With respect to their materials, the same rule may be followed for the hollow as for the solid rammers. The lengths, the heads, and other circumstances, are also the 'same ; but, as these are always to be used with mallets, the whole set, from the smallest upwards, re quire to be of the shorter proportions, or so made as to exceed the length of the cases by two or three diame ters only. As, however, there are only two kindi of fireworks in which boring is required, namely, wheel cases and rockets, it is unnecessary to have any hollow rammers of smaller or larger sizes than the dimensions at either extreme which are intended for these. Thus, as neither rockets nor wheel-cases of less than a quar ter of a pound dimensions arc commonly required, nor of more than two pounds, which take a rammer of about one inch and five-tenths diameter, it is not necessary to be provided with any beyond these two extremes.
The description of the rammers required for driving rockets will serve for that of all others, with so few alterations, that we shall first mention the construction of these, Plate CCCCLXXII. Fig. 3. We may also assume a diameter of an inch, and a length of nine inches, as all others may be reduced to this scale. In this, the length of the composition from the choke is five inches and a quarter, and the complete rammer intended for it must contain a conical cavity exactly fitted to the spindle Fig. 2, which, for this length, is four inches long. The diameter of this cavity or bore, at the bottom, is half an inch, or, in all dimensions, half the diameter ; and it tapers regularly to the extremity, which is some what blunt.
Now, as in driving, the rammer rises as the composi tion mounts up in the case, it is plain that, after a short time, the spindle will no longer reach the bottom of the bore. Hence the composition accumulates in it, and becomes hard driven on the top of the spindle, so as to render it a matter of some trouble to clear it out again. At the same time, as the rammer mounts upwards in the ease, the protruded part becomes so long, that it is difficult to give the same firm blows above, or in the upper part of the composition, as were given in the lower, in consequence of which the action of the rocket becomes irregular. It becomes necessary, there fore, to have a succession of rammers for one rocket, each, in turn, shorter than the preceding, and with a shorter bore at the same time : the last and shortest is to be quite solid. A set of five is sufficient ; but, if economy is a great object, four may be made to answer the purpose.
For wheels, one bored rammer will be sufficient, as the bores of these are not required to be long. It is not always, indeed, that they require any boring ; and in complicated movements of works, where it is possible to apply machinery to turn them, instead of trusting to their own recoil alone, it is much better to do so, as greater regularity is thus ensured.
On Boring Fireworks.
As the hollow rammers require occasional boring to keep them clean, we may as well introduce the whole subject of boring in this place, as there are some cases in which it is indispensable. There is a peculiar ma chine sometimes used for this purpose by the makers of fireworks, but no complicated contrivance is necessary. For cleaning out the bores of the hollow rammers, a drill moved by a drill-bow is quite sufficient; because the quantity of composition is so small, that if it were to take fire it can do the operator no harm. In metal rammers, it is fully more convenient to burn it out by means of a bit of priming or quick match, or else it may be washed, out by soaking in hot water, though this method is somewhat tedious. Neither of these methods, however, is applicable to wooden rammers, for obvious reasons.
In boring those single-case wheels which turn on a hole in their own centres, a common gimblet answers every purpose, as it is barely necessary to perforate the paper. Small tourbillons may also he bored in the same way ; but it is necessary that tallow be used with the gimblet, partly to make it work easily, and partly to pre vent the risk of taking fire. For large tourbillons, however, the drill becomes necessary ; as the labour of boring these is very great, in consequence of the hard ness of the composition. These works cannot he driven on spindles, on account of the complicated directions of the bores. But the system of boring, whether for rockets or large wheel-cases, ought to be abandoned altogether in favour of driving on spindles. The latter method is the safest, and does not require more time. It is quite possible for a work to take fire under the drill, which may be attended with serious inconveniences ; besides which, there is danger that the composition in a rocket may be disturbed, the consequence of which would be for it to burst on firing. We, therefore, recommend that drilling should be limited to tourbillons, as we have already mentioned. For this purpose, nothing answers better than a common foot lathe, with the drill fixed in the chuck. If the bore is to be made in the axis of the firework, that may also be fixed in the opposite one, and brought gradually up by means of the screw ; but the tourbillons require to be guided by the hand, as it is impossible, by any methods of fixing them, to give a right direction to the holes. Care must be taken that the drills be kept well greased with tallow ; and the drilling-engine ought also to be out of doors, or in a separate outhouse or tent.