Why? Because
the old fashioned bloomeries and Catalan forges could produce blooms
only at a high cost, and because the new processes introduced failed
to turn out good blooms. Those produced were invariably "red short,"
that is, they contained unreduced oxide of iron, which prevented the
contact of the metallic particles, and rendered the welding together
of these particles to form a solid bloom impossible.
The process of puddling cast iron, and transforming it by
decarbonization into wrought iron, has, as everybody knows, been in
successful practical operation for many years, and the direct process
referred to so closely resembles this, that a short description of the
theory of puddling is not out of place here.
The material operated on in puddling is iron containing from 21/2 to 4
per cent. of carbon. During the first stage of the process this iron
is melted down to a fluid bath in the bottom of a reverberatory
furnace. Then the oxidation of the carbon contained in the iron
commences, and at the same time a fluid, basic cinder, or slag, is
produced, which covers a portion of the surface of the metal bath, and
prevents too hasty oxidation. This slag results from the union of
oxides of iron with the sand adhering to the pigs, and the silica
resulting from the oxidation of the silicon contained in the iron.
This cinder now plays a very important part in the process.
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