INDIGO

A blue substance much used as a dye-stuflf. The best indigo is obtained from an Asiatic and American plant, the In dig of era. The plant is bruised and fermented in vats of water, during which it deposits indigo in the form of a blue powder, which is collected and dried, so as to form the cubic cakes in which it usually occurs in commerce. Indigo is quite insoluble in water; when heated it yields a purple vapour, which condenses in the form of' deep blue or purple acicular crystals. When indigo is exposed to the action of certain deoxidizing agents, it becomes soluble in alkaline solutions, losing its biue colour and forming a green solution, from which it is precipitated by the acids white; but it instantly becomes blue by exposure to air. This white indigo has been termed indigo gene, and indigo appears to be its oxide. It is best obtained by mixing 3 parts of finely powdered and pure indigo with 4 of green \-itriol. 5 of slaked quicklime, and 100 of water, repeatedly shaking the mixture. In about twenty-four hours the supernatant liquor, which is transparent, and of a green colour, is to be decanted off, and pourod into dilute muriatic acid, when the deoxidized indigo is thrown down; but in order to prevent its absorbing oxygen and becoming blue, it must be most carefally excluded from the contact of air, which may be effected by syphoning it off into the acid, collecting it in ve els filled with hydrogen, and washing it with water deprived of air and holding in solution a little sulphate of ammonia. In this white state indigo gene absorbs between 11 and 12 per cent, of oxygen to become blue indigo. It would appear from Dumas' experiments that indigo gene is a compound of Atoms. Equivalents. Carbon - - - 45 = 270 Hydrogen - - 15 a= 15 Nitrogen - - - 3 = 42 Oxygen -. 4 = 32 T "359 and that indigo consists of 1 atom of indigo gene =<= 359, Qq 2 [s. 608]