ncentrated on a
negative electrode.

Radium-B 21 minutes no rays Soluble in strong acids;
volatile at a white heat; more
volatile than A or C.

Radium-C 28 minutes alpha, beta, Soluble in strong acids; less
gamma rays volatile than B.

Radium-D about 40 years no rays Soluble in strong acids; volatile
below 1000 deg C.

Radium-E 6 days beta, gamma Non-volatile at 1000 deg C.
rays

Radium-F 143 days alpha rays Volatile at 1000 deg 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 disappears
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 impossible
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
alpha-rays. Uranium-X decays to half value in 22 days, giving out beta-
and gamma-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.

With this idea in mind we see at once the significance of the
constitution of uranium minerals. Formed in the remote antiquity of
past geological ages, these minerals must become store-houses of all
the products of uranium except those which may have escaped as gases
or possibly liqui