On Trilasic Phosphoric Acid. 19 7 



upon the ammonio-phosphate of magaesia. The results arc as 

 follows : 



(a)— 1.03S (b)— 1.051 (c)— 1.0201 



Al 2 O 3 =19.03 

 HO =48.28 



These analyses go to confirm what 1 have already expressed 

 regarding the value of the methods. \ have nothing farther 

 to add to this subject; and as the other sesquioxyds, that would 

 have to be separated from iron and phosphoric acid, rarely oc- 

 cur as such in iron ores, I make no mention of them, and will 

 only add a few words on the determination of phosphoric acid. 

 The main point in the case at issue is always to have the phos- 

 phoric acid in the tribasic modification : its determination is 

 then sufficiently easy, and is best effected in the form of am- 

 monio-phosphate of magnesia. 



