THE FARM, AND OUR FOOD SUPPLIES 153 



It is to be kept in mind that the protein of plant growth (such as 

 gluten), and of the animal foodstuffs (such as albumen of eggs, casein 

 of milk, the fibrin of meat), are principally tissue-building material, 

 while starch and the sugars are chiefly body fuels. 



5. When to some baking soda in a test tube hydrochloric 

 acid was added a little at a time (paragraph 4 under Car- 

 bonates), what gas formed? 



Mix thoroughly a very little baking powder with a tea- 

 spoonful of flour. Make a thick dough out of it with cold 

 water ; knead it well with the fingers, and then bake it in a 

 spoon. Explain the "rising" of the loaf. Why does the 

 loaf retain its shape? 



6. Dissolve some baking powder in a little water and heat 

 to boiling. Observe the character of the liquid when rubbed 

 between the fingers, and infer its meaning. Wet a strip of 

 filter paper in the liquid, and test with the iodine solution. 



(b) The Sugars 



1. Describe all changes as the teacher cautiously pours 

 concentrated sulphuric acid into some thick hot sirup of 

 cane sugar in an evaporating dish. The sulphuric acid 

 takes hydrogen and oxygen from the sugar (as H 2 0), leav- 

 ing the carbon (C). 



2. Note the results carefully when a few drops of Fehling's 

 solution are added to a solution of grape sugar (glucose, or 

 corn sirup) in a test tube, and the liquid is heated to boiling. 



State the results when the same test is made (a) with a 

 solution of cane sugar ; (b) with a starch solution. 



3. Crush and dissolve some samples of candies, and test 

 for (a) grape sugar; (b) starch. State your results, and 

 their significance. 



