REESE LIBRARY
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UNIVERSITY OF CALIFOPx
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QUANTITATIVE
CHEMICAL ANALYSIS
BY
ELECTROLYSIS
BY
DR. ALEXANDER CLASSEN
PRIVY COUNCILLOR "'
Professor of Petrochemistry and Inorganic Chemistry in the Royal School of
Technology at Aachen
IN CO-OPERATION WITH
DR. WALTER LOB
Lecturer orrflectrochemistry in the Royal School of Technology at Aachen
AUTHORIZED TRANSLATION
TH1D ENGLISH FROM THE REVISED AND GREATLY
ENLARGED FOURTH GERMAN EDITION
BY
WILLIAM HALE HERRICK, A.M.
Formerly Profeor of Chemistry in Iowa College and in the Pennsylvania State College
AND
BERTRAM B. BOLTWOOD, PH.D.
Instructor in j,alytical Chemistry in the Sheffield Scientific School of Yale University
NEW YORK
JOHN WILEY & SONS
LONDON : CHAPMAN & HALL, LIMITED
1898
QUANTITATIVE
CHEMICAL ANALYSIS
BY
ELECTROLYSIS
BY
DR. ALEXANDER CLASSEN
PRIVY COUNCILLOR '^
Professor of Electrochemistry and Inorganic Chemistry in the Royal School of
Technology at Aachen
IN CO-OPERATION WITH
DR. WALTER LOB
Lecturer on Electrochemistry in the Royal School of Technology at Aachen
AUTHORIZED TRANSLATION
THIRD ENGLISH FROM THE REVISED AND GREATLY
ENLARGED FOURTH GERMAN EDITION
WILLIAM HALE HERRIOK, A.M.
Formerly Professor of Chemistry in Iowa College and in the Pennsylvania State College
AND
BERTRAM B. BOLTWOOD, PH.D.
Instructor in Analytical Chemistry in the Sheffield Scientific School of Yale University
NEW YORK
JOHN WILEY & SONS
LONDON : CHAPMAN & HALL, LIMITED
1898
QTM15
C (o
Copyright, 1898,
BY
WILLIAM HALE HERRICK
AND
BERTRAM B. BOLTWOOD.
f 32.
BOBKRT DRUMMOND, ELECTROTYPER AND PRINTER, NEW YORK.
PREFACE TO FOURTH EDITION.
THE present edition, revised with the assistance of Dr.
Lob, differs from the previous editions in that the Introduc-
tion has been augmented by the insertion of a section devoted
to theory. This was made the more necessary, since the in-
vestigations of recent years have been chiefly devoted to the
explanation of the reactions in solutions, and the determina-
tion of the electrical magnitudes. The necessity of specific
directions concerning electrode tension, current strength and
decomposition tension has been demonstrated. The author,
with the co-operation of his assistants, has experimentally
determined these electrical magnitudes, not only for his own
methods for the determination and separation of the metals,
but also for a number of other methods, and has incorporated
them in the text. Additional methods by other authors, in
which directions concerning these important factors are want-
ing, have been omitted, in consideration of the fact that these
are either uncertain or entirely impractical ; mention of them
has, however, been made in the references to the literature.
The book has been made more complete by the description
of various measuring instruments, sources of current and
apparatus ; together with an explanation of simple and com-
plete appliances for carrying out electrolytic experiments.
These have been illustrated by a large number of new cuts,
in the text and in the appended tables.
The publishers have spared neither pains nor expense to
make these new illustrations as perfect as possible; I feel
called upon to express here my full appreciation of this fact.
A. CLASSEN.
AACHEN, January 18, 1897.
iii
TRANSLATORS 1 PREFACE.
THE Author's Preface to the Fourth Edition points out so
fully the improvements over preceding editions, that the
translators need add nothing. It is plainly a more complete,
scientific and logically arranged work than heretofore.
The translators have made some additions, as had their
senior in previous editions; and have corrected some errors
in the German edition, apparently the result of hasty com-
pilation. The " Special Part" of former German editions
(which is omitted in the fourth) has been retained in the
form of an appendix, and has been revised and brought up to
date. In addition to this a carefully prepared index has been
added, and the translators believe that the value and con-
venience of the work is thereby much enhanced.
WILLIAM HALE HERRICK.
BERTRAM B. BOLTWOOD.
January, 1898.
CONTENTS.
SECTION I.
GENERAL PART.
PAGE
INTRODUCTION 1
ION THEORY 6
FARADAY'S LAW 10
OHM'S LAW 12
TENSION AND ITS SIGNIFICANCE 13
SIGNIFICANCE OF CURRENT STRENGTH 17
SIGNIFICANCE OF RESISTANCE 19
THEORY OF ELECTROLYTIC PRECIPITATION , 21
DETERMINATION OF 'THE CURRENT MAGNITUDES :
1. MEASUREMENT OF THE CURRENT STRENGTH 23
Oxyhydrogeu-gas Voltameter 24
Weight Voltameter 26
Tangent Galvanometer 26
Sine Galvanometer 28
Other Forms of Galvanometers 29
Spring Galvanometer 31
Amperemeter 31
2. MEASUREMENT OF THE TENSION 32
Voltmeter .... 32
Torsion Galvanometer 33
Lippmanu Capillary Electrometer 35
Quadrant Electrometer 37
SOURCES OF CURRENT 38
PRIMARY GALVANIC ELEMENTS :
Leclanche Cell 39
Meidinger Cell 41
Daniell Cell 43
Gravity Cell 43
vii
viii CONTENTS.
PAGE
Grove Cell 44
Bunsen Cell 45
Cupron Element 46
Edison-Lalande Element 47
SECONDARY GALVANIC ELEMENTS (ACCUMULATORS, OR STORAGE
BATTERIES) ... 47
General Rules for the Handling of Accumulators 54
PHYSICAL METHODS OF PRODUCING THE CURRENT :
Electromagnetic Machines 60
Thermo-electric Piles 64
REGULATION OF THE CURRENT 73
PROCESS OF ANALYSIS 83
HISTORICAL .. 101
ARRANGEMENTS FOR ANALYSIS 107
Arrangement for Smaller Experiments 108
Former Equipment of the Electrochemical Institute at Aachen.. . . Ill
Present Equipment of the Electrochemical Institute at Aachen. ... 124
SECTION II.
SPECIAL PART.
QUANTITATIVE DETERMINATION OF THE METALS.
IRON 137
COBALT 141
NICKEL 143
ZINC 144
MANGANESE 148
ALUMINIUM, URANIUM, CHROMIUM, BERYLLIUM 153
COPPER 153
BISMUTH 162
CADMIUM , 163
LEAD . 166
THALLIUM 170
SILVER 172
MERCURY 174
GOLD 177
ANTIMONY 178
PLATINUM 182
PALLADIUM 183
TIN.. . 183
CONTENTS.
PAGE
ARSENIC. . . ...... ...... ........... . . ................. ........... 188
POTASSIUM, AMMONIUM (NITROGEN) ........ ... ..................... 188
DETERMINATION OF NITRIC ACID IN NITRATES ............ . ....... 189
DETERMINATION OF THE HALOGENS.
CHLORINE, BROMINE, IODINE ...................... . .............. 190
SEPARATION OF THE METALS.
IRON .................................................. . ...... 191-204
Iron Cobalt .................................................. 191
Iron Nickel ...... ........................................... 192
Iron Zinc .................................................. 193
Iron Manganese ....................... ...................... 194
Iron Aluminium ............................................. 196
Iron Uranium ............................................... 198
Iron Chromium .......................................... ... 199
Iron Aluminium Chromium ....... . ......................... 200
Iron Chromium Uranium ............................ . ....... 200
Iron Beryllium . ............................................. 201
Iron Beryllium Aluminium .................................. 201
Iron Copper ................................................. 202
Iron Lead ................................................... 204
COBALT ...................................................... 204-206
Cobalt Zinc ............................................... 204
Cobalt Aluminium ........................................... 204
Cobalt Uranium ............................................ 204
Cobalt Chromium . . ........................................ 204
Cobalt Uranium Chromium ............. .................... 204
Cobalt Copper ............................................... 205
Cobalt Bismuth ........ ... .................................. 205
Cobalt Lead ................................................ 206
Cobalt Mercury ....... . ...................................... 206
NICKEL ....... . ............ . .............................. 206,207
Nickel Manganese ......................................... 206
Nickel Aluminium ................. '. ......................... 206
Nickel Uranium ...... , ..................................... 206
Nickel Chromium ......... .................................. 206
Nickel Copper .............................................. 206
Nickel Lead ............................................... 207
Nickel Mercury ................... ......................... 207
S CONTENTS.
PAGE
ZINC 208-211
Zinc Manganese 208
Zinc Aluminium 208
Zinc Copper 208
Zinc Cadmium 209
Zinc Lead 210
Zinc Silver 210
Zinc Mercury 210
MANGANESE 211, 212
Manganese Copper 211
Manganese Cadmium 212
COPPER 3i2-21?
Copper Cadmium 212
Copper Lead 213
Copper Silver 215
Copper Mercury 216
Copper Arsenic 217
CADMIUM 217,218
Cadmium Lead 217
Cadmium Mercury 218
LEAD 218,219
Lead Silver 218
Lead Mercury 218
Lead Antimony 219
SILVER 220
Silver Antimony , 220
Silver Arsenic 220
MERCURY 220, 221
Mercury Antimony 220
Mercury Arsenic 221
ANTIMONY 221-228
Antimony Tin 221
Antimony Arsenic 224
Antimony Tin Arsenic 225
TIN PHOSPHORIC ACID 228
PLATINUM IRIDIUM 228
SEPARATION OF GOLD FROM OTHER METALS 228
POTASSIUM SODIUM 229
SODIUM AMMONIUM. . . 229
CONTENTS. XI
APPENDIX.
SOME APPLIED EXAMPLES OF ELECTROCHEMICAL
ANALYSIS.
PAGE
BRASS 231
SILVER COIN 233
NICKEL COIN 233
GERMAN SILVER 234
BRONZE , 235
PHOSPHOR-BRONZE 235
MANGANESE PHOSPHOR-BRONZE 236
SOLDER 236
WOOD'S METAL 237
HARD LEAD, TYPE-METAL. 237
ALLOY OF ANTIMONY AND TIN 238
ALLOY OF ANTIMONY AND ARSENIC 238
ALLOY OF ANTIMONY, TIN AND ARSENIC 239
SPATHIC IRON-ORE 239
HEMATITE 240
LIMONITE 241
CLAY IRON-ORE , 242
BOG IRON-ORE 242
CHROME IRON-ORE 242
PSILOMELANE 244
SPHALERITE (ZINC BLENDE) 247
CALAMINE AND SMITHSONITE 249
ULTRAMARINE , 249
REFINERY SLAG 250
COPPER AND LEAD SLAGS 250
BLAST-FURNACE, CUPOLA, AND BESSEMER SLAGS 252
ZIRCON 253
ARSENOPYRITE 253
CHALCOPYRITE 254
NICKEL MATTE, COPPER MATTE 255
COPPER SPEISS, LEAD SPEISS . . 256
PYRARGYRITE 257
TETRAHEDRITE 257
FURNACE "Sows" - 258
STIBNITE (ANTIMONY GLANCE). 259
ULLMANITE 259
BOURNONITE . 260
Xll CONTENTS.
PAGE
ZlNKENITE 260
LlNN^EITE 261
CoBALTITE . 261
COBALTIFEROUS ARSENOPYRITE 262
CERUSSITE 263
GALENA ... 263
PYROMORPHITE 264
LEAD MATTE 264
CINNABAR , 265
SOFT LEAD (CRUDE LEAD) 265
ANTIMONY 268
SPELTER (CRUDE ZINC) 268
BLISTER COPPER 269
REFINED COPPER 272
TIN . 272
SILVER . . 273
COMMERCIAL NICKEL 274
PIG IRON, STEEL, SPIEGEL, FERROMANGANESE 275
TABLES FOR CALCULATION OF ANALYSES 280-283
REAGENTS 284-287
POTASSIUM OXALATE 284
AMMONIUM OXALATE 284
OXALIC ACID 285
AMMONIUM SULPHATE 285
SODIUM SULPHIDE 285
ALCOHOL 286
INDEX OF AUTHORS 287
INDEX OF SUBJECTS.. 293
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
PAET L-GEKEKAL PAET.
INTRODUCTION.*
WATER acidified with sulphuric acid is decomposed into
its elements, hydrogen and oxygen, when a galvanic current
is passed through it; a large number of compound sub-
stances conduct themselves in a similar manner. This gal-
vanic decomposition is called electrolysis, and the substances
which are decomposed by the electric current are known as
electrolytes. The substances into which electrolytes are
separated by the electric current are naturally divided into
two groups : Those which separate at the positive electrode,
or anode (connected with the + pole of the source of the
current), and which are therefore the electro-negative con-
stituents, are called anions; those which separate at the
negative electrode, or cathode (connected with the pole
of the source of the current), the electro-positive constitu-
ents, are called cathions.
The metalloids, or electro-negative acid groups, therefore
appear at the positive electrode, while the metals are sepa-
rated at the negative electrode.
* An elementary knowledge of galvanic action is assumed.
2 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
For instance, if the electric current is passed through
the solution of a haloid salt, the halogen is separated at the
anode, the metal at the cathode.
CuCl 2 = C1 2 + Cu,
ZnCl 2 = C1 2 + Zn.
Oxygen salts act in a similar manner.
CuS0 4 = S0 4 + Cu,
Cu(N0 3 ) 2 = (N0 3 ) 2 + Cu.
Many acids are decomposed in a similar manner.*
H 2 S0 4 = S0 4 + H 2 ,
2HC1 = C1 2 + H 2 .
The substances formed by electrolytic decomposition,
however, generally undergo further chemical change, or are
acted on by the electrodes ; various secondary reactions take
place.
In the electrolysis of a solution of copper sulphate between
platinum electrodes, the secondary process consists in the re-
action with water of the group SO 4 , which cannot exist
uncombined.
SO 4 + H 2 O = H 2 S0 4 + O.
The evolution of oxygen gas, which is partially due to this
secondary reaction, is observed at the positive pole. Pri-
marily the water itself splits off oxygen in the electrolysis of
aqueous solutions.
* Some acids are not decomposed by the electric current ; e.g., silicic,
carbonic, and boric acids.
INTRODUCTION. 3
In the electrolysis of hydrochloric acid, the chlorine set
free at the anode reacts with water, forming hypochlorous
acid, chloric acid, perchloric acid, etc. Similar secondary
reactions are observed in the electrolysis of chlorides. If a
solution of ammonium chloride, for example, is submitted to
electrolysis the nascent chlorine acts on the un decomposed
salt, with the production, among other substances, of nitro-
gen, or nitrogen chloride. Haloid salts of the alkaline earths
show similar phenomena.
Nitric acid, on electrolysis, gives in the first place
SHINTO, = 4H 2 (cathion) + 8E"O 3 (anion).
The latter then splits up further:
4N 2 O 6 = 4^1,0. + 2O 2 (anion).
The oxygen is given off, while the anhydride forms nitric
acid again with water:
4N A + 4H 2 o = SHNO,.
The hydrogen, on the contrary, which appears as cathion,
is not set free but acts reducingly on the nitric acid present :
4H, + mro s = NH 3 + 3H a O.
In the presence of sulphuric acid, or a sulphate, this de-
composition is complete, the final product being ammonium
sulphate.
This decomposition of nitric acid is of practical importance
in chemical analysis. From a nitric acid solution which con-
tains copper and zinc, the former metal only is reduced ; this
fact can be utilized for the separation of the two metals. If,
4 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
now, the current is allowed to pass for a long time after the
reduction of the copper, the nitric acid is gradually converted
into ammonia, and the zinc then separates from the solution.
If the salts of metals which decompose water at ordinary
temperatures (alkalies and alkaline earths) are electrolyzed,
secondary reactions occur at the negative electrode :
K 2 SO 4 = SO 4 (anode),
K 2 (cathode),
(S0 4 + H 2 = H 2 S0 4 + 0),
K a + 2H.O = 2KOH + H a .
The decomposition products, then, are sulphuric acid and
oxygen at one electrode, potassium hydroxide and hydrogen
at the other. It must be borne in mind, however, that a
small portion of the hydrogen and oxygen formed owes its
existence to the primary electrolysis of the water.
The metals disengaged at the negative electrode may yield
secondary products by acting on the substances in solution.
So, for instance, in the electrolysis of cupric chloride, the
separated copper reacts with the cupric chloride to form
cuprous chloride; copper acetate yields, at the cathode, a
mixture of copper and cupric (or cuprous) oxide.
In the electrolysis of organic compounds, the groups set
free at an electrode may be decomposed in a manner analo-
gous to that noted in inorganic compounds, and yield various
products.
The electrolysis of potassium acetate should yield, as iinal
products, potassium (potassium hydroxide) and acetic acid.
Instead of this, the acetic acid splits either into carbon
dioxide and ethane, or ethylene is formed by the action of
oxygen on the ethane.
Potassium valerate yields, in addition to valeric acid,
INTRODUCTION. 5
carbon dioxide and octane; the latter is oxidized by con-
tinued electrolysis to isobutylene and water.
Sodium snccinate yields, among other products, ethylene
and carbon dioxide ; potassium lactate breaks up into carbon
dioxide and acetaldehyde.
For the purposes of quantitative chemical analysis, only
such solutions are adapted, as indicated by the foregoing, as
are decomposed completely by the current without the forma-
tion of injurious intermediate products. Solutions which
contain a free inorganic acid are well adapted to electrolysis,
because of their high conductivity.
Of all compounds of the metals, the double oxalates are
the best adapted to quantitative analysis.* Oxalic acid is
decomposed by the electric current :
C 3 H 2 O 4 = 2CO 2 (anode),
H 2 (cathode).
When potassium oxalate is subjected to electrolysis, the
principal decomposition -products are:
K 3 C,O 4 = 2CO 3 (anode),
K 2 (cathode),
K 3 + 2H a O = 2KOH + H 2 (cathode),
2KHO + 2CO, = 2KHCO 3 .
When ammonium oxalate is used, the decomposed solu-
tion contains hydrogen ammonium carbonate. The latter
partly decomposes into ammonia and carbon dioxide.
In the electrolysis of double oxalates, e.g., of zinc ammo-
* Classen, Ber. d. ch. Ges., 14, 1622, 2771; 17, 2467; 18, 1104, 1687; 19,
323 ; 20, 504 ; 21, 2900.
6 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
nium oxalate, decomposition takes place as follows : Zinc
oxalate breaks up into zinc and carbon dioxide, and ammo-
nium oxalate into ammonium and carbon dioxide. The car-
bon dioxide, which separates at the positive pole, combines
with the ammonium to form hydrogen ammonium carbonate,
as above explained.
In the decomposition of oxalates there are no unfavora-
ble secondary reactions. All oxalates are decomposed by the
electric current with greater or less ease, and the reduced
metals are not attacked by the decomposition-products, even
when the current becomes weaker during the reaction. When
the reaction is complete, the solution can be poured off at
once, and the weight of the separated metal determined. (See
further details later.)
THE ION THEORY.
Before proceeding to a description of the appliances and
methods of quantitative analysis, the reactions which take
place in solutions during their decomposition, together with
the magnitudes which here come into consideration, should
be made perfectly clear.
The ion theory, proposed in connection with the researches
of van't Hoff, by the Swedish investigator Arrhenius, furnishes
us with a comprehensive picture of the same. According to
this theory, a partial splitting up of the dissolved compounds
into their component parts takes place in aqueous solutions ;
a dissociation which, in contradistinction to the ordinary, is
called electrolytic dissociation.
In tlie case of a sodium chloride solution, for example,
many phenomena, such as the osmotic pressure, the lowering
of the freezing- point, and others, necessitate the assumption
that, besides the particles of undecomposed Nad, separate.
THE ION THEORY. 7
particles of "N& and Cl are present in the solution. The
latter are entirely different from atomic Na and Cl, since it
is of course impossible to conceive of a Na atom, which reacts
violently with water, as existing free in an aqueous solution.
The difference between these electrolytic dissociation
products and atoms lies in an unlike content of energy. This
of course materially affects the other properties.
While the atom in itself must be considered non-electric
(containing as much positive as negative electricity), it is
necessary to attribute a certain electric charge to the products
of electrolytic dissociation. These electrically charged par-
ticles are called ions (iovres, the wandering), a name given
to them by Faraday.
The phenomena of the osmotic pressure and the depression
of the freezing-point, already mentioned, have identified with
electrolytic dissociation, and accordingly with ions, certain
classes of chemical compounds, namely, acids, bases, and
salts, but not indifferent organic compounds. Since it has
been shown that the former compounds, and indeed only these
and no others, conduct the electric current in aqueous solu-
tions, the existence of ions and the characteristic of being decom-
posed by the electric current have been brought into causal
relation.
The substances which are electrolytically dissociated in
solution, and therefore conduct the electric current, are called
electrolytes ; those which are not dissociated into ions and do
not permit the passage of the current, non-electrolytes.
Acids, bases, and salts are accordingly electrolytes ; all other
substances, such as chloroform, benzene, ether, sugar, etc.,
non-electrolytes.
Relative to the formation of ions, all acids exhibit a com-
mon characteristic in yielding hydrogen ions ; correspondingly
all bases give hydroxyl ions.
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
An acid is accordingly dissociated as follows :
HC1
into
H
Cl .
H 2 S0 4
into
H 2
S0 4
HN0 3
into
H
N0 3
C 2 4 H 2
into
H 2
C,0 4
CH 3 COOH
into
H
CH 3 COO, etc.
By the electrolytic dissociation of acids, therefore, all of
those hydrogen atoms, which are replaceable by metals on
neutralization with bases, are brought into the state of ions ;
at the same time the corresponding acid radicals pass over
into the ionic condition.
The dissociation of bases is analogous :
JSaOH into Na OH
NH 4 OH into NH 4 OH
Ca(OH) 2 into Ca (OH),, etc.
All the hydroxyl groups, which are replaceable by acid
radicals on neutralization with acids, change to the ion con-
dition; and simultaneously the basic radicals, i.e., the metals.
Salts are accordingly dissociated into metal and acid ions.
When the current passes, a part of the ions migrate to the
positive electrode, a part to the negative electrode. Since the
ions possess an electric charge, those attracted by the positively
charged electrode must be negatively charged (anions), and
those attracted by the negative electrode positively charged
(cat/lions).
Hydrogen and all metals are electro-positive ; halogens and
acid radicals, electro-negative. The former are cathions, the
latter anions. Therefore when a salt of a metal is electrolyzed.
the metal separates at the negative electrode, the acid radical
at the positive electrode.
THE ION THEORY/S^f TAH ai\K^^ 9
It h&s been demonstrated that the electrolytic dissociation
increases with the dilution, and proportionally to it the elec-
trical conductivity of the ions also. Arrhenius therefore drew
the conclusion that the ions alone conduct the current, and that
the undissociated portion takes no part in the electrolysis.
This assumption has been proved correct, and through it elec-
trolytic dissociation presents an entirely different aspect.
The primary products which are set free at the electrodes
are not separated by the current , but existed previously in
the solution in the form of cathions and anions.
Since the substances separate at the electrodes in an atomic,
non-electric condition, while the ions possess an electric charge,
a discharge of the ions must take place at the electrodes. Such
is in fact the case. The negatively charged electrode attracts
the positively charged cathions, and on their coming into
contact a neutralization of equivalent parts of positive and
negative electricities takes place, accompanied by the dis-
appearance of electricity. The separation of the substance in
an atomic form is then possible. The work done by the elec-
tric current consists in the attraction and discharge of the ions,
but not in the decomposition of the dissolved compound.
What has been said of the cathion naturally applies in a
similar manner to the anion.
The degree of dissociation at a certain concentration [and
temperature] is a fixed magnitude for every substance. Here
the objection might be raised, for example, that in a copper
sulphate solution in which ^ of the copper sulphate is split up
into Cu and SO 4 ions and f is present as undissociated salt,
the electrolysis must come to a standstill after the third of the
copper has been removed, since there are no more copper
ions present. Experiment shows that all the copper may be
separated. This phenomenon is explained by the law of mass
action, according to which the product of the ion con-
10 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
centrations remains constant at a fixed concentration of the
solution. In other words, if copper ions disappear from the
solution owing to the removal of the metal, the undissociated
salt present dissociates and furnishes new copper ions. This
process continues until all the copper ions have been removed
by precipitation as atoms. What is true of copper sulphate
is true of all acids, bases, and salts, and anions behave similarly
to cathions.
FARADAY'S LAW.
This law, which is named from its discoverer and is the
basis of all electrolytic phenomena, includes the two following
propositions :
1. The quantities of ions separated at the electrodes during
equal intervals of time are directly proportional to the
current strength.
2. Equal quantities of electricity separate the ions in pro-
portion to their chemical equivalent weights.
The truth of the first statement may be readily demon-
strated by electrolyzing a copper sulphate solution for ten
minutes with a current of certain strength and determining
the weight of the separated copper. If now in a second
operation a current of twice the former strength be passed
through the same solution for an equal length of time, the
weight of the copper separated in the second case will be
twice as great as that precipitated in the first experiment.
The second proposition, called in brief Faraday's Law,
is proved experimentally by passing the same current simul-
taneously through a series of solutions of metallic salts and
weighing the quantities of metals which separate. It will then
be found that the weights are proportional to the chemical
equivalent weights of the metals. Accordingly solutions of
silver nitrate, cupric chloride, and ferric chloride when decom-
FARADAY'S LAW. 11
posed by the same current, yield precipitates of metals, the
weights of which bear the following ratio to one another :
108 - 63 - 55 ' 9
8 -" -~-
The ratio when silver nitrate, cuprous chloride, and fer-
rous chloride are used is correspondingly
108:63:^,
so that the equivalent weight is dependent upon the valence
of the metal in the compound employed. That which may
be conveniently carried out in the case of the metals, i.e.,
the cathions, holds true similarly in the case of the anions.
The law of Faraday, regarded in the light of the ion
theory, leads to a series of new conclusions. It declares that
equal currents of electricity always separate equal quantities
of univalent, half the quantities of bivalent, and one- third the
quantities of trivalent ions. This separation consists in the
discharge of the electrically charged ions ; therefore it follows
that equal quantities of univalent ions are the carriers of equal
electric charges, that the same quantities of bivalent ions bear
twice, of trivalent ions three times, as great charges.
Consequently all univalent ions, independent of their
chemical nature, bear equal quantities of electricity, all biva-
lent ions twice the quantity, etc. The magnitude of this
charge is considerable. Experiment has shown that by the
action of 96,500 coulombs of electricity on an electrolyte, a
quantity of ions equal in grams to their atomic weight divided
by their valence always passes over into the atomic condition,
or, as it may be stated, by 96,500 coulombs a gram equiva-
lent of ions will be discharged, or, better, neutralized on the
electrode. For this neutralization the ions must carry a
12 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
quantity of electricity equal, but opposite in sign, to that
supplied by the source of current to the electrodes. A gram
equivalent of ions must therefore be the bearer of 96,500
coulombs.* This conclusion, arrived at by v. Hehnholtz,
leads to the assumption that every bond of valence of an ele-
mentary or complex ion is charged with the same quantity of
positive or negative electricity, which, similarly to an electric
atom, cannot be further divided.
OHM'S LAW.
Ohm's Law holds good for solutions as it does for metals:
C = |, E = 0-K.
"When suitable units are chosen, the current strength is
equal to the quotient of the electromotive force divided by
the resistance.
The ampere serves as the unit of current strength, and is
that current strength by which, in one second, 0.328 nag. of
copper will be precipitated, f The unit of resistance is the
resistance (at 0) of a column of mercury having a length of
106.3 cm. and a cross-section of 1 sq. mm. It is called the
ohm. The unit of electromotive force is the volt, and is
defined by the equation
1 ampere X 1 ohm = 1 volt,
volt
ampere = , .
ohm
* " The quantity of electricity necessary for the separation of a gram
equivalent, i.e., 96,540 coulombs, is to be denoted by the symbol F, in
remembrance of Faraday." Report of Commission on Electrical Units,
Deutsche Elektrochemische Gesellschaft. Zeit. f. Elektrochemie, 1897-98,
p. 36. Trans.
f An ampere may be also defined as the strength of the current which
flows through a resistance of 1 ohm when the electromotive force is equal
to 1 volt. Trans.
TENSION AND ITS SIGNIFICANCE. 13
An electromotive force of one volt with a resistance of one
ohm gives a current strength of one ampere.
Every source of current furnishes a certain electromotive
force ; it possesses a certain tension. If the two poles of a
source of current are connected by a conductor, there takes
place along this connection a fall of potential which is pro-
portional to its resistance. If an electrolyte, into which ex-
tend two electrodes, is included in the circuit, there arises a
difference of potential between the electrodes which is called
the electrode tension. This tension at the electrodes is of con-
siderable importance in electrolysis, since it denotes that elec-
tromotive force which comes into action in the cell itself.
Each of the three factors given in Ohm's Law is of signifi-
cance for quantitative electrolysis ; we will next proceed to
their consideration.
TENSION AND ITS SIGNIFICANCE FOR ELECTROLYSIS.
As quantitative electrolysis is employed chiefly for the
determination of metals, it will be w r ell to here consider some
of the general properties of solutions of metallic salts.
In accordance with present theory, the origin of an electro-
motive force is explained as follows : If a strip of metal, zinc
for example, be dipped into an electrolyte, say zinc chloride,
the zinc ions present in the solution will have a tendency to
discharge their electricity upon the zinc and to pass over into
an atomic condition. This tendency may be considered as a
pressure directed from the liquid toward the metal, and is
known as the osmotic pressure of the ions. The metallic zinc,
however, exerts a pressure in the opposite direction, which is
due to the tendency of the zinc atoms to pass into the solution
and assume the condition of ions, and is opposed to the sepa-
ration of the ions already present, which strive to leave the
14 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
.electrolyte as atoms. This latter pressure is known as the
electrolytic solution pressure.
Since the ions are bearers of electric charges, it is evident
that the simultaneous action of these two pressure-forces is
intimately connected with the production of electricity, and
experience has taught that the electromotive force between
the liquid and the metal may be considered a function of these
two pressures.
Osmotic pressure of the ions and electrolytic solution pres-
sure cause currents in opposite directions. The positively
charged ions of the salt solution tend, as a result of the osmotic
pressure, to give up their charges to the exposed metal and to
charge this positive ; while, on the other hand, the electrolytic
solution pressure forces positive ions out from the metal and
into the solution, leaving an equivalent negative charge upon
the metal itself.
If a similar course of reasoning be applied to the case
where an electric current is passed between two platinum
electrodes which dip into a solution of a metallic salt, the
following conditions will be recognized. A definite difference
of potential will exist between the electrodes, as a result of
which metal will be separated on the negative pole, and, in
general, oxygen on the positive pole. As soon, however, as
the metal and oxygen have passed over into the atomic condi-
tion, the electrolytic solution pressure of each comes into
action and operates to drive them back into the form of ions.
An electromotive force opposed to that of the primary cur-
rent is thereby set up. This electromotive force, which may
under certain conditions have a tension higher than that of
the primary current, is the cause of a current called the
polarization current. Polarization must always appear when
unattacked electrodes, as those of platinum, which are exclu-
sively used in quantitative electrolysis, are employed.
TENSION AND ITS SIGNIFICANCE. 15
The tension required for electrolysis may always be deter-
mined from the consideration of the above conditions. It
must in all cases be greater than the resulting polarization
current, for otherwise, at the commencement of decomposition,
the electromotive force of the primary current would be
counterbalanced by the polarization tension and electrolysis
would be entirely prevented.
Le Blanc, who made a careful study of the values of the
tensions required for the decomposition of various solutions,
directed attention to the fact that for the continued electrolysis
of any solution a definite minimum tension, dependent directly
upon the polarization phenomena, is required.
This so-called decomposition tension value is often given
as a measure in quantitative electrolysis, and by it is denoted
that electromotive force at which the current is just able to
pass through the cell. If the electromotive force of the
primary current be denoted by E, the current strength by
C, the resistance by R, and the polarization tension by P,
then
E must satisfy this equation without C being equal to ;
then only can the current continuously decompose the solution.
Le Blanc determined the following values for the deeoin-
,ST
position tension of y solutions :
ZnSO 4 .............. 2.35 volts. Cd(NO,) a ............ 1.98 volts.
ZnBr a .............. 1.80 " CdSO 4 .............. 2.03 "
NiS0 4 .............. 2.09 " CdCl, .............. 1.88 "
NiCL, .............. 1.85 " CoS0 4 .............. 1.92 "
Pb(NO,) a ........... 1.52 " CoCl a ............... 1.78 "
AgNO, ............. 0.70 "
16 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ACIDS.
Sulphuric acid 1.67 volts. Pyroracemic acid 1.57 volts*
Nitric acid 1.69
Phosphoric acid. ...1.70
Monochloracetic acid 1.72
Dichloracetic acid .. 1.66
Malonic acid 1.69
Perchloric acid 1.65
Dextrotartaric acid . . 1.62
Trichloracetic acid... 1.51
Hydrochloric acid 1.31
Hydrazoic acid 1.29
Oxalic acid 0.95
Hydrobromic acid 0.94
Hydriodic acid 0.52
BASES.
Sodium hydroxide. . . . 1.69 volts. Methylamine 1.75 volts.
Potassium hydroxide. . 1.67 " Diethylamiue 1.68 "
N
Ammonium hydroxide 1.74 " ^- Tetramethyl ammo-
nium hydroxide.. 1.74 "
The sulphates and nitrates of the alkalies and alkaline
earths have all nearly the same decomposition tension value,
namely, about 2.20 volts.
The values of the decomposition tension for solutions of
metallic salts are of decided importance for quantitative
electrolysis, since by them is given the minimum tension re-
quired for the precipitation of a metal, and also the conditions
under which several metals may be quantitatively precipitated
from the same solution by simply altering the tension of
the current. For example, zinc is not precipitated from a
IS" r
ZnSO 4 solution by a current having a tension of less than
N
2.35 volts, while a silver nitrate solution is decomposed
at 0.70 volts. The silver may therefore be separated at a ten-
sion of less than 2.35 volts, the zinc remaining meanwhile in
solution. After the separation of the silver, the electromotive-
SIGNIFICANCE OF CURRENT STRENGTH. 17
force may be increased to over 2.35 volts and the zinc
precipitated as metal.
Kiliani, whose early death is to be greatly lamented, was
the first to point out the importance of the tension for elec-
trolytic separations. Somewhat later, Freudeiiberg, basing
his work on Le Blanc's studies, carried out, in Ostwald's
laboratory, a careful investigation of the exact relations. The
results which he obtained will be given in the Special Part, in
connection with the discussion of the determination and
separation of the respective metals.
SIGNIFICANCE OF CURRENT STRENGTH.
Although the choice of tension makes the electrolytic
separation of a metal possible, the condition of the resulting
precipitate is first of all dependent upon the strength of the
current which flows through the cell.
This follows from Faraday's law, since the number of
ions w T hich, by discharging on the electrodes, separate in the
atomic condition, in the unit time, depends solely on the cur-
rent strength.
Irrespective of the tension employed, a current of double
strength will precipitate twice the quantity of metal in the
same time. The current strength therefore determines the
number of ions which will discharge within a given time, and
correspondingly the rate of deposit on the electrode. With
relation to the latter, however, a second factor, namely, the
size and si i ape of the electrodes, is of decided importance,
since the manner in which the metal is deposited by a certain
current strength depends entirely on this. If the area of the
electrode surface is small and the current density great, the
individual atoms of metal are deposited one upon the other in
such rapid succession that the precipitate does not adhere
firmly to the electrode, but scales off. In quantitative elec-
IS QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
trolysis, the firm adherence of the precipitate to the electrode
is most essential for the determination of the weight of the
separated material.
When, on the other hand, a very large surface is offered
for the deposition, and a current of low current strength is
employed, it is impossible for a compact layer to form and
the metal will coat the surface in isolated patches. These
conditions of precipitation are also useless for quantitative
determinations.
The real significance of the current strength lies in its
ratio to the area of the electrode surfaces. This is known as
the current density, and as unit, a current strength of one
ampere for 100 square centimeters electrode surface, has been
chosen.
In this book, therefore, the current density will always be
given with reference to 100 square centimeters of electrode
surface, and will be expressed by the symbol ND ]00 .
If, for example, a current of 3 amperes flows through a
cell, the electrode surface of which is equal to 250 sq.cm., an
equal distribution of the lines of the electric current being as-
sumed, the current of 3 amperes will be distributed over the
250 sq.cm., and therefore every 100 sq.cm. receives a current
o
of ampere. The current density, therefore, ND 100 = 1.2
2 . 5
ampere.
Although the current strength is the same at every point
in the circuit, the current density of the cathode and anode
have the same value only when the two electrodes have
exactly equal dimensions.
In the determination of metals it is usually sufficient to
know the current density at the cathode alone. On the other
hand, to determine the halogens, for example, a knowledge of
the current density at the anode is required.
SIGNIFICANCE OF THE KESISTANCE. 19
The current strength, in the form of the current density,
accordingly occupies an important place in quantitative elec-
trolysis.
SIGNIFICANCE OF THE RESISTANCE.
The third factor in Ohm's Law, the resistance, is to be
considered chiefly in the selection of the solvent which will he
most suitable for the experiment, and the proper substances
to be added to the electrolyte.
It is evident that with a certain given tension, which in
very electrolysis may vary within certain limits, the speed of
the operation depends upon the resistance of the solution,
since by this the current strength is determined according to
the equation
E
It is therefore necessary to have the conductivity of the
solution as high as possible. Since aqueous solutions are ex-
clusively employed in quantitative electrolysis, this is accom-
plished by the addition of certain substances, the natures of
which are dependent upon the chemical properties of the metals
in the solution. In some cases acids are used ; in others,
bases or salts. The proper substances can only be determined
by experience.
A fundamental requirement of the substance added and
one which is independent of the chemical properties of the
metal to be precipitated may, however, be stated. It must
be a good conductor of the current and must form no decom-
position products which are insoluble or are detrimental to the
analysis. Alkalies and acids, which after their decomposition
are again regenerated at the electrodes, are therefore suitable,
20 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
as are also organic acids, the decomposition products of which
are given off in a gaseous form. This last condition is fulfilled
by oxalic acid, which, on account of its great solubility, is of
special importance in the electrolysis of metals, particularly in
the form of double salts.
[A few words on the theory of the conductivity of solu-
tions will perhaps be in place here. Since the passage of
electricity through an electrolyte is always accompanied by the
transference of material, the power which a solution has for
conducting the electric current must depend directly upon the
nature of the substances which are held in solution. As has
already been stated, the ions alone are bearers of electric
charges, the undissociated molecules taking no part in the
transportation of electricity. The conductivity of a solution
therefore depends upon the number of ions which it con-
tains, and upon the nature of the ions themselves. If, in two
equal volumes of a solution of the same substance, one contains
twice as many ions as the other, the other physical conditions of
both being the same, the conductivity of the former will be
twice that of the latter.
The ratio of the dissociated part to the total amount of
substance present is called the degree of dissociation. The
degree of dissociation varies for different substances, but in
all cases for fairly concentrated solutions increases with
dilution. For very concentrated solutions the degree of dis-
sociation is very low. Concentrated sulphuric acid, for
example, is practically a non-conductor, although a dilute
solution of the same possesses a relatively high conductivity.
The ease with which a current can pass through a cell
containing two electrodes immersed in an electrolyte depends
then upon the distance by which the electrodes are separated,
and upon the number and nature of the ions which are be-
tween them.
THEORY OF ELECTROLYTIC PRECIPITATION. 21
The resistance of the cell may be decreased in a variety
of ways. For example, a substance possessing a high degree
of dissociation may be added to the solution, and, provided
that it does not materially influence the degree of dissociation
of the substance already present, the number of ions between
the electrodes will be accordingly increased, and thereby the
conductivity of the solution. The solution may also be
warmed. The effect of this is generally to slightly increase
the degree of dissociation, but more especially to decrease the
viscosity of the solvent, as a result of which the ions experi-
ence less resistance to their movements through the solution,
and the passage of the current is thus expedited. Another
means at hand is to diminish the distance between, or to in-
crease the size of, the electrodes. The effect of the former is
readily understood, and by the latter a greater number of ions
are brought within the sphere of action.
A word more as to the influence of ions themselves.
Since the electricity is transported by the ions, the fate of
migration of the same must be ar^ important factor of the
conductivity. Hydrogen of all ions has tke highest velocity of
migration. Accordingly all highly dissociated acids are good
conductors. The hydroxyl ion comes next, which explains
the relatively high conductivity of the bases. The conduc-
tivity of a solution is indeed nothing more than a function
of the rates of migration of the cathion and anion. Trans.~\
THEORY OF ELECTROLYTIC PRECIPITATION.
When viewed from the standpoint of the theory of elec-
trolytic dissociation the processes of quantitative electrolysis
may be generalized as follows. Quantitative determinations
may be divided into two classes according to whether the de-
termination of a cathion (metal) or an anion (halogen or
22 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
metal peroxide) is concerned. What takes place in the former
case is evident without further explanation. The metal ions.
migrate in the direction of the positive current, to the
cathode ; discharge, and separate on the electrode in the form
of a smooth metallic coating. The halogens may be separated
in a similar manner ; but since some of them are gaseous or
liquid, it is not practical to weigh them directly. Instead,
therefore, of using inert platinum electrodes as are used with
metals, silver electrodes are employed. With these the
halogen atoms combine, at the moment of discharge, to form
halogen silver compounds which adhere firmly to the elec-
trode. The increase in weight of the electrode gives directly
the quantity of the halogen which has separated.
The process in the separation of metal peroxides (only
lead and manganese peroxides will be here considered) is.
somewhat more complicated. Formerly the formation of
PbO a and MnO 2 was attributed to an oxidation brought about
by the electrolytically generated oxygen. The investigations,
of Liebenow* and Lobf have made it appear that lead peroxide
ions and manganese peroxide ions are already present in the
solutions. Since the peroxides separate from strong nitric
acid solutions, it must be assumed that through the oxidizing
power of this acid oxygen ions are formed in the solutions,
and that these combine with the lead or manganese ions to-
form peroxide ions. Since in the peroxides of the bivalent
metals the two positive charges of the metal are combined
with the four negative charges of the two oxygen atoms, the
resulting peroxide ion therefore possesses two negative charges
and consequently behaves like a bivalent anion. It is precipi-
tated on the positive electrode as a smooth, adherent coating
* Zeitschr. f. Electrochemie, 1895-96, pp. 420, 653.
fZeitschr. f. Eleclrocbemie, 1896-97, p. 100.
DETERMINATION OF THE CURRENT MAGNITUDES. 23
in a form similar to that of a metal. The details of the reac-
tions will be given in the Special Part.
From what has been said, the necessity of accurate data in
the performance of electro-analyses is obvious, for unless all
the important conditions are determined and recorded the ex-
periment cannot be accurately repeated.
Since the determination of the resistance of the liquid in
the cell is beyond the scope of analytical work, therefore, in-
stead of this, the exact volume and composition of the solu-
tion, as well as the size and shape of the electrodes, must be
stated. In addition to this the tension at the electrodes, the
current strength as read directly on the amperemeter, and the
calculation of the current density from the current strength,
for the electrode on which the quantitative precipitation has
taken place, must be given. All electrical relations are influ-
enced by the temperature, so that an exact knowledge of this
is most essential. The length of time required for the elec-
trolysis and the nature of the source of current having been
specified, all adequate and necessary data are at hand to enable
every one to repeat the analysis under exactly similar condi-
tions.
DETERMINATION OF THE CURRENT
MAGNITUDES.
1. MEASUREMENT OF THE CURRENT STRENGTH.
The current strength is measured either by means of the
chemical or the electromagnetic action of the current. The
chemical instruments are the oxyhydrogen gas voltameter and
the weight voltameter ; the first of which depends upon the
volume of gas produced, the second upon the weight of
metal precipitated.
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
THE OXYHYDROGEN GAS VOLTAMETER.
The construction of the apparatus is shown in Fig. 1.
The cylindrical vessel g is partly filled with pure dilute 33
FIG. 1.
per cent sulphuric acid. The platinum wires d and d' welded
to the platinum strips p and p* are fused into the walls of
the vessel g. This latter stands in a large cylinder C of water
which serves to cool it. The platinum wires end in the screws
*In the apparatus used by the author, the platinum electrodes are
31 X 13 mm., aiid are distant from each other 20 mm.
THE OXYHYDBOGEN GAS VOLTAMETER. 25
s and s', wliich are connected with the battery. The oxy-
hydrogen gas, as it is formed, passes through the tube /, which
contains a little water, and is then collected in the measuring-
tube K, which is graduated into -^ cc, and filled with water.
To measure an electric current with the voltameter, the water
over which the gas is collected is first saturated with oxyhy-
drogen gas, and then, by the use of a watch with second-hand,
the volume of gas is observed which the current yields in a
minute, or, if the current is weak, in a longer time. To
compare observations, the volume should be reduced to
and 760 rnm. pressure.
v = observed volume of oxy hydrogen gas ;
v l = normal volume (at and 760 mm.);
t observed temperature ;
h pressure reckoned in mm. of mercury.
1 + 0.00367* '760*
Let I indicate the height of the column of liquid, s the
density of the liquid, and I the barometric height ; then
h = b - I
-x-
13.6*
The oxyhydrogen gas voltameter, which unfortunately is
still frequently used, is quite unsuited to the purpose for
which it is intended, since, among other disadvantages, it
possesses a high tension which under some circumstances may
be much greater than that of the experiment. In addition to
this, the comparison of measurements made with different oxy-
hydrogen gas voltameters is only possible when the instru-
* 13.6 sp. g. of mercury
""HF^
UNIVERSITY
^CALIFOR^,
26 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ments correspond absolutely with one another in construction,
a condition not possible in practice.
THE WEIGHT VOLTAMETER.
The weight voltameter, which is used in the form of a
copper or silver voltameter, has
found quite as little application in
electrolytic laboratories. Its con-
struction is given in Fig. 2.
Both methods have been sup-
planted by the electromagnetic
measuring instruments, some of
which make use of the deflection of
the magnetic needle caused by the
current, and others of the magnetic
properties induced in a soft iron
core. To the former class belong the
sine and tangent galvanometers ; to
the latter, the instrument most used
in practice, i.e., the amperemeter.
FIG. 2.
THE TANGENT GALVANOMETER.
In the tangent galvanometer (Fig. 3) there is a small mag-
net which has its plane of swing horizontal and at right angles
to the plane of a ring shaped circuit. The actual position of
the magnet when at rest, as well as that of the plane of
the windings of the circuit, is the magnetic meridian.
When a current flows through the wire ring, there results
a deflection of the magnetic needle, the amount of which
depends upon the strength of the current and the number
of windings. If H denotes the horizontal component of
THE TANGENT GALVANOMETER. 27
the earth's magnetic field, n the number of turns of wire in
the ring, r the radius of the ring, and the angle of deflection
FIG. 3.
caused by the current, then the current strength
C = H tan0.
n
is a constant for each instrument, which may be
determined by connecting it witli a source of known current
strength, according to the equation
r C
n H tan
28 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
The current strength to be determined may then be easily
found ; it is C = K H tan (p.
THE SINE GALVANOMETER.
The sine galvanometer (Fig. 4) differs from the tangent
galvanometer in that the plane of the windings is not fixed in
the meridian, but is turned in the direction of the needle dis-
FIG. 4.
placed by the current, until the position of the latter again
corresponds with the plane of the circuit. The angle through
which the current circle has been turned from its original
position in the magnetic meridian is then read off. The cur-
rent strength is
C = K - H - sin 0,
where K denotes the constant reduction factor of the instru-
ment.
OTHER FORMS OF GALVANOMETERS.
OTHER FORMS OF GALVANOMETERS.
The galvanometers which are used for making the most
accurate measurements depend likewise upon the displacement
FIG. 5.
of the magnetic needle by a circular current. Here, however,
the needle is suspended by a fine cocoon fiber, between spools
containing a very large number of turns of wire. In order to
remove the magnet from the influence of the earth's magnet-
ism, a pair of so-called astatic needles are frequently em-
30
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ployed. Two exactly similar magnets are rigidly connected
with one another, so that the north pole of the one is situated
exactly over the south pole of the other, and correspondingly
the south pole of the first above the north pole of the second.
By this arrangement the effect of the earth's magnetism is
neutralized by the two needles.
FIG. 6.
FIG. 7.
The angle of displacement is read by means of a telescope
and a mirror which swings with the needle. The scale,
which is rigidly clamped to the telescope, shows the divisions
which correspond to the deflection of the needle.
Figures 5 and 6 show two practical galvanometers.
The effect of the magnetism induced in a soft-iron core is
made use of in the two instruments, most useful for electrol-
SPRING GALVANOMETER AMPEREMETER. 31
jsis; the Kolilrauscli spring galvanometer and the ampere-
meter (often called ammeter).
THE SPRING GALVANOMETER.
In this apparatus of Kohlrausch (Fig. 7), a hollow cylin-
der of sheet iron is suspended within a vertical solenoid
by a spiral spring. When a current is passed through the
instrument, the iron cylinder is drawn down into the solenoid
until the force of attraction is equalized by the tension of the
spring. A small pointer attached to the spring moves over a
scale which is empirically graduated and gives the current
strength directly in amperes.
THE AMPEREMETER.
In the amperemeter (Fig. 8) the solenoid is usually placed
horizontal and carries eccentrically a bent piece of thin sheet
FIG. 8.
iron which is provided with a long pointer. This pointer
moves over a scale. These instruments under suitable con-
ditions are extraordinarily sensitive.
32 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
2. MEASUREMENT OF THE TENSION.
For measuring the tension a great number of instruments
are in use, the application of which depends upon the fineness
of the measurement which is to be carried out. Two instru-
ments are employed in electrolysis, the voltmeter and the
torsion galvanometer, while for exact determinations of dif-
ferences of potential, especially small ones, the Lippmann
capillary electrometer and the quadrant electrometer, lately in
the form improved by Nernst, have been generally adopted.
THE VOLTMETER.
Since, according to Ohm's Law, E = C E, every measure-
ment of tension may be referred to a measurement of the
current strength provided that the resistance R remains con-
stant. This is done in the voltmeter, which has the external
form of an amperemeter, by giving the solenoid a very high
resistance, 1000 ohms for example. In this way, the resist-
ance of the connecting wire may be left out of consideration,
and the fall in tension is confined practically to the coils of
the solenoid alone. Further, the voltmeter is always connected
on a shunt circuit.
If the resistance in this shunt is low, then the greater part
of the current passes through it, causing a fall to take place
in the tension at the cell under measurement. The cor-
responding value obtained for the tension will therefore be
too low.
If, however, the resistance of the voltmeter is very high,,
then the current will pass through the cell with almost un-
altered tension and only an extremely small fraction will go
through the measuring instrument itself. The scale is so
THE TORSIOX GALVONOMETEK. 33
constructed with reference to the resistance that the amperes
are converted directly into volts,
according to the equation, which
for the solenoid mentioned would
be
E = 1000 -C.
A most excellent form of
apparatus is the voltmeter of
Weston (Fig. 9). This gives the
value accurately to -^ volt and
allows of approximation to T fg- volt. A mirror, placed below
the scale over which the pointer moves, prevents parallax
in reading.
THE TORSION GALVANOMETER.
The principle of this instrument is electromagnetic.
A light bell magnet swings between two parallel and perpen-
dicular coils containing many windings of wire. These two
spools are so connected with one another that the current
flowing through each of them tends to deflect the magnetic
needle in the same direction. The magnet, the swinging of
which is usually retarded by copper damping, is suspended
from the cover of the case by a spiral spring. To this spring
a horizontally moving pointer, which is just beneath the glass
cover of the instrument, is attached. A second pointer is
fastened directly to the magnet.
The instrument is used as follows : By revolving the case
the needle is brought into the magnetic meridian, so that the
two pointers correspond to the zero point of the scale on the
glass cover. Care must be taken that the magnet swings
entirely free, which is insured by setting the instrument
exactly horizontal by means of the foot-screws. If the
34
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
binding-screws of the galvanometer are now connected with
the source of current or with the cell, the tension of which is
to be determined, the magnet will be deflected from its
position of rest and the pointer attached to the spiral spring
must be turned a certain distance in order to bring the pointer
rigidly connected to the magnet back to the zero point on
FIG. 10.
the scale, and thereby to return the magnet itself to its former
position. In this operation the pointer fastened to the top of
the spiral spring has been moved through a certain number
of divisions on the scale, and this scale is empirically calibrated,
so that by the position of the pointer the tension is given in
_i_ volt. By interposing resistance, the sensitiveness may be
THE LIPPMANN CAPILLARY ELECTROMETER. 35
so decreased that the divisions correspond to tenths or to
whole volts. Fig. 10 shows a torsion galvanometer of the
type manufactured by Siemens & Halske (Berlin).
The principle of the construction of the instrument is
similar to that of the voltmeter. The deflection of the needle
is of course proportional to the current strength, but since the
resistance of the spool windings is very high and remains
constant, a strict proportion exists between the intensity and
the tension, so that the direct reading in volts is made possible
by the use of the equation
THE LIPPMANN CAPILLARY ELECTROMETER.
This instrument is chiefly employed in the measurement of
electromotive forces by the Poggendorf compensation method,
most practical in the arrangement described by Ostwald.
In this a known electromotive force is opposed to the one
which is to be measured, and the former is modified through
alterations of the resistance by certain known amounts, until
the two electromotive forces are equal and compensate one
another.
In practice, an element of known electromotive force is
so connected with a resistance-box, which contains for
example 1000 ohms, that the whole fall in potential takes
place through the 1000 ohms. Every resistance of 10 ohms
is provided with a clamp to which a wire may be connected.
If the known electromotive force is for example 1 volt, this
will be distributed over the resistance in such a way that the
1000 ohms will represent a fall of 1 volt, every 100 ohms
one of 0.1 volt, and every 10 ohms one of 0.01 volt. The
electromotive force to be measured is now connected with the
36 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
two clamps of the resistance-box in such a manner that it will
be opposed to the known electromotive force and the resist-
ance between the two clamps is varied, until the two electro-
motive forces are equal and compensate one another. If, for
example, the resistance between the clamps is 100 ohms, then
the electromotive force to be measured is equal to 0.1 volt, for
110 ohms it would be 0.11 volt, for 120 ohms 0.12 volt, etc.
In order to determine when the electromotive force which
is being measured is equal to the opposed electromotive force,
a Lippmann electrometer of the form given by Ostwald * is.
employed. (Fig. 11.)
FIG. 11.
' ' A platinum wire, partly encased in a glass capillary,
leads from an insulated binding- screw and extends into the
mercury at the bottom of the bulb 5, which also contains
above the mercury a 10 per cent sulphuric acid solution.
The capillary tube c opening into the bulb ~b is filled in its
upper part with acid ; its lower part contains mercury, like-
wise the tube d, which is in connection with a second binding-
screw. The position of the mercury in the capillary tube o
may be regulated through altering the inclination of the capil-
lary by means of the screw at /. That this apparatus may
*Ztschr. f. pbys. Chem., 1890, p. 471.
THE QUADRANT ELECTROMETER. 37
give satisfactory results it should be short- circuited just before
use, and consequently it was connected with a switch so con-
structed that on breaking the current the electrometer was always
short-circuited, and on making the current this connection
within itself was destroyed . In measuring electromotive forces,
so much of the resistance of the box was brought between the
movable clamps that the mercury remained at rest on closing
the circuit. A millimeter scale placed beneath the capillary,
and a lens above it, aided in the reading. It w r as possible
to approximately estimate to a thousandth volt. One hun-
dredth volt corresponded to 3 divisions on the scale."
The Lippmann capillary electrometer, the theory of which
cannot be entered upon here, depends upon the fact that the
surface tension of mercury alters under varying electrical con-
ditions. When the two opposed electromotive forces are
equal, then the mercury is electrically neutral and the menis-
cus returns to its normal position.
THE QUADRANT ELECTROMETER.
The quadrant electrometer, which was constructed in the
most varied forms by "W. Thomson and 'is very generally used
for the measurement of potentials, has the following general
construction.
Four separated sectors of a flat, cylindrical metal box rest
upon four insulating glass supports. Each of these sectors is
called a quadrant. Each pair of oppositely located quadrants
is in metallic connection. Within the hollow space formed by
the four quadrants the so-called needle, a thin, horizontal plate
of aluminium, is suspended by a fine wire which also carries
a mirror for reading. A wire leads from the needle to a vessel
filled with sulphuric acid, situated beneath the quadrants.
In using the instrument, the aluminium needle is charged
to a comparatively high potential by connecting it with some
38
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
FlG. 12.
source of electricity, usually a Leyden jar, through the wire
dipping into the sulphuric acid. One pair
of quadrants is then grounded, and the
other pair is connected to one pole of the
electromotive force to be measured, the
second pole of the electromotive force being
connected with the earth. So long as all the
quadrants have the same potential, the
aluminium needle remains at rest ; the
difference between the potential of the earth
and the one under consideration is deter-
mined from the deflection of the needle
measured by means of the mirror and scale.
Nernst and Dolezalek * have made the
employment of this instrument more simple
and accurate. They avoid the operation of
charging the aluminium needle before use,
by employing a small perpendicularly hung
Zamboni pile having a tension of about
1400 volts. (Figs. 12 and 13.)
A small Zamboni pile Z, suspended by
the quartz fiber /*, has fastened to its two-
poles the electrometer needles N, and N 2 ,
which swing in the quadrant boxes Q, and Q 3 , placed one
above the other.
The measurement of a difference of potential is carried
out by comparing the instrument with a normal tension, or by
the compensation method.
SOURCES OF CURRENT.
Two classes of current supply are employed in electrolysis,,
chemical and physical. The first class is represented by the
*Ztschr. f. Electrochemie, 1896-97, p. 1.
FIG. 13.
LECLANCHE CELL.
39
galvanic elements, which are further divided into primary
and secondary elements, according as the difference of poten-
tial is directly due to a chemical reaction or to a polarization
current (accumulators).
To the second class belong the electromagnetic machines
and thermopiles. The most important apparatus will be
briefly described in the following section.
1. PRIMARY GALVANIC ELEMENTS.
LECLANCHE CELL.
This is a one-fluid cell using a solution of ammonium
chloride, which surrounds the negative pole, the zinc. The
FIG. 14.
cell is much used in the form shown in Fig. 14:. In the jar,
which is square in section, with a rounded projection at
40
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
one corner, stands a porous clay cup, from which projects a
block of carbon K surrounded by coarsely pulverized man-
ganese dioxide, or a mixture of manganese dioxide and retort
carbon. In the projecting rounded corner is a stout rod Z
of amalgamated zinc. The carbon and zinc are both provided
with binding screws, and are immersed in a concentrated
solution of ammonium chloride.
Leclanche* also uses, in place of the powdered man-
ganese dioxide, compressed prisms (shown in Fig. 15) con-
FIG. 15.
sisting of 40 parts manganese dioxide, 55 parts gas carbon,
arid 5 parts shellac ; a little potassium sulphate is also
added to increase the conductivity. The porous cup is
thus dispensed with. This cell has an electromotive force of
1.48 volts.
MEIDINGER CELL.
41
MEIDINGER CELL.
In contrast to the Leclanche* cell, that of Meidinger con-
tains two liquids, solutions of magnesium and copper sul-
phates. The element is constructed as follows : In the glass
vessel G (Fig. 16) stands a smaller glass #, and in this a
copper cylinder K to which an insulated copper wire D is
fastened.
A second cylinder Z of zinc, to which the projecting wire
D 1 is fastened, is placed in the upper part of the vessel G.
The balloon-shaped glass
B, filled with crystals of
copper sulphate, closes the
cell. The cell is filled to
about three-fourths of its
capacity w r ith a solution
of 1 part crystallized mag-
nesium sulphate in 7 parts
of water ; and the balloon-
shaped flask containing
copper sulphate is filled
up with water, closed with
a stopper fitted with the
glass tube r, and, as the
FIG. 16. cut shows, inverted in
the cell.
Electromotive force about 1 volt.
42 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
DANIELL CELL.
In a jar of glass (Fig. IT) is a porous clay cup T, and in
this a cylinder of cast zinc, the negative pole (Fig. 18). The
FIG. 17. FIG. 18.
porous cup is surrounded by a cylinder of sheet-copper K>
the positive pole.
The cylinder of amalgamated zinc * stands in dilute sul-
* The zinc is easily amalgamated by plunging it into mercury, on the
surface of which a little hydrochloric acid has been poured. The amalga-
mated cylinder is then placed in a vessel of water to remove the hydrochloric
acid, and allow the excess of mercury to drop off.
DANIELL CELL. 43
plmric acid (1 : 20), and the copper cylinder in a solution of
copper sulphate ; the sulphuric acid may be replaced by a
solution of zinc sulphate.
The element has an electromotive force of 1.079 volts.
[The modification of the Daniell cell known as the gravity
cell is the form commonly in use for telegraph batteries in
this country, and is the cheapest and most convenient cell
for constant batteries to yield currents of moderate strength
in scientific laboratories. It is very generally thus used.
The copper is placed at the bottom of the jar ; an insulated
copper wire is riveted to it, long enough to pass up through
the solutions and connect with a binding screw on the zinc
of an adjacent cell, or with the wire which serves to conduct
the current to the solution for electrolysis. The bottom of
the jar, about the copper, is filled with copper sulphate ; the
zinc, a heavy casting with large surface, is suspended a few
inches below the top ; and the jar is filled with water some-
times acidulated with sulphuric acid. After standing a few
hours, the copper 'sulphate dissolves ; copper is precipitated,
and zinc dissolved ; and the jar, in its normal working state,
thus contains two solutions ; the heavier, of copper sulphate,
below, and the lighter, of zinc sulphate, above. The porous
cup of the Daniell cell is thus dispensed with, and the zinc
does not require amalgamation.
The cut (Fig. 19) shows one of the simplest gravity cells,
having the zinc in the so-called " crow-foot " shape, hanging
directly on the edge of the jar, and furnished with a binding-
screw.
The outfit of the chemical laboratory of the Pennsylvania
State College, while under the translator's charge, was found
44
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
convenient, and sufficient for the needs of an ordinary labora-
tory for instruction. Some twenty "crow-foot" gravity cells
were kept in working condition, and eight Grove cells could
be set up if needed for a strong current. Four sets of con-
necting-wires were run from the battery-room to the labora-
tory desk set apart for electrolytic work, each set being so
arranged with binding-screws as to be quickly connected with
any desired number of cells. (See under " Secondary Bat-
teries," p. 47.) Trans.']
FIG. 19.
GROVE CELL.
The positive pole is a sheet of platinum foil of the form
shown in Fig. 20 ; this is placed in a porous cup filled with
nitric acid. The negative pole is a cylinder of amalgamated
zinc placed in a glass jar containing dilute sulphuric acid
(1 : 20). Fig. 21 shows the arrangement of the cell.
Electromotive force 1.81 volts.
BUNSEN CELL.
45
FIG. 20.
FIG. 21.
BUNSEN CELL.
In the Bunsen cell, the platinum is replaced by a prism
of retort carbon (Fig. 22) standing in a porous cup filled with
nitric acid. The negative electrode, as in the Grove cell, is
a cylinder of amalgamated zinc placed in a glass jar filled
with dilute sulphuric acid (1 : 20). The screw-clamp shown
in Fig. 23 is often used to fasten a metallic connection to the
carbon prism. It has, however, the disadvantage that the
clamp is quickly oxidized by the decomposition products of the
nitric acid, and the contact thus broken. It is better, there-
fore, to insert in the carbon a metallic socket (Fig. 24), the
stem of which is closely covered with platinum foil.
46
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Fig. 25 shows the Bimsen cell in its most common form.
Electromotive force 1.80 volts.
FIG. 22.
FIG. 23.
FIG. 24.
FIG. 25.
CUPRON ELEMENT.
A copper oxide plate and a zinc plate dip into an aqueous
sodium hydroxide solution, as shown in Fig. 26. When a
current is produced the following re -
actions take place :
II. CuO + 2H = Cu + H 2 O.
The current ceases as soon as all
5 the copper oxide is reduced or all the
zinc is dissolved. In the type intro-
FIG. 26. duced on the market by TJmbreit &
Matthews (Leipzig), when the copper oxide plate has been
FIG. 27.
GALVANIC SECONDARY ELEMENTS. 47
reduced it may be reconverted into copper oxide by allowing
the plate to stand for 15 hours in a warm place.
The element has an electromotive force of 0.8 volt, with
an internal resistance of 0.05 ohm.
[EDISON-LALANDE ELEMENT.
This element, having a form differing
somewhat from the above cuprori element,
but depending for the production of the
current upon a similar chemical reaction,
has come largely into use in the United
States.
Elements of this type, with capacities of
from 50 to 600 ampere-hours, are manufactured, and furnish
a very convenient primary source of electricity. (Fig. 27.)]
GALVANIC SECONDARY ELEMENTS.
(ACCUMULATORS, OR STORAGE BATTERIES.)
While the primary elements previously described furnish
electrical energy through chemical reactions which involve a
gradual using up of their component parts, the characteristic
of accumulators lies in the fact that by passing an electric
current through them they are brought into a condition which
makes it possible for them to furnish a polarization current,
and thereby to return to their original condition. Elements
of this class are called reversible elements.
Accumulators are therefore instruments which alternately
convert chemical energy into electrical energy, and electrical
energy into chemical energy.*
The principle of their construction depends upon the
behavior of lead plates in dilute sulphuric acid on the passage
of a current. If we have two such plates dipped in sul-
* Elbs, Die Akkumulatoren, 1896.
48
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
phuric acid, one serving as cathode, the other as anode, it
will be observed, upon closing the current, that a brown coat-
ing forms upon the positive electrode, spongy lead separating
out at the same time on the negative plate. This phenome-
non is due to the formation, at both poles, of a saturated solu-
tion of lead sulphate, the lead ions of which discharge upon the
cathode as spongy lead, while at the anode the lead and oxygen
ions separate in the form of lead peroxide. If the primary
current be broken and the polarization current allowed to
discharge by establishing metallic connection between the two
plates, the following reaction takes place : The sulphuric acid
dissolves the spongy lead at the negative pole ; the hydrogen
ions thus made available migrate to the anode with their posi-
tive charges and reduce the lead peroxide there present to
lead oxide, which again forms lead sulphate with the sulphuric
acid. As soon as all the spongy lead is dissolved and all the
lead peroxide is reduced, the polarization current ceases, the
accumulator is discharged, and the original condition is again
reproduced. By means of a new primary current (charging
current) the accumulator may be again brought into an avail-
able condition.
Jar.
Anode.
Anode Plates.
Cathode Plates.
Cathode.
FIG. 28.
In the construction of accumulators, the longest possible
continuation of the polarization current is aimed at, together
with the lowest possible internal resistance of the element.
The electromotive force between lead and lead peroxide in
dilute sulphuric acid is approximately 2 volts. In order to
GALVANIC SECONDARY ELEMENTS.
49
arrive at the most practical construction, a number of parallel
plates are metallically connected together and hung as cathodes
in a trough containing sulphuric acid. Similarly, an equal
number of anode plates are hung in and so arranged that each
cathode plate is between two anode plates and vice versa, each
anode between two cathode plates. (Fig. 28. View from
above.)
The time required for charging depends upon the area of
the plates and the condition of the spongy lead and lead per-
oxide. In order to satisfy all requirements the so-called
PIG. 29.
FIG. 30.
" active material " (i.e., the spongy lead and lead peroxide) is
attached to a solid lead frame by the employment of a series of
processes (''forming," etc.), which
cannot be discussed here. Fig. 29
shows a negative, Fig. 30 a positive
plate, while Fig. 31 gives an accumu-
lator of the form commonly used.
The first experiments with accumu-
lators for the purposes of quantitative
analysis were conducted in the Aachen
laboratory, with apparatus especially
constructed by Professors Farbaky and
Scheneck * in Schemnitz (Hungary). Fio. 81.
* Compare Ueber die elektrischeu Akkumulatoren von Farbaky und
50 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
These gentlemen had the kindness to place two accumu-
lators at the author's service for testing, and he made his
first experiments in 1888, working with R. Schelle, at that
time professor in the Schemnitz Royal School of Mines.
These accumulators have 6 negative and 5 positive lead-plate
electrodes, each 6 mm. thick. The weight of the electrodes
is 15.5 kg., the volume of the 33$ sulphuric acid 3.5 1., the
total weight of each cell 35 kg. The active surface of the
electrodes is 3133 sq. cm., so that the internal resistance is
very low, measuring between 0.0166 and 0.017 ohm. The
accumulators can be charged at a 20 to 25 ampere rate, and
yield in discharge at 23, 30, 40, and 60 ampere rates respec-
tively 150, 148, 140, and 125 ampere-hours, with a fall of
not over 10$ in the voltage. If the discharge is lighter, and
the fall in the electromotive force less than for lighting pur-
poses, as in electrolytic analyses, an accumulator may yield
over 250 ampere-hours.
Two such accumulators were fully charged, until OH gas
was obviously disengaged, by a current of 20 to 25 amperes
from the dynamo. The current was measured by a Kohlrausch
galvanometer, made by Hartmann & Braun, Bockenheim,
Frankfurt a. M. , the scale of which read from to 60 amperes.
A second Kohlrausch amperemeter, divided from to 15 am-
peres, was used to measure the current taken from the accu-
mulators for the analyses.
A Siemens torsion galvanometer showed a tension, for each
charged accumulator, of 2.05 volts.
By the use of these two accumulators, four to eight analyses
were carried on simultaneously, and the accumulators kept in
Scheneck (Dingier polyt. Journ., 257, 357); further, Bericht tiber die Ak-
kumulatoren von Farbaky und Scheneck von A. v. Waltenhofen. Zeitschr.
f. Elektrotechnik, 1886.
GALVANIC SECONDARY ELEMENTS. 51
constant use day and night, except for the short intervals
needed to change the solutions for analysis.
The results of analyses extending over a period of six days
are subjoined.
FIRST DAY.
Tension 2.55 volts.
Determination of Copper from Nitric-acid Solution.
Taken CuSO 4) 5H 2 O. Found Cu.
4.0140 g 1.0170 g = 25.33^
4.1376 " 1.0480 " = 25.33
2.2340 " 0.5661 " = 25.34
2.3575 " 0.5978 " = 25.35
Tin from the Acid Ammonium Double Oxalate.*
Taken 8nCl 4 2NH 4 Cl. Found Sn.
1.8450 g. 0.5964 g. =32.33
2.0210 0.6548 " =32.39
Antimony from Solution in Sodium Sulphide. f
Taken Sb 2 S 3 . Found Sb.
0.2404 g. 0.1720 g. = 71.50
0.2551 " 0.1827 = *1.60
* Classen's method : see Tin.
t " ""... " Antimony.
52 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
SECOND DAY.
Tension 1.95 volts.
2.0490 g.
NiS0 4 +(NH 4 ) 2 S0 4 ,6H 2 gave 0.3053 g.
Ni = 14.90^*
2.0180 "
" 0.3000 "
" =14.91
2.3400
CoSO 4 + K 2 SO 4 ,6H 2 O " 0.3440 "
Co = 14.70f
2.1200 "
" 0.3120 "
" =14.71
1.8920 "
FeSO 4 +(NH 4 ) 2 SO 4 ,6H 2 O " 0.2697 "
Fe = 14.25^
2.1240 "
" 0.3027 "
" =14.25
1.0
CuSO 4 ,5H 2 O " 0.2533 "
Cu = 25.33^
1.0
" 0.2533 "
" =25.33
1.0
" 02534 "
" =25.34
1.0
" 0.2537 "
" =25.37
1.9210 "
SnCl 4 + 2NH 4 Cl " 0.6219 "
Sn = 32.371
2.1320 "
" 0.6900 "
" =32.36
THIRD DAY.
Tension 1.95 volts.
(Six simultaneous analyses.)
1.0050 g.
CuS0 4 ,5H 2 O gave 0.2550 g.
Cu = 25.37
1.0170 "
" 0.2580 "
" =25.36
1.0006 "
" 0.2539 "
" =25.37
1.0013 "
" 0.2540 "
" =25.37
1.5680 "
SnCl 4 +2NH 4 Cl " 0.5070 "
Sn = 32.34
2.4520 "
" 0.7946 "
" = 32.40
* Classen's method : see Nickel.
f " "Cobalt.
\ " " " Iron.
From the acid double oxalate, Classen's method.
| From the acid ammonium double oxalate.
GALVANIC SECONDARY ELEMENTS.
FOURTH DAY.
53
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
2.20
2.45
2.1340
2.4350
g. CuSO 4 ,5H a O
Tension 1.95 volts.
gave
NiS0 4 -KNH 4 ) 2 S0 4 ,6H 2
< < 1 1
CoSO 4 +K 2 SO 4 ,6H 2 O
0.2532
0.2535
0.2532
0.2536
0.2535
0.2538
0.2539
0.2537
0.3277
0.3650
0.3148
0.3587
g. Cu =
Ni
Co
25.32?
25.35
25.32
25.36
25.35
25.38
25.39
25.37
1489
14.89
14.75
14.73
FIFTH DAY.
Tension 1.95 volts.
1.0 g. CuS0 4 ,5H 2
1.0
2.4120
2.2130
FeSO 4 -f(NH 4 ) 2 S0 4 ,6H 2
gave 0.2537 g. Cu = 25.37^
" 0.2537 " " =25.37
" 0.3438 " Fe = 14.25
" 0.3156 " " =14.26
SIXTH DAY.
Tension 1.92 volts.
(Eight simultaneous copper determinations.)
1.0 g. CuSO 4 ,5H 2 O gave 0.2533 g. Cu = 25.33$
1.0 "
1.0 "
1.0 " "
1.0 "
1.0 "
1.0
1.0 "
((
0.2534
"
"
= 25.34
(
0.2536
tt
<t
= 25.36
ti
0.2533
tt
tt
= 25.33
tt
0.2537
tt
= 25.37
tt
0.2534
tt
tt
= 25.34
tt
0.2536
tt
n
= 25.36
tt
0.2535
tt
= 25.35
54 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Fifty determinations, it is seen, were made in six days.
At the end of the sixth day the tension had fallen to 1.85
volts ; the accumulators were therefore fully charged by a
10-ampere current, receiving an addition of 5tt ampere-hours.
Since the total capacity of such an accumulator is over 250
ampere-hours, it is safe to assume that 60 to TO determina-
tions may be made from one charge ; and the experience of
years confirms this assumption.
To ascertain whether accumulators in use still retain electric
energy, their tension may be measured, or the specific gravity
of the sulphuric acid in the accumulator may be determined,
as this is higher when the accumulator is charged.
Still another advantage in the use of accumulators is found
in the fine quality of the precipitated metal, resulting from the
constancy of the current, which much exceeds that from a
primary battery or a dynamo. In the Aachen laboratory four
pairs of accumulators have been constantly in use since 1888,
without need of repair. Four accumulators are used in the
analytical laboratory, for which they have proved entirely
sufficient, and four in the author's private laboratory.
GENERAL RULES FOR THE HANDLING OP
ACCUMULATORS .
The accumulators which are employed for the purpose of
quantitative analysis are not shipped from the factory ready
mounted for use, as in the case of the smaller types of bat-
teries, but the glass jars, cathode and anode plates, and the
acid are packed separately. After the glass jars have been
carefully cleaned, the plates are set in and the jars are filled
with pure dilute acid (sp. g. 1.15), so that the plates are com-
pletely covered by the liquid. The density of the acid is not
so important as its purity. Either absolutely pure (chlorine-
free) acid must be obtained direct from the manufactory, or
RULES FOR THE HANDLING OF ACCUMULATORS. 55
must be prepared by passing hydrogen sulphide gas for several
minutes into the " commercially pure " acid. By this opera-
tion the traces of metals in solution, which would otherwise
prove extremely detrimental to the accumulators, will be pre-
cipitated. After the precipitate has subsided and the acid
has been decanted, the dissolved hydrogen sulphide is removed
by warming the acid for a short time or by blowing in air.
As soon as the accumulators have been set up they are
ready for charging. This is done from a suitable source of
current according to the number of accumulators at hand.
The charging current should under no circumstances be
allowed to exceed the one given for the particular model by
the manufactory. It must therefore always be controlled by
measuring instruments. The current from a dynamo or
thermopile may be most practically used for charging, but in
case of necessity Bunsen or the so-called i i gravity batteries ' '
may be employed. The peroxide plates are connected with
the positive, the lead plates with the negative pole, of the
charging current.
If a number of accumulators are to be charged, they are
connected in series ; the charging current must therefore have
an electromotive force proportional to the number of
accumulators.
The so-called "capacity" of the accumulator determines
the period required for charging. By this is understood its
production in ampere-hours. For example, an accumulator
of 100 ampere-hours capacity, with a maximum rate of
discharge of 10 amperes, may be discharged at a rate of
10 amp. for 10 hours,
or 5 " " 20 " ,
or 1 " " 100 " , etc.*
* Anleitung zu elektrochemischen Versucheu vou Dr. Felix Oettel,
1894.
6 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
The period of charge is therefore given by the current
strength of the charging current when the capacity is known.
As already stated, accumulators are reversible elements, and
therefore the same number of ampere-hours must be expended
in charging them as they themselves are able to furnish when
fully charged. The termination of the charging must be
determined either by a measurement of the tension, since
every accumulator when fully charged hag a tension of about
2.2 volts, or the appearance of the formation of gas (so-called
4 ' boiling ' ' of the acid) may be taken as the point for stopping
the primary current. The appearance of hydrogen shows
that the gas is no longer used up to reduce the lead sulphate
at the negative pole, and that the reaction upon which the
action of the accumulator depends is completed.
When the batteries are charged for the first time it is
found best to continue the supercharging (generation of gas)
for one hour or over.
On discharging, the tension of each accumulator falls
rapidly to 2 volts and there remains constant. As soon as the
tension falls below 2 volts the batteries must be recharged.
The manner and method of connecting up the batteries on
charging depends upon the nature of the source of current.
If a dynamo is at disposal, the accumulators are so coupled in
series that the tension of the dynamo exceeds by a small
amount the opposed tension of the accumulators (2 volts
each). If the electromotive force of the primary current is
too high, then it must be reduced, either by introducing
resistance or by the employment of a transformer.
If a Giilcher thermopile having a tension of 4 volts is
used for charging the batteries, the cells must be differently
connected. They are then arranged in parallel, i.e., the
similar poles are connected with one another, so that the
whole system acts like a single accumulator with a tension of
ETJLES FOR THE HANDLING OF ACCUMULATORS. 57
2 volts. Owing to the small number of amperes furnished
by a thermopile, a considerable time is required for charging
(8 cells of 8 ampere-hours' capacity each require 32 hours).
To insure the durability of the accumulators, the follow-
ing rules must be observed : *
1. They must be protected from short circuit.
2. The maximum rate of discharge given by the manu-
facturers must not be exceeded.
3. Each element must not be discharged below 1.85 volts.
4. The elements must not be allowed to stand in an un-
charged condition ; also when not in use they must be charged
once every 3 or 4 months.
5. Violent shaking must be avoided, since it is apt to cause
the falling out of the active material.
[The Electric Storage Battery Co. of Philadelphia, Pa.,
manufacture a number of types of accumulators which are
particularly suited fur electrolytic work. Fig. 32 shows a
cell of the so-called type E, a form of cell especially suited for
small storage plants. The plates are provided with very long
lugs which allow the connections to be made at such distance
from the acid that the possibility of corrosion is entirely
removed. The plates themselves are prepared by the so-
called ' ' chloride process, ' ' which gives to them great durability.
In employing this type of battery in the laboratory, it is best
to seal the jars with paraffine. This is done by pouring
melted paraffine over the acid in the jar. A good-sized rubber
stopper is held with its lower end just touching the surface of
the acid, and the melted paraffine is allowed to flow around it.
When the paraffine has completely solidified, the stopper is
withdrawn or may be allowed to remain loosely in the orifice.
* Of. Anleitimg zu elektrochemischen Versuckeii voii Dr. Felix Oettel,
1894.
58
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Spattering and evaporation are thus prevented and the cell
may be moved about without danger of slopping.
The same Company also make a portable cell (Fig. 33).
The accumulators are put up in sealed rubber jars, enclosed
FIG. 32.
in neat hard -wood cases provided with handles and binding-
posts. Various capacities are furnished. These cells are
especially convenient for small laboratories or others which
possess no plant suitable for charging. In such cases the
RULES FOR THE HANDLING OF ACCUMULATORS. 59
portable accumulators may be charged outside of the building
at some power station at a reasonable figure. With four such
FIG. 33.
cells of, say, 100 ampere-hours capacity each, and the simple
arrangement described on page 108, any of the analyses
described in this book may be carried out.
The translators are indebted to the Electric Storage
Battery Company for their kindness in furnishing the illus-
trations here given.
The translators have omitted some 20 pages of the German
text, devoted to an elaborate argument to prove that secondary
batteries are superior to primary galvanic cells as a proximate
source of electricity for electrochemical analysis. They con
sider that fact as fully established in the minds of all who are
likely to make use of their work.
It may be as well to say a few words in this connection as
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
to the source of current. Granted that the secondary battery
is the best proximate source, the question remains as to the
charging of these batteries. In the great majority of cases,
arrangements can be made for using a current that is main-
tained for other purposes, either sending out the cells to be
jcharged, or charging in the laboratory, using resistances or
transformer, according to suggestions elsewhere in this work.
Where recourse must be had to a source contained within the
laboratory, it may be possible, in technical laboratories, to
have a small dynamo run by a belt from shafting belonging
to the factory.
In case 110 dynanlo current is at hand, either primary bat-
teries or a thermopile may be employed. A chemist in so
isolated a location could either prepare a sufficient number of
Daniell cells of the "gravity" type, perhaps making large-
sized cells by using pails of moulded fiber, now universally
sold, as containers, or could with little trouble and expense
construct a thermopile of the Paget type that he would find
sufficient for his needs. Trans.]
PHYSICAL METHODS OF PRODUCING THE
CURRENT.
ELECTROMAGNETIC MACHINES.
For electrochemical processes, uniform continuous cur-
rents of great quantity (low intensity) are required.
The author used for electrolytic analysis, during the years
1881-5, a magneto-electric machine made by Siemens &
Halske of Berlin.
A pulley was fixed on the nxis of this machine, and con-
nected to a second pulley on a counter-shaft. The counter-
shaft carried a cone pulley with 5 steps of 30, 25. 20. 15, and
10 cm. diameter, corresponding to a similar cone pulley on a
second counter-shaft. This second counter-shaft was provided
with fixed and loose pulleys, and was directly connected with
PHYSICAL METHODS OF PRODUCING THE CURRENT. 61
the source of power. The change of connection of the cone
pulleys, therefore, changed the velocity of revolution of the
magneto-electric machine.
The observed velocities of the machine, with this arrange-
ment, were TOO, 500, 300, 200, and 100 revolutions per
minute.
To control still more closely the strength of the current,
a regulator was inserted provided with resistance-spirals and 6
contacts, giving resistances of 0.01, 0.02, 0.06, 0.6, 1.45, and
3 ohms ; thus the machine was made available for all deter-
minations and separations.
This arrangement is adapted, as will be seen, to carry
on simultaneously only similar determinations ; it is not
possible, e.g., to determine together iron and antimony or
copper.
The firm of Siemens & Halske has constructed, for the
laboratory of the author, an apparatus which allows a large
number of the most unlike determinations to be carried on
together without interference. The action of the apparatus
depends essentially on an arrangement by which the full
current of the machine is sent through an artificial resistance
with many subdivisions, and the tension of these subdivisions
is kept constant ; that is, each subdivision has a constant
known tension, which remains unchanged, if a side current
of comparatively little strength is taken to carry on a deter-
mination.
Before describing the details of the apparatus, it must be
premised that the current is produced by a dynamo machine
of the form shown in Fig. 25. This machine, at 1,000 revo-
lutions per minute, furnishes a current of 60 amperes with a
tension of 10 volts ; it requires to run it something more
than one-horse power.
Siemens & Halske describe the action of the dynamo
as follows: A current is produced in a closed electric con-
62 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ductor when a portion of it is passed between opposite poles,
which may be developed in fixed or in moving masses of iron.
The direction of this current depends on the position of the
magnetic poles with reference to the direction of the motion.
The conductor, by the motion of which the electric current
is produced, is insulated copper wire wound in several divi-
FIG. 34.
sions of many turns each about an iron core, so as to cover it
completely, even on the faces. This core is a hollow cylinder
of soft iron wires or plates, which revolves on an axis passing
longitudinally through it (Fig. 35, nn, ss'). Partly sur-
rounding this hollow cylinder on either side, and conforming
to it in shape, are iron bars, "IW, SS 7 , the straight project-
PHYSICAL METHODS OF PRODUCING THE CURRENT. 63
South
North
ing portions of which are wound with insulated copper wire,
and connected by the bars m and O, thus forming horseshoe
electro- magnets, NmS and
N'OS', with their similar
poles opposite to each other.
By the action of the
electro - magnets, powerful
opposite magnetic poles are
formed in the iron bars to
the right and left of the
rotating wire-covering of
the core.
The iron core becomes,
by induction, a transverse
magnet always opposing its
poles to those of the outer
electro - magnets. The in-
termediate spaces, in which
revolves the wire cylinder
covering the core, become
magnetic fields of great in-
tensity. Every revolution
of the wire cylinder pro-
duces in each turn of the
wire, as it passes through the two magnetic fields, two cur-
rents in opposite directions. By means of a commutator
which is connected in a peculiar manner with the single coils,
a continuous current (constant in one direction) is produced
from the combined action of these single alternating currents.
The commutator C (Fig. 34) consists of a number of insulated
copper plates, which, taken together, form a cylinder sur-
rounding the axis of the iron core and revolving with it.
Brushes of copper wire transmit the current from the com-
mutator to the wire that forms the circuit.
FIG. 35.
64 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
According to the fundamental principle of the dynamo,
the electric current which is produced is itself utilized for
strengthening the magnetism which is necessary to the
machine, the weak magnetism remaining in the iron being
sufficient to begin the action when the machine is started.
The current, to this end, traverses the wires which are wound
about the electro- magnets, as well as the external circuit in.
which it is utilized.
THERMO-ELECTRIC PILES.
The principle upon which the construction of this form
of apparatus is based, is that at the points where two metals
are soldered together a difference of potential arises, if the
junctions are maintained at different temperatures. Of the
various forms of thermo-electric piles which have been brought
before the public, those of diamond, Noe and Giilcher have
found practical application.
diamond's pile (shown in Figs. 36 and 37) is built up
of a large number of elements, each consisting of a bar of an
antimony and zinc alloy, and a strip of tinned sheet-iron ; the
iron strips are fastened to the bars as shown in Fig. 38, thus
serving to connect the elements. Both the single elements
and the superimposed rings of elements are separated by
layers of asbestus.
Binding- screws are attached to the poles of each ring
of elements. The current is produced by heating with
illuminating gas which burns from a perforated cylinder
of clay or porcelain, standing in the middle of the pile (Fig.
39, one-third natural size). This tube-burner is cemented
in the cylinder with a mixture of powdered asbestus and
water-glass, and can be replaced in case of accidental break-
age. To keep the flow of gas constant, and prevent exces-
THERMO-ELECTRIC PILES.
65
Fio. 37.
66
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
sive heating of the burner, the gas is first passed through a
regulator filled with water (r, Fig. 36), the valve of which
partly closes the orifice when the pressure rises, and opens
it wider when the pressure falls. The water in the regu-
FIG. 38.
FIG. 39.
lator must be replaced as it evaporates. The current attains
its full strength when the gas has been burning about one
hour.
After using the pile, care must be taken not to cool the
tube-burner too quickly. To this end, the cylinder opening
at C (Fig. 37) is first closed with an iron plate d ; after that
the cock is closed.
The elements of Noe's thermopile are rods of an alloy con-
taining 63 per cent antimony and 37 per cent zinc, about 7
THERMO-ELECTRIC PILES. 67
mm. in diameter and 27 mm. long (Fig. 40), to each of which
FIG. 42
is attached a smaller pointed iron rod (e) to conduct the heat
68 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
to it. The elements are arranged in a circle, on a ring of
ebonite, with the iron point resting on a plate which serves
to spread the flame of the gas-burner (Fig. 41). The con-
nection of the elements by German- silver strips, nn, etc. , is
shown in Fig. 42. The elements are soldered to copper
plates set in a circle, which are bent in spiral form, and
serve to support the elements, and also to cool their outer
ends. Fig. 43 gives a general view of the Noe thermopile.
If it is only moderately heated, the air cools it sufficiently ;
if more strongly heated, it must be placed in a vessel of
water.
FIG. 43.
According to v. Waltenhofen, a pile of 128 elements in
4 groups of 32 each is equal in electromotive force to about
2 Daniel! cells.
Kecently a thermopile of new construction, devised by
THERMO-ELECTRIC PILES. 69
Oiilcher, has proved especially adapted to the requirements
of electrolysis. Along the upper side of the pipe which con-
ducts the gas, and which extends lengthwise through the
apparatus, are situated two rows of nickel tubes having at the
tops small openings which permit the escape of the gas.
On the upper ends of the nickel tubes, where the flames are
ignited, are soldered plates of an antimony alloy, from which
copper strips extend to the bottom of the adjoining nickel
tubes, so that considerable differences of temperature exist
between the top of one tube and the bottom of the next.
FIG. 44.
Fig. 44 shows an apparatus of the model constructed by the
firm of Julius Pintsch (Leipzig). This thermopile, consuming
170 liters of gas per hour, furnishes an electromotive force
of 4 volts and has an internal resistance of 0.6-0.7 ohm, so
that it may be used for charging accumulators.
Wing-like plates of sheet metal are attached to each of
the nickel tubes, and from these fractional parts of the entire
tension of the apparatus may be taken off.
The constancy of the tension of the thermopile depends
upon the uniformity of the gas-pressure, which in cities
is often liable to great fluctuations. Such a condition of
70 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
things may often be extremely deceptive, as in the case, for
example, where an experiment is continued unobserved
throughout the night. Of the many regulators which have
been devised to prevent these variations in the gas-pressure,
that constructed by Danueel (Gottingen) excels all others
in simplicity of construction and operation, as well as in
precision.*
The arrangement of the apparatus is readily seen from
the adjacent sketch (Fig. 45). The solenoid S
receives its current directly from the thermopile,
or, if desired, from the pole- clamps of the bath.
It iits exactly over the glass tube which encloses
the apparatus, and draws downward the magnet
M on an increase of the tension. The opposing
force is furnished by a spring so arranged that it
will not be too greatly stretched by the weight
of the core, and still may respond to slight
attraction. The spring is attached at its upper
end to a thread which is connected with an ad-
justing mechanism plainly shown in the drawing,
FIG. 45. by which the tension of the spring can be easily
increased. On the iron core is hung the plate of the plate
valve. The gas flows in through the base B, and out to the
thermopile through A. C is an adjustable screw ending in a
cone, which is used for closing a second passage for the gas
from B to A, so far that the current of gas passing through
is just sufficient to keep the lights of the thermopile from
being extinguished when the valve is completely closed. The
thermopile is provided with an attachment for regulating the
air-supply, in order to prevent the snapping back of the flames
when the gas-supply is low. The apparatus is mounted on a
* Ztschr. f. Elektrochemie, 1896-97, p. 81.
,7
FIG. 46.
FIG. 47.
FIG. 48.
To face page 71.
THERMO-ELECTRIC PILES. 71
base provided with adjusting-screws. On this is a regulating
resistance which allows any desired tension to be taken off
direct from the apparatus. The thermopile, which in con-
trast to most other sources of current can stand short-cir-
cuiting, is short-circuited through a variable resistance of
coiled wire, and by the adjustment of a curved lever connected
with this the desired tension is obtained. Varying the ten-
sion in this manner is far more convenient than the usual
method of attaching clamps to the vanes of the separate
thermo-elements.
The Giilcher thermopile, in combination with accumulators,
appears to be particularly suited to the requirements of small
electrolytic experiments. An especially convenient arrange-
ment of this sort is described by K. Elbs.*
[Another thermopile worthy of mention is that invented
by Dr. Leonard Paget of New York. Although patented,
it has not been made in commercial quantities and put on the
market, and any chemist or electrician is free to prepare and
use one. The inventor has expressly authorized the trans-
lators to make this statement, and will answer any inquiries
made through them.
The Paget thermopile is very simple in construction, so
that it can be made by or under the direction of any chemist
or electrician, wherever the services of an ordinary black
smith or similar metal-worker are to be procured.
It consists of thin annular disks of copper and German
silver, buckled or dished (Fig. 46), and placed alternately, one
above the other, upon the gas-tube g (Fig. 47), so that adjacent
disks are held in contact by their own elasticity.! The whole
system is held between annular iron plates pp (Fig. 48) with
* Chem. Ztg., 1893, pp. 66 and 97.
f The gas-tube g in this small pile is conveniently made of asbestus
sheet, shaped into tube form about a stick of the desired diameter.
72 QlANTri ATIVE ANALYSIS BY ELECTROLYSIS.
asbestus washers ww, by three long bolts b ; these bolts are
prolonged to serve as legs. Heat is supplied by a Bunsen
burner. The disks are some 3 or 4 inches in diameter, with
an opening 1 inch in diameter.
This thermopile can be taken apart at any time by re-
moving three nuts, and the contact edges of the disks bright-
ened by sand-papering. This will be found desirable after
several weeks' use, and can be done in an hour by unskilled
labor.
A larger form, used with great success in copper deter-
minations at the Chicago Copper Refining Works, consisted
of disks 8 or more inches in diameter, with a 3-ii:ch opening,
and was heated by charcoal, the gas-tube g being furnished
with a simple grate and extended upward to produce a
draught. This latter form has been used in the works re-
ferred to, in preference to an available side current from a
dynamo.
Fig. 49 shows a still larger form, heated by coke on the
base-burning principle, which was constructed and used in
1892.
The tire-bnx is 1 foot in diameter. The annular copper
plates c are extended to form cooling plates ; all air used in
combustion being drawn over them, as indicated by arrows.
The cylinder was 2 ft. high, with 8 pairs of elements to the
inch, and the output in actual work was 11 volts and 72 am-
peres.
Various modifications will suggest themselves under
special conditions, e.g., the adaptation of the size of the disks
to the use of one of the more powerful oil lamps as a source of
heat.
The sheet metal used for the disks in the smaller sizes is
Jg- of an inch in thickness. About 35 pairs of the smaller
size described give an E.M.F of 1 volt, so that to charge
two secondary cells would require about 200 pairs.
REGULATION OF THE CURRENT.
73
FIG. 49
REGULATION OF THE CURRENT.
The relation of the current strength to the resistance is
explained by Ohm's Law ; from which it follows that it is
never possible to alter either one of the two quantities in-
dependently of the other. Variation of the current strength
as well as of the tension, as has been previously explained, is
of the greatest importance for quantitative electrolysis, and
the means at hand for the accomplishment of this are
numerous.
"When accumulators or primary elements are employed,
the tension may be varied by connecting a greater or less
74
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
number of them in series. If one element has a tension of a
volts, then n elements in series give na volts.
In the case of dynamos, the number of revolutions of the
FIG. 50.
armature, as well as the number of windings of the magnet,
has a great influence, so that by an alteration of either of
these the most varied tensions can be obtained.
A convenient method of altering the tension, which is
applicable to every source of current, is the introduction of a
shunt circuit, or the use of resistance in the main circuit.
The theory of the shunt circuit is based upon the follow-
ing considerations : Suppose that the positive and negative
poles of a source of current are connected by a wire 100
meters in length, and that the electromotive force is 1 volts.
Then along the 100 meters of wire a fall in tension of 10
volts will take place, which will be proportional to the resist-
ance of the connecting wire. If the wire is of equal cross-
section throughout and of uniform material, the resistance and
correspondingly the fall in tension will be proportional to the
length. The fall in tension for every ten meters will there-
REGULATION OF THE CURRENT. 75
fore be 1 volt, for every 1 meter 0. 1 volt, etc. If a branch
circuit be now attached to two points about 20 meters apart
this will have an electromotive force of about 2 volts, and in
this manner any desired tension within the limit of the source
of current can be obtained. Of course at the same time a
corresponding change in the current strength takes place ac-
cording to Ohm's Law, but since the current strength, at a
given tension in the branch circuit, depends upon the resist-
ance of the electrolytic cell, this latter is variable, and with it
the current strength with the given tension.
The simple apparatus described in the following has been
constructed by the author for this purpose. A plan of it
appears in Fig. 50.
The current from the battery enters at &, circulates through
the German-silver resistance N", and returns to the battery
through b. In making electrolytic determinations the plati-
num dishes serving as negative electrodes may be attached to
any one of the binding- screws 1-20, while the platinum foils
serving as positive electrodes are attached to the binding-screws
marked with the 4- sign. The apparatus, therefore, is suited
to carry on eight different determinations simultaneously.
Its value for analytical purposes is shown by the following
experiments. To determine directly the current strength at
the binding- screws 1-20, 150 cc of a 15$ copper sulphate
solution was placed in each of 6 platinum dishes of equal
size, copper anodes* were used, and the current was passed
for 7. minutes in each case.
The current was produced by a battery of 5 Bunsen cells.
As already stated, the current strength in the shunt cir-
cuit is proportional to the tension, if the resistance remains
* 6 cm. in diameter, 2 mm. thick. The diameter of the platinum dishes
was 9 cm., the distance of the electrodes from each other 2.5 cm.
76 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
constant. This fact permits of accurate determination of the
changes in the tension from the measured variations of the
current strength.
FIEST EXPERIMENT.
g. Cu. Amperes.
Binding-screw 1 0.5064 = 3.75
2 . * ... 0.3507 = 2.617
3 0.2873 = 2.085
4 ..... -0.2358 = 1.711
5 0.1857 = 1.348
6 0.1453 = 1.054
u 7 0.1341 = 0.973
8 0.1128 = 0.818
SECOND EXPERIMENT.
g. Cu. Amperes.
Binding-screw 7 ..... 0.2213 = 1.606
8 0.1622 = 1.177
9 0.1356 = 0.984
10 0.1083 = 0.786
11 0.0846 = 0.614
12 0.0744 = 0.576
13 0.0506 = 0.367
14 , 0.0410 = 0.225
REGULATION OF THE CURRENT. 77
THIRD EXPERIMENT.
g. Cu. Amperes.
Binding-screw 13 0.1983 = 1.446
14 -. .... 0.1304 = 0.946
" 15 . j. , . . 0.1276 = 0.926
" 16 . . . . . 0.0855 = 0.620
" 17 ..... 0.0605 = 0.439
" 18 0.0385 = 0.280
" 19 ..... 0.0314 = 0.227
" 20 ... . . 0.0136 = 0.098
From a number of quantitative determinations, which
were made by Norrenburg with this apparatus, the following
are selected :
SERIES I.
The apparatus was attached to a battery of 5 Bunsen cells,
and eight iron determinations were made simultaneously.
The precipitation was complete in 6 hours.
Taken Found Binding cc.
FeSO 4 ,2(NH 4 ) 2 SO 4? 6H 2 O. Fe. Screw. OH Gas.
1.2918
g-
0.1846 g.
= 14.30^ \
( 24.0
1.4360
u
0.2059 "
= 14.33 L
2 1 25.0
1.1926
(1
0.1708 "
= 14.32 j
(24.0
1.1964
it
0.1700 "
= 14.30 }
( 16.8
1.2945
u
0.1851 "
= 14.30 V
3 ] 16.6
1.3218
tt
0.1892 "
= 14.31 )
( 17.2
1.2931
1.3255
u
(4
0.1854 "
0.1895 "
= 14.34 )
= 14.30 )
j 13.2
4 J13.4
* The measurements given here, taken from earlier experiments con-
ducted with tlie oxy hydrogen gus voltameter, now entirely abandoned, per-
mit of the recognition of the correct variations of the intensity, since the
same instrument was used in all, and in each case but a short time.
78 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
At the close of the experiment the battery (without resist-
ance) still yielded 50 cc OH gas.
SERIES II.
Three nickel and five copper determinations were con-
ducted simultaneously. The current from 5 Bunsen cells
yielded 65 cc OH gas.
Taken
Nickel Ammon. Sulph.
1.2848 g.
1.4341 "
1.2008
Copper Sulphate.
1.1531 g.
0.9787 "
1.0092 "
0.9938 "
1.0088 "
Found
Nickel.
0.1963 g. = 15.
0.2201 " =15.35
0.1842 " = 15.34
Copper.
0.2910 g. = 25.23;
0.2476 u = 25.30
0.2556 " =25.32
Binding cc.
Screw. OH Gas.
0.2515
0.2550
= 25.30
= 25.27
SERIES III.
This established the applicability of the process to the
simultaneous determination of nickel, antimony, and copper.
The number of analyses again was eight. The battery, of
5 Bunsen cells, yielded 65 cc OH gas per minute.
REGULATION OF THE CURRENT
79
Found
Nickel.
Binding
Screw.
cc.
OH Gas.
15.30JH
( 21.0
15.27
3
] 22.0
15.32 j
( 22.0
Antimony.
71.44$ \
71.47 l
9
j i:o
71.49 )
\ 1.0
Copper.
25.30 I
25.30 j
7
) 3.6
j 3.6
Taken
Nickel Ammonium Sulphate.
1.3022 g.
1.1520 "
1.4391 "
Antimony Trisulphide.
0.1609 gm.
0.1691 "
0.1626 "
Copper Sulphate.
0.2527 g.
0.2550 "
The current strength of the battery at the close of the last
two series was about half that at the beginning.
These experiments show plainly the practical advantage
of this rheostat. To perform eight iron determinations
(Series I ) simultaneously without this rheostat would require
8 ordinary rheostats and at least 16 cells. For three nickel
and five copper determinations would be needed 16 Bunsen
cells and 8 rheostats, or 6 cells, 3 rheostats, and 5 Meidinger
batteries of 3 or 4 cells each, the latter for the copper deter-
minations. The conditions would be similar with the third
series.
[Prof. Edgar F. Smith uses a simple apparatus (Fig. 51),
the accompanying figure and description of which he kindly
permits the translator to copy :
"The writer has for some time employed a much simpler
current- reducer, which has the advantage of cheapness and
ready construction to recommend it. It consists of a light
wooden parallelogram, about 6 feet in length. Extending
from end to end, on both sides, is a light iron wire, measuring
80
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
in all about 500 feet. With the binding-posts at a and &, and
a simple clamp, it is possible to throw in almost any resistance
that may be required. It answers all practical purposes."
' c Electro-chemical Analysis. ' ' Trans. ]
FIG. 51.
A direct alteration of the current strength is in general
brought about by the introduction of resistance into the main
circuit. It may, however, take place in the elements them-
selves, whereby several elements are connected in parallel, i.e.,
REGULATION OF THE CURRENT. 81
the similar poles connected with one another. This has the
effect of increasing the electrode surface, and consequently
decreases the internal resistance.
With dynamos such a parallel coupling is of course not
practical.
A much more general method for varying the current
strength is through alterations of the external resistance, which
can be carried out to a certain extent in the cell itself, by
placing the electrodes further apart or by the addition to the
solution of substances which increase or decrease its conduc-
tivity. Outside of the cell " rheostats " are employed. These
are metallic resistances, portions of which may be switched
in or out as desired.
Of the innumerable different models, many of which are
described in the text-books of physics, only one, of a con-
struction similar to those used for a long time in the Aachen
laboratory, will be mentioned.
For the reduction of the current strength, plug rheostats
deserve special recommendation. As ordinarily constructed,
these are ill adapted to laboratory use, for the plugs are
quickly attacked by acid vapors from the cells or the
vapors of the laboratory, and the resistance introduced is
thus changed. The ordinary apparatus has also the fault
that the plugs are liable to become loose. Both difficulties
are met by the use of mercury contacts, instead of plugs, to
connect the metallic plates. Fig. 52 shows the arrangement
of such a rheostat.* By inserting the contact bars CC in
the mercury cups or removing them, any resistance from 0.5
to 80 ohms may be inserted by intervals of 0.5 ohms.
The following results of experiment show the action of
this rheostat. A current from three Bunsen cells yielding
* This rheostat is made, at the author's suggestion, by Frans Brothers in
WiiMsiedel.
82 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
in the voltameter 28 cc oxyhydrogen gas per minute was
reduced as follows:
Ohms inserted.
cc Oxyhydrogen
Gas per Minute.
Ohms inserted.
cc Oxyhydrogen
Gas per Minute.
0.5
16.00
15.0
2.20
1.0
12.50
20.0
1.30
1.5
9.75
30.0
1.10
2.0
7.00
40.0
0.80
3.0
6.00
50.0
0.70
4.0
5.00
60.0
0.60
5.0
4.90
70.0
0.50
7.5
4.00
80.0
0.45
10.0
3.50
A current of 16 cc Oxyhydrogen gas per minute (yielded
by two Bun sen cells) was reduced by 40 ohms to 0.4, and by
80 ohms to 0.15 cc oxyhydrogen gas.
More recently the author has used the simplified form of
rheostat shown in Fig. 53, in which brass plates are dispensed
with, and the contact with the German-silver coils is made
directly by mercury.
The following results of experiment show how constant
is the current from Bunsen cells when a rheostat is used. In
the separation of antimony from tin, the current from two
Bunsen cells was reduced to 0.6 and 2 cc oxyhydrogen gas
per minute.
Columns A and B give the strength of the two Bunsen
elements ; columns C and D, that obtained by use of the
rheostat.
A and C were measured before the experiments; B and
D, after them (lapse of time, 14 hours).
FIG. 52.
FIG. 53.
To face pa (je 8~ l .
THE PROCESS OF ANALYSIS.
83
A.
B.
C.
D.
cc OH Gas.
cc OH Gas.
cc OH Gas
cc OH Gas.
17
16.0
0.6
0.3
24
19.0
0.6
0.4
18
11.5
0.6
0.3
17
15.5
0.6
0.4
THE PROCESS OF ANALYSIS.
The performance of a quantitative anatysis by electrolysis
requires, above all things, extreme cleanliness. As it is impos-
sible, in electro-plating, to obtain a metallic coating on any
surface which is not most carefully cleaned before it is placed
in the bath, so a quantitative analysis cannot be successfully
carried out unless the metallic surface serving as cathode is
previously perfectly cleaned and freed from fat. The same
care must be used with the battery connections, the stand
which serves to conduct the current, etc. ; otherwise it is
impossible to avoid the weakening or breaking of the current.
It is plainly desirable that the surface of the cathode
should be large in order that the separated metal may be
more firmly attached to it. If a metal separates from a solu-
tion in dense form, as is the case in the electrolysis of double
oxalates, the possibility of the oxidation of the metal is
scarcely increased by enlarging the cathode.
In the separation of peroxides (e.g., lead and manganese
peroxides), which are much less firmly attached, the size of
the electrode on which they are deposited is of especial
importance.
It is not desirable, therefore, to employ a platinum cruci-
ble for electrolytic precipitation if more than a few milli-
grams are to be determined ; not only is the surface of the
84 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
cathode too small, but the electrodes are not widely enough
separated to facilitate the separation of the metal in a dense
form.
For these reasons, the author uses as the negative electrode
a thin platinum dish of 35-37 grams weight, 9 cm. diameter,
4.2 cm. depth, and about 250 cc capacity. The dish has tho
form shown, in about one-half natural size, in Fig. 54 Dishes
which have become, in the course of time, rough, scratched,
or bent, cannot be used for electrolysis.
Some metals separate less readily in hammered dishes
than in those which are spun and polished on the lathe*
FIG. 54.
If, for instance, hammered dishes are used for the reduction
of zinc from the double oxalate, there always remains, after
the solution of the metal in acid, a gray, closely adherent
coating of platinum black, which is with difficulty removed
even by melted potassium hydrogen sulphate, and which
makes further determination of metals in the dish difficult.
For many purposes, as for example the determination of
lead in the form of peroxide, the firm adherence of the pre-
cipitate to the dish can only be secured by the use of a plati-
num dish, the inner surface of which has been roughened with
a sand-blast.
It is to be recommended that under all circumstances the
dishes used for electrolysis be reserved exclusively for their
intended purposes.
The great flexibility of pure platinum dishes has been
THE PROCESS OF ANALYSIS. 85
recently overcome by the use of platinum -iridium dishes.
The iridium, of which about 10 per cent is added to the
platinum, gives a much greater hardness and resistibility to
the utensils made from this alloy than is possessed by pure
platinum articles.
As anode (positive electrode), the author uses a plate of
moderately thick platinum foil, about 4.5 cm. in diameter,
FIG. 55, FIG. 56.
which is fastened to a tolerably stout platinum wire (Fig. 55).
It is desirable, in order to insure uniformity of the solution
during electrolysis, to make a few holes in the platinum foil
with a cork-borer. If this is neglected, a large bubble of gas
may form under the anode by the union of several smaller
ones, and this bubble, on escaping, may cause spirting and loss.
The author has used as positive electrode, in addition to
86 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
the one shown in Fig. 55, a platinum dish of the form shown
in Fig. 54, 50 mm. in diameter and 20 mm. deep. To
secure better circulation of the solution, and more rapid re-
duction, the electrode has five openings in it. This form of
electrode is specially adapted to the determination of such
metals as have the tendency to separate in a spongy state, e.g.,
cadmium and bismuth.
Two standards were formerly used, as shown in Fig. 59, to
support the two electrodes. The author substituted a single
standard (Fig. 56) provided with a metallic ring to which
three short contact wires of platinum are riveted for the plati-
num dish to stand on, and an insulated arm a of glass to sup-
port the positive electrode. The use of this stand has the
drawback that the brass rod to which the metallic ring and
glass arm are clamped is readily corroded by the laboratory
vapors, and this may lead to the breaking of contact. The
stand shown in Fig. 57 has given good service for a long time.
King and arm are clamped to a glass rod Gr, and n is connected
with the negative and p with the positive pole. The posi-
tive electrode is clamped in place at e. If a platinum cone
is used instead of a platinum dish for the deposition of the
metal (as described later), two arms are clamped to the glass
standard, as shown in Fig. 58. This arrangement is also
convenient when a metal is to be precipitated from an acid
solution ; the standard with the electrodes is removed quickly
from the solution and plunged into a vessel of water, and the
water is finally removed from the negative electrode by 'wash-
ing with alcohol.
[It is, of course, not necessary to use a special standard
constituting a part of the conductor, as shown in the figures.
The platinum dish may be placed on the table or the base of
a wooden standard, on a coil of platinum or bright copper
wire which is connected with the negative pole of the bat-
THE PROCESS OF ANALYSTS-
87
terj; and the positive electrode may be held in a wooden
clamp on such a standard, and connected directly with the
wire from the positive pole. See also pp. 89-92. Trans. ,]
When a platinum dish is used it may be placed on a metal-
FIG. 57. J^io. 58.
lie tripod in a beaker, and the acid displaced by a stream of
water from a wash-bottle after the reduction is complete.
Fia. 59.
88 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
FlG. 61.
FIG. 62.
FIG. 63.
THE PROCESS OF ANALYSIS.
The electrodes used almost exclusively for copper deter-
minations at the Mansfeld smelting- works are shown in Figs.
59 to 64. According to the quantity of metal to be deter-
FIG. 64.
mined, the cylinder of platinum foil shown in Fig. 60 (one-
half natural size), or the platinum cone shown in Fig. 61
(one-fourth natural size) is used. The positive electrode is
either a thick platinum wire wound in spiral form (Fig. 62),
or has the form shown in Fig. 63. The arrangement of the
several parts is shown in Figs. 59 and 64.
[An apparatus described by v. Malapert* is specially
adapted to the use of the above-described electrodes, and
particularly to carrying on simultaneously several similar
determinations.
As shown in Fig. 65, a single wooden standard A sup-
ports the apparatus for several electrolytic determinations, the
lower board B carrying the vessels containing the solutions
to be electrolyzed, and the upper board C the apparatus for
directing the current as desired. In the apparatus described,
* Zts. anal. Ch., 26, 56.
90
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
the two boards are 18 cm. apart, and the upper board 7 cm,
wide.
Fig. 66 shows, on a larger scale, the arrangement for
directing the current, connected with each pair of electrodes.
The two strips lib of brass are
1 cm. wide, 2 mm. thick, and
their centres 3 cm. apart. The
binding-screws aa serve for
the attachment of the elec-
FIG. 65.
FIG. 66.
trodes ; to cc are attached the conducting-wires. The switch
d establishes or breaks connection between the two strips
according as it is in the position shown in the cut (closed), or
is moved to bear on the curved strip of hard rubber e (open).
When the apparatus is arranged, as shown in Fig. 65, with
the conducting-wires from the battery connected with the
end binding-screws, and adjacent binding-screws throughout
connected by wires, the current passes unhindered so long as
the switches are closed. To insert any desired number of
similar solutions for electrolysis, it is only necessary to place
the solutions and electrodes in position, and open the corre-
sponding switches ; the current is then forced to pass through
the solutions.
If dissimilar determinations are to be made, the connecting-
wires between adjacent pairs of brass strips are removed, and
THE PROCESS OF ANALYSIS. 91
the conducting-wires from each battery in use are brought
directly to the binding-screws cc of one pair of strips.
To remove acid solutions without interrupting the cur-
rent, v. Malapert uses beakers of heavy glass 8 cm. in diam-
eter and 12 cm. high, with a side tubulure near the top, as
shown in Fig. 65. A cork is inserted in the hole between
the brass strips shown in Fig. 66, through which passes with
little friction a glass tube connected by rubber tubing with a
reservoir of water. When the precipitation is complete, a
stream of water is turned on, and the acid solution displaced,
passing off through the tubulure. A common beaker with
siphon can, of course, be used.
A resistance coil of German-silver wire is shown in Fig.
65 connected to the pair of binding-screws at the extreme
right. Any desired resistance can be thus conveniently
inserted.
An apparatus, made according to this description, was
prepared for use in the chemical laboratory of the Pennsyl-
vania State College, with an addition, devised by the trans-
lator, which makes it equally convenient when a platinum
dish is used as the negative electrode.
Fig. 67 shows the nature of the addition referred to. The
brass strip connected with the negative electrode is extended
downward, at the rear (G, Fig. 67), to the lower board. Here
it is connected with the brass plate H, which is set into the
board B so as to be flush with its upper surface, and has a
shallow saucer-shaped depression, the centre of which is
directly beneath the binding-screw to which is attached the
positive electrode. The plate H and the entire strip were
cut, in the apparatus originally made, from a single sheet of
brass.
A platinum dish placed in the saucer-shaped depression is
firmly supported, and is in good metallic connection with the
92 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
negative pole of the battery ; the positive electrode is attached
as in the original form of the apparatus. All the adjustments
of the original apparatus are retained, and the brass plate
offers no impediment to the use of a beaker with cone-shaped
negative electrode, as shown in Fig. 65. Trans.']
FIG. 67.
Herpin uses, for electrolysis, the apparatus shown in
Fig. 68. The platinum dish P standing on the tripod F is
connected with the negative pole, the platinum spiral S
(shown separately in Fig. 69) with the positive. The dish is
covered with a glass funnel T to avoid loss by spirting of
the solution.
Eiche uses, as cathode, a platinum cone (Fig. TO) open
at both ends, having the form of a crucible, and provided
THE PROCESS OF ANALYSIS.
93
with a bail. Oblong openings are made in the cone to facili-
tate a uniform concentration of the liquid during reduction.
The cone is placed in a platinum crucible so that it is 2 to
4 mm. from it. The whole arrangement is seen in Fig. 71.
FIG. 68.
FIG. 69.
To return to the consideration of the actual electrolysis:
sulphates are best adapted to conversion into double ox-
alates (see p. 5), chlorides less so, and nitrates entirely
unadapted. If chlorides have been used, and the smell of
chlorine is observed during the electrolysis, ammonium oxa-
late must be gradually added to the solution till the odor
94 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
disappears. Sometimes potassium oxalate, sometimes ammo-
FIG. 70.
FIG. 71.
mum oxalate, and often a mixture of the two, is used for the
preparation of the double salt.
As hot solutions conduct the current more readily, solu-
tions are often heated before they are submitted to electro-
lysis. In some cases, however, as in the determination of
antimony, it is necessary that the solution should be of the
ordinary temperature.
In certain determinations and separations, it is best to keep
the solution to be electrolyzed at moderate heat, not above 50
THE PROCESS OF ANALYSIS.
C. The following experiments show the influence of heat on
the time required for electrolysis. Nearly equal weights of
iron and nickel were precipitated, under as equal conditions
as possible (strength of current, concentration, etc.), from
solutions kept respectively at 50 and 15:
IKON.
Taken.
Found.
Strength of Current.
Time.
cc OH Gas.
h. m.
j ( 0.2385 g Fe 2 O 3
(Cold) .
0.2384
11
4 20
' 1 0.2345 g Fe 2 O 3
(Warm),
0.2342
11
2 10
n (0.2246
(Cold) .
0.2244
10
4 10
' (0.2369
(Warm),
0.2369
10
2 15
NICKEL.
Taken.
Found.
Strength of Current.
Time.
cc OH Gas.
h. m.
I ( 0.2660 g Ni
(Cold) .
0.2660
13
7 25
' ( 0.2660 g Ni
(Warm),
0.2659
13
2 20
n ( 0.2660 g Ni
(Cold) .
0.2661
13
7 30
' 1 0.2660 g Ni
(Warm),
0.2660
13
2 20
It also results from the foregoing experiments, that the
current-strength can be greatly reduced by the use of hot solu-
tions, in case there is no occasion for hastening the electrolysis.
The statements in this book apply to solutions at the
ordinary temperature, except when the contrary is stated.
For heating the solution to about 50 (it must on no
account be heated to boiling, else the reduced metal will
flake off from the platinum, and cannot be determined), the
burner shown in Fig. 72 is used. The tube of a Bunsen
burner may also be unscrewed, and the luminous jet issuing
from the opening at the bottom, reduced to a few millimetres
in height, used to heat the solution. The distance of the
96 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
dish from the burner must be about 15 cm. To insure
uniform distribution of the reduced metal on the dish, it
must be uniformly heated. This is most simply accomplished
by placing under the dish a piece of thin asbestos paper cut
through at the points of contact of the dish with the contact
wires of the standard. The use of asbestos paper also dimin-
ishes the danger of boiling.
FIG. 72.
In order to obtain a uniform, easily regulated heating,
Engels* recommends, as a result of investigations conducted in
the Aachen laboratory, the use of an asbestus board at a dis-
tance of 2 cm. above which the dish is held by the standard,
and under which there is an ordinary Bunsen burner. The
dish is thus maintained in an air-bath, the temperature of which
can be easily kept constant, and the heating is quite uniform.
Such is not the case, however, in the other methods of warm-
ing. There, at the points where the dish and stand are in
direct contact, a higher temperature arises, and as a result a
greater precipitation takes place at these points than on the
other portions of the dish.
* Ztschr. f. Electrochemie, 1895-96, p. 413.
THE PROCESS OF ANALYSIS. 97
When the current acts for a long time it is impossible to
prevent some evaporation of the solution, whereby a part of
the reduced metal is exposed to the action of water-vapor
and air. To prevent the oxidation of metal laid bare by
evaporation, a little water is poured from time to time on
the glass cover of the dish, so that the metal remains always
covered by the solution.
After precipitation is complete, the solution remaining in
the dish is poured into a beaker, with care to avoid loss, the
dish washed three times with about 5 cc of cold water, and
then three times with pure absolute alcohol. The dish is
dried some five minutes in an air-bath at 70-90 C, allowed
to cool thoroughly in a desiccator, and weighed.
The apparatus hitherto described have, without exception,
been the result of work conducted in the Aachen laboratory.
Other forms of apparatus, which to a limited extent have
also found application, have mostly originated from v.
Klobukow. He describes a universal stand (Fig. 73) which
carries upon a rod screwed into the work- bench all the ap-
paratus necessary for electrolysis.
" If a platinum dish is used as electrode in performing
the electrolysis, then the ring 7?, to which three platinum
points are soldered, serves as a holder for the dish s. The
second electrode E is clamped into the holder d, the latter
being adjustably attached by means of the sleeve D to the
cross-arm TT, of hard rubber. The path of the current is
as follows : From m to the dish s by means of the metallic
rod, from there to the electrode ^and thence along d to the
binding-screw n fastened at the end.
' ' The conducting wires are connected to the rocker TF,
firmly fastened to the work-bench and coupled into the cir-
cuit from the source of current. In addition there are wires
attached to the voltmeter, the ends of which may be properly
98
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
connected with s and E for the measurement of the potential
differences at the electrodes.
"Additional parts of the ' universal 'stand' are: the
micro-burner B, which serves to warm the liquid in s during
the electrolysis, and the bottle F^ provided with a siphon of
special construction, and containing the liquid to be used for
FIG.
washing the metallic precipitate in the dish. The construction
of the siphon mentioned is such, that by opening the cocks
A, A,, A 2 in proper order the washing liquid is on the one
hand introduced into the dish, and on the other hand the con-
tents of the dish are transferred to the beaker 6r."
THE PKOCESS OF ANALYSIS.
99
The form of the electrode E given by v. Klobukow
differs from that described by the author, in that
it is convex on its lower surface, the curvature
corresponding exactly to that of the bottom of the
dish. FIG. 74.
This construction is, indeed, in accordance with jthe theo-
retical principles, but from the author's experience it is not
necessary. It is curious that the metallic precipitates gener-
ally have a better appearance when flat, rather than curved,
electrodes are employed. (See Fig. Y4.)
For his universal apparatus, v. Klobukow proposes at
the same time the use of a stirring attachment. With this
FIG. 75.
a slow rotary motion is given to the electrode E by means
of a suitable motor connected with it. (See Fig. 75.)
100 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
FIG. 76.
For the special purposes of electrolysis, in addition to the
electrodes and dishes described, there have been made a large
number of suggestions which are all based more or less upon
the same principle. The elbow apparatus, also originated by
v. Klobukow, deserves mention. This allows the gases set
free at the electrodes to be separately collected, and accord-
ingly permits of a quantitative examination of the same. The
apparatus is readily understood from Fig. 76. The corks,
which are preferably paraffined , carry
thick platinum wires to which the
round flat plates which serve as elec-
trodes are welded at angles of 45.
The form of the electrodes is, of
course, not confined to any particular
one ; v. Klobukow also suggests
round fluted platinum foils, spirally-wound wire, or pointed
electrodes.
In case the anode and cathode
liquids are to be kept separate by
a porous membrane, v. Klobukow
proposes the arrangement shown in
Fig. 77. The two separate arms
have close-fitting ground faces,
which are cemented into a brass
mounting. A tight joint is ob-
tained by a hinge and screw.
An electrolytic apparatus, depending upon another prin-
ciple and serving other purposes, which nevertheless might
be useful for quantitative work, is described by Hofer.*
Fig. 78 shows two electrode chambers of glass provided with
inlet and outlet tubes for the electrolyte, which is con-
FIG 77.
* Ber. deutsch. chem. Ges., 27, 461.
HISTORICAL.
101
FIG. 78.
ducted in a continuous stream through the apparatus. There
is also an escape tube for the
gases generated. The two halves,
between which parchment paper
or other porous diaphragm is in-
terposed, are fastened together by
means of a firmly cemented con-
nection provided with a screw.
The electrodes have the form of
spirals of platinum wire, 0.8 mm.
in thickness, or of small platinum
plates attached to wires. The con-
necting wires pass through the gas
outlet tubes, and in case the gases are to be collected, they
are carried on through T tubes placed at the top and made
tight with rubber stoppers.
The liquid to be electrolyzed is contained in a dropping-
funnel, the tube of which is connected by rubber tubing to
the lower inlet tube of one section of the apparatus. The
liquid is thus continuously brought to the particular electrode
and is made to circulate through the cell from the bottom to
the top. It flows out through the outlet tube, thence through
a piece of rubber tubing provided with a screw pinch-cock
for regulating the flow, and into a vessel placed at a lower
level.
This piece of apparatus, which has hitherto been used only
for the study of organic decompositions, might perhaps be
suitable for the quantitative determination of gases.
HISTORICAL.
As in every other new branch of science, the development
of electrolysis has been purely empirical. From a great number
of observations, collected with diligence and perseverance, in
102 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
course of time the most suitable conditions were determined,
while the nature of the reactions was not always exactly under-
stood. It was reserved to the most recent development of
electro-chemistry to throw light upon the important factors
of quantitative electrolysis, and to make clear the significa-
tion and value of the current magnitudes and other con-
ditions.
The first researches on the electrolytic determination of
metals were of a purely qualitative nature. Shortly after the
discovery of the decomposition of water by the electric cur-
rent, Cruikshank (1801) brought forward the conjecture,
based on observations of copper separation, that the galvanic
current might be used for the qualitative determination of
metals. Very little interest was taken in his suggestion.
Fischer (1812) identified arsenic by electrolysis, Cozzi (1840)
the presence of metals in general in animal fluids ; also Gaul-
tier de Claubry (1850) recommended the employment of the
current for discovering poisonous metals in mixtures which
contain organic substances.
Charles L. Bloxam (1860) took up Gaultier's researches
and worked out many methods which attempted to make pos-
sible the identification of arsenic and antimony in the presence
of other metals. He was able to rely to a certain extent upon
the directions of Morton (1851) for the separation of metals
from mixtures.
It had already been observed by Becquerel (1830) that lead
and manganese often separated, not as metals at the negative
pole, but at the positive pole in the form of oxides, a fact
which permitted of the ready separation of these metals from
others. A series of investigations on the decomposition of
inorganic metallic salts then followed by Despretz (1857), by
Nickles (1862), and by Wohler (1868), of entirely qualitative
nature. Likewise the summary of the electro-chemical in-
HISTORICAL. 103
vestigations of A. C. and E. Becquerel only gave a synopsis of
the qualitative electrolytic reduction of the metals.
The results in this direction were accordingly so abundant,
that, based upon them, quantitative electrolysis developed with
comparative rapidity.
The field of quantitative investigation was first opened by
W. Gibbs (1864), who carried out an investigation on the
electrolytic determination of copper and nickel, which included
a description of the methods for the determination of silver
and bismuth in the form of metals, as well as of lead and
manganese in the form of peroxides. He also published
studies on the separation of zinc, nickel, and cobalt. The
possibility of the quantitative determination of copper was
confirmed by Luckow (1865), who had worked at it for a
number of years. The quantitative electrolytic determination
of metals was entitled by him " electro- metal-analy sis. " This
author published at the same time a series of directions for
the method of using the current for analytical work, and by
these precise instructions laid the foundation for many later
researches.
The attention of investigators was now directed principally
towards the chemical reactions taking place in the cell with
the use of different sources of current and under varying
physical conditions. The questions as to the suitable salts of
the metals and the appropriate solvents to be used and the
proper substances to be added to the solutions were investi-
gated and determined. Wrightson (1876) called attention to
the fact that the presence of other metals influences the accu-
racy of copper determinations, and ascertained the limits for
which the presence of antimony in copper still permitted the
accurate determination of the latter. The results obtained
with cadmium, zinc, and other metals were as yet unsatisfac-
tory.
104 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
At the same time as the announcement of the electrolytic
determination of gallium in alkaline solutions by Lecoq de
Boisbaudran (1877), the first investigation of Parodi and
Mascazzini appeared (1877). In the latter, notice was given
of the determination of zinc from the solution of its sulphate,
to which had been added an excess of ammonium acetate.
The authors also found it possible to quantitatively precipitate
metallic lead from an alkaline tartaric acid solution containing
an alkali acetate.
To Richert (1878) we owe the first accurate directions
concerning tho determination of manganese. He observed
that this metal may be completely separated from solutions of
the nitrate in the form of an oxide at the positive pole. This
characteristic made possible the electrolytic separation of
manganese from other metals, as copper, cobalt, nickel, zinc,
etc.
Some of the papers appearing at the same time by Luckow,
F. W. Clarke, and J. B. Haunay treat of the electrolytic
determination of mercury, which readily separates from solu-
tions of its chlorides or solutions of inercurous sulphate.
F. W. Clarke (1878) succeeded in finding a method for
the electrolytic determination of cadmium by separating the
metal from solutions of its acetate, a circumstance which Yver
(1880) employed for separating cadmium from zinc. Cadmium
is not precipitated in the presence of nitric acid, by which the
same author succeeded in separating this metal from copper.*
Beilstein and Jawein (1879) satisfactorily employed solu-
tions of the double cyanides in the determination of zinc.
According to Fresenius and Bergmann (1880), nickel and
cobalt were successfully separated from solutions which con-
tained an excess of free ammonia and ammonium sulphate.
* This method, however, is uot quantitative.
HISTORICAL. 105
Smith (1880) started upon the first of his series of investi-
gations with the electrolysis of uranium acetate, which allowed
the quantitative separation of the uranium in the form of a
hydrated sesquioxide, a property which is shared by molyb-
denum in solutions of ammonium molybdate containing free
ammonia. * Further investig; tio:is of this well-known chemist
include the electrolysis of salts of tungsten, vanadium, and
cerium, and more recently experiments on the separation of
metals from potassium cyanide solutions, f
Luckow (1880) rendered special service in the publication
of his observations on the reactions which take place during
electrolysis in addition to the reduction of the metals. He
pointed out the reduction from higher states of oxidation
to lower in the case of chromic acid, iron, and uranium salts.
He showed, on the other hand, that sulphites and thiosulphates
are oxidized to sulphates. Luckow embodied the results of
his observations in the law, that in general the action of the
electric current on acid solutions is that of reduction, on
alkaline solutions that of oxidation.
A. Classen and his students, in the year 1881, began in-
vestigations on quantitative analysis by electrolysis, which
embraced the observation of nearly all the metals. Classen
first pointed out the value of oxalic acid and of the oxalates
in the form of double salts with metals (1881).;): He also
* According to the investigations undertaken by M. Heidenreich (Ber.
deutsch. -chera. Gesell., 29, 1587) this method gives unsatisfactory results.
f Compare experiments given in the special part.
\ Smith, in his Electrochemical Analysis (p. 44), states that Parodi and
Mascazzini (Gazetta chim. it., vol. 8, p. 178), in the year 1879, therefore
two years before the appearance of the author's publication, had already
announced that iron and antimony could be separated in a dense form, if
solutions of the sulpho-salts of antimony and chloride of iron containing
acid ammonium oxalate were electrolyzed. The article by Parodi and Mas-
cazzini referred to states as follows: " Questi due metalli si depongono
106 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
worked out a large number of electrolytic methods, the details
of which will be given under the corresponding metals.
At about the same time Reinhardt and Ihle recommended
the oxalic acid double salts for the determination of zinc.
Gibbs attempted (1880), by the use of a mercury cathode,
to determine the metals through the increase in weight of the
mercury, a method which Luckow (1886) applied also to the
analysis of zinc.
Since the year 1886 a great number of publications have
annually appeared, the enumeration of which would require
too great space.
Nevertheless the experiments of Vortmann (1894) on the
electrolytic determination of the halogens by the employment
of a silver cathode are worthy of mention. The silver halides
adhere firmly to the electrode, the increase in weight of which
gives directly the quantity of halogen which has separated.
Greater stress was laid on the physical relations in the-
investigations which originated exclusively from the observa-
tions of Kiliani (1883) on the significance of the tension in
electrolytic experiments. Le Blanc was the first to determine
the decomposition tension values for solutions of various metals,
and through his work laid the foundation based upon which
Freudenberg (1891) conducted a separation of several metals
by a mere variation of the tension.
sotto forma elementare compatti e perfettamente aderenti sul polo negative
in platino e cive : 1'antimonio dal chloruro diluito nel tartrato ammonico
busico ed auche dalle dissoluzioni dei solfosoli ; il ferro dal sesquiossido
disciolto nel 1'ossalato acido di amtnouiaca." It is therefore evident that
the authors used tartaricacid solutions for antimony. Tlie author (Classen)
first proposed the use of ammonium oxalate in the detenu nation of iron.
The acid ammonium oxalate employed for this purpose by Parodi and
Mascazzini is not at all suited for the determination of iron, since, in the
first place, it forms no soluble ferrous double salts, and, in the second place,
from solutions of the ferric double salts not even a trace of iron is precipi-
tated until the acid ammonium oxalate has been decomposed by the current.
ARRANGEMENTS FOR ANALYSIS. 107
As the methods of electrolysis were gradually developed,
apparatus suitable to the special requirements were con-
structed. The instruments and arrangements for quantitative
electrolysis at present in general use have originated in the
Aachen laboratory, where, moreover, both dynamos and ac-
cumulators were for the first time employed as sources of
current.
ARRANGEMENTS FOR ANALYSIS.
The question as to the most practical equipment for elec-
trolytic research does not permit of a general answer, owing
to the many details, such as the construction of the "building,
the arrangement of rooms, etc., upon which it depends.
After solving the problem as to the most serviceable source
of current, and deciding in favor of accumulators in combina-
tion with a dynamo or thermopile, the details of the equip-
ment can only be described from a certain point of view,
according to the requirements which must be fulfilled. The
laboratory at Aachen has followed the development of quan-
titative electrolysis, and beginning with the smallest and
simplest equipment has gradually attained a most elaborate
one. Three equipments may therefore be profitably de-
scribed; first, the simplest and most useful arrangement for
small requirements; second, the former; and third, the pres-
ent electrolytic outfit of the Technical High School at Aachen.
Kriiger * has published a general review of the equipment
of electrolytic laboratories, which contains many valuable sug-
gestions, the repetition of which, however, would occupy too
great a space. The choice of special apparatus depends so
much upon the individual taste that exact directions are
* Elektrochem. Ztsckr., 2, pp. 73, 104, 129, 174, 207, 251 ; 3, 7, 76, 129.
108 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
practically impossible. Indeed Kr tiger warmly recommends
a set of instruments the practical advantages of which have
not been confirmed in the Aachen laboratory.
ARRANGEMENT FOR SMALLER EXPERIMENTS.
The equipment needed for carrying out a single electro-
lytic experiment when a constant source of current is at hand
is an extremely simple one.
A standard, with a dish and electrode, and instruments for
measuring the tension and current strength, are all that are re-
quired. Since, however, it is often desirable to conduct several
experiments simultaneously on a small scale, an arrangement
will be described which has the advantage that it may be con-
structed by every one who makes use of electrolysis.
The chief requirement is that it shall be possible to con-
stantly observe the tension and strength of the current. This
may be accomplished with the use of one amperemeter and
one voltmeter for any number of experiments, in the follow-
ing manner :
A wooden block, /(Fig. 79), is placed before the binding-
post to which the negative pole of the source of current is at-
FIG. 79.
tached. This block has a number of holes bored in its upper
side, and into these holes are set inverted thimbles filled with
ARRANGEMENT FOR SMALLER EXPERIMENTS. 109
mercury. These mercury-cups are arranged so that there are
five in a row along one edge and four along ;
the other. (Fig. 80..)
<&> <r> <=> <=>
A resistance-box for the regulation of the
current is required for each separate experi-
ment. The description will be limited to four simultaneous
electrolyses.
The rheostats w^ w^ w t , w 41 of the form designated in the
sketch, are then placed in front of the block 7, and a second
block, 77, having four mercury-cups on one side and one on
the other, is added. An amperemeter and a voltmeter com-
plete the outfit.
The connections are made as follows (Fig. 79) : Four short
wires extend from the negative pole into the mercury-cups 1,
2, 3, 4, of board /, the fifth cup of which, #, is connected
directly with the amperemeter. The second binding-screw
of the amperemeter is connected by a wire to the negative
pole. Four short wires lead from the corresponding mercury-
cups of board 7, 1', 2', 3', 4', to the resistance- boxes w^ w
w w 4 , the other binding-posts of which are connected both
with the electrolytic cells and also with the mercury-cups s l9
*> * 8 ? *45 of board 77, in the corresponding manner. The mer-
cury cup s, situated by itself on board 77, opposite the four
mercury-cups just mentioned, is connected with the instru-
ment for measuring the tension ; and the second binding-post
of the latter is connected by a wire to the positive pole. In
order to complete the circuit it is only necessary to connect the
cups 1-1', 2-2', 3-3', 4-4' by short bent wires. For the
cell 1, for example, beginning at the negative pole, the cur-
rent pursues the following path: Negative pole, 11', 0,,
cell 1, positive pole. The current travels likewise in the
other experiments. In order at the same time to measure the
current strength, the wire connection is laid from a to 1' (2',
110 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
3', 4/) and the connection 1-1 ' is broken (correspondingly 2-2',
3-3', 4-4/). By this arrangement the current, in passing
from the negative pole, is forced to flow through the ampere-
meter, thence over a-V to the rheostat, etc. In order that
the correct value for the current strength may be obtained by
this operation, the wires which make the connections 1-1',
2-2', etc., must have a resistance equal to that of the am.
peremeter, while the connections a-V ', #-2', etc., must be
made with wires having practically no resistance. (For fur-
ther details see p. 122.) '
From the electrolytic cells the circuit is completed, on
the one hand by wires having extremely low resistances run-
ning to the positive pole, and on the other hand by similar
wires connected to the binding-posts of the resistance -boxes,
or what amounts to the same thing, to the cups $ 1? s 2 , s 3 , s 4 .
Between one of the latter and the positive pole the tension
must be measured, since here the fall in tension is due to the
resistance of the cell only. It is accordingly sufficient to
make the connection s 1 s, s 2 s, etc., in order to imme-
diately obtain the difference of potential in the corresponding
cell. The 'simultaneous measurement of several cells is of
course out of the question.
This simple appliance, the principles of which recur in the
following descriptions, can be prepared by anyone from the
simplest materials, so that, as already stated, it is very suit-
able for students, since by working with it they become ac-
quainted with the methods of making connections and the
manipulation of more elaborate apparatus.
The resistance- boxes permit of a variation of the tension
and current strength sufficient for most purposes.
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. Ill
FORMER EQUIPMENT OF THE ELECTRO-CHEMICAL
INSTITUTE AT AACHEN.
This system is based upon the employment of a dynamo
of the type described on page 62, the current from which can
be employed both directly and for charging accumulators.
As already stated, the machine described has a tension of
10 volts with 1,000 revolutions. The tension, while the
machine is in use, is measured by a galvanometer or other
instrument which shows the tension directly. In Fig. 81, the
tension indicator marked G is connected with both ends of
the brass resistance MM r
Siemens & Halske describe the tension indicator as
follows : It consists of an electro-magnet, beside one pole of
which stands on edge a piece of iron which has the same
polarity, and is therefore repelled by it in proportion to the
strength of the magnetism, and so of the electric current
which passes around the instrument. The extent of the
repulsion is measured on a scale on which plays an index
attached to the piece of iron which is repelled. The indica-
tions of the instrument are not entirely independent of the
residual magnetism ; the direction of the current in the
instrument must therefore be alwaj^s the same. This result-
is accomplished by a small adjustable permanent magnet in
front of the lower pole of the electro-magnet ; this shows the
direction of the current in the instrument, and stops the
index if the current is in the wrong direction. (See Z,
Fig. 81.) If this occurs, the wires leading the current to
the instrument must be interchanged.
The instrument is supplied with a brass ring, which,
before the current passes, is placed on the round weight of
the index, and must then turn the index to the zero point.
If this is not the case, the instrument is not plumb. When
the instrument is in use, the ring is removed.
112 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
As already stated, the laboratory apparatus constructed
by Siemens & Halske is capable of carrying on, at the same
time, a large number of electrolytic determinations on the
small scale, requiring currents, differing in strength and ten-
sion, so that each determination is independent of the rest.
According to the description of Siemens & Halske, this
THE ELECTROCHEMICAL INSTITUTE AT AACHEN. 113
result is obtained essentially by passing far the greater part
of the current through a brass wire-gauze resistance,* the
individual determinations being made by small branch cur-
rents which may be independently varied in intensity by
attaching their conductors to different portions of the wire-
gauze resistance.
The dynamo machine is connected by short heavy con-
ductors to the ends M Mj of the zigzag brass wire-gauze
resistance. These ends of the resistance are also connected,
by smaller wires, with the instrument which shows directly
the tension at the resistance. Care must be taken that this
instrument always shows the same tension, i.e., that the
velocity of the machine is uniform. If the tension at the
ends of the resistance is 6 volts, and the resistance is made
up of 24 equal parts, the ends of which are connected with
binding-screws, the difference in tension between any two
adjacent binding-screws is ^ = ^ volt. If the tension at
the first screw is 0, the tensions at the following screws are
i> f i f > 1? f > etc., volts ; that is, the whole interval of 6 volts
is divided into portions of J volt each.
If, now, a current, small in proportion to the current
passing through the resistance, is taken out between any two
binding-screws for an electrolytic determination, the tension
between the screws is not materially changed ; the wires
carrying this current can be connected with any binding
screws without any change in the main current ; moreover,
* When the same source of current is used for carrying on a number
of dissimilar experiments simultaneously, the employment of resistances
and the loss of a part of the energy is unavoidable. The apparatus con-
structed by Siemens and Halske has the advantage that it makes use of
only a single resistance, while with all other arrangements as many sepa-
rate resistances are required as experiments are conducted.
114 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
the introduction of a number of such currents does not
materially change the tension, and the tension for any given
determination can be varied at will without affecting the
others,
In the apparatus used by the author, Fig. 81 (one-
twentieth natural size), the brass wire gauze resistance is
divided into 20 equal parts marked 1, 2, 3, etc. As already
stated, the machine, at 1 5 000 revolutions, has a current-
strength of 60 amperes and a tension of 10 volts. Of the 60
amperes, 40 are conducted through the resistance, so that 20
remain for electrolytic determinations.
The difference of tension between two adjacent binding-
screws is J = volt. The tension, that is, at the screw
marked 19, is volt, at 18 = 1, at 17 = 1J, at 16 = 2, at
= 10 volts.
The current from the machine enters by a heavy copper
conductor at the screw marked 0, and passes out at that
marked 20.
On the board BBBB are fastened 6 T-shaped galvanized-
iron strips, S x , S 2 , S 3 , S 4 , S 5 , S 6 , six resistances of 0.1 ohm
each, W x , W 2 , W 3 , W 4 , W 5 , W 6 (to allow the strength of
current in single experiments to be measured), and the brass
strip M 2 . S 1 is connected by a wire with W x , S 2 with W 2 , S 3
with W 3 ,' S 4 with W 4 , S 5 with W 5 , and S 6 with W 6 . The iron
strips may be connected with the binding-screws 1, 2, 3, etc.,
by means of wires and the brass screws K 1? K 2 , etc. If the
apparatus is used as shown in the cut, and 1, 2, or 3 is
connected with S 1? 4, 5, or 6 with S 2 , 7, 8, or 9 with S 3 , 10,
11, or 12 with S 4 , 13, 14, 15, or 16 with S 5 , and one of the
others with S 6 , the strongest current is at W v and the weakest
at W 6 . Any strip may, of course, be connected with any
binding-screw.
In performing electrolysis, the solutions to be acted on
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 115
are placed in connection with a negative pole n v n v or
w 3 , etc. (on the resistances W v W 2 , or W 3 , etc.), and a
positive pole p v p^ or p%, etc., on the brass strip M 2 , the
connections being made according to the strength of current
desired.
Moreover, as shown by the examples given later, several
determinations requiring the same strength of current may
be connected with any pair of poles, n^ and p v n 2 and p^, etc.
In order to connect more conveniently with the platinum
dishes containing the solutions for electrolysis, n^ and p v for
instance, may be connected with a brass strip Z (the con-
nection with n^ only is shown in the cut), to which are
attached a number of binding-screws, z v 2 2 , etc.
The tension and the strength of the current may be
measured at each dish. For example, if the tension at the
dish connected with W 2 is to be measured, the plugs from
the galvanometer are inserted at 5 2 and c 2 ; if they are
inserted at 2 and 5 2 , the tension in the resistance is meas^
ured, which, multiplied by 10, gives, in amperes, the strength
of the current acting on the solution connected with W 2 .
In order to test the working of the apparatus, the tension
at the divisions of the wire-gauze resistance was directly
measured by a torsion galvanometer, with the following
results :
116 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Resistance marked
Connected with Binding
Screw, marked
Tension in Volts.
w,
1
10.300
w,
2
9.900
w,
3
9.400
W 2
4
8.950
W 2
5
8.300
w a
6
7.750
W 8
7
7.200
W 8
8
6.650
w $
9
5.950
W 4
10
5.500
W 4
11
5.050
w.
12
4.500
W 6
13
4.000
W 6
14
3.450
W 6
15
2.850
W 6
16
2.300
W 6
17
1.700
W 6
18
1.100
w.
19
0.560
W 6
20
0.007
For the measurement of the strength of the current at
the screws 1 to 20, a cell was used which had a copper elec-
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 117
trode,* and contained 150 cc. of a 15 per cent solution of
copper sulphate ; this cell was connected to the resistance W 6
(binding-screws, n e and p Q ). The screws 1 to 20 were then
successively connected with the bar S 6 , and the deflection of
the galvanometer read, the plugs connecting it being placed
in # 6 and b 6 . After this reading, the tension in the cell was
read, for each screw connection, by placing the plugs in > 6
and c Q .
In order to control the rate of the machine during the
-experiment, p l and n l on the resistance W 1 were connected
through a rheostat ; and the tension at the binding-screw 1
(connected with Sj) was determined by a second torsion
galvanometer, the plugs from which were inserted at b^
and c r
The results of these experiments are given in the following
table in the columns included under I.
A second series of experiments was conducted to deter-
mine the strength of the current by the quantity of copper
precipitated.
Six platinum dishes, as nearly alike as possible, were
filled with 150 cc each of a 15 per cent solution of copper
sulphate, supplied with copper eiectrodes (see note below),
and different quantities of copper precipitated in the same
time. These experiments were conducted in three series, as
follows :
Series 1. I., IV., VIII., XII., XVI., XIX.
Series 2. II., V., IX., XIII., XVII., XX.
Series 3. III., VI., X., XL, XIV., XVIII.
* The cell consisted of a platinum dish, and the positive electrode was a
round piece of sheet-copper (of the form of the platinum electrode shown in
Fig. 55), 6 cm. in diameter and 2 mm. thick. The electrodes were 2.5 cm.
apart.
118 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Of the columns included under II., A gives the strength
of the current as determined from the precipitated copper ;
B, the results, in a few cases, of the measurement of the
strength of current by a torsion galvanometer ; and C,
the tension measured at the same time with the torsion
galvanometer.
Binding
Screw.
I.
II.
Amperes.
Volts,
Experi-
ment.
Volts,
Machine.
A,
Amperes.
B, Am-
peres.
c,
Volts.
I.
II.
18.018
15.352
7.900
7.400
10.90
9.90
15.97
14.04
9.200
9.000
III.
13.231
7.100
10.10
10.86
10.800
7.900
IV.
11.615
6.650
10.10
8.87
-
7.400
V.
10.302
6.350
10.30
8.00
-
7.100
VI.
9.595
6.010
10.40
6.04
-
5.500
VII.
VIII.
8.383
6,565
5.710
5.300
10.50
10.60
4.97
_
5.000
IX.
5.757
5.100
10.60
4.21
3.800
4.500
X.
4.747
4.700
11.1-0
4.03
- 3.800
XI.
4.040
4.250
10.90
3.75
3.700
3.100
XII.
XIII.
3.838
3.535
3.800
3.400
11.00
10.90
3.54
3.47
:
2.900
2.500
XIV.
3.030
2.850
10.90
3.09
2.700
2.300
XV.
2.520
2.400
11.05
-
-
-
XVI.
2.120
1.900
11.00
1.85
-
1.200
XVII.
1.560
1.500
11.00
1.35
-
1.050
XVIII.
0.759
0.890
10.90
0.76
0.605
0.600
XIX.
0.396
0.290
11.00
0.54
-
0.360
XX.
0.000
. ^
0.007
11.10
^^ ^ ^
0.00
0.007
i ^~m
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 119
The following sixteen experiments were made simulta-
neously under the same conditions as before. The numbers
in column A express the quantities of copper precipitated in
6.5 minutes ; those under B, the tensions measured with the
torsion galvanometer.
A, Copper.
B, Volts.
f 0.7616 g ]
Binding screw I. to W l
1 0.7415 "
I 0.8286 "
7.10
Screw IV. to W 2 ....
( 0.6021 "
0.5716 "
5.30
1 0.4788 " J
0.4155 "
Screw VIII. to W 3 . . . .
< 0.3510 "
3.30
. 0.3535 "
C.2648
Screw XII. to W 4 ....
< 0.2963 "
1.80
. 0.2652 "
Screw XVI. to W 5 ....
j 0.1435 " |
( 0.1470 " f
0.90
Screw XIX. to W 6 . . . .
( 0.0363 " )
( 0.0260 4t )
0.23
In order to reach a conclusion as to the value of the
apparatus for the purposes of quantitative analysis, twelve
determinations were carried on simultaneously, at the author's
request, by Dr. Kobert Ludwig, formerly assistant in the In-
organic Laboratory. The solutions used for these experi-
ments were of iron, cobalt, tin, antimony, and copper, metals
120 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
which, as will be shown later, require currents of widely
different strengths for their separation. The results of one
series of these experiments are subjoined.
Taken.
Found.
I.
0.3546 g
Fe 2 O 3
0.2479
g Fe = 0.3541 g Fe 2 O 3
II.
0.3836 "
Fe 2 3
0.2691
" Fe = 0.3844 " Fe 2 O 3
III.
0.2624 "
Co
0.2619
" Co
IY.
0.2234 "
Co
0.2231
" Co
V.
0.1145 "
Sn
0.1142
" Sn
VI.
0.2290 "
Sn
0.2290
" Sn
VII.
0.2025 "
Sb 2 S 3
0.1444
" Sb = 0.2019 " Sb 2 S 3
VIII.
0.1890 "
Sb 2 S 3
0.1348
" Sb = 0.1885 " Sb 2 S 3
IX.
0.1670 "
Sb 2 S 3
0.1189
" Sb = 0.1663 " Sb 2 S 3
X.
0.8374 "
CuSO 4
0.2133
" Cu = 25.47 % Cu
XI.
0.8768 "
CuSO 4
0.2225
" Cu = 25.31 % Cu
XII.
0.7905 "
CuSO 4
( 0.1991
" Cu = 25.29 % Cu
I
Calculated 25.39 % Cu
In general the current of the dynamo was not directly
employed, bu{; was used to charge four accumulators, which
sent their current of 8 volts to the electrolytic work-bench.
The current thus transformed was employed in the following
manner (Table I).
The connection of the cells with the positive conductor,
which carries the current of the four accumulators to the
electrolytic table, is effected by means of six binding-screws
(marked 1, 2, 3, 4, 5, 6). For connecting the cells with the
negative pole of the source of current, wooden blocks bearing
separate binding-posts and mercury-cups (in the diagram 6)
are made use of. The arrangement of such a board is shown
in Fig. 82 (f actual size).
The cups marked 1, 2, 3, 4 are connected with the four
binding-posts JT, cups 5 and 6 with the negative conductor
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 121
from the source of current, and cup 7 with one conductor
from the amperemeter. The connections between the cups
are made by plain copper forks while the current is being
measured, and otherwise by forks upon which resistances
O
K
1-7
Binding posts.
Mercury cups.
Cup 7 is connected through
the measuring circuit with
the amperemeter.
O
FIG. 82.
equal to the resistance of the measuring instrument are rolled.
A fork of this description (resistance-roll) is shown separately
in Fig. 83. An instrument made by Hartmann & Braun
(Bockenheim -Frankfurt a. M.) serves for measuring the cur-
rent strength. This instrument, especially constructed for
the laboratory of instruction, is provided with two scales and
pointers (one on fech side), which allow of its being observed
from all points on the work-bench. The pointer of the
122 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
amperemeter moves over a scale having a radius of 16 cm.
The instrument permits of the measurement of currents up to
2 amperes in decimals of 0.05 ampere. By the use of a
resistance which may be connected in shunt, the range of
measurement is increased tenfold. The resistance of the
instrument itself is 0.32 ohm. An exactly equal resistance is
contained in the resistance-roll.
The measurement of the current strength in the cell is
conducted as follows : A moderately high resistance of, say,
60 ohms is 'inserted in the circuit of the connected rheostat
and a wire from a positive binding-screw is connected with
Resistance-roll having a resistance
equal to that of the amperemeter.
FIG. 83.
the anode of the cell. A wire running to one of the neg-
ative binding- screws (for example, 5, Table I, Fig. 1) i&
now attached through the rheostat to the cathode. The
arrangement is seen from Table I, Fig. 1. It only remains
to connect the mercury-cups 4 and 7 (the latter connected
with the amperemeter) by means of a copper fork. With a
resistance of 60 ohms in the circuit the amperemeter will
show only a small deflection, which may be increased to the
required value by reducing the resistance in the rheostat.
This having been done, a resistance- roll is inserted between the
cups 4 and 6 and the copper fork between 4 and 7 is removed,
which breaks the connection with the amperemeter. Since
the resistance of the amperemeter and roll are equal, a current
1-6 POSITIVE BINDING POS1
. SEPARATE NEGATIVE B
MERCURY CUPS.
. POSITIVE CONDUCTORS
NEGATIVE CONDUCTORS
I CIRCUIT CONNECTED W
\ MEASURING INSTRUMEN
PLAN OF WORK-BENCH 1
tf
1
00
p '
j 1
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TABLE I
[NG ARRANGEMENT FOR MEASURING THE CURRENT
THE USE OF A SINGLE J
FIG. 1.
r^
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CONNECTION FOR MEASUREMENT
CABLE FROM THE DYNAMO WITH T( J AMPER ^ METER
OR ACCUMULATORS j 1
WITH THE RESISTANCE \
%
ELECTROLYTIC CELL
CELL
BORATORY OF THE ROYAL TECHNICAL HIGH SCHOOL AT AACHEN.
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ENGTH OF EACH SEPARATE ELECTROLYSIS WIT
REMETER.
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UNIVERSITY
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 128
corresponding to the one measured flows through the cell. To
observe the current strength during the electrolysis, the copper
fork is placed in the cups 4 and 7, and the resistance- roll is
removed. It is, therefore, possible to measure the current
strength at any time without interrupting the current through
the cell. As is evident from Table I, Fig. 1, the construc-
tion of the electrolytic table allows 24 separate electrolyses to
be conducted simultaneously. If at least four accumulators,
with a tension of 8 volts, are used, a considerable number
of experiments may be carried out at the same time quite in-
dependently of one another.
The former equipment of the private laboratory is, with-
out further comment, evident from Table II. It includes a
special connection for using the current from the dynamo
directly, as well as for working with the 8 accumulators.
The wire-gauze resistance, described on p. 113, serves to
reduce the current when charging the accumulators, or in the
direct employment of the same. The conductors from the
dynamo and accumulators pass from the private laboratory to
the electrolytic tables in the laboratory of instruction. An
amperemeter shows the current which is there being used,
while another amperemeter serves to control the current used
for charging the accumulators. The complete arrangement
of the plant is explained by Table I, Fig. 2.
That accumulators furnish the most suitable source of
current for electrolysis is to-day beyond question. These
instruments, since they can also be charged with a thermopile,
are more practical and convenient for small laboratories than
primary batteries, which furnish either insufficient or incon-
stant currents.
The torsion galvanometer has long served in this labora-
tory for measuring the tension at the electrodes. Since a
knowledge of the tension is of great importance, both for the
124 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
quality of the precipitated metal and for the separation of
different metals, it must always be possible, as has been
repeatedly stated, to determine the tension as. well as the cur-
rent strength. How this may be accomplished with a single
voltmeter, in the performance of several simultaneous ex-
periments by means of a common source of current, is clear
from the diagram, Table I, Fig. 2.
When this method is used, special care must be taken that
the rheostat is connected between the cell and the negative
pole, since otherwise the tension of the accumulators and
not that of the cell will be measured. In carrying out the
measurement, only the cathode should be connected with the
voltmeter circuit, if a deflection at the voltmeter is expected.
The manner of attaching the cell is readily seen from the
sketch. Since the measurement of several tensions cannot be
conducted at the same time, owing to one interfering with the
other, it must always be ascertained, before switching in the
voltmeter, that it is not in use elsewhere.
PRESENT EQUIPMENT OF THE ELECTROCHEMICAL
INSTITUTE OF THE TECHNICAL HIGH SCHOOL.
Although the electric current of the former equipment
was furnished by an independent generating plant, such is not
the case in the present one. It was considered desirable to be
as independent of a power plant as possible, since these are
by nature uneconomical, and moreover are not always ready
for use.
The solution of the problem was made possible by the fact
that the city of Aachen has an electric-power station, the
cables of which extend to the Technical High School. It
was decided, therefore, to take the electricity for the new
installation from the city mains.
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 125
The current, as taken from the city system, could not, of
course, be used for all experiments without modification. As
is well known, for carrying out many electro-analyses, only
very low tensions, included within the limits 0.5-8 volts, are
required.
The current furnished by the Aachen Electrical Works,
operating on the three- wire direct-current system, has a ten-
sion of about 108 volts between the middle wire and an out-
side wire, and a tension of about 216 volts between the two
outside wires.
It was therefore necessary, in connection with the experi-
ments previously mentioned, to reduce the high tension of
the power wire in some suitable manner to the low tension
required for experiment. Moreover it should at all times be
possible, without special preparation, to carry out experiments
with high tension, as for example in experiments where the
current must be forced through materials having a high
resistance, or for performing experiments with the electric arc.
For the reduction of the high tension to a low tension in
the case at hand, a direct- cur rent transformer was considered,
The economical working of a double- dynamo combination of
this description, its quiet and convenient operation, together
with the small space which it occupies, all speak for the
choice of the direct-current transformer. The question as
to the method of obtaining the low tension required for
electrolytic experiments was thus solved.
Before proceeding to the description of the plant installed
by the firm of Schuckert & Co., proprietors of the Aachen
Electrical Works, the nature of the different experiments and
investigations carried out will be briefly sketched in order
that what follows may be more readily comprehended.
126 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
1. EXPERIMENTS WITH Low TENSION.
The experiments with low tension are chiefly confined to
the electro-analysis of solutions of metallic salts. In addition
to this the precipitation of metals on a large scale is also
undertaken as an introduction to the study of electroplating.
2. EXPERIMENTS WITH HIGH TENSION.
The experiments with high tension begin at about 45
volts, required for the production of the Davy arc ; the high-
est available tension of the supply circuit, that between the
two outside wires, is about 216 volts. The high-tension
current is chiefly employed for fusion experiments, as well
as for the decomposition of gases and other bodies of high
resistance.
In addition to the above purposes, the current is also
used for running an electric projection lantern, as well as a
number of arc and incandescent lights.
The distribution of the current to the various rooms, and
also the operation of the transformer, is controlled from a
central switchboard. The centralization of the whole plant
was desirable for many reasons, chief among which was the
fact that a valuable and complicated switchboard might thus
be placed under competent supervision in a room not open to
every one. This would prevent unauthorized persons from
taking off current, and besides would allow a general super-
vision of the whole plant.
From the central switchboard currents are carried to the
following places:
1. Private laboratory.
2. Large lecture-room.
3. Laboratory for electro-analysis.
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 127
4. Laboratory for experiments on a large scale with high
and low tension.
The circuits running to the different rooms are distin-
guished, according to the purpose for which the current they
carry is intended, as :
a. Lighting circuits,
1). High-tension circuits,
c. Low-tension circuits,
and are entirely independent of one another.
The lighting circuits run to the private laboratory and to
the large lecture-room.
The circuits for the high-tension current extend to the
private laboratory, to the large lecture-room, and to the
laboratory for experiments with high- and low-tension.
The circuits for low-tension current extend to. the private
laboratory, the large lecture-room, the laboratory for electro-
analysis, and the research room for high and low tension,
In addition to the above circuits, which are intended for
direct current transmission, there are also to be mentioned
the circuit for charging the two batteries of accumulators and
the circuit for running the transformer.
The switches, resistances, controlling, and measuring
apparatus belonging to the different circuits are located on
the central switchboard.
1. PRIVATE LABORATORY.
Concerning the special arrangements, the private labora-
tory will next be mentioned. As already stated, the central
switchboard, with the apparatus for the control of the whole
plant, is placed in the private laboratory. In tins room there
is also located a battery of accumulators.
Table III gives a photographic view showing the arrange-
ment of this laboratory. In the middle may be seen the
128 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
central switchboard upon which the various instruments are
mounted; to the left stands the glass closet containing the
battery of accumulators. On the wall by the window are two
work-benches, one intended especially for electro-analytical
work with low tensions and small currents, and the other for
experiments with high tensions and large currents.
The arrangement for electro-analysis is as follows: On
the back of the corner bench is a slanting wooden frame, on
the face of which are fastened the switches and branch bind-
ing-posts, while the connecting wires are attached to the back
There are altogether five work-places on this bench, each of
which will permit of the performance of two analyses simul-
taneously, so that in all ten experiments may be carried on
at the same time.
The installation of these work-places, as well as of the
second work-bench, is in accordance with the scheme for
current distribution shown in Table IY.
Each work-place is connected in parallel to the positive
and negative conductors, which are run through the work-
bench.
The current for every analysis can be independently varied
by means of the regulating resistance at the work-place. A
single amperemeter, which can be thrown into the circuit of
any analysis by means of a switch placed at each work-place,
serves for measuring the current strength. When the am-
peremeter is cut out, its place is taken by a resistance, in or-
der that the current strength may not be altered (see p. 122).
The measurement of the tension is carried out in a similar
manner by a single voltmeter, which may at will be switched
into the circuit of any analysis in operation.
A lead safety fuse is inserted in the circuit of each of the
ten branches, to guard against the possibility of too great cur-
rent strength.
32
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THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 129
The connections of the electrolytic apparatus to the small
switchboards of the work-bench are made with very flexible
rubber-insulated copper leads, the ends of which are provided
with small copper links to allow of a more convenient attach-
ment to the apparatus.
For setting up experiments where large currents of high
or low tension are required, two cases furnished with locks
are affixed to the second work-bench. That for low tension,
contains two branch plates which carry a number of binding-
posts, thus allowing several different pieces of apparatus to be
connected at the same time.
The case for high tension contains three plates, connected
with the two outside leads and the middle lead of the three-
wire system respectively, whereby a maximum tension of
about 216 volts is obtainable. These plates also carry several
binding-posts, which permit the use of several pieces of appa-
ratus at one time.
The two accumulator batteries are comprised of four cells
each. One battery, with the cells connected in series, requires
a charging current of 90 amperes ; the other, similarly con-
nected, requires 25 amperes.
The batteries are charged from the transformer.
The small battery furnishes current to the private labora-
tory only, while the large one supplies the rest of the plant.
Each of the batteries is provided with a cell switchboard for
four cells, so that by cutting out separate cells the tension of
the current may be reduced and the use of higli external re-
sistances avoided.
As a protection against the possibility of the current re-
versing, during the process of charging, and flowing back
through the transformer, each battery circuit is provided with
an automatic cut-out.
The tension of the separate cells is controlled by a special
130 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
voltmeter having contact plugs, which allows the tension of
each cell to be independently measured at the cell switch-
board.
For the measurement of the battery tension and the
strength of the charging and discharging currents a special
voltmeter and amperemeter are provided. Further, that the
operation of charging and discharging may be more closely
observed, indicators for showing the direction of the current
are attached to the corresponding circuits.
2. LARGE LECTURE-ROOM.
The installation of the large lecture-room is especially in-
tended for the performance of lecture experiments, which
comprise the demonstration of electrolysis, the decomposition
of gases and liquids by the Davy arc, and fusion experiments.
Besides this, provision is made for the running of an
electric projecting lantern, as well as for a number of incan-
descent and arc lamps.
3. LABORATORY FOR THE ELECTRO- ANALYSIS OF METALS.
In this room the transformer is placed. It also contains
a large experiment table having ten work -places, for carrying
out electro-analytical experiments with low tensions. (Gf.
Table Y.)
The transformer will next be described. This consists
of a combination of two direct-current dynamos, with their
shafts coupled directly together. One of the dynamos, ar-
ranged as a motor, is driven by the current from the two
outside wires of the three-wire system, by a tension, there-
fore, of about 216 volts. The circuit is run to the trans-
former from the central switchboard. The dynamo which is
coupled to the motor, and which furnishes the low-tension
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 131
current, is so arranged that the tension at the poles may be
varied from about 4.5-9 volts, the corresponding current
strengths being respectively 360 and 180 amperes. The con-
ductors carrying the low-tension current from the dynamo
run to the central switchboard. The tension of 9 volts is
the one generally used, the lower tension "of 4.5 volts being
employed for larger electrolytic experiments, such as the prep-
aration of pure metals.
The alteration in the tension of the current is brought
about by connecting the two halves of the double armature,
with which the transformer is provided, either in series or in
parallel. This is done by merely changing the corresponding
connections on the frame of the transformer.
Further concerning the construction of the transformer, it
should be mentioned that the machine is very solidly cast, and
the magnets protected within the frame, so that a mechanical
injury to the magnet-coils is out of the question. The lubri-
cation of all parts is carried out by means of ring-lubrication,
which has proved very satisfactory. Such delays as often
occur when other mechanical contrivances are employed are
here impossible. Owing to its construction, the transformer,
which for protection is enclosed in a special covering, can run
for hours without particular attention.
The action of the transformer, in spite of its speed of about
1300 revolutions per minute, is so quiet and free from any
jarring or shaking, that its running can scarcely be detected
even in- the immediate neighborhood.
It should be stated that there is a switchboard near the
transformer, by which direct currents of low tension can be
taken off in this room, without making use of the central
switchboard. Such currents are required when experiments
with high current strength and low tension are performed ;
132 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
and in such cases short cables are run from this switchboard
to the nearest work-bench, where the apparatus is set up.
The arrangement of the large work-bench, a photograph
of which is given in Table Y, corresponds in general to that
of the table for conducting analyses in the private labora-
tory.
Here, on either side of the bench, there are five work-
places, each of which allows of the simultaneous performance
of two analyses, so that in all twenty experiments may be
carried on at the same time.*
Table IY shows the method employed for measuring the
current strength and tension of an analysis. The ampere-
meter and voltmeter are above. The current strengths are
regulated by means of the rheostats (I, II, III, and IY).
These consist of slate slabs into which are fixed metal knobs,
which are attached to separate resistance spirals. By turning
the lever in the direction indicated by the arrow, the resist-
ance is cut out and the current strength correspondingly
increased.
The switches for the amperemeter A (I( n> m IV) , f or the
electrolyses i E (I| IIt IIIt IV) , and the safety-fuses B (Ii n> IIIf IV) are
located under bronzed metal cases.
%, ii, in, iv) are the binding-posts to which the electrolyses
are connected, Y is a double-pole switch used in measuring
the tension. In the position o the voltmeter is cut out ; at
i, n, in, iv the corresponding electrolysis is connected with
the voltmeter. As already stated, there is only one ampere-
meter and one vo.ltmeter to every table with 10-20 dishes,
and therefore only one electrolysis can be measured at a time.
The four figures on Table IY are designed to make the
explanations clearer.
* Two other work-benches have been recently added, so that there are
now twenty work-places for electro-analysis.
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 133
In position I, where the keys A r and E r are horizontal,
the circuit is closed. In II, A n is perpendicular; the
amperemeter is in circuit. The lever of the rheostat at II
may be turned in the direction of the arrow until the meas-
uring apparatus registers the desired current strength. A is
then brought into the position A m and E to E m . The cur-
rent now flows no longer through the amperemeter, but
through a roll of wire, the resistance of which is equal to
that of the amperemeter. The current strength remains the
same as that previously shown by the amperemeter.
Y serves for measuring the tension at the poles of the
electrolytic vessel, as shown at Y IV . In this operation the
position of A and E is the same as in III. The two metal
strips (SS) are pushed to the right or left (in the figure to
the right, iv), whereupon the voltmeter shows the tension
existing at that time at the poles of the corresponding elec-
trolysis. The instruments should be cut out immediately
after use.
4t. LABORATORY FOR PERFORMING EXPERIMENTS ON A LARGE
SCALE WITH Low AND HIGH TENSIONS.
As already mentioned, special cases w r hich receive their
currents from separate conductors running from the central
switchboard are arranged for high and low tension.
Within the case for high tension there are three separate
plates corresponding to the three wires of the three- wire
system, providing currents at tensions of 108 and 216 volts
accordingly.
The case for low tension contains two connections, with
possible tension at the poles up to 9 volts.
From both of the cases separate branch circuits run to the
four work-benches, where they end in terminal boxes pro-
134 QUANTITATIVE ANALYSIS BY ELECTEOLYSIS.
vided with locks. By this arrangement each table is pro-
vided with both high and low tension.
Each of the branches running to the tables is supplied
with a safety fuse and a switch; each table is therefore
independent of the others.
A set of transportable resistances and measuring instru-
ments for regulating the current is used in carrying out
experiments.
Large and cumbersome resistances are required to produce
appreciable variations in the tension. A simple appliance in
use in the Aachen laboratory overcomes this difficulty in the
case of experiments of short duration, where economical use
of the current is not an essential feature. This scheme,
originated by Lob and Kaufmann,* permits the convenient
splitting up of the current of 216 or 108 volts into separate
independent currents having the required lower tension.
A number of lead plates are hung parallel to one another
in a large porcelain trough filled with sulphuric acid (Fig. 84),
in such a manner that they cut
all the lines of the current.
They must therefore almost
touch the sides and bottom of
the trough. When the current
passes, these lead plates act as
intermediate conductors, the sum
of their separate tensions being
equal to the tension of the main
current. The arrangement is of course impractical as an
accumulator, since the polarized plates immediately short-
circuit through the electrolyte and are reduced to the poten-
tial of the electrodes.
FIG. 84.
* Zeitschr. f. Elektroch., 1895-96, p. 345. Ibid., p. 664.
THE ELECTRO-CHEMICAL INSTITUTE AT AACHEN. 135
The immersed lead plates can be slid along the length of
the trough on the glass rod by which they are hung. By
moving the plates toward or away from the electrodes the
tension is varied, and any desired tension may be obtained by
making a connection between a terminal electrode and one of
the plates. The arrangement is given in Fig. 84. E de-
notes the source of current ; T, the trough filled with sul-
phuric acid ; A and K, anode and cathode ; M, the five plates.
The wires to S show the removal of three separate currents
of different tensions. A large number of such connections
are possible. On account of the gases given off, the trough
should be kept under a hood.
In addition to the details of the equipment which have
been described, some general facts in connection with the
management of the entire plant should be stated.
Since the apparatus is much used, and is not always
placed in experienced hands, it was considered desirable to
have all parts solidly constructed and intended for continu-
ous use.
The switches and regulating instruments, as well as the
branch plates, are all mounted on bases of fire-proof material.
All connections are made with the best rubber-covered
wire, fastened to large porcelain brackets, so that most perfect
insulation of the conductors is assured.
To secure against improper use, all switch-cases are pro-
vided with safety-locks, so that currents can nowhere be
taken off without the permission of the director of the
laboratory.
SECTION II.
SPECIAL PART.
QUANTITATIVE DETERMINATION OF THE
METALS. *
IRON.
LITEEATUBE I
Wrightson, Zeit. f. analyt. Chem., 15, 305.
Luckow, Zeit. f. analyt. Chem., 19, 18.
Classen and v. Keiss, Ber. deutsch. chem. Ges., 14, 1622.
Classen, Zeit. f. Elektrochemie, vol. I.
Moore, Chem. News, 53, 209.
Smith, Amer. Chem. Jour., 10, 330.
Brand, Zeib. f. analyt. Chem., 28, 581.
Drown and Meckenna, J. of Analyt. and Applied Chem., 5, 627.
Smith and Muhr, ibid., 5, 488.
Rudorff, Zeit. f . angew. Chem., 15, 198.
Vortmann, Monatshefte f. Chem., 14, 542.
Heidenreich, Ber. deutsch. chem. Ges., 29, 1585.
If the solution of a ferrous salt f is treated with potassium
* Of the methods existing in the literature, reference will be made only
to those which give the necessar} r and complete details concerning the
conditions of experiment.
f As stated on p. 5, sulphates are best adapted to this treatment, chlo-
rides less so, while nitrates must be avoided. The presence of phosphoric
acid is not harmful.
137
138 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
or ammonium oxalate, there is produced an intensely yellow-
ish-red precipitate of ferrous oxalate, soluble in an excess of
the reagent to a yellowish-red solution of the double salt.
The above-named oxalates do not precipitate ferric salts ;
but, if added in sufficient quantity, a solution of the double
ferric salt is produced having a more or less green color. If
this solution is submitted to electrolysis, there is first produced
the double ferrous, salt, which is then decomposed with separa-
tion of metallic iron ; the green liquid therefore becomes first
red, and then colorless. Because of this action, the determina-
tion of iron is more rapidly performed in solutions of ferrous
than of ferric salts. Potassium iron oxalate is not adapted to
electrolysis, because the potassium carbonate which is pro-
duced precipitates iron carbonate, and thus complete reduc-
tion is prevented. The electrolysis of the ammonium double
salt, when ammonium oxalate is in sufficient excess, proceeds
smoothly, with no separation of an iron compound. If the
solution contains free hydrochloric acid, it is best to remove it
by evaporation on the water- bath.
Free sulphuric acid may be neutralized with ammonia,
since the ammonium sulphate thus produced only increases
the conductivity of the solution. Nitrates are converted by
evaporation with sulphuric acid into sulphates, or by repeated
evaporation with hydrochloric acid into chlorides.
The determination is conducted as follows: Assuming
that 1 g of iron may be present in the solution to be elec-
trolyzed, 68 g of ammonium oxalate are dissolved by heat in
as little water as possible, and the iron solution is gradually
added, with constant agitation.* The solution is then diluted
* It is not desirable to add ammonium oxalate solution to a ferrous
solution, as difficultly soluble ferrous oxalate separates, and can be dis
solved to the double salt only by long heating. With a ferric solution this
precaution is unnecessary.
IRON. 139
with water to 100-150 cc, and the positive electrode is im-
mersed in the liquid until it is just covered by the solution.
The electrolysis is conducted according to the special direc-
tions which are given below.
The end of the reaction is determined by taking out a
small portion of the colorless solution with a capillary tube,
acidifying strongly with hydrochloric acid, and testing with
potassium sulphocyanate. When the reaction is ended the
positive electrode is removed from the solution, which is
poured off, and the dish washed three times with cold water
(about 5 cc each time), and three times with absolute alcohol,
dried a few moments in the air-bath at a temperature of 70 to
90, and weighed after cooling.
The separated iron has a steel-gray color and brilliant
lustre, is firmly attached to the dish, and can be preserved in
the air without oxidation for a full day.
CONDITIONS OF EXPERIMENT.*
Temperature of the liquid: Although the maintenance
of a certain uniform temperature is not essential to the suc-
cess of the experiment, it has been found in practice that
the ordinary temperature of the solution (20-40) is the
most favorable to the rapid completion of the analysis.
Current density, ND 100 : For solutions at ordinary tem-
perature, 1-1.5 amp.; for warm solutions (40-65), 0.5-1
amp.
Electrode tension : For warm solutions, with the stated
current density, 2.0-3.5 volts; otherwise, 3.6-4.3 volts.
* Method of the author. In all of the author's methods the statements
refer to the use of the electrodes described on p. 85; the current densities
refer only to the dish given in Fig. 54.
140 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
For the quality of the precipitated metal, polished or
roughened dishes answer equally well.
EXPERIMENT.
Used 2.1-2.5 g FeSO 4 (NH 4 ) 2 SO 4 .6H 2 O, 6-8 g ammonium
oxalate, 120 cc of liquid.
Current Density,
Amperes.
1 -1.5
Electrode Tension,
Volts.
3.85-4.3
Temp.
20-40
Time.
2 hr. 15 m.
Found.*
14.21 %
1 -1.05
3.6 -4.2
36
3 " 50 "
14.21 "
1 -1.08
3.05-3.52
65
2 " 30 "
14.28 "
0.5-0.55
2.0 -2.3
50-52
3 " 30 "
14.24 "
Used 2.6-2.8 g ferric potassium oxalate (Fe a (C 2 O 4 ),.
3K 2 C 2 O 4 .6H 2 O), 6-7 g ammonium oxalate.
1.5-1.7 3.55-4.25 35-40 2 hr. 54 m. 11.39 %'\
1.0-1.1 3.9 -4.0 30-40 3 " 15 " 11.35 "
0.5-0.8 2.4 -2.8 50 6 " 15 " 11.25 "
Edgar F. Smith precipitates iron from a solution of am-
monium citrate to which a few drops of citric acid have been
added. The author's experiments in earlier years on the
separation of iron from other metals in citric and tartaric
acid solution, demonstrated that in the presence of fixed
organic acids the precipitated metal always contains carbon.
Heidenreich has recently shown, by experiments conducted
in the Aachen laboratory, that iron may be quantitatively
determined under certain conditions, namely: 0.2 g ferrous
ammonium sulphate, 50 cc of a 10 per cent solution of
sodium citrate, 2 cc of a saturated solution of citric acid;
entire volume of liquid, 120 cc; temperature of room;
ND 100 = 0.75-0.9 amp.; electrode tension, 5 volts; time,
4r-6 hours. The iron, however, always contains carbon.
[Theory 14.29*.] t [Theory 11.40*.]
COBALT. 141
COBALT.
LITEKATUKE I
Gibbs, Zeit. f. anal. Chem., 3, 336 ; 11, 10 ; 22, 548.
Merrick, Amer. Chemist, 2, 136.
Wrightson, Zeit. f. anal. Chem., 15, 300, 303. 333.
Schweder, ibid., 16, 344.
Cheney and Richards, Amer. Jour, of Science and Arts, [3] 14, 178.
Ohl, Zeit. f. anal. Chem., 18, 523.
Luckow, ibid., 19, 314.
Riche, ibid., 21, 116.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622. 2771.
Classen, ibid., 27, 2061 ; Zeit. f. Elektrochemie, 1894-95, Heft 1.
Schucht, Zeit. f. anal. Chem., 21, 493.
Eohn and Woodgate, Journ. Soc. Chem. Indust., 8, 256.
Riidorff, Zeit. f. angew. Chemie, 1892, p. 6.
Brand, Zeit. f. anal. Chemie, 28, 588.
Le Roy, Compt. rend., 112, 722.
Vortmann, Monatsh. f. Chem., 14, 536.
Oettel, Zeit. f. Elektrochemie, 1894-95, p. 195.
Fresenius and Bergmann, Zeit. f. anal. Chem., 19, 329.
Cobalt may be very easily precipitated from a solution of
cobalt ammonium oxalate containing an excess of ammonium
oxalate (method of the author). The metal separates rapidly
at the negative electrode, in a compact adherent coating,
showing its characteristic metallic properties. The operation
is performed as in the determination of iron. 4-5 g am-
monium oxalate are dissolved by heating in the solution, the
volume of which should be about 25 cc ; it is then diluted to
100-120 cc, warmed, and electrolyzed at 60-70.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : The period of electrolysis is
considerably shortened by warming, so that a temperature of
60-70 is suitable.
142 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Current density : The proper current density for warmed
solutions is KD 100 = 1 amp.
Electrode tension : 3.1-3. 8 volts.
The condition of the surface of the cathode has no effect
upon the quality of the precipitated metal.
EXPERIMENT.
Used 2.2-2.6 g CoSO 4 .K 1 SO 4 .6H,O, 4-5 g ammonium
oxalate, 120 cc solution.
A.mperes.
jtLiieciroue lensi
Volts.
Temp.
Time.
Found.*
1 -1.1
3.1 -3.78
60-65
2 br. 15 ra.
13.36
0.5-0.52
2.7 -2.95
60-65
3 " 30 "
13.49"
1 -1.2
3.9 -4.1
15-35
4 " 30 '
13.43"
0.5-0.53
3.46-3.9
15-27
6 " 35 "
1325"
According to a method given by Fresenius and Bergmann,
the cobalt solution, after the addition of 15-20 cc of an
ammonium sulphate solution (300 g (NH 4 ),SO 4 to the liter)
and 40 cc ammonia sp. g. 0.96 (where more than 0.5 g
cobalt is present in the solution, 50-60 cc NH 4 OH), is
diluted with water to 150-170 cc, and electrolyzed with a
current of I^D 100 = 0.7 as a maximum at ordinary tempera-
tures. The presence of chlorides and nitrates is unfavorable
to the reduction. Fixed organic acids (citric acid, tartaric
acid) and also magnesium compounds act injuriously.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : The separation is not hastened
by warming.
Current density: JSTD IOO = 0.5-0.7 amp.
Electrode tension : With the given current density and at
ordinary temperatures, this equals 2.8-3.3 volts.
F. Oettel proposes the following method for the determina-
tion of cobalt : The salt is dissolved in water and a quantity
* [Theory 13.43^.]
NICKEL. 143
of ammonium chloride, equal to four times the weight of the
salt taken, is added. The volume of the liquid is 150 cc,
-J- of which is an ammonia solution (sp. g. = 0.92). After
electrolyzing for 14 hours the cobalt is quantitatively pre-
cipitated if 100 cc of solution do not contain more than 0.25
g of the cobalt salt.
NICKEL.
LITERATURE I
Gibbs, Zeit. f. anal. Chem., 3, 336 ; 11, 10 ; 22, 558.
Merrick, Amer. Chemist, 2, 136.
Wrightson, Zeit. f. anal. Chem., 15, 300, 303, 333.
Schweder, ibid., 16, 344.
Cheney and Richards, Amer. Journ. of Science and Arts, [3] 14, 178.
Ohl, Zeit. f. anal. Chem., 18, 523.
Luckow, ibid., 19, 314.
Riche, ibid., 21, 116.
Classen and v. Keiss, Ber. deutsch. chem. Ges., 14, 1622, 2771.
Classen, ibid., 27, 2061 ; Zeit. f. Elektrochemie, 1894-95, Heft 1.
Schucht, Zeit. f. anal. Chem., 21, 493.
Kohn and Woodgate, Journ. Soc. Chem. Indust., 8, 256.
Riidorff, Zeit. f. angew. Chem., 1892, p. 6.
Brand, Zeit. f. anal. Chem., 28, 588.
Le Roy, Compt. rend., 112, 722.
Vortmann, Monatsh. f. Chemie, 14, 536.
Campbell and Andrews, Journ. Am. Chem. Soc., 17, 125.
Oettel, Zeit. f. Elektrochemie, 1894-95, p. 192.
Fresenius and Bergmann, Zeit. f. anal. Chem., 19, 320.
Nickel may be reduced under conditions similar to those
requisite for cobalt ; the metal is precipitated from the solu-
tion of the double oxalate containing ammonium oxalate in
excess, by the action of a similar current, as a thick, bright
coating on the negative electrode. The end of the reaction
is ascertained by testing with ammonium sulphide or potas-
sium sulphocarbonate, and the precipitate is treated as pre-
viously directed.
144 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
CONDITIONS OF EXPERIMENT .
The conditions of experiment are the same as in the
separation of cobalt. Here also polished or roughened dishes
serve equally well.
Used 1.2-2.1 g 'NiSO 4 .(]N T H 4 ) 2 SO 4 .6H 2 O, 4-5 g ammo-
nium oxalate, 120 cc liquid.
Current Density, Electrode Tension, Temp Time Found.*
ArnpGrGS. vtMio.
0.9-1 3.1-2.9 65-70 2 hr. 50 m. 15.13 #
0.5-0.6 3.38-3.4 17 5" 15.11"
0.9-1 4.09-4.35 15-30 3 " 35 " 15.05"
05-0.53 2.7-2.85 60-65 4" 15.17"
The condition of the precipitate is best when the elec-
trolysis is conducted at a temperature of 60-70, with a
current of ND 100 = 1 amp.
According to Fresenius and Bergmann, nickel, like cobalt,
may be precipitated completely from a solution treated with
ammonium sulphate and ammonia (see Cobalt).
The method given by Oettel for the determination of
cobalt may also be used for nickel. For this purpose the
nickel salt is dissolved in 20-40 cc ammonia (sp. g. 0.92) to
which 10 g ammonium chloride are added, and after diluting
to about 120 cc, the nickel is precipitated in 7-8 hours with
a current of ND 100 = 0.45 amp.
Campbell and Andrews dissolve nickel hydroxide in 30 cc
of a 10 per cent solution of di-sodium phosphate, to which 30
cc of a concentrated ammonia solution are added, and, with a
distance of 5 mm between the electrodes, separate out the
nickel by the use of a current of KD 100 = 0.14 amp.
ZINC.
LITERATURE I
Wrightson, Zeit. f. anal. Chem., 15, 303.
Parodi and Mascazzini, Ber. deutsch. chem. Ges., 10, 1098 ;
Zeit. f. anal. Chem., 18, 587.
* [Theory 14.87$ Ni.]
ZINC. 145
Riche, Zeit. f. anal. Chem., 17, 216.
Beilstem and Jaweiu, Ber. deutsch. chem. Ges., 12, 446 ;
Zeit. f. anal. Chein., 18, 588.
Riche, Zeit. f. anal. Chem., 21, 119.
Reinhardt and Ihle, Journ. f. prakt. Chem., 24, 193.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622.
Classen, ibid., 27, 2060. x-
Gibbs, Zeit. f. anal. Chem/ 22, 558.
Luckow, ibid., 25, 113.
Brand, ibid., 28, 581.
Warwick, Zeit, f. anorg. Chem., 1, 290.
Vortmann, Ber. deutsch. chem. Ges., 24, 2753.
Riidorff, Zeit. f. angew. Chem., 1892, p. 197.
Vortmann, Monatsh. f. Chemie, 14, 536.
Jordis, Zeit. f. Elektrochemie, 1895-96, pp. 138, 565, 655.
Millot, Bull, de la Soc. chim., 37, 339.
The metal may be easily and quickly separated from the
double salts of zinc ammonium oxalate and zinc potassium
oxalate (method of the author).*
The reduced metal has a bluish-white color, and under
proper conditions adheres firmly to the negative electrode.
Indeed, the metallic zinc often adheres so firmly to the
platinum dish that, after being cleaned with water and alco-
hol, and dried, it is with difficulty dissolved by warming
with acids. Generally, after this operation, a dark coating of
platinum- black remains which can only be removed by ignit-
ing the dish and again treating with acids. It is therefore
desirable, before weighing the dish, to precipitate upon it a
thin coating of copper, tin, or, better, silver. In laboratories
* The reduction of zinc from a solution of zinc ammonium oxalate is
very often credited to Reinhardt and Ihle. The author, however, described
this method in Fehling's " Handworterbuch " before the research of the
above-named investigators appeared in the Journal f lir praktische Chemie,
to the editor of which, Kolbe, the author especially stated the facts at the
time.
146 QUANTITATIVE ANALYSIS BY ELECTKOLYSIS.
in which many zinc determinations are performed, silver
dishes may be advantageously employed.
A bright, thick coating of copper can be obtained in a few
minutes if a saturated solution of copper sulphate is treated
with an excess of ammonium oxalate to form the double salt,
acidified with oxalic acid, warmed to 70-80, and decomposed
by a current of 1 ampere. The preparation of the double
salt in a beaker, and the transfer of the clear, hot solution to
the platinum dish, is to be recommended.
For silvering the dish it is best to precipitate the silver
from a solution of the same in potassium cyanide (see Silver).
In determining zinc by this method, the zinc salt is dis-
solved in a little water by warming, about 4 g of potassium
oxalate or an equal amount of ammonium oxalate is added,
and the whole is brought into solution by warming and, if
necessary, by the addition of small quantities of water.*
The liquid is now transferred to a platinrtm dish coated with
copper or silver, and electrolyzed. The author has demon-
strated by experiments that the separation of the zinc in a
dense, shiny condition is possible if the solution be kept acid
during the process of analysis.
For acidifying the solution, a cold saturated solution of
oxalic acid, or, better, a solution, of tartaric acid (3 : 50) is em-
ployed. At the start the solution is electrolyzed for about
3-5 minutes without addition of acid, and then the acid is
permitted to flow in drops (about 10 drops per minute) from
a burette with a fine outlet, upon the watch-glass covering
the dish. The acid flows through the holes in the watch-
glass into the dish itself. After the reduction is completed
* If the alkali oxalate be added to a dilute solution of a zinc salt, there
first forms a precipitate of zinc oxalate which is not completely converted
into the soluble zinc double salt if the solution of the alkali oxalate is too
dilute.
ZINC. 147
(this is determined with potassium ferrocyanide), the metal
must be washed without interrupting the current.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : This must be from 50-60.
Current density : ND 100 = 0.5-1 amp.
Electrode tension : 3.54.8 volts.
Roughened or polished dishes answer equally well.
Time : About 2 hours.
EXPERIMENT.
Used 1.8-2 g zinc ammonium sulphate, 4 g potassium
oxalate, 120 cc liquid.
CUr AmpSes 8ity ' Electr ^ ts Tension ' Temp. Time. Found.*
0.5-0.55 3.5-4.0 55-60 2 hr. 16.44#
0.9-1 4.7-4.8 60 1 " 50 m. 16.42 "
According to v. Miller and Kiliani, 4 g potassium oxa-
late and 3 g potassium sulphate are dissolved in water, the
neutralized zinc solution (sulphate or nitrate containing not
more than 0.3 g Zn) carefully added, and electrolysis effected
without heat, by a current of ND 100 = 0.3-0.5 amperes.
The reaction is complete in 2 to 3 hours.
N. Eisenbergf obtained the following results by the above
method :
Current Electrode Condition
Density, Tension, Temp. Time. Found. of
en - Amperes. Volts. Metal.
1.8312 0.4-0.35 3.95-4.00 25 -26 4 hr. 16.35$ partly spongy
1.8312 0.40-0.35 4.15-4.25 28.5-30 4 " 15 m. 16.01 " spongy
Remark: (1) Rough dish; (2) Polished dish.
The agitation of the liquid by means of a stirring appli-
ance is recommended for this method.
According to Jordis, zinc, when present in the form of
sulphate, chloride or nitrate, may be separated from a lactic
* [Theory 16.29^ Zn.] \ Inaugural-Dissert. Heidelberg, 1895.
148 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
acid solution. The ease with which this method may be car-
ried out appears from the directions of the author, which
read as follows :* " 2 g ammonium sulphate and 5-7 g ammo-
nium lactate are added to the neutral solution containing not
less than 0.3-0.5g zinc, and it is acidified with 'a few drops
of lactic acid. A stirring attachment is employed, and the
solution is electrolyzed with a current of !ND 100 = 1.0-1.5
amp. After 40-60 minutes the electrolyte is poured into a
second dish and the separation completed in this. With a
current of the above density this requires 20-25 minutes. A
somewhat more concentrated solution of about 120-150 cc
is advantageous.
4 c Since the lactic acid is but very slowly decomposed
during the electrolysis, its regeneration resulting from the
action of the sulphuric acid formed upon the ammonium
lactate, the electrolyte remains acid until the end and requires
no further attention."
MANGANESE.
LITERATURE I
Riche, Ann. d. China, et Pliys., [5], 13, 508.
Luckow, Zeit. f. anal. Chem., 19, 17.
Schucht, ibid., 22, 493.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622.
Moore, Chem. News, 53, 209.
Smith and Frankel, Journ. Anal. Chem., 3, 385 ;
Chem. News, 60, 262.
Brand, Zeit. f. anal. Chem., 28, 581.
Riidorff, Zeit. f. angew. Chem., 15, 6.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Engels, Zeit. f. Elektrochemie, 1895-96, p. 413 ; 1896-97, p. 286.
Groeger, Zeit. f. angew. Chem., 1895, p. 253.
* Zeit. f . Elektrochemie, 1895-96, p. 656
MANGANESE. 149
From the results of experience in the Aachen laboratory,
none of the methods long in use are applicable for the direct
quantitative determination of this metal as peroxide. It is gen-
erally assumed that the peroxide when dried at about 68 has
the composition MnO a .H a O, an assumption which the author
cannot confirm. If the attempt be made to convert the
hyd rated peroxide into anhydrous peroxide by prolonged
drying at a higher temperature, a strongly hygroscopic sub-
stance results which rapidly increases in weight during the
process of weighing. It is therefore necessary to convert the
dried peroxide into mangano-manganic oxide by ignition, an
operation conducted with ease and safety. After determin-
ing the necessary conditions for the separation of large quan-
tities of lead peroxide, the author was induced to assume that
manganese behaved similarly to lead. Investigation proved,
however, that strong inorganic acids interfere with complete
precipitation, and even make it impossible. Of the organic
acids, acetic acid alone is suitable, although the precipitation
of large quantities, even when roughened dishes are used,
cannot be successfully carried out, since it is impossible to
obtain firmly adhering precipitates.
As will be stated under lead, the separation of lead takes
place from nitric acid solutions in the presence of other
metals. The hope that manganese in the presence of iron
might be separated and determined in an acetic acid solution
has not been fulfilled. Innumerable experiments, conducted
under the most varied conditions and with the most diverse
substances, have given no satisfactory results. In view of the
great importance which a method for the direct determina-
tion of manganese in the presence of iron, etc., would pos-
sess, this investigation will be continued.
150 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : 50-70.
Current density : ND ]00 = 0.3-0.35 amp.
Electrode tension: 4.3-4.9 volts.
Time: 3 hours.
EXPERIMENT.
Used about 0.5 g MnSO 4 .(NH 4 ) a SO 4 .6H a O, which was
dissolved in about 75 cc water and eleetrolyzed after the ad-
dition of 25 cc acetic acid sp. g. 1.069 (20).
Current Density, Electrode
Amperes. Tension, Temp. Time. Found.
Volts.
0.3-0.3 4.4-4.9 50-68 3 hr. 0.1035 g Mn 3 O 4 14.94$*
0.3-0.35 4.3-4.6 56-62 3" 0.1045 g Mn 3 O 4 15-04''
An equally rapid and complete separation was secured by
Engels, as a result of investigations conducted in the Aachen
laboratory. The method is as follows : 1-2 g of the manga-
nese salt is dissolved in about 125 cc of water, and 10 g am-
monium acetate and 1 . 5-2 g chrome alum are also added.
The clear solution is then eleetrolyzed. Chlorides must not
be present, since the evolution of chlorine interferes with the
separation of the manganese. If they are present, the pro-
cess is carried out according to the directions given under the
separation of manganese and copper.
CONDITIONS OF EXPERIMENT.
Temperature of liquid : 80.
Current density: ND 100 = 0.6-1 amp.
Electrode tension : 2.8-4 volts.
Time : About 1 J hours.
Note : Roughened dishes must be used.
* [Theory 14.07$ Mn. Probably impure salt was used. Trans ]
MANGANESE. 151
EXPERIMENT.
In the determinations given below, 10 g ammonium ace-
tate and 1.5-2 g chrome alum were added to the solution.
TT \ /o/^ \ z-cr r\ Current Density Electrode m,^ T i mp Found*
Mn(NH 4 ),(S0 4 ) a .6H,0. NDloo , Amp. Tension, Temp. Time. Mn,O 4 ,
en, ,
Volts. g. Per cent.
1.1522g 0.6-0.5 2.8-3.1 80 |br. 0.2235 19.39
1.2554" 0.6-0.5 2.8-3.1 80 " " 0.2436 19.40
1.2994" 0.6 3. 83 " " 0.2520 19.39
1.8099" 1.1 3.7-4.1 80 " " 0.3513 19.40
In the determination of manganese in the salts of perman-
ganic acid, the solution of the latter is decomposed, accord-
ing to Engels, with 5 cc acetic acid and enough hydrogen
peroxide to completely decolorize it. Since the presence of
even small quantities of hydrogen peroxide prevents the sepa-
ration and the firm adherence of the precipitate, the excess
of hydrogen peroxide must be removed. This may be most
easily accomplished by the addition of small quantities of
chromic acid, until further addition no longer causes the evo-
lution of gas; generally 0.3-0.5 g is sufficient.
EXPERIMENT.
50 cc of a potassium permanganate solution were decom-
posed with 5 cc acetic acid and 10 cc of a weak solution of
hydrogen peroxide. The excess of H a O 2 was removed with
Cr0 3 .
Current Density. Tension. Time. Temp. Mn 3 O 4 .
I. 1.5 amp. 2.8 volts 1 hr. 85 0.1217 g
II. " 1.65 " 3.15 " 1 " 85 0.1220"
III. 1.78 " 3.4 " 1 " 80 0.1220"
The current strength available varies between compara-
tively wide limits. Weak currents also give rapid and satis-
factory results.
* [Theory 19.52# Mn 3 O 4 .]
152 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
EXPERIMENT.
Three dishes, each containing manganese sulphate solu-
tion, 10 g ammonium acetate and 1 g chrome alum, were con-
nected in parallel, and the current from a thermopile passed
through. The tension at the electrodes at the beginning of
the electrolysis was 3 . 2 volts, the entire current strength 1.5
amp., so that each dish received about 0.4 amp. The man-
ganese salt used contained 20.45$ Mn 8 O 4 .
Time. Found.
1.1955 0.22 3.2 80 2hrs. 30 min. 20.45
0.9009 0.22 3.2 80 2 " " " 20.44"
1.2012 0.22 3.2 80 2 " " " 20.40"
Since manganese separates as peroxide from a cold solution
to which ammonium acetate has been added, at 1.25 volts,
and when warmed to 80 as low as 1-1.1 volts, the electroly-
sis may therefore be conducted with low electromotive forces.
The constancy of the latter may be assured by connecting in
shunt (page 73). The lower the tension, the longer the time
required for the separation. With the maximum tension of
1.8 volts it takes from 4 to 5 hours. For the firm adher-
ence of the precipitate a temperature of 80 is essential.
In those cases (i.e., in the presence of silver) where the
chrome alum produces a precipitate in the solutions, it may be
replaced by 10 cc of alcohol, which in general is not as effi-
cient as the chrome alum for separating the manganese perox-
ide.
When alcohol is used, the electrolysis is conducted at a
temperature of 75-80, with a maximum tension of 2 volts,
which gives a current density ND JOO = about 0.15 amp. Time
required for the electrolysis, about 5 hours.
ALUMINIUM, URANIUM, CHROMIUM, BERYLLIUM. 153
ALUMINIUM, URANIUM, CHROMIUM, BERYLLIUM.
If a solution of aluminium ammonium oxalate containing
ammonium oxalate in excess is submitted to the action of the
electric current, the ammonium oxalate is changed into car-
bonate, and the aluminium separates as hydroxide. When the
oxalate is decomposed, the solution is heated until there is only
a faint odor of ammonia, the hydroxide filtered off, washed
with water, and converted, by ignition, into A1 2 O 3 ,
Uranium is acted on in the same way as aluminium.
Chromium ammonium oxalate is oxidized by the current
with formation of ammonium chromate. To determine the
chromic acid, the ammonium carbonate is decomposed by
boiling, the* solution acidified with acetic acid, and the chromic
acid determined as lead or barium chromate.
When beryllium ammonium oxalate is subjected to elec-
trolysis, the beryllium is kept in solution by the hydrogen
ammonium carbonate produced, provided the solution is cold.
The behavior of aluminium, chromium, uranium, and be-
ryllium can be made use of, as explained later, to separate
them from each other and from all metals which separate
from their double oxalates in the metallic state at the nega-
tive electrode.
COPPER.
LITERATURE :
Gibbs, Zeit. f. anal. Chem., 3, 334.
Boisbaudran, Bull. d. 1. Soc. Chiin., 1867, p. 468.
Merrick, Amer. Chemist, 2, 136.
Wrightson, Zeit. f. anal. Chem., 15, 299.
Herpin, ibid,, 15, 335.
Ohl, ibid., 18, 523.
Classen, Ber. deutsch. chem. Ges., 14, 1622, 1627.
154 QUANTITATIVE ANALYSIS BY ELECTIIOLYS13.
Classen and v. Keiss, Zeit. f. anal. Chem., 14, 246.
Hampe, Berg- und Hiittenm. Ztg., 21, 220 ; 25, 113.
Riche, Zeit. f. anal. Chem., 21, 116,
Mackintosh, Am. Chem. Journ., 3, 354.
Riidorff, Ber. deutsch. chem. Ges., 21, 3050 ;
Zeit. f. angew. Chem., 1892, p. 5.
Luckow, Zeit. f. anal. Chem., 8, 23.
Warwick, Zeit. f. anorg. Chem., 1, 285.
Smith, Am. Chem. Journ., 12, 329.
Croasdale, Journ. of Anal, and Appl. Chem., 5, 133.
Foote, Am. Chem. Journ., 6, 333.
Meeker, Journ. of Anal, and Appl. Chem., 6. 267.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Heidenreich, ibid., 29, 1585.
Regelsberger, Zeit. f. angew. Chemie (1891), 16, 473.
Oettel, Chemiker-Zeitung, 1894, p. 879.
Schweder, Berg- und Huttenmann. Ztg., 36 (5) 11, 21.
/ If copper be reduced from a solution containing an excess
of ammonium oxalate, it is not always possible to obtain the
metal in a compact form. For this reason the author, as
long ago as 1888,* began experiments on the determination
of this metal from a solution of the acid double oxalate.
Further experiments in this direction have shown that coher-
ent, bright red copper precipitates can be obtained when cop-
per is reduced from such solutions at a temperature of about
80. The solution containing the copper is treated with a
cold-saturated solution of ammonium oxalate, heated as di-
rected, and at first electrolyzed for a few minutes without the
addition of oxalic acid. A cold- saturated oxalic acid solu-
tion is then run in from a burette. The method of proced-
ure here is similar to that described under Zinc (page 147).
In the analysis of substances low in copper, the solution
may be made acid at the start ; in concentrated solutions, on
the contrary, the electrolysis must be conducted in solutions
*Ber. deutsch. chem. Ges., 21, 2898.
COPPER. 155
which are as nearly neutral as possible, since otherwise diffi-
cultly soluble oxalate of copper will separate out, owing to
the free oxalic acid present. The end of the reaction is de-
termined by testing with potassium ferrocyanide a small por-
tion of the solution strongly acidified with hydrochloric acid.
The precipitate must be washed without stopping the current.
The metal is dried in an air-bath after treating with water
and alcohol.
The precipitated copper has a bright red color, adheres
firmly to the dish, and has little resemblance to the copper
precipitated from nitric acid solutions (see below). The
chief advantage of this method is the rapidity with which it
may be conducted.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : 80.
Current density:, JSD 100 = 0.5-1 amp. Most favorable
current density ND 100 = 1 amp.
Electrode tension: 2.5-3.2 volts.
Time of electrolysis; 2 hours.
EXPERIMENT. *
Used 1 g copper sulphate, 4 g ammonium oxalate, 120 cc
liquid.
CUr Amp?r e e n s Sity ' Elect ^J ensioa < Temp. Time. Found. Taken.
1.0-0.8. 2.8-3.2 80 2 hr. 0.2531 g 0.2529 g
0.45-0.35 2.5-2.8 80 2J " 0.2528 " 0.2529 "
Copper precipitate bright red.
As has been observed by Luckow, copper may also be
precipitated from a solution to which nitric acid has been
added.
* Separation of copper from a solution of the ammonium double
oxalate in the presence of free oxalic acid.
156 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
The reduction of copper from a nitric acid solution de-
pends upon the presence of a certain quantity of nitric acid
and the absence of chlorides. To about 200ccof solution,
containing the copper as sulphate, 20 cc of nitric acid * (sp.
g. = 1.21) are added and the liquid is subjected to electrolysis.
The end of the reaction is determined with ammonia.
The presence of chlorides is to be avoided. In the pres-
ence of antimony, arsenic, mercury, silver, tin, and bismuth,
traces of these metals come down with the copper ; but iron,
cobalt, nickel, cadmium, manganese, and zinc can be separated
from copper by this method.
According to the researches of Schroder large quantities
of iron are detrimental, since a secondary reaction may take
place between the ferric salt formed and the precipitated cop-
per, which causes the copper to redissolve.
Copper separates in a crystalline form from solutions
warmed to 50-60 ; it is nevertheless impossible to separate
the last traces of copper at this temperature.
CONDITIONS OF EXPERIMENT.
Temperature of solution : 20-30.
Current density: ND 100 = 0.5-1 amp. The latter only
when no other metal than copper is present in the solution.
Electrode tension : 2.2-2.5 volts.
Time : 4-5 hours. Agitating the solution with a stirring
attachment hastens the operation.
EXPERIMENT.
Used about 1 g copper sulphate and 5$ by volume nitric
acid. Entire volume of liquid 120 cc.
* Such a large quantity of nitric acid is required only when the separa-
tion of copper from other metals is to be carried out. If no other metal
than copper is present in the solution, 2 or 3 per cent by volume of nitric
acid is sufficient.
COPPER. 157
Electro ^J t e s nsion ' Temp. Time. Found. Taken.
1.1-1.0 2.2-2.5 25-30 5 hr. 0.2490 g Cu 0.2495 gCu
1.0-0.95 2.25-2.3 30-32 5" 0.2505"" 0.2510""
A solution containing free nitric acid may also be used
for separating such metals as are not reduced in the presence
of this acid, or which are set free at the positive electrode in
the form of peroxides. In such cases, however, it must be
kept in mind that the nitric acid is gradually converted into
ammonia, on account of which, after the current has acted
for some time, nitric acid must be occasionally added.
Copper may be separated from a solution containing am-
monium oxalate or one containing free nitric acid, in the
presence of small quantities of antimony and arsenic. If,
however, the amounts of the latter are considerable, then,
after continued action of the current, antimony and arsenic
are deposited upon the copper, causing the negative electrode
to appear more or less dark-colored. In order to determine
the copper in such cases, the dried electrode is ignited for a
short time, as a result of which the copper is oxidized and
the antimony and arsenic are driven off. The residue of
oxide is dissolved in nitric acid and again submitted to elec-
trolysis.*
In general the presence of chlorides causes the copper to
separate in a spongy condition. To avert this action and to
secure an adherent precipitate, Riidorff adds 2-3 g ammonium
nitrate and 20 cc ammonia (sp. g. 0.96), dilutes with water to
100 cc, and electrolyzes this solution. At the close of the re-
duction the solution is acidified with dilute acetic acid, the
dish filled to overflowing with water, emptied, shaken to re-
move the last drops of water, and dried at 100 in the air-
bath.
In the laboratory of the Technical High School at Munich
* Mansfeld'scbe Hiittendirection.
158 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
the preceding method is carried out under the following con-
ditions : Ammonia is added in slight excess until the precipi-
tate which at first appears is redissolved. Then 20-2 5 cc
ammonia, sp. g. 0.96, are added, in case not more than 0.5g
copper is present.* In this solution 3-5 g ammonium nitrate
are dissolved and the electrolysis is conducted with a current
of OT) JOU 2 amperes. The precipitate must he washed
without interrupting the current.
Oettel, who also carried out experiments on the quantita-
tive determination of copper from ammoniacal solutions,
found that by the addition of ammonium nitmte 0.2-0. 25 g
of copper sulphate were quantitatively reduced in 6-8 hours
at ordinary temperatures. The results of his investigation are :
" 1 . That copper can be separated in a compact form
from weakly ammoniacal solutions containing ammonium
nitrate, by currents of ]STD 100 = 0.07-0.27 ampere. With too
little ammonium nitrate, as well as in the presence of large
quantities of free ammonia, the precipitate shows a tendency
to a spongy structure.
"2. The highest concentration of the solution is 0.8 g
copper per 100 sq. cm. electrode surface, with the employ-
ment of a wire-shaped positive electrode.
"3. The presence of chlorine, zinc, arsenic, and small
quantities of antimony is without detrimental action ; when the
solution contains lead, bismuth, mercury, cadmium, or nickel,
the results of the determinations are somewhat too high."
E. F. Smith f precipitates copper from a solution which
contains sodium phosphate and free phosphoric acid.
Heidenreich, who tested the method in the Aachen laboratory,
obtained the following results.
* If as much as 1 g Cu is present, the quantity of ammonia is increased
to 30-35 cc.
f Electrochemical Analysis, p. 92.
COPPER. 159
EXPERIMENT.
100 cc of a solution of NaJIPO 4 (1.0358 g) and 3.o cc
of a solution of phosphoric acid (1.347 g) were diluted with
water to 110 cc. To this solution the copper solution was
added.
Taken. Volts. Time. Found.*
0.3959 g 2.4-2.6 17 hr. 25.41
0.3982 " 2.4-2.6 17 " 25.26 "
The copper separated at first brilliantly metallic, but as
the electrolysis proceeded it became dark red and spongy.
Variations of the conditions, such as increasing the tension,
led to no better results. Owing to the spongy condition of
the precipitate, the results came too high.
For the special determination of copper, in copper-alumin-
ium alloys, liegelsberger suggests dissolving 3-5 g of the
alloy in nitric acid and evaporating the solution down to the
consistency of sirup. The sample is diluted, and a measured
quantity (corresponding to 0.6-1 g substance) is poured into
the electrolytic cell. An excellent precipitate is obtained if
the acid solution is neutralized with ammonia and 10 cc of
dilute nitric acid (sp. g. 1.2) are added to 200 cc of the
liquid. The clear solution is electrolyzed with a current den-
sity ND IOO OA amp. When the solution is warmed the
separation is completed in about three hours.
A rapid and accurate method for the determination
of copper has been worked out by Carl Engels in the
Aachen laboratory. This method has the advantage over the
use of nitric acid solutions that it can be more rapidly per-
formed, and that, in separations, it also dispenses with the
tedious conversion of the nitrates into sulphates. This method
is based upon the addition of urea.
The separation of copper from solutions containing sul-
* [Theory 25.33# Cu.]
160 QUANTITATIVE ANALYSIS BY ELECTKOLYSIS.
phuric acid is possible also if hydroxylamine be added. The
method is as follows :
If the separation is to be carried out with weak currents,
say during the night, the addition of 2 cc concentrated sul-
phuric acid and about J- g hydroxylamine sulphate is recom-
mended. A fine crystalline precipitate and absolutely accurate
results are obtained with a current strength of OT3 100 =
0.08-0.18 ampere. The tension at the poles of a shunt cir-
cuit was 1.8-2.2 volts; after connecting the dish the tension
sank to 1.1-1.3 volts, with a current of 0.1-0.2 amp.
EXPERIMENT.
Taken Current Density Tension, T , Found. p ^
CuS0 4 .5H 2 O. 'ND 100 . Volts. me ' Cu.
1.0130g. 0.1 amp. 1.1 Night 0.2574 25.41
1.7065 " 0.12 " 1.3 " 0.4335 25.40
1.1893 " 0.1 " 1.2 " 0.3021 25.41
If stronger currents are used, the amount of sulphuric
acid must be increased. 1015 cc of cone, sulphuric acid
are poured into the solution of the salt, it is diluted to 150
cc, and 1 g hydroxylamine sulphate is added. If 0.3-0.5
g Cu is present, with a current strength of ND JOO 1 amp.,
the separation is finished in 1^ to 2 hours. The condition of
the precipitated copper is much better and much more suited
for quantitative determination than the copper obtained under
similar conditions without the addition of hydroxylamine.
Urea exerts a far more satisfactory action than hydroxyl-
amine upon the separation of copper from solutions contain-
ing sulphuric acid. "With a current strength of OT) ]00 = 1
ampere, not the slightest tendency toward a spongy separa-
tion is exhibited, but a bright-red crystalline coating is
obtained on the negative electrode. The analysis, with the
stated current density, is completed in 1J hours.
10-15 cc concentrated sulphuric acid and 1 g urea are
* [Theory 25.33$ Cu.]
.;urreui ueusity
NDjooi Amp.
JLVU81OU,
Volts.
Temp.
Time.
Found.*
1.05
3.1
25
1 hr. 15 m.
25.09 %
1.2
3.1
55
1 " 15 "
25.09"
0.75
2.7
65
1 " 45 "
25.09"
COPPER. 161
added to the solution of the copper, which is then diluted to
150 cc.
CONDITIONS OF EXPERIMENT.
Temperature of liquid : Most suitable, 60-70.
Electrode tension : 2.7-3.1 volts.
Current density: KD 100 = 0.8-1 amp.
Time : 1 J- hours.
EXPERIMENT.
Used CuSO 4 .5H 2 O.
Quantsub
1.1364
0.9671
1.3972
The current may be interrupted in washing the precipitate.
The separated copper contains traces of carbon, and also plat-
inum which dissolves from the anode. These admixtures
can be determined by dissolving the copper in dilute nitric
acid (1 : 10). A thin dark coating remains on the dish,
which may be washed with water, but not with alcohol, with-
out becoming loosened. The weight of the dish, determined
after washing and drying in the air-bath, is used as a basis
for calculating the weight of the separated copper.
With weaker currents the length of time required is of
course greater. With a current density of ND 100 = 0.2 am-
pere, the precipitation of from 0.3 to 0.4 g Cu is completed
in 3- 4 hours. It is desirable in this case to add less sul-
phuric acid to the solution; 5 cc cone. H a SO 4 to each 150
cc, is the proper proportion.
Four dishes were connected in parallel, and for every 150
cc of solution of the copper salt which they contained 1 g
urea and 5 cc cone. H,SO 4 were added. The four electroly-
* [Theory 25.33^]
162 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ses were then conducted in the cold, with the current from
a thermopile. The entire current strength was !ND 100 = 0.8
ampere, so that each dish received a current of ND 100 = 0.2
ampere. The analyses were completed in 4 hours. The per
cent, of copper in the salt used was 25.08.
Used CuSO 4 .5H 2 O. Found Cu. Found %.
l.OlOlg 0.2533g 25.07
1.0815 " 0.2709 " 25.05
1.0320 " 0.2589 " 25.08
1.0111 " 0.2535 " 25.07
BISMUTH.
LITERATURE :
Luckow, Zeit. f. anal. Chem., 19, 16.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622.
Thomas and Smith, Am. Chem. Journ., 5, 114.
Moore, Chem. News, 53, 209.
Smith and Knerr, Am. Chem. Journ., 8, 206.
Schucht, Zeit, f. anal. Chem., 22, 492.
Eliasberg, Ber. deutsch. chem. Ges. , 19, 326.
Brand, Zeit, f. anal. Chem., 28, 596.
Vortmann, Ber. deutsch. chem. Ges., 24, 2749.
Kiidorff, Zeit. f. angew. Chem., 1892, p. 199.
Smith andi Saltar, Zeit. f. anorg. Chem., 3, 418.
Smith and Moyer, Journ. of the Am. Chem. Soc., 15, 28, 101.
Smith and Knerr, Am. Chem. Journ., 8, 206.
Schmucker, Zeit. f. anorg. Chem., 5, 199.
Up to the present time it has been found impossible to
quantitatively precipitate bismuth in a compact metallic form.
It separates in a more or less spongy form from all its com-
pounds. A discussion of the directions given by the different
investigators will therefore be omitted.
G. Vortmann has attempted to separate bismuth as an
amalgam. Since, however, the directions for the conditions
of experiment are not given, the mere mention of this method
will be sufficient.
CADMIUM. 163
CADMIUM.
LITERATURE :
Smith, Am. Phil. Soc. Pr., 1878.
Clarke, Zeit. f. anal. Chem., 18, 104.
Beilstein and Jawein, Ber. deutsch. chem. Ges., 12, 759.
Smith, Am. Chem. Journ., 2, 43.
Luckow, Zeit. f. anal. Chem., 19, 16.
Wrightson, ibid., 15, 303.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1638,
Warwick, Zeit. f. anorg. Chem., 1, 258, 291.
Moore, Chem. News, 53, 209.
Smith, Am. Chem. Journ., 12, 329.
Vortmann, Ber. deutsch. chem. Ges., 24, 2749.
Eiidorff, Ztschr. f. angew. Chem., 1892.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Heidenreich, ibid., 29, 1586.
The separation* of this metal in a compact brilliant form
has been shown, by experiments carried out at the Aachen
laboratory, not to be possible by any of the methods hitherto
described. It may bo accomplished, however, by the elec-
trolysis of a warm solution of the double oxalate which is
kept acid with oxalic acid during the electrolysis. (A cold-
saturated solution of oxalic acid is employed.) (See direc-
tions for Zinc.)
To prepare the double salt, the cadmium compound is
dissolved in 20-25 cc water, by warming in a platinum
dish ; a hot solution, which should be previously filtered, of
10 g ammonium oxalate in 80-100 cc water is added and the
solution is electrolyzed. As soon as the action of the current
has begun, several cubic centimeters of oxalic acid are poured
upon the watch-glass covering the dish, and the liquid is kept
* The metallic condition of the precipitated cadmium, all the conditions
of the experiment being preserved, depends upon the absolute cleanliness
of the surface of the cathode.
164 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
weakly acid during the electrolysis. The end of the reaction
is determined with hydrogen sulphide, by testing a small por-
tion of the solution acidified with hydrochloric acid. The
metal must be washed without interrupting the current.
(Method of the author.)
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : 70-75.
Current density: !ND 100 = 0.5-1 amp.
Electrode tension: 3-3.4 volts.
Period of electrolysis : About 3 hours.
Maximum quantity of metal which can be precipitated :
0.15-0.16 g.
EXPERIMENT.
Used 0.3-0.4 g cadmium sulphate, 10 g ammonium oxa-
late, 120 cc liquid.
CU Tmper e e n S Sity ' Electr ^ o e lt T s ension ' Temp. Time. Found.
0.6-0.5 2.75-3.4 73-76 3 hr. 30m. 0.1472 g 49.07 #*
1.0-0.8 3.0-3.4 68-73 3" 0.1474 g 49.13"
Precipitate brilliantly lustrous.
"With regard to further experiments by this method and
for data on the use of polished and roughened dishes, of which
the former are in this case to be preferred, the dissertation of
N. Eisenberg f should be consulted.
Smith and Luckow recommend the precipitation of cad-
mium from a solution of the chloride or sulphate, which has
been saturated with sodium acetate. Eliasberg, who tested
this method in the Aachen laboratory, found that the reduc-
tion took place readily when the solution, of about 100 cc
volume, was treated with about 3 g sodium acetate and a few
*[The salt taken was probably CdSO 4 .H 2 O containing 49.67$ Cd. Trans.]
f Eisenberg, Inaugural-Dissertation, Heidelberg, 1895
CADMIUM. 165
drops of acetic acid, and the electrolysis wab carried out at a
temperature of 40-50.
In the laboratory of the Munich High School the forego-
ing method is practised as follows : The solution, neutralized if
necessary, containing not more than 0.5 g cadmium, is treated
with 3 g sodium acetate, and made weakly acid with acetic
acid. The solution is warmed to 45, and decomposed with
a current of ]SD 10o 0.02-0.07 ampere. The metal is
washed without interrupting the current, and quickly dried
at 100.
During the electrolysis the solution should not be warmed
above 50, on account of the formation of basic salts. Cad-
mium is only partly precipitated from solutions strongly
acidified with acetic acid. By this method 0.2 g of cadmium
may be separated in about five hours. The presence of
nitrates is detrimental.
According to Beilstein and Jawein, the determination of
cadmium may be conducted from a solution of the double
salt with potassium cyanide. Aside from the fact that the
necessary directions are not given, this method possesses no
advantages, the precipitation of 0.2 g cadmium requiring
about 12 hours.
Vortmann attempted the determination of cadmium by a
method similar to that used for the determination of bismuth
and zinc, by precipitation from a solution of the ammonium
double salt in the form of amalgam.
E. F. Smith determines cadmium by dissolving the oxide
in acetic acid, evaporating, taking up in water, and electro-
lyzing the solution thus obtained. Heidenreich, who carried
out in the Aachen laboratory a series of varied researches on
this subject, obtained no satisfactory results, either in the
condition of the precipitate or in the quantitative separation
of the metal.
166 QUANTITATIVE ANALYSIS BY ELECTROLYSIS."
A further method by E. Smith depends upon the reduc-
tion of cadmium from a solution to which sodium phosphate and
free phosphoric acid have been added. Here also the quanti-
tative separation of the cadmium does not take place, not even
when the current is increased to 1 ampere.
Finally, Smith * has proposed a method for the separation
of cadmium from a solution containing free acetic acid.
According to the statements of Heidenreich, cadmium is pre-
cipitated from a solution containing 10 cc acetic acid (50$)
to 120 cc of solution, by a current density of 0.4 ampere
and a tension of 4.5 volts, in the form of small crystalline
plates which cannot be washed without loss. Variations of
the conditions of experiment (addition of less acetic acid
[2-10 cc], employment of current densities of from 0.1 to
0.4 ampere and tensions of 4-7. 5 volts, as well as different
temperatures) gave no satisfactory results.
LEAD. *
LITERATURE :
Kiliani, Berg- u. Hiittenin.-Zeitung, 1883, p. 253.
Luckow, Zeit. f. anal. Chem., 19, 215.
Kiche, Ann. d. Chim. et Phys., 13, 508; Zeit. f.anal. Chem., 21, 117.
Classen, Zeit. f. anal. Chem., 21, 257.
Hampe, Zeit. f. anal. Chem., 13, 183.
Parodi and Mascazzini, Ber. deutsch. chem. Ges., 10, 1098;
Zeit. f. anal. Chem., 16, 469; 18, 588.
Kiche, Zeit. f. anal. Chem,, 17, 219.
Schucht, Zeit. f. anal. Chem., 21, 488.
Tenny, Am. Chem. Journ., 5, 413.
Smith, Am. Phil. Soc. Pr., 24, 428.
Vortmann, Ber. deutsch. chem. Ges., 24, 2749.
RMorff, Zeit. f. angew. Chem., 1892, p. 198.
* Electrochemical Analysis, p. 95.
LEAD. 167
Warwick, Zeit. f. anorg. Chem., 1, 258.
Classen, Ber. deutsch. chem. Ges., 27, 163.
Kreichgauer, ibid., 27, 315; Zeit. f. anorg. Chem., 9, 89.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Medicus, ibid., 25, 2490.
Neumann, Chemiker-Zeitung, 1896, p. 381.
If a solution of a lead salt containing an excess of ammo-
nium oxalate be electrolyzed warm, the lead separates at
the negative electrode, adheres closely, and shows its char-
acteristic metallic properties ; but it oxidizes partially on wash-
ing with water and alcohol, so that the results are always too
high. The precipitation of lead as amalgam presents some
difficulties, inasmuch as some lead peroxide separates at the
positive electrode and must be dissolved. According to G.
Yortmann, the aqueous solution of the lead salt, containing
sufficient mercuric chloride to produce the amalgam, is treated
with 3-5 g sodium acetate and a few cubic centimeters of
concentrated potassium nitrite solution. The precipitate pro-
duced by the latter reagent (which is added to prevent the
formation of peroxide) is dissolved in acetic acid, and the
clear yellow solution diluted and electrolyzed. If lead per-
oxide appears on the positive electrode during the reaction,
more potassium nitrite is added. The close of the reaction is
determined by testing with ammonium sulphide. As lead
amalgam oxidizes rather readily when moist, it is quickly
washed with water, alcohol, and ether, dried by the warmth
of the hand and by blowing upon it, and finally in the desic-
cator.
The amalgam may also be separated from an aqueous solu-
tion acidified with nitric acid. However, as free nitric acid
favors the formation of lead peroxide, more frequent addition
of potassium nitrite is necessary, and complete precipitation
is thereby seriously hindered.
168 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
In a solution containing free nitric acid, lead is acted on
like manganese; it is oxidized, and separates as hydrated
peroxide at the positive electrode. If there is no other metal
in the solution, it must contain at least 10 per cent free nitric
acid, according to Luckow ; in the presence of other metals
{mercury, copper, etc.), the oxidation is complete even in
presence of little nitric acid.
In the Munich laboratory experiments have been con-
ducted as to the quantity of nitric acid, sp. gr. 1.36, and have
demonstrated that this depends on the temperature and
the current density which is used. The current density
depends in turn on the condition of the surface of the positive
electrode. If this is very smooth, a current of ND 100 = 0.05
is sufficient, otherwise one of NDi 00 = 0.5 is needed to pro-
duce an adherent precipitate. When ND ]00 0.05 ampere,
2 per cent by volume of nitric acid should be added when the
solution is heated, and 10 per cent by volume at ordinary
temperatures. "When ED 100 = 0.5 the vohime-percentages
are, respectively, 7 and 20 for heated and cool solutions.
Heating the solution to about 50 materially assists the
separation. ' The precipitate may be washed without loss, after
the current is interrupted.
Chlorine compounds urns*, not be present in the solution
for electrolysis.
Even when the stated conditions are observed, the quan-
tity of lead which can be precipitated as peroxide in an
adherent form is relatively small.* The rapid separation of
large quantities of lead peroxide, firmly adherent like a metal,
may only be carried out without difficulty, as the author's
* From experience in the Aachen laboratory, the greatest possible quan-
tity is 0.15 gPbO 2 per 100 sq. era. surface, while according to the statements
of Dr. Cohen (Chem. Ztg., 1893, No. 98) as much as 0.3 g can be precip-
itated.
LEAD. 169
researches have shown, when the inside of the platinum dish
serving as anode is roughened with a sand-blast.* By the
use of such dishes, it is possible, with a current of 1.5 ampere,
to precipitate in a few hours as much as 4 g of lead peroxide
on 100 sq. cm. of surface.
For conducting the determination of lead, after the solu-
tion of the lead salt has been accomplished, 20 cc nitric acid
(sp. g. 1.35-1.38) are added, the solution is diluted to about
100 cc, warmed to 60-65, and electrolyzed with a current
of ND 100 = 1.5-1.7 amperes. If the warming is continued
during the electrolysis, the precipitation of quantities up to
1 . 5 g lead peroxide is completed in about 3 hours ; with larger
quantities in about 4-5 hours. Complete precipitation is
insured by adding about 20 cc of water and observing
whether the freshly wetted surface of the electrode becomes
darker. Incase no blackening is observed at the end of 10-15
minutes, the current is stopped, and the precipitate is washed
with water and alcohol, and dried at 180-190. The residue
is anhydrous peroxide.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid: 60-65.
Current density: ND JOO = 1.51.7 amp.
Electrode tension: 2.5 volts. The tension is without
influence upon the condition of the peroxide, and may vary
within wide limits.
EXPERIMENT.
Used Pb (NO 3 ) a dissolved in 100 cc water, with the ad-
dition of 20 cc nitric acid (sp g. 1.35-1.38).
* The platinum refinery of G. Siebert in Hanau has faultlessly carried
out the roughening in the desired manner at the request of the author.
Such roughened dishes are of course applicable to all other electrolytic
determinations.
170 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Current Density,
Amperes.
Electrode Tension,
Volts.
Temp.
Time.
Found.*
1.55-1.45
2.43-2.4
60-65
1 hr. 5 m.
72.20 %
1.6 -1.58
2.48-2.43
60-65
1 " 10 "
72.19"
1.6 -1.65
2.41-2.36
60-65
1 " 5 "
72.20"
The preceding method permits of the separation of lead
from zinc, iron, nickel, cobalt, manganese, copper, cadmium,
gold, mercury, antimony, and aluminium ; in the presence of
silver and bismuth, traces of these metals in the form of
peroxides pass over into the lead peroxide.
THALLIUM.
Tins metal may be completely precipitated from an am-
monium oxalate solution.
The properties of thallium,
however, are similar to those of
lead ; its determination therefore
requires special consideration.
G. Neumann, in connection
with a research on certain double
salts of thallium in the Aachen
laboratory, has also investigated
the quantitative determination of
the metal. As his method is of
value in the investigation of
thallium compounds, it is here
described. The process is based
on precipitation of the thallium
as metal, and determination of
the volume of hydrogen set free
by its solution in hydrochloric
acid.
The apparatus shown in Fig.
K is a flask of about 100 cc
FIG. 85.
85 is used for the process.
* Theory 7221
THALLIUM. 171
capacity, containing platinum- foil electrodes of 9 sq. cm.
surface, terminating in con tact- wires fused into the glass.
The thallium salt and about 5 g ammonium oxalate are dis-
solved in this flask, and electrolyzed, after dilution, with a
current of 0.1 ampere. The completion of the reaction is
ascertained by testing with ammonium sulphide. As the
FIG. 86.
ammonium oxalate is converted into carbonate by the current,
and the measuring-tube would be insufficient to contain
the disengaged carbon dioxide, the solution remaining in the
flask is removed after the reaction. This may readily be
done by the use of two siphons. Neumann's automatic
arrangement for this purpose is shown in Fig. 86 ; it is
very convenient where many determinations are to be per-
172 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
formed, and its operation is easily seen from the figure.
The washing is conducted without interrupting the current.
To remove the gas-bubbles clinging to the electrode it is
desirable to heat the flask a short time after the washing is
complete. The flask is then connected to the measuring-
tube, the thallium dissolved, and the hydrogen collected ani
measured in the usual way,
SILVER.
LITERATURE :
Luckow, Dingl. polyt. Journ., 178, 43 ; Zeit. f. anal. Chem., 19, 15.
Fresenius and Bergmann, Zeit. f. anal. Chem., 19, 324,
Krutwig, Ber. deutsch. chem. Ges., 15, 1267.
Schucht, Zeit. f. anal. Chem., 22, 417.
Einnicutt, Am. Chem. Journ., 4, 22.
Riidorff, Zeit. f. angew. Chem., 1892, p. 5.
Eisenberg, Dissertation. Heidelberg, 1895.
Of the methods proposed for the determination of silver,
the one suggested by Luckow (separation of the silver from
the potassium double cyanide) is probably the most suitable.
If insoluble silver compounds (silver chloride, silver oxalate)
are to be analyzed, they are dissolved in potassium cyanide
solution. For conducting the method, 3 g potassium cyanide,
are added to the solution, which is then diluted to 100-120 cc.
Eisenberg, who tested the method in the Aachen laboratory,
was convinced that the success of the same, as well as the
metallic condition of the precipitated silver, depends upon the
purity of the potassium cyanide used. Even the so-called
" purissimum " potassium cyanide of commerce is unsuited.
It is therefore desirable to prepare pure potassium cyanide by
passing hydrocyanic acid gas into an alcoholic solution of
potassium hydroxide.
SILVER. 173
CONDITIONS OF EXPERIMENT,
Temperature of the liquid : 20-30.
Current density: ND 100 0.2-0.5 amp.
Electrode tension : 3.7-4.8 volts.
Time of electrolysis : In the presence of equal quantities
of silver, with current densities ND 100 = 0.2-0.5 ampere,
this varies from 5 to 1 j- hours.
For this determination, roughened dishes give best results.
EXPERIMENT.
(a) Experiment with the so-called " purissimum " potas-
sium cyanide of commerce. Used silver sulphate.
C,,KO* Current Electrode Condition
Dsc - Density, Tension, Temp. Time. Found.* of Remark,
taken. Amp ' Vokg Metal
0.8660 0.4-0.2 3.35 23-24 6 hr. 68. 91# } Not firmly j Rough dish.
0.8660 0.3-0.1 3.55 22-24 6" 68. 91 ") adherent ( Polished "
(b) Experiment with pure potassium cyanide. Used silver
sulphate.
O,,K-- Current Electrode Condition
Dsr - Density, Tens., Temp. Time. Found. of Remark,
taken. Amp /' volts! Metal.
0.4369 0.3-0.23 3.72 22 5 hr. 69.08$ ) Firmly (Roughened
0.4370 0.52-0.54 4.6-4.8 20-30 1 " 40 m. 69.00 "J adherent 1 dish.
0.4369 0.32-0.21 3.70 22 5" 69.12") (( i Polished
0.8742 0.55-0.53 4.0 23 2 " 40 " 68.98 " f \ dish.
J. Krutwig treats the solution of the silver salt with
ammonia in slight excess, adds ammonium sulphate, and
electrolyzes.
In the Munich laboratory the following conditions have
been determined for the preceding process. The solution,
which must not contain more than 0.5 g silver, is treated
* [Theory 69.22* Ag.]
174 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
with 20 per cent by volume of ammonia (sp. gr. 0.96) and 5$
ammonium sulphate solution (1 : 10), warmed, and electrolyzed
with a current of ND 100 = 0.02 0.05 ampere. After the
current is stopped the precipitate must be very thoroughly
washed to completely remove the ammonium sulphate.
Fresenius and Bergmann have found that silver can also
be precipitated in a dense form from a solution containing
nitric acid: 20 cc of nitric acid (sp. g. 1.2) are added to the
silver solution, which is then diluted with water to about
200 cc and electrolyzed.
According to results in the Munich laboratory, it is desir-
able to add to the solution, which may contain as much as OA
g silver, 3 per cent by volume of nitric acid, sp. gr. 1.36, and
to electrolyze the heated solution with a current of ND ]00 =
0.04-0.05 ampere. The silver must be carefully washed
without interrupting the current, to prevent loss. An insuf-
ficient quantity of nitric acid may lead to the formation of
peroxide.
MERCURY.
LITERATURE :
Clarke, Am. Journ. of Sci. and Arts, 6, 200.
Classen and Ludwig, Ber. deutsch. chem. Ges., 19, 323.
Hoskinson, Am. Chem. Journ., 8, 209.
Smith and Knerr, ibid., 8, 206.
Smith and Frankel, Am. Chem. Journ., 11, 264.
Smith, Journ. Anal. Chem., 5. 202.
Vortmann, Ber. deutsch. chem. Ges., 24, 2749.
Brandt, Zeit. f. angew. Chem., 1891, p. 202.
Riidorff, ibid., 1892, p. 5.
Eisenberg, Dissertation. Heidelberg, 1895.
Frankel, Journ. Franklin Inst., 131, 144.
Rising and Lenher, Berg* und Hiittenm. Ztg., 55, 175.
The metal can be readily separated from solutions of the
mercuric salts to which 4-5 g ammonium oxalate have been
MERCURY.
175
added (method of the author). If the mercury is present as
chloride in the solution, the electrolysis is continued until
mercurous chloride disappears from the positive electrode^
CONDITIONS OF EXPERIMENT.
Temperature of liquid : Ordinary temperatures.
Current density: NT) 100 = 0.1-1.0 amp.
Electrode tension: 2.5-5.5 volts.
Time : Dependent on the current density.
Roughened dishes are preferable to polished, on account
of the more uniform distribution and firmer adherence of the
mercury to the cathode. On polished dishes the mercury
separates in the form of small globules.
EXPERIMENT.
Subst.
used.
HgCl a .
g-
Current
Density,
Amperes.
Electrode
Tension,
Voles.
Temp.
Time,
hrs. m.
Found '* Remark.
0.4068
0.2 -0.15
2.6 -3.35
30-23
5
15
73.74)
0.4073
1.02-0.93
4.05-4.75
29-37
1
30
73.63
0.4076
1.08-0.92
4.42-4.88
25-40
2
5
73.77
Roughened
0.4080
1.15-1.09
4.97-5.05
18-40.5
2
5
73.87
Dish.
0.4080
1.12-0.93
4.95-4.85
18-38
2
5
73.84
0.4080
1.52-0.48
3.65-4.65
16-27
3
55
73.67- 1
0.4070
0.2 -0.23
2.89-3.75
28^24
5
15
73.80
0.4073
1.06-0.95
4.45-5.00
30-39.5
1
30
73.29
0.4076
1.16-1.09
5.32-5.53
23-40
2
5
73.93
Polished
0.4080
1.20-0.99
4.70-4.90
18-43
3
73.55
Dish.
0.4075
1.51-0.48
3.87-4.50
16-30
3
55
73.85
Mercury may also be quantitatively precipitated from a
solution containing nitric, sulphuric, or hydrochloric acid.
If no other metal than mercury is present, 1-2 per cent by
volume of nitric acid is sufficient ; while in the presence of
other metals, which are not precipitated from solutions con-
* [Theory 73.85# Hg.]
176 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
taining free acid, 5 per cent by volume is required. In the
latter case a current density not greater than 0.5 ampere is
employed ; in the former the current density may be raised
to 1 ampere.
If hydrochloric acid is used, only a few drops are added,
since larger quantities have a detrimental action on the separa-
tion of the metal. Large quantities of chlorides have an
action similar to that of large quantities of hydrochloric acid.
Insoluble mercury compounds may be easily electrolyzed
by suspending them in water slightly acidified with hydro-
chloric acid, or in a dilute solution of sodium chloride (about
10 per cent). This process, originated by the author, is
used at Almaden for determining the amount of mercury
contained in cinnabar.
Edgar F. Smith precipitates mercury from the solution of
the same in potassium cyanide. The solution of the mercuric
salt, which may contain about 0.2 g mercury, is decomposed
with 0.25-2 g potassium cyanide, diluted with water to 175
cc and electrolyzed.
Heidenreich, in the Aachen laboratory, determined the
conditions of experiment for this method.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid : Ordinary temperatures.
Current density : KD 100 = 0.03-0.08.
Electrode tension : 1 . 6 5-1 . T 5 volt.
Time : Dependent on the current density.
m , Current Dens. Tension, m._, & j *
Taken - ND 100 , Amp. Volts. Time " Found.*
0.2501 g HgCU, 2-3 g KCN 0.08-0.04 1.65-1.69 5 hr. 73.61$ Hg
0.2655 " " " " " 0.03 1.75 14 " 73.50" "
The metal reduced by this method must be washed with
water only, and not with alcohol, since, on washing with
* [Theory 73.85$ Hg.]
GOLD. 177
the latter, small quantities of the mercury will become loos-
ened and be carried away.
GOLD.
LITERATURE I
Luckow, Zeit. f. anal. Chem., 19, 14.
Brugnatelli, Phil. Magazin, 21, 187.
Smith and Muhr, Ber. deutsch. chem. Ges., 23, 2175.
Smith and "Wallace, Proceed. Chem. Soc. Franklin Inst., 3, 20.
Smith, Am. Chem. Journ., 13, 206.
Persoz, Annal. Chem. Pharm., 65, 164.
Riidorff, Zeit. f. angew. Chem., 1892, p. 695.
Gold may be separated in a compact form from solutions
of gold salts in potassium cyanide. To form the double
cyanide, about 3 g of potassium cyanide are added. The
solution is then electrolyzed at ordinary temperatures or at
temperatures between 50 and 60. Since the gold can be
removed from the platinum dish with aqua regia only (an
operation by which the platinum is also dissolved), platinum
dishes coated with a thin deposit of silver have previously been
used for this determination. According to a private commu-
nication from Dr. "W. Dupre of Stassfurt, the gold may be
readily removed from the platinum dishes by warming with a
solution of chromic anhydride in saturated sodium chloride
solution. The author can confirm this statement; in this
operation gold only, and no platinum, goes into solution.
Since the conditions of experiment for the separation of
gold from double cyanides had not been previously determined,
they were ascertained by Dr. v. Wirkner at the suggestion of
the author.
CONDITIONS OF EXPERIMENT.
Temperature of the liquid: Ordinary temperatures; or
better 50-60, since at ordinary temperatures a brownish
decomposition product of potassium cyanide often separates.
178 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Current density : ND 100 = 0.3-0.8 amp.
Electrode tension : 2.7-4 volts.
EXPERIMENT.
A solution of chloride of gold of unknown strength was
used. The electrolyses were carried out in roughened plat-
inum-iridium dishes without a coating of silver. Used 3 g
potassium cyanide, 120 cc liquid.
Taken, cc
Gold Chlo-
ride Sol.
Current
Density,
Amperes.
Electrode
Tension,
Volts.
Temper-
ature.
Time,
hr. m.
15
0.3
3.5-3.9
20-27
5
15
0.35
3.9-4.0
22-28
14 (overnight)
30
0.37
3.6-3.9
20-28
4 15
15
0.38
2.7-3.8
52-55
1 30
15
0.38
2.7-3.4
53-54
1 20
15
0.39
2.7-3.8
52-56
1 30
15
0.85
4.0-4.1
52-56
1 30
Found,
g-
0.0545
0.0548
0.1099
0.0544
0.0546
0.0545
0.0544
ANTIMONY.
LITERATURE I
Wrightson, Zeit. f. anal. Chem., 15, 300.
Parodi and Mascazzini, ibid., 18, 588.
Luckow, ibid,, 19, 13.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622 ;
ibid., 17, 2467; 18, 1104.
Lecrenier, Chemiker Zeitung, 13, 1219.
Vortmann, Ber. deutsch. chem. Ges., 24, 2762.
Rudorff, Zeit. f. angew. Chem., 1892, p. 199.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Antimony is precipitated from hydrochloric acid solution,
but not in an adherent form. If potassium oxalate is added
to the solution of the trichloride, antimony is easily reduced,
but adheres even less closely than in the other case. An
adherent metallic deposit can be obtained by adding potassium
tartrate, but the separation is then too slow.
ANTIMONY. 179
The precipitation of antimony from the solutions of its
sulpho-salts is complete and satisfactory. If ammonium sul-
phide is used to produce a double salt, it must contain neither
free ammonia nor polysulphides. Ammonium hydrosulphide,
therefore, is convenient for the determination ; it is kept in
small, tightly corked bottles.
When a solution of antimony containing ammonium sul-
phide is electrolyzed, there is formed over the metal a coating
of sulphur which cannot be washed off with water. When
the metal is washed afterward with alcohol, the thin coating
of sulphur can be removed by rubbing with the finger or a
handkerchief moistened with alcohol, without danger of loss.
The use of ammonium sulphide has the disadvantage that,
when several determinations are made together, the odor
becomes unbearable. For this reason the author has made a
series of experiments with potassium and sodium monosul-
phide and hydrosulphide, the results of which show that the
precipitation of antimony from double salts with these com-
pounds proceeds satisfactorily. As sodium sulphide (Na 2 S) is
the one of the salts named which is most desirable for facilitat-
ing the separation of antimony from tin and arsenic, the
following particulars relate exclusively to the use of this salt *
for the determination of antimony.
The following equations probably represent the reactions
which take place in the electrolysis of the antimony sulpho-
salt. The current first decomposes water :
3H a O = 6H + 30.
At the cathode :
Sb a S, + 3Na a S +6H = 2Sb + 6NaHS.
At the anode :
3O = 3Na 3 S a + 3H 2 O.
* For the preparation of this salt, see section on Reagents.
180 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
The reduction of antimony from the prepared sulpho-salt&
can be carried out as well at ordinary as at higher tempera-
tures. In the first case the determination requires 17-18
hours, in the latter about 2 hours. If the separation is con-
ducted in polished dishes, only relatively small quantities of the
metal can be made to adhere firmly to the dish, and the em-
ployment of weak currents is necessary. In recent experi-
ments roughened dishes have been used, and the reduction has
been conducted from hot solutions and with stronger currents.
To carry out the analysis, 80-100 cc of a solution of
sodium monosulphide (sp. g. about 1.14) are added to the
antimony solution, which is diluted with water to 120 cc, and
electrolyzed. If the metal is precipitated from a warm solu-
tion, it must be washed without interrupting the current.
The end of the reaction can only be determined with certainty
by the use of another electrode which is dipped into the liquid
and brought into contact with the dish, i.e., the cathode.
The dish with the separated antimony is treated in the
usual way with water and perfectly pure absolute alcohol,
dried for a short time in the air-bach at 80-90, and weighed.
CONDITIONS OF EXPERIMENT.
A. Temperature of the liquid : Ordinary temperatures.
Current density: ND 100 = 0.3-0.35 ampere.
Electrode tension: 1-1.8 volts.
Remark : It is best to use roughened dishes only.
EXPERIMENT.
Used tartar emetic.*
Subst.
taken,
Current
Density,
Electrode
Tension,
Time.
Found,
Condition
of the
g-
Amp.
Volts.
%'
Metal.
0.7892
0.7894
0.35
0.35
1.70-1.06
1.80-1.00
17 hr. 30 m.
17 " 30 "
37.84
37.80
( bright rae-
< tallic, adher-
( ent.
* [Probably impure anhydrous, KSbC 4 H 4 O7 containing about 37.12$
Sb. Trans.]
ANTIMONY.
181
B. Temperature of the liquid : 55-70.
Current density: KD 100 = 1.0-1.5 amp.
Electrode tension : 1-2 volts.
Subst.
taken,
Current
Density,
Electrode
Tension,
Temp.
Time.
Found,
Condition
of the
g. Amp.
Volts.
hr.
m.
%
Metal.
0.7895
1.
00-1,
2
1
.45-1.25
55-60
2
5
37.64
(
0.7895
1.06-1,
25
1
.35
65-70
2
15
37.57
1
bright
0.7898
1.
50
1
.42
70
1
45
37.85
J \
metallic
1.5873
1.
50
1
.80
70-80
2
30
37.84
The method of determining antimony in solutions of the
polysulphides of the alkalies is very simple. The solution
containing polysulphides is treated with an excess of hydrogen
peroxide and heated till it becomes colorless. If a great
excess of hydrogen peroxide is used, it may happen that the
alkali sulphide is entirely decomposed and antimony sulphide
precipitated. If the solution is entirely colorless, or if a pre-
cipitate of antimony sulphide has already appeared, the solu-
tion is cooled, 80 cc of a solution of sodium monosulphide
are added, the whole is diluted with water to about 120-150
cc, and electrolyzed as above directed.
[Chittenden and Blake * have applied the electrolytic
method to the determination of very small quantities of anti-
mony in a large amount of organic matter. In test experi-
ments, 100 g of beef or liver were finely divided, a few cubic
centimeters of a standard antimony solution added, the mixture
thoroughly oxidized with hydrochloric acid and potassium
chlorate, all free chlorine removed by heat, and the antimony
precipitated by hydrogen sulphide. The precipitate containing,
together with antimony sulphide, some sulphur and organic
matter, was dissolved in cold sodium monosulphide, and directly
submitted to the action of a current from four gravity cells of
* Trans. Conn. Acad. Arts and Sci., 7, 276.
182 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
moderate size. The electrolytic action was continued till all
the organic matter and sulphur was oxidized (eighteen to forty-
eight hours), and the deposited antimony washed without
breaking the current. Results satisfactory, and much better
than those obtained by any other process.
Chittenden and Blake also found that antimony in small
quantities was deposited quantitatively from urine by acidify-
ing with sulphuric acid (1 cc dilute H 2 SO 4 to 25 cc urine),
and submitting directly to electrolysis. The battery used
was the same as before. Trans. ]
PLATINUM.
LITERATURE :
Luckow, Zeit. f. anal. Chem., 19, 13.
Classen, Ber. deutsch. cheni. Ges., 17, 2467.
Smith, Am. Chem. Journ., 13, 206.
Eudorff, Zeit. f. angew. Chem., 1892, p. 696.
The compounds of platinum are very readily decomposed
by the electric current, the metal being precipitated. Accord-
ing to the determinations made by Dr. W. Gobbels in the
Aachen laboratory, if a solution of a platinum salt containing
2-3 per cent by volume of sulphuric acid is used for the de-
composition and is electrolyzed with a current of N"D ]00 = 0.1-
0.2 ampere, all the platinum separates in a short time in the
form of platinum-black. If, however, a solution heated to
60-65 is electrolyzed with a current of ND 100 = 0.05 amp.
and 1.2 volts tension, the platinum separates quantitatively
and in a very compact form. The reduced metal is so dense
that it cannot be distinguished from hammered platinum.
If the quantity of platinum is about 0.4 g, the solution of
the platinum salt, according to the practice in the Munich
laboratory, is treated with 2 per cent by volume dilute sul-
PALLADIUM TIN. 183
phuric acid (1:5), heated, and electrolyzed with a current of
ND 100 = 0.01 0.03 ampere; the precipitation is complete
in about 5 hours.
Iridium is not reduced from its solutions by a current of
ND 100 = 0.05 amp. and 1.2 volts tension: this property may
be used for the quantitative separation of platinum, from irid-
ium (Classen).
PALLADIUM,
LITER AT CTRE I
Wohler, Lieb. Ann., 133, 357.
Schucht, Zeit. f. anal. Chem., 22, 242.
Smith and Knerr, Am. Chem. Journ., 12, 252.
Smith, ibid., 8, 206 ; 14, 435.
Palladium is determined in the same way as platinum.
If a current of ND 100 = 0.05 ampere, with a tension of 1.2
volts, is used for the reduction, the palladium is obtained in
an excellent metallic condition.
TIN.
LITERATURE I
Luckow, Zeit. f. anal. Chem., 19, 13.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622.
Gibbs, Chem. News, 42, 291.
Classen, Ber. deutsch. chem. Ges., 17, 2467 ; 18, 1104.
Bongartz and Classen, ibid., 21, 2900.
Rudorff, Zeit. f. angew. Chem., 1892, p. 196.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Engels, Zeit. f. Elektrochemie, 1895-96, p. 418.
Freudenberg, Zeit. f. phys. Chem., 12, 121.
Heideureich, Ber. deutsch. chem. Ges., 28, 1586.
Tin separates completely from a solution containing the
ammonium double oxalate, or from an ammonium sulphide
solution. Sodium and potassium sulphides cannot be used,
184 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
as tin separates only partially from a dilute solution of the
corresponding sulpho-salt, and not at all from a concentrated
solution.
If tin is precipitated from the ammonium double oxalate,
a separation of stannic acid readily occurs, especially when
much tin is present, which must be redissolved by addition
of oxalic acid. The reduction of tin may be carried out
without difficulty, however, if acid ammonium oxalate is used
instead of the neutral oxalate. The results obtained by this
process are so accurate that the author has found it adapted
to the determination of the atomic weight of tin.*
The solution of tin is treated with a cold saturated solu-
tion of acid ammonium oxalate in the proportion of 20 cc to
0.1 g tin. The solution is diluted to about 150 cc and elec-
trolyzed. The tin is completely precipitated as a closely ad-
herent, shining, silver- white metal, even when as much as 6 g
is present. The current is interrupted, and the metal washed
as usual with water and alcohol, and dried at 80-90.
CONDITIONS OF EXPERIMENT.
Temperature of liquid : Ordinary temperatures.
Current density : ND 100 = 0.2-0.6 amp.
Electrode tension: 2.7-3.8 volts.
Time of experiment : 8-10 hours.
EXPERIMENT.
Used 0.9-1 g SnCl 4 .2NH 4 Cl[32.10# Sn], 120 cc of a satu-
rated solution of acid ammonium oxalate.
Current Density,
Amperes.
Electrode Tension,
Volts.
Temp.
Time.
Found.
02-0.3f
2.7-3.8
25
8 hr. 5. m.
32.062
0.3-0.6
2.8-3.8
30-35
9 " 45 "
32.00"
* Bongartz and Classen, Ber. deutch. chem. Ges., 21, 2900.
f Finally increased to 0.5 ampere.
TIN. 185
If larger quantities of the tin salt are used, it is necessary to
add acid ammonium oxalate from time to time, on account of
the decomposition of the acid ammonium oxalate, which
causes the solution to react alkaline. According to recent
investigations, the determination of tin may be carried out
by treating the solution of the tin salt with neutral ammonium
oxalate to form the double salt, acidifying .with oxalic acid
and electrolyzing warm.
Heidenreich, who tested this method in the Aachen
laboratory, found that the determination of tin can be com-
pleted in 4-4^ hours. 4 g ammonium oxalate to every
0.3 g tin present are added to the solution, which is then
acidified with 9-10 g oxalic acid, warmed to 60-65, and
electrolyzed with a current of ND 100 = 1-1.5 amperes. The
precipitate must be washed without interrupting the current.
Instead of oxalic acid, acetic acid may be used ; it possesses,
however, no advantages. 100 cc of a saturated solution of
ammonium oxalate are added to the solution of the tin salt,
which is then acidified with 25 cc acetic acid (sp. g. 1.0615;
about 50$). The metal is precipitated in the form of radi-
ated crystals, in contrast to the precipitate from acid ammo-
nium oxalate solutions. Tin adheres better to roughened
than to polished dishes.
The following experiments were conducted by the acetic
acid method :
Current Density, Electrode Tom Timo i?rmn,i
Ampere. Tens., Volts. 3mp '
0.3 increased to 0.5 3.2-3.8 25 6 hr. 15 m. 32.00$
0.5 " " 1.0 3.6-4.2 25-30 5 " 45 " 32.01"
In these experiments the tin in the polished dishes ap-
peared brilliantly crystalline, and in the roughened dishes
silver- white.
Since tin, like zinc, is dissolved with difficulty from the
186 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
platinum dishes by acids, it is necessary to use fused acid
potassium sulphate to remove it. It is therefore best to pre-
cipitate the tin in coppered dishes (see Zinc).
Engels worked out the following method in the Aachen
laboratory : The tin salt is dissolved in water containing a
few cubic centimeters of oxalic acid, and 0.3-0. 5 g hydroxyl-
amine, 2 g ammonium acetate, and 2 g tartaric acid are added
for every 0.5-1.2 g tin salt taken. The solution is then
diluted to 150 cc.
CONDITIONS OF EXPERIMENT.
Temperature of liquid : 60-70.
Current density: ND 100 = 0.99-1 amp.
Electrode tension : 4-5 volts.
Time : 3-5 hours.
EXPERIMENT.
SnCl 4 .
2NH 4 01,
g-
0.9175
Current
Density,
Amp.
1-0.8
Electrode
Tension,
Volts.
5.2-5.6
Temp.
70
Time.
3hr.
g. F Percent. Calculated.
0.2970 32.37 32.37#
0.9859
1-0.8
4.8-5.3
63
3 "
0.3195
32.40
0.9050
1-0.9
5.0-5.6
65
3 "
0.2931
32.39
1.1879
0.5
5.1-6.0
45
6 "
0.3847
32.38
1.0026
0.7
3.4
60
3 "
0.3238
32.36
0.9940
0.7
4.0
60
3"
0.3219
32.38
1.0024
0.8
4.6
60
3 "
0.3250
32.42
1.0022
0.8
4.2-4.4
60
3 "
0.3252
32.44
In the solution of the ammonium sulpho-salt tin behaves
like antimony. The tin solution (if necessary after neutraliza-
tion with ammonia) is treated with ammonium sulphide free
from ammonia (no more is added than is needed to form the
sulpho-salt), diluted to 150-175 cc, warmed to 50-60, and
electrolyzed with a current of 1-2 amperes, at a tension of 3. 5-
4 volts. Under these conditions 0.3-0.4 g of tin can be
reduced in an hour. Sometimes a deposit of sulphur adheres
so strongly to the tin at the edge of the dish that it cannot be
TIN. 187
washed off with water ; it may, however, be easily removed,
after washing with alcohol, by gentle rubbing with a linen
cloth.
In gravimetric analysis tin is often separated from other
metals by sodium sulphide instead of ammonium sulphide.
In order to determine the tin electrolytically in such cases,
the sodium sulphide must be converted into ammonium sul-
phide.* To accomplish this, the solution is treated with
about 25 g pure ammonium sulphate free from iron, and
heated very carefully, with the dish covered, till the hydrogen
sulphide has all escaped ; the solution is then kept in gentle
ebullition for about fifteen minutes. Complete conversion
into ammonium sulphide is shown by the greenish-yellow
color of the solution. If the heating is continued too long,
tin sulphide may separate ; it can be dissolved in ammonium
sulphide. After it is completely cooled, any sodium sulphate
that may have separated is dissolved by addition of water,
and the solution electrolyzed.
The determination of the tin is much more simply and
easily accomplished by converting the solution of tin sulphide
in sodium sulphide into the acid oxalate. This conversion
may be accomplished in two ways ; either the sulpho-salt is
decomposed with dilute sulphuric acid to remove the greater
part of the sulphur as hydrogen sulphide, and the separated
tin sulphide oxidized with hydrogen peroxide f until the stan-
nic acid which is produced appears clear white, or the heated
alkaline solution is treated directly with hydrogen peroxide
(of which a great quantity is needed), then acidified with sul-
phuric acid to precipitate stannic acid, neutralized with
* Sodium sulphide cannot be replaced by potassium sulphide in the
separation from other metals, because the latter produces difficultly soluble
potassium sulphate when ammonium sulphide is formed.
f Classen and Bauer, Ber. d. ch. Ges., 16, 1062.
188 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ammonia, and treated with more hydrogen peroxide. In
either case the solution is heated to decompose the excess of
hydrogen peroxide, and the stannic acid allowed to settle and
then filtered off. The precipitate is washed with the oxalate
solution from the filter into a beaker, the filter washed with
hot oxalic acid solution, and the stannic acid in the beaker
dissolved by heating. Sometimes there is a residue of sulphur,
which is removed by filtration. The filtrate is collected in
the weighed platinum dish to be used for the electrolysis, and
the sulphur is washed with a cold saturated solution of am-
monium oxalate or acid ammonium oxalate. The solution
for electrolysis must contain at least 4 g of the oxalate.
ARSENIC.
LITERATURE I
Luckow, Zeit. f. anal. Ohem., 19, 14.
Classen and v. Reiss, Ber. deutsch. chem. Ges., 14, 1622.
Moore, Chem. News, 53, 209.
Vortmann, Ber. deutsch. chem. Ges., 24, 2764.
Arsenic cannot be quantitatively separated either from
aqueous solutions or from solutions containing hydrochloric
acid, ammonium oxalate, or alkali sulphides. From aqueous
as from oxalic acid solutions a part of the metal is reduced,
while from hydrochloric acid solutions, if the current is al-
lowed to act for a sufficient length of time, all of the arsenic
passes off in the form of arseniuretted hydrogen.
The behavior of arsenic (present as arsenic acid) in a con-
centrated solution of sodium sulphide permits the separation
of arsenic from antimony, as will be shown later.
POTASSIUM, AMMONIUM. (NITROGEN.)
Potassium and ammonium may be determined, as is well
known, by converting them into potassium or ammonium pla-
tinchloride, and weighing the precipitate, dried at 110, on a
tared filter. This method, which is almost universally em-
DETERMINATION OF NITKIC ACID IN NITEATES. 189
ployed in the separation of potassium from sodium, has many
disadvantages. It is preferable, after precipitating and wash-
ing the platinum salt as usual, to dissolve it in water, and
determine the platinum as directed on p. 182.
DETERMINATION OF NITRIC ACID IN NITRATES.
As is well known, nitric acid is often converted into am-
monia, and the latter determined. The action of the galvanic
current converts nitric acid into ammonia, as explained in the
Introduction (p. 3). If the solution of an alkali nitrate, acid-
ified with dilute sulphuric acid, is exposed to the action of the
galvanic current, no ammonia is formed.
Luckow discovered that reduction of the nitric acid always
takes place when a salt from which the metal is precipitated
by the current is also present in the solution. Copper salts
are best adapted for this purpose. G. Vortmann has deter-
mined in the Aachen laboratory the conditions for the quan-
titative determination of nitric acid in nitrates. The solution
of the nitrate is treated with a sufficient quantity of copper
sulphate (in the analysis of potassium nitrate, e.g., half as
much crystallized copper sulphate as potassium nitrate), acidi-
fied with dilute sulphuric acid, and electrolyzed cold. When
the reaction is complete the solution is poured off, sodium hy-
droxide solution is added, and the ammonia distilled off and
determined volumetrically in the usual way. For this pur-
pose one-fifth normal solutions of ammonia and sulphuric
acid -are used. To standardize the sulphuric acid, a weighed
quantity (0.5 g) of crystallized copper sulphate is decom-
posed electrolytically, and the resulting free acid tit-
rated with ammonia. G. Vortmann decomposed 0.4876 g
CuSO 4 . 5H 2 O, and used, for the neutralization of the acid set
free, 19.6 cc of ammonia of a strength equal to the one-
fifth normal sulphuric acid. 1 cc of the latter corresponds
therefore to 0. 0028017 g of nitrogen in the form of ammonia.
190 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
DETERMINATION OF THE HALOGENS.
Chlorine, Bromine, Iodine.
LITERATURE :
Vortmann, Monatshefte f. Chem., 15, 280; 16, 674 ;
Elektrochem. Zeit., 1894 (1), p. 137.
The method originated by Yortmann depends upon the
principle that the halogens are set free from solutions of
halogen salts by the electric current, and while in the ion
state combine with a silver anode to form insoluble silver
halide. The increase in weight of the anode gives directly
the quantity of halogen which has separated. The comple-
tion of the analysis is determined by replacing the original
silver anode by a second weighed silver anode and noting its
increase in weight.
For an experimental test of the method, a weighed quantity
of iodide is dissolved in water, 6-10 cc of a 10$ solution of
sodium hydroxide added, and the solution diluted to 100-150
cc. The silver anode, having the form of a watch-glass 6 cm.
in diameter, is fixed about 5 mm. from the bottom of the cop-
per dish which serves as cathode.
The cold solution is electrolyzed with a current strength
of 0.03-0.07 ampere and a tension of 2 volts. After 4-5
hours the greater part of the iodine has been converted into
silver iodide, and the remainder may be separated on a fresh
silver anode, after the addition to the solution of sodium po-
tassium tartrate. The liquid is warmed to 50-70 and elec-
trolyzed with a current having a tension of 1.2-1.3 volts and
a current strength of 0.01-0.02 ampere.
SEPARATION OF METALS. 391
SEPARATION OF METALS.
IRON.
Iron Cobalt,
LITERATURE.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
The two metals may be determined by electrolyzing the
solution of the double oxalates, as directed under Iron (p.
138), weighing the iron and cobalt together, and determin-
ing the former volumetrically.
After weighing the iron and cobalt, the deposit is dis-
solved in dilute sulphuric acid (dilute sulphuric acid is poured
over the metals, and concentrated acid gradually added, so
that the solution becomes heated), and the iron is titrated in
the platinum dish with potassium permanganate. To over-
come the red color of cobalt sulphate, a sufficient amount of
nickel sulphate is added before the titration. The end of
the reaction is easily recognized.
The residue of cobalt and iron may also be dissolved in
hydrochloric acid, the iron oxidized with hydrogen peroxide,
and titrated with stannous chloride, after removing the excess
of hydrogen peroxide by boiling.
EXPERIMENT.
Used 1 g each of CoSO 4 .K,SO 4 .6H 9 O and Fe 3 (C a O 4 ),.
3K 2 C,O 4 .6H 2 O, and 8 g ammonium oxalate. Yolume of
liquid, 120 cc.
192 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Current Electrode Found,
Density, Tension, Temp. Time. & , c, n Calculated. Titrated.
Amperes. Volts.
2.0-1.6 3.0-3.6 65-70 1 hr. 40 m. 0.2658 g 0.1141 g Fe* 0.1140 g Fe
0.1517 "Co
0.2658 g
1.55-1.43.2-3.6 62-65 1 " 20" 0.2650" 0.1138 g Fe 0.1140""
0.1517 " Co
0.2655 g
1.0-0.85 2.85-3.1 60-65 2 " 30" 0.2585" 0.1137 g Fe 0.1140""
0.1451 " Co
0.2586 g
0.5-0.4 2.0-2.7 60-67 4 " 0.2593" 0.1136 g Fe 0.1133""
0.1452 " Co
0.2588 g
0.5-0.45 2.35-2.7 58-62 4 " 0.2617" 0.1189 g Fe 0.1141""
0.1477 "Co
0.2616 g
Iron Nickel.
LITERATURE :
Vortmann, Monatshefte f. Chem., 14, 536.
Classen, Ber. deutsch. chem. Ges., 27, 2060.
The method of determination is exactly like the preceding.
Iron and nickel separate in the form of a beautiful white alloy
scarcely distinguishable from the platinum. This alloy resists
strongly the action of acids, and is only very slowly attacked
by dilute sulphuric or hydrochloric acid.
Since the precipitation of the last trace of nickel takes
place very slowly, the use of a current of at least ND 100 = 1
ampere is to be recommended. Toward the end of the opera-
tion the current strength should be increased to 1 ampere.
To determine the iron, the precipitate in the dish must be
heated with concentrated hydrochloric acid ; and if the iron
is to be titrated with permanganate, the solution must be
* The numbers placed under the heading " Calculated " are the quanti-
ties of iron and cobalt in the two salts taken, which were separately deter-
mined by electrolysis.
IKON.
193
reduced by nascent hydrogen. It is more simple to oxidize
with hydrogen peroxide, and, after removing the excess,
titrate the ferric chloride with stannous chloride.
EXPERIMENT.
Used 1 g each of NiSO 4 .(NH 4 ) t SO 4 .6E t O and Fe,(C 2 O 4 ) 3 .
3K a C 2 O 4 .6H,O, and 8 g ammonium oxalate. Volume of
liquid, 120 cc.
Current Dens., Electrode
Amperes.
2.2-1.75
Tens., Volts.
3.45-4.0
Temp.
70-65
Time,
hr. m.
Found.
Fe4-Ni.
0.2760 g
2.0-1.75 335-3.9 69-67 2 0.2654
1.1-0.7 2.6-3.1 65-71 430 0.2675'
0.5-0.4 2.6-3.0 68-71 5 0.2664
Calculated.
0.1135 gFe*
0.1622" Ni
0.2757g
0.1135 gFe
0.1527"Ni
0.2662 g
0.1135 g Fe
0.1550"Ni
0.2683 g
0.2664 g
Yortmann adds 4-6 g sodium potassium tartrate and an
excess of sodium hydroxide to the solution, and precipitates
the iron with a current of OT) 100 0.3-0.5 ampere in three
to four hours, the nickel remaining in solution.
Iron Zinc.
LITERATURE :
Vortmann, Monatshefte f. Chem., 14, 536.
If the double oxalates of iron and zinc are submitted to
electrolysis, an alloy of the two does not separate, but zinc,
with a little iron, is first precipitated on the negative elec-
trode. The electrolysis proceeds very satisfactorily, and the
*The numbers placed under the heading " Calculated" are the quanti-
ties of iron and cobalt in the two salts taken, which were separately deter-
mined by electrolysis.
194 QUANTITATIVE ANALYSIS BY ELECTROLYSIS,
united weight of the two metals may readily be determined
if there is less than one-third as much zinc as iron in the solu-
tion. If the proportion of zinc is greater, the zinc dissolves
with the evolution of gas as the action proceeds, and a pre-
cipitate of iron oxide is formed.
Vortmann proposes the following method : Several grams
of potassium sodium tartrate and an excess of a 10-20$ solu-
tion of sodium hydroxide are added to the solution of the
metals, and the liquid is electrolyzed at an electrode tension of
2 volts, with a current strength of KD 100 = 0.07-0.1 ampere.
It is best to raise the temperature at the close of the operation
to 50-60. After several hours the iron will be precipitated,
the zinc remaining in solution.
Iron Manganese.
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 18, 1787.
A solution of ammonium oxalate is decomposed by elec-
trolysis, as stated in the introduction, mainly into hydrogen
and hydrogen ammonium carbonate. The latter is partly
decomposed into ammonia, most of which remains in solution,
and carbon dioxide. In the electrolysis of a hot solution of
ammonium oxalate, the ammonium carbonate produced by the
current is partly neutralized as a result of dissociation of
ammonium oxalate; carbon dioxide is rapidly liberated at the
positive electrode.
If a solution of the double oxalates of iron and manganese
is subjected to electrolysis without the previous addition of a
great excess of ammonium oxalate, the characteristic color of
permanganic acid appears immediately at the positive elec
trode, manganese dioxide gradually separates at the posi-
tive electrode, and iron at the negative. If the electrolysis
is conducted under these conditions, it is impossible to obtain
IRON. 195
a quantitative separation of the two metals, since the manga-
nese dioxide carries down witli it considerable quantities of
ferric hydroxide. The complete separation of the metals is
possible only when the separation of the manganese dioxide is
delayed till most of the iron is precipitated. If a solution of
the double oxalates of iron and manganese, which contains a
great excess of ammonium oxalate, is electrolyzed in the cold,
the greater part of the manganese dioxide is precipitated only
after most of the ammonium oxalate is decomposed. In this
case, however, the separation of the manganese dioxide is in-
complete, because by the action of the current a considerable
quantity of ammonium carbonate or ammonia is produced
which acts on the manganese double salt, causing a portion of
the precipitate (a mixture of dioxide and a lower oxide) to pass
into solution.
The rapid dissociation of ammonium oxalate when heated
gives a simple means of delaying, or entirely preventing, the
formation of a manganese precipitate during electrolysis.
The double oxalate is prepared by the method given under
iron, with the difference only that 8 to 1 g ammonium oxa-
late are dissolved in the liquid, which is warmed to 70, and
electrolyzed with a current of NT) 100 = 0.5 amp.
When the reduction is complete, the solution is poured
off, the dish washed repeatedly with water, and this, together
with traces of the dioxide precipitate, removed by alcohol ; it
is sometimes necessary to rub the dish gently with the finger.
The preceding method gives satisfactory results when the
percentage of manganese is not too high. For the analysis of
manganiferous iron (f erro-manganese, for example) this method
has no practical value, since the per cent of manganese is here
required, while by this method the iron is determined directly
and the manganese must be determined in the liquid from
which the iron has been separated.
196 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
To obtain a complete separation, the solution, containing
suspended manganese dioxide, is heated with a solution of
pure potassium or sodium hydroxide in a porcelain dish,
till the ammonium carbonate produced by electrolysis is de-
composed and the solution no longer has the odor of ammonia ;
and then sodium carbonate and a small quantity of sodium
hypochlorite, or, better, hydrogen peroxide, are added. The
manganese dioxide quickly falls to the bottom, and can be
filtered off. The precipitate is best washed with hot water to
which a little ammonium nitrate has been added, and is either
converted into mangano-manganic oxide (Mn 3 O 4 ) by ignition,
or, better, into manganese sulphate (MnSO 4 ).
The conversion into manganese sulphate is accomplished
by moistening the precipitate in the crucible with a little pure
concentrated sulphuric acid, arid igniting very gently, so that
the bottom of the crucible is barely red.
If it is desired to determine the manganese as manganese
sulphide, the solution is boiled till the ammonium carbonate
is decomposed, the remaining ammonia is neutralized with
nitric acid, and ammonium sulphide added till the precip-
itation is complete. The manganese sulphide is either deter-
mined as such, by ignition in a stream of hydrogen, or, more
simply, converted into manganese sulphate by heating with a
few drops of sulphuric acid.
Iron Aluminium.
LITERATURE:
Classen, Ber. deutsch. chem. Ges., 18, 1795 ; 27, 2060.
When a solution containing the above-named metals and
a great excess of ammonium oxalate is electrolyzed in the
cold, iron is deposited on the negative electrode, while the
aluminium remains in solution as long as ammonium oxalate is
present in the solution in greater proportion than the ammo-
IRON. 197
mum carbonate formed from it. If a precipitate of aluminium
hydroxide finally appears, it is only when the solution is al-
most free from iron. A small portion withdrawn by a capil-
lary tube is tested, from time to time, with ammonium sul-
phide or another reagent already mentioned, and the current
is stopped as soon as no reaction is obtained.
The process is as follows: The aqueous or weakly acid
solution (in the latter case neutralized with ammonia) of the
sulphates (the chlorides are not as well adapted to the process)
is treated with ammonium oxalate in excess, and enough solid
ammonium oxalate added (with gentle warming if necessary)
to give the proportion of 2 3 g ammonium oxalate to 0.1 g
of the metals. The entire volume of the solution should be
150-175 cc. If the temperature of the solution is not over
4:0, it may be submitted to electrolysis at once, since it grad-
ually cools under the action of a current of the given strength.
It is not best to continue the action of the current longer
than , is necessary to reduce the iron ; for, otherwise, a large
part of the aluminium is precipitated as hydroxide, and
clings so closely to the negative electrode that it cannot be
removed.
In such a case it is necessary to bring the aluminium hydrox-
ide into solution by acidifying with oxalic acid, and, in case
too much acid has been added, to pass the current till the
last traces of the redissolved iron have been again precipitated.
The oxalic acid is poured gradually down the glass which
covers the platinum dish, without interrupting the current,
till there is no more ebullition, and the aluminium precipitate
is dissolved.
If the quantity of the aluminium is not greater than that of
the iron, the method gives good results without further treat-
ment. In other cases, the precipitate of aluminium hydrox-
ide is dissolved, without interrupting the current, by careful
198 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
addition of oxalic acid, and the electrolysis repeated until
the iron is completely precipitated. To determine the alu-
minium in the solution poured off from the iron, it is heated
in a porcelain dish till the ammonia is driven off, filtered,
and the aluminium hydroxide converted, by ignition, into
A1.0.-
EXPERIMENT.
Usedl g each of Fe 2 (C 2 O 4 ) 3 .3K 2 C 2 O 4 .6H 2 O and A1 2 (SO 4 ) 3 .
K 2 SO 4 .24rH 2 O, and 8 g ammonium oxalate. Yolume of
liquid, 120 cc.
Current
Density,
Amperes.
Electrode
Tension,
Volts.
Temp.
Time
hr. m.
Found,
g-
Taken,
1.95-1.6
4 3 -4.4
31-42
2 35
0.1143 Fe
0.1135 Fe
1.65-1.35
3.8 -4.1
30-48
3
0.1159 "
0.1150 "
1.00-0.84
3.55-3.8
31-36
4 30
0.1138 "
0.1135 "
0.50-0.42
2.75-3.1
30-32
5 40
0.1139 "
0.1135 "
In order to avoid the separation of aluminium hydroxide
(small quantities of which often adhere to the iron) strong
currents, which raise the temperature of the solution, should
not be used.
The effect of strong currents and high temperatures is
illustrated in the above experiment.
Iron Uranium.
The separation of iron from uranium depends upon the
same principle as the separation from aluminium. It is nec-
essary to have a great excess (8 g) of ammonium oxalate present
in the solution, in order to retain the uranium in the form
of the double salt until all of the other metals are reduced.
The process is conducted in the same manner as in the separa-
tion of aluminium from iron. When a strong current is
employed, especially when there is an insufficient quantity of
ammonium oxalate present, it may happen that, as a result of
IRON. 199
the decomposition of the hydrogen ammonium carbonate by
the heat produced, the uranium is precipitated as hydroxide.
The uranium solution, after the other metals have been
separated, is freed from oxalic acid by further electrolysis, and
finally the ammonium carbonate is decomposed by heating.
To bring the finely divided precipitate of uranium hydrox-
ide into suitable condition for filtration, nitric acid is added, the
solution is heated till the precipitate is wholly dissolved, and
ammonia is added to reprecipitate the hydroxide. The pre-
cipitate is converted into uranium oxide by ignition in a
stream of hydrogen.
Iron Chromium.
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 27, 2060.
If a solution which contains an excess of ammonium oxa-
late, and chromium as sesquioxide, that is, as chromium
ammonium oxalate, be submitted to electrolysis, all of the
chromium is converted into a chromate. If iron is also pres-
ent, it is precipitated in the metallic state on the negative
electrode ; the metal has a peculiarly characteristic lustre.
When the precipitation is complete, the liquid is poured
off from the precipitated metal and is boiled to decompose
ammonium carbonate, and the chromic acid reduced by boiling
with hydrochloric acid and alcohol. The chromium is then
precipitated as hydroxide with ammonia.
The hydroxide is converted into Cr 3 O, in the usual mariner,
and weighed.
EXPERIMENT.
A. Used 1 g each of Fe,(C 2 O 4 ) s .3K,C a O 4 .6H a O and
3K,C,O 4 .Cr,(C,O 4 ) 3 .6H a O, and 8 g ammonium oxalate. So-
lution diluted to 120 cc.
200 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Amperes.
Electrode
Tension,
Volts.
Temp,
Time,
hr. m.
Found
Fe.
Taken
Fe.
2.00-1.60
3.4-3.6
62-68
^
0.1123 g
0.1120 g
1.60-0.95
3.2-3.8
66-68
5 -
0.1135 "
0.1135 "
1.95-1.50
3.3-3.7
62-65
3
0.1130 "
0.1135 "
B. Used 2 g chrome alum, 1.5890 g ferrous ammonium
sulphate, and 8 g ammonium oxalate.
1.5 3 65 4 14.19$ Fe 14.28$ Fe
C. Used 2 g chrome alum, 1 g Fe 2 (C,O 4 ) 3 .3K 2 C a O 4 .6H 2 O,
and 8 g ammonium oxalate.
1.50-1.60 3.0-3.2 65 4 11.35* Fe 11.40$ Fe
Iron Aluminium Chromium.
LITERATURE :
Classen, Ber. deutsch. chem. (res., 14, 2771.
The separation is performed as above. To separate the
aluminium from chromium, the solution poured off from the
precipitated metals is boiled till it has only a weak odor of am-
monia, the aluminium hydroxide filtered off, and the chro-
mium precipitated as above.
Iron Chromium Uranium.
LITERATURE :
Classen, Ber. deutsch. chem. Ges, 14, 2771; 17, 2483.
The separation is accomplished by the precipitation of
iron as metal, from the double oxalate solution, and the oxi-
dation of chromium to chromic acid by the current. Uranium
is separated as hydroxide, while chromium remains in solution
as ammonium chromate. To accomplish the quantitative sep-
aration of chromium from uranium, the electrolysis must be
continued till the oxalic acid is completely oxidized.
IRON. 201
The solution is boiled to decompose the resulting ammo-
nium carbonate, and allowed to stand six hours. The chromi-
um is determined, as above, in the filtrate from the uranium.
Iron Beryllium,
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 14, 2771,
The separation of these two metals offers no difficulties
whatever if the soluble double salts with ammonium oxalate
are prepared, and if care is taken to have an excess of ammo-
nium oxalate present. The iron is precipitated according to
the directions given under the separation of aluminium from
iron.
Strong currents are not advisable lest the solution become
heated, and thus the ammonium carbonate, which holds the
beryllium in solution, be decomposed. The beryllium hy-
droxide may, in any case, begin to precipitate before the iron
is fully deposited. The determination of beryllium in the
solution poured off from the iron is very simple; the solution
is boiled to decompose the hydrogen ammonium carbonate,
and the heating continued till the solution has only a weak
odor of ammonia. The beryllium hydroxide is filtered, washed
with hot water, and converted into BeO by ignition in a
platinum crucible.
Iron Beryllium Aluminium,
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 14, 2771.
The process is precisely like the foregoing. When the
iron is reduced, the solution is poured into a second platinum
dish, and the action of the current is continued till all the
202 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
oxalic acid is decomposed, and the aluminium is precipitated
as hydroxide. The beryllium is precipitated from the filtrate
as hydroxide by boiling.
It is advisable to redissolve the aluminium hydroxide,
to convert it again into the double oxalate, and to repeat the
electrolysis.
Iron Copper.
LITERATURE :
Vortmann, Monatshefte f. Chem., 14, 536.
Classen, Ber. deutsch. chem Ges., 27, 2060.
The separation may be accomplished according to the
method given by Luckow (p. 156), if the operation is conducted
at ordinary temperatures. * To determine the iron in the solu-
tion from which the copper has been removed, it is evaporated
to dryness with the addition of sufficient sulphuric acid to
convert the iron into sulphate, and the double oxalate is pre-
pared by the method given on page 138.
EXPERIMENT.
Used about 1 g each of copper sulphate and ferrous am-
monium sulphate and 5 cc nitric acid (sp. g. 1.35). Volume
of liquid, 120 cc.
Current Dens., Electrode T omn Time, Found Taken
Amperes. Tens., Volts. ^ mp ' hr. m. Cu. Cu.
1.0-0.9 3.0-3.3 19-32 4 0.2518 g 0.2528 g
1.1-1.0 2.6-3.2 18-32 3 30 0.2430 " 0.2450 "
The free sulphuric acid in the decanted liquid was neu-
tralized with ammonium hydroxide, and 8 g ammonium oxalate
were added.
Current Dens., Electrode T Time, Found Taken
Amperes. Tens., Volts. hr. m. Fe. Fe.
1.30-0.8 2.7-4.5 31-42 3 0.1416 g 0.1406 g
145-11 3.0-3.5 60 330 0.1438" 0.1435"
IRON. 203
A similar separation may also be carried out in the pres-
ence of sulphuric acid instead of nitric acid. Three cubic
centimeters of the concentrated acid are used, the other con-
ditions being the same.
Current Dens., Electrode Tm^ Time, Found Taken
Amperes. Tens , Volts. hr.m. Cu. Cu.
1.05-1.20 3.0-2.85 22-30 210 0.2534 g 0.2539 g
1.00-0.95 2.5-2.45 56-59 2 0.2504" 0.2510"
The determination of the iron was conducted as before.
Fe. Fe.
1.55-1.32 3.4-3.8 33-40 4 0.1419 g 0.1421 g
1.60-1.40 3.0-3.5 61-64 3 0.1625" 0.1675"
The separation of iron and copper may be performed if
the copper is precipitated from a hot solution of the double
oxalate containing free oxalic, tartaric, or acetic acid. A
saturated solution of oxalic acid is used, and one of tartaric
acid which contains 6 g acid in every 100 cc.
EXPERIMENT.
Used about 1 g each of copper sulphate and ferric salt,
6 g ammonium oxalate. The copper must be washed without
interrupting the current.
Amperes. Volts. Temp. Time.
1.1-1.0 2.95-3.5 51-62 3 hr. 0.2525 g 0.2528 g
0.7-0.7 3.20-285 62 3" 0.2532" 0.2530"
The iron was determined in the solution which was poured
off from the copper, the free acid being first neutralized with
ammonium hydroxide.
Fe. Fe.
1.4-1.3 3.0-3.2 68-70 2} hr. 0.1431 g 0.1435 g
1.0-0.9 3.1-3.3 30-40 3 " 0.1425" 0.1429"
204 QUANTITATIVE ANALYSIS BY ELECTEOLYSIS.
Yortmann dissolves the oxides of both metals in an am-
moniacal solution, to- which are added several grams of ammo-
nium sulphate, and electrolyzes with a current of OTD 100 =
0.1-0.6 ampere. Only copper is precipitated, the ferric
hydroxide remaining unaltered in solution.
Iron Lead.
The separation is based on the separation of lead as per-
oxide in the presence of nitric acid (p. 168). The iron is
.determined as above.
COBALT.
Cobalt Zinc.
LITERATURE I
Vortmann, Elektrochem. Zeit., 1, 6.
Smith and Wallace, Journ. of anal. Chem., 1893, p. 183.
According to Yortmann, an excess of a 10-20$ solution
of sodium hydroxide is added to the solution containing the
metals. Several grams of sodium potassium tartrate are then
added and the electrolysis is conducted with a current of
NI) 100 = 0.07-0.1 ampere and an electrode tension of 2
volts. The cobalt is precipitated, but the addition of potas-
sium iodide is necessaiy in order to prevent the separation of
cobaltic oxide at the anode.
Cobalt Aluminium.
The method is carried out similarly to that of iron from
aluminium.
Cobalt Uranium ; Cobalt Chromium ; Cobalt Uranium Chromium
The methods employed are similar to those of the corre-
sponding separations from iron (p. 200).
COBALT. 205
Cobalt Copper.
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 27. 2060.
Rudorff, Zeit. f. angew. Chem., 1894, p. 388.
Warwick, Zeit. f. anorg. Chem., 1, 299.
The separation of these two metals can only be satisfac-
torily carried out by the electrolysis of solutions containing
oxalic, tartaric, or dilute acetic acid, at a temperature of 50-
60, and at an electrode tension of not less than 1.1 or more
than 1.3 volts. In order to have the tension constant and to
be able to regulate it conveniently, it is best to insert the wire-
gauze resistance described on page 113 in the main circuit,
EXPERIMENT.
Used 1 g copper sulphate, 1 g cobalt ammonium sulphate,,
and 6 g ammonium oxalate.
trorle Tension,
Volts.
Temp.
Time,
hr. m.
Found*
g Cu. % Cu.
1.24-1.30
50-60
3
50
0.2602
25.36
1.20-1.35
50-60
3
30
0.2531
25.29
1.20-1.29
50-60
4
0.2522
25.28
Cobalt Bismuth.
LITERATURE :
Smith and Wallace, Journ. of Anal. Chem., 1893, p. 183.
Smith and Moyer, Zeit. f. anorg. Chem., 4, 268.
According to Smith and Wallace, and also Smith, and
Moyer, a separation of these metals may be satisfactorily con-
ducted in a solution containing nitric acid. Since, however,
the required conditions of experiment are not given in the
respective publications, the methods will be here omitted.
* [Theory 25 33g Cu. ]
206 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Cobalt Lead.
The solution, to which nitric acid has been added, is
electrolyzed (see Lead).
Cobalt Mercury.
Similar to the above.
NICKEL.
Nickel Manganese.
What has been said with reference to the separation of
iron from manganese applies also to the separation of nickel
from manganese.
Nickel Aluminium.
Similar to the separation of iron from aluminium.
Nickel Uranium ; Nickel Chromium.
See Iron (pp. 198-199).
Nickel Copper.
LITERATURE I
Classen, Ber. deutsch. chem. G-es., 27, 2060.
The separation takes place under the same conditions as
the separation of cobalt from copper.
If 1 g each of copper sulphate and nickel sulphate are
taken, 6 g ammonium oxalate are required. Larger quantities
of metal require correspondingly greater quantities of the
ammonium oxalate.
NICKEL. 207
EXPERIMENT.
Elec.Tens., Time, Found*
Volts. hr. in. g Cu. % Cu. Remark.
1.11-1.3 3 50 0.2552 25.40
1.20-1.3 3 0.2559 25.37 Acidified with oxalic acid.
1.20-1.3 3 30 0.2591 25.38 Acidified with tartaric acid.
J Acidified with acetic acid. The
1 copper contained nickel.
1 Q4_1 A^ Q ^O n 9^7Q
1.20-1.6 350 0.2595 25.33 The copper contained nickel.
Nickel Lead.
The separation corresponds to the method given under
Cobalt.
Nickel Mercury.
LITERATURE I
Kudorff, Zeit. f. angew. Chem., 1894, p. 388.
Smith, Am. Chem. Jouru., 12, 104.
Heidenreich, Ber. deutsch. chein. Ges., 28, 1585.
The method for the separation of these two metals is
similar to that of cobalt from mercury. According to the
statements of Smith, the separation may be carried out from
a solution of the double cyanides. Heidenreich, who de-
termined in the Aachen laboratory the proper conditions
of experiment, found that only the mercury is precipitated
when the tension at the electrodes is 1.2-1.6 volts.
EXPERIMENT.
Used about 1 g nickel ammonium sulphate and 3 g potas-
sium cyanide.
Taken
f HgCI 2 .
Current Density,
Amperes.
El. Tension,
Volts.
Time.
Found t
per cent Hg.
03687
08-0.03
1.2-1.6
5 hr.
73.65
0.3702
0.05-0.93
1.4-1.5
overnight
73.62
0.3000
0.05-0.03
1.4-1.5
"
73.66
[Theory 25.33^ Cu.] f [Theory 73.80 Hg.]
208 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
ZINC.
Zinc Manganese.
This separation, similar to that of copper from cobalt,
takes place from hot solutions containing free oxalic acid,
which prevents the separation of manganese peroxide.
Zinc Aluminium.
Conditions similar to the above.
Zinc Copper.
LITERATURE I
Riidorff, Zeit. f. angew. Chem., 1893, p. 452.
Smith and Wallace, Journ. of Anal. Chem., 1893, p. 183.
Heidenreich, Ber. deutsch. chem. Ges., 28, 1585.
For this separation, Smith and Wallace recommend the
precipitation of the copper from a solution to which nitric
acid has been added. Heidenreich, who determined in the
Aachen laboratory the proper conditions of experiment, found
that if the solution contains about 4 cc nitric acid (sp. g. = 1 . 3)
to 120 cc of liquid, and the tension of 1.4 volts is not
exceeded, the copper only is precipitated. The greater part
of the copper separates in a short time, but the precipitation
of the last trace proceeds very slowly. The analysis therefore
requires from 18 to 20 hours.
EXPERIMENT.
Used copper sulphate (containing 25.29$ Cu) to which
was added 0. 8 g zinc ammonium sulphate.
ZINC.
Taken
CuS0 4 .5H 2
g-
Current
, Density,
Amperes.
Electrode
Tension,
Volts.
Time,
hr. m.
Found
Cu,
%
0.4476
0.2
1.00-1.10
6
30
24.31
0.3857
0.2-0.3
1.00-1.20
8
25.00
0.4244
0.2
1.00-1.15
15
30
25.19
0.4689
0.2
1.00-1.15
15
30
25.25
0.4728
0.2-0.15
1.00-1.20
18
25.25
0.5049
0.20-0.15
1.13
18
25.31
0.4660
0.5
1.20
2
25.22
0.4775
1.05-0.9
1.50
2
25.84
) contained
0.4826
1.00-0.8
1.35-1.98
18
25.80
) zinc
0.4576
0.50-0.4
1.15-1.23
6
30
25.19
Zinc Cadmium.
LITERATURE.
Smith, Am. Chem. Journ., 11, 352.
Yver, Bull. Soc. Chern., 34, 18.
Eliasberg, Zeit. f. anal. Chem., 24, 550.
Smith and Knerr, Am. Chem. Journ., 8, 210.
A. Yver recommends the use of a solution of the ace-
tates or sulphates treated with an excess of sodium acetate
and a few drops of acetic acid ; the electrolysis to be con-
ducted hot, using two Daniell cells.
In the laboratory of the Technical High School in Munich
the following directions are given for Tver's method : To the
sulphuric acid solution of the two metals add sodium hydrox-
ide solution until a permanent precipitate is obtained, dissolve
the precipitate in the smallest possible quantity of dilute sul-
phuric acid, dilute the solution to about 70 cc, and reduce the
cadmium with a current of ND 100 = 0.07 ampere. When the
greater part of the metal is precipitated, neutralize the free
sulphuric acid with sodium hydroxide, add 3 g sodium acetate,
heat to about 45, and subject to the action of a current of
ND )00 =0.3 ampere. The latter direction assumes that the
electromotive force is not over 3.6 volts; if more, it is to be
reduced to about 2.4 volts.
210 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Zinc Lead.
The separation is conducted from a nitric acid solution,
the lead being precipitated as peroxide (see Lead, p. 168).
To determine the zinc, it is converted into the sulphate in
the manner described under the separation of iron from copper
on page 202, and is precipitated by the method given on
page 146.
Zinc Silver.
LITERATURE :
Smith and Wallace, Zeit. f. Elektrochemie, 2, 312;
Journ. of Anal. Chem., 1892, p. 87.
Heidenreich, Ber. deutsch. chem. Ges., 28, 1585.
The separation, according to Smith and Wallace, is con-
ducted from a solution of the double cyanide. The proper
experimental conditions were acertained by Heidenreich in the
Aachen laboratory, with the result that the separation was
best carried out at a temperature of 60-70, and with a ten-
sion at the electrodes of 1.9-2 volts.
EXPERIMENT.
Taken Current Density, Electrode Tens., rp PTnn Timfk Found*
gAgN0 3 . Amperes. Volts. % Ag.
0.4046 0.05 1.9-2.03 60 28 hr. 63.34
0.4149 0.03 2.1-2.05 " 22 " 63.31
0.3260 0.08 1.9 " 16 " 63.23
0.3739 0.08-0.05 3.0-2.15 " 15 " 63.31
0.2949 0.05-0.02 1.8-2.05 " 6 " 63.36
Zinc Mercury.
LITERATURE I
Smith and Wallace, Zeit. f. Elektrochemie, 2, 312.
Heidenreich, Ber. deutsch. chem. Ges., 28, 1585.
Smith and Wallace conduct the separation from a solution
of the double cyanide. According to the experiments carried
* [Theory 63.52$ Ag.J
MANGANESE. 211
out in the Aachen laboratory by Heidenreich, the mercury
is precipitated free from zinc.
In performing the experiments, Heidenreich observed
also that the dishes used suffer severely from the combined
action of the mercury and potassium cyanide on the platinum.
EXPERIMENT.
Taken Current Density, Elec. Tension, m-^ Found*
gHgCl 2 . gKCN. Ampere. ' Volts. Hg.
0.2501 2-3 0.08-0.04 1.65-1.69 5 hr. 73.61
0.2655 2-3 0.03 1.75 14 " 73.51
MANGANESE.
Manganese Copper.
The separation is conducted similarly to that of copper
from cobalt. The copper is precipitated from a hot solution
containing free oxalic acid which prevents the separation of
manganese peroxide. The liquid containing the manganese
is poured off from the copper. Generally this is not suited
for direct electrolytic determination, since the substances
previously added interfere with the precipitation of the
manganese, and the volume of the liquid has become too
great as a result of washing the copper without interrupt-
ing the current. According to the directions of Jannasch
the manganese is then precipitated with ammonia and hydro-
gen peroxide. The precipitate is allowed to settle and the
solution is filtered. The precipitate is dissolved in a mixture
of 5 cc of acetic acid, 5 cc hydrogen peroxide, and 25 cc
water, and this solution is submitted to electrolysis after the
excess of hydrogen peroxide has been removed with chromic
oxide. The same method is employed when the solution
contains manganese chloride, since the presence of the
chlorine also interferes with the separation of the peroxide.
The following experiment was performed as above directed
by Dr. Oarl Engels in the Aachen laboratory.
* [Theory 73.80#Hg.]
212 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
EXPERIMENT.
The solution contained (NH 4 ) 2 MnCl 4 .7H 2 O.
(NH 4 ) 2 MnCl4.7H a O Current Electrode ,. Found*
taken, Density, Tension, Temp. . f Mn 3 O 4 ,
g. Amp. Volts. g. %
0.8619 0.63 2.8 80 1 45 0.2153 24.98
0.9550 0.62 2.8 82 1 45 0.2385 24.98
0.9562 0.70 2.9 83 1 45 0.2394 25.03
1.0131 0.72 3.1 80 1 30 0.2536 25.03
0.8580 0.80 3.1 80 1 15 0.2151 25.01
1.1383 0.78 3.1 85 1 15 0.2848 25.02
Manganese Cadmium.
This is conducted similarly to the separation of manganese
and copper, and the manganese is determined according to the
directions of Engels, which are given above.
COPPER.
Copper Cadmium.
LITERATURE I
Freudenberg, Zeit. f. phys. Chem., 12, 97.
Heidenreich, Ber. deutsch. chem. Ges., 28, 1585.
Smith and Wallace, Journ. of Anal. Chem., 1893, p. 183.
Smith and Moyer, Zeit. f. anorg. Chem., 1, 299.
According to the statements of Freudenberg, the two
metals may be separately precipitated from a sulphuric acid
solution (1020 cc. of dilute sulphuric acid) by a variation of
the tension. With a tension of 2 volts the copper is precipi-
tated, all the cadmium remaining in solution.
Heidenreich tested this method in the Aachen laboratory,
and found that the separation is best conducted with a tension
not exceeding 1.85 volts.
* [It seems probable that the salt taken was not pure. MnCl 8 .2NH4Cl.
7H a O contains 21.270 of Mn 3 O 4 . Trans.]
COPPER. 213
EXPERIMENT.
The volume of the liquid was 120 cc, containing 15 cc
dilute sulphuric acid (sp. gr. = 1.09).
Taken Current Density Electrode ,. Found*
CuS04.5H.jO, CdS0 4 .8H 2 O, ND 100 , Tension, L F^' Cu,
g. g. Amperes. Volts. %
0.7078 0.4 0.07-0.05 1.7-1.76 24 25.27
Experiments in which it was attempted to replace the
sulphuric acid by nitric acid yielded no satisfactory results.
Copper Lead.
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 27, 2060.
Nissenson, Zeit. f. augew. Chem., 1893, p. 452.
To separate copper from lead, 20 cc of nitric acid (sp. g.
1.35) are added to the solution, which is then diluted to
75 cc, warmed and electrolyzed with a current of 1.1-1.2
amperes (corresponding to ND 100 = 1.5-1.7 amperes). At the
end of one hour the greater part of the lead has separated as
peroxide (98-99$ when not more than 0.5 g is present in the
solution), and the current is then interrupted, no trace of
copper as yet appearing at the cathode. The liquid is then
transferred to a second tared dish, the lead peroxide is washed
with water, and after drying is weighed. The washings from
the lead peroxide are added to the copper solution, which is
then treated with ammonium hydroxide until the well-known
deep blue color appears, and about 5 cc nitric acid are added.
The platinum dish is connected with the negative pole of the
source of current, and one of the perforated platinum bucket
electrodes, described by the author, is employed as anode to
* [Theory 25 33^ Cu.]
214 > QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
take up the remainder of the lead peroxide. This electrode
should have a roughened surface. It is weighed before the
experiment. After the solution has cooled, it is diluted to
120-150 cc, and electrolyzed with a current of OT3 100 1.0
1.2 amp. At the end of 3 to 4 hours the copper (if about
0.25 g is present), together with the rest of the lead, is pre-
cipitated.
This' method, which is of great value in technical work, is
not only rapid (45 hours as compared to 14 hours or more),
but allows of the complete precipitation of both metals,
irrespective of the relative quantities present.
When this method is employed for the analysis of sub-
stances containing sulphur, the lead sulphate resulting from
the oxidation is troublesome. The operation of dissolving
this may often require more time than the analysis itself.
Accordingly, if lead sulphate is formed, either as a result
of the oxidation of sulphur or of double decomposition between
lead nitrate and copper sulphate, a slight excess of ammonia
is added and the solution is warmed for several minutes.
The dense lead sulphate is hereby converted into porous lead
hydroxide, The liquid is poured little by little into the
platinum dish, which contains about 20 cc of warm nitric
acid, and constantly stirred with the electrode. The lead
sulphate which reappears either dissolves immediately, or if
the quantity is large the greater part of it goes immediately
into solution, and the remainder disappears on warming for a
short time. The vessel in which the decomposition of the
lead sulphate is conducted is first washed with a little nitric
acid and then with water.
EXPERIMENT.
Usetf about 1 g each of lead nitrate and copper sulphate,,
and 20 cc nitric acid.
COPPER. 215
Current
Density,
Amperes.
Electrode Tension,
Volts.
Beginning. End.
Temp.
Time,
hr.
Found
PbO a ,
g-
Taken
PbO,,
g-
1.1 -1.1
1.4
1.4
60-63
1
0.7266
0.7260
1.55-1.45
1.4
1.4
66-72
1
0.7310
0.7303
The liquid was poured off from the lead peroxide, made
alkaline with ammonia, and 5 cc. nitric acid were added.
The copper was then separated by electrolysis.
Current Electrode Timp Found Taken
Density, Tension, Temp. ^r c ' Cu, Cu,
Amperes. Volts. g. g.
1.1-1.0 2.2 -2.5 25-30 5 0.2490 0.2495
1.0-0.95 2.25-2.3 30-32 5 0.2505 0.2510
H. Nissenson, who employed the preceding method for
determining the copper and lead in copper matte, gives the
following directions for carrying out the analysis :
1 g copper matte is dissolved in 30 cc nitric acid (sp. g.
1.4) and the solution is diluted to 180 cc. The electrolysis
is so conducted that the lead is precipitated on the dish, a
perforated platinum plate which serves as cathode receiving
the copper. The electrolysis is started at ordinary tempera-
tures with a current density of 0.5 ampere, which at the end
of an hour is increased to 1.5-2 amperes. Both metals are
completely precipitated in 6-7 hours.
For technical analyses, where the determination is con-
ducted from nitric acid solutions, the presence of small
quantities of silver and bismuth may be neglected. Where
lead is precipitated from nitric acid solutions containing
arsenic, selenium, or manganese, even in very small quanti-
ties, the results are not accurate.
Copper Silver.
LITERATUEE I
Freudenberg, Zeit. f. phys. Chem., 12, 97.
Smith and Wallace, Zeit. f. Elektrochemie, 5, 312.
Heidenreich, Ber. deutsch. chem. Ges., 28, 1585.
216 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Freudenberg employs a solution containing a few cubic
centimeters of nitric acid (sp. g. 1.2) for the separation of the
silver, which is quantitatively precipitated at a tension of
1.3-1.4: volts. The copper remains in solution and is first
decomposed at a higher tension (2-3 volts).
According to E. Smith, these two metals may be sepa-
rated from a solution of the double cyanides. 4. 5 g of potas-
sium cyanide are added to a solution of about 0.4 g of the
mixed metals. The solution is diluted to about 120 cc and
electrolyzed. If the solution be warmed to 6575, the pre-
cipitation of the silver is greatly hastened. M. Heidenreich
tested this method in the Aachen laboratory and determined
the following conditions of experiment.
EXPERIMENT.
Used silver nitrate containing 63.42$ silver, and copper
sulphate. About 0.7 g of copper sulphate was added.
Taken
gAgN0 3 . gKCN.
0.2379 2
Current
Density,
Amperes.
0.07-0.03
Electrode
Tension,
Volts.
1.0-1.2
Time, Found
hr. m. % Ag.
8 63.34
^0.2303
2
0.04
1.0-1.28
8
63.43
3099
2
0.03
1.0-1.39
6
30 63.40
0.3327
2
0.09
1.2-1,3
4
warmed 63.27
0.6037
6
0.19-0.08
1.2-1.3
6
U3.33
Copper Mercury.
LITER AT ORE :
Smith, Journ. of Anal. Chem., 3, 254 ; 5, 489.
Am. Chem. Journ., 11, 104, 264.
Freudenberg, Zeit. f. phys. Chem., 12, 113.
According to E. Smith, the separation may be conducted
from a solution of the double cyanides. The temperature
CADMIUM. 217
should be about 65. With the ordinary conditions of con-
centration, about 2 g potassium cyanide are added, and the
solution is electrolyzed with a current of ND 100 = 0.06-0.08
ampere. The decomposition requires about 4 hours for every
0.2 g of the combined metals. The copper remains in solu-
tion, the mercury being deposited.
Freudenberg found that at a tension of 2.5 volts the
mercury, in the presence of 2-4 g potassium cyanide, sepa-
rates brilliantly white and completely free from copper.
Copper Arsenic.
LITERATURE :
Freudenberg, Zeit. f. phys. Chem., 12, 97.
Schmucker, Zeit. f. anorg. Chem., 5, 199.
Although formerly it was necessary to remove the arsenic
before precipitating the copper, Freudenberg has shown that
a separation may be satisfactorily conducted from a sulphuric
acid solution (10-20 cc dilute sulphuric acid) if the tension is
not allowed to exceed 1.9 volts. It is immaterial whether
the arsenic is added in the form of trioxide or pentoxide. A
second method of the same author is the following: Am-
monia is added to the solution containing the metals in the
form of higher oxides, until there is an excess of about 30 cc
of a 10# ammonia solution. The electrolysis is conducted
with a current tension of 1.9 volts, and is continued until the
solution is completely decolorized, requiring generally 6-8
hours.
This method is not suitable for the separation of copper
and antimony.
CADMIUM.
Cadmium Lead.
This process is the same as the separation of lead from
copper. The lead is separated as peroxide from a nitric acid
218 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
solution. To determine the cadmium in the solution from
which the lead has been removed, the nitric acid is evapo-
rated off on the water-bath, the cadmium converted into sul-
phate, and treated according to the directions on page 164.
Cadmium Mercury.
LITEEATUEE I
Freudenberg, Zeit. f. phys. Chem., 12, 97.
According to Freudenberg, the separation proceeds best
from a solution of the salts of both metals, containing 0.5-1
g potassium cyanide. With a tension of 1.8-1.9 volts
mercury only is precipitated. After the separation of the
mercury, the cadmium is precipitated from the solution by a
current of higher tension.
LEAD.
Lead Silver.
This separation is conducted like that of lead from copper
(see page 213). To determine the silver, the solution is
evaporated down on the water-bath, and the silver is precipi-
tated according to the directions given on page 173.
Lead Mercury.
LITEEATUEE I
Smith and Moyer, Zeit. f. anorg. Chem., 4, 267.
Heidenreich, Ber. deutsch. chem. Ges., 28, 1585.
The method corresponds to that used for the separation
of copper from lead. Smith and Moyer attempt to deter-
mine the lead and mercury at the same time. They add
5 cc nitric acid (sp. g. 1.3) to the solution of the two metals,
and dilute the liquid to 180 cc. The electrolysis is con-
LEAD. 219
ducted witli a current of 1.7 cc of oxy hydrogen gas per
minute.
Heidenreich determined the conditions of experiment for
the preceding method, and found that 20-30 cc nitric acid
(sp. g. 1.3-1.4) must be present for every 120 cc of the
solution to be electrolyzed, since otherwise the lead peroxide
scales off and cannot be accurately determined. A current
of ND 100 = 0.2-0. 5 ampere may be used. The fact that greater
quantities of lead could not be precipitated in an adherent
form was due to the condition of the surface of the platinum
disk which was used as anode.
Lead Antimony.
LITERATURE I
Neumann and Nissenson, Chemiker Zeitung, 1895, No. 49.
For the electrolytic determination of both metals in alloys
(stereotype-metal, type-metal), Neumann and Nissenson rec-
ommend that 2.5 g of the alloy be dissolved by warming
with a mixture of 10 g tartaric acid, 4 cc nitric acid (sp.g. 1.4),
and 15 cc water. 4 cc cone, sulphuric acid are then added,
the solution is diluted with water, allowed to cool, and filled
up to exactly one quarter liter. If the liquid is now filtered
off from the separated lead sulphate, it will contain all of the
antimony. 50 cc of this filtrate are made strongly alkaline
with sodium hydroxide, 50 cc of a saturated solution of sodium
monosulphide are added, the solution is filtered immediately,
washed from the precipitate, and electrolyzed according to the
method given on page 180.
For the determination of the lead, the lead sulphate is
treated as in the separation of lead from copper (page 213).
220 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
SILVER.
Silver Antimony.
LITERATUEE I
Freudenberg, Zeit. f . phys. Chem. , 12, 97.
If the antimony is present as pentoxide, the separation
may be carried out from an ammoniacal solution to which
several grams of ammonium sulphate have been added.
The silver is precipitated at a tension of 1.7-1.8 volts.
Silver Arsenic.
LITERATUEE I
Freudenberg, Zeit. f. phys. Chem., 12, 97.
According to Freudenberg, this separation is conducted in
the same manner as the separation of silver from antimony.
MERCURY.
Mercury Antimony.
LITEEATUEE I
Freudenberg, Zeit. f. phys. Chem., 12, 97.
The antimony must be added in the form of a pentavalent
salt, since a reduction of the mercuric salt present would
otherwise occur. A mixture of the chlorides of the two
metals is brought into solution by the use of 0.5-1 g tartaric
acid. The solution is diluted with water, made neutral with
ammonia, and then about 20 cc of a 10# solution of ammonia
are added until the solution is perfectly clear. The electrolysis
is conducted at a tension of 1.6-1.7 volts. After the mercury
ANTIMONY. 221
is deposited, the solution is made acid and hydrogen sulphide
is passed in. The antimony sulphide may be either directly
determined, i.e., weighed, or determined by electrolysis (see
page 179).
Mercury Arsenic.
LITERATURE I
Freudenberg, Zeit. f. phys. Chem., 12, 97.
According to Freudenberg, the separation is conducted
from a nitric acid solution (see page 175) from which the
mercury is precipitated at a tension of 1.7-1.8 volts.
ANTIMONY.
Antimony Tin.
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 17, 2245 ; 18, 1110 ; 28, 2060.
The separation of antimony from tin by the ordinary
gravimetric methods, which, as is well known, is difficult, and
gives uncertain results, may be accomplished by electrolysis
with ease and accuracy. Antimony may be completely pre-
cipitated, in the presence of tin, from a concentrated solution
of sodium sulphide, to which is added a certain amount of
sodium hydroxide.
The crystallized sodium monosulphide of commerce, aside
from the fact that its purity is otherwise uncertain, is not
pure monosulphide, but is a mixture of several sulphides with
varying amounts of sodium hydroxide. This explains the
large amount of alumina which it always contains. If, there-
fore, commercial sodium sulphide is to be used, it must first
be dissolved, and the solution, with exclusion of air, com-
pletely saturated with pure hydrogen sulphide gas. It is then
filtered from the precipitated impurities, and evaporated in a
222 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
large platinum or porcelain dish. The further treatment is
given in full in the chapter on reagents. As the condition
of the sodium sulphide solution is of great importance to the
success of the process, it is preferable to prepare the solution
as directed in the chapter referred to.
The process of separation is as follows : A mixture of the
pure sulphides,* or the residue obtained by evaporating a
solution of the two metals, is treated in a platinum dish with
about 80 cc of a sodium sulphide solution saturated at ordinary
.temperatures, and enough concentrated solution of pure
sodium hydroxide f to furnish 1-2 g NaOH. If solution does
not take place at once, it is hastened by heating over a low
Aflame, the watch-glass covering the dish is rinsed with 10-15
cc water, and the solution is allowed to cool thoroughly. It
is then submitted to electrolysis.
When weak currents (ND 100 0.2 amp.) are employed,
the separation of the antimony requires about 14 hours, so that
the electrolysis must be continued through the night. Ex-
periments recently undertaken by the author have shown
that, for the precipitation of antimony in the presence of tin,
the solution may be warmed to 50-60 and a current density
of ND 100 0.5 ampere employed. It is thus possible to
complete the precipitation within 2 hours.
When the action begins, the whole surface of the dish,
which is in contact with the solution, becomes quickly covered
with a dark coating of antimony, which soon takes on a
brilliant metallic appearance.
* The solution of a mixture of the metallic sulphides and sulphur in
sodium sulphide is to be treated like a solution of polysulphides (see
further on).
f The sodium hydroxide used must be absolutely pure, and must show
no cloudiness when warmed with sodium sulphide. Otherwise the results
obtained for the antimony will be too high, owing to the inclusion of the
precipitate.
ANTIMONY. 223
In the earlier part of the process, the entire solution ap-
pears to be filled with small gas-bubbles which rise slowly,
break at the surface, arid cover the watch-glass with minute
portions of the solution. In the course of two hours the dis-
engagement of gas is ended, and the solution is completely
clear. To avoid loss, it is best, at this time, to wash re-
peatedly the under surface of the watch-glass with a drop of
water which is finally allowed to run down the positive elec-
trode. When the reduction is completed, the antimony is
washed without interrupting the current, and is treated accord-
ing to the directions already given (p. 180).
As tin cannot be reduced from a sodium sulphide solu-
tion (as stated on p. 184), but can be completely precipitated
from solution in ammonium sulphide, the sodium sulphide,
after the separation of antimony, must be converted into
ammonium sulphide according to the directions given on
p. 187.
If the two metals are to be determined in the yellow
solution of polysulphides of the alkalies, the solution is
decolorized with ammoniacal hydrogen peroxide (see Anti-
mony, p. 181), and evaporated nearly to dryness; about 80
cc sodium sulphide solution and the necessary amount of
sodium hydroxide are then added, and the process carried on
as above directed.
In the following experiment, antimony was precipitated
from both warm and cold solutions containing tin.
EXPERIMENT.
Used about 1 g antimony potassium tartrate, an equal
quantity of NH 4 CLSnCl 4 , 80 cc sodium sulphide solution,
and about 2 g sodium hydroxide.
Current
Density,
Amperes.
Electrode
Tension,
Volts.
Temp.
hrs?
1.5-1.45
0.9-0.8
57-67
2
1.5-1.6
0.8-0.9
58-60
2
0.4-0.2
0.7-0.55
30-24
15
224 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Found Taken
Sb, Sb,
g. g.
0.3790 0.3780
0.3787 0.3780
0.3775 0.3780
The antimony precipitate appeared gray and shiny, and
contained no tin.
Antimony Arsenic.
LITEKATUKE I
Classen and Ludwig, Ber. deutsch. chem, Ges,, 19, 323.
In an alkaline solution, arsenions acid is oxidized to
arsenic acid by the galvanic current. If, however, a solution
containing antimony and arsenious acid is clectrolyzed, a
mixture of antimony with arsenic is deposited. The action
is different if the arsenic is present in the solution as arsenic
acid ; in the presence of a free alkali, the antimony alone is
deposited from a concentrated sodium sulphide solution. The
arsenic, therefore, if present as arsenious acid, must be oxi-
dized to arsenic acid before the metals can be separated. It
is heated with concentrated nitric acid or aqua regia, the acid
completely removed by evaporation on the water-bath, the
residue treated with 80 cc of a cold saturated sodium sul-
phide solution, a concentrated solution of sodium hydroxide
(containing about 1 2 g IsaOH) added, and the solution
electrolyzed. The separation is conducted precisely like that
of antimony from tin.
The electrolysis may be conducted either warm or at ordi-
nary temperatures. If antimony and arsenic are to be deter-
mined in a solution of polysulphides of the alkalies, the solu-
tion is treated as described on p. 181. To determine arsenic,
the antimony-free solution is acidified with dilute sulphuric
acid, heated in the water-bath to remove hydrogen sulphide.
ANTIMONY. 225
filtered, and the precipitate dissolved in hydrochloric acid
with the addition of potassium chlorate. This solution is
treated with ammonia in excess, and the arsenic acid precip-
itated as magnesium ammonium arsenate with magnesium
mixture.
The precipitate may be dried, at 110, on a weighed filter,
and weighed, or converted into magnesium pyro-arsenate by
careful ignition in a porcelain crucible.
EXPEKIMENT.
Used about 1 g of antimony potassium tartrate, 1 g
sodium arsenate, 80 cc sodium sulphide solution, and 2.5
g sodium hydroxide.
Current
Density,
Amperes.
Electrode
Tension,
Volts.
Temp.
Time,
hr. m.
Found
Sb,
g.
Taken
Sb,
g.
1.55-1.5
1.75-1.1
54-57
3 30
0.3778
0.3773
1.60-1.5
2.10-1.45
25-38
6
0.3770
0.3773
0.5 -0.4
1,75-0.8
21-24
overnight
0.3770
0.3770
Antimony Tin Arsenic .
LITERATURE :
Classen, Ber. deutsch. chem. Ges., 17, 2245; 18, 1110; 28, 2060.
Classen and Ludwig, ibid., 19, 323.
If arsenic is present as arsenic acid, antimony alone is
precipitated from a concentrated alkaline solution of the three
metals in sodium sulphide ; tin and arsenic remain in solution.
The arsenic is converted into arsenic acid, and the antimony
precipitated, exactly as heretofore described.
For the separation of tin from arsenic, the solution poured
off from the antimony is treated with dilute sulphuric or
hydrochloric acid to decompose the sulpho-salts, the mixture
of arsenic and tin sulphides and sulphur is filtered off and
oxidized with hydrochloric acid and potassium chlorate, and
226 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
the arsenic separated as described below. To determine the
tin, the solution freed from arsenic is saturated with hy-
drogen sulphide, filtered, and the tin sulphide dissolved in
ammonium sulphide. The tin is determined electrolytically
as directed p. 186.
In the analysis of a substance which contains arsenic,
antimony, and tin, the arsenic may also be first eliminated
according to the method of E. Fischer-Hufschmidt simplified
by R. Ludwig and the author,* and antimony and tin sepa-
rated in the arsenic-free solution.
If the sulphides of the metals are to be separated, they
are oxidized with concentrated hydrochloric acid and potas-
sium chlorate, and the acid evaporated on the water-bath.
The residue is washed with fuming hydrochloric acid into
a flask of 500-600 cc capacity, f treated with 20-25 cc of a
saturated solution of ferrous chloride, or, better with about
25gof ammonium ferrous sulphate [FeSO 4 .(NH 4 ) 2 SO 4 .6H 2 O],
and fuming hydrochloric acid added till the volume is 150
to 200 cc. A strong current of hydrochloric acid gas is now
passed into the solution, and kept up for at least half an hour
after the solution seems fully saturated. Then the solution
is reduced to about 50 cc by distilling off the liquid, without
a condenser, in a stream of hydrogen chloride gas. A flask
of about 1 liter capacity, containing 400-500 cc water, is
used as a receiver. If the flask is well cooled during the
distillation, not a trace of arsenic passes over into a second
receiver, even when as much as 0.5 g, reckoned as As 2 O 3 , is
present.
The arsenic in the distillate may either be saturated with
sodium carbonate and titrated with iodine solution, or pre-
* Ber. d. ch. Ges., 18, 1110.
| A convenient apparatus is illustrated in the author's " Handbuch der
Quantitative Analyse," 4th edition, p. 78.
ANTIMONY. 227
cipitated as As 3 S 3 with hydrogen sulphide, and determined
as such on a weighed filter, or the arsenic calculated from the
amount of sulphur in the precipitate. The process, in the
latter case, is as follows : The distillate is mixed with twice
its volume of water, air expelled by a strong current of
carbon dioxide, and the arsenic precipitated by passing in
pure hydrogen sulphide gas. The excess of hydrogen sul-
phide is removed by passing a strong current of carbon
dioxide till lead acetate paper is not colored by the escaping
gases. The arsenic sulphide is allowed to subside, and the
clear solution siphoned off. The remaining strongly acid
solution is saturated with ammonia, which dissolves the
arsenic sulphide ; the solution is then boiled with an excess
of hydrogen peroxide free from sulphuric acid. The solution
is acidified with hydrochloric acid, and the sulphuric acid
produced by the action of the hydrogen peroxide determined
as barium sulphate in the usual way (Classen).
To determine the antimony and tin, the strong acid solu-
tion in the flask, which contains the iron, is diluted with
three times its volume of water. Antimony and tin are pre-
cipitated with hydrogen sulphide. After the precipitate has
subsided, the clear solution is poured on a filter, the pre-
cipitate washed several times by decantation, and afterwards,
on the filter, with hot water, till free from hydrochloric acid.
Portions of the sulphides often adhere to the walls of the flask
in which the precipitation took place. These are washed out
with concentrated sodium sulphide solution, and the solution
is poured on the filter containing the sulphides. The filtrate
is collected in a weighed platinum dish. The filter, on which
some iron sulphide always remains after the solution of the
antimony and tin sulphides, is washed with sodium sulphide
solution, the necessary amount of sodium hydroxide is added
228 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
to the filtrate, and the antimony and tin are separated electro-
lytically as already directed.
TIN PHOSPHORIC ACID.
In the determination of metals, in the presence of phos-
phoric acid, the latter is often removed as tin phosphate.
The phosphoric acid is then usually determined in a separate
portion, as its determination in the tin precipitate is too
difficult and slow a process. The precipitate of tin oxide
and tin phosphate may, however, be dissolved by digesting
with ammonium sulphide, the solution diluted, the tin pre-
cipitated by electrolysis, and the phosphoric acid determined
as usual.
PLATINUM IRIDIUM.
As stated on page 182, platinum can be separated from a
hydrochloric acid solution by a current of ]STD 100 = 0.05 am-
pere and 1.2 volts.
This property of platinum may be used for separating it
from iridium, which under similar conditions remains in solu-
tion.
The platinum is deposited free from iridium. (Classen.)
SEPARATION OF GOLD FROM OTHER METALS.
LITERATURE :
Smith and Muhr, Ber. deutsch. chem. Ges., 23, 2175.
Smith and Wallace, ibid., 25, 779 ;
Journ. of Anal. Chem., 1892, p. 87.
As has already been frequently stated, Edgar F. Smith
has made an exhaustive study of the action of the galvanic
current on the cyanides of the metals, and has applied this
SODIUM AMMONIA. 229
method to the separation of gold from palladium, copper,
nickel, zinc, and platinum.
The same conditions may also be employed for the separa-
tion of silver from platinum and mercury from platinum.
Smith gives but incompletely the conditions of experi-
ment necessary for conducting these operations, and therefore
a consideration of them in detail will be omitted.
POTASSIUM SODIUM.
The ordinary method of determining potassium and so-
dium in the same solution is to weigh the mixed chlorides,
and the potassium as platinchloride ; the sodium is thus deter-
mined by difference. The errors of the work, therefore, all
fall on the sodium. The potassium may be determined, as
already directed (p. 188), by precipitating as potassium platin-
chloride, and determining the platinum in the latter by elec-
trolysis. To determine the sodium directly, the filtrate from
the potassium platinchloride is evaporated on the water-bath
to remove alcohol, the residue dissolved in water with the
addition of a little hydrochloric acid, and the platinum re-
moved by electrolysis. The sodium chloride in the solution
poured off from the platinum is determined by evaporating to
dry ness, and weighing the residue.
SODIUM AMMONIUM.
The direct determination of both is accomplished as with
potassium and sodium ; the ammonium is precipitated as ammo-
nium platinchloride, and the process conducted as described
above.
APPENDIX.
SOME APPLIED EXAMPLES OF ELECTBO-
CHEMICAL ANALYSIS.*
BRASS.
Alloy of Copper and Zinc (Lead, Tin, Iron).
For the separation of the copper from the other metals, it
is necessary to precipitate it from an acid solution. A nitric
or sulphuric acid solution may be used. The employment of
a solution containing free nitric acid has the disadvantage
that if the action of the current is continued for too long a
period after all the copper has been precipitated, the nitric
acid is reduced to ammonia, and zinc is precipitated. It has
the further disadvantage that enough ammonia is often formed
to prevent the complete precipitation of the zinc by sodium
carbonate, a method often employed in practice. The pres-
ence of nitric acid or a nitrate also prevents the electrolytic
separation of the zinc. If this acid is used, therefore, the
solution, after removal of the copper, must be repeatedly
* The applied examples of electro- analysis here given appeared in the
third German and second English editions of this work, but are not con-
tained in the fourth German edition. Owing to the practical advantages of
these schematic outlines, the translators have thought it best to include
them in the present edition, and have, at the same time, made such altera-
tions as the recent advances along the variouj^Uww^wJd^eem to justify.
231
232 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
evaporated to dryness with hydrochloric acid to convert the
nitrates into chlorides.
For the analysis of the alloy, 0.1-0.2 g is dissolved in as
little dilute nitric acid as possible, and evaporated to dryness
on the water-bath. The residue is then treated with a few
cubic centimeters of water, and 20 cc nitric acid (sp. g. = 1.27)
are added. The solution is now diluted to about 100 cc, and
any stannic oxide which may be present is filtered off and de-
termined gravimetrically. From the solution, the final vol-
ume of which should be 120 cc, the copper is precipitated by
electrolysis according to the directions given on page 156.
The current is continued as long as a drop of the solution
gives a blue color with ammonia.
If lead is present in the alloy it may be determined at the
same time as the copper, since it separates on the positive
electrode in the form of peroxide. A weighed positive elec-
trode is employed, and the precipitated peroxide is washed
and treated according to the directions on page 169. The
separated lead peroxide and copper are washed without inter-
rupting the current.
The zinc is best determined in the solution by adding
about 5 cc dilute sulphuric acid and evaporating on the water-
bath until no odor of nitric acid can be detected. The residue
is dissolved in a small quantity of water, and a slight excess
of ammonia added. If iron is present it will be precipitated
as hydroxide, which may be filtered off from the solution and
determined gravimetrically. Ammonium oxalate or lactate is
now added, and the separation of the zinc conducted under
the conditions * given on page 147.
When a sulphuric acid solution is employed for the sepa-
* The same electrode upon whicli the copper has been precipitated may
be used for receiving the zinc. By this the necessity of especially prepar-
ing a copper-plated electrode is avoided.
APPENDIX. 233
ration of the copper, it is best to first dissolve the alloy in
dilute nitric acid and filter off any stannic oxide as before,
xln excess of sulphuric is then added, and the solution is
evaporated until all nitric acid is driven off. The residue is
now treated with water, any lead which is present being then
found in the form of sulphate, which can be removed by
filtering and determined gravimetrically. The solution is
diluted to 115 cc, 5 cc nitric acid (sp. g. == 1.21) are added,
and the precipitation of the copper conducted under the con-
ditions given on page 156. After the copper has been sep-
arated, the solution is evaporated to drive off nitric acid, and
the separation of the zinc is carried out as in the previous
case.
SILVER COIN.
Alloy of Copper and Silver.
The alloy is analyzed by dissolving 0.1-0.2 g in dilute
nitric acid, evaporating off the acid on the water-bath, dis-
solving the residue in water, and treating the solution accord-
ing to the directions on page 216.
NICKEL COIN.
Alloy of Copper and Nickel.
About 0.4 g of the alloy, best in the form of small cut-
tings, is dissolved in dilute nitric acid, 8 cc of dilute sulphuric
acid (50 per cent) is added, and the solution is evaporated on
the water-bath until all nitric acid is removed. The residue
is then taken up in 150 cc of water, and electrolyzed with a
current of ND 100 = 1 ampere, and an electrode tension of
2.75-3 volts.
After the removal of the copper the solution is neutralized
with ammonia, an excess of 40 cc ammonia (sp. g. 0.96) is
234 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
added, and the nickel is precipitated by a current of OT3 100 =
0.5-1.5 amperes, and a tension at the electrodes of 2.8-3.3
volts.
GERMAN SILVER.
Alloy of Copper, Zinc, Nickel (Tin, Lead).
For the analysis of this alloy about 0.3 g of the metal is
dissolved in nitric acid, 10 cc concentrated nitric acid added,
the solution diluted to 150 cc, and electrolyzed at ordinary
temperatures with a current of !ND 100 = 0.5-1 ampere, and
an electrode tension of 2.5-2.8 volts. The solution from
which the copper has been removed is evaporated to dryness
with sufficient sulphuric acid to convert the nitrates present
into sulphates, and the residue is dissolved in water.
To the solution containing the zinc and nickel 5 g potas-
sium sodium tartrate is added, and the solution is made alka-
line with sodium hydroxide. The zinc is now precipitated
with a current of ND 100 = 0.3-0.6 ampere, and an electrode
tension of 2 volts.* The zinc may be precipitated on the
electrode bearing the copper precipitate. In this operation
oxide of nickel may separate on the positive electrode, or may
form in the solution in sufficient quantities to slightly discolor
the precipitated zinc. This may be avoided by adding to the
solution a small quantity of potassium iodide.
The solution, containing now only nickel, is acidified with
sulphuric acid, an excess of ammonia added, and the nickel
separated according to the directions for cobalt given on page
142. Another method is to add 25 cc ammonia and 15-20 g
ammonium carbonate directly to the nickel solution, and elec-
trolyze with a current of KT> 100 = 0.8-1 ampere, at a temper-
ature of 50-60. f
* Vortmann, Monatsh. f. Chem., 14, 536.
f Neumann, Analytiscben Elektrolyse, Halle, 1897.
APPENDIX. 235
BRONZE.
Alloy of Copper and Tin.
The alloy in a finely divided form is treated with aqua
regia, and the solution is evaporated to dryness. The residue
is digested with a concentrated solution of sodium sulphide,
the tin being dissolved. The copper sulphide which remains
after filtering is washed thoroughly with sodium sulphide and
then with hydrogen sulphide solution, dissolved in the proper
quantity of nitric acid, and the copper precipitated under the
conditions given on page 156.
The solution of tin in sodium sulphide is brought to a
volume of about 150 cc, 2530 g ammonium sulphate is
added, and the solution is boiled for about one half hour to
convert the sodium sulphide into ammonium sulphide (see
page 187). The solution thus obtained is treated as described
on page 186. .
Accurate results may also be obtained* by treating
0.2-0.4 g of the alloy, best in the form of fine turnings,
with 6 cc nitric acid (sp. g. = 1.5), and adding 3 cc water.
When the reaction is over, the solution is heated to boiling,
diluted with 15 cc boiling water, and the stannic oxide filtered
off. To the solution containing the copper, 5-10 cc of nitric
acid is added, and the copper is precipitated as directed on
page 156. The stannic oxide is dissolved in ammonium sul-
phide and determined electrolytically (page 186).
PHOSPHOR-BRONZE.
Alloy of Copper, Tin, Zinc, and Phosphorus.
When the alloy is digested with concentrated nitric acid
as stated under Bronze, a precipitate remains, which consists
* Neumann, 1. c.
236 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
of a mixture of tin oxide and tin phosphate, with small quan-
tities of copper oxide. It is filtered off, washed with water
containing nitric acid, and heated with a concentrated solution
of sodium culphide. The residue of copper sulphide is dis-
solved in nitric acid, and added to the principal solution.
The tin is determined by converting the sodium sulphide
into ammonium sulphide, and electrolyzing as directed p. 186.
The phosphoric acid is determined in the filtrate in the usual
manner.
The nitric acid solution contains the copper and zinc.
They are separated according to directions for the analysis of
brass (p. 231).
MANGANESE PHOSPHOR-BRONZE.
Alloy of Copper, Tin, Zinc, Manganese, and Phosphorus.
The process is similar to that given for Phosphor- Bronze ;
the manganese remains with the zinc, and is finally separated
as directed p. 208.
SOLDER.
Alloy of Tin and Lead.
About 0.4 g of the alloy in the form of small pieces is
treated with 6 cc nitric acid (sp. g. 1.5) and 3 cc water.
When the reaction is completed the solution is heated to boil-
ing, and diluted with 15 cc hot water, the precipitate of stan-
nic oxide allowed to settle, filtered oft', and washed with water
containing a little nitric acid. The stannic oxide may be
determined gravimetrically, or may be dissolved in ammonium
sulphide and determined by electrolysis according to the direc-
tions given on page 186. The lead contained in the filtrate
may be determined by the method given on page 169.
APPENDIX. 237
WOOD'S METAL.
Alloy of Tin, Lead, Bismuth, and Cadmium.
The alloy is treated similarly to solder, the tin being sepa-
rated and determined in the same manner. Since it is impos-
sible to separate lead and bismuth by electrolysis, it is necessary
to evaporate the solution to a sirup on the water-bath, add
water and repeat the operation until the odor of nitric acid
can be no longer detected. The solution is then treated with
dilute ammonium nitrate solution, and the basic bismuth
nitrate is filtered oft'.* A sufficient excess of nitric acid is
added to the filtrate, and the lead is determined by electroly-
sis. The cadmium is precipitated by one of the methods
given under Cadmium.
HARD LEAD. TYPE-METAL.
Alloy of Lead and Antimony (Copper).
The two metals may be separated, either by oxidizing with
nitric acid, evaporating to dryness, and digesting the residue
with sodium sulphide, or by heating the finely divided alloy
with ten times its weight of anhydrous sodium thiosulphate in
a covered porcelain crucible, over a very low fiame, till the
mixture is sintered together, and extracting with water. In
either case, lead sulphide remains undissolved, and is filtered
off, and washed first with sodium sulphide, and then with hy-
drogen sulphide, solution. It may be determined directly as
sulphide, or as directed p. 169.
The antimony is determined, in the filtrate from lead sul-
phide, exactly as directed p. 180.
The following method is recommended by Neumannf :
2.5 g of the alloy are brought into a 250-cc graduated flask,
* Neumann, Analytisclien Elektrolyse, Halle, 1897.
f Analytischen Elektrolyse, Halle, 1897.
238 QUANTITATIVE ANALYSIS BY ELECTKOLYSIS.
10 g tartaric acid, 15 cc water, and 4 cc strong nitric acid are
added, and solution is effected by warming. To the clear
solution 4 cc of concentrated sulphuric acid is added, it is di-
luted somewhat, allowed to cool, and then diluted to the mark.
50 cc of the filtrate, corresponding to 0.5 g of the substance,
is made strongly alkaline with sodium hydroxide, treated with
50 cc saturated sodium sulphide solution, heated to boiling,
and immediately filtered. The filtrate, while still hot, is
electrolyzed with a strong current according to the directions
given on page 181. For the determination of the copper
which is present, the residue remaining after treating with
sodium sulphide is dissolved in nitric acid, the solution is di-
luted, and the copper separated as given on page 156. If the
percentage of lead is also required, 0.5 g of the alloy may be
taken and the precipitated lead sulphate determined gravi-
metrically ; it is more satisfactory, however, to treat the solu-
tion of the metals directly with sodium hydroxide and sodium
sulphide. The residue, consisting of the sulphides of lead
and copper, is then dissolved in nitric acid, and the separation
of the two metals is conducted under the conditions given on
j)age 213.
ALLOY OF ANTIMONY AND TIN.
The method of analysis has been already given on p. 121.
The alloy is oxidized with nitric acid, and the residue, after
evaporation, dissolved in a concentrated solution of sodium
sulphide, sodium hydroxide added, and the process followed
throughout as given on p. 122.
ALLOY OF ANTIMONY AND ARSENIC.
It has already been stated (p. 224) that the two metals
can be separated under conditions similar to those in the
APPENDIX. 239
separation of antimony from tin ; the method requires the
arsenic to be oxidized to arsenic acid. The alloy is digested
with aqua regia, the acid removed by evaporation, the residue
dissolved in concentrated sodium sulphide, sodium hydroxide
added, and the directions given on p. 225 followed throughout.
ALLOY OF ANTIMONY, TIN, AND ARSENIC.
When this alloy is oxidized with aqua regia, and a solu-
tion in sodium sulphide prepared as above, antimony alone is
electrolytically deposited in presence of tin. The method is
described on p. 225.
SPATHIC IRON ORE.
Constituents : Ferrous Carbonate, -with Manganese, Calcium,
and Magnesium Carbonates (Gangue).
All the constituents of the mineral may be determined in
the same solution. About 0.5 g of the dry mineral is
dissolved in a porcelain dish, in the least possible amount of
hydrochloric acid, the acid removed by evaporation, and the
residue taken up with water to which a little hydrochloric
acid is added. If insoluble gangue is present, this is filtered
off, washed with water, and weighed. The metals are con-
verted into oxalates by treatment with potassium and ammo-
nium oxalate, and the insoluble residue of calcium oxalate
filtered off, and washed with hot water. If manganese is pres-
ent, the calcium oxalate always carries down some manganese
oxalate.* When the precipitate is ignited, a mixture of CaO
and MTi 2 O 3 is obtained. It is weighed, and the manganese in
it determined volumetrically.f
The iron and manganese are separated as directed on p. 195,
* Classen, Zts. anal. Ch., 16, 318.
f Classen, Quant. Anal., 4th ed., p. 128.
240 QUANTITATIVE ANALYSIS BY ELECTKOLYSIS.
the manganese finally precipitated as sulphide, and the mag-
nesium in the filtrate as magnesium ammonium phosphate.
If magnesium is absent, the manganese is determined as
mangano-manganic oxide or sulphate (p. 196).
HEMATITE.
Constituents: Ferric Oxide, Manganic Oxide (Copper Oxide, Alumina,
Lime. Magnesia), Phosphoric Acid, Sulphuric Acid.
The iron, manganese, and calcium are determined a&
above. If copper is present, it is first separated from
the other metals by submitting the double oxalate solution
to a very weak current. If, in addition to iron (copper,
if present) and manganese, phosphoric and sulphuric acids
are to be determined, the metals are converted into double
oxalates, and iron and manganese completely removed (see
separation of Iron and Manganese, p. 195); the two acids
may now be determined in the solution entirely free from
manganese. If only one acid is to be determined, the whole
filtrate can be used ; otherwise it is diluted to a known
volume, and aliquot portions taken for analysis. In the
determination of either acid, the solution is first acidified
with hydrochloric acid,* and then treated either with barium
chloride, or with one-third its volume of ammonia, and mag-
nesium mixture. About 1 g of the mineral is needed for
the determination of sulphuric and phosphoric acids.
If alumina, as well as phosphoric acid, is present in
hematite (its presence is shown by a white turbidity f of
* If the acid carbonates produced from the oxalates are not decomposed,
small hard crystals of acid carbonates are precipitated together with am-
monium magnesium phosphate. These crystals are difficultly soluble in
ammonia, and may make the results too high.
t A turbidity often appears when the solution is first heated, caused by
the driving off of ammonium compounds.
APPENDIX. 241
aluminium phosphate and hydroxide in the solution under-
going electrolysis), the manganese must always be converted
into sulphide. The iron-free solution is boiled to decompose
hydrogen ammonium carbonate, tartaric acid or a solution of
a tar tr ate added till the precipitate of aluminium hydroxide
disappears, and the weakly ammoniacal solution precipitated
hot with ammonium sulphide.
The green manganous sulphide is determined as hereto-
fore directed. The phosphoric acid may be determined with
magnesium mixture, in the filtrate from the manganese sul-
phide.
To determine sulphuric acid in presence of alumina,
iron and manganese are removed, by electrolysis, from a
separate portion, the solution is poured off, the ammonium
carbonate decomposed by heat, the solution acidified with
hydrochloric acid, and the sulphuric acid determined with
barium chloride.
Determination of Iron, Manganese, Copper, Calcium, Magnesium,
Phosphoric Acid, and Sulphuric Acid.
The method of determining iron, manganese, etc., in the
same solution has already been given. If it is desired to
determine magnesium and phosphoric and sulphuric acids,
in the filtrate from manganese peroxide, it is diluted to a
known volume, magnesium is determined in an aliquot part
with ammonium phosphate, and phosphoric and sulphuric
acids in two other portions.
LIMONITE.
Constituents : Ferric Hydroxide, together with Manganese Oxide
(Lime, Magnesia), Phosphoric Acid, Sulphuric Acid, Silica,
and Gangue.
The analysis may be conducted like those of hematite
and spathic iron ; but care must be taken, at the outset, to
242 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
convert the silica into the insoluble modification by evapo-
rating the solution, and drying the residue.
CLAY IRON-ORE.
Constituents : Iron Oxide, Alumina, Manganese, and Water.
The mineral is digested with concentrated hydrochloric
acid till it is completely decomposed, the insoluble residue is
filtered off, the filtrate evaporated to remove free acid, the
residue dissolved in water with a few drops of hydrochloric
acid, and the iron separated from aluminium and manganese
as directed pp. 194-198.
BOG IRON-ORE.
Mixture of Ferric Hydroxide -with Ferrous and Ferric Silicates,
Manganese, Alumina, Copper, Calcium, Magnesium, Sulphuric
Acid, Phosphoric Acid, Arsenic Acid, Organic Matter, and
Gangue.
The analysis of the mineral is easily understood from the
foregoing.
Arsenic and copper are best determined by eliminating
the former as chloride, as directed p. 226, and precipitating
the copper with hydrogen sulphide in the greatly diluted
residue left in the distillation flask. The copper sulphide is
dissolved in nitric acid, and determined electrolytically as
directed p. 156.
CHROME IRON ORE.
Constituents : Chromium Oxide, Ferrous and Ferric Oxides,
Alumina, Manganese, Calcium, Silica.
The finely powdered mineral is fused for a long time with
sodium carbonate and potassium chlorate, and the fused mass
APPENDIX.
extracted with water. The residue contains oxides of iron.,
manganese, calcium, magnesium, and aluminium, and traces
of chromium and silica ; the solution, chromic acid, silica,
and some alumina and lime. The residue is dissolved in
hydrochloric acid, the solution evaporated to dryness to
separate silica, the residue treated with water and a little
hydrochloric acid, and filtered. The metals in the filtrate
are converted into double oxalates. If manganese is present,
the precipitate of calcium oxalate must be treated as directed
p. 239. The filtrate from the calcium oxalate, which contains
iron, manganese, aluminium, and chromium, is treated as
directed pp. 194199. The aqueous solution from the fused
mass is evaporated to separate silica, the calcium precipitated as
oxalate, and the aluminium and chromic acid separated accord-
ing to previous directions.
Edgar F. Smith recommends the use of the galvanic cur-
rent for the decomposition of chrome iron ore. The process,
according to his directions, is conducted as follows : Thirty
or forty gin. potassium hydroxide are heated in a nickel
crucible until the mass is in a condition of quiet fusion. The
chrome iron ore for decomposition (about 0.5 gm.) is finely
pulverized, weighed on a watch-glass, and gradually added,
with the help of a camel's-hair pencil, to the crucible contain-
ing the fused alkali. The crucible is then covered with a
perforated watch-glass and connected with the anode of the
battery or other source of current. The kathode employed is
a thick platinum wire, which is plunged through the opening
in the watch-glass into the fused mass. To regulate the current
an amperemeter (p. 31) is inserted, and a switch is also placed
in the circuit, so adjusted as readily to produce the reversal of
the current, which is necessary toward the close of the process.
The current strength must not exceed 1 ampere. After about
30 minutes the current is reversed by the switch, so that the
244 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
crucible becomes the kathode, and the platinum wire the anode.
The object of this reversal is to oxidize completely the last
traces of the mineral, minute portions of which may have been
protected by metallic iron which had been deposited by the
current. After the current has acted in this direction for 10
minutes, the decomposition is complete. The fused mass
of course contains the chromium as chromate.
The author pursued similar researches some years since,
and can confirm Smith's results.
PSILOMELANE.
Constituents : Manganous Oxide, Copper Oxide, Ferric
Oxide, Nickel Oxide, Cobalt Oxide, Alumina, Lime,
Potash, Soda, and Lithia.
Determination of Manganese, Copper, Iron, Aluminium,
Nickel, Cobalt, and Calcium.
A weighed portion of the mineral is dissolved in hydro-
chloric acid, evaporated to dryness, dissolved in water with
a^ few drops of hydrochloric acid, converted into double
oxalates, calcium oxalate filtered off, and the calcium and
manganese in the precipitate determined as directed p. 239.
In the filtrate, the copper is first determined electrolyti-
cally (p. 155). After the precipitation of the copper is
complete, the solution, which contains the other metals,
is decanted from the copper precipitate, and is then again
submitted to electrolysis for the precipitation of iron, co-
balt, nickel, and manganese, the latter as dioxide at the
positive electrode. After the electrolysis is completed, the
solution is decanted from the precipitated metals, and the
remaining manganese completely precipitated, according to
directions given on p. 196. If only the weight of nickel
and cobalt together is desired, the precipitate containing the
APPENDIX. 245
three metals is dissolved in hydrochloric acid, and the iron
determined by titration with potassium permanganate as
directed p. 191. Otherwise the cobalt and nickel must first
be separated from the iron. The precipitate of the metals is
dissolved in hydrochloric acid, the acid removed by evapora-
tion, the residue oxidized with hydrogen peroxide or bromine
water, dissolved in water with a few drops of hydrochloric
acid, and the metals converted into double oxalates by addi-
tion of potassium oxalate in slight excess. From the boiling
solution, which should have a volume of 80-100 cc, the
cobalt and nickel are precipitated as oxalates by concen-
trated acetic acid. A great excess of acetic acid must be
used, and the solution, after the filtrate has subsided, must
be tested with the reagent for a further precipitate. The
filtrate from the cobalt and nickel oxalates contains all the
iron as potassium iron oxalate.*
The precipitate of nickel and cobalt oxalates is washed
with a mixture of equal parts of alcohol, acetic acid, and
water, and, after drying to remove acetic acid and alcohol, is
dissolved on the filter with hot water containing potassium
and ammonium oxalates. The solution is electrolyzed as
directed p. 141. The sum of nickel and cobalt is determined,
the metals dissolved in hydrochloric acid, evaporated to dry-
ness, the residue dissolved in a few drops of water, potassium
hydroxide added in slight excess, and the resulting precipi-
tate dissolved in concentrated acetic acid. The cobalt is
precipitated with a saturated solution of potassium nitrite
acidified with acetic acid. The precipitate, after standing
twenty-four hours,, is filtered off, washed with potassium
nitrite, and dissolved in hydrochloric acid, the solution is
* Classen, Zts. anal. Ch., 18, 189
246 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
evaporated to dryness, and the residue converted into the
double oxalate, and electrolyzed. The nickel is determined
by difference. The nickel may also be determined, instead
of, or in addition to, the cobalt, by precipitating nickel with
potassium hydroxide, in the filtrate from the cobalt potas-
sium nitrite, filtering, dissolving in hydrochloric acid, and
separating nickel electrolytically as directed p. 144.
To determine the iron in the filtrate from cobalt and
nickel oxalates, the alcohol and acetic acid are completely
removed by evaporation, the residue dissolved in water, and
the iron electrolytically deposited from the solution of the
double oxalate (p. 138).
Determination of Potassium, Sodium, Lithium, Calcium, and
Magnesium.
The mineral is dissolved in hydrochloric acid, evaporated
to remove acid, and treated with an excess of ammonium
oxalate. The filtrate from calcium oxalate is electrolyzed,
iron, nickel, cobalt, and copper separating as metals, man-
ganese as dioxide, and aluminium as hydroxide. The filtrate
from the manganese dioxide and aluminium hydroxide con-
tains only alkalies, magnesium, and a little manganese. It is
boiled to 'remove the hydrogen ammonium carbonate formed
by the electrolytic decomposition of ammonium oxalate, con-
centrated to about 50 cc ? heated to boiling, and at least an
equal volume of concentrated acetic acid added. The pre-
cipitate consists of manganese and magnesium oxalates. It
is filtered off, washed with a mixture of equal volumes of
alcohol, acetic acid, and water, and ignited. The residue is
MgO + Mn 2 O 3 . It is weighed, dissolved in hydrochloric
acid, and the manganese determined by electrolysis as
dioxide (p. 150).
APPENDIX. 247
The alkalies are determined in the filtrate from the man-
ganese and magnesium oxalates. It is evaporated to dryness,
the ammonium salts removed by gentle ignition, the residue
dissolved in water, the solution filtered, and evaporated to t
dryness after addition of a little hydrochloric acid. The
residue is washed into a small stoppered flask with absolute
alcohol, an equal volume of water-free ether added, and
allowed to stand twenty-four hours. The solution is then
filtered from the residue, the alcohol and ether evaporated,
and the lithium chloride converted into sulphate and weighed.
The residue of potassium and sodium chlorides is dissolved
in water, and both metals directly determined as directed
p. 229.
SPHALERITE (ZINC BLENDE).
Constituents : Zinc Sulphide, also Determinable Quantities of
Iron, Manganese, Copper, Arsenic, Antimony, and Gangue.
In most cases, it is only necessary to determine the zinc.
The process is then as follows: About 0.5 g of the finely
powdered mineral is digested with concentrated nitric acid
till fully decomposed, the acid evaporated off, and the nitrates
converted into chlorides by evaporation with hydrochloric
acid. The residue is dissolved in about 25 cc water and
10 cc hydrochloric acid, and hydrogen sulphide passed
through the solution. The precipitate of sulphides of lead,
copper, etc., is filtered off, washed with water containing
hydrogen sulphide and hydrochloric acid, and the, filtrate
evaporated -to dryness. The residue contains chlorides of
zinc, iron, manganese, calcium, and magnesium. It is dis-
solved in water with a little hydrochloric acid, converted
into double oxalates (p. 138), the calcium oxalate filtered oft',
and the filtrate electrolyzed. Zinc and iron separate at the
248 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
negative electrode, and manganese, as dioxide, at the positive.
The two metals are weighed, dissolved in hydrochloric acid,
and the iron determined by titration with potassium per-
manganate (p. 191).
It is stated on p. 194 that the precipitation of iron and
zinc from the same solution is complete only when there is
less than one-third us much zinc as iron, arid that it can be
successfully performed, in other cases, by adding a weighed
quantity of an iron salt before the electrolysis.
Determination of Lead, Copper, Arsenic, Antimony, Zinc, Iron,
Manganese, and Gangue.
As when zinc alone is to be determined, the mineral is
oxidized with nitric acid, the gangue filtered off, and the acid
solution of chlorides treated with hydrogen sulphide. The
precipitated sulphides are washed first with hydrogen sulphide
water containing hydrochloric acid, and afterward with pure
hydrogen sulphide water.
The antimony and arsenic are separated from lead and
copper by digestion with a concentrated solution of sodium
sulphide ; the residue is washed with the same solution, and
afterward with hydrogen sulphide solution. The sodium
sulphide washings are added to the solution for determina-
tion of arsenic and antimony, and the hydrogen sulphide
washings separately collected.
The necessary amount of sodium hydroxide is added to
the sodium sulphide solution, and the antimony and arsenic
separated and determined as directed p. 224.
The sulphides of lead and copper are dissolved in nitric
acid, and the metals determined as directed p. 213.
Iron, zinc, and manganese are determined according to
previous directions.
APPENDIX. 249
CALAMINE AND SMITHSONITE.
Constituents: Zinc (Cadmium), Copper, Lead, Arsenic, Antimony,
Iron, Manganese, Calcium, Magnesium, Silica, Carbonic Acid,
Water.
Zinc and the other constituents are determined as already
directed. If the mineral contains cadmium, copper and
lead are first precipitated from the nitric acid solution, the
decanted solution evaporated to dry ness, the cadmium nitrate
converted into chloride, and cadmium determined as directed
1>. 103.
ULTRAMARINE.
Constituents : Alumina, Potassium, Sodium, Iron, Calcium,
Sulphur, Silica, Sulphuric Acid, Chlorine.
A weighed portion of the substance is dissolved in hydro-
chloric acid, evaporated to dry ness to separate silica, the
residue dissolved in water with a few drops of hydrochloric
acid, filtered from the silica, the free acid neutralized with
ammonia, and a great excess of ammonium oxalate added.
The calcium oxalate is filtered off, iron and aluminium deter-
mined electrolytically, the solution filtered from the alu-
minium hydroxide, evaporated to dryness, the ammonium
salts removed by gentle ignition, the residue dissolved in
water, and the alkalies converted into chlorides by evapora-
tion with hydrochloric acid. Potassium and sodium are
determined as directed p. 229.
250 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
REFINERY SLAG.
Constituents: Ferrous and Ferric Oxides, Metallic Iron, Copper,
Aluminium, Calcium, Magnesium, Silica, Sulphuric and Phosphoric
Acids,
A portion of the substance (0.5-1 g) is dissolved in
hydrochloric acid, evaporated to remove silica, the residue
dissolved in hydrochloric acid, evaporated to remove free
acid, and the metals converted, as usual, into double oxalates.
Calcium oxalate is filtered off, and the manganese in the
precipitate determined as directed p. 239. The copper is
separated by the action of a weak galvanic current (p. 156),
and the iron, manganese, and aluminium separated in the
copper-free solution as directed pp. 194198.
For the determination of magnesium and sulphuric and
phosphoric acids, see Hematite, p. 240.
To determine the metallic iron, about 5 g of the finely
powdered slag is placed in a small platinum or porcelain dish,
and treated with an aqueous solution of copper sulphate. A
quantity of metallic copper equivalent to the iron is precipi-
tated (CuSO 4 + Fe = FeSO 4 -f Cu). The decomposition
is hastened by frequent stirring ; the copper and undecom-
posed slag are finally filtered off, washed thoroughly, and
digested in the water-bath for a long time with nitric acid.
In the solution, after filtration, the copper is electrolytically
determined, and the quantity of iron calculated from it.
COPPER AND LEAD SLAGS.
Constituents : Copper, Lead, Iron, Manganese, Barium, Calcium,
Magnesium, Silica, Sulphuric Acid, Sulphur, and ordinarily
small quantities of Arsenic, Antimony, Bismuth, Cobalt,
Nickel, and Zinc.
The slag is decomposed by digestion with nitric acid,
evaporated to dryness, the residue taken up with water and
APPENDIX. 251
a little hydrochloric acid, and the solution filtered from the
residue of silica and barium sulphate, which are separated as
usual. The calcium is separated by adding ammonium oxa-
late in great excess ; the calcium and the manganese it may
contain are determined as directed p. 239. Copper is then
precipitated (p. 155), and afterward iron and manganese
(p. 194:), and magnesium and sulphuric acid are determined as
directed p. 240.
In the presence of arsenic, antimony, etc., the hydrochloric
acid solution, after separation of silica, is treated, first hot
and then cold, with hydrogen sulphide gas, and the precipi-
tated sulphides are washed with hydrogen sulphide water,
and treated with a concentrated solution of sodium sulphide.
The insoluble sulphides of lead, copper, etc., are washed first
with sodium sulphide, and then with hydrogen sulphide
(see p. 237), and antimony and arsenic are separated in the
solution as directed on p. 224.
The residue of lead sulphide, etc., is digested with nitric
acid till thoroughly decomposed, and lead and copper sepa-
rated from the solution as directed p. 213. The nitric acid is
evaporated off, and bismuth determined as directed p. 237.
The solution filtered from the hydrogen sulphide precipi-
tate, which contains iron, manganese, etc., is evaporated
almost to dryness to remove hydrogen sulphide and most of
the hydrochloric acid, and the metals finally converted into
double oxalates. Calcium oxalate is filtered oif, and the
precautions described on p. 239 are observed in its deter-
mination. By electrolysis of the filtrate, iron, cobalt, nickel,
and zinc are obtained as metals, and manganese, in part, as
dioxide; magnesium remains in solution. The two latter
are determined as directed p. 241.
The iron, cobalt, etc. , are dissolved in concentrated hydro-
chloric acid, the solution evaporated to dryness, the residue
252 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
chloric acid, the solution evaporated to dryness, the residue
dissolved in water with a few drops of acetic acid, potassium
oxalate added in sufficient quantity to form the double oxa-
lates, the solution diluted to 25-30 cc, and precipitated,
at boiling heat, with concentrated acetic acid in great excess.
After standing about six hours in a warm place, the oxalates
of cobalt, nickel, and zinc are filtered off, washed with a
mixture of equal volumes of acetic acid, alcohol, and water,
and the oxalates converted, by very gentle heating, into
oxides. The mixed oxides are dissolved in hydrochloric
acid, and zinc separated from nickel and cobalt as directed
on p. 234. Iron is determined, in the filtrate from the oxa-
lates, as directed on p. 246.
BLAST FURNACE, CUPOLA, AND BESSEMER SLAGS.
Constituents : Ferrous and Ferric Oxides, Metallic Iron, Man-
ganese, Aluminium, Copper, Lead, Zinc, Calcium, Magnesium,
Alkalies, Silica, Sulphuric and Phosphoric Acids, Sulphur
(as Calcium Sulphide).
The method of analysis is so similar to the foregoing that
it needs only brief mention. The slag is digested with
fuming hydrochloric acid, or aqua regia, till completely
decomposed, the solution evaporated on the water-bath to
dryness, the residue dissolved in water and a little hydro-
chloric acid, and the silica filtered off. After conversion into
double oxalates, the calcium oxalate, which may contain
manganese, is filtered off (p. 239), copper and lead first
precipitated (p. 213), then iron and zinc with aluminium and
the rest of the manganese ; iron and zinc are determined as
directed p. 193, and manganese, aluminium, and magnesium
as directed p. 241. The alkalies and sulphuric and phos-
phoric acids are determined as heretofore directed.
APPENDIX. 253
ZIRCON.
Constituents : Zirconia, Iron Oxide, Lime, Silica.
The mineral is decomposed by long-continued fusion
with sodium carbonate, the fused mass dissolved in hydro-
chloric acid, the solution evaporated to dryness, the residue
taken up with water acidified with hydrochloric acid, the
silica filtered off, and the filtrate treated with a great excess
of ammonium oxalate. To overcome the injurious effect of
sodium chloride, about 10 g ammonium oxalate must be
dissolved by heating in the solution diluted to about 200 cc.
The separation of iron and zirconium is carried out under con-
ditions similar to those given for Iron-Beryllium, p. 201. If
calcium is present, the calcium oxalate precipitate is, of
course, to be filtered off before electrolysis, and determined.
ARSENOPYRITE.
Iron, Arsenic, Antimony, Sulphur, Gangue.
A portion of the finely powdered mineral is oxidized with
aqua regia till fully decomposed, the gangue filtered off, and
the solution evaporated to dryness. The chlorides are con-
verted into sulphates by moistening and heating with sul-
phuric acid, water is added, the solution heated to 70-80,
and hydrogen sulphide passed till it has cooled completely.
After -standing some twelve hours at a moderate heat, the
sulphides of arsenic and antimony are filtered off, and sepa-
rated as directed p. 224.
To determine the iron, the hydrogen sulphide is driven off
from the solution, which is then treated as directed p. 138.
254 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
CHALCOPTRITE (COPPER PYRITES).
Constituents: Copper, Iron, Sulphur, Gangue.
The mineral is oxidized with nitric acid, the gangue
filtered off, and copper precipitated in the filtrate (p. 156).
To determine iron, nitric acid is removed by evaporation,
concentrated hydrochloric acid added, the solution again
evaporated, and finally iron is precipitated, after formation
of the double oxalate, according to directions on p. 138.
Sulphur* may be determined in the same portion by pre-
cipitating sulphuric acid with barium chloride, and removing
the excess of the latter by careful addition of sulphuric acid.
Copper is then separated from iron in sulphuric acid solution,
and the latter determined as usual.
As already stated on p. 157, copper cannot be precipitated
from either nitric or sulphuric acid solution in the presence
of any considerable quantity of arsenic and antimony without
being contaminated by them.
If only the copper is to be determined, the nitric acid
solution of the mineral is evaporated to dry ness, the residue
dissolved in water with a little acetic acid, and potassium
oxalate added in excess. The solution is filtered hot from
the gangue, the residue washed with water containing potas-
sium oxalate, and the filtrate brought to a volume of about
50 cc. After cooling, almost all the copper crystallizes out
as potassium copper oxalate ; the rest is precipitated by
addition of much concentrated acetic acid. The precipitate
is washed with a mixture of equal volumes of water, acetic
acid, and alcohol, dissolved in ammonium oxalate, and elec-
trolyzed.
If arsenic and antimony are present in larger proportion,
the finely pulverized mineral is mixed with four times its
APPENDIX. 255
weight of ammonium chloride, and heated gently in a
covered crucible. Arsenic and antimony, and the greater
part of the iron are volatilized as chlorides.*
The residue is dissolved in nitric acid, and treated as
before.
NICKEL MATTE. COPPER MATTE.
Nickel, Cobalt, Zinc, Iron, Copper, Lead, Arsenic, Antimony,
Sulphur, Gangue.
The substance is decomposed with aqua regia, evaporated
to dryness, the residue dissolved in hydrochloric acid, and
filtered from the gangue. In this solution, the metals pre-
cipitable by hydrogen sulphide are precipitated by heating to
70-80, and passing hydrogen sulphide gas till the solution
becomes cold. The precipitate is filtered off, washed first
with a solution containing hydrogen sulphide and hydro-
chloric acid, then with pure hydrogen sulphide solution, and
treated with a concentrated solution of sodium sulphide as
directed p. 222, and the arsenic and antimony separated and
determined as directed p. 224.
The sulphides of lead and copper left undissolved by
sodium sulphide are digested with nitric acid, and deter-
mined as directed p. 213. The filtrate from the hydrogen
sulphide precipitate is evaporated to dryness to remove
hydrogen sulphide and hydrochloric acid, the residue dis-
solved in water with a little acetic acid, potassium oxalate
added in excess, and the solution of 50-100 cc precipitated
boiling hot with a great excess of concentrated acetic acid
(at least an equal volume). The precipitate of nickel, cobalt,
and zinc oxalates is filtered off, washed with a mixture of
equal volumes of alcohol, acetic acid, and water (p. 214),
* Classen, Zts. anal. Ch., 18, 388.
256 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
dried, and converted, by gentle ignition, into the oxides. The
residue is dissolved in hydrochloric acid, and zinc, cobalt,
and nickel separated, and determined as directed pp. 204 and
245.
Iron is determined, in the filtrate from the mixed oxalates,
as directed p. 245.
COPPER SPEISS, LEAD SPEISS.
Antimony or Arsenic Compounds of Iron, Cobalt, and Nickel,
together with Sulphur Compounds of Copper, Lead, Silver,
Bismuth, Iron, and Zinc.
It is best to decompose the finely powdered substance in
a suitable apparatus * with chlorine gas, volatilizing arsenic,
antimony, iron, and zinc, as chlorides, and collecting them in
a receiver containing equal volumes of hydrochloric and
tartaric acids. The free chlorine is expelled, by heat, from
the solution in the receiver, and hydrogen sulphide passed
into the still hot solution until it cools. The sulphides are
filtered, washed, treated with sodium sulphide, and arsenic
and antimony determined in the solution, as directed p. 224.
The insoluble sulphides of iron and zinc are dissolved in
hydrochloric acid, evaporated to dryness, the residue dis-
solved in water with a few drops of hydrochloric- acid, and
iron and zinc determined as directed p. 193.
After the decomposition with chlorine, the non-volatile
chlorides of copper, lead, silver, bismuth, cobalt, and nickel,
and a part of the iron and zinc, remain in the bulb. They
are dissolved in dilute hydrochloric acid, and lead, copper,
silver, and bismuth precipitated with hydrogen sulphide.
The sulphides are digested with nitric acid till completely
* Classen, Quantitative Analyse, 4th ed. p. 187.
APPENDIX. 257
dissolved, and copper and silver precipitated as metals, and
lead as peroxide, by electrolysis. Copper and silver are
separated as directed p. 216, and bismuth from some residual
lead as directed p. 237.
The separation of cobalt and nickel from iron and zinc is
given on pp. 204 and 244.
PYRARGYRITE.
Silver, Antimony (Arsenic), Sulphur, Gangue.
The mineral may be decomposed by chlorine gas, or by
heating with anhydrous sodium thiosulphate. In the former
case, the chlorides of antimony and arsenic (and sulphur) go
into solution, while silver chloride remains in the bulb tube.
In the latter case, when the fused mass is treated with water,
silver sulphide remains unclissolved, and may be dissolved in
nitric acid, and the silver deposited, as metal, from the solu-
tion (p. 174).
To determine antimony, and separate it from arsenic, the
solution of sodium pentasulphide is oxidized with hydrogen
peroxide, evaporated, and treated as in the determination of
antimony in presence of tin (p. 225).
TETRAHEDRITE.
Copper, Antimony, Arsenic, Silver, Lead, Iron, Zinc, Sulphur,
Gangue.
The mineral may be decomposed as heretofore described.
When chlorine gas is used, the receiver contains chlorides of
antimony, arsenic, iron, and zinc (and sulphur) ; the bulb-
tube, copper, lead, silver, and gangue, with a portion of the
iron and zinc. The metals are separated as already described*
258 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
FURNACE "SOWS."
Alloys of Iron (the principal constituent), Copper, Silver, Lead,
Molybdenum, Vanadium, Cobalt, Nickel, and Zinc, with
Sulphides and Phosphides of these Metals, and varying
amounts of Carbonic Acid and Silica.
The substance is best decomposed by chlorine gas. The
quantity of iron is so great, however, that two bulb-tubes
of the most infusible glass should be used, in the second of
which is deposited most of the iron chloride. The substance
is heated in a stream of chlorine as long as iron chloride
sublimes ; then it is certain that all the molybdenum
chloride will have been carried over into the receiver, which
also contains vanadium, sulphur, and phosphorus chlorides.
Hydrogen sulphide is passed into the solution collected in
the receiver until the supernatant liquid is colorless. The
precipitate of molybdenum sulphide is filtered off, washed,
oxidized with nitric acid, the solution supersaturated with
ammonia, and molybdenum oxide precipitated by electrolysis.
The filtrate from molybdenum sulphide contains vana-
dium and iron. Hydrogen sulphide and hydrochloric acid
are evaporated off, double oxalates formed, and the two
metals separated electrolytically, according to the method
given for the separation of Beryllium-Iron, p. 201. To
determine vanadium in the solution decanted from the iron,
it is evaporated to dryness, the ammonium salts driven off
by careful ignition, and the residue of vanadium oxide
converted, by fusion with potassium nitrate, into potassium
vanadate. The fused mass is dissolved in water, nitric acid
added not to acid reaction, then a concentrated solution of
ammonium chloride, and then alcohol in the proportion of
one volume to three of the solution. After standing forty-
eight hours, the ammonium vanadate is filtered off, and
washed with a concentrated solution of ammonium chloride.
APPENDIX. 259
and then with alcohol. The salt is heated first in the air,
then in a stream of oxygen, and leaves a residue of pure
vanadic acid which is weighed.
The chlorides remaining in the bulb-tube are heated with
hydrochloric acid ; a residue of silver chloride and carbon
remains. It is heated with potassium cyanide, the carbon
filtered off, and the silver determined by electrolysis.
The methods of separation and determination of the
metals in the hydrochloric acid solution have already been
given.
STIBNITE (ANTIMONY GLANCE).
Constituents: Antimony and Sulphur, and usually small
quantities of Iron, Lead, Copper, and Arsenic.
The simplest method of analyzing the mineral is to mix
with four or five times its weight of anhydrous sodium
thiosulphate, and heat for a long time in a covered crucible
(p. 237). The fused mass is extracted with water; the
solution contains antimony and arsenic, and is treated for
decomposition of sodium pentasulphide and determination of
the two metals as directed p. 224 ; the undissolved sulphides
of lead, copper, and iron are oxidized with nitric acid, and
the metals separated according to foregoing directions.
ULLMANITE.
Antimony, Nickel, and Sulphur.
The finely powdered mineral is decomposed in a stream
of chlorine (p. 256), all the antimony passing into the
receiver as chloride, and nickel chloride remaining in the
bulb-tube. The latter is determined by dissolving the con-
tents of the bulb in hydrochloric acid, evaporating, convert-
ing into the double oxalate, and precipitating by electrolysis.
260 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
Antimony is precipitated, as sulphide, by passing hydro-
gen sulphide gas into the solution, in hydrochloric and tar-
taric acids, dissolved in concentrated sodium sulphide, the solu-
tion diluted with water and submitted to electrolysis (p. 179).
If the mineral contains iron, it passes over, as chloride, into
the receiver ; it may be determined, in the filtrate from
antimony sulphide, after supersatu ration with ammonia, by
precipitation as sulphide with ammonium sulphide. The
sulphide thus obtained is dissolved, converted into the
double oxalate, and iron determined electrolytically (p. 138).
The analysis is made more simply if the mineral is
decomposed by heating with sodium thiosulphate ; when the
proportion of antimony is large, it is necessary to repeat
the process with the residual nickel sulphide. Antimony is
determined in the aqueous solution of the fused mass as
directed p. 181. If, on treatment with hydrogen peroxide,
or addition of sodium monosulphide, some nickel sulphide
separates, it is added to the principal portion.
The sulphides of iron and nickel are oxidized with nitric
acid, the nitrates converted into chlorides, and the two
metals separated as directed (p. 192).
BOURNONITE.
Antimony, Lead, Copper (Iron), and Sulphur.
The finely powdered mineral is heated either with
chlorine or anhydrous sodium thiosulphate, and the analysis
conducted as already described.
ZINKENITE.
Antimony, Lead (Silver, Copper, Iron), Sulphur.
The mineral is most simply decomposed by heating
with anhydrous sodium thiosulphate. After extracting with
APPENDIX. 261
water, the residue of undissolved sulphides is dried, the
filter burnt, and fusion with thiosulphate repeated. Anti-
mony is determined according to directions on p. 179. The
sulphides of lead, silver, etc., are oxidized with nitric acid;
copper and silver precipitated electrolytically, and separated
as directed p. 216. A portion of the lead is separated, as
peroxide, by the electrolysis of the nitric acid solution, and
is determined as such. The rest is precipitated with hydro-
gen sulphide, the filtrate neutralized with ammonia, ammo-
nium oxalate added, and iron determined by electrolysis.
LINN-3EIITB.
Constituents : Cobalt and Sulphur.
The analysis of this mineral is very simple. It is dis-
solved in aqua regia, the free acid evaporated off, and
chlorides formed by repeated evaporation with hydrochloric
acid.
The aqueous solution of the residue is treated with an
excess of ammonium oxalate, and cobalt precipitated electro-
lytically (p. 141). If iron is present, the two metals are
separated as directed p. 191.
In the solution decanted from the metallic cobalt, ammo-
nium carbonate is decomposed by boiling, hydrochloric acid
is added, and the sulphur determined by precipitation with
barium chloride.
COBALTITE.
Cobalt, Iron (Copper, Antimony), Arsenic, and Sulphur.
The mineral may be decomposed by heating with nitric
acid, or with sodium thiosulphate. If nitric acid is used,
the free acid is evaporated off, and the nitrates converted
262 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
into chlorides. In the hydrochloric acid solution, arsenic,
antimony, and copper are precipitated, as sulphides, by pass-
ing hydrogen sulphide into the hot solution till it cools; the
sulphides are digested with sodium sulphide, and the solution
treated as directed p. 224. The residue of copper sulphide is
dissolved in nitric acid, and the copper separated by elec-
trolysis (p. 156). The filtrate from the hydrogen sulphide
precipitate is freed from hydrogen sulphide and hydro-
chloric acid, and iron and cobalt are separated as directed
p. 191.
If the mineral is heated with anhydrous sodium thio-
sulphate, and extracted with water, antimony and arsenic go
into solution, and are determined as directed p. 224.
The sulphides insoluble in water are dissolved in nitric
acid, and copper first precipitated (p. 156); the nitrates are
then converted into chlorides, and cobalt and iron deter-
mined (p. 191).
Finally, arsenic and antimony may also be determined by
removing the arsenic first. The nitric acid solution is heated
with sulphuric acid to convert nitrates into sulphates. The
arsenic is driven off from this, as chloride, by treatment with
ferrous chloride or sulphate, and distillation in a stream of
hydrochloric acid (p. 226). To determine antimony, the
residue in the flask is saturated with hydrogen sulphide, and
filtered ; the precipitate is washed, and treated with sodium
sulphide (p. 227).
COBALTIFEROUS ARSENOPYRITE.
Cobalt, Iron, Arsenic, and Sulphur.
The mineral is analyzed in the same manner as co-
baltite.
APPENDIX. 263
CERUSSITE.
Lead, Iron, Calcium, Carbonic Acid.
The pulverized mineral is dissolved by heating with nitric
acid, and the lead determined, as peroxide, by connecting
the platinum dish with the positive pole of the battery
(p. 169V
The solution decanted from the lead peroxide is evapo-
rated to dryness with hydrochloric acid, the residue taken up
with water and a few drops of hydrochloric acid, treated
with ammonium oxalate in great excess, calcium oxalate
filtered off, and iron determined electrolytically in the filtrate
(p. 138).
GALENA.
Lead (Antimony, Arsenic, Copper, Silver, Gold, Zinc, Iron),
Sulphur, Gangue.
Galena rich in antimony is decomposed either by chlorine,
or by heating with anhydrous sodium thiosulphate. When
decomposed with chlorine, the receiver contains antimony,
arsenic, iron, and zinc. These metals are separated as
directed p. 256. The chlorides remaining in the bulb-tube
are dissolved in hot dilute hydrochloric acid, and evaporated
on the water-bath, with addition of sulphuric acid, till the
hydrochloric acid is all driven off. The residue is diluted
with water, one-third its volume of alcohol added to the
solution, and the lead sulphate filtered off. In the filtrate,
copper and silver are precipitated with hydrogen sulphide,
the sulphides oxidized with nitric acid, and determined as
directed p. 216.* The filtrate from the hydrogen sulphide
* AS silver and gold are present only in small quantities, they are
ordinarily determined by cupellation.
264 QUANTITATIVE ANALYSIS BY ELECTKOLYSIS.
precipitate is evaporated, and iron and zinc determined as
directed p. 193.
By heating galena with sodium thiosulphate, and extract-
ing with water, antimony and arsenic (and gold) are found
in the solution, and are separated as already directed ; the
sulphides of lead, silver, copper, zinc, and iron remain undis-
solved. The proportion of lead is so great that it cannot
well be determined, as dioxide, in -nitric acid solution ; it is
converted into sulphate, and the analysis completed as before.
PYROMORPHITE.
Lead Phosphate and Chloride, sometimes Sulphate and
Arsenate.
The finely pulverized mineral is digested with nitric acid,
and evaporated to dryness with hydrochloric acid. The
residue is moistened with hydrochloric acid, dissolved in hot
water, the clear nitrate poured off, and the lead chloride,
which had crystallized out, brought into solution by repeated
boiling with water. Lead and arsenic are precipitated by
passing hydrogen sulphide into the hot solution till it cools,
filtered hot after long standing, and the precipitate washed
and digested with sodium sulphide. Arsenic is determined
in the solution as directed p. 223. The lead sulphide is
oxidized with nitric acid, and lead determined, as peroxide,
as directed p. 168. Phosphoric acid is determined, in the
usual way, in the filtrate from the hydrogen sulphide
precipitate.
LEAD MATTE.
Lead, Copper, Iron (Silver, Antimony, Nickel, Zinc), Sulphur.
If the mineral is decomposed by heating in chlorine, iron
and antimony pass over into the receiver. The analysis is
conducted according to directions for copper or lead speiss.
APPENDIX. 265
CINNABAR.
Constituents : Mercury, Manganese, Copper, Alumina, Iron,
Calcium, Sulphur.
The mineral is decomposed by heating with aqua regia,
the solution evaporated on the water-bath, and the metals
converted into nitrates by repeated evaporation with nitric
acid. Mercury and copper are precipitated from the nitric
acid solution (p. 175), the two metals redissolved in nitric
acid, converted into the double cyanides, and determined
according to the directions on p. 216. The small amount of
manganese present is precipitated, as dioxide, in the elec-
trolytic process, and may be weighed as such.
To determine iron, aluminium, and calcium, the solution
decanted from the metals is evaporated to dryness on the
water-bath, the nitric acid removed by repeated evaporation
with hydrochloric acid, the weak acid solution of the residue
treated with ammonium oxalate in great excess, calcium
oxalate filtered off, and iron and aluminium determined as
directed p. 197.
SOFT LEAD (CRUDE LEAD).
In addition to Lead, small quantities of Silver, Copper, Bismuth, Anti-
mony, Arsenic, Cadmium, Iron, Zinc, Cobalt, Nickel.
According to the purity of the metal, 200 to 500 grams
are taken. The weighed quantity, cleaned and rolled into
thin plates, is digested with a mixture of about 250 cc con-
centrated nitric acid, sp. gr. 1.4, and 500-600 cc water. The
solution is hastened by careful heating on a sand or water
bath. If the acid works very actively, the flask is removed
from the bath, but not long enough for crystals of lead
266 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
nitrate to separate from the cooled solution. If there is not
more than 0.02-0.03 per cent of antimony, a perfectly clear
solution is finally obtained. If the filtrate is turbid from the
presence of lead antimonate, the precipitate is filtered off,
and washed thoroughly with water (residue I).
The nitric acid solution is transferred into a 2 -liter
measuring-flask, about 170 cc of dilute sulphuric acid are
added (1 part concentrated sulphuric acid and 2 parts
water), thus precipitating all the lead as sulphate, and the
flask is filled to the mark. The contents of the flask are
thoroughly shaken, the precipitate allowed to settle, and the
greater part of the solution siphoned off, taking care not to
disturb the lead sulphate.
1,750 cc of the clear solution are evaporated till white
fumes of sulphuric acid appear; 50-60 cc of water are
added after cooling, and the small amount of lead sulphate
that may remain undissolved is filtered off. As this latter
may contain antimony, it is digested with concentrated
sodium sulphide, and the solution siphoned off (solution I).
The filtrate from lead sulphate is heated to about 70,
and hydrogen sulphide passed in till it cools. When the
precipitate, after long standing on the sand-bath, has com-
pletely subsided, it is filtered off, washed thoroughly with
water containing hydrogen sulphide, and digested with a
concentrated solution of sodium sulphide. The residue
marked I is also treated with sodium sulphide, and the
dissolved portion, together with solution I, added to the
principal solution. Antimony and- arsenic are then separated
and determined as directed p. 224.
The sulphides insoluble in sodium sulphide (copper,
cadmium, etc.) are digested with nitric acid till completely
oxidized, and copper and silver are separated from the
solution, as metals, by electrolysis, and any remaining lead
APPENDIX. 267
as peroxide. The copper and silver are separated and
determined as directed p. 216.
To determine bismuth arid cadmium, the nitric acid is
completely removed by evaporation, the residue dissolved in
water with a few drops of dilute hydrochloric acid, potassium
cyanide added, and the solution gently heated on the water-
bath ; the potassium bismuth cyanide is filtered off and washed
with water. The bismuth may then be determined gravi-
metrically.
Cadmium can be directly electrolyzed from the solution
of cadmium potassium cyanide (p. 165).
The filtrate from the original hydrogen sulphide precipi-
tate, which contains zinc, iron, cobalt, nickel, etc., is heated
to boiling and oxidized with bromine- water. An excess of
sodium hydroxide is added, and the metals, with the excep-
tion of zinc, are precipitated as hydroxides. The solution is
filtered off, and the zinc precipitated by electrolysis, either
directly from the filtrate, or after being first converted into
some other salt. The hydroxides are dissolved in dilute sul-
phuric acid, the iron is precipitated with ammonium hydroxide
and determined either gravimetrically or by electrolysis. The
nickel and cobalt are determined in the solution, from which
the iron has been removed, by electrolysis under the condi-
tions given on p. 144.
In calculating the analysis, the space occupied by the lead
sulphate in the solution is to be taken into account. 100 g
lead converted into sulphate occupy a space of 23 cc; 200 g,
therefore, 46 cc. Accordingly in making the calculation,
1750 cc are to be reduced, not to 2000 cc, but to 2000 46
= 1954 cc, or to 179.12 g lead.
Crude lead is also analyzed by the foregoing method;
10 to 50 g is a sufficient quantity for the analysis.
268 QUANTITATIVE ANALYSIS BY ELECTKOLYSIS.
ANTIMONY.
Metallic antimony may be treated in the same way as
hard lead, p. 237.
SPELTER (CRUDE ZINC).
Zinc and determinable quantities of Lead, Iron, Cadmium, Arsenic,
Antimony, Tin, and Copper.
In the analysis of crude metals, the determination of the
impurities is of more importance than that of the metal. As
the quantity of other metals is so small, it is necessary to
dissolve a large quantity of zinc. According to its purity,
25 to 100 g are taken, and dissolved, in a flask, by gradual
addition of hydrochloric acid, some zinc, however, being left
undissolved. If the zinc comes in sticks, a stick may be
fastened to a platinum wire, and dipped partly into the
solution, and the undissolved zinc removed, cleaned, and
weighed.
In both cases, zinc only goes into solution , the other
metals, with the exception of arsenic and antimony, being
left as spongy masses. It is necessary, however, to filter the
solution of zinc at once, and to wash the residue. The
latter is digested with nitric acid, and carbon and silica, with
all the tin oxide and small quantities of antimony (most of
it was volatilized during the solution in hydrochloric acid)
and lead, remain undissolved. To determine the tin, the
residue is heated with concentrated hydrochloric acid, carbon
and silica are filtered off, the filtrate is evaporated to dry ness,
and the residue digested with a concentrated solution of
sodium sulphide. The antimony and tin in the filtered
solution are separated as directed p. 221.
The nitric acid solution of the metals is evaporated, the
APPENDIX. 269
residue dissolved in dilute hydrochloric acid, diluted with
water, and hydrogen sulphide passed into the hot solution
till it lias thoroughly cooled. The precipitate, after settling,
is filtered off, washed with water, and digested with concen-
trated sodium sulphide. The sulphides of lead, copper, etc.,
remain, are dissolved in nitric acid, and separated as in the
analysis of soft lead.
The filtrate from the hydrogen sulphide precipitate is
heated to boiling and treated with bromine- water ; and the
metals present, iron, zinc, nickel, cobalt, etc., determined as
in the analysis of soft lead.
Antimony and arsenic must be determined in a separate
portion of zinc, which is dissolved in aqua regia. The aqua
regia is evaporated off, the residue treated with concentrated
hydrochloric acid, and again evaporated, and finally dissolved
in dilute hydrochloric acid. Hydrogen sulphide is passed
into the solution as before, the sulphides are filtered off after
long standing, washed thoroughly with water, and digested
with a concentrated solution of sodium sulphide. Antimony
and arsenic and tin, if present, are determined as directed
pp. 225 ff.
BLISTER COPPER*
Copper, Iron, Lead, Silver, Antimony, Arsenic, Bismuth, Zinc,
Nickel, Cobalt
grams of blister copper must be taken to determine
the impurities ; it is analyzed in two separate portions of
* Process of analysis partly after W. Hampe ( " Beitriige zur Metal lurgie
des Kupfers"), Zts. fiir Berg-, Hiltten- und Salinenwesen, 27, 205.
270 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
25 g each. Each portion of 25 g of bright copper cut-
tings is digested with a mixture of about 175 cc nitric
acid, sp. gr. 1.2, and 200 cc water, till no metallic residue
is left ; and after cooling, whether the solution is clear or
not, 25 cc of concentrated sulphuric acid are carefully added.
The solution is evaporated on the water-bath, and heated on
the sand-bath till the excess of sulphuric acid is driven off.
After cooling, 20 cc nitric acid is added, the solution is
diluted with 300 or 400 cc water, and heated to dissolve
copper sulphate.
This solution is treated with exactly enough* of a titrated
solution of hydrochloric acid to precipitate the silver, and
allowed to stand twenty-four hours, after which the precipi-
tate (I.) of silver chloride, lead sulphate, antimony oxide,
etc., is filtered off and washed with water.
The filtrate is brought to a volume of 400-450 cc, and
the copper separated by electrolysis. For this purpose,
either a larger platinum dish is used, or the platinum cone
shown in Fig. 61, p. 88; and the current is continued only
so long as is necessary to remove the copper, as otherwise
it might be contaminated with antimony and arsenic. If
the copper is darkened by these metals, the process given
on p. 157 must be followed.
There is usually a slight deposit of lead peroxide on the
positive electrode which is determined as directed p. 169.
The precipitated copper contains bismuth. To determine
the latter, the copper precipitated from both 25-g portions
is dissolved in about 350 cc nitric acid, sp. gr. 1.2; a great
excess of concentrated hydrochlowc acid added, and the
solution boiled till all the nitric acid is driven off. It is
evaporated on the water-bath till the residue has a brown
* Silver must be previously determined in a separate portion of 25 g 1 .
APPENDIX. 271
color, and then poured into a large quantity of boiling water
to separate the bismuth as oxychloride. The bismuth oxy-
chloride is generally contaminated with some basic copper
salt. If the color shows the quantity of the latter to be
considerable, the precipitate, after standing twenty-four
hours, is filtered off, dissolved again in concentrated nitric
acid, diluted with water, and copper precipitated electro-
lytically (p. 156).
The bismuth in the solution is determined gravimetrically.
The solution siphoned off from the main portion of the
copper is evaporated to dryness, and the sulphuric acid set
free by the precipitation of copper removed by heating on
the sand-bath, so that the residue contains only traces of acid.
After cooling, it is dissolved in hydrochloric acid and water,
any silica from the glass vessels filtered off, and hydrogen
sulphide passed into the solution, heated to 70-80, till it is
thoroughly cool. The precipitate, which consists mostly of
arsenic and antimony, is filtered off after long standing on
the sand-bath, and washed ; the filtrate, containing iron,
cobalt, etc., is retained (II.).
Another portion of the antimony is in residue I., which
was left on the solution of the blister copper in nitric acid.
Both precipitates are digested with a concentrated solution
of sodium sulphide, filtered, and antimony and tin determined
as directed p. 222. The sulphides insoluble in sodium sulphide
are oxidized with nitric acid, silver (p. 172), and lead (p. 169)
precipitated from the solution, the solution siphoned off,
evaporated to remove nitric acid, and bismuth determined
gravimetrically.
Solution II. filtered from the hydrogen sulphide precipi-
tate, which contains iron, cobalt, etc., is evaporated to
remove hydrogen sulphide, etc., and the metals are deter-
mined in the residue as directed p. 267.
272 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
REFINED COPPER.
This contains, in addition to the metals present in blister
copper, cuprous oxide. The metals are determined as in
blister copper. The determination of the cuprous oxide is
based on the fact that it reacts with a dilute neutral silver
solution, with the formation of metallic silver and basic
copper nitrate, which precipitate, and normal copper nitrate,
which remains in solution.
3Cu 2 O + 6AgNO 3 + 3H 2 O
= 2Cu 2 (OH) 3 N0 3 + 2Cu(N0 3 ) 2 + 6Ag.
The process is as follows: About 2 g silver nitrate is
dissolved in 100 cc water, and about 1 g of the copper to
be tested is added. When the reaction is ended in the cold,
the precipitate is filtered off, and washed thoroughly with
water ; either the copper or the silver in it may be deter-
mined electrolytically. The nitric acid is removed by
evaporation, and copper and silver separated as directed
p. 216. If copper is to be determined, silver is precipitated
as silver chloride from the aqueous solution of the residue,
the excess of acid removed, and copper precipitated, by
electrolysis, from solution of copper ammonium oxalate
(p. 155).
TIN.
The Impurities are usually Copper, Lead, Bismuth, Iron, Zinc,
Arsenic, and Antimony.
By oxidation of the metal with nitric acid, the tin is
completely converted into insoluble oxide, while the other
APPENDIX.* 273
metals remain, for the most part, in solution. The tin oxide
contains, however, detenninable quantities of lead, copper,
antimony, and arsenic. The methods already described are
used for their separation ; the tin oxide is digested with a
concentrated solution of sodium sulphide, or fused with
anhydrous sodium thiosulphite in a porcelain crucible.
The insoluble sulphides of copper and lead are oxidized
with nitric acid, and the solution added to the principal
solution of the metals. The rest of the process is in
accordance with previous directions.
SILVER.
Traces of Gold, also Lead, Copper, Antimony, and Arsenic.
The gold remains undissolved when a large quantity of
silver is dissolved in nitric acid entirely free from hydro-
chloric acid. To determine copper and lead, the silver is
precipitated from the largely diluted solution by hydro-
chloric acid, the silver chloride filtered off, and copper and
lead separated, after removal of hydrochloric acid, as directed
p. 213.
As antimony and arsenic can only be present in very
small quantities, they are determined in a larger weight of
silver. The silver is precipitated as chloride, and the metals
precipitable by hydrogen sulphide by passing the gas into
the hot filtrate. Antimony and arsenic are separated from
the other metals by digestion with sodium sulphide, and
determined as usual (p. 224).
274 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
COMMERCIAL NICKEL.
Nickel, Copper, Arsenic, Antimony, Iron, Cobalt (Carbon,
Silica, Sulphur).
The nickel is dissolved in nitric acid, the insoluble residue
filtered off, the nitric acid removed by evaporation, the resi-
due dissolved in hydrochloric acid, and hydrogen sulphide
passed in to remove the metals which it will precipitate. It is
best to redissolve the sulphides and repeat the precipitation.
Antimony and arsenic are separated from copper by digest-
ing the sulphide with sodium sulphide, and determined as
usual* It is to be noted, in determining antimony, that the
insoluble residue (silica, etc.) may contain antimony, and
must be tested for it.
To separate cobalt and nickel from iron, the filtrate from
the hydrogen sulphide precipitate is evaporated to dryness,
the residue oxidized with hydrogen peroxide or bromine
water, and dissolved in water with addition of acetic acid.
The metals are then converted into double oxalates by
addition of potassium oxalate, and cobalt and nickel precipi-
tated by a'cetic acid. The two metals, and the iron in the
filtrate, are determined as directed p. 245.
If only iron is to be determined, the three metals are
precipitated from the double oxalate solution by electrolysis,
the weight ascertained, and the iron determined volumetri-
cally in hydrochloric acid solution (pp. 191-193).
APPENDIX. 275
PIG IRON, STEEL, SPIEGEL, FERROMANGANESE.
Constituents : Iron, Manganese, Copper, Zinc, Cobalt, Nickel,
Chromium, Aluminium, Titanium, Arsenic, Antimony, Cal-
cium, Magnesium, Silicon, Phosphorus, Sulphur, Carbon.
If a complete analysis of iron is to be made, it is best to
dissolve a large quantity, dilute to a known volume, and use
aliquot parts of the solution. In many cases, only copper,
or manganese, or certain other metals are to be determined.
The complete analysis will first be described, and afterward
the special determination of certain metals. 5 or 10 grams
of the pure iron, in powder or turnings, are dissolved in
hydrochloric acid in a capacious platinum or porcelain dish,
and the solution evaporated to dryness. The residue is
moistened with dilute hydrochloric acid, allowed to stand for
a time that the acid may act, dissolved in water, and the
insoluble residue of graphite, silica, and compounds of iron
with titanium, chromium, phosphorus, and carbon, filtered
off. The precipitate is ignited with the filter, fused with
about its own weight of a mixture of equal parts of sodium
carbonate and potassium nitrate, dissolved in water with
addition of hydrochloric acid, and the solution evaporated
on the water-bath. The residue is heated for a short time on
the sand-bath to insure separation of silica, moistened, after
cooling, with hydrochloric acid, treated with water, heated,
and the silica filtered off, weighed, and tested for titanium.
The filtrate contains chromium, together with the rest of
the silica and titanium, and small quantities of iron and
aluminium. To completely separate silica and titanium, the
solution is evaporated to dryness, the residue treated with
276 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
dilute sulphuric acid, and heated till all the hydrochloric
acid is driven off; water is then added, silica filtered off,
and titanic acid precipitated by long boiling. The filtrate
from titanic acid is concentrated by evaporation, the free
sulphuric acid neutralized with ammonia, iron, aluminium,
and chromium converted into the double oxalates, and
chromium separated as directed p. 153.
For the determination of iron, aluminium, zinc, cobalt,
nickel, manganese, copper, calcium, and magnesium, an aliquot
part of the hydrochloric acid solution is saturated with
hydrogen sulphide, and the precipitate filtered off after long
standing in a warm place.
Since arsenic and antimony are ordinarily present only in
very small quantities, the copper sulphide can usually be
oxidized with nitric acid, and the copper determined electro-
lytically. If the precipitated copper is blackened by the
presence of antimony or arsenic, it is treated as directed
p. 157.
The filtrate from the hydrogen sulphide precipitate is
freed from hydrogen sulphide and hydrochloric acid by
evaporation, oxidized with hydrogen peroxide or a little
bromine water (by no means with nitric acid), dissolved in
water with addition of a little acetic acid, and the metals
converted into double oxalates by the use of potassium (not
ammonium) oxalate. The insoluble calcium oxalate is filtered
off, and separated from the manganese precipitated with it as
directed p. 239. The filtrate is diluted * with water, heated
to boiling, and an excess of concentrated acetic acid added,
whereby all the zinc, cobalt, nickel, and magnesium, and a
portion of the manganese, are precipitated as oxalates ; iron,
aluminium, and the rest of the manganese remain in solution
* Fifty cc of the dilute solution should contain 0.4-0.5 g iron.
APPENDIX. 277
as double oxalates. The beaker is covered, and left standing
in a warm place for six hours ; the precipitate is then filtered
off, washed with a mixture of equal volumes of acetic acid,
water, and alcohol, and dissolved, after drying, in ammonium
oxalate. Zinc, cobalt, and nickel are separated from man-
ganese and magnesium as directed p. 251. The filtrate from
the oxalates is completely freed from alcohol and acetic acid by
evaporation, and iron, aluminium, and manganese separated
as directed pp. 194-198. As the quantity of zinc, cobalt,
etc. , is generally very small, it is best, in order to facilitate the
separation of the oxalates and the collection of the precipi-
tate, to add about 0.2 g magnesium in the form of chloride,*
so that magnesium oxalate is precipitated with the other
oxalates. In this case, the magnesium in pig iron, if present
at all, is determined in another portion, together with some
other metal (e.g., copper). If magnesium is used, all the
manganese is found in the precipitate produced by acetic acid.
To determine manganese alone in pig iron, either an
aliquot part of the hydrochloric acid solution, or a separate
portion of 0.2-0.5 g iron may be taken, and the determina-
tion conducted as directed under Spathic Iron Ore, p. 239.
If copper is to be determined, the solution freed from acid
and preferably oxidized is treated with ammonium oxalate
in great excess, and electrolyzed as already directed. The
hydrochloric acid solution may also be precipitated with
hydrogen sulphide, and the copper determined in nitric acid
solution (see p. 156).
Determination of Arsenic and Antimony.
Since these metals are present only in very small quantity,
about 10 g pig iron are used for their determination, and
* Dissolve magnesium oxide in hydrochloric acid, and remove the free
acid by evaporation.
278 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
digested with aqua regia. When solution is complete, the
aqua regia is removed by evaporation, the residue treated
with hydrochloric acid, and heated till no nitric acid remains.
The solution is diluted, heated, and hydrogen sulphide
passed into it until it is thoroughly cool (p. 253) ; the precipi-
tated sulphides of arsenic, antimony, and copper are filtered
off, thoroughly washed, and digested with sodium sulphide.
The solution is treated like one containing polysulphides,
and arsenic and antimony separated as directed p. 224.
Determination of Phosphorus.
About 2 g of iron is digested with nitric acid, sp. gr.
1.2, till decomposition is complete. If a carbonaceous residue
is left, the nitric acid solution is poured off, and the residue
heated with aqua regia. Nitric acid and aqua regia are
completely removed by evaporation to dryness, and the
nitrates converted into chlorides by repeatedly moistening
with concentrated hydrochloric acid, and evaporating to
dryness. ' The residue is treated with water, heated, and
the iron brought into solution by the addition of the least
possible quantity of hydrochloric acid. To convert the iron,
etc., into double oxalates, six or eight times the weight of
the iron, reckoned as oxide, of a mixture of 1 part potassium
oxalate and 5-6 parts ammonium oxalate, is dissolved by
heating in the solution, it is diluted to 250-300 cc, and
electrolyzed at a temperature of about 80, The heating
is maintained during the reaction ; the solution must by no
means be heated to boiling, lest the iron scale off. The solu-
tion is poured off when the reduction is complete, and phos-
phoric acid determined as magnesium pyrophosphate.
Two grams of iron are enough for tiie determination of
APPENDIX. 279
phosphorus, even when the percentage is small. If a larger
quantity is taken, it is best to divide the solution, after
conversion into oxalates, and precipitate in several dishes.
As it is not necessary to determine the iron, it may be
precipitated just as well in a beaker; in this case, the
negative electrode is a large piece of light platinum foil
which is attached by a platinum wire to the negative pole of
the source of current.
Determination of Sulphur.
About 2 grams of iron is oxidized, with aqua regia, to
convert sulphur into sulphuric acid, and the insoluble resi-
due filtered off. As a portion of the sulphur may be left
in the residue, it is fused with a small quantity of a mixture
of sodium carbonate and potassium nitrate, the fused mass
dissolved in hydrochloric acid, and the solution thus obtained
added to the other. The aqua regia is removed, the nitrates
converted into chlorides, and the latter into double oxalates,
as already directed. After removing the iron by electrolysis,
the solution is poured off, boiled to remove ammonia, acidified
with hydrochloric acid, and the sulphuric acid precipitated
with barium chloride.
280 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
TABLES FOR CALCULATION OF ANALYSES,
A t.ATVI 1 f>
Weight.
Found.
Required.
Factor.
Aluminium .
27.04
A1A
Al
0.5304
Antimony . .
119.6
Sb
Sb a O.
1.20017
Sb 2 S 3
1.40108
Arsenic . . .
74.9
As
AsA
1.31962
AsA
1.53271
As. 2 S 3
1.64192
Barium
136.86
BaSO 4
Ba
0.58819
Ba00 3
Ba
0.69574
| BaO
0.77688
Beryllium . . 9.08
BeO
Be
0.36262
Bismuth . . . 208.4
Bi
BiA
1.11488
Boron . . . . 10.9
KBF 4
B
0.08639
BA
0.27613
Bromine! . . . 79.76
AgBr
Br
0.42556
Cadmium . . . 111.7
Cd
CdO
1.14288
CdS
1.28630
Caesium .
132.7
Calcium .
39.91
CaO
Ca
0.71433
CaCO 8
Ca
0.40006
CaO
0.56004
Carbon
11.97
CO 2
C
0.272727
Ca00 3
C0 2
0.43995
Cerium . . .
141.2
Chlorine .
35.37
AgCl
Cl
0.24729
Ag
Cl
0.32853
Chromium . .
52.0
CrA
Cr
0.81419
CrO 3
1.18581
1
TABLES FOR CALCULATION OF ANALYSES.
281
Atomic
Weight.
Found.
Required.
Factor
Cobalt . . .
58.60
Co
CoO
L27116
Copper . . .
63.18
Cu
CuO
1.25261
CuS
Ic25309
Diclymium . .
145.0
Erbium .
166.0
Fluorine .
19.06
CaF 2
F
0.48853
Gold ....
196.7
Au
Aa 2 O e
1.12171
Hydrogen
1
H 2
H
0,11136
Iodine. .
126.54
Agl
I
0.54031
Ag
I
1.17546
Iron ....
55.88
Fe
FeO
1.28561
Fe 2 8
1.42842
Lanthanum . .
138.5
Lead ....
206.39
PbO 2
Pb
0.86605
PbO
0.93303
PbCl 2
1.16289
Lithium . . .
7.01
LiCl
Li
0.165408
Li 2
0.35370
Li 3 P0 4
Li
0.18156
Li 2 O
0.38824
LiCl
1.09764
Magnesium .
23.94
Mg 2 P 2 7
Mg
0,21614
MgO
0.36024
Manganese . .
54.8
Mn 3 4
Mn
0.72029
MnO
0.93007
-
Mn 2 O 8
1.03496
Mn0 2
Mn
0.63192
MuO
0.81596
Mn 2 O 8
0.90798
MnS0 4
Mn
0.36383
MnO
0.46979
Mn 2 O 8
0.52277
282 QUANTITATIVE ANALYSIS BY ELECTEOLYSIS.
Atomic
Weight.
Found.
Required.
Factor.
Mercury . . .
199.8
Hg
Hg 2
1.03994
HgO
1.07988
HgCl
1.17703
Hg 2 S
1.08003
HgS
1.16006
Molybdenum
95.9
MoS 8
Mo
0.49989
Nickel. . . .
58.6
Ni
NiO
1.27116
Niobium . . .
93.7
Nitrogen .
14.01
Pt
N
0.14411
NH 3
0.17497
NH 4
0.18526
Osmium .
195
Palladium . .
106.2
Phosphorus .
30.96
Mg 2 P 2 O 7
P
0.27952
P 2 O 5
0.63976
Platinum . . .
194.43
Pt
Pt0 2
1.16417
Potassium . .
39.03
Pt
K
0.40129
K 2 O
0.48848
. 1 ".
KC1
0.76495
K 2 S0 4
0.89389
Rhodium . . .
104.1
Rubidium
85.2
Ruthenium . .
103.5
Selenium .
78.87
Silicon
28
Si0 2
Si
0.46729
Silver ....
107.66
Ag
Ag 2
1.07412
AgCl
1.32853
Sodium ,
22.99
NaCl
Na
0.39393
Na 2 O
0.53067
Na 2 SO 4
1.21488
Strontium
87.3
SrS0 4
Sr
0.47673
SrO
0.56389
TABLES FOR CALCULATION OF ANALYSES.
263
Atomic
Weight.
Found.
Required.
Factor.
Sulphur . . .
31.98
BaSO 4
S
0.13744
S0 8
0.34322
S0 4
0.41181
Tantalum . .
182
Tellurium . .
127.7
Thallium .
203.7
T1 2 O
Tl
0.9623
Thorium .
231.96
Tin ....
118.8
Sn
SnO 2
1.26869
Titanium . . .
50.25
Ti0 2
Ti
0.61154
Tungsten .
183.6
W0 8
W
0.79316
Uranium .
239.8
UO 2
U
0.88249
U 8 8
1.03916
Vanadium
51.1
V 2 O 5
V
0.56154
Yttrium .
89.6
Zinc ....
65.1
Zn
ZnO
1.24516
ZnS
1.49124
Zircon
90.4
Zr0 2
Zr
0.73904
284 QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
REAGENTS.
POTASSIUM OXALATE.
The crystallized potassium oxalate of commerce always
contains determinable quantities of iron and lead. To purify
it, one part of the salt is dissolved in three parts of water in
a porcelain dish, and ammonium sulphide is added drop by
drop, as long as a precipitate forms. The solution is now
heated on the water-bath till the precipitate settles, and
filtered through a plaited filter. To decompose the slight
excess of ammonium sulphide, a current of air is conducted
through the solution till it is perfectly colorless, and no
longer gives a reaction with sodium nitroprusside. The
separated sulphur is allowed to settle, and the clear solution
siphoned off.
AMMONIUM OXALATB.
The same impurities are present as in potassium oxalate.
The salt is purified by precipitating the hot saturated solution
with ammonium sulphide. It is heated over a naked flame till
the precipitate coheres together, and filtered hot by the use
of a hot-water funnel. The greater part of the ammonium
oxalate crystallizes from the filtrate on cooling. The solution
is poured off, and the crystals dried by placing them in a
funnel stopped with asbestos, and connecting with a filter-
pump.
REAGENTS. 285
OXALIC ACID.
The impurities are similar to those of the alkali oxalates ;
it is purified by repeated recrystallization.
AMMONIUM SULPHATE.
This salt is purified in the same way as ammonium
oxalate.
SODIUM SULPHIDE.
The crystallized sodium sulphide of commerce is not only
exceedingly impure, but is not inonosulphide at all, but
a mixture of polysulphides and sodium hydroxide. The
presence of the latter explains that of alumina, which is
always found in abundance. If commercial sodium sulphide
is used, its solution must first be completely saturated, without
access of air, with hydrogen sulphide gas. It is better,
however, to prepare the substance, in which case the process
is as follows : Sodium hydroxide purified by alcohol is
dissolved in water to a solution of sp. gr. 1.35. The solution
is divided into two equal parts, and one half, with exclusion
of air, saturated with the purest possible hydrogen sulphide
gas till the volume ceases to increase. The hydrogen sul-
phide is purified by passing it through a wash-bottle of water,
and several tubes filled with cotton or wadding. When
completely saturated, the solution is filtered from the pre-
cipitate formed, and mixed with the other half of the, sodium
hydroxide solution. Hydrogen sulphide is again passed into
the mixture, with exclusion of air, and it is filtered again.
The nearly colorless filtrate is evaporated in a capacious
platinum or porcelain dish, over a strong free flame as quickly
as possible. It boils without bumping if a platinum spiral is
QUANTITATIVE ANALYSIS BY ELECTROLYSIS.
placed in it. As soon as a thin crystalline pellicle forms on
the surface, the boiling is stopped, and the solution poured
while hot into small flasks with well-ground glass stoppers
which must be filled full. It is best to completely exclude
the air by melted paraffine. For the separation of antimony
and tin, the solution should have a sp. gr. of 1.22-1.225.
ALCOHOL.
The alcohol used for washing metals must be free from
acid, and, as nearly as possible, absolute. It is left standing
in a large flask, for twelve hours, over quicklime, and then
distilled off on a water or steam bath. The distillate must
leave no residue on evaporation.
INDEX OF AUTHORS.
PAGE
Andrews and Campbell 143, 144
Arrhenius 6, 9
Bauer and Classen 187
Becquerel 102
Bergmaun 104
and Fresenius 141, 142, 143, 144, 172, 174
Beilstein 104
and Jawein 145,163,165
Blake and Chittendeu 181
Bloxam 102
Boisbaudran 104-153
Bongartz and Classen 183
Brand 137, 141, 143, 145, 148, 162, 174
Brugnatelli 177
Bunseu 45
Campbell and Andrews. .. 143, 144
Cheney and Richards 141, 143
Chittenden and Blake 181
Clamoud 64
Clarke, F. W 104, 163, 174
Classen 105, 135, 137, 141, 143, 148, 153, 154, 163, 166, 167, 178, 182,
183, 191, 192, 194, 196, 199, 200, 201, 202, 205, 206, 213, 221, 224, 225,
2-27, 228, 239, 245, 255, 256
Classen and Bauer 187
and Bongartz 183
" and Lud wig , 174, 225
" and v. Reiss, 137, 141, 143, 145, 148, 154, 162, 163, 168, 178, 183, 188
Cozzi 102
Croasdule 154
Cruikshauk 102
287
288 INDEX OF AUTHORS.
PAGk.
Daniell 42
Danueel 70
Despretz 102
Dolezalek 38
Drown and Mackeima. 137
Duprfc 177
Eiseiiberg 147, 164, 172, 174
Elbs 47, 71
Eliasberg 162, 164, 209
Eugels 96, 148, 150, 151, 159, 183, 186, 211
Faraday 7, 10, 12
Farbaky 49
Fischer 102
Fischer-Hufschmidt 226
Foote 154
Fraukl 174
" and Smith 148
Fresenius 104
andBergmami 141, 142, 143, 144, 172, 174
Freudeuberg 17, 106, 183, 212, 215, 216, 217, 218, 220, 221
Gaultier 102
Gibbs 103, 106, 141, 143, 145, 153, 183
Gobbels 182
Groeger.... 148
Grove 44
Gillcher...;. 69
Hampe 154, 166, 270
Haunay 104
v. Helmholtz 12
Heidenreich 105, 137, 140, 154, 158, 163, 166, 176, 183, 185, 207, 208,
210, 212, 215, 216, 218
Herpiii 92, 153
Hofer 100
Hoskinson 174
Ikle 106
" and Reinhardt 145
Jannasch * 211
Jawein 104
and Beilslein 145,163,165
INDEX OF AUTHORS. 289
PAGE
Jordis 145,147
Knufmann 134
Kiliani 17, 106, 166
" and v. Miller 147
Kinnicutt 172
v. Elobukow 97, 99
Knerr aud Smith 162, 174, 183, 209
Koliu and Woodgate 141, 143
Krcichgauer 167
Kriiger 107
Ki utvvig 1 73
Le Blanc 15, 106
Leclanche 40
Lecreuier 178
Leuher and Rising , . . . . 174
Le Roy 141 , 143
Lob 134
Luckow 103-106, 137, 141, 143, 145, 148,154, 155, 162-164, 166, 168,
172, 177, 178, 182, 183, 188. 189, 202
Ludwig 226
aud Classen 174,225
Mackintosh 154
v. Malapert . . . 89, 91
Mascazziui and Parodi 104, 144, 166, 178
Meckenna and Drown 137
Medicus 167
Meeker 154
Meidiuger . .- 41
Merrick 141, 143, 153
v. Miller and Kiliani 147
Millot 145
Moore 137, 148, 162, 163, 188
Morton: 102
Moyeraud Smith 162, 205, 212, 218
Muhrand Smith 137, 177, 228
Xernst 38
Neumann 167, 170, 284, 235, 237
andNissenson 213, 215, 219
Nickles.. . 102
290 INDEX OF AUTHORS.
PAGE
Nissenson and Neumann 213 215 219
Noe ' 66
Oettel 55, 141-144, 154, 158
Obi 141, 143, 153
Ohm 12
Ostwald 35
Paget 71
Parodi and Mascazzini 104, 144, 166, 178
Persoz 177
Regelsberger 154, 159
Reinhardt 106
" and Ihle 145
v. Reiss and Classen.... 137, 141, 143, 145, 148, 154, 162, 163, 168, 178,
183, 188
Richards and Cheney. 141, 143
Riche 92, 141, 143, 145, 148, 154, 166
Richert 104
Rising arid Lenher 174
Rudorff.... 137, 141, 143, 145, 148, 154, 157, 162, 166, 172, 174, 177, 178,
182, 183, 205, 207, 208
Saltar and Smith 162
Schelle, R 50
Scheneck 49
Schmucker 162, 217
Schroder 156
Schucht 141, 143, 148, 162. 166, 172, 183
Schweder 141, 143, 154
Smith, E. F. ... 79, 105, 137, 140, 154, 158, 163-166, 174, 176,177,182,
183, 207, 209, 216, 228, 243
and Frankel 145, 174
" Knerr 162,174,183,209
" Moyer 162, 205, 212, 218
" Muhr 137,177,228
" Saltar 162
" " Thomas 162
" Wallace 177, 204, 205. 208, 210, 212, 215, 228
Tenny..'. 166
Thomas and Smith 162
Thomson, W 37
INDEX OF AUTHORS. 291
PAGE
van't Hoff 6
Vortraaun.... 106, 137, 141, 143, 145, 162, 163, 165-167, 174, 178, 180-190,
192-194, 202, 204, 234
Wallace and Smith 177, 204, 205, 208, 210, 212, 215, 228
v. Waltenhofeu 68
Warwick 145, 154, 163, 167, 205
Wirkner 177
Wohler 102, 183
Woodgate and Kohn 141, 143
Wrightson 103, 137, 141, 143, 144, 153, 163,178
104, 209
INDEX OF SUBJECTS.
PAGE
Accumulators 47
action of 48
charging of 56
general rules for the handling of 54
tests of 51
Acids, decomposition tension value for 16
dissociation of 8
Alcohol as reagent 286
Alloy, analysis of, containing antimony and arsenic 238
antimony and tin 238
antimony, tin, and arsenic 239
antimony and lead 237
copper and nickel 233
copper and silver 233
copper and tin 235
copper, tin, zinc, and phosphorus 235
copper, tin, zinc, manganese, and phos-
phorus 236
copper and zinc 231
copper, zinc, and nickel 234
tin and lead 236
tin, lead, bismuth, and cadmium 237
Aluminium, determination of 153
separation from cobalt 204
iron 196
iron and beryllium 201
iron and chromium ...... 200
nickel 206
zinc 208
Ammonium, determination of. 188
separation from sodium 229
293
294 INDEX OF SUBJECTS.
PAGE
Ammonium, oxalate as reagent 284
sulphate as reagent 285
Ampere, definition of 12
Amperemeter 31
Analysis, arrangements for 107 ff
process of 83
Anions 1 ? 8
Antimony, determination of 178
separation from arsenic 224
arsenic and tin 225
lead 219
mercury 220
silver 220
tin 221
glance, analysis of 259
metallic, analysis of 268
Arsenic, determination of 188
separation from antimony 224
antimony and tin 225
mercury 220
silver 220
Arsenopyrite, analysis of 253
Bases, decomposition tension value for 16
dissociation of 8
Beryllium, determination of 153
separation from aluminium 201
iron 201
Bismuth, determination of 162
separation from cobalt. 205
Bog-iron ore, analysis of 242
Bournonite, analysis of 260
Brass, analysis of 231
Bromine, determination of 190
Bronze, analysis of 235
Buusen cell 45
Cadmium, determination of 163
separation from copper 212
lead 217
manganese 212
mercury. 218
zinc.. . 209
INDEX OF SUBJECTS. 295
PAGE
Calamiue, analysis of 249
Calculation of analyses, tables for 280-2S3
Cathions , 1, 8
Cerussite, analysis of 263
Chalcopyrite, analysis of 254
Chlorine, determination of 190
Chrome-iron ore, analysis of 242
Chromium, determination of 153
separation from iron 199
iron and aluminium 200
iron and uranium 200
iron, uranium, and cobalt 204
iron and nickel 206
Cinnabar, analysis of 265
Clay-iron ore, analysis of 242
Cobalt, determination of 141
separation from aluminium 204
bismuth 205
chromium 204
chromium and uranium 204
copper ..205
iron 191
lead 206
mercury 206
uranium 204
zinc 204
Cobaltiferous arsenopyrite, analysis of 262
Cobaltite, analysis of 261
Conductivity of solutions, theory of 20
Copper, determination of 153
separation from antimony and arsenic 157
arsenic 217
cadmium 212
cobalt 205
lead 213
manganese 211
mercury 217
nickel 206
silver 215
zinc 206
Copper, blister, analysis of 269
matte, analysis of 215, 255
296 INDEX OF SUBJECTS.
PAGE
Copper, refined, analysis of 272
speiss, analysis of 255
Cupron element 46
Current density, calculation of 18
specific directions concerning 139
distribution, scheme of 126
strength, measurement of 17, 28
during analysis 109, 122, 132
apparatus for regulation of 73, 75
Daniell cell 42
Decomposition, tension value of, for acids and bases 15
Double oxalates, general advantages of, for quantitative analysis 5
Dynamo, action of 62
Edison-Lalaude element , 47
Electrochemical equivalent 12
Institute at Aachen, former equipment of Ill
present " " 124
Electrodes 84, 85, 88, 89, 92-94
Electrode tension 13
measurement of 110, 124
Electrolysis, influence of temperature on 94, 95
special apparatus for 100, 101
Electrolytic dissociation 6
of acids 8
bases 8
salts 8
Electrolytic dissociation , degree of 9, 20
precipitation, theory of 21
solution pressure 14
Electrometers 35-37
Faraday's law 10
Ferromangauese, analysis of 275
Furnace "sows," analysis of 258
Galena, analysis of 263
Galvanometers 29
German silver, analysis of 234
Gold, determination of 1?7
separation from other metals 228
Gravity cell 43
Grove cell.. 44
INDEX OF SUBJECTS. 297
PAGE
Halogens, determination of 190
precipitation of 22
Heating, arrangements for 95, 96
Hematite, analysis of , , 240
High tension, laboratory for experiments with 133
Historical 101
Iodine, determination of , . . 190
Ions 7
" osmotic pressure of 13
Ion theory 6
Iridium, separation from platinum 228
Iron, determination of 137
separation from aluminium 196
aluminium and beryllium 201
aluminium and chromium 200
beryllium , 201
chromium 199
chromium and uranium 200
cobalt 191
copper 202
lead 204
manganese 194
nickel. ... 192
uranium 198
zinc 193
Laboratory, private 12?
for the electro-analysis of metals 130
for experiments with high and low tensions 133
Lead, determination of 166
separation from antimony 219
cadmium 217
cobalt 206
copper 213
iron 204
mercury 218
silver ' 218
zinc 210
crude, analysis of 265
hard, " 219,237
matte, " " 264
soft, " " .265
298 INDEX OF SUBJECTS.
PAGE
Lead, speiss, analysis of 256
Leclanche cell 39
Lecture- room 130
Limonite, analysis of 241
Linnseite, " 261
Lippmann electrometer 35
Manganese, determination of 148
separation from cadmium 212
copper 211
iron 194
nickel 206
zinc 208
phosphor-bronze, analysis of 236
Meidinger cell 41
Mercury, determination of 174
separation from antimony 220
cadmium 218
copper 217
lead 218
nickel 207
zinc 210
Nickel, determination of 143
separation from aluminium 206
chromium 206
copper 206
iron 192
lead 207
manganese 206
mercury 206
uranium 206
coin, analysis of 233
commercial, analysis of 274
matte, " " 255
Nitric acid, electrolysis of 3
in nitrates, determination of 189
Ohm 12
Ohm's law 12
Organic compounds, electrolysis of 4
Osmotic pressure of the ions 13
Oxalic acid, as reagent 285
Oxyhydrogen gas voltameter 24
INDEX OF SUBJECTS. 299
PAGE
Palladium, determination of 183
Peroxides, precipitation of 22
Phosphor-bronze 235
Phosphoric acid, separation from tin 228
Pig iron, analysis of 275
Platinum dishes as electrodes 84
determination of 182
separation from iridiuin 228
Poggendorf compensation method 35
Polarization current, explanation of 14
Potassium oxalate, as reagent 284
sulphate, electrolysis of 4
determination of 188
separation from sodium 229
Psilomelane, analysis of 244
Pyrargyrite, " " 257
Pyromorphite, " " 264
Quadrant electrometer 37
Reagents, preparation of 284-286
Resistance for high tensions 134
roll 122
significance of , 19
wire-gauze 113
Rheostats 81
Salts, decomposition tension value of 15
Secondary elements (see Accumulators) 47
reactions 3, 4
Separation of metals, directions for the 191
Shunt circuit, theory of 74
Silver, determination of 172
separation from antimony 220
arsenic 220
copper 215
lead 218
zinc 210
coin, analysis of. ... 233
commercial metal, analysis of 273
Sine galvanometer 28
Smithsonite, analysis of 249
Slag, blast-furnace, cupola, and bessemer 252
300 INDEX OF SUBJECTS.
PAGE
Slag, copper and lead 250
Slags, refinery 250
Sodium, separation from ammonium 229
potassium 229
sulphide as reagent 285
Solder, analysis of 236
Solutions, requirements of, for quantitative electrolysis 5
Spathic iron-ore, analysis of 239
Spelter, " " 268
Sphalerite, " " 247
Spiegel, " " 275
Spring galvanometer 31
Standards for electrolysis 86, 87
v. Klobukow's universal 98
Steel , analysis of 275
Stibnite, " " 259
Storage-batteries (see Accumulators).
Tables for calculation of analyses 280
Tangent galvanometer 26
Tension 1*2
measurement of 32, 109, 124, 128, 182
Tetrahedrite, analysis of .- 257
Thallium, determination of 170
Thermopiles 64
Clamoud's 64
Noe's 66
Gulcher's 69
Paget's 71
regulator for 70
Tin, determination of 183
separation from antimony 221
arsenic 225
phosphoric acid 228
analysis of commercial 272
Torsion galvanometer 33
Transformer, direct-current 125
Transformation of current 125
Type metal, analysis of 219, 237
Ullmaiiite, analysis of 259
Ultramarine, " " 249
Uranium, determination of 153
INDEX OF SUBJECTS. 301
PAGE
Uranium, separation from cobalt 204
cobalt and chromium 204
iron 198
iron ami chromium 200
nickel 206
Volt 12
Voltameter, oxy hydrogen gas 24
weight 26
Voltmeter 32
Wood's metal, analysis of 237
Zinc blende, analysis of 247
crude, " " 268
determination of 144
separation from alumin iuin 208
cadmium 209
cobalt 204
copper 208
iron 193
lead 210
manganese 208
mercury 210
silver 210
Zinkenite, analysis of 260
Zircon " . 253
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14
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16
UNIVERSITY OF CALIFORNIA LIBRARY
THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW
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tP25 1316
JUL 30 1917
7>llS*
