102 THE INVISIBLE WORLD 



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The process of this conversion is simple and 

 quickly told. The essential quality of vinegar is 

 acetic acid. It is this acid which gives vinegar its 

 sharp taste. But the essential quality of cider is 

 its alcohol. Now the making the cider into vine- 

 gar is simply turning the alcohol into the acid. 

 This is done by the microbe. 



As the microbe lives only in the air, it can do 

 its work only on the surface of the cider. A com- 

 paratively large surface of the cider must there- 

 fore be exposed to the air. The more surface, the 

 more microbes employed, and the quicker the work 

 is done. 



By reason of this fact the vinegar of commerce 

 is usually made by the quick process. The liquor 

 is spread out over a large surface. Great room 

 brings great numbers of workers. The work is 

 done quick. But the liquor employed is rarely or 

 never made like cider, from apple juice, but from 

 other materials; and the vinegar is not so good. 

 Home made vinegar from cider is the best. In the 

 first place, the cider is home made, and is genuine. 

 Then the work is done slowly and well. The re- 

 sult is excellent. 



The barrel lacks a couple of gallons of being full. 

 The bung is open. This admits air to a sufficient- 

 surface. The microbes come in from the air and 

 begin their work. Little patches of a thin film 

 collect at different points on the surface. These 

 patches grow larger and larger until the thin film 



