( 409 ) 



If one of tliem has reinaineil, the Ciii-lher siihliiiuilion lakes i>hu'e 

 at a ('OJistantly iiiereasiji;»' teniperatiire until the jioint of tlie line 

 F J'J or (>' /-J is reached, wliich cori-esponds witji the original eon- 

 centralioii of the mixture. 



The wliole tigure is quite analogous with that representing the 

 solidilieation or fusion of binary mixtures in whieli only the two 

 components occur as solid phases, J'J F am] HE resemble the mel- 

 ting point lines, E the eutectie poiiit. 



The analogy also holds good for the initial parts of the sublimation 

 lilies, for whose direction a formula similar to that for the loweriii"- 

 of the melting point may be deduced. 



For the equilibrium of a single solid substance with its vapour 

 we have the relation 



<:llp__Q_ 

 dt ^2P 



which is true for the increase of the sublimation pressure, when 



Q represents the molecular heat of evaporation of the solid substance. 



If \\-Q now assume that a small part of this line is straight and 



that Q is constant, then if the pressure^; is diminished by A p =z 0.01 n 



the sublimation temperature will diminish by L T, for ^vhich we tlnd : 



Q Lp 

 ^r X— ^ = — = 0.01 



02 T' 

 LT ^ 



Q 



If we now add to the vapour of the solid substance, which has 

 at T — L T a pressure j) — 0.01/), 1 inol. % of the vapour of a 

 second substance, the total ])ressure again becomes j) and 7' — L T 

 is therefore, at that })ressure, the sublimation temperature of the 

 solid substance with 1 mol. "/„ of admixture. Consequently A T is 

 also the lowering of that sublimation temperature by 1 mol. "/„ of 

 admixture. 



The formula for the decrease therefore corresponds perfectly with 

 that for the molecular lowering of the freezing point, provided that 

 we take for Q the molecular heat of sublimation. 



The formula, however, only applies in the case of exceedingly 

 small quantities of admixture, as the supposition that thej>,Mine for 

 the equilibrium of a single solid substance with its vapour is a 

 straight one, is incorrect. 



If we take into consideration its curvature, it follows that the 

 sublimation lines of each solid substance of the mixture are concave 

 to the .t;-axis. 



