Descendants of Uranium 



577 



Of these products, A, B, and C constitute that part of the active 

 deposit of the emanation which suffers rapid decay and nearly dis- 

 appears in a few hours. Radium-D, continually producing its short- 

 lived descendants E and F, remains for years on surfaces once exposed 

 to the emanation, and makes delicate radio-active researches im- 

 possible in laboratories which have been contaminated by an escape 

 of radium emanation. 



A somewhat similar pcdigi'ee has been made out in the case of 

 thorium. Here thorium-X is interposed between thorium and its 

 short-lived emanation, which decays to half its initial quantity in 

 54 seconds. Two active deposits, thorium A and B, arise successively 

 fi-om the emanation. In uranium, we have the one obvious derivative 

 uranium-X, and the question remains whether this one descent can 

 be connected with any other individual or family. Uranium is long- 

 lived, and emits only a-rays. Uranium-X decays to half value in 

 22 days, giving out /3- and 7-rays. Since our evidence goes to show 

 that radio-activity is generally accompanied by tlie production of new 

 elements, it is natural to search for the substance of uranium-X in 

 other forms, and perhaps under other names, rather than to surrender 

 immediately our belief in the conservation of matter. 



37 



D. 



