We now introduce a spoonful of earth, and choak and bind as before. It is then finished by charging it with 7/12ths of an inch of composition. The remainder of the case is cut, and the composition primed.
Cases, thus prepared, are afterwards treated in the following manner: We pierce three holes in the sides of each, one a little above the last choak, another through, or into the case, to penetrate the last charge, and the third through the first charge. These holes have a communication with each other by means of quickmatch; so that, when the match is set on fire, the two extremes are inflamed at the same time, and being opposed to each other, give a rotary motion to the tourbillon, which, when the powder inflames, terminates by an explosion. The holes ought to be covered with three or four turns of pasted paper. It is then ready to be put into the pots de chasse. When completed, the tourbillon should not exceed 10/12ths of an inch in diameter.
The pots de chasse (mortars somewhat similar to those described) should be made of pasteboard, prepared with eight thicknesses of paper, and moulded upon a roller of 11/12ths of an inch in diameter. They are mounted in the same manner as fire-pots, and are also primed in the same way.
Into each pot there is put four drachms of broken grain powder, and a slip of pasteboard, pierced with five or six holes, which is introduced by means of a stick. A little meal-powder is then put into the pot, and afterwards the tourbillon, the primed end of which must be above the chasse. It is then closed with paper, made into a wad or ball, and the pot is secured with a slip of pasteboard, pasted on it.
Composition of Mosaic Tourbillons.
| 1. | Meal powder, | 16 | oz. |
| Charcoal, | 3 or 4 | dr. | |
| 2. | Meal powder, | 16 | parts. |
| Charcoal, | 3⅓ | —— |
Common tourbillons differ in many respects from the mosaic, although their motion is the same. There are two methods of forming them as well as their appendages, both of which we purpose to describe. The first is the following: Having filled some cases within about 11/2 diameters, drive in a handful of clay, prepared, of course, in the manner described in the first part of the work; then pinch their ends close, and drive them down with a mallet. Then find the centre of gravity of each case; where you nail and tie a stick, which should be 1/2 an inch broad at the middle, and run a little narrower to the ends; these sticks must have their ends turned upwards, so that the cases may turn horizontally on their centres. At the opposite sides of the cases, at each end, bore a hole close to the clay, with a gimblet the size of the neck of a common case of the same nature. From these holes, draw a line round the case, and, at the under part of the case, bore a hole with the same gimblet, within half a diameter of each line, towards the centre; then from one hole to the other, draw a right line. This line divide into three equal parts, and bore a hole near to each of the ends; then from these holes to the other two, lead a quick-match, over which paste a thin paper.
It is to be observed, that there is a stick about the length of the case, which goes across it, and is securely fastened by a cord, that the whole lies flat upon a table before it is fired, and hence, it is sometimes named the table tourbillon; and, that the leader should be carried from one side hole to the other, the holes being made at the opposite sides, as before mentioned. When tourbillons are fired, they must lay upon a smooth table, with their sticks downwards, the leader being set on fire in the middle with a port fire. They should spin two, three, or four seconds round the table, before they rise, which is about the time the composition will be burning from the side holes to those at the bottom.
Reports, or detonating cases, may be fixed to tourbillons, if so required. In this case, we make a small hole in the centre of the case at top, and in the middle of the report make another. Then place them together, and tie on the report, and, with a single paper, secure it from fire. By this method, small cases of stars, rains, &c. may be fixed on tourbillons, being careful, nevertheless, that they are not overloaded.
One-eighth will be a sufficient thickness for the sticks, and their length equal to that of the cases.