r 230 ) 



Physics. — "'TJit' ff/iii/ihriinn hctirctni a solid bod;/ and a jïnld 

 Il/ut SI', i'sjiecuillij UI till' iwii/h/joni'/wod of tlw critical state." 

 \\\ l'iof. .1. D. VAN i)i:i{ Waai,s. 



After tlic piihlk'iUiüJi of the experiiiieiils of Dr. A. Smits in the 

 proceedings of the September meeting, cnmmiiiiicated hy l'rof. IIakiiiis 

 Roozeboo:m, I had a (hscnssioii with the laller cliiclly on liie (piestion 

 if and in wiiat wav the licpnd eipiilihrinms and the gas cqnilihrinnis 

 wliich may exist hy tiie side of a soüd phase, must l)e tiionglit to 

 be connected by a theoretic ciirxe at given temperatnre, in conse- 

 cjnence of the continuity betuceii U(|iiid and gas. It is in agreement 

 willi tlie wisli of Prof. Hakihis Roozehoom, that I cominunicate the 

 foUowing ol)ser\ations. 



liCt us imagine the x|*-surface of a binary nii.xlure, anlhrai|uinone 

 and etiier, in which we Avili call ether tiie second substance, at a 

 temperature sliglitly above Tk for clher. Then there is a liquid- 

 vapour plait, closed on tlie side for ether. 



Let us add the if>cnrve or the tf'-surface foi- the solid state, 

 tlie if'-curve \\ hen the solid state has an inxariable concentration. 

 If only |>nre anthraqninoiie sliouhl be possible in the solid state, 

 this i|--curve would lie in the surface for wliich .*• = (). For the sake 

 of perspicuity we shall start from this hypothesis in our first descrip- 

 tion. Then we lind the jdiases wliicii coexist with the solid anthra- 

 (piinone, by rolling a j)lane over the U"-surface and the conjugate 

 \V-v\\v\v. 



( )n account of llic slight conqtressibility of the solid body, we 

 can describe a cone, indcss tiie pressure be excessively high. This 

 surface enables us to lind the coexisting phases; its vertex lies viz. 

 in the point ,/=(), /=/•,, and i|-3=i|',, if I's represents the molecidar 

 volume of the solid anthraipiinone and i|'^. tlie value of the free 

 energy, both at the temperature considered. The cnrve of contact 

 of this cone and the V'-^'ii"ti^(*c re[)resents then the coexisting phases. 

 For shortness' sake we Avill use for it the name of contact-curve, 

 thougli it is properly speaking also a connodal cnrve on the if'-surface 

 of tlie binary mixture having its second or conjugate branch on the 

 i|*-surface of the solid state. 



INow^ we can have three cases for the course of this contact-curve, 

 'i^t . It may remain wholly outside the li(|nid-vapour-plait, and will 

 form then a perfectly continuous curve. 2"^'. It may pass through 

 that plait, in which case one [lart of this curve will represent gas 

 phases aii<l aiiolhcr li(|nid phases, wliich Iwit pans \\ ill be connected 

 by a tliii-(l pari lying bclwecii llic two branches of ihc connodal 



