Chemical Properties of Uranium

Metallic uranium exhibits considerable chemical activity. Although unchanged at ordinary temperatures in dry air, the brightly polished metal becomes considerably tarnished after a few days exposure to the atmosphere; it burns briskly at 170° C., forming uranous oxide. It burns in sulphur vapour at 500° C., and also in selenium vapour. The halogens react vigorously; the metal inflames immediately in fluorine in the cold, in chlorine at 180° C., in bromine at 210° C., and in iodine vapour at 260° C. Dry hydrogen chloride and hydrogen iodide attack at a dull red heat. Nitrogen combines at 1000° C. to produce a yellow nitride, and the metal decomposes ammonia, liberating hydrogen and yielding a black crystalline powder. With carbon the metal yields a well-defined crystalline carbide. According to Moissan, finely divided uranium readily decomposes water; Lely and Hamburger, however, found the metal stable towards water and towards alkalies. Dilute hydrochloric and sulphuric acids dissolve uranium with vigorous evolution of hydrogen; concentrated sulphuric acid yields sulphur dioxide; nitric acid forms the nitrate. Uranium displaces the following metals, in part even in the cold, from solutions of their salts: mercury, silver, copper, tin, platinum, and gold.