Appendix. ^^ 



Other relations than those of place may be represented geomet- 

 rically, with advantage. 



The aromatic hydrocarbons, together, are known as the 

 benzoles — the chief liquid distillates from coal tar — coal tar 

 naphtha. Among the distillates from coal tar are two other 

 hydrocarbons, which are solid, and are of unusual importance in 

 industry, namely : naphthalene and anthracene. These are not 

 homologous with benzene, as members of the same series 

 (CnHjo-e), but belong each in another series related progressively 

 to the benzene series, with mathematical harmony, as follows : 



I 

 C 



// \ 



Benzene CgHg or — C C — 



CnH2„_6 Single | || 



Hexagon P q 



^ / 



C 



C C 



// \ / \ 



Naphthalene CioHg -C C C— 



or C„H., 



n*--'-2n— 2x6 



Double Hexagon — p P P 



\ ^ \ // 



C C 



