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The Preparation of Substances 

 Important in Agriculture 



SUPERPHOSPHATE 



Superphosphate is made from the natural 

 rock phosphate, finely ground, and sulfuric 

 acid, the phosphate being acted upon as 

 shown in equation (1) which follows: 



(1) CagPsOs + 2H2SO4 • aq = CaH4Po08 • H2O 

 + 2CaS04 • 2H2O. ^^^"^ 



Calcium sulfate (gypsum) , , ^ 



phosphate 



Two-thirds of the calcium of the tricalcium 

 phosphate are replaced by the hydrogen of the 

 acid. Chamber sulfuric acid is used. It is 

 necessary to calculate the actual amount of 

 tricalcium phosphate in the material at hand, 

 the amount of sulfuric acid to act on 200 

 grams of this material and the amount of 

 water that must be added to the sulfuric acid 

 to make it of the proper strength. 



Calculations. — (a) Note the purity of 



the phosphate rock and calculate the number 



of grams (a) of the tricalcium phosphate in 



1 



