of Molybdenum and some of its Compounds. 527 



ant part accordingly as we have to do with a-, b-, or c-phos- 

 phoric acid. 



We adopted this method for the preparation of the inso- 

 luble yellow compound in order to be perfectly certain of ob- 

 taining a pure preparation ; however, as the following analyses 

 will show, the salt can be prepared more quickly in a much 

 more simple manner. Molybdic acid is dissolved in an ex- 

 cess of ammonia and a few drops of a solution of phosphate 

 of soda added, the liquid heated and mixed with an excess 

 of one of the above-mentioned acids, when the yellow salt is 

 instantly precipitated. To ascertain the composition of this 

 salt we made the following analyses: — 



I. 1*2258 grm. salt, prepared according to the first method, 

 and dried at 212°, gave on calcination, with the addition of a 

 few drops of nitric acid, 1*1095 molybdic and phosphoric acid. 

 This residue was dissolved in ammonia, the molybdenum pre- 

 cipitated as sulphuret, and the phosphoric acid determined 

 in the filtered solution, after it had been somewhat evaporated 

 and mixed with chloride of ammonium, by magnesia. The 

 weight of the ignited phosphate of magnesia amounted to 

 00699 = 0-0445 phosphoric acid. 100 parts of the salt con- 

 sequently contained — 



Oxide of ammonium -f water . .- 9*488 



Phosphoric acid 3631 



Molybdic acid 86*881 



II. 4*7247 grms. salt, prepared according to the second 

 method, and dried at 212°, lost on ignition 0-478 grm. oxide 

 of ammonium and water; the phosphoric acid was not deter- 

 mined. 100 parts contain — 



Oxide of ammonium + water . 10*117 

 Molybdic and phosphoric acids . 89833 



In this analysis the loss on ignition is too high owing to the 

 difficulty of oxidizing the residual mass, which consisted 

 partly of oxide of molybdenum. 



It seems to follow from analysis I. that the phosphoric acid 

 in this salt is not an essential constituent according to the or- 

 dinary laws of chemical combination, and if it be neglected, 

 the two analyses agree tolerably well with the theoretical com- 

 position of a pentamolybdate of ammonia, which contains — 



a. 

 1 at. Oxide of ammonium 324*980 

 1 at. Water . . . .112*479 

 5 at. Molybdic acid . 4444-8 30 



4882*289 100-000 4816604 100*000 



