During the seventeenth century, chemists needed a broad conceptual system to explain what caused the chemical reactions they observed. The phlogiston theory of combustion was the first comprehensive theory of chemistry and it served to satisfy the need for a broad system of explanation. This theory was based on phlogiston, a substance that chemists thought was contained in all combustible substances. The phlogiston theory was the first theory of chemistry that was able to explain a wide range of phenomena.

An example of a reaction that the phlogiston theory could explain is the preparation of metals from their ores by heating with charcoal (smelting). The transformation of an earthy substance, the ore, into a metal by this process appeared to be much the same whether the metal involved was iron, tin, or copper. The fact that metals became ores when heated and could be changed back into metals...