A white, crystalline acid (C 7 H
6 O 5 ), that occurs widely
in plants both in the free form, as in GALLS and combined in
tannins, from which it may be obtained by the
action of molds or an alkali. It is used
principally in the manufacture of pyrogallol
tannins, dyes, and writing inks. See also: VEGETABLE TANNINS .