Researches on the molecular dissymmetry of natural organic products : presented to the Chemical Society of Paris, January 20 and February 3, 1860 / by L. Pasteur ; translated from "Leçons de chimie professées en 1860" by W.S.W. Ruschenberger.

  • Pasteur, Louis, 1822-1895.
Date:
[1862]
Catalogue details

Licence: Public Domain Mark

Credit: Researches on the molecular dissymmetry of natural organic products : presented to the Chemical Society of Paris, January 20 and February 3, 1860 / by L. Pasteur ; translated from "Leçons de chimie professées en 1860" by W.S.W. Ruschenberger. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    constitution. In quartz the phenomenon results from the mode of aggregation of the crystalline particles. These are the physical precedents, if I may so express myself, of the researches with which I propose to entertain you. Here are their mineralogical precedents. II. Hemihedrity* is assuredly, among the peculiarities of crys- tallization, the one which is the easiest to seize in its external manifestation : consider, for example, a species of mineral crystal- lizing in the cubic form. This form, as all know, may surround different kinds of determinate forms by the law of symmetry, a law so natural that it is, so to speak, a physical axiom. The expression of this law is, that a form being given, all others compatible with it may be obtained by a contrivance which would consist in modifying, truncating, as Rome* de Lisle said, at the same time and in the same manner the identical parts. The identical edges are those which are at the intersection of faces respectively identical, mutually cutting at the same angle; and solid identical angles, those which are formed by dihedral angles respectively equal and similarly placed. For example, in the cube there is bat one kind of solid angles and one kind of edge3. Let one of the solid angles be truncated by a face equally in- clined to the three faces of the solid angle, and the seven other angles should be, at the same time, by a face of the same na- ture. This is observed in alum, in galena, and generally in all cubic species. Let us consider a right prism with a rhomb base. The eight edges of the bases are identical. If one is truncated, the seven others should be, and in the same manner. The four vertical edges are of another kind. Generally they will not be truncat- ed at the same time as tthose of the bases, and if they are, it will be differently. These examples alone will suffice to explain the law of symme- try and its application. Nothing is more simple than to have a clear idea of hemi- hedrity. Experiment has long since shown, Haiiy was ac- quainted with the most celebrated instances, that, in a crystal, * Emisus, half ; edron side.