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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
164
The
probability
that
one
element
might
be
changed
into
another
was
increased
by
the
demonstration
of
the
connexions
between
uranium
and
radium.
The
metal
uranium
has
been
classed
with
the
elements
since
it
was
isolated
in
1840.
In
1896,
Becquerel
found
that
compounds
of
uranium,
and
also
the
metal
itself,
are
radio-active.
In
the
light
of
what
is
now
known
about
radio-activity,
it
is
necessary
to
suppose
that
some
of
the
minute
particles
of
uranium
emit
particles
lighter
than
themselves,
and
change
into
some
substance,
or
substances,
different
from
uranium;
in
other
words,
it
is
necessary
to
suppose
that
some
particles
of
uranium
are
spontaneously
disintegrating.
This
supposition
is
confirmed
by
the
fact,
experimentally
proved,
that
uranium
emits
[alpha]-rays,
that
is,
atoms
of
helium,
and
produces
a
substance
known
as
uranium
X.
Uranium
X
is
itself
radio-active;
it
emits
[beta]-rays,
that
is,
it
gives
off
electrons.
Inasmuch
as
all
minerals
which
contain
compounds
of
uranium
contain
compounds
of
radium
also,
it
is
probable
that
radium
is
one
of
the
disintegration-products
of
uranium.
The
rate
of
decay
of
radium
may
be
roughly
expressed
by
saying
that,
if
a
quantity
of
radium
were
kept
for
ten
thousand
years,
only
about
one
per
cent.
of
the
original
quantity
would
then
remain
unchanged.
Even
if
it
were
assumed
that
at
a
remote
time
the
earth's
crust
contained
considerable
quantities
of
radium
compounds,
it
is
certain
that
they
would
have
completely
disappeared
long
ago,
had
not
compounds
of
radium
been
reproduced
from
other
materials.
Again,
the
most
likely
hypothesis
is
that
compounds
of
radium
are
being
produced
from
compounds
of
uranium.
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