SUPERPHOSPHATE 61 



formation of ferric and aluminie phosphate. The pro- 

 portion of reduced phosphate present in a super- 

 phosphate is estimated by making use of the fact that, 

 though insoluble in water, reduced phosphate is soluble 

 in a solution of citrate of ammonium. Eeduced phos- 

 phate has an agricultural value between soluble and 

 undissolved phosphate. 



Superphosphate is at present principally made from 

 mineral phosphates imported from Algeria, Tunis, 

 Florida, South Carolina, and Belgium. Ordinary super- 

 phosphate will contain about 26 per cent, of soluble 

 phosphate, with 2 — 3 per cent, of undissolved phos- 

 phate, or about 13 per cent, of total phosphoric acid. 

 Higher qualities are made for special purposes. 



Superphosphates form the basis of almost all manu- 

 factured manures. By using bones, or ground horn, 

 or by adding shoddy or crude ammonium salts, turnip 

 manures are produced containing a small amount of 

 nitrogenous matter. By mixing with the superphos- 

 phate a larger amount of ammonium salts, and in some 

 cases potassium salts, the articles sold as corn, grass, 

 mangel and potato manures are prepared. Super- 

 phosphate made largely from bones is known as dis- 

 solved bones. 



When superphosphate is applied to a soil containing 

 carbonate of calcium the soluble phosphate is gradually 

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

 of plants. In most cases the phosphoric acid is finally 

 converted into basic phosphate of iron, a substance less 

 easily assimilated by the roots; fresh applications of 

 phosphates are thus more effective than the residues 

 of previous manuring. 



Superphosphates are naturally more speedy in their 



