( 268 ) 



If we now take the simplest case, the stable unary melting equili- 

 brium will be lowered in temperature bj addition of S,j, so that 

 lines can be diawn over the melting-point surface and oxer the mixed 

 crystal surface of >S'j/, starting from 4 I'esp. from S^, which indicate 

 the liquid and solid phases which coexist with internal equilibrium 

 between Sr and Sm on increase of the Sy. -content. The same thing 

 holds for the metastable unary melting-point equilibrium. Here too 

 we get two lines starting from /^ and *Si, which traverse the meta- 

 stable part of the melting-|)oint surface resp. mixed crystal surface 

 of Sr. And finally we get something of the same kind for the 

 transition eqnilibrium. If this too is lowered by addition of Sy. , 

 lines will start from the points ;S'/ and ,S'./, which traverse tiie mixed 

 crystal surfaces of Sr and S^/ . 



If we now consider the case that there is alwiiys internal ecpiili- 

 brium between S],t and Sy, and that Sr behaves as a true component 

 or in otiier words is not converted, we assume here that also the 

 unary melting-point equilibrium indicated by the points /, and S^, is 

 lowered by addition of ;S7;, so that lines will start from these points 

 /j and -S', running over the melting-point surface and the mixed 

 crystal surface of S,]/. 



At the point where the liquid lines starting from /, and I^, meet, 

 we shall have a solidifying liquid, in which the three pseudo- 

 components are in internal equilibrium with each other, so that this 

 point indicated by L in the drawing, is the liquid point of the stable 

 unary pseudo-ternary melting-point equilibrium while the point of 

 intersection of the lines starting from S, and /S'3, gives the mono- 

 clinic sulphur, which is in internal equilibrium and coexists with the 

 liquid L at the unary melting-point temperature. This point is denoted 

 by S. 



We find in the same way that L' and S' denote the liquid and 

 the solid phase, which are in equilibrium with each other in the 

 metastable unary melting point of the rhombic sulphur. 



In the same way as the line for the infernal equilibria which exist 

 in the liquid phase at higher temperatures starts from L, the line 

 for the internal equilibria in the solid monoclinic sulphur starts in 

 S, and this line runs to smaller concentrations of Sy with fall of 

 temperature. The same holds for the line for the metastable internal 

 equilibria in the solid rhombic sulphur, which starts from S'. 



When a meeting of tliese lines and the transition surfaces takes 

 place, as drawn here, this means that a point of transition occurs 

 in the unary pseudo ternary system. The monoclinic mixed crystal 

 phase Sj is converted into the rhombic mixed crystal phase S;,, with 



