139 
Mg)” | My)? 
When ( ; u is not very small, l a will always be very 
(Mg)* ME) 
great positive. Now (M/“) can however, not be arbitrarily great, 
though (MF) can, indeed, be arbitrarily small. 
It follows from this that the very great value of the fraction 
_-— is caused by the small value of (M/”) in the case supposed 
here. 
If we now call the total concentration of the ions C, practi- 
cally M7 will be = C. 
In this case we can therefore write for (21): 
BEK u gee aes ¥ & 
A= ay ae ee (ES hr VE EN 
y,F Re v,F Ae (A 
ip 
It then follows from this equation that when the total ion con 
centration Cis constant, the potential difference in the metal will 
become more strongly negative on increase of the concentration of 
the base ion M™, in the metal and more strongly positive on 
decrease of this concentration. 
7. The metal assumes internal equilibrium. *) 
Now we shall suppose that in the electrolyte the equilibrium sets 
in between atoms, ions, and electrons, which is accompanied with 
a setting in of the internal equilibrium in the metal. If the metal 
is in internal equilibrium, its state is perfectly determined for 
definite temperature and pressure, i.e. the concentrations of the 
atoms, ions, and electrous in the metal are then under these cir- 
cumstances constant quantities. (Mx) and (Me) are, constants; hence 
in connection with (25) 
will hold for the coexisting electrolyte. 
We can also arrive at this conclusion by another way. When 
internal equilibrium prevails in the metal, the same equilibria will 
occur in the coexisting electrolyte as in the metal, viz. : 
1) The internal equilibrium may be defined as the equilibrium in a phase of 
a unary system. 
