The crumbling facade of a century-old theory finally came crashing down on 5th September 1775, when French chemist Antoine Lavoisier presented his findings to the French Academy of Science, effectively debunking the phlogiston theory that had dominated scientific understanding for nearly a century. This 'matter of fire' – believed to be a colourless, odourless, tasteless and weightless element present in all flammable materials – was a cornerstone of 17th-century German thought, born from the work of professors Johann Joachim Becher and Georg Ernst Stahl.
Becher initially proposed that metals and minerals were compounds releasing a 'fatty, flammable earth' (terra pinguis) during combustion, leaving behind their true forms. Stahl refined this concept in 1700 by replacing terra pinguis with phlogiston, derived from the Greek word for flammable. He further elaborated on his ideas in his 1708 work, 'The True Theory of Medicine', suggesting that phlogiston was not only released during combustion but also through living organisms' respiration, producing 'phlogisticated air' that plants absorbed.
Charcoal's minimal residue upon burning led proponents to believe it contained almost pure phlogiston. The theory even suggested rusting iron was a slow release of phlogiston, causing it to revert to its elemental form. British scientist Joseph Priestley, inventor of the fizzy drink and discoverer of several gases, described 'dephlogisticated air' as being exceptionally beneficial for combustion, observing a candle's increased brightness and a mouse's prolonged survival in this gas. He communicated his findings to Lavoisier.
Lavoisier's own investigations led him to a different conclusion, however. Presenting his findings on 5th September 1775, he declared that Priestley's 'dephlogisticated air' was the true combustible body and that no massive quantities of fixed fire were needed in combustible materials. He renamed this gas 'pure air', later rebranding it as 'oxygen', fundamentally altering our understanding of combustion and laying the groundwork for modern chemistry.
This historical shift from phlogiston to oxygen marked a critical turning point in scientific thought, demonstrating how empirical evidence and rigorous experimentation can challenge deeply held theories. Lavoisier's contributions not only revolutionised chemistry but also reflected the evolving nature of science, which relies on an unyielding pursuit of truth and evidence.