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Platinum Arsenides

Platinum and arsenic combine readily on heating; Gehlen observed deflagration when the spongy metal was heated with excess of arsenic. The system Pt-As, up to about 28 per cent, of arsenic, has been studied. There is a eutectic containing 13 per cent, of arsenic solidifying at 597° C., and from the times of eutectic solidification indications of the probable existence of the arsenide Pt2As3 were obtained. The formation of an arsenide of composition Pt3As2 was described by Tivoli who, by the action of arsine on aqueous platinic chloride, obtained black crystalline scales which he considered to be a hydroxy arsenide, PtAs(OH). This substance could be dried at 130° C. without decomposition, but above that temperature it yielded the arsenide in accordance with the equation:

6PtAs(OH) = As2O3 + 2Pt3As2 + 3H2O

Wohler, however, has shown that the product of the interaction of arsine and an aqueous solution of platinic chloride or potassium chlor-platinite is a mixture of variable composition, and he was unable to obtain the hydroxyarsenide.

Platinum Di-arsenide, PtAs2

Platinum Di-arsenide, PtAs2, occurs in Nature as the rare mineral sperrylite, and may be prepared in the laboratory by heating a mixture of the elements in a sealed tube at 270° C. The reaction is explosive, but can be moderated by using a large excess of arsenic, which is afterwards removed in a stream of carbon dioxide at 500° C. The residual grey powder resembles natural sperrylite, and is attacked with difficulty by concentrated nitric acid or aqua regia. The di-arsenide has also been obtained in a pure form by heating platinic chloride with an excess of arsenic in a current of hydrogen. The crystal structure has been investigated by the powder method; a = 5.957 ± 0.003 A.

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