26 BOILER TESTS. 



the same. The rate of combustion is slightly larger in the 

 case of the vertical boiler. The temperature of the escaping 

 gases is 104.1 degrees higher in the vertical boilers than in the 

 horizontal boilers. The evaporation per pound of combustible 

 is 15.7 per cent, larger in the horizontal boilers than in the ver- 

 tical boilers, and the latter superheat the steam 68 degrees. 

 Assuming as before that the saturated steam contains 1 per 

 cent, of moisture, the superheating represents a gain in effi- 

 ciency of 8.2 per cent., and there is left for the net superiority 

 of the horizontal boilers 7 per cent. 



A more satisfactory comparison may be made if those of the 

 horizontal tubular boilers, which are called " double-deck," 

 are discarded, as also those in which the heating surface is de- 

 ficient. Throwing out for this reason Nos. 17, 22, 24, 42, 43, 

 and 45 , the average quantities for the remaining ten examples 

 are as follows : ratio, 40 ; ash, 12.6 per cent. ; rate of combus- 

 tion, 10.6 pounds ; temperature of escaping gases, 382 degrees ; 

 water per pound of combustible from and at 212 degrees, 

 10.90 pounds. Comparing the vertical boilers now with this 

 new average, we have a difference of 110 degrees in the tem- 

 perature of the gases, and 17.2 per cent, in the. evaporation 

 per pound of combustible. This makes the net superiority of 

 the horizontal boilers 8.3 per cent. 



The superior economy thus shown is evidently due in the 

 main to the saving produced by the low temperature of the 

 escaping gases. A difference of 110 degrees is sufficient to 

 account for a considerable difference in the results. For ex- 

 ample, refer to the tests on Boiler Xo. 46, which give the 

 effect produced by utilizing the heat of the gases in warming 

 the feed-water. Here a reduction of 107 degrees in the tem- 

 perature of the gases secured an increase in the evaporation per 

 pound of coal amounting to 7 per cent. The indication of tem- 

 perature is not, however, according to the best vieiv of Ihe 

 subject, a full measure of the extent of the loss in the waste 

 gases. Owing to the brick setting with which the boilers are 

 provided, and the tendency which hot brick-work has to be- 

 come unsound by age, it is probable that, in ordinary use, a 



