542 PRINCIPLES OF CHEMISTRY 



osride of this metal, as "water is in -the case of hydrogen. Although the 

 peroxide H 2 2 is derived from hydrogen, and Na 2 O 2 from sodium, 

 yet there are no corresponding salts known, and if they are formed 

 ihey are probably as unstable as hydrogen peroxide. Although carbon 

 forms carbonic oxide, CO, still it has only one .salt-forming oxide 

 carbonic anhydride, CO 2 . Nitrogen and chlorine both give several 

 fialt-forming oxides and types of salts. But of the oxides of nitrogen, 

 NO and NO 2 do not form salts, as do NgOg, N 2 O 4 , and N a O 6 , although 

 H 2 O 4 does not form special salts, and N 2 5 corresponds with the 

 highest form of the saline compounds of nitrogen. Such distinctions 

 between the elements, according to their power of giving one or several 

 saline forms, is a radical property of no less importance than the basic 

 or acid properties of their oxides. Sodium as a typical metal does 

 not form any acid oxides, whilst chlorine, as ft typical non-metal, does 

 not form bases with oxygen. Therefore sodium as an dement may be 

 thus characterised : it forms one very stable salt-forming oxide, Na 2 0, 

 having powerful basic properties, and its salts are of the general 

 formula, NaX, therefore in its compounds it is, like hydrogen, a basic 

 and univalent element. 



On comparing sodium and its analogues, which will be described later 

 with other metallic elements, it will be seen that these properties, 

 together with the relative lightness of the metal itself and its com- 

 pounds, and the magnitude of its atomic weight comprise the most 

 essential properties of this element, clearly distinguishing it from 

 Others, and enabling us easily to recognise its analogues. 



