Figure S4 shows the composition dependence of the (a) mass density, (b) glass transition temperature, and (c) dissolution rate (DR) found in the work of Mosner et al. for the (Nb2O5)_x(Na2O)_{0.4}(P2O5)_{0.6-x} glass series. In (b) and (c), the curves show the effect on model I of changing the paramater kappa from 2.75 to 4.