822 Mr. F. B. Young on the 



h x and h of gasons to liquid ons in the vapour and liquid phases 

 respectively are in the final state functions of the temperature 

 only, the functions being different for the respective phases. 

 If the law of Avogadro is assumed to hold for both kinds of 

 molecules, the temperature of uniform density is that at 

 which the ratios become identical. As the temperature is 

 raised the establishment of equilibrium involves a continuous 

 reduction in the value of hi and a continuous increase in the 

 value of h ; the adjustment is produced by a combined process 

 of diffusion and of transformation of one kind of molecule 

 into the other. A lag in this adjustment will sufficiently 

 account for the prolonged differences of density which have 

 been observed. 



Since this theory differs from the classical theory in its 

 predictions concerning observable phenomena only in respect 

 to the time required for the establishment of equilibrium, it 

 is only possible to decide between them by observation of the 

 time-factor. Though the fact that the transition zone may 

 be reproduced by heating the upper portion decisively proves 

 that diffusion must play a minor part in the establishment of 

 uniformity, it cannot be regarded as crucial evidence agains 

 the validity of the liquidogenic theory : the objection may 

 reasonably be raised that the changes of temperature and 

 pressure which are produced tend to produce dissociation in 

 the heated portion and possibly association in the lower 

 portion. It is, however doubtful whether the time-factor 

 must be necessarily greater on the assumption of the liquido- 

 genic hypothesis than on the assumption of Andrews's theory. 

 According to the latter, if we accept Villard's explanation of 

 the transition zone as of predominant importance, the denser 

 substance must expand and the less dense substance be com- 

 pressed against the external pressure and the intramolecular 

 forces combined : this involves virtually the transmission of 

 energy from the upper to the lower part of the substance, 

 the transmission probably occurring mainly through the walls 

 of the tube. In addition to this, sufficient heat must pass to 

 bring the substance to the temperature of the thermostat. 

 The liquidogenic theory seems to differ from Andrews's theory 

 only in substituting the force of chemical affinity for the 

 cohesive force, and the time-factor involved will only differ 

 greatly on the assumption that the energy absorbed in the 

 disintegration of the liquidons is much greater than that 

 absorbed in separating the molecules against the cohesive 

 force. 



In Table II. are given readings for plotting by means of 

 Yan der Waals's equation the isobar which passes at the 



