12 CHEMISTRY OF FARM PRACTICE 



the action of an external agent other than the Oxidizer. 

 Heaps of finely divided coal may in the same way be set 

 on fire by the spontaneous combustion occasioned by the 

 oxidation of their sulphur or oil content. 



12. Reduction. This process is the reverse of oxidation. 

 It is the subtraction from a compound of oxygen or of the 

 element which plays the role of oxygen. The extraction 

 of the common metals from their ores is a process of re- 

 duction. This process is brought about by subjecting the 

 material to be reduced to certain reducing agents which 

 have a stronger affinity for the oxygen part of the compound 

 than does the metal originally combined with that part. 

 The most useful of these reducing agents are carbon, in 

 the form of charcoal or -goal, hydrogen and the hydro-carbon 

 compounds and certain active metals, such as sodium or 

 aluminium. Carbon monoxide gas, which needs more 

 oxygen so as to make itself into carbon dioxide, a more 

 stable compound, is a very valuable reducing agent. In 

 the highly heated areas of the blast furnace in the process 

 of iron reduction, the carbon monoxide takes away the oxy- 

 gen of the iron ore and leaves metallic iron. 



