  Very recent measurements of the electrical conductivity of solid systems AgX
- CdX$_2$ (where X$\equiv$Cl,Br) that form large areas of solid solutions, have
shown that maximum conductivity occurs for a concentration around 20 mol\% of
the cadmium halide. Here, we suggest a quantitative explanation of this
phenomenon based on a model that was suggested (J. Appl. Phys. 103, 083552,
(2008)) for estimating the compressibility of multiphased mixed crystals. In
addition, explicit conditions are obtained which predict when such a
conductivity maximum is expected to occur.
