26 



Material. I,ime. P-zOs sol. in i per Per cent of 



cent citric acid. total. 



Prec. Ferric Phos i gram 24.95% 65.3 



Prec. Ferric Phos i gram 24.90% 65.2 



Prec. Ferric Phos 0.5 gram 358o% 93.7 



Prec. Ferric Phos 0.5 gram 35-8o% 93.8 



Prec. Ferric Phos 0.25 gram 37-oo% 96.9 



Prec. Ferric Phos 0.25 gram 36.90% 96.6 



Dufrenite i gram 0.45% 2.8 



Dufrenite i gram 0.47% 2.9 



The following table shows the comparative solubility of the 

 phosphoric acid (P 2 O 5 ) in i per cent citric acid, with and without 

 the addition of lime : 



Material. Without lime. With lime. 



It is seen from the above tables that the action of lime on 

 the natural ferric phosphate was not very marked. In the case 

 of the precipitated ferric phosphate the lime caused a considerable 

 increase in the solubility. The larger quantities did not cause 

 as great an increase as the smaller quantities. This fact indi- 

 cated the formation of the more soluble calcium phosphates with 

 the smaller quantities. With an excess of lime, as in the experi- 

 ment in which i gram was used, tri-calcium phosphate was 

 probably formed, and this compound is much less soluble in i 

 per cent citric acid than the di- and mono-calcium compounds. 



It is to be remarked that the reaction was fairly rapid. 

 Within one hour after the addition of lime, a red compound began 

 to separate. This compound was probably ferric hydroxide. 'An 

 attempt was made to separate the products formed in the reaction. 

 Various solvents were tried, but it was found impossible to effect 

 a separation of calcium and ferric phosphates in the presence of 

 ferric hydroxide. In the course of these trials a 5 per cent solu- 

 tion of neutral potassium oxalate was observed to act on precipi- 

 tated ferric phosphate, dissolving both the iron and the phos- 



