( 216 ) 



differences found are to be ascribed to admixtures or to differences 

 in the pressure or the temperature of the phases compared appeared 

 already when Kuenen (Comm. n°. 11, Verslag Kon. Ak. v. Wet. 

 May and June 1894) repeated Galitzine's experiments (Wied. Ann. 

 50, 1893), and found but trifling differences remaining. Afterwards 

 when de Heen (Bull. Ac. Belg. 3e S. t. XXXI '96) had again found 

 the differences of density in question by another way, it was shown 

 by repetition of his experiments at Leiden (Comm. N°. 68, These 

 Proc. April 1901 p. 628 and p. 691), that also these differences of 

 density vanish almost entirely for pure CO a when attention is paid 

 to the differences of temperature. In the last few years, however, it 

 has been particularly Teichner's ] ) experiments that have given new 

 support to the opinion that after all these differences of density really 

 exist (Drudes Ann. 13, 1904). 



In the first place we have repeated de Heen's experiment in 

 different ways. Already with the earlier repetition (1901) thermo- 

 elements had been introduced for the determination of the difference 

 in temperature of the two metal reservoirs of the apparatus, which 

 were separated by a cock, the apparatus for the rest resembling that 

 of de Heen as closely as possible. One of the thermo-elements, however, 

 was damaged during the experiments. Though it could be ascertained 

 that the differences in density even without correction for the tem- 

 perature were considerably smaller than those found by de Heen, 

 probably on account of the greater purity of the CO,, the exact 

 amount of the difference remaining after temperature correction 

 could not be determined. To replace these measurements by better ones 

 a new, improved apparatus with thermo-elements was built, resembling 

 for the rest de Heen's apparatus as closely as possible, and with 

 this apparatus we made the observations communicated in $ 3. 

 They confirm that the differences in density derived by de Heen from 

 his experiments do not exist for a pure substance when temperature 

 and pressure are uniform 2 ). 



x ) In the Teichner's tube the same differences of density which Galitzine and 

 Wilip (Gongr. Intern, de Physique I 668, 1900) had found were shown by Gilbert- 

 Faraday's density-bulbs. What holds for Teichner's experiments applies therefore 

 also to those of Galitzine and Wilip. 



8 ) So if there exist processes as meant in p. 215 note 1, they pass so quickly that 

 it is not possible to demonstrate them by methods which require that the equili- 

 brium of pressure and temperature has first been established. As yet nothing 

 has been found that points to the fact that the establishment of the temperature 

 equilibrium is retarded an appreciable time on account of changes of energy which 

 increase in course of time to a definite limiting value, the volume remaining constant. 



It was demonstrated in Comm. N°. 68 that admixtures and differences of tem- 



