38 Rankin and Wright — Ternary System CaO-A\0 \-SiO \. 



tinue to boil more vigorously as the temperature rises. Most 

 of a twenty gram charge will boil out of a 100 cc platinum 

 crucible. If large lumps of this compound or ternary mix- 

 tures of which this compound is a considerable part are melted, 

 this phenomenon does not occur. The reason for this boiling 

 we have not fully investigated, but it is probably due to 

 absorbed gas which is liberated only at melting. What we do 

 know is that this boiling is distressing when it occurs in a 

 charge on which we wish to take a heating curve. (2) The 

 unstable form of 5Ca0.3Al 2 3 appears and disappears in melts 

 in the ternary, as in the binary system. This causes uncertain 

 and irregular breaks on heating which may occur at almost any 

 temperature. For these reasons satisfactory heating curve 

 breaks for these two eutectics are impossible except for those 

 compositions containing but a small amount of 5Ca0.3Al 2 3 , 

 in which case so small an amount of the eutectic is present 

 that the break is not very sharp. 



Quintuple Points not Eutectics. The data for quintuple 

 points not eutectics are presented in the same way as those 

 for eutectics ; that is, the complete series of observations on 

 which is based the temperature of a single point is given but 

 only one value (the mean of a large number of determinations) 

 for each of the other points. The number assigned to each 

 quintuple point corresponds to the number in tig. 6. 



Point 4 is the quintuple point for 2CaO. Al 2 3 .Si0 2 , /3Ca 2 SiG 4 

 and 3Ca0.2Si0 2 (CaO 48*2, A1 2 3 11-9, SiU 2 39*9). Its melt- 

 ing temperature, 1335°d= 5°, is based on the values obtained 

 from various compositions as given in Table XII. 



Table XII. 



Melting temperature: quintuple point 4 for /?2CaO.SiO a + 2CaO.Al 2 3 .Si0 2 -|- 



3Ca0.2Si0 2 as determined from various compositions. 





CaO 



60 



55 



45 



55 



48*5 



Composition 

 Wt. per cent 



A1 2 3 

 SiO, 



5 



35 



10 

 35 



30 



25 



5 

 40 



12- 



39-5 



Temperature 





1333 



1337 



1334 



1333 



1337 







1334 



1337 



1337 



1336 



Quench 







1334 



1338 



1337 



1333 









1332 



1339 

 1340 

 1341 



1336 

 1336 







Mean 





1333 



1338 



1336 



1333 



1337 



Point 3 is the quintuple point for a2CaO.Si0 2 , /32CaO.Si0 2 and 

 3Ca0.2Si0 2 . (CaO 53 0, A1 2 3 4-2, Si0 2 42*8); 14 1 5 ± 5°. 



Point 8 is the quintuple point for a2CaO.Si0 2 , /?2CaO.Si0 2 and 

 2CaO.Al 2 3 .Si0 2 . (CaO 49, A1 2 3 14-4, Si0 2 36-6); 1415° ± 5°. 



