272 



APPLIED BIOLOGY 



(2) Now, wash out the tubes with clean water. Again put lime- 

 water in the bottom of the larger tube. Into the smaller tube 

 put some molasses-solution (about half full), and put in some yeast. 

 Lower the small tube into the larger one, and insert the stopper. 

 Set in a warm place, and after the fermentation has continued for 

 an hour or more look for changes in the lime-water. (If the teacher 

 has ready a pan of water, heated as much 

 as the hand will bear with comfort, and 

 the tubes are prepared from growing yeast 

 at the beginning of a two-hour session 

 and placed in the warm water, it will be 

 possible to get results before the close of 

 the session ; but examine the tubes again 

 after they stand a day or more in a warm 

 place . ) What does this experiment prove ? 

 Compare with similar experiments pre- 

 viously performed (26). 



Experiment 4. (D) Conducting the gas 

 into lime-water. Prepare apparatus shown 

 in Fig. 84. In tube a put lime-water, in 

 tube b put some molasses-solution with 

 yeast. Set in a warm place, and when 

 active fermentation begins notice bubbles 

 of gas rising through the lime-water and its effect. Compare with 

 Experiment 3. 



Experiment 5. (D) Collecting gas from fermentation. (1) Arrange 

 apparatus shown in Fig. 85. In the flask y put molasses-solution 

 with yeast; fill the 

 bottle with water be- 

 fore inverting and 

 suspending in posi- 

 tion shown in the 

 figure. Set in warm 

 place. When gas is 

 evolved from the 

 flask it will be col- 



FIG. 85. Apparatus for collecting gas evolved by 

 yeast, y, flask or bottle with yeast in molasses- 



FIG. 84. Two glass bottles 

 connected by a bent glass 

 tube (0, inserted through 

 the cork (c). Tube a con- 

 tains yeast in molasses-so- 

 lution (y) , and tube b con- 

 tains lime-water (w). 



solution; w, water partly displaced by gas (c). 



lected in the bottle, 



the bubbles rising 



and displacing the 



water. When the bottle is full of the gas, that is, when all the water 



has been displaced, carefully insert a stopper before raising the mouth 



of bottle above the surface of the water. (2) Holding the bottle in 



