1908-9.] 
169 
Note on a Study of Polarisation. 
resistance and low-resistance cells, which at first sight suggested variation 
of polarisation with potential difference of electrodes, may have been 
largely, and possibly wholly, due to differences in the area of the electrodes. 
Additional observations would need to be made, with exactly cut electrodes 
and more complete precautions against the sources of error mentioned 
above, before a test of this kind would be completely satisfactory. But 
it may be concluded at least that this experiment showed no evidence 
of variation of the electromotive force of polarisation with the difference 
of potential of the electrodes. 
2. Wiedeburg’s Formula for the Variation of Polarisation with 
Time during the Flow of the Current. 
Wiedeburg,* making simple assumptions as to the way in which the 
polarisation itself occurs, and as to the occlusion and diffusion which go on 
at the same time, has developed the formula: 
_ 1 - e~ yt 
J a - be~ yt 
for the polarisation, as a function of the time, during the passage of the 
polarising current, the circuit being of constant resistance and containing a 
cell of constant electromotive force, and the electrodes being of ecpial area. 
The a, b, and y in his formula are functions of one or more of the electro- 
motive force of the galvanic cell, the resistance of the circuit, etc., and of 
the initial conditions. 
To test this formula, I passed a current from a secondary cell through the 
same circuit as in the former case ; but instead of observing all four electrodes 
I watched only one, thus being able to keep the electrometer permanently 
attached to one platinum electrode and the corresponding calomel electrode. 
Consequently the deflections were much more accurately determined. 
Three of the series of observations thus made are given graphically in 
fig. 2. It will be seen that, even with an ordinary watch, the curves 
can be followed quite a considerable distance from the bend towards the 
origin by means of the Dolezalek electrometer. 
Wiedeburg tested his formula by the aid of the law, obtained empiri- 
cally by Bouty,f that the polarisation within very short intervals of time 
from the starting of the polarising current is given by the formula : 
at 
T 
where a and (3 are constants. 
* IVied . Ann ., li. 302, 1894. 
t G . R , cxvi. 628, 1893. 
