COMBUSTION. 145 



the more serviceable it is in this respect. But even hot 

 water is of some service in this way; for it is not as hot as 

 the fire is. The fire converts it into steam, and thus parts 

 with a great deal of heat, which is rendered latent as the 

 steam forms, as noticed in Part L, Chapter XIIL And then, 

 for the purpose of shutting out the oxygen, hot water an- 

 swers as well as cold. Some other means are often resorted 

 to for extinguishing fires, all of them acting by excluding 

 the air. For example, we put an extinguisher over a candle 

 to put it out. So, also, if a person's clothes take fire, and no 

 water be at hand, we wrap some clothing or other article 

 quickly and closely around him. Such expedients, in com- 

 mon language, are said to smother the fire, but in scientific 

 language to prevent the oxygen of the air from coming in 

 contact with the combustible substance. 



186. Fire Under Water. If we put a very combustible 

 substance under water, we can make it burn 



there by giving it a good supply of oxygen. 



In Fig. 60 we have an experiment of this 



kind represented. A bit of phosphorus, #, 



is put in a glass of hot water, and a stream 



of oxygen gas is directed upon it through 



the tube, a. A brilliant combustion occurs. 



It is necessary that the water should be hot Fi s- <>. 



to make the phosphorus burn, or, in other words, unite with 



the oxygen. 



187. Fire Extinguishers. Since carbonic anhydride is not 

 a supporter of combustion, it may be used for extinguishing 

 fires. It is usually employed in solution in water under 

 pressure, and various contrivances have been made for gen- 

 erating the gas quickly when needed, and throwing a stream 

 of it mixed with water in any direction desired. The " plain 

 soda-water" sold in apothecary shops would serve just as 

 well, for it is really the same thing. The pure dry gas has 



G 



