Energy. 475 



be desired, indicating an error of somewhat less than 1 per cent. Difficulties 

 attending the control of the temperature of the room in which the experiments 

 have been made and minor discrepancies in the manipulation of the apparatus 

 by assistants with varying degrees of skill have undoubtedly introduced errors 

 of slight magnitude that are not compensated and are not absolutely known. 

 It is believed that in a large majority of the experiments here reported, the 

 accuracy of the heat measurement is well within 1 per cent. In some instances 

 the error may be greater than this but in no case could it have amounted to 

 5 per cent. 



Heat can leave the body in a number of different ways. The larger portion 

 of the heat is lost by radiation and conduction; a certain amount is used to 

 warm the inspired air; the urine and feces carry away measurable amounts 

 of heat; finally large quantities are necessary to vaporize the water eliminated 

 from the lungs and surface of the body. Aside from the measurement of these 

 factors, there are the numerous corrections which have to deal with the actual 

 heat production during the period of the study, corrections which receive spe- 

 cial subsequent treatment. 



The heat lost by radiation and conduction, together with that required to 

 warm the inspired air is measured by the amount of water passing through the 

 heat absorbers and the temperature through which this water is raised. The 

 amount of heat thus measured, however, includes also the heat lost from the 

 urine and feces that are allowed to cool to the temperature of the calorimeter 

 before being removed. From the weights and specific heats of urine and 

 feces and the difference between the body temperature and the temperature of 

 the calorimeter, the amount of heat lost by this means can be computed. It 

 is recorded for the experiments here published in table 231, column c. The 

 amount of heat required to warm the inspired air from the temperature of the 

 calorimeter to that of the body may be obtained by the use of four factors: 

 the total ventilation of the lungs, the weight of a liter of air, the specific heat 

 of air, and the difference between the temperature of the calorimeter and that 

 of the body. The volume of the inspired air has been computed and the total 

 ventilation of the lungs is given in column a of table 220. Since these results 

 are recorded in liters reduced to standard conditions of temperature and 

 pressure, the weight of air warmed is obtained by multiplying the total venti- 

 lation by 1.293, the weight of a liter of air at standard conditions of tempera- 

 ture and pressure. From the weight of air, its specific heat 16a and the 

 difference between the body temperature and that of the chamber, the amount 

 of heat actually required to warm this inspired air may readily be computed. 



Deducting from the total heat brought away by the water current the heat 

 from the feces and urine and that required to warm the inspired air, leaves the 

 heat of radiation and conduction, which is recorded in the first column of 

 table 231. 



182 The specific heat of air has been taken as 0.237. 



