![]() ![]() Curie made a new determination of its atomic weight and prepared metallic radium. The work proved exceedingly difficult in practice on account of the great quantities of material that had to be treated. The separation of barium was made by a process of fractional crystallisation. Curie succeed in preparing the first decigram of pure radium salt and made a determination of its atomic weight. ![]() Though the existence of these new substances was certain, they were present only in a very small proportion in the products obtained at that time yet Demarçay was able to detect in the barium-radium mixture three new lines belonging to radium. Bémont published the discovery of radium. Curie published the discovery of polonium, the element accompanying bismuth in Dec. The method they used in that work was entirely new the result of the separations made by the ordinary process of chemical analysis was controlled by tests of the activity of every fraction the activity was measured quantitatively by the current produced by the substance when placed in a special “ionisation chamber.” Thus concentration of the radioactive property was traced in two fractions of the treatment, the fraction containing bismuth and the fraction containing barium. By the hypothesis of the existence of a very radioactive unknown substance present in very small quantity, she undertook, with Pierre Curie, research for this substance in the uranium mineral called pitchblende. But she found that uranium minerals were much more active than could be predicted from their uranium content. Curie proved that this property, later called radioactivity, is characteristic of the atom of uranium and is possessed also by thorium. Becquerel discovered that uranium emits spontaneously a radiation that produces an impression on a photographic plate through a sheet of black paper, and ionises the air.
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