DISSOCIATION OF STRONG ELECTROLYTES 131 



neutral salt (which alone occurs in Bjerrum's approximation equation 

 for the activity factor), but is also greatly affected by its specific 

 nature. Thus the influence of the alkali cations increases in the 

 series Rb K Na Li; with anions it increases from ^ SO4 to CI; Br 

 appears to have the same effect as CI. 



The most important for physiology is the reduced constant of 

 carbonic acid, for it represents one of the most significant constants 

 of nature. It will be dealt with in greater detail in a subsequent 

 section. 



With the change of pk' accompanying variations of the salt- 

 content, the entire dissociation curve {a- or p-curve) is simply 

 displaced horizontally through the presence of the neutral salt. 

 With the perception of this phenomenon the study of ionic equi- 

 librium was greatly advanced, especially for the physiologists.^^'' 



37. Another exposition on the effect of strong electroljrtes^^ 



It appeared necessary in the presentation of this entire chapter to 

 follow the historical development of this subject which is still in 

 progress. But now we may attempt to find another method of repre- 

 sentation, which comprises the physiologically important problems 

 just as well, and which avoids many difficult complications. 



The concentration of hydrogen ions is measured by means of the 

 concentration chain. One solution whose unknown [H+] = hi is 

 in contact with a hydrogen-platinum electrode, and its potential \i 



TTi = 0.058 log r , where ho denotes that hydrion concentration which 



Ho 



the solution would have if tt = 0. The second solution of hydrion 



concentration ha is in contact with the second hydrogen-platinum 



h2 

 electrode, and here the potential is 1:2 = log 7-. It is usually assumed 



that the ho values in the first and second equations are identical, 

 and hence the electromotive force E of the chain is 



/ hi h,\ 



E = TTi - 7r2 = 0.058 I log log — ) 



\ ho ho/ 



'^ Concerning recent conceptions of the reduced constants see E. Warburg 

 (Biochem. Journ. 16, 153, 1922). 



15 This section is based upon the theory of concentration chains which is 

 detailed in a later chapter. 



