RADIUM.
Professor and Madame Curie investi gated the residue from pitchblende after the uranium had been extracted from it, and found that it was more radio-active than uranium itself. Eventually a body was isolated from the residue which was 300 times more active than uranium. This was named potonitim. Another new sub stance was isolated, which the Curies named actinum, and finally radium was discovered, possessing one million times the activity of Becquerel's salts. Radium, from its extreme rarity, as well as its properties of emitting heat and light without any perceptible diminution in its bulk, has aroused great interest, and has been the subject of so many articles in newspapers and other publications that it is not necessary here to devote much space to its peculiar properties. It is separated from the residue of pitchblende by a series of complicated chemical opera tions, one ton of material yielding only a few grains of radium in the form of the wrapped in black paper, placed in a box, and covered with three earrings, was exposed to a tube of radium chloride for twenty-four hours. Fig.
923 shows the impression produced upon a similar plate placed at the same time outside the box, above the perforated silver lid of a soap box belonging to a dressing case. Neither the X-rays nor radium radiations are stopped by the interposition of a photographic film, so that no image can be printed on a plate from an ordinary negative. But if a negative with a plate or paper beneath it bromide or chloride of the metal. Radium has the highest. atomic weight of all the elements, namely-, 223. A glass tube con taining radium is shown by Fig. 921.