( l«ö ) 



The Joule-Kelvin effect, which plays such an important part in 

 the liquefaction of gases whose critical temperature lies below the 

 lowest temperature down to which we can permanently cool down, 

 may be calculated from the isotherms, at least if the specific heat 

 in the gas state is not unknown, and its determination, though more 

 lengthy than that of the isotherms, may be an important test of our 

 measurements. If there is to be question of statical Liquefaction of 

 the gas by means of the Joule- Kelvin effect, this must at all events 

 give a decrease of temperature at the lowest temperature already 

 reached, which, as was demonstrated in the above communication, 

 will be the case to a corresponding amount for gases with the same 

 number of atoms 1 ) in the molecule at corresponding states, while a 

 mon-atomic gas compared with adi-atoinic one will be in more favourable 

 circumstances for liquefaction (Comp. also Comm. N°. 66, 1900). 



But the sign of the Joule-Kelvin effect under certain circumstances 

 does not decide the question whether an experiment on the statical 

 liquefaction of a gas will succeed. Speaking theoretically, when by the 

 Joule-Kelvin effect, at a certain temperature a decrease of temperature 

 however slight can be effected, liquid may be obtained by an adia- 

 batic process with a regenerator coil and expansion cock with 

 preliminary cooling down of the gas to that temperature. But as long 

 as we remain too near the point of inversion the Joule-Kelvin effect 

 will have a slight value; accordingly the processes by which really 

 gas was liquefied in statical state with an apparatus of this kind, as 

 those which were applied to air by Linde and Hampson, and to 

 hydrogen by Dewar, start from a much lower reduced temperature, 

 viz. from about half the reduced temperature at which the sign of the 

 Joule-Kelvin effect at small densities is reversed, or more accurately 

 from somewhat below the BoYLE-point, i.e. that temperature at which 

 the minimum of pv is found at very small densities. [Experiments from 

 which could be derived at how much higher reduced temperature 

 the process still succeeds with mon-atomic gases are lacking]. So 

 according to the above theorem it is practically the question whether 

 the lowest temperature at our disposal lies below this BoYLE-point 3 ) 



1 ) [The inversion points of the effect having reference to the amount and 

 therefore being independent of the number of atoms in the molecule, are at 

 corresponding states, and the inversion point for small densities is at corresponding 

 temperature for all gases as far as they obey the law of corresponding states. 

 This is easily deduced from the considerations of Comm. N°. 23J. 



2 ) [The Boyle point, as well as the Joule-Kelvin inversion point for small 

 densities is a corresponding temperature and both temperatures are therefore pro- 

 portional theoretically. In the present question it is better to refer to the Boyle 

 point than to the Joule-Kelvin inversion point considering the deviations of the 

 law of corresponding states]. 



