The object of this is to make the
metal soft while the shoulder and neck of the vessel are formed. To
accomplish this, the heated open end of the cylinder is laid
horizontally upon a kind of semicircular cradle, and is held there by
tongs handled by two men. Another workman places over the open end a
die of the form shown in Fig. 4, and while the cylinder is slowly
turned round in its cradle, two sledge hammers are brought down with
frequent blows upon the die, closing in the end of the cylinder, but
leaving a central hole as shown in Fig. 5. Further operations reduce
the opening still more until it is closed altogether, and a projection
is formed as shown at Fig. 6. This projection is now bored through,
and the cylinder is ready for testing.
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
[Illustration: FIG. 6.]
The cylinder is submitted to a water test, the liquid being forced in
until the gauge shows a pressure of two tons to the square inch.
Cylinders have been known to give way under this ordeal, but without
any dangerous consequences. The metal simply rips up, making a report
at the moment of fracture as loud as a gun. The wonderful strength of
the metal employed may be gauged by the circumstance that the walls of
the cylinder designed to hold 100 feet of gas are only five-sixteenths
of an inch in thickness.
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