The numerous electrical, thermometric, and chemical measurements
necessary in the full conduct of an experiment with the respiration
calorimeter has often raised the question of the desirability of making
at least a portion of these observations more or less automatic. This
seems particularly feasible with the observations ordinarily recorded by
the physical observer. These observations consist of the reading of the
mercurial thermometers indicating the temperatures of the ingoing and
outcoming water, records with the electric-resistance thermometers for
the temperature of the air and the walls and the body temperatures, and
the deflections of the thermo-electric elements.
Numerous plans have been proposed for rendering automatic some of these
observations, as well as the control of the heating and cooling of the
air-circuits. Obviously, such a record of temperature measurements would
have two distinct advantages: (1) in giving an accurate graphic record
which would be permanent and in which the influence of the personal
equation would be eliminated; (2) while the physical observer at present
has much less to do than with the earlier form of apparatus, it would
materially lighten his labors and thereby tend to minimize errors in the
other observations.
The development of the thread recorder and the photographic registration
apparatus in recent years led to the belief that we could employ similar
apparatus in connection with our investigations in this laboratory. To
this end a number of accurate electrical measuring instruments were
purchased, and after a number of tests it was considered feasible to
record automatically the temperature differences of the ingoing and
outcoming water from the calorimeter. Based upon our preliminary tests,
the Leeds & Northrup Company of Philadelphia, whose experience with such
problems is very extended, were commissioned to construct an apparatus
to meet the requirements of the respiration calorimeter. The conditions
to be met by this apparatus were such as to call for a registering
recorder that would indicate the differences in temperature between the
ingoing and outcoming water to within 0.5 per cent and to record these
differences in a permanent ink line on coordinate paper. Furthermore,
the apparatus must be installed in a fixed position in the laboratory,
and connections should be such as to make it interchangeable with any
one of five calorimeters.
After a great deal of preliminary experimenting, in which the Leeds &
Northrup Company have most generously interpreted our specifications,
they have furnished us with an apparatus which meets to a high degree of
satisfaction the conditions imposed. The thermometers themselves have
already been discussed. (See page 30.) The recording apparatus consists
of three parts: (1) the galvanometer; (2) the creeper or automatic
sliding-contact; (3) the clockwork for the forward movement of the roll
of coordinate paper and to control the periodic movement of the creeper.
Under ordinary conditions with rest experiments in the chair calorimeter
or bed calorimeter, the temperature differences run not far from 2° to
4°. Thus, it is seen that if the apparatus is to meet the conditions of
the specifications it must measure differences of 2° C. to within 0.01°
C. Provision has also been made to extend the measurement of temperature
differences with the apparatus so that a difference of 8° can be
measured with the same percentage accuracy.