Also called Trinitrophenol. An explosive, corrosive, poisonous material used in the manufacture of explosives. It is highly shock, heat and friction sensitive, and is both a "class A" explosive and a flammable solid. It can be used to produce hugely volatile picrate salts which can be made to explode just by lookng at them. Well, almost.
Flash point: 150°C
Auto-ignition temperature: 300°C
If you find yourself in possession of picric acid or its byproducts, do not mess with it. Call the local bomb disposal unit, ASAP.
Picric acid has also seen use in the manufacture of yellow dye, as an antiseptic, and as an insecticide.
It was instrumental in The Halifax Explosion of 1917.