402 SECTION MECHANICS. 



cooling ; but it is chiefly to be attributed to the greater heating power 

 of the hydrogen, of which such oils largely consist, than that of carbon. 

 As Dr. Percy has pointed out, though the great weight, and the high 

 specific heat, of the gases resulting from the combustion of hydrogen 

 in air, lower the theoretical maximum temperature produced to a little 

 under that due to the combustion of carbon, yet if the products of 

 combustion pass off at any ordinary furnace temperature, considerably 

 below the theoretical maximum, the number of available units of heat 

 produced by the combustion of hydrogen is much greater than that 

 obtained from an equal weight of carbon. Thus, if the burned gases 

 pass off at 1500 C., the available heating effect of hydrogen is nearly 

 four times as great as that of carbon. 



It does not appear that any trials have been made of working re- 

 generative furnaces either with mineral oil or with natural gas ; nor, 

 indeed, even of burning these fuels with air moderately heated, such 

 as is used in Head's or Price's furnace ; though the advantage of thus 

 making use of the waste heat, to increase still further the temperature 

 of the flame, would evidently be great. It is not too much to say. that 

 a regenerative furnace, with regenerators, of course, only for heating 

 the air, and fired either with hydrocarbon gas, or with liquid fuel, on 

 such a plan as either of those above referred to, would far surpass any 

 furnace now in use, (except those, such as Deville's, in which the fuel 

 is burned by a current of oxygen,) in the weight of material that it 

 would heat with a given consumption of fuel. 



In nearly all furnaces, the amount of heat that is utilized is an ex- 

 tremely small proportion of the total heat due to the combustion of 

 the fuel ; the greater part being carried off by the burned gases, or lost 

 by conduction and radiation. M. Gruner calculates, in a recent paper 

 published in the "Annales des Mines," on the proportion of heat that 

 is utilized in furnaces of different kinds, that in the fusion of steel, in 

 crucibles, in ordinary coke furnaces, the heat utilized does not exceed 

 1 7 per cent, of the total amount that the fuel would be capable of 

 giving out, if perfectly burned ; and that even on the extreme suppo- 

 sition that half of the fuel is burned only to CO, the heat utilized 

 amounts to only 2'6 per cent, of that evolved. In flame furnaces, the 

 proportion of heat utilized is higher ; reaching, as a maximum, fifteen to 

 twenty per cent, of the total heat due to the amount of coal burned, in 



