BOILERS AND GENERATION OF STEAM 321 



that the blow-off cock is in order and closed, that the ash pit 

 is clear of ashes, that the tubes are clean, and that the safety 

 valve is raised off its seat, or that some valve or cock is open 

 to the atmosphere until steam issues from it. The grate 

 bars should be covered with coal from the bridge wall toward 

 the furnace door for about 3 ft. The fireman should then 

 put some light wood on the grate in front of the coal and with 

 a little oily waste set fire to it. When the fire has thoroughly 

 kindled the wood a little coal may be put on it. During this 

 time the ash pit should be closed and the furnace door left 

 open a little so that the flames may be communicated to the 

 coal at the back of the furnace. 



As soon as a good fire is burning in the front of the furnace, 

 the front coals may be pushed back a little and the ash pit 

 damper opened. The fire should not be forced, but should 

 be allowed to work up gradually. An unequal strain through 

 forcing the fire when the boiler is cold may cause leakage and 

 make expensive repairs necessary. The fires should be main- 

 tained level and of a uniform thickness, but the thickness 

 must be determined by the demand for steam, the condition 

 of the chimney draught, and by the quality and nature of the 

 fuel. 



362. Firing the Boiler. Firing can best be done when 

 combustion is good, as but little dense smoke then is given 

 off. Dark spots in the fire, abundance of smoke, unsteady 

 steam pressure, unsteady water line, dirty tubes, and coal in 

 the ash heap are all evidences of careless firing, and should 

 not be tolerated. Experience is the only guide to the best 

 methods of handling the different kinds of fuel under the 

 different conditions to be met with in practice. 



The coal should be put in lightly at regular intervals in 



