This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
When small ulcerations occur in the buccal mucous membrane, and when there is gingivitis or sponginess and inflammation of the gums, dried alum, applied in the form of powder, or a lotion containing it with myrrh and spirits of wine, is very useful. Salivation is also restrained by its moderate use, and injurious effects on the gums during a mercurial course may be prevented by keeping a piece of alum in the mouth for a few minutes occasionally. At Aix-la-Chapelle, patients are ordered to use alum gargles and washes frequently during the mercurial treatment.
In Catarrhal Angina and "relaxed throat," especially for relaxed uvula, the gargle of Riviere (1 dr. of alum to 6 oz. of water) is still a frequent prescription. It is said, however, to be injurious to the teeth, and plain water should be used after it.
In Hoarseness, a gargle containing 2 dr. of alum in 6 oz. of barley water has been found useful for professional singers (Bennati): the remedy is still better applied in the form of spray (10 gr. to 1 oz.).