28 Rankin and Wright— Ternary System CaO-Alfi-SiO^ 



used; in such cases the results obtained by both methods 

 checked within the limit of error (=b 5°). For certain composi- 

 tions it was not possible to determine the melting temperature 

 by either method. 



We shall now consider the fields separately, the numbers 

 and letters used to designate them being those given in iig. 6. 

 In the tables only mean values obtained from a large number 

 of determinations are given. 



I. The field of silica (SiO,)— -K-A-2-1- J.— -Within the 

 region where Si0 2 is the stable primary phase it exists in two 

 forms, tridymite and cristobalite ; K-10 is the boundary curve 

 above which cristobalite is the stable form and below which 

 tridymite is the stable form. Owing to the extreme viscosity 

 of the melts within this field, satisfactory melting temperatures 

 could not be obtained either by heating curves or quenchings ; 

 but an idea of the general slope of the melting surface of this 

 field was obtained from the slope of the curves bounding it, 

 which are the equilibrium curves — A-2 ; 2-1 ; \-J\ «/-SiO a ; 

 Si0 2 -.4. 



II. The field of CaSiO,—{A-B-6-5-%).— -Though there are 

 two forms of CaSi0 3 yet only one of these appears in the 

 ternary system as a primary phase, for the reason that the 

 temperature at the eutectics 2 and 5 is higher than the inver- 

 sion temperature of /3 to aCaSi0 3 . This inversion tempera- 

 ture varies somewhat with the gross composition of the ternary 

 mixture, because CaSi0 3 takes up in solid solution to a small 

 extent — not over 2 per cent— each of the compounds with 

 which it is associated at the boundary curves ; this variation is 

 illustrated by the following table : 



Table I. 

 To show the change of the inversion temperature a 



(3 CaSi0 3 caused 









by the presence of additional solid phases. 





Composition 









Weight percentage 





tempera- 









Weight percentage 



ture 



CaO 



A1 2 3 



Si0 2 







48-2 





51-8 



100$ CaSi0 3 . 



1200°±2° 



45 





55 



90$ CaSiO s . 10$ Si0 2 . 



1210°±5° 



50 





50 



83$ CaSi0 3 . 13$ Ca,Si 2 7 . 



1190°±5° 



51-2 



0-9 



47-9 



97$ CaSi0 3 . 3$ CaAl 2 Si 2 O fi . 



1195°±5° 



46-3 



0'9 



52*8 



94$ CaSi0 3 . 3$ Si0 2 . 3$ CaA1 2 Si 2 8 . 



1165°±5° 



35 



10 



55 



60$ CaSi0 3 . 15$ Si0 2 . 25$ CaAl 2 Si 2 8 . 



1165°±5° 



48 



2 



50 



94$ CaSiO s . 6$ Ca 2 Al 2 Si0 7 . 



1175°±5° 



45 



5 



50 



86$ CaSi0 3 . 10$ CaAl 2 Si 2 8 . 4$ Ca o Al 2 Si0 7 



1155°±5° 



