The anomalous behavior of H+ in exchange reactions of soil colloids has been known for many yrs. From the postulation that H+ is adsorbed on colloids with forces other than pure electrostatic forces of ordinary strength, the authors conclude that the calculation of a dissociation constant for adsorbed H is essential. By plotting fH (adsorbed) against H (adsorbed) for a given absorbent, (where [mu] is a function of the other adsorbed ions), one can, theoretically, calculate, by means of the graph and equilibrium data, a satisfactory exchange constant for any ion pair involving H. fH (adsorbed) will vary linearly with the amt. of absorbent and this fact must be considered in the calculation of equilibrium constants. fH (adsorbed) is different from the pH of the suspension since it is independent of particle size and the kind of complementary ions.