VOLUME XXX NUMBER 8 



THE 



JOURNAL OF GEOLOGY 



November-December 1022 



THE PHYSICAL CHEMISTRY OF THE CRYSTALLIZATION 



AND MAGMATIC DIFFERENTIATION 



OF IGNEOUS ROCKS 



J. H. L. VOGT 



Trondlijem, Norway 



VI 



THE INTLUENCE OP THE LIGHT VOLATILE COMPOUNDS 

 (H2O, CO2, ETC.) 



The physico-chemistry of the light volatile compounds in the 

 magmas has lately been explained in two treatises published at the 

 same time and independently of each other, namely: 



P. Niggli. Die leichtfliichtigen Bestandteile im Magma. Preisschrift 

 von der Furstlich Jablonowkischen Gesellschaft zu Leipzig, 1920. 



Th. Vogt. Lecture in the Society of Science, Kristiania Meeting, 

 April 16, 1920. 



Referring to these two treatises and to H. E. Boeke's "Grund- 

 lagen der physikalisch-chemischen Petrographie " (191 5, especially 

 pp. 256-63), we will begin with a general orientation. 



We will discuss a binary system at constant pressure, in which 

 we think of a very high pressure, between A and B, with melting 

 point, respectively critical temperature, Sa, Ka and Sb, Kb where Sb 

 lies notably higher than Ka (illustrated by Fig. 52). The "critical 

 curve" cuts the curve of the gas phase. In this system, when 



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