Franklin, Benjamin, Experiments and Observations on Electricity at Philadelphia in America (London, England: Francis Newberg, 1769), p. 92. From p. 92: "A small cartridge is filled with dry powder, hard rammed, so as to bruise some of the grains; two pointed wires are then thrust in, one at each end, the points approaching each other in the middle of the cartridge till within the distance of half an inch [1.27 cm]; then, the cartridge being placed in the circle [i.e., circuit], when the four [Leyden] jars are discharged, the electric flame leaping from the point of one wire to the point of the other, within the cartridge amongst the powder, fires it, and the explosion of the powder is at the same instant with the crack of the discharge."
