( 327 ) 



shaped border-curves of the mixtures which touch the plaitpoint 

 curve in the plaitpoint. In the critical point of contact the tangent 

 is parallel to the p-axis. 



In this figure I have also drawn the vapour-pressure curve 

 of pure carbonic acid, as determined bj- Amagat i). By con- 

 necting the plaitpoints with the critical point of carbonic acid : 

 < = 31°,35, /) =: 72,9 atm., we obtain a part of the plaitpoint curve. 

 This plaitpoint curve rises steeply. It is probable that it also rises 

 steeply from the critical point of hydrogen: t = — 234°,5, p = 20 

 atm. 2). 



The course of the plaitpoint curve found thus agrees with Kundt's^) 

 observations on the influence of the pressure of compressed hydrogen 

 on the surface-tension of liquids in contact with it, if they are 

 understood as van Eldik *) has explained in his doctor-paper. Van 

 Eldik points out that the pressure at which the surface-tension 

 would become zero is the plaitpoint pressure which corresponds to 

 the temperature of observation. Moreover he has investigated the 

 law of the surface-tension as a function of the pressure. He con- 

 cludes that the plaitpoint pressure for hydrogen and ether at the 

 ordinary temperature would be no less than 750 atm , from which 

 follows a steep rising of the plaitpoint curve for ether and hydrogen 

 on the etherside. 



The experiments communicated in this paper are not the first 

 that have been made on the critical phenomena in mixtures of hy- 

 drogen and carbonic acid. Cailletet '") has made experiments with 

 a mixture containing about 5 mol. of CO^ on 1 mol. of H^. They 

 were undertaken in order to show, with a view to Jamin's expla- 

 nation of the critical phenomena, that by increase of hydrogen-pres- 

 sure the carbonic acid is bound to disappear. Cailletet has found 

 that this really occurred and this at a higher pressure as the tem- 

 perature was lower; for instance at 245 atm. at 15°, and at 153 

 atm. at 25°. But when we have to construct the border-curves and 

 the plaitpoint-curve we can set no value upon these observations, 

 as Cailletet did not secure the equilibrium of the phases by 

 stirring ; and only since Kuenes '^) has avoided the appearing of 



') Coiuptes rendus, 114, p. 1Ü'J3, 1893. 



*) See Olszewski, VVied. Ann., 56, p. 183, 1893. 



■') Ber. d. Kön. .\cad. v. Wiss. Berlin, il Oct. 1880. 



^) Van Eldik, Dissertation, Leideu 1S98. Communie. Leiden N». 39. 



') Comptes rendus, 96, p. 1448, 1883. 



"j KuENLN, Dissertation, Leiden 1892. Communie. Leiden N". 4. 



