x 



eO BOILER TESTS. 



working with a heater, unless the temperature of the gases is 

 excessive. If the temperature is excessive and the full capac- 

 ity of the chimney is required, there is some doubt whether a 

 heater could successfully be used. 



The quantities given in Table No. 10 show the draught 

 power of chimneys of different heights, supplied with gas of 

 various temperatures. In this connection it may be added 

 that the draught of another chimney having a height of 230 

 feet, supplied with gas at a temperature of 500 degrees, 

 amounted to 1.6 inches. This and all the observations referred 

 to were made in cold weather. 



The effect of changing the proportions of air space in the 

 grates is shown by the tests on Boiler No. 10. With anthra- 

 cite Lehigh coal, of which 8.7 pounds were consumed per 

 square foot of grate per hour, the grates having 50 per cent, 

 air space, secured about 2 per cent, more evaporation per 

 pound of combustible than those having 60 per cent, air space. 

 With about one-half as much coal burned in a given time the 

 gain was 8 per cent, in favor of the smaller air space. The 

 results of repeated tests corroborated these figures. Consider- 

 ing that whatever air passes through the grate, beyond that 

 needed for chemically perfect combustion, produces a loss of 

 economy, and that an excess of air to a greater or less extent 

 always attends combustion, the effect may be explained on the 

 ground that the reduced amount of opening in the grates tends 

 to cut off this source of waste. The effect appears to be 

 greatest when the rate of combustion is low. In the case 

 mentioned the rate was much below that required to work the 

 boiler to its nominal capacity. The effect is small at the 

 higher rate and the conclusion may be drawn that it is only 

 under special conditions of work that the matter is of much 

 importance. 



The tests on Boiler No. 10 furnish a case of economy pro- 

 duced by automatic regulation of the draught over hand 

 regulation. The automatic regulation secured an increased 

 evaporation amounting to 3.7 per cent. The hand regulation 

 consisted in alternately opening the damper wide and changing 



