24 



Nature of Mineral Phosphates 



has also been produced by calcining Tunisian phosphate. The 

 ratio in the 2nd citric extract again corresponds to the phosphate 

 4Ca3P208 . 3CaO, whilst the ratio in the 4th and 5th extracts cor- 

 responds to the phosphate 2Ca3P208 . CaO present in Makatea Island 

 phosphate. It is probable that the 3rd citric extract contains the 

 phosphate SCagPgOg . 2CaO present in calcined Belgian and calcined 

 Gafsa phosphate. 



The results obtained by submitting 5 grams of apatite to consecutive 

 half-hour extractions with 2 per cent, citric acid are given in the 

 following table. 



Apatite, SCagPgOg . CaFg. 



Passes "100" sieve 



% % Ratio 



P,Ob CaO P,0;; : CaO 



* After subtracting 2-84 per cent. CaO present as CaCOg. 



These results show that the phosphoric acid and hme are dissolved 

 out in the same ratio as they are present in the mineral. 



Conclusions. 



Five different mineral phosphates have been examined and the 

 results secured indicate the presence of three distinct compounds of 

 phosphoric acid and lime. 



