G. P. (George Payn) Quackenbos.

A natural philosphy: embracing the most recent discoveries in the various branches of physics .. online

. (page 18 of 42)
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mosphere being removed from its surface, the water soon boils; but it comes
to rest the moment that air is readmitted. For the same reason, water boils
at a lower temperature on the top of a mountain than at its base, as has often
been observed by travellers.

44 If beer is placed under a receiver and the air exhausted, it begins to
foam. This is owing to the elasticity of the carbonic acid in the liquid, rush-
ing out to till the vacuum. If the air is readmitted, the beer resumes its
usual appearance.

443. A shrivelled apple in an exhausted receiver is puffed out to its full
size by the expansion of the air within.

444. If a vessel of water containing a piece of wood, a vegetable, oral-
most any solid substance, is placed under a receiver, and the air is exhaust-
ed, minute globules of air can be seen forming on the surface of the solid,
and sometimes even bubbling up through the water. This proves the poros-
ity of solids and the presence of air in their pores.

445. A lighted candle in an exhausted receiver is extinguished, and the
smoke falls because it is heavier than the rarefied air. If a mouse, rabbit, or
other living creature, is placed under a receiver and the air is drawn off, it
immediately shows signs of distress, and soon dies.

446. These experiments show that air is everywhere
present, and is essential to life and combustion. In a vac-
uum, animals die, vegetation ceases, and sound can not be
produced.

TIae Condenser.

447. The Condenser (Fig. 200) is an instrument used
for forcing a large quantity of air into a given vessel.

Like the single-barrelled air-pump, the condenser con-
sists of a cylinder, A, with a valve at its base, V, and a pis-
ton, P, which also contains a valve, tightly fitted to it.



ing apparatus, and the experiment with it. 441. At what temperature does boiling
commence in a vacuum, compared with that at which it commences in the air?
How is this shown ? What is said of the boiling of water on the top of a mountain ?
442. What phenomenon is presented when beer is placed under a receiver and the air
exhausted.' 4t5. When a shrivellel apple is so placed? 444 How is the presence
of air in the pores of solids proved with the air-pump? 445. How is it shown with
the air-pump that air is necessary to combustion and animal life ? 447. What is the



THE CONDENSER.



185




Instead of opening upward, however, as in the Fi ?- 20 -
air-pump, these valves open downward.

448. Operation. The condenser having been
screwed to any strong vessel in which it is desired
to condense air, the handle is worked np and
down. A vacuum being produced below the pis-
ton, as it ascends, its valve is opened and air
rushes in ; while the valve in the cylinder is closed
by the pressure of the air in the vessel. When
the piston descends, its valve is closed by the
pressure of the air in the cylinder, while the other
valve opens and allows this air to be driven into the vessel.
"With every ascent of the piston, therefore, the cylinder is
filled with air, and with every descent Fig. 201.

this cylinder-full of air is forced into
the vessel.

Air is condensed in the chamber of
the air-gun (described in 399) by the
use of this instrument.

449. Experiment. An interesting experiment
may be performed with the condenser and the ap-
paratus represented in Fig. 201. A is a globe half
full of water, with a tube, B, reaching nearly to the
bottom, and extending upward through an air-tight
cap till it terminates in a screw just above the stop-
cock D. The condenser, having been screwed on,
is worked till a large quantity of air is forced into
A. The stop-cock is then closed, the condenser is
unscrewed, and a jet-pipe, C, is put on in its place.
The stop-cock is now opened, when the pressure of
the condensed air, being greater than that of the
atmosphere, forces the water in A up through the
jet, making a beautiful fountain. This experiment
shows that the elasticity of air is increased by
condensing it.




Paieumatic and Hydraulic MacMsies.

450. THE SIPHON. The Siphon, represented in Fig.



Condenser? Describe it. 443. How does the condenser operate ? 449. Describe an
experiment with the condenser and the apparatus represented in Fig. 201. 450. "What




186 PNEUMATICS.

202, is a simple instrument for drawing off liquids from a
higher to a lower level. It is nothing more than a bent
tube, with one leg longer than the other.

Fi- 202 ^ use ^ e s 'phon, fill it with some liquid and then invert

it, stopping the long end with the finger, and setting the short
cue in the liquid to be drawn off. Remove the finger, and the
liquid will commence flowing from the long end. The upward
pressure of the atmosphere is counterbalanced by its down-
ward pressure on the surface of the liquid to be drawn off, and
the liquid in the tube will therefore flow in the direction of its
greatest weight. As it flows, a vacuum is formed in the tube,
and fresh liquid is constantly forced up into the short leg.
The flow continues till the liquid falls below the extremity of
the short leg.

451. Some siphons, like that in the figure, have an addi-
tional tube, open at the upper end and at the lower communi-
cating with the long leg. This saves the trouble of turning
the siphon, every time it is used, to fill it with liquid ; for,
a-iiE SIPHON. the long leg being stopped with the finger and the mouth ap-
plied to this additional tube, the liquid may by suction readily be made to
fill both legs.

452. TANTALUS'S CUP. Fig. 203 represents Tantalus's
Cup, which is simply a goblet containing a siphon, the short
Fig. 203. leg of which reaches nearly to the bottom,
while its long leg passes through the bottom
and extends below. The siphon is concealed
by a figure, which seems to be trying to
drink. Water is poured in ; but, the mo-
ment it reaches the lips of the figure, it re-
cedes, because just then it passes the turn
of the siphon and begins to be discharged
below.

TANTALUS'S CUP. 453. THE LIFTING-PUMP. The Lifting-

pump was invented by Ctesibius \te-sib' -e-us], who flourished
at Alexandria, in Egypt, 250 B. c. Though the son of a
barber and brought up to his father's calling, he attained
distinction by his mechanical abilities. Several ingenious

is the Siphon? How is it used? Explain the principle on which it works. 451. What
improvement is attached to some siphons? 452. Describe Tantalus's Cup, and the
principle on which it works. 45-3. Who invented the Lift! ng-pump? What is said
of Ctesibius ? 454 Of what does the lifting-puinp consist? 455. Describe its mode




THE LIFTING-PUMP.



187



contrivances for raising water are attributed to this philos-
opher, besides the clepsydra already described.

454. The common Lifting-pump is rep- Fig. 204.
resented in Fig. 204. It consists of a cyl-
inder, B C, to which is fitted the air-tight
piston G, containing a valve opening up-
ward. A is called the suction-pipe ; it
must be long enough to reach the water
that is to be raised. In the top of the
jjuction-pipe is the valve H, opening upward
into the cylinder. E Is a handle, by which
the piston may be worked. F is a spout,
from which the water is discharged.

455. Operation. To work the pump, raise the pis-
ton. As it ascends, it leaves a vacuum behind it, and
the water under the pressure of the atmosphere rushes
up through A, opens H, and fills the cylinder B C. The
piston, having reached the top, is now forced back.
Its downward pressure at once closes the valve H, so
that the water can not return into the suction-pipe ; but
the valve in the piston opens, and through it the water
rushes above the piston. When the piston has reached
the bottom of the cylinder, it is again raised ; its valve
being now closed by the downward pressure, the water
is lifted by the piston into the reservoir D, whence it is
discharged by the spout. Meanwhile, the second time
the piston rises, a vacuum is formed below it as before,
and the whole operation is repeated.

456. Thus we see that water is raised in pumps by at-
mospheric pressure. The air will support a column of wa-
ter from 32 to 34 feet high. To this elevation, therefore,
water can be raised with the lifting-pump ; for greater dis-
tances, the forcing-pump must be used.

457. THE FORCING-PUMP. The Forcing-pump, after rais-
ing a liquid through its suction-pipe, does not discharge it
from a spout above, but by the pressure of the returning
piston drives it through an opening in the side below. The




THE LIFTING-PtTMP.



of operation. 456. By what a'Ten^y is water raised in pumps? TTow hicrh a column
will atmospheric pressure support ? To raise water to a greater height, what must



188



PNEUMATICS.



Fig. 205.



liquid is thus forced, either directly or by means of the
pressure of condensed air, to a greater height than it could
otherwise attain.

458. Fig. 205 represents one form of
the forcing-pump. It has a cylinder, pis-
ton.and suction-pipe, like the lifting-pump
just described ; but there is no valve in
the piston. Near the bottom of the cylin-
der enters the pipe M, which communi-
cates with the air-chamber K, by the valve
P, opening upward. The tube I, open at
the bottom and terminating at the upper
end in a jet, passes through the air-tight
top of the chamber K, and extends nearly
to its bottom.

459. Operation. To work the forcing-
pump, raise the piston. A vacuum is
formed ; and water, from the reservoir
below, rushes through the suction-pipe,
opens H, and fills the cylinder. The pis-
ton is now pushed back, when H at once
closes. The water in the cylinder is forced
into M, raises P, and enters the chamber
K. The water in K soon rises above the
mouth of the tube I, and begins to con-
dense the air in the upper part of the chamber. The higher
the water rises in K, the more the air is condensed, and its
elasticity increases in proportion. Its pressure, therefore,
soon becomes greater than that of the atmosphere, and drives
out the liquid through the jet.

Some forcing-pumps have no air-chamber, but drive out
the liquid by the direct pressure of the descending piston. In
that case, the discharge is by successive impulses ; but, when
made from an air-chamber, it is continuous.

460. THE FIRE-EXGINE. The Fire-engine is a combina-
tion of two forcing pumps, with a common air-chamber
and suction-pipe. Its operation will be understood from
Fig. 206.

The pistons, C, D, are attached to a working-beam, A B, turning on the




THE FORCING'

PUMP.



be used? 457. What is the principle on which the Forcinsr-pump acts? 458. De-
scribe the form of forcinjr-purnp represented in Fig. 205. 459. Explain its operation.
When there is no air-chamber, how does the forcing-pump drive out the liquid?
460. Of what does the Fire-engine consist ? Describe its operation with Fig. 206.



THE FIRE-ENGINE.



189




pivot K, so that one rises as the other ^^^ Fig. 206 -

descends. They are driven up and
down by Imkes attached to the beam
and worked by a number of men on
each side. F is the suction-pipe. H
is the air-chamber, and E a pipe ris-
ing from it, to which a flexible leather
hose is attached, so that the stream
can be turned in any direction. The
piston D in Fig. 206 is ascending, fol-
lowed by a stream of water from the
reservoir below, the valve I leading
into the air-chamber being closed.
The piston C, on the other hand, is
descending; its lower valve is closed,
and the water drawn into the cylinder

during its previous ascent, is now being forced into H, through the open
valve J.

461. The fire-engine is one of the most powerful forms of the forcing-
pump, since water is being constantly forced into the air-chamber by one of
the pistons, and the air is violently compressed. With a good engine, a
stream can be thrown more than 100 feet high.

m
462. THE CENTRIFUGAL

PUMP. The Centrifugal Pump
(Fig. 207) is an instrument
for raising water by the com-
bined efl'jct of the centrifugal
force and atmospheric pres-
sure.

It consists of a vertical
axle, AB, and one or more
tubes, C, C, fastened to it,
extending into a reservoir of
water below, and branching
off towards the top so as to
bring their mouths over the
circular trough D. E is a
spout for discharging the wa-




TIIE CENTRIFUGAL PUMP.



401. What is said of the power of the fire-engine ? HOT- high can a stream be thrown
with a good engine ? 462. What forces are brought to bear iu the Centrifugal Tump i



190



PNEUMATICS.



ter from the trough. Near the top and bottom of each
tube is a valve opening upward.

463. Operation. When the pump is to be worked, the tubes are filled
with water, which is prevented from escaping by the lower valves. A rotary
motion is then communicated to the tubes by means of a handle attached to
the axle. The centrifugal force at once acts on the water within, causing it
to open th'e valves and rush forth from the mouths of the tubes. As it as-
cends, a vacuum is left behind it, into which water is driven by atmospheric
pressure from the reservoir below. Streams are thus kept pouring into the
trough as long as the rotary motion is continued.

A large centrifugal pump, worked by steam, has raised no less than 1,800
gallons a minute to a considerable height.

464. THE STOMACH PUMP. The Stomach Pump is an
instrument for injecting a liquid into the stomach of a poi-
soned person and withdrawing it, without removing the
apparatus. The stomach is thus rinsed out, and life is often
saved.

Fig. 208.
C




THE STOMACH PTTMP.



Fig. 208 represents the stomach pump. A syringe, A,
is screwed into a cylindrical box, B, where it communicates
with a short metallic tube. This tube leads on either side
into a bulb, which is connected with a tube of india rubber.
Each bulb contains a movable circular valve of metal, which
fits either extremity, and may be made to close either by
raising the opposite side of the instrument.

Operation. To work the pump, turn the syringe so as to depress C and
elevate D ; and then introduce the tube F into the patient's stomach, and E
into a basin of warm water. The metallic valves fall to the lowest part of

Of what does the centrifugal pump consist? 463. What is its mode of operation ?
What has been effected with a large centrifugal pump worked by steam? 4G4. For
what is the Stomach Pump used ? Describe its parts. How is it worked ?



EXAMPLES FOR PRACTICE. 191

their respective bulbs, which brings them directly opposite where they are in
the Figure. Now draw out the handle of the synuge. A vacuum is pro-
duced ; and the warm water, under atmospheric pressure, rushes up to fill
it, all communication with F being cut off by the valve. The syringe being
thus charged, the handle is pressed back, and the water, prevented from re-
turning into E by the valve, is forced through F into the stomach. Without
removing the India rubber tube from the stomach, now turn the instrument,
so as to raise the side C and depress D, as shown in the Figure. The metal-
lic valves are thus thrown to the opposite extremities of their bulbs, and by
working the syringe with them in this position, the contents of the stomach
are drawn off and discharged into the basin. The syringe is thus always
charged through the depressed tube and emptied through the elevated one.

465. The consideration of the steam-engine, the great-
est of pneumatic machines, is deferred till we shall have
treated of the mode of generating steam by heat, a subject
which belongs to Pyronomics.

EXAMPLES FOR PRACTICE.

1. (See 39S.) Under a pressure of one atmosphere, a body of oxygen fills 24

cubic inches, and its specific gravity is 1.111. What space will it occupy,
and what will be its specific gravity, under a pressure of three atmos-
pheres ?

2. Some hydrogen, by a pressure of 20 pounds to the square inch, is forced

into a space of one cubic foot. How great a pressure will compress it
into half a cubic foot, arid how will its density then compare with what
it was before?

3. Into what space must we compress 10 cubic inches of air, to double its

elastic force?

4. (See 401.) 'What is the weight of 600 cubic inches of air? What is the

weight of the same bulk of water?

5. A vessel, full of air, weighs 1,061 grains; exhausted, it weighs but 1,000

grains. How many cubic inches does it contain ?

6. (See 41-4.) What is the downward atmospheric pressure on the roof of a

house containing 115,200 square inches ? What is the upward atmos-
pheric pressure on the same roof?

7. What amount of atmospheric pressure is supported by a boy whose body

contains 1,000 square inches of surface?

8. (See 40S.) When the mercury in the barometer stands at 29 inches, at

what height will a column of water be supported by the atmosphere?

[Solution,. T7te specific gravity of water is 1 ; that of mercury, 13.5(5?.
A column of water will be supported at the height of 29 X 13.;"6H inches.~\

9. When the atmosphere supports a column of water 32 feet high, how high

a column of mercury will it support?

1C. (See Fig. 183.) How far above the earth's surface would the mercury
stand only two inches high in the barometer?



1 92 PYBONOMICS.



CHAPTER XIII.

PYRONOMICS.

466. PYEONOMICS is the science that treats of heat.

Nature of Meat.

467. Heat is the sensation experienced on approaching
a warm body.

The invisible agent that produces this sensation is also
called Heat. Another name for it is Ca-lor'-ic.

4G8. Cold is the opposite of heat. It is not a positive
agent, but merely implies a greater or less deficiency of
heat. There is heat in all substances ; but in those which
we call cold, it exists in an inferior degree.

4G9. There are two kinds of heat ; Free, or Sensible,
and Latent.

Free or Sensible Heat is heat that can be felt. Latent
Heat is heat that can not be felt. The heat of a fire is Free,
or Sensible ; the heat in ice is Latent.

470. The Temperature of a body is the amount of sen-
sible heat that it contains.

We can not always judge correctly of a body's temperature by the sensa-
tion it produces when we touch it. In the same room, for instance, are a
bar of iron and a piece of cloth ; they must be of the same temperature, but
the iron is cold to the touch while the cloth is not. This is because the iron
carries off the heat more rapidly from the part that touches it. So, if one
hand be cold and the other warm, a substance which to the former seems
hot, to the latter may appear just the reverse. Our sensations, therefore, are
not proper criterions by which to judge of a body's temperature.

466. What is Pyronomics ? 4G7. What is Heat? What other signification has the
tcrmheatf What other name is therefor it in this sense? 4fiS. What is Cojd?
463. How many kinds of heat are there ? What is Free or Sensible Ilea' ? What is
Latent Heat? Give examples. 470. What is the Temperature of a body? Can \ve
judge of a body's temperature by the sensation it produces when we touch it? Stato



NATURE OF HEAT. 193

471. What heat is, we do not know.

Some think that it is not a material substance, but results from the vibra-
tions of the particles of bodies. Others believe it to be an exceedingly sub-
tile substance, whose particles repel each othei-, and thus give it a tendency
to diffuse itself, while they have a strong affinity for other matter. This sub-
stance, they think, enters into every body, and keeps its particles from com-
ing into absolute contact. As long as it remains at rest, it may be latent ;
but, when a colder body approaches, there is a tendency to equalize the tem-
perature ; a series of vibrations are produced in the subtile atmosphere around
each particle, and the heat which was before latent becomes sensible.

Heat seems to be closely connected with light. The one is generally ac-
companied by the other ; and to some extent, as will appear hereafter, they
are governed by the same laws.

472. Heat has no weight.

Balance a piece of red-hot iron with weights in a sensitive pair of scales ;
the same weights will exactly balance it when it has become cold. Heat,
therefore, must be imponderable ; or the loss of so much of it would occa-
sion a perceptible difference in the weight of the iron. So, if a piece of ice
is balanced and then allowed to melt, the water formed will weigh precisely
the same as the ice.

Sources of Meat.

473. The principal Sources of Heat fire four in number :
the Sun, Chemical Action, Mechanical Action, and Elec-
tricity.

474. THE SUN, A SOURCE or HEAT. The Sun is the great
source of heat, as well as light, to the earth.

What the sun is composed of, that it has thus for thousands of years
poured forth undiminished supplies of heat, astronomers can not determine.
Some think that the whole of its immense mass is heated to such a degree as
to make it luminous. According to others, the great body of the sun is not
luminous, but its surface is covered with flames from which rays of heat and
light arc constantly emitted. In either case, it is hard to explain how com-
bustion can be continued so long without exhausting the material by which
it is supported.

475. The heat at the sun's surface is supposed to be
more intense than any with which we are acquainted. By

some facts to prove this. 471. What is heat ? What do some think it results from ?
What do others believe it to be ? How do the latter account for its being sometimes
latent and sometimes sensible? With what is heat connected? 472. What is tho
weight of heat ? Prove this. 473. What are the principal sources of heat ? 474. What
Is the great source of heat to the earth ? What two theories have been advanced to
account for the sun's heat ? 475. How great is the heat at the sun's surface supposed
9



194



the time it reaches us, modified by the immense distance it
has traversed, it is just sufficient to warm the earth into
fertility.

The sun does not heat all parts of the earth alike. This is because its
rays strike some portions perpendicularly and others obliquely. The per-
pendicular rays are absorbed more than the oblique ones, and therefore pro-
duce a greater degree of heat in the parts on which they strike. For the
same reason, it is hotter about noon than any other time of day, the sun
being then more directly over head.

The variety of productions in different parts of the earth is owing to th
difference in the amount of heat received from the sun. The trees and plants
of the tropics are quite different from those of the temperate regions, and
these again are unlike those of cold climates. In the far north and south, so
little heat is received that vegetation entirely ceases. '

Fig. 209. 4*76. The sun's heat may be increased

by collecting a number of its rays into
one point called a Focus. This may be
done with a convex lens, or glass of the
shape represented in Fig. 209. With
such a lens, three feet in diameter, the
metals have been melted.




A similar effect may be produced with concave
mirrors, so arranged as to reflect the rays that strike
them to one and the same focus. When the Romans
were besieging Syracuse, 213 B. c., Archimedes is
said to have used a number of metallic mirrors with
such effect as to set fire to their fleet. The experi-
ment has been repeated in modern times. Buffou,
with a combination of 168 mirrors, showed that

tarred planks could be set on fire at a distance of 150 feet, and that at 60 feet

silver could bo fused.

477. Heat below the Earths Surface. The sun's heat,
even when it falls perpendicularly on the surface, does not
penetrate into the earth farther than 100 feet. Beyond
this depth, all the heat that is felt, comes, not from the
sun, but from the interior of the earth.



to bo ? Why is it less intense when it reaches us ? "Why does not the sun heat all
parts of the earth alike ? To what is the variety of productions in different parts of the
earth owing ? 476. How may the sun's heat be increased ? In what other way may a
similar effect be produced ? What did Archimedes accomplish with a number of me-
tallic mirrors ? Qivo an account of Buffon's experiment. 4TT- What is the greatest



SOURCES OF HEAT. 195

As we descend below the earth's surface, the temperature increases about
one degree for every 45 feet. At this rate, water would boil at a depth of
less than two miles, and at 125 miles all known substances would be melted.
It is thought, therefore, that the great mass of the interior of the earth is in
a state of fusion. The discharge of melted earthy matter, called lava, during
the eruption of volcanoes, goes to prove this ; while the hot springs in differ-
ent parts of the world (particularly numerous in Iceland) show that a high



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 18 of 42)