All the members of this series are well- 

 known bodies. The first is called chemically 

 methane, or from its natural occurrence, 

 marsh gas. The second is called methyl 

 chloride, the group (CH 3 ) united to the single 

 atom of chlorine forming a characteristic 

 group in organic chemistry which goes into 

 and comes out of compounds as if it were a 

 single univalent atom ; such a group is 

 called an organic radical. The third member 

 with two chlorine atoms is called di-chlor- 

 methane, for obvious reasons. The fourth 

 member with three chlorine atoms is the 

 well-known anaesthetic, chloroform ; its chemi- 

 cal name is tri-chlor-methane. The fifth 

 member where all the hydrogen has been 



