KCl serves for the detection and isolation of platinum, and vice versa,
for the detection of ammonium or potassium compounds. (Comp.
Ciiapter II.)

Platinum is capable of forming a lower chloride, vii., plafcmous chloride,
"Pt"Cl2, in which the platinum acts as a djad. This salt is obtained by heating
the platinic chloride for some time in an air- or oil-bath up to 204i° C, as long as
any chlorine is evolved ; or hy acting with sulphurous acid upon a solution of
platinic chloride, until the latter ceases to give a precipitate with ammonic
chloride. PtCl2 is a greenish-grey powder, insoluble in water, but soluble in hydro-
chloric acid.
Several reactions in the wet way for platinum are based upon the power
which its salts possess, of oxidizing other bodies which have some bonds left
unsatisfied ; but as platinic salts are not so easily reduced as gold salts, a solution
of the latter metal is generally preferred. After what has been stated under
gold, the following reax;tions will be readily understood : —

PtCl4 produces with SnCl2 only a dark brownish-red colour, owing to the
reduction of the platinic to platinous chloride.
PtCl4 is reduced by S02i^'eo" only after long-continved boiling.
COTT » ^^ heating, if the free

acid be neutralized with sodic carbonate.
Metallic zinc precipitates metallic platinum.
It is obvious that platinous chloride could act as a reducing agent, but it is
rarely employed for this purpose.
\V'henever platinum and gold are contained in a solution, together with other
metals of Group II, precipitable by sulphuretted hydrogen, it is preferable to
remove the gold, by means of oxalic acid (which does not reduce platinic chloride),
before removing the platinum by evaporation with ammonic chloride.
QUESTIONS AND EXERCISES.
