If you read the responses carefully, you'll see that the answer is no. You can't rapidly, or reasonably quickly dissolve steel, with something you can carry in a small tube.
Conc. sulfuric acid will rapidly char organic materials, turning paper, wood, or living tissue into carbon and steam. But iron would be inert to it -- a different reaction would be needed, we'd want a strong solution, not a concentrated one, and still, it would corrode thin steel, over time, not attack dimensional steel. Likewise, phosphoric acid is a weak acid, no matter how strong it is, it doesn't hurt iron -- it is , like P:
has alluded to, very good at reacting with the coating of rust on the outside of the iron, and making a thin coating of iron phosphate, like Borek:
We understand that you're new to chemistry, and you're trying to learn. But we'd like to think that you'd be able to think of things in terms of scale. Consider: a tube full of some magic juice (not a chemical, given the properties assigned to it,) can soften bars. What if you had a jar full? You'd be able to melt vault doors with it. A shell, of the size the US Air Force can drop would be able to liquefy a half a dozen armored tanks, leaving some badly burned people sitting confused on the ground. A tanker truck of it, driven into a building, would melt it down. Yes things like that do happen, but not with a chemical, with lots of heat, and effort to get the attack into place. Otherwise, we'd never be able to build anything that could hold anyone. Moderate amounts of acid, like acid rain, would be destroying our structures in a few years, instead of taking centuries. We wouldn't even have the same sort of culture and civilization we have now, if nothing could endure long enough.
Now, I saw on Mythbusters
, they tested the story, that someone in a Mexican prison, broke out by dissolving his bars with the vinegar content of his daily salsa ration, perhaps augmented by oxidation caused by wiring his bars electrically. Adam and Jamie didn't have the luxury of months of effort, so they weren't very successful. But I don't doubt the myth strongly, if bars are neglected, if maintenance isn't constantly performed, sure, moderate effort may have result -- I don't know if that was worked into the storyline. I do know, for some prisoners, there are no bars -- prisoners in the kitchen staff may take a delivery from the back, with no bars -- just 50 yards to the woods, and nothing to stop them. Just the guard, in a tower, with a rifle. The person watching them will even tell them, "Feel free to give it a try." It's just another example, things in this world we live in are designed so that, if you want an extraordinary benefit, you need extraordinary effort. Many newbs on this forum do not seem to be able to respect that, and want a superlative result, for little effort.
For a shorter explanation along these lines, see this post:http://www.chemicalforums.com/index.php?topic=27366.0