The chair calorimeter was designed for experiments to last not more than
6 to 8 hours, as a person can not remain comfortably seated in a chair
much longer than this time. For longer experiments (experiments during
the night and particularly for bed-ridden patients) a type of
calorimeter which permits the introduction of a couch or bed has been
devised. This calorimeter has been built, tested, and used in a number
of experiments with men and women. The general shape of the chamber is
given in fig. 26. The principles involved in the construction of the
chair calorimeter are here applied, _i. e._, the use of a
structural-steel framework, inner air-tight copper lining, outer zinc
wall, hair-felt insulation, and outer asbestos panels. Inside of the
chamber there is a heat-absorbing system suspended from the ceiling, and
air thermometers and thermometers for the copper wall are installed at
several points. The food-aperture is of the same general type and the
furniture here consists simply of a sliding frame upon which is placed
an air-mattress. The opening is at the front end of the calorimeter and
is closed by two pieces of plate glass, each well sealed into place by
wax after the subject has been placed inside of the chamber. Tubes
through the wall opposite the food-aperture are used for the
introduction of electrical connections, ingoing and outgoing water, the
air-pipes, and connections for the stethoscope, pneumograph, and
telephone.
The apparatus rests on four heavy iron legs. Two pieces of channel iron
are attached to these legs and the structural framework of the
calorimeter chamber rests upon these irons. The method of separating the
asbestos outer panels is shown in the diagram. In order to provide light
for the chamber, the outer wall in front of the glass windows is made
of glass rather than asbestos. The front section of the outer casing can
be removed easily for the introduction of a patient.
In this chamber it is impossible to weigh the bed and clothing, and
hence this calorimeter can not be used for the accurate determination of
the moisture vaporized from the lungs and skin of the subject, since
here (as in almost every form of respiration chamber) it is absolutely
impossible to distinguish between the amount of water vaporized from
bed-clothing and that vaporized from the lungs and skin of the subject.
With the chair calorimeter, the weighing arrangements make it possible
to weigh the chair, clothing, etc., and thus apportion the total water
vaporized between losses from the chair, furniture, and body of the man.
In view of the fact that the water vaporized from the skin and lungs
could not be determined, the whole interior of the chamber of the bed
calorimeter has been coated with a white enamel paint, which gives it a
bright appearance and makes it much more attractive to new patients. An
incandescent light placed above the head at the front illuminates the
chamber very well, and as a matter of fact the food-aperture is so
placed that one can lie on the cot and actually look outdoors through
one of the laboratory windows.
[Illustration: FIG. 26.--Cross-section of bed calorimeter, showing part
of steel construction, also copper and zinc walls, food-aperture, and
wall and air-resistance thermometers. Cross-section of opening,
cross-section of panels of insulating asbestos, and supports of
calorimeter itself are also indicated.]
Special precaution was taken with this calorimeter to make it as
comfortable and as attractive as possible to new and possibly
apprehensive patients. The painting of the walls unquestionably results
in a condensation of more or less moisture, for the paint certainly
absorbs more moisture than does the metallic surface of the copper. The
chief value of the determination of the water vaporized inside of the
chamber during an experiment lies, however, not in a study of the
vaporization of water as such, but in the fact that a certain amount of
heat is required to vaporize the water and obviously an accurate measure
of the heat production must involve a measure of the amount of water
vaporized. So far as the measurement of heat is concerned, it is
immaterial whether the water is vaporized from the lungs or skin of the
subject or the clothing, bedding, or walls of the chamber; since for
every gram of water vaporized inside of the chamber, from whatever
source, 0.586 calorie of heat must have been absorbed.
The apparatus as perfected is very sensitive. The sojourn in the chamber
is not uncomfortable; as a matter of fact, in an experiment made during
January, 1909, the subject remained inside of the chamber for 30 hours.
With male patients no difficulty is experienced in collecting the urine.
No provision is made for defecation, and hence it is our custom in long
experiments to empty the lower bowel with an enema and thus defer as
long as possible the necessity for defecation. With none of the
experiments thus far made have we experienced any difficulty in having
to remove the patient because of necessity to defecate in the cramped
quarters. It is highly probable that, with the majority of sick
patients, experiments will not extend for more than 8 or 10 hours, and
consequently the apparatus as designed should furnish most satisfactory
results.
In testing the apparatus by the electrical-check method, it has been
found to be extremely accurate. When the test has been made with burning
alcohol, as described beyond, it has been found that the large amount of
moisture apparently retained by the white enamel paint on the walls
vitiates the determination of water for several hours after the
experiment begins, and only after several hours of continuous
ventilating is the moisture content of the air brought down to a low
enough point to establish equilibrium between the moisture condensed on
the surface and the moisture in the air and thus have the measured
amount of moisture in the sulphuric acid vessels equal the amount of
moisture formed by the burning of alcohol. Hence in practically all of
the alcohol-check experiments, especially of short duration, with this
calorimeter, the values for water are invariably somewhat too high. A
comparison of the alcohol-check experiments made with the bed and chair
calorimeters gives an interesting light upon the power of paint to
absorb moisture and emphasizes again the necessity of avoiding the use
of material of a hygroscopic nature in the interior of an apparatus in
which accurate moisture determinations from the body are to be made.
The details of the bed calorimeter are better shown in fig. 4. The
opening at the front is here removed and the wooden track upon which the
frame, supporting the cot, slides is clearly shown. The tension
equalizer (see page 71) partly distended is shown connected to the
ingoing air-pipe, and on the top of the calorimeter connected to the
tension equalizer is a Sondén manometer. On the floor at the right is
seen the resistance coil used for electrical tests (see page 50). A
number of connections inside the chamber at the left are made with
electric wires or with rubber tubing. Of the five connections appearing
through the opening, reading from left to right, we have, first, the
rubber connection with the pneumograph, then the tubing for connection
with the stethoscope, then the electric-resistance thermometer, the
telephone, and finally a push button for bell call. The connections for
the pneumograph and stethoscope are made with the instruments outside on
the table at the left of the bed calorimeter.