34 ORGANIC AGRICULTURAL CHEMISTRY 



The alcoholic fermentation of sugar, then, is due to the action 

 of the enzyme zymase which is secreted by the yeast cell. In 

 grapes both the sugar and enzyme are present and the juice 

 therefore ferments naturally with the formation of alcohol, 

 the resulting alcoholic liquid being known as wine. As wine 

 has considerable commercial value in itself it is not the source 

 from which pure or high percentage alcohol is obtained. 



EXPERIMENT STUDY VIII 

 Alcoholic Fermentation 



Place 150 c.c. of glucose sirup (Karo Corn Sirup) in a 1000 c.c. 

 flask with 500 c.c. of water. Add 20 c.c. of nutritive solution^ (a 

 solution of salts for the nutrition of the yeast plant). Mix about 

 I cake of yeast with a little water to make a thin mixture. Add this 

 yeast to the sugar solution and place stopper in flask with bent glass 

 and rubber connection. Connect the rubber tube with a straight 

 glass tube and introduce this glass tube into a graduated cylinder 

 containing 50 c.c. of limewater, Ca(0H)2. Pour about i c.c. of kero- 

 sene upon the surface of the limewater to exclude air. Set the whole 

 apparatus on the shelf and let it remain at 25° C. until the next exer- 

 cise, examining in the interval if possible. What is the precipitate 

 formed in the cylinder? What gas does this prove to be given off? 

 After the fermentation is over pour off 150 c.c. of the clear liquid 

 into a 300 c.c. distilling flask and distill over 100 c.c. Test the 

 distillate for alcohol as in VII, 4. What are the two products of 

 the yeast fermentation of sugar? Test the specific gravity of the 

 distillate and calculate the amount of alcohol present in it. As 

 this distillate contains all of the alcohol present in the 150 c.c. of the 

 fermentation liquid calculate the amount of alcohol present in the 

 fermentation liquid. This is the method of determining the alcohol 

 content of alcoholic liquors. 



Diastase. — The chemical substance which is the ultimate 

 source of industrial alcohol is starch. Recently cellulose has 



^ Pasteur salt solution is made as follows : 



Potassium phosphate, 2.0 parts " 



Calcium phosphate, 0.2 parts , , r. ^ . 

 TIT • 1 u X ^ ) + water, 857.6 parts 



Magnesium sulphate, 0.2 parts 



Ammonium tartrate, lo.o parts . 



