W^ 6N EVAFOllATlNG FURNACUS. 



On the com- rife of the temperature, whence it refults that the heat wtilcft 

 ^JcTnftruaL '•'' in<ufiicient to produce a complete combuftion of the inflam- 

 of furoaccs. mable particles, will rather produce gazification than oxigi- 

 nation. This volatilization of the particles of combuftible 

 bodies which efcape combuftion, and which pafs fucceffively 

 into the ftate of permanent gales, will alfo abforb a quantity 

 of heat neceffary to their gafeous conftitution, which, together 

 with tlie effcds of the current of air, will tend to lower the 

 interior temperature of the furnace, and to impede the procefs 

 of combuftion. 



Thefe remarks, which perfeftly agree with all the pheno- 

 mena: of combuftion, fliew that the oxigen of the atmofphere 

 does not a£l with much efficacy on combuftible bodies, except 

 when they are immerfed in it at an high temperature, and that 

 to apply an intenfeand uniform heat to an evaporating furnace 

 without lofs of the combuftible, it (liould be produced in a fire- 

 place, having a current of air, and fo far dillant from the boiler 

 that the temperature may be raifed gradually and at pleafur«. 

 By this means all the particles of the combuftible matter will 

 be in a ftate favourable to their oxigination ; and the whole 

 quantity of radiant heat produced by the readion of the oxi- 

 gen upon the combuftible, will be difengaged and employed 

 without lofs. 



That which under fimilar circumftances conduces ftill farther 

 to encreafe the a6tion of the oxigen, is its continual renewal. 

 For the higher the temperature of a furnace is raifed the more 

 eafily the outer air will enter; and fo likewife when the igni- 

 tion is carried to a high degree, it becomes necefTary and ad- 

 vantageous to check the current of air, not by clofing the door 

 or lower opening of the furnace, as is generally done, but ra- 

 ther by contrafting or even clofing the upper aperture of the 

 chimney. By this means the heat becomes concentrated in 

 the body of the furnace, and has no other pafl'age than through 

 the liquid in the boiler. 



This remark on the method of checking the current of air 

 by the top of the chimney, may alfo be applied to furnaces of 

 fufion, and in cafes where it is required to maintnn the heat 

 of a metal without expofing it to the oxigenating adion of a 

 current of air in a ftate of ignition. 



General 



