The Imperfect Crystallisation of Common Things¹

Abstract

MANY things consist of, or contain, agglomerations of small crystals which are plain to the eye or may be made evident by the use of the microscope. Many more are only discovered to be of similar composition when they are examined with the aid of X-rays, as for example, fats, cotton and silk. In some cases the small crystals are in complete disorder. In others there is a partial arrangement; some one odirection related similarly to each crystal has a tendency to orient itself more or less in a certain direction related to the body of which the crystals form part. When this happens there must necessarily be a cause for it. The body may have been subjected to strain or mechanical treatment of some sort, as when a metal sheet is hammered or rolled, or when a metal wire is drawn. Or again the body may have been formed under conditions which favour orientation, as when a substance is deposited electrolytically. Yet another case of great interest is that of animal or vegetable structure; the general orientation of the crystallites in cotton, silk, animal scales and spines, teeth and the like, has features which are clearly associated with growth.²