22 VINEGAR, CIDER, AND FRUIT-WINES. 



other bodies are formed from the alcohol can be readily detected 

 in a vinegar manufactory by the sense of smell. 



By treating alcohol with pyrolusite and sulphuric acid hence 

 by the action of oxygen at the moment of its liberation from a 

 combination (in its nascent state) Dobereiner obtained a body 

 which he called "light oxygenated ether" (leichter Sauer- 

 stoffather). Liebig, later on, studied the nature of this com- 

 bination more accurately, and found that, as regards its composi- 

 tion, it differed from that of alcohol only by containing two 

 atoms less of hydrogen. He applied to it the term " aldehyde." 



Aldehyde is composed of C 2 H 4 O, and its formation is repre- 

 sented by the formula 



C 2 H G + <> = C 2 H 4 + H 2 



Alcohol. Oxygen. Aldehyde. Water. 



In the examination of the properties of aldehyde it was shown 

 that it is readily converted into acetic acid by the absorption of 

 oxygen, and, based upon these facts, Liebig established a theory 

 of the formation of vinegar which was for many years considered 

 correct. 



Essentially Liebig's theory is as follows : 

 By the exposure, under suitable conditions, of alcohol to the 

 action of the atmospheric oxygen, one-third of the entire quantity 

 of hydrogen contained in it is withdrawn, and aldehyde is formed. 

 The latter, however, immediately further combines with oxygen, 

 and is converted into acetic acid; the formation of vinegar from 

 alcohol being, therefore, a partial process of combustion. 



From the present stand-point of our knowledge as regards the 

 formation of acetic acid from alcohol, the correctness of this 

 theory is about parallel with that according to which alcohol and 

 carbonic acid are formed by the alcoholic fermentation of sugar. 

 This latter process can also be illustrated by an equation in as 

 simple a manner as the conversion of alcohol into acetic acid by 

 aldehyde. At the present time the processes taking place in the 

 formation of acetic acid from alcohol must, however, be considered 

 as far more complicated than supposed by Liebig. According to 

 the latter, a simple oxidation, i. e., a simple chemical process, 

 takes place; but, according to the now universally accepted view, 

 the formation of vinegar is due to a cheniico-physiological pro- 



