One of the most beautiful and entertaining uses of fire occurs in firework displays. Fireworks need a source of combustible material for energy such as black powder, a mixture of charcoal, sulfur, and saltpeter (an old name for potassium nitrate), or smokeless powder such as cellulose nitrate. In addition, fireworks contain substances that give off bright, colorful light when heated. Chemical ingredients of fireworks are chosen to produce specific colours. Barium compounds produce green colours when heated, copper salts produce green and blue flames, sodium salts are yellow in flame, lithium compounds produce red colours, magnesium metal produces brilliant white light when burned, and strontium compounds produce brilliant red colours. Barium salts give a green colour in fireworks, due to a series of emission lines between 505 and 535 nanometers.
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