The Beginnings of Modern Chemistry

The Beginnings of Modern Chemistry

For about two centuries after Boyle, scientists continued to make useful discoveries but made little progress in understanding the true nature of matter or chemical behavior. Perhaps the greatest source of confusion and defeat in these centuries was a theory of burning (combustion) called the phlogiston theory. It was originated by the German chemists Johann Joachim Becher and Georg Ernst Stahl in the late 1600s. According to this theory, phlogiston, an “essence” like yellowness or hardness in the theories of the ancient philosophers, escaped from substances during the burning process. By this time, chemists were learning to gain knowledge the modern way: by testing theories with experiments (see science). But such tests failed to confirm the existence of phlogiston.

The first clue to a more useful theory came when an English chemist, Joseph Priestley, discovered in 1774 that a gas (now known as oxygen) was essential to the burning process. (Oxygen was also discovered by the Swedish chemist Carl Wilhelm Scheele at about the same time.) A few years earlier another English scientist, Henry Cavendish, had identified hydrogen as an element. The French chemist Antoine-Laurent Lavoisier used the discoveries of Priestley and Cavendish in a series of experiments from which he formulated the presently accepted theory of combustion. He also showed that burning, the rusting of metals, and the breathing of animals are all processes in which oxygen combines chemically with other substances. Lavoisier's most significant finding was that the products of a chemical reaction have the same total mass as the reactants, no matter how much the substances are changed. This means that, even when chemical changes take place, something essential stays the same. These contributions are often considered to mark the beginning of modern chemistry.