Tungsten Arsenide, WAs₂

When tungsten and arsenic are heated together in a sealed tube at 620° for 5 days, a product of composition WAs_1.95 and of density 10.95 at 25° C. is obtained. Defacqz described the di-arsenide as a black crystalline mass of density 6.9 at 18° C. This product he obtained by heating pure tungsten hexachloride in a current of arsine, the temperature being maintained at 150° to 200° C. for a time and then gradually raised to 350° C. The arsenide is stable in air at the ordinary temperature; at red heat it is readily oxidised, leaving a residue of yellow tungstic anhydride. It readily combines with chlorine, sulphur and phosphorus when heated. It is quite insoluble in water, carbon disulphide and the usual organic solvents; solutions of hydrofluoric and hydrochloric acids have no action upon it, but nitric acid and aqua regia oxidise it on warming. Fused alkalis and alkali carbonates act upon it, forming arsenate and tungstate. Tungsten chlorarsenide, W₂AsCl₉, is obtained by heating a mixture of tungsten hexachloride and liquid arsine in a sealed tube at 60° to 75° C. It forms bluish-black, hygroscopic crystals, and is readily decomposed by water, acids and alkalis.