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.
In inflammation, with patches of ulceration about the mucous membrane of the mouth and gums, hydrochloric acid, diluted with an equal part of glycerin, and applied to the sloughing spots will induce healthy action. In mercurial stomatitis, and in the aphthous conditions that occur in children, or during advanced disease, lotions containing 1 part of acid in 10 of rose-water, either alone or with chlorate of potash and glycerin, are very serviceable. The acid is also valuable given internally in such cases. To avoid possible injury to the teeth, plain or alkalized water should be used immediately afterward.