How did Cannizzaro’s work help create the modern system of atomic weights and molecular formulas?

Stanislao Cannizzaro was instrumental in resolving the mid-19th-century chaos surrounding atomic weights and molecular formulas by championing the long-neglected theories of Amedeo Avogadro.1

During the 1850s, chemists lacked a unified system, leading to incompatible atomistic models. In his 1858 pamphlet, Sunto di un corso di filosofia chimica, Cannizzaro demonstrated that applying Avogadro’s hypothesis—which used vapour densities to infer relative weights—created a consistent theoretical structure that aligned with empirical evidence. He argued that this approach allowed for a single, reliable system of atomic weights, explaining that elementary gases consist of molecules with varying numbers of atoms.1

Cannizzaro’s logic gained widespread acceptance following the 1860 Karlsruhe Congress. His eloquent presentation and the distribution of his pamphlet convinced the international chemical community to adopt his reformed system. This standardization provided the essential foundation for subsequent breakthroughs, including the development of the periodic table of the elements by Dmitry Mendeleev.12