The Discovery of Radium.
§ 87. Mme. Curie[102] determined the radioactivity of many uranium and thorium compounds, and found that there was a proportion between the radioactivity of such compounds and the quantity of uranium or thorium in them, with the remarkable exception of certain natural ores, which had a radioactivity much in excess of the normal, and, indeed, in certain cases, much greater than pure uranium. In order to throw some light on this matter, Mme. Curie prepared one of these ores by a chemical process and found that it possessed a normal radioactivity. The only logical conclusion to be drawn from these facts was that the ores in question must contain some unknown, highly radioactive substance, and the Curies were able, after very considerable labour, to extract from pitchblende (the ore with the greatest radioactivity) minute quantities of the salts of two new elements—which they named “Polonium” and “Radium” respectively—both of which were extremely radioactive.
[102] See Madame Sklodowska Curie’s Radio-active Substances (2nd ed., 1904).
M. Debierne has obtained a third radioactive substance from pitchblende, which he has called “Actinium.”