( 47. s ) 



The followiiiü- iij;i\ Ik' ;i<Me<i iii fiii-llior o\|>l;iii;\tioii : tlioie is a 

 well «lelinod coiili-ast henvceii llie Iwo jdails as i-('Liai*<Is the cansos 

 (if Iheii- ('xisleiMV. The ci'oss-plail (h'|>«'ii(ls hu' il> exisleiice on the 

 shape <>t' the «('-curves \\tv ihe scjiarale hoiiioueiieoiis niixlures. the 

 liqiiid-plait on the olhei- hand is (hie lo liie manner in whieh these 

 riirxes chanu-e with tlu» composition. In the formation of the hitter 

 idail association se<Mns to l>e the principal factor. Ihit iiotw ilhsiaii(hnu- 

 this (Hstinct contrast there must he a nnndier (»f cases in w liich it 

 ^^ill he impossilile to sav w hicii kind of |)lail one is dealinu' NNilh 

 and t(» which sort of |dait a Liiven plaitpoijil Ixdoiiiis. We shall 

 presenth come across a strikimi' instance <d' this kind where a 

 ci-oss-plait with its |ilail|>oint üiadnallv chaiiLi-es into a jilail with its 

 piaitpoini turned towards the ./•-a\i> fiom which it is impos.^ijilc to 

 withhold the name litpnd-plate. 



Let Us no\N consider the case of meth\ lalcoh(»l and ethane. 

 Before commuincaliiiLi the new resull> I will discn>s Prof, vw i)i:i{ 

 \Va.vi>'s views of these mixture^, lie assumes that the critical curxc 

 is aiiain a continnons (»ne hut with a loop lurne*! upwards this time 

 instead of downwards a> with the luLiher term>. ' There are some 

 >erious ohjectioirs to this llieorv. 



The critical curve, startini:- at the critical |)oinl of ethane (\, 

 disappears from the practical |iart of the surface at A. as in the 

 former ca<e. and the pari hevoud can therefor*' oidv represent a 

 Iheorelical jdaitpoim which remain> hidden, hecause at hi.Liher tem- 

 peratures no three phases coexist. l*n'Voud A the cur\(' should there- 

 foi-e he dotted throuLihout . and it cannot he interprele<l as in pait 

 i-,>al. In this ca>e as in the (»lher the shape of the curxc was 

 declnced h\ keepinu' in \ iew lh<' homoiieneoiis critical point and a 

 slrikiuLi' instance is alforded of how this curve does iiot Liixe us 

 an\ clue as to the shape of the i-eal critical curve. 



In the second jdace 1 thiidc the hendinü" npwai-<ls of the critical 

 cur\<' assumed in this case is open !<• flouht. At somewhat hiizh 

 Iemj»eratures theiv is prohahlv no ahnormalit v on the surface and 

 no jdait except the cross-jilait : as the temperature falls a closed 

 curve develops one of whose plaitpoints pierces the main |)lail at 

 .1 and moves from there towards ( ^. As in the othei- ndxlures the 

 three-phase pressure is lower than the \apour pressure of ethane: 

 it follows that the snhsidiary plait[toint is turned towards the .r-axis 

 and represents a maxininm |>i-essure on the closed |»lail. This heiny 

 s«( the simplest suppositioji to make is that the othei- piaitpoini (»1 



1) Comp. his <li;t^rain K.m. Ak. v. Wettuscli, Amst. March -J.jth. 1»9Ü p. 5. 



