62 SCIENTIFIC AGRICULTURE. 



It exists in several plants, but is found in most abundance in 

 the camphor tree. It is highly inflammable, and resembles in 

 some respects the resins : it is nearly insoluble in water, but 

 dissolved by alcohol and oils. 



CAOUTCHOUC. 



Caoutchouc, or India Rubber, is the product of several 

 trees in tropical countries, from which it exudes in tlie form of 

 a milky juice which hardens by contact with the air. It is 

 insoluble in water or alcohol, and dissolves but imperfectly in 

 ether; its proper solvent is volatile oils: oil of turpentine dis- 

 solves it, but it dries imperfectly afterwards. At a tempera- 

 ture a little above that of boiling water it melts and never 

 resumes its elasticity : in its properties, it possesses considera- 

 ble resemblance to the resins: it may be^converted into a 

 volatile oil by distillation. 



FIXED OILS. 



Oils are divided into two classes, viz: fixed and volatile: 

 the former are capable of being distilled without decomposi- 

 tion, the latter are not. The animal and vegetable oils agree 

 in their properties very nearly in every respect. The fixed 

 oils are obtained by pressure, from the seeds of various plants, 

 as the castor bean, flax seed, <fcc. 



They have little taste or odor, are lighter than water, con- 

 geal at a lower temperature, and require a higher heat than 

 that of boih'ng water to evaporate them. They are highly 

 nutricious, and combine with soda to form soap: by contact 

 with air they become rancid and gummy : they are all inso- 

 luble in water, and, with the exception of castor oil, but 

 slightly so in alcohol: they dissolve easily in ether and the 

 volatile oils. 



VOLATILE OILS. 



Volatile or essential oils are numerous in the vegetable 

 kingdom, and give to plants their peculiar odors: they are 



