306 
Pieric acid. 
EE em EERE ETE LP ESE ES ET 
Cones era: | sil GLE aa Cone Ky 
03 N la = 0-00135 
: 0:0031 N 9°67 0:00139 
3 0:0050 N 6.00 0.00141 
; 0:0513 N 0:58 0-00173 
8 0:0778 N 0:38 0-00160 
: 0-1161 N 0:25 0-00153 
ki 0:1597_N 0-18 0.00134 
: 03066 N 0:09 0:00122 
It will be evident from the foregoing tables that the velocity 
coefficients do not decrease proportionally with the decrease in the 
concentration of the hydrogen ions. In the case of oxalic acid the 
velocity coefficients fall off with the concentration of potassium 
oxalate; whilst in the case of picric acid the addition of sodium 
picrate produces at first an increase in the velocity coefficient and 
then when the concentration of sodium picrate reaches the value of 
0-159 N, the velocity coefficients begin to fall off. This is explicable 
on the assumption that even undissociated acids are catalytically 
active in the hydrolysis of esters. But in view of the work of 
Wa.pen (Jour. Amer. Chem. Soc. 1912, 35, 1649) on the measure- 
ment of the di-electric constants of solutions, a different interpretation 
of these results is possible. WALDEN has shown with non-aqueous 
solutions that the di-electric constant and the ionising power of a 
solvent are enormously increased when electrolyts are dissolved in 
it. Naturally the degree of ionisation of the dissolved acid and along 
with it the concentration of hydrogen ions are also increased. Thus 
by the addition of salts of the same acids, there are two effects: 
1. The diminution of hydrogen ions due to the increase of the 
common negative ion. 
2. The increase in the concentration of the hydrogen ions due to 
the greater ionisation of the acid caused by the increase in the 
di-electric constant of the solvent. 
It is evident that these two effects counteract each other. 
In the case of potassium oxalate the first effect preponderates 
over the second and hence the velocity coefficient falls off with the 
concentration of potassium oxalate, whilst in the case of picric acid 
