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Physics. "Contributions to the knowledge of the xy-surface oj 



van der Waals. XVI. On the gas phase sinking in the liquid 

 phase for binary mixtures in the case that the molecules of 

 one component exert only a feeble attraction." By Prof. H. 

 Kamerlingh Onnes and Dr. W. H. Keesom. Supplement N°. 16 

 to the Communications from the Physical Laboratory at Leiden. 



§ 1. Introduction. In Comm. N°. 96*, These Proc. Dec. J 906, 

 p. 501 a gas phase sinking in a liquid phase 1 ), the barotropic pheno- 

 menon, was treated for binary mixtures for a gas liquid plait, which 

 crosses the ip-surface as a transverse plait at lower temperature. Then the 

 treatment for temperatures, at which the appearance of a longitudinal 

 plait brings about a disturbance, was deferred to a later communi- 

 cation. Moreover, more special cases, as the appearance of minimum 

 or maximum critical temperature or minimum or maximum pressure 

 of coexistence, were left out of consideration, and the discussion 

 was restricted to the case that retrograde condensation of the first 

 kind occurs. 



When for binary mixtures the conditions for the sinking of a gas 

 phase in a liquid phase were treated in Comm. N°. 96'', These Proc. 

 Dec. '06, p. 508 and Febr. '07 p. 660, it appeared in the first place 

 that at least if the hypotheses mentioned there are valid, and pairs of 

 substances are found with proper a 2 2M/a\\M> b>2M/bi\M and M,/M l 

 the theory of van dek Waals' ^-surface leads us to expect that 

 barotropic plaitpoints s ) will occur. 8 ) Further that for mixtures with 



1 ) Considerations which are not in accord either with the limited compressibility 

 of a gas at high pressures, first stated by Natterer in 1844, or with our present 

 views on the mixing of two substances, induced Jamin, G.R. 96 (1883) p. 1448, 

 Journ. de phys. (2) 2 (1883) p. 389 to raise the question whether it should be 

 possible that with compression of a mixture of G0 3 with air or with hydrogen, a 

 liquid phase would collect above the gas phase. Cailletet (Jamin I.e.) did not succeed 

 in realizing this. 



2 ) On the peculiar phenomena which are met with in ease of a barotropic 

 plaitpoint, we hope shortly to make a communication. 



• 3) That the barotropic plaitpoint found in Comm. N'. 96c, Dec. '06 §5 belongs 

 o the gas liquid plait (cf. Comm. N° 96c, Febr, '07, p. 660 footnote 1) was derived 

 rom the shape of the spinodal curve for this case, in connection with the course 

 of the plaitpoint curve. The same thing may appear as follows : By applying the 

 criterion (.3) in Suppl. N '. 15, March '07, p. 796, we find that mixtures of a pair of 

 substances of ratios indicated in the mentioned § belong to case (c), (cf. p. 276) 

 while we may derive from van Laar's fig. 22, Arch. Teyler (2) 10 (1907) 

 p. 138, These Proc. Sept. '06, p. -J26, fig. 1, that the plaitpoint curve crosses from 

 the side x = to the side v = b (van Laar's type I). 



