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chemistry. And yet he persisted, secure in his faith in the pre- 

 dictions of pure chemistry. Who would say whether his triumph, 

 \vhich revolutionized one of our fundamental chemical indus- 

 tries, should form a further leaf in the laurels of pure chem- 

 istry or in those of applied chemistry? It would be impossible 

 to say which parts of Professor Baeyer's classical researches at 

 the University of Alunich on the structure and artificial synthe- 

 sis of indigo must be credited to the efforts of pure chemistry, 

 which to the domain of" applied chemistry ; the investigations 

 did, as a mater of fact, after some thirty years of conscious effort 

 by Baeyer, Heumann and others, lead to the successful exploi- 

 tation of the manufacture of artificial indigo on a scale which 

 must finally bring about the disappearance of the natural arti- 

 cle from the markets and make vast areas formerly used for 

 the cultivation of the indigo plant available for the production 

 of food. At the same time, besides these ultimate utilitarian 

 results, these same researches of Baeyer led to such pro- 

 profound questions of pure chemical interest as the problem 

 of the real structure of the benzene nucleus, the problem of 

 polymethylene rings, of unsaturated carbon valences, of tauto- 

 merism as shown in enolic and ketonic forms, of acid am.ides 

 and amido acids ; all present day organic chemistry is permeat- 

 ed with results of that work on the structure and synthesis of 

 indigo. 



The same difficulty that confronts us when we attempt to 

 distinguish in such great investigations between pure and ap- 

 plied chemistry and their relations to the progress of knowledge 

 and to practical affairs meets us if we attempt to 

 assign our great investigators to one field or the other : 

 A. W. iHofman was equally successful in extending the 

 lines of discovery into the great domain of organic nitrogen 

 bases, which before him, had been practically a "dark contin- 

 ent" and in developing extensive and profitable manufactur- 

 ing of aniline dyes: Baeyer pre-eminently a disciple of pure 

 chemistry was, as we have seen, the originator of the line of 

 work which has established the commercial preparation of arti- 

 ficial indigo: Bernthsen, professor of organic chemistry at 



