1822.] Tin Ores in Cornwall and Devonshire. 455 



the bottom at the back of the cyhnder is provided to admit the 

 blast, and another, lower down and opposite to it, suffers the 

 metal to flow out regularly as it is reduced. 



A strong blast is kept up by bellows, or, in more improved 

 works, by pistons working in cylinders, and the air is conducted 

 by a proper pipe so as to blow into the orifice in the furnace. 



The only purification it seems to require is to separate from it 

 such substances as are mechanically suspended in it, and for this 

 purpose it is laded into an iron pan or kettle where the fusion is 

 kept up by a gentle fire underneath, and a complete agitation of 

 the mass is effected by plunging into the melted metal pieces of 

 charcoal, which have been soaked in water, and by means of an 

 iron tool, keeping them at the bottom of the kettle. The water 

 in the charcoal is rapidly converted into vapour, which rushing 

 through the metal, gives it the appearance of rapid ebullition. 

 After this is over, and the whole has rested some little time, the 

 scum, which is thrown up to the surface, is taken off, and the tin, 

 which is peculiarly briUiant in appearance, is removed by ladles 

 into proper moulds to form the blocks in which it is generally 

 sold. 



Grain Tin is, however, sometimes put into a different form by 

 breaking it : for this purpose the blocks are heated to such a 

 degree as is known to render the metal brittle ; they are then 

 raised a considerable height from the ground,and, being suffered 

 to fall, the whole divides into fragments, which assume a very 

 peculiar appearance. 



The smelting by a strong blast is injurious to metals that are 

 volatilizable by heat, as they have in this mode no protection 

 from the slag, which in reverberating furnaces floats on their 

 surface, and protects them from oxidation and evaporation. 

 The old practice of melting lead in what are called Ore Earths, 

 is, on this account, giving way, and reverberating furnaces are 

 coming into general use, by which the produce of metal from the 

 ore is considerably increased. Tin, though volatile to a certain 

 degree, is not affected by the process in any important manner, 

 but as some flies off in white fumes, it is usual to construct a long 

 horizontal flue, which is made to communicate with and pass 

 through a kind of chamber, in which a considerable part of these 

 fumes is condensed and collected. 



