INTRODUCTION. 11 



of combustion, in connection with hy- 

 drogen, which is very inflammable, are 

 we indebted for the only material capa- 

 ble of arresting the progress of com- 

 bustion, water. Thus, then, the 

 same materials, differently combined, 

 support life and combustion, and de- 

 stroy them. Most metals have the 

 property of decomposing water, by 

 uniting with its oxygen ; when the 

 hydrogen, being liberated, is again set 

 free in the form of gas. If this latter 

 gas is again inflamed, it will unite with 

 the oxygen of the atmosphere, and 

 water will be formed. During the in- 

 tense heat evolved from burning build- 

 ings, if a small quantity of water be 

 thrown upon them, the fire is increased, 

 the water is decomposed, the oxygen 

 unites with the combustible substance, 



