274 CHEMICAL TRANSFORMATIONS. 



Fermentation and putrefaction are examples of the kind of de- 

 composition which we have named transformations ; the elements 

 of the bodies capable of undergoing these changes arrange them- 

 selves into new combinations, in which the constituents of water 

 generally take a part. 



Eremacausis (or decay) differs from fermentation and putre- 

 faction, inasmuch as it cannot take place without the access of 

 air, the oxygen of which is absorbed by the decaying bodies. 

 Hence it is a process of slow combustion, in which heat is uni- 

 formly evolved, and occasionally even light. In the processes 

 of decomposition termed fermentation and putrefaction, gaseous 

 products are very frequently formed, which are either inodorous, 

 or possess a very offensive smell. 



The transformation of those matters which evolve gaseous 

 products without odor, are now, by pretty general consent, desig- 

 nated by the term fermentation ; whilst to spontaneous decom- 

 position of bodies which emit gases of a disagreeable smell, the 

 term putrefaction is applied. But the smell is, of course, no 

 distinctive character of the nature of the decomposition, for both 

 fermentation and putrefaction are processes of decomposition of 

 a similar kind, the one of substances destitute of nitrogen, the 

 other of substances containing that element. 



It has also been customary to distinguish from fermentation 

 and putrefaction a particular class of transformations, viz. those 

 whose conversions and transpositions are effected without the 

 evolution of gaseous products. But the conditions under which 

 the products of the decomposition present themselves are purely 

 accidental ; there is therefore no i eason for the distinction just 

 mentioned. 



