Combustion Codiscoveries Oxygène Commentary

Uppsala, London, Paris—Joseph Priestley, Carl Wilhelm Scheele, Antoine Lavoisier elements

Combustion

• The “pneumatic” chemists studied air.
• What, they asked, was in it
• that let things burn?
• Since the alchemist Johann Joachim Becher
• proposed the existence of phlogiston in 1667,
• most thought that things burned
• because of the phlogiston in them.
• Becher taught that phlogiston was an element
• contained in combustible materials
• and that fire was the release
• of phlogiston.
• Air, phlogistonists thought, absorbed phlogiston.
• The purpose of breathing
• was to remove phlogiston from the body.
• Phlogistonists said
• that what remained after burning
• was “dephlogisticated”; that is, in burning,
• all its phlogiston had been released.
• Because burning stops in an airtight container
• air, they thought, could absorb
• only a limited amount of phlogiston.
• Thus replete, air, they said, was phlogisticated.
• When Priestley discovered oxygen,
• he found it permitted things to burn
• longer than usual,
• so he thought oxygen must be air with its phlogiston removed.
• Made sense.

Codiscoveries

• Carl Wilhelm Scheele discovered oxygen three years before Priestley,
• but Priestley was first to publish.
• Neither thought that oxygen disproved phlogiston theory
• and both called it dephlogisticated air.
• Antoine Lavoisier, however,
• having read papers by Priestley and Cavendish
• and personal letters from Scheele,
• showed that dephlogisticated air had weight
• and this weight was added to metals when rusted.
• This overthrew phlogiston theory.
• Combustion, breathing, and rusting
• could now all be seen as degrees of oxydation.

Oxygène

• Antoine Lavoisier named oxygène
• “acid-former” in Greek
• because he wrongly thought
• it was required in the composition of acids.
• Fire, breath, life itself
• depends on the biting element in air.
• Let it go to your head;
• without it you are dead.
• Too much, however,
• can burn you up.