CRBAMBRY MECHANICS 279 



FIRING 01^ BOILER. 



The immense amount of heat stored in wood and coal 

 is rendered effective in the boiler by burning (combus- 

 tion). To understand how to fire a boiler intelligently we 

 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 ignite 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- 

 burned in the form of gases. If, on the other hand, too 

 much air is admitted the excess simply passes through 

 the chimney, absorbing heat as it passes through the 

 boiler. The problem of firing becomes, therefore, a difii- 

 cult one. 



Burning Coal and Wood. When hard coal is burned 

 the fire should be thin. A thickness of three to four 

 inches on the grates gives very satisfactory results. For 

 best results with soft coal a thickness of six to seven 

 inches is recommended. Whenever fresh coal is added 

 it should be placed near the front and the hot coals pushed 

 back. 



In case wood is burned the fire box should be kept well 

 filled, care being necessary to keep every part of the grate 

 well covered. 



