160 



BOILEE TESTS. 



room, and the water line is carried up to about the middle 

 point in this shell. The area of heating surface for a given 

 amount of grate surface, and the area through the tubes, is 

 much larger in this form of boiler than in the ordinary type. 

 In this respect the boiler, from an engineering point of view, 

 possesses its chief characteristic. The brick setting is arched 

 over the top of the drum, as shown in the cut, and the whole 

 of the shell is exposed to the heat of the escaping gases on 

 their way to the chimney. The boiler is thus provided with a 

 small amount of steam-heating surface. 



BOILER No. 41, LONGITUDINAL SECTION. 



Dimensions of Boiler No.. 41. 



Diameter of lower shell, 54 in. 



Diameter of upper shell, 32 in. 



Length of shells and tubes, 12 ft. 



Number of tubes (3 inches diameter), 118 



Area of water-heating surface, 1,221 sq. ft. 



Area of steam-heating surface, 60 sq. ft. 



Area of grate surface, . 20 sq. ft. 



Area through tubes, 4.9 sq. ft. 



Ratio of water-heating surface to grate, . . . . 61 to 1 



Ratio of steam-heating surface to grate, 3 to 1 



Ratio of grate to tube area, ... 4.1 to 1 



