82 



PHYSIOLOGICAL CHEMISTRY. 



injected into the blood circulation it passes unchanged through 

 the kidneys into the urine ; the same thing happens when large 

 quantities of white of egg are eaten. It seems to escape diges- 

 tion in this latter case and be absorbed in pure condition, to be 

 later discarded by the kidneys. These various points of beha- 

 vior indicate, then, a rather marked difference between the two 

 kinds of albumin. 



Ex. So-called pure egg albumin may be obtained in this way : The 

 white of egg is shaken in a bottle with some broken glass to thoroughly 

 break up the membranes. The foamy mass is filtered through fine, unsized 

 muslin, and to the filtrate an equal volume of saturated ammonium sul- 

 phate solution is added. This 

 produces a precipitate of globu- 

 lin which after 24 hours is fil- 

 tered off. Ammonium sulphate 

 in this strength does not pre- 

 cipitate the true albumin. To 

 this filtrate a little more satu- 

 rated ammonium sulphate is 

 added and until a precipitate or 

 turbidity just begins to show. 

 This is caused to disappear by 

 the cautious addition of water, 

 a few drops at a time. Filially, 

 acetic acid of ten per cent 

 strength saturated with ammo- 

 nium sulphate is added until a 

 turbidity again appears, and 

 then the mixture is allowed to 

 stand 24 hours in a cool place. 

 A part of the albumin separates 

 in the crystalline form. This is 

 collected, redissolved in a very 

 little cold water and reprecipi- 



FIG. 8. Form of Graham dialyzer fre- 

 quently used in purification of proteins. 

 The simple parchment tube dialyzers now 

 obtainable are more efficient. 



tated with ammonium sulphate 

 and acetic acid as before. The 



crystals are collected on a filter, then transferred to a dialyzer with water 

 lor the separation of the sulphate by dialysis. In this way a nearly pure 

 albumin may be obtained in solution, but the crystallized substance has 

 not been secured free from salts. 



White of egg contains in the mean about 86 per cent of 

 water, 13 per cent of proteins, 0.6 per cent of mineral matters 

 and a little fat. The yellow of egg is a substance of very 



