FOODS 



EXPERIMENT 20. THE PRESENCE OF STARCH IN SOME 

 COMMON FOODS 



(a) Put a pinch of powdered starch into a test tube and 

 fill the test tube half full of water, shaking it thoroughly. 

 Then add one or two drops of iodine and note whether 

 the color of the starch-and-water mixture changes. If 

 the application of dilute iodine to a substance produces 

 a beautiful blue color, starch is present. 



(b) Put a pinch of powdered starch in a tube and add 

 water as before; then boil the mixture (Fig. 24), noting 

 any change which occurs. If the 



starchy paste is too thick, thin it 

 with hot water and shake vigorously. 

 After the starch has cooled, add 

 iodine as before and compare the 

 result with (a). 



(c) Scrape some raw potatoes into 

 a test tube and add sufficient water to 

 thin the pulp considerably. .T est 

 this with iodine, and state whether 

 starch is present in the potato. 



In a similar manner test rice, oat- 



. . FIG. 24. Boiling starch. 



meal, cracker. 



(d) Scrape some potato as in (c), but boil the pulp before 

 testing it with iodine. Is there any noticeable difference 

 between the action of iodine on raw and cooked starch ? 



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