Lit·mus n. 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.
Note: ☞ 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.
Roc·cel·lic a. Chem. Pertaining to, or designating, a dibasic acid of the oxalic series found in archil (Roccella tinctoria, etc.), and other lichens, and extracted as a white crystalline substance C17H32O4.
1. A violet dye obtained from several species of lichen (Roccella tinctoria, etc.), which grow on maritime rocks in the Canary and Cape Verd Islands, etc.
2. The plant from which the dye is obtained. [Written also orchal and orchil.]
n : a source of the dye archil and of litmus [syn: roccella]