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chemists. An additional impetus was given to the movement when 

 it was joined by Laurent, who, though often so much at variance with 

 Dumas, as to become, more especially in consequence of questions of 

 priority as to certain collateral ideas, his declared opponent, has 

 nevertheless, by amplifying the original conceptions and by pre- 

 senting in his unremitting researches ever new and welcome illus- 

 trations of them, assisted more perhaps than any other chemist in the 

 propagation of the theory of substitution. 



We cannot, of course, attempt to examine the several experimental 

 researches, extending over a considerable space of time and embracing 

 a great variety of subjects, which served as scaffolding to Dumas 

 when building up his substitutional and typical conceptions ; all we 

 can do is to allude in a few words to the experiments which furnished 

 him with his principal illustrations.. 



Proceeding chronologically, we should have to refer in the first 

 place to Dumas' experiments on cinnamon oil and cinnamic acid. 

 Again, excellent illustrations of substitution are furnished by his work 

 on olefiant gas and ordinary ether. 



His examination of the action of chlorine upon alcohol, too, served 

 to illustrate his theory ; although in these experiments he was fore- 

 stalled by Liebig, who by his researches had been led to the discovery 

 of chloral and chloroform. But if Dumas lost the discovery of these 

 two compounds, he had at all events the satisfaction of establishing 

 their true composition, and of thus supplying the key to the correct 

 interpretation both of the formation of chloral from alcohol and 

 of its decomposition, first pointed out by Liebig, into formic acid 

 and chloroform, when submitted to the action of alkalies. 



But the inquiry, which more perhaps than any other has contri- 

 buted to establish Dumas' ideas in the minds of chemists, is his 

 splendid investigation of the action of chlorine upon acetic acid. The 

 trichloracetic acid formed in this reaction retains all the characteristic 

 properties of the mother compound, its salts and its ethers resemble 

 those of acetic acid, and when Berzelius and the champions of dualistic 

 views still endeavoured, by constrained interpretation, to prove acetic 

 and chloracetic acid to differ in constitution, Dumas showed that even 

 their metamorphoses are strictly analogous. 



Among the numerous researches undertaken with a view of eluci- 

 dating the theory of substitution, a joint inquiry of Dumas and Stas 

 on the action of alkalies on alcohols and ethers must not be forgotten. 

 They prove that the alkalies act as oxidising agents, hydrogen being 

 evolved, whilst the acids belonging to the alcohols are simultaneously 

 produced. Amylic alcohol, then just brought to light by Dumas and 

 Cahours' researches, is thus formd to yield valeric acid, up to that time 

 obtained only from Valeriana officinalis. 



A few years later Dumas returned once more to the acids generated 



