218 James W. Helps on some 



preserving railroad sleepers, &c., by soaking them with the 

 creosote or heavy oils from coal-tar. 



Still, however, the lighter oils were little used, except for 

 burning and for dissolving india-rubber ; their day came when 

 A. W. Hoffman, in 1845, showed in them the presence of 

 Benzene, and when two years later his pupil, C. B. Mansfield, 

 described the composition of these oils, and also a method 

 of preparing pure benzene on a practical scale. His devotion to 

 this research unfortunately cost him his life, for he was burnt to 

 death through the bursting of an experimental still at which he 

 was working. These discoveries were soon followed by the pre- 

 paration of NiTKO-BENZENE or oU. of viirbane, frequently used as a 

 substitute for the essential oil of bitter almonds. 



Coal-tar still failed to attain any commercial value ; but all 

 this was changed when, in 1856, Mr. W. Perkm succeeded in 

 producing the first aniline colour, especially as the starting- 

 point for this, viz., Benzol, was exclusively derived from coal-tar. 



I have said that Aniline, under the name of Crystalline, was 

 found out by Unverdorben, and Eunge found in coal-tar a sub- 

 stance called Kijanol; the latter also found that a solution of this 

 substance in water formed a dark purple on the addition of 

 chloride of lime or bleaching powder, a rather strange result, as 

 bleaching powder usually destroys rather than produces colour ; 

 but it was Hoffman, however, who proved that Cnjstalline, 

 Kyanol, and Aniline, were one and the same thing. Now, 

 Perkin, failing in some experiments he was making with Aniline, 

 turned his thoughts in another direction, and the idea occurred 

 to him that the purple colour obtained by the mixture of aniline 

 and chloride of lime, could be fixed and used as a dye. He dis- 

 solved some aniline in sulphuric acid, added bi-chromate of potash, 

 and obtained a dirty -looking precipitate ; this he treated with 

 alcohol, and produced a solution which imparted to his quill-pen, 

 when boiled in it, a most brilliant purple. Mr. Perkin made this 

 colour on a large scale, and thus founded the industry known as 

 the Aniline Colour Trade, Naturally, his success set other 

 chemists to work, and it is hardly surprising that the number of 

 derivatives from the tar-oils, &c., increased with great rapidity, 

 and has gone on doing so ever since. Let me draw your atten- 

 tion to the chart, or " tar-tree," as it is called, showing over 600 

 different products, nearly all brought to light during the past 50 

 years. 



Having now given you a brief history of the chief derivatives 

 from coal-tar, I must give you some idea of the manner in which 

 they are obtained. The first step is to distil the tar; this is 

 done in wrought-iron stills of various forms, one of which is 

 shown set in brickwork on drawing No. 1. A. is the still, 



