20 i! Method of extracting Molyldic yield 



in a stronger heat, and which, after coohng, exhibited a 

 radiant whitish gray mass perfectly similar to fused pure 

 molybdic acid. The residuum collected after the digestion 

 of the calcined )no!ybdcna with the ammonia weighed twenty 

 grains: I subjected it to the following experiment. 

 Experhnenl XV. 



T boiled the residuum above mentioned with two gros of 

 nitric acid to perfect evaporation, and digested the new re- 

 sicuum with two gros of liquid ammonia. The residuum 

 was then filtered, washed, and dried. It w^eighed sixteen 

 grains. The liquid was evaporated, and alter incandescence 

 i obtained four grains of molybdic acid. The residuum of 

 this experiment, like those of Nos. X. XI. and XII. con- 

 tained oxide of iron, alumine, and quartzy sand. 



After these experiments I will not hesitate to prefer the 

 method of separation by anunonia to that by soda, espe- 

 cially in operating with pure soda. For it may happen that 

 the molvbdena will enter into vitreous fusion with the fo- 

 rcion bodies contained in its ore, and then ammonia would 

 not be capable of separating the molybdic acid from that 

 combination. However, this inconvenience may be pre- 

 vented by not making the fire too strong towards the end 

 of the calcination. When the method by ammonia is pro- 

 perly considered, it will be readily perceived that it would 

 'be impossible to devise one more expeditious and less ex- 

 pensive. 



The molybdena may be deprived of its sulphur without 

 the aid of the nitric acid or of nitrate of potash. The mo- 

 lybdic acid formed is purified from the oxide of iron with 

 which it is naturally united, and from the quartz and argil 

 with which they are accidentally mixed, by digesting it with 

 ammonia ; which can be done only with dilHculty by means 

 of nitric acid. Molybdate of ammonia is decomposed by a 

 heat of incandescence, which separates from it the alkali in 

 the state of purity aiul without being decomposed. It may 

 therefore be collected without great loss in a distilling ap- 

 paratus, and the acid, almc^st without any decrease, will be 

 found in the retort. So many advantages ui\ited are cer- 

 tainly not to be found in any other method, not even iu 

 tliat of separation by soda. 



By following these ditiercnt indications we arc led to the 

 following process, which is the most advantageous for pre- 

 paring molybdic acid. 



New Method nf preparing pure Mohjhdic Acid. 



Take the purest sulphuret of molybdena that can be found, 



and 



