LECTURE XII.] HISTORY OF CHEMISTRY. 223 



up, whilst those deducible from the hydrogen type are pre- 

 served : 



c H i r H n 



V^ 47 1 J. r L /"\ V* o -i- -1 r V^ A 



Ethyl sulphuric acid SOJ gives SO CL 



H} -id 



while benzene sulphonic acid SO 2 ^Q gives SO 9 C1 



H J ~HQ 



It was by means of the theory of mixed types (the last 

 consequence of this mode of regarding substances) that Ger- 

 hardt's system first attained that uniform character in which it 

 dominated organic chemistry for several years. But after the 

 idea of the types had been recognised, 7 they themselves became 

 unnecessary. The theory of types was only a formal con- 

 ception, which lost its importance as soon as its real teaching 

 had been grasped. It had been necessary, however, for the 

 origination of the views as to atomicity then in process of 

 development. Particularly active in this connection were 

 Williamson, Wurtz, Odling, and especially Kekule that is to 

 say, the chemists who had already taken an important part in 

 establishing the theory of types. Simultaneously, however, 

 such important services were rendered, from an altogether 

 different side (that is, from the opponents of Gerhardt and 

 successors of Berzelius), both by means of theoretical specula- 

 tions and of experimental investigation, that before we turn to 

 the theory of atomicity and the views arising from it as to the 

 mutual relations of the atoms, we shall look more closely at 

 the labours of that school which had sprung up from the ruins 

 of the system of Berzelius. 



In doing so, I may be permitted to go a long way back and 

 state the facts which, in my opinion, led from the copulse of 

 Berzelius to the important views of Kolbe. 



Magnus had shown, at the beginning of the fourth decade 

 of the century, 8 that the salts of ethyl sulphuric acid, dried 



7 Ann. Chim. [3] 44, 304 ; compare also Hunt, loc, cit, 8 Pogg. 



Ann. 27 267. 



