Abstract: The electrochemical properties of clays are discussed under four rules which arise from considerations of the bonding energy of ions associated with charged surfaces. The mean free bonding energy of a cation associated with a negatively charged surface is determined by calculation from conventional potentiometric measurements with membrane electrodes.
The first three rules are concerned with the effects of valency upon ionization. They arise directly from the method of calculating cationic mean free bonding energies, applicable to monofunctional surfaces as regards Rule 3, and to polyfunctional surfaces also as regards Rules 1 and 2.
The fourth rule (Jarusov's rule) deals with mixtures of cations on polyfunctional surfaces. It may be expressed verbally by stating that the cation with the higher mean free bonding energy preempts those positions on the surface which manifest greater mean free bonding energy.
The incidence of each rule is examined, using data from studies of cationic activities in clay systems. The factors which cause deviations from these idealized rules are discussed. Graphical data are presented for Wyoming bentonite, Arizona bentonite (montmorillonite), and Putnam clay (montmorillonite group); illite, kaolinite and attapulgite.