HYDROCARBONS AND THEIR HALOGEN DERIVATIVES. 465 



The above table shows that the paraffins form an homologous 

 series; the first four members are gases, most of the others liquids, 

 regularly increasing in specific gravity, boiling-point, viscidity, and 

 vapor density, as their molecular weight becomes greater. 



The paraffins are saturated hydrocarbons, the constitution of which 

 has been already explained; they are incapable of uniting directly 

 with monatomic elements or residues, but they easily yield sub- 

 stitution-derivatives when subjected to the action of chlorine or bro- 

 mine, hydrogen in all cases being given up from the hydrocarbon. 



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 bond only, we can arrange the atoms in the compounds, 

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



/ H 

 ^H 



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

 the structure of the molecule, namely, these : 



CEBH 3 



C=:H 2 C=H 3 



(j=tiy O^=Ii 3 OH G^^-tl 3 . 



LH 



L/ r 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: 



C=H 3 



C=H a CEEH 3 



| C=H 3 -C-H. | 



C=H 2 | C=H 3 C C^H, 



C=H 2 | _ O=H 3 . 



C^5iHj| 



C=H 3 



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

 the number of possible isomers rises rapidly according to the law of permuta- 

 30 



