EXPLANATION OF TABLES. 21 



1,110, which is the total heat of steam of 70 pounds pressure, 

 reckoned from 100 degrees. 



The observations of the boiler pressure, the various tempera- 

 tures, and the draught suction are made every half hour 

 while the boiler is doing normal work, and the results are 

 averaged. 



The water evaporated " per pound of coal from and at 212 

 degrees" is computed by multiplying the quantity evaporated 

 per pound of coal by the total heat of the steam, reckoned 

 from the temperature of the feed- water, and dividing the 

 product by 966. 



The water evaporated " per pound of combustible from and 

 at 212 degrees" is computed by dividing the " water per pound 

 of coal from and at 212 degrees," by the percentage of com- 

 bustible in the coal ; that is, by 100, less the percentage of ash, 

 and multiplying the result by 100. 



In the tables of dimensions, the area of heating surface given 

 is that exposed to the fire and products of combustion, and not 

 that exposed to the water or steam. 



No attempt has been made in these tests to determine, by 

 chemical analysis, the constituent elements in the composition 

 of either the coal or the escaping gases. 



The evaporative results expressed in pounds of water evap- 

 orated per pound of coal, include no allowance for superheat- 

 ing in cases where superheating exists, and are not corrected 

 for moisture when the steam is found to be w r et. The quanti- 

 ties given as " water evaporated " are feed- water supplied and, 

 presumably , evaporated . 



DISCUSSION OF RESULTS. 



Having now considered in a brief manner the general sub- 

 ject of boiler tests, and pointed out the method of conducting 

 the particular tests under notice, we may pass to the chief 

 object of the paper; viz., a review of the various results, and 

 a consideration of the general subject of econom}^ in the gen- 

 eration of steam, as revealed by the tests. 



