MAXUKES. 81 



made, or if the original mineral contained much ferric 

 oxide or alumina. 



The value of a superphosphate chiefly depends on the 

 percentage of " soluble phosphate" present. By this term 

 analysts do not mean monocalcic phosphate, but the quan- 

 tity of tricalcic phosphate rendered soluble. 



The best mineral phosphate found in England is Cam- 

 bridge coprolite. This is largely used for making super- 

 phosphate. Other coprolites are also employed, but they 

 are less suitable. Immense quantities of mineral phos- 

 phates are imported, principally from South Carolina, 

 Spain, Bordeaux, and Canada, besides considerable quan- 

 tities of phosphatic guano. 



The superphosphates richest in soluble phosphate (40 

 to 45 per cent.) are prepared from phosphatic guanos. 

 Bone ash, and some phosphorites, also yield high quality 

 manures. The great bulk of our superphosphates is at 

 present prepared from Carolina phosphate or coprolite ; 

 such manure will contain 23 to 27 per cent, of soluble 

 phosphate. 



Superphosphates form the basis of almost all manufac- 

 tured manures. By using bones, or by adding shoddy or 

 crude ammonium salts, turnip manures are produced con- 

 taining a small amount of nitrogen. By mixing with the 

 superphosphate a larger amount of ammonium salts, or 

 nitrate of sodium, the articles sold as corn, grass, mangel, 

 and potato onanures are prepared. Superphosphate made 

 largely from bones is known as dissolved hones. 



When superphosphate is applied to a soil containing 

 carbonate of calcium, the soluble phosphate is speedily 

 precipitated, but in a form easily taken up by the roots oi 

 plants. In most cases the phosphoric acid is finally con- 



