334 P. Eskola — Silicates of Strontium and Barium. 



match those of two or more members in the set of refrac- 

 tive liquids. The dispersions of the whole series of 

 liquids used having been determined and expressed 

 graphically, it now remains simply to locate, on the dia- 

 gram, the points determined and to read the refractive 

 index for any wave-length desired. The values obtained 

 in favorable substances are dependable in the third deci- 

 mal place, provided due care is taken for variations in the 

 temperature. 



In the present work the indices of refraction are given 

 for. four wave-lengths corresponding with the spectral 

 line F(a = 486/*/*), T1(A = 535^),- D( = 589^) and 

 C(A = 656/*/*). Jn the actual determinations wave- 

 lengths between 500 and 625 were commonly used, there- 

 fore the values for F and C may sometimes have an 

 uncertainty of ± 0.001 or a little more, due to enlarge- 

 ment of the errors in extrapolation. 



The System SrO-Si0 2 . 



The results of a thermal study of this system are given 

 in table I. 



Table I. 



Composition 



* 



wt. per 



cent 



Temperature Time Eesulting phases 



SrO 



Si0 2 



°C. minutes 



Liquidus of eristobalite 



40 



60 



1636 15 Glass 



40 



60 



1600 60 Glass and eristobalite 

 ■Eutectic tridymite-SrSi0 3 



53.82 



46.18 



1368 ... 30 Glass 



53.82 



46.18 



1361 60 - Glass and a little tridymite 



53.82 



46.18 



1356 60 Tridymite, SrO.Si0 2 , trace of 

 . glass 



50 



50 



1363 25 SrO.Si0 2 and glass 

 Liquidus. of SrO.SiO, 



50 



50 



1430 30 Glass 



50 



50 



1420 60 Glass and SrO.SiOo 



60 



40 



1571 60 Glass 



60 



40 



1552 45 Glass and SrO.SiO, 

 Melting point of SrO.Si0 2 



63.22 



36.78a 



1584 15 Glass 



63.22 



36.78 



1580 ' 15 SrO.Si0 2 and glass 



63.22 



36.78 



1575 15 SrO.SiO, only 



