286 The Soluhility of Calcium Fhosphafes in Citric Acid 



By calculation the above appears to consist of: 



CaO H2O PoOs Water 



Dicalcic phosphate (CaO)oHoOP205 6-116 0-983 7-754 — = 14-853 



Tricalcic phosphate (CaO)3P,05 ... 40-244 — 34-016 — =74-260 



Water of crystallisation ... ... — — — 10-887 = 10-887 



46-360 0-983 41-770 10-887 =100-000 



If the whole of the water of crystallisation be contained in the 

 dicalcic phosphate only, then the formula of this would correspond to 

 (CaO)2H20P.205llH20, but if, as is more probable both the di- and 

 tri-salts contain water of crystallisation, and if the di-phosphate be 

 CaHP042H20 the tricalcic phosphate would correspond to the formula 

 CagPaOg l-eiHaO. Thus: 



(CaO)2H20P205 4H2O 18-785 



(CaO)3P205l-61H,0 81-215 



100-000 



Preparation No. 8a was found upon analysis to consist of : 



Lime (CaO) 41-386 



Phosphoric acid {F-P:-,) 50-596 



Water 8-018 



100-000 

 By calculation the above appears to be a mixture of : 



CaO H2O P2O5 Water 



Dicalcic phosphate ... 36-949 5-938 46-846 — = 89-733 



Tricalcic phosphate ... 4-437 — 3-750 — =8-187 



Water of crystallisation ... — — — 2-080 = 2-080 



41-386 5-938 50-596 2-080 = 100-000 



If all the water of crystallisation be associated with the dicalcic phos- 

 phate only, its formula would correspond to (CaO)2H2OP2O5 0--35H2O. 

 The tricalcic phosphate would be Ca3P208. 



It was considered probable that in the last experiments (prepara- 

 tions No. 7 and No. 8) hydrolysis of the salts originally produced might 

 easily have occurred, owing to the lapse of time between the mixing of 

 the lime and phosphoric acid, and the separation of the precipitates 

 formed, from the fluid portion. It was therefore decided to repeat this 

 portion of the work, and to remove the precipitate formed after the 

 lapse of an hour. Preparation of the solution of phosphoric acid (H3PO4) : 



About 43 grams pure phosphorus pentoxide was dissolved in water 

 and made up to 500 c.c. 



A titration of this to methyl-orange, using caustic soda, gave 



