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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
151
The
fact
that
there
is
a
very
definite
connexion
between
the
values
of
the
atomic
weights,
and
the
properties,
of
the
elements,
lends
some
support
to
the
hypothesis
that
the
substances
we
call,
and
are
obliged
at
present
to
call,
elements,
may
have
been
formed
from
one,
or
a
few,
distinct
substances,
by
some
process
of
progressive
change.
If
the
elements
are
considered
in
the
order
of
increasing
atomic
weights,
from
hydrogen,
whose
atomic
weight
is
taken
as
unity
because
it
is
the
lightest
substance
known,
to
uranium,
an
atom
of
which
is
240
times
heavier
than
an
atom
of
hydrogen,
it
is
found
that
the
elements
fall
into
periods,
and
the
properties
of
those
in
one
period
vary
from
element
to
element,
in
a
way
which
is,
broadly
and
on
the
whole,
like
the
variation
of
the
properties
of
those
in
other
periods.
This
fact
suggests
the
supposition--it
might
be
more
accurate
to
say
the
speculation--that
the
elements
mark
the
stable
points
in
a
process
of
change,
which
has
not
proceeded
continuously
from
a
very
simple
substance
to
a
very
complex
one,
but
has
repeated
itself,
with
certain
variations,
again
and
again.
If
such
a
process
has
occurred,
we
might
reasonably
expect
to
find
substances
exhibiting
only
minute
differences
in
their
properties,
differences
so
slight
as
to
make
it
impossible
to
assign
the
substances,
definitely
and
certainly,
either
to
the
class
of
elements
or
to
that
of
compounds.
We
find
exactly
such
substances
among
what
are
called
the
rare
earths.
There
are
earth-like
substances
which
exhibit
no
differences
of
chemical
properties,
and
yet
show
minute
differences
in
the
characters
of
the
light
which
they
emit
when
they
are
raised
to
a
very
high
temperature.
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