ISO 
Iron . 
gen, which prevents its becoming a perfect metal * and it 
is employed in adding a further dose of carbon to the pure 
iron, which thereby becomes much more fusible. The 
carbon in crude iron supercarbonated, is in a great degree 
mechanically mixed with the iron as the surface of highly 
carburetted kishy iron, shews : in steel, the carbon is 
chemically united to the iron. Good fresh charcoal may 
be considered as containing seven eighths of carbon. 
12thly, The limestone is in proper proportion, if the 
slag is thin and does not retain any particles of metallic 
iron enveloped in it. Otherwise, the heat has not been 
sufficient ; or the limestone is not in proper proportion ; 
or the charge has descended too soon ; or the blast has not 
been sufficient in quantity, strength, and regularity, to 
consume the coal ; or it may also be in too great proper- 
tion for the coal, thereby cooling the metal or the slag in 
its ascent from the tweer ; for the blast that is not em- 
ployed in producing heat with the charcoal, will produce 
cold: and still worse, it will re-oxygenate the iron. 
The skill of the man who manages the furnace is shewn, 
in his proportioning his flux to his ore, so that there shall 
be thin fusion with as small a quantity of coal as possible 
—in using none but well burnt dry coal, that none may 
be wasted— in using coal enough and no more to give the 
required heat and carbonization ; for which purpose the 
air thrown in and the coal thrown in, must consume each 
other. If the air be in too great proportion, the charge 
will be cooled : if in too small a proportion the charcoal 
will not be used up. W herever great lumps of charcoal 
are seen floating on the slag or enveloped with it, there is 
want of skill in adjusting the proportions. 
1 Sthly, The charcoal to be entirely consumed without 
waste, should not be thrown into the furnace in large 
lumps, for there is not time in this case during its descent, 
for the air and the iron to decompose it. 
