P. Eskola — Silicates of Strontium and Barium. 335 



65 



35 



65 



35 



65 



35 



67 



33 



67 



33 



67 



33 



72 



28 



77.46 



22.54& 



o- — 



SrO.SiO, 



h — 



2SrO.Si6 2 



Eutectic SrO.Si0 2 -2SrO.Si0 2 * 

 1554 15 Glass 



1546 30 Glass and SrO.SiO. 



1538 15 SrO.Si0 2 and 2SrO.SiO, 



1544 15 SrO.Si0 2 and 2SrO.SiOo 



Liquidus of 2SrO.Si0 2 

 1617 15 Glass 



1600 15 Glass and 2SrO.Si0 2 



1628 15 Glass and 2SrO.SiO, 



1634 5 Sr 2 SiO, only 



The equilibrium diagram (fig. 1) is based on the above 

 results ; the melting point of cristobalite has been placed 

 at 1710°, according to the determinations of Ferguson 

 and Merwin, 7 and the inversion point cristobalite-tridy- 

 mite at 1470° according to Fenner. 8 . 



The liquidus curve of the silica minerals has the same 

 general shape as formerly found in all the other binary 

 systems with silica as one component : starting from the 

 eutectic point first a very steep rise a little above 1600°. 



The eutectic tridymite-SrO.Si0 2 . — I prepared inciden- 

 tally a mixture of 46.18 per cent SrO and 53.82 per cent 

 Si0 2 , corresponding to the proportion Sr0.2Si0 2 , to find 

 out whether there was any disilicate of strontium, analo- 

 gous to the barium disilicate known formerly. The 

 result was negative, and this happened to be almost 

 exactly the eutectic composition. The tridymite liquidus 

 lying only about five degrees above the solidus, the 

 eutectic composition can be located with a fair degree of 

 accuracy at 46.5 per cent SrO and 53.5 per cent Si0 2 . 

 The temperature is 1358 ± 4°. 



Strontium metasiiicate, SrO.Si0 2 . — Strontium metasili- 

 cate was found in only one form which shows a very close 

 resemblance to a-CaSi0 3 , or pseudowollastonite. Its 

 melting point was determined as 1580 ± 4°, in agreement 

 with Jaeger and Van Klooster's result, 1578 =1= 1°. It is 

 apparently of dihexagonal pyramidal symmetry, uniaxial 

 and positive, and its characteristic habit is thick-tabular 

 .parallel to (0001). There is a fairly good basal cleavage. 



7 J. B. Ferguson and H. E. j&erwin, this Journal, 46, 417, 1918. 



8 C. N. Fenner, this Journal, 36, 337, 1913. 



