( 267 ) 



in the system Sm -f Su, wliieli equilibrium is indicated by tlie points 

 ƒ, (/, /, we see that the temperature of this three-phase equilibrium 

 is lowered by addition of Sr till the eutectic line cy„ is reached. 

 At this meeting the liquid layers are also saturate with regard to 

 the rhombic mixed ci'ystal phase, and a four phase equihbrium 

 invariant at constant pressure occurs between the two mixed crystal 

 phases /\ and /\, and the two liquid layers g^ and h^. It is clear 

 that we get the same four phase equilibrium starting from the three 

 phase equilibrium between ihe rhombic mixed crystal phase and 

 the two liquid layers in the plane for Sr -\- Sy. indicated by f\gih^ 

 and so we see that the eutectic line which meets the region ofnon- 

 miscibility at (/^, skips to h^, from where it pursues its course to the 

 ternary eutectic point indicated by /g. 



After this explanation we can proceed to the discussion of the 

 lines for the different internal equilibria. 



The line kL^ in the plane for Sr -\- Sj/ indicates the internal liquid 

 equilibria in this pseudo-binary system ; 4 and S.^ are the liquid and 

 solid phases which coexist at the unary meltingpoint temperature ; 

 from S.^ starts the line for the solid internal equilibria, which meets 

 the mixed crystal line of the pseudobinary system in *SV, so that at 

 this place the transition point in the system Sr -}- Sm occurs with 

 unary behaviour. Then >S/ is formed by the side of S^', and below 

 the transition temperature the solid phase, which is in internal equi- 

 librium, moves along the line S/Sq. 



So it is supposed here that in the pseudo-binary sj^stem Sr -j- Sm 

 a point of transition occurs, but not between the pure pseudo- 

 components, but between two mixed crystal phases, one of which 

 is rhombic and the other monoclinic. 



Before we proceed it may be pointed out here that the points 

 /j and >Si represent the metastable unary melting-point, and that, 

 as was mentioned before, the line for the internal equilibria in the 

 rhombic moditication, which does not become stable until below the 

 transition point, starts from /S'l. 



In the other two pseudo-binary mixtures the liquid and solid 

 phases which are in internal equilibrium are also indicated, but 

 transition points need not be assumed in these systems. 



The question which called for a solution tirst of all was this: 

 "what shall w^e get when to the system Sr + S^J, which is thought 

 to be continually in internal equilibrium we add Su, of which substance 

 we suppose for a moment that it cannot be converted to rhombic 

 or monoclinic sulphur, and wdiich, accordingly, behaves as a real 

 component. 



