84 HOW CROPS GROW. 



their properties. They differ more or less in taste, odor, 

 and consistency, as well as in their chemical composition. 

 The "oils" are the simplest in chemical composition, 

 and have the lowest melting points. The "fats" have 

 larger content of carbon, and higher points of fusion. 

 The varieties of wax are most complex in composition, 

 and have the highest melting points and greatest content 

 of carbon. These differences are mostly gradational. In 

 chemical constitution these bodies are alike. 



EXP. 39. Place a handful of fine and fresh corn or oatmeal, which has 

 been dried for an hour or so at a heat not exceeding 212, in a bottle. 

 Pour on twice its bulk of ether, cork tightly, and agitate frequently for 

 half an hour. Drain off the liquid (filter, if need be) into a clean porce- 

 lain dish, and allow the ether to evaporate. A yellowish oil remains, 

 which, by gently wanning for some time, loses the smell of ether and 

 becomes quite pure. 



The fatty oils must not be confounded with the ethe- 

 real, essential, or volatile oils, which, however, do not occur 

 to much extent in agricultural plants. The former can 

 not evaporate except at a high temperature, and when 

 brought upon paper leave a permanent "grease spot." 

 The latter readily volatilize, leaving no trace of their 

 presence. The former, when pure, are without smell or 

 taste. The latter usually possess marked odors, which 

 adapt many of them to use as perfumes. 



In the animal body, fat (in some insects, wax) is formed 

 or appropriated from the food, and accumulates in con- 

 siderable quantities. How to feed an animal so as to 

 cause the most rapid and economical fattening is one of 

 the most important questions of agricultural chemistry. 



However greatly the various fats may differ in external 

 characters, they are all mixtures of a few elementary fats. 

 The most abundant and commonly-occurring fats, espe- 

 cially those which are ingredients of the food of man and 

 domestic animals e.g., tallow, olive oil. and butter con- 

 sist mainly of three substances, which we may briefly 

 notice. These elementary fats are Stearin, Palmitin, 



