09 July 2004

Fireworks

Forrest M. Mims III

The first anniversary of the signing of the Declaration of Independence was celebrated in Philadelphia on July 4, 1777.

According to an article two weeks later in the Virginia Gazette,"The evening was closed with the ringing of bells, and at night there was a grand exhibition of fireworks, which began and concluded with thirteen rockets on the commons, and the city was beautifully illuminated....Thus may the 4th of July, that glorious and ever memorable day, be celebrated through America, by the sons of freedom, from age to age till time shall be no more."

The tradition of celebrating the Fourth of July rapidly spread. Bonfires were ignited and church bells were rung. If fireworks weren't available, rifles and canons were fired. In fact, they were often fired anyway. One report claims that several hundred people were killed each year during Fourth of July celebrations.

By the twentieth century, citizens were prohibited from discharging firearms and using fireworks in major cities. My grandfather over in Houston didn't know about this. He used to fire his pistol into the ground on the Fourth of July while we kids were setting off firecrackers.

The black powder that made fireworks possible was invented by the Chinese more than fifteen hundred years ago. There are various historical accounts of what happened next. What is known for sure is that the Chinese used firecrackers made from black powder in religious and other ceremonies.

Black powder also has a very long and deadly military history, for the Chinese also used it in various kinds of rocket propelled arrows and explosives.

Fireworks used in displays once provided only a few colors, which were always shades of yellow and orange. Pyrotechnics manufacturers found that adding powdered metallic salts to their explosive shells would create brilliant colors.

Copper produces blue and barium provides green. Strontium produces red. Powdered magnesium provides intensely bright flashes of white. Magnesium burns so brightly that it's also used in military illumination flares.

The U.S. is the world's largest consumer of fireworks. We also have the most large scale fireworks displays. As people living nearby can attest, these displays can produce considerable air pollution.

A new development is the use of compressed air to propel exploding shells skyward. This invention was necessitated because of the huge amount of air pollution created by fireworks displays at Disney theme parks.

The web has some terrific articles about fireworks. Begin your visit at www.zambellifireworks.com.


Forrest M. Mims III and his science are featured online at http://www.forrestmims.org/.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.