Litmus
Litmus , noun
[Dutch lakmoes; lak lacker + moes a thick preparation of fruit, pap, prob. akin to English meat: compare German lackmus. See Lac a resinous substance.]
(Chemistry) 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.
Collocations (1)
Litmus paper (Chemistry) , unsized paper saturated with blue or red litmus, -- used in testing for acids or alkalies.