28 ROYAL SOCIETY OF CANADA 



VIII. Summary of Results. 



1. It has been shewn that the activity of uniform layers of active 

 potassium salts was directly proportional to the area of the salt 

 exposed. 



2. With uniform layers of a number of potassium salts the 

 activity was found to increase with the thickness of the layer, and 

 maximum activities were obtained with all the salts examined with 

 layers of the salt from 2 to 3 mm. in thickness. 



3. Such wide variations were found in the activities of different 

 potassium salts, and of potassium salts of the same composition 

 obtained from different sources, as to practically preclude the view 

 that the activity was due to a normal atomic property of the potassium. 



4. The rays from the potassium salts, which were found to be 

 heterogeneous and to possess considerable penetrating power, ex- 

 hibited characteristics similar to those of the /? radiation emitted 

 by uranium X. The penetrating power of the latter, however, is 

 somewhat greater than that possessed by the potassium rays. 



5. Experiments have been described which go to shew that the 

 activity of potassium salts is not due to the excitation of a secondary 

 radiation in the salts by the activity of penetrating rays coming from 

 external sources. 



6. By various tests it was found impossible to trace the activity 

 of potassium salts to the existence in them of minute quantities of 

 any of the known radioactive elements or their active products. 



7. Of all the elements in the alkali group, potassium alone has 

 been found to exhibit marked radioactivity. Both sodium and all 

 of its salts were found to be quite inactive, and although a sample of 

 rubidium alum exhibited an activity which was extremely small, and 

 a specimen of caesium chloride one which was only just measurable, 

 no evidence was adduced which would support exclusively the view 

 that the activity observed was due to any physical property of the 

 metallic constituents of these salts. 



In conclusion we wish to express our very great indebtedness to 

 Prof. Lang and to Prof. Lash Miller, as well as to other members of 

 the staff in Chemistry, for their kindness in placing at our disposal a 

 number of the specimens of the salts examined. 



