(From the Arabic term Hindi, India). The indigo blue plant; also called indigo, anil, nil, isatis, and coronilla Indica, emerus Americanas, glastum Indicam, Ameri, coaachira Indorum, colutea Indica, herbacea, enger,gali,herva de anil Lusitanis,hin-aivaru; Indigofera tinctoria Lin. Sp. Pi. 1061, is a native of South Carolina, but was known to the ancients. It seems to have been indigenous in Malta, and was certainly produced in large quantities in Egypt; and the name anil (al-nil) seems to show that it was known to the Arabians. It requires a tropical temperature, but is found within forty degrees on each side of the equator. We are now supplied from the continent and islands of America, though some indigo is prepared in France. This substance is a faecula, or starch, separated from the plant by the powerful action of fermentation. It is not agreed how far this process should proceed. It certainly goes beyond the spirituous, since ammoniacal salts are found in indigo, but, by complete putrefaction, it is spoiled. Some oil is used in the preparation, though with no very decided object. We suspect its chief advantage to arise from its power of moderating the too violent fermentation, or preventing the escape of the carbonic acid gas. Various species of this plant, and various processes for separating the faecula, are employed, which it is not our object to detail. It is brought to us in flat cakes of a moderate thickness, moderately hard, of a deep violet colour: the best kind swims on water, and when broken hath no white spots in it. That which is reddish, on being rubbed with the nail, and hath dust and broken pieces in it, is far inferior. Such white spots are found in the common indigo of the shops, which is an adulteration of the genuine kind by the mixture of flour.
The plant is said to be detergent, of some use when applied to ulcers, or to kill lice.
There is another plant which is called anil, vised by way of decoction in nephritic colics, and suppressions of urine; but we have not been able to determine the species.
See Raii Historia Plantarum. Neumann's Chert). Works,