The fairy tales of science/A Little Bit
A Little Bit.
"Many a little, makes a mickle."—Old Proverb
In the foregoing pages we have assumed that all things are made up of very little bits, called atoms. This view of the nature of matter is purely conjectural, but it agrees so well with the truths revealed by Science, that we must admit it to be highly probable. Let us descend for a while from the realms of imagination, and lay before our reader the facts upon which the beautiful theory of atoms is based.
The word "atom" is derived from the Greek language, and signifies "that which cannot be cut,"—a very appropriate term, for an atom being the smallest possible particle of a substance, must necessarily be indivisible. The existence of half an atom is inadmissible, because the mind cannot form an idea of a particle smaller than the smallest.
Philosophers are divided in their opinions respecting the nature of the ultimate particles of matter: some maintain that they are hard and solid, and therefore of a definite size and weight, though so minute as to defy all our optical instruments to enable us to perceive them; others hold them to be mere points or centres of force, destitute of solidity and magnitude. What is an atom? This is a problem which the human mind can never solve, it can only throw out shrewd guesses at the truth. We will, however, take it for granted that the ultimate particles of matter are indivisible and indestructible, without wasting our time on metaphysical subtleties.
Though we can form no conception of the absolute size of atoms, the wonderful divisibility of matter furnishes many proofs of their extreme minuteness. The gold-beater hammers out a single grain of the precious metal until it covers forty-nine square inches. Now, each square inch of this gold leaf may readily be cut into a hundred strips, and each strip into a hundred pieces, each of which is distinctly visible to the unaided eye. A single grain of gold may thus be subdivided into 490,000 visible parts. But this is not all; if attached to a slip of glass the leaf may be subdivided still further, as ten thousand lines may then be ruled in the space of a square inch, and in this manner the entire leaf, weighing but a grain, may be cut into 4,900,000,000 fragments, each visible by means of the microscope. As we require no less than ten figures to express the number of parts into which a grain of matter may be subdivided by mechanical means, and as each of these parts must contain a vast number of particles, we see that an atom must be a very little bit indeed! But gold furnishes a still more remarkable instance of the extension of matter. The gilt wire used in embroidery is formed by extending gold over the surface of silver. A very little gold is made to go a very long way, for each grain is spread over a surface of nearly ten thousand square inches.
In the animal and vegetable kingdoms we meet with some surprising instances of the divisibility of matter. The microscope reveals the existence of animals so wonderfully minute that it takes a hundred millions of them to weigh a grain, yet each creature is possessed of distinct organs, and must be composed of innumerable atoms.
The spores of the lycoperdon or puff-ball are found to be little orange-coloured globes, and although each spore is capable of becoming a living plant, no less than 125,000 of them would be requisite to form a single globe of the diameter of a human hair.
The sense of smell enables us to perceive particles of whose magnitude we can form no adequate conception. Odour is simply the disengagement of the volatile particles of a substance, yet a single grain of musk has been known to perfume a large room for the space of twenty years!
We may rest assured, then, that the atoms of matter are exceedingly minute, though their actual size can never be determined by our powers of perception. Let us now consider the aggregation of these little bits into masses.
The force which holds the atoms together is called cohesion; it is greater in solids than in liquids, while in aëriform bodies it seems to be altogether absent.
We have every reason to believe that the ultimate particles of a body are never in actual contact, but are placed at a certain distance from each other, so that there exists around every individual particle a space void of matter. All bodies are more or less compressible, and unless we acknowledge the existence of these empty spaces we must suppose that two or more particles are capable of occupying the same place at the same time: a supposition which is opposed to the notion of an atom having a definite size.
A volume of air can be compressed into a space a thousand times smaller than that which it originally occupied, and we must therefore conclude that the atoms of air are separated by wide intervals. Solids and liquids must also have interstices or pores between their particles, as they invariably expand when heated and contract when exposed to a low temperature.
The porosity of gold was demonstrated some two hundred years ago by the famous Florentine experiment. A hollow ball of the precious metal, filled with water, was submitted to a great pressure, by which the fluid was made to ooze through its pores and bedew its outer surface.
The distance between the particles of matter is greater in liquids than in solids, and greatest in gases and vapours. It is highly probable that all bodies, even the densest metals, contain more space than matter—in other words, that the atoms are much smaller than the spaces which separate them. Some of our greatest philosophers have held the atoms of matter to be immeasurably small, compared with their surrounding spaces.
Newton thought that the whole material world might be compressed into the space of a single cubic inch, provided that its particles could be brought into actual contact.
Sir John Herschel compares a ray of light penetrating glass, to a bird threading the mazes of a forest; and says that there is no absurdity in imagining the atoms of a solid to be as thinly distributed through the space it occupies as the stars that compose a nebula.
We need scarcely say that these hidden truths do not fall within the sphere of scientific inquiry, but can only be subjects for the exercise of speculation. All our instruments are far too clumsy to help us to a knowledge of atomic magnitudes; the compasses that can measure the interval that separates particle from particle, and the scale that will turn with the weight of an atom, do not belong to man, though the imagination may picture such delicate contrivances in the laboratory of a scientific fairy.
These considerations lead us to a subject about which we do know something, namely, the relative weights of the ultimate particles or atoms of bodies.
Chemistry has revealed the existence of some sixty-three elementary bodies, or, according to the atomic theory, sixty-three different kinds of atoms. Now, although we cannot ascertain the actual weight of a single atom, we have good grounds for believing that an atom of oxygen is heavier than an atom of carbon and lighter than one of sulphur. Before we enter into this subject, we have a few words about the great man who revived the ancient theory of atoms, and made use of it to explain the mysterious laws of chemical combination.
John Dalton was born in Westmoreland, in the latter portion of the last century, and belonged to the sect of Quakers. When very young he resided with Mr. Gough, of Kendal, a blind philosopher, to whom he read, and whom he assisted in his scientific investigations. It was here that he acquired a considerable part of his education, particularly his taste for mathematics. From Kendal, Dalton went to Manchester, and commenced teaching elementary mathematics to young men. In this way, together with a few courses of chemical lectures which he occasionally delivered, he contrived to support himself during a long and useful life. His slender income was always equal to his wants, and in his contempt for riches he resembled the sages of antiquity.
His kind heart and powerful mind gained him many friends and admirers, and in course of time he came to be regarded as a great philosopher, though he still continued to earn his bread as a tutor. Such was the founder of the beautiful atomic theory of Chemistry, which is so well adapted to render certain natural laws intelligible to our understanding.
In examining the so-called four elements, we alluded to the fact that bodies united to form compounds in definite proportions. Let us explain this matter more fully. Water invariably contains oxygen and hydrogen, in the proportion of eight parts by weight of the former element to one part of the latter, whether these parts represent tons, pounds, grains, or any other quantities. The whole of the oxygen contained in the ocean is exactly eight times heavier than the hydrogen with which it is combined, and the weights of the two gases bear the same relation to each other in the dew-drop. If we take any other chemical compound, we shall find that the proportions by weight of its constituents are invariable; thus there is a broad distinction between such a compound and a mere mixture in which the ingredients are present in indefinite proportions.
Water is not the only compound that can be formed of oxygen and hydrogen. We can compel one part of hydrogen to combine with sixteen parts of oxygen, and the result of their union is a colourless liquid, less volatile than water, and having a metallic taste. This liquid, called peroxide of hydrogen, and water, are the only compounds that can be formed of the two gases. This fact is well worthy of consideration. Hydrogen will combine with eight or with sixteen parts of oxygen, but in no other proportions. Let us now glance at some other compounds. The poisonous gas known as carbonic oxide, contains six parts of carbon and eight of oxygen; but six parts of carbon also combine with sixteen of oxygen to form carbonic acid. Again, in ordinary coal-gas we find one part by weight of hydrogen united to six of carbon.
How can we account for these recurrent numbers? What relation subsists between the number 8 or its multiple 16, and oxygen; between 1 and hydrogen; between 6 and carbon? Why should these three bodies combine in fixed numerical proportions?
According to the beautiful atomic theory of Dalton, these numbers express the relative weights of the ultimate particles of matter. Let us consider the composition of water in this light. The smallest possible particle of water is composed of one atom of hydrogen gas and one atom of oxygen, the latter being eight times heavier than the former. Now, it is evident that whatever may be the number of particles in a given volume of water, the relative weights of the two gases will remain constant. The smallest particle of the peroxide of hydrogen contains one atom of hydrogen and two atoms of oxygen; accordingly, there can be no compound of hydrogen and oxygen between water and the peroxide, unless we admit the existence of half-atoms. We have only spoken of three of the elementary bodies, as we wished our remarks to be as simple as possible; each of the sixty-three elements has, however, a definite combining proportion or atomic weight.
How admirably this atomic theory explains the laws of chemical combination; how intelligible it renders those fixed, invariable weights in which the elements unite to form compounds. All is shown to depend on the properties with which those inconceivably small particles of matter are invested.
We have told the reader all we know about atoms (at least all we think we know, for we can never be certain that atoms exist). They are immeasurably minute; they are separated from each other by wide intervals, and they have a definite weight.
A German chemist has endeavoured to render the atomic theory intelligible by a very ingenious illustration. He compares atoms to the heavenly bodies, which, in comparison with the extent of the space in which they are suspended, are infinitely small: that is, are atoms. Innumerable suns, with their planets and attendant satellites, move in infinite space, at definite and measured distances from each other. They are individually indivisible, inasmuch as there exists no force capable of separating them into parts, tearing off from them anything material, or altering their size or form in such a degree as to be perceptible, or to impair or disturb their relations to the other heavenly bodies. In this sense the whole universe coalesces into one immense body, the atoms of which—that is, suns, planets, and satellites—are indivisible and unchangeable!
There are many things in nature which the human mind will never be able to comprehend; and foremost among them we must place our Little Bit.