Calcium Arsenide, Ca₃As₂

Soubeiran obtained a little Calcium Arsenide, Ca₃As₂, mixed with arsenite by passing arsenic vapour and hydrogen over heated quicklime. It is best prepared by the reduction of calcium arsenate by carbon in the electric furnace, but it may also be formed by the action of liquid arseniuretted hydrogen on metallic calcium or on calcium ammonium, or by the direct combination of calcium and arsenic.

It forms a reddish-brown fused mass with a crystalline structure. Its density is 2.5, and in hardness it lies between calcite and glass. It is readily attacked by the halogens, and the higher the atomic weight of the latter the higher the temperature necessary. It remains unchanged in dry air or oxygen, but when heated with oxygen or sulphur, combination readily takes place. With oxidising agents there is a vigorous heat evolution. Hydrogen does not affect the arsenide even at 700°-800° C. Water decomposes it in the cold with the evolution of arseniuretted hydrogen and formation of calcium hydroxide. Fuming nitric acid does not attack it in the cold, but there is a rapid reaction on heating. Cold concentrated sulphuric acid is reduced to sulphurous acid. Boron and carbon are without action at 1000° C., but the latter can decompose it completely at the temperature of the electric furnace. Sulphuretted hydrogen and gaseous halogen acids react at red heat, giving arsenic and a calcium salt. A number of metallic salts are decomposed by the arsenide.