Iron . 
133 
When splint- coal coaks are used in the blast-furnace, 
the blast admits of being thrown in under the highest pos- 
sible pitch of compression ; the uncommon density of the 
charcoal sustains a very powerful discharge of blast before 
it is dissipated to facilitate the general descent. Most fre~ 
quently, large masses of these cinders pass through the 
whole ignited cavity, and are thrown out below, possess? 
mg all the acuteness of their original form and fracture. 
This quality of coal is used in all the Corson blast-fur- 
naces, where, to ensure a respectable produce, the air is 
discharged under a pressure equal to 3 1-4 pounds upon 
the square inch, or 6 1-2 inches of mercury. 
The same quality of coal was used at the Devon iron- 
works, where, at one time, having all the blast of a 48 
inch cylinder engine thrown into one furnace, the column 
of mercury supported was upwards of 7 inches ; the quan- 
tity of air discharged under such an impelling power, I 
found to exceed 2600 cubical feet per minute. 
The coals used at the Cleugh, Cleland, and Clyde iron- 
works, are nearly of the same quality at each— a mixture 
of splint and soft coal. The Muirkirk and Glenbuck iron- 
works have a coal different from any of the former, and in 
some particular spots it considerably resembles the Eng- 
lish clod-coal. 
2d, The various methods of procuring air for the blast- 
furnace may be reduced to the following 1st, That pro- 
cured by cylinders, and discharged into the furnace by 
means of a floating piston heavily loaded, and working in 
a large receiver or regulating cylinder : 2d, That wherein 
pumping cylinders only are used, and the air thrown into 
chests inverted in water, called the water -vault: 3d, That 
mode wherein the air is discharged from the pumping or 
forcing cylinder into an air-tight house, called the air -vault. 
The first method is the original mode of blowing, and 
h still much used at those iron-works whose erection has 
