Manchester Memoirs, Vol. liii. (1908), No. "X 



II. Some Properties of the Radium Emanation. 

 By E. Rutherford, F.R.S. 



Received and jcad JVo7h-?ii/)cr jid, igoS. 



In 1906 {Nature, Oct. 25), I drew attention to the 

 fact that tlie emanations of radium, thorium, and actinium 

 were completely absorbed by cocoanut charcoal at 

 ordinary temperatures. I have had occasion recently to 

 repeat these experiments with much larger quantities of 

 radium emanation and have found that the actual volume 

 of emanation capable of absorption by charcoal at room 

 temperature is very small. For example, several grams of 

 cocoanut charcoal are required to absorb completely the 

 emanation from 200 mgs. of radium at ordinary tempera- 

 ture although the volume of the gas is only one-tenth of a 

 cubic mdlimetre. As was to be expected, the absorptive 

 power of charcoal for the emanation increases rapidly with 

 lowering of the temperature. This was investigated as 

 follows : — A quantity 0"8 gram of cocoanut charcoal, which 

 absorbed about 4 c.cms. of air at the temperature of liquid 

 air, was connected with a pump and the air completely 

 removed by heating the charcoal. The charcoal 

 was then surrounded by a pentane bath at -I50°C., 

 and the purified emanation from 83 mg. of 

 radium (about 05 cubic mm.) absorbed in it. As the 

 temperature of the bath slowly rose, the unabsorbed 

 emanation was allowed to expand into an exhausted 

 receiver of about 50 c.cms. capacity. This was pumped out 

 at different temperatures of the charcoal, and the emanation 



November igth, igo8. 



