148 CHEMICAL COMPOSITION OF VEGETABLES. 
elementary bodies, differing in the proportion in which these 
are present, : 
' 580. Organic substances are remarkable for their tendency 
to spontaneous decomposition. When their elements are no 
longer held together by the principle of life, they are re- 
solved into carbonic acid, water, carbonic oxide, and the dif- 
ferent kinds of carbureted hydrogen. Ammonia is also 
formed when nitrogen is present. The carbon and hydrogen 
have a constant tendency to unite with oxygen to form car- 
bonic acid and water ; but as there is never a sufficient quan- 
tity of oxygen to convert all the carbon into ¢arbonic acid, and 
all the hydrogen into water, the carbureted hydrogen, which 
requires no oxygen, and the carbonic oxide, which requires = 
less than the carbonic acid, are formed. 
581. It has been ascertained by MM. Gay-Lussac and 
Thenard, that those vegetable products in which the oxyge? 
and hydrogen exist in the proportions in which they unite 
form water, are of a mild and inoffensive nature, being neither 
acid, resinous, nor oily ; that when there is more hydroget 
than is necessary to form water with the oxygen, the product 
is resinous or oily ; and that when there is more oxygen than 
would be necessary to form water with the hydrogen, the pro 
duct is in general of an acid nature. Besides these, there i§ 
a newly discovered class of vegetable principles called alkalis, 
many of which contain a considerable quantity of nitroge? 
and there are several vegetable compounds which cannot be 
included in any of the preceding classes. Under these 
heads, we shall now proceed to describe the leading products 
of the vegetable world. 
