VIII. Bakerian lecture.–Optical rotatory dispersion.–Part II. Tartaric acid and the tartrates

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Abstract
The optical rotatory power of tartaric acid was discovered in 1832 by Biot (‘Mém. Acad. Sci.,’ Paris, 1835, vol. 13, Table G, p. 168; paper read November 5, 1832), who devoted one of his longest memoirs (‘Mém. Acad. Sci.,’ 1838, vol. 15, pp. 93-279; paper read January 11, 1836) to a detailed account of its properties when mixed with water, with alcohol and with wood-spirit. Biot found that tartaric acid, when “dissolved in different fluid media, exercises on the planes of polarisation of light a special power, which distinguishes it from all the other substances hitherto studied.” These had agreed with quartz in obeying, at least approximately, Biot’s Law, according to which “the rotation of the different simple rays is reciprocal to the square of their wave-lengths” ('Mém. Acad. Sci.,’ 1817, vol. 2, pp. 49, 57 and 135; paper read September 22, 1818). This agreement had been verified in the case of turpentine, alone and mixed with ether, and of cane-sugar dissolved in water (i.) by comparing the tints with those produced by equivalent plates of quartz, and (ii.) by eliminating the effects of rotatory polarisation with the help of a quartz plate of opposite sign acting as a compensator (‘Mém. Acad. Sci.,’ 1817, vol. 2, pp. 103-114). When tartaric acid was compared with quartz,however, no such parallelism was observed, the rotations for the chief colours being as follows :—

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