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.
The local use of iron in ringworm is an old practice, which has been recently revived (British Medical Journal, i., 1877). After cleansing the part, tincture of perchloride may be painted upon it three or four times, at a day or two's interval; a brown scale forms, which should be left undisturbed, glycerin will lessen the sense of dryness and constriction. I have found this treatment succeed in slight and recent cases; also in old ones, after more active remedies had been used, and it has the advantage of being not so unpleasant as some other applications.