332 P. Eskola — Silicates of Strontium and Barium. 



carried out thermal investigations by the cooling curve 

 method on the binary systems of the metasilicates of 

 sodium and lithium with those of strontium and barium. 

 He gives the melting point of SrSi0 3 , 1529° and of 

 BaSi0 3 , 1490°. All his melting diagrams resulted in the 

 type of complete solid solutions with a minimum. 

 P. Lebedew, 3 for the system BaSi0 3 -CaSi0 3 , also found a 

 melting curve of the complete solid solution type with the 

 melting point of BaSi0 3 at 1438° and a minimum at about 

 1000°. Smolensky, 4 who studied the system BaSiO.- 

 BaTi0 3 , found the melting point of BaSi0 3 at 1470°. 



All these results were obtained by the cooling-curve 

 method, using carbon crucibles and porcelain tubes to 

 protect the thermo-elements. No quantitative optical or 

 other physical diagnostics for the crystalline phases were 

 given. In the absence of such characteristics, and in 

 view of the poor agreement of the results, the melting 

 diagrams merely based upon cooling curves are subject 

 to large corrections and often entirely erroneous. The 

 melting point determinations are, in fact, all considerably 

 too low. 



Very accurate determinations were carried out by 

 Jaeger and Van Klooster, 5 who found the melting point of 

 SrSi0 3 , 1578 ± 1°, and of BaSi0 3 , 1604 ± 0.5°. They, 

 also, emphasize the unreliability of the cooling-curve 

 method and illustrate this by experimental evidence. 

 They determined further some physical constants of the 

 compounds named. Their results will be mentioned 

 later. 



The entire field of the physical chemistry of the 

 strontium and barium silicates being open, the first task 

 was to investigate the two binary systems SrO-Si0 2 

 and BaO-Si0 2 . Among the further problems, those 

 regarding the relations of the metasilicates to the well- 

 known wollastonite minerals seemed to me most interest- 

 ing and were chosen for study. For still further com- 

 parison with corresponding calcium compounds I tried 

 to synthesize the strontium and barium compounds analo- 

 gous to two important lime silicate minerals, diopside 

 and anorthite. 



3 P. Lebedew, Z. anorg. Chem., 70, 301, 1911. 

 4 S. Smolensky, Z. anorg. Chem., 73, 293, 1912. 



5 F. M. Jaeger and H. S. Van Klooster, Proc. Kon. Akad. Amsterdam, 6, 

 XVIII, 896, 1915. 



