Brass . 
77 
both the materials are in great abundance. The ores of 
zinc are several species of calamine and of blende , called 
by the miners Black-Jack , which are found abundantly in 
Devonshire, Derbyshire, and North- Wales, generally ac- 
companying lead ores. These are chiefly oxyds or car- 
bonated oxyds of zinc, and require a previous calcination 
before they are fit for brass-making. Blende is a sul- 
phured 
At Holywell, in Flintshire, the calamine which is re- 
ceived raw from the mines in the neighbourhood, is first 
pounded in a stamping mill, and then washed and sifted 
in order to separate the lead, with which it is largely ad- 
mixed. It is then calcined on a broad shallow brick 
hearth, over an oven heated to redness, and frequently stir- 
red for some hours. In some places a conical pile is com- 
posed of horizontal layers of calamine alternating with 
layers of charcoal, the whole resting on a layer of wood in 
large pieces, with sufficient intervals for the draught of air. 
It is then kindled, and the stack continues to burn till the 
calamine is thoroughly calcined. The calamine thus pre- 
pared is then ground in a mill, and at the same time mix- 
ed with about a third or a fourth part of charcoal, and is 
then ready for the brass -furnace. In some places pit- coal 
is ground with the calamine instead of charcoal, but this 
is found to injure the malleability of the brass obtained. 
The brass-furnace^ has the form of the frustum of a 
hollow cone, or a cone with the apex cut off horizontally. 
At the bottom of the furnace is a circular grate or perfo- 
rated iron plate, coated with clay and horse- dung, to de- 
fend it from the action of the fire. The crucibles stand 
upon the circular plate, forming a circular row with one 
in the middle. The fuel, which in England is coal, is 
thrown round the crucibles, being let down through the 
f Keirin a note to the article Bran in Macquer s s Chem, Diet. 
