BEN'ZENE, or BEN'ZOL (for derivation see 1.3E8zoiN), Ca,. One of the most important of the compounds of carbon. Large quantities of it are industrially converted into nitro-benzene, from which, in turn, all of the aniline of com merce is manufactured. The luminosity of a coal gas flame is largely due to the presence of con siderable quantities of benzene in the gas. Be sides, benzene is an excellent solvent for fats, resins, iodine, and other substances, and is much used for cleaning purposes. The importance of benzene in pure chemistry is due to the fact that a very large number of substances are derived from it. the derivatives constituting the so-called aromatic compounds. Benzene may be obtained in a variety of ways; it is produced by passing the vapors of ordinary alcohol, ether, and many other organic substances through a tube heated to redness: it is one of the constituents of the tar obtained by heating wood. peat, and shale out of contact with air, etc. Faraday first dis covered it (1825) in oil-gas, and in 1845 Hof mann found it in eoal-tar, from which all the benzene of commerce is at present obtained. The process by which benzene is obtained industri ally was first worked out by a pupil of Hof mann's, Charles Mansfield, whose death was caused (1856) by a large quantity of benzene taking fire during a distillation. Most of the benzene produced by the destructive distillation of coal forms a constituent of illuminating gas, while the remaining benzene is found in the por tion of the coal-tar that distils over below 110° C. When this portion, called light oil, is redistill ed, a liquid consisting mainly of benzene and a similar substance called toluene passes over be tween 82° and 110° C. This portion is purified by washing consecutively with sulphuric acid, water, and soda; it is then subjected to further fractional distillation. In this manner still somewhat impure benzene is obtained. To purify it, the liquid is cooled to crystallization, and the benzene crystals are separated and again dis tilled. Thus benzene is rendered pure enough
for all practical purposes. It still contains, how ever, a small quantity of the compound called thiophcnc whose presence may be best demonstrated by the so-called indophenin reac tion, causing a blue coloration to appear when a little sulphuric acid and isatin are added to ordinary benzene. As thiophene is more readily soluble in sulphuric acid than benzene, it may be eliminated from the latter by repeatedly agi tating with the concentrated acid at the ordi nary temperature. A better method, however, consists in boiling benzene for about half an hour with some aluminium chloride, and then distill ing. In this manlier perfectly pure benzene may be prepared for scientific purposes. Pure benzene Is a light, colorless liquid, having a peculiar odor and a burning taste. At low temperatures it solidifies, forming colorless crystals that melt at 6° C., and boil at 80.5° C. The vapors burn with a smoky flame. owing mainly to the high percentage of carbon contained in benzene. Ben zene floats on water, but mixes readily with ether, anhydrous alcohol. petroleum, and many other organic liquids. When treated with strong nitric acid, it is converted into nitro-benzene, ac cording to the following equation: HNO, = + Benzene Nitric Acid Water The French chemist Berthelot succeeded in converting acetylene gas into benzene by heating the former at a dull-red heat, the conversion taking place according to the following simple chemical equation: = Acetylene Benzene As acetylene (q.v.) can be made directly from carbon and hydrogen, it may be said that benzene, too, can be made from its ekenents. For an account of the chemical constitution of ben zene and its derivatives, see CARBON COMPOUNDS.