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210
The Fairy-Land of Science
·
Arabella B. Buckley
49
Perhaps
you
will
say,
If
oxygen
is
so
useful,
why
is
not
the
air
made
entirely
of
it?
But
think
for
a
moment.
If
there
was
such
an
immense
quantity
of
oxygen,
how
fearfully
fast
everything
would
burn!
Our
bodies
would
soon
rise
above
fever
heat
from
the
quantity
of
oxygen
we
should
take
in,
and
all
fires
and
lights
would
burn
furiously.
In
fact,
a
flame
once
lighted
would
spread
so
rapidly
that
no
power
on
earth
could
stop
it,
and
everything
would
be
destroyed.
So
the
lazy
nitrogen
is
very
useful
in
keeping
the
oxygen-atoms
apart;
and
we
have
time,
even
when
a
fire
is
very
large
and
powerful,
to
put
it
out
before
it
has
drawn
in
more
and
more
oxygen
from
the
surrounding
air.
Often,
if
you
can
shut
a
fire
into
a
closed
space,
as
in
a
closely-shut
room
or
the
hold
of
a
ship,
it
will
go
out,
because
it
has
used
up
all
the
oxygen
in
the
air.
So,
you
see,
we
shall
be
right
in
picturing
this
invisible
air
all
around
us
as
a
mixture
of
two
gases.
But
when
we
examine
ordinary
air
very
carefully,
we
find
small
quantities
of
other
gases
in
it,
besides
oxygen
and
nitrogen.
First,
there
is
carbonic
acid
gas.
This
is
the
bad
gas
which
we
give
out
of
our
mouths
after
we
have
burnt
up
the
oxygen
with
the
carbon
of
our
bodies
inside
our
lungs;
and
this
carbonic
acid
is
also
given
out
from
everything
that
burns.
If
only
animals
lived
in
the
world,
this
gas
would
soon
poison
the
air;
but
plants
get
hold
of
it,
and
in
the
sunshine
they
break
it
up
again,
as
we
shall
see
in
Lecture
VII,
and
use
up
the
carbon,
throwing
the
oxygen
back
into
the
air
for
us
to
use.
Secondly,
there
are
very
small
quantities
of
ammonia,
or
the
gas
which
almost
chokes
you
in
smelling-salts,
and
which,
when
liquid
is
commonly
called
"spirits
of
hartshorn."
This
ammonia
is
useful
to
plants,
as
we
shall
see
by
and
by.
Lastly,
there
is
a
great
deal
of
water
in
the
air,
floating
about
as
invisible
vapour
or
water-dust,
and
this
we
shall
speak
of
in
the
next
lecture.
Still,
all
these
gases
and
vapours
in
the
atmosphere
are
in
very
small
quantities,
and
the
bulk
of
the
air
is
composed
of
oxygen
and
nitrogen.
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