These chemists isolated two compounds which they named alizarin and purpurin.
In the roots three coloring matters are obtained: alizarin and purpurin, which are both red, and xanthin, which is yellow.
The only dyes in this group which appear somewhat behind the rest in point of fastness are purpurin and alizarin maroon.
Madder contains two closely allied colouring matters, namely, alizarin and purpurin.
The purpurin, like some of the murices, when mutilated, exude a reddish-purple fluid.
The same operations have also another end--to transform the purpurin into its hydrate, which is brighter and more solid.
We may remark that purpurin has not been obtained by direct synthesis.
purpurin pur·pu·rin (pûr'pyə-rĭn')
A reddish crystalline compound used as a biological stain.