16 PLANT BIOLOGY 



thus formed a few drops of iodine. What color is 

 produced ? 



2. Try the effect of iodine on each of the other food sub- 



stances as follows : Put a small amount of grape sugar 

 into a test tube; into a second tube put some white 

 of egg (protein) ; into a third some fat or oil ; into a 

 fourth some mineral matter (salt) ; and into a fifth some 

 water. Add a little water to each and boil as in 1 

 above to cook each nutrient. Add a drop or two of 

 iodine solution to each test tube. 



Do any of the colors thus produced resemble at all the 

 color resulting from the addition of iodine to starch ? 



3. From the preceding, state how you can determine whether 



or not a substance contains starch. 



4. (Optional home work.) Test as many foods as you can (e.g. 



oatmeal, flour, raw meat, milk, parsnip, potato, onions, ap- 

 ples, beans, rice, pepper) in the following way : Put a small 

 amount of a given food into a test tube or in a sauce pan, add 

 a little water, and boil to cook each food, then add a few 

 drops of iodine. Before making each test make sure that the 

 test tube or saucer is clean. Prepare in your note-book a 

 table like the following, and fill in under each head the names 

 of the foods you have proved to contain or to be without 

 starch. 



24. To test foods for grape sugar. Laboratory Study 

 No. 9. 



Materials : Grape sugar, corn starch, white of egg, fat or oil, salt, 

 water ; various food substances common in home kitchen ; Fehling's 

 solution (see below) ; test tubes, gas burner or alcohol lamp. 



