phlogiston+theory

In the late 1600's to mid-1700's, a number of alchemists and other scientists derived a theory to attempt to describe the chemical composition and chemical properties of air. More specifically, they were interested in its ability to support combustion. This theory was called //phlogiston theory//.



Some important observations that had been made were:
 * Some substances are flammable in air, others are not; in general, organic plant or animal material (wood, paper, coal, oil, wax, fats, etc.) were flammable and were considered to contain a substance called //phlogiston.//
 * Once burned in air, these substances were converted to lighter materials (smoke, soot, ash). In the process, they gave off heat and light energy, and were thought to have released their phlogiston.
 * This phlogiston entered the air; in fact, a sealed container around a burning candle, for example, would eventually contain too much //phlogisticated air,// causing the candle to go out. Therefore phlogisticated air would not support combustion.
 * Animals also released phlogiston in respiration, and produced heat, and were thought to get this combustion from plant or animal foods.
 * Air that supported combustion was called //dephlogisticated air//.

Some interesting experiments helped to verify the theory:
 * A burning candle or a mouse inside a sealed container would create phlogisticated air, eventually extinguishing the candle or suffocating the mouse.
 * Placing a mouse inside the sealed container with the burning candle would cause the flame to extinguish faster, and the mouse would suffocate faster.
 * Placing a plant inside the sealed container with the mouse or the candle would result in longer burning time, or the mouse would not suffocate. This reinforced the idea that plant life absorbed phlogiston from the air (and were therefore flammable).
 * A plant in phlogisticated air would thrive. This air would then be able to absorb more phlogiston later (it would support combustion).

One major flaw that led to the demise of phlogiston theory was its application to metals.
 * Steel wool inside a sealed container would create phlogisticated air over time as it rusted.
 * But instead of getting lighter by releasing phlogiston, the metal actually got heavier, which was unexplainable using this theory.

Eventually, phlogiston theory was made obsolete by the works of Antoine Lavoisier, who first used the element oxygen to explain combustion. Phlogisticated air was found to contain nitrogen and carbon dioxide; dephlogisticated air contiained elevated levels of oxygen gas.