BOILER AND MANAGEMENT 163 



ing particles. When, therefore, heat is applied to the bot- 

 tom of a vessel containing water, the particles at the 

 bottom do not communicate their heat to the particles next 

 above them, but expand and rise, cool ones taking their 

 places. . This gives rise to convection currents which tend 

 to equalize the temperature of the water in the vessel. 

 When the water has reached a uniform temperature of 

 212° F. the particles begin 'to fly off at the surface in the 

 form of vapor, and this we call steam. To generate steam 

 in a boiler, then, it is necessary to impart to the water in it 

 a considerable amount of heat, which is produced by 

 burning fuel in the fire box. 



FIRING OF BOILER. 



The immense amount of heat stored in wood and coal 

 is rendered elifective in the boiler by bui-ning (combus- 

 tion). To understand how to fire a boiler intelligently 

 one must first learn what the process of burning consists 

 of. 



Process of Burning. Anything will burn when the 

 temperature has been raised high enough to cause the 

 oxygen of the air to unite with it. Thus, in "striking" 

 a match the temperature is raised high enough by the 

 friction produced to cause the match to burn. The burn- 

 ing match will produce heat enough to ignitq the kind- 

 ling, which in turn, produces the necessary heat to ignite 

 the wood or coal in the fire box of the boiler. Burning 

 may, therefore, be defined as the union of the oxygen of 

 the air with the fuel. In burning a pound of coal or wood 

 a definite amount of air must be admitted to furnish the 

 necessary oxygen for complete combustion. When oxygen 

 is lacking part of the fuel passes out of the chimney un- 



