Thermal expansion of sodium nitrate (I)

The thermal expansion coefficients, α, of sodium nitrate have been measured along the trigonal axis of the crystal (α∥) and in a direction perpendicular to this axis (α⊥) by means of a Fizeau interferometer in the temperature range 77-300 K. α∥ is large, while α⊥ is relatively small, showing a large anisotropy. The results have been compared with earlier observations and the possible origin of large anisotropy has been suggested. Some details are given of the cryostat used for this experiment. © 1986.