HYDROCARBONS. 301 



stitution-derivatives when subjected to the action of chlorine or 

 bromine. 



Most of the paraffins are known in two (or even more) modifications ; there 

 are, therefore, other homologous series of hydrocarbons of the same composition 

 as the above normal paraffins, which show some difference from the normal 

 paraffins in boiling-points and other properties. In these isomeric paraffins the 

 atoms are arranged differently from those in the normal hydrocarbons, which 

 fact may be proven by the difference in decomposition which these substances 

 suffer when acted upon by chemical agents. 



No isomeric hydrocarbons of the first three members of the paraffin series are 

 known, which fact is in accordance with our present theories. Assuming that 

 the quadrivalent carbon atoms exert their full valence, and that they are held 

 together by one atomicity only, we can arrange the atoms in the compounds, 

 CH 4 , C 2 H 6 , and C 3 H 8 , not otherwise than thus : 



TT O^^-LiQ 



CEEH 3 | 



^1 U. 



C H 3 



In the next compound, butane, C 4 H 10 , we have two possibilities explaining 

 the structure of the molecule, namely, these : 



C=H 2 C=H 3 



C=H 2 C=H 3 CH-CEEH 3 . 



C=H 3 



Both these compounds are known, and termed normal butane and isobutane, 

 respectively. 



The next member, pentane, C 5 H 12 , shows three possibilities of constitution, 

 thus : 



3 



U 

 * 



I C=H 3 



H. 



C^H 3 C CEEH. 



H 2 



C=H 2 



0=H 2 | 



I C=H 3 



CEH 3 



These compounds also are known. With the higher members of the paraffins 

 tne number of possible isomeres rises rapidly according to the law of permuta- 

 tion, so that we have of the seventh member 9, of the tenth 75, and of the 

 thirteenth member 799, possible isomeric hydrocarbons. 



Methane, CH 4 (Marsh-gas, Fire-damp). This hydrocarbon has 

 been spoken of in Chapter 13, where it was stated that it is a color- 

 less, combustible gas, which is formed by the decay of organic matter 

 in the presence of moisture, during the formation of coal in the 



