EXERCISE 30 (Continued) 



What substance is shown to be absent from the original stock 

 of starch paste ? What is the evidence ? 



Was the substance which you found in the dilute starch 

 paste present also after the malt extract had been added ? Was 

 any substance present after malt extract was added that was 

 not originally present in the starch paste ? If so, how do you 

 account for its presence ? 



Write a full account of the experiment, giving your explana- 

 tions of the changes observed and the reasons for your opinions. 



NOTE. Some sugar is always present in the malt extract and is carried 

 into tubes 3 and 4 with the malt. The relative amount may be determined 

 with sufficient accuracy if to an inch of water in a fifth tube is added malt 

 extract and Fehling's solution in quantity equal to that placed in tube 4. 

 Upon boiling, a red precipitate is formed, its quantity indicating the 

 amount of sugar present in the malt extract. 



Reference 



BERGEN and CALDWELL. Introduction to Botany, p. 46. 



[35] 



