Thermal expansions of sixteen zinc single crystals have been measured in the temperature range, 25° to 100°C by an optical lever method. The dependence on orientation followed the expected cosine-squared symmetry relation. The principal coefficients, parallel and perpendicular to the hexagonal axis, were found to be: ${\alpha }_0=64.2\mathrm{}$ and ${\alpha }_{90}14.1\times {10}^{-6\mathrm{}}$ per degree C. Slight differences in purity did not affect the values of the expansion coefficients, nor did optically mosaic crystals differ from true singles. Permanent strain lowered the coefficients slightly.

• Received 24 February 1942

DOI:https://doi.org/10.1103/PhysRev.61.653