Rankin and Wright — Ternary System CaO-Al 2 O z -Si0 2 . 23 



ary diagram. These quadruple points are the starting points 

 of the boundary curves which enter the triangle from the sides, 

 but nothing definite as to the course of these boundary curves 

 can be predicted from the binary systems, except that the 

 direction of falling temperature will be from the sides of the 

 triangle toward the interior. 



However, it is of great assistance in locating these boundary 

 curves to know their starting points ; to know that they limit 



3Ca02S.0 2 

 2CaO.S.O, 



3C«O.SiO. 



3Ca0>l z 0, 



Fig. 5. Composition of binary compounds and quadruple points pro- 

 jected on the ternary diagram. 



in certain directions the fields of stability for those compounds 

 which occur as primary phase both in the binary and ternary 

 systems and that for each of these fields there will be two such 

 boundary curves. If these two boundary curves start, one 

 from either side of the composition of a compound, then that 

 compound is stable at its melting point and its composition lies 

 inside the field within which it is the primary phase. Such 

 stable binary compounds are the following : CaO. Si0 2 ; 2CaO. 

 Si0 2 ; 5Ca6. 3A1 2 3 ; CaO. A1 2 3 ; 3Ca0.5Al 2 3 ; A1 2 3 . Si0 2 ; 

 the three components behave likewise. If, on the other hand, 

 the starting points of both boundary curves are on the same 



