( 230 ) 



It is in harmony with this that a tolerably sharply defined critical 

 density can be assigned. We derive 0.460 from the density of vapour 

 and liquid in the third experiment for it, which agrees with the 

 mean which would follow from experiment 1 at 2 h 15, i.e. 0.450, 

 and 0.470, derived from experiment 3 on account of the appearance 

 of the meniscus at 25 (cf. further § 6 p. 223 footnote J). 



Differences of density as Teichner finds, were also found by us; it 

 was in the second experiment at the moment that the meniscus disappears 

 with comparatively rapidly rising temperature. However, after the tube 

 has been kept at the same temperature above the critical temperature 

 for 3 hours, and the temperature in the tube has become uniform 

 probably up to less than 0°,0J 0\9 above the critical temperature, 

 they have been reduced to less than 0,466 — 0,450, or less than 

 3,5 %> i. e. after correction for gravity <[ 3,3 % ovei ' 10 em. 



The remaining difference in the first experiment 0°,23 above the 

 critical temperature after 6 hours' heating above the critical tempe- 

 rature can be derived from the fact that bulb 0.450 floats 5.6 cm. 

 above 0,466. This difference is no more than 3,5 %> an ^ corrected 

 for gravity 2,9 %. 



From Verschaffelt's calculations follows that at 0°,23 above the 

 critical temperature 0,0001 molecule of admixture may cause about 

 12 °/o difference of density. Differences of temperature and admixtures 

 which may account for remaining differences such as those just treated 

 are scarcely to be avoided even with the precautions taken by us. 



Nothing has been observed of an "Entmischung" by cooling when 

 the critical temperature is approached, as Traube I.e. p. 477 mentions. 



Teichner observed that, after the disappearance of the meniscus, at 



the place where it was found last a transition zone exists towards 



which the differences of density concentrate, whereas outside it the 



changes are only insignificant. In our observations the contrary 



appeared, and the changes in density continue regularly with increase 



of temperature, only the motion of the bulbs was slightly accelerated 



as they approach the top of the tube, and they cover the last 1 or 



2 cm. very rapidly. In a less degree but in the same way this takes 



place with the bulbs which descended. We consider these phenomena 



lo be connected with heating and cooling of phases by compression 



and expansion : ). 



state with simultaneous change of the pressure of coexistence (cf. note 1 p. 1 § 1). 

 But the absence of subsequent rise of pressure in the repetition of de Heen's 

 experiment (see § 3) has taught us, that already after a very short time after- 

 changes of the density no longer occur. 



') They just as the "Entmischung" assign that the temperature differences within 

 the tube in the experiments of Teichner were probably greater than in ours. 

 [Note added in the English translation]. 



