Ultimate elements of universe—Built up by polarity—Experiment with magnet—Chemical affinity—Atomic poles—Alkalies and acids—Quantivalence—Atomicity—Isomerism—Chemical stability—Thermochemistry—Definition of atoms—All matter built up by polar forces. I almost fear that by this time some of my readers may think that I have seduced them under false pretences to read long chapters of dry science, when they had been led from the introduction to anticipate discussions on the more immediately interesting topics of morals, religions, and philosophies. My excuse must be that these scientific subjects are really of extreme interest in themselves and indispensable as a solid basis for the superstructure to be raised on them. How can I attempt to show that the law of polarity extends to the more complex problems of human thought and life, if I fail in establishing its application to the simpler case of inorganic force and matter? It must be recollected also that among the primitive polarities is that of author and reader. It is my part to endeavour to present the leading facts and laws of the material universe in such plain and popular language that the ordinary reader who has neither time nor faculty for special studies may apprehend them clearly without excessive effort, or extraordinary intelligence. But it is the reader’s part to supply a fair average amount of attention, and above all[66] to feel an interest in interesting matters. Cleverness and curiosity are very much convertible terms, and the clearest exposition is thrown away on the torpid mind which views the marvellous universe in which he has the privilege to live, with the stupid apathy of the savage, taking things as they come without caring to know anything about them.
For the reader’s part of the work I am not responsible; but for my own I am, and I proceed therefore to give in my own way, and with the best faculty that is in me, a clear summary of such of the fundamental facts and laws of nature as seem necessary for the work I have undertaken.
From the preceding chapters we are now able to realise what are the ultimate elements of the material universe, and it remains to show how they are put together. The elements are ether, energy, and matter.
First, ether: a universal, all-pervading medium, imponderable or infinitely light, and almost infinitely elastic, in which all matter, from suns and planets down to molecules and atoms, float as in a boundless ocean, and whose tremors or vibrations, propagated as waves, transport the different forms of energy, light, heat, and electricity, across space.
Secondly, energy: a primitive, indestructible something, which causes motion and manifests itself under its many diversified forms, such as gravity, mechanical work, molecular and atomic forces, light, heat, electricity, and magnetism, all of which are merely Protean transformations of the one fundamental energy, and convertible into each other.
Thirdly, matter: the ultimate elements of this are atoms, which combined form molecules, or little pieces of[67] ordinary matter with all its qualities, which are the bricks used in building all the varied structures of the organic and inorganic worlds. Of these atoms some seventy have never yet been divided, and therefore, although we may suspect that they are merely combinations or transformations of one original matter, we must be content for the present to consider them as elementary. In like manner we may suspect that matter is in reality only another form of energy, and that the impression of solidity is given by the action of a repellent force which is very energetic at short distances. If this were established we might look forward to the generalisation that energy was the one reality of nature; but for the present it is a mere speculation, and we must be content with over seventy elementary atoms as ultimate facts. In any case this much is certain, that matter, like energy, is indestructible. We have absolutely no experience of either of them being created or annihilated. Nay, more, we have no faculties to enable us even to conceive how something can be made out of nothing, and all we know, or can ever know, about these primitive constituents of the universe is of their laws of existence, their evolutions and their transformations.
Minute as the atoms and molecules are, we must conceive of them not as stationary and indissolubly connected, but rather as little solar systems in which revolving atoms form the molecule, and revolving molecules form the matter, held together as separate systems by their proper energies and motions, until some superior force intruding breaks up the system and sets its components free to form new combinations.
What is the principle which thus forms, un-forms, and re-forms the various combinations of atomic and[68] molecular systems by which the world is built up from its constituent elements? It is polarity.
As I began with the illustration of the magnet introducing order and harmony into the confused mass of iron filings, let me take this other illustration from the same source. If we place an iron bar in contact with the pole of a magnet, the bar becomes itself a magnet with opposite poles to the original one, so that as opposite poles attract, the iron bar adheres to it. Bring a lump of nickel in contact with the further end or free pole of the iron bar, and the nickel also will be magnetised and adhere. Let the lump of nickel be as large as the pole of the iron bar is able to support, and now bring a lump of soft iron near this pole. It will drop the nickel and take the iron. This is exactly similar to those cases of chemical affinity in which a molecule drops one of its factors and takes on another to which its attraction is stronger. If iron rusts in water it is because the oxygen atom drops hydrogen to take iron just as the magnet dropped nickel.
The polarity of chemical elements is attested by the fact that when compounds are decomposed by the electric current, the different elementary substances appear at different poles of the battery. Thus, oxygen, chlorine, and non-metallic substances appear at the positive pole; while hydrogen, potassium, and metals generally, appear at the negative one. The inference is irresistible that the atoms had in each case an opposite polarity to that of the poles to which they were attracted. This is confirmed by the fact that the radicals, i.e. the elementary atoms or groups of atoms which have opposite polarities, combine readily; while those which have the same polarity, as two metals,[69] have but slight affinity for each other. Like therefore attracts unlike, as in all cases of polarity, and the greater the degree of unlikeness the stronger is the attraction. Thus, the radicals of all alkalies are electro-positive, and appear at the negative pole of a battery; while those of acids are all electro-negative, and the higher each stands in its respective scale of polarity the more strongly does it show the peculiar qualities of acid or alkali and the more eagerly does it combine with its opposite.
Acids and alkalies are, in fact, all members of the same class of compounds called hydrates, because a single atom of hydrogen is a common feature in their composition. This atom is coupled with a single atom of oxygen, which may be conceived of as the central magnet holding the hydrogen atom at one pole, while at the other it holds either a single atom of some metallic element, such as potassium or sodium, or a group consisting of such an element together with atoms of oxygen, so constituted as to present a single pole to the attraction of the central oxygen atom. Thus, if K stands for kali or potassium, N for nitrogen, O for oxygen, and H for hydrogen, we may have the compounds
H—O—K
and
 
The former is the molecule of potassic hydrate, which is the most caustic or strongest of alkalies; the latter, that of nitric acid, the most corrosive or powerful of acids. These are the extremes of the series, of which there are many intermediate members, all being more or[70] less alkaline, that is caustic and turning litmus-paper blue, when the third element is a simple metallic atom; and acid, corrosive, and turning litmus-paper red, when it is a compound radical of a group of metallic and oxygen atoms. This shows to what an extent whole classes of substances may have a general resemblance in their constitution, and yet differ most widely in their qualities by the substitution of one element for another.
These special qualities may be made to diminish and finally disappear by mixing the two opposite substances, or, as it is called, neutralising an acid by an alkali or an alkali by an acid. Thus, if hydrochloric acid, HCl, be poured into a solution of sodic-hydrate, Na—O—H, the alkaline qualities of the latter diminish and finally disappear, the result of the neutral solution being water, H—O—H, and sodic-chloride, or common salt, Na—Cl. It is evident that this result has been produced by the hydrogen atom in H—Cl and the sodium atom in Na—O—H changing places, the former preferring to unite with oxygen to form water, while the displaced sodium atom finds a refuge with chlorine. The oxygen atom has dropped sodium and taken hydrogen, just as the magnet dropped nickel and took iron.
This polarity of chemical elements manifests itself in different ways. In some cases it appears like that of a magnet, in which there are two opposite poles, and two only, one at each end. Thus oxygen (O) is bipolar, and its atom holds together two atoms of hydrogen (H) in forming the molecule of water, which may be represented as H+-O+-H, which is equivalent to drawing of a magnet. Others again, like hydrogen and chlorine, seem to have only a single[71] pole, as in the case of electricity in an excited glass rod, and have to create for themselves the opposite pole, which is the indispensable condition of all polarity, by induction in another body. Thus, muriatic or hydrochloric acid is formed by the union of a single atom of chlorine, which is strongly negative, with a single atom of hydrogen, in which it appears to have induced a positive pole: though the combination is not a very stable one, for if an element with a stronger positive pole of its own is presented to the chlorine, it drops the hydrogen, just as the magnet drops the nickel. Other atoms are multipolar, and seem as if made up of more than one magnet, or rather as if the atom had regular shape like a triangle, square, or pentagon, and each angle was a pole, thus enabling it to unite with three, four, five, or more atoms of other substances. Thus, one atom of nitrogen unites with three of hydrogen, one of carbon with four of hydrogen, and so on. Every substance has, therefore, what is called its ‘quantivalence,’ or power of uniting with it a greater or less quantity of other atoms, and conversely that of replacing in combinations other atoms, or groups of atoms, the sum of whose quantivalence equals its own. Thus, one atom of carbon, which has four poles, combines with four atoms of hydrogen or chlorine, which is unipolar, but with only two of oxygen, which are bipolar; while the oxygen atom combines with two of hydrogen, and that of chlorine with one atom only of hydrogen. The analogy between the single atomic and electrical poles on the one hand, and the dual and magnetic poles on the other, will be evident if we consider what occurs if a pith-ball, electrified positively, is brought near a similar ball electrified negatively.[72] They attract each other, and the one becomes the pole of the other; but if separated, each carries with it its own electrical charge. But the separate balls or poles, though no longer influencing each other, are not isolated, for each draws by induction an electrical charge opposite to its own to the extremity of the nearest conductor, and thus creates for itself a new or second pole. Polarity, in fact, involves opposition of relations, or two poles, and electrical only differs from magnetic polarity in the fact that in the latter the two poles are in the same body, while in the former they are in separate bodies.
For pith-balls read atoms, and we have an explanation of the univalent atoms like those of chlorine and sodium which act as single poles; and this is confirmed by the fact that such atoms are never found isolated, but are always associated in a molecule with at least one other atom which forms the opposite pole of the molecular system. Bivalent or magnetic atoms, on the other hand, which have two poles, like those of mercury and zinc, may constitute a complete polar system and be found isolated, and form the class of molecules which consist of single atoms.
This conception of the polarity of atoms enables us to understand the way in which the almost infinite variety of substances existing in the world is built up from a comparatively few simple elements. Atoms and radicals, which are multipolar, can attract and form molecules with as many other atoms or radicals as they have poles. This is called their degree of atomicity, which is the same as their quantivalence; and each of these atoms or radicals may be replaced by some other atom or radical, which presents to any pole a more powerful[73] polarity. Thus, compounds may be built up of great and varied complexity, for the quality of any compound may be greatly altered by any one of the substitutions at any one of the poles. And the molecules, or small specimens of matter, may be thus built up into very complex aggregations of atoms, some single molecules containing more than a hundred atoms. Thus, carbon has four poles, or is quadrivalent, and its atoms possess the power of combining among themselves to an almost indefinite extent and forming groups of great stability. Thus, carbon radicals may be formed in very great number, each affording a nucleus upon which compound radicals may be built up, so that carbon has been aptly called the skeleton of almost all the varied compounds of the more complex forms of inorganic matter as well as the principal foundation of organic life.
Nor is this all, for the qualities of substances depend not only on the qualities of their constituent elements, but also on the manner in which these elements are grouped. Two substances may have exactly the same chemical composition and yet be very different. We may suppose that the same elements affect us differently according as they are grouped. Thus, the same bricks may be built up either into a cube or pyramid, which forms are extremely stable and can only be taken in pieces brick by brick; or into a Gothic arch, which all tumbles to pieces if a single brick forming the keystone is displaced. As an instance of this, butyric acid, which gives the offensive odour to rancid butter, has exactly the same composition as acetic ether, which gives the flavour to a ripe apple. They consist of the same number of atoms of the same elements—carbon,[74] hydrogen, and oxygen—united in the same proportions. This applies to a number of substances, and is called Isomerism, or formation of different wholes from the same parts.
The principle of polarity, therefore, aided by the subsidiary conditions of quantivalence, atomicity, and isomerism, gives the clue to the construction of the inorganic world out of some seventy elementary substances. Of the substances thus formed, whether of molecules or of combinations of molecules, some are stable and some unstable. As a rule the simpler combinations are the most stable, and instability increases with complexity. Thus the diamond, which is merely a crystal of pure carbon, is very hard and indestructible; while dynamite, or nitro-glycerine, which is a very complex compound, explodes at a touch.
The stability of a substance depends partly on the stable structure of its component elements, and partly on their mutual affinity being strong enough to keep them together in presence of the attractions of other outside elements, which, in the case of most natural substances at the surface of the earth, consist principally of air and water. Thus, the rocks, earths, metallic oxides, water, carbonic dioxide, and nitrogen are extremely stable, and resist decomposition, or chemical union with other substances, with great energy. With regard to all substances this law holds good, that the tendency is to fall back from a less stable to a more stable condition, and that such a falling back is always attended with an evolution of heat; while, on the other hand, heat is always absorbed and disappears whenever the elements of a more stable substance are made to enter into a less stable condition. Thus, when wood[75] burns, there is a falling back from a substance unstable, on account of its affinity for the oxygen in the air, into the stable products, carbonic dioxide and water, and the heat evolved is the effect of this fall.
As the tendency of all changes is towards stability we arrive at the following law, which is one of the most recent generalisations of modern chemistry: In all cases of chemical change the tendency is to those products whose formation will determine the greatest evolution of heat.
This, however, does not imply that the tendency may not be overcome and unstable products formed, for just as a weight may be lifted against the force of gravity, so may the chemical tendency be overcome by a sufficient energy acting against it. Heat is the principal means of supplying this energy, and by increasing it sufficiently not only are molecules drawn apart and most solids converted into fluids and finally into gases, but there is reason to believe that at extremely high temperatures, such as may prevail in the sun, all matter would be resolved into isolated or dissociated atoms. Thus, water at a temperature of 1,200° is resolved into a mixture of oxygen and hydrogen atoms no longer chemically united into water-molecules; and iodine-vapour, which below 700° degrees consists of molecules of two atoms, above that temperature consists of single atoms only.
The subject might be pursued further, but enough has been said for the present purpose to show that the universe consists of atoms which are endowed with polarity, and that as diminished temperature allows these atoms to come closer together and form compounds, matter in all its forms is built up by the action of polar forces.