a snowy white camphor-like mass, or when very slowly refrigerated, to beautiful transparent cruciform leaflets, which aggregate together into forms resembling fern-fronds; remelts at 40-1° Fahr.; and when solidifies burns, like camphor, without previous fusion. Sp. gr. ·850;[158] sp. gr. of vapour, 2·770.[159] It is unaffected by the ordinary hydrated acids, and has no action on the alkaline metals. Highly concentrated nitric acid readily dissolves it, and from this solution nitrobenzol is precipitated on the addition of water. Its vapour is dangerously inflammable, and, when mixed with the air, is highly explosive. Its solvent power extends over a numerous list of substances. Commercial benzol has a less agreeable odour, and not unfrequently a slight colour, with other modifications of the properties just enumerated, depending on the relative amount of impurities contained in it.
[157] Fownes, Mansfield, Muspratt, and others; 186°—Mitscherlich 187°—Mr C. G. Williams (in Ure’s ‘Dict. of A. M., & M.,’ 5th ed. See next note.)
[158] Williams, Ure, Muspratt; ·885—Fownes, Mitscherlich. The different sp. gr. and boiling-points assigned to benzol, by authors, can only be accounted for by samples of different degrees of purity having probably been examined. The numbers given in the text are those not usually adopted; but we are not prepared to say, that they are definitely settled. On the contrary, we think it not unlikely that further investigations may show that the apparently greater levity of the benzole obtained from naphtha may arise from the presence of some other hydrocarbon which has hitherto escaped detection.
[159] Theoretically, 2·738.
Pur.—1. It should be colourless, without action on either litmus or turmeric paper, and have the boiling-point, sp. gr.,[160] &c. already indicated:—2. A few drops thrown on a slip of glass or a piece of white paper should rapidly and entirely evaporate by simple exposure to the air without leaving a stain behind, or evolving any disagreeable or foreign odour:—3. Agitation with a little sulphuric acid should not discolour it:—4. It should not perceptibly lose weight or volume by agitation with a little cold water.
[160] If it has a less sp. gr. than ·850, it is probably adulterated with the naphtha obtained from the Torbane-hill mineral or Boghead-coal, of which the sp. gr. is only ·750.
Detec.—1. From the physical and other properties already enumerated:—2. By converting it into aniline and then testing it accordingly. For this purpose a little of it is dissolved in concentrated nitric acid, and the nitrobenzol thus formed is precipitated by the addition of water. The fluid is then agitated with ether, to dissolve out the nitrobenzol, and the resulting ethereal solution is mixed with an equal bulk of alcohol and hydrochloric acid and a little granulated zinc at once added. Hydrogen is evolved, and by its action the nitro-compound is converted into aniline. The liquid is next alkalised with potassa in excess, and the alkaline fluid agitated with ether. The ethereal solution, on evaporation, leaves a residue (aniline), which, after the addition of a little water, may be tested with a few drops of solution of chloride of lime, when a characteristic purple colour will be developed, provided the original liquor was benzole, or contained it. In this way very minute traces of benzol may be detected.
Uses, &c. In its impure or commercial form, chiefly as a solvent for gutta percha and india rubber; but it leaves the first in a spongy, friable state, and the latter glutinous or sticky, unless heat is applied to it for some time; also as a solvent in the manufacture of varnishes, as a diluent in lieu of oil of turpentine, for oil-paints, as a material for the production of artificial light, &c., &c. In the pure or nearly pure form it is largely employed in the laboratory and in chemical analysis as a solvent of many resins,[161] mastic, wax, camphor, fat, the fixed and essential oils, sulphur, phosphorus, iodine, several of the alkaloids,[162] &c., &c. Under the name of BENZINE and BENZINE-COLLAS it has been recently extensively vended for the removal of spots of grease, paint, &c., from woven fabrics, which it does most readily and completely, without detriment to the material. As a source of artificial light it has been the subject of innumerable applications and patents. It may be burned in a ‘wickless’ lamp, provided a proper cap-burner be employed. Alcohol or pyroxilic spirit containing 1-3rd, or even 1-4th of it, burns with a rich white flame. Air driven through it becomes sufficiently inflammable to serve as illuminating gas; whilst ordinary coal-gas by merely passing over it yields a flame of greatly increased brilliancy; but in all these applications the greatest possible care is necessary to prevent accidents.[163] See Naphtha (Coal-tar).
[161] Anime and copal are scarcely affected by it in the fluid state, but readily dissolve in its vapour at the point of condensation.
[162] Particularly quinine, which it dissolves readily, but not cinchonine. Hence it is invaluable for the separation of them. It may be economically and conveniently substituted for ether in the preparation of many alkaloids, with the advantage of being applicable in many cases in which ether cannot be employed.