( 604 ) 



happened that phenomena^) al the critical point have heen descrilted 

 as abnormal and as l)eiM,U' at \ariancc with Ihe \ie\vs of ANnRKWs- 

 VAN DEK Waals, in eases whei-e ihe therniodynaniic e(piilil)riuiii 

 had not yet been attained eitlier l)ecaiise small differences in com- 

 position had remained owing to the slow ditfusion of very small 

 quantities of admixtnre (Kienen Comnis. N". 8, Oct. '93, N". 11, 

 May and Jnne '94), or because differences of temperature resulting 

 from variations of volume in different portions of the substance 

 during the passage from one condition of temperature and pressure 

 to the next had not yet been equalized (Kamerlingh Onne», Comm. 

 N". 68, March and April 'OJ and Kamerlingh Onnes and Fabius, 

 N". 98, May '07). 



When the thermodynamical equilibrium is obtained either by 

 keeping the substance in the neighbourhood of the critical point 

 during a long time at a constant temperature or by repeated rever- 

 sals of the sealed tube containing the substance (Gouv), or by 

 stirring it electromagnetically (Kuenkn) we must pay regard to the 

 gravitation which on account of the great compressibility of the 

 substance in that condition becomes of great influence *) and also 

 to small quantities of admixture which may occur and of which the 

 nature and the quantity are known ^). 



The consideration of these influences and those of capillai-ity and 

 absorption phenomena near the walls of the vessel ^), things which in 

 other cases are hardly to be considered, is indispensable at the critical 

 point liquid-gas for the determination of tlie exijerunetitdl equation 

 of state of a substance, i. e. the relation between [), r and T for 

 a substance consisting of one conq)onent in thermodynamic equili- 

 brium subject to no other external forces than the pressure on the 

 walls of the vessel. 



§ 2. In this communication w'e intend to bring into connection 

 some peculiarities in the experimental equation of state in the 

 neighbourhood of the critical state with the great compressibility 



1) For a survey of these phenomena comp. Graetz, Winkelmann's Handbuch, III, 

 2le Aufl. p. 837. 



2) GouY, G. R. 115 (1892) p. 720 and 11(>, p. 1289. J. P. Kuenen, Gomm. N". 17 

 May '95. 



3) Gf. Gomm. N". 75, Nov. '01, N". 79, March "02, N^. 88 Nov. '03 (Keesom), 

 N''. 81, June and Sept. '02, Suppl. N^. 6, Febr. and May '03, N . 18, Dec '04, 

 N'\ 12, Jan. '07 (Verschaffelt). On the influence of gravity a small quantity of 

 admixture being present, cf. Kuenen, Gonnn. N'. 17, May '95 and Keesom, Gomm. 

 N'. 88 VI, Nov. 'O:;. 



*) Gomp. VAN DER Waals, i.e. p. 106 and 107. 



