There can be hut two modes of ornamental fire, namely, flame and sparks, however these may be varied and combined, whether as to colour, or quality, or quan tity, or mixture, or alternation, or, according to their mechanical disposition in vat-ions kinds of work. A se parate management of the composition is required in each of these.
In compositions which are merely to flame, slowness of burning is necessary, and all sparks are excluded, as purity of colour, steadiness, and duration, are the principal objects. Hence the basis of all these compo sitions must exclude charcoal as far as it is possible to do without it, and the mixtures must also be as minute and intimate as can be effected. Thus, wherever char coal is necessary, it is introduced in the form of mewled powder, as it is there so fine as to yield no sparks, while the requisite degree of feebleness or dilution is obtained by diminishing the dose of nitre. Such is the general basis of all compositions merely luminous, whether in the shape of cases or stars; and to it the several ingredients intended to modify the colours of the flame are added. All of these must also be most finely powdered and intimately mixed, as it is only in this manner that steadiness and clearness of flame can be produced.
In compositions that are intended to sparkle, the or dinary mixture used for recoil forms the basis. Even this may be rendered sufficiently brilliant by increasing the charcoal, and using it in the state of a coarse pow der ; but it is also modified by the addition of other sparkling substances, and principally of iron. As this ingredient is extremely brilliant in its effect, it may also be united to the simpler bases intended for flaming compositions ; by which means its peculiar effects are obtained in a state of purity. It is so easy to under stand how these different kinds of composition may be united or alternated, that it is almost superlluous to men tion it. Yet we may give one instance as an illustration, by saying, that if iron be mixed with the antimonial com position for a blue flame, the result will be a firework discharging a blue flame, accompanied by brilliant white sparks.
Of the General Mechanical arrangement of Fzreworks.
THE mere fires of works in Pyrotechny being thus limited in point of variety, it is chiefly by their mecha arrangements and combinations that all their splendid effects are produced. In some cases these arrangements are simple and inherent in the very na ture of the firework ; in others they are complicated in various modes, so that there is scarcely any end to the varieties which an ingenious artist can produce. As it
would be impossible within the limits of our article, to describe even a small part of the arrangements of which they arc susceptible, we shall here give a sketch of the general principles by which they arc guided, so that artist of any resource will be able to produce new effects without difficulty. Hereafter, the few varieties which we shall select for consideration will serve for examples of what may be done in this department of the art ; and on which, after such general remarks and exam ples, it would be as little necessary to enlarge as it would be to us impossible.
The leading distinction among fireworks is between those which arc characterised by rest, and those to which motion is essential. In the former, the effect depends solely on the quantity, the shape, and the colours of the fire, if they are simple, and on the various ways in which that is directed and combined in compound and complicated works. Gerbes, which throw out a spark ling fire, offer a good example of the simpler kinds, which arc indeed rarely used in this manner, without being at least relieved by others, if not united aml in termixed with them. It is evident, however, that in numerable varieties may be produced, merely by the combination and disposition of the simplest fireworks. Thus, for example, a bright star may be made by five or six small flaming lights, or speckles, radiating from a centre. In greater number, many such stars may be dis posed in various forms, either alone, or in combination with other bodies. When in still greater numbers, such illumination lights may be arranged in lines, or crosses, or circles, or triangles, or in any other figures, and those also may be intermixed in various ways. Be coming more compounded still, they may serve to de fine the architectural lines of a pyrotechnic building, the other ornaments of which may exhibit all the varie ties of fire of which the art is susceptible. Lastly, that we may not dwell unnecessarily on this subject, they may be disposed in the form of letters, so as to express the names of individuals, or any sentence connected with the particular object of the firework which is dis played.