A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 235
§ 17. The Lower Oxides of Platinum and their Hydrates
P. Klason * observed that when a hot soln. of potassium chloroplatiiiite is
evaporated, platinic chloride, and a derivative of a lower oxide, probably platinum
suboxide, or platinum hemioxide, Pt2O, are formed. G. Neumann said that
J. W. Dobereiner's datum on the amount of oxygen occluded by platinum corresponds
with 3-05 per cent., and that the value calculated for Pt2O is 3*85 per
cent. This is probably a coincidence, although it has been taken to be an indication
that a hemioxide is formed. P. T. CIeve prepared platinous dihydroxytetramniine,
Pt2(NH3)4(OH)2, by boiling platinous cis-dichlorotetrammine with soda-lye,
and drying the product at 100°. The dirty white powder is insoluble in water ;
hydrochloric acid forms a mixture of cis-dichlorodiammine and dichlorotetrammine ;
whilst nitric and sulphuric acids form the corresponding nitrate and sulphate ;
and aqua regia forms platinic tetrachlorotetrammine. C. W. Blomstrand discussed
the nature of the compound.
W. Manchot and G. Lehmann treated a 1 per cent. aq. soln. of potassium platinocyanide
with 3 per cent, sodium amalgam, and obtained a colourless solution
which reduced an ammoniacal soln. of silver, cadmium salt soln., mercuric chloride,
bismuth salt, litmus, anthraquinonesulphonate, and acidic indigotin. If exposed
to air, the reducing power of the soln. slowly disappears. .Reduction can also be
effected by potassium amalgam, calcium filings, electrolytically, or by aluminium
and potassium hydroxide. Barium platinocyanide may be used or potassium
chloroplatiiiite or chloroplatinate in presence of the equivalent amount of potassium
cyanide. Attempts to concentrate the reduced soln. on a water-bath or in vacuo
are accompanied by an evolution of gas, and potassium platinocyanide separates.
The soln. is supposed to contain univalent platinum.
According to L. Gmelin, platinum monoxide or platinous oxide, PtO, is probably
formed during the " combustion " of platinum which occurs at the m.p. and
which is attended with sparking, the emission of fumes, and the formation of a
dirty green dust. The " combustion *' does not occur at an ordinary white heat,
but only in the oxyhydrogen flame, the oxy-alcohol flame, or when a thin platinum
wire is explosively spluttered by an electric current. The alleged nature of the
product is very doubtful. According to L. Wohler, 2 the oxygen associated with
platinum black is probably present in great part as platinous oxide or its hydrate.
The preparation of oxygenated spongy platinum is best conducted at 510°, and
not above 560°. P. Laffitte and P. Grandadam obtained the oxides PtO and
PtO2 by heating the metal in oxygen to 100° to 560° at a press, of 8 to 2OO atm.
W. F. .Bruce discussed the subject. J. J. Uerzelius said that the hydrate can be
deprived of its water by a gentle heat ; and C. Engler and L. Wohler added that the
water is difficult to drive off, and requires a temp, of at least 300°. L. Wohler
found that the expulsion of the water is attended by some decomposition of the
oxide so that the pure oxide free from hydrate cannot be so prepared.
J. W. Dobereiner heated calcium chloroplatinate, Ca2Pt2O5Cl2.7H2O, in a covered
crucible, and obtained a violet powder which becomes very hot when treated with
water ; the lime and calcium chloride can be removed by water and dil. nitric
acid, and there remains platinous oxide.
J. W. Dobereiner's product is a violet powder ; J. J. Berzelius' product is a
grey powder ; and L. Wohler's, velvety black. P. Laffitte and P. Grandadam
gave 14-9 for the sp. gr. at 15°. H. G. Howell and G. 33. Rochester studied the
band spectrum. Li. Wohler said that platinous oxide is perceptibly decomposed
at 430° ; P. Laffitte and P. Grandadam said that it decomposes at 560° ; and,
according to J.J. Berzelius, the oxide is completely decomposed at a red-heat so
that the product of the operation above cited by L. Gmelin is not likely to have
been the monoxide. J. J. Berzelius also observed that when the monoxide is
mixed with powdered charcoal, and heated to redness, there is a strong detonation.
L. Wohler observed that the oxide very slowly dissolves in boiling hydrochloric