THE PHYSICAL CHEMISTRY OF THE CRYSTALLIZATION 



AND MAGMATIC DIFFERENTIATION 



OF IGNEOUS ROCKS 



J. H. L. VOGT . 



Trondhjem, Norway 



VII 



VISCOSITY, SIZE OF CRYSTALS, SPEED OF CRYSTALLIZATION, FORMA- 

 TION OF GLASS, INFLUENCE OF TIME, UNDERCOOLING (OR 

 SUPERSATURATION), and equilibrium of MIX-CRYSTALS 

 BETWEEN THE SOLID AND LIQUID PHASE, ETC. 



We have only empirical methods for the measurement of viscosity, 

 e.g., submersion of a ball of a certain weight for a certain period, 

 resistance to stirring, the length of an out-pulled thread, etc. 



At one and the same temperature the various silicate melts 

 (at one atmosphere pressure) are characterized by greatly varying 

 viscosity.^ To be convinced of this, laboratory experiments are 

 not needed, as we only need to refer to the well-known phenomena 

 seen in the large, molten masses at smelting-plants, glassworks, etc. 

 As I have had a rather considerable experience in this matter for 

 the judgment of the temperature supported by measurements 

 with Le Chatelier's and optical pyrometers, I shall give a review 

 of the degree of viscosity of various siHcate melts, mainly metal- 

 lurgical slags and several glasses. 



At first, according to an old experience that is also confirmed 

 by laboratory measurements, we notice that the viscosity decreases 

 with increasing temperature, though in a highly varying degree 

 for the various melts. 



' Cf. especially E. Greiner, "Ueber die Abhangigkeit der Viscositat in 

 Silikatschmelzen von ihrer chemischen Zusammensetzung," Ing Diss., Jena, 1907 

 (with references to the previous literature) . Further the chapter "Ueber die Beziehimg 

 zwischen Viskositat, Krystallizationszeit und Krystalgrosse " and "Weshalb ist das Glas 

 eine feste Losung?" in Silikatschmelzldsimgen 1904, I, 156-69, besides earlier treatises 

 by J. H. L. Vogt, especially one in Zeitschrift fiir praktische Geologic (1893), p. 275. 



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