286 HISTORY OF CHEMISTRY. [LECTURE XIV. 



These and other facts, which seemed to place beyond 

 doubt the relations of several natural bases to pyridine, 86 led 

 Wischnegradsky to the opinion stated above regarding the con- 

 stitution of the alkaloids ; 8T and this was more fully discussed 

 and established, a year later, by Konigs. 88 Since then, this 

 view has gained ground more and more ; especially as a series 

 of facts have been discovered in support of it. Thus Weidel 

 obtained a pyridine-tricarbonic acid by the oxidation of ber- 

 berine ; s9 Gerichten was able to prepare pyridine-dicarbonic 

 acid from narcotine, 90 and Ladenburg dibromo-pyridine from 

 atropine; 91 while Hofmann converted coniine into propyl- 

 pyridine. 92 



The results which attended this view of pyridine and of 

 quinoline, and the recognition which they met with, led to the 

 introduction of a similar view concerning many other sub- 

 stances. In the first place it is necessary to consider the 

 formula which was assigned as early as 1869, by Baeyer and 

 Emmerling, 93 to indol,' 14 the starting-point for most of the 

 indigo derivatives : 



According to this formula indol is represented as a double 

 nucleus resembling naphthalene and quinoline. This mode of 

 representing it acquired greater significance when Baeyer and 

 Emmerling, 95 somewhat later, regarded pyrrol also as a "ring." 

 The same relation was now assumed between pyrrol and 



86 Weidel, Annalen. 173, 76; Ramsay and Dobbie, Berichte. II, 324. 

 87 Ibid. 12, 1506; compare also Ladenburg, ibid. 12, 947. ^ Studien 

 uber die Alkaloide, Munich 1880. 8<J Berichte. 12, 410. ! ' Annalen. 

 210, 101. 91 Ibid. 217, 148. K Berichte. 17, 825. QS Ibid. 2, 

 679. 94 Baeyer, ibid. I, 17. 95 Ibid. 3, 517. 



