The measurements of heat eliminated by man, as made by this apparatus,
are based upon the fact that the subject is inclosed in a heat-proof
chamber through which a current of cold water is constantly passing. The
amount of water, the flow of which, for the sake of accuracy, is kept at
a constant rate, is carefully weighed. The temperatures of the water
entering and leaving the chamber are accurately recorded at frequent
intervals. The walls of the chamber are held adiabatic, thus preventing
a gain or loss of heat by arbitrarily heating or cooling the outer metal
walls, and the withdrawal of heat by the water-current is so controlled,
by varying the temperature of the ingoing water, that the heat brought
away from the calorimeter is exactly equal in amount to the heat
eliminated by radiation and conduction by the subject, thus maintaining
a constant temperature inside of the chamber. The latent heat of the
water vaporized is determined by measuring directly the water vapor in
the ventilating air-current.
In the construction of the new calorimeters a further and fundamental
change in construction has been made in that all the thermal junctions,
heating wires, and cooling pipes have been attached directly to the zinc
wall of the calorimeter, leaving the outer insulating panels free from
incumbrances, so that they can be removed readily and practically all
parts inspected whenever desired without necessitating complete
dismantling of the apparatus. This arrangement is possible except in
those instances where connections pass clear through from the interior
of the chamber to the outside, namely, the food-aperture, air-pipes,
water-pipes, electrical connections, and tubes for connections with
pneumograph and stethoscope; but the apparatus is so arranged as to have
all of these openings in one part of the calorimeter. It is possible,
therefore, to remove all of the outer sections of the calorimeter with
the exception of panels on the east side.
This fundamental change in construction has proven highly advantageous.
It does away with the necessity of rolling the calorimeter out of its
protecting insulating house and minimizes the delay and expense
incidental to repairs or modifications. As the calorimeter is now
constructed, it is possible to get at all parts of it from the outside,
with the exception of one small fixed panel through which the above
connections are passed. This panel, however, is made as narrow as
possible, so that practically all changes can be made by taking out the
adjacent panels.