6 Preparation of Substances 



The fertilizer manufacturer must determin 

 the exact amount of sulfuric acid to be used 

 for each substance present in the ground rock. 

 The student is not askt to do this. How- 

 ever, to insure the presence of sufficient acid 

 to combine with all these substances, the 

 calcium phosphate content of the floats as 

 given to the student is increased 5 to 10 per 

 cent. 



The strength of sulfuric acid used will vary 

 according to the source and composition of 

 the natural rock. If large amounts of cal- 

 cium compounds other than phosphate are 

 present a more dilute acid is used so that 

 there will be water enuf to hj^drate the 

 land plaster (calcium sulfate) formd in the 

 reaction. 



The calcium fluorid present reacts with 

 the sulfuric acid producing the disagreeable 

 poisonous hydrofluoric acid gas. Avoid 

 breathing the fumes from the mixture. 



Notice that after standing the mass crum- 

 bles easily in the hand. After storing several 

 weeks, during which time the action of the 

 sulfuric acid continues until the insoluble 

 phosphates are reduced to a fraction of one 

 per cent, the material is ground, if necessary, 

 and put on the market or used as a ''base," 

 i.e., one of the substances from which fer- 

 tilizers are made. 



