88 
contains no mercury, but the solution outside the boundary layer 
does, the precipitation of mercury will continue, and at last the 
mixed erystal phase s in the surface will have been entirely converted 
to the mercury / (see Fig. 2). At this moment the electrode will be 
perfectly shiny, but the deposition of mercury has not stopped yet, 
so that now a fall of the potential of the liquid mercury phase 
will occur, till the electrolyte and the liquid mercury phase are in 
equilibrium, or in other words, the process continues till practically 
all the mercury from the electrolyte has been precipitated, and the 
end-potential will have approached the mercury potential the more 
as the surface liquid phase contains less aluminium. 
In order to represent this interesting change of the electrical 
potential of aluminium through mercury in the most striking way, 
we have first modified the experiment somewhat, and then registered 
the phenomenon photographically. 
3. The modification in the experimentation consists in this that 
the aluminium electrode was directly immersed in an aqueous solution 
of an aluminium salt, to which a little of a mercury salt was added. 
This solution was brought into contact with the same solution, but 
without mercury salt by means of a siphon, and this solution also 
contained an aluminium electrode, so that the potential of the ex- 
perimental electrode was measured with respect toaluminium. Pure 
nitrogen was led through both solutions, which prevented the very 
troublesome disturbance which always accompanies attack by oxygen. 
Fig. 1 gives a clear representation of the first part of the pheno- 
_menon. The line ab indicates the position of the light image, when 
Be 
riem es ‘ sh ienie ie emelten wg a erp eni edities 
! ner SEC ' as f : I 
Ek. 
Fig. 1. 
