EXERCISE 34 



Protein, a class of substances present in all protoplasm, and in lean meat and fish, can be found by a 

 more difficult test. The teacher should perform this as a demonstration. 



Problem. How does protein act when treated with the materials used in the xanthoproteic ("yellow- 

 protein ") test? 



What to use. Protein, such as white of egg or cottage cheese ; test tube ; a source of heat ; water ; 

 concentrated nitric acid ; ammonia. 



What to do. Place a small amount of protein in the tube, add a drop of concentrated nitric acid, 

 rinse with water ; boil ; let cool ; add several drops of strong ammonia. 



Results. Note color after addition of nitric acid ; then again after addition of ammonia. The 

 appearance of these two colors indicates presence of protein. 



NOTE i. No other known substances produce these same color changes after treatment with nitric acid and ammonia. 



Record. Describe results and give your conclusions. 



Problems to work out. (i) Is there protein in the cotyledons of the bean ? (2) in the endosperm of 

 the corn ? (3) in the cotyledon of the corn ? Try white feathers, wool, skin of finger. 



NOTE 2. Another test for protein that is often convenient is to burn or singe a bit of the material and then to smell 

 for the characteristic odor of burnt hair. 



Question. How do you account for this same odor in a blacksmith's shop ? 



[39] 



