“We must expect the discovery of many as yet unknown elements-for example, elemen…” — Dmitri Mendeleev

The establishment of a law, moreover, does not take place when the first thought of it takes form, or even when its significance is recognised, but only when it has been confirmed by the results of the experiment.

The elements which are the most widely diffused have small atomic weights.

The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.

Elements which are similar as regards their chemical properties have atomic weights which are either of nearly the same value (eg. Pt, Ir, Os) or which increase regularly (eg. K, Ru, Cs).