P. Eskola — Silicates of Strontium and Barium. 359 



BaO.SiO,. I found in both cases «(D) = 1.683 ± 0.003; 

 e(D) = 1.669 ± 0.003. The results are not significantly 

 different from those of the pure compound. 



The invariant point CaO.Si0 2 -2CaO.Ba0.3Si0 2 -melt. — 

 In a mixture containing 50 per cent of CaO.Si0 2 and as 

 much BaO.Si0 2 the crystals of 2CaO.Ba0.3Si0 2 break up 

 into a-CaO.Si0 2 and liquid before melting entirely. In 

 another mixture with 47.5 per cent CaO.Si0 2 the last 

 crystals before complete melting consist of the double 

 compound. The invariant point therefore is between 

 these limits, and the course of both liquidus curves meet- 

 ing there indicates it to be at 52 per cent BaO.Si0 2 and 

 •48 per cent CaG.Si0 2 , with the temperature of complete 

 melting 1320 ± 4°. 



The liquidus of 2CaO.Ba0.3Si0 2 has, from the 

 invariant point, a regular course towards a eutectic. I 

 followed its course very closely, because it was suspected 

 that another double compound, CaO.Ba0.2Si0 2 , might 

 possibly form here, its composition corresponding to 

 35.26 weight per cent CaO.Si0 2 and 64.74 weight per cent 

 BaO.Si0 2 . But no such compound could be isolated, and 

 the corresponding mixture crystallized within an interval 

 of 32 : into a verv fine mixture of BaO.SiOo and 2CaO. 

 Ba0.3Si0 2 . 



The liquidus of BaO.Si0 2 was determined, with only a 

 few quenches, to have a steep course towards the high 

 melting point of the barium metasilicate. 



The crystals of this compound in melts containing 75 to 

 80 per cent BaO.Si0 2 were not equant grains as in the 

 system BaO.Si0 2 , but needle-like, sharp at both ends. 

 As they have formed at much' lower temperatures than 

 the crystals in BaO-SiO? melts, it may be possible that 

 they represent another form of BaO.Si0 2 . The refrac- 

 tive indices, however, so far as they could be determined, 

 were identical, and experiments carried out to establish 

 the transformation expected failed, even when minerali- 

 zers were applied (cf. p. 352). 



The Properties of the Glasses. 



The physical properties of representative glasses 

 studied in the present work are tabulated below. 



