A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 303
platinum is warmed with a little dil. hydrochloric acid in order to remove iron, and
is then transferred to the electrolytic apparatus, where it is washed and afterwards
covered with cone, hydrochloric acid. The electrodes are composed of sheet
platinum. The precipitated platinum thus forms the anode of an electrolytic cell.
On concentrating the soln. of hydrochloroplatinic acid resulting from the electrolysis,
a small quantity of chlorine is introduced in order to ensure the absence of platinous
compounds. H. Precht described the preparation of hydrochloroplatinic acid from
platinum residues. L. N. Vauquelin passed chlorine into warm water containing
ammonium chloroplatinate in suspension until all the ammonia is decomposed—
there is here a possibility of forming explosive nitrogen chloride. L. Pigeon employed
this process.
On slowly evaporating the soln. of hydrochloroplatinic acid prepared by one
of these processes—say over calcium oxide and cone, sulphuric acid as recommended
by R. Weber—brownish-red, deliquescent crystals of the hexahydrate are formed.
H. W. Hake said that the maximum quantity of water absorbed during a few days'
exposure to atmospheric air amounts to 47-82 per cent.—i.e. H2PtCl6.21H2O.
R. Engel said that the salt is relatively stable. When heated, it loses hydrogen
chloride and water, and then some chlorine is given off and platinous chloride is
formed. H. Topsoe observed that some hydrogen chloride, and chlorine are lost
at 110°, and, added J. J. .Berzelius, at a higher temp., platinous chloride and
platinum are formed. According to TJ. Pigeon, no platinous chloride is formed
when the hydrochloroplatinic acid is heated 5 hrs. in vacuo at 170° ; at 280°, a
small proportion of platinous chloride is formed, but more is produced at 358°.
When heated in vacuo in the presence of potassium hydroxide, the first product
of the action is HPtCl5.2H2O, and afterwards platinous chloride appears. The
heat of formation (2HC1.6H20, PtCl4)—20-46 CaIs., (HC1.4H.,0, HPtCl5.2H2O)
— lOOO CaIs., and (PtCl4, 2HCl)-=24-8 CaIs. ; the heat of soln. is 4-34 CaIs.
J. Thomsen gave (Pt, Cl4, 2HCl, Aq.) ^84-62 CaIs.; (Pt, O2, GHCl, Aq.) = 64-06 CaIs.
Y. Shibata and K. Ilarai, and R. Samuel and A. R. Despande. studied the absorption
spectrum.
K. Seubert said that the aq. soln. of the purified salt is golden-yellow, and
J. J. Berzelius added that if some iridium salt is present, the colour may be reddishyellow,
or brown. According to A. Hantzsch, eq. soln. of hydrochloroplatinic acid
and of sodium chloroplatinate, containing the complex PtCl6"-ion, in the same
solvent, are optically identical—that is, they show the same absorption spectrum,
and the molecular absorption is independent of the degree of ionization. The
light absorption of the acid and of the salt is also unaffected by changes of temperature.
The solvent does not appear to exercise any influence on the absorption
in the blue and violet parts of the spectrum, but does so to a very slight extent in
the green and ultra-violet. The temp, coeff. of the absorption spectrum is very
small. F. Kohlrausch observed that the behaviour of soln. of hydrochloroplatinic
acid in light resembles that of soln. of platinic chloride—vide sujtra.
The electrical conductivity of soln. of 0-IiV-H2PtCl6 changes in light owing to
hydrolysis ; but more cone. soln. are stable, and are not affected by light. A
freshly-prepared soln. with 0-0002 gram-equivalent per litre had an eq. conductivity
380, and when hydrolyzed in light, 1048, showing that all the chlorine
is probably present as hydrochloric acid. J. A. Prins and A. Fonteyne studied
the X-ray diffraction of aq. soln. The eq. conductivities, A, of soln. of the following
concentration in gram-equivalents per litre, at 18°, were :
00002iV- O-OOIJV- 00022V- O OliV- O IJV- O 37iV- 0-88A- 205iV-
A/Not insolated. 380 367 362 352 325 302 265 155
"\ lnsolated . 1048 1036 776 365 — - —
F. Braun succeeded in converting up to 49 per cent, of the heat of combination
into electrical energy. S. Nagami measured the lowering of the f.p., the ionic