‎"CROOKES, WILLIAM - SEPARATING URANIUM AND CREATING URANIUM X.‎
‎""Radio-activity of Uranium.""‎

‎(London, Harrison and Sons, 1900). Without wrappers. Extracted from ""Proceedings of the Royal Society of London"", Vol. 66. Pp. 409-422 a. 1 photographic plate.‎

Reference : 47429

‎First printing of an importent paper which pawed the way to the understanding of radioactivity. Crookes showed by using photographic plates as indicators of activity that if uranium was purified, it could be separated chemically into a nonactive portion and a radioactive portion that he called uranium X. ""In May 1900 Sir W.Crookes showed (the paper offered) that it was possible by chemical means to separate from uranium a small fraction, which he called uranium X, which possessed the whole of the photographic activity of the original substance. He found, moreover, that the activity of the uranium X gradually decayed, while the full activity of the residual uranium was gradually renewed, so that after a sufficient lapse of time it was possible to separate from it a freh supply of uranium X. These facts had an importent share in the formation of the theory (of radioactivity)."" (Whittaker ""A History of the Theories of Aether and Electricity"" Vol. II, p. 5.).‎