796 



Mr. F. B. Young on the 



in the lower for two or three hours after the temperature 

 had been raised above the Cagniard-Latour temperature. 

 Eversheim (6) observed similar effects in ammonia and S0 2 , 

 whilst the dielectric constant for H 2 S differed also in similar 

 fashion. If, however, the density differences can be explained 

 in accordance with Andrews's theory these latter forms of 

 evidence become inconclusive. For though, by definition, 

 the liquid and vapour cease to exist above the Cagniard- 

 Latour temperature, there is no cogent reason why their 

 peculiar properties should forthwith disappear. The diagram 

 of Andrews is apt to give an impression of discontinuity at 

 6 C which in practice is nonexistent. The ordinate AB (fig. 1), 



Fig. 1. 



I 



V 



for which v is equal to the critical volume V c , appears in 

 meeting the saturation curve to strike a point of sudden 

 transition ; this is because of the impossibility of realizing 

 the theoretical isothermals within that curve. In practice, 

 however, as the explanations of both Gouy and Villard 

 indicate, the bulk of the substance does not, during rise of 

 temperature, pass through C along the isothermal AB, but, 

 roughly speaking, along two ordinates DC and EF, for 

 which v < V c and v> V c respectively. In this case the dis- 

 continuity at 6 C ceases to be apparent. Hence it is not 

 unreasonable to assume that the continued difference of 

 density will be accompanied by a continued difference of 

 properties; and if adequate causes for the observed persistency 

 of the density difference can be found which are in accord- 

 ance with Andrews's theory, the same causes may be held 

 to produce indirectly the observed differences of electrical 

 and chemical properties. 



