[Illustration: FIG. 7.--Horizontal cross-section of chair calorimeter,
showing cross-section of copper wall at A, zinc wall at B, hair-felt at
E, and asbestos outer wall at F; also cross-section of all upright
channels in the steel construction. At the right is the location of the
ingoing and outgoing water and the thermometers. At C is shown the food
aperture, and D is a gasket separating the two parts. The ingoing and
outcoming air-pipes are shown at the right inside the copper wall. The
telephone is shown at the left, and in the center of the drawing is the
chair with its foot-rest, G. In dotted line is shown the opening where
the man enters.]
[Illustration: FIG. 8.--Vertical cross-section of chair calorimeter,
showing part of rear of calorimeter and structural-steel frame. N,
cross-section of bottom horizontal channel supporting asbestos floor J;
H, H, upright channels (at the right is a side upright channel and to
the left of this is an upright rear channel); M horizontal 8-inch
channel supporting calorimeter; Zn, zinc wall; Cu, copper wall; J,
insulating asbestos.]
The respiration chamber used in Middletown, Connecticut, was designed to
permit of the greatest latitude in the nature of the experiments to be
made with it. As a result, it was found at the end of a number of years
of experimenting that this particular size of chamber was somewhat too
small for the most satisfactory experiments during muscular work and, on
the other hand, somewhat too large for the best results during so-called
rest experiments. In the earlier experiments, where no attempt was made
to determine the consumption of oxygen, these disadvantages were not so
apparent, as carbon dioxide could be determined with very great
accuracy; but with the attempts to measure the oxygen it was found that
the large volume of residual air inside the chamber, amounting to some
4,500 liters, made possible very considerable errors in this
determination, for, obviously, the subject could draw upon the oxygen
residual in the air of the chamber, nearly 1,000 liters, as well as upon
the oxygen furnished from outside sources. The result was that a very
careful analysis of the residual air must be made frequently in order to
insure that the increase or decrease in the amount of oxygen residual in
the air of the chamber was known accurately at the end of each period.
Analysis of this large volume of air could be made with considerable
accuracy, but in order to calculate the exact total of oxygen residual
in the air it was necessary to know the total volume of air inside the
chamber under standard conditions. This necessitated, therefore, a
careful measurement of temperature and pressure, and while the
barometric pressure could be measured with a high degree of accuracy,
it was found to be very difficult to determine exactly the average
temperature of so large a mass of air. The difficulties attending this
measurement and experiments upon this point are discussed in detail
elsewhere.[5] Consequently, as a result of this experience, in planning
the calorimeters for the Nutrition Laboratory it was decided to design
them for special types of experiments. The first calorimeter to be
constructed was one which would have general use in experiments during
rest and, indeed, during experiments with the subject sitting quietly in
the chair.
[Illustration: FIG. 9.--Vertical cross-section of chair calorimeter from
front to back, showing structural steel supporting the calorimeter and
the large balance above for weighing the subject inside the calorimeter.
The chair, method of suspension, and apparatus for raising and lowering
are shown. Part of the heat-absorbers is shown, and their general
direction. The ingoing and outgoing air-pipes and direction of
ventilation are also indicated. The positions of the food-aperture and
wire mat and asbestos support are seen. Surrounding the calorimeter are
the asbestos outside and hair-felt lining.]
It may well be asked why the first calorimeter was not constructed of
such a type as to permit the subject assuming a position on a couch or
sofa, such as is used by Zuntz and his collaborators in their research
on the respiratory exchange, or the position of complete muscular rest
introduced by Johansson and his associates. While the body positions
maintained by Zuntz and Johansson may be the best positions for
experiments of short duration, it was found, as a result of a large
number of experiments, that subjects could be more comfortable and quiet
for periods of from 6 to 8 hours by sitting, somewhat inclined, in a
comfortable arm-chair, provided with a foot-rest. With this in mind the
first calorimeter was constructed so as to hold an arm-chair with a
foot-rest so adjusted that the air-space between the body of the subject
and the walls of the chamber could be cut down to the minimum and thus
increase the accuracy of the determination of oxygen. That the volume
has been very materially reduced may be seen from the fact that the
total volume of the first calorimeter to be described is less than 1,400
liters, or about one-third that of the Middletown apparatus.