The purpose of these preparations is to make it possible, in all cases where laboratory crystals are obtained from supersaturated solutions, to carry out an optical study in parallel with the goniometric one with the most accurate possible orientation of the axes of the optical ellipsoid. Until recent years, I used homemade preparations, composing them from scraps of cover slips, cut and glued onto a slide so as to create the required wedge space for crystallization. Now I have settled on a relatively simple and very convenient type for research, which is quite clear from the attached plan and section of a microscopic specimen (see article).
