332 HEAT-BALANCE. 



A. Helmholtz was the first to estimate numerically the amount of heat produced by a 

 man : 



(1) Heat-income. (a) A healthy adult, weighing 82 kilos., expires in 



twenty-four hours 878*4 grms. C0 2 (Scharling). The combustion of 



the C 'therein into CO, produces " 1,730,760 cal. 



(b) Rut he takes in more than reappears in the C0 2 ; the excess is 



used in oxidation -processes, e.g., for the formation of H 2 0, by 

 union with H, so that 13,615 grms. H will be oxidised by the 

 excess of 0, which gives 318,600 ,, 



2,049,360 cal. 



(c) About 25 per cent, of the heat must be referred to sources other 



than combustion (Dulong), so that the total =2,732,000 ,, 



2,732,000 calories are actually sufficient to raise the temperature of an adult, weighing 

 80 to 90 kilos., from 10 to 38 or 39 C, i.e., to a normal temperature. 



(2) Heat-expenditure. (a) Heating the food and drink, which 



have a mean temperature of 12 C 70,157 cal. = 2*6 per cent. 



(b) Heating the air respired = 16,400 grms. with an initial 



temperature of 20 C 70,032 = 2-6 



( When the temperature of the air is 0, 140,064 cal. =5*2 per cent.) 



(c) Evaporation of 656 gnus, water by the lungs, . . 397,536 cal. =14'7 ,, 



(d) The remainder given off by radiation and evaporation of 



water by the skin, (77*5 per cent. fo) = 80 - l ,, 



B. Dulong. (1) Heat-income. Dulong and others sought to estimate the amount of heat 

 from the C and H contained in the food. As we know that the combustion of 1 grm. C = 8040 

 heat-units, and 1 grm. H = 34,460 heat-units, it would be easy to determine the amount of heat 

 were the C simply converted into CC\, and the H into H 2 0. But Dulong omitted the H in the 

 carbohydrates (e.g., grape-sugar = C 6 Hi 2 6 ) as producing heat, because the H is already com- 

 bined with O, or at least is the proportion in which it exists in water. This assumption is 

 hypothetical, for the atoms of C in a carbohydrate may be so firmly united to the other atoms, 

 that before oxidation can take place their relations must be altered, so that potential energy is 

 used uj>, i.e., heat must be rendered latent; so that these considerations rendered the following 

 exam [ile of Dulong's method given by Vierordt very problematical : 



An adult eats in twenty-four hours, 120 grms. proteids, 90 grms. fat, and 340 grms. starch 

 (carbohydrates). These contain : 



Proteids,. . . . 120 grms. contain 64*18 C. and 8*60 H. 



Fat, . . . 90 70*20 10*26 



Starch, . . . . 330 ,, ,,146-82 



281-20 and 18-86 

 The urine and faeces contain still unconsumed, . .29-8 ,, 6 3 



Remainder to be burned, . . . 251 # 4 and 12'56 



As 1 grm. C = 8040 heat-units and 1 grm. H = 34,460 heat-units, we have the following cal- 

 culation : 



251-4 x 8,040 = 2,031,312 (from combustion of C). 

 12-56x34,460= 432,818 ( ,, H). 



2,464,130 heat-units. 

 (2) Heat- expenditure : 



1. 1900 grms. are excreted daily by the urine and freces, and they 



are 25 warmer than the food, ..... 



2. 13,000 grms. air are heated (from 12 to 37 C.) (heat-capacity 



of the air -0-26), 



3. 330 grms. water are evaporated by the respiration (1 grm. =582 



heat-units), ...... 



4. 660 grms. water are evaporated from the skin, . 



Total, ...... 



Remainder radiated and conducted from the skin, 



TT*t i,nit Per cent - of 



Heat-units. theexcreta> 



47,500 1-9 



84,500 3-38 



192,060 7-68 



384,120 15-37 



708,180 

 1,791,820 71-67 



2,500,000 100-00 



Total amount of heat-units given off, 

 C. Heat-income. Frankland burned the food directly in a calorimeter, and found that 

 1 grm. of the following substances yielded : 



