Georg Ernst Stahl and the Phlogiston Theory

Just to keep things balanced, I have an engraving of Georg Stahl hanging on my office wall right near my Priestley likenesses, some of these likenesses I have blogged about earlier.  I have Georg hanging there to put things in perspective.  

Georg Ernst Stahl (1659-1734) was born at Ansbach. He was an eminent chemist and physician and is best know as the foremost proponent of the now defunct and discredited phlogiston theory.  

The phlogiston theory was originally postulated by Johann Becher in 1667. It hypothesized that flammable materials contained phlogiston, a substance without any discernible properties, including, mass, or any other physical properties whatsoever.  When the flammable material was combusted the phlogiston dissipated and the material returned to its "dephlogisticated" state called the calyx or true state.

Joseph Priestley was also a lifelong proponent of the phlogiston theory, and, in fact, upon isolating a substance from mercuric oxide with heat, called it "dephlogisticated air" (oxygen).

It was Antoine Lavoisier in France who showed that combustion requires a gas that has weight. This substance he named oxygen, and in demonstrating that it did have mass he had made the phogiston theory obsolete.  The fact that Lavoisier became obsolete after the French Revolution by losing his head is the subject of a blog yet to be composed.

In any case, the conclusion is that even great minds make mistakes. In Priestley's case it was his clinging to an obsolete theory even after it had been clearly discredited.  In Scientific Correspondence of Joseph Priestley the letters Priestley wrote of his observations from experiments he had performed show his numerous mistakes and ill formed conclusions. Yet, through it all, through all the imperfect observations and incorrect thinking, he was able to accomplish so much. It is a lesson to be learned by all.  Mistakes are normal in the course of discovery. They are essential!  And every assumption must be treated with suspicion.