CONTRIBUTIONS FROM . THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



ON THE APPLICABILITY OF THE LAW OF CORRESPOND- 

 ING STATES TO THE JOULE-THOMSON EFFECT IN 

 WATER AND CARBON DIOXIDE. 



By Harvey N. Davis. 



Presented by John Trowbridge, December 8, 1909; Received December 30, 1909. 



In" the classical plug experiments of Joule and Kelvin certain gases 

 were forced by pressure through a porous plug under circumstances 

 which permitted the accurate measurement of any small resulting 

 change in their temperature. It can easily be shown that a perfect 

 gas would show no such change. As a matter of fact, hydrogen was 

 found to be slightly warmer on the low pressure side of such a plug 

 than on the high pressure side, while air, oxygen, nitrogen and carbon 

 dioxide were slightly cooler. The ratio of the observed drop in tem- 

 perature to the drop in pressure in such a plug has ever since been 

 called the Joule-Thomson coefficient. 



The results of such experiments afford the best known means of 

 computing corrections for reducing the temperature scale of a gas 

 thermometer to Kelvin's absolute thermodynamic scale. For this pur- 

 pose one must know the Joule-Thomson coefficient of the gas in the 

 thermometer at all temperatures between 0° C. and the t° C. at which 

 the correction is desired. Unfortunately, none of the experiments 

 either of Joule and Kelvin or of any of their successors are at temper- 

 atures other than between 0° C. and 100° C, except for certain inver- 

 sion points of Olschewsky obtained under circumstances not yet fully 

 understood. These are not enough to give a direct determination of 

 the absolute thermodynamic scale above 100°. In order to get one 

 indirectly, it has been customary to assume that, at least in the five 

 gases, hydrogen, oxygen, nitrogen, carbon dioxide and air, the Joule- 

 Thomson effect obeys the law of corresponding states. That is, it is 

 assumed that if the coefficient for each gas is expressed in terms of the 

 critical pressure and temperature of that gas as units, and if the 

 results are plotted against the temperature expressed in the same 



