So, I've wound up in jail again (not my fault - I didn't start that fire, honest!) and I need to get out of here before the mayor has a chance to check his safe. Unfortunately, I left my lockpicks in my other pants.
Luckily, I happen to be carrying a little vial of metal-be-gone. A few drops on the hinges, and in a matter of minutes it's eaten through the metal, and I can escape. But it gets me wondering... Just what is in that vial?
Question: Is there a liquid which can be safely carried (probably in a glass container), and which will rapidly dissolve iron? Preferably something that does not release toxic fumes. If so, what is it, and how could someone (or some group) produce (ideally with a medieval level of technology) or obtain it?