There the vessels were unloaded and their cargo carried by railway to Stony Hill, and about the middle of January the enormous mass of metal was delivered at its destination.
It will easily be understood that 1,200 furnaces were not too many to melt these 60,000 tons of iron simultaneously.

Each of these furnaces contained about 1,400,000 lbs.

of metal; they had been built on the model of those used for the casting of the Rodman gun; they were trapezoidal in form, with a high elliptical arch.

The warming apparatus and the chimney were placed at the two extremities of the furnace, so that it was equally heated throughout.

These furnaces, built of fireproof brick, were filled with coal-grates and a "sole" for the bars of iron; this sole, inclosed at an angle of 25 deg., allowed the metal to flow into the receiving-troughs; from thence 1,200 converging trenches carried it down to the central well.
The day following that upon which the works of masonry and casting were terminated, Barbicane set to work upon the interior mould; his object now was to raise in the centre of the well, with a coincident axis, a cylinder 900 feet high and nine in diameter, to exactly fill up the space reserved for the bore of the Columbiad.