620 MOLYBDENUM. 



Molybdous oxide, MoO, 698.5 or 55.96. This oxide is ob- 

 tained by adding to the concentrated solution of any molybdate, 

 so much hydrochloric acid as to redissolve the molybdic acid 

 which is at first thrown down, and placing zinc in the liquid ; 

 this becomes first blue, then reddish-brown, and finally black, 

 and contains the chloride of zinc and protochloride of molyb- 

 denum. To separate the oxide of molybdenum from the oxide 

 of zinc, ammonia is added to the liquid in quantity no more 

 than sufficient to precipitate the former, while the latter remains 

 in solution. The molybdous oxide carries down with it a por- 

 tion of oxide of zinc, from which it may be freed by washing 

 with ammonia : it is thus obtained as a hydrate of a black 

 colour. The hydrate of molybdous oxide dissolves with diffi- 

 culty in acids, forming solutions which are almost black and 

 opaque, and which do not yield crystallizable salts. It is not 

 dissolved by potash, nor by the fixed alkaline carbonates 5 but, 

 on the contrary, is soluble in carbonate of ammonia, when 

 freshly precipitated. Molybdous oxide resists, after ignition, 

 the action of all acids. 



Molybdic oxide, MoO 2 ; 798.5 or 63.96. This oxide may be 

 obtained by igniting molybdate of ammonia in a covered cruci- 

 ble, but mixed with a little molybdic acid. It is better pro- 

 cured by igniting rapidly, in a covered crucible, a mixture of 

 anhydrous molybdate of soda (which may contain an excess of 

 soda) with sal ammoniac. Water poured upon the fused mass 

 dissolves common salt, and leaves a brown powder almost 

 black. But molybdic oxide prepared in this way is insoluble in 

 acids. The hydrated oxide may be obtained in various ways, 

 one of which consists in digesting molybdic acid with hydro- 

 chloric acid and copper, till all the molybdic acid is dissolved. 

 From the solution, which is of a deep red colour, molybdic oxide is 

 precipitated in appearance exactly similar to the hydrated per- 

 oxide of iron, by ammonia, added in sufficient excess to retain 

 all the oxide of copper in solution. The hydrate has a certain 

 degree of solubility in pure water, and should, therefore, be 

 washed with a solution of sal ammoniac, and lastly by alcohol. 

 This hydrate reddens litmus paper, but possesses no other pro- 

 perty of an acid. It is not dissolved by the hydrated alkalies, 

 but is soluble in their carbonates, like several earths and metallic 

 oxides. It dissolves in acids and forms salts, which are red 

 when they contain water of crystallization, and black when an- 



