The fairy tales of science/The Four Elements
The Four Elements.
"Do not our lives consist of the four elements?"
What is the world made of? According to the ancient doctrine of the Four Elements, all things are formed of fire, air, earth, and water; and the varieties and differences in the properties of bodies depend entirely on the proportion in which these great principles are mingled.
While we confine our observations to the external properties of matter, this beautiful doctrine seems incontestable. If we kindle a few dry sticks on a cool hearth, we may remark that while the wood burns there rises smoke or air; the smoke is followed by flame or fire; moisture or water is deposited on the hearth; and ash or earth remains.
Everywhere can we detect the presence of the mighty elements. Fire can be set free from innumerable substances; air penetrates the pores of all bodies, and covers the world like a mantle; water forms the all-embracing sea, and nourishes every plant and animal: while earth enters into the composition of all solids, and gives form and stability to the universe.
Man himself seems to be built up of the four elements, and according to the first theoretical system of medicine, health indicates their perfect balance, and disease, the preponderance of one of them.
Such is the old doctrine of the Four Elements, simple and concise enough, but unfortunately false.
Modern science has satisfactorily demonstrated the compound nature of fire, air, earth, and water, and they can no longer be regarded as elements. By the term element, we understand any kind of matter which up to the present time has never been decomposed into constituents, and which consequently appears to have a simple nature. The true elementary bodies may be compared to the letters of the alphabet, and the diversified compounds which compose the material world to the words which form a language.
Let us examine the imaginary elements of the ancients, and see whether they will help us to arrive at the true solution of the problem—what is the world made of?
A candle in burning seems to disappear completely, and when the combustion is over, an insignificant trace of ash from the wick is all that remains to the eye. According to the Greek philosophers, tallow contains an ethereal substance called Fire, which being set free, takes the form of flame; the gradual decrease of the candle is therefore accounted for by the dissipation of its chief constituent. Before we can accept this explanation we must be quite satisfied that Fire is a substance.
Wherever we perceive light and heat emanating simultaneously from a combustible body, we say—there is fire—but we can bring forward no proof of the material existence of this so-called element. We cannot weigh it, measure it, or put it in a bottle; nor can we imagine it existing apart from a burning substance. Fire, after all, may be nothing but a name for certain phenomena of heat and light. These two great forces are intimately connected; thus, whenever we raise a solid object to a high temperature it becomes luminous; first it emits a dull red light, which changes as the temperature increases to orange, then to yellow, and finally to full white.
The flame of a candle is a white hot cone of volatile matter, which we vaguely term Fire—if we can discover the real nature of this cone we shall be able to define Fire with some degree of accuracy.
The chemist tells us that nothing can be absolutely destroyed, and that what we call destruction is merely the conversion of a visible body into an invisible one. To reconcile this statement with the gradual disappearance of the burning candle, we are forced to conclude that the tallow is changed into an invisible gas or vapour, and escapes into the air. Now as no solid can become aëriform without the agency of heat, the question naturally arises—whence comes the heat that vaporizes the tallow?
Everybody is familiar with the fact, that a considerable amount of heat is evolved when water is poured upon quicklime, a fact which illustrates the great chemical law, that no union of two bodies can take place without a change in their temperature.
The intense heat emitted by the flame of a candle may be traced to chemical action. If we cover a lighted candle with a glass shade, the flame will soon begin to languish, and in a few minutes it will expire. The flame seems to rob the confined air of a certain virtue which is essential to its continued existence. This is the true interpretation of the phenomenon. The air contains a wonderful gas called oxygen, which combines with the vaporized tallow, just as water combines with quicklime, and their union is attended by a development of heat.
The phenomena presented by a burning candle may now be easily understood. The tallow is melted and sucked up to the top of the wick, where it is boiled and converted into vapour. This vapour combines rapidly with the oxygen of the surrounding atmosphere, and the heat evolved is such as to render the vapour luminous. To bring about the combustion of the candle it is necessary to apply heat to the wick, but afterwards the heat which is liberated is more than sufficient to sustain the action.
We have now arrived at a tolerably clear conception of Flame; it is merely volatile combustible matter heated to whiteness. Fire is simply a convenient word which we make use of to denote the extrication of light and heat during combustion, and the ancient notion that it is one of the primordial constituents of the material world is no longer tenable.
Fire is often spoken of as the destroying element, but we must bear in mind that combustion only alters the state of bodies; there is no actual destruction or loss of weight when a body is burned, though the products of combustion may be invisible.
If we set fire to a small fragment of phosphorus and cover it with a dry tumbler, dense white fumes will arise, which will condense on the sides of the glass in snow-like flakes. If we collect this white substance and weigh it, we shall find that it is more than twice as heavy as the phosphorus. How is this? The explanation of this apparent anomaly is simple enough. The phosphorus, in burning, combines with the oxygen of the atmosphere to form this white compound, which is known to chemists by the name of Phosphoric Acid, the weight of the oxygen is therefore added to that of the phosphorus.
Some of our readers will doubtless receive this information with astonishment. It seems scarcely credible that a substance having the appearance of snow should be produced by the union of an invisible gas and a yellow wax-like solid. Chemistry is a science of marvels, and this wonderful dissimilitude between a compound body and its constituents is anything but an exceptional case; in fact it is this change of properties that distinguishes chemical union from mere mechanical mixture.
Our tallow candle is composed of two invisible gases and a black solid, and is therefore a much more extraordinary compound than the white phosphoric acid. When a candle is burned, the products of the combustion are invisible gases; these gases can nevertheless be collected by the chemist, and are found to weigh more than the original candle. Coal, coke, wood, and other combustibles which are employed as fuel, likewise form gaseous compounds with the oxygen of the atmosphere. This is a very significant fact, for were the products of combustion invariably solid, like phosphoric acid, the world would long since have been buried in ashes.
We have examined the first of the so-called elements of the ancients, and have proved it to be a manifestation of intense chemical action between two or more bodies. Let us now proceed to consider the nature of Air.
"There exists a certain thing," says a philosopher of the sixteenth century, "which we do not perceive, and in the midst of which is plunged the whole universe of living beings. This thing comes from the stars, and we call it air. Fire, in order that it may burn, requires wood, but it also requires air. The air, then, is the life, for if air be wanting all living beings would be suffocated and die." In all ages the atmosphere has been regarded as the great source of life, and long before the famous dogma of the Four Elements was propounded, a Grecian sage declared that air was the one universal principle from which everything proceeded.
We have already alluded to the fact that combustible bodies combine with a certain gas called oxygen, which is contained in the atmosphere; our readers will not, therefore, be surprised when we tell them that air is a mixture of dissimilar gases, but they will marvel greatly when we describe the properties of its constituents.
If we boil some mercury or quicksilver in a closed glass vessel, in a few hours the metal will undergo a very extraordinary change. It will lose its metallic character entirely, and in place of the glistening fluid we shall find a heap of bright red scales. As these scales weigh more than the original mercury, we may safely conclude that something has been abstracted from the air contained in the vessel.
If we now take a lighted match and plunge it into the air that remains, it will be instantly extinguished; it is therefore evident that the abstracted something is oxygen.
Let us close the vessel once more and apply to it a strong heat; the red scales are now converted into metallic mercury, and the air regains its property of supporting combustion.
This beautiful experiment proves air to be a mixture of oxygen and a certain gas in which no ordinary combustible will burn. This gas has been named azote or nitrogen.
Oxygen forms about one-fifth of the atmosphere, and nitrogen nearly the remaining four-fifths; to these components must be added about one two-thousandth part of a gas called carbonic acid, and traces of another body called ammonia. Though these two last-named constituents bear such a small proportion to the others, we shall presently see that they have important duties to perform in the economy of nature.
The composition of the atmosphere is everywhere uniform; we may bring down air from the summit of the highest mountain and collect it in the deepest valley, but we shall not be able to detect the slightest variation in its composition.
The same uniformity is apparent whether we examine the air of the polar regions or that of the tropics; whether we collect it in the densely populated city or in the untrodden forest. This fact seems all the more wonderful when we consider the contaminating influence of the countless exhalations that are continually rising into the atmosphere. The clouds of smoke poured forth by our chimneys, the expired breath of animals, and the gases that proceed from decaying matters, do not perceptibly disturb the equilibrium of the constituents of the atmospheric ocean.
We must remember that this aërial ocean is some forty-five miles in depth, and that the vapours which arise from the earth are rapidly diffused throughout its entire extent.
The atmosphere exerts a pressure upon the earth's surface equal to about fourteen and a half pounds upon each square inch; and it has been calculated that its entire weight amounts to more than five thousand one hundred and fourteen billions of tons—a sum which words may express, but which the human mind cannot appreciate. Our readers will gain a clearer conception of this enormous sum when we tell them that it is equivalent to the weight of a solid globe of lead some sixty miles in diameter!
We have said that the atmosphere contains an aëriform body called carbonic acid. Let us now see how this fact may be proved. When quicklime is exposed to the air it gradually loses its caustic properties, and increases in weight; this increase of weight depends on the absorption of carbonic acid from the surrounding atmosphere.
We may expel this gas from the altered lime by heat, and collect it in suitable vessels for examination. We find it to be much heavier than ordinary air—so heavy, indeed, that we may pour it from one vessel to another, like water. If we plunge a lighted taper in it the flame will be instantly extinguished; and if we substitute a mouse or any other small animal for the taper, the poor creature will be suffocated.
This gas is the chief product of combustion; our candles and fires are continually pouring it forth into the atmosphere, animals expire it from their lungs, and it is produced in every case of putrefaction and fermentation.
Carbonic acid, so fatal to animal life, is essential to the life of plants; indeed the existence of the whole vegetable kingdom depends on the presence of this gas in the atmosphere. Carbonic acid is a compound of oxygen and carbon or charcoal, which substance is the principal constituent of all plants. Every green leaf may be compared to a little chemical laboratory, in which the carbonic acid of the air is decomposed, the carbon being retained by the plant, while the pure oxygen is cast forth into the atmosphere.
Vegetables absorb the carbon which is exhaled in combination with oxygen by animals, and the two great divisions of organized beings are thus indissolubly connected by the interchange of substances necessary to their existence.
The old fable of the Hamadryads who presided over the trees of the forest, and who died when the trees were cut down, shadowed forth a deep truth. In the fairy-tales of science we read that the lives, not merely of wood-nymphs, but of all living creatures, are dependent on trees and herbs!
The atmosphere invariably contains a minute portion of ammonia, another compound body, its constituents being nitrogen and a gas called hydrogen. Ammonia is absorbed by water, and it is therefore brought down to the earth by rain, where it forms a valuable manure for plants; its importance may be conceived when we state that the nutritious qualities of grain and other vegetable substances are mainly derived from the nitrogen contained in this aërial manure.
Watery vapour is constantly present in the atmosphere, though we can scarcely call it a constituent of air. Its presence can be easily demonstrated by putting some ice in a tumbler, for when the glass is sufficiently cool, the vapour will be condensed upon its outer surface in the form of dew.
We have resolved air into its component gases, and have thus exploded the old notion of air being an element.
Our investigations have brought to light certain bodies which may be justly considered elements, namely oxygen, hydrogen, nitrogen, and carbon. These substances have never yet been resolved into constituents, but we do not dogmatically assert that they are absolutely simple in their nature. We call them elements because we cannot prove them to be compounds, though it is not impossible that they may turn out to be such at some future time.
That a mixture of four dissimilar elements should produce the life-supporting atmosphere is a fact that may well excite our wonder. Who would suspect that the mild and genial air which envelopes our planet could be formed of ingredients which separately exhibit such striking peculiarities, and which combine in other proportions to form compounds all more or less fatal to life?
An atmosphere of pure oxygen would be too exciting to be compatible with long life in animals, even if we could imagine the existence of life in a blazing world; for not only those substances which are generally spoken of as combustibles, but even the metals, burn with great violence in oxygen.
In an atmosphere of nitrogen, animals could not exist at all; indeed this gas formerly went by the name of azote, the literal significance of which is "fatal to life."
Two volumes of oxygen mixed with eight of nitrogen form "the breath of life," but when these gases are combined in other proportions they form compounds which have very different properties.
One of these compounds is the protoxide of nitrogen, a gas which may be inhaled for a few minutes without danger, but which is incapable of supporting life for any length of time. When breathed it produces great mental excitement, and occasions a total loss of volition. The person who inhales it performs a hundred strange antics; he talks incoherently, laughs wildly, sings, dances, and sometimes fights; he feels that he is lighter than the atmosphere, and sees all things under a new aspect.
In old times these extraordinary effects would probably have been ascribed to some mischievous demon contained in the laughing gas, and the "bell, book, and candle," would have been deemed indispensable for its exorcism.
Another compound is a colourless and invisible gas so poisonous that animals plunged into it instantly expire; a third, a corrosive orange-coloured vapour, equally noxious; and a fourth, the well-known liquid called aqua-fortis, a powerful acid which dissolves copper and other metals, and which destroys all organic substances.
Such are the compounds of nitrogen and oxygen, the very elements which we draw into our lungs at every inspiration, and without which we could not exist.
Carbonic acid gas though incapable of supporting life is not poisonous, and its presence in the atmosphere does not disturb our vital functions. Animals may be drowned in pure carbonic acid, but they cannot be poisoned by it. If the atmosphere contained another compound of carbon and oxygen, namely, carbonic oxide, in place of this innocuous gas, the world would be a lifeless desert, as carbonic oxide is an active poison, and a very small quantity of it would suffice to infect the air.
The philosopher who declared that air came from the stars, figuratively expressed a great truth. We have only to examine the wondrous constitution of the gaseous mixture to be convinced that it must have had a celestial origin, and that the potent elements of which it is composed must have been mingled by an all-wise and beneficent Power.
We have resolved Fire into the phenomena of light and heat, and have separated the constituents of Air; let us now summon Water into our presence, and compel that supposed element to reveal its true nature.
Water, like Air, was once regarded as the origin of all things; indeed this belief in the universality of moisture may be said to have laid the foundation speculative philosophy among the Greeks.
Water exists in the three physical states—the solid, liquid, aëriform. By adding heat to liquid water we convert it into aëriform water, or steam; by abstracting heat from it, we change it into solid water, or ice; in either case the chemical composition of water remains unaltered.
We can demonstrate the compound nature of Water by analysis or by synthesis; in plainer language, by resolving it into its elements, or by forming it from its elements. Let us first see how its analysis may be effected.
Some chemical compounds, the red mercurial scales, for example, are decomposable by heat, but Water is merely vaporized by this potent agent. To overcome the attractive force or affinity which binds the elements of Water together, we must call in the aid of some substance which has a superlative affinity for one of these elements.
Such a substance is potassium, the lightest of our metals. When exposed to the air potassium rapidly loses its metallic character by combining with oxygen, with which gas it forms potash; we therefore conclude that potassium has a strong affinity for oxygen.
If we throw a small fragment of this metal into water, it takes fire and burns, while swimming about on the surface of the liquid, with a brilliant light of a violet-red colour. When the combustion is over, no vestige of the potassium remains, but we find that the water has acquired the acrid taste of potash. The chemist thus interprets the phenomenon:—Water is a compound of oxygen and a highly inflammable gas called hydrogen; when potassium is thrown into Water it combines with a portion of its oxygen to form potash, and the heat which attends their union sets fire to the liberated hydrogen. It is not the metal that burns so furiously, but one of the constituents of water.
Here is a revelation far more wonderful than anything we find in our old story books!
Oxygen gas is the great supporter of combustion; even the metals will burn away in it like tinder. Hydrogen is the lightest gas known; it is very inflammable, and gives out an intense heat while burning. Water, the great antagonist of Fire, is built up of these two fiery elements!
Wherever we find Water we may be sure that these two elements are present. We may detect them in the water of the boundless ocean, the placid lake, and the murmuring rivulet; in the floating cloud and the jagged iceberg; in the raindrop, the hailstone, and the snow-flake; in the jewel that glitters upon the bosom of the rose, and in the tear that falls from the mourner's eye!
Potassium is not the only substance that decomposes water. Everybody is familiar with the fact that iron rusts when placed in water. Now the rusting of iron is a similar phenomenon to the conversion of potassium into potash; they both depend upon the absorption of oxygen. At a red heat, iron decomposes water very rapidly. When steam is made to pass through a long red-hot iron tube it is resolved into its elements. The oxygen unites with the iron to form rust, and the hydrogen is set free. By weighing the tube before and after the operation, the chemist is able to determine the proportion in which the two elements are combined.
In a hundred parts by weight of water he invariably finds eighty-nine of oxygen and eleven of hydrogen.
We may employ our old friend the Amber Spirit to separate the elements of Water, as this versatile being is a most skilful analytical chemist. The Spirit can set free the oxygen and hydrogen in two distinct streams of bubbles; whereas, the human operator can only liberate one of these gases by forcing the other to combine with some new body.
We have spoken of the inflammable nature of hydrogen, but we have not yet explained the phenomena which attend its combustion. This gas when pure burns with a very pale flame, the product of its combustion being water, which escapes into the atmosphere in the form of an invisible vapour. If a cool tumbler be inverted over the flame this vapour will be condensed into minute drops, which will trickle down the inner surface of the glass. The combustion of hydrogen is therefore a manifestation of the intense affinity of this gas for the oxygen of the air.
If we mix the two gases in the proportion in which they combine to form water, and apply a lighted match to the mixture, the gases will instantly unite with a deafening explosion. All the water produced will merely suffice to damp the surface of the vessel in which the .explosion takes place, as no less than 2550 measures of the gaseous mixture are required to form one measure of water.
Here is another marvellous revelation! The two gases have separately resisted every attempt made by the joint efforts of cold and pressure to liquify them, yet they combine and form water, the type of liquidity!
According to the dogma of the Four Elements, everything that is neither fire, air, nor water, is necessarily earth. Now a moment's consideration will convince us that innumerable bodies having the most diverse properties are comprised in this definition of the so-called element.
We cannot therefore deal with Earth as we have dealt with its mighty brethren; we cannot deduce any general conclusions as to its nature from the analysis of a single sample. We may resolve a particular handful of soil into its elements, but we dare not assert that these elements are common to the multitudinous handfuls which constitute the solid portions of our planet.
How, then, are we to proceed with our investigations? Were we to examine in regular order the various compounds included in the ancient conception of earth, our fairy tale would assume the character and proportions of an encyclopaedia. To preclude such a result, we must abandon the analytical method of inquiry, and be content to accept certain comprehensive truths that chemistry has revealed regarding the constitution of different kinds of earth.
The diversified compounds which form the material world have been resolved by the chemist into sixty-three elementary bodies, fifty of which are metals. These elements are rarely found in a state of purity, owing to their strong tendency to combine with each other.
The principal ingredients of Earth, are compounds of oxygen with certain elementary bodies that are never found pure in nature.
Silica, the most widely-diffused compound, contains oxygen, and another of the metalloids, or nonmetallic elements, called silicon, which can be isolated as a dark-brown powder. Sand, flint, and quartz consist almost entirely of silica; so do the granitic and siliceous rocks which form, so large a portion of the earth's crust.
The highest and most extensive mountain ranges are huge masses of silica, and the deserts of Africa and Asia are vast plains of the same abundant substance. Silica forms the sand and shingle of the sea-shore, and enters into the composition of every soil; it is the chief ingredient of some of our most precious jewels; of the invaluable transparent glass; and of the stones with which we pave our streets and build our temples.
Alumina is a compound of oxygen with a very extraordinary metal named aluminium, of which we shall have to speak in another of our fairy tales. Alumina is the basis of every kind of clay, and is only second in importance to silica. It is also a constituent of our rocks and soils, of our gems, and our building materials; and we make use of it to form earthenware, a substance which rivals glass in usefulness.
Lime is another abundant metallic oxide or rust, its base being calcium, a beautiful silver-white metal, which burns brilliantly when heated in the air. In nature, lime is generally found in combination with carbonic acid, one of the constituents of the atmosphere. The well-known substance, chalk, which forms our far-famed white cliffs, the compact limestones used in architecture, and all the elegant varieties of marble, are examples of this union.
The solid portions of our globe are almost as rich in oxygen as the atmosphere and ocean. Every rock is a compound of oxygen with certain metallic and non-metallic bodies. Silica contains about half its weight of this abundant element; alumina no less than one-third; and lime two-fifths.
In some compounds oxygen is replaced by another metalloid. Common salt, the chief saline matter of sea-water, is a compound of sodium, a metal closely allied to potassium, with chlorine, a remarkable gaseous body, which in some respects resembles oxygen. The glistening yellow mineral called iron pyrites, contains iron, and the metalloid sulphur. The variegated crystalline substance known as fluorspar, is a compound of calcium, the metallic base of lime, with fluorine, a mysterious body which the chemist has never yet been able to procure in a separate state.
The so-called noble metals—namely, gold, silver, mercury, platinum, and a few others—are usually found in a state of purity; sulphur is frequently met with uncombined; and carbon is found pure in the diamond. With these few exceptions, the material world may be said to be an assemblage of compounds formed by the union of thirteen metalloids with fifty metals.
Plants and animals are almost wholly composed of oxygen, hydrogen, nitrogen, and carbon; hence these metalloids have been styled the organogens, or organ-forming elements. The chemist tells us that wood, sap, starch, muscle, blood, nerve, and all other organized substances, result from the combination of these four principles in varying proportions.
Vegetables feed upon inorganic matter; they derive their carbon from carbonic acid, their nitrogen from ammonia, and their oxygen and hydrogen from water.
Animals are dependent upon the vegetable kingdom for their sustenance. A large number of races feed directly upon herbs and fruits; others prey upon the bodies of these vegetable-feeders. When animals die, their bodies suffer decomposition, and their original constituents—water, ammonia, and carbonic acid, return to the atmosphere, to nourish another generation of plants, for another generation of animals to feed upon.
The elements are indestructible, and death merely alters the arrangement of their atoms.
The ancient philosopher contended that all things were formed out of four elements: the modern philosopher declares that the two great organic kingdoms spring from a few invisible gases. The theory seems almost as credible as the fact! The following words from the pen of a celebrated chemist, read like a page of some wild romance, and yet they deal with facts that are incontrovertible: "Man is formed of condensed air (or solidified and liquefied gapes). He lives on condensed as well as uncondensed air, and clothes himself in condensed air. He prepares his food by means of condensed air, and by means of the same agent moves the heaviest weights with the velocity of the wind. But the strangest part of the matter is, that thousands of these tabernacles formed of condensed air, and going upon two legs, occasionally, and on account of the production and supply of those forms of condensed air which they require for food and clothing, or on account of their honour and power, destroy each other in pitched battles by means of condensed air."
We have now arrived at a true solution of the great problem—what is the world made of?
The three kingdoms of nature are built up of some sixty-three elementary bodies, endowed with the most diverse properties and affinities; each being destined to perform some important part in the great system of creation. Truly has it been said, that the powers of not one element could be modified without destroying at once the balance of harmonies, and involving in one ruin the economy of the world!
Although the ancient doctrine of the Four Elements has been exploded by chemistry, we must still honour the mighty sages by whom it was propounded. The doctrine is not wholly false, and were we to confine our observations, as they did, to the external properties of matter, we should be forced to acknowledge the justice of their conclusions.
In some sense the world is really made up of the four elements. Fire may be said to represent the imponderable agents—heat, light, and electricity; the remaining elements, the three physical states of ponderable matter, namely, the gaseous, liquid, and solid. The difference between our present views and those of the ancients consists in this, we regard these states as mere modes of existence, while they believed them to be distinct principles.
We must now take leave of the Four Elements, as we fear our readers are growing impatient for another story from the plenteous budget of Science.