MOLYBDENUM, m6-1113'de-ntim, a pure white metal, softer than steel, malleable and capable of being forged and welded. It can be filed and polished and may be drawn into ribbons arid fine wire. Metallic molybdenum is used in various electrical contact making and breaking devices, in X-ray tubes, in voltage rectifiers, in the form of wire for filament sup ports in incandescent electric lamps, for wind ing electric resistance furnaces and in dentistry. It is also employed in the manufacture of chemical reagents, dyes, glazes and disinfect ants. The principal use of molybdenum is in the manufacture of special alloy steels, usually in conjunction with chromium,manganese, nickel, cobalt, tungsten or vanadium. These steels are used for self-hardening and high speed machine tools, for crank-shaft and pro peller-shaft forgings, high-pressure boiler plate, armor-piercing projectiles, permanent magnets and wire. During the World War the main uses were for gun-linings, armor plates, pro jectiles and in the motor industry, especially in the crank-shafts and connecting-rods of Liberty motors. The purest molybdenum is produced from wulfenite, but practically the whole of the world's supply of the metal and its com pounds is obtained from molybdenite (q.v.). Molybdenite resembles galena in some respects and owes its name to this fact, the word being based upon the Latin name for galena. It was first clearly distinguished from galena by Scheele in 1778, and in 1782 Hjelm obtained the element molybdenum in the metallic form. Molybdenum may be prepared by reducing the oxide by hydrogen, carbon or potassium cyanide, as well as by various other methods. It has a specific gravity of about 8.6 and a specific heat of about 0.0659. Its melt
ing point is higher than that of platinum. Molybdenum is not affected by air or moisture at ordinary temperatures, but oxidizes slowly when heated in air, and at high temperatures it burns, whether heated in air or in steam. Chemically, molybdenum behaves both as a metal and as a non-metal. It has the chemical symbol Mo and an atomic weight of 96 if 0=16, or 95.3 if H=.. I. It forms several oxides, of which the trioxide, MoO,, is the most important. This is the oxide that is formed when the metal is burned in air, and it may also be prepared by roasting the native sulphide in air. The trioxide occurs native in small quan tities, as ochre,( or Metallic molybdenum combines directly with chlorine to form Mons, and with bromine to form MoBr.; but it does not combine directly with iodine. Unlike the other metals, molyb denum does not readily replace the hydrogen of acids to form definite salts, but its oxides dissolve in acids with the formation of com pounds which have, as yet, been but little stud ied. The trioxide combines with water to form substances of the nature of acids, and which are, in fact, called amolybdic acids?' These further combine with metallic bases to form an extensive series of compounds known as Ammonium molybdate is used in the laboratory as a reagent for the detection of phosphoric acid, a yellow precipitate being thrown down when a nitric acid solution of ammonium molybdate is added to a solution containing a phosphate. Consult Wolf, H. J., 'Molybdenum' (Golden, Colo., 1918) ; Wilson, A. W. G., (Molybdenum" in The Mineral In dustry (luring 1916,' Vol. XXV.