A. A. Ramsay 281 



(CaO)2HoOP205 1-4 H2O or CaHP04 0-7 R^O. This preparation there- 

 fore appears to be a mixture of 78-059% dicalcic phosphate and 

 14-777 % tricalcic phosphate with water of crystalhsation. 



No. 3. Calcii Phosphas B.P., also purchased locally. 

 Upon analysis the following figures were obtained : 



Lime(CaO) 41-15 



Phosphoric acid (P2O5) 42-20 



Water lG-65 



100-00 



Per cent. 



Loss in weight on drying in desiccator over sulphuric acid IG hours 1-920 



Loss in weight on drying in desiccator over sulphuric acid 112 hours 2-760 



Loss on drv'Tng at 100° C. : 2 hours 5-.38 %. 4 hours 5-38 %. 6 hours 5-45 "o^ 1 i lionrs 5-52 

 Loss on Ignition ... 



By calculation we find the lime and phosphoric acid exist in the 



following combination : 



CaO H,() P,05 Water 



Dicalcic phosphate {CaO)oH,OP,0, 17-554 2-821 22-256 - =42-631 



Tricalcic phosphate (CaO)3P,05 - 23-596 - 19-944 - =43-540 



Water of crystallisation — ^ — — 13-8 29 - 13-829 



41-150 2-821 42-200 13-829 100000 



Assuming that all the water of crystallisation is associated with the 

 dicalcic phosphate only, this would conform to the formula 

 (CaO)2H20P2054-9H20 or CaHP042-45H20. 



The above sample therefore appears to be a mixture of 42-631 % 

 dicalcic phosphate with 43-540 % tricalcic phosphate with water of 

 crystallisation. 



None of these three compounds are what they purport to be. but 

 are mixtures of varying amounts of di- and tricalcic phosphates. 



Having been unsuccessful in procuring pure tricalcium phosphate by 

 purchase, the preparation of this substance was undertaken, following 

 recognised authorities, 



Roscoe and Schorlemmeri state : " pure calcium phosphate CagPoOg 

 is obtained as a white precipitate by adding an excess of common 

 sodium phosphate to an ammoniacal solution of chloride of calcium." 

 This method was adopted by Warington2 i^ preparing pure tricalcic 

 phosphate for his investigations on the action of water on this substance. 



1 Treatise on Chemistry, Vol. n, Part i, p. 205. 



2 "On the decomposition of tricalcium phosphate by water," Journal Chemical Society, 

 Vol. XXVI (entire series), p. 983. 



