|Building Needed||Army Staff College|
This small copper container holds a chemical mixture that reacts explosively when hit; the flash is used to ignite a main gunpowder charge.
A percussion piece has less to go wrong than a flintlock during firing: there is no flint to become loose; no need to charge the pan with loose powder and less to get wet in bad weather. Instead a small cap is fitted over the end of a small tube at the breech end of the barrel. The cap is filled with fulminate of mercury, a most volatile substance. When it is struck by the hammer it explodes, but in a small way. The flash travels down the tube and ignites the main charge of gunpowder, and the musket fires.
Historically, the percussion cap was the invention of a Scottish clergyman, Alexander John Forsyth (1769-1843), who was looking for a solution to a hunting problem. The flintlock's flash in the pan before the main charge fired alerted birds that they were about to be shot, causing them to fly away in a decidedly unsporting fashion. The newly discovered and very unstable fulminate of mercury gave him an invisible spark that didn't warn his feathered victims!