S26 M. Dumas on the Lata of Substitutions, 



we may take away 1, 2, 3 equivalents of hydrogen, and sup- 

 ply their places by I5 2, 3 equivalents of chlorine, bromine, 

 iodine, or oxygen. It indicates that these substitutions will 

 give birth to new bodies, the properties of which it is often 

 possible to foresee. It makes known that these actions [re- 

 actions) are the easiest, the most frequent, the least changing 

 (alteratites) that a body can undergo. 



Before the law of substitutions was published, no one could 

 have foreseen how a hydrogenated body would have acted 

 under the influence of chlorine or oxygen. Now every one 

 knows it, and a chemist performs in a few days, by means of 

 this guide, operations which would have required years of 

 labour before he had learned its use. 



Ask the theory of equivalents what ought to take place 

 when ether is subjected to the action of chlorine, and it will 

 certainly reply that it knows nothing of the matter; or indeed, 

 what comes to the same thing, it will show you a hundred 

 possible cases between which you will have to choose. 



For ether ma}' lose in succession the five equivalents of 

 hydrogen which it contains without gaining anything, which 

 gives five new bodies ; for it may, without losing anything, 

 absorb 1, 2, 3, 4, 5, and many more equivalents of chlorine 

 besides ; which makes ten, twenty, thirty new bodies, if we 

 desire it ; for it may, in losing a single, or even two, or 

 three equivalents of hydrogen, absorb equivalents of chlorine 

 more or less in number; and in this third hypothesis, the 

 number of compounds will become almost innumerable. 



In fine, we should fall upon almost infinite varieties of 

 combinations, if we add that the oxygen of ether may be 

 eliminated, either free, in the form of water, or in the form 

 of carbonic acid. 



Thus the theory of equivalents announces the production 

 of a prodigious quantity of compounds: provided the ele- 

 ments which the ether loses and those which it gains are 

 represented by equivalents, it is sufficient. 



It is otherwise with the law of substitutions. With regard 

 to that, when ether loses hydrogen, it must receive chlorine. 

 There are then only five compounds which are possible, of 

 which the composition is perfectly foreseen. 



Q4 C4 Q4 C* C4 C4 



H^ H4 Ch H3 Ch2 H2 Ch^ H Ch^ Ch^ 

 000000 



Amongst them, three are already known, and there is not 

 the smallest risk to run when we predict the probable dis- 

 covery of the two others. 



