( 561 ) 
these cases some mercury is solved and a saturated though very 
diluted solution of Hg, SO, or Hg, Clo!) is formed. 
The mercury and the solution assume 
therefore a different potential. The dif- 
ference between those potentials I call 
„natural difference of potential”. The con- 
dt 
centration of the solved Hgs-ions being 
greater than that, at which the Hg-electrode 
and these ions are in equilibrium, some 
aaa 
Ki Hgs-ions are deposited on the mercury, 
where they ‘aie discharged immediately. So at the separating surface 
between the mercury and the solution is established a so called electric 
double-layer: on the side of the mercury + electrons, on the side 
of the solution — ions SO, or Cl. The thus established difference of 
potential be V;—V,;=Apo. (I always indicate the solution by means 
of the index 2). In the normal case this quantity is negative. 
We know however, that the absolute value of this difference of 
a 
potential will decrease, when the concentration of the Hes ious in 
the solution decreases. When we extend the dilution beyond a 
certain point, the difference reverses its sign, the potential of the 
mercury becoming —, that of the solution +, so the electric be- 
haviour of mercury becomes comparable to that of zinc. 
How can this dilution at one of the electrodes be brought about? 
To that purpose we apply an electromotive force ZE in a manner 
as is indicated by the figure. In consequenee of the transport of 
++ ; 
ions, the concentration of the Hg -ions in the solution near the 
large mercury surface will become greater, that le de small 
surface will decrease. At this latter surface namely, ie (and ee K) 
will be continually deposited in consequence of the transport of 
SO, or Cl towards the large surface; but when the current of the 
inserted cell has only passed for a very short time, the concentration 
os ; tee 
of the Hgz-ions near the large surface will practically not have 
varied, near the small surface however it will have varied conside- 
rably in consequence of the much greater density of the current. 
+ 
1) Not HgCl. The mercuro-ion being proved to be ta ga and not Hg. (See eg 
Oee, Zeitschr, f, Ph, Ch, 27, 298 (1898). 
