When zinc is used in fire-works, it should be remarkably fine. The powder may be very readily formed, by heating it, until it is about to fuse, and pulverizing it while hot, in a warm mortar. It is generally considered, however, that the best method of obtaining the powder of zinc, although a longer time is required, is by filing it; but the filings are more or less coarse, according to the file which is used. They may be sifted, and thus obtained of any degree of fineness. In various blue lights, in the blue flame of the parasol and cascades, and other descriptions of fire-works, it is used. It gives a more brilliant light than any other substance used for this purpose. It is frequently mixed with other substances; but, as to its peculiar properties, they remain the same. By the combustion of zinc, which follows in fire-works, it always produces an oxide. In this state, it is expelled, or thrown off.
Acetate of zinc appears to possess advantages over zinc-filing, especially as it produces the same colour, may be more readily mixed, and with more accuracy, and does not deliquesce or absorb moisture, a circumstance which must always be guarded against in artificial fire-works.
Sec. XLIII. Of Brass.
This is a mixed metal, composed of copper and zinc. This alloy, according to the proportion of the metals, is more or less yellow, or reddish-yellow. The yellow copper, or laiton of the French, the similor, Manheim gold, prince Rupert's metal, &c. are alloys of the same metals.
Zinc readily unites with copper; and the usual manner of forming brass by brass-founders, is to make a direct union between the two metals. The process, however, generally consists in mixing together granulated copper, calamine, or carbonated oxide of zinc, and charcoal in powder, and melting them in a crucible. The charcoal reduces the zinc, which then unites with the copper. The heat is kept up for five or six hours, and towards the last of the process, is raised. Zinc, in small proportion, renders copper pale, and in the proportion of one-twelfth, inclines its colour to yellow. The yellow colour increases in intensity with the zinc, until the weight of this metal in the alloy equals that of the copper. An increase of zinc, afterwards makes the alloy white. English brass contains one-third of its weight of zinc. In Germany and Sweden, the proportion of zinc varies from one-fifth to one-fourth of the copper. Twenty to forty parts of zinc, with eighty to sixty parts of copper form the cuivre jaune, laiton, or yellow copper of the French.
Dutch metal, or Dutch gold, is a fine kind of brass, and comes in leaf, which is about five times as thick as gold leaf. This brass is made by the cementation of copper plates with calamine, and hammered out into leaves.
According to Thenard (Traité de Chimie, tome i, p. 478), the French use 50 parts of calamine, mixed intimately with 20 parts of charcoal, and stratified in a crucible with 30 parts of laminated, or granulated copper. British brass consists of two parts of copper, and 11/8 parts of zinc, by weight.
The filings of brass are much employed in fire-works. They communicate to stars, rains, &c. a flame between a blue and green. In some, the filings of copper alone are used. A beautiful green fire, for instance, is produced by 16 ounces of gunpowder, and 31/4 ounces of copper-filings. Verdigris is also employed for the same purpose; but the effect is not so striking, as in that preparation, the copper is already oxidized. The effect of copper in fire-works, it is to be recollected, depends, like that of other metals, on its combustion, and consequent oxidizement. The product of the combustion of brass, is oxide of copper, and oxide of zinc.
Sec. XLIV. Of Bronze.
The union of copper with tin, in various proportions, forms gun-metal, bell-metal, the mirrors of telescopes, and bronze.