The volume of air in the food-aperture between the two glass doors is
approximately 5.3 liters. When the door on the inside is opened and the
material placed in the food-aperture and the outer door is subsequently
opened, there is by diffusion a passage outward of air of the
composition of the air inside of the chamber, and the food-aperture is
now filled with room air. When the inner door is again opened this room
air enters the chamber and is replaced by air of the same composition as
that in the chamber. It is seen, then, that there may theoretically be
an interchange of air here which may have an influence on the results.
In severe work experiments, where the amount of carbon dioxide in the
air is enormously increased, such interchange doubtless does take place
in measurable amounts and correction should undoubtedly be made. In
ordinary rest experiments, where the composition of the air in the
chamber is much more nearly normal, this correction is without special
significance. Furthermore, in the two forms of calorimeter now in use,
the experiments being of but short duration, provision is made to render
it unnecessary to open the food-aperture during the experiment proper.
Consequently at present no correction for interchange of air in the
food-aperture is made, and for the same reason the slight alteration in
volume resulting from the removal or addition of material has also not
been considered here.