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COALFIELDS AND COLLIERIES OF AUSTRALIA. 



connect the three upper drums together (Fig. 171). All the 

 tubes are bent slightly, so as to allow them to enter the drums, 

 normal to their periphery, and provide for expansion and con- 

 traction. The steam spaces of all the upper drums are con- 

 nected, while the water spaces of only the front and middle 

 drums communicate. All parts subject to pressure are of 

 wrought metal, and either spherical or cylindrical in form, so 

 as to mitigate the tendency to distortion under pressure. By 

 suitably disposed fire-brick baffle walls, the gases from the 

 grate are led up among the first bank of tubes, thence down 

 the middle bank, up the rear bank, and on to the chimney, so- 

 they have every opportunity of giving up their heat to the 

 water. The feed water enters the boiler at the coolest point; 



Fig. 171. Sectional Arrangement of the Stirling Boiler, Side 



Elevation. 



that is, lit the rear steam drum. The lime salts in the water 

 that are rendered insoluble bv the heat, settle in the mud 

 drum, and can be blown oil' as required. The mud drum is 

 protected from the heat of the furnace by the bridge wall. 

 Every tube has an outlet to the steam drum equal to its full 

 area. The removal of one manhole door from the end of each 

 drum renders every part of the interior accessible for cleaning. 

 The tubes being only slightly inclined from the vertical, there 

 i.s little opportunity for soot or dust to collect on the outside 

 surfaces of the tubes, and as the tubes are arranged in parallel 

 rows, they can be thoroughly cleaned on the outside by means 

 of a steam hose. The bent tube performs the same function 

 as the expansion loop or bend in a steam main, inasmuch as 



