300 



.MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



is our custom to reduce all these measurements of heat to the calorie at 20 c C. To this end it is 

 necessary to multiply the number of calorics of heat removed in the water current at the mean 

 difference of temperature between the incoming and outgoing current by the mean specific heat 

 of water for that range. The product gives the corrected heat measured in terms of calorics at 

 2ii C. or C .,„. These corrected values appear in the first column of Table XIII. For a more 

 detailed discussion of this subject see page 55 of Bulletin 63, above referred to. 



The heat measured in terms of C° 20 does not represent all of the heat given off by the subject 

 during a given period, but must be corrected for changes in temperature of the calorimeter and 

 for the heat introduced or removed by articles of food and drink taken into or removed from the 

 chamber, and for the heat required to vaporize the excess of water given off in the outgoing as 

 compared with the incoming air current; i. e.. latent heat of vaporization of water given off from 

 the lungs and skin. 



The temperatures of the inner walls of the calorimeter are observed at the beginning and end 

 of each period. If these walls are warmer at the end than at the beginning of the period, some 

 heat has been absorbed. If they are cooler, some heat has been added to the air of the chamber. 

 For a rise in temperature of 1 : C. it has been found that the walls absorb 60 calories of heat, and 

 vice versa, in cooling 1° they give up 60 calories of heat. The changes of temperature are, 

 however, kept so nearly constant as to vary rarely more than a tenth of a degree between the 

 beginning and end of any period. 



The temperature of the drink is taken immediately before it is passed into the chamber, and 

 corrections are made for heat introduced by the hot coffee, or required to bring the cold water 

 to the temperature of the chamber. The temperature of the food is brought as nearly as possible 

 to that of the chamber before being sent in to the subject, so that little or no heat is added to or 

 removed from the apparatus in this way. The corrections for temperature of food and drink and 

 the dishes containing them are shown in column d of Table XIII. 



From the best data available it appears that 0.592 calorie of heat is required for the vapor- 

 ization of one gram of water at the temperature of C ; ,„. Water which condenses on the absorl >ers 

 and is removed as drip gives up this latent heat of vaporization within the chamber and it is 

 measured by the water current. The water which passes out from the chamber in the form of 

 vapor in the ventilating air current carries out. however, a considerable quantity of latent heat. 

 The amount of water vaporized is found by taking the algebraic difference between the total 

 excess of water in the outgoing air, as shown in column </ of Tabie XII. and the gain or loss of 

 water vapor in the air of the chamber, as shown in the fourth column of Table X. The amount 

 of water thus vaporized multiplied by 0.592, the heat of vaporization of 1 gram, gives the total 

 heat removed by the vaporization of water within the chamber. 



The heat carried away in the water current, as measured in terms of C° 20 , corrected for change 

 in temperature of calorimeter and for temperature of food and drink introduced into the chamber. 

 added to the amount removed in the water vapor, gives the total heat determined, as shown in 

 column (/ of Table XIII. 



Table XIII. — Summary of calorimetric measurements — Metabolism experiment No. J-'. 



