A Comprehensive Treatise on Inorganic and Theoretical Chemistry

244 INORGANIC AND THEORETICAL CHEMISTRY
platinate by means of acetic acid. M. Blondel obtained the polymer, which he
called metaplatinic acid, (PtO2-H2O)5, by the action of mineral acids on the salt
Na20.5Pt02.9H20, and he found it to be sparingly soluble in dil. hydrochloric
acid. The dihydrate varies in colour from rust-yellow to amber-brown, and,
according to L. Pigeon, the particles are crystalline and polarize light. L. Wohler
obtained the trihydrate, PtO2.3H2O, from the higher hydrate as a precipitate from
boiling soln. ; E. Prost, by adding water to a soln. of platinic nitrate ; but Li. Wohler
always found the product to contain some basic nitrate, as was also the case with
the anodic deposit obtained in the electrolysis of a soln. of platinic nitrate in
nitric acid. The colour of the trihydrate ranges from ochre-yellow to nankeenyellow.
E. Fremy obtained the tetrahydrate, PtO2.4H2O, by boiling a soln. of
platinic chloride for a long time with an excess of sodium hydroxide, and precipitating
the hydrate -with acetic acid. L. Wohler, and, I. Bellucci employed a
similar process. I. Bellucci dissolved the dihydrate in molten potassium or sodium
hydroxide, and neutralized the product "with acetic acid ; and he also neutralized
a soln. of the alkali salts—K2Pt(OH)6, or Na2Pt(OH)6—with acetic acid. M. Blondel
treated Pt(OH)4.2HCLwH2O with water in a dialyzer. The colour of the tetrahydrate
is white.
Li. Wohler observed that hydrogen does not reduce the monohydrate perceptibly
at ordinary temp., but when feebly warmed the reduction proceeds vigorously,
and if some platinous oxide is present, such as occurs if the hydrate has been
preheated to 400°, the reduction proceeds rapidly at ordinary temp., until it is
retarded by the protective action of the platinum formed on the surfaces of the
grains. The hydrates lower than the dihydrate make electrolytic gas explode, but
the trihydrate only glows in the gas. The decomposition of hydrogen dioxide proceeds
slowly in the presence of the hydrated dioxide, and this even in acidic or
alkaline boiling soln. when stirred. The freshly-precipitated hydrate was found by
W. H. Wahl, C. Marie, and Li. Wohler to be soluble in cone, hydrochloric acid,
but after being dried on a water-bath, it is no longer completely soluble. L. Wohler
observed that dissolution occurs immediately if the hydrate has been reduced
with stannic chloride, or with sulphurous acid. W. Bersch observed that the
dihydrate produces an alkaline reaction with a soln. of potassium iodide, but it
has no perceptible action on soln. of potassium chloride or bromide. W. H. Wahl
found that the freshly-precipitated hydrate is soluble in sulphuric acid, and
\A. Wohler added that if the hydrate has been dried on a water-bath, dissolution
is incomplete. C. Marie said that the hydrate is not perceptibly soluble in dil.
sulphuric acid—except in the presence of reducing agents like sulphurous acid
or alcohol. If the hydra ted dioxide be heated with cone, sulphuric acid, it loses
water, and darkens in colour. For the compound with ammonia, vide infra, fulminating
platinum. W. H. Wahl observed that the freshly-precipitated hydrate
is soluble in nitric acid, but L. Wohler added that after the hydrate has been dried
on a water-bath, it becomes insoluble in that acid. W. H. Wahl observed that a
dil. aq. soln. of phosphoric acid dissolves a small proportion of the hydrated dioxide
in the cold, and much more when heated ; the solubility also increases as the cone,
of the acid is increased. The hydrated dioxide is soluble in formic acid, and very
sparingly soluble in acetic acid. Boiling acetic acid gradually decomposes the
hydrated dioxide. J. W. Dobereiner, E. Fremy, and H. Topsoe said that different
reports as to the solvent action of acetic acid are based on differences in the degree
of hydration of the specimen under observation. The best solvent for the hydrated
dioxide was found by W. H. Wahl to be oxalic acid. Dissolution takes place
rapidly even in the cold, and when aided by heat platinic oxalate is formed, and
some carbon dioxide is evolved owing to the decomposition of the acid. IJ. Wohler
also found that if boiled for 4 hrs. with iV-soln. of oxalic acid, the hydrated dioxide
is reduced to metal. W. Bersch observed no reaction with potassium thiocyanate.
R. Adams and co-workers, and F. D. Aguirreche discussed the use of platinic oxide
as a catalyst in organic hydrogenations, etc. Dil. aq. soln. of sodium hydroxide,