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 power of the remedy in this disease depends much on the mode of its application; the mere drawing of a line of caustic round the inflamed margin (as sometimes practised) is illusory. The best method is that of Mr. Higginbottom, who advises previous cleansing of the part with soap and water, then with pure water, and afterward the thorough application of a saturated solution (20 gr. in each fluid drachm) two or three times over the whole affected surface, and beyond it on the healthy skin for about two inches. This is effective in the superficial forms of erysipelas, but not, according to my experience, when much oedema or cellulitis are present, and I am reluctant to advise it over an extensive surface, or in the idiopathic form. It causes severe burning pain, and in the latter condition, at least, does not always stay the inflammation, so that I prefer milder applications and appropriate internal medication.