40 Scientific Proceedings^ Royal Dublin Society. 



(3.) Reduction by another Metal. 



Certain ores are capable of reduction by being heated in con- 

 tact with another metal which is more easily obtainable, or less 

 costly, than that to be extracted. 



The following are examples : — 



Lead Smelting : — 



PbS + Fe = Pb + FeS + (23-8 - 17-1) heat-units. 

 Heat evolved = 6 units. 



Reduction of Mercury Ores : — 



HgS + Fe = Hg + FeS + (23-8 - 19-8) heat-units. 

 Heat evolved = 4 units. 



Special Action of Sodium. — Magnesium and aluminium are in- 

 capable of reduction from their oxides, and are therefore converted 

 into chlorides, from which compounds they may be separated by 

 the action of metallic sodium when the material is heated sufficiently 

 to initiate the reaction. 



Reduction of Magnesium from its Chloride: — 



MgCls + 2 Na = Mg + 2 NaOl + (194-6 - 151) heat-units. 

 Heat evolved = 43"6 units. 



Reduction of Aluminium from its Chloride : — 



AICI.3 + 3 Na = Al + 3 Na CI + (291-9 - 160-9) heat-units. 

 Heat evolved = 131 units. 



(4.) AlR-EEDUCTION pROCESS. 



It is to be observed that, in combining with sulphur, metals 

 evolve less heat than in uniting with oxygen, and also that oxygen 

 can decompose sulphides yielding an oxide. 



If the oxide is only feebly exothermic the metal will be pro- 

 duced by the action of heated air upon the sulphide, thus : — 



