LECTURE XIV.] HISTORY OF CHEMISTRY. 295 



molecule of a substance becomes converted into a new mole- 

 cule by parting with some of its atoms, which unite to form 

 such a molecule as H.>, HC1, H.,O, NH 3 , etc. ; />., reactions 

 which occur within a molecule. As applied to such reactions, 

 the word condensation so far retains its meaning, that the atoms 

 are related more intimately (that is, by a greater number of 

 valencies) to one another. Amongst these reactions there are 

 many processes which have long been known, such as the 

 formation of ethylene from alcohol, of C C1 4 from C 2 C1 6 , of 

 aldehydes or of ketones from alcohols, of ethylene oxide from 

 glycol, of anhydrides from polybasic acids, etc. But the for- 

 mation of the anhydrides of monobasic acids, of the lactones 

 and of the lactone acids, which have been minutely studied by 

 Fittig, comparatively recently, must also be regarded as internal 

 condensations. To the same class of reactions belong, further, 

 the formation of cumarine, and that of the oxycumarines 

 (umbelliferone, daphnetine, etc.), of isatine, indol, rosaniline, 

 of rosolic acid, of the phthale'ines, of the aldehydines, of 

 quinoline, naphthalene, anthracene, etc. Consequently these 

 processes have played an important part in more recent 

 investigations, and they will engage our attention here a little 

 longer. 



The formation of ethenyl-xylene-diamine and of ethenyl- 

 toluylene-diamine by the reduction of nitro-acet-xylid and of 

 nitro-acet-toluid, observed by Hobrecker, 170 first attracted 

 Pliibner's attention to this matter. The latter chemist prepared 

 a large number of analogous compounds, and was able to show 

 that this abnormal course of the reduction only occurred with 

 the ortho-benzene derivatives, and not with the meta- or para- 

 derivatives. 171 This was entirely confirmed by Ladenburg's 

 investigations. 17 - The latter chemist discovered quite a number 

 of reactions which proceed altogether differently in the ortho- 

 series from the way in which they proceed in the other isomeric 

 series. In the case of the diamines, he showed, by means of 



170 Berichte. 5, 920. 171 Ibid. 8, 471 ; Annalen. 208, 278 ; 209, 339; 

 2IO, 328. 172 Berichte. 8, 677 ; 9, 219 and 1524; 10, 1123, 1260, etc. 



