Descendants of Uranium 577 
Time of 
half decay Radio-activity Properties 
Radium about a rays Element chemically analogous 
2600 years to barium. 
Emanation 3°8 days a rays Chemically inert gas; con- 
denses at — 150°C. 
Radium-A 3 mins. a rays Behaves as a solid deposited 
on surfaces; concentrated 
on a negative electrode. 
Radium-B 21 mins. no rays Soluble in strong acids; vola- 
tile at a white heat; more 
volatile than A or C. 
Radium-C 28 mins, a, B, y rays Soluble in strong acids; less 
volatile than B. 
Radium-D about no rays Soluble in strong acids ; vola- 
40 years tile below 1000 C. 
Radium-E 6 days B, y rays Non-volatile at 1000 C. 
ee 143 days w rays Volatile at 1000 C. Deposited 
from solution on a bismuth 
plate. 
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 pedigree 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 
from 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 @- and y-rays. Since our evidence goes to show 
that radio-activity is generally accompanied by the 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. 
D. 37 
