( 497 ) 



We shall conclude with ^oiuc i-cmnrks on the determination of 

 tli(> |)hiit|)oinl- or critical IcmpcfaluiHv 



As is known, the critical pliononuMion for binary inixliii'es can 

 only he observed, when before the region L-\-(l is left, tliere is 

 exactly tlie same (|iiatitily of li(|iiid as of xapoiii', or in otluM- xNords, 

 when tlie \-oliinie is exactly tlie same as (he plaitpoint xobime (sco 

 tig. 4). In this case we enter the j;as region at the [)lait|)oinl /'. In 

 general every concentration requires then another volume If the volume 

 is greater or smaller than the |)lait|)oint volume, we do not observe 

 a critical [dienomenon. In the first case we come to the gas branch 

 of the binodal curve, and conse(|uently total evaporation of the li(iuid 

 takes place when the temperature rises slowly; the liquid mass 

 decreases more and more and disapj)ears in the lower part of the 

 tube. In the second case we reach the li(piid bi-anch of the binodal 

 curve and the whole tube is finally filled with liquid. 



A sudden transition from the region L-\-(t into the gas region, 

 in consequence of the fact that the liquid and the gas phase become 

 identical is only observed for a xolume e(pial to the plaitpoint volume, 

 also when the temperature rises Aery slowly. Yet for other volumes 

 phenomena may be observed, closely resendiling the critical ones, 

 but this is oidy to be attrilmted to the fact that the temperature rises 

 too quickly for the equilibrium to be established. 



For a simple substance the plaitpoint temj)erature is the highest, 

 but this is not the case for binary mixtures. The highest temperature 

 for a binary system will be observed foi- the volume of the critical 

 tangent /?, so for a volume lai-gei- than the plaitpoint volume (see 

 tig. 4). For still larger volumes the litpiid will again disappear at 

 lower temperatures, so that from the plaitpoint volume to larger 

 volumes the temperature, at which all the liquid has disappeared, 

 and which we might also call condensation temperature, passes 

 through a maximum value. If the volume is smaller than the plait- 

 point volume, the tube is completely filled with liquid, but the tem- 

 perature at which this takes place, is always lower than the plait- 

 point temperature. 



Amsti'rdam, Dec. 1003. 



Chemical Laboratorv of the University. 



