562 N.I. Bowen — The Binary Syst 



em. 



sion point and C 2 = concentration of the solution below. In 

 the present case, as has been stated, the concentration below 

 the inversion point (nephelite) is much greater than that above 

 (carnegieite), therefore C 2 — C 1 is positive and relatively large 

 and so also A T. This corresponds well with the sharp rise in 

 the inversion temperature of nephelite occasioned by the solid 

 solution of CaAl 2 Si 2 8 . Qualitatively, the facts fill the require- 

 ments of thermo-dynamic theory. 



The Nephelite Solidus and Liquidus {Table 11 (b) and 

 (c) ). — The melting-interval of the nephelite solid solutions has 

 already been mentioned. The solidus C F and the liquidus 

 B G have the same significance in this connection as have E C 

 and E D with respect to the inversion interval. 



In mineral work it is not possible to locate solidus and 

 liquidus by the method of separating solid and liquid phases 

 from an equilibrium mixture at various temperatures and 

 determining the composition of each phase. The solidus was 

 located by finding the temperature at which nephelite mix- 

 crystals of different compositions first showed signs of melting 

 and the liquidus by finding the temperature at which melting 

 was barely completed. After location of the curves in this 

 manner the composition of liquid and solid in equilibrium with 

 each other at various temperatures can be predicted with the 

 degree of accuracy attained in the location. 



The u Knickpunkt" {Table II {/)). — Breaks were obtained 

 on some of the heating curves at 1352° (approx.). Quench- 

 ings show that this is the temperature at which the two 

 solid phases, carnegieite and nephelite, are in equilibrium 

 with liquid. The carnegieite has the composition Cg 95 

 An 5 (D), nephelite JS T e 82 An J8 (C) and the liquid has 28*5 per 

 cent CaAl 2 Si 2 8 (B), the compositions being known from the 

 positions of these points determined by quenchings and not 

 from analysis (Table II (a), (b), (c) and (1). 



The Eutectic {Table II (g) ). — Breaks were obtained on 

 many of the heating curves at 1302° (approx.). Quenchings 

 proved that at this temperature nephelite (JN"e 65 An 35 ) and 

 anorthite (An 98 Ne 2 ) are in equilibrium with a liquid with 45*5 

 per cent CaAl 2 Si 2 8 (eutectic). The exact composition of the 

 eutectic mixture was obtained by holding the furnace slightly 

 above the eutectic point and hanging in it four or five charges 

 of the same mixture, one above another, on a platinum wire. 

 The charge at one end of the wire is in the hottest part of the 

 furnace a few degrees above the eutectic temperature and for 

 compositions close to the eutectic is completely molten. The 

 one at the other end is in a cooler part of the furnace a few 

 degrees below the eutectic and completely crystalline. One or 

 more of the intermediate charges is at a temperature only very 



