LECTURE XII.] HISTORY OF CHEMISTRY. 233 



them, " that the properties of an organic compound are de- 

 pendent upon the position and not .upon the nature of its 

 single atoms," I cannot altogether agree with him in this. 

 Since the investigations of Hofmann 43 on substituted bases, 

 the idea of substitution was no longer held, even by Laurent, 

 in the absolute sense in which the latter had at one time stated 

 it. 44 The chlorinated ethers previously prepared by Malaguti 45 

 could not by any means be brought into harmony with com- 

 plete invariability of the type ; and when Williamson referred 

 ether, alcohol, and acetic acid to the water type, it was plain 

 that he used the word type more in the sense of the mechanical 

 than of the chemical types. 



By this paper of Frankland's the first step was taken in 

 the approach towards one another of the heretofore separated 

 schools, and the way to a mutual understanding was provided. 

 It was destined to lead to a fusion of the different opinions, 

 out of which the theory of valency then arose. The change 

 of opinion on the part of Frankland was a gain to the supporters 

 of the theory of types, since he brought with him novel ideas 

 which were capable of being turned to excellent account. I 

 do not assert that they might not themselves have been able 

 independently to make the last great advance that is, the 

 step to the classification of the atoms according to their valence. 

 In the way in which the development actually took place, the 

 influence of Kolbe, and more particularly that of Frankland, 

 upon the supporters of the Gerhardt-Williamson school (VVurtz, 

 Kekule, and Odling) can hardly fail to be recognised. Both 

 schools were required, in order to raise the significance of 

 the formulae to what it subsequently became; especially as 

 Williamson, the only one who desired, even at that time, to 

 write anything more than decomposition formulae, withdrew 

 from the further development of chemistry. 



It may now be expedient to explain at once the transition, 

 for which the way had been prepared by Frankland, from the 

 theory of copulae to that of types ; and then, when I enter 



43 Annalen. 53, I. 44 Comptes rendus par Laurent et Gerhardt, 1845. 

 45 Annalen. 24, 40 ; 56, 268. 



