Mr Bevan, On the Joule-Thomson Effect 127 



On the Joule-Thomson Effect. By P. V. Bevan, M.A., Fellow 

 of Trinity College. 



[Received 20 February 1903.] 



The method which at first sight appears best adapted to 

 determine empirically the characteristic equation for gases depends 

 on the observations of the Joule-Thomson effect in gases forced 

 through a porous plug. We shall see however that with the 

 experimental results which we possess at present we are led to an 

 equation which does not agree well with direct experiment on the 

 pressure and volume of gases. 



The well known expression for the change of temperature for 

 a gas streaming steadily through a porous plug is 



\ dd/p J G p 



where A6, Ap are the small changes of temperature and pressure, 

 from one side of the plug to the other, O p the specific heat at 

 constant pressure, and p, v and 6 are as usual the pressure, volume 

 and temperature of the gas measured on the absolute scale. In 

 actual experiments which have been performed the change of 

 pressure from one side of the plug to the other has always been 

 large so that the observed temperature change is 



<H) = 





C p 



where the limits of the integral are the values of the pressure on 

 the two sides of the plug. 



From Joule and Thomson's experiments the temperature 

 change observed was found to be approximately proportional to 

 the difference of pressure on the two sides of the plug, so that 



assuming this proportionality to hold, we should have -r— inde- 

 pendent of p ; in other words that 



Op 



is a function of the temperature only. 



