224 BOILER TESTS. 



absorbed, as the comparatively low flue temperature indicates. 

 The rate of combustion is somewhat low for the water tube 

 type of boiler, the draught being deficient, and this, coupled 

 with the possibility of an inferior quality of fuel used 

 furnishes a partial, and perhaps a full explanation of the 

 inferior character of the result. 



Boiler No. 68. 



Kind of boiler Water tube. 



Number used, . . . . . Two. 



Horse-power ( collective, basis 12 sq. ft. ), Two hundred and sixty. 



Kind of coal, George's Creek Cumberland. 



Age, . Two years. 



Boiler No. 68 consists of a plant of two water tube boilers 

 of the form shown in longitudinal section in the cut of Boiler 

 No. 64. The brick side walls of the furnaces are fitted with 

 perforated tiles, through which air is admitted over the fuel, 

 as shown in the cut referred to. This plant is provided with 

 a flue heater, the location of which with reference to the boilers 

 and chimney is shown in the following cut. The heater con- 

 sists of a cluster of vertical cast iron pipes, similar to that in 

 use on Boiler No. 33. The heating surface exposed by these 

 pipes is about half as much as the total heating surface of the 

 two boilers. 



Dimensions of Boiler No. 68. 



Number of tubes 4 inches outside diameter, .... 144 



Length of tubes, 18 ft. 



Diameter of drums (2 ),. . . . . . 36 in. 



Mean length of drums, 17 ft., 6 in. 



Area of heating surface, . . . . . . 3,126 sq. ft. 



Area of grate surface, 50 sq. ft. 



Area through flue, 11 sq. ft. 



Height of chimney, 80 ft. 



Width of air spaces and metal bars in grates, Air 1-2 in., metal 11-16 in. 

 Ratio of heating surface to grate surface, .... 62.5 to 1 



Ratio of grate surface to flue area, . ..... 4.5 to 1 



Area of heating surface in flue heater, .... 1,600 sq. ft. 



