Now, let us consider two limits of the surface potential in order to get a few simplifications,

Case – 1: potential is very large

In this regime,

Under this condition, from Eq -10.6

(10.7)

This relation is called as the Schultz-Hardy rule.

This dependence of CCC on valence of the counter-ions is very strong, and just doubling the charge on ions (Z' = 2Z), reduces the CCC by a factor of 64. ()

Case – 2: potential is very small

Under this approximation, tanh could be approximated by

or,

Thus, which suggests that no has weaker dependence on z.