428 MM. Svanberg and Struve on the Atomic Weight 



Bimolybdate of the Oxide of Ammonium, NH 4 0, 2M0O 3 . — 

 When an ammoniacal solution of molybdic acid is strongly 

 concentrated, always however smelling of ammonia, this salt 

 gradually separates as a white crystalline powder. 



Analysis. — 1*0448 grm. salt left on ignition 0*8824 molybdic 

 acid. 



a. Calc. A. Calc. Found. 



1 at. Oxide of ammonium... 32498 15-544 324-98 15-649 



2 at. Molybdic acid 1777-932 84-456 1751658 84-35184-456 



2102-912 100000 2076638 100000 



Double salt between the Bimolybdate and the Trimolybdate of 

 the Oxide of Ammonium, NH 4 0, 2Mo0 3 +NH 4 0,* 3M0O 3 

 + 3HO. — This salt is formed when a solution of molybdic acid 

 in ammonia is evaporated by heat to crystallization, or the solu- 

 tion left to spontaneous evaporation. It forms large six-sided 

 prisms with two truncations ; the crystals are perfectly trans- 

 parent, and are not altered by exposure to the air. 



Analysis. — I. 3*0623 grms. salt lost 0*2001 by desiccation in 

 a current of dry air at 212°, the water however carried with 

 it traces of ammonia. The residue left on ignition 2*503 mo- 

 lybdic acid. 



II. 3*550 grms. salt gave 2*8998 molybdic acid. 



III. 0*381 grm. salt gave 0*3095 molybdic acid. 

 100 parts of the salt therefore contain — 



I. II. III. Mean. 



Molybdic acid . . . . 81*725 81*685 81*234 81*548 

 Water 6-534 



On comparing these numbers with the theoretical compo- 

 sition, we have — 



a. 



2 at. Oxide of ammonium 649960 

 5 at. Molybdic acid 4444*830 



3 at. Water 337*437 



5432-227 100 000 5366542 100-000 



Several other salts may be prepared by the action of nitric 

 acid upon solutions of molybdic acid in ammonia ; among 

 others there exists, as with potash, a double salt which on so- 

 lution in water is decomposed into a readily soluble salt, and 

 an insoluble one, which separates in minute acicular crystals. 



By the partial precipitation of a solution of crude molybdic 

 acid, i. e. as obtained by exhausting the roasted mineral in 

 ammonia, a nearly pure molybdic acid may be obtained; it 

 contains mere traces of phosphoric acid. This method is 

 very simple, and may be employed in many cases. 



