A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 243
platinic chloride ; C. Marie, that the hydrate is formed by the action of oxidizing
agents—acid soln. of potassium permanganate, dichromate, chlorate, or ferrocyanide—on
platinum ; L. Wohler, by heating platinic nitrate to constant weight
at 380°, boiling the product with cone, nitric acid, and drying it at 380° to constant
weight ; L. Wohler and W. Frey, by boiling cone. soln. of platinic chloride and
sodium carbonate ; A. Rosenheim, by boiling a soln. of platinic chloride supersaturated
with sodium hydroxide ; and the replacement of the chlorine in hydrochloroplatinic
acid, H2PtCl6, by OH-groups by treatment with alkali hydroxide
was studied by W. Hittorf, and F. Kohlrausch. L. Wohler boiled platinic chloride
with an excess of 2JV-NaOH, and neutralized the cold soln. with acetic acid when the
hydroxide H2Pt(OH)6 is precipitated as a yellow powder, which, when heated, turns
brown and then black. When the precipitated hydroxide is boiled for a long time,
it is converted into the compound PtO2.3H2O, which, when left over sulphuric
acid in a desiccator, is converted into the compound PtO2.2H2O. The latter
hydroxide, when heated at 100°, becomes dark coloured, with the formation of the
compound PtO2.H2O, which parts with its water with great difficulty. The monohydrate
is insoluble in aqua regia and in hydrochloric acid.
M. Blondel, and H. Topsoe found that the tetrahydrate loses 2 mols. of water
slowly at 100° and becomes yellowish-brown ; at 120°, another mol. of water is given
off; and at 150°,it darkens in colour owing to reduction. These results do not agree
with the observations of L. Wohler, who found that when the white hydrate precipitated
from a cold soln. is dried in air, it is coloured straw-yellow or nankeenyellow,
and it contains 4 mols. of water ; if precipitated from boiling soln., the
product is ochre-yellow, and it contains 3 mols. of water, and the same results
are obtained if the product is dried a short time over calcium chloride ; if dried
for a long time over cone, sulphuric acid, or a short time on a water-bath, the
product is rose-yellow or amber-brown, and contains 2 mols. of water ; and if
dried for a long time at 100°, the colour is dark brown or deep black, and it contains
1 mol. of water. The last mol. of water is difficult to remove, for after 10 days
at 180°, the product contained 6*3 per cent, of water ; after 8 days at 250°, 4-6 per
cent. ; after 24 hrs. at 410° to 450°, 3 per cent. ; after heating in oxygen at 400°,
2*6 per cent. ; and it decomposes into its elements when heated in oxygen above
510°. F. Becker was unable to dehydrate the hydrated dioxide without some
decomposition. C. Marie also noted that the oxide is decomposed at a dull red-heat.
As just indicated, Li. Wohler obtained the monohydrate, PtO2.H2O, from a higher
hydrate ; and E. von Meyer, by evaporating a mixed soln. of platinic chloride and
an excess of sodium carbonate, to dryness, -washing the residue with hot water,
digesting the solid with dil. acetic acid, and then washing with hot water. The
product is black. M. Blondel reported the polymer, (PtO2-H2O)5, to be formed by
the action of boiling water for 14 days on (Pt02)6.2HC1.9H20, and drying the
product at 100° to 105°. E. von Meyer reported the hemilrihydrate, PtO2-I^H2O,
to be formed by drying at 110° the product of the action of sodium carbonate on
platinic chloride. H. Topsoe prepared the dihydrate, PtO2.2H2O, by heating the
higher hydrate at 100°, and it was obtained by L. Wohler by drying the higher
hydrate for a long time over cone, sulphuric acid. J. J. Berzelius observed that
alkalies precipitate basic double salts from soln. of most platinic salts, but with
platinic nitrate and potash-lye, the hydrate is first precipitated, and, after that,
the double salt. L. Pigeon heated a mixture of platinic chloride and sodium
hydroxide in a sealed tube for many hours at 180°, and after washing the precipitate
with water, dried it in vacuo at ordinary temp. H. Topsoe evaporated a
soln. of platinic chloride mixed with an excess of sodium carbonate to dryness on
a water-bath, washed the product with water, then -with acetic acid, and finally
with hot water. G. C. Wittstein obtained the dihydrate by adding calcium carbonate
to a soln. of platinic sulphate, and washing the excess of calcium carbonate
from the precipitate by acetic acid, and the calcium sulphate, by water.
J. W. Dobereiner obtained the dihydrate by dissolving the alkali from sodium