http://www.ck12.org Chapter 1. Introduction to Chemistry
more than the original magnesium metal. The explanation offered was that phlogiston had negative weight in this
case. Can the same material have both a positive weight and a negative weight? When mercuric oxide was heated
in the absence of any charcoal, it returned to its pure metal form. The phlogiston theory would require that charcoal
(thought to be essentially pure phlogiston) be present to provide the phlogiston for restoring the metal.
The French scientist Antoine Lavoisier (Figurebelow) carried out studies on oxygen (which had originally been
discovered by Joseph Priestley, an ardent supporter of the phlogiston theory). Lavoisier found that when mercury
was heated, it would become mercuric oxide and gain weight. When the mercuric oxide was heated, it returned to
mercury and released a gas he identified as oxygen. He also carried out a number of experiments that conclusively
demonstrated the essential role of oxygen in combustion processes.
FIGURE 1.12
Antoine Lavoisier and his wife Marie-Anne Pierrette Paulze, who was also
a chemist and made contributions to the work of her husband.FIGURE 1.13
The device used by Lavoisier to study the decomposition of mercuric
oxide.Eventually the phlogiston theory was replaced by the oxygen-based combustion ideas developed by Lavoisier and
others. Today the theory is studied as an example of how to approach a scientific question and how one theory can
be supplanted by another theory that more closely fits the data. It should also be noted that the phlogiston idea took
time to develop, it took time to become accepted, and it took time for researchers to discard it in favor of a better
theory.
Lesson Summary
- The early Greek philosophers spent a great deal of time talking about nature, but they did little or no actual
exploration or investigation. - Inductive reasoning means developing a general conclusion from a collection of observations.
- Deductive reasoning means making a specific statement based on a general principle.
- Scientific method is a process consisting of making observations, developing a hypothesis, and testing that
hypothesis. - Phlogiston theory is the disproven idea that materials lost phlogiston when they burned.