58 Buddington — Natural and Synthetic Melilites. 



plotted against the compositions, and curves are drawn 

 connecting mixtures which show equal birefringence. 

 The results are similar to those obtained in the case of 

 mixtures of 2CaO.Mg0.2Si0 2 , 2CaO.Al 9 3 .Si0 2 , and 

 3CaO.Al 2 3 .3Si0 2 . 



Fig. 8. 

 2 CaO-Al 2 3 -S0 2 



2 CaO*MgO*2SiO 



40 60 



WT. PERCENT 



90 [3CaO-Al 2 3 «3S0 2 ] 

 10 [3Na 2 0-Al 2 3 -3S0 2 ] 



8. — Triangular concentration diagram showing the compositions of 

 preparations investigated. Lines connecting similar indices of refraction 

 have been plotted for those mixtures which show complete homogeneity 

 within a definite temperature range above 980° (the lowest temperature of 

 experiments). Lines of equal birefringence also plotted. 



Mixttjkes of 10 Percent 3Na 2 O.Al 2 3 .3Si0 2 with Vary- 

 ing Amounts of 3CaO.Fe 2 3 .3Si0 2 , 3CaO.Al 2 3 .3Si0 2 , and 

 2CaO.Mg0.2Si0 2 . 



Mixtures made up by maintaining the compound 

 3Na 2 O.Al 2 3 .3Si0 2 at a constant ratio of 10 percent and 

 varying the percentages of 3CaO.Fe 2 3 .3SiOo, 3CaO. 

 Al 2 3 .3Si0 2 , and 2CaO.Mg0.2Si0 2 gave a very limited 



