LECTURE VIII.] HISTORY OF CHEMISTRY. 143 



reacted upon him, and he went his own way, and became 

 gradually more incomprehensible, particularly in consequence 

 of a nomenclature which was used almost exclusively by himself. 

 Many of his clever and original ideas were thus lost to our 

 science, or are now ascribed to the services of others. A great 

 deal, on the other hand, was supplied to us first by Gerhardt, 

 who was a friend and collaborator of Laurent for many years, 

 and who combined a clear mode of expressing and of regarding 

 chemical matters with probably more perspicuity and less 

 genius. 



At an early period, Laurent had begun to occupy his 

 attention with the phenomena of substitution. He first studied 

 naphthaline and its derivatives ; 3S then, simultaneously with 

 Regnault, the derivatives of ethylene chloride ; 39 afterwards 

 the action of chlorine upon compound ethers, 40 and upon the 

 products of the distillation of tar, especially on phenol, 41 etc. 



He very soon satisfied himself, by means of these various 

 investigations, that the form which Dumas had given to the law 

 of substitution was not a generally accurate one. He found 

 that in very many instances there are more or fewer equivalents 

 of chlorine or of oxygen taken up than there are of hydrogen 

 eliminated, and vice versa ; and that this is the case even with 

 substances which do not contain oxygen, so that the exceptions 

 cannot be explained by Dumas' second rule. 42 At the same 

 time, however, Laurent points out that the substituted product, 

 when it is produced by replacement of equivalent by equivalent, 

 still exhibits certain analogies with the original substance ; arid 

 he asserts that the chlorine introduced takes the place, and to a 

 certain extent plays the part, of the hydrogen eliminated. His 

 opinion may be stated somewhat in the following manner : 43 



Many organic substances when treated with chlorine lose a 

 certain number of hydrogen atoms, which escape as hydrochloric 



38 Annalen. 8, 8 ; 19, 38 ; 35, 292 ; 41, 98 ; 72, 297 ; 76, 298, etc. 

 39 Ibid. 12, 187 ; 18, 165 ; 22, 292. 40 Ibid. 22, "292. 41 Ibid. 22, 292 ; 

 23, 60; 43, 200, etc. 4 ' J Sec p. 141. 43 Laurent, Methode de Chimie. 

 242 ; E. 199 ; These de docteur, Paris, 20 Dec. 1837, n, 88 and 102 ; Ann. 

 Chim. [2] 63, 384; Comptes Rendus. 10, 413; Revue Scientifique. I, 161. 



