Of Roman Candles.
These are also known by the name of fire-pumps. They are very much used on all occasions of public display, as they are exceedingly ornamental; as well as on the most common occasions, by the people, and by school-boys. Though apparently simple, they are by no means easy to make so as to act well, and re quire, therefore, considerable attention, and very parti cular directions.
It is requisite that the cases should be exceedingly strong, as they have to bear considerable force without, at the same time, running any hazard of bursting. All the paper, therefore, which enters into the case, should be pasted at every turn, and well rolled, that it may be as hard as a board, and as strong as a piece of ordnance, which it is, in fact, as far as its use is concerned. Those who have frequent occasion to use this firework, for public purposes, that recur often, will find it good economy to have iron cases as strong as gun barrels, which, of course, must be carefully cleaned and greased when out of use. The length of the case should not be less than twelve diameters; and as this firework, from its nature, cannot be very durable, it may even range as far as fifteen, if carefully made, beyond which the length becomes inconvenient, as the sparks have too far to travel through it before they make their appearance.
Before beginning to fill it, it is necessary that all the compositions which are to be introduced into it, should be ready arranged under the operator's hand, as it is necessary to keep an accurate account of their succession and proportions. Four kinds of fire arc all that can be introduced, but three at least arc neces sary. These are the common sparkling fire from charcoal; that from iron; the blue antimonial light; and the white light, the receipts for which may be selected at the operator's pleasure, from the table of composi tions, with this recollection, that the sparkling fires need not be of a very strong kind, as there is no recoil wanted, and nothing but a stream of sparks. The stars for this purpose may also be taken from the compositions described for stars in general ; but blue and white ones will be sufficient. It is requisite, how ever, that the stars used for Roman candles should be short cylinders, moulded in a case of the same dimen sions, that they may take up as little room as possible, and run the least risk of being broken in the driving of the case. In point of thickness they need not ex
ceed one quarter of the diameter of the charge, as it is a great object to save room, and as the star ought, if possible, to be burnt out before it falls to the ground. Thus we will here suppose, that the case is an inch in the interior diameter, when its length will be twelve inches, and the length of each star a quarter.
The case is closed at the lower extremity, and is filled from above; and as much force cannot be used, it may be driven without the precaution of using a mould. The first thing to be introduced is powder in the grain, to the amount of a diameter, on which is to be placed a star, or two or three, should the artist prefer it. But care must he taken that there be not powder enough to burst the case, as that would spoil the effect. If the artist is desirous that there should be a report at the end, it is better to attach a separate maroon, or a number of these, or else a folded cracker, which must communicate with the end of the charge, by a proper touch-hole.
On the top of the star must now be placed the amount of a diameter or more, of the brightest spark ling fire, which must be rammed down es hard as cats safely be done, without breaking the star. But none of these compositions will bear so much driving as wheels or sky-rockets, for that reason. Another charge of powder, and another star, may then be in troduced, and so on alternately, at the discretion of the operator; taking care to vary the fires as the firework proceeds, by means of the charcoal fires, and the slow flaming compositions. But it is a general rule, that the brighter and stronger fires must be at the bottom, where the length of the case requires it, and that the slow ones should only be introduced high up in the case, as their flames would otherwise be half suffocat ed. The operator must also remember, that wherever a slow composition is introduced, it need not occupy so much space as a quick one; and he must also take care that one species of composition is firmly settled before another is introduced, that their effects on burn ing may be preserved distinct. With these attentions he cannot fail ; and we shall only yet remark, that a twelve inch case may carry from six to eight or ten stars.