ON FURNA CES. 403 



well-arranged regeneiative gas furnaces for reheating iron. In those 

 arrangements in which there is little heat lost by external cooling, and 

 in which the heat of the products of combustion is most fully utilized, 

 the useful effect is much higher : thus, in large blast furnaces, 

 M. Gruner estimates that it is as much as seventy to eighty per cent, 

 of the heat actually developed in the furnace and introduced into it 

 by the blast, or between forty and fifty per cent, of the total heat that 

 the fuel could evolve if completely burned ; and in the annular 

 Hoffmann brick kiln, it is estimated to amount also to between 

 seventy and eighty per cent, of that given out by the fuel. 



A greater proportion of the heat evolved is lost, in the burned gases, 

 the less the difference is between the temperature of the flame and that 

 required to be maintained in the working chamber ; for as soon as any 

 portion of the flame is cooled down to the temperature of the matters 

 lo be heated, however high this may be, it can impart no more heat to 

 them, and must be drawn away and replaced by hotter flame from the 

 fire. Hence, a small increase in the initial temperature of the flame, 

 such as that obtained by effecting the combustion of the fuel by means 

 of moderately heated blast, or a small diminution in the proportion of 

 heat lost from the working chamber by external cooling, effects a great 

 saving in the consumption of fuel that is required to do a given 

 amount of work. 



The effect of a high flame temperature, on the proportion of heat 

 utilized, is strikingly shown by the very economical working of fur- 

 naces on Deville's system, that of burning coal gas with oxygen, instead 

 of with air. The theoretical temperature of such a flame, if not limited 

 by dissociation, would probably amount to 7000 or 8000 C, and it is 

 in any case far above the fusing point of platinum, which is estimated 

 at about 1900 C. In an example, of which M. Gruner gives particulars, 

 in the paper above referred to, of the fusion of a charge of 250 kilo- 

 grammes of platinum by this method, the cold furnace was heated up, 

 and the metal melted in it, in one and a quarter hours, and with a 

 consumption of only twenty-four cubic metres (848 cubic feet) of gas ; 

 the proportion of heat actually utilized, in the fusion of the metal, 

 being fourteen per cent, of that due to the combustion of the gas. 

 Thus, on account of the intense heat of the oxyhydrogen flame, as 

 good an economical result was obtained, in this little furnace, as in the 



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