The amount of benzol contained in a sample of tar will, under ordinary circumstances, depend upon the amount of refrigeration to which the gas is submitted. The reader's attention is called to Lake's patent method of obtaioing be,nzol from gas (No. 488, 1869); if the figures therein given can be sustained in practice, an enormous amount of benzol and toluol can by this method be recovered from coal-tar. Coal-tar naphtha boiling at 130° (266° F.) is worth about Is. 9d. a gall., whilst petroleum boiling at 149° (300° F.) is worth about 9d. a gall.; 60 per cent. benzol is worth 3s. a gall. If it is possible to recover, say, 12 per cent. of the liquid used in washing the gas, there should be 2i to 5 gall. of a product worth from 3s. to 4s. a gall. from every 10,000 cub. ft. of gas, so that it would be more economical to carburet the gas with such liquids if necessary. This fact is important to gas manufacturers, and not without interest to gas consumers. lf the sole object in distilling coal were to use the gas as fuel, there could be no advantage in this process. It appears quite possible that, by selecting the coal and arranging the heats, the tar may be enriched in benzol, with only a slight sacrifice in the quantity of gas produced. The production of liquid hydrocarbons from coal, as a source of profit, does not seem to have occurred to gas companies. The comparative poverty of the highly bituminous coals in benzol and anthracene places many dis tillers of English tar at a disadvantage in the manufacture of these two products.
Toluol, Toluene, or Diethyl Benzol. CGE15,CH.,.—Toluol was discovered by Pelletier and Walther in rosin-oil, and was called by them " Retinnaphthe The name" toluol " was given to the liquid by Deville, who obtained it by the distillation of Tolu-balsam. It exists in wood-tar ; but its commercial source is coal-tar. It is met with in commerce as "rectified toluol," " commercial toluol," " rosaniline beuzol," Sm. Its highestdegree of rectification would be exhibited by the fluid obtained in preparing benzol by refrigeration ; but commercially it is procured from the distillate of naphtha which comes over between 107° and 121° (225° aud 250° F.); some samples contain a dis tillate going over at higher temperatures. It is a colourless, limpid, oily liquid, which does not solidify when cooled to any ordinary temperature. In odour, solvent properties, and miscibility with other hydrocarbons, it resembles benzol. By oxidation, it becomes benzoic acid. Its sp. gr. is 0.88 at 0° (32° F.), and 0 . 87 at 24° (75°F.); it boils at 110° (230° F.). The value of commercial samples is found in the same way as benzol. It is best stored in galvanized iron drums, or glass carboys, as benzol.
Xylol, Xylene, or Di-methyl Benzols. C6H, {CH3.—When purified coal-tar naphtha CH, is submitted to fractional diAillation, a liquid boiling at 139° to 140° (282° to 284° F.) is obtained. This was at first regarded as a pure compound ; but recent researches have shown it to be a mixture of two di-methyl benzols, which, having nearly the same boiling-point, cannot be separated by dis tillation. They are known as " methyl-toluol " and " iso-xylol " ; the latter forms the principal
ingredient of the solvent naphtha used by indiarubber manufacturers. Commercial xylol contains a little toluol, as it is the product of the higher distillation after the commercial toluols have been drawn over, and consequently forms the bulk of the second liglat oils. It is prepared by Beilstein an,d Wahlfoss by treating the naphtha distillate which comes over at 141° (286° F.) with fuming sulphuric acid, after repeated treatment with acid and alkali, as in preparing benzol, naphtha, Ste. ; this dissolves the xylol, which is subsequently extracted by dry distillation.
. Creosote.—The portion of the distillate wlaich is collected 0,s creosote oils is generally sold as " creosote," without ally further treatment. It is a thick, black liquid, containing principally carbolic acid and naphthalene. Its consistency varies with the proportion of the latter ; creosote from London tar is particularly rich in it, and, in cold weather, frequently solidifies. The principal use to which creosote is applied is the preservation of timber. Its value for this purpose depends, according to Dr. Letheby, upon the following points :—It ahould have a density of 1.015-1.055; it should not deposit any cryatalline matter at 4°-5° (40° F.) ; it should not yield less than 5 per cent. of crude carbolic acid to a aolution of caustic potash at 1.070 (14' Tw.); and it ahould furnish 90 per cent. of liquid oil when distilled at 315° (600° F.). Some contracts issued in 1867, by the Dutch Government, stipulated that the ereoaote ahould be clear, and not yield more than 40 per cent. of naphthalene when cooled to 0° (32°F.), and kept at that temperature for twenty-four hours. It should dry up with little loss, and ahould harden by oxidation when imbibed by porous substances. This fraction is also worked on for carbolic acid.
The cremate of the druggists ia a totally different product, derived from the distillation of wood.
Creosote oils accumulate in a works in excess of requirements ; they may be utilized as fuel, in accordance with the patented plan of Edward Dorsett (No. 176, 1868). Crude creoaote is worth 2/. to 2/. 5s. a ton.
Naphthalene. Cioll..—This aubatanee was discovered by Garden, in 1820, in coal-tar. It is formed by the destructive diatillation of many organic bodiea, especially when their vapoura aro pasaed through tubes heated to redness. It is found in wood-tar, and also in Rangoon petroleum ; it has been produced aynthetically by paasing the vapaur of phenyl-butene dibromide through a red-hot tube. Its commercial LiOUree is coal-tar. It exists most abundantly in tars from bituminous coals ; in lignite and boghead tars, and also the better classes of cannel tar, it is replaced by paraffin.