Besides the above products obtained from aniline, a series of colours have been obtained from phenol, or carbolic acid, another substance obtained from coal tar.
Picric Acid. This is obtained by treating in a suitable apparatus, with proper precautions, carbolic acid with nitric acid. It is a pale yellow crystalline acid, forming dark orange explosive salts, and dyeing silk a fine yellow.
Isopurpurate of Potassium. Grenate Brown. Grenate Soluble. By treating picric acid with cyanide of potassium a very explosive salt is obtained, used to dye wool a dark maroon colour.
Aurine, or Rosolic Acid. This is obtained by heating a mixture of sulphuric, oxalic, and carbolic acids, and purifying the
products. It is a beautiful reddish, resinous substance, with a pale green lustre, and yielding an orange coloured solution, changed by alkalies to a splendid crimson. Owing to the difficulty in using it, however, it is not very extensively employed.
Peonine, or Coralline. This dye is formed when rosolic acid and ammonia are heated to between 248° and 284° Fahr. (120° to 140° C.). It is a fine crimson dye, forming shades similar to safflower on silk, but, owing to the bad effects of acids, not much used.
Azuline. Prepared by heating coralline and aniline together. A coppery coloured resinous substance, soluble, in alcohol, and with difficulty in water, and dyeing silk a blue colour. The aniline blues, however, have superseded it to a great extent.
There are other substances obtained from coal tar that have been employed to form dyes, but of which we shall only refer to one—naphthaline. By treating this in exactly the same manner as benzol, it is converted into aniline. A solid crystalline white base, termed naphthylamine, is produced. From this substance is obtained the following dye.
Dinitronaphthal, or Manchester Yellow. Naphthylamine is converted into diazynaphthol by treatment with nitrate of potassium, and the latter, when heated with nitric acid, yields the colour. It is a weak acid, and the salt employed in commerce is the beautiful yellow crystalline calcium salt which dyes silk and wool a magnificent golden-yellow colour.
TARPAU′LIN. Syn. Tarpawling. Canvas covered with tar or any composition to render it waterproof.