Hydrofluoric acid is a solution of hydrogen flouride (HF) in water.  It has many industrial uses, providing flourine in chemical reactions in pharmaceuticals and other substances, like teflon.  However, both the liquid and gaseous forms are highly damaging to human tissue, particularly the cornea and lungs.  It can also interfere with metabolism and can be toxic even with exposure to the skin . In addition, it is one of the few acids that will actually have a dangerous reaction with glass, meaning it must be stored in plastic containers.  

In Nobody's FaultBill Koppelman is exposed to hydrofluoric acid when a science experiment explodes.

Hydrofluoric acid at Wikipedia

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