Plagioclase Feldspars. 



591 



278 = 104*2. Akerman and Vogt have found by direct 

 measurement that the latent heat of melting of anorthite is 

 105 cal. per gram, which agrees well with the calculated value. 

 The extraordinary agreement is, of course, in part pure 

 accident. No direct determinations of the latent heat of melt- 

 ing of albite have been made. 



The value calculated from the 



Fig. 3. 



1400 



1320 



1240 



1160 



ANORTHITE 



AO 60 



MOL PERCENT 



ALBITE 



Fig. 3. ACB and ADB calculated curves (see text), o, experimentally 

 determined points. 



present results is 12740 -f- 263 = 4S # 5 cal. per 

 using the formula weight. 



If the values 29000 and 12740 calories are taken as the molal 

 latent heats of melting of anorthite and albite and the tempera- 

 tures 1550° C. and 1100° C. as their melting points, complete 

 solidus and liquidus curves can be calculated from these data. 

 Actual calculation gives the curves ADB and ACB of fig. 3. 

 The small circles of this figure indicate the experimentally deter- 



