116 Ferguson and Merwin — The Ternary System. 



must be a maximum on the line 8, 9, at B although due to 

 the slight temperature gradient we have been unable to 

 detect It. The field B, 9, 11, C is the field of the solid 

 solution D and the field B, 8, 10, C is the field of the solid 

 solutions with compositions on the line DM. The exact 

 liquidus-solidus relations cannot be determined because 

 of the difficulties inherent in the microscopic examination 

 of these solutions. The decomposition temperatures 

 along DM are evidently all lower than the temperature at 

 D but one cannot say if they change gradually from D to 

 M or if they pass through a minimum between D and M. 

 If a minimum is present then the point 10 represents a 

 glass which can coexist with a solid solution of an 



Fig. 14. 



Fig. 14. — An enlargement of that part of the diagram given in fig. 8 

 which deals with the monticellite solid solutions with some additions 

 designed to aid in the discussion of these solid solutions. 



intermediate composition to D and M. If a minimum 

 is not present this may or may not be the case and the 

 pure compound may be stable in the presence of the glass 

 10. Our inability to prepare the pure compound cannot 

 be reconciled to this latter theoretical possibility and it 

 would therefore appear reasonably certain that the glass 

 10 corresponds to a solid solution with a composition 

 intermediate with D and M. The crystallization of a 

 glass M of the composition CaO.MgO.Si0 2 would be: 



1. Liquid. 



2. Magnesia and liquid. The liquid composition varies 

 from M to E along ME. 



3. Magnesia, a2CaO.Si0 2 and liquid. The liquid com- 

 position follows the line E 10 to 10. 



