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1
177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
157
Radio-active
substances
are
constantly
giving
off
energy
in
the
form
of
heat,
sending
forth
rays
which
have
definite
and
remarkable
properties,
and
producing
gaseous
emanations
which
are
very
unstable,
and
change,
some
very
rapidly,
some
less
rapidly,
into
other
substances,
and
emit
rays
which
are
generally
the
same
as
the
rays
emitted
by
the
parent
substance.
In
briefly
considering
these
three
phenomena,
I
shall
choose
radium
compounds
as
representative
of
the
class
of
radio-active
substances.
Radium
compounds
spontaneously
give
off
energy
in
the
form
of
heat.
A
quantity
of
radium
chloride
which
contains
1
gram
of
radium
continuously
gives
out,
per
hour,
a
quantity
of
heat
sufficient
to
raise
the
temperature
of
1
gram
of
water
through
100°
C.,
or
100
grams
of
water
through
1°
C.
The
heat
given
out
by
1
gram
of
radium
during
twenty-four
hours
would
raise
the
temperature
of
2400
grams
of
water
through
1°
C.;
in
one
year
the
temperature
of
876,000
grams
of
water
would
be
raised
through
1°
C.;
and
in
1800
years,
which
is
approximately
the
half-life
period
of
radium,
the
temperature
of
1,576,800
kilograms
of
water
would
be
raised
through
1°
C.
These
results
may
be
expressed
by
saying
that
if
1
gram
(about
15
grains)
of
radium
were
kept
until
half
of
it
had
changed
into
inactive
substances,
and
if
the
heat
spontaneously
produced
during
the
changes
which
occurred
were
caused
to
act
on
water,
that
quantity
of
heat
would
raise
the
temperature
of
about
15½
tons
of
water
from
its
freezing-
to
its
boiling-point.
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