25 



dried. Phosphoric acid was determined by the gravimetric 

 method, and ferric oxide by the volumetric bi-chromate method. 

 The following results were obtained : 



Fe 2 0,, --------------------------------------------- 41.53% 



P 2 5 -------------------------------------------- 38.20% 



H 2 O ____________________________________________ 20.08% 



Correcting for hygroscopic moisture, the figures agree with 

 the formula FePO 4 .2H 2 O. 



The only natural ferric phosphate that could be obtained 

 was a sample of Dufrenite containing 16.01 per cent of P 2 O 5 . 

 This is a basic ferric phosphate. 



The solubility of these materials was first determined by 

 placing i gram in a small flask, adding 100 c.c. of i per cent 

 citric acid solution, and allowing to stand twenty-four hours at 

 room temperature, shaking once each hour. The insoluble resi- 

 due was then filtered off, washed with cold water, and the phos- 

 phoric acid determined. The following results were obtained : 



Material. fzOo sol. in Per cent of 



i per cent citric acid. total. 



Precipitated Ferric Phos __________ 12.20% 31.9 



Precipitated Ferric Phos ---------- 12.05% 3 r -5 



Dufrenite ________________________ -O7% 0.4 



Dufrenite ________________________ 0.09% 0.5 



The effect of lime on the solubility of these phosphates was 

 then determined. For this purpose i gram of each of the ma- 

 terials was placed in a flask, pure slaked lime (free from phos- 

 phoric acid) added, and enough water to make a thin paste. 

 After twenty-four hours the contents of the flask were treated 

 with 100 c.c. of i per cent citric acid solution and an additional 

 amount of the crystallized acid to neutralize the excess of lime. 

 The solubility in the citric acid was then determined as in the 

 first instance. The following table contains the results. 



