Ammonium Magnesium, Phosphate of Analysis. 195 



provided the magnesia mixture is present in sufficiently large 

 excess. 



Table V. 



P 2 5 in 



HNa 2 P0 4 



taken. 



Magnesia 

 mixture. 



Volume. 



NH 4 C1. 





grm. 



cm 3 . 



cm 3 . 



grm. 



Precipitation. 



0*0005 



10 



100 



._ 



Visible at once 



0*0005 

 O-0005 



50 



10 



100 

 100 



10 



throughout the liquid. 



a 



0-0005 



10 



200 



60 



a 



o-oooi 



50 



250 



60 



a 



o-oooi 



10 



100 



.. 



tt 



0*0001 



10 



100 



10 



a 



o-oooi 



50 



200 



10 



a 



o-oooi 



10 



250 



60 



tc 



o-oooi 



50 



300 



60 



Visible after 



o-oooi 



50 



500 



60 



settling out. 



This conclusion was further substantiated by an actual test (by 

 the molybdate method) of the ignited residue, obtained by evap- 

 orating a filtrate from ammonium magnesium phosphate 

 (equivalent to 0*8614 grams of the pyrophosphate) precipitated 

 by a faintly ammoniacal solution of magnesia mixture in pres- 

 ence of sixty grams of ammonium chloride, which gave a 

 precipitate of ammonium phosphomolybdate yielding 0*0002 

 grams of magnesium pyrophosphate. It is evident, therefore, 

 that any considerable deficiencies of weight of the magnesium 

 phosphate obtained by precipitating equal amounts of a soluble 

 phosphate by magnesia mixture in presence of varying amounts 

 of ammonium chloride, cannot be attributed to varying solu- 

 bility of the magnesium phosphate under changing proportions 

 of the ammonium chloride. 



The results recorded in section A of Table VI were obtained 

 by treating definite volumes of the pure solution of hydrogen 

 disodium phosphate with magnesia mixture, in slight excess 

 above the amount required to bring down the phosphate, and 

 making the solution distinctly ammoniacal. After thorough 

 subsidence, the precipitate was filtered off on asbestos under 

 pressure in a perforated platinum crucible, washed in water 

 faintly ammoniacal, dried, ignited and weighed. In experi- 

 ments (1), (5) and (6), only the ammonium chloride present in 

 the magnesia mixture was used ; in the other cases weighed 

 portions were added. In the experiments of section B, the 

 precipitate was dissolved in hydrochloric acid after filtering off 

 the supernatant liquid, brought down again in dilute solution 

 by ammonia in distinct excess, and thereafter treated as in the 

 experiments of section A. The experiments of section C 

 were conducted similarly to (1), (5) and (6) of A excepting 



