40 THE CHEMISTRY OF THE FAEM. 



bridge coprolite. This is not at present much used, 

 cheaper phosphates being imported. Immense quantities 

 of mineral phosphates are imported from South Carolina, 

 Belgium, Spain, 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 ; such manure 

 will contain 23 to 27 per cent, of soluble phosphate. 



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 nitro- 

 gen. By mixing with the superphosphate a larger 

 amount of ammonium salts, and in some cases potassium 

 salts, the articles sold as corn, grass, mangel, and potato 

 manures are prepared. Superphosphate made largely 

 from bones is known as dissolved bones. 



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 

 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 

 effect than manures consisting of undissolved phosphate. 

 A small quantity of phosphoric acid applied as super- 

 phosphate will generally have as great immediate effect 



