[johnstoxe] emanating POWER OF MINERALS 109 



treated in the manner described in this paper is once measured in 

 terms of some standard of radium, it may thereafter be used as a 

 standard of radium emanation. The value of the activity of the 

 equilibrium amount of emanation evolved will be practically inde- 

 pendent of the usual variations in laboratory temperature and it will 

 remain practically constant, provided the humidity of the air con- 

 tained in and passing through the tube is always maintained at the 

 value it possessed when it was standardized. 



Summary 



1. The variation with the temperature of the emanating power 

 of certain specimens of carnotite and uraninite has been determined. 



2. By heating the minerals to a high temperature, the temperature 

 coefficient of the emanating power is greatly decreased so that for 

 ordinary ranges of laboratory temperature it may be assumed to be 

 negligible. 



3. A secondary emanation standard has been suggested which 

 can be easily and simply prepared, which is not subject to appreciable 

 variations under ordinary conditions and which is more convenient 

 to use, particularly in the field, than either the customary standard 

 radium solution or a uranium mineral of known composition. 



