EDWIN JOSEPH COHN 721 



SUMMARY. 



1. Two proteins of the globulin type, serum globulin and tuberin, 

 and the protein of milk, casein, have been purified (a) of the other 

 proteins and (b) of the inorganic electrolytes with which they exist 

 in nature. The methods that were employed are described. 



2. All three proteins were found to be only very slightly soluble in 

 water in the pure uncombined state. The solubility of each was ac- 

 curately measured at 25.0° ± 0.1°C. The most probable solubility 

 of the pseudoglobulin of serum was found to be 0.07 gm. in 1 liter; 

 of tuberin 0.1 gm. and of casein 0.11 gm. The methods that were 

 employed in their determination are described. 



3. Each protein investigated dissolved in water to a constant and 

 characteristic extent when the amount of protein precipitate with 

 which the solution was in heterogeneous equilibrium was varied within 

 wide limits. The solubility of a pure protein is therefore proposed as 

 a fundamental physicochemical constant, which may be used in identi- 

 fying and in classifying proteins. 



4. The concentration of protein dissolved must be the sum of the 

 concentration of the undissociated protein molecule which is in hetero- 

 geneous equilibrium with the protein precipitate, and of the con- 

 centration of the dissociated protein ions. 



5. The dissociated ions of the dissolved protein give a hydrogen ion 

 concentration to water that is also a characteristic of each protein. 



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