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2. (Chem.) A blue dyestuff obtained from several plants belonging to
very different genera and orders; as, the woad, Isatis tinctoria,
Indigofera tinctoria, I. Anil, Nereum tinctorium, etc. It is a dark
blue earthy substance, tasteless and odorless, with a copper-violet
luster when rubbed. Indigo does not exist in the plants as such, but is
obtained by decomposition of the glycoside indican.
Commercial indigo contains the essential coloring principle indigo blue
or indigotine, with several other dyes; as, indigo red, indigo brown,
etc., and various impurities. Indigo is insoluble in ordinary reagents,
with the exception of strong sulphuric acid.
Chinese indigo (Bot.), Isatis indigotica, a kind of woad. -- Wild
indigo (Bot.), the American herb Baptisia tinctoria which yields a poor
quality of indigo, as do several other species of the same genus.
In"di*go (?), a. Having the color of, pertaining to, or derived from,
indigo.
Indigo berry (Bot.), the fruit of the West Indian shrub Randia
aculeata, used as a blue dye. -- Indigo bird (Zoöl.), a small North
American finch (Cyanospiza cyanea). The male is indigo blue in color.
Called also indigo bunting. -- Indigo blue. (a) The essential coloring
material of commercial indigo, from which it is obtained as a dark blue
earthy powder, with a reddish luster, C16H10N2O2, which may be
crystallized by sublimation. Indigo blue is also made from artificial
amido cinnamic acid, and from artificial isatine; and these methods are
of great commercial importance. Called also indigotin. (b) A dark, dull
blue color like the indigo of commerce. -- Indigo brown (Chem.), a
brown resinous substance found in crude indigo. -- Indigo copper
(Min.), covellite. -- Indigo green, a green obtained from indigo. --
Indigo plant (Bot.), a leguminous plant of several species (genus
Indigofera), from which indigo is prepared. The different varieties are
natives of Asia, Africa, and America. Several species are cultivated,
of which the most important are the I. tinctoria, or common indigo
plant, the I. Anil, a larger species, and the I. disperma. -- Indigo
purple, a purple obtained from indigo. -- Indigo red, a dyestuff,
isomeric with indigo blue, obtained from crude indigo as a dark brown
amorphous powder. -- Indigo snake (Zoöl.), the gopher snake. -- Indigo
white, a white crystalline powder obtained by reduction from indigo
blue, and by oxidation easily changed back to it; -- called also
indigogen. -- Indigo yellow, a substance obtained from indigo.
||In`di*gof"e*ra (?), n. [NL., from E. indigo + L. ferre to bear.]
||(Bot.) A genus of leguminous plants having many species, mostly in
||tropical countries, several of them yielding indigo, esp. Indigofera
||tinctoria, and I. Anil.
||
In"di*go*gen (?), n. [Indigo + -gen.]