Arsenic Pentasilicide, AsSi₅

Arsenic Pentasilicide, AsSi₅, has been prepared, however, by the action of hydrochloric acid on zinc silico-arsenide. The product was very impure, containing zinc, silica and arsenic monohydride; the last was removed by heating in a stream of hydrogen, and the zinc and silica were removed by treating with boiling nitric acid and aqueous alkali respectively. It remained as microscopic dark grey needles, stable when heated in air, and unattacked by concentrated acids or aqua regia.

A series of complex silico-arsenides has been obtained by melting metals with silicon and an excess of arsenic under a layer of molten cryolite and sodium chloride. The following have thus been prepared: copper silico-arsenide, a grey crystalline brittle mass; zinc silico-arsenide, which behaved as above with hydrochloric acid; iron, cobalt and nickel silico-arsenides, of composition M₂Si₉As₄, similar in appearance to the copper compound. When platinum was treated in the same way, a hard white product of indefinite composition was obtained, almost insoluble in nitric acid.