THE PROPERTIES OF MATTER—IMPENETRABILITY.
In the present state of our knowledge it seems to be universally agreed, that we cannot properly commence even popular discussions on astronomy, mechanics, and chemistry, or on the imponderables, heat, light, electricity, and magnetism, without a definition of the general term "matter;" which is an expression applied by philosophers to every species of substance capable of occupying space, and, therefore, to everything which can be seen and felt.
The sun, the moon, the earth, and other planets, rocks, earths, metals, glass, wool, oils, water, alcohol, air, steam, and hosts of things, both great and small, all solids, liquids and gases, are included under the comprehensive term matter. Such a numerous and varied collection of bodies must necessarily have certain qualities, peculiarities, or properties; and hence we come in the first place to consider "The general powers or properties of matter." Thus, if we place a block of wood or stone in any position, we cannot take another substance and put it in the space filled by the wood or stone, until the latter be removed. Now this is one of the first and most simple of the properties of matter, and is called impenetrability, being the property possessed by all solid, liquid, and gaseous bodies, of filling a space to the exclusion of others until they be removed, and it admits of many amusing illustrations, both as regards the proof and modification of the property.
Thus, a block of wood fills a certain space: how is it (if impenetrable) that we can drive a nail into it? A few experiments will enable us to answer this question.
Into a glass (as depicted at fig. 1) filled with spirits of wine, a quantity of cotton wool many times the bulk of the alcohol may (if the experiment is carefully performed) be pushed without causing a drop to overflow the sides of the vessel.
Fig. 1.
Here we seem to have a direct contradiction of the simple and indisputable truth, that "two things cannot occupy the same space at once." But let us proceed with our experiments:—
We have now a flask full of water, and taking some very finely-powdered sugar, it is easy to introduce a notable quantity of that substance without increasing the bulk of the water; the only precaution necessary, is not to allow the sugar to fall into the flask in a mass, but to drop it in grain by grain, and very slowly, allowing time for the air-bubbles (which will cling to the particles of sugar) to pass off, and for the sugar to dissolve. Matter, in the experiments adduced, appears to be penetrable, and the property of impenetrability seems only to be a creation of fancy: reason, however, enables us to say that the latter is not the case.
Fig. 2.
A nail may certainly be hammered into wood, but the particles are thrust aside to allow it to enter. Cotton wool may be placed in spirits of wine because it is simply greatly extended and bulky matter, which, if compressed, might only occupy the space of the kernel of a nut, and if this were dropped into a half-pint measure full of alcohol, the increase of bulk would not cause the spirit to overflow. The cotton-wool experiment is therefore no contradiction of impenetrability. The experiment with the sugar is the most troublesome opponent to our term, and obliges us to amend and qualify the original definition, and say, that the ultimate or smallest particles or atoms of bodies only are impenetrable; and we may believe they are not in close contact with each other, because certain bulks of sugar and water occupy more space separately than when mixed.
Fig. 3.
If we compare the flask of water to a flask full of marbles, and the sugar to some rape-seed, it will be evident that we may almost pour another flask full of the latter amongst the marbles, because they are not in close contact with each other, but have spaces between them; and after pouring in the rape-seed, we might still find room for some fine sand.
The particles of one body may thus enter into the spaces left between those of another without increasing its volume; and hence, as has been before stated, "The atoms only of bodies are truly impenetrable."
This spreading, as it were, of matter through matter assumes a very important function when we come to examine the constitution of the air we breathe, which is chiefly a mechanical mixture of gases: seventy-nine parts by volume or measure of nitrogen gas, twenty-one parts of oxygen gas, and four parts of carbonic acid vapour in every ten thousand parts of air having the following relations as to weight:—
| Specific gravity. | |
| Nitrogen | 972 |
| Oxygen | 1105 |
| Carbonic acid | 1524 |
It might be expected that these gases would arrange themselves in our atmosphere in the above order, and if that were the case, we should have the carbonic-acid gas (a most poisonous one) at the bottom, and touching the earth, then the oxygen, and, last of all, the nitrogen; a state of things in which organized life could not exist. The gases do not, however, separate: indeed, they seem to act as it were like vacuums to one another, and "the diffusion of gases" has become a recognised fact, governed by fixed laws. This fact is curiously illustrated, as shown in our cut, by filling a bottle with carbonic acid, and another with hydrogen; and having previously fitted corks to the bottles, perforated so as to admit a tube, place the bottle containing the carbonic acid on the table, then take the other full of hydrogen, keeping the mouth downwards, and fit in the cork and tube: place this finally into the cork of the carbonic-acid bottle, which may be a little larger than the other, in order to make the arrangement stand firmer; and after leaving them for an hour or so, the carbonic acid, which is twenty-two times heavier than the hydrogen, will ascend to the latter, whilst the hydrogen will descend to the carbonic acid. The presence of the carbonic acid in the hydrogen bottle is easily proved by pouring in a wine-glassful of clear lime-water, which speedily becomes milky, owing to the production of carbonate of lime; whilst the proof of the hydrogen being present in the carbonic acid is established by absorbing the latter with a little cream of lime—i.e., slacked lime mixed to the consistence of cream with some water—and setting fire to the hydrogen that remains, which burns quietly with a yellowish flame if unmixed with air; but if air be admitted to the bottle, the mixture of air and hydrogen inflames rapidly, and with some noise.
Fig. 4.
One of the most elegant modes of showing the diffusion of gases is by taking a large round dry porous cell, such as would be employed in a voltaic battery, and having cemented a brass cap with a glass tube attached to its open extremity, it may then be supported by a small tripod of iron wire, and the end of the glass tube placed in a tumbler containing a small quantity of water coloured blue with sulphate of indigo. If a tolerably large jar containing hydrogen is now placed over the porous cell, bubbles of gas make their escape at the end of the tube, because the hydrogen diffuses itself more rapidly into the porous cell than the air which it already contains passes out. When the jar is removed, the reverse occurs, hydrogen diffuses out of the porous cell, and the blue liquid rises in the tube.
This diffusive force prevents the accumulation of the various noxious gases on the earth, and spreads them rapidly through the great bulk of the atmosphere surrounding the globe.
Fig. 5.
a. The porous cell. b. The jar of hydrogen. c. The brass cap and glass tube d, the end of which dips into the tumbler containing the solution of indigo e. f f. The wire and stand supporting the porous cell and tube in tumbler.
Although air and other gases are invisible, they possess the property of impenetrability, as may be easily proved by various experiments. Having opened a pair of common bellows, stop up the nozzle securely, and it is then impossible to shut them; or, fill a bladder with air by blowing into it, and tie a string fast round the neck; you then find that you cannot, without breaking the bladder, press the sides together.
It is customary to say that a vessel is empty when we have poured out the water which it contained. Having provided two glass vessels full of water, place each of them in an empty white pan, to receive the overflow, then lay an orange upon the surface of the water of one of them, and being provided with a cylindrical glass, open at one end, with a hole in the centre of the closed end, place your finger firmly over the orifice, and endeavour, by inverting the glass over the orange, and pressing upon the surface of the water, to make it enter the interior of the glass cylinder; the resistance of the air will now cause the water to overflow into the white pan, whilst the orange will not enter. The orange may now be transferred to the other vessel of water, and on removing the finger from the orifice of the cylindrical glass, and inverting it as before over the orange, the air will rush out and the orange and water will enter, whilst there will be no overflow as in the preceding experiment. The comparison of the two is very striking, and at once teaches the fact desired.
| Fig. 6 represents the water overflowing, as the glass, with the orifice closed, is pressed down, proving the impenetrability of air. | Fig. 7. The orange has entered the glass vessel, and the air having passed from the orifice, no water overflows. |
Whilst the vessels of water are still in use, another pretty experiment may be made with the metal potassium. First throw a small piece of the metal on the surface of the water, to show that it takes fire on contact with that fluid; then, having provided a gas-jar, fitted with a cap and stop-cock, and a little spoon screwed into the bottom of the stop-cock inside the gas-jar, place another piece of potassium in the little spoon, and, after closing the stop-cock, push the jar into one of the vessels of water: as before, the impenetrability of the air prevents the water flowing up to the potassium; but, on opening the stop-cock, the air escapes, the water rushes up, and directly it touches the potassium, combustion ensues.
| Fig. 8. Gas-jar with stop-cock closed, and potassium in ladle; air prevents the entrance of the water. | Fig. 9. Gas-jar; stop-cock open; the air passes, the water enters, and the potassium is inflamed. |
Having sufficiently indicated the nature and meaning of impenetrability, we may proceed to discuss experimentally three other marked and special qualities of matter—viz., inertia, gravity, and weight.
INERTIA, OR PASSIVENESS.
Inertia is a power which (according to Sir Isaac Newton) is implanted in all matter of resisting any change from a state of rest. It is sometimes called vis inertiæ, and is that property possessed by all matter, of remaining at rest till set in motion, and vice versâ; and it expresses, in brief terms, resistance to motion or rest.
A pendulum clock wound up and ready to go, does not commence its movements, until the inertia of the pendulum is overcome, and motion imparted to it. On the other hand, when seated in a carriage, should any obstruction cause the horse to stop suddenly, it is only perhaps by a violent effort, if at all, that we can resist the onward movement of our bodies. To illustrate inertia, construct a metal tray, about three feet long, two feet wide, and two inches deep, with a glass bottom, and arrange it on a framework supported by legs, like a table, and having filled it with water, let the room be darkened, and then place under the tank a lighted candle, at a sufficient distance from the glass to prevent the heat cracking it. If a piece of calico or paper, stretched on a framework, be now held over the water at an angle of about thirty degrees, all that occurs on the surface of the water will be rendered visible on such screen. Attention may now be directed to the quiescence, or the inertia of the water, while the opposite condition of movement and formation of the waves may be beautifully shown by touching the surface of the water with the finger; the miniature waves being depicted on the screen, and continuing their motion till set at rest by striking against the sides of the tin tray.
Fig. 10.
Tin tray, with glass bottom, full of water; candle placed underneath.
Fig. 11.
Fig. 11. Same tray, with calico screen; showing the waves as they are produced by touching the surface of the water with the finger.
Should the above experiment be thought too troublesome or expensive to prepare, inertia may be demonstrated by filling a tea-cup or other convenient vessel with water, and after moving rapidly with it in any direction, if we stop suddenly, the rigidity of all parts of the cup we hold brings them simultaneously to a state of rest; but the mobility of the liquid particles allows of their continuing in motion in their original direction, and the liquid is spilled. Thus, carelessness in handing and spilling a cup of tea (though not to be recommended) serves to illustrate an important principle. The inertia of bodies in motion is further and lamentably illustrated by the accidents caused from the sudden stoppage of a railway train whilst in rapid motion, when heads and knees come in contact with frightful results.—It is more especially demonstrated by the earth, the moon, and the other planets continuing their motion for ever in the absence of any friction or resistance to oppose their onward progress. It is the friction arising from the roughness of the ground, the resistance of the air, and the force of the earth's attraction, which puts a stop to bodies set in motion about the surface of the earth.
GRAVITATION.
Inertia represents a passive force, gravitation, an active condition of matter; and this latter may truly be termed a force of attraction, because it acts between masses at sensible or insensible distances: it is illustrated by a stone, unsupported, falling to the ground; by the stone pressing with force on the earth, and requiring power to raise it from the ground: indeed, it is commonly reported that it was by an accident—"an apple falling from a tree"—that the great Newton was led to reflect on the universal law of gravitation, and to pronounce upon it in the following memorable words:—
"Every particle of matter in the universe attracts every other particle of matter with a force or power directly proportional to the quantity of matter in each, and decreasing as the squares of the distances which separate the particles increase."
These words may appear very obscure to our juvenile readers; but when dissected and examined properly, they clearly define the property of gravitation. For instance, "every particle attracts every other with a force proportional to the quantity of matter in each." This statement was verified some years back by Maskelyne, who, having sought out and discovered a steep, precipitous rock in the Schichallion mountains, in Scotland, suspended from it a metal weight by a cord, and going to a convenient distance with a telescope, and observing the weight, he found that it did not hang perpendicularly, like an ordinary plumb line, but was attracted, or impelled, to the sides of the rock by some kind of attraction, which, of course, could be no other than that indicated by Newton as the attraction of gravitation.
Fig. 12.
The Schichallion Rocks. The dotted line and weight a represent the ordinary position of a plumb line, whilst the line of the weight b indicates (of course, with some exaggeration) the attractive power of the mass of the rock drawing it from the perpendicular.
This truly wonderful power of attraction pervades all masses; and being, as before stated, proportional to the quantity of matter, if a man could be transported to the surface of the sun, he would become about thirty times heavier: he would be attracted, or impelled, to the sun with thirty times more gravitating force than on the surface of the earth, and would weigh about two tons. Of course, nursing a baby on the sun's surface would be a very serious affair with our ordinary strength; whilst on some of the smaller planets, such as Ceres and Pallas, we should probably gravitate with a force of a few pounds only, and with the same muscular power now possessed, we should quite emulate the exploits of those domestic little creatures sometimes called "the industrious fleas," and our jumping would be something marvellous.
There is no very good lecture-table experiment that will illustrate gravitation, although attention may be directed to the fact of a piece of potassium thrown on the surface of water in a plate generally rushing to the sides, and, as if attracted, attaching itself with great force to the substance of the pottery or porcelain; or, if a model ship, or lump of wood, be allowed to float at rest in a large tank of water, and a number of light chips of wood or bits of straw be thrown in, they generally collect and remain around the larger floating mass.
A very good idea, however, may be afforded of the universal action of gravity maintaining all things in their natural position on the earth by taking a hoop and arranging in and upon it balls, or a model ship, or other toy, and wires, as depicted in our diagram.
Fig. 13.
a. The centre ball, representing the earth's centre of gravity. w w w w. Four wires fixed into centre ball, and passing through and secured in the hoop, projecting about one foot from the circumference. b b b b. Two balls—a model ship and toy—working on the wires like beads, with vulcanized India-rubber straps attached to them and the circumference of the hoop.
With this simple apparatus we may illustrate the upward, downward, and sideway movement of bodies from the earth, and the counteraction by the force of gravitation of any tendency of matter to fall away from the globe, which is represented in the model by the india-rubber springs pulling the balls and toys back again to the circumference of the hoop.
The attraction of gravitation decreases (quoting the remainder of Newton's definition) as the squares of the distances which separate the particles increase—i.e., it obeys the principle called "inverse proportion"—viz., the greater the distance, the less gravitating power; the less the distance, the greater the power of gravitation. Gravitation is like the distribution of light and other radiant forces, and may be thus illustrated.
Fig. 14.
Place a lighted candle, marked a, at a certain distance from No. 1, a board one foot square; at double the distance the latter will shadow another board, No. 2, four feet square; at three times, No. 3, nine feet square; at four, No. 4, sixteen feet; and so on.
To make the comparison between the propagation of light and the attraction of gravitation, we have only to imagine the candle, a, to represent the point where the force of gravity exists in the highest degree of intensity; suppose it to be the sun—the great centre of this power in our planetary system. A body, as at No. 1, at any given distance will be attracted (like iron-filings to a magnet) with a certain force; at twice the distance, the square of two being four, and by inverse proportion, the attraction will be four times less; at thrice the distance, nine times less; at the fourth distance, sixteen times less; and so on. With the assistance of this law, we may calculate, roughly, the depth of a well, or a precipice, or a column, by ascertaining the time occupied in the fall of a stone or other heavy substance. A falling body descends about 16 feet in one second, 64 feet in two seconds, 144 feet in three seconds, 256 feet in four seconds, 400 feet in five seconds, 576 feet in six seconds; the spaces passed over being as the squares of the times.
Suppose a stone takes three seconds in falling to the surface of the water in a well, then 3 × 3 = 9 × 16 = 144 feet would be a rough estimate of the depth. The calculation will exceed the truth in consequence of the stone being retarded in its passage by the resistance of the air.
All bodies gravitate equally to the earth: for instance, if an open box, say one foot in length, two inches broad, and two inches deep, be provided with a nicely-fitted bottom, attached by a hinge, a number of substances, such as wood, cork, marble, iron, lead, copper, may be arranged in a row; and directly the hand is withdrawn, the moveable flap flies open, and if the manipulation with the disengagement of the trap-door is good, the whole of the substances are seen to proceed to the earth in a straight line, as shown in our drawing.
Fig. 15.
Fig. 16.
If a heavy substance, like gold, be greatly extended by hammering and beating into thin leaves, and then dropped from the hand, the resistance of the air becomes very apparent; and a gold coin and a piece of gold-leaf would not reach the earth at the same time if allowed to fall from any given height. This fact is easily displayed by the assistance of a long glass cylindrical vessel placed on the air-pump, with suitable apparatus arranged with little stages to carry the different substances; upon two of them may be placed a feather and a gold coin, and on the third, another gold coin and a piece of gold-leaf.
Fig. 17.
In arranging the experiment, great care ought to be taken that the little stages are all nicely cleaned, and free from any oil, grease, or other matter which might cause the feathers or the gold-leaf to cling to the stages when they are disengaged, by moving the brass stop round that works in the collar of leathers. Sometimes these leathers are oiled, and in that case, when the vacuum is made, the oil, by the pressure, is squeezed out, and, passing down, may reach the stages and spoil the experiment, by causing the feathers and gold-leaf to stick to the brass, producing great disappointment, as the illustration, usually called the "guinea and feather glass experiment" takes some time to prepare. The air-pump being in good order, the long glass is first greased on the lower welt or edge, and then placed firmly on the air-pump plate. The top edge, or welt, may now be greased, and the gold coins, feathers, and gold-leaf arranged in the drop-apparatus; this is carefully placed on the top of the glass, and firmly squeezed down. The author has always found a tallow candle, rolled in a sheet of paper (so as to leave about half the candle exposed), the best grease to smear the glass with for air-pump experiments; if the weather is cold, the candle may be placed for a few minutes before an ordinary fire to soften the tallow. Pomatum answers perfectly well when the surfaces of glass and brass are all nicely ground; but as air-pumps and glasses by use get scratched and rubbed, the tallow seems to fill up better all ordinary channels by which air may enter to spoil a vacuum.
Fig. 18.
The apparatus being now arranged, the air is pumped out; and here, again, care must be taken not to shake the gold off the stages. When a proper vacuum has been obtained, which will be shown by the pump-gauge, the stop is withdrawn from one of the stages, and the gold and feather are seen to fall simultaneously to the air-pump plate. Another stage, with the gold-leaf and coin, may now be detached; both showing distinctly, that when the resistance of the air is withdrawn, all bodies, whether called light or heavy, gravitate equally to the earth. Then, the screw at the bottom of the pump barrels being opened, attention may be directed to the whizzing noise the air makes on entering the vacuum, and when the air is once more restored to the long glass vessel, the last stage may be allowed to fall; and now, the gold coin reaches the pump-plate first, and the feather, lingering behind, loses (as it were) the race, and touches the plate after the gold coin; thus demonstrating clearly the resistance of the air to falling bodies.
Another, and perhaps less troublesome, mode of showing the same fact, is to use a long glass tube closed at each end with brass caps cemented on. One cap should have the largest possible aperture closed by a brass screw, and the other may fit a small hand-pump.
Fig. 19.
a b. Glass tube containing a piece of gold and a feather, which are placed in at the large aperture a. c. Small hand-pump.
If a piece of gold and a small feather are placed in the tube, it may be shown that the former reaches the bottom of the tube first, whilst it is full of air, and when the air is withdrawn by means of the pump, and the tube again inverted, both the gold and the feather fall in the same time.
For this reason, all attempts to measure heights or depths by observing the time occupied by a falling body in reaching the earth must be incorrect, and can only be rough approximations. An experiment tried at St. Paul's Cathedral, with a stone, which was allowed to fall from the cupola, indicated the time occupied in the descent to be four and a half seconds: now, if we square this time, and multiply by 16, a height of 324 feet is denoted; whereas the actual height is only 272 feet, and the difference of 52 feet shows how the stone was retarded in its passage through the air; for, had there been no obstacle, it would have reached the ground in 4-3/20ths seconds.
Fig. 20.
The force of gravitation is further demonstrated by the action of the sun and moon raising the waters of the ocean, and producing the tides; and also by the earth and moon, and other planets and satellites, being prevented from flying from their natural paths or orbits around the sun. It is also very clearly proved that there must be some kind of attractive force resident in the earth, or else all moveable things, the water, the air, the living and dead matters, would fly away from the surface of the earth in obedience to what is called "centrifugal force." Our earth is twenty-four hours in performing one rotation on its axis, which is an imaginary line drawn from pole to pole, and represented by the wire round which we cause a sphere to rotate. All objects, therefore, on the earth are moving with the planet at an enormous velocity; and this movement is called the earth's diurnal, or daily rotation. Now, it will be remembered, that mud or other fluid matter flies off, and is not retained by the circumference of a wheel in motion: when a mop is trundled, or a dog or sheep, after exposure to rain, shake themselves, the water is thrown off by what is called centrifugal force (centrum, a centre, fugio, to fly from).