In all the smaller works, or even up to two inch diameters, the upper cylinder may thus be made in one piece with a bore. But when port-fires are to be driven, the length of the cases is such as to render it difficult to introduce them, and nearly impossible to withdraw them, in consequence of their extension within the mould. Such moulds, therefore, are best made of two half cylinders well fitted, and held together by driving two or three metal hoops on them. The outsides should be somewhat conical, to admit of their being the more easily taken off when the case is removed, by separat ing the two parts of the mould. Moulds like these are best made of metal, and as they require neither nipples nor spindles, being burnt without a choke at the ends at which they are driven, they may be altogether sunk within a hole of the block fitted to receive and retain them firmly. Other cases that burn without chokes, such as illumination lights, small serpents, &c. may be treated in the same manner.
Similar divisible moulds are also most convenient for large rockets in cases of whatever nature, as they are both most easy to fit and to remove. These may be made of wood, and secured from splitting by hoops and gun metal in the same manner.
It is not now necessary to be particular with respect to the simpler moulds, since the principles applied to those of port-fires are nearly applicable to all. In the smaller cases, such as serpents, the bores may be made for many different sizes in one block of wood; and if many bores of the same size also are made, much time will be saved. These bores, which constitute the moulds for such cases, must pass quite through the block, as the case cannot be withdrawn as it entered, but must be driven through. A mould thus made, re quires only to be placed on the block, to which it may be securely fastened by two loops and pins, as well as in 'many other ways that are too obvious to require description.
On the making of Cases.
This is an important branch of the general matters which concern all fireworks alike. We shall have occa sion to mention the sizes and proportions of these for different kinds of fireworks when those are described; but, in the mean time, the same general principles being applicable to all, they will with more brevity be all condensed under this general head.
Materials for Cases.
Paper, wood, and metal arc the only materials appli cable to the making of cases, and the uses of the two latter are so very limited that a few words will suffice respecting them. For throwing paper shells a metallic mortar is to be preferred, at least in the hands of those artists who are frequently called on for exhibitions, as they are steady, and last for ever. They need not be
very strong, as the charge of powder which they carry is commonly trifling, and they may be fixed in their beds in a position about two or three degrees off the perpendicular, to permit the shell to fall out of the way of the spectators. A common square box of stout elm, well dove-tailed and nailed, serve the same purpose fon discharges of serpents and stars. We shall have occa sion to speak of iron cases for rockets under the division of military fireworks.
For paper cases, three or four sorts at least are wanted. For the spiral wheels it is necessary not only that the cases should be flexible, but that they should burn with the composition, as the wheel would other wise burst and fly off from the support. The paper for these is such as is used for musket cartridges ; this being made of new hempen materials, so as to be very strong and tough. If made with the common gray paper of the shops, they are apt to burst in attempting to give them the spiral form. A thicker kind of gray paper is required for illumination cases which are of a small size, as well as for all the inferior sizes of fireworks of whatever description. This is com monly termed cartridge paper, being used for cartridges for small ordnance. For the larger sizes of fireworks a harder and thicker quality is necessary; and if larger rockets are to be made, the artist should only use what is properly called rocket paper, which is still thicker, and is condensed by rolling in the mill, iti the manner of pasteboard. For the very largest sizes of all, pasteboard itself is preferable, as there is much time saved in the making, and as the work is much firmer.
In making cases, both paste and glue are required ; but the first is chiefly wanted. Paste for this purpose must be made as thick as it is for the use of bookbinders and shoemakers. It is usual to put rosin into it, which serves no purpose unless it be that of preserving it longer without moulding. Alum, which is also com monly introduced, is of very little usc, except as it may render the cases somewhat less combustible; and glue, if it is in sufficient quantity to have any effect at all, only serves to render it intractable. To keep it from moulding, a little oil of turpentine is the most ef fectual substance, and a small quantity of corrosive sub limate prevents rats and mice and cockroaches from de stroying the fireworks when they are to be stored away for any time.