160 NATURE STUDY BY GRADES 



LESSON XXXIII 

 WHEAT CONSTITUENTS 



Experiment i. Add a few drops of tincture of iodine to 

 some starch stirred in water. Note the purple color. This 

 is a test for starch. Pulverize wheat and other seeds, scrape 

 a potato or turnip, etc., mix with water, and test these sub- 

 stances for starch. 



Test a small piece of bread in the same way. 



Explain that starch forms a large and necessary part of 

 our foods, and is very abundant in wheat and flour and bread, 

 as well as in many of our vegetables and in some of our 

 fruits. 



Experiment 2. Wash in water for a long time a piece of 

 dough made from wheat flour. Chewing for a long time 

 a mouthful of wheat will produce the same result. When 

 all the starch is washed out, a gummy substance is left. This 

 is mostly gluten, and is useful food. This is also what makes 

 the dough tough or tenacious and holds the gas made by the 

 yeast, making the bread light. 



Experiment j. Explain how the gas bubbles in the yeast 

 are caught and retained throughout the loaf by the gluten in 

 the dough. Make some soap bubbles. Compare the action 

 of the gluten with the office of soap in making soap 

 bubbles. 



Baking powder acts in a similar way. Bicarbonate of 

 soda mixed with an acid like cream of tartar, when moistened, 

 will emit the same gas. 



' This gas, however, is mostly driven off in baking, but not 

 until it has made the dough light, and the heat has made the 

 loaf rigid. 



