328 M. Dumas on the Law of Subsfittitions, 8^c. 



These are the foresights, always justified by experience, 

 which characterize the law of substitutions. If it be connected 

 with the theory of equivalents, it then results that every 

 chemical phsenomenon is represented by equivalents, and that 

 the facts of substitution are chemical phsenomena ; that every 

 possible event in chemistry is translated into the language of 

 equivalents, and that after all a true fact must be a possible 

 fact. Ill the same manner that the possible comprehends the 

 true, ill like manner, and not otherwise, the theory of equiva- 

 lents comprehends the law of substitutions. 



So far, I have reasoned as if the law of substitutions only 

 applied in reality to the substitution of hydrogen, which has 

 furnished the first examples of it. But chemists know that 

 in an organic substance not only can hydrogen undergo sub- 

 stitution, but also oxygen and azote, of which it would be 

 easy to cite numerous examples. 



Still more, we can cause carbon to undergo real substi- 

 tutions, which sufficiently shows how artificial that classifi- 

 cation of organic substances would be, which would rest 

 solely on the permanency of the number of the equivalents of 

 carbon in all the compounds of the same family. 



In an organic compound, all the elements may then be 

 displaced, and others substituted for them in succession. Those 

 which disappear most easily, abstraction being caused by 

 certain conditions of stability which we cannot yet foresee, are 

 those of which the affinities are the most energetic. This is 

 why hydrogen is one of the easiest to subtract and have an- 

 other element substituted for it; this is why carbon is one of 

 the most rebellious, for we know few bodies which can act 

 upon carbon and not upon hydrogen. 



In fine, I add that the law of substitutions allows us not 

 only to foresee the disappearance of a certain number, or of 

 all the elements of the organic compound, and new elements 

 being substituted for them, but also the intervention, playing 

 the part of the same elements, of certain compound bodies. 



Thus, cyanogen, carbonic oxide, sulphuric acid, the 

 binoxide of azote, nitrous gas, amidogen, and many other 

 compound groups may intervene as the elements would do, 

 take the place of hydrogen, and give rise to new bodies. 



The law of substitutions is then an almost inexhaustible 

 source of discoveries. It guides the hand of the chemist 

 who trusts to it, it rectifies his errors by showing him the 

 cause of them; and in a number of possible but uncertain 

 actions, it points out some which are proximate, easy to pro- 

 duce, and of the highest interest. 



This future, so rich in facts which may be realised, so full 



