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The stress‐optic coefficients or Brewster constants C'λ001 and C'λ110 of mixed crystals of KClKBr are measured in the wavelength range 3000 to 6200 Å using a modified Filon method. The percentage dispersion of C'λ001 and C'λ110 increases with increasing KBr content, reaches a maximum around equimolar concentration, and finally falls off to the value of pure KBr. Also, at a given wavelength, the C'λ vary nonlinearly with the composition of the mixture, the deviation being larger in the ultraviolet.

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Following the theoretical approach of Bansigir and Iyengar, the expression for P44 for the crystals of CsC1 type is developed. Polarizabilities of some ions at 5890 A are evaluated with experimental values ofp44 and are found to be in good agreement with reported values. Polarizabilities of the ions in CsI at different wavelengths in the range 3000 to 5890 A are also evaluated.The results are given for the calculation of the profile function of the scattering curve and the calculated primary extinction factor for a crystal in the form of a square-section parallelepiped as a function of its size 7:, expressed in extinction length units. The calculations are based on the equations of the dynamical theory of diffraction. Asymmetry of the scattering curve and a shift of its principal maximum to larger angles, with r and the Bragg angle increasing, are found. Approximate expressions for calculating the primary extinction factor as a function of r are given.