PROPERTIES OF MATTER.
17. =Variety in the Properties of Matter.=--All matter has
properties or qualities. Some of these are different in the
different kinds of matter. Thus its three forms have different
properties, as you saw in Chapter I. There is variety also in the
properties of substances of the same class. Thus liquids are unlike
each other in some respects. Some, for example, are lighter than
others. Oil is lighter than water. Gaseous substances also differ
in this and in other respects. But the variety in the properties
of solids is greater than in those of gases or liquids. This will
appear as I proceed.
18. =Divisibility of Matter.=--Any visible portion of matter can
be divided into parts. Even if it be so small that you can see
it only with a powerful microscope, it could still be divided if
you could have an instrument sufficiently fine for the purpose.
_Divisibility_, then, is said to be a _general_ property of matter;
that is, a property belonging to all kinds of matter.
19. =Examples of Minute Division of Matter.=--There are numerous
examples in which the division of matter is carried far beyond that
which can be effected by any cutting instrument. Some of these I
will notice:
A gold-beater can hammer a grain of gold into a leaf covering a
space of fifty square inches. So thin is it that it would take
282,000 of such leaves, laid upon each other, to make the thickness
of an inch. And yet so even and perfect is this thin layer of
gold, that when it is laid upon any surface in gilding it has the
appearance of solid gold. A fifty millionth part of this grain of
gold thus hammered out can be seen by the aid of a microscope which
magnifies the diameter of an object ten times. But the division of
gold is made even more minute than this in the manufacture of the
wire of gold-lace. It is done in this way: A bar of silver weighing
180 ounces is covered with a layer of gold weighing an ounce. It is
then drawn through a series of holes in a steel plate, diminishing
in diameter, till it at length comes out a very fine wire 4000 feet
long. Each foot of it then has only the one 4000th part of the
ounce of gold, and yet the silver is well covered.
A soap-bubble is a beautiful example of the minute division of
matter. That thin wall which incloses the air which you have blown
into it is composed of particles of the soap and of the water
mingled together. It is supposed to be less than one millionth of
an inch in thickness.
The thread of the silk-worm is so minute that the finest
sewing-silk is formed of many of these threads twisted together.
But the spider spins much more finely than this. The thread by
which you see him letting himself down from any height is made up
of about 6000 threads or filaments, each coming from a separate
hole in his spinning machine. A quarter of an ounce of the thread
of a spider's web would extend 400 miles.
A grain of blue vitriol, dissolved in a gallon of water, will
make the whole blue. Such a diffusion could not be without an
exceedingly minute division of the particles.
Perhaps the most minute division of matter is exemplified in odors.
A grain of musk will scent a room for years, and yet have no
perceptible loss of weight. But all this time the air is filled
with fine particles coming from the musk.
The microscope reveals to us many wonderful examples of the
minuteness of the particles of matter, both in the vegetable and
the animal world.
If you press a common puff-ball a dust flies off like smoke.
Examined with a microscope, each particle of this dust, which is
the seed of the plant, is a perfectly round orange-colored ball.
This ball is of course made up of very many particles, arranged in
this regular form. Beautiful examples of various arrangements of
the minute particles of matter we have in the pollen of different
plants, as seen with the microscope.
Each particle of the dust which adheres to your fingers as you
catch a moth is a scale with fine lines upon it regularly arranged.
And if you look through the microscope at the wing of the moth, you
will see, where the dust is rubbed off, the attachments by which
the scales were held standing up from the surface of the wing, like
nail-heads on a roof where the shingles have been torn off.
The organization of exceedingly small animals, as revealed by the
microscope, furnishes us with wonderful examples of the minute
division of matter. A little of the dust of guano, examined through
a powerful microscope, is seen to contain multitudes of shells
of various shapes. These shells are the remains of animalcules
that lived in the water, their destiny seeming to be in part to
furnish food to other animals larger than themselves. In the chalk
formations of the earth are seen multitudes of such shells. They
have been discovered even in the glazing of a visiting-card; for
they are so small that the fine grinding up of the chalk does not
wholly destroy them. There are animals, both in the air and in the
water, so small that it would take millions of them to equal in
bulk a gram of sand, and a thousand of them could swim side by side
through the eye of a common-sized needle. Now in all these animals
there are organs, constructed of particles of matter, which are
arranged in them with as much order and symmetry as in the organs
of our bodies. How minute then must these particles be!
How do such facts extend our views of the power of the Deity! The
same power that moulded the earth, sun, moon, and the whole "host
of heaven," gave form, and life, and motion to the millions which
sport in every sunbeam; the same eye that watches the immense
heavenly bodies as they move on in their course, looks upon one and
all of these legions of animals in earth, air, and water, though
they are unseen by human eyes, seeing that every particle shall
take its right position, so that this part of creation may with all
the rest be pronounced very good; and the same bountiful hand that
dispenses the means of life and enjoyment to the millions of the
human race, forgets not to minister to the brief life and enjoyment
of each one of these myriads of animalcules, though they seem to be
almost nothingness itself.
20. =Pores and Spaces in Matter.=--In all matter there are spaces
about the particles. Those bodies which are called porous have
quite large spaces in them. But even in those which are not
commonly considered porous the particles are by no means close
together. A celebrated experiment tried in Florence a long time
ago showed that there are spaces among the particles of so dense
a substance as gold sufficiently large to let water through them.
A hollow golden globe containing water was subjected to great
pressure, and its surface was bedewed with the water that came out
through the pores of the gold. In all substances in which there are
pores visible to the naked eye, or by the aid of the microscope,
there are other spaces or interstices among the particles around
the pores. Indeed, it is supposed that there is space around every
ultimate particle or atom, and that no two of these atoms are
in actual contact. The fact that substances which have no pores
can be compressed into a smaller space than they usually occupy
shows that there are spaces or interstices in them. Solids can be
thus compressed, some more than others. But the most compressible
substances are the gases and vapors. The amount of space between
their particles must be very large to allow of so great compression.
[Illustration: Fig. 1.]
21. =Space in Gaseous Substances.=--We can have some idea of
the great amount of space in a gaseous or aeriform substance by
observing the difference between water in its liquid and in its
aeriform state. A cubic inch of water, when it becomes steam,
occupies 1696 times as much room as it did when it was water. The
difference in proportion is exhibited in Fig. 1, the inner circle
representing the water, and the outer the steam into which it is
converted. Now the water is not altered at all in its nature by
being changed into steam. The particles are simply put farther
apart by the heat, and as soon as the heat is withdrawn they
come together again to form water, or, in other words, the steam
is condensed into water. It is plain, therefore, that the space
between the particles is 1696 times as great in steam as it is in
the water from which the steam is made.
22. =Solutions.=--When any substance, as sugar or salt, is
dissolved in water, its particles are diffused through the spaces
that exist between the particles of the water. So also when water
evaporates (§ 12), the particles of water are diffused through the
spaces between the particles of the air. In like manner are the
particles from an odorous substance diffused in these spaces, and
thus mingled with the particles of the air they are carried into
the nostrils, and strike upon the minute extremities of the nerve
of smell.
23. =Relation of Heat to the Spaces of Matter.=--The variation
in the amount of space between the particles of matter in any
substance generally depends on the variation of the amount of
heat present. Thus heat expands iron; that is, it increases the
spaces between the particles of the iron. So also heat increases
the spaces between the particles of mercury, and thus makes it
occupy more room in the thermometer. This effect of heat will be
considered more fully hereafter.
The general views which I have given of the constitution of
matter will throw light upon the different qualities of different
substances, some of which I will notice.
24. =Density and Rarity.=--The density of a substance depends upon
the quantity of matter it contains in a given space. The more
dense, therefore, a substance is the greater is its weight. A piece
of lead is forty times heavier than a piece of cork of the same
size. Mercury is nearly fourteen times heavier than an equal bulk
of water. You see, then, that density must depend on the nearness
of the atoms to each other. In so dense a substance as gold the
atoms are all very close together; in wood there are spaces, some
of which are so large that you can see them; and in air, steam, and
the gases there is a great deal of space among the particles (§
21), so that we speak of their _rarity_ instead of their density.
25. =Tenacity.=--The power of holding together, termed tenacity,
depends on the degree of attraction between the particles. By
attraction I mean a disposition in particles to come together, this
disposition being manifested in opposition to any force tending
to draw them apart. I shall soon speak of this more particularly.
Tenacity does not exist at all in gaseous substances. The particles
of air and of steam, for example, show no disposition to cling
together; that is, have no tenacity. This property is weak in
liquids. It is only strong enough in water to enable its particles
to hang together in the shape of a drop. It is strong in solids,
enabling their particles not only to hold together in large
quantities, but to hold up also heavy weights suspended to them.
It is stronger in iron than in any other solid. It is stronger in
wrought iron than in cast iron; and strongest of all in steel.
26. =Comparative Tenacity of Substances.=--Various metals and other
substances have been tested in reference to their comparative
tenacity. It was done in this way: Wires were made of the metals,
all of the same size. Weights were suspended to them, and additions
were made to the weights by little and little till the wires broke.
The table underneath was made by placing against each metal the
greatest weight that its wire would hold:
Cast steel 134 pounds.
Best wrought iron 70 pounds.
Cast iron 19 pounds.
Copper 19 pounds.
Silver 11 pounds.
Gold 9 pounds.
Tin 5 pounds.
Lead 2 pounds.
Oak wood, tried in the same way, was found to hold up 12 pounds,
one more pound than silver. Some animal substances have great
tenacity, as the thread of the silk-worm, hair, wool, and the
ligaments and tendons of our bodies and of other animals.
27. =Value of Tenacious Substances.=--"The gradual discovery," says
Dr. Arnot, "of substances possessed of strong tenacity, and which
man could yet easily mould and apply to his purposes, has been of
great importance to his progress in the arts of life. The place of
the hempen cordage of European navies is still held in China by
twisted canes and strips of bamboo; and even the hempen cable of
Europe, so great an improvement on former usage, is now rapidly
giving way to the more complete and commodious security of the iron
chain--of which the material to our remote ancestors existed only
as useless stone or earth. And what a magnificent spectacle is it,
at the present day, to behold chains of tenacious iron stretched
high across a channel of the ocean, as at the Menai Strait between
Anglesea and England, and supporting an admirable bridge-road of
safety, along which crowded processions may pour, regardless of
the deep below, or of the storm; while ships there, with sails
full-spread, pursue their course unmolesting and unmolested."
28. =Hardness.=--This property seems to depend upon some peculiar
arrangement of the particles of matter. We should suppose that the
densest substances would be the hardest. But it is not so. Iron
is the hardest of the metals, but its particles are not so close
together as those of gold, which is quite a soft metal. And gold
is five times as heavy as the diamond, which is so hard as to cut
glass easily. Common flint is hard enough to scratch glass, but
will not cut it like the diamond.
[Illustration: Fig. 2.]
29. =Flexibility and Brittleness.=--If you bend a flexible body as
a piece of wood, as represented in Fig. 2, it is obvious that the
particles on the upper or convex side must be put a little farther
apart, while those on the under or concave side are brought a
little nearer together. But the wood does not break, because the
particles that are thus moved a little apart still retain their
hold upon each other. This is the explanation of what we call
flexibility. On the other hand, the particles in a rod of glass
can not be put farther apart in this way. They are not actually in
contact any more than the particles of the wood are (§ 20), but
they are in a _fixed_ relative position; that is, a position which
can not be disturbed without a _permanent_ separation of particles.
If you attempt to bend the rod there is no slight separation of
many particles, as in the bent wood, but a full and permanent
separation in some one part of the rod. We call the property on
which this result depends brittleness. Brittle substances are
generally hard. Glass, while the most brittle of all substances,
is hard enough to scratch iron. Brittle substances also have much
tenacity. A rod of glass can hold up a heavy weight, although a
slight blow suddenly given would break it.
30. =Flexible and Brittle Steel.=--There are two kinds of steel,
flexible and brittle. The steel of most cutting instruments is
brittle. The steel of a sword-blade is quite flexible, and that
of a watch-spring is so much so that we can wind it up in a coil.
This difference is owing to a difference in the mode of cooling
the steel. If it be cooled suddenly, it is brittle; if slowly,
it is flexible. The process by which it is cooled slowly is
called _annealing_. The explanation of all this is quite plain.
The steel being expanded by heat--that is, its particles being
put farther apart than they usually are--when they are suddenly
brought together again they have not time to arrange their relative
position properly. Brittleness is therefore the result. But, on the
other hand, when the cooling is effected gradually, time is given
for the arrangement.
31. =Tempering of Steel.=--Steel suddenly hardened is too brittle
for common use. A process called tempering is therefore resorted
to for diminishing the brittleness. The steel is reheated after
the hardening, and is then allowed to cool slowly. The degree in
which the brittleness is lessened depends on the degree of heat to
which the steel is subjected. It can be entirely removed by a red
heat, for then the particles have a full opportunity to readjust
themselves; and the more the heat comes short of this point the
less thorough will be the adjustment, because the less perfectly
are the particles released from their suddenly-taken position. In
lessening the brittleness we lessen hardness also, and therefore
the tempering is varied in different cases according to the degree
of hardness which is desired.
32. =Annealing of Glass.=--Glass is always annealed. If this
were not done our glass vessels and windows would be exceedingly
brittle, and would therefore be constantly breaking. Articles made
of glass are annealed by being passed very slowly indeed through
a long oven which is very hot at one end, the heat gradually
lessening toward the other end.
[Illustration: Fig. 3]
33. =Prince Rupert's Drops.=--We have a striking example of
brittleness induced by sudden cooling in what are called Prince
Rupert's drops. These are made by dropping melted green glass into
cold water, and they are of the shape represented in Fig. 3. If
you break off ever so small a bit of the point of one of these
drops, the whole will at once shiver to pieces. That is, the sudden
arrangement of the particles is so slight and unnatural that the
disturbance of the arrangement in a small part suffices to destroy
the arrangement of the whole, very much as a row of bricks falls
over from the fall of the first in the row. Mr. Farraday says that
these drops were not, as is commonly supposed, invented by Prince
Rupert, but were first brought to England by him in 1660. They
excited much curiosity at that time, and were considered "a kind of
miracle in nature." But you see that this, like many other wonders,
receives with a little thought an easy explanation.
34. =Malleability and Ductility.=--Those metals which can be
hammered into thin plates are called malleable. Gold furnishes us
with the best illustration of this property. Silver, copper, and
tin are quite malleable. Most of the other metals are very little
so, and some of them are not at all, breaking at the first blow.
A substance is said to be _ductile_ when it can be drawn out into
wire. The principal metals that have this quality are platinum,
silver, iron, copper, and gold, and in the order in which I have
named them. Melted glass is very ductile. It can be drawn out in
a very fine thread, and when this thread is cut and arranged in
branches it resembles beautiful white hair. In hammering metals
into plates, or drawing them into wire, there is a considerable
change of relative position in the particles, similar to that which
we have in fluids, though nothing like as free. In this change of
position those particles that do remain in close neighborhood have
a remarkable tenacity or attraction, preventing their separation.
In welding two pieces of iron, which is done by the blacksmith by
hammering them together when red-hot, there must be enough movement
among the particles to have those of one piece mingle somewhat with
those of the other.
35. =Compressibility.=--Porous substances can be considerably
compressed. Force applied to them can bring their particles
nearer together, making them to fill up in part their pores. The
most familiar example you have of this is in sponge. The more
porous wood is the more can it be compressed. But even such dense
substances as the metals can be compressed in some degree; that is,
the interstices between their particles can be made smaller. Medals
and coins have their figures and letters stamped upon them by
pressure, just as impressions are made upon melted sealing-wax. The
heavy and quick pressure required to do this actually compresses
the whole piece of the hard metal, putting all the particles nearer
together, so that it occupies less space than it did before it was
stamped.
36. =Incompressibility of Liquids.=--We should suppose, from the
freeness with which the particles of liquids move among each
other, and from the spaces (§ 22) which exist among them, that
these substances could be easily compressed. But it is not so. The
heaviest pressure is required to compress them even in a slight
degree. Water can be compressed so very little that practically it
is regarded as incompressible.
37. =Influence of Heat on the Bulk of Liquids.=--Although the
interstices between the particles of liquids can not be varied by
mechanical pressure, they can be by variations of temperature.
Liquids are dilated or expanded by heat; that is, their particles
are put farther apart. They are contracted or compressed by cold;
that is, their particles are brought nearer together by the
abstraction of heat. The most familiar example that we have is
in the thermometer. The mercury rises in the tube when the heat
increases the interstices between its particles; and it falls when
the loss of heat allows the particles to come near together. The
same effects are seen when alcohol is used in the thermometer,
as is done in the arctic regions, because mercury may freeze
there. A thermometer with water in it would answer if we wished
only to measure temperatures between the freezing point and the
boiling point of water. The expansive influence of heat will be
particularly treated of hereafter.
38. =Compressibility of Aeriform Substances.=--Aeriform bodies
are more compressible than any other substances, showing that in
their ordinary condition there is a great deal of space among their
particles. While they are thus unlike liquids in compressibility,
they are affected by heat in the same way that liquids are.
[Illustration: Fig. 4. Fig. 5.]
39. =Elasticity.=--Closely allied with the compressibility
of matter is its elasticity. We see this property strikingly
exemplified in India-rubber. It occasions the rebounding of a ball
of this substance when thrown down. Observe flow exactly what
occurs in this case. The ball as it meets the resistance of the
floor is flattened, as represented in Fig. 4. Then, as it assumes
the round shape, as seen in Fig. 5, it pushes downward upon the
floor. It is this sudden pushing downward that makes it rebound.
It is as if there were a compressed spring between the ball and
floor. It may be likened also to jumping. When one jumps he bends
his limbs at the thigh and knee joints, and then, in straightening
himself up, gives a sudden push, like that given by the ball as
it assumes its round shape, and so is thrown forward or upward,
according to the direction in which the pushing force is made.
The same flattening occurs in an ivory ball, though not to the
same degree. You can prove that it does occur by experiment. Let a
marble slab be wet and drop the ball upon it. Quite a spot will be
made dry by the blow of the ball, showing that it touched more of
the marble than it does when it is merely placed upon it.
40. =Elasticity Shown in Other Ways.=--If a stick be bent, as in
Fig. 2, as soon as the bending force is withdrawn the stick becomes
straight again from its elasticity. It is this elastic force of the
bow, straightening it, that speeds the arrow. Observe in this case
that while the particles on the concave side of the bent bow are
brought nearer together or compressed, those on the convex side are
moved apart. This moving apart of the particles is often shown in
India-rubber. You can see how very far apart particles that are in
near neighborhood may be carried, if you will stick two pins close
together in a strip of India-rubber before you stretch it.
41. =Degrees of Elasticity in Different Substances.=--Some
substances have so very little elasticity that they are practically
considered as having none. Lead is one of these. A rod of lead
when bent remains so, and a leaden ball does not rebound. While
aeriform substances are the most compressible of all, they are also
the most elastic. Air compressed returns to its usual condition
the moment that it is relieved from the pressure, and with a force
proportioned to the amount of the pressure. So it is with steam
and the gases. The varied results of this quality of aeriform
substances will claim our attention more particularly in some
other parts of this book.
42. =Definition of Elasticity.=--You see from the illustrations
that have been given that elasticity is _that property of matter
by which its particles, when brought nearer together or carried
farther apart by any force, return to their usual condition when
the force is withdrawn_.
43. =Usefulness of Variety in Properties of Matter.=--The
various properties of matter brought to view in this chapter are
providential adaptations to the necessities of man. Each substance
has those properties which best fit it for his use. Iron, for
example, designed by the Creator to be both the strongest and most
extensively useful servant of man among the metals, is therefore
provided in great abundance, and has those strong, decided, and
various qualities which fit it for the services it is to perform.
Gold and silver, on the other hand, designed for services less
extensive, lighter, and in a great measure ornamental, are provided
in very much less quantity, and have properties admirably adapting
them to the services for which they are so manifestly intended.
The same can be substantially said of all other substances, and
especially of those very abundant ones, air and water. And it
may be remarked also that the ingenuity of man is continually
discovering new modes of bringing the various properties of matter
into his service. I will give but a single illustration--the
tempering of steel. "This discovery," says Dr. Arnot, "is perhaps
second in importance to few discoveries which man has made; for it
has given him all the edge-tools and cutting-instruments by which
he now moulds every other substance to his wishes. A savage will
work for twelve months with fire and sharp stones to fell a great
tree and to give it the shape of a canoe, where a modern carpenter,
with his tools, could accomplish the object in a day or two."