Effect of Salts on Hydration of Acetic Anhydride. 113 



acetic acid. He concluded that, with equivalent quantities of anhy- 

 dride and water, the reaction was niono-molecular. 



Rivett and Sidgwick, 1 using dilute aqueous solutions, followed the 

 hydration by measuring the electrical conductivity. The measure- 

 ments were made at 25. The velocity of hydration showed that the 

 reaction was mono-molecular and was not catalyzed by hydrogen ions ; 

 and that beyond a certain point the constant decreases steadily with 

 increasing concentration. 



Orton and M. Jones 2 concluded that the hydration of acetic anhy- 

 dride in acetic acid as a solvent is a slow reaction of the second order; 

 that on dilution the increase in velocity was approximately proportional 

 to the amount of water present, and that the relation of the velocity 

 factor to the temperature was normal. The effect of catalysts was also 

 studied. It was found that acids were powerful catalysts of the hydra- 

 tion. The effect was most obvious in media containing but little water, 

 diminishing as the proportion of the water increased, being least obvious 

 in pure water. The value of the velocity factor was a linear function 

 of the concentration of the acid. Alkalies and hydrolyzed salts were 

 also found to act as powerful catalysts to the hydration in aqueous 

 solutions. 



Philip 3 made a study of the reaction between acetic anhydride and 

 water in glacial acetic acid, by determining the freezing-points of the 

 mixture taken at frequent intervals. 



Wilson and Sidgwick 4 studied the rate of hydration of a number of 

 acid anhydrides. The rate of formation of the acid was determined 

 by measuring the increase in the electrical conductivity of a solution 

 of the anltydride in water. 



NEUTRAL SALT ACTION. 



There has been but little experimental work done on the problem of 

 the effect of the neutral salt on the hydrolysis by water alone. Most 

 of the work has had to do with the effect exerted by a neutral salt on the 

 activity of an acid used to catalyze the reaction. This latter is what 

 we generally understand by the term " neutral salt action." It has 

 been studied mainly in two reactions: (1) the rate of inversion of cane 

 sugar in the presence of acids, and (2) the catalytic hydrolysis of esters. 

 In general it has been found that neutral salt action is not greatly 

 influenced by temperature, and that the influence of neutral salts is 

 regarded as independent of the acid employed as catalyst. 



Practically the only work done on the effect of neutral salts on hydra- 

 tion alone is that due to Kellogg, published in a series of three articles. 5 

 He showed that the rate of hydrolysis of ethyl acetate by water is 



Mourn. Chem. Soc., 97, 733, 1677 (1910). Mourn. Chem. Soc., 103, 1959 (1913). 



a /6td., 101, 1708 (1912). *Ibid., 31, 403 (1909) ; 886 (1909) ; 35, 396 (1913). 



"Proc.Chem.Soc.,28, 259. 



