racy; 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