fire composition fireworks oxygen employed motion substances stars combustion paper
PYROTECHNY is the art of producing pleasing scenic effects by means of fire. It is not held to include the manufacture of inflammable and explosive substances for other purposes. The use of fireworks for purposes of display is not a modern invention, for it appears to have existed in China in very ancient times ; but the secret of constructing them remained unknown in Europe till about the 13th century, when the knowledge of GUNPOWDER (q.v.) crept in from the East. In modern times the art has been gradually improved by the work of specialists, who have had the advantage of being guided by scientific knowledge. The value of such knowledge to the pyrotechnist is extremely great ; for he must be governed by the principles of chemistry in the selection of his materials, and his various contrivances for turning them to the best account are subject to the laws of mechanics. As in all such cases, however, science is useless without the aid of practical experience and acquired manual dexterity.
Many substances have a strong tendency to combine with oxygen, and will do so, in certain circumstances, so energetically as to render the products of the combination (which may be solid matter or gas) intensely hot and luminous. This is the general cause of the phenomenon known as fire. Its special character depends chiefly on the nature of the substances burned and on the manner in which the oxygen is supplied to them. As is well known, our atmosphere contains oxygen gas diluted with about four times its volume of nitrogen ; and it is this oxygen which supports the combustion of our coal and candles. But it is not often that the pyrotechnist depends wholly upon atmospheric oxygen for his purposes ; for the phenomena of combustion in it are too familiar, and too little capable of variation, to strike with wonder. Two cases, however, where he does so may be instanced, viz., the burning of magnesium powder and of lycopodiurn, both of which are used for the imitation of lightning in theatres. Nor does the pyrotechnist resort much to the use of pure oxygen, although very brilliant effects may be produced by burning various substances in glass jars filled with the gas. Indeed, the art could never have existed in anything like its present form had not certain solid substances become known which, containing oxygen in combination with other elements, are capable of being made to evolve large volumes of it at the moment it is required. The best examples of these solid oxidizing agents are nitrate of potash (nitre or saltpetre) and chlorate of potash ; and these are of the first importance in the manufacture of fireworks. If a portion of one of these salts be thoroughly powdered and mixed with the correct quantity of some suitable combustible body, also reduced to powder, the resulting mixture is capable of burning with more or less energy without any aid from atmospheric oxygen, since each small piece of fuel is in close juxtaposition to an available and sufficient store of the gas. All that is required is that the liberation of the oxygen from the solid particles which contain it shall be started by the application of heat from without, and the action then goes on unaided. This, then, is the fundamental fact of pyrotechny, - that, with proper attention to the chemical nature of the substances employed, solid mixtures (compositions or fuses) may be prepared which contain within themselves all that is essential for the production of fire.
If nitre and chlorate of potash, with other salts of 'nitric and chloric acids and a few similar compounds, be grouped together as oxidizing agents, most of the other materials used in making firework compositions may be classed as oxidizable eubstances. Every composition must contain at least one sample of each class : usually there are present more than one oxidizable substance, and very often more than one oxidizing agent. In all cases the proportions by weight which the ingredients of a mixture bear to one another is a matter of much importance, for it greatly affects the manner and rate of combustion. The most important oxidizable substances employed are charcoal and sulphur. These two, it is well known, when properly mixed in certain proportions with the oxidizing agent nitre, constitute gunpowder ; and gunpowder plays an important part in the construction of most fireworks. It is sometimes employed alone, when a strong explosion is required ; but more commonly it is mixed with one or more of its own ingredients and with other matters. In addition to charcoal and sulphur, the following oxidizable substances are more or less employed : - many compounds of carbon, such as sugar, starch, resins, Sze. ; certain metallic compounds of sulphur, such as the sulphides of arsenic and antimony ; a few of the metals themselves, such as iron, zinc, magnesium, antimony, copper. Of these metals iron (cast-iron and steel) is more used than any of the others. They are all employed in the form of powder or small filings. They do not contribute much to the burning power of the composition ; but when it is ignited they become intensely heated and are discharged into the air, where they oxidize more or less completely and cause brilliant sparks and scintillations.
Sand, sulphate of potash, calomel, and some other substances, which neither combine with oxygen nor supply it, are sometimes employed as ingredients of the compositions in order to influence the character of the fire. This may be modified in many ways. Thus the rate of combustion may be altered so as to give anything from an instantaneous explosion to a slow fire lasting many minutes. The flame may be clear, smoky, or charged with glowing sparks. But the most important characteristic of a fire - one to which great attention is paid by pyrotechnistsis its colour, which may be varied through the different shades and combinations of yellow, red, green, and blue. These colours are imparted to the flame by the presence in it of the heated vapours of certain metals, of which the following are the most important : - sodium, which gives a yellow colour; calcium, red ; strontium, crimson ; barium, green ; copper, green or blue, according to circumstances. Suitable salts of these metals are much used as ingredients of fire mixtures ; and they are decomposed and volatilized during the process of combustion. Very often the chlorates and nitrates are employed, as they serve the double purpose of supplying oxygen and of imparting colour to the flame.
The number of fire mixtures actually employed is very great ; for the requirements of each variety of firework, and of almost each size of each variety, are different. Moreover, every pyrotechnist has his own taste in the matter of compositions. They are capable, however, of being classified according to the nature of the work to which they are suited. Thus there are rocket-fuses, gerbefuses, squib-fuses, star-compositions, &c. ; and, in addition, there are a few which are essential in the construction of most fireworks, whatever the main composition may be.
Such are the starting-powder, which first catches the fire, the bursting-powder, which causes the final explosion, and the quick-match (cotton-wick, dried after being saturated with a paste of gunpowder and starch), employed for connecting parts of the more complicated works and carrying the fire from one to another. Of the general nature of fuses an idea may be had from the following two examples, which are selected at hazard from among the numerous recipes for making, respectively, tourbillion fire and green stars : - Tourbillion. Green Stars.
Meal gunpowder 24 parts. Chlorate of potash ...16 parts.
Nitre 10 „ Nitrate of baryta ...48 „ Sulphur 7 „ Sulphur 12 „ Charcoal 4 „ Charcoal 1 „ Steel filings 8 „ Shellac 5 ,, Calomel 8 II Sulphide of copper 2 „ Although the making of compositions is of the first importance, it is not the only operation with which the pyrotechnist has to do ; for the construction of the cases in which they are to be packed, and the actual processes of packing and finishing, require much care and dexterity. These cases are made of paper or pasteboard, and are generally of a cylindrical shape. In size they vary greatly, according to the effect which it is desired to produce. The relations of length to thickness, of internal to external diameter, and of these to the size of the openings for discharge, are matters of extreme importance, and must always be attended to with almost mathematical exactness and considered in connexion with the nature of the composition which is to be used.
There is one very important property of fireworks that is due more to the mechanical structure of the cases and the manner in which they are filled than to the precise chemical character of the composition, i.e., their power of motion. Some are so constructed that the piece is kept at rest and the only motion possible is that of the flame and sparks which escape during combustion from the mouth of the case. Others, also fixed, contain, alternately with layers of some more ordinary composition, balls or blocks of a special mixture cemented by some kind of varnish ; and these stars, as they are called, shot into the air, one by one, like bullets from a gun, blaze and burst there with striking effect. But in many instances motion is imparted to the firework as a whole, - to the case as well as to its contents. This motion, various as it is in detail, is almost entirely one of two kinds, - rotatory motion round a fixed point, which may be the centre of gravity of a single piece or that of a whole system of pieces, and free ascending motion through the air. In all cases the cause of motion is the same, viz., that large quantities of gaseous matter • are formed by the combustion, that these can escape only at certain apertures, and that a backward pressure is necessarily exerted at the point opposite to them. When a large gun is discharged, it recoils a few feet. Movable fireworks may be regarded as very light guns loaded with heavy charges ; and in them the recoil is therefore so much greater as to be the most noticeable feature of the discharge ; and it only requires proper contrivances to make the piece fly through the air like a sky-rocket or revolve round a central axis like a Catherine wheel. Beauty of motion is hardly less important in pyrotechny than brilliancy of fire and variety of colour.
The following is a brief description of some of the forms of firework most employed :- Fixed Fires. - Theatre fires consist of a slow composition which may be heaped in a conical pile on a tile or a flagstone and lit at the apex. They require no cases. Usually the fire is coloured, - green, red, or blue ; and beautiful effects are obtained by illuminating buildings with it. It is also used on the stage ; but, in that case, the composition must be such as to give no suffocating or poisonous fumes. Bengal lights are very similar, but are piled in saucers, covered with gummed paper, and lit by means of pieces of match. Marroons are small boxes wrapped round several times with lind cord and filled with a strong composition which explodes with a loud report. They are generally used in batteries, or in combination with some other form of firework. Squibs are straight cylindrical cases about 6 inches long, firmly closed at one end, tightly packed with a strong composition, and capped with touch -paper. Usually a little bursting-powder is put in before the ordinary composition, so that the fire is finished by an explosion. The character of the fire is, of course, susceptible of great variation in colour, &c. Crackers are characterized by the cases being doubled backwards and forwards several times, the folds being pressed close and secured by twine. One end is primed ; and when this is lit the cracker burns with a hissing noise, and a loud report occurs every time the fire reaches a bend. If the cracker is placed on the ground, it will give a jump at each report ; so that it cannot quite fairly be classed among the fixed fireworks. Roman candles are straight cylindrical cases filled with layers of composition and stars alternately. These stars are simply balls of some special composition, usually containing metallic filings, made up with gum and spirits of wine, cut to the required size and shape, dusted with gunpowder, and dried. They are discharged like blazing bullets several feet into the air, and produce a beautiful effect, which may be enhanced by packing stars of differently coloured fire in one case. Gerbes are choked cases, not unlike Roman candles, but often of much larger size. Their fire spreads like a sheaf of wheat. They may be packed with variously coloured stars, which will rise 30 feet or more. Lances are small straight cases charged with compositions like those used for making stars. They are mostly used in complex devices, for which purpose they are fixed with wires on suitable wooden frames. They are connected by leaders, i.e., by quick-match enclosed in paper tubes, so that they can be regulated to take fire all at the same time, singly, or in detachments, as may be desired. The devices constructed in this way are often of an extremely elaborate character ; and they include all the varieties of lettered designs, of fixed suns, fountains, palm-trees, waterfalls, mosaic work, Highland tartan, he.
Rotating Fireworks. - Pin or Catherine wheels are long paper cases filled with a composition by means of a funnel and packing-wire and afterwards wound round a disk of wood. This is fixed by a pin, sometimes vertically and sometimes horizontally ; and the outer primed end of the spiral is lit. As the fire escapes the recoil causes the wheel to revolve in an opposite direction and often with considerable velocity. Pastiles are very similar in principle and construction. Instead of the case being wound in a spiral and made to revolve round its own centre point, it may be used as the engine to drive a wheel or other form of framework round in a circle. Many varied effects are thus produced, of which the fire-wheel is the simplest. Straight cases, filled with some fire-composition, are attached to the end of the spokes of a wheel or other mechanism capable of being rotated. They are all pointed in the same direction at an angle to the spokes, and they are connected together by leaders, so that each, as it burns out, fires the one next it. The pieces may be so chosen that brilliant effects of changing colour are produced ; or various fire-wheels of different colours may be combined, revolving in different planes and different directions - some fast and some slowly. Bisecting wheels, plural wheels, caprice wheels, spiral wheels, are all more or less complicated forms ; and it is possible to produce, by mechanism of this nature, a model in fire of the solar system.
Ascending Fireworks. - Tourbillions are fireworks so constructed as to ascend in the air and rotate at the same time, forming beautiful spiral curves of fire. The straight cylindrical case is closed at the centre and at the two ends with plugs of plaster of Paris, the composition occupying the intermediate parts. The fire finds vent by six holes pierced in the case. Two of these are placed close to the ends, but at opposite sides, so that one end discharges to the right and the other to the left ; and it is this which imparts the rotatory motion. The other holes are placed along the middle line of what is the under-surface of the case when it is laid horizontally on the ground ; and these, discharging downwards, impart an upward motion to the whole. A cross piece of wood balances the tourbillion ; and the quick-match and touch-paper are so arranged that combustion begins at the two ends simultaneously and does not reach the holes of ascension till after the rotation is fairly begun. The skyrocket is generally considered the most beautiful of all fireworks ; and it certainly is the one that requires most skill and science in its construction. It consists essentially of two parts, - the body and the head. The body is a straight cylinder of strong pasted paper and is choked at the lower end, so as to present only a narrow opening for the escape of the fire. The composition does not fill up the case entirely, for a central hollow conical bore extends from the choked mouth np the body for three quarters of its length. This is an essential feature of the rocket. It allows of nearly the whole composition being fired at once ; the result of which is that an enormous quantity of heated gases collects in the hollow bore and the gases, forcing their way downwards through the narrow opening, urge the rocket up through the air. The top of the case is closed by a plaster-of-Paris plug. A hole passes through this and is filled with a fuse, which serves to communicate the fire to the head after the body is burned out. This head, which is made separately and fastened on after the body is packed, consists of a short cylindrical paper chamber with a conical top. It serves the double purpose of cutting a way through the air and of holding the garniture of stars, sparks, crackers, serpents, gold and silver rain, he., which are scattered by bursting fire as soon as the rocket reaches the highest point of its path. A great variety of beautiful effects may be obtained by the exercise of ingenuity in the choice and construction of this garniture. Many of the best results have been obtained by unpublished methods which must be regarded as the secrets of the trade. The stick of the sky-rocket serves the purpose of guiding and balancing it in its flight ; and its size must be accurately adapted to the dimensions of the case. In winged rockets the stick is replaced by cardboard wings, which act like the feathers of an arrow. A girandole is the simultaneous discharge of a large number of rockets (often from one hundred to two hundred), which either spread like a peacock's tail or pierce the sky in all directions with rushing lines of fire. This is usually the final feat of a great pyrotechnic display.
For a description of rockets used in war, see AMMUNITION.
See Chertier, Sur les Fees d' Artifice (Paris, 1841; 2d ed. 1854); Mortimer, Manua/ of Pyrotechny (London, 1856); Tessier, Chinas pyrotechnique, ou naite pratique des Feux Colores (Paris, 1858); Richardson and Watts, Chemical Technology, ay. "Pyrotechny" (London, 1863-67); Thomas Kentish, The Pyrotechnist's Treasury (London, 1878); Websky, Luftfeuencerkkunst (Leipsic, 1878). (0. 31.)