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 strumous ulceration of superficial and indolent character, with livid undermined edges, and affecting extensive surfaces on the trunk or extremities, caustic potash lightly applied to the margin often stimulates to satisfactory healing.
For destroying unhealthy growths, the edges of strumous ulceration, etc., caustic soda has been sometimes used. It is less deliquescent than potash, but yet is very diffusible, and readily extends its action: it therefore requires the precaution of protecting adjacent parts, and of neutralizing with weak vinegar or oil after application.