Harrisburg telegraph. [volume] (Harrisburg, Pa.) 1879-1948, 1918-11-15
BE- Gnrrett p, servlss

By Garrett ~ beFNisS
am asked by a reader to write
an article on "atoms. molecules, cleo
irons and IONS" These names APP
pear so frequently now In news
papers, magazines and books that
, everybody ought to have an elemen-
tary knowledge Of the things Tor
which they stand. Bome of them
were never heard OF In schools which
people now in middle life attended.
Atoms is an old word conveying
an old idea, viz, that of the exis-
tence of ultimate, indlvlsible par
ticles of which all things are COM
posed. II is easy to see how the
notion of atoms arose. You find
that everything can be divided and
split up into smaller and smaller
particles. The finest particles of
dust into which rock might be
divided may be separately Invisible
without a microscope, But both
experience and reason Indicate that
that is not the end of the division,
but that the dividing process may
be almost without limit,
The question then ariseA Is there
actually a limit? Can matter be
reduced to particles SO small that
further division is impossibleS Even
the ancient Greek philosophers con-
cluded that there was such limit,
and they called the fnaL indlvisible
particles atoms" |. e., things that
cannot be cut, but without under
taking to say Just how small they
were.
This idea lived through the ages
springing up again after every tenn
porary recession of man into bar
barism and ignorance, and at last
1t became one of the corner stones
of modern science, The late Lord
Kelvin made a celebrated calcula-
ton OF the probable size OF an atom.
He, so to speak, put 1t on the view
lng-stage of the microscope of the
Imagination by means of a graphic
comparison.
Imagine" he said. "a raindrop
or a globe of glass as large as a
pea to be magnihed up to the size
of the earth each constituent atom
Che used the word moieeule, but we
may substitute atom for our present
purpose) being magnided In the same
proportion. The magnified structure
would be more coarse grained than
n heap OF small shot but probably
less coarse grained than a heap Of
cricket balls" More recent calcula-
tions give the diameter of the small
est atom as about one-three- e-hundred-
millionth OF an inch, The largest
kind may have many times that.
With the atom 1t was until recently
supposed that subdivision ceased.
1t was adopted as the chemists
unit" and practically remains so
still, although, as we shall see, the
theory OF its indivisibllity has proved
to be erroneous. The great service
that the conception of ultimate
atoms has rendered to chemistry Is
in making clear tho difference be-
tween elementary and compound sub
stances, and rendering 1t possible to
study, the laws OF chemical action,
Every substance made up OF only
one kind of atoms Is an element
About eighty-three chemical ele-
ments are now known; consequently
there are eighty-three different kinds
of atoms.
Molecules are groups of atoms, SO
that molecule Is larger than an
atom OF the same kind OF substance.
There are two sorts of molecules,
viz. those which consist Of only one
kind. or species, OF atoms, and those
kinds united together The first sort
which consist of atoms OF different
kinds united together The first sort
of molecules is found only in ele-
mentary substances, and the second
only in compound substances, 1. e.
substances made up of two or more
chemical elements,
For the sake of clearness IL Is best,
for ordinary purposes, to think of
molecules only as tho constituent
particles of compound substances.
Being composed OF atoms of different
kinds, when such molecules are
broken up the compound substance
formed of them loses Its identity,
and the separated atoms go back
into their elements,
Water, for instance. is a COM
pound substance, each OF whose
molecules consists OF one atom of
the element oxygen combined with
two atoms OF the element hydrogen.
When water IS chemically decom-
posed. its individual molecules are
broken up and from each OF them
Is released one atom Of oxygen and
two atoms of hydrogen. but there
the ordinary process OF decomposl-
tlon ceases and we cannot make an
other division by breaking up the
atoms.
Within quite recent times. how
ever, it has been discovered that the
apparently indivisible and unbreak-