On the electrostatic interaction across a salt solution between two bodies bearing unequal charges.

We consider two parallel planar charged surfaces bearing unequal surface charge densities interacting across a region in ionic equilibrium with a neutral salt solution. Combining rules are derived appropriate for interactions across distances of separation greater than the characteristic Debye length. When ions are excluded from the regions behind the interacting surfaces there can be repulsion between charged surfaces of opposite sign; but surfaces bearing charges of the same sign never attract one another. Also, surfaces bearing electrostatic potential of like sign can attract.