SMOKE; ITS CAUSE AND PREVENTION 



99 



tained in the combustion chamber to burn the volatile matter 

 completely (Figs. 74 and 75). 



In the UNDERFEED furnace, fresh coal is introduced at the 

 bottom of the fire bed. Distillation of the volatile matter 



FIG. 77. Showing the feed cylinder tilted forward and filled with coal. 

 The apron closes the opening in the center of the grate through which the 

 coal is forced upward into the fire box. 



takes place therefore at the bottom of the fire, where the oxygen 

 supply may be more abundant than on top of the fire, and 

 hence it is more completely burned (Figs. 76, 77 and 78). 

 Moreover, in passing through the glowing coke above, the 

 volatile matter is sure to be heated to the kindling temperature. 



FIG 78. Showing the fresh coal forced into the fire box and the burning 

 coal resting on the top of the fresh coal. 



In steam boiler plants MECHANICAL STOKERS are often 

 employed. With the mechanical stokers, the aim is to feed 

 the fuel to the fire gradually by some device. In the stoker 

 shown (Fig. 79), which is a chain grate stoker, the coal is fed 



