OILY AND ETHEREAL PRODUCTS. 291 



being dried, is moistened with water, tied together 

 in small bundles, and placed in heaps, a peculiar 

 process of decomposition takes place. Fermentation 

 commences, and is accompanied by the absorption of 

 oxygen ; the leaves now become warm and emit the 

 characteristic smell of prepared tobacco and snuff. 

 When the fermentation is carefully promoted and 

 too high a heat avoided, this smell increases and 

 becomes more delicate ; and after the fermentation 

 is completed, an oily azotised volatile matter called 

 nicotine is found in the leaves. This substance 

 nicotine, which possesses all the properties of a 

 base, was not present before the fermentation. The 

 different kinds of tobacco are distinguished from 

 one another, like wines, by having very different 

 odoriferous substances, which are generated along 

 with the nicotine. 



We know that most of the blossoms and vegeta- 

 ble substances which possess a smell, owe this pro- 

 perty to a volatile oil existing in them ; but it is 

 not less certain, that others emit a smell only when 

 they undergo change or decomposition. 



Arsenic and arsenious acid are both quite in- 

 odorous. It is only during their oxidation that they 

 emit their characteristic odour of garlic. The oil 

 of the berries of the elder-tree, many kinds of oil 

 of turpentine, and oil of lemons, possess a smell 

 only during their oxidation or decay. The same 

 is the case with many blossoms ; and Geiger has 



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