The constituent parts of indigo are Carbon, 73.22, Nitrogen 11.26, Oxygen 12.60, and Hydrogen, 2.92, = 100.
When indigo is digested in concentrated sulphuric acid, it is converted into a peculiar blue substance, commonly called sulphate of indigo; this colouring matter has been, however, lately named Cerulin, by Mr. W. Crum, who has made many experiments on it; (see notes to Bertholet, vol. ii. p. 357. et seq.) he observes that cerulin dissolves more abundantly in sulphuric acid than water; but this does not prove the formation of a compound entitled to be called sulphate of indigo; that, such a solution differs in no respect from that of resins in acids or in alcohol. Another substance has been also obtained from indigo by Mr. Crum, of a purple colour, which he calls Phenicin; it dissolves both in water and alcohol.
Iron rarely in its metallic state enters into the manipulations of dyeing, but its sulphate, muriate, acetate, &c. as well as its oxides contribute largely to the dyer's art.
Sulphate of Iron, or green copperas, as it is commonly called, is too well known to need description; it is in green crystals of different sizes, and is used for various purposes in dyeing, &c.
Peracetate of Iron, or Acetate of Iron, forms a reddish-brown uncrystallizable solution, much used by the calico printers, and is prepared by keeping iron turnings or pieces of old iron for six months immersed in redistilled pyrolignous acid. It may be also prepared in a more expeditious way by boiling filings of iron with the acid.
Lac dye and LAC LAKE are two articles now regularly imported from the East Indies, and employed for dyeing scarlet. They both appear to be the colouring matter of seed-lac, obtained from it in India by a process not generally known. Both these articles are in lumps or cakes of a dark-reddish or blackish colour.
Muriatic acid, or spirit of salt, as it was formerly called, is obtained from common salt or muriate of soda, by distillation with sulphuric acid. When this acid is pure it is perfectly colourless, but it generally has a yellow hue arising from a little iron. It gives out, at all temperatures, a large quantity of a fuming suffocating gas of a peculiar smell. Its usual specific gravity is about 1.160. For the basis of this acid see Oxymuriatic acid.
Nitric acid is composed of oxygen and nitrogen: it is usually obtained from nitre, (the chemical name of which is nitrate of potash,) by distilling three parts of it with two of sulphuric acid. When pure, nitric acid is a colourless, extremely sour, and corrosive liquor. Its specific gravity is 1.42; it always contains more or less water, which modifies its specific gravity. It is usually coloured with nitrous acid gas. It forms a variety of compounds with numerous other bodies. Aqua fortis is this acid diluted more or less with water; when strong it is called double, when weak single aqua fortis. For Nitrogen, see forwards.
Nitro-muriatic acid, or AQUA REGIA, is a mixture of nitric and muriatic acids. It is usually made by dissolving sal ammoniac or common salt in nitric acid. When the former is employed the usual proportion is one of the salt to four of the acid; but equal parts will be necessary to dissolve platinum. Aqua regia is the only menstruum which will dissolve gold.
Orpiment, REALGAR, or SULPHURET of ARSENIC has been lately applied to the purposes of dyeing a yellow colour. Sulphur may be combined with arsenic in different proportions. Realgar is red, and occurs native in Germany and Switzerland; it is also produced by art. Orpiment is commonly produced by art and is of a yellowish colour; native orpiment is also occasionally found; it is of a bright lemon colour.