Steel-dust.
5. Steel-dust is another important ingredient in fire-works, for being mixed with mealed powder or some other composition, and the mixture inflamed in a proper tube, or case, the jet of fire produces a most brilliant appearance by the sparks arising from the ignition of the iron in the oxygen gas of the nitre.
Iron-filings, (for this Steel-dust is nothing more than pure iron reduced into small particles by filing or some other method,) when free from rust, and not mixed with any impurities, answer very well; but fire-work makers generally prefer cast-iron reduced to powder, by beating thin plates of it on a cast-iron anvil with a heavy hammer, and sifting the broken particles through sieves of brass or iron wire, of different degrees of fineness, so as to separate the particles into grains of various sizes, according to the magnitude of the pieces. The grains thus sorted have been called iron-sand, and have been distinguished into sand of three or four orders, according to their respective fineness; thus the sand that passes through the finest sieve, is called sand of the first order; and that which passes through the second, sand of the second order; and so on to the fourth, which is generally very coarse. The finest is calculated for fire-works of the smallest size, the second for pieces somewhat larger, and that of the last order, only for pieces of the largest size, such as gerbes of six or eight pounds, the composition of which being of proportionate strength to bring such large particles into a state of ignition.
As these grains are very apt to rust by keeping, they should be preserved either in close stopped bottles, well dried, or in boxes that shut close, and are lined with paper moistened in linseed oil. It sometimes happens that fire-works may be required to be kept a long time, or sent abroad; neither of which could be done with the brilliant fires, if made with filings unprepared, for this reason, that the salt-petre being of a damp nature it causes the iron to rust; the consequence of which is, that when the works are fired there will appear but very few brilliant sparks, but instead of them a number of red and drossy sparks; and besides, the charge will be so much weakened that if this were to take place in wheels, the fire would scarcely be strong enough to force them round; but to prevent such failures in the firing of them, the filings, or iron-sand, may be thus prepared:—