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MESSRS. THOMAS MARTIN LOWRY AND PERCY CORLETT AUSTIN 
used for tartaric acid. Potassium and ammonium tartrates and Rochelle salt give 
similar dispersion curves, but deviate more widely from Biot’s law. 
4. A number of solutions which give negative rotations have been examined for a 
range of wave-lengths, and the corresponding dispersion-curves have been plotted. 
5. In presence of an excess of boric acid the rotatory dispersion of tartaric acid is 
no longer complex but simple, and can be expressed over a wide range of wave-lengths 
by the equation 
h 
CL - -r, • 
x 2 -\ 0 a 
Tartar emetic also gives a simple dispersion curve. 
6. When tartar emetic is dissolved in an excess of potassium hydroxide, or when a 
corresponding solution is prepared with bismuth in place of antimony, strongly kevo- 
rotatory solutions are obtained, but these are again characterised by a simple rotatory 
dispersion. 
7. It is suggested that d-tartaric acid, like nitro-camphor, exists in solution in two 
labile isomeric forms, and that the anomalous dispersion of the acid and of many of its 
derivatives is due to the presence of two isomeric compounds of opposite rotatory power 
and unequal dispersion. Derivatives which give simple rotatory dispersion are assumed 
(like the salts of nitro-camphor) to be fixed in one of these forms. 
List of Tables. 
I. Specific and Molecular Rotatory Power of Tartaric Acid in Aqueous Solutions at 20° C. 
II. Specific Rotatory Power of Tartaric Acid, Observed and Calculated. Linear and Parabolic 
Laws. 
III. Rotatory Dispersion of Tartaric Acid in Aqueous Solutions at 20° C. 
IV. Molecular Rotatory Power of Tartaric Acid in Aqueous Solutions (Observed and Calculated). 
V. Rotatory Dispersion in"Aqueous Solutions of Tartaric Acid at 20° C. Constants and Anomalies. 
VI. Rotatory Dispersion of Sodium Tartrate in Aqueous Solution at 20° C. 
VII. Rotatory Dispersion of Potassium Tartrate in Aqueous Solution at 20° C. 
VIII. Rotatory Dispersion of Rochelle Salt in Aqueous Solution at 20° C. 
IX. Rotatory Dispersion of Ammonium Tartrate in Aqueous Solution at 20° C. 
X. Molecular Rotatory Power of Tartrates in Aqueous Solution at 20° C. 
XI. Dispersion-constants and Dispersion Ratios of Tartrates in Aqueous Solution at 20° C. 
XII. Dispersion-constants and Dispersion Ratios of other Substances. 
XIII. Constants of Drude’s Equation for Tartrates in Aqueous Solution at 20° C. 
XIV. Rotatory Dispersion of Potassium and Sodium Tartrates at 20° C. in presence of an excess of 
Alkali. 
XV. Rotatory Dispersion of Potassium and Sodium Tartrates at 20° C. in presence of Alkali. 
XVI. Rotatory Dispersion of Tartar Emetic in Aqueous Solution at 20° C. 
XVII. Rotatory Dispersion of Tartar Emetic in presence of excess of Alkali at 20° C. 
XVIII. Rotatory Dispersion of Potassium and Hydrogen Arsenyl Tartrates at 20° C. 
XIX. Rotatory Dispersion of Potassium Bismuthyl Tartrate in presence of excess of Alkali at 20 C. 
XX. Rotatory Dispersion of Boro-tartaric Acid in Aqueous Solutions at 20° C. 
