DISSOCIATION OF ACIDS AND BASES 147 



It could be doubted if the conception of "a constant reduced to a 

 definite salt content" would still hold, if the premise of the total 

 dissociation of all salts were invalidated. It has been shown that 

 such doubt is unjustifiable. Only it cannot always be distinguished 

 in individual cases whether the apparent change of k to k' is based 

 upon an activity effect or upon true salt-formation. As far as the 

 physiological utilization of the "reduced constant" is concerned this 

 is of no import; for our ionic equilibria can still be calculated if only 

 the "reduced dissociation constants" of the acid for the corresponding 

 neutral salt content of the solution is known, no matter how com- 

 phcated the theoretical derivation of this constant may be. In any 

 event, by using the properly reduced constant, the amount of un- 

 dissociated acid molecules can be irrefutably calculated. What 

 remains undetermined are the relative amount of the remaining acid 

 molecules dissociated into ions and those bound into true salt 

 molecules. 



All of the above considerations are valid for the univalent ions, 

 but if a weak acid forms a salt with a divalent ion (as, for example, 

 acetate buffer + CaCl2), then not only does the horizontal displace- 

 ment of the p-curve ensue, but the curve simultaneously also becomes 

 steeper. Concerning the more detailed calculation of these relations 

 the original article' should be referred to. Special complications 

 also arise when we assume the acid molecules in solution are asso- 

 ciated with two or more molecular species and approach the col- 

 loidal state. Concerning this aspect also the above mentioned 

 original article should be consulted. 



3 L. Michaelis, Biochem. Zeitschr. 106, 83 (1920). 



