ELECTRO-ANALYSIS
SMITH
ELECTRO-ANALYSIS
BY
EDGAR F. SMITH
M
PROFESSOR OF CHEMISTRY, UNIVERSITY OF PENNSYLVANIA
FOURTH EDITION, REVISED AND ENLARGED
WITH FORTY-TWO ILLUSTRATIONS
OF T
UNIVEF
'F.-
PHILADELPHIA
P. BLAKISTON'S SON & CO.
1012 WALNUT STREET
1907
COPYRIGHT, 1907, BY P. BLAKISTON'S SON & Co.
PREFACE TO FOURTH EDITION.
It appeared advisable to omit from this edition the sev-
eral sections relating to the various sources of the current,
particularly those in which the older forms of battery were
described. It is true that the use of these sources of elec-
tric energy will probably continue, but their construction,
treatment and efficiency are so well understood that any
particular information about them is best obtained from
publications devoted especially to them.
The greater portion of the new material, presented in
the pages which follow, refers to the rapid precipitation
and separation of metals, the use of a mercury cathode
with rotating anode and the employment of a new cell in
the determination of cations and anions. To give this
material the space it so abundantly deserves suggested the
elimination of the minute directions found in the various
electrolytes used with stationary electrodes, "but it devel-
oped that beginners in electro-analysis learn much from
the execution of details, the handling of deposits and other
points which arise constantly in work of this character.
Further, there will always be persons who, from prefer-
ence or from the lack of facilities to carry out the newer
methods, will make determinations and separations with
stationary electrodes. Indeed, these earlier methods con-
stitute a fundamental step in the development of analysis
through the agency of the current, and are therefore re-
tained in their original forms, except where experience has
recommended alterations. So long as the time factor con-
174618*
VI PREFACE
tinues to be of no moment the older procedures will appeal
to the analyst.
It may be stated that the rapid methods of analysis set
forth in detail in this text, including those in which the
mercury cathode plays an important role, have been sub-
jected to rigorous tests in this laboratory and have invari-
ably brought success to all working with ordinary care.
The section describing the determination of cations and
anions cannot fail to excite interest and inquiry. That
the estimation, for example, of barium and chlorine, in
barium chloride, may be made in an hour or less, while
hours would be required by time-honored methods, will
naturally lead one to pause. The neatness and accuracy
of such determinations also recommend them. The deter-
mination of the ferro- and ferri-cyanogen and other anions
indicates still greater possibilities in the application of the
current to analysis.
The very latest proposals regarding the value of graded
potential in separations and the possibility of effecting
organic combustions by means of the electric current re-
ceive ample consideration.
The paragraphs on theoretical considerations will throw
much light upon the deportment of metals in solution and
assist in explaining many heretofore obscure reactions.
Confident that the latest advances in electro-chemistry
will win many additional friends to this most interesting
field of investigation, these prefatory observations may be
concluded with an acknowledgment of great indebtedness
and profound gratitude to the many students and friends
who have shared in this particular study and made thereby
possible the appearance of the present volume.
S.
THE JOHN HARRISON
LABORATORY OF CHEMISTRY, 1907.
TABLE OF CONTENTS.
INTRODUCTION I
SOURCES OF ELECTRIC CURRENT Magneto-Electric
Machines, Dynamos, Thermopile, Storage Cells. 2-5
REDUCTION OF THE CURRENT Rheostats, Resistance
Frame , 5-9
MEASURING CURRENTS Voltameter, Amperemeter.,
An Electro-chemical Laboratory 9~ J 9
HISTORICAL SKETCH 1 9~3 2
THEORETICAL CONSIDERATIONS 3 2 ~4 l
RAPID PRECIPITATION OF METALS IN THE ELECTRO-
LYTIC WAY 4!~55
USE OF MERCURY CATHODE 55-63
SPECIAL PART.
1. DETERMINATION OF METALS 63-181
2. SEPARATION OF METALS 181-274
3. ADDITIONAL REMARKS ON METAL SEPARATIONS. . 274-285
4. DETERMINATION OF THE HALOGENS IN THE ELEC-
TROLYTIC WAY 285-289
5. DETERMINATION OF NITRIC ACID IN THE ELECTRO-
LYTIC WAY 289-296
6. SPECIAL APPLICATION OF THE ROTATING ANODE
AND MERCURY CATHODE IN ANALYSIS 296-314
7. OXIDATIONS BY MEANS OF THE ELECTRIC CURRENT 314-319
8. THE COMBUSTION OF ORGANIC COMPOUNDS 3 I 9~33
INDEX 331-336
vii
ABBREVIATIONS.
AM. CH The American Chemist.
AM. CH. JR = American Chemical Journal.
AM. JR. Sc. AND AR. American Journal of Science and Arts.
AM. PHIL. Soc. PR. = Proceedings of the American Philosophical Society.
ANN = Annalen der Chemie und Pharmacie.
BER = Berichte der deutschen chemischen Gesellschaft.
BERG-HUTT. Z = Berg- und Hiittenmdnnische Zeitung.
B. s. CH. PARIS . . . . Bulletin de la Societe Chimique de Paris.
CH. N = Chemical News.
CH. Z = Chemiker-Zeitung.
C. R = Comptes Rendus.
DING. P. JR Dingier s Polytechnisches Journal.
ELEKTROCH. Z = Elektrochemische Zeitschrift.
G. CH. ITAL Gazetta chimica italiana.
JAHRB = Jahresbericht der Chemie.
J. AM. CH. S Journal of the American Chemical Society.
JR. AN. CH Journal of Analytical and Applied Chemistry.
JR. F. PKT. CH = Journal fur praktische Chemie.
JR. FR. INS = Journal of the Franklin Institute, Phila.
M. F. CH = Monatsheft fur Chemie.
PHIL. MAG = Philosophical Magazine.
WIED. ANN = Wiedemann's Annalen.
Z. F. A. CH = Zeitschrift fur analytische Chemie.
Z. F. ANG. CH = Zeitschrift fur angewandte Chemie.
Z. F. ANORG. CH. . . = Zeitschrift fur anorganische Chemie.
Z. F. ELEKTROCHEM. = Zeitschrift fur Elektrochemie.
Z. F. PH. CH = Zeitschrift fur physikalische Chemie.
Vlll
UNIVERSITY
.
ELECTRO-ANALYSIS.
INTRODUCTION.
Many chemical compounds are decomposed when exposed
to the action of an electric current. Such a decomposition
is called Electrolysis. The substance decomposed is termed
an electrolyte. The products of the decomposition are the
anions and cations, or those ( i ) which separate at the anode,
the positive electrode or pole (-)- P), and (2) those sepa-
rating at the cathode, the negative electrode or pole ( P)
of the source of the electric energy.
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.
This method of analysis analysis by electrolysis has
been designated electro-chemical analysis or, better, Electro-
analysis. It is especially inviting, since it permits of clean,
accurate and rapid determinations where the ordinary meth-
ods yield unsatisfactory results. This statement will at once
be confirmed on recalling the gravimetric methods usually
employed in the estimation of copper, mercury, cadmium,
bismuth, tin, or almost any metal.
ELECTRO-ANALYSIS.
i. SOURCES OF THE ELECTRIC CURRENT.
The electric energy required for quantitative analysis has
been variously derived from batteries of well-known types
(see Ayrton's Practical Electricity), magneto-electric ma-
chines, dynamos (see Oettel's Electrochemical Experi-
ments), thermopiles (Z. f. a. Ch., 15, 334; Z. f. ang. Ch.
(1890), Heft 18, 548; Electrotechnische Zeitschrift, u,
187; Z. f. a. Ch., 14, 350; 17, 205; Ding. p. Jr., 224,
267; Z. f. a. Ch., 18, 457; 25, 539), and electrical accumu-
lators or storage cells, which unquestionably are the best
source. The current from them is constant. Cells of this
kind can be charged from primary batteries, or, better, by
means of a dynamo or thermopile. In any community
where electric lighting 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 number of
cells could be kept in condition for work. The iron esti-
mations required by any establishment 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. Consult the following
literature upon storage batteries :
Wied. Ann., 34 (1888), 583 ; Proceedings of the Royal Society, June 20,
1889 ; -Transactions of Am. Inst. Mining Engineers (Electrical Accumula-
tors, Salom), Feb., 1890. Elektrotechnische Zeitschrift, Jahrg. 1890;
Heppe, Akkumulatoren fur Elektrizitat, Berlin, 1892; Z. f. ang. Ch.,,
1892, p. 451 ; Ch. Z., Jahrg. 17, 66; Die Akkumulatoren, Elbs, 2te Auflage,
1896, Leipzig; Introduction to Electrochemical Experiments, F. Oettel
(translation by Smith), Philadelphia, 1897; Pfitzner, Die elektrischen
Starkstrome, Leipzig; Dolezalek, Theory of the Lead Accumulator.
SOURCES OF THE ELECTRIC CURRENT. 3
Stillwell 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 communi-
cation, in which is emlxxlied all that is essential for those
H
H
<
a
desirous of adopting this method, will be found in the fol-
lowing quotation : " The whole apparatus can be made from
a few yards of insulated copper wire, some 16 wooden lamp
sockets, and blackened lamps, say six 5o-candle power, three
4 ELECTRO-ANALYSIS.
32-candle power, six 24-candle power, and six i6-candle
power. . . . 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 necessary
if ordinary currents are required. If, however, two or three
different determinations, or some requiring very small cur-
rents, 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 represent the proper position of
the solutions to be electrolyzed by these side currents. By
this arrangement three unlike determinations can be simul-
taneously 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 elec-
trolyzed." (Jr. An. Ch., 6, 129.) Any other arrangement
can be adopted. That just described can be adjusted to the
parallel system.
The current may be derived from an Edison three-wire
system or from any other incandescent system.
See Herlant, Bull, de TAssoc. beige des Chim., 18, 232.
Hart has devised a resistance frame to be used when the
electric light current is employed for electrolytic purposes.
REDUCTION OF THE CURRENT. 5
It is simpler in construction than that described in the pre-
ceding paragraph. Particulars in regard to it can be ob-
tained from Baker & Adamson, Easton, Pa.
2. REDUCTION OF THE CURRENT.
It is often necessary to reduce strong currents. Persons
acquainted with practical physics will promptly suggest the
FIG. 2.
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 from
time to time. A few of these later appliances may be
mentioned :
ELECTRO-ANALYSIS.
The current may be sent through a saturated solution
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 b (Fig. 2), and in the next
from b to a. " The rod b, with one zinc pole, is pushed
toward the zinc pole a, until the current reaches the desired
FIG. 3.
strength." It is 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. 3) (Ber., 21, 359). In this apparatus the current
enters at a, travels the German silver resistance AT, and
returns through b to the battery. In the performance of
electrolytic depositions the platinum vessels, serving as nega-
tive electrodes, may be connected with any one of the bind-
ing-posts from i to 20. This makes it possible for the
analyst to execute eight different determinations at the same
time. To show the influence of this apparatus, a current
from five Bunsen cells, generating 68 c.c. of oxyhydrogen
REDUCTION OF THE CURRENT.
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 amperes; at 3, 2.085 amperes; at 4, 1.911 amperes,
etc., until at 20 it was only 0.098 of an ampere.
To better understand these figures it should be remem-
bered that an ampere equals 10.436 c.c. of oxyhydrogen gas
per minute, or it is equivalent to a current which will pre-
cipitate 19.69 mg. of metallic 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. Figs. 4 and 5 rep-
resent other forms of convenient and helpful rheostats.
FIG. 4.
FIG. 5.
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, meas-
uring in all about 500 feet (Fig. 6). With the binding-
8
ELECTRO-ANALYSIS.
posts at a and b, and a simple clamp, it is possible to throw
in almost any resistance that may be required. It answers
all practical purposes.
FIG. 6.
LITERATURE. v. Klobukow, Jr. f. pkt. Ch., 37, 375 ; 40, 121 ; Oettel's
Electrochemical Experiments (Smith), P. Blakiston's Son & Co., Phila.
MEASURING CURRENTS.
3. MEASURING CURRENTS, VOLTAMETER,
AMPEREMETER.
In every analysis by electrolysis it is advisable that the
strength of the acting current should be known. The Bun-
sen voltameter may be used for this purpose. Voltameters
of this description are, however, only in rare cases adapted
for current measurement by introduction into the circuit.
To read them the current must generally be interrupted, and
they augment the resistance of the circuit to a marked
degree, hence many chemists substitute a galvanometer
(tangent or sine) for the voltameter. The deflection of the
needle by the current measures the strength of the latter.
" In order to express in terms of chemical action the deflec-
tion 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 electrolytic gas (reduced to o and
760 mm. pressure) which is produced in a minute. Plac-
ing the volume equal to v, the quotient ^- a gives the
standard value for the galvanometer. If this standard
value is denoted by R, the strength, I, of a current which
produces the deviation a is I = R tan. a."
The writer has found the amperemeter of Kohlrausch
very satisfactory, especially in cases where strong currents
are employed. In this instrument the current travels
through an insulated wire surrounding a bar of soft iron.
The latter, in its magnetized state, attracts a needle or indi-
cator and causes it to move over a vertical, graduated scale
(in amperes), and. its deflection gives at once the strength
of the current in amperes. The Weston milliamperemeters
and ammeters will also prove most valuable in this connec-
tion.
IO ELECTRO-ANALYSIS.
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 unpleasant difficulties. It is neces-
sary to know just what energy is required, and then so
regulate the current that the same is approximately main-
tained throughout the entire determination.
When metals were first determined electrolytically no
attention was given to certain very important factors.
" Strong " and " feeble " currents, or currents from a two-
cell bichromate battery, or five large Bunsen cells, etc., were
indicated. Measuring instruments were seldom used.
Rarely was anything said of the size of the cathode upon
which the metal was deposited, or of the forms of the anode,
the degree of dilution of the solution, and similar facts.
Confusion naturally arose and contradictory statements of
one kind and another were numerous. But in this, as in
all other questions where there was a real desire to arrive
at the truth, honest experiment soon pointed the way in
which changes were necessary and also demonstrated the
conditions to be observed in order that satisfactory results
might be obtained. Probably then, as at present, the metal
depositions were mainly made in platinum dishes, or upon
cylinders or cones. These receptacles, as well as the vari-
ous anode forms, will receive thorough consideration later.
It is the purpose of the writer at this point to merely empha-
size the most essential features in an electrolytic determina-
tion or separation. Hence note :
i. The current density. To this end the inner surface
of the platinum dish in which the electrolysis is made should
be known in cm 2 ; its contents, too, should be given in cm 3
for various heights. N.D 100 is the normal density of the
MEASURING CURRENTS. I I
current; this is equivalent to the current strength for 100
cm 2 of the electrode surface. The density (D) therefore
is dependent upon the current strength, as well as upon the
surface (E) of the electrode upon which the metallic deposit
is precipitated, i. e., D ^.
When the surface upon which the metal is deposited
equals E, the corresponding current strength can be deduced
from the formula C (N.D 100 ) . See, further, Miller
and Kiliani, Lehrbuch der analyt. Chemie, 4th ed., pp.
17-24.
2. The potential across the poles, the pole pressure,
which is best determined by means of a Weston voltmeter
(p. 64). This is a very important factor. A number of
interesting separations have been made by carefully regu-
lating the pressure voltage. See Z. f. ph. Ch., 12, 97;
also p. 32.
3. The form of the anode whether a flat spiral, a disk
of platinum, or a smaller perforated dish, suspended in the
electrolyte should also be observed, as well as its distance
from the cathode.
4. The total dilution of the electrolyte and its tempera-
ture are items of value.
5. The ammeter and voltmeter should always be in the
circuit.
Under the individual metals these points will be taken
up more fully. By strict adherence, however, to these car-
dinal features no one need fear the outcome. It will in
every way be satisfactory.
As the importance of electro-analysis has become evident,
there has been marked improvement in the various forms
of apparatus used in this work, and increased facilities for
the same are noticed on all sides. In every well-appointed
laboratory provision is made for this field of study, and in
12
ELECTRO-ANALYSIS.
certain institutions rooms are set aside and especially equip-
ped to carry out such work. Here at the University of
Pennsylvania, where electro-analysis was practiced as early
as 1878, with no special appointments and with the most
primitive forms of apparatus, there has been a gradual evo-
lution and development in apparatus and facilities according
to demands and with increased knowledge, until recently an
installation has been made for this as well as for other lines
of work in electro-chemistry, which is characterized by great
completeness and such simplicity that a brief sketch of the
plant may be well introduced here.
AN ELECTRO-CHEMICAL LABORATORY.
This laboratory will accommodate at least sixteen stu-
dents, working continuously. The room available for this
purpose (Fig. 7) is fifteen feet by twenty-six feet, thus
FIG. 7-
ELECTRO-CHEMICAL LABORATORY,
MEASURING CURRENTS. 13
affording each individual three feet by twenty inches of
table space.
Storage cells supply the energy. Those in use have a
capacity of 120 ampere-hours, with a normal discharge rate
of 15 amperes and a maximum rate of 30 amperes. The
compartments, indicated at the end of the room, contain
BATTERY ROOM.
two groups of twenty-four cells each. They supply their
respective sides of the room. They are supported on racks
of four shelves each, six cells per shelf. Each shelf is
thoroughly paraffined and a half-inch layer of ground quartz
is placed around the jars. Fig. 8 shows one of these com-
partments with the lead wires and cut-outs for each cell.
The switchboards are three in number, two of them each
controlling the six places on their respective sides of the
ELECTRO-ANALYSIS.
room, and the third controlling the four places in the centre.
The face of one of these boards is shown in Fig. 9, the
letters on the face referring to the working tables controlled.
FIG. 9-
DISTRIBUTING BOARD.
The switchboard on the east side of the room consists of
a slab of enameled slate twenty-four by thirty-four inches,
one inch thick, and contains, for each of the six outlets to
be controlled, one circle of twenty-five contact pieces, and
has two spring levers, insulated from each other and mov-
MEASURING CURRENTS. 15
ing about a common centre, sweeping over them. The con-
tact blocks are numbered consecutively from o to 24 and a
stop is provided to prevent the levers from sweeping past
the zero. Cell No. i is connected between blocks numbered
o and i in each of the six circles, cell No. 2 between blocks
numbered i and 2, and so on for the remainder of the
twenty-four cells in that group, so that all blocks similarly
numbered on the one board are connected together, and but
a single wire leads from the six similarly numbered blocks
to the junction between two cells. In this lead is provided
the usual fuse. The circles are lettered A, B, C, etc., con-
secutively, corresponding with the letters at the outlets to
be controlled.
Should the operator at the outlet E, for instance, need
two cells, he goes to this board, and finding that the cells
from the twelfth cell forward are not being used in any of
the circles, he places one of the levers on contact block No.
12 and the other one on No. 14. There is thus very little
chance of doing anything wrong, or for persons to inter-
fere with one another, because there is no necessity to use
the same cells, and at a glance one can observe which cells
are in use. Fig. 10 shows the electrical connections from
one of these distributing boards to the cells and outlets on
the working tables. The levers themselves are too narrow
at their outer ends to reach across from one block to an-
other, to prevent short-circuiting the cells, so they are pro-
vided with fibre extensions on each side to prevent their
falling between the blocks, and also to prevent their making
contact with each other..
The switchboard on the west wall is exactly similar to
the one just described. It contains the circles G, H, I, K,
L, and M, while the third one, which controls the four out-
lets on the centre table, is only twenty-four inches square,
i6
ELECTRO-ANALYSIS.
but has twenty-six contact blocks in each circle. They are
numbered o, 24, 25, 26, and so on to 48. Between the
two blocks numbered o and 24 are connected the cells of the
group on the east side of the room; between the blocks 24
and 25 is connected cell No. i of the west side of the room,
while cell No. 2 is connected between blocks numbered 25
and 26. This arrangement connects the two groups of
cells in series, and permits the use of from one to forty-
eight cells at the centre table when necessity requires. It
FIG. 10.
CONNECTIONS TO WORKING TABLE.
will, perhaps, have been noticed that there is no provision
made for connecting cells in parallel, and this is not neces-
sary, as the maximum discharge rate of the cells exceeds
the greatest estimated current needed by one operator.
All brass parts on the back of the board, as well as the
bared ends of the wires, are thoroughly coated with P. and
B. paint, while the brass parts on the front are heavily lac-
quered to prevent corrosion. The surface of the contact
blocks can easily be cleaned with fine sandpaper.
The measuring instruments, after some deliberation, were
MEASURING CURRENTS. \J
chosen of the switchboard type. While this necessitated
procuring at least one-third more instruments, yet the initial
cost was considerably lower than if portable instruments
had been provided, and experience with portable instruments
has shown that a greater accuracy will be attained with
switchboard instruments of a good form, if not immediately,
yet surely after the first six months of use.
Each outlet is provided with a fused switch, a voltmeter,
two ammeters, a rheostat, and a terminal board. They are
connected as shown in Fig. 10. The positive lead after
passing through the variable resistance runs directly to the
positive binding-post. The wire coming from the negative
binding-post runs to the low-reading ammeter and thence
to the negative side of the switch, while the negative post
marked 25 is connected to the same switch terminal, but
through the ammeter of large capacity. The anode of the
electrolytic cell is therefore always connected to the middle
binding-post and the cathode either to post i or 25, depend-
ing upon the strength of current it is intended to pass
through the cell. The voltmeter, being connected as shown,
measures the potential differences at the terminals of the
cell, except for the addition of the small fall of potential
through the ammeters.
The voltmeters on the side of the room have scales rang-
ing from o to 50, and divided to 1-2 volts. Those on the
centre table range from o to 120.
The ammeters ranging from o to i ampere are divided
to i-ioo, and those reading from o to 25 are divided to
1-5 amperes. The three instruments are mounted side by
side on an oak backboard extending the whole length of
the room and are covered by an air-tight case with a glass'
front, as shown in Fig. n. The cases have neither doors
nor a back, but are simply screwed against a backboard with
3
i8
ELECTRO-ANALYSIS.
a heavy felt gasket, making the joint. The wires come out
through hard rubber tubes sealed at their outer ends by
insulating tape.
FIG. ii.
WORKING TABLE.
The rheostats are of the enameled type, chosen because
of their being impervious to fumes. They have a total
resistance of 172 ohms, divided into 51 steps in such a way
that their resistances form a geometrical progression, the
first step and the sum of all the steps being chosen in
accordance with data of the resistances of the baths deter-
mined for the work done under an earlier system.
The wires, both those in the battery rooms and those in
the laboratory proper, are covered with rubber, and those
in the laboratory are further encased in oak moulding, but
this rather for the sake of appearance than for protection.
The whole installation, as well as the other fittings of the
HISTORICAL. 19
room, has a very neat and finished appearance. (Science,
I 3 697 (1901).) The following references may also be
consulted :
Z. f. Elektrochem., 8, 398, 445; 9, 496; 10, 238. H. Nissenson..
Einrichtungen von elektrolytischen Laboratorien, etc. Verlag von W.
Knapp in Halle a. S. Elektrochemische Zeitschrift 10, 267; Gazzetta
chimica italiana, 36, 401; Abegg, Z. f. Elektrochem., 12, 109; Foerster,
ibid., 12, 183.
Before taking up the description of the details to be ob-
served in the electrolytic precipitation of individual metals,
it may not be uninteresting to briefly trace the history of
the introduction of the electric current into chemical analysis.
4. HISTORICAL.
Although the early years of last century show consider-
able activity in electrical studies, the efforts were mainly
directed to the solution of the physical side of electrolysis.
Cruikshank (1801), observing the readiness with which
the metal copper was precipitated by the current, first sug-
gested it as a possible agent in the detection of metals.
Fischer (1812) detected arsenic, and Cozzi (1840) the
metals generally in animal fluids by this means, while Gaul-
tier de Claubry (1850) directed his efforts wholly to the
isolation of metals from poisons by depositing the same
upon plates of platinum. When the precipitation was con-
sidered finished the plates w r ere 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 reli-
able in all instances, but especially recommends it for the
20 ELECTRO-ANALYSIS.
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 deposited, from solutions of
these metals, upon the positive electrode of the battery;
. . . that the point of a platinum wire, when attached to
the anode of a cell, 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
experiment : A piece of iron, in connection with the positive
electrode of the battery, is introduced into a V-shaped glass
tube containing a concentrated solution of potassium hy-
droxide, 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 cer-
tain 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. Potassium antimonyl tar-
trate gave a crystalline metallic deposit of antimony at the
cathode, and upon the anode a yellowish-red coating, sup-
posed to be anhydrous antimonic acid. Bismuth nitrate
HISTORICAL. 2 1
yielded a reddish-brown deposit at the positive electrode.
Despretz concludes his paper by stating that although the
facts were few in number, yet they were new in so far as
they concerned lead, antimony, and manganese; and, fur-
thermore, that the separation of copper from lead by the
current was almost perfectly complete.
Three years later (1860) 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 (1851), in his work on electrometallurgy,
asserts that Morton was the first person to employ the elec-
tric current for the isolation of metals from poisonous mix-
tures. 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 large 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 containing
dilute sulphuric acid. The jar with its contents stood in
a wide beaker, filled with water, into which dipped the posi-
tive 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-
22 ELECTRO-ANALYSIS.
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. Nickles (1862) 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 constituted the negative
electrode. The silver separated upon this. The current
was very feeble, for hydrogen was not liberated at the
cathode. Nickles also suggested 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 constructed 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 electrolytically, by
Nickles, from textiles.
In 1862 A. C. and E. Becquerel resumed their electro-
chemical investigations, first begun some thirty years pre-
viously. Their experiments seem to have been aimed chiefly
toward the reduction of metallic solutions upon a large
scale, caring not for the quantitative estimation of metals,
but seeking rather a rapid and satisfactory technical isola-
tion 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
HISTORICAL. 23
covered with alternating, bright, steel-like colors. He re-
garded 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 alkali 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 decomposed with difficulty under ordinary cir-
cumstances, 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 deposit of metal slowly
makes its appearance upon the negative pole.
The experiments thus far described are qualitative in their
results. The first notice of the quantitative estimation of
metals electrolytically was that of Wolcott 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 1860 employed the electric current for the deposi-
tion of copper quantitatively in various analyses." It was
Luckow who proposed the name Elektro-Metall Analyse
for this new method of quantitative analysis. According
to this writer the current may be applied as follows :
i. To dissolve metals and alloys in acids by which they
would not be affected unaided by the electric current.
24 ELECTRO-ANALYSIS.
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 man-
ganese, from zinc, iron, cobalt and nickel.
4. To deposit and estimate metals quantitatively, in acid,
alkaline, and neutral solutions.
5. For various reductions, c. g., silver chloride, basic
bismuth chloride, and lead sulphate, in order that the metals
in them may be determined. To reduce chromic acid to
oxide, e. g., potassium bichromate acidulated with dilute
sulphuric acid.
These applications embrace nearly all that has since been
accomplished by the aid of the current. In the same article
in which Luckow calls attention to the facts recorded above,
he describes minutely the method pursued by him in the
precipitation of metals. Reference to these early experi-
ments 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 positive 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 electrolyzed in the presence of
other metals, the latter greatly influenced the separation 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. Notwithstanding, a complete separation of the
two metals can be effected when the quantity of the anti-
mony is small. A somewhat similar behavior was noticed
with other metals. The deposition of cadmium, zinc, cobalt,
and nickel was apparently not satisfactory.
HISTORICAL. 25
Lecoq cle Boisbaudran (1877) electrolyzed the potassium
hydroxide solution of the metal gallium, using six Bunsen
elements with 20-30 c.c. of the concentrated liquid. The
deposited metal was readily detached when the negative
electrode was immersed in cold water and bent slightly.
The unpromising behavior of zinc solutions, observed by
Wrightson, was fortunately overcome by Parodi and Mas-
cazzini (1877), who employed a solution of the sulphate,
to which was added an excess of ammonium acetate. Lead
was also deposited in a compact form from an alkaline tar-
trate solution of this metal in the presence of an alkaline
acetate.
After Luckow's experiments upon manganese, little at-
tention appears to have been given this metal until Riche
(1878) published his results. While confirming the obser-
vations of Luckow, he discovered that manganese was not
only completely precipitated from the solution of its sul-
phate, but also from that of the nitrate, thus rendering pos-
sible an electrolytic separation of manganese from copper,
nickel, cobalt, zinc, magnesium, the alkaline earth, and the
alkali metals. Riche recommended that the deposited diox-
ide 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 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
4
26 ELECTRO-ANALYSIS.
platinum dish, using six Bunsen cells. Mercurous chloride
was at first precipitated, but it was gradually reduced to the
metallic form. J. B. Hannay (1873) had previously rec-
ommended precipitating this metal from solutions of mer-
curic 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 solu-
tions of its sulphate, contrary to an earlier observation of
Wrightson. At the same time copper was completely sepa-
rated from cadmium by electrolyzing their solution in the
presence of free nitric acid.
A very successful determination of both zinc and cad-
mium was published by Beilstein and Jawein in 1879. They
employed for this purpose solutions of the double cyanides.
Heinrich Fresenius and Bergmann (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 (.1880) showed that if uranium acetate solu-
tions were electrolyzed the uranium was completely precipi-
tated as a hydrated protosesquioxide ; and, further, that
molybdenum could be deposited as hydrated sesquioxide
from warm solutions of ammonium molybdate in the pres-
ence of free ammonia. Very promising indications were
obtained with salts of tungsten, vanadium and cerium.
HISTORICAL. 27
In a more recent (1880) communication from Luckow,
to whom we are indebted for much that is valuable in elec-
trolysis, 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 pro-
duced. Arsenic and arsenious acid behave similarly. The
same is true also of the soluble ferro- and fern-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 alka-
line 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 decomposi-
tion, 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 alka-
line 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 bro-
mates and iodates are formed when metals of the first two
28 ELECTRO- ANALYSIS.
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. Dilute nitric acid alone, or even in
the presence of sulphuric acid, is not reduced to ammonia.
(See also Z. f. anorg. Ch., 31, 289.) If, however, dilute
nitric acid be present in a copper sulphate solution under-
going electrolysis, copper will separate upon the negative
electrode and ammonium sulphate will be formed. Solu-
tions of nitrates containing sulphuric acid behave analo-
gously. Phosphoric acid sustains no change. Silicic acid
separates as a white mass, and boric acid, in crystals unit-
ing to arborescent groups, at the positive electrode.
In the Ber. d. d. chem. Gesellschaft, 14 (1881), 1622,
Classen and v. Reiss presented the first of a series of papers
upon electrolytic subjects, which continued through subse-
quent issues of this publication. Their early work was
devoted to the precipitation of metals from solutions of
their double oxalates. They also elaborated excellent meth-
ods for antimony and tin. Many very serviceable forms of
apparatus, intended for electrolytic work, were devised and
described 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 meth-
ods proposed by Classen and his co-laborers will receive due
mention under the respective metals.
Quite independently of Classen, Reinhardt and Ihle pro-
posed zinc-potassium oxalate for the estimation of zinc elec-
trolytically ; and in this connection it may not be improper
to mention that as early as 1879, Parodi and Mascazzini
(Gazetta chimica italiana, 8, 78) wrote " finally, we may
HISTORICAL. 29
add, that the electrolytic determination of antimony and
iron in their derivatives must be considered an accomplished
fact judging from the experiments we have happily initiated
in this important subject; namely, that antimony is fully
precipitated from its chloride dissolved in basic ammonium
tartrate, and also from the solutions of its sulpho-salts,
while the iron is deposited from a ferric solution in the pres-
ence of acid ammonium oxalate."
Both of these suggestions have since been amplified and
vastly improved by Classen and his students.
In 1883 Wolcott Gibbs " gave an account of a method of
electrolysis for the separation of metals from their solutions
by the employment of mercury as negative electrode, the
positive electrode being a plate of platinum. Under these
circumstances, and with a current of moderate force, it was
found possible to separate iron, cobalt, nickel, zinc, cadmium,
and copper so completely from solutions of the respective
sulphates that no trace of metal could be detected in the
liquid. In addition it was found that phosphates of these
metals dissolved in dilute sulphuric acid were easily resolved
into amalgams and free acid, and the advantages of the
method were pointed out in at least a certain number of
cases. The author had in view both the determination of
the metal by the increase in weight of the mercury, and in
particular cases of the molecule combined with the metal,
either by direct titration or by known gravimetric methods."
The experiments were purely qualitative, such being in the
author's opinion sufficient -to establish the correctness of the
principle involved. " It is to be hoped that the determina-
tion quantitatively of the electro-negative atoms or mole-
cules united with the metal will also attract attention, the
method having been originally intended to serve the double
purpose." This method is not applicable in the case of anti-
mony and arsenic.
3O ELECTRO-ANALYSIS.
Three years later (1886) Luckow recommended a very
similar procedure for the estimation of zinc.
Moore (1886) also published new data upon the estima-
tion of iron, cobalt, nickel, manganese, etc., full notice of
which will appear under these metals.
Whitfield (1886) suggested an indirect determination
of the halogens electrolytically, which has proved useful.
Brand (1889) succeeded in effecting separations by util-
izing solutions of the pyrophosphates of different metals.
Smith and Frankel (1889) 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 investigations in this direc-
tion are given in detail in the following pages.
Other publications relating to electrolysis are that of
Warwick on metallic formates (Z. f. anorg. Ch., i, 285),
that of Frankel on the oxidation of metallic arsenides (Ch
N., 65, 54), and that of Vortmann (Ber., 24, 2749)
upon the electro-deposition of metals in the form of amal-
gams, together with a series of critical reviews of electro-
lytic methods by Rudorff in the Z. f. ang. Ch., 1892.
In the years immediately following the recording of
the preceding experiments the efforts in electro-analysis
had for their chief purpose the perfecting of methods.
The absence of reliable working conditions necessitated
a careful review of earlier suggestions, with the result
that while some have been abandoned, the greater num-
ber have been re-enforced and -have been given a more
favorable and extended use. Freudenberg (1893) revived
the idea to which Kiliani first called attention, viz. : that by
the application of suitable decomposition-pressures metal
separations could be easily executed in the electrolytic way.
This contribution, published in the Z. f. ph. Ch., 12, 97,
HISTORICAL. 3 1
and epitomized on pp. 33-39, should be seriously studied
by all persons interested in electro-analysis. Singularly
enough, the separations therein indicated had been previ-
ously made by Smith and Frankel (1889), and the state-
ment also appears that by the use of the double cyanides the
field of separations was widely extended. (See also J. Am.
Ch. S., 16,93.)
The direct determination of the halogens electrolytically
has been worked out by Vortmann, Specketer and others.
Other contributions have considered the availability of
known electro-chemical methods to technical analysis, and
many, too, have been almost wholly controversial in their
character, so that they may be omitted here. The literature
references to them appear in their appropriate places.
The most recent advances in electro-analysis embrace
the rapid determination of metals by agitation of the electrp-
lyte, and the use of a mercury cathode. A complete account
of the results achieved by these means will appear upon the
subsequent pages.
The preceding paragraphs give a brief outline of what
has been accomplished in the field of analysis by electroly-
sis ; for further information consult the following :
LITERATURE. Jahrb., 1850, 602 ; C. r., 45, 449 ; Jr. f. pkt. Ch., 73, 79 ;
Chem. Soc. Quart. Journ., 13, 12; Jahrb., 1862, 610 ; Ann., 124, 131; C. r.,
55, 18; Ann., 146, 375 ; Z. f. a. Ch., 3, 334; Ding. p. Jr. (1865), 231 ; Z. . a.
Ch., 8, 23 ; n, i, 9 ; 13, 183 ; Am. Jr. Sc. and Ar. (36 ser.), 6, 255 ; Z. . a.
Ch., 15, 297; Ber., 10, 1098; Annales de Ch. et de Phy., 1878; Am. Jr. Sc.
and Ar., 16, 200; Am. Phil. Soc. Pr., 1878; Z. f. a. Ch., 15, 303; Am. Ch.
Jr., 2, 41 ; Berg-Hutt. Z., 37, 41 ; Z. f. a. Ch., 19, i, 314, 324; Am. Ch. Jr.,
i, 341; B. s. Ch. Paris, 34, 18; Ber., 12, 1446; 14, 1622, 2771; 17, 1611,
2467, 2931; 18, 168, 1104, 1787; 19, 323; 21, 359, 2892, 2900; Jr. f. pkt.
Ch., 24, 193; Z. f. a. Ch., 18, 588; 22, 558; 25, 113; Ch. N., 28, 581;
53, 209 ; Ber., 25, 2492 ; Z. f. ph. Ch., 12, 97 ; Ber., 27, 2060 ; Z. f. Elektro-
chem., 2, 231, 253, 269; Z. f. a. Ch. (1893), 32, 424. And the following
will be found worthy of careful study : Ann., 36, 32 ; 94, i ; Z. f. a. Ch.,
32 ELECTRO-ANALYSIS.
19, i; Berb-Hiitt. Z., 42, 377; Z. f. a. Ch., 22, 485. Pa week, Elektro-
technische Zeitschrift x, 243 ; Foerster and M ii 1 1 e r , Z. f. Elektroch.,
8, 515; Medicus, Z. f. Elektroch., 8, 696; Z. f. Elektroch., 8, 569;
Per kin, Electrolytic apparatus, Ch. N., 88, 102; J. E. Root, Electro-
chemical Analysis and the Voltaic Series, Jr. phys. Chem., 7, 428 ; H o 1 -
lard, Influence of the Nature of the Cathode on the Quantitative Separa-
tion of Metals by Electrolysis, Ch. N., 88, 5 ; ibid., 89, no ; 87, 193.
5. THEORETICAL CONSIDERATIONS.
In the following pages, forms of apparatus and their
arrangement in carrying out metal determinations will be
carefully considered. As the details for estimations and
separations will be amply given, and electrolytes of various
descriptions will be suggested, a preliminary section may be
here introduced, in which will be set forth some of the views
entertained, at present, for the different behavior of metals
in electrolytes which have met with widest use.
It is due Kiliani (1883) to say that he showed by
attention to differences in decomposition pressure, how
the separation of metals could be readily made in the elec-
trolytic way. He used pressures corresponding closely to
the thermal values of the salts undergoing electrolysis.
Uncertainty prevailed as to whether the precipitation of
a metal first began when a definite pressure was reached, or
whether it took place with the very lowest pressure and
gradually advanced to the maximum. On this point Kili-
ani's study gave no decisive answer.
In 1891, Le Blanc (Z. f. ph. Ch., 8, 299) conclusively
demonstrated that every electrolyte, under normal condi-
tions, showed a decomposition-pressure peculiar to it, and
that this pressure might be accurately determined.
Freudenberg, guickd by these facts (Z. f. ph. Ch., 12,
97) classified the metals as follows:
THEORETICAL CONSIDERATIONS. 33
1. Those which, by proper pressure, cannot be separated
from aqueous solutions : the alkali metals, the alkaline earth
metals, etc.
2. Those generally precipitated on the anode by the cur-
rent in the form of peroxides : lead, manganese and thallium.
3. Those deposited in metallic form upon the cathode.
These three groups may be easily separated. In this in-
stance, electromotive force (pressure) has little influence.
But Freudenberg observed :
" The third or last group may be separated into sub-
groups, easily separable one from the other, the important
point being the magnitude of their discharge potential in
comparison with that of hydrogen.
" According to Le Blanc the decomposition value of all
acids and bases reaches its maximum at 1.7 volts. This is
due to the fact that at this point the ions of water can dis-
charge themselves. Therefore, all those metals whose salt
solutions cannot be decomposed till the pressure exceeds 1.7
volts, must have a greater electric cohesion than the hydro-
gen of water. Since then, in electrolysis, those ions will
be first deprived of their charge, which require the least
expenditure of energy to accomplish this, the metals of the
last group will not be precipitated from solutions in which
the hydrogen ions, in proportion to the current density, are
present in excess. This end is reached by the presence of
strong acids, e. g., nitric acid. Weak acids will not answer,
because the concentration of hydrogen ions in them is too
slight.
" Alkalies and alkali salts cannot exercise any influence
upon the precipitation of metals. This is because the alkali
metal in them plays the role of a cation and is therefore
not to be considered in the discharge. The most important
metals, which show in their salt solutions a more ready
34 ELECTRO-ANALYSIS.
decomposability than the corresponding acids, are gold,
platinum, silver, mercury, copper, bismuth, antimony, ar-
senic and tin. As previously mentioned, the ratio of their
decomposition values (being independent of the anion) will
be the same in all cases, if there is only present in the solu-
tions a sufficient number of metal ions. This condition is
almost invariably realized; because, as a rule, metallic salts
are strongly dissociated. The condition, however, is not
met when dealing with complex salts. And it is especially
true in the case of the metal double cyanides; e. g., potas-
sium copper cyanide. Its formula indicates it to be the
potassium salt of hydro-cupro-cyanic acid. If this salt were
absolutely complex, then it could only contain ions of CuCy 4
and potassium. Upon electrolysis CuCy 4 would pass to the
anode and potassium to the cathode. A precipitation of
copper could not occur. As a matter of fact, however, this
double cyanide, like its analogues of the other heavy metals,
is not a perfect complex, but in aqueous solution is slightly
resolved into copper cyanide and potassium cyanide, which
are further dissociated into their components. Hence, cop-
per ions must be assumed as present in the solution of potas-
sium copper cyanide; but they are so few in number that
their presence cannot be chemically demonstrated. In other
double cyanides, e. g., that of silver, the degree of dissocia-
tion is sufficient to render possible a chemical test for silver
ions. There is then a gradual transition from complex
salts to double salts. The best means of distinguishing be-
tween these two classes of bodies is their electric behavior.
This is so because (the most important consideration) they
influence characteristically the pressure necessary for the
separation of the metal in them. According to a theory
proposed by Nernst (Z. f. ph. Ch., 4, 129) the potential
difference of a solid metal in contrast to a liquid is dependent
THEORETICAL CONSIDERATIONS. 35
not only upon its solution-tension, but also upon the concen-
tration of the ions present in the solution ; it increases with
increasing dilution. Just as a solid in contrast with a liquid
shows a greater tendency to dissolve, the less of it there
already is in solution (the less in consequence is the oppos-
ing osmotic pressure), so a metal in contrast to a liquid
shows a greater difference in potential the fewer ions there
are of it in the latter. Conversely, the electromotive force
intended to throw out the metal ions in solution must, there-
fore, be chosen larger in proportion, as it is less supported
or aided by the osmotic pressure of the same, and the less
also the concentration of the ions. It must become endless
if the number of ions is infinitely small. Therefore, theo-
retically speaking, metals can never be completely precipi-
tated from their solutions by the galvanic current. Yet,
as seen from the formula of Nernst, under normal condi-
tions, the rise in polarization with dilution is so very slow
that in practical work it is negligible. In the complex cya-
nides, however, the number of metallic ions is so extremely
small that they are capable of very appreciably influencing
the difference in potential requisite for their separation.
The degree of this influence depends, in addition to the
specific property of the double cyanide, upon the quantity
of potassium cyanide present in the solution, inasmuch as
the presence of the latter retards the dissociation of the
metallic cyanide. Further, the water may show an abnor-
mal rise of polarization in consequence of the small number
of its ions. In neutral salts, not having ions similar to those
of water, its decomposition value is about 2.2 volts, because
of the formation of base and acid at the electrodes. Acids
and alkalies, however, show normal pressure. In their
electrolysis, unlike that of the alkali salts, concentration
changes alone occur at the electrodes. It is therefore im-
36 ELECTRO-ANALYSIS.
portant with the double cyanides, in whose solutions the
higher decomposition value of water (2.2 volts) comes into
consideration, whether in them the abnormal potential of
the metals is able to raise itself above that of water, or
whether it remains below. If the first be the case, by regu-
lated pressure, the hydrogen alone will be discharged and
the metal cannot be precipitated. The number of hydrogen
ions is, indeed, very small, but as the number of the metal
ions is also extremely small, therefore, the separation of the
former is favored in consequence of their lower potential.
" Precipitation under these conditions becomes possible
only by using, on the one hand, a higher pressure and suffi-
cient current density, or, upon the other hand, by decom-
posing the potassium cyanide present, thus lowering the
potential of the metal which it is desired to precipitate.
" Another group of metals, namely, those sufficiently dis-
sociated in their double cyanide solutions, are not able to
raise their potential above that of hydrogen, hence they can
at once be precipitated from a potassium cyanide solution.
" The earlier view by which the metals were regarded as
a secondary precipitation, caused by the potassium set free
by electrolysis, leads to contradictions. For example, it
does not well explain why the current precipitates some
metals readily from solutions containing an excess of potas-
sium cyanide, and others only with difficulty. If it be a
fact that potassium is discharged and it is then in a condi-
tion to produce a secondary reaction, why does it act in this
manner with certain metals and not with the others ? Fur-
ther, the intimate connection, existing between the precipi-
tation of metals and their chemical detection by hydrogen
sulphide, argues most clearly in favor of the first theory.
" This variation in the behavior of metals in potassium
cyanide solutions leads to another division, which rests upon
THEORETICAL CONSIDERATIONS. 37
entirely different principles, not identical with those answer-
ing for acid solutions. Metals readily reduced from a
potassium cyanide solution are gold, silver, mercury and
cadmium. Examples of the opposite class are copper,
platinum, arsenic, nickel, cobalt, iron and zinc. It is worthy
of note how the potential of metals, originally constant in
consequence of the specific cohesion of the ions, may be
increased at will and altered in its order of magnitude by
diminishing the number of ions.
''' There is another instance, besides the double cyanides,
which has found practical application and is explainable by
this same principle. Certain metals, e. g., arsenic and anti-
mony, able to act both as bases and acids, may be more or
less completely robbed of their ionic condition by dissolving
them in alkalies, thus imparting to them the role of an acid.
Thereby their potential rises above that of hydrogen in a
manner perfectly analogous to that of the double cyanides,
and they are then no longer reducible by the current.
" At this point may be recalled the fact which well repre-
sents the behavior of the metals upon electrolysis it is the
great analogy between their precipitation by the galvanic
current and by hydrogen sulphide. The cause for this is
that the tendency of metals and hydrogen to form ions in
general repeats itself in their sulphur derivatives. In a solu-
tion containing an excess of hydrogen ions there will be
just as few metals precipitated by hydrogen sulphide as by
the current if the ionizing tendency of the metals is greater
than that of .hydrogen. In an alkaline solution, in which
the ionizing tendency of the hydrogen attains an abnormal
value, all those metals will be precipitated both by the cur-
rent and by hydrogen sulphide whose ionizing tendency is
lower than that of hydrogen. Finally, in a potassium cya-
nide solution, in which the potential has been greatly in-
3 ELECTRO-ANALYSIS.
creased, only those metals will be precipitated by hydrogen
sulphide which are immediately precipitated by the current.
True, the analogy between the two series is not absolute in
any sense. Thus, hydrogen sulphide precipitates cadmium
from a solution containing nitric acid, but this is not the
case with the current. But it follows it in so far that in
metallic mixtures, hydrogen sulphide, as well as the current,
causes a partial precipitation. In slightly acid solutions,
hydrogen sulphide precipitates cadmium at once; should,
however, copper be simultaneously present in the solution,
at first this metal only will be precipitated and not until the
major portion of it has been thrown out of solution will
any cadmium appear. Could, therefore, the action of
hydrogen sulphide be regulated as the current is regulated,
a separation of the two metals might be possible in this
way.
" The behavior of metals contrasted with that of hydro--
gen in reference to their potential in different solvents made
possible the simplest separations, and the early methods were
almost exclusively based on this fact. Because the main-
tenance of a definite pressure was not necessary, it is nat-
ural that it should not occur that it was important, hence it
was almost wholly ignored. Formerly, in most precipita-
tions, equal voltage was used, and the current strength was
regulated in accordance with the influence exerted by the
gas evolution upon the deposit. This was done by the in-
troduction or removal of resistances. Under particularly
favorable conditions, by this means alone, metal separations
were effected. The current density was so low that the
ions of the more readily reducible metal continued to the
end to take upon themselves the discharge of electricity, so
that only after the removal of the same was it possible for
the second metal to participate in the electrolysis. It is,
THEORETICAL CONSIDERATIONS. 39
however, in every respect more practicable to lower the cur-
rent density, not by increasing the external resistance but
by lowering the pressure, because in this way is not only the
precipitation of the second metal prevented, but the current
density may be allowed to increase appreciably more than
by the former procedure. Only arrange the pressure so
that it exceeds enough the polarization of the one metal
while it continues below that of the other. A reliable sepa-
ration of metals may be attained in this manner independ-
ently of the length of action of the current.
" It is obvious that the importance given the pressure, by
use of this method, in contrast to current density must lead
to many alterations in regard to method and apparatus in
electrolysis. First of all, the oxy-hydrogen voltameter,
which heretofore has afforded us information regarding the
current energy employed, will lose its importance as a meas-
uring instrument, etc."
Bancroft ( International Congress (1903), Band 4,
703), commenting upon the separation of metals by atten-
tion to their difference in pressure, adds :
" As a matter of fact, this method is not used in most
of the standard separations which are rather to be classed
as constant current separations, even though the current may
not be held absolutely constant. In order to prevent the
second metal precipitating as soon as the first is all down,
it is essential that hydrogen shall be set free by the current
instead of the second metal. The essential feature, there-
fore, of a constant current separation is that the decomposi-
tion voltage for hydrogen in any solution shall lie below
the decomposition voltage of one. of the two metals. Since
most separations were originally made without a voltameter
in circuit, no satisfactory results were obtained until a solu-
tion was found which permitted of a constant current sepa-
ELECTRO-ANALYSIS.
ration, and, for this reason, all, except some of the most
recent separations, are constant current separations."
Root (Jr. phys. Ch. (1903), 7, 428), under the direction
of Bancroft, studied the conditions of a number of metal
separations from solutions of cyanides, oxalates, phosphates,
and tartrates. The following tables give most of the im-
portant separations for silver, mercury, copper, bismuth,
lead, tin, nickel, iron, cadmium and zinc.
TABLE I.
TABLE II.
SILVER OR MERCURY FROM
COPPER FROM
Cu
Nitric acid
V
V
Bi
Cyanide -f- citrate
C
C
Cyanide
C
C
bismuth precip-
Bi
Nitric acid
V
V
itates
Pb
Excess nitric acid
C
C
Pb
Excess nitric acid
C
C
Sn
Sulphide
Sn
NH 3 -f tartrate
C
C
(Ag 2 S insoluble)
Fe
Acid, phosphate,
C
C
Fe
Nitric acid
C
C
or oxalate
Cyanide
C
C
Ni
Acid, phosphate
C
C
Ni
Acid
C
C
Oxalate
V?
C
Cyanide
C
C
Cd
Acid
V?
C
Cd
Nitric acid
C
C
Phosphate
C
C
Cyanide
V?
C
Cyanide
Zn
Cyanide
C
C
cadmium precip-
itates
C
C
Zn
Acid, phosphate
C
C
TABLE III. TABLE IV.
BISMUTH FROM
IRON FROM
Pb
None
Ni
None
Sn
NH 3 -j- tartrate
C
C
Cd
Alkaline cyanide
Fe
Acid sulphate
C
C
cadmium pre-
Ni
Acid sulphate
C
C
cipitates
C
C
Cd
Acid
C
C
Acid (NH 4 ) 2 SO 4
Zn
Acid
C
C
cadmium pre-
cipitates
C
C
Phosphate, cad-
mium precipi-
tates
C
C
Zn
Alkaline cyanide,
zinc precipi-
tates
C
C
RAPID PRECIPITATION OF METALS.
TABLE V.
TABLE VI.
NICKEL FROM
t ADMIUM FROM
Cd
Alkaline cyanide
Zn
Sulphate
C
C
cadmium pre-
Cyanide
C
C
cipitates
C
C
Phosphate
C
C
Acid (NH 4 ) 2 S0 4 ,
Oxalate
C.
V?
cadmium pre-
cipitates
C
C
Zn
NaOH -f tartrate,
zinc precipitates
C
C
"The first column gives the metal and the second the solu-
tion. In the third column C means that a constant current
separation is used and V a voltage separation. In the
fourth column the same letters refer to the method of sepa-
ration as predicted from measurements of decomposition
voltage.
" As was to have been expected, practically all the deter-
minations are constant current separations, and the few that
are not are of minor importance."
A most interesting contribution, along this same line, has
been made by Danneel (Internationaler Congress fur angw.
Ch. (1903), 4 Band, 680-687). Consult also Hollard, Ch.
N., 87, 193; 88, 5; 89, no, 125; Centralblatt, I. (1903),
600. See, further, F. Foerster, Z. f. ang. Ch., 19 (1906),
1842-1849. Ibid., 29, 1889.
6. THE RAPID PRECIPITATION OF METALS IN
THE ELECTROLYTIC WAY.
While engaged in perfecting old and seeking new electro-
methods, the writer, watching the precipitation of molyb-
denum in its electrolytic separation from tungsten, observed
delicate, blue-colored, thread-like masses extending, or
5
4 2 ELECTRO-ANALYSIS.
reaching out, from the cathode toward the anode a flat
platinum spiral which, as they approached the latter, im-
mediately vanished. These threads of a blue-colored tung-
sten oxide, formed in the vicinity of the cathode by reduc-
tion, were reoxidized upon coming into the field of oxidation
surrounding the anode. Immediately the thought sug-
gested itself that by agitating the electrolyte the unwished-
for reduction of the tungstic acid would not take place.
Then arose the question as to how this might best be done.
The passage of an air current did not, for numerous rea-
sons, recommend itself, so that the next thought was to
rotate the anode. This was tried. All this occurred in
1901. The results were disappointing. But on applying
the idea in the same year to other metals, it was soon found
that copper, silver and mercury were precipitated in excel-
lent form, and further, that by causing the anode to rotate
at a high speed, greater current intensity and higher voltage
might be applied with an attending, more rapid precipitation
of the respective metals. The time period was astonishingly
reduced. The results were carefully noted, but the earlier
question of the separation of molybdenum from tungsten
continued to persistently obtrude itself. Hoping to solve it,
further work with copper and other metals along the lines
just described was interrupted and not resumed, except at
short intervals in 1902, until early in 1903, when the writer
directed Dr. Franz F. Exner, then a student in this labora-
tory, to repeat the experiments upon the metals, rotating the
anode while applying currents of great intensity and high
voltage. The results of these trials were embodied in Ex-
ner's doctoral thesis published in June, 1903, and in con-
densed form in the Journal of the American Chemical
Society, Vol. 25, 896. They were of such a remarkable
character that many chemists considered the field of electro-
RAPID PRECIPITATION OF METALS. 43
analysis to have been truly revolutionized by them. In the
opinion of the writer, they represent at least a new depart-
ure in this domain. Metals which, until this study was com-
pleted, were determined electrolytically under the most
favorable circumstances (from o. i to 0.2 grams) in periods
from two to four hours are now estimated in quantities vary
ing from 0.25 to 0.5 gram and more in from five to ten min-
utes. But before discussing minutely these results of Exner
and those obtained along similar lines by other students of
the writer, it is proposed to sketch briefly the allied efforts
of other chemists along similar lines.
The fact that agitation of the electrolyte favors the
electro-deposition of metals has long been recognized in the
great technical field of electrolysis. For some mysterious
reason it has not impressed itself very strongly upon the
minds of analysts, although it is only just and proper to
record that v. Klobukow (J. pr. Ch., 33 (Neue Folge), 473,
1886) particularly emphasized the importance of agitating
the electrolyte during the passage of the current. Indeed,
he made this matter his special study, devising various forms
of agitators to achieve his ends. He deprecated the blow-
ing of gases through the electrolytes because it was impos-
sible to distribute them evenly, and the superficial appear-
ance of the bubbles, he thought, exerted a harmful effect
upon the metal depositions near the edge of the electrolyte
and perhaps occasioned undesirable oxidations. In his
efforts to contrive mechanical devices he rotated the cathode
and then the anode; indeed, he even held the electrodes sta-
tionary while moving the electrolyte itself. At last he
declared himself partial to a rotating anode and announced
that the results obtained in this way by him in electrolysis
were most astonishing. However, those results were never
given -to the public; so that students were permitted to rely
44
ELECTRO-ANALYSIS.
on their imaginations to picture the character of the novelty,
v. Klobukow's chief thought was the agitation of the elec-
trolyte. The use of high currents with high speed of rota-
FIG. 12.
tion of the electrode was not discussed. In his preferred
form of apparatus a platinum dish served as the cathode.
The anode was attached as shown in Fig. 12. The power
was derived from a water motor. The anode performed
RAPID PRECIPITATION OF METALS. 45
not more than 150 revolutions per minute. The apparatus
is sketched here because historically it holds first place
among the various forms of apparatus devised for agitation
in electro-analysis, and too much credit cannot be given to
v. Klobukow for it. It is essentially the form employed
by the author, by Exner and others in this laboratory,
v. Klobukow used a platinum disk as anode.
FIG. 13.
Levoir (Z. f. a. Ch., 28, 63), also, appreciated the
advantages arising from agitation of the electrolyte during
the precipitation of metals by the current, for it is to him
that we are indebted for the thought represented in the
apparatus pictured in Fig. 13. The positive electrode is
46 ELECTRO-ANALYSIS.
the larger dish ; in it is suspended the smaller dish the
negative electrode. By this arrangement it is expected that
the electrolyte will be agitated by the oxygen bubbles arising
from the positive electrode, v. Klobukow's criticism of
Levoir's suggestion was that the requisite energetic libera-
tion of oxygen would not always be attainable in metal pre-
cipitations; further, it may not be advisable to have the
deposited metal come in contact with oxygen. Unnecessary
oxidations in the electrolyte might very easily occur, so that
all things considered, it would seem wisest to utilize the
positive electrode as an agitator, rotating it slowly about
its axis.
So far as the writer's knowledge extends, the idea of
Levoir has met with nothing like general adoption in
electro-analysis.
The preceding paragraphs contain no reference to the use
of high currents and high voltage, which was the dominant
idea with the writer and his corps of students when they
began in 1901 to rotate the anode in electrolysis. That is,
v. Klobukow and Levoir were content to agitate the electro-
lyte and to stop there. The possibility of using higher inten-
sity of current and greater voltage escaped their thought.
This idea first appeared in print in an article published
by Gooch and Meclway (Amer. Jr. of Science [4th Series],
15, 320), when they said:
" So far as we are aware, however, no attempts have been
made, heretofore, to apply the rotary cathode in analytical
operations, in which it is the object to remove the metal
completely from solution. In such processes the soluble
anode is not used, and the comparatively high electromotive
force necessary to overcome the resistance and to throw
down the metal with rapidity liberates hydrogen from the
water solution simultaneously with the metal, and the con-
RAPID PRECIPITATION OF METALS.
47
FIG. 14.
TO REV. COUNTER
48 ELECTRO-ANALYSIS.
sequence is the production of a deposit lacking in compact-
ness and adhesiveness. This interference on the part of the
evolved hydrogen with the regularity of deposition appears
to be the chief reason why low intensity of current must be
used in the ordinary electrolytic processes of analysis. We
have made some experiments, therefore, to see whether it
is not possible to so far avoid the interfering action of hydro-
gen by the use of the revolving cathode as to secure with
high currents and in a short time deposits sufficiently adher-
ent and homogeneous for analytical purposes."
The cathode was a platinum crucible of 20 c.c. capacity.
It rotated at a speed of from 600 to 800 revolutions a min-
ute. It was driven by an electric motor fastened so that its
shaft was vertical (Fig. 14). The crucible was attached
to the shaft by pressing it over a rubber stopper bored cen-
trally and fitted tightly on the end of the shaft. " To secure
electrical connection between crucible and shaft a narrow
strip of sheet platinum is soldered to the shaft and then
bent upward along the sides of the stopper, thus putting the
shaft in contact with the inside of the crucible when the last
is pressed over the stopper. The shaft is made in two parts
as a matter of convenience in removing the crucible and is
joined, with care. to make a good contact between the two
pieces of shafting, by a rubber connector of sufficient thick-
ness to prevent the crucible from wabbling when rotated."
A platinum plate was the anode. It dipped in the salt solu-
tion contained in the beaker. Copper, silver and zinc salts
were studied in this way. The results were indeed most
satisfactory.
It must be remembered that the cathode was rotated in
these trials, and when their publication was made Exner's
experiments were well advanced, results having been ob-
tained, not only with copper, zinc and silver, but with vari-
RAPID PRECIPITATION OF METALS.
49
ous other metals ; so that the writer felt justified in privately
communicating to Prof. Gooch the outcome of Exner's
work. As the latter used the rotating- anode with high
current and high pressure, suggested by the writer, and
Gooch, the rotating cathode, there appeared no good reason
why each should not continue to pursue, undisturbed, his
own original plan, and this has been done with marked suc-
cess in both cases.
It was only natural to expect that modifications in forms
of apparatus would soon follow. One of the best sugges-
FIG. 15.
< 5?.__.
tions in this direction was that of E. S. Sheppard in the
Journal of Physical Chemistry, 7, 568. It is used in the
Cornell Laboratory (Fig. 15).
" Instead of a platinum crucible, I have used the ordinary
disk anode, shortening the stem to about 6 cm., and fastened
it by a screw connector directly to the shaft of the armature.
The connection to the battery is made through the iron
6
50 ELECTRO-ANALYSIS.
frame of the motor. The motor used is a toy motor, a very
poor affair in its way, but sufficient for the purpose, and
cheap enough to permit each cathode having its own motor.
The use of belts as suggested by Gooch is very unsatisfac-
tory, owing to the slipping, etc. It was found best to ar-
range a rheostat for each motor, since no two motors run
on the same current, and it is also desirable to slacken the
speed when removing the beaker and washing the cathode.
" This rheostat consisted of one zero, two one-ohm and
two two-ohm coils connecting through the switch (S), the
other motor connection being through the wire leading to
M, and a no-volt circuit lamp may of course replace this
form of rheostat.
" The cathode connection was made through four 8-volt
6-C. P. lamps in multiple (L) for storage battery work, or
these are replaced by the ordinary no-lamp for dynamo
circuit. The current was then regulated by loosening or
tightening the lamps in their sockets. No difficulty was
experienced in getting a good connection through the motor
frame to the cathode.
" The beaker containing the electrolyte was supported by
the wood support (C) on the brass posts (D). The screw
for tightening the collar of (C) should be of such a size
as to allow manipulating this support with one hand, leav-
ing the other free to manage the wash bottle, etc.
" The anode was a stiff platinum wire held in the usual
electrode holder, connection being made through the brass
posts (D) . The distance from the motors to the base board
is about 30 cm., and between the motors 10 cm.
" The disk electrode was used because we happened to
have that form in stock. A more desirable form would be a
disk of platinum gauze, thus allowing a stronger current to
be used and shortening the time required.
RAPID PRECIPITATION OF METALS. 51
" The brass conductor which connects the cathode to the
shaft is protected from corrosion by a rubber tube. A fin-
ger stall does very well." .
Very satisfactory determinations of the copper content of
chalcopyrite and the zinc content of sphalerite were carried
out by means of this device.
FIG. 1 6.
Still other schemes have appeared (Fig. 16). This is
taken from Perkin's Practical Methods in Electro-Chemis-
try. Here :
" The support for the cathode consists of a gun-metal
arm, the end of which is drilled to allow a spindle to pass.
This spindle carries a small chuck (such as is used in fixing
small drills) which is used for holding the rotator. The
grooved pulley, which is fastened on to the upper end of the
spindle, bears on the top of the arm, which is ground
smooth. The whole arrangement is driven by means of a
belt from a water turbine or electric motor. This arrange-
5 2 ELECTRO-ANALYSIS.
ment is found to give very perfect contact and to work with
very little friction. The parts should be only slightly lubri-
cated, the best lubricant being a mixture of graphite and oil.
" The cathode, as is seen from the figure, is a small sand-
blasted cylinder of platinum gauze, which has a combined
surface of about 25 cm. The anode is in the form of a
double circle of stout platinum wire, and has four little baf-
fles placed at intervals around it, to prevent the liquid from
rotating with the cathode. A double coil of stout platinum
wire serves equally well. Of course for peroxide deposits
the rotating electrode would be the anode. A cylinder of
sheet platinum also gives very good results, but in this case
very little metal is deposited upon the inner surface. Lon-
gitudinal slits, however, partially get over this difficulty, but
with gauze as shown in the figure the deposition is practi-
cally equal inside and outside."
R. Amberg (Z. f. Elektrochem., 10, 853) and Fischer and
Boddaert (ibid., 945) write at some length upon the rapid
precipitation of metals, although their results were in the
main anticipated by previous investigators in this new field.
Consult Sherwood and Alleman, J. Am. Ch. Soc., 29,
1065, upon the use of tin as a cathode for the rapid quan-
titative electrolytic deposition of zinc, etc.
As minute details in the use of the rotating anode will
be given under the various metals, it will not be necessary
here to occupy further space for their consideration save to
add that Henry Sand (Z. f. Elektrochem., 10, 452) remarks,
in explanation of this rapid precipitation of metals, that
" it is most probable the high current densities are possible
and dependent solely upon the rapidity of renewal of the
liquid at the electrodes. It is extremely likely that in metal
precipitation the potential at the cathode is independent of
the current density. The great variations observed when
RAPID PRECIPITATION OF METALS. 53
applying different current densities are almost wholly the
consequence of local concentration changes. The great role
which such changes, under circumstances, can play I showed
four years ago in the electrolysis of copper sulphate solu-
tions containing sulphuric acid (Z. f. ph. Ch., 35, 641).
Just as long as copper ions, in appreciable concentration,
were present at the surface of the touched electrode, those
alone were precipitated, when, however, they had practically
disappeared from this touched surface, all the copper migrat-
ing in that direction was, by diffusion, set free simultane-
ously with the hydrogen. In all instances, as a consequence
of local exhaustion of copper sulphate, in spite of the con-
vection, heating, hydrogen evolution, etc., over 60 per cent,
of the current was consumed in liberating hydrogen. On
agitating the solution energetically, copper alone was pre-
cipitated. Had the purpose of these trials been to deter-
mine copper, that metal would, in the first instance, have
separated in a pulverulent form ; in the second, as a coherent
precipitate.
' The conditions upon which the local concentration
changes at the electrode are dependent are well known and
were adequately emphasized by Danneel (Z. f. Elektrochem.,
9, 763). In the mind of the writer of those lines, how-
ever, in the mere enumeration of those factors, we fail to
place their functions in the true light. Thus, if it be said
of diffusion that it acts in opposition to concentration alter-
ations at the electrode, there is, thereby, not expressed the
idea that diffusion renders possible current conductivity,
and is indissolubly connected with it, and that without dif-
fusion the concentration of a metallic salt at the electrode
would fall at once to zero. Such an enumeration also
expresses just as little the fact that diffusion alone without
54 ELECTRO-ANALYSIS.
convection is never able to completely cancel the alterations
in concentration at the electrode.
" The relative function, attaching to the individual fac-
tors, may be best represented by an expression for the time
which expires until the concentration at the electrode with-
out any convection or artificial disturbance of the liquid
falls to zero, or at least diminishes by a definite amount.
" This time period follows immediately from equation
2 in the cited article :
Here, Ac is the value to which the concentration of the salts
under consideration may fall (for analytical purposes this
is always the concentration of the salt) ; K is the diffusion
coefficient of the salt ; y the number -~ -* ^ * } - ; i the current
density and n c the conversion number of the precipitated
metal in the larger sense, i. e., the ratio of the equivalent of
metal, directed by the current to the cathode, to the entire
number of equivalents carried by the current. In the case
of a complex salt in which the metal wanders from the
cathode in the form of an anion, a negative value must be
introduced n c . In experimenting with a sample of copper
sulphate containing free sulphuric acid, it was demonstrated
that the expression is sufficiently accurate when a conduct-
ing electrolyte is present. It may easily happen that with
a given apparatus and with a given rotation velocity, on
electrolyzing different solutions with varying current densi-
ties satisfactory results will always be obtained if the mag-
nitude given above does not exceed a definite value. The
expression, omitting the constant y, may be viewed as char-
acteristic for the behavior of a solution under electrolysis.
It is evident from it how far conducting salts favor decrease
USE OF MERCURY CATHODE. 55
in concentration (by reducing n c ), and that in this particu-
lar complex formation can act more unfavorably (by the
negative value of n c ). It may be further concluded that,
ceteris paribus, at higher concentration of the electrolyte, a
proportionately higher current density is admissible than at
lower concentration. In fact, in the rapid galvanoplastic
methods, solutions are applied in as concentrated form as
possible, with little conducting electrolyte. In rapid analy-
sis, by electrolysis, it may, however, be advisable to keep
the volume as small as possible and at the same time lower
the current strength and have it as nearly proportional as
possible with the diminishing average concentration. If
the current strength be held constant, in spite of decreasing
concentration, then the efficiency of the stirrer should be
increased in inverse square ratio to the latter."
See also R. Amberg, Z. f. Elektrochem., 10, 385 and 853 ;
Classen, Z. f. Elektrochem., 13, 181.
7. USE OF A MERCURY CATHODE.
LITERATURE. J. Am. Ch. S., 25, 884.
Most work in electro-analysis has been performed with
platinum cathodes. These have had a variety of shapes :
dishes, cones, cylinders, gauzes, etc. Wolcott Gibbs (1880)
(p. 29) first suggested the possibility of using metallic mer-
cury as a cathode. He recommended weighing out in a
small beaker a definite amount of metallic mercury which
was, by means of a platinum wire, connected with a battery
and made the cathode, while in the salt solution, contained
in the beaker, was suspended a strip of platinum, serving
as the anode. The currents used varied greatly in strength.
Three years later (1883) the same chemist (Am. Ch.
56 ELECTRO-ANALYSIS.
Jr., 13, 571) again directed attention to " the employment
of mercury as negative electrode, the positive electrode
being a plate of platinum. ... It was found possible to
separate iron, cobalt, nickel, zinc, cadmium, and copper so
completely from solutions of the respective sulphates that no
trace of metal could be detected in the liquid . . . the
author had in view both the determination of the metal by
the increase in weight of the mercury, and in particular cases
of the molecule combined with the metal, either by direct
titration or by known gravimetric methods (p. 29)." The
experiments were purely qualitative, such being, in the
author's opinion, sufficient to establish the correctness of
the principle involved.
In 1886, Luckow (Chemiker-Zeitung, 9, 338, and Z.
a. Ch., 25, 113), cognizant of the difficulties attending
the determination of zinc in the electrolytic way, described
a course (p. 30) for this purpose which consisted in weigh-
ing out in a platinum dish a quantity of metallic mercury
or its oxide, introducing the zinc salt solution and then
electrolyzing, when the zinc, combined with the mercury,
spread over the inner surface of the dish as a beautiful,
adherent amalgam.
Nothing further was done towards developing the pre-
ceding ideas until 1891, when Vortmann (Ber., 24, 2749)
described, at considerable length, the determination of
several metals in the form of amalgams. His plan con-
sisted in adding a weighed quantity of mercuric chloride
to the solution of the salt to be electrolyzed, the metals being
then precipitated together. The results were quite interest-
ing and seemed to offer decided advantages, but later experi-
ence demonstrated that, except in a few cases, this method
of analysis, as elaborated by Vortmann, was in nowise super-
ior to the usual procedure in determining metals electrolyt-
ically.
USE OF MERCURY CATHODE. 57
A few months later, in the same year (1891), Drown and
McKenna (Jr. An. Ch., 5, 627), striving to find a method
suitable for the estimation of small amounts of aluminium
in the presence of a preponderance of iron (p. 142), had re-
course to the suggestion of Wolcott Gibbs. They accord-
ingly weighed a beaker containing a layer of mercury (the
cathode), and introduced into the solution of the metals a
platinum plate (the anode). The current was allowed to
act through the night and the iron was completely precipi-
tated in the mercury. Several difficulties were encountered
in pursuing this course. The platinum wire projecting into
the mercury often had iron precipitated upon it, so that it
became necessary to weigh the wire, enclosed in a glass tube,
together with the beaker containing the mercury. Further,
much annoyance was experienced in the efforts to dry the
amalgam and obtain constant weights.
The thought of the writer had many times dwelt upon the
facts just mentioned, until at length it was determined to
conduct a series of experiments with mercury as cathode to
establish two points : (a) The determination of the negative
radical in various salts, as well as the metals combined with
them, and (b) the possibility of effecting the separation of
certain metals.
To this end, practically the same device as that used by
Drown and McKenna was adopted. Into the mercury,
serving as cathode, there extended a glass tube from the
lower end of which projected a carbon pencil, I mm. in
length. This pencil of carbon was preferable to the plati-
num wire ; metals did not adhere to it ; and, therefore, it was
not necessary to weigh it together with the beaker and the
mercury. The glass tube was nearly full of mercury, into
which dipped a copper wire connected with the negative
binding-post. Such was the form of apparatus first used,
ELECTRO-ANALYSIS.
FIG. 17.
and the results obtained were quite satisfactory, although
difficulty was experienced in drying the amalgam (J. Am.
Ch. S., 25, 885). It seemed at the beginning that this
USE OF MERCURY CATHODE. 59
might prove deterimental to the general adoption of the
method in ordinary analysis. It was, however, successfully
overcome, for it was found that the amalgam could be
washed with alcohol and ether, thus removing the final traces
of water, and that not more than fifteen minutes would then
be necessary for the drying of the metal. A number of care-
fully conducted tests established this point. In the mean-
time, William M. Howard of this laboratory devised the
following form of apparatus to eliminate the use of the
anode of Drown and McKenna, as well as the carbon pencil.
It is an extremely simple contrivance, consisting of a
small beaker (50 c.c. capacity), (Fig. 17), near the bottom
of which there is introduced, through the side, a thin plati-
num wire. Internally it dips into the mercury, while ex-
ternally it touches a disk of sheet-copper on which the beaker
rests and which is connected with the negative electrode of
a cell, thus making the mercury the cathode. By adopting
this device and by washing the amalgam with alcohol and
ether, the two chief disturbing factors were removed.
How this device was applied will be indicated under the
several metals. Its modifications and uses in the determi-
nation of anions will be sufficiently outlined in connection
with this special chapter on electro-analysis.
Frary in a very recent issue of the Z. f. Elektrochem.
(1907), No. 23, 308, presents a new form of apparatus
(Fig. 18) to be used in the rapid precipitation of metals.
A motor is not necessary. No parts of the apparatus are
at any time in motion. The parts, given in the vertical
section, are the spool (S), wound about a cylinder (E)
of thin sheet copper through which passes the electrolyzing
current. The cylinder is large enough to conveniently
accommodate a beaker (B) of 150 c.c. capacity. The
spool is surrounded, for practical reasons, with a rather
6o
ELECTRO-ANALYSIS.
thick cylinder of sheet iron (D), and the entire system
placed on a piece of sheet iron in order to augment the
magnetic field in the beaker. C is the gauze cathode. A
is the anode of platinum wire. The electrolyte must not
extend beyond the upper end of the cathode. The spool
is made from i kilogram of insulated copper wire of i.i
mm. diameter. Its resistance is about 2 ohms. The cath-
ode may be a cylinder of platinum, silver, or copper gauze.
Another device (Fig. 19), for use with the mercury
cathode, consists of a U-shaped electromagnet, the spool
(S) of which is wound about the bend of the magnet. In
the upper limb (pole) of the magnet is an opening 4 cm.
in width, through the middle of which passes an iron rod,
one centimeter in diameter, leading to the other pole, into
which it is screwed. The electrolyzing vessel (E) is ring-
shaped and fits into the opening between the ring-shaped
end of the upper hole and the iron rod. A is the ring-
shaped anode of platinum wire. C is the mercury cathode,
forming contact with the copper plate (P) by means of the
USE OF MERCURY CATHODE.
6l
two platinum wires. B is a shield of asbestos, designed
to prevent contact between the plate and the iron rod.
In the first apparatus (Fig. 18) there is a vertical mag-
netic field with radial current lines, while in the second
(Fig. 19) there is a radial field with vertical current lines.
FIG. 19.
The agitation or movement is particularly energetic in the
second form of apparatus, because of the iron core and the
very narrow air space.
Frary, using the first form of apparatus, precipitated
0.8500 gram of copper from 100 c.c. of a copper sulphate
solution, acidulated with ten drops of concentrated sul-
phuric acid, in fifteen minutes. The current equalled 6 to
7 amperes and the pole pressure was about 6 volts.
62 ELECTRO-ANALYSIS.
With the second form of apparatus o.i gram of iron was
precipitated from ferrous sulphate in ten minutes, using a
current of 4 amperes.
See also Ashcroft, Electrochemical and Met. Industry, 4,
145-
The advantages claimed by Frary for these forms of
apparatus are : they are inexpensive ; they may be run with-
out noise, and they require little or no attention.
The writer inclines to the opinion that all of these points
are features of the devices now in use in this laboratorv.
SPECIAL PART.
i. DETERMINATION OF THE DIFFERENT
METALS.
COPPER.
LITERATURE. Gibbs, Z. f. a. Ch., 3, 334; Boisbaudran, B. s. Ch.
Paris, 1867, 468; Merrick, Am. Ch., 2, 136; Wright son, Z. f. a. Ch..
15, 299; Herpin, Z. f. a. Ch., 15, 335; Moniteur Scientifique [3 ser.], 5,
41; Ohl, Z. f. a. Ch., 18, 523; Classen, Ber., 14, 1622, 1627; Classen
and v. Reiss, Z. f. a. Ch., 24, 246; 25, 113; Hampe, Berg-Hiitt. Z., 21,
220; Riche, Z. f. a. Ch., 21, 116; M akin tosh, Am. Ch. Jr., 3, 354;
Rudorff, Ber., 21, 3050; Z. . ang. Ch., 1892, p. 5; Luckow, Z. f. a.
Ch., 8, 23; Warwick, Z. f. anorg. Ch., i, 285 ; Smith, Am. Ch. Jr., 12,
329; Cro as dale, Jr. An. Ch., 5, 133; Foote, Am. Ch. Jr., 6, 3335 G. H.
Meeker, Jr. An. Ch., 6, 267; Classen, Ber., 27, 2060; Heidenreich,
Ber., 29, 1585 ; Regelsberger , Z. f. ang. Ch., 1891, 473 ; Oettel, Ch. Z.,
1894, 879; Schweder, Berg-Hiitt. Z., 36 (5), n 21; Fernberger and
Smith, J. Am. Ch. S., 21, 1001 ; Wagner, Z. f. Elektrochem., 2, 613;
Oettel, Ch. Z. (1894), 47, 879; Foerster and Seidel, Z. f. anorg.
Ch., 14, 1 06; Head, Trans. Am. Inst. Mining Engineers, 1898; Rev ay,
Z. f. Elektrochem., 4, 313-329; Ullmann, Ch. Z., 22, 808; Ho Hard,
C. r., 123, 1003 (1896) ; Kollock, J. Am. Ch. S., 21, 923; Richards and
Bisbee, J. Am. Ch. S., 26, 530; Gooch, Am. Jr. Sc., xv, 320; Ch. News,
87, 284; Foerster and Coffetti, Z. f. Elektrochem., 10, 736;
Denso, Z. f. Elektrochem., 9, 463; Medway, Am. Jr. Sc. [4th Series],
xviii, 1 80; Heath, J. Am. Ch. S., 26, 1120-1125; Spitzer, Z. f.
Elektrochem., n, 391; Koch, Z. f. a. Ch., 41, 105; Danve, J. pharm.
Chim., [6], 16, 371; Kufferath, Z. f. ang. Ch., 17, 1785; Interna-
tionaler Congress fiir angew. Ch., [Berlin] Band 4, 677; Guess, Eng.
Min. Jr., 81, 328 (1906); Exner, J. Am. Ch. S., 25, 897; Fischer and
Boddaert, Z. f. Elektrochem., 10, 947; Foerster, Z. f. ang. Ch., 19,
1890 (1906); Smith, J. Am. Ch. S., 26, 1614; Kollock and Smith,
Am. Phil. Soc. Pr., 44, 143; Flanigen, J. Am. Ch. S., 29, 455;
63
6 4
ELECTRO-ANALYSIS.
Langness, ibid., 29, 460 ; K o 1 1 o c k and Smith, Am. Phil. Soc. Pr., 45,
257-
Dissolve 19.6 grams of pure copper sulphate in water,
and dilute to i liter. Place 50 c.c. of this solution (= 0.25
gram of metallic copper) in a clean platinum dish, pre-
viously weighed. Arrange the apparatus as in the ac-
FIG. 20.
companying sketch (Fig. 20), the voltmeter being to the left
of the dish and the milliamperemeter and the rheostat to the
right-hand side of the same; and having done this, add 9-10
drops of concentrated nitric acid to the solution of the
electrolyte; dilute to 125 c.c. with water; heat to 70, and
electrolyze with a current of N.D 100 = 0.09 ampere and 1.9
volts. Cover the vessel with a perforated watch-crystal
during the decomposition. Four to five hours will suffice for
the precipitation. To ascertain when the metal has been
completely precipitated, add water to the dish; this will
expose a clean, platinum surface, and if in the course of half
DETERMINATION OF METALS COPPER. 65
an hour no copper appears upon it, the deposition may be
considered as finished. Or, a drop of the liquid may be
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.
As the precipitation has been made in an acid solution 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 metal will be sufficient to
cause some of the latter to pass into solution. To obviate
this, siphon off the acid liquid. As the acidulated water is
conveyed away by the siphon, pour distilled water into the
dish. Empty the platinum dish twice in this way ; the cur-
rent can then be interrupted without 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 exceeding 100 C. ; an air-bath, an asbes-
tos plate, or warm iron plate will answer for this purpose.
Do not weigh the dish until it is perfectly cold, and has at-
tained the temperature of the balance-room.
In heating the dish containing the electrolyte, do not apply
a direct lamp flame; attach a circular piece of thin sheet-
asbestos to the lower side of the ring, supporting the plati-
num dish, and under it place an ordinary Bunsen burner, or
one reduced in size. Water-baths are not needed for heat-
ing purposes.
Riidorff 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 at-
tack the copper, which can be at once washed and treated as
just described.
7
66 ELECTRO-ANALYSIS.
Copper is very readily precipitated from solutions con-
taining free nitric or sulphuric acid. Hydrochloric acid
should never be used.
A platinum dish, 50 mm. in diameter and 20 mm. in depth,
may be substituted for the spiral anode. There are openings
in the dish to facilitate circulation and accelerate the precipi-
tation of the metal.
The deposition of the copper can also be made in a plati-
num crucible, or upon the exterior surface of the same.
This is sometimes convenient. Place the liquid undergoing
electrolysis in a beaker (capacity 100-250 c.c.), and suspend
the crucible in it, supporting it there by a tight-fitting cork,
through which passes a stout copper wire, 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 adding water to the
solution in the beaker. No further appearance of copper on
the newly exposed platinum indicates the end of the precipi-
tation. 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 presence
of sulphuric acid, copper sulphide may be produced. Black
spots on the surface of the copper deposit indicate this.
Instead of using either of the suggestions first offered,
substitute the apparatus of Riche if convenient. This con-
sists 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.
Engels recommends the addition of urea or hydroxyl-
amine sulphate to the copper sulphate solution, as it seems
to favor the deposition of the metal. He, therefore, pro-
DETERMINATION OF METALS COPPER. 6/
ceeds as follows: Add 1015 c<c - f concentrated sulphuric
acid and 1.5 grams of hydroxylamine sulphate, or i gram
of urea, to the salt solution, dilute to 150 c.c. with water,
heat to 70, and electrolyze with a current of N.D 100 = 0.8-
i.o ampere and 2.7-3.1 volts. The metal will be precipi-
tated in one and one-half hours.
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 excess of a satu-
rated solution of ammonium oxalate diluted to 120 c.c. with
water; heated to 60 and electrolyzed with N.D 100 = 0.35--
i.o ampere and 2.5 to 3.2 volts. As the metal begins to sepa-
rate, and the original deep blue color of the liquid disappears,
add 20-30 c.c. of a cold saturated solution of oxalic acid.
This should be added gradually from a burette. Avoid the
precipitation of insoluble copper oxalate. 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. The precipitation is generally com-
plete after three hours. Use ferrocyanide of potassium to
learn whether all the metal has been precipitated.
E. Wagner recommends the following procedure in the
precipitation of copper from an oxalate solution : Pour the
copper solution into the ammonium oxalate solution (4
grams of ammonium oxalate in 60 grams of water for
I gram of copper sulphate) ; at the beginning electrolyze
with a current of 0.05 ampere for one-half hour, then in-
troduce 5 c.c. of a cold saturated solution of oxalic acid,
and at the expiration of five minutes increase the current
to 0.3 ampere. The temperature of the electrolyte should
equal 60. In the following eighty minutes, during four
intervals, 5 c.c. of oxalic acid are added at each period and
the maximum current of 0.4 ampere is applied. Two hours
68
ELECTRO-ANALYSIS.
after the close of the circuit neither ammonia nor potassium
ferrocyanide will show the copper reaction with the solution.
The liquid should be siphoned off without the interruption
of the current. The deposit of copper should be washed and
dried as previously indicated.
Copper can also be determined quite accurately in solu-
tions of the phosphate in the presence of free phosphoric
acid, or in a formate solution containing free formic acid.
The following example is given to show the applicability
of an acid phosphate solution for this particular purpose
To a solution of copper sulphate ( =0.1239 gram of cop-
per) were added 20 c.c. of a solution of disodium hydrogen
phosphate (sp. gr. 1.0358) and 5 c.c. of phosphoric acid
(sp. gr. 1.347). It was then diluted to 225 c.c. with water,
heated to 65, and electrolyzed with a current of N.D 100 =
0.035-0.068 ampere and 2.2-2.6 volts. The precipitation
was completed in six hours. The deposit of copper weighed
0.1238 gram. It was washed and dried as previously di-
rected, p. 65.
Riidorff obtained excellent results with the following con-
ditions : 0.1-0.3 gram of metallic copper in 150 c.c. of water,
to which were added 2-3 grams of potassium or ammonium
nitrate and 20 c.c. of ammonium hydroxide (0.91 sp. gr.).
Electrolyze at the ordinary temperature with a current of
N.D 100 = i ampere and 3.3-3.6 volts. It is claimed that
by observing the preceding conditions copper can be fully
precipitated in the presence of chlorides. An excess of ace-
tic acid should be added to the solution before the current is
interrupted.
Oettel remarks on the precipitation of copper from
ammoniacal solutions that the metal can be quantitatively
deposited from a slightly ammoniacal liquid, containing
ammonium nitrate, with a current density of 0.07-0.27
DETERMINATION OF METALS COPPER.
6 9
ampere per square decimeter. When ammonium nitrate is
absent and the quantity of ammonia is large, the metal de-
posits become spongy. He found the most satisfactory
concentration to be 0.8 gram of copper for 100 c.c. of liquid
when using a wire-form anode with a cylinder or cone as
cathode. Chlorine, zinc, arsenic, and small amounts of
FIG. 21.
antimony were without deleterious effect. In the presence
of lead, bismuth, mercury, cadmium and nickel the results
were high.
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, electrolyzes the warm (70) solution.
In using this electrolyte care should be taken to interrupt the
;o
ELECTRO-ANALYSIS.
current just as soon as the copper has been fully precipitated,
otherwise metallic platinum may be deposited upon the
copper.
In this laboratory it was observed that the electrolysis
can be best and most satisfactorily executed by dissolving
the sulphide in as small a volume of potassium cyanide as
possible, diluting to 150 c.c. with water, heating to 65,
FIG. 22.
and electrolyzing with N.D 100 = 0.15-0.8 ampere and
3-4.5 volts. The metal will be fully precipitated in from
two to three hours.
It has been asserted from time to time that in an alkaline
cyanide solution there is great probability that the anode will
suffer loss and that the dissolved platinum will reappear in
the cathode. This point has been most carefully considered
DETERMINATION OF METALS COPPER.
in this laboratory with the result that if the quantity of
cyanide added to the copper solution be not more than
enough to precipitate and redissolve the metallic cyanide
there will be no solution of the platinum anode. Heating
the solution to 65 favors the deposition of the copper. It
was further ascertained that in the presence of a definite
amount of ammonium hydroxide there is absolutely no loss
sustained by the anode in the cyanide electrolyte, and that
the precipitation of metal is much accelerated. Two ex-
amples illustrate this :
COPPER
IN
GRAMS.
POTASSIUM
CYANIDE
IN GRAMS.
AMMONIUM
HYDROXIDE
IN C.C.
N. D IOO
AMP.
VOLTS.
TEMPERA-
TURE.
TIME
IN
HOURS.
GRAMS OF
COPPER
FOUND.
0.2015
i-5
IO
I.OO
5
65
I
0.2014
0.2015
i*5
IO
0.66
5
65
I
0.2015
FIG. 23.
72 ELECTRO-ANALYSIS.
In the analysis of commercial copper Luckow employed
the apparatus pictured in Fig. 21. The beaker 1 contains the
electrolyte, and the metal is precipitated upon the cylinder
of platinum. It is a very satisfactory device for almost any
kind of electrolytic work. Either one of the arrangements
pictured in Figs. 22 and 23 will answer for the same pur-
pose. The platinum gauze cathode in Fig. 23 is much
favored by analysts. An anode of similar material and form
can be used to advantage. To calculate the approximate
surface of a cylindrical gauze cathode use the formula
5= nd2v'nlb
in which d is the diameter of the wire, n the number of
meshes per square centimeter, / the length and b the width
of the strip of gauze used (height of the cylinder).
(Winkler, Ber., 32, 2192.)
The Rapid Precipitation of Copper With the Use of
a Rotating Anode.
Arrange the apparatus and dish as pictured on p. 44.
Use an anode of the form in Fig. 24. To the solution of
the copper salt, placed in the dish, add one cubic centimeter
of dilute sulphuric acid (i : 10), dilute the solution to 125
c.c., thus exposing a cathode area of 100 sq. cm., cover the
dish with suitable glass covers, heat the liquid almost to
boiling, remove the lamp, start the rotator, giving the anode
a speed of 600 to 700 revolutions per minute, and let a cur-
rent of five amperes and five volts pass. When the electro-
lysis is complete (indicated by the colorless solution), stop
the rotator, and reduce the current by throwing in resistance
from the rheostat. Add distilled water to cover any ex-
posed metal and thus prevent oxidation. Siphon off the
acid liquor, keeping the dish, however, full by the addition
DETERMINATION OF METALS COPPER.
73
of water from a wash bottle. Disconnect the dish, wash
the deposit of copper with warm water, alcohol and ether.
Dry and weigh. With the conditions just outlined, 0.4994
gram of metal was frequently deposited in five minutes.
Miss Langness, working in this laboratory, precipitated
FIG. 24.
FIG. 25.
0.5035 gram of copper in seven minutes by the use of ten
volts and 5 to 13 amperes. The deposits of metal were
perfectly adherent, dark red in color and had a beautiful
velvet-like appearance.
Rate of precipitation:
In i minute 0.1493 gram of metal
In 2 minutes 0.3019 gram of metal
In 3 minutes 0.4371 gram of metal
In 4 minutes 0.4925 gram of metal
In 5 minutes 0.5029 gram of metal
Or, there may be used a dish (Langness, J. Am. Ch.
S., 29, 460) anode with the form shown in Fig. 25 so
constructed as to be about 7 cm. in diameter and 3 cm. deep.
conforming throughout with the cathode. In its sides are
8
74
ELECTRO-ANALYSIS.
ten slits perpendicular to the edge, each slit being 1.8 cm.
long and 0.5 cm. wide. Free circulation of the electrolyte
is insured by these openings and through a circular open-
ing, 1.3 cm. in diameter, in the bottom of the dish. The
anode is held in position by a stout platinum rod. The
anode is so adjusted that it is equidistant from the sides of
the cathode. The electrolyte, during the rotation of the
anode, is all contained within the space bounded by the
cathode and the outer surface of the anode. There is none
within the inner dish. The dilution, therefore, is less than
when using a spiral anode. When properly adjusted this
anode occasions absolutely no splashing and no loss of
electrolyte is sustained. To show the result, on employing
this anode, five actual experiments are here introduced :
No.
("u PRESENT
IN GRAMS.
VOLTS.
AMPERES.
TIME, MIN.
WT. OF ( u IN
GRAMS
I
0.4884
7+
IO-I5
4
0.4883
2
0.4884
8
10-15
3
0.4884
3
0.4884 | 8
10-15
5
0.4887
4
0.4884
8
10
2
0.4634
5
0.4884
8
10
I
O.2OIO
The electrolyte in each instance did not exceed sixty cubic
centimeters in volume. The character of the metal deposits
was the same as when using the spiral anode. The volume
of free sulphuric (i: 10) was i c.c. in all the trials just
described.
It may be preferred to use a nitric acid electrolyte. If so,
proper working conditions can be readily formed by obser-
vation of the following experiments:
DETERMINATION OF METALS COPPER.
75
No.
COPPER
PRESENT
IN GRAMS.
ACID IN
c.c SP. GR.
I 2.
DILUTION
IN C C.
VOLTS.
AMPERES.
TIME IN
MINUTES.
COPPER
IN GRAMS
FOUND.
I
0.4876
0-5
125
8
7
15
0.4878
2
0.4876
0-5
I2 5
8
7
15
0.4877
3
0.4876
o-5
125
8
8
15
0.4875
4
0.4876
0-5
125
8
8
IO
0.4875
The spiral anode was used in these trials. The metal de-
posits were brilliant, adherent and crystalline.
Rate of precipitation:
In i minute 0.1507 gram of metal
In 2 minutes 0.25 1 8 gram of metal
In 3 minutes 0.3418 gram of metal
In 4 minutes 0.3960 gram of metal
In 5 minutes 0.4486 gram of metal
In 6 minutes 0.4654 gram of metal
In 8 minutes 0.4852 gram of metal
In 10 minutes 0.4875 gram of metal
See also J. Am. Chem. S., 25, 898.
In an ammoniacal electrolyte, containing 0.4967 gram of
copper, 1.2 gram of ammonium nitrate, total dilution 125
c.c., a current of 9 amperes and 8 volts, using the rotating
spiral anode, precipitated 0.4963 grams of metal in fifteen
minutes. The deposits were perfectly adherent and very
bright in color. In this same electrolyte, if the dish anode
be substituted and a current of seventeen amperes and six
volts be employed, 0.4824 gram of copper can be com-
fortably precipitated in six minutes. (See also J. Am.
Chem. S., 25, 898.)
The preceding conditions answer well for the determi-
nation of copper in chalcopyrite. The latter having been
reduced to a fine powder is rapidly decomposed in a small
beaker by boiling with concentrated nitric acid. When the
76 ELECTRO-ANALYSIS.
decomposition is complete the solution is quickly evaporated
to dryness, the residue moistened by a few drops of pure
nitric acid, water added, the solution heated and then fil-
tered into a weighed platinum dish where it is mixed with
an excess of ammonium hydroxide. The iron will, of
course, be precipitated as hydroxide but without paying-
attention to it the anode is put in motion and the solution
electrolyzed. There is no danger of any of the ferric
hydroxide attaching to the deposit of copper. The thorough
agitation of the electrolyte prevents this. Numerous de-
terminations have been made in this laboratory and the re-
sults have been most concordant. Of course if the plan is
not approved by the analyst ammonium hydroxide may be
added directly to the acidulated (HNO 3 ) water solution
of the mineral before filtering out the gangue, thus bring-
ing the latter and the resulting ferric hydroxide together
upon the filter. The blue colored ammoniacal filtrate will
contain an abundance of ammonium nitrate so that one may
proceed at once with its electrolysis as just directed.
An advantage possessed by this electrolyte is that in the
ordinary course of analysis copper is very frequently got
in the form of nitrate. See separation of copper from
nickel (p. 197).
From an alkaline cyanide electrolyte the precipitation of
copper proceeds rapidly and well. Thus, to a solution con-
taining 0.2484 gram of metal there was added just enough
potassium cyanide to precipitate copper cyanide and then
dissolve it. On dilution, the liquid, being brought to boil-
ing, was electrolyzed with a current of N.D 100 = 6 amperes
and 1 8 volts. The precipitation was complete in eighteen
minutes. The deposit was deep red in color and shone as
if it had been polished. The deposition of metal from this
electrolyte is even more rapid, when using the dish anode
DETERMINATION OF METALS COPPER. 77
(p. 73). Thus, to a solution of potassium copper cyanide
( := 0.4882 gram of copper) were added 10 c.c. of ammo-
nium hydroxide (sp. gr. 0.93 at 24) and it was electrolyzed
with a current of 15 amperes and seven volts. In a period
of six minutes 0.4883 gram of copper was precipitated.
Here, again is an admirable means of determining the
copper content of minerals. Boil down to dryness a
weighed (0.5 gram) amount, for example, of finely divided
chalcopyrite with aqua regia. Take up the residue with a
little hydrochloric acid and water; filter and supersaturate
the filtrate w r ith hydrogen sulphide gas ; filter out the copper
sulphide and having washed it with hydrogen sulphide
water, dissolve it from off the filter in as little warm dilute
potassium cyanide as possible, collect the cyanide filtrate in
a weighed platinum dish and electrolyze as directed in the
preceding paragraph. The results will be perfectly satis-
factory.
The Rapid Precipitation of Copper With the Use of
the Rotating Anode and Mercury Cathode (J. Am. Ch.
S., 25, 883; J. Am. Ch. S., 26, 1595; ibid., 26, 1614; Am.
Phil. Soc. Pr., XLIV. (1905), 137; J. Am. Ch. S., 27,
1527; Myers, J. Am. Ch. S., 26, 1124).
In the introduction (p. 58) reference was made to the
form of cell or cup which may be used with advantage when
mercury is applied as a cathode in electro-analysis. Such
cups can easily be made from ten-inch test tubes of soft
glass. Into a tube of this kind introduce a layer of mercury
sufficient to cover the platinum wire fused through the bot-
tom or side of the cup. Re-weigh the cup, place it upon a
plate of sheet copper, connected with the negative electrode
of a battery, whereby the mercury becomes the cathode.
Introduce a solution of copper sulphate, add a drop or two
of sulphuric acid and suspend the anode (see p. 58) from
/ ELECTRO-ANALYSIS.
the rotator. Provide the cup with cover-glasses, notched
so as to allow the passage of the anode. These glasses can
be readily made from the slides used in microscopic work.
The anode is now rotated precisely as when making pre-
cipitations upon a platinum dish cathode (p. 72). When
high currents are used the solution of the metal will fre-
quently be heated to boiling. Some of the liquid will, of
course, be carried to the sides of the cup and to the cover
glasses by the escaping gases or by the agitation of the
liquid. Experience has shown that it is not necessary to
wash down this portion, because the condensed steam con-
tinually frees the sides from the solution. The cover-
glasses should now and then be tilted against the sides of
the tube in order to run off the water which collects in large
drops.
It has been repeatedly observed that the greater the con-
centration of the electrolyte, the greater the rapidity of depo-
sition, but the last traces of metal separate slowly, so after
a solution has become colorless, continue the electrolytic
action several minutes in order to precipitate the minute
amount remaining unprecipitated.
When the metal has been completely deposited, stop the
rotator, remove the cover-glasses and fill the decomposition
cell with distilled water. This should then be siphoned off
to the level of the spiral and the liquid replaced by distilled
water until the current drops to zero. This wash water
should always be put aside and tested to ascertain that the
metal has been completely removed. Next interrupt the
current, remove the tube and wash its contents again with
distilled water, inclining and twirling the cell in order to
more completely wash the amalgam. As much of the water
as possible should be poured from the cell and the amalgam
then be washed twice with absolute alcohol and twice with
DETERMINATION OF METALS COPPER.
79
ether. It should be wiped dry on the outside and after the
volatilization of the ether be placed in the desiccator and
weighed as previously described.
The following experiments are taken from a laboratory
notebook. They show that by the method just described
rapidity and accuracy are obtained without any difficulty
whatsoever. Even inexperienced chemists get very satis-
factory estimations not only of copper, but of other metals,
as will be observed later.
h
%
U 2
S5 W
2
" </i
ID
H
*i
2 g S
2 S3
S
2
6
z ^
B t3
3u
u
H
s z 5
W D
tJ
^
3p
Pi
Ir
O
PH PH
II
r "
i
w
i
0.7890
.25
12
3-5
6
1200
10
0.7900
-LO.OOI
2
0.3945
12
4
6
1081
5
0.3941
0.0004
3
0.3945
'25
12
3-5
6
1200
6
0-3942
0.0003
4
0-3945
12
5
6.5
1200
5
0.3944
-O.OOOI
5
0-3945
.00
10
2-4
9-7
1200
6
0.3946
+ 0.0001
6
0.3945
.17
10
3-5
8.5
1200
4
0-3944
O.OOOI
7
0.3945
.17
10
4
6
1080
5
0.3946
+ 0.0001
Rate of Precipitation. In a solution of copper sulphate
(5 c.c. in volume and containing 0.3945 gram of metallic
copper) slightly acidulated with sulphuric acid a current of
5 amperes and 6 volts precipitated the metal as follows :
In i minute 0.1800 gram
In 2 minutes 0.3400 gram
In 3 minutes 0.3664 gram
In 4 minutes 0.3945 gram
In 5 minutes 0.3945 gram
Remarks. The following experiment was made to deter-
mine what loss, if any, was suffered by the mercury while
standing in the desiccator. A cell filled and prepared as
above was weighed. It was then returned to the desiccator
80 ELECTRO-ANALYSIS.
and reweighed at intervals of twenty-four hours. A loss
of o.oooi gram per day was observed during the first week.
The rate of loss then decreased to such an extent that the
total loss after a period of twenty-six days amounted to
only 0.0015 gram. It was frequently found upon reweigh-
ing a cell in the morning that no loss had occurred, the cell
having remained in the desiccator over night.
It is necessary to keep the inside of the cell absolutely
clean, otherwise the amalgam shows a tendency to cling to
the glass. Losses may occur from this source, as exceed-
ingly small globules of mercury are often detached by the
wash water, as well as by the alcohol and ether.
An interesting experiment that students should perform
consists in dissolving a weighed amount of pure copper sul-
phate in a small volume of water (5 to 10 cubic centimeters)
and electrolyzing the solution in the manner just outlined
with a mercury cathode and a rotating anode. Do not add
any sulphuric acid. When the solution is colorless care-
fully siphon out the acid liquid into a beaker. Wash the
amalgam as before, combining the wash water and the liquid
first removed, after which titrate this solution with a TO nor-
mal sodium carbonate solution. The sulphuric acid con-
tent of the salt is thus obtained with great accuracy. The
increase in weight of the mercury cup naturally gives the
copper so that a complete analysis of the salt (water of crys-
tallization excepted) may be executed in a very few minutes.
A metallic nitrate may be analyzed as under Nitric Acid,
p. 289.
For the estimation of the halogen content of metallic
halides see p. 89.
DETERMINATION OF METALS CADMIUM. 8 I
CADMIUM.
LITERATURE. Ber., 11,2048; Smith, Am. Phil. Soc. Pr., 1878; Clarke,
Z. f. a. Ch., 18, 104; Beil stein and Jawein, Ber., 12, 759; Smith,
Am. Ch. Jr., 2, 42; Luckow, Z. f. a. Ch., 19, 16 ; Wright son, Z. f. a.
Ch., 15, 303; Classen and v. Reiss, Ber., 14, 1628; Warwick, Z. f.
anorg. Ch., i, 258; Moore, Ch. News, 53, 209 ; Smith, Am. Ch. Jr., 12,
329; Vortmann, Ber., 24, 2749; Riidorff, Z. f. ang. Ch., Jahrg. 1892;
Classen, Ber., 27, 2060; Heidenreich, Ber., 29, 1586; Wallace and
Smith, J. Am. Ch. S., 19, 870 ; ibid., 20, 279 ; Balachowsky , C. r., 131,
384; Miller and Page, Z. f. anorg. Ch., 28, 233; Kollock, J. Am. Ch.
S., 21, 911 ; A very and Dales, J. Am. Ch. S., 19, 380 ; M ed way , Am.
Jr. Science [4th series], 18, 56; Flora, Am. Jr. Science [4th series],
20, 268; Z. f. anorg. Ch., 47, 13; Danneel and Nissenson, Internation-
aler Congress fur angw. Ch., (1903) Bd. 4, 680; Exner, J. Am. Ch.
S., 25, 902; Diavison, J. Ani. Ch. S., 27, 1275; Kollock and Smith,
J. Am. Ch. S., 27, 1528; Fischer and Boddaert, Z. f. Elektrochem.,
10, 948; Foerster, Z. f. ang. Ch., 19, 1890; Kollock and Smith,
Am. Phil. Soc. Pr., 45, 260.
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 suitable, weighed
platinum vessel. Add one gram of pure potassium cyanide;
dilute with water to 125 c.c., heat to 60, and electrolyze
with N.D 100 = 0.06 ampere and 3.2 volts. The metal will
be completely deposited in five hours, or the decomposition
may be begun in the evening and by morning the metal will
be fully precipitated. To ascertain whether the precipita-
tion 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; also with alco-
hol and ether. Dry upon a warm iron plate (temperature
not exceeding 100 C.).
This metal can be deposited from the solution of its phos-
82
ELECTRO-ANALYSIS.
phate in phosphoric acid. The conditions that follow gave
very satisfactory results; a current of N.D 100 = o.o6
ampere and 3-7 volts acted upon 0.1656 gram of cadmium
as sulphate, 30 c.c. of sodium phosphate (1.0358 sp. gr.),
and iy 2 c.c. of phosphoric acid (sp. gr. 1.347). The total
dilution equaled 100 c.c. The temperature of the solution
was 50. The precipitated cadmium weighed (a) 0.1654
gram and (b) 0.1657 gram. The current for the last hour
of the decomposition should be increased and the deposit be
washed before breaking the current.
Cadmium may also be precipitated from a solution of its
sulphate containing a small amount of free sulphuric acid
(2 c.c. H 2 SO 4 , sp. gr. 1.09 for o.i gram of cadmium).
Heat to 50 and electrolyze with N.D 100 = o.i5 ampere
and 2.5 volts. Siphon off the acid liquid before interrupting
the current. Treat the deposit as previously directed.
Cadmium can also be deposited quite readily, and in a
crystalline form, from its acetate solution. An example will
indicate the proper conditions for a successful determina-
tion : 0.1329 gram of cadmium oxide was dissolved in acetic
acid, the solution was evaporated to dryness, and the residue
dissolved in 30 c.c. of water. The liquid was then heated
to 50 and electrolyzed with a current of 0.02 ampere for
37 sq. cm. of cathode surface and a pressure of 3.5 volts.
The metal was completely precipitated in four hours. It
was crystalline and adherent. The acid liquid should be
siphoned off without interrupting the current. Good results
can be obtained and the period of precipitation be reduced
by adding i gram of ammonium acetate to the solution after
the current has acted for an hour. 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.
DETERMINATION OF METALS CADMIUM. 83
Balachowsky, in precipitating cadmium, makes use of a
silver-coated platinum dish. Dissolve from 1.5 to 2 grams
of cadmium sulphate in 100 c.c. of water, add 5 c.c. of
acetic acid for every gram of salt, heat to 60 and electrolyze
with a current of 0.004 ampere per sq. cm. and 2.8 volts.
Later increase the current to 0.006 ampere and 3.5 volts.
The deposited metal should be treated as already described.
The same chemist also obtained very satisfactory results
by adding formaldehyde, acetaldehyde, or urea to the solu-
tion of cadmium sulphate. The liquid was then heated to
60 and electrolyzed with a current of 2.5-3.3 v lts and
0.003 to 0.006 ampere per sq. cm.
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.
When using the oxalate solution, add to it for every 0.3
to 0.4 gram of sulphate, 10 grams of ammonium oxalate,
dilute to 1 20 c.c. with water, heat to 75, and electrolyze
with N.D 100 = 0.5-1.5 amperes and 3-3.5 volts. The time
necessary for complete precipitation will be three and one-
half hours.
Avery and Dales employed the formate solution. Their
recommendation is : Add 6 c.c. of formic acid (sp. gr. 1.20)
to the solution of cadmium sulphate, then potassium car-
bonate until a slight permanent precipitate is formed, which
is just dissolved in formic acid, after which i c.c. of the same
acid is introduced, the liquid diluted to 150 c.c. and electro-
lyzed with N.D 100 = 0.15-0.20 ampere and 2.6-3.4 volts.
Vortmann has determined several metals quite satis-
factorily in the form of amalgams. In applying his recom-
mendation to cadmium, add to the solution of its salt a
solution of mercuric chloride and 5 grams of ammonium
84 ELECTRO-ANALYSIS.
oxalate. Effect the solution of the latter salt without the
aid of heat. This procedure is only good when small
amounts of cadmium are present; cadmium ammonium
oxalate is not very soluble. The current employed for the
precipitation should at the very beginning of the decompo-
sition equal from 0.6 to 0.8 ampere. When the amalgam
of mercury and cadmium commences to separate reduce the
current to 0.3 ampere, 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 solution
undergoing electrolysis be ammoniacal. To this end add tar-
taric acid (3 grams) and an excess of ammonia to the liquid
containing the mercury and the cadmium. Dilute to 200
c.c. with water. Allow the current to act until a portion of
the liquid remains clear when tested with ammonium sul-
phide.
In the usual course of gravimetric analysis cadmium is
obtained as sulphide. To prepare it for electrolysis dissolve
the same in nitric acid, and after expelling the excess of the
latter, add a small amount of potassium hydroxide (suffi-
cient to precipitate the cadmium), and follow this with an
excess of potassium cyanide (i to 2 grams). Proceed fur-
ther as already directed.
The Rapid Precipitation of Cadmium With the Use of
a Rotating Anode.
Arrange apparatus as outlined under COPPER. To the
solution of cadmium sulphate ( = 0.2756 gram of cad-
mium), add 3 c.c. of sulphuric acid (i : 10), dilute to 125
c.c. with water, heat to incipient boiling, remove the lamp,
rotate the anode at the rate of 600 revolutions per minute
and electrolyze with a current of N.D 100 = 5 amperes and
DETERMINATION OF METALS CADMIUM. 85
8 to 9 volts. In ten minutes the precipitation of cadmium
will be complete. In one actual experiment 0.2756 gram
was found, and in another where 0.5512 gram metal was
present 0.5508 gram was precipitated in fifteen minutes.
The deposits are grey in color, crystalline and adherent.
Much sulphuric acid retards the complete deposition of
metal. It was also found in the presence of 0.5 c.c. sul-
phuric acid (1:10) by using a current of N.D 100 4
amperes and 14 volts that as much as 0.5762 gram of metal
could be precipitated in eight minutes.
Rate of precipitation:
In i minute o.i 190 gram
In 2 minutes 0.2245 gram
In 3 minutes 0.3417 gram
In 5 minutes 0.5217 gram
In 7 Y 2 minutes 0.5760 gram
In 8 minutes 0.5762 gram
The deposition of cadmium from an ammoniaeal electro-
lyte with stationary electrodes never gave satisfaction. By
using a rotating anode, however, this electrolyte may be
employed. To the solution of the cadmium salt add ammo-
nium hydroxide sufficient to precipitate the metallic hydrox-
ide and to redissolve it. To this solution add a solution of
10 c.c. sulphuric acid (1:10) neutralized with ammonia,
dilute to 125 c.c. and electrolyze with N.D 100 = 5 amperes
and 6 l / 2 volts. In ten minutes the deposition will be com-
plete. In this electrolyte the rate of precipitation was as
follows :
In i minute 0.1312 gram
In 2 minutes 0.2708 gram
In 3 minutes 0.2868 gram
In 4 minutes 0.2889 gram
In 5 minutes 0.2887 gram
86 ELECTRO-ANALYSIS.
As observed in a preceding paragraph a formate electro-
lyte answers well for the precipitation of cadmium. Upon
introducing the rotating anode in connection with it the
cadmium is deposited in a very few minutes. This is evi-
denced by one from a number of examples :
To a solution, containing 0.2898 gram of cadmium as
sulphate add five grams of sodium carbonate and 16 c.c. of
formic acid (sp. gr. 1.06), after which dilute to 125 c.c.,
heat the electrolyte to boiling, remove the flame, rotate the
anode at 600 revolutions per minute, and apply a current of
N.D 100 = 5 amperes and 5 volts. In fifteen minutes 0.2900
gram of metal was precipitated.
Again to a solution containing 0.2898 gram of cadmium
add 1.25 gram of sodium carbonate, 5 c.c. of formic acid
(sp. gr. i. 06) and electrolyze with N.D 100 = 5 amperes
and 9 volts, when the entire quantity of metal will be pre-
cipitated in five minutes. Thus from this electrolyte there
was deposited.
In i minute 0.1645 gram of cadmium
In 2 minutes 0.2816 gram of cadmium
In 3 minutes 0.2891 gram of cadmium
In 4 minutes 0.2896 gram of cadmium
In an electrolyte containing ammonium formate in the
presence of either ammonium hydroxide or formic acid the
deposition of cadmium takes place equally well. Thus,
with 0.2898 gram of metal in the presence of 5 c.c. of
ammonium hydroxide, - and 10 c.c. of formic acid (sp. gr.
i. 06) a current of N.D 100 = 5 amperes and 6 volts, the
anode making 690 revolutions per minute, there was
precipitated :
In i minute .. .0.1612 gram
In 2 minutes 0.2850 gram
In 3 minutes 0.2904 gram
DETERMINATION OF METALS CADMIUM. 8/
The deposits of metal resembled those from the sodium
formate electrolyte.
One of the very first electrolytes suggested for the precip-
itation of cadmium was sodium acetate in the presence of
free acetic acid. The results from it have been most satis-
factory. By employing the rotating anode the time factor
may be reduced to a few minutes. Starting with a cadmium
sulphate solution containing 0.3984 gram of metal add to
it 3 grams of sodium acetate and 0.25 c.c. of dilute acetic
acid, dilute to 125 c.c. and electrolyze with a current of
N.D 100 = 5 amperes and 8.5 to 9 volts. The anode should
perform 600 revolutions per minute. With these conditions
the rate of precipitation will be
In i minute 0.1601 gram of cadmium
In 2 minutes 0.2863 gram of cadmium
In 3 minutes 0.3963 gram of cadmium
In 4 minutes 0.3987 gram of cadmium
Ammonium acetate may be substituted for the sodium
salt. In such cases it is advisable to have acetic acid present
from the very beginning.
With an alkaline cyanide electrolyte follow the conditions
of an actual experiment : Add to a solution of cadmium
sulphate ( = 0.4568 gram of metal) , 3 grams of pure potas-
sium cyanide, i gram of sodium hydroxide, dilute to 125
c.c. with water and electrolyze with N.D 100 = 5 amperes
and 5.5 volts. The rate of precipitation will then be
In i minute 0.1808 gram of metal
In 2 minutes 0.2585 gram of metal
In 3 minutes 0.3291 gram of metal
In 5 minutes 0.3778 gram of metal
In 7}/2 minutes 0.4348 gram of metal
In i o minutes 0.4534 gram of metal
In 15 minutes 0.4568 gram of metal
88 ELECTRO-ANALYSIS.
The cadmium deposits were here lustrous and of a silver-
white color.
Ammonium and sodium acetates are not very good elec-
trolytes for this metal, while ammonium succinate in the
presence of a slight excess of succinic acid yielded good re-
sults, the deposits being similar to those from a formate or
an acetate electrolyte. With sodium succinate free acid is
not favorable to the character of the deposit. As much as
0.4 gram of metal can be deposited in a period of ten
minutes.
The Rapid Precipitation of Cadmium With the Use of
the Rotating Anode and Mercury Cathode.
Use the apparatus described under COPPER (p. 77).
Weigh the cup with its layer of mercury, introduce an
aqueous solution of cadmium sulphate ( = 0.9480 gram of
metal), and apply a current of 1.5 to 3.5 amperes and 10 to
7 volts. At the expiration of fifteen minutes the precipita-
tion of the cadmium will be finished. Wash and dry as
directed under COPPER. The anode should make 360 revo-
lutions per minute. The amalgam will be quite bright in
appearance. The rate of precipitation of the cadmium is as
follows :
In i minute 0.1531 gram
In 2 minutes 0.4984 gram
In 7 minutes 0.8707 gram
In 9 minutes 0.9480 gram
In i o minutes 0.9484 gram
One cubic centimeter (40 drops) of concentrated sul-
phuric acid will retard the deposition of this metal quite
markedly. Half of this volume of acid will do no harm.
Under the preceding metal, COPPER, mention was made of
the mercury cathode and the rotating anode in the analysis
DETERMINATION OF METALS MERCURY. 89
of metallic sulphates and nitrates. How the halogens may
be simultaneously determined will be outlined later (p. 285).
At this point, however, it seems advisable to indicate the
course of procedure in the analysis of a metallic halide when
the determination of the halogen element is of secondary
importance while that of the metal is of chief importance.
Using the apparatus, just employed with the sulphate, with
halides, there will under the influence of high current densi-
ties be a copious evolution of halogens and these will attack
the rotating anode most energetically. To offset these un-
favorable conditions place a layer of toluene or xylene upon
the solution of the metal halide. Either liquid will com-
pletely absorb the liberated halogen. Chlorides of cobalt,
gold, iron, mercury and tin were quickly analyzed in this
way with the utmost ease and satisfaction. In the case of
cadmium the bromide was used. Its solution was so pre-
pared that 5 c.c. of it contained 0.2212 gram of metal.
After the addition of 10 c.c. of toluene the liquid was elec-
trolyzed with a current of 2 amperes and 5 volts. The
toluene became red in color but later changed to yellow.
The odor of bromine was not detected. In ten minutes
0.2215 " ram of metal was precipitated.
See also J. Am. Ch. S., 27, 1547, and Journal of the
Chemical Society (London), 87, 1034.
MERCURY.
LITERATURE. Ber., 6, 270; Clarke, Am. Jr. Sc. and Ar., 16, 200;
Classen and L u d w i g , Ber., 19, 323 ; Hoskinson, Am. Ch. Jr., 8, 209 ;
Smith and Kn er r , ibid., 8, 206 ; Smith and Fr ankel, Am. Ch. Jr., n,
264; Smith, Jr. An. Ch., 5, 202; Vortmann, Ber., 24, 2749; Brandt.
Z. f. a. Ch., 1891, p. 202; Riidorff, Z. f. ang. Ch., 1892, p. 5; Eisen-
berg, Thesis, Heidelberg, 1895; Schmucker, J. Am. Ch. S., 15,
204; Fr ankel, Jr. Fr. Ins., 1891; Rising and Lenher, Berg-Hiitt. Z..
55, J 75 ; Wallace and Smith, J. Am. Ch. S., 18, 169 ; F e r n b e r g e r and
9
9O ELECTRO-ANALYSIS.
Smith, J. Am. Ch. S., 21, 1006; Kollock, J. Am. Ch. S., 21, 911;
Bindschedler, Z. f. Elektrochem., 8, 329; Glaser, Z. f. Elektrochem.,
9, ii ; Matolcsy, Ch. Blatt., 77 Jahrg. (1906), 166 ; Exner, J. Am. Ch.
S., 25, 901; Kollock and Smith, J. Am. Ch. S., 27, 1537; R. O.
Smith, J. Am. Ch. S., 27, 1270; Fischer and Boddaert, Z. f.
Elektrochem., 10, 949.
In preparing solutions for experimental purposes, use
either mercuric nitrate or chloride. To a definite portion
of such a solution add 3 c.c. of concentrated nitric acid,
dilute to 125 c.c., heat to 70, and electrolyze with a cur-
rent of N.D 100 = 0.06 ampere and 2 volts. The metal will
be fully precipitated in four hours. The deposit will be
drop-like in appearance. The acid liquid must be re-
moved before the interruption 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 sul-
phuric acid (0.5 c.c. of sulphuric acid), diluted to 125 c.c..
heated to 65, and electrolyzed with a current of N.D 100 =
0.4-0.6 ampere and 3.5 volts, will yield all its metal in
one hour. Always wash the deposited metal with cold
water. Rudorff recommended the addition of the follow-
ing substances to the liquid containing the mercury salt:
0.5 gram of tartaric acid and 10 c.c. of ammonium hydrox-
ide (sp. gr. 0.91), or 5 c.c. of nitric acid, 10 c.c. of a
saturated solution of sodium pyrophosphate, and 10 c.c. of
ammonium hydroxide. A current of 0.02 ampere will pre-
cipitate the mercury in a compact, adherent form.
From experiments made in this laboratory the writer
prefers and would especially recommend solutions of the
double cyanide of mercury and potassium for the electro-
lytic deposition of mercury. To the mercury salt solu-
DETERMINATION OF METALS MERCURY. 9!
tion add I gram of pure potassium cyanide for every o.i-
0.2 gram of metal, dilute with water to 100 c.c., heat to
65, and electrolyze with a current. of N.D 100 = 0.02-0.07
ampere and 1.6-3.2 volts. As much as 0.25 gram of metal
can be deposited in three hours. This procedure 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. In all precipitations of mercury it is advis-
able to have this metal deposited upon a layer of metallic
silver, hence invariably coat the platinum dishes with this
metal.
Classen recommends the double oxalate solution for
electrolytic purposes, and to that end adds to the mercuric
chloride solution from 4 to 5 grams of ammonium oxalate,
dilutes with water to 120 c.c., and electrolyzes at 29-37
with a current of N.D 100 = i ampere and 4.05-4.7 volts.
The mercury comes down in a perfectly adherent form,
the time depending entirely upon the pressure.
The precipitation is also very satisfactory in a phosphoric
acid solution, as is seen in the following example : To a
solution, containing 0.1159 gram of mercury, were added
30 c.c. of sodium phosphate (sp. gr. 1.038) and 5 c.c. of
phosphoric acid (sp. gr. 1.347), after which it was diluted
to 175 c.c. with water, heated to 50, and electrolyzed for
four hours with a current of N.D 100 = o.O4 ampere and
1.6 volts. The deposit of mercury weighed 0.1162 gram.
It was treated in the usual manner.
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
92 ELECTRO- ANALYSIS.
that such a solution can be electrolyzed without difficulty;
the mercury is deposited from it in a very compact form.
An actual analysis conducted in this laboratory will best
present the proper conditions for a successful determina-
tion: 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 125 c.c. with
water. This was acted upon with a current of N.D 100 =
o.i i ampere and 2.5 volts for five hours. The temperature
of the solution was 70. The weight of the precipitated
mercury was 0.1902 gram. It was further treated as ad-
vised in the preceding paragraphs. It is best to use a plati-
num dish as the negative electrode and a platinum spiral
(p. 73) for the anode. Dry the deposit on a moderately
warm plate or over sulphuric acid.
Several determinations of mercury in cinnabar were
made to test the general applicability of the method.
Samples of the mineral, analyzed in the usual gravimetric
way, showed the presence of 85.40 per cent, of metallic
mercury. Portions of the same mineral were weighed out
in platinum dishes and after solution in 20 to 25 c.c. of
sodium sulphide of the specific gravity previously men-
tioned, were diluted with water to 125 c.c. and electrolyzed
at 70, with the conditions recorded in the preceding para-
graph. The period of time allowed for the precipitations
never exceeded three hours. The results were:
CINNABAR, IN MERCURY, IN MERCURY
GRAMS. GRAMS. PERCENTAGE.
0.2167 0.1850 85.37
0.2432 0.2077 85.40
The platinum dishes were covered during the electrolytic
decomposition. It should be done in the determination
of every metal. Its purpose here was to prevent evapora-
DETERMINATION OF METALS MERCURY. 93
tion, thereby exposing a rim of metal, which, if in part not
volatilized, would yet be changed to mercury sulphide, indi-
cated by a dark-colored film.
The Rapid Precipitation of Mercury With the Use of
a Rotating Anode.
In a nitric acid electrolyte with 0.5840 gram of mercury
as mercurous nitrate and one cubic centimeter of concen-
trated nitric acid, a current of N.D 100 = 7 amperes and 12
volts precipitated the whole of the metal in seven minutes.
The anode performed 700 revolutions per minute.
To show the rate of precipitation from this electrolyte
a solution containing 0.5120 gram of metal was exposed
to the action of the current with the following results :
Metal deposited in 2 minutes 0.3612 gram
Metal deposited in 4 minutes 0.4772 gram
Metal deposited in 8 minutes 0.5077 gram
Metal deposited in 10 minutes 0.5122 gram
Metal deposited in 12 minutes 0.5121 gram
Metal deposited in 20 minutes 0.5119 gram
In these speed trials the pressure never exceeded 7 volts.
It was usually 6.5 volts. The total dilution of the electro-
lyte was 115 cubic centimeters.
Upon using an alkaline sulphide electrolyte it was found
to answer admirably in the precipitation of mercury with
the help of a rotating anode. Thus to a mercuric chloride
solution, containing 0.2603 gram of metal, were added 10
c.c. of a sodium sulphide solution of sp. gr. 1.17, diluted
to 115 c.c., and electrolyzed with a current of N.D 100 = 6
amperes and 7 volts, the anode being rotated as indicated
in the preceding paragraph. In fifteen minutes 0.2602
gram of metal was precipitated.
94 ELECTRO-ANALYSIS.
The rate of precipitation was found to be :
Metal deposited in 2 minutes 0.1371 gram
Metal deposited in 5 minutes 0.2198 gram
Metal deposited in 8 minutes 0.2538 gram
Metal deposited in 10 minutes 0.2554 gram
Metal deposited in 12 minutes 0.2596 gram
Metal deposited in 13 minutes 0.2601 gram
Metal deposited in 15 minutes 0.2602 gram
Metal deposited in 20 minutes 0.2604 gram
This scheme may be applied in determining the mercury
in cinnabar as described in an earlier paragraph. For ex-
ample, an ore that showed the presence of 46.20 per cent,
mercury, when analyzed by the distillation method, gave
46.40, 46.46, 46.40, 46.41, 46.40, 46.46 per cent, by the
procedure just outlined. The deposits of mercury were all
that could be desired. The time necessary for each determi-
nation, from the weighing of the ore until the mercury
deposit itself was weighed, did not exceed an hour and
thirty minutes. The quantity of ore varied from 0.3000
gram to 0.5000 gram.
It is not too much to say that, in the light of many simi-
lar experiences had in this laboratory, the electrolytic method
is vastly superior to the time-honored methods generally
employed in the estimation of mercury.
The Rapid Precipitation of Mercury With the Use of
the Rotating Anode and Mercury Cathode.
Use the same apparatus here as described under cadmium
and copper. A mercurous nitrate solution contained
0.3570 gram of mercury in five cubic centimeters. Nitric
acid, sufficient to prevent the formation of a basic salt, was
also present. Using a current of 3 amperes and a pressure
of 7 to 5 volts the rate of precipitation was :
DETERMINATION OF METALS BISMUTH. 95
In i minute 0.2777 gram of mercury
In 2 minutes 0.3542 gram of mercury
In 3 minutes 0.3572 gram of mercury
Dilution with water to 25 c.c. prolonged the period of
complete precipitation to 8 minutes. The addition of too
much free nitric acid also exerted a retarding influence.
Mercuric chloride may also be analyzed in this way, ap-
plying, however, the precautionary method of adding
toluene (p. 89) so that the anode is not attacked by the
liberated chlorine. Thus, to 5 c.c. of this salt, equivalent
to 0.2525 gram of mercury, were added 10 c.c. of toluene
and the decomposition made with a current of from i to 3
amperes and 10 to 7.5 volts. In ten minutes the metal was
completely deposited.
Trials recently conducted in this laboratory prove that
if cinnabar is decomposed with aqua regia, the solution
evaporated to dryness, the residue taken up with water and
filtered from gangue the liquid may be electrolyzed in the
manner just described with good results.
BISMUTH.
LITERATURE. Luckow, Z. f. a. Ch., 19, 16; Classen and v. Reiss,
Ber., 14, 1622; Thomas and Smith, Am. Ch. Jr., 5, 114; Moore, Ch.
N. 53, 209; Smith and Knerr, Am. Ch. Jr., 8, 206; Schucht, Z. f. a.
Ch., 22, 492; Eliasberg, Ber., 19, 326; Brand, Z. f. a. Ch., 28, 596;
Vortmann, Ber., 24, 2749 ; Riido r f.f , Z. f. ang. Ch., 1892, 199 ; Smith
and Saltar, Z. f. anorg. Ch., 3, 418; Smith and Moyer, J. Am. Ch. S.,
15, 28; ibid., 15, 1 01 ; Wieland, Ber., 17, 1612; Smith and Knerr,
Am. Ch. Jr., 8, 206; Schmucker, Z. f. anorg. Ch., 5, 199; J. Am. Ch.
S., 15, 203; Kollock, J. Am. Ch. S., 21, 925; Wimmenauer, Z. f.
anorg. Ch., 27, i; Brunck, Ber., 35, 1871; Balachowsky, C. r., 131,
179-182; Ho Hard and Bertiaux, C. r., cxxxix (1904), 839; Exner.
J. Am. Ch. S., 25, 901; KoUock and Smith, J. Am. Ch. S., 27, 1539;
Fischer and Boddaert, Z. f. Elektrochern., 10, 947.
9 ELECTRO-ANALYSIS.
The electrolytic determination of bismuth has received
much attention. Numerous electrolytes have been sug-
gested. Most of them have failed in that the deposits of
metal, unless very small in amount, have almost invaria-
bly been dark in color and have shown a tendency to spongi-
ness. Yet they were in nearly all cases adherent. There
has been an additional objection in many of the methods
to the separation of' peroxide upon the anode. In short,
the appearance of bismuth at both poles has been very dis-
turbing. For these reasons many of the earlier suggestions
have been abandoned, and will be omitted from the present
text.
Vortmann prefers the amalgam method, in accordance
with which dissolve 0.5 gram of bismuth trioxide and 2
grams of mercuric oxide in sufficient nitric acid for the
purpose, dilute with water to 150 c.c., and at the ordinary
temperature electrolyze with N.D 100 = i ampere and 3.5
volts. The amalgam, when the ratio is 4Hg to iBi, will
be silver-white in color. It should be washed without in-
terrupting the current, then carefully dried and weighed
The method is said to be especially well adapted for the
precipitation of large quantities of bismuth.
Wimmenauer has reviewed the different methods pro-
posed from time to time, and from his experience recom-
mends the following procedure: Dissolve 0.1-0.3 gram of
bismuth nitrate in 2-4 c.c. of a glycerol solution (i part
of commercial glycerol and 2 parts of water), dilute with
water to 150 c.c., and electrolyze at 50, in a roughened
dish, with a current of N.D 100 = o.i ampere and 2 volts.
The anode is rotated during the decomposition. This can
be accomplished by a small electric motor, as shown in
Fig. 26. The rotation is supposed to prevent the forma-
tion of peroxide, because the latter, by the movement of
DETERMINATION OF METALS BISMUTH.
97
the anode, is immediately brought in contact with dilute
nitric acid, in which it dissolves. When the anode is at
rest, a protective layer of gas forms about it, and this is
favorable to the deposition of peroxide.
FIG. 26.
A. L. Kammerer, who has very recently made an ex-
haustive study on the electrolytic determination of bis-
muth in this laboratory, where he has tried every form of
cathode and anode with varying electrolytes, concludes that
the following conditions may be relied upon to yield satis-
factory results: 0.10-0.15 gram of metal in i c.c. of nitric
acid (sp. gr. 1.42), 2 c.c. of sulphuric acid (sp. gr. 1.84),
i gram of potassium sulphate, 150 c.c. total dilution
N.D 100 = o.02 ampere, V 1.8. Temperature, 45-5o;
time, 6-7 hours.
The current should be increased the last hour to 0.15
10
98 ELECTRO-ANALYSIS.
ampere. Heat is absolutely essential in order to get a
bright metallic deposit of metal. The deposit should be
washed without interrupting the current, just as has been
recommended with other metals when precipitated from
an acid solution. Close-fitting cover-glasses should always
be used to reduce the evaporation to a minimum. The
metal seemed to be deposited as well upon smooth as upon
roughened surfaces.
The many successful determinations made in accord-
ance with the directions just described indicate that the
method is perhaps the best which has ever been applied in
the case of this particular metal.
In determining bismuth Balachowsky keeps in view the
following points: (a) A slightly acid solution; (b) the
absence of large amounts of the halogens; (c) the use of a
low current density (not exceeding 0.06 ampere per square
decimeter) ; (d) a roughened dish; (e) the addition of urea
or aldehyde; and offers this example: 0.06-1.7 grams of
bismuth sulphate, 5-7 c.c. of nitric acid, 150 c.c. of water,
3.5-5 grams of urea; N.D 100 = 0.04-0.06 ampere and 1-2
volts. Temperature, 6o 76 ; time, 6-10 hours.
When it is necessary to use an alkaline citrate or citric
acid solution in the precipitation of bismuth, observe the
following conditions: 0.1822 gram of bismuth, 3 grams of
citric acid, 125 c.c. total dilution; N.D 100 = o.O3 ampere,
volts = 2. Temperature, 65; time, 6 hours. 0.1820
gram of bismuth was found. Weigh the anode before and
after the electrolysis.
The Rapid Precipitation of Bismuth With the Use of
a Rotating Anode.
As much as 0.5510 gram of the metal, in the presence of
i c.c. of concentrated nitric acid, may be precipitated in
DETERMINATION OF METALS BISMUTH. 99
twenty minutes with a current of N.D 100 = i ampere and
2.5 volts. The anode should rotate at the rate of 700 to
900 revolutions per minute. At first the deposit of metal
will be white and crystalline, becoming loose and black
later but sufficiently adherent for washing and weighing
purposes.
It is preferable, however, to precipitate the bismuth in
the presence of mercury as an amalgam. Thus to a solu-
tion of bismuth nitrate, equivalent to 0.2970 gram of metal
add as much mercury in the form of mercurous nitrate
and i c.c. of concentrated nitric acid. Heat the solution
to boiling and electrolyze with a current of N.D 100 = 5
amperes and 8.5 volts. Complete precipitation of the metals
as an amalgam will occur in from eight to ten minutes.
The Rapid Precipitation of Bismuth With the Use of a
Rotating Anode and a Mercury Cathode.
Frequent reference has been made in preceding para-
graphs concerning the difficulty experienced in the pre-
cipitation of the metal bismuth and emphasis laid repeatedly
on the strict observance of the working conditions which
proved satisfactory so that naturally the analyst uncon-
sciously turns from the electrolytic procedure when esti-
mating this metal. However, with the simple device of
a mercury cup and rotating anode as outlined and used with
the preceding metals the determination can be made with-
out trouble.
To a solution of 0.2273 gram of metal, not exceeding
12 c.c. in volume, add 0.5 c.c. of concentrated nitric acid and
electrolyze with a current of 4 amperes and 5 volts. All
the metal will be precipitated in twelve minutes. Use a
perfectly smooth anode. When it is rough peroxide, in
slight amount, may at the beginning of the experiment
IOO ELECTRO-ANALYSIS.
appear on it but it will rapidly go away. The rotation of
the anode should be quite rapid, so that the mercury may
take up the bismuth which is deposited quickly, as it often
collects in a black mass beneath the anode.
The rate of precipitation from this electrolyte is :
In i minute 0.1305 gram of metal
In 3 minutes 0.2274 gram of metal
In 5 minutes 0.2515 gram of metal
In 8 minutes 0.2732 gram of metal
In 10 minutes 0.2751 gram of metal
In 1 2 minutes . . 0.2775 gram of metal
The substitution of sulphuric for nitric acid makes very
little difference in the rate at which bismuth is precipitated :
In 5 minutes 0.2409 gram
In 10 minutes 0.2764 gram
In 1 5 minutes 0.2770 gram
LEAD.
LITERATURE. Kiliani, Berg-Hiitt. Z., 1883, 253; Luckow, Z. f.
a. Ch., 19, 215; Riche, Ann. de Chim. et de Phys. [5 ser.], 13, 508; Z.
f. a. Ch., 21, 117 ; Classen, ibid., 257; Hampe, Z. f. a. Ch., 13, 183 ; May,
Am. Jr. Sc. and Ar. [3 ser.], 6, 255; also Z. f. a. Ch., 14, 347; Parodi
and Mascazzini, Ber., 10, 1098; Z. f. a. Ch., 16, 469; 18, 588; Riche,
Z. f. a. Ch., 17, 219; Schucht, Z. f. a. Ch., 21, 488; Tenny, Am. Ch.
Jr., 5, 413; Smith, Am. Phil. Soc. Pr., 24, 428; Vortmann, Ber., 24,
2749; Riidorff, Z. f. ang. Ch., 1892, p. 198; Warwick, Z. f. anorg. Ch.,
i, 258; Classen, Ber., 27, 163; Kreichgauer, Ber., 27, 315; Z. f.
anorg. Ch., 9, 89; Classen, Ber., 27, 2060; Medicus, Ber., 25, 2490;
Neumann, Ch. Z. (1896), 20, 381; Hollard, B. s. Ch. Paris, 19, 911;
Linn, J. Am. Ch. S., 24, 435; Marie, Ch. Z., 24, 341, 480; Nissenson
and Neumann, Ch. Z., 19, 1143; Elbs and Rixon, 2. f. Elektrochem.,
9, 267; Danneel and Nissenson, Internationaler Congress fur angew.
Ch. (1903), Band 4, 677; Hollard, B. s. Ch., Series 3, 31, No. 5; Ch.
N., 89, 278; Meillere, J. Phar. Chim., [6] 16, 465; Guess, Eng.
Min. Jr., 81, 328 (1906); Hollard, Ch. Z., 27, 141 (1903); Exner, 25,
DETERMINATION OF METALS LEAD. IOI
J. Am. Ch. S., 25, 904; R. O. Smith, J. Am. Ch. S., 27, 1287; Fischer
and Boddaert, Z. f. Elektrochem., 10, 949; Vortmann, Ann., 351,283.
The metal may be obtained by electrolyzing solutions
of the double oxalate (see Copper and Cadmium), the
acetate, the oxide in sodium hydroxide, or the phosphate
dissolved in the latter reagent or in phosphoric acid of 1.7
specific gravity. While the metal separates well from
either one of these solutions, difficulty is experienced in
drying the deposit, for the moist metal almost invariably
suffers a partial oxidation, thus rendering the results high.
The deposit can be dried, without oxidation, in an atmos-
phere of hydrogen, but for the inexperienced operator
this procedure offers little satisfaction. It is, therefore,
better to utilize the tendency of lead to separate, from
acid solutions, as the dioxide. For trial purposes make
up a definite volume of lead nitrate. Electrolyze several
portions (=0.1 gram lead each) in a platinum dish con-
nected with the anode, using a current of N.D 100 = 1.5-1.7
amperes and 2.36 to 2.41 volts. The volume of the elec-
trolyte should be 100 c.c., and its temperature 5O-6o. 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 20 c.c. of nitric acid of specific gravity
1.35-1.38. This quantity of acid is required when lead
alone is present in solution. To hasten the solution of
any metal which may have found its way to the cathode
interrupt the current for a short time five seconds about
the middle of the determination and again for a brief period
before the precipitation is finished. Chlorides must be
absent. In the presence of other metals the complete depo-
sition of the lead as dioxide occurs with even less acid.
At the end of the precipitation siphon off the acid liquid
102 ELECTRO-ANALYSIS.
and wash in the dish, then dry the deposit at i8o-i9O C,
and weigh. The weight multiplied by 0.866 gives the
quantity of metallic lead present. Numerous experiments
made in this laboratory showed that the deposits of lead
dioxide will weigh too much unless they have been dried
for definite periods at a temperature ranging from 200-
230 C. It is not probable that the excessive weight is due
to the formation of a higher oxide than the dioxide but to
adherent and included water, expelled with difficulty. From
a series of results made upon the drying of the dioxide at
different temperatures it would seem as if the factor with
which to multiply the dioxide should be 0.8643. The de-
posit can be readily dissolved in nitric acid to which oxalic
acid is added, or cover it with dilute nitric acid and insert
a rod of zinc or copper. Henz recommends a nitrite solu-
tion, acidified with nitric acid, for this purpose. Reference
to the literature shows that May preferred, after drying the
deposit, to carefully ignite it and finally weigh as lead oxide
(PbO). This precipitation of lead as dioxide affords an
excellent method by which to separate it from other metals,
e. g. } mercury, copper, cadmium, silver, and all those solu-
ble in nitric acid, or those which, in a nitric acid solution,
are deposited upon the cathode.
Use in these determinations a Classen dish, the inner
surface of which has been roughened by having had a sand
blast projected against it. The deposition of the dioxide
will 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 2 surface with a current of 1.5 am-
peres. Wash with water and alcohol, then dry as pre-
viously directed.
The presence of arsenic in the solution lowers the lead
results. When its quantity is very trifling the discrepancy
may be disregarded. Selenium has a similar effect.
DETERMINATION OF METALS LEAD. 1 03
Lead dioxide, like manganese dioxide (p. 135), 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.
In the analysis of lead ores Nissenson and Neumann
dissolve 0.5 gram of the material in 30 c.c. of nitric acid of
1.4 specific gravity, boil, dilute with water, filter into a
platinum dish, and electrolyze at 6o-7o with a current
of N.D ]00 i ampere and 2.5 volts. The dioxide is
washed and dried as indicated above. One hour is suffi-
cient for the precipitation.
The suggestion made by Vortmann that lead should be
precipitated as an amalgam is not feasible, owing to cer-
tain difficulties. His method, however, will serve for the
separation of the lead from a few metals.
The Rapid Precipitation of Lead Dioxide With the Use
of a Rotating Electrode.
Exner added 20 c.c. of concentrated nitric acid to a solu-
tion of lead nitrate, giving a total volume of about 125 c.c.
and acted upon the same with a current of N.D 100 = 10
amperes and 4.5 volts. The rotating electrode (cathode)
performed 600 revolutions per minute. The deposits had
a uniform, velvety black color. There was no tendency
on the part of the deposit to scale off though more than a
gram of the dioxide was precipitated. The time varied
from ten to fifteen minutes. A platinum dish with sand-
blasted inner surface was used as anode.
R. O. Smith in using a current of N.D 100 = 1 1 amperes
and 4 volts upon a solution of lead nitrate containing 0.4996
gram of lead or 0.5787 gram of dioxide found the rate
of precipitation to be :
104 ELECTRO-ANALYSIS.
In 5 minutes 0.4940 gram lead dioxide
In 10 minutes 0.5708 gram lead dioxide
In 15 minutes 0.5747 gram lead dioxide
In 20 minutes 0.5770 gram lead dioxide
In 25 minutes 0.5787 gram lead dioxide
In 30 minutes 0.5789 gram lead dioxide
The maximum time period for a quarter of a gram of
metal is fifteen minutes, and the maximum time for a half-
gram of metal is twenty-five minutes.
SILVER.
LITERATURE.- Luckow, Ding. p. Jr., 178, 43; Z. f. a. Ch., 19, 15;
Fresenius and Bergmann, Z. f. a. Ch., 19, 324; K rut wig, Ber., 15,
1267; Schucht, Z. f. a. Ch., 22, 417; Kinnicutt, Am. Ch. Jr., 4, 22;
Rudorff, Z. f. ang. Ch., Jahrg. 1892, p. 5; Eisenberg, Thesis, Heidel-
berg, 1895; Smith, Am. Ch. Jr., 12, 335; Fulweiler and Smith, J.
Am. Ch. S., 23, 583; Exner, J. Am. Ch. S., 25, 900; Gooch and
Medway, Am. Jr. Sciences, 15, 320; ibid., Ch. N., 87, 284; Kollock
and Smith, J. Am. Ch. S., 27, 1536; Langness, J. Am. Ch. S., 29, 464;
Fischer and Boddaert, Z. f. Elektrochem., 10, 949.
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 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 electrolysis
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 de-
DETERMINATION OF METALS SILVER.
105
FIG. 27.
posit was compact 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 following conditions
were adopted : The total dilution of the solution was 200
c.c. ; in this there were 0.03-0.04 gram of silver, and 3-6
grams of free nitric acid. The poles were separated about
i cm. from each other, while the current at 5O-6o was
N.D 100 = 0.04-0.05 ampere,
and at the ordinary tempera-
ture it was N.Dj oo = 0.1-0.2
ampere and 2 volts.
In the experiments of Fre-
senius and Bergmann appa-
ratus similar to that in Fig. 27
was employed. It has some de-
cided advantages. Both spiral
(a) and cone (b) are con-
structed of platinum. The
metallic deposition, it will be
understood, occurs upon the
cone, the sides of which are
perforated, so that a uniform
concentration of liquid is preserved throughout the decom-
position. 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 openings. 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 ammonium sul-
phate to the silver solution, previously made alkaline with
io6
ELECTRO-ANALYSIS.
ammonium hydroxide, and employs a current of N.D 100 =
0.02-0.05 ampere and 2.5 volts. In this way, o.i gram of
silver may be precipitated in two hours.
The writer's experience has chiefly been with solutions
of silver containing an excess of a pure alkaline cyanide.
With these peroxide separation does not occur, and a very
weak current will precipitate 0.15-0.20 gram of 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.D 100
= 0.07 ampere. Several examples from a student's note-
book will show how well the method works :
SILVER.
GRAM.
DILUTION.
c.c.
POTASSIUM
CYANIDE.
GRAMS.
CURRENT.
N.D 100 .
VOLTS.
TEMPERA-
TURE.
TIME
HOURS.
SILVER
FOUND.
GRAM.
!
0.2133
125
2
0.03 A
2-5
65
4
0.2132
2
0.2133
125
2
0.03 A
2-5
60
3
0.2133
3
0.2133
125
4
0.04 A
2-5
60
3
0.2131
4
0.2133
125
2
O.O25A
2.7
60
4
0.2134
5'
0.2133
1^5
2
O.O25A
2.7
60
3
0.2135
6
0.2133
125
2
O.O25A
2.7
60
4
0.2125
In trials i and 2 the metal was precipitated upon a dish,
while in 3 and 4 a plate cathode, and in 5 and 6 a cone was
used to receive the silver, which was very adherent, and
brilliant in lustre. It was washed with water, alcohol, and
ether.
Chlorine, bromine, and iodine can be indirectly estimated
electrolytically by first precipitating them as silver salts,
then dissolving the latter in potassium 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
DETERMINATION OF METALS SILVER. IO/
dish, serving as the negative electrode, covering it with
dilute sulphuric or acetic acid, and allowing the positive
electrode to project into the solution. Four Meidinger cells
were strong enough to reduce o.i gram of silver chloride
in ten minutes. The deposit, 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 experiments; also, Prescott and Dunn, Jr. An.
Ch., 3, 373-)
The Rapid Precipitation of Silver With the Use of a
Rotating Anode.
To a solution of silver nitrate, containing 0.4990 gram
of metal, add 2 grams of potassium cyanide, heat the solu-
tion (125 c.c.) almost to boiling and electrolyze with a cur-
rent of N.D 100 = 2 to 2.8 amperes and 5 volts. The metal
will be precipitated in the form of a dense white deposit in
nine to ten minutes. Have the anode perform 700 revo-
lutions per minute.
The rate of precipitation, with a flat spiral anode, from
this electrolyte was as follows :
In i minute 0.2046 gram
In 2 minutes 0.3391 gram
In 3 minutes 0.4858 gram
In 4 minutes 0.5043 gram
In 5 minutes 0.5225 gram
In 7 minutes 0.5270 gram
In 10 minutes 0.5301 gram
By using the dish anode described on p. 73 the 0.53 gram
of silver present was precipitated in two minutes, all but a
very small quantity being deposited in the first minute.
Thus with 5 volts and nine to ten amperes the rate of precipi-
tation was :
108 ELECTRO-ANALYSIS.
In i minute 0.5116 gram
In 2 minutes 0.5304 gram
In 3 minutes 0.5306 gram
In 4 minutes 0.5306 gram
One fails to see how any gravimetric method followed in
the precipitation of silver could give results like the preced-
ing. The time factor is almost eliminated. Every part of
the procedure is satisfactory.
Gooch and Meday also obtained very excellent determina-
tions of silver by depositing it upon a rotating cathode
(P- 47)-
The Rapid Precipitation of Silver With the Use of a
Rotating Anode and Mercury Cathode.
In determining silver in this manner have it in the form
of nitrate. An example will illustrate the best conditions.
To 5 c.c. of silver nitrate solution (=0.2240 gram of
silver) add 5 drops of nitric acid (30 drops equaled i c.c.).
Rotate the anode at a speed of 1200 revolutions per minute.
At the end of five minutes the precipitation will be complete.
Then proceed as directed in all determinations made in this
way.
An anodic deposit will show itself in the first minute
or two, but it will entirely disappear in four or five minutes.
The anode should have a high speed to insure agitation of
the mercury thereby making the absorption of silver more
certain. It is not advantageous to have a greater concen-
tration than 0.3500 gram of silver in 5 cubic centimeters.
The rate of precipitation in this electrolyte was :
In i minute 0.1874 gram of silver
In 2 minutes 0.2178 gram of silver
In 3 minutes 0.2207 gram of silver
In 4 minutes 0.2240 gram of silver
DETERMINATION OF METALS ZINC. ICK)
ZINC.
LITERATURE. Wright son, Z. f. a. Ch., 15, 303; Parodi and Mas-
cazzini, Ber., 10, 1098; Z. f. a. Ch., 18, 587; Riche, Z. f. a. Ch., 17,
216; Beilstein and Jawein, Ber., 12, 446; Z. f. a. Ch., 18, 588;
Riche, Z. f. a. Ch., 21, 119; Reinhardt and I hie, Jr. f. pkt. Ch. [N.
F.], 24, 193; Classen and v. Reiss, Ber., 14, 1622; Gibbs, Z. f. a.
Ch., 22, 558; Luckow, Z. f. a. Ch., 25, 113; Brand, Z. f. a. Ch., 28,
581; Warwick,'Z. f. anorg. Ch., i, 258; Vortmann, Ber., 24, 2753;
Rudorff, Z. f. ang. Ch., Jahrg. 1892, 197; Vortmann, M. f. Ch., 14,
536; v. Malapert, Z. f. a. Ch., 26, 56; Her rick, Jr. An. Ch., 2, 167;
Jordis, Z. f. Elektrochem., 2, 138, 563, 655; Millot, B. s. Ch. Paris.
37, 339.' v. Foregger, Dissertation, Bern, 1896; Rider er, J. Am. Ch.
S., 21, 789; Nicholson and A very, J. Am. Ch. S., 18, 659; Pa week,
Berg-Hiitt. Z., 46, S7o~573 ; Pa week, Ch. Z. (1900), 24, No. 80;
Ho Hard, B. s. Ch. Paris (Series 3), 29, 262; Ch. N. (1903), 87, 259;
Amberg, Ber., 36, 2489 (1903); Spitzer, Z. fur Elektrochem., n,
391; C : urrie, Ch. N., 91, 247; Danneel and Nissenson, Interna-
tionaler Congress fur angew. Ch. (1903), 4, 679; Price and Judge,
Ch. N., 94, 18; Ingham, J. Am. Ch. S., 26, 1269; Jene, Ch. Z., 29,
801 ; Exner, J. Am. Ch. S., 25, 899; Langness, J. Am. Ch. S.,
24, 463; Kollock and Smith, Am. Phil. Soc. Pr., xliv, 137 (1905);
Fischer and Bod'daert, Z. f. Elektrochem., 10, 946; Foerster, Z. f.
angw. Ch., 19, 1889 (1906); Kollock and Smith, Am. Phil. Soc. Pr.,
45, 256.
Much has been written upon the electrolytic estimation
of zinc. The personal experience of the writer inclines
him to give preference to the method suggested 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 4 c.c. of a solution of ammonium
acetate, 20 c.c. of 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 millimeters.
The precipitation can be made in a beaker, using a weighed
platinum cone (Fig. 27) as the cathode. The current for
this purpose should be 0.5 ampere and 5.9-6.3 volts. At
IIO ELECTRO-ANALYSIS.
5O-6o, with a current of 0.5 ampere, the pressure will
be 4.8-5.2 volts and the deposit of metal will be most satis-
factory. When the precipitation of metal has ended, which
may be ascertained by removing a small quantity of the
liquid with a capillary tube and bringing 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 precipitated 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, Rii-
dorff). It "is exceedingly difficult to remove, and to pre-
vent its occurrence it is best to coat the platinum dish with
a thin layer of copper or silver before precipitating the
zinc (p. 113).
Beilstein and Jawein add sodium hydroxide to the solu-
tions of zinc nitrate or sulphate, until a precipitate is pro-
duced, dissolve it in potassium cyanide, and dilute with
water to 150 c.c. The decomposition is carried out in a
rather large beaker, the cathode being either the platinum
cone already described (p. 105), or a rather large platinum
crucible suspended from a cork, perforated by a copper
wire, touching the inner surface of the crucible. If the
decomposition takes place at the ordinary temperature, use
a current of N.D 100 = o.5 ampere and 5.8 volts. The
precipitation will be complete in from two to two and one-
half hours. It may be reduced to one and one-half to
one and three-quarter hours by heating the electrolyte to
60 and applying a current of the density just given and
5 volts. Wash the deposit as instructed above.
Reinhardt and Ihle have objected to nearly all the
methods which have been proposed for the electrolytic
DETERMINATION OF METALS ZINC. I I I
estimation of zinc. They say of the Beilstein and Jawein
method . . . that the results are fairly good, . . . but a
strong current is necessary, otherwise the precipitation of
the zinc is slow and incomplete, . . . the positive pole di-
minishes in weight very appreciably, . . . finally, work-
ing 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 suggested by Reinhardt and Ihle is, however, very
excellent 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 sul-
phate or chloride, neutral as possible, with an excess of
neutral potassium oxalate, until the precipitate, which appears
at first, redissolves. Or, observing the recommendation of
Classen, add 4 grams of potassium or ammonium oxalate
to the solution, acidulate the latter with tartaric acid
(3:50), dilute to 150 c.c. with water, heat to 60, and
electrolyze in copper-coated platinum dishes with N.D 100 =
0.5-1.5 amperes and 3.5-3.8 volts. Two hours will be
sufficient for complete precipitation.
The immediate decomposition of the zinc oxalate is into
zinc and carbon dioxide (two molecules), and the potas-
sium oxalate into carbon dioxide (two molecules) and
potassium; the latter then reacts with the water, so that
while an abundant liberation of hydrogen occurs at the
cathode, the alkali simultaneously set free is converted into
acid potassium carbonate by the carbon dioxide at the
anode :
ZnC 2 O 4 + K 2 C 2 O 4 = (Zn ;+ 2 KOH + H 2 ) + 4 CO 2 .
Cathode. Anode.
2KOH + 2 CO, = 2
I I 2 ELECTRO-ANALYSIS.
Therefore, just as long as zinc oxalate is being decom-
posed, considerable evolution of gas is noticeable at the
positive electrode, and when this diminishes, and occa-
sional bubbles escape, the decomposition 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 quantity of 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 car-
bonate produced during the decomposition offers great
resistance to the current; it is, therefore, advisable to add
potassium sulphate to the solution to increase its conduc-
tivity. Reinhardt and Ihle recommend the following solu-
tions for use in decompositions like that just described: 166
grams of potassium oxalate in i liter of water; 250 grams
of potassium sulphate in i liter of water, and a solution of
oxalic acid saturated at 15 C.
Experiments. (i) 40 c.c. of a solution of zinc sulphate
( =0.1812 gram of metallic zinc), to which were added 50
c.c. of potassium oxalate and 100 c.c. of potassium sulphate,
were electrolyzed with a current of N.D 100 = 0.3 ampere
and 3.9-4.2 volts, at the ordinary temperature. After three
to four hours the current was interrupted. The precipitated
zinc weighed 0.1814 gram. (2) 2.1867 grams of brass
(containing tin, copper, lead, and zinc) were dissolved in
nitric acid and the tin determined in the usual gravimetric
way. Its quantity was found to be 0.04 per cent. In the
filtrate, containing nitric acid, lead and copper were deter-
mined simultaneously by electrolysis (the copper separated
upon the cathode and the lead as dioxide upon the anode) :
r a __ .8s% Pb and 64.60% Cu.
* oun(1 \fc_- 0.85% Pb and 64.62% Cu.
DETERMINATION OF METALS ZINC. 113
The acid liquid was siphoned off from the deposits, evap-
orated to dryness with sulphuric acid, neutralized with
caustic potash, and then to this ( 100 c.c. in volume) solu-
tion 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 plati-
num cone for the cathode (p. 105). To avoid the peculiar
spots which electrolytic zinc shows upon a platinum sur-
face, it will be best to first coat the negative 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 depositions. 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.
Jordis prefers lactic to oxalic acid in the electrolysis of
zinc salts. To the solution containing 0.2 gram of metallic
zinc he added 5 grams of ammonium lactate, 2 grams of
lactic acid, and 5 grams of ammonium sulphate. The liquid
was diluted to 230 c.c. and acted upon at 60 with a current
of N.Dj 00 = o.io-o.23 ampere and 3.4-3.9 volts. The
electrolyte was usually agitated (p. 97). The anode and
cathode were 1.5 cm. apart. The time for complete preci-
pitation occupied four and a quarter hours. A copper-
plated platinum dish was used as cathode.
Nicholson and Avery, adopting the suggestion of War-
wick, add 3 c.c. of formic acid to the zinc salt solution, then
nearly neutralize with sodium carbonate, dilute to 150 c.c.,
and electrolyze at the ordinary temperature with a current
varying from 0.5 to I ampere.
Millot, Kiliani, and v. Foregger use sodium zincate as
n
114 ELECTRO-ANALYSIS.
electrolyte, giving the following example : To the solution
of i gram of zinc sulphate add 2 to 4 grams of sodium
hydroxide, dilute to 125 c.c. with water, heat to 50, and
electrolyze with N.D 100 = 0.7-1.5 amperes and 3.9-4.5
volts. All of the metal will be deposited in two hours. The
character of the deposit is improved with the increase in
the quantity of sodium hydroxide. In applying this method
to the determination of zinc in its ores, Jene proceeds as fol-
lows : Dissolve 0.5 gram of the ore in aqua regia, evaporate
to dryness, add I to 2 c.c. of dilute sulphuric acid ( i : i )
which expel by heat. When the mass is cold, add water,
boil, filter and wash the residue with hot water. The filtrate
should not exceed 80 to 100 c.c. in volume. It is ready
for electrolysis. Add to it 4 to 7 grams of solid sodium
hydroxide, allowing the latter to dissolve completely. Heat
to 50 C, and electrolyze without any regard to the hydrox-
ides swimming in the solution. Use a copper-plated plati-
num dish with N.D 100 = i ampere and a pressure of from
3.8 to 4.2 volts. The deposition will be finished in from
ij to 2 hours. The end of the decomposition is ascertained
by suspending a perfectly clean strip of sheet copper over
the edge of the dish and observing whether, after fifteen
minutes, it has become coated with any zinc.
Riche employs " a solution of the acetate with an excess
of ammonium acetate, obtained by supersaturation 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 3 grams of sodium
acetate and 10 drops of ordinary acetic acid. When there
is an insufficiency of acetic acid, the zinc deposit becomes
spongy. Ammonium acetate may be substituted for the
sodium salt. After two hours 0.1063 gram of metallic
DETERMINATION OF METALS ZINC. IIS
zinc was obtained, the required quantity being 0.1072 gram.
The temperature should be 60 and the current N.D 100 =
0.5 ampere and 4.8-5.2 volts.
Moore seems to have obtained exceedingly satisfactory
results by precipitating a solution of zinc sulphate with
sodic phosphate, then adding an excess of ammonium car-
bonate, and after dissolving the precipitate in potassium
cyanide, the solution was electrolyzed at a temperature of
80. (See method of Beilstein and Jawein.) The metal
was deposited upon a silver-plated electrode. An excellent
procedure, originating with Luckow and previously noticed
in the Historical section, consists in introducing 0.5 gram of
metallic mercury into the dish in which it is intended to elec-
trolyze the solution of the zinc salt. It is, of course, under-
stood that the platinum dish and the drop of mercury are
weighed together. A zinc amalgam is precipitated ; it dis-
tributes itself in a beautiful adherent layer over the surface
of the dish.
Paweck believes that in the amalgam method suggested
by Vortmann much inconvenience is experienced in weigh-
ing out the mercuric chloride and subsequently re-calcu-
lating it into metal ; further, that by frequent use the surface
of the platinum cathode changes to spongy platinum, thus
giving rise to considerable loss. To avoid these disadvant-
ages he suggests the use of amalgamated zinc or brass elec-
trodes in gauze form. The introduction of these eliminates
the addition of a mercury salt, while the gauze form favors
the deposition and prevents the collection of hydrogen bub-
bles on the under side of the cathode, whereby a spongy
zinc deposit is likely to be produced. The gauze electrodes
are semi-cylindrical in shape, 6 cm. in diameter, two being
attached to a brass rod at a distance of 12 mm. After they
have been cleaned, they are amalgamated or coated with
I 1 6 ELECTRO-ANALYSIS.
mercury by electrolyzing a solution containing 0.6 gram of
mercuric chloride. The amalgam is washed with alcohol,
ether, dried and weighed. The electrolyte contains the
zinc salt, Seignette salt and alkali. It may be electrolyzed
with a current of 0.1-0.5 ampere and 2.6-3.6 volts. The
deposit should be dried at 3O-4O. (See p. 65.)
Vortmann has found that zinc may be readily precipitated
from its solution in the presence of an excess of sodium
hydroxide and sodium tartrate. The deposit is gray in
color and adheres well to the dish. The current density
(N.D 100 ) 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.
The Rapid Precipitation of Zinc With the Use of the
Rotating Anode.
In an alkaline electrolyte (NaOH) proceed as follows:
To 25 c.c. of solution ( = 0.2490 gram of zinc) add 8
grams of solid sodium hydroxide, dilute to 125 c.c. with
water, heat almost to boiling then remove the flame and
electrolyze with N.D 100 = 5 amperes and 6 volts. The
anode should make about 600 revolutions per minute. The
precipitation will be complete in twenty minutes. The de-
posit will be adherent, smooth, hard and gray in color. The
amount of sodium hydroxide may vary within quite wide
limits.
In all precipitations of zinc in platinum vessels coat the
latter with silver. If this is clone one such coating will
serve through a number of precipitations. After the dish
and its deposit have been weighed fill the dish to the brim
with sulphuric acid previously diluted with about fifty times
its volume of water, then set the dish aside until the action
ceases. Next pour the solution into a beaker, rinse the dish
DETERMINATION OF METALS ZINC. I I/
with water and heat it to faint redness over a free flame
while holding it in a nickel forceps. Cool under a faucet,
fill a second time with dilute acid, rinse after a few minutes,
heat as before and give a third treatment with the same
acid. Finally, after rinsing with clean water, wipe dry
externally, ignite, cool in a desiccator and weigh. The
entire time in cleaning the dish need not exceed six minutes.
One coat of silver sufficed for more than a hundred deter-
minations of zinc.
The rate of precipitation of zinc from the preceding elec-
trolyte, using a current of 5 amperes and 8 volts, was
In i minute 0.1028 gram
In 2 minutes 0.1847 gram
In 3 minutes 0.2921 gram
In 4 minutes 0.3498 gram
In 5 minutes 0.421 7 gram
In 7 minutes -. 0.4691 gram
In i o minutes 0.4740 gram
In 1 2 minutes 0.4780 gram
In 1 5 minutes 0.4780 gram
In an alkaline acetate electrolyte the deposition is also
very rapid. An example will show this
A solution of zinc sulphate, equivalent to 0.5004 gram of
metal, containing 3 grams of sodium acetate and 0.2 c.c. of
acetic acid (30 per cent.), was diluted with water to 125 c.c.
and electrolyzed with a current of N.D 100 = 4 amperes and
10 volts. In fifteen minutes 0.5002 gram of zinc was pre-
cipitated on the silver-plated platinum dish. The deposit
was light blue in color and crystalline. The anode per-
formed 600 revolutions per minute.
Ingham determined the rate of precipitation of zinc from
this electrolyte:
1 1 8 ELECTRO- ANALYSIS.
In i minute . . .. 0.0933 gram
In 2 minutes 0.1500 gram .
In 3 minutes 0.2326 gram
In 4 minutes 0.2957 gram
In 5 minutes 0.3773 gram
In 7 minutes 0.4645 gram
In i o minutes 0.4736 gram
In 1 5 mihutes 0.4766 gram
In 20 minutes 0.4779 gram
when the amount of metal in the electrolyte equaled 0.4780
gram.
The formate electrolyte was prepared as follows :
To the salt solution (= 0.2490 gram of zinc) were added
5 grams of sodium carbonate and 4.6 c.c. of formic acid,
sp. gr. 1.22. The solution was diluted with water to 125
c.c., heated to boiling and acted upon with a current of
N.D 100 = 5 amperes and 8 volts. In twenty minutes the
entire amount of metal was precipitated. The deposit was
fine-grained and very adherent.
The rate of precipitation was found to be :
In i minute 0.0839 gram of metal
In 2 minutes 0.1418 gram of metal
In 3 minutes 0.1723 gram of metal
In 5 minutes 0.2095 gram of metal
In 7 minutes 0.2244 gram of metal
In 10 minutes 0.2464 gram of metal
In 12 minutes 0.2483 gram of metal
In 1 5 minutes 0.2490 gram of metal
In 20 minutes 0.2490 gram of metal
In an ammomacal electrolyte it is possible to precipitate
the metal very satisfactorily by using a rotating anode. It
is well established that with stationary electrodes the same
electrolyte is impracticable. To use it proceed in the fol-
lowing manner :
Add to the zinc salt solution 5 c.c. of hydrochloric acid
DETERMINATION OF METALS ZINC. I -1 9
(sp. gr. 1.21), 25 c.c. of ammonium hydroxide (sp. gr.
0.95) and one gram of ammonium chloride. Let the total
dilution be 125 c.c. Electrolyze with N.D 100 = 5 amperes
and 5 volts. In twenty minutes a quarter of a gram of
metal will be fully precipitated. The deposit will be all
that one can wish. There is no likelihood of the anode
being attacked by the chlorine. This electrolyte can be
used in estimating the zinc content of zincblende. Weigh
off 0.5 gram of the powdered ore into a No. 5 porcelain
dish, moisten it with water, add nitric acid (sp. gr. 1.41)
sufficient to cover it and digest upon an iron plate. In
about twenty minutes after action has ceased raise the cover
enough to let the fumes escape and rapidly evaporate the
liquid to dryness. Cover the residue with pure hydro-
chloric acid (sp. gr. 1.21) and again evaporate to dryness.
Repeat the treatment with hydrochloric acid, taking care
to avoid overheating and volatilization of any chloride.
Finally, moisten the dry salts with strong hydrochloric acid
and take up with hot water. This operation need not re-
quire more than an hour and ten minutes. Having filtered
out the gangue, precipitate the iron with ammonium hy-
droxide, receiving the filtrate from it in the customary sil-
vered and weighed platinum dish, the precipitate not being
washed with water, but after the substitution of a porcelain
vessel for the platinum the iron hydrate should be dissolved
from off the moist filter in warm dilute acid and reprecipi-
tated with ammonium hydroxide. Two precipitations will
be necessary to free the iron completely from zinc. To the
solution in the platinum dish add 0.5 gram of ammonium
chloride, preferably in the dry form, and electrolyze the
solution (125 c.c. in volume) with a current of 5 amperes
and 6 volts. Twenty minutes are sufficient for the precipi-
tation. The deposit will be crystalline, adherent but not
spongy.
1 20
ELECTRO-ANALYSIS.
By this method the zinc content of a blende may be made
in a little more than two hours from the time of weighing
off the powdered ore to the weighing of its zinc content.
If the iron in the ore, after removal of the gangue, is
precipitated as the basic acetate or formate, the filtrate from
it can be used for the electrolytic determination of the zinc,
using the rotating anode. The results will be most satis-
factory.
The Rapid Precipitation of Zinc With the Use of the
Rotating Anode and Mercury Cathode.
This metal is especially readily determined in this manner.
Perhaps no better evidence of this can be given than may be
found in the accompanying table where varying condition?
are presented in detail.
ZINC.
6
z
L
(/} 5
Q
U u
<C U
Z
U
IN C-C.
H in
z a
o
m *
[INUTES
z
Q .
R
K
O
w <
w
tf w
J
p S 5
^;
O <
z
X
P-0
U
-> H
X
iJ
o
a!
o
P a z
F
U
Z
o
X
N
*
H
N
I
0.2025
15
7
750
30
0.2027
+ 0.0002
2
0.2025
15
7
750
25
0.2030
-f 0.0005
3
O.2O25
15
7
750
25
0.2015
O.OOIO
4
O.2O25
o
15
7
750
25
0.2020
O.OOO5
5
0.2025
o
15
7
750
25
0.2025
6
o. 2025
o
IO
7
750
25
O.2O24
O.OOOI
7
O.2O25
.25
IO
7
750
30
o. 2027
+ O.OOO2
8
0.4040
.25
20
5
6
750
45
0.2054
+ O.OOO4
9
0.2025
25
10
5
750
25
o 2025
10
0.2025
25
10
5
750
25
/> r*
0.2029
+ 0.0004
1 1
O'2O25
25
* 5
75
2 5
o. 2025
12
0.2025
.25
15
5
750
20
0.2027
+ O.OOO2
13
O.2O25
25
15
2
6
750
15
0.2030
-j- O.OOO5
O.2O25
25
15
2
6
750
15
0. 2020
O.OOO5
15
O.2O25
25
2
6
750
15
0.2021
O.OOO4
16
0.4050
.25
15
5
8
1,400
6
0.4057
+ O.OO07
17
0.4050
25
15
5
8
480
6
0.4045
- 0.0005
18
0.4050
25
15
5-6
7-5
480
8
0.4042
O.OOOS
19
0.4050
25
10
5
7
640
5
0.4050
DETERMINATION OF METALS ZINC. 121
The rate of precipitation is interesting :
With a current of one ampere and five volts acting upon
15 c.c. of a zinc sulphate solution, containing 0.2025 gram
of metal, there was precipitated :
In 5 minutes o.i 196 gram
In 10 minutes , 0.1774 gram
In 15 minutes 0.1897 gram
In 20 minutes 0.2002 gram
In 25 minutes 0.2027 gram
With a like volume of solution, to which had been added
0.4 c.c. of concentrated sulphuric acid; a current of two
amperes and seven volts, precipitated :
In 5 minutes 0.1860 gram of zinc
In 10 minutes 0.1998 gram of zinc
In 1 5 minutes 0.2020 gram of zinc
On dissolving double the quantity of zinc in 15 c.c.,
adding 0.25 c.c. of concentrated sulphuric acid, a current of
1.5 amperes and 10 volts, and an anode rotating at the rate
of 800 revolutions per minute, precipitated :
In 10 minutes 0.3701 gram
In 1 5 minutes 0.3997 gram
In 20 minutes 0.401 1 gram
In 30 minutes 0.4058 gram
The same mass of zinc in twenty cubic centimeters was
electrolyzed with a current of 2 amperes and 6 volts, other
conditions being identical, at this rate :
In 10 minutes 0.3352 gram
In 15 minutes 0.4010 gram
In 20 minutes 0.4030 gram
In 30 minutes 0.4050 gram
An anode rotating at 440 revolutions per minute and
again at 1000 revolutions made no apparent difference in
12
122 ELECTRO-ANALYSIS.
the rate at which the metal was deposited. The mercury
should not be allowed to accumulate too much of the metal
when it does, results are not obtained so quickly. Con-
centration of the electrolyte is most favorable to rapid and
satisfactory depositions of the zinc metal.
NICKEL AND COBALT.
LITERATURE. Gibbs, Z. f. a. Ch., 3, 336; Z. f. a. Ch., n, 10; 22, 558;
Merrick, Am. Ch., 2, 136; Wright son, Z. f. a. Ch., 15, 300, 303, 333;
Schweder, Z. f. a. Ch., 16, 344; Cheney and Richards, Am. Jr. Sc.
and Ar. [3], 14, 178; Ohl, Z. f. a. Ch., 18, 523; Luckow, Z. f. a. Ch.,
19, 16 ; Bergmann and Fresenius, Z. f. a. Ch., 19, 314; Riche, Z.
f. a. Ch., 21, 116, 119; Classen and v. Reiss, Ber., 14, 1622, 2771*;
Schucht, Z. f. a. Ch., 22, 493; Kohn and Woodgate, Jour. Soc.
Chem. Industry, 8, 256; Riidorff, Z. f. ang. Ch., Jahrg. 1892, p. 6;
Brand, Z. f. a. Ch., 28, 588; Le Roy, C. r., 112, 722; Vortmann, M.
f. Ch., 14, 536; v. Foregger, Dissertation, 1896, Bern; Campbell and
Andrews, J. Am. Ch. S., 17, 125; Oettel, Z. f. Elektrochem., i, 192;
Fresenius and Bergmann, Z. f. a. Ch., 19, 320; Foster, Z. f. Elektro-
chem., 6, 160; W inkier, Z. f. anorg. Ch., 8, 291; Hollar d, B. s. Ch.
[Series 3], 29, 22; Danneel and Nissenson, Internationaler Congress
fur angw. Ch., (1903) 4, 679; Per kin and Preble, Ch. N., 90, 307;
Exner, J. Am. Ch. S., 25, 899; Smith, J. Am. Ch. S., 26, 1595;
Kollock and Smith, Am. Phil. Soc. Pr., 44 (1905), 137; Fischer
and Bod'daert, Z. f. Elektrochem., 10, 946; Foerster, Z. f. angw.
Ch., 19, 1889 (1906); Kollock and Smith, Am. Phil. Soc. Pr., 45,
262; Fischer, Z. f. Elektrochem., 13, 361.
These metals are precipitated from solutions of their
double cyanides, double oxalates, and sulphates mixed with
alkaline acetates, tartrates, and citrates, or from ammoni-
acal 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 series
of experiments with nickel and cobalt, give the following
as satisfactory conditions: 50 c.c. nickel solution (= 0.1233
DETERMINATION OF METALS NICKEL, COBALT. 123
gram of nickel), 100 c.c. of ammonia (sp. gr. 0.96), 10 c.c.
of ammonium sulphate (305 grams of the salt in i liter
of water), 100 c.c. of water; separation of the electrodes
J J cm.; time, four hours. The current was N.D ]00 =
0.5-0.7 ampere and 2.8-3.3 v l ts at tne ordinary tem-
perature. The nickel found weighed 0.1233 gram. Ap-
paratus suitable for the decomposition just described is
FIG. 28.
represented in Fig. 28. The metal is deposited upon the
weighed platinum cone in the beaker, C. The vessel is
covered with a glass lid having suitable apertures for the
positive 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 sulphocarbonate. If the latter
causes only a faint rose-red coloration the deposition of
metal may be considered complete. If the electrolysis is
unnecessarily prolonged, metallic sulphide may be produced
1 24 ELECTRO-ANALYSIS.
(Lehrbuch der analyt. Chemie, Miller and Kiliani). It
is not advisable to interrupt the current or to remove the
cone from the electrolyzed 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 ; x is a doubly bent tube extending 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
electrolyzes with a current density of N.D 100 = 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 Berg-
mann, is here given as a guide in determining cobalt: 50
c.c. of cobalt sulphate (= 0.1280 gram of cobalt), 100 c.c. of
ammonia, 10 c.c. of ammonium sulphate, 100 c.c. of water;
current N.D 100 = 0.5-0.7 ampere and 2.8-3.3 vo ^ ts at tne
ordinary temperature; separation of electrodes, J-J cm.
Time, five hours. The deposited cobalt weighed 0.1286
gram.
Use potassium sulphocarbonate to test when the metal
is fully reduced; it gives a wine-yellow coloration with
even the most dilute solutions of cobalt salts.
When too little ammonia is present in the electrolyte the
results are bad; too much of this reagent retards the deposi-
tion of the cobalt.
v. Foregger adds 15 to 20 grams of ammonium car-
bonate to the solution of i gram of nickel sulphate, dilutes
with water to 150 c.c., heats to 60, and electrolyzes with
N.D 100 = 1-1.5 amperes and 3.5-4 volts. Two hours will
be required for the precipitation.
DETERMINATION OF METALS NICKEL, COBALT. 125
Oettel observed that nickel could be, contrary to gen-
eral statements, as well precipitated from an ammoniacal
chloride as from an ammoniacal sulphate solution. With
a current of N.D-, 00 = 0.45 ampere in the presence of 40
c.c. of free ammonia '(sp. gr. 0.92), 10 grams of ammonium
chloride and nickel chloride equivalent to 1.0456 grams of
metal, total dilution 200 c.c., he succeeded in throwing
out 1.0462 grams of metal in six and one-quarter hours.
Nitric acid should not be present. More difficulty was
experienced with cobalt. The most favorable results were
obtained with a current of N.D 100 = 0.4-0.5 ampere.
The quantity of ammonium chloride should be at least
four times that of the cobalt and the solution should con-
tain one-fifth of its volume of free ammonia (sp. gr. 0.92).
When precipitating these metals from the solutions of their
double oxalates, the conditions should be: 4 to 5 grams of
ammonium oxalate, 120 c.c. total dilution, temperature 60 -
70, with N.D 100 = i ampere and 4 volts.
The writer has electrolyzed cobalt compounds contain-
ing an excess of an alkaline acetate (see Zinc) with per-
fectly satisfactory results, and would recommend such solu-
tions for this particular metal.
In this laboratory the following conditions are observed
in precipitating nickel from a cyanide solution: Add o.i
gram more of alkaline cyanide than is necessary for the
precipitation and re-solution, 2 grams of ammonium car-
bonate, dilute to 150 c.c., heat to 60, and electrolyze with
N.D 100 =i.5 amperes and 6-6.5 volts. The nickel will
be fully precipitated in three and one-half hours. Cobalt
may be precipitated under similar conditions.
Sodium pyrophosphate precipitates a greenish-white pyro-
phosphate from nickel solutions, an excess of the reagent
dissolves the precipitate, while the liquid becomes yellow-
1 26 ELECTRO-ANALYSIS.
green in color. The latter is changed to green by am-
monium carbonate, and to blue by ammonium hydroxide.
When electrolyzing 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 of 0.5 to 0.8
ampere will be sufficient to throw out the nickel in nine
hours. This method will serve equally well for the estima-
tion of cobalt.
In determining nickel, Campbell and Andrews dissolve
nickel hydrate in 30 c.c. of a 10 per cent, solution of
sodium phosphate, add 30 c.c. of ammonia to the same,
dilute to 125 c.c. and electrolyse with N.D 100 = o.i4 am-
pere, the electrodes being separated 5 mm. The precipita-
tion is complete in twelve hours.
The Rapid Precipitation of Nickel With the Use of a
Rotating Anode.
The results obtained by Exner in the precipitation of
metals with the aid of a rotating anode have led to a most
careful investigation of the best conditions for each metal.
This study, with nickel, has developed most interesting
data in the hands of West, J. Am. Ch. S., 26, 1596. The
details are given under several electrolytes. The condi-
tions there described, if adhered to, will lead to the most
satisfactory .results. The dilution of the various electro-
lytes ranged from 100 to 125 c.c., representing a cathode
surface of 100 sq. cm., while the anode performed 500 to
600 revolutions per minute. From solutions containing an
excess of ammonia the nickel deposits were crystalline and
gray in color, while in acid solutions the metal was brilliant
and very metallic in appearance closely resembling the
platinum. Sometimes peroxide appeared on the anode.
DETERMINATION OF METALS NICKEL, COBALT. I2/
It was made to disappear, in ammoniacal solutions, by add-
ing more ammonium hydroxide to the electrolyte, and if it
occurred in acid solutions by lowering the current toward
the end of the decomposition, and after a few minutes again
increasing it, or by introducing into the acid liquid a few
drops of a mixture consisting of 5 c.c. of glycerol, 45 c.c.
of alcohol and 50 c.c. of water.
In an ammoniacal acetate electrolyte the working condi-
tions should be :
For 0.4444 gram of nickel, 25 c.c. of ammonium hydrox-
ide (sp. gr. 0.94), 10 c.c. of acetic acid and 125 c.c. dilu-
tion, a current of N.D 100 = 5 amperes and 4.6 volts. In
twenty minutes the metal will be completely precipitated.
In the presence of sodium acetate and free acetic acid the
precipitation is slower. Thirty minutes were necessary for
the precipitation of the quantity of metal mentioned in the
preceding paragraph.
In an electrolyte of ammonium hydrate and ammonium
sulphate, which is the time-honored solution for the deposi-
tion of nickel, conditions like these will answer:
Electrolyze the salt solution (containing i.oioo gram of
metal), 1.2 gram of ammonium sulphate and 30 c.c. of
ammonium hydroxide (sp. gr. 0.94) with a current of 5.2
amperes and 6.5 volts. The precipitation will be complete
in twenty-five minutes.
The rate of precipitation, using a solution containing
0.5050 gram of metal, with a current of N.D 100 = 4 am-
peres and 5.5 volts was:
In i minute 0.0571 gram
In 2 minutes o.i 164 gram
In 3 minutes o. 1 549 gram
In 4 minutes 0.2000 gram
In 5 minutes 0.2510 gram
128 ELECTRO-ANALYSIS.
In 7^2 minutes 0.3580 gram
In 10 minutes 0.4450 gram
In 15 minutes 0.5007 gram
In 20 minutes 0.5050 gram
A formate electrolyte answers admirably for the precip-
itation of nickel.
To a solution containing 0.4444 gram of metal, add 20
c.c. of ammonium hydroxide (0.094 sp. gr.) and 10 c.c. of
formic acid, then electrolyze with a current of N.D 100 = 5
amperes and 4 volts. All of the metal will be precipitated
in fifteen minutes.
Or, the metal may be completely precipitated with sodium
carbonate and the precipitate be dissolved in an excess of
formic acid. For example, to a solution of nickel sulphate
(0.4444 gram of nickel) add five grams of sodium carbon-
ate and 22 c.c. of formic acid (25 per cent.), then elec-
trolyze with a current of N.D 100 = 5 amperes and 4 volts.
In 30 minutes the metal will be completely precipitated.
The rate of precipitation in this electrolyte was, with a
current of 5 amperes and 4 volts, as follows :
In 5 minutes 0.2474 gram
In 7^ minutes 0.3260 gram
In 10 minutes 0.3688 gram
In 1 5 minutes , 0.4323 gram
In 20 minutes 0.4394 gram
In 30 minutes 0.4448 gram
Nickel is quite easily determined in an electrolyte of
ammonium lactate. Dilution and speed should be the same
as in the preceding electrolytes.
Conduct a current of 5 amperes and 7.5 volts through
the solution (containing 0.4444 gram of nickel), in which
are present 25 c.c. of ammonium hydroxide (sp. gr. 0.94)
and 2.5 c.c. of lactic acid. The precipitation will be com-
plete in twenty minutes. The rate of precipitation is :
DETERMINATION OF METALS NICKEL, COBALT. I
In 5 minutes 0.3 151 gram
In 75/2 minutes .0.4056 gram
In 10 minutes 0.4344 gram
In 1 5 minutes 0.4443 gram
In 20 minutes 0.4443 gram
The Rapid Precipitation of Nickel With the Use of the
Rotating Anode and Mercury Cathode.
In the experiments given in the subjoined table a solu-
tion of nickel sulphate, equivalent to 0.4802 gram of metal
in ten cubic centimeters, was used.
NICKEL.
I
tfi t/5
a
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a
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i
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1 i
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35
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5
H
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s S
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H
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W
^
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ai
H
W
j
0.4802
25
18
2
7
600
18
0.4802
2
0.4802
2 5
12
3-5
7
600
16
0.4799
0.0003
3
0.4802
25
12
2-4
6.5
600
IO
0.4806
-(-0.0004
4
0.4802
25
12
6
5
500
7
0.4804
-fO.0002
5-
0.4802
25
12
5
6.5
600
IO
0.4796
0.0006
6
o. 9604
25
IO-3O
4
6
1,100
IO
0.9597
o 0007
7
0.4802
25
12
3
7-5
I,IOO
IO
0.4806
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8
0.4802
25
12
3
7
I,IOO
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0.4796
0.0006
9
o. 9604
25
12
3-5
7
I,IOO
16
o. 9604
10
0.4802
25
12
5
7
640
12
0.4809
-f 0.0007
ii
0.4802
25
12
5
6
880
8
0.4806
4- 0.0004
12
0.4802
25
7
6
5
1,200
9
0.4801
O.OOOI
13
0.4802
25
7
6
6
I,2OO
7
0.4801
O.OOOI
The rate of precipitation, when using a current of 2
amperes and 7 volts, was found to be :
In 2y 2 minutes 0.2017 gram of metal
In 7^2 minutes 0.4095 gram of metal
In 10 minutes 0.4651 gram of metal
In \2y 2 minutes 0.4774 gram of metal
In 1 5 minutes 0.4802 gram of metal
1 3O ELECTRO-ANALYSIS.
A nickel solution became colorless in four minutes when
exposed to a current of 6 amperes and 5 volts. Not a
trace of the metal was present in the solution siphoned off
after seven minutes.
Nickel amalgam is very bright in appearance. A gram
of the metal combined with the usual quantity of mercury
(40 grams) imparts to the amalgam the consistency of
soft dough.
The Rapid Precipitation of Cobalt With the Use of a
Rotating Anode.
Various electrolytes have been studied by Miss Kollock
(J. Am. Ch. S., 26, 1606) to fix more definitely the con-
ditions so successfully used by Exner. The results con-
clusively demonstrate that the introduction of the rotat-
ing anode has given the electrolytic method of estimating
cobalt a very superior value. The details in procedure are
analogous to those described under nickel.
To precipitate it from a sodium formate electrolyte, add
to a cobalt sulphate solution (=0.3535 gram of metal)
2.5 grams of pure sodium carbonate and 4 c.c. (94 per
cent.) formic acid. Heat the solution to boiling, remove
the flame and electrolyze with a current of N.D 100 5
amperes and 6 volts. The precipitation will be complete
in thirty minutes. The deposit of cobalt is so brilliant that
it is difficult to distinguish it from the platinum on which
it is precipitated. In this electrolyte a slight anodic deposit
may occur. The glycerol mixture, referred to under nickel,
causes it to disappear or prevents its formation. However,
it is preferable to lower the current to one ampere for a
few minutes when the solution has nearly lost its color.
Just as soon as the peroxide has disappeared from the
anode restore the current to its original strength. Much
DETERMINATION OF METALS NICKEL, COBALT. 13!
formic acid retards the precipitation. If the liquid becomes
alkaline the deposition is very rapid and the metal is spongy,
hence add the acid drop by drop from time to time.
The rate of precipitation in a solution containing 0.3152
gram of cobalt was :
In 5 minutes 0.1470 gram of metal
In 7 */2 minutes 0.2096 gram of metal
In 10 minutes 0.2570 gram of metal
In 1 5 minutes 0.3066 gram of metal
In 20 minutes 0.3092 gram of metal
In 25 minutes 0.3142 gram of metal
In 30 minutes 0.3152 gram of metal
By applying a current of 6.5 amperes and 7 volts to a
solution containing 0.3152 gram of cobalt in the presence of
20 c.c. of ammonium hydroxide and 3.5 c.c. of formic acid
(94 per cent.) all of the metal will be precipitated in twenty
minutes. If the solution is alkaline the metal deposit will
be very compact in form and dull in appearance, while
if the liquid is acid the cobalt will separate in a very brilli-
ant form, but more slowly than from an ammoniacal solu-
tion. In this electrolyte formate there is little tendency
to anodic deposition.
A very satisfactory electrolyte is that containing am-
monium acetate.
Conduct a current of 5 amperes and 6 volts through a
solution of cobalt sulphate (0.3310 gram of metal), con-
taining 25 c.c. of ammonium hydroxide and 10 c.c. of 20
per cent, acetic acid. The metal will be fully deposited in
twenty-five minutes. It will be brilliant in appearance and
there will be no sign of anodic precipitation. A solution
in which 0.2980 gram of metal was present gave the follow-
ing rate of precipitation:
I 3 2 ELECTRO-ANALYSIS.
In 5 minutes 0.2235 gram of cobalt
In 10 minutes 0.2778 gram of cobalt
In 1 5 minutes 0.2950 gram of cobalt
In 20 minutes . . . . 0.2980 gram of cobalt
In 25 minutes 0.2980 gram of cobalt
An electrolyte of lactic acid or a lactate will also answer
admirably in the estimation of this metal. Peroxide pre-
cipitation does not take place. The cobalt deposits are most
adherent and exceedingly brilliant in appearance. A large
excess of lactic acid retards the precipitation.
Add to the solution of cobalt sulphate (=0.3152 gram
of metal), 2.2 grams of sodium carbonate and 5 c.c. of
concentrated lactic acid, and with a current of N.D 100 = 5
amperes and 8 volts the precipitation will be complete in
twenty-five minutes.
In an ammonium lactate solution the results are, if any-
thing, superior to those in the preceding electrolyte. As
a rule the solution becomes colorless in twenty-five minutes.
To a solution of the sulphate (= 0.3310 gram of metal),
add 30 c.c. of ammonium hydroxide and 7 c.c. of lactic
acid and electrolyze with N.D 100 = 6 amperes and 5 volts.
Twenty-five minutes will suffice for complete precipitation.
The rate of precipitation was found to be :
In 5 minutes 0.2215 gram of metal
In 10 minutes 0.3060 gram of metal
In 15 minutes 0.3230 gram of metal
In 20 minutes 0.3290 gram of metal
In 25 minutes 0.3310 gram of metal
In 30 minutes 0.3310 gram of metal
An electrolyte of ammonium succinate can be employed.
Some carbon is apt to be precipitated with the cobalt.
Sodium succinate should not be used.
DETERMINATION OF METALS NICKEL, COBALT. 133
The Rapid Precipitation of Cobalt With the Use of the
Rotating Anode and Mercury Cathode.
Cobalt does not seem to enter the mercury with the same
rapidity as the nickel under like conditions. The appended
table presents a list of experiments. By duplicating any
one of them satisfactory results may be expected. Cobalt
sulphate was the salt used :
COBALT.
h
Z
M
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u
o
8
Q
t/i
x
ft.'
c/) ,/j
Is
(j
z
is
g
IS-
D
Z
1 "
PC
O
X
K
K H
M
S w
tj
Hyp
0Q
K
z
w
hO
5
S
s
J Q j*
Z
S^
M
< Z
a. a
J
5x
> z ^
M
ffl ^
O
m "
Q
D K
o
U *^
S
, "
Cfl 3 "
^
^
H
^
M
I
0.3525
35
15
5
7
I25O
15
0.3522
0.0003
2
0.3525
25
15
3
5
980
18
0.3524
O.OOOI
3
0.3525
25
15
4
6
600
14
0.3523
O.OOO2
4
0.3525
25
IO
4
6
860
16
0.3530
4-0.0005
5
0.3525
5
IO
4
6
IOOO
15
0-353
4- 0.0005
6
O.3525
.0
IO
4
6
1240
16
0.3528
4-0.0003
7
0.3525
25
IO
3
6
I2OO
IO
0.3521
0.0004
8
0.3525
5
IO
6
6
I2OO
IO
0.3.530
4-0.0005
9
0.3525
25
IO
5
8
800
IO
0.3522
0.0003
10
0.3525
25
IO
3
8
I4OO
12
0.3523
0.0002
ii
0.35 2 5
5
IO
6
5
800
II
0.3530
4-0.0005
12
O.7O5O
-5
15
6
1200
30
0.7052
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13
o. 1762
35
10
4
8
560
7
0.1762
J
A solution of cobalt chloride may also be used (p. 89).
Thus, introduce into the mercury cup 5 c.c. of a cobalt
chloride solution (= 0.1250 gram of metal), cover the same
with 10 c.c. of pure toluene and electrolyze with a current
of from 2 to 4 amperes and 5 volts. In five minutes the
liquid will be colorless, and the metal will be completely
precipitated in 7 minutes.
1 34 ELECTRO-ANALYSIS.
MANGANESE.
LITERATURE. Z. f. a. Ch., n, 14; Riche, Ann. de Chim. et de Phys.
[5th ser.], 13, 508; Luckow, Z. f. a. Ch., 19, 17; Schucht, Z. f. a. Ch.,
22, 493; Classen and v. Reiss, Ber., 14, 1622; Moore, Ch. N.,
53, 209; Smith and Frankel, Jr. An. Ch., 3, 385; Ch. N., 60, 262;
Brand, Z. f. a. Ch., 28, 581; Riidorff, Z. f. ang. Ch., Jahrg. 15, p. 6;
Classen, Ber., 27, 2060; En gels, Z. f. Elektrochem., 2, 413; 3, 286;
Groeger, Z. f. ang. Ch. (1895), 253; Kaeppel, Z. f. anorg. Ch., 16,
268; Currie, Ch. N., 91, 247; Koster, Z. f. Elektroch. 10, 553;
Scholl, J. Am. Chem. S., 25, 1045, Koster, Z. f. Elektrochem., 10
(1904), 553-
The electric current causes this metal, when in solution
as chloride, nitrate, or sulphate, to separate as the dioxide
upon the anode (see Lead). In a solution of nitric acid,
the hydrogen set free reduces the acid to oxides of nitro-
gen and, finally, to ammonia. Under such conditions com-
plications may arise, particularly if other metals are present
in the solution. For this reason a solution of the sulphate,
slightly acidulated with two to six drops of sulphuric acid,
is preferable for electrolytic purposes. Neumann prefers
the mineral acid solutions for these depositions, and gives
the following as illustrative examples :
(a) To the solution containing 0.3 gram of manganese
nitrate, add 2 c.c. of concentrated nitric acid, dilute to 150
c.c. with water, and electrolyze with N.D 100 = 0.3 ampere
and 3-3.5 volts for two hours. It is advisable to acid the
acid during the course of the electrolysis. When its quan-
tity exceeds 3 per cent, the permanganic acid reaction shows
itself.
(b) Add 0.5 c.c. of concentrated sulphuric acid to the
solution of 0.3 gram of manganese sulphate, dilute to 150
c.c., heat to 60 -70, and act upon the solution for four
hours with a current of 0.4-0.6 ampere and 4 volts.
DETERMINATION OF METALS MANGANESE. 135
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 protosesquioxide (Mn 3 O 4 ) before weighing.
Groeger has demonstrated by iodometric tests, that the com-
position of the precipitate only approximates the formula
MnO 2 .H 2 O usually assigned it. Further, it is useless to
try to obtain a definite compound by drying. The product
is so extremely hygroscopic that ignition alone to the pro-
tosesquioxide will give definite and concordant results.
In the presence of large quantities of iron, this precipita-
tion 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 sulphocyanide also prevents its
formation, and if added to solutions in which dioxide is
already precipitated, it causes the same to redissolve.
Classen maintains that strong mineral acids, such as nitric
and sulphuric, retard the complete deposition of the manga-
nese. He regards acetic acid as the most suitable of all
the organic acids for use in this precipitation. The condi-
tions given are : 25 c.c. of acetic acid of specific gravity
1.069; 75 c - c - f water; temperature, 5o-68 ; N.D 100 =
0.3-0.35 ampere; = 4.3-4.9; time, 3 hours; roughened
dish.
Engels dissolves the manganese salt in 50 c.c. of water,
adds 10 grams of ammonium acetate and ij 2 grams of
chrome alum, then dilutes with water to 150 c.c., heats to
80, and applies a current of N.D 100 = 0.6-0.9 ampere and
3-4 volts. The deposit is washed with water and alcohol,
then dried and ignited. The deposition was made in rough-
1 36 ELECTRO-ANALYSIS.
ened dishes of platinum. Alcohol (5-10 c.c.) may be sub-
stituted for the chrome alum, but more time will then be
required for the precipitation.
Kaeppel has given the precipitation of manganese
thoughtful consideration, fie confirms the experience of
Engels, and adds that acetone is a very desirable addition.
This method of procedure consists in heating the electro-
lyte to 55, adding 1.5 to 10 grams of acetone, and electro-
lyzing with a current of N.D 100 = 0.7-1.2 amperes and
4-4.25 volts for a period of from two to five hours. The
acetone is converted into acetic acid, and it is the transi-
tional formation of the latter that the author regards as
more beneficial in the deposition than if it be added directly
to the electrolyte.
In this laboratory a formate electrolyte has been used
with good results. Thus, to a manganous sulphate solu-
tion (= o.i 100 gram of metal) were added five cubic
centimeters of formic acid (specific gravity 1.06), 10 c.c. of
a sodium formate solution ( = i gram of the salt), the
whole was diluted to 130 c.c. with water and electrolyzed
with a current of N.D 100 =i.4 ampere and a pressure
ranging from 12 volts at the beginning to 8.6 volts at
the end. The precipitation was finished at the expiration
of one and a half hours. The deposit of dioxide was very
adherent.
Later it was observed that the deposition could be satis-
factorily made in the presence of free formic acid alone.
The pressure was at the start high, because of the low con-
ductivity of the formic acid. It fell in the course of an
hour. An example from many will give the conditions.
To a solution containing 0.2068 gram of manganese there
were added: 5 c.c. of formic acid (sp. gr. 1.09) and it was
electrolyzed at room temperature with N.D 100 = 0.8 to i
DETERMINATION OF METALS MANGANESE.
37
ampere and 6.8 volts. The time required was five hours.
The manganese weighed 0.2069 gram. The deposit from a
formate electrolyte is very adherent. Formic acid is supe-
rior to acetic acid as an electrolyte. For the separation of
manganese from iron and from zinc see pp. 262, 266.
FIG. 29.
The apparatus devised by Herpin (Fig. 29) can be well
applied in the decomposition of manganese salts. It con-
sists of a platinum dish, A, resting upon a tripod, B, in con-
nection 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
13
I3 8 ELECTRO-ANALYSIS.
prevented by this means. The anode is a platinum spiral
C. In estimating manganese it must not be forgotten to
connect the dish with the anode of the battery employed for
the decomposition.
The Rapid Precipitation of Manganese With the Use
of a Rotating Electrode.
The experiments made in this direction, in this laboratory,
were not successful. Koster has proposed the following :
To the electrolyte, about 130 cubic centimeters in volume,
containing the manganese salt (not the chloride) add 5 to
10 grams of ammonium acetate, 2 to 3 grams of chrome
alum and several cubic centimeters of alcohol. Heat the
solution to 75 C., remove the flame and electrolyze with
N.D 100 = 4 to 4.5 amperes and a pressure of 7 volts.
Another suggestion from the same chemist consists in add-
ing to the solution of the manganese salt 10 grams of
ammonium acetate and about 10 cubic centimeters of 96
per cent, alcohol. The current density and pressure to be
used are dependent upon the quantity of manganese present.
For example, in the case of 0.2 gram of manganese or less,
use a current of N.D 100 = 4 to 4.5 amperes and 7 to 8
volts; when there is a larger quantity use but 2 amperes
and 4 to 5 volts. The author declares that in the presence
of more than 0.3 gram of manganese neither suggestion, as
given above, can be relied upon, because oxide will detach
itself even from a sand-blasted electrode. The time re-
quired for precipitation varies from 20 to 25 minutes.
IRON.
LITERATURE. Wright son, Z. f. a. Ch., 15, 305; Parodi and Mas-
cazzini, G. ch. ital., 8, 178; also Z. f. a. Ch., 18, 588; Luckow, Z. f. a.
Ch., 19, 18; Classen and v. Reiss, Ber., 14, 1622; Classen, Z. f.
DETERMINATION OF METALS IRON. 139
Elektrochem., i, 288; Moore, Ch. N., 53, 209; Smith, Am. Ch. Jr.,
!O, 330; Brand, Z. f. a. Ch., 28, 581 ; Drown and McKenna, Jr. An.
Ch., 5, 627 ; Smith and M u h r , Jr. An. Ch., 5, 488 ; Rtidorff, Z. f. ang.
Ch., 15, Jahrg., p. 198; Vortmann, M. f. Ch., 14, 536; Heidenreich,
Ber., 29, 1585; A very and Dales, Ber., 32, 64, 2233; Verwer and
Groll, Ber., 32, 37, 806; Goecke, Dissertation, Bonn, 1900; Kollock,
J. Am. Ch. S., 21, 928; Exner, J. Am. Ch. S., 25, 903; Kollock
and Smith, Am. Phil. Soc. Pr., 44, 149; ibid., 45, 261.
The suggestion of Parodi and Mascazzini relative to the
precipitation of iron (p. 28) has since been elaborated by
Classen, and by him applied to many other metals. Fol-
lowing the recommendation of this chemist, about six to
seven grams of ammonium oxalate 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 electrolyzed at the ordinary tem-
perature with a current of N.D 100 = 1.5 amperes and 2-4.5
volts, or at the temperature of 4O-65 with 0.5-1.0 ampere
and 2-3.5 volts. If ferric hydroxide should separate during
the electrolytic decomposition, it can be redissolved by add-
ing oxalic acid drop by drop. Test the clear liquid, acidu-
lated with hydrochloric acid, with potassium sulphocyanide.
The deposited iron has a steel-gray color; it should be
washed with water, alcohol, and ether. Avoid the presence
of chlorides and nitrates. By carefully complying with the
conditions recommended by Classen good results are sure
to follow. To show that persons with but little experience
do succeed with the preceding method the two following
determinations, made by a student, are given : A quantity
of ferric ammonium sulphate (=0.0814 gram of iron)
was dissolved in 200 c.c. of water, and to this were added 8
grams of ammonium oxalate. The solution was heated to
80, and in two hours, with a current of 1.5 amperes,
0.0814 gram of iron was obtained. In a second experi-
ELECTRO-ANALYSIS.
ment the quantity of iron was doubled ( =0.1628 gram of
iron), while the ammonium oxalate was n grams, tem-
perature 66, and the current i ampere. 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 ( =
0.1277 gram of metal), 10 c.c. sodium citrate (1.8 grams)
with 3 c.c. of citric acid (0.059 g ram )> tnen diluted with
water to 250 c.c., and electrolyzed with a current of N.D 100
= 0.8 ampere and 7-8 volts at 50 for four and one-half
hours. The iron deposit weighed 0.1280 gram. It con-
tained 0.94 per cent, of carbon. The deposit was washed
as already directed. In several determinations aluminium
and titanium were present with the iron, but the latter was
precipitated free from the other two. For this reason the
writer regards the method as useful. E. F. Kern, working
in this laboratory with the view of arriving at some knowl-
edge in regard to the carbon deposition, after long and
painstaking experimentation, recommends the following
conditions as favorable for the getting of iron deposits free
from the carbon impurity : Add i gram of sodium citrate
and o.i gram of citric acid to the solution of iron sulphate
(o.i gram of metal), dilute to 150 c.c,, heat to 60, and
electrolyze with N.D 100 = 0.8-1.3 amperes and 9 volts.
Just as soon as the iron is precipitated, siphon off the liquid
and wash without interruption of the current. The opinion
exists that prolonged action of the current after the metal is
all deposited tends to increase the carbon content of the iron.
From ammoniacal tartrate solutions iron is also precipi-
tated, but carries carbon with it. It would therefore not be
advisable to use this electrolyte except in cases where sepa-
rations were desired, which were possible only in solutions
of this character.
DETERMINATION OF METALS IRON. H!
A third method, originated by Moore, advises that glacial
phosphoric acid (15 per cent, acid) be added to the distinctly
acid solution of ferric chloride or sulphate, until the yellow
color fully disappears, then a large excess of ammonium
carbonate is added and a gentle heat, is applied until the
liquid becomes clear. On electrolyzing the hot (70) solu-
tion with a current of 2 amperes, the iron is rapidly and
completely deposited at the rate of 0.75 gram per hour.
Avery and Dales, on the other hand, claim that with a cur-
rent of N.D 100 = 2 amperes and 5 volts they were not able
to precipitate more than 0.2 gram of iron in five hours.
The end of the decomposition is recognized by testing a
portion of the solution with ammonium sulphide. Wash
the deposit as already directed.
Recently, quite a little discussion has been had upon the
deposition of iron and its enclosures. Avery and Dales
question whether the metal is fully precipitated from any
one of the electrolytes described in the preceding para-
graphs; furthermore, they affirm that even from an oxalate
solution the iron carries down carbon with it; that oxalic
acid is converted in part, at least, into glycollic acid, and that
iron salts in the presence of the latter acid yield upon elec-
trolysis a metal strongly contaminated with hydrocarbons.
As to Moore's method, they assert that phosphorus is always
present in the deposit of iron. Goecke concurs with these
chemists in their views on the cathodic contaminations.
Verwer and Groll think that iron, from an oxalate solution,
is absolutely free from carbon, while Classen attributes the
trifling amounts of carbon, which have been observed, to
carelessness and inexperience in the execution of the pre-
scribed directions.
Consult Blum and Smith, Am. Phil. Soc. Pr., 46, 59,
on the cathodic precipitation of carbon.
142 ELECTRO- ANALYSIS.
Drown, pursuing a suggestion made by Wolcott Gibbs
in 1883 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 ammo-
nium 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 precipi-
tation equaled about 2 amperes per minute. The author
remarks that if these conditions be observed, as much as 10
grams of iron can be precipitated in from ten to fifteen
hours.
The decomposition was carried out in beakers. Care
should be exercised in drying, so that no mercury is vola-
tilized.
The Rapid Precipitation of Iron With the Use of a
Rotating Anode.
The only electrolyte from which this metal was deposited,
while using a high current and high pressure, was that of
ammonium iron oxalate. The anode performed 800 revo-
lutions per minute and the other conditions may be learned
from two actual trials.
i. To a solution of ferric ammonium sulphate (0.2461
gram of iron) were added 7.5 grams of ammonium oxalate
and one cubic centimeter of a saturated solution of oxalic
acid. This was then electrolyzed after heating to boiling
with a current of N.D 100 = 7 amperes and 7.5 volts. In
twenty-five minutes 0.2461 gram of iron was precipitated.
The deposit of metal was very dense and so light in color
DETERMINATION OF METALS IRON. 143
that it resembled the polished platinum dish on which it was
precipitated.
2. In this trial all the conditions were like those in i,
excepting the quantity of iron equaled 0.4922 gram. In
thirty-five minutes this exact amount of metal was obtained.
No attempt thus far has been made to determine the rate
of precipitation of iron from this electrolyte.
The Rapid Precipitation of Iron With the Use of the
Rotating Anode and Mercury Cathode.
In carrying out this precipitation an example will give the
most satisfactory information :
Five cubic centimeters contained 0.2075 gram of iron.
Three drops (40 drops = i cubic centimeter) of concen-
trated sulphuric acid were added to it, when it was electro-
lyzed with a current of 3 to 4 amperes and 7 volts. The
anode made from 500 to 900 revolutions per minute. The
iron was completely deposited in seven minutes. The
water was then siphoned off and the amalgam washed as in
all previous cases with alcohol and water.
The rate of precipitation, under the conditions just men-
tioned, was :
In 2 minutes 0.1760 gram of iron was deposited
In 4 minutes 0.2000 gram of iron was deposited
In 6 minutes 0.2050 gram of iron was deposited
In 8 minutes 0.2075 gram of iron was deposited
The following table exhibits conditions which can be re-
lied upon :
144
ELECTRO-ANALYSIS.
B-
Q ' '
u
s*
s
Is
g
Q
M
<
2 'I
2
Z [I]
K BJ
B
O H
S S
O
M
o 5
2;
s z
^ s
o
3 o 5
g
fe K
zO
M
o2
ft< M ^
j
u<
^ ^
M
o
M
s
O
M
M
M
M
M
w J*
*
H
W
I
0.2075
7
5
4 -5
8 -7
520
14
0.2072
o. 0003
2
0.2075
4
5 -4
6.5-5
680
H
0.2078
-(-0.0003
3
0.2075
5
5-10
3-2-4
6-5
680
15
0.2077
0.0003
4
0.2075
3
5
2 -2.5
7-6
680
15
0.2073
0.0002
5
0.2075
3
5
4
6-5
680
IO
0.2080
40.0005
6
0.2075
3
5
3 -4-5
7-6
92O
7
0.2078
40.0003
7
0.2075
3
5
2 -3
6
740
9
0.2076
4O.OOOI
8
0.2075
3
5
2 -4
6-5-5-5
700
9
0.2076
4 0.0001
When the metal exists as chloride this salt may be electro-
lyzed with ease, taking the precaution to add to the electro-
lyte a layer of pure toluene (p. 89). For example, to 5
cubic centimeters of a pure ferric chloride solution
(=0.1030 gram of iron), were added 10 cubic centimeters
of toluene and the liquid electrolyzed with a current of
two to four amperes and nine volts. In twelve minutes
the total quantity of metal had entered the mercury.
CHROMIUM.
LITERATURE. Myers, J. Am. Chem. S., 26, 1128; Kollock and
Smith, Am. Phil. Soc. Pr., 44, 146.
This metal has never, until recently, been determined in
the electrolytic way. Upon experimenting with a solution
of its sulphate it was found that chromium would enter or
attach itself to a mercury cathode, accordingly a solution
of this salt was electrolyzed in the mercury cup (p. 58),
using stationary electrodes. Ten cubic centimeters of the
salt solution contained 0.1080 gram of chromium. The
working conditions are shown in the following table:
DETERMINATION OF METALS CHROMIUM.
</i
2
I
J
M O
CONDITIONS
SO
II
J
J2
1
S Z
o ~
|E
h w
S H "
H
i
i
H
M
M
12'
X Q
H
J
j
rj W
O
^ C/2 W
s
0.
O
E
H
g
55
s > ^S
H
1
>
jj
1
04
fa
^ ^
I
O.IO8O
0.1079
2
2
3
o-3
7
0-55
5-5
2
O.IO8O
0.1080
I
3
14
0.3
7
-55
5-5
3
0.2160
0.2157
I
4
14
0.4
7-5
0.7
6
4
0. 2 1 60
0.2160
I
4
0.4
7-5
0.7
6
5
0.3240
0.3235
I
8
30
0.7
7
2.
6.5
6
0.3240
0.3222*
1
6
30
0.65
7
2-5
8
The initial voltage and amperage are given to the left in
the table. The acid liberated, during the course of the elec-
trolysis, causes the potential to fall and the current to rise
to the final voltage and amperage exhibited on the right.
Chromium amalgam is not very stable. Water rapidly
decomposes it with the separation of metallic chromium as
a fine black powder on the surface of the mercury. The
amalgam must, therefore, be washed as rapidly as possible.
A given amount of mercury should not be used for more
than one decomposition. The appearance of an oxide of
chromium in the electrolyte indicates an insufficient amount
of acid.
The Rapid Precipitation of Chromium With the Use of
the Rotating Anode and Mercury Cathode.
To 10 cubic centimeters of chromium sulphate (= 0.1180
gram of metal), add three drops of concentrated sulphuric
acid (40 drops = I cubic centimeter), and electrolyze with
a current of from 4 to 5 amperes and 6 volts, the speed of
the anode being 400 revolutions per minute. Six minutes
will more than suffice for the complete precipitation of the
* Some chromium floated off in wash water.
14
146
ELECTRO-ANALYSIS.
metal. Siphon off the acid liquid, and wash the amalgam
as quickly as possible with anhydrous alcohol and ether.
The following table shows conditions which may be relied
upon to yield results that will be satisfactory in every way :
g u !
u
h
o
g
a
</>
H
Z
U
IN
1;
u
z
z' &
in K
*S
|
^ <
' o
K
H
III
1
w
p
I!
K O
3 | 5
Z
If '
w
u 1 ^ .5
"s3
tJ
o
u.<-
$<
u
S
K
.
7.^
M
H
u
w -
J
0.1180
5
10-15
3-4
7
280
15
0.1186
40.0006
2
0.1180
3
10-15
2-4
n -9
280
15
0^1187
4-0.0007
3
o. 1 1 80
3
10-15
9
640
20
0.1185
-J-O.OOO5
4
o. 1180
3
8-15
'5-3
10 -8
220
15
0.1186
-j- O.OOO6
5
o. 1180
3
10-15
ii -9
520
20
0.1186
4-O.OOO6
6
o. 1180
3
5-15
1-2
ii -9
640
17
0.1175
O.OOO5
7
0.1180
3
5-15
2-4
9 -8
480
15
o. 1180
8
0.2360
3
5-15
2-5
10
520
50
0.2355
O.OOO5
9
0.1180
5
5-15
3
7.5
400
15
0.1179
O.OOOI
10
0.1180
3
7-15
4 -5
8
640
6
0.1175
0.0005
T T
at T 8r*
7T C
3 A
tc\ n
f\AC\
IO
oil 80
1 1
. 1 1 OU
1 J
~"4
ILJ y
\JQ\J
12
o. 1180
7
7-15
3 -4
io -8
200
13
0.1187
4 0.0007
13
0.1180
3
5-15
3-5
8
640
II
0.1177
0.0003
0.2360
4
5-15
3
12
640
35
0.2359
O.OOOI
15
o. 1180
3
5-15
3 -4
io -8
32O
ii
0.1179
O.OOOI
16
0.1180
3
5-15
3 -4
IO
540
u
o. 1182
40.0002
The rate of precipitation, deduced from these figures,
would be :
In 2 minutes 0.0480 gram of metal
In 4 minutes 0.0850 gram of metal
In 6 minutes o.idoo gram of metal
In 8 minutes. o.i 105 gram of metal
In 9 minutes 0.1185 gram of metal
In io minutes 0.1185 gram of metal
URANIUM.
LITERATURE. L u c k o w , Z. f. a. Ch., 19, 18; Smith, Am. Ch. Jr., i,
329; Smith and Wallace, J. Am. Ch. S., 20, 279; Kollock and
Smith,J. Am. Ch. S., 23, 607 ; K e r n , J. Am. Ch. S., 23, 685 ; Wherry
and Smith, J. Am. Ch. S., 29, 806.
DETERMINATION OP METALS URANIUM.
For electrolytic purposes use the acetate, the sulphate,
or -the nitrate. Connect the dish in which the deposition
is made with the negative electrode of the battery. The
uranium separates as yellow uranic hydroxide upon the
cathode; by the continued action of the current it changes
to the black hydrated protosesquioxide. As soon as the
solution becomes colorless, interrupt the current, wash
with a little acetic acid and boiling water; dry, ignite, and
weigh as protosesquioxide. If any of the hydrate becomes
detached, collect the same upon a small filter, and ignite
the latter together with the dish contents. Conditions lead-
ing to successful results are contained in the following
examples :
ELECTROLYSIS OF URANIUM ACETATE.
f j
l/l
H"
H
U
u
o
K '
a - .
s
1
U
h
u
H
I
O
ffi
P S
o <
M
00
U
o
1
X
X
^
H)
<
z
w'
g
ocO
z
tt
o
**
0.
^
J . M
)
M (J
Q
H
^
K
"*<
H
W , ,
0.0986
0.2
I2 5
ND -02 9 A
16.25
70
5
0.0988
-f 0.0002
0.0986
0.2
125
N;D^ = b.3 A
12.2
70
5
0.0989
-f 0.0003
0.1972
0.2
125
N.D 107 --^o. 3 A
10-75
70
6
o. 1970
0.0002
0.2298
O.I
N.D 107 ^o.o 9 A
4-25
70
6
0.2297
-0.000 1
0.2298
0.2
125
4.25
70
sX
0.2299
-f 0.0001
ELECTROLYSIS OF URANYL NITRATE SOLUTIONS.
U 3 8
PRESENT,
IN GRAMS.
DILUTION
c.c.
TEMPERA
TURK C.
CURRENT.
VOLTS.
TIME.
HOURS:
U 3 8
FOUND IN
GRAMS.
0.1222
0.1222
125
125
H
N.D )07 = o.o 3 5A
N.D 107 = o.o 4 A
4.6
2.25
5^
7^
0.1225
O.I2I8
Quantitative results were also obtained by the electrol-
ysis of the sulphate. The neutral salt solution was diluted
148
ELECTRO-ANALYSIS.
to 125 c.c. and heated to 75 C, when a current of from
0.02 to 0.04 ampere for 107 sq. cm. of cathode surface and
2.25 volts was conducted through the liquid.
ELECTROLYSIS OF URANYL SULPHATE.
h*
u
u
JS
.
1
03
p
!/>
H
H *j
u
H
<!
8
w
O <;
^O
o
CURRENT.
O
oo'J
5
I
3
1
>
u
5
M
o
&
Q
H
H
M
0.1320
125
75
N F> n n? A
2
6X
0.1320
IM.1J I07 - 0.02 A
0.1320
125
75
N.D ]07 r=:0.02 A
2
5/4
o. 1322
+ 0.0002
o.i393
125
75
N.D lW =o.04 A
2.25
5
0.1395
+ 6.0002
o.i393
125
70
N.D, 07 =o.o 3 8A
2.25
7
0.1392
0.000 1
This method affords an excellent separation of uranium
from the alkali and alkaline earth metals (p. 271).
H
Q
z
2
Q
6
U
U
ISi
u w
1
5 S
H 5
OH*
|1
fc
^o
h u
O H K
si
o
7. Z
H
co^
S
u
^
0^
HS
"
I
0.1527
O.2
2/2
3
H
18
ord.
O.I5I3
2
0.1527
0.2
4/4^
3
12
15
"
O.I52 5
3
0.2613
0.25
5/^
7
15
8
60
O.26II
4
0.2613
0.25
4K
4
12
3
50
0.0344
5
0.2613
0.25
4)4
4
12
15
50
0.0530
6
0.2613
0.25
4/4
4
12
IO
50
0.1074
7
0.2613
0.25
4/4
4
12
18
50
0.1935
8
0.2613
0.25
4 1 A
4
12
25
50
0.2467
9
0.2613
0.25
4/2
4
12
30
50
0.26II
a .
H -y)
<JP
< Z
U M
IO
0.2613
I
5
15
25
o. 2600
II
0.2613
2
5
13
3
0.2613
DETERMINATION OF METALS THALLIUM. 149
The Rapid Precipitation of Uranium With the Use
of a Rotating Anode (performing 600 revolutions per
minute) may be seen in the results on the preceding page,
obtained when using a uranyl sulphate solution.
Either of the two electrolytes mentioned here will prove
quite satisfactory, and the procedure cannot fail to com-
mend itself to mineral analysts.
THALLIUM.
LITERATURE. Schucht, Z. f. a. Ch., 22, 241, 490; Neumann, Ber.,
21, 356; Heiberg, Z. f. anorg. Ch., 35, 346.
This metal separates as sesquioxide, from acid solutions,
upon the anode, while from ammoniacal liquids it is de-
posited partly as metal and partly as oxide. From oxa-
late solutions and from its double cyanides it separates
only as metal when the current is feeble. However, diffi-
culty 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 originally present. For suitable apparatus to carry
out this method consult the literature cited above.
The recommendation of Heiberg is that to a solution of
thallium sulphate (0.2 to i.oooo gram of salt) in 100 c.c.
of water there be added 2 to 6 c.c. of normal sulphuric
acid and 5 to 10 c.c. of acetone. Use a roughened dish
which is made the anode during the decomposition. Heat
to 55 C., and electrolyze with a current ranging from 0.02
to .05 ampere and pole pressure of 1.7 to 2.3 volts.
The precipitation is finished when |- c.c. of the electrolyte
produces no opalescence on bringing it into 3 to 5 c.c. of
I O ELECTRO-ANALYSIS.
a five per cent, solution of potassium iodide. Pour out
the liquid quickly from the dish and wash the deposit of
oxide several times with water, alcohol, and ether. Dry
for twenty minutes at i6o-i65 in an air bath. Cool in
a desiccator. The time for precipitation is about seven
hours. The oxide is T1 2 O 3 .
Recently, G. W. Morden, working in this laboratory,
found that the most satisfactory course to pursue in esti-
mating thallium electrolytically consists in precipitating it
with the aid of the rotating anode and mercury cathode.
If the metal is precipitated directly into the mercury the
resulting amalgam will on washing give up a portion of
its thallium content to the water. This, however, may be
absolutely prevented by precipitating a little zinc simul-
taneously in the mercury. Indeed, as small a quantity as
0.0007 " r am of zinc will prevent any oxidation of as much
as 0.1305 gram of thallium. To the solution of the sul-
phates contained in the mercury cup add a few drops of
sulphuric acid (specific gravity 1.8) and electrolyze with
a current of 5 amperes and n volts. In 10 minutes as
much as 0.2250 gram of thallium may be precipitated and
the amalgam washed and dried in the customary way.
INDIUM.
LITERATURE. T'hiel, Z. f. anorg. Chemie, 39, 119; Dennis and
Geer, Ber., 37, 175; J. Am. Ch. S., 26 (1904)^ 438.
Thiel asserts that indium may be determined in the elec-
trolytic way with great accuracy. He recommends that
it be deposited on a silver-plated platinum cathode.
Dennis and Geer found that this metal may be readily
precipitated from solutions of its chloride or nitrate in the
presence of pyridine, hydroxylamine or formic acid. The
DETERMINATION OF METALS PLATINUM. I$I
depositions from oxalic or oxalate solutions were not very
satisfactory. The metal separated from an acetate elec-
trolyte in a dark, spongy form, while from solutions con-
taining pyridine it was brilliant white in color and very
compact.
In making a determination dissolve the yellow oxide in
one-sixth normal sulphuric acid, avoiding an excess. Add
to this solution 25 cubic centimeters of formic acid (spe-
cific gravity 1.20) and 5 cubic centimeters of ammonia
(specific gravity 0.908), then dilute to 200 cubic centimeters,
and electrolyze with a current of N.D 100 = 9 to 12 amperes.
The quantity of metal varied from 0.2 to 1.5 gram. It was
deposited on a rotating cathode a roughened dish. The
cathode will not be attacked so long as the electrolyte con-
tains formic acid.
PLATINUM.
LITERATURE. Luckow, Z. f. a. Ch v 19, 13; Classen, Ber., 17, 2467;
Smith, Am. Ch. Jr., 13, 206; Riidorff, Z. f. ang. Ch., 1892, 696;
Langness, J. Am. Ch. S., 29, 466.
The solutions of platinum salts, slightly acidulated with
sulphuric acid, and acted upon by a feeble current, give
up the metal as a bright, dense deposit upon the dish,
frequently so light as to be scarcely distinguished 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, K 2 PtCl 6 . This
operation requires time and care. Rather dissolve the
double salt in water, slightly acidulate the solution with
sulphuric acid (2 to 3 per cent, by volume), and electro-
IS 2 ELECTRO-ANALYSIS.
lyze with a current of N.D 100 = 0.1-0.2 ampere. The
deposit will be spongy. On heating to 6o-65 and elec-
trolyzing with N.D 100 = o.O5 ampere and 1.2 volts, the
platinum will be completely precipitated in from four to
five hours in a perfectly adherent form. It is often so
dense as to be distinguished from hammered platinum with
difficulty.
In the Munich laboratory the platinum salt solution is
mixed with 2 per cent, (by volume) of a dilute sulphuric
acid (i : 5), heated to 70, and electrolyzed with N.D 100 =
0.01-0.03 ampere. The precipitation will be complete in
five hours.
The following experiment executed in this laboratory
demonstrates that the precipitation of platinum from solu-
tions containing sodium phosphate and free phosphoric
acid is complete. The volume of the liquid was 150 c.c.
It contained 0.1144 gram of metallic platinum, 30 c.c. of
disodium hydrogen phosphate (sp. gr. 1.0358), and 5 c.c.
of phosphoric acid (sp. gr. 1.347). The current equaled
0.8 ampere. 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.
The Rapid Precipitation of Platinum With the Use of
the Rotating Anode.
In making the trials to obtain a rapid precipitation of
metal a solution of potassium platinum chloride was used.
Twenty-five cubic centimeters of this solution contained
0.0953 gram of platinum. The metal was deposited on a
silver coated dish. The rotating dish anode (p. 73) was
used in this electrolysis.
DETERMINATION OF METALS PALLADIUM.
153
No.
H 2 SO 4
(DlL I.IO)
VOLTS
AMPERES
TIME,
MIN.
WT. OF PT.
IN GRAMS.
IN C C.
,
5
5
10
7
0.0953
2
2.5
10
16
3
0.0952
On doubling the volume of the solution the following
results were obtained :
No.
H 2 S0 4
(Diu x:io)
IN C.C.
VOLTS.
AMPERES.
TIME,
MIN.
WT. OF PT.
IN GRAMS.
I
2-5
10
17
I
0.1158
2
2.5
10
18
2
0.1734
3
2.5
10
16
3
0.1855
4
2.5
10
18
4
0.1903
5
25
10
17
5
0.1904
The rate of precipitation is very evident from these
figures.
PALLADIUM.
LITERATURE. Wohler, Ann., 143, 375; Schucht, Z. f. a. Ch., 22,
242; Smith and Keller, Am. Ch. Jr., 12, 252; Smith, Am. Ch. Jr.,
13, 206; 14, 435; Joly and Lei die, C. r., 116, 146; Z. f. anorg. Ch.,
3, 476; Amberg, Z. f. Elektrochem., 10 (1904), 386; Annalen, 341,
271 ; Langness, J. Am. Chem. S., 29, 467.
Palladium can be deposited from solutions of the same
kind and in the same manner as platinum. A bright
metallic deposit will be obtained by the use of a current
of N.D 100 = 0.05 ampere and 1.2 volts; otherwise it is
spongy.
It has been discovered, in this laboratory, that this
metal can be rapidly and fully precipitated from ammoni-
acal solutions of palladammonium chloride, Pd(NH 3 Cl) 2 ,
which may be prepared by adding hydrochloric acid to an
1 54 ELECTRO-ANALYSIS.
ammonium hydroxide solution of palladious chloride. To
show the accuracy of this method, several actual determi-
nations are here introduced: (i) A quantity of the double
salt (=0.2228 gram of palladium) was dissolved in am-
monium hydroxide; to this solution were added 20-30 c.c,
of the same reagent (sp. gr. 0.935) anc ^ IO c - c - f water.
A current of 0.07-0.1 ampere acted upon this mixture
through the night, and deposited 0.2225 gram of palladium.
(2) In another experiment, with conditions similar to those
just mentioned, excepting that the quantity of the pallad-
ammonium chloride was doubled, and the current held at
0.7 ampere, the quantity of metal precipitated equaled
0.4462 gram instead of 0.4456. Oxide did not separate
upon the anode. The deposit, 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 no 115. It is best to deposit the palla-
dium in platinum dishes previously coated with silver.
The Rapid Precipitation of Palladium With the Use of
a Rotating Anode.
Amberg mentions having electrolyzed palladosammine
chloride in sulphuric acid solution with a current of 0.3
ampere and 1.25 volts, when he succeeded in precipitating
one gram of palladium upon a roughened dish in three
hours. The anode performed from 600 to 650 revolutions
per minute. The electrolyte was heated to 65. The
deposit of metal was perfectly adherent and resembled
platinum. This chemist abandoned the silver or gold
coated platinum cathode, preferring to deposit the palla-
dium directly upon the platinum from which he later dis-
solved it by means of a saturated potassium chloride solu-
tion (7o-8o) to which were added crystals of chromic
DETERMINATION OF METALS PALLADIUM.
155
acid. This freshly prepared solution was poured over the
palladium and the dish rocked constantly so that the plati-
num was only superficially attacked if affected at all.
In this laboratory perfectly analogous results were ob-
tained by electrolyzing an ammoniacal solution of pallad-
ammonium chloride. The anode was the dish (p. 73)
used to such advantage in many other instances. Portions
of such a solution ( 10 cubic centimeters contained 0.2680
gram of metal) were mixed with 20 cubic centimeters of
boiling ammonium hydroxide, diluted with water to 60 cu-
bic centimeters and electrolyzed.
RESULTS.
No.
VOLTS.
AMPERES.
TIME, Mm.
WT. OF Pd.
IN GRAMS.
!
5-6
2 +
1-8
0.2682
2
II
5
10
0.2680
3
17
7
5
0.2682
4
17
10
3
0.2678
5
17
10
2
0.2678
6
17
10
2
0.2683
7
17
10
2
0.2680
8
17
10
2
o 2681
The deposits were gray in color and perfectly adherent.
In the last three the palladium was deposited directly on the
platinum dish. It was later removed by the mixture to
which reference has been made.
In a second series the quantity of metal present equaled
in each instance 0.5360 gram.
RESULTS.
' No.
NH 4 OH INC c.
DILUTION.
VOLTS.
AMPERES.
TIME,
Mm.
WT. OF P.
m GRAMS
I
20
60 c.c.
15
14
3
0.5358
2
20
60 c.c.
17
14-20
2
0-5357
3
20
60 c.c.
17
14-20
I
0.4966
156 ELECTRO- ANALYSIS.
The deposits were almost like platinum in appearance.
This procedure is particularly satisfactory with palladium;
the time element is almost annihilated.
RHODIUM.
LITERATURE. Smith, Jr. An. Ch., 5, 201; Joly and Lei dip, C. r.,
U2, 793; Langness, J. Am. Ch. S., 29, 469.
Few attempts have been made to determine this metal
electrolytically. Its separation from an acid phosphate
solution is very rapid and complete. A current of o.iS
ampere will answer perfectly 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 finished. The deposition of the
rhodium should be made upon copper-coated dishes. The
metal is generally black in color, very compact, and per-
fectly adherent. Hot water may be used for washing
purposes.
Joly precipitates the metal from solutions acidulated with
sulphuric acid.
The Rapid Precipitation of Rhodium With the Use of
a Rotating Anode.
The electrolyte consisted of an aqueous solution of rho-
dium sodium chloride (0.0576 gram of metal) to which
were added 2.5 c.c. of sulphuric acid (dil. i : 10). It
was diluted to 100 c.c. with boiling water, and electrolyzed,
using a spiral (p. 73) anode; while in the last three de-
terminations a dish (p. 73) anode was employed. The
rhodium was deposited on a silver-coated platinum dish.
DETERMINATION OF METALS MOLYBDENUM.
157
No.
VOLTS.
AMPERES
TIME, MIN
WT. OF RH. IN
GRAMS.
I
7
8
15
0.0577
2
7-5
8
IO
0.0580
3
8
9
10
0.0575
4
8
9
7
0.0576
5
8
15
4
0.0573
6
6
ii
4
0.0563
7
7
14
4
0.0567
The deposits were adherent and black in color.
The rate of precipitation was determined with a solution
containing- 0.1153 gram of metal. The current equaled
15 amperes and the pressure 7 volts. The results were:
In i minute 0.0896 gram of metal
In 2 minutes 0.1006 gram of metal
In 3 minutes o.i 104 gram of metal
In 4 minutes 0.1128 gram of metal
In 5 minutes o.i 141 gram of metal
In 8 minutes 0.1152 gram of metal
In 10 minutes 0.1153 gram of metal
MOLYBDENUM.
LITERATURE. Gahn, Gilbert's Ann., 14, 235; Feree, C. r., 122,
733 ; Smith, Am. Ch. Jr., i, 329 ; Hoskinson and Smith, ibid., 7, 90 ;
Kollock and Smith, J. Am. Ch. S., 23, 669; Exner, J. Am. Chem.
S., 25, 904; Myers, J. Am. Chem. S., 26, 1129; Chilesotti, Gazz.
Chim. ital., 33, 349, 362; Z. f. Elektrochem., 12, 146; Chilesotti and
Rozzi, Gazz. Chim. ital., 35 (1905), 228; Wherry and Smith, J.
Am. Ch. S., 29, 806; Chilesotti, Z. f. Elektrochem., 12, 146.
When the electric current acts upon ammoniacal or
feebly acid solutions of ammonium 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. At the
158 ELECTRO-ANALYSIS.
time when these observations were made, experiments were
instituted to determine the metal. The results, while
quantitative in character, were obtained with the consump-
tion of too much time to permit of the method being
generally applied. Recently attention has again been
given to the subject in this laboratory. Sodium molyb-
date (Na 2 MoO 4 .2H 2 O) was dissolved so that 0.1302 gram
of molybdenum trioxide was present in 125 c.c. of solution,
which was exposed for several hours to the action of a
current of o.i ampere and 4 volts. The temperature of
the electrolyte was 75 C. No precipitation occurred upon
either electrode. Upon adding two drops of concentrated
sulphuric acid to the liquid, it at once assumed a dark blue
color. As the current continued to act, this color dis-
appeared and the cathode was coated with a black deposit
the hydrated sesquioxide. On removing the colorless liquid
and testing it with ammonium thiocyanide, zinc, and hydro-
chloric acid, evidences of the presence of molybdenum
failed to appear. The deposit was brilliant black in color
and so adherent that it could be washed without detaching
any particles. Usually the colorless liquid was removed
with a siphon, cold water being introduced without inter-
rupting the current. The deposit was not dried, but dis-
solved while moist from off the dish in dilute nitric acid,
and the solution carefully evaporated to dryness, the residue
being heated upon an iron plate to expel the final traces of
acid. White molybdic acid remained. If blue spots ap-
peared in the mass, they were removed by moistening the
residue with nitric acid and evaporating a second time to
dryness. This procedure was adopted in all the experi-
ments. It was not possible to obtain concordant results
by merely drying the hydrate at a definite temperature.
The same was true in regard to the ignition of the hy-
DETERMINATION OF METALS- MOLYBDENUM.
59
drate to trioxide. Loss occurred from sublimation and
volatilization.
RESULTS.
y
U
OS
u *
Z Q ., [/)
K Q
u
M
2
D
o
Z Q ~ tfl
n 5 ^ ^
S Q .
Z
^
fri
aTS
s'sl'J
3^
O
g
1
CURRENT.
ij
o
g||j
<
as 7
o H as
C/3 U
_)
M
X
o H ft,
M
S
Q
H
H
2
0.1302
O. I
I2 5
70
N.D 107 =O.O22A
2.O
4/4
0.1299
0.0003
0.1302
O.I
125
80
N.D 107 ^=0.045 A
2.25
2 i/
0.1302
0.1302
O. I
I2S
70
N.D 107 =o.04 A
2.2
4 1^
0.1302
o. 2604
0.2
125
75
N.D 107 =o.04 A
2.O
7
0.2603
O.OOOI
O.I54I
0.2
125
85
N D o 04 A
1.9
2|
0.1541
O.I54I
0.2
125
80
N.-D 107 =o.o 3 5A
2. I
4
0.1540
0.0001
The method is accurate, is easy of execution, and re-
quires comparatively little time.
Chilesotti and Rozzi have applied this method in the
estimation of molybdenum and have met with excellent suc-
cess. At first, in the presence of alkali metals, they observed
that these were carried into the molybdenum sesquioxide,
but subsequently discovered that by addition of sulphuric
acid any alkali co-precipitated with the molybdenum was
reduced to nil. In the presence of 0.75 per cent, of potassium
sulphate, 0.4 per cent, to 0.50 per cent, of sulphuric acid
was sufficient to arrest all alkali precipitation.
^It seemed that the method could be made useful in the
determination of the molybdenum content of the mineral
molybdenite. By fusing the latter with a mixture of pure
alkaline carbonate and nitrate, sodium molybdate and sul-
phate would be formed. If the sulphur is not to be deter-
mined, after dissolving out the fusion with water, and
filtering off the insoluble oxides, acidulate the alkaline
liquid with dilute sulphuric acid and proceed with the elec-
i6o
ELECTRO-ANALYSIS.
trolysis; but in cases where an estimation of the sulphur
is desired, it was thought that acetic acid would answer
for the purpose of acidulation. To ascertain the latter
fact the experiments given below were instituted. The
solution, acidified with this acid, does not acquire a blue
color on passing the current through it. The deposit of
hydrated oxide is very adherent and readily washed. A
longer time is necessary for the complete precipitation. It
is also advisable not to add the entire volume of acetic acid
at first, but to introduce it gradually from time to time,
from a burette.
RESULTS.
!
U
H
in
s
} M S
S U
u
Eti
s
o a ss
^
D
H
o
R 3 * as
g H g
ji . H
5 .
1
S
EC
glil
if"
05 o w 5;
h Q
^
;
o
o <
2 S u O
5 w^
H
^
w
S r S o
x O
^^ a
3
i
CJ
S
H
S ^
M U
Q
H
H
S
O.I54I
I
I2 S
85
N.D 107 ^ 0.075 A
4.4
7^
0.1541
0.1541
I
125
85
N.D 1OT = 0.075 A
44
3
0.1540
O.OOOI
0.1541
I
I2 5
80
N.D 107 =o.o S A
2-5
6
0.1543
-[-O.OOO2
In the last experiment, 5 grams of sodium acetate were
added in order to increase the conductivity of the solution
and to ascertain what effect an excess of this salt would
have, because, if the acetic acid were used to acidify the
alkaline solution obtained by the decomposition of molyb-
denite, a great deal of this salt would be present. The
concordant results justified the next step, which was to
decompose weighed amounts of pulverized molybdenite
with sodium carbonate and nitrate, then take up the fusion
with water, filter out the insoluble oxides, acidify with
acetic acid, boil off the carbon dioxide, and electrolyze.
The liquid poured off from the deposit of the sesquihy-
DETERMINATION OF METAL'
-MOLYBDENUM.
161
droxide was heated to boiling and precipitated with a hot
solution of barium chloride.
MOLYBDENITE,
IN GRAMS.
MOLYBDENUM FOUND,
IN PER CENT.
SULPHUR FOUND,
IN PER CENT.
I
2
3
0.2869
0.1005
0.1388
57-37
57-15
56.83
38.28
38.33
37-87
The Rapid. Precipitation of Molybdenum Sesquioxide
With the Use of a Rotating Anode.
The procedure was the same as described under all the
other metals. The solutions were acidulated with sulphuric
acid and the conditions were as given here.
a
H
Z .
W r,
JN
Z
s M
^
M tA
Q
i
o
||
w ^ u
325
s *
5 s
w ^ 3
H S
2 ^
M td
H
J
M
g
fe
&
~"Z
a||
S53
*JJ
iS
5^
O
H
o
i
J~
s
I
O.I 2OO
2
5
16
30
0.1197
2
O. I2OO
2
5
16
5
0.0335
3
O. I2OO
2
5
16
9
0.0603
4
O. I2OO
2
5
16
15
o. 1026
5
O. I2OO
2
5
16
20
0.1190
6
O. I2OO
2
5
16
25
0.1198
The total dilution never exceeded 100 cubic centimeters.
The rapidity with which the oxide separates and the ease
with which the estimation is made make this electrolytic
procedure vastly superior to other methods of determina-
tion.
1 62
ELECTRO-ANALYSIS.
The Rapid Precipitation of Molybdenum With the Use
of a Mercury Cathode.
On electrolyzing an aqueous solution of molybdenum
trioxide, acidulated with sulphuric acid, with a cathode of
mercury, molybdenum itself enters fully into the cathode
and forms with it a brilliant white amalgam. Therefore
this metal can be directly weighed in this way. A water
solution of sodium molybdate, acidulated with sulphuric
acid, will serve also for this purpose. Accordingly, portions
of sodium molybdate (10 cubic centimeters of which con-
tained 0.0950 gram of metal) were electrolyzed under the
following conditions. The anode was stationary.
DETERMINATION OF MOLYBDENUM.
<ft
**<
s Si-
Q
\
Q S2
u^.
CONDITIONS.
S
w
lo
S3
H)
^^Q
00 M
*
S5
J
a H *
rf
ri
> H
r"
u
B.ffe
W K
i
M
H
M
M
i
J S5
- a
h
a S g
% ^
ID
s
M
3
O H
o z
o
fcC/3 S
PH
E
o
SIS
K
OH
s l
6
^
ga
fi
hffi
M
<3
^
I
<U
I
O.O95O
0.0950
3
13
14
1.2
6
1.6
6.5(2 hrs. )
2
O.O95O
0.0950
3
13
22
1.2
6
1.6
6 ( 2 hrs. )
3
O.I9OO
0.1906
2
30
18
1.6
5-5
1.4
7 (4 hrs.)
4
O.I9OO
0.1903
2
25
2O
1.6
5-5
7 (4 hrs.)
The ordinary steps, observed in treatment of the amalgam
with other metals, are observed here.
This method of determining molybdenum affords an
excellent means of separating it from other metals (see
p. 272).
GOLD.
LITERATURE. Luckow, Z. f. a. Ch., 19, 14; Brugnatelli, Phil.
Mag., 21, 187; Smith, Am. Ch. Jr., 13, 206; Smith and Muhr, Am. Ch.
Jr., 13, 417; Smith, Jr. An. Ch., 5, 204; Smith and Wallace, Ber.,
DETERMINATION OF METALS GOLD. 163
2 5> 779J Frankel, Jr. Fr. Ins., 1891; Persoz, Ann. Chim. Pharm., 65,
164; Riidorff, Z. f. ang. Ch., 1892, p. 695; Exner, J. Am. Ch. S.,
2 5 95; Medway, Am. Jr. Science [4th series] 18, 58; Per kin and
Preble, Electrochemische Zeitschrift, u, 69; Mill'er, J. Am. Ch.
S., 25, 896; Wi throw, J. Am. Ch. S., 28, 1350; J. Am. Ch. S.,
27, 1545-
This metal can be completely deposited from solutions
containing it in the form of a double cyanide, sulphaurate,
and sulphocyanide, as well as in the presence of free phos-
phoric acid. In this laboratory the cyanide and sulphaurate
have received the most consideration. An example will
illustrate the conditions with which good results may be
obtained from the double cyanide: A solution contained
o.i 162 gram of metallic gold; to it were added 1.5 grams of
potassium cyanide and 150 c.c. of water. It was heated to
55 and electrolyzed with a current of N.D 100 = o.38 am-
pere and 2.7-3.8 volts. The precipitation was complete in
one and one-half hours. 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 potas-
sium cyanide into the dish, and then connect the latter with
the anode of a battery yielding a very feeble current.
Perkin and Preble dissolve the gold from off the platinum
by pouring into the dish 100 c.c. of water containing two to
three grams of potassium cyanide and adding to this five
cubic centimeters of hydrogen peroxide. In the cold two to
three minutes will be required for the solution of the gold.
One minute is sufficient if the solution be gently heated.
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 equal 0.1-0.2 ampere
164
ELECTRO-ANALYSIS.
for a total dilution of about 125 c.c. The precipitated metal
is very adherent and of a bright yellow color.
The Rapid Precipitation of Gold With the Use of a
Rotating Anode.
Use a double cyanide electrolyte and follow the condi-
tions given in the subjoined table.
Q
z ^
*d
61
.
u*
R
3 i/i
3<
fcS
g 8
5
M g
3
S3
So
o
h|
S3
O
O
0.0290
I.O
5
II
IO
0.0289
0.0725
2.0
5
II
II
0.0725
0.1450
i-5
5
II
7
0.1447
The anode should perform 500 revolutions per minute.
In the examples given the deposits were excellent.
Withrow, in developing this study, found the following
results :
jf
C/5
P
u
%
^T r j)
td *
i
8
.1 2*
K
o
H
011 H
u"
o S
O
H <
O
D b
|s
J
Q g
a z
S P
.- <
M
Q rj
fc
J
^ s
E~* M
Q (^
M
Q
CJ^J
C/2
S
O
^
O
i
0.5222
5
60
IO
io -8
800
IO
0.5216
2
0.5222
5
60
10 -10.2
10 -7.3
800
12
0.5226
3
0.5222
2-5
55
10 -10.8
14.5-9.6
800
IO
0.5222
4
0.5222
2-5
55
10 -10.3
14 -9.4
810
12
0.5234
5
0.5465
3-5
60
10 -10.5
8.3-7
790
12
0.5461
6
0.5465
5
60
10 -10.2
9-3 8.3
790
I 0.1891
7
0.5465
5
60
10.2-10.5
8.3-7
800
3 0.4341
8
0.5465
5
60
10 -10.3
9.6-7.1
825
5 0.5286
9
0.5465
5
60
IO
8.6-6.7
780
7 0.5437
IO
o 5465
5
60
10.3-10
8.3-6.3
790
ii i o. 5468
ii
0.5465
5
60
16
7.8-6.8
790
12
0.5467
DETERMINATION OF METALS GOLD.
,6 5
The rate of precipitation is readily determined from these
data.
In an alkaline sulphide electrolyte results may be obtained,
which are just as satisfactory. In using this electrolyte
bring the alkaline sulphide into the cathode dish, rotate the
anode and then run in from a pipette the solution of gold
chloride.
RESULTS.
B-
CJ
z
M
c/3
z
6
|
u
in
H U
W M
K "
o
Bfi
li
5
z
Ii
Q *
o
O
$
Q
**
r
I
0.2878
15
60
10 - 8.8
7.6- 7.2
810
7
0.2891
2
0.2878
30
60
10.1-10.3
6.9- 6
840
7
0.2879
3
0.2878
30
60
9.8-10.1
7.8
830
7
0.2897
4
0.2878
15
60
10 - 9.8
11.6-n.i
840
7
0.2898
5
0.2878
20
60
10
ii. 6- 9
800
7
0.2905
6
0.2878
3
60
10.2-10 5
8.8- 7.4
830
7
0.2883
7
0.2878
20
60
IO.I-IO
9.1- 8.2
850
7
0.2885
8
0.2878
15
60
10
11.5-10
840
7
0.2887
9
0.2878
30
60
IO.I-IO
9-4- 8.5
850
0.1165
10
0.2878
30
60
10
8 - 7
850
6
0.2870
ii 0.2878
30
60
10 -10.2
9 - 7-9
850
3
0.2365
The Rapid Precipitation of Gold With the Use of a
Rotating Anode and Mercury Cathode.
Introduce the gold chloride solution into the mercury cup.
Place upon it 10 cubic centimeters of toluene. Electrolyze
with a current of from 2 to 3 amperes and 10 volts. The
gold is precipitated very rapidly. The other details of
manipulation are analogous to those recited under preceding
metals.
Five minutes are more than enough to precipitate from
0.15 to 0.2 gram of metal.
1 66 ELECTRO-ANALYSIS.
TIN.
LITERATURE. Luckow, Z. f. a. Ch., 19, 13; Classen and v. Reiss,
Ber., 14, 1622; Gibbs, Ch. N., 42, 291; Classen, Ber., 17, 2467; 18,
1104; Bongartz and Classen, Ber., 21, 2900; Riidorff, Z. f. ang. Ch.,
1892, 199; Classen, Ber., 27, 2060; Engels, Z. f. Elektrochem., 2,418;
Freudenberg, Z. f. ph. Ch., 12, 121; Heidenreich, Ber., 28, 1586;
Campbell and Champion, J. Am. Ch. S., 20, 687; Klapproth, Dis-
sertation, Hannover, 1901; Classen, Z. . Elektrochem., i, 289;
Henz, Z. f. anorg. Ch., 37, 40; Fischer and Boddaert, Z. f. Elektro-
chem., 10, 951; Medway, Am. Jour. Science [4th series], 18, 57;
D a n n e e 1 and Nissenson, Internationaler Congress fur angew. Chemie
(1903) Band, 4, 678; Exner, J. Am. Chem. S., 25, 905; Kollock
and Smith, J. Am. Ch. S., 27, 1532 and 1546; Witmer, J. Am. Ch.
S., 29, 473.
Tin may be deposited from a solution of ammonium tin
oxalate. It is advisable not to use potassium oxalate in
the electrolysis, for then a basic salt is liable to separate upon
the anode.
Classen adds 120 c.c. of a saturated ammonium oxalate
solution to the liquid containing 0.9-1.0 gram of stannic
ammonium chloride, then electrolyzes at 3O-35 with a
current of 0.3-0.6 ampere and 2.8-3.8 volts. Acid am-
monium oxalate must be added from time to time if large
quantities of metal are to be precipitated. The tin separates
in a brilliant, white, adherent form. It is washed and dried
in the usual way. The time required for precipitation is
generally nine hours. This factor, however, can be re-
duced, as is evident from the following example: Acidulate
the solution containing 0.4 gram of tin and 4 grams of
ammonium oxalate with 9-10 grams of oxalic acid; heat
to 6o-65, and electrolyze with N.D 100 = 1-1.5 amperes.
Acetic acid may replace the oxalic acid. Fusion with potas-
sium acid sulphate will remove the tin from the dish.
Henz dissolves the tin deposit in nitric acid, containing
DETERMINATION OF METALS TIN. 167
an excess of oxalic acid, or fills the dish with dilute hydro-
chloric acid and adds metallic zinc.
Campbell and Champion use the oxalate method in deter-
mining tin in its ores. Fuse I gram of the ore with 5-6
grams of a mixture of equal parts of soda and sulphur for
an hour and a half, at full red heat. This is done in a
porcelain crucible, placed within a second crucible of the
same material. Dissolve the sulphostannate in from 40-50
c.c. of hot water, filter, and re-fuse the residue as before.
Add hydrochloric acid, to faint acid reaction, to the com-
bined solutions of sulpho-salts. Stannic sulphide will be
precipitated. Boil off the hydrogen sulphide, add 10 c.c.
of hydrochloric acid (sp. gr. 1.20), and then gradually
introduce 2-3 grams of sodium peroxide until a clear liquid
is obtained. Boil for three minutes, filter out the separated
sulphur, add ammonia water to permanent precipitation and
50 c.c. of a 10 per cent, acid ammonium oxalate solution.
Electrolyze with a current of N.D 100 = o.i ampere and 4
volts. Allow the current to act through the night. The
deposit will be light in color and very adherent.
Classen has discovered that a tin solution containing 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 solu-
tion then carefully warmed in a covered vessel until the
evolution of hydrogen sulphide ceases ; after which the
liquid is heated to incipient ebullition for fifteen minutes.
Allow it to cool, dissolve any sodium sulphate which may
1 68 ELECTRO-ANALYSIS.
have separated by the addition of water, and electrolyze.
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. Having potassium sulphostannate,
Classen considers it advisable to convert the tin into oxalate
and then electrolyze. He employs two methods. One will
be given here :
Decompose the greater portion of the sulpho-salt with
dilute sulphuric acid (the liquid must remain alkaline) to
get rid of most of the sulphur as hydrogen sulphide, then
oxidize with hydrogen peroxide until the metastannic acid
produced is pure white in color. Acidulate with sulphuric
acid, neutralize with ammonia water, and again add hydro-
gen peroxide. Filter out the stannic acid when it has sub-
sided, dissolve in oxalic acid and ammonium oxalate, and
electrolyze with the conditions given in the preceding para-
graphs.
According to Carl Engels add 0.3 to 0.5 gram of hy-
droxylamine hydrochloride or sulphate, 2 grams of ammo-
nium acetate, and 2 grams of tartaric acid to the solution
of the tin salt, dilute with water to 150 c.c., heat to 6o-7O,
and electrolyze. with N.D 100 = i ampere.
The Rapid Precipitation of Tin With the Use of a
Rotating Anode.
In this laboratory no difficulty was experienced in using
a solution of stannous ammonium chloride containing an
excess of a hot saturated solution of ammonium oxalate.
The anode performed 300 revolutions per minute. The
proper conditions are shown in a few examples which fol-
low :
DETERMINATION OF METALS TIN.
169
AMMONIUM
TIN PRESENT
IN GRAMS.
OXALATE HOT,
SATURATED
SOLUTION
CURRENT
N. D. 100 IN
AMPERES.
VOLTS.
TIME.
MINUTES.
FOUND TIN
IN GRAMS.
IN C.C.
0.5396
100
5
5
13
0-5392
0.2193
100
5
5-5
15
0.2193
0-4355
100
5-8
5-5-6-5
1 8
0-4353
1.0800
IOO
5
4-5
20
I.oSoi
In using an ammonium sulphide electrolyte a definite
volume of the alkaline sulphide was placed in the cathode
dish and the solution of stannous chloride pipetted into it.
Hot water was then added to give 100 cubic centimeters
volume to the liquid. The anode was made to rotate 500
times per minute, the dish was covered and the current ap-
plied. The conditions are exhibited in the following experi-
ments :
AMMONIUM
SULPHIDE
(Sp. GR. 0.985).
CURRENT
N I). ,00 IN
AMPERES.
VOLTS.
TIME IN
MINUTES.
TIN PRESENT
IN GRAMS.
TIN FOUND
IN GRAMS.
An excess.
5-4
7
10
0-1357
0.1052
4
7-5
20
0.1357
0.1350
4
7-5
20
o 1357
0.1354
7 c.c.
4-5
8
25
0.1357
0.1358
H '
5-4
7-5
25
0.2714
0.2717
The deposits were like polished silver. When stannic
chloride was the salt used, the metal deposit was slightly
crystalline but perfectly adherent. The speed of rotation
of the anode had little or no effect on the character of the
deposit.
The best conditions for 0.2 gram of metal were found to
be 15 to 20 cubic centimeters of ammonium sulphide (sp.
gr. 0.985) and a current of N.D 100 = 5.5 amperes and 9
volts.
16
I ;o
ELECTRO-ANALYSIS.
The rate of precipitation was determined with a solution
containing 0.5070 gram of metal. It was found to be:
In i minute 0.0704 gram
In 2 minutes 0.1276 gram
In 3 minutes 0.1922 gram
In 4 minutes 0.2475 gram
In 5 minutes 0.2927 gram
In i o minutes 0.4796 gram
In 1 5 minutes 0.49 1 7 gram
In 20 minutes 0.5070 gram
The current in these trials was N.D 100 = 5 amperes and 7.5
to 10 volts.
The Rapid Precipitation of Tin With the Use of .a
Rotating Anode and Mercury Cathode.
Arrange the mercury cup as under the preceding metals.
Introduce into it the tin salt, preferably the sulphate ( 5 cubic
centimeters = 0.4 1 06 gram), add a little concentrated sul-
phuric acid and electrolyze with a current of from 2 to 4
amperes and 5 to 4 volts. Conditions almost analogous to
these are found in the following examples. They are re-
liable and give results that are dependable.
ri
H
u u
Q
M
W
w
K U
X
11
[5
gi
Z .
D g
o <
!l
a.
X
z
1"
Q
11
o
*=!
K
2
w
H
H
I
0.4106
5
0.2
2-4
5
10
0.4109
-f 0.0003
2
0.4106
5
0.2
4
5
9
0.4114
.-f 0.0008
3
0.4106
5
0.2
4
5-4-5
9
0.4109
+0.0003
o 4106
6
O. !
6
0.4106
5
0.4106
5
0.25
.'
4
5
6
0.4106
6
0.8212
10
6
5-5
9
0.8210
O.OOO2
7
0.4106
10
0.75
5
5
8
0.4107
+ O.OOOI
8
0.4106
7
0.05
5
5
7
0.4106
9
0.4106
7
0.25
5
5
10
0.4107
+ 0.0001
DETERMINATION OF METALS ANTIMONY. I /I
The rate of precipitation is :
In 2 minutes 0.2997 gram of tin
In 4 minutes 0.3974 gram of tin
In 5 minutes 0.4060 gram of tin
In 6 minutes 0.4106 gram of tin
On using a current of 5 amperes and 5 to 4 volts, 0.8212
gram of tin was precipitated in eight minutes.
Stannous chloride may also be used as the electrolyte if
the layer of toluene (p. 89) is placed over it. To illustrate,
the following examples may be cited :
1. Five cubic centimeters of stannous chloride (=0.0800
gram of tin) and 10 cubic centimeters of toluene were elec-
trolyzed with a current of 2 to 3 amperes and 7 to 6 volts.
In ten minutes (a) 0.0798 gram and (b) 0.0806 gram of
metal were precipitated.
2. Ten cubic centimeters of stannous chloride ( 0.1600
gram of tin) and ten cubic centimeters of toluene were
electrolyzed with a current of 2 to 3 amperes and 7 to 6
volts. In fifteen minutes 0.1595 and 0.1600 gram of metal
were obtained.
ANTIMONY.
LITERATURE. Wrightson, Z. f. a. Ch., 15, 300; Parodi and Mas-
cazzini, Z. f. a. Ch., 18, 588; Luckow, Z. f. a. Ch., 19, 13; Classen
and v. Reiss, Ber., 14, 1622; 17, 2467; 18, 1104; Lecrenier, Ch. Z.,
13, 1219; Chittenden, Pro. Conn. Acad. Sci., Vol. 8; Vortmann,
Ber., 24, 2762; Riidorff, Z. f. a. Ch., 1892, 199; Classen, Ber., 27,
2060; Henz, Z. f. anorg. Ch., 37, 29; Ost and Klapproth, Z. f. ang.
Ch. (1900), 827; Ho Hard, B. Soc. Chim. [series 3], 29, 262 and C.
N., 87, 282; Fischer, Ber., 36, 2348; Z. fur anorg. Ch., 42, 363;
Law and Per kin, Trans. Faraday Society (1905), i, 262; Danneel
and Nissenson, Internationaler Congress fur angewandte Ch. (1903),
Band 4, 678; Exner, J. Am. Ch. S., 25, 905; Fischer and Bod-
daert, Z. f. Elektrochem., 10, 950; Langness and Smith, J. Am.
Ch. S., 27, 1524; Dormaar, Z. f. anorg. Ch., 53, 349; Foerster
and Wolf, Z. f. Elektrochem., 13, 205; Sand, Z. f. Elektrochem., 13, 326.
172 ELECTRO-ANALYSIS.
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 potassium antimony 1 tartrate. Its de-
position from a cold ammonium sulphide solution is satis-
factory, but the use of this reagent for this purpose is not
pleasant, especially when several analyses are being carried
out simultaneously. For this reason potassium or sodium
sulphide has been substituted. The alkaline sulphide used
must not contain iron or alumina.
The antimony solution mixed with 80 c.c. of sodium
sulphide (sp. gr. 1.131.15), should be diluted with water
to 125 c.c. and acted upon at 6o 65 with a current of
N.D 100 = i ampere and 1.1-1.7 volts. The metal will be
fully precipitated in two hours. The deposit should be
treated in the usual way with water and pure alcohol.
Dry at 90. To ascertain when all of the metal has been
deposited, incline the dish slightly, thus exposing a clean
platinum surface. If this remains bright for half an hour
the precipitation is finished. In separating antimony from
the heavy metals e. g., lead it happens that alkaline sul-
phides 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, the solution of sodium monosulphide,
and electrolyze as previously directed.
Lecrenier writes as follows relative to the preceding
method: The precipitation is all that one can desire, pro-
viding the solution of the sulpho-salt is absolutely free
from polysulphides; otherwise, it is incomplete. The anti-
DETERMINATION OF METALS ANTIMONY. 173
mony sulphide obtained in the ordinary course of analysis
always contains sulphur, and this must be eliminated. To
remove the various inconveniences connected with the
method add 50-70 c.c. of a 25 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 conducted
through the liquid. This can rise to 0.5 ampere without
impairing the result; but it is not best, as the precipitated
metal is then very coherent. It is better to use a current
of 0.25 ampere. When the quantity of antimony does not
exceed 0.2 gram, the deposit will be adherent and free
from sulphur; wash with water, alcohol, and ether. Sul-
phur will separate upon the anode, despite the presence of
an excess of sodium sulphite. This, however, does not
affect the result.
The method of Classen suffers in several points :
1. The bath pressure falls as the electrolysis proceeds,
because of the accumulation in it of sodium polysulphide.
2. If the electrolysis is not interrupted at the proper
moment, antimony already precipitated will be again dis-
solved by the polysulphide which has diffused toward the
cathode (Z. f. ang. Ch., 1897, 325). Ost and Klapproth
have sought by the use of a diaphragm to circumvent
these objectionable features. To this end they use (Fig.
30) a roughened dish, a, in which is suspended a dish-
shaped diaphragm, b (a Pukall porous cup, Ber., 26, 1159).
A strip of platinum, c, within the diaphragm, is the anode,
while the platinum dish itself constitutes the cathode.
Cover-glasses are placed over both dishes. The liquids
experimented upon were a solution of Schlippe's salt
(=0.0985 gram of antimony in 10 c.c.) and a solution of
pure sodium sulphide (195 grams Na 2 S = 200 grams
ELECTRO-ANALYSIS.
NaOH to the liter). In the first experiments the anti-
mony was equally distributed in the whole electrolyte.
The cathode chamber contained 85 c.c. and the anode
FIG. 30.
chamber 40 c.c. of the solution, which had 0.0985 gram of
antimony in 125 c.c., with varying amounts of sodium
sulphide. The liquid covered about 100 sq. cm. of the
surface of the dish :
BATH PRESSURE AT
CURRENT STRENTH
EXPERI-
Na 2 S
TEMPER-A-
ONE AMPERE.
IN AMPERES.
ANTIMONY
MENT.
TION.
TURE.
BEGINNING
END
AT
AT
TATED.
VOLTS.
VOLTS.
BEGINNING.
END.
I
5 c.c.
7
3-8
3-9
0.7
0-3
0.0675
2
50 -
Cold.
1.9
3-8
o-5
0.4
0.0725
3
80
70
2-5
i-7
I.O
I.O
0.0685
4
80 "
70
i-7
i-3
I.O
I.O
0.0720
When the electrolysis was finished, antimony could not
be found in the cathode liquid from any one of the four
experiments, whereas in the anode chamber it was still in
solution, and in experiment I it had been precipitated on
the anode in the form of antimony pentasulphide.
DETERMINATION OF METALS ANTIMONY.
175
These experiments indicated then that the current is
not able to carry antimony ions from the anode into the
cathode chamber.
In the next series of experiments the 10 c.c. of antimony
solution (=0.0985 gram of metal) were placed in the
cathode chamber alone :
BATH PRESSURE AT ONE
EXPERI-
Na 2 S
SOLU-
TEMPERA-
AMPERE.
ANTIMONY
MENT
TION.
TURE.
BEGINNING
AT END
TATED.
VOLTS.
VOLTS.
I
50 c.c.
Cold.
4.2
3-7
5 hours.
0.0970
2
50 c.c.
70
2.O
3-8
3 "
0.0984
Temp. 32
3
80 c.c.
70
2-5
1.7
2 "
0.0990
4
50 c.c.
70
1.8
1.8
iK"
0.0990
The results show a quantitative precipitation of the anti-
mony. None of it could be found either in the cathode or
anode liquid.
On placing the antimony in the anode chamber alone,
not a particle of metal was deposited on the cathode.
When the antimony was placed in the cathode chamber
only and varying quantities of sodium sulphide solution
were mixed with it, remarkable differences were observed.
In the presence of much sodium sulphide and accompany-
ing low bath pressure all of the antimony was precipitated
at the cathode, while with little sodium sulphide and con-
sequent high bath pressure, a small amount of antimony
wandered through the diaphragm and was deposited at the
anode in the form of antimony sulphide.
These experiments show how a successful antimony de-
termination may be made. No difficulties attend its esti-
mation in this way.
1 76 ELECTRO-ANALYSIS.
To dissolve the antimony deposit from off the dish, Ost
recommends nitric acid, containing tartaric acid.
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 its solution in sodium
sulphide, with his knowledge that antimony could be pre-
cipitated from a similar solution, and hence recommends
the determination of the antimony in the form of an amal-
gam. No difficulties 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 oxide ;
to this end digest the antimonious solution with bromine
water, and afterward add the sodium sulphide containing
sodium hydroxide. Electrolyze with a current of from
0.2 to 0.3 ampere. The amalgam can be washed in the
usual way.
Law and Perkin recommend precipitating antimony from
an ammoniacal solution of its tartrate. To this end they
heat the electrolyte to 75 and act upon it with a current
of N.D 100 = o.2 to 0.5 ampere and 2.5 to 3 volts.
Almost every analyst has experienced at the out-start,
difficulties similar to those described and many have made
suggestions of value to escape them. Thus, Henz, recog-
nizing the virtue of the methods adopted by Lecrenier and
Ost and Klapproth to get rid of the disturbing influences
due to the polysulphide, found an excellent reducing agent
in potassium cyanide. Hollard (1900), however, was the
first to use this reagent, antedating Henz, Fischer and
Exner. Potassium cyanide rapidly reduces polysulphides
to monosulphide, forming a sulphocyanide :
KCN + Na 2 S 2 = KCNS + Na 2 S.
DETERMINATION OF METALS ANTIMONY.
177
In this respect one gram of potassium cyanide will be
as effective as four grams of sodium sulphite. It is also
much more soluble. One to two grams will suffice to
keep colorless the bath for the precipitation of o.i gram of
antimony.
While Henz obtained most satisfactory deposits of anti-
mony in this way he observed as have others that often
the results were high; in some instances from 2 to 3 per
cent. He thought possibly there was here a constant for
which allowance could be made. Dormaar has since given
this point very careful study and found that the apparent
increase in the found antimony, rising with the current
strength and the quantity of metal present, is due in large
part to the presence of oxygen in the deposit and some
occluded sodium sulphide.
It is probable that working with from o.i to 0.2 gram of
metal this oxidation has been too slight to affect the final
result, so it has been usually neglected. '
The Rapid Precipitation of Antimony With the Use of
a Rotating Anode.
Exner, working in this laboratory, first performed this
determination. He added to a solution of antimony chlo-
ride a slight excess of sodium hydroxide, sodium hydro-
sulphide and potassium cyanide, then electrolyzed with con-
ditions like those given below.
SbCl 3
EQUAL TO
ANTIMONY
IN GKAMS.
NaOH
10$ SOLU-
TION INC.C.
NaSH
c.c.
2O
KCN
GRAMS
CURRENT
N.D 100 =
AMPERES.
VOLTS.
TIME IN
MINUTES.
Sb.
0.3042
30
2
5
4-5
2O
0.3042
178 ELECTRO-ANALYSIS.
The anode made 400 to 500 revolutions per minute.
Later Miss Langness proceeded as follows in applying
the above procedure. To a solution of antimony chloride
(=0.2405 gram of metal) were added 15 cubic centi-
meters of sodium sulphide (sp, gr. 1.18), 3 grams of po-
tassium cyanide, i cubic centimeter of sodium hydroxide
(10 per cent.), the solution was diluted with water to 70
cubic centimeters, heated nearly to boiling and electrolyzed
with N.D 100 = 6 amperes and 3.5 to 4 volts. The metal
was all deposited in fifteen minutes. Numerous determi-
nations were made. The deposits in all of them were per-
fectly adherent. There was no sponginess. The metal
was bright gray in color. On using sand-blasted platinum
dishes from 0.4847 gram to i.oooo gram of metal could be
precipitated in a beautiful and very compact form in from
twenty to twenty-five minutes.
The rate of precipitation, determined with a current of
6.5 amperes and 3.5 volts, was as follows:
In i minute 0.0652 gram of antimony was obtained
In 2 minutes 0.1007 gram of antimony was obtained
In 3 minutes ..0.1575 gram of antimony was obtained
In 4 minutes 0.1969 gram of antimony was obtained
In 5 minutes 0.2140 gram of antimony was obtained
In 6 minutes 0.2251 gram of antimony was obtained
In 7 minutes ....0.2331 gram of antimony was obtained
In 8 minutes 0.2369 gram of antimony was obtained
In 15 minutes 0.2405 gram of antimony was obtained
The omission of the sodium hydroxide from the electro-
lyte works no harm. It is possible also to reduce the volume
of sulphide to ten cubic centimeters, but there should then
be a reduction of the alkaline cyanide to 2 grams. The
reduction of the latter without a corresponding reduction
of sulphide is apt to alter somewhat the character of the
deposit.
DETERMINATION OF METALS TELLURIUM.
This method was tried out under the most varied con-
ditions, and then applied to the mineral stibnite. Very
pure samples of the latter were reduced to powder and 0.5
gram portions digested with 20 cubic centimeters or more
of sodium sulphide (1.18 sp. gr.), filtered from the insoluble
part, and after the addition of 3 grams of potassium cyanide
and one cubic centimeter of sodium hydroxide (10 per
cent.), heated to boiling and electrolyzed with N.D 100 =7
amperes and 3 volts. The results were perfectly satis-
factory. The time required to precipitate all the antimony
did not exceed twenty-five minutes. See also separation
of antimony from arsenic (p. 251).
TELLURIUM.
LITERATURE. Pellini, Gaz. chim. ital., 34 (I.) 128; Gallo, Gaz. chim.
ital., 34 (II.) 404-409; Gallo (Atti R. Accad. dei Lincei Roma [5]
I3> [*] 7i3; Gazz. chim. ital., 35, 514 (1905); Schucht, Ch. Z.
(1880), 292, 374; Jahresb. 1880, p. 174, 1143; Schucht, Ch. N., 41,
280; Jahresb. (1880) 1143, 1144; Schucht, Z. f. analyt. Ch., 22 (1883)
495 ; Whitehead, J. Am. Ch. S., 17, 849 ; Ch. N., 82, 203.
Dissolve the tellurium in nitric acid and evaporate. Heat
the residue on a water bath after the addition of ten cubic
centimeters of sulphuric acid, introduce 30-40 cubic centi-
meters of a saturated solution of acid ammonium tartrate
to complete solution, dilute with water to 250 cubic centi-
meters, rotate the anode at the rate of 800 to 900 revo-
lutions per minute and electrolyze with N.D 100 0.12 to
0.09 ampere and 1.8 to 1.2 volts. The electrolyte should
be heated to 60 C. Wash the deposit promptly with water
free from oxygen, then with alcohol and dry at about 90
C. Rather large quantities of tellurium can be precipitated
in this way.
ISO ELECTRO-ANALYSIS.
Gallo recommends dissolving distilled tellurium in sul-
phuric acid, using a sand-blasted dish, then evaporating to
the appearance of white fumes. The tellurium dissolves
as tellurous acid. When cold add several cubic centimeters
of boiled water, free from carbon dioxide, to the white
residue, dilute to 150 cubic centimeters with a ten per cent,
solution of sodium or potassium pyrophosphate. Heat
gradually to 60 C., use a spiral anode, and electrolyze with
a current of N.D 100 = 0.025 ampere and 1.8 to 2 volts.
About twenty-five milligrams of tellurium will be precipi-
tated per hour.
ARSENIC.
LITERATURE. Luckow, Z. f. a. Ch., 19, 14; Classen and v. Reiss,
Ber., 14, 1622; Moore, Ch. N., 53, 209; Vortmann, Ber., 24, 2764;
Schulze, Inaugural Dissertation, Berlin (1900); Thorpe, Jr. Ch. Soc.,
London, 83, 974; Sand and Hackford, Jr. Chem. Soc. London (1904),
1018; Mai and Hurt, Ch. Z., 29, Heft 20 (1905), Z. f. Untersuch.
Nahr. Genusen. 9, 193 to 199; Frerichs and Rodenberg, Arch, der
Pharmacie, 243, 348; Thorpe, Ch. N., 88, 7; Trotman, Jr. Chem.
Society 23, 177.
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.
Its separation from oxalate solutions is incomplete; nor do
the sulpho-salts answer for electrolytic purposes.
From a solution containing 0.2662 gram of arsenious
oxide Vortmann obtained 0.18527 gram of metallic arsenic,
equivalent to 69.59 P er cent - The trioxide contains 75.78
per cent, of arsenic. This precipitation was effected by the
amalgam method.
The facts relating to the electrolytic behavior of vana-
dium (Truchot, Ann. Chim. Anal. (1902), 7, 165) tungs-
SEPARATION OF METALS COPPER. l8l
ten, and osmium are, at the present writing, few in number
and will not be introduced here.
2. 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 indicated.
It will be noticed that the electrolytes vary. The mineral
acid and the double cyanide solutions are best adapted for
the purpose. The greatest number of separations have
been made by means of them. Some of the organic acids,
too, answer quite well as will be seen in the succeeding
paragraphs.
COPPER.
Inasmuch as the electrolytic precipitation of copper gives
the analyst such an excellent means of determining this
metal quantitatively, its separations from other metals are
of prime importance. Such separations, so far as they have
been carefully worked out in the most essential points, are
given in detail in the following paragraphs. It is needless
to add that acid solutions mainly are best adapted for these
separations.
i. From Aluminium:
(a) In nitric acid solution. Dilution, 200 c.c.; 5 c.c. of
nitric acid (sp. gr. 1.30) ; temperature, 32; N.D 100 =
i ampere and 3.3 volts; time, 4 hours.
1 82 ELECTRO-ANALYSIS.
With a rotating anode. Arrange the apparatus as
described on p. 72. Dilute the solution to 125 c.c.,
add i c.c. of nitric acid (sp. gr. 1.43) and electrolyze
with a current of N.D 100 = 3 amperes and a pressure
of 4 to 5 volts. The anode should perform 300 to 400
revolutions per minute. The time allowed the precip-
itation should not exceed twenty minutes. Copper
present 0.2874 gram and aluminium 0.2500 gram. The
copper found equaled (a) 0.2873 gram, (b) 0.2874
gram and (c) 0.2874 gram. J. Am. Ch. S., 26,
1284.
(b) In sulphuric acid solution. Dilution, 150 c.c. ; 3 c.c.
of concentrated sulphuric acid; temperature, 59;
N.D 100 =. i ampere and 2.5 volts; time, 2 hours.
With a rotating anode. With apparatus arranged
as given on p. 72 introduce the solution of salts of the
two metals into a dish, dilute to 125 c.c., add i c.c. of
sulphuric acid (sp. gr. -1.83) and electrolyze with a cur-
rent of N.D 100 = 4 to 5 amperes and a pressure of 14
to 8 volts. Time ten minutes. With a mercury cath-
ode and rotating anode. This separation was accom-
plished in the presence of 0.5 cubic centimeters of sul-
phuric acid (i.i), when the current registered i
ampere and 4 volts. In four minutes the solution was
colorless. The current was allowed to act for ten
minutes.
Volume of the solution = 10 cubic centimeters.
Copper sulphate 00.1150 gram copper.
Aluminium sulphate O o.i gram aluminium.
Sulphuric acid (i.i) =0.5 cubic centimeter.
Current = 1-1.6 ampere.
Pressure =4-4.5 volts.
Time 10 minutes.
Copper found 0.1150 gram, 0.1153 gram, 0.1152 gram.
SEPARATION OF METALS COPPER. 183
(c) In phosphoric acid solution. Dilution, 225 c.c. ; 5
c.c. of phosphoric acid (sp. gr. 1.347) ; temperature,
77 C. ; N.D 100 == 0.068 ampere and 2.6 volts; time, 6
hours. Sixty cubic centimeters of disodium hydro-
gen phosphate (sp. gr. 1,0338) were present for 0.1239
gram of copper and o.iooo gram of aluminium. The
precipitated copper weighed 0.1240 gram (J. Am.
Ch. S., 21, 1002).
In this electrolyte the separation with the aid of a
rotating anode is also possible when observing these
conditions: Dilution 125 c.c., with 10 c.c. of phosphoric
acid (sp. gr. 1.085), 5 c - c - f a IO P er cent - solution
of disodium hydrogen phosphate, and a current of
N.D 100 = 5 amperes and 6 volts. Time 10 minutes.
A slight amount of phosphorus, not sufficient to affect
the weight materially, was always found in the deposit
of copper.
2. From Antimony:
In tartrate solution. In the presence of one-tenth
of a gram of each metal, making certain that the anti-
mony is in its highest state of oxidation, add 8 grams
of tartaric acid and 30 c.c. of ammonia (sp. gr. 0.91).
Electrolyze at 50 with a current of N.D 100 = o.o8-
o.io ampere and 1.8-2 volts. Total dilution 150 c.c.
The ordinary temperature. Time, 5 hours (J. Am.
Ch. S., 15, 195).
Smith and Wallace (Jr. An. Ch., 7, 189; Z. f. anorg.
Ch., 4, 274) have also used this separation with emi-
nent success. They, too, emphasize the necessity of
having the antimony in its highest form of oxidation.
Several examples will illustrate their method of pro-
cedure :
1 84
ELECTRO-ANALYSIS.
Z
_^
i .'
" a
JjH
o
off
S 2 w
P
S
H
S K
3
o
O
o o
sis
CL,
1
Q
>< i
Ufa
0.0670
0.1449
175 c.c.
15 c.c.
3-4
1.8
O.I
0.0670
0.1341
0.1449
175 "
15 "
3-4
2.0
O. I
0.1341
0.1341
0.2898
175 "
15 "
3-4
2.0
0.08
0.1344
The deposited metal showed no antimony.
See also Puschin and Trechzinsky, Ch. Z., 28, 482;
also Elektrochemische Zeitschrift, 14, 47.
From Arsenic :
(a) In ammoniacal solution. McCay (Ch. Z., 14, 509)
observed that a current conducted through a potas-
sium arsenate solution, made distinctly ammoniacal,
had no effect upon the arsenic, while with copper under
like conditions the metal was quantitatively precipi-
tated. Upon this behavior he has based a very excel-
lent separation of the two metals. Care should be
taken not to introduce too much ammonia water. In
this laboratory the method of McCay, with the condi-
tions here presented, has repeatedly given excellent
results :
Add 20 c.c. of ammonium hydroxide (sp. gr. 0.91)
and 2.5 grams of ammonium nitrate to the solution
containing 0.2121 gram of copper and 0.1540 gram of
arsenic; dilute to 125 c.c. with water, heat to 5o-6o,
and electrolyze with N.D 100 = o.5 ampere and 3.5
volts. The copper, precipitated in three hours, weighed
0.2123 an d 0.2121 gram. Drossbach (Ch. Z., 16, 819)
and Oettel confirm (Ch. Z. (1890), 14, 509) (also see
Copper) McCay's experience.
Freudenberg, who adopted the suggestion of Kili-
SEPARATION OF METALS COPPER. 185
ani, of giving more attention to the pressure than to
the amperage, succeeded in separating copper and
arsenic (latter existing as arsenate) by arranging to
have in their solution, 30 c.c. in excess of a 10 per
cent, ammonium hydroxide solution and then elec-
trolyzing with a current of 1.9 volts until the liquid
became colorless, which usually occurred after from
6-8 hours (Z. f. ph. Ch., 12, 118).
With a rotating anode (p. 72). Dilute the solution
to 125 c.c., add 25 c.c. of ammonium hydroxide (sp.
gr. 0.74), and 2.5 grams of ammonium nitrate, then
electrolyze with N.D 100 = 5 amperes and 7 volts.
Fifteen minutes will suffice to precipitate 0.2742 gram
of copper from an equal amount of arsenic. The de-
posit will be smooth and adherent (J. Am. Ch. S.,
26, 1285).
Schmucker separated copper from arsenic with con-
ditions similar to those indicated for copper and anti-
mony in ammoniacal tartrate solution (see above).
(b) In potassium cyanide solution. Add the copper
solution to that of the alkaline arsenite or arsenate, and
then introduce a solution of potassium cyanide until the
precipitate first produced is just dissolved; the liquid
will then show a slight purple tint. Electrolyze with
the following conditions: N.D 100 = 0.25-0.26 ampere;
volts = 2. 4-3. 6; dilution, 150 c.c.; time, 3 hours;
temperature, 60.
(c) In acid solution. Freudenberg adds 1020 c.c. of
dilute sulphuric acid to the solution of the metals in
question and then electrolyzes with a current having a
tension of 1.9 volts. The arsenic existed partly as
trioxide and partly as pentoxide. The precipitation
was made during the night (Z. f. ph. Ch., 12, 117).
17"
1 86 ELECTRO-ANALYSIS.
Copper present, 0.3000 gram; found, 0.2997 gram;
arsenic present, 0.3531 gram. The copper was always
brilliant in color.
The separation can also be made in nitric acid solu-
tion with the same voltage. It is inferior to the first
method.
By using the rotating anode and following the con-
ditions recommended in the separation of copper from
aluminium by the same procedure (p. 182) excellent
results may be obtained (J. Am. Ch. S., 26, 1285).
4. From Barium, Strontium, Calcium, Magnesium, and
the Alkali Metals. The conditions given for the sepa-
ration of copper from aluminium in nitric acid solution
(p. 181) will serve for its separation from these metals.
5. From Bismuth. See the separation of bismuth from
copper, p. 227.
6. From Cadmium:
(a) In nitric acid solution. It was in a solution contain-
ing free nitric acid that these two metals were first
separated electrolytically (Am. Ch. Jr., 2, 41). The
results have been frequently confirmed. An idea of
the proper working conditions may be obtained from
the following: To a solution in which were present
0.0988 gram of copper and 0.1152 gram of cadmium
were added 2 c.c. of nitric acid of sp. gr. 1.43. The
total dilution of the liquid equaled 100 c.c. It was
heated to 50 and electrolyzed with N.D 100 = o.io
ampere and 2.5 volts. In 3 hours the copper was
completely precipitated. It was bright in color and
weighed 0.0988 gram. It contained no cadmium (J.
Am. Ch. S., 19, 873; also Jr. An. Ch., 7, 253).
When the copper has been precipitated, washed,
SEPARATION OF METALS COPPER. 187
dried, and weighed, make the residual liquid alkaline
with sodium hydroxide, add sufficient potassium cy-
anide to redissolve the precipitate, and electrolyze as
directed on p. 81.
This separation may be performed in a few minutes
with the rotating anode by following the conditions pre-
scribed under the separation of copper from aluminium
(p. 182) in the same electrolyte (J. Am. Ch. S., 26,
1285).
(b) In sulphuric acid solution. From solutions in
which there is free sulphuric acid the copper may be
electrolytically precipitated, leaving the cadmium.
This is evidenced by the following examples : Total
dilution, 100 c.c. ; 10 c.c. of sulphuric acid, sp. gr.
1.09; 0.1975 gram of copper and 0.1828 gram of cad-
mium; N.D 100 0.05-0.07 ampere and 1.70-1.76
volts; at the ordinary temperature. The precipitate
of copper weighed 0.1976 gram (Am. Ch. Jr., 12,
no). By heating the electrolyte the time can be re-
duced to 8 hours.
The separation has also been made by strict atten-
tion to difference in potential (Freudenberg, Z. f. ph.
Ch., 12, 116). Ten to twenty cubic centimeters of
dilute sulphuric acid are added to the solution con-
taining the two metals and the liquid is then electro-
lyzed with a current not exceeding 2 volts. The cop-
per will be deposited very rapidly and be free from
cadmium.
COPPER TAKEN.
0.2734 gram
0.4101 gram
0.3000 gram
CADMIUM TAKEN.
0.2560 gram
0.2958 gram
0.4437 gram
COPPER FOUND.
0.2729 gram
0.4098 gram
0.3003 gram
These separations were conducted during the night.
1 8 8 ELECTRO-ANALYSIS.
Heidenreich (Ber., 29, 1585) met with success in ap-
plying Freudenberg's suggestion, but asserts that the
tension should not exceed 1.8 volts for N.D 100 =
0.07-0.05 ampere. See also Denso, Z. f. Elektrochem.,
9, 469.
(c) In phosphoric acid solution. The separation of the
two metals in the presence of free phosphoric acid has
often been made in this laboratory with satisfaction.
Favorable conditions will be found in the example
which appears here: Dilution of solution, 125 c.c. ;
0.2452 gram of metallic copper and 0.1827 gram of
metallic cadmium; 20 c.c. of disodium hydrogen phos-
phate, sp. gr. 1.0353, an d 10 c.c. of phosphoric acid,
sp. gr. 1.347; temperature, 60; N.D 100 = 0.07-0.08
ampere and 2.5 volts; time, 3 hours (Am. Ch. Jr., 12,
329)-
7. From Calcium. See the separation of copper from
barium, p. 186.
8. From Chromium. See copper from aluminium, p. 182,
for the conditions of separation when the metals are
present in nitric or sulphuric acid solution. This state-
ment also holds true if the rotating anode be used in the
same electrolytes (J. Am. Ch. S., 26, 1285).
(a) In phosphoric acid solution. Volume of solution
(containing 0.1239 gram of metallic copper and 0.1403
gram of metallic chromium as sulphates) 225 c.c., 60
c.c. of disodium hydrogen phosphate (sp. gr. 1.033)
and 8 c.c. of phosphoric acid (sp. gr. 1.347) ; N.D 100 =
0.062 ampere and 2.5 volts; temperature, 65; time, 6
hours (J. Am. Ch. S., 21, 1003).
When using the rotating anode follow the instruc-
tions laid down for the separation of copper from
aluminium in this electrolyte (p. .183) (J. Am. Ch.
SEPARATION OF METALS COPPER. 189
S., 26, 1285). The copper will contain traces of phos-
phorus.
From Cobalt:
(a) In the presence of nitric or sulphuric acid the sepa-
ration of these two metals may be accomplished by ob-
serving- the conditions given for the separation of cop-
per from aluminium in the presence of the same acids
(see p. 182). Dr. Wolcott Gibbs employed mineral
acid solutions for this purpose many years ago (Z. f. a.
Ch., 3, 334). Most analysts prefer the sulphate solu-
tion. Neumann is of this number. He dissolves, for
example, i gram each of copper sulphate and cobalt
sulphate in the requisite volume of water, adds 3 c.c. of
concentrated sulphuric acid, dilutes to 150 c.c., and
electrolyzes with N.D 100 = i ampere at the ordinary
temperature. The time required for the complete pre-
cipitation of the copper varies from 2^-3 hours. The
filtrate or solution poured off from the deposit of cop-
per need only be mixed with an excess of ammonia
water and then be exposed to a stronger current in
order to precipitate the cobalt. See Z. f. angw. Ch.,
17, 892.
(b) In oxalic acid solution. The double oxalates have
also been used. The method requires a strict adher-
ence to the prescribed voltage (1.11.3) to yield a
satisfactory result. Classen, with whom the method
originated, advises the addition of 6 grams of am-
monium oxalate to the solution of the salts and acid-
ulates the liquid with oxalic acid, acetic acid, or
tartaric acid. Four hours are required for the pre-
cipitation of 0.25 gram of copper (Z. f. Elektrochem.,
i, 291, 292; Ber., 27, 2060). Also Puschin and
Trechzinsky, Z. f. angw. Chemie, 19, 892.
ELECTRO-ANALYSIS.
(c) In phosphoric acid solution. An example will
afford an idea of the method of procedure : Total
dilution, 225 c.c. ; 60 c.c. of sodium hydrogen phos-
phate (sp. gr. 1.033) ; 10 c.c. of phosphoric acid (sp.
gr. 1.347); N.D 100 = 0.035 ampere and 1.5 volts;
temperature, 62 ; time, 6 hours. Copper present,
0.1239 gram; cobalt present, o.iooo gram. Copper
found, 0.1243 gram (J. Am. Ch. S., 21, 1003; Am.
Ch. Jr., 12, 329; Jr. An. Ch., 5, 133).
In using the rotating anode to bring about the sepa-
ration of copper from cobalt an electrolyte containing
sulphuric or phosphoric acid should not be employed.
In a nitric acid electrolyte the separation is all that
can be desired. Use the conditions described in the
separation of copper from aluminium (p. 182) (J. Am.
Ch. S., 26, 1286).
10. From Gold. See p. 247.
11. From Iron:
(a) In nitric acid solution. The conditions given for
the separation of copper from aluminium (p. 182) will
answer here. When much iron is present, difficul-
ties will be encountered. The copper tends to redis-
solve (Schweder, Berg-Hutt. Z., 36, 5, n, 31).
(b) In sulphuric acid solution. Experience has dem-
onstrated that the separation of the metals in ques-
tion is best and most accurately made in the presence
of free sulphuric acid, observing the conditions as
described on p. 182 for copper from aluminium. When
the copper has been fully precipitated, which usually
requires 2j hours, the residual solution is poured off,
the copper is washed, and the liquid reduced to a
suitable volume, neutralized with ammonia, and 4-6
SEPARATION OF METALS COPPER. IQI
grams of ammonium oxalate introduced into the
liquid, which is then electrolyzed at 3O-4O with a
current of N.D 100 1-1.5 amperes and 3.4-3.8 volts.
The iron will be fully precipitated in 3-4 hours (Clas-
sen, Neumann).
(c) In phosphoric acid solution. In this laboratory suc-
cess has attended the use of the phosphates in the
presence of free phosphoric acid. Recently the proper
conditions as to current density and voltage have
been carefully determined. It will be seen from the
appended example that the results are most satisfac-
tory : Total dilution, 225 c.c. ; disodium hydrogen phos-
phate, 60 c.c. (sp. gr. 1.0358) ; 10 c.c. of phosphoric
acid (sp. gr. 1.347); temperature, 53 C. ; N.D 100 =
0.04 ampere and 2.4 volts; time, 7 hours. Copper
present, 0.1239 gram; found, 0.1237 gram (Am. Ch.
Jr., 12, 329; Jr. An. Ch., 5, 133; J. Am. Ch. S., 21,
1002).
The use of the rotating anode may be resorted to
in each of the preceding electrolytes with most satis-
factory results, if the conditions mentioned on p. 182
for the separation of copper from aluminium be care-
fully observed (J. Am. Ch. S., 26, 1286).
(d) In animoniacal solution. In such a solution Vort-
mann separates the copper from a large quantity of
iron. The liquid containing the two metals is mixed
with ammonium sulphate and an excess of ammonia
water. The author maintains that the ferric hydrox-
ide, which is of course precipitated, does not interfere
with the deposition of the copper. The latter is free
from iron. The current employed in this separation
should be N.D 100 0.1-0.6 ampere (M. f. Ch., 14,
552).
1 92 ELECTRO-ANALYSIS.
It is doubtful whether the copper is really free
from iron. The opinion presented under the separa-
tion of nickel from iron (p. 264) and the experiences
there recorded certainly make this recommendation
very questionable. Indeed, in this laboratory it was
found in 'separating the copper from iron in chalco-
pyrite by this method that if the precipitation of the
former took place in a platinum dish it was invariably
contaminated with iron. On the other hand, if the
solution of metals was placed in a beaker and a
vertical platinum plate was made the cathode, then
the copper deposited was free from iron. The ferric
hydrate floating about in the platinum dish and in im-
mediate contact with the precipitate is partially reduced
to the metallic form.
(e) In oxalic acid solution. This procedure is due to
Classen (Ber., 27, 2060), who adds to the solution
containing both metals in the form of sulphates from
6-8 grams of ammonium oxalate and sufficient oxalic,
acetic, or tartaric acid to render the liquid acid. The
total dilution is 150 c.c. N.D 100 = i ampere; voltage,
2.9-3.4 at 50-6o. Time, 3 hours. It is absolutely
necessary to replace the oxalic acid as it is decomposed,
otherwise iron will separate upon the copper. The
method requires the strictest attention to details, other-
wise its results will be far from satisfactory. Indeed,
its omission from the last edition of Classen's " Quanti-
tative Electrolysis " would seem to indicate that its
author had lost faith in its efficacy.
(/) To a solution of copper sulphate and pure ferrous
sulphate add 1.5 gram of pure potassium cyanide and
10 c.c. of ammonia (sp. gr. 0.94), then dilute to 100
c.c., rotate the anode about 400 revolutions per minute
SEPARATION OF METALS COPPER. 1 93
and electrolyze with a current of N.D 100 = 9 to n
amperes and 10 volts. The copper will be fully pre-
cipitated, free from iron, in ten minutes (J. Am. Ch.
S., 29, 455).
12. From Lead. The separation of these two metals has
great value from the technical standpoint. It is fortu-
nate, therefore, while both separate under the influence
of the current in a nitric acid solution, that they are
deposited at opposite poles. Very considerable atten-
tion has been paid to the conditions which ought to pre-
vail during the deposition. Many writers have con-
tributed their experience on this point, and from them
is gathered the following: The liquid electrolyzed should
equal 150 c.c. in volume. It should contain 15 c.c. of
nitric acid and be heated to about 60 and acted upon
with a current of N.D 100 1-1.5 amperes and 1.4 volts.
In the course of an hour all the lead will have been pre-
cipitated upon the anode, which in this separation should
be a dish with roughened surface, but not all of the
copper will have been deposited on the cathode a smaller,
perforated dish. It will be noticed in the course of the
decomposition that the lead separates first and the copper
more slowly. When the lead is fully precipitated, wash
without interrupting the current, proceed further as di-
rected on p. 101, and after placing the liquid and wash
water, reduced to 130 c.c., into another weighed dish,
make the latter the cathode and suspend in it the smaller
dish upon which some copper had been deposited, making
it the anode. The solution will give up its copper on
passing the current and the metal will be deposited on the
larger vessel (the cathode). It may be well to add that
the liquid poured from off the lead dioxide will be quite
18
1 94 ELECTRO-ANALYSIS.
acid, therefore neutralize it with ammonium hydroxide
and add 10 c.c. of nitric acid. The electrolysis can then
be conducted with N.D 100 = i ampere and 2.2-2.5 volts,
at the ordinary temperature.
13. From Magnesium. See the separation of copper from
barium, etc., p. 186.
Copper may be separated from magnesium in an elec-
trolyte containing nitric, sulphuric or phosphoric acid,
with the help of the rotating anode, by observing the
conditions given under the separation of copper from
aluminium, pp. 182, 183 (see J. Am. Ch. S., 26, 1286).
14. From Manganese:
(a) In sulphuric acid solution. It should be remem-
bered that from such a solution the manganese will
be deposited upon the anode as peroxide (see p. 134) ;
therefore, in the electrolysis let the larger dish, with
rough inner surface, be made the anode to receive
the manganese. The solution containing the two
metals is diluted to 130-150 c.c. with the addition
of 10 drops of concentrated sulphuric acid. Let the
current be N.D 100 = 0.5-1.0 ampere. The most favor-
able temperature is 5o-6o. The time required is
usually 2-3 hours. Experience has taught that too
much manganese must not be present. When the de-
position is finished, treat the deposit as already des-
cribed on p. 135. The washing should be performed
without interrupting the current.
(b) In nitric acid solution. The separation can also be
effected in the presence of free nitric acid. If the
content of the latter, however, exceeds 3 to 4 per
cent., instead of having the manganese precipitated
on the anode it remains in solution and a red color
SEPARATION OF METALS COPPER. 195
appears at the anode due to permanganic acid. In
the actual analysis, the solution of the two metals
ought to be acidulated with a few cubic centimeters
of acid and then electrolyzed at 60 with the same
current conditions as given in a.
It will be wise here to observe the statement made
upon page 135 as to the influence of the strong min-
eral acids. Indeed, if this be true, then the preced-
ing separations are worthless and should be discarded,
as has been done with the separation in oxalate so-
lutions. In the writer's personal experience the sepa-
ration in sulphuric acid solution does give satisfac-
tory results. The subject deserves further investi-
gation.
The rotating anode may be used in both a sulphuric
or nitric acid electrolyte to effect this separation if the
conditions under copper from aluminium (p. 182) are
observed (J. Am. Ch. S., 26, 1287).
(c) In phosphoric acid solution. When free phosphoric
acid is present in the solution containing salts of these
metals, no question need arise as to the result, for
oft-repeated tests, made in this laboratory, have amply
demonstrated the accuracy of the procedure. The
appended example will illustrate: N.D 100 = o.o5 am-
pere; voltage =2. 5; temperature, 56; time, 6 hours;
dilution, 225 c.c. ; copper present, 0.1239 gram; copper
found, 0.1236 gram; manganese present, 0.1200 gram:
60 c.c. of disodium hydrogen phosphate (sp. gr.
1.038) ; 10 c.c. of phosphoric acid (sp. gr. 1.347) (J.
Am. Ch. S., 21, 1004, and Am. Ch. Jr., 12, 329).
The copper deposit in this, as well as in the many
other trials conducted under practically the same con-
ditions, was deep red in color and very adherent. It
196 ELECTRO-ANALYSIS.
contained no manganese. The latter does not even
appear at the anode, except as an amethyst color, indi-
cating the formation there of permanganic acid.
15. From Mercury. See the separation of mercury from
copper, pp. 218, 219.
1 6. From Molybdenum. Add 1.5 grams of pure potas-
sium cyanide to the solution of the two metals ; dilute
with water to 150 c.c., heat to 60, and electrolyze with
N.D 100 = o.28 ampere and 4 volts. The copper will
be completely precipitated in 5-6 hours.
17. From Nickel:
(a) In acid solution. This separation may be realized
by observing the conditions given for the separation
of copper from aluminium (p. 182) or those noted
under copper from cobalt (p. 189). That is, in nitric
or sulphuric acid solution (Wolcott Gibbs, Z. f. a. Ch.,
3, 334), the separation is all that the analyst can ask.
The separation in oxalate solution, as recommended
by Classen (Z. f. Elektrochem., i, 291, 292), must also
be executed with conditions analogous to those indi-
cated for copper from cobalt, b (p. 189). Also Z.
f. Elektrochem., 9, 469.
(b) In phosphoric acid solution. The writer has found
that in the presence of free phosphoric acid this separa-
tion can be made with ease and the confidence of
securing a favorable result: copper present, 0.1239
gram; copper found, 0.1241 gram; nickel present,
0.1366 gram; 60 c.c. of disodium hydrogen phosphate,
sp. gr. 1.033; IO c - c - of phosphoric acid, sp. gr. 1.347;
total dilution, 225 c.c.; N.D 100 = 0.035 ampere; ten-
sion = 1.5 volts; time, 6 hours; temperature, 62 C.
(J. Am. Ch. S., 21, 1003). For the conditions when
SEPARATION OF METALS COPPER. 197
iron, cobalt, zinc, and copper are present together in
phosphoric acid solution, see J. Am. Ch. S., 21, 1004.
In attempting to separate these two metals in a sul-
phuric or phosphoric acid electrolyte, using a rotating
anode, the results were poor, but in an electrolyte con-
taining nitric acid, they were most satisfactory.
To the solution containing 0.2500 gram of each
metal add 0.25 cubic centimeter of concentrated nitric
acid and three grams of ammonium nitrate. Elec-
trolyze with a current of N.D 100 = 4 amperes and a
pressure of 5 volts. In fifteen minutes the separa-
tion will be complete. The speed of rotation of the
anode should be about 600 revolutions per minute.
To show how helpful this separation may be an
analysis of a nickel coin will be here given :
Dissolve the coin (4.925 grams in weight) in 20
cubic centimeters of concentrated nitric acid diluted
with an equal volume of water. Exactly neutralize
with ammonium hydroxide, transfer to a 250 cubic
centimeter measuring flask and fill this to the mark
with water. Transfer 25 cubic centimeters of this
liquid to a weighed platinum dish, and add three grams
of ammonium sulphate, then dilute with water to 125
cubic centimeters, heat almost to boiling and electro-
lyze with a current of N.D 100 = 5 amperes and a
pressure of 5.5 volts for twenty minutes. (The pre-
cipitated copper in this particular analysis weighed
0.3691 gram = 74.95 per cent, of the coin.) Pre-
cipitate the nickel from the solution with sodium hy-
droxide and bromine water, filter and wash. Dissolve
the precipitate in 2 cubic centimeters of concentrated
sulphuric acid diluted with water, add 30 cubic centi-
meters of concentrated ammonium hydroxide, dilute to
198 ELECTRO-ANALYSIS.
125 cubic centimeters, heat and electrolyze with a cur-
rent of N.D 100 = 6 amperes and a pressure of 5
volts. (In twenty minutes 0.1217 gram, correspond-
ing to 24.71 per cent, of nickel, was precipitated.) The
solution from the nickel deposit should be filtered to
get the iron in this particular case it weighed 0.0026
gram, equivalent to 0.35 per cent, of metallic iron.
Two and one-half hours will suffice for the complete
analysis (J. Am. Ch. S., 25, 906).
1 8. From Palladium. See the following separation:
19. From Platinum. Add 1.5 grams of pure potassium
cyanide and 5 grams of ammonium carbonate to the
solution of the two metals, dilute with water to 125 c.c.,
heat to 70, and electrolyze with N.D 100 = o.2 ampere
and 2-2.5 volts. The copper will be precipitated in
6 hours.
In using the rotating anode add to the solution of the
two metals, 3 grams of potassium cyanide and 10 to 20
c.c. of ammonia. Electrolyze with a current of N.D 100 =
3 amperes and 5 volts.
20. From Potassium. See copper from barium, etc. (p.
186).
21. From Selenium.
(a) In cyanide solution. To the solution containing
0.0745 gram of copper and 0.2500 gram of sodium
selenate add i gram of potassium cyanide, dilute to
150 c.c., heat to 60 C., and electrolyze with N.D 100 =
0.2 ampere and 4 volts. The precipitation will be
finished in five hours.
(b) In nitric acid solution. To a solution containing
the quantities of metal as in (a) add I c.c. of nitric
acid (sp. gr. 1.43), dilute to 150 c.c, and electrolyze at
SEPARATION OF METALS COPPER. 1 99
65 C, with a current of N.D 100 = 0.05 to 0.08 am-
pere and 2 to 2.5 volts.
(c) In sulphuric acid solution. Add one cubic centi-
meter of concentrated sulphuric acid to the solution
of the metals and electrolyze with N.D 100 =o.O5 to
o.io ampere and 2.25 volts at 65 C. The separa-
tion will be complete in five hours.
22. From Sodium. See copper from barium, p. 186.
23. From Strontium. See copper from barium, p. 186.
24. From Silver. See silver from copper, p. 240. Classen
proposed to precipitate the two metals with ammonium
oxalate, silver oxalate being insoluble in an excess of
the precipitant, while the copper salt was soluble. The
former was to be filtered off, dissolved in potassium
cyanide, and electrolyzed, while the filtrate containing
the copper was to be subjected to a separate electrolysis.
This is really not an electrolytic separation, as was shown
by others (J. Am. Ch. S., 16, 420). Further, the copper
deposits were invariably found to contain silver, so that
it is best not to follow this procedure.
25. From Tellurium:
(a) In nitric acid solution. For several years, at inter-
vals, experiments have been made in this laboratory by
D. L. Wallace, upon the electrolytic separation of these
metals. The results have been uniformly good with
the following conditions: Copper, in grams, 0.1543;
tellurium, in grams, o.uoi ; dilution, 100 c.c. ; 0.5 c.c.
nitric acid (sp. gr. 1.42) ; N.D 100 = o.io ampere and
2.06 volts ; temperature, 66-7O ; time, 5 hours. Cop-
per found: (a) 0.1541 gram; (b) 0.1546 gram; (c)
0.1543 gram; (d) 0.1542 gram.
(b) In sulphuric acid solution. Add one cubic centi-
200 ELECTRO-ANALYSIS.
meter of concentrated sulphuric acid to the solution of
the metals, dilute to 150 c.c., heat to 65 C, and elec-
trolyze with N.D 100 = 0.05 to o.i ampere and 2 to 2.25
volts. Six hours will suffice for the precipitation of
the copper (J. Am. Ch. S., 25, 895).
26. From Thallium. No attempt has been made to effect
this separation.
27. From Tin. Schmucker demonstrated (J. Am. Ch.
S., 15, 195) that, having tin in its highest oxidation
form, it is possible to precipitate and separate copper from
it by adding to the solution 8 grams of tartaric acid and
30 c.c. of ammonia water (sp. gr. 0.91), then electrolyz-
ing at 50 C. with N.D 100 = o.O4 ampere and 1.8 volts.
If a tenth of a gram of each metal be present, the copper
will be precipitated in 5 hours. The total dilution was
175 c.c.
As observed in preceding paragraphs, this method was
utilized by Schmucker in the separation of copper from
arsenic and copper from antimony. The same author
also separated copper from a mixture of antimony,
arsenic, and tin, using the conditions as described above.
Or, when antimony, arsenic, and tin are associated
with copper, treat the four sulphides with sodium sul-
phide. The resulting alkaline sulphide solution can then
be employed for the separation of the first three (p. 251),
while the insoluble copper sulphide may be dissolved and
treated as described on p. 70.
28. From Tungsten. The conditions given for the sepa-
ration of copper from molybdenum (p. 196) may be used
for this separation.
29. From Uranium:
(a) In nitric acid solution. Add 0.5 c.c. of concentrated
SEPARATION OF METALS COPPER. 2OI
nitric acid to the solution, dilute to 150 c.c., heat to
60, and electrolyze with N.D 100 = 0.14-0.27 ampere
and 2-2.4 volts. The copper will be precipitated in
3 hours.
(b) In sulphuric acid solution. The solution of these
metals should be mixed with 2 c.c. of concentrated sul-
phuric acid, diluted to 150 c.c. with water, heated to
50-6o, and electrolyzed with N.D 100 = 0.16 ampere
and 2 volts. The precipitation will be complete in 4
hours.
The separation of copper from uranium may be
readily carried out with the help of a rotating anode by
observing the conditions given for the separation of
copper from aluminium in the same electrolytes (p.
182) (J. Am. Ch. S., 26, 1287).
30. From Vanadium. A method of separation is lacking.
31. From Zinc:
(a) In nitric acid solution. The conditions mentioned
under a in copper from aluminium (p. 181), and under
copper from cobalt (p. 189) and nickel (p. 196), will
answer here in getting a satisfactory separation. The
solution must be kept acid during the decomposition.
To this may be added, that to a solution containing
0.1341 gram of copper and equal amounts of zinc,
cobalt, and nickel, 5 c.c. of nitric acid were added, the
liquid was diluted to 200 c.c., and electrolyzed with
0.04 ampere, when 0.1339 gram of copper was obtained.
In using the rotating anode in conducting this sepa-
ration add to the solution of the metals 3 grams of
ammonium nitrate and 0.25 c.c. of concentrated nitric
acid, then electrolyze with a current of N.D 100 = 5
amperes and 9 volts. Time, 15 minutes.
202 ELECTRO-ANALYSIS.
(b) In sulphuric acid solution. The conditions are
analogous to those employed for the separation of
copper from aluminium (p. 182), cobalt (p. 189), and
nickel (p. 196).
In this electrolyte also the separation is greatly
accelerated by the use of the rotating anode. Dilute
the solution to 125 c.c., add i c.c. of sulphuric acid of
sp. gravity 1.83 and electrolyze with N.D 100 = 3 to 5
amperes and 5 volts. Time, 10 minutes.
(c) In oxalate solution. This method (Ber., 17, 2467)
is no longer recommended. Only the most careful
observance of the conditions given will yield anything
like a satisfactory result.
(d) In phosphoric acid solution (Am. Ch. Jr., 12, 329;
Jr. An. Ch., 5, 133). The early suggestions that these
metals be precipitated as phosphates and the latter be
then dissolved in phosphoric acid and the resulting solu-
tion be electrolyzed were not favorably received.
Here, in this laboratory, where the separation had been
repeatedly performed, the method gave satisfaction.
To extend its application the most favorable conditions
have been worked out and repeated. They are given
in the example which follows :
To the solution of the sulphates, containing 0.1239
gram of copper and a like quantity of zinc, were added
60 c.c. of disodium hydrogen phosphate (sp. gr. 1.033)
and 10 c.c. of phosphoric acid (sp. gr. 1.347). It was
diluted to 225 c.c., heated to 60, and electrolyzed with
N.D 100 = 0.035 ampere and 2.5 volts, for 5 hours,
when 0.1244 gram of copper was obtained, free from
zinc.
By following the conditions given in the separation
of copper from aluminium (p. 183) in this electrolyte
SEPARATION OF METALS CADMIUM. 203
a rotating anode will prove most helpful. Traces of
phosphorus will appear in the copper deposits.
Another interesting separation, properly belonging
here, was that of copper from a mixture of iron, cobalt,
and zinc. The solution diluted to 225 c.c. contained :
0.1239 gram of copper
0.1007 gram of cobalt
o.i ooo gram of iron
0.1200 gram of zinc
30 c.c. of Na,HPO 4 (sp. gr. 1.0358)
15 c.c. of H 3 PO 4 (sp. gr. 1.347)
It was electrolyzed at 57 with a current of N.D 100 =
0.04-0.05 ampere and 2.3 volts. In six hours the
copper was fully precipitated. It weighed 0.1240 gram
and contained none of the other metals (J. Am. Ch. S.,
21, 1003, 1004).
CADMIUM.
The ordinary gravimetric methods for the determination
of this metal are such that they can frequently with advan-
tage be replaced by the electrolytic process. The same is
true when it comes to the separation of cadmium from the
metals usually associated with it, as well as those with which
it occasionally occurs. The writer prefers the electro-
lytic course whenever it is available. To what extent the
various suggestions offered for the electrolytic determination
of the metal can be applied in separations may be gathered
from the following paragraphs :
i. From Aluminium:
(a) In sulphuric acid solution. In this separation it is
only necessary to add to the solution of the salts of the
metals 3 c.c. of sulphuric acid, of specific gravity 1.09,
2O4 ELECTRO-ANALYSIS.
dilute to 125 c.c. with water, heat to 65, and electro-
lyze with N.D 100 0.078 ampere and 2.61 volts.
The cadmium will be deposited in the course of from
4-4/2 hours. It should be washed without interrupt-
ing the current. In one case o. 1 1 1 1 gram of Cd in-
stead of 0.1105 was found; in another, 0.1181 instead
of o.i 1 88 gram; and in a third, 0.1604 instead of
0.1599 gram.
To demonstrate the advantage in using a rotating
anode in making this separation an example in actual
experimentation may be here introduced :
To a solution containing 0.2727 gram of cadmium
and 0.2500 gram of aluminium add I c.c. of sulphuric
acid (sp. gr. 1.83), dilute to 125 c.c. with water and
electrolyze with a current of N.D 100 = 5 amperes and
5 volts. Time ten minutes. The deposits are per-
fectly adherent (J. Am. Ch. S., 26, 1288). Or, by
using a mercury cathode and rotating anode with a
current of 3 amperes and 7 volts, total volume of the
solution being 10 c.c., this separation may be made in
twenty minutes.
(b) In phosphoric acid solution. Add an excess of di-
soclium hydrogen phosphate (sp. gr. 1.0358) to the
solution of the metals and then sufficient phosphoric
acid (sp. gr. 1.347) to leave about 1.5 c.c. of the latter
in excess. Dilute with water to 100 c.c., heat to 50,
and electrolyze with N.D 100 = 0.06 ampere and 3 volts.
Time, 7 hours. See p. 82 for further details (J. Am.
Ch. S., 20, 279; Am. Ch. Jr., 12, 329; 13, 206).
When using the rotating anode dilute the solution
of the metal salts to 125 c.c. after adding 10 c.c. of
phosphoric acid, and 50 c.c. of a 10 per cent, solution
of disodium hydrogen phosphate solution and elec-
SEPARATION OF METALS CADMIUM. 2O5
trolyze with a current of N.D 100 = 5 amperes and 7
volts for 10 minutes (J. Am. Ch. S., 26, 1288).
2. From Antimony. Schmucker (J. Am. Ch. S., 15, 195)
used for this purpose the method described on p. 183
for the separation of copper from antimony, observing
the same conditions. The results were perfectly satis-
factory. In washing the cadmium deposit water alone
was used. The deposition was made during the night,
but by heating the electrolyte the time factor can be
much reduced.
3. From Arsenic:
(a) In animoniacal tartrate solution. Proceed precisely
as directed on p. 184 in the separation of copper from
arsenic (J. Am. Ch. S., 15, 195).
(b) In alkaline cyanide solution. After converting the
arsenic into its highest state of oxidation, add from
2 to 3 grams of potassium cyanide to the solution con-
taining the metals and electrolyze with a pressure not
exceeding 2.6 volts (Am. Ch. Jr., 12, 428; Z. f. ph.
Ch., 12, 122).
4. From Barium, Strontium, Calcium, Magnesium, and
the Alkali Metals. No records of any such separations
have been made.
5. From Beryllium. There is no record of this separation.
6. From Bismuth. See separation of bismuth from cad-
mium, p. 225.
7. From Chromium. The conditions given for the sepa-
ration of cadmium from aluminium will answer equally
well in this case; also when applying a rotating anode
in a phosphoric acid electrolyte (J. Am. Ch. S., 26, 1288).
In the presence of 3 cubic centimeters of concen-
trated sulphuric acid, using the mercury cathode and
2O6 ELECTRO-ANALYSIS.
rotating anode, this separation is easily made with a
current of 2 to 3 amperes and 3.5 to 4 volts. Time 25
minutes.
8. From Cobalt:
(a) In sulphuric acid solution. Use the conditions pre-
scribed for the separation of cadmium from aluminium
(p. 204). It may be well to add that the addition of
ammonium sulphate to the solution is advantageous.
The voltage should not exceed 2.8-2.9.
(b) In alkaline cyanide solution. Add 4-5 grams of
pure potassium cyanide to the solution of the metals,
dilute to 200 c.c., and electrolyze with N.D 100 = o.3
ampere and 2.6 volts (Am. Ch. Jr., 12, 104; Z. f. ph.
Ch., 12, 116). See also J. Am. Ch. S., 27, 1286.
9. From Copper. See also copper from cadmium, pp. 186,
187, 1 88. In addition to the methods used in separat-
ing these metals, in which the copper is precipitated, we
may add the following : Introduce 5 to 6 grams of pure
potassium cyanide into the solution of the metals for
every 0.2-0.4 gram of cadmium and copper. Dilute
the solution to 200 c.c. and electrolyze with a current
of N.D 100 = 0.02-0.04 ampere and 2.6-2.7 volts. The
cadmium will be deposited; the copper will remain
dissolved (Jr. An. Ch., 3, 385; Z. f. ph. Ch., 12, 122).
Rimbach (Z. f. a. Ch., 37, 288) has tried this separa-
tion with marked success in the analysis of aluminium-
cadmium-tin alloys containing copper as impurity. In
case the nitrate of cadmium is used it will be necessary
to increase the current to N.D 100 = 0.4 ampere.
10. From Gold. This separation is not recorded. It is
probable that it can be executed in a hot alkaline cy-
anide solution.
SEPARATION OF METALS CADMIUM. 2O/
IT. From Iron:
(a) In sulphuric acid solution.' Follow the directions
given in a under cadmium from aluminium, p. 204.
It may be observed that this is the procedure used,
too, in separating cadmium from chromium. See the
separation of cadmium from aluminium (p. 204) for
the conditions to be used when applying a rotating
anode (J. Am. Ch. S., 26, 1288).
(b) In phosphoric acid solution. Again the conditions
noticed in b under cadmium from aluminium (p. 204)
will prove to be very satisfactory in this particular
case (J. Am. Ch. S., 26, 1289).
(c) In potassium cyanide solution. Dissolve a mixture
of cadmium and ferrous sulphates in 100 c.c. of water,
previously acidulated with a few drops of dilute sul-
phuric acid, introduce 2 to 3 grams of pure potassium
cyanide, and heat gently until perfect solution ensues.
If considerable time elapses before the liquid becomes
yellow in color, add a few drops of caustic potash.
Dilute the liquid to 200 c.c. and electrolyze the cold
solution with a current of N.D 100 = 0.05-0.1 ampere.
The deposit of cadmium will be very satisfactory (W.
Stortenbeker, Z. f. Elektrochem., 4, 409).
It is possible, by using the rotating anode, to per-
form this separation in twenty minutes by electrolyz-
ing the solution of mixed salts, after the addition of
12 grams of potassium cyanide and 2 grams of sodium
hydroxide, with a current of N.D 100 = 5 amperes
and a pressure of 5 volts. It is well to use a quarter
of a gram of each metal (J. Am. Ch. S., 27, 1285).
12. From Lead. See lead from cadmium, p. 234.
13. From Magnesium. See cadmium from barium, etc.,
p. 205. In this connection it may be stated that Rim-
208 ELECTRO-ANALYSIS.
bach (Z. f. a. Ch., 37, 289) effected this separation in a
potassium cyanide solution. The precaution is made
that not too much magnesia be present, ammonium
chloride also being added to the solution to hold up the
magnesia. The current strength best adapted for this
separation proved to be N.D 100 = 0.02-0.05 ampere.
The time was 14 hours.
In a formic acid solution. To the solution of the
salts of the two metals add 0.2 gram of sodium carbon-
ate and 12 c.c. of formic acid of sp. gr. 1.06, then elec-
trolyze with a current of N.D 100 5 amperes and 6
volts. The anode should perform about 600 revolu-
tions per minute. Ten minutes will answer for the full
precipitation of the cadmium (J. Am. Ch. S., 27, 1285).
In electrolytes of sulphuric and phosphoric acid the
conditions applicable here are found under cadmium from
aluminium, p. 204.
14. From Manganese:
(a) In sulphuric acid solution. As manganese sepa-
rates readily from a sulphate solution in the presence
of a slight excess of sulphuric acid, and then, too,
upon the anode (p. 134), it is only necessary to add
from 2 to 3 c.c. of sulphuric acid (sp. gr. 1.09) to the
solution of the metals, dilute to 125 c.c., and electro-
lyze with the current and voltage given under cad-
mium from aluminium, a. As the manganese is pre-
cipitated upon the anode as dioxide, make the larger
dish the receiving vessel for it; further, let its inner
surface be roughened. The cadmium is deposited
upon the cathode. The method has been used in this
laboratory with success.
(b) In phosphoric acid solution. An idea of the ac-
curacy of the method can be best obtained from an
SEPARATION OF METALS CADMIUM. 2OQ
actual example. The conditions also for work will be
most satisfactorily learned from it. Twenty cubic
centimeters of disodium hydrogen phosphate (sp. gr.
1.0358) and 3 c.c. of phosphoric acid (sp. gr. 1.347)
were added to a solution containing 0.2399 gram of
cadmium and o.iooo gram of manganese and the
liquid then diluted with water to 150 c.c. and electro-
lyzed at the ordinary temperature with a current of
i ampere. In 12 hours 0.2394 gram of cadmium was
precipitated. There was not the slightest deposition
of manganese at the anode. The cadmium deposit
was crystalline in appearance. It was washed with
hot water. Before the final interruption, the cur-
rent ought to be increased and allowed to act for an
hour. The acid liquid should be removed with a
siphon before disconnecting (Am. Ch. Jr., 13, 206).
In using the rotating anode as an aid in this sepa-
ration, according to (a) and (b) follow the condi-
tions given under the separation of cadmium from
aluminium, p. 204 (J. Am. Ch. S., 26, 1289).
15. From Mercury. See mercury from cadmium, p. 217.
1 6. From Molybdenum. The alkaline cyanide solution
is well adapted for this purpose. Add from 1.5 to 3
grams of pure potassium cyanide, dilute to 200 c.c., and
electrolyze at 40 C, with N.D 100 = 0.03-0.04 ampere
and 2.25-3.0 volts. The conditions are practically
those used in the separation of cadmium from arsenic
(Am. Ch. Jr., 12, 428).
17. From Nickel:
(a) In sulphuric acid solution. To the solution of salts
of the two metals add 2 to 3 c.c. of sulphuric acid, sp.
19
2 1 ELECTRO-ANALYSIS.
gr. 1.09, also ammonium sulphate, and electrolyze
with the current density and voltage mentioned in
the separation of cadmium from aluminium, a, p. 204.
The conditions favorable to the use of the rotating
anode in this separation are analogous to those out-
lined under the separation of cadmium from alu-
minium, p. 204.
(b) In phosphoric acid solution. 0.1827 gram of cad-
mium and 0.1500 gram of nickel (both as sulphates)
were precipitated by 40 c.c. of disodium hydrogen
phosphate, dissolved in 3 c.c. of phosphoric acid (sp.
gr. 1.347), diluted to 125 c.c., and electrolyzed at the
ordinary temperature with N.D 100 = 0.035 ampere
and 2.5-3.0 volts. The precipitated cadmium weighed
0.1820 gram. It was washed and treated as directed
upon p. 81.
(c) In alkaline cyanide solution. The solution contain-
ing the double cyanides of the two metals is well
suited for this separation, but it is absolutely neces-
sary to have a little free sodium hydroxide present.
The conditions would be then about as follows : Add
to the solution containing 0.1723 gram of cadmium,
and 0.1600 gram of nickel, 2 grams of potassium or
sodium hydroxide and 3 grams of potassium cyanide.
Dilute to 175 c.c. and electrolyze at 40 with N.D 100 --
0.03-0.04 ampere -and 2.25-3.0 volts (Am. Ch. Jr.,
12, 104; Freudenberg, Z. f. ph. Ch., 12, 122).
1 8. From Osmium. The only recorded separation of
these two metals was made in a solution of potassium
cyanide. The quantity of cyanide was 1.5 grams for
0.3 gram of the combined metals. The dilution of the
solution equaled 170 c.c.; it was electrolyzed with a
SEPARATION OF METALS - CADMIUM. 211
current of N.D 100 = o.26 ampere and 3-4 volts. Time,
10 hours; temperature, 25 (Jr. An. Ch., 6, 87).
An electrolytic separation of cadmium from plati-
num and palladium is not known (Am. Ch. Jr., 12, 428;
ig. From Selenium. This separation has not been made.
20. From Silver. See p. 239, for silver from cadmium.
21. From Sodium. See the separation of cadmium from
barium, etc., p. 205.
22. From Srontium. See the separation of cadmium from
barium, etc., p. 205.
23. From Tellurium. There is no known electrolytic
separation.
24. From Tin. They have not been separated electro-
lytically.
25. From Tungsten. The conditions detailed in the sepa-
ration of cadmium from arsenic (p. 205) and under
cadmium from molybdenum (p. 209) in cyanide solu-
tion will answer here.
26. From Uranium. The current has not been used in
their separation.
27. From Vanadium. They have not been separated in
the electrolytic way.
28. From Zinc. As these two metals are so frequently
found together, both in natural and in artificial prod-
ucts, it is not surprising that electrolytic methods have
been sought to effect their separation in such a manner
as to leave no doubt in the mind of the analyst. They
should be and indeed are preferable to the ordinary
gravimetric procedures.
2 I 2 ELECTRO-ANALYSIS.
The first method proposed and published was that by
Yver (B. s. Ch. Paris, 34, 1 8). It is based upon the
fact that cadmium separates well
(a) In acetate solution. Convert the metals into ace-
tates by the addition of 2 to 3 grams of sodium
acetate to their solution, followed by several drops of
free acetic acid. Dilute the liquid to 100 c.c. and
warm to 70 C. Electrolyze with N.D 100 =o.io
ampere and 2.2 volts. Time, 3-4 hours. The cad-
mium (0.2 gram) will be precipitated in a crystalline
form and free from zinc (Am. Ch. Jr., 8, 210).
The zinc in the liquid from the cadmium deposit
may then be precipitated by the method of Riche
(p. 114).
Mention may be here made of the fact that Smith
and Knerr (Am. Ch. Jr., 8, 210) electrolyzed a solu-
tion of cadmium and zinc to which 3-4 grams of
sodium tartrate and tartaric acid had been added,
with a current of N.D 100 = 0.3-0.4 ampere and 2.25-
3 volts. The temperature of the solution was 60.
(b) In oxalic acid solution. Eliasberg (Z. f. a. Ch., 24,
55) proposed this method, second in point of time,
and recommended the following procedure: Dissolve
the metallic oxides in hydrochloric acid, evaporate
their solution to dryness, take up the residue in water,
add to the liquid 8 grams of potassium oxalate
(C 2 O 4 K 2 ) and 2 grams of ammonium oxalate
((NH 4 ) 2 C 2 O 4 ), dilute to 120 c.c., heat to 8o-85,
and electrolyze with N.D 100 = 0.01-0.02 ampere and 3
volts. The cadmium will be precipitated free from
zinc. See also Waller, Z. f. Elektrochem., 4, 241-
247. From 6 to 7 hours are required for the deposi-
tion of 0.2 gram of cadmium.
SEPARATION OF METALS CADMIUM. 213
(c) In sulphuric acid solution. To the liquid containing
the salts of the two metals add 3 to 4 c.c. of a concen-
trated ammonium sulphate solution and follow with
2 to 3 c.c. of dilute sulphuric acid. Dilute to 100 c.c.
and electrolyze with N.D 100 = 0.08 ampere and 2.8-
2.9 volts (Neumann's Elektrolyse, p. 189). See
Denso, Z. f. Elektrochem., 9, 469.
In the electro-chemical laboratory of the Univer-
sity of Munich the separation of cadmium from zinc
is in a certain sense a combination, of c and a. For
example, sodium hydroxide is added to the sulphates
of the metals until a permanent precipitate is formed;
this is then dissolved in as little sulphuric acid as pos-
sible, the solution is diluted to 70 c.c. and the cad-
mium precipitated by a current of N.D 100 =0.07 am-
pere. When the greater portion of this metal has
been thrown out of the solution, the free sulphuric
acid is neutralized with sodium hydroxide and 2 to 3
grams of sodium acetate are introduced into the
liquid, which is heated to 45 and electrolyzed with a
current of N.D 100 = 0.03 ampere and 3.6 volts.
(d) In phosphoric acid solution. Total dilution, 125
c.c. ; cadmium, 0.1827 gram; zinc, 0.1500 gram; di-
soclium hydrogen phosphate (sp. gr. 1.038), 40 c.c.;
phosphoric acid (sp. gr. 1.347), 3 c.c.; N.D 100 = 0.035
ampere; V= 2.5-3.0. Cadmium found, 0.1820 gram.
The ordinary temperature. Time, 10 hours (Am. Ch.
Jr., 12, 329).
(e) In potassium cyanide solution. This separation
originated in this laboratory (Am. Ch. Jr., n, 352).
Example: 0.2426 gram of cadmium as sulphate,
0.2000 gram of zinc as sulphate; 4.5 grams of po-
tassium cyanide; total dilution, 200 c.c. Ordinary
214 ELECTRO-ANALYSIS.
temperature. N.D 100 = 0.03 ampere ; volts = 2.8-
3.2. 0.2429 gram of cadmium found.
In the filtrate the zinc may be precipitated by in-
creasing the current. Freudenberg used this method
with success, applying a current corresponding to an
electromotive force of 2.6-2.7 volts.
MERCURY.
Experience has proved that this metal is most accu-
rately determined, and most satisfactorily separated from
the metals usually found with it by the use of electrolytic
methods which in this instance are preferable in every
particular to the ordinary gravimetric courses ; hence all the
known separations in the electrolytic way will be given, in
the paragraphs which follow, with such detail that no doubt
need remain as to the final results.
While mercury is very quickly determined with the help
of the rotating anode it is almost impossible to separate it
from other metals, owing to the readiness with which it
forms amalgams. It was, however, separated in a beauti-
ful mirror-like form from aluminium and magnesium.
i. From Aluminium:
(a) In nitric acid solution (p. 181). Add 3 c.c. of con-
centrated nitric acid to the solution of the two salts,
dilute to 125 c.c. ; heat to 70 C., and electrolyze with
N.D 100 = 0.06 ampere and 2 volts. Time, 2 hours.
The solution in the. dish must be siphoned off before
the interruption of the current.
(b) In sulphuric acid solution (p. 182). Add i c.c. of
sulphuric acid to the solution of the salts; dilute to 125
c.c., heat to 65 and electrolyze with N.D 100 = 0.4-0.6
SEPARATION OF METALS MERCURY. 21 5
ampere and 3.50 volts. The mercury (0.1500 gram)
will be precipitated in an hour. Wash it with cold
water and proceed as directed on p. 92.
From Antimony. Add to the solution, containing
about equal amounts of the two metals, 5 grams of tar-
taric acid and 15-20 c.c. of ammonia water (10 per
cent.) ; dilute to 175 c.c., and electrolyze with N.D 100 =
0.015-0.085 ampere and 2.2-3.5 volts. The temperature
should be 50. About 6 hours will be required for the
precipitation (J. Am. Ch. S., 15, 205). The antimony
must exist in solution as an antimonic compound. The
method was first worked out by Schmucker ( loc. cit. ) and
was later successfully confirmed by Freudenberg in his
study of the differences in potential (Z. f. ph. Ch., 12,
112), when he employed an electromotive force of 1.6-1.7
volts. Mercury used, 0.2362 gram; mercury found,
- 2 356 gram; antimony present, 0.2600 gram.
The liquid from the deposit of mercury, after acidula-
tion, may be precipitated with hydrogen sulphide and the
resulting sulphide be dissolved in sodium sulphide and
treated as described on p. 172 for the determination of
the antimony.
From Arsenic:
(a) In nitric acid solution. The solution of the metals
should contain a few cubic centimeters of free nitric
acid and then be acted upon with an electromotive
force of 1.7-1.8 volts: Mercury taken, 0.2380 gram;
mercury found, 0.2380 gram; arsenic present, 0.2516
gram (Freudenberg, Z. f. ph. Ch., 12, in).
(b) In potassium cyanide solution. Add 3 grams of
pure potassium cyanide to the liquid containing 0.5
gram of combined metals, dilute to 200 c.e., and elec-
2l6 ELECTRO-ANALYSIS.
trolyze with N.D 100 = 0.015 ampere and 2.2-3.5 volts
for 5 hours at 65 (Am. Ch. Jr., 12, 428). It is im-
material whether the arsenic is present as an arsenite or
arsenate.
(c) In alkaline sulphide solution (p. 92). An example
will best illustrate the method : To the solution of mer-
cury add 25 c.c. of sodium sulphide (sp. gr. 1.19),
dilute with water to 125 c.c., heat to 70 C., and elec-
trolyze with a current of N.D 100 = o.n ampere and
2.5 volts. The time for precipitation is usually 5 hours.
See Jr. Fr. Ins., 1891.
4. From Barium, Strontium, Calcium, Magnesium, and
the Alkali Metals. Use method a under mercury from
aluminium (p. 214) for this purpose.
5. From Bismuth. The statements with reference to the
separation of these two metals are contradictory. The
experiments conducted in this laboratory (Jr. An. Ch.,
7, 252) showed that the metals were coprecipitated from
a nitric acid solution, as .one from many examples will
illustrate: The solution contained 0.1132 gram of mer-
cury and 0.0716 gram of bismuth. Ten cubic centi-
meters of nitric acid of specific gravity 1.2 were added
and the liquid diluted with water to 200 c.c., and elec-
trolyzed with a current of N.D 100 = o.O4 ampere and
1.6 volts.
The precipitation of the metals was complete, but the
mercury contained bismuth. This was one of eight trials
which resulted similarly. They were made to disprove a
statement which had appeared repeatedly in three editions
of Classen's Quantitative Analyse durch Elektrolyse (p.
147, 2d ed.), despite the fact that the same writer had de-
clared previously (Ber., 19, 325) : " Bismuth cannot be
SEPARATION OF METALS MERCURY. 217
separated from mercury in this manner. Both metals
are precipitated simultaneously from an acid solution. "
After this study had been made, Freudenberg (Z. f.
ph. Ch., 12, in), by adherence to the idea of the differ-
ences in potential, gave results which would indicate a
complete separation ; a few cubic centimeters of nitric acid,
of sp. gr. 1.2, and 2-4 grams of ammonium nitrate are
added to the nitrate solution of the two metals and the
electrolysis conducted with a potential of 1.3 volt. Mer-
cury used, 0.2380 gram; mercury found, 0.2376 gram;
bismuth present, 0.2694 gram. As Neumann (Elektro-
lyse, p. 181) remarks, the possible current strength is ex-
ceedingly low, hence a long time is required for the pre-
cipitation of the mercury.
While the writer has never tested the recommendation
of Freudenberg, his experience gathered from numerous
attempts on the part of his students inclines him to say
that the procedure is worthy of further study at least.
6. From Cadmium:
(a) In acid solution. The nitric acid and sulphuric acid
solutions lend themselves quite well to this separation.
The proper conditions for the obtainment of satisfac-
tory results are given in the section on mercury from
aluminium, paragraphs a and b (p. 214).
(b) In alkaline cyanide solution. The solution contained
0.1182 gram of mercury and 0.2206 gram of cadmium.
Two and one-half grams of pure potassium cyanide
were added, and the liquid was then diluted with water
to 125 c.c., heated to 65, and acted upon with a .cur-
rent of N.D 100 = o.oi8 ampere and 1.7 volts. The
precipitation was complete in 7 hours at the ordinary
temperature (J. Am. Ch. S., 21, 919 also 17, 612).
20
2 I 8 ELECTRO-ANALYSIS.
7. From Calcium. See the separation of mercury from
barium (p. 216).
8. From Chromium. The methqds recommended for the
separation of mercury from aluminium, p. 214, will an-
swer for this particular purpose.
9. From Cobalt:
(a) In acid solutions. See p. 214, under mercury from
aluminium.
(b) In alkaline cyanide solution. The solution con-
tained 0.1216 gram of mercury and o.iooo gram of
cobalt. The liquid was diluted to 100 c.c. ; 2 grams
of potassium cyanide were added to it and the liquid,
then heated to 65, was electrolyzed with N.D 100 =
0.025-0.03 ampere and 2.06-2.7 volts for 5 hours.
The mercury found equaled 0.1213 gram and 0.1217
gram. Too much potassium cyanide exercises a re-
tarding influence on the precipitation of the mercury
(J. Am. Ch. S., 21, 918; Am. Ch. Jr., 12, 104).
10. From Copper:
(a) In nitric acid solution. Freudenberg (Z. f. ph. Ch.,
12, in), with attention to voltage alone, separates
these metals as follows : To their solution (the nitrates)
add several cubic centimeters of nitric acid (sp. gr.
1.2) and 2 to 4 grams of ammonium nitrate, after
which electrolyze with a current having a pressure of
1.3 volts. Mercury present, 0.2380 gram; copper
present, 0.1356 gram; mercury found, 0.2377 gram;
copper found, 0.1358 gram. The separation was made
during the night.
(b) In alkaline cyanide solution. It was in a solution of
the double cyanides of these metals that they were
first separated successfully in the electrolytic way (Am.
SEPARATION OF METALS MERCURY. 2 19
Ch. Jr., ii, 264). At the time it was thought that the
separation could not be regarded as yielding trust-
worthy results when the copper exceeded 20 per cent.,
but about two years subsequently it was shown (Jr.
An. Ch., 5, 489) that by careful adjustment of the cur-
rent strength the quantity of copper could not only
equal, but exceed, that of the mercury almost indefi-
nitely (Spare and Smith, J. Am. Ch. S., 23, 579).
The time, however, was still an important factor, and
it was not reduced by Freudenberg, who electrolyzed
the double cyanides with a pressure of 2.5 volts, in the
presence of 2 to 4 grams of potassium cyanide (Z. f.
ph. Ch., 12, 113). The reduction of this factor was
made in 1894 (J. Am. Ch. S., 16, 42) by gently warm-
ing the electrolyte. It then became possible to fully
precipitate the mercury in three and one-half hours.
Since then the separation has been repeatedly made
both with mercury and copper (J. Am. Ch. S., 21,
917), and with mercury, copper, cadmium, zinc, and
nickel simultaneously present. The following condi-
tions will prove satisfactory for this separation : Mer-
cury present, 0.1216 gram; copper present, equal
amount; total dilution, 125 c.c. ; potassium cyanide,
2-3 grams; temperature, 65 ; time, 2^3 hours. Mer-
cury found, 0.1215 -gram (Revay, Z. f. Elektrochem.,
4, 313).
11. From Gold. This separation has not been made. See
Z. f. ph. Ch., 12, 113.
12. From Iron:
(a) In nitric acid solution. Use the conditions indi-
cated under a, mercury from aluminium (p. 214).
(b) In sulphuric acid solution. See b under mercury
from aluminium.
22O ELECTRO-ANALYSIS.
(c) In alkaline cyanide solution. Dissolve ferrous am-
monium sulphate in water; conduct sulphur dioxide
through it to reduce any ferric salt which may be
present, nearly neutralize the excess of acid with sodium
carbonate, mix with the solution of the silver salt, and
add from 2.5 to 4 grams of potassium cyanide for 0.2-
0.4 gram of the combined metals ; then electrolyze with
N.D 100 = 0.02-0.05 ampere and 2.5 volts, with a tem-
perature of 70. The total dilution should equal 125
c.c. Time, 3-4 hours (J. Am. Ch. S., 21, 920).
13. From Lead. To the solution, containing the two
metals add from 25 to 30 c.c. of nitric acid (sp. gr. 1.3),
dilute to 175 c.c. with water, and electrolyze with a cur-
rent of N.D 100 = 0.13 to 0.18 ampere and 2 volts, at 30
for 4 hours. It will, of course, be understood that the
lead is deposited as dioxide upon the anode while the
mercury is simultaneously precipitated on the cathode.
Use a dish as anode (Smith and Moyer, Jr. An. Ch., 7,
252; Z. f. anorg. Ch., 4, 267; Heidenreich, Ber., 29, 1585;
Z. f. Elektrochem., 3, 151).
14. From Magnesium. See the separation of mercury
from barium, etc., p. 216.
15. From Manganese :
(a) In nitric acid solution. See the conditions under
which manganese is precipitated as dioxide (p. 134).
The mercury separates at the cathode.
(b) In sulphuric acid solution. The conditions which
should be observed in depositing manganese from a
solution containing free sulphuric acid will answer in
this particular separation (p. 134). The larger dish
must, of course, be made the anode. The quantities
of the two metals must not be too large.
SEPARATION OF METALS MERCURY. 221
1 6. From Molybdenum. The separation is readily ef-
fected in an alkaline cyanide solution, using the conditions
prescribed under b in the separation of mercury from
arsenic (p. 215).
17. From Nickel:
(a) In nitric acid solution. Follow the conditions given
under a in the separation of mercury from aluminium,
p. 214.
(b) In sulphuric acid solution. Reproduce the condi-
tions of b in the separation of mercury from aluminium,
p. 214.
(c) In alkaline cyanide solution. An example will illus-
trate : Mercury present, 0.1216 gram; nickel present,
0.1500 gram; potassium cyanide, 2-2.5 grams; total
dilution, 125 c.c. ; N.D 100 = o.O4 ampere; volts = 1.7-
2.2; temperature, 65; time, 4 hours. The mercury
found equaled 0.1213 gram (J. Am. Ch. S., 21, 918;
Am. Ch. Jr., 12, 104).
1 8. From Osmium. Follow the directions for the separa-
tion of mercury from arsenic in an alkaline cyanide solu-
tion, p. 215. In this separation the quantity of alkaline
cyanide should not exceed 1.5 gram for 0.2 gram of
metal (Am. Ch. Jr., 12, 428; 13, 417; Jr. An. Ch., 6, 87).
19. From Palladium. Let the conditions be the same as
those given for the separation of mercury from platinum
(see below) (Am. Ch. Jr., 12, 428).
20. From Platinum. Example: Mercury present, 0.1373
gram; platinum present, o.iooo gram; total dilution, 125
c.c. ; potassium cyanide, 3 grams; N.D 100 = 0.04-0.05
ampere; V = 2.i; temperature, 65-75; time, 4 hours.
The mercury found equaled 0.1372 gram (Am. Ch. Jr.,
13, 417; J. Am. Ch. S., 21, 920).
222 ELECTRO-ANALYSIS.
21. From Potassium. See mercury from barium, etc.,
p. 216.
22. From Selenium. To the solution of the two metals,
each about one quarter of a gram in amount, add one
gram of potassium cyanide, dilute to 150 c.c. with water,
heat to 60 C., and electrolyze with N.D 100 = 0.03 am-
pere and a pressure of 3 volts. The precipitation of
the mercury will be complete in five hours.
In a nitric acid electrolyte the separation is conducted
with ease by observing the conditions followed in the
separation of silver from selenium, p. 245.
23. From Silver. These metals cannot be separated elec-
trolytically either in an acid or alkaline cyanide solu-
tion. Classen precipitates them together, and after ascer-
taining their combined weight expels the mercury by
ignition and weighs the residual silver.
24. From Sodium. See barium, p. 216.
25. From Strontium. See mercury from calcium, etc.,
p. 218.
26. From Tellurium. In a cyanide solution the separa-
tion cannot be made. Most favorable results were ob-
tained in a nitric acid electrolyte. An example will illus-
trate. To a solution containing 0.1272 gram of mer-
cury and 0.2500 gram of sodium tellurate, three cubic
centimeters of nitric acid (sp. gr. 1.43) were added.
After dilution to 150 c.c. with water it was heated to
60 C., and electrolyzed with a current of N.D ]00 =
0.04 to 0.05 ampere and a pressure of 2 to 2.5 volts. In
five hours the precipitation was finished (J. Am. Ch. S.,
25, 895).
27. From Tin:
(a) In alkaline sulphide solution. The conditions men-
SEPARATION OF METALS MERCURY. 223
tioned under mercury (p. 92) will answer perfectly
for this separation (Jr. Fr. Ins., 1891). To change
the sodium sulpho-salt in the filtrate into ammonium
sulphostannate consult p. 167.
(b) In ammoniacal tartrate solution. A solution of the
two metals was made by adding mercuric chloride to
tartaric acid, followed by ammonia water and then
diluting with water. This solution was then mixed
with the tin salt solution and the combined liquids
electrolyzed with a current showing a pressure of from
1.6-1.7 volts. (See the separation of mercury from
antimony in tartrate solution, p. 215; also J. Am. Ch.
S., 15, p. 204.)
It may be of interest to state that the conditions
given for the separation of mercury from antimony
(p. 215), and those just employed above for the sepa-
ration of mercury from tin have been successfully
applied by Schmucker (J. Am. Ch. S., 15, 204) for
the electrolytic separation of mercury from a solu-
tion containing arsenic, antimony, and tin, the only
change being in the addition of an increased amount
of tartaric acid and ammonium hydroxide. Example :
Mercury, 0.0933 gram; arsenic, 0.1009 gram; anti-
mony, 0.1031 gram; tin, o.iooo gram; tartaric acid,
8 grams; ammonium hydroxide 30 c.c. ; dilution, 175
c.c. ; N.D 100 =:o.O5 ampere; volts = 1.7. The pre-
cipitation made at 60 was complete in 6 hours.
28. From Tungsten. Use conditions corresponding to
those employed in the separation of mercury from
arsenic in an alkaline cyanide solution (p. 215).
29. From Uranium. There is no recorded electrolytic
separation of these metals, but it is quite probable that
2 24 ELECTRO-ANALYSIS.
methods a and b, under mercury from aluminium (p.
214), would be applicable in this case.
30. From Vanadium. They have not been separated by
the current.
31. From Zinc:
(a) In acid solutions (nitric or sulphuric) the conditions
mentioned under a and b, in the separation of mer-
cury from aluminium, will prove perfectly satisfac-
tory (p. 214).
(b) In alkaline cyanide solution. This separation has
been made repeatedly with excellent success, so that
perhaps an actual example will give all the data neces-
sary to guide others in making the separation : Mer-
cury present, 0.1158 gram; zinc present, o.iooo gram;
potassium cyanide, 1.5 to 2 grams; dilution, 125 c.c. ;
N.D 100 = 0.025-0.05 ampere; V = 25 to 3; time,
4 hours; temperature, 60. Mercury found, 0.1155
gram (J. Am. Ch. S., 21, 919; Jr. Fr. Ins., 1889).
(c) In phosphoric acid solution. An example from
many results will show the conditions which should
be pursued in conducting the separation in a solution
such as just indicated : 25 c.c. of mercuric chloride
= 0.1159 gram of metal; 25 c.c. of zinc sulphate =
o.ioio gram of metal; 60 c.c. of disodium hydrogen
phosphate (1.038 sp. gr.) ; 10 c.c. of phosphoric acid
(1.347 sp. gr.) ; total dilution, 175 c.c.; temperature,
60; N.D 100 = o.oi ampere; V=i-5; time, 4-5
hours. Mercury found, 0.1163 gram (J. Am. Ch. S.,
21, I006).
SEPARATION OF METALS BISMUTH. 225
BISMUTH.
The separations of this metal from other metals in the
electrolytic way are not numerous, but they are, notwith-
standing*, of decided help to the analyst, and therefore
will be here presented in such detail as is known.
1. From Aluminium. The conditions give.n under bis-
muth for its determination in a nitric (p. 96) or sul-
phuric acid (p. 97) solution can be here used for its
separation from aluminium. Its precipitation as an
amalgam (p. 96) is well adapted for this purpose.
2. From Antimony. To the solution containing the two
metals add 5 grams of tartaric acid, 15 c.c. of ammo-
nium hydroxide, dilute to 175 c.c. with water, and elec-
trolyze with a current of N.D 100 = 0.022 ampere and
1.8 volts at 50 for 6 hours (J. Am. Ch. S., 15, 203).
3. From Arsenic. The course just outlined for the sepa-
ration of bismuth from antimony will answer in this
case (J. Am. Ch. S., 15, 202). Neumann (Elektro-
lyse, p. 185) states that the two metals, if in sulphate
solution, can be separated with a current having an E.
M. F. of 1.9 volts.
4. From Barium. The conditions for the precipitation of
bismuth from nitric acid solution (p. 96) will answer for
this separation.
5. From Cadmium. This separation may be conducted
in the presence of free nitric acid (p. 96), by the amal-
gam method (p. 96), or in a sulphuric acid solution.
If using the last electrolyte, proceed as follows: Dis-
solve 0.1500 gram of cadmium metal in 2 c.c. of concen-
trated sulphuric acid (sp. gr. 1.84) and to this solution
add another of 0.15 gram of bismuth and i c.c. of con-
226
ELECTRO-ANALYSIS.
centrated nitric acid, i gram of potassium sulphate, and
dilute with water to 150 c.c., heat to 50, and electro-
lyze with a current of N.D 100 = 0.025 ampere and 2
volts. Time, 8 hours. The bismuth will be deposited
in a bright, metallic form (Kammerer).
6. From Calcium. The conditions given on pp. 96, 97
for the determination of bismuth may be relied upon in
making this separation.
7. From Chromium. Use a nitric acid solution (p. 96),
or adopt the method given in the following paragraph :
To a solution of bismuth containing 0.1500 gram of
metal and I c.c. of nitric acid (sp. gr. 1.42) add 0.5 gram
of potassium sulphate, 2 c.c. of sulphuric acid (sp. gr.
1.84), and a quantity of chrome alum equivalent to
0.1500 gram of chromium. Dilute to 150 c.c. with water
and electrolyze with a current strength of N.D 100 =
0.025 ampere and 2 volts, the temperature being main-
tained at 50 C. After 8 hours the deposition will be
complete and the bismuth will be free from chromium.
RESULTS.
a
X .
H 55
X Q
g
M
H
5 n
5!
O
H
H
o
H
h
S W
S
D 2;
|
1
|j
x 2
H
H
s
H
a
H a
gg
pqH
03*
X
C/3
Q :
s
H
LO" 5 "
H
Grm.
Grm.
Grm.
Grm.
r.c.
C.c.
Hours.
o c .
Amp.
0.1434
0.1430
O.I5OO
0-5
2
200
9
50
003
2
Gauze.
0.1434
o. 1428
0.1500
0-5
2
150
9
50
0.025
2
Basket.
0.1434
o. 1434
0.1500
0-5
2
200
8^
50
0.025
2
Gauze.
0.1434
0.1428
0.1500
0-5
2
150
8/^
50
O.O2
2
Basket.
0.1434
o. 1430
O.I5OO
0-5
2
8/4
50
O.O2
2
Spiral.
0.1434
0.1429
0.1500
0-5
2
IS
9
50
O.O25
2
The chromium salt seems to exert a beneficial influ-
ence on the character of the deposit. Much of the
SEPARATION OF METALS BISMUTH. 227
chromium, during the electrolysis, is oxidized to chromic
acid. Especially is this true when gauze electrodes are
used (Kammerer).
8. From Cobalt. Proceed as in the separation from alu-
minium (p. 225), or from chromium (above).
g. From Copper. In a nitric acid solution copper and bis-
muth cannot be separated electrolytically. This state-
ment has been the subject of considerable controversy
in past years (Z. f. anorg. Ch., 3, 415; 4, 234; 5, 197;
6, 43; Z. f. ph. Ch., 12, 117), so that all that remains to
chemists is the suggestion made in the Am. Ch. Jr., 12,
428 viz., add from 3 to 4 grams of citric acid to the
bismuth solution, supersaturate the latter with sodium
hydroxide, and into this mixture pour the copper salt
solution, containing a slight excess of potassium cyan-
ide, and electrolyze at the ordinary temperature with a
current of N.D 100 = 0.05 ampere and 2.7 volts. In 9
hours the bismuth will be fully precipitated and will
not contain any copper.
Hollard and Bertiaux, Ch. Z., 28, 782, describe a sepa-
ration of bismuth from copper which is essentially an
ordinary gravimetric precipitation for they add an excess
of phosphoric acid to a boiling solution of the two sul-
phates. The solution is allowed to stand over night.
The bismuth phosphate is filtered off and washed with
dilute phosphoric acid (i volume of acid of sp. gr. 1.711
diluted to 20 volumes). The final washing is per-
formed with ammonium sulphydrate and potassium
cyanide. The bismuth phosphate is dissolved in nitric
acid and the solution then evaporated in the presence of
12 c.c. of sulphuric acid until fumes escape. Now dilute
to 300 c.c. and electrolyze with a current of N.D =
228 ELECTRO-ANALYSIS.
o.i ampere. Twenty- four hours will be necessary for
the precipitation.
10. From Gold. There is no recorded electrolytic sepa-
ration of these metals.
11. From Iron. The acid solutions and conditions, given
on pp. 96, 97, 98, will answer in this case. It may be
remarked here that the deposition of bismuth from sul-
phuric acid solutions containing iron is attended with
considerable difficulty. The iron present seems to exert
an influence on the bismuth, tending to hold it in solution
and prevent its deposition by the current. Especially is
this true when the salt used is a ferric salt. This ten-
dency of bismuth to be held in solution is shown even in a
more marked degree when the liquid contains besides
ferric alum an equal quantity of chrome alum. A cur-
rent of o.io ampere will often not cause the slightest pre-
cipitation of bismuth. It was thought that this behavior
of bismuth could be used to separate other metals from it.
It was hoped that the bismuth would be held back by the
iron and chrome alums and such metals as mercury, cop-
per, and silver be deposited from the solution. These
hopes were not realized. As soon as another metal is
introduced the condition of affairs is changed, and both
the metal and the bismuth are precipitated. Deposits of
silver, however, were obtained containing but very little
co-precipitated bismuth. Further investigation in this
direction might lead to some very interesting and valuable
results.
The best conditions for the separation of bismuth from
iron were found to be as follows : To the bismuth solution
containing 0.15 gram of bismuth and i c.c. of concentrated
nitric acid, add 2 c.c. of sulphuric acid (sp. gr. 1.84), 0.5
SEPARATION OF METALS BISMUTH.
229
gram of potassium sulphate, and a quantity of ferrous
sulphate or ammonium ferric alum equivalent to 0.15
gram of iron. This solution should be diluted to 150 c.c.
and electrolyzed at a temperature of 45 C. If a ferrous
salt is used, the current strength should be 0.03 ampere,
but if a ferric salt is in solution, a higher current strength
should be employed, 0.05 ampere, the voltage in both
cases being 2.0. In eight hours the deposition will be
complete. The precipitated bismuth is free from iron
( Kammerer) .
In several cases the separation was made in the presence
of urea nitrate, but its addition was no advantage.
RESULTS.
TAKEN.
FOUND
1
i
TRATE.
||
o
Q
U
U
H
w
PC
G
u
Q
X
5
s
|
H
z
M
\\
o u
Q
s
D
X
Bi
s
H
MPEK^
ft
S
o
U
ts>
M
J
H
m
P
CO
H
&
Grm
Grm.
Grm
Grm.
Grm
C.c.
C.c.
Hours.
c.
Amp.
O.H34
0.1429
0. 1500 1
0.5
150
2
8^
50
0.025
1.5
Spiral.
0.1431
0. 1500 1
0.6
150
2
7 1 A
45
0.03
2
11
0.1435
o. I500 1
-5
I 5
2
24
45
0.03
2
"
0.1430
o. I500 1
0-5
'5
2
24
45
0.03
1.7
Basket.
0.1395
0.1394
o. I500 1
0-5
0.2
150
2
8
45
0.035
2
"
0.1400
o. I500 1
0.5
0.2
150
2
8
0.035
2
Spiral.
0.1393
o. I500 1
05
O.2
200
2
8
45
.5
2
Gauze.
0.1397
O.I500 2
0.5
150
2
9
45
O.O7
2
Spiral.
0.1395
o.i 5 oo 2
I
150
2
9
45
O.O6
2
"
0.1394
O.I500 2
I
200
2
8
45
O.O6
2
Gauze.
0.1395
o.i5oo 2
3-0
0-5
150
2
9
45
0.035
2
Spiral.
12. From Lead. Experiments made in this laboratory
(Jr. An. Ch., 7, 252) have demonstrated that the gener-
ally accepted statement that the metals could be separated
1 Ferrous sulphate.
2 Ferric ammonium sulphate.
230 ELECTRO-ANALYSIS.
in the presence of free nitric acid is not correct. The
lead dioxide invariably contained bismuth. We are,
therefore, for the present at least, without an electrolytic
method for their separation.
Hollard and Bertiaux B. Soc. Ch., 31, 1133 (1904)
recommend adding to the two nitrates 12 c.c. of sul-
phuric acid plus the requisite amount of this acid to com-
bine with the two metals, viz., for lead 0.3 c.c. and for
bismuth 0.5 c.c., then evaporate until white fumes arise.
Cool. Add water to 300 c.c. and 35 c.c. of absolute
alcohol. Electrolyze with a current of o.i ampere for a
period of 48 hours.
13. From Magnesium. The acid solutions and conditions
given for the separation of bismuth from aluminium
(p. 225) will serve to effect this particular separation.
14. From Manganese. To the bismuth solution contain-
ing 0.1500 gram of metal and I c.c. of nitric acid (sp. gr.
1.42) add 3 c.c. of sulphuric acid (sp. gr. 1.84), 0.5 gram
of potassium sulphate, and a quantity of manganous sul-
phate equivalent to 0.1500 gram of manganese. Dilute
this solution to 150 c.c. with water and electrolyze with a
current of N.D 100 = 0.025 ampere and 2 volts, keeping
the temperature at 45 C. The bismuth will be deposited
in 9 hours in a beautiful form, free from manganese.
At first the solution assumes a dark red color due to the
oxidation of some of the manganese into permanganic
acid. After an hour or two the color begins gradually to
fade away and the solution again becomes colorless. A
considerable quantity of hydrated oxide of manganese
deposits on the anode during the electrolysis. This de-
posit was always examined for bismuth, but in no case
was it found to contain any of this metal (Kammerer and
Am. Ch. Jr., 8, 206).
SEPARATION OF METALS BISMUTH. 2JI.
15. From Mercury. See the separation of mercury from
bismuth, p. 216. ,
1 6. From Molybdenum. At present no electrolytic
method is know for this purpose.
17. From Nickel. The directions recorded on pp. 96, 97
for the determination of bismuth in acid solutions may be
followed with confidence in making this separation (Am.
Ch. Jr., 8, 206; Jr. An. Ch., 7, 252; Z. f. anorg. Ch., 4,
270).
1 8. From Palladium and Platinum. Separations are not
known.
19. From Potassium. Follow the methods given for the
determination of bismuth itself, pp. 96, 97, 98.
20. From Selenium. There is no existing electrolytic
method.
21. From Silver. Freudehberg (Z. f. ph. Ch., 12, 108)
uses the nitrates of the two metals, adds to their solution
several cubic centimeters of nitric acid of sp. gr. 1.2 and
from 2 to 4 grams of ammonium nitrate, then electrolyzes
with a current having a potential of 1.3 volts. The silver
is precipitated through the night. The liquid containing
the residual bismuth may be worked for the determination
of the bismuth by the amalgam method, p. 96, although it
would appear that Freudenberg always determined it by
evaporation of the nitric acid solution and ignition of the
residue, weighing finally bismuth oxide. The results
obtained by him are:
Silver used, 0.3790 gram ; Bi = 0.3080 gram
Silver found, 0.3793 gram ; Bi = 0.3073 gram
Silver used, 0.2916 gram; Bi = 0.3080 gram
Silver found, 0.2914 gram; 61 = 0.3072 gram
232 ELECTRO-ANALYSIS.
22. From Sodium. Any one of the methods pursued in
the determination of bismuth when alone will do for this
purpose (pp. 96, 97, 98).
23. From Strontium. See the separation of barium from
bismuth, p. 225.
24. From Tellurium. There is no recorded electrolytic
separation.
25. From Tin. The solution contained 0.0518 gram of
bismuth and 0.1031 gram of tin. To it were added 5
grams of tartaric acid and 15 c.c. of ammonium hydrox-
ide, and the liquid then diluted to 175 c.c. with water
and electrolyzed at the ordinary temperature with N.D 100
= 0.02 ampere and 1.8 volts, during the night (J. Am.
Ch. S., 15, 204).
The chemist who proposed the preceding method also
separated bismuth from a mixture of arsenic, antimony,
and tin. The solution with which he operated contained
0.0518 gram of bismuth, 0.1009 f arsenic, 0.1024 gram
of antimony, "and 0.1031 gram of tin. To it were added
8 grams of tartaric acid and 3 c.c. of ammonium hydrox-
ide, then diluted to 175 c.c. with water and electrolyzed
with a current of N.D 100 = 0.02 ampere and 1.9 volts, at
the ordinary temperature. The precipitation was made
during the night. The time factor can probably be re-
duced by the application of a gentle heat. The bismuth
precipitates rapidly and in an adherent form.
26. From Tungsten. There is no recorded separation.
27. From Uranium. The conditions presented on p. 97
for the determination of bismuth in sulphuric acid solu-
tion will serve excellently in making this separation (Am.
Ch. Jr., 8, 206). See also bismuth from chromium.
28. From Vanadium. There is no recorded separation.
SEPARATION OF METALS LEAD. 233
29. From Zinc. The conditions given in the determination
of bismuth in nitric acid (p. 96), sulphuric acid (p. 97),
and as amalgam (p. 96) will be found satisfactory in this
separation (Am. Ch. Jr., 8, 206; Jr. An. Ch., 7, 255).
See also bismuth from cobalt.
LEAD.
The importance of lead industrially makes not only its
accurate determination of interest and value, but its separa-
tion from the metals frequently associated with it becomes
a matter of deep concern. It will be generally conceded that
lead is a metal that is best determined by the electrolytic pro-
cedure; this is vastly better than the ordinary gravimetric
processes, and this, too, increases the value of its separations.
1. From Aluminium. As aluminium is not precipitated
electrolytically from a nitric acid solution and the latter is
especially well adapted for the deposition of lead in the
form of its dioxide upon the anode, the conditions laid
clown upon p. 103 will be found to answer admirably in
effecting the present separation.
2. From Antimony. A purely electrolytic procedure is at
the present not known for the separation of these metals.
In the Ch. Z., 19, 1142 (1895), Nissenson and Neu-
mann described a method for the analysis of an alloy of
antimony and lead, which deserves attention here. It is
not an electrolytic separation in any sense of that term,
but a helpful suggestion.
The finely divided alloy is brought into solution with
4 c.c. of nitric acid (sp. gr. 1.4), 15 c.c. of water, and 10
grams of tartaric acid. Four cubic centimeters of con-
centrated sulphuric acid are added to the clear solution,
21
234 ELECTRO-ANALYSIS.
which is then diluted with water, allowed to cool, and
filled up to the mark of the ^-liter flask. On filtering
from the lead sulphate, which has separated, the filtrate
will contain all of the antimony. None will remain in
the lead sulphate. Remove 50 c.c. of the filtrate with a
pipette, render it strongly alkaline with caustic soda, add
50 c.c. of a cold saturated sodium sulphide solution, boil,
filter at once, wash and electrolyze the hot solution with
a current of N.D 100 = 1.5-2.0 amperes. An hour at the
most will be required for the deposition of the antimony.
The lead sulphate should be digested for a few minutes
with ammonia water. This changes it to hydroxide,
which can be gradually introduced into a platinum dish
containing 20 c.c. of nitric acid, in which it slowly dis-
solves. The liquid is then electrolyzed with the conditions
indicated on p. 103.
3. From Arsenic. Neumann (Ch. Z., 20, 382) records
his experience in attempting to separate these metals elec-
trolytically, from which the conclusion may be deduced
that in the presence of arsenic the lead determinations are
not reliable. They are too low. When there is only a
fraction of a per cent, of arsenic present, the results can
be used, although the time then necessary for the complete
precipitation of the lead as dioxide is prolonged to an un-
warrantable degree. The experiments of Neumann were
all conducted in nitric acid solution.
4. From Barium, Strontium, Calcium, Magnesium, the
Alkali Metals, Beryllium, Cadmium, Chromium, Iron,
Uranium, Zirconium, Zinc, Nickel, and Cobalt the sep-
aration of lead is easily made by observing the conditions
given (p. 101) for its determination. There should be
from 1 5 to 20 per cent, of concentrated nitric acid present.
SEPARATION OF METALS LEAD. 235
The liquid poured off from the deposit of lead peroxide
is changed into the most favorable salt for the precipita-
tion of the particular metal and the electrolysis proceeded
with in the usual way.
5. From Bismuth. See p. 229.
6. From Copper. This separation has always been made
in the presence of free nitric acid. The details of pro-
cedure are described under copper from lead, p. 193.
7. From Gold. This combination of metals has not re-
ceived any attention, apparently, in the electrolytic way
as the separation can be made more satisfactorily in other
ways.
8. From Manganese:
(a) In nitric acid solution. It is well known thai man-
ganese can be precipitated from solutions in which the
quantity of free nitric acid does not exceed from 3 to 5
per cent. Greater quantities of the acid prevent its
appearance, its presence being made evident by the pink
tinge of permanganic acid about the anode. As lead
is completely deposited even in the presence of from
15 to 20 per cent, of acid, it would seem as if the sepa-
ration could be made under the latter conditions. Until
recently it has not been undertaken. Neumann recom-
mends heating the solution containing the two metals
and 20 per cent, of concentrated nitric acid to 70, then
electrolyzing with a current of from 1.5 to 2 amperes
and 2.5 to 2.7 volts. It is absolutely essential to use hot
solutions, strong currents, and not too large quantities
of manganese (0.03 gram of manganese at the most in
150 c.c. of liquid). When large amounts are employed
and the electrolysis prolonged the liquid will very prob-
ably become turbid, owing to the separation of dioxide
of manganese (Ch. Z., 20, 383).
2 3 6
ELECTRO-ANALYSIS.
(b) In phosphoric acid solution. Linn adds to the solu-
tion of the two nitrates a little more disodium hydro-
gen phosphate than necessary for complete precipita-
tion. The phosphates are then dissolved in an excess
of pure phosphoric acid (sp. gr. 1.7) and the solution
electrolyzed with N.D 100 .003 to .006 ampere and
a pressure of from 2 to 3 volts. Wash the deposit of
lead with water, alcohol and ether, then dry at 100-
110 C. (J. Am. Ch. S., 29, 82).
9. From Mercury. The details of this separation are given
under mercury from lead, p. 220.
10. From Selenium. As selenium materially affects the
deposition of lead as dioxide from a nitric acid solution,
it may be of interest to present some results from Neu-
mann's experiments (Ch. Z., 20, 383). They are instruc-
tive and suggestive. He used solutions of lead nitrate
containing sodium selenite. The first experiment was
with lead alone, the others contain the two metals :
LEAD
PRESENT.
SELENIUM
PRESENT.
NITRIC
ACID.
LIQUID.
TIME.
AMPERES.
VOLTS.
LEAD
FOUND.
0.2238
O.OOOO
30 C.C.
150 C.C.
I hr.
0.8
3
0.2238
0.2238
o 0050
3
150
I
0.8
3
0.2208
0.2238
0.0100
30
ISO
I
0.8
3
0.2156
0.2238
0.0200
30
150
I
0.8
3
0.1886
0.2238
0.0500
30
150
1
0.8
3
0.0327
As the quantity of selenium was increased, the amount
of lead dioxide deposited grew less. This was the case
with lead and arsenic. The cathode also carried a deposit
consisting of metallic lead and selenium.
ii. From Silver:
In nitric acid solution. An example, taken from a num-
ber made in this laboratory, will give the best condi-
SEPARATION OF METALS LEAD. 237
tions for carrying- out this separation : To a solution
containing 0.1028 gram of silver and lead equal to
0.0144 gram of dioxide were added 15 c.c. of nitric acid
of 1.3 specific gravity. After dilution to 200 c.c. it
was electrolyzed with a current of N.D 100 = o.i8 am-
pere and 2.25 volts. The deposit of silver weighed
0.1023 gram and that of the dioxide 0.0144 gram. It
is probably not necessary to say that the depositions
were simultaneous and that the precautions described
under the individual metals were carefully observed.
It must be borne in mind that silver quite often separates
in the presence of nitric acid both as peroxide at the
anode and as metal at the cathode, so that Luckow
recommends the presence of at least 18 per cent, of
nitric acid and also introduces several drops of oxalic
acid, thus hindering the precipitation of silver dioxide
(Jr. An. Ch., 7, 252; Z. f. ang. Ch., 1890, 345). See
also Arth and Nicholas, B. S. ch. de Paris [3], Tome
29-30, p. 633.
12. From Tellurium. This separation has not received
any attention.
13. From Tin. In this instance the usual gravimetric pro-
cedure is the preferable course to adopt in making the
separation.
SILVER.
The current has proved a most valuable reagent in the
separation of this metal from many others which occur
associated with it. The ease and accuracy of these various
separations recommend them,
i. From Aluminium. The conditions given on p. 105 for
the precipitation of silver from a nitric acid solution will
answer for this separation.
238 ELECTRO-ANALYSIS.
In using the rotating anode dilute the solution to 125
c.c., add i c.c. of nitric acid of sp. gravity 1.43 and i gram
of ammonium nitrate, then electrolyze with N.D 100 = 3
amperes and 3.5 volts. The time will be fifteen minutes
for a quarter of a gram of metal or more. This same
procedure will serve in the rapid separation of silver from
cadmium, chromium, cobalt, iron, lead, magnesium, man-
ganese, nickel and zinc (J. Am. Ch. S., 26, 1290).
2. From Antimony:
(ft) In ammoniacal solution. In accordance with the
suggestion of Freudenberg (Z. f. ph. Ch., 12, 109), if
the antimony be raised to its highest state of oxidation
it will only be necessary to add ammonium sulphate and
ammonia water to the solution of the combined metals
and electrolyze with a current having a pressure vary-
ing from 1.2 to 1.3 volts. The precipitated metal will
not adhere well to the dish, so that the method will be
used only when special reasons demand it.
(b) In acid solution. To the nitric acid solution add
tartaric acid, after having converted all the antimony
into pentoxide, and electrolyze with a pressure not
exceeding 1.4 to 1.5 volts. Freudenberg remarks that
the deposit of silver is not well suited for weighing.
( c ) In potassium cyan ide so hi tion. The anti mony should
exist as pentoxide. After adding tartaric acid to the
cyanide solution ( i gram of pure potassium cyanide for
every o.i gram of metal), electrolyze with a pressure
of from 2.3 to 2.4 volts.
Fischer found procedures (b) and (c) very satis-
factory, Ber., 36, 3297 and Z. f. Elektrochem., 9, 993.
3. From Arsenic. The methods just described for the
separation of silver from antimony will be found appli-
cable in this case (Am. Ch. Jr., 12, 428).
SEPARATION OF METALS SILVER. 239
4. From Barium. Follow the instructions given on p. 105
for the determination of silver.
5. From Bismuth. See p. 231, bismuth from silver.
6. From Cadmium:
(a) In nitric acid solution. To the solution of the salts
of the two metals add 15 to 20 c.c. of nitric acid of
specific gravity 1.3, heat to 60, and electrolyze with a
current having a pressure of from 2 to 2.2 volts. The
silver will be precipitated and should be treated as di-
rected on p. 107. The acid filtrate can, by the addition
of an excess of sodium acetate, be changed to a suitable
form for the deposition of the cadmium. See p. 82.
(b) In potassium cyanide solution. Add 2 grams of
pure potassium cyanide to the solution, containing o. i
0.2 gram of each metal, dilute to 125 c.c., heat to 65-
75, then conduct a current of N.D 100 = 0.02-0.025
ampere and 2.1 volts through the liquid. The silver will
be completely precipitated at the expiration of from 4 to
5 hours. After removing the liquid from the precipitat-
ing "dish it should be reduced in volume, introduced into
a second weighed platinum dish, and electrolyzed as
directed on p. 81 for the deposition of the cadmium.
7. From Calcium and Chromium. See p. 237.
8. From Cobalt. An example will show the conditions
which have been found very satisfactory in this particular
separation: To the solution of the silver salt (0.1024
gram of silver) were added o.i gram of cobalt as nitrate
and 2.75 grams of pure potassium cyanide. The liquid
was diluted to 125 c.c. with water, heated to 65 C., and
electrolyzed with N.D 100 = 0.038 ampere and 2 volts.
At the expiration of 5 hours the silver was completely
deposited. It weighed 0.1027 gram. It contained no
240 ELECTRO-ANALYSIS.
cobalt (J. Am. Ch. S., 21, 915). This procedure is pref-
erable to the deposition of silver from a nitric acid solu-
tion.
g. From Copper:
(a) In nitric acid solution. Freudenberg added 2 to 3
c.c. of nitric acid of 1.2 specific gravity to the solution
of salts of the two metals, then electrolyzed with a
pressure of 1.3-1.4 volts, and a current of o.i ampere.
The silver was deposited free from copper (Z. f. ph.
Ch., 12, 107; Berg-Hutt. Z. (1883), 375).
At the ordinary temperature this separation will re-
quire 7 hours, while at 60 the precipitation of the
silver will be finished in 4 hours. The liquid siphoned
off from the silver, after the addition of nitric acid, can
be electrolyzed in a beaker in which a platinum cone
is suspended. The copper is precipitated on the cone.
A current ranging from 0.5 to i.o ampere will be re-
quired for this. The solution should be heated to
6o-65.
The plan is ideal, but those who have attempted to
repeat Freudenberg's work have encountered difficulties,
and naturally modifications of the procedure have been
proposed. Kuster and v. Steinwehr (Z. f. Elektro-
chem., 4, 451), in particular, have made an exhaustive
investigation of the precipitation of silver from nitric
acid and its separation from copper in the presence of
the latter acid. Their conclusion is briefly that the
solution should contain from i to 2 c.c. of nitric acid
(sp. gr. 1.4), and that to it should be added 5 c.c. of
alcohol. Further, that the potential of the electrolyte
should be kept constantly at 1.35-1.38 volts. An ex-
ample will show how they operated : A weighed piece
(0.3161 gram) of silver coin was dissolved in 2 c.c. of
SEPARATION OF METALS SILVER. 24!
nitric acid (sp.gr. 1.4), the liquid was diluted to 150 c.c.,
5 c.c. of alcohol were added, and the solution then heated
to 55 and electrolyzed with 1.36 o.oi volt. They
obtained 0.2839 gram of silver = 89.83 per cent.
(b) In potassium cyanide solution. This separation was
first made by Smith and Frankel (Am. Ch. Jr., 12,
104) and has been carried out over a hundred times in
this laboratory by experienced persons and by those
who lacked experience, but in all cases the results have
been most satisfactory.
Add 2 grams of pure potassium cyanide to the solu-
tion of mixed salts, heat to 65, and electrolyze the
liquid (125 c.c.) with a current of N.D 100 = o.O3^
0.058 ampere and i.i 1.6 volts. The silver will be
precipitated in from 4 to 5 hours. It will, of course, be
understood that if there be a great preponderance of
copper over the silver the quantity of potassium cyanide
will have to be increased. Example: A solution con-
tained 0.1066 gram of silver and 0.5265 gram of cop-
% per. Four grams of pure potassium cyanide were
added, the liquid was heated to 60 and electrolyzed for
3! hours with a current of N.D 100 = 0.02-0.03 ampere
and 1.2 volts. The silver deposit weighed 0.1066
gram. The total dilution was 125 c.c.
The presence of three or four metals besides the
silver also requires the addition of more alkaline
cyanide (J. Am. Ch. S., 23, 582, also Brunck, Ber., 34,
1604; Revay, Z. f. Elektrochem., 4, 313).
In the preceding electrolyte it is easy to separate sil-
ver from copper when using a rotating anode. To the
solution of the metals add 2 grams of potassium cyan-
ide, heat almost to boiling and electrolyze with N.D 100
22
242
ELECTRO-ANALYSIS.
= 0.4 to o.i ampere and 2.5 volts. Fifteen minutes
will suffice for the precipitation.
To show how this procedure may be applied in the
rapid analysis of a coin an example from the notebook
of Miss Langness, working in this laboratory, may be
here introduced.
A dime was cleaned and cut into four parts. One
part was then weighed (0.7070 gram), dissolved in the
least possible amount of nitric acid, the excess of acid
evaporated, and the residue dissolved in water and
diluted to 100 c.c.. To 25 c.c. of this solution was
added \ gram of potassium cyanide. The silver was
first removed with a low current, and the decanted
liquid after evaporation electrolyzed for the copper.
The conditions used and results obtained are tabulated
below.
No.
VOLTS.
AMPERES.
TIME. MIN.
WT. OF METAL.
PER CENT. OF METAL.
I
3-2.5
.4-. 06
35
o.i589g. Ag.
89.90 percent, silver.
10
5
IO
0.0177 g- Cu.
10.01 " " copper.
2
3-2.5
.4-. 06
45
0.1588 g. Ag.
89.84 " " silver.
10
6
IO
0.0180 g. Cu.
10. 18 " " copper
The complete analysis, including the weighing of the
coin and the final weighing of the deposits, required
about two and a half hours.
If two portions are taken, depositing the metals to-
gether in the one, and the silver alone in the other, the
complete analysis can be made in an hour and a half,
providing two dishes are available. One determination
was made in that way. The coin weighing 0.5638
gram was dissolved in a small amount of nitric acid
(less than i c.c.). Part of the excess of acid was
SEPARATION OF METALS SILVER. 243
evaporated and a few drops of ammonia added to neu-
tralize the remaining excess. Two grams of potassium
cyanide were then introduced and the solution diluted
to 100 c.c. Twenty-five cubic centimeters of this
solution diluted to about 125 c.c. were electrolyzed for
the silver and copper combined, and a second portion
for the silver alone.
VOLTS
AMPERES
TIME MIN
7
2-5
2
.5-. 07
18
25
o. 1409 combined weight of Cu and Ag 99.94 percent,
o. 1268 weight of silver 90 oo per cent.
10. From Gold. No successful method has yet been
found. See Jr. An. Ch., 6, 87.
11. From Iron. When the iron is present as a ferrous salt
in the mixture of salts, introduce into the solution 3 grams
of potassium cyanide, dilute to 100 c.c. with water, heat
to 65, and electrolyze with a current of N.D 100 := 0.04
ampere and 2.7 volts. The silver will be fully precipi-
tated in 3 hours, or in a few minutes by use of the rotating
anode.
The separation of these metals can also be made in nitric
acid solution by observing the conditions laid down on
pp. 104, 105.
12. From Lead. Consult p. 236, where the separation of
lead from silver is described. See also Arth and Nico-
las, Ch. N. 88, 309.
13. From Lithium. See silver from barium and the alka-
line earth metals, p. 239.
14. From Magnesium. See silver from barium, p. 239.
15. From Manganese. See lead from manganese, p. 235.
1 6. From Mercury. There is no known electrolytic
244 ELECTRO-ANALYSIS.
method for the separation of these metals. It is true that
both can be precipitated from a nitric acid solution (p.
222), their joint weight be determined, after which the
mercury can be expelled by heat and the silver residue
be reweighed.
17. From Molybdenum, Tungsten, and Osmium. Fol-
low the conditions recommended as satisfactory in the
separation of silver from cobalt, p. 239.
1 8. From Nickel. Add 1.5 gram of pure potassium cy-
anide to the solution containing equal amounts of the
metals (0.1-0.2 gram), dilute to 125 c.c. with water,
heat to 6o 65, and electrolyze with a current of
N.D 100 = 0.02-0.03 ampere and a pressure of 1.6-2.0
volts. The period of precipitation is usually 3 hours (J.
Am. Ch. S., 21, 915).
To reduce the time factor use the rotating anode. To
the solution of the salts of the metals add 1.5 gram of
pure potassium cyanide and electrolyze with a current
of N.D 100 0.4 to 0.07 ampere and 2.5 volts. The
separation will be finished in 20 minutes.
19. From Palladium. The electrolytic separation of
silver from palladium has not yet been made with any
satisfaction.
20. From Platinum. To the solution of the combined
metals add (for 0.2 gram of each metal) 1.25 gram of
pure potassium cyanide, dilute to 125 c.c. with water,
heat to 70, and electrolyze with a current of N.D 100 =
0.04 ampere and 2.5 volts. The precipitation will be
complete at the end of 3 hours (J. Am. Ch. S., 21, 913).
To hasten this separation use a rotating anode with
a current of N.D 100 = 0.25 to .05 ampere and 3 volts.
Twenty minutes will suffice for the deposition of the
silver.
SEPARATION OF METALS SILVER. 245
21. From Potassium, the other Alkali Metals, and Alka-
line Earth Metals. See the separation from 'barium.
P- 2 39-
22. From Selenium:
(a) In cyanide solution. Meyer (Z. f. anorg. Ch., 31,
393) pursued a course in the determination of the atomic
weight of selenium, in which he electrolyzed silver sele-
nite in cyanide solution. The silver was precipitated
free from selenium, so that this method may be regarded
as furnishing a satisfactory separation of the two
metals. As working conditions were not given by Meyer
those used with success in this laboratory will be here
introduced :
Add to the solution of the two metals 3 grams of
potassium cyanide, heat to 60 C, and electrolyze with
a current of N.D 100 =0.02 ampere and 2.5 volts. The
separation will be finished in 6 hours.
(b) In nitric acid solution. Add i c.c. of nitric acid
(sp. gr. 1.43) to the solution of the metals, heat to 60
C., and electrolyze with a current of N.D 100 = 0.015
ampere and 1.25 to 2 volts. Time, 3 hours.
23. From Tellurium. In a cyanide solution this separa-
tion did not succeed.
Add to the solution of the two metals one cubic centi-
meter of nitric acid (sp. gr. 1.43), dilute to 150 c.c., heat
to 60 C., and electrolyze with a current of N.D 100 =
o.oi to 0.015 ampere and 1.25 to 2 volts. Time, 3!
hours.
24. From Tin. When tin and silver are present together,
digest their sulphides with ammonium sulphide, which
will bring the tin into a proper condition to effect its
determination electrolytically (p. 167). Dissolve the
insoluble silver sulphide in nitric acid, and after the
246 ELECTRO-ANALYSIS.
excess of the latter is expelled, add an excess of potas-
sium cyanide and proceed as directed on p. 106. The
silver will be deposited as a dense coating, and may be
washed with hot water.
This same course, which is not a strict electrolytic pro-
cedure, has also been recommended for the separation of
silver when associated with arsenic, antimony, and tin.
25. From Uranium. See aluminium from silver, p. 237.
26. From Zinc. Add i gram of pure potassium cyanide
to the liquid containing at least o.i gram of each metal,
dilute to 125 c.c. with water, and electrolyze at 70
with a current of N.D 100 == 0.032-0.038 ampere and
2.76 volts. The silver will be fully precipitated in 3
hours. Treat as described on p. 106 (J. Am. Ch. S., 21,
By using the rotating anode, in the presence of 2.5
grams of potassium cyanide, a current of N.D 100 = o.3
ampere and 3 volts will precipitate the silver in twenty
minutes.
GOLD.
Separations of gold from certain metals have been car-
ried out in the electrolytic way with marked success.
As they may prove helpful, it was deemed advisable to
describe them here in sufficient detail to make them gener-
ally applicable.
1. From Antimony. Add 0.5 to i gram of tartaric acid
to their solution, followed by 3 to 4 grams of pure po-
tassium cyanide; then electrolyze with the conditions
given under the separation of gold from copper.
2. From Cadmium:
In phosphoric add solution. Add 40 c.c. of disodium
hydrogen phosphate (sp. gr. 1.028) and 10 c.c. of phos-
SEPARATION OF METALS GOLD. 247
phoric acid (sp. gr. 1.35) to the solution of the metals,
dilute to 125 c.c., heat to 60 C, and electrolyze with
a current of N.D 100 = 0.03 ampere and i to 2 volts.
Time 4 hours.
3. From Cobalt.
(a) In cyanide solution. In the early experiments made
in the separation of these metals some difficulties were
encountered, so that it will be necessary to follow the
directions, given below, with the utmost care. After
adding 4 grams of pure potassium cyanide to the solu-
tion, dilute to 125 c.c., heat to 65, and electrolyze
with a current of N.D 100 = 0.05-0.08 ampere and
1.7-2 volts. Before interrupting the current intro-
duce i c.c. of a 2 per cent, sodium hydroxide solution
and increase the current to o.io ampere. The time
necessary to effect this separation is usually 6 hours
(J. Am. Ch. S., 21, 922).
(b) In phosphoric acid solution. Let the total dilution
of the solution be about 200 c.c. There should be
present 30 c.c. of disodium hydrogen phosphate (sp.
gr. 1.028) and 6 c.c. of phosphoric acid (sp. gr. 1.35).
Heat to 60 C. Electrolyze with a current of N.D 100
= 0.03 to 0.04 ampere and a pressure of from i to 2
volts.
4. From Copper. The alkaline cyanide solution is best
adapted for this separation. To the liquid contain-
ing 0.1665 g ram f gold and a like amount of copper
4 grams of potassium cyanide were added. The solution
was diluted to 250 c.c. with water, heated to 6o-65,
and electrolyzed with a current of N.D 100 = 0.05-0.08
ampere and 1.7-1.9 volts. At the expiration of two
and one-half hours 0.1667 gram of gold, free from
24-8 ELECTRO-ANALYSIS.
copper, was precipitated. The liquid poured off from
the gold, after the addition of an excess of ammonium
carbonate, can be acted upon with a more powerful
current and the copper be thus obtained (p. 70). See
J. Am. Ch. S., 21, 921 ; J. Am. Ch. S., 26, 1268.
5. From Iron.
(a) In cyanide solution. Dissolve pure ferrous am-
monium sulphate ( 0.1300 gram of iron) in water
and run this solution into a solution of three grams
of pure potassium cyanide. Next add this potassium
ferrocyanide solution to the gold salt, dilute with
water to 125 c.c., heat to 65 C., and electrolyze with
a current of N. D 100 - 0.36 ampere and 2.3 to 3 volts.
Two and one-half hours will serve for the complete
precipitation of gold (J. Am. Ch. S., 26, 1259).
(b) In phosphoric odd solution. To the solution con-
taining the two metals add 40 c.c. of disodium hydro-
gen phosphate (sp. gr. 1.028) and 10 c.c. of phos-
phoric acid (sp. gr. 1.35), then dilute to 150 c.c., heat
to 65 C.> and electrolyze with a current of N.D 100 =
0.02 to 0.08 ampere and i to 2.7 volts. Five hours
will be required for the precipitation (J. Am. Ch. S,,
26, 1266).
6. From Nickel.
(a) In cyanide solution. Follow the conditions ob-
served in the separation of gold from cobalt (see
above).
(b) In phosphoric acid solution. Follow the conditions
given for the separation of gold from iron (see above)
in this electrolyte (J. Am. Ch. S., 26, 1268).
7. From Palladium. To their solution add 2 grams of
pure potassium cyanide, dilute to 150 c.c. with water,
heat to 65, and electrolyze for 5 hours with a current
SEPARATION OF METALS GOLD. 249
of N.D 100 =o.03 to 0.06 ampere and 2.5 volts. The
gold will be precipitated free from palladium. In using
the rotating anode with a cyanide electrolyte, containing
equal amounts of the two metals, apply a current of two
amperes and six volts. The gold will be precipitated in
ten minutes.
8. From Platinum. Add to the solution, containing
equal quantities of the two metals, about 1.5 gram of
pure potassium cyanide, dilute to 250 c.c. with water,
heat to 70, and electrolyze for 3 hours with a current
of N.D 100 o.oi ampere and 2.7 volts (J. Am. Ch. S.,
21, 923). A current of 2.5 amperes and 6 volts will
effect this separation in fifteen minutes if the rotating
anode be employed.
9. From Zinc:
(a) In cyanide solution. In this separation the points
to be observed are the quantity of potassium cyanide
(4 grams), the current density, N.D 100 = o.o6 am-
pere, and the pressure, which should be about 2.6
volts. The dilution and other conditions are similar
to those followed in the separation of gold from
copper, p. 247 (J. Am. Ch. S., 21, 923).
(b) In phosphoric acid solution.- To the solution of the
metals add 30 c.c. of disodium hydrogen phosphate
(sp. gr. 1.028) and 6 c.c. of phosphoric acid (sp. gr.
1.35). Dilute to 150 c.c., heat to 65 C, and elec-
trolyze with a current of N.D 100 = 0.2 ampere.
It may be here stated that the conditions given for
the separation of gold from copper will serve just as
well for the separation of gold from molybdenum,
tungsten, and osmium. The conditions observed in
the precipitation of gold from a sulphaurate solution
25O ELECTRO-ANALYSIS.
(p. 163) can be used with the certainty of good re-
sults in the separation of gold from arsenic, molybde-
num, and tungsten, while its deposition from a phos-
phoric acid solution (p. 163) will prove of value in
its separation from zinc and cobalt (Am. Ch. Jr., 13,
206).
THE PLATINUM METALS.
In this group of metals separations are not very numer-
ous. Further research is needed in this particular direction.
For instance with platinum there are lacking separations
from aluminium, antimony, arsenic, the alkaline earth met-
als, bismuth, lead, manganese, molybdenum, selenium, tellu-
rium, thallium, tin, tungsten, uranium and vanadium. Con-
sequently, those from which it has been separated in the elec-
trolytic way are few : zinc, cadmium, iron, nickel and cobalt,
in acid solution (with a current of N.D 100 = o.O7 to 0.08
ampere and 1.8 to 2.0 volts), copper (p. 198), gold (p.
249), mercury (p. 221) and silver (p. 244).
Platinum may be separated from iridium in a slightly
acidulated solution with a current of N.D 100 = 0.05 ampere
and 1.2 volts (Classen).
In the case of Palladium the only separations of it seem
to be from copper (p. 198), mercury (p. 221), silver (p.
244) and iridium by the method given for its determination
on p. 153.
The separations of the metals, comprising the platinum
group, one from the other, have thus far received scant at-
tention, but from qualitative trials they promise interesting
results.
The method given on p. 156 for the precipitation of
Rhodium has not been applied to effect any separations.
SEPARATION OF METALS - ANTIMONY.
ANTIMONY, ARSENIC, AND TIN.
Under the metals which precede this group will be found
the methods that experience has shown are best adapted for
their separation from any one member of this group. So
far as the latter itself is concerned, much credit is due
Classen and his co-laborers for valuable data upon the
electrolytic separation of its members.
1. Antimony from Arsenic. The metals, or compounds
of the same, are evaporated to dryness with aqua regia,
the residue dissolved in 2 to 3 c.c. of water ; concentrated
sodium hydroxide is added so that there will be 2.5 grams
of alkali present in the liquid and then 80 c.c. of sodium
sulphide (sp. gr. 1.13-1.15) are introduced and the whole
solution is diluted to 150 c.c., temperature 25-38, and
electrolyzed with N.D 100 = 1.5-1.6 amperes and 2.1 volts
(beginning) to 1.45 volts (at end). The time required
for the separation of the antimony is usually 6 hours (Z.
f. Elektrochem., i, 291).
Or, to a solution containing 0.1268 gram of antimony
and 0.2000 gram of arsenic, add 15 c.c. of sodium sul-
phide of specific gravity 1.18, three grams of potassium
cyanide and water to increase the total volume of liquid
to 70 c.c., then apply a current of 6 amperes and 4 volts
with the rotating anode. The antimony will be com-
pletely precipitated in 20 minutes.
2. Antimony from Tin. The sulphides (or residue from
a solution of the metals) are placed in a weighed plati-
num dish and covered with 80 c.c. of sodium sulphide
of specific gravity 1.13-1.15, to which are added 2 grams
of sodium hydroxide. Dilute to 125 c.c. with water, heat
to 57-67, and electrolyze with a current of N.D 100 =
252 ELECTRO-ANALYSIS.
1.45-1.50 ampere and 0.9-0.8 volt. The precipitation
will be complete at the expiration of 2 hours (Z. f.
Elektrochem., I, 291). Pour off the liquid into a second
dish. Treat the deposit of antimony as previously di-
rected (p. 172). To prepare the tin solution for elec-
trolysis, proceed as described (p. 167) for the conversion
of the sodium into ammonium sulphide (Ber., 17, 2245;
18, mo).
This separation has not always, in the hands of chem-
ists, given the results that were confidently expected.
There are disturbing features connected with it. It is
not certain that these have been absolutely eliminated,
although strenuous efforts have been put forth to arrive
at such a result. Very recently Ost and Klapproth (Z. f.
ang. Ch., 1900, p. 827) conducted experiments in a cell
provided with a diaphragm (p. 174). These demon-
strated that by using a concentrated sodium sulphide solu-
tion the current, as a rule, mainly decomposes the sodium
sulphide, and the antimony, if the bath pressure is low,
does not participate in the electrolysis. It is precipitated
as a secondary product by the sodium ion. When the
pressure is great and the antimony salt assists in con-
ducting the current, then the antimony wanders in the
form of a complex anion, SbS 4 , to the anode. Disturb-
ances also arise from the commingling of the anode and
cathode liquids, so that these investigators have worked
out the following piece of apparatus, to be used in this
separation, which in their hands has yielded very satis-
factory results. The sketch (Fig. 31) gives a perfect
idea of their scheme, a is a low beaker; the cylindrical
diaphragm (a Pukall porous cell), b, stands in it. The
anode is a rod of carbon, c, placed within the diaphragm-
cell, while a bent sheet of platinum or a platinum gauze, d,
SEPARATION OF METALS ANTIMONY. 253
serves as cathode. The beaker and cell are covered with
suitable cover-glasses. The diaphragm-cell above the
liquid is covered with a suitable rubber ring, e, so that the
drops of liquid falling from the cover-glass are returned
to the cathode chamber. The diaphragm, thoroughly
FIG. 31.
cleansed, should always be preserved under water. The
anode liquor should be introduced into the diaphragm-cell
some time before the electrolysis begins and the apparatus
should not be connected up until this liquor has penetrated
through the walls of the diaphragm. During the electrol-
ysis the level of the anode solution should stand from 0.5
254
ELECTRO-ANALYSIS.
to i cm. higher than that of the cathode solution. The
anode chamber contains from 40 to 50 c.c., and the
cathode chamber 150 c.c. The total volume of the elec-
trolytes is about 150 c.c. The available surface of the
cathodes equals i sq. dm.
To illustrate the practical working of this idea, several
results taken from Klapproth"s doctoral thesis (Die
Fallung cles Zinns und seine Trennung vom Antimon
durch Elektrolyse, Hannover, 1901) may here be in-
corporated :
SEPARATION OF ANTIMONY AND TIN. DIAPHRAGM AND
CARBON ANODE.
af
A
E
SOLUTION OF NINETY c c. IN
h
O
H
Q*
u-^
CATHODE CHAMBER
H
,1 M
O
D to
K
SOLUTION OF FIFTY
1
I
fa
^
Z
c.c. IN ANODE
CHAMBER.
DH
"1
w"
M
|a
K^T
I " H
2
Z g
^
g
s z
2 ^
yfi
*"
ZK
H
H
S"
i
w
K
H "
2
55
H
y.
W)
8
PH
b
Q
40
0.1500
0.2500
30 Na 2 S
20
0.08
0.9
0.1505
16
35
0.1500
0.2500
30 Na 2 S
20
0.19
I.IO
0.1446
7
60
0.1500
0.5000
( 20(NH 4 ) 2 S I
I 3 o(NH 4 ) 2 S0 4 /
20
0.2
o.5
O.I5OO
16
40
0.3000
0.2500
/ 20(NH 4 ) 2 S \
\ 3 o(NH 4 ) 2 SOj
20
0.15
1.2
o. 2990
7
5 o
o. 1 500
0.2500
f 20(NH 4 ) 2 S )
\ 3 o(NH 4 ) 2 S0 4 f
20
I.O
o. H95
16
The solution, freed from antimony, can now be changed
to one suitable for the precipitation of the tin by digesting
it with ammonium sulphate (p. 167). If this is to be
done in the absence of the diaphragm, then the latter must
be removed from the solution, placed over the cathode
beaker, and be washed for one-half hour, by allowing
water to run through it. The liquid is later concentrated
and electrolyzed (see p. 172).
SEPARATION OF METALS TIN. 255
But the tin may be estimated without removing the
diaphragm. To this end the cathode liquor is reduced to
a volume of 40 c.c. and the anode solution is renewed.
The precipitation of the tin is then made at 70. As
much as 0.25 gram of the metal will be precipitated in
from 2 to 3 hours. The pressure should not exceed 2
volts.
When antimony, arsenic, and tin are present together,
expel the arsenic from their solution by the Fischer-
Hufschmidt method (Ber., 18, mo), and separate the
antimony from the tin as already described on page 251.
See also Fischer, Z. f. anorg. Ch., 42, 363-417.
In general analysis phosphoric acid is frequently pre-
cipitated as tin phosphate. The latter, of course, con-
tains tin oxide. Dissolve the precipitate in ammonium
sulphide. On electrolyzing the solution the tin will be
precipitated, and the filtrate will contain all of the phos-
phoric acid; this can be estimated in the usual way
(Classen). By observing this suggestion the determina-
tion of the phosphoric acid in a separate portion of the
material will not be required.
Tin from Manganese. Dissolve 0.5 gram of tin in
a solution of bromine in hydrochloric acid, neutralize with
ammonium hydroxide, add the solution of manganese sul-
phate and introduce this mixture into 25 c.c. of a satu-
rated ammonium oxalate solution. Next add 100 c.c. of
a saturated oxalic acid solution and electrolyze with a
current of one ampere per i qdm. and a pressure of 2.5
volts. The tin will be precipitated in satisfactory form.
Puschin, Ch. Z., 30, 572; Z. f. Elektrochem., 13, 153.
256 ELECTRO-ANALYSIS.
IRON, MANGANESE, NICKEL, ZINC, COBALT,
ALUMINIUM, CHROMIUM, AND PHOS-
PHORIC ACID.
Electrolytic methods for the separation of these metals
are neither so numerous nor so thoroughly worked out as
with the metals already considered. Their separation from
the heavy metals has been outlined under the same, and it
only remains to describe the courses which may be pursued
with this group of metals when present together.
i. Iron from Aluminium. Add sufficient ammonium oxa-
late to the solution of the salts of the metals (preferably
not chlorides) so that it will contain from 2 to 3 grams
of oxalate for each o.i gram of metal. Dilute to 175 c.c.,
heat to 40, and electrolyze with N.D 100 = 1.95-1.6
amperes and 4.3-4.4 volts. The iron will be precipitated
in two and one-half hours (Ber., 18, 1795; 27, 2060; Z.
f. Elektrochem., i, 292). It is not advisable to allow the
current to act longer than is necessary for the reduction
of the iron. Towards the end of the electrolysis alumin-
ium hydroxide is apt to separate and will coat the iron
deposit. When the latter is dry, this adhering material
can be removed with a handkerchief. The aluminium
must be determined gravimetrically. The separation of
aluminium hydroxide can be avoided if ammonium or
potassium tartrate ( i gram) or citrate be added to the
solution of the two metals, and it be heated to 60 -, then
electrolyzed with N.D 100 = i ampere and 4-5 volts. It
is true that the iron will probably contain small amounts
of carbon. These will not be excessive and will not affect
the results seriously. See p. 141. Consult Hollard and
Bertiaux, C. r., 136, 1266.
Drown and McKenna have endeavored to utilize the
SEPARATION OF METALS IRON. 257
method described on p. 142 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 diffi-
culty in separating iron from aluminium or iron from
phosphoric acid. It is expected that the process will give
equally good results in the separation of iron and some
other metals from titanium, zirconium, columbium, and
tantalum (Wolcott Gibbs, Am. Ch. Jr., 13, 571 ; see also
pp. 29, 57). To determine iron in the presence of alu-
minium in steel they recommend the following procedure :
" Dissolve 5-10 grams of iron or steel in sulphuric acid,
evaporate until white fumes of sulphuric anhydride begin
to come off, add water, heat until all the iron is in solu-
tion, filter 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 volume
of the solution should be from 300 to 500 c.c. Connect
with battery or dynamo in such a way that about 2
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 aluminium is determined in this filtrate
(Jr. An. Ch., 5, 627). For the separation of iron from
titanium and aluminium consult also Magri and Ercolini,
Atti. R. Accad. dei Lincei, Roma [5], 16, I. 331.
By modifying the preceding scheme in accordance with
the outline given on p. 57, and observing the steps and
precautions detailed under copper, p. 77, iron may be
easily separated quantitatively, with the aid of a mercury
cathode.
23
258
ELECTRO-ANALYSIS.
From Vanadium. The details are best given in ex-
amples so that a tabulated series of results may be here
introduced :
H
ii
P
G j.
CONDITIONS.
a
M
* i
o <
ll
O)
1
|
t/>
o
fc ^
- -
M O tj \ (~\
M
PH
OS
c
5 2
9 *
<i H
&4 -^ S
9
M
5
p
O M
K HI
s
Q
Hi
Q
K
5~
H
s
g
I
O.IO56
o. 1054
0.1002
12
7
0.4
7
I
8. 5
2
O.IO56
0.1051
0.1002
13
1 4
0.6
7
I
9
3
O.2II2
0.2113
0.0200
5
14
0-3
7
I
7-5
4
O.2II2
O.2II2
0.0200
5
H
0.4
7
1
7
The dilution of solution in each of these trials equaled
20 cubic centimeters.
From Beryllium. From the readiness with which
iron may be separated from aluminium with the aid of
a mercury cathode it was reasonable to suppose that its
separation from beryllium could be made without diffi-
culty. The series given in the appended table sets forth
the conditions of successful operation. They appear
just as they were carried out :
H
Z
Q
M
a
S 2
w
Q
rS
Q
M
CONDITIONS.
i ^
D >i
O ^
O M
r>Pu *
5
2
gfia
S ^
"^ 2 "
O
m
d
fc .,
go
3 S3
^ on
X 2 wQ
H
M
M
B
H
K
H
O
z
i
M
M
J
I-J
i*
j^li
H
h
g
o
BH
o
PQ
M
PQ
Cfl
^
i
0.1056
0.1057
0.0818
O.O82I
2
7
0-5
7
0.5
6.5
2
o. 1056
0.1059
0.0818
0.0820
2
14
-5
7
0-5
6.5
3
0.0105
0.0105
0.1636
0.1633
2
4/4
0.6
8
0.6
8
4
O.O2OO
0.0208
0.1636
0.1630
2
H
0.6
8
0.6
8
5
0.2112
0.2113
0.0082
0.0082
2
0.4
6.5
1.4
7
6
0.2112
O.2II2
0.0082
0.0083
2
H
0.4
6.5
1.4
7
See J. Am. Chem. S., 26, 1128.
SEPARATION OF METALS IRON.
259
After discovering the rapidity with which metals were
deposited in a mercury cathode with the help of a rotating
anode (p. 72) it was proposed to try out the separation of
iron in this way from other metals with which it is often
associated and from some of which by ordinary gravi-
metric methods it is separated with difficulty. The speed
of the anode was 600 revolutions per minute. The metals
were present either as sulphates or nitrates. The work-
ing conditions are sufficiently indicated in the appended
experiments.
a. IRON FROM URANIUM.
W
H
ij
D
H)
Q
gj
X
i
w
fii
u o 6
gjjj
s
i
Q
2
ft!
O
4*
K *<
o
S 01 M
5 2
g 5
U- *^
C/3 g
PH ^*
u z
DO II
&
o
ft!
C^
J ^
g *
i 2
x z "
3 8
K*
w
^O
g
O
| 3
U* 1 !
s
ft!
as
OS
<
W
o
H
O.2
0.1777
7
2
3-5
7-5
, s
0.1777
O.I
0.1777
6
2
2-5
7-5
15
0.1772
0.0005
O.2
0.1777
7
3
2-5-5
7-5
o. 1769
0.0008
O.2
0.1777
7
2
2.5-3.5
7-5
J 5
0.1775
O.OOO2
&. IRON FROM ALUMINIUM.
i
Q
Ji
H
o
U ^
a
gj
<
2 ^
S s
^ "
u'^o
a
75
ui
j
o
^> ^
OS <j
o
HH 2
g
S ^
O j
S H
Q "
K S
o
cH z
CH
ctf
M CH
so
M M
|I
o
3 H
,2o
'vJ<J
Jg
o
M
DH
<*
^
O
D ^
in
M
0.2
0.1777
7
2
2-5
9-7
15
0.1777
:_
O.2
0.1777
7
2-4
9-7
15
0.1782
-)-O.OOO5
O.2
0.1777
7
2
2-5
9-7
15
o. 1781
-f O.COO4
0-3
0.1777
8
2
2-4.5
7-6
15
0.1782
-fo.oco5
260
ELECTRO-ANALYSIS.
c. IRON FROM THORIUM.
s
a
4
t
u
a
3
THORIUM NIT
GRAM.
IRON PRESE
GRAM.
VOLUME, c
SULPHURIC A
IN DROPS
(30 i c.c.
CURRENT
AMPERES
o
TIME.
MINUTES
r
M
0.2
0.1777
7
2
2-4
7-6
15
0.1777
0.2
0.1777
7
2
3-5
6-5
15
0.1777
0-3
0.1777
8
2
3-4
7-5
15
0.1777
0.2
0.1777
7
2
3-4
7-5 15
0.1777
O.OOOI
d. IRON FROM LANTHANUM.
J
Q
5
u
a
s
<
*S
H g
u o 6
"
a
-8
2
S
O
z
< M
2
u
Z
Ha;
i "
k)
SD
r" Z
^ K
sS
^^
3
x 2
^
>
^
ZO
o
"3
O
K
o
D *-"
M
M
W
0.2
0.1220
10
2
2-4
8-6
15
O.I22I
-4 o.ooo I
0.15
0.1220
10
2
2-4
8-6
15
0.1226
+0.0006
0.25
0.1220
10
2
2-4
8-6
15
0.1226
+0.0006
?. IRON FROM PRASEODYMIUM.
a
^
h
U
a
gj
SH
S;
u
y u
ii
H
W (H
o*
C6
O
o s <:
O a, as
M
SQ M
is
O
=>
z o
x z II
" s
u
H
! 5
<W
o
M
O
j "^
**
K
h
C/5
W
0.25
0.1235
7
2
2-4
8-5
2O
0.1240
+0.0005
0-3
0.1235
8
2
3-5
9-6
2O
0.1234
O.OOOI
0.1235
8
2
2-4
8-5
20
0.1229
0.0006
0.25
0.1235
7
2
2-4
8-5
20
0.1230
0.0005
SEPARATION OF METALS IRON.
261
/. IRON FROM NEODYMIUM.
a
grf
h
3
u
u
Sa'o
UM
4
Q
2
3
HI
|P
ISs
u <
PL, DC
H
1
D
K8<J
gQ -
X2"
si
^
o
si
PJJ
I?
* BS
2O
K
">
O
M
>
S~&
3 v -'
W
U<1
7$
O
M
K
W
o. 16
0.1235
7
2
3-4
7-5
20
o. 1242
-f- 0.0007
0.24
0.1235
8
2
3-5
9-5
20
O.I236
-f 0001
0.24
0.1235
8
2
3-5
9-7
20
0.1237
-f 0.0002
o. 16
0-1235
7
2
3-5
9-5
20
0.1237
-^0.0002
g. IRON FROM CERIUM.
Q
CERIUM
SULPHATE.
GRAM.
IRON PRESENT
GRAM.
VOLUME, c.c
SULPHURIC Aci
IN DROPS
(30 = 1 c c.).
CURRENT.
AMPERES.
i
TIME.
MINUTES.
Q
la
1
ERROR. GRAM
0.12
0.1235
8
2
2-4
9-6
20
0.1237
4-O.OOO2
0.24
0.1235
9
2
2-4
9-6
20
0.1236
-f O.OOOI
0.36
0.1235
IO
O
2-5
10-7
25
0.1230
O.OOO5
h. IRON FROM ZIRCONIUM.
a
H
u
g
ZIRCONIUM
SULPHATE.
GRAM.
RON PRESEN
GRAM.
VOLUME, c.
JLPHURIC A(
IN DROPS
(30=1 C.C.)
h
H
VOLTS.
TIME.
MINUTES.
2 O
OS
5
I
w
U
0.2
0.1235
7
o
2-4
7-5
2O
o. 1238
-1-0.0003
0-3
0.1235
8
i
2-4
7-5
2O
o. 1230
-(-O.OOO5
0-5
0.1235
10
2
2-5
6-5
25
0.1238
-fO.0003
The conditions under thorium will answer for the sepa-
ration of iron from titanium and from yttrium.
J. Am. Ch. S., 25, 888; ibid., 27, 1547.
262 ELECTRO-ANALYSIS.
2. From Chromium. They can be separated in oxalate
solution with conditions like those given above for the
separation of iron from aluminium, the only difference
being that the temperature should be about 65 (Z. f.
Elektrochem., 1/292). The chromium during the elec-
trolysis is converted into chromate. It must be deter-
mined gravimetrically. The second course, tartrate or
citrate solution, also lends itself well to this separation.
The requisites are given above under iron and aluminium.
It may be added here that just as iron is separated in
tartrate or citrate solution from aluminium and chromium,
so can it also be separated from titanium.
3. From Cobalt. Classen (Ber., 27, 2060) adds about 8
grams of ammonium oxalate to the solution of the
metals, dilutes with water to 120 c.c., heats to 65 70,
and electrolyzes with N.D 100 = 1.6 2.O amperes and
electrode pressure of 3.0-3.6 volts. The time required
for complete deposition varies from 2 to 4 hours. The
metals are precipitated together, their combined weight
ascertained, then they are dissolved in acid, and the
quantity of iron is found by titration. The cobalt is ob-
tained by difference.
Vortmann suggests adding 3 to 6 grams of ammo-
nium sulphate and a moderate excess of ammonium
hydroxide to the solution of the metals, then electro-
lyzing with a current of N.D 100 = 0.4-0.8 ampere and
4-5 volts. He remarks that by contact with the ferric
hydroxide the deposit of cobalt will contain traces of
iron, which can be fully eliminated by a second precipi-
tation. (See iron from nickel.)
4. From Manganese. In considering this separation it
should be remembered that objections have repeatedly
SEPARATION OF METALS IRON. 263
been offered to the suggestion of Classen (Ber., 18, 1787) ;
hence to obtain results at all satisfactory it is advisable
to carry out the separation exactly as given by this
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 oxa-
late ... it is impossible to obtain a quantitative sepa-
ration of the two metals, because the manganese dioxide
carries down with it considerable quantities of ferric
hydroxide. The complete separation of the metals is
possible only when the separation of the dioxide is de-
layed till most of the iron is precipitated." The elec-
trolysis in the cold is not favorable; the large amount
of ammonium carbonate, or ammonia formed in the
decomposition of the excessive ammonium oxalate, dis-
solves the precipitated dioxide. " The rapid dissociation
of ammonium oxalate when heated, however, gives a
simple means of delaying, or entirely preventing, the
formation of a manganese precipitate during the elec-
trolysis." The solution containing the two metals is
treated with 8 to 10 grams of ammonium oxalate and
while hot (70) is acted upon with a current of N.D 100
= 0.5 ampere and 3.1-3.8 volts. Treat the iron deposit
as directed on p. 139. Boil the liquid, poured off from
the iron, with sodium hydroxide, to decompose the am-
monium carbonate present, after which add sodium car-
bonate and a little sodium hypochlorite. The manga-
nese is precipitated as dioxide, and after solution in
hydrochloric acid is finally weighed as pyrophosphate.
Classen mentions that the method affords good re-
sults if the manganese content is not too high. In the
analysis of ferromanganese, for example, it possesses
no practical value (Ber., 18, 1787). Engels has tried
264 ELECTRO-ANALYSIS.
to use the plan he describes for the deposition of man-
ganese (p. 135) in effecting the separation of the latter
from iron (Z. f. Elektrochem., 2, 414), but it has been
observed that while the manganese was completely de-
posited as dioxide, it invariably contained as much as
0.02 gram of iron. See Koster, Ber., 26, 2746; Hpllarcl
and Bertiaux, C. r., 136, 1266.
Scholl, working in this laboratory, separated iron and
manganese and determined them simultaneously by the
following procedure : Ten cubic centimeters of a manga-
nese sulphate solution (=0.0988 gram of manganese)
were introduced into a roughened platinum dish. To
this were added 10 c.c. of a ferric ammonium sulphate
solution (=0.0996 gram of iron), 5 c.c. of formic acid,
sp. gr. i. 06, and 10 c.c. of ammonium acetate. A basket
electrode (the cathode) was then suspended in the liquid
and a current of N.D 100 =i.i amperes and 3.9 volts
was allowed to act for five hours. The precipitation of
each metal was complete, the manganese of course sepa-
rating as dioxide (J. Am. Ch. S., 25, 1045).
5. From Nickel. Classen deposits nickel and iron together
(same as cobalt and iron) as an alloy, which is weighed,
then dissolved in concentrated hydrochloric acid, the iron
oxidized with hydrogen peroxide, and the ferric so-
lution titrated with a stannous chloride solution. The
current may vary from 1.75 to 2.2 amperes and the volt-
age from 3.4 to 4.0. The temperature of the liquid is
usually 65-7o. Two hours will be sufficient time for
the precipitation of 0.2 gram of the combined metals.
Under iron from cobalt mention was made of a
method which can be pursued in separating the metals
now under discussion. To repeat, it consists in oxidiz-
SEPARATION OF METALS IRON. 265
ing the iron with bromine, then introducing into the
solution from 3 to 6 grams of ammonium sulphate and
a moderate excess of ammonium hydroxide. From
this solution the nickel will be deposited in from 2 to 3
hours, with a current of N.D 100 = 0.4-0.8 ampere. As
in the case of the cobalt, traces of iron will appear in the
nickel. This occlusion, so to speak, of iron has become
a subject -of discussion among those using electro-
lytic methods. Neumann (Ch. Z., 22, 731) remarks
that it has tacitly been understood that the nickel car-
ries down no iron with it. Indeed, Engels (Thesis,
Bern) claims to have obtained perfectly correct results.
Vortmann, as indicated, and also Ducru (Ch. Z., 21,
780; C. r., 125, 436; B. s. Ch. Paris, 17, 1881) recom-
mend the solution of the nickel and the determination
of any iron present. So well satisfied is Ducru that he
employs this method for the estimation of nickel in
steel, asserting that the amount of enclosed iron is fairly
constant (varying between i and 2 mg.), and that for
technical or commercial purposes it may be ignored.
Neumann, on the other hand, maintains the absolute
necessity of determining the amount of iron co-precipi-
tated. In the analysis of nickel steel and nickel matte
he proceeds as follows :
Dissolve the substance in dilute sulphuric acid, and
after a brief period introduce hydrogen peroxide into
the solution to oxidize the carbon and the iron, thus
obtaining a clear, yellow solution. Now add ammonium
sulphate and ammonium hydroxide, boil and continue
the addition of ammonium hydroxide to an excess, then
dilute to a definite volume. Filter out 100 c.c. of this
solution, mix with it ammonium sulphate and ammonium
hydroxide, dilute to 175-200 c.c., and electrolyze the hot
24
266 ELECTRO-ANALYSIS.
liquid with N.D 100 = 1-2 amperes and 3.4-3.8 volts
The electrolysis will be finished at the expiration of from
ij to 2 hours.
For another method by Vortmann applicable here,
see zinc from nickel in the presence of Rochelle salt
(p. 268).
6. From Phosphoric Acid. If the iron has been precipi-
tated from an oxalate solution (p. 139), from a citrate
solution, or from an ammoniacal tartrate solution, the
liquids poured off from the iron deposit will contain
the phosphoric acid, which can then be removed as am-
monium magnesium phosphate. Or, if the iron phos-
phate be dissolved in sulphuric acid the iron may be de-
posited in a mercury cathode, using at the time a rotat-
ing anode (see p. 143).
7. From Titanium. The method described on p. 140, and
also p. 261, with the conditions given there, will answer
perfectly in making this separation.
8. From Uranium. (Ber., 14, 2771; 18, 2483.) In
making this separation, follow the directions outlined
on p. 256 for the separation of iron from aluminium.
The uranium is precipitated in the form of hydroxide.
The separation with the use of the mercury cathode and
rotating anode (p. 259) is decidedly preferable.
9. From Zinc. Add to the solution of the metals 1-3
c.c. of a solution of potassium oxalate (1:3) and 3 to 4
grams of ammonium oxalate and electrolyze the liquid
with a current of N.D 100 = i to 1.2 amperes. The zinc
is deposited first, and no difficulty is experienced, pro-
viding 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
SEPARATION OF METALS COBALT. 267
in excess. Vortmann (M. f. Ch., 14, 536) suggests two
methods :
(a) Add potassium cyanide to the solution of the
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.D 100
0.3-0.6 ampere.
(b) Several grams of Rochelle salt are introduced
into the solution of the metals and then an excess of
10-20 per cent, sodium hydroxide, after which the elec-
trolysis is conducted at 5o-6o with a current of N.D 100
= 0.07-0.1 ampere and an electrode pressure of 2 volts.
1. Cobalt from Manganese. The course generally recom-
mended for this separation is precisely like that given
for the separation of iron from manganese. Owing to
the great tendency of the manganese, toward the close
of the decomposition, to separate out as dioxide which
settles on the cobalt deposit, the method can hardly
be regarded as being accurate.
2. From Nickel. To the acetic acid solution of the metals
add 10 grams of ammonium sulphocyanide, 3 grams
of urea, and from 3 to 6 c.c. of ammonium hydroxide to
neutralize the excess of acid. Dilute the solution to 300
to 350 c.c. and electrolyze with a pressure of not more
than one volt and 0.8 ampere at 70 -80 C. The time
of precipitation is one and one-half hours. Nickel and
sulphur pass to the cathode, while the cobalt remains
unprecipitated. The nickel should be dissolved in acid
and reprecipitated according to the method described on
268 ELECTRO-ANALYSIS.
p. 126, to obtain it pure. The liquid poured off from the
first nickel deposit should be evaporated to dryness several
times with nitric acid, the residue taken up in water,
and the solution treated as directed on p. 133 (Bala-
chowsky, C. r., 132, 1492; also M. f. Ch., 14, 548).
3. From Zinc. Add several grams of Rochelle salt and
an excess of a dilute sodium hydroxide solution to the
liquid containing the metals. Warm to 65 and electro-
lyze with N.D 100 = 0.3-0.6 ampere and 2 volts. Usually
there is a deposit upon the anode, hence it is advisable
to previously weigh the latter and again at 110 after
the precipitation is complete (Elektrochem., Z., i, 7).
1. Nickel from Manganese. What was said of the sepa-
ration of cobalt from manganese applies here in every
particular.
2. From Zinc:
1. Add 4 to 6 grams of Rochelle salt to the solution of
the two metals, then a concentrated solution of sodium
hydroxide. Electrolyze the mixture with a current
of N.D 100 = 0.3-0.6 ampere. The precipitation of
the zinc will be finished in a period of from 2 to 4
hours. Pour off the alkaline liquid, wash the zinc
deposit with water and alcohol; dry at 100 C.
2. Add 10 grams of ammonium sulphate, 5 grams of
magnesium sulphate, 5 c.c. of a saturated solution of
sulphurous acid and an excess of 25 c.c. of ammonia
(sp. gr. 0.924) to the solution containing the two
metals as sulphates ; dilute to 300 c.c. and electro-
lyze at 90 with a current of o.i ampere. At the
expiration of four hours one to two cubic centimeters
of the liquid should not turn black on the addition of
ammonium sulphydrate. Continue the electrolysis for
SEPARATION OF METALS ZINC. 269
an hour longer. Ch. Z., 27, 1229 (1903) ; Ch. Z., 28,
645; C. r., 137 (1903). 8 53; Mid., 138 (1904), 1605.
Puschin and Trechzinsky outline a method in the
Z. f. angw. Ch., 17, 892, for the separation of tin
from nickel, which may be regarded as worthy of
some consideration, although it in no wise is superior
to the ordinary course of analysis.
i. Zinc from Manganese. A solution contained 0.5074
gram of zinc sulphate and 0.1634 gram of manganese
sulphate. To it were added 5 grams of ammonium
lactate, 0.75 gram of lactic acid, and 2 grams of ammo-
nium sulphate. It was diluted to 200 c.c. and electro-
lyzed at 2o-25 C. with a current of N.D 100 = 0.24-0.26
ampere and 3.7-3.9 volts. In 4 hours 22.786 per cent,
of zinc was found, while theory required 22.78 per cent.
(Riderer, J. Am. Ch. S., 27,789).
Scholl recommends adding to the solution of the two
metals in the form of sulphates, 10 c.c. of formic acid
of sp. gr. i. 06 and 5 c.c. of an ammonium formate solu-
tion, then electrolyzing with a current of i ampere and
5.4 volts, using a sand-blasted dish as anode and a basket
shaped cathode. Ten hours are usually required for the
separation as the electrodes are stationary.
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 precipi-
tation with barium carbonate. Dissolve the iron precipi-
tate in citric acid, and electrolyze the solution according
to the directions given upon p. 140. The filtrate, con-
taining the zinc, manganese, nickel, and cobalt, together
with a little barium salt, is carefully treated with just
sufficient dilute sulphuric acid to remove the barium.
27O ELECTRO-ANALYSIS.
After filtering, electrolyze the filtrate in a platinum .dish,
connected with the anode of a battery, with a current of
0.3-0.5 ampere. A weighed piece of platinum foil will an-
swer for the cathode. The manganese is deposited as
dioxide (p. 136) ; the other metals remain dissolved and can
only be separated by one of the usual gravimetric methods ;
or perhaps the suggestion of Vortmann (p. 268), for the
separation of zinc from nickel and cobalt, would be appli-
cable here, and these two might then be separated as out-
lined on p. 268. 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 solution containing
these two metals be very slightly acid with sulphuric acid,
they can be precipitated simultaneously the zinc at the
cathode, and manganese dioxide at the anode.
URANIUM.
Smith has called attention to the separation of uranium
in the electrolytic way from the alkali metals and from
barium (p. 147). Actual results are given. It seemed
desirable to amplify the suggestion; hence the presenta-
tion of the results given below. It may be said here,
that in attempting to separate uranium from nickel and
cobalt no satisfaction could be obtained, so that even-
tually that particular line of experiment was abandoned.
During the precipitation of the urano-uranic hydrate the
dish should be \vell covered so that as little evapora-
tion as possible occurs. It was observed that in case of
evaporation there was danger of other salts separating
upon the exposed metal, and on refilling with water the
SEPARATION OF METALS URANIUM.
2/1
uranium precipitate was apt to enclose the same and thus
carry with it a slight impurity. This precaution is espe-
cially necessary in the separation from zinc (J. Am. Ch.
S., 23, 608).
i. FROM BARIUM .(ACETATES).
z
z
.. u
:')
".
H"
a u u
u
o
t/5
2
i
w .
Bl
? fe 2
fc*
5
p
j
M
S
O
W
j
M
o
as al
S
H g<J
o
2
M
2
PH ^
s ^
MCJ U
^
u
O
a!
cc
D
,J
U
g
B
H u w
PH "
Q
H
H
M
^
H
o. 1116
0.1 I
o-5
125
70
N.D 107 = o.02A
2
51^' O.III9
-j-0.0003
0.1116
O.I I
0-5
!25
70
N.D, 07 =:0.04 A
8
51^' 0.1117
-f O.OOOI
o. 1116
O.I I
0.2
125
70
N.D; o7 = o.i A
4-54
0.1117
-[-O.OOOI
2. FROM CALCIUM (ACETATES).
M
?
W u
r) .
z
u
o
z
H
tn
fe
U
ni
X
o
.-
W t/5
OS ",
' Q
M
g
z '^
W 5
Sjj
' "
5
b)
H
W
D <
as
SO
U
3
O
fa K
<-
^O
5 2
b
W
P
^
g
o
O
a
"s
Q
g
H
&
^
s
M
o. 1116
O.I
0.2
125
70
N.D ]07 = 0.025 A
2.25
6*
0.1113
-0.0003
o. 1116
O. I
0.2
I2.S
70
N.D 107 ^r o 04 A
2.2
5^
0.1114
0.0004
o. 1116
O.I
0.2
125
70
N.D 107 = o.os A
2.25
4^
0.1113
0.0003
o. 1116
O.I
0.2
125
70! N.D ]07 =^ 0.025 A
2.0
4|
0.1115
O.OOOI
3. FROM MAGNESIUM (ACETATES).
z
H
Z
w
d
|
gj
U
r 5
u
3
t/i
g
g
H
z
u .
fa
U
63
Lj
OS
D
Q* .
M
w tn
PH S
f-' Q
%
O
Z f>
O
83
g as
z
Q
9
&E)
^
H
ffi
1
2;
"^ V
^ O
r\ <J
<
M
O
fa as
"^
C^
t/5
_
H
K
a
U
O
as*
CD
td ^
os M
P
U
y
g
Q
o
o
Z "
" j-
^J
Ok
as
o
Pu H
fl
U
H
p
OS
1
$<
H
0.1116
O.I
O.I
125
70
N.D ]07 = o.o26A
2.22
6
O.III5
O.OOOI
O.I 102
O.I
O.I
I2 5
70
N. D ]07 = 0.05 A
2-25 s\
O.IIO4
-f O.OQO2
O.I 120
O.I
O.I
125
70
N.D 107== o.i 5 A
4.0 4
O.III9
O.OOOI
272
ELECTRO-ANALYSIS.
4. FROM ZINC (ACETATES).
z
8
w u
So
.
5 2
If.
is
H
Z u
U
Z
w
u
s
h
z
'7J
(H
tf
Q"
'"^
o
x
w <
tt 3;
3<
o
H
<
x
St
11
z
PH Q
P*O
<* y
&
K
p
u
o
X
Z
" H
j
Q
i
g
H
o n
o
X
&
**
N
^
H
W
O 1 1 2O
O I
O I
I2C
7O
N D o 021 A
2 2C
5
0. 1 102
O.2
0.2
1 ^J
125
70
N. U 107 0.017 A
^^3
2.25
6
0.1099
0.0003
0. 1 102
O.I
O.I
"5
70
N.D 107 ^=o.o2 A
2.2
6
O. IIOO
O.OOO2
O.I 102
O.I
O.I
125
75
N. D ]07 = 0.025 A
4.4
4*
o. 1 103
4 o.oooi
O.I 102
0.15
O.2
125
75
N.I) 10T = o.oi A
2.2
6
0.1105
-f 0.0003
O.I 102
O.2
O.2
125
75
N.D 107 =^o.o2 A
2.25
6
0.1099
0.0003
MOLYBDENUM.
Under the various metals conditions have been given by
which molybdenum may be easily separated from them.
The fact, however, that the latter metal can be readily
deposited in mercury (p. 162) has made it possible to sepa-
rate it from vanadium, and yield results which are per-
fectly satisfactory. The salts employed were sodium molyb-
FROM VANADIUM.
MOLYBDENUM
PRESENT IN GRAMS.
MOLYBDENUM
FOUND IN GRAMS
8
3 z
O,
No. OF CELL USED.
SULPHURIC ACID
(>PG. 1.832)
PRESENT IN DROPS
1
H
g
H
2O
18
18
20
CONDITIONS.
t/5
U
a
0,
g
1.6
2
1.6
1-4
d
O
K^OT^ Cn AMPERES.
s
o
I
2
3
4
0.0950
0.0950
0.1900
0.1900
0.0950
0.0940
0.1895
0.1887
1002
0.1002
0.0100
0.0100
2
3
2
2
2O
2O
3
3
6-5
5
4-5
4-5
5-5
6
5-5
(3 hrs.)
(3 hrs.)
(3 hrs.)
(3 hrs.)
1 Neutralized with caustic potash to 15 drops of sulphuric acid and then
run under final conditions for time given.
2 Neutralized with caustic potash to 20 drops of sulphuric acid and then
run under final conditions for time given.
.SEPARATION OF METALS CHROMIUM.
2/3
date and sodium vanaclate. As indicated in experiments
Nos. 3 and 4 in the table, it was found best to neutralize,
with potassium hydroxide, a portion of the sulphuric acid
present after all the molybdenum, but the last traces, had
been deposited. Large amounts of the acid seem to exert a
retarding influence on the final traces of molybdenum. On
the other hand the neutralization must not be carried too far,
as an oxide of vanadium appears at the anode, when in-
sufficient acid is present. When the molybdenum is com-
pletely deposited the solution will be green in color. This
may serve as an indication for the interruption of the
current.
CHROMIUM.
Since it is possible to precipitate this metal in mercury
(p. 144) it is natural to pursue this plan in effecting sepa-
rations from other metals, especially where these separations
are an improvement on earlier procedures. Thus, when in
the form of sulphates, it is comparatively easy to separate
chromium from aluminium by using the mercury cathode
and stationary anode as described on p. 58. The conditions
are sufficiently given in the subjoined examples.
i. From Aluminium.
<
s
" "*
1
<
<! K
J
JJ
oi
CONDITIONS.
DO
Ho
zO
r'n
w
TO 1
o
s2
la
s^
h
s
w
8
,
3
m
02 H
K
D H
5 HH
o
D d z
H
H
H
5
X Q
B
D
o
6
^5
D tt
s
H
w
s
E
ti
5>
0,
h
On
l - 4
C/J Q,
I
0.1080
o. 1080
0.1421
0.1423
I
6
14
0-35
6
0.8
6. 5
2
o.io^'o
o. 1081
0.1421
0.1426
2
4
14
0-3
6
0.8
6.5
3
0.0108
0.0107
0.2842
I
6
2
o-3
5-5
0.7
7
4
0.0108
0.0107
0.2842
3
5
i/4
-3
5-5
0.85
7-5
5
o. 2160
0.2162
0.0142
I
6
24
0.6
6
1.8
7-5
6
0.2160
0.2158
0.0142
I
5
14
0.4
8
i
7-5
274
ELECTRO-ANALYSIS.
2. From Beryllium.
A wide range in the time necessary for this separation is
permissible without injury to the deposit. No deleterious
effects are produced by the prolonged action of the current.
The requisite conditions are sufficiently given in the follow-
ing table:
1 [
S Z
a z .
s
j
a
Q
ur as
2 CONDITIONS.
D
D r. rj5
2 W g
03* U ,J
O ;
* H <
|g<
U
5 H Id O
K 1 -5
,
as *
g *
KiD *
P
K ^ "Q
.
X
H
!/3
H
5|
CJ fa
o
J^fe
"
3
o
E
H)
O
W
H
3
3
*
I
o. 1080
o. 1079
0.0818
I
4
14
0.4
6
3-5
5
2
o. 1080
0.1078
0.0818
I
4
4-5
0.3
6
3-5
5
3. ADDITIONAL REMARKS ON METAL
SEPARATIONS.
In the preceding pages the greater number of recorded
separations have been made with stationary electrodes,
although it will be observed that there are numerous records
of such as have been conducted with the help of the rotating
anode. This number will be greatly augmented in the
course of time, as opportunity for further study in this direc-
tion is had. That this field of investigation is attractive
and that suggestions of all kinds are sure to be made is
most certain. While the writer has not had time to person-
ally investigate all suggestions which have already been
made along the line cited he feels constrained to insert at
this point the main features of a scheme for metal separation
recently proposed by H. J. Sand. In doing this he would
emphasize the fact that all separations referred to by Sand
ADDITIONAL REMARKS ON METAL SEPARATIONS. 2/5
FIG. 32.
have been already carried out after the plan developed in this
laboratory for the rapid precipitation of single metals, and
are given full expression in the preceding pages. The basal
thought of Sand is the " sepa-
ration of metals by graded
potential."
A description of the appa-
ratus is as follows :
" Figs, i a, ib, ic illustrate
the apparatus (Fig. 32) de-
signed to meet these require-
ments. It consists of a pair
of platinum gauze electrodes,
an inner rotating electrode, ic,
and an outer electrode, ici,
which surrounds it on all sides
except the bottom. The two
are kept in position relatively
to each other by means of the
glass tube, ib, which is slipped
through the collar A and the
ring B of the outer electrode.
It is gripped firmly by the for-
mer, but passes loosely through
the latter. The hollow platinum-indium stem A of the
inner electrode is passed through the glass tube, in which it
rotates freely. The inner electrode is designed to produce a
maximum amount of rotation of the liquid, and for this
purpose has a vertical partition, P. It is open at the bottom
and as open at the top as the requirement of rigidity in the
construction of the frame will allow. The mesh of the
gauze is I4 2 per sq. cm. The gauze of the outer electrode
almost completely stops the rotation of the liquid. While
2/6 ELECTRO-ANALYSIS.
the electrolyte is therefore ejected rapidly from the center
of the inner electrode by centrifugal force, it is continually re-
placed by liquid drawn in from the top and the bottom. So
great is the suction thus produced that when the electrode is
moving rapidly, chips of wood or paper placed on the surface
are drawn down to the top of the outer electrode. The
circulation is practically independent of the size of the beaker
employed. As the outer electrode surrounds the inner com-
pletely, the lines of flow of the current are contained between
the two, and even when strong currents are employed the
potential of the electrolyte anywhere outside the outer elec-
trode is practically the same as that of the layer of liquid in
immediate contact with it. This is a matter of great im-
portance when an auxiliary electrode is employed, as it
enables the potential difference electrode-electrolyte to be
measured at any point in the liquid outside the outer elec-
trode. The space between the surfaces of the two electrodes
is about 3 mm. The weight of the outer electrode is about
40 grams, that of the inner electrode about 28 grams. Fig.
33 shows the stand. It will be seen that the beaker con-
taining the electrolyte is always placed on a tripod support.
The outer electrode is gripped by a V-clamp, the cork
from the flat side of which has been removed and replaced
by platinum foil so as to obtain metallic contact. The inner
electrode is held by a small chuck which is flexibly attached
to the pulley from which the motion is derived. The figure
will fully explain this, as well as the mode of electrical con-
nection by means of the mercury contained in the glass and
rubber tubes C and F. There is thus practically no resist-
ance in the rotating contact, and no chance of its being
affected by the air of a chemical laboratory, a matter espe-
cially important when the potential difference of the two elec-
trodes is measured for the purpose of separations. All
ADDITIONAL REMARKS ON METAL SEPARATIONS.
movable connections are made on the base of the stand on
two sets of double terminals which are permanently joined
to the holders of the electrodes by heavy flexible wire.
Those parts of the stand which are exposed to the vapors
FIG. 33.
G-
A, Clamp to grip outer electrode; B, chuck to grip inner electrode;
C, glass tube rotating in glass tube D ; E, oil trap on C ; F, thick
rubber tube; G, amalgamated copper wire dipping into mercury con-
tained in C and F ; H, cord made of violin string; /, pulley made of
rubber tube.
2 7 8
ELECTRO-ANALYSIS.
from the electrolyte are painted with several coatings of
celluloid in amyl acetate. In order to reduce the amount of
platinum required for the apparatus, attempts were made
FIG. 34-
FIG. 35.
FIG. 34. INNER ELECTRODE WITH GLASS FRAME. A, Copper wire
held in position in glass stem by slightly burnt glass tube ; B, C , mer-
cury; D, piece of gauze fused through the glass, and, E, wire forming
connection between C and outer gauze; G, partition cut from micro-
scope slide held in position by wire F.
FIG. 35. INNER ELECTRODE, No. 2. Stem and mercury as in Fig.
34. A, Bulb to spread out gas bubbles ; B, gauze fused into glass to
make connections; C, wire forming metal surface of electrode; D, D,
vanes for stirring.
to construct the frame of the inner electrode of glass and at
the same time to retain its essential features. Fig. 34 shows
the result of these attempts. The electrode there depicted
ADDITIONAL REMARKS ON METAL SEPARATIONS. 279
was in continual use for a month, after which the stem broke.
The weight of platinum was less than 5 grams.
To avoid the use of platinum, it might be possible to
make the outer electrode of silver when it is used as the
cathode. It is probable that the metals deposited on it might
be removed after electrolysis by the method of graded poten-
tial, although experiments in this direction have not yet been
made.
The electrodes ic (Fig. 34) and 2 (Fig. 35) are not
suitable for solutions containing metals which very read-
ily pass from one stage of oxidation to another, such as
copper in ammoniacal liquids, iron, tin, etc. In this case,
an anode with a smaller oxidation and stirring efficiency is
necessary. The former is obtained by making the surface
of the electrode much smaller. Fig. 35 shows the electrode
which was designed for this purpose. It is made almost
entirely of glass, the total weight of platinum being ij
grams.
The Auxiliary Electrode. The auxiliary electrode al-
ways used for the present investigation was a mercury-
mercurous sulphate-2N sulphuric acid electrode. As an
auxiliary electrode has hitherto not been employed in analy-
sis, a special form (Fig. 36) suitable for this purpose was
designed. The distinctive feature of this electrode lies in
the funnel F and connecting glass tube A B. It will be
seen that the two-way tap T will allow the funnel F to be
connected with either half of the glass tube A B, or will close
all parts from each other/ The half A permanently con-
tains the 2N-sulphuric acid solution of the electrode. The
half B, on the other hand, is filled for each experiment from
the funnel F with a suitable connecting liquid, generally
sodium sulphate solution. The end of B is made of thin
28O ELECTRO-ANALYSIS.
tube of about ii mm. bore, and is bent round several times
to minimize convection, as will be seen from the figure.
While the electrode is in use, the tap, which must be kept
free from grease, is kept closed, the film of liquid held round
the barrel by capillary attraction making the electrical con-
FIG. 36.
nection, but towards the end of a determination a few drops
are run out in order to expel any salt which may have dif-
fused into the tube. The normal electrode is held in a
separate stand so that it can easily be brought to or removed
from the solution undergoing electrolysis.
Electrical Connections. For separations by graded po-
tential the electrical connection must be made as shown in
ADDITIONAL REMARKS ON METAL SEPARATIONS. 28 1
Fig. 37. The battery is connected directly to the two ends
of a sliding rheostat, the electrolytic cell to one of them and
the slider. It is manifestly essential that the sliding con-
FIG. 37-
attjery
Rheostat
/WV\
^ f electrodes) (Am-meterJ >
tact should be very good. A rheostat by Ruhstrat of
Gottingen, with a carrying capacity of 15 amperes and a
resistance of 2.6 ohms, proved very satisfactory. It was
protected from the atmosphere of the laboratory by a coat-
ing of vaselin.
The arrangement (Fig. 38) adopted for the measure-
ment of the potential difference auxiliary electrode-cathode
is the one most usually employed at the present time in
electrochemical research. The electromotive force to be
measured is balanced against a known electromotive force
by means of a capillary electrometer. The known elec-
tromotive force is drawn from a sliding rheostat, the ends
of which are connected with one or two dry cells. The
value of the E. M. F. is read directly on a delicate volt-
meter (range, 1.5 volts). For potential difference greater
than 1.5 volts a Helmholtz T volt cell was interposed be-
tween the auxiliary electrode and the rheostat. The ar-
2 5
282
ELECTRO-ANALYSIS.
rangement allows the voltage to be measured almost
instantaneously, a matter of great importance in the present
case. Owing to the very great advances made in recent
years in the construction of quadrant electrometers and their
adjuncts, it seems probable that an electrometer might be
permanently fitted up in such a manner as to be used as
a direct-reading electrostatic voltmeter (range required, i
volt; sensitiveness, i centivolt). If this were the case it
FIG. 38.
athode
Electrometer Auxiliar
electrode.
would become as simple a matter to read the potential
difference between the cathode and the electrolyte as that
between the cathode and the anode.
Method of Carrying out an Experiment. Where not
especially stated to the contrary, the metal was always de-
posited on the outer electrode. To carry out an experiment
the cathode, anode, and auxiliary electrode are placed in
position, the electrolyte is heated to the required tempera-
ture and covered with a set of clock glasses having suitable
openings for the electrodes. For the purpose of a sepa-
ration the current is usually started at about 3-4 amperes
ADDITIONAL REMARKS ON METAL SEPARATIONS. 283
and the potential of the auxiliary electrode noted. As a
rule this is only slightly above the equilibrium potential.
The current is then regulated so that the potential of the
electrode may remain constant. When no by-reactions
take place the current falls to a small residual value (gener-
ally about 0.2 ampere), as the metal to be separated dis-
appears from the solution. The auxiliary electrode is then
allowed to rise o.i to 0.2 volt, according to the metal.
It is obviously a matter of great importance to know
when all the metal has been deposited. Under the condi-
tions just assumed the amount deposited per unit of time
may be taken as roughly proportional to the amount still
in solution. This being so, it follows that the amount in
solution will decrease in geometrical ratio during successive
equal intervals of time. If we, therefore, make the safe
assumption that the concentration of the metal has fallen
to under i per cent, of its original value in the time during
which the potential and the current have been brought to
their final value, it is clear by continuing the experiment
half as long again, the concentration of the metal will fall
to under o.i per cent., so that the deposition can then be
considered finished.
In cases where by-reactions occur, the current does not
fall to zero, but it generally attains a constant value which
allows one to see when all the metal has been removed. In
certain cases, the absence of the latter can be roughly tested
for chemically, and by continuing the experiment for about
half as long again as this reaction demands, the metal may
be safely assumed to have been deposited completely. This
method may be adopted, for example, in the separation of
lead from cadmium, the former being roughly tested for
by sulphuric acid. If none of these methods is available,
the metal must be deposited to constant weight or else the
284 ELECTRO-ANALYSIS.
separation must be carried out under very carefully defined
conditions for a length of time proved more than sufficient
by previous experiment.
Interrupting an Experiment. A short time before
completing the analysis, the inside of the tube 6 , the sides
of the beaker, and the clock glasses are washed by the aid
of a wash-bottle and a few drops of liquid run out of the
connecting limb of the auxiliary electrode. To interrupt
the experiment, the auxiliary electrode and the clock glasses
are removed, the tripod is then taken from under the
beaker and the latter lowered until the surface of the
liquid is just below the outer electrode. During this time
the latter is washed. The stirrer is now stopped before
lowering the beaker any further. The latter is then re-
placed by a slightly larger one, the tripod put back and the
electrode again washed. It is then disconnected, shaken,
dipped first into a jar containing alcohol, shaken, then into
another containing ether, and then dried for about a minute
over a Bunsen burner. The collar A is carefully dried by
a silk cloth before weighing. The remaining liquid is
washed into the larger beaker and is then ready for the
deposition of the next metal.
When only one metal is contained in the solution under-
going analysis, it is simpler to stop the stirrer, take away
the beaker, and replace it by two successive ones containing
distilled water. In both cases the current is left on during
the process of interruption.
The beaker in which the first deposition of a separation
is carried out was only slightly wider than the electrode
and the amount of the liquid roughly 85 c.c. In the second
separation the amount was usually 130 c.c. and so on.
The rate of stirring varied very considerably from one
DETERMINATION OF THE HALOGENS. 285
experiment to another without greatly affecting the result.
It may be taken as having been between the limits of 300
and 600 revolutions per minute." Sand, J. Ch. S. (Lon-
don), 91, 374.
Consult also A. Fischer, Z. f. Elektrochem., 13, 469;
Z. f. angw. Ch., 20, 134 (1907).
4. DETERMINATION OF THE HALOGENS
IN THE ELECTROLYTIC WAY.
LITERATURE. Whit field, Am. Ch. Jr., 8, 421; Vortmann, Elek-
troch. Z., i, 137; 2, 169; E. Miiller, Ber., 35 (1902), 950; Specketer,
Z. f. Elektrochem., 4, 539; With row, J. Am. Ch. S., 28, 1356.
Whitfield proceeds as follows : The silver halide is col-
lected in a Gooch crucible and dried directly over a low
Bunsen flame. After weighing it is dissolved by intro-
ducing the crucible and asbestos into a concentrated po-
tassium cyanide solution. The silver is then deposited in
a platinum dish of 100 cm 2 surface with a current of 0.07
ampere. It is not advisable to work with more than 2
grams of silver halide.
Vortmann has developed an electrolytic scheme for the
direct determination of the halogens. As he has given the
most attention to 'iodine, its method of estimation will be
presented here.
To the aqueous solution of potassium iodide were added
several grams of Seignette salt and 16-20 c.c. of a 10 per
cent, solution of sodium hydroxide. The liquid was then
diluted to 150 c.c. and placed in a crystallizing dish or in
a platinum dish. If the first was used, then a platinum
disk, 5 cm. in diameter, was made the cathode, whereas
in the second instance the dish itself became the cathode,
'286 ELECTRO-ANALYSIS.
the anode being a circular plate of pure silver, 5 cm. in
diameter, or a plate of platinum of like size, coated with
silver. The electrolysis was made with a current of 0.03-
0.07 ampere and 2 volts. It was found expedient, after
several hours, to replace the anode coated with silver
iodide with another, and the electrolysis was continued
until the anode ceased to increase in weight. This change
in anodes is absolutely necessary when the quantity of
iodine exceeds 0.2 gram. The iodine may exist as iodide
or iodate. The alkaline tartrate is introduced to prevent
the silver iodide from becoming detached.
#. Determination of Iodine in the Presence of Bromine
and Chlorine.
The method is based on the fact that an iodide in the
presence of a soluble chromate in alkaline solution is oxi-
dized to iodate at a pressure insufficient for the conversion
of bromides and chlorides into their corresponding oxy-
salts. The iodate produced is estimated by titration with
thiosulphate, and the quantity of thiosulphate used by the
known amount of chromate present is then deducted. Chro-
mate, even in small amounts prevents reduction at the
cathode. Further, periodate is not produced. It is neces-
sary always to platinize anew the platinum cathode. A
pressure of 1.6 volts does not form bromate in a o.i to
o.oi normal solution, while all of the iodine is changed to
iodate. The following solutions were used in the analysis :
1. A potassium chromate solution, of which i cubic centi-
meter =10.6 c.c. i/ioo N thiosulphate solution.
2. Normal caustic potash.
3. Solution of potassium iodide, of which i cubic centi-
meter = 9.13 cubic centimeters i/ioo N silver
nitrate solution.
DETERMINATION OF THE HALOGENS. 28/
In determining iodine in the absence of the other halo-
gens mix: 2 cubic centimeters of solution i; I cubic centi-
meter of solution 2; 10 cubic centimeters of solution 3 and
90 cubic centimeters of water. Electrolyze for a peroid
of twenty hours with a pressure of from 1.6 to 1.61 volts.
Titration with sodium hyposulphite solution gave 0.11594
gram and 0.11632 gram of iodine instead of 0.1158 gram.
In the presence of chlorine, use :
2 cubic centimeters of solution i
i cubic centimeter of solution 2
1 cubic centimeter of solution 3 and
100 cubic centimeters of a saturated sodium chloride solution.
Time 20 hours, Volts 1.59 to 1.60.
Result: 0.01163 and 0.01167 instead of 0.1158.
In the presence of bromine use:
2 cubic centimeters of solution i
i cubic centimeter of solution 2
i cubic centimeter of solution 3 and
100 cubic centimeters of a normal potassium bromide solution.
Time, 22 hours. Pressure, 1.6 to 1.61 volts.
Results: 0.01158 and 0.01170 instead of 0.01158.
Test the reagents beforehand with potassium iodide and
sulphuric acid to ascertain whether they liberate iodine.
This often occurs with the alkali solutions of trade. The
anode must be wholly immersed in the solution, because
if iodine is separated directly at the surface, it readily
vaporizes. The point of contact of the conducting wire
with the solution should be covered with glass. Alkaline
earths should be absent.
b. Separation of the Halogens.
Metals have been separated by graded potential (Kiliani,
Freudenberg, etc.). This principle has been applied re-
cently to the halogens. In the hands of Specketer good
N
288 ELECTRO-ANALYSIS.
results have been obtained. The electrolysis is carried out
in sulphuric acid solution of normal concentration. The
method of conducting the experiment is briefly as follows :
Use a Giilcher thermopile. It possesses superior advan-
tages for this particular kind of work, as constancy of
current is an absolute necessity. The pressure of the form
used by Specketer was three volts. The vessel in which
the electrolysis is performed should be narrow and tall,
something like a measuring cylinder, so that nothing is
lost by spattering, occasioned by conducting hydrogen
through the electrolyte during the analysis, and in order
that the washing of the anode may be directly done in the
cylinder, the latter should be closed with a cork, carrying
the cathode of sheet platinum and an anode of silver gauze,
and sufficiently large to permit of the passage of a gas
delivery tube through it. The hydrogen finds its exit im-
mediately back of the cathode plate. A voltmeter should
be in circuit. The conclusion of the analysis is indicated
by a delicate Edelmann galvanometer so arranged that it
can readily be thrown in or out of the circuit. The salts
used were pure potassium chloride, bromide and iodide.
i. Separation of Iodine from Chlorine.
PRESSURE =. 0.13 volt.
a. IODINE USED. b. IODINE FOUND.
0.29087 gram 0.2992 gram
0.2394 gram 0.2386 gram
0.0481 gram 0.0480 gram
0.1543 gram 0.1532 gram
When the iodine was completely precipitated, the current
was interrupted, the anode washed off in the cylinder and
then dried at 120. The chlorine was determined in the
residual liquid by the Volhard method.
DETERMINATION OF NITRIC ACID. 289
2. Separation of Bromine from Chlorine.
PRESSURE = 0.35 volt.
a. BROMINE PRESENT. b. BROMINE FOUND.
0.19437 gram 0.1940 gram
0.2735 gram 0.2736 gram
0.1962 gram 0.1958 gram
0.1899 gram 0.1906 gram
The chlorine was again determined volumetrically.
3. Separation of Iodine from Bromine.
PRESSURE 0.13 volt.
a. IODINE PRESENT. b. IODINE FOUND.
0.1706 gram 0.1685 gram
0.1636 gram 0.1610 gram
0.2029 gram 0.2036 gram
It should be constantly borne in mind that to make these
separations successfully air must be absolutely excluded,
the source of current must be constant and a definite acid
concentration must be maintained.
5. DETERMINATION OF NITRIC ACID IN
THE ELECTROLYTIC WAY.
LITERATURE. Vortmann, Ber., 23, 2798; East on, J. Am. Chem.
S., 25, 1042 ; I ngham , J. Am. Ch. S., 26, 1251.
To the solution of the nitrate, in a platinum dish, add a
sufficient quantity of copper sulphate. Acidulate the
liquid with dilute sulphuric acid and electrolyze with a cur-
rent of o.i to 0.2 ampere. When the deposition of the
copper is completed, 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 determined
by the quantity of nitric acid present. If potassium nitrate
is the salt undergoing analysis, add half of its weight in
copper sulphate.
26
290- ELECTRO-ANALYSIS.
Easton gave the following as satisfactory conditions,
when using stationary electrodes : an equal weight of copper
nitrate and copper sulphate, 30 c.c. of sulphuric acid of
specific gravity 1.062, a dilution of 150 c.c., a platinum
anode, a cathode of lead or copper, or a platinum dish of
200 c.c. capacity, 0.15 to 3 amperes, 3 to 8 volts, and one
and a quarter to eight and one half hours.
The Rapid Determination of Nitric Acid With the Use
of a Rotating Anode.
This method has been most carefully elaborated by Leslie
H. Ingham in this laboratory. The results of his experi-
ments are given here in considerable detail.
Employ in this determination the apparatus described on
p. 72 in estimating copper.
Use the following solutions :
1. A fifth-normal solution of sodium carbonate. This
solution constitutes the basis of value of the subsequent solu-
tions.
2. A dilute solution of sulphuric acid, containing about
20 cubic centimeters of acid of specific gravity 1.84 in 4 liters
of water. Standardize this on the sodium carbonate solu-
tion.
3. A dilute ammonia solution, containing about 50 cubic
centimeters of ammonium hydroxide of specific gravity 0.95
in 4 liters of water. This is about equivalent in strength
to the standard acid solution. Obtain its exact ratio by
titration.
4. A solution of copper sulphate, containing about 80
grams of CuSO 4 .5H 2 O in 2 liters.
Six electrolytic determinations of the value of this solu-
tion were made, using the conditions : 25 cubic centimeters
of copper solution, 25 cubic centimeters of standard acid,
DETERMINATION OF NITRIC ACID.
125 cubic centimeters dilution, 5 amperes, 10 volts, ten
minutes, resulting in the following as the copper content of
25 cubic centimeters of the sulphate solution :
GRAM. GRAM.
0.2532 0.2530
0.2532 0.2536
0.2535 0.2534
The average of these values, or 0.2533 gram, was used.
The acid solution and the ammonium hydroxide solution
were now compared with each other and with the sodium
carbonate solution, litmus or methyl orange being used as
indicators. The average of eight concordant results is as
follows :
Ten cubic centimeters N/5 sodium carbonate = 10.22
cubic centimeters, sulphuric acid = 9.960 cubic centimeters
of ammonium hydroxide solution. As much as 50 cubic
centimeters were sometimes consumed in one titration and it
is believed that the results are correct for three figures at
least.
An additional independent standardization of the ammon-
ium hydroxide solution was made by titrating the sulphuric
acid liberated by the electrolysis of 25 c.c. of the copper
solution in the presence of 25 cubic centimeters of standard
acid. In the average of four concordant determinations the
total free acid, after electrolysis, was found to be exactly
neutralized by 64.42 cubic centimeters of the ammonium
hydroxide solution; deducting the 24.38 cubic centimeters,
which are equivalent to the 25 cubic centimeters of standard
acid present, there remain 40.04 cubic centimeters of am-
monium hydroxide used in neutralizing the sulphate, com-
bined with 0.2533 gram of copper. This gives a ratio of
N/5 sodium carbonate to the ammonium hydroxide solution
of 10 : 9.958, agreeing well with that obtained by direct titra-
tion.
292 ELECTRO-ANALYSIS.
Experimental Part.
Weigh off the desired quantity of potassium nitrate and
dissolve it in a small amount of water in a clean platinum
dish; then pipette from the stock solution the necessary
amount of copper sulphate and add a measured amount of
standard acid, sufficient to make the electrical resistance low
and to insure the solution remaining quite strongly acid dur-
ing the reduction of the nitrate.
Dilute to about 125 cubic centimeters and electrolyze with
about 4 to 5 a'mperes and about 10 volts. The exact condi-
tions are stated in a number of experiments in the appended
tabular exhibit.
During the course of the electrolysis the copper is de-
posited on the cathode and its equivalent of sulphuric acid
is liberated and added to the acid already present, whereby
the conductivity is increased and the pressure falls. As the
nitric acid is gradually reduced to ammonia the free acid
becomes neutralized and if the current be maintained con-
stant by the rheostat the pressure will gradually rise for
about twenty-eight minutes and then become stationary,
thereby indicating the end of the reduction. This rise is
usually from 5 to 7 volts, and the voltages given in the table
are those read at the outset of each experiment, to which the
above is to be added to obtain the final voltage.
Stop the motor, siphon off the liquid in the dish into a
beaker and replace it by distilled watef while the current
passes; the dish, anode and cover glasses are well washed,
the electrical current interrupted, and the washings added
to the liquid in the beaker. It is unnecessary to weigh the
deposited copper, so the platinum dish is merely rinsed with
nitric acid and washed under the faucet, when it is ready for
use again.
Rapidly neutralize the contents of the beaker, in the pres-
DETERMINATION OF NITRIC ACID. 293
ence of litmus or methyl orange by the standard ammonia
solution from a burette. The indicators named were found
to give identical results. Note that in the reaetion of reduc-
tion one molecule of potassium nitrate gives rise to a mole-
cule of potassium hydroxide and one of ammonia; hence
two equivalents of alkali are produced from one equivalent
of nitrate, and allowance must be made for this by having
the results obtained by titration. The use of a o. 5-gram
sample for analysis just offsets this. The calculation of the
standard ammonia solution to its equivalent of N/5 sodium
carbonate solution and thence to nitrogen is obvious.
To learn the best conditions a number of experiments may
here be introduced from a notebook.
(a) Time. The first ten experiments were made with
reference to the time of reduction. Using 25 cubic centi-
meters of copper sulphate solution, 25 cubic centimeters of
acid solution and 0.5 gram of nitrate, 5 amperes gave 5.63
per cent., 9.83 per cent., 9.91 per cent., and 11.26 per cent,
of nitrogen respectively in ten, fifteen and twenty minutes,
the theoretical percentage of nitrogen in potassium nitrate
being 13.86.
Increasing the time, with 4 amperes, gave 13.64 per cent,
in twenty-five minutes and 13.83 per cent, in thirty minutes.
(b) Amount of Copper Sulphate. The above results
were obtained with 25 cubic centimeters of copper sulphate.
Two experiments with 50 cubic centimeters gave 8.79 per
cent, in twenty minutes and 12.96 per cent, in thirty min-
utes, showing that the increased amount of copper is not an
advantage. Two experiments with but 15 cubic centimeters
of copper sulphate solution and 30 c.c. of standard acid
resulted in a reduction of 11.93 per cent, and 13.55 per cent,
in twenty and thirty minutes respectively. Increasing the
amount of acid to 50 cubic centimeters with the same
294 ELECTRO-ANALYSIS.
amount of copper gave better results, viz., 13.10 per cent,
and 13.83 per cent, in twenty and thirty minutes respectively.
(c) Strength of Current. An experiment with 5
amperes gave 13.38 per cent, of nitrogen in twenty-five
minutes, while 6 amperes gave only 13.19 in twenty minutes.
From this it appears that 4 amperes is sufficient current,
since that will yield complete reduction in thirty minutes and
more current will not do the work in less time.
(d) Speed. Two experiments with the speed of rota-
tion of the anode increased to about 560 revolutions per
minute gave 12.91 per cent, and 13.19 per cent, in twenty
and thirty minutes respectively; the voltage needed was 40,
since the contact between the anode and the liquid was poor
at this velocity. So much heat was produced that .the
liquid boiled freely, but no advantage in increased speed
was found.
?
The results and detailed conditions of this work are found
in the subjoined tabular exhibit. They indicate that the con-
ditions of Experiment 8 are to be preferred. To confirm
this a series of ten determinations was made in accordance
with these conditions, namely, 25 cubic centimeters of cop-
per sulphate solution, representing 0.2533 gram of metallic
copper, 25 cubic centimeters of the standard sulphuric acid,
0.5 gram of potassium nitrate, 4 amperes, 10 volts at the
outset, or 17 volts at the end of reduction, slowest speed and
thirty minutes. The dish was not warmed at the outset of
the experiment, nor was external heat applied during elec-
trolysis, although the liquid was considerably warmed by
the current, the final temperature being about 65 C. This
continuous series was made in a single afternoon and no
results were rejected; consequently the latter may be taken
to represent the probable error of the method.
DETERMINATION OF NITRIC ACID.
295
The following are the percentages of nitrogen found, the
theoretical value being 13.86:
PER CENT.
13.81
13-79
13-83
13-83
13-94
PER CENT.
13-86
13-92
13.92
13-86
13-89
Mean of the series of ten, 13.865.
TAKEN.
CONDITIONS
CALCULATION.
o
K
H
H
**
H
c/i
y
a
Q
<! < H
Q
W
o o
" w
H (/i
*P
3
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t> "Z.
a
u
<
||
|
i
[INUTI
Q g <
lit
*
a u a
H Jj
< H<
az z
g H Q 5
h z
O &
x
COPPER Si
SOLUTIOJ
Ij
fe
STANDARD
X
1
o
a
s
S
H
(3***
u
AMMONIA
EQUIV.'
TO CO
AMMC
EQUIVAL
STANDAR
g ^ H
U < u
u > J W
i|3 d
PERCENTA
GKN
NUMBER o
25
0.5000
25
0-2533
12
5
IO
44-5
4O.O
24.4
19.9
20. i
5.63
I
25
0.5000
25
0-2533
12
5
15
29-5
40.0
24.4
34.9
35.1
9.83
2
25
0.5000
25
0-2533
12
5
15
29.2
40.0
24.4
35-2
35-4
9.91
3
25
0.5000
25
0-2533
12
5
2O
24-4
40.0
24.4
40.0
40.2
11.26
4
25
0.5000
25
0-2533
8
3
2O
32.4
40.0
24.4
32.0
32.2
9.O2
5
25
0.5000
25
0-2533
IO
4
2O
15.9
40.0
24.4
48.5 48.7
13.64
6
25
0.5000
25
0.2533
IO
4
25
15.9
40.0
24.4
48.5
48.7
13.64
7
25
0.5000
25
0-2533
9
4
30
15.2
40.0
24-4
49-2
49 4
13.83
8
25
0.5000
25
0-2533
9
4
30
15-4
40.0
24.4
49.0
49-2
13.78
o
25 0.5000
25
0.2533
9
4
30
15.5
4O.O
24.4
48.9
49-1
13-75 10
50 0.5000
25
0.5066
10
4
20
73-2
80.0
24.4
31-2
3L4
8-79,11
50 0.5000
25
0.5066
10
4
30
58.3
80.0
24.4
46. i
46-3
12.9612
15
o 5000
3
0.1520
10
4
20
10.9
24.O
29-3
42.4
42.6
II 93113
15
0.5000
30
o. 1520
10
4
30
5* i
24.O
29.3
48.2
48.4
13.55 H
15
0.5000
50
o. 1520
10
4
20
26.2
24.0
48.8
46.6
46.8
13.1015
15
o. 5000
50
0.1520
IO
4
30
23.6
24.0
48.8
49-2
49-4
13.83 16
15
0.5000
50
0.1520
16
6
2O
25-9
24.0
48.8
46.9
47.1
13.19 17
15
0.5000
0.1520
12
5
2 5
25-2
24.O
48.8
47 6
47-8
13.3818
25
0.5000
25
0.2533
40
4
2O
18.5
4O.O
24-4
45-9
46.1
12.91 19
25
0.5000
25
0.2533
40
4
30
17-5
4O.O
24.4
46.9
47-i
13.19 20
This method for the determination of nitrates compares
quite favorably with other methods in point of accuracy.
Its advantages in simplicity and speed are worthy of care-
296 ELECTRO-ANALYSIS.
ful consideration, as a complete determination of the nitric
acid content of an alkali nitrate may be made in thirty-five
minutes from the time of weighing off the sample.
Recent experiments, made in this laboratory, have dem-
onstrated that to determine the nitric acid content of such
salts as zinc nitrate, cobalt nitrate, nickel nitrate, etc., it
is advisable to precipitate the metal with sodium carbonate,
filter out the precipitate and electrolyze the filtrate contain-
ing the sodium nitrate.
6. SPECIAL APPLICATION OF THE ROTAT-
ING ANODE AND MERCURY CATHODE
IN ANALYSIS.
Determination of both Cations and Anions.
In the preceding pages numerous examples have been
given of the determination of metals with the help of the
simple device pictured (Fig. 17) on p. 58. Under copper,
for instance, it is suggested that the student perform the
analysis of copper sulphate, depositing the metal in the
mercury, then siphoning off the colorless solution into a
beaker and determining the acid by titration with a N/io
solution of sodium carbonate. To this it may be added
that no more satisfactory method can be adopted in the
analysis of zinc sulphate. Both constituents can be rapidly
and accurately estimated. In the ordinary gravimetric
determination of the sulphuric acid content of white vitriol
the precipitate of barium sulphate is very apt to contain
zinc, so by this electrolytic procedure the analyst gains great
advantage. The simplicity of the procedure appeals strongly
to those who are called upon to perform analyses of salts
DETERMINATION OF CATIONS AND ANIONS. 297
like those just mentioned. Indeed, any soluble metallic
sulphate may be analyzed in this manner. The results have
been most satisfactory. When the method was first applied
to them, the anode was stationary (J. Am. Cherri. S., 25,
883); subsequently it was rotated (p. 58) (J. Am. Chem.
Soc., 26, 1614; Am. Phil. Soc., Pr. XLIV, 137 (1905);
J. Am. Chem. S., 27, 1527; Myers, J. Am. Ch. S., 26,
1124.).
Having reached a high degree of success in the analysis
of sulphates in the direction outlined in the preceding para-
graphs, it occurred to the writer that possibly chlorides
might be analyzed equally well in this way if provision were
made to catch or fix the chlorine ions. Accordingly, a
solution of sodium chloride was subjected to decomposition
in the little cup (Fig. 17, p. 58). The anode consisted
of a silver-plated strip of platinum, which later was replaced
by a weighed, silver-coated platinum gauze suspended in
the aqueous solution (40 c.c.) of the sodium chloride.
Almost immediately the silver, on passage of the current,
began to darken in color from the lower edge of the gauze
upwards. When this ceased, the decomposition was as-
sumed to be at an end, whereupon the gauze was raised
from the solution, rinsed with water and further washed
with alcohol and ether. It was weighed after drying for
a short time. For the gauze a platinum spiral was sub-
stituted in the residual liquor in the beaker ; the current was
reversed, the layer of mercury being made the anode, when
the sodium was rapidly driven into the water. All this
occupied about twenty minutes, after which the alkaline
liquor was titrated with standardized acid.
A solution of salt, containing 0.0606 gram of chlorine
and 0.390 gram of sodium gave:
298 ELECTRO-ANALYSIS.
No. C GRAM. Na GRAM
I 0.0606 0.0389
2 0.0610 0.0384
Six hours were allowed for the decomposition. The cur-
rent showed 0.0325 to 0.03 ampere and 2 volts.
On electrolyzing a solution of barium chloride, in the
same way, there were obtained :
Ba Cl Ba Cl
PER CENT. PER CENT. PER CENT. PER CENT.
55.87 28.69 instead of 56.14 29.09
56.07 29.31
Strontium bromide was analyzed with just as much suc-
cess. The same is true of other halides. Indeed, both
sodium chloride and barium chloride were electrolyzed suc-
cessfully without the use of the mercury cathode. A flat,
platinum spiral was made to take its place. The alkaline
liquors, observing proper current conditions, did not inter-
fere with the deposition of the halogen upon the silver gauze.
In the preceding example the time factor was somewhat
prolonged and difficulty was experienced in determining the
end of the reaction. Hildebrand, working in this labora-
tory, found that in spite of the extreme care in keeping the
mercury and the interior of the cell absolutely clean so as
to minimize secondary decomposition of the amalgam some
caustic was formed and after the halide had been completely
decomposed it was possible to increase the weight of the
gauze indefinitely by the production of silver oxide from the
electrolysis of the caustic. To learn the end of the decompo-
sition the following scheme was pursued : the gauze was
suspended, at the beginning of the operation, within about
5 mm. of the surface of the mercury and the liquid so
diluted as to cover only about one-third of the gauze. The
pressure (voltage) was kept constant during the electrolysis
DETERMINATION OF CATIONS AND ANIONS.
299
so that the fall in current strength, as the action progressed,
indicated the completeness of the decomposition. When
it reached from 0.005 to 0.02 amperes, the liquid level was
raised a few millimeters from time to time, and as soon
as the fresh surface showed the formation of brown silver
oxide which could easily be distinguished from the bluish
chloride the gauze was removed, immersed in alcohol,
then in ether, dried and weighed. This procedure gave con-
secutive concordant results. In every case the amalgam
was washed into a beaker and, after it had decomposed, the
alkali was titrated with tenth normal sulphuric acid, using
methyl orange as an indicator.
Analysis of Sodium Chloride.
The following table shows the results obtained for this
salt. The current in amperes, at the beginning and end of
each decomposition, is given in the third column.
SODIUM IN GRAMS.
CHLORINE IN GRAMS.
TIME.
Vni T^
.
MINUTES.
, V OL T S.
AMPERES.
PRESENT.
FOUND.
PRESENT.
FOUND.
J 35
3-5
.o8-.oi
0.0460
0.0461
0.0708
0.0713
2IO
3-5
.09-. 003
0.0460
0.0456
0.0708
o 0706
1 S
3-5
.20-. 005
0.0460
0.0460
0.0708
o.o;o6
22O
3-5
.24-. 005
0460
o 0458
0.0708
00705
2OO
3-5
.21-. 005
0.0460
0.0462
0.0708
0.0709
1 2O
3-5
.i6-.oi
o. 0460
0.0459
0.0708
0.0712
130
3-5
.20-. 02
0.0460
0.0461
0.0708
0.0705
70
3-5
.I5-.04
0.0460
0.0459
0.0708
0.0707
&s
.14-. 03
0.0460
0.0463
0.0708
0.0711
3-5
.I3-.02
0.0460
0.0463
0.0708
0.0710
The deposits were perfectly adherent in character unless
the silver coating was too thin. No attempt was made to
protect it from the light, so that the deposits both here and
with other substances were always very dark colored; in
300
ELECTRO-ANALYSIS.
fact, with several other salts if the silver salt was formed
so rapidly as to show its true color at places, it was often
not very adherent.
Analysis of Sodium Bromide.
SODIUM IN GRAMS.
BROMINE IN GKAMS.
TIME.
VOLTS
A
MINUTES.
AMPERES.
PRESENT.
FOUND.
PRESENT.
FOUND.
60
4-0-3-5
.13-. 02
.0232
' -0235
.0804
*
.0794
45
4.0-3.5
.IJH.OS
.0232
.0237
.0804
.0806
50
3-5
.12-. 03
.0232
.0231
.0804
.0806
100
3.5
.i3-.oi
.0232
.0237
.0804
.0812
60
3-5
.I2-.05
.0232
.0238
.0804
.0804
3-5
.09
.0232
.0230 .0804
.0805
Analysis of Sodium Iodide.
TIME.
MINUTES.
VOLTS.
AMPERES.
SODIUM IN GRAMS.
IODINE IN GRAMS.
PRESENT.
FOUND.
PRESENT
FOUND.
70
70
45
4 -3-5
3.5
3.5-3
.10-. 02
.05-.OI
.10-. 02
.0154
.0154
.0154
.0156
.0156
.0154
.0850
.0850
.0850
.0850
.0857
.0845
Analysis of Potassium Sulphocyanide.
This salt proved more troublesome because the potassium
amalgam usually started to decompose rapidly near the
end of the electrolysis.
POTASSIUM IN GRAMS
CNS IN GRAMS.
TIME.
VOLTS
.
PERES.
MINUTES.
PRESENT.
FOUND.
PRESENT.
FOUND.
45
3-5
.IO-.O6
0375
.0371
.0558
.0558
120
3-5
.o7-.o 4
0375
0379
.0558
.0560
105
4-3-5
.IO-.OI
0375
0379
.0558
.0560
135
3-5
.06-. oi
0375
0375
0558
.0566
65
4-3-5
.09-. oi
0375
.0373
.0558
0553
DETERMINATION OF CATIONS AND ANIONS. 3OI
It was soon after found that silver ferro- and ferri-
cyanides could be formed and, what seemed still more re-
markable, silver carbonate. In the last instance the decom-
position was complete, there being no traces of carbon
dioxide liberated at the anode. The deposit, afterwards
immersed in dilute sulphuric acid, liberated carbon dioxide
with effervescence. However, it was impossible to make
these depositions quantitative, because the silver salts were
not very coherent and at the edge of the gauze near the
mercury, where the deposit was thick, part of it always
became detached.
The difficulty here mentioned was overcome by devising
a new anode. This consisted of two circular disks of plati-
num gauze 5 cm. in diameter and having 300 meshes per
square centimeter. The circumference was slightly fused
in the blowpipe. These were mounted 5 mm. apart on a
stout platinum wire i mm. in diameter and 10 cm. long
which passed through the centers of the disks perpendicular
to them. Each disk was attached to this axial wire by
means of two smaller wires fitting tightly into two adjacent
holes drilled at right angles to each other through the large
wire. These anodes weighed about 16 grams apiece. The
total surface of each pair of disks is about 100 sq. cm. which
is at least doubled when coated with several grams of silver.
These anodes were always supported when not in use by
fastening the axis in a clamp so that the gauze might not
come in contact with anything which might bend it. In
order to suspend them from the balance beam in weighing, a
loop of fine platinum wire was soldered to each axial wire
about 2 cm. from the top.
Silver Plating the Anode. In plating the anodes with
silver the rotator was always used, as a coating from 3 to 4
grams of silver could thus be deposited. A number of de-
302 ELECTRO-ANALYSIS.
terminations could then be made without replating the gauze,
the deposited silver chloride being merely dissolved off by
immersing for a few moments in potassium cyanide, thus
exposing a fresh surface of silver. The plating was done
in a beaker, the anode being a platinum wire passing
through a glass tube to the bottom of the beaker where it
was bent into a flat horizontal spiral. A strong stock solu-
tion of silver potassium cyanide was kept in a bottle and
portions added to the beaker from time to time as the sil-
ver in the electrolyte was deposited. No particular care is
necessary in this plating as the conditions may be varied
rather widely without injuring the deposit; about 5 volts
and i to 2 amperes were the ordinary conditions. When
the coating was sufficiently heavy the gauze was removed,
washed by immersing in distilled water, followed by alco-
hol and ether.
To avoid the necessity of centering the anode each time
it was placed in the rotator, a small piece of copper foil was
rolled into a cylinder about the axis of the anode and then
put permanently into the tip of the rotator. The anode was
thus always centered when put in position.
The Cell. In principle it resembles the Castner-Kellner
process for caustic soda, the amalgam being formed in one
compartment and decomposed in another. The outer cell
is a crystallizing dish n cm. in diameter and 5 cm. deep.
Inside of this is a beaker 6 cm. in diameter with the bottom
cut off and the edge rounded so that a ring is formed 4.5 cm.
high. This rests on a large Y of thin glass rod on the
bottom of the crystallizing dish and is kept in position by
three rubber stoppers fitting radially between it and the
inside of the dish. In the outer compartment thus formed
there is a ring of about six turns of nickel wire provided
with three legs which are fastened to the ends of the glass Y
DETERMINATION OF CATIONS AND ANIONS. 303
and serve to support the ring about i cm. above the surface
of the mercury when sufficient of the latter is poured in
FIG. 39-
to seal off the two compartments. The cell and anode are
shown in Fig. 39.
3C4
ELECTRO-ANALYSIS.
In using this cell, which must be kept scrupulously clean,
pure clean mercury is poured in so that its level is about 3
mm. above the lower edge of the bottomless beaker. The
solution to be electrolyzed is then put into the inner com-
partment; into the outer is placed enough distilled water to
cover the nickel wire, and to this is- added a cubic centimeter
of a saturated solution of common salt. By this arrange-
ment the amalgam formed in the inner compartment is im-
mediately decomposed in the outer, which acts as a cell
whose elements are amalgam-sodium chloride-nickel wire.
The sodium chloride serves merely to make the liquid a con-
ductor so that the action may proceed more rapidly at the
beginning. Without this scheme the amalgam is not en-
tirely decomposed in the outer compartment as pure water
does not attack it rapidly enough to prevent a partial decom-
position in the inside cell. The mercury is connected with
the negative pole of the battery by means of the glass tube
bearing the copper and platinum wires described above,
which dips into the outer compartment. After the electrol-
ysis is complete the entire contents of the cell are poured
into a beaker, the cell rinsed and the alkali titrated. After
titration the mercury is washed, the water decanted and the
metal poured into a large separatory funnel, from which it
can be drawn off clean and dry. To show how well this
new arrangement of anode and new cell worked in the
analysis of sodium chloride the following results attest :
TIME.
MINUTES
VOLTS.
AMPERES.
SODIUM IN GRAMS.
CHLORINE IN GRAMS.
PRESENT.
FOUND.
PRESENT
FOUND.
30
4.0-2.5
.50-02
.0461
0459
.0708
.0704
45
3-5-2-5
.34-01
.0461
.0708
.0706
40
3 5-3-0
.50-01
.0461
.0708
.0704
45
4-0-3-5
.65-01
.0461
.0708
.0716
3
4.0-2.5
.76-02
.0461
.0708
0713
55
3-0
. 26-O2
.0461
.0708
.0709
DETERMINATION OF CATIONS AND ANIONS.
305
Thus far the anode has remained stationary. Hence-
forth, all results given will be those obtained with the help
of the rotating 1 anode.
The weighed gauze anode should be clamped 'to the shaft.
Lower the latter in the cell till the lower gauze is about 5
mm. from the surface of the mercury. Adjust the motor
and the belt, start the motor and turn on the electrolyzing
current. The most convenient speed for the motor would
be about 300 revolutions per minute.
Do not wash the anode after the salt is decomposed as the
water remaining is pure. This avoids any loss by the usual
washing in water, alcohol and ether, although the two may
be used where it is desired to still further reduce the time.
Dry the gauze over a steam radiator.
Analysis of Sodium Bromide.
Let the dilution of the salt solution be about 25 cubic
centimeters. Only the lower gauze needs to be immersed
as it will afford surface sufficient for the quantity of bromide
generally used in experiments.
RESULTS.
TIME.
MINUTES.
VOLTS.
AMPERES.
SODIUM IN GRAMS.
BROMINE IN GRAMS.
PRESENT.
FOUND.
PRESENT.
FOUND.
30
30
5-
5-o
.65-.OI
.65-.OI
0231
.02JI
0233
0233
.0800
.0800
.0798
.0802
Analysis of Sodium Carbonate.
In this determination it is well to have the silver anode
surface slightly roughened. This can be obtained by stop-
ping the rotator several minutes before removing the gauze
anode from the silver plating bath.
27
306
ELECTRO-ANALYSIS.
RESULTS.
SODIUM IN GRAMS.
CO 3 IN GRAMS.
MINUTES.
VOLTS.
AMPERES
PRESENT.
FOUND
PRESENT.
FOUND.
60
3-5-5-0
.i5-.oi
-0323
.0325
.0420
.0416
90
4.0-5.0
. 15-. 01
0323
.0324
.0420
.0419
50
5-o
.65-.oi
.0346
0349
.0450
.0448
70
3-5-5-0
.15-01
.0346
.0450
.0447
In this instance the easiest way to clean the gauze is to
ignite it gently instead of the usual washing with potassium
cyanide, water and then drying.
Analysis of Potassium Ferrocyanide.
TIME.
MINUTES.
VOLTS.
AMPERES.
POTASSIUM IN GRAMS.
Fe(CN) 6 IN GRAMS.
PRESENT.
FOUND.
PRESENT.
FOUND.
30
4.0-4.5
.i5~.oi
.0391
.0384
.0531
053 1
30
3 0-5.0
.i5-.oi
.0391
.0389
0531
0532
30
4.0-5.0
.2O-.OI
.0391
.0387
.0531
.0527
Analysis of Potassium Ferricyanide.
POTASSIUM IN GRAMS.
Fe(CN) 6 IN GRAMS.
TIME.
MINUTES.
VOLTS.
AMPERES.
PRESENT.
FOUND.
PRESENT.
FOUND.
35
2 -5
.20-.OI
.0392
.0710
.0714
30
4 -5
.40-. oi
.0392
.0389
.0710
.0712
40
4-5-5
.3o-.oi
.0392
.0389
.0710
.0713
Analysis of Trisodium Phosphate.
Trisodium phosphate gave a deposit which was satis-
factory at 4 volts but not completely adherent at 5 volts
The lower voltage and the smaller conductivity made a
longer time necessary to get out the last traces. To avoid
this, in the last two determinations a second anode was used
near the end to receive these traces.
DETERMINATION OF CATIONS AND ANIONS.
307
SODIUM IN GRAMS.
l'O 4 IN GRAMS.
TIME.
MINUTES.
VOLTS.
AMPERES.
PRESENT.
FOUND.
PRESENT.
FOUND.
75
5-4
50
0343
0343
.0472
0473
120
4
30
0343
0343
.0472
.0468
60
4
30
0343
.0340
.0472
.0470
70
4
.40
0343
.0472 .0478
See Hiklebrancl, J. Am. Ch. S., 29, 447.
Finding that halides of the alkali metals were so readily
analyzed in the manner outlined, it was but a step to the
application of the same procedure to the alkaline earth
metals. The appended results were obtained, in this labora-
tory, by. Hiram S. Lukens and Thos. P. McCutcheon, Jr.
Thus, on dissolving a definite amount of barium chloride
in water and electrolyzing with a current of 0.3 ampere
and 2.5 to 3 volts, it was discovered that as much as 0.2
gram of metal and its equivalent of halogen could be readily
determined in from thirty to forty minutes.
EXAMPLES.
BARIUM PRESENT.
BARIUM FOUND.
CHLORINE
PRESENT.
CHLORINE FOUND
0.2277 gram
0.2276 gram
0.1180 gram
0.1177 gram
0.2274
0.1178
0.2277
o. 1181
0.2278
0.1180
0.2277
o. 1180
0.2277
0.1181
The bromide was used in the determination of strontium.
The conditions were those used under barium chloride.
308 ELECTRO-ANALYSIS.
EXAMPLES.
STRONTIUM PRESENT. STRONTIUM FOUND.
0.0727 gram 0.0725 gram
0.0727 gram
0.0727 gram
0.0726 gram
0.0725 gram
The barium and strontium amalgams passed freely into
the outer dish and there quickly decomposed.
Upon electrolyzing a solution of pure magnesium chloride
large quantities of magnesium hydrate were formed in the
inner dish or compartment, while not a trace of magnesium
could be detected in the outer compartment.
Mixtures of calcium chloride and magnesium chloride,
consisting of one half as much magnesium as calciu'm or of
equal amounts, gave like results. Not even traces of calcium
or magnesium were found in the outer dish, provided the
current did not exceed 3.5 to 4 volts.
Separation of Sodium from Calcium and Magnesium.
As the amalgams of calcium and magnesium decomposed
so easily, it was thought that this separation could be made.
Accordingly the chlorides of the three metals were dissolved
in water and the solution placed in the inner dish. It was
then exposed for a period of fifty minutes to the action of a
current of 0.25 ampere and 3.5 volts.
Calcium present in grams 0.0222
Magnesium present in grams 0.0210
Sodium present in grams 0.0474
Sodium found in grams 0.0471
Sodium found in grams 0.0474
Sodium found in grams 0.0476
Sodium found in grams 0.0474
DETERMINATION OF CATIONS AND ANIONS.
309
Separation of Potassium from Calcium and Magnesium.
Using like amounts of calcium and magnesium in the form
of chlorides, and substituting potassium chloride for sodium
chloride, while applying the same current as in the preceding
separation, the following quantities of potassium were found
in the outer dish :
GRAM.
0.0582
0.0583
0.0580
GRAM.
0.0579
0.0580
0.0580
The quantity of potassium present equaled 0.0580 gram.
Separation of Barium from Calcium and Magnesium.
Dissolve the chlorides in 30 cubic centimeters of water,
add one drop of hydrochloric acid (i : 10) to this solution
and electrolyze with a current of 0.3 ampere and 3.5 to 4
volts for a period of seventy-five minutes.
EXAMPLES.
BARIUM PRESENT
IN GRAMS.
CALCIUM PRESENT
IN GRAMS
MAGNESIUM
PRESENT IN
GRAMS.
BARIUM FOUND
IN GRAMS.
0.0455
0.0222
0.0210
0.0456
0.0455
0.0454
0.0454
0.0455
0.0454
0.0454
o.o
910
0.0910
0.0911
0.0910
0.0912
0.0910
When calcium and magnesium are present together as
chlorides their electrolysis leads to amalgam formation.
3IO ELECTRO-ANALYSIS.
These amalgams, however, decompose in the inner cell,
forming hydroxides. Under such conditions, viz., the
presence of magnesium and working with a pressure not
exceeding five volts, the calcium is retained within the inner
cell. The separation of barium from calcium and mag-
nesium was thus made possible, as previously outlined. If,
however, calcium chloride be subjected to a higher pressure
(8 volts), it will be fully decomposed, the chlorine attach-
ing itself to the silver-plated anode and the metal forming
an amalgam, passing into the outer dish or compartment.
Numerous determinations proved this.
Electrolysis of a Mixture of Barium, Calcium and
Magnesium Chlorides.
Let the solution contain 0.0691 gram of barium, 0.0278
gram of calcium and 0.0220 gram of magnesium. Electro-
lyze the solution, after the anode has begun to rotate, with
a pressure of 3.5 volts. In two hours the barium amalgam
will have formed and completely decomposed to hydrate,
in the outer compartment. Titrate this hydrate, then in-
crease the pressure to 9 volts, the current ranging from
0.30 to 0.02 ampere. In three hours the calcium will be
completely removed to the outer cell, and may there be
titrated with tenth normal acid. One illustration of the
results from a solution, constituted as above indicated,
showed the barium found to be 0.0691 gram, the calcium
0.0276 gram, leaving of course as residuum the quantity
of magnesium originally added.
Consult also Coehn and Kettembeil, Z. f. anorg. Chem.,
38, 198 tO 2T2.
Separation of Strontium from Calcium and Magnesium.
Use the conditions given in the separation of barium
from the same metals. Results like the following were
obtained.
DETERMINATION OF CATIONS AND ANIONS. 3 I I
STRONTIUM PRESENT IN GRAMS. STRONTIUM FOUND IN GRAMS.
0-0565 0.0563
0-0565 0.0565
0.0565 0.0564
0-0565 0.0565
0.0565 0.0566
0-0565 0.0565
Barium from Magnesium.
Use the chlorides in water solution. Let the current
equal 0.3 ampere and 3.5 volts. The anode should per-
form 300 revolutions per minute. The current will not
fall below 0.03 ampere, due to the traces of magnesium
hydrate which have passed into solution. Several results
show the accuracy of the method.
BARIUM PRESENT
MAGNESIUM PRESENT
I>ARIUM FOUND
IN GRAMS.
IN GRAMS.
IN GRAMS.
0.0455
0.0358
0-0455
0.0455
0.0358
0.0456
0.2277
0.0358
0.2277
0.2277
0.0358
0.2277
Strontium from Magnesium.
Use the same conditions as were employed in the pre-
ceding separation.
Barium from Iron.
Electrolyze the solution of the chlorides as neutral as
possible with a current of 0.3 ampere and 3 to 5 volts for
a period of fifty minutes. The iron amalgam decomposes
at once within the inner compartment, forming ferric hy-
drate, while the barium amalgam passes into the outer cup
and rapidly decomposes there. The results were most
satisfactory.
Strontium, Potassium and Sodium may be similarly
separated from Iron. The results in all instances were
excellent.
3 I 2 ELECTRO-ANALYSIS.
Barium, Strontium, Potassium and Sodium were, with
conditions like those given under barium from iron, sepa-
rated most satisfactorily from Aluminium.
Sodium from Uranium.
Use the chlorides, apply a current of 3.5 volts and 0.3
to 0.02 ampere. The time is usually three hours. The
chlorine collects on the silver-plated anode. The inner
compartment will be filled with yellow colored uranium
hydroxide which gradually assumes a black color. The
sodium hydroxide, formed in the outer dish or compart-
ment, should be titrated with tenth normal hydrochloric
or sulphuric acid, using methyl orange as an indicator.
Sometimes it is more convenient to remove the anode when
the decomposition is finished, siphon out the liquid and the
hydroxide formed there, wash out the inner compartment
thoroughly with pure water, then pour the contents of the
cell into a large beaker, and there make the titration with-
out the slightest difficulty.
Potassium and lithium may be separated, under like
conditions, from uranium. When making the separation
of lithium use a current of 0.3 to o.oi ampere and 5 volts.
Time one hour.
Barium from Uranium.
This separation may be made in one hour by employing
a current of 1.5 to o.oi amperes and 5 volts. It is well
to acid a definite volume of tenth normal hydrochloric acid
to the water in the outer dish. Any barium hydroxide or
carbonate that might form there is at once dissolved and
at the conclusion of the experiment it is only necessary to
titrate the residual acid.
In separating strontium from uranium follow the pre-
DETERMINATION OF CATIONS AND ANIONS. 313
ceding plan and use a current of 0.4 to 0.02 ampere and 5
volts. Two hours will suffice for the separation.
With a current varying from 0.4 to o.oi ampere and a
pressure of 4 to 5 volts, it is possible, using chlorides, to
separate barium completely, in a period of two hours, from
cerium, lanthanum, neodymium, thorium and titanium.
The amalgams of the rare earth metals form hydroxides at
once -in the inner cell, while the barium amalgam, passing
into the outer compartment, there decomposes. Consult
also Kettembeil, Z. f. anorg. Ch., 38, 213.
The Analysis of Sodium Sulphide.
Coat the platinum disks with cadmium, then carefully
dry, weigh and suspend them in the aqueous solution of a
known amount of sodium sulphide. Use a current of o.i
to 0.03 ampere and 3.5 volts. In fifteen minutes the an-
alysis will have been completed. At first the solution in
the inner cup will assume a yellow color. After a few
minutes, however, it will be colorless. In a sample con-
taining 0.0253 gram of sulphur there was found :
0.0252 gram of sulphur
0.0252 gram of sulphur
0.0251 gram of sulphur
The deposit of cadmium sulphide is very adherent. It
should be dried at about 115 C., before weighing.
In the analysis of alkaline fluorides the anode disks may
be coated with calcium hydrate. On electrolyzing sodium
fluoride the halogen will attach itself to the calcium hy-
drate on the anode, forming there an adherent layer of
calcium fluoride. The alkali metal will pass out into the
larger compartment of the cell, decomposing to hydroxide
and be there titrated. Numerous decompositions have
28
314 ELECTRO-ANALYSIS.
been successfully made in this laboratory, but as the study
is still in progress, this mere mention will be here made.
7. OXIDATIONS BY MEANS OF THE
ELECTRIC CURRENT.
LITERATURE. Smith, Ber., 23, 2276; Am. Ch. Jr., 13, 414; Frankel,
Ch. N., 65, 64.
When natural sulphides, e. g., chalcopyrite, marcasite,
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 sul-
phuric acid (Jr. Fr. Ins., April, 1889; Ber., 22, 1019).
The metals (iron, copper, etc.) originally present in the
mineral separate as oxides and metal on dissolving the
fused alkaline mass in water. This method of oxidation
eliminates many other disagreeable features of the old
methods. Its rapidity and accuracy entitle it to the fol-
lowing brief description :
Place about 20 grams of caustic potash in a nickel
crucible ii inches high and if inches wide. Apply heat
from a Bunsen burner until the water has been almost en-
tirely expelled, when the flame is lowered so that the tem-
perature is just sufficient to retain the alkali in a liquid
condition. The crucible is next connected with the nega-
tive 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, ex-
OXIDATIONS BY MEANS OF ELECTRIC CURRENT. 315
tends a short distance below the surface of the fused mass.
When the current passes, a lively action ensues, accom-
panied with some spattering. To prevent 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. Invaria-
bly examine the residue for sulphur by dissolving it in
nitric acid 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 hydro-
chloric 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 ap-
pearance as a white turbidity. The caustic potash em-
ployed in these oxidations 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 de-
ducted from that actually found in the analysis.
The arrangement of apparatus employed in the oxida-
tions just outlined is represented in Fig. 40. 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 bind-
ing 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
316
ELECTRO-ANALYSIS.
OXIDATIONS BY MEANS OF ELECTRIC CURRENT. 3 I/
enclose unattacked sulphide, so that by reversing the
current (the poles) any precipitated metal will be detached,
and the enclosed sulphide be again brought into the field
of oxidation. Cinnabar is a sulphide which has a tendency
to mass together, and it could only be decomposed and its
sulphur thoroughly 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 (.v) in it contain a few drops of mercury, into
which the side binding screws (a) project. The mercury
cups are made to communicate with each other by a cap of
wood, D, carrying two 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 ( * ) or
horizontal ( >), the crucible or the platinum wire extend-
ing into the fused mass can be made the anode or cathode
in a few seconds. is a Kohlrausch amperemeter and R
the resistance frame (Fig. 6).
Storage batteries furnish the most satisfactory current
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 bind-
ing-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 resistance frame, R, where it is fixed
by an ordinary metallic clamp.
For most purposes the strength of current need not
exceed 11.5 amperes; however, it may be necessary
occasionally to increase it to 4 amperes. Pyrite, FeS 2 , is
even then not completely decomposed. This particular
case requires the addition of a quantity of cupric oxide
equal in weight to the pyrite and a current of the strength
3 1 8 ELECTRO-ANALYSIS.
last indicated before all of its sulphur is fully converted
into sulphuric acid.
By increasing the number of crucibles it will be possible
to conduct at least from four to six of these decompositions
simultaneously, and by using a volumetric method of esti-
mating the sulphuric acid, a sulphur 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.
Frankel has conclusively demonstrated that the arsenic
contained in metallic arsenides, e. g., arsenopyrite, rammels-
bergite, etc., can be entirely converted into arsenic acid by
the above method. He recommends conditions analogous
to those employed with the sulphides.
The current will also completely decompose the mineral
chromite. For a quantity of material varying from o.i-
0.5 gram use from 30-40 grams of stick potash and a cru-
cible slightly larger than that recommended in the oxida-
tion of sulphides and arsenides. The current should not
exceed one ampere. Thirty 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 excess of iron with a standardized bichromate solution,
using potassium ferricyanide as an indicator. Upon oxi-
dizing 0.4787 gram of chromite by the above process
51.77 per cent, of chromic oxide was obtained, while a sec-
ond sample of the same mineral, oxidized by the Dittmar
method, gave 51.70 per cent, of chromic oxide. If the
chromium be estimated volumetrically, the chromium con-
tent in a chrome ore may be ascertained in less than an
hour.
COMBUSTION OF ORGANIC COMPOUNDS. 3 ! 9
8. THE COMBUSTION OF ORGANIC
COMPOUNDS.
LITERATURE. Carrasco, R. Ace. d. Lincei (5), 14, 608; Taylor
Thesis (Johns Hopkins University, 1905).
For the combustion of organic bodies Carrasco employs
an ordinary combustion tube in which there is heated a wire
of platinum-iridium. An atmosphere of oxygen is main-
tained throughout the entire experiment which usually occu-
pies not more than fifteen minutes. The device of Taylor
in its simplest form is seen in Fig. 41. " It consists of a
thin glass combustion tube A closed at one end, 300 mm. in
length and 15 mm. in internal diameter. Through the rub-
ber stopper in its open end there pass : ( i ) the porcelain
tube C , which has a length of 250 mm. and a diameter of
6 mm. ; (2) the glass tube K, through which the products of
combustion enter the absorption apparatus; (3) the rather
stout platinum wire, which extends from F to /. The por-
celain tube C is joined outside of the stopper, by means of
rubber tubing, to the branched glass tube D. The latter is
provided with a stopper, G, through which passes the plati-
num wire E, which extends into the porcelain tube to the
point H, where it is joined to a smaller platinum wire. The
small wire has a length of about 1.75 meters and weighs,
approximately, 2.5 grams. It extends from its junction with
the larger wire at H, through the porcelain tube to the inner
end of the latter and then returns on the outside, in a series
of suspended coils, to the point /, where it joins the larger
wire F. Thicker wire is used from F to / and from E to H
in order to avoid any overheating of the rubber stopper by
the current. The roll of copper wire gauze B, about 60 mm.
in length, is inserted between the end of the porcelain tube
and the boat containing the substance to be burned.
320
ELECTRO-ANALYSIS.
FlG - 4i. " The coil is prepared by first
heating the wire, while stretched
slightly, either by passing it through
a flame or by connecting its ends
with electric terminals and passing
a current through it. The danger
of the former method, which is ob-
viated by the latter, is that the wire
will have its resistance changed at
some one spot by being drawn out
there through uneven heating. This
also serves the purpose of straight-
ening the wire and removing some
of the temper, making it easier to
wind. It is then wound upon a
screw thread of such size that the
coil will have an approximate diame-
ter of 9 mm. During the winding
the tension of the wire should be
kept as nearly constant as possible.
After all the wire has been placed
upon the thread it may be easily re-
moved by turning the screw, the
wire being held firmly by the fingers.
.From this method an even coil
should result which is ready to be
placed upon the porcelain stem for
use. After the wire has been used
for a few combustions it loses its
temper and the coil can then be
reformed by simply winding it
around a glass rod of the proper
diameter.
COMBUSTION OF ORGANIC COMPOUNDS. 321
1 The heavy wire from / to F is sharpened at one end and
with a pair of forceps forced through the rubber stopper.
By regulating its length in the combustion tube the coils
may be brought so near the end that all the moisture will be
driven over and yet not near enough to burn the stopper.
The longer wire from H to E, forming the second terminal,
is passed through the stopper in the branched tube D at G
and the end of the tube filled with sealing-wax. The sec-
ond end of the branched tube is slipped over the end of the
porcelain tube and closed with thick rubber tubing tied with
waxed shoemaker's thread.
' The pure oxygen or air enters the apparatus at D and
while passing over the portion of the small wire which is
within the porcelain tube has its temperature raised more or
less according to the rate of its flow. It is, therefore,
already hot when it enters the tube C ', where the combustion
is to be effected. The completeness of the combustion is
probably due, to a large extent, to the temperature to which
the oxygen is heated before it comes in contact with the
vapors to be burned. This hot oxygen is also of especial
advantage not only in keeping the roll of copper gauze next
to the porcelain tube thoroughly oxidized at all times, but
in heating the roll to such a temperature that it can be acted
upon readily by the vapors of the substance to be burned.
The excess of oxygen and the products of the combustion
of the substance pass together over the heated coils on the
outside of the porcelain tube, completing the burning of any
unoxidized material coming from the rear.
" The coils are supported by unglazed porcelain tubes.
They are very durable and they are not hygroscopic to an
appreciable degree.
" The roll of copper wire gauze, B, while not absolutely
necessary has some advantage because much less care is re-
322 ELECTRO-ANALYSIS.
quired in the management of the combustion with it than
without it. If the substances are liquids, or if they readily
yield large quantities of inflammable vapors when heated,
it must be inserted between the material and the end of the
porcelain tube through which the oxygen enters.
' The combustion is conducted in the following manner :
" Having placed, in the positions indicated in the figure,
the boat containing the material and the roll of copper wire
gauze (which, in the beginning, may or may not be oxidized)
and having joined the tube K to the usual train of absorption
apparatus, a slow current of dry and purified oxygen is
admitted and the electric circuit is closed through a regulat-
ing rheostat. Starting with a current of about one ampere
the flow is gradually increased, at the rate of 0.2 ampere
every two or three minutes, until the coils assume a bright
red color or until 3.6 amperes are reached. While the coils
are being heated a lamp having a broad, thin flame is
brought under the roll of copper wire gauze and raised
gradually until the blue portion of the flame touches the glass
tube on its under side. The substance in the boat is then
heated with the same lamp, or with another which is held in
the hand. The rate of heating and the flow of oxygen are
so regulated with respect to each other that at least one half
of the roll of wire gauze is kept in the oxidized condition
during the entire combustion. After the formation of vola-
tile products has ceased, the reoxidation of the copper pro-
gresses rapidly and the oxygen enters the rear compartment,
burning any residue of carbon upon the boat or upon the
glass.
" Having finished the combustion of the substance, the
current of oxygen is replaced by one of dried and purified
air, and the flow of the latter continued until the products of
the combustion have all been expelled from the space behind
COMBUSTION OF ORGANIC COMPOUNDS. 323
the wire gauze. It is here that a miscalculation is likely to
be made. The time required for the complete removal of
these products depends, principally, upon the freedom of
diffusion through the gauze and for this reason it should
not be rolled too tightly.
" The apparatus, already described, is adapted to the com-
bustion of those solids and liquids which consist of carbon
and hydrogen, or of carbon, hydrogen and oxygen.
' The heating of the roll of wire gauze B, and, at times, of
the substance also, is facilitated by inverting over the tube,
at a little distance above it, a trough of asbestos board, the
side of a trough, at the back, being much deeper than in
front. This arrangement is supported in its position by a
rod, which is inserted in a heavy block, resting upon the
work table behind the tube. The device is also of advantage
in protecting the tube from draughts of cold air during the
combustion and during the subsequent cooling period. The
portion of the glass tube which is occupied by the porcelain
tube and the platinum wire is protected, on the bottom, by
a semi-circular strip of asbestos board which is inserted in
the clamp between the lower jaw and the glass. To protect
the upper portion of the tube in the same region, a semi-
circular trough of mica is inverted over it, behind the clamp,
in such a manner that the lower edges of the mica rest in
the trough below. The mica is made to keep its curved form
by fastening it to narrow strips of metal and bending the
latter to the required shape.
" The cooling of the tube requires some care. The cur-
rent should be reduced quite gradually, following the reverse
of the heating process, and it is well, also, as soon as the
combustion is finished, to cover the portions of the glass
tube which is beyond the porcelain one with the soot from a
smoky flame and to take any other measures for the protec-
324 ELECTRO-ANALYSIS.
tion of the tube which will contribute toward the proper
annealing of the glass. Care must likewise be taken never
to allow the platinum coils to come in contact with the glass
either while heating or cooling the tube, since, in the former
case, the metal is likely to stick to the glass, while in the
latter, the tube is quite sure to crack at some lower temper-
ature. Further, the coils, after being used for some time,
show a tendency to increase in size towards the end of the
porcelain tube, and, if they approach too nearly the inner
diameter of the combustion tube, the wire must be taken out
and rewound. The difficulty of keeping the coils away from
the glass while they were hot, led to the placing upon the
inner end of the porcelain tube of a small platinum disk.
The porcelain tube was ground down at the end until it was
practically square and the disk, which was a little smaller
than the internal diameter of the combustion tube, was fitted
eccentrically upon it so that the coils were held the same
distance from the glass tube at all points. Small holes were
drilled in the disk to allow the free passage of the vapors.
As the small wire of the coils only comes in contact with
the platinum disk at one point it does not heat the latter hot
enough to affect the glass tube injuriously. The porcelain
tube and coils are thus always kept in the same relative posi-
tion to the glass tube while the combustion is not in any way
interfered with. With the proper care a good piece of
glass tubing can be used for a large number of combustions.
" The time required for a combustion does not, ordinarily,
exceed half an hour, and it may be reduced to twenty
minutes, or even less, if the substance to be burned is of such
a character that the roll of wire gauze can be dispensed with.
Its omission is not, however, recommended at any time,
except to those who have had some experience with the
method.
COMBUSTION OF ORGANIC COMPOUNDS.
325
" At the highest temperature employed
during the combustion (at a bright red,
but not a white heat), especially when the
wire is new, there is a sensible volatiliza-
tion of the platinum. This volatilization
of platinum in an atmosphere of oxygen,'
even at comparatively moderate tempera-
tures, has been repeatedly noticed by others.
The volatilized metal settles upon the sur-
face of the glass and porcelain tubes as i
dark deposit, which, at first, may be mis-
taken for carbon. The presence of such
films of volatilized platinum upon the in-
ner surface of the tube is, of course, by
its catalytic action, of some assistance in
the combustion.
" The objections to and difficulties in
the use of the short, closed combustion
tube represented in Fig. 41 are wholly ob-
viated by using a somewhat longer tube
which is open at both ends, as represented
in Fig. 42. In this arrangement the boat
is introduced from the rear and there is
placed behind it a second roll of copper
wire gauze, about 60 mm. in length. The
stopper in the front end of the combustion
tube, the forward roll of copper wire gauze
and also the apparatus as a whole, are
never disturbed. Each roll of wire gauze
is heated by a lamp giving a broad, thin
flame and there is inverted over both rolls
and the space between them the asbes-
tos shield already described. The lamps
FIG. 42.
326 ELECTRO-ANALYSIS.
should be raised until the bottom of the tube is just within
the blue region of the flames. To prevent any sagging of
the combustion tube while hot, it is supported at a point
beneath the end of the porcelain tube by a forked or notched
standard, which is placed under the asbestos trough in which
the front portion of the apparatus lies.
' The combustion is conducted in the same manner as in
the short, closed tube, except that a slow current of oxygen
or air is admitted from the rear during the entire experi-
ment. This prevents any accumulation of volatilized mat-
ter in the back part of the tube and aids in the expulsion of
the products of combustion from the space occupied by the
boat.
" If the substance to be burned is very volatile, it is ad-
visable to introduce air and not oxygen in the rear, and to
employ, behind the boat, a roll of gauze which is only par-
tially oxidized. In this way the vapors of the substance
may be diluted with nitrogen to any desired extent.
" With this apparatus a Marchand tube, filled with calcium
chloride, is used to absorb the water vapors formed, because
the end of the tube can be placed directly in the stopper of
the combustion tube, thus doing away with the connection
tube K. No trouble is experienced with this arrangement in
getting the water vapor ready to weigh by the time the com-
bustion is completed. When the Marchand tube is re-
moved from the absorption train its ends are closed by small
pieces of rubber tubing carrying glass plugs.
" The clamp at the rear is required only as a support and
it should not grip the tube so tightly as to prevent the free
movement of the latter, back and forth through the former.
" In the following determinations of carbon and hydrogen
in cane-sugar, which were made for the purpose of testing
the method, the short, closed tube was employed and the
COMBUSTION OF ORGANIC COMPOUNDS.
32;
roll of wire gauze was omitted. A clay tobacco pipe stem
served for the introduction of oxygen and the effect of its
use is evident in the high percentages of hydrogen which
were obtained in the first four analyses. In the last two
analyses, in which normal quantities of hydrogen were
obtained, the pipe stem was thoroughly burned out in a
current of oxygen before beginning the combustion :
WEIGHT OF
SUGAR. GRAM.
CARBON FOUND.
PER CENT.
HYDROGEN
FOUND. PER CENT
TIME OCCUPIED IN
COMBUSTION.
MINUTES.
0.1364
41-95
6.86
25
O.II88
42.03
6.63
18
o. 1227
42.03
6.65
18
0.1382
42.07
6-73
18
O.II54
42. II
6.47
18
o. 2809
42.03
6.46
45
Theoretical, 42.09
6-47
" The current at the highest temperature was 2.6 amperes
at 48 volts. In these combustions a coil of No. 32 wire
(B. & S. gauge) was used, but, as is stated later, it was
found advisable to exchange this, in the combustions of
naphthalene, for a greater length of larger wire.
" Careful management is required, even in the combustion
of such substances as sugar, when the roll of wire gauze is
omitted. On several occasions, when it was attempted to
reduce the time consumed in combustion to fifteen minutes
or less, small explosions occurred. To avoid the explosions,
which always resulted in unburned material escaping, the
combustion tube was lengthened slightly and the previously
mentioned roll of wire gauze was inserted between the boat
and the end of the porcelain tube. Combustions of toluene
and two of naphthalene were made with the modified ap-
paratus with the following results :
328
ELECTRO-ANALYSIS.
TOLUENE.
WEIGHT OF
CARBON FOUND
HYDROGEN FOUND.
TIME OCCUPIED IN
SUBSTANCE. GRAM.
PER CENT
PER LENT.
COMBUSTION.
MINUTES.
0.1057
90.91
8.62
35
0.0650
91.25
8.80
35
Theoretical, 91.24
8.76
NAPHTHALENE.
WEIGHT OF
SUBSTANCE. GRAM.
CARBON FOUND.
PER CENT.
HYDROGEN FOUND.
PER CENT.
TIME OCCUPIED IN
COMBUSTION.
MINUTES.
o 1184
0.1252
93-54
93-49
Theoretical, 93.70
6.36
6 -39
6.36
55
55
The Combustion of Substances Containing Nitrogen.
" For the determination of carbon and hydrogen in com-
pounds containing nitrogen, there are placed in the combus-
tion tube: (i) a roll, 100 mm. in length, of wire copper
gauze which has been reduced in the usual way by methyl
alcohol; (2) a roll, 80 mm. in length, of wire gauze which
has been well oxidized; (3) the boat containing the sub-
stance; (4) a short roll of wire gauze also well oxidized.
" During the combustion each of the three rolls is heated
by a burner giving a broad, thin flame, the last lamp serving
also for heating the substance. The portion of the tube
occupied by the copper is covered with a screen of asbestos
board, to insure a sufficiently high temperature for the re-
duction of the nitric oxide. The flow of the oxygen through
the porcelain tube is so regulated that only about one-quarter
of the copper roll (i) is oxidized, while at the rear it is
admitted as rapidly as may be necessary to keep a portion
of the second roll (2) at all times in an oxidized condition.
COMBUSTION OF ORGANIC COMPOUNDS. 329
The Combustion of Halogen Compounds.
' To prepare the apparatus for the analysis of substances
containing the halogens, a piece of silver foil, about 50 mm.
in width, is rolled up with a sheet of thick paper, which is
afterwards withdrawn. The silver roll is placed in the tube
quite close to the end of the porcelain tube and is not directly
heated during the combustion. In other respects the arrange-
ments are the same as for the combustion of non-nitrogenous
compounds. A roll of well-oxidized copper wire gauze fol-
lows the one of silver, then the boat containing the sub-
stance and, finally, a second roll of oxidized copper wire
gauze.
" During the combustion there is formed a quantity of
fusible cuprous-halogen salt, which deposits itself, more or
less, upon the inner surface of the glass tube, but does not,
at any time, get beyond the silver foil into the space occu-
pied by the porcelain tube and platinum wire. On cooling,
the cuprous-halogen salt, in accordance with the well-known
behavior of such compounds, absorbs large quantities of
oxygen, only to give it up again when the apparatus is
reheated in a succeeding experiment. At the same time
the copper wire, in the oxidized rolls, grows thinner and be-
comes quite brittle.
" The quantity of cuprous salt accumulates, after a few
combustions, to such an extent that the time required for
its oxidation is considerable. Hence, it is well frequently
to cleanse the combustion tube and to renew, at the same
time, the oxidized rolls of copper wire gauze.
The Combustion of Sulphur Compounds.
" The determination of carbon and hydrogen in com-
pounds containing sulphur presents no difficulty. The only
29
33O ELECTRO-ANALYSIS.
change which it is necessary to make in the simple arrange-
ment for non-nitrogenous and non-halogen compounds, in
order to adapt the method to the combustion of sulphur
compounds, is to substitute lead chromate for the roll of
oxidized copper wire gauze which is nearest the end of
the porcelain tube. Instead of maintaining the lead chro-
mate in its position in the tube by means of plugs of asbestos
or of wire gauze, it has been found more convenient and
better for the glass tube to introduce it in the form of a
cartridge. This is prepared by filling, with the loose, granu-
lar "chromate, a shell made from very fine copper wire
gauze."
INDEX.
Accumulator, 2
Ammeters, 9, u, 17
Ampere, 7
Amperemeter, i, 9
Anions, I
determination of, 296
Anode, i, n
dish, 73
spiral, 73
Antimony, determination of, 171-
177
rapid precipitation of, 177-
179
separation from arsenic, 251
bismuth, 225
copper, 183, 184
lead, 233
mercury, 215
silver, 238
tin, 251-255
Arsenic, determination of, 180
oxidation of, 318
separation from antimony, 251
bismuth, p 225
cadmium, 205
copper, 184, 185, 186
lead, 234
mercury, 215
silver, 238
tin, 255
Barium, determination of, 307
separation from calcium and
magnesium, 309, 310
separation from iron, 311
separation from magnesium,
3ii
separation from uranium, 312
Battery, Bunsen, 10
storage, 2, 13
Bismuth, determination of, 95-98
rapid precipitation of, 98, 99
rapid precipitation with mer-
cury cathode, 99-100.
Bismuth, separation from alumin-
ium, 225
antimony, 225
arsenic, 225
barium, 225
cadmium, 225
calcium, 226
chromium, 226, 227
cobalt, 227
copper, 227
gold, 228
iron, 228, 229
lead, 229, 230
magnesium, 230
manganese, 230
mercury, 231
molybdenum, 231
nickel, 231
palladium and platinum,
231
potassium, 231
selenium^ 231
silver, 231
sodium, 232
strontium, 232
tellurium, 232
tin, 232
tungsten, 232
uranium, 232
vanadium, 232
zinc, 233
Board, distributing, 12
switch, 12
Bromine, separation from chlor-
ine, 289
Bunsen cell, 10
Cadmium, determination of, 81-84
rapid precipitation oi, 84-88
rapid precipitation of, with
mercury cathode, 8^-89
separation from aluminium,
203, 204
antimony, 205
arsenic, 205
331
332
INDEX
Cadmium, separation from barium,
strontium, etc., 205
beryllium, 205
bismuth, 205
chromium, 205
cobalt, 205
copper, 186, 187, 188, 206
gold, 206
iron, 207
lead, 207
magnesium, 208
manganese, 208, 209
mercury, 209
molybdenum, 209
nickel, 209, 210
osmium, 210, 211
selenium, 211
silver, 211
sodium, 211
strontium, 211
tellurium, 211
tin, 211
tungsten, 211
uranium, 211
vanadium, 211
zinc, 211, 212, 213, 214
Cations, I
determination of, 296
Cathode, i
mercury, 55
Chromite, oxidation of, 318
Chromium, determination of 144-
145
rapid precipitation with mer-
cury cathode, 145, 146
separation from aluminium,
273
beryllium, 274
Cobalt, determination of, 122-126
rapid precipitation of, 130-
.133
with mercury cath-
ode, 133
separation from bismuth, 227
cadmium, 206
copper, 189, 190
iron, 262
manganese, 267
mercury, 218
nickel, 267
silver, 236
zinc, 268
Combustion of organic com-
pounds, 319-330
Copper, determination of, 63-72
rapid precipitation of, 72-77
with mercury cath-
ode, 77-80
separation from aluminium,
181, 182, 183
antimony, 183, 184
arsenic, 184, 185, 186
barium, strontium, mag-
nesium, etc., 185.
bismuth, 186
cadmium, 186, 187, 188
calcium, 188
chromium, 188
cobalt, 189, 190
gold, 190
iron, 190, 191, 192, 193
lead, 193, 194
magnesium, 194
manganese, 194, 195
mercury, 196
molybdenum, 196
nickel, 196, 197, 198
palladium, 198
platinum, 198
potassium, 198
selenium, 198, 199
silver, 199
sodium, 199
strontium, 199
tellurium, 199, 200
thallium, 200
tin, 200
tungsten," 200
uranium, 200, 201
vanadium, 201
zinc, 20 1, 202, 203
Current, action upon compounds, I
density, 10
electric light, 3
measuring of, 9
reduction of, 5, 7
separations, 39
Decomposition pressure, 32, 33
Determination of metals, 63
Distributing board, 14
Dynamos, 2
Electric current, sources of, 2
light current, 3
motor, 96
Flectro-analysis, I
Electro-chemical laboratory, 12
INDEX
333
Electrode, auxiliary, 279
Electrolysis, defined, i
Electrolyte, I
Galvanometer, 9
sine, 9
tangent 9
Gold, determination of, 162, 164
rapid precipitation of, 164,
165
with mercury cath-
ode, 165
separation from antimony, 246
arsenic, 250
cadmium, 246, 247
cobalt, 247
copper, 247
iron, 248
molybdenum, 249, 250
nickel, 248
osmium, 249
palladium, 248
platinum, 249
tungsten, 249, 250
zinc, 249
Halogen compounds, combustion
of, 329
Halogens, determination of, 285
separation of, 287
Historical account, 19-31
Indium, determination of, 150, 151
Iodine, determination of, 286
separation from bromine, 289
chlorine, 288
Ions, 33
Iron, determination of, 138-142
rapid precipitation of, 142,
143
with mercury cathode,
1.43, 144
separation from aluminium,
256, 257, 259
beryllium, ?s8
bismuth, 228, 229
cadmium, 207
cerium, 261
chromium, 262
cobalt, 262
copper, 190, 191, 192
lanthanum, 260
lead, 234
manganese, 262, 263, 264
Iron, separation from mercury,
219
neodymium, 261
nickel, 264, 265, 266
phosphoric acids, 266
praseodymium, 260
silver, 243
thorium, 260
titanium, 261, 266
uranium, 259, 266
vanadium, 258
yttrium, 261
zinc, 266, 267
zirconium, 261
Laboratory, electrochemical, 12
Lead, determination of, 100-103
rapid precipitation of, 103-104
separation from alkali metals,
barium, beryllium, cad-
mium, calcium, cobalt,
iron, magnesium, nickel,
uranium, zinc, zircon-
ium, 234
aluminium, 233
antimony, 233
arsenic, 234
bismuth, 235
copper, 235
gold, 235
manganese, 235, 236
mercury, 236
selenium, 236
silver, 236, 237
tellurium, 237
tin, 237
Magneto-machines, 2
Manganese, determination of, 134-
138
rapid precipitation of, 138
separation from aluminium,
.134
bismuth, 230
cadmium, 208, 209
cobalt, 267
copper, 194, 195
iron, 262, 263, 264
mercury, 220
nickel, 268
zinc, 269
Measuring currents, 9
Mercury, determination of, 89-93
rapid precipitation of, 93-94
334
INDEX
Mercury, rapid precipitation with
mercury cathode, 94-95
separation from aluminium,
214, 215
antimony, 215
arsenic, 215, 216
barium, strontium, etc.,
216
bismuth, 216, 217
cadmium, 217
calcium, 218
chromium, 218
cobalt, 218
copper, 218, 219
gold, 219
iron, 219, 220
lead, 220
magnesium, 220
manganese, 220
molybdenum, 221
nickel, 221
osmium, 221
palladium, 221
platinum, 221
potassium, 222
selenium, 222
silver, 222
sodium, 222
strontium, 222
tellurium, 222
tin, 222, 223
tungsten, 223
uranium, 223, 224
vanadium, 224
zinc, 224
Metals, separation of, 181, 274
additional remarks, 274
Milliamperemeter, 9
Molybdenum, determination of,
157, 161
rapid precipitation of, 161
with mercury cath-
ode, 162
separation from cadmium, 209
mercury, 221
silver, 244
vanadium, 272
Nickel, determination of, 122-126
rapid precipitation of, 126-129
with mercury cath-
ode, 129, 130
separation from aluminium,
264
Nickel, separation from bismuth,
231
cadmium, 209, 210
cobalt, 267
copper, 196, 197
iron, 264, 265
lead, 234
manganese, 268
mercury, 221
silver, 244
zinc, 268, 269
Nitric acid, determination of, 289
rapid determination of, 290-
296
Normal density denned, 10
Organic compounds, combustion
of, 319-330
Osmium, 181
Oxidations by means of the cur-
rent, 314
Palladium, determination of, 153
rapid precipitation of, 154-
156
separation from iridium, 250
mercury, 221, 250
Phosphoric acid, separation, etc.,
266
Platinum, determination of, 151
rapid precipitation of, 152
metals-, 250
separation of, 250
separation from iridium, 250
Pole pressure, n
Potassium ferricyanide, analysis
of, 306
ferrocyanide, analysis of, 306
separation from calcium and
magnesium, 309
. iron, 311
sulphocyanide, analysis of, 300
Potential across the poles, n
Precipitation of metals, rapid, 41
Resistance coils and frames, 6,
7, 8
Rheostat, 6, 7, 17, 281
Rhodium, determination of, 156,
250
rapid precipitation of, 156,
157
INDEX
335
Rotating anode, 42
and mercury cathode, 58,
296
cathode, 46, 49, 51
Separation, constant current, 39,
4i
Separation of metals, 181, 274
Silver, determination of, 104-107
rapid precipitation of, 107-108
with mercury cath-
ode, 1 08
separation from aluminium,
237, 238
antimony, 238
arsenic, 238
barium, 239
bismuth, 231, 239
cadmium, 239
calcium, 239
chromium, 239
cobalt, 239, 240
copper, 240, 241, 242, 243
gold, 243
iron, 243
lead, 236, 243
lithium, 243
magnesium, 243
manganese, 243
mercury, 244
molybdenum, 244
nickel, 244
osmium, 244
palladium, 244
platinum, 244
- - potassium, 244
selenium, 245
tellurium, 245
tin, 245, 246
tungsten, 244
uranium, 246
zinc, 246
Sodium bromide, analysis of, 300
305
carbonate, analysis of, 305
chloride, analysis of, 294
iodide, analysis of, 300
separation from calcium and
magnesium, 308
iron, 311
uranium, 312
sulphide, analysis of, 313
Storage cells, 2, 13
Strontium, determination of, 307
separation from calcium and
magnesium, 310
iron, 311
magnesium, 311
Sulphur compounds, combustion
of, 329
Sulphur, oxidation of, 314
Switchboard, 14
Table, working, 18
Tangent galvanometer, 9
Tellurium, 179, 180
Thallium, determination of, 149,
150
Theoretical considerations, 32
Thermopile, 2
Tin, determination of, 166-168
rapid precipitation of, 168-
170
with mercury cath-
ode, 170-171
separation from antimony,
251-255
arsenic, 255
bismuth, 232
cadmium, 211
copper, 200
lead, 237
manganese, 255
mercury, 222
Trisodium phosphate, analysis of,
306
Tungsten, 41, 180
Uranium, determination of, 146-
148
rapid precipitation of, 149
separation from barium, 270,
271
calcium, 271
magnesium, 271
zinc, 272
Vanadium, 180
Voltage, ii
Voltameter, 9
Voltmeter, 11, 64
\Vorking table, 18
Zinc, determination of, 109-116
rapid precipitation of, 116-
120
136
INDEX
Zinc, rapid precipitation with mer-
cury cathode, 120-122
separation from aluminium,
270
bismuth, 233
cadmium, 211-214
copper, 201-203
Zinc, separation from iron, 266,
267
lead, 234
manganese, 269, 270
mercury, 224
silver, 246
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