1 68 HISTORY OF CHEMISTRY. [LECTURE IX. 



uniform whole, which might undergo change from the fact that 

 one atom could take the place of another. Dumas compares 

 it with a planetary system ; the atoms here represent the indi- 

 vidual planets, and they are held together by affinity instead of 

 by gravitation. The atoms in this system can be replaced by 

 others : so long as the number of the equivalents and the relative 

 positions of the atoms are preserved, the system is unchanged. 



According to the theory of types, the properties of a com- 

 pound were affected far more by the arrangement than by the 

 nature of the atoms; and this doctrine which Dumas now 

 defends as confirmed by experiment, leads him to an attack 

 upon the electro-chemical theory. This is how he expresses 

 himself : 45 



" One of the most immediate consequences of the electro- 

 chemical theory is the necessity of considering all chemical 

 compounds as binary substances. It is necessary to find out, 

 in every one of them, the positive and the negative constituents, 

 or the groups of particles to which these two distinctive char- 

 acters are ascribed. No view was ever more fitted to retard 

 the progress of organic chemistry." And in another place : 46 

 "In general, when the, substitution theory and the theory of 

 types assume similar molecules, in which some of the elements 

 can be replaced by means of others without the edifice be- 

 coming modified either in form or outward behaviour, the 

 electro-chemical theory splits these same molecules, simply and 

 solely, one may say, in order to find in them two opposite 

 groups, which it then supposes to be combined with each 

 other in virtue of their mutual electrical activity." 



Dumas does not deny the influence of electrical forces 

 upon chemical reactions. On the contrary, chemical and 

 electrical forces might, according to him, even be identical. 

 What he attacks is the electro-chemical theory of Berzelius, in 

 accordance with which hydrogen is supposed to be always 

 positive, and chlorine always negative. He believes that in 

 the formation or decomposition of compounds he can recognise 



45 Annalen. 33, 291. Ibid. 33, 294. 



