438 METALLIC ELEMENTS. 



rides are then to be associated with those salts of oxygen-acids 

 usually denominated subsalts (page 169); the oxichlorides of 

 lead and of copper, Pb Cl + 3 Pb O and Cu Cl + 3 Cu O, with 

 the subacetates and subsulphates of the same metals. 



Arrangement of metallic elements. A distribution of the 

 metals into three classes is generally made, composed respec- 

 tively of the metals of the alkalies and alkaline earths, the me- 

 tals of the earths, and the metals proper. The latter class 

 again is subdivided, according to the affinity of the metals con- 

 tained in it for oxygen, into the two groups, the noble and 

 common metals, the oxides of the former, such as gold, silver, 

 &c., abandoning their oxygen at a high temperature, while the 

 oxides of the latter, lead, copper, &c., are undecomposable by 

 heat alone. In treating of the metals, I shall introduce them in 

 the order which appears to facilitate most the study of their 

 combinations, with a general reference to that old classification. 

 For subdivisions, I shall avail myself of the natural families 

 into which the elements have been arranged (page 142), which 

 have the advantage of bringing together those metals of which 

 the compounds are most frequently isomorphous. The different 

 metals will therefore be grouped under the following heads : 



I. Metallic bases of the alkalies three metals : 



Oxides. 



Potassium . . . Potash. 

 Sodium . . . Soda. 



Lithium . . , Lithia. 



II. Metallic bases of the alkaline earths four metals : 



Oxides. 



Barium . . . Barytes. 



Strontium . . . Strontian. 



Calcium . . . Lime. 



Magnesium . . . Magnesia. 



III. Metallic bases of the earths proper five metals : 



Oxides. 



Aluminum . . . Alumina. 



Glucinum . . . Glucina. 



Zirconium , . . . Zirconia. 



Yttrium . . . Yttria. 



Thorium Thorina,. 



