380 CHEMISTRY. 



CHAPTER XXX. 



FERMENTATION. 



535. Different Kinds of Fermentation. The word fermen- 

 tation is applied to various decompositions and changes 

 which occur in organic substances. We have the alcohol- 

 ic fermentation, producing alcohol; the acetous, producing 

 vinegar, etc. It is of these two kinds that we shall speak 

 in this chapter. By the alcoholic fermentation sugar is 

 converted into alcohol, and by the acetous alcohol is con- 

 verted into acetic acid, the sour principle of vinegar ; or, 

 strictly speaking, alcohol is made from sugar, and acetic 

 acid from alcohol. 



Putrefaction and fermentation are really the same thing, 

 only the former name is given to the decomposition when 

 accompanied by an offensive odor. Some fermentations 

 give rise to evolution of gases, derived from the constitu- 

 ents of the decomposing substance ; when these gases have 

 a disagreeable odor, as sulphuretted hydrogen, certain hy- 

 drocarbons, and ammonia, for example, produced in the 

 decomposition of animal matter, the term putrefaction is 

 used. Nitrogenous bodies are the most disposed to this 

 kind of decomposition. Substances which arrest fermen- 

 tation already begun, or deprive bodies of the power of 

 fermenting, are called antiseptics. Such are ferric chlo- 

 ride, arsenious anhydride, carbolic acid, etc. 



536. Ferments. There must always be a fermenting 

 agent to produce the change. Neither sugar nor alcohol 

 has any tendency to ferment of itself, but they very readily 



