Amadeo Avogadro 1776-1856

When the American Chemical Society (ACS) celebrated its centenary in 1974 it issued car stickers that proclaimed: 'I know Avogadro's Number is 6.022 ? 10²³. The implication was that, like C. P. Snow's claim for knowledge of the Second Law of Thermodynamics as a mark of good education, familiarity with Avogadro's number provides a similar test. The irony is that Avogadro never calculated the number and the eponym was only made 50 years after his death. The eponym, however, is justified on the grounds that Avogadro was one of the founders of modern molecular theory and of the standardisation of atomic weights.