122 
Iron* 
always announced by a partial fusion, and the dropping 
of lava through the iron- bars, introduced to support the 
incumbent materials while those on the bottom are carried 
away. The filling above is regularly continued, and when 
the furnace at the top has acquired a considerable degree 
of heat, it is then judged time to introduce the blast ; the 
preparations necessary for which are the following : 
The dam-stone is laid in its place firmly imbedded in 
fire-clay ; the dam-plate is again imbedded on this with 
the same cement, and is subject to the same inclination, 
on the top of this plate is a slight depression, of a curved 
form, towards that side farthest distant from the blast, for 
the purpose of concentrating the scoria, and allowing it 
to flow off in a connected stream, as it tends to surmount 
tlie level of the dam. From this notch to the level of the 
floor a declivity of brick- work is erected, down which 
the scoria of the furnace flows in large quantities. The 
opening betwixt the dam and side-walls of the furnace* 
called the faidd , is then built up with sand, the loose 
bricks are removed, and the furnace bottom is covered i; 
with powdered lime or charcoal-dust. The ignited coaks 
are now allowed to fall down, and are brought forward i 
with iron -bars nearly to a level with the dam. The space 
between the surface of the coaks and the bottom of the 
tymp-plate is next rammed hard with strong binding sand ; 
and these coaks, which are exposed on the outside, are co- 
vered with coak-dust. These precautions being taken, the 
tuyere-hole is then opened and lined with a soft mixture of 
fire-clay and loam : the blast is commonly introduced into 
the furnace at first with a small discharging-pipe, which 
is afterwards increased as occasion may require. In tw r o 
hours after blowing, a considerable quantity of lava will 
be accumulated ; iron bars are then introduced, and per- 
forations, made in the compressed matter at the bottom of 
the furnace ; the lava is admitted to all parts of the hearth, 
