LECTURE IX.] HISTORY OF CHEMISTRY. 167 



sulphuric anhydride, carbonic oxide being evolved. Dumas 

 regarded this acid as camphoric acid in which one atom of 

 carbon was replaced by the group SO 2 . 



If the conception of the molecular type is regarded in its 

 widest sense, it may be said that this idea of Dumas as to the 

 replacement of carbon, was wholly justified by subsequent 

 experiments. Wohler has pointed out a substitution of carbon 

 by silicon; 42 and by means of reactions quite analogous to 

 those employed for converting a hydrocarbon into the corre- 

 sponding alcohol, Friedel and Crafts have transformed ethyl 

 silicide into silico-nonyl alcohol which, as the name indicates, 

 they look upon as nonyl alcohol in which one atom of carbon 

 is replaced by one atom of silicon. 43 More recently, silicon 

 compounds have been discovered which are not only to be 

 regarded as analogous to certain carbon compounds, but which 

 behave in a manner similar to the latter. This is particularly 

 the case with triethyl silicol. 44 



I may also remark here that the view of Dumas concerning 

 the replacement of carbon was in contradiction to the nucleus 

 theory of Laurent, and rendered difficult the classification of 

 organic substances according to the number of their carbon 

 atoms. The ideas of the two chemists approach each other 

 more closely as regards the conception of the radical than as 

 regards its composition. Dumas now expressly slates also that 

 the radical is not an unalterable group, but that in it, just as in 

 all compounds, the atoms are replaceable by others. Gerhardt 

 had, however, advanced similar views two years earlier, and we 

 shall, therefore, have to deal fully with this point afterwards in 

 another lecture. 



The first, and probably the most important consequence of 

 the theory of types was that it demanded a unitary mode of 

 regarding substances. The compound was no longer to be 

 regarded as consisting of two parts. It constituted, rather, a 



42 Annalen. 127, 268. 43 Comptes Rendus. 6l, 792 ; also Annalen. 

 138? J 9 > compare further Friedel and Ladenburg, Annalen. 143, 118; 

 145, 174 and 179; 147, 355 ; and Comptes Rendus. 66, 816. 44 Laden- 

 burg, Annalen. 164, 300. 



