EXERCISE 41 

 WHAT IS THE NATURE OF THE YEAST PLANT? 



Materials. Cake of compressed yeast ; molasses or sugar ; bottles ; rubber and glass tubing ; 

 limewater. 



Directions. Dissolve some sugar or molasses in water. Do not make the solution stronger than 

 10 per cent. Add a little yeast which has been thoroughly mixed with water. 



From day to day note the bubbles which rise and the increasing amount of sediment and scum. 



Place some of the solution and sediment in a bottle and close the bottle with a one-holed rubber 

 stopper through which a glass tube has been passed. Attach a rubber tube and collect some of the 

 gas which escapes, as you did in Exercise 29. It may take a day or more to fill a bottle. Test the 

 collected gas with a flame, with limewater, and by any other means that you think of, to find out 

 whether it is one of the gases with which you are familiar. 



When you have discovered what gas it is that is coming from the sugar solution, try to explain 

 how it may have been produced. 



Additional problems. If a compound microscope is available, examine the sediment to see what the yeast 

 plant is. How are new yeast plants formed ? 

 How does yeast cause bread to " rise " ? 



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