The new substances were proved to be compounds chemically very similar to salts of barium.

Their compositions were determined on the supposition that they were salts of an unknown metal closely allied to barium.
Because of the great radio-activity of the compounds, the hypothetical metal of them was named _Radium_.

At a later time, radium was isolated by Madame Curie.

It is described by her as a white, hard, metal-like solid, which reacts with water at the ordinary temperature, as barium does.
Since the discovery of radium compounds, many radio-active substances have been isolated.

Only exceedingly minute quantities of any of them have been obtained.