in Aqueous Salt- Solutions. 369 



Now, in the general equation (1) G x —x the concentration of 

 the base is what we now call A, so that we may re-write it in 

 the form 



dx _J_ 1 a) 



dt 'C-x'k V 



Combining (3) and (4) we get 



dx _1_ 1 = K(C a -aQ (5) 



dt 'C—x'k x ' 



which on integration gives the solution : 



loff nat. ^p Q — pj — jpY- log nat. 



C-U 2 g ' C 2 -^ C-C 2 & C-^ 

 K= " Kh-h) • < 6) 



k, the specific coefficient of velocity, is known, and for potash 

 at 24°*2 C. is numerically equal to 6*22. Having got K from 

 equation (6) all that remains to be done in order to know how 

 much free potash is present in the solution at the commence- 

 ment is the calculation of A from equation (2). At the 

 beginning, when x = 0, 



A 2 = K(C 2 -A), (7) 



from which we get A in gram-molecules per litre. 



The percentage amount of potassium cyanide which has 

 been decomposed by the water is therefore 



100 A 



C 2 ' 



It is here unnecessary to describe in detail the apparatus 

 and method which I used to determine the velocity of the 

 saponification of ethyl acetate by the salt-solutions, as it was 

 precisely similar to that which has already been employed by 

 Ostwald (Journ. f. pr. Ch. [2] vol. xxxv. p. 112, 1887), 

 Arrhenius [Zeits.f. pkysikal. Chemie, vol. i. p. 110, 1887), and 

 others. Measured volumes of a known strength of salt-solu- 

 tion and of ethyl acetate were mixed at the temperature of the 

 thermostat. (For the construction of the thermostat, &c. 

 see Zeits. f. physikal. Chemie, vol. ii. p. 564, 1888.) From 

 time to time small fractions of the mixture were withdrawn 

 by means of a pipette and titrated as expeditiously as possible. 



In calculating the concentration of the salt at the com- 

 mencement, it has been assumed that the volume of the mixed 

 solutions of salt and ester is the sum of the volumes taken 

 separately. This is of course, strictly speaking, not true, but 

 the deviation from the truth is so small as to be entirely 

 negligible. I shall now proceed to give the experimental 



