170 Ferguson and Merivin — The Ternary System. 



(3) Material fully crystallized containing no pseudo- 

 wollastonite but trace of calchim ortho silicate, composi- 

 tion CaO 56, Si0 2 44. 



(a) Heated two hours at 1150° C. Unchanged. 



(b) Heated two hours at 1185 °C. Largely 

 inverted. 



From these inversion temperatures and rates it 

 would appear that the composition CaO 54, Si0 2 46, has 

 a lower inversion than the composition CaO 51, Si0 2 49, 

 and also probably that the inversion temperatures of 

 the compositions CaO 54, Si0 2 46, and CaO 56, SiG 2 44, 

 were approximately the same. We have therefore 

 placed the limit of the wollastonite solid solution at the 

 composition CaO 47.5, Si0 2 52.5, or approximately 45 

 per cent of the compound 3Ca0.2Si0 2 . This figure is 

 not at all exact but seems the most probable value and is 

 given in order to emphasize the fact that the extent of 

 these wollastonite solid solutions is much greater than 

 the earlier observations indicated. The most concen- 

 trated of these solutions inverts, or perhaps better, 

 decomposes, at about 1170 °C or about 30 °C below the 

 inversion temperature of the pure compound. 



In discussing these and the other solid solutions it is 

 somewhat difficult to draw the line between the use of 

 the words inversion and decomposition. In what follows 

 we will apply the word " inversion' ' to the phenomenon 

 in which one solid phase changes into another, and 

 " decomposition' ' to the phenomenon in which one solid 

 phase changes into two or more phases, one of which at 

 least is solid. Thus some of the wollastonite solid solu- 

 tions with 3Ca0.2Si0 2 invert to form solid solutions of 

 pseudowollastonite, and others decompose to form mix- 

 tures of a pseudowollastonite solid solution and the 

 compound 3Ca0.2Si0 2 . 



Solid Solutions of CaO.Si0 2 with Diopside. — Solid 

 solutions between pseudowollastonite and diopside have 

 not been previously observed. The following experi- 

 ments indicate that such solid solutions exist and extend 

 to a composition containing about 16 or 17 per cent of 

 diopside by weight. 



(1) A charge with composition CaO 44, MgO 3.5, Si0 2 

 52.5, was heated 16 hours at 1370 °C. It then contained 

 a small amount of glass with pseudowollastonite. 



