323 
M. Dumas on the Law of Substitutions^ 8^c. 
and take exactly an equivalent volume of chlorine to that of 
the hydrogen set free, I had myself subjected oil of turpen- 
tine to similar trials, and was convinced, agreeably to M. De- 
vielle’s late re-examination of the subject, that it easily loses 
eight volumes of hydrogen and takes in their place eight 
volumes of chlorine, thus constituting the compound 
Ch^, derived from the original oil of turpentine 
At the same time, I studied the composition of some ex- 
traordinary products obtained from alcohol, viz. chloral, 
chloroform, bromoform, iodoform, of which I gave an ex- 
act analysis, and endeavoured to explain their formation.. 
This work was the occasion of the law of substitutions 
being developed for the first time. But as it was then be- 
lieved that certain organic matters, and alcohol in particular, 
contained water ready formed, the law of substitutions, in 
the form in which I first presented it, attributed a function 
to this water, which gave rise to many objections. To re- 
turn to the details of this point, would be without interest at 
the present time, for those chemists who admit the reality of 
substitutions, have in general given up the supposition of the 
existence of ready-formed water in the compounds in which 
these substitutions are observed.^ 
Although the function which I had attributed to the water 
may be reconciled to the general phaenomena of chemistry, 
as it is now become useless, we must limit the law of substi- 
tutions to the following expression: — “When a hydro- 
genated organic substance is treated with chlorine, bromine, 
iodine, or oxygen, &c., these bodies generally remove hydro- 
gen from it, and for an equivalent of hydrogen so removed, 
an equivalent of chlorine, bromine, iodine, or oxygen is sub- 
stituted in the compound. 
Is this phaenomenon general ? has it a peculiar character ? 
This is what we are about to examine. 
At the present time every one knows that in the reciprocal 
action of bodies certain relations of weight are observed, and 
that it is not enough to say that sulphur or oxygen combine 
with or act upon zinc or lead, but that a quantity of sulphur 
weighing 201, and of oxygen weighing 100, act upon or 
combine with a quantity of zinc weighing 403, and of lead 
* It may however be observed, that when I admitted that chlorine de- 
composed this water, seized the hydrogen, and left the oxygen in the com- 
pound, I made a very logical supposition. An analogous case presents 
itself when the benzoate of silver is decomposed by bromine, giving bromide 
of silver, the oxygen of the oxide uniting with the benzoic acid. 
When I added that oxygen itself could decompose the water fixed in 
the compounds, I was guided by the theory of cementation, in which we 
admit that iron decomposes carburet of iron, 
Y2 
