560 JY. I. Boiven — The Binary System. 



latter form is that of bringing out clearly the analogy between 

 the two components. No knowledge of the molecular weight 

 is implied. Diagram II is the only diagram here contained on 

 which certain points are lettered, and when these points are 

 referred to by letter in the text, it has not always been con- 

 sidered necessary to specify Diagram II. 



Discussion of Table II and Equilibrium Diagram. 



Inversion Phenomena {Table II (a)). — In the heating curve 

 work a break was obtained with nephelite (Ne) at 1305°. 

 The heat effect was small and undoubtedly due to inversion. 

 In the quenchings it was, however, found that nephelite will 

 go over to carnegieite at a temperature considerably below 

 1305°. Held at 1245° for 6 hours there was no formation of 

 carnegieite, but at 1252° for only one hour the charge was 

 largely converted to carnegieite. These results indicate an 

 inversion temperature between 1245° and 1252°. By starting 

 with carnegieite (Cg) confirmatory results were obtained. 

 Crystallized at a high temperature and then held at successively 

 lower and lower temperatures, it was found that at 1252° no 

 change took place in 6 hours, but that at 1245° partial con- 

 version to nephelite was observed within one hour. From 

 these results the inversion temperature is shown to lie between 

 1245° and 1252° or at 1248° (approx.). Close to the transition 

 temperature the inversion is only partial in either direction, 

 after several hours. At a temperature (about 1300°) more 

 removed from the transition point nephelite is converted 

 entirely to carnegieite within an hour. The reverse change 

 does not proceed to completion so readily, but was effected by 

 heating carnegieite over a Bunsen burner for 60 hours. 



Glass of composition NaAlSi0 4 crystallizes as carnegieite 

 at any temperature above 1248°. At temperatures only a 

 few degrees below 1248° where nephelite is the stable 

 phase glass crystallizes as both nephelite and carnegieite, 

 whereas nephelite itself shows no tendency to change to 

 carnegieite at these temperatures. It seems possible that the 

 unstable glass in assuming the stable form nephelite passes 

 through the "less unstable" form carnegieite which may 

 persist for a considerable time and is therefore found in the 

 quenched products. Glass held at temperatures considerably 

 below 1248° crystallizes only as nephelite. If the "less 

 unstable" form, carnegieite, is formed at these temperatures it 

 inverts quickly to nephelite. 



With the nephelite mix-crystal (Xe 90 An 10 ) a small heat effect 

 suggestive of inversion was obtained at 1335°, somewhat higher 

 than that in Ne. The results of quenchings indicate again 



