COAL AND THE COAL-TAR COLORS. 205 



of the cleansing agents. They are then put into the market as illu- 

 minating oils. They may also be used for solutions of India-rubber, 

 but sulphuret of carbon is preferred for that purpose. 



Faraday discovered benzine in 1825 among the products arising 

 in the manufacture of oil-gas, and called it bicarbureted hydrogen. 

 Mitscherlich, in 1825, in treating benzoic acid with soda, obtained a 

 volatile liquid which he called benzine. Hofmann, in 1825, demon- 

 strated that these two substances were the same. Berthelot explained 

 the formation of the substance, and made a synthesis of it by heating 

 acetylene, its molecule being composed of three molecules of that gas 

 united, or of twelve atoms of carbon and six of hydi'ogen. Benzine 

 is a type of a class of organic bodies that furnish, by substitution, 

 innumerable series of derivatives. They are like buildings from which 

 we can take the stones one at a time and replace them with others. 

 They are the organic radicals, in which a number of atoms of carbon 

 and hydrogen are associated in such a way that the energy of one 

 atom of hydrogen is left free. In benzine, for instance, Ave may sub- 

 stitute for each atom of hydrogen an atom of chlorine and get benzine 

 monochloride, benzine dichloride, etc., or an atom of bromine or iodine 

 and get benzine bromide and benzine iodide ; or another radical, such 

 as methyl or ethyl, and get methylbenzine or ethylbenzine, dimethyl- 

 benzine, trimethylbenzine, and so on. These theories permit us to 

 account for the long series of bodies which organic chemistry has re- 

 vealed, many of which are now employed in industry. 



Benzine, as everybody knows, is a light liquid, perfectly colorless, 

 and having a nauseous odor. It nevertheless furnishes perfumes and 

 dyes. Charles Mansfield, who was the first person to utilize benzine, 

 and make it on a large scale, announced in 1847 that he had found 

 among the derivatives of stone-coal an oil that might take the place of 

 the oil of bitter-almonds. It was nitrobenzine. Mitscherlich had pre- 

 viously produced, by the lively reaction of nitric acid on benzine, a 

 colorless liquid, in which a compound molecule of nitrogen and oxygen 

 was substituted for one of the six atoms of hvdrosren in benzine, but 

 his experiment never got beyond the laboratories. It was attended by 

 too great dangers. Nevertheless, Mansfield ventured to repeat it in 

 his shop, and succeeded in basing an industrial operation upon it. 

 Nitrobenzine can not be pure unless the benzine was pure, and that is 

 rarely the case with the commercial article. In the mixture of hydro- 

 carbons, of which naphtha is constituted, are some very nearly alike in 

 composition and in respect to their boiling-point, and it is difiicult, 

 even with the best distilling apparatus, to arrest the passage of some 

 of them. Toluene, for example, nearly always comes over with ben- 

 zine. Like it, it is attacked by nitric acid and then yields a nitro- 

 toluene. There has also been found, associated with nitrobenzine, a 

 peculiar yellowish-colored acid, endowed with the smell and taste of 

 the pineapple ; and its ethers taste like the strawben-y or the rasp- 



