164 BOILEE TESTS. 



of the escaping gases in the two cases is 482 degrees and 392 

 degrees, respectively. The reduction is evidently due in a 

 measure to the increased amount of heating surface which the 

 double-deck boiler provides. There is 5,850 square feet of 

 surface in this boiler, against only 4,056 square feet in the 

 common boilers. While an improvement might be expected 

 from this cause, the whole of the improvement cannot be attri- 

 buted to the difference in the type of boiler, because the 

 double-deck boilers were new and clean, while the common 

 boilers were old and presumably somewhat inefficient from 

 long usage. It is quite probable that the whole of this trinall 

 improvement (which, as noted, is only 3.5 per cent. ) maybe 

 attributed to the difference in age and condition of the heating 

 surfaces, rather than to the change in the type of boiler. 



The results of Tests No. 83 and No. 84 may be compared to 

 show the relative economy of Lacka wanna coal, broken size, 

 and George's Creek Cumberland coal. The bituminous coal, 

 considered by itself, gave exceptionally good results. The 

 large draught area through the tubes appears to be a favorable 

 condition in cases like this, where the gaseous element of com- 

 bustion forms so* prominent a feature. If this be so, the com- 

 parison between the economy of the two fuels shows a larger 

 difference in favor of the bituminous coal than would be shown 

 on some different type of boiler. Taking the figures as they 

 stand, however, there is a difference of 11.55 9.65 = 

 1.90 pounds of water in favor of the performance of the 

 bituminous coal, which is a gain of nearly 20 per cent, over 

 that of the anthracite coal, and this gain represents a saving 

 in the quantity of bituminous coal required to do a given 

 amount of work of 16.4 per cent. 



In comparing the two kinds of fuel used on Tests No. 83 and 

 No. 84, a marked difference is to be observed in the quantity 

 of ash. The percentage of ash in the anthracite coal is 12.3 

 per cent, and that in the bituminous coal 6.7 per cent. 



