EXERCISE 79 

 WHAT FOOD MATERIALS ARE PRESENT IN PLANTS'.' 



Materials. The following are convenient for this exercise : potato, turnip, carrot, radish, apple, 

 orange, rice, beans, oat grain, wheat grain, corn grain, or the products of these, as oatmeal, flour, 

 commercial starch, etc.; iodine solution; Fehling's solution; nitric acid; ammonia; some test tubes. 



Directions. The tests for food substances which may be made most readily are the following : 



a. Starch. Crush or scrape some of the material to be investigated, and boil it in water in a test 

 tube. When cool, add iodine and note the resulting color. If commercial starch is used, first the re- 

 actions may be seen with material that is known to be starch, and later tests for the presence of starch 

 in other materials will be made more accurately. 



b. Grape sugar. Crush or scrape, add water, boil, add 1 or 2 cubic centimeters of Fehling's solu- 

 tion, and boil again. If grape sugar is present, the solution will soon be clouded by a red precipitate, 

 which will settle to the bottom. 



c. Protein. Crush or scrape the material and boil in water to which a few drops of nitric acid 

 have been added. A yellow color indicates protein, and this is changed to an orange by the addition 

 of ammonia. Since most of the plant proteins encountered are not soluble, the color will appear upon 

 the fragments rather than in the solution. 



In the above experiments record your results in the blanks given below, checking for each material 

 the food substances which are found to be present: 



MATKIUAI, TKSTKI> 



Additional problems lor this exercise may !< added indefinitely by testing such plant materials as are 

 available. 



[112] 



