232 METALS. 



quire the stimulus of an acid, or of heat. Except in 

 the case of manganese, the heat must be sufficient to 

 convert the water into steam. Strictly speaking, there- 

 fore, they do not decompose water, but steam. 



Describe Class 5 ?3. CLASS IV. TlN AND ANTIMONY.- 



IV - Tin and antimony tarnish less readily than 



the metals of the previous class. To enable them to 

 decompose water, and appropriate its oxygen, they re- 

 quire the stimulus of a red heat. An acid, or mode- 

 rate heat will not suffice. 



Describe Class ^74. CLASS V. COPPER, BISMUTH, AND 



LEAD. Although copper and lead become 

 tarnished, or covered with a thin film of oxide, rather 

 more readily than the metals of the last two groups, 

 their affinity for oxygen under other circumstances is 

 less. This is evident in the fact that a red heat ena- 

 bles them to decompose water and appropriate its oxy- 

 gen, but feebly. Acids will not suffice. Bismuth 

 does not tarnish so readily as copper or lead. 



Describe Class 5 ?5. CLASS VI. MERCURY, SILVER, PLA- 



VL TINUM, AND GOLD. The metals of this 



class do not tarnish, and do not decompose water under 

 any circumstances. Even if made to combine with 

 oxygen by other means, they yield it again very readily, 

 and return to the condition of metals. They are called 

 the noble metals. 



