OIL-CAKE. 



229 



extraordinary extension, and in all probability it will 

 import for some time to come more of the same 

 kind of produce from neighboring countries. In 

 several districts, a custom that deserves the highest 

 commendation has been introduced very generally 

 into trade, by which the farmer sends his seed to 

 the oil-mill upon condition that the cake produced 

 from it is returned to himself. 



1. Constituents and Operation of Oil-Cake. 



The following figures may, first of all, show in 

 what way the seeds of oleaginous crops differ in 

 point of chemical composition from their strictly 

 vegetable parts, or straw : — 



According to this analysis, rape-stravj is richer in 

 valuable manuring substances than the straw of the 

 various kinds of grain, whose composition has been 

 stated in page 144. Besides the constituents just 

 enumerated, it often contains considerable quantities 

 of common salt and gypsum, which of course en- 

 hance its worth as a manure. As, however, from its 

 woody nature, it is in its natural state incorporated 

 20 



y 



