ceous matter has penetrated the ore, or united to the metal* 
to constitu fusibility. I shad adduce an example, as be* 
ing most illustrative of this doctrine. 
S pp s a c ast-fumace, 35 feet high, 11 feet wide at 
the boshes, properly burdened, and producing No. 1, pig- 
iron. Let the dischar ge of air be supposed equal to a 
pressure two and a half pounds upon the square inch, or 
equivalent to l-6th of the atmosphere, or 5 inches of mer- 
cury : under these circumstances let it farther be suppos- 
ed, that 1500 cubical feet of air are discharged in one min- 
ute ; and that the diameter of the discharging-pipe is 2*625, 
the area of which is equal to 6*890625 circular inches^ 
Let the discharging-pipe be increased to 3 inches diame- 
ter, and let the same quantity of air be passed into the fur- 
nace ; it is evident that as the area of the discharging-pipe 
is increased to 9 circular inches, or nearly l-3d more than 
formerly, the compression of air must be proportionally 
diminished. This alteration is soon perceivedby its effects ; 
the quantity of scoria increases from the furnace, whilst 
die consumption of the materials above is also considera- 
bly augmented. In a few hours the scoria will have un~ 
dergone a complete change, from pure white, enamelled 
with various blue shades, to a green, brown, or black co- 
lour, considerably charged with the oxyd of iroiA The 
same effects will continue, in greater or lesser degree, till 
all the materials are reduced which were existing in the 
furnace at the period of diminished compression. The phi- 
losophy of this fact may be accounted for in the following 
manner 
While the just association of proportions remained, the 
air was discharged under such a degree of compression as 
to excite proper combustion : the decomposition of the 
air by means of the ignited fuel, was not effected in imme- 
* Tee metal will have lost nearly all its carbon, and have become 
inferior in value 25 to 30 fier cent . 
