328 BESEAnCHES ON EVAPORATION AND DISSOCIATION. 



equation for a perfect gan, pv — Jl(l + at). Btit neither the 

 equation as proposed by Van der Waals, nor as modified 

 by ClausiiTS, Sarrau, and others, give rcmiltH which are 

 more than approximately correct; indeed, at very higli 

 pressures, the deviations become very largo. 



A step in this direction has been made by the diwcovcry 

 of a simple relation between the pressure and temperature 

 of a substance in cither the liquid or gaseous state at con- 

 stant volume, which may be expressed by the equation 

 J) = 6 y - rt, whore ^' is the absolute temperature, and /) and a 

 are constants depending on the substance and on its 

 volume. An equation eqiiivalent to this was found by 

 Amagat to l)e applicable to gases ; wo find that it holds 

 good for both ll(]uids and gases, at any rate within the 

 limits we have been able to reach in our experiments. In 

 order to construct an equation which shall represent the 

 results when, volume, as well as pressure and teniporaturo, 

 is variable, it is necessary to discover the relation of the 

 constants a and h to the volume, but this relation appears 

 to be a very complex one. 



