406 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



a joint report on the subject was to be prepared in response 

 to a request from the Liverpool meeting of the British 

 Association, and from 1838 to 1841 Dumas and Graham 

 appeared as collaborators with Liebig in the publication of his 

 Annalen. This happy collaboration was to be made effec- 

 tive by training a new generation of chemists ; it was there- 

 fore no mere coincidence that resulted, ten years later, in 

 the association together of Auguste Laurent (1807-1853, 

 pupil of Dumas) and Charles Gerhardt (1816-1856, pupil 

 of Liebig) in another campaign to establish a rational system 

 of atomic weights and formulae in chemistry ; only the early 

 death of these two workers prevented them from seeing the 

 triumph of their ideas through the masterly exposition of 

 Cannizzaro. 



D. THE THEORY OF SUBSTITUTION. 



Dumas (1834) on substitution or metalepsy. In the 



second part of his Researches in Organic Chemistry, " On 

 the Action of Chlorine on Alcohol. The Law of Substitu- 

 tions or Metalepsy," read before the Academy of Sciences 

 at Paris, on Jan. 13, 1834, Dumas directed attention to the 

 fact that 



"Chlorine possesses the remarkable power of seizing 

 hold of the hydrogen of certain substances, and replacing 

 it atom by atom; This law of nature, this law or theory of 

 substitutions, has seemed to me to be worthy of a special 

 name. I propose to call it metalepsy, from //,TaAr?i/as, which 

 expresses well enough that the body on which one acts, has 

 taken one element in the place of another, chlorine in place 

 of hydrogen, for example" (Mem. Inst., 1838,! 15, 548). 



The laws of substitution were set out in the following 

 year in his Treatise on Chemistry as follows : 



" i. When a hydrogenated compound is submitted to 

 the dehydrogenating action of chlorine, of bromine, of 



1 This passage does not appear in the paper as published four years 

 earlier in the Ann. Chim. Phys., 1834, 56, 1-13-154. 



