134 ON THE SETTING OF STEAM BOILERS. 



the object of the setting of a boiler, and what are tho con- 

 ditions under which that object is best attained? Tlie 

 object is, to bring the flame and heated products, generated 

 in the furnace, in contact with tho surface of the boiler ; and 

 it is best attained — (1) when the greatest amount of surface 

 is exposed to the flame ; (2) when the greatest amount of 

 exposed surface is horizontal, or in the most favourable 

 direction for the flame to impinge upon it ; (3) when the 

 passage of the gases through the flues is least impeded by 

 contracted area or by obstructions in them ; and (4) when 

 tho gases can be kept in contact with the surface long 

 enough to part with all or practically all their heat without 

 checking the draught into the furnace. 



Keeping these points in mind, I will now notice the most 

 usual forms of setting in vogue, as applied to the two types 

 of land boilers almost universally used — the Lancashire and 

 the Cornish types. I may dismiss the Egg-end boiler as 

 almost obsolete, except in tho case of rolling mills, where 

 it is heated by the Waste heat from tho puddling furnaces, 

 and in the case of collieries, where coal is so plentiful that 

 it matters little what kind of setting is adopted. 



The most usual forms of sotting arc but two — the q)lit 

 draught and the wheel draught. 



Eegarding these critically, to find out their weak points, 

 as it is the Engineer's business to do, you will notice the 

 draught is split either at the back to traverse the side flues, 

 or, as is most usual, it traverses the bottom first, is split at 

 the front, and returns by the side flues. The latter is 

 perhaps tho one to be preferred, as tho bottom or horizontal 

 part of the boiler is exposed to the gases at the time when 

 they are hottest, and the circulation of the water is increased 

 by the more rapid generation of steam from the bottom. 

 But seeing that the gases will, by natural law, always take 



