

The Phosphates of America. 157 



The weight of the Mg 2 P 2 O 7 X .6396 X 2 equals the total phos- 

 phoric anhydride in one gramme of the substance. 



The three following determinations have now been made : 



1. The P 2 O 5 soluble in water. 



2. The P 2 O 5 insoluble in ammonium citrate. 



3. The total P 2 O 5 contained in the substance. 



The figures obtained in the first two cases, added together and 

 deducted from the last, will therefore show the amount of citrate- 

 soluble phosphoric acid in one gramme of the substance ; as for 

 example : 



Total P 2 O 5 in one gramme 0.160 gramme 



P 8 O 5 soluble in water 0.140 



P 2 O 5 insoluble in water and ammonium citrate . . 004 .144 " 



P 2 O. soluble in ammonium citrate 016 * 



and the manner in which we should state the result of such an 

 analysis as this in our reports would be as follows : 



Moisture ? 



Water-soluble phosphoric anhydride (P 2 O 5 ) 14.00 



Citrate-soluble or assimilable phosphoric anhydride (P 2 O 5 ). 1.60 



Insoluble phosphoric anhydride (P 3 O 5 ) 0.40 



Equal to 34 per cent, of bone phosphate made soluble. 



THE VOLUMETRIC ESTIMATION OF PHOS- 

 PHORIC ACID. 



While we have long discarded the use, in our commercial labor- 

 atory, of all volumetric processes of determining phosphoric acid 

 for commercial purposes, we nevertheless have always found the one 

 that we shall now describe of considerable value in the factory. 

 With a little practice it is possible to observe the end reaction with 

 great accuracy, and provided not more than one per cent, of com- 

 bined iron and alumina is present, the results are tolerably reli- 

 able. 



The formulae for preparing the standard solutions required are 

 given on another page, and the principle on which the method is 

 based is the fact, that phosphoric anhydride and uranic oxide com- 

 bine together to form a compound insoluble in acetic acid. 



P 2 5 -f 2 Ur 2 3 = Ur 4 P 2 O n 



142 -f 576 = 718. 



