THE MEASUREMENT OF PH AND TITRATABLE ACIDITY 



79 



pH 6 



PER CENT DISSOCIATION 



Fig. 1. Ionization curves of some sulfonphthalein indicators, illustrating the general 

 relationships among the acid-base indicators and the applications of Eq. (5). Note: In 

 some cases, the positions of the curves on the pH ordinate are approximate. Table 2 

 should be consulted for accurate values of pK'. 



