HEAT. 



37 



form current of any "gas, the specific 

 heat of which was to be ascertained, to 

 issue from a gasometer, and pass 

 through a pipe forty inches long, which 

 was inclosed in a larger pipe, con- 

 stantly filled with the steam of boiling 

 water, by which it was heated ; and its 

 temperature being determined, it was 

 made to pass slowly through a spiral 

 tube, immersed in a quantity of cold 

 water; the cylindrical vessel contain- 

 ing the water, and the spiral tube, 

 being called the calorimeter. When 

 the gas issued from this tube, its tem- 

 perature was indicated by a thermo- 

 meter at the extremity, to be always 

 the same as the water in the calori- 

 meter ; and the specific heat of the gas 

 operated upon was judged of by the de- 

 gree of heat which it imparted to the 

 water in being cooled to the same tem- 

 perature. 



An extract from a translation of the 

 memoir in which the researches alluded 

 to were made known, will assist in 

 giving a clear idea of the methods by 

 which Berard and Delaroche estimated 

 the specific heats of different gases. 

 Speaking of their calorimeter, they say, 

 " Now, let us conceive a thin copper 

 cylinder, six inches long, and three in 

 diameter, filled with distilled water, 

 and traversed by a serpentine of about 

 five feet in length, forming eight spiral 

 turnings, the two ends of which open 

 without the vessel, the one at the top 

 and the other at the bottom. If we 

 make a regular current of gas traverse 

 this serpentine, maintained before its 

 entrance at an elevated and constant 

 temperature, this current may be con- 



sidered as an uniform source of heat, 

 and the water in the cylinder as the 

 body heated. Of course, if we repeat 

 the same experiment upon each of the 

 gases, each current will raise the tem- 

 perature of the cylinder to a fixed point, 

 where it will remain stationary : and it 

 follows from the principles announced 

 above, that, reckoning from this point, 

 the excess of the temperature of the 

 cylinder above that of the ambient air, 

 will be proportional to the quantity of 

 heat given out by the current of gas 

 that passed through the cylinder. 

 Hence, we shall obtain by this method, 

 with great exactness, the relative spe- 

 cific heats of the gases subjected to this 

 kind of experiment. There are like- 

 wise two methods of comparing them 

 with water. The first consists in sub- 

 jecting the cylinder which we call the 

 calorimeter to the action of a current of 

 water, perfectly regular, and so slow 

 that it will hardly produce a greater 

 effect than the current of the different 

 gases. The second method consists in 

 determining by calculation the real 

 quantity of heat which the calorimeter, 

 come to its stationary temperature, can 

 lose in a given time ; for since, after it 

 reaches this point, it does not become 

 hotter, though the source of heat con- 

 tinues to be applied to it, it is evident 

 that it loses as much heat as it re- 

 ceives." Annals of Philosophy, vol. ii. 

 page 2 12. 



The ingenious and delicate arrange- 

 ment used by Delaroche and Berard 

 in the experiments, is shown at Jig. 

 14 : a is the vessel for containing the 

 water, so contrived, that an uniform 



Fig. 14. 



