COMBINING CAPACITY 197 



intermediate values which are determined by the alkahnity or 

 acidity (H+ concentration) of their solutions. 



In applying this method to the comparison of the acidity or 

 alkalinity (H+ concentration) of solutions the terminal electrodes 

 must be hydrogen. A hydrogen electrode can be obtained by 

 employing a saturated solution of hydrogen in a metal, e.g., 

 platinum. In order to obtain a large surface, platinum gauze 

 coated with platinum black is usually employed and a stream 

 of pure hydrogen is passed over or through the gauze. The 

 potential between the two acid or alkaline solutions themselves 

 (as distinguished from that between the hydrogen electrodes and 

 these solutions) may be abolished or at any rate greatly diminished 

 by connecting them by means of a U-tube filled with agar satu- 

 rated with KCl (3) (1). 



I have utilized this method in determining the combining 

 capacities of casein and of ovomucoid for acids or bases in solu- 

 tions of varying acidity and alkalinity (59) (60). For further 

 details regarding the technique employed and the precautions to 

 be taken in carrying out such determinations in solutions which 

 contain proteins, the reader is referred to the appendix. 



In the following tables, which enumerate the results of these 

 experiments, the symbols which are employed have the following 

 significance : 



hi = The concentration of a solution of base in which protein 



is dissolved, 

 ai = The concentration of a solution of acid in which protein 



is dissolved. 

 TT = The potential of the chain : 



H, 



acid or base 

 plus protein 



H. 



acid or base 

 alone 



in volts. At 30 degrees, with monacid bases or mono- 

 basic acids 



= 0.0601 logio ^ or 0.0601 logio -• 

 a 



h = The hydroxyl concentration (unneutralized base) in the 



solution of base containing protein. 

 a = The hydrogen concentration (unneutrahzed acid) in the 



solution of acid containing protein. 

 m = bi — h or ai — a = the concentration of base or acid 



neutralized by the protein. 



