Alizarin , a red colouring matter obtained from the madder root (Rubia tinctorum), in which it exists in the form of a glucoside termed Ruberythric Acid, a substance which is split up by a natural process of fermentation into Alizarin and Glucose. Alizarin, identical in chemical composition with that obtained from the madder root, is now prepared artificially from the Anthracene of coal tar. It is a red crystalline substance which is little acted on by water, but readily dissolved by benzine and ether. It acts as a weak acid, forming Alizarates with metallic bases. Is of great importance in dyeing.