( 281 ) 



Van der Waals, These Proc. Jan. '07 p. 528 calls attention to the 

 influence of i i5 &,, on the occurrence of barotropic phenomena by 

 stating this rule: "When the most volatile substance has the greatest 

 limiting density, the gas phase can be specifically heavier than the 

 liquid phase." In connection with what was discussed above we 

 may now supplement this rule as follows: If of a binary mixture 

 the more volatile component lias the greater limiting density, the 

 gas phase will be made to sink in the liquid phase by compression 

 with suitable concentration and temperature, provided the more 

 volatile component has so feeble an attraction that pressing in of 

 this latter component cannot make the liquid phase of the less volatile 

 component dissolve in the gas phase at definite ') temperatures even 

 at the highest (comp. p. 277 note 1) pressures. 3 ) It is implied in the 

 terms of this rule that it has been supposed that no two liquid phases 

 occur. 



It is not excluded that also in other cases sinking of the gas phase 

 in the liquid phase might occur. n ) 



If we apply this rule to pairs of substances of which data are 

 available for a., 2M , a nv ail <l b.>« M , b nu , it appears that only for 

 He — II, it may be expected on reasonable grounds *) that barotropic 

 phenomena occur at not too high pressures 5 ). Further investigations will 

 have to reveal whether for mixtures of pairs of substances as nitrogen 



*) Also at higher temperatures than these barotropic phenomena may then occur. 



2 j In the case of compression of a gas above a liquid, starting from the pure 

 substance in the way as was done in Kundt's experiments we describe on the 

 •i-surface a curve the r, ^-projection of which is a straight line joining a point of 

 the line X= with the point V = 0, x= [. For the liquid phase to disappear at 

 a definite, suitable temperature just under plaitpoint circumstances, we must start 

 from a definite quantity of liquid so that the volume id represented by SQ (see 

 fig. G). If the quantity of liquid from which we start, is smaller, the liquid phase 

 will evaporate (be dissolved in the gas phase' 1 , if it is larger the gas is dissolved 

 in the liquid phase (cf. van der Waals, Cont. II, p 130). Only if the diffusion 

 is not rapid enough to ensure equilibrium all through the tube, solution of the 

 liquid under plaitpoint phenomena may be observed also witlT'other quantities of 

 liquid as corresponding with vq, as has been set forth by Kuenen's experiments 

 on the influence of phenomena of retardation. 



3 ) See e.g. § 1, p 375, note 1. 



4 ) Though for mixtures of e.g. helium and acetonitril the available data with 

 application of the special hypotheses assumed in this § (concerning the equation 

 of state etc.) would point to the fact that at high pressures barotropic phenomena 

 might still just occur, it is impossible to express a definite expectation with regard 

 to this on account of the influence of the uncertainties, both in the data and in 

 the validity of the mentioned suppositions. 



,i This was mentioned in Cornm. No. 966 Dec. '06 p. 501. 



