HEAT EQUIVALENT OF NUTRIENTS OF FOOD. 599 

 II. FAT.i 



Fats of the animal body. — According to tlie investigations of Schultze 

 and Eeinecke^, who investigated the fatty tissues of oxen, sheep, swine, 

 dogs, cats, and man, fat has an ahuost uniform composition, though it 

 be taken from various parts of the body and though it may have beeu 

 formed under the most varied condition of life. The composition is: 



Per cent. 



Carbon 76. 50 



Hydrogen 12.00 



Oxygen 11.50 



100.00 

 Our investigations with the calorimeter, at first while using the potas- 

 sium chlorate method, and later with Berthelot's bomb, have shown the 

 heat equivalent to be so nearly the same for fat of all kinds of animals that 

 it is impossible to find a noticeable variation for any particular sort. 

 The first twenty three substances investigated included different kinds 

 of fat from swine, oxen, horses, men, dogs, geese, and ducks. The 

 mean value for fat obtained by the potassium chlorate method is 9,365 

 small calories per gram. Eepeating the experiments with the Berthelot 

 bomb gave, when a reduction to constant pressure was made, 9,500 

 small calories i)er gram; and the greatest variation from this value was 

 not more than i 0.2 per cent. The number, 9,500 calories, can therefore 

 be considered the true mean value for animal fat. The relation between 

 the earlier value and the correct one is as 98.57: 100. 



If we assuiwie that animal fat is composed of equal molecules of tri- 

 stearin, triolein, and tripalmitin, or what is just the same, that it is a 

 mixed glycerin ether of the following comijosition: 



i Cl8H:,503 



C3H5 < C18H3302 

 ( C16H3103 



the empirical formula of such an ether would be C55H104O6 and the 

 perceuj;age comi)osition : 



Per cent. 



Ccarhon 76.75 



Hydrogen 12. 09 



Oxygen 11 . 16 



100. 00 



This agrees very well with the mean value obtained by Schultze and 

 Eeinecke. We can calculate the heat equivalent of such an ether and 

 thus have a control on the value which we find by experiment. The 

 real heat equivalent of fat is found when from the snm of the heat equiva- 

 lent of the glycerin and the acids which form the ether a small constant 

 is deducted. This constant is very small in comparison to the whole 



iJour. prak. Clicni., 2d ser., 31, p. 275 j 42, p. 361. 

 »Aun. Cheui., 142, p. 191. 



