Picric acid

Picric acid is the common term for the chemical compound 2,4,6-trinitrophenol; the material is a yellow crystalline[?] solid. Like other highly nitrated compounds (eg. Trinitrotoluene TNT), picric acid is an explosive. When picric acid is dry, it is extremely sensitive to shock and friction, so laboratories that use it store it in bottles under a layer of water, rendering it safe. Glass bottles are required, as picric acid can form metal picrate salts that are even more sensitive and hazardous that the acid.

Uses

By far the largest use has been in in munitions and explosives; it was known in World War I as Lyddite or Melinite

The principal laboratory use is in microscopy, where it is used as a reagent for staining samples, e.g. Gram staining.

Picric acid was one of the agents in the Halifax explosion.