As a general rule, all bodies, whether solid, liquid, or gaseous, are
expanded by caloric. This may be shown by experiments in each form of
matter.
Have a small iron rod made, which when cold just passes through a hole
in a plate of metal; heat it, and it will no longer pass; after a time
the rod will return to its former temperature, and then will go through
the hole as before. The rod increases in length as well as width; if
you have a gauge divided into 1/100 of an inch, and place the rod in it
when cold, noting its position, on heating it will extend to a greater
length in the gauge, returning to its former place when cool.
The effect of caloric in causing fluids to expand is actually employed
as a measure of quantity in the thermometer, the rise of the fluid
in the tube when heated depending on the increased bulk of the fluid
occasioned by the addition of caloric. The same fact is to be noticed
every day when the cook fills the kettle, and places it on the fire. As
the water becomes warmer it expands, that is, takes up more room than
it did before, and the water escapes by slow degrees, increasing as the
heat increases, up to the point of boiling, when a sudden commotion
takes place from the condensation of a portion of the water into steam.
But it is in the form of vapor or gas (which, by the bye, is not the
same thing), that the expansive force of caloric is most obvious. The
gigantic powers of the steam-engine depend entirely on the tendency of
vapor to expand on the addition of caloric; and this force of expansion
appears to have no limit; boilers made of iron plates an inch or even
more in thickness, and the buildings or ships containing them, having
been torn to pieces and scattered in all directions by the expansive
power of steam. Take a bladder and fill it about half-full of air, and
tie the neck securely; upon holding it to the fire it will swell out
and become quite tense from the expansion of the contained air.
The principal source of caloric is the sun, whose beams, diffused
through all nature by the refractive property of the atmosphere,
are the source of vitality both to vegetables and animals, and when
concentrated by a large convex lens, produce the most intense heat,
sufficient to light a piece of diamond, and melt platinum. Caloric
is also produced or evolved by combustion, by friction, percussion,
chemical combination, electricity, and galvanism.
The evolution of heat by friction may be witnessed daily in a
thousand instances. Lucifer matches are lighted by rubbing the highly
inflammable substances with which they are tipped against a piece of
sand-paper. Nearly all savage people procure fire by rubbing a piece
of hard wood violently against a softer piece. The axle-trees of
steam-engines, and even of carriages, have been known to be so heated
by friction as to endanger burning the carriage; and it is very usual
to be obliged to pour a quantity of cold water on the iron axle of the
carriages of an express train after an hour of constant and rapid work.
If you merely rub the blade of a knife rapidly on a piece of wood it
will become hot enough to burn your hand.
Percussion is merely a more energetic kind of friction, and is often
resorted to by the blacksmith to light his furnace. He places a nail or
other piece of soft iron on his anvil, and beats it rapidly with the
hammer, when it becomes actually red hot. The production of sparks by
striking flint against steel, or two pieces of flint one against the
other, are familiar instances of heat produced by percussion.
One of the most powerful means of producing heat is the process of
combustion.
Combustion, as the word imports, is the _burning together_ of two or
more substances, a chemical union of oxygen generally with carbon
and hydrogen in some shape or other. In our ordinary fires we burn
coal, a hydro-carbon as it is called; and the gas which is now so
universally used for the purpose of illumination, is a compound of the
same bodies--so wax, tallow, oil of various kinds, both of animal and
vegetable origin, are all hydro-carbons.
On the application of a sufficient heat, and a free access of
atmospheric air, or of some other gas containing oxygen in a certain
state of combination, these bodies take fire, and continue to burn
either with flame, or a red or even white heat without flame,
until they are consumed; that is, until they have entered into new
combinations with the oxygen, and are converted into carbonic acid and
water, the carbon forming the first product, the hydrogen the other.
The following experiment shows the productions of heat by chemical
action alone. Bruise some fresh prepared crystals of nitrate of copper,
spread them over a piece of tin foil, sprinkle them with a little
water; then fold up the foil tightly as rapidly as possible, and in a
minute or two it will become red-hot, the tin apparently burning away.
The heat is produced by the energetic action of the tin on the nitrate
of copper, taking away its oxygen in order to unite with the nitrate
acid, for which, as well as for the oxygen, the tin has a much greater
affinity than the copper has.
Combustion without flame may be shown in a very elegant and agreeable
manner, by making a coil of platinum wire by twisting it round the stem
of a tobacco-pipe, or any cylindrical body, for a dozen times or so,
leaving about an inch straight, which should be inserted into the wick
of a spirit-lamp; light the lamp, and after it has burnt for a minute
or two extinguish the flame quickly; the wire will soon become red-hot,
and, if kept from draughts of air, will continue to burn until all the
spirit is consumed. Spongy platinum, as it is called, answers rather
better than wire, and has been employed in the formation of fumigators
for the drawing-room, in which, instead of pure spirits, some perfume,
such as lavender water, is used; by its combustion an agreeable odor is
diffused through the apartment. These little lamps were much in vogue a
few years ago, but are now nearly out of fashion.
Experiments on combustion might be multiplied almost to any amount, but
the above will be sufficient for the present. When we come to treat of
the properties of the gases and some other substances, we shall have
occasion to recur to this subject.
The production of caloric by chemical combination may be exhibited by
mixing carefully one part of oil of vitriol with two of water, when
sufficient heat will be produced to boil some water in a thin and
narrow tube, which may be used as a rod to stir the mixture.
The production of heat by electric and galvanic agency belongs to
another subject.