Crystallography: Crystals of Potassic Racemate

Abstract

ACCORDING to De la Provostaye, potassic racemate crystallises in the rhombic system; but M. des Cloiseaux, in a communication to the Annales de Chimie (xvii. 365), disputes the truth of that statement. All the crystals with which he worked (some being presented to him by Pasteur, some by Lamy and Gernez), are really derived from an oblique rhomboidal prism of 96° 56′. The base of this prism is always highly developed, and its inclined diagonal makes an angle of 92° 28′ with the anterior vertical edge. The plane of the optic axes is perpendicular to the plane of symmetry; the acute bisectrix is negative and normal to g. The revolving dispersion is considerable, as shown by the distance which separates the plane where the red axes are situated from that containing the blue. It is easily found by the polarising microscope across fine sections, normal to the acute bisectrix. The proper dispersion of the axes is rather strong, with p < v. For their apparent distance in