Ferguson and Merwin — The Ternary System. 169 



A. Experiments with the Pseudowollastonite Solid Solutions. 



(1) A charge of composition CaO 49, SiO ? 51, was 

 heated some hours at 1450°C. No 3Ca0.2Si0 2 could 

 then be observed. 



(2) A charge of composition CaO 50, Si0 2 50, was 

 heated several hours at 1460 °C ; a small quantity of glass 

 was then visible. 



The pseudowollastonite solid solutions extend there- 

 fore to between the compositions CaO 49, Si0 2 51, and 

 CaO 50, Si0 2 50, and the latter composition may be taken 

 as the approximate limit. This represents about 20 per 

 cent of the 3Ca0.2Si0 2 compound. 



B. Experiments with the Wollastonite Solid Solutions. 



Glasses with compositions ranging from pure wol- 

 lastonite to CaO 54, Si0 2 46, when crystallized at 

 temperatures below 1000 °C, usually contain little if any 

 pseudowollastonite, but even after prolonged heating at 

 temperatures just below the inversion temperatures 

 ( 1170-1200° C) are so fine-grained that positive identifi- 

 cation of the phases present is impossible. A charge 

 with the composition CaO 56, Si0 2 44, when crystallized 

 at low temperatures, was found to contain traces of cal- 

 cium orthosilicate which is here unstable, but no other 

 phases could be made out. These facts made necessary 

 a different method of attack than that of the crystalliza- 

 tion of the undercooled glasses, and for the purpose a 

 study of the inversion and decomposition temperatures 

 seemed the only feasible method. The following signi- 

 ficant experiments were made in this study. 



(1) Material — Composition CaO 51, Si0 2 49, fully 

 crystallized but containing practically no pseudowollas- 

 tonite. 



(a) Heated all night about 1180° C. Mostly 



changed to pseudowollastonite. 

 (6) Heated two hours at 1164 ± 2°C. Unchanged. 

 (c) Heated two hours at 1182 ± 2°C. Signs that 



the inversion had started. 



(2) Material — Similar to material (1) but with compo- 

 sition CaO 54, Si0 2 46. 



(a) Heated two hours at 1164 ± 2°C. Unchanged. 



(b) Heated one hour at 1182 ± 2°C. Largely 

 inverted. 



