This information comes from Ayers' Every Man His Own Doctor
The wart is an excrescence from the cutis or outer skin--a horny tumor formed upon it; it is not generally so painful as it is disagreeable and unsightly, coming nearly always upon the hands, or some other conspicuous place. The best treatment is to touch it with some caustic, or escharote. Nitrate or silver is the most effectual, but this turns the skin black, which is in many cases very objectionable. Caustic potash will answer the purpose, so will acetic acid, if of extra strength, and nitric acid. The application should be made daily, and the decayed part pared off, or cut with scissors. If it can be conveniently done, a ligature of silk tied tightly around the base of the wart will cause it to decay, and eventually drop off. Another simple method is to bind a leaf of a house leek upon it, from which you have removed the skin, for a few nights in succession, and the wart will disappear.