Chapter VI: 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_.