Spherical Cases.
These are only required for paper shells, and they are to be made in the spherical former already describ ed. Being fixed in its stand, which is to form the fuse hole, it must first be soaped that the paper may come off easily when the shell is finished. The paper must then be cut into stripes, which are to be laid to meet round it in various circles like the great circles in a sphere. Other pieces being afterwards laid on in gores till the former is covered, the work may proceed with rapidity until it has acquired the requisite thickness, which may vary from half an inch upwards, according to the size of the shell. But it must not be so far completed upon the former but that it may still admit of more coats after it has been removed. Being thus brought up to a sufficient size, it must be suffered to dry in its place, when it is to be cut into two hemi spheres by a saw well greased, and removed from the block. After this, by pasting on a few more coats of paper, the hemispheres are secured, and the shell brought up to the required strength and size. Care must be taken that it be made thus strong enough to bear the explosion of the mortar, as there is no fear but that it will be split by the bursting charge which it is to contain.
Cylindrical Cases.
These are of various kinds, and require some dif ferences in the management, while they all demand considerable attention. 1 he cases for small spiral or firew heels as they are called, must be made by rolling the paper round a wire, which is slightly greased or soaped. Two or three turns of paper, according to its strength, arc sufficient for these, as if they are too thick, they will either break in the turning or burst in the firing. The last turns must be pasted, but with as thin and little paste as possible, for the sante reasons, and the paper ought to be parallel, so that the case through out may be of an equal thickness. The cases for leaders to conduct quick match must be made in the same way ; but the paper for these should be of a much thicker quality, that it may bear rough handling and bending, as well as the paint with which these must generally be cowered. In the wheel-cases, lengths from fifteen to eighteen inches ate sufficient ; but those for leaders may be made of all imaginable lengths, as they are required for so many different purposes.
In making rocket or other cases that are required to fit eh sely in the moulds, it is proper to ascertain first by trial what length of paper is necessary to make the case of the requisite thickness. Thus all risk of waste
or error is avoided, which is important when there is much work to be done. The paper is then to be cut to the requisite size, taking care to have it a little too large in that direction which corresponds to the dia meter of the case, that there may be an allowance for that irregularity at the ends which is unavoidable in rolling. At one of the other sides which correspond to the length of the case, the paper must be carefully cut at right angles; that when it is rolled, the line within may be parallel to the axis, without which the rammer may lay hold of the edge, and force it down in driving. This is an accident carefully to be avoid ed, as it may spoil the effect of a firework altogether. Ott the opposite side of the paper, the cut Is made oblique at an angle of ten or twelve degrees ; so that, w hen rolled up, the edge forms a spiral round the case of about one turn. The wider part being placed at the bottom, is secured by the string which forms the choke; and thus the case is tight at the outer joint, and does not unfold in driving or otherwise. If the case is so thick that more sheets of paper than one arc necessary, all except the last may have both the longi tudinal sides parallel.
In making up the cases a flat smooth table is re quired, with a rolling board, which may be about a foot and a half or two feet broad, and which must at any rate exceed the length of the case. It is furnished above with a handle, by which it may be easily held. In pasting the paper, it is better that the last or inner most turns should remain dry, because, if wetted, or if any paste adheres to the former, it will be difficult to withdraw it. When pasted it is laid near the edge of the table, and the former is laid in it with its handle beyond the table. The case is then rolled up as well as can he done by hand, and then it must be placed un der the rolling board. By pressing hard on this, and continuing to roll the case thus pasted on the table, it can be condensed to a great degree of firmness ; hut care must be taken always to roil in one direction, for if that were reversed, the paper would be loosened, and the case be rendered spungy. This operation is completed by the addition of as much paper as may be necessary to bring it to the requisite thickness.