CHAPTER VIII 

 MANUFACTURE OF SUPERPHOSPHATE 



THE manufacture of superphosphate comprises 

 three principal operations: 1. Grinding the raw ma- 

 terial. 2. Rendering the ground raw phosphate 

 soluble by sulphuric acid. 3. The drying of the 

 superphosphate. 



Raw phosphate should be carefully ground, be- 

 cause it is found that the fineness of the phosphate 

 contributes to a great extent to a perfectly suc- 

 cessful superphosphate. Thus the powder should 

 not leave more than 10 per cent of residue on a 

 70 mesh sieve, and this residue should not exceed 

 the size of groats; it is only at this cost that all the 

 phosphoric acid is rendered soluble. Certain 

 phosphates are delivered ground, others in lumps 

 of the size of the fist. To lend itself well to grind- 

 ing the phosphate should be dry. Florida phos- 

 phate especially should not contain more than 1 

 per cent of moisture, while Algerian phosphate 

 grinds very well with 5 per cent of water. When 

 dealing with phosphate drenched with sea water 

 in transit or accidentally in the warehouse it is 

 extended on a drying platform of sheet iron heated 

 by the combustion gases or over flues from the 

 boiler furnaces. For the grinding of phosphate at 



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