( 233 ) 



mentioned in § 2 might be applied, have been given for some helium 

 mixtures. 'J\ m lias here been calculated according to van dek Waals 

 Cont. II, p. 43 (cf. § 6), Td,,i according to the formula mentioned 

 in § 7, pd r i from the equation of state with the just mentioned 

 Tdpi and the Vd p t also represented in formula in § 7 '). 



The reduced temperature of the double plaitpoint Td p i 'l'i,,, men- 

 tioned in this table, nixes an idea in how far the phases in its 

 neighbourhood behave as compressed gas-phases. 



The values of a and b of the different components have been borrowed 

 from Kohnstamm, Landolt-Börnstein-Meyerhoffer's Physik. Chem. 

 Tabellen-, for those of helium see above; for neon we have made use 

 of the ratio of its refractive power '-) to that of helium according to the 

 determinations of R\msav and Travers'), and of the estimation con- 

 cerning the critical temperature by Travers, Senteb and Jaquerod 4 ). 



It appears from table II that when the gas-gasplaii can make its 

 appearance, the range of temperature within which this is the case 

 .between Ti :m and 7',/,,/), on the mentioned suppositions is small for 

 most of these pairs of substances, for some even exceedingly narrow. 



For the pressures on the gasplai! higher values than pjpi will have 



') Though originally we did not consider the developments which led us to the 

 explicit expressions for the double plaitpoint mentioned These Proc. March '07 

 pp. 796 and 798 of sufficient importance, now that van Laar (see These Proc. 

 May '07 p. 41) thinks the derivation of such like expressions impossible there 

 is a reason for communicating them on a following occasion. 



a ) Happkl, Habilitationsschrift Tubingen 1906, p. 30, found that the refractive 

 power for argon, crypton and xenon would yield values for b which greatly deviate 

 from the b's derived from the critical data. When according to the principle of 

 the corresponding states (cf. Happel loc. cit. p. 31, note 1) we compare the ratios 

 of the refractive powers for these gases with those of their critical volumes 

 (derived from pk and 27,) the deviations are far less considerable. So with regard 

 to this property, these one-atomic gases form a group, just as is the case with 

 the bi-atomic and with a great many more-atomic substances (Guye, Journ. de 

 phys. (2) 9 (1890) p. 312). 



:! ) Ramsay and Travers, Phil. Trans. A197 (1900; p. 81. Yet we must 

 remark that when comparing this ratio for helium and argon according to Ramsay 

 and Travers with the ratio of ÖHe according to our estimation and b\ derived 

 from pt and Tt , we should find an importaut deviation (.cf. note 1). Also in 

 view of this the data concerning mixtures of helium and neon are very uncertain. 



4 ) Travers, Senter and Jaquerod, Phil. Trans. A 200 (1902) p. 177. Then- 

 views, however, on a connection between atomic weight and critical temperature 

 lead to an unlikely result for the critical temperature of helium. 



The determinations of isotherms of neon by Ramsay and Travers, loc. cit. 

 have been of as little use to us as those of helium for the determination of a and 

 /' (different particulars in the course of the isotherms of the one-atomic gases 

 given by these scientists in plate 2 loc. cit. do not seem very probable to us). 



