Benzole, a peculiar product of coal tar, important in the manufacture of aniline colors. (See Benzine.) Its chemical formula isC12 H6 (old), or C6H6 (new). Its synonymes are benzol, benzin, benzene, bicarburetted hydrogen, and bydrite of phenyl (Fr. phene). There ore numerous methods for the preparation of benzole, but the only one of practical value, invented by Mansfield in 1847, is founded upon the distillation of coal tar. The crude tar, as it comes from the gas works, is first subjected to regulated distillation, so as to obtain separately naphtha or light oil (oily liquid lighter than water); secondly, after all the naphtha has passed, dead oil or heavy oil (oily liquid sinking in water); and thirdly, pitch, which remains behind in the retort. From the light oil the benzole is separated by further fractional distillation. The resulting product, which is far from being absolutely pure, is the well known preparation for removing grease stains from articles of dress. It is also extensively used as a solvent of caoutchouc and resins. When required for the production of aniline, it must be rectified by subjecting it to further operations.
The boiling point of pure benzole is 80oC (170° F.), whereas commercial benzole boils from 80° to 120° C, and is therefore a mixture of several compounds. The transformation of benzole into nitro-benzole is accomplished by dissolving benzole in fuming nitric acid and mixing the clear liquid with water, when the nitro-benzole is precipitated as a dense yellow liquid. Nitro-benzole has for some years been sold under the trade name of essence de mirhane, or artificial oil of bitter almonds. Nitro-benzole when submitted to the actio* of reducing agents is converted into aniline. The successive changes of benzole are thus expressed in chemical symbols:
First change, transformation of benzole into nitro-benzole:
C6H6 + 4NO3 = C6H5NO2 + H2O.
Benzole. Nitric acid. Nitro-benzole. Water.
Second change, transformation of nitro-benzole Into aniline:
C6H5NO2 + 3H2S = C6H7N + 2H2O + 3S Nitro-benzole. Sulphuretted Aniline. Water. Sulphur. hydrogen.
On the large scale, instead of sulphuretted hydrogen, nascent hydrogen produced from iron turnings and acetic acid is employed as the reducing agent. The inhalation of nitro-benzole produces insensibility to pain, but from some slight irritation it was found to occasion when the experiments were made, it has not come into general use as an aniestlictie. - At ordinary temperatures benzole is a limpid, colorless, strongly refracting oil, of specific gravity 0.85 at 15.5° 0. When cooled to +3° C. it solidifies into fern-like tufts or into masses like camphor, which melt at 5.5° C, expanding one eighth of their volume, and freezing again at 0° C. Prof, Hoffmann takes advantage of the freezing of benzole to obtain it pure. For this purpose the impure article is placed in a tin or brass vessel, in which an iron rod, having attached a close-fitting piston perforated with numerous small holes, is made to play. On forcing down the plunger the liquid portions ascend and can be drawn off, and on melting the frozen benzole it will be found to be nearly pure. Cooled to - 18° C, benzole becomes so hard and brittle that it can be pulverized in a mortar. It boils at 80° C, and volatilizes undecomposed.
The oil has a pleasant ethereal smell, and when breathed produces insensibility attended by convulsions; internally it acts as a violent poison. The density of its vapor is 2'75 (calculated 2.704). It is not soluble in water, although it imparts a color and odor to that liquid. Alcohol, wood spirit, acetone, and ether are good solvents of benzole. It dissolves fats, the fixed and essential oils, camphor, wax, india rubber, gutta percha, resins, asphaltum, sulphur, phosphorus, iodine, and picric acid; gum lac, copal, anime, and gamboge in small quantity; quinine, somewhat readily; strychnine and morphine in small quantity; cinchonine, not at all. It is inflammable, and burns with a bright smoky flame; and when its vapor is added to illuminating gas, it materially contributes to the illuminating power; hence it finds extensive application in carburetting or carbonizing poor gas, and in the manufacture of "air gas." The jiame phene was proposed for it by Laurent in allusion to its high value as an illuminating agent, from to emit light. It is now nearly superseded for this purpose by petroleum benzine, on account of the comparatively great expense of benzole. A mixture of one volume of benzole with two volumes of alcohol forms a very good lamp oil; more benzole gives rise to a smoky flame. When benzole is passed through a red-hot tube, it is decomposed into solid carbon and a gaseous hydrocarbon. Under favorable circumstances 100 lbs. of coal will yield 10 3/4 lbs. tar, 8 1/2 oz. tar naphtha, 3 oz. benzole, 4 1/2 oz. nitro-benzole, and 2 1/2 oz. aniline. Benzole has been found ready formed in the native petroleum of Rangoon, and has been made synthetically by Prof. Schulze by the direct oxidation of carbon by means of permanganate of potash. As benzoic acid, from which benzole was originally distilled by Mit-scherlich, has also been made artificially, it is not impossible that a synthetical method for the manufacture of benzole may eventually be discovered.