1903.] on Perfumes, Natural and Artificial, 269 



aliphatic series ; and Thiemann, through his studies of vanilline, oil 

 of iris and of irone, arrived at the synthesis of vanilline and ionone, 

 or artificial violet. Many more might be mentioned as having con- 

 tributed to our knowledge of this subject. 



The chief sources of natural perfumes are the flowers, plants, 

 aromatic roots, the sweet spices of the East, etc., from which the 

 active principle, the essential oil, is extracted in diflferent ways. 

 The oldest method which is still in use for substances readily de- 

 composable, and to which distillation with steam cannot be applied 

 without destruction, is to treat the blossoms with vaseline or with 

 molten fat, or press them between two sheets saturated with fat until 

 the perfume has been completely dissolved in the fat {enfleurage). 



The perfume can be separated from its fatty solvent by cold 

 alcohol, in which the fats are insoluble. The essential oils of jasmine 

 and tuberoses are, for instance, prepared in this manner. The mode 

 is practically identical with the one described by Plinius in the 

 second half of the first century. 



The second mode of obtaining esssential oils, and the one which 

 is most generally used, is to distil the blossoms with steam. Attar 

 of roses, oil of neroli, oil of lavender and many others are produced 

 by this process. There are three distinct operations : 



(1) Preparation of the raw material. 



(2) Distillation. 



(SJ Purification of the crude oil. 



The distillation can be carried out 



(a) With high-pressure steam ; 

 (h) With superheated steam; 

 (c) With water ; 



all of which may be used, but the selection must always depend on 

 the properties of the oil. 



The purification of the distillate is very important and must 

 depend on the special impurities which may contaminate the oil. 



A third mode of obtaining the perfimie is to extract it from the 

 raw material with low boiling liquids such as ether, petroleum ether 

 or acetone, and to remove the solvent by evaporation, which is usually 

 effected in vacuo. 



An effort has been made to explain the fragrant properties of 

 scents by the presence of aromatophoric groups in a similar way as 

 the colour of substances is due to chromophoric groups, but not 

 sufficient data have been collected to allow of any fixed conclusions. 



A variety of classes of compounds have been isolated from essen- 

 tial oils such as hydrocarbons, alcohols, ethers, aldehydes, ketones, 

 acids and their esters. 



The most important hydrocarbons belong to the class of terpenes, 

 and their complex structure has been explained by a series of clas- 



