Since the experiments to be made with this chamber will rarely exceed 6
to 8 hours, there is no provision made for installing a cot bed or other
conveniences which would be necessary for experiments of long duration.
Aside from the arm-chair with the foot-rest suspended from the balance,
there is practically no furniture inside of the chamber, and a shelf or
two, usually attached to the chair, to support bottles for urine and
drinking-water bottles, completes the furniture equipment. The
construction of the calorimeter is such as to minimize the volume of air
surrounding the subject and yet secure sufficient freedom of movement to
have him comfortable. A general impression of the arrangement of the
pipes, chair, telephone, etc., inside the chamber can be obtained from
figs. 7 and 9. The heat-absorber system is attached to rings soldered to
the ceiling at different points. The incoming air-pipe is carried to the
top of the central dome, while the air is drawn from the calorimeter at
a point at the lower front near the position of the feet of the subject.
From this point it is carried through a pipe along the floor and up the
rear wall of the calorimeter to the exit.
With the perfect heat insulation obtaining, the heat production of the
man would soon raise the temperature to an uncomfortable degree were
there no provisions for withdrawing it. It is therefore necessary to
cool the chamber and, as has been pointed out, the cooling is
accomplished by passing a current of cold water through a heat-absorbing
apparatus permanently installed in the interior of the chamber. The
heat-absorber consists of a continuous copper pipe of 6 millimeters
internal diameter and 10 millimeters external diameter. Along this pipe
there are soldered a large number of copper disks 5 centimeters in
diameter at a distance of 5 millimeters from each other. This increases
enormously the area for the absorption of heat. In order to allow the
absorber system to be removed, added to, or repaired at any time, it is
necessary to insert couplings at several points. This is usually done at
corners where the attachment of disks is not practicable. The total
length of heat-absorbers is 5.6 meters and a rough calculation shows
that the total area of metal for the absorption of heat is 4.7 square
meters. The total volume of water in the absorbers is 254 cubic
centimeters.
It has been found advantageous to place a simple apparatus to mix the
water in the water-cooling circuit at a point just before the water
leaves the chamber. This water-mixer consists of a 15-centimeter length
of standard 1-inch pipe with a cap at each end. Through each of these
caps there is a piece of one-eighth-inch pipe which extends nearly the
whole length of the mixer. The water thus passing into one end returns
inside the 1-inch pipe and leaves from the other. This simple device
insures a thorough mixing.
The air-pipes are of thin brass, 1-inch internal diameter. One of them
conducts the air from the ingoing air-pipe up into the top of the
central dome or hood immediately above the head of the subject. The air
thus enters the chamber through a pipe running longitudinally along the
top of the dome. On the upper side of this pipe a number of holes have
been drilled so as to have the air-current directed upwards rather than
down against the head of the subject. With this arrangement no
difficulties are experienced with uncomfortable drafts and although the
air enters the chamber through this pipe absolutely dry, there is no
uncomfortable sensation of extreme dryness in the air taken in at the
nostrils, nor is the absorption of water from the skin of the face,
head, or neck great enough to produce an uncomfortable feeling of cold.
The other air-pipe, as suggested, receives the air from the chamber at
the lower front and passes around the rear to the point where the
outside air-pipe leaves the chamber.
The chamber is illuminated by a small glass door in the food aperture.
This is a so-called "port" used on vessels. Sufficient light passes
through this glass to enable the subject to see inside the calorimeter
without difficulty and most of the subjects can read with comfort. If an
electric light is placed outside of the window, the illumination is very
satisfactory and repeated tests have shown that no measurable amount of
heat passes through the window by placing a 32 c. p. electric lamp 0.5
meter from the food aperture outside. More recently we have arranged to
produce directly inside the chamber illumination by means of a small
tungsten electric lamp connected to the storage battery outside of the
chamber. This lamp is provided with a powerful mirror and a glass shade,
so that the light is very bright throughout the chamber and is
satisfactory for reading. It is necessary, however, to make a correction
for the heat developed, amounting usually to not far from 3 calories per
hour.
By means of a hand microphone and receiver, the subject can communicate
with the observers outside at will. A push-button and an electric bell
make it possible for him to call the observers whenever desired.