Ah yes,the Dewberry-Firkin.
Well, its an organic Petard,first invented by a Mr Dewberry oh,about 1638,or thereabouts,on the 15th of August.The Firkin being a barrel of Ale.Mr Dewberry(may his shadow ever be jointed at the elbow) found at considerable personal risk,that such a barrel,left under a wall,in the sun,during a siege,would not only drive the besieged mad with thirst(thus making it one of the earliest known weapons of psychological warfare),but would also aid rapid fermentation.This resulted in the eventual explosion of the Firkin,showering the besieged with over-fermented Ale, splinters,and froth.The Ale woulD,if left long enough on the castle walls,eat away at the mortar,thus weakening the structure. The weapon is not as well known as it deserves to be,due to the habit of the rude soldiery of the time of *drinking* the Ale and replacing it with water,or worse.(I beleive the fermentation rate of horse-pee is too slow to create a satifactory bang). The soldiery saw no good reason to chuck good Ale at the enemy, or,for that matter,bad Ale either,so they invented Gunpowder, and chucked rocks instead.