Heat 



97 



bicarbonate of soda or certain other fire-extinguishing solutions, 

 such as calcium chloride, also depend upon the cooling principle 

 for their effect. 



Special methods are necessary in fighting serious oil fires 

 because the oil is lighter and will float on water and many other 

 extinguishing agents. A method has been developed in recent 

 years which is very efficient in fighting oil fires; it is called the 



Underwood & Underwood. 



FIGHTING FIRE 



"Firefoam" method. Chemicals are placed in separate compart- 

 ments, as in the soda and acid extinguisher. When the extin- 

 guisher is inverted, the chemicals mix and the action that follows 

 gives off a foam which is made up of small bubbles filled with 

 carbon dioxide. This foam is very light and will float on the 

 surface of the oil. It is a very poor conductor of heat so that 



