G. S, Robertson 



21 



for the increased total solubility of the calcined Florida pebble phosphate 

 compared with the uncalcined, because, as has already been pointed 

 out, Makatea Island phosphate is more soluble in citric acid than 

 Florida pebble phosphate. 



With regard to the phosphate in the first calcined citric extract, it 

 is interesting to note that the phosphoric acid, calcium oxide and silica 

 are dissolved in exactly the same proportion as they are present in the 

 phosphate (Ca3P208)2 2CaO.Si02. 



Algerian Phosphate. 



CaO in the various citric acid extracts obtained 

 from Algerian phosphates are given in the following table. 



The ratios P2O5 



Refuses "100" sieve 



Passes "100" sieve 



* Excluding first extract. 



If the first citric extracts in both portions are excluded a constant 

 ratio of 1 : 1-58 is obtained for the phosphoric acid and hme dissolving 

 in the ei^ht citric extracts. The calcium oxide and phosphoric acid 

 are dissolved out in the 2nd, 3rd, 4th and 5th extracts in exactly the 

 same proportion as they are present in the phosphate Ca3P208 . CaO. 



Calcining produces a marked decrease in the solubility of Algerian 

 phosphate in citric acid, and a still more marked alteration in the 

 ratios in which the phosphoric acid and lime dissolve out in the various 

 extracts. 



Calcined Algerian Phosphate. 



