PERFUMES AND ESSENTIAL OILS 343 



long used in confectionery. Here again it would be possible to 

 proceed from the elements carbon, hydrogen, and oxygen. This, 

 however, would necessitate several roundabout processes, and 

 fortunately nature provides, in the substance called eugenol, a 

 convenient and not too expensive material. Eugenol is the chief 

 constituent of oil of cloves, and by acting on it with oxidising 

 agents vanillin is produced. 



The reader may be reminded that many years before such 

 achievements could be placed on record the chemist had already 

 learned that some of the fragrant essences so lavishly provided 

 in fruit and flower and leaf could be reproduced by purely 

 laboratory operations. As soon as organic chemistry began to 

 be seriously studied nearly a century ago, among the earliest 

 results was the production of what used to be called compound 

 ethers, by the action of various acids on common alcohol, on the 

 alcohol from wood spirit, and on the alcohol from fusel oil 

 separated in the rectification of whiskey. Among these products 

 were speedily recognised such odours and flavours as those of 

 the pineapple, the jargonelle pear, and others. Pineapple owes 

 its fragrance to ethyl butyrate, the pear to amyl acetate, winter- 

 green (largely used in the United States) to methyl salicylate, 

 while the strawberry and raspberry contain mixtures of several 

 such ethereal compounds. These are now common articles of 

 commerce. 



These, however, were not alone, for already in those early 

 days the odour developed when bitter almonds are crushed with 

 water was found to be due to the formation of another kind of 

 substance already mentioned in previous pages, namely, benz- 

 aldehyde. Similarly the flowers of the meadowsweet contain 

 salicylic aldehyde, the barks of cinnamon and cassia yield 

 cinnamic aldehyde, the hawthorn and many garden flowers 

 secrete other characteristic aldehydes. Nor were the older 

 chemists altogether ignorant of the constitution of the essences 

 to which the pungency of mustard, garlic, onions, and horse- 

 radish are due. These are also ethereal salts or compound ethers 

 which are characterised by the presence in them of sulphur 

 associated with a radicle called allyl in reference to their frequent 

 presence in plants of the genus Allium, belonging to the onion tribe. 



There is perhaps no department of applied organic chemistry 

 which has attracted during the last thirty years a larger number 

 of workers, nor one in which a larger amount of definite progress 



