824 Mr. F. B. Young on the 



between the intensity of the opalescence and the density of 

 the substance is also desirable, but owing to the difficulties 

 of purification of the ether and of exact measure inents at the 

 critical temperature, this of itself would involve lengthy 

 research. 



General Conclusions. 



The experiments described have perhaps served rather to 

 demonstrate the difficulty of realising theoretical conditions, 

 than to lead to a decisive conclusion concerning the nature 

 of the Cagniard-Latour phenomena. The results of the 

 investigation, however, clearly favour the retention of the 

 classical theory of Andrews. 



It has been found that by the introduction of a temperature 

 difference, the Cagniard-Latour phenomena may be repro- 

 duced with similar opalescent effects and approximately the 

 same persistency. 



The last traces of gaseous impurity have proved most 

 difficult to eliminate, and extremely slight traces of such 

 impurity have visibly accentuated the phenomena or delayed 

 the establishment of equilibrium. 



Since the differences of temperature involved are so slight, 

 the period required for the establishment of equilibrium does 

 not seem unduly long. 



The intensity of the opalescence depends greatly upon the 

 density of the substance, so that any cause which produces 

 a small difference in density will produce visible qualitative 

 effects which are great in proportion to that cause. 



The investigation of the nature of the opalescence, so far 

 as it has been carried, tends to favour the kinetic explanation 

 of Kiister rather than that of Altschul or Donnan, and thus 

 far decides the Cagniard-Latour temperature to be the true 

 critical temperature of vaporization. 



It may be noted that the more recent investigations have 

 in general tended to show that the more violent discrepancies 

 from the predictions of Andrews's theory concerning the 

 critical phenomena have been due to causes which are not 

 out of accordance with Andrews's theory. Owing to the 

 peculiar properties of the substance at the critical tempera- 

 ture, the approach to conditions which permit of theoretical 

 results must of necessity be asymptotic, and therefore to 

 formulate an hypothesis for the purpose of explaining such 

 discrepancies as may now be considered to remain seems un- 

 necessary, except perhaps in the case of those liquids whose 

 surface-tensions point to association of their molecules 



