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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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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    known, published a handsome work on the crystalline forms of tartaric acid, paratartaric acid, and their saline combinations. I took hold of this memoir. I crystallized tartaric acid and its salts, and I studied the forms of their crystals. But, in my progress, I perceived that a very interesting fact had escaped the teamed physicist. All the tartrates I studied afforded de- cided indications of hemihedric faces. This particularity of form in the tartrates was not very evi- dent. This may be readily conceived, since it had not yet been observed. But when, in one species, it appeared in doubtful characters, I always succeeded in rendering it more manifest, by recommencing the crystallization and slightly modifying the conditions. Sometimes the crystals bore all the faces re- quired by the law of symmetry, but hemihedrity had credit for an unequal development of one half the faces. This was seen for example in the ordinary tartar emetic. It may be said that what adds to the difficulty in recognising hemihedrity, are the frequent irregularities of crystals which are never easily de- veloped. Hence their results, deformities, arrests of develop- ment in this or that direction, faces accidentally suppressed, kc. Except under circumstances almost exceptional, the ascer- taining of hemihedrity, especially in crystals of the laboratory, requires a very attentive study. Besides that, although hemi- hedrity may be possible in a form, although it may be a function of the internal structure of the body, it may not be externally manifest, any more than is found upon every crystal of the cubic species all the forms compatible with the cube. But be that as it may, I repeat, I found hemihedric tartrates. This observation would have been barren, probably, without the following :— Let a, 6, e, be the parameters of the crystalline form of any tartrate; a, ,?, y, be the angles of the crystallographic axes. These are ordinarily right angles or a little oblique. Besides, the relation of the two parameters, such as a and b, is nearly the same in the different tartrates, whatever may be their com- position, the quantity of their water of crystallization, the nature of their bases ; y, alone differs sensibly. There is a kind of semi-isomorphism among all the tartrates. One might say that the tartaric group prevails and impresses a stamp ofresem-