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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
165
Uranium
is
a
substance
which,
after
being
rightly
classed
with
the
elements
for
more
than
half
a
century,
because
it
had
not
been
separated
into
unlike
parts,
must
now
be
classed
with
the
radium-like
substances
which
disintegrate
spontaneously,
although
it
differs
from
other
radio-active
substances
in
that
its
rate
of
change
is
almost
infinitively
slower
than
that
of
any
of
them,
except
thorium.[12]
Thorium,
a
very
rare
metal,
is
the
second
of
the
seventy-five
or
eighty
elements
known
when
radio-activity
was
discovered,
which
has
been
found
to
undergo
spontaneous
disintegration
with
the
emission
of
rays.
The
rate
of
change
of
thorium
is
considerably
slower
than
that
of
uranium.[13]
None
of
the
other
substances
placed
in
the
class
of
elements
is
radio-active.
[12]
The
life-period
of
uranium
is
probably
about
eight
thousand
million
years.
[13]
The
life-period
of
thorium
is
possibly
about
forty
thousand
million
years.
On
p.
192
I
said,
that
when
the
radio-active
substances
had
been
labelled
elements,
the
facts
of
radio-activity
led
some
chemists
to
the
conclusion
that
the
other
bodies
which
had
for
long
been
called
by
this
class-name,
or
at
any
rate
some
of
these
bodies,
are
perhaps
not
true
elements,
but
are
merely
more
stable
collocations
of
particles
than
the
substances
called
compounds.
It
seems
to
me
that
this
reasoning
rests
on
an
unscientific
use
of
the
term
element;
it
rests
on
giving
to
that
class-name
the
meaning,
substances
asserted
to
be
undecomposable.
A
line
of
demarcation
is
drawn
between
elements,
meaning
thereby
forms
of
matter
said
to
be
undecomposable
but
probably
capable
of
separation
into
unlike
parts,
and
true
elements,
meaning
thereby
groups
of
identical
undecomposable
particles.
If
one
names
the
radio-active
substances
elements,
one
is
placing
in
this
class
substances
which
are
specially
characterised
by
a
property
the
direct
opposite
of
that
the
possession
of
which
by
other
substances
was
the
reason
for
the
formation
of
the
class.
To
do
this
may
be
ingenious;
it
is
certainly
not
scientific.
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