satisfactorily when the amount of zinc present is less than
one-third that of the iron.
Vortmann has recommended the use of a solution con-
taining a sufficient excess of potassium cyanide to hold the
cyanides of the metals in solution, and sodium hydrate. 2
This latter forms sodium ferrocyanide with the iron, and
this salt is not decomposed by the current in presence of
free alkalies. Too great an excess of potassium cyanide
delays the deposition of the zinc.
A current density of from -30 to '60 ampere is
employed. As regards the practical utility of this method,
the remarks under 'Iron Nickel' apply here.
Iron from Manganese. A great number of experi-
ments have been carried out with all forms of salts, in
order to discover a reliable method for obtaining a complete
separation of these two metals, but without success. In
1 Electrolyse. 2 Monats. f. Chem. 14, 536.
212 THE ELECTROLYTIC PROCEDURE
most of these experiments the aim has been to obtain the
manganese as peroxide at the anode, or to keep it in
solution while the iron is deposited at the kathode. The
results obtained showed that the deposition of the iron was
incomplete (at least for the first deposition), and that when
the manganese was separated as peroxide this latter con-
This difficulty arises in connection with the method
proposed by Classen. 1 The solution of the two metals is
prepared by treating it with 6 or 8 grms. ammonium
oxalate, and after heating to 50 or 60 C., the electrolysis
is conducted with a current of 1 ampere in density, and
of 3-1 to 3-8 volts as regards E.M.F. Only a small
portion of the manganese is obtained at the anode as per-
oxide under these conditions. If less ammonium oxalate
be used, permanganic acid and its salts will be formed at
first at the anode, and later a peroxide deposit will be ob-
tained containing iron. As a rule the liquid is rendered
completely turbid by a brown flocculent precipitate, which
partly settles in adherent form upon the kathode. The
method gives inexact results in spite of all assertions to the
The method proposed by Brand, 2 in which a solution
containing sodium pyrophosphate and ammonium oxalate is
used, also yields inaccurate results.
If one attempt to effect the separation of iron from
manganese in a solution containing 20 to 30 grms. ammonium
acetate, an incomplete deposition of the manganese as per-
oxide occurs, owing to the formation of a ferrous salt which
dissolves the peroxide again at the anode. Engels has proposed
to add oxidising agents in order to overcome this difficulty. 3
If chromic acid be used to oxidise the ferrous salt, a com-
plete deposition of the manganese as peroxide can be
obtained, but the deposit will be found to contain up to '02
grm. iron, probably in the form of oxide.
1 Electrolyse. 2 Zeitschr. f. anal. CJwm. 28, 581.
3 Zeitschr. f. Elektrochem. 2, 414.
SEPARATION OF METALS 213
Iron from Aluminium. If a solution of an iron salt
containing alum be treated with 8 grms. ammonium oxalate
and be then electrolysed, a deposit of iron alone will be ob-
tained at the kathode at the commencement of the electro-
lysis. As aluminium can in no case be deposited from an
aqueous solution, the separation is complete. In course of
the electrolysis of solutions containing ammonium oxalate,
carbonic acid is formed at the anode.
This leads to the formation of ammonium carbonate in
the electrolyte, and to the precipitation by the latter of
aluminium as a flocculent hydroxide.
The separation of aluminium hydrate does not produce
any impurity in the deposit of iron. The electrolysis is
conducted at the normal temperature, with a current that
does not exceed 1 ampere in density. Stronger currents
than 1 ampere heat the electrolyte and accelerate the for-
mation of ammonium carbonate.
The E.M.F. required will lie between 3 and 3-8 volts, and
about four hours will be demanded for the deposition of -10
As a rule a smooth deposit of iron is obtained, but
towards the end of the electrolysis the aluminium hydroxide
has a tendency to adhere to the deposit on the kathode.
When this has occurred, it may be removed without
injury to the coating of iron by wiping with a cloth. The
aluminium must be estimated by gravimetric methods.
If it be thought necessary to avoid the separation of the
aluminium as hydroxide in the electrolyte, the solution
containing the iron salt and the alum is treated with 1 grm.
potassium tartrate, and after heating to 50 or 00 0. is
electrolysed with a current of about 1 ampere in density.
The E.M.F. required will be from 4 to 5 volts, and about
five and a half hours will be requisite for -10 grm. iron.
This solution will remain clear to the end of the electro-
lysis. A bright deposit of iron will be obtained, but it will
be found to contain some carbon. The amount of this
latter impurity does not exceed 1 mg. for the above-
214 THE ELECTKOLYTIC PKOCEDUEE
named weight of potassium tartrate, so that the results
obtained are only slightly erroneous.
Iron from Chromium. A solution of either a ferric or
ferrous salt containing any soluble salt of chromium sesqui-
oxide may be prepared for electrolysis by adding 8 grms.
The solution is then heated to 60 C., and is electrolysed
by means of a current of from 1 to 2 amperes in density.
The E.M.F. required will be from 3-3 to 3'7 volts ; in order
to deposit '10 grm. iron from three to four hours will be
necessary. The deposit obtained is bright and metallic.
The chromium salt is raised to the chromic acid state of
oxidation during the electrolysis, and the chromium is
determined in this solution by gravimetric methods.
COBALT AND NICKEL
Since cobalt and nickel belong to the group of metals
which as a general rule cannot be deposited in acid solutions
by means of the electric current, the separation of these
two metals from many of the others is easily accomplished.
The methods in use have already been described under the
headings of the different metals, and a few methods of
separation from metals of the same group have also already
Cobalt and Nickel from Copper. See p. 172.
Cobalt and Nickel from Silver. See p. 192.
Cobalt and Nickel from Mercury. See p. 196.
Cobalt and Nickel from Bismuth. See p. 200.
Cobalt and Nickel from Lead. See p. 190.
Cobalt and Nickel from Cadmium. See p. 206.
Cobalt and Nickel from Iron. See p. 209.
Cobalt from Nickel. Yortmann has proposed two
methods } for effecting the separation of these two metals, so
closely allied in their general properties and characteristics.
The first consists in the use of a solution of the neutral
sulphates of the two metals to which sulphates of the
1 D. R. P. Kl. 40, 78236. Monatsheftc f. Chemie. 14, 548.
SEPAKATION OF METALS 215
alkali or alkaline earth metals have been added, together with
a soluble chloride salt. The solution is then electrolysed with
a current, the direction of which is continually changed,
oxidation and reduction alternately occur at the electrode,
and the cobalt is said to separate as hydrate while the
nickel remains in solution.
The method is unsuitable for the purpose of electrolytic
analysis, since quantitative results cannot be expected with
it. The other method depends upon the use of solutions
containing tartrates of the alkali metals, and a little potas-
sium iodide. The results obtained with this method are also
unsatisfactory, and a reliable electrolytic procedure for the
separation of cobalt and nickel does not therefore exist.
Cobalt and Nickel from Zinc. There are two ways in
which the separation of these metals can be effected.
Either the nickel or the zinc may be deposited, while the
second metal remains in solution. According to Vortmann,
in order to deposit the zinc from such a mixture of salts,
the solution, which should contain about '20 grm. each of
the concerned metals, should be treated with 5 to 6 grms.
sodium potassium tartrate and with an excess of sodium
hydrate, and should then be diluted to a volume of 150
c.cms. * The electrolysis is conducted at the normal tempera-
ture with a current of from '30 to '60 ampere in density.
From two and a half to three and a half hours will be required
in order to deposit the whole of the zinc.
Nickel monoxide often separates at the anode during
this electrolysis. Towards the end of the deposition of zinc
it frequently happens that a flocculent precipitate of nickel
hydrate separates in the electrolyte, and ultimately this
hydrate may settle upon the zinc at the kathode in fine
brown streaks. This, however, can only occur when the
electrolysis has been permitted to continue for too lengthy
a period of time. The most simple manner of determining
whether the whole of the zinc has been deposited is to hang
a narrow strip of brass over the edge of the basin electrode
1 Mwatsch. /. Clicinie, 14, 536.
216 THE ELECTROLYTIC PROCEDURE
and to note whether any deposition of zinc occurs upon it.
The solution remaining after the whole of the zinc has been
removed is acidified with sulphuric acid, and, after addition
of excess of ammonium hydrate, is made use of for the
deposition of the nickel by the ammonium sulphate method
described under ' Nickel.' The solution may also be treated
with 25 c.cms. ammonium hydrate, and 15 to 20 grms.
ammonium carbonate, and electrolysed at a temperature of
50 to 60 C., with a current of from -80 to 1-0 ampere in
density. From one to two hours will be required in order
to deposit '20 grm. nickel.
A method of separation depending upon the deposition
of the nickel has been proposed by von Foregger. 1
The electrolyte is prepared by treating the solutions of
the two sulphates, which should contain about '20 grm. of
each metal, with 10 grms. ammonium sulphate, 10 grms. am-
monium carbonate, and 10 c.cms. strong ammonium hydrate.
The mixed salt solution is then diluted to 150 c.cms., and is
electrolysed at a temperature of 50 or 60 C., with a
current which at first does not exceed "30 to '50 ampere in
density, but which is later increased to a density of 1 '0 to
The nickel separates as an adherent deposit at the
kathode, whereas the zinc remains in solution even at the
higher current density.
It is striking that the deposit of nickel is sometimes of
a brownish colour, due not to admixed zinc but to enclosed
This, when it occurs, renders the results too high. The
electrolyte remaining after the separation of the nickel can
be prepared for the electrolytic determination of the zinc
by treating with an excess of sodium hydrate. The depo-
sition of the zinc from this solution is then carried out at
60 or 70 C., with a current of from -80 to 1*0 ampere in
density. About three and a half hours will be required to
deposit the zinc.
1 Dissertation, Bern, 18UO.
SEPARATION OF METALS 217
The methods of zinc deposition depending upon the use
of the cyanide or oxalate double salts may also be used, if
the necessary steps be taken to convert the zinc present in
the solution that remains after deposition of the nickel, into
The two methods given above may also be used together ;
that is to say, the zinc is deposited according to the first,
and the nickel in the remaining electrolyte is then deposited
in accordance with the directions of the second.
Cobalt and Nickel from Manganese. Classen has prot
posed to use a solution of the sulphate salts of these metals,
to which about 8 grms. ammonium oxalate have been
added, for effecting their separation. 1 The deposition of
the nickel or cobalt is then effected similarly to that of
iron from a corresponding solution, at a temperature of
Between 50 and 60 C., by means of a current of about
1-0 ampere in density. The E.M.F. required will be
from 3*1 up to 3'6 volts. The cobalt or nickel separate
at the kathode, whilst the deposition of the manganese
is prevented by the ammonium oxalate present in the
A formation of a dark-brown flocculent precipitate of
manganese compounds occurs, however, and these settle
upon and adhere to the metallic coating on the kathode.
It is impossible wholly to avoid this precipitation, either by
altering the temperature at which the electrolysis is carried
out, or by varying the amount of ammonium oxalate used.
The method is inexact.
Brand has proposed to separate cobalt fro*m manganese in
solutions containing sodium pyrophosphate, 2 but the method
does not lead to successful results. Nickel may, however,
be separated from manganese in such a solution if the
amount of the two metals present is very small, and if the
electrolyte contains in addition to the sodium salt 15 per cent,
Neither of the two methods described for the separation
1 Electrolyse. * Zeitttchr. f. anal. Client. 28, 581.
218 THE ELECTKOLYTIC PKOCEDURE
of cobalt and nickel from manganese can be recommended
Nickel and Cobalt from Aluminium and Chromium.
The separation of these metals is effected in the same way
as that of iron from aluminium and chromium.
Since zinc also belongs to that group of metals which
are separated from their salts with greater difficulty than
hydrogen is separated from its salts (the acids), it follows
that the separation of zinc from many of the metals is easily
accomplished. The methods used to effect such separations,
and also other separations from the metals of the same
group, have already received mention as follows :
Zinc from Copper. See p. 167.
Zinc from Lead. See p. 190.
Zinc from Silver. See p. 192.
Zinc from Mercury. See p. 196.
Zinc from Gold. See p. 198.
Zinc from Bismuth. See p. 200.
Zinc from Cadmium. See p. 205.
Zinc from Iron. See p. 211.
Zinc from Cobalt and Nickel. See p. 215.
Zinc from Manganese, Aluminium, and Chromium.
The methods described under iron and cobalt for the
separation of these metals from manganese, aluminium,
and chromium may also be used to effect the separation of
zinc from the latter metals. The remarks concerning the
trustworthiness of the methods also apply in the case of
Manganese, which is nearly always deposited as
peroxide, can be separated in acid solutions from a con-
siderable number of the metals. These separations have
already received full description, under the concerned
PRACTICAL EXAMPLES 219
metals. The separation of manganese from those metals
which cannot be deposited in acid solutions is attended by
difficulties, and the results obtained in most cases are un-
These separations have likewise received mention under
the individual metals.
SEPARATION OF SEVERAL METALS
If many metals be present in one solution, the methods
of electrolytic separation employed are varied according to
the electrolytic character of the metals present.
Magnesium, aluminium, chromium, calcium, barium,
strontium, potassium, and sodium always remain in
solution, as they cannot be deposited at the kathode under
the ordinary current conditions.
The remaining metals can be easily separated into two
large groups by electrolysing solutions containing a definite
excess of certain acids.
In this way it may occur that many of the metals are
deposited together ; a separation of the metals in such a
composite deposit is only possible after redissolving.
For example, if a solution containing silver, copper,
cadmium, and zinc be obtained for analysis, one would
first deposit the silver and copper together, and then
dissolve this mixed kathode deposit in order to effect the
separation of the silver from the copper. If lead be
present in such a mixed acid solution, the method of
separation is also again very simple.
After electrolysis, those metals which can be deposited
in the presence of free acid will be found at the kathode,
the lead as peroxide at the anode, and the metals of the
group Zinc-Iron will be found still in solution. In some
cases, dependent upon the metals present, similar group
separations are possible in solutions of the cyanides or other
It is more advantageous, however, in practical analytic
work, when dealing with solutions which contain several
220 THE ELECTROLYTIC PROCEDURE
metals, to separate these by purely chemical methods to
such an extent, that either the electrolytic work is confined
to depositions of single metals, or to separations for which
definite data are available.
Examples of these combined chemical and electrolytic
methods of analysis are given in Part III. D.
D. PRACTICAL EXAMPLES
Alloys of Copper and Zinc, containing Lead and Iron
as Impurities (Brass, Tombac). About -50 grm. of the
sample obtained by boring or filing the alloy is dissolved,
with the aid of gentle heat, in dilute nitric or sulphuric
acid The amount of acid requisite for the later electro-
lysis is 5 to 10 c.cms. strong nitric acid, or 3 to 5 c.cms. cone,
sulphuric acid. The warm solution of the alloy is diluted to a
volume of 150 c.cms., and is electrolysed either in a beaker
with a cone electrode, or in the platinum basin, with a current
of about 1 ampere in density, and under the conditions given
in detail under Copper-Zinc on p. 167.
If the alloy under analysis be brass containing lead as
an impurity, a nitric acid solution should be used with
an anode that has been previously weighed. The lead
separates upon the latter as peroxide ; and as lead is only
present in very small amounts in brass, the smaller
electrode will in this case serve to receive it.
When the whole of the copper has been deposited
(three to four hours will be requisite for this) the electrodes
are removed from the electrolyte in the beaker, or the
basin electrode is washed out before breaking the current
The remaining solution of zinc in nitric acid is treated
with a small amount of sulphuric acid, and is evaporated
in order to drive off the free and combined nitric acid.
The sulphates of zinc and iron thus obtained are dissolved in a
small quantity of water, and the latter is precipitated as
PRACTICAL EXAMPLES 221
hydroxide, most simply by addition of a slight excess of
ammonium hydrate to the aqueous solution of the
This iron is then determined by the gravimetric method,
or the hydroxide may be dissolved, and the iron deter-
mined electrolytically in an ammonium oxalate solution.
The sulphuric acid solution of zinc and iron that
remains when the copper has been deposited from a
sulphuric acid electrolyte is treated in the same manner
in order to separate the iron. The slightly alkaline am-
moniacal zinc solution obtained in either case is treated with
a few grams of pure potassium cyanide, or with ammonium
oxalate or lactate, according to one of the methods de-
scribed under zinc on pp. 113-122, and the zinc is deposited
as metal upon an electrode which has been previously coated
with copper or silver. The preparation of the deposits of
copper and zinc for weighing is, of course, carried out as
already described in detail under these metals.
It is more convenient to precipitate the iron by means
of ammonia, and to estimate it separately, than to electro-
lytically deposit zinc and iron together, and then to use
the unsatisfactory electrolytic method for separation of
these two metals.
Brass is composed as a rule of 65 per cent, copper and
35 per cent. zinc. Lead and iron are generally only present
as impurities in very small amounts.
Alloys of Copper and Silver (Mint-Silver). In order
to carry out this analysis '20 to '60 grm. of the borings or
filings of the alloy are dissolved in a small amount of
nitric acid. This solution is then either directly used for
the electrolytic separation of the silver and copper under
the conditions described on p. 182, or it is neutralised
with sodium hydrate, treated with excess of pure potas-
sium cyanide, and electrolysed as described under this
method on p. 183.
1 [If much zinc be present, a larger excess of ammonium hydrate
will be required to keep this metal in solution. Translator's note.'}
222 THE ELECTROLYTIC PROCEDURE
The German and United States mint-silver contains
90 per cent, of the metal ; that used in France varies from
83'5 per cent, up to 90 per cent. ; while there is 92-5 per
cent, silver in the coinage-silver used at the mint in
Alloys of Copper and Nickel (Mint-Nickel). The
solution of this alloy for electrolysis is obtained by
dissolving -30 to *50 grm. of the prepared sample in dilute
nitric or sulphuric acid, and by adding in the former case
still another 5 .c.cms. cone, nitric acid. The deposition of
the copper is then carried out under the current con-
ditions detailed under Copper-Nickel (see p. 173). In
order to determine the nickel in the remaining electrolyte,
the nitric acid is removed by evaporation with an excess of
sulphuric acid, and, after treatment with an excess of
ammonium hydrate, the nickel is deposited directly from
the resulting ammoniacal solution of sulphate salts. When
sulphuric acid has been used to dissolve the alloy, more
time is required to effect this, but the later evaporation
with this acid is unnecessary ; and after deposition of the
copper in the acid solution, one can simply add excess of
ammonium hydrate, and proceed at once to deposit the
The details of the procedure will be found on p. 106.
If small amounts of iron be present as an impurity in
the alloy, this will cause a precipitate of ferric- hydrate to
form when the ammoniacal solution of nickel is being pre-
pared for electrolysis.
This is removed from the solution by nitration, and the
iron in it is determined either by the gravimetric method,
or by redissolving and deposition from an ammonium
The nickel coins used as currency in Germany contain
75 per cent, copper and 25 per cent, nickel.
Alloys of Copper, Zinc, and Nickel (German-Silver).
Three different methods may be employed to effect the
electrolytic separation of the metals that occur in this
PRACTICAL EXAMPLES 228
alloy. First, one may use a nitric acid solution, to de-
posit the copper alone, and then separate the nickel and
zinc in the remaining electrolyte. Or, one can make use
of an alkaline sodium potassium tartrate solution, and
deposit the zinc and copper together as an alloy, while
the nickel remains in solution to be later deposited alone.
The third method depends upon the use of an am-
moniacal solution containing ammonium carbonate, from
which on electrolysis copper and nickel are deposited as an
alloy, zinc remaining in solution.
In order to carry out the first method, between -20 and
40 grm. of the alloy, preferably in the form of thin
shavings, is dissolved in dilute nitric acid in a beaker.
When the solution is complete, a further 20 to 30 c.cms.
cone, nitric acid are added, the solution is diluted to 150
c.cms., and after cooling to the normal temperature it is
electrolysed either in the beaker with a cone electrode, or
in the platinum basin.
The density of current used should be from -50 to I'O
ampere. The E.M.F. required will be from 2-5 to 2-8 volts,
and the time from two to three hours. The remaining
solution is then evaporated with sulphuric acid in order to
remove the nitric acid and to convert the nitrates into
sulphates, and after neutralising it is treated by either of
the methods detailed on pp. 215, 216. In the one case zinc
is first deposited ; in the other, the nickel is determined
first, and the zinc in the remaining electrolyte.
The second method is carried out as follows : To the
solution of '20 to -40 grm. of the alloy in nitric acid, after
evaporation with sulphuric acid to convert the salts into
sulphates, 6 grms. sodium potassium tartrate and 4 to
5 grms. sodium hydrate are added, and the mixture is
then diluted to 150 c.cms. and heated to 40 or 50 C. The
solution is then electrolysed with a current of -60 to -70
ampere in density. The whole of the copper and zinc will
be deposited as an alloy in three to four hours. As the
copper is deposited more rapidly than the zinc, the red
224 THE ELECTROLYTIC PROCEDURE
colour of the coating on the kathode will gradually pass
into a grey. The mixed deposit after washing is dissolved in
a few cubic centimetres of dilute nitric or sulphuric acid, and
the separation of the copper and zinc in this solution is then
undertaken as described under Copper-Zinc (see p. 168).
The current used should be about 1 ampere in density ;
the time required will be from two to three hours.
The solution containing the nickel is treated with