OILS. 143 



ARTICLE V. 



Oils* 



The oils are fat, unctuous bodies, of various degrees of 

 fluidity, insoluble in water, forming soap with the alka- 

 lies, and burning and evaporating at different tempera- 

 tures. It is the last characteristic, particularly, which es- 

 tablishes that difference amongst them by which they are 

 divided into fixed and volatile oils. The fixed oils are 

 contained in seeds and fruits, from which they are ex- 

 tracted by pressure. The first portion which is expressed 

 is the purest, and is known by the name of virgin oil ; 

 that which follows is rendered more or less impure by the 

 mixture of other principles contained in the fruit submit- 

 ted to compression. It is particularly by the mucilage, 

 which is found in a greater or less quantity in all vegetables, 

 that the purity of oil is affected. 



After all the oil, which can be extracted by pressure, 

 has been drawn off, it is customary to moisten the mash 

 with boiling water, and to subject it to another and more 

 powerful pressure; but the oil thus obtained carries with 



* I make use of the generic term oil, by which two substances, 

 differing widely from each other, have been for a long time known ; 

 but I ought to observe, that the properties which are common to 

 them, are not sufficient to authorize their being included under one 

 name, and that in all their relations they present 30 great a difference 

 as to entitle them to be considered as two kinds of products, and to be 

 designated by specific names. 



1 . The fixed oils are insoluble in alcohol ; the volatile oils are 

 soluble. 



2. The fixed oils have generally neither odor nor flavor ; the vola- 

 tile oils are pungent, caustic, and very odoriferous. 



3. The property of burning, common to the two oils, belongs like- 

 wise to all vegetable substances properly so called. 



4. The fixed oils are obtained only from seeds and fruits ; many 

 volatile oils are extracted from all parts of plants. 



5. The fixed oils are for the most part employed as food ; the vola- 

 tile oils are useful only in the arts. 



6. The fixed oils evaporate only at a high degree of temperature ; 

 the volatile oils are dissipated entirely at the temperature of the 

 atmosphere. 



7. The characteristic of forming soap does not belong exclusively 

 to the oils; it is possessed by many other substances, animal ana 

 vegetable. 



Thus wfiat are called volatile oils are only liquid or concrete 

 iromas, and it is in the class of aromas that they ought to be ranked. 



