A CENTURY OF CHEMISTRY. 87 



forms coincide. Even at that time, the same number 

 of atoms was assumed to be present in both acids, 

 and thus Mitscherlich arrived at the idea that it was 

 similarity of atomic constitution which gave rise to 

 identity of form." * 



This discovery was utilised by Berzelius in the 

 following rule : — " When one substance is isomor- 

 phous with another in which the number of atoms 

 is known, then the number of atoms in both is known, 

 because isomorphism is a mechanical consequence of 

 similarity of atomic construction." 



" The chemical edifice which Berzelius erected 

 was a wonderful one, as it stood completed (for in- 

 organic substances) at the end of the third decade of 

 the century. Even if it cannot be said that the fun- 

 damental ideas of the system proceed exclusively 

 from himself, and if he is indebted to Lavoisier, 

 Dalton, Davy, and Gay-Lussac for a great deal, still 

 it was he who moulded these ideas and theories into 

 a connected whole, adding also much that was origi- 

 nal. His electro-chemical hypothesis no doubt had 

 points of similarity with that of Davy, but, in spite 

 of that, it was essentially different from it. Besides, 

 the first method of atomic weight determination, of 

 moderately general applicability, proceeded from 

 Berzelius; and this method was so extraordinarily 

 servicable that it rendered possible the fixing of these 

 most important numbers, so that alteration was nec- 

 essary in only a few cases. " f 



It is important to notice, however, that about 1840 



an error of about 2 per cent, was discovered in the 



estimate which Berzelius had made of the atomic 



weight of carbon. This raised suspicions and further 



*Ladenburg, 1900, p. 96. 

 fLadenburg, 1900, pp. 101-102. 



