How did Stanislao Cannizzaro help settle questions about atomic and molecular masses?

By the mid-19th century, chemistry was in a state of confusion regarding atomic weights and molecular formulas, largely because John Dalton’s original atomic theory lacked a standardized method for determining these values. While Amedeo Avogadro had proposed a solution as early as 1811, his ideas were largely ignored for decades.12

Stanislao Cannizzaro helped resolve this by demonstrating that a consistent and robust theoretical structure could be built by fully returning to Avogadro’s hypotheses. In an influential 1858 pamphlet, he showed that these principles fit nearly all available empirical evidence, allowing for the construction of a single, reliable atomistic system.2

Cannizzaro’s most significant impact occurred at the 1860 Karlsruhe Congress, where his logical presentation and the distribution of his pamphlet convinced many leading chemists to adopt a unified system of atomic weights. This reform replaced the chaotic, competing systems of the time and provided the foundation necessary for later breakthroughs, such as the development of the periodic table by Dmitry Mendeleev.23