168 Ferguson and Merwin — The Ternary System. 



had been crystallized at low temperatures by Mr. E. S. 

 Shepherd of this Laboratory, was examined and found 

 to contain wollastonite with definite traces of silica. The 

 weight percentage composition of wollastonite is CaO 

 48.2, Si0 2 51.8. 



(2) A glass with composition CaO 46, Si0 2 54, was 

 heated for 40 hours at 1000 °C. Upon examination it was 

 found to have crystallized to a milky wollastonite and 

 had minute traces of pseudowollastonite in it. The 

 charge appeared under the microscope quite brown as 

 did the previous charge but in this case no absolute iden- 

 tification of silica could be made. 



(3) A glass with composition CaO 47, Si0 2 53, was 

 heated 16 hours at 1065°C. The glass originally con- 

 tained a trace of pseudowollastonite. After the heat 

 treatment much wollastonite could be identified but no 

 silica. 



(4) A similar glass to that used in (3) was heated for 

 several hours at 1400 °C. It crystallized to pseudowol- 

 lastonite and silica. The silica could be positively iden- 

 tified. 



These experiments indicate that wollastonite takes up 

 about 3 per cent 7 of silica (figured on the total weight) 

 in solid solution, and that pseudowollastonite takes up 

 less than 2 per cent, 



Solid Solutions of CaO.Si0 2 with 3Ca0.2Si0 2 . — Some 

 confusion has arisen over the nomenclature of these solu- 

 tions. Their compositions have generally been given on 

 a component oxide basis and thus they have been 

 referred to as solutions of lime in the metasilicate. In 

 reality they are solid solutions with the compound 3CaO. 

 2Si0 2 . When their compositions are given upon an 

 oxide basis their true character is concealed since a solid 

 solution containing a few per cent excess lime over the 

 metasilicate composition is in reality a solution contain- 

 ing many per cent 8 of the compound 3Ca0.2Si0 2 and 

 thus what is really a concentrated solution is made to 

 appear as a somewhat dilute one. 



7 Percentages of silica on the diagrams refer to total composition on an 

 oxide basis. Three per cent on a metasilicate basis would be about 1% per 

 cent on an oxide basis. 



8 One per cent excess lime on an oxide basis represents, when referred 

 to the compounds present, approximately 10 per cent of 3Ca0.2Si0 2 . Unless 

 otherwise stated per cent always means weight per cent. 



