22 Nature of Mineral Pliosphates 



All the free lime was removed by the two sugar extracts and the 

 phosphate dissolving in the first citric extract is therefore one with a 

 very high calcium oxide content and is also combined with siUca. The 

 ratio P2O5 : CaO of 1 : 2-59 and the ratio SiOg : CaO of 1 : 4-05 are in 

 agreement with the formula (2Ca3P208 . CaO) SSiOa . 6CaO. The second 

 citric extract contains no siUca and the ratio P2O5 : CaO is precisely the 

 same as the ratio P2O5 : CaO in the second extract of calcined Florida 

 pebble phosphate, and corresponds to the formula 4Ca3P208 . 3CaO, 

 the phosphate present in uncalcined Florida pebble phosphate. The 

 ratio P2O5 : CaO of 1 : 1-38 in the 3rd, 4th and 5th extracts corresponds 

 with the phosphate 2Ca3P208 . CaO which was found to be present in 

 Makatea Island phosphate, and in the 3rd, 4th and 5th extracts of 

 calcined Florida pebble phosphate. 



Belgian and Gafsa Phosphates. 



The results secured with Belgian and Gafsa phosphates are very 

 similar to those recorded for Algerian phosphate. The ratio of phos- 

 phoric acid to lime is also 1 : 1-58, a ratio which corresponds to the 

 formula Ca3P208 . CaO. 



With the calcined Belgian phosphate the following figures were 

 obtained. 



The ratios in the 1st citric extract correspond to the phosphate 

 (Ca3P208 . CaO)4 6CaO . 3Si02. The ratio in the 2nd extract again 

 corresponds to the formula 4Ca3P208 . 3CaO, whilst the ratio in the 

 3rd, 4th and 5th extracts corresponds to the phosphate 3Ca3P208 . 2CaO, 

 which also occurs in calcined Gafsa phosphate and calcined Tunisian 

 phosphate. 



