498 



THE STEAM-ENGINE. 



Fig. 55. 



ducts the flame in contact with the side from the back to the front; it then passes 

 through the flue K across the front, and returns to the back by the other side- 

 flue L. The side-flue is represented, stripped of the masonry, in fig. 52, and 

 also appears in the plan in fig. 55, and in the cross section in fig. 54. The 

 course of the air is represented in fig. 55, by the arrows. From the flue L the 

 air is conducted into the chimney at M. 



By such an arrangement, the flame and heated air proceeding from the grate 

 are made to circulate round the boiler, and the length and magnitude of the 

 flues through which it is conducted should be such, that when it shall arrive 

 at the chimney its temperature shall be reduced, as nearly as is consistent 

 with the maintenance of draught in the chimney, to the temperature of the 

 water with which it is in contact. 



The method of feeding the furnace, which has been described above, is one 

 which, if conducted with skill and care, would produce a much more perfect 

 combustion of the fuel than would attend the common method of filling the 

 grate from the back to the front with fresh fuel, whenever the furnace is fed. 

 This method, however, is rarely observed in the management of the furnace. 

 It requires jhe constant attention of the stokers (such is the name given to 

 those who feed the furnaces). The fuel must be supplied, not in large quanti- 

 ties, and at distant intervals, but in small quantities arid more frequently. On 

 the other hand, the more common practice is to allow the fuel on the grate to 

 be in a great degree burned away, and then to heap on a large quantity of fresh 

 fuel, covering over with it the burning fuel from the back to the front of the 

 grate. When this is done, the heat of the ignited coal acting upon the fresh 

 fuel introduced, expels the gases combined with it and, mixed with these, a 

 quantity of carbon, in a state of minute division, forming an opaque black 

 smoke. This is carried through the flues and drawn up the chimney. The 

 consequence is, that not only a quantity of solid fuel is sent out of the chimney 

 unconsumed, but the hydrogen and other gases also escape unburnt, and a 

 proportional waste of the combustible is produced ; besides which, the nuis-ance 

 of an atmosphere filled with smoke ensues. Such effects are visible to all 

 who observe the chimneys of steam-vessels, while the engine is in operation. 

 When the furnaces are thus filled with fresh fuel, a large volume of dense 

 black smoke is observed to issue from the chimney. This gradually subsides 

 as the fuel on the grate is ignited, and does not reappear until a fresh feed is 

 introduced. 



This method of feeding, by which the furnace would be made to consume 

 its own smoke, and the combustion of the fuel be rendered complete, is not 



