The ultrasonic velocities of a molten stratifying mixture composed of 0.5 AgI and 0.5 NaCl (the composition corresponding to the top of the miscibility gap) were measured along the saturation line for a wide temperature range via the pulse method to establish the characteristics of mixing salts with different chemical bonds. We show that the difference, Delta u, between the magnitudes of the sound velocities for the coexisting phases decreases with increasing temperature and becomes zero at 1064 K. This temperature corresponds to the critical phase transition point, T-c. The temperature dependence of the sound velocity difference, Delta u, is described by the equation Delta u approximate to (T-c - T)(Theta), where Theta = 0.896, which is less than that found for alkali halide melts (Theta = 1.02), in which long-range Coulomb forces between ions prevail. The results are discussed in terms of the peculiarity of the chemical bond in silver iodide. (c) 2013 Elsevier Ltd. All rights reserved.