These isotherms were commonly divided into four regions as reported earlier. Region I was a region of low adsorption densities and sometimes referred to as the Henry’s law region. In region I the surfactants were adsorbed as monomers and did not interact with one another. The adsorption in this zone resulted primarily from electro- static forces between surfactant ions and the charged solid surface. Region II was indicated by the sharp increase in the slope of the isotherm. In the region II, the adsorption was due to the electrostatic attraction between the ions and the charged solid surface and hemimicelles association of hydrocarbon chains. For example, in case of adsorption of sodium dodecyl sulfonate on alumina, when sulfonate ions equivalent in number to the surface sites had been adsorbed, the contribution due to the electrostatic attraction disappeared, and the further increase in adsorption would be only due to the association between the hydro- carbon chains. Micelle-like aggregates were formed on the solid surface in this region. The transition from region I to region II had been given designations analogous to the critical micelle concentration (CMC), as critical admicelles concentration (CAC) or hemimicelle concentration (HMC). The differences in terminology emphasized different views of the morphology of the aggregates at