Radio-Activity (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ...is blown out, the excited activity remains behind on the surface, but rapidly loses its activity in the course of a few hours. After several hours, the intensity of the residual radiation is very small. These effects and their connection with the emanation are discussed more fully in chapter IX. Giesel1 has recorded some interesting observations of the eftect of the radium emanation on a screen of phosphorescent zinc sulphide. 1 Ber. dtr deuttch. Chem. Ges. p. 3608, 1902. a. r.-A. 14 When a few centigrams of moist radium bromide were placed on a screen, any slight motion of the air caused the luminosity to move to and fro on the screen. The direction of phosphorescence could be altered at will, by a slow current of air. The effect was still further increased by placing the active material in a tube and blowing the air through it towards the screen. A screen of barium platino-cyanide or of Balmain's paint failed to give any visible light under the same conditions. The luminosity was not altered by a magnetic field, but it was affected by an electric field. If the screen were charged the luminosity was more marked when it was negative than when it was positive. Giesel states that the luminosity was not equally distributed, but was concentrated in a peculiar ring-shaped manner over the surface of the screen. The concentration of luminosity on the negative, rather than on the positive, electrode is probably due to the excited activity, caused by the emanation, and not to the emanation itself. This excited activity (see chap. IX) in an electric field is concentrated chiefly on the negative electrode. The electric field, probably, does not act on the emanation itself but concentrates the excited activity, due to the emanation present, on to the...