Burnt ALUM, is that melted in a fire-shovel, or crucible, where it is allowed to bubble till it becomes a white hard substance.
The watery part of the alum being thus expelled,
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the remainder is left possessed of all its acids, less clogged, and more in a condition to exert its effects. It proves a gentle escharotic, and is used in small quantities, mixed with other ingredients, in tooth-powders.