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Application of the Scientific Application of the Scientific MethodMethod

An ExampleAn Example

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Why do some things burn?Why do some things burn?

ObservationsObservations1.1. Things would stop burning when placed in a Things would stop burning when placed in a

closed containerclosed container

2.2. Many metals burn to form a white powder Many metals burn to form a white powder called a called a calxcalx

3.3. Metals could be recovered from their calx by Metals could be recovered from their calx by roasting it with charcoalroasting it with charcoal

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Why do some things burn?Why do some things burn? Phlogiston Theory Phlogiston Theory

Explanation of combustion in early/mid Explanation of combustion in early/mid 1700’s1700’s

Combustible substances contained a Combustible substances contained a substance they called substance they called phlogistonphlogiston..

When a substance burned it released all When a substance burned it released all or some of its or some of its phlogistonphlogiston into the air into the air

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How does Phlogiston Theory Explain How does Phlogiston Theory Explain the Observations?the Observations?

When substance is burned in open, all the When substance is burned in open, all the phlogistonphlogiston is released. is released.When substance is burned in closed container, When substance is burned in closed container, phlogistonphlogiston is released until it saturates the is released until it saturates the container, then combustion stops.container, then combustion stops.A metal’s A metal’s calxcalx is what is left after it releases all is what is left after it releases all its its phlogistonphlogiston..When roasted with charcoal the When roasted with charcoal the calxcalx reacquires reacquires phlogistonphlogiston from the charcoal. from the charcoal.– Charcoal is rich in Charcoal is rich in phlogistonphlogiston, that’s why charcoal burns, that’s why charcoal burns

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How was Phlogiston Theory How was Phlogiston Theory Put to the Test?Put to the Test?

Prediction of Phlogiston Theory – if Prediction of Phlogiston Theory – if phlogistonphlogiston is lost when metals burn, then metals should is lost when metals burn, then metals should lose weight when burnedlose weight when burned

Morveau’s Experiments showed that when a Morveau’s Experiments showed that when a piece of metal burned, the resulting piece of metal burned, the resulting calxcalx weighed more than the original metalweighed more than the original metal

Do Morveau’s observations validate or Do Morveau’s observations validate or invalidate the Phlogiston Theory?invalidate the Phlogiston Theory?

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How was Phlogiston Theory How was Phlogiston Theory Put to the Test?Put to the Test?

Prediction of Phlogiston Theory – if a Prediction of Phlogiston Theory – if a calxcalx is is heated, it should remove heated, it should remove phlogistonphlogiston from the from the air as the air as the calxcalx is converted to the metal is converted to the metal

Lavoisier roasted many Lavoisier roasted many calxcalx with a large lens with a large lens and observed that material he called “fixed and observed that material he called “fixed air” was released into the air air” was released into the air

Do Lavoisier’s observations validate or Do Lavoisier’s observations validate or invalidate the Phlogiston Theory? invalidate the Phlogiston Theory?

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A Better Theory of CombustionA Better Theory of Combustion

Lavoisier proposed an alternative theory Lavoisier proposed an alternative theory of combustionof combustion

When materials burn, they remove and When materials burn, they remove and combine with “fixed air” from the air.combine with “fixed air” from the air.

Does Lavoisier’s idea explain all the Does Lavoisier’s idea explain all the previous observations?previous observations?

How could you test Lavoisier’s idea? How could you test Lavoisier’s idea?