Ultrasonic velocity and absorption have been measured in molten (Li,Ag)NO 3 , (Na,Ag)NO 3 , (K ,Ag)NO 3 , (Cs,Ag)NO 3 , (Li,Rb)NO 3 , and (Na ,Rb)NO 3 , and (Na,Rb)NO 3 as functions of composition in the temperature range 230 to 300 °C. An improved pulse transmission device was applied. The obtained accuracy was 2‰o for the velocity and 2-4% for the absorption data. The ultrasonic velocity and absorption coefficient (25 MHz) were found to depend linearly on temperature. The dependence of the velocity on the mole fraction could be represented by a cubic polynomial. For the absorption values (referred to the square of frequency) a reasonable general dependence on composition could not be given. The adiabatic compressibility of all mixtures has been calculated from the measured sound velocity. The ratio bulk/shear viscosity and the bulk viscosity itself follow from the measured absorption values together with the velocity values. The conclusion from these data is that ultrasonic absorption in the six investigated systems is governed by the bulk viscosity and that structural rearrangements rather than structural relaxation of the molecules, are the reason for high bulk viscosities in ionic melts.