392 PLANTS AND MAN 



on natural camphor supplies has stimulated attempts at cultiva- 

 tion of camphor trees elsewhere in tropical regions of the world. 

 The United States is one of the world's principal users of cam- 

 phor, and is attempting to grow camphor on a large scale in 

 southern Florida where some thousands of acres are under 

 cultivation at the present time. In addition to being employed 

 in a variety of medical uses and in perfumery, its most important 

 use is in the manufacture of plastics — celluloid anid other nitro- 

 cellulose products. Synthetic camphor from oil of turpentine 

 has been a war time development in both Germany and the 

 United States, and may rival natural camphor. 



Fixed Oils 



Fatty oils, as they are also called, differ from the volatile oils 

 in that they are incapable of being distilled or evaporated with- 

 out being changed in composition. They are closely related 

 chemically to animal fats (see p. 134), and may be liquid at 

 ordinary temperatures, in which case they are commonly called 

 oils, or if they are solid at ordinary temperatures they are called 

 fats. These differences are due to the kind of acid which, with 

 glycerin, goes to make up the compound. Fixed oils are found in 

 many plant families, chiefly in the seeds where they constitute a 

 light, highly concentrated form of stored food for use by the 

 embryo plant contained within. As a rule fixed oils are lacking in 

 strong tastes or odors, and many are used as foods by man. 



In the extraction of fixed oils, the seed coats are first removed, 

 and the kernels reduced to a meal, after which the oils are 

 removed by solvents, or by hydraulic pressure which squeezes the 

 oils out of the cells. Edible oils are generally extracted by the 

 latter method; lower grades of the same oils are secured by pres- 

 sure with the addition of heat which causes a somewhat higher 

 yield but a lower quality. Such oils are used in the industries 

 discussed later in connection with the various oils. The "cake" 

 remaining after the oil has been removed is high in protein con- 

 tent, and in most cases is very valuable as a stock food. In a few 

 instances, poisonous substances in the meal preclude their use as 

 animal food. The fixed oils are generally classified according to 

 their ability to absorb oxygen from the air and dry into thin, 



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