Tests for the Validity of the X-Ray Crystal Method for DeterminingNandewith Aluminum, Silver and Quartz

Abstract

The principal objections to the x-ray crystal method of determining $N$ and $e$ are that the presence of a mosaic effect or superstructure will not affect the lattice parameters as determined by x-ray diffraction but will affect the density, and further that the x-rays measure the lattice constant of only a very superficial layer which might not be characteristic of the interior of the crystal. The crystal structure of two polycrystalline metals, silver and aluminum, and one single crystal, powdered quartz, were precisely measured with the Seeman-Bohlin spectrograph. The crystallites were small enough so that the radiation penetrated them completely and the effect of distortion of the metal crystals on the density and crystal structure was investigated. The following values of $N$ and $e$ were found where the two different values for quartz are for two different values of the molecular weight of silicon and the error is that due to internal consistency only. When the results of Tu are expressed in absolute units we find After examining these deviations from a consistent value of $N$ and $e$ and the effect of distortion on the metal crystals the authors believe that there is perhaps a small mosaic (or superstructure) effect that renders the value of $N$ and $e$ uncertain by 0.04 percent and that the best value of $e$ is perhaps slightly lower than that obtained with macroscopic calcite, say 4.801 ±0.0002 × ${10}^{-10\mathrm{}}$ e. s. u.