PROTEINS 237 



should give a negative protein test as saturating with ammonium 

 sulphate even in neutral solution precipitates both albumins and 

 globulins. To a portion of the filtrate add 1-2 drops of acetic 

 acid. No precipitate should form, since the albumin already has 

 been precipitated. 



(c) To a small portion of blood serum add an equal volume of 

 saturated ammonium sulphate solution, thus producing a mix- 

 ture half saturated with this salt ; this will have the same effect as 

 saturating with magnesium sulphate. 



viii. Pour 2 or 3 drops of blood serum into a large beaker of 

 distilled water. The cloudiness is due to the precipitation of a 

 protein (globulin) which is soluble in the blood serum because of 

 the presence of certain salts. On dilution the protein precipi- 

 tates. The same results may be obtained if the salts are removed 

 by dialysis. 



Individual Groups Simple Proteins 



1. Albumins. The solution of egg white, and also the blood 

 serum used for the general protein tests contained both albumins 

 and globulins. These two classes of proteins may be separated 

 from one another by saturating with magnesium sulphate, or half 

 saturating with ammonium sulphate in neutral solution. Either 

 method causes globulin to precipitate. Saturating with mag- 

 nesium sulphate will precipitate both groups if the solution is 

 acid. Saturating with ammonium sulphate throws down both 

 groups in neutral solution. Some of the plant albumins and 

 globulins are exceptions to the above statements. 



i. Preparation of Albumin Crystals. Beat up 5 c.c. of white 

 of egg to break the reticulum. Dilute with ten volumes of water 

 and strain through gauze. Add an equal volume of saturated 

 ammonium sulphate. Label with your name and leave in the 

 ice box until the next laboratory period. Filter off the precipi- 

 tated globulin and to the filtrate add saturated ammonium sul- 

 phate until the liquid becomes turbid. Now add distilled water 

 in very small portions until the turbidity has just disappeared. 

 Add drop by drop 10% acetic acid saturated with ammonium 



