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ELECTRO-CHEMICAL 
ANALYSIS. 

SMITH. 



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RicHTER's Chemistries. 

AUTHORIZED TRANSLATIONS. 

BY EDGAR F. SMITH, F.C.S.. M.A., PH.D., 

■^inpr i>/ CktmUlry, Unwirsify of Pinniflvania ; Membtr 0/ Ckim. 



INORGANIC CHEMISTRY. Fourth American, from ihe Sfilh 
German Edition, thoroughly revised, and in many parts rewritten. 
With 89 Illustrations and a Colored Plate of Spectra. i2mo. 

Cloth, (2.00 

THE CHEMISTRY OF THE CARBON COMPOUNDS, 
or Organic Chemistry. A Text-Book for Students. Second 
American, from the Sixth German Edilion. Illustrated. 1040 
pages. Cloth, J4,oo 

Prof Riehter's methods of arrangement and teaching have proved 
their superiority by the large sale of his books throughout Europe and 
America, translations having been made in Russia, Holland, and Italy. 
They are now used by many of the most prominent schools and colleges 
in the United Slates, by those giving a high technical education, as well 
as those who aim to give but a groundwork in the science of chemistry; 
this shows iheir wonderful adaptiveness to all grades of teaching. 



TO BE USED IN OONNECTION WITH 

RtCHTER'S INORGANIC CHEMISTRY. 

SMITH AND KELLER. EXPERIMENTS. Arranged for 
Students in General Chemistry. By Edgar F. Smith, Professor 
of Chemistry, University of Pennsylvania, and Dr. H. F. Keller, 
Professor of Chemistry, Philadelphia High School. Second Edition- 
Uluslrated. Qoth, Nit. .60 

P. BLAKISTON, SON & CO., PUBLISHERS, 

1012 Walnut Street, Philadelphia. 



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ELECTRO-CHEMICAL 
ANALYSIS. 



EDGAR F. SMITH. 



SECOND EDITION, REVISED AND ENLARGED. 



W[TH TWENTV-SEVEN ILLUSTRATtONS. 



PHILADELPHIA: 

P. BLAKISTON, SON & CO 

I0I2 WALNUT STREET. 
1894. 



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(university! 
v library^ 



Copyrighi, 1894, by P. Blakiston, Son & Co. 



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PREFACE 

TO THE SECOND EDITION. 



Since the appearance of the first edition of this 
book electro-chemical methods of analysis have been 
widely adopted, especially in technical establishments. 
Thousands of analyses are now made annually by 
these methods; they are in many cases superseding 
the ordinary gravimetric methods, because of their 
extreme accuracy. 

In sending forth this little volume a second time, 
the writer has taken pains to incorporate in it such 
new material as experience has demonstrated to be 
entitled to consideration. While the various sources 
of electric energy are mentioned, the storag e cell is 
best adapted for all the work outlined in.the.text. 
Rm phasis should also be laid upon the suggestion 
made by other writers on electrolysis, — that i t is pre- 
ferable to fgpgrt th_at_results have been obtained by a 
currenj; of. definite density., rather than by a current 
yielding a certain number of cubic centimetres of 
electrolytic gas per minute. By observing this sug- 
gestion it is hoped that many contradictory state- 

V 

D,nitiz.!.o,GoOglc 



VI PREFACE TO THE SECOND EDITION. 

merits will disappear from the literature of electrolysis, 
and that chemists everywhere will be able to repeat 
published experiments without finding it necessary to 
continually emend earlier directions.. 

In conclusion, the author would acknowledge his 
great indebtedness to friends for help, suggestions, and 
kindly criticisms, and to his students for their very 
material aid in the development of methods used in 
the determination and separation of the metals dis- 
cussed in the following pages. S. 



UnrversUy of Pennsylvania, iSg4. 



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PREFACE 

TO THE FIRST EDITION. 



In preparing this little volume the author has had 
constantly in view the needs of a large class of stu- 
dents of analytical chemistry desirous of becoming 
acquainted with the methods of quantitative analysis 
by electrolysis ; these are daily acquiring greater im- 
portance, and being introduced and applied wherever 
possible. 

The larger texts devoted to analysis have omitted 
electrolysis from their pages, thus rendering its special 
treatment necessary and desirable. 

The plan adopted in the following pages in present- 
ing this subject has been to give a brief Introduction 
upon the behavior of the current toward the different 
acids and salts, a short description of the various 
sources of the electric energy ; its control and measure- 
ment; after which follow a condensed history of the 
introduction of the current into chemical analysis, and 
sections relating to the determination and separation 
of metals, as well as the oxidations possible by means 
of the electric agent. 

In using this book as a gu ide, the student is ear- 
vii 

- D,nitiz.!.o,GoOglc 



nestlyrecommended to perform the determinations of 
each metal as indicated jn the tex t. The details have 
been made sufficiently full, and clear enough, it is 
hoped, for the most inexperienced analyst. Addi- 
tional skill and valuable experience are acquired 
with each trial, so that, when the section treating 
of separations is reached, the work there outlined will 
be performed without difficulty. Before commencing 
the determination s of any one metal_read, i f po ssible, 
jts literature. 

The methods of determination and separation given 
preference are not those of any onejndividuaj, but 
have been selected from _all sources after an experience 
ofjnany^ears, care being taken to present only_th^e 
which actual tests have shown to be reliable and tj;ust- 
worthy. 

It has not been considered advisable to include an 
outlined electrolytic analysis of alloys and minerals in 
the text, inasmuch as the experience gained in perform- 
ing the analyses already described there will have given 
the analyst such a fund of experience that the course to 
be pursued in special cases will readily suggest itself. 

The author would here acknowledge his indebted- 
ness to the various writers on electrolysis, whose 
publications he has freely used, to the editors of the 
different journals consulted, to friends who have made 
kindly suggestions, and to his brother, Dr. Allen J, 
Smith, who prepared all the drawings from which the 
illustrations of the text were made. S. 

Ukivrrsiiy of Pfnna. 

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TABLE OF CONTENTS. 



Introduction, 9-10 

AcTioNOFTHE Electric Current UPON Acids and Salts, 10-13 

Ohm, Volt, Ampere, »3-i4 

Sources op Evectric Current — 

Greael Balleij, LecUncht Cell, Dankll Cell, Meldinger 
Cell, Crowfool Cell, Bunsen and Grove Batteries, 
Magneto- Electric Machine^ Storage Cells, Ther- 
iDopile, The Electric-light Current in Electrolysis, . 14-Jo 
Reduction of the Current — 

Rheostat, Resistance Frame 30-34 

HRASitRiNG Current — 

Voltameter, Amperemeter 34-37 

Historical Sketch 3^51 

SPECIAL PART. 

I. Determinations OF Metals, 53-'°7 

3. Separation OF Metals, 107 132 

3. Determination of Nitric Acid bv Electrolysis, . . 133 

4. Oxidations bv Means of the Electric Current, . . 133-139 
Index 141 



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ABBREVIATIONS. 



= Jahrtibtrickt der Chimit. 
— Comptis Rendus. 
= Journal fur prailUekt ChimU. 
= Annalen der Chimie und Pharviacu. 
. — Ziilsckriflfur analytUche Chtmir. 

Bctichti dtr deutsrhtn chcmischtn Cesill- 
scAaJi. 
American Journal of SHittd and Arts. 
Proceedings of tkt Amtrican Philosophical 



Am. Ch. Jr. 

Jr. An. Ch. . . 
Jr. Fr. Ins. . . 
Berg-HOtt. Z. 
B. s. Ch. Paris 
Ch. Nei^. 
Ding. p. Jr. 

G. CH. ITAL, 

Ch. Z. . . 



-. American Cke 
= J-hiA 



ncal Journal. 
1 Ciemi,!. 



. — Journalof Analytical and Applied Ckanislry. 

= Journal if the Franklin Inititule, Phlla. 
. ^ Strg- und HatlenmSnnische Zeilung. 

= Bulletin de !a Soiiitl Chimique de Paris. 

- Chemical News. 

- Dinglet's Polytechnisches Journal. 

- Gaietia ehttnica italiana. 
= Chetiiiker-Zditing. 

: Zeilschrififiir angivendete Chiiide. 

- Zeiischrift f&r anorganische Chtmie. 

^ Journal of the American Chemical Society. 

- Mottatshefifur Chemie. 



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ELECTRO-CHEMICAL 
ANALYSIS." 



INTRODUCTION. 

Many chemical compounds are decomposed when 
exposed to the action of an electric current. A de- 
composition of this kind is called electrolysis, while 
the substance undergoing change is termed an electro- 
lyte. The products of the decomposition are the 
anions and cathions, or those (i) which separate at the 
anode, the positive electrode or pole (+ P) of the bat- 
tery, and (2) those separating at the cathode, the nega- 
tive electrode or pole ( — P) of the battery. 

This behavior of compounds has become of great 
service to the analyst, inasmuch as it has enabled him 
to effect the isolation of metals from their solutions, 
and by carefully studying the electrolytic behavior of 
salts it has been possible for him to bring about 
quantitative determinations and separations. 

The electrolytic method of analysis is especially 
inviting, since it permits of clean, accurate, and rapid 
B 9 



10 ELECTRO-CHEMICAL ANALYSTS. 

determinations where the ordinary methods yield ug- 
satis factory results. This statement is readily con- 
firmed on recalling the gravimetric methods usually 
employed in the estimation of copper, mercury, cad- 
mium, bismuth, tin, etc., etc. That this assertion may 
be the conviction of every student of analysis, the 
writer would call attention, first, to the course of the 
current in solutions of some of the more frequently 
occurring salts ; after which will follow a brief account 
of the various modes of obtaining theelectric current, 
how it maybe measured, and how controlled. Finally, 
all the metals which have been studied electrolytically 
will be taken up in detail, and their various determina- 
tions will be followed by a sufficient number of sepa- 
rations to show, at least in part, how w idely the elec- 
trolytic method of analysis may be applied. 



I. ACTION OF THE ELECTRIC CURRENT UPON 
ACIDS AND SALTS. 

At Ihe At the 

— Pole. + Pple. 

HjNlrochloric add + the caireut ^ Hydrogen -(- Chlorine. 
Copper chloride + " « = Cu -|- Cl^ 

Zinc cliloride ^ .■ .< = Zn -|- 01,. 

Nilric acid ^ « « = H -I- NO, -|- O. 

In this last case the hydrogen further acts upon more 
nitric acid and produces ammonia (NHj) and water. 
Lead nittale -|- ihe correDt = Pb -|- NO, + O. 

The oxygen liberated here attacks a second molecule 

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ACTION OF CURRENT UPON ACIDS AND SALTS. 11 

of lead nitrate, and produces lead peroxide, Pb(N03)j 
+ Oj = PbOj, which deposits upon the positive elec- 
trode. 



Copper nitrate -|- the enireal = Cu -|- (NO,),. 
Sulphuric acid + " " i^ H, + SOj. 

Secondary changes frequently occur in these de- 
compositions ; thus, iathelast example the SO, reacts 
with the water present : SO, -|- HjO = HjSO, + O, 
the oxygen going to the positive electrode. In the 
electrolysis of copper sulphate, which is analogous to 
sulph uric acid, secondary changes also occur. 



Potusium milphale + lh« caireot = K, + SO,. 

In this decomposition the litwrated potassium acts 
upon water, with the liberation of hydrogen and the 
formation of potassium hydroxide. 

Bourgoin observed the following changes with 
formic, acetic, and oxalic acids, and their salts : — 

I. Formic Acid. — The decomposition may be ex- 
pressed in two equations — 

(fl) CH,0, = H + (CHO -1- O). 

— Pole + Pole 

(*) 2(CH0 + O) = CH,0, + CO,. 

The decomposition of sodium formate yields carbon 
dioxide and formic acid at the anode, and hydrogen 
and sodium hydroxide at the cathode. 



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12 ELECTRO-CHEMICAL ANALYSIS. 

2. Acetic Acid. — The electrolysis of the dilute ac id 
affords hydrogen at the negative electrode, and at 
the positive electrode a mixture of oxygen, carbon 
dioxide, and a small quantity of carbon monoxide. 

3. Oxalic Acid. — The electrolysis of this acid with 
a current obtained from four Bunsen cells pave de- 
compositions which may be expressed as follows ; — 

C,H,0,.lH,0 + current = 3H, + iCO, + O, ; 
— Pole. -I- Pole. 

the oxygen reacts upon additional acid : — 
aC,H,0, + iH,0 + O, = 4CO, + 4H,0, 

SO that the final products are pure carbon dioxide at 
the positive electrode and hydrogen at the opposite 
pole. The decomposition of potassium oxalate may 
be formulated in the following way: — 

C,K,0, = K, + aC(^ ; 
-Pole. +Pole. 

the liberated metal and the carbon dioxide then react 
further: — 

aH,0 + K, = aKOH + H, and iCO, + aKOH = iKHCO,. 
When exposed to the same influence ammonium 
oxalate yields hydrogen at the negative electrode, and 
hydrogen ammonium carbonate at the positive elec- 
trode. The latter compound further breaks down 
into ammonia and carbon dioxide. 

Succinic acid is electrolysed with difficulty . In its 
decomposition the products which have generally been 



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OHM, VOLT, AND AMPERE. 1 3 

observed at the positive electrode were oxygen and 
the two oxides of carbon. By electrolysing sodium 
succinate KekuU obtained hydrogen at the cathode, 
and carbon dioxide and ethylene at the anode. 
Tartaric acid + the current gave at 
— Pole. _ + Pole, 

hydrogen acetic acid, carbon dioxide, 

carbon monoxide, and oxygen ; 
while with potassium tartrate the products were hy- 
drogen and potassium at the cathode and acid potas- 
sium tartrate, carbon dioxide, carbon monoxide, and 
oxygen at the anode. An alkaline solution of potas- 
sium tartrate gave hydrogen at the cathode and at the 
anode, acetic acid, the oxides of carbon, oxygen, and 
ethane (QHj). 

The above examples will suffice to indicate the na- 
ture of the decomposition due to the current ; they 
will assist very materially in understanding the 
changes occurring in ordinary electrolytic analyses. 
For further particulars in this direction, consult 
Tommasi's Traiti Theorigue ei pratique it fyectrochimie. 



3. OHM, VOLT, AND AMPERE. 
These terms may be defined as follows : — 
The okm is the unit of resistance. Its value is rep- 
resented by a column of mercu ry i sq. mm. in cross- 
section, and 106.2 cm . in length at the temperature 
O-'C. 



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14 ELECTRO-CHEMICAL ANALYSIS. 

The volt is the unit of electromotive force (E. M. F.). 
It is the E. M. F, which gives a current of one ampere 
through a resistance of one ohm. 

The ampere is the unit of current. It is the 
current which, under an electromotive force of one 
volt, flows through a circuit offering a resistance 
of one ohm. 

V 

A=— . 

O 



3. SOURCBS OF THE ELECTRIC CURRENT. 

The electric energy required for quantitative analy- 
sis has been variously furnished by batteries of well- 
known types, magneto -electric machines, dynamos, 
thermo-piles, and electrical accumulators or storage 
cells, A brief descriptlbn of some of these may be 
properly introduced here. 

The Grenet cell or Bichromate Battery (Fig. l) con- 
sists of two plates of carbon (K) and one of zinc (Z), 
movable by means of the handle, a. This is a con- 
venient arrangement, as it allows of easy interruption 
of the current. The liquid to be used in this cell con- 
sists of potassium bichromate(i lb.), strong sulphuric 
acid (2 lbs.), and water ( 1 2 lbs.). In mixing these, the 
probable chemical change is : — 

K,Cr,0, + tHjSO, = aCrO, + K,SOj + H,0 + 6H,S0,. 

D,nitiz.!.o,GoOglc 



SOURCES OP THE ELECTRIC CURRENT. IJ 

The chemical action in the cell, when the current 
passes, may be expressed by the equation: — 

aCiO, + 6H^, + 3Zn = Cr,(SOJ, + jZnSO, + 6H,0. 

The writer found foju: cells of this type ( capacity 
two^uarts) very serviceable in the electrolysis of solu- 
tions of cadmium, uranium, molybdenum, and other 



metals. No disag r eeable fumes arise from _cells of 
tbis__clas§. The electromotive force is about two 
volts, and the internal resistance low. The Grenet 
cell loses in intensity when used for long periods, but 
regainsjts value when it has remained out of action 
for some time. 

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l6 ELECTRO-CHBHICAL ANALYSIS. 

Leclancke Cell (Figs. 2 and 3). — ^Two forms of this 
cell are in use. In the first, to the left of the 
figure, there is a zinc rod, immersed in a solution 
of ammonium chloride, and a carbon plate inside 
a porous cup, tightly packed with a mixture of 
manganese dioxide and broken gas carbon. The 





porous cup is only int ended to hold the mixture 
in pos ition. There is but one liquid, and that a 
strong solution of ammonium chloride. The E. M.F. 
of this cell equals 1 .47 v olts; it decreases ra pidly 
when sending stron g currents. It is infen^ to the 
Dan iell c ell when a steady current is desired for a 
lOTii£_£eriod. 



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SOURCES OF THE ELECTRIC CURRENT. 1/ 

The chemical action in cells of this kind Ayrton 
expresses as follows : — 

(Bdbre sending the cuTrent) — 

iC + / (MnO,) + /» (NHjCl) + « Zn. 
(After sending the cuirenl)— 
iC +(/- iHMnO,) + (« - *)(NH,C1) + (Mn.O.) + i(NH,) 
+ (H,0) + (ZnCI.) + (n - l)(Zn). 

The letters i, /, m, n represent indefinite amounts 
of the acting substances. 

In the modified Leclanche cell the porous cup is 
not needed, as compressed prisms of manganese diox- 
ide, gas carbon, and shellac are used around the 
carbon plate. 

The Daniell cell (Fig. 4) consists of a glass jar, the 
porous cup T, and a cylinder of zinc (Z), the negative 
pole. Outside of the porous cup is the sheet-copper 
cylinder K. The zinc is the negative electrode, and 
the copper the positive electrode. The zinc stands in 
dilute sulphuric acid (i : 20), and the copper in copper 
sulphate. Zinc sulphate often replaces the sulphuric 
acid. The chemical action in the cell is probably:— 

* (Cu) + / (CuSOJ. ( Before lending-l | m (ZnSOJ + n (Zn). 



The E. M. F. of this cell is about 1.07. The Meid- 
/Kf«-{Fig. s) and Crowfoot (Fig. 6) cells are modifica- 
tions of the Daniell, and very serviceable in electrolytic 



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is electro-chehical analysis. 

Fig. 4. 



^ 



^ 




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SOURCES OF THE ELECTRIC CURRENT. 19 

work when currents of low intensity are desired. In 
the sketch of the Meidinger cell, G is a large glass 
jar ; £; a small glass vessel, in which stands the copper 
cylinder, K (+ P). Z (— P) is a cylinder of zinc. 
B contains the supply of copper sulphate crystals. 

The current from either of these batteries remains 
quite constant for long periods. The cells themselves 
do not require much attention. Haifa dozen of either 
of these forms will do nearly all the electrolytic work 
of an ordinary laboratory. The " Crowfoot " form 
can be readily and cheaply prepared. Rejected acid 
bottles, after removing the neck and upper portions, 
answer well as jars. 

If currents of greater E. M. F. are required, the 
Bunsen (Fig. 7) or Grove cell (Fig. 8) should be used. 
In the former there is zinc in dilute sulphuric acid, or 
a mixture of potassium bichromate and sulphuric acid, 
and a carbon plate in a cupof nitric acid. It is a less 
expensive cell than the Grove, as platinum is not 
employed. It is not so readily handled, and cqfi- 
sumes more nitric acid. Its electromotive force is 
somewhat less than that of the Grove form. In the 
latter there is a strip of platinum (P) in concentrated 
nitric acid (in the porous cup, ^ ), and zinc (ZZ) in 
dilute sulphuric acid (one pint acid and ten pints 
water). The E. M. F. is 1.93 volts. When acting, 
N,04 is set free ; this can be in a measure suppressed 
by adding ammonium chloride to the nitric acid. 
The chemical changes occurring in the Bunsen and 

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20 ELECTRO<HBUICAL ANALVStS. 

Grove cells are very similar. Ayrton expresses them 
as follows : — 



«(H,SOJ + »(2b). 



*(Pt) + /(HNOJ. 
(After HndlDf ciutoit)— 
*(Pt)+(/-.MHNOJ + (N^J + (,B/)). f («-i)(H,SOJ + (ZiiSO,) ^ 

Fig. 8. 



W~- 





The internal resistance of the Grove cell is small. 
To obtain good results both the Bunsen and Grove 
cells require constant attention. 



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SOURCES OF THE ELECTRIC CURRENT. 21 

In amalgamating the zincs in any of the preceding 
batteries, first allow them to remain over night in very 
dilute hydrochloric acid, then immerse in mercury, 
and with a wet cloth rub the latter into the metal. 
This should be done once a week, when the cells are 
in daily use. For further information upon batteries, 
consult Ayrton's Practical Electricity. 

Magneto-electric machines and dynamos have been 
used to some extent in electrolytic decompositions, 
but a detailed description of their construction will not 
be given. It will be sufficient to add that a dynamo 
with a tension of 5 volts will answer for about all 
the determinations, separations, and oxidations which 
are carried out electrolytically. 

Thermo-piles have also been used to furnish cur- 
rents for electrolytic work. Their use has been 
objected to upon the ground that the currents afforded 
by them are rarely strong enough for the greater num- 
ber of determinations and separations, and again they 
are easily broken and difficult to repair. The forms 
generally met with are those recommended by Cla- 
mond and Noe. 

The Clamond thermo-pile is pictured in Fig. 9, i 
is a perspective view of the same ; 2 represents a ver- 
tical section, and 3 a basal section, showing the bars 
and armatures. The elements consist of bars of a zinc 
and antimony alloy and a strip of sheet-iron. These 
are arranged in circles, as indicated in 3 ; they are 
placed one above the other. In 3, B represents the 

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22 BLECTRO-CRBHICAL ANALYSIS. 



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SOURCES OF THE ELECTRIC CURRENT. 2$ 

bars of zinc and antimony alloy, while the tinned 
sheet-iron plates are marked L. The sheet-iron serves 
to conduct the current from one element to the other ; 
hence, these strips rest upon the bars B. Heat ex- 
pands the latter, and in consequence renders the con- 
tact more intimate. The single elements, as well as 
the circles of elements, are separated from each other 
by plates of asbestos (see r in 2). The cylinder itself 
consists of a series of such circles. The welded points 
of the bars are all directed to the centre of the cylin- 
der. The gas flames are prevented from coming in 
immediate contact with them by the asbestos lining 
of the cylinder. As gas is employed to furnish the 
necessary heat, in the middle of the cylinder will be 
observed a clay tube {A) provided with apertures (2 
and 3). The gas enters through the Giroud regulator 
C(i and 2), which makes it possible to maintain a 
uniform temperature and a constant current. From 
Cit is conducted to A, through T, into which air is 
admitted by suitable apertures. The mixture of air 
and gas burns at the openings in A. Additional 
air is supplied through D. Light the gas jets from 
above, after removing the cover. The poles of each 
ring of elements end in binding screws, thus en- 
abling the operator to connect any number of them, 
depending upon the external resistance (Z. f a. Ch., 
^5> 334)- When in excellent condition, these thermo- 
piles are said to yield a current equivalent to 400-500 
c.c. oxyhydrogen gas per hour. The form of thermo- 

D,nitiz.!.o,GoOglc 



24 ELECTRO-CHEMICAL ANALYSIS. 

pile recently devised by Giilcher (Z. f. ang. Ch., Heft 
i8, 548; Electrotechnische Zeitschrift, n, 187) pos-' 
sesses marked advantages over the types j ust described. 
It is decidedly more durable. The largest form con- 
sumes hourly 170 litres of gas and develops an electro- 
motive force of 4 volts, with ati internal resistance of 
0.6-0.7 ohms. Those who have used this modified 



thermo-pile consider it extremely valuable in charging 
storage-cells for use in electro-chemical analysis. 

Liter ATUBE,—E. f. «. Ch., 14, 350; 17,305; Ding. p. Jr., az4, 
367 ; Z. f. a. Ch., 18, 457 ; 35, 539 1 Z. f. ang. Ch., Hefl iS, 548. 

The best source of electric energy, for electrolytic 
purposes, is unquestionably the storage cell (Fig- 10). 



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SOURCES OF THE ELECTRIC CURRENT. 2$ 

The illustration represents a cell of the Julien type. 
It contains nineteen alternating plates of lead and lead 
dioxide. Each of these is five and three-fourths inches 
square. The exciting liquid is sulphuric acid of sp. 
gr. 1.2. The E.M.F.oi such a cell is a little more 
than two volts. The current is very constant. 

Another form of storage cell that has been developed 
recently deserves mention. It is known as the " Chlo- 
ride Accumulator" (Fig. ii); it is of the Plante type. 
The largely increased surface of available plate for 
corrosion by the current is secured by casting a frame 
of lead around square or circular tablets of lead chlo- 
ride mixed with zinc chloride, and then reducing these 
to metallic lead by means of zinc in an acid zinc 
chloride solution. In this way a plate is obtained 
which is readily " formed " by the action of the cur- 
rent, the oxygen rapidly converting its porous portion 
into peroxide. An uneven number of these peroxi- 
dized or positive plates are placed with an even num- 
ber of the metallic lead or negative plates, to form a 
battery, the total number of plates being fixed by 
the capacity required. Thus, one positive plate 7j^ 
inches square, placed between two negative plates of 
the same size, and immersed in sulphuric acid of 
.specific gravity 1.275, forms a battery having * normal 
storage capacity of 50 amperp-hours. The weight of 
the plates in this cell is 1 3 pounds. The resistance 
of the "Chloride Accumulator" is very low. The 
great merit of the cell lies in its wide adaptability to 



o,Googlc 



26 EL.ECTRO-CHEMICAL ANALYSIS. 

the conditions of use. It can be charged and dis- 
charged at varying rates without injury, and shows 
no sulphating when discharged below its normal min- 



imum voltage. It is manufactured by the Electric 
Storage Co., of Philadelphia. 

Cells of this kind can be charged from primary 
batteries, or, better, by means of a dynamo or thermo- 

D,nitiz.!.o,GoOglc 



SOURCES OF THE ELECTRIC CURRENT. 2/ 

pile (p. 2l). In any community where electric light- 
ing is employed it is possible to have the charging 
done at little expense, and in factories, where there is 
always sufficient power, a small dynamo could easily 
be arranged for this purpose, so that almost any num- 
ber of cells could be kept in condition for work. The 
iron estimations required by any estabh'shmcnt could 
be rapidly and accurately made with three cells of 
this type; little attention would be demanded from 
the chemist. While storage cells can be used in almost 
every description of electrolysis, there are a great 
many cases where economy would suggest the use of 
the cheaper batteries, e. g., the Crowfoot. Consult 
the following literature upon storage batteries: — 

Proceediags of the Rojal Society, Jaoe 30, 1S89; Transaction* of 
Am. Inst. Mining Engineers (Eleclrical Accumulatori, Salom), Feb., 
1890. Z. f. ang. Ch., 1S92, p. 451 ; Ch. Z., Jabrg. 17, 66; Die Ak- 
knmDlatoren, Elbs, Leipzig, 1893 ; Anleitnng zu EldclTOchemischen 
Vertocben, F. Oettel, Fieiberg, (894. 

Stillweil and Austen have recently suggested the 
use of the electric light current for the determination 
of metals in the electrolytic way. That portion of 
their communication, in which is embodied all that is 
essential for those desirous of adopting this method, 
will be found in the following quotation : " The whole 
apparatus can be made from a few yards of insulated 
copper wire, some 16 wooden lamp sockets, and black- 
ened lamps, say six so-candle power, three 32-candle 
power, six 24-candle power, and six i6-candle power. 



o,Googlc 



ELECTKO-CHEMICAL ANALYSIS. 



~-B^' 




o,Googlc 



SOURCES OF THE ELECTRIC CURRENT. 29 

. . . . Binding screws, connections, and plugs 
will also be necessary in addition to those which are 
put in with the electric wires. 

The main wires +, +, — , are furnished with sockets 
A, B, C for the introduction of safety plugs, which, for 
the small currents used in electrolytic work, need not 
exceed 6 lamp leads. The main wires terminate in 
binding screws, by which they are connected with the 
series of sockets i, 2, 3, 4, 5. In these lamps for 
reducing the main current are placed, and if only one 
determination or like determinations are required to 
be made, only this series will be neces.sary if ordinary 
currents are required. If, however, two or three dif- 
ferent determinations, or some requiring very small 
currents, are to be made, side currents can be formed 
as around sockets 2 and 4, and the current brought 
to the desired size by the introduction of resistances 
in the series of sockets E and F. K and L will rep- 
resent the proper position of the solutions to be elec- 
trolysed by these side currents. By this arrangement 
three unlike determinations can be simultaneously 
made, one in the main circuit, and one in each of the 
side-series. If more determinations are required, 
other sets of sockets may be put up and potentials be 
taken over other lamps. The sockets may be placed 
on the wall above the desk, the wires leading down 
to the solutions to be electrolysed." Jr. An, Ch., 6, 
129. Any other arrangement can be adopted. That 
just described can be adjusted to the parallel system. 

D,nitiz.!.o,GoOglc 



30 ELECTRO-CHEMICAL ANALYSIS.. 

The current may be derived from an Edison three- 
wire system or from any other incandescent system. 

Dr. Hart, of Easton, Pa., has devised a resistance 
frame to be used when the electric light current is 
employed for electrolytic purposes. It is simpler in 
construction than that described in the preceding 
paragraph. Baker & Adamson, of Easton, manu- 
facture this frame ; particulars in regard to it can be 
obtained from them. 

Having thus briefly described the more important 
current-producers, the means of regulating the current 
may be next considered. 



4. REDUCTION OF THE CURRENT. 

When a battery gives a current that generates 10 
c.c. oxy-hydrogen gas per minute, and work is to be 
done which can easily be performed by an expenditure 
of energy not exceeding 3 c.c. oxy-hydrogen gas per 
minute, it will become necessary to reduce the strong 
current. Persons acquainted with practical physics 
will promptly suggest the resistance coils found in 
physical laboratories as suitable for this purpose. 
They are, on the whole, quite satisfactory, and have 
been thus utilized, although simpler and more con- 
venient current-reducers have made their appearance 
in recent years. A few of these later appliances may 
be mentioned : — 

I. The current may be sent through a solution 



o,Googlc 



REDUCTION OF THE CURRENT. 



31 



(saturated) of zinc sulphate, contained in a large glass 
cylinder, about 22 cm. long and 8.5 cm. in diameter. 
In one experiment the current is passed from a to ^ 
(Fig. 13), and in the next from b to a. " The rod i, 
with one zinc pole, is pushed toward the zinc pole a, 
until the current reaches the desired strength." It is 



Fio. 13. 




well to amalgamate the zincs from time to time. We 
are indebted for this piece of apparatus to Classen, 
who has also described another simple rheostat (Fig. 
14) (Ber., 31, 359). In this apparatus the current 
enters at a, travels the German silver resistance », and 
returns through d to the battery. In the performance 
of electrolytic depositions the platinum vessels, serv- 



o,Googk' 



32 ELECTKO'CHEHICAL ANALYSIS. 

ing as negative electrodes, may be connected with any 
one of the binding-posts from 1—20. This makes it 
possible for the analyst to execute eight different de- 
terminations at the same time. To show the influence 
of this apparatus, a current from five Bunsen cells, 
generating 68 c.c. oxy-hydrogen gas per minute, was 
allowed to act upon copper solutions contained in six 
vessels. The current at binding-post I was found to 
be equal to 3,75 amperes; at 2, it equaled 2.617 

Fio. 14. 



amperes; at 3, 2.085 amperes; at 4, I.911 amperes, 
, etc., until at 20 it was only 0.098 of an ampere. 

To better understand these figures it should be re- 
membered that an ampere equals 10.436 c.c. oxy- 
hydrogen gas per minute, or it is equivalent to a 
current which will precipitate 19.69 mg. of metaUjc 
copper, or 67.1 mg. of metallic silver in one minute. 

For a larger form of apparatus somewhat similar to 
that described above, see Ber., 17, 1787. 



o,Googlc 



REDUCTION OF THE CURRENT. 33 



b, Google 



34 ELECTRO-CHEHICAL ANALYSIS. 

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 six 
feet in length. Extending from end to end, on both 
sides, is a light iron wire, measuring in all about 500 
feet (Fig. 15). With the binding-posts at a and b, and 
a simple clamp, it is possible to throw in almost any 
resistance that maybe required. It answers all prac- 
tical purposes. It can be procured from Queen &Co., 
Philadelphia, Pa. 

LiTEKATURB. — T. Klobolco w, Jr. f. pkt. Gi., 37, 375; 40, 131. 



In every analysis by electrolysis it is advisable that 
the strength of the acting current should be known. 
The simplest and most convenient apparatus for this 
purpose is the Bunsen voltameter (Fig. 16), The 
inner tube a, containing sulphuric acid of sp. gr. 1.22, 
stands in a large cylinder of water to cool it. The 
liberated hydrogen and oxygen are collected over 
water in the eudiometer tube R; p and p' are platinum 
electrodes. In all accurate experiments the volume 
of gas should always be reduced to 0° and 760 mm, 
pressure. Some chemists substitute a galvanometer 
(tangent or sine) for the voltameter. The deflection 
of the needle by the current measures the strength of 



o,Googlc 



MEASURING CURRENTS. 35 

the latter. " In order to express in terms of chemical 
action the deflection of the needle, it is placed in the 
same current with a voltameter, and the deviation of 
the needle is observed, as well as the volume of elec- 
trolytic gas (reduced to o° and 760 mm. pressure) 



which is produced in a minute. Placing the volume 
equal to v, the quotient ~-^ gives the standard value 
for the galvanometer. If this standard value is de- 
noted by R, the strength, I, of a current which pro- 
duces the deviation a is I = R tan. a." 

The writer has found the amperemeter of Kohl- 

D,nitiz.!.o,GoOglc 



36 ELECTRO-CHEMICAL ANALYSIS. 

rausch (Fig. 17) very satisfactory, especially in cases 
where strong currents are employed. In this instru- 
ment the current travels through an insulated wire 
surrounding a Bar of soft iron. The latter, in its 
magnetized state, attracts the needle C, attached to a 
spiral. C moves over a graduated face (in amperes). 



and its deflection gives at once the strength of the 
current in amperes. 

In electrolytic work of any kind it is advisable 
that the apparatus intended to measure the current 
strength should be in the circuit during the entire 
decomposition, for it is only in this way that we can 
expect to effect separations without encountering un- 

D,nitiz.!.o,GoOglc 



MEASURING CURRENTS. 37 

pleasant difficulties. It is necessary to know just what 
energy is required, and then to so regulate the current 
that the same is approximately maintained throughout 
the entire determination. 

Different writers upon electro-chemical analysis 
have advised, instead of indicating that a determina- 
tion has been made by a current liberating a definite 
volume of electrolytic gas per minute, that it would 
be better, from a practical standpoint, to indicate the 
current density. To this end the inner surface of the 
platinum dish in which the electrolysis is made should 
be known in cm* ; its contents, too, should be given 
in cm' for various heights, N.D,gi,^ the normal den- 
sity of the current; this is equivalent to the current 
strength for loo cm' of the electrode surface. The 
density (D) therefore is dependent upon the current 
strength, as well as upon the surface (E) of the elec- 
trode upon which the metallic deposit is precipitated. 

When the surface upon which the metal is deposited 
equals E, the corresponding current strength can be 
deduced from the formula C = (N.Di„,).^. See, 
further, Miller and Kiliani, Lehrbuch der analyt 
Chemie, p. ii. 

Before taking up the description of the details to 
be observed in the electrolytic precipitation of indi- 
vidual metals, it may not be uninteresting to briefly 
trace the history of the introduction of the electric 
current into chemical analysis. 

D,nitiz.!.o,GoOglc 



38 ELECTRO-CHEMICAL ANALYSIS. 

6. HISTORICAL. 

Although the early years of this century show con- 
siderable activity in electrical studies, the efforts were 
mainly directed to the solution of the physical side of 
electrolysis. To Gautticr de Claubry probably be- 
longs the credit of having first (1850) applied the cur- 
rent to the detection of metals when in solution. His 
efforts were wholly directed to the isolation of metals 
from poisons by depositing the same upon plates of 
platinum. When the precipitation was considered 
finished the plates were removed, carefully washed, 
and the deposited metals brought into solution with 
nitric acid, and there tested for and identified by the 
usual course of analysis. The current was evidently 
very feeble, as the time recorded as necessary for the 
deposition varied from ten to twelve hours. Gaultier 
considered this method reliable in all instances, but 
especially recommends it for the separation of copper 
from bread. In testing for zinc he employed a strip 
of tin as anode, but states that a platinum plate will 
answer as well. 

In Graham-Otto's Lehrbuch der Chemie (1857) it 
is stated that the oxygen developed at the positive 
electrode readily induces the formation of peroxides ; 
. . . that lead and manganese peroxides are de- 
posited, from solutions of these metals, upon the posi- 
tive electrode of the battery ; . , . that the point of 
a platinum wire, when attached to the anode of a cell, 

D,nitiz.!.o,GoOglc 



HISTORICAL. 39 

is therefore a delicate means of testing for manganese 
and lead. In the same text the oxidizing power of 
the anode is nicely shown by the following simple ex- 
periment: A piece of iron, in connection with the 
positive electrode of the battery, is introduced into a 
V-shaped glass tube containing a concentrated solu- 
tion of potassium hydroxide, while a platinum wire 
running from a negative electrode projects into the 
other limb of the vessel. In a short time ferric acid 
appears around the anode, and is recognized by its 
color. 

C. Despretz (1857) described the decomposition of 
certain salts by means of the electric current, and 
remarked that, while operating with solutions of the 
acetates of copper and lead, he expected both metals 
would be deposited upon the negative pole, and was 
much surprised to find that the lead separated as oxide 
upon the anode at the same time that the copper 
was deposited upon the cathode. The results were 
the same when experiments were conducted with 
the nitrates and pure acetates. With manganese no 
deposition took place upon the negative electrode, but 
a black oxide appeared at the opposite pole. Potas- 
sium antimonyl tartrate gave a crystalline metallic 
deposit of antimony at the cathode, and upon the anode 
a yetlowish-rcd coating, supposed to be anhydrous 
antimonic acid. Bismuth nitrate yielded a reddish- 
brown deposit at the positive electrode. Despretz 
concludes his paper by stating that although the facts 

D,nitiz.!.o,GoOglc 



40 ELECTRO-CHEUICAL ANALYSIS. 

were few in number, yet they were new in so far as 
they concerned lead, antimony, and manganese ; and, 
furthermore, that the separation of copper from lead 
by the current was almost perfectly complete. 

Three years later (i860) Charles L. Bloxam recom- 
mended the process of Gaultier for the detection of 
metals in organic mixtures, although it may not be 
improper to add that Smee (185 1), in his work on 
electrometallurgy, asserts that Morton was the first 
person to employ the electric current for the isolation 
of metals from poisonous mixtures. However this 
may be, the fact remains that Bloxam did use the 
current quite extensively for this purpose, and while 
he claims no quantitative results for the method, the 
apparatus employed by him and his subsequent work 
in this direction deserve great credit. 

To detect arsenic electrolytically Bloxam made use 
of a glass jar, four cubic inches in capacity, closed 
below by parchment, which was tightly secured by 
means of a thin platinum wire. In the neck of the 
jar was a targe cork, through which passed a glass 
tube bent at a right angle. This tube was intended 
to serve as a means of escape for the gases liberated 
within the jar. The platinum wire from the negative 
electrode was also held in position by the cork. The 
portion of the wire within the jar was attached to a 
platinum plate dipping into the arsenical mixture con- 
taining dilute sulphuric acid. The jar with its contents 
stood in a wide beaker, filled with water, into which 

D,nitiz.!.o,GoOglc 



HISTORICAL. 41 

dipped the positive electrode of the battery. Under 
the influence of the current, metals like antimony, 
copper, mercury, and bismuth separated upon the 
platinum plate of the negative electrode, while arsine 
was liberated and escaped through the exit- tube into 
some suitable absorbing liquid. To ascertain what 
metal or metals had separated upon the cathode, 
the plate attached thereto was removed, after the 
interruption of the current, and treated with hot 
ammonium sulphide. Upon evaporating this solution 
an orange -colored spot remained if antimony had been 
previously present. If a metallic deposit continued to 
adhere to the foil the latter was acted upon by nitric 
acid to effect the solution of the remaining metals. 

J. Nicklis( 1 862) precipitated silver with the current 
obtained from a zinc-copper couple. The positive 
electrode consisted of a piece of graphite, taken from 
a lead-pencil, while a thin, bright copper wire consti- 
tuted the negative electrode. The silver separated 
upon this. The current was very feeble, for hydrogen 
was not liberated at the cathode. Nickles also sug- 
gested the reduction of large quantities of silver from 
the solution of its cyanide by this means. To obtain 
the silver he advised using a cylindrical cathode con- 
structed from some readily fusible alloy, so that after 
the reduction was finished the other metals might be 
easily melted out and leave a silver plate. Copper, 
lead, bismuth, and antimony were separated electro- 
lytically, by Nickles, from textiles. 
D 

D,nitiz.!.o,GoOglc 



42 ELECTKO-CHEHICAL ANALYSIS. 

In 1S62 A. C. and £. Becquerel resumed their 
electrochemical investigations, first begun some thirty 
years previously. Their experiments seem to have 
been aimed chiefly toward the reduction of metallic 
solutions upon a large scale, caring not for the quanti- 
tative estimation of metals, but seeking rather a rapid 
and satisfactory technical isolation process. 

Wohler (1868) found that when palladium was 
made the positive conductor of two Bunsen cells, and 
placed in water acidulated with sulphuric acid, it 
immediately became covered with alternating, bright, 
steel-like colors. He regarded the coating as palladium 
dioxide, since it liberated chlorine when treated with 
hydrochloric acid, and carbon dioxide when warmed 
with oxalic acid. Black amorphous metal separated 
at the cathode. Its quantity was slight. Under 
similar conditions lead also yields the brown dioxide, 
and the same may be said of thallium. Osmium, in 
its ordinary porous form, at once becomes osmic acid. 
When caustic alkaU is substituted for the acid the 
liquid rapidly assumes a deep yellow color, while a 
thin deposit of metal appears upon the cathode. 
Ruthenium behaves similarly when applied in the 
form of powder. Osmium-iridium, a compound de- 
composed with difficulty under ordinary circum- 
stances, immediately passes into solution when brought 
in contact with the positive electrode of a battery 
placed in a solution of sodium hydroxide, and imparts 
a yellow color to the alkaline liquid. A black de- 

D,nitiz.!.o,GoOglc 



HISTORICAL. 43 

posit of metal slowly makes its appearance upon the 
negative pole. 

The experiments thus far described are qualitative 
in their results. The Brst notice of the quantitative 
estimation of metals electrolytically was that of Gibbs 
(1864), when he published the results he had obtained 
with copper and nickel. Luckow, in alluding to this 
work a year later (1865), says : " I take the liberty to 
observe that so far as the determination of copper is 
concerned, I estimated that metal in this manner 
more than twenty years ago, and as early as 1S60 
employed the electric current for the deposition of 
copper quantitatively in various analyses." It was 
Luckow who proposed the name Eiektro-Metall Ana- 
lyse for this new method of quantitative analysis. 
According to this writer the current may be applied 
as follows : — 

1. To dissolve metals and alloys in acids by which 
they would not be affected unaided by the electric 
current. 

2. To detect metals like manganese and lead 
(silver, nickel, cobalt) ; separating them in the form 
of peroxides; also manganese as permanganic acid. 

3. To separate various metals, e. g., copper and 
manganese, from zinc, iron, cobalt, and nickel. 

4. To deposit and estimate metals quantitatively, 
in acid, alkaline, and neutral solutions. 

5. For various reductions, t. g., silver chloride, basic 
bismuth chloride, and lead sulphate, in order that the 

D,nitiz.!.o,GoOglc 



44 ELECTRO-CHEMICAL ANALYSIS. 

metals in them may be determined. To reduce chro- 
mic acid to oxide, e. g., potassium bichromate acidu- 
lated with dilute sulphuric acid. 

These applications embrace nearly all that has since 
been accomplished by the aid of the current. In the 
same article to which Luckow calls attention to the 
facts recorded above, he describes minutely the method 
pursued by him in the precipitation of metals. Refer- 
ence to these early experiments will show with what 
care and accuracy every detail was worked out. 
Luckow also announced "that all the lead contained 
in solution was deposited as peroxide upon the posi- 
tive electrode, and might be determined from the 
increased weight of the latter." This observation 
was fully confirmed by Hampe, and later by W, 
C. May. 

Wrightson (1876) called attention to the fact that 
if solutions of copper were electrolysed in the presence 
of other metals, the latter greatly influenced the sepa- 
ration of the former. For example, with copper and 
antimony, the deposition of the copper was always 
incomplete when the antimony equaled one-fourth to 
two-thirds the quantity of the former. Notwithstand- 
ing, a complete separation of the two metals can be 
effected when the quantity of the antimony is small. 
A somewhat similar behavior was noticed with other 
metals. The deposition of cadmium, zinc, cobalt, and 
nickel was apparently not satisfactory. 

Lecoq de Boisbaudran ( 1 877) electrolysed the potas- 

D,niiiz.!.o,GoOglc 



HISTORICAL. 45 

sium hydroxide solution of the metal gallium, using 
six Bunsen elements with 20-30 c.c. of the concen- 
trated liquid. The deposited metal was readily de- 
tached when the negative electrode was immersed in 
cold water and bent slightly. 

The unpromising behavior of zinc solutions, ob- 
served by Wrightson, was fortunately overcome by 
Farodi and Mascazzini (1877), who employed a solu- 
tion of the sulphate, to which was added an excess of 
ammonium acetate. Lead was also deposited in a 
compact form from an alkaline tartrate solution of this 
metal in the presence of an alkaline acetate. 

After Luckow's experiments upon manganese, little 
attention appears to have been given this metal until 
Richi (187S) published his results. While confirming 
the observations of Luckow, he discovered that manga- 
nese was not only completely precipitated from the 
solution of its sulphate, but also from that of the 
nitrate, thus rendering possible an electrolytic sepa- 
ration of manganese from copper, nickel, cobalt, zinc, 
magnesium, the alkaline earth, and the alkali metals. 
Rich£ recommended that the deposited dioxide be 
carefully dried, converted by ignition into the proto- 
sesquioxide, and weighed as such. According to this 
chemist the one-millionth of a gram of manganese, 
when exposed to the action of the current, gave a 
distinct rose-red color, perceptible even when diluted 
tenfold. 

In zinc depositions Riche gave preference to a 

D,nitiz.!.o,GoOglc 



46 ELBCTRO-CHEUICAL ANALYSIS, 

solution of zinc-ammonium acetate containing free 
acetic acid. 

Luckow was the first to mention that the current 
caused mercury to separate in a metallic form, from 
acid solutions, upon the negative electrode. F. W, 
Clarke (1878) used a mercuric chloride solution, 
feebly acidulated with sulphuric acid, for this purpose. 
The deposition was made in a platinum dish, using 
six Bunsen cells. Mercurous chloride was at first pre- 
cipitated, but it was gradually reduced to the metallic 
form. J. B. Hannay (1873) had previously recom- 
mended precipitating this metal from solutions of 
mercuric sulphate, but gave no results. 

Clarke, also, gave some attention to cadmium ; his 
results, however, were not satisfactory. A few 
months later the writer (1878) succeeded in depositing 
cadmium completely and in a very compact form 
from solutions of its acetate. Upon this behavior 
Yver (1880) based his separation of cadmium from 
zinc. Furthermore, the writer found {1880) that the 
deposition of cadmium could be made from solutions 
of its sulphate, contrary to an earlier observation of 
Wrightson. At the same time copper was completely 
separated from cadmium by electrolysing their solu- 
tion in the presence of free nitric acid. 

A very successful determination of both zinc and 
cadmium was published by Beilstein and Jawein in 
1879. They employed for this purpose solutions of 
the double cyanides. 



o,Googlc 



HISTORICAL. 47 

Heinrich Fresenius and Bergmanti (1880) found 
that the electrolysis of nickel and cobalt solutions 
succeeded best in the presence of an excess of free 
ammonia and ammonium sulphate. 

Their experience with silver demonstrated that 
the best results could be obtained with solutions 
containing free nitric acid, and by the employment of 
weak currents. 

The writer showed (1880) that if uranium acetate 
solutions were electrolysed the uranium was com- 
pletely precipitated as a hydrated protosesquioxide ; 
and, further, that molybdenum could be deposited as 
hydrated sesquioxide from warm solutions of am- 
monium molybdate in the presence of free ammonia. 
Very promising indications were obtained with salts 
of tungsten, vanadium, and cerium. 

In a more recent (1880) communication from 
Luckow, to whom we are indebted for much that is 
valuable in electrolysis, is given a full description of 
his observations in this field of analysis, from which 
the following condensed account is taken. While it 
relates more particularly to the qualitative behavior 
of various compounds, its importance demands careful 
study. 

When the current is conducted through an acid 
solution of potassium chromate, the chromic acid is 
reduced to oxide ; whereas, if the solution of the oxide 
in caustic potash be subjected to a like treatment 
potassium chromate is produced. Arsenic and 

D,nitiz.!.o,GoOglc 



48 ELECTRO-CHEMICAL ANALYSIS. 

arsenious acid behave similarly. The same is true 
also of the soluble fcrro- and ferri-cyanides and nitric 
acid. In the presence of sulphuric acid ferric and 
uranic oxides are reduced to lower states of oxidation. 
Sulphates result in the electrolysis of the alkaline 
sulphites, hyposulphites, and sulphides.and carbonates 
from the alkaline organic salts. . In short, the current 
has a reducing action in acid solutions, and the 
opposite effect in those that are alkaline. In the 
electrolysis of solutions of hydrogen chloride, bromide, 
iodide, cyanide, ferro- and ferri-cyanide and sulphide, 
the hydrogen separates at the electro-negative pole, 
and the electro-negative constituents at the positive 
electrode. Cyanogen sustains a more thorough de- 
composition, the final products being carbon dioxide 
and ammonia. In the electrolysis of ferro- and ferri- 
cyanogen Prussian blue separates at the positive 
electrode. In dilute chloride solutions hypochlorous 
acid is the only product, whereas chlorine is also 
present in concentrated solutions. In alkaline chloride 
solutions chlorates are produced as soon as the liquid 
becomes alkaline. In the iodides and bromides iodine 
and bromine separate at the positive electrode, while 
bromates and iodates are formed when metals of the 
first two groups are present. Potassium cyanide is 
converted into potassium and ammonium carbonates. 
Concentrated nitric acid is reduced to nitrous acid ; 
however, when its specific gravity equals 1.2, this does 
not occur, at least not when a feeble current is used. 



o,Googlc 



HISTORICAL. 49 

Dilute nitric acid alone, or even in the presence of 
sulphuric acid, is not reduced to ammonia. If, how- 
ever, dilute nitric acid be present in a copper sulphate 
solution undergoing electrolysis, copper will separate 
upon the negative electrode and ammonium sulphate 
will be formed. Solutions of nitrates containing sul- 
phuric acid behave analogously. Phosphoric acid 
sustains no change. Silicic acid separates as a white 
mass, and boric acid, in crystals uniting to arborescent 
groups, at the positive electrode. 

In the Ber. d. d. chem. Gesellschaft for 1881 (Vol. 
14, 1622), Classen and v. Reiss presented the first ot 
a series of papers upon electrolytic subjects, which 
continued through subsequent issues of this publica- 
tion. Their early work was devote"d to the precipita- 
tion of metals from solutions of their double oxalates. 
They also elaborated excellent methods for antimony 
and tin. Many very service^le forms of apparatus, 
intended for electrolytic work, were devised and de- 
scribed by them, and it must be conceded that through 
the activity of the Aachen School electrolysis acquired 
more importance in the eyes of the chemical public 
than it ever before possessed. The details of the 
more important methods proposed by Classen and 
his co-laborers will receive due mention under the 
respective metals. 

At the same time with and quite independently of 
Classen, Reinhardt and Ihle proposed the double oxa- 
lates for the estimation of zinc electrolytically ; and 

D,nitiz.!.o,GoOglc 



50 EX,ECTRO-CHEMICAL ANAI.YSIS. 

in this connection it may not be improper to mention 
that as early as 1879, two years prior to the publica- 
tion of Classen's first communication, Parodi and Mas- 
cazzini (Gazetta chimica italiana, Vol. 8) announced 
that antimony and iron could be deposited completely 
and in compact form by electrolysing the solutions 
of the sulpho-salts of the former and the chloride 
of the latter in the presence of acid ammonium 
oxalate. 

In 1880, Gibbs recommended placing solutions of 
the metals in a beaker glass, on the bottom of which 
was placed a layer of mercury, which served as the 
negative electrode. Knowing the combined weight 
of the beaker and mercury, the increased weight, after 
precipitation and removal of the liquid, will give the 
quantity of metal under examination. This method 
is not applicable in the case of antimony and arsenic. 

Six years later (1886) Luckow recommended a 
very similar procedure for the estimation of zinc 

Moore (1886] also published new data upon the 
estimation of iron, cobalt, nickel, manganese, etc., full 
notice of which will appear under these metals. 

Brand (1889) succeeded in effecting separations by 
utilizing solutions of the pyrophosphates of different 
metals. 

Smith and Frankel (1S89) made an extended study 
of the double cyanides, and found thereby a number 
of very convenient methods of separation heretofore 
unrecorded. The results of their numerous investiga- 



o,Googlc 



HISTORICAL. 51 

tions in this direction are given in detail in the follow- 
ing pages. 

The most recent publications relating to electrolysis 
are that of Warwick on metallic formates (Z. f. anorg. 
Ch., 1, 285), that of Frankel on the oxidation of metal- 
lic arsenides, Ch, News, 65 , 54, and that of Vortmann 
(Ber., 24, 2749) upon the electro-deposition of metals 
in the form of amalgams, together with a series of 
critical reviews of electrolytic methods by Riidorfrin 
the Zeit.f. angew. Chemie, 1892, 

The preceding paragraphs give a brief outline of 
what has been accomplished in the field of analysis by 
electrolysis; for further information consult the fol- 
lowing : — 

Literature. — Jahrb., 1850,602) Ct.,4S,449; Jr. f. pkt. Ch., 73, 
791 Chem. Soc. Quart. Joum., 13, 12; Jabrb., 1S62, 610; Ann., 134, 
131 ; C. r.. 55, iS i Ann., 146, 375 ; Z. f. a. Ch., 3, 334 ; Ding. p. Jr. 
(iS65],33i; Z. f. a. Ch., 8, 23; 11, 1, 9; 13, 183; Am. Jr. Sc. and 
Ar. (3d >er.),6,l55; Z. f. a. Ch., 15, 297; Ber., 10, 1098; Annilei 
deCh. etde Ph;., 1878; Am. Jr.Sc.and Ar., iC, 200; Am. Phil. Soc. 
Ft., 1878 ; Z. f. a. Ch., 15, 303 ; Am, Ch. Jr., a, 4" i BerE-HUil. Z., 
37,41; 7.. r. a. Ch., 19, 1,314, 3M; Am. Ch. Jr., 1,341; B. s. Ch. 
Parii,34,lS; Ber., 12, 1446; 14,1622,2771; 17,1611,3467,2931; 
tS, 168, 1104, 1787; 19.323; "!> 359. 2892, 2900; Jr. f. pkt. Ch,, 
24, 193; Z. f. a. Ch., 18, 588; 22, 558; »5, 113; Cbem. News, a8, 
5^1; S3<i(>9; Ber,, as, 2492 ; Z. f. ph. Ch., la, 97. Aad the fallow- 
ing will be found worthy of carerul study : Ann., 36, 32 ; 94, i ; Z. f. 
a. Ch., 19, I ; Be^-Hau.Z.,4a, 377; Z. f. a. Cb., ai, 485. 



b, Google 



b, Google 



SPECIAL PART. 



I. DETERMINATION OF THE DIFFER- 
ENT METALS. 

COPPER. 
Literature.— Gibbs, Z. f. a. Ch., 3, 334; Boisbaudran, B. i. 
Ch., Paris, 1867, p, 46S; Merrick, Am. Cb., a, 136; Wrightson, 
Z. f. a. Ch., IS, 399 ; Herpin, Z, f. a, Cb., 15, 335 ; Maniteui Scien- 
lifique [3 aer.], 5, 41; Oh1,Z. f. a. Cb., 18, 523; Classen, Ber., 14, 
t63Z, 1627; Clasien and v. Reiss, Z. f. a. Cli., 34, 346; 35, 113; 
Kicbi.Z. f. a. Ch., 11, 116; Makintosh, Am. Ch. Jr., 3,354; 
RQdorff, Ber., zi, 3050; Z. f. ang. Ch., 1S92, p. 5; Luckow.Z. f. 
a.. Ch., 8, 23; Warwick, Z. f. anorg. Ch., 1,385; Smith, Am. 
Ch. Jr., 12,339; Croasdale, Jr. An. Ch., 5, 133. 

Dissolve 19.6 grams of pure copper sulphate in 
water, and dilute to i litre. Place soccof this solu- 
tion {= 0,25 gram of metallic copper) in a c/ean plati- 
num dish, previously weighed. Connect the dish with 
a battery, whose current is sufficiently strong to effect 
the complete precipitation of the copper in the course 
of ten or twelve hours. The apparatus may be 
arranged as in the accompanying sketch (Fig. 18), 
page 54. 

A is an ordinary filter stand, upon the base of which 
53 

D,nitiz.!.o,GoOglc 



ELECTRO-CHEMICAL ANALYSIS, 



b, Google 



DETERMINATION OF METALS — COPPER. 55 

is fixed a binding-post, :r, to which is attached a heavy 
copper ring for the support of the platinum vessel. It 
is in connection with the negative electrode of the bat- 
tery. The arm, y, has been shortened, and at its 
extremity there is a second binding-screw, // the lat- 
ter holds the positive pole (a heavy platinum wire 
bent into a flat spiral at its lower end), and the copper 
wire from the anode of the battery (the copper plate 
in a " Crowfoot " cell). It will be noticed that the 
current passes through the vessel, B (a Bunsen volta- 
meter), in which acidulated water is undergoing de- 
composition, the resulting gases being collected in d. 
Their volume serves to measure the strength of the 
acting current. Copper is very readily precipitated 
from solutions containing free nitric or sulphuric acid. 
Hydrochloric acid should never be present 

A platinum dish of go mm. diameter and 20 mm, 
depth may be substituted for the spiral anode. Open- 
ings are made in the dish to facilitate circulation and 
accelerate the precipitation of the metal. 

Having arranged the apparatus as just described, 
add 9-10 drops of concentrated nitric acid to the solu- 
tion of the electrolyte ; cover the vessel with a perfo- 
rated watch crystal during the decomposition. To 
ascertain when the metal has been completely precipi- 
tated, add water to the dish ; this will expose a clean, 
platinum surface, and if in the course of half an hour 
no copper appears upon it, the deposition may be con- 
sidered as finished. Or a drop of the liquid may be 

D,nitiz.!.o,GoOglc 



56 ELECTRO-CHEUICAL ANALYSIS. 

removed and brought in contact with a drop of 
ammonium hydroxide or hydrogen sulphide, when, if 
a blue coloration or black precipitate is not produced, 
the deposition can be considered ended. 

Fig. 19. 



As the precipitation has been made in an acid solu- 
tion, the current should not be interrupted until the 
acid liquid has been removed, for in many cases the 
brief period during which the acid can act upon the 

D,nitiz.!.o,GoOglc 



DETERMINATION OF HETALS COPPER. J/ 

metal will be sufficient to cause some of the latter to 
pass into solution. To obviate this, siphon oUT the 
acid liquid. The sketch (Fig. 19) shows how this can 
be done. A rubber tube of small diameter may be 
substituted for the glass siphon. As the acidulated 
water is conveyed away by the latter, pour distilled 
water into the dish. Empty the platinum dish twice 
in this way; the current can then be interrupted with- 
out loss of copper. Finally, disconnect the dish, wash 
the deposit with hot water and then with alcohol. Dry 
the precipitated copper at a temperature not exceed- 
ing 100° C; an air-bath, an asbestos plate, or warm 
iron plate will answer for this purpose. Do not weigh 
the dish until it is perfectly cold, and has attained the 
temperature of 'the balance-room. 

Rudorff suggests the addition of ten drops of a 
saturated sodium acetate solution to the acid liquid 
from which the copper has been precipitated before 
interrupting the current. The acetic acid, which is 
liberated, will not immediately attack the copper, which 
can be at once washed and treated as just described. 

In the ordinary precipitations of copper from dilute 
nitric or sulphuric acid solution a current, giving 
0.3-0.5 c.c. oxy-hydrogen gas (electrolytic gas) per 
minute, will be amply sufficient. The deposition can 
also be made in a platinum crucible, or the copper can 
be precipitated upon the exterior surface of the same. 
This is sometimes convenient. Place the liquid under- 
going electrolysis in a beaker glass (capacity 100-250 

E 

D,nitiz.!.o,GoOglc 



58 ELECTRO-CHBHICAL ANALYSIS. 

ex.), and suspend the crucible in it (Fig. 20), support- 
ing it there by a tight-fitting cork, through which 
passes a stout copper wire, w, in connection with the 
negative electrode of a battery. The positive electrode 
is a platinum plate projecting into the liquid. The end 
of the decomposition may be learned by pressing down 




upon w, or by adding water to the solution in the 
beaker. No further appearance of copper on the ntfwly 
exposed platinum indicates the end of the precipita- 
tion. Raise the crucible from the liquid, wash the 
copper with water, then detach the vessel carefully 
from the cork, and dry as already directed. 
If the current be permitted to act too long in the 



o,Googlc 



DETERMINATION OF U ETA LS— COPPER. 59 

presence of sulphurif acid copper sulphide may be 
produced. (Miller and Kiliani, Lehrbuch d. analyt. 
Chemie.) 

Instead of using either of the suggestions first 
offered, substitute the apparatus of Riche (Fig. 21) if 
convenient. This consists in suspending a crucible 
within a crucible. The sides of the inner vessel are 
perforated so that the liquid will maintain uniform 
concentration. It is practically the same as the device 
just described above. 

Copper can also be precipitated from the solution of 
ammonium-copper oxalate. To this end the copper 
solution (sulphate or chloride) is treated with an ex- 
cess of a saturated solution of ammonium oxalate. 
The current acting upon this solution should liberate 
from 3-4 c.c. of electrolytic gas per minute. As the 
metal begins to separate, and the original deep blue 
color of the liquid disappears, add 20-30 c.c. of a cold 
saturated solution of oxalic acid. When the decom- 
position is finished decant the solution, and wash the 
deposit of copper repeatedly with water and then with 
alcohol. Dry as previously directed. 

If the double oxalate solution be heated to 40-50° 
and held at that temperature it will be possible to pre- 
cipitate as much as two grams of copper in from three 
to four hours. Use ferrocyanide of potassium to learn 
whether all the metal has been precipitated. Wash 
and dry as already instructed. 

Copper can also be determined quite accurately in 

D,nitiz.!.o,GoOglc 



6o 



ELECTRO-CHEMICAL ANALYSIS. 



solutions of the phosphate in the presence of free 
phosphoric acid, or in a formate solution containing 
free formic acid. 

Rudorff obtained excellent results with the follow- 
ing conditions : 0.1-0.3 gram of metallic copper in loo 
c.c. water, to which were added 2—3 grams of potas- 




sium or ammonium nitrate and 20 c.c. of a 
hydroxide (0.91 sp. gr.). A current giving 0.5 c.c. 
oxy-hydrogen gas per minute will throw out the cop- 
per from this solution. It is claimed that by observ- 
ing the preceding conditions copper can be fully pre- 
cipitated in the presence of chlorides. An excess of 



o,Googlc 



DETERMINATION OF METALS — CADMIUM. 6l 

acetic acid should be added to the solution before the 
current is interrupted, 

Moore advises dissolving the recently precipitated 
copper sulphide, obtained in the ordinary course of 
analysis, in potassium cyanide ; and, after the addition 
of an excess of ammonium carbonate, electrolyses the 
warm (70°) solution. 

In the analysis of commercial copper Luckow em- 
ployed the apparatus pictured in Fig. 22. The beaker 
(a) contains the electrolyte, and the metal is precipi- 
tated upon the cylinder of platinum (i). It is a very 
satisfactory device for almost any kind of electrolytic 
work. 

Foote (Am. Ch, Jr., 6, 333) has described a very 
excellent improvement in the apparatus intended for 
the electrolytic precipitation of copper. Consult also 
G. H. Meeker, Jr. An. Ch., 6, 267. 



CADMIUM. 
LiTERATUKK.— Ber., It, 204S; Smith, Am. PhiL Soc. Pr., 1S78; 
Clarke, Z. f. a. Ch., tS, 104; Beil stein and Jawein, Ber., la, 
7591 Smith, Am. Ch. Jr., a, 43; Luckow, Z. f. 1. Ch., ig, 16; 
Wiighlson, Z. f. a Ch., 15,303; Classen and v. Reiss, Ber., 
14,1628; Warwick, Z.f.aDorg.Ch., 1,158; Sm ith. Am. Ch. Jr., 
13,329: Vortmaan, Ber., 14 2749; Rfldorff, 2. f. ang. Ch., 
Jab^. 1893. 

Cadmium can be determined electrolytically as 
readily as copper. Prepare a solution of the chloride 
or sulphate of definite strength. Remove 50 c.c. to a 



o,Googlc 



62 ELECTRO-CHEHICAL ANAU'SIS. 

suitable, weighed platinum vessel. Add one gram of 
pure potassium cyanide ; dilute with water to 150-200 
C.C., and then connect with five or six " Crowfoot " 
cells in the same manner as directed under copper. 
Introduce the voltameter as there indicated. It is well 
to commence the decomposition in the evening, and 
by morning the metal will be fully deposited. A 
current yielding 0.3 c.c. electrolytic gas per minute 
will precipitate 0.2 gram metal in this time. To ascer- 
tain whether the precipitation is complete, raise the 
level of the liquid in the platinum dish. In washing, 
it will not be necessary to siphon off the supernatant 
liquid ; it can be poured off, after interruption of the 
current, without loss of metal from re-solution. Wash 
the deposit with cold and hot water. Dry upon a 
warm iron plate (temperature not exceeding 100° C), 

This metal can be deposited from the solution of 
its phosphate in phosphoric acid. The conditions that 
follow gave very satisfactory results; a current liber- 
ating 0.6 c.c. of electrolytic gas per minute acted upon 
0.1 827 gram cadmium, as sulphate, an excess of sodium 
phosphate (1.0358 sp. gr.), and i ^ c.c. of phosphoric 
acid (sp. gr. 1.347). The total dilution equaled 100 
c.c. The precipitated cadmium weighed 0.1820 gram. 
Increase the strength of the current for the last hour 
of the decomposition, and wash the deposit before 
breaking the current. 

Cadmium may also be precipitated from a solution 
of its sulphate containing a small amount of free sul- 

D,nitiz.!.o,GoOglc 



DETERMINATION OF METALS — CADMIUM. 63 

phuric acid (2 c.c. HjSOj, sp, gr. 1,09 for 0.1 gram 
cadmium). When operating with a solution of this 
character, use a current generating ; c.c. electrolytic 
gas per minute. Two Bunsen cells will answer, 
although it may be necessary to reduce the current to 
some degree : this can be accomplished by introduc- 
ing one of the resistances described on pages 32 and 
33. Arrange the apparatus as under copper. The 
precipitation takes place at the ordinary temperature. 

Cadmium can also be deposited quite readily, and 
in a crystalline form, from its acetate solution. In 
this case the liquid, containing an excess of free acetic 
acid, is heated to 50-60° during the decomposition. 
The apparatus can be arranged as in Fig. 23. The 
platinum dish is placed in a water bath, and the current 
made to pass through R (resistance frame) and V 
(voltameter). An asbestos plate may be substituted 
for the water bath. The current should give i J^— 2 
c.c. of oxy-hydrogen gas per minute. This will insure 
the precipitation of 0.12-0.15 gram of cadmium in 
five to six hours. When the precipitation is completed, 
detach the dish, wash the deposited metal first with 
warm water, then with absolute alcohol, and finally 
with ether. Dry upon a moderately warm plate. 

If desired, the metal can also be precipitated from 
the solution of the double oxalate of ammonium and 
cadmium (see Copper), or from a formate solution 
in the presence of free formic acid. 

Vortmann has determined several metals quite sat- 

D,nitiz.!.o,GoOglc 



64 elex;tro-chehical analysis. 

isfactorily in the form of amalgams. In applying his 
recommendation to cadmium, add to the solution 
of its salt a solution of mercuric chloride and 
5 grams of ammonium oxalate. Effect the solu- 
tion of the latter salt without the aid of heat. The 



FIG. 33. 




current employed for the precipitation should at 
the very beginning of the decomposition liberate 
from 6-8 c.c. of electrolytic gas per minute. When 
the amalgam of mercury and cadmium commences 
to separate reduce the current to 3 c.c. per min- 



o,Googlc 



DETERMINATION OF METALS — MERCURY. 65 

ute, but gradually increase it until at the end of 
the decomposition it has its initial strength. If the 
quantity of cadmium exceeds 0.3 gram, let the solu- 
tion undergoing electrolysis be ammoniacal. To this 
end add tartaric acid (3 grams) and an excess of am- 
monia to the liquid containing the mercury and the 
cadmium. Dilute to 200 c.c. with water. The cur- 
rent is allowed to act until a portion of the liquid 
remains clear when tested with ammonium sulphide. 
In the usual course of gravimetric analysis cad- 
mium is obtained as sulphide. To prepare it for elec- 
trolysis dissolve the same in nitric acid, and after 
expelling the excess of the latter, add a small amount 
of potassium hydroxide (sufficient to precipitate the 
cadmium), and follow this with an excess of potassium 
cyanide (i to 2 grams). Proceed further as already 
directed. 

MERCURY. 
Literature.— Ber„ 6, 270 ; Clarke, Am. Jr. Sc. and Ar., 16. 200; 
Classen and Lud wig, B«., 19, 323; H oskinion, Am. Ch. Jr., 
8, zog; Smith and Kneir, ibid.; Smith and Frankel, Am. 
Cb. Jr., 11,264 ; Smilb, Jr. An. Ch,, s, zozi VoTtmsnii, Ber., 34, 
3749; Brandt, Z. f. an. Ch., 1891, p. 201; RUdorff, Z. f. ang. 
Ch., 189Z, p. 5 ; F[aDkel,Jr. Fr. In., 1891. 

In preparing solutions for experimental purposes, 
use either mercuric nitrate or chloride. A current 
equivalent to 0.5-1.0 c.c. electrolytic gas per minute 
will precipitate 0.3 gram of mercury from such solu- 

D,nitiz.!.o,GoOglc 



66 ELECTRO-CHEMICAL ANALYSIS. 

tions(add a slight amount of free nitric acid) in twelve 
hours. The deposit will be drop-like in appearance. 
Even in the presence of considerable free nitric acid 
it has been found that a current of 4 c.c. electrolytic 
gas per minute will suffice to precipitate as much as 
0.10 gram of metal in 30 to 45 minutes. In such cases 
the acid liquid must be removed before the interrup- 
tion of the current occurs, or sodium acetate should 
be added ; then the liquid can be decanted without the 
possibility of loss from resolution of the mercury 
(Rudorff). 

A mercuric chloride solution, feebly acidulated 
with sulphuric acid, gradually yields its metal to a 
current, giving 5-6 c.c. oxy-hydrogen gas per minute. 
Always wash the deposited metal with cold water. 
Rudorff adds the following substances to the liquid 
containing the mercury salt: 0.5 gram tartaric acid, 
and 10 c.c. of ammonium hydroxide (sp, gr,, 0.91), or 
S c.c. of nitric acid, loc.c. of a saturated solution of 
sodium pyrophosphate, and 10 c.c. of ammonium 
hydroxide. A current liberating 2 c.c. of electrolytic 
gas per minute will precipitate the mercury in a 
compact, adherent form. 

From experiments made inthislaboratorythe writer 
prefers and would especially recommend solutions of 
the double cyanide of mercury and potassium for the 
electrolytic deposition of mercury. A current of 0,2 
c.c. electrolytic gas per minute will precipitate from 
0.10-0.20 gram of metal in twelve hours. The pre- 

D,nitiz.!.o,GoOglc 



DETERHINATION OF HETALS — HBRCURV. 6/ 

cipitation may be considerably accelerated by heating 
the solution to 65-70" C. As much as 0.25 gram of 
metal can be deposited in three hours. This pro- 
cedure requires no further attention after it is once 
set in operation. The deposit is always compact, 
and gray in color. Use water only in washing it, 
for alcohol seems to detach some of the metallic 
film. The quantity of alkaline cyanide present may 
vary from 0.26-2.6 grams (KCN) for every gram of 
mercury. 

In general analysis mercury is frequently obtained 
as sulphide. Its determination in this form requires 
time and exceeding care. It is, however, soluble in 
the fixed alkaline sulphides containing free alkali. 
The writer has discovered that such a solution can be 
electrolysed without difficulty ; the mercury is depos- 
ited from it in a very compact form. An actual 
analysis conducted in this laboratory will best present 
the proper conditions for a successful determination : 
20 c.c. of a sodium sulphide solution (sp. gr., 1.19) 
were added to a mercuric chloride solution (^0.1903 
gram of mercury), and the whole then diluted to 150 
c.c. with water. The current acting upon this mixture 
liberated l c.c. of electrolytic gas per minute. In 
twelvehourso.i902gramof mercury was precipitated. 
It was further treated as advised in the preceding para- 
graphs. It is best to use a platinum dish as the 
negative electrode and a platinum spiral (p. 54) for the 
anode. Dry the deposit on a moderately warm plate, 

D,nitiz.!.o,GoOglc 



68 ELECTRO-CHEMICAL ANALYSIS. 

or over sulphuric acid. " Crowfoot " cells are well 
adapted for decompositions of this kind. 



BISMUTH. 
LiTBKATuaa. — Luckow, Z. f. ■. Ch.,ig.i6; CI nssen and v.Reiss, 
Bef., 14, 1622; Thom> sand Smilh, Am. Ch. Jr., 5, 114; Moore, 
Ch. Newi, 53, Z091 Smith and Knetr, Am. Ch. Jr., 8, zo6 ; 
Schucbt.Z. f. a. Ch., 31,492; Eliasberg, Ber., 19,326; Brand, 
Z. f. a. Ch., a8, 596 ; Vorimann, Ber., 14, 2749; Riidorff, Z. f. 
tug. Ch., 1S93, 199; Smith and Sallar, Z. f. anorg. Ch,, 3, 418; 
SmithandMoyer, Jr. Am. Ch.S., 15. 28; iiii/., 1$, 101. 

Prepare a solution of definite value as directed 
under the preceding metals. To a portion of it add 
an excess of a cold ammonium oxalate solution, and 
act upon the mixture with a current of 0.10 c.c. oxy- 
hydrogen gas per minute. Those who have employed 
this method find that the deposit is not very adherent, 
and great care must be taken to expose as large a pla- 
tinum surface as possible. If inetallic particles do 
separate, collect them upon a small filter and weigh 
alone. 

Eliasberg advises bringing the solution of the metal 
into a weighed platinum dish, and then adding lo c.c, 
of a potassium oxalate solution ( 1 : 3). Heat is applied, 
and solid ammonium oxalate is introduced until com- 
plete solution ensues. Dilute to 170-180 c.c, and 
warm to 70-80^ C, while the current acts. The latter 
should be so feeble that the liberation of gas in the 



o,Googlc 



DETERMINATION OF UETALS — BISMUTH. 69 

voltameter is scarcely perceptible. In sixteen hours 
the greater portion of the metal will have separated, 
and then oxalic acid is added to distinct acid reaction. 
As soon as the metal is fully precipitated, interrupt 
the current and wash the deposit with water. Take 
special pains in drying, so that the metal does not 
oxidize. 

Experiments made in this laboratory demonstrate 
that by electrolysing the sulphate, an alkaline citrate 
solution, or one containing free citric acid, the bis- 
muth will be rapidly-and completely precipitated. In 
some cases the deposits were made in small platinum 
crucibles, while others were thrown upon the exterior 
surface of the crucibles arranged as under Copper. If 
peroxide should separate upon the anode in the electro- 
lysis of citrate or sulphate solutions of bismuth, it will 
disappear before the decomposition is fully ended. 
Heat is not required. The best results were obtained 
with solutions of the sulphate, containing free sul- 
phuric acid. For example: 0.1542 gram of bismuth, 
as sulphate, 3 c.c. sulphuric acid (1.09 sp. gr.), and 150 
c.c. of water, required a current giving 3 c.c. oxy- 
hydrogen gas per minute, for a period of three hours, 
to effect the complete separation of the metal. The 
latter was quite compact and offered no difficulty in 
washing with water and alcohol. An air-bath was 
used for drying purposes. 

Moore recommends the following method : Add 
sufficient tartaric acid to the bismuth solution to 

D,nitiz.!.o,GoOglc 



70 ELECTRO-CHEUICAL ANALYSIS. 

prevent the precipitation of a basic salt, then, after 
rendering the solution slightly alkaline with ammo- 
nium hydroxide, add a considerable excess of glacial 
phosphoric acid, so that the solution has a strong acid 
reaction. The current should give 0.33-0.50 c.c. 
electrolytic gas per minute at first, but this must be 
increased at last to 7.5 c.c. per minute. The deposit 
at the beginning of the deposition is loose, but 
gradually becomes hard and compact. 

Brand's recommendation consists in adding to a 
somewhat dilute acid solution of bismuth from four 
to five times as much sodium pyrophosphate as will 
be necessary to form the double salt. Ammonium 
carbonate is then carefully introduced until the re- 
action of the liquid is distinctly alkaline, when 3-5 
grams of ammonium oxalate are added. The total 
dilution should be about 200 c.c. The electrolysis is 
commenced with a current giving o.i-i.O c.c. electro- 
lytic gas per minute, although toward the close it will 
be necessary to increase the same to 2-3 c.c. per min- 
ute. By following these instructions 0.2500 gram of 
bismuth can be precipitated in twelve hours. When 
considerable quantity of metal is present in solution a 
feeble current should be used at first. If the peroxide 
appears upon the anode in the course of tlie decompo- 
sition, redissolve it in a few drops of a concentrated 
solution of oxalic acid. However, this should not be 
done until there is no further separation of metal upon 
the cathode. The final reduction is ascertained by 

D,nitiz.!.o,GoOglc 



DETERMINATION OF METALS — BISMUTH. 7I 

testing with hydrogen sulphide. The metal is said 
to sustain a superficial oxidation, hence it is converted 
into oxide and weighed as such. 

In the presence of 5 c.c. of nitric acid (sp. gr. i.i), 
bismuth can be fully precipitated by a current liber- 
ating 1 c.c. of electrolytic gas per minute. The de- 
posit was found to be very adherent. It was washed 
with water and with alcohol. 

Vortmann determines this metal in the following 
manner : The compound containing the bismuth is 
brought into solution with hydrochloric acid. A 
weighed amount of mercuric chloride, dissolved in 
the same acid, is added, and then about 50 c. c. of 
alcohol (96 per cent.). Water is gradually added 
until the surface of the liquid is i cm. below the edge 
of the dish. The current strength required for the 
deposition of cadmium as metal will be sufficient in 
this case. The method is said to be especially well 
adapted for the separation of large quantities of bis- 
muth. 

Rudorff, experiencing difficulties with the various 
methods that have been proposed, advises the follow- 
ing course: presuming the presence of a quantity of 
bismuth not exceeding o.i gram in a solution con- 
taining very little nitric acid, add sufficient sodium 
pyrophosphate to precipitate, and redissolve the pre- 
cipitate which is produced. Next add 20 c.c. of a 
saturated potassium oxalate solution, 20 c.c. of potas- 
sium sulphate, and sufficient water to increase the 

Dinitizedo, Google 



72 ELECTRO-CHEMICAL ANALYSIS. 

volume of liquid to 120" c. c. Apply a very feeble 
current for the decomposition. The precipitation will 
be complete in twenty hours. 



LEAD. 
Literature.— Lnckow.Z. r. a. Cb., ig, 215; Richi, Ann. de 
Chim. etdePhys. [5 kt.], 13,508; Z. f . ». Ch., ai, 117; Classen, 
ai/.,z57; Hampe, Z. f. a. Ch., 13, 183; May, Am. Jr. Sc. and 
Ar. [3ser,], 6, 255. also Z. f. aCh., 14, 347; Parodiand Maaeai- 
iini, Ber„io, 1098; Z. f. a. Ch., 16, 469 ; 18, s88; Rich*, Z. f. a. 
Ch., 17,219; SchuchE, Z. f, a. Ch., 11, 488; Tenny, Am. Ch. 
J'., S, 413; Smith, Am. Phil. Soc. Pr.,34,4zS; Vortwana, Ber., 
34, ?749i Rfldorff, Z. r. ang. Ch., 1892, p.198; Warwick.Z. f. 
boot:. Ch., I, 258; Classen, Ber., 27, 163; Kreichgaaer, Ber., 
"7. 3"5. 

The metal may be obtained by electrolysing so- 
lutions of the double oxalate (.^ff Copper and Cadmium), 
the acetate, the oxide in sodium hydroxide, or the 
phosphate dissolved in the latter reagent, A current 
of 0.1-0.2 c.c. electrolytic gas per minute is sufiRcient 
for this purpose. While the metal separates well from 
either one of these solutions, difficulty is experienced 
in drying the deposit, for the moist metal almost in> 
variably suffers a partial oxidation, thus rendering the 
results high. The deposit can be dried, without oxid- 
ation, in an atmosphere of hydrogen, but for the in- 
experienced operator this procedure offers little satis- 
faction. It is, therefore, better to utilize the tendency 
of lead to separate, from acid solutions, as the dioxide. 



o,Googlc 



DETERMINATION OF METALS — LEAD. 73 

For trial purposes make up a definite volume of lead 
nitrate. Electrolyse several portions (= o. i gram lead 
each) in a platinum dish connected with the anode of a 
battery, giving o. 1-0.2 c.c. electrolytic gas per minute. 
In order that the lead may be precipitated wholly 
as dioxide upon the positive electrode and none in 
metallic form upon the cathode, it is necessary that 
the solution being analyzed should contain from ten 
to twenty per cent, of free nitric acid. This quantity 
of acid is required when lead alone is present in so- 
lution. In the presence of other metals the complete 
deposition of the lead as dioxide occurs with even 
less acid (eight per cent.). At the end of the precipi- 
tation siphon off the acid liquid and wash in the dish, 
then dry the deposit at 1 10" C, and weigh. Reference 
to the literature shows that May preferred, after dry- 
ing the deposit, to carefully ignite it and finally weigh 
as lead oxide (PbO). This deportment of lead affords 
an excellent method by which to separate it from 
other metals, ^,;f., mercury, copper, cadmium, silver, 
and all those soluble in nitric acid, or those which, in 
a nitric acid solution, are deposited upon the electro- 
negative pole of a battery. 

Riidorff, assuming that the metal exists as nitrate 
and that its quantity does not exceed 0.1 gram, 
recommends that an addition of 2-3 c.c. of nitric acid, 
and I C.C. of a copper nitrate solution (100 c.c. con- 
taining 1 gr. of copper) be made to the lead salt. 
Water is then added until the total dilution equals 
F 

DinitizetiovGoOglc 



74 BLGCTRO-CHEHICAL ANALYSIS. 

I20 c.c. A current from four " Crowfoot " cells will 
be all-sufficient for the deposition of the lead as diox- 
ide in a very adherent form. The copper will not be 
entirely precipitated. The decomposition requires a 
period of twelve hours. 

Classen claims that, if the inner surface of the plati- 
num dish used as anode in the deposition of lead 
dioxide be roughened by having a sand blast pro- 
jected against it, the deposition of the dioxide can 
be much accelerated, e. g., a few hours (4-5) will 
be sufficient for the precipitation of as much as 
4 grams of dioxide upon 100 cm' surface with a 
current of i.J ampere. Wash with water and alcohol, 
then dry at 180-190°. 

The suggestion made by Vortmann that lead should 
be precipitated as an amalgam is not feasible, owing 
to certain difficulties. His method, however, will serve 
for the separation of the lead from a few metals. 



SILVER. 
Literature,— Luckow, Dbg. p. Jr., 178, 43, Z, f. a. Cb., ig, 

15; Freseniusand Bergmann, Z.f. B, Ch., 19,324; Krutnig, 
Ber, 15, 1267; Schucht, Z. r. a. C)i.,2a, 417; Kionicult, Am. 
Ch. Jr., 4. 12; R ad ot f f, Z. f. ang. Cb., Jahrg. 1892, p. J. 

The experiments of Luckow showed that this metal 
could be deposited from solutions containing as high 
as eight to ten per cent, of free nitric acid. The 
deposit was spongy, and there was a simultaneous 



o,Googlc 



DETERMINATION OF METALS SILVER. 75 

deposition of silver peroxide at the anode. This was, 
however, prevented by adding to the solution some 
glycerol, lactic or tartaric acid. A voluminous mass 
was also obtained from silver solutions, containing 
an excess of ammonium hydroxide or carbonate, 
and peroxide appeared at the same time upon the 
anode. 

Fresenius and Bergmann, who have given the elec- 
trolysis of acid solutions of silver particular study, 
observed that the tendency of the metal to sponginess 
is most marked when the electrolyte is concentrated 
and acted upon by a strong current. In a dilute 
liquid, the current being feeble, the deposit was com- 
pact and metallic in appearance (free acid should be 
present). From neutral solutions, although very 
dilute, the metal is separated in a flocculent condition 
by the feeblest currents. Therefore, to obtain results 
that would answer for quantitative analysis, the fol- 
lowing conditions were adopted: The total dilution 
of the solution was 200 c.c. ; in this theie was 0.03 , 
gram^04 gram silver, and 3-6 grams of free nitric 
acid. The poles were separated about 1 cm, from 
each other, while the current gave 100-150 c.c. elec- 
trolytic gas per hour. 

In the experiments of Fresenius and Bergmann 
apparatus similar to that in Fig. 24 was employed. 
It has some decided advantages. Both spiral (fi)and 
cone {b) are constructed of platinum. The metallic 
deposition, it will be understood, occurs upon the 

D,nitiz.!.o,GoOglc 



76 ELECTRO-CHEMICAL ANALYSIS. 

cone, the sides of which are perforated, so that a uni- 
form concentration of liquid is preserved throughout 
the decomposition. When liquid electrolytes contain 
much iron, it is essential that the oxygen liberated 
within the cone should be equally distributed over its 
outer surface. This is made possible through open- 
ings. The shape of the cone also prevents loss from 




the bursting of the bubbles arising from the platinum 
spiral in connection with the anode. 

Krutwig advises adding a large excess of ammo- 
nium sulphate to the silver solution, previously made 
alkaline with ammonium hydroxide, and employs a 
current giving 150 c.c. electrolytic gas per hour, but 
after half an hour the latter is increased to 300 c.c. of 



DinitizetiovGoOglc 



DETERMINATION OF METALS — SILVER. T} 

gas per hour. In this way, 0.1 gram of silver is 
precipitated in two hours. 

The writer's experience has chiefly been with solu- 
tions of silver containing an excess of alkaline cyanide 
(i gram KCN for 0.2-0.3 gram silver). With these 
peroxide separation does not occur, and a very weak 
current will precipitate 0.15-0.20 gram metal in ten 
hours from a cold solution. If the liquid be heated 
to 65° C, during the decomposition as much as 0.2-0.3 
gram of metal may be precipitated in three and one- 
half hours. The current density for this precipitation 
should be N.Dko = 0.07 ampere. The precipitation 
can be made either in a platinum dish or crucible as 
cathode. 

Riidorff met with little success when using the 
Krutwig method, but obtained very satisfactory re- 
sults with the cyanide method. 

Chlorine, bromine, and iodine can be indirectly 
estimated electrolytically by first precipitating them 
as silver salts, then dissolving the latter inj)otassium 
cyanide, and exposing the resulting solution to the 
action of a current from three to four "Crowfoot" 
cells. 

Luckow reduced silver chloride by placing it in a 
platinum dish, serving as the negative electrode, cov- 
ered it with dilute sulphuric or acetic acid, and allowed 
the positive electrode to project into the solution. 
Four Meidinger cells were strong enough to reduce 
0.1 gram silver chloride in ten minutes. The deposit, 

D,nitiz.!.o,GoOglc 



78 ELECTRO-CHEHICAL ANALVStS. 

while spongy, was adherent It was washed with 
water and then thoroughly dried to insure the absence 
of any acid, (See the reference to Kinnicutt's experi- 
ments; also, Prescott and Dunn, Jr. An. Ch., 3, 373.) 



ZINC. 

Literature.— Wrigbtson, Z. t. *. Ch., 15, 3031 Parodi and 
Mascaiiini.Ber., 10, io98,Z.f ..Ch,, 18, 587; Rieh*,Z.f.«.Ch., 
17, Il6; BeiUlein ■ndj* wEiu, Ber., I9, 446,2. f. «. Ch., l8, 588; 
Rich«, Z. f.a.Cb., 21, 119; Rcinhatdt >ad Ihle, Jr.f.pkt.Ch., 
[N. F.],a4, 1931 Classen *iidv. Reiss, Ber., 14, i6zzi Gibbs, 
Z.r.B.Ch., 33,558; Luckow, Z. f. a. Ch., 15, iij; Brand, Z.f. 
a. Ch., 38, 581; Warwick, Z.ranorg.Cb., 1,258; Vortmann, 
Ber., 34, 2753 ; RUdorff, Z. £ ang. Cb., Jah^ I8ga, p. 197 ; Vort- 
mann, M. f. Ch., 14, 536. 

Much has been written upon the electrolytic esti- 
mation of zinc. The personal experience of the writer 
inclines him to give preference to the method sug- 
gested by Parodi and Mascazzini. They recommended 
that the metal be present in solution as sulphate; its 
quantity may vary from 0.1-0.25 gram. To it add 4c.c. 
of a solution of ammonium acetate, 20 c.c. citric acid, 
and dilute to 200 c.c. with water. The electrodes are 
then introduced into the liquid, their distance apart 
being not more than a few millimetres. The precipi- 
tation can be made in a beaker glass, using a weighed 
platinum cone (Fig. 24) as the cathode. The current 
for this purpose should give 250-300 c.c. electrolytic 
gas per hour. When the precipitation of metal has 



0, Google 



DETERMINATION OF UETALS — ZINC. 79 

ended, which may be ascertained by removing a small 
quantity of the liquid with a capillary tube and bring- 
ing it in contact with a drop of a solution of potassium 
ferrocyanide, remove the bulk of the liquid with a 
siphon. Wash the deposit with water and alcohol. 
There is no danger of oxidation during the drying 
process. It will be discovered on dissolving the pre- 
cipitated zinc that the platinum is covered with a black 
powdery layer, insoluble even in hot hydrochloric or 
hot nitric acid. This is platinum black (Vortmann, 
Riidorff). It is exceedingly difficult to remove, and 
to prevent its occurrence it is best to coat the pla- 
tinum dish with a thin layer of copper before precipi- 
tating the zinc (p. 82). 

Beilstein and Jawein add sodium hydroxide to the 
solutions of zinc nitrate or sulphate, until a precipitate 
is produced, and 'dissolve it in potassium cyanide. 
The decomposition is carried out in a rather large 
beaker glass, the cathode being either the platinum 
cone already described (p. 76), or a rather large plati- 
num crucible suspended from acork(p. 58), perforated 
by a copper wire, touching the inner surface of the 
crucible. Four Bunsen cells (usual size) are sufficient 
for the precipitation. Wash the deposit as instructed 
above. 

Reinhardt and Ihle have objected to nearly all the 
methods which have been proposed for the electrolytic 
estimation of zinc. They say of the Beilstein and 
Jawein method .... that the results are fairly good, 

D,nitiz.!.o,GoOglc 



80 ELECTRO-CHEMICAL ANALYSIS. 

.... but a strong current is necessary, otherwise the 

precipitation of the zinc is slow and incomplete 

the positive pole diminishes in weight very appreciably, 
.... finally, working with potassium cyanide is very 
unpleasant. The writer's experience has proved that 
a current considerably less than that which Beilstein 
and Jawein first recommended will throw out all the 
zinc in the course of a night, and further that the 
anode is not appreciably affected. The method sug- 
gested by Reinhardt and Ihle is, however, very excel- 
lent and deserves trial by all interested in the electro- 
lytic estimation of zinc. Its essential features, taken 
from their publication, are these: Mix the solution of 
zinc sulphate or chloride, neutral as possible, with an 
excess of neutral potassium oxalate, until the precipi- 
tate, which appears at first, redissolves. A current 
giving 90 c.c, electrolytic gas per hour will answer 
for complete precipitation. 

The immediate decomposition of the zinc oxalate 
is into zinc and carbon dioxide (two molecules), and 
the potassium oxalate into carbon dioxide (two mole- 
cules) and potassium ; the latter then reacts with the 
water, so that while an abundant liberation of hydro- 
gen occurs at the cathode, the alkali simultaneously 
set free is converted into acid potassium carbonate by 
the carbon dioxide at the anode: — 

ZiiC,0, -f K,C,0, = (Zn + 2K0H + H.) + 400^ 
2KOH -I- 2CO, = aCO^Q^. 

D,nitiz.!.o,GoOglc 



DETERMINATION OF METALS — ZINC, 8 1 

Therefore, just as long as zinc oxalate is being 
decomposed, considerable evolution of gas is notice- 
able at the positive electrode, and when this dimin- 
ishes, and occasional bubbles escape, the decomposi- 
tion is complete, and the deposition of metal may be 
considered finished. 

Free oxalic acid, or any other acid, is not injurious 
if there is a sufficient quanityof potassium oxalate 
present. Nitric acid, however, free, or combined, 
should be avoided; it gives rise to ammonium salts, 
which prevent the zinc from separating in a dense form. 
The acid potassium carbonate produced during the 
decomposition offers great resistance to the current; 
it is, therefore, advisable to add potassium sulphate to 
the solution to increase its conductivity. Reinhardt 
and Ihle recommend the following solutions for use 
in decompositions like that just described : i66 grams 
of potassium oxalate in i litre of water; 250 grams 
of potassium sulphate in i litre of water, and a solu- 
tion of oxalic acid saturated at 15° C. 

Experiments. — (i) 40 c.c. of a solution of zinc sul- 
phate (^ O.1812 gram metallic zinc), to which were 
added 50 c.c. of potassium oxalate and loo c.c. of 
potassium sulphate, were electrolysed with a current 
giving 109 c.c. of electrolytic gas per hour. After 
five hours the current was interrupted. The precipi- 
tated zinc weighed 0.1814 gram. (2) 2.1867 grams 
brass (containing tin, copper, lead, and zinc) were dis- 
solved in nitric acid and the tin determined in the 

■ D,nitiz.!.o,GoOglc 



02 ELECTRO-CHEUICAL ANALYSIS. 

usual gravimetric way. Its quantity was found to be 
0.04 per cent. In the filtrate, containing nitric acid, 
lead and copper were determined simultaneously by 
electrolysis (the copper separated upon the cathode 
and the lead as dioxide upon the anode) : — 



The acid liquid was siphoned off from the deposits, 
evaporated to dryness with sulphuric acid, neutral- 
ized with caustic potash, and then to this (100 c.c. in 
volume) solution were added 50 c. c. of a solution 
of potassium oxalate and 100 c.c. of a solution of 
potassium sulphate. The zinc found equaled 34.50 
per cent. 

When using this method employ a stout platinum 
wire, wound to a spiral at the one end, for the anode, 
and a platinum cone for the cathode. To avoid the 
peculiar spots which electrolytic zinc shows upon a 
platinum surface, it will be best to first coat the nega- 
tive electrode with copper (5 grams). In dissolving 
the precipitated zinc, use rather dilute nitric acid. 
The copper layer will be but slightly attacked, and 
after washing and drying will serve for further depo- 
sitions. Wash the zinc deposit with water, alcohol, 
and ether ; dry in a desiccator. Oxidation is liable to 
occur if an air bath be used for the drying. 

Riche employs "a solution of the acetate with an 
excess of ammonium acetate, obtained by supersatu- 



o,Googlc 



DETERMINATION OF HETALS — ZINC. 83 

ration with ammonia and acidifying with acetic acid." 
This method affords good results, as may be seen 
from the following determination : 0.4736 gram of zinc 
sulphate was dissolved in 200 c.c. of water, to which 
were added three grams of sodium acetate and ten 
drops of ordinary acetic acid. The current gave 3 c,c, 
of electrolytic gas per minute. After two hours 0.1063 
gram of metallic zinc was obtained, the required 
quantity being 0.1072 gram, 

Moore seems to have obtained exceedingly satis- 
factory results by precipitating a solution of zinc sul- 
phate with sodic phosphate, then adding an excess 
of ammonium carbonate, and after dissolving the 
precipitate in potassium cyanide, the solution was elec- 
trolysed at a temperature of 80° with a current giving 
1000 c.c. electrolytic gas per hour. The metal was 
■ deposited upon a silver-plated electrode. An excel- 
lent procedure, originating with Luckow and pre- 
viously noticed in the Historical section, consists in 
introducing 0.5 gram of metallic mercury into the 
dish in which it is intended to electrolyse the solu- 
tion of the zinc salt. It is, of course, understood that 
the platinum dish and the drop of mercury are 
weighed together. A zinc amalgam is precipitated ; it 
distributes itself in a beautiful adherent layer over the 
surface of the dish. 

Vortmann has found that zinc may be readily pre- 
cipitated from its solution in the presence of an excess 
of sodium hydroxide and sodium tartrate. The de- 

D,nitiz.!.o,GoOglc 



84 ELECTRO-CHEMICAL ANALYSIS. 

posit is gray in color and adheres well to the dish. 
The current density (N. Dim) may vary from 0.3-0.6 
ampere. To determine when the precipitation is 
complete, remove a few drops of the liquid and warm 
with ammonium sulphide. 

A very convenient stand for electrolytic work and 
suitable in the zinc depositions has been described by 
V. Malapert (Z. f a. Ch. 36, 56) and since conve- 
niently modified by Herrick (Jr. An. Ch., 3, 167). 



NICKEL AND COBALT. 
LiTERATUKE— Gibbs. Z. f. a. Ch., 3, 336 ; Z. f ft. Ch,, U,IC 
558; Mertick,Ain. Ch., a, 136; Wri ghison, Z. f.a.Ch., is. 300, 
303. 333; Scbweder,Z. (.ft. Ch., 16, 344; Cheney and Richa 
Am.Jr.Sc. and Ar. [3].i4. t78;Ohl,Z.f. B.Ch., i8,5i3;Luc] 
Z.r. a.Ch., 19, 16-, BergmariDand Fres e d i u s, Z. f. a'Ch., 19, 
3141 Riche, Z. ra.Ch.,ai, 116, 119; CUsaen and v. Reisi, Ber. 
14, i6:z,277iiSchucht, Z. r. a. Ch., 21,493; Kohnand Wood- 
e ate. Jour. Soc. Cbem, Industry, 8, 256 ; RUdorfl, Z. f. ang. Ch,, 
Jahrg. 1892, p. 6; Brand, Z. f. a. Ch., 28, 588; Le Roy, ComplCS 
rendus,Iii, 7ZJ; Votimant,, M. f. Ch., 14, 536. 

These metals are precipitated from solutions of their 
double cyanides, double oxalates, and sulphates mixed 
with alkaline acetates, tartrates, and citrates, or from 
ammoniacal solutions. The latter seem best adapted 
for nickel depositions, the presence of ammonium 
sulphate or sodium phosphate being favorable to the 
precipitation. 

Fresenius and Bergmann, who have carried out a 



o,Googlc 



DETEKHINATION OF HETALS — NICKEL, COBALT. 85 

series of experiments with nickel and cobalt, give the 
following as satisfactory conditions : 50 c.c. nickel 
solution (= 0.1233 gram nickel), 100 c.c. ammonia 
(sp. gr. 0.96), 10 c.c. ammonium sulphate (305 grams 
of the salt in i litre of water), 100 c.c. of water ; sepa- 
ration of the electrodes }4-}i cm. : time, four hours. 




Current, 300 c.c. electrolytic gas per hour. The nickel 
found was 0.1233 gram. Apparatus suitable for the 
decomposition just described is represented in Fig. 25. 
The metal is deposited upon the weighed platinum 
cone in the beaker glass, C. The vessel is covered 
with a glass lid having suitable apertures for the posi- 



o,Googlc 



86 ELECTRO-CHEHICAL AKALY51S. 

live and negative electrodes. As soon as the blue- 
colored liquid becomes colorless, an indication that 
the metal is completely precipitated, remove a few 
drops and test with a solution of potassium sulpho- 
carbonate. If the latter causes only a faint rose-red 
coloration the deposition of metal may be considered 
complete. If the electrolysis is unnecessarily pro- 
longed metallic sulphide may be produced (Lehrbuch 
der analyt. Chemie, Miller and Kiliani). It is not ad- 
visable to interrupt the current or to remove the cone 
from the electrolysed liquid until the latter has been 
replaced by water. This Is effected by the vessels to the 
left of the figure : A is an aspirator, filled with water ; 
B is air-tight and empty ; ;f is a doubly bent tube ex- 
tending to the bottom of C. Open p and the liquid 
in C is gradually transferred to B. Add fresh water 
in C. Ammonium chloride should not be present in 
the solution undergoing electrolysis. 

Vortmann adds tartaric or citric acid and an excess 
of sodium carbonate to the solution of the nickel salt, 
then electrolyses with a current density of N. Dio, = 
0.3-0.4 ampere. The deposit may contain traces of 
carbon. 

The statements upon nickel also apply to cobalt. 
An experiment, taken from the article of Fresenius 
and Bergmann is here given as a guide in determin- 
ing cobalt: 50 c.c. of cobalt sulphate {= 0.1286 gram 
cobalt), 100 c.c. of ammonia, ro c,c. of ammonium 
sulphate, 100 c.c. water ; current 300 c.c. electrolytic 

Dinitizedo, Google 



DETERMINATION OF METALS — NICKEL, COBALT. 87 

gas per hour ; separation of electrodes, )4-}i cm. 
Time five hours. The deposited cobalt weighed 
0.1286 gram. 

Use potassium sulpho-carbonate to test when the 
metal is fully reduced ; it gives a wine-yellow colora- 
tion with even the most dilute solutions of cobalt salts. 

When too little ammonia is present in the electro- 
lyte the results are bad; too much of this reagent 
retards the deposition of the cobalt. 

When precipitating these metals from the solutions 
of their double oxalates, the conditions should be 
similar to those indicated under Iron (p. 91). 

The writer has electrolysed cobalt compounds con- 
taining an excess of an alkaline acetate {see Zinc) with 
perfectly satisfactory results, and would recommend 
such solutions for this particular metal. 

Sodium pyrophosphate precipitates a greenish -white 
pyrophosphate from nickel solutions, an excess of the 
reagent dissolves the precipitate, while the liquid be- 
comes yellow-green in color. The latter is changed 
to green by ammonium carbonate, and to blue by 
ammonium hydroxide. When electrolysing a nickel 
solution add to it 20 c.c. of a sodium pyrophosphate 
solution, 25 c.c. of ammonia (0.91 sp.gr.), and 150 c.c. 
of water. A current from six Meidinger cells will be 
sufficient to throw out the nickel. This method will 
serve equally well for the estimation of cobalt. 



b, Google 



88 ELECTRO-CHEMICAL ANALYSIS, 

MANGANESE. 

LlTERATlTRK — Z. t. a. Ch., II, 14; Rich i, Ann. deChim.etde 
Phys. [5ih ser ], 13. 508 i Lucko w, Z. f. a. Ch., 19, 17 ; Schucht, 
Z. f. ■ Ch., aa, 493; Classen and ». Reisa, Ber., 14, i6m ; 
Moore, Ch. News, 53, 209;Smith and Fr ank e I. Jt. An, Ch , 3, 
38s; Cb. News 60, 262; Brand, Z. f. a. Ch. aS. 381 ; RUdorff, 
Z, I. ang. Ch., Jahtg. 15, p. 6. 

The electric current causes this metal, when in solu- 
tion as chloride, nitrate or sulphate, to separate as the 
dioxide upon the anode {s£e Lead). In a solution of 
nitric acid, the hydrogen set free reduces the acid to 
oxides of nitrogen and, finally, to ammonia. Hence, 
when the liquid becomes alkaline or only slightly acid, 
peroxide will also separate upon the cathode ; it will 
be necessary to remove this by means of a strip of 
paper, and ignite the same along with the greater bulk 
of dioxide, weighing all finally as Mnj04. As long 
as manganese alone is present in the solution, this 
separation at both electrodes will not cause a serious 
result ; but in electrolysing a nitric acid solution con- 
taining manganese, magnesium, or aluminium, the re- 
sults will be high. For this reason a solution of the 
sulphate, slightly acidulated with two to six drops of 
sulphuric acid, is preferable for electrolytic purposes. 
Riche advises connecting a platinum crucible or dish 
with the anode of a battery, warming the solution, 
during the deposition, upon a water-bath (7o''-90''), 
and then electrolyses with a current generating 



o,Googlc 



DETERMINATION OF METALS — MANGANESE. 89 

3 c.c. of oxy-hydrogen gas per minute. Arrange 
the apparatus as directed under Cadmium. As 
soon as the manganese has been fully precipitated 
as dioxide, the current is interrupted, the deposit 
washed with water, and should any of the dioxide 
become detached, it must be caught upon a small 
filter, then dried, ignited, and weighed, together with 
the adherent dioxide, which is changed to MnjOj 
before weighing. RiJdorff advises drying the deposit 
in a desiccator, containing sulphuric acid, after which 
it is exposed to an air-bath temperature of 60° C, 
for a period of forty minutes. The weight will then 
be constant. The composition of the deposit is rep- 
resented by the formula Mn02,H80. Multiply its 
weight by 0.523 ; the product will be the quantity of 
metal present in the oxide. Then remove the man- 
ganese dioxide from the dish, add dilute sulphuric acid 
and a solution of hydrogen peroxide. 

In the presence of large quantities of iron, this 
precipitation is unsatisfactory; therefore, first remove 
the iron with barium carbonate. Tartaric, oxalic, and 
lactic acids retard the formation of manganese dioxide. 
The same is true of phosphoric acid. Potassium sul- 
phocyanide also prevents its formation, and if added 
to solutions in which dioxide is already precipitated, 
it causes the same to redissolve. 

The apparatus devised by Herpin (Fig. 26) can be 
well applied in the decomposition of manganese salts. 
It consists of a platinum dish. A, resting upon a tripod, 

G 

DinitizetiovGoOglc ■ 



90 



ELECTRO-CHEMICAL ANALYSIS. 



B, in connection with the cathode of a battery. The 
upper portion of the dish is so constructed that it 
will support an inverted glass funnel, D. Any loss 
from the bursting of bubbles is prevented by this 




means. The anode is a platinum spiral C. In esti- 
mating manganese it must not be forgotten to connect 
the dish with the anode of the battery employed for 
the decomposition. 

. D,nitiz.!.o,GoOglc 



DETERMINATION OF METALS — IRON. 9I 

IRON. 

Literature. — Wrightson, Z. f, a. Ch., 15,305; Parodi and 
Mascazzini, G. Ch. hal., 8;r1soZ. f. a.Ch., 18,588; Lnckow, Z. 
f. a. Cb., 19, lS; Classen and v. Reiss, Ber., 14, 1622; Moore, 
Ch, News, 53, 209 ; Smith, Am. Cb. Jr., 10, 330 ; B r a n d, Z. (. a. 
Chem , a8, 581 ; Drown and McKenna, Jr. An. Ch., 5, eajj ; 
SmilhandMuhr,Jr. An.Ch.,5, 488; R Udorf f, Z. f. ang. Cb., 15 
Jahi^., p. 198; Vortmann, M. f. Ch., 14, 536. 

In the historical sketch (p. $0) it was mentioned 
that Parodi and Mascazzini found that iron could be 
precipitated from solutions of its double oxalates. 
This suggestion has since been elaborated by Classen, 
and by him applied to many other metals. Following 
the recommendation of this chemist, about six grams 
of ammonium oi^alate are dissolved in as little water 
as possible, and the iron salt solution gradually added 
to it with constant stirring. The liquid is then diluted 
with water to 150-175 c.c, and electrolysed with a 
current generating S-io c.c, of electrolytic gas per 
minute. It is necessary to increase this to 12-15 ^■'^■ 
toward the end of the reduction, to insure the com- 
plete deposition of the metal. If ferric hydroxide 
should separate during the electrolytic decomposition 
it can be redissolved by adding oxalic acid drop by 
drop. Test the clear liquid, acidulated with hydro- 
chloric acid, with potassium sulphocyanide. The 
solution should be hot (70°} during the decomposi- 
tion. The deposited iron has a steel-gray color ; it 
should be washed with water, alcohol, and ether. 



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92 ELECTRO-CHEHICAL ANAL,rsiS. 

Avoid the presence of chlorides and nitrJUes. By 
carefully complying with the conditions recommended 
by Classen good results are sure to follow. To show 
that persons with b ut little fvpfjricnrff can obtain 
satisfactory results with the preceding method the 
two following determinations, made by a student, are 
given : A quantity of ferric ammonium sulphate (^ 
0.0814 gram iron) was dissolved in 200 c.c. of water, 
and to this were added eight grams of ammonium 
oxalate. The solution was heated to 80°, and in two 
hours, with a current of 15 c.c. electrolytic gas per 
minute, 0.0814 gram of iron was obtained. In a sec- 
ond experiment the quantity of iron was doubled {= 
0.1628 gram iron), while the ammonium oxalate was 
1 1 grams, temperature 66°, and the current 10 c.c. 
electrolytic gas per minute. The precipitated iron 
weighed 0.1619 gram instead of 0.1628. 

The writer found the following procedure admirably 
suited for iron determinations: 10 c.c. iron solution 
(= 0.0300 gram metal), 20 c.c sodium citrate (28 
grams in J^litre) with a little free citric acid, then diluted 
with water to 150 c.c. Current, 12 c.c. electrolytic 
gas per minute. In four hours O.0303 gram iron was 
precipitated from the cold solution. The deposit was 
washed as already directed. In several determina- 
tions aluminium and titanium were present with the 
iron, but the latter was precipitated free from the 
other two. The deposit of iron sometimes contains 
carbon. 

D,nitiz.!.o,GoOglc 



DETERMINATION OP METALS — IRON. 93 

A third method, originated by Moore, advises that 
glacial phosphoric acid ( 1 5 per cent, acid) be added to 
the distinctly acid solution of ferric chloride or sul- 
phate, until the yellow color fully disappears, then a 
large excess of ammonium carbonate added and gently 
warme d until the liquid becomes clear. On electrolys- 
ing the hot (70° ) solution by a current equal to 1200 
c.c. electrolytic gas per hour, the iron is rapidly and 
compl etel y deposited at the rate of 0.75 gram per hour. 
The end of the decomposition is recognized by test- 
ing a portion of the solution with ammonium sulphide. 
Wash the deposit as already directed. 

Drown, pursuing a suggestion made by Gibbs in 
1880 relative to the precipitation of metals in the form 
of amalgams, has applied it to the determination of 
iron. The trial tests were made with a solution of 
ferrous ammonium sulphate, slightly acidulated with 
sulphuric acid, to which a large excess of mercury 
was added (not less than fifty times the weight of the 
iron to be precipitated). A large platinum anode was 
used, while, the mercury cathode was brought into 
the circuit by means of a platinum wire enclosed and 
fused into one end of a glass tube which passed 
through the liquid. The current employed for the 
precipitation equaled about two amperes per minute. 
The author remarks ' that if these conditions be 
observed, as much as 10 grams of iron can be precip- 
itated in from 10-15 hours. 

The decompositions were carried out in beaker 



94 ELECTRO-CHEHICAL ANALYSIS. 

glasses. Care should be exercised in drying, so that no 
mercury is volatilized. 

Experiments made in this laboratory show that iron 
can be fully precipitated in the cold from ammoniacal 
tartrate solutions. The iron, however, carries down 
carbon with it. If the metal be dissolved, after weigh- 
ing, in dilute sulphuric acid, it can be accurately esti- 
mated by titration with permanganate. A current of 
2.5 c.c, electrolytic gas per minute is sufHcient to 
precipitate the metal. 



Literature.— Luckov, Z. f. a. Ch., 19, 18 ^ Smitb, Am. Ch. 
Jr., I, 329- 

For electrolytic purposes use the acetate or any of 
the salts to which an alkaline acetate has been added 
in large excess, together with a few drops of free acetic 
acid. The dish in which the deposition is made is 
placed upon a water-bath, and connected with the 
negative electrode of a battery giving 2— 3,c.c. of elec- 
trolytic gas per minute (see Cadmium). Heat the 
liquid to 70° throughout the entire decomposition. 
The uranium separates as yellow uranic hydroxide 
upon the cathode ; by the continued action of the 
current it changes to the black hydrated protosesqui- 
oxide. As soon as the solution becomes colorless, 
interrupt the current and quickly pour the clear liquid 
upon a small filter, to catch any detached particles of 



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DETERMINATION OF HETALS — THALLIUM, 95 

oxide. Wash with a little acetic acid and boiling 
water ; dry, ignite, and weigh as Ur30,(UrjOg). This 
method affords an excellent separation of uranium from 
the alkali and alkaline earth metals. 



THALLIUM. 
Literature. — Schucht, Z. f. a. Ch., aa, 341, 490; Neumann, 
Ber., ai, 356. 

This metal separates as sesquioxide, from acid solu- 
tions, upon the anode, while from ammoniacal liquids it 
is deposited partly as metal and partly as oxide. From 
oxalate solutions and from its double cyanides it sepa- 
rates only as metal when the current is feeble. How- 
ever, difficulty is experienced in drying the deposit 
without having it oxidized. In this respect it is even 
more troublesome than lead, Neumann utilizes the 
current to separate the metal, dissolves the latter in 
acid, and measures the liberated hydrogen ; from its 
volume he calculates the quantity of thallium origi- 
nally present. For suitable apparatus to carry out 
this method consult the literature cited above. 



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9D ELECTRO-CHEMICAL ANALYSIS. 

PLATIHUM. 
LlTEBATURE.— Luckow, Z. f. B. Ch., 19, 13; CUssen, Ber., 17, 
2467; Smith, Am. Ch. Jr.,i3,ao6; Rfldorff, Z. f.uig. Ch.,i893, 
696. 

The solutions of platinum salts, slightly acidulated 
with sulphuric acid, and acted upon by a feeble cur- 
rent, give up the metal as a bright, dense deposit upon 
the dish, frequently so light as to be scarcely dis- 
tinguished from the latter. In using platinum vessels 
for this purpose, first coat them with a rather thick 
layer of copper, upon which afterward deposit the 
metal. Wash the deposit with water and alcohol. 

In ordinary gravimetric analysis, potassium is 
frequently estimated as potassio-platinum chloride, 
KiPtOfl. This operation requires time and care. 
Rather dissolve the double salt in water, slightly acidu- 
late the solution with sulphuric acid, and electrolyse 
with one Bunsen cell. The deposit will be black 
and spongy if the current is too strong. From the 
quantity of platinum found calculate the potassium. 

The following facts have been taken from Classen's 
article (jc^ Literature): A platinic chloride solution, 
containing 0.6 gram platinum, was diluted to 200 c.c. 
with water and electrolysed. In five hours 0.4581 
gram platinum had separated. When mixed with 
ammonium oxalate 0.0996 gram platinum was pre- 
cipitated in two hours. From a solution, feebly acidu- 
lated with hydrochloric acid, four Meidinger cells 



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DETERMINATION OF HETALS — PLATINUM. 97 

precipitated O.737 gram platinum in the course of 
twenty-four hours. On dissolvingO-S gram ammonio- 
platinum chloride in lOO c.c. water and mixing with 
ammonium oxalate the current from one Bunsen cell 
precipitated 0.208 gram platinum in five hours, 0.6042 
gram potassio-platinum chloride was dissolved in 150 
c.c. of water, acidulated with thirty drops of dilute sul- 
phuric acid (i :6), and in six hours gave 0.201 7 gram 
platinum to the action of the current; O.5015 gram 
of the same salt gave 00956 gram metal in two 
hours; while 0,4545 gram of the double chloride 
dissolved in 100 c.c. water, and not acidulated, gave 
0.0688 gram platinum in three hours. 

The following experiment executed in this labora- 
tory demonstrates that the precipitation of plati- 
num from solutions containing sodium phosphate 
and free phosphoric acid is complete. The volume 
of the liquid was 150 c.c. It contained 0,1 144 gram 
of metallic platinum, 30 c.c, of NaiHPO, (sp, gr. 
■■0358), and 5 c,c, of phosphoric acid (sp, gr, 1.347). 
The current gave 0.8 c.c. of electrolytic gas per minute. 
The deposit of platinum weighed 0.1140 gram. It 
was precipitated upon a copper-coated platinum dish. 
It was washed with water and alcohol. Ten hours 
were required for the deposition. 



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ELECTRO-CHEMICAL ANALYSIS. 



PALLADIUM. 
Literature.— web I er, Ann., M3<375; Sehucht, Z. f. ■ Ch., 
13, 343; Smith and Keller, Am. Ch. Jr., la, 251; Smith, Am. 
Ch. Jr., 13, 206; 14,43s- 

Palladium can be deposited from solutions of the 
satne kind and in the same manner as platinum. The 
use of a feeble current gives a bright metallic de- 
posit; otherwise it is spongy. 

It has been discovered, in this laboratory, that this 
metal can be rapidly and fully precipitated from 
ammoniacal solutions of palladammonium chloride 
by a current liberating 0.7 c.c. electrolytic gas per 
minute. Palladammonium chloride, Pd(NH3Cl)t. is 
prepared by adding hydrochloric acid to an ammo- 
nium hydroxide solution of palladious chloride. To 
show the accuracy of this method, several actual de- 
terminations are here introduced; (i) A quantity of 
the double salt (= 0.2228 gram palladium) was dis- 
solved in ammonium hydroxide; to this solution 
were added 20-30 c.c, of the same reagent (sp. gr. 
0935) and 100 C.C, of water, A current, giving 
09 c.c, electrolytic gas per minute, acted upon this 
mixture through the night, and deposited 0,2225 
gram palladium, {2) In another experiment, with 
conditions similar to those just mentioned, except- 
ing that the quantity of the palladammonium chlo- 
ride was doubled, and the current reduced to 0.7 
C.C. electrolytic gas per minute, the quantity of metal 



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DETERMINATION OF HETALS — RHODIUM. 99 

precipitated equaled 0.4462 gram instead of 0.44S6. 
Oxide did not separate upon the anode. The de- 
posit, when dry, showed the same appearance as is 
ordinarily observed with this metal in sheet form. 
It was washed with hot (70°) water, and dried in an 
air-bath at i io°-ii5°. It is best to deposit the pal- 
ladium in platinum dishes previously coated with 
silver. 

RHODIUM. 
LiTEBATDRE. — Smith, Jr. An. Ch., 5, 201 ; Joly aod Leidit, 
Conptcs rendos, 113, 793. 

Few attempts have been made to determine this 
metal electrolytically. Its separation from an acid 
phosphate solution is very rapid and complete. A 
current liberating 1.8 c.c. of electrolytic gas per 
minute will serve very well for the purpose. As 
the decomposition progresses, the beautiful purple 
color of the liquid gradually disappears, and the 
solution is colorless when the precipitation is fin- 
ished. The deposition of the rhodium should be 
made upon copper- coated dishes. The metal is 
generally black in color, very compact, and perfectly 
adherent Hot water may be used for washing pur- 
poses. 

Joly precipitates the metal from solutions acidu- 
lated with sulphuric acid. 



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electro-cremiCal analysis. 



MOLYBDENUM. 
LiTEitATURK. — Smith, Am. Cb. Jr., i, 339; Hoskinion uid 
Smith, iiiJ., i, 90. 

When the electric current acts upon ammoniacal 
or feebly acid solutions of ammoniuni molybdate, a 
beautiful iridescence appears ; as the action continues 
this assumes a black color, and the deposit becomes 
more dense. It is the hydrated sesquioxide which is 
precipitated ; after washing with hot water it is dried, 
carefully ignited to molybdic acid, and weighed. The 
precipitation can take place in a platinum crucible, in 
connection with the cathode of a battery liberating 
3-4 c.c. of electrolytic gas per minute. The tempera- 
ture of the solution should not fall below 70° ; its 
volume may vary from 25 C.C.-125 c.c. Three hours 
were required for the precipitation of 0.0329-0.1000 
gram of oxide. 

GOLD. 

LrrEKATURE.— L u c k o w, Z. f. «. Cb., 19, 14; Smi t b. Am. Cb. Jr., 

13, Jo6j Smith and Muhr, Am. Ch. Jr., 13,417; Smilb, Jr. 

An. Ch., 5, 204; Smith and Wallace, Ber., 25, 7791 Fran- 

kel, Jr. Frank. Inst, 189I; Radorff, Z. f. fltiE- Ch„ 189*, p. 695. 

This metal can be completely deposited from solu-; 
tions containing it in the form of a double cyanide, 
sulphaurate, and sulphocyanide, as well as in the 
presence of free phosphoric acid. In this laboratory 
the cyanide and sulphaurate have received the most 



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DETERMINATION OF METALS — GOLD. lOI 

consideration. An example will illustrate the condi- 
tions with which good results may be obtained from 
the double cyanide: A solution contained 0.1162 
gram of metallic gold; to it were added one and one- 
half grams of potassium cyanide and 1 50 ex. of water. 
The current that acted upon this solution gave 0.8 
c.c. to I cc. of electrolytic gas per minute. The 
gold deposit weighed 0.1163 gram. It was washed 
both with cold and hot water. The metal may 
be precipitated upon silver-coated or copper-coated 
platinum vessels, or directly upon the sides of the 
platinum dish. If the last suggestion is followed, 
dissolve off the gold, after weighing, by introducing 
very dilute potassium cyanide into the dish, and 
then connect the latter with the anode of a battery 
yielding a very feeble current. 

The deposition of gold from a sodium sulphide 
solution (sp. gr. 1.18) is just as satisfactory as that 
described in the last paragraph. The current should 
liberate from 2-3 cc. of electrolytic gas per minute. 
The precipitated metal is very adherent and of a 
bright yellow color. 

The facts relating to the electrolytic behavior of 
vanadium, tungsten, and osmium are, at the present 
writing, few in number and will not be given here. 



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ELECTRO-CHEMICAL ANALYSIS. 



LlTEBATUBE,— Luckow, Z. f. a. Ch., IQ, 13; Classen ■nd v. 
Reiss, Ber., 14, 16221 Gibbs, Ch. News, 4a, 291; Classen, 
Ber., 17, 2467 ; 18, 1104) Riidorff, Z, f. aog. Cb., i8gi, 199. 

Tin may be deposited either from a solution of its 
chloride, or from that of ammonium tin oxalate. It 
is advisable not to use potassium oxalate in the elec- 
trolysis, for then a basic salt is liable to separate upon 
the anode. Three to four grams of ammonium oxa- 
late will be sufficient for the decomposition. The 
current should liberate 3 c.c. electrolytic gas per 
minute. When electrolysing acid tin solutions do 
not interrupt the current until the free acid is first 
removed; this is not necessary when operating with 
oxalate solutions. 

Rudorff claims that the very best results are 
obtained by electrolysing the tin salt in the pres- 
ence of primary ammonium oxalate. It is imma- 
terial whether the metal exists in the solution as 
a stannous or stannic salt, but its quantity should 
not exceed 03 gram. If the liquid is acid, neutralize 
with ammonium hydroxide, and add 10 c.c. of a 
saturated ammonium hydric oxalate solution for 
every O.I gram of metallic tin present. Should the 
liquid not be clear, apply heat, dilute with water to 
120 c.c, and electrolyse with a current liberating from 
2—3 c.c. of electrolytic gas per minute. Wash the 
metal deposit with water and dry at 80° C. 



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DETERMINATION OF HETALS TIN. IO3 

Classen has discovered that a tin solution contain- 
ing an excess of ammonium sulphide, largely diluted 
with water, yields a quantitative deposition of the 
metal when exposed to the action of a current from 
two Bunsen cells. In dilute sodium or potassium 
sulphide solution the tin precipitation is incomplete, 
and whenever such conditions exist, the sodium 
or potassium salt must be converted into ammonium 
sulphide. To this end the liquid is mixed with 
about 25 grams of ammonium sulphate, free from 
iron, and the solution then carefully warmed in a 
covered vessel until the evolution of hydrogen sul- 
phide ceases; after which the liquid is heated to 
incipient ebullition for fifteen minutes. Allow it to 
cool, dissolve any sodium sulphate which may have 
separated by the addition of water, and electrolyse 
with a current of 9-10 c.c. oxy-hydrogen gas per 
minute. The tin separates in a gray, dense layer. 
Wash it with water and alcohol. At times sulphur 
sets itself upon the tin deposit; this is difficult to > 
remove, but can be detached, after washing the 
deposit with alcohol, by gently applying a linen 
handkerchief. 



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ELECTRO-CHEMICAL ANALYSIS. 



ANTIMONY. 
Literature. — Wright so n, Z. f. a. Ch., 15, 300; Parodi and 
Mascftiiioi, Z. f. «, Ch, 18, 588; Lucko w, Z, f.a. Ch., 19, 13; 
C1ass«aaail t. Reiss, B«r., 14, i6ii; 17, 3467 ; 18,1104; Lecre- 
nier.Chemiker Zeitung, 13, 1219; Chine nd en, Pro. Conn. Acad, 
Sci,, Vol, 8; Vorlraann, Ber., H. 2761; Rildorff, Z. f. a. Ch., 
1891, 199. 



Antimony, when precipitated from a solution of its 
chloride, or from that of antimony potassium oxalate, 
does not adhere well to the cathode. It is deposited 
very slowly from a solution of potassio-antimony 
tartrate. Its deposition from a cold ammonium sul,- 
phide solution is satisfactory, but the use of this 
reagent for this purpose is not pleasant, especially 
when several analyses are being carried out simulta- 
neously. For this reason potassium or sodium sul- 
phide has been substituted. The alkaline sulphide 
used must not contain iron or alumina. 

The antimony solution, mixed with sodium sulphide, 
is largely diluted with water. A more rapid reduction 
follows in consequence of the dilution. A current 
giving 2-3 c.c. of electrolytic gas per minute will pre- 
cipitate O.I gram of antimony in four or five hours. 
To ascertain when all the metal is deposited incline 
the dish slightly, thus exposing a clean platinum sur- 
face. If this remains bright for half an hour the pre- 
cipitation is finished. In separating antimony from 
the heavy metals, e.g., lead, it happens that alkaline 



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DETERMINATION OF METALS — ANTIMONY. lOJ 

sulphides containing polysulphides are used, or are 
produced. To remove these Classen proposed adding 
to the antimony-polysulphide mixture, already in a 
weighed platinum dish, an ammoniacal solution of 
hydrogen peroxide, and warming the same until the 
liquid becomes colorless. When this is accomplished, 
even if a precipitate has been produced, add, after 
cooling, 10 C.C, of a concentrated solution of sodium 
monosulphide, and electrolyse with a current of 1.5-2 
C.C. electrolytic gas per minute. Wash the deposit 
with water and alcohol. 

Lecrenier writes as follows relative to the preceding 
method : The precipitation is all that one can desire, 
providing the solution of the sulpho-salt is absolutely 
free from polysulphides ; otherwise, it is incomplete. 
The antimony sulphide obtained in the ordinary 
course of analysis always contains sulphur, and this 
must be eliminated. To remove the various incon- 
veniences cotlnected with the method add 50-75 C.C. 
of a 20 per cent, solution of sodium sulphite to the 
solution after the addition of the excess of sodium 
sulphide, then heat the liquid to complete decoloriza- 
tion; allow to cool, after which the current is con- 
ducted through the liquid. This can rise to 5 c.c. per 
minute without impairing the result ; but it is not best, 
as the precipitated metal is then not very coherent. 
It is better to use a current giving not more than half 
of the above volume of electrolytic gas per minute. 
When the quantity of antimony does not exceed 0.2 

H 

D,nitiz.!.o,GoOglc 



I06 ELECTRO-CHEMICAL ANALYSIS. 

gram the deposit will be adherent and free from sul- 
phur; wash with water, alcohol, and ether. Sulphur 
will separate upon the anode, despite the presence of 
an excess of sodium sulphite. This, however, does 
not affect the result. 

Vortmann, recognizing the fact that it is difficult to 
obtain an adherent deposit of antimony when the 
quantity of metal in solution exceeds 0.16 gram, has 
combined the method of Smith, who first pointed out 
that mercury could be deposited very satisfactorily 
from the solution in sodium sulphide, with his knowl- 
edge that antimony could be precipitated from a simi- 
lar solution, and hence recommends the determination 
of the antimony in the form of an amalgam. No dif- 
ficulties attend this procedure. Two parts of mercury 
should be present for every part of antimony. The 
latter must also be present in solution as higher ox- 
ide ; to this end digest the antimonious solution with 
bromine water, and afterward add the sodium sul- 
phide containing sodium hydroxide. Electrolyse 
with a current of 2—3 c.c. electrolytic gas per minute. 
The amalgam can be washed in the usual way. 



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SEPARATION OF METAI-S. 



ARSENIC. 



Literature.— L u c k o w, Z. f. a. Cb., ig, 14 ; C 1 a s s e n and v. 
Reiss, Ber., 14, 1622; Moore, Ch. News, 53, 109; Vor t mann, 
Ber., 34, 2764. 

A successful method for the complete deposition of 
arsenic is not known. The current acting upon the 
chloride causes complete volatilization of the metal 
in the form of arsine. Us separation from oxalate 
solutions is incomplete ; nor do the sulpho-salts an- 
swer for electrolytic purposes. 

From a solution containing 0.2662 gram arscnious 
oxide Vortmann obtained 0.18527 gram metallic 
arsenic, equivalent to 69.59 per cent. The trioxide 
contains 75.78 per cent, of arsenic. This precipita- 
tion was effected by the amalgam method. 



a. SEPARATION OF THE METALS. 

Electrolysis, to be of value, must not only furnish 
the analyst with methods suitable for the complete 
deposition of metals, but it should, in addition, enable 
him to separate metallic mixtures. The data given 
in the preceding pages will serve for this purpose, but, 
as a special treatment is required in some instances, a 
brief outline of a series of separations will be indi- 
cated. 



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-CHBHICAL ANALYSIS. 

COPPER. 

We recall, first of all, that this metal can be de- 
posited electrolytically from solutions in which free 
nitric acid is present (page 55), This behavior renders 
the separation of copper from cadmium possible (Am. 
Ch. jr., 3, 42). Place the solution containing the two 
tnetals in a beaker glass of 200 c.c. capacity ; suspend 
(p. 58) a weighed platinum crucible in the liquid, 
and precipitate the copper upon it. The total dilution, 
during the decomposition, should not exceed 1 50 c.c. 
As much as 5 per cent, of nitric acid can be present; 
the current should give 0.5 c.c. electrolytic gas per 
minute. When all the copper is precipitated, washed, 
dried, and weighed (p. 57), make the residual liquid 
alkaline with sodium hydroxide, and add sufficient 
potassium cyanide to redissolve the precipitate. Elec- 
trolyse as directed p. 65 (also consult p. 114). Very 
recent experiments, made in this laboratory, show that 
also in the presence of an excess of free sulphuric 
acid the current will precipitate copper free from cad- 
mium : e.g., 0.1975 gram of metallic copper, and 
0.1828 gram of cadmium, both as sulphates, were 
dissolved in 20 c.c. of water ; to this were added 10 
c.c. of sulphuric acid of 1.09 sp. gr. and 100 c.c. ol 
water. The current gave 0.30 c.c. electrolytic gas 
per minute. The precipitated copper weighed 0.1976 
gram ; it contained no cadmium. 

The separation is also possible when the metals are 



SEPARATION OF METALS COPPER. IO9 

present together with an alkaline phosphate and free 
phosphoric acid. Thus, a solution contained 0.2452 
gram of copper, 0.1827 gram of cadmium, 20 c.c. of 
disodic hydrogen phosphate (sp. gr. = 1.0358), and 10 
C.C. of phosphoric acid (sp. gr. 1.347), with a total 
dilution of 125 c.c. A current of 0.1 c.c. electrolytic 
gas per minute precipitated the copper, free from cad- 
mium, in twelve hours. The deposit was washed and 
dried as previously described. 

It is not possible to separate these metals when 
present together in an oxalate solution. 

The precipitation of copper in nitric acid solutions 
further enables us to separate it from iron, aluminium, 
chromium, cobalt, nickel, zinc, the alkaline earth, and 
the alkali metals. The separation from the first six 
can also be made in a solution containing free sul- 
phuric acid. A solution containing 0.1341 gram of 
copper and an equal amount of zinc was mixed with 
S c.c. of nitric acid (sp. gr. 1.3), then diluted to 200 
c.c. A current of i c.c. of electrolytic gas per min- 
ute acted upon this mixture. The precipitated copper 
weighed 0.1 345 gram. A second solution witho.1341 
gram of copper and equal amounts of zinc, cobalt, 
and nickel, 5 c.c. of nitric acid, and total dilution of 
200 c.c. gave 0.1339 gram copper to a current of 0,4 
c.c. electrolytic gas. 

The conditions mentioned in the first example will 
also serve for the separation of copper from iron. 
Vortmann, however, separates copper from a large 

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1 lO ELECTRO-CHEMICAL ANALYSIS. 

quantity of iron by adding ammonium sulphate 
and an excess of ammonium hydroxide to the 
liquid in which these metals are present. The ferric 
hydroxide, which is precipitated, does not inter- 
fere with the deposition of the copper. The latter is 
free from iron. The current employed in this separa- 
tion should be N.Dioo = 0.I-0.6 ampere (M. f. Ch., 
H. 536). 

Copper can also be separated from iron, aluminium, 
chromium, zinc, cobalt, and nickel in solutions of their 
phosphates in phosphoric acid. The most satisfac- 
tory conditions for the separation of any one of these 
metals from copper may be learned from the following 
example: 0.0996 gram copper, 0.1500 gram zinc, 30 
c.c. of sodium phosphate, and 3 c.c, phosphoric acid 
(sp.gr. 1.347) ^'^h ^^^^^ dilution of 125 c.c. were 
electrolysed with a current of 0.6 c.c. electrolytic gas. 
The precipitated copper weighed 0.0993 gi'^'n (Am. 
Ch. Jr., 12, 329; Jr. An. Ch.. 5, 133). 

From mercury, silver and bismuth the copper can- 
not be separated in the presence of nitric or sulphuric 
acid.* For the electrolytic separation of copper from 
mercury see p. 118. Its separation from bismuth has 
only recently been made possible by combining the 
behavior of copper in the presence of an excess of 
alkaline cyanide, and that of bismuth where it exists 
as a double citrate in an alkaline solution (p. 69). 

•Jr. An. Ch„ 7, liS, 

D,nitiz.!.o,GoOglc 



SEPARATION OF METALS COPPER. 1 1 1 

Add 3—4 grams of citric acid to the bismuth solution, 
SO that upon the later addition of sodium hydroxide 
to alkaline reaction a precipitate is not produced. 
Into this liquid introduce the cyanide copper solution, 
and electrolyse with a current giving 0.15 c.c. electro- 
lytic gas per minute. 

In a solution of copper and lead, containing 5 per cent. 
of nitric acid, the former will be deposited completely 
at the cathode, while the latter is fully precipitated as 
dioxide at the anode (p. 73}. This course is adopted 
when separating these metals in alloys or minerals. 

The separation of copper from manganese should 
be conducted in solutions containing a slight excess 
of sulphuric acid. While the copper is deposited as 
such upon the cathode, the manganese separates upon 
the anode as dioxide (p. 89). A platinum foil may be 
used as anode in this separation. Another method, 
applicable here, is based on the observation that man- 
ganese remains dissolved in the presence of phos- 
phoric acid, while the copper is deposited in its usual 
form. For example, 0.1770 gram copper and 0.1500 
gram manganese, both as sulphates, were treated with 
30 c.c. of sodium phosphate, of sp. gr. 1.0388, and 10 
c.c. phosphoric acid, of sp. gr. 1.347, t^^" diluted to 
J50 c.c. with water and electrolysed with a current 
giving I c.c. of electrolytic gas per minute. The pre- 
cipitated copper weighed o 1765 gram. Manganese 
did not separate, even as dioxide. (See Am. Ch. Jr., 
12, 329.) 

D,nitiz.!.o,GoOglc 



112 ELECTRO-CHEHICAL ANALYSIS. 

It is only recently that a satisfactory electrolytic 
separation of copper from antimony has been found. 
The antimony is oxidized to the antimonic condition 
by bromine, after which it is added to the solution of 
the copper salt. Tartaric acid and an excess of am- 
monium hydroxide are next introduced. The depo- 
sition of the copper is then readily effected with a 
current of 0.8 c,c.-i.4 c.c. of electrolytic gas (Jr. 
An. Ch., 7, 4; Z. f. anorg. Ch., 4. 273). 

As to the separation of copper from arsenic, Classen 
remarks (Ber., 15, 297) that when the arsenic exceeds 
0.20 per cent, the deposited copper is more or less 
dark in color, and the result will be high. Some 
chemists have advised that after the copper deposit 
has been dried, it should be heated to volatilize the 
arsenic; the residual cupric oxide is redissolved and 
its solution again electrolysed. This procedure will 
be satisfactory when arsenic is present in traces, other- 
wise it is worthless. The arsenic in copper ores can 
be entirely removed by evaporating their acid solution 
with bromine, when it will be expelled as bromide. 
The copper results are then satisfactory. 

McCay (Chemiker Zeitung, 14, 509) has observed 
that when the current from 4-6 Meidinger cells is con- 
ducted through a potassium arsenite solution, made 
distinctly alkaline with ammonium hydroxide, this 
salt sustains no change. With copper, under like con- 
ditions, the .separation of the metal is quantitative. 
Upon this behavior he bases a very excellent separa- 

DinitizetiovGoOglc 



SEPARATION OF METALS COPPER. 1 1 3 

tion of these two metals. The only care necessary is 
to see that not too much ammonia is employed. In 
this laboratory like results were obtained', but prefer- 
ence has since been given to the following course: 
Add the copper solution to that of the alkaline arsen- 
ite or arsenate, and follow it with a solution of potas- 
sium cyanide until the precipitate first produced is 
just dissolved; the liquid will then show a slight 
purple tint, A current of 0.25 c.c. electrolytic gas 
per minute precipitates the copper quite rapidly 
under these conditions ; the deposit will contain no 
arsenic (Am. Ch. Jr., la, 428). 

When antimony, arsenic, and tin are associated with 
copper, treat the sulphides with sodium sulphide. 
The resulting alkaline sulphide solution can then be 
employed for the separation of the first three (p. 1 24), 
while the insoluble copper sulphide may be dissolved 
and treated as described on page 61. 

Schmucker has demonstrated that, when arsenic 
antimony, and tin, all in their highest oxide form, are 
present with copper, the latter can be precipitated free 
from even traces of the other three, by adding to their 
solution eight grams of tartaric acid and 30 c.c. of 
ammonia (sp gr. 0.91), then electrolysing with a cur- 
rent of 0.8-1.0 c.c. electrolytic gas per minute. If a 
tenth of a gram £>{ each metal be present the copper 
will be precipitated in five hours (Jr. Am. Ch. S,, 
15. 195)- 



b^Googlc 



1 14 ELECTRO-CHEUICAL ANALYSIS. 

CADMIUM. 

We mayadd the following method for the separation 
of cadmium from copper to those already described 
under the latter metal : Add 5-6 grams of potassium 
cyanide to the solution of the metals for every 0.2- 
04 gram of cadmium and copper. Dilute the solu- 
tion to 200 c.c. and electrolyse with a current of 0.28 
c.c. electrolytic gas per minute. The cadmium is 
deposited while the copper remains undissolved 
(Jr. An. Ch.. 3, 385). 

A solution containing free nitric acid is used 
for the separation of cadmium from silver, mercury, 
lead, and bismuth ; the latter is also separated from it 
by using a solution in which there is a slight excess 
of sulphuric acid (p. 69). When these metals have 
been removed from their solution, neutralize the " 
excess of acid with potassium hydroxide, add a slight 
excessof potassium cyanide, and electrolyse the liquid 
for the estimation of the cadmium as directed on 
page 62. 

When there is an excess of but 2 c.c. of sulphuric 
acid, of sp. gr. 1.09, cadmium can be precipitated 
(p. 63), and thus separated from iron, aluminium, chro- 
mium, zinc, cobalt, nickel, and manganese (the latter 
deposits at the same time as dioxide.upon the anode, 
p. 89). Or, the method described on p. 62 for the 
deposition of cadmium from an acid phosphate solu- 
tion will suffice for the separation of this metal from 



o,Googlc 



SEPARATION OF METALS— CADMIUM. II5 

zinc, nickel, iron, chromium, manganese, and alumi- 
nium. The conditions there given will answer for any 
one of these cases (Am. Ch. Jr., la, 329; 13, 206), 

Another method which serves for the separation of 
cadmium from either zinc or cobalt consists in having 
these metals in solution in the form of double 
cyanides with the alkaline cyanides. The volume of 
the aqueous solution should be at least 200 c,c. ; to 
this add 4j^ grams of potassium cyanide, and electro- 
lyse the liquid with a current giving 0,30 c.c. electro- 
lytic gas per minute (Am. Ch. Jr., 11, p. 352). It is 
singular that cadmium, under the preceding condi- 
tions, cannot be separated from nickel. If, however, 
the method be modified as indicated in the example 
about to be given, satisfactory results can be easily 
obtained. A current of 2.2 c.c of electrolytic gas 
acted through the night upon a solution containing 
0.1723 gram of cadmium, 0.1600 gram of nickel, 2 
grams of potassium hydroxide, and 2.5 grams of po- 
tassium cyanide. The total dilution of the liquid 
equaled 175 c.c. The precipitated cadmium was free 
from nickel and it weighed 0.1723 gram (Jr. An. Ch,, 

6. 8;). 

Under the special methods given for the estimation 
of cadmium (p. 61) it was mentioned that it separates 
well from solutions of the acetate. Yver (B. s. Ch. 
Paris, 34, 18) has employed this behavior to separate 
cadmium from zinc. The method is this: the metals 
are converted into acetates by the addition of 2-3 

D,nitiz.!.o,GoOglc 



1 16 ELECTRO-CHEUICAL ANALYSIS. 

grams of sodium acetate to their solution, followed 
by several drops of free acetic acid. This liquid is 
then exposed to the current from two ordinary Daniell 
cells. Heat (70°) the solution during the decomposi- 
tion. The precipitated cadmium contains no zinc. 
Three to four hours are necessary for the reduction of 
0.18-0.210 gram of cadmium. Remove the zinc from 
the filtrate by the method of Riche (p. 82). Smith 
and Knerr (Am. Ch. Jr., 8, 210) have tried this separa- 
tion, and recommend that the current should not 
exceed 0.1-0.2 c.c. of electrolytic gas per minute. It 
is also essential that the liquid be held at a nearly uni- 
form temperature (70°) during the reduction. The di- 
lution of the liquid should not exceed 100 c.c. 

The same chemists also (Am. Ch. Jr., 8, 210) found 
that upon electrolysing a solution of these two metals, 
to which 3-4 grams of sodium tartrate and tartaric 
acid had been added, with a current of 3-4 c.c. elec- 
trolytic gas per minute, the cadmium was deposited 
completely from the warm solution, and contained no 
zinc. 

Eliasberg (Z. f. a. Ch., 24, 550) has also proposed a 
method for the separation of cadmium from zinc : 
Dissolve the metallic oxides in hydrochloric acid, 
evaporate their solution to dryness, add 8—10 grams 
of potassium oxalate, and 2-3 grams of ammonium 
oxalate, diluting finally to lOO c.c. ; heat to boiling 
and electrolyse the warm (not boiling) liquid with a 
current equal to 0.15 c.c. electrolytic gas per minute. 

D,nitiz.!.o,GoOglc 



SEPARATION OF METALS — CADMIUM. II 7 

Cover the vessel in which the decomposition is made. 
Six to seven hours will be required for the complete 
deposition of 0.15 gram of metal (cadmium). The 
electrolytic separation of these two metals is also pos- 
sible in a solution of their 'phosphates, dissolved in 
phosphoric acid (Am. Ch. Jr., 13, 329). 

A direct separation of cadmium from arsenic is 
possible, but that the cadmium may be precipitated 
absolutely free from arsenic, the latter must be present 
in the solution as an arsenate. Upon adding two to 
three grams of potassium cyanide to such a solution, 
and electrolysing the same with a current equal to 
0.3 C.C. of electrolytic gas per minute, the cadmium will 
be completely precipitated in ten hours. The reduc- 
tion is made in cold solutions (Am. Ch, Jr., 13, p. 428). 

Schmucker has employed with success the method 
described {p. 113) for the separation of cadmium from 
arsenic, antimony, and tin. 

The conditions mentioned in the cyanide separation 
of cadmium from arsenic will also answer for the 
separation of this metal from molybdenum and tung- 
sten (Am. Ch. Jr., 12, 428). 

In separating cadmium from osmium observe the 
following conditions : add 1.5 gram of potassium 
cyanide for 0.3 gram of combined metals, dilute to 
170 c.c, and electrolyse with a current of 2.6 c.c. of 
electrolytic gas per minute. 

An electrolytic separation of cadmium from plati- 
num and palladium is not known. 

D,nitiz.!.o,GoOglc 



ELECTRO-CHEMICAL ANALYSIS. 



MERCURY. 

This metal is deposited quite rapidly from solutions 
containing free nitric acid (p. 66), hence under such 
conditions it may be separated from cadmium, iron, 
aluminium, chromium, zinc, nickel, cobalt, barium, 
strontium, calcium, magnesium, and the alkalies. 
When lead and mercury are exposed, in a solution of 
nitric acid, to the action of the current, they are de- 
posited simultaneously, the lead as dioxide at the 
anode (p. 73), and the mercury as metal upon the 
cathode. Manganese and mercury are separated to 
the best advantage in solutions containing free sul- 
phuric acid (p. 88). Mercury cannot be separated in 
the electrolytic way from silver and bismuth. From 
copper, the separation can be made in a cyanide so- 
lution (Jr. An. Ch.. 3, 254 ; 5, 489). As an example, 
it may be stated that 0.1018 gram mercury, as chlo- 
ride, and .2500 gram copper, as sulphate, with 3-4 
grams potassium cyanide, were diluted to 200 c.c. 
with water, and then electrolysed in the cold, with a 
current giving 1.3 c.c. of electrolytic gas per minute. 
At the end of sixteen hours 0.1018 gram mercury had 
separated. The time limit may be reduced to 3-4 
hours by heating the solution undergoing decom- 
position to 65° C. 

More recent experiments, made in this laboratory, 
prove that mercury may be readily separated in the 
same way from zinc, nickel, and cobalt. The quan- 



o^Googlc 



SEPARATION OF METALS — MERCURY. I IQ 

tity of alkaline cyanide to be used in these separations 
may vary from three to four grams, although when 
cobalt is to be separated from mercury good results 
will not be obtained if more than three grams of po- 
tassium cyanide are present for 0.3-0.4 gram of metal. 
The current should not exceed o.S c.c, of electrolytic 
gas per minute (Am. Ch. Jr., 12, 104). 

In separating mercury from tin and antimony, pre- 
pare their sulphides, and digest these with ammonium 
sulphide, dissolving out the first two. The residual 
mercury sulphide is then dissolved in aqua regia, and 
after neutralizing the excess of acid with an alkaline 
hydroxide, potassium cyanide is added in sufficient 
quantity to form the double cyanide, which is then 
electrolysed as described, p. 66; or, dissolve the sul- 
phide in sodium sulphide containing sodium hydrox- 
ide and electrolyse, as directed p. 67. Mercury is 
separated from arsenic similarly to cadmium from 
this metal, although it is immaterial whether the ar- 
senic exists in the solution as an arsenite or arsenate 
(p. 117). The same procedure may be followed in its 
Separation from molybdenum, tungsten, palladium, 
platinum, and osmium, although in case of the latter 
metal it is advisable that the quantity of cyanide 
should not exceed 1.5 gram for 0.2 gram of metal 
(Am. Ch. Jr., la, 428 ; 13, 417 ; Jr. An. Ch., 6, 87). 

Mercury can be separated from tin by electrolysing 
the solution of their sodium sulpho-salts, p. 67. 

For the separation of mercury from arsenic, anti- 

D,nitiz.!.o,GoOglc 



I20 ELECTRO-CHEMICAL ANALYSIS. 

mony, and tin, when all are present in a solution, 
consult the method of Schmucker, p. 113. 



BISMUTH. 
At present there is no .satisfactory electrolytic 
method known for the separation of this metal from 
mercury, silver, and lead (consult Freudenberg, Z. f. 
phys. Ch,, 12, 97), Its separation from cadmium is 
effected in solutions containing free sulphuric acid 
(j-io c.c. of sp. gr. 1.09), p. 6g. This course will also 
serve to separate it from iron, manganese, zinc, nickel, 
cobalt, aluminium, chromium, uranium, magnesium, 
and the alkaline metals (p. 69). The method of Elias- 
berg (p. 68) may also be used for the separation of 
bismuth from zinc, nickel, cobalt, and uranium. In 
separating bismuth from those metals, the sulphides 
of which are soluble in alkaline sulphides, it is neces- 
sary to have the usual gravimetric course precede the 
electrolytic reduction. Consult method of Schmucker, 
p. 113. 

LEAD. 
The deposition of lead as dioxide upon the anode 
(p. 73) in the presence of at least five per cent, of 
nitric acid affords a method for its separation from 
mercury, silver, copper, cadmium, iron, chromium, 
aluminium, zinc, nickel, cobalt, uranium, the metals 
of the alkaline earths, and the alkaline metals. It 



o,Googlc 



SEPARATION OF METALS — SILVER. 121 

will be remembered, of course, that some of these 
metals separate as such upon the cathode simultane- 
ously with the lead upon the anode. Lead, in some 
respects, is much like manganese, from which it can- 
not be separated electrolytically. Its deposition re- 
quires no special description, as the conditions already 
described upon p. 73 are to be observed in the per- 
formance of the separations just indicated. Ivead,tin, 
antimony, and arsenic are separated as directed under 
the preceding heavy metals. Follow the ordinary 
gravimetric course. 

Lead dioxide, like manganese dioxide (p. 89), is 
not separated from solutions containing an excess of 
an alkaline sulphocyanide, and, if already precipitated 
as dioxide, will redissolve upon the addition of the 
sulphocyanide. 

SILVER. 
To separate silver and copper electrolytically, mix 
equal quantities of the two metals, in the form of 
nitrates, with four and one-half grams of potassium 
cyanide, dilute to 200 c.c. with water, and electrolyse 
with a current, giving 0,15-0.80 c.c. electrolytic gas 
per minute (Am. Ch. Jr., 12, 104}. As much as 0.2 
gram of silver will be deposited in 12-14 hours. The 
time limit can be reduced to 3-4 hours by heating 
the solution, while electrolysing, to 65° C. If desir- 
able, expose the filtrate containing the copper to the 
action of a stronger current (3 c.c. 0-H gas per min- 



o,Googlc 



122 ELECTRO-CHEUICAL ANALYSIS. 

ute); as soon as the excess of alkaline cyanide is 
decomposed, the copper will be deposited in a dense 
and brilliant coating. The analysis of a silver coin 
can be made by this method without any dif^culty. 
Thtf results will be very satisfactory. Proceed as 
directed (p. 114) in separating silver from cadmium. 
There is no known electrolytic method for the sepa- 
ration of silver from mercury. It is true both can be 
precipitated from a nitric acid solution (pp. 56, 75), 
their joint weight determined, after which the mer- 
cury can be expelled by heat and the silver residue 
be re-weighed. 

There is no electrolytic method known for the 
separation of silver from bismuth. The separation of 
silver from lead is made in a nitric acid solution (p. 
73). A similar solution is used to separate it from 
the metals of other groups. 

When antimony, tin, and silver are present together, 
digest their sulphides with sodium sulphide, which 
will bring the antimony and tin into a proper condi- 
tion to effect their separation electrolytically (p. 104). 
The insoluble silver sulphide is dissolved in nitric 
acid, and, after the excess of the latter is expelled, 
potassium cyanide is added in excess and the result- 
ing liquid electrolysed at 65° C. The silver is depos- 
ited as a dense coating, and may be washed with hot 
water. ' 

It is possible to separate silver from arsenic in the 
presence of three grams of potassium cyanide, pro- 

D,nitiz.!.o,GoOglc 



SEPARATION OF METALS — SILVER. 1 23 

viding the arsenic exists in the solution as an 
arsenate. 

A current giving 0.30 cc, electrolytic gas per 
minute will be sufficient for the metallic reduction. 
Determine the arsenic in the residual liquid by the 
usual gravimetric method (Am. Ch. Jr., 12, p. 
428). 

The course just described (above) for the separation 
of silver from copper will answer admirably for the 
same purpose with silver, zinc, nickel, and cobalt. 
Not more than three grams of potassium cyanide are 
required for 0.2 gram of each metal. The total 
dilution! should not be less than 200 cc, and the 
current not stronger than 0.3 cc. electrolytic gas per 
minute. 

In separating silver from tungsten and molybdenum 
the current should not exceed 0.7 cc. of electrolytic 
gas per minute. Use 1.5 gram of potassium cyanide 
for .2-3 gram of metal. The total dilution should be 
about 200 cc. When separating silver from platinum 
increase the cyanide to 2.5 grams, and the current to 
I cc. of electrolytic gas per minute ; while for the 
deposition of silver in the presence of osmium reduce 
the quantity of cyanide to 1.4 cc. of electrolytic 
gas. 

Palladium and silver cannot be separated electrolyt- 
ically in a cyanide solution. 

Much credit is due Classen and his co-laborers for 



o,Googlc 



I 24 ELECTRO-CHEMICAL ANALYSIS. 

valuable data upon the electrolytic separation of the 
following metals : — 



ANTIMONY FROM TIN. 
The sulphides (or residue from a solution of the 
metals) are placed in a weighed platinum dish, and 
covered with 60 c.c, of sodium monosulphide, to which 
is added one gram of sodium hydroxide. If imme- 
diate solution does not occur, apply heat, then cool_ 
Conduct a current of 1.5— 2.0 c.c. of electrolytic gas 
per minute through this mixture. When the reduc- 
tion is finished, pour off the liquid into a second dish. 
Treat the antimony deposit as already directed (p. 
106). To prepare the tin solution for electrolysis, pro- 
ceed as described (p. 103) for the conversion of the 
sodium into ammonium sulphide (Ber., 17, 2245 \ '^' 
1 1 10). 

ANTIMONY FROM ARSENIC. 

These metals, or compounds of the same, are evapor- 
ated to dryness with aqua regia, the residue dissolved 
in 2—3 c.c. of water ; concentrated sodium hydroxide is 
added so that there will be one gram of alkali present 
in the liquid, and finally add 60 c.c. of sodium mono- 
sulphide. Electrolyse as in the separation of anti- 
mony from tin (Ber. 19, 323), 

If antimony, arsenic, and tin are present together. 



I ai.:,.:,G00glc 



SEPARATION OF IRON FROM MANGANESE. 125 



the arsenic is expelled from their solution by the 
Fischer-Hufschmidt method (Ber., i8, ilio), and the 
separation of the tin and antimony made as already 
directed on the preceding page. 

In general analysis phosphoric acid is frequently 
precipitated as tin phosphate. The latter, of course, 
contains oxide of tin. Dissolve the precipitate In 
ammonium sulphide. On electrolysing the solution 
the tin is precipitated, and the filtrate will contain all 
the phosphoric acid ; this can be estimated in the 
usual way (Classen). By observing this suggestion 
the determination of the phosphoric acid in a separate 
portion of the material will not be required. 



Electrolytic methods for the separation of these 
metals are not either so numerous nor so thoroughly 
worked out as with the metals already considered. 
Their separation from the heavy metals has been out- 
lined under these, and it only remains to describe the 
courses which may be pursued with this group of 
metals when present together. 

Concerning the separation of iron from manganese, 
it should be remembered that objections have been 
offered to the suggestion of Classen (Ber., i8, 1 787), 
hence to obtain results at all satisfactory it is advisable 
to carry out the separation exactly as given by this 



o,Googlc 



r26 ELECTRO-CHEMICAL ANALYSIS. 

chemist : " 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 it is impossible to obtain a 

quantitative separation of the two metals, beca use the 
manganese dioxide carries down with it considerable 
quantities of ferric hydroxide. The complete sepa- 
ration of the metals is possible only when^the sega- 
ration of the dioxide is delayed till most of the .iron 
is^precipitated,," The electrolysis in the cold is not 
favorable; the large amount of ammonium carbonate, 
or ammonia formed in the decomposition of the ex- 
cessive ammonium oxalate, dissolves the precipitated 
dioxide. " The rapid dksociatj^orLof ammonium oxa- 
late when heated, however, gives a simgle ineans o£ 
delaying, or entir ely preventing, the formation of a 
m^ilganese precipitate during the electrolysis." The 
solution containing the two metals is treated with 5-6 
grams of ammonium oxalate, and while hot is acted 
upon with a current giving 15-20 c.c. of electrolytic 
gas per minute. Treat the iron deposit as directed 
on p. 91. Boil the liquid, poured off from the iron, 
with sodium hydroxide, to decompose the ammonium 
carbonate present, after which add sodium carbonate 
and a little sodium hypochlorite. The manganese 
is precipitated as dioxide, and finally weighed as the 
protosesquioxide. Nickel and manganese are sepa- 
rated from each other in a similar manner. Cobalt 
and zinc, when present with manganese, are separated 

Dinitizedo, Google 



SEPARATION OF IRON FROM ZINC. 12/ 

from it by a current of lO c.c. oxy-hydrogen gas per 
minute, acting in the cold. Oxalic acid is added 
toward the end of the reduction to redissolve any 
separated manganese dioxide. 

To separate iron from zinc, add 1-3 c.c. of a solu- 
tion of potassium oxalate (i : 3) and 3-4 grams of 
ammonium oxalate to their solution and electrolyse 
the liquid with a current liberating 10-12 c.c, electro- 
lytic gas per minute. The zinc is deposited first, and 
no difficulty is experienced, providing its quantity is 
less than one-third that of the iron present. Classen 
provides for this condition by adding a weighed 
amount of pure ferrous ammonium sulphate in excess. 
The same chemist precipitates iron and cobalt simul- 
taneously from their double oxalate solution (condi- 
tions as above), takes the combined weight of the 
metals, dissolves them in acid, and determines the iron 
by titration; the cobalt is found by difference. Nickel 
and iron are also deposited together (same as cobalt 
and iron) as an alloy, which is weighed, then dissolved 
in concentrated hydrochloric acid, the iron oxidized, 
and the ferric solution titrated with a stannous chloride 
solution. It will be observed that an electrolytic 
separation of cobalt from nickel is wanting. 

In the Monatskeft fur Ckemie,\^, 536, Vortmann 
writes as follows in regard to the separation of zinc 
from nickel r Add 4-6 grams of Rochelle salts to the 
solution of the two metals, then a concentrated solu- 
tion of sodium hydroxide. Electrolyse the mixture 



o^Googk 



I2i) ELECTRO-CHEMICAL ANALYSIS. 

with a current of N.Dmo = 0.3-0.6 ampere. The pre- 
cipitation of the zinc will be finished in a period of 2- 
4 hours. Pour off the alkaline liquid, wash the zinc 
deposit with water and alcohol ; dry at 100° C. 

Iron can be separated from nickel in the manner 
just described. 

To separate zinc from iron the same writer recom- 
mends adding potassium cyanideto the solution of the 
two metals until the precipitate formed at first has 
dissolved, then introduce sodium hydroxide. The 
iron is present in the solution as ferrocyanide, which 
in the presence of free alkali is not decomposed by the 
current. Avoid too large an excess of potassium 
cyanide, as it retards the separation of the zinc. The 
current should be N.Di^ = 0.3-0.6 ampere. 

To separate cobalt or nickel, or both of them, from 
iron, Vortmann oxidizes the iron by bromine to the 
ferric state, then adds 3-6 grams of ammonium sul- 
phate, and a moderate excess of ammonium hydroxide. 
Ferric hydroxide will, of course, be precipitated, but 
the author has discovered that its presence is not 
harmful, and that the precipitated cobalt or nickel will 
contain but traces of iron, which can be fully elimi- 
nated by asecond precipitation. The deposition of the 
cobalt or nickel will not require more than from 2-3 
hours, with a current of N.Dim ^= 0.4-o.S ampere. 

The writer would recommend the following course 
in separating the metals of this group: Separate the 
iron from the manganese, zinc, nickel, and cobalt by 



o,G(">oglc 



SEPARATION OF IRON FROM ZINC. 129 

precipitation with barium carbonate. Dissolve the 
iron precipitate in citric acid, and electrolyse the solu- 
tion according to the directions given upon page 92. 
The filtrate, containing the zinc, manganese, nickel, and 
cobait, together with a little barium salt, is carefully 
treated with just sufficient dilute sulphuric acid to re- 
move the barium. After filtering, electrolyse the 
filtrate in a platinum dish, connected with the anode 
of a battery yielding 3-5 c.c. of electrolytic gas per 
minute. A weighed piece of platinum foil will answer 
for the cathode. The manganese is deposited as di- 
oxide (p. 88) ; the other metals remain dissolved and 
can only be separated by one of the usual gravimetric 
methods. This course proved quite satisfactory in the 
analysis of the mineral franklinite,where, after having 
obtained the iron and manganese as described, the zinc 
was also determined electrolytically in the liquid 
poured off from the manganese deposit. If the solu- 
tion containing these two metals be very slightly acid 
with sulphuric acid, they can be precipitated simultane- 
ously — the zinc at the cathode, and manganese dioxide 
at the anode. 

Iron can be further separated, in citrate solution, 
from aluminium, chromium, and titanium (p. 92). The 
deposition should occur in a cold solution, with a cur- 
rent liberating 12 c.c. electrolytic gas per minute. 
This method will also serve to separate iron from 
chromium and phosphoric acid. The precipitation of 
iron as metal from an ammoniacal tartrate solution 



o,Googlc 



130 ELECTRO-CHEMICAL ANALYSIS. 

(p. 94) ajifords an excellent means of separating it from 
aluminium, chromium, and phosphoric acid. Classen 
separates iron, cobalt, nickel, and zinc from manganese, 
chromium, and aluminium by electrolysing their hot 
oxalate solution in the presence of a large excess of 
ammonium oxalate. The first four are deposited as 
metals, while the manganese dioxide upon the anode 
has carried with it some chromium, and should be dis- 
solved, and the manganese reprecipitated by sodium 
hydroxide and sodium hypochlorite (p. 126). The 
main solution from the metals is digested until the 
excess of ammonia is expelled, when the aluminium 
hydroxide is filtered off; the chromate solution, then 
reduced with hydrogen sulphide in the presence of an 
acid, is precipitated with ammonium hydroxide. In 
all case s where it is necessary to add oxalic acid to re- 
dissolve the aluminium hydroxide, or manganese 
dioxide, the acid should be introduced without the 
interruption of the current. When phosphoric acid is 
present with the iron and manganese it will be found 
in the liquid (oxalate) from which the metals have 
been previously precipitated, and may be removed as 
ammonium magnesium phosphate. 

Drown and McKenna have endeavored to utilize the 
method described p. 93 for the separation of iron from 
other elements. The conditions favorable for the 
deposition of the Iron they found unfavorable for its 
separation from manganese. They experienced no 
difliculty in separating iron from aluminium or iron 



o,Googlc 



SEPARATION OF GOLD PROM COPPER. I3I 

from phosphoric acid. To determine iron in the 
presence of aluminium in steel they recommend the 
following procedure : — 

" Dissolve 5-10 grams of iron or steel in sulphuric 
acid, evaporate until white fumes of sulphuric anhy- 
dride begin to come off, adJ water, heat until all the 
iron is in solution, 61ter off the silica and carbon, and 
wash with water acidulated with sulphuric acid. 
Make the filtrate nearly neutral with ammonia, and add 
to the beaker in which the electrolysis is made about 
100 times as much mercury as the weight of iron or 
steel taken. The bulk of the solution should be from 
300-500 c.c. Connect with battery or dynamo in such 
a way that about two amperes may pass through the 
solution over night. . . When the solution gives 
no test for iron it is removed from the beaker with a 
pipette while the current is still passing." The alumi- 
nium is determined in this filtrate (Jr. An. Ch., 5, 627). 



GOLD. 

The fact that this metal can be deposited electrolyti- 
cally from its solution in sodium sulphide (p. lOi) 
affords a means of separating it from arsenic, molyb- 
denum, and tungsten. The conditions described 
under the determination of the metal will serve in 
these separations. 

To separate gold from copper add i ^-3 grams of 
potassium cyanide to the solution containing equal 



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132 ELECTRO-CHEMICAL ANALYSIS, 

quantities of the two tnetats; dilute to 150 ex., and 
electrolyse with a current of 0.4-0.8 c.c. electrolytic 
gas per minute. The same conditions will prove sat- 
isfactory in the separation of gold from cobalt, nickel, 
and zinc. 

In separating gold from platinum, in cyanide solu- 
tion, increase the current to i c.c. electrolytic gas, 
and the quantity of potassium cyanide should equal 
2}i grams for 0.15 gram metal. The separation of 
gold from osmium was made as follows: 0.1277 gram 
gold, 0.1500 gram osmium, 0.75 gram potassium. 
cyanide, with a dilution of 150 c.c. and a current of 
2.4 c.c. electrolytic gas. 



THE PLATINUM METALS. 
The separations in this group of metals are not 
numerous. Palladium can be separated from iridium 
by means of the method described on p. 98 for the 
determination of palladium. Platinum can be sepa- 
rated from iridium in similar manner. Although 
rhodium can be fully precipitated from an acid phos- 
phate solution (p. 99), it cannot be thus separated from 
iridium. 



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OXIDATIONS BY MEANS OF CURRENT. I33 

3. DETERMINATION OF NITRIC ACID IN 
THE ELECTROLYTIC WAY. 

Literature. — V or 1 man a, Ber., 23, 2798. 

To the solution of the nitrate, in a platinum dish, 
add a sufficient quantity of copper sulphate. Acidu- 
late the liquid with dilute sulphuric acid and electro- 
lyse with a current of 1-2 c.c. of electrolytic gas per 
minute. When the deposition of the copper is com- 
pleted, pour off the liquid, reduce it to a small volume, 
and distil off" the ammonia in the usual manner. The 
quantity of copper sulphate added should be deter- 
mined by the quantity of nitric acid present. It 
potassium nitrate is the salt undergoing analysis, add 
half its weight in copper sulphate. 



4. OXIDATIONS BY MEANS OF THE 

ELECTRIC CURRENT. 
Literature. — Smith, Ber., »3, 2176; Am. Ch. Jr., 13, 414; 
Frankel, Ch. News, 65,54. 

When natural sulphides, e.g., chalcopyrite, marca- 
site, etc, are exposed to the action of a strong current 
in the presence of a sufficient quantity of potassium 
hydroxide their sulphur will be quickly and fully 
oxidized to sulphuric acid (Jr. Fr. Ins., April, 1889; 
Ber., 22, 1019). The metals (iron, copper, etc.) origi- 
nally present in the mineral separate as oxides and 



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134 ELECTRO-CHEMICAL ANALYSIS. 

metal on dissolving the fused alkaline mass in water. 
This method of oxidation eHminates many other 
disagreeable features of the old methods. Its rapidity 
and accuracy entitle it to the following brief descrip- 
tion ; — 

Place about 20 grams of caustic potash in a nickel 
crucible l % inches high and i yi inches wide. Apply 
heat from a Bunsen burner until the water has been 
almost entirely expelled, when the flame is lowered so 
that the temperature is just sufficient to retain the 
alkali in a liquid condition. The crucible is next 
connected with the negative pole of a battery, and the 
sulphide to be oxidized is placed upon the fused 
alkali. As some natural sulphides part with a portion 
of their sulphur at a comparatively low temperature, 
it is advisable to allow the alkali to cool so far that a 
.scum forms over its surface before adding the weighed 
mineral. 

The heavy platinum wire, attached to the anode, 
extends a short distance below the surface of the 
fused mass. When the current passes a lively action 
ensues, accompanied with some spattering. To pre- 
vent loss from this source, always place a perforated 
watch crystal over the crucible. After the current 
has acted for 10-20 minutes interrupt it. When the 
crucible and its contents are cold place them in about 
200 c.c. of water, to dissolve out the excess of alkali 
and alkaline sulphate. Filter. Invariably examine 
the residue for sulphur by dissolving it in nitric acid 



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OXIDATIONS BY MEANS OF CURRENT. I3S 

and then testing with barium chloride. The alkaline 
filtrate is carefully acidulated with hydrochloric acid, 
and after digesting for some time is precipitated with 
a boiling solution of barium chloride. When the 
hydrochloric acid is first added, care should be taken 
to observe whether hydrogen sulphide or sulphur 
dioxide is liberated. If the oxidation is incomplete 
sulphur also makes its appearance as a whits tur- 
bidity. The caustic potash employed in these oxida- 
tions should always be examined for sulphur and 
other impurities. As it is difficult to obtain alkali 
perfectly free from sulphur compounds, a weighed 
portion should be taken and its quantity of sulphur 
deducted from that actually found in the analysis. 

The arrangement of apparatus employed in the 
oxidations just outlined is represented in Fig. 27. 
The crucible A is supported by a stout copper wire 
bent as indicated, and held In position by a binding 
screw attached to the base of a filter stand. The arm 
of the latter carries a second binding screw holding 
the platinum anode in position. While the platinum 
rod is generally the positive electrode, it is best to 
make it the negative pole for at least a part of the 
time during which the current acts. This is advisable 
because in many of the decompositions metals are pre- 
cipitated upon the sides of the crucibles, and can 
readily enclose unattacked sulphide, so that by re- 
versing the current (the poles) any precipitated metal 
will be detached, and the enclosed sulphide be again 

D,nitiz.!.o,G(")Oglc 



136 ELECTRO-CHEMICAL ANALYSIS. 



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OXIDATIONS BY MEANS OF CURRENT. 1 37 

brought into the Held of oxidation. Cinnabar is a 
sulphide which has a tendency to mass together, and 
it could only be decomposed and its sulphur thor- 
oughly oxidized by reversing the current every few 
minutes. To reverse the current use the contrivance 
C; this is nothing more than a square block of wood 
fastened to the top of the table, T, by a screw or nail. 
The four depressions {x) in it contain a few drops of 
mercury, into which the side binding screws (a) pro- 
ject. The mercury cups are made to communicate 
with each other by a cap of wood, D, carrying two 
metallic wires, which pass through it and project a 
slight distance on its lower side. By raising the cap 
and turning it so that the wires are vertical (l)of 
horizontal (a»-+-), the crucible or the platinum wire 
extending into the fused mass can be made the anode 
or cathode in a few seconds, .fis a Kohlrausch am- 
peremeter {Fig. 17) and R the resistance frame 
(Fig. IS). 

Storage batteries furnish the most satisfactory cur- 
rent for work of this character. In the sketch the 
cells stand beneath the table ; the wire from the anode 
passes through a hole in the table-top, and is attached 
to one of the binding posts of the block, C, while the 
positive wire is attached to a binding post at the end 
of the table-top, and from here it passes to the resist- 
ance frame, R, where it is fixed by an ordinary metal- 
lic clamp. 

For most purposes the strength of current need not 

D,nitiz.!.o,GoOglc 



138 ELECTRO-CHBHiCAL AHALYSIS. 

exceed 1-1.5 amperes per minute; however, it may 
be necessary occasionally to increase it to 4 amperes 
perminute. Pyrite.FeSu, is even then not completely 
decomposed. This particular case requires the addi- 
tion of a quantity of cupric oxide equal in weight to 
the pyrite and a current of the strength last indicated 
before all ofits sulphur is fully converted into sulphuric 
acid. 

By increasing the number of crucibles it will be pos- 
sible to conduct at least from four to six of these de- 
compositions simultaneously, and by using a volume- 
tric method for estimating the sulphuric acid, a sul- 
phur determination can easily be executed in forty 
minutes. 

Experience has demonstrated that 0.1-0.2 gram of 
material will require about 20-25 grams of caustic 
potash. 

Dr. K. Frankel has conclusively demonstrated 
that the arsenic contained in metallic arsenides, e^.^ 
arse no pyrite, rammelsbergite, etc., can be entirely 
converted into arsenic acid by the above method. 
He recommends conditions analogous to those em- 
ployed with the sulphides. 

The current will also completely decompose the 
mineral chromite. For a quantity of material varying 
from 0.1-0.5 gram use from 30-40 grams of stick 
potash and a crucible slightly larger than that recom- 
mended in the oxidation of sulphides and arsenides. 
The current should not exceed one ampere. Thirty 

D,nitiz.!.o,GoOglc 



OXIDATIONS BY MEANS OF CURRENT. 1 39 

minutes will be sufficient for the oxidation. At the 
expiration of this period allow the mass to cool, take 
up in water, filter off from the iron oxide, acidulate the 
filtrate with sulphuric acid, add a weighed quantity of 
ferrous ammonium sulphate, and determine the ex- 
cess of iron with a standardized bichromate solution, 
using potassium ferricyanide as an indicator. Upon 
oxidizing 0.4787 gram chromiteby the above process 
51.77 per cent, chromic oxide was obtained, while a 
second sample of the same mineral, oxidized by the 
Dittmar method, gave 51.70 per cent, chromic oxide. 
The writer believes that if the chromium be estimated 
volu metrically the chromium content in a chrome ore 
can be obtained in an hour. 



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INDEX. 



ACCUMULATOR, a; 
Amperemeler, 34, 3S, 36 



uipjMt.i.a, 113 

jilverlua ' 
i1d, 134 
Anenic, delemination of, ic? 

BATTERY, Bunsen, 19 
LKllDcb'j, 16 

Mcidinger, 17 
BinnuUi, dctcrminiiiiiHi of, 6B-71 



^ leparalion from ilumlaium, inii- 
mon^. anenic, iHimutk, cobalt. 



oEmmnV/niDlybdcDuin, and 

cSihode%' 

ChiomiM, oiidulon of, 13B, im 

Cobalt, dcterminalwn of, »i-^ 

copp«, .^9. 110 
iron, uj, ii8, 159 

lilvct, 113 
Copper, deunninaiion of, 5)-<' 

oabUli^Tnin, 'leaS', nickel, 



rjYNAMOS. 91 

CLECTROLYSlS,definei 

GOLD, deierminalion of, 
separation from aiMUK 



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INDEX. 

Mercury, d 



H' 

IRON,< 

1 ICPUT 



I EAI 






mergPH', "> 
nickel .a;, laB 
phcAphoiic acic 



copper, 108, ■ 



lion of, 6;-6a 



Motybdenum, dewrminaiion of, loo 

W ICKEL, delermiiiBtioii of, B4-aT 
cadiKium. iM, >>5 



^ Osmium, 41 

PALLADIUM, deienninalion of, 9S 
sepa radon from ir^ium, 139 

Platinun, doteralnalLoD of, 96-97 
nuupboJ 

RHODIUM, d 
R«i>tu.ce 



SILVER, delermlnalioD of, ■n-Ji 
HpacBtion fmn Aluminium, ™pper, 
iron, lesd, manguKtc, 



pluTn'um.matybdenuni ,aDd 
.xidationof, 1J3-13B 

DinitizetiovGoOglc 



r ThiUmm, d 
ThermCHSleclric pili.ii-i. 
Tiii,d.H!Ttiiiniiii™of, loj.ioj 

IJRANIlIM,deIeiinimlionof,94 



INDEX. 

V%I(i,.,.„ 

7mC, diMrmiiution of, 78-84 



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Fuel and its Applications, 

BVE. J. MILLS, d.s...i'.i<.3.,andF, J. ROWAN, e.E., ASSISTED 
BY OTHERS, INCLUDING Mh. F, P. DEWEY, OF THE 
SMITHSONIAN INSTITUTE, WASHINGTON, D. C. 



7 PLATES AND 607 OTHER ILLUSTRATIONS. 



Royal Octavo, Pages, xx + Soz. Handsome Cloth, $7.50. 
Half Morocco, Jg-oo. 



CHEMICAL TECHNOLOGY; or, chemistry in ns 
application to arts and manufactures, edited by 

CHARLES EDWARD GROVES, i-.R.c, *hd WILLIAM THORP, n s. 



There is no other item of expense that enters more largely 
into the cost of producing than that of Fuel. The importance, 
therefore, of being acquainted with the latest and most economi- 
cal methods of usine and applying it is apparent, and in no 
other branch of manufacturing has there been greater advance- 
ment made than in our knowledge of combustion, and the 
economical distribution and utilization of heat. 

The work has been prepared with great care, so that every- 
thing of value pertaining to the subject might receive proper 
treatment. It appeals generally to all interested in the use of 

— . [OVER.) 

p. BLAKJSTOir, BOn ft CO., Soientiflo and Hsdioal FnblUliera, 
laii WalDut Stieet, phJUdelphla. 



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a MILLS ON FUEL AND ITS APPLICATIONS. 

Fuels, and specially to the manufacturers of Iron, Steel and 
their various products : tools, stoves and heating apparatus of 
all kinds, steam and gas fittings, etc., etc.; the manufaaurers 
and users of Coke, Illuminating Gas, Charcoal, Petroleum and 
other Minor Fuels. The Sections on Heat, its theory and ap- 
plication ; on Blast and other Furnaces ; the Analytical Tables, 
etc.; the Relative Values of Coal and other Fuels, will be 
found of great use in the preparation of estimates, etc. 

It is not too much to say that many patents owe their exist- 
ence to ignorance concerning what has been done in the matters 
of which they treat ; the historical information contained in this 
volume will therefore be of great use by saving much laborious 
searching through Patent OfGce records. 

SYNOPSIS OF CONTENTS. 







Domestic Heating. 






Heating by Meaiis of Hot . 


Tu»f or Pe,t. 




Kot.blaai Stoves. 


Coal. 




Heatine by Water and Stei 


Effect of Hc*t OD Fu.li. 




Application of Fuel to Vapor 


Wood Charcoal. 




VapoTiiation. 


Coke. 






DisiillatioD of Peat. 




DiBtiUalion. 


ArMficial or Patent Fuel, Briqi 




1. Drying, 






Ovens for Baking Bread. 


Liquid Fuel. 




Brick aod Porcelain Kilns. 


Minor Fuels. 




Furnaces. 


Theory of Heat. 






Flame. 




The Practical Effect of Fu. 


On the Application of Fuel. 




Analytical Tables of Variou 
of Coal and Other Fuel. 


Appendii— On the Qeneri 


ilPrii 


iciples of Coal Washing. Ind 



19-A complete List of Contents, the Preface and a List of 
the Plates and 607 Illustrations will be sent, free, upon appli- 



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MILLS ON FUEL AND ITS APPLICATIONS. B 

RECOMMENDATIONS FROM VARIOUS SCIENTIFIC 
AND TRADE JOURNALS. 



From ike Journal of the Franklin IngUtute. 

" This splendid royal octavo of 8oj pages ia a work of the highest 
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"It is without doubt the most useful and comprehensive book in the 
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of every intelHgeot and progressive manufacturer." 

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founded on that written by Richardson and Renolds, and subsequently 
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1 MILLS ON FUEL AND ITS APPLICATIONS. 

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