cent., is in fusion. From the huge crucible runs a conduit to the pit,
at the side of which the furnace is constructed, and in which is
placed the mould. A metallic plug intercepts communication. A quick
blow with an iron rod removes this plug and the tapping is effected.
This operation, which seems simple at first sight, is extremely
delicate in practice and requires a very skillful workman. A host of
technical words designates the dangers that it presents. Before the
tapping, it is necessary to calculate at a glance the function of the
gate pit. And what accidents afterward! But we need not dwell upon
these. After the cooling of the metal comes the cleaning, which is
done with scrapers and special instruments.

The casting is preceded by two operations--the designing and the
moulding. The design rests upon a basis generally furnished by
experience, and which the founders have transmitted from generation to
generation. The thickness of the rim of the bell taken as unity
determines the diameters and dimensions. The outline most usually
followed gives 15 rims to the large diameter, 7½ to the upper part of
the bell, and 32 to the large radius that serves to trace the profiles
of the external sides.

[Illustration: THE CASTING OF THE GREAT BELL OF THE BASILICA OF THE
SACRED HEART.]

The moulding is done as follows: In the pit where the casting is to be
done there is constructed a core of bricks and a clay shell, separated
from each other by a thickness of earth, called false bell. This
occupies provisionally the place of the metal, and will be destroyed
at the moment of the casting.