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177
The Story of Alchemy and the Beginnings of Chemistry
·
M. M. Pattison Muir
137
[11]
I
have
considered
the
law
of
the
conservation
of
mass
in
some
detail
in
Chapter
IV.
of
The
Story
of
the
Chemical
Elements.
By
accepting
the
accuracy
of
this
generalisation,
and
using
it
in
every
experiment,
Lavoisier
was
able
to
form
a
clear
mental
picture
of
a
chemical
change
as
the
separation
and
combination
of
homogeneous
substances;
for,
by
using
the
balance,
he
was
able
to
follow
each
substance
through
the
maze
of
changes,
to
determine
when
it
united
with
other
substances,
and
when
it
separated
into
substances
simpler
than
itself.
CHAPTER
XIII.
THE
CHEMICAL
ELEMENTS
CONTRASTED
WITH
THE
ALCHEMICAL
PRINCIPLES.
It
was
known
to
many
observers
in
the
later
years
of
the
17th
century
that
the
product
of
the
calcination
of
a
metal
weighs
more
than
the
metal;
but
it
was
still
possible,
at
that
time,
to
assert
that
this
fact
is
of
no
importance
to
one
who
is
seeking
to
give
an
accurate
description
of
the
process
of
calcination.
Weight,
which
measures
mass
or
quantity
of
substance,
was
thought
of,
in
these
days,
as
a
property
like
colour,
taste,
or
smell,
a
property
which
was
sometimes
decreased,
and
sometimes
increased,
by
adding
one
substance
to
another.
Students
of
natural
occurrences
were,
however,
feeling
their
way
towards
the
recognition
of
some
property
of
substances
which
did
not
change
in
the
haphazard
way
wherein
most
properties
seemed
to
alter.
Lavoisier
reached
this
property
at
one
bound.
By
his
experimental
investigations,
he
taught
that,
however
greatly
the
properties
of
one
substance
may
be
masked,
or
altered,
by
adding
another
substance
to
it,
yet
the
property
we
call
mass,
and
measure
by
weight,
is
not
affected
by
these
changes;
for
Lavoisier
showed,
that
the
mass
of
the
product
of
the
union
of
two
substances
is
always
exactly
the
sum
of
the
masses
of
these
two
substances,
and
the
sum
of
the
masses
of
the
substances
whereinto
one
substance
is
divided
is
always
exactly
equal
to
that
mass
of
the
substance
which
is
divided.
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