LECTURE X.] HISTORY OF CHEMISTRY. 187 



Gerhardt's activity was perhaps of still greater importance 

 in connection with another question ; that is, with the fixing of 

 the atomic and molecular weights. Although the movement 

 for the revision of these most important numbers originated 

 with him alone, still he was influenced in the further elabora- 

 tion of the work by Laurent, with whom he was at that time in 

 very intimate communication. Indeed, I might almost say that 

 it was Laurent who first clearly stated 40 what Gerhardt wished 

 to advance. It is, however, extremely difficult to separate from 

 one another the services of the two chemists, because they 

 published a great deal conjointly, and probably discussed 

 everything together. I would ask, therefore, that my statements 

 with respect to this matter may not be taken too literally. 



Gerhardt's first paper on the subject in question dates from 

 the year i842. 41 In this paper he frequently employs the word 

 equivalent in a sense in which it was introduced into chemistry 

 by Wollaston and Gmelin, although this sense is one of which 

 we cannot any longer approve. With Gerhardt the word is 

 one whose signification he does not seek for in its origin, other- 

 wise he could not call H 2 SO 4 and HC1 one equivalent each ; 

 for he himself wishes to prove that sulphuric acid is dibasic, in 

 which case it is not equivalent to hydrochloric acid. What 

 Gerhardt wishes to determine are atomic and molecular 

 weights, which, however, he does not yet understand how to 

 distinguish from each other, and for which he uses the word 

 " equivalent," at the same time designating as " atomic weights " 

 the numbers which he is attacking. 



Gerhardt's equivalents, so-called, are not really equivalent, 

 but merely comparable quantities ; and in determining them, 

 the most various points of view which can be of consequence in 

 estimations of atomic and molecular weights and of equivalents, 

 are taken into consideration. 



It must appear striking and peculiar to any unprejudiced 

 person, that the numbers which Gerhardt proposes as the 



40 Ann. Chim. [3] 18, 266. 41 J. pr. Chem. 27, 439 ; also Ann. 

 Chim. [3] 7, 129; 8,238. 



