Molybdenum, a metal usually obtained from the native bisulphide (molybdenite). It is also found as a molybdate of lead. Its symbol is Mo; atomic weight, 96; specific gravity, 8.6. The resemblance of the bisulphide ore to graphite gave the metal its name (Gr. , a piece of lead). It was first distinguished from graphite by Scheele in 1778, but was first obtained in the metallic form by Hjelm in 1782. The most complete investigations of its properties and combinations were made by Berze-lius. The metal may be obtained by roasting the native sulphide in a free current of air, by which impure molybdic acid is produced in the form of a gray powder. This is digested in ammonia, the solution filtered and evaporated to dryness, the residue dissolved in nitric acid and again evaporated to dryness, pure molybdic acid being left. This being made into a paste with oil and charcoal and heated to whiteness, the oxygen is abstracted and the metal remains. It may also be obtained by passing hydrogen over molybdic acid at a red heat in a porcelain tube. It is a white metal, brittle, and difficult to melt. When heated to whiteness in the air or in oxygen, it forms a crystalline sublimate of molybdic acid. It is easily oxidized by nitric acid, with evolution of nitrous acid fumes, and if ignited in a stream of aqueous vapor hydrogen is evolved.
Molybdenum forms alloys with tin, lead, iron, copper, silver, gold, and platinum, rendering them less fusible, more brittle, and, except the silver, whiter. It forms three oxides: protoxide, MoO (or according to Rammelsberg, who doubts the existence of MoO, sesquioxide, Mo2 03); the dioxide, Mo02; and a third, molybdic anhydride, Mo03. The first two possess basic characters, while the last is an active acid. The protoxide (or sesquioxide) is obtained by dissolving molybdic acid in hydrochloric acid, and placing in the solution zinc or one of the metals capable of decomposing water, and afterward treating with excess of ammonia. The dioxide is obtained by heating a mixture of sal ammoniac and molybdate of soda and digesting the residue in caustic potassa. Molybdenum forms with bromine dibromide, tri-bromide, and tetrabromide, and with chlorine and sulphur corresponding salts; and there may also be formed chloro-bromides. The iodine compounds are molybdous and molybdic iodides. Molybdic anhydride forms salts with various bases, called molybdates. The molybdate of ammonium is used as a delicate test for phosphoric acid. The solution suspected to contain the phosphate is acidulated with nitric acid, and the molybdate is added.
If phosphoric acid is present, either free or uncombined, a yellow crystalline precipitate is formed, consisting of molybdic and phosphoric acids in combination with ammonia. Arsenic acid forms a similar compound with amnionic molybdate when the solutions are boiled. A mixture of sulphuric and molybdic acids yields a beautiful purple with pure morphia or its salts. The oxygen salts of molybdenum are not well enough known or of enough importance to require notice here.