“Our theories are crutches”: what chemists got wrong

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Antoine Lavoisier conducting an experiment related to combustion generated by amplified sun light. Source: History of Science

The classical elements

The four classical elements of antiquity, as taught by the Greek philosopher Plato (428–348 BC), were earth, water, air and fire (a very easy to memorise periodic table).

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Seventeenth century alchemical emblem showing the four Classical elements in the corners of the image, alongside the tria prima on the central triangle. Source: Deutsche Fotothek

Phlogiston theory

The theory that air was one of the basic elements persisted well into the 17th century. Dutch physician and naturalist Herman Boerhaave (1668–1738) suspected that there was some life-supporting ingredient in air, as did Anglo-Irish scientist Robert Boyle (1627–1691), who said it was probably related to the substance needed to maintain a flame. The discovery that both oxygen and hydrogen are elemental gases was delayed by the theory of phlogiston, an early attempt to explain combustion.

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Georg Ernst Stahl. Line engraving, 1715. Source: Wellcome Collection gallery (2018–03–29)

Caloric theory

The nature and source of heat were long pondered by scientists throughout history. We now understand heat to be a form of energy, but it wasn’t always this way. Phlogiston theory hints at why heat was once also believed to be a physical substance.

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Engraving of James Joule’s apparatus for measuring the mechanical equivalent of heat, in which altitude potential energy from the weight on the right is converted into heat at the left, through stirring of water. Source: Harper’s New Monthly Magazine, № 231, August, 1869

In retrospect

These three superseded theories are some of the most famous examples of scientific misconceptions. While they may amuse and even arouse disdain now, they serve as an excellent reminder that “theories cannot claim to be indestructible”. This timeless observation on science comes from French chemist and Nobel prize-winner Paul Sabatier (1854–1941). Fellow Frenchman and chemist Jean-Baptiste Dumas (1800–1884) had the following insight to share: “In chemistry, our theories are crutches; to show that they are valid, they must be used to walk.”

Chemistry PhD candidate, science communicator and freelance science writer based in Sydney, Australia.

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