CHAPTER V 

 PROTEINS 



All poteins contain carbon, hydrogen, oxygen and nitrogen; 

 some contain also sulphur, phosphorus, iron or other elements. 

 These elements may be detected by the methods described in the 

 chapter on the elements. 



General Protein Reactions 



The general tests for the detection or isolation of the proteins 

 are divided into two groups, color reactions and precipitation 

 reactions. 



1. Color Reactions. 



i. Biuret Test. Prepare two test tubes each containing a few 

 cubic centimeters of water. To one test tube add a few drops of 

 egg albumin solution. To each tube add 1-2 c.c. saturated 

 sodium hydrate and a few drops of copper sulphate solution 

 which has been diluted until it has only a faint blue color. Such 

 a copper sulphate solution can be prepared by adding a few 

 drops of copper sulphate solution to a half test tube of distilled 

 water. Notice the lavender or violet color in the albumin tube, 

 and compare it with the color of the control. This reaction is 

 very delicate. It also may be performed by adding the alkali 

 to the protein solution, inclining the test tube slightly and allow- 

 ing the copper sulphate solution to flow down the side of the 

 tube so as to form a layer on the surface of the liquid. A lav- 

 ender ring forms at the juncture of the two liquids. The biuret 

 test is given by any substance, protein or otherwise, which con- 

 tains two CONH 2 groups joined either directly or by a single 

 carbon or nitrogen atom, and also by some other similar group- 

 ings. The test is named from the fact that it is given by biuret, 



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