[ROCKETS.]
Rockets are charged in choked cases, on a spindle, to leave a hollow up the middle, through which the fire may be communicated to nearly the whole of the composition at once: this causes the sudden generation of an enormous quantity of elastic vapour, which, being unable to escape instantly through the contracted aperture left for its exit, exerts its pressure in the contrary direction, and hurries the rocket forward. A stick, attached to it, guides it, like the rudder of a vessel, or tail of a bird, or fish; while its weight and leverage keep the centre of gravity a little below the case, and prevent the rocket from pitching over. Its manufacture, therefore, from the commencement of cutting the paper for the case, to its finish of fitting on the stick, requires an accurate adjustment of all its parts. Disregarding the trade names of pound, ounce, &c., which, now that moulds are dispensed with, are useful only for enabling the makers, from tradition, to understand each other; the internal diameter, instead of the external, as formerly, may be selected, from which to compute the relative measures. Taking the bore of the case as unity, the proportions will be as follow:—
| 1 | Internal diameter of case. |
| 11⁄2 | External diameter. |
| 8 | Length of case. |
| 6 | Length of spindle. |
| 3⁄5 | Bottom diameter of spindle. |
| 64 | Length of stick. |
| 1⁄2 by 1⁄2 | Thickness and breadth of stick. |
These proportions are most readily calculated by taking the diameter in eighths of an inch. Selecting, for instance, a 6⁄8 rocket, we have, 6⁄8, inner diameter; half as much again, 9⁄8, outer diameter.
Taking the numerator as inches: 6 inches, length of case; 3⁄4 of this, or, which is the same, 1⁄2 the outer diameter, as inches, 41⁄2 inches, length of spindle; putting 20 for the denominator, instead of 8 (8 being 2⁄5 of 20), 6⁄20 of an inch, bottom diameter of spindle; 6 × 8, (numerator multiplied by denominator) = 48 inches, length of stick; 3⁄8 by 3⁄8, size of stick.
The following table exhibits the usual sizes in inches.
| Name of Rocket. | Inner Diameter. | Outer Diameter. | Length of Case. | Length of Spindle. | Bottom Diam. of Spindle. | Length of Stick. | Size of Stick. |
| 10/8 | 10/8 | 15/8 | 10 | 71⁄2 | 10/20 | 10 times 8=80 | 5/8 by 5/8 |
| 9/8 | 9/8 | 131⁄2/8 | 9 | 63⁄4 | 9/20 | 9 times 8=72 | 41⁄2/8 by 41⁄2/8 |
| 8/8 | 8/8 | 12/8 | 8 | 6 | 8/20 | 8 times 8=64 | 4/8 by 4/8 |
| 7/8 | 7/8 | 101⁄2/8 | 7 | 51⁄4 | 7/20 | 7 times 8=56 | 31⁄2/8 by 31⁄2/8 |
| 6/8 | 6/8 | 9/8 | 6 | 41⁄2 | 6/20 | 6 times 8=48 | 3/8 by 3/8 |
| 5/8 | 5/8 | 71⁄2/8 | 5 | 33⁄4 | 5/20 | 5 times 8=40 | 21⁄2/8 by 21⁄2/8 |
| 41⁄2/8 | 41⁄2/8 | 63⁄4/8 | 41⁄2 | 33⁄8 | 41⁄2/20 | 41⁄2 times 8=36 | 21⁄4/8 by 21⁄4/8 |
| 4/8 | 4/8 | 6/8 | 4 | 3 | 4/20 | 4 times 8=32 | 2/8 by 2/8 |
| 3/8 | 3/8 | 41⁄2/8 | 3 | 21⁄4 | 3/20 | 3 times 8=24 | 11⁄2/8 by 11⁄2/8 |
To Make a 6⁄8 Rocket.
Have the former, fig. 7, a brass tube 6⁄8 of an inch external diameter; the gauge, fig. 8, with a 9⁄8 aperture; procure some imperial brown paper, 70 lb. or 84 lb., the thicker and heavier the better. The best kind is made of old ropes, is air-dried, and rough. This is not easily obtained now. The smooth machine-made, cylinder-dried answers very well. The sort used for laying under carpets, and which is 5 feet broad, is almost equal to the original rough imperial, and should be procured, if possible, in preference to the smooth. Cut it into strips 6 inches wide. Paste the pieces well, and roll the cases as hard as possible, with the rolling board fig. 6, till they fit the gauge. Lay them by for a few hours to get partially dry. They must, then, be choked or strangled, about half a diameter from one end of the case, that end that lay nearest to the left hand in rolling, till they assume the shape of the neck of a vial. For this purpose have a cylindrical piece of deal, alder, or any kind of wood, fig. 24, about 9 or 10 inches long, made to fit easily into the case; cut it into 2 pieces, a and b; b may be an inch and a half long; round off the ends, just cut. In a, fasten a screw, the solid wire, or uncut part of which, is 1⁄4 of an inch thick; saw, or file off the head, and slightly taper the part projecting; in the piece b bore a hole to just fit the wire of a. Slip b upon a, and push them into the case, so that the interval between the two reaches within about 1⁄2 an inch of one end of the case; slightly draw out b, to leave a neck, or hollow, round which to form the choke; fix a staple, or screw-eye in a post: tie to it one end of a piece of cord, about a yard long, and 1⁄10 of an inch thick; fasten the other end round the middle of a stick, for a handle; take hold of the stick with the right hand; hold the case in the left; pass the cord round the space left vacant and gradually tighten it, turning the case round and round, so as to pinch it in equally on all sides, till it assumes the shape of fig. 23. Hitch a piece of string, about 1⁄16 of an inch thick, a few times round the neck, until it is filled up flush with the other part of the case, remove the choker, and hang the case up to dry. A hitch is made by simply bending the string backwards into a loop, like fig. 22; passing it round the choke; pulling it tight; looping it again, again passing it round the choke, and so on. The first loop is called a half hitch, and will not hold of itself; the second loop completes the hitch, and makes it hold: the remaining hitches are for filling up the choke, and restoring the cylindrical shape. Practise, by hitching the string upon your thumb, 4 or 5 times: it will hold after the second loop; but push it off at the end, and it will all fall loose again.
A case must not be choked when wet, or it will tear; nor must it be too dry, or it will be difficult to choke it at all. The drier, however, it can be choked, the better. Experience is the only guide. If properly dry, the wrinkles of the choke will be small, and perfectly regular. Should the string stick to the case, chalk it; but this is not likely to occur unless the paper is too wet. Have a foot, fig. 16, turned of ash, or beech, or box, with a hemispherical nipple, 6⁄8 of an inch diameter, as drawn. Bore it with a twist drill, or nosebit, to the depth of an inch and a half. Procure a brass, iron, or steel wire, but preferably brass, 6 inches long, and 3⁄10 of an inch diameter, and perfectly straight. Cut, on one end of it, a screw, 11⁄2 inch long, fix it in a vice, wet the screw with glue, and screw the foot on. File the 41⁄2 inches gradually tapering. The object of tapering it is simply to make it deliver. A cylindrical hollow up the rocket would answer as well, but the spindle could not be got out. The more conically true it is tapered, of course, the better. Finish it off with a very fine file, and smooth it with glass paper. The block into which it is screwed may be larger than drawn; the bottom should be turned slightly concave, to make it stand firm, on the same principle as the bottoms of plates, cups, &c., are made with a rim. The block and spindle are better if cast in gun-metal, in one solid piece: the pattern to give to the caster should be in one solid piece of wood. After casting, the rough parts must be filed smooth; not many turners will be found willing to undertake to turn it.