[ 536 ] 



XLIII. On the Specific Heat of Saturated Vapours. 

 By John P. D Alton, M.A., Carnegie Research Scholar*. 



A 



A. According to van der Waals's Equation. 



WELL-KNOWN thermodynamic relation is expressed 

 by the equation 



dv 

 where h s is the specific heat of the saturated vapour, and jm 



is calculated along the saturation line. 



Hence 



7, -r + BT dv 

 *.- c .+.,-=& , 5T' 



or, in " reduced " magnitudes, 



^6 day 



h=C v + 



3co-ld0' 



points, i. e. at points where the specific 

 heat of the saturated vapour changes its sign, /^ g = 0. The 

 curve o£ inversion points is, therefore, determined by the 

 equation 



_ 9l _ _§_ ^ 



Now, the law of corresponding states does not involve the 

 correspondence of thermal quantities. But, considering that 

 C„ does not vary with the volume, and probably comparatively 

 little with the temperature, C v may be assumed constant and 

 equal to C v=v >. At infinite volume the gas laws are obeyed, 

 hence 



R=<Wr.-i) > 



where y^ = Q>pjO v at large volume. 



The equation to the curve of inversion points may now be 

 written in terms of 7, 



1 3a> — 1 IdO 



Using the saturation constants given in a previous paper, 

 ■j- was calculated by means of Stirling's interpolation formula, 

 and the right member of the above equation evaluated. 



* Communicated by Prof. J. P. Kuenen, Ph.D. 



