IRON. 191 
are those in Great Britain and France. After iron t>re i$ 
dug out of the earth, it is crushed or broken into small 
pieces, by machinery. It is next washed, to detach the 
grosser particles of earth which adhere to it. This ope- 
ration ended, it is roasted in kilns, formed for the pur- 
pose, by which the sulphur, and some other substances 
that are capable of being separated by heat, are de- 
tached. It is then thrown into a furnace, mixed with a 
certain portion of limestone and charcoal, to be melted. 
Near the bottom of the furnace there is a tap-hole, 
through which the liquid metal is discharged into fur- 
rows made in a bed of sand. The larger masses, or 
those Which flow into the main furrow, are called 
sows ; the smaller ones are denominated pigs of iron ; 
and the general name of the metal in this state is cast 
iron. 
With us iron is employed in three states, of cast iron, 
wrought iron, and steel. 
Cast iron is distinguishable, by its properties of being, 
in general, so hard as to resist both the hammer and the 
file ; being extremely brittle, and for the most part, of 
a dark grey or blackish colour. 
A great number of useful and important articles are 
formed of cast iron, such as grates^ chimney backs, pots, 
boilers, pipes, and cannon shot. These are made by 
casting ladles full of the liquid metal into moulds that 
are shaped, for the purpose, in sifted sand. 
Wrought iron. The process of converting cast iron 
into wrought or malleable iron, is called blooming. The 
cast iron is thrown into the furnace, and kept melted by 
the flame of combustibles which is made to play upon 
its surface. Here it is suffered to continue for about 
two hours, a workman constantly stirring it, until, not- 
.withstanding the continuance of the heat, it gradually 
acquires consistency, and congeals. It is then taken 
out, while hot, and violently beaten with a large ham- 
mer worked by machinery. In this state it is formed 
into bars for sale. 
The value of iron is beyond all estimate, and infinitely 
