494 
Proceedings of Royal Society of Edinburgh. [sess. 
yening dilution was then obtained from a curve in which the 
velocity constants per equivalent were plotted against the corre- 
sponding concentrations. The following are the results obtained in 
this way for a series of dilutions. 1 G is the concentration of the 
acid : — 
c 
h per equivalent. 
0-01 
606 
0*025 
545 
0-05 
493 
0T 
441 
0-2 
411 
0*35 
407 
0-5 
403 
Correction op the Velocity Constants. 
As the neutral salts in the solutions employed in these experi- 
ments do not of themselves bring about the catalysis of the etliylic 
acetate, this being affected only by the hydrogen ions arising from 
the free acid present at the same time, the velocity constant 
obtained with any solution gives a measure of the free acid which 
it contains. The standard of comparison is the velocity constant 
measured in the case of sulphuric acid alone, of the same con- 
centration. A constant obtained for sulphuric acid alone, on the 
one hand, and that for a solution containing sulphuric acid and a 
neutral sulphate on the other, are not, however, immediately com- 
parable. Each must be corrected in a manner which I will now 
indicate. 
It is known that when a neutral salt is added to a solution of 
the corresponding monobasic acid, the velocity with which the acid 
effects the catalysis of an ester is increased. As this influence of 
the neutral salt is considered to be of a physical nature, and due 
in the first instance to the action of the dissociated part of the 
added salt, it must be supposed, when the catalysis is performed with 
a dibasic acid like sulphuric acid, to which a neutral sulphate has 
been added, that the influence exists here also ; and that, although 
in this latter case the velocity actually measured is less than that 
obtained with sulphuric acid alone, (owing to the formation of the 
