1 66 HISTORY OF CHEMISTRY. [LECTURE IX. 



another molecular type, the law of substitution is no longer 

 adhered to during the reaction." And further: "Alcohol, 

 acetic acid, and chloracetic acid belong to the same natural 

 family ; acetic acid and chloracetic acid to the same species." 

 It may therefore be said that, so far as the idea goes, mechani- 

 cal type and nucleus amount to the same thing; both comprise 

 the substances which arise from one another or which can, at 

 least, be looked upon as arising from one another by equivalent 

 substitution. 



Dumas, as may have been observed, has now arrived at the 

 opinion that his law of substitutions is not applicable to all 

 reactions, and that an equivalent of another element is not 

 always taken up even for the hydrogen removed. He is all 

 the more obliged to admit this, since he now no longer assumes 

 the existence of ready formed water in organic substances 

 (alcohol, for example 36 ) whereby his second rule ceases to 

 hold. 37 He is obliged, in consequence, to recognise, and he 

 does it explicitly, that the phenomenon of substitution is not a 

 general one ; he even finds in this one of its most essential 

 features. 38 



While he thus limits the applicability of the law of substi- 

 tution, the validity of the law in another direction is enhanced. 

 It is not only the hydrogen of an organic substance that can, 

 according to Dumas, be replaced, but all the elements which 

 it contains. True substitution of the oxygen, of the nitrogen, 

 and even of the carbon may be accomplished ; 39 and these 

 elements may be replaced, not only by others, but also by 

 compound groups such as cyanogen, carbonic oxide, sulphurous 

 acid, nitric oxide, nitrous acid, amide, etc. The assumption 

 of the replaceability of carbon, which at that time met with the 

 most vigorous contradiction as a silly hypothesis, and was, in 

 Germany, made the subject even of ridicule, 40 was a conse- 

 quence of the experiments of Walter 41 who had obtained sulpho- 

 camphoric acid by the treatment of camphoric acid with 



36 Annalen. 33, 261. :<7 Compare p. 141. 38 Annalen. 33, 264. 

 Ibid. 33, 269. 40 Ibid. 33, 308. 41 Ibid. 36, 59. 



