‘Atomic weight, triads, and Prout’ discusses the shift in chemical thinking from qualitative analysis to quantitative analysis. John Dalton, drawing on the work of Antoine Lavoisier and Benjamin Richter, was the first to put forward the ideas of modern atomic theory. Avogadro realized that gases could exist as diatomic molecules, and Von Humboldt and Gay-Lussac postulated that these molecules reacted in a ratio. Prout also realized that atomic weight rose in multiples of the weight of hydrogen. Döbereiner introduced the concept of triads of similarly reacting elements, but developments of this system were flawed. It was Kremers who first started to relate elements that were chemically dissimilar, thus paving the way for periodicity.