P. Eskola — Silicates of Strontium and Barium. 357 



14.45 



50.25 



35.30 



30 



70 



1270 



2CaO.BaO.3SiO, and glass 



14.45 



50.25 



35.30 



30 



70 



1268 



2CaO.Ba0.3Si0 2 and BaO. 

 Si0 2 



13.25 



52.04 



34.71 



27.5 



72.5 



1274 



Glass 



13.25 



52.04 



34.71 



27.5 



72.5 



1271 



Glass 



13.25 



52.04 



34.71 



27.5 



72.5 



1268 



2CaO.BaO.3SiO, and BaO. 

 Si0 2 



12.05 



53.83 



34.12 



25 



75 



1275 



BaO.SiO, and glass 



12.05 



53.83 



34.12 



25 



75 



1267 



BaO.SiO, and 2CaO.BaO. 

 3SiO, 



9.63 



57.42 



32.95 



20 



SO 



1267 



BaO.SiO, and 2CaO.BaO. 

 3SiO, 



. Liquidus of BaO.SiO, 



12.05 53.83 34.12 25 75 1300 Glass 



12.05 53.83 34.12 25 75 1292 Glass and BaO.SiO, 



9.63 57.42 32.95 20 80 1367 Glass and BaO.SiO, 



The melting diagram resulting from these facts is 

 given in fig. 12. 



The liquidus curve of a-CaO.Si0 2 was followed to 50 per 

 cent BaO.Si0 2 . The a-CaO.Si0 2 which always separated 

 in the form of thin crystals tabular parallel to the basal 

 plane did not seem to take any BaO.Si0 2 in solid solution, 

 as the crystals in all cases showed the indices of refrac- 

 tion characteristic of pure pseudowollastonite : <*(D) = 

 1.609 ± 0.002; y(D) =1.652 ± 0.002. 



Dicalcium barium silicate, 2CaO.Ba0.3Si0 2 . — When 

 the mixture composed of 50 per cent BaO.Si0 2 and 50 per 

 cent CaO.Si0 2 was allowed to crystallize on cooling, it 

 formed a coarsely crystalline, fibrous mass, almost like 

 natural wollastonite. The fibers were speckled with 

 minute crystals of another substance (BaO.Si0 2 ). 

 Supposing the fibrous crystals to have the composition 

 2CaO.Ba0.3Si0 2 I prepared such a mixture, which was 

 now found to crystallize as homogeneous crystals and on 

 heating to break up at 1320 ± 4° into a-CaSi0 2 and 

 liquid. 



The crystals are uniaxial and negative, probably hex- 

 agonal, and have good cleavages in their prismatic zone. 

 A crystallizing mass develops negatively elongated 

 fibers. 



The indices of refraction were determined as follows : 





0) 



c 



F ... 



;". 1.690 



1.678 



Tl ... 



.. 1.685 



1.672 



D ... 



.. 1.681 



1.668 



C ... 



.. 1.677 



1.664 



