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Why was Joseph Black slow to accept Lavoisier’s oxygen theory?

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Joseph Black Joseph Black, detail of an engraving by J. Rogers after a portrait by Sir Henry Raeburn

Joseph Black was reluctant to accept Antoine-Laurent Lavoisier’s oxygen theory because he remained committed to the long-standing phlogiston theory of combustion.2

The phlogiston theory, which posited that burning substances emit an invisible, weightless principle called phlogiston, was the prevailing scientific framework during much of Black's career. Although Black’s own students argued in favor of Lavoisier’s new system—which identified oxygen as the active agent in combustion—Black did not formally abandon the phlogiston hypothesis until 1790, after he began corresponding with Lavoisier.12

While Black’s earlier experimental work on "fixed air" (carbon dioxide) provided a foundational methodology that Lavoisier later utilized to develop his own revolutionary system, Black’s own views on combustion became increasingly outdated toward the end of his life. His eventual acceptance of the oxygen theory marked a transition toward the modern chemical understanding that replaced the phlogistonist perspective.234