LECTURE XIV.] 



HISTORY OF CHEMISTRY. 



287 



indol as between pyridine and quinoline or between benzene 

 and naphthalene : 



H 



The analogues are : 



C H (; 

 Benzene. 



C 5 H 5 N 



1'yridine. 



C 4 H 5 N 



Pyrrol- 



C 10 H S 

 Naphthalene. 



C 9 H,N 



Quinoline. 



C 8 H 7 N 



Indol. 



At the same time, tetra-phenol % (furfuran), C 4 H 4 O, dis- 

 covered by Limpricht, was represented by a formula analogous 

 to that for pyrrol, the NH group of the latter being regarded 

 as replaced by O. Related to furfuran, there is thiophen, 

 C 4 H 4 S, 1)>r (discovered more recently by V. Meyer), which is 

 looked upon as thiofurfuran, and which has already become of 

 great importance on account of its numerous derivatives. In 

 the case of thiophen the resemblance exhibited by it and its 

 derivatives to benzene and the benzene derivatives is particularly 

 noteworthy. 



Carbazol, 98 discovered by Fritzsche, may also be mentioned 

 here a substance which Grabe 91 ' regards as fluorene, in which 



CH., is replaced by NH, thus: j 



NH. Further, there is 



C H 



acridine, 100 found in crude anthracene by Gra'be and Caro, 

 which is regarded as a derivative of anthracene 1G1 or of phen- 



96 Berichte. 3, 90. 97 Ibid. 16, 1465. 98 J. pr. Chem. 73, 286; 101, 



342. " Annalen. 167, 125 ; 174, iSo. 10 Ibid. 158, 265. 

 Berichte. 16, 1609; Bernthsen and Bender, ibid. 16, 1803. 



Riedel, 



