803 



within an angle smaller tlian 180°. The coexistences between 

 immediately following four-phase lines have been omitted for the 

 sake of clearness. 



If we know the situation of the five phases in the plane of con- 

 centration, it is easy to construct the subjoined P-T figures. The 

 five points can namely lie in three different ways : they can form a 

 triangle with two points inside, a quadrangle with one point inside 

 it, or a pentagon. 



These three cases correspond resp. with the figures 8, 9, and 10. 

 For the first case the figure is e.g. constructed in the following way. 

 We consider a certain division of the triangle in three phase 

 regions; this situation is then possible in one angle at the quin- 

 tuple point. If we now pass round the quintuple point it is possible 

 that by the side of three of the coexisting phases a fourth exists. 

 This fourth phase can lie inside or outside the three-phase coexistence 

 in question. We then get either a quadrangle, of which the four 



phases can exist simultaneously, or a triangle with a point inside 

 it. which are all at the same time stable. If we take a definite 



