Muriatic Acid - sealed, in a bag, in a steel drawer - looks like rust under the bag!?

[bruce.desertrat]

Muriatic acid is volatile-ish (HCl is a gas, after all), and will certainly do the things you're describing, especially if it's in an un-cooled area in the summer. Under humid conditions you'll see the 'wet' you're talking about, because as a gas it is hydrophilic.

Why the 'rust' inside the bag is another question, but any kind of steel or iron that gets in there will cause that. It doesn't have to be more than a bit of steel wool or swarf.

in the (climate controlled) chem lab we would store it in glass bottles with tightly fitting caps with teflon liners, and we'd still end up with rusty acid cabinets.

Personally I'd be leery of keeping acids of any kind in a cabinet with solvents....way too much opportunity for , ahem, unintended reactions; were your dad alive, he'd probably regale you with all the exciting ways it could go wrong.