248 CONSIDERATION OF CARBON COMPOUNDS. 



The explanation regarding the formation of an homologous 

 series is to be found in the above-described property of carbon 

 to form chains. By saturating, for instance, the affinities in the 

 open carbon chains mentioned above, we obtain the compounds 

 CH 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 , etc. 



H HH HHH HHHH 



H C H, H C C H, H C C C H, H C C C C H , etc. 

 H HH HHH HHHH 



Many homologous series of various organic compounds are 

 known, as, for instance : 



Types. It has been proposed to select some substances in 

 which the arrangement of atoms in the molecules may be taken 

 as representative of whole classes of other substances, the mole- 

 cules of which have a similar arrangement, and these normal 

 substances have been termed types. Most substances may be 

 classified under the following five types : 



I. II. III. IY. Y. 



Hydrogen. Water. Ammonia. Methane. Phosphoric chloride. 



H = H ' Cl 



H H, H O H, 1ST H, C , P Cl. 



By replacing the constituents of these types by other elements 

 or residues of equal valence, most of the compounds known 

 (both organic and inorganic) may be classed in one of these 

 types. 



The following five substances may, for instance, be said to 

 have an atomic arrangement similar to the types above stated : 



