Features of homogeneous and heterogeneous Lux acid-base reactions Me2+ + O2- in alkaline halide melts are analysed using logarithmic diagrams: E-p Theta (p Theta = -log/(0)(Me2+) - mO(2-)0/) and E-pm(O2-)(0) where m is molarity. This allows division into regions of unsaturated and saturated solutions for the estimation of dissociation constants and solubility products of oxides. Cases of incomplete dissociation of oxide, levelling acidic properties of cations and the precipitation of oxide formed by the most acidic constituent cations of melts are considered.