(24) 
according to equation (12), from which follows that in this case the 
metal ions in the metal are in equilibrium with those in the solution, 
no potential difference existing between metal and solution. This 
equilibrium is therefore an equilibrium of saturation and the concen- 
tration of the metal ions in the solutions will therefore be a concen- 
tration of saturation. Therefore the product A77 (Ms) represents 
the saturation concentration of the metal ions at definite temperature 
and pressure. 
That under the said circumstances this product is really a con- 
stant follows from this that not only A’y;, but also (Ms) is a 
constant quantity in case of unary behaviour of a metal at the 
same temperature and pressure. 
If we now represent this concentration of saturation of the metal 
ions or in other words the metal ion solubility by Ayy:, then 
KES TRICE) eG eee eh  {(2453) 
and then equation (17a) becomes: 
RT Ky 
2h, = 
Ff (M1) 
This is NerNsT's equation, in which instead of the Lösungstension 
P, the metal ion solubility Ayy,;- occurs. 
On purpose we have followed this course in order to show that 
the well known relation for the potential difference is found when 
L (26) 
we only take the metal ions into account, whereas the role of the 
electrons is at least equally important. 
Accordingly we get a much deeper insight when we also take 
the electrons into account. 
For this we must also make use of equation (18a). In this equa- 
tion first a simplification can, however, be applied. Just as we have 
been able to demonstrate just now that the product A’ (Ms) 
represents the concentration of saturation of the metal ions, we can 
show in entirely the same way that the product A’;(%,) indicates 
the concentration of saturation of the electrons. 
If for this quantity we again introduce a simple symbol e.g. 
Ks (0) = Ke. se ee ee (27) 
equation (18a) is simplified to: 
FT “on 
We see from this that for a base metal (@/) is greater than AK. 
It is here the place to draw attention to an exceedingly remark- 
96 
Proceedings Royal Acad. Amsterdam, Vol. XVIII. 
