( 540 ) 



point. Ill llie pai'tinilai' case that the compound was perfectly pure, 

 liquid and \aponr sliould appear both together at the boiling point. 

 This may be made plain by tiie example of I Clj. Tlie whole 

 <, .x'-tigure at 1 atm. is schematically represented by tig. 7. 



'..J. 



a, JCL X 



/? a. 



Fiff. 7. 



Fig. 8. 



in which A, represents the temperature (64) in question. In tiie ditferent 

 regions (t represents vapour and L liquid. The further parts of the 

 tigure are entirely dominated in tluur relative situation by that of 

 the three-phase lines. On this entirely depends which branches of a 

 particular three-phase line will be intersected at the same pressure. 

 In tig. 1 (previous communication) a simultaneous intersection of the 

 brandies \ti and \h is only possible on the three-phase line of the 

 compound. If, however, as with ICI3, the melting point 7^ lies at a 

 high pressure, a simultaneous intersection of \h with 2 or 3 is 

 possible. This is why in Fig. 7, besides the boiling point t.^ on branch 

 2, ^1 also occurs as boiling point on branch \h. 



The pressure of 1 atm. is also higher for I CI or I than their 

 three-phase line, consequently for these compositions, melting and 

 boiling phenomena occur quite separately and the melting point lines 

 of ICl and I run quite below the boiling point line. 



If we take a pressure somewhat lower than 100 mm. we obtain 

 a ^, ,y-tigure fS. Fur ICl., we now liave again ^i as boiling point 

 on brancii \l) and /., as Imijinn- poiiil (in branch o. For 1 CI, melting 

 iind boiling are still quite distinct but at a pressure below 100 nun. 



