NOV. 22, I915 
Improved Respiration Calorimeter 
315 
OBSERVER’S TABLE 
The Wheatstone bridge described above and the telephone mentioned 
, on page 302 are located on the table beside the chamber (PI. XXXVI, 
fig. 1) at which the observer sits while controlling the apparatus. The 
same bridge is employed in the determination of other temperatures, as 
described beyond. Other devices on the table serve to indicate and 
regulate temperature conditions inside and outside the chamber, as 
explained in detail in the sections which follow. 
DETERMINATION OF THE QUANTITY OF HEAT PRODUCED IN THE 
CHAMBER 
Energy expended by the human body for any purpose, such as the 
performance of muscular work, the maintenance of body temperature, or 
whatever, results in the production of heat, which is eventually dissipated 
from the body; hence, the measurement of the quantity of heat dissipated 
by the body under given conditions affords data for the determination of 
the quantity of energy expended. Heat escapes from the body in two 
ways: As latent heat of water vaporized from the lungs and skin and as 
sensible heat, by conduction, convection, and radiation from the surface 
of the body to the air and to objects in the chamber. Both latent heat 
and sensible heat are carried out of the chamber and measured. 
measurement or latent heat 
The water vaporized by the lungs and skin leaves the chamber in the 
outgoing air, unless it is precipitated by contact with some object in the 
chamber whose temperature is below the dew point for the conditions 
prevailing, but the temperature of the air and of objects in the chamber 
is controlled so that precipitation is not likely to occur. The quantity 
of heat leaving the chamber as latent heat of water vapor in any given 
period is determined by multiplying the weight of the water vapor 
absorbed from the outgoing air during the period by the factor 0.586, 
which according to determinations made by Smith (18), represents the 
number of Calories of heat required to vaporize a gram of water at 20° C. 
All measurements of heat with the calorimeter are expressed in terms of 
Calories at 20° C., 1 Calorie being taken as the amount of heat required 
to raise the temperature of 1 kgm. of water i° C.—i.e.,from 19.5^0 20.5 0 , 
the specific heat of water being taken as unity at 20° C. The determina¬ 
tions by Smith were made in accordance with the conclusion by Barnes (7) 
that the mean small calorie is equivalent to 4.1877 international joules. 
Dickinson, Harper, and Osborne (io), in work on the latent heat of 
fusion of ice, assumed 4.187 international joules equal to 1 small calorie 
at 15 0 , in which case 4.183 joules would be equivalent to 1 small calorie 
at 20 0 C. The latter value is used in these investigations (p. 342), but 
the difference between this and the value by Barnes has no significant 
effect upon the factor for latent heat here employed. 
9841°—15 - 2 
