Chromium, METALLURGY

OF. Principal ore is chromite, compound of chromic oxide and oxide of iron, widely distributed, especially in serpentine rocks. The pure metal is not well-known, as it is very difficult to prepare pure, and the alloy of iron and chromium has been its only industrial application. Wöhler first isolated it, as a powder, by reducing its oxide by zinc. Deville reduced the oxide by carbon at a very high temperature, in a lime crucible. Bunsen electrolyzed a concentrated solution of chromium chloride, and obtained the pure metal. Placet electrolyzes a solution of chrome alum, pota ium sulphate, and sulphuric acid. This last proce has arisen in France (1892), and large ingots of chemically pure chromium are being put on the market at a moderate price. The alloy of iron and chromium used for making chrome steel is made by intensely heating in a crucible a mixture of carbon, iron oxide, and pota ium bichromate. When this alloy is added to steel it produces an intensely hard metal, suitable for chisels, punches, dies, etc. Pure chromium is white, sp. gr. 6.8, very hard, le fusible than platinum, m, and resists attack by the strong acids except hydrochloric. Metallic chromium is also electroplated upon engraved steel plates, to give them a harder surface. See STEEL.