1. 18th Century Chemistry

2. Joseph Priestley (1733-1804) Theologian, chemist, and teacher
Moved to the United States because he opposed the beliefs of the Church of England
Invented soda water
Discovered oxygen (which he called “dephlogisticated” air)
Defender of “Phlogiston” theory

3. Antoine Lavoisier ( )
French
Wealthy nobleman
“Father” of modern chemistry
Executed by guillotine during the French revolution

4. Antoine Lavoisier (1743-1794) Scientific accomplishments
Helped develop the metric system
Wrote the first list of elements
Developed a naming system for chemical compounds
Wrote the law of conservation of mass
Overthrew “Phlogiston” theory

5. Phlogiston Theory-18th Century Science
THE established theory of combustion in the 1700’s.
Universities, schools, etc. all taught phlogiston theory extensively.
Was overthrown in the late 1700’s by Lavoisier and others.
Many thinkers died believing firmly in phlogiston theory and rejecting Lavoisier’s ideas about the so-called element “oxygen”

6. Phlogiston Theory
Phlogiston = an element contained in flammable substances that is released when the substance is burned.
Phlogisticated air = air that is completely saturated with phlogiston (flame goes out)
Dephlogisticated air = air with no phlogiston in it, will cause very bright flames

7. Phlogiston Theory “Evidence” and explanations of phlogiston theory
When you burn things, their mass gets smaller (they give off phlogiston)
Plant material burns easily because plants absorb phlogiston from the air
When you put a flame in an enclosed space, it burns out because the air has been saturated with phlogiston

8. Priestley vs. Lavoisier
Joseph Priestley discovered what we now call oxygen
He called it “dephlogisticated air”
Antoine Lavoisier suggested that phlogiston theory was wrong
He called the “dephlogisticated air” oxygen, and claimed it was a newly discovered element.
He proposed that oxygen in air is what allows things to burn.

9. Evidence for Lavoisier’s Theory
When he burned things in an enclosed space, he found that the mass did not change
When some things burn, they INCREASE in mass (directly conflicts with phlogiston theory!)

10. Phlogiston vs. Oxygen
Eventually, oxygen theory won out over phlogiston theory
Priestley and many others died believing firmly in phlogiston theory and rejecting oxygen theory