514 



N. L. BOWEN 



In the present paper it is proposed to discuss the behavior of 

 inclusions with special reference to these questions. By application 

 of the principle of the reaction series, as developed in a former 

 paper/ it is hoped to effect a certain amount of reconciliation of 

 these extreme views. 



HEAT EFFECTS OF SOLUTION 



Since one of the important questions involved is that relating 

 to the heat effects resulting from solution it is desirable to consider 



the information available on 

 these effects. The ordinary- 

 equilibrium diagram, commonly 

 regarded as a freezing-point dia- 

 gram, is at the same time a solu- 

 bility diagram. It gives the 

 change of solubility of any phase 

 with temperature. But the 

 change of solubility with temper- 

 ature depends mainly^ on the 

 heat effect involved in solution 

 and the equilibrium diagram 

 contains complete information 

 on this heat effect. Unfortu- 

 nately the information may be 

 very dijS&cult of extraction; in 

 the present state of knowledge, 

 often impossible. One solubiUty 

 diagram, that of the plagioclase 

 feldspars, has proved particularly simple in this respect. This dia- 

 gram is shown in Figure i, the curves being calculated on the basis 

 of a latent heat of 104.2 cal. per gram for anorthite and 48.5 cal. per 

 gram for albite. The determined points are given by the small circles 

 and their correspondence with the calculated curves is very remark- 

 able. Since the curves were calculated on the basis of constant 

 latent heats (solution heats) this correspondence simply means that 



^ N. L. Bowen, Jour. GeoL, Vol. XXX (1922), pp. 177-98. 



2 The volume change is involved also but is relatively unimportant. 



ANORTHITE 



Fig. I. — Equilibrium diagram of the 

 plagioclase feldspars. The circles indicate 

 determined points. ACB and ADB are 

 calculated curves assuming no heat of 

 mixing. 



