70 Conductivities and Viscosities in Pure and in Mixed Solvents. 



to the effect of the neutral salt. From this it might be concluded that 

 Kj would be largest for those solutions containing the greatest amount 

 of neutral salt. A study of the separate tables, table 40 for instance, 

 shows that just the reverse is true. The solution that contains the 

 largest amount of neutral salt always gives the smallest concentration 

 of hydroxyl ions, and the K, value for such a solution is much lower 

 than for a solution containing less neutral salt but a greater concen- 

 tration of hydroxyl ions. It is thus evident that K; varies not only 

 with the concentration of the neutral salt, but also with the concen- 

 tration of the hydroxyl ions. From the above it will be seen that if 

 the neutral salt had no effect, the variation of K> in the separate tables 

 would be much greater than it actually is. It is therefore obvious 

 that the equilibrium equations, based on the assumption that phenol- 

 phthalein acts as a monobasic acid, do not hold. 



Wegscheider concludes that these variations may be accounted for 

 by regarding phenolphthalein as a dibasic acid. The results of Rosen- 

 stein make it appear very probable that this indicator does act as a 

 dibasic acid. The limitations of this method and the presence of 

 neutral salts made it impossible for him to determine satisfactorily the 

 ionization constant for phenolphthalein, and the question must there- 

 fore be regarded as still open. 



The radiometric method has thus far been applied for determining 

 the hydrolysis and ionization constants of indicators. Knowing these 

 values, it is possible, by radiometric means, to determine from them 

 the hydrolysis constants of many salts. The calculation of the ioni- 

 zation constants of weak acids and bases formed by the hydrolysis of 

 these salts is then a simple matter. 



This method has been applied in a preliminary way to aluminum 

 sulphate, using methyl orange as the indicator. It is assumed that the 

 secondary and tertiary hydrolysis of this salt can be neglected, and, 

 on this assumption, the ionization constant of the base formed by the 

 primary hydrolysis has been calculated. 



The calculations of the constants are based on two fundamental 

 equilibrium equations, the symbols representing gram-ions per liter. 

 Expressing the equilibrium relation for the primary hydrolysis of 

 aluminum sulphate, we have 



AiOH X H K 7y 



+++ = x, ^ ' 



Al 



In the hydrolysis equation for methyl orange, 



AzOH X H _ K. 

 Q+ K, 



