
174 PROPERTIES OF THE RADIATIONS [cH. 
Chemical actions. 
115. 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 
a and 8 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. Goldstem 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. 
The cause of these colorations by cathode and radium rays 
has been the subject of much discussion. Elster and Geitel? 
observed that a specimen of potassium sulphate, coloured green by 
radium rays, showed a strong photo-electric action, 2.e. it rapidly 
lost a negative charge of electricity when exposed to the action of 
ultra-violet light. All substances coloured by cathode rays show 
a strong photo-electric action, and, since the metals sodium and 
potassium themselves show photo-electric action to a very remark- 
able degree, Elster and Geitel have suggested that the colorations 
are caused by a solid solution of the metal in the salt. 
1 §. and P. Curie, C. R. 129, p. 823, 1899. 
* Giesel, Verhandlg. d. d. phys. Ges. Jan. 5, 1900. 
3 Phys. Zeit. p. 113, No. 3, 1902. 
