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]
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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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    of bestowing epithets appropriate to each variety of a species, applied the term plagihedral to the variety of quartz having the face x. Crystals in which the face x inclined to the right, are designated under the name right plagihedrals, the crystal being adjusted in a suitable manner ; and those crystals in which the face x inclined in an opposite direction are termed left plagihe- drals. Nothing is more variable than this character. Here it ex- ists ; there it is absent. Upon the same crystal there are angles which bear the face x ; others which should have it, have it not. Sometimes we find plagihedral faces to the right and to the left. Nevertheless, all persons versed in a knowledge of crystals, ad- mit that there is in quartz a true hemihedrity in two opposite directions. Here is placed a very ingenious approximation due to Sir John Herschell, communicated to the Royal Society of London, in 1820. M. Biot, as I previously said, made the remarkable observa- tion, that among the specimens of quartz, some deviated in the direction of the plane of polarized light, and others in an opposite direction, to the right and to the left. This stated, John Herschell associated the crystallographic observation of Haiiy with the physical remark due to M. Biot. Experiment confirmed the idea of a relation, in fact, between the right and left plagihedrals and the right and left optical deviations. Specimens of quartz which bear in one direction the face x, deviate the plane of polarized light in the same direction. Such is an exposition of the principal facts which have pre- ceded the researches, an abridged history of which I have to relate. III. When I began to devote myself to particular pursuits I sought to fortify myself in the study of crystals, anticipating that I would derive assistance from it in my chemical researches. The most simple means, it seemed to me, was to take a somewhat extensive work upon crystalline forms, to repeat all the measure- ments and to compare my determinations with those of the author. In 1841, M. de la Provostaye, whose exactness is well