The bottle-shaped bomb is made of ½-in. wrought steel, and has a
capacity of 30 liters. On opposite sides near the top are bored
apertures, one for the exhaust valve for obtaining a partial vacuum
(about 20 mm., mercury column) after the bomb has been charged, the
other for inserting the plug through which passes the fuse wire for
igniting the charge. The bomb is closed with a cap, by which the chamber
may be made absolutely air-tight. It is 30 in. high with the cap on,
weighs 158 lb., and is handled to and from the immersion vessel by a
small crane.

The inner receiver is made of 1/16-in. sheet copper, 30⅞ in. deep, and
with an inner diameter of 17⅞ in. It is nickel-plated, and strengthened
on the outside with bands of copper wire, and its capacity is about 70
liters. The outer tub is made of 1-in. lumber strengthened with four
brass hoops on the outside. It is 33 in. deep, and its inner diameter
is 21 in.

The stirring device, operated vertically by an electric motor, consists
of a small wooden beam connected to a system of three rings having a
horizontal bearing surface. When the apparatus is put together, the
inner receiver rests on a small standard on top of the base of the outer
tank, and the rings of the stirring device are run between the bomb and
the inner receiver. The bomb itself rests on a small standard placed on
the bottom of the inner receiver. The apparatus is provided with a
snugly fitting board cover. The bomb is charged from the top, the
explosive being suspended in its center. The air is exhausted to the
desired degree of rarification. The caps are then screwed on, and the
apparatus is set together as described.

[Illustration: PLATE IX.