ECONOMY OP FUEL EOE STEAM MACHINERY. 339 



thrown in, is unconsumed gas, decomposed from the fuel without 

 enough oxygen to burn, although there may have been a sufficient 

 supply of heat-" 



" A second cause why the whole value of the produced heat is not 

 obtained, is that so much is abstracted from the gases in passing 

 through long tubes, that there is not enough left to continue the 

 combustion, although the inflammable gas is still there. That a tube 

 or any substance in the way of the gas does absorb heat enough to 

 prevent the burning of the gases, is proved by the action of Davy's 

 safety lamp. This is a common light, surrounded by a wire gauze, 

 which so absorbs the heat from the flame, as to extinguish the latter 

 at the gauze, by applying fire above the gauze the gas is again kindled, 

 showing plainly that want cf heat above had extinguished the flames." 



To remedy the waste of heat resulting from these causes Mr. Mc- 

 Connell of the London and North "Western Hailway (England) intro- 

 duced in some of his Locomotives what he termed a " Combustion 

 Chamber" dividing his flues into two lengths — into this chamber a 

 sufficient quantity of fresh air was introduced to produce the combus- 

 tion of the gases ; escaping unburned from the first length of tubes — 

 in fact producing precisely the same phenomena in the combustion 

 chamber as we frequently notice at the top of steamboat funnels. 

 The arrangement is said to have produced the most satisfactory results 

 as regards economy, though the practical difficulties in carrying it 

 out, have prevented its introduction to general use ; enough was done, 

 however, to demonstrate the correctness of the theory, and there is no 

 doubt but a duly regulated supply of oxygen in the tubes at that point 

 in the length where the heat of the escaped gases would be just suffi- 

 cient to ignite the mass, would be productive of a more complete ab- 

 sorption of the heat generated, than is affected in flues of the ordinary 

 construction. 



A most important influence is exercised on the consumption of fuel 

 by the form and position of the heating surfaces through which the 

 heat is transmitted to the water. Mr. Armstrong found that " a cubi- 

 cal metallic box submerged in water, and heated from within, generated 

 steam from its upper surface more than twice as fast as from the sides 

 when vertical, and the bottom yielded none at all. By slightly in- 

 clining the box, the elevated side much more easily parted with the 

 steam, and the rate of evaporation was increased, while in the depressed 

 side the steam hung so sluggishly, as to cause overheating of the 

 metal."* 1 Lence the advantages resulting from inclining the lire box 



• Tredgold ou the Steam Engine, vol. 1, 1850. 



