322 APPLIED SCIENCE 



order to fire the green coal in the front of the furnace and 

 to allow the smoke to pass over a bed of incandescent fuel at 

 the back, and be consumed. Later the coal in front may be 

 pushed back and new coal added to take its place. 



Side-firing, i.e., keeping one side of the fire always brilliant 

 while firing green coal on the opposite side, works very well. 

 No established rule, however, can be set for every condition, 

 and much must be left to the judgment of the fireman in each 

 individual case. When firing or cleaning fires where the 

 chimney draught is very strong, it is advisable to check the 

 stack damper to prevent too great a quantity of cold air 

 entering the furnace and causing undue contraction of the 

 plates. In boilers having a large furnace, it is well when 

 cleaning fires to clean one side at a time. 



The feed water should be kept constantly on, and the water 

 line maintained at the proper level all the time. Every day 

 the steam pressure should be raised to the blowing-off point, so 

 that the fireman may know that the safety valve is in work- 

 ing order. If at any time, from any cause, the gauge should 

 show the pressure increasing rapidly up to or past the limit, 

 the feed should at once be put on and the draught checked. 



363. Chimneys and Flues. A chimney is a vertical flue, 

 usually of iron or brick, for conveying the heated air and 

 combustion gases from the fire to the outer air. It usually 

 extends some distance above the tops of buildings. The 

 height of the chimney determines the intensity of the draught. 

 The capacity of the chimney depends upon its height and 

 area. A draught may be natural, induced, or forced. 



A natural draught is produced by a chimney alone, and is due 

 to the difference between the weight of a column of the hot 

 inside the chimney and an equal column of air on the 



