( 224 ) 



deviations from the law of Henry for this pair of substances, investigate 

 the variations of this absorption with a small variation of temperature 

 and finally find for the same temperature the pressure to which 

 KuNDT ought to have gone in his experiments ^) on the removal of 

 the capillary ascension of liquid by pressing gas on it in order to 

 see the meniscus of ether disappear under the pressure of hydrogen, 

 which, as has been remarked in van Eldik's thesis for the doctorate 

 p. 7, comes to a determination of the plaitpoint pressure of the 

 mixture of ether and hydrogen of which the plaitpoint lies at this 

 temperature ^). 



In such cases we can only obtain solutions by means of the 

 graphical treatment described in Comm. N". 5da (»Sept. 1900). It 

 is true that the graphical method lacks the general character of 

 the approximate solutions just mentioned, yet by means of it a better 

 numerical agreement may be obtained for each special case. ^) By 

 a proper choice of special cases some data may also be derived 

 for the qualitative charactei's of phenomena in mixtures "). 



If we only aim at such qualitative results we may simplify the 

 graphical treatment as well as the analytical by introducing dilFerent 

 approximations according to the nature of the problem, while it lies 

 at hand to derive wanting experimental data or results of calcula- 

 tions from empirical formulae on a larger scale tlian in tiie analytical 

 treatment. For instance, everything that may be neglected in the 

 analytical treatment may also be neglected in the graphical method. 

 Occasion for this exists only, however, with problems which neither 

 qualitatively are solved by means of the analytical method. 



If we do not want to neglect to such an extent as in the 

 analytical treatment, we might for instance retain the neglection of 

 the deviations mentioned sub 2" of different normal substances and 

 mixtures of normal substances from the law of corresponding states, 

 which first occurs in Comm. N". 59a and is kept up in this whole 

 series of contributions.' 



1) Repeated by van Eldik (thesis for the doctorate; Leiden 1898) for hydrogen- 

 ether and ethylene-metliylchloride. 



3) Gomp. also van der Waals, Die Gontinuitat etc. II, p. 136. 



3) For instance, one of us and Reinganum have derived (Gomm. N''. 59& Sept. 1 900) 

 a numerical fairly approximate representation of the retrograde condensation 

 observed by Kuenen with mixtures of raethylchloride and carbon dioxide from the 

 isothermals observed by him at other temperatures. 



^) So for instance the character of the retrograde condensation (comp. note 2), 

 and also the peculiarity in the conditions of coexistence in mixtures of which the 

 critical temperature varies almost linearly with the composition, far below the 

 critical temperature. Gomp. ^these contributions Gomm. N^. 59a § 8 at the end 

 and III, Gomm. N'^. 64. Hartman, Livre jubil. Lorentz, p. 640. 



