166 C. A. WATKINS ON YEAST AND OTHER FERMENTS. 



The ferments themselves suffer differently, being always reduced 

 to the simplest combinations. 



Looking at the result of a fermentation, it would appear that the 

 ferment and the matter fermented did not enter into combination, 

 but that its transformation is due to the force generated in the 

 decomposition of the ferment with which it is in contact. It is, 

 however, clear that the changes which take place in the two sub- 

 stances are collateral, for the same ferment will produce various 

 chemical transformations of a substance according to the phase of 

 its own decomposition. " Thus diastase, when fresh, converts 

 starch into sugar ; if kept for a few days, it converts it into gum 

 instead of sugar ; while at another period it converts the starch 

 first into sugar, and then transforms it into lactic acid." 



Therefore the transformations always depend on, and are relative 

 to, the peculiar changes which take place in the ferment. 



The commercial production of vinegar appears to be due to the 

 agency of one or more microscopic organisms, the mass being called 

 the vinegar plant, which, as I have said, is not regarded as a true 

 ferment by chemists, and for this reason ; all the ferments proper, 

 such as I have described, produce the transformations entirely 

 within the solutions, receiving nothing from, nor imparting any- 

 thing thereto ; but the conversion of alcohol into vinegar is a case 

 of simple oxydation, in which the oxygen is derived from the 

 atmosphere, each equivalent of alcohol absorbing four equivalents of 

 oxygen to become acetic acid, according to the following formula : 



Alchol. Aldehyd. Water. 



CHO + 20 = CHO + 2HO 



4 6 2 4 4 2 



Aldehyd. Acetic Acid. 



CHO + 20 = CHO+ HO 



4 4 2 4 3 3 



In countries where no duty is imposed on the manufacture of 

 alcohol, it can be made into vinegar cheaply and rapidly. The 

 alcohol diluted with water, and a small quantity of some azotised 

 substance added, is allowed to trickle over beech shavings placed in 

 a vat, so arranged, that a current of air circulates freely through- 

 out. 



For some days the process goes on very slowly ; but the shavings 

 become gradually covered with a slimy fungus, called mother of 

 vinegar, and then acetification proceeds much more rapidly. 



Pure dilute alcohol, exposed to the air, undergoes no chemical 

 change ; and its conversion into vinegar is undoubtedly due to some 



