14 Prof. Rutherford and Miss Brooks : Comparison of 



It was found that in the case of thorium compounds the 

 emanating power increased to three or four times before a dull 

 red heat of the platinum tube was reached, and remained con- 

 stant if the temperature was unchanged. On heating to a 

 white heat the emanating power was to a large extent 

 destroyed. 



The amount of emanation from radium increased over 

 10,000 times by heating below a red heat. Like thoria, if 

 the temperature was raised to a white heat, the emanating 

 power could not be recovered on cooling. 



Unlike the thoria emanation, the radium emanation loses 

 its radioactive power very slowly, with time. 



The emanation kept in a closed metal vessel still preserved 

 appreciable radioactivity after an interval of 14 days. The 

 rate of decay of the emanation from radium does not appear 

 to be the same under all conditions. The emanations from 

 the two different radium compounds showed appreciable 

 differences in this respect. The rate of decay also seems to 

 depend on the temperature at which the emanations are 

 produced. 



Further experiments on this subject are delayed until 

 preparations of radium of more definite composition are 

 obtained. 



Connexion between Emanation and Excited Radioactivity. 



There is a very close connexion between the emanation 

 from radium and thorium and their property of causing 

 excited radioactivity. The presence of the emanation is 

 necessary to produce excited radioactivity, and the amount 

 of the latter depends upon the amount of emanation present. 



Thoria, for example, which has been ignited to a white 

 heat loses its power, to a large extent, of giving off an eman- 

 tion, and its power of producing activity is diminished in a 

 like ratio. 



Excited radioactivity can be produced at long distances 

 from the radioactive material provided the emanation is 

 carried to that point. Intense excited radioactivity can be 

 obtained from a radium emanation which has been left 

 standing in a closed vessel for over a week, far removed 

 from the radium compound from which the emanation was 

 originally obtained. 



Excited radioactivity is due to the conveyance of some 

 kind of radioactive matter to surrounding bodies. This 

 radioactive material is either derived from the radioactive 

 emanation itself, or in some way produced by it out of* the 

 surrounding gas. 



