COMPARISON OF DIFFERENT KINDS OF BOILERS. 39 



desired end must be secured by reducing the length of the tubes 

 and increasing their number, using a larger shell. The test 

 gives no indication of the result which would follow this change 

 of construction. 



The double-deck boilers No. 42 and No. 45, burning anthracite 

 coal with high rates of combustion, give an average evaporation 

 of 11.05 pounds. Those numbered 42 and 44, burning bitu- 

 minous coal, give an average of 12.22 pounds. One is slightly 

 below the standard of the common tubular boiler and the other 

 slightly above it. Here the benefit with bituminous coal is 

 due undoubtedly to favorable proportions. 



With all the various modifications in the type of horizontal 

 tubular boiler to which the tests refer, some of which it must 

 be admitted give excellent results, there is no other conclusion 

 to be drawn than that the form of horizontal boiler, which with 

 suitable proportions and operation can be depended upon to 

 give the highest evaporation, is the common horizontal return 

 tubular boiler, so widely used in New England factories. 



Passing to the boilers of the other types named, the first is 

 the plain cylinder. Little need be said of this boiler, it is of 

 such evident inferiority as an economical generator of steam. 

 The ratio of heating surface to grate surface is in no case above 

 10.9 to 1. If 36 square feet of heating surface is required for 

 economical results, nothing can be expected from a proportion 

 of less than *one-third of this quantity, and it is probably out 

 of the question to institute a re-arrangement in this type of 

 boiler which will secure the desired end in any practical way. 



The next form is the vertical boiler. This has already been 

 taken up under the head of superheating boilers, and only the 

 conclusions there derived require mention. These are, that if 

 suitable attention is given to the design of the boiler, the ver- 

 tical tubular compares favorably with the horizontal boiler. 

 The example afforded by Boiler No. 60, using Cumberland 

 coal, corroborates this view in the most positive manner. The 

 result obtained in this one case, when reduced to the basis of 

 horizontal boilers giving steam containing one per cent, of 

 moisture, in the manner pointed out for superheating boilers, 



