M. Dumas 071 the Laiv of Stibstiiutzo?is, S^c. 323 



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 C^^H*^'* 

 Ch^, derived from the original oil of turpentine C**^ H^^. 



At the same time, J 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 tlie 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 



