THE CONSTRUCTION OF SUBSTANCES.
In order to understand the chemical construction of substances it is
necessary to consider three terms much used by the chemist: these terms
are,
Mass,
Molecule,
Atom.
Evidently the words relate to three grades of magnitude in which matter
is capable of existing; it is equally plain that of the series the mass
represents the largest individual portion of substance, and the atom
the smallest, while the molecule represents the intermediate one.
The Chemical Use of the Term Mass.
Whoever looks about him sees substances existing in masses. This is
true of vast mountain chains and equally true of the smallest grains of
matter that are recognized as the humblest components of those peaks.
But the smallest of these _visible_ masses is made up of particles
still more minute—yet perhaps of precisely the same kind. For the
chemist possesses means of subdivision of substances by which he may
make them into minute fractional parts that are measurable and are all
just alike, and he may continue this process long after the portions
have sunk below the reach and range of ordinary vision. A lump of pure
sugar as big as a cubic inch may be _mechanically_ divided by any
one into many smaller ones, each little one being easily recognized
by the ordinary senses as possessing the sweetness, the crystalline
construction, the whiteness, the solidity, the brilliancy, the power
of dissolving in water and indeed a great many other well-known
characteristics that pertain to sugar. But the chemist is able to
continue the subdivision of the sugar much further. This he does by
recourse to processes not exactly mechanical though closely allied to
them: by processes often called _physical_ as distinguished from purely
mechanical ones. He may thus reduce the sugar to fragments of such
extreme minuteness that while they do not impress our senses as larger
portions do, yet each fragment is capable of displaying to a competent
scientific observer the certain and sure chemical properties that
always belong to sugar, whether in large lumps or in small ones, and
which in fact belong to nothing but sugar.
Speaking generally, all particles producible by mechanical subdivision
are masses, while the same is true of most particles producible by
physical subdivision.
The Chemical Use of the Term Molecule.
But there is a point where any attempt at further scientific
subdivision results in a new and startling change: at this stage the
last individual that can properly be called sugar is dissected and
loses entirely the characteristics of sugar. The fragments produced by
the wreck of the last particle are of a new kind. They are
portions of carbon,
portions of hydrogen,
portions of oxygen.
This last particle of sugar is separated into its ultimate constituents
only by _chemical_ processes. This last particle before it is broken up
is called the _molecule_, the word meaning a little portion. The single
individual thing it refers to cannot be detected by the eye, nor can it
be in any way appreciated except by scientific means. But a chemical
change of _the last multitude of molecules at once_, is practicable
to everybody, and it is to a certain extent recognized by every one
who heats sugar until it turns to a charred mass. This charred mass is
mainly carbon—one of the components of the now ruined sugar—and it is
very unlike sugar in every way. The chemist can show that when sugar is
charred, the oxygen and the hydrogen go off mostly in the form of gases
or vapors, and that on this account they escape detection at the hands
of all ordinary observers.
The Chemical Use of the Term Atom.
It appears then that the chemist is able to subdivide molecules into
smaller parts. But he finds that further division is at a certain stage
forbidden him. He can take the oxygen out of the sugar, but he cannot
take anything but oxygen out of oxygen; he can take hydrogen out of
sugar, but he cannot take anything but hydrogen out of hydrogen; he can
take carbon out of sugar, but he cannot take anything but carbon out of
carbon.
As a result of all chemical study of common sugar the chemist has fixed
upon the following as expressing most closely the facts as he knows
them:
The formula
of one molecule of pure cane sugar, is
C₁₂H₂₂O₁₁
The chemical formula of any substance expresses much more than the
reader would at first imagine. Thus the formula C₁₂H₂₂O₁₁ conveys at
once to the chemist a series of facts, some of which may be amplified
as follows:—one molecule of sugar contains three kinds of substance:
carbon, hydrogen and oxygen:—each of these kinds of matter exists in
the molecule in separate minute portions such as in the present state
of human knowledge are divisible only in a limited way: thus the carbon
of one molecule of sugar is divisible into twelve parts, _and no
further_;
the hydrogen of one molecule of sugar is divisible into
twenty-two parts, _and no further_;
the oxygen of one molecule of sugar is divisible into
eleven parts, _and no further_.
Definition of the Term Atom.
Now at last the atom has been reached. It is that portion of any kind
of matter that is to human beings indivisible _in fact_. It has already
been stated that there are only sixty-six different kinds of atoms,
it appears then that there are only sixty-six kinds of matter that at
present cannot be chemically subdivided into different components.
It is true that some persons consider that certain intricate chemical
processes suggest that what have been here called indivisible atoms
are themselves really capable of yet further decomposition. Without
attempting here to sustain or to demolish this proposition or to say
what the future of chemical investigation may reveal, it may be safely
remarked that adequate proof has not yet been offered of the ability
of any one to successfully accomplish a decomposition of the sixty-six
atoms enumerated.
Plainly then just as bricks may be made into a building, and a series
of buildings may make a city, and a series of cities may exist in a
state, so atoms may combine together to form molecules, and molecules
may cohere together to form a mass, and visible masses may be placed
side by side and give rise to the ordinary objects recognized about
us. True the comparison suggested is not strictly carried out in all
particulars. But the difficulty not a serious one: for a city _might_
contain a multitude of houses each one so similar that no difference
could be distinguished between them, just as a mass of sugar does
in fact contain molecules of which each one is so like its neighbor
that the most refined chemical methods discover no difference between
them. Again these same houses _might_ be composed of combinations of
brick and other materials differing among themselves, but closely
corresponding in every house. So the molecule of sugar does contain
atoms of carbon, hydrogen and oxygen, the atoms of one kind differing
distinctly and absolutely from the atoms of the other kind.
But here the parallelism seems to cease. For while all bricks and
other components of a building are capable of being split into smaller
portions, the atoms composing the molecule are found by the chemist to
be absolutely indivisible in the present state of knowledge.
Employing still further the illustration already in hand it may be
added that just as the walls of a dwelling might contain bricks either
of the same kind as to their color, shape and weight, or else differing
in these or other respects, so a molecule may be a little group of
atoms of the same kind, or it may be a group of atoms of different
kinds. Thus the hydrogen gas molecule is composed of two atoms each
just alike, and each being hydrogen. This molecule is represented by
the formula
H₂ or H—H.
So a molecule of chlorine gas is composed of two atoms each just alike
and each being chlorine. This molecule is represented by the formula
Cl₂ or Cl—Cl.
Everything Built up of Atoms.
Now each of the sixty-six elementary substances has molecules composed
of atoms, and each molecule of a given element is composed of atoms
of the same kind. And further all the vast and countless myriad of
compound substances, whether buried in the heart of the solid earth,
whether drifting in the wandering courses of the ocean’s currents,
whether floating in the airy mass which is wrapped about our globe,
whether components of distant planets of unknown constituents, whether
parts of the seething mass which pours its volcanic torrents millions
of miles out from the surface of our central sun—all these substances
are constructed, so far as we know, of inconceivably minute atoms of
varying kinds bound together by chemical attraction into molecules, the
molecules being piled one upon another into those masses whose reaction
our dull senses can appreciate.
Atoms and Molecules Manifest Chemical Affinity.
But to the chemist, atoms, molecules and masses possess an interest of
another kind. Each atom and each molecule is endowed with an invisible,
occult power called _chemical affinity_. This power acts like an unseen
spirit possessed of likes and dislikes. By reason of it an atom of
hydrogen for example instantly binds itself to an atom of chlorine
whenever opportunity offers, but will never, even under the most
favorable circumstances, combine with an atom of gold.
Finally this attractive force is a kind of energy of which no true
explanation can be offered. All that human beings can do is to
attentively study it as it manifests itself in the relations of
elementary substances and compound substances one toward another.
Indeed one of the principal offices of chemistry is to study these
relationships as they develop. It is the multitude of possible
relationships and actions of which the numberless substances known are
capable, that gives to chemistry its great scope and variety and that
makes it such a vast field for experiment, for discovery of facts, and
for industrial application of them.
READING REFERENCES.
Atoms and Molecules.
=Barker=, G. F.—Amer. Chemist. Nov. 1876. p. ms. 164.
=Stoney=, Johnstone.—Phil. Mag. xxxvi, 141.
=Clerk=-Maxwell, J.—Encyclopædia Britannica,
_article_ Atoms.
———— Theory of Heat. New York. 1872.
=Thompson=, Sir Wm.—_Nature_. Mch. 1870.
=Tait=, P. G.—Recent Advances in Physical Science. London.
1876. p. 283.
=Mayer=, A. M.—Lecture Notes on Physics. p. 52.
=Cooke=, J. P.—The New Chemistry. New York. 1881. pp. 29-43.
———— American Cyclopædia, _article Molecule_.