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You will probably recollect that I sent you some time since a small portion of an alkaloid, which at that time was called quinidin in Germany, but it has since been distinguished from it and named cinchonidin. You then examined it for epipolism or fluorescence, and you pronounced the opinion that it possessed this property only in a minor degree, and you imagined that this arose from the presence of a small per-centage ofα -quinine. I have since obtained, through the kindness of Mr. J. E. Howard, specimens of the perfectly pure alkaloids quinidin and cinchonidin, and find that quinidin, which I can now identify as theβ -quinine of Von Heijningen, possesses the phenomenon of fluorescence or epipolic dispersion as powerfully asα -quinine; whilst cinchonidin, if perfectly pure, is devoid of it altogether; and recent experiments have shown me that a small per-centage of quinidin was the cause of the epipolic dispersion found by you in the specimen of cinchonidin sent by me.

proceedings of the royal society of london

II. On the optical characters of certain alkaloids associated with quinine, and of the sulphates of their iodo-compounds. By William Bird Herapath, M. D., in a letter to Professor Stokes, Sec. R. S. Communicated by Professor Stokes