BOILERS No. 20 and No. 21. 



125 



3 

 75 



sq. ft. 

 ft. 



3-8 in. 



Area through flue, ..... 

 Height of chimney, ..... 

 Width of air spaces and metal bars in grates, 

 Distance of grate to shell, 

 Distance of flat bridge wall to shell 

 Ratio of heating surface to grate surface 

 Ratio of grate surface to tube area, 



Results of Tests, Boilers No. 20 and No. 21. (Average of 2 runs. ) 



NOTE. The coal when fired contained 3 1-2 per cent, of moisture. 



The tests on Boilers No. 20 and No. 21 were made to deter- 

 mine the economy of admitting air to the furnace over the fuel, 

 when using a mixture of pea and dust and Cumberland coal. 

 The two tests were conducted .simultaneously with fuel which 

 had been thoroughly mixed so as to obtain the same quality 

 for both boilers. The evaporative results show that the use 

 of air above the fuel, in Boiler No. 20, was attended with a 

 loss of 4.5 percent, based on coal, and 4.8 per cent, based on 

 combustible. Boiler No. 21 was subsequently tried with 

 anthracite broken coal, containing 13.3 per cent, of ash, and 

 burning 10.5 pounds of coal per square foot of grate per hour, 

 with a draught of 0.29 of an inch, and gave an evaporation of 



