On the Experimental Evidence of the Mosaic Structure of Bi-Single Crystals.

It is known that the description of the structure of a normal crystal as given by the theory of the atomic and molecular lattices is not complete without taking into account a certain kind of irregularities, the presence of which is dependent on the imperfection of the crystal. Thus the conception of the mosaic crystal rose, first given by Ewald and Smekal and others. In two recent papers, ZwickyL2 gave theoretical reasons for the assumption that the mosaic structure in a crystal is a regular one, its period depending on the character of the substance and the lattice. Thus, he obtains the aspect that a crystal has a definite structure-a kind of a secondary lattice-superposed to the molecular or atomic arrangement in the primary lattice. The experimental facts previously known which can be interpreted in favor of this theory are not very many, and of a more or less indirect kind and mostly taken from non-metallic substances. There are only two phenomena known which may count as visible evidences of the mosaic structure. One is observed by Wood'0 on potassium chlorate crystals, explained by him as a periodical occurrence of twinning, the other concerns ultra-microscopic observations by Traubes of the "submicronic" state of crystals of very complex molecules during the act of solution into an almost saturated solvent. The fact that a crystal dissolves first into a large number of particles being within the visibility of an ultra-microscope before being dissolved in molecular dispersions, may be due to the presence of a mosaic block-structure. The following is a partial report of observations of two different kinds, one dealing with microscopic measurements on Bi single-crystals, the other concerning a study of the conditions in which the orientation and perfection of a growing crystal can be predetermined by inoculation with a seed-crystal. Inasmuch as the ways in which these measurements were obtained differ considerably, the xeports shall be published separately. The present paper deals with the microscopic investigation.