Mr. J. Taylor's Lectures on Metallurgy. 4,55 



iiaces at a high degree of heat, and the slag is raked oflP in a 

 rluid state. 



Lead and tin ores are treated in nearly a similar manner. 

 _ Iron smelting is carried on in blast furnaces of very laro-e 

 dimensions, in which coke is employed as fuel, and limestone 

 is used as a flux. Copper of the first flowing is in part com- 

 bmed with sulphur, so as to require subsequent calcinations 

 and repeated fusions before it comes to the refining process. 



Lead is generally produced pure in one operation from the 

 reverberatory furnace, and also from the blast-furnace, where 

 the sulphur is dissipated pardy by the application of heat, and 

 partly by combining with the 'lime which is used. 



Tin being produced from an oxide, some carbonaceous 

 matter, such as smallcoal, is used in mixture Avith the ores; the 

 carbon unites with the oxygen and leaves the metal pure, ex- 

 ce})t as it may happen to be mixed with other metallic sub- 

 stances. 



By the operations which have been described, the whole 

 metallic contents of die ores are produced in a separate state, 

 the volatile part being dissipated by calcination, and the earthv 

 part by being converted into slag, which is easily detached 

 from the metal: it is evident however, that if more metals than 

 one exist in the ores, they will all be reduced by the same 

 li-eatment, and therefore we may, and often do, procure an 

 alloy more or less complicated. 



The purification of the metals is performed by various 

 processes of refining, which are suited to their several qualities, 

 and advantage is taken of the different properties in each to 

 effect this. 



Thus, some metals are refined by their having less affinity 

 for oxygen than others ; such as gold, silver, "and copper : 

 these not being easily oxidized in the fire, may be exposed to 

 a strong and continued heat, which converting the inferior 

 metals into oxides, they ri-^e to the surfeceof the melted mass, 

 from which they may be- removed by various means. An 

 exam]>le of this is the separation of lead from silver. This 

 operation is called Testing or Cupellation. 



Another mode of refining is, when one metal is more fusi- 

 ble than another, whereby a separation of the two may be 

 elFected : — Thus tin of the first melting often contains some 

 iron or coj)per, but being melted at a very low heat, the tin 

 exudes, leaving the others, which do not flow but at a higher 

 tein})eratare. Silver is separated irom copper when it Is in 

 small jjroportions by adding lead to the whole infusion. The 

 silver unites with the lead and is separated with it afterwards 



by 



