Sulphuric Acid acts on trousers and carpets. Wooden desks seem remarkably immune.

Found out after getting an actual chemical and chemistry set from a deceased relative. Parents didn't check what was in it, just "chemistry is educational, good he's learning".

I was either dropping magnesium or potassium into a beaker of sulphuric acid as both of them were in the set too. And I was either a butterfingered lummox, or the act of dropping the metal into unbalanced the beaker knocked it over and the sulphuric acid cascaded onto my jeans eating through them and making my leg itchy, and bubbling the carpet into a stinky white then grey foam. I can still picture-ish that sight; and I'm normally not very visually minded, a testament to the deep impression the experience left on me.

Was much more sensible after that: just burning magnesium and chucking potassium into tub of water in the garden like you do in Chemistry class from time to time.