ALCOHOLIC FERMENTATION 57 



5. Set two Dewar flasks side by side where they 

 will not be subject to great or unequal changes 

 of external temperature. 



6. At frequent intervals (e.g., twenty minutes) during 

 the next two hours, record the temperatures of 

 the two fluids. Continue the records over as long 

 a period as convenient, not exceeding twenty-four 

 hours. 



7. Tabulate the results, and from the figures con- 

 struct two " curves," showing the rate and amount 

 of temperature change in each flask. 



8. State your inferences from this experiment. 

 B. The gaseous exchange in alcoholic fermentation: 



Experiment 34. To ascertain what gaseous exchange 

 accompanies alcoholic fermentation. 



1. Place 250 c.c. of fermenting mixture into a tall 

 glass cylinder, and 250 c.c. of distilled water into 

 a similar adjacent cylinder, as a control. At 

 once test the air in the cylinders above the liquid 

 with lime water, to see if the latter turns milky, 

 as a result of the formation of a precipitate of 

 carbonate of lime. 1 



2. After the test for COz, test the air in both cylinders 

 with a lighted splinter or taper, to see if it contains 

 sufficient oxygen to support combustion. The 

 taper should be rapidly lowered into and removed 

 from the cylinder. Why? 



1 If the members of the class are not familiar with the effect of CO 2 on 

 lime water, this should be demonstrated by the instructor, using both 

 chemically prepared CC>2 and the breath from the lungs, before proceeding 

 with the experiments in fermentation and respiration. 



The air in the cylinder may conveniently be tested by first dipping a 

 small wire loop (e.g., 10 mm. in diameter) into lime water. A film of the 

 lime water will form across the loop, and may thus be transferred into the 

 cylinder. 



