254 



CRYPTOGAMS 



the gas above the liquids. How do they differ? Test with 

 limewater by holding a glass rod on which hangs a drop of 

 limewater. 



What gas is given off by substances in which yeast is 

 working ? Repeat this Experiment using a small portion of 

 bread dough. 



215. YEAST 



Object. To prove that carbon dioxide is given off in 

 fermentation. 



Apparatus. Test tubes, limewater, perforated stopper, and bent 

 tube as shown in Figure 112. 



Method. Fit up an apparatus like that shown in Figure 

 112, filling one tube half full of the molasses preparation 



mentioned in the preced- 

 ing Experiment. Fill the 

 other tube with limewater 

 and let the gas from the 

 fermentating sirup pass 

 through the limewater. 

 Result? 



Conclusion. What does 

 Molasses this show as to the gas 

 & Yeast, given off when fermenta- 

 tion takes place? 



Note. Alcohol also is produced in this experiment and re- 

 mains dissolved in the solution. Its presence can be detected by 

 the odor, and it can be obtained if the substance.is distilled. It is 

 hardly advisable, however, to take the time to distill it although 

 that is an interesting and instructive experiment. 



Cider and fresh fruit juices may be substituted for molasses, 



Limewater. 



Coa 



FIG. 112. 



