SicrioN III., 1906 [ 189 ] Trans. R. S. C. 



XU. — ^1 Method of Determining the Specific Heat of a Gas at Constant 



Pressure. 



i 

 By H, F. Dawes, M.A., University of Toronto. 



(Communicated by Prof. J. C. McLennan, and read May 23, 1906.) 



The classical determination of this constant for several gases wa? 

 made l)y l^cgnault.^ His method consisted in passing a stream of heated 

 gas through an ordinary water calorimeter and determining the quantity 

 of heat given up by observing the rise in temperature of the water. Th-3 

 (|iiantity of gas used in any experiment was determined from observations 

 on the pressure, and the temperature of the gas together with the volume 

 of the reservoir in which it was stored. The gas was heated by passing 

 it through a long spiral tube of copper immersed in a bath of 

 boiling oil. From the heating bath it passed directly into the calori- 

 meter traversing it in a spiral copper tube. It was assumed that the air 

 entered the calorimeter at the temperature of the oil bath, and left it at 

 the temperature of the water. 



Besides the heat given up by the gas a certain amount was com- 

 municated to the calorimeter by conduction and by radiation both from 

 the bath and from other bodies in the room. In order to determine the 

 amount of heat derived from these sources observations were made on 

 the temperature of the calorimeter for a certain time before the gas was 

 allowed to pass through and again after the flow was stopped. 



Defects. 



In attempting to repeat this experiment with apparatus precisely 

 similar to that used by Regnault it was found that the arrangement had 

 several disadvantages. In the first place the calorimeter used was not 

 very delicate, i.e., it required a comparatively large quantity of heat to 

 make a sufficiently great difference between the initial and final tempera- 

 tures of the calorimeter. 



Since both the specific heat and the density of a gas are very small, 

 it is necessary to use a large quantity of gas and to make the initial tem- 

 'perature very high in order to have the required quantity of heat avail- 

 able. To obtain a sufficiently high temperature, boiling oil was used in 

 the heating bath and this made the experiment very disagreeable an I 

 difficult to work with. 



' Regnault. Mémoires de l'Académie des Sciences de l'Institut Imperial 

 de France. Tome XXVI. pp. 1-112. 



