A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 327
Ag2PtCl6, by melting silver chloride in an atm. of chlorine in a platinum vessel.
L. N. Vauquelin obtained a yellow precipitate by adding silver nitrate to a eoln.
of hydrochloroplatinic acid, and J. E. Herberger said that ammonia extracts
only a part of the silver chloride contained in the precipitate. K. Birnbaum found
that if silver chloride be dissolved in hydrochloroplatinic acid, the silver salt
crystallizes out unchanged when the soln. is evaporated. The salt was prepared
by A. Commaille, S. A. Norton, and S. M. Jorgensen. L. Pigeon reported the formation
of silver chloroplatinate from a soln. containing the theoretical proportions
of silver nitrate and hydrochloroplatinic acid ; and A. Miolati added that if an
excess of silver nitrate be present, Ag2Pt(OH)2Cl4 is formed. According to
W. Ostwald, the silver salt is formed quantitatively when the theoretical proportion
of silver nitrate is added to a soln. of sodium chloroplatinate. Li. Pigeon gave for
the heat of formation (2AgCl, PtCl4) ==7-7 CaIs. According to S. M. Jorgensen, and
A. Miolati, cold water slowly decomposes the salt, forming silver chloride and
H2Pt(OH)2Cl4, and with hot water the reaction proceeds rapidly. W. Peters
observed that the salt absorbs about 10 mols. of dry ammonia, forming silver
octamminochloroplatinate, Ag2PtCl6.8NH3; and in vacuo, this forms silver
tetramminochloroplatinate, Ag2PtCl6.4NH3 ; K. Birnbaum obtained silver diamminochloroplatinate,
Ag2PtCl6.2NH3, by mixing freshly-prepared hydrochloroplatinic
acid with an ammoniacal silver chloride soln. and washing the yellow product
rapidly with cold water, and drying it over sulphuric acid. The salt loses
water at 100°, and at a higher temp, forms platinum and silver chloride. It is
insoluble in water. Ammonia is evolved when the product is treated with potashlye
; when boiled with sodium carbonate, a dirty yellow precipitate is formed
containing a part of the silver and part of the platinum.
W. Peters found that when a mixed soln. of auric chloride and hydrochloroplatinic
acid is evaporated, no sold chloroplatinate is formed since the gold
separates out in the metallic state. A. Cahours and H. Gal prepared platinic
quatertriethylphosphinechloroaurate, [Pt{P( C2H5)3}4] AuCl4.
P. A. von BonsdorfE 26 prepared Calcium chloroplatinate, CaPtCl6.6H2O, in
small, orange-red prismatic crystals by evaporating a mixture of hydrochloroplatinic
acid with an excess of calcium chloride, and separating mechanically the
crystals of the oclohydrate from those of calcium chloride. P. Rohland, and
H. Topsoe prepared the enneahydrate, CaPtCl6.9H2O, by evaporating a soln. of
theoretical proportions of the component chlorides over sulphuric acid. L. Pauling
found that the crystals of the hexahydrate are rhombohedral with a,= 112° 0'.
P. A. von BonsdorfT, and W. Peters said that the water can be expelled by heating
to 170°, and a yellow powder remains. The crystals of the hydrate are freely
soluble in water ; H. Precht observed that the sat. alcoholic soln. contains 53 per cent,
of salt ; P. Rohland added that the salt is soluble in methyl alcohol of sp. gr.
0-79O at 15°, and in ethyl alcohol of sp. gr. 0-8035 at 15°, and the salt is decomposed
in soln. into its component chlorides. It is insoluble in ether. W. Peters said that
when the anhydrous salt is exposed to dry ammonia it forms calcium dodecamminochloroplatinate,
CaPtCl6.12NH3, and that in vacuo, this forms calcium hezamminochloroplatinate,
CaPtCl6.6NH3. P. A. von BonsdorfE prepared strontium chloroplatinate,
SrPtCl6.8H2O, as in the case of the calcium salt. The rhombic prisms
are stable in air, but effloresce in warm air. The salt is freely soluble in water.
H. Precht found that the salt is decomposed by absolute alcohol.
A. von Mussin-Puschkin, and P. A. von BonsdorfE also prepared barium
chloroplatinate* BaPtCl6.6H2O, by the spontaneous evaporation of a mixed soln.
of hydrochloroplatinic acid with an excess of barium chloride. P. Rohland used
theoretical proportions of the two constituents. H. Topsoe added that it is difficult
to prevent contamination with barium chloride since there is a slight decomposition
of the salt during recrystallization. The salt was also prepared by J. J. Berzelius.
The hexahydrate forms orange-yellow, monoclinic prisms and plates which, according
to H. Topsoe, have the axial ratios a : b : c=0-9645 : 1 : 14949, and £=102° 15'.