138 NATURAL MANURES. VI. 



An American product horn and hoof waste contains on 

 the average 



Water ... ... 10-17% 



Nitrogen ... ... 13-25% 



Phosphorus pentoxide ... 1-83% 



Wool, hair, and horn suffer decomposition in the soil only 

 very slowly ; consequently they are not quick in their action, 

 hut afford a slow supply of nitrogen for a long period, in some 

 cases for five or six years. They are used in the preparation 

 of certain "mixed manures," and especially in the cultivation 

 of hops. Feathers, which resemble hair in composition, are 

 also used as manure in Ireland. 



Soot. The soot collected from the imperfect combustion of 

 coal contains a portion of the nitrogen of the coal in the form 

 of ammonium salts and as organic nitrogenous compounds of 

 an amine character. Its usefulness as a manure depends 

 upon the nitrogen which it contains ; this varies from very 

 little up to 3 or 4% ; on an average perhaps 1-8 or 2% will be 

 present. Soot is useful as an insecticide. 



Oil-cakes. These, the residue of husks, &c., left after the 

 oil is expressed from certain seeds, are often highly nitro- 

 genous and generally contain considerable quantities of 

 phosphates and potash, indeed, of all forms of plant food. 

 Usually they are used as food for animals; but in some cases, 

 owing to the presence in the seed of poisonous or unpalatable 

 substances, they are only fit for manurial purposes. 



Eape, mustard, cotton, and castor cakes are the principal 

 ones used for manure, and of these cotton cake but rarely. 

 The percentages of the important constituents in such cakes 

 are given in the following table : 



Indian Cotton-seed meal : Castor 

 rape cake. undecorticated. cake. 



Water ... ... 12-0 9-5 



Nitrogen ... ... 5 - 5 4-3 5*5 



Potash ... ... 1-5 1-1 



Phosphorus pentoxide ... 3'1 1-7 



Oil 10-3 5-0 4-0 



