CLASSIFICATION OF ORGANIC SUBSTANCES. 305 



isting. The bodies marked ? are not as yet known to 

 chemists. 



At the head of each column is placed an algebraic for- 

 mula expressing the formula of the series in general terms. 

 By making n=l, n=2, n = 3, etc., each member of the ho- 

 mologous series can be obtained. Two sets of names are 

 given : the first are in general use among chemists, and the 

 second is a very ingenious plan proposed by Dr. A. W. 

 Hofmann, where the vowels a, e, i, o, and u are successively 

 used in the final syllable to indicate the position of any 

 member of the isologous series. The Marsh Gas Series, or 

 Paraffin Series, as it is called, and the Olefin Series, are of 

 first importance, next comes the Benzol Series ; of benzol 

 itself you will learn more farther on. 



421. Substitution. Marsh gas, you know, is CH 4 , but it 

 may be considered as CHHHH, which is really the same 

 thing. Each H represents one atom of hydrogen. Now 

 certain bodies, as chlorine, bromine, cyanogen, etc. (provided 

 they are monatomic ; see 44), may take the place of these 

 atoms of H ; or, as we say, may be substituted, by means of 

 appropriate processes, for each atom of H in the compound 

 CHHHH; this substitution may take place all at once or 

 gradually, as shown below : 



CHHHH or CH 4 (1) 



CHHHC1 or CH 3 C1 (2) 



CHHC1C1 or CH 2 Cl a (3) 



CHC1C1C1 or CHC1 3 (4) 



CC1C1C1C1 or CC1 4 (5) 



thus giving rise to a large number of so-called substitution 

 compounds. The bodies numbered (1), (2), (3), (4), and (5) 

 really exist, one of them, (4), being the well-known and 

 valuable substance chloroform. Thus you see how the 

 theory of substitution is made use of to explain the forma- 

 tion of organic bodies. One more example, however, will 

 be given. 



