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Updated: June 27, 2025
The so-called aniline colours are not all derived from aniline, such colouring matters being in some cases derived from other coal-tar products, such as benzene and toluene, phenol, naphthalene, and anthracene, and it is remarkable that although the earlier dyes were produced from the lighter and more easily distilled products of coal-tar, yet now some of the heaviest and most stubborn of the distillates are brought under requisition for colouring matters, those which not many years ago were regarded as fit only to be used as lubricants or to be regarded as waste.
I pointed to benzene or benzol in the table as a hydrocarbon, C H , which forms a principal colour-producing constituent of coal-tar. If you desire to produce chemical appetite in benzene, you must rob it of some of its hydrogen. This is the first step in the formation of aniline.
This, in its unrefined condition, is a light spirit which distils over at a point somewhat below the boiling point of water, but a delicate process of rectification is necessary to produce the pure spirit. Other products of the same light oils are toluene and xylene. Benzene of a certain quality is of course a very familiar and useful household supplement.
If these treatments are ineffectual, resort to diluted oxalic acid or Javelle water, a careful rinsing to follow the application. Grass stains may be treated in a like manner, or washed in alcohol. Ammonia and water, applied while the stain is fresh, will often remove it. Remove paint stains with benzene or turpentine, machine oil with cold water and Ivory soap, vaseline with turpentine.
After the distillation of benzene from the crude coal-naphtha is completed, the chief impurities in the residue are charred and deposited by the action of strong sulphuric acid. By further distillation a lighter oil is given off, often known as artificial turpentine oil, which is used as a solvent for varnishes and lackers.
The isolation of aniline from coal-tar is expensive, in consequence of the small quantities in which it is there found, but it was discovered by Mitscherlich that by acting upon benzene, one of the early distillates of coal-tar, for the production of nitro-benzole, a compound was produced from which aniline could be obtained in large quantities.
The valuable constituents actually extracted are then these: benzene, toluene, xylene, naphthalene, anthracene, and phenol or carbolic acid. One ton of Lancashire coal, when distilled in gas retorts, yields about 12 gallons of coal-tar. Let us now learn what those 12 gallons of tar will give us in the shape of hydrocarbons and carbolic acid, mentioned as extracted profitably from tar.
Here they arrange themselves into two layers, the top of which consists of the nitrobenzene which has been produced, together with some benzene which is still unacted upon. The mixture is then freed from the latter by treatment with a current of steam. Nitrobenzene presents itself as a yellowish oily liquid, with a peculiar taste as of bitter almonds.
These assist in increasing the illuminosity, which is sometimes greatly enhanced, too, by the presence of a small quantity of benzene vapour. These illuminants, however, constitute but about 6 per cent. of the whole. Added to these, there are four other usual constituents which in no way increase the value of gas, but which rather detract from it.
Emetics, purgatives, and stimulants. Many of the synthetical coal-tar products now so largely employed as analgesics are powerful toxic agents. =Phenazone, Antipyrine, or Analgesin=, is a complex benzene derivative prepared from aniline, aceto-acetic ether, and methyl iodide. It is in colourless, inodorous, scaly crystals, which have a bitter taste. It is soluble in its own weight of water.
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