( &17 ) 



Further we have repeated Teichner's experiment ') with more 

 precautions than had been taken by this observer. Especially a 

 thermoelement (platinum-platinum-iridium not to sacritice the security 

 which the glass apparatus offers for the preservation of the purity 

 of the substance) was adjusted in the upper and in the lower end 

 of the Teichner tube, just as in de Heen's modified apparatus, 

 to enable us to follow the differences of temperature in the tube.*) 

 By using CO, for the experiment, a high degree of purity could be 

 reached, and we came into a region where the temperature could 

 be kept constant up to a very small amount. 



If we wish to prevent diffusion between the higher phases and 

 the lower ones, the modified Teichner tube (at least when not a 

 capillary constriction has been made in it ') is inferior to the 

 modified apparatus of de Heen. Moreover when we wish to reach 

 the equilibrium of temperature quickly, the bad conductivity of 

 heat of the glass is a drawback, but it has the great advantage, that 

 the changes of density can be observed at the same time with the 

 other phenomena for the critical state. With regard to these pheno- 

 mena Travers and Usher (Ztschr. f. phys. Chem. 57, p. 365, 1906) 

 and Young (ibid p. 262) published important papers, after we had 

 made the experiments mentioned in § 7. In the main points our 

 observations agree with the descriptions given by Travers and 



peralure lead to systematic disturbances as in de Heen's experiments. Both give 

 rise to disturbances of the same character. In the discussion of the influence of 

 the differences of temperature the valuable paper by Villard Ann. d. Gh. et d. 

 Phys (7) 10. 1897 has been overlooked there. That Teichner's results might be 

 ascribed to small admixtures has appeared in details from the calculations by 

 Verschaffelt (Comm. Suppl. n'. 10, (Dec. l'J04). 



To the influence of admixtures on phenomena in the neighbourhood of the 

 critical point attention has also been drawn by Young Journ. de Ghim. Phys. 4 

 (1906) p. 475. To this may be added that Keesom, Comm. No. 88, These Proc. 

 Jan. 1904 p. 593 did not only consider the increase of the pressure during conden- 

 sation with constant temperature as a proof of the presence of admixtures, but 

 that it served him further to arrive at an opinion on the quantity of the admixture. 



'1 This was already mentioned Comm. Suppl. No. 10 These Proc. Dec. 1904. 

 Lately Traube strongly urged the advisability of a repetition. 



2 ) In a Cagniard-Latour tube thermometers were fused by Villard. Our tube 

 may just as well be called a Villard tube with density-bulbs as a Teichner tube 

 with thermo-elements. 



s ) Such an apparatus, if necessary provided with a valve which is worked 

 magnetically might be serviceable in the investigation of the variation of density 

 with temperature. [After this was printed we noticed that the device of a capillary 

 constriction was used by Ramsay, Proc. Roy. Soc. 30 (1880) p. 327. Note added 

 in the translation]. 



