In order to communicate with the interior of the chamber, maintain a
ventilating air-current, and provide for the passage of the current of
water for the heat-absorber system and the large number of electrical
connections, a number of openings through the walls of the chamber were
necessary. The great importance of maintaining this chamber absolutely
air-tight renders it necessary to minimize the number of these openings,
to reduce their size as much as possible, and to take extra precaution
in securing their closure during an experiment. The largest opening is
obviously the trap-door at the top through which the subject enters,
shown in dotted outline in fig. 7. While somewhat inconvenient to enter
the chamber in this way, the entrance from above possesses many
advantages. It is readily closed and sealed by hot wax and rarely is a
leakage experienced. The trap-door is constructed on precisely the same
plan as the rest of the calorimeter, having its double walls of copper
and zinc, its thermal-junction system, its heating wires and
connections, and its cooling pipes. When closed and sealed, and the
connections made with the cooling pipes and heating wires, it presents
an appearance not differing from any other portion of the calorimeter.
The next largest opening is the food-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 not in use, a solid
rubber stopper on a brass rod is drawn into this opening, thus
producing an air-tight closure. When in actual use during the process of
weighing, a thin rubber diaphragm prevents leakage of air through this
opening. The escape of heat through the weighing-tube is minimized by
having this tube of hard rubber.