OXIDATION AND COMBUSTION 19 



formed are called oxides. For example, a chemist would 

 describe the formation of carbon dioxide as the oxidation 

 of carbon to form an oxide. In every case the formation 

 of an oxide is accompanied by the production of heat, but 

 sometimes the union of the elements takes place much 

 more rapidly than at others, and when this occurs the 

 amount of heat produced is large and often accompanied 

 by flames or light. Such rapid unions are called rapid 

 oxidation or combustion, to distinguish them from slower 

 unions or slow oxidation. All burning then may be ex- 

 plained as the rapid oxidation of the substance burned, 

 and it is evident, therefore, that burning cannot take 

 place in the absence of oxygen. Further, since in burn- 

 ing the oxygen combines with the substance to form an 

 oxide, it follows that for a substance to continue burning 

 implies a continuous supply of oxygen until the substance 

 has entered completely into combination. It is for these 

 reasons that we supply our stoves with draughts which 

 win permit the continuous entrance of oxygen. This 

 explanation of the true nature of combustion also explains 

 the methods of extinguishing fires, all such methods aim- 

 ing to separate, through the aid of some substance which 

 does not combine with oxygen, the burning substance 

 from its air or oxygen supply. In short, pouring water on 

 a fire puts an incombustible substance between the burn- 

 ing matter and the air, and thus prevents further oxida- 

 tion. Water is more frequently used than sand or dirt 

 for this purpose because it is easier to handle, but in 

 theory one is as effective as the other. 



The special interest of oxidation to the physiologist 

 consists in the fact that it furnishes a means for the pro- 

 duction of heat, and we shall learn later how the body 



