( 184 ) 



to say a few words about it in connection with the appearance of 

 retrograde solidification. 



If in fig. 3 tlie ^M/'-loop 

 cIckeR represents tlie liquids 

 and \'ai)Ours which may 

 coexist at a given lenipera- 

 tnre, but of which a series 

 of liquids and vapours are 

 not lo be realized in a stable 

 stale because of tlie ai)pear- 

 ance of the threephase pres- 

 sure curve ^), then several 

 cases are possii)lc. If the 

 threephase pressure curve, 

 as drawn in fig. 4 lies above 

 the critical [)oint of contact 

 y" R, then no retrograde con- 

 densation will occur, not- 

 withstanding its possibility is 

 strongly i)ronounced in the 

 character of llie />-/'-h)op, because the part giving rise to the retrograde 

 condensation lies in tlio nietastable region. Now this occurs in the 

 system ether-anlhracpiinone from 247° to 26()\ 



The dotted vapour and liquid curves below (he liireephase-pressure 

 curve ecf are nietastable; the stable state here is solid B by the 

 side of a fluid phase, and now tlie question was raised: "how is 

 this part of the isotherm of solubility situated?" Evidently this stable 

 curve must lie left of the nietastable curve dRe or in other 

 words towards smaller j5-conceiit rations. This conclusion is of great 

 importance for us, for from it follo\vs that, if the thrcephase-pre.ssiu'e- 

 cun-e lies above the critical point of contact of the vapour curve 

 coe.vistim/ ivitlt liquid and for that reason the retrotjrade condensation 

 falls in tlie Nietastable re^/ion, retrograde solidification nmst occur 

 instead of retrograde condensation, and this retrograde solidification 

 must be stronger than the retrograde condensati(^n would have been. 

 If the threephase-pressurecurve passes exactly through the critical 

 point of contact, retrograde solidification is no longer necessary. 

 Resuming, we conclude that, given the case that the plaitpoint- 



1) I propose to give this name to the curve that in a 2>''section denotes llie 

 pressure at which the three |)hases coexist. This curve refers therefore to one 

 temperature, wliilst the threepJiasecurve emhraces a series of temperatures. 



