446 INCOME AND EXPENDITURE OF HEAT. 



B. According to Dulong. 



(1.) Heat-income. Dulong, and after him Boussingault, Liebig and Dumas, 

 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 = 8,040 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 CO 2 and the H into H 2 O. But Dulong omitted the H in 

 the carbohydrates (e.g., grape-sugar = CgH^Oe) as producing heat, because 

 the H is already combined with 0, 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 up, i.e., heat must be 

 rendered latent; so that these considerations rendered the following example of 

 Dulong's method given by Vierordt very problematical. 



An adult eats in 24 hours, 120 grm. proteids, 90 grm. fat, and 340 grm. starch 

 (carbohydrates). These contain: 



Gram. C. H. 



Proteids, .... 120 contain 64,18 and 8,60 



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. = 8,040 heat-unite and 1 grm. H = 34,460 heat-units, we have the 

 following calculation: 



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: 



Heat-units. Per cent, of 

 the excreta. 



1. 1,900 grm. are excreted daily by the urine and 



faeces, and they are 25 warmer than the food, 47,500 1'S 



2. 13,000 grm. air are heated (from 12 to 37C.) 



(heat-capacity of the air = 0'26), . . . 84,500 3'5 



3. 330 grm. water are evaporated by the respiration 



(1 grm. = 582 heat-units), .... 192,060 7 '2 



4. 660 grm. water are evaporated from the skin, 384,120 14*5 



Total, 708,180 



Remainder radiated and conducted from the skin, 1,791,810 72 



Total amount of heat-units given off, . 2,500,000 100 



C. Heat-income, according to Frankland. 



Frankland burned the food directly in a calorimeter, and found that 1 grm. of 

 the following substances yielded: 



Albumin, ..... 4,998 heat-units. 



Grape-sugar, . . ^, . 3,277 

 Ox fat, ..... 9,069 



