Emily Dickinson Lexicon

LIT'MUS, or LAC'MUS, n.

A blue pigment, formed from Argol orchal or archil, a lichen, the Roccella tinctoria. [See Archil.] It is prepared by bruising the archil, and adding quick lime and putrefied urine, or spirit of urine distilled from lime. The mixture, after cooling and the evaporation of the fluid, becomes a mass of the consistence of paste, which is laid on a board to dry in square lumps. – Encyc.