62 TL L. Bronson — Decay of Deposit from, Radium. 



hour, the deca}< curve of the active deposit from radium is 

 satisfactorily explained by assuming two successive products, 

 radium B and radium C ; the matter B giving rise to no rays, 

 and the matter C to <x, (3 and 7 rays. Taking twenty-eight 

 minutes as the decay period of one of these, he calculated that 

 the period of the other must be twenty-one minutes. Theoret- 

 ically it makes no difference whether the longer period belongs 

 to the matter B or C, but the above mentioned experiments of 

 Curie and Danne supplied the evidence which decided this 

 question in favor of the matter C. 



The fact that so many of the values of #, obtained after 

 heating the deposit, were in the neighborhood of twenty-one 

 minutes, made it seem quite possible that the matter C had 

 the shorter period, and not that its period had been changed 

 by heating. Also the fact that the rayless change in the active 

 deposits from thorium and actinium each have a longer period 

 of decay than the change immediately following, possibly is 

 evidence in the same direction. If this be the case, then all 

 the larger values of must have been produced by mixtures of 

 the two kinds of matter, B and C, in different proportions. 

 This, however, would not give an exponential decay curve, but 

 the period would continue to increase, since the ratio of the 

 matter having the longer period to that having the shorter 

 would increase with the time. 



In order to see if this were the case, the decay of the activ- 

 ity of the heated deposit was measured over a long period of 



