P. Eskola — Silicates of Strontium and Barium. 371 



form a double compound CaCl 2 .BaCl 2 which shows an 

 incongTuent melting, breaking np into crystals of BaCL, 

 and liquid. These relations are in all particulars, except 

 in the molecular proportion of the double compound, 

 strictly analogous to those of a-CaO.Si0 2 to the metasili- 

 cates of strontium and barium. 



In the lime-silica system there occur the basic silicates 

 3CaO.SiO L , and 3Ca0.2Si0 2 the analogs of which were not 

 found in the systems strontia-silica or baryta-silica. The 

 last-named system, on the other hand, is the only one in 

 which occur silicates more acid than the meta silicate, 

 namely, 2Ba0.3Si0 2 and Ba0.2Si0 2 . Among the alkali 

 metals, in a similar way, the one having the lowest atomic 

 weight (lithium) forms the most basic silicates and those 

 with higher atomic weights (potassium, etc.) more acid 

 silicates. 



Summary. 



Fig. 17 gives a synoptical view of the melting diagrams 

 for the three binary systems CaO-Si0 2 , SrO-Si0 2 , and 

 BaO-Si0 2 . To make the diagrams really comparable 

 they are all expressed in terms of molecular percentages. 



The compositions and melting or decomposition points 

 of the compounds and eutectics, etc. in the three systems 

 are listed in table XI. Table XII gives all the impor- 

 tant properties determined for the strontium and barium 

 silicates. 



In the svstem SrO-SiOo the following compounds were 

 found: SrO, 2SrO.Si0 2 ,~SrO.Si0 2 and Si0 2 . With the 

 exception of silica each of them was found in one form 

 only, although the temperature of formation of the 

 strontium silicates was varied from the melting points 

 down to about 900°. 



Especial interest was taken in the strontium metasili- 

 cate, SrO.Si0 2 , which was found to be closely isomor- 

 phous and optically very similar to a-CaO.Si0 2 . It there- 

 fore probably belongs to the monoclinic crystal system, 

 but its crystals agree so closely with the hexagonal 

 system that, judging only from its own properties, it 

 would seem to belong to this system. The crystals are 

 apparently hemimorphic and might belong to the dihexa- 

 gonal pyramidal or, if they are monoclinic, to the mono- 

 clinic domatic class. 



