HYDROCARBONS. 265 



use of the difference in their boiling-points and specific gravi- 

 ties, or of their solubility or insolubility in various liquids, or, 

 finally, of their basic, acid, or neutral properties. 



Olefines. The hydrocarbons of the general formula C n H 2n , 

 are termed defines. To this series belong : 



Ethene or ethylene, C 2 H 4 . 



Propene or propylene, C 3 H 6 . 



Butene or butylene. C 4 H 8 . 



Pentene or atnylene, C 5 H 10 . 



Hexene or hexylene, C 6 H 12 . 

 etc. 



Methene, CH 2 , the lowest term of this series, is not known. 

 The hydrocarbons of this series are not only homologous, but 

 also polymeric with one another. 



Of special interest is the first known member of the series, 

 ethene or olefiant gas, on account of its normal occurrence in 

 illuminating gas as well as in most common flames, the lumin- 

 osity of which depends greatly on the quantity of this compound 

 present in the burning gas. 



Benzene series or aromatic hydrocarbons. The members of 

 a series of hydrocarbons having the general composition 

 C n H 2n _ 6 and all the derivatives of this group, including the 

 alcohols, acids, etc., are generally termed aromatic substances 

 on account of the peculiar and fragrant odor possessed by many 

 of them. To the benzene series belong : 



B. P. 



Benzene, C 6 H 6 , 80 



Toluene, C 7 H 8 = C 6 H 5 .CH 3 , 110 



Xylene, C 8 H 10 = C 6 H 4 .2CH 3 , 142 



Cumene, C 9 H 12 = C 6 H 3 3CH 3 , 151 



Cymene, C 10 H, 4 = C 6 H 2 .4CH 3 , IT 5 



Laurene, C n H 16 = C 6 H.5CH 3 , 188 



The structure of the closed carbon chain of benzene has been 

 referred to, and will be more fully considered in connection with 

 the other aromatic compounds. 



The most important member of the above series is benzol or 

 benzene, C G H 6 , which is chiefly obtained from coal-tar. It is a 

 colorless, highly volatile and combustible liquid, and an excel- 



