452 Professor Sir Henry E. Boscoe [April 16, 



ducts from tlie coal are obtained in the form of paraffinoid bodies 

 mainly, and hence are useless for colour-making purposes. Amongst 

 the few coking processes in which the heat is suddenly applied, and 

 consequently a yield of colour-giving hydrocarbons is obtained, may 

 be mentioned the patented process of Simon-Carves, the use of which 

 is now spreading in England and abroad. The tar obtained in this 

 process is almost identical in composition with the average gas-works 

 tar, whilst the coke also appears to be equal for iron-smelting purposes 

 to that derived from other coke-ovens. A third source of these oils 

 yet remains to be mentioned, viz. those obtained as a by-product in 

 blast furnaces fed with coal. 



Another condition has, in addition, to be considered in thisindustry, 

 and that is the nature of the coal employed for distillation. It is a 

 well-known fact that if Lancashire cannel be exclusively employed in 

 gas-making a highly luminous gas is obtained, but the tar is too rich 

 in paraffins to be a source of profit to the tar-distiller, whilst, on the 

 other hand, coal of a more anthracitic character, like that from New- 

 castle or Staffordshire, yields a tar too rich in one constituent, viz. 

 naphthalene, and too poor in another, viz. benzene. It is also known 

 to those engaged in carbonising coal principally for the sake of the 

 tar that the coal from diflferent measures, even in the same pit, yields 

 tars of very different constitution. That under these varying con- 

 ditions products of varying composition are obtained is a result that 

 will surprise no one who considers the complicated chemical changes 

 brought about in the jDrocess of the destructive distillation of coal. 



History of Benzene and its derivatives. — Having thus sketched the 

 principles upon which the formation of these valuable tar colours 

 depends, we should do wrong to pass over the history of the discovery 

 of benzene (CqHq), which contributed so much to the unlocking of 

 the coal-tar treasury. 



Faraday in 1825 discovered two new hydrocarbons in the oils 

 obtained from portable gas. One of these was found to be butylene 

 (C4H8) ; to the other Faraday gave the name of bicarburet of hydrogen, 

 as he ascertained its empirical formula to be C2H (C = 6). By ex- 

 ploding its vapour with oxygen, he observed that one volume contains 

 36 parts by weight of carbon to 3 parts by weight of hydrogen, and 

 its specific gravity compared with hydrogen is therefore 39.* 



Mitscherlich, in 1834, obtained the same hydrocarbon by distilla- 

 tion of benzoic acid, C7II6O2, with slaked lime, and termed it benzin. 

 He assumed that it is formed from benzoic acid simply by removal of 

 carbon dioxide. Liebig denied this, adding the following editorial 

 liOte to Mitscherlich's memoir: — " We have changed the name of the 

 body obtained by Professor Mitscherlich by the dry distillation of 

 benzoic acid and lime, and termed by him benzin, into benzol, 

 because the termination ' in ' ajipears to denote an analogy between 

 strychnine, quinine, &c., bodies to which it does not bear the slightest 



* i p 



Phil. Trans.; 1825, p. 440. 



