CHEMISTRY OF INDUSTRIAL SUBSTANCES 165 



in the presence of a supporter of combustion like air, to the 

 point of ignition by some external agent, such as a match. 

 When a substance oxidizes with great rapidity, a great deal 

 of heat is evolved and a flame is formed. The temperature 

 at which the flame forms is known as the point of ignition 

 or the kindling point. 



Certain kinds of damp organic matter, such as soft coal 

 or cotton rags containing oil, confined tightly may absorb 

 enough oxygen to raise their temperature to the kindling 

 point. The result is spontaneous combustion. The quan- 

 tity of heat is the same whether the combustion is slow or 

 fast. A quantity of wood that decays gives off exactly the 

 same quantity of heat as if the same amount of wood were 

 burned in a furnace, provided in both cases the wood is 

 completely destroyed. The products of combustion are 

 exactly the same. 



195. Chemical Solution for Extinguishing Fires. The 

 most effective method of extinguishing fire is by means of a 

 solution used in chemical fire apparatus. This solution is 

 much more efficient for fire-extinguishing purposes than 

 plain water, because the chemical solution does everything 

 that water can do exactly in the same way and for exactly 

 the same reasons. In addition, it forms a considerable 

 blanket of fire-extinguishing gases which are heavier than 

 air and better supporters of combustion, and in this manner 

 'shuts off much more effectively the access of air (oxygen) 

 to the fire. 



Chemical fire-extinguishing solution extinguishes fire more 

 by smothering than by cooling. The only drawback is 

 that the supply of chemical solution must necessarily be 

 comparatively limited. However, a reasonable supply of 



