158 FERMENTATION. 



all substances which possess the power of causing 

 fermentation, contain nitrogen ; they are compounds 

 of carbon, oxygen, hydrogen, and nitrogen, and are 

 accordingly very liable to decompose. During the 

 fermentation of any liquid, the azotized matters 

 present, which constitute the ferment, and are in an 

 active state of decomposition, gradually separate, 

 either rising to the surface or falling to the bottom. 

 This ferment, yeast, or barm, may then be removed 

 and added to any other solution, the fermentation of 

 which it is desired to excite. In most cases, there is 

 more azotized matter present than is require^ to in- 

 duce the fermentation of all the sugar, and hence 

 there is generally a quantity of ferment left over, 

 when the operation is finished. 



367. Most varieties of sugar are capable of under- 

 going fermentation, but it appears that, in all cases, 

 they previously pass into a state of grape sugar. 

 When a solution containing sugar and ferment is 

 kept for some time at a moderate temperature, the 

 sweet taste of the sugar gradually disappears, much 

 gas is given off, the mixture froths up from the escape 

 of carbonic acid, and, when the fermentation is com- 

 plete, spirit is found in place of sugar. When such 

 a fermented liquor is distilled, the spirit passes over 

 before the water, being more volatile; at least, the 

 first portions of the liquid which pass over contain 

 the greater part of the spirit. 



368. Common spirit of wine is a mixture of alcohol 

 and water ; by repeated distillation with substances 



