To the theatre in Hereford, to see Young Bloods' "The Canary Girls", about the munitions workers at the Rotherwas Munitions Factory in the first and second world wars. During World War I, 4000 women worked at the factory, packing explosives into shells.  They had to do this by hand to reduce the likelihood of explosion, pressing the explosives into the shells with their thumbs, which caused painful skin damage.  The picric acid made the workers' skin go yellow and caused liver disease. 

Read more about it from the BBC here

These days, picric acid is used in fireworks because it makes a whistling noise as it burns in air.