94 HISTORY OF CHEMISTRY. [LECTURE VI. 



a way that the quantities of the latter in the one constituent 

 stand to those in the other as i to i, 2, 3, 4, 5, 6, etc. ; as 3 

 to 2 or 4 ; or finally, as 5 to 2, 3, 4, 4^, and 6. 20 



It is interesting to see how, by the aid of these rules, 

 Berzelius determines the number of atoms contained in a 

 compound. As an example, I choose the oxygen compounds, 

 which are unquestionably of the greatest importance. 



Berzelius believes he has discovered (especially from the 

 consideration of the proportions by volume in the case of gases) 

 that it is usually the electro-negative constituent of which 

 several atoms occur, and, therefore, in the case to be examined 

 here, the above mentioned rules take the following form. 21 



I. When an element or radical forms several oxides, and 



the quantities of oxygen in these, as compared with 



a given quantity of the other element, stand to each 



other as i to 2, it must be assumed that the first 



compound consists of i atom of radical and i 



atom of oxygen ; the second, of i atom of radical 



and 2 atoms of oxygen (or 2 atoms of radical and 



4 atoms of oxygen). When the proportions are 



as 2 to 3, the first compound consists of i atom 



of radical and 2 atoms of oxygen ; the second, of 



i atom of radical and 3 atoms of oxygen, and so on. 



In conformity with this rule, Berzelius, in 1819, writes 



soda NaO 2 , and the peroxide NaO 3 ; and his formulae for the 



other oxides are similar. Thus it comes about that the atomic 



weights which he proposes for the metals at this period, are 



double those which he definitely adopts afterwards (i828). 2 ' 2 



Influenced by reasons which we shall immediately learn, he 



makes, in his Text-book, the following addition to Rule I : 23 



When the proportion of the quantities of oxygen in 



two compounds is as 2 to 3, then in the first, i 



atom of radical can also be combined with i atom 



of oxygen, and, in the second, 2 atoms of radical 



can be combined with 3 atoms of oxygen. 



20 Lehrbuch. 3, part I, 40. 21 Essai etc. 118. - 2 Berzelius, Jahres- 

 bericht 1828, 73. - 3 Lehrbuch. 3, part I, 90. 



