CALORIMETRY. 423 



part of the chamber ; one of them (0) supplies the air which is necessary for combus- 

 tion, it reaches almost to the bottom of the chamber ; the second tube (a) is fixed in 

 the middle of the lid, and is closed above with a thick glass plate, and on this is 

 placed, at an angle, a small mirror (s) which enables an observer to see into the 

 interior of the chamber, and to observe the process of combustion at c. The 

 third tube (d) is used only when combustible gases are to be burned in the chamber. 

 It can be closed by means of a stop-cock. A lead tube (e, e) with many twists on it, 

 passes from the upper part of the chamber through the water, and finally opens at 

 g. The gaseous products of combustion pass out through this tube, and in doing 

 so help to heat the water. The cylindrical vessel with the water is closed with a 

 lid which transmits the four tubes. The water cylinder stands on four feet within 

 a large cylinder (M), which is filled with some good non-conductor of heat, and 

 this again is placed in a large vessel filled with water (W). This is to prevent 

 any heat reaching the inner cylinder from without. A weighed quantity of the 

 substance (c) to be investigated, is placed in the combustion chamber. When 

 combustion is ended, during which the inner water must be repeatedly 

 stirred, the temperature of the water is ascertained by means of a delicate 

 thermometer. If the increase of the temperature and the amount of water are 

 known, then it is easy to calculate the number of heat-units produced by the 

 combustion of a known weight of the substance (see Introduction). 



The ice-calorimeter may also be used. The inner cylinder is filled with ice 

 and not with water, and ice is also placed in the outer cylinder to prevent any 

 heat from without from acting upon the inner ice. The heat given off from the 

 combustion chamber causes a certain amount of the ice to melt, and the water 

 thereby produced is collected and measured. It requires 79 heat-units to melt 

 1 grm. of ice to 1 grm. of water at 0C. 



Just as in a calorimeter, although much more slowly, the food-stuffs 

 within our body are burned up, oxygen being supplied, and thus 

 potential energy is transformed into kinetic energy, which, in the case 

 of a person at rest i.e., when the muscles are inactive, almost completely 

 appears in the form of heat (see Introduction). 



Favre, Silbermann, Frankland, Rechenberg, B. Danilewsky, and others have 

 made calorimetric experiments on the heat produced by food. Thus, there are 

 produced by 



1 grm. Albumin 4,998 heat-units / Completely dried and completely 

 1 ,, Ox-flesh 5,103 I burned. 



f When burned to urea (i.e., the heat-units 



1 grm. Albumin 4,263 ,, corresponding to the urea (1 grm. =2,206 



1 ,, Ox-flesh 4,368 j calories) is deducted from those of the 



^ albumin and flesh. 



1 gramme of the following dry substances yields heat-units : 



