Action of Hydrated and Nonhydrated Salts on Saponification. 85 



The above physical difference in the action of combined and of free 

 water, in their power to absorb light, led us to study solutions of 

 slightly hydrated salts and strongly hydrated salts to see if a corre- 

 sponding chemical difference existed between water in the combined 

 and in the free state in other words, to study the effect of free water 

 on some chemical reaction in which water is one of the reacting sub- 

 stances, a solution of a slightly hydrated salt containing an amount of 

 water equal to the free water, and a solution of a hydrated salt con- 

 taining an amount of water equal to the free water. 



REACTION CHOSEN. 



Berthelot and Pean de Saint Gilles, 1 as early as 1862, showed that the 

 formation of an ester from an alcohol and an acid 



CH 3 COOH + HOC 2 H 5 ^ CH 3 COOC 2 H 5 + H 2 O 



proceeded in a slow, progressive manner towards a limit, and that 

 the speed of the reaction was dependent on the amounts of the sub- 

 stances present and on the temperature. This was also shown to be 

 a reversible process. 



The reaction of the saponification of an ester has been studied by 

 Ostwald 2 and Reicher, 3 as a method for determining the strengths of 

 acids and bases. Bases were found to saponify the ester more rapidly 

 than acids. The strengths of the acids and bases determined by this 

 method agreed with the strengths as determined by conductivity. In 

 other words, it is the hydroxyl ion of the base and the hydrogen ion 

 of the acid which do the saponifying. The velocities of the reactions 

 studied by Ostwald and Reicher were so much greater, on account of 

 the large number of ions furnished by the acids and bases, in contrast 

 with the small number of ions in those studied by Berthelot and Saint 

 Gilles. 



We decided to use the saponification of an ester in the study of the 

 action of free water and of combined water for the following reasons : 



In the first place, as Berthelot and Saint Gilles showed, the speed 

 of the reaction is dependent on the relative amounts of the substances 

 used. By keeping the amount of the ester constant, we could study 

 the effect of the water in solutions of salts containing the same amounts 

 of water. 



Secondly, the reaction proceeds slowly and its velocity could there- 

 fore be easily measured. 



Thirdly, the speed of the reaction is dependent on the temperature. 

 However, as the temperature rises the hydrates become less complex. 



J Ann. Chim. Phys., 65, 385 (1862); 66, 5, 110 (1862); 68, 225, (1865); 14 ,437 (1878); 15, 220 

 (1878). 

 J Jour. prakt. Chem., 28, 449 (1883) ; 35, 112 (1887). 3 Lieb. Ann., 228, 257 (1885). 



