368 Dr. J. Shields on Hydrolysis 



hydrate, the velocity of the reaction is represented at every 

 instant by the general equation 



J =£(0-40(0!-*), (i) 



where k is the coefficient of velocity of reaction, C and Oj the 

 concentrations of the ester and base respectively at the com- 

 mencement, and x the quantity of ester which has undergone 

 change during the time t. 



In the case of the salt-solutions we wish to determine the 

 concentration of the base, i. e., the amount of active free 

 alkali at the commencement, the coefficient of velocity for the 

 various bases being already known. On dissolving potassium 

 cyanide in water we get 



KOH + HCN^=±: KCN + HOH 



(quantity KOH x diss, ratio) x (quantity HON x diss, ratio) 



= (quantity KCN x diss, ratio) X (quantity HOH x diss, ratio). 



The dissociation ratios of potassium cyanide and potassium 

 hydrate, water and hydrogen cyanide, do not alter appreciably 

 with change of concentration in the solution, and may conse- 

 quently be regarded as constant. (Arrhenius, Zeits.f.physikal. 

 Chemie, vol. v. p. 17, 1890.) 



The quantity of water as compared with the other substances 

 is supposed to be infinitely great and regarded as a constant 

 K. The saponification of ethyl acetate by means of aqueous 

 potash takes place according to the equation : — 



CH 3 COOC 2 H 5 + KOH=CH 3 COOK + C 2 H 5 OH . 



and if we represent by C 2 the initial concentration of the 

 potassium cyanide, by A the concentration of the free 

 potassium hydrate, and by x that of the potassium acetate 

 formed, then C 2 — x— A will represent the actual concentration 

 of the potassium cyanide, and A + x that of the hydrocyanic 

 acid : all of course being expressed in the same unit, namely, 

 gram-molecules per litre. From the equilibrium, 



KOH + HCN^=±:KCN + HOH 



we now get, using our new symbols, the equation 



A(A + *)=K(C 8 -tf-A), . .... (2) 



which represents what takes place at any stage of the reaction. 

 After the first few moments, however, when A becomes very 

 small compared with x, we may write the equation thus : — 



A.^-" (3 



x 



\ 



