Lĭt'mus, n.

Lĭt'mus, n. [H. Ger. lackmus, L. Ger. lackmās, lackmōs, D. lakmoes, N. Lat. lacca musica, from Ger. lack, D. lak, lac, lacker, and Ger. mus, D. moes, a thick preparation of fruit, pap.] A purple dye obtained from a lichen, the archil, and from a euphorbious plant, Cryophora (Croton) tinctoria, common in the south of Europe. It turns blue with alkalies and red with acids. See ARCHIL.

Litmus paper (Chem.), unsized paper, colored with litmus, and used as a delicate test of acidity in chemical experiments.