18h 15min, nov 2, 1817 y - Döbereiner's Triads

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Döbereiner, German Scientist makes law of Triads.
He arranges elements in groups of three according to appearance and chemical properties.
Scientists started to discover the atomic masses of elements and Döbereiner realised that the middle one of his three atoms would have an atomic mass equal to the average of the other two.

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