554 



JIT. L. Bow en — The Binary Syst 



em. 



vals, and temperature is plotted against time. If there is no 

 energy change within the charge, its temperature also rises reg- 

 ularly, but at the appearance of a new phase the rate of heating 

 of the charge (the gradient of the heating curve) experiences a 

 change depending upon the energy involved in the change of 

 phase. 



During the change of phase, on account of heat absorption, 

 the temperature of the charge either remains constant or rises 

 more slowly than the temperature of the furnace, but upon 

 completion of the change of phase the temperature rises rap- 

 idly to that of the furnace. It is this sudden increase in the 

 rate of heating of the charge which is commonly termed a 

 'break' on the heating curve. The temperature at which a 

 break occurs is, then, the temperature at which the disappear- 

 ance of a phase of the system is completed. In Table I the 

 temperatures at which breaks were obtained on heating curves 

 are given opposite the corresponding composition. 



Table I. 



Wt. % Upper point 



CaAl 2 Si 2 8 



0.._ ___ 1527 



0.. 1525 



10 1473 



10 _.. 



20. _ 



20 



30 



40 



50 ... 



50 



60 



70 1437 



80 1484 



90. _. 1522 



100. _ 1550 



100 1549 



Eutectic Inversion Knickpunkt 



1304 

 1305 

 1335 



1352 

 1354 

 1360 

 1352 

 1349 



1310 c 



1305 



1304 



1302 



1307 



1306 



These results are plotted on the temperature-composition 

 diagram (Diagram I). 



In the diagram each circle shows a temperature at which a 

 break occurred on the heating curve for the corresponding 

 composition. The general form of the equilibrium diagram is 

 suggested. There is a eutectic point at about 1302°. Another 

 triple point, possibly a ' knickpunkt,' occurs at about 1352°. 

 The general form of the liquidus curves is indicated. Small 

 heat effects obtained in the pure sodium compound and in the 



