Metals. 231 



lead gains ten pounds in the hundred, or more. 

 This is evidently owing to the quantity of oxy- 

 gen absorbed by the metal, and exactly corre- 

 sponds with it. Again, by submitting the me- 

 tallic oxides to a strong heat in contact with any 

 substance which has a stronger attraction for 

 oxygen, as charcoal, or most of the combusti- 

 bles, the metal will be robbed of the oxygen, 

 and restored to its metallic state. This opera- 

 tion is called the reduction of metals. All com- 

 bustible substances will reduce metals, except 

 sulphur. 



The common method is to mix the oxide to 

 be reduced with charcoal, or any combustible 

 substance capable of sustaining a strong heat. 

 Heat is then applied, the violence of which must 

 be different in different cases : the oxide imme- 

 diately recovers its metallic form, often with the 

 phenomena of ebullition and effervescence. 



The metals can also be restored by means of 

 each other. Thus we may reduce oxide of lead 

 by melting it, and throwing in a quantity of 

 iron or ?teel filings ; and the oxide of copper find 

 some others by throwing in a quantity of lead, 

 which is suddenly oxidized, while the copper is 

 reduced, the lead having a stronger attraction 

 for the oxygen than the copper. 



The metals themselves will, upon the same 

 principles, recover some of the inflammable 

 substances. Thus phosphorus, after burning, 



