BURNING 



139 



There are some gases, like nitrogen, which do not support com- 

 bustion. These gases are used in fire extinguishers, as the gas 

 surrounds the burning material, shutting off the supply of oxygen. 

 The fire extinguisher "Pyrene" contains carbon tetrachloride, a liquid 



KOUAHTFIRE EXTINGUISHER 



FIG. 106. 



FIG. 107. 



FIG. 108. 



which readily changes to a gas when heated. This gas surrounds 

 the burning object, preventing the oxygen from uniting with the 

 material. 



The ordinary fire extinguisher uses a gas called " carbon dioxide," 



