OIL-CAKES. 139 



These substances decompose slowly in the soil, so that they 

 are not quick-acting manures. They give better results as a 

 rule on clay soils than on light sandy ones. 



When the oil has been extracted by solvents the cake is of 

 greater value as a manure, since not only is it richer in the 

 proportion of valuable ingredients, but the absence of oily 

 matter permits of more ready access of water and thus favours 

 oxidation. 



