A Manual of Pyrotechny; or, A Familiar System of Recreative Fire-works

by G. W. Mortimer

Sky Rockets.

1. Sky-rockets.—Sky-rockets, in regard to size, are divided into three kinds, namely, those the calibre or internal diameter of which does not exceed that of a pound bullet; or having their orifice equal to a leaden bullet, which weighs exactly one pound; for the relative magnitude of Rockets is estimated by the diameter of lead balls or bullets, after the manner taught in the Article Gerbes. Those, therefore, the calibre of which does not exceed a pound bullet, are termed small-size Rockets; those whose calibre is from one to three pounds are of the middle size; and those whose calibres exceed the last dimensions, are termed Rockets of the largest size; or are named after their weight, estimated as above.

We now proceed to describe the moulds and apparatus requisite for making Rockets, for on the due proportion of which (as was before observed) depends much of the goodness of the article. These moulds are also requisite in order that any number of Rockets may be prepared of the same size and force. As Rockets are made of various sizes, it is evident that moulds of different diameters must be produced.

[Fig. 1, plate 1], represents a mould made and proportioned by the diameter of its calibre, which is divided into equal parts and rendered into scale, by which the relative proportions may be understood, merely by a contemplation of the figure. Thus A B is the calibre, or diameter; C D its whole height, including the foot complete, and equal to eight diameters, as per scale: E is the thickness of the mould, and may be about half a diameter; it should be made of some hard wood, such as lignum vitæ, or box, and may be either ornamented or plain; F is an iron pin, which serves to fix the cylinder firm to its foot. [Fig. 2], is the foot detached from the cylinder, and drawn in true proportion as per scale; G, H, I, J, is the base, and may be about one and half diameter high; K, the choak, which serves to connect the cylinder to the foot; L is the nipple, which is half a diameter high, and in thickness equal to the former, or five-eighths diameter; M is the piercer, whose height is three diameters and a-half from the nipple, and at the bottom one third or fourth diameter, from thence tapering to one-sixth diameter in thickness. This piercer should be of iron, and inserted firmly into the foot; its purpose is to preserve a vacuity in the centre of the charge, the nature of which we shall hereafter explain. [Fig. 3], is a former in two pieces, connected by an iron pin, (in diameter equal to the bottom of the piercer,) to which both ends are rounded off, in order that the choak or contraction in the cartridge may be effected more easily; the diameter of this former must be the same as that of the nipple, or suppose the diameter of the mould be divided into eight equal parts, (which is done on one part of the scale,) then the diameter of the former must be equal to five of these parts.

The length of this former, or roller, is not particular, providing it be long enough to admit of good hand-hold in the rolling of the cases; the short part of the former A may be two diameters in length, and should have a line B marked round it in the middle, or one diameter from the end; the longer part may be seven or eight diameters, which will give good hand-hold in the rolling.

[Fig. 4 and 5], are rammers, or drift pins, used in loading the cases, which must be pierced lengthwise to fit on to the piercer.

[Fig. 4]. The first rammer should be pierced the whole length of the piercer, the second rammer should be pierced one and a half diameter; when the case is loaded and rammed above the piercer, a short solid rammer must be used, and these rammers should be a little less than the former, to prevent injury to the inside of the cartridge, when driving in the charge. They should be made of some hard wood, and their extremities secured by ferrels of brass, or any other metal, which will keep them from splitting or extending: their lengths are of little consequence, providing they do not much exceed the relative depths of the cartridge; for, as the workmen say, the longer the rammer the less will be the pressure on the composition by the blow given by the mallet.

The proportion between the length of Rockets and their calibre, is not the same in Rockets of greater or less dimensions than those given above, but should vary nearly as their magnitude; that is to say, their length should be diminished as their calibre is increased. The length of the mould for small Rockets should be six times the calibre, but for Rockets of the mean and larger size, it will be sufficient if the length of the mould be five times, or even four times that of the calibre.

The following is a table computed to regulate the height and diameter of the mould according to the weight of the Rockets, when they are driven solid, or without the use of a piercer. It is extracted from an old treatise on fire-works by Lieutenant Robert Jones; and inserted for the assistance of those who may wish to construct Rockets without the piercer, a practice we would never recommend to those for whom our “Manual” is designed. To those who manufacture fire-works for sale it is certainly the most expeditious method to ram them solid, and with the machine to bore or pierce them afterwards; but to those who make Rockets for their own private recreation, it is by far the most eligible to load them over a piercer, for by the other method it will require a very expensive apparatus,[9] and at first more skill to use it than what the Tyro will possess, and at last he will never be certain that he has made a good article.