98 LABORATORY EXERCISES. 



hole pass a glass tube, allowing it to pro- 

 ject just inside the flask. Connect this 

 glass tube with rubber tubing to a con- 

 denser (used in distillation). Place the 

 flask over a water-bath, and keep the 

 temperature at the point where the ther- 

 mometer registers 78 C. Collect the liq- 

 uid which comes from the condenser. 



a. What is the smell and taste of the liq- 



uid? 



b. Apply a lighted match to a little of it. 



Will it burn?* 



c. What kind of substance is formed 



when yeast "works," or when fer- 

 mentation takes place? 



B. Into a half-pint of water put a spoonful of the 



thin yeast mixture (of yeast and water) ; set 

 aside in a warm place beside the other mix- 

 ture. Examine at the end of 12 hours. 



1. Do you see any evidence of activity in the 



mixture? 



2. What kind of substance was present in the 



preceding experiments which is absent in 

 this experiment? 



3. What do you infer from this experiment? 



C. Summary. 



1 . What conditions are necessary for the rapid 



growth of yeast ? 



2. What changes are caused by the yeast in a 



mixture in which it is growing? 



*The experiment will be more successful if the liquid is distilled 

 a second time. 



