ON CONSUMPTION OF FUEL AND PREVENTION OF SMOKE. Il7 



Stated, to 10 times the volume of gases it contains. Now, from a number of 

 well-conducted experiments on the waggon-shaped, and the improved boilers 

 with double flues, it was ascertained that the following proportions of per- 

 manent openings for the admission of air behind the fire-bridge were the 

 nearest approach to perfect combustion*. 



Summary of Results obtained from 17 Experiments with fixed apertures for 

 the admission of air behind the bridge of two 40-horse power Boilers. 



It therefore appears that about 26 square feet, and 32^ inches of perma- 

 nent aperture for the admission of air, is the mean of the old and improved 

 boilers. 



This proportion must not however be taken as a criterion for every boiler, 

 as much depends upon the principle on which they are constructed, and it 

 will be safer to adopt the mean results of the experiments as shown in the 

 table, than to apply them without exception to every description of boiler 

 and furnace. Taking therefore the mean of the whole experiments, we may 

 safely administer the following supply of air behind the bridge. 



For cylindrical waggon-shaped and every description of boiler of the usual 

 construction, give permanent opening for the admission of air of 1^ square 

 inch to every square foot of grate-bar ; and for every square foot of grate-bar 

 surface in the double furnace and double-flued boiler, give half a square inch, 

 or '5 for the same purpose. 



Practically considered, this will be found a near approximation to the 

 correct quantity of air required for the support of effective combustion in 

 each, and provided necessary attention is paid to considerations involving 

 the consumption of bituminous coal, of different kinds, we may reasonably in- 

 fer a greatly improved process in the use and absorption of our mineral fuels. 

 In the combustion of splint and slaty coal, a different treatment will be 

 required as respects either the anthracite and the bituminous kinds ; the one 

 is obdurate and hard, the other is compact, and in some instances liquefies 

 like pitch. Now the splint and slaty specimens burn open and rapid, and 

 therefore require less air, exclusive of what is taken through the grate-bars. 



* It is due to Mr. John Wakefield (formerly of Manchester, now of Farnworth near Bolton) 

 to state, that he was amongst the first who turned his attention to the admission of air at the 

 biidge, behind the furnace, for the purpose of consuming the smolie as it escaped into the 

 flues. His first furnace was constructed on a plan of his own, having a hollow bridge closed 

 at the top, and thus rendering it an air-chamber connected with openings on each side of the 

 furnace. On this plan the air w.ts heated by the passing currents, and by a communication 

 from the air-chamber to an opening in the arch-plate over the furnace door, tlie air thus rare- 

 fied was forced downwards, by the form of tlie opening in the plate, direct upon the fire. A 

 variety of other scliemes were tried by Mr. Wakefield, some of them successfully ; and it is only 

 justice to that gentleman to state, that a considerable portion of his life was devoted to im- 

 provements in steam-boiler furnaces, and the abatement of a nuisance wliich at that period 

 (nearly thirty years ago) was justly complained of. 



