Ferguson and Merwin — The Ternary System. 175 



These results indicate a considerable area of solid solu- 

 tion of wollastonite and that this area is probably even 

 more extensive at low temperatures. The increased 

 solubility of diopside at low temperatures has been pre- 

 viously noted by others. 12 



The 5Ca0.2Mg0.6Si0 2 Solid Solutions.— The solid 

 solutions which we have been discussing in nowise 

 explain the wollastonite liquidus relations found by us 

 and given in a previous paper. 13 These relations indi- 

 cated the existence of two wollastonite fields, one corre- 

 sponding to an optically positive and the other to an 

 optically negative wollastonite. The latter, decompos- 

 ing at about 1340° C, was evidently the solid solution of 

 17 per cent of diopside in wollastonite, but the former, 

 stable below 1365 °C, corresponded to nothing which we 

 had then found existent in the ternary system. 



Fortunately the finding of a maximum on the wollas- 

 tonite-diopside boundary line (then so-called) enabled us 

 to say that the composition of the solid solution inverting 

 at 1365 °C lay on a line which was an extrapolation of the 

 line joining the diopside composition with the composi- 

 tion of the maximum on the boundary line. Now this 

 line ran through the 5Ca0.2Mg0.6Si0 2 composition, and 

 therefore experiments were made in order to determine 

 if a homogeneous product could be obtained in the region 

 at and near this composition recorded in Table V. 



Table V. 

 Experiments upon the 5Ca0.2Mg0.6Si0 2 solid solutions. 

 Time 

 Composition wt. % Temp. in Phases present 



CaO MgO SiO, °C. hours 



38 11 51 1360 0-5 5Ca0.2Mg0.6Si0 2 + trace pseudo- 



wollastonite-)-a small quantity of glass 



38 12 50 1360 0-5 Some glass -f crystals 



39 11 50 1350 0-5 A homogenous product 1 



1360 0-5 Part decomposed into pseudo- 



wollastonite and glass 

 42-4 8-8 48-8 900 15 All wollastonite 



1275 0-5 Not decomposed 



1300 0-5 Not decomposed 



1325 0-5 Not decomposed 



1345 0-5 Barely started to decompose but 



clearly started 



5Ca0.2Mg0.6Si0 2 would be CaO 38.9, MgO 11.1, Si0 2 50. 



2 Allen, White, Wright, and Larsen, this Journal 27, 20, 1909. 



3 See fig. 1. 



