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 various forms of sore throat, sulphurous acid in gargle, or preferably in fine spray, is exceedingly useful, relieving pain, lessening inflammation, destroying parasitic growth, and cleansing unhealthy suppurating surfaces. It is, in my experience, of great value in aphthous conditions such as occur during phthisis or other exhausting diseases, as well as in the ordinary form common during infancy; it often relieves the pain, tension, and ulceration of scarlatinal and variolous throats, and I have seen it of the greatest service in chronic syphilitic ulceration of the fauces.
In the acute inflammatory stage of catarrhal angina, it is not always well borne, but will be found to answer better in such cases when used of full strength, if only for a very short time, than if diluted; in the latter case, it has seemed to irritate the mucous membrane without controlling inflammation, but there is no one rule, a short trial will be the best guide; young children do not usually bear it well. Fergus, on the other hand, says it is good "in all forms of inflammation of the throat and tonsil;" it should change the turgid redness to a light pink during the application.