485. The friction-tube is not put into the vent until the piece is about to be fired.
FUZES.
486. The wooden fuzes used at present for the 13-inch bombs are in sections, and marked according to the estimated distance in practice, viz.:
Seven inches extreme length; and each section one inch, giving a flight for every section of seven seconds, and a total of forty-nine seconds.
487. The plugs are of the proper size for the fuze-hole; the axis bored cylindrically from the large end down, to within a short distance of the small end, which is left solid; the orifice is filled with composition pressed hard and evenly as possible. At the large end a cup is hollowed out and filled with mealed powder moistened with alcohol.
488. The rate of burning is ascertained by experiment, and marked on a water-proof cap, which is tied over the cup.
489. A fuze-saw must be at hand during practice to cut the fuze the required length.
490. Fuzes for sea-coast mortars are also driven in a conical paper case, which is inserted in a metal or wooden plug previously driven in the fuze-hole and accurately reamed out.
491. The paper-case fuze is marked with the number of seconds it burns per inch, and it may be cut, where no danger from ignition can take place, with a sharp knife.