S26 M. Dumas on the La'w of Substitutions^ 
we may take away 1, 2, 3 equivalents of hydrogen, and sup- 
ply their places by 1, 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 
{alterantes) 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 may 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 wdth 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. 
C4 QA QA QA QA QA 
H^Ch FPCh^ H^Chs HCh^ Ch^ 
O O O O O O 
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. 
