10. Litmus. 10a. Orchil. 10b. Cudbear.
10. LITMUS.—A fermented coloring extract from various species of lichens (e.g., Lecanora tartarea), other varieties of which also yield the dyes orchil and cudbear. Habitat: Northern Europe and African coast, and adjacent islands. Litmus is in about ½ to 1 inch rectangular cakes, blue, light, friable, finely granular. Unlike most vegetable dyes, it is not turned green by alkalies. It is turned red by acids, for which it is used as a test in the form of infusion (tincture), or litmus paper, made by dipping unsized paper in the strong infusion.
- 10 a. Orchil is a purplish-red, thickish liquid, with an ammoniacal odor.
- 10 b. Cudbear (Persio, N.F.) is a purplish-red powder, sometimes used to color preparations.