22 FOOD MATERIALS AND HOW TO DETECT THEM 



Heat the test tube gently over the flame. What change 

 takes place in the color and general appearance of the starch ? 



Now add a drop of iodine solution to the starch paste. 

 What happens? Heat. What happens? Cool again. Does 

 the color return ? 



Test potatoes, flour, and other things mentioned, also 

 milk, meat, eggs, etc. Which ones contain starch and which 

 do not? 



Conclusion. State in one sentence how starch may be 

 recognized. 



9. STARCH (optional) 



Object. To find out something of the appearance of 

 starch grains- 



Apparatus. Various kinds of starch which can be obtained 

 from corn, wheat, rice, cannas, potatoes, etc., a compound micro- 

 scope, and a razor for cutting thin sections. 



Method. Mount a drop of water containing starch of 

 any sort and examine with a low power. Note the shape 

 and structure of a grain. Draw starch grains. 



In a similar manner mount and examine other kinds of 

 starch. Wherein do these starches differ ? In what respects 

 do they agree ? Cut thin sections of potato tubers and mount 

 them in water. Note the starch grains packed in the cells. 



Place a drop of iodine solution on the slide at the edge 

 of the cover glass. Watch the solution as it works under 

 and note the effect as it comes in contact with the starch 

 grains. 



Note. Canna rootstocks contain very large starch grains. 



Suggestions. Scrape as finely as possible one or two 

 large potatoes. Put the potato pulp in a large bottle with 



