The elastic constants of sodium chloride and rubidium chloride in the range 140-300 K

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.