ORPIMENT, RED.—This compound of arsenic and sulphur is chiefly used for producing the white colour in signal lights, commonly known by the name of Ben gal lights, and used either for military purposes, or in surveying, or lastly in ornamental fires. The light which it gives, though white, and accompanied by much smoke, is not nearly so bright as that produced from zinc; while it is extremely poisonous wherever the operators are exposed to the smoke or burning. For these two reasons its use ought to be exploded alto gether.
ZiNc.—The use of this beautiful ingredient is scarce ly known to any of the pyrotechnists, although, as a substance for light, it is far superior to any of the me tals. The light which it yields on burning, is as bright as that of the sun, and as white, so that the eye can scarcely endure it; and the effect is much increased by tire great quantity of silvery smoke caused by its volatile oxyd; which reflects the fire, and thus widely increases the sphere of illumination. For signal lights it far exceeds any other substance ; a case of an inch in diameter producing a flame that has been seen at seventy miles, and would probably be visible at one hundred. As a military light for discovering the ope rations of besiegers in their trenches, or for other ob jects of nocturnal discovery, it has no rival. It is also
very applicable for ornamental works, where it serves to vary the colours and effects of light and of sparkling fires. It is used in the shape of filings, and has the advantage of being much more durable than iron when made up.
COPPER.—The effect of copper is to give a greenish light; but it is not easy to produce, as the colour is destroyed by too active an inflammation. The nitrate and other salts of this metal will answer this purpose; but they are expensive, and have not been introduced by the firework makers. In the form of filings, it is apt to fail, and the common practice is to use verdigris. Brass filings are recommended, in some books, to pro duce red sparks; but they are burnt in the explosion, so as to produce only light and smoke, partaking in some degree of the effects of zinc. We may add, that some other modifications of colour may be produced by some others of the metals; but they are expensive, nor are the effects such as to be worth purchasing at a great price.