COMPARISON OF DIFFEEENT KINDS OF BOILERS. 37 



economy of different types of boilers, these principles should 

 be remembered, and the comparison based on the performance 

 of the boiler when suitable conditions exist for the attainment 

 of the best result. There is on]y one case where this cannot be 

 done, and that is where the construction of the boiler forbids 

 the attainment of those conditions. 



A large proportion of the boilers treated of in the paper 

 are, in one form or another, of the horizontal tubular type. The 

 number of these is 46. Of this number, there are 31 of the 

 common return tubular type ; 1 is what may be termed a direct 

 tubular with common furnace ;2 are direct tubular with detached 

 furnace ; 1 has two furnaces for alternate firing ; 2 are provided 

 with a water leg for the front of the furnace ; 3 have such 

 an arrangement of tubes that there is a double passage of the 

 products of combustion through the boiler ; 6 are of the double- 

 deck type. 



Of the remaining boilers, 3 are plain cylinder, 10 vertical 

 tubular, 3 cast-iron sectional, 8 water-tube, and 1 Galloway. 



The most favorable results with the common horizontal boiler 

 are those obtained on No. 10 with anthracite coal, andonNos. 

 31,32, and 40 with Cumberland coal. The first is 11 .37 pounds, 

 and the average of the second 12.17 pounds. The conditions 

 in all these cases were favorable. 



The direct tubular boiler with common furnace, No. 14, 

 cannot be compared with these on account of the different kinds 

 of coal used; but this boiler can be compared with No. 13, 

 which is of the common type and which used the same kind of 

 fuel. In this comparison it stands at a disadvantage, but there 

 seems to be a reason for it in the fact of the unfavorable pro- 

 portion of heating surface to grate, which is only 27.7 to 1. 



The direct tubular boilers with detached furnace, Nos. 8 and 

 36, cannot both be brought into the comparison, since the 

 former used a mixture of screenings and bituminous coal. The 

 latter, No. 36, which was tested with both anthracite and Cum- 

 berland coal, can be used. The anthracite coal gave an evap- 

 oration of 11.33 pounds, and the bituminous coal 11.99 pounds. 

 Both of these are nearly as good results as the high-grade 



