THE METALS: THE METALLIC OXIDES 57 



the boiling point. The chemical activity in respect to oxygen 

 would seem to be greater in the case of copper, and this is also 

 shown by the fact that while oxide of mercury is decomposed 

 by heat, oxide of copper is not. In determining the composition 

 of water, evidence has already been obtained that heated 

 copper has no action on steam. In fact, under no conditions 

 are these metals oxidised by water. 



Study the oxidisability of gold, silver, and platinum. Note 

 that under no conditions does direct oxidation take place 

 (hence noble metals as distinguished from base metals). In 

 fact, the oxides of these metals when formed by indirect 

 methods are all decomposed on heating. 



It is now possible to arrange the metals in the following 

 groups : — 



1. The metals of the alkalies (potash, soda, etc.), e.g, 



potassium, sodium. 



2. The metals of the alkaline earths (lime, strontia, baryta), 



viz. calcium, strontium, barium. 



3. The metals of the earths (magnesia, etc.), e-g. magnesium, 



zinc, iron. 



4. The heavy metals, e.g. copper, mercury. 



5. The noble metals, e.g. silver, gold, platinum. 



This arrangement shows that the metals fall into natural 

 groups, the members of each of which have several properties 

 in common. Thus the metals that belong to the first group, 

 because most oxidisable, form oxides both of which are cha- 

 racterised by their great solubility, while the metals which are 

 classed in the second group, on account of their feebler 

 oxidisability, all form oxides which are slightly soluble in 

 water. In physical as well as in chemical properties this 

 grouping often holds good. Thus sodium and potassium are 

 found to be both characterised by low specific gravity and low 

 melting point, and gold and silver are both characterised by 



