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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
108
That
he
might
bring
into
one
point
of
view,
and
compare
the
various
changes
effected
by
the
agency
of
fire,
Stahl
invented
a
new
Principle,
which
he
named
Phlogiston,
and
constructed
an
hypothesis
which
is
generally
known
as
the
phlogistic
theory.
He
explained,
and
applied,
this
hypothesis
in
various
books,
especially
in
one
published
at
Halle
in
1717.
Stahl
observed
that
many
substances
which
differed
much
from
one
another
in
various
respects
were
alike
in
one
respect;
they
were
all
combustible.
All
the
combustible
substances,
he
argued,
must
contain
a
common
principle;
he
named
this
supposed
principle,
phlogiston
(from
the
Greek
word
phlogistos
=
burnt,
or
set
on
fire).
Stahl
said
that
the
phlogiston
of
a
combustible
thing
escapes
as
the
substance
burns,
and,
becoming
apparent
to
the
senses,
is
named
fire
or
flame.
The
phlogiston
in
a
combustible
substance
was
supposed
to
be
so
intimately
associated
with
something
else
that
our
senses
cannot
perceive
it;
nevertheless,
the
theory
said,
it
is
there;
we
can
see
only
the
escaping
phlogiston,
we
can
perceive
only
the
phlogiston
which
is
set
free
from
its
combination
with
other
things.
The
theory
thought
of
phlogiston
as
imprisoned
in
the
thing
which
can
be
burnt,
and
as
itself
forming
part
of
the
prison;
that
the
prisoner
should
be
set
free,
the
walls
of
the
prison
had
to
be
removed;
the
freeing
of
the
prisoner
destroyed
the
prison.
As
escaping,
or
free,
phlogiston
was
called
fire,
or
flame,
so
the
phlogiston
in
a
combustible
substance
was
sometimes
called
combined
fire,
or
flame
in
the
state
of
combination.
A
peculiarity
of
the
strange
thing
called
phlogiston
was
that
it
preferred
to
be
concealed
in
something,
hidden,
imprisoned,
combined;
free
phlogiston*
was
supposed
to
be
always
ready
to
become
combined
phlogiston.
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