402 Mr. S. Rafcner on some Properties of the 



1 min. 25 sec, one after another. Column A shows the 

 activity of the disks measured immediately after their re- 

 moval from the apparatus, columns A 3 , A 6 , and A 9 their 



Table I. 



A . A 3 . A 6 . A 9 . 



1 95 48 25 13 



II 48 24 13 7 



III 25 14 75 4 



IV 15 8 5 3 



activities measured 3, 6, and 9 min. after the first mea- 

 surement. From column A the period T for RaA can be 

 deduced, while the rows I, II, III, and IV give the analysis 

 of active matter on the corresponding disks. On the disk IV 

 the presence of RaB and RaC is well marked, since at the 

 time of its exposure the RaA on the plate had already 

 disintegrated to a large degree. 



In the case of RaB and RaC the period T is by far not so 

 constant, and varies from one series of experiments to another 

 within large limits, viz. 10-40 min. (Some experiments 

 carried out with pure RaB and RaC show that on the average 

 the period T is smaller for RaB than for RaC. This is clearly 

 seen in the case of Ra(B 4- C) on the plate R, when the 

 analysis of the activities on the disks usually shows that in 

 the active matter expanding from the plate the ratio of RaC 

 to RaB increases with time. In some experiments, when 

 the plate R was introduced into the apparatus 3 or 4 hours 

 after its exposure to emanation, almost pure RaC could . be 

 obtained on the collecting disks. It must be pointed out, 

 however, that this effect is not always observed. 



4. Discussion on the nature of the Phenomenon. — The results 

 given in the previous section seem to be very complicated, and 

 throw but little light on the nature of the phenomenon. It 

 appeared of interest therefore to test experimentally different 

 assumptions which may be put forward for the interpretation 

 of the phenomenon. First, the usual assumption that the 

 active deposit of radium is slightly volatile at ordinary tem- 

 peratures was investigated. In a series of experiments the 

 disks, while exposed in the apparatus, were heated in a gas- 

 flame to about 300°-400° C, and the amount of active matter 

 deposited on them compared with that acquired by cold disks 

 under the same conditions. It was found that the high 

 temperature of the disks does not prevent the active matter 

 from being deposited on them. It is obvious that the 



