In 26th December 1948, Pierre and Marie Curie announced the discovery of this element. It had been distinguished from polonium due to the likeliness of its chemical properties with those of barium. Its sulfate and carbonate were insoluble and the chloride was soluble in water but insoluble in hydrochloride acid or in alcohol. However, this element was not identical to barium, and could easily be separated.
The existence of a second element, demonstrated by its radioactive properties, was confirmed by a foggy line in the spectrum of barium. This new element was called "radium".
Some years later, in 1902, Madame Curie performed a series of fractional crystallizations starting from a considerable amount of uraninite residues, and was able to isolate about 0,1 grams of chloride of almost pure radium, with an activity about 3 million greater than that of uranium.
The announcement of the discovery of polonium and of radium triggered a series of research works, leading to the discovery of another radioactive elements associated to uranium and thorium.