BITUMEN, ROSIN, TALLOW, PITCH, COAL,—..The for mer four are used only in military fireworks, and re quire no particular notice. Coal is recommended in many of the receipts for ornamental works, as produc ing dark, and even black flames. It is always either useless or pernicious. The flame which it gives, if thoroughly burnt by using nitre enough, is white; and if this is in an under proportion, it yields nothing but smoke, and is even apt to be extinguished.
CAMPHOR.—This is recommended to make a white flame. It is both useless and expensive. The flame which it gives is not perceptible in the burning com pound; and a true white flame can be procured only by means of zinc, as we shall hereafter see.
GLASS.—Pounded glass is recommended in some re ceipts for producing red sparks. It is not only, how ever, useless for this purpose, but is a dangerous in gredient in driving, as it is hard enough to set the com positions on fire in the hands of the workmen: while red sparks, or red fire, as it is called, is produced in a more perfect manner by charcoal. It is very necessary, and full time, that many of these absurd processes should be simplified.
Ithen.—Mica in scales, as it is often found among decomposed granite, is also recommended for produc ing what is called red and yellow rain ; but there are no virtues in yellow or brown mica more than in other colours, as is asserted in the receipt books. The fire which it produces is distinguishable from that of char coal, but that only at very small distances; and as it is an expensive or difficult substance to procure, it may in almost all cases be safely omitted.
litor:.—This metal is the chief ornamental ingredient in pyrotechny, from the property which it has of burn ing with brilliant sparks when highly heated. It is the soul of Gerbes, and is introduced into all fiery showers. But the effects of different kinds of iron dif fer much, and it is important to distinguish them for use. It is common to recommend iron filings for must works, particularly for the smaller ones. But malleable iron is far less combustible than steel or cast iron; or the carburetted varieties yield the most sparks, and the finest light. Hence if filings are required, as is the
case for the small wheels and other similar works, they should be those of steel at least, as there are not many -varieties of cast iron that are easily filed. But in the larger works, it is necessary that the iron should be in particles somewhat larger than it can be procured by means of any file in common use. It is therefore re commended to pound it in a mortar, a thing which is scarcely practicable in any species of iron. It is more easy to procure particles of the requisite bulk by pound ing iron turnings; the thickness of which is easily re gulated, and which are indeed to be procured abund antly in all iron manufactories. There are two advan tages in the use of large particles, as they can longer be preserved from rusting in the case, and as they yield, in burning, much more complicated sparks. Cast iron is also in itself less liable to rust than malleable, and hence it is attended with another advantage. We may add that the best iron for this purpose is what is technically called black pig; very distinguishable, from its dark gray colour, as it is the most highly carburetted variety. White pig has the advantage of being more brittle; but if this be more easy to pound, it is more hard to turn. We may add, that it is possible to di minish the tendency of iron to rust when thus used, by means of lac varnish.
ANTIMONY.—This metal is largely used in fireworks for the production of blue light. It is a mistake to Auppose that this can be done by means of sulphur, as when this substance burns rapidly its light is white. Whether the sulphuret of antimony or metallic anti mony is used, in both cases it is the burning of the metal which produces the colour. The sulphuret, com monly called antimony, is used for the stars of rockets and common blue fires, but the light which it yields is not so blue or clear as that from the regulus or me tallic antimony. This therefore is introduced into the compositions for small ornamental or figured lights. commonly called speckles. In all cases antimony must be powdered; but it need not be extremely fine except for the last purpose.