How did oxygen affect a burning candle in Joseph Priestley’s experiment?

In Joseph Priestley’s 1774 experiment, he discovered that a candle would burn in the gas he had isolated by heating red mercuric oxide.1

Because Priestley adhered to the phlogiston theory, he did not initially identify this gas as oxygen. Instead, he named it "dephlogisticated air," believing that ordinary air became saturated with phlogiston—a hypothetical "principle of inflammability"—once it could no longer support combustion or life. By observing that a candle burned brightly in this new air, he concluded that the gas was free of phlogiston, thereby allowing it to absorb the substance released by the burning candle.12