192 M. Dumas on the Law of Substitutions. 



nomena ; and to explain by a last word the meaning which 

 I attach to their respective functions, I shall say that in 

 chemistry the nature of the molecules, their weight, their form 

 and their situation, must each exercise a real influence on the 

 properties of bodies. 



It is the influence of the nature of molecules that Lavoisier 

 has so well defined, it is that of their weight which Berzelius 

 has characterized by his immortal labours. It might be said 

 that the discoveries of Mitscherlich relate to the influence of 

 their form, and the future will prove whether the present la- 

 bours of the French chemists are destined to give us the key 

 to the function which belongs to their position. 



We subjoin to the preceding memoir by M. Dumas, a 

 translation of an extract of a letter from M. Baudrimont, 

 published in the Comples Rendus, for March 16. 



" M. Dumas says, that the law of substitutions, and the 

 theory of chemical types, are unconcerned in the reclama- 

 tions of M. Baudrimont, who does not admit them. This re- 

 quires an explanation from me. 



" I cannot admit M. Dumas's law of substitutions ; first, 

 because it has not the character of a physical law ; secondly, 

 because it is but the strict expression of an order of facts, 

 much more extended than M. Dumas supposes ; but I admit 

 chemical substitutions; for substitution is only one of the modes 

 by which bodies may enter into combination. 



" I should without doubt do more than M. Dumas in say- 

 ing to the Academy : Chemical compounds are produced, either 

 by direct combination or by displacement, or by substitution, 

 or lastly, by several of these modes united. Substitution may 

 be non-equivalent, equivalent, isotypic, isorhythmic, or isomor- 

 phtc ; let me be pardoned this neologism. But this formula, 

 which is true, has not the character of a law ; it is but the 

 general expression of facts which are within the knowledge 

 of all men, ever so little versed in chemistry ; for chemical 

 substitutions have been known ever since we arrived at the 

 knowledge that one metal can precipitate another, taking its 

 place in a saline solution ; ever since hydrogen was first ob- 

 tained by displacing it by iron or zinc in the pretended sul- 

 phuric and chlorhydric acids diluted with water; ever since 

 we knew that chlorine displaces bromine and iodine ; ever since 

 we knew isomorphism by substitution ; and ever since M. 

 Beudant made more than a thousand applications of them 

 to the calculation of the composition of minerals.... I admit, 

 then, chemical substitution ; but I repudiate the pretended 

 law of M. Dumas, for the reasons I have just set forth. 



