The temperature dependences from 4·2 to 300 K of the seven adiabatic elastic constants of CaWO4 have been determined by measurements of ultrasound wave velocities using the `sing-around' and pulse superposition methods. The adiabatic elastic constants have been calculated from the measured ultrasound wave velocities by a perturbation method using just seven of the eleven measured velocities and by an iterative method using all the measured velocities; agreement has been found between the two sets of values. The complementary data on the thermal expansion and heat capacity at constant pressure of CaWO4 have been used with the present results to find the isothermal elastic constants, the heat capacity at constant volume, the Grüneisen parameters, and the Debye characteristic temperature at 0 K. The Debye characteristic temperature has been found from the heat capacity at constant volume from 10 to 300 K after subtraction of the Einstein heat capacity terms from the total heat capacity.

Measurements of the adiabatic elastic constants of NaCl from 190 to 300 K and of RbCl from 140 to 300 K have been made using the `sing-around' system to an absolute accuracy of ±0·2% and with a relative accuracy of ±0·05%. The elastic constants of NaCl agree with other recent measurements. The measurements of the elastic constants of RbCl agree with other work for C 11 and C 44 but the variation of C 12 with temperature disagrees with the other measurements. The decrease in C 12 of RbCl with decreasing temperature is in accordance with the variation of C 12 in other alkali chlorides. The reasons for the disagreement of the variation of C 12 are examined and it is shown that the observed decrease is real.

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