CHAPTER IX 



THE COMBINING CAPACITY OF THE PROTEINS 



1. The Electrochemical Determination of the Combining 

 Capacity of the Proteins. — The potentiometric method was 

 employed by Bugarszky and Liebermann (5) for the purpose of 

 demonstrating that proteins possess a true combining capacity 

 for acids and bases. I have utiHzed this method in determining 

 the relationship of the combining capacity of the proteins to the 

 alkalinity or acidity as well as the absolute concentration of their 

 solutions (54) (59) (60). In brief, the principles upon which the 

 method depends are as follows : * 



When a metal or hydrogen is brought into contact with a liquid 

 a certain amount of the metal tends to pass over into the liquid 

 and it strives to do so with a certain measurable and character- 

 istic force, analogous to gas- or osmotic-pressure, which Nernst 

 (47) (48) has termed the solution pressure. The particles which 

 this pressure tends to bring into solution are all, in the case of 

 the metals and hydrogen, charged electropositively. The number 

 of these particles which actually pass into solution, provided no 

 current is allowed to traverse the hquid and the metal, and no 

 chemical work is performed, must be very small and, in proportion 

 to weighable qualities, quite evanescent; for as the positively 

 charged particles pass out into the liquid an electrostatic tension 

 is necessarily developed. The film of liquid which is in immediate 

 contact with the metal becomes positively charged; the metal, 

 having lost positive charges, acquires a corresponding negative 

 charge, and the force driving fresh metal or hydrogen ions into 

 the liquid becomes balanced by the electrostatic repulsion of the 

 positive ions, from the film of liquid which is in contact with the 

 metal into the surface of the metal again. Hence there is quickly 

 developed a certain constant difference of electric potential be- 



* For a fuller discussion of these principles and of the forms of apparatus 

 used the reader is referred to standard works of general physical chemistry 

 (21) (41) (64) (67). 



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