Solubilities of Gaseous Species in Silicate Melts

Before examining in detail the present-day knowledge of the solubihties of various gaseous species in magmas, it is necessary to describe solubility in terms of reactivity of gaseous species with melt components. A simple heterogeneous equilibrium between gas and melt involves the inert gas Ar  

This can be conceived as mechanical solubility, which does not imply either reactivity or modifications of the molecular structure of the compound of interest. Several gaseous species do not exhibit solubility of the type exemplified by equation 9.63, but more or less complex reactions with melt components. For instance, in the case of CO2, 

Homogeneous equilibrium 9.66 modifies the stoichiometry, structure, and properties of the component of interest. 

Generally, in the case of mechanical solubility, an extended Henry s law field is observed, whereas homogeneous equilibria of type 9.66 usually imply precocious deviations from ideality (Battino and Clever, 1966 Wilhem et al., 1977). 

There are several ways of expressing the solubilities of gaseous species in melts or hquids. The Bunsen coefficient defines the volume of reduced gas at T = 273.15 K, P = 1.013 bar adsorbed by a unit volume of solvent at T of interest and P = 1.013 bar. The equation used to calculate the Bunsen coefficient is 

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