Rockets may be driven solid, or over a piercer. In the latter case, they must not have so much composition put in them at a time. The piercer, accompanying a greater part of the bore of the case, would cause the rammer to rise too high; so that the pressure of it would not be so great on the composition, nor would it be driven equally. For rockets rammed over a piercer, let the ladle, or copper scoop, hold as much composition, as, when driven, will raise the drift one-half the interior diameter of the case; and, for those driven solid, let it contain as much as will raise the drift one-half the exterior diameter of the case. Ladles are generally made to go easily into the case, and the length of the scoop is about one and a half of its own diameter.
The charge of rockets must always be driven one diameter above the piercer, and, on it, must be rammed, one-third of a diameter of clay; through the middle of which a small hole must be bored to the composition, so that, when the charge is burnt to the top, it may communicate its fire, through the hole, to the stars in the head. (See [plate, fig. 14.]) Great care must be taken to strike, with the mallet, with an equal force, giving the same number of strokes to each ladleful of composition; otherwise the rocket will not rise with a uniform motion, or burn equally and regularly, for which reason, they cannot carry a proper tail. It will break, in this case, before the rocket has ascended to its extreme height, where the rocket should break and disperse the stars, rain, or whatever is contained in the head. When in the act of ramming, the drift or driver must be kept constantly turning or moving; and when the hollow rammers are used, the composition is to be knocked out every now and then, or the piercer will split them. To a rocket of four ounces, give to each ladleful of charge, 16 strokes; to a rocket of 1 lb. 28; to a 2 pounder, 36; to a 4 pounder, 42; to a 6 pounder, 56. But rockets of a larger sort cannot be driven by hand, and must be rammed with a machine similar to a pile-driver.
The method of ramming wheel cases, or any other sort, in which the charge is driven solid, is much the same as that used for sky-rockets; for the same proportion may be observed in the ladle, and the same number of strokes given, according to their diameters, all cases being distinguished by their diameters. In this manner, a case, whose bore is equal to that of a rocket of four ounces, is called a four ounce case; and one which is equal, in bore, to an eight ounce rocket, an eight ounce case, &c. The method of ramming cases, without moulds, will answer for strong pasted cases, and save the expense of making so many moulds. In filling any case, it must be placed on a perpendicular block of wood, in order to keep it firm and solid; otherwise the composition would be rammed unequally.
When cases are to be filled without moulds, procure some nipples, made of brass or iron, in proportion to the cases, to screw or fix in the top of the driving block. When the nipple is fixed in, make, at about one and half inches from it, a square hole in the block, six inches deep, and one inch in diameter. Then have a piece of wood, six inches longer than the case intended to be filled, and two inches square. On one side of it, cut a groove, almost the length of the case, whose breadth and depth must be sufficient to cover near one-half the case. Then cut the other end, to fit the hole in the block; but take care to cut it, so that the groove may be at a proper distance from the nipple. This half mould being made, and fixed tight in the block, cut, in another piece of wood, nearly of the same length as the case, a groove of the same dimensions as that in the fixed piece. Then put the case on the nipple, and, with the cord, tie it, and the two half moulds together; and the case will be prepared for filling. The dimensions of the above half moulds are proportionable for cases of eight ounces; but they differ in size in proportion to the cases.
Sec. IV. Of the Boring of Rockets.
The machine, for boring rockets, is similar, in some respects, to a lathe. The rocket is confined in a box, and, by means of a wheel, which is made to turn a second one, an auger rammer is put in motion. The rammer must be of a size, proportionate to the rocket, and of the same diameter, as the top of the bore intended, and continue of that thickness, a little longer than the depth of the bore required. The thick end of each rammer must be made square, and all of the same size. The rammer is made to move backward, and forward, so that, after the rammer is marked three and a half diameters of the rocket, from the point, set the guide, allowing for the thickness of the front of the rocket box, and the neck and mouth of the rocket. When the rocket is fixed in the box, it must be pushed forward against the rammer, and, when the scoop of the rammer is full, draw the box back, and knock out the composition. A little oil is sometimes used, to prevent the friction from setting fire to the rocket. Having bored a number of rockets, taps must be used. These taps are similar to the common spicket. When employed, it is necessary to mark them three and a half diameters from the point, allowing for the thickness of the rocket's neck.
There are several contrivances for the boring of rockets. The operation is sometimes done, by confining the rocket in a box, and boring it with a borer, fixed in a brace, using, at the same time, a proper director. This brace is like the common brace, used by carpenters, or formed on that principle, and made of iron. The motion, given by the hand, performs the operation.
Sec. V. Of the Preservation of Steel or Iron Filings.
When treating of iron, we mentioned, that it has the property of oxidizing rapidly, when exposed to the air and moisture; and that its effects in fire-works, in that case, would be either destroyed, or considerably diminished. And even fire-works, in which iron enters as a component part, will, if kept long, lose some of their effect, in consequence of the change, which the iron suffers; for, instead of producing brilliant sparks, which is their intention, it would impart a dull red appearance.
Two methods are recommended for the preservation of iron. The one is to melt a portion of sulphur, and throw the filings into it, and afterwards to separate the extraneous sulphur. The other consists in wrapping them up in oiled paper. As to the first method, we may apprehend the effect of the sulphur, combining with some of the iron, instead of coating it, forming thereby a sulphuret, which, besides, is readily decomposed by the contact of air and moisture, producing sulphate of iron. The second method, of wrapping them in oil, or, in fact, covering them with oil, is certainly a greater preventive from rust, for where the oil is in contact, no oxidizement can take place.