( 506 ) 



§4. Disturbances by capillary action. As is always tacitly assumed 

 in the application of the tp-surfaee when the reverse is not expressly 

 stated, the curvature of the surfaces of separation of the phases is put 

 zero in the foregoing' discussion. If the curvature may not be ne- 

 glected, e. g. at the compression of a mixture in a narrow tube, 

 then, when the barotropic pressure is exceeded, the phase which has 

 thus become heavier, will only sink through the lighter phase under it, 

 when the equilibrium has become labile taking the capillary energy of 

 the surface of separation into account. For this it is required that 6 P 



has become larger than — to an amount of A0 ca/ ,, which will depend 



on the capillary energy of the surface of separation and the diameter 

 of the tube in which the experiment is made. Thus capillarity causes 

 a retardation of the appearance of the barotropic phenomenon: both 

 with increase and with decrease of pressure the barotropic tangent- 

 chord must be exceeded by increase or decrease of pressure to a 

 certain amount, before the two phases interchange positions. In this 

 way the difference of pressure mentioned in Comm. X". 96', (Nov. 

 J906, p. 460) between the sinking of the gas phase chiefly consisting 

 of helium and its rising again at expansion (49 and 32 atms.) is 

 e.g. to be explained by the aid of the following suppositions which 

 are admissible for a first estimation. 



1. that at - 253° and 32, resp. 49 atms. He is in corresponding 

 state with H 3 at 150° and 1(50. resp. 245 atm., in agreement with the 



assumptions MueVkHe = —Mnvku according to the ratio of the molecular 



refractive powers, l,. He — l\b (according to Olszewski <1°.7); if 

 the gas phase consisted only of He (molec. weight 4), the density 

 at the temperature and pressures mentioned would be 0.062, resp. 

 0.081, and if moreover the liquid phase had the same density with 

 the two pressures, LH cap would have to correspond to a diJference 

 of density of ±0.01; owing to the fact that the two last mentioned 

 suppositions are not satisfied, the difference of density will be smaller ; 



2. that the capillary energy of the surface of separation between 

 the phases coexisting at the above temperature and pressures is not 

 many times smaller (or greater) than that of liquid hydrogen at that 

 temperature in equilibrium with its saturated vapour, and that the latter 

 may be derived from that of nitrogen *) by the aid of the principle 

 of corresponding states. The gas bubble will then in a tube like 

 that in which the experiment described in Comm. N°. 96a was made 

 (int. diam. 8 mm.) only sink through the liquid or rise again, when 



i) Baly and Donnan, Trans. Chem. Soc. 81 (1902) p. 907. 



