EXERCISE 30 



DIGESTION OF STARCH 



Materials. Starch paste ; malt extract ; Fehling's solution ; iodine 

 solution ; funnel ; filter paper ; test tubes. 



To prepare the starch paste, place in a test tube a lump of starch 

 half as large as a grain of corn, add a small amount of water, and 

 boil until all lumps have disappeared and a transparent, slightly 

 milky fluid is obtained. Dilute the starch paste thus obtained with 

 three or four ounces of cold water. 



Crush a spoonful of germinated barley grains and soak in one or 

 two ounces of water for an hour or longer. Filter off the water and 

 set it aside as stock malt extract. 



Directions for work. To determine whether starch can be 

 changed into sugar experimentally, proceed as follows: Select 

 four large test tubes and label them numbers 1, 2, 3, and 4. 

 Place in each about one inch of the dilute starch paste. To num- 

 bers 3 and 4 add about two cubic centimeters each of the malt 

 extract. Set all four aside for at least ten minutes preferably 

 an hour. At the end of this time treat each tube as directed 

 below and record observations. Remember (Exercise 29) that 

 Fehling's solution gives the test for sugar only after boiling. 



What substance do you know by experimental evidence to 

 be present in the original starch paste ? What is the evidence ? 



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