Researches on the molecular asymmetry of natural organic products (1860).

  • Pasteur, Louis, 1822-1895.
Date:
1905
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Credit: Researches on the molecular asymmetry of natural organic products (1860). Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    be assumed that the two differently coloured rays from the incident beam of white light are polarised in different planes on leaving the plate of quartz. Arago did not continue the study of these striking phenomena, and Biot, from 1813 onward, enunciated the physical laws governing them, carefully isolating them from all those with which they seemed to have been confused by Arago. Biot produced the polarised ray with light from each of the parts of the simple spectrum separately, and found that the original plane of polarisation was deviated through an angle proportional to the thickness of the plate; that this angle was different for each of the primary colours and increased with the refrangibility according to a fixed law. He also made the exceedingly curious observa- tion that of plates obtained from different crystals of quartz, some deviated the plane of polarisation to the right and others to the left, in each case according to the same laws. But Biot's most remarkable discovery in connection with this kind of phenomena is undoubtedly that of the deviation of the plane of polarisation produced by a number of natural organic products, such as oil of turpentine, solutions of sugar, of camphor, and of tartaric acid. The first mention of this fact occurs in the bulletin of the Societe Philomatique for December 1815. To understand this Lecture it is essential particularly to recollect the existence of this rotative property in tartaric acid, and its absence in paratartaric or racemic acid, an acid isomeric with tartaric acid. There exist, therefore, organic products which, when themselves liquid, or when dissolved in water, possess the rotative property, and resemble in this respect solid crystallised quartz. But it must be noted here that the analogy with quartz is superficial only. The deviation of