler is added to the original solution,

or 70 c.c. on the water bath. The

.tracted several times with chloro-

lime, the precipitated calcium
once with water. Tlie wash wai
and the whole evaporated to Cc
concentrated solution is now e:

form ; the chloroform is then distilled off, when there i
yellowish crystalline residue. This crystalline residue is dissolYed
in a small quantity of lo-per-cent. hydrochloric acid, and the
solution shaken out with chloroform ; tliis dissolves out the colour-
ing matter, and any unchanged caffeine which may have escaped
reduction. The solution is now made alkaline with caustic alkali,
and again extracted several times with chloroform. On evapo-
rating the chloroform the desoxy caffeine is obtained in a very
pure condition, in the foroi of colourless crystals. It can be
further purified by crystallisation from ethyl acetate. 'I'he desosy-
caffeine so obtained contains i mol of water of crystallisation
CsHuNjO.RjO; m.p. 118". When dried over sulphuric acid in
vacuo the water of crystallisation is given up, and the m.p. rises
to 148°. The water-free substance can be distilled undeconiposed
ift xiaciio. The yield of the pure product is about 70 per cent.

XXXV. Preparation of EthyNo=toluidineJ

Another interesting case of reduction of the carbonyl groufifl
the reduction of the acetanilides as, for example, acetanilid§, wli)
is converted into ethylaniline.

QHjNH . CO . CH^ + 4H - QH.NH . CH, . CH, -\- Vlfi
The acet-toluidines yield ethyl toluidines, ilius ortliotoluidi
gives etliy 1-0- tolui dine.

NH.CO.CH,

4-4H =

NH.CH, CH,

-HjO J

Dissolve 10 grm. of acetyl-o-toluidine in a mixture ol
concentrated sulphuric acid and 45 c.c. of water This is t
' T. B. Bailiie and J. Tafel, Ber., 32, 6S.

Reduction of Organic Compounds.

electrolysed in a porous cell as cathode space, with a prepared
lead electrode. The porous cell is placed in a lead vessel, which
acts as anode, and is filled with 20-per-cent. sulphuric acid. If
preferred, the cell can be placed in a beaker, and a cylinder of
lead be employed as anode. The whole apparatus is placed
in cold water, otherwise considerable heating takes place. A
current of about 5 amperes is passed ; the current density is
not of great importance, provided the temperature does not rise
too high— it should not be allowed to rise above 25°.

QHiiNO + 4H = QHijN + H,0

10 grm. of acet-toluide requires just over 7 ampere hours for
complete reduction; about S^s ami)ere hours of current is passed
and the electrolysis stopped.

The cathode solution is diluted with about \\ times its volume
of water, and allowed to stand overnight. Some unchanged
acet-toluide crystallises out; this is filtered off, and the filtrate
rendered alkaline with caustic alkali, and steam-distilled. In
order to purify the product, the distillate is made acid, and sodium
nitrite added a little at a time, the mixture at the same time being
cooled, to convert the ethyl toluidine into the nitrosamine. The
oily nitrosamine is then separated from the solution, and reduced
with tin and hydrochloric acid, by which means it is reconverted
into the ethyl-o-toluidine, which after making the solution alkaline
is extracted with ether. The boiling-point of the ethyl-o-toluidine
is ai3° to ai4°. Yield, about 60 per cent, of the theory.

XXXVI. Preparation of Piperidine (Hexa^
hydropyridine).

Dissolve 2o grm. pyridine in 200 c.c. of lo-per-cent. sulphuric
acid. Place this solution in a glass electrolysing cell with a lead
cathode, and a rather smaller anode also of lead. As neither
pyridine nor piperidine are oxidised to any extent by the anode
current, it is not necessary to separate the anode and catliode.

26o Practical Electro-Cliemistry.

CONDITIONS.

CD lo to 12 amperes.

E.M.F 6 lo 8 volts.

Tem]3 Normal ; rises during electroljrsis to

50° or 60°

When the circuit is first closed there is scarcely any hydrogen gas
given off at the cathode, almost the whole of it being used up to
reduce the pyridine to piperidine.

QH,N + 6H = C5H10NH

But as the electrolysis is continued more and more, gas is given off
at the cathode until finally the evolution of gas is quite vigorous.
When rather more than the theoretical amount of current has
been passed, it is switched off. The solution is then rendered
alkaline with caustic soda, and steam-distilled. The piperidine
passes over with the steam, which should be vigorously driven into
the solution, and the distilling flask should also be heated on a sand
bath. The strongly alkaline distillate, which possesses the peculiar
and characteristic odour of piperidine, is acidified with hydrochloric
acid and evaporated to dryness. The solid piperidine hydrochloric
is then decomposed with a strong solution of caustic potash. If
the mixture does not separate into two layers, a few small pieces
of solid caustic potash are added. The upper layer consisting
of piperidine is then separated, dried with solid caustic potash
and fractionated. The boiling-point of piperidine is 106°.

LITER A TURK
Ahrens, ZeiLf, Elektrochem.^ 2, 577. Merck, D.R.P,y 1896, 90308.

CHAPTER XV.

OXIDATION OF ORGANIC COMPOUNDS.

The number of compounds which have been successfully prepared
by electrolytic oxidation is comparatively small. The chief
difficulty in oxidising is to stop tbe reaction at the right point.
One might suppose this to be a comparatively easy matter, it
being only necessary to pass the current sufficiently long to
liberate a given amount of oxygen, and that then the oxidation
should be complete. For example, if one atom of oxygen is
required to oxidise a certain substance, then, if 2 faradays or
96,540 X 3 coulombs of electricity is passed, the oxidation will
have taken place. But here, as with all oxidations, the reaction
often proceeds too far : a portion of the substance only may have
been attacked, and attacked much too vigorously— in other words,
burnt up ; whereas a portion will have been altogether unacted
upon. To exactly state what are the conditions necessary for
successful electrical oxidation is an impossibility ; generally speak-
ing, it seems important to keep the E.M.F. as low as possible:
other conditions, hot or cold, acid or alkaline solutions, and so
forth, will vary with the substance to be oxidised.

XXXVd. Preparation of Purpurogallin.

Ci,H,0.
Dissolve 38 grm. (i oz.) pyrogallol in 500 c.c, of a 15-per-
cenL solution of sodium sulphate. Place this solution in a
rectangular glass jar, which should stand in a basin of cold water.

At ihc two o]iposite comers of the jar fix two tliin pieces of com-
position pipe, to each of which a piece of copper wire has been
soldered. Connect these wires together, .and join them up with
ihe negative pole of the electrical supply. The anode must be of
platinum, and it is best to have it rotating. If a rotating platinum
anode is not to be had, then hang two pieces of platinum foil at
opposite sides of the jar, and vigorously agitate the solution
by means of a glass or wooden stirrer. The anode surface should
not be less than r square decimeter, but is better to have double
that surface.

CD I's lo a amperes.

E.M.F 4'3 lo 4*5 volls.

Temp Nnrmal.

With a current of z amperes the electrolysis is completed in 6 to 8'
hours. As soon as the current is switched on, the solution
becomes yellow, and in a short time a yellow or orange yellow
precipitate of purpurogallin begins to separate out. The solution
should not be allowed to become hot, otherwise a brown impure
product is obtained ; it is therefore advisable lo stand the electro-
lysing cell in a basin of cold water. After the electrolysis is
finished, allow the product to stand overnight, then filter and
wash with water ; finally .spread on a porous plate to dry. The
purpurogallin so obtained is of a bright yellow colour, and is quite
pure.

Yield about lo grm. It can be crystallised from hot glacial
acetic acid, from which it separates, on cooling, in dark yellow
needles or plates. If a very small quantity of purpurogallin
is shaken up with water containing a drop or two of ammonia or
caustic alkali, a magnificent blue colour is produced, which
gradually becomes brown ; this reaction only shows in dilute
solutions. Purpurogallin has well-marked tinctorial properties,
giving with mordants much the same shades as alizarine. The
interesting point about purpurogallin is, that in it we have a
benzene derivative passing by simple oxidation into a derivativ<»

Oxidation of Organic Compounds.

of naphthaline. The exact constitutional formula of purpurogallin
is not at present knoivn.

LITERA TUBE.

A, G. Perkin, Chsm. Soc. (rgos), 83, 192; A. G. Perkin and
F. M. Perkin, Cheni. Soc. (1904), 85, 243.

XXXVIII. Preparation of Iodoform.

Cllls.

From Alcohol.

Dissolve zo grm. dry sodium carbonate and zo grm. potas-
sium iodide in 200 c.c. water, then add 50 c.c. of absolute
alcohol. Metiiylated spirit which has been purified by distillation
over caustic soda and lime may be used instead of the absolute
alcohol.

Anode. — Sheet platinum.

Cathode. — Platinum or nickel ; it should be in the form of
a spiral of stout wire, and the surface should be considerably less
than the anode surface.

Heat the solution to a temperature of 60' lo 70°, and then
electrolyse with an anode current density of r to 3 amperes. The
beaker employed should be a high one, so that the upper surface
may help to condense the alcohol, which is otherwise apt to
volatilise. During the electrolysis a slow stream of carbonic acid
gas should be conducted through the mixture in order lo prevent
the solution becoming too alkaline, owing to the liberation of
sodium at the cathode. It is also advantageous to agitate the
Solution vigorously by means of a mechanical stirrer — a rotating
platinum anode serves this purpose very well. If during the
electrolysis the solution should become brown, owing to liberation
of iodine, the passage of the carbonic acid gas must be stopped
until the brown colour disappears, because the appearance of the
brown coloration shows that the carbonic acid gas is being
passed too rapidly.

The reaction which takes place is representee] by the following
equation : —

CH, . CH, . OH 4- lol + H5O = CHI, + CO, + 7HI

The hydrogen iodide produced recombines with the liberated
sodium and potassium at the cathode to reform potassium iodide,
The iodine shown in the above equation is, of course, obtained
from the electrolysis of the potassium iodide.

The electrolysis may be allowed to continue for three hours,
at the end of which time the current is cut off and the solution
allowed to stand for two or three hours, or better over night,
when the iodoform is filtered off. The iodoform so obtained
is in the form of small crystals, and is very pure. The current _
eiBciency is between 75 and So per cent.

The solution which is left over may ^ain be employed bd
adding a fresh quantity of alcohol and potassium iodide, s<
the process can be made practically continuous ; this is, of o
important when the operation is conducted on a manufacturii
scale. _

During the electrolysis, a certain portion of the iodidi
becomes oxidised to iodate. A certain amount of reductioi
of the iodoform always takes place at the cathode, so Eibs sug-
gests surrounding the cathode with parchment paper; but when
large quantities of iodoform are required, it is better to employ
a porous cell for the cathode department. In a continuous
process, the anode solution may be changed to the cathode after
each filtration, as the iodate thus becomes reduced to iodide
again, and is then ready to be again placed in the anode t
partment. The disadvantage in using a porous cell is that tJ
E.M.r. is slightly raised.

With Acetone.

In the equation already given for the production of iodofonj
from alcohol and iodine, it is seen that for every molecule (
iodoform produced, 10 atoms of iodine is required. With aceton^

Oxidation of Organic Compounds.

the otlier hand, only 6 atoms of iodine is requited to produce
s molecule of iodoform.

CHa

~ CO + 61 + H,0 = CHI. + CHs . COOH + 3HI

CH/

When alcohol is oxidised, i ampere hour will theoretically yield
I '467 grm. of iodoform; but with acetone, 1 ampere hour gives
2'444 grm. It follows, therefore, that if acetone can be substi-
tuted for alcohol, there would be a great saving in the current
required : furthermore, acetone is cheaper than alcohol- When
a mixture of potassium iodide, sodium carbonate, and acetone is
electrolysed under tlie same conditions as those set out above for
the preparation of iodoform from alcohol, only very small quan-
tities of iodoform are-^oduced. But it has recently been shown
by Abbot that fairly good results can be obtained by allowing the
acetone to run in very slowly during the course of the electrolysis.
The following method, due to T. E. Teeple, gives extremely good
results, the yields often being up to 95 per cent, of the theoretical.
In the commercial chemical process for m'Snufacturing iodoform
from acetone, according to the method of Suilliot and Raynand,
the production of the iodoform depends upon the formation of
potassium hypoiodite by the action of a hypochlorite upon potas-
sium iodide.

Kl + KCIO = KCl -!- KIO
3KIO ->r (CVi,)^CO = CHI, -j- CH.COOK + 2KOH

If DOW a solution of potassium iodide is electrolysed at ordinary
temperatures, potassium hypo iodide is produced.

aKI + 2H2O = aKOH -|- 2I -|- 2H
6K0H -I- 61 = 3KI -1- 3KIO + 3H,jO

If acetone is also present, it will react with the hypoiodide in the
following manner : —

3KIO 4- (CH,),jCO = Cr,. CO . CH, -i- 3KOH
CL, . CO . CH, -I- KOH = CHI, -j- CH, . COOK

In order to olitain a good yield of iodoform, it is necessary to

neutralise the excess of caustic potash formed in the reaction
this may either be done by passing in carbonic acid gas, neutralis-
ing with hydrochloric acid, or, better still, with iodine.

= KIO + Kl + H,0
= CHI, + CH,. COOK -

sKOH

■aKOH + z
3KIO + (CH„),CO

It will be seen that caustic potash is again set free by the further
electrolysis, and we therefore obtain a continually decreasii^
quantity, i+J+jj + ... = 5, It follows, therefore, that the
necessary quantity of iodine to add is exactly half as much as
the quantity which the electric curront liberates.

Process. — Dissolve 25 grni, of potassium iodide in 225 to
250C.C. water, add 3 c. c. of acetone, and electrolyse with aiplatinum
cathode — a spiral of stout wire — and a platinum anode of from
J to 1 square decimeter. It is best to employ a rotating anode,
or to thoroughly agitate the solution by means of a glass stirrer.

CONIlITKiN-S.

E.M.F 3'5'o37

Tt-mp Normal.

The electrolysis may be conducted for about 90 minutes, during
which time i'56 grm, of iodine is added in small quantities at
a time, sufficiently quickly to keep the solution just brown i
colour, After the electrolysis has proceeded for about 45 minutes,
anotlier 3 cc. of acetone may be added.' At the end of 90
minutes or so the electrolysis is stopped, and the mixture allowed
to stand for about an hour and a half. After which the iodoformj
is filtered off and washed with a fittle water,
colour it should be also washed witli small quantities of a dilute ,
solution of sodium carbonate. Yield of iodoform, 92 to 94
per cent

Instead of adding iodine, a fairly rapid stream of carbonic
acid gas may be conducted through the electrolyte during the;

' Teeple only recommends ihe aildillon of 2
intliQr has, however, ohtaineil better results by pio.

Oxidation of Organic Compounds.

first fifty minutes of the electrolysis, after which it is discontinued.
The solution will probably be very brown in colour, and the
colour may not have comjjletely disappeared when the current
is stopped. In about an hour's time after the current has been
cut oiF, the brown colour will probably have completely vanished.
The iodoform is obtained in the form of a fine crystalline
powder. It can be obtained in large crystalline plates by crystal-
lizing from acetone. But the colour of the product keeps better
when the iodoform is crystallised from alcohol,

L/TERA TURK.

Elbs und Heri, Zeit. f. Eliklrockem., 4, 113; A. Foerster and
Meves, Zeit. /, Elektrochsm., 4, n68 ; Schering, D.R.P., 29771;
Howe Abbot, Journ. Physical Chem., 1003, S4. Teeple, Journ.
Amer. Chem. Soc. (1904), XXVI. 170.

XXXIX. Preparation of Bromoform.'

Sixty grams of potassium bromide and o'3 grm. of potassium
chromate is dissolved in 150 c.c. of water, and to the solution is
added 20 c.c. of acetone. This solution is then placed in a
beaker capable of holding about 200 c.c.

The anode should be of sheet platinum, bent cylindricaliy,
so that when placed in the beaker it fits almost against the
walls of the vessel. Tiie active anode surface may be about
go sq. cm. — practically only the inner surface of the anode,
when arranged as here described, will be active. The cathode,
which is a spiral of stout platinum wire capable of carrying 4 or
5 amperes without becoming hot, is placed in the centre of the
beaker, so that it is surrounded by the cyhndrical anode. A
cylinder, such as is used for electro -analytical purposes, ser\-es very
well as anode.

In order that the temperature may not rise above 18" to -zo"
the beaker is placed in a basin tlirough which cold water is caused
to circulate during the experiment. A current of about 3 amperes

' E. Midler and R. Loche, Zfit.f. Elrhlrochem., 1904, X,, 409.

is passed ; the E.M.F. will be about 4 lo 4"2 volts. During the
electrolysis a rapiil stream of c.irbonic acid gas is conducted
through the solution. The tube from which the carbonic acid gas
is delivered should pass to the bottom of the beaker, so that the
hraraoform, as it is formed, may, as weU as the solution, be
agitated. In order to obtain a thorough agitation, the delivery
tube may consist of a T tube bent twice at right angles, the ends
of the tube being drawn out into narrow openings.

After the passage of about 14 ampere hours the current is
stopped, when the bromoform, strongly coloured with bromine,
settles to the bottom of the beaker. The mixture is transferred
to a separating funnel, and separated from the electrolyte. It is
then shaken up in the separating funnel with a mixture of acetone,
and sodium carbonate solution. This solution is added in small
quantities at a time, the addition being continued until the brown
colour disappears. The brown coloration due to the bromine
varies very much in intensity in different experiments ; sometimes
the bromoform is coloured a deep red, at other times it is only
light brown. The cathode should not be nickel, because the
liberated bromine acts upon it, and the yield of bromoform is very
much less than when the cathode is of platinum. There seems
also a tendency with a nickel cathode for bro mo-ace tones to be
produced, and these are extremely irritating to the eyes.

The bromoform is finally washed with a little water, aud its
volume measured, the weight being obtained by multiplying the
number of cubic centimeters obtained by i-g, the sp.gr. of bromo-
form. So obtained, the bromoform always contains a trace of
moisture, which causes it to be cloudy. In order to render it
anhydrous, the bromoform must be dried over calcium chloride,
and distilled; the b.p. is 151°, and the m.p. 7*6°.

The reaction which takes place in the formation of bromoform
may be represented by the equation^

CU, . CO . CH, + 6Br + H^O = CHBrj + CH, . COOH + aHBr.

In the electrolytic production of bromoform from potassium
bromide and acetone, potassium hydroxide is produced, and itL

Oxidation of Organic Compounds.

is to rendtr this innoxious that carbonic add gas Js passijd through
tin; electrolyte. The addition of the potassium chroniate is to
prevent, as far as possihle, the reducing action of the hydrogen j
the employment of a high cathode density also helps in this
direction.

XL. Preparation of Anthraquinone.

C„H„0,

The electrolytic oxidation of aiithracine is attended with
certain difficulties, because anthracine is a solid substance which
is only very difficultly soluble in organic reagents: the only one
which can be employed is acetone, but with this solution it is
not possible to obtain very satisfactory yields of anthraquinone.
Recourse is therefore had to oxidation of an emulsion of the solid
anthracine which has been ground to a very fine powder,

Anthracine is a substance which it is very difficult to wet satis-
factorily, but unless it is thoroughly wetted a good emulsion
cannot be formed, By dissolving it in acetone or in acetic acid,
and pouring into water, a good mixture can be obtained. Perhaps,
however, the best method to adopt is to rub the finely powdered
anthracine through a wire gauze of very fine mesh with warm
water; this is a somewhat tiresome procedure, but it gives vei^
satisfactory results.

If a mixture of anthracine in sulphuric acid or in caustic
alkali is subjected to the oxidising action of the electric current,
only a very small amount of oxidation takes place. It is found,
however, that if an oxygen-carrier is added to the mixture, over
80 per cent, of the anthracine can be oxidised to anthraquinone.
Various oxygen carriers have been suggested, such as manganese
chromium or cerium salts, all of which give satisfactory results.

Procedure. — A circular lead vessel is made the anode ; it
should have a capacity of about 1500 c.c. of solution. The cathode,
wliieh should be capable of very vigorous rotation, is also of lead,

£^. a lead paddle (p. 198); the entire cathode surfaci; should ni
exceed half a square decimeter.

Mix ao gmi. of anthracine with water in the maimer ju
described, and wash it into the anode vessel ; dilute to 900 c.c, an
add 100 c.c. concentrated sulphuric acid. The oxygen-carrier it
now added, and may be 150 grm. chrome alum, 20 grni. potassium
chromate, 100 grm. manganese sulphate, or i"5 grm. eerie
sulphate. The total exposed anode surface will be from 5 to fr
square dec i meters.

CUNDITION^.

CD I (uz amperes.

E.M.F 3-8 to 3-5 volts.

Temp 75° to 90°

The cathode must be very rapidly rotated in order that lh0
anthracine may be thoroughly incorporated with the solution.

When an oxygen- carrier is used, there Seems very Utde
advantage in employing a porous cell to separate the anode and
cathode, so long as the anode siurface is very large in comparison
to the cathode. From the equation it will be seen that every
gram of anthracine requires about i ampere hour to oxidise .
anthraquinone,

C,.H,„ +30 = CuH^O, + H^O

After the current has been passed for about 22 ampere hours, the
electrolysis is stopped. Towards the end of the reaction it is.
advisable to cut the current down to about \ ampere per square
decimeter, and to raise the temperature to 100^, When a cerium
salt is used as oxygen-carrier, the end of the operation is kaowi^
by the solution retaining a permanent yellow colour, due
unreduced eerie sulphate.

When cool the mixture is filtered and the anthraquinone
washed with water until the filtrate is no longer acid. It is then'
spread on a porous plate, and when dry may be crystallised froitt
toluene or benzene or a mixture of acetone and toluene. Since):
there is still from 10 to 12 per cent, of anthracine present, the,
mother liquor should be poured oflT from the anthraquinone, which

Oxidation of Organic Compounds. 271

separates out first, before it is quite cold. One crystallisation, if
tills ])recaution is taken, is generally sufficient to give a perfectly
pure product. The anthraquinone is obtained in the form of
beautiful light yellow siiky needles ; m.p. 274°.

It is a rather interesting point, that, although without a
diaphragm (even when a small cathode and large anode surface is
employed), it is only possible to oxidise a comparatively small
quantity of chromic salt to a chromate. Yet in spite of this it
makes a very satisfactory oxygen- carrier for oxidising organic
substances such as anlhracine. It is quite likely that the lead
peroxide produced at the anode may also take part in the
oxidation. In fact, one very rarely notices any deposit of lead
peroxide on the anode vessel when the reaction is finished.

LITERA TURE.

Darmstadtcr (1897), D.R.P., 109,012; Htichst Farben Fabrik,
D.R.P. (189S, 103,860) ; Le Blanc, Zeit.f. Elektrotkan. (1900), 7, 292 ;
I and Darsielliiiig dfs Chroiits., A. Fontana and F, M. Perkin, Eieclre-

chemist {1904.), III. 656.

PREPARATION OF DYES.
XLl. Preparation of Canarine.'

When potassium or ammonium thiocyanate is eleclrolytically
oxidised in presence of hydrochloric acid, a yellow precipitate
called canarine is produced, the constitution of which has not yet
been determined, but which has had the formula QH^HSj assigned
to it. This substance, which is insoluble in acids and in the
ordinary organic solvents, dissolves in alkali carbonates and
hydroxides and in borax solution. Silk and wool, when immersed

' Ptochoroff und Mailer, Dingier' s yaiinml, 263, 130; Markognikoff,
/otirn. Russian Cliem. Soc, 1884, 380 ; Lindow, Ibid., 1884, 271 ; refeiences
\a Ber., 17, K. 275 and 522 ; and Bcr., 18, R. 676.

272 Practical Electro-Chemistry.

in solutions of caiiarinc, are dyed a yellow, the intensity of t
colour depending upon the amount of canarine in the solutioi
Whtn cotton goods are impregnated with this dye, it acts i
mordant toward basic colouring matters.

Preparation. — Dissolve 30 grm. ammonium or poCassiul

thiocyanate in about 300 to 400 c.c. of distilled water,
this solution to a narrow beaker, fitted with a cork through whicfi
passes a glass stirrer {Fig 62). On either side of the glass stirrer
is hung an electrode of sheet platinum, about \ square decimeter

in surface, and on the other two sides spirals of platinum i
one of which is shown in the diagram (diameter about 075 |
I mm.). The two larger electrodes act as anodes and the bid
electrodes as cathodes. Before commencing the electrolysis, ti
solution is heated to 75° or 80°, and then 30 cc. of strong hydro-
chloric acid run in by means of a thistle funnel, which passes
through a hole in thu cork ; the current is then switched on.

Oxidation of Organic Compounds. 273

CONDITIONS.

CD 5 to 6 amperes.

E.M.F 3-oti)3-5 voUs.

Temp So"

The best form of glass stirrer to use is that described by
W. Lob ; ' this form of stirrer is exceedingly efficient, and never
wobbles.* Fig. 62 shows the arrangement of the cell. If the
cell is not kept enclosed during the course of the electrolysis, the
vapours which come off are extremely unpleasant and poisonous,
and produce headache. A tube, not shown in the diagram,
passes through the cork, so that the gas evolved can be led off or
collected, as may be desired. Shortly after the electrolysis has
commenced, a light yellow precipitate commences to fall out, and
the mixture assumes a uniform yellow tint. Af^er the current has
been passed for about four hours, the electrolysis is stopped.
The mixture is allowed to stand until cold, and then filtered off.
The canary yellow precipitate is washed several times with warm
water, and then spread upon a porous plate, in order to remove
the last traces of moisture. Yield about 5 grra.

Azo- Com pounds.

W. Lob ^ finds that, when an amine, a nitrite, and a coupling
substance, such as a phenol, are mixed tc^ether, and subjected
to electrolysis in the anode compartment, azo-colouring matters
are produced. It must be presumed that a dia/o-com pound is
first formed by the action of the NOa ions at the moment of
their liberation, for which we may write the equation —
R . NH, + NO.; -* R . N = N . OH + OH'
The main difficulty in the reaction is the unstable character of the
diazo-compound under the influence of the electric current. It
is therefore necessary to have the coupling ageut present from the

' Zeit.f. EUklracliein., 7, 117 (1900).

' When it is desired 10 keep the eleclrolylic cell absolutely gas-lijihl, ihen
the vessel A is partially filled with mercury, as shown in the figure.
' Zeit.f. Eleklmcktm., 1904. X. 237 : D.N.p., 761, jro, 1904.

very commencement, so iliat the azo-compound is forined.
this means it is precipitated, or, if not precipitated, converted ir
the more stable substance, and thus removed from the farther I
action of the electric current.

An amine cannot be employed as coupling or fixing agent,!
because the amine itself will react with the discharged NO^' ions. I
I^b finds, however, that phenols may be very satisfactorily 1
employed. The sodium nitrite, amine, and a phenol are mixed 1
together, and electrolysed in the anode compartment with al
platinum electrode. It is necessary to vigorously agitate theJ
solution.

XLII. Preparation of Orange 11.

(Tropaolin OOO No. I.)

y3. Naphihol-a^obenzenemonosulphonate.

H SO, . C„H. . N = N . C,„H, , OH

Add 1 9-5 grm. of the sodium salt of sulphanilic acid (p-iunii
benzene sulphonic acid), 14*4 grm. of j8. naphthol, and 6-g grro.
sodium nitrite' to 150 c,c. of water. Place this mixture in the anode
compartment, which may consist of a beaker or a rectangulat
battery jar.

The cathode compartment should consist of two small porous'
cells, of such a size that either a platinum or glass stirrer can be
rotated between them. The cathode solution may consist of 10-"
per-cent. caustic soda.

The cathode should be either nickel or platinum wii
anode either a stirrer of platinum or a sheet of platinum;
latter case a glass stirrer {Fig. 62, p. 272) must be employed,
because, as the substances use^ are not all soluble in water, it is
essential to have a very thorough agitation of the mixture. The
whole apparatus is placed in a basin through which cold water is

' It is necessary to first test the quality of the sodiiim nitrite, because tlw
ordinary proiluct is rarely pure. The above nambers refer tg (he lOO-per-ceoL

Oxidation of Organic Compounds. 375

passed — it is, in fact, an advantage to surround the electrolysing
apparatus with ice.

]f the anode mixture is placed in a porous cell, the outer cell
acting as cathode, there is considerable difficulty in keeping the
temperature of the mixture
sufficiently low. When larger
quantities than the above ate
prepared, the apparatus de-
picted in Fig. 63 may he
employed.

The apparatus consists of
a rectangular battery jar, on
cither side of which is placed
a porous cell, containing the
cathode solution. The anode
consists of a platinum rotator,

and, in order to increase the anode surface, a sheet of platinum
is fixed at the bottom of the vessel, as shown in the figure. Or
two sheets of platinum may be hung about i cm. from each side
of the cathode cells, and a glass stirrer can be employed. The
whole apparatus is placed in a vessel of cold water, to which ice
is added in order to maintain as low a temperature as possible.

CONDITIONS.

E.M.F iS to 15 volls.

As the sodium nitrite gets used up in the reaction, the E.M.F. is
inclined to rise. Therefore Lob recommends the employment of
sodium nitrate as the cathode solution ; the only drawback to this
is that, as the electrolysis proceeds, the anode solution gets acid
from the migration of the NO^, ions. This can be prevented by
occasional addition of small quantities of dilute causric soda.

In order to complete the reaction, about twice the theoretical
amount cff current should be passed.

If during the electrolysis frothing lakes place, it can be
prevented by adding a few cubic centimeters of dilute caustic soda.

276

When the electrolysis is carried out at a temperature of □
a considerable quantity of the colouring matter crystallises out,
which can be filtered off; it usually contains, however, smallA
amounts of ^. naphtbol, for this reason it is advisable to addl
sufficient water to dissolve all the orange II. and filter from tiift.l
unchanged jj. naphthol. Excess of alkali must not be ]
otherwise the (3. naphthol will also dissolve.

The colouring matter can be obtained from this solution by 1
evaporating to dryness on the water hath and extracting with I
alcohol. On evaporating off the alcohol the orange is obtained I
as a dark yellow powder. Or the colouring matter may be precipl-'l
tated in the form of its insoluble barium salt by the addition of fl
barium chloride. The barium salt fonns a yellow powdery '
precipitate, which can be filtered off and washed with water.
Again, the colouring matter may be salted out by addition of
excess of sodium chloride.

On a technical scale the colouring matter can be estimated by
making direct quantitative dyeing experiments with the anode
solution. Orange II. dyes wool and silk a brilliant yellow.

By using a. naphthol as coupling substance instead of |
p. naphthol, Orange I. or TropaoHn OOO No. II. is produced.

XLIII. Preparation of Dianisidine Blue.'

C,„H„OH
C,„H,OH

CH3O . CbH.N =

CH,0 . CbHsN =

24'4 gim. dianisidine, aS'S grm. ^. naphthol and tj'S grm, of 1
sodium nitrite .ire mixed with 350 c.c. water, and placed i
anode cell, and treated in exactly the same manner as that J
described in the preceding preparation, the C.D. and all the othCT I
particulars being similar.

During the electrolysis the dianisidine blue precipitates com- J
pletely out. It is purified by dissolving it in caustic alkali, '
e particulars o:

:lrolytic prepnrntio
e by Dr. L^b, to iv

y thanks s:

Oxidation of Organic Compounds,

I precipitating with dilute sulphuric or hydrochloric acici, and
washing with water.

The reaction may be expressed by the following equation, in
which the action of the NO^' anions is represented as producing
the diazo-compound upon acting upon the dianisidine {dimethoxy-
benzidine).

CH,0.C5H,.N =

1
CH,O.CH,.N =

N.OH + OH'
N.OH + OH'
ouples up with

CH.O.CsH,NH,+ NO;

I
CH,0.q,H,NH,+ NO;

The dia/odianisidine in presence of ^. naphthol
this, and forms the dianisidine blue.

CH,0 . C„H,. N = N . OH + C,„H;OH

I
CH,0 . C„H, . N = N . OH + C,„H;OH

CHjO . C„Ha . N = N . C,„H„OH

> I + 2H.jO

CHjO . C„Hs N = N . Ci„H„OH

A similar reaction applies in the case of the preparation of orange
II.

Other aiO-colouring matters can be prepared in a similar
manner.' I'or example, —

Ponceau 2. G, benzene-aM-z-naphthol-3 : 6 disulphonic acid.

C„H, - N = N

/SO,H(6)
- C„H,-S0,H{3)
^0H(2)

The anode bath in this case consists of lo parts by weight of
aniline, 327 parts of p. naphthol disulphonic acid (R. acid), and
9*1 parts of potassium nitrite.

SO,Na(a)

qh^-n = n-c,„h/

I ^NH.j{a)

Congo red.

I NH,(a)

C„H,-N = N -Q,Hs'

SO,H(a)

■i'.A',/'., 761,310, 1904.

278

Practical Eleclro-Chemistry.

This substance can be prepared by electrolysing, in tbe anode
compartment, lo parts of benzidine, 33 parts of the sodium sah
of naphtbionic acid (r, 4 Naphtylamine sulphonic acid), and
9'3 parts jjotassiuni nitrite. The bath being kept at a temperature
of 60' to 90°. During the electrolysis the bath should not be
allowed to become acid, therefore the cathode solution should
consist of 10-15 P^"^ ceni. caustic soda.

OXIDATION OF BENZENE DERIVATIVES.

Wlien toluene, the xylenes, or the mesitylcnes are oxidised
with platinum electrodes — to a less extent with peroxidised lead
electrodes — the methyl group, or one of the metliyl groups, is
oxidised to the aldehyde group. This oxidation to aldehyde,
i.e. the second ttage of oxidation, is unusual, most oxidising
agents carrying the oxidation a stage further to produce the
carboxyl group. The influence of the position of the methyl
groups to each other is also of interest, for whereas with toluene,
generally speaking, the yield of benzaldehyde is not more than
13 to 14 per cent., with ortho- and para-xylene between 30 and 35
per cent, of tbe corresponding mono^ldehydes can be obtained.
With meta-xylene, however, the yield is very poor, rarely exceeding
10 or 15 per cent., and it may often be less.

The influence of a negative group is also very strikmg; it is
a well-known fact that ordinary oxidising agents have very little
action upon the methyl group in the cresols, the negative hydroxyl
exerting a protective action. With electrolytic oxidation a similar
difficulty is met. The electrolytic oxidation of the nitrotoluenes
is also of interest when these substances are oxidised under similar
conditions to those which yield benzaldehyde or the toluene
aldehydes, only a very small quantity of the nitroaldehyde is pro-
duced, the bulk of the substance being unacted upon. Elbs ' and
Pierron ^ have found that when para- and ottlio-nitro toluene are
dissolved in acetic acid and subjected to electrolytic oxidation,
' Zdl.f. Elektrockem., 2, 511.
' Bidl. Soc. Chcm., 25, 853.

Oxidtition of Organic Compounds. 279

the chief product is the corresponding nitrobenzyl alcohol.
Pierron, ioc. tit., has further found that with in eta -nitro toluene the
aldehyde is produced.

XLIV. Preparation of Benzaldehyde.

For the preparation of benzaldehyde an apparatus with a
stirrer, similar to that employed for the preparation of canarine
(p. 272, Fig. 6z), should be used. When this apparatus is employed,
it is not necessary to use a diaphragm or porous cell to separate
the anode from the cathode, because the anodes are so much
larger than the cathode. Under these circumstances the cathodic
hydrogen exerts very little reducing action. The anode surface
should he from i to z square decimeters in area ; the cathode,
about 2 to 4 square centimeters.

Process. — Weigh out 50 grm. of toluene into the electro-
lysing cell, and add zoo c.c. of lo-per-cent. sulphuric acid and
350 to 300 c.c. of acetone. Stand the cell in a basin through
which cold water can be circulated, and connect up the electrodes.

CONIllTIONS.

CD 1 '5 to 2 amperes.

E.M.F S to 5 volts.

Temi) Not ibove 20°

The stirring must be sufficiently vigorous to keep the mixture
in a thorough emulsion. From the equation it is seen that

CsHj . CH3 4- 2O - CpHs . CHO + H,0

5 grm. of toluene requires the passage of about 58 ampere hours.
In order to make sure that the toluene is all oxidised, about 65
ampere hours of current should be passed, but a large excess of
current is not advisable.

When the electrolysis is finished, the mixture is transferred to
a flask, the excess of acid neutralised with sodium carbonate
(the solution must not be made strongly alkaline), and the
acetone distilled off. The residue is then steam-distilled, when

Practical EUctrcCkemistry.

the benzatdehyde and any unchanged toluene passes over, a coii-
considerable quantity of a resinous substance remaining behind
in the flask. In order to purify the benzaldehyde, and separate
il from unchanged toluene, the distillate is extracted with ether
and shaken up with sodium hydrogen sulphite. After allowing to
stand overnight, the bisulphite compound is filtered off, washed
with alcohol and ether, and placed in a flask, A little dilute
caustic soda solution is added, after which it is steam-distilled.
On extracting the distillate with ether, drying over calcium
chloride, and distilling off the ether, the benzaldehyde is obtained
in the pure condition. Yield, 7 to 8 grra.

'I'he ethereal solution obtained when the bisulphite compound
is filtered off, contains a small quantity of a neutral substance
which may either be benzyl alcohol or a condensation product of
partially oxidised toulene.

The oxidation of ortho- or para-xyiene gives very good results;
but owing to the expense of these substances, the oxidation of
toluene has been given. The method of procedure with the
xylenes is exactly the same as with toluene. 'J

LITERATURE. V

Renard, Compl. Rimliis, Bl, 175 ; Merzbacher and Smith, AfHif:
ChetH. So/:., 23, 723 ; K. Puis, C/ieni. Ziituni;, 25, 263 ; H. D. Law
and F. M. Perkin, Trans. Faraday Society, 1904, 31.

XLV. Preparation of Para=nitrobenzyl
Alcohol.

A porous cell is used as anode compartment, and in this is
placed an anode of sheet platinum or of platinum gauze. The
anode solution consists of So c.c. glacial acetic acid, 8 c.c. con-
centrated sulphuric acid, and 15 grm. of para-nitro toluene.

The porous cell is placed in a beaker and surrounded with
a cylindrical cathode of sheet lead, the electrolyte being sulphuric
acid, i'6 to i'7 sp. gr. The whole apparatus must stand in a
water bath, which is kept at boiling temperature during the
electrolysis.

Oxidation

of Organic

Compounds.

CONDITION

M.V. . .

It will be noticed that during thu electrolysis very little
hydrogen is evolved at the cathode, because it is mainly required
to reduce the strong sulphuric acid which forms the electrolyte,
and, as a consequence, sulphur separates out. Three times as
. much current must be passed into the mixture as is theoretically
required.

At the end of the operation the mixture is steam-distilled, hy
which means unchanged pa ra-nitro toluene is driven over : a small
portion of the p-nitrobeuzyl alcohol also passes over. The oily
content of the flask is now filtered, while still hot, through a wet
double filter paper; by this means the main portion of a resinous
material remains behind ; this is then twice washed with hoi
water and the washings added to the filtrate.

On cooling, crude p-nittobenzyl alcohol crystallises out in
long dirty yeUow needles ; these are filtered off, and the mother
liquor shaken out with ether. The ethereal solution contains a
mixture of p-nitrobenzyl alcohol and p-nitrobenzyl acetic esttr
(CHs . CO . OCH, . CaH.NO,). The ether is distilled off, and the
residue extracted with small quantities of alcohol. The alcoholic
extract contains only the p-nitrobenzyl alcohol.

The crystals and the product from the alcohol are then mixed
together and purified by boiling with water and animal charcoal ;
on filtration the pure product crystallises out. Yield, 35 to 40
per cent.

NO.J

NO-j
C0H4.; + O - QHj

CH, CH„.OH

Preparation of Some of the Reag-ents and
Materials.

Solution of Sodium Monosulphide, Na^S. — Dissolve
sufficient sodium hydroxide — purified from alcohol — in water, lo
form a solution of sp. gr. i'z4 to I'sfi. Saturate Che solution with
sulphuretted hydrogen. In spite of the sodium hydroxide being
purified, there is generally more or less precipitate produced ; filler
this off. Now evaporate the solution down in a porcelain basin
placed on a sand bath, until about one quarter of it has evaporated
away. The solution should be poured into bottles while still hot,
and the bottles closed with rubber stoppers. Glass stoppers areJ
liable to become fixed and immovable.

Ammonium Borate and Ammonia. — Dissolve 35 g
of ammonium borate in 700 c.c. of water — it may be necessary b
warm the mixture ; and when cool add 300 c.c, of ammoniui
hydrate, sp. gr. o'88. This solution is used in the analysis c
nickel and cobalt (pp. 95 and 9S).

Cobalt Ammonium Sulphate. — Dissolve equi-molecula
proportions of cobalt and of ammonium sulphate in separah)
quantities of hot water; the solutions should be made nearljiij
saturated. Mix the two solutions while still hot, and place ii
beaker surrounded with cold water. While ihe solution is cooling,!
it should be vigorously stirred with a glass rod. The cobal
double salt separates out in the form of a fine pink crystallii
powder. When quite cold, filter off", wash with a small quantity ol
cold water, and spread on a plate to dry. The salt so obtained 11
quite pure, and does not require further purification.

Other double salts can be prepared in a similar n

Preparation of Reagents, 283

Solution for Copper Coulommeter, and for Proof of
Faraday's Law.— Octtel recommends the following solution as
being the most satisfactory for the coulommeter.

150 Eti". crysialliscd copper sulphate.
50 „ sulphuric a/AA [codc.)
I SO II alcohol.

I litre distilled water.

COOCHs
Potassium Ethyl MalonatejCHj''

— Add i6o grm. diethyl malonate to 130 c.c. alcohol, and to
this solution add a concentrated alcoholic solution of 56 grra.
potassium hydroxide.' This is half the quantity of potassium
hydroxide necessary to hydrolyse the two ethyl groups

-COOQHi ,COOK

CH,-;; + KOH = CH./ + CHjOH

COOC2H, ^COOC~H;

The mixture becomes warm, and the potassium salt is precipi-
tated out, a semi-solid mass being obtained. Allow it to stand
for three or four hours, and then evaporate nearly to dryness on
the water bath, at the same time passing a rapid stream of carbonic
acid gas through the mass.

Now take up with just sufficient water to dissolve the solid
substance, and if any unchanged diethyl malonate separates out,
extract with a little ether, otherwise reduce again by evaporation
to about one-third of its bulk. This mixture may now without
further treatiiient be employed for electrolysis, in the preparation
of diethyl succinate (p. 231}.

CH, - COOQHs
Potassium Ethyl Succinate, |

CH, - COOK

— Treat 174 grm, diethyl succinate, dissolved in 150 c.c. alcohol,

the polassiuni hydroxide to contaJQ IC30 per cent,
correspoadinj^ly larger quantities must

284 Practical Electro-Chemistry.

with a concentrated alcoholic solution of 56 grm. potassium
hydroxide, exactly as described above in the preparation of
potassium ethyl malonate. The concentrated solution of potassium
ethyl succinate obtained at the end of the process may be
employed, without further treatment, to prepare diethyl adipic
acid (p. 231).

Acet-toluide, C«H/

CH,

\NH.CO.CH,

— Take 50 grm. of ortho-, para-, or meta-toluidine, and add to the
toluidine about twice the theoretical quantity of glacial acetic acid
to convert it into the acetyl compound

C6H,(CH3)NH2 + CH3. COOH

= C6H4(CH3)NH . CO . CH3 + HaO

The mixture is contained in a flask, to which is fitted a long tube to
act as a reflux condenser, placed on a sand bath, and heated to
gentle boiling for from twelve to fifteen hours. It is then, while
still hot, poured into cold water, and the more or less oily mixture
allowed to stand overnight. It will by this time have solidified to a
colourless or pinkish solid ; this is filtered off, and washed with
water until free from acetic acid. In order to further purify it, the
acet-toluide may be recrystallised from alcohol.

NOTE TO p. 104.

Further experiment shows that the remarks made on page 104, in which the
use of a gold electrode for the analysis of mercury is recommended, require to be
modified. The first few results obtained with a gold electrode gave very fair
results. Extended work, however, shows that the results obtained when this elec-
trode is used are almost invariably from i to 2 per cent, too high. It has not up
to the present been found possible to assign a reason for the abnormality, but the
subject is still under investigation.

On the other hand, it has been found that the mercury adheres to a well-
roughened (sand-blasted) flag-electrode, not in the form of globules, as is usually
the case with a basin electrode, but in the form of a homogeneous amalgam,
which may be washed with alcohol without in any way detracting from the
accuracy of the results. The electrode amalgamates better after it has been used
a few times. It is essential that it should be sand-blasted on the gauze as well as
on the rim.

Some Useful* Data.

When a current of i ampere intensity has passed through an
electrolyte for i hour, 3600 coulombs of electricity have passed
through the electrolyte.

A current of electricity of i ampere passing for 26*65 hours
(in round numbers 27 hours) is equivalent to 96,540 coulombs
or I faraday of electricity.

Twenty-seven ampere hours, i,e, a current of electricity of i
ampere of intensity passing for 27 hours, will liberate the
hydrogen equivalent of an element, e.g. 1 grm. of hydrogen, 8
grm. of oxygen, or 107 '9 grm. of silver.

I foot . . . .

= 30-47 cm.

I inch. . . .

= 2*54 cm.

I inch. . .

= 25*40 mm.

I metre . . .

= 39*37 inches.

I metre . . .

= 3-28 feet.

I lb. (avoirdupoi

is) = 7000 grains = 453*6 grm

I kilogram .

= 2*205 ^bs.

I ounce . . .

= 28-35 grm.

I gram . . .

= 15*43 grains.

I grain . . .

= 0*0648 grm.

I cubic foot of water at 62° F. (16*6° C.) weighs 62*24 lbs.
I cubic foot of water =6*24 gals.
I cwt. of water = i*8 cubic feet = ii'2 gals.
I ton of water = 35*9 cubic foot = 224 gals.
I gallon = 0*1604 cubic foot = 10 lbs. water at 62° F. = 4*536
litres.

286 Practical Electro- Chemist fy.

I fluid ounce = 28*38 c.c.

I cubic foot of air at o** C. and 760 mm. pressure, weighs

0*0807 lb.
I cubic foot of hydrogen at 0° C. and 760 mm. pressure, weighs

0-00559 lb.
I atmosphere pressure = i\*i lbs. per square inch = 2 116 lbs.

per square foot = 760 mm. of mercury = ro* dynes

per square centimeter (approximately).
A column of water 2*3 feet high corresponds to a pressure of

I lb. per square inch.
I foot-pound = 1*3562 X 10^ ergs.
I horse-power hour = 33000 X 60 foot-pounds.
I horse-power = 33000 foot-pounds per minute = 746 watts (see

P- 29).
I kilowatt = 1*36 horse-power (see p. 29).
I watt = I volt-ampere second (see p. 28).
I kilowatt = 1000 watt hours,
volts X amperes = watts.

TT = 3*1416.

. . . . = 0*3183.

TT^ = 9*8696.

The following formulae will be found useful in calculating
electrode surfaces : —

Area of a circle . . = ttt^; or, (diameter)' x 0*7854.

Volume of a cylinder . = irf^h.

Surface of a sphere . = 4 Trr^.

Volume of a sphere . = f ttH.
Circumference of a circle = diam. x tt or r X 2ir,

Diameter x o 88623 . = side of an equal square.

Diameter X 0*7071 . = side of an inscribed square.

Circumference X 0*3183 = diameter.

Useful Data. 287

Relation between Centigrade and Fahrenheit thermometric
scales : —

To find F." = f C + 32
To find C.° = (F - 3a) %
1 litre of hydrogen at o' C- and 760 mm. pressure, weighs
0-0896 grm. {o-o9 approx.) ; this weight is called the
crith.
The weight of i litre of any gas at N.T.P. is obtained by multi-
plying the density of the gas by the crith (0-0896 grm.).
1 12 litres of hydrogen at N.T.P. weigh i grm.

A gas expands 0-003665 {.^^-^ of its volume for every degree
through which it is heated.

The following formula is employed for calculating tlie volume
of gas:—

_ v^ _ p

'■"~ I + 0003665/ 760
where v^ is the volume at standard pressure, and v the volume of
gas measured at pressure/, or by employing fractions
_ VKpy. 373
"" 760 X {273 + ')

NOTE TO CURVE, FIG. 64 (NEXT PAGE),

Attenlion has been called in several places in this book to Uie importance of

knowing the electrode surface. The curve on the next page gives ii ready way of

finding both the area and the volume, and from the volume the weight of a wire

following examples illustrate the manner of using the curve.

I. To find the area of tlie Burface of a platinum wire 1-26 mm.

diameter and SO cm. long :-

Find the appro-timate position of the point laS on the left V(
this Irnce the inmginary horizontal Une throcgh the point 1-36 Uimi 11 iiiLciBcuia
Ihe "area" line, and through the point of intersection trace a vertical linetfown-
loards and read its value on the ^Am^iu-iian/'i/'iM. This is 0-395. This number
represents the area of Ihe surface of 1 cm. length of the wire iu aq, cru. -The total
area is ihorefore 0395 X 30 = 11*86 sq. cm.

IL To find the Tolume of the same wire :—

Find the approximate posiiion of the point 1-26 on the left vertical numbered
line. Through this point follow an imaginary horiiontal line until it intersects the
" volume " curve, and through the point of intersection trace a vertical lineu/warrfi
and read its value on Kix top hiriximlal Uni. This is 0-0125. This number is Ihe
volume of 1 cm. iMigth of the wire, and the total volume of the wire, therefore, is
0-0125 X 30 = 0-87fS cc.

The weisht of this qttanliiy of metal is found by multiplyin;; the volume by
Ihe sp. gr. ofthe metal. R.g.. if the wire is plalinum. Ihe sp. gr, of which is 2iSi
then Ihe weiglil of the wire is 0-3750 X 31-5 = 8-06 grm.

( 2

ig )

TABLE IX.

International Table of Atomic Weights. ■

0=16

H-i

D-.6

H-,

Ncodymiuui

. Nd 143-6

1425

Antimony . Sb IM'2

II9-3

39'o

Neon . .

. Ne zo-o

19-9

Argon. . . A 39'9

Nickel .

. Ni s8 7

5S-3

Arsenic . . Aa 7S'0

74-4

Nitr<^en .

. N 1404

13-93

Barium . , Ila 137'4

13C-4

Osmium .

. Os 191-0

iSg-6

BisIDUlh , . Hi 2oS'5

206-9

Vadium'

. o Te-o

Boron. . .1! ii-0

lo-g

. Pd 106-5

105-7

Bromine . . Br 79-96

79"36

Phosphorus

. p 310

3077

Cadmium . Cd li2'4

111-6

riatinum .

. Pt 1548

<93-3

Caesium . . Cs 133'0

132-0

Potassium

. K 39' 15

38-86

Calcium . . Ca 40'!

39-8

Prascody-

Pr 140-5

'39'4

Carbon . . C i2'o

:i-9i

CcriuQ. . . Ce 140-0

139-0

Kadium .

Ra 225-0

223-3

Chlorine . . CI 35-45

35-'8

Rhodium .

Rh 103-0

102-2

Chromiam . Cr 52'i

517

Rubidium

Rb 85-5

84-9

Coball . . Co 59-0

58-56

Ruthenium

Ru 101-7

100-9

Sm 150-3

149-2

(Niobium ).Cb[Nb]94'o

93-3

Scandium

sc U-i

43-8

Copper . . Cu 63'5

63- >

Seleninm .

Se 79'2

7S-6

Erbium . . E i66'o

1648

Silicon .

Si 28-4

28-2

Fluorine . . F 19-0

]8-9

Silver. .

Ag 107-93

107-12

155-0

Sodium .

Na 33-05

2Z-88

Gallium . . Ga 70-0

69-5

Strontium

Sr 87-6

86-94

Germanium . Ge 72-5

71-9

Sulphur .

S 32-06
Ta ig3-o

3>-83

Glncinum

Tantalum

181-6-'

[Beryllium) Gl[Be]9-l

9'03

Tellurium

Te 127 -6

126-6

Gold . . . Au 197-2

i9S"7

Terbium .

Tb i6o-o

158-8

HeliQin . . He 4-0

4-0

Thallium .

. Tl 204-1

202-6

Hydrogen . H 1008

. Th 232-5

114-1

Thulium .

. Tm 171-0

Iodine ... I 126-97

12601

Tin . .

Kn 119-0
. Ti 4S-r

Iridium . . Ir 193-0

■91 5

Titanium ,

47-7

Iron . . , Fe 5S'9

SS'S

Tungsten .

W 1840

182-6

Krypton . . K 8r8

81-2

Uranium .

u 238-5

236-7

Lanthanum . La 138-9

'37'9

Vanadium

V 5'-2

50-8

l.ead . . . Pb 2069

«>S"35

Xenon

X 118-0

127-0

Lithium . . Li 7-03

6-98

Ytterbium

¥b 173-0

171-7

Magnesium . Mg 14-36

24-18

Vtulum .

Yt '4-0

88-3

Manganese . Mn 55-0

54-6

Zinc . .

. Zn 65-4

64-9

Mercury . . Hg 200-0

1985

Zirconium

. Zr 90-6

89-9

95-3

1 ^1

290

Practical Electro-Chefnistry.

TABLE X.

Theoretical Percentage of the MetaHic
Elements in Some Metallic Compounds.

Compound.

Ammunio-stanni chloride
Ammoniuni aurichloride .
Ammonium mulylxlate
Ammonium platini chloride
Antimonious oxide . .
Antimony tctroxide . .
Antimonyl potassium tartrate (tartar
emetic)

Bismuth nitrate

Bismuth oxide

Cadmium sulphate

Cobalt ammonium sulphate . . .

Cobalt chloride

Cobalt potassium sulphate . . .

Cobalt sulphate

Copper chloride

Copper sulphate

Ferrous ammonium sulphate . . .

Ferrous sulphate

Iron alum (ammonium) ....

Iron alum (potassium)

Lead nitrate

Manganese chloride

Manganese sulphate

Mercuric chloride

Mercurous chloride

Molybdenum oxide (Molybdic acid)
Nickel ammonium sulphate . . .

Nickel chloride

Nickel sulphate

Nickel potassium sulphate . . .
Potassium auri chloride ....
Potassium permanganate
Potassium platini chloride . .

Silver nitrate

Stannous chloride

Uranium oxide

Zinc sulphate

Formula.

SnCl^, 2NII,C1 .

(NH,)AuCl„3n,0

(NIIJ,Mo,0,,.4H20

(NH,),PtCl,

Sb^O,

SbjO^

C4ll40,K(SbO),iII,0

Bi(N0,)„5H,0
Bi,0,

CdS04,4H,0
; sCdSO^, 8H,0
:(NH,)2S04,CoS04.6H,0

CoCI„6H,0
, K,S04,CoS04,6H,0

CoS04,7H,0

CuCl2,2H,0

CuS04,5HjO
(NlI,)jS04,FeS04,6H80

FeS04,7H,0
I NlI^Fe(S04)„i2H,0
; KFe(S0J„i2H,0
I Pb(NO,)2

' MnCl2,4H,0

MnSO^jyHjO
HgCl,
HgCl
M0O3
(N H j2S04,NiSO„6H20
I NiCJ2,6H20

i NiS04,7H20

K2S04,NiS04.6H20

j KAuCloSHgO

KMnO,

KgPtClg

AgNO,

SnCl2,2H,0

U3O8
ZnSO^, 7H0O

Percentage of
Metal.

32*36 Sn
47*98 An
54*36 Mo
43*92 Pt
71*34 Sb
78-84 Sb
36*16 Sb

4303
8669

39*94

4277
14*94

24*80

13*49
20'99

37*17

25*33
14*28

21*18

11*62

ii'ii

62*52

72*21

27*79

19*85

73*82

84*90

54*84
14-87
24*70
20*90

1343
45-65
37*77
39*93
63*51
41*84
83*72
22*78

Pb,

PbO,

Ag
Sn

U
Zn

Note. — The percentages are calculated taking O = 16.

THE USE OF LOGARITHMS.

Much of the arithmetical work required in quantitative chemistry
may be simplified by the use of logarithms. Those la common
use are calculated to the base io,so ihaXthe logtirilhm of a number
is ikepmver lo which lo is raised to cblain thai number.

For example, the logarithm of loo is 2. This means that
10'^ = 100. It is usually written log 100 = 2. In the same way
log 1000 = 3, but the logarithms of numbers between 100 and
1000 lie between 2 and 3^that is, t!iey are 3 plus a decimal
quantity; e.g. log 500 = 2*69897, because 500 = 10'™*'.

To find the Logarithm of a Decimal Quantity.

Therefore log o'os = ~'(i^'&^i, where 2 is a negative quantity and
o'GgSgy is positive. It is convenient to keep it in this form.

The appended tables give the decimal portion, or mantiaaa,
of the logarithm, and the integral portion, or characteristic, is
obtained by inspection.

For numbers greater than unity the characteristic of the
logarithm is one less than the number of figures in the integral
portion of the number for which tlie logarithm is required, t'or
example, to obtain log aa^S look in the tables for the mantissa
of log zaS, which is o"35793. The characteristic is i, therefore
log za'8 = 1-35793. Likewise log 2-28 = 035793.

For numbers less than unity the characteristic is obtained by
adding one to the number of noughts between the decimal point
and the Jirst significant figure, and it is negative, e^. log o-228 =
•■35793 and log o'oo228 = 3'3S793.

292

Practical Electro- Chemistry,

To obtain log 37-376.— First consider thi= number 37376.'
On p. 303 look for 373 in thu first column headed "Number,"
and its mantissa is given in ihe same horizontal row in the next
column, headed " o," and is 57171. The mantissa for 3737 is
given in the same horizontal row in the column headed "7,"
- and is 57252. The ne.vt mantissa in the same row is that
for 3738, and is 57264. For an increase of i in the fourth figure
of the number the increase in the mantissa is 12. The fifth figure
in the number represents tenths of a unit in the fourth place, so
the same number of tenths of the difference between the mantissfe
of the tirst four figures {3737), and of that number increased by
unity (3738), is added to the mantissa of the lower number (3737)-
These tenths are worked out in the column headed " Difference."
The mantissa for log 37376 is 57252 + 8'4 or 57260-4 and loj
37'376 = i'5726o4. In the same way log 0-0376 ~ 2-572604.

To obtain log 6 or log o-6 look in the tables for the mantissa
of log 600, and to obtain log 66, or log o-65, look in the tables
for the mantissa of log 660. The characteristics are obtained
by inspection according to rule,

log 6 = I
? 0-6 =

■77815

log 66= r8i9S4

■77815

log 6-6 = 0-81954

■77815

log o'o66 = 2'8i954

tissa
ined

uired^^

To multiply two or more numbers together, add the logl

rithms of the numbers, and the sura is the logarithm of the required
product. To divide a number by another, subtract the loga-
rithm of the divisor (or denominator of a fraction) from the loga-
rithm of the dividend (or numerator of a fraction), and the d
is the logarithm of the quotient. The following example
illustrate the method of procedure.

The Use of Logarithms. 293

= 0*755218 — r6oo32
= 1154898

15473 is the mantissa for 1428

15503 » » n 1429
30 is the difference for i

i6-8 „ „ „ 0-56

.*. 154898 is the mantissa for 142856
or correct to the fifth figure, 14286

As the characteristic is i the number of integral figures will be
two, and 1 '154898 is the logarithm of i4*286. The value of
the fraction is therefore 14*286.

Example 2. — In the analysis of a sample of lead nitrate
(p. 136) the following data were obtained.

Weight of basin electrode = 53*1814 grm.

„ + lead nitrate =54*2228 „
„ + deposit of PbOa = 53*9342 „

)) 9)

Find the percentage of lead in the lead nitrate.

Weight of lead nitrate = 1*0414 grm.
„ „ deposit of PbOg = 0*7528 „

238*9 grm. of Pb02 contain 206*9 g^m. of Pb.

0*7528 X 206*9
.*. the weight of lead in the deposit is V-i^-T^ — g"^'i ^ind

this was obtained from 1*0412 grm. of Pb (N03)2.

^ , , 100 X 0*7528 X 206*9
.-. the percentage of lead = f.— ^ ^ ^-^:^ - "

IPC X 0*7528 X 206 -9
log ro4i4 X 238-9
= log 100 + log 07528 + log 2o6*9 - log 10414 - log 238*9
= 2 + 1*87668 + 2-31576 — 0*017618 — 2-37822
= 4*19244 - 2*395838
= 1*796602

294 Practical Electro-chemistry.

79657 is the mantissa for 6260

79664 „ „ „ 6261
7 is the diflference for i
32 „ „ „ 4 (approx.)

.*. 796602 is the mantissa for 62604
and 1796602 is log 62*604

The percentage of lead is therefore 62*604.

Example 3. — In the preparation of azobenzene (p. 241)
according to the equation, 8 grm. of hydrogen will be required
to reduce twice the gram-molecular weight of nitrobenzene to
azobenzene. How many coulombs will be required to reduce
50 grm. of nitrobenzene ?

The gram-molecular weight of nitrobenzene is i23'o8 ;

/. 8 grm. of hydrogen reduce 2 X 123*08 grm. of nitro-
benzene, and 8 grm. of hydrogen will be liberated by

96540 X 8 coulombs (p. 7).

.*. the quantity of electricity required to reduce 2 X 123*08
grm. of nitrobenzene is 96540 x 8 coulombs; and 50 grm. of
nitrobenzene will require

96540 X 8 X 50 . . r J .

- - -.0 coulombs for reduction
2 X 123-08 ,^

^ 96540 X 8 X 50 96540 X 100 \

^^g 2 x"I^*o8 " = ^^^ 61^4 ' j

= log 96540 + log 100 - log 61-54 ^

= 4-98471 + 2 — I-78916

= 5'i9555

19535 is the mantissa for 1568

19562 „ „ „ 1569
27 is the difference for i
20 „ „ „ 0-74

.*. 19555 ^s the mantissa for 156874
and 5-9555 is log 156874

.*. the quantity of electricity required is 166874 coulombs.

The Use of Logarithms, 295

Example 4. — From a gas coulommeter 900 c.c. of a mixture
of hydrogen and oxygen at 21° C. and 742 mm. was evolved.
What quantity of electricity had passed through the coulommeter ?
(See p. 15).

First find the volume of the mixed gases at N.T.P.

900 X 273 X 742 ,^ „ ,

^0 = L^ —X \^ \1 (See p. 287.)
(273 + 21) X 760 ^ ^ * '

I ampere-hour, or 3600 coulombs, evolve 626*4 c.c. of the
mixed gases at N.T.P. (see p. 15) ;

.*. the above quantity z'o will be evolved

, 3600 900 X 273 X 742 , ,

by ^ i- X / ,— \ -- c coulombs.
^ 626-4 (273 + 21) X 760

All operations of addition and subtraction must be
performed before taking logarithms.

, 3600 X 900 X 273 X 742

Jo*' ,"

*^ 626*4 X 294 X 760

= log 3600 + log 900 + log 273 + log 742
— log 626*4 — log 294 — log 760

= 3*55630 + 2-95424 + 2-43616 + 2-87040

— 279685 — 2-46835 — 2-88o8i
= 11*81710 — 8-14601
= 3*67109

67108 is the mantissa for 4689
671 17 „ „ „ 4690

9 is the difference for i

I „ „ „ o-i (approx.).

67109 is the mantissa for 46891
.'. 3*67109 is log 4689-1

.'. the quantity of electricity that had passed through the
coulommeter was 4689*1 coulombs.

It is hoped that the above examples will be found sufficient
to explain the use of logarithms even to those who may never

296 Practical Electro-Chemistry,

have employed them before. For further information upon the
theory of the subject, students must study standard works upon
algebra or trigonometry.

The following logarithm tables have been carefully checked,
both against five-figure tables and seven-figure tables, and where
any discrepancies were found, the numbers have been recalculated,
I am greatly indebted to Mr. F. Hart, B.Sc, for kindly under-
taking this laborious work, and also for calculating the worked-out
examples on the preceding pages.

FIVE-FIGURE LOGARITHMS

Five-figure Logarithms.

(MK) U13 087 lat 173
i^'l 4TR h\% Slil mi
vm U0.1 M5 9tl8 isao I

1 284 326 U68 410 452

703 745 787 B2B 870

31)3 34li ilSO
9 732 775 817

1 JSr J99 3£9

B 578 ()2<) U<i2

8 119 ItiO 202 243 281

531 572 612 653 RiH
e38 U7B Oif 060 iOO

3 342 383 423 463 503

743 782 822 862 902

1 139 179 218 258 297

532 571 610 C5U 6ail
922 961 9!)9 ms 0?7

5 308 346 385 428 461

_690_729_7C7 805 843

3 07O 108 14a 183 221

44G 4!«3 521 558 595

S25 3«t;
735 778
141 IBl
943 588
941 981 Oai 060 100

a 4U7 440 190
B 816 857 898
1 1122 962 803

:B6 876
727 766
lie 154

633 670
004 041
372 408
73777:)
099 135
45S 493

415 454 493
805 844 883

19a aai 369

576 614 652
956 994 033
'333 371 408
707 744 781
078 115 151

9 314 350 388 422

6 672 707 743 778

i 026 061 096 132 167 202

a 877 412 447 482

814 8

1 726 760 795 830
7 "72 lOG 140 175

415 449 483 517

1 755 789 823 856
9 093 126 lliO 193

9 934 9118 003
a 278 312 346
5 fiU) (iG3 1587
4 958 iH)2 025
294 327 361

4 428 461 494 528
7 700 793 826 860
7 090 123 156 189

5 418 4fi0 483 510
(} 743 775 808 840

893 926 9
222 254 2

648 581 6

4 628 6

I 992 034

44 ■ 43

S-8 ; S'6

13-3

2b-4

.,-8

39-6 ! 38-7

16 137

435
732

17 026

3 066 098 130 162

4 380 418 460 481

2 704 736 767 799

8 019 OBI 082 114
1_333_364 395_426

3 644 675 706 737
2 953 983 014 MB 1

9 259 290 320 351

4 564 594 625 655

6 B60 89 7 927 957

7 167 m 227 256

5 405 495 624 554
2 7G1 791 820 850

056 085 114 143
346 377 406 435

4 226 258 200 322
3 546 577 609 640

862 89S 925 956

5 17S 20s 239 270

7 489 520 551 582

8 799 82'J 860 891
S 106 1ST 168 198

1 412 442 473 503
S 715 746 776 806
7 017 047 077 1 07

286 316 346 376 406
584 613 643 673 702
879 909 938 967 9!»7
173 202 231 260 281)
464 493 522 651 580

a6'6 25-9 ■ 2yx
30-4 : 29'6 I 28-8
K''i33'3' 3^'4

10- 1

14-0

ire

'7-'i

170

i!o-4

24 -n

2M-0

3i'5

30'6

Five figure Logarithms.

17 609 G38 667 696 725 '
138 026 95S 984 QIS i

18 184 213 241 270 298 ;
4G9 4dS 526 554 i)83 <
752 7B0 808 837 865 :

le 033 061 089 117 145
312 340 368 396 424
590 618 645 673 700

2 811 840 869
Odd 137 im

5 384 412 441

667 691! 724

1 949 97 7 005
1 229 257 285
9 507 53S 562

3 811 a

aO 140 167 194 2

B 976 003 030 058 085 113

548 575
817 844
085 112

8 775 801 827 854

1 037 063 089 115

2 298 324 350 376

602 629 656
871 898 925
139 165 193
405 431 458

032 958 985
194 220 246
453 479 505
712 737 763
891 917 943 968 994 019

S 608 634 660 6

34 055 080 105 130 155
J04 329 353 378 403
351 576 601 625 650
797 822 846 871 895
H2 066 091 lis 139
i85 310 334 358 382
)27 551 57fl 600 624
?68 792 816 840 864
107 031 055 079 102
i45 269 293 316 349
182 505 529 5 53 576
717 741 764 788 811
)51 975 998 OSl 0«F
184 207 231 254 277
116 439 462 485 508 .
346 669 692 715 738 '
175 898 921 944 967
103 126 149 171 194
130 8S3 375 398 421
iK 578 601 623 646
780 803 825 847 870
)03 026 048 070 092
i26 248 270 292 314 .
147 469 491 513 5:^5 .
iff? 688 710 732 754 '
i85 907 929 951 973

2'8

I4-0

IQb

2s:?_

Five-figure Le^tritkms

{

No.
im

21)1

l->B, 1 :i :i 4

5 7 8 9

Differenoes.

30 103 125 146 16H 190

320 i»l 303 3M 41)0
535 aST 578 <H)0 621
750 771 702 HU 835

wa !)H4 (mm 0^

211 23:t 255 270 298
428 440 471 492 514
642 664 6I«5 707 728
850 878 899 920 942

oes 091 m m jm

3
4

S
9

14
i6
i8

3
4

1
I

2US
206

208
li09
210
211
212
213
2U

81 176 197 218 239 2tiO
387 408 429 450 471
597 618 039 660 681
806 827 848 869 890

32 015 035 056 077 098

281 302 323 345 366

492 513 534 555 576
702 723 744 705 785
911 931 952 973 994
118 139 160 181 201

222 243 mi 234 305
428 449 469 490 610
634 654 673 695 715
8:« 858 879 899 919
33 041 002 082 102 122

325 346 366 S87 403
531 552 572 593 613
73G 766 777 797 818
WO 960 980 OOi Oai
148 163 183 203 224

i
I

8-0
I8-0

215
216
217
2ItJ

2in

220'
221
222
223
224
226
226
227
228
22S

244 264 284 804 325
445 465 186 506 526

646 666 686 706 726

846 860 885 905 925

34 014 004 0S4 104 124

345 365 385 405 425
546 566 586 606 626
746 766 786 806 826
945 9G5 985 005 OSe
143 163 183 203 223

242 262 282 3U1 321
4:19 459 479 #98 518
035 655 674 094 713
830 850 809 889 908
35 025 044 064 083 102
218 238 257 27<i 205
411 430 449 408 488
003 622 041 660 679
793 813 832 851 870
984 QQS 021 040 059

341 361 380 400 420
537 557 577 596 016
733 753 772 792 811
928 947 967 986 006
122 141 160 180 199
315 334 353 372 392
507 526 645 501 583
698 717 736 755 771
889 908 927 046 966
078 097 116 IBB 1S4

1
I

9-5
11-4
■3-3
rS-2
«7->

230
231
232
233
234
235
236
237
233
23il
240
241
242
243
244

Se 173 192 211 229 248
361 380 399 418 486
549 568 580 005 624
736 754 773 791 810
922 940 959 977 991!

37 107 125 144 1U2 181
291 310 328 346 365
475 493 5U 530 548
658 670 094 712 731
840 858 876 894 912

267 286 305 324 342
455 171 493 511 530
612 001 080 698 717
829 847 866 881 903
014 033 051 mo 088
199 218 236 251 373
383 401-420 438 457
566 585 603 021 630
719 767 785 803 822
931 919 967 985 003

38 021 030 057 075 093
202 220 238 250 274
382 399 417 435 453
561 578 596 G14 032
739 7;i7 775 792 810

112 130 148 106 184
292 310 328 346 364
171 489 507 525 513
650 668 686 703 721
828 810 863 881 899

3-5
S"4

9-0
10-8

12-6

245
2-lG
2+7
248

917 934 952 970 987
39 094 111 129 146 164
270 287 305 322 340
445 463 480 498 516
020 637 655 072 690

006 033 MI OSS 076
182 199 217 235 252
358 375 893 410 428
533 660 568 585 002
707 724 712 759 777

Five-figure Logarithms. 30I

■

No.

r-og. 1 2 3 1

6 C 7 S 9

Dlff<!TeUCl«.

250
251
252
253
25+

30 7IH Mil W29 M-16 HOB
!N.7 985 002 019 037

40 Uf) 157 175 192 209
^12 329 31(J 3G1 381
483 500 518 585 S52

881 898 915 933 950
(mori 088 106 im

226 243 261 278 295
398 115 432 449 406
569 58G G03 620 037

1
8

3-6
7 -2
lo'S

12-6
lt,-2

■255
25e
257
258
250
■iGO^
2G1
2G2

2r^
261

651 671 688 705 722
824 841 858 876 892
993 010 027 Oti 061
41 16a 179 196 212 229
3:111 :«7 363 380 397

739 756 773 790 807
909 92G 943 959 976
ore 09B 111 128 146
246 263 280 296 313
114 430 447 464 181

497 511 531 517 56*
604 G81 697 714 731
83(1 847 863 880 896
99(1 013 039 WJ 062
42 160 177 193 210 226

581 597 614 631 647
747 764 780 797 814
913 929 916 963 979
078 095 111 m 14i
243 259 275 292 308

265
266
267
2ti8
2W

325 311 357 374 390
488 504 521 537 553
(Si 667 681 700 716
813 830 816 802 878
im 9S1 008 034 040

400 423 439 456 472
570 586 602 619 635
732 719 765 781 797
894 911 927 913 969
OBS 072 088 104 120

\
I

'7
3"4

6-8

IS "3

270
271
272
273
274

43 136 152 169 185 201
297 313 329 315 361
457 173 189 505 B21
G16 632 618 661 680
775 791 807 823 838

217 233 219 265 281
377 393 409 425 111
537 553 569 584 000
696 712 727 713 759

854 870 886 902 917

275
276

277
278
279
2'80
281
282
283
281

933 919 905 981 996
44 091 107 122 138 151
248 261 279 295 311
404 420 436 451 167
560 576 592 607 628
716 731 717 762 778
871 886 902 917 »32
46 025 010 056 071 086
179 194 209 225 210
332 347 862 378 393

012 038 044 069 076

170 185 201 217 232
326 342 358 373 389
483 198 511 52B 545
638 651 660 685 700
793 809 824 840 855
048 963 979 994 010
102 117 133 118 163
255 271 288 301 317
108 423 439 151 469

3
4

6-4
8o
9;6

iiS

144

285

286
287

181 500 515 530 545
637 652 667 682 697
788 803 818 831 819
939 951 969 981 000
46 1)90 1U5 120 135 150

561 576 591 606 621
712 TC8 743 758 773
861 879 894 909 921
015 030 046 060 075
105 180 195 210 225

290
291
292
293
291

21(1 255 270 285 300
389 404 419 434 449
538 563 568 583 598
687 702 716 731 746
835 850 864 879 894

315 330 814 359 374
464 479 494 509 523
613 627 642 657 672
761 776 790 805 820
909 923 938 953 9H7

1-5

6-0

io'5

295

296
297
298
299

982 997 013 026 041
47 129 144 159 173 188
276 290 305 319 334
122 436 451 465 180
567 532 506 6U 625

mS 070 085 100 114
202 217 232 210 261
319 363 378 392 407
491 509 524 538 553
610 654 669 683 698

■50*-

No.

Log. 12 3 4

5 6 7 8 S

Differenoe.

SOU
301
302
803

304

47 712 727 741 75G 770

857 871 885 BOO SU

48 001 015 029 044 058
144 15U 173 187 202
•iH7 3U2 310 33U 344

781 799 813 828 812
929 943 958 972 986
073 087 101 116 130
210 230 244 259 273
359 373 387 101 116

305
30C
307

30H
3I>0
^IIJ

aia

313

430 441 458 473 487
572 586 601 615 629
714 728 742 756 770
855 869 883 897 911
<MG 010 024 OSa 0S2

501 515 530 544 558
643 657 671 686 700
785 799 813 827 811
026 940 954 968 982

oee oaooM loa isa

200 220 231 218 262

310 360 371 388 102
185 499 513 527 541
621 638 651 665 679

762 776 790 803 817

48 130 I5U 164 178 192
27(i 290 304 31» 332
415 429 443 457 471
554 508 582 59B 610
693 707 721 734 748

i
I
1

316
316

ai7

318
H19
320
3U

323
324
3-Z5
326
327

a-is

329

831 845 859 872 880
969 982 996 010 024

50 106 120 133 147 161
243 256 270 284 297
3T9 393 406 42U 433
515"529 642 556 669'
650 664 678 691 705
786 799 813 826 839
920 934 947 961 971

51 054 0G8 081 095 108

900 914 927 911 955
037 (St OSS 079 092
171 188 202 215 229
311 325 338 852 365
417 161 174 488 501

583 696 610 623 637
718 732 716 756 778
853 866 880 898 907
087 001 014 038 041
121 135 148 162 175

188 202 215 228 242
322 335 348 362 375
455 408 481 195 508
587 601 OH 627 040
720 733 746 759 773

256 268 282 295 308
388 402 415 428 441
521 534 548 501 574
654 667 080 693 706
7B6 799 812 825 838

330
331
332
333
334
335

337
33S
339

851 805 878 891 904

983 mioos ozaoss

6S 114 127 140 153 166
244 257 270 284 297
375 388 401 411 427

917 930 943 957 970
043 061 075 038 101
179 192 205 218 231
310 323 336 349 362
440 153 466 479 492

7
8

3-9

10-4
117 1

504 517 530 513 556
634 647 660 673 686
763 776 789 802 815
892 905 917 930 013
53 020 033 046 058 071

569 582 595 608 B21
699 711 724 737 750
827 840 853 866 879
056 969 982 994 007
084 097 110 122 135

3-10
341
342
343
344
345
346
347
348
349

148 161 173 186 199
275 288 301 314 326
103 415 428 441 453
529 542 555 567 580
056 668 081 694 706

212 224 237 250 263
339 352 364 377 390
466 479 491 504 517
593 605 618 631 643
719 732 741 757 769

782 794 807 820 832
908 920 933 915 958
54 033 045 058 070 OKI
158 170 183 195 208
283 295 307 320 332

816 857 870 882 895
970 983 995 008 OX
095 108 120 133 145
220 233 245 258 270
345 357 370 382 394

■

Ftve-figure Logarithms. 303

No,

i^.g, 1 '2 3 4

5 6 7 8 9

Difforoncos.

350
351
352
353
351
355
35lt
357

Bse

S&9

54 407 119 432 141 15G
531 543 555 5i;8 580
G54 667 679 691 704
777 791) 802 811 827
900 913 925 937 919

469 181 191 506 518
593 605 617 630 642
716 728 741 753 765
839 851 864 876 888
962 974 986 998 Oil

6B 023 035 047 OGO 072
145 157 169 182 194
267 279 291 303 315
388 400 113 425 137
509 522 534 546 558

084 096 108 121 133
206 218 230 242 255
328 3-10 852 364 376
449 461 473 485 197
570 582 594 606 618

1
I

3-9

7'8
9'
10-4
117

360
B61
362

363
3i>4

630 642 6S4 666 678
751 763 775 787 799
871 883 895 907 919
991 QOS 015 027 038
56 110 122 134 146 158

691 703 715 727 739
811 823 835 847 859
931 913 955 007 979
050 063 074 088 098
170 182 194 205 217
289 30i 312^324 336
107 119 431 443 455
526 538 549 561 573
644 656 667 679 691
761 773 785 797 808

365
360
367
3B8
3GB

229 241 253 265 277
346 360 372 384 396
467 478 490 502 511
585 597 60S 620 632
703 711 726 738 750

370
371
372
373
37*

820 832 844 855 8(i7
937 949 961 972 984
57 054 066 078 089 101
171 183 194 200 217
287 299 310 322 334

879 891 902 914 920
996 008 019 031 043
113 121 136 118 159
229 211 252 2ill 276
315 357 368 380 392

_ 9.

4-8
8-4

375
376
377
37S
379

403 115 426 138 149
519 530 542 553 565
634 646 057 669 680
749 761 772 784 795
861 876 887 898 910

461 473 184 196 507
576 588 600 611 623
692 703 715 726 738
807 818 830 841 852
921 933 944 955 967

380

381

3S3

978 990 001 013 034
68 092 104 115 127 138
206 218 229 210 252
320 331 343 354 365
133 144 456 467 478

03S <M7 058 070 081
119 161 172 184 195
263 271 286 297 309
377 388 399 410 422
490 501 512 524 535

386
386
887
388

3110
391

393
3M

546 557 569 580 591
659 670 681 692 704
771 782 794 805 816
883 801 906 917 928
995 006 017 008 040

602 614 625 636 647
715 726 737 749 760
827 838 850 861 872
939 950 061 973 984
051 062 073 084 095

4
5
6
7
8

4'<J

77
8'S
9-9

68 106 118 120 140 151
218 229 240 251 262
329 310 351 362 373
439 450 161 472 183
550 561 572 583 594

162 173 184 195 207
273 284 295 306 318
384 395 406 417 128
191 506 517 528 539
605 616 627 638 619

S9S
896
397
39S
399

660 671 682 693 704
770 780 791 802 813
879 890 901 912 923
988 999 010 021 033
60 097 108 119 130 141

715 726 737 748 759
824 835 846 857 868
934 945 956 966 977
043 054 065 076 086
152 163 173 184 195

No.

U,B. U 1 2 3 1

vta

aO 206 217 228 239 349

260 271 282 293 304

«ii

B14 325 33« 347 358

369 379 390 461 412

423 43B 444 455 4C6

477 487 498 500 520

*(13

530 541 552 M3 574

584 595 6(Hi 617 627

403

638 MS 060 6711 681

692 703 713 724 735

2-2

745 756 707 778 788

799 810 820 831 842

loe

853 863 874 885 895

906 917 927 938 949

3-3

407

9S9 970 981 Wtl OB

013 033 034 04S 05S

4oa

ai 0«W 077 087 (Hffi 109

119 130 140 151 162

5 '5

40a

410

172 18:{ 191 2(H 215

225 236 247 257 268

6-6

278 289 m> 310 321

331 342 352 363 374

411

381 395 4()n 41G 42G

437 448 458 469 479

t.-8

412
41»

49U 500 511 521 532
595 606 C16 Om 037

542 553 563 574 584

048 658 669 679 690

_9".9

4U
415

700 711 721 731 742

752 763 773 784 794

805 815 826 8:W 847

857 868 878 888 899

416

909 920 930 941 951

961 972 982 993 OOS

417

62 014 024 034 045 055

066 076 086 097 107

41S

lie 128 138 149 159

170 180 190 201 211

419

221 232 242 252 20^

273 284 294 304 315

420

325 335 348 356 3e«

377 387 397 408 418

421

428 439 449 459 469

480 490 500 511 521

422

531 642 552 562 572

583 593 603 613 G24

423

(;34 644 655 665 675

685 696 706 716 726

424

737 747 757 767 778

788 798 808 818 829

425

839 849 859 870 880

890 900 910 921 931

426

941 9Sl 961 972 982

992 008 Oia 083 033

427

eS 043 053 083 073 083

OM 104 114 124 134

428
429

144 155 165 175 185
246 256 266 276 286

195 205 215 225 23(1
296 306 317 327 337

90 1

IST

347 357 367 377 387

397 407 417 428 438

431

448 458 468 478 488

498 508 518 528 538

132

54S 558 568 579 589

599 609 619 629 639

433

649 659 669 679 689

699 709 719 729 739

434

749 759 769 779 789

799 809 819 829 839

849 859 869 879 889

899 909 919 929 939

436

949 959 969 979 988

998 008 018 OaS 058

0-9

437

64 048 058 068 078 088

098 108 118 128 137

I'S

438

147 157 167 177 187

197 207 217 227 237

439

246 256 2G6 276 286

296 306 316 326 335

3-6
4-5

440

346 355 365 375 885

395 404 414 424 434

441

444 454 464 473 483

493 503 518 523 532

442

542 552 562 572 582

591 601 611 621 631

443

G40 650 660 670 680

689 899 709 719 729

444

738 748 758 768 777

787 797 807 816 82G

9 „.

445

S36 646 856 865 875

885 896 904 914 924

44C

933 943 953 963 972

982 992 002 Oil 021

447

B6 031 040 050 060 070

079 089 099 108 118

448

128 137 147 157 167

176 18G 196 205 215

419

225 234 244 254 263

273 283 292 302 312

Five-figure Logarithms.

7 4*7 466 4fiH 475

3 543 552 562 571

9 639 648 658 667

5 734 744 753 763

901 SU 820 &
896 WM! 916 ff
992 001 Oil a

ee 087 09G 106 1
ISl 191 200 2
276 285 295
370 380 389
464 474 483
558 567 577 5
652 661 071 6
745 755 704 7
839 848 857 »
932 941 950 S

67 025 034 043
117 127 136 1
210 219 228 2
302 311 321 3
394 403 413
486 495 504
578 587 596

422 431
514 523
605 614

761 770 779 7
852 861 870 8
943 952 061 9

i 034 043 052
124 133 142 1
215 224 233 2
305 314 323 3
395 404 413 4
485 494 502 5
574 583 592 6
664 G73 681 G
753 762 771 7
842 851 S6D 8
931 940 949 9

i 020 028 037
loe 117 126 1
197 205 214 2
285 294 302 3

3 487 496
6 574 583
3 062 071

485 499 504
581 591 6
677 686 606
772 782 702

304 314

398 408
492 502

9 068068 or?
3 153 162 172
8 247 257 2 66
2 342 351 3
7 436 445 455
I 630 539 549

i 596 605 814 ii24 633 642
699 708 717 727 736
792 801 811 820 829
885 894 D04 913 922
978 9S7 9
071 080
104 173 1
256 265 2
348 357 3
440 449 4
532 541 S

624 633 042 661 660

6 916 925 934

7 006 OlS 0.

8 097 106 1

8 187 196 205

9 278 287 296
» 368 377 386
9 458 467 470
8 547 556 565
8 637 646 6

7 726 735 744

8 966 97 5 984 9

055 064 073

5 144 152 161

3 232 241 249

170 179 1

258 267 270

346 355 364

4S4 443 452

2 601 609 618 627 '

679 688
767 775
854 862

697 705 714 i
784 793 801 I
871 880888

306

Five-figure Logarithms.

No.
iini

302

r)03
rm

Log. 12 3 4

5 6 7 8 S

—

69 K<)7 90c 014 fril 932
984 'J92 001 010 018

70 1170 079 088 096 105
157 165 174 183 191
243 252 260 269 278

940 949 958 966 97S
Oil!' 036 044 063 Oea
114 122 131 140 148
200 209 217 226 234
286 295 S03 313 3S1

50s

506
507
508
509
510
511
512
513
51i
515
Sli!
517
518
519_
520
521
522
523
524

329 388 346 35S 304
415 424 432 441 449

501 509 518 526 535
586 595 603 612 621

672 680 889 697 706

372 381 389 »98 406
458 467 475 484 492 '
544 552 561 569 S7S
629 638 646 655 663

714 723 731 740 748

757 766 774 783 701
842 851 859 868 876
927 983 944 952 961
71 012 020 029 037 046
096 105 113 122 130
181 m\'M 206 214
265 273 282 290 209
349 357 3Wi 374 383
433 441 450 458 466
517 525 533 542 550
(MH) 609117 025 634
084 092 7(K) 70!i 717
767 775 784 792 800
850 858 867 875 883
933 941 950 958 966

800 808 817 825 834
885 893 902 910 919
969 978 986 995 003
054 062 071 079 088
139 147 155 164 172
223 231 240 248 257
307 315 324 332 341
391 309 408 416 425
475 483 492 500 508
559 567 575 584 592
642 650 659 067 676
725 734 742 750 759
809 817 825 834 842
863 900 908 917 925
975 98:) 991 999 »U

7
S
9

■

625
5Z6
827
528
529

79 016 024 032 041 040
09Q 107 115 123 132
181 189 198 206 214
203 272 280 288 290
346 354 362 370 878

057 066 074 082 090
140 148 156 185 173
222 230 239 247 255
304 313 321 329 837
387 395 403 411 419

530
531
532
538
531
535
536
537
538
539

428 436 444 452 460
509 518 526 334 542
591 599 607 616 624
673 681 689 697 705

754 762 770 779 7S7

469 477 485 493 501
550 558 567 575 583
632 640 648 656 665
713 722 730 7BS 746
795 803 811 819 827

3
4

i
I

835 843 852 860 868
916 925 933 941 949
997 006 014 022 030
78 078 086 094 102 111
159 167 175 183 191

870 884 892 900 908
957 965 973 981 989
(138 046 054 062 070
119 127 135 143 151
199 207 215 223 231

540
541
542
543
544

239 247 255 263 272
320 828 336 344 352
400 408 416 424 432
480 488 49l> 504 512
560 5I>8 576 584 592

280 288 296 B04 312
860 368 376 384 S92
441) 448 456 464 472
520 32S 536 544 552
600 608 616 624 632

545

546
547
548
549

640 648 066 664 672
719 727 737 743 751
799 807 815 823 830
878 886 894 902 910
957 965 973 981 989

679 687 695 703 711
759 767 775 783 791
838 846 854 862 870
918 926 933 941 949
997 005 013 020 03fl

-i

Five-figure Logarithms. %o',

■

No.

Log. 1 2 3 *

5 6 7 8 9; Differenoes,

550
551
552
553

554

74 036 044 052 OfiO 068
115 123 131 139 147
194 20a 210 217 225
273 280 28S 296 304
351 359 367 374 382

076 084 092 099 107
155 162 170 178 186
233 241 249 257 205
312 320 327 335 343
390 398 406 414 421

555
556
557
558
559

429 437 445 453 461
507 515 523 581 539
586 593 601 609 617
663 671 679 687 695
741 749 757 764 772

408 476 484 492 500
547 564 502 570 578
624 032 040 648 65G
702 710 718 72S 733
780 788 796 803 811

560
561

562

5<U
505

507
568
569

819 827 834 842 850
896 904 912 920 927
974 981 989 997 «M
76 051 059 066 074 082
123 136 143 151 159

858 865 873 881 889
935 913 950 958 966
01% 030 028 035 043
089 097 105 113 120
166 174 182 189 197

t
6
7
8
9

8
6

K
6

■205 213 220 228 236
282 289 297 305 312
358 366 374 381 389
435 442 450 458 465
511 519 52G 534 542

243 251 259 266 274
320 328 B35 343 351

397 404 412 420 427
473 481 *S8 496 504
549 557 565 572 580

570
571
572
673
574
575
576
577
578
579
5H0
581
5S2
583
584

587 595 603 610 618
664 671 079 6B6 694
740 747 755 762 770
815 823 831 838 84G
891 899 906 914 921

626 033 Oil 648 656
702 709 717 724 732
778 785 793 800 808
853 361 369 S76 884
929 937 941 952 959

967 974 982 989 997
76 042 050 057 0C5 072
lis 125 133 140 148
193 200 208 215 223
268 275 283 290 298

005 oia 000 oar osb

080 087 095 103 110
155 163 170 178 185
230 238 245 253 200
305 313 320 828 335

343 350 358 365 373
418 425 433 440 447
492 500 507 515 522
567 574 582 589 597
641 C49 656 664 671

380 388 3£I5 403 410
455 462 470 477 485
530 537 544 552 559
604 612 619 020 034
678 6a6 693 701 708

4
I
I
9

07
I '4
z-8
3;5

585
586
587
588
589

718 723 730 738 745
790 797 805 812 819
864 871 879 886 893
938 045 952 960 %^
77 012 019 026 034 041

753 760 768 775 782
827 834 842 849 856
901 908 916 923 930
975 982 989 097 OM
048 050 003 070 078

590
^1
592
593

085 093 100 107 115
159 166 173 181 188
232 240 247 254 262
305 313 320 327 335
379 386 393 401 408

122 129 137 144 151
195 203 210 217 225
269 270 283 291 298
342 349 357 364 371
415 422 430 437 444

595
596
597
598

599

452 459 406 474 481
525 532 539 546 554
597 605 012 019 627
670 677 685 692 699
743 750 757 764 772

488 495 503 510 617
561 568 576 583 590
634 641 648 056 663
706 714 721 728 735
779 786 793 801 808

Five-figure Logarithms.

No.

Log. 12 3 4

5 6 7 8 9

DifFerencBft

600

815 822 S30 837 844

851 859 866 873 S80

601

K87 895 902 90H 916

924 931 938 915 952

602

960 967 974 'JSl 988

996 OOS 010 017 035

603

7e 032 039 046 UA3 061

068 075 082 089 096

601

104 111 118 125 132

140 117 154 161 168

60B

176 183 190 197 204

211 219 226 283 210

606

247 254 262 269 270

283 290 297 305 312

607

319 326 333 340 317

355 362 369 376 383

608

390 897 405 412 119

426 133 440 447 455

609

463 469 476 4^ 490

497 504 512 519 526

Gilt

533 540 547 564 661

569 676 583 590 597

611

G04 611 618 625 633

640 647 654 661 668

612

675 682 689 698 704

711 718 725 732 739

'■4

613

716 758 760 767 774

781 789 796 803 810

2-1
2-8

3 5

614

817 824 881 838 815

852 859 866 873 8S0

615

883 895 902 009 916

923 930 937 914 951

61Q

958 965 072 979 986

993 000 007 Oii 021

617

7B 020 036 043 U60 057

064 071 078 085 092

618

099 106 113 120 127

131 111 148 155 162

619

169 176 183 190 197

204 211 218 225 232

620

239 246 253 260 267

274 281 288 295 302

021

309 316 323 330 337

344 331 358 365 372

379 386 303 400 407

414 421 428 435 442

623

449 456 463 470 477

181 191 498 505 511

624

513 525 532 539 546

553 560 567 571 681

G25

588 595 602 609 616

623 630 637 644 650

657 664 671 678 685

692 699 706 713 720

627

727 781 741 748 751

761 768 775 782 789

caa

796 803 810 817 824

831 837 844 851 858

865 872 879 886 893

900 906 913 920 927

631

934 941 948 955 962
80 003 010 017 024 030

969 975 9S2 989 906
037 014 051 058 065

0-6

C32

072 079 085 092 099

106 113 120 127 134

110 117 154 161 168

175 182 188 195 202

1-3

634

209 216 223 229 236

243 250 257 261 271

4
1

2'4

3 '6

635

277 284 291 298 305

312 318 325 332 339

346 353 359 366 373

380 387 393 400 107

637

114 421 428 431 441

448 455 462 168 475

638

182 489 496 502 509

516 523 530 536 513

4-8

639

550 557 S64 570 577

584 591 598 604 611

G40

618 625 632 638 645

652 659 665 672 679

641

686 693 699 706 713

720 726 7a! 740 717

642

753 760 767 774 781

787 791 801 808 811

643

821 823 835 S41 848

855 862 868 875 882

644

889 895 902 909 916

922 929 936 W2 919

645

956 963 969 976 983

990 996 0C8 OJO 017

646

81 023 030 (»37 043 050

057 064 070 077 084

C17

090 097 104 m 117

124 131 137 144 151

G18

157 164 171 178 184

191 198 204 211 218

224 2:^l 238 245 251

2.58 20.-5 271 278 285

Five-figitre Logarithms. 309

No.

L(«. u 1 2 3 4

5 6 7 8 9

DilTurouuuB.

(150
651

G53

654

81 291 298 805 3U 31B
358 365 371 378 385
425 431 438 445 451
491 498 505 511 518
558 S64 571 578 584

325 331 338 345 351
391 398 405 411 418
458 465 471 478 485
525 531 538 544 551
591 598 604 611 617

655
656
657
658
6R9

C24 631 637 644 631
690 697 704 710 717
757 763 770 776 783
823 829 836 842 849
889 895 902 908 915

657 S64 671 677 684
728 730 737 743 750
700 796 803 809 816
856 862 869 875 882
921 928 935 941 948

ti(!(l
Hill

Utii

954 961 9G8 974 981
83 020 027 033 040 OIG
086 092 099 105 112
151 168 1H4 171 178
217 223 230 230 243

987 994 000 007 014
053 060 066 073 079
119 12S 132 138 145
184 191 197 204 210
249 256 253 269 276

3
4
S
6
7

0-7

2-8
3'5

6G6
667

ces

G69

282 289 295 302 308
347 354 360 307 373
413 419 426 432 439
478 484 491 497 504
543 549 556 562 569

315 321 828 334 341
880 387 393 400 406
445 452 458 465 471
510 517 523 530 636
576 682 588 696 601

670
671
672
673
674
675
676
677
678
679
680"
681
6li2
683
68i

607 614 620 627 633
672 679 685 692 698
737 743 750 756 763
802 808 814 821 827
806 872 879 885 892

640 646 653 659 666
705 711 718 724 730
769 776 782 789 795
83* 840 847 853 860
898 906 911 918 924

930 937 943 950 956
995 mi OCe 014 030
83 059 06S 072 078 085
123 129 136 142 149
187 193 200 206 213

963 9G9 975 982 988
OX 033 040 046 052
091 097 104 110 117
155 161 168 17* 181
219 225 232 238 244

251 257 264 270 276
315 321 327 334 340
378 386 391 398 404
442 448 455 461 467
506 512 518 525 531

283 289 296 302 308
347 353 359 366 372
410 417 423 429 436
474 480 487 493 499
637 544 650 556 563

I
9

4
6

UR5
6H6
087
688

569 575 582 588 594
632 639 6-45 651 658
696 702 708 715 721
759 765 771 778 784
822 828 836 641 847

601 607 613 620 626
664 670 677 683 G89
727 734 740 746 753
790 797 803 809 816
853 860 866 872 879

690
691
6i»li

m-i

694
1^
696
6B7
698
699

885 891 897 904 910
948 954 960 967 973
84 Oil 017 023 029 036
073 080 086 092 098
136 142 148 155 161

916 923 929 935 942
979 985 992 998 0(M
043 048 055 001 087
105 111 117 123 130
167 173 180 186 192

198 205 211 217 223
261 267 273 280 286
323 330 336 342 348
386 3D2 398 404 410
448 454 460 466 473

230 23G 242 248 255
292 298 30S 311 317
354 361 367 373 379
417 423 429 435 441
479 485 491 497 504

Five-Jigttre Logarithms.

N.>.

I>T(. 1 2 y 4

5 6 7 8 9

1 DiffereDoet.

71>ci
701
702
703
704

84 510 516 822 528 535

572 578 SM 590 697
IBM 640 ft»i (152 058
«9« 702 708 714 720

757 7ia 770 77(! 782

Ml 547 553 558 566
6113 609 613 621 628

66S 671 677 6BS 889
726 733 730 745 761

788 794 800 807 813

705
70(i
707

708
70it
710

712
713

714

8IU 825 831 837 844
880 887 8lfS 8!>9 1N)5
942 948 1)54 INiO 9t;7
86 WXA OO!) Olli (J22 028
IH15 071 077 08:4 089

850 856 862 868 874
911 917 924 930 936
973 979 1*86 991 997
034 040 046 052 058
095 101 107 114 120

12G 132 138 144 I.W
187 193 l&B 205 211
248 254 200 2(1H 272
309 315 821 327 333
370 37C 382 388 SM

156 163 169 175 181
217 224 230 236 242
278 285 291 297 303
839 345 352 358 364
400 406 412 418 425

0-6
I -a
i-S
2-4

S-4

715

718
719

431 437 44H 449 455

491 497 503 509 5IR
652 558 51)4 570 67R
012 618 625 ti:il o:t7
{.73 B79 685 ISUI K!17

461 467 47H 479 486
522 528 e;ii 640 646
582 588 694 600 606
64S 649 055 661 667
703 709 715 721 727

720
7-11
722
7^3
724

733 739 743 751 757
794 800 SlHi 812 818
854 860 866 872 878
E>14 920 926 082 I>38
974 980 B86 992 998

763 709 775 781 787
824 830 836 842 848
884 890 89(5 902 908
944 950 966 9(!2 968

OM 010 016 (m oas

725
72G
727
728
729
730
731
732
733
734
735
736
737
738
739

7*0
741
742
743
744
745
74(;
747
718
749

86 (KM 04U 046 052 058
UH4 100 106 112 118
153 159 165 171 177
213 219 225 231 237
273 279 28fl 291 297
332 338 344 360 356
392 398 404 410 416
451 157 463 409 475
510 flic 522 528 534
570 570 681 687 593

064 070 076 082 088
124 130 136 141 147
ISa 189 195 201 207
243 249 255 261 267
803 308 314 820 326
362 368 374 380 386
421 427 433 439 445
481 487 493 499 604
540 546 552 558 664
599 605 611 617 623

3
4

1
I

2-5
3-0

3-5

4-0

lay 035 641 646 652
68S (i94 700 705 711
747 753 759 764 770
806 812 817 823 829
864 870 876 882 888
923 929 935 941 947
982 988 994 1«19 (W5
87 040 046 1)52 058 064
099 106 111 116 122
167 163 169 175 181
216 221 227 23:J 239
274 280 286 291 297
332 338 344 340 355
390 B96 102 408 413
448 454 460 466 471

658 604 670 676 682
717 723 729 785 741
776 782 788 704 800
835 841 847 853 859
894 900 906 911 917
953 958 9(14 970 970
Oil 017 033 039 035
070 075 ONI 087 093
128 134 140 146 151
186 192 198 204 210
246 251 256 262 2(58
308 309 315 320 32(i
301 307 373 37it SS4
419 425 431 437 442
477 483 480 495 500

Five-figure Logarithms.

No.
75U

Lug- 12 3 1

5 U 7 8 9

Diff^!^c!llC^^B.

87 506 S12 H18 923 529

535 541 547 652 558

751

564 570 576 681 587

593 599 604 610 616

752

622 628 K13 639 H45

651 656 662 668 671

75H

679 685 691 697 703

708 714 720 726 731

754

737 743 749 754 760

706 772 777 783 780

755

795 800 806 812 818

823 829 835 841 846

756

852 858 864 869 875

881 887 892 898 904

757

910 915 921 927 933

938 944 950 953 961

758

967 973 978 98* 990

996 OOi 007 OIB 018

759

88 024 030 036 041 047

053 058 064 070 076

7«0

7t;i

OKI 087 093 098 104
138 144 150 156 161

110 116 121 127 133
167 173 178 184 190

7(i2

195 201 207 213 218

224 230 235 241 247

252 258 264 270 275

281 237 292 298 301

764

309 315 3-il 32G 332

338 313 349 355 360

■3

765

366 372 377 383 389

395 400 406 112 417

766

423 429 434 440 446

451 457 163 468 471

767

480 48S 191 497 502

508 513 519 525 530

768

536 512 547 553 559

561 670 576 681 587

v±

760

593 598 604 610 615

621 627 632 638 643

770

649 665 660 606 672

677 683 689 691 700

771

705 711 717 7!2 728

734 739 745 750 756

772

762 767 778 779 781

790 795 801 807 812

773

818 824 829 835 8«P

846 852 857 868 868

774

871 880 885 891 897

902 908 913 919 925

775

930 936 941 947 9r.3

958 964 969 975 981

776

986 992 997 003 009

014 030 oaa oai 087

777

88 042 018 053 059 064

070 076 081 087 092

778

098 104 109 115 120

126 131 137 143 148

779
780

154 159 165 170 176

182 187 193 198 204

209 215 221 226 232

237 213 248 254 260

781

265 271 276 282 287

293 298 804 310 315

o-S

321 396 332 337 343

848 864 360 365 371

783

XIG 382 387 393 398

104 409 115 121 426

I'S

784

4;J2 l:i7 143 448 454

459 165 470 17S 181

7
S

785

187 492 498 504 509

515 620 526 531 5S7

786

512 548 553 559 561

570 575 681 586 502

3-s

7S7

597 603 009 614 620

625 631 636 642 647

788

653 GSa 661 669 675

680 086 691 697 702

A'"

789

708 713 719 724 730

735 741 716 752 757

=jj

^'S

790

763 768 774 779 785

790 796 801 807 812

791

818 823 829 834 840

845 851 856 862 867

792

873 878 883 889 891

900 905 911 916 922

793

927 933 93H 944 919

955 960 »U6 971 S77

794

982 988 993 998 OOi

009 oiBoaooao osi

795

eO 037 012 048 058 059

0G4 069 075 080 OSli

796

091 097 102 108 113

119 124 120 i;!r. Uii

797

146 ISl 157 162 168

m 179 184 IMl l;-.-.

798

200 206 211 217 222

227 233 23H ^11 -^i'.'

799

255 260 266 271 276

282 287 293 'MS 3U1

312

Fwe-jigt

tre Logarithms. ■

No.

I>«. 1 2 3 4

5 C 7 8 9 ' Uiffuroncoa. Ifl

801
802

801

90 ;w)y ;ii4 320 :i25 331
363 bta 37* 380 385
417 423 428 434 439
472 477 482 488 403
521! 531 5;W 542 547

336 342 347 352 358
390 396 401 407 412
444 450 455 461 466
490 501 609 515 520
553 558 663 669 574

805
SOti
807
808
809
810
811
812
813
614
8IS
8IU
817
818
810
820
821

823
824

580 585 590 S96 601
634 639 644 650 655
687 693 698 703 709

741 747 752 757 703
795 800 806 811 810

607 612 017 623 628

C60 666 671 677 682
714 720 725 730 736
768 778 779 784 789
822 827 832 838 643

848 854 859 865 870
902 907 913 918 32:-l
956 961 966 972 977
91 009 014 020 025 030
062 068 073 078 084
116 121 126 132 137
169 174 180 185 190
222 228 233 238 243
275 281 286 291 297

875 881 886 891 897
929 934 940 945 950
982 988 893 998 OM
036 041 016 0S2 057
089 094 100 105 110

3
4

1
S

- s

o-e ■

112 148 153 158 164
196 201 206 212 217
249 251 259 265 270
302 307 312 318 823

381 SH7 392 397 103
434 140 145 450 455
487 492 498 508 608
540 545 551 556 561
593 598 603 609 614

108 113 418 424 429
461 166 471 477 482
514 510 624 529 535
566 572 577 582 687
fll9 621 630 635 640

825
826
827
828
829

645 651 656 561 666
698 703 709 714 719
751 756 761 766 772
803 808 114 819 824
855 8G1 866 871 876

672 677 682 687 693
724 730 735 740 715
777 782 787 793 798
829 831 810 845 860
882 887 892 897 903

830
831

S32
833
834

908 913 918 923 929
960 965 971 976 981
ea 012 018 023 028 033
065 070 075 080 085
117 122 127 132 137

931 939 941 950 B65
986 991 997 008 007
038 044 049 054 059
091 096 101 106 111
113 148 153 158 163

1
1

835
837
830

169 174 179 1B4 189
221 226 231 236 241
273 278 283 288 293
324 330 335 340 345
376 381 387 392 397

195 SOO 205 210 215
247 252 257 262 267
298 304 309 314 319
350 355 361 366 371
402 107 412 418 423

840
841
842
843
844

428 433 438 443 449
480 185 490 195 500
531 536 542 547 552

633 588 593 598 603

634 639 646 650 636

454 459 164 469 474
505 511 516 621 626
557 662 567 572 678
G09 614 619 624 829
660 665 670 675 681

845
846
847
848
849

686 691 690 701 706
737 742 747 752 758
788 79:j 79a 81)4 809
810 845 850 855 860
891 896 901 906 911

711 716 722 727 732
763 768 773 778 783
814 819 824 829 834
865 870 875 881 880
916 021 027 932 037

^^^^^J

Five-fignte Logarithms.

N.,.
HDD

Log. (1 1 ■; 3 4

5 6 7 8

DifferouoL.s,

92 912 9i7 9S2 957 962

967 973 978 983 988

851

993 998 (m 008 013

018 OZi 039 034 033

S52

83 044 049 054 059 064

069 075 080 085 090

853

095 100 105 110 115

120 125 131 136 141

854

146 151 156 161 166

171 176 181 186 192

855

197 202 207 212 217

222 227 232 237 242

850

247 252 258 263 268

373 278 283 288 293

857

298 303 308 313 318

323 323 334 339 344

8SS

349 354 859 364 369

374 379 384 389 394

859

399 404 409 414 420

426 430 435 440 445

450 455 460 465 470
500 505 510 515 520

475 480 485 490 495
526 531 536 541 546

861

I'O

862

551 556 561 566 571

576 581 586 591 596

863

601 606 611 616 621

626 631 636 641 646

3'o

661

651 656 661 666 671

676 682 687 692 697

665

702 707 712 717 722

727 732 737 742 747

866

752 757 762 767 772

777 782 787 792 797

3'S

867

S02 807 812 817 822

827 832 837 842 847

4-0

852 857 862 867 872

877 882 887 892 897

860

002 007 912 917 922

927 932 937 942 947

"btT

952 957 962 967 972

977 982 987 992 997

871

84 002 007 012 017 022

027 032 037 042 047

872

052 057 062 067 072

077 082 086 091 096

873

101 106 111 116 121

126 131 136 141 146

874

151 156 161 166 171

176 181 186 191 196

875

201 206 211 216 221

226 231 236 240 245

876

250 255 260 265 270

275 280 285 290 295

877

300 305 310 315 320

325 330 336 340 344

878

349 354 359 364 369

374 379 384 389 394

879

399 404 409 414 419

424 429 433 438 443

880

448 453 458 463 468

473 478 483 488 493

498 503 507 512 517

522 527 532 537 542

547 552 557 562 567

571 676 581 586 591

596 601 606 611 616

621 626 630 635 640

884

645 650 655 060 665

670 675 680 685 689

;

885

694 699 704 709 714

719 724 729 734 738

886

743 748 753 758 763

768 773 778 783 787

887

792 797 802 807 812

817 822 827 832 336

841 846 851 856 861

866 871 876 880 885

880
890

890 895 900 905 910

915 919 924 929 934

i^ - 1

939 944 949 954 959

963 968 973 078 983

891

988 993 998 oaa 007

013 01? OSm 037 032

892

86 036 041 046 051 056

061 066 071 075 080

893

085 090 095 100 105

109 114 119 124 129

894

131 139 143 148 153

158 163 168 178 177

895

ia2 167 192 197 202

207 211 216 221 226

896

231 236 240 245 250

255 260 265 270 274

897

279 28-4 289 294 299

303 308 313 318 323

328 332 337 342 317

352 357 361 366 371

899

376 381 386 300 395

400 406 410 415 419

314

Five-figure Logarithms.

N...

1->e. 11 1 2 :i 4 5 6 7 8 9

900
901

ooa

!HM
903

WP7
Olio

M 424 420 434 4S9 444 448 4S3 458 463 408
472 477 482 487 492 407 501 506 511 516
521 f>25 fiW 535 540 545 550 654 559 564
569 574 578 583 588 603 598 602 807 612
617 622 626 631 636 641 046 650 655 660

863 670 674 679 684 l'*0 694 698 703 708
713 718 792 727 732 7»7 742 746 751 756
761 766 770 775 780 785 780 79* 799 804
800 813 818 823 828 832 837 842 847 SS2
858 881 866 871 875 880 885 890 89S 899

OUI

oil

012

013
OM

904 909 914 918 923 928 933 938 943 947
952 967 961 966 971 976 980 983 990 B96
999 «M 009 OM 0J9 033 OSB OSS (»S 0«
M 047 052 057 061 066 071 076 080 085 090
095 099 104 109 114 118 123 128 133 137

91.-)

Mia
017

OIH
010
920
921

92a

924

142 147 152 156 161 166 171 175 180 185
190 194 199 204 209 213 218 223 227 232
237 242 246 251 258 261 285 270 275 280
284 289 294 298 303 308 313 317 822 327
332 338 341 34<1 350 3M 360 365 369 374

379 383 388 393 398 402 407 412 417 421
420 431 435 440 445 450 454 459 46* 468
473 478 483 487 402 497 501 506 511 B15

520 525 530 634 539 544 548 663 556 562
567 572 577 581 586 591 596 600 605 609

025
926
027
928
920

614 619 024 628 6ft3 638 842 647 652 656
661 666 670 67S 680 68S 089 694 699 708
708 713 717 722 727 731 736 741 745 750
755 759 764 769 774 778 783 788 792 797
802 806 811 816 820 825 830 834 830 844

930
931
932

848 853 858 862 887 872 876 881 886 800
895 900 904 909 914 918 923 928 932 937
i»42 946 951 956 960 965 970 974 979 984
988 993 997 003 OW Oil 016 021 006 030
fl7 035 039 044 049 053 058 003 087 072 077

I
I

935
936
937
938

081 086 09O 095 100 104 109 114 118 123
128 132 137 141 146 151 155 160 165 169
174 179 183 188 192 197 202 206 211 216
220 225 230 234 239 243 248 253 257 262
267 271 278 280 283 290 294 299 304 308

040
041
942
943
944

313 317 322 327 331 336 340 345 350 854
359 364 388 373 377 382 387 891 398 400
405 410 414 419 424 428 433 437 442 447
451 468 460 465 470 474 479 483 488 403
497 502 508 511 616 620 525 529 634 539

945
9411
917

543 548 552 557 562 566 571 575 580 585
589 594 69S 603 007 612 617 821 626 830
635 040 044 649 653 658 663 667 672 876
881 685 890 695 699 704 708 713 717 722
727 781 736 740 745 749 754 759 783 768

Five-figitre Logaritlnns.

No.

!I5I1

Log. 1 2 y -1 5 6 7 8 9

Difforonce?.

97 772 777 7H2 786 791

795 800 804 S09 813

»5I

81« K-23 827 832 83ti

841 845 850 855 859

952

86-1 868 873 877 882

886 891 896 900 905

Dsa

900 014 918 923 928

932 937 911 946 050

5154

955

955 959 9H-1 9G8 973

978 982 987 091 996

98 000 005 000 014 019

023 028 032 037 041

956

04G 050 055 059 004

068 073 078 083 087

il57

091 U9C 100 105 1U9

114 118 123 127 132

958

137 141 146 150 155

159 161 168 173 177

959

182 186 191 195 200

204 209 214 218 223

9tiil

227 232 23«t 241 243

250 254 259 263 268

°'5 "~

9i>]

272 277 281 286 290

295 299 304 308 313

318 322 327 831 336

340 345 349 354 358

963

363 367 372 376 881

385 390 394 399 403

!Hi4

408 412 417 421 426

430 435 439 444 448

3-0

965"

453 457 462 466 471

475 480 484 489 493

96a

498 502 507 511 516

520 525 529 534 538

967

543 547 552 556 581

565 570 574 579 583

968
969
970

588 592 597 601 605
032 637 641 646 650

610 611 619 623 628
655 659 S64 668 673

677 682 686 691 695

700 704 708 713 717

971

722 726 731 735 740

714 719 753 758 762

972

767 771 776 780 784

789 793 798 802 807

973

811 816 820 825 829

831 838 813 847 851

974

856 860 865 869 874

878 883 887 892 896

975

900 906 909 914 918

923 927 932 936 911

976

945 919 954 958 963

967 972 976 981 985

977

989 944 998 003 007

01% 016 021 tm 039

97H

99 034 038 043 047 052

05(! (Mil 065 069 074

979

078 083 087 092 096

imi 105 109 114 118

980

123 127 131 136 140

145 149 154 158 162

4
8

i»81

167 171 176 180 185

189 193 198 202 207

982

211 216 220 224 229

233 238 242 247 251

9B3

255 260 264 269 273

277 282 286 291 295

984

300 304 308 313 317

322 326 330 335 339

985

314 348 352 357 361

366 370 374 379 383

980

388 392 396 401 405

110 411 119 123 127

987

432 436 441 445 449

451 458 163 167 171

988
989

476 480 484 489 493
520 524 528 533 337

498 502 606 511 515
542 546 550 555 559

ill I

990

564 568 572 577 581

586 590 594 599 603

991

607 C12 610 621 625

629 634 638 642 647

902

651 656 660 664 669

673 677 682 686 691

993

Km tm 704 708 712

717 721 726 730 734

094

739 743 747 752 756

700 765 769 774 778

995

782 787 791 795 800

801 808 813 817 822

996

826 830 835 839 843

818 852 856 861 865

997

870 874 878 883 887

891 896 900 901 909

998

913 917 922 926 930

935 939 943 048 952

999 1

957 961 965 970 974

978 983 987 901 996

INDEX

The references in heavy type refer to the preparations or special analysis

of the substances.

Accumulator, charging of, 55

, chemical process of, 53, 60

, discharging of, 55

, Edison, the, 60

, lead, the, 53

Accumulators, 52
Acetanilide, 258
Acet-toluide, 283
Acheson graphite, 199
Acid, acetic, 228

, adipic, 231

, diethyl adipic, 231, 283

, trichloracetic, 227

Agitating electrode, 198
Agitation of solutions, 198
Alcohol, 87, 236, 241, 245, 251, 263

, isopropyl, 252, 254

, methyl, 228, 232

, para-nitrobenzyl, 278, 280

Alloys, analysis of, 185
Alteration of decomposition value, 152
Alternating currents, rectification of, 61
Aluminium from iron, 167
Amalgam, bismuth, 134

, cadmium, 133

, lead, 136

Amalgamation, 223
Amalgams, 132
Amidophenol (para-), 238
Ammeters, 22
Ammonium borate, 95, 98, 282

, cobalt sulphate, 282

, thiocyanate, 271

Analysis of alloys, 185
Aniline, 236
Anion, 5
Anode, 5
Anthracine, 269

Anthraquinone, 269

Antimony, 108

from arsenic, 184

copper, 181

lead, 180

mercury, 175

silver, 178

tin, 181

Apparatus, 76

Arrhenius, 33

Arsenic, 147

from antimony, 184

copper, 184

mercury, 175

Artificial alteration of decomposition
value, 152

Atomic and electro-chemical equiva-
lents, 9

Atomic weights, table of, 288

Azobenzene, 241

Azoxybenzene, 240

Back E.M.F., 37, 73

Balachowsky, 117

Basin electrode, 77

Bell metal, 186

/3. naphthol, 274, 276

/3. naphthol - azo - benzenemonosulpho-

. nate, 274
p. naphthol disulphonic acid (R. acid),

277
Benzaldelyde, 279
Benzene derivatives, oxidation of, 278
Benzidine, 243

Benzilidene-phenylhydroxylamine, 246
Berthelot, 200
Bertiaux, 168
Bindschedler, 108

3iS

'34

Raard of Trade Unii, 39
Sonite of ammonia, 95, 98. 3B3
fiomwl S65

Brituinia metal, 190
Bnimale of pDlnssiimi, aia
Bromororm. 907
Ilrown. A. Cmm, 327

Biinspti, 34

celr, 44

sulphi

copper, 156
silver, 17G
221

yellow. S

r:nffeine,.257
Canarine, 127, S
Calhode, 5

Cell, I

— , chromic iicid, 45
— , Clark. 39
~, eiipron, 47
— , Daniell, 43
— , Leclanuhe, 46

iinc, 39
00.73

, porous, preparation of,

, standard, 39

. Weslon, 41

Cells, primary, 39
Cliaplin SI?

Charging accumulators, 55
Chlorate polosimm, 9U

, sodium, ai2

Chlorates. 310
Chloroanilines, 247
Chroma tc. lead, 3i3
potassium, 319

mereury, 173

nickel, 170

Coebn, 170
Commercial lend, 189
Compk-S cyanides, 91

Conductors, 3
Congo red, 177
Copper. 88
and gold, 186

-, gas, 13, 14. IS

Cruikshank. 85
Cupron element, 47, 159
Current density (CD,), So

-diBtributton,t,5

, sources of, 34

Cylindrical gauie electrode, 7B

DaseellccII, 42. 53

Davy, ,, 34

Decom posit

onofw

ter, 6

value, artificial

alteration

Ubte of,

— ba^e

, table of

^^H

Index. 3i^^^^B

Gasconlommelers, .3. 14. 15 H

Detonaling gaa coulommeter, 13

German silver, 188 . B

DiagniTn of current dislribulion, 65

Glaser, t?" ■

Dianisidine blue, 276

Cold, 1S3 H

dimelhoxybeniidine. a??

electrode, 104 H

Dielectric polarisalion, 6i

from mercury, 174 ^1

Diethyl adipic acid, 281

, sterling, 1B6 ■

succinate. 331

Gooch. 81 H

Core, 108 ^H

Gram equivalent, 11 ^^^^^B

Graphite, Acheson, 199 ^^^^^^^

Groupint; cells, 49, 50 ^^^^^^1

DyQBmo, 37, 34. sa, 56

Gun melaJ, 186 ^^^^^^^H

Edison storage cell. 60

Habeb. 935. 339 H
Hackford. Set Arsenic flpparalus, 150 H

Electrical equivalent of heal, 98

positions, table of, 37

Heat, electrical equivalent of, aS ■

quantities, 8

, meclmnicnl eiiuivalcni oF, 28 ^H

Electrode, agitating, 198

Hddenreich, 156 ■

, fiag. 79

Hempel's burette, aog ^1

, gHUie, 79

Hexahydropyiidine, 269 ,^H

, rotating. So, ig8

Historical, 3 ^^^B

Electrodes, 4

, preparalion of. 8a, 198. 250

- ^^^^H

Electrolysis, i

of oi^anic acids, 225

Horse power, 29 ^^^^^^H

Electrolytes, 4

Electrolytic cell, resistance of, 7a

Hydrochloride of hydrosylMmine. 222

— meter. Wright's, 20

rediflcation of alternating currents,

Hydrorides metallic, 220

1' 61

Eleclromoliveforce(E.M.F.|, 37, 39, 73

HydroxyUmine hydrochloridt-, 222

1 — . bBck, 39. 73

, Energy, 27

iNTERNATroNAI. wblc of atomic

Engels, 139

weights, 288

Ethane, 238

Ethylaniline. 258

from alcohol, 283

Ethylene, 230

acetone, 264

EUiyl-o-toluidine, 368

lanisation, 2

Ethyl poLissium malonate, 283

Ions, 5

- — succinate, 283

Iron, 100, 103

^ chromium. 166

Fab A DAT, I, 7

definition of a, 7

cobalt. 165

Faraday's Law, 7. 12

. lend, 170

; experimental proof of, 10

Fischer, 109, (47

Flag electrode, 79

nickel, 165

Friedberger, 215

silver, 162

— ^inc, .64

Isopnipyl alcohol. 368, 254

Galvanising b.illi, residues from. 191

Kilowatt, a8
Kohn, 117, 147
Kolloch, 141, 143
Kom, 141

Le Blanc, 6. 33
Lead, 136

accumulator, 53

amalgam, 135

chromate, 31B

elecirodes. preparalion of. 330

from anliniony. 180

1, 173

I MonoBulphidi! of sodium, 381
' Moore, 135
I Milller, 144, ai;

I Nalder ammeier. 22

L Naphthionic acid, 378

Naphlhol. fi,, 374, 376
' Naiure of cathode, influence of, 153
[ NpRafive pole, 35

and positive electricity. 35

i Nickel, 92

I coinage, 187

Uhfeldl, 7, 33

I-iquid resijlaDce, 7s
Lijl), i3Si "73
Lognriihm lablos, agi
Luckow, 13a, ai6

Magnus, 85

nickel, 173

Mercury, IM. 107

coulommeter, ao

from antimon)', 175

r.geU..'274
Organic iic Ids. eleclroiysis of. 335

OKidation, 261

radicals, 103

Origin of eleclroohemisiry, 3
Oriho-chloronniline, S47

tin, ,^

inphntmncenticiil preparations, 107

Metallic hydroxides 320

sulphides, S&l
Meier "Wright's electrolytic, 20
Melliod for regulating potential, 158
Methyl aicohol, 933

Mirror arsenic, 149

lation of beniene derivatives, 378

Palladium, 139

a-amidapheiio1,238

- -chloroaniline, 247

- -nilroboniyl alcohol, 27B, 380

- -phcnylenediamliii-. 344

- -xylene, 278, 3B0
allel grouping, 49. 50

Peri

metallic compo
table of. 286
crniJinganate. potassium, 218

W ^^^ka^m^

^^H

\ ^ Index.

321

Residues, linc in, 191

— - potassium, 203

Resislance liquid, 7j

of electrolytic cell, 72

-^, Ubieof. 70

, estimation of, aoj

wire, 69, 74

Pliarmacemical preparations, mercmy

Resistances. 68. 69, 72-75

in, IC7

Rhodium, 126

Phenol, para-amido, 388

Rotating electrode. Bo

Phenylenedianiine, para-, 344

Pinacone, 354

Sand and Hackford's arseni

appa-

Piperidine, 269

rams. 150

Plan,*, 53

Separation methods, Hollard's.

■5"

Plaiinum. 138

'. by variadon of polen

al,.5.

PolariBalion, 37, 38

of Hallides, 143

. "11, 73

-^metals, 151

Pole pnpers, 68

^ — ■ : nature of cathod

upon,

Ponceau 2. G, 377

153

Porous cells, preparation of, 251

Series grouping of cells, 49, 50

Potassium bromale, 312

Shunt circuit, 23, 24

chlorate, 211

Silver. 121

ehromale, aig

coulommeler, 17

from antimony, 17B

ethyl-succinale, 3S3

■ cadmium, 176

iodftte. 213

cobalt, .71

copper, 157

perchlorate, 214

^ — - iron, i6a

^^^^^^H

permanganate, 218

lead, 177, 189

petsulphatc, 303

mercury, 174

nickel, 171

Potential, regutelion of, 158

. German, 188

, sterling, 163

dyes, 371

.Smith, E., 107, 135, 139, '4': 14

=, 1.0,

electrodes, 83, 198, 250

lead electrodes 350

Sodium bromate, 313

1 porous cells, 351

I Preparations. 195

1 Primary cells, 34

Solenoid, 23

Solution, agitation of, 198

i Purone, 256

Purpurogallin, 261

Sptcific resistance. 70

Pyrogallol, 309, 361

Speculum metal, 186
Spencer, 160

Ratleigh, Lord, 40

Standard iirsenic mirror. 149

sulphuric acid, 146

1 Rectification of alternating currents, 61

Sterling gold, 186

Reduction in acid solution, 336

silver, IBs

alkaline solution, 339

Stirring electrode, 198

, of earbonyl group, 349, 253, SS8

Storage battery, Edison, 60

nitro group, 333

Clonic compounds, 235

Succinate diethyl , 231

! Regulation of current, 69

Sulphanilic acid, 274

322

Sulphating, 59
Sulphides, metallic. 221
Sulphur heptoxide, 200
Sulphuric acid, standard, 146

Tables of logarithms. 292
Tafel. 223. 253. 255. 256
Teeple, 265
Tellurium, 180
Temperature coefficients, 70, 71
Thallium, 181

as oxide, 140

Theoretical percentage of metals

salts. 289
Thorpe's arsenic apparatus, 148

Tin, 112

Tin from antimony, 181

mercury, 176

silver, 177

Toluene, 278, 279
Toluidines; 238. 258
Trade. Board of, cell, 40
Trichloracetic acid, 227
TropaoUn OOO I., 274, 276

000 II., 276

Trotman, S. R., 150
Truchot, 143

Uranium, 141
Uric acid, 256
Useful data, 285

Index.

Valencies of ions, 4

Values of acids, decomposition, 32

• bases, decomposition, 32

: r salts, decomposition, 32

Vanadium, 148

Variable potential, 151

Volta, I, 12

Voltage, decomposition values of, 29

polarisation, 73

Voltameter, 12, 25
Volt-coloumb, 27
Voltmeter, 24
Vortmann, 132, 143

Walker, 227

Wallace, 125, 156

Watt, 28

Watt-kilo, 28

Weight coulommeter, 17
j Weston ammeter, 28. 26

1 cadmium cell, 41

i White lead, 216

I Wimmenaneur, 117

i Wright's electrolytic meter, 20

Zinc, 118

from cobalt, 172

copper, 157

iron, 164

nickel, 172

silver, 179

residues in galvanising bath, 191

THE END

FSIMTBD BY WILLIAM CLOWBS AND SONS, LIMITED, LONDON AND BECCLES.