+--------+----------++--------+----------++--------+----------+

Weight.

Diameter.

Weight.

Diameter.

Weight.

Diameter.

+--------+----------++--------+----------++--------+----------+

1 dram

264

1 oz.

664

1 lb.

1672

+--------+----------++--------+----------++--------+----------+

2 drams

332

2 "

836

1 "

18

+--------+----------++--------+----------++--------+----------+

4 "

418

4 "

1056

1 "

191

+--------+----------++--------+----------++--------+----------+

8 "

528

8 "

1328

1 "

202

+--------+----------++--------+----------++--------+----------+

12 "

604

12 "

152

2 "

2112

+--------+----------++--------+----------++--------+----------+

And 2/3 of the above numbers multiplied by 8, give the correct names for rockets in eighths of an inch.

Required the true size of a half-pounder.

1328 2 8 ------------- = 708.

3

A trifle above 7/8, as before stated.

A cast-iron ball 6 inches in diameter weighs 30lb.

Cast iron is about 40/63 the weight of lead.

5280 feet = 1 mile; 3280 feet = 1 kilometre.

_WHEEL AND FIXED CASES._

Wheel cases may be 5-5/8 inches long. Cut the paper, without waste, into 4 strips, each 29 inches long. Fixed cases may be 7-1/4 inches long: cut the paper the other way of the sheet, into 4 strips, each 22-1/2 inches long. The extra length, for fixed cases, is to allow of their being reported; that is, filled at the end, with an inch, or more, of grain powder, to make a bang like a squib. The cases are to be gauged to the thickness of roman candle cases, but choked like rockets; 5/8 internal, and 7/8 external, are a good size. Two solid drifts will be required for wheel cases; one 5-1/2 inches long, besides the head; the other 3 inches: for the fixed cases it will be necessary to have one of 7-1/4 inches. They may be turned of box, beech, or ash; but gun-metal drifts are best, though by no means indispensable. If they are cast in gun-metal, they will simply require filing in the rough places. The cases are to be rammed solid throughout, on a foot, fig. 42, turned in one piece, with a nipple, and a pin 1/3 of a diameter thick, and just high enough to keep the choke clear.

In all wheel and fixed cases, whatever the remainder of the fuse may be, begin by putting in one scoop of starting fire; this, when malleted firmly in, should fill about 3/8 of an inch in the case. The subsequent fuse can be selected from the Tables. The choke may be protected with a little clay, before the starting fire, like rockets, if thought desirable: no clay is to be used anywhere else. Wheel cases containing steel-filings are termed brilliant.

To prime the cases, very slightly damp some meal powder, by sprinkling it with a few drops of water; mix and chop it up, or mince it, as it were, with a knife: put a little into the mouth of the case, press the nipple, fig. 42, into it, and work it round; this will prime the choke and the mouth at once, still leaving the choke clear; or, paint the choke and mouth with the sash-tool, with meal paste, just sufficient to wet them, then plunge them into dry meal, give them a rap to shake off the superfluous dust, and lay them by to dry.

Wheel and fixed cases need not be choked at all, but plugged 1/4 of an inch, with plaster of paris, as directed for roman candles. When dry, charge them by setting them flat on the block, without using the foot.

Mallet in a scoop of starting fire, then the other. Afterwards, when a number are charged, bore through the centre of the plaster, with a sh.e.l.l-bit, 1/3 the diameter of the case; insert a piece of match in the hole; wash the face of the plaster over with meal paste, and plunge into dry meal. A sheet of double-crown makes 8 wheel case envelopes (2.2.2) 10 by 7-1/2, so that the void at each end, to receive the match, is nearly 1 inch.

It is not possible to devise a formula that will indicate the exact quant.i.ty required for wheel cases, as the fuses vary; but, representing the length, in inches, by I; and the diameter in eighths by e, the following will help to serve as a guide.

(I e)/7 = drams.

Suppose a wheel case 5-5/8 inches long, and 4 eighths diameter,

(5? 4 4)/7 = 90/7 = 13 drams.

Suppose a fixed case 7-1/4 inches long, and 5 eighths diameter,

(7 5 5)/7 = 181/7 = 26 drms. = 1 oz. 10 drms.

_GERBES._

Gerbes, so called from the French word for wheat-sheaf, which they resemble, are fixed choked cases: they do not show well on wheels. As they contain grains of iron, they must not be under 6/8; for private exhibitions a good size is 9/8, 9/8 internal diameter; 12/8 external; 3/8 the diameter of the choke; 11-1/4 inches, length of case. Charge the case on a nipple, exactly like a wheel case. It is advisable to put in, first, a little clay, to protect the choke, as the fire, being fierce, would, otherwise, enlarge it, and diminish the ascent of the sparks.

Upon the clay drive in a scoop of starting fire, and fill up with gerbe composition. This, when containing iron borings, is termed Chinese fire; the pieces, Chinese trees.

The most magnificent of all, however, is the coloured gerbe. For this, some green, blue, and crimson grains, or small stars must be prepared.

They may be quarter-inch cubes, cut as directed for the chopped nitre stars. A far better way, however, of preparing them, is to remove the pin a, of fig. 2, up to c, so that the stars, driven in the tube, will be 5/8 inch diameter, and 3/8 thick. When these are dry, chop them into 4 pieces, by holding a knife, or chisel, across them, and giving it a smart blow with the mallet. They are harder made this way.

To charge the cases: having driven in the clay, and the starting fire, put in 7 or 8 stars, then a scoopful of fuse No. 1 or 2, then 7 or 8 more stars, and another scoop of fuse; mallet the whole 4 layers down firm, with blows not too heavy at a time, but many times repeated. Then put in 7 or 8 more stars, another scoopful, 7 or 8 more stars, and another scoop, and mallet the 4 layers as before; and so repeat. The two layers and the two scoopfuls may fill up, when malleted in, 3/4 of an inch, in a 9/8 case.

Instead of choking the cases, plaster of paris is far preferable. Let it be 3/8 of an inch thick, and well dried, before charging. After the cases are charged, bore a hole through the plaster, 1/3 of a diameter, that is, with a 9/8 case, 3/8 of an inch diameter. For this purpose it is not necessary to have another sh.e.l.l-bit; bore it with the 3/16, and enlarge it with a penknife. It is better arched under, till conical, as shown in fig. 48. Prime with 4 or 5 pieces of match, and wash with the sash-tool.

The gerbe being finished, make a cylindrical box, or paper bag, of 2 or 3 thicknesses of paper: fill it with a number of crackers, and a scoopful of meal powder, and fasten it to the gerbe.

No single piece is more effective than a coloured gerbe; the stars will be projected 30 feet, or more: they may be put in, mixed; or, one layer may be blue, another green, another crimson. Twist a piece of wire, deprived of its elasticity, round the neck, and another piece round the bottom, and leave long ends; it can then be fastened by them to the top of a post. To remove the elasticity from iron wire, lay it in the fire till red hot; withdraw it with the tongs, and put it aside, to cool slowly. If copper wire is used, it will bend without preparation. String must not be employed, as it might burn, and let the case fall. Common pins, patent short whites, deprived of their elasticity, are useful for connecting the parts of l.u.s.tres together.

_FLOWER POTS._

These are choked cases, charged with spur fire: the fire is somewhat slow, so the cases must be short: 4 inches long, and 5/8 diameter is a good size. Rub the composition thoroughly up in the mortar; the vegetable black produces beautiful star-like sparks, totally dissimilar to any other. Put a little composition, at a time, into the case, and jolt it with the roman candle rammer.

Vegetable black, introduced into a star, causes it to tail, like linseed oil. Light such star on the hob; it will burn, and leave a residue, unaltered in shape; blow upon this continuously with the mouth, or, better still, with a pair of bellows: the supply of oxygen will cause it to boil up, in a state of fusion, when it will begin to throw out cl.u.s.ters of the peculiar starlike sparks, before mentioned, bright and yellow as new sovereigns.

Vegetable black is a pure lamp black; some samples of lamp black make equally good stars, but others are worthless. Greater reliance can be placed upon vegetable black. Vegetable black and lamp black must not be mixed with linseed oil, as such mixture is liable to spontaneous combustion.

Roll up a tube for pill boxes, of two thicknesses of brown paper. When dry, cut it into pieces about 1-1/8 inch long: choke one end, like a wheel case; set it on a nipple,and charge it with spur fire, till full within 1/16 of an inch: fill up flush with a little plaster of paris, pressed in flat with a knife: prime the choked end, and put a number of such cases into a rocket head, or sh.e.l.l.

_PORT FIRES AND Sh.e.l.l FUSES._

These are unchoked cases, like roman candles; 6 inches long, 3/8 internal, (4-1/2)/8 external, is a good size. They should be rammed, as hard as possible; and, for this purpose, it is best to have a mould.

Now, if a case is rolled of such a size that it will exactly fit into a bra.s.s tube, and is charged, in it, very hard, it will swell, and it will be almost impossible to get it out again; but if it be made a trifle smaller, so as to just slip through the tube; then, if a piece of writing paper be rolled, dry, round it, once or twice, so as to make it a tight fit, and the case is charged, it can be pushed out, like a pellet from a popgun, leaving the writing paper, generally, in the tube, or mould, and the case will come out without a wrinkle.

Let the composition be put in, very little at a time, and well driven with a solid rammer and mallet. Fig. 59 represents the mould; the foot b fits the tube a; the tenon c fits the case; a wire, d, goes through 2 holes in the bra.s.s tube, and a hole through the foot; a nut, e, to keep the wire from jarring out, is made of a piece of indiarubber: make a hole through it, with a bradawl, and slip it on the wire; or, a screw-eye may be pa.s.sed through and held with a leaden, or wooden nut.

_TOURBILLIONS._[A]

A tourbillion, so called from the French word for whirlwind, is a case made to rotate and ascend at the same time, forming a spiral of fire, and ending in the shape of an umbrella.

TO MAKE A TOURBILLION.