404 SECTION MECHANICS. 



best of the flame furnaces used in ordinary metallurgical work ; though 

 the proportionate loss of heat from the surface cooling of so small a 

 furnace, (a little trough not more than thirty inches long,) must have 

 been enormous, the products of combustion cannot have escaped at a 

 lower temperature than 2000 C., and neither the coal gas nor the 

 oxygen was heated. 



The system of working furnaces under high pressure, on which some 

 experiments were made a few years ago by Mr. Bessemer, offers a 

 possible method of increasing, considerably, the temperature of com- 

 bustion of ordinary fuels, and with it the proportion of available heat ; 

 but since the first experiments were made, of which an account was 

 published in the technical journals in 1869, nothing further has been 

 done to test the practical value of the scheme. 



The diminished proportion of heat that is lost by suiface cooling, in 

 the case of large furnaces, and the consequent higher temperature of 

 their flame, render them in all cases much more economical in fuel than 

 furnaces of smaller size. In the case of ordinary puddling furnaces, for 

 instance, when the coal consumption in those working five-hundred- 

 weight charges is about twenty-three and a half hundredweight per ton 

 of bar produced, the consumption is reduced to eighteen hundred- 

 weight per ton in working ten-hundredweight charges, and to fifteen 

 hundredweight per ton in still larger furnaces working charges of 

 fifteen hundredweight ; and in the welding furnaces, in use at Wool- 

 wich Arsenal, the larger the furnace is, the higher by actual experiment 

 is the temperature of the flame as it passes over the bridge, and the 

 smaller is the amount of coal required per ton of metal heated. A 

 furnace of ordinary size, heating six tons at a charge, consumes about 

 eight hundredweight of coal per ton ; a larger furnace, heating a charge 

 of thirteen tons, does the workr with only seven hundredweight per 

 ton ; and the largest of all, capable of heating at once a mass of iron 

 weighing sixty-five tons, gets this up to a full welding heat with a coal 

 consumption of only five and a half hundredweight per ton. In copper 

 smelting, in glass making, and in other work, large furnaces are 

 similarly found to use less fuel, in proportion to the work done ia 

 them, than furnaces of smaller size. 



The Conference then adjourned, 



