A Comprehensive Treatise on Inorganic and Theoretical Chemistry

248 INORGANIC AND THEORETICAL, CHEMISTRY
baryta water, or sod a-lye ; it is soluble in acids, but cold acetic acid has no action,
whilst the hot acid forms barium acetate and hydrated platinum dioxide.
For the tin platirtcU.es, vide 7. 46, 14 ; the vanadium platinates, 9. 54, 6 ; chromium
platinates, 11. 60, 15 and 16; the molybdenum platinates, 11. 61, 11 ; and the tungsten
platinates, 11. 62, 12.
According to E. Prost, 3 an oxide, Pt5O1I-IlH2O, is obtained by boiling a soln.
of hydrated platinum dioxide in cone, nitric acid. "Lt. Wohler could not prepare
this product, and considered it to be a mixture of different hydrated oxides.
Ja. Wohler 4 and co-workers, C. Marie, M. Ie Blanc, and R. Ruer showed that
the oxide film which was observed by F. Kohlrausch to form on the anode during
the electrolysis of a soln. of platinic chloride is possibly platinum trioxide, PtO3 ;
and that the same film is formed when the metal becomes passive. E. Haber and
S. Grinberg showed that it liberates iodine from potassium iodide. According to
Li. Wohler and F. Martin, when the yellow soln. of hydrated platinum dioxide in
2iV-KOH is oxidized anodically whilst the soln. is well-cooled, the anode soon
becomes covered with a golden yellow, amorphous deposit, which peels off in thin,
silky plates. It is potassium platinic decoxide, K20.3Pt03. The trioxide can be
obtained from this salt by treatment with ice-cold 0-5iV-acetic acid. The reddishbrown
product contained slightly less oxygen than that necessary for the trioxide,
owing to the fact that it readily parts with some of its oxygen as soon as
all the alkali has been removed. On keeping, the percentage of oxygen gradually
decreases, but it never falls to that necessary for the dioxide, probably because a
solid solution of the trioxide in the dioxide is formed. Platinum trioxide is not
acted on by dil. sulphuric, nitric, or acetic acids. It slowly liberates chlorine from
dil. hydrochloric acid. Sulphurous acid dissolves it with the formation of a colourless
complex. Cone, sulphuric and nitric acids slowly decomposed it with the formation
of the dioxide. On gently heating, it gives the dioxide. In the cold it has no
action on alcohol or acetic acid. The oxidation which takes place on warming is
due to the dioxide which is formed. It does not decompose into hydrogen dioxide,
and must therefore be classed as a polyoxide or peroxide of platinum of the
constitution
G. Grube, 5 in his study of the behaviour of the oxygen electrode, found that
potentials from 1*5 volts downwards are due to solid soln. of platinum trioxide
in platinum dioxide, or of platinum dioxide in platinum monoxide. Since, however,
platinum electrodes can be polarized up to potentials of 2 volts, G. Grube suggested
that an unknown platinum tetroxide, PtO4, is formed.
REFERENCES.
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