Phlogiston

3 Pages 681 Words

Kirby L. Foote
In 1770, G.E. Stahl, a German physician, proposed a theory that received widespread acceptance. He claimed that all inflammable objects contained a material substance that he called "phlogiston," from a Greek word meaning "to set on fire." When an object burned, it poured its content of phlogiston into the air, and when all its phlogiston was gone, it stopped burning. Wood lost its phlogiston very rapidly, so that its passage into air was visible as flames.
Stahl suggested that the rusting of metals also depended on the loss of phlogiston to surrounding air, except that metals lost their phlogiston so slowly that rusting was a gradual process. When metal is calcined, or roasted in the presence of air, it turns to a powdery substance called a calx (now known as an oxide). This reduction in weight was explained as a loss of phlogiston into the air. For the smelting of an ore, the process reversed. Charcoal was believed to be rich in phlogiston and so, when charcoal was burned with this powdery calx, phlogiston supposedly passed from the charcoal to the calx restoring the metal.
Experiments to learn more about the principles of combustion were made in 1772 by Scottish chemist, Joseph Black, and his student, Daniel Rutherford. They tried burning candles in closed containers of air and found that the candles eventually went out even though the containers still held a large amount of air. Mice put into these containers promptly died. Holding to the phlogiston theory, Rutherford came to the conclusion that the burning candles emitted phlogiston but a given volume of air could hold only a certain amount of phlogiston. When the saturation point was reached in the closed container, the air would not accept any more phlogiston and the candle would go out because it could not continue to emit phlogiston. Rutherford believed that, in like manner, a living creature gives up phlogiston while breathing and when placed in air t...