of Molybdenum and some of its Compounds. 427 



the action might not gradually proceed further; this however 

 was by no means the case, as the results obtained show. 



We found on treating a soluble molybdate of potash with 

 ah excess of concentrated nitric acid in the cold, that salts in- 

 stantly separated with a greater amount of molybdic acid ; this 

 is not the case with the soda salt. When an excess of nitric 

 acid is added to a cold solution of molybdate of soda, no pre- 

 cipitate results even after several days, but on heating the 

 liquid it instantly becomes turbid, and gradually deposits a 

 bulky yellow precipitate. On collecting this upon the filter, 

 it easily passes through the paper on being washed with 

 water, which may however be prevented by adding a few 

 drops of nitric acid to the water. The washing is very slowly 

 and imperfectly effected, as the precipitate adheres closely to 

 the filter. When dry it appears amorphous and yellow, except 

 at the edges and on the surface, where the colour is bluish- 

 green, produced by the escape of the nitric acid in drying. 

 When a portion of the precipitate is heated in a platinum cru- 

 cible, the greater part is volatilized at a strong red heat. 

 This had been observed by Buchholz, and may in some cases 

 serve for the preparation of pure molybdic acid. 



Salts of the Oxide of Ammonium. 

 The series of these salts is quite as numerous as that of the 

 salts of potash. We have not examined these combinations 

 so accurately, as in all the analyses the amount of molybdic 

 acid only has been determined by carefully heating the salt 

 in a counterpoised platina crucible, and in no instance that of 

 the ammonia or of the water ; by these determinations, and 

 partly by the preparation of the corresponding salts of baryta, 

 we are enabled to establish the following definite compounds. 



Neutral Molybdate of the Oxide of Ammonium, NH 4 0, 

 MoO 3 . — This salt was prepared by dissolving molybdic acid 

 in an excess of highly concentrated solution of ammonia in a 

 stoppered vessel, and precipitating with alcohol of 0*942 spec, 

 grav. The salt so precipitated is collected as quickly as 

 possible upon a filter and dried over caustic lime. 



When seen under the microscope, it has the form of small 

 four-sided prisms with two truncations. When a little of this 

 salt moistened with water is placed under the microscope, it is 

 quickly seen to change into the acid salt. It is anhydrous. 



Analysis. — 0*8095 grm. salt gave 0*594 molybdic acid; the 

 per-centage composition of the salt is therefore — 



a. Calc. b. Calc. Found. 



1 at. Oxide of ammonium 32498 26? 71 324*98 27*063 



1 at. Molybdic acid 888*966 73*229 875*829 72937 73-379 



1213*946 100000 1200*809 100*000 

 2 F2 



