Iron . 237 
N, the interior of the stalk or chimney, 30 inches square, 
OO, the lire brick- work, 9 inches thick. 
PP, space of 2 inches for stuffing with sand 
QQ, common brick building. 
RR, cast-iron lintels, over which are thrown double 9~ 
inch arches, so that at any time the inferior building can 
be taken down to make repairs, without shaking or in the 
least injuring the chimney. 
S. The dotted lines here are meant to represent what 
is called the tapping-hole. When a large piece of goods 
is to be cast, lifting the metal with ladles would be im- 
practicable. A sharp-pointed bar is driven up this open- 
ing. The iron then flows freely out into a large bason of 
sand made for its reception. It is then conducted, by col- 
lateral channels, into the mould. 
The space under the curved dotted line from G to L, 
| by S, is filled with a mixture of sand and ashes. When 
the furnace is prepared to melt, the whole of the bottom 
receives a stratum of sharp clean sand about two inches 
thick. This is broken up at night, and fresh sand is sub- 
stituted for it before the fire is kindled in the morn in 
Fig. 3. is a horizontal section of the chimney or stalk, 
taken where the flues assume a perpendicular direction. 
The letters in this figure correspond to those in the vertical 
section, fig. 2. The height of the chimney ought not to 
be less than 45 feet : if 50 feet, the effect will be sooner 
and of course better produced. 
Remarks upon the Melting of Ron in these Furnaces . 
The effect wished to be produced in air furnaces is the 
fusion of a certain portion of pig or cast-iron for the pur- 
pose of being poured or run into moulds to form articles 
of almost every description. 
