184? M. Dumas on the La*w of Substitutions > and the 



powers of bodies. Now, that hydrogen can perform the func- 

 tion of chlorine exactly, is what I can hardly admit. 



"Allow me to ask you if chemists are not rather easy {facile) 

 when they group their symbols in every way. There is in this 

 facility of permutation something which does not completely 

 satisfy us physicists, and which appears to lend itself rather too 

 complacently to all combinations. Is there not something ar- 

 bitrary in the manner in which chemists make these choices? 

 To attack the electro-chemical theory you group your formulae 

 in a certain manner; immediately to defend this theory M. 

 Berzelius groups them in another manner ; where is the law 

 of nature?"* 



I shall be pardoned for quoting this letter ; it depicts the 

 opinions of philosophers upon questions still new to many 

 minds, and in all cases very obscure to those persons who have 

 not followed them step by step in their development. 



Those who have taken a part in the experimental researches 

 of which we are speaking, know well that the electro-chemical 

 theory guided my first studies, that I professed and admitted 

 it for a long time on the faith of its inventors. They also know, 



* [It is proper to add here, that M . de la Rive, in the Bibliotheque Uni- 

 versellehr February 1840, p. 193, after reciting the passage extracted from 

 his letter by M. Dumas, as above, makes the following remarks on the sub- 

 ject of it and the comments of M. Dumas : — 



" In writing these lines to M. Dumas, I sought, as he himself remarked, 

 to satisfy myself concerning a question which becomes every day more ob- 

 scure. On the one hand, we cannot help recognizing that in organic 

 chemistry, especially the electro-chemical theory, or rather the chemistry 

 which connects the development of electricity with the play of the affini- 

 ties with which it is always accompanied, has on its side powerful argu- 

 ments, even when we do not admit on this point all the views of M. Ber- 

 zelius. On the other hand, there are certainly some phenomena, espe- 

 cially in organic chemistry, in which the function of the same elements in 

 the formation of compounds seems to change its nature in a manner so 

 complete and so extraordinary, that we cannot admit of their possessing a 

 previous predisposition to conduct themselves in such and such a chemical 

 manner, or what comes to the same thing, an absolute electro-chemical 

 power. Would not the result of this seem to be that the electro-negative 

 or electro-positive properties do not previously exist in bodies? That 

 they do not exist until the bodies are presented to each other, and that 

 from that time instead of being absolute they are i-elative, that is to say, 

 depend for the same body on the relations which exist between its own 

 nature and that of other bodies in the presence of which it is found ? 

 This point of view can only be thoroughly examined by means of direct 

 experiments. I shall return to it when I have finished bringing together 

 a number of facts sufficiently considerable for its justification, if, as I pre- 

 sume, I find it to be founded. I shall be glad to try thus to reconcile, at 

 least in part, the function which M. Berzelius attributes to electricity in 

 the chemical phenomena with the very remarkable laws at which M. 

 Dumas seems to have arrived."] 



