235 
Iron 9 
MISCELLANEOUS ESSAYS RELATING TO IRON. 
On the Kind of Air-Furnaces employed in Iron Foundries 
for casting large pieces of Ordnance, ShaJ-ts for Mills , 
Cylinder s y and other heavy Articles . By Mr . David 
Mushet, of the Calder Iron f Forks- 15 Ph. Mag. 
THE furnaces about to be described are employed 
for melting pig-iron with the flame of pit-coal. Fur- 
Inaces of this kind are constructed of various sizes ac- 
ii 
cording to circumstances. The small sizes will run down 
i ° 
ji from seven to ten hundred weight, and are used in small 
j foundries for what the trade call jobbing. 
Fig. 1. (Plate IV.) a ground plan of two large air-fur- 
s naces, and chimney for melting pig or cast-iron with the 
flame of pit- coal. 
The letters ABC D point out the exterior dimensions 
|| of the stalk or chimney, which is first erected, leaving two 
openings or arches into which the fore-part of the furnaces 
are afterwards built. The breadth of the chimney at the 
particular place which the plan exhibits is 16 feet from A 
to B, and from A to D or from B to C 6 feet 6 inches. 
! f 
The plan is drawn at that elevation where the flame enters 
the chimn,ey by the flue or throat, narrowed on purpose 
to throw back part of the flame, and keep the furnace 
I equally hot throughout, as may be more particularly view- 
ed in the vertical section, fig. 2. 
EE, the furnace bars on which the coals rest and 
where the combustion is maintained. 
FF, openings called teasing-holes, by which the coals 
are introduced to repair the fire. 
GG, fire-brick buildings called bridges. These are 
meant to concentrate the flame, that it may act as violent- 
ly on the metal as possible. Upon the height of the 
bridge much depends in fusing the metal speedily, and 
