As the effect of Chinese fire on wheels depends greatly on the motion of the wheel, its velocity should therefore be accelerated; which, although the duration of its effect would be shorter and more brilliant, may be produced by employing several cases of white fire, and communicating their fire one to the other by leaders in the usual manner.
There is no doubt, that the accelerated motion of the wheel causes the composition to burn more rapidly, in the same way as a bellows excites the heat of a blast-furnace; and, therefore, the increased brilliancy of the fire may be attributed to the greater rapidity of the combustion, which necessarily produces, in a shorter time, the oxidizement of the iron, and, at the same time, the combustion of the other substances.
With respect to the comparative force of compositions, or that power by which cases, as rockets, &c. ascend, or which gives motion to vertical and horizontal wheels, we may observe generally, that these effects depend on the compositions employed; and that the recoil, in such instances, is proportionate to the impelling power; for the resistance with which the fire meets from the air, in the immediate vicinity of the caliber of the case, causes a reaction, which produces the recoil, and consequently the motion of the wheel. That this effect depends, in a greater or less degree, on the composition we use, and the manner the case is charged, is very evident. (See [General Theory of Fire-Works.] Part 1.)
Composition of Chinese Fire for calibers under ten-twelfths of an inch.
It may be proper to remark, that the above formulæ are all approved; as they have been used in France, and are given on the authority of Morel and Bigot. We are informed, indeed, that these proportions produce the most perfect fire, which surpasses the fire of the Chinese. From the many experiments made in France, instituted with the view of determining the best proportions, and leading, in fact, to the improvement of the original composition, we do not hesitate to give them the preference over all others.
In the composition of wheel-cases, Chinese fire is sometimes used, and then only for decoration; but in nearly all the compositions employed, in wheel-works, for standing or fixed cases, sun-cases, &c. steel-dust forms a constituent part. The proportion it bears to other substances is various: viz. to meal-powder, as one to five, one to ten, &c. In one of the formulæ for brilliant fire, the proportion is still greater, and in another less; but by mixing seven and a half ounces of steel-dust with meal-powder, saltpetre, and sulphur in the proportion of eleven pounds, one pound two ounces, and four ounces respectively, a composition is formed, calculated to produce a brilliant fire. But as this subject will be considered, when we treat of wheel-works, standing pieces, &c. and the different compositions appertaining thereto, we would only observe, that Chinese fire should always be preferred, where the object is decidedly appearance, with brilliancy and splendour.
Sec. IV. Of Bengal Lights.
We have had occasion to mention heretofore, that metallic as well as the crude, or sulphuret of, antimony, entered as a component part into some compositions, in order to vary the effect and appearance of the flame. That this is the effect, in the composition, which constitutes the Bengal lights, is a fact well known, and to which its particular character is owing.
Bengal lights, in consequence of the whiteness and brilliancy of their flame, are considered as highly important in fire-works. The composition was a long time kept secret, and artists were at a loss to compound it, for those who possessed the secret, it appears, would not divulge it. Simple as it is, it was not known, until many experiments were made, which proved its identity with the original Bengal composition; and, since that time, it has been confirmed by the original formula. Morel assures us, that he purchased the secret.