Chemical science. Colouring Matters of Madder.

The Year-Book of Facts in Science and Art
Exhibiting the Most Important discoveries and Improvements of the past year,
in mechanics and the useful arts; natural philosophy; electricity; chemistry; zoology and biology; geology and geography; meteorology and astronomy.
By John Timbs,
editor of "the Arcana of Science and Art."
London:
David Bogue, Fleet Street,
MDCCCXLIX (1849)Mr. J. Higgin, in a paper read to the British Association, after describing the three Colouring Matters of Madder-xanthin, rubiacin, and alizarin, and the means he employs to separate them in a pure form, - proceeds to show that the opinion usually entertained — that it is the alizarin only which is the valuable part of madder — is incorrect; and several experiments were adduced to prove that in proper circumstances, such as obtain in ordinary madder dyeing, the xanthin and rubiacin contribute very materially to the effect. They are shown not to act directly, but become changed into alizarin, which then combines with the mordants. This change is considered by the author to be induced by a peculiar azotized ferment found in madder, whereby xanthin becomes rubiacin, and this latter alizarin; and the opinion is held out that all colouring matter in madder is derived primarily from xanthin.