Appendix. 57 



Wright with oils of lemon, orange and nutmeg, reported to the 

 London Chemical Society, in i873. 8 ^ seems, then, strongly 

 probable, if not yet fully established, that the terpenes, extend- 

 ing as they do widely through the vegetable kingdom, are all 

 built upon the benzene nucleus, being, however, somewhat com- 

 plex extensions of that nucleus. 



From this standpoint, too recent to be secure, no small 

 share of the most simple carbon compounds which plants con- 

 tain those destitute of oxygen and nitrogen belong to the aro- 

 matic group. It has long been well known that plants contain 

 oxidized aromatic compounds very closely related to hydrocar- 

 bons, so that the latter are easily obtained from plant constitu- 

 ents. Benzene itself took its name from the abundant educt ben- 

 zoic acid, from which Mitscherlich first obtained it in 1834, by 

 heating with lime or by stronger heat with iron. It is obtained 

 by dry distillation or by more gentle treatment from the most of 

 the aromatic compounds, and by harsher methods from bodies 

 not built upon it ; having been discovered by Faraday in 1825 

 among the vapors distilled at a high temperature from fats. 

 Toluene was obtained by Deville, who first examined it and 

 named it, by distilling Tolu balsam ; and it is obtained with es- 

 pecial ease by the moderate action of heat upon a large number 

 of resins this being one of the many indications that most 

 resins contain the aromatic nucleus. Xylene is also easily ob- 

 tained from resins. The reverse of these transformations, the 

 constant production of resins from terpenes by atmospheric ox- 

 idation in balsams and turpentines, will require mention further 

 on. And the manufacture of aromatic hydrocarbons, on the 

 large scale, from coal, will be noticed with the methods of pro- 

 duction from inorganic sources. 



After the hydrocarbons, we next inquire as to the distribu- 

 tion of the oxidized products of the aromatic group : phenols, 

 acids, aldehydes, etc. 



(8) Jour. Qhem. 8oc., xi., 686-701. 



