BOILER No. 18. 

 Results of Tests, Boiler No. 18. 



121 



The tests on Boiler No. 18 had for an object the determina- 

 tion of the economy produced by alternate firing in the double 

 furnace system which was here employed. Two kinds of coal 

 were used, viz : Cumberland coal on test No. 52, and anthra- 

 cite Lehigh on Test No. 53. The Cumberland coal gave an 

 evaporation of 10.93 pounds of water from and at 212 degrees 

 per pound of combustible, and the boiler developed somewhat 

 more than its rated capacity. This result is much below the 

 highest obtained from boilers which are set and operated in 

 the usual manner. The cause of the low performance may be 

 attributed in part to the somewhat high degree of waste heat 

 escaping to the chimney, the temperature of the gases being 472 

 degrees, though there does not appear to be a sufficient loss in 

 this alone to wholly account for it. It is probable that the use 

 of a furnace at each end of the boiler, and the arrangement 

 of flues required in this system, is attended with a greater loss 

 from radiation than ordinarily occurs, and that this loss more 

 than offsets the advantage which might otherwise be obtained 



