122 GENERAL SCIENCE 



iodine solution. For example, take a piece of bread and 

 put on it some weak iodine solution. The color of the 

 bread will become blue or bluish purple. Beans and 

 cereals of all kinds can be tested in this way for carbo- 

 hydrates. (To learn just the effect of iodine solution 

 on starch in foods, put a little corn starch into a test 

 tube and add some water, then put into the test tube a 

 few drops of iodine solution and observe the color. 

 This will serve as a sample color in testing foods for 

 starch.) 



To test foods for protein, observe the following: Take 

 a piece of bread, put on it some strong nitric acid; if 

 protein is present the bread will turn yellow. Now add 

 some ammonium hydroxide and the yellow portion will 

 change to orange if it is protein. Other foods can be 

 tested for protein in the same manner. 



Foods can be tested for fats thus : Take a small quantity 

 of corn meal, place it on white paper, and put the white 

 paper with the corn meal on it into an oven which is not 

 quite hot enough to scorch the paper. The oil in the 

 meal will make a spot on the paper. Other foods can be 

 tested for fats in the same manner. 



To test foods for sugar, place a small quantity of the 

 food in a test tube with some water, and put into it 

 a few drops of Fehling's solution. Heat the mixture 

 slowly over a Bunsen burner or alcohol lamp and watch 

 the color of the contents in the test tube as the tempera- 

 ture rises. If sugar is present the color will first be a 

 greenish yellow, changing to yellow, and finally to brick- 

 red when the substance begins to boil. (To be sure of 

 the colors in the test for sugar with Fehling's solution, 

 make a. weak solution of sugar and test it with Fehling's 

 solution, observing the colors.) 



