| Trichromium Silicide, Cr3Si, has been prepared by heating a mixture containing 140 parts each of copper and aluminium with 200 parts of chromium sesquioxide in a fireclay crucible; on adding a small quantity of aluminium filings an energetic action occurs, and on cooling, a metallic ingot is obtained containing crystals of the silicide, which can be separated from the metal by treating with aqua regia and then washing with water. It has also been obtained by fusing a mixture of copper and chromium with a relatively small quantity of silicon in an electric furnace, and digesting the resulting button in nitric acid. It forms grey, prismatic, arborescent crystals, of density 6.52 at 18° C., hard enough to scratch glass, but not quartz. Acids have no action on it, except hydrofluoric acid; it is only slightly attacked by sulphur, potassium chlorate, or fused potash; chlorine and bromine decompose it at red heat, and it is rapidly attacked by a mixture of potassium chlorate and nitric acid. |