248 SCIENCE PROGRESS 



The atmosphere of careful chemical research which char- 

 acterised the first few years of the industry in England seemed 

 to disappear with the departure of Hofmann, with the excep- 

 tion of Perkin's Greenford Green works, and the scientific 

 method gave way little by little to empiricism and rule of thumb. 



However it may be, the fact remains that with the loss of 

 Hofmann the dye industry in Great Britain seemed to lose 

 its nucleus, and by degrees the other German dye chemists 

 left the country and returned to Germany, where they felt 

 that their abilities in research would be recognised and utilised. 



In 1866 Caro returned to Germany, and a couple of years 

 later joined the little group of chemists and manufacturers at 

 Mannheim which in 1865 had taken the name of the " Badische 

 Anilin und Soda Fabrik," and was persuaded to become 

 Technical Director. 



In 1865 also Professor Kekule announced his famous " ring 

 theory " of the structure of benzene, which in Caro's words 

 came " like the breaking dawn to lighten the hitherto dark 

 paths of industry, and to assist its progress upon clear lines 

 towards a definite objective. Technical chemistry felt that it 

 must keep abreast with the advance of the science to which 

 it owed its origin and whose leaders were also its own." 



From this date onwards it may be said that the manufacture 

 of coal-tar dyes ceased altogether to be a business conducted 

 by rule-of-thumb methods, and became simply an application 

 of scientific chemistry on a large scale. 



From 1865 to 1868 there was a period of diminished activity 

 as regards the preparation of new dyes either in England or 

 abroad, attention being chiefly devoted to the development 

 of existing dyes, and in fact the years 1 856-1 868 form a very 

 definite initial period in the coal-tar industry. 



The Second Period : 1 868-1 884. Synthesis of Alizarine ; 



Beginnings of Azo Dyes 



A new era of activity was inaugurated in 1 868 by the dis- 

 covery of Graebe & Liebermann in Berlin that alizarine, the 

 colouring matter of madder, was directly related to the hydro- 

 carbon anthracene, which under the name of " paranaphtha- 

 lene " had been shown to be present in coal-tar as far back 

 as 1832 ; and it will also be recalled that Perkin had begun 



