LECTURE VI.] HISTORY OF CHEMISTRY. IOI 



ing the formulae HC1 and NH :? for hydrochloric acid and 

 ammonia ; but that afterwards, influenced especially by Dumas' 

 investigations, 41 he placed much less reliance upon this law, 

 and applied it to the permanent (and elementary) gases alone. 42 

 He was then no longer prevented from believing in an agree- 

 ment between equivalent and atom, even in these substances, 

 and he employed only the formulae Hi and NH 3 . 



It follows,. from the foregoing, that Berzelius did not admit 

 the distinction between the physical and the chemical atom, 

 and he thereby establishes an essential difference between ele- 

 ments and compounds. According to him, the atoms of the 

 elementary gases occupy, in general, one half (or one quarter) 

 the space occupied by the atoms of the compound gases. 

 Whilst similarity in behaviour with respect to changes of pres- 

 sure and of temperature was a sufficient reason for assuming 

 the same number of atoms in equal volumes of hydrogen and 

 of oxygen, the same reason was insufficient to justify the same 

 conclusion with regard to chlorine and hydrochloric acid. 

 There was an inconsequence in this, but it was of no material 

 importance, since the experiments bearing most closely upon 

 the matter appeared to negative any general applicability to it 

 of the law of gaseous volumes. 



The chemical edifice which Berzelius erected was a wonder- 

 ful one, as it stood completed (for inorganic substances) at the 

 end of the third decade of the century. Even if it cannot be 

 said that the fundamental ideas of the system proceed exclu- 

 sively 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 original. 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 



41 Ann. Chim. [2] 49, 210; 50, 170. 42 Lehrbuch. Third Edition, 



5,8*, 



