What is "erythrolitmin"

Erythrolitmin \E*ryth`ro*lit"min\, n. [Gr. 'eryqro`s red + E. litmus.] (Chem.) Erythrolein. [1913 Webster] ||

n. (context chemistry English) A particular fraction of litmus.

Erythrolitmin (also called erythrolein) is the active ingredient extracted from the Litmus lichen, used in chemistry as a pH indicator. The erythrolitmin molecule is related to the orceins, and consists essentially of several phenoxazone and orcinol residues.