L64 PROCEEDINGS OP THE AMERICAN ACADEMY. 



volume does i lot appear to tend to become zero at the zero of tempera- 

 ture, but rather to approach aa a limit Borne definite volume. As the 

 kinetic tore- become less there must be some other force which enters 

 to oppose the attraction between tin ■ molecules. If it is permissible 

 tu consider the limiting case where the motion of the molecules cea 

 there must exist at the absolute zero a condition in which the total ex- 

 ternal pressure and all the attractive forces betweeu the molecules are 

 ther balanced by some sort of outward force which is equal to their 

 sum. This would be greater than the attractive forces alone and the 

 difference would depend upon the external pressure. In other words, 

 there would !><■ a resultant repulsive force equal to the external pressure. 

 A- to whether this force is of the nature of elasticity, or of some action 

 at a distance, it would he presumptuous to speculate. From these con- 

 siderations, which must be admitted to be very hypothetical, it would 

 seem that at ordinary temperatures there should be analogous conditions 

 in which the repulsive forces would he greater the higher the pressure. 

 According to equation 1 16), in all liquids the resultant attractive pressure 

 diminishes with increasing external pressure, and finally changes Bign at 

 the poiut where mi the P V diagram the equation of condition cuts the 

 hyperbola of thermal pressure; that is. at the point where the volume is 

 the same as it would he if the substance were to behave as a perfect gas 

 under the same pressure. Similarly, at high pressures probably all gas< a 

 have a greater volume than corresponds to the gas law. and according to 

 our theory their particles repel each other under these conditions. At 

 at spheric pressure, on the other hand, almost all ga8e8 have too small 



a volume, but hydrogen still has a volume which corresponds in our 

 theory to an intermolecular repulsion. It is interesting, therefore, to 

 oote that in the experiments of Joule and Thomson, while other ga 

 Bhowed an increase oi internal energy on expansion, hydrogen showed a 

 sliL.ditdecre.a-c-. Helium is in all probability another gas which has too 



: a volume: and it ha- been shown by Donnan * \\- his experiments 



on the effusion of gases, that probably helium also ha- a beating effect on 

 free ion. like hydrogen. Such a beating effect can be explained 



in no other way so simply a- by a-sumiiiL r that there i- a repulsion 

 between the molecules in both helium and hydrogen. Finally, a similar 

 repulsion could explain the phenomenon observed in the experiments 

 oi Ramsay \ on the distribution of hydrogen between two Bpaces, one of 

 which contained hydrogen alone, the other hydrogen and nitrogen, lie 



I'lal. !.l\ I2i Phil Mag., XXXVII] 206 L894) 



