292 The Solubility of Calcium Phosphates in Citric Acid 



would be submitted for the determination of "citrate soluble" phos- 

 phoric acid, which would contain more than 50 % calcium carbonate. 



Before discussing further the results of these experiments on the 

 action of the prescribed 2 % citric acid solution on tricalcic phosphate 

 and mixtures of these with calcium carbonate, it will perhaps be well 

 to give here, the results of investigations of the action of 2 % citric acid 

 solution on the substances which were sold and purchased as tricalcic 

 phosphate, but which chemical analysis showed to be mixtures of di- 

 and tricalcic phosphates in varying amounts. For this purpose phos- 

 phates No. 1 and No. 2 were selected, the former containing 78 % tri- 

 and 14 % dicalcic phosphate, and the latter 78 % di- and 14 % tri- 

 calcium phosphate. 



The results of these two examinations will now be given. 



Extraction of 5 grams of the phosphate of Ume (No. 1) with 500 c.c. 

 of a 2 % citric acid solution for 30 minutes. 



This powder was shown to consist of : 



Dicalcic phosphate CaHPOj 

 Tricalcic phosphate Ca3P208 

 Water of crystallisation 



14-188 



78-271 



7-541 



100-000 



containing lime (OaO) 48-26 % and phosphoric acid (P2O.5) 43-26 %, 



48-33 



43-26 



Actually present 48-26 — 



In the first extraction this salt appears to have gone into solution 

 as a mixture of tri- and dicalcic phosphates, the tricalcic phosphate 

 predominating, since the lime found is less than that necessary to com- 

 bine with the P2O5 found to form CagPgOg. 



In the second extraction the phosphate appears to have gone into 

 solution as tricalcic phosphate. There is a very minute excess of lime 

 which probably indicates calcium citrate. 



Extraction of 5 grams of the Calcii Phosphas B.P. (No. 2) with 

 500 c.c. of a 2 % citric acid solution for 30 minutes. 



