THE NATURE AND NEEDS OF LIVING MATTER 25 



Method b. Add 5 cc. of Benedict's second solution to 

 about 8 drops of the solution under examination ; such as 

 the glucose solution. Boil the mixture for one or two minutes 

 and let it cool slowly. 



Observation. What changes in color do you notice ? Note. 

 If grape sugar is present the liquid will be filled with a precipi- 

 tate, which may be red, yellow, or green in color, depending upon 

 the amount of sugar present. The positive test is the precipitate, 

 not the color. 



c. Fats and Oils 



Materials. Nuts or animal fat, white paper, watch glass or 

 other shallow vessel, and ether, chloroform, or benzene. 



Method a. Rub the nut or material to be tested on a piece 

 of paper, and hold to the light. 



Observation. What effect do you notice when the nut is 

 rubbed on paper ? Note. If oil is present, a translucent 

 grease spot will appear. 



Method b. Put the substance to be tested on a piece of 

 plain white paper and put it in a warm place, as on a radia- 

 tor or in an oven. 



What happens when nuts are so tested ? 



Method c. Grind or crush the substance to be tested, as 

 flaxseed; place it in a watch glass, add ether or benzene, and 

 allow it to stand until it evaporates. 



Observation. Do you note anything sticking to the sides of 

 the vessel ? Note. Ether, etc., dissolves and extracts oils 

 from substances, and on evaporation leaves the oil on the 

 container. 



d. Proteids or Nitrogenous J Foods 



Materials. Raw and hard-boiled white of egg, feather or 

 leather, nitric acid, ammonia, test tubes, spirit lamp. 



Method a. Place the substance to be tested in a test tube, 

 and add a little strong nitric acid. Note any color that ap- 



1 Nitrogenous foods contain nitrogen, other foods do not. Good examples 

 are peas, beans, white of egg, cheese, and lean meat. 



