Action of Hydrated and Nonhydrated Salts on Saponification. 109 



(2) The effect of salts with water of crystallization decreases, on 

 dilution, much more than the salts without water of crystallization. 



(3) Among the metals with common anions, as magnesium, calcium, 

 strontium, and barium chlorides or nitrates, the curves are arranged 

 in the order of the decreasing atomic weights of the cations. 



We therefore conclude that between salts with water of crystalliza- 

 tion and salts without, on the saponification of esters, the difference 

 in action is probably due to the chemical difference between hydrated 

 and nonhydrated salts or between free and combined water. As an 

 explanation of this difference in action we offer the suggestion that 

 the combined water is more highly ionized than free water, and with 

 hydrated salts we have this effect added to the salt effect shown in 

 the case of nonhydrated salts. 



Pearce 1 shows that the cations are the ones that are most strongly 

 hydrated, the anions, if hydrated at all, being only slightly so. 



The curves we find for the halides of potassium show that in the 

 saponification of esters the anions play an important part. This is in 

 line with what Kellogg 2 found. It therefore seems probable that the 

 anions are also hydrated to a certain extent. 



But how can the larger temperature coefficient of reaction velocity of 

 the hydrated salts be accounted for, since with rise in temperature the 

 hydrates become less complex? A study of figures 8 and 1 1 shows that, 

 temperature being constant, the amounts of ester saponified in the 

 presence of the hydrated salts, as the time increases, is much greater 

 than the amounts saponified in the presence of the non-hydrated salts. 

 This is probably due to the larger amount of acid formed by the 

 saponification of the ester by combined water. With rise in tempera- 

 ture the larger amount of acid would give us a larger temperature 

 coefficient. Another factor to be taken into consideration is the 

 hydrolysis of the hydrated salts, which, though negligible at low tem- 

 perature, increases greatly as the temperature rises. The increased 

 fluidity of the solution must also be taken into account, the hydrates 

 becoming less complex with rise in temperature. These three factors 

 would probably offset the decomposition of the hydrates, giving less 

 combined water, with the result that we should have a larger tempera- 

 ture coefficient of reaction velocity for the hydrated than for the non- 

 hydrated salts. 



From the standpoint of hydrates breaking down with rise in tem- 

 perature, let us consider the effect of such rise on chemical reactions 

 in general. The influence of temperature on the velocity of reactions 

 is usually very great. 



Berthelot 3 showed that the velocity with which an ester is formed is 

 about 22,000 times as great at 200 as at 7. 



'Carnegie Inst. Wash. Pub. No. 180, 57 (1913). 



"Journ. Amer. Chem. Soc., 31, 886 (1909); 35, 396 (1909). 



'Essai de Mecanique Chiinique, 2, 93 (1879). 



