Ferguson and Merwin — The Ternary System. 171 



(2) A charge with composition CaO 44.4, MgO 3.1, 

 Si0 2 52.5, was heated 16 hours at 1370°C. Only pseudo- 

 wollastonite could then be found in the charge. 



(3) A charge with composition CaO 44.8, MgO 2.8, 

 Si0 2 52.4, was given the following two heat treatments : 



(a) Heated for 15 minutes at 1500 °C. Charge 

 contained crystals of pseudowollastonite with 

 a little glass. 



(b) Heated for 15 minutes at 1510 °C. Charge 

 now glass with a few crystals scattered 

 through it. 



Wollastonite is known to form solid solutions with 

 diopside taking up a maximum of 17 per cent of the latter 

 at the higher temperatures. The decomposition tem- 

 perature 9 of the most concentrated solution lies between 

 1336 and 1352 °C. Our experiments confirm these earlier 

 observations. They are given in Table I. 











Table I. 







The wollastonite-diopside solid solutions. 











Time 



Composition 



wt. % 



Temp. 



in Phases present 



CaO 



MgO 



Si0 2 



°C. 



hours 



44-8 



2-8 



52-4 



1290 



15 No diopside 



44-4 



31 



52-5 



1340 

 1346 

 1336 

 1352 



15 Homogeneous wollastonite 

 0-75 Trace pseudowollastonite and (?) 

 2 Wollastonite 



0-5 Part charge changed to pseudo- 

 wollastonite and (?) 



44 



3-5 



52-5 



1300 



15 Wollastonite -j- diopside (less than 5% ) 



46-6 



16 



51-8 1 



1225 

 1245 



15 Practically all wollastonite 



15 Wollastonite and pseudowollastonite 



1 Not quite on the line. 



Solid Solution toward Akermanite. — Solid solutions 

 occur to a considerable extent in the binary system cal- 

 cium metasilicate-akermanite. The evidence that pseu- 

 dowollastonite forms such solid solutions is as follows : 



9 We cannot say whether the extent of the solid solutions of diopside in 

 pseudowollastonite is the same as, slightly greater than, or slightly less than 

 that of the solid solutions in wollastonite since the limits are so close 

 together. However, we have assumed that pseudowollastonite takes up a 

 little less of diopside than does wollastonite and hence use the term decompo- 

 sition temperature. Assumptions of this character are made, in this paper, 

 purely to aid in the presentation of the experimental matter, the writers 

 believing that in these cases a thorough discussion of all the possible inter- 

 pretations of all of the evidence is unnecessary if one interpretation is given 

 and other possible interpretations indicated but not worked out. 



