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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
144
A
chemical
element
was
thought
of
by
Lavoisier
as
"the
actual
term
whereat
analysis
has
arrived,"
a
definite
substance
"which
we
cannot
subdivide
with
our
present
knowledge,"
but
not
necessarily
a
substance
which
will
never
be
divided.
A
compound
was
thought
of
by
him
as
a
definite
substance
which
is
always
produced
by
the
union
of
the
same
quantities
of
the
same
elements,
and
can
be
separated
into
the
same
quantities
of
the
same
elements.
These
conceptions
were
amplified
and
made
more
full
of
meaning
by
the
work
of
many
who
came
after
Lavoisier,
notably
by
John
Dalton,
who
was
born
in
1766
and
died
in
1844.
In
Chapter
I.,
I
gave
a
sketch
of
the
atomic
theory
of
the
Greek
thinkers.
The
founder
of
that
theory,
who
flourished
about
500
B.C.,
said
that
every
substance
is
a
collocation
of
a
vast
number
of
minute
particles,
which
are
unchangeable,
indestructible,
and
impenetrable,
and
are
therefore
properly
called
atoms;
that
the
differences
which
are
observed
between
the
qualities
of
things
are
due
to
differences
in
the
numbers,
sizes,
shapes,
positions,
and
movements
of
atoms,
and
that
the
process
which
occurs
when
one
substance
is
apparently
destroyed
and
another
is
produced
in
its
place,
is
nothing
more
than
a
rearrangement
of
atoms.
The
supposition
that
changes
in
the
properties
of
substances
are
connected
with
changes
in
the
numbers,
movements,
and
arrangements
of
different
kinds
of
minute
particles,
was
used
in
a
general
way
by
many
naturalists
of
the
17th
and
18th
centuries;
but
Dalton
was
the
first
to
show
that
the
data
obtained
by
the
analyses
of
compounds
make
it
possible
to
determine
the
relative
weights
of
the
atoms
of
the
elements.
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