litmus

A water-soluble bluish powder derived from certain lichens that changes to red with increasing acidity and to deeper blue with increasing basicity.

A peculiar coloring matter procured from Roccella tinctoria and some other lichens.

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.

unsized paper saturated with blue or red litmus, — used in testing for acids or alkalies.

A dyestuff extracted from certain lichens, that changes color when exposed to pH levels greater than or less than certain critical levels.

A simple test of acidity in a liquid using litmus, usually in the form of litmus paper.

A simple test of any attribute; a litmus test.

a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator