^Appendix. 51 



acid, cinnamon oil, cuminic acid and cummin oil, with a con- 

 siderable number of artificial derivatives from these bodies, 

 nearly all having penetrating aromatic odors. The possession of 

 aromatic odors, however, is not especially characteristic of the 

 very great number of bodies now classified in this group. The 

 present definition of the aromatic group, is, in briefest terms, the 

 series of bodies built upon benzene. 



Benzene (also termed benzole), containing if carbon and 

 -fa hydrogen, may be formulated as C 6 H 6 : being in vapor 39 

 times heavier than its volume of hydrogen, its molecular weight 

 is 78 and it must be formulated as C 6 H 6 . Carbon, here as 

 almost everywhere, is a tetrad, and the six tetrad atoms of car- 

 bon have twenty-four bonds of chemical union. As only six of 

 these are occupied by the six monad atoms of hydrogen, 

 eighteen bonds must (it is believed) connect carbon with car- 

 bon, forming nine lines (or movements? 1 ) of union between 

 carbon atoms. As it is found in certain compounds that each 

 one of the six carbon atoms behaves alike, it appears that each 

 must hold the same relations to its fellows, and they must be dis- 

 posed in a ring, as first proposed by Kekule, in 1865. The nine 

 H lines of union between the six atoms 



of carbon (if not connecting alternate 

 or opposite atoms, *'. *., if disposed in 

 // \ the ring) require the alternate unions 



pj Q [ to be made by double lines. Then 



each atom of carbon in the ring has 



one bond of union free to be held by 



TT^p /" TT 



atoms (or semi-molecules) outside of the 



^ / carbon ring : so that as regards other 



C elements each atom of carbon is a 



I monad. 



H By substitutions, for one or more of 



the six hydrogen atoms, of other (monad) atoms or radicals, the 

 formulae of the various aromatic compounds are obtained : the 

 graphic symbol being always a hexagon. 



(1) KEKULE, Ann. Chem. u. Pharm., clxii, 77. LADENBURG, Deut. Chew. 

 Ges. Her., Y., 322. Watts' Dictionary of Chem., 2nd Supplement, 132. 



