Superphosphate 5 



neither scale bears any relation to true specific 

 gravity. See Thorp, Inorganic Chemical 

 Preparations, p. 32. 



The solubility of the natural rock phosphate, 

 or floats, in a short time under most soil 

 conditions, is so sUght that it has become a 

 common practise to ''dissolv" it, that is, 

 to convert it into the water-soluble acid 

 phosphate having only one-third of the ori- 

 ginal amount of calcium. Under ordinary 

 business conditions one-half of all the sul- 

 furic acid made in this country is used in this 

 process. 



Tricalcium phosphate, whether as rock 

 phosphate, bones or the mineral apatite, is 

 always associated with fluorin and generally 

 chlorin. In addition rock phosphate is gen- 

 erally associated with calcium and magnesium 

 carbonates, and sometimes iron and alumi- 

 num phosphates so that the reactions which 

 take place with the sulfuric acid are more 

 complicated than that given at the beginning 

 of this exercise. The following are the more 

 important : 



(2) 2Ca3P208 • Ca2FP04 + 7H2SO4 • aq = 



3CaH4P208 • H2O + 7CaS04 • 2H2O 

 + 2HF. 



(3) CaCOs + H2SO4 . aq = CaS04 • 2H2O 



+ CO2. 



(4) 2AIPO4 + 3H2SO .aq = 2H3PO. + 



2A1(S04)3 • I8H2O. 



