e violence, scattering the
burning and scintillating metal in every direction around.

[Illustration: THE EXPLOSION.]

When the casting is completed it is of course allowed to remain
undisturbed until the iron has had time to cool, and then the whole mass
is to be dug out of the pit in which it is imbedded. So much heat,
however, still remains in the iron and in the sand surrounding it, that
the mould itself and the twenty or thirty men engaged in disinterring
it, are enveloped in dense clouds of vapor which rise all around them
while the operation is proceeding.

[Illustration: DIGGING OUT THE CYLINDER.]

It is necessary that the sand which surrounds these moulds should be
rammed down in the most compact and solid manner to sustain the sides of
the mould and enable them to resist the enormous pressure to which it is
subject, especially in the lower portions, while the iron continues
fluid. In the case of iron, the weight of four inches in height is
equivalent to the pressure of a pound upon the square inch. In a pit,
therefore, eighteen feet deep, as some of the pits at this foundry are,
we should have a pressure at the bottom of fifty-four pounds to the
inch. Now, in the most powerful sea-going steamers, the pressure of
steam at which the engines are worked, is seldom more than _eighteen_
pounds to the inch; that of the Cunard line is said to be from twelve to
fifteen, and that of the Collins line from fifteen to eighteen. In other
words there is a pressure to be resisted at the lower ends of these long
castings equal to three times that at which the most powerful low
pressure engines are worked, and which sometimes results in such
terrific explosions.

When the cylinder is freed from the pressure of the sand around it, in
its bed, the great iron cross by which the mould was lowered into the
pit, as seen in the engraving of the Casting, is once more brought down
to its place, and the stirrups at the tops of the iron rods seen in the
engraving below, are brought over the ends of the arms of the cross. The
lower ends of these rods take hold of a frame or platform below, upon
which the whole mould, together with the cylinder within it, is
supported. The arm of the crane is then brought round to the spot. The
hook pendant from it is attached to the ring in the centre of the cross,
and by means of the wheels and machinery of the crane, the whole is
slowly hoisted out, and then swung round to some convenient level, whe