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of potassium iodide.

J. PARKES' * METHOD ; AND H. FLECK'S f MODIFICATION.

PARKES' expeditious method is based on the action of potassium
cyanide on ammoniacal copper solution. On adding potassium
cyanide to the azure-blue fluid, the color disappears, CuCy,
NII 4 Cy, and KOII being formed, while one equivalent of cyanogen
is liberated, and acting on the free ammonia present, yields urea,
urea oxalate, ammonium cyanide, and ammonium formate (LIE-
BIG :f). The decomposition is not always uniform, however, the
quantity and strength of the ammonia having considerable in-
fluence ; see LIEBIG (loc. cit.\ as also my experiments (2u>. 73, ),
from which it appears that the neutral ammonium salts present
modify the results. See also FLECK (loc. cit.), v. WOLFSKRON,
STEINBECK,! and KIRPITSCHOW.^

FLECK proposed the following modification : Instead of am-
monia, a 1 : 10 solution of ammonium sesquicarbonate is used at a
temperature of 60, the end of the reaction being rendered more
readily determined by adding 2 drops of a 1 : 20 potassium-fer-
rocyanide solution, neither the blue color nor its transparency be-
ing affected by this addition. The potassium-cyanide solution is
standardized against a copper solution of known strength, before
being employed for solutions of unknown strength. On adding
the potassium-cyanide solution by drops to the blue solution
warmed to 60, the odor of cyanogen becomes quite distinct,
while the color of the solution becomes gradually paler. As soon
as the copper double salt is decomposed, the red color of copper
ferrocyanide becomes visible without any precipitate forming,
and on adding the last drop of the potassium-cyanide solution
this color fades away also and leaves a perfectly colorless liquid.

* Mining Journal, 1851. f Polytechn. Centralbl., 1859, 1313.

f Annal. d. Chem. u. Pharm., xcv. 118.
Zeihchr. f. analyt. Chem., v. 403. | Ibid., vm, 1C.

^Zeitschr.f. Chem. (II), vn, 207.



119.] COPPER. 379

This modification yields results wliicli while concordant are yet
only approximate.* Where sucli suffice, the method may be used,
as it is quite convenient.

I have found that in this method also, ammonium salts, if
present, have an influence on the results (see Exp. No. 73, ),
hence the method appears to be useful only when the standard-
ization of the potassium-cyanide solution and the analytical proc-
esses are performed under similar circumstances.

On this principle is based STEINBECK'S f method, which was
devised for estimating the copper in the Mansfeld shales, and
which received a premium from the Mansfeld Ober-Berg-und
Hiitten-Direction. It depends upon the precipitation of metallic
copper from a hydrochloric-acid solution by zinc in contact with
platinum. After being washed, the metallic copper is dissolved
in a definite quantity of nitric acid, a definite quantity of am-
monia added, and the standard solution of potassium cyanide
then added until decolorization is effected. Since, in this
method, only definite quantities of ammonia and ammonium
nitrate are present, the results obtained are very concordant, and
also very nearly correct if the cyanide solution is standardized
against a copper solution the strength of which is approximately
like that of solution to be operated upon. The cyanide solution
should be made of such strength that 1 c. c. of it is the equiva-
lent of 0*005 grm. of copper.

c. METHODS DEPENDING UPON THE PRECIPITATION OF COPPER
13 Y SODIUM SULPHIDE.

PELOUZE supersaturates the neutral or acid copper solution with
ammonia, heats the solution to between 60 and 80, and adds so-
dium sulphide until the blue color just disappears. The precipitate
that forms at this temperature has the composition 5CuS -|- CuO.
As the temperature is not without influence on the composition
of the precipitate, and as the moment of disappearance of the
blue color is not very marked, FR. MOHR ^ and KUNZEL have

* FLECK used in 6 tests, in which varying quantities of ammonium carbonate
were purposely taken for 100 c. c. of copper solution, a minimum of 15'2 c. c.
and a maximum of 15 75 c. c., an average of 15'46 c. c. of potassium-cyanide
solution.

\ Zeitsclir. f. analyt. CJiem., vin, 8.

t Lehrbucli der TitrirmelJiode , 3. Aufl., 429.

Jour.f. prakt. Ghem. t LXXXVIII, 486; ZeitscJir. f. analyt, Chem., n, 373.



380 DETERMINATION. [ 119.

modified the method. The former precipitates in the cold
(whereby cupric sulphide is formed), and ascertains the incipient
excess of sodium sulphide by using alkaline-lead solution. The
latter precipitates at the boiling temperature (the oxysulphide
formed in this case rapidly settles), and ascertains when the pre-
cipitation of copper is complete by bringing a drop of the
fluid into contact with freshly precipitated hydrated zinc sulphide
(it should not be colored brown). The sodium-sulphide solution
should be diluted so that 1 c. c. will precipitate about 01 grm.
copper. It may be standardized by using a solution containing
10 grm. of copper per litre. 20 c. c. are taken, representing 0*2
grin, of copper, supersaturated with ammonia, then diluted with
water, heated to boiling, and sodium-sulphide solution then added
until the reaction is complete. The zinc sulphide required is pre-
pared by dissolving ordinary zinc in hydrochloric acid, adding an
excess of ammonia, and boiling with a small quantity of sodium-
sulphide solution, whereby any lead present is precipitated. Suf-
ficient sodium-sulphide solution is now added to precipitate nearly
all of the zinc (leaving a small quantity unprecipitated) ; the
magma obtained is uniformly spread out over several layers of
blotting-paper.

According to KUNZEL the method, if carefully carried out,
gives errors not exceeding 0*25 per cent. ; hence it is perfectly
suitable for technical purposes.

d. METHODS DEPENDING UPON THE REDUCTION OF CUPKIG
CHLORIDE BY STANNOUS CHLORIDE.

E. MULDER * was the first to base upon this reaction a method
of estimating copper, using indigo-carmine as an indicator. FR.
WEIL f found that if sufficient hydrochloric acid is present, the
end of the reaction is indicated by the decolorization of the hot
liquid. He prepared the stannous-chloride solution by dissolving
6 grm. of tinfoil in 200 c. c. of hot hydrochloric acid and diluting
the solution with boiled water to make 1 litre. The copper solu-
tion, against which the stannous-chloride solution must be stand-
ardized before every fresh series of estimations, is prepared by

*Ja7tresber. von Korr u. WILL, 1860, 613.
\Zeitschr.f. analyt Chem., ix, 297.



119.] COPPER. 381

dissolving 7-854 grin, of copper sulphate (=2 grm. Cti.), pow-
dered and dried by pressure between blotting-paper, in water to
make 500 c. c. 25 c. c. of this solution (containing O'l grm. cop-
per) are then introduced into a 100-c. c. flask, 5 c. c. of pure,
concentrated hydrochloric acid added, the whole heated to gentle
boiling, and stannous-chioride solution added to the boiling liquid,
rapidly at first, but towards the last by drops, until the fluid
is perfectly colorless. 5 c. c. of hydrochloric acid are again
added ; if a slight color develops, it is discharged by adding a
few drops of stannous-chioride solution. The further certainty
that the reaction is complete is afforded on adding a few drops of
mercuric-chloride solution to a small quantity of the cooled solu-
tion ; if no turbidity is noticeable there is no excess of stannous
chloride present, hence a little of the latter may be added until
a faint precipitate of mercurous chloride is developed. In this
case, however, there must be deducted 0- 05 c. c. from the quantity
of stannous-chioride solution used. In titrating a copper solu-
tion proceed similarly. Any nitric acid present must be evap-
orated off after adding an excess of sulphuric acid. If any fer-
ric salt is present, it will be reduced with the cupric chloride.
In such a case precipitate the copper in a second portion of the
solution with zinc and platinum wire in the heat, determine the
ferrous salt with potassium permanganate or chromate ( 112),
and calculate how much of the stannous-chioride solution had
been used to reduce the ferric salt: the remainder will be that
used up for the cupric chloride ; or wash the precipitated cop-
per, dissolve it in sulphuric acid, and then reduce it with stan-
nous chloride. The test analyses cited by WEIL show very satis-
factory results.

e. SCHWARZ * precipitates cuprous oxide from the solution of
potassio-cupric tartrate by heating with grape sugar, filters off
the precipitate, washes it, warms it with ferric chloride and hy-
drochloric acid, and, according to the equation Cu 2 O -f- Fe 2 Cl 6 -f-
2HC1 = 2CuCl 2 + 2FeCl 2 + H 2 O, estimates the ferrous chloride
formed by means of potassium permanganate. f



* Annal d. Chem. u. Pharm . LXXXIV, 84.

f Potassium chromate is not eligible for use because the cupric chloride im-
pairs the distinctness of the end reaction.



382 DETERMINATION. [ 120.

f. E. FLEISCHER * precipitates the copper as cuprous sulpho-
cyanate ( 119, 3, J), boils the washed precipitate with potassa
lye, and thus obtains cuprous oxide ; or he adds stannous chloride
and potassium iodide and obtains a precipitate of cuprous iodide.
In either case the precipitate is brought into contact with ferric-
sulphate solution, the ferrous salt formed estimated, and from
this the copper calculated.

g. F. FLEITMANN f precipitates the copper with zinc, brings
the washed precipitate into contact with ferric chloride and hy-
drocholoric acid, and estimates the ferrous chloride formed
(Cu + Fe,Cl. = CuCl, + 2FeCl f ).

h. H. SCHWARZ \ adds potassium xanthogenate to the acetic-
acid solution of copper until no further precipitate forms. Since
the other heavy metals, excepting zinc, are also precipitated by
the reagent from acetic-acid solutions, the copper must be separated
from the precipitate.

As noted, the methods e to h require the previous precipita-
tion or isolation of the copper in one way or another; they can-
not therefore be preferred to gravimetric methods, excepting in
very special cases.

120.
6. BISMUTH.

a. Solution.

Metallic bismuth, bismuth trioxide, and all other compounds
of that metal, are dissolved best in nitric acid more or less diluted.
It must be borne in mind that hydrochloric-acid solutions of bis-
muth, if concentrated, cannot be evaporated without loss of
bismuth chloride.

b. Determination.

Bismuth is weighed in the form of trioxide^ chromate, sul-
phide, or arsenate, or in the metallic state. The compounds of bis-
muth are converted into trioxide by ignition, by precipitation as
basic carbonate, or by repeated evaporation of the nitric-acid solu-



* ZeitscJir. /. analijt. Ghem. t ix, 255.
f Annal. d. Ckem. u. Pharm., xcvirr, 141

^Dingl. polyt. Journ., cxc, 220 and 295; also Zeitschr. f. analyt. Chem.,
Vlii, 462.



120.] BISMUTH. 383

tion. These are sometimes preceded by separation as sulphide.
The determination as metallic bismuth is frequently preceded by
precipitation as sulphide or as basic chloride.
We may convert into

1. BISMUTH TRIOXIDE:

a. By Precipitation as basic Bismuth Carbonate. All com-
pounds of bismuth which dissolve in nitric acid to nitrate, no other
acid remaining in the solution.

1). By Ignition.

a. Bismuth salts of readily volatile oxygen acids.

' ft. Bismuth salts of organic acids.

c. By Evaporation. Bismuth in nitric-acid solution.

d. By Precipitation as Bismuth Trisulphide. All compounds
of bismuth without exception.

2. BISMUTH CHROMATE. All compounds named in 1, a.

3. BISMUTH TRISULPHIDE. The compounds of bismuth without
exception.

4. METALLIC BISMUTH : The trioxide and oxygen salts, the
sulphide, the basic chloride, in which latter form the bismuth may
be precipitated out of all its solutions.

1. Determination of Bismuth as Trioxide.

a. By Precipitation as Bismuth Carbonate.

If the solution is concentrated add water, taking no notice of
any precipitate of basic nitrate that may be formed. Mix with
ammonium carbonate in very slight excess, and heat for some time
nearly to boiling ; filter, dry the precipitate, and ignite in the man-
ner directed 116, 1 (Ignition of lead carbonate) ; the process of
ignition serves to convert the carbonate into bismuth trioxide. For
the properties of the precipitate and residue, see 86. The method
gives accurate results, though generally a trifle too low, owing to
the circumstance that bismuth carbonate is not absolutely insoluble
in ammonium carbonate. Were you to attempt to precipitate
bismuth, by means of ammonium carbonate, from solutions con-
taining sulphuric acid or hydrochloric acid, you would obtain
incorrect results, since with the basic carbonate, basic sulphate or
basic chloride would be precipitated, which are not decomposed by
excess of ammonium carbonate. Were you to filter off the precipi-
tate without warming, a considerable loss would be sustained, as



384 DETERMINATION. [ 120.

the whole of the basic carbonate would not have been separated
(Expt. No. 74).

b. By Ignition.

ex. Compounds like bismuth carbonate or nitrate are ignited in
a porcelain crucible until their weight remains constant.

ft. Salts of organic acids are treated like the corresponding
compounds of copper ( 119, 1, c).

c. By Evaporation. .

The solution of the nitrate is evaporated, in a porcelain dish on
the water-bath, till the neutral salt remains in syrupy solution;
add water, loosen the white crust that is formed with a glass rod
from the sides, evaporate again on a water-bath, reprecipitate with
water, and repeat the whole operation three or four times. After
the dry mass on the water-bath has ceased to smell of nitric acid,
it is allowed to cool thoroughly, and then treated with cold water
containing a little ammonium nitrate (1 in 500) ; after the residue
and fluid have been a short time together, filter, wash with the
weak solution of ammonium nitrate, dry and ignite ( 53). Eesults
very satisfactory (J. LOWE*).

d. By Precipitation, as Bismuth Trisulphide.

Dilute the solution with water slightly acidulated with acetic
acid (to prevent the precipitation of a basic salt), and precipitate
with hydrogen sulphide water or gas ; allow the precipitate to
subside, and test a portion of the supernatant fluid with hydrogen
sulphide water: if it remains clear, which is a sign that the
bismuth is completely precipitated, filter (the filtrate should smell
strongly of H a S), and wash the precipitate with water containing
hydrogen sulphide. Or mix with ammonia until the free acid is
neutralized, then ;i<l<l ammonium sulphide in excess, and allow to
digest for some time.

The washed precipitate may now be weighed in three different
forms, viz., as trisulphidi-, as metal, or as trioxide. The treatment
in the two former cases will be described in 3 and 4 : in the latter
case proceed as follows :

Spread the filter out on a glass plate and remove the precipitate
to a vessel by means of a jet of water from the wash-bottle or, if
this is not practicable, put the precipitate and filter together into
the vessel and heat gently with moderately strong nitric acid

* Journ. f. prakt. Chem., LXXIV, 844.



120.] BISMUTH. 385

until complete decomposition is effected ; the solution is then
diluted with water slightly acidulated with acetic or nitric acid,
and filtered, the filter being washed with the acidulated water; the
filtrate is then finally precipitated as directed in a.

2. Determination of Bismuth as Chromate (J. LOWE*),
Pour the solution of bismuth, which must be as neutral as

possible, and must, if necessary, be first freed from the excess of
nitric acid by evaporation on the water-bath, into a warm solution
of pure potassium dichromate in a porcelain dish, with stirring,
and take care to leave the alkali chromate slightly in excess.
Rinse the vessel which contained the solution of bismuth with
water containing nitric acid into the porcelain dish. The precipi-
tate formed must be orange-yellow, and dense throughout ; if it is
flocculent, and has the color of the yolk of an egg, this is a sign
that there is a deficiency of potassium dichromate; in which case
add a fresh quantity of this salt, taking care, however, to guard
against too great an excess, and boil until the precipitate presents
the proper appearance. Boil the contents of the dish for ten
minutes, with stirring ; then wash the precipitate, first by repeated
boiling with water and decantation on to a weighed filter, at last
thoroughly on the latter with boiling water ; dry at about 120,
and weigh. For the properties and composition of tlie precipitate,
see 86. Results very satisfactory.

3. Determination of Bismuth as Trisulphide.
Precipitate the bismuth as trisulphide according to 1, d. If

the precipitate contains free sulphur, extract the latter by boiling
with solution of sodium sulphite, or by treatment with carbon
disulphide (compare the determination of mercury as sulphide,
118, 3), collect on a weighed filter, dry at 100, and weigh.

The drying must be conducted with caution. At first the
precipitate loses weight, by the evaporation of water, then it gains
weight, from the absorption of oxygen. Hence you should weigh
every half hour, and take the lowest weight as the correct one.
Compare Expt. No. 52. Properties and composition, 86, g.

The bismuth sulphide cannot be conveniently converted into
the metallic state by ignition in hydrogen, as its complete decom-
position is a work of considerable time. As regards reduction
with potassium cyanide, see 4.

* Journ. f. prakt. Chem., LXVII, 464



386 DETERMINATION. [ 120.

4. Determination of JSismuth as Metal.
The oxide, sulphide, or basic chloride to be reduced is fused
in a porcelain crucible with five times its quantity of ordi-
nary potassium cyanide. The crucible must be large enough
In the case of oxide and basic chloride, the reduction is completed
in a short time at a gentle heat ; sulphide, on the other hand,
requires longer fusion and a higher temperature. The operation
has been successful if on treatment with water metallic grains are
obtained. These grains are first washed completely and rapidly
with water, then with weak and lastly with strong alcohol, dried
and weighed. If you have been reducing the sulphide, and on
treating the fused masswith water a black powder (a mixture of
bismuth with bismuth sulphide) is visible, besides the metallic grains,
it is necessary to fuse the former again with potassium cyanide.

It sometimes happens that the crucible is attacked, and particles
of porcelain are found mixed with the metallic bismuth ; to prevent
this from spoiling the analysis, weigh the crucible together with a
small dried filter before the experiment, collect the metal on the
filter, dry and weigh the crucible with the filter and bismuth again.
Results good (H. ROSE*).

The precipitation of bismuth as basic chloride, and the reduc-
tion of the latter with potassium cyanide, has been recommended
by II. RosE.f The process is conducted as follows : Nearly neu-
tralize any large excess of acid that may be present with potassa,
soda, or ammonia, add ammonium chloride in sufficient quantity
(if hydrochloric acid is not already present), and then a rather large
quantity of water. After allowing to stand some time, test whether
a portion of the clear supernatant fluid is rendered turbid by a
further addition of water ; and then, if required, add water to the
whole till the precipitation is complete. Finally filter, wash com-
pletely with cold water, dry and fuse according to the directions
just given with potassium cyanide. It is less advisable to dry the
precipitate at 100, weigh and calculate the metal present from the
formula BiOCl, as washing causes a slight alteration in its com-
position (unless a little hydrochloric acid is added to the wasli-
water, which is inconvenient when the precipitate is collected on
a weighed filter), and if precipitated in the presence of sulphuric,
phosphoric acids, &c., it is liable to contain small quantities of
these acids. Results accurate.

*Pogg. Annal., xci, 104, and ex, 136. \lb. ex, 425.



121.] CADMIUM. 387

5. Determination of Bismuth as Ar senate.
H. SALKOWSKI * recommends the determination of bismuth as
ai arsenate (BiAsO 4 .H,O) which is dried at 100 to 120, the
method being based on the observation by SCHEELE that bismuth
arsenate is perfectly insoluble in nitric acid. The solution of
bismuthic nitrate is acidulated with nitric acid (but must be free from
other acids), precipitated by a moderate excess of arsenic acid,
and stirred, avoiding touching the sides of the beaker with the
rod (otherwise the crystalline precipitate will adhere fast to the
parts touched). The whole is then allowed to stand, without
warming, for a few hours, then the precipitate is collected on a
filter previously dried at 120, and washed until the washings
begin to pass slightly turbid. Then dry at 120 and weigh.
Ignition of the precipitate is not advisable, as the carbon of the
filter exercises a reducing action even when ammonium nitrate is
used. The test analyses made by SALKOWSKI gave 99 '88 to
100-02 instead of 100.

121.

Y. CADMIUM.
a. Solution.

Cadmium, its oxide, and all the other compounds insoluble in
water, are dissolved in hydrochloric acid or in nitric acid.

1). Determination.

Cadmium is weighed either in the form of oxide, or in that of
sulphide ( 87). It may also be weighed as sulphate, and in the
absence of other bases precipitable by oxalic acid, it may be esti-
mated volumetrically.

"We may convert into

1. CADMIUM OXIDE:

a. By Precipitation. The compounds of cadmium which are
soluble in water ; the insoluble compounds, the acid of which is
removed upon solution in hydrochloric acid ; cadmium salts of
organic acids.

1. By Ignition. Cadmium salts of readily volatile or easily
decomposable inorganic oxygen acids.

2. CADMIUM SULPHIDE : All compounds of cadmium without
exception.

* Journ. f. prakt. Cftem., civ, 170; Zeitschr. /. analyt. Chem., vm, 205.



388 DETERMINATION. [ 121.

3. CADMIUM SULPHATE : All compounds of cadmium, in the
absence of other non-volatile substances.

1. Determination as Cadmium Oxide.

a. By Precipitation.

Precipitate with potassium carbonate, wash the precipitated
cadmium carbonate, and convert it, by ignition, into oxide. The
precipitation is conducted as in the case of zinc, 108, 1, a. The
cadmium oxide which adheres to the filter may easily be reduced
and volatilized ; it is therefore necessary to be cautious. In the
first place choose a thin filter, transfer the dried precipitate as com-
pletely as possible to the crucible, replace the filter in the funnel,
and moisten it with ammonium nitrate solution, allow to dry, and
then burn carefully in a coil of platinum wire. Let the ash fall
into the crucible containing the mass of the precipitate, ignite
carefully, avoiding the action of reducing gases, and finally weigh.
It is difficult to remove the last portions of carbonic acid ; you must
therefore repeat the ignition till the weight remains constant
Properties of precipitate and residue, 87. Results generally a
little too low.

I). By Ignition.

Same process as for zinc, 108, 1, c.

2. Determination as Cadmium Sulphide.
It is best to precipitate the moderately acid solution with hydro-
gen sulphide water or gas, which must be used in sufficient excess.
The presence of a considerable quantity of free hydrochloric or
nitric acid may especially if the solution is not enough diluted
prevent complete precipitation, hence such an excess should be
'avoided, and the clear supernatant fluid should in all cases be tested,
by the addition of a relatively large amount of hydrogen sulphide
water to a portion, before being filtered. Alkaline solutions of
cadmium may be precipitated with ammonium sulphide. If the
cadmium sulphide is free from admixed sulphur, it maybe at once
collected on a weighed filter, washed first with diluted hydrogen
sulphide water mixed with a little hydrochloric acid, then with
pure water, dried at 100, and weighed : it', on the contrary, it eon-
tains free Hilphur, it may be purified by boiling with a solution of
sodium sulphite, or by treatment with carbon disulphide (see Mer-
curic Sulphide, 118, 3). Results accurate. The precipitation of
sulphur may occasionally be obviated 1>\ adding to the cadmium



122.] PALLADIUM. 389

solution potassium cyanide till tlie precipitate first formed is redis-
solved, a*nd then precipitating tins solution with hydrogen sulphide.



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