It may not be improper, before noticing the arrangement of wheel-cases, to give in this place the compositions, which are used for charging them, reserving, however, the notice of some preparations, when we treat of such works, in which they are particularly employed.
Wheel-cases from two ounces to four pounds.
| Slow fire for wheels. | |||||
| 1. | Saltpetre, | 4 | oz. | ||
| Sulphur, | 2 | — | |||
| Meal-powder, | 1½ | — | |||
| 2. | Saltpetre, | 4 | oz. | ||
| Sulphur, | 1 | — | |||
| Antimony, | 1 | — | 6 | dr. | |
| 3. | Saltpetre | 4½ | oz. | ||
| Sulphur, | 1 | — | |||
| Meal-powder, | 1½ | — | |||
| Dead fire for wheels. | |||||
| 1. | Saltpetre, | 1¼ | oz. | ||
| Sulphur, | ¼ | — | |||
| Lapis calaminaris, (prepared calamine,) | ¼ | — | |||
| Antimony, | 2 | dr. | |||
| Sun cases. | |||||
| 1. | Meal-powder, | 8½ | lbs. | ||
| Saltpetre, | 1 | — | 2 | oz. | |
| Steel-dust, | 2 | — | 10 | — | |
| Sulphur, | 4 | — | |||
| 2. | Meal-powder, | 3 | lbs. | ||
| Saltpetre, | 6 | oz. | |||
| Steel-dust, | 7½ | — | |||
| Crowns or globes. | |||||
| 1. | Saltpetre, | 6 | oz. | ||
| Sulphur, | 2 | lbs. | |||
| Antimony, | 4 | oz. | |||
| Camphor, | 2 | — | |||
This view of the compositions used in fixed and turning pieces, exhibits the various compounds which have been employed, and, therefore, may be relied upon. Notwithstanding they are considered the standard formulæ; yet we must observe, that in some, particularly in the turning sun, with variations, changes are required, in order to produce a variety in the effect. This is accomplished, by making, in the first place, a particular composition, and mixing a given quantity of it with meal-powder, which forms the second change. Of this second composition, combined in a given proportion, with meal-powder, we form a third change; and, in like manner, we employ the third along with more powder, to form a fourth, and the fourth to form a fifth. The particular manner of making these changes will be described in a future section.
Sec. II. Of Single, Vertical, Horizontal, Spiral, and other wheels.
Of the different kinds of vertical wheels, we may mention, that some have their fells of a circular form, others, in the form of a hexagon, octagon, or of a figure of a greater number of sides, according to the length of the cases designed for the wheels. The spokes being fixed in the nave, nail slips of tin, with their edges turned up, so as to form grooves for the cases to lie in, from the end of one spoke to another. Then tie the cases in the grooves head to tail, in the same manner as those on the horizontal water-wheel; so that the cases successively taking fire from one to another, will keep the wheel in an equal rotation. Two of these wheels are very often fired together, one on each side of a building, and both lighted at the same time, and all the cases filled alike to make them keep time together. This may be accomplished in the following manner. In all the cases of both wheels, except the first, and on each wheel, drive two or three ladles full of slow fire, in any part of the cases, but be careful to ram the same quantity in each case; and in the end of one of the cases on each wheel, one ladle full of dead-fire composition, which must be very lightly driven. Many charges of fire may be made by the same method.
The hole in the nave of the wheel may be lined with brass, and made to turn on a smooth iron spindle. On the end of this spindle, let there be a nut to screw off and on. When we have placed the wheel on the spindle, screw on the nut, which will keep the wheel from flying off. Let the mouth of the first case be a little raised.