warmer than co l ore( } fabrics are warmer when made into ear-
light ones ? .
ments than those ol light color.
733. Snow or ice will melt under a piece of black cloth, while
it would remain perfectly solid under a white one. The farmers in
some of the mountainous parts of Europe are accustomed to spread
192 NATURAL PHILOSOPHY.
black earth, or soot, over the snow, in the spring, to hasten its
welting, and enable them to commence ploughing.
What effect has heat 734 rr he density of all substances is aug-
upon the density of , .,. . .
tubstances? mented by cold, and diminished by neat.
There is a remarkable exception to this remark, and that is in tho
Cd,<?e of water ; which instead of contracting, expands at the freez-
ing point, or when it fc frozen. This is the reason why pitchers,
ihd other vessels, containing water and other similar fluids, are so
often broken when the liquid freezes in them. For the same reason,
ice floats instead of sinking in water ; for, as its density is dimin-
ished, its specific gravity is consequently diminished. Were it not for
this remarkable property of water, large ponds and lakes, expose'
to intense cold, would become solid masses of ice ; for. if the ice,
when formed on the surface,* were more dense (that is, more heavj)
than the water below, it would sink to the bottom, and the water
above, freezing in its turn, would also sink, until the whole body
of the water would be frozen. The consequence would be the total
destruction of all creatures in the water. But the specific gravity
of ice causes it to continue on the surface, protecting the water
below from congelation.
735. Cold is merely the absence of heat ; or rather.
co/rf? more properly speaking, inferior degrees of heat are
termed cold. (See par. 1463.)
736. The effect of heat and cold, in the expansion and contrac
tion of glass, is an object of common observation ; for it is this
expansion and contraction which cause so many accidents with glasb
articles. Thus, when hot water is suddenly poured into a cold glass
of any form, the glass, if it have any thickness, will crack ; ano
on the contrary, if cold water be poured into a heated glass vessel
the same effect will be produced. The reason of which is this ;
Heat makes its way but slowly through glass ; the inner surface,
therefore, when the hot water is poured into it, becomes heated,
and, of course, distended before the outer surface, and the irregular
expansion causes the vessel to break. There is less danger of frao-
ture, therefore, when the gjass is thin, because the heat readily pen-
etrates it, and there is no irregular expansion.
737. The glass chimneys, used for oil and gas burners, are often
broken by being suddenly placed, when cold, over a hot flame. The
danger of fracture may be prevented (it is said) by making a mi-
nute notch on the bottom of the tube with a diamond. This precau-
tion has been used in an establishment where six lamps were lighted
ttvery day, and not a single glass has been broken in nine years
What bodies retain 738. Different bodies require different quan-
heat the longest ? tides of heat to raise them to the same tern-
perature ; and those which are heated with most difficulty retain
their heat the longest.
Thus, oil becomes heated more speedily than water, and it
likewise cools more quickly. (See par. 1471.)
739. The most obvious and direct effect of heat on a bodj
is to increase its extension in all directions.
740. Coopers, wheelwrights and other artificers, avail themselves
of this property in fixing iron hoops on casks, and the tires or irons
on wheels. The hoop or tire, having been heated, expands, and,
being adapted in that state to the cask or the wheel, as the metal
contracts in cooling it clasps the parts very firmly together.
741. From what lias been stated above, it will be seen that an
allowance should be made for the alteration of the dimensions in
metallic beams or supporters, caused by thedilatation and contraction
effected by the weather. In the iron arches of Southwark Bridge,
over the Thames, the variation of the temperature of the air causes
a difference of height, at different times, amounting to nearly an inch.
A happy application of the expansive power of heat to the mechanic
arts was made some years ago, at Paris. The weight of the roof of a
building, in the Conservatory of Arts and Trades, had pressed out-
wards the side walls of the structure, and endangered its security
The following method was adopted to restore the perpendicular
direction of the structure. Several apertures were made in the
walls, opposite to each other, through which iron bars were intro-
duced, which, stretching across the building, extended beyond the
outside of the walls. These bars terminated in screws, at each end,
to which large broad nuts were attached. Each alternate bar was
then heated by means of powerful lamps, and their lengths being thus
increased, the nuts on the outside of the building were screwed up
close to it, and the bars were suffered to cool. The powerful con-
traction of the bars drew the walls of the building closer together
and the same process being repeated on all the bars, the walls were
gradually and steadily restored to their upright position.
742. The Pyrometer is an instrument to
What is the , ^ . , ,. , , ..
Pyrometer] show the expansion oi bodies by the applica-
tion of heat.
It consists of a metallic bar or wire, with an index connected
with one extremity. On the application of heat, the bar expands,
and turns the index to show the degree of expansion.
743. Wedgewood's pyrometer, the instrument commonly used
for high temperatures, measures heat by the contraction of
194 NATURAL PHILOSOPHY.
What effect ^^ ^ e ex P ans i n caused by heat i.i
has heat on solid and liquid bodies differs in different sub-
^ ITthe stances ' bu * ag riform fluids all expand alike,
w/idf, liquid and and undergo uniform degrees of expansion at
triform state? ^.^ temperatujm
745. The expansion of solid bodies depends, in some degree, on
the cohesion of their particles ; but, as gases and vapors are desti-
tute of cohesion, heat operates on them without any opposing power.
746. When heat IP. applied to water or other
What effect liquids, it converts them into steam or vapor. The
the f f deprivation of heat reconverts them into the liquid
liquid bodies ? form. It is on this principle that distillation takes
What is a 747. The vessel employed for distillation is called
***?' a Still.*
Explain 748. Fig. 107 represents a Still. A liquid being
Fig. 107. poured into the large vessel a, heat is applied below,
which converts the liquid gradually into steam or vapor, which,
having no other outlet, passes through the spiral tube, called the
worm, in vessel &, and from 5 through another worm, in c. The
worm, being surrounded with cold water, condenses the vapor in
the tube or worm, and reconverts it to a fluid state, and it flows
* The subject of distillation properly belongs to the science of Chemistry,
but it is here introduced for the benefit of those who cannot readily refer
to a treatise on that subject.
out at e in a tepid stream. The worm is of different lengths, and
its only use is to present a large extent of surface to the cold
water, so that the vapor may readily be condensed.
749. The process of distillation is sometimes used to purify a
liquid, as the vapors which rise are unmixed with the impurities of
the fluid. Important changes are thus made, and the still becomes
highly useful in the arts.
At what tem- 750. When water is raised to the tempera-
w^Tonvert- ture of 212 of Fahrenheit's thermometer, it
ed into steam ? is converted into steam. It is then highly
elastic and compressible.
What effect ^^' ^e elastic force of steam is increased
has heat upon by heat ; and decrease of heat diminishes it.
The amount of pressure which steam will exert
depends, therefore, on its temperature.
^^ . 752. The temperature of steam is always the
temperature same with that .. of the liquid from which it is
of confined formed, while it remains in contact with that liquid ,
and when heated to a great degree, its elastic force
will cause the vessel in which it is contained to burst, unless Jt
is made sufficiently strong to resist a prodigious pressure.
753. It has already been stated that water is converted into
steam at the temperature of 212. When closely confined it may be
raised to a higher temperature, and it will then emit steam ol
greatly increased elastic force.
How is steam 754:. When any portion of steam comes in
condensed? contact with water, it instantly parts with its
heat to the water, and becomes condensed into water. The
whole mass then becomes water, increased in temperature
by the amount of heat which the steam has lost.
On what property 755. This is the great and peculiar
tSW^ PPerty of steam, on which its me-
depend? chanical agencies depend namely, its
power of exerting a high degree of elastic force, and losing
196 NATURAL PHILOSOPHY
How may the ^^' There are two ways in which steam
mechanical is made instantly to lose its mechanical force ;
force of steam , * '- f n i
le instantly namely, first, by suddenly opening a passage
destroyed? f or j^ s escape into the open air, where it iinnift-
iiately becomes visible,* by a sudden loss of part of its heat,
tfhich it gives to the air ; and secondly, by conveying it to
i vessel called a condenser, where it comes directly into
s.tmtact with a stream of water, to which it instantly gives
up its heat and is condensed into water.
757. Steam occupies a space about seven-
does steam teen hundred times larger than when it is con-
occupy f verted into water. But the space th&t a given
quantity of water converted into steam will occupy depends
upon the temperature of the steam. The more it is heated
the greater space it will fill, and the greater will be its
WJiaf is the 758. THE STEAM-ENGINE. The Steam-
Steam-engme ? en gj ne j s a mac hine moved by the expansive
force of steam.
In what man- 759. The mode in which steam is made to act
ner is steam is by causing its expansive force to raise a solid
made to act ? piston accurately fitted to the bore O f a cylinder,
like that in the forcing-pump. The piston rises by the impulse
of expanding steam, admitted into the cylinder below. When
the piston is thus raised, if the steam below it be suddenly con-
densed by the admission of cold water, or withdrawn from under
* Steam in a highly elastic state that is, when at a high temperature
Is perfectly dry and invisible. The reason that we are able to see it after it
has performed its work and issues from the steam-engine is, that as soon as it
eoines in contact with the air it immediately parts with a portion of its
heat (and, because air is not a good conductor, only a portion), and is con
densed into small vesicles, which present a visible form, resembling smoke
Its expansive force, however, is not wholly destroyed; for the vesicles them
selves expand as they rise, and soon become invisible, mingling with other
vapors in the air. Could we look into the cylinder, filled with highly elastic
steam, we should be able to see nothing. But, that the steam is thcve, and
ir. its invisible form exerting a prodigious force, we know by the movement?
of the piston
it, a vacuum will be formed, and the pressure of the atmosphere
on the piston above will drive it down. The admission of more
steam below will raise it again, and thus a continued motion ot
the piston, up and down, will be produced. This motion of the
piston is communicated to wheels, levers, and other machinery,
in such a manner as to produce the effect intended.
760. This is the mode in which the engine of
How was the
steam-engine Thomas Newcomen, commonly called the atmos-
of Neiccomen pheric engine, was constructed. It was called
constructed? . .
the atmospheric engine because all of the work
was done by the pressure of the atmosphere namely, in the
downward motion of the piston.
761. The celebrated James Watt introduced
ments did Watt two important improvements into the steam-
make in the engine. Observing that the cooling of the cylin-
steam-cngine ? , . ,_ . . .. .,_
der by the water thrown into it to condense the
steam lessened the expansibility of the steam, he contrived a
method to withdraw the steam from the principal cylinder, after
it had performed its office, into a conden sing-chamber, where it
is reconverted into water, and conveyed back to the boiler. The
other improvement, called the double action, consists in substitut-
ing the expansive power of steam for the atmospheric pressure.
This was performed by admitting the steam into the cylinder
above the raised piston at the same moment that it is removed
from Mow it ; and thus the power of steam is exerted in the de-
scending as well as in the ascending stroke of the piston ; and a
much greater impetus is given to the machinery than by the
former method. From the doulle action of the steam above as
well as Mow the piston, and from the condensation of the steam
after it has performed its office, this engine is called Watt's
double-acting condensing steam-engine. [See also No. 766.]
Explain 762. Fig. 108 represents that portion of the steam-
Fig. 108. engine in which steam is made to act, and propel such
machinery as may be connected with it. It also exhibits two
improvements of Mr. Watt.
The principal Darts are the
noiler, the cylinder and its
piston, the condenser, the
air-pump, the steam-pipe,
the eductiou-pipe, and the
cistern. In this figure, A
represents the boiler, G
the cylinder, with H the
piston, B the steam-pipe, with two branches* communicating
with the cylinder, the one above and the other below the piston.
This pipe has two valves, F and G, which are opened and -closed
alternately by machinery connected with the piston. The steam
is carried through this pipe by the valves, when open, to the
cylinder, both above and below the piston. K is the eduction-
pipe, having two branches, like the steam-pipe, furnished with
valves, &c., which are opened and shut by the same machinery.
By the eduction-pipe the steam is led off from the cylinder, as
1-he piston ascends and descends.
L is the condenser, and a stop-cock for the admission of cold
water. M is the pump. N is the cistern of cold water in which
the condenser is immersed. R is the safety-valve. When the
valves are all open, the steam issues freely from the boiler, and
circulates through ail the parts of the machine, expelling the
air. This process is called blowing out, and is heard when a
steamboat is about starting.
Now, the valves F and Q being closed, and G and P remain-
ing open, the steam presses upon the piston and forces it down
As it descends, it draws with it the end of the working-beam,
which is attached to the piston-rod J (but which is not repre
sented in the figure). To this working-beam (which is a lever
of the first kind) bars or rods are attached, which, rising and
falling with the beam and the piston, open the stop-cock 0, ad-
* The steam and the eduction pipes are sometimes made in form? differing
from those in the figure, and they differ much in different tmgines.
initting a stream of cold water, which meets the steam from the
cylinder and condenses it, leaving no force below the piston to
oppose its descent. At this moment the rods attached to the
working-beam close the stop-cocks Gr and P, and open. F and Q.
The steam then flows in below the piston, and rushes from above
it into the condenser, by which means the piston is forced up
again with the same power as that with which it descended.
Thus the steam-cocks Gr and P and F and Q are alternately
opened and closed ; the steam passing from the boiler drives the
piston alternately upwards and downwards, and thus produces
a regular and continued motion. This motion of the piston,
being communicated to the working-beam, is extended to other
machinery, and thus an engine of great power is obtained.
The pump M, the rod of which is connected with the working-
beam, carries the water from the condenser back into the boiler,
by a communication represented in Fig. 109.
The safety-valve R, connected with a levej* of the second
kind, is made to open when the pressure of the steam within the
boiler is too great. The steam then rushing through the aperture
under the valve, removes the danger of the bursting of the boiler.
How is the 7^3. The power of a steam-engine is gen-
power of a ,, 111
steam-engine erally expressed by the power ot a horse,
estimated? which can raise 33,000 Ibs. to the height of
one foot in a minute. An engine of 100 horse power is
one that will raise 3,300,000 Ibs. to the height of one foot
in one minute.
What are the 764. The steam-engine is constructed in va-
r ^ ous forms, and no two manufacturers fol low-
one? how do they ing exactly the same pattern ; but the two priri-
dijferi c -p a j kj nc [s are the high and the low pressure
engines, or, as they are sometimes called, the non-condensing and
the condensing engines. The non-condensing or high-pressure,
engines differ from the low-pressure or condensing engines in
having no condenser. The steam, after having moved the piston,
200 NATURAL PHILOSOPHY.
is let off into the open air. \s this ki-nd of engine occupies Jese
space, and is much less complicated, it is generally used on rail-
roads. In the tow-pressure or condensing engines, the steam,
after having moved the piston, is condensed, or converted into
water, and then conducted back into the boiler.
765. The steam-engine, as it is constructed
Who were the .
principal im- at tae present day, is the result of the inventions
provers of the and discoveries of a number of distinguished indi-
iteam-mgine? vidualgj at different periods. Among thosa who
have contributed to its present state of perfection, and its ap-
plication to practical purposes, may be mentioned the names o^
Somerset, the Marquis of Worcester, Savery, Newcomeu, Fulton,
and especially Mr. James Watt.
766. To the inventive genius of Watt tne engine is indebted foi
the condenser, the appendages for parallel notion-* the application <f
the governor, and for the double action. In the words of Mr. Jeffrey,,
it may be added, that, " by his admirable contrivances, and those of
Mr. Fulton, it has become a thing alike stupendous for its force and
its flexibility ; for the prodigious power it can exert, and the ease
and precision and ductility with which it can be varied, distributed,
and applied. The trunk of an elephant, that can pick up a pin, or
rend an oak, is as nothing to it. It can engrave a seal, and crush
masses of obdurate metal before it; draw out, without breaking, a
thread as fine as gossamer, and lift up a ship of war like a baublo
in the air. It can embroider muslin, and forge anchors ; cut steel
into ribands, and impel loaded vessels against the fury of the winds
Explain 767. Fig. 109 represents Watt's double-acting condens-
Fig. 109. j n g s t eam _engine, in which A represents the boiler, con-
taining a large quantity of water, which is constantly replaced as
fast as portions are converted into steam. B is the steam-pipe,
conveying the steam to the cylinder, having a steam-cock b to
admit or exclude the steam at pleasure.
C is the cylinder, surrounded by the jacket c c, a space kept
constantly supplied with hot steam, in order to keep the cylinder
from being cooled by the external air. D is the eduction-pipe,
communicating between the cylinder and the condenser. E is
the condenser, with a valve e called the injection-cock, admitting
a jet of cold water, which meets the steam the instant that tho
steam enters the condenser. F is the air-pump, which is a com-
mon suction-pump, but is here called the air-pump because it
removes from the condenser not only the water, but also the air,
and the steam that escapes condensation. G G is a cold-water
cistern, which surrounds the condenser, and supplies it with cold
water, being filled by the cold-water pump, which is represented
by H. I is the hot well, containing water from the condenser ;
K is the hot-water pump, which conveys back the water of con-
densation from the hot well to the boiler.
L L are levers, which open and shut the valves in the chan-
nel between the steam-pipe, cylinder, eduction-pipe, and con-
denser ; which levers are raised or depressed by projections
attached to the piston-rod of the pump. M M is an apparatus
for changing the circular motion of the w'orking-beani into par-
aliel motion, so that the piston-rods are made to move in a straight
line N N is the working-beam, which, being moved by the
rising and falling of the piston attached to one end, coinmuoi-
cates motion to the fly-wheel by means of the crank P, and from
the fly-wheel the motion is communicated by bands, wheels or
levers, to the other parts of the machinery. is the governor.
The governor, being connected with the fly-wheel, is made to
partake of the common motion of the engine, and the balls will
remain at a constant distance from the perpendicular shaft so
long as the motion of the engine is uniform ; but, whenever the
engine moves faster than usual, the balls will recede further froni
the shaft, and by partly closing a valve connected with the
toiler, will diminish the supply of steam to the cylinder, and
thus reduce the speed to the rate required.
The ^team-engine thus constructed is applied to boats to, turn
wheels having paddles attached to their circumference, which
answer the purpose of oars. [See Fig. 110.] It is used also
in work-shops, factories, &c. ; and different directions and veloc-
ities may be given to the motion produced by the action of the
steam on the piston, by connecting the piston to the beam with
wheels, axles and levers, according to the principles stated
under the head of Mechanics.
Steamboats are used principally on rivers, in harbors, bays, and on
the coast. They are made of all sizes, and carry engines of different
power, proportioned to the size of the boat.
The steamship [See Fig. Ill], in addition to its steam -engires
^04 NATUBAL PHILOSOPHY.
nd paddles, is rigged with masts and sails to increase the speed. 01
to make progress if the engines get out of order.
The Propeller differs from a steam-boat or steam-ship, by having
an immense screw projecting from under the stern of the ship, instead
of paddle-wheels. The screw is caused to revolve by means of steam-
engines, and forces the vessel forward by its action on the water.
What is the ^^* ^e locomotive engine is a high-
locomotive pressure steam-engine, mounted on wheels,
steam-engine? ^ uged t() draw 1()adg Qn ft ra ji roa( J ) CI ot h el
level road. It is usually accompanied by a large wagon.
called a tender, in which the wood and water used by the
engine are carried.
Explain 769. Fig. 112 represents a side view of the internal
Fig. 112. construction of a locomotive steam-engine ; in which
F represents the fire-box, or place where the fire is kept; D
the door through which the fuel is introduced. The spaces
marked B are the interior of the boiler, in which the water
stands at the height indicated by the dotted line. The boiler is
closed on all sides, all its openings being guarded by valves.
The tubes marked p p conduct the smoke and flame of the fuel
through the boiler to the chimney C C, serving, at the same
time, to communicate the heat to the remotest part of the boiler.
By this arrangement, none of the heat is lost, as these tubes are
all surrounded by the water. S S S is the steam -pipe, open at
the top V S, having a steam-tight cock, or regulator, V, which
is opened and shut by the lever L, extending outside of tbe
boiler, and managed by the engineer.
The operation of the machine is as follows: The steam being
generated in great abundance in the boiler, and being unable to
escape out of it, acquires a considerable degree of elastic force.
If at that moment the valve V be opened, by the handle L, the
steam, entering the pipe S, passes in the direction of the arrow,
through the tube, and enters the valve-box at X. There a
tsliding-valve, which moves at the same time with the machine,
opens for the steam a communication successively with each end