135 
the same interval by determination in a liquid of known p9". As 
a gradual change in the electromotive force of the same combination 
was generally noticed on returning to it after the two other estima- 
tions, the influence of this change could at any rate be eliminated 
for the greater part by interpolation. 
The value, determined in this way for the negative logarithm of 
ke in 8°/, phosphate solutions, was in the mean 
13,78. 
As to the long standing problem, why the potential of the OH 
electrode is usually found about 0,15 Volt too low, some information 
may be derived from the following observation. 
If the blackened platinum electrode had been polarised kathodi- 
cally in dilute sulphuric acid, the value found for its potential was 
too low, in accordance with the experience of previous investigators. 
If, however, the electrode had been the anode in sulphurie acid, 
the determination of its potential showed a value, by nearly the 
same amount too high. 
The following estimations were carried out with the same 8 °/, 
phosphate solution (py = 6,92). 
Oxygen electrode kathodically polarised : 
> ae 
MH + calomel = 0,658 Volt 
<_ > 
HOH + calomel —= — 0,421 Volt 
ay + 70H = 1,08 Volt 
Oxyden electrode anodically polarised: 
—-> => 
TH a= Tealomel S= 0,653 Volt 
_ == ; 
HOH + Healomel = — 0,736 Volt 
AH +2%0R = 1,39 Volt 
The theoretical value for the electromotive force of the oxygen- 
hydrogen-cell at room temperature is 123. Volt 
This fact appears to indicate, that the difference between the 
potential, observed at the oxygen electrode and the theoretical value 
is due to a polarisation phenomenon, as it can be quantitatively 
reversed by reversing the state of polarisation of the electrode. 
