Andersen — System Anorthite-Forsterite-Silica. 433 



temperatures below the melting point. The diagram in fig. 7 

 represents a case where the course of the boundary curve j o 

 is such that no tangent to this curve can be drawn through the 

 point D. The two-component system A-B contains the 

 unstable compound D. The relations of such a system have 



Fig. 7. 



> 



<r 



B 



D 



been explained before.* In all mixtures between j and A, in 

 this binary system, the compound D is decomposed on heating 

 at the temperature of the pointy'. The product of the decom- 

 position is A and liquid. The other binary systems of the 

 diagram fig. 7 are of the simple eutectic type. 



Qualities ofhoundary curve j o. — The only principal differ- 

 ence between the present ternary system and the preceding 



*P. 17. 



487, 1914. 



See also N. L. Bowen and Olaf Andersen, this Journal (4), xxxvii, 



