198 PROFESSOR E. RUTHERFORD ON THK 



Miss GATES* showed that this active matter was volatilized from a platinum wire 

 above a red heat and deposited on the surface of a cold cylinder surrounding the wire. 

 CURIE and DANNE extended these results by subjecting an active platinum wire for a, 

 aliort time to the action of temperatures varying between 15 C. and 13oO C., and 

 then examining at room temperatures the decay curves not only for the active matter 

 remaining on the wire, but also for the volatilized part. They found that the 

 activity of the distilled part always increased after removal, passed through a 

 maximum, and finally decayed according to an exponential law (half value in 

 28 minutes). At a temperature of about 630 C. the active matter left behind on 

 the wire decayed at once according to an exponential law, falling to half value in 

 28 minutes. P. CURIE and DANNE showed that the matter B is much more volatile 

 than C. The former is completely volatilized at about 600 C., while the latter is 

 not completely volatilized even at a temperature of 1300 C. The fact that the 

 matter C, left behind when B is completely volatilized, decays at once to half value 

 in 28 minutes shows that the matter C itself and not B is half transformed in 

 28 minutes. 



CURIE and DANNE also found that the rate of decay of the active matter varied 

 with the temperature to which the platinum wire had been subjected. At 630 C. 

 the rate of decay was normal, at 1100 C. the activity fell to half value in about 

 20 minutes, while at 1300 C. it fell to about half value in about 25 minutes. 



I have repeated the experiments of CURIE and DANNE and obtained very similar 

 results. It was thought possible that the measured rate of decay observed after 

 heating might be due to a permanent increase in the rate of volatilization of C at 

 ordinary temperatures. This explanation, however, is not tenable, for it was found 

 that the activity decreased at the same rate whether the activity of the wire was 

 tested in a closed tube or in the open with a current of air passed over it. 



These results are of great importance, for they indicate that the rate of change of 

 the product C is not a constant, but is affected by differences of temperature. This 

 is the first case where temperature has been shown to exert an appreciable influence 

 on the rate of change of any radioactive product. 



22. Effect of the First Rapid Change. We have seen that the law of decay of 

 activity, measured by the j3 or y rays, can be very satisfactorily explained if the first 

 3-minute change is disregarded. The full theoretical examination of the question 

 given in sections 10 and 11 and the curves of figs. 8 and 9 shows, however, that the 

 presence of the first change should exercise an effect of sufficient magnitude to be 

 detected in measurements of the activity due to the succeeding changes. The 

 question is ot great interest, for it involves the important theoretical point whether 

 the substances A and B are produced independently of one another, or whether A is 

 the parent of B. In the latter case, the matter A which is present changes into B, 



* ' Phys. Rev.,' p. 300, 1903. 



