Fireworks

I

Introduction

Fireworks, incendiary devices or materials used for signaling or entertainment, and sometimes known as pyrotechnics. The term pyrotechnics also connotes the skills involved in the making and employment of such illuminative materials. Fireworks include substances or devices that produce, when ignited or activated, sound, smoke, motion, or a combination of these; thus military flare and smoke devices are also considered fireworks.

II

Constituents of Fireworks

The essential constituents of most fireworks are a substance such as potassium nitrate (saltpeter) that supplies oxygen, and substances such as charcoal and sulfur that combine with the oxygen, producing heat and light. A mixture of saltpeter, sulfur, and charcoal constitutes black powder, used for pyrotechny before it was adapted for military purposes (see Gunpowder). By the 17th century, elaborate displays of such fireworks accompanied important celebrations. Shortly after 1800 potassium chlorate was substituted for some or all of the potassium nitrate in the explosive mixture, and potassium chlorate or perchlorate is still a key part of most fireworks mixtures.

A large number of flammable substances, such as starch, gums, sugar, shellac, and various petroleum derivatives, are frequently used in the mixture in place of charcoal and sulfur. Color is given to the fire by incorporating compounds of various metals.

III

Types of Fireworks

Most fireworks are made by incorporating a suitable mixture in a paper case. Among the best-known types of fireworks are the following: firecrackers, used primarily to produce sound; Roman candles, cylindrical containers that are placed in the ground and emit balls or stars of fire at intervals; Catherine wheels and pinwheels, groups of fireworks mounted around the periphery of a wheel that, when discharged, force the wheel to rotate by rocket effect; suns, similar wheels in which the fireworks are discharged outward from the center of the wheel and hence do not produce any rotation; and pastilles, spirally coiled tubes that rotate when lighted. The most elaborate and spectacular of the fireworks is the skyrocket, a rocket-propelled projectile that explodes high in the air to produce any of several types of display.

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IV

Military Flares and Smoke Screens

Pyrotechnics provide an excellent means of signaling, particularly at night. The Very pistol, for example, invented by the American naval officer Edward Wilson Very in 1877, looks like an ordinary pistol with a short barrel of large caliber; it shoots small, colored star shells or balls of fire similar to those produced by a Roman candle. A red Very shell has the universal significance of danger, and various combinations of red, green, and white shells have various meanings according to standard codes. Flares that are fired into the air and then descend by parachute have also been used in military operations for illumination purposes. The most important military pyrotechnics, however, are smoke and smoke screens.

During the period between World War I and World War II, smudge pots (similar to those used to protect orange groves against frost) were developed, as were chemical smokes that produced heavy clouds when ejected into the air. These smokes consisted of some chemical such as chlorosulfonic acid, hexachloroethane, or titanium tetrachloride, which reacted with the water vapor in the air to produce an opaque cloud. In 1940 several American scientists, including Irving Langmuir, began a theoretical and experimental study of smoke. They discovered that an efficient smoke must consist of particles of a particular size, and all of the same size. They also found that a black or colored smoke absorbs light, whereas a white smoke scatters light, and that in many cases the latter is preferable for military screening because the scattered light confuses the observer.

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