od-aperture, which is a large
sheet-copper tube, somewhat flattened, thus giving a slightly oval form,
closed with a port, such as is used on vessels. The door of the port
consists of a heavy brass frame with a heavy glass window and it can be
closed tightly by means of a rubber gasket and two thumbscrews. On the
outside is used a similar port provided with a tube somewhat larger in
diameter than that connected with the inner port. The annular space
between these tubes is filled with a pneumatic gasket which can be
inflated and thus a tight closure may be maintained. When one door is
closed and the other opened, articles can be placed in and taken out of
the chamber without the passage of a material amount of air from the
chamber to the room outside or into the chamber from outside.

The air-pipes passing through the wall of the calorimeter are of
standard 1-inch piping. The insulation from the copper wall is made by a
rubber stopper through which this piping is passed, the stopper being
crowded into a brass ferule which is stoutly soldered to the copper
wall. This is shown in detail in fig. 25, in which N is the brass ferule
and M the rubber stopper through which the air-pipe passes. The closure
is absolutely air-tight and a minimum amount of heat is conducted out of
the chamber, owing to the insulation of the rubber stopper M. The
water-current enters and leaves the chamber through two pipes insulated
in two similar brass ferules soldered to the copper and zinc walls. The
insulation between the water-pipe and the brass ferule has been the
subject of much experimenting and is discussed on page 24. The best
insulation was secured by a vacuum-jacketed glass tube, although the
special hard-rubber tubes surrounding the electric-resistance
thermometers have proven very effective as insulators in the bed
calorimeter.

A series of small brass tubes, from 10 to 15 millimeters in diameter,
are soldered into the copper wall in the vicinity of the water-pipes.
These are used for electrical connections and for connections with the
manometer, stethoscope, and pneumograph. All of these openings are
tested carefully and shown to be absolutely air-tight before being put
in use.

In the dome of the calorimeter, and directly over the head of the
subject, is the opening for the weighing apparatus. This consists of a
hard-rubber tube, threaded at one end and screwed into a brass flange
heavily soldered to the copper wall (fig. 9). When