From the solubility minimum the value of the basic ionization constant of sulfanilic acid is shown to lie probably between the values 1.7 x 10–15 and 3.2 x 10–15. From solubility measurements the value of this same constant is shown to lie probably between 2.0 and 2.2 x 10–15, and the isoelectric point of sulfanilic acid is thus at a cH of 0.056 or a pH of 1.25. From conductivity ratios the acid ionization constant of sulfanilic acid is shown to be 7.05 x 10–4 at room temperature (21°C.).
Calculations are made, from data published in preceding papers, of the ionization constants of glycine, Ka being 2.3 x 10–10, and Kb being 2.2 x 10–12.