92 BOILER TESTS. 



and when the mixture of equal parts of screenings and Cum- 

 berland coal was burned, it was nearly one-third larger. Com- 

 pared among themselves the Cumberland coal developed 36 

 per cent, more power than the anthracite coal and 50 per cent, 

 more power than the mixture. 



The relative economy of these fuels is not fairly shown 

 because of the large difference in the conditions as to capacity, 

 especially in the case of the test of the Cumberland coal. The 

 low result produced here is no doubt due to the loss attending 

 the large capacity, this being shown in the comparatively high 

 temperature of the escaping gases. Considering the large 

 amount of power developed in the case of the test with anthra- 

 cite coal, the result in this case shows a high degree of 

 economy. The high rate of combustion, viz., 14 pounds per 

 square foot of grate per hour, and the low temperature of the 

 escaping gases, which was 349 degrees, are the two vital ele- 

 ments which contributed to this result. 



A subsequent test was made to determine the effect produced 

 upon the economy of the boiler by dispensing with the admis- 

 sion of air at the bridge wall. The test was made when 

 using Cumberland coal, and the principal results obtained were 

 as follows : 



Coal per hour per square foot of grate, .... 18.8 Ibs. 



Percentage of ash, 7 per cent. 



Horse-power developed, 135 H. P. 



Temperature of feed-water, ...... 40 cleg. 



Temperature of escaping gases, ..... 486 deg. 



Water per pound of coal, 7.94 Ibs. 



Water per pound of coal from and at 212 degrees, . 9. 02 Ibs. 



Water per pound of combustible from and at 212 degrees, 10.34 Ibs. 



Comparing the results of this test with those of test Xo. 16, 

 made with air in use, it appears that the evaporation per pound 

 of coal was reduced nearly 8 per cent. 



Boiler No. 1 O. 



Kind of boiler, Horizontal return tubular. 



Number used, . . . . . . One. 



Horse-power (basis 12 square feet ), . . Fifty-five. 



Kind of coal, Anthracite Lehigh, broken. 



Age, Several years. 



