LECTURE XVI.] HISTORY OF CHEMISTRY. 355 



mentioned. The latter formerly constituted one of the most 

 confused sections of organic chemistry, whereas Wallach has 

 now succeeded in systematising them by his extended and 

 careful researches. 133 But the most important thing about 

 them, the elucidation of their constitution, is still wanting ; for, 

 in spite of some fortunate attempts by Baeyer, 134 which led to 

 the synthesis of substances resembling terpenes, no one has 

 yet succeeded in making this clear. 



The discovery of the iodo-, iodoso-, and iodonium-com- 

 pounds, for which we are indebted to Willgerodt 13rj and to 

 Victor Meyer, 1315 is also important, and these compounds supply 

 new knowledge concerning the nature of iodine. The dis- 

 covery of antipyrine by Knorr 13T was of great importance in 

 medicine, and through it the pyrazol group 138 came to be 

 simultaneously explored. 



The preparation of the so-called substantive azo-dyes has 

 become of technical importance; 139 and that of synthetic 

 indigo, according to a method discovered by Heumann, 140 

 promises to become so. 



Great advances have likewise been made in the preparation 

 of artificial perfumes. Vanilline has already been referred to. 

 The manufacture of piperonal U1 (heliotropine), and especially 

 the synthesis of ionone by Tiemann and Kriiger, 142 must be 

 mentioned in this connection. 



This account of the most recent phases in the develop- 

 ment of our science must not be concluded, however, without 

 reference being made to the valuable, although unfinished, re- 

 searches which were carried out under the direction of Friedel, 

 and which aimed at the introduction of a new nomenclature 

 into organic chemistry. 143 Although it has not yet been 



133 Annalen. 225-306 (46 papers). 134 Ibid. 278, 288 ; Berichte. 26, 232. 

 1:w J. pr.Chem. [2] 33, 154 ; Berichte. 25, 3495 ; and 26, 1802. 136 Ibid. 

 25, 2632 ; 26, 1354 ; 27, 1592 ; 28, Ref. 80. 1:f7 Ibid. 17, Ref. 148 and 149. 

 Also Ibid. 17, 2032, etc. 1:M Annalen. 279, 188 ; 293, I. 13<J German 

 Patent No. 32958, 1884. 14 Berichte. 23, 3043, 3431. 141 Annalen. 

 152, 25. 14 ' 2 Berichte. 26, 2675 ; 28, 1754. 143 Compare the report by 

 Tiemann, Berichte. 26, 1595. 



