THE STEAM-ENGINE--_continued_.
[Illustration: Fig. 391. The first steam-boat, the _Comet_, built by
Henry Bell, in 1811, who brought steam navigation into practice in
Europe.]
"So shalt thou instant reach the realm assign'd
In wondrous ships, _self-mov'd_, instinct with mind.
* * * * *
Though clouds and darkness veil the encumbered sky.
Fearless, through darkness and through clouds they fly,
Tho' tempests rage,--tho' rolls the swelling main,
The seas may roll, the tempests swell in vain;
E'en the stern god that o'er the waves presides,
Safe as they pass, and safe repass the tides,
With fury burns; while careless they convey,
Promiscuous, ev'ry guest to ev'ry bay."
These lines, from Pope's translation of the "Odyssey," were very aptly
quoted twenty-five years ago by Mr. M. A. Alderson, in his treatise on
the steam-engine, for which he received from Dr. Birkbeck, the [Page
419] originator of Mechanics' Institutions, the prize of 20_l._, being
the gift of the London Mechanics' Institution, and these lines seem to
indicate some sort of rude anticipation by the ancients of that free
passage of the ocean by the agency of steam which has rendered ships
almost independent of wind and weather.
Homer's description, as above, of the Phoenician fleet of King
Alcinous, in the eighth book of the "Odyssey," is certainly an ancient
record of an _idea_, but nothing more. In a work written by Hero of
Alexandria, about a hundred years B.C., and entitled "Spiritalia seu
Pneumatica," a number of contrivances are mentioned for raising liquids
and producing motion by means of air and steam, so that the first
steam-engine is usually ascribed to Hero; and the annexed cut displays
the apparatus. (Fig. 392.)
[Illustration: Fig. 392. Hero's steam-engine. A. The boiler in which
steam is produced, and then passes through the hollow support B, from
which there is no outlet but through the two apertures, C C. The
reaction of the air on the issuing steam produces a rotatory motion in
the jets, C C, attached to a centre but hollow axle.]
It is a remarkable circumstance that Sir Isaac Newton applied the same
principle in a little ball, mounted on wheels, containing boiling water,
and provided with a small orifice; and in his description he says: "And
if the ball be opened, the vapours will rush out violently one way, and
the wheels and the ball at the same time will be carried the contrary
way." From the time of Hero, there does not appear to be any record or
mention made of steam apparatus till the year 1002, when, in a work
called "Malmesbury's History," mention is made of an organ in which the
sounds were produced by the escape of air (query, steam) by means of
heated water. It is strange that, in these days of steam application,
the Calliope, or steam organ, should be an important feature at the
present moment at the Crystal Palace; and it only shows how the same
ideas are reproduced as novelties in the ever-recurring cycles of years.
On the revival of classical learning throughout Gothic Europe, the work
of Hero began to attract attention, and it was translated and printed in
black letter, and most likely first from the Arabic character, as in the
year 1543 the first fruits appeared in Spain, where Blasco de Garay, a
sea captain, propelled a ship of 200 tons burden, at the rate of three
miles per hour, before certain commissioners appointed by the Emperor
Charles the Fifth. Alas for inquisitorial Spain! had she looked deeper
into the matter, and performed her _auto-da-fées_ on the boilers of
[Page 420] steam engines instead of the bodies of poor human beings,
what lasting glories would have been her reward. The invention made its
_début_ in Spain, the commissioners reported, the worthy inventor was
rewarded, but the mighty giant invoked was put to sleep again for at
least 150 years. The steam giant was disturbed with dreams; one Mathias,
in 1563, gave him a nightmare; Solomon de Caus, in 1624, nearly woke him
up; Giovanni Bianca, in 1629, did more; and the Marquis of Worcester, in
the middle of the seventeenth century, as the evil genius of Spain,
carried off the giant bodily and made him the slave of England; at
least, he experimented, and wrote such wondrous tales of his new motive
power, that in 1653 we read of steam being fairly tethered to its work,
and set to draw water out of the Thames at Vauxhall; and Cosmo de
Medici, a foreigner who inspected the apparatus in 1653, says, "It
raises water more than forty geometrical feet by the power of one man
only, and in a very short space of time will draw up full vessels of
water through a tube or channel not more than a span in width, on which
account it is considered to be of greater service to the public than the
other machine near Somerset House, which last one was driven by _two
horses_."
What would the Marquis of Worcester and Cosmo de Medici have thought of
Blasco de Garay on the ocean, and ruling 12,000 steam horses? Write the
name of the brave and prudent Captain Harrison, in the good ship _Great
Eastern_, date 1859, instead of that of the gallant Spaniard, and our
brief history is finished.
The first really useful steam-engine was made, not by a plain Mr., but
again by a captain--namely, Captain Savery, who appears to have been the
first inventor who thoroughly understood and applied the _vacuum_
principle. (Fig. 393.)
[Page 421]
[Illustration: Fig. 393. Savery's engine.]
A A. The furnaces which contain the boiler. B 1 and B 2. The two
fireplaces. C. The funnel or chimney, which is common to both furnaces.
In these two furnaces are placed two vessels of copper, which I (Savery)
call boilers--the one large as at L, the other small as D. D. The small
boiler contained in the furnace, which is heated by the fire at B 2. E.
The pipe and cock to admit cold water into the small boiler to fill it.
F. The screw that covers and confines the cock E to the top of the small
boiler. G. A small gauge cock at the top of a pipe, going within eight
inches of the bottom of the small boiler. H. A large pipe which goes the
same depth into the small boiler. I. A clack or valve at the top of the
pipe H (opening upwards). K. A pipe going from the box above the said
clack or valve in the great boiler, and passing about one inch into it.
L L. The great boiler contained in the other furnace, which is heated by
fire at B 1. M. The screw with the regulator, which is moved by the
handle Z, and opens or shuts the apertures at which the steam passes out
of the great boiler at the steam-pipes O O. N. A small gauge cock at the
top of a pipe, which goes half way down into the great boiler. O 1, O 2.
Steam pipes, one end of each screwed to the regulator; the other ends to
the receivers P P, to convey the steam from the great boiler into those
receivers. P 1, P 2. Copper vessels called receivers, which are to
receive the water which is to be raised. Q. Screw joints by which the
branches of the water-pipes are connected with the lower parts of the
receivers. R 1, 2, 3, and 4. Valves or clacks of brass in the
water-pipes, two above the branches Q and two below them; they allow the
water to pass upwards through the pipes, but prevent its descent; there
are screw-plugs to take out on occasions to get at the valves R. S. The
forcing-pump which conveys the water upwards to its place of delivery,
when it is forced out from the receivers by the impelled steam. T. The
sucking-pipe, which conveys the water up from the bottom of the pit to
fill the receivers by suction. V. A square frame of wood, or a box, with
holes round its bottom in the water, to enclose the lower end of the
sucking-pipe to keep away dirt and obstructions. X is a cistern with a
bung cock coming from the force-pipe, so as it shall always be kept
filled with cold water. Y Y. A cock and pipe coming from the bottom of
the said cistern, with a spout to let the cold run down on the outside
of either of the receivers, P P. Z. The handle of the regulator to move
it by, either open or shut, so as to let the steam out of the great
boiler into either of the receivers.
[Page 422]
This is Savery's own description (taken from the "Miner's Friend,"
printed in 1702), of his water-engine, which differs from that suggested
by the Marquis of Worcester, in the fact that he made the _pressure of
the air_ carry the water up the first stage. Savery's patent was "for
raising water and occasioning motion to all sorts of mill-work by the
impellant force of fire;" and the patent was granted in the reign of
King William the Third of glorious memory.
Thus Savery overcame, as he remarks, the "oddest and almost insuperable
difficulties," and introduced a steam apparatus or engine, a good many
of which were constructed, and employed for raising water. The
mechanical skill required to construct the boiler, the very _heart_ (as
it were) of the iron engine, had not been acquired in the time of
Captain Savery, and hence the weakness of the boilers, and the danger of
working them. As the pressure required was very considerable to overcome
the resistance of a lofty column of water, these engines were gradually
relinquished for those of another clever mechanician--viz., for those of
Thomas Newcomen, an ironmonger of Dartmouth, who, about the year 1705,
constructed and introduced the _cylinder_, from which the transition was
gradually made to the mode of condensing by a jet of cold water, the use
of self-acting valves, and the construction of self-acting engines by
Smeaton, Hornblower, and finally by the illustrious Watt, whose portrait
heads the first chapter on Heat in this book.
Newcomen was assisted in his work by one Cawley, a glazier; and their
persevering labours were crowned with a successful result of the most
memorable importance in the history of the steam-engine.
In the engine by Savery, the operation of the steam was twofold--namely,
by the direct pressure from its elasticity, and by the indirect
consequence of its condensation, which affords a vacuum. This last may
be said to be the only principle used by Newcomen, who employed a boiler
for the generation of steam, and conveyed it by a pipe to the bottom of
a hollow cylinder, open at the top, but provided with a solid piston,
that moved up and down in it, and was rendered tight by a stuffing of
hemp, like the piston of a boy's common squirt. It can readily be
understood, that if the jet of the latter was connected with a tight
little boiler, and steam blown into it, that the piston of the squirt
would rise to the top of the barrel in which it works, being thrust up
by the pressure or force of the steam; but unless the steam was cut off,
and cold water applied to the interior of the barrel, the piston could
not descend again. As soon, therefore, as Newcomen had thrust up the
piston by the action of steam, he introduced a jet of cold water,
supplied from an elevated cistern beneath the piston, when the steam was
condensed into water, and a vacuum or void space obtained. The piston
being free to move either up or down, was now forced in the latter
direction by the pressure of the air, which is a constant force equal to
fifteen pounds on the square inch; and thus the piston in Newcomen's
engine was raised by _heat_--viz., by steam, and thrust down by
_cold_--i.e., by the condensation of the steam producing a vacuum. The
void obtained in this manner was very considerable, because one cubic
_foot_ of [Page 423] steam at 212° condenses into one cubic _inch_ of
water. The production of a vacuum with the aid of steam is quickly
effected by boiling some water in a clean camphine can, and when the
steam is issuing freely from the mouth of the latter it is then corked,
and cold water thrown over the exterior. Directly the temperature is
lowered, the steam inside the tin vessel is condensed suddenly into
water, and a void space being suddenly obtained, the whole pressure of a
column of air of a breadth equal to the area of the vessel, and of a
height of forty miles, is brought suddenly down like a sledge-hammer
upon the sides of the tin vessel, and as they are not sufficiently
strong to offer a proper resistance, they are crushed in like an
egg-shell by the giant weight which falls upon them.
The barometer, or measurer of the weight of the air, consists of a glass
tube about thirty-three inches in length, hermetically sealed at one
end, and containing mercury that has been carefully boiled within it,
and being perfectly filled the tube is inserted in a cistern of clean
mercury, when it gravitates to a height equal to the pressure of the
air, leaving a space at the top called the torricellian vacuum. As the
atmospheric air decreases in density by admixture with invisible steam
or vapour, any given volume becomes specifically lighter: hence the
column of mercury falls to a height of about twenty-eight inches; whilst
if the aqueous vapour diminishes, the weight of the air becomes greater,
and the barometer may rise to a height of about thirty-one inches.
Having thus secured a "reciprocating motion," Newcomen applied it to the
working of a force-pump by the intervention of a great beam or lever
suspended on gudgeons (an iron pin on which a wheel or shaft of a
machine turns) at the middle, and suspended like the beam of a pair of
scales; and, in fact, he invented that method of supporting the beam
which is in use to the present day. Supposing we compare Newcomen's beam
to a scale beam, he attached to the extremities (instead of scale pans)
a water pump and his steam cylinder--the latter being at one end, and
the former at the other. The beam played at "see-saw:" by the primary
action of the steam on the bottom of the piston in the _cylinder_ it was
pushed up at this end, and of course suffered an equal fall at the
other, to which the pump piston was attached; and when the motion was
reversed by the condensation of the steam, down went the piston again by
the pressure of the air, whilst that of the water pump was again raised,
and being provided with proper valves, the water was pumped slowly out
of the mine, although the steam power used was very moderate, and only
just sufficient to counterpoise the weight of the atmosphere. Newcomen
made the end attached to the water pump purposely heavier than the steam
piston of the other end of the beam, and by this means the work of the
steam, by its elasticity, was very moderate, whilst the actual lift of
the water from the mine was performed by the pressure of the air, equal
(as already stated) to fifteen pounds on every square inch of the
surface of the steam piston. This engine is called the atmospheric
engine, and in the next cut we have a picture taken from a photograph by
the "Watt Club" of the actual model of the Newcomen engine in the [Page
424] Hunterian Museum of the University of Glasgow; the dimensions
being--length, 27 in.; breadth, 12 in.; height, 50½ in.; from which, "in
1765, _James Watt, in seeking to repair this model_, belonging to the
Natural Philosophy Class in the University of Glasgow, _made the
discovery of a separate condenser_, which has identified his name with
that of the steam-engine." (Fig. 394.)
[Illustration: Fig. 394. Model of the Newcomen engine, in which the
furnace and boiler, the steam cylinder, beam, water-pump, and elevated
cistern of water, are apparent.]
In Newcomen's engine, the opening and shutting of the cocks required the
vigilant care of a man or boy, and it is stated on good authority that a
boy who preferred (like nearly all other boys) _play_ to work,
contrived, by means of strings, a brick, and one or two catches on the
working beam, to make the engine self-acting.
This poor boy's ingenious contrivance paved the way for the improved
[Page 425] methods of opening and shutting the valves, which were
brought to a great state of perfection by Beighton, of Newcastle, about
1718. Between that time and the year 1763, we find honourable mention
made of Smeaton in connexion with the steam-engine, but the name of the
great James Watt at this time began to be appreciated, and by a series
of wonderfully simple mechanisms, he at last perfected the machine whose
origin could be traced back not only to the time of Blasco de Garay, in
1543, but even to the days of the ancient mechanicians, such as Hero,
who lived 130 B.C.
In 1763, James Watt was a maker of mathematical instruments in Glasgow,
and his attention was drawn to the subject of the steam-engine by his
undertaking to repair a working model of Newcomen's steam-engine, which
was used by Professor Anderson, who then filled the Chair of Natural
Philosophy, and subsequently founded the Andersonian Institution. The
repairs required for this model induced Watt to make another, and by
watching its operation, he discovered that a vast quantity of heat, and
therefore fuel, was wasted in the constant and successive heating and
cooling of the steam cylinder. About two years after, when Watt was
twenty-nine years of age, he had made so many experiments, that he was
enabled to put into a mechanical shape his original ideas, which are
embodied in his patent of 1769, as follows:--
"My method of lessening the consumption of steam, and consequently fuel,
in fire-engines, consists of the following _principles_:
"First: That vessel in which the powers of steam are to be employed to
work the engine, which is called the cylinder in common fire-engines,
and which I call the steam-vessel, must, during the whole time the
engine is at work, _be kept as hot as the steam that enters it_--first,
by enclosing it in a case of wood or any other materials that transmit
heat slowly; secondly, by surrounding it with steam or other heated
bodies; and thirdly, by suffering neither water nor any other substance
colder than steam to enter or touch it during that time.
"Secondly: In engines that are to be worked wholly or partially by
condensation of steam, the steam is to be condensed in vessels
_distinct_ from the steam-vessels or cylinders, although occasionally
communicating with them; _these vessels_ I call _condensers_; and whilst
the engines are working, these condensers ought at least to be kept as
cold as the air in the neighbourhood of the engine, by application of
water or other cold bodies.
"Thirdly: Whatever air or other elastic vapour is not condensed by the
cold of the condenser, and may impede the working of the engine, is to
be drawn out of the steam-vessels or condensers by means of pumps
wrought by the engines themselves, or otherwise.
"Fourthly: I intend in many cases to employ the expansive force of steam
to press on the pistons, or whatever may be used instead of them, in the
same manner as the pressure of the atmosphere is now employed in common
fire-engines. In cases where cold water cannot be had in plenty, the
engines may be wrought by this force of steam only, by discharging the
steam into the open air after it has done its office.
"Lastly: Instead of using water to render the piston or other parts of
[Page 426] the engines air and steam-tight, I employ oils, wax, resinous
bodies, fat of animals, quicksilver, and other metals in their fluid
state.
"And the said James Watt, by a memorandum added to the said
specification, declared that he did not intend that anything in the
fourth article should be understood to extend to any engine when the
water to be raised enters the steam-vessel itself, or any vessel having
an open communication with it."
"About the time he obtained his patent, Watt commenced the construction
of his first real engine, the cylinder of which was eighteen inches in
diameter, and after many impediments in the details of the work he
succeeded in bringing it to considerable perfection. The bad boring of
the cylinder, and the difficulty of obtaining a substance that would
keep the piston tight without enormous friction, and at the same time
resist the action of steam, gave him the most trouble, and the
employment of a piston rod moving through a stuffing-box was a new
feature in steam-engines at that time, and required great nicety of
workmanship to make it effectual. While Watt was contending with these
difficulties, Roebuck's finances became disarranged, and in 1773 he
disposed of his interest in the patent to Mr. Boulton, of Soho. As,
however, a considerable part of the term of fourteen years, for which
the patent was granted, had already passed away, and as several years
more would probably elapse before the improved engines could be brought
into operation, it was judged expedient to apply to Parliament for a
prolongation of the term, and an Act was passed in 1775 granting an
extension of twenty-five years from that date, in consideration of the
great merit of the invention." (Bourne's "Treatise on the
Steam-engine.")
In Fig. 395 (p. 427) we give an illustration of a low-pressure
condensing engine and boiler of eight-horse power, constructed on the
principle of Boulton and Watt, as the latter had fortunately united his
skill, learning, originality, and experience with Mr. Boulton, of Soho,
near Birmingham, whose metal manufactory was already the most celebrated
in England.
During the explanation of this eight horse-power engine, the opportunity
may be taken to discuss occasionally the special improvements effected
by Watt. The steam-pipe A conveys the steam generated in the boiler B to
the slide-valve C, which is kept close to the surface, against which it
works by the pressure of the steam.
Here we notice some of the valuable improvements of Watt in the
admission of steam _above_ as well as _below_ the piston, by which he
increased the power of his engine, and no longer confined it to the
force of the atmospheric pressure. It is also necessary to remark the
beautifully simple mechanism of the slide-valve, by which steam is
admitted alternately above and below the piston. Want of space prevents
us tracing out the gradual improvements effected by Watt, and therefore
we take his invention as it stood in the year 1780, and refer our
readers to Bourne's "Treatise on the Steam-engine" for the full and
minute particulars of the improvements to that date.
[Page 427]
[Illustration: Fig. 395. An eight-horse power condensing steam-engine,
after the principle of Boulton and Watt, and explained in pages 426 to
432.]
[Page 428]
At that time it occurred to Watt that the _condensation_ of the steam
from the _cylinder_ after it had done its work, might be made more
perfect if a _perpetual vacuum_ was maintained beneath the piston, while
an alternate steam-pressure and vacuum were produced above it. (Fig.
396.)
[Illustration: Fig. 396. "E E is the cylinder. J. The piston, _a._ The
steam-pipe. _b._ The regulating or throttle valve, _e._ The eduction and
equilibrium single valve, performing the functions of both. _c._ The
upper, and _f_ the under, portholes, by which passages only the steam
can enter and pass away. _d, j, g._ The eduction-pipe by which the steam
passes from above the piston during every returning stroke to the
condenser, a perpetual exhaustion being maintained beneath it."--From
BOURNE _on the Steam-engine_.]
Instead of obtaining a specific advantage the contrary occurred, and
Watt was obliged in this case to return to the ponderous Newcomen
counterweight to balance the difference in the vacuum above and below
the piston, consequently this form of the cylinder and valves was
abandoned. The juvenile reader will perceive in the above drawing that
the superior arrangement of Watt's cylinder to that of Newcomen arises
from the steam operating above and below the piston, and that the piston
rod works air-tight in a _stuffing box_ at the top of the cylinder. A
most important improvement in the employment of steam as a motive power
has been discovered in the mode of using it "expansively," by which the
steam, at a pressure say of sixty pounds on the square inch, is admitted
below the piston, and then cut off and allowed to expand and drive up
the latter without the expenditure of any more fuel, and leaving, after
lifting the piston to a height say of three feet, an average or mean
power of thirty pounds on the square inch.
Returning to the eight-horse condensing engine, D is the steam cylinder
surrounded by a case to prevent the steam cooling and to maintain in
the [Page 429] cylinder the same, or nearly the same, temperature as
that of the steam in the boiler, according to the condition of Art. I.
of Watt's Patent, quoted at p. 425 of this book. The same outer case is
apparent around the cylinder in Fig. 396; E, the piston, which, by
stuffing with hemp or other proper material, fits the interior of the
cylinder in the most accurate manner, and prevents the escape of steam
by its sides: _e_ is the piston rod attached to the parallel motion.
This clockwork-like piece of mechanism has often been quoted as one of
the masterpieces of Watt, and in its greatest perfection is called the
_complete_ parallel motion, and may be found in all the best land beam
steam-engines. The object of the parallel motion is to cause the piston
and pump rods to move always in straight lines, never deviating to
either side. (Fig. 397.)
[Illustration: Fig. 397. A B is half the beam, A being the main centre,
B E. The main links connecting the piston-rod F with the end of the
beam. G D. The air-pump links, from the centre of which the air-pump rod
is suspended. C D and E D produce the parallelism, because C D is
moveable only round the fixed centre C, whilst E D is not only moveable
round the centre D, but the centre itself in the arc described by C D,
and by this action E D corrects the distorting influence of its own
radius. The dotted lines and letters above enable the observer to see
the effect of the movement of the beam on the parallel motion.]
In the eight horse-power engine shown in page picture, _e_ is also
attached to the piston E, which moves the beam F, and the other end of
this beam, by the connecting rod _g_, gives motion to the heavy fly
wheel G, by means of the crank _h_.
H is an eccentric circle on the axle of the fly wheel G, it gives motion
to the slide valve, which admits the steam alternately above and below
the piston. The slide valve and its seat are contained within an oblong
box or case, large enough to permit the easy motion of the valve within
it, and usually forming an enlargement in the course of a pipe.
The valve rod by means of which the valve is opened and shut, passes out
through a stuffing box; or, instead of such a rod, a valve of moderate
size often has a nut fixed to it, within which works a screw on the end
of an axle which passes out through a bush, and has shoulders within and
without to prevent it from moving longitudinally, and a square on the
outer end on which the key fits that is used in turning it. I is the
throttle valve inside the steam pipe and lever connected with a governor
for regulating the admission of steam into the cylinder.
Here, again, we pause in the description of our eight horse-power engine
to illustrate more particularly this admirable contrivance of [Page
430] Watt, which remains to the present day without any material
alteration even in the best steam-engines. (Fig. 398.)
[Illustration: Fig. 398. A. The seat of the throttle valve, Z. The valve
itself turning on a spindle, which passes through its centre. _a_ is the
steam pipe. _w._ The throttle valve lever on which the rod H, proceeding
from the governor, acts. D D. The spindle of the governor revolving by a
belt acting on the pulley _d_. E E. The balls hung on the ends of the
arms, which cross each other at _e_ like a pair of scissors. When D D is
set in motion, the balls fly out by centrifugal motion, and in doing so
draw down the collar into which the lever F works by means of the links
_f h_. When F is depressed, of course H rises, and the valve Z is partly
closed, and the supply of steam reduced.]
In the eight-horse engine already partly explained, _k_ is the cylinder
of an air-pump to remove any air, and the water which condenses the
steam, from the condenser L. There is also the eduction pipe, which
conducts the steam from the cylinder to the condenser L. O is the pump
that supplies cold water to the cistern S, in which the condenser and
air-pump stand, P is a rod connected with the injection cock for
admitting a jet of water into the condenser from the cistern, and which
is continually flowing during the working of the engine, Q Q, cast-iron
columns, four of which support the principal parts of the engine.
We now come to the boiler of the steam-engine, which is of course of
almost equal importance with the engine itself; and the one in our
page-picture is a good type of one of the favourite boilers used by
Messrs. Boulton and Watt, and is called the "Wagon boiler." The boiler
is made of wrought-iron plates rivetted together, and properly
strengthened where necessary; and the steam-pipe A conveys the steam to
the engine. It may be remarked here that the cylindrical [Page 431]
boiler--consisting of two cylinders, one within the other, of which the
former contains the fire, whilst the furnace-draught circulates outside
the latter, and the space between the two cylinders being filled with
water--is the form of boiler which is most highly approved of, and is
employed in the famous economical steam-engines of the Cornish mines.
As the water evaporates in the form of steam, the boiler must be
continually supplied with fresh water, which comes (as will be noticed
by inspecting the page picture) from the _hot well_ S, by means of the
_hot-water pump R_, attached to the beam F. The water is pumped to the
top of a column rising above but connected with the boiler. There is a
cylindrical float, inside the column of water, connected with the
boiler, suspended ever a pulley by a chain passing to the damper of the
furnace. The damper and float balance each other, and when the water in
the boiler rises to too high a temperature, it causes the float to rise
in the column of water, which lowering the damper or shutter that stops
the draught of the chimney of the furnace T, diminishes the intensity of
the heat, and reduces the formation of steam. On the other hand, as the
temperature diminishes, the float descends and the damper rises, and
permitting more air to rush to the burning fuel in the fire, a greater
quantity of steam is generated.
There is likewise a stone float inside the boiler, for regulating the
supply of water by the feed pipe, or column of water, which latter must
always be sufficiently lofty to press with greater force than the steam
produced in the boiler, or else the power of the steam might, under
certain circumstances, eject or blow out the water from the top of the
column. The stone is suspended by a brass wire which works through a
stuffing box, and is connected with a lever, to which is attached a
heavy counterpoise, so adjusted that when the stone is immersed to a
certain depth in water (according to the principle of a solid body
losing weight in a fluid, explained in the article on specific gravity,
page 48), it shall exactly balance the latter, but when the water sinks
in the boiler, and the stone is no longer surrounded with water, it
becomes heavier, and sinking down opens a conical plug, ground so as to
fit water-tight into a hole in the bottom of the column of water or feed
pipe, and directly the plug opens, water rushes into the boiler; being
cut off again as the stone rises when immersed or surrounded with the
proper height of water. Unless our juvenile readers refer to the article
on specific gravity, they will not understand the otherwise seeming
anomaly of a _stone float_.
A large hole, called the man-hole, covered with an iron plate and
securely fastened with screws, is provided for the purpose of allowing
the engineer to enter the boiler, when cold, for the purpose of clearing
out the incrustation and dirt arising from the water. To prevent the
incrustation of lime and other earthy matters, it is sometimes usual, on
the principle "_that prevention is better than cure_" to put a large log
of "logwood" inside the boiler, as it is found that the colouring matter
curiously prevents the earthy matter, so well known as the "fur" in iron
"tea-kettles," sticking to the sides of the boiler. Sal ammoniac [Page
432] and other salts also have the same property, but neither are much
used, the mechanical labour of chipping out the boiler and stopping its
work for a day or so, being preferred to the _prevention plan_ already
described.
There is also a valve opening inwards to prevent the consequences of a
sudden condensation in the boiler, and also a safety valve and lever
with weights opening outwards, and allowing the steam to escape when it
reaches a dangerous excess, and in order to look as it were at the state
of the pressure inside the iron boiler, a proper steam gauge is
provided, also two cocks--viz., a water and steam cock, to enable the
engineer to ascertain if the water is up to, and does not exceed, the
proper height, because when turned, supposing that all is going on
properly, the former, No. 7, should eject water, the latter, No. 8,
steam.
It is truly wonderful, considering the number of safeguards and warnings
provided, that accidents ever happen to boilers, but the statistics of
deaths and annual destruction of property show that science is
powerless, nay, absolutely dangerous, when handled by ignorant and
careless persons. The great fly-wheel, which is usually such an
awe-inspiring and marvellous exhibition of strength in an engine of any
great power, is employed for the purpose of storing up force, so that if
any parts of the engine work indifferently (they all work with
resistance), it shall equalize the wants of the whole, and by its
inertia it will continue to move until its motion is stopped by a
resistance equal to its momentum.
In starting an engine, the engineer may sometimes be observed labouring
to move the "fly-wheel," and when once he succeeds in getting it to
move, the resistance of the other parts of the machinery is soon
overcome. Mr. Alderson, in his prize essay, remarks that "it is in the
property which the steam-engine possesses of regulating itself, and
providing for all its wants, that the great beauty of the invention
consists. It has been said that nothing made by the hand of man
approaches so near to animal life. Heat is the principle of its
movement; there is in its tubes circulation, like that of the blood in
the veins of animals, having valves which open and shut in proper
periods; it feeds itself, evacuates such portions of its food as are
useless, and draws from its own labours all that is necessary to its own
subsistance. To this may be added, that they are now regulated so as not
to exceed the assigned speed, and thus do animals in a state of nature.
That the safety valves, like the pores of perspiration, open to permit
the escape of superfluous heat in the form of steam. The steam gauge, as
a pulse to the boiler, indicates the heat and pressure of the steam
within; and the motion of the piston represents the action and the power
of which it is capable. The motion of the fluids in the boiler
represents the expanding and collapsing of the heart; the fluid that
goes to it by one channel is drawn off by another, in part to be
returned when condensed by the cold, similar to the operation of veins
and arteries. Animals require long and frequent periods of relaxation
from fatigue, and any great accumulation of their power is not obtained
without great expense and inconvenience. The [Page 433] wind is
uncertain; and water, the constancy of which is in few places equal to
the wants of the machinist, can seldom be obtained on the spot where
other circumstances require machines to be erected. To relieve us from
all these difficulties, the last century has given us the steam-engine
for a resource, the power of which may be increased to infinitude: it
requires but little room; it may be erected in all places, and its
mighty services are always at our command, whether in winter or summer,
by day or by night, on land or water; it knows no intermission but what
our wishes dictate."
The _high-pressure_ steam-engine appears to have been first brought into
general use by Trevethic and Vivian, although the primary notion of such
a modification of the Newcomen or water-engines did not originate with
them. As the name implies, the steam is brought to a much higher
temperature and pressure than is required in the condensing engines of
Boulton and Watt. It consisted, in the first place, of a cylinder open
at the top, and provided with a piston. To save heat the cylinder was
fixed _inside_ the boiler, and was provided with a two-way cock worked
by a crank, for the purpose of supplying and cutting off the steam. The
downward stroke was produced by the atmosphere, and the steam having
done its work, was simply blown away and wasted in the air.
The engine was provided with a fly-wheel, to which the piston-rod was at
once attached, producing a continuous rotatory movement without the
assistance of the heavier parallel motion, or hot and cold water pumps.
This form of engine was soon adopted for pumping work--such as that of
draining fens; and in 1804 Mr. Richard Trevethic used it for propelling
the first carriage on the Merthyr Tydvil rail or tram way, and it was
then speedily adopted in all the coal districts where the levels were
moderate. Stephenson the elder, succeeded by the late lamented Robert
Stephenson, followed with inventions and improvements of the locomotive
steam-engine; and we are told in "Once a Week" that,
"One of those best qualified to speak to the latter's contributions to
the development of the locomotive engine, states that from about five
years from his return from America, Robert Stephenson's attention was
chiefly directed to its improvement. 'None but those who accompanied him
during the period in his incessant experiments can form an idea of the
amazing metamorphosis which the machine underwent in it. The most
elementary principles of the application of heat, of the mode of
calculating the strength of cylindrical and other boilers, of the
strength of rivetting and of staying flat portions of the boilers, were
then far from being understood, and each step in the improvement of the
engine had to be confirmed by the most careful experiments before the
brilliant results of the Rocket and Planet engines (the latter being the
type of the existing modern locomotive) could be arrived at.'
"Stephenson's time was not, however, so fully taken up during the above
interval as to preclude attention to his other civil engineering
business, and he executed within it the Leicester and Swannington,
[Page 434] Whitby and Pickering, Canterbury and Whitstable, and Newton
and Warrington Railways; while he also erected an extensive manufactory
for locomotives at Newton, in Lancashire, in partnership with the
Messrs. Tayleur. About the middle of the above period, also, the first
surveys and estimates for the London and Birmingham Railway were framed,
leading eventually to the obtaining of the Act. Then followed the
execution of that line, and here Robert Stephenson had an opportunity of
showing his great talent for the management of works on a large scale.
This was the first railway of any magnitude executed under the contract
system; perfect sets of plans and specifications (which have since
served as a type for nearly all the subsequent lines) were prepared--no
small matter for a series of works extending over 112 miles, involving
tunnels and other works of a then unprecedented magnitude.
"Many other railways in England and abroad were executed by him in rapid
succession; the Midland, Blackwall, Northern and Eastern, Norfolk,
Chester and Holyhead, together with numerous branch lines, were executed
in this country by him; and among railways abroad may be enumerated as
works either executed by him or recommended in his capacity of a
consulting engineer, the system of lines in Belgium, Italy, Norway, and
Egypt, and in France, Holland, Denmark, India, Canada, and New Zealand.
"Robert Stephenson first saw the light in the village of Willington, at
a cottage which his father occupied after his marriage with Miss Fanny
Henderson--a marriage contracted on the strength of his first
appointment as "breaksman" to the engine employed for lifting the
ballast brought by the return collier ships to Newcastle. Here Robert
was born on the 17th of November, 1803. As the cottage looked out upon a
tramway, the eyes of the child were naturally familiarized from infancy
with sights and scenes most nearly connected with his future
profession."
In locomotive steam-engine boilers, the principal object is to generate
steam with the greatest rapidity; hence the boiler consists of two
parts--viz., a square box containing the fire, and around which a thin
stratum of water circulates, whilst the draught for the fire rushes
through a number of copper tubes placed in the second or cylindrical
part of the boiler. By the use of these tubes an immense _surface_ of
water is exposed to the action of the fire, and the steam is not only
generated with amazing rapidity, but is also maintained at a very high
pressure.
Within the last few years "superheated steam" has been favourably
mentioned, and employed economically for driving certain engines. The
principle consists in first generating steam, and then passing it
through coils of strong wrought-iron pipe, by which it acquires
additional heat, and we have therefore combined in steam the ordinary
principle of evaporation of water with the heated-air principle of
Stirling, described at p. 367. We give a drawing of Scott's patent
generator and superheated steam engine. (Fig. 399.)
The apparatus is used as follows:--A fire is made in the furnace, and so
soon as a pyrometer connected with that indicates about 800 degrees,
[Page 435] a little water is pumped into the coils by hand, which is
immediately converted into steam. The donkey engine is then started,
which maintains the necessary feed of _air_ and water. The generator
produces a copious supply of elastic mixed gaseous vapour, at a pressure
of 250 pounds on the square inch; and it is stated that this engine
works satisfactorily, and is started in the incredibly short time of
from three to five minutes, so that for marine engines in war vessels,
expecting to be ordered out suddenly, no fuel need be burnt till the
moment required.
[Illustration: Fig. 399. Scott's patent generator, or new _versus_ old
steam.]
Experiments with superheated steam have already been tried most
successfully on board the Peninsular and Oriental Company's ship the
_Valetta_, whereby it is stated that a saving of thirty per cent. in
fuel [Page 436] is obtained. The engine to which the superheated steam
was adapted was constructed by Penn and Sons, and the vessel attained a
speed of nearly sixteen knots per hour, and under the most adverse
circumstances had an abundance of steam to spare.
"A most important experimental improvement in steam machinery was on
Thursday last tried for the first time down the river, on board the
Peninsular and Oriental Company's ship, the _Valetta_. The actual nature
of the improvement may be described in a few words as consisting of a
simple apparatus for working marine engines by means of superheated
steam; but it is not too much to say that in the success or failure of
this experiment are involved results so important as to affect
materially all ocean-going steamers, and, indeed, steam machinery of all
kinds. To be able to work machinery with superheated steam, means to
command increased power with a thirty per cent. reduction in the
consumption of fuel. A principle which can effect such important changes
in the universal application of steam has not remained undiscovered to
the present day. The want of superheated steam has long been felt, and
the enormous comparative advantages of working engines on such a plan
have long been known. A simple and effective working of the principle,
however, has been an engineering difficulty which various
expedients--all, however, sufficiently successful to show the value of
the improvement--have failed to obviate entirely. This obstacle has now,
we believe, been effectually overcome by Mr. Penn, and the value of the
improvement so clearly demonstrated, that the general application of the
principle to steam machinery of every kind may now be regarded as
certain.
"The idea of working engines by superheated steam, and the immense
saving of fuel and increase of power it would effect, was, we believe,
first started many years ago by Mr. Howard, and subsequently by Dr.
Haycraft. The difficulties, however, in the way of its adoption at that
time, and the undue estimate of the importance of the principle,
prevented those gentlemen from realizing very great practical results.
At a later period the matter was again taken up by an American
engineer--Mr. Weatherhead--who, however, only superheated a portion of
the steam and mixed it with common steam in its way to the cylinders.
The success which attended even this partial application of the process
again revived the idea, and encouraged other engineers to turn their
attention to the subject. The result of these renewed efforts is that
several methods of securing the great economy to be effected by
superheating the steam are now under trial, and there is no doubt that a
most important step in the progress of steam, especially as applied to
ocean navigation, is now at last on the point of being successfully
accomplished.
"The value of the improvement on the score of economy in working may be
best illustrated by a single fact--namely, that the Peninsular and
Oriental Company's bill for coal annually amounts to the enormous sum of
700,000_l._, and that by working their vessels with superheated steam
properly applied, it is become almost certain that, without any [Page
437] detriment to the machinery, from 28 to 30 per cent. of this
gigantic outlay can be saved. As to the various proposed methods of
superheating steam, it may be briefly explained, that the conditions
required to be fulfilled are perfect simplicity of arrangement with
ready control over the apparatus; that it should be so placed as not to
be liable to accidental injury in the engine-room; and that the heat
employed for superheating the steam should be waste heat which has
already done its duty in the boilers and is passing away.
"All these conditions have been most satisfactorily fulfilled by Mr.
Penn in the new engines on board the _Valetta_, which were tried down
the Thames for the first time on Thursday. The _Valetta_, as our readers
may remember, was for many years the mail-boat between Marseilles,
Malta, and Constantinople. While thus employed, she had Penn's engines
of 400 horse-power, and to work these up to an average speed of 15 miles
an hour required a consumption of fuel of from 70 to 75 tons of coal per
day. At no time was it less than from 45 to 55 tons. These engines have
now been removed to a vessel nearly double the tonnage of the _Valetta_,
and the latter fitted with engines by Mr. Penn on the superheating
principle. We may mention that, besides this alteration, the _Valetta_
has been considerably improved. A poop and forecastle have been added,
increased accommodation given to passengers, and the whole vessel fitted
up in the richest style. The saloon is one of the simplest and
handsomest things of the kind we have seen, sufficiently lofty and
capacious, and above all, admirably ventilated on the system which is
now being adopted on all sea-going steamers, and the merit of devising
which belongs to Mr. Robinson, of the Peninsular and Oriental Company.
"To return, however, to the engines. Mr. Penn, at the repeated request
of Mr. Allen, the Managing Director of the Peninsular and Oriental
Company, undertook to apply to them the principle of superheating, to
which his attention had many years before been seriously directed by Dr.
Haycraft. His method of doing this is to place in the smoke-box of the
boiler, through which the hot air from the furnace first passes, as
large a number of small pipes as is consistent with allowing a free
draught from the furnaces. Through these all the steam from the boilers
passes in its way to the cylinders. By this plan an immense heating
surface in the pipes is secured, the steam is in a subdivided form, so
as to be readily acted on, and the waste heat from the furnace is
utilized at the point where its intensity is greatest, and where the
greatest conveniences exist for applying the apparatus. By means of
three ordinary stop-valves, the whole contrivance can be shut in or off
from the engines at pleasure. In ordinary engines steam leaves the
boilers at about 250°, but declines from this temperature in its way to
the engines to 230°, undergoing from condensation a still greater and
more serious diminution of heat in the cylinders. From these causes, and
also from the immense quantity of waste heat which escapes through the
smoke-box and up the funnels, there has always been a theoretical loss
of steam power amounting to forty per cent., as [Page 438] compared
with the coal consumed. It is this loss of power and waste of heat which
the superheating process is intended to prevent, and which will, of
course, allow a reduction of from twenty-eight to thirty per cent. on
the fuel now consumed. By the superheating process the steam is raised
in passing along the pipes in the smoke-box (where the heat is about
650°) from a temperature of 250° to 350°, and so enters the cylinders at
100° in excess of the temperature due to its pressure. This extra heat
is, of course, rapidly communicated to the metals, and prevents the
condensation in the cylinders or other parts of the engines, which would
otherwise, of course, take place. Singularly enough, a smaller amount of
cold water is required to condense the steam at this high temperature of
350° than when at the ordinary heat of common steam.
"The trial trip of the _Valetta_ on Thursday was most satisfactory,
not only as regards the engines, but still more so as to the
application for the superheating process. At the measured mile at
the Lower Hope, near the Nore, the result of repeated runs gave an
average speed of nearly 14½ knots per hour, thus realizing with
engines of 260 horse-power, and a small consumption of fuel, the
same rate of speed as had been gained with her previous engines of
400 horse-power, and a consumption of seventy-five tons of coals per
day. The superheating apparatus evidently effected a most important
saving in fuel, but until an average of many days' working can be
obtained, it would be difficult to estimate the exact amount
economized. There seems, however, every reason to believe that an
average of fourteen knots an hour can be obtained with a consumption
of only from twenty-four to twenty-six tons per diem. The
thermometer during the trial indicated in the steam pipes an
addition to the ordinary temperature of 100°, which Mr. Penn
believes to be enough for all practical purposes of superheating.
Even when making from thirty-three to thirty-four revolutions per
minute, and driving the vessel against a strong head wind and tide,
it was impossible to consume all the steam generated, which was
blowing off from both boilers all the trip. The engines are
remarkable for the extraordinary beauty and simplicity of their
proportions, qualities well known in all engines from Penn and Sons,
and which, combined with the strength of the materials and
perfection of the workmanship, make this firm the foremost in the
world for machinery of this description. Both cylinders are
oscillating, of sixty-two inches diameter, and with a stroke of four
feet six inches. The paddles are on the feathering principle, and
the boilers of Lamb and Co.'s patent. During the whole course of the
trials, and when going at one time nearly sixteen knots, there was
no perceptible vibration, even at the end of the saloon nearest to
the engines. When it is remembered that the superheating process
which can effect such important results is capable, as we have said,
of application to steam machinery of every kind, including even
locomotives, it cannot be doubted that the trial of Thursday and its
great success is one of the most important events for the progress
of steam which we have had to chronicle for many years." (_The
Times_, April 23rd. 1859.)
[Page 439]
Whilst speaking of the application of this somewhat novel condition of
steam, it may be observed that many inventors, who have paid little or
no attention to _first principles_, have proposed to apply the vapours
of alcohol, ether, or turpentine, instead of that of water; and they
have founded their notions on the idea that in consequence of the less
latent and sensible heat of alcohol, ether, and turpentine vapour, and
of the small quantity of fuel required to boil them, that they would
compete advantageously with steam. This view of the case, however, is
soon proved to be a very shortsighted one, because the _amount_ of
_expansion_ has been quite overlooked; and if it was desirable, by way
of comparison, to produce a cubic foot of steam, alcohol, ether, or
turpentine, the steam would stand first for cheapness, and would require
the least quantity of fuel to produce it, so that if the more expensive
of combustible liquids could be obtained for nothing, it would still be
cheaper to employ water.
Latent heat, or
equivalent
for fuel.
A cubic foot of water yields 1700 cubic feet of steam = 1000°
A cubic foot of alcohol produces 493 cubic feet = 457°.
Then, by rule of proportion, 493 cubic inches : 457
:: 1700 : 1575°
A cubic foot of ether yields only 212 cubic feet of
vapour = 312°, and 212 : 312° :: 1700 : 2500°
A cubic foot of the oil of turpentine affords 192 cubic
feet of vapour = 183°, and 192 : 183 :: 1700 : 1620°
It will therefore be seen that water, when converted into steam, expands
eight times as much as sulphuric ether, and nearly three times and a
half as much as alcohol.
The application of steam for the purpose of propelling vessels has
already been mentioned in connexion with the Spanish inventor, Blasco de
Garay, in the year 1543. The first patent in this kingdom granted for
that purpose was that of Mr. Jonathan Hull in 1773. In 1787, Mr. Miller
tried a number of important experiments in the propulsion of vessels by
steam-engines, and it would appear that Lord Cullen advocated his ideas,
and endeavoured to secure the co-operation of the great firm of Boulton
and Watt, who, occupied with their land engines, could not pay attention
to it; and twenty years elapsed after the reply of Watt to Lord Cullen's
application, before the real novelty appeared of a first successful
experiment with a steam-boat in "the open sea," by Henry Bell, in 1811.
A picture of this boat, called the _Comet_, which was afterwards
wrecked, is shown at p. 418. Henry Bell's _novelty_ was _success_, and
he is fairly entitled to the merit of first introducing steam navigation
into Europe.
In 1811, the public stared with mingled astonishment and satisfaction at
the realization of that which was called a fable. Only forty-seven years
afterwards another generation spontaneously exhibits the liveliest
interest in the gigantic private speculation of the _Great Eastern_.
[Page 440] Henry Bell's vessel of 1811 was 40 feet keel, 10 feet 6
inches beam, and 25 tons burthen! The _Great Eastern_ of 1859 is 692
feet long, 83 feet wide, 60 feet deep, and 24,000 tons burthen!! The
whole nation with one voice wish her God speed in her projected voyage
across the Atlantic, as the embodiment of that great goodwill which
every generous-hearted Englishman feels towards the enlightened
free-born people of the United States.
Should the author's little vessel, with its humble freight of science,
meet with the approbation of his good friends, the boys and their
advisers, another and another, if health permits, shall be launched for
their benefit. _Vale._
[Illustration]
THE END.
Transcriber's Notes.
Words and phrases in italics are indicated with
underscores thus:- _italics_.
Chapter XV. Experiment one is not indicated by a title heading.
Page 99. "the pulse is raised forty or fifty beats per second" changed
to "the pulse is raised forty or fifty beats per minute"
Page 148. "it is allowed to dry spontaneously, and being coated with
amber varnish (a solution of amber in chloroform) is now ready to print
from. It is, perhaps, hardly necessary to add, that the
sensitizing and developing processes must be performed in a dark room."
Fig. 123. is irrelevant to this section. The reference has been deleted.
Page 365. "an air thermometer has been employed by Sir John Leslie,
under the name of the "Differential Thermometer," in his refined and
delicate experiments with heat. (Fig. 401.)" Ref. to (Fig. 401.)
removed. Fig. 401. not in original hard copy version.
End of Project Gutenberg's The Boy's Playbook of Science, by John Henry Pepper