STUDY OF NUTRIENTS 27 



water and egg mixture slowly. What form does the white 

 of egg take now? Is this form soluble in water? 



Put a second portion of the egg in a test tube. Add 

 dilute nitric acid to it. What happens to the white of egg? 

 Compare the action with that in boiling water. * 



(This action of acid and heat on a proteid like egg albu- 

 min is called coagulation.) Why does a piece of meat 

 (which is composed mainly of a proteid like white of egg) 

 become more solid under heat? 



5. Xanthoproteic Test. Place a little coagulated white of 

 egg in a test tube and cover with dilute nitric acid. Heat 

 to boiling and then add enough ammonia to neutralize the 

 acid and give an alkaline test. The white of egg (proteid) 

 takes what color? Treat in the same way some olive oil, 

 some common salt, and any other substance that does not 

 contain proteid. Do any of these take the same color as 

 the white of egg? 



C. Milton's Test. Add enough Millon's reagent to a little 

 coagulated white of egg to cover, and boil. What color does 

 the egg and the solution become? Treat the other sub- 

 stances mentioned in B in the same way. Do they act like 

 the egg? 



D. Biuret Test, or Piotrowski's Reaction. Add caustic soda 

 in concentrated solution to some white of egg, in a test tube. 

 To this add a few drops of a solution of copper sulphate. 

 What color do you get? Boil. What change takes place 

 in the color? Test other substances mentioned in B in the 

 same way. 



(Of the three chemical tests for proteid given above, the 

 xanthoproteic is best for general use. There are many 

 forms of proteid, but these tests will indicate its presence 

 whatever its form may be.) 



