1 72 Ferguson and Merwin — The Ternary System. 



(1) A charge with composition CaO 46.7, MgO 3.1, 

 Si0 2 50.2, was given the following heat treatments : 



(a) Heated 15 minutes at 1500 °C. All glass. 



(b) Heated 15 minntes at 1490 °C. All consists of 

 crystals of pseudowollastonite. 



(2) A charge with composition CaO 46, MgO 5, Si0 2 

 49, was heated for several hours at 1425 °C and then 

 found to contain considerable quantities of glass. 



The approximate limit, therefore, assigned to the 

 pseudowollastonite solid solutions is the composition 

 CaO 46.5, MgO 3.5, Si0 2 50, or about 23 per cent of 

 akermanite. 



The experiments upon the wollastonite solid solutions 

 are somewhat unsatisfactory since charges free from 

 pseudowollastonite were so fine-grained that the phases 

 then present could not be identified. Charges ranging 

 from pure wollastonite to the composition CaO 43.5, 

 MgO 10, Si0 2 46.5, when free from pseudowollastonite 

 appear homogeneous, but a charge with a composition 

 CaO 42, MgO 13, Si0 2 45, after an all-night heat treat- 

 ment at 950 °C, appeared brownish and not at all homo- 

 geneous, although no akermanite could be definitely 

 identified. We have placed the approximate limit of the 

 solutions at the composition CaO 43.5, MgO 10, Si0 2 46.5, 

 which is very near the composition 3CaO.Mg0.3Si0 2 , and 

 corresponds to a composition containing between 60 'and 

 70 per cent of akermanite. There is no conclusive evi- 

 dence to show whether these solutions are in reality 

 solutions containing akermanite or an unstable com- 

 pound 3CaO.Mg0.3Si0 2 , and lacking such evidence we 

 have preferred to omit reference to this possible com- 

 pound in the former paper and will in this paper assume 

 it to be non-existent. The inversion and decomposition 

 temperatures of these solutions are indicated by the 

 quenches given in Table II. 



Table II. 



Quenches which indicate the inversion and decomposition temperatures of 

 the wollastonite-akermanite solid solutions. 

 Time 

 Composition wt. % Temp. in Phases present 



CaO MgO Si0 2 °C. hours 



46-7 3-1 50-2 2103 0-5 Initial charge of wollastonite 



unchanged 

 1213 0-5 Inversion started 

 1225 20 All pseudowollastonite 

 43-5 10 46-5 1200 0-5 Initial charge unchanged 

 1213 0-5 Initial charge unchanged 



1225 0-5 All decomposed 



