18 



Nature of Mineral Phosphates 



The curves representing the rate of extraction of phosphoric acid 

 from each of the portions are shown in Fig. 1. They are of a fairly 

 definite nature, and are certainly not what would be derived from a 

 mixture of phosphates. 



12 3 4 5 



Extractions 



1. Passes " 100 " sieve. 2. Refuses "90" sieve. 



3. Refuses " 60 " sieve. 4. Refuses "30" sieve. 



5. Refuses " 1 mm." sieve. 



Pig. 1. Makatea Island Phosphate. 



The solubihty of the phosphate has been greatly decreased by 

 calcining, and an examination of the relationship P2O5 : CaO in the 

 five extracts suggests that a change in the composition of the phosphate 

 has been brought about by calcining. 



