( ^-(^ ) 



coiTesponding willi tlic outcclic tompenitiirc, deiioted In /^ in tlio 

 /*,7'-projection, we gel \vlia( is i'epreseiik'il in liu'. 2. 'l'lic Iwo iIut'C 

 phase pressure lines Sa + ^'' + ^^ 'i'"' '"^^ + ^- + ^' l"^^'*' ''•^♦'' 

 descended, llie former, however, sironger than the inlter, and Ihov 

 have (inally coincided. 



The two solubilitv i.sotiiernis intersect besides in the nnslable region, 

 also in the points G and L. While the point of intersection (r indi- 

 cates tiie possil)ilily of a coexistence of ,S'i -|- S/i ~\- (r, tiie second 

 point of intersection Ij indicates the jjOssibiUly of a coexistence of 

 ,S'.j -|- *S'b + L, and when at a delinite teniperatnre, as is liie case 

 here the two points lie on the same j)ressüre line, this means that 

 at that teniperatnre the four phases Sa + <Sb + ^ + ^^ f*" coexist, 

 provided the pressure be equal to that indicated by tiie horizontal 

 line which joins the four coexisting states. At a higher pressure the 

 regions for Sa + -^ iind .S'.i -j- L are separated by the triangular 

 region for L. 



In order to get a clear idea of tiie form wiiicli the y>,r-section 

 assumes at a temperature /,, lying somewhat below the eutectic 

 temperature, it is necessary to draw the metastable branches of the 

 lines for ,SU + Lab + ^aij, Xoy Sb-}- Lad-\-Oab and for La + (-a . 

 as has been done in fig. 1. We see then, that the situation of the 

 fii'st two tiiree phase lines is Just the reverse of that of the stable 

 branches. For the stable branches that for ,S i + La/j + Gab lies, 

 namely, above that for S/j -{- Lab + ^''.i/;- for the metastable branches 

 the reverse is the case. If, taking this into consideration, we now 

 draw the pr-section corresponding with the temperature /,, we gel 

 fig. 4, from Avhich we see that the lirst point of intersection of 

 the two solubility isotherms lias moved upwards, and the second 

 downwards. The first point of intersection denotes, as has been 

 said, the coexistence of ^S'^i -|- Su -\- G, and the second the coexistence 

 Qt" ,S'^ +»'>'/;+ L\ at constant temperature these tliree phase e(iuilil»ria 

 are only possible at one pressure, because we haxe here a system 

 of two components, hence for pressures between tlie two |)oints of 

 intersection mentioned there must be change of the three phase 

 equilibria into a two phase system, where the two three phase 

 pressure lines form the limits of a new hen p/iuse nu/lon, viz. for 



SA-\-Sn. 



The second |)oint of intersection of the solubibty isotherms which 

 causes the occurrence of Ihe three phases N-i +>'/;+ /- hi'^^ 1'"^'''' 

 in agreement with the (hilted line traced in tlie /^ 7-projeclion for 

 the temperature t^ at a pressure beh)w that of liie supercooled liquid 

 of pure A. 



