SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 35 



also been used, as will be referred to later. The material from 

 which the starch is obtained is generally one of the cereal grains 

 or potatoes. Starch, however, is not acted upon by the enzyme 

 zymase, so that it cannot be used directly for the alcoholic 

 fermentation. When one of the cereal grains, or in general 

 any starch-containing seed, sprouts or begins to grow, there is a 

 gradual conversion of the starch present in the grain into sugar. 

 This change is brought about by the presence in the germinating 

 grain of two other enzymes, viz. diastase and maltase. The 

 diastase converts the starch into a sugar, maltose, and maltase 

 converts the maltose into glucose. When, therefore, these 

 enzymes have acted upon starch, it is converted into a sugar 

 upon which the alcoholic enzyme Z3nTiase can act. In practice 

 the grain, usually corn, rye or barley, is allowed to sprout in a 

 warm room (6o°-63°) , ground, and water added, making a thin 

 mush or mash. This is next treated with yeast and allowed to 

 stand at about 25°. Temperatures above ^,7,° are injurious to 

 the enzyme. After the fermentation the mash, or wort as it is 

 now called, is either placed in retorts and the alcohol distilled 

 off directly or the liquid of the wort is separated by filtration. 

 The amount of alcohol present in the liquid of the wort is usually 

 about 5 per cent, but in some fermenting liquids as in grape 

 juice it may reach as high as 14 per cent. Above this it cannot 

 go because a stronger solution of alcohol is destructive to the 

 enzyme. The distillation of the fermented liquid takes place 

 in a still built in several sections so that the alcoholic vapor 

 is continually condensed and redistilled (fractionated). By a 

 direct distillation from such an apparatus a solution of alcohol 

 is obtained of about 90 per cent. This may contain small 

 amounts of higher boiling alcohols, propyl and amyl alcohols. 

 The non-volatile substances present in the fermentation liquid, 

 the principal ones being glycerol and succinic acid, are left 

 behind in the retort. For the still greater purification of the 

 alcohol it is first mixed with water, making about a 50 per cent 

 solution. This allows the separation of some of the amyl 

 alcohols as an oily layer. After separation it is now distilled 



