The spontaneous Brillouin scattering has been used to measure the hypersonic velocity and its temperature dependence in a temperature range covering about 100thinsp;deg;C above the melting point in the nitrates: LiNO3, NaNO3, KNO3, RbNO3, CsNO3, and AgNO3. The investigations were performed in a frequqncy interval below any relaxation frequency in LiNO3and NaNO3, while in KNO3and AgNO3the investigations were performed above some relaxation frequency according to comparisons with ultrasonic data. The measurements in CsNO3and RbNO3do not indicate any dispersion of the sonic velocity within the investigated frequency range and no conclusions can be drawn about relaxation effects as these molten alkali nitrates have neither been investigated hypersonically nor ultrasonically before. The measured hypersonic velocities were used for calculating the adiabatic and isothermal compressibilities as well as the specific heat at constant volume.
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