Periodisches System der Elemente (1904-1945, now at the Gdansk University of Technology): lack of elements: 84 polonium Po (though discovered as early as in 1898 by Maria Sklodowska-Curie), 85 astatine At (1940, in Berkeley), 87 francium Fr (1939, in France), 93 neptunium Np (1940, in Berkeley) and other actinides and lanthanides. Old symbols for: 18 argon Ar (here: A), 23 antimony Sb (D), 43 technetium Tc (Ma, masurium, 1925, dismissed as an error and finally confirmed in 1936, Palermo), 54 xenon Xe (X), 86 radon, Rn (Em, emanation).