of the boiler, immediately below the mouths of the tubes: a
powerful draft of air, passing through the fire, carries with it
ashes and cinders, which are driven violently through the tubes,
and especially the lower ones, situated near the fuel. These tubes
are, by this means, subject to rapid wear, the cinders continually
acting upon their interior surface. After a short time it becomes
necessary to replace single tubes, according as they are found to
be worn, by new ones; and it not unfrequently happens, when this
is neglected, that tubes burst. After a certain length of time the
engines require new tubing. This wear of the tubes might possibly
be avoided by constructing the fire-place in a lower position, so
as to be more removed from their mouths; or, still more
effectually, by interposing a casing of metal, which might be
filled with water, between the fire-place and those tubes which
are the most exposed to the cinders and ashes. The unequal
expansion of the tubes [Pg361] and boilers appears to be an
incurable defect, if the present form of the engine be retained.
If the fire-place and chimney could be placed at the same end of
the boiler, so that the tubes might be recurved, the unequal
expansion would then produce no injurious effect; but it would be
difficult to clean the tubes, if they were exposed, as they are at
present, to the cinders. The next source of expense arises from
the wear of the boiler-heads, which are exposed to the action of
the fire.
A considerable improvement was subsequently introduced into the
method of tubing, by substituting brass for copper tubes. I am not
aware that the cause of this improvement has been discovered; but
it is certain, whatever be the cause, that brass tubes are subject
to considerably slower wear than copper ones.
(196.) The expense of locomotive power having so far exceeded what
was anticipated at the commencement of the undertaking, it was
thought advisable, about the beginning of the year 1834, to
institute an inquiry into the causes which produced the
discrepancy between the estimated and actual expenses, with a view
to the discovery of some practical means by which they could be
reduced. The directors of the company, for this purpose, appointed
a sub-committee of their own body, assisted by Mr. Booth, their
treasurer, to inquire and report respecting the causes of the
amount of this item of their expenditure, and to ascertain whether
any and what measures could be devised for the attainment of
greater economy. A very able and satisfactory report was made by
this committee, or, to speak more correctly, by Mr. Booth.
It appears that, previous to the establishment of the railway,
Messrs. Walker and Rastrick, engineers, were employed by the
company to visit various places where steam power was applied on
railways, for the purpose of forming an estimate of the probable
comparative expense of working the railway by locomotive and by
fixed power. These engineers recommended the adoption of
locomotive power; and their estimate was, that the transport might
be effected at the rate of ·278 of a penny, or very little more
than a farthing per ton per mile. In the year [Pg362] 1833, five
years after this investigation took place, it was found that the
actual cost was ·625 of a penny, or something more than a
halfpenny, per ton per mile, being considerably above double the
estimated rate. Mr. Booth very properly directed his inquiries to
ascertain the cause of this discrepancy, by comparing the various
circumstances assumed by Messrs. Walker and Rastrick, in making
their estimate, with those under which the transport was actually
effected. The first point of difference which he observed was the
_speed_ of transport: the estimate was founded on an assumed speed
of ten miles an hour, and it was stated that a four-fold speed
would require an addition of 50 per cent. to the power, without
taking into account wear and tear. Now, the actual speed of
transport being double the speed assumed in the statement, Mr.
Booth holds it to be necessary to add 25 per cent. on that score.
The next point of difference is in the amount of the loads: the
estimate is founded upon the assumption, that every engine shall
start with its full complement of load, and that with this it
shall go the whole distance. "The facts, however, are," says Mr.
Booth, "that, instead of a _full load_ of profitable carriage
_from_ Manchester, about half the waggons _come back empty_; and,
instead of the tonnage being conveyed the whole way, many thousand
tons are conveyed only half the way; also, instead of the daily
work being uniform, it is extremely fluctuating." It is further
remarked, that in order to accomplish the transport of goods from
the branches and from intermediate places, engines are despatched
several times a-day, from both ends of the line, _to clear the
road_; the object of this arrangement being rather to lay the
foundation of a beneficial intercourse in future, than with a view
to any immediate profit. Mr. Booth makes a rough estimate of the
disadvantages arising from these circumstances, by stating them at
33 per cent. in addition to the original estimate.
The next point of difference is the fuel. In the original
estimate, _coal_ is assumed as the fuel, and it is taken at the
price of five shillings and ten-pence per ton: now the act of
parliament forbids the use of coal which would produce smoke; the
company have, therefore, been obliged to use _coke_, at [Pg363]
seventeen shillings and sixpence a ton.[32] Taking coke, then, to
be equivalent to coal, ton for ton, this would add ·162 to the
original estimate.
These several discrepancies being allowed for, and a proportional
amount being added to the original estimate, the amount would be
raised to ·601 of a penny per ton per mile, which is within one
fortieth of a penny of the actual cost. This difference is
considered to be sufficiently accounted for by the wear and tear
produced by the very rapid motion, more especially when it is
considered that many of the engines were constructed before the
engineer was aware of the great speed that would be required.
"What, then," says Mr. Booth, in the Report already alluded to, "is
the result of these opposite and mutually counteracting
circumstances? and what is the present position of the company in
respect of their moving power? Simply, that they are still in a
course of experiment, to ascertain practically the best
construction, and the most durable materials, for engines required
to transport greater weights, and at greater velocities, than had,
till very recently, been considered possible; and which, a few years
ago, it had not entered into the imagination of the most daring and
sanguine inventor to conceive: and farther, that these experiments
have necessarily been made, not with the calm deliberation and quiet
pace which a salutary caution recommends,—making good each step in
the progress of discovery before advancing another stage,—but
amidst the bustle and responsibilities of a large and increasing
traffic; the directors being altogether ignorant of the time each
engine would last before it would be laid up as inefficient, but
compelled to have engines, whether good or bad; being aware of
various defects and imperfections, which it was impossible at the
time to remedy, yet obliged to keep the machines in motion, under
all the disadvantages of heavy repairs, constantly going on during
the night, in order that the requisite number of engines might be
ready for the morning's work. Neither is this great experiment yet
complete; it is still going forward. But the most prominent
difficulties have been in a great measure surmounted, [Pg364] and
your committee conceive that they are warranted in expecting, that
the expenditure in this department will, ere long, be materially
reduced,—more especially when they consider the relative
performances of the engines at the _present time_, compared with
what it was two years ago."
In the half year ending 31st December, 1831, the six best engines
performed as follows:—
Miles.
Planet 9,986
Mercury 11,040
Jupiter 11,618
Saturn 11,786
Venus 12,850
Etna 8,764
——————
Making in all 66,044
——————
In the half year ending 31st December, 1833, the six best engines
performed as follows:—
Miles.
Jupiter 16,572
Saturn 18,678
Sun 14,552
Etna 17,763
Ajax 11,678
Firefly 15,608
——————
Making in all 95,851
——————
(197.) Since the date to which the preceding observations refer,
the locomotive engine has undergone several improvements in detail
of considerable importance; among which, the addition of a third
pair of wheels deserves to be particularly mentioned. An engine
supported on three pair of wheels has great security in the event
of the fracture of any one of the axles,—the remaining axles and
wheels being sufficient for the support of the machine. Connected
with this change is another, recommended by Mr. Robert Stephenson,
by which the flanges are removed from the driving wheels, those
upon the remaining pairs of wheels being sufficient to keep the
engine in its position upon the rails. We shall now describe a
locomotive engine similar in construction to those almost [Pg365]
universally used at present on railroads, as well in this kingdom
as in other countries.[33]
The external appearance of the engine and tender is shown in the
engraving at the head of this chapter. In _fig._ 97. is exhibited
a vertical section of the engine made by a plane carried through
its length; and in _fig._ 98. is exhibited a corresponding section
of its tender,—the tender being supposed to be joined on to the
engine at the part where the connecting points appear to be broken
in the drawing. In _fig._ 99. is exhibited the plan of the working
machinery, including the cylinders, pistons, eccentrics, &c. which
are under the boiler, by the operation of which the engine is
driven. _Fig._ 100. represents the tender, also taken in plan.
In _fig._ 101. is represented an elevation of the hinder end of
the engine next the fire-box; and in _fig._ 102. is represented a
cross vertical section through the fire-box, and at right angles
to the length of the engine, showing the interior of the boiler
above and beside the fire-box, the rivets and bolts connecting the
internal and external fire-boxes, the regulator, steam funnel, and
steam dome.
In _fig._ 103. is represented an elevation of the front of the
engine next the smoke-box, showing the cylinder covers W, buffers
T, &c.; and in _fig._ 104. is represented a section of the
interior of the smoke-box, made by a vertical plane at right
angles to the engine, showing the tube plate forming the foremost
end of the boiler, the branches S of the steam-pipe leading to the
cylinders, the blast-pipe _p_, the cylinders H, and the chimney G.
The same letters of reference are placed at corresponding parts in
the different figures.
The boiler, as has been explained in the engines already
described, is a cylinder placed upon its side, the section of
which is exhibited at A, _fig._ 97. The fire-box consists of two
casings of metal, one within the other. The fire-grate is
represented at D. The tubes by which the products of combustion
are [Pg366] drawn from the fire-box to the smoke-box F are
represented at E. Upon the smoke-box is erected the chimney G. In
the engine from which this drawing has been taken, and which was
used on the London and Birmingham Railway, the boiler is a
cylinder 7-1/2 feet long, and 3-1/2 feet in diameter. It is formed
of wrought-iron plates 5/16 of an inch in thickness, overlapping
each other, and bound together by iron rivets 7/8 of an inch in
diameter and 1-3/4 inch apart. One of these rivets, as it joins
two plates, is represented in _fig._ 95. The boiler is clothed
with a boarding of wood _a_, an inch in thickness, and bound round
by iron hoops screwed together at the bottom. Wood being a slow
conductor of heat, this covering has the effect of keeping the
boiler warm, and checking the condensation of steam which would
otherwise be produced by the rapid motion of the engine through
the cold air.
[Illustration: _Fig._ 95.]
[Illustration: _Fig._ 96.]
The external fire-box, B B, is a casing nearly square in its plan,
being four feet wide outside, and three feet seven and a half
inches long, measured in the direction of the boiler. It is
constructed of wrought-iron plates, similar to those of the
boiler. This box descends about two feet below the boiler, the top
being semi-cylindrical, as seen in _fig._ 102., of a somewhat
greater diameter than the boiler, and concentrical with it. The
front of the fire-box next the end of the boiler has a circular
opening equal in size to the end of the boiler. To the edge of
this opening the boiler is fastened by angle irons, and rivets in
the manner represented in _fig._ 96. These rivets are seen in
section in _fig._ 97.
The internal fire-box C, _fig._ 97., is similar in shape to the
external, only it is flat at the top, and close every where except
at the bottom. Between it and the external fire-box an open space
of three inches and a half is left all round, and on the side next
the boiler this space is increased to four inches. This internal
fire-box is made of copper plates, 7/16 [Pg367] of an inch in
thickness, every where except next the boiler, where the thickness
is 7/8.
As the sides and front of the external fire-box, and all the
surfaces bounding the internal fire-box, are flat, their form is
unfavourable for the resistance of pressure. Adequate means are,
therefore, provided for strengthening them. The plates forming the
internal fire-box are bent outwards near the bottom, until they
are brought into contact with those of the external fire-box, to
which they are attached by copper rivets, as represented at _f_ in
_fig._ 97. The plates forming the bounding surfaces of the two
fire-boxes are fastened together by stays represented at _k_ in
_figs._ 97. and 102. These stays, which are of copper, have a
screw cut upon them through their whole length, and holes are made
through the plates of both fire-boxes tapped with corresponding
threads. The copper screws are then passed through them, and
rivets formed on their heads within and without, as seen in _fig._
102. These screw rivets connect all parts of the plating of the
two fire-boxes which are opposed to each other: they are placed at
about four inches apart over the sides and back of the internal
fire-place and that part of the front which is below the boiler.
[Illustration: _Fig._ 97.
LONGITUDINAL VERTICAL SECTION OF A LOCOMOTIVE ENGINE.]
[Illustration: _Fig._ 98.
LONGITUDINAL VERTICAL SECTION OF THE TENDER.]
[Illustration: _Fig._ 99.
PLAN OF THE WORKING MACHINERY OF A LOCOMOTIVE ENGINE.]
[Illustration: _Fig._ 100.
PLAN OF THE TENDER.]
[Illustration: _Fig._ 101.
ELEVATION OF THE HINDER END OF A LOCOMOTIVE ENGINE.]
[Illustration: _Fig._ 102.
CROSS VERTICAL SECTION OF THE ENGINE THROUGH THE FIRE-BOX.]
[Illustration: _Fig._ 103.
ELEVATION OF THE FOREMOST END OF THE ENGINE.]
[Illustration: _Fig._ 104.
CROSS VERTICAL SECTION OF ENGINE THROUGH THE SMOKE-BOX.]
As the top of the internal fire-box cannot be strengthened by
stays of this kind, ribs of wrought-iron, which are seen in their
length at _l_, in _fig._ 97., and of which an end view is seen in
_fig._ 102., are attached by bolts to it. These ribs are hollowed
out, as seen in _fig._ 97., between bolt and bolt, in order to
break their contact with the roof of the fire-box, and allow a
more free passage to the heat through it. If they were in
continuous contact with the fire-box, the metal composing them
would become more highly heated, and would soon wear out, besides
intercepting heat from the water. This part of the fire-box is
subject to rapid wear, unless care be taken that the level of the
water be preserved at its proper height in the boiler. Even when
the boiler is properly filled, the depth of water above the roof
of the fire-box is not considerable, and on the least neglect the
roof may be exposed to the contact of steam, in which case it will
soon be destroyed.
To prevent accidents arising from this cause, a leaden plug,
[Pg368] represented at _m_, _figs._ 97. and 102., is inserted in
the roof of the internal fire-box. If the water be allowed to
subside, this plug will melt out before the copper is very
injuriously heated, and the steam rushing out at the aperture will
cause the fire to be extinguished.
Copper fire-boxes are almost universally used; but sometimes, from
the consideration of cheapness, the internal fire-box is
constructed of iron.
In the plating which forms the back of the external fire-box, an
oval aperture is formed, as represented in the back view of the
engine, _fig._ 101., for the fire-door _g_. The plating of the
internal fire-box around this aperture is bent at right angles to
meet that of the external fire-box, to which it is fastened by a
row of copper rivets. The fire-door is formed of two plates of
wrought-iron, riveted together with a space of nine inches and a
half between them. The air between these plates being an imperfect
conductor of heat, keeps the outer plate of the fire-door at a
moderate temperature.
In that part of the surface of the internal fire-box which forms
the end of the boiler, holes are made to receive the extremities
of the tubes, by which the air proceeding from the fire is drawn
to the smoke-box at the remote end of the boiler. These tubes are
represented in longitudinal section at E, _fig._ 97., and their
ends are seen in the surface of the internal fire-box in _fig._
102., and in the remote end of the boiler where they terminate in
the smoke-box in _fig._ 104. These tubes are formed of the best
rolled brass, and their thickness in the engine, to which we now
refer, is 1/13 of an inch. After the brass plating is bent into
the form of a tube, and being overlapped, is properly soldered
together, and the edges smoothed off, the tubes are made perfectly
cylindrical by being drawn through a circular steel die.
[Illustration: _Fig._ 105.]
The tube-plates (as those parts of the boiler ends in which the
tubes are inserted are called) are bored with holes in corresponding
positions, truly cylindrical, and corresponding in magnitude to the
tubes, so that the tubes, when passed into them, will be just in
contact with them. The length of the tubes is so regulated, that
when extending from end to end of the boiler, and passing through
the holes, they shall [Pg369] project at each end a little beyond
the holes. The manner of fastening them so as to be water-tight is
as follows:—A steel hoop or ferrule, made slightly conical, a
section of which is exhibited at C. _fig._ 105., the smaller end of
which is a little less than the internal diameter of the tube, but
which increases towards the outer end, is driven in as represented
in the figure. It acts as a wedge, and forces the tube into close
contact with the edges of the hole in the tube-plate.
When particular tubes in a boiler are worn out, and require to be
replaced, their removal is easily effected. It is only necessary
to cut the steel ferrule on the inside, and to bend it off from
contact with the tube, by which means it can be loosened and
withdrawn, and the tube removed.
In the engine to which this description refers there were one
hundred and twenty-four tubes, the external diameter of which was
1-5/8 inch. The distance between tube and tube was 3/4 of an inch.
The number of tubes vary in different engines, some having so many
as one hundred and fifty, while the number in some is less than
ninety. The evaporating power of an engine greatly depends on the
proper number and magnitude of its tubes; and the experience which
engineers have had on railways have led them gradually to increase
the number of tubes, and diminish their magnitude. In the Rocket,
already mentioned as having gained the prize on the opening of the
Liverpool and Manchester Railway, the number of tubes was
twenty-four, and their diameter three inches; but in all the
engines subsequently made their number was augmented, and their
diameter diminished. The practical inconvenience which limits the
size of the tubes is their liability to become choked by cinders
and ashes, which get wedged in them when they are too small, and
thereby obstruct the draft, and diminish the evaporating power of
the boiler. The tubes now in use, of about an inch and a [Pg370]
half internal diameter, not only require to be cleared of the
ashes and cinders, which get fastened in them after each journey,
but it is necessary throughout a journey of any length that the
tubes should be picked and cleaned by opening the fire door at
convenient intervals.
The substitution of brass for copper tubes, which has been already
mentioned as so great an improvement in the construction of
locomotive engines, is ascribed to Mr. Dixon, who suggested them
in 1833, being then the resident engineer of the Liverpool and
Manchester Railway. They are said to last six or eight times as
long as copper tubes of the same dimensions.
When tubes fail, they are usually destroyed by the pressure of the
water crushing them inwards: the water enters through the rent made
in the tube, and flowing upon the fire extinguishes it. When a
single tube thus fails upon a journey, the engine, notwithstanding
the accident, may generally be made to work to the end of its
journey by plugging the ends of the broken tube with hard wood; the
water in contact with which will prevent the fire from burning it
away.
Tubes of the dimensions here referred to weigh about sixteen
pounds, and lose from six to seven pounds before they are worn
out. Their cost is about one pound each.