MANUAL OF NATURB SfUDY. 69 



a warm place, temperature of a summer day, twen- 

 ty-four hours, and watch it "work," fermentation. 



The effervescence which you see is caused by 

 the escape of carbon dioxide gas formed therein. 

 The alcohol is formed at same time, but does not 

 escape so readily as the gas unless warmed to a 

 much higher temperature, as in baking light bread. 



In secondary fermentation the alcohol escapes, 

 thus leaving acetous acid or vinegar. In the first, 

 or primary fermentation, the sugar in the juice is 

 changed to alcohol ; in the second fermentation the 

 alcohol is changed to vinegar. 



Alcohol does not exist in the fruit, or sugar, 

 neither does vinegar exist in the alcohol. A fossil 

 made of limestone preserves the form of 

 a once living animal or plant, but the limestone 

 did not exist in the living tissues of the animal or 

 plant ; no more does alcohol exist in living corn, 

 or grape, or apple. 



Fresh oysters are wholesome food, but fossil 

 oysters would lie rather heavy on the stomach. 



Fresh com is an excellent food, but, when 

 changed by fermentation into whiskey, it is poison- 

 ous to the system. 



To make this illustration vivid, the teacher 

 should show some fossil plants or animals, oysters, 

 if possible, so that children may see that nature 

 makes a complete change in quality and properties. 



