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Physics. — Repetition of de Heen's and Teichner's experiments on 

 the critical state", by Prof. H. Kameklingh Onnes and G. H. 

 Fabius. Communication N°. 98 from the Physical Laboratory 

 at Leiden. 



(Communicated in the meeting of April 26, 1907). 



§ 1. Introduction. Experiments have been repeatedly made from 

 which the conclusion was drawn, that a substance can assume different 

 densities above its critical temperature with the same pressure and the 

 same temperature, which densities it can retain for hours according to 

 some investigators '). That in reality this is not the case, and that the 



!) Traube Ztschr. f. phys. Chem. 58 p. 477. 1907, cf. also Mathias, Le point 

 critique des corps purs p. 250. 



When with change of density dissociations or variations of volume of the 

 molecules themselves should made their appearance which clearly require more time 

 than the establishment of temperature equilibrium through conduction of heat and 

 convection, we should when a phase was kept at constant volume after having 

 suffered variation of density, have to find an increase of the pressure both for 

 liquid and vapour phases and for phases above the critical temperature; theimo- 

 dynamically it follows from this that the density of liquid in equilibrium with 

 vapour would then have to be a function of the time. 

 . Cf. Travers and Usher on variations of density in consequence of false equilibria. 



