Hartley — A Study in Thermo- Chemistry. 37 



dioxide (CO2), and this gas is converted into carbon monoxide (CO) 

 bj contact with more red-hot fuel. 



In either case the following functions are performed : — 



(a) Initiation of the reducing process by heating the ore, 



that is by raising it to a suitable temperature. 



(b) Reduction of the ore by carbon monoxide gas (00). 



(c) In certain cases, in which the reducing process consists 



of feebly exothermic reactions, to maintain the 

 reducing process by the continuous supply of 

 extraneous heat. 



All reducing processes are not of the same nature, and it will 

 be convenient to consider them in the following order : — 



1. Reduction accomplished by means of furnace gases. 



2. Reduction by carbon. 



3. Reduction by another metal. 



4. Air reduction processes, or those in which air, acting 



upon a sulphide, removes the sulphur as sulphur 

 dioxide while the metal itself is reduced. 



Furnace gases, which operate in reducing processes, consist 

 chiefly of carbon monoxide (CO), and some hydrogen. The 

 difference in the heat evolved by the combustion of various sub- 

 stances is considerable, as may be understood by the following 

 equations : — 



(1.) H2 + = HoO gaseous + 58-2 heat-units. 



(2.) + = CO „ +28 



(3.) CO + = CO3 „ + 69 „ 



(4.) +0.= C02 „ +97 



The production of the so-called " water-gas " can take place 

 only at very high temperatures because it involves a loss of heat ; 

 the reaction is endothermic. 



0^+ H2O = CO + H2 + (28-58-2) heat-units. 



As the heat evolved by the formation of water amounts to 58-2 units, 

 and that of carbon monoxide to only 28 units, it follows that to bring 



