16 THE PRODUCTION OF VOLATILE OILS AND PEEFUMEEY PLANTS. 



oil, however, is not formed until the mustard is brought in contact 

 with water, thus enabling the vegetable ferment to hydrolj^se the glu- 

 cosid, with the results specified. 



These instances are cited here simply to nuike clear the fact that 

 not all volatile oils preexist in plants and that some of our most valu- 

 able oils are obtained from plants entirely devoid of odor, which, 

 however, develops when the proper conditions are supplied. The 

 number of these special cases is comparatively few Avhen Ave consider 

 the vast number of plants which contain volatile oils existing as such 

 in their tissues and depending for their development in the plant only 

 on conditions of growth and nourishment. 



EXTRACTION OF AROMA. 



For the separation of the aromatic principle from a plant, several 

 methods are in vogue, depending for their efficiency and practicability 

 largely upon the nature of the odors to be extracted. The properties 

 of the various odorous substances are such that in order to separate 

 them in their entirety onl}^ such methods can be applied as will bring 

 about the least possible change in the fragrant constituents. Because 

 of the facility with which certain aromatic principles undergo change 

 it is necessary at times to extract the perfume Avithout exposing the 

 materials to high temperatures and to other conditions which would 

 tend to change their chemical nature. For this reason several meth- 

 ods are emploj'ed at the present time for the extraction of volatile 

 oils and perfumes, each of which possesses adA-antages and disad- 

 vantages. 



The following general methods find application in commerce for 

 the separation of the odoriferous principles from plants and plant 

 products: (1) Solution, (2) expression, and (3) distillation. 



SEPARATION OF PERFUMES BY SOLUTION. 



The method of solution as applied in practice is subdivided into 

 three modifications, viz, by volatile solvents, by liquid fats, and by 

 solid fats. 



EXTKACTION WITH VOI.ATILE SOLVENTS. 



The method of extraction Avith vohitile soh^ents, such as ether, 

 chloroform, benzene, petroleum ether, acetone, etc., is adaptable only 

 to flowers, because of the comparatively small quantity of other kinds 

 of extractive matter soluble in any one of these soh'ents. The method 

 would be A'ery impractical for the extraction of perfumes or oils from 

 a AA'hole plant or from the leaA^es of a plant, since whole plants or 

 plant parts other than floAvers contain considerable other matter 

 besides the essential oil solublo in these soh'ents. 

 195 



