Compounds of Short-lived Radioactive Elements. 133 



actinium B being deposited between 615° and 675°. This is 

 shown clearly in the following table : — 



Interval of time between insertion of the active wire and 

 removal of the mica, 15 minutes. 



Length No. 



Temperature. 



Activity 

 in div. per min. 







Greater than 960° 

 945°-960° 

 925°-945° 

 880°-925° 

 820°-880° 

 760°-820° 

 675°-760° 

 615°-675° 

 555°-615° 

 385°-555° 

 200°-385° 



8 



1 



8 



2 



9 



3 



5 



4 



3 



5 



4 



6 



84 



Half of 7 



Half of 7 



8 



780 



5 



10 



9-11 



5 







Similar results were obtained with thorium B and 0. 

 Since the decay of thorium C is much slower than that of 

 the corresponding member of the actinium series, it was 

 possible to determine the ratio of the amounts of B and 

 deposited at different temperatures. Thorium B was de- 

 posited almost pure on the hotter parts of the strip, thorium 

 C on the cooler. The latter product is consequently more 

 volatile in hydrogen than the former. Further experiments 

 on this point are in progress. 



Conclusion. 



It has been shown that the radioactive matter when once 

 volatilized condenses on a surface at a much lower tempera- 

 ture in an atmosphere of hydrogen than in an atmosphere of 

 air. This suggests that the active matter forms compounds 

 in the presence of air which are less volatile and conse- 

 quently easier to condense than the reduction products 

 obtained in hydrogen, which are perhaps the elements, i. e. 

 the metals themselves. The assumption is in agreement 

 with the behaviour of common metals and their oxides, the 

 former being generally more volatile than the latter. 



The fact that the volatilization of actinium B from 

 platinum, as shown above, takes place over a long range of 



