134 Studies on Solution. 



hydrogen ions; to be basic, an excess of hydroxyl ions. To determine 

 whether a solution is neutral or not, we therefore make use of indicators, 

 such as litmus, methyl orange, phenolphthalein, which give evidence 

 by their color changes. 



When a normal salt is dissolved in water, partial hydrolysis takes 

 place, yielding free acid and free base. Whether the solution will 

 react acid or alkaline will depend on the degree of dissociation of these 

 products of hydrolysis. It follows, therefore, that there are four types 

 of salts which may undergo hydrolysis: (1) salts derived from strong 

 acids and strong bases; (2) salts of weak acids and strong bases; 

 (3) salts of strong acids and weak bases; (4) salts of weak acids and 

 weak bases. All salts except those of the first type are hydrolyzed to 

 a considerable extent, due to the small degree of dissociation of one or of 

 both of the products of hydrolysis. Salts of strong acids and strong 

 bases under ordinary conditions do not undergo hydrolysis. 



The determination of the degree of hydrolysis is not accomplished 

 without difficulty. The free acid or base can not be directly titrated 

 with a standard solution, for equilibrium would be destroyed at once 

 and neutrality would be reached only when the salt was completely 

 decomposed. A method must then be employed which will not destroy 

 the hydrolytic equilibrium. The methods most generally used are: 1 

 (1) the determination of the velocity constant for the hydrolysis of an 

 ester, for this is proportional to the amount of free acid or alkali 

 present; (2) the determination of the rate of inversion of cane sugar; 



(3) the determination of the electrical conductivity of the solution; 



(4) the determination of the coefficient of distribution between two 

 solvents. There are also many other methods of more or less limited 

 applicability. 



Only those salts were used in this investigation which were proved 

 by the above methods to be nonhydrolyzed. For these salts the values 

 of k calculated according to the equation 



(Salt) k_ 



(Acid) X (Base) H2 o 



are so small that they need not be taken into account. The salts were 

 further tested according to an observation made by Salm, 2 that salts 

 which give no reaction with litmus have a concentration of H + and 

 OH~ ions less than 1 X 10~ 6 , a value so small that it is negligible. 



NEUTRAL SALT ACTION. 



In a discussion of neutral salt action one must distinguish clearly 

 between the effect produced by a neutral salt on the catalytic activity 

 of an acid (or alkali), and the effect of the neutral salt on hydrolysis 

 by water alone. It is the latter effect in which we are most interested 



R. C. Farmor: B. A. Reports, 240 (1901). 2 Zeit. physik. Chcm. 57, 471 (1907). 



