Phosphates 



assimilable, measuring their assimilability by their 

 solubility in water, and experimenting on bones; 

 and two years later, after successful experiments on 

 bones and mineral phosphates, Lawes established 

 the first factory at Deptford. 



Superphosphates, therefore, are the result of 

 treating the substances contained in tricalcic phos- 

 phates [Ca3(P04)2], with sulphuric acid [H2SO4], and 

 so rendering them super-assimilative by the following 

 method. A suitable quantity of sulphuric acid is 

 made to react on tricalcic phosphates, mineral phos- 

 phates for example. Theoretically one ought to get 

 — Ca3(P04)2 -f 2H2SO4 = CaH4(P04)2 + 2CaS04 = 

 plaster. But m practice one finds that a little free 

 phosphoric acid has been formed and that a portion 

 of tricalcic phosphate has not been touched, and 

 the more foreign matter the mineral phosphate 

 contams the more will this be the case. 



This difficulty is partially met, however, by 

 grinding the mineral phosphate very fine, and adding 

 water to the sulphuric acid in such a manner as to 

 make it thoroughly penetrate the mixture. In this 

 way a good superphosphate ought not to contain 

 more than 2 per cent, insoluble phosphate. In any 

 case the insoluble phosphate is not counted in the 

 super in fixing the price of the latter. 



The mixture at this point is doughy, but the 

 great quantity of plaster formed in the first reaction 

 combines itself with the water and the whole 

 becomes hard through the formation of gypsum. 

 Before being applied to agricultural uses the 

 superphosphate should first be ground. 



Nearly 800,000 tons of superphosphate are made 



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