Often this felsitic devitrified glass is so fine-grained that its constituents cannot be directly determined even with the aid of the microscope, but chemical analysis leaves little doubt as to the real nature cf the minerals which have been formed.
In the same way artificial glass can be devitrified if it be kept at a temperature slightly below the fusing point for some days.
In this way is produced the crystalline, devitrified material, known as Reaumur's porcelain.
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