NECESSARY FOODS 235 



the alimentary canal wherever the food has been suffi- 

 ciently prepared. 



110. Necessary Foods. Experiment 118. Place in different 

 test tubes small amounts of (1) corn starch, (2) grape sugar, 



(3) scrapings from a raw potato, (4) flour, and (5) the white of an 

 egg. Pour in a little water and shake thoroughly. Drop into each 

 tube a few drops of the iodine solution prepared in Experiment 100. 



Experiment 119. Place in test tubes small quantities of (1) the 

 white of a hard-boiled egg, (2) tallow or lard, (3) grape sugar, and 



(4) any other food which may be handy. Pour a little concentrated 

 nitric acid into each tube and allow to stand for a minute. Be care- 

 ful not to get the nitric acid on the clothes or hands. Pour the acid 

 out into a slop jar and wash the substances with a little water. Pour 

 off the wash water and pour on a little strong ammonia. If the sub- 

 stances turn a yellow or orange color, proteins are present. Which 

 substances contain proteins ? 



Experiment 120. Gasoline vapor is very inflammable, so be sure 

 in this experiment that there is no flame in the room. Place about a 

 spoonful of (1) both the white and the yellow of an egg, (2) flaxseed 

 meal, (3) yellow corn meal, (4) white flour, and (5) other foods it is 

 desired to test in separate evaporating dishes or beakers near an open 

 window. Pour on to these enough gasoline to more than cover them 

 and stir thoroughly. Cover the evaporating dishes and -allow to stand 

 for ten or fifteen minutes. Pour the gasoline off into a beaker and 

 set the beaker outside the window until the gasoline has evaporated. 

 If there is anything .left it must have been dissolved from the food. 

 If a substance remains, place a drop of it on a piece of paper. Smell 

 of it. Try to mix it with water. Rub it between the fingers. Try 

 any other fat or oil test of which you can think. 



Experiment 121. In a place where there is a good draft so that 

 odors will not penetrate the room, burn in an iron spoon over a Bun- 

 sen burner (1) small pieces of meat, (2) a little condensed milk or 

 milk powder, (3) part of an egg, and (4) any other food. Is there a 

 residue left after burning ? If so, this is mineral matter. 



In Experiments 118-121 we found that our ordinary 

 foods are of three great groups of chemical compounds, 

 carbohydrates (starches and sugars), proteins, and fats or 



