The principal adiabatic and isothermal elastic moduli and elastic constants of NaCl, KCl and MgO have been measured over the temperature ranges 80°K to 270°K (Balamuth and Rose) and 270°K to 480°K for NaCl; 80°K to 280°K for KCl; and 80°K to 560°K for MgO. The Debye characteristic temperatures of these substances at 80°K, calculated from the adiabatic elastic constants, are 320°K, 246°K and 946°K, respectively. The variation of the isothermal $c_{11}$ and $c_{44}$ with temperature is described very accurately by the formula: ${\left(c_{\mathrm{ii}}\right)}_u={\left(c_{\mathrm{ii}}\right)}_0\exp (-A_{\mathrm{ii}}{F}_{\mathrm{ii}}\mathrm{}(u\left)\right)$, where $u=\left(\frac{T}{\theta }\right)$, $T$ is the absolute temperature and $\theta$ the characteristic temperature, ${\left(c_{\mathrm{ii}}\right)}_0$ denotes the value at absolute zero, $A_{\mathrm{ii}}$ is a constant of the material, and $F_{\mathrm{ii}}\mathrm{}\left(u\right)\mathrm{}$ is a function of $u$ which assumes the value unity when $u=1\mathrm{}$, and which is the same for all three substances. Experimental values of $F_{11}\mathrm{}\left(u\right)\mathrm{}$ and $F_{44}\mathrm{}\left(u\right)\mathrm{}$ are given for values of $u$ between 0.1 and 1.5. The isothermal $c_{12}$ does not vary with temperature, over the specified ranges, by more than the error of measurement.

• Received 29 June 1936

DOI:https://doi.org/10.1103/PhysRev.50.449