THE METALS: THE METALLIC OXIDES 53 



which appears to be a compound of the two oxides employed, 

 for it has lost the distinctive properties of each. 



Repeat the operation with the solution of lime and oxide of 

 phosphorus, pouring the latter into the former till a neutral 

 mixture is obtained. The " salt " appears in this case to be a 

 white insoluble compound of the two oxides. Filter and 

 evaporate the filtrate to dryness. Should there be no residue, 

 this must be the case. 



The conclusions arrived at from these two instances are true 

 for the oxides of other elements. They may be stated thus : — 



Basic oxides are oxides of metallic elements; if dissolved 

 by water they form alkaline liquids, and they unite with acidic 

 oxides forming salts. 



The oxides of non-metallic elements are usually acidic; 

 if dissolved by water they form acids, and they unite with 

 basic oxides to form salts. 



Salts are compounds formed by the admixture of basic ana 

 acidic oxides ; if dissolved by water they usually form neutral 

 solutions. 



It will be observed that water is a neutral oxide. Thus basic and acidic 

 oxides can be dissolved in water without their properties being affected. 

 The element hydrogen, in fact, in its chemical behaviour, stands inter- 

 mediate between metals and non-metals. 



XIII. THE METALS: THE METALLIC OXIDES 



In order to compare the chemical activity of the metals, a study 

 may be made of their oxidisability and the methods by which 

 their oxides may be produced. Two methods have already 

 been found available for preparing oxide of iron from metallic 

 iron, viz. (i) the action of the free oxygen of the air and (2) 



