DOILEE No. 54. 195 



the effect which the admission of air above the fuel has 

 upon the economy and capacity of the boiler. The 

 damper was kept in a constant position for both tests, 

 and there was a steady draught of 0.7 inch on the chimney 

 side of the damper. The eifective draught in the boiler flue 

 was 0.26 inch when the air was admitted and 0.32 inch when 

 it was excluded, and, as a consequence, the power developed 

 was increased, by excluding the air,from 209.2 horse power to 

 236.2 horse power, an increase of 13 per cent. In the matter 

 of economy, the exclusion of air was followed by an increase 

 of 4.3 per cent, in the evaporation per pound of coal, and of 

 2.3 per cent, per pound of combustible. 



Test No. 110 taken in connection with tests No. Ill and No. 

 11 2, form a series of tests which show the relative economy 

 of different kinds of fuel. On each of these three tests the 

 air ducts remained closed. The evaporation per pound of 

 Cumberland coal was 16.6 per cent, greater, and that per 

 pound of mixed fuel 4 per cent, less, than the performance 

 with anthracite coal. The cost of fuel required to evaporate 

 30,000 pounds of water from and at 212 degrees, at the prices 

 which ruled at the time of the tests, is as follows : 



From this it appears that the cost of Cumberland coal 

 required to do a given amount of work was 15.5 per cent, 

 less, and that of the mixture 34.7 per cent, less, than the cost 

 of anthracite coal. 



The relatively small amount of draught required in burning 

 the standard grades of coal is noticeable, although the boiler 

 developed somewhat less than the rated power, and the rate of 

 combustion was low. The draught on test No. 112 is less 

 than one-sixth of the full capacity of a good chimney. The 

 Cumberland coal required a slightly stronger draught than the 



