G. P. (George Payn) Quackenbos.

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

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or zero, it is 32 degrees below the freezing-point. In Reau-
mur's scale the freezing-point is called 0, the boiling-point 80.
In the Centigrade the freezing-point is 0, the boiling-point 100.
When degrees of the thermometer are mentioned, it is usual
to indicate the scale referred to by the letters F., R., or C., as
the case may be. Thus 40 F. means 40 degrees on Fahren-
heit's scale; 15 R., 15 degrees -on Reaumur's scale, &c. In this country,
when no scale is mentioned, Fahrenheit's is meant.

545. Imperfect thermometers were in use at the beginning of the seven-
teenth century. It is uncertain whether the honor of their invention belongs
to' Sanctorio, an Italian physician, Drebbel, a Dutch peasant, or Galileo.
Various liquids have been tried ; the astronomer Roemer was the first to use
mercury, the advantages of which are such that it has superseded all others.

546. The Differential Thermometer. This instrument,



THE THER-
MOMETER.



is the Thermometer? Of what does it consist ? How is the scale of the thermome-
ter formed ? 544. What is said of the number of degrees into which the scale is di-
vided? Name the three principal scales, and tell where each is used. What are the
freezing-point and the boiling-point respectively called in Fahrenheit's scale ? What,
in Reaumur's scale ? In the Centigrade scale ? How are the different scales indi-
cated ? 545. When were thermometers first used ? To whom does the honor of their
invention belong? What liquid has superseded all others in the thermometer? Who



THE DIFFERENTIAL THERMOMETER.



215



Ffc. 217.



30?



o



represented in Fig. 217 V measures minute dif-
ferences of temperature.

It consists of a long glass tube, bent twice at right an-
gles, somewhat in the form of the letter U. One arm is
furnished with a scale of 100 degrees, and each terminates
in a bulb. The tube contains a small quantity of sulphu-
ric acid, colored red, and so disposed that when both
bulbs are of the same temperature it stands at on the
scale. Let either bulb be heated ever so little more than
the other, and the expansion of the air within will drive
the liquid down and cause it to ascend the opposite arm to
.a distance measured by the scale. Ordinary changes of
temperature do not affect the instrument, because both
bulbs are acted on alike.

547. THE PYROMETER. The Pyrometer
(see Fig. 218) is used for measuring variations
in elevated temperatures, and comparing the
expansive power of different metals for a
given degree of heat.

Fig. 218.



THE DIFFERENTIAL
THERMOMETER.

A metal bar is fixed
in an upright at one
end by means of a
screw, and left free to
expand at the other.
It there touches a pin
projecting from a rod
which rests against an
opposite upright, in a
circular support at
each side. This rod

terminates at one end in an arm bent at right angles, which is connected by
a cord and pulley with an index traversing a scale marked with degrees.
Near its extremity is a ball, the weight of which, under ordinary circum-
stances, keeps the index at the highest point of the scale. When lamps are
placed beneath and the bar expands, it pushes against the pin, turns the rod

first used it ? 546. For what is the Differential Thermometer employed ? Describe
the differential thermometer, and its operation. 547. For what is the Pyrometer





THE PYROMETER.



216 PYRONOMICS.

more or less around, and thus raises the arm containing the ball and moves
the index along the scale. The relative degree of heat applied to the bar is
thus indicated. By keeping the heat the same, and using rods of different
metals, we can ascertain their relative expansive power.

Specific Meat.

548. Put a pound of water and a pound of olive oil in
two similar vessels, and apply heat. It will take twice as
long to raise the water to a given temperature as it will the
oil. Let them cool, and the water will be twice as long in
parting with its heat as the oil. Water, therefore, must
receive twice as much heat as olive oil in reaching a given
temperature.

The relative amount of heat which a body receives in
reaching a given temperature is called its Specific Heat, or
its Capacity for Heat.

549. In estimating the specific heat of bodies, that of water is taken as a
standard. Beckoning the specific heat of water as 1, that of iron is about
1 / g , and mercury only J /33- As a general thing, the densest bodies have the
ieast specific heat ; solids have less than liquids, and liquids less than gases
and vapors.

550. As the elastic fluids expand, they are rarefied, and their specific heat
becomes greater. that is, it requires more heat to raise them to a given tem-
perature. This is one reason why the upper regions of the atmosphere are
colder than the lower, as is found by those who ascend mountains.

Steam.

551. GENERATION OP STEAM. Water is rapidly turned
into steam at its boiling-point, which in an open vessel at
the level of the sea is 212 F. After it commences boiling,
water can not be raised to any higher temperature, because
all the heat subsequently applied is absorbed by the steam
and passes off with it.

used ? Describe the Pyrometer. 543. How is it proved that water must receive twice
as much heat as olive oil in reaching a given temperature ? What is meant by Spe-
cific Heat? 549. In estimating the specific heat of bodies, what is taken as a stand-
ard? What is the specific heat of iron? Of mercury? As a general thing, what
bodies have the least specific heat? 550. Under what circumstances is the specific
heat of elastic fluids increased ? What fact is thus explained ? 551. How is steam
genarated ? Why can not water, after it commences boiling, be raised to any higher



STEAM.



217



If the water is in a close vessel, the steam first formed,
being confined, presses on the water and prevents it from
boiling as soon as before. It may now be raised to a more
elevated temperature, for heat is not withdrawn by the
formation of steam till it reaches a higher point.

552. Steam has the same temperature as the water from
which it is formed, the heat absorbed in the process of for-
mation becoming latent. When it is generated from wa-
ter in an open vessel, its temperature is 212; in a confined
vessel it will be higher, according to the pressure on the
surface of the water.

553. Steam is colorless and invisible. "When cooled by
contact with the atmosphere, it begins to turn back into a
liquid state, and assumes a grey mist-like appearance. Look
at the spout of a tea-kettle full of boiling water. For half
an inch from the extremity nothing can be seen ; beyond
that, the steam, cooling and beginning to

condense, becomes visible.

554. The generation and properties of steam may
be understood from Fig. 219. AB represents the in-
side of a tall glass tube, the section of which has an
area of one square inch. The tube is closed at its
lower end, and contains a cubic inch of water, D, and
resting on it a tightly-fitting piston, C. A cord, fast-
ened to the piston, is carried round the wheel E, a-ad
attached to the weight F. F is made just heavy enough
to counterbalance the piston and its friction against
the tube. Suppose a thermometer to be placed in
the water, and apply heat at the bottom of the tube.
As soon as the thermometer indicates a temperature
of 212, the piston begins to rise, leaving a space ap-
parently empty between it and the water. The fire
continues to impart heat to the water, but the mer-
cury in the thermometer remains stationary at 212;
the piston keeps rising, and the water begins to di-
minish. If the process were continued and the tube
were long enough, the piston would at last reach a



Fig. 219.




temperature ? Under what circumstances may water be raised to a higher tempera-
ture than 212 ? 552. What is the temperature of steam ? 553. What is the color of
Btcaro ? Explain the mist-like appearance a short distance from the spout of a boiling
tea-kettle. 554. With the aid of Fig. 219, show the process of generating steam, and

10



218 PYRONOMICS.

height of nearly 1,700 inches, by which time the water would entirely disap-
pear. If the tube were then weighed, though nothing could be seen in it but
the piston, it would be found to have exactly the same weight as at first.
The water would simply be converted into steam, and thus increased in vol-
ume 1,700 times. The piston, with the pressure of the atmosphere on it
(which is 15 pounds, the area of the piston being one square inch), would be
raised 1,700 inches.

All the time steam is forming, a uniform amount of heat is applied to the
tube. As the mercury in the thermometer rises no higher than 212, it is
evident that the heat imparted after it reaches that point is absorbed by the
steam and becomes latent. To determine the amount of this latent heat, we
must compare the time required to raise the water from the freezing to the
boiling point with the time that elapses from the commencement of boiling
till the water disappears. We shall find that the latter interval is 5Va times
as great as the former ; and, since from the freezing-point (32) to the boiling-
point (212) is 180, we conclude that the amount of heat absorbed is 5Va
times 180, or nearly 1,000 degrees. That is, the heat applied would have
raised the water to a temperature of nearly 1,000, if it could have remained
in the liquid state.

555. If, besides the pressure of the atmosphere on P, a weight of 15 pounds
were placed on it, it would be said to have a pressure of two atmospheres.
Steam, in this case, would not commence forming till the water reached a
temperature of 251 1 / 2 degrees ; and, when the whole was evaporated, the pis-
ton would stand only about half as high as before. Under a pressure of three
atmospheres, the piston would be raised about one-third as high, <fcc. ; the
mechanical force developed in the evaporation of a given quantity of water
remaining nearly the same. This force, for a cubic inch of water, is suffi-
cient to raise a ton a foot high.

556. Steam has a high degree of elasticity and expansi-
bility. Under a pressure of two atmospheres, or 30 pounds
to the square inch, it would raise the piston in the above
experiment about 850 inches; if 15 pounds were removed
from the piston, the expansive force of the steam would
drive it up 850 inches farther.

557. CONDENSATION OF STEAM. Steam retains its form
only as long as it retains the latent heat absorbed. The

describe some of its properties. When water is converted into steam, how many
times is its volume increased? How is this proved with the apparatus just de-
scribed ? Prove that heat becomes latent in the steam. How can the amount of
latent heat be determined? 555. When is steam said to have a pressure of two at-
mospheres? How high would the piston then be raised ? How high would the piston
bo raised under a pressure of three atmospheres? How great is the mechanical force
developed in evaporating a cubic inch of water? 556. Prove the expansibility of
fcteam. 557. How long does steam retain its form ? When 5s it condensed? Show



THE STEAM-ENGINE. 219

moment it is forced to part with this heat, it is turned back
into the liquid form, or condensed.

In the above experiment, after the piston has been raised 1,700 inches, let
the fire be removed, and cold water be applied to the surface of the tube.
The latent heat will be abstracted, and the steam will be condensed and form
once more a cubic inch of water at the bottom of the tube. As the steam
condenses, successive vacuums are produced ; and the piston, forced down
by the pressure of the atmosphere, descends, and finally rests on the water
as at first.

By applying heat again, the process may be repeated. An up-and-down
motion may in this way be communicated to the piston ; and the piston may
be connected with machinery, which will thus be set in motion by the al-
ternate evaporation of water and condensation of steam. This was the prin-
ciple of the Atmospheric Engine, which was once extensively used, but has
now been superseded.

TIae Steam-Engine.

558. HERO'S ENGINE. Steam and some of its proper-
ties appear to have been known to the ancients centuries
before the Christian era. Hero, of Alexandria, who flour-
ished about 200 years B. c., has left us a description of a
steam-engine by which machinery could be set in motion.

Fig. 220 represents Hero's Fig. 220.

engine. A hollow metallic
globe is supported by pivots,
and provided with a number
of jets equally distant from
the pivots, and bent at right
angles near their outer end.
As soon as steam is introduced
into the globe, it issues vio-
lently from the mouth of each
jet, while on the opposite side
of each it presses without be-
ing able to escape. This un-
balanced pressure makes the
globe revolve. Machinery may HERO'S STEAM-ENGINE.

be set in motion by means of a band connected with this apparatus.

559. Hero's was a simple rotatory engine. No use was made of it for

how it may be condensed in the above experiment. What follows the condensation
of the steam? How may an up-and-down motion be communicated to the piston?
What engine was constructed on this principle ? 553. How long ago was steam
known? Who has left us a description of a steam-engine? Describe Hero's engine.




220 PTEONOMICS.

2,000 years ; but the principle involved has been revived, and is applied in
rotatory engines at the present day.

560. DE GAKAY'S ENGINE. In 1543, a Spaniard, by the
name of De Garay, undertook to propel a vessel of 200 tons
in the harbor of Barcelona by the force of steam. He kept
his machinery a secret, but it was observed that a boiler
and two wheels constituted the principal part of his appa-
ratus. The experiment succeeded. The vessel moved
three miles an hour, and was turned or stopped at pleasure ;
but the Emperor Charles V., by whose order the trial was
made, never followed the matter up, and De Garay and his
invention were forgotten.

561. ENGINES OP DE CAUS AND BRANCA. In 1615, De
Caus, a French mathematician, devised an apparatus by
which water could be raised in a tube through the agency
of steam. A few years afterwards, an Italian physician,
named Branca, ground his drugs by means of a wheel set
in motion by steam. The steam was led from a close ves-
sel, in which it was prepared, and discharged against flanges
on the rim of the wheel.

562. THE MARQUIS OF WORCESTER'S ENGINE. The Mar-
quis of Worcester,, by many regarded as the inventor of the
steam-engine, greatly improved on the imperfect attempts
of those who had preceded him.

Some say that Worcester derived his ideas from De Caus. Others claim
that his invention was purely original, and the result of reflections to which
he was led during his imprisonment in the Tower of London, in 1G56, for
plotting against the government of Cromwell. Observing how the steam kept
moving the lid of the pot in which he was cooking his dinner, he could not
help thinking that this power could be turned to a variety of useful purposes,
and set about devising an engine in which it might be applied to the raising
of water.

The Marquis of Worcester generated his steam in a boiler, and led it by
pipes to two vessels communicating on one side with the reservoir from
which it was to be drawn, and on the other with the cistern into which it
was to be discharged.



559. What sort of an engine was Hero's, and what is said of it ? 5CO. Give an account
of De Garay's engine, and the experiment made with it. 5G1. Give an account of De
Caus's engine. Of Branca's. 562. Whom do many regard as the inventor of the steam-
engine ? "What claim has he to the honor ? How was he led to reflect on the subject ?



THE STEAM-ENGINE. 221

563. PAPIN'S ENGINE. The next step was taken by Pa-
pin, who devised the mode of giving a piston an up-and-
down motion in a cylinder by alternately generating and
condensing steam below a piston.

564. SAVERY'S ENGINE. Captain Thomas Savery, in
1698, constructed an engine superior to any before invent-
ed. He was led to investigate the subject by the following
occurrence. Having finished a flask of wine at a tavern, he
flung it on the fire, and called for a basin of water to wash
his hands. Some of the wine remained in the flask, and
steam soon began to issue from it. Observing this, Savery
thought that he would try the effect* of inverting the flask
and plunging its mouth into the basin of cold water. "No
sooner had he done this than the steam condensed, arid the
water rushing into the flask nearly filled it. Confident that
he could advantageously apply this principle in machinery,
Savery rested not till he invented an engine which was em-
ployed with success in drawing off the water from mines.

565. The principle on which Savery's engine
worked, may be understood from Fig. 221. S is a
pipe connecting a boiler in which steam is genera-
ted (and which does not appear in the Figure) with
a cylindrical vessel, C, called the receiver. I is known
as the injection-pipe, and is used for throwing cold
water into the receiver to condense the steam. The
steam-pipe, S, and the injection-pipe, I, contain the
stop-cocks, G, B, which are moved by the common
handle, A, so arranged that when one is opened the
other is closed. F is a pipe which descends to the
reservoir whence the water is to be drawn, and is
commanded by the valve V, opening upward. E D
is a pipe leading from the bottom of the receiver up
to the cistern, into which the water is to be discharged. This pipe contains
the valve Q, opening upward.

Operation. To work the engine, open the stop-cock G, which of course
involves the shutting of B. The steam rushes in through S, and fills the re-
ceiver C, driving out the air through the valve Q. When C is full, shut G



How was the Marquis of Worcester's apparatus arranged ? 563. Who took the next
step ? What was Papin's improvement ? 564. Who constructed a superior engine in
1698? Eelate the circumstances that led Savery to investigate the subject. 565. With
the aid of Fig. 221 , describe tho parts of Savory's engine, Explain its operation.




222 PYKONOMICS.

and open B. Cold water at once enters through the injection-pipe and con?
denses the steam in C. A vacuum is thus formed, and the water in the res-
ervoir or mine, under the pressure of the atmosphere, forces open the valve
V, and rushes up through Finto G, till the receiver is nearly filled. G is then
opened and B closed; when the steam again enters through S, and by its
expansive force opens the valve Q, and drives the water up through E D into
the cistern.

566. NEWCOMEN'S ENGINE. Savery's engine was em-
ployed only for raising water ; but Newcomen, an intelli-
gent blacksmith, extended its sphere of usefulness, by con-
necting a piston, worked up and down on Papin's principle,
with a beam turning on a pivot, by means of which ma-
chinery of different kinds could be set in motion.

567. About this time, also, the engine was made self-acting through the
ingenuity of Humphrey Potter, a lad employed to turn the stop-cocks Pre-
ferring play to this monotonous labor, he contrived to fasten cords m the
beam to the handle of the stop-cocks, in such a way that the latter were
opened and closed at the proper times, while he was away, enjoying himself
with his companions. His device was after a time found out, and saved so
much labor that it was at once adopted as an essential part of the machine.

568. WATT'S ENGINE. The genius of James Watt
brought the steam-engine to such perfection that but little
improvement has since been made in it. Gifted with re-
markable mathematical powers and a reflective mind, he
commenced his experiments in 1763. Having been em-
ployed to repair one of Newcomen's engines, he soon per-
ceived that there was a great loss in consequence of having
every time to cool down the receiver from a high degree
of heat before the steam could be condensed. This diffi-
culty he remedied by providing a separate chamber called
a condenser, to which the steam was conveyed and in which
it was condensed. He also made the movement of the pis-
ton more prompt and effective by introducing steam into the
cylinder alternately above and below it. The Double-
acting Condensing Steam-engine, as improved by Watt, and

566. What was the only purpose for which Savery's engine was employed ? Who ex-
tended its usefulness, and how ? 567. Give an account of Humphrey Potter's im-
provement, and the circumstances under which it was devised. 56S. Who brought
the steam-engine to comparative perfection ? When did Watt commence his exper-
iments? What disadvantage did he perceive that Newcomen's engines labored un-
der? How did he remedy the difficulty ? What other improvement did he make ?



THE STEAM-ENGINE.



223



now generally constructed for manufacturing establishments,
is represented in Fig. 222.

5G9. Description of the Parts. A. is the cylinder, in which the piston T
works. This piston is connected by the piston-rod R with the working-beam

Fig. 222.




THE DOUBLE-ACTING CONDENSING STEAM-ENGINE.

V W, which turns on a pivot, U. The other end of the working-beam, 0,
imparts a rotary motion to the heavy fly-wheel X Y, by means of the connect-
ing-rod P and the crank Q. The fly, as explained on page 125, regulates the
motion, and is directly connected with the machinery to be moved. Steam

669. Describe the parts of Watt's Double-acting Condensing Engine. Show how the



224



PYEONOMICS.



is conveyed to the cylinder A from the boiler (which is not seen in the fig-
ure), through the steam-pipe B, which is commanded by the throttle-valve C.
This valve is connected with the governor D, in such a way as to be opened
when the supply of steam is too small and closed when it is too great.

Communicating with the cylinder at its top and bottom on the left, are
two hollow steam-boxes, E, E, each of which is divided into three compartments
by two valves. F is called the upper induction-valve, and opens or closes
communication between the steam-pipe and the upper part of the cylinder,
so as to admit or intercept a supply of steam. G, called the upper exhaustion-
valve, opens or closes communication between the upper part of the piston
and the condenser K, so that the steam may either be allowed to escape into
the latter or confined in the cylinder. The lower induction-valve g, and the
lower exhaustion-valve f, stand in the same relation to the lower part of the
cylinder, the former connecting it with the steam-pipe, and the latter with
the condenser K. These valves are connected by a system of levers with a
common handle, H, called a spanner, which is made to work at the proper in-
tervals by a pin projecting from the rod L, which is moved by the working-
beam. The spanner works so as to open and close the valves by pairs. When
it is pressed up, it opens F and/, and closes G- and g ; when pressed down,
it closes F and/ and opens G and g.

Below is the condensing apparatus, consisting of two cylinders, I and J,
immersed in a cistern of cold water. A pipe, K, having an end like the rose
of a watering-pot, conveys water from the cistern to the cylinder I (the sup-
ply being regulated by a stop-cock), and thus condenses the steam which is
from time to time admitted into I. The other cylinder, J, called the air-pump,
contains a piston with a valve in it opening upward, which works like the
bucket of a common pump, and draws off the surplus water that collects at
the bottom of the cylinder I into the upper reservoir S. The hot-water pump
M then conveys this water to the cistern that supplies the boiler. To keep
the water around the condensing apparatus at the right temperature, a fresh
supply is constantly introduced through the cold-water pump N ; which, like
the hot-water pump and the air-pump, is kept in operation by rods connected
with the working-beam.

570. Operation. The working of the engine is as follows : Let the piston
be at the top of the cylinder, and all the space below be filled with steam.
The upper induction-valve and the lower exhaustion-valve are then opened
by the spanner, while the upper exhaustion-valve and the lower induction-
valve are closed. By this means steam is introduced above the piston, while
the steam beneath is drawn off into the condenser, where it is converted into
water. The pressure of the steam above at once forces the piston to the bot-
tom of the cylinder. Just at this moment the spanner is moved in the oppo-
site direction, and the valves that were before opened are closed, while those
that were previously closed are opened. The steam is now admitted beneath



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 21 of 42)