274 PHYSIOLOGICAL CHEMISTRY 



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 



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. 



17. 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 nitrate 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 

 sulphate until a precipitate is obtained. Again place in the ice 

 box until the next period. On standing, the precipitate, which 

 is at first amorphous, will become crystalline. Examine under 

 the microscope. The crystals are small, and look much like sand 

 grains. If similarly prepared, serum albumin and lactalbumin 

 crystals may be obtained. 



18. Solubility of Egg Albumin. Test the solubility of pow- 

 dered egg albumin in water and 10% HC1. Recall notes on solu- 

 bility determinations under dextrose. A filtrate may best be 

 tested for protein by one or more of the color reactions. Recall 

 that albumins are precipitated in neutral solution by saturating 

 with ammonium sulphate, but not with magnesium sulphate, or 



