Physical Properties of Radium

Since metallic radium can only be said with certainty to have been separated once, and that in very small quantity, no very precise account of its properties can be given.

It is a brilliant white metal of melting-point 700° C. It is much more volatile than barium, and the vapour attacks quartz energetically. In its behaviour towards chemical reagents it closely resembles metallic barium. It is attacked by both the nitrogen and the oxygen of the air, forming the nitride and the oxide respectively. It is decomposed by cold water, the heat of reaction probably being about 90 Cal. per gram atom. In contact with organic matter, paper for instance, the latter is charred.

Radium differs from the other alkaline earths in the luminescence which it has in common with its salts, and which is a consequence of the radioactive properties to be discussed later.

The following are the chief lines of the spectrum in Angstrom units: -

Spark: Ultra-violet: 2709.05, 2813.84, 3649.8; Visible: 3814.6, 4340.83, 4436.49, 4533.33, 4682.36, 4826.12, 4856.25, 5400.31, 5406.78, 5502.07, 5601.72, 5616.73, 5660.81, 5729.2, 5958.4, 6167.4, 6200.6, 6446.3.

Arc: Visible: 3814.6, 4682.4.

Runge and Precht studied the flame spectrum of radium and obtained the following as the most important lines: -

Flame: 4826; strong bands between 6130 and 6330; 6349; strong band between 6530 and 6700; 6653 Å.

The fluorescent light from radium compounds gives a banded spectrum of nitrogen superimposed on a faint continuous spectrum due to the fluorescence of the crystals. In an evacuated tube no nitrogen bands are obtained, and in an atmosphere of helium three helium lines are observed.