LITMUS

litmus. Litmus, n. a blue pigment used in painting

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Lit″mus (?), n. [[D. lakmoes; lak lacker + moes a thick preparation of fruit, pap, prob. akin to E. meat: cf. G. lackmus. See Lac a resinous substance.]] (Chem.) A dyestuff extracted from certain lichens (Roccella tinctoria, Lecanora tartarea, etc.), as a blue amorphous mass which consists of a compound of the alkaline carbonates with certain coloring matters related to orcin and orcein. ☞ Litmus is used as a dye, and being turned red by acids and restored to its blue color by alkalies, is a common indicator or test for acidity and alkalinity. Litmus paper (Chem.), unsized paper saturated with blue or red litmus, — used in testing for acids or alkalies.