Phlogistons

Part of speech: noun

Definitions

1. A theoretical substance once believed to be released during combustion processes
2. An 18th-century hypothesis proposing that this element was the essence of fire
3. A concept used to explain oxidation before the modern understanding of chemical reactions was established

Etymology: Phlogiston was a substance that 18th-century chemists believed every combustible material contained, and that escaped as flame when the material burned. The idea was formalised by the German chemist Georg Ernst Stahl, who coined the name in 1702 from New Latin "phlogiston," itself taken from Ancient Greek "phlogistón," the neuter form of "phlogistós," meaning "burnt up" or "inflammable." That Greek root goes back to "phlóx," meaning "flame," and "phlogízō," "to set fire to." The name was built to describe something invisible: a material that left the burning object and carried away its fire. Because the theory explained why wood shrank and metals changed when heated, it was widely accepted for most of the century. Its supporters thought a substance losing phlogiston should weigh less afterwards, which made the idea seem testable. The plural "phlogistons" refers to more than one such hypothesised substance, or to the idea as it appeared in different versions. It is the plural of "phlogiston," so it carries the same origin.