BEN′ZOL

(-zōle). C 6 H 6 . [ benz (oin)- oleum. ] Syn. Ben′zene *, Ben′zĭne , Ben′zōle *, Hydrĭde of phe′ny̆̆l *, Phe′ne †, .; Benzo′leum , L.; Benzine , Fr.; Benzöl , Ger. A peculiar ethereal hydrocarbon discovered, by Faraday, among the products of the destructive distillation of whale oil and other organic substances ( A.D. 1825); and subsequently shown, by Mitscherlich, to form the principal ingredient in the distillate procured by the action of heat on a mixture of benzoic acid and hydrate of lime. In 1849, Mr C. B. Mans field [154] discovered its presence in coal-tar naphtha, from which the benzol of commerce is now chiefly, if not wholly, obtained. [154] This unfortunate chemist lost his life (Feb. 25, 1855), in consequence of being severely burned whilst experimenting on benzol. Prep. 1. Pure :— a. A mixture of benzoic acid, 1 part; fresh-slaked lime, 3 parts; is submitted, in a coated gla or earthenware retort, to a heat slowly raised to redne ; the oily portion of the resulting distillate is then separated from the water, and carefully rectified, with the proper precautions, at a temperature not exceeding 190° Fahr. The product is usually stated to be pure benzol; but to ensure this it may be submitted to one refrigeration and rectification, in the manner and at the temperature noticed below. b. From good commercial benzol, agitated with 1-4th or 1-5th of its weight of concentrated sulphuric acid, and, after repose and decantation, rectified at a temperature under 195° Fahr.; the resulting distillate is exposed to a temperature below [155] 32° Fahr., and the ma of crystals that form are thrown on a funnel, kept at the same temperature, to drain, after which they are pre ed between folds of bibulous paper, [156] and then allowed to liquefy by simple exposure, in a close ve el, to the ordinary temperature of the atmosphere. The product, after rectification at a temperature not exceeding 190,° is nearly pure benzol. It may be rendered absolutely pure by repeating the refrigeration a second and a third time, followed by a final rectification at 180-185° Fahr. [155] Preferably considerably below. If the distillate be not rich in benzol, a temperature so low as 8 or 10°, or even 4-5°, Fahr. may be nece ary or, at all events, advantageous. [156] Filtration under pre ure is thought by some chemists to be preferable. For this purpose a ‘Beart’s Coffee-pot’ (or a similarly constructed apparatus), was often employed by Mans field, and is recommended by Prof. Muspratt. 2. Commercial :—By submitting light coal-tar naphtha to distillation, either at once, or after it has been agitated with a little oil of vitriol, and decanted, care being taken that the temperature does not exceed 200° Fahr. A drawing and description of the apparatus invented by Mans field for the preparation of benzol from coal-tar naphtha is given below. IMG:596405606043057898_i300-1.png: A is the still placed on a furnace R; C is filled with cold water. As soon as the oil in the still boils, the vapours are condensed in B, and flow back into A; this continues until the water in C has been heated to a certain temperature, when the vapours are condensed in the cooler D, the liquid flowing at n into the carboy S. As soon as the water in C begins to boil, all the substances contained in the coal-tar naphtha and volatile at 212° Fahr. are condensed and collected in S. A very pure benzol is obtained by this apparatus. By opening the tap m , the hydrocarbons which boil over 212° Fahr. can be rectified. The stopcock i is used for opening the still. In the benzol works the apparatus shown below is employed. A is the still, B the condenser, C a water-tank. At the commencement of the operation the water in C is heated by means of the steam-pipe D which communicates with the steam boiler. The tube G is attached to the still; i is a contrivance for filling, b for emptying it. The condensed water is carried off by means of H. By freezing benzol and pre ing the solid substance obtained, it may be rendered quite pure. IMG:596405606043057898_i300-2.png: Prop. Pure benzol is a clear, colourle , very mobile liquid, having a strong, characteristic, and rather agreeable ethereal odour. It is neutral to test-paper; exceedingly volatile at all temperatures; insoluble in water; miscible with alcohol and with ether; highly inflammable; burns with a brilliant flame, emitting clouds of smoke, which rapidly condense and fall as a shower of fine sooty, carbonaceous matter; boils at 176° Fahr.; [157] solidifies, at 32°, to a snowy white camphor-like ma , 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 di olves it, and from this solution nitro benzol 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 le 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, Mans field, 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 a igned 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 colourle , without action on either litmus or turmeric paper, and have the boiling-point, sp. gr., [160] . already indicated:—2. A few drops thrown on a slip of gla 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 le 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 di olved in concentrated nitric acid, and the nitro benzol thus formed is precipitated by the addition of water. The fluid is then agitated with ether, to di olve out the nitro benzol, 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 pota a in exce , 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, . In its impure or commercial form, chiefly as a solvent for gutta perch a and india rubber; but it leaves the first in a spongy, friable state, and the latter glutinous or sticky, unle 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, ., . 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 e ential oils, sulphur, phosphorus, iodine, several of the alkaloids, [162] ., . Under the name of BENZINE and BENZINE-COLLAS it has been recently extensively vended for the removal of spots of grease, paint, ., 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 ‘wickle ’ 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 pa ing over it yields a flame of greatly increased brilliancy; but in all these applications the greatest po ible care is nece ary to prevent accidents. [163] See Naphtha (Coal-tar). [161] Anime and copal are scarcely affected by it in the fluid state, but readily di olve in its vapour at the point of condensation. [162] Particularly quinine, which it di olves 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. [163] Workmen constantly exposed to the vapour of benzol are very subject to nervous irritability, and, where the apartment is ill-ventilated, even fits of nervous prostration and trembling, of a truly alarming character. In two or three cases which we have seen, the symptoms, to the inexperienced eye, closely resembled those occasionally resulting from the long-continued use of very minute doses of strychnia, or of the alcoholic extract of nux vomica.