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No. 1515:

Today, let's try to find out who discovered oxygen. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

In his 1962 bombshell-book about scientific change, The Structure of Scientific Revolutions, Thomas Kuhn gave us a whole new way to think about priority. Kuhn showed that revolutionary scientific change was never the work of a single genius. Rather, it occurs when new communities form around wholly new scientific outlooks.

Kuhn does this best when he talks about the "discovery" of oxygen. You and I know perfectly well that the oxygen in air reacts with other materials when they burn. But eighteenth-century chemists thought burning materials were simply releasing an invisible fluid called phlogiston, which caused heating. No one supposed burning had anything to do with the air itself. They had no idea that oxygen, which makes up one fifth of air, was the active agent.

Three people finally pinned oxygen down as a separate element in the 1770s: an English cleric named Priestley, the French chemist Lavoisier, and a Swedish pharmacist named Scheele. When Priestley isolated oxygen in 1774, he thought he had laughing gas. A year later he decided he'd actually taken the phlogiston out of air. At the same time, Lavoisier (who knew about Priestley's work) also isolated oxygen. He thought it was very pure air.

Two years later, Lavoisier realized he'd actually separated a component of air; but he thought it was something that came into existence only when air was heated. Meanwhile, the Swede Scheele had been working quietly. He published a book titled Air and Fire just after Lavoisier uttered his final word on the matter. Based on work he'd done before either Priestley or Lavoisier, Scheele realized that oxygen was a separate part of air.

Kuhn uses this muddle to undercut all our talk about who got there first -- to show how squabbles over who gets credit cloud the real story. Should we credit Priestley, who isolated oxygen -- then went to his death thinking it was something else? Lavoisier, who saw it was part of air but didn't know it was a new element? And what can we say about Scheele, who was slow to publish his results?

The fact is that oxygen couldn't possibly have been understood in terms that you and I find acceptable. Scientists first had to change their whole view of matter. Priestley started a scientific revolution that couldn't be finished until John Dalton built oxygen into the atomic theory of matter thirty years later.

The idea that burning meant new combinations of atoms was too great a leap for any one person to make. Pieces of the puzzle added up until an unexpected new picture suddenly burst free. Oxygen wasn't discovered at all. Oxygen as we know it couldn't've been perceived, much less discovered, until a whole new science was forged to accommodate it. Priestley, Lavoisier, Scheele, and Dalton each added new insights, but the game couldn't be concluded until it'd added up to a major scientific revolution.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Kuhn, T. S., The Structure of Scientific Revolutions. Chicago: The University of Chicago Press, 1970.

This is a greatly revised version of Episode 86.

Joseph Priestley

Joseph Priestley
From Dibner, B., Early Electrical Machines. Image courtesy of the
Burndy Library, Dibner Institute for the History of Science and Technology