Tests of the Validity of the X-Ray Crystal Method for Determining "e"

Citation

Bollman, Vernon Leroy (1936) Tests of the Validity of the X-Ray Crystal Method for Determining "e". Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/644d-vg91. https://resolver.caltech.edu/CaltechTHESIS:10162024-213147638

Abstract

To establish the validity of the x-ray crystal method for determining "e", the density of microscopic powdered calcite and the x-ray diffraction angles for several sets of planes of a sample of the same powdered calcite were measured.

The density of powdered calcite was determined pycnometrically to be

ρ = 2.71022 ± 0.00035 gms/cc

in agreement with macroscopic calcite.

X-ray diffraction rings of the Ni Kα, and Kα₂ lines for planes (330), (677), (233) and (163) (crystallographic system of axes) were observed using a Seeman-Bohlin powder camera. The observed rings all occur at diffraction angles near 90° thus affording extremely high precision in the lattice constant determinations. The parameters found for powdered calcite from these data are

C = 12.8197 ± 0.0016 A (Siegbahn Scale)

and β = 101 54' 18" ± 48".

The grating space of the cleavage planes calculated from these data is

d₁₀₀ = 3.0282 A (Siegbahn Scale of wavelengths)

in agreement with d₁₀₀ for macroscopic calcite within the experimental error of 0.05 percent.

From the known grating wavelength of Cu Kα, and the experimental data for powdered calcite the value

e = 4.799 ± 0.007 x 10^-10 e.s.u.

was obtained.

This measurement constitutes the first high precision lattice determination on calcite ever made by the powder method. It is free from the objection frequently raised in the case of determinations on large calcite crystals that the density determination may not be representative of the thin layer at the surface of a crystal involved in x-ray reflection.

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