BOILER No. 68. 227 



best class of shell boilers. The proportion of heating surface 

 to grate surface is ample, so also is the rate of combustion. 

 The temperature of the escaping gases is not excessive. The 

 quality of the coal, judging from the low percentage of ash, is 

 excellent. With all these conditions, which would ordinarily 

 be considered favorable, it is difficult to assign a cause for the 

 inferior result, unless it be the loss produced by the admission 

 of air over the fuel through the passages in the walls, and that 

 which may have entered through openings in the brick work 

 due to the somewhat long service to which the boiler had been 

 subjected. The admission of air in this manner makes the 

 actual loss from the waste heat in the gases greater than that 

 apparently indicated by the temperature. 



Previous to the introduction of the flue heater a test was 

 made upon the plant when the boilers had been in use but a 

 few weeks, the coal employed being Powelton bituminous 

 mixed with one-fourth of its weight of pea and dust coal. 

 The grate surface on this occasion had a much larger area, 

 being 70 square feet and the proportion of heating surface to 

 grate surface was thereby reduced to 44.7 to 1. The principal 

 results were as follows : 



Coal per hour per square foot of grate surface, . . 16.7 Ibs. 



Percentage of ash, 9.0 per cent. 



Water per hour per square foot of heating surface, . . 3.7 Ibs. 



Horse-power developed, 403.3 H. P. 



Boiler pressure, 77.0 Ibs. 



Temperature of feed-water, . . . . . . 38.0 cleg. 



Temperature of escaping gases, 402.0 deg. 



Draught suction, ......... 0.5 in. 



Water per pound of coal, 9.75 Ibs 



Water per pound of coal from and at 212 degrees, . 11.86 Ibs 



Water per pound of combustible from and at 212 degrees, 13.01 Ibs 

 NOTE. The coal when fired contained 4.5 per cent, of moisture. 



This test is remarkable on account of the high character of 

 the result. Compared with the later test it shows the 

 effect which age may produce upon the performance of a 

 boiler. Although the boiler developed nearly 50 per cent, 

 more than that on test No. 134, the heat was so much 

 better absorbed by the new and clean surfaces that the 



