The electrical conductivity was measured from the melting point to 1280 K for molten 0.7 LiF-0.3 KBr (its composition corresponds to the top of the miscibility gap) containing (2.3, 4.4, 6.5, 8.8, and 11.2) mol % KCl or (1.2, 2.5, 5.5, and 10.2) mol % CsCl to establish the influence of this solute on the stability of the two-phase system. These results indicate that the temperature dependences of the conductivity along the saturation lines for all of the mixtures studied herein are similar to one another. Hence, this demonstrates that small additions of KCl and CsCl to the dissolving melt of LiF-KBr do not exert a substantial influence on its type of criticality. In the vicinity of the critical point, the temperature dependence on conductivity differences for melts is investigated and is described by the equation Delta kappa approximate to (T-c - T)(k), where k is the critical exponent (k = 0.98). The critical temperature changes as a function of the mixture composition and depends on the ion size of the salt added. The critical temperature increases continuously with the addition of CsCl to molten LiF-KBr, whereas it decreases as the fraction as KCl is added. This circumstance must occur during the organization process, as salts accumulate in the dissolving molten mixture, and they prevent the confluence of the phases at a given operating temperature. To interpret the experimental results, the charged hard sphere model for ionic melts in the Debye-Hiickel approximation was used with an account of the excluded volume.