By experimental titration measurements - which were conducted on alpha-Ca-3(PO4)(2)/H2O (1) dispersions to follow H+/OH-adsorption from aqueous solution onto the solid surface - an unexpected shape transition (S-->L, in the Giles classification) was observed in the adsorption isotherm when the solid mass concentration reached the (critical) value c(Nc)=0.54+/-0.01. This phenomenon did not occur when acid/basic aqueous solutions containing Ca2+ and PO43- ions were employed as titrants. Formulation and application of an Ising-based model suggested that solid solubility phenomena can influence the adsorption mechanism by inducing an additional (inhomogeneous) hydration pressure, which seems to be related to interfacial order perturbations produced by the surface dissolution, In the end, the predicted critical solid mass concentration was <(c(Nc))over tilde>=0.53+/-0.01 and, correspondingly, extrapolated values from the model of water correlation length were in agreement with the current literature concerning TCP (tricalcium phosphate) wettability and inhomogeneous structural forces. (C) 1997 American Institute of Physics.