492 



SCIENCE. 



[Vol. XIII. No. 333 



boiler under test, in connection with one other boiler of usual form ; 

 and although all the machinery of the works, including about 35 

 horse-power used in running generators for electric lights, was 

 thrown on the engine, no difficulty was found in holding the steam- 

 pressure required, with the flue damper one-third open, and fire- 

 doors closed or placed ajar for a considerable portion of the time. 

 The boiler showed considerable reserve capacity for an increase of 

 power, whenever a demand was made upon it. 



In the matter of safety it would seem that this construction is 

 safer than the ordinary form. The crown sheet over the furnace 

 has usually the least depth of water over it of any plate in a boiler 

 exposed to the action of the fire, and is at the same time exposed 

 to the fiercest temperature of the tire. The result of low water, 

 should the crown sheet not be covered, would be, in the ordinary 

 case, to burn the plate, with a resulting bulging of the sheet, or 



great a quantity of air, which would be heated and wasted ; or (3) 

 by too strong a draught in the flue to the chimney, which would 

 take off the hot gases before there was time for the absorption of 

 their heat by the boiler. At the beginning of the test, the flue 

 damper was open, and the temperature in the uptake was 590° F. 

 On closing the damper to about one-third opening, at which point 

 it was kept during the remainder of the trial, temperatures varying 

 from 330° to 375° F. were obtained. At the steam-pressure car- 

 ried, the temperature of the steam and water in the boiler was 

 about 330° F., showing that the loss of heat above this temperature 

 throtigh the chimney was very small, varying from nothing to at no 

 time more than about 40° F. 



The firing was skilfully managed, and, so far as could be deter- 

 mined, no unnecessary amount of air was admitted. The percent- 

 age of refuse to the coal burned (9 91) shows that the coal, which 



COMPLETE COMBUSTION BOILER. 



perhaps the explosion of the boiler. In this boiler the hottest tem- 

 perature of the fire is beneath the grate, where all the surrounding 

 surfaces are protected by water, which instantaneously absorbs 

 the heat coming in contact with them ; while the direction of the 

 draught being downward and away from the crown sheet, and the 

 latter being still further cooled by the entering air used for com- 

 bustion, the crown sheet is kept comparatively cool, with, in any 

 case, little probability of burning. Should the water-level be low- 

 ered below the grate, the grate-tubes would burn off, and destroy 

 the fire. 



An important advantage in supplying the air above the grate is 

 that it is never necessary to open the combustion-chamber to the 

 outside air, which cools the entire boiler, and causes loss of heat in 

 the ordinary boiler whenever the furnace is fired. Throughout the 

 trial the ash-pit doors were kept closed. 



The boiler was covered with asbestos, brick setting being unne- 

 cessary on account of the use of the internal furnace. Since the 

 radiation from the steam and water surfaces of the boiler was re- 

 duced by the covering to a minimum, the only losses of heat that 

 could occur were either (i) by not supplying air in the right quan- 

 tity or manner to consume the coal perfectly ; (2) by admitting too 



was the best dry Cumberland to be had, was quite perfectly con- 

 sumed. 



From the above considerations and conditions, it would be ex- 

 pected that this boiler, properly run, would give high economical 

 results. These were an evaporation from an average temperature 

 of 53-J-° F. into steam of an average gauge pressure of 80 pounds, 

 of 9.82 pounds of water per pound of coal. The equivalent evapo- 

 ration, reduced to the standard of from and at 2r2° F. was 11.78 

 pounds, and per pound of combustible, 13.08 pounds. The average 

 result of a large number of tests made with different boilers at the 

 Centennial Exhibition of 1876 was 10.99 pounds of water per pound 

 of combustible. 



The boiler shows, as above, good proportions ; and the condi- 

 tions of setting, draught of chimney, etc., were favorable. The 

 steam appeared to be of excellent quality, free from moisture, and 

 there was no priming. The coal was charged as dry coal, no de- 

 duction being made for moisture. The water-consumption was 

 accurately obtained by weighing all the water fed to the boiler, and 

 there was no leakage. The water-level in the boiler was the same 

 at the beginning and end of the test, and the steam-pressure 

 made uniform at both times. 



