3I 6 CALORIMETRY. 



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-evlinder stands on four feet within a large cylinder (M), which is filled with 

 some <*ood non-conducter of heat, and this again is placed in a large vessel filled with water 

 (W) ^This is to prevent any boat reaching the inner cylinder from without. A weighed quan- 

 tity of the substance (<) to be investigated is placed in the combustion-chamber. When com- 

 bustion 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 tempera- 

 ture and the amount of water are known, then it is easy to calculate the number of heat-units 

 produc.-.l by the combustion of a known weight of the substance (see Introduction). 



The icecalorimeter 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 beat 

 given oft* 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 C. 



[The amount of heat produced by a 

 living animal is similarly measured. 

 The animal (fig. 227), in a cage, is 

 placed in a large vessel, which is placed 

 within another vessel, and the inter- 

 space filled with water. The whole 

 should be enclosed in a large box packed 

 with fur, shavings, feathers, or other 

 bad conductor of heat. A tube, D, 

 opens into the inner space, and from 

 /.*0&#* it; tnere * s an exi t-tube, D, which winds 

 many times in the water-space beneath. 

 Fig. 227. Air passes in through D and out by 



"Water-calorimeter of Dulong. D'. The temperature of the water is 



ascertained by thermometers T and T', while the water is moved by a stirrer (S) placed between 

 the two.] 



Just as in a calorimeter, although much more sloivly, the food-stuffs within our 

 body are burned up, oxygeu being supplied, and thus potential energy is trans- 

 formed into kinetic energy, which, in the case of a person at rest, almost completely 

 appears in the form of heat. 



Heat-Units. Favre, Silbermann, Frankland, Rechenberg, B. Danilewsky, and others have 

 made calorimetric experiments on the heat produced by food. According to Danilewsky, 1 

 gramme of the following dry substances yields heat-units : 



Palmitin, . 8883 



Olein, . 8958 



Stearin, . 9036 



Ox-fat, . 9686 



Glycerine, . 4179 



Starch, . 4479 



Dextrose, . 3939 



Maltose, . 4163 



Milk-sugar. 4162 



Cane-sugar, 4173 



oxidised to the stage of urea, we must deduct the heat-units obtainable 

 from urea from those of albumin, and as 1 part of albumin yields in round numbers about ^ of 

 urea, we obtain about 5100 calories [ = 2170 kilogram-metres] for 1 grm. of albumin. i 



Isodvnamic foods, i.e., those that produce an equal amount of heat; 100 grms. animal 

 albumin (after deducting the heat-units of urea) = 52 fat = 114 starch = 129 dextrose; 100 

 grms. fat are isodvnamic with 243 dry flesh or 225 of dry syntonin (Buhner); 100 grms. of 

 vegetable albumin -=55 fat = 121 starch = 137. dextrose (Danileivsky). Rubner calculated that 

 in man, with a mixed diet, the available heat-units for 1 grm. of albumin = 4100 ; 1 grm. 

 fat 9300 ; and for 1 grm. carbohydrate 4100 calories. 



When we know the weight of any of the above-named substances consumed by a 

 man in twenty-four hours, a simple calculation enables us to determine how many 





