A uniform procedure is suggested for calculation of the pH_t value(s) separating equilibrium solid phases in pH scale, at an excess of the precipitating agent. The pH_t value, related to pairs of precipitates formed from the species   and  , fulfils the relation , where F is a constant value involving pK_so’s for solubility products (K_so’s) of these precipitates, and the equilibrium data, related to the species composing these precipitates.