31 6 Journal of Agricultural Research voi. v. No. s 



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 -wall 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- 3i3)> ^^^ 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 >8-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 1 1 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. 



