230 CHEMICAL TRANSFORMATIONS 



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 

 uniformly evolved, and occasionally even light. In 

 the processes of decomposition, termed fermenta- 

 tion and putrefaction, gaseous products are very 

 frequently formed, which are either inodorous, or 

 possess a very offensive smell. 



The transformations of those matters which 

 evolve gaseous products without odour, are now, 

 by pretty general consent, designated by the term 

 fermentation ; whilst to the spontaneous decompo- 

 sition 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 which contain it. 



It has also been customary to distinguish from 

 fermentation and putrefaction a particular class of 

 transformations, viz., those in which conversions and 

 transpositions are effected without the evolution of 

 gaseous products. But the conditions under which 

 the products of the decomposition present them- 

 selves are purely accidental ; there is therefore no 

 reason for the distinction just mentioned. 



