316 
Journal of Agricultural Research 
Vol. V, No. 8 
MEASUREMENT OF SENSIBLE HEAT 
The energy eliminated from the body as sensible heat, which is much 
greater in amount than that latent in water vaporized from the body, * 
is practically all carried out in a current of water which circulates in the 
chamber through a device called the “heat absorber,” though a small 
quantity of it may become latent in water vaporized from objects in the 
chamber, in which case it may leave the chamber as latent heat of water 
vapor in the outgoing air. If the weight of the water that flows through 
the absorber during a given period, as stated in kilograms, is multiplied 
by the difference between the temperature of the water as it enters and 
that as it leaves the absorber, as measured in degrees centigrade, the 
product will show the quantity of heat removed as expressed in Calories, 
at the mean temperature of the. water flowing in the absorber. These 
are converted into Calories at 20° by making due allowance for the 
specific heat of water at the mean temperature of the flow as compared 
with that at 20° (4, p. 56; 19, p. 229). 
The rate at which heat is removed from the chamber is regulated to 
prevent fluctuations in the temperature of the air of the chamber, which 
falls when the rate is too fast and rises when it is too slow. To avoid 
chance for error in the determination of the volume of air in the chamber, 
which depends upon the accuracy of the measurement of its temperature 
(p. 313), and to some extent also for the comfort of the subject, it is 
desirable to keep the temperature of the air as constant as possible. 
The temperature to be maintained depends upon the nature of the 
experiment, but it is commonly not far from 20° C. Whatever the 
requirement may be, by proper control of the temperature at which the 
water enters the heat absorber, and of the rate at which it passes 
through the absorber, the removal of heat from the chamber may be 
made to accord with its production within it to such an extent that the 
temperature of the air of the chamber may be kept constant within 
narrow limits. The most convenient practice is to maintain a constant 
rate of flow and to vary the temperature of the water entering the heat 
absorber according to the amount of heat to be absorbed. 
Heat Absorber 
The heat absorber, which is suspended near the ceiling of the chamber, 
about 10 cm. from the sides, consists of brass pipe of 7 mm. internal 
diameter (so-called >^-inch pipe), along which disks of sheet copper 5 
cm. in diameter are soldered 3 mm. apart to increase the area of the heat- 
absorbing surface. The total length of pipe in the absorber is not far 
from 11 meters, and there are more than 2,500 disks on it, so that several 
square meters of surface are exposed to the air of the chamber. Though 
the total quantity of water in the absorber is not over 400 c. c., it is 
possible, by control of the temperature and rate of flow of the water, 
to vary the rate of removal of heat from the chamber within wide limits. 
