Chemical science was in a state of confusion in the mid-nineteenth century. About 60 elements were known, and new ones were being discovered on a regular basis. The very concept of an element was itself in doubt since no one really knew how many of these "basic substances" existed or whether they were somehow related to each other. Chemists realized that some organizing principle was badly needed.

Probably the first attempt to find a logical connection among the elements was made by Johann Döbereiner beginning in 1817. Döbereiner found that certain groups of elements with similar chemical properties had atomic weights that were mathematical progressions of each other. His Law of Triads was largely ignored by colleagues, however.

Over the next four decades, other attempts to organize the elements were made by P. Kremers, M. von Pettenkofer (1818-1901), J. H. Gladstone (1827-1902), J. P...