P. Eskola — Silicates of Strontium and Barium. 349 



The variation of the refractive indices in this solid 

 solution series appears from table III and from fig. 9. 



As may be seen from fig. 9, the indices of refraction, in 

 the series of crystals between Ba0.2Si0 2 and 2BaO. 



Fig. 9. 



T1650 



1.625 

 Kti 



Kd 

 fc 



Jfa 



(3d 



600 

 «n 



CXd 











>~~ 











' ><; 



/ 









^c 



__ 





/ y 









^< 







'/ / / 



x^~- 









/// 







y 



^ ^ 



''-;> 



// 





_ -« ' 







J 



__ __ _- ■ 



/■* 







1 





f. 



~~ • 



— - 1~"~~ / 



^^*^ 











/ 











y . 











y 





*^ > 



/ 









r> 





, ^ 













20 



100 Ba0-2St0g 



40 



Wt# 



60 



80 



100 



2BaO-3SiCfe 



Fig. 9. — Variation of the indices of refraction in the series of mix crystals 

 of barium disilicate and dibarium trisilicate. * 



3Si0 2 , change gradually along with the composition, and 

 all of them increase towards the latter end member, but 

 their intermediate relations and hence the optic axial 

 angles have rather complicated variations. 



