Nov. 22, 191S 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. i) 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 OF I^ATENT 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 Hkely 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, i Calorie being taken as the amount of heat required 

 to raise the temperature of i kgm. of water 1° C. — i.e., from 19.5° to 20.5°, 

 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 (10), in work on the latent heat of 

 fusion of ice, assumed 4.187 international joules equal to i small calorie 

 at 15°, in which case 4.183 joules would be equivalent to i small calorie 

 at 20° 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. 



