i52 Mr. J. Taylor's Lectures on MctaUurgjj'. 



large dimensions. Of a smaller size they are very commonly 

 used in iron foundries, where pig-iron is simply melled for 

 making various articles of cast-iron ; and similar furnaces are 

 in use in what are called the blowing-houses in Cornwall, for 

 the finer kind of tin called Grain-tin. Blast furnaces of a small 

 kind, called Hearths, are much employed also in Cumber- 

 land and Yorkshire for melting lead ore; but they are nearly 

 confined to this district, as the Derbyshire and Welsh smelters 

 prefer air furnaces. 



The fuel is mostly in use for the blast furnaces is coke, 

 or coal charred so as to drive ofl" its bituminous part; this is 

 common for iron. In lead ores the principal iiiel is peat or 

 turf with a small mixture of coal. And for tin ores they em- 

 ploy wood charcoal ; coal would not answer, as it would cake 

 together and prevent the proper action of the furnace. 



Air furnaces fqr smelting are of a construction which is 

 usually called a Reverberatory, though they have also some 

 other local appellations. It is not unlike a large flat oven with 

 the fire-place at one end and the chimney at the other; so that 

 the matter to be acted upon being placed in the bottom be- 

 tween the flame playing over it, and reverberating upon it, 

 produces the effect desired. These furnaces are used with 

 a gentle draught and a moderate red heat for calcining or 

 roasting, and with a stronger draught and an intense heat for 

 fusion or flowing, and also for refining. They are the fur- 

 naces for copper ores, for lead ores in many places, and for 

 the greater part of the tin ores. Connnon coal is the fuel 

 used in them, and is the best adapted for them, as the strong 

 flame it gives is just what is rec|uired, and the fire-places are 

 so constructed that the fire can be stirred and supplied at 

 pleasure. 



The first operation which we shall notice, as it is the first 

 in order in the large way, is that of calcination. The object 

 here is to evaporate the volatile substances, or such as may be 

 driven off* b}' lieat or converted into a gaseous or atuiibrm 

 state. These are most commonly sulphur and arsenic, and 

 occasionally some acids. 



Another effect is often produced by roasting or calcination ; 

 which is the oxidizing some inferior metal : when the subse- 

 quent fusion takes place, it is got rid of by its combining with 

 the earthy matter in the form of an impure glass called scoi'ia 

 or slag. This happens in the calcination of copper ores, 

 where the iron is oxidized, while the copper is not much al- 

 tered. 



Calcinaiiuii of copper, lead and lin ores is performed in re- 

 verberatory 



