METALS 283 
furnace. The Lime acts as a flux, causing the earthy 
impurities in the Ore to become liquid and separate 
from the Iron. Hot air is driven in through the burning 
mass until the heat in the lower part is so great that 
the contents become fluid. At intervals of half-an-hour 
or so fresh charges are introduced, and in this way 
the furnace is kept constantly full. As the mass becomes 
liquid, it runs down to the part of the furnace called the 
crucible—here the Iron proper, being heavier than the 
liquid slag, sinks to the bottom, and is drawn off at 
regular intervals. This process consists in exposing a 
small hole, and allowing the liquid Iron to flow out into 
specially prepared moulds. Each of the moulds is known — 
as pig, and the Iron it contains is called Pig Iron. — It is 
this which is re-melted and used in making Cast Iron 
articles. 
Wrought Iron made from Pig Iron. During the 
process of smelting, the Pig Iron absorbed a portion of the 
Carbon of the fuel—it is this which makes the Iron so 
brittle ; hence it is necessary to get rid of the Carbon in 
order to render the Iron malleable and ductile. With this 
object it is placed in a furnace constructed in such a way 
that the metal is melted without coming in contact with 
the fuel. This prevents it from absorbing any more Carbon 
and allows it to get rid of what it already contains. When 
melted it is well-stirred and hammered and finally formed 
into bars by being rolled out between steel rollers. It 
now possesses all the properties which make it so valuable 
as malleability, ductility, tenacity, as also the power of 
being welded together at a red heat. 
Steel made from Wrought Iron. The bars of 
Wrought Iron are placed in vessels filled with charcoal ; 
these are closed and heated until a certain temperature is 
reached. This heat is maintained for about a week, when 
