Isotherms of equivalent conductivity, activation energy of ionic migration and molar volume show only slight deviations from linearity for the systems NaN02 + NaN03 CdI2 + CdC12 and KI + NaCl in which the phase diagrams indicate that no intermediate phases occur in the solid state. Similar effects are observed for the system KN03 + KBr for which the phase diagram indicates the formation of incongruently melting KNO3 . KBr.Hence, in all four systems, the molten mixtures do not exhibit any appreciable increase of covalent character compared with the individual molten constituents.