APATITE. 29 



and a part of the sulphate of lime are extracted with 

 water, and separated as in No. 12. The sulphate of 

 lime remaining undissolved is ignited and weighed. 

 The phosphoric acid solution is mixed with water, the 

 alcohol evaporated, and the phosphoric acid then pre- 

 cipitated by sulphate of magnesia and ammonia as in 

 No. 6. 



A third method, based upon the insolubility of 

 phosphate of binoxide of tin in nitric acid, is as fol- 

 lows : The weighed bone-ash is heated in a flask, with 

 moderately strong nitric acid, and several times its 

 weight of pure tin (tin-foil), the weight of which must 

 be accurately known ; the contents of the flask are 

 heated to ebullition, diluted with water, and the binox- 

 ide of tin, which contains the whole of the phosphoric 

 acid, is filtered off, washed, dried, ignited and weighed. 

 The difference between the weight of this precipitate 

 and that of the binoxide of tin which should be fur- 

 nished, by the amount of metal employed, is due to 

 phosphoric acid. The separation of the lime and mag- 

 nesia contained in the solution is effected as in No. 12. 



A fourth method, applicable in general for the sepa- 

 ration of phosphoric acid from bases, consists in dis- 

 solving the substance to be analyzed in a small quan- 

 tity of nitric acid, adding nitrate of silver, some car- 

 bonate of silver, and shaking the mixture. All the 

 phosphoric acid combines with the oxide of silver and 

 is precipitated, while the bases remain in solution and 

 may be separated from the excess of silver by hydro- 

 chloric acid. 



14. APATITE. 

 3 (3 CaO, P0 5 ) + CaCl (or + CaF). 



For the determination of the chlorine, a weighed por- 

 tion of the mineral (which need not be powdered) is 



5* 



