The modified stability ratio, W', and the critical coagulation concentration, CCC, of a colloidal dispersion containing spherical particles are analyzed theoretically. We consider the case where the surface of a particle is capable of regulating its charged condition through the dissociation of functional groups, the exchange of ions with the Liquid phase, or both. An amphoteric surface is assumed for the former. The analysis leads to an approximate analytic expression for the electrical interaction energy between two particles. We show that the smaller the (pK(-) - pK(+)), K- and K+ being the dissociation constants, the greater the interaction energy. It is found that a system may have two different CCC's and two different electrolyte concentrations at which W' = 1. However, the greater the (pK(-) + pK(+)), or the greater the (pK(-) pK(+)), the less the significance of the second CCC and the electrolyte concentration at which W' = 1. The number of CCC and that of electrolyte concentration at which W' = 1 may not be the same, and we show that W' provides a more realistic description of the qualitative behavior of a colloidal dispersion than does CCC.