preLavoisier

PreLavoisier is a historiographic term used to describe the body of chemical knowledge and practice that existed before Antoine Lavoisier’s reforms in the late 18th century. It encompasses the alchemical and early chemical traditions, including theories of combustion, the nature of air, and the development of chemical language, before a coherent, quantitative framework was established.

The period was dominated by theories such as the phlogiston theory of combustion and the caloric theory of heat, with a primarily qualitative approach to substances and reactions. Phlogiston, imagined as a substance released during burning, shaped explanations of oxidation, calcination, and respiration. During this era, investigators identified and studied gases and vapors, but the interpretations were diverse and often inconsistent. Notable figures included Joseph Priestley and Carl Wilhelm Scheele, who discovered gases such as what Priestley called dephlogisticated air and Scheele’s oxygen, and Henry Cavendish, who conducted quantitative experiments on gases and reactions.

The concept of chemical elements and the proper categorization of substances were still developing, and standardized methods for weighing or balancing reactions were not universally applied. The discovery of carbon dioxide by Joseph Black in 1754 and other quantitative observations gradually pushed the field toward measurement-based reasoning, but a comprehensive theory of oxidation and combustion remained elusive.

The turning point came with Lavoisier’s experiments in the 1770s and 1780s. He demonstrated that mass is conserved in chemical changes and identified oxygen as a central reactant in combustion, prompting a redefinition of elements and compounds. His Traité élémentaire de chimie (1789) articulated a new chemical language and a modern framework, marking the beginning of the chemical revolution and ending the preLavoisier era.