867 
in Cornwall and Devonshire . 
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 brilliant 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 ap- 
pearance. 
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 
Vol. V. 3 a 
