Weighing Authority. Lavoisier’s and Séguin’s Reassessment of Santorio’s Experiments on Transpiration

This chapter explores how Lavoisier and Armand Séguin reassessed Santorio Santori’s experiments on insensible perspiration in order to advance both a new chemical physiology and the authority of the “new chemistry.” Although Lavoisier lacked formal medical training, his commitment to precision instruments and quantitative measurement led him to reinterpret respiration and transpiration as chemical processes governed by oxygen and caloric exchange. While openly praising Santorio as a pioneer of medical quantification, Lavoisier and Séguin criticized his experimental inaccuracy and, above all, his ignorance of modern pneumatic chemistry. Their replication of Santorio’s protocol with improved balances and controlled conditions allowed them to position themselves simultaneously as heirs and correctors of the medical tradition. The chapter argues that this ambivalent engagement was not merely technical but rhetorical: by acknowledging Santorio yet exposing the limits of pre-chemical medicine, Lavoisier and Séguin asserted the epistemic superiority of chemistry over medicine. In doing so, they contributed to constructing Lavoisier’s scientific authority and redefining disciplinary hierarchies at the end of the eighteenth century.