P. Eskola — Silicates of Strontium and Barium. 363 







Table 



IX. 











Glasses in the 



system CaO.Si0 2 - 



-SrO.Si0 2 . 







;.% CaO.SiO, 



100 



87.5 



62.5 



43.75 



37.5 







;. % SrO.SiO., 







12.5 



37.5 



56.25 



62.5 



100 



n{¥) 



1.635 



1.634 



1.634 



1.636 



1.637 



1.640 



rc(Tl) 



1.631 



1.630 



1.630 



1.633 



1.632 



1.636 



n(D) 



1.628 



1.6265 



1.627 



1.628 



1.628 



1.632 



■n(C) 



1.625 



1.6245 



1.625 



1.625 



1.626 



1.629 



Table X. 



Glasses in the system CaO.Si0 2 -BaO.Si0 2 . 



Wt. % CaO.SiO, 100 75 60 50 40 25 



Wt. % BaO.SiO, 25 40 50 60 75 100a 



?i(F) 1.635 1.643 1.649 1.6525 1.658 1.6655 (1.681) 



n(Tl) 1.631 1.638 1.6435 1.647 1.653 1.6605 (1.675) 



n(D) 1.628 1.6345 1.6395 1.644 1.649 1.657 (1.672) 



?i(C) 1.625 1.6305 1.636 1.640 1.645 1.653 (1.668) 



Density 3.633 



a Extrapolated. 



Absence of Diopside Analogs. 



A few experiments were made to ascertain whether 

 strontium and barium metasilicates form double com- 

 pounds with magnesium metasilicate, analogous to diop- 

 side, the calcium compound, CaO.Mg0.2Si0 2 . Mixtures 

 corresponding to these proportions were prepared and 

 quenched from different temperatures. 



A mixture corresponding to SrO.Mg0.2Si0 2 gave only 

 glass at temperatures above 1320 and, at temperatures 

 down to about 1200°, glass and crystals that from their 

 optical properties may have consisted of clinoenstatite. 

 Another mixture of the composition 2SrO.Mg0.3Si0 2 

 gave SrO.Si0 2 as a primary phase. It therefore seems 

 that the metasilicates of strontium and magnesium do not 

 form any double compound at all. At any rate, there is 

 no compound SrO.Mg0.2Si0 2 , analogous to diopside. 



Furthermore, I made a mixture of 25 weight per cent 

 SrO.Mg0.2Si0 2 and 75 weight per cent CaO.Mg0.2Si0 2 , 

 heated it above 1400° and let it cool slowly. The product 

 contained diopside, showing a(D) = 1.665 ± 0.002; 

 /?(D) =1.675 ± 0.003; y(D) =1.695 ± 0.002 and 2V = 

 60°. These properties agree perfectly with those of 

 pure diopside and consequently the crystals do not 

 contain any strontium compound as isomorphous mix- 



Am. Jour. Sci. — Fifth Series, Vol. IV, No. 23. — November, 1922. 

 24 



