MOLYBDENUM. 621 



hydrous. The oxalate of molybdic oxide can be obtained in 

 crystals by spontaneous evaporation. 



Molybdic acid., MoO 3 ; 898.5 or 71.96. The native sulphuret 

 of molybdenum, in fine powder, is roasted in an open crucible, 

 with constant stirring, at a heat not exceeding low redness, so 

 long as sulphurous acid comes off. It leaves a dull yellow 

 powder, which is impure molybdic acid. This is dissolved in 

 ammonia, and the molybdate of ammonia purified by evapora- 

 tion, during which some foreign matters are deposited, and 

 crystallized. The crystallized salt, exposed to a moderate heat, 

 sq as to avoid fusion, loses its ammonia, and leaves molybdic 

 acid in a state of purity. The acid thus prepared is a white and 

 light porous mass, which may be diffused in water, and divides 

 into little crystalline scales of a silky lustre. It fuses at a red 

 heat, and forms on cooling a straw-coloured crystalline mass, of 

 which the density is 3.49. This acid forms no hydrate. It 

 requires 570 times its weight of water to dissolve it. Before 

 being ignited, it is soluble in acids, and forms a class of com- 

 pounds, in which it appears to play the part of base, but of 

 which not much is known. When boiled with bitartrate of 

 potash, molybdic acid dissolves, even after being fused by heat. 



When a solution of bichloride of molybdenum is poured into 

 a solution saturated, or nearly so, of molybdate of ammonia, a 

 blue precipitate falls, which is a molybdate of molybdic oxide, 

 MO 2 , 2MO 3 . This compound is likewise readily formed in a 

 variety of other circumstances.* The salts of molybdic acid are 

 colourless, when their base is not coloured. When they are 

 treated with other acids, molybdic acid precipitates, which dis- 

 solves, however, in an excess of the acid, except in nitric acid. 

 It forms both neutral and acid salts with the alkalies. Molyb- 

 date of potash is formed by dissolving molybdic acid in car- 

 bonate of potash ; it is easily soluble in water and crystallizable. 

 Molybdate of soda has the same form, and resembles in proper- 

 ties the ttmgstate of soda. Bimolybdate of soda crystallizes in 

 large fine crystals, which effloresce in air. Molybdate of magnesia 

 is soluble in twelve or fifteen times its weight of water, and 

 may be crystallized. Molybdate of lead occurs finely crystallized 



* It will be observed, that the atom of this compound contains three atoms 

 of metal, so also does the remarkable combination of tungstic oxide and soda, 

 (page 618) ; both thus containing a sali-molecule of metal, like the compound 

 oxide of iron, which appears to be a condition of stability. 



