USE OF BACTERIA IN THE ARTS. 5 1 



rial action. Some of them we should unhesitat- 

 ingly look upon as fermentations, while others 

 would hardly be thought of as belonging to the 

 fermentation industries. 



VINEGAR. 



The commercial importance of the manufac- 

 ture of vinegar, though large, does not, of course, 

 compare in extent with that of the alcoholic fer- 

 mentations. Vinegar is a weak solution of acetic 

 acid, together with various other ingredients 

 which have come from the materials furnishing 

 the acid. In the manufacture of vinegar, alcohol 

 is always used as the source of the acetic acid. 

 The production of acetic acid from alcohol is a 

 simple oxidation. The equation C 2 H 6 O-j-O 2 = 

 C 2 H 4 O 2 -fH 2 O shows the chemical change that 

 occurs. This oxidation can be brought about by 

 purely chemical means. While alcohol will not 

 readily unite with oxygen under common condi- 

 tions, if the alcohol is allowed to pass over a bit 

 of platinum sponge the union readily occurs and 

 acetic acid results. This method of acetic-acid 

 production is possible experimentally, but is im- 

 practicable on any large scale. In the ordinary 

 manufacture of vinegar the oxidation is a true 

 fermentation, and brought about by the growth of 

 bacteria. 



In the commercial manufacture of vinegar 

 several different weak alcoholic solutions are 

 used. The most common of these are fermented 

 malt, weak wine, cider, and sometimes a weak so- 

 lution of spirit to which is added sugar and malt. 

 If these solutions are allowed to stand for a time 

 in contact with air, they slowly turn sour by the 



