Pierre and Marie Curie set about working to search for the unknown element. They ground up samples of pitchblende, dissolved them in acid, and began to separate the different elements present, using the standard analytical chemistry techniques of the time. Eventually, they extracted a black powder 330 times more radioactive than uranium, which they called polonium . Polonium was a new chemical element, atomic number 84.
When the Curies investigated further, they found that the liquid left behind after they had extracted polonium was still extremely radioactive. They realised that pitchblende contained another new element, far more radioactive than polonium, but present in even smaller quantities.
In 1898, the Curies published strong evidence supporting the existence of the new element – which they called radium – but they still had no sample of it. Pitchblende is an expensive mineral, because it contains valuable uranium, and Marie needed a lot of it.