308 Shepherd, Rankin, Wright — Binary Systems of 



necessary 

 any way 



Fig. 



to determine whether or not these changes were in 

 related to the stable phases present in this region. 

 Quenching experiments made by removing 

 the charge from the furnace and chilling in 

 water were found to be too slow. Obviously, 

 from a field like E F O, where we have the 

 phase CaO.Al 2 3 in contact with the melt, 

 great speed in cooling is necessary to prevent 

 the whole mass from crystallizing in the 

 presence of the excellent nuclei furnished by 

 the solid phase. Therefore a special device 

 was needed to secure more rapid cooling. 

 The system adopted is shown in fig. 7. 

 Passing through the furnace is a tube, A. 

 Within this tube is placed the element, E: 

 The charge is contained in a small platinum 

 cup, B, suspended by a small porcelain ring 

 from the fine platinum wire, C. This wire is 

 attached to two heavy platinum leads marked 

 + and — . The tube is closed at the bottom 

 by the removable plug, D. F is a dish of 

 mercury with a layer of water above it. In 

 operation the charge is brought to the 

 desired temperature and held for a suitable 

 length of time. The plug J) is removed and 

 a strong current passed through the wire C. 

 The current fuses the wire, dropping the 

 charge into the vessel, F. The porcelain 

 ring C prevents the wire of B from sticking 

 to the suspending wire at C. 



By this method we were able to quench 

 samples of the partly melted charge, obtain- 

 ing well-formed crystals of the primary 

 phase imbedded in glass. In other words, we were able to 

 bring the charge to room temperature rapidly enough to pre- 

 vent its changing over. The results of this study are given 

 below : Time is the time during which the charge was held 

 at the temperature, T, before quenching ; IB, traces of 

 unstable form of 5Ca0.3Al 2 3 ; |j present ; tr, trace. 



isw^NsssssSa 



41$ A1 2 3 i 



Time 

 30 min. 



60 

 30 

 60 

 90 



T 

 1544° 

 1513° 

 1487° 

 1457° 

 1454° 

 1427° 

 1394° 



Glass CaO 



5CaO . 3A1 2 S 



II 

 II 

 II 

 II 

 II 

 II 



IB 3CaO . Al 2 O s 



