( "I ) 



represented in fig. 2 by the branches 7L1C' and OD, to the left of 



it — — <^ 0, to the right > 0. If in consequence we talve .1 as tlie 

 dx 



component with the lower critical temperature, in other words : if 



we put Tj ^ 1, there must be a minimum plaitpoint temperature 



when the second component lies in the area AGCABDHA ; in 



general this will again occur when the critical temperatures dift'er 



little, whereas the critical pressures difler much'). This does not 



prove, however, that there may not be other circumstances for which 



tlie plaitpoint temperature reaches a minimum. 



If on the other hand we take ^4 as a component witli the higlier 



critical temperature, there must be a maximum plaitpoint tem[)erature 



when the second component lies in the area OHK. ') Neither liere 



is it proved that the phenomenon is restricted to that area. 



9. The boundary between '^^ > and ''''''' < is formed bv the 



dx (I. I' 



curve 



T^ (3._1^^ _ 2tc' (ör-1) + 4c' = 0, 



represented in tig. 2 bv EAF; — -^ is negative wiihiii lluU line and 



dx 



positive beyond it. Whence follows that a minimum plaitijoiul pres- 

 sure is impossible, at least iillle prolial)le, while a maximum |plail- 

 poiut pressure must occur when the second component lies wilhin 

 the area ALEAFr OMA; this will therefore in general be the 

 case when the critical temperatures difler much, which is confirmed by 

 experiment. 



10. Finally, in order to show by means of an example that (he 

 suppositions whence we started in the main represent precisely the 



') Cf. also VAN Laar, loc. cit., p. öS5. 



-) This is again the same condition as for the existence of a minimum critical 



1 CdT^„i\ 1 dl'i 



temperature; but as -;— I '— = a + —; ((3 — 4z)-, — ~~ may be positive with 



J^ok\ dx yg lb dx 



negative x, in other words: a minimum plaitpoint temperature requires a minimum 



critical temperature, but not reversely. This may also be seen from fig. ^, where 



I have once more drawn the line GAH of fig. 1 (doited line). 



*) An instance of this is probably not to be found, 



