27 
Copper . 
phur- chamber is cleared out four times, after which the 
ore is sufficiently roasted. The old sulphur-chambers are 
on a level with the kilns and of the same length and height, 
or in fact they are a prolongation of the kilns : but the 
more modem and improved chambers are like lime-kilns, 
the ore being at the bottom, and the sulphur subliming at 
the top, with a contrivance to take out the roasted ore, and 
thus to keep up a perpetual fire. 
The richest part of the roasted ore is exported without 
further preparation, but the poorest part is smelted on the 
spot. It still contains a vast quantity of sulphur and other 
impurities. The smelting houses are a range of large re* 
verberatory furnaces, thirty-one of which are under the 
same roof, ranged side by side in a single long row. They 
are all air furnaces, the chimneys of which are 41 feet 
high, which causes a most powerful draught through 
them. The fuel is coal, which is burned on a grate at the 
anterior part of the furnace, and the flame in drawing up 
the chimney passes over the bed of the reverberatory, in- 
to which is put 12 cwt. of the roasted ore, previously mix* 
ed with a small portion of coal dust. The ore is here 
melted and reduced into a very impure regulus, and when 
sufficiently fused it is drawn off through a plug-hole into 
earthen moulds. A single charge of the furnace, or 12 
cwt. yields 1-2 a cwt. of rough copper, which by further 
purification affords about 50 per cent, of pure malleable 
metal. The furnaces work off a single charge about eve* 
ry five hours. 
The copper furnaces in Cornwall are also of the rever- 
beratory kind. The ore when drawn up from the mine 
is first broken into pieces no bigger than a hazle-nut, 
which operation is called cobbing , and the better sort is 
picked out by hand. The reduction begins by the pro- 
cess of roasting in large reverberatory furnaces 14 feet by 
16, the bottom or bed of which is made of fire-bricks and 
covered to the thickness of about two feet with silicious 
