DISSOCIATION OF STRONG ELECTROLYTES 129 



buffer acid is varied, then fa will remain for this 'particular buffer acid 

 a constant value; and hence fa depends upon: 1. the nature, and 

 especially the valence, of the buffer acid, but not upon its concentra- 

 tion, as long as it remains relatively small, and 2. the kind, especially 

 the valence, of the ions, and the concentration of the neutral salt in 

 excess. 



In equation (3) above we may designate 



-la 



and then instead of (3) introduce as the corrected buffer equation the 

 important equation 



^ [Na - salt of the acid] ^ ' 



and the k' which is substituted for the previous k we shall designate 

 as the reduced dissociation constant of the acid, which has a well 

 defined value for every NaCl concentration of the solution, k' 

 may be operated with as well as k. Since k' > k, the entire effect 

 of the influence of the neutral salt is such as to make it appear as 

 if ike dissociation constant of the acid were increased by it, i.e., as if the 

 acid has become stronger. 



36. The reduced constants of physiologically important acids 



If we should wish to apply our buffer equation developed above to 

 physiological problems, we must know not only the k-values for the 

 CO2, phosphoric acid and sunilar buffers, but also their k'-values 

 reduced to the corresponding content of sodium chloride and other 

 neutral salts. 



It has been experimentally confirmed that in a dilute buffer solu- 

 tion containing a constant amount of NaCl in excess k' is a constant. 

 Therefore it is entirely possible to render the field of experimental 

 physiology entirely independent of the theory of activity; and all 

 that is necessary for this purpose is to determine experimentally the 

 k' values for every physiologically important acid and for every 

 significant concentration of neutral salt. 



There are still very few exact data on this subject, and it is a 

 pressing task for the immediate future to make available numerical 

 data. Michaehs and Kruger^^ determined the following k' values for 

 acetic acid. 



" L. Michaelis and R. Kruger, Biochem. Zeitschr. 119, 307 (1921). 



