Steel- 
273 
md a quarter to two and three quarters wide. The com- 
pression of air which is necessary is equal to a column 
bf water four feet and a half high.* The ore melts as it 
passes through the fire, and is collected at the bottom , 
|Where it is maintained in a liquid state. The slag* which 
falls down with the fused metal, is let off by means of an 
ppening in the side of the furnace, at the discretion of the 
workmen. When a sufficient quantity of regulus, or im- 
perfectly reduced metal, is accumulated at the bottom of 
the furnace (which usually happens every eight hours,) it 
is let off into moulds, to form it for the purposes intended, 
isuch as cannon or pig iron. — -Crude iron is distinguished 
into white, black, f and grey. The white is the least re- 
duced, and more brittle than the other two ; the black is 
that with which a large quantity of fuel has been used ; 
and the grey is that which has been reduced with a sufficient 
quantity of fuel, of which it contains apart in solution. Fhe 
operation of refining crude iron consists in burning the com- 
bustible matter which it holds in solution ; at the same time 
that the remaining iron is more perfectly reduced, and am 
quires a fibrous texture. For this purpose, the pigs of cast 
iron are taken to the forge, where they are first put into 
what is called the refinery ; which is an open charcoal fire, 
urged by a pair of bellows, worKed by water or a steam- 
engine f but the compression of air in the refinery ought 
to be less than that in the blast-furnace. After the metal 
is melted, it is let out of the fire by the workmen to dis- 
charge the scoriae, and then returned and subjected to the 
blast as before. This operation is sometimes repeated two 
or three times before any appearance of malleability (or 
what the workmen call coming into nature) takes place; 
this they know by the metal’s first assuming a granular 
appearance, the particles appearing to repel each other, or 
* This ought t© be 6 inches of mercury, or 6 feet of water 
■f Mottled. 
M M 
