Page:Radio-activity.djvu/235

 source of light is brought near it. This should evidently be the case, since the face coated with radium should reach a slightly higher temperature than the other. This experiment has been tried, but the effect seems too small to produce rotation of the vanes.

Chemical actions.

123. Rays from active radium preparations change oxygen into ozone. Its presence can be detected by the smell or by the action on iodide of potassium paper. This effect is due to the α and β rays from the radium, and not to the luminous rays from it. Since energy is required to produce ozone from oxygen, this must be derived from the energy of the radiations.

The Curies found that radium compounds rapidly produced coloration in glass. For moderately active material the colour is violet, for more active material it is yellow. Long continued action blackens the glass, although the glass may have no lead in its composition. This coloration gradually extends through the glass, and is dependent to some extent on the kind of glass used.

Giesel found that he could obtain as much coloration in rock-salt and fluor-spar by radium rays, as by exposure to the action of cathode rays in a vacuum tube. The coloration, however, extended much deeper than that produced by the cathode rays. This is to be expected, since the radium rays have a higher velocity, and consequently greater penetrating power, than the cathode rays produced in an ordinary vacuum tube. Goldstein observed that the coloration is far more intense and rapid when the salts are melted or heated to a red heat. Melted potassium sulphate, under the action of a very active preparation of radium, was rapidly coloured a strong greenish blue which gradually changed into a dark green. Salomonsen and Dreyer found that plates of quartz were coloured by exposure to radium rays. When examined minutely, plates cut perpendicular to the optic axis showed the presence of lines and striae, parallel to the binary axes. Adjacent portions of the striated system differed considerably in intensity of