C. Remigius Fresenius.

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will not always entirely prevent the coprecipitatiori of the zinc.
KIVOT and BOUQUET * declare a complete separation of copper
from zinc by means of hydrogen sulphide altogether imprac-
ticable. CALVERT f states that he has arrived at the same con-
clusion. On the other hand, SPIRGATIS ^ concurs with H. EOSB
in maintaining that the complete, separation of copper from
zinc may be effected by means of hydrogen sulphide in presence
of a sufficient quantity of free acid.

In this conflict of opinions, I thought it necessary to subject
this method once more to a searching investigation. I there-
fore had R. GRUNDMANN make a series of experiments in the
matter in my laboratory with a view to settling the question.!

The following process is founded on the results which we
obtained :

Add .to the COPPER and ZINC solution a large amount of
hydrochloric acid (e.g.^to 0'4 grin, oxide of copper in 250 c.c. of
solution, 30 c.c. hydrochloric acid of 1*1 sp. gr.), conduct into
the fluid at about 70 hydrogen sulphide largely in excess, filter
before the excess of hydrogen sulphide has had time to escape
or become decomposed, wash with hydrogen sulphide water,
dry, roast, redissolve in nitrohydrochloric acid, evaporate nearly
to dryness, add water and hydrochloric acid as above, and pre-
cipitate again with hydrogen sulphide. This second precipi-
tate is free from zinc ; it is treated as directed in 119, 3.

If CADMIUM is present, it is well to have less acid present,
e.g., to 0*4 grm. oxide of cadmium in 250 c.c. of solution add 10
c.c. hydrochloric acid of I'l sp. gr. If the quantity of zinc is
considerable, dissolve the first precipitate of cadmium sulphide
in hot hydrochloric acid, evaporate nearly to dryness, add 10
c.c. hydrochloric acid and about 250 c.c. water, and precipitate
again. In this way the results are quite satisfactory.

y. The other metals of the fifth group comport themselves
in this respect similarly to cadmium, i.e., they are not com-
pletely precipitated by hydrogen sulphide in presence of too
much free acid in a concentrated solution. Lead requires the
least amount of free acid to be retained in solution ; then follow
in order of succession, cadmium, mercury, bismuth, copper, sil-
ver (M. MARTIN |[). A portion of the filtrate should, if neces-

* Annal. d. Chem. u. Pharm., Exxx, 364. f Journ.f. prakt. (J hem. , LXXI, 155.
t lb., LVII, 184. 2b., LXXIII, 241. || lb., LXVII, 371.

678 SEPARATION. [ 162.

sary, be tested by addition of a large quantity of hydrogen sul-
phide to see if the precipitation of the fifth group was com-

d. If hydrochloric acid produces no precipitate in the
solution, it is preferred as acidifying agent, otherwise sulphuric
or nitric acid must be used. In the latter case the fluid must
be rather largely diluted. ELIOT and STOKER * arrived at the
same conclusion as ourselves, and showed that the cause of
CALVERT'S unfavorable results was the too large dilution of his
solutions. For, to prevent the precipitation of zinc you have
not merely to preserve a certain proportion between the zinc
and the free acid, but also a certain degree of dilution.
Although I agree with the above-named chemists in the opinion
that it is possible to produce a condition of the fluid, under
which one precipitation will effect complete separation, still it
appears to me better, for practical purposes, to precipitate twice,
as this is sure to lead to the desired result.

e. A somewhat extended experience in the separation of COP-
PER from NICKEL (and COBALT) which so frequently occurs has
led me to the opinion that a double precipitation is unnecessary.
If the solution which is to be treated with hydrogen sulphide
contains enough free hydrochloric acid and riot too much water,
the copper falls down absolutely free from nickel, while, on the
other hand, if the quantity of free acid is not too large, the fil-
trate will be quite free from copper. The method of sepa-
rating copper from zinc given in (3 is also to be recommended
in this case.

C- CADMIUM and ZINC may, according to FOLLENIUS, f also be
completely separated by a single precipitation, if the metals are
present in a sulphuric acid solution containing 25 or 30 per
cent, of dilute acid of 1'19 sp. gr. Precipitate with hydrogen
sulphide at 70. Collect the precipitate on a weighed asbestos
filter, dry in a current of heated air, ignite gently in a stream
of pure hydrogen sulphide (to convert small quantities of cad-
mium sulphate into sulphide), remove the small quantity of
separated sulphur by gentle ignition in a current of air, and
weigh .

*On the Impurities of Commercial Zinc, etc. Memoirs of the American
Acadi my >f Arts and Sciences. New Series. Vol. 8.
j- Zeitschr. f. analyt. Chem., xiu, Part 4.

162.] BASES OF GEOUP V. 679

B. Special Methods.


1. SILVER is most simply and completely separated from the 128
METALS OF THE FIRST FOUR GROUPS by means of hydrochloric
acid. The hydrochloric acid must not be used too largely in
excess, and the fluid must be sufficiently dilute ; otherwise a
portion of the silver will remain in solution. Care must be
taken also not to omit the addition of nitric acid, which pro-
motes the separation of the silver chloride. The latter should

be treated according to 115, 1, a.

2. The separation of MERCURY from the METALS OF THE 129
FIRST FOUR GROUPS may be effected also by ignition, which will
cause the volatilization of the mercury or the mercurial com-
pound, leaving the non-volatile bodies behind. The method is
applicable in many cases to alloys, in others to oxides, chlorides, .
or sulphides. If the mercury is estimated only from the loss,
the operation is conducted in a crucible ; otherwise in a bulb-
tube, or a wide glass tube with porcelain boat. In the latter
case it is well to use a current of hydrogen (compare 118,

1, a ; also Examination of Mercury Ores in the Special Part).
The precipitation of mercury as mercurous chloride with
phosphorous acid, according to 118, 2, is also well adapted for
its separation from metals of the first four groups. If the mer-
cury is already present as a mercurous salt, it may be separated
and determined in a simple manner, by precipitation with
hydrochloric acid ( 117, 1).

WITH SULPHURIC ACID, LEAD may be readily separated by that
acid. The results are very satisfactory, if the rules given in

116, 3 are strictly adhered to.

If you have lead in presence of barium, both in form of
sulphates, digest the precipitate with a solution of ordinary
ammonium sesquicarbonate, without application of heat. This
decomposes the lead salt, leaving the barium salt unaltered.
. Wash, first with solution of ammonium carbonate, then with
water, and separate finally the lead carbonate from the barium
sulphate, by acetic acid or dilute nitric acid (H. ROSE*). The

* Journ.f. prakt. Chern., LXVI, 166,

680 SEPAKATIOK. [ 162.

same object may also be attained by suspending the washed
insoluble salts in water and digesting with a clear concentrated
solution of sodium thiosulphate at 15 20 (not higher). The
barium sulphate remains undissolved, the lead sulphate dis-
solves. Determine the lead in the filtrate (after 116, 2) as
lead sulphide (J. LOWE *). The method recommended by
RIVOT, BEUDANT, and DAGUIN f for separating lead by adding
sodium acetate to the solution, heating, and passing in chlo-
rine gas, requires to be carried out with great caution, ac-
cording to IT. ROSE,:): since portions of other metals, even
such as are not converted into higher oxides e.g., zinc are
very likely to be precipitated with the lead.


a. Free the solution as far as possible from hydrochloric 131
and nitric acids by evaporation with sulphuric acid. Dilute if
necessary, boil, and add sodium thiosulphate as long as a black
precipitate continues to form. As soon as this has deposited,
and the supernatant fluid contains only suspended sulphur,
the whole of the copper is precipitated. The precipitate is
cuprous sulphide (Cu a S), and may be readily washed without
suffering oxidation. Convert it into anhydrous cuprous sul-
phide by ignition in hydrogen ( 119, 3). The other metals
are in the filtrate and washings. Evaporate with some nitric
acid, filter, and determine the metals in the filtrate. || Results
good. The method requires practice, as the end of the pre-
cipitation of the copper is not so easy to hit as when hydro-
gen sulphide is employed.

If the solution contained hydrochloric or nitric acid, and
this was not first removed before the addition of the thiosul-
phate, the precipitant would be required in much larger quan-
tity ; in the presence of hydrochloric acid because the cuprous

*Journ. f. prakt. Chem., LXXVII, 75. f lb. t LXI, 136.

\ Pogg. Annal., ox, 417.

The commercial salt is often not sufficiently pure, in which case some
sodium carbonate must be added to its solution and the mixture filtered.

|| As far back as 1842. C. HIMLY made the first proposal to employ sodium
thiosulphate for the precipitation of many metals as sulphides (Annal. d Chem.
u. Pharm., XLIII, 150). The question, after long neglect, was afterwards takm
up again by VOIIL (Annal. d. Chem. u. Pharm., xcvi, 237), and SLATER (Chem.
Oaz., 1855. 369) FLAJOLOT, however, made the first quantitative experiment
(Annal des Mines, 1853, 641: Journ. f. prakt. Chem., LXI, 105). The results
obtained by him are perfectly satisfactory.

162.] BASES OF GKOUP V. 681

chloride produced is only decomposed by a large excess of
thiosulphate, in the presence of nitric acid because the thio-
sulphate does not begin to act on the copper salt till all the
nitric acid is decomposed.

I. Precipitate the copper as cuprous sulphocyanate 132
according to 119, 3, J, or 119, 4, e\ the other metals
remain in solution (Kivox). If alkalies were present and it
were desired to determine them in the filtrate, ammonium
sulphocyanate must be used instead of the potassium salt
usually employed. This method is particularly well adapted
for the separation of copper from zinc. The zinc can be
precipitated at once from the filtrate by sodium carbonate.
The method is also suitable for separating copper from iron
(H. ROSE *) ; in this case it is unnecessary that ferric salts be
completely reduced by the sulphurous acid added ; the sepa-
ration may be effected, even if the solution becomes blood-
red on the addition of the precipitant.

c. The method proposed by FLAJOLOT,-)- and which has 133
been so frequently recommended, consisting in precipitating

the copper by adding a solution of iodine in aqueous sul-
phurous acid, after removing the greater part of the free acid
present and adding sulphurous acid, gives inaccurate results,
according to H. ROSE,;); because a not inconsiderable quantity
of copper remains dissolved in the sulphurous liquid. This
difficulty may be avoided by adding to the hydrochloric-acid
solution, containing a slight excess of acid, an excess of
stannous chloride, ammonium chloride, and potassium iodide,
until this last just predominates (E. FLEISCHER ). As, how-
ever, the excess of stannous chloride in the filtrate and the
stannic chloride formed must first be removed before the
bases of groups 1 to 4 can be determined, this method offers
no advantages.

d. If the solution is not too dilute, the bases being pres- 134
ent as sulphates, while hydrochloric and nitric acids are
absent, the copper may also be completely precipitated by

* Pogg. AnnaL, ex, 424.

f AnnaL des Mines, 1853, 641; Journ.f. prakt. Chem., LXI, 1QO,

\Pogg. AnnaL, ex, 425.

Zeitschr.f. analyt. Chem., ix, 350,



[ 162.

means of an alkali hypophosphite. At about 70 copper
hydride is precipitated, and this, on heating to a still higher
temperature, which should not, however, exceed 90, decom-
poses into copper and hydrogen. The precipitation is com-
plete when a drop of the liquid is no longer colored brown
by hydrogen sulphide. Wash the spongy copper by decan-
tation, dry, and ignite in a current of hydrogen. The sepa-
ration is complete (W. GIBBS and R. CHAUVENET *). The
method is adapted particularly for separating copper from
the metals of group 4, which may be precipitated from the
filtrate by ammonium sulphide.

e. The solution should be free from hydrochloric acid, 135
and should contain a certain quantity of free nitric acid (20
c. c. nitric acid of 1*2 sp. gr. to 200 c. c.) and some sul-
phuric acid. Throw down the copper by a galvanic current,
so that the metal may be firmly deposited on a platinum ves-
sel (preferably a platinum cone), which forms the negative
pole. Take care that the current is strong enough, and,
without interrupting it, remove the cone from the fluid
occasionally to see when the copper is all precipitated. With
proper execution the separation of copper from all metals of
groups 14 is thorough. All metals of groups 1-4 remain dis-
solved, except manganese, which separates as dioxide at the
positive pole. The method requires practice and strict atten-
tion to tlie conditions which have been determined by a long
course of experiments. It is particularly suited for mining
assays and manufacturers. The electrolytic method of sepa-
rating copper was, I believe, first recommended by GIBBS, f
and afterwards improved by LUCKOW. ; LECOQ DE BOISBAU-
DRAN, ULLGREN,|| and MERRICR^ have also written on this
subject. Finally the method was very accurately and
minutely described by the Mansfelder Ober-Berg- und Iliit-
tendirection at Eisleben,** who, after giving a prize to
LUCKOW'S method, afterwards adopted it, and still further

* Zeitschr. f. analyt. Chem., vu, 2o6. f lb., in, 834.

% Dingier s polyt. Journ., CLXXVII, 296, and (in detail) Zeitschr. f. analyt.
Chem., vin, 25.

Zeitschr. f analyt. Chem., vu, 253, and ix, 102. | lb., 7, 255.

'^American Chemist, ji, 136. ** Zeitechr. f. analyt. Chem. t xi, 1

162.] * BASES OF GROUP V. 683

improved it. I must refer the reader for details to the last
mentioned memoir and LUCKOW'S paper.


a. BOBIEKRE * employed the following method with satis- 136
factory results in the analysis of many alloys of zinc and
copper : The alloy is put into a porcelain boat lying in a por-
celain tube, and heated to redness for three-quarters of an
hour at the most, a rapid stream of hydrogen gas being con-
ducted over it during the process. The zinc volatilizes, the
copper remains behind. If the alloy contains a little lead
(under 2 to 3 per cent.) this goes off entirely with the zinc,
and is partly deposited in the porcelain tube in front of the
boat; if more lead is present part only is volatilized, the rest
remaining with the copper (M. BUESTYN f).

5. A. W. HOFMANN'S method given below (159) for 137
separating copper from cadmium (boiling the precipitated
sulphides with dilute sulphuric acid, whereby the cadmium
sulphide is dissolved while copper sulphide remains behind),

is also adapted for separating copper from zinc (G. C.



One of the oldest methods of separating the oxides con- 138
sists in precipitating the solution with ammonia and filtering
off the precipitated iron hydroxide from the amrnoniacal
copper solution. To obtain accurate results by this method,
however, the precipitation must be repeated according to the
quantity of copper present, two or even three times, or until
the filtrate is no longer blue, otherwise the iron hydroxide
will contain copper.


Evaporate the nitric-acid solution, if it be such a one, 139
with hydrochloric acid to dry ness, dissolve the chlorides in
water, add about twice as much pure potassium tartrate as
there are metals present, warm slightly to facilitate solution,

* Compt. rend., xxxvi, 224; Journ.f. prakt. Chem., LVIII, 380.
\Zeitschr.f. analyt. Chem., xi, 175.

\ Vierteljahresschr. f. prakt. Pharm., xvn, 461 ; Zeitschr. f analyt. Chem.,
vin, 202.



[ 162.

and then add gradually alcoholic solution of potassa until the
hydrated oxides precipitated redissolve. After cooling, add a
solution of pure grape sugar, and boil for one or two minutes.
The copper is precipitated as cuprous oxide. Make certain
that precipitation is complete by adding a drop of grape-
sugar solution to the clear liquid, then filter, and determine
the copper as oxide, either by ignition (treating with nitric
acid and reigniting), or as cuprous sulphide ( 119, 3, c), or
volu metrically ( 119, 4, e). Evaporate the liquid contain-
ing the nickel to dryness, ignite the residue, remove the
potassium carbonate by washing, reignite, dissolve the resi-
due in nitrohydrochloric acid, and precipitate the nickel with
potassa solution, as in 110, 1, a (DEWILDE*). The cu-
prous oxide must be rapidly filtered off and washed, otherwise
a part will redissolve. The method is inconvenient, and is
by no means more accurate than the separation by hydrogen


Precipitate the bismuth according to 120, 4, as bismuth 140
oxy chloride, and determine it as metal ; all the other basic
metals remain completely in solution. Results very satis-
factory (H. RosEf).


Prepare a hydrochloric- or nitric-acid solution of the- two 141
oxides as neutral as possible, add a sufficient quantity of tar-
taric acid, then solution of potassa or soda, until the reaction
of the clear fluid is distinctly alkaline. Dilute now with a
sufficient quantity of water, and boil for 1^-2 hours. All
the cadmium precipitates as hydroxide, free from alkali (to be
determined as directed in 121), whilst the whole of the zinc
remains in solution ; the latter metal is determined as directed
in 108, 1, J (AuBEL and RAMDOIIR ;):). The test-analyses
communicated are satisfactory. As the separation only suc-
ceeds when the substances are present in correct proportions,

* Chem. News, 1863, vn, 49; Zeitschr. f. analyt. Chem., n, 72.

t Pogg, AnnaL, ex, 429. \ Annal. d. Chem, u. Pharm., cm, 33.

163.] BASES OF GROUP V. 685

I will give the quantities employed by AUBEL and RAMDOHR
with especially good effect. About 1 grin, oxide of zinc
and 1 grm. oxide of cadmium were dissolved in hydrochloric
acid, 30 grm. solution of tartaric acid (containing 0*23 grrn.
acid in 1 grm.), 50 grrn. soda solution of 1-16 sp. gr., and
120 grm. water added, and the whole boiled 2 hours. (The
boiling must on no account be done in glass; a platinum or
silver dish should be used.)


If the' solution contains a manganous salt and one of the 142
other bases, precipitate the hot solution with sodium carbonate,
wash the precipitate first by decantation, then on the filter,
with boiling water, dry, ignite for some time, weigh, and in
a portion of the residue estimate the manganese volumetric-
ally (72). If sufficient bismuth, lead, cadmium, or copper is
present, the residue will have the formula Mn 2 O 3 -[- ccMO,
or MnO 2 + a?Bi 2 O, (KRIEGER*). Never neglect testing the
filtrate by adding ammonium sulphide, to ascertain whether
the metals have been completely precipitated by the sodium
carbonate. When precipitating copper by alkali carbonates,
dilute the liquid so that it contains about 1 grm. per litre,
add the alkali carbonate in very slight excess, and boil the
mixture for about half an hour, whereby the bluish-green
basic carbonate becomes dark, granular, and more easily
washed (W. GIBBS and E. E. TAYLOR f).




INDEX. (The numbers refer to those in the margin.)

Silver from copper, 143, 148, 150, 164, 165.
" cadmium, 143, 148, 150.

bismuth, 143, 147, 150, 161.
uiercuricum4 143, 148, 150, 158, 160.
lead, 143, 146, 147, 150, 155, 164, 165.

* Annal. de Chem. u. Fharm., LXXXVII, 264.
\Zeitichr.f. analyt. Chem., VIT, 258.

\ For the sake of brevity the terms " mercuricum " and " mercurosum " are
used to designate respectively mercury in mercuric and mercurous compounds.



[ 163.

Mercuricum* from silver, 143, 148, 150, 158, 160.
41 mercurosum,* 144.

" lead, 145, 146, 147, 150, 158, 160.

bismuth, 145, 147, 150, 151, 158.
" copper, 145, 149, 150, 158, 160.

cadmium, 145, 150, 158.
Mercurosum* from mercuricum, 144.
" copper, 144.

" cadmium, 144.

lead, 144, 146.

Compare also mercuricum from other metals.
Lead from silver, 143, 147, 150, 155, 164, 165.

" mercuricum, 145, 146, 147, 150, 158, 160.
mercurosum, 144, 146.
copper, 146, 147, 150, 152.
" bismuth, 146, 147, 152, 161, 162.

cadmium, 146, 147, 150.
Bismuth from silver, 143, 147, 150, 161.

lead, 146, 147, 152, 161, 162.
copper, 147, 150, 151, 153, 161.
cadmium, 147, 150, 151, 152, 157.
mercuricum, 145, 147, 150, 151, 158.
Copper from silver, 143, 148, 150, 164, 165.
lead, 146, 147, 150, 152.
bismuth, 147, 150, 151, 153, 161.
mercuricum, 145, 149, 150, 158, 160.
" mercurosum, 144.

cadmium, 149, 150, 152, 154, 156, 159.

Copper in cupric from copper in cuprous compounds, 163, 165.
Cadmium from silver, 143, 148, 150.
lead, 146, 147, 150.
bismuth, 147, 150, 151, 152, 157.
copper, 149, 150, 152, 154, 156, 159.
" mercuricum, 145, 150, 158.
" mercurosum, 144.

1. Methods based upon tfie Insolubility of certain of ih6
Chlorides in Water or Alcohol.


a. To separate silver from copper, cadmium, and bismuth, 143
add to the nitric acid solution containing excess of nitric acid,
hydrochloric acid as long as a precipitate forms, and separate
the precipitated silver chloride from the solution which con-
tains the other metals, as directed 115, 1, a. In the presence

*For the sake of brevity the terms "mercuricum" and "mercurosum" are
used to designate respectively mercury in mercuric and mercurous compounds.

163.] BASES OF CROUP V. 687

of bismuth, after pouring off the supernatant fluid, heat again
with nitric acid, and wash with dilute nitric acid before wash-
ing with water.

ft. If you wish to separate mercuricum from silver by
hydrochloric acid, special precautions must be taken, as a solu-
tion of mercuric nitrate possesses the property of dissolving
silver chloride (WACKENRODER, v. LIEBIG,* H. DEBRAyf).
Although the silver chloride in solution for the most part
separates on the addition of enough hydrochloric acid to con-
vert the mercuric nitrate into chloride, or on addition of
sodium acetate, still we cannot depend upon the complete pre-
cipitation of the silver. On this account, mix the nitric acid
solution which must not contain any mercurous salt, and is
to be in a sufficiently dilute condition and acidified with nitric
acid with hydrochloric acid, as long as a precipitate forms.
Allow to deposit, filter off the clear fluid, heat the precipitate
to free it from any possibly coprecipitated basic mercuric
salts with a little nitric acid, add water, then a few drops of
hydrochloric acid, and filter off the silver chloride. In the
filtrate determine the mercury as sulphide ( 118, 3), and
finally test this for silver, by ignition in a stream of hydrogen
any silver that may happen to be present will remain behind
in the metallic state.

y. In the separation of silver from lead, the precipitation
is advantageously preceded by addition of sodium acetate.
The fluid must be hot and the hydrochloric acid rather dilute;
ho more must be added of the latter than is just necessary.
In this manner, the separation may be readily effected, since
lead chloride dissolves in sodium acetate (ANTHON). The sil-
ver chloride is washed with hot water. The lead is thrown
down from the filtrate with hydrogen sulphide. If you desire
to prevent the occasionally injurious influence of sodium ace
tate, great care must be given to the washing of the silver
chloride. It is also well to reduce the weighed chloride by
gentle ignition in a current of hydrogen, and to test the silver
obtained for lead. Regarding the estimation of very small
quantities of silver in lead, compare " Analysis of Refined
Lead ' : in the Special Part.

* Annal. d. Chem. u. Pharin., LXXXI, 128.

f Compt. rend., LXX, 847 ; Zeitschr.f. analyt. Chem., xiu, 349.


tf. The volumetric method ( 115, 5) is usally resorted to in
mints to determine the silver in alloys. In presence of a mer-

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