the Radioactive Emanations oy Charcoal. 375 



It was pointed out by Professor Rutherford, in a letter to 

 4 Nature,' October 6th, 1906, that this property of coconut 

 charcoal also holds for the radioactive emanations ; and in 

 his letter are accounts of experiments demonstrating the 

 fact. Professor Rutherford found that a slow current of 

 air charged with the emanations of radium, thorium, or 

 actinium is deprived of some or all of its emanation in the 

 passage through a tube filled with coconut charcoal, and 

 for this purpose the charcoal need only be at ordinary 

 temperature. The complete withdrawal of the emanation 

 only takes place when the air is passed very slowly 

 through the charcoal ; if the speed is increased, the amount 

 of emanation emeroino- is increased also. In another 

 experiment, Rutherford found that if a tube containing 

 less than a gramme of the charcoal is open to a vessel 

 containing the emanation from several milligrammes of 

 radium bromide, in the course of time the emanation is 

 absorbed by the charcoal. If some powdered willemite 

 is mixed with the charcoal, the gradual absorption is shown 

 by the increasing brilliancy of phosphorescence of the 

 willemite. It is not necessary to heat or exhaust the char- 

 coal previously, but when either is done the emanation is 

 more rapidly absorbed. The charcoal retains the emanation 

 at ordinary temperature, but the greater part of it is expelled 

 by heating to a low red heat. 



The phenomenon of the absorption of emanation is not only 

 of much interest in itself, but also in the fact that, it may be 

 of use in determining directly the amount of emanation 

 ■existing in any particular gas. Mr. Eve, of this laboratory, 

 is now utilizing the method io determine the amount of 

 radium emanation existing in the free atmosphere. 



It may be noted that, since the emanation must be mixed 

 with some gas, there is special interest in studying the 

 information contained in the papers of Devvar and Ramsay 

 concerning the absorption of the inert gases of the argon 

 family which exist in the atmosphere. The cases are 

 analogous in that the emanations are believed To be che- 

 mically inert gases, and are mixed with the containing gas 

 in extremely small proportions ; but there is the distinctive 

 difference that the emanations decrease in amount with time, 

 while the gases of the argon family do not. 



It is important to determine the laws which govern the 

 absorption of the radioactive emanations, to know how far it 

 depends on the speed of the containing gas through the 

 absorbent, the temperature of the absorbent, and other con- 

 ditions. An investigation of these points is the main object 

 of this paper. 



