URANIUM, a metallic chemical element, symbol U, atomic weight 238.5, specific gravity 18.6. It was discovered by Klaproth (1789) in the mineral pitchblende and named by him in honor of Herschel's discovery of the planet Uranus. The body discovered by Klaproth was really the oxide of uranium, the free metal being first isolated by Peligot (1842). It is one of the rarer elements and occurs in nature only in combination with other elements. The prin cipal minerals containing it in any considerable quantity are uraninite or pitchblende (75 to 85 per cent U20.), a greenish mineral coming chiefly from Joachimsthal in Bohemia, though found in other places; gummite, a hydrated cal cium lead uranium silicate; uranosphcerite, a hydrated bismuth uranite; torbernite, a hy drated copper uranium phosphate from Saxony and Cornwall; autunite, a hydrated calcium uranium phosphate from the same regions; uvanite, a hydrated compound of uranium and vanadium; and carnotite, a potassium uranium vanadate. Carnotite is the most important ore in the United States. The latter carries im portant amounts of radium (q.v.). Deposits
are worked in Colorado and Utah. The most important European deposits are at Joachimsthal in Austria and at various points in Saxony. The metal is prepared by heating a mixture of uranium chloride, sodium chloride, and carbon or of uranium chloride, sodium chloride and metallic sodium. It is a malleable white metal looking like nickel. It oxidizes very slowly in the air at ordinary temperatures, but rapidly burns to when heated above 400° F. Is soluble in mineral acids. It acts both as an acid and a basic element. We have uranous salts such as UCl4, uranyl salts in which the group UO, acts as a basic radical, example uranyl chloride (UO2)C1, and uranates which are formed by the combination of the oxide U01 with strong bases. Sodium uranate, or ura nium yellow, is used in glass and china painting and in the manufacture of beautiful fluorescent uranium glass. Metallic uranium and minerals containing its compounds possess marked radio activity. See MINERAL PRODUCTION OF THE UNITED STATES; RADIUM.