Chapter XXII: Part I: Locomotives (1)

As the locomotive engine is the power by which railroads are worked, and as its proportions and dimensions are so intimately connected with the physical character of the road, it is thought proper to take space enough at this point to examine the general principles of its construction, and of its adaptation to the work required of it upon railroads.

Under the general principles, we recognize the production and consumption of steam, the disposition of weight upon the several pairs of wheels which shall secure the necessary adhesion, the application of the power generated in the boiler to the moving of the wheels, and that general arrangement of parts which shall render the use of power economical.

BIRTH AND GROWTH OF THE LOCOMOTIVE.

294. The first idea of the application of steam to locomotion, is due to the unfortunate Solomon de Caus, of Normandy (France), who was confined in a madhouse for insisting that steam could be made to move wheeled carriages.

295. In the year 1784, William Murdoch, the friend and assistant of James Watt, built a non-condensing steam locomotive engine, on a scale of about one inch per foot, having

Cylinders, ¾ × 2 inches,
Wheels, 9½ inches,
and Weight, 10 lbs.

This little engine, however, accomplished the speed of ten miles per hour.

296. In 1802, Richard Trevethick patented the application of the non-condensing steam-engine to the propelling of carriages on railroads; his engine was fitted with one horizontal cylinder, which applied its power to the wheels by means of spur gear.

297. In 1825, the truck was first applied, to relieve the driving wheels of a part of the weight, and to enable the engine to pass freely around curves.

298. In 1827, Timothy Hackworth applied the blast pipe, for the purpose of draft. He applied, also, spring balances to the safety-valves, and used the waste steam to heat the feed water. This engine drew one hundred tons, at five miles per hour, and forty-five tons on a fifty feet grade.

299. In 1828, M. Seguin (France) introduced the multitubular boiler.

300. In 1829, the directors of the Liverpool and Manchester Railroad offered a premium for the best locomotive, which should draw three times its own weight, at ten miles miles per hour. The “Rocket,” by Robert Stephenson, of Newcastle on Tyne, was the successful competitor, and drew the load required, seventy miles, at an average speed of 13.8 miles per hour; its maximum velocity was twenty-nine miles per hour; it evaporated 5.4 lbs. of water per pound of coke, and 18.24 cubic feet per hour of water.

301. From 1830 to 1840, the changes that were made were rather those of dimension, proportion, and arrangement, than of essential elements of steam producing.

302. In 1840, several truck frame engines were sent to England from the Norris Works of Philadelphia. These locomotives would draw a load of one hundred and twenty tons over a sixteen feet grade, at the rate of twenty miles per hour.

303. In 1845, the Great Western Railroad, of England, was supplied with an engine of twenty-two tons weight, having cylinders 15¾ × 18, wheels 7 feet, heating surface 829 square feet. This locomotive carried seventy-six and one half tons at a velocity of fifty-nine miles per hour. The consumption of coke was 35.3 lbs. per mile, and of water, 201.5 cubic feet per hour.

THE ENGLISH LOCOMOTIVE OF 1850.

304. The “_ne plus ultra_” for the seven feet gauge (Great Western Railway) by Gooch, has inside cylinders 18 × 24 inches, one pair of eight feet driving wheels, grate area twenty-one square feet. Fire-box surface, one hundred and fifty-three feet. Three hundred and five two inch tubes, giving 1,799 feet of surface. Total heating surface, 1,952 square feet. Weight of engine, empty, thirty-one tons; of tender, eight and one half tons; whole weight with wood and water, fifty tons. Evaporating power, three hundred cubic feet of water per hour. This engine can draw two hundred and thirty-six tons, at forty miles per hour.

The maximum for the London and North-western Railroad, four feet, eight and one half inches gauge (Crampton’s patent), has cylinders 18 × 24 inches; wheels, eight feet; two hundred two and three sixteenths inch (outside diameter) tubes; grate, twenty-one and one half square feet; fire surface, one hundred and fifty-four feet; tube surface, 2,136 feet; whole heating surface, 2,290 square feet; weight, loaded, thirty-five tons; twelve tons upon driving wheels; tender, twenty-one tons, loaded; whole weight, fifty-six tons.

THE AMERICAN LOCOMOTIVE OF 1855.

305. The engine “Charles Ellet, Jr.,” drew on the 9th of August, 1854, forty tons, over a grade of two hundred and seventy-five feet per mile, and over grades of two hundred and thirty-eight feet, upon curves of three hundred feet radius. This engine has wheels four and one half feet in diameter coupled seven feet apart; cylinders 14 × 26 inches; and weighs, including wood and water, 53,058 lbs. This is a tank locomotive, the tender is dispensed with, and in its room a tank containing one hundred cubic feet of water, and one cord of wood is used. This engine was built by Richard Norris and Son.

An engine built by the Cuyahoga Steam Furnace Co. of Cleveland, Ohio, performed the following feat.

An ordinary passenger train was carried one hundred and one miles, over a total ascent of 1,255 feet of grades, making twenty stops, at an average speed of twenty-five miles per hour, with a consumption of only ninety cubic feet of wood.

The same engine drew an average load of three and one third cars four hundred and thirty miles, making seventy-five stops, surmounting a total ascent of 5,439 feet, averaging twenty-five miles per hour, with one tender full of wood only.

In the months of July and August, 1856, two engines upon the Pacific Railroad (Missouri), one by R. K. and G., and one by Palm & Robertson, ran each one hundred and twenty-five miles, with three passenger and one baggage cars, using only one cord of wood.

NOTE.—For an interesting example of what can be done by the American
locomotive, and an illustration of engineering peculiarly American,
the reader is referred to a description of the “Mountain top track”
at the Rock-fish Gap crossing of the Blue Ridge (Va.), by the
Virginia Central Railroad, given by the engineer under whose
direction the work was proposed and executed (Charles Ellet, Esq.),
from which is extracted the following:—

“The eastern slope is 12,500 feet long, and rises 610 feet; the
average grade being 2574/10 feet, and the maximum 29568/100 feet per
mile. The least radius of curvature 234 feet; upon which curve the
grade is 2376/10 feet per mile. The western slope is 10,650 feet
long, and falls 450 feet; the average grade being 223⅒, and the
range 27984/100 feet per mile.

“The engines, which have taken loads ranging from twenty-five to
fifty tons up one slope at seven and one half miles per hour, and
down the opposite one at six miles per hour, making four trips of
eight miles per day for three years, were designed and built by M.
W. Baldwin & Co., Philadelphia, and have three pair of forty-two
inch wheels all coupled, the flange base being 9′ 4″, cylinders 16½
× 20 inches, weigh, with wood and water, 55,000 lbs., or
twenty-seven and one half tons. They run without a tender, the
engine carrying its own feed; thus gaining the double advantage of
increasing the adhesion of the engine, and avoiding the resistance
of a tender.”

GENERAL DESCRIPTION.

306. The locomotive is a non-condensing, high pressure engine, working at a greater or less degree of expansion, according to the labor to be performed, and placed upon wheels which are so connected with the piston, that any motion of the latter is communicated to the former, by which the whole is moved.

The power exerted in the cylinder and referred to the circumference of the driving wheel, is called _traction_; its amount depends upon the cylinder diameter and steam pressure, upon the diameter of wheel and stroke, this latter being the distance between the wheel centre and point of application of power.

The means by which the “traction” is rendered available for moving the engine and its load, is the resistance which the wheel offers to slipping on the rail, or its bite, and is called adhesion; it is directly as the weight applied to the wheels, but depends also upon the state of the rails. It varies from nothing, when there is ice on the rail, to one fifth of the weight upon the driving wheels when the rail is clean and dry, and in some cases has reached as high as nearly one third. It should be enough to resist the maximum force of traction, that is, the wheel should not slip when the engine is doing its greatest work.

_Steam producing_, _Traction_, and _Adhesion_, are the three elements which determine the ability of an engine to perform work. The proportions and dimensions of the machine depend upon the duty required of it; sufficient adhesion for a required effect should be obtained rather by a proper _distribution_, than by _increase_ of weight.

Fig. 150 shows the relative position of parts in the locomotive engine as at present constructed in America.

1 2, Grate upon which the fuel is placed. 1 2 3 4, Interior fire-box. 5 6, Exterior fire-box. 7 7 8 8, Shell of the boiler. 9 9, Boiler flues. 10 11 12 13, Exhaust chamber, or smoke box. 14, Steam dome, entrance to steam pipe. 15, Steam pipe. 16, Piston. 18, Piston rod. 19, Connecting rod. 20, Crank. 21, Driving wheel. 22, Blast pipe. 23, Chimney. 27 28, Leading wheels, supporting the front end of the engine, turning on a swivel, 29. 30, “Blow off” safety-valve.

307. The operation of generating and applying steam for the production of motion is as follows:—

The boiler and the space between the two fire-boxes being filled with water, (high enough at least to cover the flues and the top of the inner box,) fire is applied to the fuel placed upon the grate; the heat which fills the fire-box and tubes, is communicated to the water and converts the same to steam; which entering the mouth of the pipe, 15, flows to the cylinder, where it forces the piston to the end of the stroke. This motion is transferred through the connecting rods and cranks to the wheels, which revolving, move the engine upon the rails. At the same time the eccentrics, placed upon the driving axle, give a motion to the valve gear, and thence to the valves, by which the admission of steam is stopped at the first end of the cylinder, and commenced at the other. The volume of steam which entered during the first half stroke is forced out of the cylinder by the returning piston, up the blast pipe, and out at the chimney, where a vacuum is produced, which can be supplied with air only from the chamber 10 11 12 13; after a few strokes the air is exhausted from the _chamber_, which can be refilled only by the external air _drawn through the fuel, furnace, and tubes_. The more complete this vacuum, the stronger the current of air drawn through the fire, which (current) is the draft. The admission of fresh air is regulated by a damper placed at 2. The fuel is placed upon the grate by means of a door in the rear of the fire-box. The necessary height of water is maintained in the boiler by pumps worked by the engine, in such a manner as to secure at all times the proper supply. The proportions and dimensions of the boiler, the engine, and the carriage, with the rules for obtaining the same will be considered shortly.

DUTIES EXPECTED OF LOCOMOTIVE ENGINES.

308. The work required of any engine depends upon the nature and amount of traffic, and upon the physical character of the road.

The nature of the traffic, whether bulky or compact, and whether requiring quick or slow transport, determines somewhat the number and size of the trains, and consequently the number and power of the engines.

A road with steep grades and sharp curves, with the same amount of traffic, will need stronger engines than a road with easy grades and large curves.

The amount of motive power and cost of working it, depends in a great degree upon the disposition of grades as regards the direction of the traffic movement. The most economically worked road will be either a level one, or one where the bulk of the traffic is moved _down_ hill.

The mineral, commercial, or agricultural nature of the country, determines the direction of the traffic, and the physical nature, the arrangement of the grades.

The different kinds of labor required of locomotives, necessitate the employment of engines of different proportions; and the different classes of railways, require engines possessing different amounts of power.

309. The classification of locomotives should be determined according to the following relations.

_Department_ depends upon commercial duty.
_Division_ depends upon character of road.
_Order_ depends upon weight of trains.
_Class_ depends upon speed of trains.

NOTE.—The general classification is given at the end of this
chapter.

High rates of speed are generally combined with light loads, and heavy trains are required to move at the lower velocities.

Great speeds require the rapid production and consumption of a large bulk of steam of but little density; large wheels and short stroke, that the ratio of velocities of piston and wheel may be as great as possible.

Heavy trains consume less steam by bulk, per mile, but of a much greater density, and combine a long stroke with a small wheel, by which great leverage is obtained.

In general, engines for winter use should be heavier than those for summer, upon the same ground, as natural causes are more liable to resist adhesion in the winter.

The locomotive engine may be so proportioned as to run at any speed from ten to sixty miles per hour, over grades from ten to two hundred feet per mile, and to carry loads from two hundred to two thousand tons.

The rules by which the necessary dimensions to perform any required duty are fixed, depend upon the very simplest mechanical laws.

NOTE.—The formulæ expressing the most proper relations to exist
between the several steam-producing and steam-consuming parts are
more reliable than the assertions of any machinist in America, and
though taken from books, are the result of the experience of the
most able and practical men for twenty years. Operatives are too apt
to despise book knowledge, forgetting that the very knowledge so
despised is the result of more practice than a lifetime can afford
them. Railroad managers are too apt to receive as indisputable, the
opinions of men who are _practical_, simply because they understand
nothing of _principle_.

Since the work of D. K. Clark (England) has appeared, any dimension
from the beginning to the end of a locomotive may be fixed, to the
eighth of an inch, with absolute correctness, and there is no excuse
for departing from the proper proportions. It does not follow that
because a locomotive does actually start off and draw the train,
that it is properly made. A race-horse can draw a plough, and a yoke
of oxen a “trotting buggy,” but this is by no means the correct
adaptation of power.

310. The elements which govern the requirements of power are

The maximum grades.
The weight of the train.
The required speed.

And the elements which govern our ability to produce the power needed,

The grate area.
The heating surface.
The cylinder diameter.
The steam pressure.
The stroke.
The diameter of wheels.
The weight upon driving wheels.

MECHANICAL AND PHYSICAL PRINCIPLES GOVERNING THE CONSTRUCTION OF THE
LOCOMOTIVE ENGINE.

RESISTANCE TO THE MOTION OF RAILROAD TRAINS.

311. The exact resistance to the motion of a railroad train cannot be determined, as some of the elements are so variable; for example, the state of the weather. An approximate estimate, near enough for practice, is easily obtained. To arrive at correct data the observations must be made upon trains working under the same conditions that they are subject to in practice.

The whole resistance is made up of several partial resistances, some of which are constant at all speeds, and some of which increase with the velocity.

The engine and tender resistance is composed of the friction of pistons, cross heads, slide valves, cranks, eccentrics, pumps, the back pressure of the blast, and various erratic movements, rolling, twisting, and pitching together with both wheel and axle friction, which is common to the engine and tender.

The atmospheric resistance is not due to the direct action of the air upon the front and sides of the train entirely, but chiefly to the exhausting action in the rear. The train has, as it were, to pull along a large column of air like the water in the wake of a ship; form or amount of frontage has little or no effect. The resistance depends upon the bulk of the train and its velocity. A train with the same frontage offers more resistance as its bulk increases.

Oscillatory resistance is caused by irregularities in the surface of the rails, and increases with the velocity, and also with increase of height of the centre of gravity of the car or engine.

Frictional resistance may be divided into wheel and axle friction. That of the axle is composed of two parts, the direct vertical friction on the journal, and the side friction on the collar, consequent upon lateral motion. The vertical friction is independent of the surface pressed or of velocity, but is directly proportional to the pressure, and the same remark applies to that of the collars. As the diameter of wheel increases, the oscillation is increased, the centre of gravity being raised. The direct cause of the vertical friction is the weight of the car or engine, and of the lateral irregularities in the surface of the rails, which cause the car to sway from side to side. Wheel friction which acts between the periphery of the wheel and the surface of the rail increases with the load, and decreases as the wheel diameter augments.

For the total resistance to the motion of a railroad train, D. K. Clark gives the following formula:—

(_V^2_)/171 + 8 = _R_,

Where _R_ is the resistance in lbs. per ton,
and _V_ the velocity in miles per hour.

From this expression we form the following table:—

Velocity in miles per hour. Resistance in lbs. per ton.
10 8.585
12 8.842
15 9.315
20 10.339
25 11.655
30 13.263
40 17.356
50 22.620
60 29.052
100 66.480

From a great number of experiments made by Mr. Clark, the relative resistance to the motion of inside and outside connected engines is as follows:—

Inside connections 17
Outside connections 14

The effect of curves, bad state of the road, and adverse winds, amounts (according to the same author) to the following percentages:—

Bad state of the road 40
Curves 20
Strong head and side winds 20
—
In all 80

The resistance due to grades depends entirely upon the rate of incline, and is quite independent of all other considerations. The _relative_ effect of grades decreases with the absolute increase of resistance on a level. Thus common roads admit of steeper grades than do railroads, because the level resistance is much more upon the former than on the latter.

The exact determination of the resistance due to any grade depends upon the very simple mechanical principle, regulating motion upon the inclined plane. For each foot rise of grade per mile, the resistance per ton is

2240 × 1/5280.

Thus the resistance to one ton upon a forty feet grade is

2240 × 40/5280 or 17 lbs.

And if we are moving at thirty miles per hour the sum of all other resistances is, by the formula, or the table at the end of Chapter XIV., part I., 13.3 lbs. per ton; whence the whole resistance to the motion of one ton, at thirty miles per hour, upon a forty feet grade, is

17 + 13.3 or 30.3 lbs.

and one hundred tons would be one hundred times as much. Table 1, at the end of Chapter XIV., part I., gives the whole resistance to the motion of trains of from fifty to one thousand tons, moving at speeds varying from ten to one hundred miles per hour, and table 2 gives the resistance upon grades from ten to one hundred feet per mile.

TRACTION AND ADHESION.

312. The whole steam pressure upon both pistons, referred by means of the crank, connecting, and piston rods, and wheel, to the rail, is called “traction.” It is the _drawing_ power of the engine. Its amount depends upon the diameter of cylinder, steam pressure, stroke, and diameter of wheel.

By increasing the steam pressure, we increase the power. By increasing the cylinder diameter, we increase the power. By increasing the stroke, we increase the power. By decreasing the wheel diameter, we increase the power. And by adjusting the dimensions of the above parts, we may give any desired amount of power to the engine.

The formula expressing the tractive power of an engine, of any dimensions, is

((2_A_) _P_ × 2_S_)/_C_.

Where _A_ = the area of one piston.
_P_ = the steam pressure in cylinder per square inch,
_S_ = the stroke in inches.
_C_ = the circumference of the wheel in inches.

The formula is expressed verbally as follows: Double the stroke and multiply it by the total steam pressure on both pistons; divide the product by the circumference of the driving-wheel in inches.

ADHESION.

313. As observed on page 307, the adhesion or the bite of the wheels upon the rail is, as an average, from one fifth to one sixth of the weight; one fifth when the rail is in a good state, and less when wet or greasy; we cannot depend upon more than one sixth in practice. Therefore, if the tractive power of an engine is 3,000 lbs. we must, to make it available, place 3,000 × 6 or 18,000 lbs. upon those wheels which are connected with the machinery, (driving wheels).

FUEL.

314. The fuels employed in the locomotive engine for the evaporation of water are wood, coal, and coke. In England the latter is used exclusively. In America the first has, on account of its cheapness, been quite generally adopted; but of late railroad companies have been turning their attention to coal and coke.

The immense beds of coal distributed throughout the United States will furnish fuel to railroad companies almost without limit. Its position as well as its amount will render its adoption practicable in nearly all of the States. Ohio alone contains more coal than all of Great Britain. The following table is from the iron manufacture of Frederick Overman.

Name of State. Area of Coal-fields.
Georgia 150 square miles.
Maryland 550 square miles.
Alabama 3,400 square miles.
Tennessee 4,300 square miles.
Michigan 5,000 square miles.
Missouri 6,000 square miles.
Indiana 7,700 square miles.
Ohio 11,900 square miles.
Kentucky 13,500 square miles.
Pennsylvania 15,437 square miles.
Virginia 21,195 square miles.
Illinois 44,000 square miles.
———————
In all 133,132 square miles.

315. The following table (also from the works of Overman) gives the nature and evaporative power of the different American coals.

┌────────────────────┬──────┬──────────┬──────────┬────────┬──────────┐ │ │State │ │ Steam of │Quantity│Percentage│ │ Name of Coal. │where │Percentage│ 212° │of heat │of coke by│ │ │found.│of carbon.│evaporated│ by │ weight. │ │ │ │ │ per lb. │volume. │ │ ├────────────────────┼──────┼──────────┼──────────┼────────┼──────────┤ │ │ │ │ │ │ │ │ _Anthracite._ │ │ │ │ │ │ │Beaver Meadow, │ Pa. │ 88.9 │ 10.4│ 94 │ │ │Forest Improvement, │ Pa. │ 90.7 │ 10.8│ 94 │ │ │Lehigh, │ Pa. │ 89.1 │ 9.6│ 94 │ │ │Lackawanna, │ Pa. │ 87.7 │ 10.7│ 94 │ │ │ │ │ │ │ │ │ │ _Coke._ │ │ │ │ │ │ │Midlothian, │ Va. │ │ 10.3│ 92 │ .66 │ │Cumberland, │ Md. │ │ 10.3│ 92 │ .75 │ │ │ │ │ │ │ │ │ _Bituminous._ │ │ │ │ │ │ │Maryland, │ Md. │ 73.5 │ 11.2│ 85 │ │ │Cumberland, │ Md. │ 74.3 │ 11.0│ 85 │ │ │Blossburg, │ Pa. │ 73.4 │ 10.9│ 85 │ .83 │ │Karthans, │ Pa. │ 73.8 │ 9.8│ 85 │ .88 │ │Cambria County, │ Pa. │ 69.4 │ 10.2│ 85 │ │ │Clover Hill, │ Va. │ 56.8 │ 8.5│ 85 │ .68 │ │Tippecanoe, │ Va. │ 64.6 │ 8.5│ 85 │ │ │Pittsburgh, │ Pa. │ 55.0 │ 8.9│ 85 │ .68 │ │Missouri, │ Mo. │ │ │ │ .57 │ └────────────────────┴──────┴──────────┴──────────┴────────┴──────────┘

316. The employment of the several varieties of wood depends more upon the commercial than the chemical character. The following table shows the specific gravity, the nature and the evaporative value of the different species.

┌────────────┬────────┬────────┬────────┬──────────┬────────────┐ │ Species. │Specific│Specific│Specific│Degrees of│ Species. │ │ │gravity │gravity │gravity │heat which│ │ │ │ green. │ air │ kiln │ may be │ │ │ │ │ dried. │ dried. │generated.│ │ │ │ │ │ │ │ │ ├────────────┼────────┼────────┼────────┼──────────┼────────────┤ │Hickory, │ │ │ │ 3000 │Hickory. │ │White Oak, │ 1.07 │ 0.71 │ 0.66 │ 3000 │White Oak. │ │Black Oak, │ │ │ │ 3000 │Black Oak. │ │Red Oak, │ 1.05 │ 0.68 │ 0.66 │ 3000 │Red Oak. │ │Beech, │ 0.98 │ 0.59 │ 0.58 │ 3000 │Beech. │ │Birch, │ 0.90 │ 0.63 │ 0.57 │ 3000 │Birch. │ │Maple, │ 0.90 │ 0.64 │ 0.61 │ 3000 │Maple. │ │Yellow Pine,│ │ │ │ 2800 │Yellow Pine.│ │Chestnut, │ │ │ │ 3000 │Chestnut. │ │Pitch Pine, │ │ │ │ 2800 │Pitch Pine. │ │White Pine, │ 0.87 │ 0.47 │ 0.38 │ 2800 │White Pine. │ ├────────────┼────────┼────────┼────────┼──────────┼────────────┤ │ Species. │Specific│Specific│Specific│Degrees of│ Species. │ │ │gravity │gravity │gravity │heat which│ │ │ │ green. │ air │ kiln │ may be │ │ │ │ │ dried. │ dried. │generated.│ │ │ │ │ │ │ │ │ └────────────┴────────┴────────┴────────┴──────────┴────────────┘

┌────────────┬──────────┬────────┬──────┬────────┬────────────┐ │ Species. │Percentage│Quantity│Weight│Relative│ Species. │ │ │ of │of heat │of one│value as│ │ │ │Charcoal. │ as to │ cord │ fuel. │ │ │ │ │volume. │ in │ │ │ │ │ │ │ lbs. │ │ │ ├────────────┼──────────┼────────┼──────┼────────┼────────────┤ │Hickory, │ 44.69 │ 25 │ 4469 │ 1.00 │Hickory. │ │White Oak, │ 21.62 │ 25 │ 3821 │ 0.81 │White Oak. │ │Black Oak, │ 23.80 │ 25 │ 3254 │ 0.71 │Black Oak. │ │Red Oak, │ 22.43 │ 25 │ 3254 │ 0.69 │Red Oak. │ │Beech, │ 32.36 │ 25 │ 3236 │ 0.65 │Beech. │ │Birch, │ │ 25 │ │ │Birch. │ │Maple, │ 27.00 │ 25 │ 2700 │ 0.57 │Maple. │ │Yellow Pine,│ 24.63 │ 23 │ 2463 │ 0.54 │Yellow Pine.│ │Chestnut, │ 25.25 │ 25 │ 2333 │ 0.52 │Chestnut. │ │Pitch Pine, │ 19.04 │ 23 │ 1904 │ 0.43 │Pitch Pine. │ │White Pine, │ 18.68 │ 23 │ 1868 │ 0.42 │White Pine. │ ├────────────┼──────────┼────────┼──────┼────────┼────────────┤ │ Species. │Percentage│Quantity│Weight│Relative│ Species. │ │ │ of │of heat │of one│value as│ │ │ │Charcoal. │ as to │ cord │ fuel. │ │ │ │ │volume. │ in │ │ │ │ │ │ │ lbs. │ │ │ └────────────┴──────────┴────────┴──────┴────────┴────────────┘

Of the relative value of wood and coal, we have the following results of experience.

In the engines of the Baltimore and Ohio Railway 2.55 lbs. of pine wood were found equal to one pound of Cumberland coal.

On the Reading Railroad (Pennsylvania), three pounds of pine wood equal to one pound of Anthracite coal.

Mr. Haswell estimates the best varieties of wood fuel to contain twenty per cent. of carbon.

Walter R. Johnson found that one pound of wood, upon an average, evaporated two and one half pounds of water.

The average percentage of coke from American bituminous coal from the above table is seventy-three per cent., and the average percentage of carbon, sixty-seven and one half per cent.

317. The following table shows the relative properties of good coke, coal, and wood.

┌───────────────────────────────────────────────────┬─────┬─────┬─────┐ │ Name of fuel. │Coke.│Coal.│Wood.│ ├───────────────────────────────────────────────────┼─────┼─────┼─────┤ │Weight per cubic foot, in lbs. │ 63 │ 80 │ 30 │ │Degrees of heat generated. │4300 │4000 │2800 │ │Percentage of carbon, in the fuel. │ 95 │ 88 │ 20 │ │Economic bulk, or cubic feet required to stow one │ 80 │ 44 │ 107 │ │ ton. │ │ │ │ │Economic, or stowage weight per cubic foot. │ 28 │ 51 │ 21 │ │Cubic feet of air to evaporate one lb. of water. │22.4 │ 32 │ 16 │ │Equivalent economic bulk, to evaporate the same │ 13 │ 10 │ 60 │ │ weight of water. │ │ │ │ │Weight of water evaporated per lb.of fuel in │ 8½ │ 6 │ 2½ │ │ ordinary practice. │ │ │ │ │Relative value as fuel, disregarding the actual │ 100 │ 71 │ 29 │ │ cost. │ │ │ │ └───────────────────────────────────────────────────┴─────┴─────┴─────┘

The power of fuel depends upon the amount of carbon in it.

Pure coke is solid carbon.

Hence its superior value as a heat generator.

OF THE PROCESS OF COKING.

318. Anthracite coal is used for locomotive fuel in its natural state. It is employed chiefly upon those roads on the eastern slope of the Alleghanies. The bituminous coal lies in the Mississippi valley, and may be found anywhere between the summits of the Alleghanies and the Rocky Mountains. This, in its natural state, contains so much pitchy matter as to render it unfit for locomotive purposes. Upon being heated, it melts, runs into a mass, and clogs the grate; requiring frequent poking and a strong draft. But when the bitumen is burnt off by slow and careful baking, (as described below,) no fuel equals it.

Just as carbonized wood is charcoal, so carbonized coal is coke. Coke is bituminous coal deprived of its bitumen, the raw coal being baked in ovens having vents so regulated as to admit air enough to char, without consuming the coal. The ovens being closed at the proper time, the fire is gradually extinguished, and the coke, compacted into large masses, requiring to be broken up before taken out. Coal may be coked by piling loosely in heaps, covering with earth, and firing through openings, which, after forty or fifty hours, are closed. In preparing coke, however, in the large quantities required for railroads, and that it may be of the very best quality, a good deal of care must be taken.

Probably in no place more or better coke is made, or the operation more skilfully carried on, than at the Camden-town station of the London and North-western Railroad, (England).

The company have built eighteen ovens, in two rows, all discharging their volatile gases into a horizontal flue terminating in a chimney one hundred and fifteen feet high; having an internal diameter of eleven feet, and being three feet thick, (making the external diameter seventeen feet). The ovens are elliptical, 11 × 12 feet inside, with walls three feet thick. The height is ten feet, the first three feet from the ground being solid, and furnished with a fire brick floor, on which the coal is placed. Each oven communicates with the flue by an opening in the top two and one half feet by twenty-one inches; which opening is closed by an iron damper, to regulate the draft. The openings for the doors are three and one half feet square outside, and two and three fourths inside, being closed with iron doors four and one half by five feet, lined with fire brick, and balanced in opening by counterweights. (The object of the chimney and horizontal flue is to carry the smoke and unburned gases so far up that they shall not be a nuisance. In America we might allow the smoke of each oven to escape through a low chimney of its own, (ten or twelve feet high,) and save the cost of a large stack; like the coking ovens in our foundries).

The operation of coking is carried on as follows:—Each alternate oven is charged between eight and ten A. M. every day, with three and one half tons of good coals. A whisp of straw is then thrown in, which takes fire from radiation from the top, and inflames the smoke then arising from the surface, by the reaction of the hot sides and bottom upon the body of the fuel. In this way the smoke is consumed at the very point of the process, where it would otherwise be the most abundant. The coking process is a complete combustion of the volatile principles of the coal. The mass of coal being first kindled at the surface, where it is supplied with an abundance of oxygen, because the doors in front and vents in the rear are open, no more smoke goes from the chimney than from that of a common kitchen fire. The gas generated from the slightly heated coal cannot escape destruction in passing up to the bright flame of the oven. Any deficiency in oxygen for consuming the smoke is supplied by the air entering the grooves of the dampers.

As the coking process advances most slowly from the top to the bottom, only one layer is consumed at a time; while the surface is covered with red-hot cinders, ready to consume any particles of carburetted or sulphuretted hydrogen gases which may escape from below. The greatest mass cannot emit more gases than the smallest heap.

The coke being perfectly freed from all smoky and volatile matters, by a calcination of forty hours, is cooled down to a moderate ignition by sliding in the dampers and opening the doors, which had been partly closed during the latter part of the operation.

The coal is now converted into a clean, crystalline, porous, columnar mass, of a steel-gray color, and so hard as to cut glass. This is broken up and taken out—coke. It is sometimes extinguished by a watering-pot. This is wrong, it ought not to be wet, and even more, ought to be immediately shut up in fire-proof boxes and bins. Even left to itself in the air, it absorbs moisture rapidly, which must be burned off in the boiler; it should by all means be kept in a dry place. Mr. Woods (England) observes, that coke may absorb as much as eight per cent. of water in going from the oven to the storehouse. The amount of absorption depends upon the nature of the coke. D. K. Clark records the following, the coke being immersed in water.

No. 1. Close-grained and good, absorbed 14.5 per cent. of water.

No. 2. Porous and ordinary, absorbed 21 per cent.

No. 3. Very close-grained and good, 9 per cent.

The time of coking may be stated generally as fifty hours, though it is somewhat improved by being allowed forty hours more; this gives time for a better consolidation, and gives a firmer, brighter, and more crystalline mass.

Mr. Gooch, of the Great Western (England) Railroad, experimented upon the time of coking with the following results.

In oven. Yield per ton of Water evaporated Result.
coal. per lb. of coke.
48 hours 12.71 cwt. 7.1 lbs. 902.
72 hours 12.00 cwt. 7.7 lbs. 924.

Thus, though the yield per ton is decreased by a greater time, the value of the coke per pound is augmented, and the increase overbalances the decrease.

Firstrate coal gives from seventy-five to eighty per cent. by weight, of compact glistening coke, weighing about 14 cwt. per chaldron, (thirty-six bushels). The bulk is increased from ten to fifty per cent.

In breaking out the coke from the ovens, a great deal is unavoidably reduced too fine for use in the locomotive furnace under a strong draft; such may, however, be used in firing up, in standing still, and at the stations.

In taking the coke from the ovens it should be separated into the three following classes.

Large coke. Cubes of 9 inches to the side.
Medium coke. Cubes of 6 inches to the side.
Small coke. Cubes of 3 inches to the side.

Pittsburgh coal carefully coked for forty-eight hours, gives seventy-five per cent., by weight, and one hundred twenty-five per cent. by bulk, of firstrate, firm, bright, clean coke.

The best test for coke is to place it in water. Water, weighing sixty-two and one half pounds per cubic foot, should not float good coke, which ought to weigh sixty-three pounds per cubic foot, therefore if the coke floats it is too light.

Much of the bituminous coal in the Mississippi valley does not coke, but burns up. A large part cokes moderately well, but not so well as the Pittsburgh coal. In estimating for a comparison of fuels, the particular coal of any location must be tested.

OF THE COMPARATIVE VALUE OF WOOD, COAL, AND COKE.

This question divides itself into two parts,

The relative cost of the different fuels,
and The relative power to produce heat.

319. It does not follow that because coke in England, anthracite in Pennsylvania, or wood in New England, is the most economical fuel, that either of the above will be so in Ohio, Indiana, or Illinois, or because wood is the cheapest in some parts of a State, that it is so throughout, or even that one fuel should be applied to the whole length of a single road.

The heat used to evaporate water in the locomotive boiler is developed by combustion; combustion is produced by chemically combining the oxygen of the air with the carbon of the fuel; whence, that material containing in a given cost the largest amount of carbon will produce heat the most economically.

From the table on page 320, we see that, by bulk, thirteen of coke are equal to sixty of wood; that one pound of coke evaporates eight and one half pounds of water; that one pound of wood will evaporate two and one half pounds of water. Tables of specific gravity give as an average weight per cubic foot of hard wood, thirty pounds. A cord of wood, by very careful measurement, contains one hundred cubic feet _solid_, or one hundred twenty-eight feet _as piled_, taking the average size of wood; whence a cord will weigh three thousand pounds. And we have as the relative evaporative efficiency of a cord of wood and a ton of coke,

2240 × 8½ = 19040,
3000 × 2½ = 7500.

Now if the cost of a cord of wood is to the price of a ton of coke as 7,500 to 19,040, it is immaterial which we use.

As an example of the use of the above proportion, when the absolute cost of wood, coal, coke, and labor are known, take the following.

If wood, cut and ready for burning, costs $3.00 per cord, how much may be given for a ton of coke?

As 7,500 is to 19,040, so is 300 to 762, or $7.62.

From the same proportion we form the following table.

Cost per cord of wood Price that may be paid
ready for burning. per ton for coke.
(Cents.) (Cents.)
200 508
225 571
250 635
275 698
300 762
325 825
350 877
375 952
400 1016
425 1079
450 1143
475 1206
500 1270

In the comparison above, the maximum evaporative power of wood has been used, 2½ lbs., and the ordinary power of coke, 8½ lbs. of water per pound of fuel.

320. In making coke in large quantities, the ovens should be at the mines, as we thus save transporting the extra weight of coal over coke.

The cost of making coke, exclusive of the cost of the coal, is approximately as follows:—

10 ovens capable of making annually 5,000 tons of coke, $5,000
Sheds, and apparatus to correspond, 3,000
——————
In all, 8,000

Annual interest at 6 per cent., 480
Annual cost of attendance, 2 men, 1,000
——————
The sum of which is, $1,480
And the cost per ton, 0.296/10

or in round numbers, thirty cents per ton; and if coal is $1.50 per ton, adding twenty-five per cent. we have $1.87 as the cost of coal that will make one ton of coke, to which add the cost of making per ton, thirty cents, and we have as the whole cost of one ton of coke $2.17; and from the rule on page 327 we see that wood must not cost over $0.85 per cord to be as economical as coke at $2.17; of course inferior qualities of coal will give less good coke and change the comparison.

COMBUSTION.

321. The combustible element in all fuels is carbon; the heat necessary for steam producing, is obtained by combining the carbon of the fuel with the oxygen of the air, forming carbonic acid gas.

Carbonic acid gas consists of

Oxygen 16} Parts by
Carbon 6} weight.

Atmospheric air consists of

Oxygen 8} Parts by
Nitrogen 28} weight.

Whence, for the combustion of one pound of carbon, we require

Carbon 1.00
Oxygen 2.66

But to obtain 2.66 of oxygen from the atmospheric air, we also use nitrogen in the proportion of 28 nitrogen to 8 oxygen; whence, for converting one pound of carbon to carbonic acid, we require

Oxygen 2.66
Nitrogen 9.31
—————
Or 11.97 lbs. of atmospheric air.

From careful observations on the gases passing through the chimneys of well-constructed boilers, oxygen is found free, varying in amount from one quarter to one half of the quantity necessary for combustion; this is owing to the mechanical obstructions to the perfect conversion of the air arising from leakage through the fuel.

More than the above 11.97 lbs. of air should, therefore, be applied to the fire for each pound of carbon consumed. Twenty-five per cent. is found by experience to be a sufficient surplus allowance to convert the carbon.

Whence, to 11.97
add 3.03
—————
and we have 15.00 lbs. of atmospheric air per lb. of carbon.

Air weighs .075 lbs. per cubic foot, whence 15/.075 or 200 cubic feet of air are necessary for the proper combustion of one lb. of pure carbon.

Knowing the necessary amount of air for one lb. of carbon, and also the percentage of carbon in the different kinds of fuel, it becomes a simple arithmetical operation to fix the bulk of air required for any species of coal, coke, or wood. The result of such a calculation is shown in the seventh column of the table on page 320.

“There are two causes why all the heat which fuel may furnish is not obtained. First, that the inflammable gases evolved by the heat are not all consumed from want of a sufficient supply of oxygen, the air drawn through the fire being only sufficient to decompose more fuel than when decomposed it could burn, or supply with oxygen. The thick smoke that escapes from a chimney when fresh fuel is thrown on a hot fire, is unconsumed gas; decomposed from the fuel, but without oxygen enough to burn—although there may have been a sufficient supply of heat. From this cause it is, perhaps, that flame is seen coming from the top of a steamboat chimney which appears to be continuous from the furnace; but which, in fact, is ignited by contact with the air, having retained sufficient heat for that purpose.

“All smoke-consuming furnaces are simply means of admitting fresh air to the unconsumed gases above the fire, which, in a common chimney, will effect the object, as so large a mass of smoke retains the necessary amount of heat. This only prevents the nuisance of smoke. To render the gases thus reheated useful in evaporating water, this supply of oxygen must be added while the gases are yet in the flues.” This might seem difficult. Mr. McConnell (England) divides the flues of his locomotives into two parts, connecting the front ends of the first part and the back ends of the second part by a space of twelve or fifteen inches, (called by him a ‘combustion chamber,’) into which he admits any required amount of fresh air. (See appendix E.)

“A second cause why the full value of the fuel produced is not obtained is, that so much is abstracted from the gases in passing through long tubes, that there is not enough left to continue combustion, although the inflammable gas is still there. That a tube or any substance in the way of the hot gases does absorb the heat enough to prevent the burning of the gas, is proved by the action of Davy’s Safety Lamp; this is a common light surrounded by a wire gauze, which so absorbs the heat from the flame as to extinguish the latter at the wire; by applying fire above the gauze, the gas is again kindled, showing plainly that want of heat above had quenched the flame.” See Stöckhardt’s Chemistry; translation by C. H. Peirce, M. D., Cambridge, Mass., 1852, page 105.

We require, then, in every boiler, first, to have a sufficient supply of oxygen to decompose the fuel; next, a quantity above the fire to consume the produced gases; third, such an arrangement of communicating surface that so much heat shall not be abstracted from the gases as to deaden their combustion, until just as they are discharged, at which period they ought to be consumed. (See appendix E.)

GENERATION OF STEAM.

322. The means of producing the power is of course of the first importance.

The heat generated in the fire-box is conducted through the tubes to the exhaust chamber; during which passage it is imparted to the metal, and from thence absorbed by the adjacent water, which being thereby made lighter, rises to the surface and gives place to a new supply. The duty of the furnace is to _generate_, and of the tubes to _communicate_, heat.

The power of a plain surface to generate steam, depends upon its position and on the ability of the material to transmit heat An experiment recorded in Clark’s Railway Machinery, gave the following results: A cubic metallic box submerged in water and heated from within, generated steam from its upper surface more than twice as fast as from the sides when vertical, while the bottom yielded none at all. By slightly inclining the box the elevated side produced steam much faster, while the depressed one parted so badly with it as to cause overheating of the metal.

Acting upon this result, most builders of engines of the present day give an inclination of from one inch to one quarter of an inch per foot to the sides of the inner fire-box. That the heat should be applied in the most effectual manner to the water, the latter should _circulate_ freely around the hot metal, carrying off the heat as soon as it reaches the surface. As the heat is applied to the _inside_ of the furnace and tubes, it must, therefore, be the _inside_ dimensions which determine the amount of heating surface.

NOTE.—If we multiply the interior surface of a tube by the intensity
of heat applied, and divide the product by the exterior surface, we
shall have the intensity at the outside. We also _apply more heat_
to the _outside_ of a tube, which, passing to the inner surface,
augments in intensity per unit of area.

The area of the inner fire-box is not all available for heating, but requires to be reduced as follows:—

For the fire-door.
For the ferrule area.
For the top stays.
For the side stay bolts.

The area is, therefore,

Sides, twice length by height, less stay bolts.
Back, height by width, less fire-door.
Front, height by width, less ferrule area.
Top, length by width, less top stays.

TUBES.

323. The tubes or flues, varying in number from one hundred to three hundred, in diameter from one and a half to three inches, and in length from eight to sixteen feet, furnish the real communicating surface. The amount of heating surface thus obtained for any length, number, and diameter, is given in table 10, Chapter XIV., Part I. The surface of a single tube is found by the formula

(_Ld_3.1416)/144.

Where _L_ = the length,
and _d_ = the diameter, both in inches.

The efficiency of circular tubes is a matter not yet fully understood. They certainly give a large amount of surface in a small boiler. Pambour considered the value of tube area per unit of surface, in terms of the furnace area, as one third only; that is, three square feet of tube surface as equal to one foot of furnace area, in power of generating steam. D. K. Clark makes no distinction between the two surfaces, but observes “there is reason to believe that in the upper semicircular part of each tube the efficiency principally resides. The winding progressive motion, observable in tubes of considerable diameter, confirms this conclusion, as it is with much probability due to the cooling of the upper portion of the gases of combustion, which, as they cool also, become heavier and descend laterally, to make room for the hotter smoke next the bottom of the flue; the general result of which is the spiral motion of the current in its progress onwards.” Certainly the upper half of the tube would part much easier with the steam than the under one, even supposing the applied heat to be the same.

At page 340 of “Overman’s Mechanics,” is the following: “The application of heat to a _concave_ surface is wrong in principle. The heat in gases is conducted to other bodies, and among themselves by _convection_ only. This quality of gases causes the convex form of a vessel to be the most profitable in absorbing the heat of ascending gases, because the motion of the gas causes a constant change of particles on the convex body. On a _concave_ surface exposed to the influence of moving gases, but little effect is produced; because the particles of gas in the concavity are at rest. A plane surface is for the same reason an imperfect form for absorbing heat; it must be exposed at an angle of 45° to obtain the best effect of the heating gases. In all cases if we wish to obtain the best effect from the fuel, we should expose a convex surface to the current of hot air. The direction of the motion of the hot gases decides the position of the metal which is to absorb the heat; if the current is horizontal the pipes must be vertical. Gases do not convey heat by radiation. Tubes and other vessels containing water must be so placed that the hot gases play around the outside.

“If we lead a current of hot air around a cylinder we shall observe that a particle of air plays but a short time upon its surface, when it gives way to another; the particles play almost around the cylinder, and a concentration or increase of density behind the pipe is the result. The relative position of pipes in the range is not indifferent, and the distance of one from the other must be related to their diameter.”

The conducting power of the metal composing the fire-box and tubes, is one condition which limits the rate of evaporation, when the heat is abundant on the one side and circulation free on the other, as the water certainly carries off the heat as fast as it arrives at the outer surface.

All the heat should be extracted if possible from the gases before they enter the smoke box. We should so arrange the flues, that without so much contracting the passage for the exit of the gases as to need too strong a blast, yet to confine the gases until their full value is extracted.

Several attempts have been made to apply the ideas of Clark and Overman, but as yet they have been very indirect and have met with only moderate success. (See Appendix, E.)

EVAPORATION, PRESSURE, TEMPERATURE, AND DENSITY.

324. The character of work to be done determines the nature of the steam to be used.

The quantity of work to be done shows the amount of steam to be produced.

The amount and character of the steam required, fixes the dimensions and proportions of the boiler.

A cubic foot of water, at a temperature of 62°, weighs 62.321 lbs.

A cubic foot of steam, generated at 212° Fahrenheit, under the atmospheric pressure (14.7 lbs. per square inch) weighs .03666 lbs.

Whence one cubic foot of water boiled at 212°, makes 1,700 cubic feet of steam.

The total heat of saturated steam (steam produced in contact with the water), consists of two parts at all temperatures; the _latent_ and the _sensible_. The sensible heat is that shown by the thermometer, and varies with the pressure. The latent heat absorbed during the generation of steam, amounts to three fourths of the whole. As the temperature at which the steam is produced increases, the bulk produced from a given unit of water _decreases_, but the pressure and the total heat increase. (See C. R. M. p. 59, 61, Regnault’s experiments.)

Table 8, Chapter XIV., Part I., gives the properties of saturated steam, produced under pressures varying from fifty to one hundred and fifty pounds per square inch.