UU Minute #51

Phlogiston: The Element that Wasn't

The phlogiston theory of combustion, first proposed in 1667, said any flammable substance contains an element called phlogiston, and burning releases it. When a log is all burned up, the fire stops because all the phlogiston has been released out of it and absorbed by the air. Growing plants then absorb this phlogiston from the air, which is why plant matter burns so well.

The phlogiston theory also explained why a fire in an enclosed space would go out: because the air in that space had absorbed all the phlogiston it could, so no more could be released into the air.

Pretty cool theory. Explains a lot. Completely wrong. We now know the process of combustion is just the opposite: when something burns, it’s not releasing something into the air, it’s taking oxygen out of the air and oxidizing with it. Which bring us back to Joseph Priestley, a founding figure of Unitarianism and famous for discovering oxygen.

Preistley focused sunlight on mercuric oxide in a glass tube, which released a gas. Priestley noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, Priestley wrote:
"The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards."
Joseph Priestley had discovered oxygen! Only he called it “dephlogisticated air.” You can see what he was thinking: that candles burn brighter because this special dephlogisticated air could better absorb phlogiston released from the candle.

Have you ever encountered something new and delightful – but got completely backwards what it was and how it worked? If so, you’re in good company.

The path of discovery, whether in science or in our spiritual lives, is a collective enterprise. We do it together. We need each other.

NEXT: The Priestley Riots

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