98 HISTORY OF CHEMISTRY. [LECTURE VI. 



that his rules, in many cases, cannot lead him to a decisive 

 determination, and that it is really in the cases of gaseous 

 elements only that they can give unequivocal results. But just 

 because he knows upon what shaky grounds he is proceeding, 

 he acts with the greatest caution ; and it is marvellous how 

 often, guided by an acute judgment, he hits upon the correct 

 number, where almost every criterion is wanting. 



In the case of the oxides, Berzelius constructs for himself 

 a series which furnishes him with the relative quantities of 

 oxygen with which certain weights of the metals combine. In 

 doing so, he does not require to construct a series of this kind 

 for every metal. By calling Mitscherlich's law to his assistance, 

 he is able to supply the places of any stages of oxidation that 

 are wanting in the case of a given element, by those of an 

 isomorphous element. The series is : 3r 



Relative Proportion 



of Oxygen. 



Cuprous oxide - i 



Cupric oxide, ferrous oxide, etc. - 2 



Ferric oxide, manganic oxide, minium - 3 



Lead peroxide, manganese peroxide - 4 



Manganic acid - 5 



I also give, below, a similar but more accurate tabulation, 

 from the year i835. 38 



Cuprous oxide - i 



Cupric oxide, ferrous oxide, etc. - 2 



Ferric oxide, manganic oxide, etc. 3 



Lead peroxide, manganese peroxide, etc. - 4 



Nitric acid, chloric acid, etc. 5 



Perchloric acid, permanganic acid, etc. 7 



In the compounds noted here, Berzelius assumes i, 2, 3, 4, 

 5 (and 7) atoms of oxygen ; thus making the simplest assump- 

 tion possible. It is then only a matter of determining, in 

 addition, the number of atoms of the radical or element that 

 is united with the oxygen. His series does not furnish any 



37 Lehrl-uch. 3, part I, 97. w Lehrbuch. Third Edition, 5, 89. 



