NUTRIENTS IN THE BEAN 



119 



vhite 

 of egg 

 in 

 solution. 



<J 



nitric 

 +acicl 

 and 

 heat 







oil will be shown by a translucent spot on the paper. Since the propor- 

 tion of oil in beans is small, it is better to try this test with a walnut. 



Demonstration 3. Test for protein. Another nutrient present 

 in the bean cotyledon 

 is protein. Several 

 tests are used to de- 

 tect the presence of 

 this nutrient. The 

 following is one of the 

 best known : 



Place in a test tube 

 a bit of hard-boiled 

 white of egg. Pour 

 over it an 80 per cent 

 nitric acid, and heat 

 the tube gently. Note 

 the color that ap- 

 pears — a lemon yel- 

 low. If a little am- 

 monium hydroxide is 

 added, the color turns 

 a deep orange. 



Cool, 



4-acCdin 



excess, 



ammonia^ 



.starch grain 



A-ceIl*wtdl 



Practical Exercise 2. Test a number of substances for the presence of 

 starch, fat, and protein. Give your findings in tabular form. What is the 

 value of knowing these tests ? 



Nutrients in the bean. If we mash up a small piece of a bean 

 cotyledon which has been previously soaked in water, and test it 

 with iodine solution, the characteristic blue-black color appears, 

 showing the presence of starch. If a little of the stained material 



is mounted in water on a glass slide 

 under the compound microscope, we 

 shall find that the starch is in the 

 form of little ovoid bodies called 

 starch grains. The starch grains and 

 other food products are made use of 

 by the embryo. 



A test of the cotyledon of a bean 

 with nitric acid and ammonium 

 hydrate shows us the presence of 

 protein. Beans are found by many 

 tests to contain about 23 per cent of protein, 59 per cent of 

 carbohydrates, and 2 per cent of oils. The young plant within 



protoplasm. 



Cells from a potato, under microscope. 

 Which part of the cell turns blue with 

 iodine? 



