390 CHEMISTEY. 



ter, there being diffused through the water also more or less 

 of some other matters. But a small percentage of the 

 whole is acetic acid. Common table vinegar contains but 

 from two to five per cent. As acetic acid is little if any 

 more volatile than water, it can not be obtained pure from 

 vinegar by distillation. The only way in which the chem- 

 ist can obtain it is to decompose some of the acetates, as 

 acetate of lead the common sugar of lead by an acid 

 which is strong enough to seize the base, and thus release 

 the acetic acid. 



552. The Acetous Fermentation. Vinegar is commonly 

 made by the exposure of some spirituous liquor, as cider or 

 wine, to the air. This occasions what is called the acetous 

 fermentation. This, like the alcoholic fermentation, can not 

 take place without the presence of a ferment. For this 

 reason, if a solution of alcohol in perfectly pure water be 

 exposed to the air, there will not be the least fermentation. 

 In the case of cider, wine, etc., there is no need of adding 

 any ferment, for there is one already present in the liquid, 

 the same which acted in its alcoholic fermentation. It is 

 the decomposition of this which produces that gelatinous 

 mass called the mother. As one of the results of this de- 

 composition we have the generation of infusoria, or vinegar 

 eels, as they are commonly called, which can often be seen 

 by the naked eye when a glass of vinegar is held up to the 

 light of the sun. When the acetous fermentation takes 

 place in liquids containing starch and sugar, it is always 

 really preceded by the alcoholic fermentation. For exam- 

 ple, when preserved fruits become acid there is first an al- 

 coholic fermentation, which passes into the acetous, pro- 

 ducing vinegar. The effervescence which occurs, causing 

 bubbles on the surface, is occasioned by the carbonic anhy- 

 dride generated by the preliminary alcoholic fermentation. 

 The more thoroughly the air is shut out from preserves the 



