171. In taking the weights, the powder is to be scooped up from the filling-chest with the measure until it is heaped, tapped twice moderately on the sides with the palms of the hands, and then struck with a wooden straight-edge. If the weight differs materially from that marked on the measure, a small compensating measure should be used to supply the deficiency or remove the excess.
CANNON-PRIMERS.
172. These are of two kinds, percussion and friction. Each percussion-primer is composed of a quill tube capped by an explosive wafer. The quills used for this purpose are first inspected by passing them through a gauge rather smaller than the vent.
The tube is filled with fine-grained powder.
The wafer is composed of a cap of cartridge-paper, enclosing a layer of fulminate of mercury combined with a small quantity of mealed powder. When pressed and perfectly dry, the wafer is coated with uncolored shellac, to preserve it from dampness.
173. Primers are to be kept in tin boxes containing fifty each, the lids of which are luted with shellac to exclude moisture until wanted for immediate use. These boxes are intended to fit in and form a lining to the primer-boxes which slip on the waist-belts worn by Captains of guns. For purposes of exercise no more of these boxes should be opened than are required; but for action a full box should be delivered to each Captain and 2d Captain of a gun.
174. A friction-primer consists of a tube charged with gunpowder, to the top of which is fastened a spur containing friction-powder, which is exploded by means of a slider pulled out by a lanyard. It is intended for use in case the lock should be out of order, or the other primers fail from any unforeseen cause. Friction-primers are packed in tin boxes in the same manner as percussion-primers. They are obtained from the Army as required.
175. Filled boxes of primers are kept in close laboratory cases, for which stowage must be provided in the general store-room of the ship, or other safe place.[1] They are on no account to be placed in the magazine, and the boxes must be so labelled before being put on board ship.
176. When primers have been returned from cruising ships, or have remained in store for one or more years, they must be tested by firing five per cent. of the number, and not issued again without special orders.
177. Damaged fuzes, primers, caps, and tubes, are always to be returned to the Ordnance Yard at Washington, in the condition in which they were received on the return of the ship.