Gelignite
Gelignite was an explosive material invented by Alfred Nobel in 1875. More stable than his earlier creation dynamite, gelignite was easily mouldable and safer to handle.
Ernie Clements kept a store of gelignite which he used for fishing. It had started to "sweat", or exude nitroglycerine, making it extremely unstable. The Fourth Doctor used a box of this explosive to destroy the Osiran war missile being created by Sutekh's servitors. Sarah was able to detonate the box by shooting it with a rifle. (TV: Pyramids of Mars)
Ace was attempting to extract nitroglycerin from gelignite when she was transported to Iceworld. (TV: Dragonfire)
Behind the scenes
In the real world, "sweating" is a common problem with old dynamite, however gelignite is much more stable, doesn't sweat and can't be exploded without a detonator.
