The only practically available raw material for 'the extraction of uranium is pitchblende (q.v.).
To extract the metal, the pitchblende is first roasted in order to remove the arsenic and sulphur.
The emission of rays like those just mentioned - as a property of some undiscovered substance, submitted pitchblende to a most careful analysis.
And Mme Curie subjected a large amount of pitchblende to a laborious process of fractionation, with the result that in 1898 they announced the existence in it of two highly radioactive substances, polonium and radium.