324< M. Dumas on the Law of SubstiitttionSf 



weighing IS^i'. These quantities are the chemical equiva- 

 lents of those bodies ; all chemical action takes place between 

 them and their multiples. 



Now, to say that from an organic compound, an equivalent 

 of hydrogen may be subtracted, and that its place may be 

 taken by an equivalent of chlorine, is manifestly announcing 

 a law in perfect harmony with the general law of the recipro- 

 cal action of bodies by equivalents. Every one comprehends, 

 that if a crystallized body could produce another, likewise 

 crystallized, by losing hydrogen and gaining chlorine, which 

 could not be represented by equivalents, we must conclude 

 from this that the theory of equivalents is false. The law of 

 substitutions ought to be in accordance with the theory of 

 equivalents, as moreover the general expression which has 

 been given to it suggests. 



But from thence to assert that the law of siibstitutions has 

 no peculiar character, that it is only a particular case of the 

 theory of equivalents, there is either an equivocation or an 

 immense leap. That this leap was made when the law of 

 substitutions was at first put forth, that nothing allowed the 

 cause of it to be foreseen, in order to connect it with a theo- 

 retical principle, 1 concede without difficulty. This also did 

 not fail to be the case, and amongst the objections of the 

 German chemists to the law of substitutions, it always figures 

 first. The philosophers who some years ago viewed it in 

 this manner, were right without doubt, but they must have 

 been very much surprised to see so many skilful men persist 

 in finding in it a special character. 



With regard to myself, if I believed in the future prevalence 

 of the law of substitutions, in its importance, five years ago, 

 when I was the only one who defended it, it is not to be sup- 

 posed that I can change my opinion, when the m.ost eminent 

 English chemist, Mr. Graham, adopts it without reserve ; 

 when M. Liebig, after sharply criticising it, now receives it 

 as admitted in science ; when so many labours, undertaken 

 often to combat it, have come within this very circle, to give 

 it a complete consecration ; when, lastly, far from seeing in the 

 law of substitutions a simple experimental fact, we are now 

 able to ascend to its cause. 



Thus, to assert, as M. Pelouze has done, that the phas- 

 nomenon of substitution, when it is observed, is only a par- 

 ticular case of the theory of equivalents, is to announce as a 

 novelty two things perfectly known, viz.: first, that in the 

 action of two bodies, substitution does not always take place; 

 secondly, that when it is effected, it takes place by equiva- 

 lents. This does not hinder the phsenomenon of substitution 



