GAS-TAR, or COAL-TAR, a thick, black. opaque liquid, which comes over and con denses in the pipes when gas is distilled from coal. It is slightly heavier than water, and has a strong, disagreeable odor. Coal-tar is a mixture of many distinct liquid and Solid substances, and the separation of the more useful of these constitutes an important branch of manufacturing chemistry. The tar is first.distilled in large malleable iron stills, when water and crude naphtha first come over; and afterwards, when the tempera ture rises, a heavy, fetid-nmelling oil, called which sinks iu water. There remains in the still a large residue of pitch, which is again distilled in brick ovens, giving off an oil called and leaving a large quantity of The crude naphtha is purified by sulphuric acid and quicklime, and re-distilled, when it is nearly as color less as water. This, then forms the refined coal-tar naphtha of commerce. It IA largely used for burning in lamps, as a solvent for india-rubber and gutta-percha, to preserve animal substances from moth, and it is also burned to produce a fine carbon for time manufacture of printing-ink. It. is from the lighter portion of naphtha, called benzole, that the beautiful mauve and magenta colors are manufactured. See BENZOLE and DYE STUFFS. Benzole is likewise used for removing stains of fat or oil from cloth. Tile dead-oil or pitch-oil is sometimes used, in its crude state, as a cheap material for afford ing light in lamps burned in the open air. It contains a considerable quantity of creo sote, and forms the best preservative for wood in damp situations. The coke-oil is not of much commercial importance, but it can be burned in lamps, and this, with the dead-oil,. when consumed in a confined atmosphere, gives a smoky flame, the soot from which constitutes lampblack. The pitch-coke is valuable as a fuel for melting iron,
being free from impurities. Pitch itself is used for making asphalt pavement, and also for roofing-felt.
From the last portion of the distillation of the crude naphtha, and the first of the dead oil, a beautiful white crystalline solid, called naphthaline, is obtained. It has been long known yithout being applied to any useful purpose, but is now beginning to be employ41 for the manufacture of colors, in a similar way to the benzoic. The dead-oil also contains considerable quantities of a yellow solid termed paranaphthaline, which is a mere chemical curiosity.
The creosote is extracted from. the dead oil by stirring it with soda; in which the creosote dissolves. When this soda solution is boiled for some hours, and then has an acid added to it, the creosote separates as an oil on the surface of the fluid, and, when distilled, is nearly pure. This treatment requires to be repeated several times to get it quite pure, and to keep its color. Most of the creosote used by druggists is made from coal-tar. The creosote from wood is a similar but quite distinct body.
Sulphuric acid extracts both from the dead-oil and the crude naphtha several volatile basic oils besides benzole—namely, toluole, xylole, cumole, and cymole, which are almost unknown in the arts, although they may yet come to be of great service. Among them is aniline, but not in sufficient quantity to pay for its extraction. There also occurs a curious body named pyrol, the vapor of which gives to fir-wood, dipped in muriatic acid, a splendid violet color. Beautiful blue colors have been made from these basic oils, but only by elaborate and expensive processes.