MOLYBDENUM (Mo). A rare metal, occurring native chiefly as the bisulphide, a mineral that, in appearance and properties, so much resembles graphite as to have been mistaken for that substance until the year 1778, when its peculiarity was first pointed out. A descrip tion of the two or three ores of molybdenum that have hitherto been discovered will be found in the NATURAL HISTORY DIVISION, article MOLYBDENUM. The method of isolating the metal from the sulphide is also there detailed. The equivalent of molybdenum is 46.
1. Protoxide of Molybdenum (Mo0).—Molybdous oxide. Obtained in the anhydrous form by the action of nascent, hydrogen, and in the hydrated condition on adding ammonia to a solution of the proto chloride. In the latter state it is soluble in solution of carbonate of ammonia but not in the carbonates or hydrates of potash or soda. Both varieties are of a black colour.
2. Biuoxide of Molybdenum oxide. Formed when molybdate of ammonia, is strongly ignited in a covered crucible. The residue should be washed with caustic potash to remove any molybdio acid. Its colour is usually dark brown, but purple in direct sunshine. It is to a certain extent soluble in water ; the solution sometimes gelatinises spontaneously. The salts of binoxide of molybdenum are red when hydrated, but in the anhydrous state are almost black. An olive green oxide, and a blue oxide of molybdenum have been described, but they are now known to be mixtures of the binoxide with molybdio atid.
3. Molybdic acid is generally obtained by the phide, at a low red heat, in clay basins, but M. Brunner recommends that the pulverised mineral should be first mixed with au equal volume of quartzose sand, and the mass then roasted in a platinum capsule until it has acquired a lemon•yellow colour. After cooling, the molybdic acid is extracted by exhausting the product with ammonia. The residue from the evaporation of the ammoniacal solution is heated to low redness to expel ammonia, when molybdic acid remains as a pale buff-coloured powder. At a very high temperature molybdio acid volatilises and condenses on cool surfaces in brilliant transparent needles. Molybdic acid combines with bases to form neutral and acid
salts called molybdates.
Molybdate of ammonia is sometimes used for detecting and even estimating phosphoric acid. It is best prepared by dissolving, with the aid of a gentle heat, two parts of pure molybdic acid and one of tartaric acid in fifteen of water and afterwards adding ten parts of ammonia (sp. gr. and fifteen of nitric acid. The whole is heated to ebullition in a porcelain basin, when about one fifteenth of the molybdic acid will precipitate, and must be separated by filtration. The solution is then ready for detecting phosphoric acid, with which it gives a yellow crystalline precipitate of phospho-molybdate of ammonia.
Molybdenum and sulphur combine in three proportions and form bisulphide of molybdenum, (MoS) already noticed ; tersulphide Of molyb denum, or sulpho-molybdie acid, (MoS,) precipitated on adding hydro chloric acid to a solution of a molybdate saturated with sulphuretted hydrogen ; and quadrisulphicle of molybdenum or persulpho-molybdic acid, (MoS,). Sulpho-niolybdate of potash crystallises in magnificent iridescent crystals.
Molybdenum and chlorine form two distinct chlorides, namely, proto chloridi and bichloride, as well as several oxychlorides that appear to contain terchloride of molybdenum.
Progoehloride of molybdenum (MoC1). Excess of hydrochloric acid is added to a concentrated solution of an alkaline molybdate and zinc then introduced. As soon as evolution of hydrogen commences, the liquid becomes of a blue colour, then reddish brown, and finally black IIy adding ammonia to the resulting solution and redissolving the washed protoxide in hydrochloric acid, a more pure protochlorido is obtained.
Biehloride of molybdenous, (MoCI,) is obtained in deliquescent crystals on evaporating a solution of the binoxide in hydrochloric acid. le appearance it resembles iodine.
The detection ofmolybdenum is best effected by producing the colours mentioned under protochloride of molybdenum. It is usually estimated in the form of hisulphide, which contains per cent. of metal.