78 GARDENING FOR THE SOUTH. 



"Rock Phosphates are known under several different 

 names which generally designate the locality from which 

 they come, as South Carolina Rock, Florida Rock, Ten- 

 nessee Rock, West India Rock, etc. Other mineral phos- 

 phates are known under the names of Apatite, Coprolite 

 and Phosphorite, which are found iu various places in 

 America and Europe, and some of which are used in 

 making commercial fertilizers. However, the greatest 

 source of supply of phosphoric acid is the phosphate rock 

 of our Southern States. The rock phosphates are exten- 

 sively used in making superphosphates. When ground 

 to a very fine flour-like powder, rock phosphates are 

 called "floats." Rock phosphates contain usually from 

 twenty-five to thirty per cent, of phosphoric acid, and 

 some as much as thirty-five to forty per cent. 



"Superphosphates are known under several different 

 names, such as acid phosphates, dissolved bone, dissolved 

 rock, etc. Superphosphates are formed by treating some 

 form of insoluble phosphate of lime, as rock phosphate, 

 bone, bone-ash, etc., with sulphuric acid. By this treat- 

 ment there are formed soluble phosphate of lime and 

 gypsum (sulphate of lime) in nearly equal proportions. 

 The value of a superphosphate depends upon the amount 

 of soluble phosphate of lime present in it, together with 

 the amount of reverted phosphate of lime. The amount 

 of soluble phosphoric acid compounds in superphosphates 

 varies with the kind of phosphate used in making the 

 superphosphate and also with other conditions, which we 

 need not mention here. A good quality of dissolved bone 

 contains twelve to eighteen per cent, of soluble phos- 

 phoric acid. Dissolved bone-black contains from below 

 fifteen to seventeen per cent, of soluble phosphoric acid. 

 Superphosphate made from rock phosphate may contain 

 from twelve to eighteen per cent, of soluble phosphoric 

 acid. 



