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VIII. Bakerian Lecture. — Optical Rotatory Dispersion.—Part IT. Tartaric 
Acid and the Tartrates. 
By Thomas Martin Lowry, F.R.S., and Percy Corlett Austin. 
Lecture delivered June 2, 1921—MS. received July 18, 1921. 
Contents. 
Page 
1. Optical Rotatory Power of Tartaric Acid and the Tartrates.249 
2. Rotatory Dispersion in Quartz and in Tartaric Acid.253 
3. The Origin of Anomalous Rotatory Dispersion.258 
4. Experimental Methods.265 
5. Specific Rotatory Power of Tartaric Acid for Light of Different Wave-lengths.266 
6. Rotatory Dispersion in Aqueous Solutions of Tartaric Acid.271 
7. Tartrates of the Alkali-Metals.274 
8. Negative Rotations in Concentrated Solutions of d-Tartaric Acid and its Salts.280 
9. Tartar Emetic.284 
10. Compounds of Arsenic and Bismuth.285 
11. Boro-tartaric Acid.286 
12. Summary.287 
1. Optical Rotatory Power op Tartaric Acid and the Tartrates. 
The optical rotatory power of tartaric acid was discovered in 1832 by Biot ( £ Mem. 
Acad. Sci.,’ Paris, 1835, vol. 13, Table G, p. 168 ; paper read November 5, 1832), who 
devoted one of Ms longest memoirs ( £ Mem. 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 ” ( £ Mem. 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 
VOL. CCXXIT.-A 601. 2 N [Published April 11, 1922. 
