The thermal expansions of certain crystals with layer lattices

Abstract

The method for the determination of linear expansion coefficients which are applicable to anisotropic substances fall into two main groups, the optical and the X-ray methods. Of these the former have hitherto been much more extensively used. They consist essentially in measuring the change in distance between two plane surfaces of the crystal. Thus, Fizeau investigated a large number of crystals by an interferometer method, and much of the subsequent work on single crystals has been done by modification of this method. An optical lever method was applied by Roberts to the measurement of the expansion of single crystals has been done by modifications of the subsequent work on single crystals has been done by modifications of this method. An optical lever method was applied by Robert to the measurement of the expansion of single crystals of bismuth. The X-ray method determines directly the change in lattice spacing of the crystal. It was first employed by Backhurst, who used an ionization spectrometer to find the expansion of diamond, and that of graphite perpendicular to its cleavage plane. The same method has been used by Goetz and Hergenrother for the expansion of bismuth crystals. Becker employed a photographic method, calculating the expansion from the shift of the lines on a powder photograph. He investigated several cubic and uniaxial substances up to temperatures of about 850­° C. A similar method was used by McLennan and Monkman to examine zinc and cadmium at liquid air and room temperature, and by Müller to find the expansion of long-chain paraffins up to their melting point.