I 
28 Copper * 
sand, which runs together by the r heat into a semi-vitrified 
mass* The chimney is from forty to fifty feet high, which 
causes such a powerful draught that the arsenic and sul- 
phur separated during the roasting pass almost entirely 
through the chimney into the open air, none of it be- 
ing collected as at Anglesea* The ore is spread over the 
bottom of the furnace about a foot thick, being thrown in 
through a kind of funnel or hopper just above. The fuel 
is Welsh coal, which, as usual, is burnt at the anterior 
part of the furnace, and its flame draws over the surface 
of the ore in its passage to the chimney. In this furnace, 
which is called the calcining furnace, and is the largest of 
all, the ore is roasted without addition with a dull red heat 
for 12 hours and is frequently in that time stirred with a 
long iron rake, introduced through a hole at the further 
end of the reverberatory, to expose fresh surfaces to the 
action of the flame. The ore is not melted here, but when 
roasted sufficiently, it is carried to another furnace exactly 
similar to the former, but smaller, that is, about 9 feet by 
6, and here it receives a fusing heat, but still without any 
addition, except that when the slag does not rise freely, a 
little calcareous sand is thrown in. At the end of every 
four hours the slag is raked out ; it is then of the consist- 
ence of soft dough and is laded into oblong moulds, and 
a little water is sprinkled upon it to make it sink down* 
after which the moulds are quite filled with it, and when 
cold it makes hard solid blocks of slag about 14 inches 
long and 12 deep and broad, which are used lor building. 
After the slag is raked off, a fresh charge of calcined ore 
is let down into the reverberatory, and the copper is tapped 
off by a hole in the side of the furnace, which before the 
fusion had been stopped up w ith a shovel full of wet clay 
mixed with about a fourth of new coal, w hich prevents the 
clay from hardening too much, so that the hole may rea^ 
dily be opened by an iron pick. 
The rough copper as it runs from the surface is con- 
