Chemical Activity of Free and Semi-Combined Water. 135 



in this investigation, although the former is what is generally under- 

 stood by the term "neutral salt action." 



EFFECT OF NEUTRAL SALTS ON THE CATALYTIC ACTIVITY OF ACIDS. 



It was early found 1 that the addition of a substance which is largely 

 ionized in aqueous solution alters the rate of hydrolysis of esters or 

 of carbohydrates by strong acids. This has been proved by the addi- 

 tion of metallic chlorides to mixtures in which hydrochloric acid is the 

 catalyst, the addition of bromides to hydrobromic acid, and of nitrates 

 to nitric acid. Those chlorides which are highly dissociated have 

 much the same effect, while a salt like mercuric chloride, which is 

 only partially ionized, has a much feebler action. Non-electrolytes, 

 such as the alcohols of sugars, have but little effect on the hydrolytic 

 activity of the hydrogen ions. 



The action of the neutral salt is not always to accelerate the hydroly- 

 sis; often there is a retardation. There are also well-defined differ- 

 ences between the influence of neutral salts on the rate of inversion of 

 cane sugar in the presence of acids and their influence in the catalytic 

 hydrolysis of esters. The velocity of the inversion of cane sugar is 

 increased to a much greater extent by the addition of certain concen- 

 trations of salts than is the velocity of the hydrolysis of esters. 



Neutral salts have in general a retarding effect upon the hydrolysis 

 of esters and amides by alkalis. Senter, 2 however, found that the 

 hydrolysis of sodium chloroacetate by sodium hydroxide was greatly 

 accelerated by the presence of neutral salts. It has been shown that 

 neutral salt action is independent of the concentration of the compound 

 hydrolyzed, is proportionally greater the more dilute the acid solution, 

 is not greatly influenced by temperature or pressure, and is independent 

 of the nature of the acid employed as catalyst. 



In addition, Poma 3 has determined that the intensity of the action 

 developed by neutral salts bears a strict relation to the chemical nature 

 of the ions of the salts and diminishes in passing from chlorides to 

 bromides to nitrates to iodides, in succession; that it is independent of 

 the chemical nature of the cations; and, finally, that it seems to be pro- 

 portional, not to the concentration of the salt in the solution, but to 

 the concentration of the ions. 



EFFECT OF NEUTRAL SALTS ON HYDROLYSIS BY WATER ALONE. 



Probably the first work done on neutral salt action in the absence of 

 an acid was by Smith, 4 who investigated the effect of neutral salts on 

 the rate of inversion of cane sugar. He found that salts of weak acids 

 had almost no effect, while potassium chloride and sodium sulphate, 

 the more nearly neutral salts, had considerable effect. 



Mourn. prakt.Chem.85,321,401 (1862). 3 Medd. K.Vetenskapsakad.Nobelinst.,2,No. 11, 1-28. 

 2 Journ. Chem. Soc. 91, 473 (1907). <Zeit. physik. Chem. 25, 144 (1898). 



