The “Missing Element” between Cadmium and Mercury

Abstract

IN NATURE (April 12) the writer of the notice of Dr. Mellor's treatise on chemistry refers to the suggestion of a missing element between cadmium and mercury. That there is no unknown element to go there is of course evident, but it is highly probable that a known one should be placed there. In 1914 Rydberg (Kong. fysiog. Sällskapets Hand. 24) proposed an arrangement of the periodic table to which little attention appears to have been paid. In directing attention to it in the Philosophical Magazine (28, p. 139, 1914) I suggested a small change which brought europium between cadmium and mercury. Indeed, the rare earths in this arrangement divide the periodic table horizontally and vertically into two parts. In this arrangement the atomic weight and number are in step with those of the other elements of group II. Whatever may be the difficulties from a chemical point of view in thus placing it, the spectral evidence in its favour appears to me to be conclusive.