GENERAL CHEMICAL CHARACTERS OF PROTEINS 43 



ments), if CH represent the concentration of the hydrogen ions, and 

 COH that of the hydroxyl ions, then according to the law of mass 

 action, 



C H . C OH = constant = K. 



In the presence of sodium hydroxide the concentration in the 



+ 



hydroxyl ions is decreased (owing to dissociation into Na and OH). 

 If now ^ H represent (as above) the concentration of the hydrogen 

 ions, and COH the concentration of the hydroxyl ions due to the 

 presence of the alkali, then (dissociation of water being negligible) 



Substituting this value in equation (i), it is found that 



P C OH 



7T = 0-059 WglO 



K 



Suppose now that the ionic concentration of the acid be altered by 

 the addition of protein which forms a salt with the acid, a change in 

 the electro-motive force will follow. The concentration of the hydro- 

 gen ions in the sodium hydroxide (CNaon) will remain unchanged. 

 If CHCI represent the ionic concentration of the original acid solution 

 and CH that after addition of protein, and E o the original electro- 

 motive force and E the changed force, then 



E = 0-059 



K 

 and E = 0-059 logio -^ 



Whence, 



E - EQ = 0-059 



C HC1 



and similarly for alkalis, E - E o = O'cKo log 



The experiments were carried out with 0*05 N acid and alkali 

 solutions with a 0-05 N sodium chloride solution interposed. The 

 electro-motive force was determined by a compensation method, 

 a Clark cell being used as standard. Values for E - E and 



1 This equation is not strictly correct, for between the sodium hydroxide and acid 

 solutions there is a layer of sodium chloride, and there are consequently potential 

 differences between the acid | salt and alkali | salt solutions. If </> represent the former 

 of these differences, and $ the latter, then the equations become 



E = 0-059 log 10 CHC1 



and E = 0-059 log w H ' 



^remaining the same in both equations and the ionic concentration in the alkali not 

 altering. Then 



HfM 



- E Q = 0-059 Iog 10 -^ - <f> - <t> . 



4>-<t> o is small compared with the other number and was neglected in calculating the 

 value ^l. 



