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If the cadmium sulphide is not to be weighed as such, warm it,
together with the filter, with moderately strong hydrochloric acid,
till the precipitate has dissolved and the odor of hydrogen sulphide
is no longer perceptible, filter and precipitate the solution as in
1, #, after having removed the excess of free acid for the most part
by evaporation.

3. Determination as Cadmium Sulphate.

Same process as for magnesium ( 104, 1). The CdSO 4 may
be rather strongly ignited without decomposition.

4. W. G-IBBS* determines cadmium volumetrically by mixing
the concentrated solution of the sulphate, nitrate, or chloride with
excess of oxalic acid and a quantity of strong alcohol, filtering,
washing with alcohol, dissolving in hot hydrochloric acid and
determining the oxalic acid with permanganate ( 137). W. Or.
LEisoNf obtained satisfactory results by this process.

Supplement to the Fifth Group.

122.
8. PALLADIUM.

Palladium is converted, for the purpose of estimation, into the
metallic state or in many separations into potassium palladia
chloride.

1. Determination as JPalladium.

a. Neutralize the solution of palladious chloride almost com-
pletely with sodium carbonate, mix with solution of mercuric
cyanide ; and heat gently for some time, until the odor of hydro-
cyanic acid has gone off. A yellowish-white precipitate of pall di-
ous cyanide will subside ; from dilute solutions, only after the lapse
of some time. Wash first by decantation, then on the filter, dry
thoroughly, ignite cautiously, finally over the gas blowpipe till the
palladium paracyanide first formed is decomposed, then ignite in
hydrogen, since the palladium has been slightly oxidized As soon
as the lamp is removed, stop the hydrogen to prevent absorption,
and weigh the metal. If the solution contains palladious nitrate,
evaporate it first with hydrochloric acid to dryness; as otherwise
* Zeitschr. /. analyt. Chern., vn, 25U. \ lb., x, 343.



390 DETERMINATION. [ 122.

the precipitate obtcained deflagrates upon ignition (WOLLASTON).
Results exact.

b. Mix the solution of palladious chloride or nitrate with
sodium or potassium formate, and warm until no more carbonic
acid escapes. The palladium precipitates in brilliant scales (Dnni;-
REINER).

c. Precipitate the acid solution of palladium with hydrogen
sulphide, filter, wash with boiling water, roast, dissolve in hydro'
chloric acid and nitric acid, and precipitate as in a.

Exposed to a moderate red heat metallic palladium becomes
covered with a film varying from violet to blue, but at a higher
temperature it recovers its lustre, which it keeps after being sud-
denly cooled, for instance, with cold water. This tarnishing and
recovery of the metallic lustre is not attended with any percepti-
ble difference of weight. Palladium which has taken up oxygen
is immediately reduced in hydrogen ; when cooled in the current
of gas, it retains some absorbed hydrogen. Palladium requires the
very highest degree of heat for its fusion. It dissolves readily in
nitrohydrochloric acid, with difficulty in pure nitric acid, more
easily in nitric acid containing nitrous acid, with difficulty in boil-
ing concentrated sulphuric acid.

2. Determination as Potassium Palladic Chloride.

Evaporate the solution of palladic chloride w r ith potassium
chloride and nitric acid to dryness, and treat the mass when cold
with alcohol of 0' 833 sp. gr., in which the double salt is insoluble.
Collect on a weighed filter, dry at 100, and weigh. Results a
little too low, as traces of the double salt pass away with the alcohol
washings (BERZELIUS). Instead of weighing the double salt you
may ignite in hydrogen, remove the potassium chloride with water
and weigh the metal obtained. This method is indeed to be pre-
ferred, as it prevents any potassium chloride in the precipitate from
affecting the result.

POTASSIUM PALLADIC CHLORIDE consists of microscopic octa-
hedra ; it presents the appearance of a vermilion or, if the crystals
are somewhat large, of a brown powder. It is very slightly solu-
ble in cold water ; it is almost insoluble in cold alcohol of the above
strength. It contains 26*89 per cent, palladium.



123.] GOLD. 391

Sixth Group.

GOLD PLATINUM ANTIMONY TIN IN STANNIC COMPOUNDS TIN IN

STANNOUS COMPOUNDS ARSENOUS AND AKSENIC ACIDS ( MO-

LYBDIC ACID).

123.

1. GOLD.

a. Solution.

Metallic gold, and all compounds of gold insoluble in water,
are warmed with hydrochloric acid, and nitric acid is gradually
added until complete solution is effected ; or they are repeatedly
digested with strong chlorine water. The latter method is resorted
to more especially in cases where the quantity of gold to be dis-
solved is small, and mixed with foreign oxides which it is wished
to leave undissolved. According to W. SKEY* tincture of iodine,
or, for larger quantities of gold, bromine water, is better than chlo-
rine water. They give solutions freer from other metals than the
chlorine water gives.

I. Determination.

Gold is always weighed in the metallic state. The compounds
are brought into this form, either by ignition or by precipitation,
as gold, or auric sulphide.

We convert into

METALLIC GOLD :

a. By Ignition. All compounds of gold which contain no fixed
acid, or other body.

1). By Precipitation as metallic gold. All compounds of gold
without exception in cases where a is inapplicable.

c. By Precipitation as auric sulphide. This method serves to
effect the separation of gold from certain other metals which may
be mixed with it in a solution.

Determination as Metallic Gold,
a. By Ignition,.

Heat the compound, in a covered porcelain crucible, very gently
at first, but finally to redness, and weigh the residuary pure gold.
For properties of the residue, see 88. The results are most
accurate.

*Z*itschr.f. analyt. Chem.. x, 221.



392 DETERMINATION. [

I. By Precipitation as Metallic Gold.

a. The solution is free from Nitric Acid. Mix the solution
with a little hydrochloric acid, if it does not already contain some
of that acid in the free state, and add a clear solution of ferrous
sulphate in excess ; heat gently for a few hours until the precipi-
tated fine gold powder has completely subsided; filter, wash, dry,
and ignite according to 52. A porcelain dish is a more appro-
priate vessel to effect the precipitation in than a beaker, as the
heavy fine gold powder is more readily rinsed out of the former
than out of the latter. There are no sources of error inherent in
the method.

ft. The solution of Gold contains Nitric Acid. Evaporate the
solution, on a water-bath, to the consistence of syrup, adding from
time to time hydrochloric acid ; dissolve the residue in water con-
taining hydrochloric acid, and treat the solution as directed in a.
It will sometimes happen that the residue does not dissolve to a
clear fluid, in consequence of a partial decomposition of auric chlo-
ride into aurous chloride and metallic gold; however, this is a mat-
ter of perfect indifference.

y. In cases where it is wished to avoid the presence of iron in
the filtiate, the gold may be deduced by means of oxalic acid. To
this end, the dilute solution freed previously, if necessary, from
nitric acid, in the manner directed in ft is mixed, in a beaker,
with oxalic acid, or with ammonium oxalate in excess, some sul-
phuric acid added (if that acid is not already present in the free
state), and the vessel, covered with a glass plate, is kept standing
for two days in a moderately warm place. At the end of that
time, the whole of the gold will be found to have separated in
small yellow scales, which are collected on a filter, washed first
with dilute hydrochloric acid, then with water, dried, and ignited.
If the gold solution contains a large excess of hydrochloric acid,
the latter should be for the most part evaporated, before the solu-
tion is diluted and the oxalic acid added. If the gold solution con-
tains chlorides of alkali metals, it is necessary to dilute largely, and
allow to stand for a long time, in order to effect complete precipi-
tation (II. RoSK).

6. The gold may also be thrown down in the metallic form by
chloral hydrate * in the presence of potassa. . Warm the solution,

* HAGUK'S Pharmac. CentralJialle, xr, 393.



124] PLATINUM. 393

add the chloral, then pure potassa in excess, and boil for a minute
or so. The gold is precipitated with evolution of chloroform.

e. Finally, gold may be thrown down by many metals, such as
zinc, cadmium, magnesium, &c. The latter has been recommended
byScHEiBLER* for the analysis of the gold salts of organic bases.
The precipitate is first washed with hydrochloric acid, then with
water.

c. By Precipitation as Auric Sulphide.

Hydrogen sulphide gas is transmitted in excess through the
dilute solution containing some free acid; the precipitate formed
is speedily filtered oif, without heating, washed, dried, and ignited
in a porcelain crucible. For the properties of the precipitate, see
88. 'No sources of error.

124

2. PLATINUM.

a. Solution.

Metallic platinum, and the compounds of platinum which are
insoluble in water, are dissolved by digestion, at a gentle heat, with
nitrohydrochloric acid.

b. Determination.

Platinum is invariably weighed in the metallic state, to which
condition its compounds are brought, either by precipitation as
ammonium platinic chloride, potassium platinic chloride, or pla-
tinic sulphide, or by ignition, or by precipitation with reducing
agents. All compounds of platinum, without exception, may, in
most cases, be converted into platinum by either of these methods.
Which is the most advantageous process to be pursued in special
instances, depends entirely upon the circumstances. The reduc-
tion to the metallic state by simple ignition is preferable to the
other methods, in all cases where admissible. The precipitation as
platinic sulphide is resorted to exclusively to effect the separation
of platinum from other metals.

Determination as Metallic Platinum,
a. By Precipitation as Ammonium Platinic Chloride.
The solution must be concentrated if necessary by evaporation

*Ber. derdoutsch. chem. Gesellsch., 1869, 295.



394 DETERMINATION. [ 124.

on a water-bath. Mix in a beaker with ammonia until the excess
of acid (that is, supposing an excess of acid to be present) is nearly
saturated ; add ammonium chloride in excess and mix the fluid
with a pretty large quantity of strong alcohol. Cover the beaker
now with a glass plate and let it stand for twenty-four hours, after
which collect in a weighed asbestos filter, or in an un weighed
paper filter, wash the precipitate with alcohol of about 80 per
cent., till the substances to be separated are removed, dry carefully,
ignite according to 99, 2, and weigh. In the case of large quan-
tities the final ignition is advantageously conducted in a stream of
hydrogen ( 108, Fig. 83), in order to be quite sure of effecting
complete decomposition. For the properties of the precipitate and
residue, see 89. The results are satisfactory, though generally a
little too low, as the ammonium platinic chloride is not altogether
insoluble in alcohol of the above strength (Expt. No. 16), and as
the fumes of ammonium chloride are liable to carry away traces of
the yet undecomposed double chloride, if the application of heat is
not conducted with the greatest care.

If the precipitated ammonium platinic chloride were weighed
in that form, the results would be inaccurate, since, as I have con-
vinced myself by direct experiments, it is impossible to completely
free the double chloride, by washing with alcohol, from all traces
of the ammonium chloride thrown down with it, without dissolving
at the same time a notable portion of the double chloride. As a
general rule, the results obtained by weighing the ammonium pla-
tinic chloride in that form are one or two per cent, too high.

J. By Precipitation as Potassium Platinic Chloride.

Mix the solution, in a beaker, with potassa, until the greater
part of the excess of acid (if there be any) is neutralized; add
potassiu:n chloride slightly in excess, and finally a pretty large
quantity of strong alcohol; should your solution of platinum be
very dilute, you must concentrate it previously to the addition of
the alcohol. After twenty-four hours collect the precipitate
weighed asbestos filter, wash with alcohol of 80 percent., dry
thoroughly at 100, convert into platinum according to 97, 4, or,
and weigh. For the properties of the precipitate and residue,
see 89.

The results are more accurate than those obtained by method a,
since, on the one hand, the potassium platinic chloride is more



125.] ANTIMONY. 395

insoluble in alcohol than the corresponding ammonium salt; and,
on the oilier hand, loss of substance is less likely to occur during
ignition. To weigh the potassium platinic chloride in that form
would not be practicable, as it is impossible to remove, by washing
with alcohol, all traces of the potassium chloride thrown down
with it, without, at the same time, dissolving a portion of the
double chloride.

c. By Precipitation as Platinic Sulphide.

Precipitate the solution with hydrogen- sulphide water or gas,
according to circumstances, heat the mixture to incipient ebulli-
tion, filter, wash the precipitate, dry, and ignite according to 52.
For the properties of the precipitate and residue, see 89. The
results are accurate.

d. By Ignition.

Same process as for gold, 123. For the properties of the
residue, see 89. The results are most accurate.

e. By Precipitation with Reducing Agents.

Various reducing agents may be employed to precipitate plati-
num from its solutions in the metallic state. The reduction is
very promptly effected by ferrous sulphate and potassa or soda
(the protosesquioxide of iron being removed by subsequent addi^
tion of hydrochloric acid, HEMPEL), or by pure zinc or magnesium
(the excess of which is removed by hydrochloric acid) ; somewhat
more slowly, and only with application of heat, by alkali formates.
Mercurous nitrate also precipitates the whole of the platinum from
solution of platinic chloride ; upon igniting the brown precipitate
obtained, fumes of mercurous chloride escape, and metallic plati-
num remains.

125.

3. ANTIMONY.

a-. Solution,

Antimonous oxide, and the compounds of antimony which are
insoluble in water, or are decomposed by that agent, are dissolved
in more or less concentrated hydrochloric acid. Metallic antimony
is dissolved best in nitrohydrochloric acid. The ebullition of a
hydrochloric acid solution of antimonous chloride is attended with
volatilization of traces of the latter ; the concentration of a solution



396 bETERMINATIONo [ 125.

of the kind by evaporation involves accordingly loss of substance.
Solutions so highly dilute as to necessitate a recourse to evapora-
tion must therefore previously be supersaturated with potassa.
Solutions of fl.ntimonous chloride, which it is intended to dilute
with water, nrast previously be mixed with tartarie acid, to prevent
the separation of basic salt. In diluting an acid solution of anti-
monic acid in hydrochloric acid, the water must not be added
gradually and in small quantities at a time, which would make the
fluid turbid, but in sufficient quantity at once, which will leave the
fluid clear.

I. Determination.

Antimony may be weighed as antimonous sulphide or anti-
mony tetroxide: in separations it is sometimes weighed as metallic
antimony ; or it is estimated volumetrically. Antimony oxides
and the salts, with readily volatile or decomposable oxygen acids,
may be converted into antimony tetroxide by simple ignition.

Antimony in solution is almost invariably first precipitated as
sulphide, which is then, with the view of estimation, converted
into anhydrous sulphide or determined volumetrically.

Of the volumetric methods the first two are applicable only
when the antimony is present as a pure tetroxide or as anti-
monous chloride.

1. Precipitation as Antimonous Sulphide.

Add to the antimony solution hydrochloric acid, if not already
present, then tartarie acid, and dilute with water, if necessary.
Introduce the clear fluid into a flask, closed with a doubly perfo-
rated cork; through one of the perforations passes a tube, bent
outside at a right angle, which nearly extends to the bottom of the
flask; through the other perforation passes another tube, bent out-
side twice at right angles, which reaches only a short way into the
flask ; the outer end of this tube dips slightly under water. Con-
duct through the first tube hydrogen sulphide gas, until it pre-
dominates strongly; put the flask in a moderately warm place, and
after some time conduct carbon dioxide into the fluid, until the
excess of the other gas is almost completely removed. If there is
no ivaxni ;i gainst it, from the presence of a large quantity of
hydrochloric acid, or from the presence of nitric acid, it is well to
heat the solution during tlu- passing of the gas, finally even boiling.



125.] ANTIMONY. 397

The precipitate is then denser, and may be very easily washed

(SlIAEPLES*).

If the amount of the precipitate is at all considerable, filter
without intermission through a weighed filter, wash rapidly and
thoroughly with water mixed with a few drops of hydrogen sul-
phide water, dry at 100, and weigh. The precipitate so weighed
always retains some water, and may, besides, contain free sulphur ;
in fact, it always contains the latter in cases where the antimony
solution, besides antimonous salts, contains antimonic acid or
antimony pentachloride, since the precipitation under these cir-
cumstances is preceded by. a reduction of antimonic to antimo-
nous compounds, accompanied by separation of sulphur (H. ROSE).
A further examination of the precipitate is accordingly indis-
pensable. To this end treat a sample of the weighed precipitate
with strong hydrochloric acid. If

a. The sample dissolves to a clear fluid, this is a proof that the
precipitate only contains Sb a S 3 ; but if

h. Sulphur separates, this shows that free sulphur is present.

In case a (in order to remove the water retained at 100) the
greater portion of the dried precipitate is weighed in a porcelain
boat, which is then inserted into a glass tube, about 2 decimetres
long ; a slow current of dry carbon dioxide is transmitted through
the latter, and the boat cautiously heated by means of a lamp,
moved to and fro under it, until the orange precipitate becomes
black. The precipitate is then allowed to cool in the current of
carbon dioxide, and weighed ; from the amount found, the total
quantity of anhydrous antimonous sulphide contained in the entire
precipitate is ascertained by a simple calculation. The results are
accurate. Expt, No. 75 gave 99-24 instead of 100. But if the
precipitate is simply dried at 100, the results are about 2 per
cent, too high see the same experiment. For the properties of
the precipitate, see 90.

In case >, the precipitate is subjected to the same treatment as
in #, with this difference only, that the contents of the boat are
heated much more .intensely, and the process is continued until no
more sulphur is expelled. This removes the whole of the admixed
sulphur; the residue consists of pure antimonous sulphide. It
must be completely soluble in fuming hydrochloric acid on heating.

* Zeitschr. /. analyt. Chem., x, 343.



398 DETERMINATION. [ 125.

If the amount of tJie precipitate is small, collect it in a weighed
asbestos filtering tube, dry in a slow current of carbon dioxide at a
gentle heat, heat finally rather more strongly till the sulphide has
turned black and any free sulphur present has volatilized, allow to
cool, replace the gas in the tube by air, and weigh. Results quite
satisfactory.*

BUNSEN recommends converting the antimonous sulphide into
antimony tetroxide.

For the method of estimating the antimony in the sulphide
volumetrically and indirectly, see 3, c.

2. Determination as Antimony Tetroxide.

a. In the case of antimonous oxide or a compound of the same
with an easy volatile or decomposable oxygen acid, evaporate
carefully with nitric acid and ignite finally for some time till the
weight is constant. The experiment may be safely made in a
platinum crucible. With antimonic acid, the evaporation with
nitric acid is unnecessary.

. If antimonous sulphide is to be converted into anntimony
tetroxide, one of the two following methods given by BUNSEN f is
employed :

fx. Moisten the dry antimony sulphide with a few drops of
nitric acid of 1*42 sp.- gr., then treat, in a weighed porcelain
crucible with concave lid, with 8-10 times the quantity of
fuming nitric acid,:): and let the acid gradually evaporate on the
water-bath. The sulphur separates at first as a fine powder, which,
however, is readily and completely oxidized during the process of
evaporation. The white residual mass in the crucible consists of
antimonic acid and sulphuric acid, and may by ignition be con-
verted without loss into antimony tetroxide. If the antimony
sulphide contains a large excess of free sulphur, this must be
removed by washing with carbon disulphide.

/3. Mix the antimony sulphide with 30-50 times its quantity



*Zeitschr.f. annlyt. Chem., vin, 155.

f Annal. d. Chem. u. Pharm., cvi, 3.

\ Nitric acid of l'42sp. gr. is not suitable for this purpose, as its boiling- point
is almost 10 above the fusing- point of sulphur, whereas fuming nitric acid boils
at 86, consequently below the fusing point of sulphur. With nitric acid of 1 -42
sp. gr., therefore, the separated sulphur fuses and forms drops, which obstinately
resist oxidation.



125.] ANTIMONY. 399

of pure mercuric oxide,* and heat the mixture gradually in an
open porcelain crucible. As soon as oxidation begins, which may
be known by the sudden evolution of gray mercurial fumes,
moderate the heat. When the evolution of mercurial fumes
diminishes raise the temperature again, always taking care, how-
ever, that no reducing gases come in contact with the contents of
the crucible. Remove the last traces of mercuric oxide over the
blast gas-lamp, then weigh the residual fine white powder of anti-
mony tetroxide. As mercuric oxide generally leaves a trifling fixed
residue upon ignition, the amount of this should be determined
once for all, the mercuric oxide added approximately weighed, and
the corresponding amount of fixed residue deducted from the
antimony tetroxide. The volatilization of the oxide of mercury
proceeds much more rapidly when effected in a platinum crucible
instead of a porcelain one. But, if a platinum crucible is employed,
it must be effectively protected from the action of antimony upon
it, by a good lining of mercuric oxide, f If the antimony sulphide
contains free sulphur, this must first be removed by washing
with carbon disulphide before the oxidation can le proceeded
with, since otherwise a slight deflagration is avoidable.

According to later experiments made by BUNSEN,$ it is some-
what difficult to obtain good results by this method, because a
temperature a little above that required to reduce Sb a O 6 to Sb,O 4
will reduce the latter Sb 2 O 3 . Ignition over a blast-lamp in a very
large covered platinum or rather large open porcelain crucible,
keeping only the bottom at a full red heat, is recommended as a

* Prepared by precipitation from mercuric chloride by excess of soda solution
and thorough washing.

f This is effected best, according to BUNSEN, in the following way: Soften the
sealed end of a common test-tube before the glass-blower's lamp ; place the
softened end in the centre of the platinum crucible, and blow into it, which will
cause it to expand and assume the exact form of the interior of the crucible.
Crack off the bottom of the little flask so formed, and smooth the sharp edges
cautiously by fusion. A glass is thus obtained, open at both ends, which exactly
fits the crucible. To effect the lining by means of this instrument, fill the crucible
loosely with mercuric oxide up to the brim, then force the glass gradually and
slowly clown to the bottom of the crucible, occasionally shaking out the oxide
of mercury from the interior of the glass. The inside of the crucible is thus
covered with a layer of oxide of mercury \ 1 line thick, which, after the removal
of the glass, adheres with sufficient firmness, even upon ignition.

\ Zeitschr. f. anal. Chem., xvm, 268.



400 DETERMINATION. [ 125.

method by which it is possible to drive off just one atom O from
Sb,0 s .

3. Volumetric Methods.

a. Oxidation of Antimonous Oxide to Antimonic Oxide by



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