At Kawasaki, Miyagi Pref., and Yasiro, Yamagata Pref., many globules of obsidian occur in perlite masses without any transition layers between them (Fig. 1). Many crystallites elongate, under the microscope, across the boundaries into both rocks, though the volatile components of the two rocks markedly differ both in their contents and their elimination processes. The main portion of these volatiles is water. This seems to indicate that most of the water in perlite is not of primary magma but is due to the secondary water, which was dissolved into the magma when it intruded.
In the present experiment, a newly designed vacuum thermobalance was applied to the study of elimination phenomena of volatile components of perlite, pitchstone and obsidian from several localities, and the conclusion, arrived at, is that these components are contained in these natural glasses in solution, not in cracks or in chemical combinations Further, it is ascertained that, for each temperature, there is a certain critical pressure neccessary for a gas to diffuse in a glass. This requires some modification of Henry's law. The relation between such a critical pressure and a temperature may be approximately shown by logarithmic curves. The resistance, which a molecule of water receives when it migrates in a glass may by calculated from the residual water for each temperature, if the gas theory may be applied to this water. Hence the data here published, may be taken as a measure of the cohesive force of a glass.
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