332 



longer than 4 or 5 cm. ^) Therefore it is absolutely essential in every 

 method inleiuled for exact measurement at high temperatures, that 

 the working-space be reduced to dimensions as small as possible. 

 With respect to the measurements of temperature under such con- 

 ditions, the available methods v^ill permit making them with an 

 accuracy of 0°,1 C, ") which is more than sufficient for the purpose. 

 On the other hand, the necessarj- measurements of the surface-energy 

 must be made in such a way, that the results will have the same 

 degree of accuracy at the highest temperatures, which they possess 

 at lower temperatures, while at the same time the liquid to be 

 studied must be restricted to a space of one or two cubic centimeters. 



§ 3. To fulfill these postulations, there is a method which can 

 be used under certain conditions, which was first projected by 

 M. Simon, and later developed by Cantor, •') while it was successfully 

 used afterwards for researches at lower temperatures by Feustel. '') 

 It appeared to be possible to develop the technical procedure in 

 such a way, that the method could be used, without any appreciable 

 loss of accuracy, up to the highest temperatures, which can be 

 measured with the platinum-platinumrhodium thermoelement. 



The principle of the method is the measurement of the maximum 

 pressure H, prevailing within a very small gas-bubble, Avhich is 

 slowly formed at the circular, knife-edge opening of a capillary tube 

 immersed in the liquid perpendicular to its surface, just at the 

 moment, when the gasbubble is about to burst. The sharp edge 

 of the capillary tube eliminates the influ-ence of the capillary angle. 

 In this way absolute measurements of the surface-energy are possible 

 in Ergs per cm^, if the radius r of the tube, the specific gravity d 

 of the liquid at the temperature of observation, and the depth of 

 immersion / of the tube into the liquid, are known. To obtain the 

 true value of H, the readings of the manometer require to be 

 diminished by the hydrostatic pressure, corresponding to this depth 

 of immersion i. 



The method evidently can only give exact results, if the final state 

 of the gasbubble represents a state of equilibrium, and is thus reached 



1) BoTTOMLEY, Journ. of the Chem. Soc 83. 1421. (1903) ; Lorenz and Kaufler, 

 B. d. d. Chem. Ges. 41. 3727. (1908;; Tkaubb, ibid. 24. 3074. (1891). Vide also: 

 MoïYLEWSKi, Z. f. anorg. Chem. 38. 410. (1903). 



2) F. M. Jaeger, Eine Anleitung zur Ausfiihrung exakter physiko-chemischer 

 Messungen bei höheren Temperaturen. (1913). p. 36, 43. 



3) M. Simon, Ann. de Ghim. et Phys. (3). 32. 5. (1851) ; Cantor, Wied. Ann. 

 47. 399. (1892). 



4) Feustel, Dmde's Ann. 16. öl. (1905); Forgh, ibid. 17. 744. (1905). 



