Indigo

(in'-dig-o) indigo. A blue pigment formed during the fermentation of Indigo/era anil, I. tinct or i a, and other species. It is insoluble in alcohol or water, but freely soluble in strong sulphuric acid; it is used mainly in the arts as a dye-stuff. Chemically, it is a mixture of several principles, the chief being a blue coloring -matter, indigotin. Therapeutically, it is an irritant to the mucous membrane of the alimentary tract, producing intense nausea. It has been used advantageously in epilepsy, chorea, and convulsions, in doses varying from 5 ij— J ij daily. Unof. I. -blue, Indigotin; a chromogen found in ordinary indigo, of which it constitutes the principal ingredient. It is also derived from wood (Is at is tinct or i a). It occurs in the plant as a glucosid, indican. Indigo-blue is a dark-blue powder with a reddish glimmer; it becomes metallic and copper-like under pre ure. It is insoluble in water, alcohol, and ether, and is odorle and tastele . It di olves in hot anilin with a blue color, and crystallizes from hot oil of turpentine in beautiful blue plates. I. -brown, a resinous substance of a brown color, obtained by boiling an aqueous solution of indican with an acid. It is composed of a mixture of indihumin, and in dir het in, the former soluble and the latter insoluble in alcohol. I.-carmin, a sodium salt of indigotin-disulphonic acid; it is used as a blue dye, a washing-blue, and is a delicate test for sugar. I.-carmin Test for Sugar; put in 30 minims of water one part each of' indigo-carmin and sodium carbonate; heat gently to solution; add one drop of urine, and boil quietly. A change to red or yellow indicates sugar. See Tests, Table of. I. Extract. See Indigo-carmin. I.-red. See Indirubin . I. -white, Indigo gen; a substance obtained by the reduction of indigo-blue. It occurs as a white crystalline powder, soluble in alcohol, ether, and the alkalies, with a yellowish color. It rapidly reoxidizes to indigo-blue by exposure to the air. I., Wild. See Baptisia .