1886.] on Dissociation Temperatures, dec. 479 



mostly by radiation in its first, and by contact in its second stage, a 

 great saving of fuel is effected, and almost no smoke produced. To 

 avoid altogether the production of smoke in this boiler, the fuel 

 should be charged on the grate in a uniform manner. It is quite 

 impossible to avoid producing smoke and waste if fuel is charged 

 unequally on the grate and at irregular intervals, however well the 

 boiler may have been arranged and constructed. Various kinds of 

 automatic and mechanical coal-feeding arrangements have been sug- 

 gested, and some have been aj)plied, but none have given full satis- 

 faction. At the London Smoke Abatement Exhibition numerous 

 apparatus of this kind were to be seen, and apparently worked 

 successfully, but when tested at other places, and under different 

 conditions, they have been found wanting, owing to the faulty manner 

 in which the flame and products of combustion were dealt with. 

 These clever appliances would, in my opinion, have worked more 

 satisfactorily if firing and heating had been carried out in them in 

 two successive stages. 



There is a very simple way of firing, which I have employed, 

 that may possibly not be quite new, but answers very well, and does 

 not require complicated constructions and appliances, always more 

 or less objectionable. It depends upon the following considerations. 

 When fresh coal is charged upon incandescent fuel, as is the case in 

 the usual mode of firing boilers, the volatile gases of the fresh fuel 

 are rapidly evolved, filling the fire-box to such an extent as to prevent 

 the ingress of air through the grate, and this occurs at the very time 

 the air-supply should be considerably increased. The result is 

 imperfect combustion and consequent waste of the very best com- 

 bustible gases, viz. the hydro-carbons, which cannot burn for want of 

 air to combine with ; free carbon is thus liberated from these gases, 

 and smoke is produced. In order to avoid smoke, and consequent 

 loss of fuel, any sudden production of volatile gases, either during or 

 after firing, must be prevented ; and sufficient air should always be 

 introduced, and so distributed, as to burn those gases as quickly as 

 the}' are produced. This can be done in the following manner : — 



Before putting on fresh coal the burning fuel should be pushed back 

 from the front part of the grate and distributed on the incandescent 

 fuel behind, care being taken that this portion of the grate is entirely 

 free from hot fuel. When the front part of the grate has become 

 comparatively cool owing to cold air passing through it, fresh coal 

 is distributed thereon. The freshly charged fuel lying on the cool 

 grate with cold air passing through it will be heated by radiation 

 only, partly from the incandescent fuel behind, partly by the flame 

 from its own gases, and partly by the surrounding hot brickwork. The 

 volatile gases will consequently be liberated at a comparatively slow 

 rate, and will combine with the air which entering through the inter- 

 stices in the fuel on the cool part of the grate will be evenly dis- 

 tributed over its surface. Gas and air will thus be supplied in nearly 

 the proper proportions for complete combustion of the fuel, and as 



Vol. XI. (No. 80.) 2 i 



