BOILER No. 51. 187 



cent. Allowing for superheating as before according to the 

 quantity of heat added, the results of the two tests are respec- 

 tively 9.94 pounds and 10.15 pounds, and the difference 

 between them is about 2 per cent. The increase in the water 

 heating surface enabled the boiler to utilize a larger propor- 

 tion of the heat of combustion of the coal to the extent of 

 about 2 per cent. 



A comparison of Tests No. 101 and No. 102 shows the 

 unfavorable effect produced upon the vertical type of boiler by 

 a high rate of combustion. The quantity of coal burned in a 

 given time in Test No. 101 was 54 per cent, larger than in 

 Test No. 102, and the evaporation per pound of coal was 

 reduced 14.4 per cent. This reduction is accounted for by 

 the increased temperature of the escaping gases, which was 

 from 480 degrees to 600 degrees. The amount of power 

 developed on the capacity test was large, and the ease here 

 shown with which the vertical boiler generates steam should 

 not be lost sight of. With a stack only 60 feet high, the 

 boilers developed 21 per cent, more than the rated capacity 

 ( without allowance for the greater efficiency of superheated 

 steam ), and the rate of combustion was 17.1 pounds of coal 

 per square foot of grate per hour. 



Boiler No. 52. 



Kind of boiler, Vertical tubular with fire-box. 



Number used, . . . . . . One. 



Horse-power ( basis 10 sq. ft. ), . . Twenty. 



Kind of coal, . . . . . . Anthracite, Lehigh, egg. 



Age, ....... Four months. 



Boiler No. 52 is of the vertical type, arranged in the manner 

 shown in the following cut. It is supported by a brick ash pit, 

 but otherwise it has no brick setting, the exterior surface being 

 covered with a non-conducting cement. The steam, before 

 leaving the boiler, passes through a chamber in the interior of 

 the shell. The top and bottom of this chamber are connected 

 by means of tubes which surround the respective fire tubes 

 of the boiler, the annular space between the two tubes 



