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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
154
Since
the
discovery
of
radium
compounds,
many
radio-active
substances
have
been
isolated.
Only
exceedingly
minute
quantities
of
any
of
them
have
been
obtained.
The
quantities
of
substances
used
in
experiments
on
radio-activity
are
so
small
that
they
escape
the
ordinary
methods
of
measurement,
and
are
scarcely
amenable
to
the
ordinary
processes
of
the
chemical
laboratory.
Fortunately,
radio-activity
can
be
detected
and
measured
by
electrical
methods
of
extraordinary
fineness,
methods
the
delicacy
of
which
very
much
more
exceeds
that
of
spectroscopic
methods
than
the
sensitiveness
of
these
surpasses
that
of
ordinary
chemical
analysis.
At
the
time
of
the
discovery
of
radio-activity,
about
seventy-five
substances
were
called
elements;
in
other
words,
about
seventy-five
different
substances
were
known
to
chemists,
none
of
which
had
been
separated
into
unlike
parts,
none
of
which
had
been
made
by
the
coalescence
of
unlike
substances.
Compounds
of
only
two
of
these
substances,
uranium
and
thorium,
are
radio-active.
Radio-activity
is
a
very
remarkable
phenomenon.
So
far
as
we
know
at
present,
radio-activity
is
not
a
property
of
the
substances
which
form
almost
the
whole
of
the
rocks,
the
waters,
and
the
atmosphere
of
the
earth;
it
is
not
a
property
of
the
materials
which
constitute
living
organisms.
It
is
a
property
of
some
thirty
substances--of
course,
the
number
may
be
increased--a
few
of
which
are
found
widely
distributed
in
rocks
and
waters,
but
none
of
which
is
found
anywhere
except
in
extraordinarily
minute
quantity.
Radium
is
the
most
abundant
of
these
substances;
but
only
a
very
few
grains
of
radium
chloride
can
be
obtained
from
a
couple
of
tons
of
pitchblende.
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