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I.CJ.UMAR

Sthna juries,

STEAM

AND THE

STEAM ENGINE

LAND, MAKINE, AND LOCOMOTIVE,

HENRY EVERS, LL.D.,

PROFESSOR OF MATHEMATICS AND APPLIED SCIENCE, CHARLES SCIENCE SCHOOL,
PLYMOUTH, AUTHOR OF "NAVIGATION," "NAUTICAL ASTRONOMY," ETC.

LONDON AND GLASGOW:
WILLIAM COLLINS, SONS, & COMPANY.

U.C.D. LIBRARY

.T •

,«*' t

PEEFACE.

THE chief aim of the author of this book has been to supply
a want that he, in common with a large body of teachers, has
experienced for many years. There is on Steam no cheap
work that a teacher can put into the hands of his pupils, to
give them at once a full and comprehensive idea of the whole
subject. The author has striven to supply this defect, and
to produce a work correct in its facts, safe in its deductions,
and containing, where possible, new and original matter, or
the old matter presented under new aspects. How far he
has succeeded is for others to judge.

An attempt has been made, not only to give the reader
an insight into the details and specialities of the different
kinds of engines employed to do man's work, but to make
him understand the various principles upon which each part
of the Steam Engine does that work, the relation these
parts bear to each other, and the life or physiology, so to
speak, of the whole.

The syllabus of the Government is covered not servilely
by -following its details, but by omitting what is unnecessary,
and adding much that is required for a full knowledge of
the subject. Originality of matter in this subject cannot
be expected. Freshness of arrangement and simplicity of

4 PREFACE.

illustration have been sought. In thus aiming to render
the subject intelligible, the author has endeavoured to avoid
all appearance of cram, so baneful to the true progress of
the student in any branch of science whatever.

The subject is divided into chapters, and the student
is recommended to peruse them in their order, taking up
the mathematical questions at the end as soon as the first
two or three chapters have been read.

To the Teacher I would say, be not content with the
expositions and details given; but seek for graphic
illustrations within your own reach, and avail yourself of
every opportunity that presents itself to make the class
acquainted with the Steam Engine at work.

H. E.

PLYMOUTH, Nov. 1872.

CONTENTS.

CHAPTER I.

INTRODUCTORY.

PAGE

Definition — Properties of Steam : Elasticity, Latent Heat —
Water is a Solid, a Liquid, and a Gas — Latent Heat of
Water — Ebullition — Latent Heat of Steam — Consumption
of Heat in Liquefaction and Vaporisation — Boiling Point
— Steam and its Properties — Superheated Steam : Density,
Volume, Expansion, ....... 9

CHAPTER II.
HEAT.

Definition — Expansion and Contraction — Expansion and Con-
traction of Water — Co-em cient of Expansion — Molecular
Power of Expansion and Contraction — Atomic Forces —
Radiation and Absorption — Conduction — Friction- — Tem-
perature and Measures of Temperature — Thermometer —
Pyrometer — Specific Heat — Calorimeter — Convection —
Heat and Work — Mechanical Equivalent of Heat, - - 24

CHAPTER III.

THE STEAM ENGINE.

Savary's — Newcomen's — Watt's — Cylinder and Crank — Single
and Double Acting Engines — Clearance — Cushioning —
Galvanic Action — Beam Engines — Parallel Motion —
Guides — Governor — Throttle Valve — Cataract — Eccen-
trics—Expansion Gear, 47

CHAPTER IV.

MARINE ENGINES.

Condensing and Non- Condensing — Side Lever — Twin Screw
Engines — Hammer Engines — Compound Engines — Con-
tinuous Expansion — Oscillating Engines — Steeple Engines.
— Maudslay's Twin Engine — Beam and Geared Engine —
Trunk Engine — Horse-Power — Duty, 78

CHAPTER V.
METHODS OF PROPULSION.

Paddle Wheels — Immersion of Paddle — Disconnecting Paddle
• — Centre of Pressure — The Screw — Definitions — Slip —
Propellers— Thrust— Hydraulic Propulsion, 97

O CONTENTS.

CHAPTER VI.
SLIDES.

PAGE

Slides— Long D Slide — Short D—Seaward's— Cylindrical-
Gridiron — Motion of Slide — Lap — Lead — Valves of Special
Pump— Rotatory Valve, ..... 113

CHAPTER VII.

OTHER VALVES.

Hornblower's Valve — Equilibrium — Escape — Snifting Valve —
Communication Valve — India-rubber Disc Valves — King-
ston's Valve — Blow-through Valve — Balanced Slides —
Facing Valves, 122

CHAPTER VIII.
THE BOILER AND ITS APPENDAGES.

Definition — Haycock, Haystack, or Balloon Boiler — Waggon
Boiler — Flue Boilers — Length and Diameter of Flue —
Plates — Marine Flue Boilers — Blast Pipe — Steam Chest —
Locomotive Boilers — Field's Boiler — Galloway's Tubes —
Tubes — Vertical Boiler — Cornish Boiler — Fusible Plugs
— Clothing Boilers — Copper Boilers — Testing — Water
Heaters — Surface Condensation — Circulating Pumps —
Ejector Condenser, 133

CHAPTER IX.
APPENDAGES TO THE BOILER.

Safety Valve — Salter's Spring Balance — Bourdon's Gauge —
Vacuum Gauge — Mercurial Gauge — Glass Water Gauge —
Vacuum Valve, 152

CHAPTER X.
SALT IN MARINE BOILERS.

Sea Water — Specific Gravity — Boiling Point — Blowing Out
— Scale — Salinometer — Hydrometer — Priming — Feed
Pumps — Giffard's Injector, - 161

CHAPTER XI.
LAND ENGINES.

The Beam Engine — Horizontal Engine — Vertical Engine —
Table Engine — Portable Engine — Ramsbottom's Inter-
medial Engine — Gas Engine — Caloric Engine — Siemen's
Regenerative Engine — Fire Engine — Cornish Pumping
Engine, 177

CONTENTS. 7

CHAPTER XII.

COMBUSTION AND PREVENTION OF SMOKE.

PAGE

Definition — Foot Pound— Combustion — Analysis of Coal — Pre-
vention of Smoke — Smokeless Coke — Rules to Avoid
Smoke and "Waste of Fuel, 191

CHAPTER XIII.

BOILER EXPLOSIONS.

Cause — Spheroidal Condition of Water — Water Purged from
Air — Hydrogen Theory — Accumulated Pressure — Incrus-
tations— Deficiency of Water — Collapsing— Bad Manage-
ment— Mr. Colburn's and Professor Airy's Theory, - - 196

CHAPTER XIV.
PRACTICAL WORKING.

Duties to Machinery when in Harbour and Getting up Steam ,
— Starting the Engines — Under Steam — Fires — Bearings —
Engines in Port — Lap on Slide Valves — How to Set the
Slides, 203

CHAPTER XV.
THE INDICATOR.

Description — Use — Diagram — Diagrams under Various Cir-
cumstances, - 209

CHAPTER XVI.

THE LOCOMOTIVE ENGINE.

DIVISION I. — History — Trevithick's Model — Adhesion of
Wheels to Rails, etc. — Tractive Force — Murray's Engine
— Hedley's Locomotive — Stephenson's Engine: "The
Rocket" — Blast Pipe — Trevithick's Claims — Contrast
between "Rocket" and Modern Engines, - - - 225

DIVISION II. — General Description of a Locomotive — Cramp-
ton's Engines — Tank Locomotive — Bogie — Locomotive
Boiler — Shell of Boiler — Through Tie Rods — Tubes-
Clearance — Fire Box — Staying the Furnace — Fire Bars —
Ash Pan— Smoke Box— Heating Surface— Safety Valves
Chimney — Damper — Steam Dome — Man Hole — Regulator
—Whistle — Pressure Gauges, 238

DIVISION III. — The Water for a Locomotive.— Water Tanks-
Water Cranes — Feed Pump — Giffard's Injector — Gauge
Cock — Glass Water Gauge — Screw Plugs — Scum Cocks —
Blow-off Cocks— Heating Cocks, 258

CONTENTS.

DIVISION IV. — Details. — The Cylinders — Water Cocks —
Grease Cocks — Piston and Piston-Rod — Connecting Rod
and Crank — Coupling Rod — Strap Gib and Cutter —
Sector — Driving Wheel Tire — Counterweight to Wheels —
Sand Cocks — Axle Boxes — Springs, Buffers, and Buffer
Springs — Brakes — Draw Bar, 266

DIVISION V. — Slide Valve and Combustion. — Stephenson's Link
Motion — Sector — Single Eccentric — Slide Valve and its
Motion — Temperature of Furnace Gases — Transmitting
Power of Metals — Coke and Coal Burning in Locomotives
— Air Required for Combustion — Steam Blow Pipe —
Beattie's Fire Box — Conclusions on Combustion, - - 279

DIVISION VI. — The Road. — Tramway — Railroads — Curves —
How the Carriages are Kept on a Curve — Rails — Fish
Joint — Gradients — Ballast — Cuttings an d Embankments
— How Rails are Laid — Two Ways — Broad and Narrow
Gauge — To Adapt one Gauge to the other — Fell's Railway
— Turn Tables — Traversers — Switchings and Crossings, - 293

DIVISION VII. — The Indicator and Diagram. —Richard's Indi-
cator— Diagram of Locomotive — Conclusion to be Drawn
from Diagrams — Examples of Diagrams — Questions and
Examinations, 303

CHAPTER XVII.
DE PAMBOUR'S THEORY.

Introduction — Work Done on a Square Inch — Horse-Power —
The Load— The Pressure— De Pambour's Theory— Rela-
tion between the Temperature and Pressure of Steam in
Contact with the Water — Relations between the Relative
Volumes and Temperatures of Steam — Velocity of Piston
under a Given Load and Horse-Power — To Determine the
Evaporative Power of a Boiler — Maximum Useful Effect
— Examples — Hyperbolic Logarithms, - - - 315

QUESTIONS, - 337

INDEX, 369

PLATES.

I. — Section of Locomotive Engine, - - - . . 240
II.— Fire Box, Fire Bars, Ash Pan, and Supports for Top of

Fire Box, 246

III. — Plan of Cylinder and Driving Gear, .... 267

IV.— Cylinders, Steam Pipe, Blast Pipe, etc., - - - 269

STEAM.

CHAPTER I.

Definition — Properties of Steam : Elasticity, Latent Heat — Water is
a Solid, a Liquid, and a Gas — Latent Heat of Water — Ebullition — •
Latent Heat of Steam — Consumption of Heat in Liquefaction and
Vaporisation — Boiling Point — Steam and its Properties — Super-
heated Steam : Density, Volume, Expansion.

1. Definition. — Steam is the invisible, elastic fluid gene-
rated from water by the application of heat.

2. Steam is Invisible. — When steam is issuing from the
spout of a kettle or from a safety valve, if we examine it
close to the spout or valve, we see nothing. It is only at a
distance from these orifices that the steam is rendered visible,
by parting with its heat to the air with which it is in
contact ; when visible it ceases to be steam, and is called
vapour. But many object to such a hard and fast line
separating vapour from steam, and say, steam is vapour and
vapour is steam. Vapour escapes from the surface, but is by
no means generated, as a rule, at the surface. Evaporation
is the escape of vapour. Vaporisation is the conversion of
liquid into vapour. The moment heat is applied to water
vaporisation commences, and evaporation takes place. It
has been suggested * that the heat applied to water produces
the single effect of converting part of the water into steam
or vapour, and not heating part of the water and turning
another part into vapour, and that the vapour thus formed
in the body of the liquid, is diffused through the whole mass,
and this vapour alone acts upon the thermometer, causing it

* By Mr. C. W. Williams.

STEAM.

to rise with the increase of its own temperature. This is
simply Dalton's law, " that all gases which enter water or
other liquids by means of pressure, and are wholly disengaged
again by the removal of that pressure, are mechanically
mixed and not chemically combined with the liquid. Gases
so mixed with water retain their elasticity or repulsive
power among their own particles, just the same in water as
out of it."

3. Vapour and Steam. — We may for convenience make the
following distinction : When water passes away insensibly
without the mechanical application of heat, it is termed
Vapour; but when heat is directly applied to produce this
vapour, we consider it Steam.

4. Steam is Elastic. — Take a cylinder or box, into which
is tightly fitted a piston, and fill it with steam. If we now
maintain the cylinder and steam at the same temperature,
and apply a sufficient force to compress the steam into half
the space, and then suddenly withdraw the force, the steam
will again expand and fill the same space as before, driving
the piston back again to its original position. The piston is
returned to its place by the elastic force of the steam. Or
we may illustrate the elasticity of steam much better thus :
Suppose our cylinder full of steam, to be steam at a pressure
of 15 Ibs. on the square inch, and let the piston be at A B,
and that from B to 1ST be sixteen inches.

If the piston be forced half-way down, or
eight inches, to C D, then the steam oc-
cupying one -half its former space its
pressure will be doubled, or on each
square inch the pressure will be 30 Ibs.
Next force the piston to E F, four inches
farther down, so as to reduce again the
volume of the steam by one-half, or to com-
press it into one-quarter of its original
volume, then the pressure will be again
doubled, and will now be 30 x 2 or 15 x 4
= 60 Ibs. on the square inch. If it be forced to G H, two
inches still farther down, or the volume again decreased one-
half, or occupying one-eighth of the original space, the pressure
is now G0x2orl5x8 = 120 Ibs. on the square inch. We

F
hi

THE EBULLITION OF WATER. 11

see by this illustration that the pressure increases as the
space decreases. This is called Mariotte's or Boyle's law, and
is generally expressed thus : The temperature remaining the
same, the volume of a given quantity of gas is in inverse ratio
to the pressure which it sustains.

5. Latent Heat. — The heat not sensible to the thermometer
is termed latent heat or hidden heat.

6. Water is a Solid, a Liquid, a Gas. — If we take a lump
of ice, we see water in its solid form, the temperature of which
may be below the freezing point. Ice is one-ninth lighter
than water. Apply heat to the lump of ice, the temperature
is soon raised to 0° C., and in whatever way we continue our
application of heat, we cannot increase the temperature, but
the whole of the heat we employ sets to work to melt the
ice; when all is liquefied, then the water will increase in
temperature, through 10° C., 20° C., 60° C., etc., till it reaches
the boiling point 100°C. ; after which, however much heat, and
however long we apply it to the water, we cannot make the
water hotter than 100° C. The additional heat simply con-
verts the water into steam or gas, and is employed in pushing
and keeping the atoms asunder, and is carried off as latent
heat.

7. Latent Heat of Water (or Ice). — If a pound of ice at
0°C., be mixed with a pound of water at 79*4°C., the water
will gradually dissolve the ice, being just sufficient for that
purpose, and the residuum will be two pounds of water at
0° C. The 7 9 *4 units of heat which are apparently lost,
have been employed in performing a certain amount of work,
i.e., in melting the ice or separating the molecules and giving
them another shape, and as all work requires a supply of
heat to do it, this 79*4 units has been consumed in perform-
ing the work necessary to melt the ice, and is called the
Latent Heat of Water. If the pound of water were re-
converted into ice, it would have to give up the 7 9 '4 units
of latent heat ; hence we see why it should be called the
latent heat of water, and not the latent heat of ice. The
three forms of water are, then, (1) a solid, as ice; (2) a
liquid, as limpid water ; (3) a gas, as steam.

8. The* Ebullition of Water. — The boiling point of water
is that temperature at which the tension of its vapour exactly

12 STEAM.

balances the pressure of the atmosphere.* The student must
bear in mind the law of convection, as explained farther on.
As part of that law of convection, he may observe, that if
water be placed in a Florence flask, and held over a gas-
burner, he will see small globules rise from the bottom and
ascend a small distance, until the colder water above destroys
their buoyancy; this continues, the globules rising higher and
higher, till the heat of the water increases to 100° C., when
they reach the top and produce what we call ebullition. It
is the heated water becoming specifically lighter, and rising
up with considerable force.

9. Latent Heat of Steam. — The latent heat of steam at a
pressure of 15 Ibs. or about thirty inches of mercury, is 5 37*2° C.
We will describe an experiment which will help to illustrate
this point, and fix the fact in the memory. Let us suppose
that we have two very small vessels connected at their tops
by a tube. Let one contain a pound of water, at the
temperature of 0° C., and the other five and a half pounds, at
the same temperature. If a spirit lamp be applied beneath
the vessel containing the one pound of water, its temperature
will gradually rise to 100° C., when ebullition will begin, and
if the heat be continued, the water will not increase in tem-
perature, but will pass off as steam along the tube to the
second vessel, where the five and a half pounds of cold water
will condense the steam and absorb the heat, which first
enters and passes from the one pound, as long as the spirit
lamp is applied to it. This operation of condensation and
absorption will continue until the one pound of water is all
converted into steam and re-converted into water. At the
moment that the evaporation of the pound of water is com-
pleted, the heat transferred by the steam from one vessel to
the other will cause the five and a half pounds of water to
boil. It will be found that there are now in the second vessel,
six and a half pounds of water, at a temperature of 100° C. As
the 1 Ib. takes 100 units of heat to make it boil, the 5-| Ibs.
take 5J x 100 = 550 units; or as there are 61 Ibs. of water in B,
the total quantity of heat is 100 x 6J = 650 units of heat. A
thermometer placed in the water would show a temperature
of 100° C. This 100° only being sensible to the thermometer,
* Tyndall's Heat as a Mode of Motion.

THE BOILING POINT OF WATER. 13

the other 550°, which we know to be there, are hidden or
latent. Exact experiments make the 5J- Ibs. 5*372. Hence
the latent heat deduced from the experiment will be
5-372 x 100 = 537°-2. This 537°-2C., or 966°-6R, is the
latent heat of steam. In making the experiment, ounces 01
smaller quantities of water are employed, and not pounds.

10. A Unit of Heat. — A unit of heat is defined as the
amount of heat necessary to raise the temperature of a pound
of water one degree. Hence the units of heat in a pound of
steam at 100° C., number 637*2.

11. Consumption of Heat in Liquefaction and Vaporisa-
tion.— This is but another way of putting the facts connected
with the latent heat of water and steam. We have seen that
the latent heat of water is 790t4C, or to liquefy a given
quantity of ice requires this Amount of heat; to raise the
water to its highest temperature consumes 100°C. more;
next, to vapourize it consumes 5 37° -20.

12. The Boiling Point of Water Depends upon Pressure;
or, the temperature at which the ebullition of water begins,
depends upon the elasticity of the air or other pressure. At
the level of the sea, the barometer standing at 29 -9 05 (or
very nearly 30) inches of mercury, water will boil at 100°C.;
but the higher we ascend above the sea level, the more the
temperature of the boiling point diminishes. For every 1062
feet of height, water will boil at a temperature 1^0. less;
because as we ascend the pressure of the atmosphere de-
creases. In precisely the same manner the pressure of steam
upon the surface of the water in a boiler will have a tendency
to raise the boiling point ; because the tension of the vapour
has a greater pressure to overcome before it can free itself
from the water. But we are here presented with another
law — the sum of the latent and sensible heat of steam is
constant. The latent heat of steam (as we have just seen), at
a pressure of 15 Ibs., is 537P'2C., and the sensible heat 100°C.,
making a total of 637° '20., or 1146°-6F. Now if water
under a pressure of 30 Ibs. boil at a temperature of 122°C.,
the latent heat of such steam is 637°-2 - 122° = 515°-2C.

This is Dr. Black's theory of latent heat, or, more correctly,
it is called Dr. Black's theory of the latent and sensible heat
of steam. It is termed his theory because, after a very large

14 STEAM.

series of experiments most carefully conducted, he was the first
to propound the theory, which was one greatly in advance of his
time, and shows him to have been a man of no ordinary mind.
The experiments of Eegnault tend to modify the above
theory advanced by Dr. Black. He has arrived at the con-
clusion that the total amount of heat in a given quantity of
steam increases slowly with every increase of temperature.
Regnault constructed the following formula, which gives
pretty nearly the total amount of heat in steam at all
temperatures : —

Actual temperature of steam- 1082QF. + -305T?.

This cannot be modified to give us the formula for degrees
centigrade, but must be entirely reconstructed. This matters
but little, seeing how easy it is to find the total amount of
heat in degrees Fahrenheit, and then to reduce it to centi-
grade. Hemember, then, that the constant number 1082°
must be increased '305 degrees Fahrenheit for each unit of
temperature, to give us the total amount of heat in steam
under any given pressure.

13. High Pressure Steam Does not Scald.— If steam at
high pressure be issuing from an orifice, and the hand be
placed in it, it will not be scalded. The reason must be that,
as it issues into the air, the pressure is decreased and reduced
to 15 Ibs. The steam, therefore, immediately takes to itself
the deficient latent heat from the air. If the pressure had
been 30 Ibs., the deficient latent heat would have been 22° C.
The steam is, therefore, busily employed in taking these 22°
of heat from the atmosphere, and even from the hand placed
in it ; and so, under the circumstances, will rather cool the
hand than scald it.

14. Measure of the Pressure of Steam. — The pressure of
steam is measured by atmospheres. Steam of 1 5 Ibs. pressure
is steam of one atmosphere, of 30 Ibs. pressure of two atmos-
pheres, etc. It is frequently used as high as six or seven
atmospheres; but even ten, or 150 Ibs. pressure, is employed.
Steam below two atmospheres is termed low pressure steam,
and all pressures above, high pressure steam.

15. Density of Steam and Specific Volume.— The density
of steam is ascertained by placing in an exhausted glass

TEMPERATURE, DENSITY, AND ELASTICITY OF STEAM. 15

globe, the capacity of which, is known, a certain weight of
water. The globe is next placed in a bath of mercury, and
heat is applied until the whole of the water in the globe is
converted into steam. The temperature at which this takes
place, the volume of the glass globe, and the weight of the
water employed, are the three elements from which the
density is calculated. The specific volume of the steam is
found by dividing the capacity of the globe by the weight
of water employed in the experiment.* At a pressure of
9 Ibs. per square inch, the point of saturation, by Sir Wm.
Eairbairn's and Mr. Tate's experiments, was 86° -80., and
specific volume 2620 ; at 274 Ibs. the point of saturation was
118g-2C., and specific volume 906; at 45-7 Ibs. the point of
saturation was 134°*8C., and specific volume 583.

16. Point of Saturation. — At the instant, in the above
experiments, when all the water is converted into steam, we
have " the point of saturation," or the temperature at which
steam at that pressure contains most vapour. Directly it
has reached the point of saturation, the steam, for every
increase of temperature, rapidly expands in volume; or, if
confined, its elasticity is greatly increased. Steam does not
accurately obey the laws of gases — the density of saturated
steam being always greater than that of gas.

17. The Ratio of the Temperature, Density, and Elasticity
of Steam when in Contact with the Water from which it is
Generated. — From what was said on latent heat it is evident
that the vapour rising from water must contain more heat
than the water. When steam is generating in a boiler, and
not allowed to escape as fresh quantities rise from the water,
the density and elasticity of the steam must increase ; at the
same time, to effect this change, heat is being constantly added
to the boiler ; we may express the result thus : — As the
temperature increases, so does the elasticity. This arises
not alone from the expansive property of steam, but from
the continual additions of more steam, generated by the
continued increase of temperature, which must add increment
after increment to the density and elasticity. The steam is
now in a state of saturation, and has in it the greatest possible

* See Fairbairn's Useful Information for Engineers, Second Series,
Lecture viii.

16 STEAM.

amount of vapour it can have at that temperature. We see
from what precedes that a certain pressure accompanies a fixed
temperature, and vice versa, so that we cannot increase or
decrease the one without a corresponding change in the
other.

18. Temperature, Density, and Elasticity when not in
Contact with the Water. — If steam be taken from a boiler,
and further heated or surcharged, the above relations of
temperature, density, and elasticity no longer hold good.
In superheating steam, as we increase the temperature we
decrease the density, for there is now no accession of watery
vapour; but the elasticity is increased in such a manner that
it follows no normal standard, or at least no law has been
discovered that will give us the relations of temperature,
density, and elasticity when heated and not in contact with
the water from which it was generated.

On these last two points, let it be remarked, that as steam
is allowed to run from the boiler to the cylinder, it is invari-
ably attended by a loss of heat from radiation ; and being
deprived of a portion of its heat, it becomes steam of a
different description to what it was when in contact with
the water from which it was generated, where it was con-
stantly receiving fresh accessions of heat. To maintain the
normal relation of temperature, density, and pressure, it
must be in contact with the water; while, when we super-
heat steam, it receives an entirely different character, and we
must have no confusion in our minds as regards this
difference.

The following table is worthy of attention : —

The temp, being - 40° F. or - 50° C. the pressure in Ibs. is '006 p. sq. in.

__ 1A"> T? ^-~ OO»1 a '021

•045

10° F. or-12°-|C.

. or

100° F. or 37°£C.
L>12-F. or 100° C.
300° F. or 149° 0.
325° F. or 162°£C.

•131
•930

15-

727
106-8

Much trouble has been taken by Dalton, Fairbaim, Arago,
u IK I Dulong to determine the above relations. The pressures
are here given as corrected by Fairbaim.

VOLUME AND DENSITY OF STEAM.

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18 STEAM.

The weight of a cubic foot of steam at various tempera-
tures is obtained by dividing 62-J- pounds, the weight of a
cubic foot of water, by its relative volume, and we are to
consider that the weights of water in the last column produce a
cubic foot of steam at the given temperatures and pressures.
In the third column the numbers are expressed so as to
show how the weights are obtained, while the denominator
of each fraction is the respective relative volume in each
case.

20. Relative Volume. — The relative volume of steam is
the quantity of steam generated from a given quantity of
water divided by that water. De Pambour's definition is,
" The relative volume of steam is the quotient of the
absolute volume of the steam by the corresponding volume
of water."

21. Expansive Working of Steam. — Steam is admitted to
the cylinder at a very high pressure, thus giving the piston
a great initial velocity, and before it has completed its
stroke the steam is cut off, or no more is allowed to enter,
the rest of the stroke being completed by the elastic force of
the steam already in the cylinder. The steam expands as the
piston moves onwards, and consequently its pressure, in con-
formity with Marriotte's law, is constantly diminishing, until
the piston is at the end of its stroke, it is thus brought
gradually to rest, when at that instant fresh steam enters,
and the process is repeated on the other side of the piston.

It is not brought gradually to rest through the diminishing
pressure of steam alone. This is effected by the cushioning,
which will be explained in its proper place.

When the steam is allowed to expand in the cylinder,
more time is given for evaporation in the boiler, so that steam
accumulates, and a saving is effected by using the smallest
possible quantity during each stroke of the piston. From a
minimum amount of steam a maximum amount of work, by
using it expansively, is obtained.

Suppose steam, whose initial pressure is 80 Ibs., is
admitted to the cylinder A N, 8 feet long, and that
the piston performs 2 feet of its stroke to a 5, when
the admission of steam is suddenly intercepted, the elastic
force of this one-quarter of a cylinder full of steam will

SUPERHEATED OR SURCHARGED STEAM,

now be called upon to complete the stroke. When the

piston gets to C D, the pressure will be one-half, or 40 Ibs.,

as the steam fills double the space; at E F

only one-third, for it then fills three

times the space, and so on. To find the

pressure at c d, F H, etc., and in fact at

every point of the stroke, the student is

referred to the questions at the end,

which should be commenced at once.

22. Superheated or Surcharged Steam.
— It has become a practice to allow the
steam, before it enters the cylinder, to
pass from the boiler into a series of
tubes, or into a strong iron chamber in
which a large quantity of vertical or horizontal tubes are
fitted; in these the steam is further heated to increase its
elasticity by the heat that is passing away up the funnel

SUPERHEATER.

20 STEAM.

or stack; thus, from a given quantity of steam a maximum
amount of work is obtained with a minimum amount
of fuel consumed. The annexed figure is one form of the
apparatus, which is generally placed in the uptake or at the
bottom of the stack.

The steam from the boiler passes through B into the series
of tubes T; in the upper figure they are seen in section, in
the lower in plan; around the tubes the heated air and gases
play, so that the steam .receives additional heat and passes by
way of D through C and C to the cylinder.

23. The Advantage of Superheated Steam is, that as we
increase the pressure the amount of work done by the
engine rapidly increases also; but the quantity of heat
contained in high-pressure steam is very little more than
that in low pressure. For instance, the units of heat in
steam at 230° F., pressure of 21J pounds, is 1152° F.; at
330° R, or 104 pounds pressure, it is 1183°R, or only
30° F. more.

Since it is heated by the waste products of combustion
passing up the funnel or stack, it is more economical than
ordinary steam, but it is by no means economical if this
heating is carried to excess. To ensure efficiency it wants
little more than drying.

In consequence of its great heat, superheated steam does
injury to the internal parts of the engine ; it burns the
packing, and eats away the cylinders, especially having an
injurious effect upon those of indifferent workmanship. As
steam is superheated so its elasticity is increased, or the
elasticity varies with the temperature. In practice many
engineers do little more than dry the steam ; for this purpose
a small chest, or outer casing, is sometimes fitted round the
bottom of the funnel, the steam passes through a short pipe
from the boiler to this casing, and is then led away to the
cylinder to do its work.

24. Law of Expansion of Superheated Steam. — Super-
heated steam near the point of saturation expands very
rnpidly and irregularly, but if the superheating be continued
the rate of expansion rapidly declines, and soon approaches
that of a perfect gas whose co-efficient of expansion is —TT for
every degree centigrade of expansion.

EXERCISES. 21

It lias been found that when the point of maximum
saturation was between 79° '4C and 82V>2C, the mean rate
of expansion was ioV;. when the superheating was continued
from 82° -'2 to 9 3° '30, the co-efficient of expansion fell from

EXERCISES FROM EXAMINATION- PAPERS (CHIEFLY).

1. What is meant by capacity for heat and latent heat?

What is the latent heat of steam under the ordinary atmo-
spheric pressure (1807)?

What weight of injection water at 80° will suffice to condense
a given quantity of steam into water at 1-0°?

Capacity for heat /.< explained hi next chapter.
The degrees are 80° F. and 120° F. - 26* f C. and 4^
Each unit of water is raised 48°£ - 26°§ = 22
The total heat in the steam is 637° '20. This has to be reduced
637?i — 48 u = 588 ;;C. (nearly).

.'. total units of water required = ^^;' — 23 J, nearly.

— -TT

It may be here observed that no unit is given for the water,
but the question is put generally; hence, if -we consider the quantity
of steam as that generated from a cubic foot, inch, or pound of water,
tho answer is 2lU- cubic feet, inches, or pounds.

2. The steam enters the condenser at a temperature of 212° F. ;
the water pumped out of the condenser is at a temperature of
110' F. What weight of injection water must be supplied for
each pound of steam which enters the condenser?

Before answering this question the student must draw attention
to the fact, that the temperature of the condensing water is not
given. He must therefore assume a temperature, say 10° C., and
answer the question as shown above. Ans. 17*81 Ibs.

:». Show, by an experiment, how the latent heat of steam may bs
ascertained.

4. What do you mean by the latent heat of water or ice? Wliieli
is the more correct expression?

«\ Show, as to a class, that steam is elastic and invisible.

6. Give a definition, of steam, and distinguish between vapour and
steam.

7. Describe the several methods by which heat is propagated.
Explain the terms capacity for heat and latent heat.

What is the latent heat of steam (1834) ?

22 STEAM.

8. Distinguish between common steam, superheated steam, sur-
charged steam, and saturated steam (1866).

!>. Deliue capacity for heat, latent heat, and unit of caloric
(18G5).

10. What is meant by superheated steam?
What advantages are gained by its use (1865)?

1 1 . What is meant by latent heat ?

Show under what circumstances heat becomes latent (186G).

12. Show how to determine the weight of injection at a given
temperature, which must be mixed with a given weight of steam,
that the whole may be reduced to water at another given tempera-
ture (1866)?

13. Compare the weights of injection water at 50° F. to be mixed
with a given weight of steam, that the temperature of the mixture
maybe 110°F. (1866)? And. 17'81 : 1.

14. What is the latent heat of steam ?
How is its amount ascertained (1867) ?

15. Distinguish between sensible and latent heat ?

What is the smallest weight of water at 32° which will be
sufficient to condense a pound of steam at the atmospheric pressure
(1858)? Am. 5-37 Ibs.

16. What is the distinction between sensible and latent heat ?
Describe an instrument for measuring the former (1868).

17. Under what circumstances generally (1) does heat become
latent, (2) does latent heat become sensible V

What amount of latent heat becomes sensible when ice is
thawed into water (1868)?

18. Two ounces of water at 60° are placed in an evaporating dish,
which is covered, except a small opening, by a glass plate. The
ilamc of a gas-burner causes the water to boil in 3^ minutes, and the
whole is evaporated after 22 minutes more have elapsed. What
should you infer as regards the latent heat of steam from this
experiment?

What is the correct numerical value given by a more exact
process?

The water is heated in 3j minutes from 60° F. to 212° F., or
through 152°F.

It is then evaporated in 22 minutes.

oo
It is evaporated in-t±-.— G'6 times the time it took to boil.

.'. heat put into the steam is 152° x G'G - 1003° '2. F.

. '. the latent heat of steam is 1003° '2 F.

The correct numerical value given by a more exact process is
967° F.

Had the time given in the experiment been 21 minutes 10
MC. .nds, the answer woulil come out !>>)')"7F., which is ay near a;;
it can be wished to get to the actual result.

EXERCISED 23

19. Describe an experiment proving that water is an extremely
bad conductor of heat.

In what way, then, can a large mass of. water, such as that in
a steam boiler, be readily heated (1869)?

20. Explain the meaning of latent heat.

State Black's law as to the latent heat of steam formed under
different pressures.

Is this law strictly verified by experiment (1869) ?

21. Under what circumstances does heat become latent ?

How much water did Watt consider necessary for the condens*
ation of a cubic foot of steam at the atmospheric pressure ?

State the considerations which led to the practical conclusion
at which he arrived in the case of a condensing steam engine (1869).
Watt supposed temperature of hot well to be 100° F.
,, ,, „ injection water 50° F.

Working this out, as in Example 1, gives 22 '24.
Therefore, he concluded, 1 cubic inch of water turned into
steam will require 22^ cubic inches of water to condense it. Watt
allowed 28 '9 cubic inches, or about a wine pint, for every cubic inch
of water evaporated, because as a practical man he knew that evert/
atom of water would not do all required of it. Hence he in practice
allowed above one quarter more than his theory allowed.

22. How can it be shown that the temperature at which water
boils depends upon external pressure ?

What is high pressure steam (1869) ?

23. Describe accurately the difference between steam in contact
with the water from which it is generated, and when not so in
contact.

State the law connecting the pressure, volume, and temperature
in the latter case ?

What is the formula employed by De Pambour as applicable to
the former (1865)? See chapter on De Pambour's theory.

24. State the laws which regulate the pressure of steam: (1) When
in contact with water; (2) When not in contact with water (1865).

25. What is meant by temperature ?

What are the general effects of adding heat to or subtracting
it from a body (1865)?

26. How much steam will be required to fill a cylinder, whose
diameter is 60 inches and length 6 feet, forty times per minute, the
volume of the steam being 1200 times that of the water from which
it was formed (1864)?

Ans. 3-927 feet, or 3;927 cubic feet of water must be evaporated
per minute to give the necessary supply of stsam.

CHAPTER II
HEAT.

Definition — Expansion and Contraction — Expansion and Contraction
of Water — Co-efficient of Expansion — Molecular Power of
Expansion and Contraction — Atomic Forces — Radiation and
Absorption — Conduction — Friction — Temperature and Measures
of Temperature — Thermometer — Pyrometer — Specific Heat —
Calorimeter — Convection — Heat and Work — Mechanical Equi-
valent of Heat.

WHEN heat is imparted to a body its atoms push each other
asunder, and the molecules commence to oscillate more or
less rapidly. The more intense the heat, the quicker the
particles oscillate; by raising the temperature you increase
the oscillations, while cooling is a decrease of vibration, or
loss of motion.

25. Bodies Expand by Heat and Contract by Cold. — The
law is almost universal that bodies expand by heat and
contract by cold.

(a). The most familiar illustration we have of this law is
in the expansion and contraction of water when under the
influence of heat and cold. Take water at a temperature of
4° C. ; after the heat has been applied for a short time, it
will begin to expand, and will continue to expand as the
temperature increases, till it reaches the boiling point 100° C.
After this, if we continue to apply heat, 110 alteration will
take place in the temperature of the water. The additional
heat that passes into the water is employed in converting the
water into steam. A cubic inch of water will supply 1660
cubic inches of steam, or nearly a cubic foot. The result of
another experiment was that a gallon of water, evaporated at
100° C., produced nearly 1800 gallons of vapour. When cold
is applied to this vapour it contracts to its original volume.

BODIES CONTRACT BY COLD. 25

(b) In building such bridges as the Albert Bridge, Saltash,
the Britannia and Conway tubular bridges, spaces are left for
the expansion and contraction of the iron. The difference
between the lengths of these bridges measured during the
extreme heat of summer and the extreme cold of winter, is
considerable.

(c) Experience has taught us that, in laying down the rails
for a railway, spaces of about three-eighths or a quarter of
an inch must be left to allow the rails to expand in length.
Were this nob done, the molecular fores of expansion would
bo sufficient to draw the spikes or lift the sleepers and rails
out of their places.

Mr. Stephenson once stated that, in consequence of laying
three or four miles of line, near Peterborough, with close
joints, the heat of the sun on a warm day caused such an
extension that the rails and sleepers were lifted in one placo
from the ballast so as to form an arch fifty feet long and three
feet high in the air.

(«:/) The simplest plan to separate a crank from a shaft on
which it has been shrunk, or, in fact, to disconnect any
rust joint, is to apply heat, when the bodies (being of different
dimensions) expand unequally and separate.

(e) Many other illustrations might be given, as, when
warehouses constructed with fire-proof floors, etc., have been
destroyed by fire, the walls of the buildings which were con-
sidered indestructible have been thrown down by the enormous
expansion of the iron girders, tic-beams, etc. Wheelwrights
and carriage builders, when they wish to place the tire upon
a wheel, expand it by placing it in a fire, then slip it upon
the wheel, and suddenly cool it, when the molecular power of
contraction holds and binds the whole wheel firmly together.

26. Bodies Contract by Cold. — This may be illustrated by
most of the foregoing instances of expansion by heat. A
cubic foot of steam becomes a cubic inch of water when con-
tracted by cold. The ends of railway rails are more widely
separated in winter than summer. This point will be further
illustrated under the heading of Molecular Force; but a good
illustration will be found in the method by which collars are
shrunk on a shaft. A neat way of putting collars on heavy
marine shafts where the journals come, is this : bosses are

20 STEAM.

turned on the shaft, and two ribs, three or four-sixteenths of
an inch high, are left on the bosses for the collars, which
must be prepared in the lathe, and then heated and slipped
over the ribs, then upon contracting with the cold they will
firmly grip the shaft.

27. The Exception to the Universal Law of Expansion
by Heat and Contraction by Cold. — Suppose we have a body
of water at 100° C., and expose it to cold, it will gradually
lose its motion or heat, cooling down through 90°, 60°, 30 u,
etc., and will contract or occupy a smaller space until it
descends to 3 '8° C.,, when it will contract no more, for it has
reached the point of maximum density. From 3°*8, as the
water becomes colder it expands, till it reaches the freezing
point 0° C., so that the ice is specifically lighter than the
water, and consequently floats upon the surface. Were it
not so, or did the water in the act of freezing become heavier,
it would sink to the bottom, and all rivers and ponds would
become frozen masses of ice in temperate and sub-arctic lati-
tudes, which could not be melted till a July sun exerted all
its influence. Consider the effects of this upon the earth : a
boreal climate would extend beyond the Straits of Gibraltar.
Every plumber, and almost every housekeeper, to the advan-
tage of the former, and the annoyance of the latter, knows
the effects of this expansion upon lead water-pipes. It splits
rocks in frozen regions, and makes enormous fissures in the
earth. We may state the fact succinctly thus : — Water
expands at the moment of freezing, or contracts on melting,
nearly 10 per cent. A cubic inch of ice gives '908 cubic
inches of water, or one cubic inch of water gives 1'102 of
ice at the same temperature. Bismuth is another exception,
it expands on cooling, and exerts an enormous force.

28. Co-efficient of Expansion. — The linear, superficial, or
cubical co-efficient of expansion is the amount a body expands
in length, surface, or volume on being heated one degree.
The superficial is twice the linear, and the cubical three times
it. All elastic fluids expand about the same, or -^\^ = '00366
part of their volume, on being heated one degree centigrade,

prefer PR

The following is a list of a few of the chief co-efficients of
expansion : —

ENORMOUS POWER OF EXPANSION AND CONTRACTION. 27

Linear. Cubical.

Glass, . - . -00000876 '0000254
Copper, - . - -0000171 '0000512

Brass, . . '0000185 '0000554

Iron (wrought)

Lead,

Tin (Cornish),

Silver,

Gold, .

Platinum,

Zinc,

•0000118 '0000354

•0000284 -0000890

•0000217 -0000690

•0000191 -0000574

•0000151 -0000453

•0000088 -0000264

•0000297 -0000890

It should be noticed in all cases how near the cubical
co-efficient is three times the linear. The superficial will be
found by simply doubling the numbers in the first column.

29. The Enormous Power of Extension and Contraction.
. — When bodies expand, the molecules of which, they arc
composed are pushed farther asunder by the oscillatory
motion communicated to them. The heat may be described
as entering the substance, and immediately setting to work,
separate the particles. The power or energy they exert
to do this is immense. The following are illustrations of the
energy of molecular forces. We have already mentioned
several under the heads expansion and contraction : —

(a) When a dry wooden wedge is driven into the crevice
of a rook, and moistened with water, the wedge swells and
splits the mass. Thus many accidents have happened to
grinders through the wedges swelling between the axle and
the stone, and causing the latter to burst. Of course, in this
case, centrifugal force assisted the wedges.

(b) When a rope is moistened, the diameter becomes
larger, and the rope shorter, for the fibres are drawn in by
this enlargement. It is said that, in lifting the statue cf
Nelson into its place in Trafalgar Square, the ropes had
stretched through the great weight, and the blocks were close
to each other. The whole operation would have failed,
although the hero was within a very short distance of his
place, had not a sailor cried out, " Wet the ropes." The hint
was immediately taken, and the work accomplished.

(c) Water is turned into steam by heat; this heat endows
the water with (atomic) force sufficient to drive the loco-
motive, to propel the steamship round the world, to work
the mill, the forge, the hammer, the pump, etc.

28 STEAtf.

(d) If the wall of a largo building be bulging out, and an
iron girder placed in a proper position, the power of contrac-
tion by cold will subserve the purpose of bringing it into the
perpendicular. It has been done on a large scale in France.
A girder (or girders) was fitted across the building with
strong wall-plates at each end, and screwed up as tightly as pos-
sible. All along the girder was applied a number of gas jets,
and as it expanded by the heat, the screws were tightened.
The girder was then allowed to cool, and the strain of its
contraction was sufficient, after repeating the process several
times, to draw the walls into the perpendicular.

(e) We may almost add, that the Gulf Stream and the
trade winds are caused by the atomic force of heat (but see
Convection).

30. Molecular Force, or Atomic Force. — All molecules
are under the influence of two opposite forces. The one,
molecular attraction, tends to bring them together; the other,
heat, tends to separate them, its intensity varies with its
velocity of vibration. Molecular attraction is only exerted
at infinitely small distances, and is known under the name
of cohesion, affinity, and adhesion.

31. Cohesion. — By the force of cohesion this paper is
held together. Heat and cohesion are directly antagonistic.
When heat predominates in liquids, they become gases; when
cohesion predominates, they become solids, or they may
assume the spheroidal form, as exhibited in the dew-drop,
a tear, etc. The manufacture of shot gives a striking illus-
tration how the two forces, cohesion and gravitation, act.
The lead for the shot is melted at the summit of a high
tower ; the molten lead, mixed with a little arsenic to give
it the exact amount of fluidity, is then, poured into a kind
of sieve. It passes through the holes by its own weight
(gravity), and in falling through the air, assumes — through
the force of cohesion acting on it, in the same way as in the
rain-drops — the form of a sphere ; by the attraction of gravi-
tation, it falls to the ground.

32. Affinity or Chemical Affinity is another form ot
molecular force. If oxygen and hydrogen be chemically
united, in the proportion of one to two, they form water.
The molecules are united by chemical affinity, but held

RADIATION AND ABSORPTION OF HEAT. 20

together by cohesion. By the same force light is produced.
The majority of light-giving substances are composed of
hydro-carbon. The oxygen of the air first combines with the
hydrogen, because it has the greatest affinity for it; the
carbon is then set free, and we have an intense light, as the
carbon passes from the hydrogen into the oxygen during the
great evolution of heat caused by the chemical combination.

33. Adhesion is the molecular force exerted between
bodies in direct contact. If two pieces of lead have their
pure metallic surfaces laid bare, and be put together with a
twist and pressure, they become united by this force. So
will steel, or iron, or brass, unite with lead, if their clean and
flat metallic surfaces be brought into contact. In. punching
out leaden bullets from the solid lead, as is done at Woolwich,
the steel dies will adhere to the lead and become one solid
mass, unless grease be used to prevent too close contact.
Two pieces of flint-glass will thus unite when truly flat and
clean. Before the introduction of the thrust-block to receive
the thrust of the screw-propeller shaft, the whole thrust
or force to drive the vessel was received upon a fixed steel
plate. Instances have been known in which the end of the
screw-shaft and the steel plate have so firmly adhered to each
other, that the shaft has broken elsewhere. This simply
resulted from the constant and enormous friction having
consumed all the oil, etc., between the two; and two pure
metallic surfaces were formed, which united under pressure.

The atomic force of heat has been sufficiently illustrated
under the headings of expansion and contraction. But we
must not omit to notice how this is connected with our sub-
ject, steam. By employing these atomic forces we obtain
the fire necessary to generate the heat required, which endows
the water with potential energy sufficient to do all our work,
and this simply by observing how they act, and making them,
by using natural laws, work for us.

34. Radiation and Absorption of Heat. — Good and bad
radiators. — Radiant heat is heat passing out of bodies into
the air in straight lines. We have also the radiant heat of
the sun, conveyed by the ether to our atmosphere, and passing
through it to the earth. Some bodies will allow radiant heat
to pass out more freely than others. The tea in an earthen-

30 STEAM.

ware teapot cools more rapidly than in one of silver. A
boiler unpainted, unclothed, or not surrounded as far as
possible by sawdust, ashes, etc., will radiate far more heat,
or require more fire to keep up steam, than one that is
protected and well surrounded by some of the substances
mentioned. Glass is a better radiator than pewter. Colour
does not effect radiation. If too much water be filled into a
boiler at first, the fires will not burn so well as if only a little
water were in the boiler ; because the fire absorbs too much
cold at a time, or too much cold is conducted from the water
to the fire to allow it to burn properly. For the same reason
too much fuel thrown, on a fire tends to put it out.

35. Absorption is the power of taking in heat. Coated
surfaces absorb more readily than uncoated. Lampblack
readily absorbs heat, and quite as readily allows it to radiate.
There is this reciprocity between radiation and absorption, —
good radiators are good absorbers, bad radiators are bad
absorbers. Take the same instance again. An earthenware
teapot is a good absorber and a good radiator. Hence good
tea is made in it. For its possessor, by placing in on the
hob, puts it where it can readily absorb heat, and so all the
flavour and strength is properly extracted from the leaves.
Coat bodies with ever so thin a layer of metal it becomes a
powerful defence against radiant heat. We thus see that
the engine driver, who keeps his cylinder covers constantly
bright, powerfully protects them from a loss of heat. Steam
pipes should be well clothed to prevent this radiation.

36. Conduction. — If we place a poker or piece of iron in
the fire, the molecules of the iron in the fire immediately
begin to oscillate, and each molecule strikes its neighbour,
passing the motion on ; so that the end of the poker out of
the fire also becomes warm. The process by which the heat
is passed up the poker is called conduction. There are good
and bad conductors. The metals are generally good conduc-
tors, and the earths, sawdust, ashes, stone, glass, chalk, etc.,
bad conductors. Silver is one of the best conductors. If
we call its power of conduction 100, that of copper is 74, of
gold 53, iron 12, lead 9, bismuth 2. A knowledge of this
property of heat will teach an engineer on what to bed or
surround his boiler, so that the least possible heat may be

FRICTION. 31

conducted out of it ; also, in what lie may case his steam
pipes, cylinder, etc., to attain the same end.

37. Friction. — Every school boy knows the effect of sharply
rubbing a metal button on the desk, and. clapping it on to his
neighbour's hand. Any amount of heat may be generated
by friction. The breaks of a railway train are constantly set
on fire by this cause. The friction caused by axles, journals,
etc., on bearings, quickly makes them hot. Oil keeps a bear-
ing cool, because it lessens the friction. No amount of oil
will keep a badly turned bearing or an improperly scraped
one cool, for the inequalities left by bad workmanship are
the best generators of heat.

The action of the lubricant is this : a thin film of the
lubricant is partially capable of preventing the surfaces of tho
two pieces of machinery coming into contact, it thus reduces
the resistance due to friction, and assists also in conducting
away the heat generated by friction.

The resistance from friction depends not alone on the
roughness of the surface, but the force of pressure, the load
or work done. On the same surface a double load will pro-
duce double the amount of friction, a treble load treble the
amount, etc. This statement must be taken within certain
limits. Friction does not at all depend upon the magnitude
of the surface in contact. Let a block of brass, weighing
100 Ibs., be placed on a flat, smooth surface of cast iron, it
will require a force of 22 Ibs., or -f^ = ~ of the whole to
draw it along. If another 100 Ibs., the same size and shape,
be attached to the side of the other, it will require 44 Ibs. to
draw it along, still -/^ = ii of the whole weight. Now, let
the second block be placed upon the first, so that with the
same weight we have only - one-half the rubbing surface,
experiments conclusively show that the friction is still
-JJ-, or it requires the 44 Ibs. still to drag the two weights
over the cast iron, although the surfaces in contact are
diminished by one-half. This ^ = '22 is called the co-efficient
of friction.

The laws of friction received great attention from Coulomb,
General Morin, etc. The following are a few of the co-effi
cients that may possibly prove of service to the engineer.
Unguents were not used in their determination : —

32 STEAM.

Oak on oak, *C2

Wrought iron 011 oak, '49 to fC2

Cast iron on oak, , '65

Wrought iron on cast, '19

Cast iron on cast, "10

Cast iron axles on Lignum Vitse bearings, ... 'IS

Copper on oak, 'C2

Iron on elm, - '25

Pear tree on cast iron, '44

Iron axles on Lignum Vitre bearings, "11 (with oil )

Iron axles on brass bearings, '07 ( ,, ,, )

The two laws of friction may be expressed tlins : — (a)
Within certain limits the friction of any two surfaces increases
'iii proportion to the force applied to press them together. (I)
The friction is entirely independent of the magnitude of the
two surfaces in contact. It must never be forgotten that the
friction of motion is wholly independent of the velocity of
motion. To reduce friction lubricants are employed, such as
grease, tallow, oil, soft soap mixed with oil, black lead, etc.,
with water and sulphur; the two latter act in a very different
manner to the lubricants, and are generally used in extreme
cases. The co-efficient of wrought iron on oak is '49 in the
dry state, but apply water it is reduced to -26, while soap
will reduce it to *21. Oil, tallow, lard, etc., have all about the
same effect, whether it be wood on wood, wood on metal, or
metal on metal, the co-efficient being -07 or -08, or lying some-
where between; but in the case of tallow interposed between
metal and metal the co-efficient rises to -1. Water reduces
the temperature of bearings, because it boils at a very low
temperature, and thus a large amount of heat is carried away
in steam as latent heat. Sulphur boiling at a temperature
108° C., acts on the same principle.

Cold water should never be thrown upon a hot axle or
bearing, there being great risk of fracture owing to the
sudden contraction of the metal.

38. Temperature and Measures of Temperature.— The
temperature of a substance is the amount of sensible heat it
contains. This heat is measured by the thermometer,
pyrometer, or calorimeter.

39. The Thermometer. — The thermometer is used for
measuring the intensity of the heat in air, water, etc. It

FAHRENHEIT'S THERMOMETER.

mainly consists of a tube with a capillary bore, and a bulb
at the end containing mercury or quicksilver. By the side
of the tube is the scale, graduated into degrees, from which
the temperatures are read off. The filling of the bulb and
part of the tube with mercury requires the nicest manipula-
tion, so that all air and moisture shall be totally excluded
from the tube, after which the end is hermetically sealed.
There are three methods of graduating the thermometer : —

(1) FAHRENHEIT'S.

(2) CENTIGRADE.

(3) REAUMUR'S.

40. (1) Fahrenheit's Thermometer. — Gabriel Fahrenheit
was born, at Dantzic, and settled at Amsterdam as an instru-
ment maker, where, in 1725, he improved the thermometer by
substituting mercury for spirits of wine, thus greatly
increasing its accuracy. The expansion by heat and con-
traction by cold of mercury, is the same for all temperatures,
at least practically so, for which a thermometer is used.
Hence the superiority of mercury over alcohol or water.
Fahrenheit named the freez-
ing point 32°, and the boiling FAHRENHEIT CENTIGRADE REAUMUR
point 212°. The reason for

this choice may be briefly
noticed. Ice in the act of
freezing, and also during its
conversion into water, retains
always the same temperature;
boiling water, under the same
pressure, also maintains the
same temperature as long as
it boils, and you cannot make
it hotter under the circum-
stances. Therefore no better
starting points for the gradua-
tion of the thermometer can be secured, especially as pure
water is always- procurable.

In Fahrenheit's time it was supposed that the greatest
.degree of cold attainable was reached by mixing snow and
common salt, or snow and sal-ammoniac. A thermometer

32°

THBEMOMETEE3.

100°

-80°

34 STEAM.

plunged into a mixture of this kind was found to fall much
below the point indicated by melting ice. The point to
which the mercury fell by contraction, when plunged in this
mixture, Fahrenheit marked 0°, the interval between this
and the freezing point he divided into thirty-two equal
divisions, hence the freezing point came to be indicated by
32°. The equal divisions were continued upwards, and the
mercury, by expansion, reaching 212° when the thermometer
was immersed in boiling water, this 212° was called the
boiling point. This is briefly the reason for Fahrenheit adopt-
ing his method of division, and why he has 212° - 32° = 180°
between the freezing and boiling points. Fahrenheit's scale
is the one used in England. A much lower temperature than
0° F. has been observed!- Mercury becomes solid at — 40° F.
This temperature, which has often been observed by Arctic ex-
plorers and others, would perhaps be a better limit to the scale,
because it would then register the utmost extremes of heat
and cold to which the mercurial thermometer is sensible.

41. (2) Centigrade Thermometer — Celsius, a Swede,
adopted another mode of division. He masked the freezing and
boiling points on his thermometer, calling the former 0°, the
latter 100°, and divided the interval between into a scale of
one hundred parts. This method of indicating the measure of
heat is called the centigrade, and is found so convenient that
it is fast superseding Fahrenheit. The sooner it displaces
the other modes the better, as the decimal and a uniform
scale seem very much wanted, and are certainly the most
convenient. This scale is mostly used in France.

42. (3) Reaumur, or Homer, introduced a much more arbi-
trary division of the scale, which is commonly used in Germany.
He called the freezing point 0°, the boiling point 80°. "We
now see that in Fahrenheit's scale there are 180° between
the freezing and boiling points, in the centigrade 100°, in
Ileaumur 80°.

Rules to compare the reading of one thermometer with
that of another : —

(1) To convert Fahrenheit's degrees to centigrade —

Subtract 32Q, then multiply by 5, and divide by 9.

(2) To convert centigrade to Fahrenheit —

Multiply by 9, divide by 5, and add 32°.

THE REGISTER. 35

(3) To convert centigrade to Reaumur —

Multiply by 4 and divide by 5, or subtract one-fifth.

(4) To convert Reaumur to centigrade —

Multiply by 5 and divide by 4, or add one-quarter.

(5) To convert Fahrenheit to Reaumur, or Reaumur to
Fahrenheit —

First bring them into centigrade, then reduce to
Fahrenheit or Reaumur, whichever may be
required.

Exercises on the reduction of the number of degrees of
cue thermometer to an equivalent number of another, will be
found at the end.

43. The Pyrometer. — The pyrometer is used for showing
the change produced in solid bodies by the application of heat,
from this chaiiga the temperature is calculated. The pyro-
meter has been brought forward in many shapes, such as the
Sevres, Wedge-wood's, Ellicott's, Guyton's, DanielFs, Lavoisier
and La Place's, etc. Wedgewood's pyrometer consisted of
two pieces of brass, each 24 inches long, fastened on a plate,
with two of tha ends five-tenths of an inch apart, and the
other two three-tenths apart. Small cylinders of carefully
cleaned and well baked clay were made so as to exactly fit
into the larger end when the clay was just red hot. On
exposure to greater and intense heat the clay shrank, and
the farther it passed down between the bars the higher the
temperature of the fire, furnace, etc. The shrinkage of clay
is not uniform at all temperatures, so Wedgewood's apparatus
has been, abandoned for Lavoisier and Laplace's, of which
a full description will be found in Mr. Balfour Stewart's
Treatise on If eat, page 2G.

44. Daniell's Pyrometer. — This is a valuable instrument,
and consists of two distinct parts —

(1) THE REGISTER.

(2) THE SCALE.

45. TliG Register. — A B consists of a solid bar eight inches
long, cut out of a piece of black-lead earthenware, clown its
centre is drilled a hole, marked by the dotted lines, reaching
nearly to the bottom. A tube of platinum (ac) is first placed
iii the hole, above this and touching it is a tube of porcelain

STEAM,

(ccZ), called the index. Hound the register at A is a strap of
platinum which can be tightened by a wedge, not shown in the

figure; when the index is forced
out by the heat expanding
the bar of platinum, the strap
prevents it from returning.

46. The Scale consists of a
frame formed of two rectangular
plates of brass, C and D, C is
joined on to D by two hinges ;
C acts as a guard to keep the
register A B in its place. The
strap also rests on the projec-
tion 6, which also performs the
same office. E is a graduated
arc formed on the end of the
arm F, which moves on a fixed
centre f, while d e is another
arm moving on its centre o,
DANIELL'S PYROMETER. and carrying a vernier, Y, and
terminating in a knife-edge at d. When about to be used, the
register is placed behind the scale, as seen in the figure, so
that the tube of porcelain just touches the arm de, the
position of the vernier is noted, then the register alone, with
the index and platinum bar in it, is exposed to the heat to
be measured; it is next taken out of the heat and allowed to
cool; after which it is applied to the scale, or placed as in the
figure, the strap preventing the index from returning to
where it was pushed by the expansion of the platinum; it is
evident that the vernier will be moved downwards through
the arm e, being moved on its fulcrum o, and indicate the
temperature corresponding to the expansion of the platinum.
The difference between the first and second readings will
be the temperature sought.

47. Mr. Houldsworth's Pyrometer,* as used in his experi-
ments on the combustion of fuel, is a useful and simple
apparatus. At the bottom it consists of a bar of copper
resting on iron pegs, placed in one of the side fiiies, and
fixed on the end of the boiler. One end of this bar comes
* See Fiurbairn's Useful Information for Engineers. First Series,

THE USE Otf TIl£ PYROMETER. 37

through the brickwork and gives motion to the short arm of
a lever, the longer arm of the lever answers the purpose of
an index, pointing to a graduated scale of temperatures. As
the bar of copper expands and contracts by the varying
temperature of the flue, it compels the index to move
backwards and forwards. To the larger arm. of the lever
is also attached a rod parallel to the former, which also
moves backwards and forwards with the change of tempera-
ture. During the oscillations this latter bar causes a lead
pencil to press on a revolving cylinder, round which is
fastened a sheet of paper, so that a line is traced indicating
the variations of temperature in the flue, as exhibited by the
expansion and contraction of the bar of copper.

48. The Use of the Pyrometer is to exhibit the tempera-
ture of furnaces, ovens, kilns, etc. Mr Houldsworth
established by it the following interesting facts : —

(1) That the admission of a certain quantity of air behind
the bridge acts most advantageously. The oxygen of the air
combines with the carbon and hydrogen of the fuel, and a
greater amount of heat is developed for generating steam.
The smoke is also consumed ; whenever smoke is seen we
have a sure sign of waste. Too much air cools the furnace,
too little gives an imperfect combustion; but when the
proper supply is maintained we have perfect combustion.
The carbon of the coal, which is seen so frequently escaping
as smoke, is converted into carbonic acid gas, and the
hydrogen, combining with a less proportion of oxygen, is
converted into vapour.

(2) A regular and continuous supply of air to the furnace
increases its heating powers 33J per cent.

(3) The supply of air may enter behind the bridge through
the bars, or through the furnace doors, so long as it is properly
regulated.

(4) The supply of air must vary ivith the nature of the
coal. With light burning fuel less air will be required than
with caking coal, because in the latter case the charge in the
furnace becomes a compact mass excluding the air, while the
former leaves clear spaces between the bars for its entry.

(5) For perfect combustion a high temperature is necessary.
This fact was established by Sir Humphrey Davy.

oS BTEAtt.

49. Specific Heat, or Capacity for Heat, is the power of
storing up heat.

50. The Calorimeter is not used to measure the tempera-
ture of a body, but to ascertain the total amount of heat in
it, or to find the specific heat.

Two similar metallic vessels are placed one within the
other, so as to leave a space between them. This space is
tilled with pounded ice, while a discharge-pipe proceeds from
the bottom of the external vessel to carry off all water that
may be produced through the liquefaction of the ice by the
external air. A third, and nearly similar vessel, is placed
within the second, leaving a space between it and the second
vessel, which is also filled with pounded ice ; a second dis-
charge-pipe (with a stop-cock) proceeds from the second
vessel without communicating with the outside one. Each
vessel is provided with its proper cover. It is obvious that
the ice in the inner space cannot be affected by the tcm-
.porature of the external air when the calorimeter is closed.
The substance, whose specific heat we wish to ascertain, is
placed, after observing its temperature, within the third or
inner vessel. It is perfectly clear that any heat the body may
contain, will communicate or lose its motion to the ice in the
second space, or the ice will take up the heat from the sub-
stance as latent heat, and become converted into water ; this
is then allowed to pass through the discharge-pipe leading
from the inner vessel, and is collected. This water will at
all times be proportional to the heat stored up in the given
substance placed within the calorimeter.

Supposing a body at 50° to be placed in the calorimeter,
and permitted to sink to 40°, or through 10°, if the quantity
of ice melted be ten grains, this would be a grain for every
degree. If we divide the weight of melted ice by the number
of degrees through which the body has fallen, we obtain the
quantity which the body would melt by falling through 1°.
This quantity expresses the specific heat of the body. By
the calorimeter, it has been ascertained that to raise the tem-
perature of water 1°, requires thirty times as much heat as
would be required to raise mercury 1°. Or the same heat
that would raise 1 Ib. of water 1°, would raise the tempera-
ture of 30 Ibs. of mercury 1°; and this is what is meant

THE CALORIMETER. 39

when we say the specific heat of mercury is -^ or -03 that
of water. Iron requires 3| more heat than lead to work in
it the same change of temperature; practically, this means
that lead will heat 3| times quicker than iron; at the same
time it will cool very much more quickly than iron. It is
obvious that to heat 2 Ibs. of water 1°, requires twice as much
heat as to heat 1 Ib. of water 1°. The relative quantity of
heat necessary to produce the same change of temperature in
different bodies is their specific heat. We said the capacity
for heat of water was thirty times that of mercury; hence
this latter substance is so well adapted for thermometers;
we see at once how sensible it must be to the least accession
or subtraction of heat. Again, the capacity for heat of air
at constant pressure, is about one quarter that of water, or
more accurately '237; hence 1 Ib. of water, whose specific
heat is 1, on losing 1Q of heat, will increase the temperature
of .^3T = 4'2 Ibs. of air 1Q. But water is 770 times heavier
than air. Hence if we compare volume instead of weight, a
cubic foot of water, on losing 1Q of temperature, will increase
that of 770 x 4-2 = 3234 cubic feet of air 1°.

Capacity for heat may be defined as the quantity of heat
necessary to raise the same weight of different substances
through the same number of degrees of temperature, but it
must not be defined as the amount of heat necessary to raise
a pound weight of a given substance one degree in tem-
perature, or else we shall confound it in the case of water
with the unit of heat. Capacity for heat is found thus : one,
two, three pounds, ounces, etc., any weight may be chosen,
of any substance, and heated so many degrees, one, two, three,
etc. (generally heated in boiling water), and then put into
the calorimeter, when according to the quantity of ice melted
we have the capacity for heat. The quantity each substance
liquefies is noted, the whole compared with water as a
standard, and the capacity for heat determined.

The following are the specific heats or capacity for heat of
a few well known substances : —

Iron, . -1098 White marble, '2158 Air, . . '2370

Mercury, '0330 Sulphur, . . '1844 Steam, . '4805

Silver, . '0557 Platinum, . '0355 Ice, . . '5040

Copper, . -0949 Glass, . . '1770 Water, . I'OOOO

STEAM.

51. Convection. — Convection is the transfer of heat by sen-
sible masses of matter from one place to another. Water
can only be heated by convection ; it is scarcely possible to
heat it by conduction. Our rooms are ventilated by convec-
tion, smoke ascends the chimney by the same principle, and all
our winds and currents, in both air and water, are caused by
this convection. The wind-sails of a ship afford an instance
in w^hich this law of nature is made available for ventilation.
If A 13 be a glass vessel or large Florence flask filled with
water, when heat is applied at A, the
water near A is immediately heated
and expanded, and becoming specifi-
cally lighter rises up, and the colder
water from above falls down to sup-
ply its place ; this continual change
goes on as long as the heat is applied
at A, and is called convection. If
a little cochineal be placed in the
water, it will sink to the bottom
of the flask, and heat being applied
as before, the cochineal directly
leaves the bottom, ascends up the
middle, and then descends by the
sides, returning again to the heat.
By this simple experiment the action
of convected water is made visible to the eye.

Let C D be a large test-tube filled with water, and held
by an holder in the position indi-
cated by the figure; then let heat be
applied at D, it will be found almost
impossible to heat the water in the
test-tube, for the heated or convected
water rises perpendicularly up from
the heat, confining itself to the top
of the tube, and scarcely any heat is
conducted downwards; for, of course,
the convected or light water cannot
run down, or mix itself with, or
rather communicate its motion to, the heavier water below.
Large masses of water can only be heated by convection,

CONVECTION OF WATER.

CONDUCTION OF WATER.

MECHANICAL EQUIVALENT OF HEAT. 41

and therefore all furnaces should be placed as low down in
the boilers as possible, while below the bars there should be
but little if any water.

A patent fire-door is used for boilers, which is nothing but
the application of the principle of convection : the doors are
made with front and back plates, and hollow within. In the
front plate are a few openings from one to one and a half
inches in diameter ; the back plate is thoroughly perforated
with smaller holes. The air goes in at the bottom of the front
plate and out at the top, carrying off the heat, thus the front
of the door is never heated to redness, the current of con-
vected air carrying off the heat. In precisely the same
way the funnels of steamers are kept cool, and passed
through the wood of the decks. A casing is placed entirely
round the funnel, passing into the engine-room, and some-
times spreading out over the boilers. A stream of air then
continually runs up between the funnel and the casing; this
air takes the heat out of the funnel as it passes upwards, and
keeps it from becoming too hot. Holes are often made at
the bottom of the casing for the passage of additional air.

52. Conversion of Heat into Work, and Work into Heat.—
A fire is lighted in the furnace of a locomotive; when the steam
is sufficiently elastic, the train moves out of the station, the con-
sumption of heat drives the train along; when it approaches a
station the driver shuts off the steam and puts on the brake,
which destroys the momentum of the train, by reconverting it
into heat, causing smoke and sparks to issue forth from the brake.

A good illustration to show that heat is consumed in
mechanical work will be found in the following : —

Let a large quantity of air be forced into a strong box,
then let it cool until it is of the same temperature as the
surrounding air, now open a hole in the box, when the air
will violently issue forth, but intensely cold. To drive out this
air, force is required, or work must be done ; to do this work
no heat can be obtained from the outside, so it consumes the
heat that it possesses within itself, and issues forth very cold.

53 Mechanical Equivalent of Heat. — (a) Heat is motion
— the motion of the ultimate particles.

(b) Whenever work is done, heat is consumed in exact
proportion to the work done.

42 STEAM.

(d) A. thermal unit is the quantity of heat necessary to
raise a pound of water 1° C. in temperature ; this is the exact
amount expended in raising 1392 Ibs. one foot high, or 1 Ib.
1392 feet high.

If the thermal unit of 1° F. be used, then the mechanical
equivalent is that this heat would raise 772 Ibs. one foot
high, or 1 Ib. 772 feet high. The mechanical equivalent of
heat has been determined by some of the most persevering
and exact experiments of modern science.

Let it be supposed that a cubic foot of gas or air is con-
tained in a vessel, with a square foot for its base and fitted with
a piston of the same dimensions, and that heat is applied to
the gas, which is at liberty to expand and drive up the piston.
If the temperature of the gas be raised through 273° C., the
gas will double its volume ; and as the piston is one square
foot in area, this square foot, or 144 square inches, will be
opposed in its ascent by the pressure of the atmosphere; and,
therefore, we shall have 144 x 15 — 2160 Ibs. lifted one foot
high by the act of the air doubling its volume. This cannot
be stated too distinctly, so it is repeated in another shape.
When a cubic loot of air is made to double its volume by
increasing its temperature 273° C., it performs 2160 units of
work.

In the experiment, if we applied the heat, but kept the air
from expanding, or compelled the volume to remain constant,
by continually adding additional weights to the piston (one
ounce for each degree), we should find that when heated
273° we had added 273 ounces, but that less heat was con-
sumed in this latter case than in the former, in the pro-
portion of 1 : 1-421, or,

Heat at constant volume, i
Heat at constant pressure, i'42i

We have now to apply these facts to water, and to show
how the additional heat required in the one case will give
the mechanical equivalent of heat*

A cubic foot of air, since its specific gravity is ^4^-, weighs
iVo°(7 °unces = 1'29 ounces.

MECHANICAL EQUIVALENT OF HEAT. 43

The capacity for heat of air is '24.

Therefore, the 273° C. of heat that were applied to the air
will heat 1*29 x -2 4 = '31 ounces of water through the same
temperature, or 1212L=I5 = 5-28 pounds one degree.

Or, *31 ounces of water heated 273Q C. is the same as 5 '28
pounds heated 1° C.

But this water is supposed to be heated under constant
pressure. Let us, therefore, find what quantity we should
have had, if it had been heated by the heat that was consumed
when the volume was kept constant. It evidently follows
from the proportion given above,

1421 : 1 : : 5-28 Ibs. : 3-72 Ibs.

Subtracting 3'72 from 5-28 gives 1'55 Ibs." This must be
the quantity of water heated by the excess of heat between
constant volume and constant pressure ; and this excess of
heat must have performed the 2160 units of work.

Since the heat necessary to raise 1'55 Ibs. of water 1°C.,
performs 2160 units of work ; therefore the heat necessary to
raise 1 Ib. of water 1°C. is equivalent to *1~ = 139 3 -5 units
of work.

Hence the heat necessary to raise 1393-5 pounds one foot
high will raise a pound of water one degree centigrade. This
1393, or more precisely 1390,* is called the mechanical equiva-
lent of heat. " Heat and mechanical energy are mutually
convertible; and heat requires for its production, and produces
by its disappearance, mechanical energy in the ratio of 1390
foot pounds for every thermal imit."t

It will help to a thorough conception of the above if the
student will endeavour, by the same course of reasoning, to
find the mechanical equivalent of heat in terms Fahrenheit.
He must use 490° for 273°, and his conclusion will be that
the heat required to raise a pound of water one degree
Fahrenheit will perform 771 '4 units of work.

Hence 772 is the mechanical equivalent of heat for each
degree Fahrenheit.

* Several of these numbers are taken as if the decimal plr.ccs are
worked out farther than shown in the context,

t Ganot's Physics, page 41 L

STEA1L

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. What do you understand by conduction and convection as applied
to heat (1867)?

2. What is meant by the following terms as applied to heat: —
Conduction, convection, radiation, and capacity for heat (1865)?

3. What do you understand by the conduction of heat? Mention
one or two good, moderate, and bad conductors of heat (1869).

4. What is meant by capacity for heat ? The capacity for heat of
mercury is '033, how much at the temperature of 240° will be suffi-
cient to raise 12 Ibs. of water from 50° to 58° (1867)?

Am. 16 Ibs.

5. £5how how to convert degrees on a centrigrade into degrees on
Fahrenheit's scale.

What temperature F. corresponds to 18°'5C. (1866)?

Ans. 65° '3 F.

6. Show how a thermometer is graduated. Compare the gradua-
tions on Fahrenheit's, Reaumur's, and the centigrade scale. Reaii-
mur's scale shows a temperature of 15°, what will the centigrade and
Fahrenheit's scales respectively show for the same temperatures
(1868)? Ans. 18J°C., 65f F.

7. Describe the calorimeter and Daniell's pyrometer. For what
purposes are these instruments respectively used (1868)?

8. A centigrade thermometer marks 5°, what will a Fahrenheit
thermometer mark (1865)? An*. 41 °F.

9. Give a few simple experiments and illustrations to show that
bodies expand by heat and contract by cold.

10. Obtain a formula for determining the weight of water which
must be mixed with a given weight of steam, in order that the mix-
ture may be reduced to a water of a given temperature (1868).

Let t = the temperature of injection water.

t'= ,, ,, ,, the water coming from the hot well.

. '. Each unit of water is raised t' - 1 degrees of temperature.
The total heat in steam is 637 '2° C., which has to be reduced
C37-2-*'.

637 '2 — t'
.'. Units of water required—-—; •

Applying this formula to the next example, we have
637'2~^_637-2-48g_

t-t -48«-]r>j ~17'G

that is, each unit of steam, be it inch, foot, or pound of water con-
verted into steam, will require 17 '6 cubic inches, feet, or pounds, to
condense it ; and as we have 20 Ibs. in the next example, the weight
of condensing water is 17 '6 x 20 = 352 Ibs.

11. What weight of water, at 60°F., must be mixed with 20 Ibs. of
steam of one atmosphere in order to produce water at 120°F. (1868)?

Ans. 17 '6 Ibs. for each pound of steam.

EXERCISES. 45

12. What is meant by capacity for heat? Show how to calculate
the temperature of a mixture of two substances whose temperatures
and capacities for heat are given. 1 Ib. of copper (capacity for heat
*095) at the temperature 520° is mixed with 2 Ibs. of water (capacity
for heat 1) at temperature 60°, what is the common temperature of
the mixture (I860)?

Let iv be the weight of one body, t° its temperature, and c its
capacity for heat.

Let w' be the weight of the second body, t'° its temperature, and
c' its capacity for heat.

Now since the capacity for heat of a body may be taken as the
amount of heat required to increase the temperature of a given weight
one degree

.'.we represents w raised one degree.
.'. iv c t° ,, iv ,, t degrees,
also w' c' t'° ,, w' ,, t' ,,
or w c t and w' c' t'° represent the total heat in w and w'.
Let x be the temperature of the mixture of the bodies w c and wr c'.
. -. w c t + iv' cr tf — x (w c + ior c')

__ w c t + w' c' t' /-.x

w c + w' c'

w' c' x - w' c' t' _ w, ct x~ t*_ _ - (°)
wt-wx ~~ w' 't-x

similarly c'=^.c.^
w t-x

Substituting in equation (1) we can solve the question thus:
1 x -095 x (520° - 32°) + 2 x 1 x (60° - 32°)

1 x -095 + 2x1
_ -095x488 + 2x28 102-36

^48'oi>

•095 + 2 ~ 2-095

.-. Ans. -
Or we might have reasoned thus :

Let x — common temperature of the mixture.
Copper is depressed (520 - x)°
Water is raised (x - 60)°

Lbs. Sp. II. of "Water. Sp. II. of Cop.

.'. (520 -x) : 2 (x - GO) :: 1 : '095
.'. 2 £-120 = 49-4- -095 x
.-. 2-095» = 169-4
.V £= 80°-S5F.

The answer in the centigrade scale would be

1x15:}

Ix -095 + 2x1
_ 511/8 O7°.i4f!
~ 18*55 -
or reduce the 80°'85F. to centigrade will give the same answer.

46 STEAM,

13. Show how to graduate a thermometer. Why is it necessary
to take the height of the barometer into account in determining the
boiling temperature (18G6)?

14. Give your reasons for concluding that heat and work are con-
vertible, the one into the other. Describe an experiment by means
of which the mechanical equivalent of heat may be ascertained, and
state its numerical value — (Honours, 1869).

15. What is the great exception to the universal law of expansion
by heat and contraction by cold? Can you give any other exception?

16. Explain what is meant by the co-efficient of expansion, and show
the enormous power of expansion and contraction by a few illus-
trations.

17. What do you mean by the molecular forces, and what are
their names?

18. How do radiation and absorption affect the steam-engine and
its working? State clearly what you mean by the reciprocity of
radiation and absorption.

19. What are the laws of friction? Give a few simple illustrations.

20. What are the instruments employed to measure temperature ?
Upon what principle are they all constructed?

21. What facts have been proved by the use of Mr Houldsworth's
pyrometer ? .Give a description of it.

22. Explain the term cushioning, and clearance (1SGG and 1SCS).

CHAPTER, III,
THE STEAM ENGINE.

Savary's — Xewcomen's — Watt's — Cylinder and Crank — Single and
Double Acting Engines — Clearance — Cushioning — Galvanic
Action — Beam Engines — Parallel Motion — Guides — Governor —
Throttle Valve — Cataract — Eccentrics — Expansion Gear.

54-. (1) Savary's Engine. — Savary's was the first steam
engine employed to pump water. He took out his patent in
1698. His engine consisted of a cylinder, in which steam was
employed to produce a vacuum only, after which he relied
upon the pressure of the atmosphere to raise the water. At
the top of his cylinder were two openings, each fitted with a
pipe and a stop-cock. These were so arranged that the
same handle opened one stop-cock and shut the other simulta-
neously. One pipe communicated with a boiler and admitted
steam to the cylinder, the other with a cistern and admitted
cold water to the cylinder. From the bottom of the cylinder
a pipe led down to the water. It acted thus : Suppose the
handle of the stop-cock moved, and steam admitted to. the
cylinder, the instant it was full the handle was pushed back,
and a dash of water from the other cock condensed the steam
and formed a vacuum ; then the pressure of the air on the
water at the bottom of the mine forced the water up into
the cylinder, which was prevented from returning by a valve
opening upwards ; on a second admission of steam, its elastic
force acting on the water drove it through a valve in the side
of the cylinder opening outwards ; this steam was again con-
densed as before, etc. We thus see the principle upon which
it acted. The water was first forced by atmospheric pressure
into a vacuum, after which the elasticity of the steam pressing
upon its surface was made to raise it still higher through

48 STEAM,

another passage. Tlie inefficiency of this machine is apparent.
Its defects were : that steam was used in a cold cylinder ; that
the steam was always in contact with cold water; and, there-
fore, the greater part of it was lost ; that the engine was
limited in its range and purpose ; that it must be always far
down in the mine from which the water was raised.

55. (2) Newcomen's Engine. — Thomas Newcomeii was a
Devonshire man, and the first to work out the idea of a piston
(at least in England). His engine was used for pumping.
In fact, the one idea of the early labourers at the steam
engine was to adapt it, or to invent a machine, to pump
water out of the Cornish mines.

Newcomeii placed his cylinder immediately above his boiler,
from which steam passed directly through a stop-cock. As
soon as the piston was at the top of its stroke, a cock was
opened and cold water admitted into the cylinder to condense
the steam ; a vacuum being thus obtained, the pressure of the
air, 15 Ibs. on the square inch, immediately drove down the
piston, which was attached by a chain to the end of a sway
beam moving on its centre. The piston being thus forced
down by atmospheric pressure pulled up the other end of the
beam at the' same time, and with it the pump-rods, water,
etc. When fresh steam was admitted it forced up the piston
against the atmosphere, while the weight of the pump-rods,
etc., at the other end assisted the steam. The weight of the
pump-rods, etc., was generally made equal to half the pressure
of the air on the piston. This engine raised 7 or 8 Ibs. for
each square inch of the piston. Newcomeii's was a siitf/Ie
acting engine, because the steam acted on one side of the
piston only.

Newcomen's engine is represented in the figure on the oppo-
site page, AP is the ashpit, FP the fireplace, B the boiler, S G
a stop-cock to admit the steam into the cylinder H from the
boiler B. The cylinder was bored as truly as possible, open at
the top and closed at the bottom, being connected with the
boiler by a short pipe containing the steam-cock. A piston p
was made to move up and down in the cylinder, as air-tight as
practicable, by packing its edges with hemp and covering the
iipper surface with wator. The piston rod r was attached by
a chain c to the circular arc c d, forming the end of the beam

KEWCOMENS ENGINE.

e d c, which was now for the first time introduced. The beam,
working on its centre C, was framed of strong timbers

KEWCOMEN S ENGINE.

firmly put together and strengthened by iron bars and straps.
The whole beam was supported on a strong brick wall, B W.
To the chain e attached to the other arc was fastened the rod
p r of the pump to be worked in the mine. The power of
the engine was in. the down stroke. The pump-rod was
made heavy enough to act as a counterpoise by attaching
weights g to it, so that it was heavier than the piston, piston-
rod, friction, etc. When the cock S C was opened and air
admitted, it would rise freely without violently jerking out
the piston p. A safety valve was placed on the top of the
boiler. The manner in which the engine worked was as
follows : —

The boiler B was filled with a proper quantity of water,
and the steam " got up " to a pressure a little above that of
the atmosphere. The cock S C was opened (supposing the
piston at the bottom of the cylinder), and the steam entered
the cylinder, when the piston ascended partly through the
force of the steam, but chieflv in obedience to the counter-

50 STEA:.!.

poising weights g. Just before tlie piston reached tho
top of the cylinder the steam-cock was shut and another
cock o was opened, which allowed water from the cistern S
to ilow through the pipe in and condense the steam in the
cylinder, producing a vacuum, when the pressure of the
external air, acting on the top of the piston, caused it to
descend with a force proportionate to its area ; and as this
force amounts to nearly 15 Ibs. on the superficial inch, it
was fully competent to raise the end of the beam e, and
with it the pump-rods and water. We thus see that the real
work was done by the atmosphere, and why it was called an
atmospheric engine.

Originally it was much less perfect than here described,
for the condensation was in the first instance performed from
the outside of the cylinder. The admission of water into the
cylinder to condense the steam was discovered accidentally,
through some holes wearing in the piston of an engine which
permitted the water placed upon it to keep it air-tight to run
through and condense the steam, although we must remember
Savary had introduced steam into his cylinder and condensed
it in the cylinder. The great difficulty of opening the cocks
at the proper moment was conquered by Humphrey Potter,'1"
who attached some strings and catches to the cocks of an
engine he was employed to work at Wolverhampton, in order
to release himself from the trouble of attending them ; his
contrivance gave the first idea of " hand gear." The greatest
nicety and attention on the part of the workman was necessary
in turning the two cocks at the proper moment ; for if steam
were permitted to enter the cylinder for too great a length of
time, the piston would be carried out of it or blown out of its
place ; while, on the contrary, if not opened soon enough, it
would strike against the bottom with sufficient force to break
the cylinder. The steam was liable to become mixed with
air, which was disengaged from the injection water. This
air, together vrith the injection water, was discharged by
a pipe n into the cistern s. The pipe n terminated in
a valve to preserve the vacuum, which valve, from the
peculiar noise it made was called the swifting valve or snift-
ing clack.

* Millington's Mechanical Philosophy.

WATT'S ENGINES.

Mr. Henry Beighton, of Newcastle- upon -Tyne, effected
most important improvements in Newcomen's engine, by
using what lie called a "plug tree" for admitting and shutting
off the steam, by introducing a small force pump to feed the
boiler, and otherwise giving a better arrangement to the
working parts. In fact, the machine was frequently known
as Beightoii's Fire Engine.

It was an atmospheric engine, because it depended upon
the pressure of the atmosphere to perform the down stroke —
in fact, to do the chief part of the work.

Its great disadvantage was that the cylinder was at one
time required to be hot and at another cold ; that the fresh
steam entered a cold, wet cylinder whose temperature
had just been reduced, thereby losing three-quarters of its
power.

56. (3) Watt's Engines. — Watt, having the model of an
atmospheric engine,
such as we have just
described, to repair,
asked himself the
question, whether it
were not possible to
prevent the wasteful
expenditure of steam.
He saw intuitively
the great defect of the
engine, and set himself
to solve the problem
of a separate condens-
er In this he com-
pletely succeeded, and
never left the steam
engine until it was

comparatively a perfect machine. The above figure is a
fair representation of the great improvements he introduced.

A B is a large casting, within which is placed the condenser
C, the air pump AP, and the hot well H W. V is the piston
or bucket of the air pump, with its two valves shut down, but
shown by dotted lines as they will appear when the piston
Y is descending. E P is the exhaust pips, to convey the

CONDENSER AND AIR PUMP.

52 STEAM.

used steam from the cylinder into the condenser C. C W is
a pipe bringing cold water from the pump, v the foot valve,
v the delivery valve. W W W W is water surrounding
the condenser and air pump, to keep the condenser cold.

Let us suppose that the steam having been used comes
from the cylinder, through the exhaust pipe E P. The
moment it enters the condenser, it is met by a scattered jet
of cold water from the rose head c, and is condensed. The
condensed steam and water fall to the bottom of the condenser,
and pass or are drawn through the foot valve v. Then
the piston or bucket Y of the air pump comes down into the
water ; the pressure of water opens the two butterfly valves,
and the water passes through the valves and so gets above
the piston. When the piston is drawn up the two valves
are closed by the weight of the water above them, which is
next forced or delivered into the hot well H W, through the
delivery valve v', from whence part of it is pumped into the
boiler through d, a part of the feed pump. As the air pump
ascends a vacuum is formed in A P, at least as good a vacuum
as exists in the condenser C, so that the condensing water
passes by gravity, etc., through the foot valve v, or "follows
the bucket." As the air pump descends we see v must close,
so must v' ; on the contrary, as it ascends both delivery and
foot valve will open.

All water contains air more or less. The heat of the
steam disengages the air from the condensing water, which
would rise through the exhaust pipe, and prevent the proper
escape of steam, besides counteracting its pressure if not got
lid of. The air pump was, therefore, added by Watt to his
invention of the condenser, to prevent air from accumulating
and obstructing the engine. Hence its name, air pump, its
office being not only to pump out the condensing water, but
to keep the condenser free from air.

57. Cylinder and Crank. — The Figure on opposite page
is a representation of a cylinder with a locomotive or three-
ported slide. Cylinders are constructed of cast iron and
bored with the nicest precision. They must be perfect cylin-
ders, the same diameter from end to end.

A B is the cylinder, P the piston, and P R the piston rod.
C E the crank, and E a section of the main shaft turned by

HOW THE ENGINE IS WORKED.

the crank and connecting rod C H. s b is the stiiiHng bo::,

and g d the gland. II is the ^

slide, and r the slide rod by
which the engine moves the
slide up and down. S is the
end of the steam pipe which
brings the steam from the
boiler to the cylinder, a is
the upper port, c the lower
port, e is the exhaust port
by which the steam escapes
from the cylinder to the con-
denser after it has done its
work.

58. How the Engine is
Worked. — Suppose the slide
is in the position shown in
the figure, and that steam
fills the valve chamber Y V,
through the steam pipe S.
Now, it cannot pass the back
of the slide into the upper
port «, because the slide is
covering it over ; neither, for
the same reason, can it pass
to the exhaust e ; but it can
pass into the lower port c in
the direction of the arrows
and drive up the piston P,
while, as the piston goes up
the steam that drove it down
and filled the cylinder on the
upper side above the piston,
is escaping freely through a,
in the direction of the arrows,
and passing off to the condenser through e the exhaust port.

When the piston has arrived at the upper end of the
cylinder, or at the top of its stroke, the slide 1 1 has moved
down lower, so that the lower port c is closed against the
admission of steam, and the upper one a opened j therefore,

CYLINDER, CONNECTING HOD, AND
CRANK

steam will enter the upper port and escape at the lower, in
a contrary direction to the arrows, the piston returning to
the bottom of the cylinder.

59. Watt's Single Acting Engine. — In this engine
A B is the cylinder, P the piston, P R the piston rod, S
the steam pipe, D leads to the exhaust, a b c are three valves
on one spindle, a is the steam or throttle valve, b the equi-
librium, and c the exhaust or eduction valve.

The following is an explanation of the action of this
engine : — Steam comes along
the steam pipe S from the boiler,
when the valves a b c, being in
the position shown in the figure,
with a and c open and b closed,
the steam enters the cylinder
A B in the direction marked by
the arrows with tails, and drives
the piston doAvn, causing the
pump valves at the other end to
ascend. Steam that may have
been under the piston in E can
freely pass away to the exhaust
D. The moment the piston is
at the bottom of its stroke the
valves move to their second po-
sition, so that a and c rest on
their seats o, while b is opened.
Thus, the steam that drove the
piston down can run through
valve b, in the direction shown

by the arrows without tails, get under the piston P, and
assist in driving it up. The pump-rods at the other end
are balanced by a counterweight to assist this expanding
steam. The action is then continuously repeated : a and c
open, steam enters through «, drives down P, and the steam
under P escapes through c, then a and c are closed, and
steam runs round through by to assist the upward motion of
the piston.

60. Double Acting Engines.— When steam drives the
piston both up and down the engine is termed double acting.

SINGLE ACTING ENGINE.

THE PISTON, AND HOW FITTED — PACKING, ETC. 55

All our modern engines are double acting ; but ZsTewcomen's
was an atmospheric and single acting engine, the piston being
driven up by steam but down by atmospheric pressure.
Watt's first engine was single acting ; the steam drove the
piston down, while the weight of .the rods, etc., at the other
end of the beam brought it up.

61. Clearance. — When a piston makes its stroke it is not
allowed to touch the top and bottom of the cylinder for fear
of knocking them off.

The space between the top and bottom of the cylinder and
the piston, when the latter is at the end of its stroke, is the
clearance.

Again, the term clearance sometimes includes the capacity
of the ports, passages, etc., with which the clearance proper
is in communication. Clearance is always accompanied by a
certain amount of loss, an average proportion of the steam
pressure which varies with the amount of expansion ; or, the
loss occasioned by clearance is decreased by an increase in the
degree of expansion.

62. Cushioning. — When the steam is shut in before the
end of the stroke, the piston acts against it as against a
cushion, and so is brought gradually (comparatively speaking)
to rest. Suppose the piston is in the position A B when the
steam is shut in, and that from A to C is

12 inches. Let us also suppose that the
elastic force of the steam remaining be-
hind is 2 Ibs., when the piston gets to
D, 6 inches down, by Marriotte's law, its
elastic force will be 4 Ibs. ; when at E,
9 inches down, it will be 8 Ibs., etc.
So we see at once the effects and advan-
tages of cushioning, and that it must bring
the piston gradually to rest, by destroying
its momentum.

63. The Piston, and how Fitted — Packing, etc.— As
the piston is a most important part of the engine, great care
and thought have been bestowed upon it. It must be per-
fectly steam tight, and, at the same time, it is required to
move easily within the cylinder. A cylindrical piece of iron
is chosen and turned about a quarter of an inch smaller in the

56 STEAM.

diameter than the bore of the cylinder, and around it is cut a
deep groove square in section; into this is fitted a metallic ring
of brass or steel, but generally cast iron; this ring either fits
steam tight against the cylinder by its own elasticity, or is
forced against it by springs or compressed air. Formerly
" packing " was much used, when some rope yarn was platted
the exact size of the square groove, the precise length was
cut off, and the ends neatly sewn, together — care being taken
that no turns were left in the yarn. The whole was well
greased before it was fitted in. Metallic piston rings arc
now most in fashion, the piston being composed of two
distinct parts, the piston proper and the junk ring. Tho
junk ring is bolted on to the piston by bolts tapped into the
piston and heads recessed into the junk ring. A metal ring
is next turned exactly the size of the cylinder, and then cut,
when cut we know such a ring will develop its elastictiy, and
some force will be required to place the ends in contact again.
It thus forms a powerful spring, and is placed between the
junk ring and the piston, where a place has been left for it.
The piston is now complete, and the spring or metal riu;.»
being compressed into its proper position, the whole is placed
within the cylinder, forming a very steam tight easy piston.

Pistons are seldom packed now, but the air pump bucket
is ; because packing is cheaper, and also because in this case
it answers better, for a large amount of galvanic action seta
in and eats away the piston of the air pump.

64. Galvanic Action and Oxidation of Metals. — Metals
p-re subject to two kinds of deterioration — galvanic action
and oxidation. When two different metals come in contact,
especially if they are constantly wet, a galvanic action sets in
between the two, and one destroys the other. For instance,
who has not observed that old iron railings are frequently
wasted away towards the bottom, close against the lead that
fastens them into the stone ? The reason is, that a galvanic
current passes from one to the other, and the soft lead wastes
away the hard iron. If we take, in the following order,
silver, copper, tin, lead, iron, and zinc, we have them in
their relative positions as regards galvanic action, and the
farther they are from one another in this list the greater the
effects of galvanic action. Those coming first in order will

BEAM ENGINES. 57

destroy any that follow them. Copper, when in contact with
tin, lead, iron, zinc, etc., will waste them away, but not
silver — the silver will eat away the copper, tin, lead, etc.
When copper pipes are fastened by iron bolts or screws, the
iron is soon destroyed, especially in damp situations.

Oxidation is a chemical action. When iron rusts we have
an instance of oxidation. The oxygen of the air combines
with the iron and forms oxide of iron (or rust). When the
oxygen of the air combines with copper we have oxide of
copper, or verdigris.

Two other facts which are closely allied to oxidation and
galvanic action may be stated, namely : — when superheated
steam is employed in jacketed cylinders, and much tallow
introduced, it is found that the tallow is decomposed, and
carbonises the piston, so that it becomes more like a piece
of plumbago than anything else. Cast iron long immersed
in sea water may be cut with a knife.

65. Stuffing Boxes and Glands. — These are used in
several parts of an engine. A good example may be seen in
the fig. in par. 58, p. 53. The piston rod enters the cylinder
through the stuffing box s b ; while the packing, the part
marked so dark within the stuffing box, is pressed down in
ibs place by the gland cj d ; bolts pass through the flanges
of both, so that when the steam leaks through the cover by
the side of the piston rod, we have only to screw the gland
down on to the packing and the leak is stopped by the
packing being forced against the piston rod. A depression
will be seen round the top of the gland close to the piston
rod, it is to hold oil or tallow to lubricate the piston rod.

66. (4) Beam Engines. — Newcomen's was a beam engine
and so was Watt's, but the latter was far more perfect * than
the former. The crank was not patented in time by Watt,
he therefore used the sun and planet wheel for a crank. The

* Notwithstanding the variety of forms into which it has been
moulded, the steam engine is still the same machine in all its sim-
plicity of principle as when it came from the hand of Watt ; it has
the same reciprocating action, the same principles of separate conden-
sation, and the same mechanical organization as it had 80 years ago.
What can exceed in beauty of contrivance the parallel motion, the
governor, and other motions by which this wonderful machine is
rendered effective. Innumerable attempts have been made at its

STEA:.I.

beam was so advantageous and so thoroughly incorporated
in the steam engine, that to early engineers it seemed an
inseparable part of it as much as the cylinder and piston,
therefore when it came to be adapted to marine propulsion,
the side lever was the only modification that presented itself.
The great advantage of the beam engine is that to the parts
requiring it, it gives a longer leverage, -and therefore greater
power ; a long connecting rod is employed, and thus an im-
mense advantage is gained. Again, a fly-wheel was used with
it to accumulate power.

A B is the beam moving on its main centre C, supported by
a frame and pillars, of which C D is a front one ; B E is
the piston rod working in and out of the stuffing box s, at the
top of the cylinder E F ; G H is the air pump rod ; II

BEAM ENGINE.

the air pump within the condenser H K (only part of which
is shown) ; L M is the feed pump rod] M the feed pump,
into which the plunger is seen descending; N O is the pump to
force up water for condensation; A K is the connecting rod\

improvement, and yet with the exception of working high pressure
steam expansively, and by this means economizing fuel, there has
been no change in the principle of the steam engine, either in its
condensing or non-condensing form. It is still the engine of Watt ;
his name is stamped as indelibly upon it as Newton's upon the law
of gravitation. — Fairbairn's Useful Information for Enyimcrs, Second
{Scries, p. 205.

THE PUMP.

H S the crank ; S the main shaft, on which is firmly fixed the
jbj wheel Y Y. The two dotted circles represent gearing.

The above are the essential parts of the engine, each of
which shall be described in detail as far as necessary. The
other parts are the governor, to open and shut the throttle
valve in the steam pipe, the slide and slide casing, the starting
gear, the parallel motion, the eccentric, etc.

67. (1) The Beam is a lever of the first kind, and needs
no description after an examination of the figure. The
power is conveyed into the cylinder which moves the piston,
the weight is the force conveyed by the crank, the fulcrum
is the main centre.

68. (2) The piston, the cylinder, the air pump, condenser,
and stuffing box, have been already described.

69. (3) The Feed Pump is an ordinary force pump with a
plunger to force the water into the boiler.

A is a solid plunger; v, v, and
v" are three valves ; b v" is the
pipe that brings the water to tho
feed pump; c o carries away the
waste; C c leads to the boiler,
while c is a cock to shut off the
feed from the boiler.

It acts thus : let us suppose
the plunger is raised up, then a
vacuum is left in the valve box
c d, therefore water rises through
the suction valve v''. Let us
suppose c d is filled, then the
descent of the plunger will force the water through the de-
livery valve v and up the feed pipe C c to the boiler. But
suppose the cock c should be closed, then the great pressure
of water will force back the strong spring and open the valve
v'. so that the water can pass down the waste water pipe c o.
Sometimes instead of this arrangement for the waste water,
the pump rod is disconnected when no feed is wanted, and
thus the power necessary to work the pump is saved ; or the
water is turned off before it reaches the feed valve box, and
the pump wastes its strength in lifting air.

70. (4) The Pump is an ordinary pump for raising water.

FEED PUMP.

CO STEAM.

71. (5) The Connecting Rod and Crank have been already
partially described. They are used for converting a rectilinear
into a circular motion. The connecting rod should be as long
as possible ; it is generally from three and a half to four times
the length of the stroke, but when cramped for room or
otherwise, a much shorter rod is made sufficient. The longer
the connecting rod the greater its advantage. It has more
leverage, and therefore does more work. A short connecting
rod gives much pressure upon the slides and a great strain on
the crank and crank-pin, but with a long connecting rod this
pressure and strain are avoided. With a short connecting
rod it is difficult to properly adjust the cut off.

72. (6) The Short and Long Connecting Rod.— That is
the best engine for its purpose, whatever that purpose may be,
that with a given total length possesses the longest connecting
rod. Marine engines frequently have the disadvantage of a
short connecting rod ; it is a main condition with a marine
engine that it should occupy but little space, while its
momentum cannot be stored up in a fly-wheel. The dis-
advantages that a marine engine labours under from having
a short connecting rod are four : —

(a) The friction is increased on the guide pieces.

(b) The friction is increased on the crank shaft bearings,
for at one time the crank thrusts the shaft downwards and at
another pulls it upwards.

(d) The steam is admitted into cylinders in such a man-
ner, that two violent initial pressures constantly and rapidly
succeed each other, consequently an irregularity of motion is
produced.

73. (7) Fly Wheel. — The fly wheel is an accumulator of
power, and assists the crank over the " dead centres." When
the crank and connecting rod are in one straight line, as they
must be twice in each revolution, the crank is said to be on
its dead centre, because there the force of the piston is dead
or ineffective. It is evident that when the crank is at right
angles to the connecting rod, that the latter has most power
on the former, but when the top or bottom dead centre is
reached there is no reason why it should not remain there ;

THE PARALLEL MOTION. 61

but the action of the fly wheel then shows itself, for having
on it a certain accumulated velocity, it cannot stop but goes
forward, carrying with it the crank over the dead centre. We
thus have through the momentum of the fly wheel no per-
ceptible variation in the velocity of the engine, but the
unequal leverage of the connecting rod is corrected, producing
a steady and uniform motion. The . fly wheel, it must be
remembered, is a regulator and reservoir and not a creator of
motion, and when, no fly wheels are used, as in marine engines,
we must recollect that smoothness of motion is not an absolute
requisite, and that the momentum of the engines themselves
carries the cranks over the dead centres ; but far more
generally a pair of engines work side by side, whose cranks
are at different angles, so that one assists the other at the
critical moment. The accumulated velocity in the fly wheel,
where the motion is required to be excessively equable,
should be six times that of the engine when, the crank is
horizontal. The efficiency of the fly wheel in producing
uniformity of velocity is materially modified by the motion
of the machinery which the engine is required to drive, and
regularity of motion is of much greater importance in some
cases than in others, so that in proportioning a fly wheel to a
given engine, attention must be paid to many particular
circumstances which cannot be given in a general rule.

74. (8) The Parallel Motion. — Although the parallel
motion has been almost superseded by simpler pieces of
mechanism, such as guides, quite as efficient, yet a descrip-
tion cannot be wholly omitted.

If the end of the piston rod g had been connected to the end
of the beam, the piston rod would have been bent alternately
to right and left as the beam rose and fell, and a continual
jarring would be going on, constantly destroying the stuffing
box, and rendering the cylinder leaky.

Let us suppose that the simple lines in the adjoining figure
represent the parallel motion, C h is half the beam, h g is the
main link, c d the radius bar or bridle rod. As h moves up
and down it describes an arc of a circle, with its convexity to
the left. Now c d, the radius bar, moves on its fixed centre c,
consequently the point d will describe an arc with convexity
to the right ; so h throws y h to the left, and c d throws d e

STEAM.

and with it cj h to the right. Therefore it is evident that if
these links and rod be proportionately adjusted, we shall

have an arrange-

1ir: -^ ^c ^ ment that will com-

pel the point #, and
with it the whole
piston rod, to move
exactly perpendicu-
larly. To accom-
plish this there are
joints at g and d.

PARALLEL MOTION".

To find the proper length of the bridle rod,

Divide C 7i in e so that

C e : c d : : d o : o e

where o is the point to which the air pump rod is attached,

fj d or h e : C e : : do : oe
.'. he : Ce : : Ce : c d
Ce*

•'• Cd=~h7

The parallel motion will work most accurately when the
radius rod from c to d is about the same length as the beam
from C to /£, they should therefore be kept as nearly equal
as circumstances will permit.

GUIDE.

75. Guides. — The parallelism of the piston red is pre-
served very frequently now by the use of guides. The above
ligiire will at once give an idea of what a guide is. P is the
cylinder, the dotted lines show the piston and piston rod con-
tinued to the cross head c h', C r is the connecting rod, and r s
the crank; the main shaft is s; the cross head c h slides be-

THE GOVERNOR.

tween tlie bars a b and ef, which guide the piston rod parallel.
Instances of the same are seen in various figures following.

76. The Governor. — The governor consists of two balls,
A and B, fixed on the ends of two arms and so arranged that
they can freely revolve round the spindle C D. Motion is
imparted to the balls either by a pulley which is driven by a
cord passing over another pulley on the main shaft by the side
of the fly wheel, or else by a pair of bevel wheels placed im-
mediately below D.

GOVERNOR AND THROTTLE VALVE.

When at rest the balls will remain close to the governor
spindle, as in the figure, but when in motion the faster it
moves the farther the balls will fly asunder by centrifugal
force. As they separate, the arms A C and B C will extend
outwards, and will bring up with them the short arms G H
and E F, which will move up the collars I L, when the arm
M N will pull point N to the left; P is a fixed joint and
P Q is firmly attached to P 1ST, so that point Q will be lifted
up and close the throttle valve Y in the steam pipe S, by
means of two arms, one of which, Q Y, is shown in the fig.

64 STEAM.

moving the valve on its spindle. Thus, the faster or slower
the main shaft moves, the faster or slower will the governor
move and close or open the throttle valve and regulate the
supply of steam, so that the engine may always be moving at
the same velocity. In flying outwards, the balls attain a
certain vertical height. How to find this height, and the
length of the pendulum, is shown in the miscellaneous
examples at the end. The weight of the balls does- not
affect the action of the governor at all, for if a heavy ball
increases the centripetal force, it also increases the centri-
fugal in the same ratio. It is called the conical pendulum,
or pendulum governor, because its motions are regulated
by the same laws as thosa which regulate the ordinary
pendulum.

77. (9) Throttle Valve. — From the last figure a good
idea can be obtained of the throttle valve. It is a circular
or elliptical plate moving on a spindle. Its opening, as
regulated by the governor, determines the volume of steam
that -shall pass to the cylinder.

78. Governors. — A good governor must be entirely self-
adjusting, and require 110 aid from the engineer. It must
also regulate the supply of steam to the valves, so as to keep
up a uniform velocity in the deliverer of work. When a
water-mill and engine are combined to drive a mill, we have
a test that will try the efficiency of a governor more than
any other. The first thing in the morning, when the water
is perhaps on a level with or running over the weir, let us
suppose the water does eight parts of the work and the
engine two. As the water is used and lowered behind the
dam, more work is gradually thrown on to the engine, so
that towards the end of the day, the engine may perhaps be
doing the eight parts and the water only two. The governor
during all this gradation of change should be so capable of
acting, that when the water-wheel loses its force, that of the
engine should increase in the same ratio, and keep the mill
moving at a uniform velocity. To effect this, the governor,
as well as working a common throttle valve, has to put in
action an arrangement of bevel wheels, to set the sluice in
motion. Yvrheii the balls fall to a certain point, they throw
into gear a system of mechanism, consisting of an ordinary

THE CATARACT. 65

clutch and bevel wheels, which move the ponderous sluice by
which the water passes to the wheel.

" This laborious duty of moving the sluice is assigned to
the water-wheel itself to perform ; and the office of the
governor is merely to suggest to the unreasoning wheel
which way to move its own sluice, so as to feed itself
properly and. regularly. This is accomplished by a very
familiar combination of two bevel wheels running loose upon
a shaft, with a clutch between them, and working into a
third — the third being the wheel that communicates with
the sluice. Each of the two wheels, when giving motion,
necessarily turns the third wheel in opposite directions; and
as the governor rises or falls by change of velocity, it
reminds the third wheel, by means of the clutch being made
to slide or move either to the one bevel wheel or to the
other, in order that the proper wheel may have the motion
which is suitable for the necessary movement; and during
the periods when the required speed of the water wheel is
maintained, both of the bevel wheels are at rest, the governor
being always sensitive and on the alert to jog the one or the
other."*

79. The Cataract. — The cataract supplies the place of the
governor in the single acting Cornish pumping engines. It
consists of a small pump plunger a and barrel b c set in a
cistern of cold water A B; d is a valve opening inwards, so
that when the plunger a ascends, the water passes through
d from A B into b c; f is a cock opened and shut by the
plug e, moved by the plug-rod g, worked by the beam over-
head. If the plunger be forced down, the water will pass
through f in proportion to the opening of f. When the
beam has moved fully up, it liberates the rod that works the
plunger; then as the chamber fills with water through d,
as the plunger ascends, so when the latter comes down the
pressure of water will close rf, and the weight of the plunger
will force the water through /as rapidly as the opening will
allow. The way it is carried away is not shown in the
figure. If the cock be shut, the plunger cannot descend; if
only slightly opened, it will descend gradually, etc. As
soon as a certain quantity of water has passed through /, its
* Anderson's Cantor Lecture, 1869.

DQ STEAM.

weight opens the injection valve, and condensation takes
place, when the engine can complete its stroke; for the
engine can only make the stroke as the water is supplied for
condensation. It thus regulates the speed of the engine; for
if the cock be fully open, condensation takes place at once,
and if only partly open, condensation will be delayed till
the water is supplied.

CATARACT.

80. Marine Governor. — Owing to the unsteady motion
of a ship, arising from pitching, rolling, etc., the ordinary
pendulum governors are unfitted to regulate the speed of
the engines. Mr. Silver has solved the problem how to
adapt a governor to a marine engine. He has employed
several arrangements for carrying out his ideas. The one of
which a section is shown in the figure on the opposite page,
seems the best adapted to the purpose.

A B is a small fly- wheel about IS inches in diameter, on
which are fixed two fliers or vanes, F. The faster the
engine goes the greater resistance will these vanes offer to
the air. P is a pulley worked by a cord and fixed on the
spindle s s, while E is an eccentric and K a lever. To E
be top of the pulley, for the position given in the figure,
is affixed a spring. The engineer has to tighten up or

MARINE GOVERNOR.

slacken this spring according to the speed at which it is
intended to drive the engines. K is the lever from which

SILVER S MARINE GOVERNOR,

the motion is conveyed to open or close the throttle
valve. Within C D are four pinions to communicate the
action necessary to effect the purpose of the contrivance.
Sometimes there are six pinions, one below b and d respect-
ively.

At the uniform speed of the engine, it revolves to-
gether in connection with the engine as the motive power;
but when accelerated by the running of the engine, as when
the screw is out of water, the increased pressure on the
governor fans, or blades, causes the motion to act on the
eccentric E, and the lever K carried on the tube d e. (We
must understand d e is not a continuation of s s.) Then the
spring attached to E or the arm to K, according to which-
ever arrangement is adopted, acts to close the throttle valve.
The pinion ft, keyed on the solid shaft s s, gearing in the
wheel a, which runs on a loose pin a c, transmits the motion to
c and to d, a pinion keyed on the tube de, which acts upon the
lever, and, as said before, regulates the speed of the engine.
It is excessively sensitive, and the least increase or retarda-
t^Lon of speed causes it to act upon the valve. When the

STEAM.

pulley is running very fast, the inertia of the fliers and the
resistance of the air will not allow the fliers to go as fast as
the pulley, so the pinion a runs as it were back on b (or b
overtakes a), and acting on the spring at E and the lever at
K, the latter closes the throttle valve. In one arrangement
of this governor, the spring itself works the valve.

81. To Close the Throttle Valve. — To maintain the
spring at the elasticity at which it is set requires a certain
speed, and when the engine falls below this speed the spring
slackens itself, and allows the valve to open.

82. Eccentric. — The eccentric consists of a disc of metal
encircled by a hoop or strap, to which is attached the
eccentric rod; in the disc is a hole to pass it on to the main
shaft. The centre of the eccentric does not coincide with
the centre of the shaft. When the shaft revolves it carries
with it the disc, which, moving with the hoop, gives a recip-
rocating motion to the eccentric rod.

ECCENTRIC, ECCENTRIC ROD, AND GEAR.

A B is the eccentric, B C the eccentric rod. a b c is the
solid disc that can move round within the strap or band
def'} o is the centre of the disc. S is the main shaft, on

TO REVERSE THE ENGINE WITH THE SINGLE ECCENTRIC. 69

which the disc is tightly keyed. As the eccentric or disc
revolves within the strap, it will be easily seen that the point
p moving round will come into the positions p p" and p'"9
and that the point C will be thrown alternately to the right
and left. C D E is a bell-crank lever supported on D, a
fixed point, and therefore since C moves alternately right
and left, E moving along the arc of a circle will receive a
vertical reciprocating motion, and alternately pull the slide s
up and down. The distance between the two centres o and
S (marked by a line in the figure), is called the throw of the
eccentric. The disc is generally keyed on one-sixteenth of
a revolution in advance of being at right angles to the crank.
The throw of the eccentric is the eccentricity, or the radius
of the circle described by its centre during a revolution of
the crank shaft.

83. To Reverse the Engine with the Single Eccentric. —
When an engine is fitted with a single eccentric, the engine
is reversed by hand. The engineer notices whether the
piston was moving up or down ; if moving up, he takes the
starting bar and admits steam to the top of the piston, so
that it immediately descends, and the shaft begins to move
in an opposite direction. The eccentric is fitted on to the
shaft, so that it can be moved halfway round, or rather there
are two stops on the eccentric, and one on the shaft. The
shaft revolving, as we have just said, moves without the
eccentric, so that the stop on the shaft leaves one of those on
the eccentric, and when the shaft has moved halfway round,
it comes against the second stop on the eccentric, which will
be then in its proper position for working the slides, and
so the motion of the engine is continued. To throw this
eccentric in and out of gear, a recess is cut in the eccentric
rod (care being taken that it is in its exact position), to this
a pin is fitted to connect it with the slide rod, or gab-lever
pin. When the engineer has started the engine by hand (by
lifting up the slide with the starting bar), and wishes to
attach the motion of the eccentric to it, he watches his
opportunity and lets the rod fall on the pin ; the pin will in
half a stroke fall into the recess. It is kept in its place by a
bar or strip of iron placed over the entrance of the recess,
held there by a spring.

STEAM.

84. The Double Eccentric, or Stephenson's Link Motion.
— This contrivance, used both in the locomotive and marine
engine, was invented by Stephenson. to enable the engineer
to quickly reverse his engine, and so go backwards or for-
wards at pleasure.

It consists of two eccentrics, H and G, with their rods
A D and C E, the one called the forward, the other the back-
ward eccentric. The two are connected by a link, D E, with
a slotway in it. In the slotway moves the block p, fastened
to the end of the valve rod a.

The bell crank lever, D E p, is to move the link up or
down. When the forward eccentric is moved so as to work
the valve rod it moves the slide, and the ship or locomotive
goes forward ; but when the backward eccentric works the
slide rod, the engine is reversed. The link motion is thus a
simple and expeditious mode of reversing the engine expe-
ditiously, and almost without trouble to the engineman.

"When we consider that the forward eccentric rod, A D,
sends the engine one way, and the backward rod, C E, sends it
the other, we see that the travel of the slide has been reversed,

STEPHENSON'S LINK MOTION.

as it were. Again, if the pin and link be placed in the position
shown in the figure, the slide has then but little travel, and
we can see that this travel is increased just in the same pro-
portion as the bell crank lever, D E p, moves the link I) E

EXPANSION GEAR FOR MARINE ENGINES. 71

tip or down from the inid position. As the amount of open-
ing for steam depends upon the motion of the slide, by leaving
p in different positions in the slot, we open and close the
port at and during varying times. This is done by not
placing the block at the extremity of the link, but at a distance
from it, and resting the lever in its proper place. For this
purpose an arc or sector with notches in it is attached to
the link motion, to fix the handle in and secure the required
opening the engineer may deem best for the speed required.
This is not expansion, but rather wire-drawing the steam.
In fact, Stephenson's link motion cannot properly be used
to give different grades of expansion, it only alters the travel
of the slide ; for when the pin is in the middle of the link,
the motion of neither eccentric is imparted to the slide rod.
The pin being at the end of the link, the slide rod will receive
full motion, and full steam will be given to the cylinder; but
when the block lies nearer to the centre of the link, less and
less steam is given to the engine, and consequently it moves
the more slowly. This point is more completely illustrated
under the heading " The manner in which the Link Motion dis-
tributes the Steam" in the chapter on the Locomotive Engine.

85. Expansion Gear for Marine Engines. — Various plans
are adopted by different makers. Some use cams placed 011
the shaft in such a position that when the valve is connected
with the cam, by an arrangement of rods, levers, etc., steam
can be admitted into the cylinder, but when not so, the ports
are closed against the admission of steam. The great objec-
tion to this arrangement appears to be, that when the roller
comes off the cam, it, together with the valve, drops with a
sudden jar, which causes a very unpleasant noise in the
engine-room, and also a great amount of wear and tear in the
machinery itself.

The best plan appears to be to have an eccentric, to which
is connected a sliding valve in the steam chest. This eccentric
is fixed to the shaft in such a position, that when the valve
is in connection with it, it shuts off steam at the required
portion of the stroke. The different grades of expansion are
regulated by a lever with recesses in it. This is among the
connections of the expansion gear. Care is taken when throw-
ing it out of gear that the expansion valve is not closed, or

72 STEAM.

else the engine will stop. In some cases the throttle valve ia
used as an expansion valve, under which circumstance the
full benefit of expansion is not gained, for that requires the
total cut-off of steam, which the common throttle valve cannot
do on account of its shape, but it wire-draws the steam. The
expansion valve and eccentric to work it are perfectly distinct
from the slide valve and ordinary eccentric.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1 . Give an account of the steam engine before the time of Watt,
with a description of his improvements (I860).

2. Explain the terms cushioning, clearance, lap, and lead (1866).
Lap and lead are explained in a succeeding chapter.

3. What is a circular inch ?

A safety valve 7 inches in diameter is loaded to 6,lbs. on the square
inch, what would be the load 011 each circular inch (1867) ?
A circular inch is a circle whose diameter is one inch.

a/uiCt'YA 3.*M39Jj jb£z:^ 4</MKll^lPv Am. 4*7124 Ibs.

4. The area of a piston is' 4S7TTr&4 squ'are inches, find the diameter,
of the air pump, which is half that of the cylinder ; find also the
capacity of the pump, supposing it similar to the cylinder (1867).

Ans. Dia. of air pump. 39'S99 inches. Cap.., 1219'21.

5. Describe with a sketch the single acting engine (1867).

(5. What is the foot valve ? Is it a necessary appendage to a steam
engine ? If it is not used, what arrangement must be made in con-
sequence (1867) ?

There need be no different arrangements made when an engine
is worked without a foot valve ; for the bucket of the air pump must
in any case come right down into the water, as there is a vacuum
both in condenser and air pump, so the water cannot in sufficient
quantities follow the bucket, but must pass through the bucket valve
in the down stroke when it plunges into the water. When 110 foot
valve is fitted it is customary to let the steam enter the condenser as
near the top as convenient, for it is found that a little more water
remains in the condenser than is generally the case. Where surface
condensation is employed you mtixt have a foot valve, because the
steam and condensing water not mixing there is a greater amount of
vapour to deal with, which is likely to expand and contract in the
passages, following the bucket, but not passing through it.

7. The area of a piston is 4476 square inches, and the diameter of
the piston-rod is one-eighth that of the piston, find it (1868).

Ans. Dia. of piston rod, 9 '43 inch.

8. The pressure of steam is 15 Ibs. on the square inch, and that of
the uncondensed vapour is 2 Ibs., compare the effective force in the
up and down stroke respectively (1868).

EXERCISES. 73

If the pressure of the atmosphere is greater than half the sum of the
pressures of steam and uncoiidensed vapour, then the pressure in the
down stroke is greater than the pressure in the up stroke, and vice
vtrsa — j *

Pressure of steam =15 + 15 — 30

Pressure of uncoiidensed vapour — 2

.-. Half their sum=30 + 2 = 16 Ibs.

Pressure of atmosphere = 15 Ibs.
. *. the pressure is greater in the up stroke than in the down stroke.

9. Describe generally the improvements introduced by Watt into
the steam engine (1868).

10. The initial pressure of steam in a cylinder whose stroke is 5
feet 4 inches, is 45 Ibs., and expansion commences when 2 feet 3
inches have been performed; find the pressure at the end of the
stroke. Find also the horse power if the area of the cylinder is 2218
square inches, and the number of strokes per minute 30 (1868).

Ans. Terminal pressure 18 '984 Ibs.
For horse power, see questions at the end.

1 1 . How is steam admitted into the cylinder ? Describe with a
sketch the usual mode in marine engines for working the gear con-
nected with the slide (1868).

12. What means are used to keep the piston rods and air pump
rods steam tight (1867) ?

13. Give an account of the principal discoveries of Watt, and the
advantages derivable from them (1867).

14. Investigate an expression for the length of the radius bar in
Watt's parallel motion.

15. A pair of double cylinder engines is substituted for single
cylinder engines of 78 inches diameter, if the total area of the
piston and length of stroke be the same in both cases, compare the
surfaces of the cylinders exposed to the friction of the pistons (1867)^

Ans. 1 : V2-

1G. Give a sketch of the feed valve box and pipes, and name the
valves. Is it necessary to have an air vessel to the exit pipe when
an overflow valve is fitted to the box (1867)?

It is not necessary to have an air vessel fitted under such circum-
stances ; the air vessel, as in the case of the fire engine and other
pumps, is to give a continuous stream of water, which is not required
in the overflow of a feed valve.

17. What are the foot valve and delivery valve ? What is meant
by blowing through? How is it effected (1868) ?

18. Describe the method adopted for keeping the cylinder, air
pump, slide valves, etc. , air and steam tight. Describe the strap,
gib, and cutter, and explain their use (1868).

Blowing through, and strap, gib, and cutter are explained in a
succeeding chapter.

19. Show how to find the work done by a crank. What force ap-
plied to the extremity of a crank at right angles to it will do the

74 STEAM.

same work as a mean pressure of 4 tons acting on a piston through-
out the up and down stroke (1868) ?

Let P be the pressure on the piston, and p be the power applied to
the extremity of the crank at right angles to it.

Then the units of work done by P in the up and down stroke
— P x 2 1, where I is the length of the stroke.

The extremity of the crank moves through a distance — 2 «r -|, for
if the length of the stroke be /, the radius of the circle described by
the end of the crank, or the length of the crank, is -£.

. '. units of work performed by p at right angles'to the end of the
crank = p x 2 V -£.

By the condition of the question these two units of work must bo
equal.

. '. P x 2 I = p x 2 v x L

. '. 2 P - p 7T.

2 P

• '•P = -£- (generally).

In the particular case given above

p - ?JU§ = 2 '546 tons,

20. Describe Newcomen's atmospheric pumping engine, and point
out its defects (1869).

21. How does the steam act in (1), a single acting condensing
engine ? (2) a double acting condensing ? (3) a high pressure engine
(1869) ?

22. Describe with a sketch some form of slide valve as connected
with the steam cylinder of an Engine, and explain its action (1869).

23. Describe the great improvement introduced by Watt into the
construction of the steam engine. Distinguish between, a single
acting and a double acting engine ; what valves are necessary for the
working of a single acting condensing engine (1869)?

24. Describe some form of steam slide valve adapted for a double
acting engine. How are the faees of such a valve prepared so as to
make it steam tight (1869) ?

For latter part of this question, see Chapter VII., par. 148.

25. Describe the construction of a piston, and explain the method
adopted for keeping the piston and piston-rod steam tight. Describe
also the strap, gib, and cutter'^ for tightening the brasses at end of
a connecting rod (1869-71).

26. The circumference of a Alston-rod being 30'5 inches, find its
diameter (1866). Ans. 9'70S.

27. The total pressure on a piair of equal pistons is 90 tons at the
rate of 45 Ibs. on each square inch, find their diameter (1866).

Ans. 53 '4 inches.

28. Explain the action of the governor and throttle valve in re-
gulating the speed of an engine (1869).

29. Find the load on the air pump bucket of a steam engine when
seventeen feet below the level of the water outside the ship, the
pressure of the atmosphere being 14| Ibs., and that of the steam-

EXERCISES. 75

within the condenser 2J Ibs. (a cubic foot of water weighing 64 Ibs.)
(1865). Ans. 19f Ibs. per square inch.

30. Enumerate the things to be clone in a double acting condensing
steam engine, and describe generally the method of accomplishing
them, so as to give a fair idea of the engine itself (Honours, 1869).

31. Explain the principle of Watt's parallel motion in its simplest
form. Show how to arrange that two or more points shall describe
parallel straight lines (Honours, 1869).

32. Describe some form of slide valve as fitted to the steam cylinder
of a double acting engine. Sketch the valve in section, with the
openings over which it slides, and give it some amount of lap on the
steam side. How is the face of such a valve made truly plane (1871)?.

33. What is done by the air pump in a steam engine ? What are
the foot and delivery valves ? and where are they placed (1871) ?

34. The cylinder of an engine is 74 inches in diameter and the
stroke is 74 feet, what is the capacity of the cylinder ? How many
pounds of water must be evaporated in order to fill such a cylinder
with steam at an actual pressure of 15 Ibs., it being given that steam
at 15 Ibs. pressure occupies a space equal to 1670 times that of the
water from which it is generated (1871) ?

Ans. Capacity 224-002 feet.

Cubic feet of water '1341.

35. Give a description of the steam engine in use before the time of
Watt, with an account of his improvements (1863).

36. Mention the distinguishing feature of the atmospheric single
acting and double acting engines. What kind of engine is generally
fitted to steam vessels? and what kind is best suited for land carriage
(1864) ?

37. The mean indicated pressure of steam from above .the piston
was 14-9 Ibs., and the vacuum pressure 3 '2 Ibs., and the corresponding
pressures from below were 15 '4 and 2 '7 Ibs. ; what were the mean
effective pressures per square inch during the up and down strokes
respectively (1864) ? Ans. 117 Ibs. and 127 Ibs.

38. The length of the stroke of a steam engine is 5 feet 6 inches,
and the boiler pressure 12 Ibs. above the atmosphere, the steam is
cut off after the piston has traversed 2 feet ; find the pressure of the
steam in the cylinder when it opens to the exhaust, which is 2 inches
before the piston arrives at the end of a stroke (1865).

The steam is cut off 2 inches from the end of the stroke ; so,
therefore, steam pressure is continued for 5 feet 4 inches = 5£ feet.

The total pressure of steam is 12 Ibs. + 15 Ibs. = 27 Ibs.

The following relation always exists : —

Initial pressure : terminal pressure : : whole stroke : part of
stroke performed.

.'. 27 : terminal pressure : : 5J : 2.

.'. terminal pressure = ±ZJl-±_=: 10J Ibs.
5 3

39. Explain the manner in which the steam acts in Watt's single
acting pumping engine. Why is this engine so much more economical
in steam than the old atmospheric (1870) ?

76 STEAM.

40. The diameter of a safety valve is 10 inches, find the difference
in total pressure of the steam to raise the valve if it be 9 Ibs. per cir-
cular inch above what it would be if it were 9 Ibs. per square inch
(1864). Ana. 193'14 Ibs. less when 9 Ibs. per circular inch.

See questions at the end.

41. What is the diameter of a valve containing 125 square inches
(1865). Am. 12-6 inches.

42. In what way is steam admitted into the cylinder ? How is the
apparatus worked (1865) ?

43. Draw in section the cylinder and the slide valve of a double
acting engine, and explain the manner in which the valve regulates
the admission and exit of the steam (1870).

44. Why is it economical to cut off the steam before the piston has
gone to the end of the cylinder ? The length of the stroke of an
engine is 8 feet, the pressure of the steam on entering the cylinder is
30 Ibs. on the inch; at what point should the steam be cut off, so that
the pressure at the end of the stroke may be 5 Ibs. per inch (1870) ?

Am. 1 foot 4 inches, or £.

45. Sketch in section the steam cylinder and valves connected with
it, as arranged in Watt's single acting pumping engine. Explain the
object and use of each valve, showing at what periods of the stroke
they should be respectively open or closed (1870).

46. Explain the principle upon which the parallel motion of a beam
engine is constructed (1870).

47. Describe the construction and arrangement of the working
parts in a double cylinder engine, and point out the advantages of
such engines in carrying out the expansive work of steam (Honours,
1870).

48. State what you understand to be the advantage of working
with superheated steam in an expansive condensing engine, explaining
what will probably occur in the interior of the cylinder, according as
the steam is superheated or otherwise (Honours, 1870).

See former chapter.

49. It was stated by Watt that neither water nor any other sub-
stance colder than steam should be allowed to enter or touch the
steam cylinder during the working of an engine. Show that this
rule was not adopted in the case of the atmospheric engine, and de-
scribe the arrangement by which Watt gave effect to it (1871).

50. There are three valves connected directly with the steam cylin-
der in Watt's single acting condensing engine, name them. During
what portions of the up and down stroke of the piston should these
valves be respectively open or shut ? and for what reason (1870) ?

51. State the principle of Watt's single acting engine as applied in
pumping. What valves are necessary for the working of the engine ?
How is the number of strokes to be made per minute regulated?
Describe the cataract employed for that purpose (1871).

52. Show that a single slide valve will suffice to work a double
acting engine in the place of two steam and exhaust valves. Explain
with a sketch the action of any slide valve (1871).

53. Describe the locomotive or three-ported valve, as applied in

EXERCISES. 77

engines of short stroke. Why is its use so restricted ? Show that
lap added to the valve produces expansive working of the steam
(1871). See Chapter VII.

54. Describe the eccentric for working the slide valve of a steam
engine. How is it thrown in and out of gear ? How is it attached
to the slide rod in an oscillating engine (1870) ?

For latter part of question, see next chapter.

55. Describe fully the double eccentric, and show how the eccentrics
are fixed on the shafts. What is meant by back lash ?

When one part of an engine runs or falls back on another with a
noise it is called back lash, as the single eccentric will sometimes do
against the stops, and one toothed wheel against another.

56. Describe the eccentric as applied in giving motion to a slide
valve. In what way must you change the position of the eccentric
pulley upon the shaft relatively to the crank in order to reverse the
motion of an engine (1871) ?

57. Describe the double eccentric with a sketch (1869).

58. The single eccentric is fitted with a weight to balance it, what
would be the effect on the slide if it were to become detached (1866)?

The slide would fall in the casing in certain positions and would be
useless ; the fact is, the engine could not be worked.

59. Describe the method of reversing a marine engine when fitted
with a single eccentric (1871).

60. How is an engine reversed when fitted with a single eccentric
(1870) ?

61. Explain how the reverse motion is obtained in engines fitted
for paddle wheels and screw vessels respectively (1871).

6*2. Describe some arrangement of expansion gear suitable for a
marine engine. What form of valve would you employ (1870) ?

63. Explain the way in which the eccentrics of marine engines are
fixed on the shaft. Explain also the method of obtaining the back
motion (186-1).

CHAPTER IV.
MARINE ENGINES.

Condensing and Non-Condensing — Side Lever — Twin Screw Engines
— Hammer Engines — Compound Engines — Continuous Expansion
Oscillating Engines — Steeple Engines — Maudslay's Twin Engine
—Beam and Geared Engine— Trunk Engine — Horse Power-
Duty.

ENGINES are first divided into two classes : —

(1) CONDENSING ENGINES, miscalled low-pressure.

(2) NON-CONDENSING ENGINES, miscalled high-pressure.

We should avoid the use of the two terms high and low
pressure, as they are scarcely applicable to engines of the
present day.

86. Marine Engines are generally divided into two classes
— those adapted to drive the paddle wheel, and those best
suited for the screw. The chief difference seems to be, that
•engines to drive the screw are direct acting, i.e., their piston-
rods are directly attached to a crank on the shaft, while
in the case of paddle wheels they are not always direct acting,
but the motion is conveyed through the intervention of side
levers. In the direct acting engine, it is often a prime object
with the engineer to obtain a long stroke. To gain this_ejid,
many of the various modifications in marine engines ntve
been suggested.

But let it be well understood that no particular engine,
perhaps with the exception of the side lever, is entirely con-
fined to either class. Every student should seek oppor-
tunities to examine the engines in his neighbourhood as
minutely as possible. An hour spent in this way will some-
times add more information to the student's repertory than
days at his books alone.

87. The Side Lever Engines, — The first engine employed

SIDE LEVEE ENGINES, 70

to drive the paddle wheel was a side lever, in which the
ordinary beam pumping engine was modified to obtain the
requisite rotatory motion, and the beam placed by the side
of the cylinder, condenser, etc., to stow it into as compact
a space as possible. In the original side lever the end A of
the beam AB was worked up and down on its centre C by the
side rods AD, while to the end B was attached the connecting
rod working the crank above.

SIDE LEVER ENGINE.

Our figure is a new arrangement of this engine, Cy is the
cylinder, in which the piston is shown by dotted lines, the
piston-rod is immediately behind AD, and not shown. As the
piston moves up or down, the end of the cross head at D lifts
up or down the beam AB by means of the side rod AD,
'atyd^urns it on its centre B; as it reciprocates on its centre B,
the connecting rod CH turns the crank US, which carries with
it the paddle shaft S.

E is the air pump, underneath which is the condenser
C' F. The air pump is worked by its side rods a d, in the
same way as the larger cylinder C?/ is worked; G can be
used both as a feed and bilge pump. B is attached to
strong framing. The whole works as a lever of the second
class.

V the valves are worked by the rod be working the bell
crank lever on its centre e, which gives an alternate upwards

STEAM,

and downwards stroke to the slide valves. The details con-
nected with be are not properly shown, c being attached
near to the main shaft.

The piston-rod is compelled to move perpendicularly by
means of the guide rod D H moving between two guides.

In all side lever engines there are two side levers and two
side rods both to cylinder and pumps; the side rods are
connected to the two ends of the piston cross head, which is
made, for this purpose, a little longer than the diameter of
the cylinder.

The condenser F C beneath the air pump sometimes ex-
tends underneath the cylinder.

TWIN SCREW ENGINES.

88. Twin Screw Engines. — Many engines placed similarly
to the above have been constructed to drive twin screws. The
propellers are fixed one on each side the rudder, and a little
in front of it. With two screws so situated a ship can very
readily be turned round — an advantage frequently of con-
siderable moment. There is great trouble in framing suffi-
ciently strong brackets to carry the screws ; all the machinery
must be in duplicate, which necessarily occupies more room
and requires more attention. H.M.S. "Abyssinia" is fitted
with engines placed somewhat in the position shown in the
above figure; but frequently engines to drive twin screws are
arranged horizontally, the port and starboard engines
forward and aft of each other,

HAMMER ENGINES,

In engines built for some Spanish gunboats, B is the surface
condenser, and is placed in that position to form a frame and
support for carrying the engines. Another arrangement is
to fix the ordinary condenser in the same position to perform
the same function. Hence, such engines will occupy but
little space.

A and A are the cylinders with their pistons PP, and piston
rods pr. C C' are the connecting rods, C' S the cranks, while '
the shafts S are shown by circles in section.

89. Hammer Engines. — These engines, which differ little
from an ordinary vertical engine, are so called because

HAMMER ENGINE.

they are supported on a frame resembling that of a steam
hammer, with the cylinder in a similar position to that
of the steam hammer — viz., overhead. They are direct
acting.

A B is the cylinder, P the piston, P B the piston rod, C B
the connecting rod, and C S the crank with shaft S. The
guides a b working in the sides of the frame preserve tho

82 STEAM,

parallelism of tlie piston rod. A P is the air pump, with its
piston-rod working in a trunk c d. The lover, D E, which
works the air pump, moves on the centre F by means
of a small rod which comes from the centre of the guide
block to the end of the air pump beam, as shown in the
figure.

The condenser is G, from whence the water is forced
out by the air pump on its down stroke. It is a single
acting air pump. This class of engine is very much used in
our commercial marine, on account of the small space they
occupy.

There is plenty of room round the engine, which is
economized, and used for the stowage of coals, stores, etc.,
and frequently for the engineers' bath and mess rooms (in
large steamers), so that they are always at hand and near
their work.

90. Compound Engines, called also High and Low Pres-
sure Engines. — A compound engine is an engine with two
cylinders, the one frequently double the diameter of the other.
Steam is admitted from the boiler into the smaller cylinder,
and after it has driven the piston up or down it is then
allowed to pass into the larger cylinder, when, by its expan-
sive property, it drives the larger piston down or up. Woolf
was the first to introduce this principle; it has been practi-
cally applied by Humphrey and others, and further modified
into what is called the continuous expansion principle by
Messrs. Stewart and Nicholson.

In Woolf and Humphrey's engines the larger cylinder is
worked entirely by the exhaust steam from the smaller; but
in Stewart and Nicholson's the steam partially acts on both
pistons at the same time; but we will presently further
explain this.

The compound engines proper are arranged in two ways,
either the cranks are placed at certain angles, or elsa when
one is at the top of its stroke the other is at the bottom.
"When one crank is set at an angle with the other, the steam
is kept back for an instant after driving the piston of the
small cylinder up or down until wanted in a receiver, to be
ready to enter the larger cylinder when its piston arrives at
the end of its stroke. This is a serious evil involving a loss

COMPOUND ENGINES.

of power. We will explain the following figure as a com-
pound engine on the two principles indicated.

(a) Woolf's or Humphrey's Compound Engine. — A is the
small cylinder, B the larger one.

The cranks are not at right angles, but when one piston is
at the top of its stroke the other is at the bottom, at least
generally it is so, but not originally as introduced by Woolf.
A whole revolution has to be performed to complete the
expansion of any given cylinder full of steam. The steam is
allowed to pass from the top of one cylinder to the bottom of
the other, being first admitted from the boiler to the smaller
cylinder. Usually the two cylinders are not distinct, but
directly connected together.

COMPOUND ENGINES.

(b) Compound Engine with Continuous Expansion. —
Let us suppose the piston of the smaller cylinder at
the top of its stroke, and that of the larger one at
the middle of its upward stroke. The steam from the
boiler is then admitted by the slide s, above the piston
a} which, therefore, commences its downward stroke; the

84 STEAM.

admission of steam is not continued beyond the middle
of the stroke, and it may be cut off at any earlier or
more convenient point by the link motion. The piston a,
as it passes the middle of the stroke, uncovers port p, then
the steam, which gave a great initial velocity to a, escapes
to the top of the larger cylinder B, the piston b of which
has continued its upward stroke and arrived at the top.
The steam has now to drive down both pistons by ex-
pansion, a from the middle, b from the top of its stroke, as
seen by a and dotted piston in B; when a gets to the bottom,
piston b is in the middle of its stroke going down, as seen by
b and dotted piston in A ; now, by valve s, steam is
admitted below a, and the exhaust in cylinder A, although
opened, is covered by a gridiron slide, so exhaust is prevented
until a has made part of its upward stroke, and b nearly
finished its down stroke. Then the intermediate slide s' closes
port p in centre of cylinder A, and immediately the upper
ends of both cylinders are open to separate exhaust passages.
By this method of regulating the supply of steam, the pressure
resisting the upward motion of a assists the downward
motion of b. Again, as the larger piston is at that time
moving faster than the other, this back pressure, if we may
so term it, will have more influence upon b than a, and so
cause a good effect upon the whole.

The amount of work lost by the opposing pressure on
piston A, is more than compensated for by the extra pressure
obtained on piston B ; but the extent to which the exhaust
may be kept back, requires much consideration and care.
The cranks are, of necessity, from the relative positions of
the pistons, at right angles, and no intermediate chamber is
employed, unless we consider sf as a travelling chamber, but
the steam is passed directly from one cylinder to the other.
The complete expansion of any given cylinder full of steam,
is completed in three-fourths of a revolution, and so is not
exposed to radiation and conduction so long as in Woolf 's
system.

General explanation : — A and B are the two cylinders. We
must consider that there are two pairs of engines to drive the
two shafts or twin screws. The action of the slides s and s has
been previously explained; d and d' are the piston rods; c and G

BALANCING THE CRANK. 85

tlie connecting rods, working e and e the cranks; ftrndf
are large pieces of cast iron to balance the cranks, and assist
them over the dead centres; S C are the surface condensers.

The air pump is shown at A P, the upper part of which is
the hot well. This air pump is worked by the lever I, from
the crosshead r of the piston.

The theory of the action of compound engines is simply
this : that a great initial velocity given to a piston does more
economical work than a pressure continued throughout the
stroke, as has been fully explained in expansive working; and
if this initial velocity be given on a small surface it does
most work, while, if the steam have less power, it will do
most work acting upon a larger surface. For convenience,
economy in working, and economy in construction, the prin-
ciples of making the initial steam act upon a small surface of
piston is the correct one, the larger surface being acted upon
by the steam when partially expanded.

91. Balancing the Crank. — It has been the practice with
a few engine makers to put a heavy piece of metal, sometimes
weighing a ton or more, opposite the crank, which they col
a balance or counterweight. The intention is, that it shall
serve to counteract the weight of the crank when not in
a perpendicular or vertical position. Some affirm that they
greatly assist in keeping the motion of the machinery firm
and smooth; other experienced men do not agree with
them, saying that when one engine is at its dead centre, the
other is at its greatest power, viz., at half stroke, and, there-
fore, the motion must be uniform, and that balances are only
so much useless metal and dead weight creating additional
friction. If the drum of the threshing machine be not
balanced it will move unsteadily. In vertical engines, such,
for instance, as the table engine, it is found necessary, in
order to produce a regular and even motion, to balance the
weight of the piston, side rods, etc., by casting the fly-wheel
in such a manner that one side shall be heavier than the
other, it is then fixed so that the heavy side is rising during
the down stroke, and falling during the up stroke, by which
means an equal and steady motion is produced, no more power
being required to lift the piston than to throw it down. The
fly-wheel of such an engine can be moved by hand, which

STEAM.

could not be done were the wheel unbalanced; this will,
perhaps, illustrate the utility of the plan.

92. Oscillating Engines are a triumph of engineering

skill. They have been
brought to their pre-
sent perfection chiefly
through the ingenuity
and skill of Penn.
Murdock, in 1785, at-
tempted an oscillating
engine, but the accu-
racy of our present
fitting .shops, and the
skilful contrivances of
modern machinists,
were not at his com-
mand, so there is no
wonder he could not
perfect his ideas.

In oscillating en-
— gines, instead of the
connecting rod oscilla-
ting to the motion of
the crank, the cylin-
ders oscillate and the connecting rod is dispensed with. It
possesses many advantages ; among others, it occupies but
little space, consists of but few parts, and is easily accessible
for repairs.

The two cylinders A B and C D vibrate, each upon two
trunnions, only one of which, «, is shown in the figure.
These trunnions are placed about the middle of the outside.
The steam enters through the outside trunnions, or those
nearest the sides of the vessel, whilst the exhaust steam
escapes at the opposite sides, or into the condenser placed
below and between the two cylinders. The air pump is
within the condenser, and is worked by a crank on the
" intermediate shaft." The shaft that stretches over the
engines from cylinder to cylinder is called the intermediate
shaft, the slide valves are worked by eccentrics on this shaft,
but the particular mode of working is explained in the next

OSCILLATING ENGINES.

paragraph. We must not omit to mention, that the steam
first passes into a belt c d on the cylinders ; and then, after
going partly round, enters the ports at the proper time. E
and F are the piston rods, G H and K H the cranks turning
the main shaft H.

93. How the Slides in Oscillating Engines are Worked.
—In oscillating engines of small power, the oscillations of
the cylinder are made to work the slide valve.

\VOHKING OF THE SLIDES IN OSCILLATING ENGINES, AND DETAILS Off
SLIDE GEAR.

(The Utters in each figure correspond.)

In oscillating engines it will not do to connect the eccentric
rod on to the slide valve rod, on account of the motion of the
cylinder. The difficulty here encountered is overcome by
having a sector B B' sliding in between two upright rods
A A'. The eccentric rod C C' is attached to the sector by
means of a pin C', so that motion is given to the sector by
the eccentric. Within the sector slides a block O, to which
is fastened the gab-lever a a (right hand figure), the spindle of
which rests on a bearing a attached to the side of the cylinder
H ; to this also is attached the valve lifter s s', which gives
motion to D, the slide valve rod, so that the movement of the
eccentric is thus transferred to the slide valve. The slotway
in the sector is an arc, the centre of which is the centre of
oscillation of the cylinder. The motion of the cylinder cannot,
therefore, have any effect on the slide valves if the block of

STEAM.

the gab-lever pin move freely in the sector, which it does.
In this manner, therefore, the eccentric works the slide
valves as in ordinary cases.

94. Steeple Engine. — Steeple engines have been intro-
duced largely on the Clyde, they also find much favour in
America. They are direct acting engines, and are very
serviceable and compact, and found to answer very well as
river steamers.

STEEPLE ENGINE.

They have not, in consequence of the high erection they
require above the deck, found any favour as sea going vessels,
but the objection against them from this cause seems more
theoretical than practical. They do certainly present a surface
to the action of the wind, but this action may very often bo
in favour of propulsion, while the surface is but small. They
acquire their name from the high erection a b, which
serves as a guide for the end of the connecting rod, which is
above the crank.

BEAM AND GEARED ENGINE.

Cv/ is the cylinder; P the two piston rods, as shown in the
figure, move the guide block G up and down, between the
guides a b. G C is the connecting rod converting the
reciprocating rectilinear motion of G into a continuous circu-
lar motion by means of the crank C K, which is thus con-
veyed to the shaft marked dark in the figure. A P is the air
pump, ap T air pump rod, worked by means of the air pump
lever C D, which receives its motion from the guide block.

95. Maudslay's Twin Engine, or Siamese Engine, or
Double Cylinder Engine, — There are two cylinders, A and 13,
and two piston-rods,

a and b. These rise
and fall simultaneous-
ly, carrying with them
the large crosshead
C D in the form of the
letter T. The part
E F descends between
the two cylinders, the
sides of which serve
as a guide, so that the
guide block F is com-
pelled to move perpen-
dicularly, and so pre-
serve the parallelism . T

of the piston-rod. To -^
F is attached the con-
necting rod FG, which
moves round the crank G H, carrying the main shaft H.

The air pump A P is worked by the lever D o, reciprocated
by the piston rod 6, and moving on its centre o. The con-
denser is low down at K ; this has proved an objection under
certain circumstances. This engine is only fitted for driving
a paddle wheel.

96. Beam and Geared Engine. — Some engineers do not

admire driving their engines at a high speed of the piston,
although it is necessary to have a high speed at the screw.
A beam engine is often put into the ship which works a
large spur wheel, from which is driven a smaller pinion.
A moderate speed of the crank shaft may be kept up, which

DOUBLE CYLINDER ENGINES.

STEAM.

will give a very fast speed to the screw, on account of the

smaller size of the screw shaft pinion compared with the

driving wheel.

Cy is the cylinder,
the piston rod (P R) of
which gives the neces-
sary reciprocating mo-
tion to A B, moving
on its centre 0. B G
is the connecting rod,
H C the crank turning
the spur wheel S W,
which works the pin-
ion P, which is keyed
on to the main shaft
s. It will thus be
seen that one revolu-
tion of the spur wheel
S W (or one stroke of

the engine) will give several revolutions to the pinion P, or

to the main shaft.

97. Trunk Engine. — Watt first gave the idea of a trunk

engine, but it was not fully developed till Penn produced the

CEAHED ENGINE WITH BEAM

TRUNK ENGINE.

direct acting horizontal marine screw engine. Each engine
is generally worked by two cylinders. The cylinder A B is
laid on its side; and down the centre, passing through both
ends of the cylinder, goes a large trunk a b, on which (all in
one piece) is cast the piston c d, so that the effective working
part of the piston is an annulus or ring. The trunk is fitted

DOUBLE ACTING PUMP. 01

steam tight by means of stuffing boxes. The connecting rod
is attached to a pin. at o, fixed in the middle of the trunk,
while the other end engages and works the crank c s, where
s is the main shaft.

C D, the rectangular figure to the right, the condenser, is
divided into the condenser proper, the hot well, and the
pump barrel. The large pipe E P is called the eduction
pipe ; its purpose is to bring the exhaust steam into the
condenser, where it is pondensed at the bottom, after which
the double acting pump p delivers the water into the hot well
HW.

98. Double Acting Pump. — A double acting pump is one
that delivers water both by the forward and backward stroke.
Perm's trunk engine is always fitted with two of these air
pumps, one to each cylinder; each is worked by a rod which
passes through the piston and cylinder cover, and there are,
of necessity, two suction (foot) valves, and two forcing
(delivery) valves, on the same principle as the India-rubber
disc valve, explained under its proper heading. The feed and
bilge pumps are worked in the same manner.

Let us suppose the air pump piston is at the end of its
stroke to the right, then the space in front of it, or near the
cylinders, will fill with water from the foot of valves 1 2; when
the piston moves to the left it will carry with it the air pump
piston by means of the rod r to the left, so that the water
rilling o will be forced through the delivery valves 3 and 4.
As the piston moves to the left a vacuum is left behind it
in y>9 s° "that water rushes through the suction valves 5 6,
while forcing valves 7 8 close by pressure from above.
In a similar manner, but by opposite action, the stroke
delivers water into the hot well H W, as the piston moves
from left to right.

Another kind of double acting pump is a simple arrange-
ment by which the same pump can be made to force water
either in or out of the ship, or in or out of the boiler. The
pump is worked by the usual arrangement of valves ; but there
are two key heads placed on the valve box which turn two
circular spaces. When turned in one direction, the suction
acts to bring water into the ship; but when turned in an
opposite way, water is forced out by simply changing the

92 STEAM.

direction from whence the water can get beneath the
valves.

99. Launch Engines. — Launch engines generally consist
of a small pair of engines either working vertically behind
the boiler, or else diagonally or vertically in front. They
are employed to propel very small river or harbour steamers.
Being first used in the Royal Navy to propel the " launch,"
they are so named. They give a large number of revolutions
per minute, and always work a screw. Both engines work
the same shaft by means of cranks. The cylinder is at the
top, and they work a shaft down close to the keel of the
vessel. There is no point in their construction calling for
explanation, as they differ in no way from a marine engine
of the ordinary type, with cylinder, connecting rod, and
crank.

100. Comparison of Engines. — Engines are compared with
each other by considering their relative performance. A
purchaser orders an engine of such and such horse-power.
An engine of 100 horse-power is calculated to do the work
of one hundred horses (but it will generally do a vast deal
more). When Watt undertook to construct an engine for
any of the mines in Cornwall, he always guaranteed it to do
the work of so many horses. He allowed that a horse can
do 33,000 units of work per minute, or lift in a minute
33,000 Ibs. 1 foot high, or 33 Ibs. 1000 feet high, or 1000
Ibs. 33 feet high. This is generally considered too much.
We have the horsepower and the nominal horse-power. The
nominal horse-power is the commercial or selling power of
an engine; or the horse-power, reckoning the pressure in the
piston to be only seven pounds. For further information on
this important point, the reader is referred to the questions
at the end, where the formula for the calculations will bo
found.

101. Duty of an Engine. — The duty of an engine is the
work it does in relation to the fuel consumed. The average
duty of the Cornish pumping engines is generally stated to
be 60,000,000 Ibs. raised one foot high by 112 Ibs. of best
Welsh coals. Some have reached a duty of 100,000,000
Ibs.

The following from the Engineer, Yol. XXXI., will give

DUTY OF AN ENGINE. 93

a good idea of what is meant by the duty cf the Cornish
engines : —

" It will be observed in the table inserted below thsft from
the period when the work performed by the engines was
commenced to be publicly reported, in 1811, there was a
continuous improvement up to 1843, when an average per-
formance of 67,000,000 Ibs. lifted one foot high, by the
consumption of 1 1 2 Ibs. of coal, was reached. Since 1843 there
has been an equally continuous retrograde course; so that at
this time the average duty of the engines has fallen off about
%6 per cent. Or, to put it in other words, at this time full
one quarter part -more coal is consumed by the engines, on the
average, than was necessary in 1843 to do the same work, an
item of no small importance, especially in such a period of
depression as the mining interest has been passing through.

"TABLE OF THE AVERAGE DUTY PERFORMED BY THE CORNISH

ENGINES PER 112 LBS. OF COAL, AT THE END OF EACH PERIOD

OF FIVE YEARS, COMMENCING WITH 1811.

Year. Duty.

1811 ... ... ... ... ... 20-4 mils.

1815 24-4

1820 34-1

1825 38-1

1830 51-5

1835 56-9

1840 G4-8

1843 67-0

1845 66-1

1850 61-8

1855 54-8

1860 • 51-6

1865 50-2

1870 (say) 50-0

" The cause of the decrease of duty which has taken place
of late years must be attributed chiefly to the careless
manner in which the engines and boilers are attended to ;
the mines have not been in a prosperous state, and in con-
sequence the engines have, many of them, been worked in a
wretched condition, perhaps after having been removed from
place to place several times ; and in many places where new
engines are badly wanted, the old ones, which have worked
some of them for thirty years, are made to answer the

94 STEAK.

purpose, to obviate a large outlay in putting down new ones.
There is also a certain carelessness on the part of the mine
managers in having their engines l reported/ so that many
of the best engines are excluded from tbe duty records.
The writer bas found the best engines very lately doing from
sixty-three to sixty-five millions with four-fifths expansion
in constant work,"

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Describe the general arrangement of the trunk engine for
driving a screw propeller. Describe also that of an oscillating engine
suitable for a paddle wheel steamer (1869).

2. Define the duty of a steam engine. What is the average duty
of the pumping engines in Cornwall? How do you explain the
increased duty obtained from such engines by employing steam at a
higher pressure and by working expansively (1869)?

3. In a steam engine the steam is used at 20 Ibs. pressure, and is
cut off at half stroke, find approximately the percentage of gain in
the work done by the consumption of a given quantity of steam by
reason of expansive working (1870).

We will find approximately the total work done. Let us suppose
the stroke is 5 feet, and divided into 10 half feet to obtcaiii a nearer
approximation.

35 Ibs. on the sq. in.
35
35
35
35

x35 = 29J
x 35 = 25

1st half foot pressure is
2nd
3rd
4th
5th
6th
7th
8th
9th
10th

x 35 = 21|
x35=19$

10)288 Ibs. on sq. in. nearly.

Total pressure,

i.e., steam whose pressure is 17i Ibs. has been made to do all the
work of 28 '8 Ibs. of steam by giving it a great initial velocity. If
therefore 17^ Ibs. does the work of 28 '8 Ibs., what is the gain per
cent. ?

As 171 : 100 : : (28'8- 17'5) o* 11;3 to Answer.

Ann. 64 '57 per cent.

Other methods for this and 5 are giveji at the end.
4. What is meant by^the nominal horse-power of an engine, and
how is it determined for patldlo wheel vessels (1867)?

EXERCISES. 95

5. The initial pressure of steam in a cylinder whose stroke is 5 feet
4 inches is 45 Ibs., and expansion commences when 2 feet 3 inches
have performed, find the pressure at the end of the stroke. Find
also the horse-power, if the area of the cylinder is 2218 square
inches, and the number of strokes per minute 30 (1867).

The terminal pressure will be found to be 1S£| Ibs. ; but, by allow-
ing the port to be opened one inch before the end of the stroke to the
exhaust, and neglecting cushioning, the terminal pressure will be
found to be 19'2 Ibs.

Dividing the piston into spaces 3 inches in length, as was done in
example 3, the average pressure will be found to be 35 Ibs. Taking
the length of the stroke as 5±- feet, area of cylinder 2218 inches, and
number of strokes per minute 30, then we have

TT _ d^ x '7854 (area of piston) x speed of piston x 35

33,000

Ans. Horse-power =752 -3.

6. Give a sketch and explanation of the oscillating engine (1867).

7. Describe with a sketch Maudslay's double cylinder engines
(1869).

8. Give a sketch and explain the working of trunk engines (1866).

9. Find the nominal horse-power of an engine of the following
dimensions : — Diameter of cylinder 57^ inches, stroke of piston 5-£
feet, number of revolutions 25 (1866).

•XT . T i d~ x speed of piston

Nominal horse-power = —

\)\)0()
_57-5x57'5x5jrx2x25

cooo"

Ans. 151-5.

10. Describe generally the side lever marine engine. What is the
object of the blow through valve, and where is it placed? Which
parts of the engine are made of brass, and which of cast or malleable
iron respectively (1870)?

11. What is the distinction between a single and a double acting
air pump? Sketch both forms of air pump, showing the valves
necessary in either case. Describe the India-rubber disc valve
(1870).

12. What is meant by a steeple engine, and to what particular
service are they generally devoted ? Give a description of one.

1.3. Describe the general arrangement of a pair of oscillating
engines in a paddle wheel sbeamer. How would you start the
engine (1865) ?

14. What is meant by the nominal horse-power of an engine, and
how is it determined for paddle wheel vessels (1865) ?

15. Find the nominal horse-power of an engine of the following
dimensions (1865) : — Diameter of cylinder 53?r inches, stroke of piston
5h feet, number of revolutions 22. Ans. H.P. 115 '44.

16. Find the horse-power of an engine whose mean steam pressure
is 15 Ibs., and vacuum pressure 2 '4 Ibs., the length of the stroke 4
feet 6 inches, the diameter of the cylinder 44 inches, and the number

96 BTEAM.

of revolutions 31 per minute, the usual allowance being made for
fricton (1366).

The pressure is 15-2'4 = 12'6 Ibs., on this the usual allowance
has to be made for friction, which is 1^ Ibs., leaving an effective
pressure of only 12*6- 1'5 — ll'l Ibs.

. TT p __ d2 x * 7854 x pressure x speed of piston

""33000

_ 44 x 44 x -7854 x 1M x 4} x 2 x 31 1/lo.^o
33000 =14269>

17. What is the nominal horse-power of a pair of engines? Given
diameter of cylinder 60 inches, stroke of piston 5 feet 4 inches,
number of revolutions 38 (1867). Am. H. P. =486 '4.

18. Why is the crank balanced in some engines? State clearly the
general idea as to its effect. Give your reasons for or against the
practice.

19. Give a sketch and explanation of the oscillating engine (1863).

20. Find the nominal horse -power when the diameter of, the
cylinder is 55i inches, stroke of piston 5 feet, and number of revolu-
tions 21 (1863). Am. 107-81.

21. The diameter of each of the engines of a steamer is 91^ inches,
the length of the stroke is 6 feet 8 inches, assuming the number of
revolutions to be 16, and the indicator pressure 16 Ibs., find the
horse-power of both engines (1863). Ans. 1360'27.

22. What is meant by the terms cushioning and clearance ? Does
the amount of clearance above the piston in a side lever engine
usually increase or diminish as the engine wears (1865) ?

The side rods and the connecting rod are shortened by wear, there-
fore the clearence must diminish.

23. The air pump is commonly double acting in screw engines ;
explain the action of such a pump. Sketch roughly in section the
condenser air pump and valves in Penn's trunk engine. How is each
separate valve made and fitted (1871) ?

24. What is meant by a hammer engine ? state clearly its dis-
tinctive features.

25. Give a sketch of a compound engine, commonly called high
and low pressure engine.

26. Describe Humphrey's engine.

27. What is meant by continuous expansion ? To what engines is
it particularly applied ?

28. State distinctly what is meant by (1) a beam engine; (2) a side
lever engine ; (3) a geared engine ; (4) a compound engine.

29. What engines are launches and small river steamers generally
fitted with ?

30. What method is adopted for comparison as to the power of
different engines ?

CHAPTER V.
METHODS OF PROPULSION.

Paddle Wheels — Immersion of Paddle — Disconnecting Paddle —
Centre of Pressure — -The Screw — Definitions — Slip — Propellers —
Thrust — Hydraulic Propulsion.

THERE are various methods of propulsion, but up to the
present time only two have done good work—

(1) PADDLE WHEELS.

(2) THE SCREW.

In addition to these two, the " Waterwitch" is driven
by a kind of turbine or hydraulic propulsion, which shall be
explained.

Vessels in every case are propelled through the water by
leverage. The only fulcrum obtainable is the water itself,
which cannot offer any resistance to the slightest pressure
applied to it without yielding to a certain extent. The
amount of yielding will vary with the pressure and the
quantity of water acted upon. Without this yielding
property of the water, no vessel could progress through it at
all. The problem to be solved in marine propulsion, is
to arrange the floats, screw, etc., that with the least amount
of slip we may attain the highest speed of progression.

102. Paddle Wheels consist of two large wheels moving on
the end of the engine shaft. They are made with iron arms
attached to two large rings, on to which are bolted the
paddles or floats. As they are turned round, the resistance
offered to them by the water causes the vessel to move, acting
precisely on the same principle as a boat oar, by them the
inertia of the water is made a means of locomotion. In
using this appliance as a motive power, its advantage greatly
depends upon the amount of immersion. When the water

98 STEAM.

approaches the centre, or reaches above, it is obvious that tho
greatest waate of power will ensue. It is quite as obvious
that the greater the diameter of the wheel the greater the
leverage, and the greater is the effect obtained. The floats
are generally made of elm or pine. There are various kinds
of pa'ddle-wheels, such as (1) the ordinary radial wheel; (2)
the Cycloidal; (3) Morgan's feathering paddle.

103. (1) The Ordinary Radial Wheel has the floats fixed
on the radial arms. It is to be observed that in this arrange-
ment the floats enter the water with the whole of
their faces presented to it; the same action takes place as
they come out. From this arises a great loss of power, for
they should evidently offer the greatest resistance to the
water when at their lowest point, and none when entering
or leaving. From, this cause, and the yielding of the water,
the ship does not move as fast as the wheel. The loss is
called slip, and is generally allowed to be 20 per cent.

Slip is the difference between the speed of the wheel and
the speed of the ship. The percentage is calculated on tho
speed of the wheel.

104:. (2) Cycloidal Wheels. — To obviate tho difficulties and
disadvantages of the ordinary wheel other forms have been
suggested, as the Cycloidal, which merely consists of dividing
the float into two strips longitudinally. The one farthest
from the centre is behind the radius, and the other in front
of it. The intention of this arrangement is, that the floats
may meet the water with more uniformity. It is a very
good form of wheel for large vessels.

In order that the floats may enter and leave the water
with the least possible resistance, they should enter in a
tangential direction to the curve which is being described by
any point in the wheel. This is, as is well known, the
cycloidal curve.

105. (3) Morgan's Feathering Paddle. — A wheel of this
kind was first patented by Galloway in 1829.

The figure at a glance gives us a good idea of the prin-
ciple of the feathering paddle. The floats are seen supported
on spurs attached to the rim of the wheel. The long levers
a a a, etc., move the short ones a a a, etc., on their centres
b b b, etc., fixed in the spurs. The levers aaa, etc., proceed to a

IMMERSION OF PADDLES.

centre C, while o is the centre of the ivheeL Thus the centre
of the floats is not coincident with that of the wheel. Tho

FEATHERING PADDLE.

centre C is either driven by an eccentric on the ship's side,
or " by a rigid bar which springs from a solid ring."* By
this plan the floats are always moved on their centres, so as
to enter and leave the water very nearly perpendicularly, and
also offer the greatest resistance at the lowest point. The
floats are, in fact, constantly at right angles to the surface of
the water when immersed.

108. Immersion of Paddles. — The great difficulty with
paddle wheels is to secure a proper immersion. As the ship
proceeds on its voyage and consumes its store of coals, the
vessel becomes lighter, and, consequently, its draught of
water decreases. Therefore, supposing a paddle is properly im-
mersed at the commencement of a voyage, it will be nearly
out of the water at the end. At the commencement of a
voyage the paddles must be too deeply immersed, at the middle
tho proper immersion will perhaps be attained, while there
will be too little towards the end of the voyage. It is usual
to allow from twelve to twenty-two inches of water over the top
of the floats, according to the size of the ship; but in river
* Goodeve's Mechanism, p. 251.

100 STEAM

steamers the usual plan is to allow only about one inch over
the floats, or that they should be just awash. A system of
reefing the paddles exists, i.e., at the commencement of the
voyage the floats are reefed, or unbolted, and fixed nearer the
centre, and as the coal is consumed they are shifted outwards
to the end of the radii.

107. Disconnecting the Paddle. — When the wind is fair
for sailing, and the ship is placed under canvas, it is usual to
disconnect the paddle wheels from the engines, and allow
them to revolve in their bearings by the resistance of the
water. Several plans have been proposed to permit this
action, as Maudslay's plan of sliding the paddle shaft with
the nearest crank out of the crank pin by means of a worm
wheel.

Braithwaite's, which consists of a cast iron disc keyed on
to the paddle shaft; surrounding the cast iron disc is a
strong wrought iron hoop, which will slide round the disc.
A projection, into which is bored an eye for the crank pin to
pass through, is forged on to the hoop; on the opposite side of
the hoop it is enlarged to cover a brass cushion; this cushion
is driven by a key tightly against the cast iron disc, when
the friction is so increased as to cause the disc to carry
round the hoop, and with it the crank, and so motion is
communicated to the wheels. Of course, if the key be
driven out, then the hoop and disc revolve independently,
and the wheel is free to move by the resistance of the
water.

108. The Centre Of Pressure. — In Morgan's feathering
paddle, as each paddle is always perpendicular to the water,
they progress with the same horizontal velocity, therefore we
may safely say that the point of maximum resistance, or
centre of pressure, is in a line passing longitudinally along
the centre of the float. But in the radial wheel this cannot
be the case, for the outside edge of the float moves much
faster than the inside ; the point where these two average
each other is taken at a distance of one-third the depth of
the board from the outer edge.

109. The Rolling Circle is that circle described by the
point in the wheel whose velocity is equal to the velocity cf
the ship. It is evident that the centre of pressure moves

THE SCREW OP, PROPELLER. 101

faster than the rolling circle j the resistance which this differ-
ence of velocity gives, is that which propels the ship.

" To the full power of the steam engine, and a certain
draught of the vessel corresponds a certain rolling circle,
which indicates the maximum performance of the vessel.
Under no circumstances whatever can this maximum
efficiency be obtained if the centre of the float of a paddle
wheel is placed on the rolling circle. Wherever beyond the
rolling circle the floats of a paddle wheel may be placed, and
however great the slip of the float, so long as the rolling
circle is kept at this maximum, slip, under such circumstances
(as, for instance, in a small float placed at a distance from
the rolling circle), is no loss of power, and does not lessen
the efficiency of the engine."''4

Paddle-wheel steamers are best adapted for propulsion on
shallow rivers and lakes, where the draught of water is
limited.

110. The Screw. — It need scarcely be said that the paddle
wheel was the first mode of propulsion used, and that paddles
possess certain advantages, under peculiar circumstances, by
which they still retain a strong hold upon marine engineers.
The comparative value of each will be considered presently.

111. The Screw or Propeller, or Screw-Propeller. — The
form is that of the screw of Archimedes, or it is a spiral
similar to the geometrical staircase. It acts at right angles
to the paddle wheel, and is fixed in the dead wood at the
stern of the vessel, a large rectangular hollow being con-
structed on purpose for its reception.

The propeller is of the same construction as the common
screw, but the narrow thread of the latter is expanded into
the large thin plate in the former, while the central cylinder
of the screw becomes small, and only a very small part
of a convolution is taken, as it has been found that one-sixth
part of a convolution is much more effective, and will do
more work than the whole. Propellers are generally made
with two blades, but they have been used with three, four,
and six blades. The former are found to answer best, being
fixed on a spindle passing through a boss.

112. Pitch, Thread, Angle, Length, Blade, Diameter,

* Engineering.

102 STEAM.

Slip. — We may suppose a screw to be formed thus:—
Take a piece of paper in the form of a right-angled triangle,

as A B C, and wrap it round a
cylinder, such as a large lead
pencil or ruler. Let us suppose
that when it is wrapped round,
the point C touches B, or the side
B C exactly fits round once.
Then A B is the pitch, B C is the
B ""^C circumference, A C the thread,

and A C B the angle. The thread on our supposed screw is
only a line; let us imagine this, as was said above, to become
a wide flat plate wound round, and that the cylinder becomes
small, and that of the whole thread only two bits are taken
opposite each other, we shall then have as good an idea of a
screw as can be given.

The Pitch is the distance that a complete convolution
takes upon the cylinder; or the pitch, as in the common
screw, is the distance between two threads; or, thirdly, the
pitch is the distance that the screw would go if turned once
completely round in some unyielding substance.

The Thread is the distance along the edge of the blade.
The Angle is the inclination of the thread of the screw
to the horizon.

The Length is the fraction of the pitch actually used.
Blade. — Each propeller consists of two or more parts,
which are called blades. The area is the surface of the
blade.

Diameter is the diameter of the cylinder from which the
screw is taken, or it is the perpendicular distance between
the extreme outside points of the blade*

Positive Slip is the difference between the speed of tho
ship and the speed of the screw. (See slip of paddle wheels,
page 98.) Slip varies from 10 to 30 per cent.

Negative Slip- — It is a curious fact that vessels have been
propelled faster by the screiv, than the screw would have gone
had it been working in an unyielding substance. The differ-
ence between the velocity of the ship and the screw under
this circumstance is called negative slip. It has been sug-
gested that the lines of the ship were such, that a large body

NEGATIVE SLIP. 103

of water followed the vessel and re-acted upon it, assisting
the screw to send the ship forward. If we consider the con-
dition of the water around the screw and behind it, we shall
see a better reason for this singular fact. The water is
thrown outwards and backwards by the propeller in the
form of a hollow cone. Obeying the usual laws of nature, the
water follows to fill tip this hollow, and it thus conies again
to the screw in two directions. First, that which follows in
the wake of the vessel ; and second, that which attempts, as
it were, to fill up the vacuum near the centre, caused by the
centrifugal action of the propeller. Both these bodies of
water will impinge upon the screw, and cause an additional
thrust. From this we can conceive that negative slip may
exist when these two forces reach a maximum, and act under
peculiar circumstances.

There are many varieties of screws, such as Griffiths',
who bends the ends of his blades forward a little, and
makes them broad at the boss. He discovered, in com-
mencing a series of experiments, that when he placed a
hollow globe, one-third the diameter of the screw, as the
boss, that thereby a positive gain was effected. The blades
of his propeller do not spring from the shaft, but from this
hollow sphere. The reason for such an apparently anomalous
arrangement will be found in what follows. To move the
central portion of the screw and blades, absorbs through their
inertia and resistance nearly twenty per cent, of the power
of the engines, while these parts do little towards the propul-
sion of the vessel. For they are nearly in a line with the
shaft, or at right angles to the water, and so cannot effect
such a displacement of water as shall react on the ship.
Griffiths constructs his blades to incline forward, the curve
beginning from the centre of the length of the blade, and
reaching to its point towards the ship.

Different engineers have given their blades the most varied
shapes. The object has been to get rid of the vibration which
communicates itself to the hull of the ship, and is the cause
of that disagreeable tremulous motion experienced in screw
vessels. This vibration must result from the screw striking
the water at intervals, and not acting as it should with a
continuous pressure. The unequal pressure is frequently

104 STEAM.

caused by the blade being too wide across the top. "Were
the speed of the ship the same as that of the screw, this
" shivering" would not occur. Engineers round off and spoil
their screws to make them cut the water instead of striking
it, when they should make the pitch finer in relation to the
diameter, and the blades narrower, but retaining their natural
form. The greatest resistance of the water is "across the
propelling side of the front surface just across the middle,
and the forward side of the leading edge of the back
surface."

113. Feathering Screws. — Several methods have been pro-
posed to feather the screw, such as Maudslay's and Bevis'
methods. To feather the propeller is to resort to such an
arrangement that the two blades can be turned into a line
with the keel of the ship, or in a fore and aft direction when
she is under canvas. Bevis' method feathers the screw by
means of two levers working in a boss on the screw shaft ;
the levers are moved by a sliding rod passing through the
hollow stern shaft. The sliding rod is worked by a nut on
the shaft, while the whole apparatus is easily accessible in
the shaft tunnel.

' 114. Twin Screws. — Twin screws are simply the use of
two screws, one on each side of the rudder, instead of one
screw in the dead wood :in front of the rudder. One screw
turns to the right hand, the other to the left. It is claimed
for this arrangement that the ship can be very quickly turned
within a small space.

115. Woodcroft's Screw is a screw of increasing pitch, i.e.,
supposing two threads to be wound round a cylinder, and
the distance between the threads to continually increase, we
shall have a screw of increasing pitch. Under Griffiths' pro-
peller, it was said that the centre does little or nothing
towards propelling the ship, so therefore nearly all the work
must be done by the extremities of the blade. For this
reason, Woodcroft sought to increase the pitch of his blades
at the ends, and thus gain power.

116. Ericsson's Propeller. — Ericsson fixed a number of
blades on a drum, so that his propeller had a hollow centre,
and the ends only of several blades were used to drive tlio
ship.

ADVANTAGES OF SCREW PROPELLERS OVER PADDLES. 105

117. Hodgson's Parabolic Propeller differs from the others,
in that the two blades are hollo w on their face, forming por-
tions of two similar parabolas. The other propellers send
away the water parallel to the axis of the screw, in the shape
of a cone, but the parabolic curves throw it to a focus in a line
with the axis. Hence, theoretically, as the action of a screw
depends upon the comparative immobility of the water, it is
evident the screw will have the greatest power when its
action is centralized towards one point.

118. Seattle's Screw Propeller. — Beattie's propeller is
placed beyond the rudder, instead of in the dead wood before
the rudder. The object of this arrangement, and it succeeded,
was to reduce the vibratory motion of the stern which is
experienced to the chagrin of all amateurs on board sea going
steam-boats.

119. The Advantages of Screw Propellers over Paddles.
— Under favourable circumstances there is but little differ-
ence between screws and paddles. In running before the
wind the paddle has the advantage; but when the wind is
ahead it is not so, for the wind acts on the paddle-boxes,
which offer great resistance, and so retard the ship. Fastened
stern, to stern, as tried with the Rattler screw and Alecto
paddle, and Niger screw and Basilisk paddle, the screw
dragged the paddle. The superiority of the screw is shown
in long voyages; for whereas the lightening of the ship may
prove detrimental to the paddle, it cannot be so to the
screw, the screw being more deeply immersed. As a vessel
rolls from, side to side the . immersion varies, and the paddle
loses its power. In men-of-war the screw gives a clear
broadside, while the paddle occupies the room of several guns.
In passenger vessels the paddles are more pleasant than the
vibrating motion of the screw, while the former will roll
more than the latter. The paddle-boxes act as outriggers,
and raise the centre of gravity so as to make the vessel
move more evenly in the water. In. lakes and rivers the
screw requires deeper water, while the weeds and plants
will be much more likely to clog the screw than the paddle.
In screw vessels the engines may be below the water line, or
at the very least much more out of the reach of shot than
those of paddle wheel steamers. With the screw the upper

10G STEAM.

deck is clear; so guns, etc., can be moved from end to end,
and there is a much better chance of arranging the masts,
sails, etc., so as to make the screw a more efficient sailing
vessel than the paddle wheel.

120. Disconnecting and Raising the Screw. — We have
stated that Maudslay makes provision for feathering his
paddle, or for arranging it so that when the ship is under
sail, it shall offer no resistance to the water. It has been
found before now, that when a ship has been under sail and
steam at the same time, that the velocity of the ship has
outstripped the velocity of the screw ; hence the screw has
dragged or become an obstacle to the progression of the
vessel. Cases have been known in which the screw has
actually been broken off backwards or away from the ship
by this dragging force. The screw also requires to be some-
times taken out for examination and repair, therefore a
necessity exists for providing means both for disconnecting the
screw from the engines, and for raising it out of its place.
Merchant vessels are generally brought alongside a quay at
high water, and at low water the screw is examined or taken
out : the process often involving considerable expense from
loss of time, etc. But in men-of-war more complete arrange-
ments exist. The screw is fixed in the centre of a frame,
supported on a short shaft. The main screw shaft can be
withdrawn, and thus the screw is disconnected from the
shaft, and is at liberty to revolve; by an arrangement of
slots, it and its frame are also perfectly free to be lifted out
vertically. This is effected by means of ropes and other
appropriate tackle, or by a rack and worm.

Admiral Hall has proposed a simpler and less expensive
plan for shipping or unshipping the propeller in any harbour
without entering a dry dock.*

The screw is fixed in a frame A B, and the screw shaft
can be withdrawn. A is the crosshead of the frame through
Which pass two rods, a and 6, which are screwed into the
tops of the bearings at d d' ; c is a strong chain to hold the
screw. First of all, the propeller is raised as high as possible
from the place sliown by the dotted lines to the position as
seen in the figure by means of the screws. Then tackling is
* A full description will be found in Engineering, Vol. VIII., p. 34.

THRUST OP THE SCREW.

107

fixed to each end of tlie blade, and c is also fastened on.
Next the rods a and b are unscrewed and taken out, when c
sustains the propeller. The tackling fixed to the ends of the
blades is supported by guys, so as to run clear of the sides

ARRANGEMENT FOR LIFTING- BG&JEW.

of the vessel. Next c is let go, and as the right chain-tacklo
is slackened, the left is wound up, bringing the propeller
out sideways and carrying it on to the deck. To ship tho
screw, these proceedings are reversed.

The same figure will also give us an idea where and how the
screw is fixed in the dead wood, and its position as regards
the rudder R.

121. Thrust of the Screw. — When we consider that the
screw acts by the resistance offered to the surface of the
blades by the inertia of the water, which is driven stern-
wards by the screw, we perceive at once that the whole force
moving the vessel is transmitted to the end of the screw-
shaft. Methods must therefore be provided to prevent thei
force or motion from being converted into heat by the
enormous amount of friction necessarily transmitted. The

103

STEA!.i.

more heat we allow the end of the screw shaft to generate,
the more power we lose. The dynamical and modern theory
of heat is, that heat is motion, and therefore the more
heat we allow to waste or develop at the end of the shaft
the more motion we lose.

The thrust of the shaft, or the reaction of that force which
pushes the ship through the water, is received on a series of

metal discs completely im-
mersed in oil. Several discs
are employed to distribute
the friction, and should two
or more set fast, by two pure
metallic surfaces coming in
contact, others may be still
free to move. By far the
best arrangement for receiv-
ing the thrust consists of a
long plummer block having
in it a series of circular
''depressions, with a square
section, into which fit a series
of collars turned on the end
of the shaft.

A B is the end of the
shaft; 1, 2, 3, 4, 5, etc., are
the collars turned on it.

These fit into the plummer block C. This figure C is a
representation of the bottom half only of the plummer
block. The cap which is removed is similar in section, and
contains the corresponding semicircular spaces to fit the
collars. The plummer block is often hollow, water circulating
within.

122. Thrust of Screw Continued. — If two pieces of lead
have their pure metallic surfaces laid bare, and are then put
together with a slight pressure and twist, they unite and
become almost as one piece; so will dissimilar metals, as
iron and lead, or steel, brass and lead, or even two pieces of
steel, or two pieces of glass truly flat and clean. When
lead bullets (as they are made at Woolwich, entirely by com-
pression, by driving the dies into the solid lead) are bcirg

(1) THRUST END OF SHAFT.

('2) LOWER END OF THRUST BLOCK.

HYDRAULIC OR JET PROPULSION. 109

manufactured, the lead will unite to the steel die, unless oil or
grease be employed to interpose between the two metals : the
pure metallic surfaces unite under pressure by the power of
cohesion. Before the thrust of the propeller was received
on a thrust block, as indicated above, it was received on a
fixed piece of steel, against which the shaft directly worked.
After wear, when the oil had been worn off, and the two
surfaces had scraped each other so as to present mutually
to each other pure metallic surfaces, the two perfectly united,
and united so firmly that the shaft twisted and broke, not
directly where the thrust was received, but elsewhere.

123. Hydraulic or Jet Propulsion. — A few years ago
attempts were made by Mr. Ruthven and others to introduce
water-jet propulsion, the main feature of which was, that a
jet of water driven out of the side of the vessel in one
direction propelled it in the other. In H.M. sloop " Water-
witch" three horizontal cylinders are arranged so that their
connecting rods are coupled to a crank, which works the
shaft of a turbined wheel placed in a case on the floor of the
engine-room. The water is led to the centre of the turbine
through openings formed in the bottom of the ship, and is
driven by the centrifugal force imparted to it by the wheel
through pipes, whose nozzles are placed outside the vessel on
its side just above the water line; or it may be explained
more exactly thus : from the circumference of the turbined
wheel, the water escapes into the surrounding casing, and is
led thence by two tangential pipes to the sides of the vessel.
There are four nozzles or jets at the ends of the pipes; one
pair pointing forward to drive the ship sternways, tho other
pointing aft to drive it forward. The water is discharged
parallel to the keel of the vessel. Four valves, that can be
worked from the deck very much like common cocks, allow-
ing a free passage of water, are fixed in the pipes. By these
the vessel can be started, stopped, backed, or moved round,
according to which valves are opened or closed, without
reversing the engine. By directing a jet of water forward on
one side and aft on the other, the vessel is turned round.

The water jet propeller has found no favour with engineers,
because it is palpably evident that there is a great loss of
power, Out of 750 II.P. of the " Waterwitch," only about

110 STEAM.

one-quarter seems to bo utilized in propulsion, so that whilst
offering advantages in manoeuvring over existing methods, it
is not economical. This arises from the inevitable losses
from friction, in pumping efficiency, and the small sectional
area of the jet.

124. Theory of Jet Propulsion. — The theory of jet pro-
pulsion is precisely that of "Barker's mill;" the same prin-
ciple is used to propel the Congreve and other rockets. The
fluid in a vessel presses horizontally and equally, and as long
as it is equal there is no tendency to communicate motion
to the vessel. But if an aperture be opened, the pressure
upon that portion of the surface is removed, and the
pressure upon the opposite portion of the surface is unsus-
tained, and will tend to produce motion in that direction.
Therefore, when water is issuing from the nozzles of the jet-
propeller, the opposite portions are unsustained, and the ship
moves.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Show how a helical surface is generated. What is meant by a
screw of increasing pitch ? How is the pitch of a screw measured
(1865)?

2. The pitch of ons of the blades of a screw propeller is 20 feet
8 inches, and the number of revolutions is 42 ; if there were no slip,
what would be the speed of the ship in knots ? Again, the pitcli
of the other blade being 21 feet 7 inches, if the speed of the screw
be that already found, what would be the slip per cent., reckoning
from the latter blade (1885) ?

Speed in knots Speed per minute x 60 _ 20§ x 42 x GO

from first blade Length of a knot ~~ ~""C08(f~

= 8^| knots = 8-566.

91 7 v <*° v fifl

Speed in knots from second blade = _^ x - - = 8 '9-13

0080

.'. Slip = -3807.
. •. Slip per cent, is found thus,
As 8-945 : 100 : : '8807 : 4-25(5, Av*.m

3. Describe some form of engine adapted for driving a screw
propeller. Define the terms pitch and length as applied to the
screw propeller (1870).

4. Describe some form of screw propeller. Define the terms
pitch, length, a.nd angle of the screw. What is the slip of the

EXERCISES. Ill

screw propeller? Tlio speed of a vessel is 12 knots, the pitch, of the
screw is 20 feet, the engines make 70 revolutions per minute, find
the amount of slip in percentage of the speed (1870).

Ans. 15 per cent.

5. Define a . screw surface, and the length and breadth of a screw
propeller. Describe the general arrangement of the boilers, engines,
screw, shafting, and propeller in a vessel. How are the engines
relieved from the thrust which propels the ship (1871).

6. How is a screw surface generated ? Define the pitch and length
of a screw propeller, and apply your knowledge of the geometrical
properties of a screw surface to deduce an approximate method of
estimating the area of the driving surface of a screw propeller by
measurement (1871).

See examples at the end.

7. Find the area of the blade of a screw propeller either by cal-
culation or approximately by measurement. In the latter case you
must explain fully the steps of the operation (1871, Honours).

See examples at end. ^

8. The length of a screw propeller is 3 feet, the pitch 20 feet, and
the diameter 16 feet, required the area of each blade (1867).

Ans. 42-48 sq. ft.

9. The pitch of a screw is 15 feet, the diameter 17 feet 6 inches,
the number of revolutions is 85 per minute, iiiid the rate of the
screw in knots and the distance traversed by a point in the circum-
ference of the screw (1867).

Ans. Rate, 12 '58 knots; distance, 58 '69 knots.

10. Find the slip of the screw of a steamer, number of revolu-
tions 60, multiple of gearing 4 to 1, pitch of screw 8 feet, speed of
ship 12 knots (1861). Ans. 5 per cent, nearly.

11. The number of revolutions of a crank is 73, find the pitch of
the screw if 25 per cent, be allowed as slip, and the speed of the ship
is 14 knots (1866). Ans. 25'91 feet.

12. Describe a screw propeller, and explain the terms pitch, length,
angle, and diameter (1866).

13. A screw ship's engine makes 65 revolutions per minute, the
pitch of the screw is 24 feet, and the rate of the ship is 14 '5 knots.
Find the slip in knots, and the amount per cent.

Ans. Slip -894 knots; 5 '809 per cent.

14. Find approximately the area of the blade of a screw propeller,
the diameter being 15 feet, the pitch 24 feet, and tho length £th of
the pitch (1866). " Ans. 46 '84 sq. ft.

15. What advantages do screw propellers possess over paddlo
wheels ?

16. Describe the common screw propeller. Define the terms pitch,
length, and angle, of the screw and slip. A ship is required to steam
at the rate of 12 knots and the engine crank is to make 76 revolutions,
what must be the pitch of the screw if 20 per cent, be allowed for
slip (1868)? Ans. 20 feet.

17. Explain a method of feathering the floats of a paddle wheel
steamer (18G9).

112 STEAM.

IS. Distinguish between (1) the ordinary radial paddle wheels •
(2) cycloidal wheels ; (3) Morgan's feathering paddle.

19. What is the proper "immersion for paddles ? " and state how
they are disconnected.

20. What is meant by "negative slip?" Can yon give any ex-
planation of it ?

21. Describe fonr different kinds of screws used in steam vessels ;
stating clearly their distinctive features.

22. What is meant by hydraulic propulsion ? Give the theory to
explain its action.

23. What do you mean by double screws, and what advantage is
claimed for them ?

Two screws are placed one behind the other on the same screw
shaft; it is asserted that by this arrangement a better grip or
leverage is obtained upon the water.

CHAPTER VI.

SLIDES.

Slides— -Long D Slide— Short D— Seaward's— Cylindrical— Gridiron
—Motion of Slide— Lap— Lead — Valves of Special Puinp — llo-
tatory Valve.

125. Slides. — The locomotive slide has been already par-
tially described, when speaking of the beam engine and the
way the steam is admitted to the cylinder. The various
slides used are the long D, short D, Sea ward's, Cylindrical,
Gridiron, etc.

126. The Locomotive Slide is represented in the annexed
figure, in which the dark shaded parts are

the slide, and the ports are marked port ;
c leads to the condenser. The whole of the
drawing is covered over by the slide casing,
and steam is brought to the back of tho
slide at A by the steam pipe, not shown.
When the steam is acting, it is clearly seen
that it presses with great force against the
back of the slide at A. The valve rod is
shown attached to the back of the slide.
When in the position as given in the figure,
it is quite evident no steam can pass into
the ports and go to the cylinder, as they
are both covered over; but when the slida
rod moves the valve up, the steam can pass
into the lower port, and drive the piston LOCOMOTIVE SLIDE.
up, while the steam that is in the upper
part of the cylinder can come out at the upper port, when
the form of the slide compels it to pass into b bf and through
c, which leads to the exhaust, hence c is called the exhaust
port. When the slide conies down again,, both ports are first

114

STEAM.

closed, then the upper one is open to steam and the lower
one to the exhaust, precisely the reverse of the first case.
As there are three ports, two steam ports and the exhaust
port, this valve is sometimes called the " three-ported slide."

127. The Long D Slide is so called because its cross sec-

tion forms the letter D. The two faces,
a and c, fit against the ports. The body,
or waist, A B, is smaller than 'the parts
a b and c d. The steam comes along the
steam-pipe, and can pass freely round the
waist of the valve, and pressing against
both back and front it is almost an equi-
librium valve. The steam cannot pass
by b, d nor a, c, because the two former
parts fit closely to the slide casing, and
the two latter press against the ports; only
when the valve A is lifted or depressed
can the steam enter the cylinder from
round the valve. When the steam
comes out of the upper port it passes
right down the slide at e to the exhaust.
This is the peculiarity of the slide, that
the exhaust passage from the upper port
is through the valve. >

128. Short D Slide may be described as consisting of the
upper and lower portions a and c of the long D, but tho
passage is closed, and they are joined together by a rod. The
ttteam is still brought to the waist, but cannot pass either
a or d unless the slide be lifted up. Its action is somewhat
similar to that of the long D, excepting that the way to the
exhaust is not through the slide. There are separate exhaust
passages from the top and bottom ports.

129. Seaward's Slides were first used by the inventor,
after whom they are named. There are four slides, two for
the exhaust and two for steam. A is the steam side of the
cylinder, and B the exhaust side. When they are in the
position in the figure, the piston is ascending. Steam enters
at C j the upper port a being closed it cannot enter the top of
the cylinder, but it can enter at the lower port 5, and drive
the piston up. As the piston ascends, c is closed and d

LOXG D SLIDE.

THE GRIDIRON VALVE.

115

open, so that the steam which drove the piston down is
escaping through d. When the piston is descending, a and c
are open, and b and d closed.
D is the way to the exhaust,
and B is called the exhaust side

of the cylinder; a and b are

called the induction ports, c and j^ £ ^

d the eduction. The slides are c-

kept against the face of the ports — i | \ ,-ff ^

by springs, so that any water

that enters the cylinder through A ft I HI L

priming can easily escape.

130. Cylindrical Slide.—
These slides have been intro-
duced and fitted to engines by
Maudslay & Field. They are

cylindrical in shape. The slide SEA WARD'S SLIDES.

faces are hollowed out con-
cave, and fifc on convex nozzles. They are placed between
the two cylinders, being used in double cylindered engines,
and when raised the steam is admitted to the top of the
cylinders, and the down stroke follows ; and when depressed,
steam enters beneath the piston, and the up stroke is effected.

131. The Gridiron Valve. — The
gridiron valve is one of the most
effective contrivances to give a large
opening for steam by a very short
movement. Each port is sub-divided
into two or more narrow ports, while
the valve face has openings to corre-
spond. The principle is the same as
that of an air grating in the floor, we
have only to give the top plate a slight
motion when it is open or shut ; the
same with this valve, except that the
motion is rectilinear and not circular.
If A B represent the ports of the
cylinder, and the dotted lines the
slide face, it is seen that by simply
lowering the slide (face) the smallest

GRIDIRON VALVE.

amount, that the

116 STEAM.

upper ports, A, are immediately open, and the lower, B,
closed; the exhaust is not shown. When the slide is
pushed back, the lower ports will be opened and the upper
closed.

Full Steam is the position of the valve when fully open,
and the piston is continuing its motion.

Cut-off is the position of the valve when it has just
closed the port against the admission of steam.

Angular Advance is the angular measurement of the
arc described by the centre of the eccentric while passing
from the place it occupies when the valve is at half stroke,
to that which it occupies at the commencement of the stroke
of the piston.

Linear Advance is the distance which the valve
moves while the centre of the eccentric is describing the
above angle.

132. The Motion of the Slide Valve.— The motion of the
slide valve when driven directly by an eccentric, or in the
ordinary gab motions, is simply rectilineal and reciprocating,
'and is precisely on a smaller scale what the motion of the
piston is on a larger. This is manifest in considering that
the eccentric is but a crank of a very small radius, which has,
like the greater crank, its own circle of revolution, its own
throw, and its own dead points, which terminate the recipro-
cations of the valve in the one case, and those of the piston
in the other. The motion of the slide valve must therefore
be considered in its relation to that of the piston. The rela-
tion of those motions is founded upon the uniform circular
motions of the crank and eccentric. These being rigidly
fixed on one shaft or axle have the same angular velocity.
Their relations, and those of the piston and valve derived
from them, may be established by following them through a
complete revolution. The rectilineal motion of the slide
valve, like that of the piston, is accelerated and retarded
during the travel.

All that is imperatively required of a slide valve in govern-
ing the distribution of the steam, is that it be at least of suffi-
cient extent to close both of the steam ports at the time of
changing the admission of the steam, in order that it (the
steam) may not enter at both ends of the cylinder at ono

THE MOTION OF THE SLIDE VALVE. 117

time, and that it release the steam from one end of the
cylinder at least as soon as it is admitted to the other end.

The valve, as shown in the next figure, meets these con-
ditions. In this position its inner and outer edges coincide
with those of the steam ports. The smallest motion either
way opens one of the ports to the steam, and the other to the
exhaust port c. The valve is now at half stroke, whilst the
piston is at the end of its stroke; and to move the piston in
the direction of the arrow, for example, the valve must move
in the same direction, and the eccentric must be set on the
shaft at right angles to the crank. From this description it
will be seen that one end of the cylinder is open to the boiler
throughout the whole of the stroke, while the other end is
open to the exhaust — a most disadvantageous result, as far
as the economical working of steam is concerned.

But these' evils may be removed, to some extent, by causing
the change of the distribution of steam to take place before
the completion of each stroke ; and this is effected by shifting
forward the eccentric on the shaft, the motion of the valve
being advanced in a like proportion. The arrival of the piston
at the end of its stroke is anticipated by the change of dis-
tribution, and the steam has thereby gained time to re-arrange
itself for the next stroke. The advantage of this is obvious,
when we remember that by this arrangement the maximum
time is afforded for these operations with the least motion of
the piston and a minimum retarding effect. While by these
arrangements a more efficient admission and exhaust are pro-
vided, nothing can be done with this valve to employ the
expansive force of the steam in propelling the piston, which
requires the confinement of the steam within the cylinder
during the latter portion of the stroke; when using such a
valve we find that the suppression and release of the steam
take place at one and the same time.

Expansion is, however, attained by simply adding to the
length of the valve, as shown in the figure, by the dotted lines
a a. Its two outer edges are, by the addition, set so much
the further apart than the extreme edges of the steam ports,
and by as much does the suppression, and, consequently, the
commencement of expansion anticipate the exhaust during
the travel of the slide valve, and while the valve describes

118

STEAM.

this portion of its stroke, the piston is moving under the
pressure developed by the expansion of the steam already in
the cylinder.

133 Lap and Lead of the Locomotive Slide. — The
width of the opening of the steam ports for the admis-
sion or for the release of the steam at the beginning of the
stroke is known as lead. On the steam side of a locomotive
slide, it is known as outside lead, or lead for the admission ;
on the exhaust side it is inside lead, or lead for the exhaust.
When the valve is placed at half stroke over the ports, the
amount by which it overlaps each steam port, either internally
or externally, is known as lap. On the steam side it is named
outside lap; on the exhaust side, inside lap. When the
terms lap and lead are employed, they are understood to
refer to outside lap and lead only.

The advance of the eccentric is a term used to denote the
angle which it forms with its position at half stroke, and
when the piston is at the commencement of its stroke.

The locomotive slide (figure annexed), as seen in section, has
neither lap nor lead, but did it extend to the
faint dotted lines b b', it would have lap on
the exhaust side to both ports; while, on
the contrary, if it reached to the clotted
lines a a, it would have lap on the steam
side. Lap is .chiefly used on the steam
side. To see what effect this will have,
( c m\ I A -^ us examine the top port, and suppose

^-^1 .WA the slide going up. It is evident if the

slide reaches to the dotted line «, as it
rises from the bottom of the upper port, it
will close it sooner against the admission
of steam than it would be otherwise if the
slide were constructed simply as drawn in
the figure; therefore the steam that has
LOCOMOTIVE SLIDE, had time to get into tlie cylinder has to
perform the rest of the stroke expansively.
Lap on the exhaust or eduction side, b b', is always less than
that on the steam side, and closes the port to the exhaust
sooner than it would otherwise be, and thus prevents all the
steam from rushing out to the exhaust; the steam remains

VALVES 0$ THE SPECIAL PU3IP. 119

behind, and the piston acts against it as against a cushion,
and so all sudden jar and stoppage is avoided. Sometimes
there is no lap, and even less than none, or negative lap; then
the valve cannot cover both ports at once. When the slide
has neither lap nor lead, the breadth of the slide face is
equal to that of the steam port, and the travel of the slide
twice the breadth of the port; but when the slide has lap,
the travel of the slide must be double the lap with double
the breadth of the steam port.

134. Lead. — Let us suppose that at the instant the piston is
at the top of its stroke, that the slide is in the position shown
in the figure of the locomotive slide, but that it extends only to
the top darkly-dotted line, then the port at that instant would
be open for the admission of steam : this is what is called the
lead of the slide. Remember the lap is when the slide is at
its middle position, but lead when the piston is at the end of
its stroke. The lap and lead of the D slide are explained in
precisely the same way, but the steam side is the inner and
the exhaust the outer. There is always more lead required
in engines that are driven at great speed, than in those which
work slowly. Again, in engines that travel fast, it is best to
open the exhaust passage before the end of the stroke, or else
the cushioning will act injuriously.

135. Valves of the Special Pump. — We describe these
valves, which are in a measure self-acting, as they seem to
involve a mode of action which may be rendered still more
effective and economical both in construction and wear and
tear.

A B is the steam chest filled -with, steam, the valves and
the contrivance for their working. There is a double set of
steam passages, a c and a c, the same as in the locomotive
slide, and e e leading from near the ends of the steam chest
to the inner end of two small cylindrical chambers, s and s',
formed in each of the cylinder covers, Both the small
chambers are fitted with a piston, as seen at s and sf, and
kept in their places by the pressure of steam on their backs.
C is an ordinary locomotive slide ; as shown in the figure it
is covering the ports, so that the right hand is open to the
exhaust, and the left for the passage of steam, consequently
the piston is moving to the right. (We have drawn it near

120

STEAM.

the end of its stroke.) On the back of the valve are a pair of
lugs, which fit between two collars, D and D', formed on one

VALVES OF SPECIAL PUMP.

spindle ; on the ends of the same spindle are two plungers,
F and F', which work in the ends of the steam chest. The
steam chest is cast cylindrical on purpose for them to work
in; but they do not work steam tight, but are fitted so as to
allow a little steam to escape beyond the plunger, which
thus gets shut up between the end of the plunger and the
steam chest.

When the piston arrives at the end of its stroke, it strikes
against the small spindle in s', when the small valve is thrown
off its seat, thereby opening the passage e, and putting it in
communication with the exhaust; so that the steam which
has escaped beyond the plunger F' runs to the exhaust, while
the steam in the chest between F and F' will obviously move
the valve to the right, and alter the position of the slide,
putting the right hand port in communication with steam,
and opening the left to the exhaust. The stroke is then
made towards the left, and the valve s thrown off its seat,
when the steam from behind F escaping to the exhaust, the
slide is moved to the left again.

136. Rotatory Valve. — A is a section of a rotatory valve
as used in Ramsbottom's "Intermedial Steam-engines." M

ROTATORY VALVE.

121

is the main shaft, a projection on the end moves the slide
round and round; the part marked black is the slide ; S is the
steam pipe ; the steam can freely enter A. As shown in the

HOTATORY VALVE.

figure, the port 2 is open for the steam to pass to the bottom
of the cylinder to drive the piston up, which is now close at
the top of its stroke. When the opening in A is turned
round, we shall see then that steam will enter 1 and pass to
the top to drive the piston down. The opening in the slide
can be very wide, so as to admit a large quantity of steam ;
and it is evident that we can allow steam to pass into the
cylinder during what part of the stroke we please. As the
dark parts revolve with the shaft, the opening near A is
alternately brought opposite to each steam passage 1 and
2, when steam will alternately pass to the top and bottom
of the cylinder to drive the hollow piston P P.

CHAPTER VII.
OTHER VALVES.

Ilornblowcr's Valve — Equilibrium — Escape — Sniftinoj Valve — Com-
munication Valve — India-rubber Disc Valves — Kingston's Valve
— Blow-through Valve — Balanced Slides — Facing Valves.

BESIDE slide valves, there are expansion valves,* such as
Hornblower's, the equilibrium and Cornish double-beat ; also
the escape valve, India-rubber disc valves, Kingston's valves,
etc., with communication or stop valve, safety valve, vacuum
valve, and blow-through valve. Any valve will constitute
£ii expansion valve, so long as it will suddenly give a large
opening for steam, and as readily cut it off. When the
throttle valve is used to regulate the steam supply, the steam
is said to be wire-drawn ; throttling is when you are using
the valve to work the engines slowly.

137. Hornblower's Valve. — As soon as high-pressure steam
came into use, a valve was wanted that would move easily,
although the pressure of steam was very great. This valve
has the " merit of affording any amount of expansion with a
rapid cut-off and absence of wire-drawing, and a fully open
passage to the condenser during the whole of the stroke."
It consists of one tube sliding within another, like telescope
tubes, with a valve fixed right across the tube; when the
edge of the inside tube comes down on the valve no steam
can pass, but directly the tube is lifted it can pass freely.
It will lift easily, because the steam can press nowhere but
upon the top circular edge of the tube.

138. Equilibrium Valves. — Equilibrium valves are those
upon which the steam presses with equal force (or very nearly
equal force) both upon the top and bottom, being ready to
move easily when required. The following figure will give a
good idea of an equilibrium valve : —

* For a good expansion valve, see Elementary Steam,

ESCAPE VALVE.

123

S is the steam-pipe, through which steam is introduced into
the valve - box A B ;
a and b are two conical
valves on one valve
spindle c d, kept in its
place by the socket d.
The steam is required to
pass at intervals along
C. This it will do with
full force when the
valves are but slightly
lifted upwards. It is
seen that if a and b be
very nearly equal, the EQUILIBRIUM VALVE.

valve is in equilibrium,

and only a small force is required to lift it, for the pressure
of steam on the top of a is counteracted by that on the
bottom of b.

139. Cornish Equilibrium, Double-beat, Crown or Drop
Valve. — A B is the valve-box.

Steam enters it, let us say, from
C, and is required to go along D, A[_
after passing the valve. It might
with equal propriety be supposed
to come from D and be passing
down C. The part drawn with
cross lines or section, is a cylin-
drical piece of iron fitting clown
on two rings, b b and b' b'. The
small squares are the sections
of the rings; suppose these to
go all round. It is evident that CORNISH DOUBLE BEAT VALVE.
when the valve is down on the

rings no steam can pass, but as soon as lifted it can rapidly
pass through the two openings marked a in the paths indi-
cated by the arrows. These openings extend all round in a
circle. A very slight movement gives a large opening for
steam. The seats b b and bf b' are called the beats. Some-
times these valves are made with three or four beats.

140. Escape Valve. — The escape valves should have been

124 STEAM.

noticed when describing the cylinder. They are fitted in the
top and bottom of the cylinder, being kept in their places by
weights or springs. Water that gets into the cylinder through
condensation or priming, as it is incompressible, would inevit-
ably break something, were not provision made to allow it to
escape through the escape valves. They are loaded with a
weight or spring greater than the pressure of steam in the
boiler. Test or pet cocks are also fitted to the tops and
bottoms of the cylinders in marine engines for the same
purpose. They are alwaj^s opened on starting the engine,
and shut when properly under way. The escape valves are
always ready to act, and are held in their places by weights,
which keep them closed only so long as the pressure in the
condenser is below that in the boiler.

141. Snifting Valve or Tail Valve. — The snifting valve
is placed in communication with the condenser, to allow the
air to -escape should the pressure of air become too great in
the condenser. It was referred to in describing Newcomen's
engine, and should have been shown in Watt's improvements
at the bottom right hand comer of the figure. Before start-
ing it is customary to " blow through," when the condenser
is cleared out, and any air there may be in the condenser is
driven out through the snifting valve, which is lifted 011 pur-
pose. A snifting valve is not always fitted to an engine,
because the air pumps take off the air.

142. Communication or Stop Valve. — The purpose of
the communication or stop valve is to allow the steam to pass
from the boiler to the engine. When it is wished to start, a
handle is turned round, which lifts generally an ordinary
conical valve from its seat, and the steam passes at once into
the steam pipe to the slide casing, etc. A communication
valve is fitted to each boiler, so that when an engine has
several boilers, any one or more can be used without the
ojbhers. The regulator in the locomotive corresponds to the
communication valve in the marine and land engine.

143. India-rubber Disc Valves. — These are employed, espe-
cially in swift running engines, for air-pump valves, instead
of the common butterfly or clack valves. They are con-
structed with a ring or disc of India-rubber covering a grating.
A B is a circular piece of good thick vulcanized India-rubber;

ELOW-TIIROUGII VALVE. 125

C D is tlie grating over which it is fixed ; the arrows show
the direction in which the water passes. The grating is
very similar in construction to
those employed for air-gratings in
floors. E is the guard to keep the
India-rubber from collapsing into
a heap. All these are bolted to- A
gether by the bolt a b. When c
water has passed through the aper-
tures in C D, and the pump ascends,
the pressure of water on and
above A B lays it flat on C D, INDIA-RUBBER DISC VALVE.
co that none can return. But on the down stroke, the
India-rubber being pliable it gives way, and the water passes
above the valve. The guard has apertures in it.

144. Kingston's Valves are conical valves with the largest
end downwards. They are fitted to every opening below the
water line in a ship. The largest end is presented to the
pressure of the outside water, so that in attempting to get
into the ship through any orifice where they are fitted, the
water actually closes it up more tightly, and so leakage is
prevented. They are opened and shut by turning a screw
by its handle ; and when open the valves come outside the
ship's bottom, but there is a guard to prevent them being
opened too far.

145. Blow -through Valve. — The blow-through valve of
an engine is used to drive out all water from the cylinders,
casings, and condensers before starting. It is placed at the
bottom of the slide casing so as directly to communicate with
the condenser. But sometimes one is placed at each end of
the cylinder, and worked by a handle from the starting
platform. Some engine-makers fit a small locomotive slide
and ports for the purpose, which can also be used to start the
engines. Before the engine is started, steam is admitted
through the blow-through valve, and the cylinder first cleared
of air and water; the steam passing on clears the condenser
in the same way, *So that as soon as the engine begins work
a good vacuum is obtained in the condenser. This last is
the chief object for which blow-through valves are fitted.

S P is the steam pipe ; the steam having been brought to

12G

STEAM.

BLOW-THROUGH
VALVE.

the back of the slide cannot enter the cylinder unless the
long D slide be lifted up or down, neither can it ga to the
condenser unless the blow-through valve B be opened by
means of the handle li. When the valve
B is lifted off its seat, then steam can
freely pass to the condenser, and blow
out all air and water that may be in it ;
when no blow-through valve is fitted,
by the tedious process of alternately
letting the steam pass to the top and
bottom of the cylinder, by raising and
lowering the slide, the steam may be sent
to the condenser, from which it will in
time expel the air and water.

146. Balanced Slides.— When steam
of a higher pressure began to be used in.
engines than was customary in the days
of Watt, the general size of the slide rods, eccentric rods,
bands, etc., were found to be too weak to perform their work;
so that in large engines, such as those that were used in our
large ocean boats, these parts were made enormously strong
and out of all proportion to the rest of the engine, from which
a great amount of power was taken to move the large
slide valves, when their whole back surfaces were exposed to
the pressure of the steam. Engine-makers seeing this took
the matter into consideration, and arrived at results which
relieve the slide valve of most, if not all, of the pressure ; by
these means the appearance of the engine has been greatly
improved. The steam-hammer was the first engine in which
it was attempted to fit a balanced valve, because, perhaps,
the slide valve being worked by hand, the evil was felt too
acutely to be longer neglected. A piston was fitted to a
cylinder, which was placed above or at the back of the slide
valve, to which it was connected by a rod. The area of the
piston was made a little less than the area of the slide valve.
a b c d ef g h is the slide casing ; V is the valve, and V R
the valve rod; to the back of the valve, by a ball and
socket joint, is attached the rod p, which is fastened in a
similar manner to the piston i. When steam enters the
valve casing through O, it will press heavily against the

PACING SLIDE VALVES.

127

back of the valve. It will also enter f e d c, and force the
piston,, i in the opposite direction. Thus the valve is
relieved of the pressure, and more readily moved to
allow steam to pass through s or to the
exhaust n.

It will thus be seen that there is just
or nearly the same force pressing against
the valve as against the piston, or the
valve is balanced.

We will now explain another and
one of the best plans yet adopted for
balancing the slide. The back of the
slide jacket cover is first planed. On
the back of the slide valve is cast a large

, ,. , . r. X1 &, BALANCED VALVE

circular recess, which is further turned OF STEAM HAMMER.
in the lathe, and into which is fitted
a metallic ring. Several strong springs are placed at the
bottom of the recess, which force the ring out against the
planed surface of the jacket. It will thus be seen that
at the back of the slide valve there is a large circular
space on which the steam cannot press at all, only on the
four corners of the valve. There is also a communication
kept open between the space inside the ring and the
condenser, by which means the condenser vacuum is in
connection with the back of the slide, and is made to help to
draw off the valve from the face of the ports, so as to coun-
teract the pressure of the steam on the four corners. In fact,
it has been calculated that when these engines are working
with a low steam pressure and a good condenser vacuum,
there is a good pressure tending to draw off the valve from
the face of the cylinder ports.

Balanced valves have been shown to possess so many good
qualities and advantages, that no large engine is made without
them now by any engineer who wishes to get the greatest
amount of work with the least possible outlay.

147. Facing Slide Valves. — The faces of the slide valves
must be so prepared that steam will not be able to find its
way between them and the nozzles of the cylinder into the latter.
The valve being cast, the faces are first planed in the planing
machine as true and smooth as that machine will make them.

128 STEAM.

Then a fine or smooth file is taken, and the faces are filed
with it till all the marks made by the tool of the planing
machine are taken out. The valve is next rubbed against a
surface plate (a truly flat surface), on which is spread a thin
covering of red lead and oil, this marks with red lead any
inequalities that may now exist on the valve face. A scrape
or scraper is then taken, which is simply a flat piece of steel
with a very fine edge finely tempered and sharpened on an
oilstone, it is held in the hand, and all marks of red lead
are scraped off from the slide with it. This is repeated till tho
valve face bears all over on the surface plate.

The valve is now covered with the red lead and oil, and
applied to the face of the port on the cylinder, when the red
lead marks left on are scraped off as before, till in its turn
the valve face bears all over the corresponding face on the
cylinder. We thus get a perfectly steam-tight slide valve face.

In the American locomotive shops it is now the practice to
put the slide valves in as they come from the planing machine,
without any other preparation whatever; after a few days'
working a very good bearing is found to have established
itself.

There appears to be a general opinion that a large amount
of time and money is wasted on the preparation of slide valve
faces by making them fit so nicely; for when hot, the amount
of expansion of the small thin part is unequal to the larger
and thicker, and thus, it is averred, the truth of the slide
valve is destroyed as soon as it is put to work.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Describe the long D slide (1867).

2. What is the use of the expansion valve ? Show by a diagram
the pressure of the steam in different parts of the stroke when \yorked
expansively (1867).

For latter part of question see chapter on the indicator.

3. Give a short description of the common D slide, the short D
slide, and Seaward's slide. What kind of slide is used for double
cylinder engines (1867) ?

4. The length of a gab lever is 10 inches, and the travel of the
slide is 12 inches ; find the travel if the gab lever be shortened 1
inch (1S67).

EXERCISES. 129

The gab lever is the lever to which the eccentric rod is attached
to work the slide.

If L and I be the length of the gab lever, and t and t' the travel of
the slide respectively, we have the following inverse proportion : —

L : I : : t' : t.

The reason is obvious, for if the gab lever be shortened the ec-
centric rod, or the throw of the eccentric, remaining the same, will
move the short gab lever through more degrees of a circle than the
longer one. Hence the shorter the gab lever the longer the travel of
the slide.

To solve the above question, since

L : I : : t' : t
.'. 10 :9 : :*':12

... *'=i^=13i inches.

5. What is meant by lap ? What is the difference in the working
of two engines, one of which has lap to the slides and the other has
not (1867) ?

6 Describe an equilibrium valve. The upper side of an equilibrium
valve is 9 inches in diameter, and the lower side 8 inches ; find the
power necessary to lift it when the steam is 16 Ibs. above that of the
atmosphere, if the space between the upper and lower valves be a
vacuum (1867). Ans. 413*9 Ibs.

7. Describe generally the side lever marine engine. What is the
object of the blow- through valve, and where is it placed ? Which
parts of the engine are made of brass, and which of cast or malleable
iron respectively (1870) ?

8. Explain the principle of an equilibrium valve, and illustrate
your explanation by referring to the Cornish double-beat or crown
valve. In a double-beat valve the internal diameters of the two seats
are 5 and 3^ inches, and the weight of the valve 68 Ibs., what head
water could be held back by such a valve, before the pressure of tho
water would cause it to lift (1870) ?

It will keep back a pressure of 5*99 Ibs. on the square inch or
15'57 feet of water nearly.

Effective area of valve x pressure = weight of valve proper.
52 - (3J) 2 x 7854 x pressure = 68 Ibs.

. '. pressure = 5 '99 Ibs.

9. What is the distinction between a single and a double acting air
pump ? Sketch both forms of air pump, showing the valves neces-
Eary in either case. Describe the India-rubber disc valve (1870).

10. Describe some form of slide valve as fitted to the steam
cylinder of a double acting engine. Sketch the valve in section with
the openings over which it slides, and give some account of lap on
tlie steam side. How is the face of such a valve made truly plane

130 STEAM.

11. For what purpose are escape valves fitted to tlie cylinders of
marine engines ? How are such valves kept closed, and what deter-
mines the least amount of load which must be put on them (1871) ?

12. Show that a single slide valve will suifice to work a double
acting engine, in the place of two steam and two exhaust valves.
Explain with a sketch the action of any slide valve which you select
(1871).

13. Define the lap of a slide valve. Explain the effect produced by
adding lap, (1) to the steam side, (2) to the exhaust side of valve,
showing what would occur if there were no lap on either side (1871).

14. A pump valve is made in the form of two rings, each 1 inch
wide, and of internal diameter 6 and 12 inches respectively, what
is the area of the openings of the seating, and what should be the
lift when the valve is full open (1871) ?

Am. Area 29 -8452 inches. Lift J inch.

15. The safety valve on the boiler of a locomotive is held down by
a lever and spring, sketch the arrangement. A safety valve 4 inches
in diameter is constructed, so that each pound of additional pressure
per square inch on the valve corresponds to 1 Ib. pressure on the
spring, what are the relative distances of the spring and valve from
the fulcrum of the lever? After the valve is set, how much additional
pressure per square inch will be necessary in order to lift it -fa of an
inch, the spring requiring 10 Ibs. to extend it 1 inch (1871) ?

Aiis. Relative distances 2 : 25, nearly.
•497 Ibs.

16. Describe the locomotive or three ported valve, as applied in
engines of short stroke. Why is its use restricted ? Show that lap
added to the valve produces an expansive working of the steam
(Honours, 1871).

17. Describe the long D slide. The cover of a valve is 1 J inches,
whereof 1 J inches is the lap on the steam side, and £ inch is the lap on
the exhaust side ; if £ inch is allowed for lead, what will be the
amount of opening of the lower part to the exhaust when the piston
is at the top of its stroke ? Why is the lap on the exhaust side made
so much less than that on the steam side (1870) ? ..

Ans. 1J inches.

18. Describe some arrangement of expansion gear suitable for a
marine engine. What form of valve should you employ (1870) ?

19. Show how to find the proper length of the eccentric rod of an
engine. The travel of a slide is to be increased from 13 to 15 inches ;
what alteration must be made in the length of the eccentric lever,
whose original length was 12 inches (1863) V

Ans. Gab lever must be shortened If inches.

20. Describe the safety valve. If a circular inch be allowed on the
area of a safety valve for every 200 square feet of heating surface,
what must be the diameter of a valve for a boiler whose heating
surface is 1,200 square feet (18G8) ? Ans. 2'45, nearly.

21. Describe the Cornish double-beat valve (18G8).

22. Describe the Cornish double-beat valve with a sketch (18GG).
£3. There are two valves, the diameter of one is 2*5 inches less.

EXERCISES. 131

than that of the other, and the sum of their area is the same as that
of a valve of 11 inches diameter, find their dimensions (1866).

Ana. 6 '4 and 8 -9.

24. How is the slide of an engine placed in the middle of its stroke
(when adjusting the slides) (1866) ?

25. What is the use of the cylinder escape valves ? The steam
pressure of a boiler is increased from 12 to 15 Ibs., how much must
the weight of the lead cylindrical weight on the valve be increased, its
diameter being the same as that of the valve, and a cubic foot of lead
weighing 710 Ibs. (1866) ? The question as it stands is absurd, the
weight would be a yard high.

Ans. 7*3 inches in length.

26. In some double acting engines the valves connected with the
steam cylinder are double-beat valves worked by cam*. State the
advantages of this system, and explain the principle of a double-beat
valve (Honours, 1871).

27. Describe the locomotive and long D slides. The travel of a slide
is 14 inches, depth of the port 6 inches, and the slide is short on the
exhaust side J inch ; when at the middle of the stroke, how far does
the slide go below the lower edgo of the port on the exhaust side at
the extreme of its stroke (1863) ?

Ans. 1| inches.

28. Describe the long D slide, and show how it is worked by the
eccentric. How is the packing of the slide at the upper and lower
ends lubricated (1864).

29. Describe the safety valve of a locomotive boiler. Explain
Bourdon's gauge for ascertaining the exact pressure of the steam in a
boiler (1869).

30. How is the scale of the barometer gauge graduated? What
error is introduced by having the scale fixed ? To what extent will a
thermometer, having its bulk inserted in the condenser, supply the
place of a barometer gauge (1863) ?

31. Give a sketch of a blow valve and a sniftiiig valve, and show
why these valves require 110 spring nor weights to keep them in their
seat (1863 and 1864).

The blow valve has steam above and a vacuum below. The snift-
ing valve, which is frequently kept in its place by a spring, has the
atmosphere above and a vacuum below.

32. Explain the meaning of the terms cushioning, lead, and lap.
On what is lead made to depend (1864)?

33. In what way is steam admitted into the cylinder ? How is the
apparatus worked (1865) ?

34. Describe with a sketch some form of slide valve, as connected
with the steam cylinder of an engine, and explain its action (1869).

35. Describe the method of working a slide valve by an eccentric
(1869).'

36. Describe Kingston's valve. Show how to ascertain the degree
of saltness of the water in a marine boiler (1869).

See chapter X.

37. Describe some form of steam sjide valve adapted for a double

132 STEAM.

acting engine. How are the faces of such a valve prepared so as to
make it steam tight (1869) ?

38. Define the lap of a slide valve. What is the object of putting lap
upon a slide ? What is meant by the lead of a valve, and what con-
siderations determine the amount of lead (1869) ?

39. Describe and explain some form of equilibrium valve. The
diameter of a steam pipe is 12^ inches, the upper and lower discs of an
equilibrium valve being 12 and 10^ inches in diameter respectively,
what will be the lift of the valve when the pipe is fully open (1869) ?

Ans. 1'736 inches.

40. Describe Kingston's valve. Sketch the arrangement of a feed
pump and the valves connected with it. How are India-rubber
annular valves made and fitted (1869) ?

41. Describe the blow valve and the snifting valve, and why the
former is not so important as formerly?* The diameter of a blow valve
is 4 '5 inches, and the steam gauge at 23 inches, what force is required
to lift it before and after a vacuum has been created in the condenser,
the barometer gauge in the latter case standing at 24 inches (1869).

Ans. 556-652 Ibs.

42. Give a description of the gridiron valve. A gridiron valve has
three openings for steam, each 16 inches by 3, find the total opening
for steam. Ans. 144 inches.

43. Describe the short D slide ; explain its action, and state in what
respect it differs from the long D.

44. Give definitions of "full steam," " cut off," "angular advance,"
"linear advance," and "travel of slide."

The travel of a slide is the sum of the distances it moves up and
down from its mid position.

45. How do Seaward's slides differ from others, and what is meant
by the steam and exhaust side of the cylinder.

46. Describe any form of valve that is self acting.

47. What is meant by a " rotatory valve ? "

48. Explain the term "balanced slide." Why do slides require
balancing, especially those of the steam hammer ?

49. Describe Hornblower's valve.

50. Give a sketch of a " snifting" and " blow- through valve.'

Higher pressure steam is used, and therefore in starting the engineer has not to
depend so much as formerly upon a good vacuum.

CHAPTER VIII.
THE BOILER AND ITS APPENDAGES.

Definition — Haycock, Haystack, or Balloon Boiler — Waggon Boiler—
Flue Boilers — Length and Diameter of Flue — Plates — Marine
Flue Boilers — Blast Pipe — Steam Chest — Locomotive Boilers —
Field's Boiler — Galloway's Tubes — Vertical Boiler — Cornish
Boiler — Fusible Plup — Clothing Boilers — Copper Boilers — Test-
ing— Water Heaters — Surface Condensation— Circulating Pumps
— Ejector Condenser.

THE boiler is the vessel in which steam to drive the engine
is generated. It has received various shapes from early and
late engineers, such as haycock or balloon, waggon, sphere,
hemisphere, ring or annular, flue, Lancashire, Cornish, and
return-tubular, Field's, etc. The early boilers were very
defective in their construction, being actually made of cast-
iroii with leaden or wooden tops, and even with wooden
shells hooped like barrels, and often with flat surfaces — the
weakest of all forms ; but then no danger arose, for the pres-
sure seldom or never exceeded twelve or fifteen pounds on the
square inch; but now, when boilers have to submit to ten or
twelve times that strain, care, thought, and diligent enquiry
are absolutely necessary.

If, in the construction of steam boilers, strength alone were
studied, the spherical form would be adopted, because it is
the strongest of all forms in which a vessel can be made if it
is to resist either internal or external pressure; but although
such boilers have been used here and there they will never
come into extensive use, because they have not a large amount
of heating surface. The cylindrical form is next to the
spherical in point of strength, and superior to it in respect of
superficial area or heating surface, hence this form is very
generally adopted.

148. The Haycock, Haystack, or Balloon jBoiler, perhaps the

134:

STEAM.

BALLOON OB HAYSTACK BOILER.

earliest used, had for its lower part the frustrum of a cone, and
its top a hemisphere. Some of these may still be seen at

old mines. It is said that
more explosions have oc-
curred with these boilers
than with any other class.
Its shape is inherently
weak.

149. The Waggon Boiler
has been more extensively
used than the last. In shape
it is somewhat like a car-
rier's waggon. The fire is
placed beneath the bottom.
It was employed very much
by Boulton and Watt; being

surrounded with brickwork flues in such a manner that the

heated air and gases could
run all round the lower
part of the boiler. These
are not strong boilers, they
require much staying.
When an explosion takes
place, they generally give
way at the bottom.

150. Flue or Cylindrical
Boilers (external pressure).
— These are a great stride
beyond the last, and ap-
proach the true shape of a truly efficient boiler. They con-
sist of a large cylinder with one or more flues passing through
their whole length, which are generally built of plates of
the same thickness as the other parts of the boiler, but
experiments prove this to be a vicious system.

FJue boilers assume many different arrangements as regards
the flues." The next figure shows the return flue boiler. At
first the flue went right through, the fireplace at one end
and the chimney at the other. It was a great improvement
and early introduced, to let the flue curve round at the
further end and return to the front, so that chimney and

WAGGON BOILER.

LENGTH OF FLUES.

135

fireplace were both at the same end. The fireplace is seen
to the left, and the chimney on the right of the front, while
the dotted lines show the
course of the flue in the boiler.
When the boiler has but one
tube running from end to end,
it is generally called a Cornish
boiler, and when two it receives
the name of Lancashire boiler ;
but we have explained a little
further on with an illustration
the real distinctive features of a
Cornish boiler, and it must not be left unstated that we may

RETURN FLUE BOILER.

LANCASHIRE BOILER.

CORNISH BOILER.

speak of a two-tube Cornish boiler; but still it is a very
common mode of distinguishing boilers
of one and two tubes from each other,
especially in the Midlands, calling
them respectively Cornish and Lanca-
shire boilers.

151. Elephant or French Boiler. —
One of the most extraordinary forms
given to boilers is shown in the annexed ([
illustration, which is not only a very bad

form of boiler, not being economical, ELEPHANT or. FEENCT

, . . , i»UlliJjlv.

but it is a dangerous one.

152. Length of Flues. — Sometimes flues are made to run
the whole length of the boiler, twenty or thirty feet, without
any supports. Three tubes were taken, four inches in
diameter, of the same thickness of iron, supported at the ends

136 STEAM.

by rings, but respectively nineteen, forty, and sixty inches
long. Pressure was brought to bear upon them, and they
collapsed at 137, 65, and 43 Ibs. per square inch. This
clearly demonstrates that the strength of similar tubes to a
collapsing pressure, is in inverse proportion to their length.
Two boiler flues forty-two inches in diameter, three-eighths of
an inch thick plate, and twenty-five and thirty-five feet long,
collapsed — the former at a pressure at 97, and the latter at
27 Ibs. on the square inch.

153. Diameter of Flues. — The greater the diameter of
a flue or cylindrical boiler, the weaker it is. Its strength
varies inversely as the diameter, i.e., double the diameter, the
strength is diminished by one half. From experiments:
three five feet tubes, four, eight, and twelve inches in diameter,
about -^V of an inch in thickness, collapsed at a pressure of 43,
20 '8, and 12*5 Ibs. on the square inch respectively.

154. Thickness of the Plates. — The strength of flue is
augmented with the thickness of the plate in a little
greater proportion than the square, i.e., if a plate one-eighth
of an inch thick bear a certain strain, then one double the
thickness, or one-fourth of an inch thick, will bear a strain
equal to 22<19, or more than four times as great. Then,
because the greater diameter of a tube the weaker it is,
and because, also, the strength of a plate increases with its
thickness, therefore the thickness of a tube plate sliotfld be
in proportion to the diameter of the tube; or, the plates of a
two feet diameter flue should be, within certain limits, double
the thickness of those of a one foot flue; or, if the plates
of a one foot flue are one-fifth of an inch thick, those of a
two feet flue should be two-fifths of an inch thick.

Mr. Fairbairn, to whom we are indebted for these impor-
tant experiments, and from whose valuable work, Useful
Information for Engineers, these facts are culled, proposes a
remedy and modification in tubular boiler tubes, which have
hitherto been constructed without a correct knowledge of the
laws of nature. He proposes that strong rings of T or angle
iron shall be riveted at intervals of 10 feet or less along the
flues, thus practically reducing them to several tubes of short
length, and, therefore, considerably increasing their strength.
He also proposes that they should not be formed with tlio

THE MARINE TUBULAR BOILER. 137

usual lap joints, but with riveted butt joints, and longitudi-
nal covering plates.

155. Boilers' Internal Pressure. — He also shows thafc the
tensile strength of a boilerplate is nearly the same whether torn
asunder in the direction of the fibre or across it ; and that
heat does not affect their strength up to 315°C., above which
they rapidly become weaker. Riveting reduces the tenacity
of a boiler or the bursting pressure from 23 tons per square
inch to 15 tons. Cylindrical boilers made of the same thick-
ness of plates throughout are more liable to give way along
the sides than at the ends.

The external shell of a boiler is three or four times stronger
than the flue, if both are constructed in the ordinary manner;
or, the outside shell more easily resists the bursting pressure
than the tubes can the collapsing. But if the flues are divided
into lengths of 10 feet or less, by strong ribs of angle iron,
their resistance is enormously increased. Cylindrical boilers
must be strengthened in the same way, but are considerably
weakened if made elliptical instead of cylindrical.

156. The Marine Flue Boiler. — In this boiler the fire-
places are within, the shell, and the flues wind backwards and
forwards until they discharge the remaining heat up the fun-
nel, the furnace (or furnaces) being at the end of the boiler,
below the middle of the water. The heat first descends to
the bottom of the boiler and towards the farther end, it then
winds back towards the furnace, and turning up and back
comes now to the bottom of the funnel, near the centre of
the boiler.

157. The Marine Tubular Boiler. — In tubular boilers the
heat is allowed to pass into and through a series of tubes
which run through the water. They are chiefly employed in
locomotive and marine engines.

The figures on next page represent (1) a longitudinal
section of a marine tubular boiler, (2) a front view —
partly in section, to give a better idea of it, and showing
four furnaces F P, with the ashpits A P. The small circles
represent the ends of the tubes, W W is the water in the boiler,
www the water around the tubes, the spaces between them,
are the tubes themselves, w L is the water level. In the left
hand figure F P is the fireplace, 13 the bridge. The coal is

133

STEAM.

first thrown on to the dead plate D to warm, it is then
pushed 011 to the fire bars a a. The fire bars are in lengths,

oooooooooooo
oooooooooooo
oooooooooooo

ooo

A P

1. Longitudinal Section. 2. Front Elevation.

TUBULAR BOILER.

and the ends are not close together, to allow for expansion.
B is the bridge to prevent the fire from getting too far back
in the furnace; the bridge sometimes forms part of the boiler
itself — a very bad practice — but is more frequently built of
Stourbridge fire-clay bricks. The heated air and gases pass
over the bridge through the lower tubes c c c c into the iire
box F B, then through the tubes c e e e into the smoke box
S B, and up the funnel or uptake F. The smoke box has a
door opening into the engine room, so that the tubes may be
cleared out should soot, etc., lodge in them. They also slant
a little, the short ones towards the fire box, the longer ones
towards the smoke box ; so that the heat may receive more
resistance in passing through, and have a better chance of
communicating its motion to the water.

The next figure is another form of marine tubular boiler,
which has been much used in compound engines. The boilers
just described are not constructed to bear a very great
pressure of steam, but those on this principle are.

In this figure the references are the same as in the last. FP
is the fire place or furnace, A P is the ashpit, W the water,
w L the water line, ccc the tubes, F the funnel — the bottom
of which in this arrangement answers both for fire box and

THE STEAM CHEST.

130

SECTION OF MARINE BOILER.

smoke box. Each fireplace has its own boiler, which can be

kept perfectly distinct, as will be explained when speaking of

the communication valve. »

A B is the superheating

apparatus ; the steam

leaves the steam chest by

the passages a a, and

passing in and out

through the tubes within

A B becomes further

heated, by the heat

passing up the funnel,

and is carried off by the

steam pipe S P to the

cylinder. At W S the

waste steam returns

through the exhaust

pipe, and rushing up the

chimney creates a

draught, answering better than a blast, and giving tho

engine-maker a chance of making his furnace small.

158. The Blast Pipe is a pipe leading from the boiler into
the funnel to create a draught while getting up steam ; but
when the engine is moving (non-condensing engines), the waste
steam passing through the waste steam pipe performs this office.
The steam rushing up the funnel leaves behind a vacuum,
when the air, rushing through the fire bars to supply its
place, gives up its store of oxygen to combine with the other
products of combustion, and intense heat is produced. It
was this contrivance that so efficiently assisted Stephenson
to win the prize of ,£500 at the memorable competition at
Hainhill, when his engine, the Rocket, now in the South
Kensington Museum, defeated the Novelty and Sanspareil.
He also used coke and a tubular boiler.

159. The Steam Chest is either a dome above the boiler, or
else the upper part of the boiler. It is a reservoir for steam,
so that should the engines be using steam faster than the
evaporation of the boiler, there is a supply to fall back
Upon.

The little squares marked with a clash (') in the figure oil

140

STEA5I.

page 139 are sections of the bearing bars which run across tho
fire places to support the fire bars.

160. Locomotive Boilers. — In the figure on page 138
suppose the fireplace reaches up higher, and that all the
tubes are of the same length, but longer, and that the smoke
box is where the fire box is, and the funnel above it, you
have then a very good idea of a locomotive boiler. The
fireplace is made of copper, being better adapted to bear the
intense heat and a better conductor than iron, it therefore
communicates the motion more readily to the water. Over the
fireplace is a part of the boiler quite flat. This is theoretically
the weakest part of locomotive boilers ; and, therefore, it is
well strengthened with angle iron, gussets, rods, etc.

LOCOMOTIVE EOILEH.

A full explanation of the locomotive boiler, with figures
of the different details, is given under the proper headings in
the chapter on the Locomotive.

161. The Field Boiler.— The Field boiler, named after its
inventor, is an ordinary boiler, with the bottom, or part
immediately over the fire, consisting of a series of vertical
tubes — or rather two tubes, one inside the other. These
come down towards the fire. The peculiar action or advantage
of this boiler depends upon convection. The heat of the fire
in contact with the tubes heats the water between the two
tubes, which immediately ascends, while other water moves
down the central tube to supply its place; so that, as tho

THE CORNISH BOILER.

141

lieatecl water and steam ascend, a constant circulation is
promoted, and other water is brought in contact with the heat.

162. Galloway's Conical Water Tubes are an application
of the same principle. They are exceedingly well adapted
for flue boilers, being used to connect the bottom water with
that above the flues ; as the water in the tubes is heated it
ascends by convection, and a constant circulation is kept up
between the lower and upper water. They are of the same
thickness as the boiler plates, and their seams are riveted;
they are, therefore, not liable to leak or split, while they act
as very strong stays.

163. Vertical Boilers. — Vertical boil-
ers assume many shapes internally,
although their outward appearance cor-
responds very much to the figure in
the margin. Vertical boilers are used
in steam cranes, hoists, and often in
portable engines, and in Samuel's ex-
press locomotive. In this figure F B
is the fire box ; the letters W W show
the water spaces, w L the water line.
It is seen that tubes leave the boiler
immediately above the fireplace, and
rejoin the water at the crown of the
furnace. Evidently from this arrange-
ment the convected water will have a
free rise, and a given quantity of heat
will produce a fair amount of evapor-
ation. In vertical boilers vertical tubes
are used, as in Samuel's locomotive
mentioned above ; but vertical tubes by
no means constitute a vertical boiler.

164. The Cornish Boiler.— The
Cornish boiler is a long cylindrical
one. Its peculiarity is in the internal
arrangement of the flues, which can

be best understood by well examining the following figures.

D is a longitudinal section, E a cross section. The lines

of shading in both figures show the water, c d ef is the flue,

in the right hand of which is the fireplace and ash pit.

VERTICAL BOILER.

142

STEAM.

Immediately behind the fire bridge B is a large tube act
running beyond the end of the boiler to a, and suspended

Longitudinal Section.

CORNISH BOILER.

within the flame and burning gases. It
communicates with the rest of the boiler
at g and h by means of two copper
pipes. Sometimes the pipe is not at g,
but leads from the end a into the top
of the boiler at b. v/ L is the water
level, and it will be observed that there
is a very large steam chest s c, and that
Cross Section. the surface of the water is large. It is
for this reason that there is no priming in Cornish boilers —
the steam having plenty of room and a large surface to rise
from. The fire and heat play everywhere within the flue, and
are brought right round under the boiler, and pass along by
D to heat the water in the bottom space d k e. The whole
is set in masonry, and the arrangements are so good that
very little heat can escape by conduction or radiation, while
the heating surface is very great. From having such a
large amount of heating surface it has been calculated that
a pound of best Welsh coal in a Cornish boiler will evapor-
ate 1 1 ^ Ibs. of water.

165. Fusible Plugs. — A precaution that should always
be adopted to prevent boiler explosions will be found in the
use of a fusible plug, or fusible metal plate, or a lead rivet
placed in the boiler immediately over the fireplace. The
lead rivet melts when the temperature of the plate is raised
to a heat the steam does not reach, 338°C.; so giving vent to

COPPER BOILERS.

143

FUSIBLE PLUG.

steam, the engineer knows of the existence of danger im-
mediately. The fusible plug in the shape of A B has the part
C consisting of an alloy of tin, lead, and bismuth, which melts
when the heat of the steam
is somewhere between 138°
and 176° C., i.e., as soon as
the pressure becomes exces-
sive.

Boilers are generally
fitted with man-hole and
mud-hole doors. The man-
hole is generally in tho
top of the boiler, and is
fastened on with bolts and
nuts. Its purpose is to
give ingress to the interior
of the boiler, so that any ne-
cessary repairs may be made. The mud-hole door is fitted in the
bottom to allow of its being easily cleansed from accumulation
of mud, salt, etc. This particularly applies to marine boilers,
and boilers in river steamers. The mud-hole door should be
fitted on inside, and the heads of the bolts should be inside,
and the nuts outside. Through inattention to these points
several accidents have happened. The nuts have become
loose and the mud-hole door given way, when the whole body
of water and steam have been driven into the engine-room
and the men scalded to death.

166. Clothing of Boiler. — Instead of boilers being allowed
to come in direct contact with the brickwork around them
they are embedded in some non-conducting substance as wood,
fine cinders, etc., so that a •minimum amount of heat may
escape by conduction from the boilers. For the same reason,
cylinders are clothed and jacketed, while the top of the
boilers are frequently covered, i.e., clothed with wood, hair-
cloth, etc., and painted to prevent radiation.

167. Copper Boilers. — Copper boilers are not so efficient
as iron boilers. At one time they were used to a consider-
able extent, but it was found that, when leaky, salt acted
injuriously, and they were soon damaged by sulphurous coal,
and became weaker the more they were heated ; but copper

144 STEAM.

being a better conductor than iron, the heat more readily
passes into the water, and consequently there is more economy
exercised. They are not quite so strong as iron, in the pro-
portion of 1G to 23, but they do not waste by scaling; and,
therefore, they retain their original strength for a long time,
while the iron ones are continually getting weaker and weaker.
In consequence of its great conductibility and not wasting
and burning at the joints, copper is used for the furnaces of
locomotive boilers.

168. Testing Boilers. — Before a boiler is put to work its
strength is tested by hydraulic pressure, also after it has been
repaired. It is thus done : Every orifice is secured or else
plugged up but one. The boiler is then filled with water,
and an hydraulic pump attached to the opening left. A
pressure gauge is attached to the pump and water is
forced in, until the pressure gauge indicates a pressure three
or four times that at which it is intended the boiler shall
work. This will find out any leaks in the boiler, and should
a part be too weak for the working strength, it is sure to bo
discovered.

I once saw a primitive way of testing a boiler. The boiler
was filled by a pipe coming from a pool on a high ridge juwt
behind the forge — the pipe being properly secured, no water
could escape from the boiler; then as the pool was about
150 feet higher than the boiler, the pressure of water from
the head severely tested its strength. 150 feet would give
a pressure of 65 Ibs. on the square inch.

169. Water Heater. — It is found very advantageous to
heat the water before it enters the boiler, and if this can be
effected by the waste steam and gases there is great economy
and saving in fuel. This figure represents a veiy good method
of carrying it into practice.* A A is a fiat cast iron pipe
fixed in the smoke box ; through this pipe the exhaust steam
passes along B B a second pipe inside A, heating the water
lying between the two pipes A and B. The water is also
heated by the waste heat round A A. The exhaust steam
after passing round goes up the blast pipe and funnel E as
usual. C is a chamber where the condensed steam water

* By Messrs. Cambridge, of Bristol. See Engineer, Aug. 5, 1870,
Vol. xxx., page 87,

WATERS FEED WATER HEATER.

1-1-5

is stopped, and passes through, tube D to be returned to
the boiler by the pump, which forces the water through the

CAMBRIDGE'S FEED WATER HEATER.

tube H into the tank at I, after which it passes through J to
boiler at K.

170. Water's Feed Water Heater is on rather a different
principle to the above, and is said to produce a good result.
A pipe brings the waste steam up through a reservoir for the
heated water. The feed water enters at the upper part of
the reservoir, being forced in fine spray through a sprinkler,
so that a great surface in a small amount of water is presented
to the steam to absorb its latent heat. At the top of the
reservoir, above the sprinkler, is a deflector, which for a

146 STEAM.

moment keeps the steam in contact with the water-spray
from the sprinkler before it escapes through the top of the
reservoir. It might be thought that part of the spray would
fall down the exhaust passage, but this can scarcely take
place to any injurious extent, because the force of steam will
balloon the spray up again until it falls into the reservoir
considerably heated. From the reservoir the water is taken
in the ordinary manner into the boiler.

171. The Amount of Water Required for Condensation. —
The proper temperature at which to keep the condenser is
as near as possible 100° E. or 38° C. At this temperature
the steam is sufficiently condensed, while the air pump has
relatively the least quantity of water to raise ; or, with a
maximum amount of useful condensation, we have a
minimum amount of water to lift.

Let us suppose the condenser is to be kept at 100° F.,
and the temperature of the condensing water is 50° F., then
out of every unit of water 100°- 50° = 50° of cold are avail-
able to condense the steam.

Watt assumed the total heat in steam to be 1112°F. (latent
and sensible heat of steam we have called 637°'2C. or 1147°F.)j
therefore there are 1112 units of heat to be overcome, which
will take 2LJJ2 = 22-24 units of water; or it will take 22J
more times water than is turned into steam. As a cubic
inch of water produces a cubic foot of steam, it will take
22 J cubic inches of water to condense one cubic foot of steam.

Watt allowed 28-9 cubic inches, or about a wine pint, for
every cubic inch evaporated.

In this calculation we have given the result arrived at by
Watt. We will now perform the calculation, using degrees
centigrade, making allowance for the heat which will be left
in the condensed steam, and using the more accurate number,
637°-2C.

Suppose the temperature of the condenser is to be maintained at
38° C., and the temperature of the condensing water is 10° C., what
amount of water will be required for condensation?

The total amount of heat in a given unit of steam is 637 '2 units C.

The amount imparted to each unit of water is 38 - 10 = 28 units C.

Of the 637*2 units of heat in each unit of steam, it, must give up
C37 '2 -38 = 599 -2 units.

. v the units of water required = 6^2 = 21 '4.

CIRCULATING PUMPS. 147

Or, a cubic foot of steam as it is produced (very nearly)
by a cubic inch of water, will require 2T4 cubic inches of
water to condense it. More is always allowed, because it
is impossible so to arrange the condenser, that every drop
of water shall at once consume its allotted amount of heat.

The temperature of the condenser will always give an
idea as to the vacuum. If the temperature of the condenser
is above 100°F., then more water must be supplied for con-
densation; if it is below 100°F., then the cocks must be
closed a little, as too much water is being used and the air
pumps will have too much work thrown upon them. "When
the air pumps are labouring too hard, it is one sign that too
much condensing water is being used. A thermometer
therefore inserted in the condenser will show the state of
the vacuum. Generally the engineman trusts to his vacuum
gauge to tell him the state of his condenser. If the vacuum
gauge is low, too little water is being used, and he must
remedy the defect accordingly.

172. Surface Condensation. — Surface condensation consists
in exposing the hot steam to large cold surfaces. Watt tried
it. A few years ago Hall introduced his surface condensers.
They did not answer originally on account of occupying so
much space, adding more parts to the engine, and the pipes
becoming furred up. They seem now to be coming more
into use, being fitted in many of our iron-clad vessels,
as the "Minotaur," "Lord Warden," "Lord Clyde," "Pallas,"
etc. The "Lord Clyde" has 13,000 vertical tubes for the
condensation of steam. Hall's surface condensers consist
of an immense number of vertical tubes or pipes placed in a
large tank. The steam, after being used in. the cylinders,
passes through these pipes. Water surrounds the tubes,
and is forced through the tank in among the tubes, either
by pressure from behind or by creating a vacuum, in front.
The cold water enters at the opposite end to the steam, and
goes out at the end where steam enters; thus the hot steam
meets the warmer water first and the colder last, by which
arrangement the water is made to carry off as much heat as
possible.

173. Circulating Pumps. — The introduction of surface
condensation has been necessarily followed by new arrange-

148 STEAM.

ments for impelling the cold water among or through the
tubes. To perfect the system circulating pumps are used.
They are worked by eccentrics on the main shaft, and often
directly from the piston by rods. Occasionally auxiliary
engines have been employed with considerable advantage to
circulate the water for the surface condensers. The water
is forced through or around the tubes in the majority of
cases, but is sometimes made to follow the vacuum.

174. Summary on Surface Condensation.* — The advan-
tages of surface condensation are : —

(1) Freedom from injurious deposits in the boiler. This
follows from using absolutely pure water, and not water that
has been used for condensation. There is no necessity to
scale the boilers or clean out salt.

(2) The boiler can be used with a higher pressure of steam.
Scale and incrustations render it almost impossible to stay
a marine boiler properly. Hence, when these evils are got
rid of, we may use boilers of improved construction and
higher pressure steam.

(3) The foulest water may be used for condensation without
risking injury to the boilers or engine.

(4) A more regular supply of feed water can be relied
upon. Under ordinary circumstances it requires constant
watchfulness to regulate the feed and the brining.

(5) The load on the air pump is more regular, so that in
heavy weather the engineer need not reduce the injection
water.

(6) Fuel is saved, as no blowing out is necessary. This
saving of coal may often amount to from 15 to 25 per cent.,
which is something very considerable on a long voyage.

(7) Being able to use high pressure steam, the economy
of increased expansion can be fully realised.

(8) The boilers do not require cleaning so frequently, so
labour is saved, and there is less wear and tear.

(9) When no scale forms on the boiler, the iron plates
more readily communicate the motion of the heat to the
water; so fuel is saved from the absorption powers of the
boiler being unimpaired.

* From a paper by Mr. J. F. Spencer, read before the Institution
of Engineers (Scotland), 5th February, 1862.

MORETON'S EJECTOR CONDENSER. 149

(10) With expansion at half stroke and superheated steam,
one-half the usual boiler surface is ample, and the boiler
power may be reduced one-fifth without any loss of indicated
power.

The mechanical disadvantages of surface condensation are
not insuperable, some existing more in imagination than
reality. They may be classified under the following
heads : —

(1) Additional pumps and machinery are required for
circulating the condensing water.

(2) Additional space is required by the surface condenser
itself and its appendages.

(3) It has been alleged that, under certain circumstances,
the constant return of the same water to the boiler creates a
tendency to corrosion in the boiler.

(4) The multiplicity of tubes in the surface condenser
creates complication.

(5) There being so many tubes and joints in the surface
condenser, there is a large increased liability to leakage.

(6) There is an increased first cost in the machinery of
from 10 to 20 per cent., with an increased cost of repairs
to additional machinery and condenser.

(7) A larger amount of condensing water is required for
surface condensation than for injection condensers.

175. Moreton's or Barclay's Ejector Condenser. — The
principle of the injector is modified to serve the office of a
condenser. A glance at the figure will in a moment show
the similarity of the two pieces of mechanism. The exhaust
steam rushes from the cylinder into the condenser, and is
met by a current of water which condenses the steam. The
water rushes into the vacuum at a velocity of more than 40
feet per second, while that of the exhaust steam is many
times greater. This force in the ordinary arrangement is lost
in the condenser, either against its sides or in agitating the
water, hence heat is developed and power lost. On an
avera,ge this loss, together with that required to work the
air pumps, is -6 Ibs., or a little more than half a pound per
square inch. Now in the ejector condenser the power in
the rush of steam and water is found to be sufficient to
carry all the water, air, and uncondensed steam into the

150

hot well at once without the intervention of an air
pump.

The cold water passes from
a tank through A to the
nozzle a, which is surrounded
by two more nozzles 6 and c,
through which pass the ex-
haust steam by way of B and
C from the two cylinders. Be-
yond the three nozzles is a
gradually widening pipe P,
which leads to the hot well.
The condensation of steam
takes place between a and c.
The action is as follows : Tide-
water enters A at a pressure
sufficient to make it flow with
a velocity of 43 feet in a
second, and rushes through a
when D is screwed up ; it is
then met by steam at b at
a much higher velocity ; the
water condenses the steam,
but partaking of its impetus,
both rush on to be joined by
more steam at c, and again
receiving more impetus, while
all the steam is condensed,
both water and .condensed
steam rush on to the hot well
by way of P.

Instead of the injection
water being started from a tank
to give it the necessary velocity,
it may be set in motion by
a small jet of steam. The part sj is on purpose for this.
The rod is screwed up, when a jet of steam mingling with
the water carries it forward to meet the exhaust. This jet
can be shut off after the apparatus is fairly acting.

It is a remarkable circumstance that the ejector in its

MOKE-TON'S EJECTOR
CONDENSER.

151

operation carries out all the air. This is doubtless on the
same principle that the Trompe carries the air into a
chamber to be afterwards used as a blast in smelting
operations in the Catalan forges in the northern part of

CHAPTER IX.
APPENDAGES TO THE BOILEE.

Safety Valve — Salter's Spring Balance — Bourdon's Gauge — Vacuum
Gauge— Mercurial Gauge— Glass Water Gauge— Vacuum Valve.

THE necessary appendages to a boiler are the safety valve,
the gauge, which may be the old fashioned mercurial gauge,
Salter's spring balance, or Bourdon's gauge; the reverse valve,
the glass water gauge, or else gauge cocks.

176. The Safety Valve is a lever of the third kind, the
fulcrum at one end, the weight at the other, while the power
is exerted between the two.

It is a conical valve fitted steam tight on its seat and kept
down by a weight. The weight is so proportioned that when
the steam exceeds a certain pressure the valve will lift and
the steam escape, and so prevent the boiler bursting, by
keeping the pressure below a fixed maximum. Its area varies
with different makers, but some engineers follow the rule of
allowing half an inch of area to each horse-power of the en-
gine. The weight is fixed by the engine-makers, and no
increase should be allowed without their express sanction.
Every boiler, when there are two or more to the same engine,
must have its own safety valve. Some safety valves are
kept on their seats by spiral springs.

177. Salter's Spring Balance is used especially in loco-
motives to exhibit the pressure of steam. Its principle is a
steel spring, well tightened, which, according to the pressure
of steam, extends after the manner of the spring steel yards
used in public by our rag and bone merchants ; or else the
increased pressure of steam acts against the spring.

Another adaptation of the spring balance is shown
by the figure on next page, where A is screwed into

BOURDON S GAUGE.

153

the boiler, or into a pipe in free communication with the
steam, so that steam can enter the cylindrical body B ; if
we suppose the dotted lines at B are a piston,
it will act against it to drive it down, which the
pressure of the spring will not allow it to do
until it overcomes its resistance. The greater
the force of the steam the more will the spring
be compressed, and the more of the graduated
part be shown. Acting on this principle it is
evident that, if it be properly graduated, the
pressure of steam in the boiler will be correctly
indicated by the scale. When used to keep
down a safety valve, it acts at one end of the
arm of a lever of the first class, and the steam
pressure at the other in one arrangement. Thus
Walter's spring balance is used in a simple man-
ner for a pressure gauge, as well as to keep the
safety valve on the seat.

178. Bourdon's Gauge. — This gauge is pro-
duced in many shapes — we give one of the most
portable and convenient in the figure on the
next page. A B is a circular plate, fitting steam
tight in 5, but still readily moving with the BALANCE.
least pressure, s is in free communication with
the boiler, by way of E ; therefore, the pressure of steam
below will cause the plate to ascend, when the rod r will move
the lever a b on its centre b, and with it the rack c d,
which moves the pinion p from right to left, and with it the
pointer P, which will indicate the number of pounds pres-
sure in the boiler on the arc.

The use of gauges, it will be gathered from what precedes,
is (1) to tell accurately the pressure of steam in boilers
when water is hotter than 100°C. ; (2) to indicate the
variation in the pressure of steam from time to time.
When we consider how much depends upon a know-
ledge of these facts, the following instance of, to say the
least, carelessness and thoughtlessness will astonish us : —
Out of 52 gauges tested for the Royal Agricultural Society,
upon the occasion of their exhibition being held at Manchester,
only 9 were correct. If this be a fair average, the deplorable

154

STEAM.

fact comes to light that only 17 -3 per cent, of the gauges in
common use give correct indications of the state of the boiler
pressure.

179. Vacuum Gauge. — The same
figure will illustrate the vacuum
gauge and its principle. This gauge
is to show the state of the vacuum
in the condenser, so is an append-
age to the condenser and not to the
boiler. E is fitted into the con-
denser. If A B be air tight, there
being a vacuum in the condenser,
when the cock V is opened the piston
will descend by reason of the pressure
of air above it. If the pointer be
directed to a particular point when
the air is acting freely on both sides
of the piston A B, then, as the
vacuum increases in the condenser,
the pointer will move from left to
right. When the gauge is used to
show a vacuum the graduation only
extends from 1 Ib. to 15 Ibs. The teacher must accustom
his pupils to draw the figure clearly, pointing out the dif-
ference of action, when used as a vacuum gauge and as a
steam pressure gauge.

180. Mercurial Gauges. — Mercurial gauges are and have
been used to show the pressure of steam and the vacuum.
But as they are very cumbersome, and nearly obsolete, it is
useless to describe them, but we may say this much —

(1) The Long Barometer Gauge. — The pressure of air
corresponds to very nearly 30 inches of mercury, which being
about 15 Ibs., 2 inches of mercury indicate 1 Ib. pressure.
A bent tube in the shape of a U, partly filled with mercury,
was taken, and one end inserted in the boiler; as the
pressure of steam increased it would drive the mercury
down one part of the tube and up the other ; a graduated
scale of 2 inches to the Ib. showed the pressure of steam in
the boiler.

(2) When used as a vacuum gauge, the mercury would

BOURDON S GAUC4E.

THE SHORT BAROMETER GAUGE. 155

follow the vacuum and rise up the part of the tube connected
with the condenser.

(3) The Short Barometer Gauge was used to show the
vacuum. It was of similar construction to the last ; but be-
tween the legs, communicating with both, was a reservoir of
mercury. As the pressure was taken off the reservoir the
mercury fell down one arm, which was short; for as the
vacuum between 10 and 15 Ibs. only was wanted, the arm
was made short, and would remain full of mercury till the
pressure fell to 5 Ibs. only ; so that when the mercury stood
10 inches high, we should have a 5 Ibs. pressure of air in the
condenser ; when 8 inches high, 4 Ibs, etc.

The mercurial or barometer gauges are old-fashioned, and
are hardly used now or fitted to new engines ; therefore we
have given no figures, merely a short description of them.
To these gauges there are scales graduated to every two
inches ; so that by looking at them the engineman can tell
at a glance the condition of his vacuum. If the mercury
stand at 20 inches, then there is |° = 10 Ibs. vacuum, or
15-10 = 5 Ibs. pressure of air in. the condenser. If the
mercury stand at 24 inches, there is a vacuum of |4 = 12 Ibs.,
or the pressure of air in the condenser is 15 — 12 = 3 Ibs.
Another form of vacuum gauge is this • An iron tube
is fixed into the condenser and bent upwards. At the
bottom near the condenser is a cock, to open or close the
communication with the condenser. Just above the cock is
a small bowl for holding mercury, the tube passing right
through the bowl, so that the mercury is round the bottom
of the tube and outside it ; the top of the tube is open.
~Now a glass tube open at the bottom and closed at the top,
a little larger in the internal diameter than the outside
diameter of the iron tube, is taken and placed right over
the iron tube, the open end coming down into the mercury.
When the communication with the condenser is opened,
there being a vacuum within the iron tube, the pressure of
the air on the outside pressing on the mercury will cause it
to ascend between the two tubes ; and, of course, the higher
it rises the better the vacuum. It will ascend two inches
for every pound. It is graduated, and a scale placed by its
side ; but as the mercury will sink in the bowl, a pointer or

156

STEAM.

piece of wire is attached to the scale, the end of which
bringing the scale lower with it, must be placed on a level
with the mercury before the state of the vacuum is read off.
Unless this precaution is taken, the reading is liable to
error.

181. Glass Water Gauge. — The best contrivance to ascer-
tain the height of the water in the boilers is the glass water
gauge ; whereby, at a glance, the engineer can see the height
of the water in the boiler. Gauge cocks are also used ; they
consist of three ordinary cocks — the lower one placed below
the level of the water, and from which water should always
flow when it is turned ; the middle on a level with the water,
from which steam and water should issue; and the third above
the level of the water, from which steam should always issue
when turned. To bring the gauge cocks within reach of the
engineman, they are placed low down or in a line, and tubes
lead up inside the boiler to the required heights, and to a

part of the boiler where the ebullition
is least.

The figure simply shows the princi-
ple of the glass water gauge, which is
often carried out by an elaborate sys-
tem of cocks to prevent the gauge from
choking, and to clean it out. B is the
boiler and w L the water line, G G the
glass gauge in communication with the
boiler at a and b. It is seen that the
height of the water in the gauge will
show the level of the water in the boil-
er, and whether it be necessary to con-
tinue or discontinue the feed .water.
There are frequently cocks at the two
ends G and G, also at c and c, to clean
out the gauge.

182. The Reverse Valve. — Vacuum valve, internal safety
valve, or atmospheric valve — for it has all these names — is
to prevent the boiler from collapsing through the external pres-
sure of air. When a boiler has been in use, we will suppose
the engine stops, and that the stop valve, safety valve, etc.,
are closed, Then, as the water cools down and steam con-

GLASS WATER GAUGE.

EXERCISES.

157

denses, a vacuum will exist in the boiler; and if means
are not taken to prevent the external pressure of 15 Ibs. on
the square inch from taking effect,
danger will ensue to it. A B
shows the general appearance of
the valve, S leads to the boiler.
The air pressing upwards in the
direction of the arrows will lift
up the valve V and open it, when
the internal pressure is at a
certain stage below that of the
atmosphere; then passing into the
boiler through S, will restore
equilibrium, or, at least, partial
equilibrium. It is generally made
of such weight that it will lift with an external pressure
of 5 Ibs. The pressure in the boiler can get below that of
the atmosphere when the supply of steam is insufficient for
the engines (if there be a good vacuum), or if a sea were
to break over a ship and suddenly condense the steam in the
boiler.

REVERSE VALVE.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Describe a cylindrical boiler with internal flues. State the
advantages of this mode of construction. Which is the weakest
part of the boiler, and how is it strengthened ? Sketch the boiler in
transverse action with the Hues, showing the probable level of the
water (1871).

2. Describe with a sketch the tubular marine boiler. Explain the
necessity for a reverse or atmospheric valve. Point out the use of
the stop valve in the steam pipe. How is this valve opened and
shut (1871)?

3. What is surface condensation as applied to marine engines?
One of the tubes used is of copper f inch outside diameter, '05 inch
thick, 5 feet 10 inches long ; find its weight, a cubic foot of copper
weighing 550 Ibs. What pumps are required when surface con-
densers are used (1871) ? Ans. 2 '012 Ibs.

4. Describe the communication valve, and explain its use? If
working with 3 boilers instead of 4, what would be the effect of
opening all the communication valves (1865)?

Ans. The steam would pass to the disused boiler, and boil the
water, so that a large amount of fuel would be wasted.

5. In the old-fashioned waggon boiler a vertical open tube, called

158 STEAM.

a stand pipe, passed through the shell of the boiler, and dipped
below the surface of the water inside. If the steam pressure inside
the boiler were 4 Ibs. per square inch, at what height would the
water stand in the pipe (1870) ? ^ns. Q.QQ feet.

6. A cylindrical boiler with flat ends is 30 feet long, 6 feet in
diameter, and has two internal flues, each 2£ feet in diameter, the
pressure of the steam in the boiler is 40 Ibs. on the inch, what is
the whole pressure on the internal surface in tons? How is the
strength of a cylindrical boiler related to its diameter, the material
being unchanged (1870) ? Ans. 2596'95 tons.

7. Describe and explain some form of vacuum gauge, which would
enable you to ascertain the pressure in the interior of the condenser
of a steam engine (1870).

8. Describe with a sketch the glass gauge for showing the height
of the water in a boiler. Point out the position and use of the three
stop cocks. For what purpose are gauge cocks fitted to a boiler
(1871)?

9. State the principal parts of a marine boiler connected with tho
generation of heat. Show the advantage of small tubes over large
ones in giving a greater amount of heating surface (1865).

k See question 13.

10. Give a description of the reverse valve. If kept in its place
by a weight of brass, what must be its thickness that it may be
opened when the pressure of steam within the boiler is If Ibs. below
the atmosphere ? The weight of a cubic foot of brass is 525 Ibs.
(1871).

Ans. Area x 1| Ibs. = area x height x •£££% . *. h = 5 '76 inches.

11. Describe a condenser gauge of an engine. The mean pressure
on a piston being 12 Ibs. above the atmosphere, and the mean vacuum
pressure 13 Ibs., what is the force exerted on a piston of 58 inches
diameter? and what would have been the force had the engine
worked without condensation of steam (1867)? The pressures are 25
and 12 Ibs. Ans. 66052-14 Ibs. ; 31705*0272 Ibs.

12. Name and give a short account of the gear connected with
marine boilers requiring the attention of the engineer (1863).

13. A circular tube is replaced by four circular tubes of the same
total volume, show that the heating surface is thereby doubled
(1863).

Let x = diameter of large tube.

y= » small ,,
a?2 x '7854 = area of large tube.

Also ?/ x 7854-

EXERCISES. 159

Heating surface of large tube = x x 3*1416 x I.
= 2y x 3-1416 xl

„ ,, small tube — y x 3*1416 xZ.

„ 4 „ =4yx 3-1416 xl.
. Heating surface of large tube _ 2y x 3 -1416 x I _ t
Heating surface of small tube 4y x 3*1416 x I
. '. Heating surface is doubled.

14. The bottom of a steam boiler is 18 feet below the level of the
sea ; find the requisite steam pressure to force the water of the boiler
through the blow out pipe (1863). Ans. 22*941 Ibs.

15. What is meant by priming ? Would you recommend in such
a case that the safety valves should be kept open (1864) ?

Ans. No ; because the pressure being taken off the water, it will
boil more furiously, and more spray will be thrown about
the boiler, and therefore it is likely to increase the priming.

16. Describe the barometer gauge in common use. Why is the
stop cock closed before blowing through (1864)?

17. Describe the steam gauge used in marine boilers (1865).

18. What are the advantages and disadvantages of tubular boilers?
and what are the peculiarities of marine boilers when contrasted with
land boilers (1866)?

19. What is meant by the grate surface of a boiler? If 1 square
foot be allowed for each horse power, how much will be necessary
for boilers to supply a pair of cylinders, each of 73 inches diameter,
the piston moving at the rate of 240 feet a minute (1866)? Find
nominal horse-power. Ans. 426*32.

20. There are 2400 tubes in a set of marine boilers, their external
diameter being 3 inches, thickness of metal J of an inch, and length
6 feet ; find the amount of power developed, 16 square feet being
equivalent to one horse-power (1866). Ans. 589*05 horse-power.

21. If the reverse valve of a boiler be a solid brass cylinder 5 inches
long, what will be the pressure to collapse a boiler, when it is on the
point of acting, the weight of a cubic foot of brass being 525 Ibs.
(1866)? Ans. 1'5 Ibs.

22. What is the usual boiler used for marine engines ? Describe
it. Why is the arrangement peculiarly useful for marine purposes
(1867)?

23. Describe the barometer gauge in common use (1867).

24. Give a description of the apparatus by which a boiler is pre-
vented from bursting and collapsing. How is the pressure of the
steam in the boiler ascertained? Can the same dependence be placed
on an old gauge as on a new one (1865)?

25. Describe the safety valve of a locomotive boiler. Explain
Bourdon's gauge for ascertaining the exact pressure of the stearn in a
boiler (1869).

26. Describe with a sketch the marine tubular boiler. What is
the object of a reverse valve, and how is it fitted ? How is a vessel
protected from the heat of the funnel (1865)?

1GO STEAM.

27. Describe tlie form of boiler first used, and how did it differ
from modern boilers ?

28. What precautions should be taken to prevent boiler flues from
collapsing ? Give an idea of the pressure they have to sustain, and
how should their thickness vary with their diameter ?

29. State the characteristics of the Field boiler and Galloway's
tubes.

30. Describe a vertical boiler, and distinguish between a Cornish
and Lancashire boiler. Give a section through any boiler with which
you are familiar.

31. What provision is made for heating the feed water of a boiler?
Why should the water be supplied as warm as possible ? Give any
plan that has been adopted for heating the feed water.

32. What are the advantages and disadvantages of surface con-
densation ?

33. Describe Moreton's Ejector Condenser.

CHAPTER X.
SALT IN MAKINE BOILERS,

Sea Water — Specific Gravity — Boiling Point — Blowing Out — Scale—
Salinometer — Hydrometer — Priming — Feed Pumps— Giffard'a
Injector.

183. Pure Water Should be Used. — Boilers, both land
and marine, are liable to become internally incrusted. If
these incrustations are not carefully removed or guarded
against great injury will ensue. All water contains solid
substances, whether it be lime, flint, salt, or sulphur, all of
which will either do, or be the means of causing, damage.
Marine boilers are generally fed with salt water. Hence
it is necessary to explain fully the constituents of sea water,
and how their evil effects may be guarded against.

The deposits and incrustations which are the source of so
much danger, are not likely to be retained as necessary evils.
If surface condensation, which, as we have already said, has
been introduced into some of our iron-clad vessels, be suc-
cessful, the condensed water, being free from all such matters,
will form no deposits. If the steam could be rapidly and
effectually condensed without mixing it with impure water,
it would itself supply almost enough water for feed, and that
of the purest quality. All the evils of deposits, incrusta-
tions, priming from impure water, and much of the wear
and tear of boilers, would be in many cases entirely and others
greatly prevented. The consumption of fuel would be less
than at present, and the air pump would be considerably
reduced in size, and therefore less power would be required
to work it, although of course we should have the circulat-
ing pumps instead, but still upon the whole there would be
a gain. As the condensed steam would contain no air, the,

162 STEAM.

function of the air pump would be exclusively confined to
the removal of the condensed steam.

184. Sea Water is both salt and bitter. Everywhere the
sea holds in solution a large quantity of solid substances,
chiefly common salt or chloride of sodium. The amount of
salt is not constant in all seas, nor even in the same sea, nor
at all depths, varying according to the amount of evapora-
tion (i.e., the heat of the climate) and the quantity of river
water running into the sea. The Keel Sea is salter than the
Mediterranean, the Mediterranean than the Atlantic, the
Atlantic than the Pacific. The water of the northern
hemisphere is not so salt as that of the southern. The
position of maximum saltness in the ocean is about 22° N*
latitude and 17° S. latitude, and the belt of ocean lying
between. We may incidentally mention that this is the
region of greatest evaporation, and that therefore the saltness
of the ocean follows from that circumstance. The Polar seas,
Baltic, and White seas, contain very little salt. Ice is free
from it, because water in the act of freezing parts with all its
impurities. Out of every 1000 parts 34-4, or about ^ of the
whole consists of solid matter; out of the 34 parts nearly 24
are common salt. We may put it thus : out of 30 gallons of
sea water, 1 gallon consists of solid matter, and of this solid
matter -|-| or y|- is pure salt ; 24 parts out of 34-4 are pure
salt, 4 parts chloride of magnesium, 4 parts sulphate of
soda; 1 part in 1000 is carbonate of lime (chalk), and 1
part in 4000 silica (flint).

ANALYSIS OF SEA WATER.

Chloride of Sodium, , 24*

Chloride of Magnesium, 4*

Sulphate of Soda, , 4*

Carbonate of Lime, '34

Silica, -OSG

Other substances,* 2-

34-426

* Bromine, Iodine, Boron, Silver, Copper, Iron, Potassium, etc,

BOILING POINT OF SALT WATER, 163

Professor Forchammer* gives the following as his analysis
of sea water : —

Chlorine, 19' parts.

Sulphuric Acid, 2'26 ,,

Lime, -56 ,,

Magnesia, 2'10 ,,

All Salts, 34-04 „

Total parts, 58 -32

Carbonic acid gas is ever present in sea water, and its
quantity increases with the depth. There is also a trace of
ammonia with atmospheric air to sustain life in the propor-
tion of from ~y to -g~j of its bulk. These facts, especially
that relating to the different quantity of salt in different '
seas, go to explain the reason why the extent of the " brin-
ing" varies in different seas.

185. The Specific Gravity of sea water differs with every
sea. In the North Atlantic Ocean it is about 1*02664,
while in the South Atlantic it is greater, 1-02672. The
Indian Ocean has a specific gravity of 1-0263 ; the Ked Sea,
1-0286; the Mediterranean, 1-0289.

186. Boiling Point of Sea Water. — In consequence of some
of the above solid substances being chemically combined and
the others mechanically suspended in sea water, especially
because of the latter, and its specific gravity being greater,
it takes considerably more heat to boil it than to boil fresh,
spring, or river water, and of course as ebullition continues
and the steam is used the water will get salter and salter ; no
salt can possibly pass away with the steam, and therefore the
amount of heat required to convert the water into steam will
have to be increased in proportion to the density of the
water, while the water itself will become saturated with salt,
or it will be incapable of holding more salt, which will be
precipitated, and form a crust on the boiler, separating the
iron boiler plates from the water, so that the boiler plates can
actually become red hot and danger is imminent, for the
plates being softened they are liable to collapse.

187. Boiling Point of Salt Water. — Salt water contain-
ng -g-jj- part of salt (it has been usual in all works on steam

* See Ansted's Physical Geography, p. 141.

164 STEAM.

to say -^¥), will boil at a temperature of 100°f C. ; if the
proportion of salt be doubled, or ^ it will boil at a tempera-
ture of 101°-| C., if -g^- or --Q- the boiling point will rise re-
spectively to 102° C. and 102° -| 0. ; when there are ^~ of salt
in the water the boiling point rises to 107°^C. •%% is the
point of saturation, when the water is so full of salt that it
will hold no more, and it is therefore rapidly precipitated.
It will assist the memory perhaps to state that in each gallon
of sea water there is more than four ounces of salt, and if
two gallons be boiled down to one, it will contain double that
amount, or more than eight ounces.

188. Blowing Out or Brining the Boilers. — Generally
the saltness of water in the boilers must be kept below three
or four thirtieths. To effect this, and to have them as free
from salt as is consistent with the economical consumption of
heat, the practice of " blowing out " is resorted to. For this
purpose blow out cocks are fitted to the bottoms of all marine
boilers, from the cocks pipes lead into the sea. Every two
hours, but generally less, the blow out cocks are opened, and
the supersalted water violently forced out of the boiler, by
the pressure of the steam, into the sea. Much heat is lost
by this blowing out, and many methods have been devised to
save it. Before showing how this is accomplished, we must
give other modes of getting rid of the impurities which
collect in a marine boiler. The brine is sent overboard,

(1) BY BLOW OUT COCKS (already explained).

(2) BY BRINE PUMPS.

(3) BY SURFACE BLOW OUT AND SCUM COCKS.

189. (2) By Brine Pumps. — To many engines are fitted
brine pumps, and at every revolution of the engine a small
portion of brine is extracted from the boiler. The size of the
brine pumps must be such that the quantity of water drawn
off added to that evaporated must be equal to the quantity
introduced by the feed pump. If the water ejected from the
boiler is to contain — of salt, or three times as much as the
feed water, then, if the feed pump supply n gallons in a given
time, the brine pumps must extract §• gallons in the same
time. The rule is, blow out from ~ to \ the amount of
feed water.

SCALE. 165

190. (3) Surface Blow Out and Scum Cocks,— The foreign
substances in a boiler are always buoyed up to the surface,
where they not alone prevent ebullition, but the formation
of steam. The steam rises from and around them, and they
remain at the surface for some time, when they gradually
descend and form a scale upon the tubes and flues. It is
therefore found quite as advantageous to blow out from the
surface as from the bottom of the water. It is done by
means of SCUHl cocks, which are inserted on a level with the
water, and are kept constantly about one-eighth open the
whole of the time, so that as fast as dirty scum and other
impurities rise to the surface they are expelled.

191. Lamb's Surface Blow Out Apparatus is a very efficient
contrivance for effecting the same object. A float in con-
nection with the bottom of the discharge pipe regulates the
feed and discharge water. The apparatus ejects the scum
and dirt at once; but in some boilers sediment collectors are
employed, one, in shape and size somewhat resembling a sugar
loaf, is placed in each boiler with the small end or apex
downwards, it is connected to a pipe leading into the
sea to carry the sediment away. The top or base of the cone
stands out of the water, and the impurities enter through
longitudinal tapering slits being ballooned into the cone,
where the water is comparatively still, by the steam as it
rises to the surface. The object of all this is to save heat.

192. Scale. — Whatever care and precaution are adopted,
scale can hardly be prevented from forming on the boiler
plates. A careful and attentive engineer can always reduce
it to a minimum. "When scale is formed on the boiler plates,
it prevents the passage of heat into the water, for salt,
gypsum, lime, etc., are exceedingly bad conductors of heat,
and will not allow its motion to pass to the water, and
therefore a waste of fuel must arise. When water is satur-
ated with salt, etc., through negligence or otherwise, it
becomes heavier, and therefore takes more heat to boil it,
which is another waste of fuel; again, the scale is occasion-
ally so hard and solid that the plates become red hot, and
are liable to be burnt as well as to give way from internal
pressure. Ammonic chloride and other chemical substances
are sometimes put into marine boilers to prevent scale, but

166 STEAM.

the utmost they do is to precipitate the foreign ingredients atf
powder, which must still be removed by blowing out. The
more of these substances there are in the water, the more
work the heat has to do to lift them, and therefore the more
heat is required for ebullition, which is waste of motion and
power.

A practical engineer, who has examined thousands of
boilers, says : " Much mischief is often done by the injudi-
cious use of compositions in the boiler which are designed to
prevent incrustations, especially where there is no blow off
cock or where its use is neglected. A hard deposit on the
boiler plates is, in the writer's opinion, not so injurious as
the soft and muddy deposit produced by the use of such
compositions. A hard scale ... is sufficiently mischievous,
but the injury to the plates is much more rapid when a
thicker but spongy deposit entirely prevents contact of the
water, and impedes the transmission of the heat. The money
spent in boiler compositions would be better applied in
securing a supply of proper water, or in filtering and purify-
ing the water before it enters the boiler. More attention
to the purity of feed water would nearly always effect
economy, and would be far cheaper than using chemical or
other ingredients to neutralize the impurity after it is in the
boiler. In. many cases simply filtering the water in some
ready way has produced very great improvement." *

A simple illustration of the formation of scale may be
seen by examining the tea-kettle, where a scale (lime or
chalk chiefly) is left on the sides and bottom of the kettle,
because steam formed from impure water is perfectly pure;
it can carry nothing away with it. We may also consider
the boiler as, or compare it to, a great salt-pan. Just as in
Cheshire and Worcestershire salt is made by the simple
process of evaporating water in large pans, so does salt, etc.,
collect in marine boilers; but there is this difference, the
scale formed on boilers is not soluble in water, while salt is.
Here, of course, we draw a distinction between salt and
scale.

An effective and expeditious, but not veiy good plan,
to scale boilers is to throw in a few wood shavings
* From Marten's Steam Boiler Explosions,

SALT AXD THE BOILING POIXT.

167

all along the bottom, and set them on fire. They quickly
heat the scale, which expands more than the shell of the
boiler; the heat cannot reach the latter, so the scale is
loosened from the plates. Precisely the same process is gone
through, with a different result, when a glass tumbler is
cracked by pouring hot water into it. The heat in the water
suddenly expands the inside of the glass, which becomes too
large for the outside, and so the glass is broken. Any scale
that remains after this must be taken off with a hammer and
chisel. This hard incrustation is formed in layers, and of
course chiefly consists of carbonate and sulphate of lime,
. gypsum and dhalk, with common salt. We have by us
pieces of scale looking like pieces of iron; in their cross
section they have the appearance of very thin alternate bands
of iron and hard crystalline rock, while other pieces are pure
salt. On this point Mr. Marten says : " The practice, espe-
cially in certain districts, of emptying the boilers immediately
the engines are stopped, and before the flues have cooled, in
order to loosen the scale by overheating the plates, has
caused much more mischief than those who persist in doing
it will believe, and has nearly ruined some otherwise good
boilers."

193. Salt and the Boiling Point.— There are several
methods of ascertaining the amount of saturation of the
water in a marine boiler : —

(1) By the THERMOMETER.

(2) 3, HYDROMETER.

(3) „ SALINOMETER.

From what has been said it will be gathered that the boil-
ing point of water depends upon the quantity of salt in it, its
specific gravity, and the pressure of the air. The strength
of a solution of salt and water has always a fixed and well-
ascertained relation to the boiling point and specific gravity;

For water with

TjV or 1° of saltness in it boils at 1000fC.

• or

r or 4°
5°
or 10°
or 12°

102° C.
102°§C.

106°! C.
107° JC.

168 STEAM.

And also as fresh water when the oarometer stands at

27 inches boils at a temperature of 97° '2 C.

28 „ „ „ 98°'1C.

29 „ „ „ 99°1C.

30 „ „ „ 100° C.

31 „ „ „ 100°-8C.

we see at once the truth of what was previously said, that
the boiling point of water depends upon its weight or specific
gravity and the pressure of the air.

If, then, water be taken from the boiler, and boiled in the
engine room under the ordinary barometric pressure of the
air, and it is found by using the thermometer that its tem-
perature at the boiling point is 103°|C., we must at once con-
clude that there are 5 degrees of saltness in the water, and that
precipitation of impurities is commencing, and blowing out
must be resorted to at once. But if by the same process it
is ascertained that the water boils at 101°J C. (in the engine
room), it is known that the boiler is comparatively safe and in
good working condition. Salt does not really deposit till ~^.
194. The Hydrometer tells us the amount of salt in water
by showing its specific gravity. The figure in the margin
D represents one. B is a hollow ball of brass or

other metal, from which rises a stem C D,
graduated ; A is a second globe filled with
mercury to make the whole swim uprightly
in the water. A acts in precisely the same
manner as the lead on a fishing line. The
lead keeps the float upright, so does A the
hydrometer. The stem C D is graduated that
we may read off how far the stem sinks in the
water. The greater the specific gravity of the
water, or the more salt there is in it, the less it
will sink, so the density is thus made a test to
exhibit the amount of salt. We read off (not
the density, but) the saltness of the water.
HYDROMETER. Each hydrometer is graduated to a particular
scale, generally 55°; i.e., when placed in distilled water at a
temperature of 55° the hydrometer sinks to the point marked
65°. This is much too low, for when water is taken from
the boiler the experimentalist has to wait a considerable time

SALIX051ETER.

160

for the water to cool clown before he can test it. 90° C.
would be a far better temperature to select. We now see
the utility of the specific gravities of sea water given on page
163, and that the hydrometer is an imperfect instrument
without the barometer ; so useless is the one without the
other, that we frequently see attempts made to combine the
two, as in the salinometer.

195. Salinometer. — The salinometer
has been presented in several shapes.
In one it consists of a thermometer and
hydrometer combined in a copper vessel,
in another, Seaward' s salinometer, of two
pith balls. Mr. Seaward affixes a glass
tube fourteen inches long, in a similar
manner and in a corresponding place to
the glass water gauge, so that when at-
tached to the boiler the water rises up
from the bottom of the boiler through
the lower cock, and remains in the glass
tube at the same level as the water in
the boiler. The taps are then closed and
the upper one opened, and two small balls
of glass or metal are dropped into the
water. The specific gravity of the first
ball is such that it will sink when there
are five degrees of saltness in the water
and swim when more, the other ball will
sink when there are less than three degrees
of saltness, but swim when four or more. -

By this methcd the state of the boiler is HOW'S SALINOMETEB.
soon ascertained.

How's salinometer consists of a cylindrical vessel, A G, con-
nected with the steam boiler by the pipe B ; the connection
on the boiler being below the surface of the water. The
quantity of water admitted to the salinometer is regulated by
the cock C in pipe B. The salinometer is most usually fixed in
the engine room, so as to be in constant view of the engineer,
but it can be fixed in any other convenient place. A ther-
mometer D is placed in the cylinder A G of the instrument,
to show the temperature of the water. A hydrometer E

170 STEAM.

floats in the water, at a height corresponding to the density
or saltness which it indicates, and is protected by the metal
guard H. An overflow pipe F takes away the surplus water,
and prevents it running over the top. I is a cock for empty-
ing the instrument through the pipe F. It should, of course,
be emptied as often as the water is tested.

196. Priming. — When the steam comes from the boiler
mixed with water, in the shape of spray or froth, it is said to
be primed. Priming exists under most diverse circumstances;
its cause cannot at all times be clearly traced.

197. Causes and Danger of Priming. — Priming takes
place more in new than in old boilers; when there is but little
water in the boiler; when the spaces between the tubes and
flues are contracted; when there is fierce ebullition, this cause
may be said to accompany all priming; in passing from fresh
water to salt or salt to fresh; when the water used is muddy,
dirty, or slimy : when there is too small a steam chest ; when
a safety valve, being situated near the steam pipe, is suddenly
opened. The clanger arising from priming is very great, and
should therefore be most anxiously guarded against. We
shall see its danger and injurious effect, if we but con-
sider that when it gets into the cylinder, and there accumu-
lates as incompressible water, something must give way
should the test cocks and escape valves act improperly.
Priming impairs the vacuum ; in consequence of this, more
water will have to be used for condensation, which will
throw a greater load upon the air pump, and more feed water
will also be required.

198. Remedy for Priming. — As priming is generally ac-
companied with great ebullition, obviously the most effectual
remedy will be to enlarge the steam chest. It is found that
boilers with plenty of water surface, or with a large steam
chest, seldom or never prime. Cornish boilers with their
large water surface give no trouble by priming. A remedy
much practised with locomotive boilers, is to open a safety
valve remote from the steam chest and pipe. Other temporary
remedies are : to partly shut the throttle valve; to work the
steam at a high pressure; to open the furnace door, thus
checking the fierce boiling ; to put down the stop valve so
that the steam rushes against it, and the water is knocked out;

REMEDY FOR PRIMING. 171

to inject tallow into the boiler by means of the donkey pump
or a syringe fitted on purpose, this is the favourite remedy, but
it is found in some boilers to increase the priming. Another
remedy is to fit a steam pipe in the boiler full of small
holes, and inside this another similar pipe, but to take care
that the perforations of one pipe are not opposite those of the
other. The steam in entering dashes against the inside pipe,
and the spray falls out. Any thing that checks furious
ebullition, or allows the steam plenty of space to rise, checks
priming. When the steam chest has to be enlarged, it is
better to fit a second on the top of the old one. Priming
arising from the use of impure water may be obviated by
liberally blowing off from the surface imtil the nuisance is
abated.

A very good plan to prevent priming is one adopted in the
engines constructed by Charles Powis & Co. Their arrange-
ment is to fit the stop valve, opening to boiler, with a disc
plate, arranged with orifices on its upper side so that dry
steam only can find its
way through the stop
valve. A C is a section
of the disc plate fitted
inside the boiler ; W L
is the water line, and
B B the top of the boiler,
so that all steam passing
to the stop valve, which
is situated just above
S Y, must pass in the
direction of the arrows,

through the small per-"" ""

forations into which the ENTRANCE TO STOP VALVE.

top arrows are entering. The water will be thrown and

knocked out of the steam before it can pass to the stop valve.

Boilers sometimes prime when the ship passes from salt
to fresh water or fresh water to salt. It has been suggested
.that in passing from salt to fresh water the cause is this :
fresh water being lighter than salt, is upon its admission to
^~ boiler more easily thrown about by the ebullition, and
efore more spray is flying ; but as the same boiler will

172 STEAM.

also prime in passing from fresh to salt water, this reason
evidently will not hold ; we have yet to seek the true cause.
May not the change of water cause a serious change in the
existing condition of the boiler, and this change being accom-
panied by a general disturbance of the equilibrium of the
water, much more spray is thrown off than usual, and prim-
ing follows.* When new boilers have primed, a good plan
adopted, is to run into harbour and blow out the boiler
several times in succession. This has often effectually pre-
vented priming.

199. Fire Grate Surface, Heating Surface, Amount of
Coal to Evaporate One Cubic Foot of Water. — In the
majority of marine boilers, it is usual now to allow three-
quarters of a square foot of fire grate surface, and about
nineteen square feet of heating surface, to each horse-power,
but some take these numbers at half a square foot and twelve
square feet. It is also calculated that six pounds of coals
should be consumed every hour for each horse-power of the
engine ; these proportions of fire grate, heating surface, and
consumption of coal, evaporate one cubic foot of water per
hour. Locomotive boilers are constructed with a much
smaller amount of fire grate surface ; to compensate for this,
the waste steam pipe is introduced into the funnel, which
causes a most intense heat in the furnace, and it is found,
the more intense the heat, or the hotter the heating surfaces
and the water are, the more heat will pass into the
water. They consume one hundred weight of coke per
hour on each square foot of grate surface, the proportion of
heating surface to this is eighty square feet; on every five or
six square feet of heating surface one cubic foot of water is
evaporated per hour. Each horse-power requires a cubic
foot of evaporated water per hour, but in high pressure work
more. The quantity of water may be generally taken as one
cubic foot per horse-power per hour, but it is in excess for
such engines as those in which advantage is taken of the
expansive force of steam. In Cornish boilers, where an
enormous duty is obtained for each engine, not more than
three and a half or four pounds of coal is burnt on each

* See Causes of Boiler Explosions — Spheroidal Condition of Water,
and Water Purged from Air.

FEED PUMPS. 173

square foot of grate surface per hour. As well as a boiler
having a due proportion of grate and heating surface to pro-
duce the necessary volume of steam, the furnace must be
sufficiently roomy to consume all the products of combustion;
the tube or flue surface, etc., must be adapted to abstract as
large an amount of heat as possible, without too much passing
away as waste, while at the same time the water spaces in
the boiler and the distances between the tubes must be large
enough to allow the steam freely to rise, or else priming may
take place. Again, the furnaces should never be too long, for
the stokers will find a difficulty in keeping the bars free from
clinkers, the clinkers as well as the fire not being fairly
within reach.

200. Feed Pumps. — The feed is supplied to the boilers in
one of the following ways : (1) By boiler hand pumps; (2)
by the donkey engine ; (3) by the feed pump proper ; or (4)
by Giffard's injector.

(1) The boiler hand pumps are fitted to marine boilers, so
that when there is 110 steam up men may fill the boiler by
hand, providing it is not sufficiently below the level of the
sea for sea water to run in freely when the Kingston valve
is opened.

(2) The donkey is a small steam pump in the engine-
room that can be set to work to fill up the boilers when the
engines are waiting for orders. The donkey has always the
steam piston and pump piston at opposite ends of the same
rod.

(3) The feed pumps which have been already explained.
In stationary engines part of the warm condensing water

is driven into the boiler as feed; the rest, by far the greater
quantity, being allowed to run away. But the feed pumps
should at all times be capable of supplying much more water
than the boiler in its normal state will use. The capacity
of the feed pump is generally about -o^-th that of the cylinder,
so that it can supply more than three times as much as is
required. While the steam pipe should be attached to the
highest point of the steam chest, the feed pipe should be
fixed as low down as possible, so that the cold water may
gradually rise. In most Government vessels the feed and
donkey pumps are made of brass.

174

STEAM.

201. Locomotive Peed. — In locomotives the feed pumps

^j are made of brass and the plunger

of iron or brass. They are worked
either from an eye on the back of
the eccentric (see fig., p. 70, G),or by
the piston crosshead. The passage of
the water from the tank to the boiler
is governed by three ball valves and
a cock or valve box close to the boiler.
The lift of the valves must never ex-
ceed -—^ or T5g- of an inch. There are
generally two pumps to each engine.
The water, when directly admitted
to the boilers, enters about the
middle of the bottom, but some-
times a pipe passes it through the
smoke box first to extract as much
heat as it can from the heated gases
before it gains admission to the
boiler. So also in the marine en-
gine, the water sometimes enters
the boiler from round the funnel.

202. (4) Giffard's Injector.—
This is a novel contrivance for feed-
ing boilers, fast superseding all
other methods of feed; but no con-
vincing explanation of its action
has yet been offered. The manu-
facturers claim for it these advan-
tages : —

(1) It is as cheap as a pump and
its connections ; (2) it saves the
wear and tear of pumps, which in
locomotives and other high pressure
engines are very considerable ; (3)
it saves the power required to work
the pumps; (4) the water enters the
boiler at a high temperature, so no
heat is lost ; (o) you can feed a
boiler without setting the engine in

GIFFAP.B'S INJECTOR.

EXERCISES, 175

motion, thus saving donkey pumps; (6) it is free from
risk of damage or stoppage by frost.

We will suppose it properly attached to the boiler, it then
works in the following manner : —

G I is the injector, N" is attached to the boiler. Steam
can pass into the injector at N. When the handle d is
moved up, steam rushes through a i at i, where it meets the
water supply coming into the injector at E. The steam
drives the water through n, and beyond the valve s, into
the boiler. When there is sufficient water in the boiler, the
valve s is forced upwards, and 110 more water can pass it;
the waste water can then pass through the overflow pipe L.
The steam to work the injector must be taken from the
highest part of the boiler, and must not be primed. The
water driven through it may be taken from a cistern over-
head, or from a tank in. the ground; but the distance from
the level of the water below to E above must not exceed
5 feet. Now it is found that the pressure of steam will
actually drive the water into the boiler, although it has to
force it against the pressure of both the steam and water in
the boiler.

A jet of steam moving with perhaps a velocity of 1700
feet per second, is instantly condensed in perhaps twelve
times its weight of water. The combined jet will then
move, by the momentum imparted to it by the steam, at one-
thirteenth its former velocity, 131 feet per second — the
motion of the steam being wholly imparted to the water.
Thus the jet properly directed enters the boiler, and we
can find an explanation of the action of the injector by
simply considering that it acts solely by the momentum

parted to the water by the jet of steam.

EXERCISES CHIEFLY FKOM EXAMINATION PAPERS.

1. Why is the hydrometer an imperfect instrument without the
thermometer (1863)?

2. What quantity of water at 56° F. would be required to condense
1500 cubic feet of steam at a pressure of 35 Ibs. per square inch above
the atmosphere, so that the temperature of the whole should be
100° F. (1865)?

17G STEAM.

Temperature of injection water is raised 100° - 56°= 44° F. = 24°f C.

100° F. = 37°£C., and temperature at 50 Ibs. pressure = 282° F.

Total heat in steam at 282° F. = 1082 + '305 x 282° = 1 168° F. = 649°C.

Relative volume at 35 Ibs. above the atmosphere, or at 50 Ibs., is
= 552.

The relative volume may be taken as the number of cubic feet of
steam produced from a cubic foot of water.

. •. Number of feet of water = -j500 = 271.

552

The steam has to give up 649 - 37£ = 611°$ C.
Since each unit gives up 24°|C.

. *. Injection water required = - — J?=25 times the water evaporated.

24g-

.'. Quantity of water required = 271 x 25 = 67*75 cubic feet.

3. When a boiler is filled with sea-water, it is the practice to test
the degree of saltness from time to time ; why is this ? Describe the
apparatus employed, and the method of using it (1871).

4. Describe Giffard's injector, and give some explanation of its
action (Honours, 1871).

5. Describe the feed pump and valves necessary for supplying the
boiler of a locomotive. What is the principle of Giffard's injector
(1869)?

6. The brine pump of a boiler being choked, how is the brine to be
got rid of, the steam gauge indicating 4 Ibs. and the upper surface of
the water being 2 feet below the level of the sea (1868) ?

Ans. There will be nearly 1 Ib. pressure per square inch to clear it.

7. Describe a method of ascertaining the degree of saltness of the
water in a marine boiler (1870).

8. How is the degree of saltness of the water in a marine boiler
ascertained ?

9. Show generally how to determine the amount of fuel lost by
the process of blowing out in marine boilers (Honours, 1871). See
questions at the end.

. 10. Give an analysis of sea water, and state clearly what is the
amount of solid matter in it.

11. How is the boiling point of salt water affected by the amount
of salt in it ?

12. Describe the manner in which the salt and impurities are
" blown off" from the surface.

13. What is How's salinometer ? also state the principle on which
Seaward's salinometer is constructed.

14. What are the remedies against priming, and what do you mean
by priming ? can you account for it taking place ?

15. Give the relation between fire-grate surface, heating surface,
and the evaporative power of the boiler in a marine engine,

CHAPTER XL
LAND ENGINES.

The Beam Engine — Horizontal Engine — Vertical Engine — Table
Engine — Portable Engine — Ramsbottom's Intermedial Engine —
Gas Engine — Caloric Engine — Siemen's .Regenerative Engine —
Fire Engine — Cornish Pumping Engine.

203. The Beam Engine has been already fully explained
in Chapter III. It is the most general form of the land

BEAM ENGINE.

jine. We have now to allude to a few of the shapes,
which for convenience, room, saving of expense, etc., have
been adopted by various makers. Merely remarking that
after the descriptions given of the beam engine, and of the
marine engine generally, there is very little to which to
direct attention, excepting the difference of arrangement.

E Horizontal Engine. — In this, which is one of the
mvenient and compact form of engine, the general
"

178

STEAM.

arrangement is as illustrated in the figure given below,
although they vary in detail with the caprice of the maker.

HORIZONTAL ENGINE.

A B is the cylinder lying horizontally on its side, v is the
valve to admit the steam from the boiler by way of the steam
pipe S P ; the head of the piston rod is seen at g, the cross-
head of which works within the guide or guide bars a b, and
to the crosshead of the piston rod is attached the connecting
rod g c, which works the crank c r. The main shaft is shown
at TJ darkened, this carries the fly wheel F W ; f is the band
working the governor G by means of pulleys, the driver being
on the main shaft ; of course the work is taken off the main
shaft r. The whole is generally supported on firm masonry
CD.

Advantages of Horizontal Engines. — The advantages
gained by the use of a horizontal instead of a beam engine
are : they require no "steadying stays" or supports, but can be
bolted to foundations; they very snugly occupy but little space,
iind give out power as near the ground as is required; they can
be made at considerably less cost, for the working parts are
fewer, and less metal is required in their construction. The
bottom parts of horizontal engines are liable to wear more
than the rest — this is an objection. The cylinder occasionally
becomes grooved out by the friction (gravity) of the piston.
Engineers guard against these defects by providing suitable
bearings, well balancing the several parts of the engine, and
constructing it of the best material and workmanship.

VEBTICAL EXGIXE,

179

205. Vertical Engine. — In many positions vertical engines
are very much better fitted to accomplish the work required
than horizontal. They seem especially adapted for cranes, and
such like services.

VEBTICAL ENGINE.

The letters in both figures correspond.

G is the cylinder, from which proceeds the piston-rocl p.
The head or crosshead, g, of the piston-rod moves in guides
g g, the connecting rod is g c, working the crank c r. The
shaft is r, which carries the fly wheel F W ; the motion is
taken from the end of the shaft at s, or sometimes F W is
used as a drum, and the work is conveyed by an endless band ;
the governor is placed at G, and the manner in which it works
is seen in the right hand figure. E is the eccentric working the
slides at s; B is the boiler, to which the framing of the
engine is attached, the boiler is generally a vertical tubular
one. It is evident from the circumstance of the engine being

180 STEAM.

attached to the boiler, that this class is not intended to give
out powerful work.

Vertical engines are frequently used where space is an
object, but they have to be rigidly supported to prevent
vibration. The slides of vertical and horizontal engines are
worked in the usual manner by eccentrics upon the main
shaft. Horizontal engines have expansion valves very
frequently, which are worked by separate eccentrics; of both
kinds of engines the boiler and boiler appendages, such as
safety valve, communication valve, pressure gauge, vacuum
gauge, gauge cocks, and arrangement of the fireplace, are all
the same. Vertical engines are generally non-condensing,
and the escape steam is utilized for the blast. Horizontal
engines are used both as condensing and non-condensing,
but generally the former.

206. Table Engine. — Before the introduction of horizontal
engines, these table engines were very common, but are now
going out of fashion, chiefly because there is a good deal of
extra gear connected with them, and they are therefore more
expensive. The cylinder stands on the top of a large cast-
iron plate or table, supported frequently by four columns,
above the cylinder is a high erection or guide for the piston-
rod to move upwards and downwards vertically, from the
crosshead of the piston-rod two side rods come down by the
side of the cylinder to work the crank which is below the
cylinder. The additional parts as compared with plain
vertical engines, are an extra connecting rod, crosshead,
crosstree, and two side rods for slide valve, two guides and
blocks for the same. As an engine it possesses great dura-
bility, but it has, as previously stated, a large amount of
extra gearing ; all its parts are well balanced.

207. Portable Engine. — A portable engine differs in no
essential particular from an ordinary horizontal engine,
excepting that provision has to be made to carry both boiler
and engine on two pair of wheels.

C is the cylinder working the piston-rod p, the crosshead
of which moves in guides or else is kept parallel by guide
bars; c e is the connecting rod to work the crank c s, the main
shaft being s, to the end of which is attached the drum or
pulley I1 Wj which also acts as a fly wheel j the slides are

DISTINCTIVE FEATURES OF THE PORTABLE ENGINE, 181

worked in the same manner as in ordinary horizontal or
other engines by the eccentric; the fireplace is at F P,

PORTABLE ENGINE.

and beneath it is the ash box ; B B' is the barrel of the
boiler, which is of the class nmltitubular ; at B' is the
smoke box and H is the chimney. The boiler in a good
many points resembles the locomotive ; the waste steam is
directed from the boiler to the funnel to create a draught, but
the cylinder is generally on the top of the boiler and not
under the smoke box ; or else the cylinder with the pipes
connected with it is placed inside the boiler, which certainly
prevents rain, frost, etc., from condensing the steam in it.
The shaft with its pulley or drum communicates the motion
of the engine, by means of an endless band, to whatever
machine it has to drive.

Distinctive Features of the Portable Engine. — Be-
sides the distinctive features which may be seen at a
glance, it is absolutely necessary that the machine should be
as light as possible, to enable it to be easily and readily taken
from place to place; hence no condensation of steam is at-
tempted, but the waste arising from non-condensation is

t/C.UJ.J^ 1/C/U.j H.

182

STEAM.

utilized as much as possible in increasing the draught. The
portable must be plain and economical, so that being used
by agricultural labourers, etc., it may not be liable to dis-
arrangement, hence all its parts are very simple and light, it
never being intended for very hard work. These engines are
also very compact and cheap, requiring no expense for brick
work, setting, etc. They are used for brick making, tile
making, pumping, winding, thrashing, crushing, chaff cutting,
and almost every other agricultural purpose.

The slides are worked by eccentrics, in the usual manner,
and steadiness is given to its motion by a governor; it seldom
or never does its work directly, but an endless band is always
employed.

208. Ramsbottom's Intermedial Engine. — B D is the
cylinder. The connecting rod A K and crank C c, as well
as the piston P P, are all within the cylinder.

The piston is long and hollow, the ends P P being con-
nected together, as seen in the figure, by a and a', so that the

HAMSBOTTOM'S INTERMEDIAL ENGINE.

crank actually works within the piston as well as within the
cylinder. The engine is evidently very compact, but is not
adapted for heavy work. The stroke is very short. The
shaft is seen at M, while the valves are explained in
their proper place. The governor is placed on the top B of

GAS ENGINE — THE ACTION. 183

the cylinder, and " much of the straggling mechanism of the
ordinary form is brought together." " This form of engine
requires little fixing, and possesses a great range of speed."

209. Gas Engine. — A gas engine is one whose motive
power is obtained by the explosion of a mixture of gas and
air, either by an electric current, as in Lenoir's gas engine,
or by external gas burners, as in Hugon's. The cylinder is
furnished with a piston like an ordinary steam engine. It
has passages on each side — one the inlet, the other the outlet
passage — each covered by its slide worked by separate eccen-
trics. The mixture of gas and air, by the explosion of which
the engine is worked, is admitted by the inlet valve. There
is a recess in the valve where the gas becomes mixed with
atmospheric air, the latter being introduced through an
opening in the top of the valve. The proportion of air to
gas used is as eleven to one. The outlet valve is very much
like the inlet valve, but the ports through the back of it
keep the recess in the valve in constant communication with
the exhaust passage. The eccentric to work this valve is set
on the crank shaft in such a position, that it uncovers each
port alternately, just before the piston has completed its
stroke either way, and releases the vapour formed by the
products of combustion. There are water spaces round the
cylinder covers and exhaust valve, to carry off the heat
generated by explosion. Forming part of the engine,
there is what is called a distributor, which regulates the
transmission of the currents of electricity to produce the
sparks which explode the mixture of air and gas in the
cylinder. An " igniter," consisting of a brass plug through
which a china cylinder passes, having two separate insulated
copper wires passing through it, is inserted at each end of
" .e cylinder. At the end of the porcelain cylinder, within
.e engine, the two wires are brought nearly into contact, so
that a spark can readily pass between them. The igniters
are of course connected with the distributor, and batteries
are employed for generating the electric current.

The Action. — In starting these engines, it is necessary
to turn the fly-wheel round quickly two or three times by
hand, then open the valves, and connect it with the dis-
tributor, etc. It should be well in motion before connected

V/M

th!

th:

184 STEAM.

with the work it has to do. Let us suppose the engine in
motion, and the piston just commencing its stroke from the
crank shaft. The port leading to the end near the crank is
uncovered by the inlet valve, the piston moves onward, and
the mixture of air and gas runs in, filling the vacuum
behind the piston. Just before the piston reaches the
middle of its stroke, the inlet valve is closed, and the current
of electricity having its circuit completed, produces a spark
which ignites the explosive compound of gas and air. A little
before the end of the stroke, the exhaust valve releases the
enclosed vapour. From indicator diagrams taken by Mr.
Smith, of the Patent Museum, South Kensington, it has
been shown that, when running at 110 revolutions per
minute, the indicated horse power was double the nominal.

210. Caloric or Hot Air Engine, or Air Engine. — Al-
though we place the air engines in this chapter, it must be
distinctly understood that Captain Ericsson's first attempt
was to adapt the caloric engine for marine purposes.

Air Engines are very similar, in all their working
parts, to the ordinary steam engine, but air expanded by
heat is the motive power employed, and not steam. In the
first attempt at a caloric engine, the air was heated to a high
temperature, and having driven the piston within the cylinder,
it was allowed to escape into the atmosphere ; the great
question has been how to save this heat, and economise the
expenditure of fuel. Messrs. Stirling effect an economy of
heat by using what they term a regenerator or economising
process. It was discovered by Dr. Stirling that if heat be
passed through a compartment filled with sieves of wire-gauze,
or even minutely divided metallic passages, it will leave a
large amount behind j this is precisely the plan adopted, the
hot air, having driven the piston down in the cylinder, passes
outwards through a chamber of fine wire-gauze, leaving a good
deal of the heat behind in the sieves and narrow passages;
other air which has to enter the cylinder next, is made to pass
inwards through the same, having had added to it a little
addition of heat, and gathering up heat also from the sieves
and narrow passages, it effects the return stroke. This being
repeated over and over again, it is evident that the same heat
will be continually doing work.

SIEMEX'S EXGINE OR REGENERATIVE EXGIX3. 185

Iii another kind of air engine compressed hot air has been
used to give the reciprocating motion to the piston. While
the name of Stirling is associated with the attempt to adopt
air engines to land purposes, Captain Ericsson has worked to
make the caloric a marine engine; although as regards the
primary object of the inventors these engines have proved
a failure, yet they have met with a certain amount of
success. Small air engines have been extensively used in
the United States for driving printing presses and other
light work.

Motive Power of Air Engines. — The motive power
of such engines is found in the circumstance that all bodies
expand by heat and contract by cold, whether it be a gas,
liquid, or metal, so therefore if they be subject to two ex-
tremes of temperature they will develop a certain amount
of power, the only question is how to utilize it. In a steam
engine, the extreme difference between the temperature of
the boiler and condenser is not very great ; now air can be
subjected to greater extremes of temperature than water, and
therefore is better adapted than water to act as a motive
power. The practical difficulties have hitherto been so great,
chiefly to prevent the enormous waste of power, and the high
tamperature to which certain parts of the engine are subjected,
that their employment has been prevented, unless under very
limited circumstances.

211. Siemen's Engine, or Regenerative Engine. — Mr.
Siemen has invented an engine in which the conversion
of heat into mechanical effect has been pretty successfully
accomplished. He obtains his motive power by alternately
heating and cooling steam, or by expansion and contrac-
tion. The regenerative engine is constructed on the same
principle as the hot air engine explained in the preceding
paragraphs. By the peculiar construction of the cylinders,
receivers, etc., the steam takes up heat and gives it out
as it passes from one cylinder to the others, of which there
are three. Two cylinders, called the working cylinders,
have plungers, and the other a piston. The steam is heated
to a high temperature in the plunger or working cylinders,
under each of which there is a fire. Part of the heat is
consumed in doing the mechanical work of lifting the

186 STEAM.

plungers, much of the rest is taken up by the regenerators
as it passes to the third or regenerative cylinder. The
regenerators have been explained in a previous page. In
the regenerative cylinder, the steam acts in the ordinary
way after its temperature has been reduced in the regenera-
tors. It then returns to the. plunger cylinders,' where it
receives additional heat and commences its round again ; so
that the same steam goes round and round, being continually
employed. The regenerative or third cylinder communicates
at one end with one working cylinder, and at the other
extremity with the second.

In justice to others, it should be remarked that Siemen's
engine resembles Stirling's, except that he uses saturated
steam instead of air in the regenerator. Could the wear and
tear caused by the heat to the heating vessels and cylinders
be prevented, these engines would come into extensive use,
as there is with them a remarkable economy of fuel, as high
as 50 per cent.

212. Fire Engine. — Theatre engine can be scarcely ranked
as a distinctive engine. It is simply a steam pump on
wheels; although, of course, there are several difficulties to
be overcome in connection with them. The two essential
qualities required are, that the steam shall be got up very
rapidly, and that they shall be able to throw water to a good
height.

Messrs. Merryweather & Sons have made these engines
quite a success. The arrangements are such that the steam
is raised in about ten minutes, while travelling to the fire.
The boilers, with the blast pipe, are of steel, with copper
tubes and large water spaces. They are fitted with the
necessary safety valves, gauges, and GifFard's injector. The
valves are arranged to allow foul and gritty water to pass,
and steam can be conducted to them so that they cannot
freeze by the winter's cold, and if they should become frozen
they are easily thawed. The engine is direct acting, with-
out fly wheels, cranks, or dead centres. The Sutherland
will throw 1000 gallons per minute 200 feet high in a 1£
or 1-| inch stream. There is, of course, an air vessel to
render the stream of water continuous, as in the common
hand fire engine.

CORNISH PUMPING ENGINE. 187

213. Cornish Pumping Engine. — Had this engine come
under our notice in the earlier part of the work, it would
have required many pages to fully describe it; but the chief
points have been already illustrated under such headings as
the Beam Engine, Single Acting Engine, Cylinder, Connect-
ing Rod and Crank, Cornish Double Beat or Crown Valve,
Cataract, Expansion, Duty, etc., to all of which headings
the student is directed to acquire a full acquaintance
with this engine. In a preceding page we remarked
that the main object of early inventors was to produce a
machine to lift the water from the mines of Cornwall and
Devon, and perhaps it is no exaggeration to say that a large
proportion of the engines of Boultoii and Watt were sent into
those counties.

Cornish Pumping Engines are generally single acting
beam engines. Three slides are used to regulate the supply
of steam in the cylinder, viz., steam or expansion, exhaust or
eduction, and the equilibrium slide. The cylinder always has
a jacket. The steam is worked at a very early " cut off," and
the greatest advantage is taken of its expansive properties ;
consequently the engine moves slowly, its stroke being regu-
lated by the cataract, although in its earliest form Watt used
the governor to give it steadiness of motion. A fly wheel is
generally employed, the steam being used to effect the down
stroke of the piston, the weight of the pump rods, etc., per-
forming the up stroke. The action of the steam is this :
the steam valve admits the steam to the top of the piston,
and after doing the duty of forcing it down, part of the
stroke is done expansively ; by means of the equilibrium
valve, the same steam is allowed to pass to the bottom of
the piston, and assist in the return stroke, after which it
escapes to the condenser through the exhaust valve. See
Single Acting Engine.

The beam is generally an unequal one, although equal
beams are occasionally employed. It is supported on two
cast-iron columns, but generally on walls of solid masonry.
The reason for using an unequal beam is to give the piston
a longer stroke without increasing the velocity at which the
pump plunger works, and thus preventing the wear and teai*
of the latter. Again, high pressure steam may be used with

188 STEAM.

a long stroke, without being obliged to strengthen the other
parts of the engine in proportion to the stroke.

The slides are not ordinarily worked in the common
manner by an eccentric, but by tappets on the air pump rod,
or else on the plug rod. As the beam goes up carrying the
air pump rod, a tappet or projection on the rod strikes the
extremity of a simple lever, lifting it up ; the other ex-
tremity opens the steam and exhaust valves, and closes the
equilibrium, and in going down it reverses the process. Thus
the slides are worked. The water is lifted on the down
stroke of the piston by the extremity of the beam by means
of a pipe passing down the mine shaft. It is not elevated
right up to the top at once, but is driven from the bottom
by an ordinary single acting valve, consisting of a plunger
of suitable size, the water being forced into a cistern or tank
at the first level, and not allowed to return by means of
valves ; the next stroke forces it up to another and higher
level, and so on. If possible, they make the water drainage
of each level run into its own tank.

To give an idea of their size, the following are the dimen-
sions of one of the engines erected by Boulton and Watt : —

Diameter of cylinder, 28 inches.

Stroke, 8 feet.

Number of strokes per minute, ... 14

Diameter of lifting pump, 17J inches.

Stroke of lifting pump, 8 feet.

Water raised, 126 feet.

The distinctive features of the Cornish single acting pump-
ing engines are: the large employment of the principle of
expansion, by which a very great economy of fuel has been
realized ; the use of the cataract to ensure a slow stroke, by
regulating the supply of condensing water; the mode in
which the valves are worked ; the employment of steam for
the down stroke, and the up stroke being performed by
the weight of the rods, etc., at the other end of the beam ;
and a plunger is employed in the pumps, and not a lift or
bucket.

The eduction valve allows the steam to escape to the
condenser, when the down stroke is to be made ; it is opened
a little before the steam or expansion valve, so that it may

EXERCISES. 189

have a longer time for condensation, and that the down
stroke may take place the instant steam is admitted.

For a general description of this engine we may consider
the figure of the beam engine, on page 177, as a Cornish
pumping engine ; but instead of the fly wheel v v, and the
small geared wheel to the right at the bottom, we must
imagine that from A descends a heavy pump rod down into
the mine from which the water is to be raised. To the same
end is attached the plug rod to work the cataract. At the
other end of the beam is first of all the cylinder E F with
the piston rod E B, while G H is the air pump rod, and PI
the air pump. L M is the hot water or feed pump rod and
pump, as the air pump rod ascends and descends it works
the valves. The water is elevated by the pump rod at the
end A by first raising it from the lowest level to a higher,
when it is delivered to the pump, then to the pump next
above, and so on until the water reaches the surface.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Give a description of a beam engine. Upon what principle
is it constructed, and how are the slides worked ?

2. Describe a simple and effective form of horizontal engine.
What advantages are gained by the use of such engines ?

3. How does a vertical engine differ from a table engine ? State
the distinctive arrangements in each case. When may vertical
engines be advantageously employed ?

4. Describe a simple form of portable engine adapted for agricul-
tural purposes. State clearly how the slides are worked, and how
the work is taken off the engine.

5. What is the general form and principle of Ramsbottom's
intermedial engine ?

6. Describe the form of engine in which gas is used as the motive
power. State clearly wherein they differ from a horizontal engine.
Give a full description of the " igniter," and the theory of its action.

7. Describe a caloric engine, and show clearly how the motive
power is treated. Can you tell what is meant by the " regenerator"
as used in these engines, and describe clearly the principle on
which it acts ?

8. How does Siemen's engine differ from the hot air engine ?

9. What are the distinctive features of a Cornish engine ? How
is the water elevated by these engines ?

10. Explain the manner in which the steam acts in Watt's single

190 STEAM.

acting pumping engine. Why is this engine so much more econ-
omical in steam than the old atmospheric engine (1870) ?

11. Explain the principle upon which the parallel motion of a
beam engine is constructed (1870). See questions at the end.

12. State the principle of Watt's single acting engine as applied
in pumping. What valves are necessary for the working of the
engine ? How is the number of the strokes to be made per minute
regulated ? Describe the cataract employed for that purpose (1871).

13. Define the duty of a steam engine. What is the average duty
of the pumping engines in Cornwall ? How do you explain the
increased duty obtained from such engines by employing steam at a
higher pressure and by working expansively (1867) ?

14. Sketch in section steam cylinder and valves connected with it,
as arranged in Watt's single acting pumping engine. Explain the
object and use of each valve, showing at what periods of the stroke
they should be respectively opened or closed (1871).

15. Give an account of the principal discoveries of Watt, and the
advantages derivable from them (1807).

16. Describe the Cornish double beat valve (1867).

17. It was stated by Watt, that neither water nor any other sub-
stance colder than steam should be allowed to enter or touch the
steam cylinder during the working of an engine. Show that this
rule was not adopted in the case of the atmospheric engine, and
describe the arrangements by which Watt gave effect to it (1872).

18. There are three valves connected directly with the steam
cylinder in Watt's singie acting condensing engine. Name them.
During what portions of the up and down strokes of the piston should
these valves be respectively open or shut, and for what reason (1872).

Several of these questions are repeated for the convenience of
the students.

CHAPTER XII.
COMBUSTION AND PREVENTION OF SMOKE.

Definition — Foot Pound— Combustion — Analysis of Coal — Prevention
of Smoke — Smokeless Coke— Pvules to Avoid Smoke and Waste
of Fuel,

214. Definition. — The combustion of a pound of coal
produces 8000 thermal units of heat.*

A thermal unit of heat is the heat necessary to raise a
pound of water one degree in temperature.

" The quantity of heat necessary to raise one pound of
water 1° Fahrenheit in temperature is equal to that
generated by a pound weight falling from a height of 772
feet against the earth, or it would raise 772 pounds 1 foot
high.

215. " Foot Pound." — The term foot pound has been
introduced to express in a convenient way the lifting of a
pound to the height of a foot. Thus the quantity of heat
necessary to raise the temperature of a pound of water 1°
Fahrenheit being taken as a standard, 772 foot pounds
constitute what is called the mechanical equivalent of heat.
Tf the degrees be centigrade, 1390 foot pounds constitute the
equivalent, "f

216. Combustion. — Combustion is chemical combination
attended with the evolution of heat and light.

A. flame is gas or vapour raised to a high temperature by
combustion. From this definition we see the reason why
the direct impact of flame against the flues and tubes of a
boiler should be avoided as much as possible.

Ganot's Physics, p. 401.
t Tyndall's Heat as a Mode of Motion, 4th Ed,, p. 40,

192 STEAM.

217. Analysis Of Coal. — Caking or bituminous coal con-
tains— -

75^ per cent, of carbon.
4£ ,, hydrogen.

10 ,, nitrogen.

4J „ oxygen.

100

All analyses vary according to the coal taken. The
quantity of carbon in different varieties of coal varies
very materially ; not only do the different kinds of coal, as
caking, splint, cannel, anthracite, etc., differ in their consti-
tuents, but the coal from the same seam will vary consider-
ably from the normal standard of that kind of coal. The
heating powers of coal vary with. the amount of carbon — the
more carbon the more heat will be yielded. The best coals
are the Lancashire, the Durham, the Staffordshire (locally
called brown coal), and the Welsh anthracite, or stone and
furnace coal. Lignite, as a rule, possesses two-thirds of the
heating power of good bituminous coal. Peat contains on
the average a little less carbon than lignite, or about 50 per
cent. • The Americans give analyses which lead to the con-
clusion that their anthracites contain more carbon than our
best coals; but it must not be forgotten that anthracite
requires an intense heat, a good supply of oxygen, and con-
siderable time for its combustion ; but we must set against
this that when it does burn the heat is very fierce.

It is plain that the quantity of air necessary for perfect
combustion will depend upon the fuel used. Caking coal, as
Welsh, which fills up the spaces between the bars, will cer-
tainly require a greater admission of artificial air than the light
burning coals from Staffordshire or Newcastle. A permanent
opening of from 40 to 50 square inches behind the bridge
has been found very effective to prevent the escape of carbon
(smoke), and resulted in a saving of 33 per cent, in fuel.

When coal burns it throws off light carburetted hydrogen,
heavy carburetted hydrogen, carbonic acid gas, carbonic oxide,
etc., each of which, as it produces heat, will combine only
with its proper proportion of oxygen ; therefore, if more be
supplied by introducing too much fresh air, it does injury
not only by cooling the internal surface of the flues, but

PREVEXriOX OF SMOKE. 193

(remembering that a high temperature is necessary to pro-
duce combustion) by preventing combustion. It has been
proved that hydrogen furnishes, weight for weight, four times
as much heat as carbon ; therefore the 4^ parts of hydrogen
in coal will produce 4J x 4 = 17 parts of heat, and the carbon
75 J ; or out of 92 parts 75 are produced by the great pre-
ponderance of the carbon, and 17 by the small amount of
hydrogen. In round numbers, we may say out of 100 Ibs.
of coal 80 Ibs. are carbon and 5 hydrogen (which latter gives
heat equal to 4 x 5 = 20). The SO Ibs. of carbon will require
2527 cubic feet of oxygen for its combustion, which will
be supplied by 12635 cubic feet of atmospheric air. The
hydrogen will require 473 cubic feet of oxygen, which will
be found in 2365 cubic feet of air, making a total of
12635 + 2365 = 15000 cubic feet of air for the combustion
of 100 Ibs. of coal. *

217. Prevention of Smoke. — Experience has proved that
it is quite possible, with a carefully contrived furnace and
skilful stoker, to prevent smoke almost entirely. In the
Rainhill competition one condition was, that the engines
were to consume their own smoke. Stephensoii therefore
used coke. In marine locomotion smoke is not a nuisance,
except in river steamers, but it is a wasteful expenditure of
fuel. Smoke is consumed by carrying out the principles of
more perfect combustion ; for this purpose, either an extra
supply of atmospheric air (oxygen) is insured, or a jet of dry
steam is sent into the mouth of the furnace. The chief object
to which the fireman has to direct his attention is to spread
his fire evenly, and when he introduces fresh fuel to keep
it close to the fire door at first, so that the carbon may
be brought in contact with sufficient heat, as it passes
over the fire, for its perfect combustion. If the coals are
at first placed near the furnace doors — this was Watt's
plan for consuming smoke — they begin at once to give
out their gases, these passing over the incandescent fuel,
farther in the fireplace, are raised in temperature suffi-
ciently for the carbon to combine with the oxygen. Coal
gives out carbon and hydrogen, with nitrogen and oxygen,
the carbon combining with the oxygen of the air gives

* See Cojburn's Locomotive Engineering for a second calculation.

194 STEAM.

out carbonic oxide; but the hydrogen combining with the
oxygen, gives intense heat, and sets the carbon free; but
the carbon next unites with the oxygen, and as it passes
from one to the other, we have intense light. The more
the oxygen the greater the heat. Hence the reason for
the construction of the Bunsen's burners, now so common
in every house under the name of gas stoves. Mr. C. W.
Williams of Liverpool has given great attention to the con-
struction of fireplaces and furnaces that shall consume their
own smoke. He admits air behind the firebridge into a
mixing chamber, where the fresh and heated air enter into
combination, and the smoke-laden flame is deprived of its
carbon by more perfect combustion.

Some engineers consume the smoke simply by paying extra
attention to the stoking. In Jukes' patent furnace the bars
are arranged as an endless chain, passing over two rollers,
which work the chain, the latter gradually carries forward
the coal from the mouth of the furnace ; as it passes under
the door, the bottom of the door prevents the entry of too
much coal at one time, or regulates the supply. A roomy
furnace has a far better chance of consuming its own smoke
than a small one. This will follow from what has been
stated above. With a roomy furnace the smoke has a larger
mass of incandescent fuel to pass over, so the gases can be
better burnt as they go along to the flues. In Pricleaux's
furnace he supplies air only as long as smoke is being pro-
duced, by the peculiar arrangement of openings in, and plates
of iron on the back of, the furnace door. These plates heat
the air as it enters the fireplace, so that no cold air can gain
admission. In practice it is found that if a continuous
stream of cold air be allowed to enter, it acts injuriously upon
the boiler plates, by causing oxidation through the excessive
heat at one moment and sudden cooling at the next. When
a jet of steam is introduced into the fireplace to promote the
consumption of smoke, it enters from a pipe placed imme-
diately across the top of and inside the door ; then as it vio-
lently rushes over the burning fuel, it does this in two ways.
Its synthesis is affected, and its own oxygen and hydrogen
combine with the other products of the coal, and create heat,
and at the same time the draught is considerably increased.

EXERCISES. 195

218. Smokeless Coal. — Anthracite coal burns without
smoke and evolves no sulphur ; for this reason it has been
introduced on the Metropolitan line. In passing through
the covered portions of the line, the exhaust steam is turned
into the tanks and condensed, while the draught is main-
tained by the moderate use of a jet of steam.

Suppose we now throw together a few of the simple rules
given under the heads Combustion of Fuel and Prevention
of Smoke.

(1) It is best to heat the coals on the dead plate first after
the Banner of Watt, or else in commencing 'firing throw the
first few shovelfuls toward the bridge, and gradually cover
the fire evenly to the door. In all cases see that the bars
are well covered.

(2) Knock out all clinkers as soon as formed, keep the
fire from caking together, and admit a proper supply of air
near the door.

(3) Regulate the draught either by the clampers or by
the ash pit and furnace doors, or by an orifice behind the
bridge. Clothe all parts of the engine and boiler that lose
heat by radiation, such as steam pipe, cylinders, boilers, etc.

EXAMINATION QUESTIONS.

1. What is a foot pound ?

2. Define combustion, and give an analysis of coal ; also state how
much air is required for the combustion of 100 Ibs. of coal.

3. Give some simple directions to a stoker to effect the consumption
of smoke when he is stoking.

CHAPTER XIII.
BOILER EXPLOSIONS.

Cause — Spheroidal Condition of Water — Water Purged from Air
• — Hydrogen Theory — Accumulated Pressure — Incrustations —
Deficiency of Water — Collapsing — Bad Management — Mr. Col-
burn's and Professor Airy's Theory.

219. Cause of Boiler Explosions. — Many theories have
been advanced to account for the sudden explosion of boilers :
such as (a) the spheroidal condition of water; (b) water
purged from air ; (c) the hydrogen theory ; (d) accumulated
pressure ; (e) incrustations ; (/) deficiency of water ; (g) from
collapsing ; (Ji) from bad management ; (i) from faulty con-
struction. The first three, a, b and c, are plausible theories.
There can be no doubt that the majority of boiler explosions
have originated in excess of pressure — the steam generated
to cause that excess arising from several of the circumstances
mentioned above.

Mr. Marten,* one of our most experienced engineers on
boiler explosions, says steam boiler explosions may be classi-
fied under two heads :

1. " Faults in the fabric of the boiler itself as originally
constructed, such as bad shape, want of stays, bad material,
defective workmanship, or injudicious setting.

2.' " Mischief arising during working, either from wear
and tear, or from overheating through shortness of water or
accumulation of scurf; or from corrosion, in its several forms
of general thinning, pitting, furrowing, or channelling of the
plates ; or from flaws or fracture in the material, or injury
by the effect of repeated strain; or from undue pressure

* See Records of Steam Boiler Explosions, by E. B. Marten, of
Stourbridge, Spon.

THE SPHEROIDAL CONDITION OF WATER.

107

through want of adequate arrangements for the escape of
surplus steam."

Experience shows the need of greater care in construction
to provide proper stays to ends; the want of stronger guards
to man holes to prevent the edge of the plate cracking with
the extra strain upon it, and the necessity of hoops or other
means of strengthening weak internally fired tubes ; and the
greater care in executing repairs so as to restore the strength,
and with sound workmanship to prevent the leakage from
corrosion so often found in boilers repaired with rough screw
patches.

220. (a) The Spheroidal Condition of Water.* — If a
drop of water be thrown upon a very hot plate, as the top
of a cooking stove, it will immediately assume a spheroidal
shape, and roll about the plate ; while if the plate be but
warm, the water will spread upon it, and soon evaporate in
steam. In the former case, the small spheres of water do
not even reach the boiling point, but between them and the
hot plate are small cushions of steam, which buoy up the
spheres and keep them from coming in contact with the hot
plate. Each sphere, as it were, projects
from its surface vapour which repels
the hot plate; but the moment they
spread abroad upon the hot surface they
disappear as steam. That steam in con-
siderable quantities may be thus formed
can be easily illustrated by experiment.
Suppose that A is a copper vessel, with a
small glass tube passing through the cork
in the neck ; place under it a spirit
lamp S L; when the vessel is heated,
pour a little water, W, into it, it will
immediately assume a spheroidal condi-
tion, the small quantity of steam de-
veloped while it remains in that state
passes through the tube. Let us remove the lamp, then
the moment the copper is cooled down sufficiently the
water loses its spheroidal form, spreads over the copper, and
a large quantity of steam is developed, sufficient to drive out
* See Tyndall's Heat as a Mode of Motion, 4th Ed., pp. 154 to 162.

198 STEAM.

the cork with great violence. Applying this to the case of*
boilers, it will bo seen that if from lack of feed the water
in a boiler should assume a spheroidal state, that an explo-
sion must inevitably follow; for as the furnace cools and the,
water spreads over the plates, a larger amount of steam will
be developed than can pass the safety valve.

221. (6) Water Purged from Air. — All water holds air ;
boiling sets it free. We may see the air bubbles rise if we
watch heating water ; this air increases the ebullition. When
air is removed the atoms of the water more firmly lock them-
selves together, or the cohesion of the particles is increased —
the cohesion is so augmented that the temperature may be
raised 30° or 40° 0. above the ordinary boiling point without
producing ebullition ; but when ebullition once commences,
the whole of the excess of heat is consumed in converting
the water into steam, and an explosion follows. Many loco-
motive boilers have exploded on quitting the shed. It lias
been suggested that the cause of this may be found in. the
above statement. The water has been purged from air by
previous boiling, and when the fires were got ready for a
journey, they, instead of generating steam, stored up a laruv,
excess of heat in water possessing a high cohesive power, so
that immediately the stop valve was opened, the equilibrium
was disturbed, the cohesion gave way, and the excess of heat
stored up produced steam sufficient to cause the explosion.

222. (c) The Hydrogen Theory. — Water consists of
hydrogen and oxygen. One pound of hydrogen combining
with eight pounds of oxygen would form nine pounds of
water. It has been suggested that when water comes in con-
tact with red-hot boiler plates, it is decomposed and separated
into its constituents of hydrogen and oxygen, and that imme-
diately the hydrogen is formed it explodes. There are serious
objections to such a theory, not the least is that before the
hydrogen explodes, it must be mixed with a due proportion
of oxygen or air ; again, it has never been proved that decom-
position does take place under such circumstances. Water
in contact with hot plates is converted into steam, which is
quite capable of causing any explosion.

223. ((/) Accumulated Pressure. — Accumulated pressure
is the cause of ninety-nine boiler explosions out of a hundred.

INCRUSTATIONS; lOO

An active fire under a boiler will generate a very large quan-
tity of steam, and if proper provision be not made for its

i} by means of the safety valve, etc., mischief must
follow. If the safety valves should be too small — if they
should get jammed on their seats — if they should be tied
clown or overloaded, for some enginemen have been found
mad enough to do that — injurious results will certainly follow

xcessive aggregation of steam. If, also, in getting the
steam ready, time after time, the boiler should be put to an
excessive strain by the safety valve being loaded too heavily
or not acting properly, the time must come when the enor-
mous elastic pressure of the steam will be greater than the
tensile strength of the boiler, and an explosion will take
place. A very large class of accidents have occurred through
the safety valve not acting, or not being large enough in pro-
portion to the evaporating power of the boiler. We have*
alluded in another place to the rapid manner in which steam
pressure accumulates when an engine is standing still and
the fires kept up as usual. When boilers burst from ex^
cessive pressure, the parts that give way are either those
immediately over the furnace, the flat ends, or where
water has been allowed to rust away the plates through
faulty setting, etc. The best security against excessive
pressure will be found in having boilers of maximum
strength and the best form, with good appendages, as safety
valves, etc.

224. (e) Incrustations. — Incrustations have been the
cause of boiler explosions, as already referred to, when speak-
ing of the salting of marine boilers. As gypsum, lime, salt,
etc., are deposited internally upon the plates of a boiler, they
form a solid hard crust. Let us suppose such a crust to be
formed. It is sometimes deposited very rapidly; and con-
sisting of earths, the incrustation is a very bad conductor of
heat, consequently the boiler plates will become red-hot
without transferring the motion to the deposit. When the
boiler plates become red-hot, the incrustation will probably
separate from the iron, through the latter expanding more
than the former; the consequence will be that the water will
ch the plates, and a sudden generation of highly elastic

a, in greater quantities than the safety valve will allow

200 STEAtf.

to pass, will cause a tremendous explosion, with consequent
loss of life and property. It is of course quite plain that the
part of the boiler likely to give way under these circum-
stances, will be the softened plates above the furnace. When
heated like this, they lose five-sixths of their strength. In fact
they will be driven into the furnace or collapse. The remedy
against incrustation is a proper amount of blowing out and
chipping off of the hard substance as it accumulates.

225. (/) Deficiency of Water. — From what was said
under 5, it is quite possible that from lack of a due supply
of water that the remainder in the boiler may assume a
spheroidal condition, which must result, when the heat
decreases, in an explosion. Such a result can hardly be
brought about if the least attention be paid to the water
cocks, the feed pumps, and the glass water gauge. Sufficient
water must always be kept in the boiler to cover every part
in immediate contact with the heat. Should these parts get
hot, as was mentioned above, they lose five-sixths of their
strength, and only one-sixth of the ordinary strength of the
boiler will be an insufficient safeguard against an explosion.
Should the engineer lose his water, he must not attempt to
open the feed valves or cocks — many a life has been thus need-
lessly thrown away to save a little scolding or dismissal. It
is a thousand times wiser and more manly to face these con-
sequences, than to risk life, limb, and far greater punish-
ment. When the valves are thus opened, a great amount of
elastic steam is immediately developed, and the softened
plates give way. Therefore risk no life, open the fire doors
and take out the fires, and then gradually ease the safety
valves. Fusible plugs are a good preventative against acci-
dents happening from a deficiency of water.

226. (y] Collapsing. — A boiler or flue is said to collapse
when it gives way to exterior pressure, or from the air or
steam acting against a vacuum or partial vacuum. In
such cases the steam enters the flues, and scalds and de-
stroys everything in the engine room. A partial vacuum
has by some means been created in the flues, then the
pressure of steam within the boiler has driven in the plates
of the tube, and an explosion has followed, or the iron has
become softened and worn, and the pressure being greater

THEORY OF BOILER, EXPLOSIONS. 201

than it can bear, the explosion has happened. To avoid
danger from this cause, the flues must be properly con-
structed, stayed, and strengthened by rings of strong angle
iron at every 10 feet. They must be round, not elliptical.
The vacuum valve must be kept in working order to prevent
boilers collapsing.

227. (A) Bad Management. — As long as ignorant and
careless men can obtain charge of boilers, accidents will
certainly happen. Let us hope that, as education spreads —
it has perhaps now a fair chance — no such persons will find
employment where so much depends upon their intelligence,
care, and attention. When men cease fastening down the
safety valve, either wilfully or by neglecting to raise it from.
its seat, and no more surreptitiously alter the weight, we
shall have fewer accidents. Such things have been done,
improbable as they may appear — the American phrase of
sitting on the safety valve is too true. Ignorance leads to
most accidents. It was only a few years ago in Plymouth
Sound, that on board one of H.M.'s vessels the water was
lost through the gaiiges not acting properly, when the
engineer, aware of what was the matter, ignorantly turned
on the feed instead of taking out the fires. The remedy for
bad management exists in education. But excellent authori-
ties say, that the introduction of cold water has nothing to
do with the explosion when plates are overheated, for they
say the water is introduced at the bottom, and only rises
slowly over the surface, and gradually cools it. The experi-
ment of putting cold water into red-hot boilers has been
repeatedly tried without producing any explosion.

228. (i) Mr. Colburn's and the Astronomer-Royal's
Theory of Boiler Explosions can hardly be called a theory
on explosions, but rather a theory to account for the large
amount of mischief that a boiler explosion creates. Mr.
Colburn is of opinion that boiler explosions take place at
but little above ordinary pressure by the rupture of a defec-
tive point close to the water line, the defect being generally
caused by corrosion ; that as soon as the rupture takes place,
immediately part of the steam escapes ; instantaneously, as
the pressure is taken off the boiler water, the large store of
heat in the water above the boiling point generates a large

202 &TEASL

amount of steam, which is at once disengaged. This large
quantity of suddenly formed steam forces off the upper shell
of the boiler, and causes all the mischief that follows. So
that the mischief is not done by the steam that was in the
boiler at the moment of explosion, but is done by that which
is created during the moment of explosion. This creating of
steam takes place throughout the instant of explosion, its
elastic force gradually diminishing till the water reaches
100° C. From careful investigations it may be stated
roundly, that the explosive energy in every cubic fobt of
water in a boiler at 60 Ibs. pressure equals that contained iix
a pound of ordinary gunpowder;

EXAMINATION QUESTIONS,

1. What are the chief causes of " boiler explosions?" What is
the hydrogen theory?

2. State distinctly what you mean by the "spheroidal condition
of water," and water purged from air. How have these theories
been connected with boiler explosions ?

3. Show how accumulated pressure and deficiency of water act to
produce a boiler explosion.

4. Account for so much steam being generated and mischief done
by boiler explosions.

5. What distinction is there between a boiler exploding and a tube
collapsing ; state the precautions to be adopted in either case.

CHAPTER XIV.
PRACTICAL WORKING.*

Duties to Machinery when in Harbour and Getting up Steam —
Starting the Engines — Under Steam — Fires — Bearings — Engines
in Port — Lap on Slide Valves — How to Set the Slides.

229. 1. Duties to Machinery when in Harbour before
Getting under Steam. — When an engineer takes charge of
the machinery of a boat, his first attention ought to be
directed to his boilers; for, being the source of power, they
may become the source of great danger if not properly looked
after. In inspecting the boilers three things require especial
notice: — (1) The thickness of the plates above the fires and
other places of importance; (2) the state of the stays; (3)
the position of the gauges, viz., the water gauge, cocks, and
glass water gauges.

(1) Respecting the first, a general plan is to drill a small
hole through the plate, and thus find its real thickness, for
it is often the case that a boiler plate may be far thicker at
the seams than in the middle. At the seams the proper
thickness cannot always be correctly ascertained on account
of the way in which they are caulked, by which a plate may
appear considerably thicker than it really is. After the hole
has served its purpose, it is tapped and plugged tightly tip
again.

(2) As regards the stays, they require a great amount of
attention ; for they are very apt to get eaten through near
the plates by oxidation.

(3) The gauge cocks are often placed just above the
highest row of tubes. Now this is a very dangerous practice,

1 it is possible for an engineer to lose his water, let him be
* AVritten by a Worldng Man.

204 STEAM.

ever so careful, when great clanger follows; while if the
cocks were placed a little higher, the loss of water would
not be necessarily followed by so much danger.

230. 2. Duties to Machinery when Steam is Getting
up. — The water in the boiler when the fires are lighted
ought to be just above the bottom of the glass. In a
large, or even moderate sized boiler, the water will expand,
and there is also not so much water to heat at first; and
we know, by reason of conduction and radiation, that small
bodies of water are heated comparatively more rapidly
than large. On first lighting the fires they should not be
kept too large, but just sufficient to cover the bars. A
large thin surface of fire is found to be the most effective on
getting under weigh.

When the fires are lighted, and the steamer is going on a
long voyage, it is the practice to rub the polished parts of
the engine over with a composition of tallow and white lead.
This prevents any rust forming on the rods, etc., from water
dropping on them which may have been used for keeping
the bearings cool.

The discharge valve is also opened now, or else on starting
the engine something will give way. Several accidents have
occurred by neglecting to do this.

The safety valves are now to be inspected to find out
whether they are fast corroded to their seatings. If so,
they must be freed and made ready to act before starting.

It is a good plan, and one much practised, to give the
engines a good blowing through whilst the steam is getting
up. This warms the cylinder, and tries any joints that may
have been made since the engines were worked last. It also
saves the steam, for if not done now (when the engine is
starting), a great amount of steam is wasted in heating the
cylinder instead of imparting its elastic force to the piston.
It is thus that boilers are sometimes taxed beyond their
powers, and the steam pressure reduced to perhaps a very
dangerous point.

231. 3. Starting the Engines. — All ships are now fitted
with the double eccentrics, or " Stephenson's Link Motion,"
by which the engines are started, or rather by this the slide
valves are under the command of the engineer, and can be

THE BOILER. 205

worked back or forward as command be given, by either a
bar, lever, or generally, in large engines, by a wheel.

The handles, by which steam is turned on and off, with
the injection cock handles, are placed beside the wheel, so
that one man can now generally start the engine.

Some large ships have a steam piston so fitted that it rises
and falls by steam admitted above or below, thus rising or
lowering the link in its motion. This is what is called steam
starting gear, and is very handy when the link is of great
weight. There is always hand gear fitted as well, which can
be used in cases of emergency. In giving injection to a
common condenser, it should be opened just after the steam
is turned on to the cylinders, or else if going slowly the
condenser may become too full of water, and the air pump
not able to perform its work properly.

In starting an engine that is fitted with surface condensers,
the only thing requiring attention before going on, is to open
both valves communicating with the sea above or below the
condenser, viz., suction to the circulating pumps and de-
livery from them.

DUTIES WHEN UNDER STEAM.

232. The Boiler. — Always keep looking at the water level.
This is oftentimes a source of great anxiety, for some boilers
require the water to be kept at a certain fixed level. If
water be too high they will not keep steam, and if too low
the steam will generate too fast. Some boilers require a
high water level, others a low one, in fact no general rule
can be given for the water level, nothing but practice can
determine it. A safe rule is to keep the glass water gauge
about two-thirds full.

Blowing out marine boilers should be practised about
every two or three hours. Practice has proved this to be a
good rule, on account of not so much water being required to
be blown out at a time, and therefore the steam pressure is
not reduced to a very great extent.

In steamers fitted with surface condensers, a little sea
water is supplied to the boilers to make up for the loss
in the steam pipes, jackets, leaks in the condensers, etc.
This iu time may injure the boiler if not counterbalanced

200 STEAM.

some way or other. The general plan is to blow out about
two or three inches every twelve hours. The water in these
boilers is never allowed to reach more than -^ of saltness.

The fires require much consideration. A furnace is best
worked with a heavy fire, but not too heavy, thicker to-
wards the back than front. The fresh fuel should be placed
in front, and then pushed back after being thoroughly heated.
Every four hours (at the least) the fires should be cleaned
out, as large clinkers or refuse of the coals adhere to the fire
bars and prevent the draught, making the fires burn dead,
especially towards the back of the furnace. Sometimes the
slag will stick fast to a furnace bar, and cannot be removed
from it. This causes a great amount of trouble, as in trying
to remove it, the fire bars are occasionally pulled out of their
places, and the greater part of the fire falls through, causing
much waste and often danger.

The principal thing to pay attention to when the engines
are under steam, is to keep the bearings cool and the glands
steam tight. Oil is generally used for keeping bearings cool,
but when larger ones are working hard, a jet of water is kept
playing upon them. This is found to answer very well when
the water is turned on before they have had time to heat.
It should not be used after they have been allowed to get
heated, for it may crack them by too sudden contraction.
A good stream of water should be kept running on the thrust,
block from the time of starting, this with the tallow, which
is always put into it before starting, keeps this all-important
bearing cool. The cap of the thrust block requires great
care in adjusting. If screwed on too tightly it is almost sure
to heat or fire, as it is termed, and if not screwed down
sufficiently tight, the unpleasant jumping shake so often
experienced in our screw ships is sure to follow.

The packing of the gland at the stern tube should be well
looked after, and kept quite tight and well tallowed.

In paddle wheel steamers there is frequently not sufficient
care taken about the outer bearing of the shafts. In very
few ships are proper means provided for lubricating these im-
portant parts. At the commencement of a voyage, the outer
bearings are well tallowed, and often put down, screwed up,
and left to look after themselves as best they may. Very

DUTIES TO MACHINERY. 207

few ships, indeed, being provided with tubes leading down
from the paddle boxes to the oil holes of the blocks, or in
which means are provided for their lubrication.

The coals in the bunkers must be carefully watched, to
prevent spontaneous combustion. The stoppers over the holes
should be kept open as much as possible, and care taken not
to keep damp coals longer in the bunkers than can be
avoided; for it is only damp coal that is liable to spon-
taneous combustion. f

In new fast running engines castor oil is a very good thing
to use on first starting. When new brasses have been fitted
into the bearings, till they form a good bearing for them-
selves, the same should be used. It appears to have a much
firmer body in it to lubricate than all other oils have. The
difference in the cost of the oil is not very much, coarse castor
oil being very little dearer than good machine oil.

233. Duties to Machinery when the Ship has Arrived in
Port. — The white lead and tallow should be rubbed off with
a piece of oily waste, and then the bright work of the engines
will give no trouble by rusting.

The engines should have a good blowing through to drive
out all water in the condensers, then the Kingston's valves,
communicating with the sea, should be shut, next open the
condenser drain cocks, which will drain out all the water left
in them. This is allowed to run into the bilges, which can
be pumped out by the donkey pump or the hand pumps if no
steam is left in the boilers.

Some engineers always blow out their boilers after steam-
ing, others do not, the latter only let the fires out and shut
the valves in the steam pipes ; both plans have their advant-
ages and disadvantages. Perhaps the majority keep the
water in the boilers, only blowing out when repairs or an
examination of the boiler is required. An engineer should
always examine for himself whether all the fires are properly
out, and not take the word of the stokers for it. A great
amount of damage may be done by the fire not being properly
put out in the ash pits. A frequent practice is to get a heap of
hot ashes together and dash some water over it ; this makes
it black outside and leaves it burning inside. The ashes
should rather be spread out evenly, and then water thrown

208 STEAM.

over gradually and gently to put the fire out effectually, and
to create as little dust and dirt as possible.

234. To Find the Amount of Lap on the Slide Valve (before
setting the slides). — Take a batten of wood, and place it on
the cylinder slide face at right angles to and over the ports.
Mark off on it the edges of the steam and exhaust ports with
a square and scriber. By placing this on the face of the
slide -valve, the amount of the lap can be at once found.

235. To Set the Slides. — Put the piston at the top or bottom
of its stroke. If the eccentric is rightly fixed on the shaft,
simply fasten the slide valve on the spindle with the required
amount of lead. Then turn the engine to the other end of
its stroke, and see if the lead is the same ; or in some engines
more lead is given at the bottom than at the top (as in ver-
tical engines). If the engine is fitted with the link motion,
the reversing eccentric is then connected and the valve tested
in like manner. Also with the link motion, the slide rod is
placed in the centre of the link; and although the position
of the eccentrics on the shaft ought to destroy any motion of the
valve, yet there is a little with a short link. This is tested
to see that the steam ports are always closed, and thus the
engines can be stopped, even if the full pressure of steam be
admitted to the back of the slide by the stop or throttle
valves.

EXAMINATION QUESTIONS.

1. Describe briefly the duties to the machinery when in harbour
before getting under steam, that require the attention of the marine
engineer.

2. To what must an engineer particularly direct his attention while
getting up the steam ?

3. When a vessel is under steam, what will then claim the especial
attention of the engineer ?

4. When a ship is to be laid up in harbour, how must the engines
be left ?

5. Show how to set the slide valves, giving the proper amount of
lap and lead.

CHAPTER XY.
THE INDICATOR,

Description — Use — Diagram — Diagrams under Various
Circumstances.

236. The Indicator, an instrument invented by Watt, is
used to ascertain the internal condition of the engine, the
state of the vacuum, the amount and variations in the
pressure of steam at every point of the stroke, the cushion-
ing, the condition of the slides, whether there be too much
or too little lap or lead, whether they are leaky or properly
set, whether ports are closed and opened at the proper time,
in fact, it tells us the power and all the faults by which
that power is impaired. It may also be attached to the air
pump, the hot well, the condenser, etc., when it will tell us
the nature of the pressures there existing. It has been very
much modified since the time of Watt, to better adapt it to its
purpose. The figure given of it is from one of Richard's
indicators, which exhibits the latest improvements.

In its simplest form, the indicator consists of a cylinder
with a piston, the top being open to the atmosphere, and a
spring to keep the piston down to its work. A diagram is
taken on a piece of paper to tell us all we wish to learn.
This piece of paper is fastened round a barrel, which moves
through nearly a whole revolution and back again as the
engine makes one stroke.

The figure is a representation of Richard's indicator. A
is a screw to fasten the indicator into the cylinder. The
handle is to open the connection between the cylinder and
the indicator, and thus allow steam to enter B D, the cylinder
of the indicator. The piston a and piston-rod b of the in-
dicator are shown by dotted lines. The slanting dotted lines

210

STEAM,

are intended to show the spring which keeps the piston down,
and against which the steam has to act in forcing up the

INDICATOR.

piston a. In the actual indicator, the piston is not so simple
as shown here, but is conical and truncated; B C is the
barrel round which the paper is wrapped. The graduated
scale is to measure the pressure of steam and the vacuum.
Within this barrel is a spring, so that when the barrel has
moved nearly round once while the piston goes up, the force
of the spring causes it to return as the indicator piston goes
down. Hound the pulley /Qc passes a string to give motion
to the barrel. This string is attached to the crosshead of
the cylinder (or the radius bar), and the motion is reduced in
its travel to suit the card barrel. While the piston of the
indicator moves up only one to two inches, the piston of the

THE INDICATOR. 211

cylinder moves several feet. The barrel lias to move round
four or five inches in the same time. The motion is reduced
by levers, when taken from the piston crosshead. If the
length of the diagram be three inches, and the stroke three
feet or thirty-six inches, we have only to proportion the
levers as 3 :36 or 1 : 12, and the required motion is found.
The indicator barrel is moved round by the string (shown in
the figure, being attached to its proper relative position on
the lever, and) actuating the pulley f G and with it the
barrel. The arm H H is to carry the parallel motion
I k L M, the pencil being at p. The reason of this arrange-
ment, i.e., of having a parallel motion, is that while the
stroke of the indicator is (say) only from 1 to 2, the pencil
is required to move up and down from the lower 15 to (say)
25 on the scale. The head of the indicator piston-rod being
attached to the lever M L at Z, multiplies the motion of
the indicator in the proportion of M Z to Z L. In Hichard's
indicator this multiplier is about three and a half; in fact,
this is the essential difference between Hichard's and other
indicators, such as M'Naught's, Maudslay and Field's, etc.,
that the motion is magnified, and therefore the pencil more
sensibly indicates the least variation of pressure or action.

The action of the indicator must now be traced. Suppos-
ing the indicator is attached to the cylinder, but not placed
in communication with it by turning the handle, and that
the cord c is fastened to a lever at the head of the piston-
rod, then it will move the barrel from right to left, and a
straight horizontal line will be drawn by the pencil, as A B
in next figure — it is generally customary to let the pencil
mark this line several times. The line is called the atmos-
pheric line, because it coincides with the atmospheric pressure;
all parts of the diagram above that line show pressure above
the atmosphere, all parts below it show the vacuum, hence
the top part of the diagram is called the " steam " and the
bottom the " vacuum." Again : supposing the barrel were
still and the steam admitted to the indicator, the pencil
would be driven straight up, or a vertical line would be
traced. We see that if the barrel only move a horizontal
line is traced, while if the indicator piston only move a
-ertical one is made; therefore when both move together wo

212 STEAM.

shall have a line compounded of the two motions, and if the
one is continually changing, it will not be a diagonal motion.
Let us suppose the indicator is attached to the top of the
cylinder, and that steam enters the upper port e as the piston
comes to the top of its stroke. The moment steam enters
the cylinder it drives the piston down, but at the same time it
enters the indicator, and drives the piston of the indicator up.

EC.-

DIAGRAM.

Let us suppose the pencil (when air is in both sides of the
piston) stands at A on the above figure, then the line A B,
which will be traced by the barrel moving nearly the whole
way round, is the atmospheric line. Now let us suppose the
top port e opened at the instant the tap of the indicator
is turned, then steam will rush in, in the direction shown
by the arrows ; in the direction y to drive down the' piston,
and in the direction z to drive up the piston of the indicator.
Steam coming in instantaneously drives up the pencil, and
the line from A to C will be drawn (C is called the starting
corner). Now steam continues rushing in at its normal
pressure and the piston of the engine goes down, while on

THE INDICATOR. 213

the indicator piston the pressure is continuous, so therefore
the pencil remains at the same height, and as the barrel
moves round the line from C to D is drawn. When the
pencil gets to D the slide has come down again and closed
the port,* so that the steam is left to expand ; and of course
as it expands its pressure decreases, the engine piston con-
tinues to go down, and the pressure, becoming less and less in
the indicator, the pencil gradually falls lower and lower to E.
When it gets to E, the slide still falling, the upper port e is
opened to the exhaust, and the steam rushes out in a con-
trary direction to the arrows, the pencil therefore im-
mediately falls to F (the eduction corner). Now there is a
vacuum above the piston of the engine, and below that in the
indicator, and the engine piston begins to rise up, all the
time it is rising there being no steam or pressure in the
indicator (or less than no pressure), the pencil having fallen
to its lowest point is still, and traces the vacuum line F G to
the lead corner G. Against the pencil gets there, the piston
has arrived at the top of its stroke, the cushioning then takes
place, and the pencil rises at once to A, or else the lead comes
into action by the rising of the slide, and drives the indicator
piston, and with it the pencil, to A.

The action of the indicator has been traced through an up
and down stroke, or a complete revolution of the crank, and
we see that the varying pressure in the cylinder is faithfully
translated by the indicator and' rendered visible to the eye.

The indicator is absolutely necessary if we are to know the
pressure of steam when it is performing its work. The
Bourdon gauge or other contrivance, when correctly graduated,
will always tell the boiler pressure, but it must be well un-
derstood that the boiler pressure seldom or never corresponds
to that in the cylinder, it is less in the cylinder. This reduc-
tion of pressure is due (1) to the friction caused as the steam
passes along the passages; (2) to radiation; (3) to loss of
power which arises when the passages are contracted; (4) when
there is a bend in the pipes and waste of steam : of course all
these causes of loss may not exist in every engine, but some

* We are supposing a long D slide is used. In reading the para-
graph, the student must consider both this figure and the last on
page 210.

STEAM.

of them certainly do in all. This diagram (page 212) is sup-
posed to be taken from the top of the cylinder, and the arrows
show the direction in which the piston of the engine is moving
when that part of the diagram is being traced. The dotted
diagram shows one taken from the bottom of the cylinder.

The indicator diagram, as we have intimated before, is
the only true way of ascertaining the action of the steam
inside the cylinder. The corners of the diagram are the
points to which attention must be directed to find out any
defects. In the diagram from a non-condensing engine, the
whole of the curve is above the atmospheric line; but in a
condensing diagram part is above the atmospheric line and
part below.

This is the normal slide diagram, and all condensing engines
in good working order with slides properly set and rods of
correct length, should give a similar diagram. We will note
what the change would be under certain conditions.

If the curve in starting from A ran to the left of C instead
of vertically, then we should know that the steam was late
in its action, or the slide (the long D) was not high enough
at the proper moment. If the curve at E were a little higher
and a little farther to the left, the exhaust would take place
too early, or the upper part of the slide would be too low.
Both the changes would take place through the slides being
too far down in the casing, or if the slide rod or eccentric rod
ivere too long. Such an evil would also be shown by the
diagram being fuller at G, or coming a little farther to the
left, and the steam would be cut off too soon at D.

If the slide rod be too short we shall have the exact opposite
effects, through it keeping the slide too high in the casing.
The upper part from A C will fall to the left at the top
and be longer from C to D, fall down lower at E, and a large
amount of cushioning will take place at G, through the port
being closed too soon, to the exhaust.

If the stop on the eccentric be too far forward we have a
diagram something similar to that given when the slide rod
is too short, because all the movements of the slide are too
early, but the corners will be sharp and angular instead of
round. There is a distinction between this case and the cases
where the eccentric rod is too long or too short. In the

THROTTLING AND EXPANSIVE WORKING. 215

case under consideration the same fault would exist in the
diagrams taken from the top and bottom of the cylinder,
but when the slide rod is in fault the opposite defects would
exist at top and bottom.

If the stop on the eccentric be not sufficiently forward the
diagram will be too full at every period, because all the
motions of the slide will be too late.

237. Throttling and Expansive Working. — If two
diagrams are taken from an engine under these two circum-
stances: first, when the steam is throttled; and second, when
the expansion valve is used; it can easily be shown that it is
far more economical to work steam expansively than thrott-
ling it; in other words, when the steam is throttled or wire-
drawn, a greater quantity is used and less work is done by
it. In throttling, hardly any of the curve will rise above the
atmospheric line, while the vacuum will be pretty full, and
show a large amount of cushioning; in expansive working the
steam line will suddenly rise to a good height, and the expan-
sion rapidly fall; and at the point E (p. 212), where the port
is opened to the exhaust, it will be found that with thrott-
ling, the line is much higher than when the expansion gear
is used, showing that there is more steam in the cylinder in
the former than in the latter case. Hence, it is always more
advantageous to use the steam at a high grade of expansion
than to throttle it.

(a) Let us suppose, for instance, that the steam is too late
for its action, or, in other words, that the piston commences
its stroke by the momentum already imparted to the engine
instead of the slide valve admitting steam through having the
requisite amount of lead. We then have, instead of an upright
line A C, a line A B slanting
towards the motion of the in-
dicator barrel. Therefore, when-
ever we find a diagram with
a line in the direction A B
instead of A C, we conclude
immediately that the steam is FIGURE 1.

too late for its action. This is corrected by advancing the
eccentric a little farther in the same direction as the motion
>f the crank, or else giving more lead to the slide. When

oi the

216

STEAM.

the slide rod is too long we have almost a similar diagram,
the steam line B D is too short while the exhaust line E A
is too long, so that steam has too short a time for its admission
and too long a time for eduction.

(b) Let us now examine the annexed figure, by looking at
corner A, which is termed the Cy
lead corner, we can tell whether
the lead be too great or properly
proportioned. A defect is ex-
hibited when instead of a

vertical' line A C being drawn

FIGURE 2.

Steam in this case enters

a line B C is drawn slantin^
off from the motion of the barrel,
too quickly. The rounding of the corner A generally exhibits
the cushioning. To remedy the defect of steam entering too
soon, less lead must be given to the slide. Had the steam
line C D been too long as well as the exhaust line E B too
short, the proper remedy would have been to lengthen the
slide rod. For these are the two defects shown by a diagram
when the slide rod is too short. A somewhat similar defect
would exist if the stop on the eccentric were too far ad-
vanced, every action of the slide would commence too soon.

(c) A good corner at the end of the full steam line, in-
dicates a good arrangement for expansion, as point D in fig.
1. Too gradual a descent from it shows that some steam
entered after it ought to have been totally cut off.

(d) A good horizontal line on the top of the diagram as
far as the expansion point D (in fig. 1), shows that steam
has free entrance to the cylinder, or, in other words, that the
steam pipes are of good size and A,.

the ports properly proportioned.

Should either of these be too small

for the size of the cylinder, the"

full steam line A C will gradually

decline from the steam corner A

to the expansion corner B. Then a FIGURE 3.

slanting line from A to B shows a defect in the ports or steam

pipe, for the full steam line A C should be perfectly horizontal,

or parallel to the atmospheric line, and not as shown by A B.

(e) A curve at the end of the expansion line before it

THROTTLING AND EXPANSIVE WORKING.

217

descends to the vacuum line, indicates that the slide valve is
a little opened to, or slightly placed in communication with,
the condenser, just before the piston has arrived at the end
of its stroke, or in fact that there is negative lead.

The two pair of high pressure diagrams, or properly,
diagrams from a non-condensing engine, below, are taken from
a pair of high pressure cylinders of lOJ inches in diameter.

HIGH PRESSURE DIAGRAMS.

Pressure of steam in the boiler, 75 Ibs; length of stroke,
1 ft. 8 in., making 150 revolutions per minute.

The first or upper card was taken from the leading engine,
which also works the pump ; the full pressure A B was allowed
for 3 J inches of the stroke, after which it was cut off by an
expansion valve at the back of the slide valve.

218 STEAM.

The second or lower card was taken from the following
engine, in which the steam A B was cut off after 2 £ inches of
the stroke were accomplished.

The leading engine is allowed ^-th of an inch lead by the
slide valve, and the following one ^Vnd.

The escape or waste steam is allowed to escape into a pipe
common to both engines, which accounts for the irregular
exhaust line ; but notwithstanding this, it is of ample size,
which is clearly proved by the exhaust line being for steam
of so high a pressure tolerably near the atmospheric line a a.
Slackness of cord as well as bad exhaust would cause the
irregularities in the lower lines.

238. Slide Diagram. — The slide diagram is omitted, as it
is perfectly useless and seldom now taken. It will tell you
nothing but what may be learnt from the diagrams taken
from the top and bottom of the cylinder.

239. Continuous Indicator. — Canon Mosley, Mr Bigg of
Chester, and others, have proposed continuous indicators.
The portion of the indicator showing the pressure and vacuum
in Mr Rigg's arrangement, is made exactly like the ordinary
indicator, with its pencil resting on a continuous web of
paper moving slowly. Suppose the pencil to have marked the
atmospheric line : the tap is so arranged that it can be opened
say during three strokes, and then remain closed for 100 or
1000, or any other pre-arranged number. The diagram so
taken consists of a succession of short strokes, across the
diagram runs one long line representing the atmospheric line,
and at right angles again are short vertical lines showing the
highest steam and lowest vacuum pressure at every 100th or
1000th stroke of the engine. The hours can be marked on
the card, and the number of revolutions in the interval
is easily ascertained according to the spaces into which the
atmospheric line is divided. An ordinary diagram, whose
steam and vacuum line correspond to any one stroke, will
give the basis for the calculation of the horse-power.

To shoiv how to Jlnd the horsepower of an engine from the
indicator diagram.

This figure consists of a pair of diagrams, one taken from
the top the other from the bottom of the cylinder by Richard's
indicator. The engine is by Maudslay & Co. (600 II. P.) : —

CONTINUOUS INDICATOR. 210

I t I 1 I I I I I i i _i i i I I I i i i i i.-i_t I i y i i i t.i I i i i t i i it
If-1 /i i +$£ l>& t & J4- fi ' «' /5

25 75

- 23-31

1220 STEAM.

2 cylinder, 76 inches in diameter, area — 4536*46; 3ft. 6 in.
stroke; 51 revolutions: 23*3 is the mean pressure as per
diagram.

To find this mean pressure we have drawn across the
diagram ten equi-distant lines. Then, in each case, taking the
length of the perpendicular lying between the steam and
vacuum lines, and applying them to the scale, we find the
pressures are 25 -75, 28-5,28-5, 28, 27, etc., which give an average
pressure of 23*92 Ibs. for the down stroke, and 22*7 Ibs. for
the up stroke, and a mean of 23*3 Ibs.

Therefore the indicated horse-power will be
4536-46 x 23-3 x 51 x 2 x 3j

33000

= 1143 '9 for one cylinder.
= 2287 '8 for two cylinder.

Notice here how widely different the nominal or mercan-
tile horse-power 600 is from the indicated 2288.

240. Dynamometer. — The dynamometer is an arrange-
ment for determining the power exerted by an engine. It
exists in several forms. In one form it consists of two
flat metal springs joined at the ends by links; the machine
or engine is applied to separate the springs. The wider they
are separated the greater the power of the machine. The
power is indicated on a dial plate.

To ascertain the power exerted by the engines of a screw
vessel, the thrust of the screw is made to bear upon the
fulcrum of a lever of the second class; by receiving the force
near the fulcrum, and having a long arm for the weight, the
force exerted by the screw is thus decreased in a great and
easily ascertained ratio, somewhat after the manner by
which in the weighing machine a small weight in the
machine house balances a considerable one on the platform.
A pulley on the shaft turns a barrel on which is fixed a piece
of paper, while a pencil, moved backwards and forwards by
the varying thrust of the screw, exhibits to the eye the
power of the engines.

The force driving a paddle wheel engine is measured by
a dynamometer fixed on shore, a rope being carried from the
vessel and fastened to the dynamometer, when the engines
are set to work and their tractive force ascertained precisely

FRICTION DYNAMOMETER.

221

as in the last case. The use of the dynamometer has greatly
furthered the mechanical improvement of screw engines, by
enabling us to estimate the thrust of the screw, and thus
ascertain if any large amount of force is being wasted.
General Morin states that a good dynamometer should have
(1) sensibility properly proportioned to the intensity of the
efforts to be measured; (2) the indications of the flexures
should be placed beyond the chronic influences of the
observer and must be given by the instrument itself; (3) the
observer should be able to estimate the effect at every point
of the path of any curve made by the instrument ; (4) the
apparatus should be constructed so as to easily give the
total amount of work expended by the engine or machine
under consideration.

241. Friction Dynamometer (Balk's). — The friction
dynamometer is employed to ascertain the horse-power of
an engine by the friction. " The strap or instrument used
for producing the friction in Balk's dynamometer is connected
with the ends of an unequally armed lever, which causes any
shifting of the strap or instrument to increase or decrease its
pressure on the friction wheel, thus adjusting it so as to
produce the exact amount of friction necessary to keep the
load up." The instrument consists of a drum, which receives
its motion from a strap connected with the engine whose
power is to be tested.
On the same axis as
the drum is affixed the
friction wheel, the
periphery of which
is turned smooth and
true, on it works the • /,,
friction band, con- n\
sisting of a hoop of /
thin copper. On the /
inside of this hoop is /
fixed a lining of wood /
(generally beech) in £Jj
pieces; to the hoop is

fastened two plates, A ~c B

from which two straps run to the ends of the lever. To

222 STEAM.

one of the plates is attached, by means of steel straps, a scale
pan, into which is put the weights. Small weights are
added to each end of the lever, until the friction of the
band is so increased as to lift the scale pan with its
weight. The instrument is tested with various loads, and
a scale obtained.

f is the friction wheel, with the friction band b round it.
The drum is not shown in the figure. The lining of wood
attached to the friction band is indicated by the blocks in
cross section. The lever is A B resting on its fulcrum C ;
the straps are seen connecting the plates p and q with the
ends of the lever. The end A C of the lever must be slightly
longer than C B. The scale pan is shown at S.

The point of suspension p of the weight W must be kept
horizontal. The power required to maintain the weight in
the position in the figure will be the velocity of the point p
per minute multiplied by the weight, which will therefore
be equivalent to the units of work done.

Let us suppose the radius of the friction wheel is 2 feet
6 inches, the number of revolutions 100 per minute, and the
weight 100 Ibs., we can then find what the horse-power
will be.

Circumference of circle .......... = 5 x 3*141 G.

•. Velocity per minute .............. = 5x3'1416x 100.

. \ Units of work done per minute = 5 x 3*1416 x 100 x 100.

,. Horse-power = ***l™™*™ - 470.

To find what weight we must use to test an engine is
evidently the reverse of this. The horse-power must be
multiplied by 33,000, and the produce divided by the number
of revolutions of the dynamometer multiplied by the circum-
ference.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. How can it be ascertained by the aid of a slide diagram if the
stop of the eccentric is properly adjusted (1867) ?

2. Describe the indicator. Show how it may be used to find the
effective horse-power of an engine (1868).

EXERCISES. 223

3. Having given a normal indicator piston diagram, show what
change would take place in its form if the injection water be shut
off; or, secondly, if the steam be throttled (1868).

4. What kind of a diagram would be obtained if the gab lever be
too long ? What kind of a diagram is obtained by fixing one end of
the string to the crosshead of the slide (1868).

5. Describe the indicator for ascertaining the horse -power of an
engine. Draw the diagram which you would expect to obtain
from a condensing engine in good working order. If the slide rod
were a little too long, describe the changes which would probably
occur in the diagrams taken at each end of the cylinder (Honours,
1869),

6. Show by an indicator diagram the advantage of working ex-
pansively over throttling (1864-5-7).

7. In what cases would you consider it necessary to take a diagram
from the top and bottom of the cylinder, and how would you from
that diagram get the work developed in the up and down strokes
respectively (1865),

8. Give a description of Richard's indicator. Do you know any-
thing of a continuous indicator ?

9. Show clearly by an illustration how the horse-power of an
engine can be found from an indicator diagram.

10. Describe the dynamometer.

11. Show by an indicator diagram the advantages of working ex-
pansively over throttling (1865).

12. Sketch a normal slide diagram, and also a slide diagram with
the eccentric stop top advanced (1865.)

13. Explain the construction and principle of the indicator (1863).

14. Give an outline of a normal slide diagram, and show by a
corresponding diagram the alternation that would take place if the
slide rod were shortened (1863).

15. Give a sketch of a normal indicator diagram. What alternation
would be produced in the upper and lower indicator diagrams if a
portion of the lap were taken from the exhaust side of the upper
slide face, and the same amount added to the lower exhaust side
(1864)?

16. Explain the construction and principle of the indicator (1865).

17. Show by slide diagrams the advantages to be gained by ex-
pansive working over the throttling when making the same number
of revolutions (1865).

18. By what apparatus can you obtain a diagram on paper which
will inform you as to the amount of the pressure of the steam or
uncondensed vapour in the cylinder during each portion of the stroke
of the piston ? what would be the probable form of the diagram in a
condensing engine (1870) ?

19. Draw the indicator diagram which would probably be obtained
from the cylinder of a condensing engine, and explain how the changes
in its form indicate what is occurring in the cylinder at different parts
of the stroke. How would you calculate the horse-power from the
diagram (1870) ?

224 STEAM.

20. Draw the indicator diagram which you would expect to obtain
from a condensing engine when the steam is cut off at one-fourth of
the stroke?

21. Draw also the diagram which would be theoretically perfect,
and show from it that the amount of work obtained from the expen-
diture of a given quantity of steam is somewhat more than twice what
it would be if the full pressure were continued till the end of the
stroke (1871).

22. Draw the indicator diagram which you would probably obtain
from the cylinder of a condensing engine. How would the curve
change if the steam passage were opened too late and the exhaust
passage too soon ? Draw also the indicator diagram which would be
taken from the cylinder of a single-acting air pump. How would the
diagram tell you when the water was being delivered (Honours, 1871)?

23. Describe the indicator with a sketch, and explain its uses.
The steam pressure before expansion is 10 Ibs. above the atmosphere,
the steam is cut off at fths of the stroke, the exhaust commences at
i^ths, the cushioning at T^ths, and there is no lead ; represent the
diagram you would expect to obtain (1865),

24. For what purposes is the indicator applied to the cylinders of
steam engines? Trace the peculiarities in the curve arising from
expansion of the steam, eduction, cushioning, and lead (1866-7).

25. Explain the construction of the indicator, and show how it may
be employed to obtain the horse-power of an engine (1866).

26. What kind of diagram would be obtained at the upper and
lower ends respectively of the cylinder if the slide rod were shortened
(1866)?

27. What is the use of the expansion valve ? Show by a diagram
the pressure of the steam in different parts of the stroke when worked
expansively (1867).

CHAPTER XYI.
THE LOCOMOTIVE ENGINE.*

DIVISION I.

History — Trevithick's Model — Adhesion of Wheels to Rails, etc. —
Tractive Force — Murray's Engine — Hedley's Locomotive —
Stephenson's Engine : "The Rocket" — Blast Pipe — Trevithick'a
Claims — Contrast between " Rocket" and Modern Engines.

. Its History. — No sooner had Watt made his im-
provements in the steam, engine, than many thoughtful
persons began to consider the practicability of turning the
new invention to the purpose of locomotion on our common
roads. Even Watt himself, although bitterly opposed to the
scheme, because he thought such a high pressure of steam
would be required, produced improvements upon steam
engines which, in his own words, " are applied to give
motion to wheel carriages for removing persons, or goods, or
other matter from place to place, and in which the engines
themselves must be portable." His boiler was to be of wood
or thin metal, even earthenware and lead were used in early
boilers, as they never dreamed of a pressure much above that
of the atmosphere ; his fireplace was to be within the cylin-
drical or globular boiler; the steam was to be discharged
into the atmosphere, or else condensed by a curious arrange-
ment for surface condensation. Two cylinders were to be

* For writing this chapter on the locomotive, the valuable work of
Colburn on Locomotive Engineering has been freely and liberally
placed at the disposal of the author by the publishers, Messrs.
Wm. Collins, Sons, & Co. , of London and Glasgow. The author has

»t scrupled to extensively avail himself of the privilege.

226 STEAM,

used, double acting, the pistons and rods of which, by the
sun and planet wheels, converted the reciprocating rectilinear
motion into rotative ; toothed wheels communicated the
motion to the axle of the wheels. Mr. Murdoch, the foreman
of Boulton and Watt, better understood the locomotive than
Mr. Watt himself. A small model made by him is still in
existence. It is remarkable for its ingenuity. The piston-
rod was connected to one end of a beam, vibrating upon a
joint at the other, an arrangement known in a certain class
of engines as the " grasshopper." The chief pioneers in the
construction and invention of the locomotive were undoubt-
edly Trevithick in Cornwall, Hedley of Wylam, constructor
of the " Puffing Billy," Murray, Hackworth of the Stockton
and Darlington Railway, and Stephenson, who, with his
" Rocket," won the <£500 prize offered by the directors of
the Liverpool and Manchester Eailway in 1829 for the best
locomotive. The conditions of competition were briefly
these : —

(1) The engine must consume its own smoke ; (2) if the
engine weigh 6 tons, it must draw after it 20 tons 10 miles
an hour; the pressure on the gauge not to exceed 50 Ibs. ;
(3) there must be two safety valves, the engine and boiler
must be supported on springs and rest on six wheels, the
height of the whole not to exceed 15 feet to the top of the
chimney; (4) it must not weigh more than 6 tons, less
weight preferred, which may draw a less weight behind it,
then it may have four wheels ; (5) the price not to exceed
£550.

243. Trevithick's Model. — Trevithick made and worked
the first tramway locomotive. The annexed drawing repre-
sents a model locomotive made by him in 1802. The cylinder
standing vertically is within the cylindrical boiler. The
large wheel is a fly wheel, evidently worked by gearing all
of which is not shown. The small hind wheel is the driving
wheel, driven by the crank, as seen on the left side of this
wheel, the connecting rod coming down from a guide and
crosshead above the cylinder. Trevithick's arrangement for
the fire was to place it within the boiler. He employed a
" force draught " created by steam for working within the
chimney. His engine worked simply by the adhesion of its

ADHESION OF WHEELS TO THE BAIL3.

227

spur-coupled driving wheels upon the smooth surface of the
tramway. His flue returned from the back through the

IREVITHICK'S MODEL.

boiler, and the chimney went up by the side of the fireplace
in front.

244. Adhesion of Wheels to the Rails. — It was a great
difficulty with early locomotive engineers as to how they
should secure a proper amount of friction between a smooth
wheel and a smooth rail. Hence in early locomotive engin-
eering we find geared wheels to the locomotives working in a
rack on the tramway. A difficulty did or does exist, for at
slow speeds with full pressure of steam on the piston, it is true
that the ordinary adhesion of a single pair of wheels loaded
with two or three tons only is nearly useless for any prac-
tical purpose. From Mr. G. Kenme's experiments on fric-
tion and the testimony of practical men, it is found that
with extremely light loads upon the driving wheels there is
not sufficient adhesion. Were we now to employ weights of
only two or three tons upon the driving wheels of locomotive
engines when working at slow speeds, means would have to

228 STEAM.

be provided to prevent slipping. Who lias not seen the
driving wheel slip when the engine is starting 1 The adhe-
sion of the wheels to the rails is reckoned at from ~ih to yV^h
of the load, according as the rails are clean, perfectly wet,
perfectly dry, or partly wet.

It has been found that a maximum adhesion upon a clean
dry rail of three-tenths, and even three-eighths of the weight
on the driving wheels is occasionally attained. This, of
course, is much more than has been counted on by engineers.
A better knowledge than was formerly possessed as to the
amount of adhesion between the driving wheels and the
rails has led to the working of steeper inclines, until, as an
extreme case, loads have been taken in practice up gradients
of one in ten, and no inclination less steep than one in forty
is now considered a serious obstacle to the practical working
of a large traffic.

245. Tractive Force. — The absolute tractive force required
to draw a carriage over a good macadamized road is -^ of
the load, but in locomotives at slow speeds on level rails it is
considered to be about ^-^ of the load. But, of course, the
more rapid the speed the greater the tractive force required.
The resistance due to the atmosphere increases very rapidly.
It is from 12 to 15 Ibs. per ton on a train moving at the
rate of 30 miles an hour. At 44 miles per hour the resist-
ance to train and engine is about 24 Ibs. per ton ; at GO
miles, 29 Ibs. per ton. On rough roads the resistance due
to the atmosphere increases as the square of the speed.

The figure (p. 229) will show the arrangements practised
by a few early engineers for securing adhesion. Mr. Blenk-
insop, of the Middleton Colliery near Leeds, took out a
patent for increasing the adhesion of the locomotive by gear-
ing. The means he employed were a pinion working in a
stout rack-rail running along one side of the line of railway.
Murray's engine worked upon such a rack, as seen in our
illustration.

The longer the crank of an engine, and the shorter the
radius of the driving wheel, the greater the proportion of the
pressure on the pistons which will be exerted as tractive
force on the rails. The tractive force varies from 6000 Ibs.)
in the case of an express engine, to 20,000 Ibs. in the case of

a FORCE.

a goods engine, and these are not the extremes. Supposing
the speed of the pistons to be the same, the express engine

MURRAY'S LOCOMOTIVE UPON BLENKINSOP'S RAILWAY, 1812.

would move fastest, because its tractive force is quite suffi-
cient and the driving wheel much larger in diameter than
that of the goods engine. To exert a great tractive force the
driving wheels of an engine must, by their friction upon the
rails, have an adhesion equal to the tractive force. For
instance, if an engine is to advance, the tractive force being
9 tons, the driving wheels must not slip until the resistance
amounts to the same 9 tons. This adhesion is secured by
providing sufficient weight upon the driving wheels. On a
clean, dry rail as much as one-fourth, and even more, of the
total weight on the driving wheel is available for adhesion.
One-sixth is, considering the ordinary condition of the
weather and other contingencies, quite enough to allow.
When half wet the adhesion is less than when thoroughly
wet. They are, in fact, what is termed greasy, and we

str

must not reckon upon more than ono-to

246. Hurray's Engine.—

nuil tine,
f i ho

other* (To secure the greatest amou : of ei the

flue 'ought to have return c hud

>lo acting steam o the enda of iho putou-

rods working in guides, while the connect! i were

!t>d to cranks, which were made to v ri^ht

KOjriea K> Midi other two on each side tho online.

is the arrangement adopted in modern K
Murray has the honour of fire: it, Tho

cylinders were upright, and are seen i it ion

luUf immersed in the boiler. The crunks drove a tvvtl:i\l
wheel on each side the engine, each of theso two NY hods
geared into another twice the diameter. On r ; tho

larger toothed wheel was a coarse pinion (the on in tho

middle front of the fivu U worked in the rack laid

along the railway. The rack rail was a clumsy affair, ami

;'.v :\\v^::v :', v i-.s ;> • o.i •..; ; . /.v; i ,:•; - • •.>. ;•-> i\ ,i\ : r

engines were constructed, and it became thoroughly uiulor-
stood thai oonsiderabto adhesion o\is:o,l between a smooth
loaded wheel and a smooth rail.

247. Hedley*s Locomotive — " The Puffiny 2Mfy:'-
Hedley, who had been employed at Wylam in altoriiu
of Trevithick's engines, first made a series of exjvrimo
ascertain whether the ordinary adhesion of tho NY hoc Is .

u> upon the smooth rails would be sufficient to
necessary amount of friction to ensure the useful application
of the tractive force of the steam. It is claimed t
that he was the first person "to ado

ing upon smooth rails." It is evident Tr had done

the same before him. Hedley constructed the f o 11 o NY
to draw coals on a colliery \-; and hero NYO NYOUUI

remark, just as the early steam engine . im-

Cornwall and Devon, so the lev

draw coals from the mouth of the pit to

and smelting furnaces at a distance. The

IIEDLEY'S LOCOMOTIVE.

231

sideration had a wrought-iron boiler and a return flue — tho
chimney being placed at the same end as the lire door. Two

HEDLEY'S LOCOMOTIVE "PUFFING BILLY," 1813 (NOW IN SOUTH

KENSINGTON MUSEUM).

vertical cylinders were used, one on each side of the farther
end of the boiler. The piston-rods were at one end linked to
brains, which were centred at the other end — an arrange-
ment known as tho " grasshopper." The two beams are seen
on the top of our figure centred close to the chimney. The
parallel motion may be noticed at the right end of the
*• grasshopper," and the connecting rods may be observed
attached to the centre of the beams (nearly). These two
connecting rods communicated the motion of the piston by
moans of tho cranks and toothed wheels to four wheels
of equal diameter. In this engine Hedley was the first
(although Trevithick had previously suggested them) to
embody two improvements of very great importance : (1) ho

232

STEAM.

employed the return flue boiler, which not only gave addi-
tional heating surface, but rendered the course of the flame
more effective on any given area ; (2) he adopted a small
diameter, about one foot for the chimney, which rendered the
draught quicker than those of 20 and 22 inches used at
Killingworth. His waste steam passed up the chimney
after being previously thrown into a cylindrical reservoir to
keep down the noise.

248. Stephenson's Engine — " The Rocket" — Stephenson's
life is the history of the locomotive engine. He found it a
small imperfect engine, and after many trials and much expe-
rience left it almost the perfect machine we see it to-day. His
first engine, made to "lead" coals from the pit, was constructed
at Killingworth in 1814; it was supported on four wheels
three feet in diameter ; it had a wrought-iron boiler with a
single flue, the fireplace was within the boiler, and the two
vertical cylinders were half immersed in the same. The
motion was conveyed to the wheels in the same manner

STEPHENSON'S DRIVING GEAR, 1814.

that Hedley had previously adopted, by the intervention of
cranks and toothed gearing. The cranks worked at right
angles to each other, and the pistons made two strokes for
each revolution of the driving wheel. As seen in the figure,
the axle of each pair of driving wheels had a 24-inch toothed
wheel keyed on to it, and the axles being 5 feet from centre
to centre they were geared together by three intermediate
wheels of one foot in diameter. The centre wheel acted as a
regulator, and preserved the two cranks at right angles, and
thus kept the propelling power in equilibrium. This engine

BLAST PIPE.

233

did not answer very well, its radical defects were the single
flue and the wide chimney; the waste steam does not appear
to have been sent into the chimney. Stephensoii soon aban-
doned the toothed gearing to convey the motion to the driving
wheels, and introduced springs to carry the weight of the
engine. Springs were first used by Nicholas Wood.

249. Blast Pipe. — The discovery of the properties of the
steam jet has been much disputed, some claiming it for one
party, some for another. Its nses were fully understood
before the year 1830.

The annexed illustrations will show how the blast pipe was
applied in the two cases of
the "Royal George" on the
Stockton and Darlington
Railway, by Hackworth, and
by Stephenson in 1827.
The principle of the blast
pipe has been previously
explained. When the steam
is introduced into the chim-
ney, it causes a very power-
ful draught by rushing up-
wards and carrying with it
the air, thus creating a partial BLAST PIPE.

vacuum, when the air rushes through the fire doors and bars
to fill up the vacuum. In this act it carries a large amount
of oxygen into the fire box, which assists in the more perfect
combustion of the coke. The steam expands as it rushes out
of the mouth of the blast pipe, and filling the chimney like a
plug it not only drives all out before it, but drags with it the
gases from the smoke box by mere contact. The degree of
exhaustion in the chimney, or the vacuum, of a locomotive,
is generally such as would support from 3 to 6 inches of water.
The force of the blast greatly depends upon the amount of
contraction given to the mouth of the blast pipe, as seen in
the foregoing left hand figure. The contraction must not be
carried too far, for it is evident that if the steam cannot freely
run out of the cylinder, a back pressure will be thrown on
the piston. As there are two cylinders, the exhaust steam is
led by a forked pipe, sometimes called a breeches pipe, toward

234

feTEAllf.

the chimney, which joins immediately before it enters the
funnel, where it stands up vertically in the centre. As the
vacuum increases in the smoke box, so there is an increase of
blast pressure. This no doubt arises from the increase of
speed, which means an increase in the rapidity at which one
puff of blast succeeds another.

250. The "Rocket." — This locomotive has been already
referred to. The annexed figure represents the engine as it
appeared when it ran in the famous Hainhill competition.

STEPHENSON'S " ROCKET. " 1S2&

It was a four-wheeled engine supported on springs, and
with a supply of water in the boiler weighed 4 tons 5 cwt.,

THE

235

•with its tender loaded it weighed 7 tons 9 cwt. Its boiler,
of which the accompanying figure is a section, was cylindrical,
6 feet long, with a diameter of 3 feet
4- inches; through it passed twenty-
five copper tubes 3 inches in diameter;
these conveyed the heated air, gases,
and other products of combustion from
the "fire box" at one end of the boiler
to the tall chimney, 12 inches in
diameter at the other end, after pass-
ing from end to end of the flue. The
heatinsc surface of this multitubular

VAV.W

boiler was 117f square feet; the use of "BOILER OF ROCKET.'*
these tubes gained Stephenson his vic-
tory, and laid the foundation of his fame. The body of
the figure on last page is the boiler barrel with the tubes
inside. The fire box or furnace is represented on the left
hand side close to the smaller wheel. It will be noticed that
a small tube goes from the boiler barrel to the furnace, this
was to allow water to run round the fire box casing; at the
top of the fire box was another tube running into the boiler
(in our figure it is omitted and hidden by the upper end of
the cylinder), to allow the steam generated in the fire box
casing to enter the boiler. The safety valve is the projection
on the top of the boiler nearest the chimney. The cylinders
were two, one on each side; one is seen to the left just above
the fire box, inclining to the rails at an angle of 45°; this
was a poor arrangement, as the pistons slightly lifted the
boiler up and down on the springs. It is seen that the con-
necting rods worked on crank pins on one of the spokes of
the driving wheels, and thus the motion of an ordinary con-
necting rod and crank was gained. The diameter of the
cylinder was eight inches, and the stroke 16J- inches. The
exhaust steam from each cylinder was carried through a pipe
and turned upwards into the chimney, but the exhaust orifice
was not contracted.

The next illustration is the " Rocket" as altered after the
trial in 1829, and as now preserved in the South Kensington
Museum, London. A glance at it will show the improve-
ments, and one or two things are plainer than in our pre-

236

STEAM.

vious figure. The long pipe running along the top of the
boiler is the exhaust steam pipe. The short pipe to the right

STEPHENSON'S "ROCKET" IMPROVED.

is the steam pipe, to allow the steam to pass from the boiler
to the slides and cylinder. The springs and crank are more
plainly visible.

251. Trevithick's Claims. — "As a 'true inventor no name
stands in so close connection with the locomotive engine as that
of Richard Trevithick. It was he who first broke through the
trammels of Watt's system of condensation, and low if not
negative pressure. It was he who first employed the internal
fireplace and internal heating surface; he was the first to
create or promote a chimney draught by means of exhaust
steam; the first to employ a horizontal cylinder and cranked
axle, and to propose two such cylinders with the cranks at
rigjit angles to each other; the first to surround the cylinder
with hot air; the first to draw a load by the adhesion of a
smooth wheel upon a smooth iron bar; and the first to mako
and to work a railway locomotive engine. Trevithick and

THE " ROCKET" AND RECENT LOCOMOTIVES CONTRASTED. 237

George Sfcepheiison were contemporaries.''4 The first loco-
motive seen by the latter was constructed by the former, and
a personal acquaintance was afterwards established between
them. Although irrelevant to the present purpose, it may
be added that Trevithick patented the screw propeller, and
specified several forms of that instrument, and various modes
of applying it, in 1815 — years before those to whom the
invention is more commonly ascribed had turned their atten-
tion to it. Justice exacts the truth, however, that Trevi-
thick's genius, brilliant as it certainly was, was of an imprac-
ticable kind, and scarcely capable of conferring any direct
benefit upon society.

" The next most deserving name in connection with loco-
motive improvement is that of Timothy Hackworth. If ho
discovered no important principles, he stamped a character
upon the structure of the locomotive engine which it still
retains. "What he did in this respect should be ever acknow-
ledged. It does not appear, however, that Hackworth was
ever placed in a position where he had to struggle against
and overcome the once strong prejudices of the public against
locomotive conveyance upon railways. It is as the champion
in that great contest that the name of George Stephenson
must ever shine above all others*; and even Trevithick and
Hackworth might have felt pride in having provided directly
or otherwise the most important aids in the final achievement
of the great victory of 1829." t

252. Contrast between the "Rocket" and Recent Loco-
motives.— The cost of the " Rocket" was not to exceed £550;
modern engines cost upwards of .£2000. It weighed 7 tons
9 cwt. with its tender; the working weight of some modern
engines and tenders exceeds 45 tons. The 'driving wheel
was 4 feet 8| inches in diameter, and cylinders 8 inches,
and stroke 16|- inches. Engines are now running with a
driving wheel 9 feet in diameter, and cylinders 18 inches,
and stroke 24 inches. The greatest speed attained by the
" Rocket" on its trial was 24 miles an hour, for a distance of
one mile arid a half. Some of the express engines on the

* Trevithick was bom April 13, 1771, and died April 22,' 1833;
George Stephenson was born June 9, 1781, and died August 12, 1848.
t Oolburu's Locomotive Engineering*

238

STEAM.

London and North- Western Railway have attained a speed
of 73 miles per hour between Holyhead and London. The
pressure on the boiler was not to exceed 50 Ibs. on the square
inch when working, although the company were to be at
liberty to test the boiler, etc., up to a pressure of 150 Ibs. on the
square inch. Now new locomotive boilers work at a pressure
rarely less than 120 Ibs. on the square inch, and many cases
140 and 150 Ibs.

The student is invited to compare the "Rocket" with the
engine on opposite page.

DIVISION II,

General Description of a Locomotive — Crampton's Engines — Tank
Locomotive — Bogie — Locomotive Boiler — Shell of Boiler —
Through Tie Hods — Tubes — Clearance — Fire Box — Staying the
Furnace— Fire Bars — Ash Pan — Smoke Box — Heating Surface
— Safety Valves — Chimney - — Damper — Steam Dome — Man
Hole — llegulator — Whistle — Pressure G auges.

253. General Description of a Locomotive. — This is ono

of the Great Western express engines, running on eight
wlioels; the large wheel is the driving wheel, the others aie

SHAH?, BROTHERS, AND CO. S ENGINE.

240 STEAM.

called the leading and trailing wheels; the chimney is seen
on the right hand, the furnace on the left, and the barrel
of the boiler with the tubes in the middle. Upon the top
of the furnace is the steam dome and the safety valve. The
springs for carrying the weight of the whole may also be
noticed.

The annexed illustration will give a much better idea of
the locomotive engine and boiler than the last one.

In this sectional elevation F is the furnace, with / the
furnace door; the furnace is seen surrounded by the outer fire
box, but the screwed stays are omitted. Above and below
B are the tubes running from the inner fire box to the
smoke box S, one only is shown; around the tubes and above
them is the water; the level of the water is called the water
line. Admission to the smoke box is gained by a door at
d\ this door is fitted as closely as possible to exclude all cold
air. At the top of the smoke box S, is seen the chimney C,
and within the smoke box is the waste steam pipe or blast
pipe, B P, the mouth of which can generally be closed, or at
least partially closed, to regulate the blast. The dome is at
D, the steam from the boiler passes up D to the mouth of a
pipe in it, this is the mouth of the steam pipe S P, generally
closed by the regulator, which admits the steam to the
cylinder; the regulator being opened, the steam passes along
S P down the smoke box by way of P to the cylinder C,
and sets the piston reciprocating; thus the engine is worked.
In our figure the handle of the regulator is at h, and the regu-
lator itself at r, the handle of course being worked by the
engineman, who stands on the foot-plate, F P, at the back of
the furnace ; the whistle is also close to his hands, whilst
one of the safety valves, s v, or S V, is under his control,
generally s v, and the other he cannot interfere with. The
man hole and man hole door are seen at M H, below the
dome; the man hole door is taken off when it is wished
to enter the boiler for examination, or to tighten the stays,
etc. The large wheel in the middle is the driving wheel,
turned by the crank, which is moved round by the con-
necting rod c, which is attached to the piston rod i, the
latter in its turn is firmly fixed to the piston. The front
wheel next the chimney is called the leading wlicol,

PLATE I .

CRAMPTON S ENGINES.

241

securely fixed on the leading axle, and the wheel to the right
the trailing wheel.

CRAMPTON'S ENGINES.

The above figure is another plan of arranging the loco-
motive. The examples given on p. 238 and Plate I. have eight
wheels, the general run is six wheels with the large driving
wheel in the middle; but in Crampton's arrangement the
large driving wheel is behind. In his engines circular
motion is first given, by inside cylinders, to a cranked
shaft, supported on bearings fixed upon the frame in the

242

STEAM.

usual manner, and motion is communicated from this shaft

to the driving wheels behind
the fire box by side rods.
When outside cylinders are
used they are placed midway
in the length of the boiler,
and connected directly to tho
driving wheel. The upper
figure is Crampton's arrange-
ment for outside cylinder, tho
lower for inside cylinders.

254. Tank Locomotive.—
Tank locomotives are advocated
in opposition to those of ex-
cessive weight to save the enor-
mous dead weight, and are
generally very light. They are
constructed with a tank usually
over the boiler, and occasion-
ally at the sides, so that they
can carry their own water,
without being compelled to
drag a tender after them, being
independent of that seemingly
fixed appendage.

255. Bogies. — The bogie is
a truck on four wheels that
will swivel round. Bogie car-
riages generally run on eight
wheels. They were invented
to meet the necessities of tho
American traffic, where, in
passing throitgh streets, it was
sometimes necessary to turn
round very sharp angles. Mr.
Stephenson constructed tho
first bogie for America. " Tho
engine was made two-wheeled,
and a small truck on four low
\yheels supported the front end,

LOCOMOTIVE BOILER.

243

being swivelled to it by a centre pin, or what the high
road people call a perch bolt. This kind of truck, known in
many places as a lorry, a trolly, and many other names, was, it
appears, called in Newcastle a bogie, and the engine was
therefore shipped as a bogie engine. It became the pattern
or type for American locomotives."* When the engine
or carriage is long, two bogies are employed with four wheels
each.

In the example here given, the engine is on two trucks.
The one end can be turned so that the double sets of wheels
are not in the same straight line. In practice it is found
that bogie carriages bring a great strain on curves. In the
" Little Wonder," which works on the Festiniog Kail way,
constructed to a gauge of 1 ft. 11|- in., or the two foot gauge,
the boiler is double, with two fire boxes, two barrels and two
sets of tubes, and two chimneys. A bogie or swivelling
truck is placed under each barrel, and each bogie has two
pairs of wheels coupled together, working independently by
a pair of steam cylinders to each.

LOCOMOTIVE BOILER.

256. Locomotive Boiler. — All locomotive boilers are of
the class termed multitubular : they consist essentially of the
barrel filled with tubes, while the two ends are named
respectively the furnace, or fire box, and the smoke box.
"piler plates should be rolled from the best iron to i "
* Cferk's Railway Ma/clmery,

244 STEAM.

three-eighths or half an inch in thickness; these form the
barrel, which has a diameter varying from three feet to four
feet three inches in different boilers, and consists of three or
six plates for each boiler, and their joints are arranged to
give as much strength as possible.

d is the barrel of tubes, f is the fire box. The fire door
is seen at the end, in front of which stands the driver and
fireman, the latter supplying the engine with coke by throw-
ing it into the furnace ; the fire door is always oval, e is the
safety valve ; there is also a second safety valve sometimes
placed on the top of c, the steam dome or chest, b is the
chimney, bolted on to the top of the smoke box a.

The shell of the boiler is usually made of best Yorkshire,
Staffordshire, or Lowmoor iron. The thickness of the plates
varies from § to J of an inch, according to the diameter of
the barrel of the boiler, which rarely exceeds 4 ft. 3 inches
inside. The joints are either lap or jump joints ; if the first
mode is adopted they are made to lap 2 inches or 2£
inches for single riveting; when jump joints are employed,
4 or 4^ inch welts are applied to the seams, and secured to
the boiler plates by two rows of rivets : the plates are or
ought to be planed at the edges. The riveting is usually
single, but for strength it should be in double rows in a zig-
zag course. The rivets in size are from f inch to -| inch in
diameter, being placed at a pitch (from centre to centre) of
from 1^ inches to 1J inches. The barrel of the boiler is
usually joined to the fire box and smoke box tube plate by a
three inch angle iron. In the fire box shell the front and
back plates are joined to the others either by three inch angle
iron, or by flanges turned on them to a four or five inch radius ;
the former is the simpler process, but the latter the stronger,
fixing them more securely, and is the plan generally followed.

257. Through Tie Rods run from the smoke box tube
plate to back of fire box; they are about one inch in diameter
and four inches from centre to centre. Their number depends
upon the size of the boiler. They are put in to stay the
boiler, and to assist the tubes in preventing the two ends from
being blown out by the force of the steam.

258. Tubes,' — The tubes may be of brass or iron; copper is
too soft, brass is also better tfem irpn for several reasons, It

TUBES.

245

conducts the heat better, or communicates the motion of the
fire more readily to the water than iron, and also resists the
abraiding action of the small coke carried through the tubes
by the draught; it resists the action of impure water outside
better, springs more easily under extra expansion, and is not
so liable to break as iron is. Economically, brass tubes are at
least as cheap as iron, as they will fetch when worn out half
their original price for old metal. Tubes are fixed in the
tube plates by widening with a mandril to fill the holes
completely, turning over their protruding ends upon the
plates. At the fire box end, ferules of wrought-iron, and
in some cases of cast-iron, about an inch in length, slightly
tapered, are inserted, and should, when driven, be left with
about a ^ inch projection into the fire box, so that should
any of the tubes spring a leak on the road they may be
tightened by a tap or two from the end of a pinch bar.
Ferules at the smoke box end are frequently omitted, which
gives a free passage for small coal and cinders into the smoke
box. Tubes are either of equal thickness throughout, or of a
tapering thickness, from No. 9 wire-gauge at the fire box to
No. 14 at the smoke box. Tubes wear unequally on the
inside, and mostly at the fire box end. The first foot or
eighteen inches should therefore be a little thicker than the
rest of the tube. The number of tiibes in a locomotive boiler
varies from about 130 to 220. The distance between the
ibes, called the clearance, is from |ths to |ths of an inch;
but the larger the tubes the greater the
clearance. The size of the tubes varies
from If to 2 inches in diameter; they
must not be too small, for fear of being
choked, nor too large, for then the heat-
ing surface is diminished. If too small
they are perhaps too numerous and
crowded, when tlie water spaces are not
of sufficient size to prevent priming,
which is a serious evil if not effectually
prevented in time, neither must they
be too long, as the evaporative power
END OF TUBE AS SEEN of the heated gases rapidly diminishes
IN FIRE BOX. as they recede from the fire box.

246 STEAM.

259. The Manner in which the Tubes are Fastened
into the Tube Plates. — This has just been explained, and
we illustrate it here : — T P represents a piece of the tube
plate ; t1 tttt' is the brass tube, which, when driven in,
projected a little beyond the tube plate, then the end was
turned over on the plate as we see it at t and t; thus
they are all left at the smoke box end, but at the fire box
end they are further secured in their places by the ferules F.

260. Clearance. — Clearance is the space between the
tubes, and between the tubes and the boiler shell. It is
required to allow a proper circulation of the water and
steam around and between the tubes, and to give the steam
plenty of room to rise, instead of remaining in contact with
the tubes.

261. Fire Box or Furnace. — The /re box consists of two
distinct parts, the external fire box, always made of wrought
iron, and the internal fire box, or furnace proper, of copper.
The staying of the fire box is a question of the greatest
importance, especially of that part immediately above the
fire. Occasionally the internal rectangular fire box is of
iron, but copper is found to answer better, because it resists
the intense combustion and conducts the heat more rapidly,
and is not so liable to be burned away and ruptured at the
thick lap joints and places where the sediment collects. Tlic
internal fire box is fastened to the external by screwed stays,
screwed through both plates, and their heads left and riveted
over. The space between the two is a water space.

In this figure (Plate II.) the part marked b b, etc., is the space
between the internal and external fire box, the latter is seen in
section on the outside, the former is seen inside the other ; the
short bolts running across are the screwed stays, many of the
ends of which are seen at the front* of the fire box at g g,
etc. The tubes B are marked by double circles above, there
are about 178 of them in this boiler. The water spaces
between the two fire boxes completely surround the inner fire
box; it will be seen closed at the bottom by a square bar

* The front of the fire box is what would be generally termed the
back, i.e., the front is the part nearest the tubes, so that the other
side, where the door is, is the back. The engineman stands at the
back of the fire box.

PLATE U.

TWO FIRE BOXES, FIRE BARS, ASH"

PAN, AND SUPPORTS FOR TOP

OF FIRE BOX.

FIRE BARS.

24?

C c, which is bent and welded to the proper form, to extend
round the bottom of the inside fire box, and is rivetted and
tightly caulked to both fire boxes. The water in the water
spaces is in free communication with the rest of the water in
the boiler.

The /re bars are seen at//, etc., and the manner in which
the top of the furnace is stayed is seen at a a a, etc.

262^ Staying of the Furnace. — The staying of the furnace
renders this end the strongest part
of the boiler. The fiat top is, of
course, equally bad with the flat
sides without the stay bolts, for all
flat surfaces in a boiler are inhe-
rently weak. The top cannot be
satisfactorily secured by stay bolts.
The following plan is adopted: —
Across the roof of the fire box are
placed nine or ten roof stays, or cross
stays; A B (fig. 3) is one of them, they
are placed four inches from centre to
centre, these roof stays are firmly
bolted to the top of the boiler, as
seen at a a a. The roof stays are
further secured by suspension stays,
or hanging stays s s, to the outer
fire box, in the manner shown very
clearly in the figure at C C. Those
in the upper figure are a Httle dif-
ferently arranged to those in the
lower, but the principle is the same
in both. The roof stays are firmly
bolted to the roof of the furnace,
then suspension stays extend from
the fire box roof stays to the top of
the outside fire box.

263. Fire Bars.— Fire bars of
wrought iron support the fire and
separate the fire box from the ash
(2) ^ pan. They are laid on a frame

which rests on bolts or brackets in the side of the fire box.

248

STEAM.

It is found that thin deep fire bars, laid close together, are
much better adapted for the purpose of a locomotive than
larger ones. The fire bars, from the intense heat of the

FURNACE STAYS.

furnace, wear or burn away very rapidly. They are
frequently bent — this arises from the softening of the iron
from intense heat — when they drop, because they are not

SMOKE BOX. 219

capable of sustaining the weight of the fire. Fire bars are
about 4 inches deep, -f of an inch thick on the lower edge,
and double that thickness at the upper, so that, they are more
widely separated on the side next the ash pan than on that
on which the fire lies ; they are so placed that the top of the
bars are above the bottom of the water spaces by 2 ^ or 3
inches. The fire bars are marked distinctly on Plate II.,
page 246, at fff, just above the ash pan A P.

264. Ash Pan. — The ash pan is placed directly under the
fire bars, and is a simple wrought iron tray about ten inches
deep, the bottom being nine inches above the level of the rails.
It must be carefully fitted and closed all round, so that the
draught shall not be impeded, while the engine driver can
use it as a damper to regulate the supply of air. Again, it
should be so arranged that when the engine is running the
air impinging against it shall be directed into the furnace.
Its purpose is to prevent cinders and live coals from falling
upon the line, for this, in early locomotion, caused several
fires. There is another reason for it, as hinted above. When
the engine is standing still it is often important to stop the
generation of steam, this is partly done by allowing as little
air as possible to gain access to the furnace, hence the ash
pan is made to fit tightly to the fire box on all sides ; but the
front side can be opened and closed at pleasure, like an
ordinary damper, which is adjusted by a rod worked from
the foot plate. "When the engine is running rapidly with
the damper opened, advantage is gained by the air rushing
into the ash pan, and thence into the furnace. At sixty
miles an hour the pressure of air would be nine pounds per
square foot, hence its advantage is at once apparent. The
ash pan is at A P in the illustration on Plate II., page 246.

265. Smoke Box. — The smoke box is at the farther end
of the engine to where the driver stands, or at the front of
the engine exactly under the chimney. The heated air and
products of combustion pass from the internal fire box
through the tubes into the smoke box, and then are carried
up the chimney. Access is given to it by means of a door,
generally swinging on two hinges, which is kept fixed in its
place as air-tight as possible, by means of bars, catches, and
handles. Sometimes the door is in two parts, folding or

250 STEAM.

overlapping in the middle, and closed by a bar, handles, and
catches also. In the smoke box is placed the blast pipe, and
the steam pipe runs down it to the cylinders at the bottom.
Its use is to contain these, and to allow the tubes to be
cleaned out, and to gather the soot, bits of coke, etc., that
may be carried through the tubes. The smoke box is seen
at SB.

266. Heating Surface of Fire Box and Tubes, and Grate
Surface. — It has been most distinctly proved by experiments,
that most of the heat passes into the water from the fire box
and the first foot or two of the tubes, and very little indeed
from the further end of the tubes, and that long boilers do
not attain any economy of fuel. Taking an average con-
sumption of fuel, the evaporation due to the first quarter of
the length of tubes is 21 per cent.; that of the second
quarter of the length of tubes, 16 per cent.; of the third, 12
per cent.; and the last quarter length 8 per cent, leaving
43 per cent, for the fire box. In the working of railways,
from 100 to 200 cubic feet of water, or from 2-8 to 5*6
tons, must be evaporated per hour to produce the necessary
steam to move an ordinary train at the usual speed. A
square foot of heating surface cannot, under any circum-
stances, transmit more than sufficient heat to evaporate ono
cubic foot of water in an hour; altogether nearly a square
yard of heating surface is requisite for the evaporation of one
cubic foot of water per hour in locomotive boilers. The total
heating surface is from 1000 to 1500 square feet. In the
fire box itself there are about 90 square feet of heating surface,
and in practice from six to twelve times this heating surface
must be provided in the tubes. The fire grate surface varies
from 12 to 30 square feet, but about 15 square feet is the
usual rule. It is easily proved that the smaller the diameter
of the tubes, by so much the more is the proportion of their
heating power increased. By doubling the diameter of a tube
we double its heating surface, but we increase the space it
occupies fourfold. In proportioning the number and diameter
of the tubes to the area of the fire box surface, it is best to
keep them to a definite proportion ; it is also considered that
there should be a certain proportion between the area of the
fire grate of the furnace and the area of the opening through

SAFETY VALVES. 25

•which, the hot gases escape from the fireplace. The size of
this opening is named the calorimeter, which is sometimes
taken as showing the evaporative power of the boiler, but
this is not a wise test, as a large calorimeter can easily be
procured by a few large tubes.

The top row of tubes — they are generally about 2 inches
in diameter, from 10 to 12 feet long, and number from 100
to 200 or more — is covered by from six to eight inches of
water. It must also be remembered, in arranging the fire box,
that more heat passes into the water from the top of the
furnace than from the sides, because the convected water and
steam can rise up more readily in the one case than in the
other. It is sometimes the practice to incline the fire box a
little.

267. Fuel and Evaporation per Hour. — The highest
rate of combustion may be taken as one hundredweight of
coke per hour on each square foot of grate surface ; this evapo-
rates, at the maximum rate, sixteen cubic feet of water per
square foot of grate surface per hour. (Taking a pound of
coke to evaporate nine pounds of water.)

268. Safety Valves. — Two openings are made in the
upper part of the boiler, which are covered by discs or valves.
These valves are held down on their seats by levers; one arm,
the shorter one, is secured directly to the boiler, while the
other arm, the longer one, is held down, by a stout spring
balance, so screwed down that the valve can only rise when
the pressure of the steam in the boiler becomes greater than
the spring can resist. These valves are named safety valves,
because by rising when the pressure of the steam exceeds the
intended limit, they allow it to escape, thus preventing any
excessive accumulation of pressure whereby the safety of the
boiler and persons around are endangered. The safety valve
does not show how much the pressure of the steam may be
below or above the proper limit; this is shown by the steam
or pressure gauge. The safety valve of a locomotive should
be placed as far from the dome as convenient, in order to
prevent priming.

There are two generally fitted, one placed beyond the con-
trol of the driver and the other near him. They are kept
in their places, one by a Salter's spring balance, and the other

252

is held down directly by a spring secured to tlie top of the
valve, and hence it has no lever; weights are inapplicable to
the case of the locomotive, because they would jerk up and
down with the vibration of the engine. The safety valves
vary in size from 1^ inches in diameter to 4 inches; but the
general size is about 3 inches. Large safety valves are not
so likely to set on their seats as smaller ones. The lever by
which the Salter's spring balance presses the valve on to its
seat is generally graduated, according to the area of the valve.
If the valve be 10 inches in area, the lever is divided into
11 parts; the safety valve lever presses on the valve at
the first division, leaving 10 divisions on the long arm
and one on the short arm; thus the pressure per square inch
on the safety valve is exhibited. They vary in shape in some
engines ; annular valves are used in which the
steam escapes round the edges of two circles.
The annexed figure illustrates a very good
valve used by Mr. Gooch. It is constructed
somewhat on the principle of the steam indicator.
To the above valve there is no lever; the
spring balance is placed on the top of the valve
itself, which is l^ inches in diameter. The
steam enters at S, when acting on a a against
the spring in the barrel B; the force of steam
compresses it until it acts by allowing the steam
to pass through b.

269. Chimney. — It is usual to term it a
chimney, not a funnel. The height must not
exceed fourteen feet above the level of the
rails ; they are made of wrought iron, and pro-
ceed directly from the top of the smoke box to
which they are bolted. Their relative sectional
area to that of the fire grate is about one-tenth,
or they should properly be a little less in
diameter than one of the two cylinders, which
is considered a good proportion. Their draught
'does not depend upon their height; or, rather,
the draught depending upon the rush of waste

steam, it matters little what height they are, so

long as they convey the steam, smoke, etc., away from the

STEAM DOME AND PREVENTION OF PRIMING. 253

driver and fireman. A damper is generally provided, as
seen in our figures, near the end of the blast pipe; but the
damper is so arranged that the nozzle of the blast pipe passes
through it. It consists of a disc of metal.

270. Dampers. — Besides the disc damper referred to
above, placed across the chimney, the front of the ash
pan is always so arranged as to act as a damper, by regu-
lating the supply of fresh air to the fire. The most effectual
dampers are those placed at the smoke box end of the tubes,
consisting either of a perforated plate with circular holes
corresponding to the number and end of the tubes, which
slides so to either completely close or leave open the ends
of the tubes, or else it consists of thin strips of metal
arranged and acting on the principle of the Venetian blind,
by these the tubes can be left fully open or closed, or partly
closed, so as to check the draught according to the judgment
of the driver.

271. Steam Dome and Prevention of Priming. — The
position of the steam dome varies, but it is always bolted to its
seating, which is riveted on to the top of the boiler, sometimes
immediately over the external fire box, and sometimes towards
the middle of the barrel of the boiler. Within the steam
dome is placed the end of the steam pipe, and it is here placed
so that the steam shall enter it as far from the water as
possible. It is sometimes known under the name of the
Separator, because by the steam entering the steam pipe
within the dome, a better chance is given for the spray pro-
duced by ebullition to separate from the steam — thus priming
is prevented. Sometimes the safety valve is placed on the
top of the steam dome, but this is considered an objectionable
practice, as it should be as far away as possible from the
steam pipe. A baffie plate of brass, shown by the line
A B in the figure (p. 255), is fixed above the water line
at the entrance to the steam dome — it is thoroughly per-
forated; as the steam runs towards the mouth of the steam
pipe M, it impinges against this perforated plate, and in
rushing against the plate and passing through the holes, the
water that has come away with the steam is knocked out — •
the whole arrangement is thus found effectually to prevent
priming. Another mode of preventing priming is, by placing

254 STEAM.

the steam pipe as near the top of the boiler as possible, and
allowing the steam to enter through holes in the top, before
which are placed a smaller baffle plate ; this has been
already explained. The dome is bolted to its seat, which
is riveted on to the top of the boiler or fire box — the former
is the more preferable plan by far — and the joint is made
steam tight, as explained under the next heading Man
Hole. Its form varies as much as its position, depending
upon the taste of the maker, but the majority are either
hemispherical or have hemispherical tops. It is usually
worked out of one plate, with a spherical top, or finished
with a dished cover of plate, or cast-iron.

272. Man Hole. — The man hole is to gain an entrance to
the interior of the boiler. No special man hole is required,
as the dome can be taken off, and admission thus gained to the
boiler ; but when fitted, it is frequently over the top of the fire
box, or near the chimney, or on the dome seating. Near the
fire box is the best place, as the stays can easily be reached. It
is about 15 inches in diameter, sufficiently large to admit a
man's body. The door of the man hole must be attached
with a steam-tight joint to the top of the boiler; it is ren-
dered steam-tight in the ordinary way, by the use of canvas
and red lead. Sometimes the molecular force of expansion
is made to render the joint steam-tight thus : — Soft copper
wire is laid on the joint, then the cover is brought down on
to it and screwed up as tightly as possible, then, when the
steam is up the heat causes the copper wire to expand ; the
greater the heat, which, in this case, may represent pressure
of steam to escape, the greater the expansion of the copper, and
the more steam-tight the joint. It is made with a necking
formed of thicker metal than that of the boiler, and flanged
to join it. The upper flange is planed to receive the cover or
dome.

273. Regulator, or Steam Regulator. — This contrivance
is to regulate the admission of steam to the cylinders from
the boiler. They are made in various forms, but are chiefly
of two classes : (1) Those formed on the principle of a conical
valve and seat ; (2) those constructed like an ordinary loco^
motive slide valve.

C is a lever, or else an eccentric worked by the regulating

STEAM WHISTLE,

255

handle, which is close to, or within easy reach of, the engine-
driver. This lever, or eccentric C, being moved, the slide M
is brought down, and free exit is given to the steam in the
boiler, so that it can readily pass down the steam pipe S P
to the cylinders. Sometimes these valves are arranged pre-
cisely on the same plan as a ventilating grate in the floor of
a building, where a very slight turn gives a large passage for
air, in this case steam.

DOME AXD STEAM REGULATOR,

274. Steam Whistle. — The steam whistle is a device
attached to locomotives for giving warning that the train
is approaching, moving, etc. It mainly consists of a pipe
fastened into the top or end of the boiler, with a cock
within easy read; of the engine driver. When the steam is
turned on, it issues violently out of $ circular opening and
strikes the rim of a bell-shaped pieoe of brass (its edge

25G

STEAM.

being placed exactly over the circular opening), with suffi-
cient force to make
the whistle heard
at a very long dis-
tance. The prin-
ciple is simply this :
— When the handle
H is turned, the
steam coming from
the boiler passes up

S P, and
round the

out all
edge of

s s through the cir-
cular opening c c,
then impinging with
great force upon the
edge of s' s it sets it
vibrating, the vibra-
tions communicate
their motion to the
STEAM WHISTLE. air and mould it in-

to a series of sonorous waves, giving us a high note of so shrill
a pitch that it can be heard at a very considerable distance.

There are generally two whistles — the shrill one for
ordinary purposes, and a deep-toned one to attract the
guard's attention. It is usual now to arrange the guard's
whistle, so that both the driver and guard can sound it.
The cord that runs along from one carriage to another is in
connection with this whistle, and if the passenger pull this
cord he will sound the deep-toned whistle.

By comparing the steam whistle we have just explained
with the next two, it will be seen that no difference in
principle exists between the first used and those with modern
improvements attached. The left hand one is a sectional
view of the first locomotive whistle ever used. It was
made in 1835; the right hand one is a section of the first
steam whistle ever employed, which was at the Dowlais Iron
Works in 1833, where it is supposed to have been invented
by William Stephens, a working man. It will be observed
that the steam is wade to pass round a tapering funnel with

PRESSURE GAUGES.

257

its wide mouth upwards, and as it conies out it is com-
pelled to impinge upon the edge of an inverted hollow
cylinder. Experience has given a thinner edge to the upper
part or cylinder.

STEAM WHISTLES.

275. Pressure Gauges. — The reader is referred back to
the gauges used in the marine steam engine, as described on
page 153, et seq.

But we would add a few remarks to these. The general
use of the steam gauge has not only given additional security
in the working of all steam engines ; but, serving as a guide
to the enginemen, it has been the means of effecting a con-
siderable saving of fuel, by enabling them to maintain the '
proper pressure without, as in old times, letting the steam
vigorously escape at the safety valves. Engine drivers once
held it to be a good sign that they were properly attending
to their fires when the safety valves were continuously
roaring, and De Pambour estimated the total steam lost on

258 STEAM.

tlie Liverpool and Manchester Hallway, by this blowing off
at the safety valves, as one-quarter of the whole steam
generated.

When steam is raised, the safety valve fixed, and the fire
under the boiler, the pressure and temperature increase very
rapidly, hence the necessity for continual watchfulness, to
see what pressure the gauges indicate, and to ascertain
whether the safety valves are properly acting. In some ex-
periments made with a locomotive boiler, the pressure being
at 32 pounds, and temperature 133J°C., and the fire kept as
regular as possible, in three minutes the pressure was 44-J
pounds, temperature 141J°C.; in three minutes more, pres-
sure was 57f pounds, temperature 149°C.; in three minutes
more, 74| pounds, temperature 155| ; or in nine minutes the
pressure increased from 32 to 74f pounds, or much more
than double its pressure — a most astonishing increase. This
will, perhaps, explain a few boiler explosions that have hap-
pened while engines were stationary.

276. A Fusible Plug is screwed into the crown of the fire
box (for description, see page 143). These plugs are not
always to be relied on, as they sometimes become encrusted
and do not operate; but, with a properly kept boiler, they
are a useful precaution against accidents.

DIVISION III.
THE WATER FOR A LOCOMOTIVE.

Water Tanks — Water Cranes — Feed Pump — Giffard's Injector —
Gauge Cock — Glass Water Gauge — Screw Plugs — Scum Cocks
— Blow-off Cocks — Heating Cocks.

277. Water. — The boiler of a locomotive engine is filled
so that the water stands a few inches above the top of the
fire box. It is admitted to the boiler by means of pumps
and ball valves, or by Giffard's injector.

278. Water Tanks.— Walls, or small buildings of sub-
stantial masonry, supporting a large tank for water, are
generally seen by the side of a railway station ; they

WATER CRANE. 250

supply the engine with water. Water tanks are usually
rectangular, from five to nine feet deep. They are, at the
bottom, at the least, twelve feet above the level of the rails,
so that there is constantly a sufficient pressure of water to
fill the tender quickly. Tanks are either filled by allowing
the water to run into them from a higher level, or by
pumping up the water by means of an engine from, a lower
level. This is the general plan when the engine, boiler,
pumps, etc., are housed under the tank. The water tanks
are made of boiler-plate iron, and supported by cast-iron
beams running in a row under each seam of the tank.
They are also made of cast-iron, supported by cast-iron
beams across the tank from side to side. The engines pre-
ferred for the purpose are vertical, and the pumps double-
acting.

279. Water Crane. — The water is drawn from the tank
at the bottom, and passes through a cast-iron pipe to the
water crane. It is allowed to pass into the mouth of this
cast-iron pipe by a valve which has the fulcrum of its
lever on the side of the tank, the valve is lifted for the dis-
charge of water by a chain hanging down outside within
reach.

Fig. 1. is a water crane of the usual construction. A B is
the swing pipe, balanced on a vertical pivot at C, within the
cast iron column C D; it will, therefore, swing round into
any position convenient for filling the tender ^v^th water. H
is a leather hose at the extremity of the swing pipe for the
convenience of the engineman. E is a shut-off screw valve,
to allow the water to pass up the column D C when the
handle is turned, and to stop the supply when sufficient has
been delivered into the tender; the valve e is screwed up
when water can pass from W. It will be seen that its
action is exceedingly simple. "Water passing from the tank
by way of the pipe W is allowed to run through the valve e
by turning the handle at the top of the shut-off screw E, it
then goes upwards through D C, along C A, and into the
tender by H. B is a weight to counterpoise that of A C, so
that no undue strain conies on the vertical pivot C; also, by
its momentum, it assists in turning the arm A C. It will be
observed at C that the pivot has a brass bearing, which has to

260

STEAM.

be fitted with considerable care. F P is a fire place, so that
in winter the column can be warmed and the water unfrozen,
or prevented from freezing; the products of combustion pass
out through a number of small apertures provided for the
A

WATER CKANE (1).

purpose at L. K is a pillar fountain, from which water can
be taken, by turning the handle at the top, for cleansing and
other purposes; an hose can be attached to it for the con-
venience of watering and cleaning.

The wall water crane is simpler in its details than the
one just described, but not always so well adapted for its
purpose, as it makes no provision for the extreme cold of
winter. It swings at the bottom A on a bracket bolted to
the wall, and at the top B it is supported by the supply
pipe D C, into which it is pivoted. The engine driver pulls
the handle H, when, by means of lever C, a sluice valve is
pushed back within D, when the waiter runs along the
supply pipe D C, and into the swing pipe, as before, to

FEED PUMPS.

261

the tender through the leather hose at the extremity of the
supply pipe. The tank is seen in its proper position.

WALL WATER CRANE (2).

280. Feed Pumps. — The feed is either supplied by
GiffarcVs injectors, fixed to the fire box, and of which a
description has been already given, or else by an ordinary
double-acting pump worked off the crosshead of the piston-
rod, or from one of the eccentrics on the crank axle. When
the former method is adopted, the ram is about If or 2
inches in diameter ; but in the latter arrangement the'ram

262

STEAlt.

must necessarily be of greater diameter, about 4 inches, as the
stroke is so much shorter.

The water is kept in the tender T. The handle at h is
turned, when the plug p is lifted and the water runs down

BALL AND TELESCOPE VALVE ON TENDER.

p 1) c by gravity. At & is a ball and socket joint, so that tho
pipe b c (this part is generally called " bags") is capable of a
slight vertical and lateral motion. From d to e is a telescopic
joint, which admits of a longitudinal motion in and out. It
is thus that all the motions of the train are provided for,

FEED PUMPS.

2G3

and that the joint is rendered water tight. At c it is screwed
011 the pipe leading to the engine and boiler. This tube
leads the water to W in the next figure, which gives us two
views of the feed pump, p is the plunger, a side view of
which is shown at A. The eye of the plunger rod is fastened
to the crosshead of the piston, but sometimes to the back of

FEED PUMP.

the eccentric to the eye at G, as seen ill fig. page 2794
The plunger is very small, not more than 2 inches in diameter.
As it moves to the right a vacuum is left behind it, and the

2G4

STEAM.

water rises through the valve v ; next, as it comes back, tho
water is forced along the delivery pipe from v to v", through
the ball valves v and v", into the boiler at B. The object of
the third valve at v" is to prevent the pressure of the steam
from forcing the water back upon the other valves. The
lift of the valves is very small, not more than -J to --% of an
inch. Above each valve is a guard to keep it down to its
seat ; for, if allowed to rise too high, the force of concussion
would be sufficiently great to destroy the valve seating. When
no feed is required the water is shut off at the tender. These
feed pumps only work when the engine is moving. Some-
times it may be noticed that engines are running backwards
and forwards a short distance near a railway station. It is
that water may be pumped into the boiler. When GiffarcVs
injector is fitted, there is no necessity for this. It was a
custom to fit a small donkey pump
for the purpose of forcing water
into the boiler when the engine
was stationary. The capacity of
the pump, i.e., the area of the
plunger or ram, multiplied by tho
length of the stroke, should bo
from Y\J to -^ of the contents of the
cylinder. Each pump or injector
should be capable, singly, of keep-
ing up the feed. Two are fitted
in case one should be disabled.

281. Gauge Cocks.— When the
boiler is first filled with water, it
is made to stand a few inches
above the fire box. In order to
know when the water is at tho-
proper height in the boiler, there
are fixed in the back or side of
the fire box two brass gauge
cocks. One is a few inches above,
and the other as much below, the
proper level of the water in the
boiler. The cocks are connected
tube, the whole forming the Glass Water

GLASS WATER GAUGE.

with a

glass

BLOW-OFF COCK. 265

Gauge. Both cocks are kept open in communication with
the boiler, so that the water can freely pass through the
bottom cock into the glass tube, and the steam as freely
through the top one. The water within the gauge has thus
the same level as that in the boiler, and the driver has only
to look at the glass to see the height of the water in the
boiler. When the feed pumps are at work, he watches it
till there is a sufficient supply in the boiler, and afterwards
he has to notice that it does not get too low through the
evaporation of the water. In addition to this there are fitted
three gauge cocks at the back or side of the fire box at different
heights, between the extreme limits admissible for the water
level. By trying these cocks successively, the engineman can
judge, according as steam or water issue from them, at what
height the water stands in the boiler.

W is the water in the boiler, w L is the water level. The
water passing from the boiler enters at a, and stands the
same height in A B, the glass water gauge. The handles H
and H, when turned, allow water or steam to issue from
the boiler, and clean the gauge out. It is the duty of the
engineman to turn these handles now and then, for fear the
gauge may be choked at a, or &', or at B and A.

282. Screw Plugs. — To facilitate the washing out of the
boiler, a screw plug, about 2 inches in diameter and slightly
tapered, should be fitted at each corner of the fire box, with
as large square heads as the plugs will admit, to bear the
strains of the screw key. The plugs should be of hard
brass, and threads cut to a fine pitch, to give them a good
hold on the metal ; sometimes a lining plate is inserted at
the corner to increase the hold of the plug, and reduce the
liability to leakage.

283. Scum Cock. — This cock is fixed on the back of the
fire box at the ordinary water level, with 1|- inch copper pipe,
carried down below the foot plate, to draw off the impurities
which rise to the surface of the water, and which, whilst there,
frequently cause the boiler to prime.

284. Blow-off Cock is also fixed at the back or side of
the fire box, but at the level of, or as near as practicable to,
the ring at the bottom of the water space between the in-
ternal and external fire boxes, and is for the purpose of

266 STEAM.

blowing the water out of the boiler when required. Thei'O
are two other cocks fitted to all locomotive boilers, viz., the
blower and the warming cock ; the former being connected
by a pipe with the chimney, for the purpose of getting up
the steam rapidly, the latter for warming the feed water in
the tender. It is generally opened while ' the engine is
stationary, when by suitable pipes the steam passes to the
tender, where it heats the water instead of blowing off to
waste. This practice was adopted in the very earliest days
of locomotive engineering. It is also a common practice to
heat the water by other methods before it enters the boilers ;
in fact, this should always be done.*

285. Warming Cocks. — Warming cocks are employed to
let any surplus steam pass into the tender to heat the water.
They are fixed near the top of the fire box, and are con-
nected with the feed pipes by an inch copper pipe. In tank
engines the pipe goes directly into the tank.

DIVISION IV.

DETAILS.

Tlic Cylinders — Water Cocks — Grease Cocks — Piston and Piston-
Rod — Connecting Rod and Crank — Coupling Rod — Strap Gib
and Cutter — Sector — Driving Wheel Tire — Counterweight to
Wheels — Sand Cocks — Axle Boxes — Springs, Buffers, and Buffer
Springs — Brakes — Draw Bar.

283. The Cylinders of locomotives are generally placed
immediately beneath the smoke box, where all condensation
from external cold is entirely prevented. Sometimes they
are fixed on the outside of the engine, such engines receiv-
ing the name of Outside Cylinder Engines. In early loco-
motives the cylinder was placed vertically. The horizontal
cylinder was finally adopted about 1830. It is unnecessary
to enter into the details of the cylinder. The student is
referred to what has been said concerning those of land and
marine engines generally, as the arrangement is the same.

* For a method of carrying out this idea, see Article on Cambridge's
Feed Water Heater.

PLATE HE.

Ct
Ul
Q

GREASE COCKS. 267

Of course they are made of good hard cast-iron. Sometimes,
from the weight and friction of the piston, there is a tendency
to groove. They are generally constructed so that both the
top and bottom of the cylinder may be removed. The piston-
rod works through a stuffing box and gland in the ordinary
manner. It is always usual to allow one-quarter of an inch,
or less, clearance at both ends of the stroke.

In Plate III., the cylinder is seen at O with its piston P.
The piston-rod is p r, and two guide blocks are at G, which
move backwards and forwards between the guide or motion
bars g g. The piston crosshead is also at G. Into the guide
blocks comes the end of the connecting rod c r. C C is the
crank moved round by the connecting rod, and carrying with
it the axle A X, and with it the driving wheel D W. It is
the eccentric, and E E the eccentric rod working the slide
rod s r, which in its turn gives the reciprocating rectilinear
motion to the slide s. The slide 8 is seen in front of the
ports, the bottom port being open to the exhaust and the
upper to the steam. The piston is just going to commence
its stroke to the left. The manner in which the connecting
rod is attached to the crosshead of the pisbon and to the
crank is explained by the illustration, a x is the axle of an
ordinary leading wheel ww\ the part marked a is the journal.

287. Water Cocks, Drain Cocks, Relief Cocks, or
Cylinder Pet Cocks. — Two drain cocks are fixed to each
cylinder, one at each end, and at the lowest part, to relieve
the cylinder from any water that may arise from condensa-
tion of steam or priming. They should be opened just before
starting, after the engine has been standing still, to get rid
of any water that may have become condensed while waiting.
They are worked by rods and levers from the footplate.
Sometimes, often after repairs, the water is greasy, and until
it is properly got rid of the engine will often prime, hence the
value of these relief cocks.

288. Grease Cocks. — A grease cock is fixed on to each
cylinder ; it communicates with the slide valve and lubricates
it; part of the tallow, as the slide moves backwards and
forwards, enters the cylinder and lubricates it also. It is
generally fixed on the valve-jacket, so that the slide valve
aild cylinder are lubricated as well.

268

289. Piston and Piston-Rod. — The crossheacl is the part to
which the farther end of the piston-rod is fitted, to this also
is attached the connecting rod, the crossheads move in guides
or between motion bars, which are two or four parallel bars.

Pistons for locomotives are fitted and packed in many
various ways. The piston-rods are made of steel or iron,
while the piston itself is of cast-iron or brass ; brass is the
better substance, because it is lighter and does not so readily
break ; some makers forge the rod and piston in one piece.
The top of the piston-rod is fastened by a cutter into a socket
with jaws ; G is the socket, the jaws are a little to the right
and left of G ; the whole is named the piston cap. Be-
tween and into the jaws comes the small end of the piston-
rod p r, which is kept in its place by the pin of the cross-
head ; the two ends of this pin are fastened into two blocks,
which move in guides or motion bars, to preserve the paral-
lelism of the piston-rod. The pin of the crosshead is seen
running under G, while the guides are marked g and g, and
the two guide blocks may be observed above and below G
at the end of the guide bars. The piston-rod works steam-
tight through the cylinder cover; between P and s b is
a short tube cast on the cylinder, with an opening a little
larger than the diameter of the piston-rod, this is called the
stuffing box, the gland is the part close to s b. The piston-
rod being in its place, the stuffing box is first filled with
hemp soaked in melted tallow, or else with other packing ;
the gland is then brought down on to it and screwed forcibly
against the packing, so as to press it tightly against the
piston-rod. Whenever any sliding rod has to work into a
space filled with steam, or with water under pressure, a
similar method is adopted to prevent any escape at the side
of the rod.

" The maximum economical speed of the piston has not
been ascertained, but it appears that, with a high speed of
piston, small driving wheels and light engines are preferable
to the very large ones which are now frequently seen. Small
wheeled engines have been found to start a train more rapidly,
and to draw it with greater regularity of motion, than engines
with from 6-J feet to 8 feet driving wheels."

290. The" Connecting Rod and Crank. — By the inter-

PLATE TZ.

YLINDERS, STEAM PIPE,
BLAST PIPE, ETC.

COUPLING ROD. 269

vention of the connecting rod and crank, the rectilinear motion
of the piston is converted into a circular motion. The con-
necting rod is c r, crank CO, and axle AX (Plate III.),
which move the driving wheel D W. The crank, or rather the
cranks — for there are two, as there are two cylinders and
pistons — are forged on the axles of the driving wheels. The
cranks are placed at right angles to each other ; only one is
seen in the figure, the other half is precisely similar to A X,
but the crank is at right angles to C C. In our illustration
C C is lying horizontally, so that when the piston P attempts
to move to the left, it will only pull the crank in a straight
line, as it were, and cannot move it, hence we see the
necessity for two cranks ; the one not shown, 'being at right
angles to C C, is just in that position where the piston will
have the greatest effect upon it ; hence the driving wheel can
be moved, which could not happen if the engine stopped
exactly as seen in the figure, and there were only one crank.
Such an axle as we have here is called a cranked axle, and
is made of wrought-iroii or steel. It must be understood
from what precedes, that when one piston is at the end of its
stroke the other is in the middle.

291. View of Fire Box, etc.— In Plate IV., C C are the
ends of the two cylinders, S P the steam pipe, B P the
blast pipe.

292. Coupling Rod. — A coupling rod is very similar in
its form to a connecting rod, but it is not so large or heavy.
Its use is for coupling the driving wheels to the leading or
trailing wheels, or both, when of course the wheels must all
be of the same diameter, as in the case of goods engines.

They are attached to cranks fixed on the outer ends of the
axles, or else to crank pins inserted in the arms of the wheels

270

STEAM.

— the former method applies to engines with outside bearings,
and the latter to those with inside bearings. They are
always outside the wheels. Generally they are made with
ends forged in one piece, and the cutters so arranged as to
preserve their length constant as the bushes wear. An oil
cup is shown in the figure; it is forged on and has a small
tube in the centre, in which to insert the wick to lubricate
the bearing.

293. Strap, Gib, and Cutter. — The ends of the connecting
rod are not, as it were, part of the rod, but are built up
upon the end of the rod itself.

Let us take the annexed illustration, which is the smaller
end of a connecting rod ; a a a a is the end of the rod with

a hole in it; first upon the
end are placed the two
brasses 1 and 2, in which
circular hole is left
for the crosshead pin to
pass through; round the
whole is placed the strap
ss; then into the hole
is placed the gib g g (in
this case we have two
gibs, #<7and#Y); then
the cutter or key c c is
driven in tightly, so

gthat the whole is held
firmly together. Some-
times c is also held in its
place by a screw and nut.
294. Driving Wheel.
— The wheels attached to
the crank axle are called the driving wheels; the front pair of
wheels of the engines, are called the leading wheels; and the
hind wheels, or those close to the fire box, the trailing wheels.
They are nearly always made of wrought-iron, and are kept
upon the rails by a flange formed on the tire. The driving
wheels in passenger engines are always made large, to increase
the speed, and the power of the engine must be increased in
the same ratio; but in goods engines they are not so l^rge,

STRAP, GIB, AND CUTTER.
SMALLER END OF CONNECTING ROD.

DRIVING WHEEL.

271

and consist of four or more coupled together by coupling
rods. The object in employing coupled driving wheels is
simply to distribute the great weight necessary for adhesion,
where great tractive force is to be exerted at moderate speed,
such as with a goods engine. The wear of wheels amounts
to about the twelfth of an inch per annum with wrought-iroii
tires. A good idea of a locomotive wheel can be obtained
by referring to the following figures.

1 HALF-CRANK.

DUNHAM'S CRANK.

Wheels are made upon various systems, the object of all
eing to give strength to the tires and prevent wear. The
ires are not cylindrical, i.e., they have not the inner ami

272 STEAM.

outer edge both the same diameter, but are made slightly
conical, which plan keeps the carriage in the centre of the
railway, and the flanges do not come in contact with the rails
unless under exceptional circumstances; in fact, conical wheels
have a self-adjusting action, which preserves the carriages in
their proper position on the rails. Again, if the wheels be
thrown into such a position that one flange is close against
the outer or large curved rail, the wheels being conical, a
larger circumference of the outer wheel will move on the rail
than on the smaller wheel (for we must recollect that the
wheel only rests on one point), consequently the larger wheel
will quickly restore the carriage to its proper position.

295. The Tire is a distinct part of the wheel, composed of
a ring of metal, either wrought-iron or steel, which is shrunk
on to the wheel, and further secured to the rim by bolts or
rivets. It forms the conical part of the wheel and the flange.
When worn, they are re-turned in the lathe to a true surface.
This is required after an engine has been running from nine
to twelve months. The tires, when new, are usually about
2J or 2 1 inches thick, and are not allowed to be worn down
to less than 1^ to 1J inches.

In each of the above wheels the tire is seen at the top and
bottom, with the flange formed on one side. Here we have
two methods differing from the ordinary one of forging the
crank on the axle. In Baldwin's half-crank, we see a simple
and cheap way of forming the crank. In the second example,
or Dunham's crank, while we have the same position of the
crank wrist, the crank is completed by adding the second arm,
or cheek, this cheek being bedded in the cast-iron driving
wheel itself.

296. Counterweights to Wheels. — The momentum of the
piston-rod, guide blocks, connecting rod, etc., is very great;
this has to be counterbalanced by the application of a
weight to the wheel. These weights are put into the rim of
the wheels between the spokes. If the student will notice
the driving wheels of a locomotive, he will see the balance
weight partially filling up the space between three or four
of the spokes. This weight depends upon the speed at which
the engine is intended to run, and the weight of the moving
parts ; 'with the engine-maker this is a matter of nice calcu-

AXLE BOXES.

273

lation. Seven-eighths of the whole disturbing weight is
allowed with outside cylinder engines, and for inside cylinder
three-fourths. Counterbalancing is done to give the engine
greater stability on the rails. It is said that engines, without
counterbalancing, will not attain the speed they will when
counterbalanced, the resistance being greater. They must be
sufficiently heavy, not only to balance the crank and
connecting rod, but the piston and its appendages.

297. Sand Cock. — To every engine there is a small sand
box, fitted either on the top of the tank, in front of the
engine on the buffer beam, or by the side of the footplate.
In connection with it is a small pipe from 1^- to 2 inches in
diameter, leading to within two inches of the rail in front
of both driving wheels, or in front of the whole if con-
nected by coupling rods. The cocks are opened in slippery
or damp weather, when the engine is starting, to assist the
wheels in biting the rails, so that they may not run round
without giving motion to the engine. The engine being
fairly started they are closed. Whenever the wheels begin
to slip, the cocks are opened till the nuisance is abated;
and are, as occasion may require, brought into use on
inclines.

AXLE BOX.

298. Axle Boxes. — The wheels are fixed securely upon
their axles, which revolve in boxes, upon which the weight
of the boiler and machinery is carried through stout springs.
~~be axle boxes can rise and fall freely, as jfar as the

274

STEAM,

springs will permit. The axle boxes are guided vertically by
suitable guides or axle guards. The part of the axle which
revolves in contact with the axle box is called the journal.
When the journals are inside the wheels they are called inside
bearings, and when outside the wheels outside bearings,
»© A

SPRINGS,

SPRINGS.

275

A is the journal (p. 2 7 3), the whole weight rests on the spring,
of which p is the spring pin, therefore the weight of the engine
rests on the top of the axle (and wheel) from a to 6; c d is
hollow, although sometimes a sponge, or some cotton waste, is
laid in to soak up the oil or grease. In the cross section it is
seen more clearly, where the weight rests upon the axle.

299. Springs. — The weight of the engine, boiler, etc., is
Sustained by springs resting upon the axle boxes. They are
formed of steel plates from three-eighths to half-an-inch in
thickness, of a number proportioned to the weight they
have to carry. Each spring of the driving axle has often to
carry from four to six tons. The plates are connected at the
centre, and slide on each other at their extremities. If we
examine the spring A (p. 274), we shall notice a rod proceeding
from the centre of the spring s to the top of the axle box at
a. The middle of the spring thus rests upon the axle box.
At p and p are two eyes, the ends of the spring pass into the
jaws of a bridle at p and p, and through them passes a pin to
keep the spring firm at p and p. Sometimes, as in figure B, the
springs are placed below the framing, when the weight of
the engine is made to rest upon the ends of the springs. In
figures A, B the weight of the engine is carried by the springs

TRANSVERSE SPRING,

8 9, the framing F F resting on the spring pins pp, the springs
then bear up tho weights, They are fastened to the axle box in
figure B by means of a pin passing through the eye of a

276

STEAM.

strap a round the middle of the spring. In the upper figure
b b are the horn plates, or axle guards, of wrought-iron,
forming part of the frame of the engine. They form a guide,
with the cast-iron slides riveted on to the wrought-iron
horn plate, for the axle box to move up and down in, as the
springs give way to the weight and jerks of the train. The
strain of the engine and carriages comes on the horn plate.

This is another method of arranging the spring : — A
transverse spring is attached to the framing at H, and
carries the weight on its centre. The ends of the spring s s rest-
ing on the top of the axle boxes at S and S. Their use is to
receive the jerks, oscillations, etc., as the engine runs, so
that the motion of the engine may be smooth, just as we
know, and can feel, the difference between riding in a cart and
a carriage, so the springs act in keeping the engine, etc., still.
300. Buffers and Buffer Springs. — Buffers are to receive
any sudden shock or strain, so as to give the passengers as
little shock as possible.

A B is bolted to the
buffer beam; within C D
are four or more cushions
of India-rubber, or India-
rubber springs, 1, 2, 3, 4,
separated from each
other by T3^ iron plates,
all of which will admit
of lateral motion. The
bar a b passes through all the plates and India-rubber springs.
When a shock is received by the buffer E, the springs are
compressed and the bar runs up A B, but it is sometimes
arranged to drive from right to left. Steel springs are as
frequently employed as India-rubber.

Here we see the arrangement of the draw bar and spring
for a carriage. At H are the India-rubber springs, L is the
hook by which the carriage is attached. The pull of the

" carriage acts on s and
draws the bar towards
L, so that the springs
are compressed.
For buffing and draw springs, many kinds have been em-

BRAKES.

27?

ployed. India-rubber springs are formed of circular discs,
the buffing and draw-rods running through them; helical
and spiral springs, made of steel, and rods acting upon ordi-
nary steel springs, are also used.

301. Draw Bar with Springs. — The draw bar with
springs is fitted to engines to receive^and take up sudden
shocks and strains.

DRAW BAR WITH SPRINGS.

h is a crook or hook, to which the carriages are coupled
on ; a a a is the draw bar, chiefly shown by dotted lines ;
b' b are two steel springs ; d and e are two transverse pieces
of the frame, firmly fixed at the same constant distance ; e is
the buffer beam ; c is a cutter to bring up the spring b',
while the spring b is brought up by d , a washer close against
a nut, as seen in the figure. The action is this, if a pulling
strain comes upon the draw bar, then the spring b' acts, and
is compressed by the cutter c ; at the same time, the washer
d compresses the spring &, thus assisting 6' to counteract the
strain. The traction spring or draw bar modifies the force
of sudden snatches by the engine, which are liable to snap
the couplings between the carriages. A plan adopted to
resist the strain on carriages, is for the two buffers to act
each on the end of an ordinary carriage spring, say from
left to right, while the draw bar, to which the carriage is
coupled, acts on its centre from right to left.

302. Brakes. — Brakes are employed to bring the train to
a standstill. They are generally worked by the fireman,
although there are brake vans with brakes worked by the
guards as auxiliaries.

Suppose the handle H pulled to the left (by a screw), then

STEAM.

the lever E is drawn towards the left, and with it the lever
A B. As A goes to the left, the arm A C jams the brake K
against the wheel, while the arm B jams K' against the other
wheel, when, friction preventing the revolutions of the wheel,
the train is brought to a standstill.

BRAKES.

The brake, which is essentially a screw and lever ap-
paratus, is generally of wrought-iron, except the part which
embraces the wheels, which is of wood. Sometimes two or
more sledges slide on the rail under the engine. The power
developed by the screw and levers is enormous, reaching as
much as 500 : 1, so therefore if a man turn the screw with the
force of half a hundred weight, it acts upon the wheels with
a force of more than twelve tons. It does not do to make the
leverage excessively great, because the force coming on the
frame of the engine, it is liable to be wrenched. The frame
must be adapted to bear such extra strains. To save the
frame, the force should be thrown on the levers as much as
possible, and not on the screw, or the screw should be coarse
in its thread, and have a short handle.

A brake used on the North London Railway is a very
good one, bringing the train to a standstill in a very short
distance. " To each vehicle two pairs of pendulous brake
blocks are hung in the usual way. The brake is worked by
a — inch chain, carried on sheaves along the centre of the
train, united by coupling hooks at each carriage. In the
centre of each carriage the chain hangs clown like a festoon,

STEPHENSON'S LINK MOTION*.

279

and passes under two pulleys attached to pulling rods fitted
to the block hangers. When the chain is tightened, the
centre pulleys are raised, and the blocks pulled on the
wheels with a collective force of about 3 tons for each
vehicle. When the chain is slackened, the pulleys, assisted
by a back weight, descend by gravity to their normal posi-
tion, and free the brake blocks. The chain is tightened from
either end of the train by means of two transverse axles,
driven by steel-faced friction wheels 20 inches in diameter,
screwed by manual power against the van wheels. The
momentum of the van is thus made to retard the whole of
the train, and is so powerful that a train of eight vehicles
can stop the largest engine under full steam."

DIVISION V.

SLIDE VALVE AND COMBUSTION.

Stcphenson's Link Motion — Sector — Single Eccentric — Slide Valve
and its Motion — Temperature of Furnace Gases — Transmitting
Power of Metals— Coke and Coal Burning in Locomotives — Air
Required for Combustion — Steam Blow Pipe — Beattie's Fire Box
— Conclusions on Combustion.

303. Stephenson's Link Motion.— The advantage of this

STEPHENSON'S LINK MOTIOK.

ontrivance is, that the engine can be reversed without any
more trouble than is entailed by moving a handle. It con-

280 STEAM.

sists of two eccentrics H and G, each having its own rod
C E and A D. When the forward eccentric works the
slides, the engine goes forward ; when the backward eccen-
tric works them, it is reversed. D E is named the link,
and it is moved up or down by the lever D E D. a is the
slide rod attached to the block p. The link motion is not
used to work the steam expansively ; it merely alters the
travel of the slide, when the engine moves slowly or quickly.
It reverses the engine by reversing the travel of the slides.

To obtain the greatly varying power required in the loco-
motive at different times, it is necessary to be able to vary
the times at which the steam shall be cut off from the
cylinder. This is effected by the link motion, which con-
sists merely of two eccentrics, as has been already explained
(page 70).

304. Single Eccentric. — The single eccentric, which is
loose on the shaft, acts on the same principle as the double
eccentric with the slot link. With the double eccentric
and link, one eccentric only works the valves at a time, or
acts on the slide valve spindle. The single eccentric is
fitted with a weight to balance it, to keep it steady on its
stop. Were it not so, it would come away from the stop on
the shaft. Were no weight fitted, when the centre of the
eccentric and centre of the shaft came in a straight line
with the valve spindle, it would have a tendency to pass too
quickly over the centre, and cause a knock or back lash at
every stroke.

305. Sector. — The sector is in the form of a sector of a
circle, and is an adjunct to the link motion. In it is a series
of notches to hold the reversing handle. When the loco-
motive is started, the handle is dropped into full throw, or
into the farthest notch. By doing this, the forward eccen-
tric at once works the slides, or the eccentric rod comes
direct on to the valve spindle, and all the strength of the
steam is at once given to the piston. When the engine is
fairly under way, the handle is brought back a notch or so
to economize the steam. There are about five notches from
the centre down, or ten altogether. The nearer the revers-
ing handle is to the centre of the sector, the less steam is
used.

ACTION OF SINGLE ECCENTRIC AND SLIDE VALVE. 281

306. Slide Valve and its Motion. — The manner in which
the steam is admitted to and released from the cylinder, and
the points of the stroke at which the events take place, can
be varied in three ways : (1) By altering the form of the
valve ; (2) by variation in the valve gear which drives the
valve ; (3) by altering the relative proportions of the con-
necting rod and crank.

307. Action of the Single Eccentric and the Slide
Valve. — The annexed is the form of valve generally employed.
It is called a locomotive or " three-ported " slide.

A and A are the steam ports or passages, by which the
steam enters the cylinder. B is the exhaust port, by which
the communication is kept up with the exhaust pipe ; C G

SLIDE AND PORTS.

are termed the bars or bridges. In the position shown in
the figure, the valve is at half-stroke, and the parts D of
the valve, extending at each end beyond the ports, is termed
the outside lap or outside cover ; and the part E, or the
distance the inner edge extends beyond the ports A A, is
called inside lap or cover.

Should the valve extend only to the dotted lines on its
inside, it would not entirely cover the ports at half-stroke
on the inside, but leaves them both partly open to the
exhaust. This is called inside clearance. Lead has already
been sufficiently illustrated on page 118.

When a slide is driven by a single eccentric, its motion is
a compound of two others : (1) Of that given by the centre of
the eccentric moving round that of the crank shaft; (2)
this motion is retarded and accelerated by the varying
inclination of the eccentric rod. As the eccentric is nothing
but a crank, we can determine the various positions of the
slide in relation to such a motion as a crank will give.

282

STEAM.

The manner in which the position" of the piston is in-
fluenced by the action of the connecting rod,
is shown by our figure, in which are repre-
sented the relative positions occupied by the
crosshead and crank, at nine points in a
half revolution of the crank shaft. In this
diagram the length of the crank is taken at
12 inches, and that of the connecting rod at 6
feet. The short lines, numbered 1 to 9 on the
upper side of the centre line, represent the
positions of the crosshead corresponding to the
similarly numbered positions of the crank.
The other lines below the centre line, lettered
a to ^ show the places the crosshead would
occupy if the connecting rod were of infinite
length ; and the spaces into which these lines
divide the stroke of course agree with the
spaces into which the diameter, k I, is divided
by the ordinates drawn to it from the points
denoting the position of the crank pin. This
diagram at once shows that if the crank shaft
rotates in the direction of the arrow, from k
to I, the motion of the piston will, during the
first half of the stroke, be retarded by the
action of the connecting rod, while during the
latter half it will be correspondingly acceler-
ated. The effect of this is, that, during the
whole of the stroke from the crank shaft, the
piston is in arrear of the position which it
would occupy if the connecting rod were of in-
finite length ; whilst, during the stroke towards
the crank shaft, it is correspondingly in ad-
vance of such position. In the example before
us, the piston travels 10*99 inches, while the
crank moves from position 1 to that marked
5, and 13 '01 inches as it rotates from 5 to 9.

308. General Principles. — The slide valves
admit and release the steam. By the lap,
means are provided for the suppression of the
steam before the end of the stroke, and the eccentric is so

MOTION OP THE SLIDE. 283

set that the valves shall open before the commencement of
the stroke, and thus release the steam before that period. It
is usual also to give a certain amount of lead to the valve,
in order that the steam, may be promptly admitted, and the
port opening be wide enough as the piston advances to
allow the pressure to be well sustained. The amount of
this varies with the speed of piston at which it is intended
the engine shall work, also to a certain extent with the
opinions of engineers, ^ inch being the usual amount in this
country, and ^ inch, or even as little as J inch, in America.
In some cases a small amount of inside lap is given for
the purpose of preventing the escape of steam too early
in the stroke ; in. other cases, inside lead is adopted in
order that the steam may have a freer escape. The former
would be suitable for goods engines exerting large tractive
force at slow speeds, and the latter for express engines work-
ing at a high speed of piston. The amount of either is rarely
over ^ inch at the most.

309. Motion of the Slide — Continued. — By these five
figures we wish to show the relation between the travel of
the slide and the path of the centre of the eccentric pulley.
The motion of the eccentric is here communicated to the
valve through a rocking shaft. This was the old method ; it
is now customary to attach the eccentric rod directly to the
slot link, which is brought down or up to the end of the valve
spindle.

" In figure 1, the piston is shown at the commencement of
its stroke by the amount due to the angular advance of its
eccentric, which, as there is no outside lead, corresponds in
this instance to a movement of the valve, equal to the lap,
which is here T\th of an inch. At the same time the steam
passage, communicating with the end of the cylinder farthest
from the piston, is uncovered to the exhaust by the amount
of the inside lead, which, as there is no inside lap, is also
•j-Q-th of an inch. Here the centre of the crank is seen in a
position at right angles to the piston rod and below it. In
fig. 2, the crank has performed one-eighth of a revolution,
and both the steam ports are partially open, the one for the
admission of steam and the other for its egress. The centre
of the eccentric has moved on in the same direction; but

284

STEAM.

notice in every case that the crank moves on in advance of
the eccentric, which is the very reverse of what would take
place if there were no rocking shaft. In all cases now the
crank of the slide rod is in advance of the larger crank. In
fig. 3, one-fourth of a revolution has been accomplished, and
both ports are fully uncovered. In fig. 4, the crank having

JTG.i .

made three-eighths of a revolution, the ports are again partially
closed, the valve having assumed a position almost similar to
that which it occupied in fig. 2. In fig. 5, the piston has
reached the end of its stroke, and the steam port, which has
hitherto been receiving steam, is uncovered -j-g-tli of an inch

SPECIFIC HEAT TRANSMITTING POWER. 285

on the exhaust side, the other steam port being entirely
closed."

310. Temperature of Furnace Gases. — The heat trans-
mitted by a solid body from a hotter medium to a colder one,
is in direct proportion to the difference of the temperature of
the two. The evaporation by any given heating surface will
therefore be increased as the temperature of the furnace gases
increases. Hence it is that coke is superior to coal, for its
products of combustion come off at a higher temperature than
those of wood or coal. In this matter we must consider the
boiler temperature as the lower. It is not a fact that the
greater the pressure of steam the less the evaporative power
of the boiler, for the gases in this case simply escape at a
higher temperature, and the pressure has nothing to do with
the transmission of heat.

311. Time of Contact. — The transmission of heat is not
alone directly proportional to the extent of heating surface
and the temperature of the furnace gases, but also to the time
of contact and the conducting power of the solid metal in con-
tact. In a locomotive, as the gases run along the tubes their
temperature rapidly diminishes ; small tubes with the blast
make the gases move rapidly, with larger ones they move more
slowly in inverse proportion. Products of combustion always
take the nearest and shortest way to the chimney. Hence
many different arrangements are adopted to keep these gases
hi contact with the heating surface, as inclining the fire box
and tubes, making the distance greater from the back of the
fire box to the tubes, than from the front part of the grate to
the tubes. In this latter arrangement the great bulk of the
air, being drawn in at the front end of the grate, would pass
through the lowest row of tubes, because it is the shortest
route, and here meets with least resistance. The grate is
inclined towards the front of the fire box; to counteract this
by equalizing the distance, more fuel is thrown on the front
of the grate, for the air, entering at the front to pass through,
is thus retarded.

312. Specific Heat Transmitting Power. — We have to
consider (1) the way in which the boiler plates and tubes
receive the heat ; (2) the conducting powers of the metal ;
(3) the emission of heat by the metal.

286 STEAM.

Let A = the absorbing unit, or the heat absorbed by one
square inch of boiler surface per minute in a locomotive.

Let B = the unit of conducting power, or the heat trans-
mitted through the boiler surface on a square inch per
minute through the thickness of one inch.

Let C = the emission unit, or the quantity of heat
given up by one square inch per minute to the water m
contact.

Let t — thickness of the plate ; then while A and C will
remain constant, B must be divided by t, for the quantity of
heat transmitted or conducted by the metal is inversely pro-
portional to the thickness of the boiler plate.

Suppose the heat within the fire box to be given off in con-
stant quantities, the plate will soon come to a stationary
temperature, and all the heat absorbed by it will be instantly
transmitted to the water, when the following equation will
exist : —

A = — = C = H (say total heat transmitted).
t

Taking the reciprocals

'.I..*

1 _ 1

'' A ~B

~ 0 H

' A.+ B

f 0"^ H

• H

^ + <]

This equation shows three things : — •

(a) That the heat-transmitting power of a boiler plate
increases with the heat absorbing, conducting, and emitting
power, (b) and decreases with its thickness, (c) but the heat
transmitting power is not inversely proportional to the thick-
ness of the plate.

In practice, it is not the thickness of the metal that is of
importance in the conduction of heat, but the heat transmit-
ting capabilities of the surface. The boiler plates become
coated with rust or oxide of iron and soot on one side, ancl
scales on the other j these lessen the absorbing and emitting
power of the boiler surfaces, Hsnce it is that thick platea
have but little influence, although thin plates with clean

TRANSMISSION OF HEAT.

287

surfaces will give the greater evaporative effect. Again,
thick boiler plates are objectionable, because they get hotter
on the outside next the fire than inside, hence burn, and their
liability to become injured by excessive heating is well known.
313. Transmission of Heat, with Decreasing Tempera-
ture of the Furnace Gases, or Transmission of Heat in
Tubes, — In showing that

we assumed that, during the time of contact, the tem-
perature of the furnace gases remained constant. This con-
dition only exists over very small areas of the boiler plate,
in tubes as the gases pass along, we must consider that the
temperature diminishes.

n nl n*

Let this represent a boiler tube surrounded with water,
and through which the gases pass.

Let us suppose n m is a very small section taken at any
particular place.

Let G- = the quantity of gas in pounds passing m n per
minute.

Let t = the temperature of the gases at m n above the
water in the boiler, which depends upon the distance of m n
from A.

Let x = the distance from m n to m1 n1,

After passing through the small space n m1, the gases
will have lost a certain amount of heat, which will be in
proportion to the length of mm1 and the difference between
the temperature of the gases and water.

Suppose we take for the unit of absorption, the heat
which would be absorbed on one inch in length in one
minute from gases 1° hotter than tho surrounding water,
tho heat absorbed by the small space n m1 is
Hj = a t (units of absorption).

288 STEAM.

Let the gases pass through the next small space nl m2 = x,
then since the loss of temperature is proportionate to the
distance they travel, they enter n* m2 with a temperature
t^= t-tx = t (l-x) .'. heat taken by second length will
be equivalent to

H2 = (t - x t) x — tx-x~ t, and

£2 = ^ -H2

.-. t2 = t-tx-tx + xH
- t-2tx + x* 1
= t(l-2x + x")
= t(l-x)*
— temperature when it enters at m2 ?i2.

In the third length we shall have

H3 = t(l-x*)x = t(x-2x'2 + x3)
.-. tQ - £o-H3 = t(I-x)*-t(x-2x'2 + cc8)
= t(l-x)*

Hence we see the law for the decrease of temperature as
the gases pass along the tubes : the temperature falls in a
geometric ratio. In passing through the first, second, third,
etc., unit of length, the temperature falls in proportion to
1-oj; (l-x)2 ; (1-a)3, etc.

These numbers are represented by hyperbolic logarithms,
thus : —

Let xm = unit of length from front end of the tube.
,, tm = the temperature of the gases above the water, less

the unit of absorption.
,, xn = whole length of tube = L
,, tn = temperature of smoke box.

Then since

Log.g t^ _ X* _. 1^
Log.j^ xn " L
Log.,£n r=L x log.ttm.

314. Coke and Coal Burning in Locomotives. — It is
usual to employ coke in locomotives, so that no smoke shall
be produced. In coal the three elements of importance in
combustion are carbon, hydrogen, and oxygen. Anthracite
contains 91*44 per cent, of carbon, 3-46 of hydrogen, 2 -5 8 of
oxygen ; the rest is nitrogen, sulphur, and ash. Good
average coal contains 73*52 per cent, of carbon, 5 '69 of
hydrogen, and 6f48 of oxygen ; the rest as above, ash, etc.
Anthracite produces 9 2 '9 per cent, of coke; average coal.

COAL BURNING. 289

57-8 per cent. A hundred pounds of coal will give out
more than a million units of heat, but the products of com-
bustion carry away nearly one quarter of this, and require
246^ Ibs. of oxygen for their consumption, or about 1068-|-
Ibs. of atmospheric air ; but as all the air cannot be made to
give up the whole of its oxygen, the supply required is'
about 1355|- Ibs. The total evaporative power of this 100
Ibs. of coal is 858 Ibs. of water. We have, in a former page,
given a similar estimate. The student must carefully con-
sider the two, and notice where they agree, and how they
differ. Both estimates are taken from leading authorities.

315. A Pound of Good Coal will in practice evaporate
74 Ibs. of water, and its heat is distributed in the following
manner : —

7400 units or 62 -2 per cent, go to form steam.

2172 ,, 18-3 ,, are wasted with products of combustion.

2375 19 '5 „ are waste.

11947 „ 100

It is calculated that the combustion of a pound of coke
produces 14,000 units of heat, and requires 2| Ibs. of oxygen,
or 12 Ibs. of atmospheric air, or 160 cubic feet, for its com-
plete combustion The 160 cubic feet become 200 in prac-
tice, and theoretically the pound of coke should evaporate
12-16 Ibs. of water.

316. One Pound of Coke. — In practice the greatest evap-
orative power of a pound of coke is 9 J- Ibs. of water, and its
heat is distributed in the following manner : —

10920 units or 78 per cent, go to form steam.
2365 ,, 16^ ,, are lost by products of combustion.
715 ,, 5| ,, are wasted by ashes, etc.

14000 „ - 100
Coke has the advantage over coal as a fuel for locomotives,
because the temperature of its products of combustion is
considerably higher than that of coal in the proportion of
about 14 : 12.

317. Coal Burning. — When coal is burnt in the loco-
motive furnace, it requires that the air shall be admitted
in a peculiar manner to perfect the combustion. As soon
as fresh coal is thrown on the fire, a gas is set free which,

290 STEAM.

when mixed with, air, burns with a clear bright flame oi
great heating power. It is therefore of importance that this
gas shall at once have its due supply of air at the spot
where it is generated, or else the draught will draw it
through the tubes, and the heating power will be lost. The
air for coal-consuming locomotives is admitted in two ways,
partly through the grate, and partly by special contrivances,
but the exact quantity depends upon the kind of coal used.
An insufficient quantity of air is exhibited by dense black
smoke issuing from the chimney. With just enough or too
much air no smoke will come out, so it requires great care
and practice. A second requisite is necessary for the com-
plete combustion of coal : the temperature should be suffi-
ciently high within the furnace in order to effect the proper
combination of the oxygen and carbon. In practice, to
prevent smoke in locomotives, engine-drivers have chiefly
relied on the ash pan, the damper, and the fire door, with
careful firing. " They have endeavoured to prevent the
formation of smoke by controlling the admission of air
through the grate, and adjusting it precisely to the require-
ments of the fuel, by similarly manoeuvring the fire door for
the admission of air above the fuel, by stoking with large
pieces of coal and deep fires for heavy duty, and smaller
coals with shallow fires for lighter duty, by firing more
frequently to lighten the duty, and at all times by keeping
the bars covered with fuel to prevent excessive local draughts
through the grate." The fire door should be pitched low ;
fresh coal must be thrown on under the fire door directly
inside, and, when partly burned, pushed forward towards the
tubes ; but when the grates are inclined, it will find its way
down by gravitation, and thus with good stoking a very
efficient system of coal burning may be carried out. It is
the usual practice now not to depend upon the stoking, but
to adopt one of these, two methods : (1) A current of air is
introduced through tubular and other openings in the sides
of the fire box, and thus uniformly distributed over the
surface of the fuel ; (2) a body of air introduced through the
doorway is deflected upon and over the surface of the fuel
by a baffle plate. Large and spacious fire boxes are also
introduced with extensive grate surface. In addition to the

BEATTIE'S COAL CONSUMING FIRE BOS.

291

above, a third method lias found considerable favour. It
may be described as follows : A steam-induced current of air
is made to pass over the incandescent fuel, thus air currents
are admitted just above the fuel by tubes or otherwise
through the sides of the fire box, and are then forcibly
accelerated by means of jets of steam, directed from the
outside through the openings into and across the fire box.*

318. Steam Blow Pipe. — The steam blow pipe in a loco-
motive corresponds to the blast pipe in a marine engine.
All engines that consume coal are fitted with the blow pipe
or auxiliary jet in the chimney, to continue the draught
when the engine is standing, and to assist in getting up the
steam when the fire is first lighted.

319. Beattie's Coal Consuming Fire Box. — In this boiler,

BEATTIE'S COAL BURNING BOILER.

signed for the use of coal only, the fire box was divided by
an inclined water partition into two compartments, each
having its own door, fire grate, ash pan, and damper. The
principal fire was maintained in the box nearest the foot-
plate. The gases arising from the coals were met by a great

* For a further explanation, see chapter on Combustion and the
Prevention of Smoke.

292 STEAM.

number of fine streams of air entering through the perforated
door, and both the gas and air rose through a grating of fire-
clay tiles into the upper part of the second fire box, on the
grate of which coal was burnt only slowly, with a slight and
carefully regulated admission of air through the front damper.
The mingling of air and gases was further deflected down-
wards by a hanging water bridge, and passed over a fire-brick
arch and through a series of fire-clay tubes into a combustion
chamber, from which the boiler tubes led into a smoke box ;
most of the arrangements are seen in the figure. In these
furnaces, arrangements are made for a sufficient admission of
air, for the intimate mixture of the air and gases, and for
the maintenance of a high temperature to complete the com-
bustion of the gases. The grating of fire-clay tiles is seen at
the lower right hand side of the figure, the hanging water
bridge is hanging down from the top of the fire box, the fire-
brick arch is seen to the left, the combustion chamber is oil
the right hand of what looks like the barrel of the boiler, the
entrance to which is through a series of fire-clay tubes not
shown (as they cannot be without putting the boiler in section).

320. Conclusions and Facts on Combustion in Locomo-
tives.— The following are the practical conclusions as to the
combustion of coke, coal, and wood in a locomotive furnace : —

"1. Successful practice requires the complete combustion of
the carbon and hydrogen available in the fuel.

"2. To find the quantity of free carbon and hydrogen, it
is necessary to deduct one part by weight of hydrogen, or six
parts of carbon from the total contents of the fuel for every
eight parts of oxygen contained in the same.

" 3. One pound of coke requires about 200 cubic feet of
air for combustion : the air may be admitted through the
grate only.

" 4. One pound of coke is capable of evaporating 9*5 ILs.
of water at 15°|-C.; in common practice, its evaporative
power is 8-£ Ibs. of water.

" 5. The temperature produced by the combustion of coke in
the hottest part of the fire box, may be estimated at 166G°C.

" 6. The gases produced by the combustion of coke carry
16|- per cent, of the total heat generated into the smoke box;
which they leave at a temperature of 333°C,

ME TfcAM OH TRAMWAY. 203

" 7. The complete combustion of coal requires tlie admission
of air both, through and above the grate ; the relative propor-
tion and the total quantity of air admitted in both ways
depends upon the percentage of gaseous components in the
coal.

" 8. Insufficient admission of air causes smoke and the loss
of heating effect by incomplete combustion. A surplus of air
reduces the temperature of flame, and causes waste of heat.

"9. The evaporative duty of coal per pound weight
averages about 6 Ibs. of water; in regular practice the
maximum being about 8 Ibs.

"10. The temperature produced by coal in the fire box is
lower than that obtained from coke.

"11. The products of combustion from coal have a higher
specific heat than those from coke : they carry off a quantity of
heat equal to 18*3 per cent, of the total heat produced. This
percentage raries with the amount of hydrogen in the coal.

" 12. The combustion of coal must be made as nearly
uniform as possible by skilful firing.

"13. Coal, when completely and properly burned in a
locomotive, affords greater economy, as compared with the
coke produced from the same.

"14. The evaporative power of dry pine wood is in prac-
tice 2£ Ibs. of water, the maximum having been found at
4 Ibs. One pound of coke is equivalent to 2 J Ibs. of wood.

"15. The temperature produced by wood is generally less
than 1111°C."

DIVISION VI.

THE ROAD.

Tramway — Railroads — Curves — How the Carriages are Kept on a
Curve — Hails — Fish Joint — Gradients — Ballast — Cuttings and
Embankments — How Kails are Laid — Two Ways — Broad and
Narrow Gauge — To Adapt one Gauge to the other — Fell's Kail-
way — Turn Tables — Traversers — Switches and Crossings.

321. The Tram or Tramway is a roadway consisting of
long pieces of wood or iron laid down in lines, and prepared

29 i STEAM;

to receive the wheels of waggons or trams. They were first
used in the North of England and South Wales for the con-
venience of carrying coals from the mouth of the pit to
seaport and other towns. The way in which they were
originally formed may be thus described : First, pieces of
oak, 5 or 6 feet long, called sleepers, were laid transversely
across the track about two feet apart; next, longitudinal
beams or rails, in lengths of 5 or 6 feet, of sycamore or larch,
were laid upon these sleepers, and secured to them by wood
pins or trenails ; next, these longitudinal pieces of wood
were supplanted by rails formed of wrought-iron plates, next
cast-iron rails were used. The trams were drawn by horses.
Some tramways are constructed of hard stone, as granite, for
sills, and flat iron bars laid upon them for rails. A good idea
of one of the earliest form of rails may be obtained by taking a
sheet of paper the size of this sheet ; first double down one-
third of the page longitudinally, turn over the paper and
double down the other side in a similar manner ; now stand
the two pieces perpendicularly to the middle, one will be
above and the other beneath. Imagine that the lower one
enters the longitudinal rail, and the middle one lies
on and is bolted to it, then the wheels of the carriage
must be supposed to run on, or within, the one standing
perpendicularly. Each part was about three inches wide,
and of iron one inch or three-quarters thick.

322. Railroad. — Kailroads are improved tramways. The
London and Birmingham Railway is about 30 feet wide
on the embankments, and 33 feet in the cuttings; it is
wider in the cuttings, because two- drains are necessary, one-
011 each side of the line. The average breadth of formation
is 18 feet for a single line, and 28 for a double. Space has
to be allowed for fencing and ditching. The width on the
narrow gauge lines is 4 feet 8| inches, as North-Western,
South-Western, Eastern Counties, etc., and 7 feet on the
broad gauge, Great Western. The space between the two
lines of rails is 6 feet 6 inches, and is often spoken of as the
" six foot way." The sleepers are laid transversely across
the road at a distance of from three feet to three feet six inches
apart. To the sleepers are fixed the chairs, which are cast-
iron supports for the rails. Sleepers are frequently creosoted,

HOW THE CAHRIAGES ARE KEPT ON A CURVE. 295

or else kyanized, to resist the action of the atmosphere,
water, etc. On the broad gauge system, the line is laid with
longitudinal sleepers and bridge rails, but the narrow gauge
with cross or transverse sleepers and double-headed rails ; the
rails in the former case being secured directly on to the
longitudinal sleepers, whereas those of the latter are supported
by cast-iron chairs secured to the cross sleepers. Longitu-
dinal sleepers have been tried on the narrow gauge system,
but have not been found to answer so well as the transverse.
At least this is the opinion of some experienced engineers.

Railways are single or double. The double consist of two
lines of rails — a down line and an up line. The down line
leads from London, the up line goes to London. To a
person looking towards London, the down line is the right
hand pair of rails, the up line the left hand pair. Single
lines consist of a single pair of rails used both for the up and
down lines. There are double lines at intervals to allow one
train to pass another. Lines are constructed on this system
for cheapness. The lines should be as level and straight as
circumstances will permit.

323. Curves should be of as large a radius as possible;
there are but few curves of less than three-eighths of a
mile, or 30 chains7 radius. The exterior rail of the curve
is always elevated — the generic term is super-elevated—
to counteract the centrifugal force, or otherwise the train
might leave the rails. Sharp curves should never be on
steep inclines, for the tendency to leave the rails at a curve
is as the square of the speed; as a rule, they should be
out in the open where they can be well seen, and not in
cuttings.

324. How the Carriages are Kept on a Curve.— As an
object moves round in a curve, the centrifugal force has a
tendency to make it fly off in a straight line* Hence railway
carriages, in passing curves, have a tendency to rtin off the
line at the outside. To prevent this, and to keep the flanges
of the wheels from the rails, the larger, or outer curve, is
raised higher than the inside one, so by this means the
carriages are thrown to the opposite side to that on which
the centrifugal force would keep them. The super-elevation
of the outer rail and the conical wheel are thus made to

296

STEAM.

balance the centrifugal force. On the narrow gauge lines,
with a wheel three feet in diameter, no super-elevation need
be made, unless the curve have a less radius than 1400 feet;
on the broad gauge line, with a four feet diametered wheel,
the least radius that can be used without super-elevation is
double this. The quicker the trains pass a curve the greater
must be the elevation of the outer rail.

325. Eails. — The rails are made in many shapes, as seen
by the following figures; all these forms are in use, but
generally those marked d and c are preferred. There are many
other forms as well as these. At a is shown one of the
earliest, a plate of iron turned up; the same figure also shows
the difference in the arrangement for the running of the
wheels on the tramway and railway. At a the purpose of

FORM OF RAILS.

one part of the rail is to confine the" wheel to the track, and
it is evident that much tractive force might be expended in.
the wheels grating against the rail; but at g, the modern
arrangement, we see that the wheel is kept on the rail by a
flange on the wheel. To the sleepers are fixed the chairs, or
chocks, of cast-iron, into which fit the rails, kept in their
places by iron spikes. The ends of the rails are secured to
each other by ajisk or fish plate, two being used, one on each
side, and bolted together by four bolts.

326. Jointing of Rails: The Fish Joint— The two ends of
any two adjoining rails are not placed close together, but a
small space is left between for expansion. The joint is
obviously the weakest part of the rail. The fish joint is
intended to give it stability.

GRADIENTS.

297

Hails are "fished" by having four holes — ct a a a —
punched in them, and then the fish plate F P is fastened on
with four bolts; the holes are larger than the bolts, to allow
a slight motion caused by the changes of temperature. The

fishes are made of wrought iron, and bear against the top
and bottom of the web of the rail, as seen in the section at
b and b. Close to each fish, on either side, are two chairs, G
and C, firmly bolted to the sleepers S S. The fish joint is
found to answer so well that its use is extending rapidly.

327. Chair, Sleeper, and Rail. — The following simple
figure will show how the rail r is fixed in the chair c c, by

CHAIK, SLEEPER, AND RAIL.

means of the wedge a] it also shows the manner in which
the flange t of the wheel W clears the chair without touching
it, and how it runs on smoothly and evenly without the
chair offering any resistance or obstruction.

328. Gradients should not exceed one foot rise in a sixty
feet length, although there are gradients double this, or that
rise two feet in sixty. Gradients are very expensive, as extra
power, which means fuel, time, and labour, is required to
ascend them. When very steep, stationary engines are em-
ployed to haul up the trains. Gradients should rise, where
practicable, on each side towards a station, for then the

298 STEAM.

weight or gravity of the train will assist the brakes in
biinging it to a standstill, while, when leaving, such an
arrangement will help to set the train moving. On long in-
clines there are occasionally level spaces, or benches, to assist
the ascending and check the descending train. It is not
allowable to place a station on an incline.

329. Ballast. — After the railway is cut, and embankments
made, the road is covered with broken hard stones, flint, dry
gravel, etc., called ballast, upon this the sleepers are laid.
The ballast serves two purposes, it allows all water to drain
away, and so the sleepers are kept dry ; it also keeps them
firm and steady.

330. Cuttings and Embankments. — To save expense, the
sides of a cutting should be as steep as possible, for then less
earth is moved, but this can scarcely ever be done ; no general
rule can be given as to what slope should be used, every-
thing depends upon the strata that is being cut through, and
not alone upon the top strata, but the bottom strata have
frequently to be considered. Most kinds of hard rock
will stand vertically, chalk requires a slope of one in three,
sand and gravel three feet in two, clay two to one; but there
are very great exceptions to every rule. The most trouble-
some cuttings are where soft clay or wet soft strata, come
under others that are harder and drier, the soft and wet give
way, or else the others slip over them, thus giving an enor-
mous amount of trouble, and adding to the expense of the
permanent way.

331. How the Bails are Laid. — Two plans, already men-
tioned, are followed in laying down rails: — (1) That with
longitudinal sleepers, which gives a continuous bearing ; (2)
that with transverse sleepers, in which the sleepers are laid
about three feet apart, and the rails supported on chairs.

(i) The Continuous Bearing. — Here the rails are firmly
secured to long baulks of timber laid in parallel lines, each
line inclines a little towards the middle. They are kept at
the proper distance apart by transverse pieces of timber, the
ends of which are let into the baulks, and then secured by
angle plates or wrought-iron knee straps. Sometimes these
longitudinal sleepers are laid on transverse or cross sleepers,
and thus the advantages of both systems are secured.

fcROAD AND NARROW GAUGE.

299

(2) The Transverse Sleeper Bearing. — This is the system
that has been most generally adopted. Sleepers of good
strong timber, twelve feet long and six or eight inches thick,
properly prepared (see page 294), are laid at intervals of
about three feet or three feet six ; on each sleeper is securely
fixed two chairs at the proper distance, in which the rails are
firmly fastened, and so kept in their places steadily > and at
a continuously equal distance. Formerly, where stone was
plentiful, large blocks of stone were used to fix the chairs
to, and thus support the rails.

332. Broad and Narrow Gauge. — The broad gauge has
a distance of seven feet between the two rails on which
the carriages run$ while the narrow gauge rails are 4 feet
8J- inches apart.

333. To Adapt Broad Gauge to Narrow Gauge. — Great
interruption and expense are entailed through railways
being of a different gauge. Instead of passengers and goods
in bulk being conveyed from the starting place to their
destination in the same carriage, much trouble and cost
are incurred in changing from one line of rails to another.
So much is this inconvenience felt, that gradually on the
Great Western and other lines a third line of rails is being
laid down, so that the inner line of rail and the third serve
for the narrow gauge carriages.

334. Fell Railway. — The progress of railway locomotion
has compelled engineers to turn their attention to steep
gradients, and how best to drive an engine and its carriages
up and down steep inclines. Practically, we have returned
to Blenkinsop's rail rack. The first plan proposed was to
have a middle rail up the steep incline and a pair of wheels
on vertical axes gripping the rail on each side, and which,

Jl.

t 11 )

A j

' R\ B

by their forcible revolution, would carry up the train where
the ordinary driving wheels would slip without effect. Mr.

300

STEAM.

Fell, for the Mount Cenis Hallway, patented a locomotive
with horizontal cylinders and two pair of coupled gripping
wheels driven direct without the inter-
vention of bevel wheels, the connecting
rods that turn the gripping wheels work-
ing in a horizontal plane. Powerful
springs press the gripping wheels against
the centre rail.

Wand W are the wheels of the engine,
B, the middle rail, A and B the gripping
wheels, a and a their axes.

335. Turn Tables.— Turn tables are
useful and necessary adjuncts to a ter-
minal station, especially when it is re-
membered that every engine upon com-
pleting a journey has to be turned round;
for the engine has to drag the train of
passengers and face any danger first. Turn
tables are divided into two classes : ( 1 )
Those employed to turn the engine and
its tender, which of course must be firm
and strong, and are generally turned by
gearing or hydraulic force ; (2) those
employed for reversing carriages, which
are not so strong, and are worked by
hand. *

In the annexed figure we have a sec-
tion of a turn table. T T is the floor
for carrying the rails, and on which
the engine or carriage stands that has
to be reversed, a the pivot, and w 10
the wheels or rollers on which the whole
turns, and by which it runs round, a
carries the centre of the floor, and w w
carry the outside circumference ; r r r r
are stay rods to bind the whole together,
and to give strength and stability to
TURX TABLE. the structure. M is the sole or sole
plate, resting on a solid foundation; the sole plate and the
wheels receive the whole weight of the turn table and what-

SWITCHES AND CROSSINGS. 301

ever is placed on it. C represents solid masonry. Turn tables
are required to be strong and steady, and to work with little
friction. They are constructed partly of cast-iron, and partly
of wrought. In some arrangements the wheels ww run simi-
larly to common railway carriage wheels. The whole is
bedded on some solid foundation, such as stone or brickwork.
Turn tables for engines and tenders have many wheels or
rollers, and are made exceedingly strong. They are turned by
gearing attached to one of the rollers. The roller path
frequently consists of an ordinary flat-footed rail inverted, so
as to present its upper table as a bearer to the rollers.

336. Traversers. — By means of a traverser, a carriage can
be taken directly across a station from the side of one
platform to that of the other. The traverser is a convenient
and cheap substitute for the turn table, consisting of a low
flat table which runs on a line of rails laid transversely to
the lines of railway. It is fitted with a line of rails on
itself, the rails overhanging at the sides, and are placed
as low as possible, so as to just clear the fixed lines.
When a carriage is run on to the top of a traverser, a
process which is rendered easy by the aid of short incline
planes attached to the ends of the table, it is then run or
traversed over any number of lines of rails, and then run
off and deposited on another line. The wheels of traversers
are placed in pairs, one a little behind the other, to enable the
traverser to pass the gaps in the traverse rails without shocks.

337. Switches and Crossings. — Switches and crossings,
or, as they are more commonly termed, points and crossings,
are used for the purpose of allowing the trains to pass or
cross over from one line of rails to the other. Several
different methods have been devised for doing this. One of
the simplest plans, and that most frequently adopted, is to
lay down a short line of rails connecting the other two, and
thus establishing the desired communication. It is, how-
ever, necessary to have ready and expeditious means of con-
necting and disconnecting this short line with the main line,
according as it is intended that the trains shall leave or con-
tinue upon the latter ; this is effected by the contrivance

Brmed a switch, which is shown in our figure.
a b and c d are portions of the rail of the main line, and

302

STEAM.

e/and g li portions of the short line branching from it. All
these parts are immovably fixed in the ordinary manner,
with the exception of the two rails fi and k I. These, which
are termed the tongues of the switch or points, are only fixed
at one of their ends f and &, on which they turn as centres ;
the other ends are tapered away to nearly a point, a slight
recess being sometimes cut in the other lines, as at i and I,
into which they fit. These tongues are connected together
by a bar m n o, by means of which they are preserved at
such a distance apart, that when either tongue is in con-
tact with the rail near it, the other shall be removed from
the one opposite a sufficient space to allow the engine or

SWITCHES.

carriage wheels to pass between. (Suppose the train to
come in the direction of the arrow.) In order to keep the
train on the main line, or to leave the same and enter the
branch line, it only becomes necessary to move the bar
mno. When mno, or the bar which moves the switch,
is in the position as shown at A, the carriages will leave the
main line ; but if shifted into the position shown at B, then
they will continue on their course along the main line. It
will assist the student to understand what has been said, if
he will consider that the flange of the wheel bears against
the inside of the rail. It is usual to have the points so
arranged that they are kept in the position shown at B
(where the main line is not interrupted) by a self-acting
weight, the attendance of a pointsman being necessary to
move them into the position A, if it is desirable that the
train should go off the main line. Two guard rails, p q and
r s, are employed to prevent the flanges of the wheels from

INDICATOR DIAGRAM OF THE LOCOMOTIVE. 303

striking against the point where the two lines intersect each
other at t.

DIVISION VII.'
THE INDICATOR AND DIAGRAM.

Richard's Indicator — Diagram of Locomotive — Conclusion to be
Drawn from Diagrams — Examples of Diagrams — Questions and
Examinations.

338. Richard's Indicator, and the slide diagrams given
on the marine engines, must be studied and mastered now.
In what is here said on the non-condensing or high pressure
diagrams of the locomotive, we have supposed the student
has mastered the early lesson there given, and that, having
some knowledge of the indicator and its action, he is now
prepared to study the locomotive diagram.

339. Indicator Diagram of the Locomotive. — The action
of the valve in the distribution of steam, as we have already
hinted, is regulated by the lap, lead, and travel. When
these are given, a diagram will show us at what point of
the stroke the steam is admitted, cut off, exhausted, and com-
pressed or shut in. "When the link motion is fitted, the
steam is cut off earlier by shortening the travel of the slide.
This is done in such a manner that, however much the travel
of the slide is reduced, the lead is always the same, or at least
as at full gear. With the shifting link, it is a little more.
When the travel is shortened, not only is the steam cut at
an earlier point of the stroke, but it is exhausted earlier,
admitted earlier, and the exhaust port is closed earlier

during the return stroke. Thus shortening the travel of

. .

the slide causes everything connected with the distribution

of steam to be done earlier.

No. 1 was taken with the shifting link in full gear in the
first notch of the sector, No. 2 in the second notch, etc.

Taking No. 1 first, we must understand that the port
began to open for the admission of steam at the point A,
about T3g- of an inch before the beginning of the steam stroke,
the line runs up instantaneously to B in time to commence

304

STEAM,

the steam stroke at the full pressure. While the pencil
runs from B to C the steam is at a continuous pressure of
38 Ibs., as shown by the scale at the side. At C the steam
is suppressed or cut off, and while the piston moves the per-

6 12

Inches of stroke.

pendicular distance between C and D (4 J inches), the enclosed
steam expands behind it, rapidly decreasing in pressure, as
indicated by the falling line C to D. At 3D, when the piston
has yet to travel the perpendicular distance from D to
G, the port is opened to the exhaust, i.e., it is opened
when the piston has yet to travel three inches, the pressure
therefore quickly decreases, as shown by the falling line
from D to E. During the return stroke, the steam continues
to exhaust into the atmosphere, and the atmospheric line
E F is traced ; but ordinarily the diagram seldom coincides
with the line, as we have it here, for there is a certain
amount of back pressure. When the piston gets to F,
within three inches of the end of the return stroke, the
exhaust port is closed, and the piston continuing its motion,
the cushioning takes place, and the pressure of the pent-up
steam increases, as shown by the rising curve F to A ; when
at A the steam is re-admitted, and the curve traced again.
We may, following the suggestion of Mr. Colbum, adopt the
following terms and points of distinction : —

A is the point of admission of the steam.

B to C is the period of admission of the steam.

C is the point of cut off or suppression.

INDICATOR DIAGRAM OF THE LOCOMOTIVE. 305

C to D is the period of expansion.

D is the point of exhaust or release.

D to E is the period of exhaust during the steam stroke.

F is the point of compression.

E to F is the period of exhaust during the return stroke.

The portion of the stroke described while A B is traced
is the period of pre-admission, or during which the lead is
taking effect.

The portion between F and A is the period of compression
or cushioning.

The same definitions apply to all four diagrams, taken
with four different notches of the sector.

(1) By considering the diagrams here given, it is obvious
that the sooner the port is closed to the admission of steam,
the sooner it is opened to the exhaust, as well as the exhaust
occupying less time, and also the sooner it is opened to
admit steam.

(2) Although every change takes place earlier, there is less
difference in the positions of the points of exhaust, cushion-
ing, and admission than in the cut off. Therefore the period
of admission being shorter, the period of expansion is longer.

(3) By shifting the link motion, the steam may be cut off
at from •£ to \ of the stroke.

(4) When we increase the expansion, though the exhaust
takes place earlier, it never commences within the first half
of the stroke.

(5) The period of cushioning, increasing as the admission
is reduced, amounts to one-half the stroke at mid gear.

(6) That the lead increases from 1 to 10 per cent, in pass-
ing from full gear to mid gear.

Let the student carefully compare these six assertions with
'the diagrams, and not leave the subject until he has mastered
them, when he will have learnt a really useful lesson. We
will take two and^tra, and try and explicitly restate them.

The period of cushioning, increasing as the admission is

"uced, amounts to one-half the stroke at mid gear.

In the first notch, the cushioning is from A to F, or meas-
uring from F to O it is 3 inches. With the second notch it
is measured by the thickly dotted line at the corner just
above A F, and takes place during 4| inches of the stroke,

306 STEAM.

reckoning from O along the atmospheric line to where the
line starts away from it. The cushioning is longer in the
proportion of the line A F and the darkly dotted line near
it, or in proportion of 3 to 4|. With the third notch, the
cushioning is shown by the fine dotted line at the same left
hand corner, and takes place during 7§ inches of the stroke.
When at mid gear the cushioning is shown by the line
commencing at 12, or it takes place during the last half of
the stroke. Thus the cushioning or compression at the

Inches.

1st notch : 2nd : 3rd : 4th : : 3 : 4| : 7| : 12.

Illustrating the second proposition : " Although every
change takes place earlier, there is less difference in the
positions of the points of exhaust, cushioning, and admission
than in the cut off Therefore the period of admission being
shorter the period of expansion is longer." The straight
horizontal lines along the top of the diagram vary in length,
that taken with the first notch being longer than the
second, the second than the third, and so on. " The
period of expansion is longer, for from C D is shorter than the
corresponding line on No. 2, and the one on No. 2 is shorter
than the one on No. 3, etc., therefore we see the expansion
increases. Again, as regards the first part of the proposition,
there is less difference between the four points corresponding
to D on the diagrams, than between the four points corre-
sponding to C on the diagrams.

The diagrams show that nearly all the time of the exhaust
(D E) is employed for the complete evacuation of the steam,
and if this be so for slow speeds, it must be, in a greater degree,
the case when the piston is running at ordinary speeds.

The following diagrams were taken when the Great Britain
was running at a velocity of 55 miles per hour under the
first, third, and fifth notch of the sector.

No. Lbs. Lbs. Lbs.

1. Mean pressure of steam 80.4, Exhaust 10.8, Effective (>0.6

3. „ „ 62 „ 11.2, „ 50.8

5. „ „ 40.9, „ 11.5, „ 29.4

Cylinder 18 by 24, driving wheel 8 feet, lap 1|- inches,
travel in full gear 4f inches, lead f inch, blast orifice 5i
inches diameter.

ISDICATOB DIAGRAM OP THE LOCOMOTIVE.

307

The marks on these diagrams show where the steam is cut
off, and where the exhaust commences. The diagrams prove

At fifty-five miles per hour.

loop

INDICATOR DIAGRAM FROM GREAT BRITAIN LOCOMOTIVE.

that the steam pressure falls very gradually during the
exhaust, especially at high speeds. The mean pressure on
the first diagram, by examining the scale and drawing equidis-
tant lines, as shown in the case of the marine diagram, amounts
to 80 pounds ; now, if we examine the curve at the bottom,
we find that the pressure of steam does not descend to the
atmospheric pressure, but remains above it, or near the
bottom line ; by taking the average of these distances from

308 STEAir.

the line, the back pressure is found to be 10-8 pounds,
leaving an effective pressure of 80*4 — 10*8 = 69*6 pounds.
The loss yielded by the early exhaust, when the link motion
is used, is of no consequence, for an early exhaust, at high
speed, is essential to a perfect exhaust during the return
stroke.

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

1. Describe the feed pump and valves necessary for supplying the
boiler of a locomotive. What is the principle of GifFard's injector
(1869)?

2. How is a locomotive engine reversed by the use of a double
eccentric and link motion. What is the object of the sector with
notches cut in it, whereby the starting lever can be held in inter-
mediate positions (1869) ?

3. State the leading features of Stephenson's invention of the
locomotive engine and boiler, pointing out the difficulties which were
overcome by this construction (Honours, 1869) ?

4. The boiler of a steam engine should be strong enough to support
the pressure of steam, the heat of the fire should not be wasted un-
necessarily, and a sufficient supply of air should be provided for the
burning of the fuel. State particularly the manner in which you
would design and set up a boiler so as to fulfil, as nearly as possible,
these requirements (Honours, 1871).

5. Describe the general construction of a locomotive boiler. Why
is the fire box made of copper ? How is it attached to the iron shell
which surrounds it? How is the roof of the fire box strengthened
(1871)?

6. Describe, with a sketch, the feed pump of a locomotive boiler.
What form of valves are used, and for what reason (1871)?

7. What form of packing rings should you prefer for the piston of
a locomotive engine? How are the brasses of the connecting rod
tightened (1871)?

8. The stroke of the piston of an engine is 24 inches, and the
diameter of the [driving wheel is 8 feet, what is the mean velocity
of the piston when the engine is running at 40 miles an hour (1871) ?

At each revolution the wheel goes 8 x 3 '1416 feet.
Forty miles per hour is 40 x 1760 x 3 feet.

. '. The train moves in feet per minute 40xl760x3

.*. Number of revolutions of wheel per minute == x *'-.*.. ?L

60x8x3-1416
But in each revolution of the wheel the piston moves 2 x 2 = 4 ft.

. •. Speed of piston =

560 feet per minute.

EXERCISES. 309

0. How does a railroad differ from a tramroad ? Describe the
method of supporting rails upon cross sleepers, and of joining them
securely (1871).

10. State what you know in respect of the arrangement and con-
struction of springs for the three different purposes for which they
are fitted to a passenger carriage, viz., as buffer, draw, and bearing
springs (1871).

11. Describe the link motion employed in reversing a locomotive
engine. Upon what principle is the power of the engine regulated
by the position of the starting lever (1871) ?

12. Describe some form of regulation valve for admitting steam
into the pipe leading into the cylinders. Where is this valve placed
(1871)?

13. Describe, with a sketch, the locomotive boiler. Why is the
fire box made of copper ? Why is it essential to discharge the waste
steam up the chimney (1869)?

14. Describe the safety valve of a locomotive boiler. Explain
Bourdon's gauge for ascertaining the exact pressure of the steam in a
boiler (1869).

15. Sketch and explain the arrangement of the feed pump and
valves connected with it, as fitted to a locomotive boiler (1869).

16. Describe generally the construction of a railroad. How are
the tires of the wheels of the carriages shaped, and for what
reason ? Describe the fish joint (1869).

17. Explain generally the nature of Stephenson's invention of the
locomotive engine and boiler. Point out the advantages resulting
from this form of construction (1869)*

18. The safety valve on the boikr of a locomotive is held down by
a lever and spring ; sketch the arrangement. A safety valve 4 inches
in diameter is constructed so that each pound of additional pressure
per square inch on the valve corresponds to 1 Ib. pressure on the
spring, what are the relative distances of the spring and valve from
the fulcrum of the lever ? After the valve is set, how much addi-
tional pressure per square inch will be necessary in order to lift it
-^th of an inch, the spring requiring 10 Ibs. to extend it 1 inch
(1871) ? Ans. 2 : 25 ; '497 Ibs.

19. State the differences in the construction of the driving axle of
a locomotive engine when inside or outside cylinders are employed.
Mention some of the advantages belonging to either mode of arranging
the engine (1871).

20. In driving a locomotive, if the valve gear were reversed before
stopping the engine what would occur, and what injury might
follow (1871)?

21. Describe generally the locomotive engine and boiler (1870). ^

22. When two equal and parallel cranks are connected by a link
attached to the end of each crank, as in the coupling link which con-
nects two driving wheels in a locomotive, will the rotation of one
crank cause the other also to rotate ? In what way does this kind of
coupling accomplish its object (1870)?

23. Explain the method of reversing a locomotive engine (1870).

310 STEA3I.

24. Describe the safety valve of a locomotive boiler, and the method
of adjusting it so as to blow off the steam at different pressures.
Explain the principle of any form of steam pressure gauge which you
would prefer to use (1870).

25. Explain the importance of balancing the cranks in a locomotive
engine. The leading wheel of an engine is 3^ feet in diameter, what
would be the pull on the centre of the wheel caused by an unbalanced
weight of 9 Ibs. upon the rim, when the engine was running at 20
miles an hour (1870) ?

/ V \2

Centrifugal force = \jw) x 9= 137*5 Ibs.

D
v — velocity per second.

26. Describe the construction of a locomotive boiler. How is the
fire box attached to the barrel of the boiler ? In what way is the
draught obtained ? In a locomotive boiler there are 156 tubes, each
2 inches in diameter and 127 inches long, what amount of heating
surface do they give (1870) ? Ans. 864 '4636 square feet.

27. Show with a sketch the method of fitting a safety valve to a
locomotive boiler. The safety valve is 5 inches in diameter, and the
bearing faces are inclined at 45° to the axis of the valve. What
should be the lift in order that the available opening for the escape
of steam may be xV^hs of a square inch? How do you account
for the fact that the pressure in such a boiler may often rise above
the amount for which the safety valve is adjusted (1870)?

As the angle is 45°, when raised the lift of the valve is equal to
the breadth of the circular space open. Hence if x — diameter of
part of valve flush with the opening, we have

(52-z2) -7854 = A

.-. a = 4-91

.-. lift.= 5-4-91 = -09 inches, Ans.

28. Show how you would allow for the weight of the lever in
adjusting the weight of the safety valve.

29. Explain the principle of construction adopted in a locomotive
boiler. How is the crown of the fire box strengthened (1870)?

30. How much air is required for the combustion of 1 Ib. of coke?
Describe the arrangements for obtaining a sufficient draught of air in
a locomotive boiler (Honours, 1870).

31. Describe Giffard's injector, and give some explanation of its
action (Honours, 1871).

32. Suppose a train of 60 tons is drawn up an incline of 1 in 100,
and the friction is 8 Ibs. per ton, find the work due to gravity, fric-
tion, and the total power required to draw the train up the incline.

If it rises 1 in 100, the force due to gravity = -_

L(}\)
' Prt

. •. Force due to gravity on a 60 ton train = — = |- tons

= 1344 Ibs.

EXERCISES. 311

Also as friction is 8 Ibs. per ton

force due to friction = 60 x 8 = 480 Ibs.
.'. Force to draw it up the incline = 1344 + 480

= 1824 Ibs.

33. With what force would it descend the incline ?
Force of gravity impels the train downwards = 1344 Ibs.

,, ,, friction resists this downward motion = 480 Ibs.
.-. There is left 1344-480 = 664 Ibs. to move it down the incline.

34. A stationary engine of 40 horse-power is situated on the top of
an incline rising 1 in 6, what weight would it draw up such an incline
(disregarding resistance of air) at a velocity of 220 feet per minute?
A horse exerts a force of 9 Ibs. to move a ton on a level road.

Work of engine per hour - 40 x 33000 x 60

Eise of incline in a mile = — - — = 880 feet

Work due to gravity in a mile = tons x 2240 x 880

= 1971200 x tons (a)

Work due to friction on a mile = tons x 9 x 5280

= 47520 x tons (b)

By adding a and b.
. •. Total work on a mile = 2018720 x tons

Kow 220 feet per minute = ?~ t x — ~ = miles per hour
5280

.-. Work to be done in one hour = 2018720 x tons x 22° x 60

5280
— Work of engine per hour

.-. Tons x 2018720 x 22° x 60 = 40 x 33000 x 60

. m 40 x 33000 x 60 x 5280 , ~ ~n .

.*. Ions — . ___ - = lo 69 tons.

2,018,720 x 220 x 60
Or thus :
Work of engine per hour = 40 x 33000 x 60

Eise of incline in one mile = - = 880 feet

Eate of work - — ^^ miles per hour

Work due to gravity on a ton p. mile = 2240 x 880 = 1971200 )

,, friction ,, ,, = 9x5280= 47520 \ ~~^

Total work on a ton per hour = 2018720 x 220 x 60

5280
*. Since work on a mile x miles per hour = work of engine

.'. Total number of tons = 40 x 33000 x 60 x 6280 = 15>69>

2018720 x 220 x 60
i5. An engine is required to draw 20 tons up an incline of one in

312 STEAM.

ten, at a velocity of 300 feet per minute; supposing the resistance due
to friction to be 8 Ibs. per ton, what is the horse-power of the engine?

Ans. 42T2T.

36. An engine of GO horse-power draws 100 tons up an incline at
the rate of 12 miles an hour; what is the gradient when friction is
10 Ibs. per ton? Ans. I in 256.

37. Find the horse-power of a locomotive engine which, running
40 miles per hour on a level track, draws a train weighing 70 tons,
taking the friction at 8 Ibs. per ton, and neglecting the resistance of
the air.

Distance train moves per minute = — 7^~~ = 3520 feet.

Kesistance due to friction = 70 x 8 = 560 Ibs.

. \ Work of friction per minute — 3520 x 560.

This must equal the horse-power in units of work.

. \ Horse-power x 33000 = 3520 x 560.

38. Find the horse-power of a locomotive to run 40 miles per
hour, to draw a train of 70 tons, while ascending a gradient of 1 in
500, allowing 8 Ibs. for friction, and neglecting the resistance of the
air.

From above work of friction per minute = 3520 x 560.

„ „ ,, „ hour = 3520 x 560 x 60

= 118272000

We next show how the work of ascending the gradient is calcu-
lated.

Rise of incline in a mile = ~^-~ - 10'56 feet.

Work due to gravity in a mile - 70 x 2240 x 10 '56

„ „ 40 miles = 70 x 2240 x 10'56 x 40

= 66232320.
Total work in one hour = 118272000 + 66232320

= 184504320
Horse-power x 33000 x 60 = 184504320.

39. A locomotive drew a train of 60 tons on a level line of rails at
a speed of 50 miles per hour, allowing friction at 8 Ibs. per ton, what
was the horse-power ? Ans. 64.

40. With what speed will an engine, whose effective horse-power
is found to be 64, draw a load of 60 tons, the rails being laid on a
level, and the usual allowance for traction assumed ?

Ans. 50 miles an hour.

41. A locomotive engine drew a train of 60 tons at a speed of 50
miles an hour up an incline of 1 foot in 440 ; if we neglect the resist-
ance of the air and allow 8 Ibs. per ton for friction, what was the
effective horse-power of the engine ? Ans. 104/T.

EXERCISES. 313

42. A locomotive engine of 100 horse-power drew a train of 60
tons at a speed of 50 miles per hour up an incline ; allowing 8 Ibs. per
ton for friction and none for the resistance of the atmosphere, what
was the gradient ? Ans. I in 498 nearly.

43. Find the horse-power to draw the train of 100 tons up the
incline of 1 in 80 at the rate of 20 miles per hour, allowing 8 Ibs. per
ton for the friction. Ans. 192 H.-P.

44. A train of 75 tons descends an incline of 1 in 400 at the rate
of 60 miles per hour; find the horse-power, the friction being 8 Ibs.
per ton. Ans. Horse-power — 28*8.

45. The stroke of an engine is 24 inches, it is making 70 revolu-
tions per minute, and the diameter of the driving wheel is 6 feet ;
what is the speed of the train.

In one stroke (forward and backwards) the wheel goes round once,
or 6x3'1416 feet.

In one minute the train goes 6 x 3*1416 x 70 (feet).

,, hour ,, ,, 6 x 3-1416x70x60 (feet).

.-. Speed per hour = 6x3^416x70x60 = 14'994 miles.

4G. What is the speed of the piston ?

The speed of the piston is the velocity at which it moves per
minute, or the distance it moves in one minute.

In 1 stroke the piston moves 2x2= 4 feet.
In 70 strokes „ ,, 4 x 70 = 280 feet.

47. An engine is running at the rate of 29 '09 miles per hour, the
diameter of the driving wheel being 5 feet, and the stroke of thfc
piston. 16 inches ; what is the speed of the piston ?

The simplest way to solve this question is first to find the number
of revolutions of the driving wheel per minute.

Train goes 29'09 x 5280 feet per hour.
29-09x5280

,, minute.

Wheel in one turn goes 5 x 3 '141 6.

•. Wheel turns -29'03 x 528°- times per minute.
60x5x3-1416

= 163 nearly.
Since each timo the wheel goes round the piston travels

16 x 2 = 32 = 2 feet 8 inches = 2§ feet.
.'. Speed of piston = 163 x 2§ = 434| feet.

48. Suppose the same engine to move at a velocity of 20 '34 miles
per hour, what is the speed of the piston ? Ans. 298 feet nearly.

49. The stroke of an engine is 25 inches, the diameter of the
driving wheel 6 feet 6 inches, what number of revolutions must it
make per minute to give a speed of 40 miles per hour, and what will
then be the speed of the piston?

Ans. 172-3 strokes, and 718 feet.

50. Tho diameter of each of n small cylinders is d, for them the en-

314 STEAM.

gineer substituted one large cylinder; show that the nibbing surfaces
or the friction was diminished, the length of the stroke being the same.
Rubbing surface of n small cylinder = d x K x I x n

Contents of small cylinder := cZ2 x !T x I

,, n „ cylinders = d2 x 5 x I x n

But this is the contents of the large cylinder.
Let D = the diameter of the large cylinder.

.*. D2 x 5 x I = contents ,, ,,

.'. D2 x ^ x I = d* x * x I x n
4 _4

.'. D -d^n

. Y rubbing surface of large cylinder = d \J n x IT Y. I
Hence, considering the friction the same as the rubbing surface,
Friction of large cylinder d \f n ir I _ 1
Friction of small cylinders • d ^ In \/n
.*. by decreasing the number of cylinders we diminish the friction.
Suppose one cylinder be substitued for four, then the friction is
diminished one half ; for in that case twice the friction of the large
cylinder is et^ual to the friction of the small ones.

51. Required the horse-power of a locomotive engine which moves
at a steady speed of n miles per hour on a level railway, the weight
of the train being W tons, and the friction ~ of the weight of the
train, the resistance of the air not being considered.

994-0 v W
The resistance to motion = - ^j—

If n be the number of miles per hour the train moves
- x 528( is the feet , min.

n x 5^80 2240 x "W
• *. The number of units of work done per min. = ! — x

••• n-p- = ^go°xx6o24x°;>v but/ = 2s° °r 8 ibs- ** ton-

60 /

: 280 c

n x 5280 x 2240 x W

33000 x 60 x 280
128 x n x W

100 x 60

CHAPTER XVIL
DE PAMBOUE'S THEORY.

Introduction — Work Done on One Square Inch — Horse-Power — The
Load — The Pressure — De Pambour's Theory — Relation between '
the Temperature and Pressure of Steam in Contact with the
Water — Relations between the Relative Volumes and Temper-
atures of Steam — Velocity of Piston under a Given Load and
Horse-Power — To Determine the Evaporative Power of a Boiler
— Maximum Useful Effect — Examples — Hyperbolic Logarithms.

340. To find the Units of Work Done on a Piston in One
Stroke, when the length of the stroke is given, the point of
cut-off, and the pressure of steam on admission.
Let I = the length of the stroke in feet
„ q = the distance moved by piston when the steam is

cut off

„ p = the pressure at which steam enters the cylinder.
„ s = the number of feet described at any part of the

stroke
„ p = the corresponding pressure

Dividing the length of the stroke into an indefinite num-
ber of parts, and taking their sum, we must have as near an
approximation as possible to the average pressure

s
ntegrating this between the limits I and q, we get

j iLEds^qpf—^ ap (log- Z-log. q)

316 STEAM.

This is the work done by the expanding steam; we must
add the work done before expansion if we wish for the total
units of work : the work done before expansion is evidently qj)%

. : Total work = qp + qp log. - = qp (\ + log. — )

Let us take an example and show the application of this
formula.

Ex. — The length of the stroke of an engine is 6 feet, the steam is
cut off at 1 foot, or £ the stroke, the pressure of steam is 60 Ibs. on
the square inch when admitted. Find the work 'done on each square
inch of the piston,

We have to substitute in qp 1 1 + log.g ~\

= ix6x60(l + log.$f )

= 1 x 60(1 + 1791759)
= 167'50554.

From this we will proceed and find the horse-power. Given
diameter of piston 35 inches, and speed of piston 25 strokes
per minute.

Area of piston = 35 x 35 x '7854

Units of work done = 35 x 35 x '7854 x 167 '50554 x 25
35 x 35 x -7854 x 167 '50554 x 25
.-. Horse-power =- -33000-

rr 122'09.

Rule to find the ivork done on each square inch of the
piston in one stroke :

Divide the length of the stroke by distance moved through
by the piston before the steam is cut off, take out the hyper-
bolic logarithm of this, and to it add one, then multiply this
sum by the steam pressure, and by the part of the stroke
performed before the steam was cut off.

The rule for horse-power is — multiply the area of the
piston by the number of strokes, and by the pressure thus
found, and divide by 33000.

341. To find the load

Let L = the load on the square inch.
.-. L x I - the work done on a square inch in each stroke
by the load, and as this must equal the work of the steam

PRESSURE. 317

. •. L or Load = 22 (l +log.f -)

to find the load:
(1) Divide the length of the stroke by the part of the
stroke at which the steam is cut off, take the hyperbolic log.
of this and add unity to it, then multiply this by the part of
the stroke and by the pressure of steam, dividing this result
by the length of the stroke we have the load.

Ex. — The length of the stroke is 6 feet, the steam is cut off at 1
foot, the pressure of steam is CO Ibs. on the square inch when ad-
mitted ; find the load.

Before qp (l + log.^-) = 1G7'50554 = work done.

Dividing this by I we have 167'5?554

.?) . =27.91759

= Load.

342. Pressure. — Given the load, the stroke, point where
steam is cut off*, to find the PRESSURE at which the steam must
be admitted.

From formula SLP (l +log. -,) = L
I * qf

From which we deduce the following rides to find the
ressure of steam :

(1) Multiply the length of the stroke by the load.

(2) Divide the length of the stroke by the part of tlio
stroke, take out the hyperbolic logarithm of this, and add
unity to it, multiply this by the part of the stroke.

(3) Divide the quantity obtained in the first rule by that
. the second, and the pressure is found.

Ex. — The load of an engine is 28 Ibs., the length of the stroke

> feet, steam is cut off when one foot of the stroke has been per-

ed ; required the pressure at which the steam was admitted.

318 STEAM,

•

Gx2SL=168 RULE II,

6-^-1 = 6

BULE III. Hyperbol. log. 6 = 1 7917594

168 1 + 1-9717594 =27917594

27917594 27917594 x 1 =27917594

= 60 '17 Ibs. pressure.

The horse-power can be also expressed in terms of the same
formula.

Let d = the diameter of the cylinder,
„ n = the number of strokes per minute.

~
.-. H.-P. = 33000

343. De Pambour's Theory. — Steam on its first admission to
the cylinder moves the engine but slowly; the motion gradually
accelerates till the engine attains a certain velocity which it
does not surpass, the steam being incapable of sustaining a
greater velocity. So long as the resistance remains constant,
it has to move the same mass. To attain this velocity
requires but a short time, and, when reached, the power is
strictly in equilibrium with the resistance. Were the power
to vary, the motion must accelerate or retard in proportion.
The pressure in the cylinder is less than that in the boiler,
therefore the steam changes its pressure in passing from the
latter to the former, because in going from the boiler along
the pipes to the cylinder, the pressure decreases, or the
steam is allowed to expand ; in the cylinder also the steam
dilates, because the area of the cylinder is larger than the
pipes and ports. The area of the cylinder is ten or twenty
times that of the pipes. At first the piston does not move;
when it does, steam continues to flow in, and the balance is
partly restored. As the piston acquires a quicker motion
and develops a greater space before the steam, the latter
dilates, till in time the piston moves as quickly as it possibly
can under the supposed pressure of steam, and equilibrium
is established between the moving power and the load or
resistance. The pressure in the cylinder can never exceed
that of the resistance of the load, and it is clear that the
pressure of steam in the cylinder is regulated by the resist-

DE PAMBOUB'S THEORY. 319

ance on the piston alone. Therefore, if P' represent the
pressure on each unit of surface, and R, the resistance against
the piston for each unit of surface, the first equality is
established, that

P' - Pu

But as the piston is in motion, the velocity as well as the
intensity of the force is to be considered. The rate at which
steam is generated in the boiler will obviously affect this
velocity, and there is necessarily an equality between the
quantity of steam used and that produced. If we let S
equal the volume of water evaporated in the boiler in a unit
of time, and m the ratio of steam formed under the pressure
P in the boiler, then m S will represent the volume of
steam generated under the pressure P in a unit of time, this
pressure P becomes P' in the cylinder. But steam in pass-
ing from pressure P to P' will increase its volume in the
inverse ratio of the pressures, therefore the volume m S of
steam from the boiler will increaso in the cylinder to a
quantity whose volume

= mS?

Now if v is the velocity of the piston and A the area of
the cylinder in square feet, therefore A v is the number of
cubic feet of steam expended in the cylinder in each unit of
time. We therefore get the equality

since the production of steam must be equal to the consump-
.on.

But before it was shown that P' = R, substituting II for
P', the equation stands thus : — •

A v = m S ?
l\i

. ? _ m S P which is the velocity of the piston under the resist-
~ ~~ '

. •. 11 — !?L — . which is the resistance with the given velocity v.

Av . .

. g _ AR v which is the evaporative power of the boiler, with
"w~P a certain load and given velocity.

320 STEAM.

These equations are sufficient to determine all ques-
tions relative to the effect of steam engines. But
they have been still further adapted to meet the re-
quirements of different engines under their varying condi-
tions.

344. Relation between the Temperature and Pressure
of Steam in Contact with the Water. — Steam generated
under the pressure of 15 Ibs. per square inch has a volume
always 1700 times that of water. If two volumes of steam
of the same iveight be compared, we institute a comparison
between their relative volumes ; for, being of the same
weight, they are produced from the same quantity of water.
The relative volume of steam being the absolute volume
divided by the volume of water from which it was produced,
the ratio of any two relative volumes of steam is the same as
the ratio of their absolute volumes.

When steam remains in contact with the water in the
boiler, the same pressure exhibited by the gauge corresponds
to the same temperature in the boiler, and the same tem-
perature in the boiler will always give the same correspond-
ing pressure of steam. So, therefore, if we increase the
temperature we increase the pressure and density, and we, of
course, get the greatest pressure and density that steam can
have at that temperature.

But if the steam be taken from the generator and further
heated in another vessel, we may increase its pressure or
elasticity as we increase the temperature to almost any
extent, but the state of greatest density ceases, for there is
no water from which to increase its density ; also, we may
increase the one without augmenting the other. The constant
ratio between temperature and pressure does not exist. This
is the great distinction between steam in contact and not in
contact with the water. We can determine the elastic force
if we know the temperature when steam is in the boiler, and
vice versa, but such is not the case when not in contact with
the water. To determine these pressures and temperatures of
steam, when in contact with the water, has required a great
number of expensive and delicate experiments. The true
theoretic law connecting the two has not been ascer-
tained ; but several formula have been proposed that give

RELATIVE VOLUMES AND TEMPERATURES OF STEAM. 321

the relative connection within certain limits of tempera-
ture.

There is a direct relation between the relative volumes
and the pressures, as long as the steam is in the boiler or in
contact with the water.

We must remember that steam in contact with the water
has its maximum density and pressure for that temperature.
The formula proposed (for the true theory has not been
yet precisely determined) is the following : — •

Let p — pounds pressure per square foot,

and v = the relative volume : then

n + qp
where for condensing engines

n = -00004227
q = -000000258

while for non-condensing engines

n = -0001421
q = -00000023.

From this formula the relative volume of steam generated
under different pressures can be calculated.

For instance, take two atmospheres 30 Ibs., the relative

volume for condensing engines will be

•00004227 + -000000258 x 30 x 144
For non-condensing engines we shall have it

= SG4-4.

= 880-5.

•0001421 + -00000023 x 30 x 144
The volume calculated by the ordinary method is 882.

345. Relation between the Relative Volumes and Tem-
peratures in Steam Taken from the Boiler. — When steam
is separated from the water, its temperature may be varied
without changing its pressure, or the pressure without alter-
ing the temperature. The density increases or diminishes
according as the elasticity or temperature is affected.

322 STEAM.

Mariotte's law is, that if the volume of a given weight of
steam be increased, the elastic force diminishes; or if the
volume be diminished, the pressure increases ; or it is affected
in an inverse ratio, i.e., if v and v be two volumes of the
same weight of steam, and p and p their pressures, then

p : p' : : vr : v (a)

Hence if r v and r v be their relative volumes, we have by
the same reasoning,

r v : r' vr : : p' : p (b)
v : v' : : r v : r' v' (c)

Gay-Lussac has shown that if the temperature of steam
not in contact with the boiler-water be increased in temper-
ature, for every degree centigrade the volume receives an
increment of -00361 ; the co-efficient of expansion is more
correctly -00366 = ^.

Hence if v and v' be two volumes of the same weight of
steam and at the same pressure with the temperatures t and
t', and Y the original volume,

v __ V + V -00366 1 _ 1 + -00366*
ff ~ V 4- V -00366 «' ~ 1 4- -00366 1''

Hence from equation (c)

rv _ 1 + -00366 1
r'v' ~ I + -00366 i7

This lav/ cannot, of course, possibly apply to steam in
contact with the water, since the pressure varies with the
temperature.

346. To Find Pressure of Steam taken from the Boiler.—
The formula for the relative volume is —

n + qp

If we, as before, suppose a volume of water S to be evapo-
rated into steam at a pressure p, whose absolute volume is Y,
we have —

Relative volume = -absolute v^ =-X = t, = J-.
vol. of water S n+qp

If the same body of steam, by passing into the cylinder,

TO FIND THE USEFUL LOAD. 323

etc., have its pressure changed to p, its volume will alter to,
suppose, V. Then, again, we have —

V 1 VI

,__ — (2) but — i —

S n + qp' >S n + qp

Dividing (1) by (2)—

__. q

v/ n + qp " n_+p

2
so, therefore, the volumes of the steam are not in. the inverse

ratio of the pressures, but in the inverse ratio of the pres-
sures plus the same constant quantity (-y).

Finding^ from the equation — — n + ^

V' n + qp
V' /n+p'g\ _ n
P V V q ' q

We now proceed —

347. To Find the Useful Load when Working Non-Ex-
pansively : —

v i

From above -«-=

S n + qp

Let L = the length of the stroke.
c = the clearance.

A = as before, the area of a section of the cylinder.
N = the number of strokes per minute.
.*. L + c is total length of cylinder filled with steam.
A (L + c) is total volume of one cylinder full of steam.
A N(L + c) is the quantity or volume of steam used per
minute.

If v be the velocity of the piston in feet per minute

/. v - NxL .-. N = JL
L

. •. Steam used per minute = ^- A (L + c) = !!A<L±£)= V

Y _ . *>A (L + c) = 1_

IS L S n + qp

T ^

n -4- = —* (a)

324 STEAM.

but the pressure p must equal the total resistance, which is
composed of R the useful load, / the friction of the unloaded
engine, a R the addition friction for the loaded engine, and
let p be the pressure of the uncondensed steam.

.-. p = E + «R
substituting in (a) above

w + 5jK(1+

solving the equation

348. To Find the Horse-Power: Working Non-Expan-
sively. — Let the whole resistance = R/, this must equal p in
equation a, by substituting R/ for p we get

Multiply each side by A v

.'. A.H'v= — \ TLS - nAv I = H.P. (c\

q I L + c _J

33000
or this is the horse-power required.

349. To Find the Velocity of Maximum Useful Effect
when Working without Expansion. — This means that we
are to find at what speed the engine should run, so that we
may get most work out of it.

This velocity will evidently be attained when the pressure
of steam in the cylinder becomes equal to that in the boiler,
and therefore is equal to p.

From our first equation (a)

LS 1

• X

A(L + c) n + qp (d)

which is the equation required, giving the velocity of maxi-
mum useful effect.

350. To Find the Useful Load when Working Expan-
sively.— Taking the same notation as when working without
expansion, and letting

Z = the length of the stroke traversed when expansion

TO FIND THE USEFUL LOAD. 325

begins, or the distance travelled by the piston before steam
is cut off.

Let lf be the distance at any point of the stroke when the
steam is expanding and its pressure falls to p.

Now from what precedes at pressure p the relative volume

S
18

n+pq

. '. At pressure p' it is =• -L-

n + qp'

. *. If V is the relative volume at the pressure p and
* » » » » » P'

but the pressure may be assumed as constant for a very
short space of the stroke (d Z'), and, therefore, the work done
while the piston traverses that small distance is =

Ap' (d I').

.'. The whole work done during expansion must be thai/
given by the following equation, which we must integrate be-
tween the limits L and I to obtain the work done during ex-
pansion : —

-A± /dl

~'\~ ' -»i j'+c . q ••

but the work done before expansion, which is A ^? ?, must
be added to this to give the total work done.

.-. Whole work=A(M-e)(-l+p) |^L + fog.g- -A-5 L(/)

but this is, of course, the resistance =: H' x L
which from what precedes — JE/(l + a)+jp/+/ JL

.'.AL JR(l + «) +p'+f\ =A(l + c)(~+p)C -A n-L (g)

*•* q

where C is substituted for — !_ + log. iliS
^ + c * ^ + c

326 STEAM.

.-. A j R(l+ .)+!>'+/ j =A (l + c] (*. + p) C-A J!

... K = * } '_+« (». + p) C- (J5 +J/ ^

1 « L N *V \

T- NA(Z+c) L

JM OW • - i - — - . . *. n 4- O T) —

- - . . . - — -
S n + qp Av(l + c)

wliich is the useful load when working expansively.

351. To Find the Horse-Pov/er when Working Expan-
sively. — From equation (g) the whole work done in one
stroke is

but if we let R/ represent the whole resistance

.-. AR'L^A^ + cf+^C-AL !1

... AR' =±(^-A!)
q ^ v '

this equation will give the horse-power when working ex-
pansively.

352. To Find the Velocity of Maximum Useful Effect
when Working Expansively. — The volume of steam used
per minute when working expansively is =

L S n + qp
LS 1

where v is the velocity of maximum useful effect required?

353. To Find the Diameter of the Cylinder to Give a
Certain Power, etc., when Working Expansively. — Equa-
tion (h) was

£L -Z { where Z=w+gr (/+/)
v )

MAXIMUM USEFUL EFFECT. 327

Solving this equation we find

* (m)

I R q (1 + *) + Z I 4

from which equation the diameter is known.

354. To Find the Evaporation when Working Expan-
sively. — From the last equation (m)

g = Av JBg(l + «X+

~~C~

355. To Find the Point at which Steam must be Cut Off
to Attain the Maximum Useful Effect. — Since

and v or velocity of maximum useful effect

SL 1

A (l+c) n+ qp

substituting this for v in the second member of the equation
we et

Differentiating with respect to I to find the value which
makes A R v a maximum, we have

_ S (

•. I = L.

We now proceed to apply the equations found. The
first three, being of no practical importance, are lightly
passed over, as engines do not work without expansion.

In equation f we have log. -, —

Log. -j^c can be found from the common logs, by multi-
ping by 2-350285 ; thus,
Log.

1 l+c l+c

328 STEAM.

To save trouble it is customary to give the log.

l ~\~ c

to the grade of expansion j in a table, but it may be

observed that it is far better to give the length of stroke,
clearance, and cut off — then all that the student has

to remember are the values of n and q in the formula ^

instead of burdening his mind with constant logarithms, or
employing unnecessary tables.

Equation c gives the horse-power when not working expan-
sively, if we make the proper substitutions for q c, etc., as
previously indicated, and dividing by 33000, we have

_ 3238686-5 S- 555 '6154 d2v
H'~P'~~ "~33000~~

= 98-14 S- -0168 d*v

Hence the rule for finding the horse-power when not working
expansively.

(1) To the log. of evaporation of number of cubic feet per
minute, add log. of 98-14.

(2) Find the natural number of this.

(3) To log. of -0168 add twice log. diameter in feet, and
log. velocity of piston per minute.

(4) Find the natural number corresponding to the sum of
this log.

(5) Then subtract the one natural number from the other,
the remainder is the horse-power.

We give no practical illustrations of these rules, because
no engineers are now so injudicious as to work their engines
without expansion.

356. To Find the Evaporation of a Boiler when we know
the horse-power, velocity, and area of piston (not working
expansively).

Hp 3238686-5 S - 555*6154 tfv

33000
H.P. =98-14 S- -0168 d*v

98*14

Equation i gives the horse-power ivhen working expansively.

AR'i; = i. /SC-A*"*\
q \ 33000 /

DE PAMBOUE/S THEORY. 329

making tlie proper substitutions, as in page 321, etc., De
Pambour's rule for finding the horse-power when working
expansively becomes

_ 339996874 SO - 555*6154 ffiv
33000

= 103 '029 SO- '0168 d-v.

Hence we obtained the following rules for finding the horse-
power of an engine under this condition : —

(1) To the log. of 103-029 add log. evaporation of cubic

feet per minute, and the log. of j * + log. ^±-c |

( t+c * I + c >

(2) Find the natural number corresponding to the sum of
the above logs.

(3) To the log. of -0168 add twice the log. of the
diameter in feet, and log. velocity of piston in feet per
minute.

(4) Find the natural number corresponding to the sum of
these logs.

(5) The difference between the natural numbers found in
(2) and (3) will give the horse-power required.

Note. — Log. j - — + log. _t? j must be calculated by itself.

(t+C * l-\-C }

"We have indicated above how log. -y^ may be found, after

$ t -f- c

which no difficulty ought to be found in finding the correct
result.

Ex. — The boilers of an engine evaporate 4 cubic feet of water per
minute, the diameter of the piston is 6 feet, the length of the stroke
5 ft., and the number of strokes per minute 20; if the steam is cut off
at J the stroke find the horse-power.

S or evaporation = 4 cubic feet per minute.

Speed of piston = 5 x 2 x 20 = 200 feet per minute.

Let the clearance at each end be 2 inches, then

JJCU l*JULC VilCctl clllUC clU

= '9375+ -657520
= 1-59502.

* Take out log. 31, subtract log. 16 from it, multiply this by 2 '302585, will give
•657520.

330 STEAM.

.-. H.-P = 103 «029x4x 1-59502- '0168x36x200
= 657-5-120-9

= 536-6

Or it may be done thus by logarithms :

EULES I AND II. RULES III AND IV. RULE V.

Log. 103-029=2-012958 Log. '0168 =2~-225309 657'5

Log. 4 = -602060 Log. dia. 6 = 778151 120-9

Log. 1-59502= -202897 '778151 H._P. ^^G.Ans.

Log. 657-5 =2-817915 Log. 200 =2-301030
Log. 120-9 =2-082641

Ex. — The boilers of an engine evaporate 270 cubic feet of water per
hour, the diameter of each piston is 66 inches, the length of stroke
6 feet, the steam is cut off at 2 feet, and the number of revolutions
of the crank is 20, allowing 2 inches for clearance determine the
horse-power.

270

S or evaporation is -— — - = 4 -5 cubic feet.

60
Speed of piston is 6 x 2 x 20 = 240 feet per minute.

__ _ __

1+ c ** I + c 2 +

= '923 + 1-040276 = 1-963276

.-. H.-P. = 103-029 x 4-5 x 1-963276- -0168 x5-52x 240
= 910-2-121-9

= 788-3, Ans.

Or it may be done thus by logarithms :

EULES I AND II. EULES III AND IV. RULE V.

Log. 103-029 =2-012958 Log. '0168 =2-225309 910-2

Log. 4-5 = '653213 Log. dia. 5J= '740363 121-9

Log. 1-963276= -292980 -740363 ^-P-WOwa.

Log. 910-2 =^959151 Log. 240 = 2-380211
Log. 121 -9 =2-086246

Equation m gives tJie area of the piston, and hence its
diameter, so that with a certain evaporation, horsepower,
velocity, etc., we may find the required dimensions of the
cylinder. Q p

Jd*=

making the proper substitutions and reducing down we
obtain the

DE PAMBOUR'S THEORY. 331

H.P. = 103-029 SO- -0168 d*v. (r)
.-. -0168 d*v = 103-029 SO- H.P.

d = (103'029SC - H.p.a

^~ -0168 x v

RULE I. — To logarithm of 103*029 add logarithm evapora-
tion of cubic feet per minute, and logarithm C, then take out
the natural number.

RULE II. — To logarithm of velocity in feet per minuto
add log. -0168, then take out the natural number.

RULE III. — Subtract the horse-power from the number
found by Rule L. and divide this by the number found in
Rule II., extract the square root of the quotient, and the
result is the diameter in feet.

Ex. — The stroke of an engine is 5 feet, number of revolutions per
minute 50, horse-power 1600, the evaporation of the boiler 390 cubic
feet per hour, the steam is cut off after the first foot of the stroke,
allowing the clearance to be f of an inch, find the diameter of the
cylinder.

The evaporation per minute = 6 '5 cubic feet.

The speed of the piston is 5 x 2 x 50 = 500 feet per minute.

Clearance g of an inch = •£% of a foot.

C or j =— - + log.g - f will be the same as in the examples on
page 333, we therefore write it down as 2-55463G.

• d - (1Q3'029SC " H.PAJ

* -0168 xv. '
_ /103-029 x 6-5 x 2-554630 - 1600\ i
V -0168 "x 500 *

... = (1714-74 -1600)^3-69,^.

Or thus by logarithms :

KULE I. RULE II.

Log. 103-02Q = 2-012958 Log. 500 = 2-698970

Log. 6-5 - -812913 Log. '0168 ="2-225309

Log. 2 -554636 = -407329 Log. 8 '4 = '924279

Log. 1714-74 = 3-234200

d = (H14-74 - 1600) J = /11474) i = 3.G9 feet<

8-4 x 8-4 '

Ex.— Find the diameter of a cylinder to give 200 horse-power when
the evaporation is 1'09 cubic feet per minute, the length of the stroke
5 feet, and number of revolutions 21, the steam is cut off at £, and
the clearance -J- inch.

332 STEAM.

The evaporation per minute is 1 -09 cubic feet.
,, Speed of the piston 5 x 21 x 2 = 210 feet per minute.
,, Clearance -fa of a foot

C or _ - . + log. -- - will be the same as in next "example.

I + c s I + c

We therefore omit this calculation altogether, merely writing
it = 2-554636.

RULE I.

Log. 103-029 ............ = 2-012958 Log. 210 ........... = 2^322219

Log. 1-09 ................. = -037426 Log. 0168 ......... - 2-225309

Log 2-554636 ........ ..... = -407329 LpgSWs ......... = '547528

Log. 286-888 ........... = 2-457713

= 5 nearly.

Equation n gives the evaporation when we know the grade
of expansion, horse-power, etc., working expansively.

s.-

without taking the trouble to substitute, we may find from (r)
above.

H.P. = 103-029 SO- -0168 d*v

103-029 C

We have, therefore, the following rules for finding the
evaporation required to produce given results when the steam
is used expansively: —

RULE I. — To log. -0168 add twice the logarithm of the
diameter and the logarithm of the speed of the piston in feet
per minute. Take out the natural number.

RULE II. — To log. 103-029 add log. C, found as before,
and take out the natural number.

RULE III. — Add the horse-power to the number found by
Rule I., and divide the sum by the number found in Rule III.
This gives the evaporation per hour.

Ex. — The stroke of an engine is 5 feet, number of revolutions per
minute 50, the horse-power 1600, the diameter of piston 42 inches,
and the grade of expansion £, and the clearance § of an inch. Find
the evaporation.

DE PAMBOUR S THEORY.

333

Velocity of piston is 5 x 2 x 50 = 500 feet per minute.
Clearance | of an inch = -^ of a foot.

C or ] — +log. , ' ( =r— i

= •9697 + 1-584936
= 2-554636

103-029 C.

1600+ -0168 x3-52x 500
103-029x2-554636

^.O i

Or by logarithms, which is a much easier method, it is done

thus —

RULE I. RULE II.

Log. '0168 =2-225309

Log.(dia.) 3.V = -544068

•544068

Log._500 = 2-698970
Los?. 102-9 = 2-012415

Log. 103-029 = 2-012958
Log.2-554636 = -407329
Log. 263-2 = 2-420287

S =

ii. -p. + -0168 d*v.
'103-029 C.

Or RULE III.

1600 + 102-9 1702-9 ft ,- , . , . . .

= = 6'47 cubic feet Per mmute.

Ex. — The diameter of a cylinder is 5 feet, the number of strokes
per minute 21, and the stroke 5 feet ; if the steam is cut off at 1 foot,
lind the evaporation, allowing g- for clearance, the horse-power
being 200.

Velocity of piston = 5 x 2 x 21 = 210 feet per minute.

Clearance -^ feet.

rb + "*.

= 2-554636, as in the last problem.

RULE I.

Log. -0168 = 2-225309
Log.(dia.)5 = -698970

•698970

Log. 210 = 2-322219
Log. 88-2 = 1-945468

S = J5i?

RULE II.

Log. 103-029 = 2-012958
Log. 2-554636 = 0 -407329
Log. 263'2 = 2-420287

+ '01C8 d-

103-029 C.
~ 200 + 88-2 _ 28^2
203-2 ~ 263T2

= 1-09 cubic feet,

334 STEAM.

Equation Jc gives the velocity of maximum useful effect,
and may be thus applied —

(I 4-c) A ) » -h-g »
.x L - !

d* x '7854 Z + c w, + </^

Ex. — The evaporation is 8^ cubic feet per minute, the pressure at
which the steam is admitted to the cylinder 31 Ibs., the diameter of
the cylinder is 7 feet, and the length of the stroke 6^ feet, the steam
is cut off at half-stroke. Find the speed of the piston or maximum
useful effect Clearance ^ feet.

Evaporation per minute in 8*5 cubic feet.

Clearance, -fa feet. Diameter, 7 feet.
Now

v = S x L x _L_

d2 x '7854 I + c n +qp

8-5 6J 1

7 x 7 x -7854 3J + -fa '00004227 + '000000258 x 144 x 31

_8-5_ 208 t 1_

~ 38-4846 105 '00119392

= 4.000 = 366'4 = No. of revolutions.

Log. 8-5 = -929419 Log. 38-4846 = 1-585286

Log. 208 = 2-318063 Log. 105 = 2-021189

< = 3-247482 Log. 00119392 = "3-Q76973

•683448 -683448

Log. 366-4 = 2-564034

.'. Speed of piston = 366'4 feet per minute.

.-. No. of revolutions! 366'4 = 28 nearly.
2 x 6i-

EXERCISES CHIEFLY FROM EXAMINATION PAPERS.

The clearance allowed in finding the answers to the following
problems is in all cases f ths of an inch, which is about the proper
quantity. The student must not use the special tables given in some

works on steam, for -- + log s -~^f-9 the clearance there

I ~\~ c I -\~ c

allowed is out of all proportion in some cases, and the true relation
between L and I is too often a matter of average, instead of proper
calculation. In every answer here given, the true quantities have
been substituted in the formula last named, and the hyperbolic
logarithm used, either taken from a table of hyrjerbolic logarithms,

EXERCISES. 335

or calculated by employing the ordinary logarithms as indicated on
page 327-

1. Investigate the relation between the useful effect of a steam
engine, the evaporation, speed, and area of the piston (1), when the
engine is not, and (2), when it is, working expansively (1863).

2. What is meant by the nominal horse-power of an engine? and
show how it is determined for paddle-wheel vessels. Find the
nominal horse-power when the diameter of the cylinder is 55| inches,
stroke of piston 5 feet, and number of revolutions 21. Find the effec-
tive evaporation of the engine whose dimensions are given above, if
the horse-power be supposed to be 120 (1863), steam cut off at i.

Ans. 107 '8 and -6962 cubic feet.

3. Wishing to construct an engine of 250 horse-power, what must
be the diameter of the cylinder that the length of the stroke may be

5 feet 10 inches, and the number of revolutions 21 (1863)?

An*. 78;24.

4. Find the quantity of water evaporated by a boiler if the initial
indicator pressure be 16 Ibs., the diameter of the piston being 3 feet

6 inches, length of stroke 4 feet, and number of revolutions 25 (1863),
steam cut off at £.

First find the horse-power = 113-72

Next find the evaporation = '904 cubio feet per minute.

5. Find the nominal horse-power of an engine of the following
dimensions : —

Diameter of cylinder 53J inches

Stroke of piston 5^ feet

Number of revolutions 22f Ans. 1 15 '44 H. -P.

6. Find the effective evaporation of the engine whose dimensions
are given above, supposing the horse-power to be 110 '6 (1865), steam
cut off at 1 J feet. Am. 82.

7. Given the evaporation of an engine, the speed and area of the
piston, investigate an expression for the horse-power (1865).

8. Investigate, according to De Pambour's method, an expression
the work done in a condensing engine when working expansively
(Honours, 1870).

9. Find an expression for calculating the effective evaporation of a
condensing engine of given dimensions and horse-power, the piston
moving with a given velocity, when working expansively (1866).

10. In a pair of engines the diameter of the cylinder is 60 inches,
length of stroke 4 feet 6 inches, the number of revolutions 63, find
the nominal horse-power, and the evaporation of a set of boilers to
supply the engines, the steam being cut off at -J of the stroke (1866).

Am. 680-4 N H.P. ; 2 '288 cubic feet.

11. Find the quantity of water evaporated by a boiler, if the initial
indicator pressure be 18 Ibs., the diameter of the piston 4 feet 6 inches,
length of stroke 4 feet, and the number of revolutions 31 (1866), steam
cut off at one half stroke. Am. 2'014 cubic feet (H.P. 262J).

12. The diameter of the cylinder of an engine is 56 inches, the
stroke of the piston 5 feet, the number of revolutions 33, find the

336.

STEAM.

effective evaporation, the horse-power being 150*8 (1867), steam cut
off at £. Ans. 1*031 cubic feet.

13. Investigate a formula for finding the diameter of a cylinder to
work at a given speed, knowing the evaporating power of the boiler
(1867 and 68).

14. Investigate an expression for the horse-power of an engine (1)
working without expansion, (2) with expansion (De Pambour's
method), (1867 and 1868).

15. Find the effective evaporation of the boiler for a pair of engines of
750 collective horse-power, the diameter of the piston being 88 inches,
the length of the stroke being 5 feet 2 inches, the number of revolu-
tions per minute 60, the steam being cut off at one-fourth of the
stroke (1868). Ans. 2*714 cubic ft. for each engine.

16. Upon what principles is De Pambour's theory of the steam engine
founded? (Honours, 1869).

17. Knowing the evaporation of an engine, the speed and the area of
the piston, show how to calculate the horse-power (Honours, 1869).

18. Pro veDe Pambour's rule for finding the horse-power of an engine,
knowing the evaporation, and speed, and area of the piston (1865).

19. What determines the nominal horse-power of an engine? What
evaporating power should a boiler have for a pair of engines of 560
collective horse-power, the diameter of the cylinder being 88 inches,
length of stroke 5 feet 9 inches, and making 17 revolutions per
minute (1865), steam cut off at £? Ans. 1*191 cubic ft. for each.

20. Calculate the work done by the steam in one stroke of the piston,
taking clearance into account, the steam being cut off at one-twelfth
of the stroke (Honours, 1871).

HYPERBOLIC LOGARITHMS.

—

•oooooo

1-446918

2-014903

6-9 =

•7917520

•223143

1-504077

2-047692 1

•9375 =

•6575042

•405465

1-558144

2-079441

Y£ or

•559615

1-609437

2-110212

2-846 =

1-060276

•693147

5 t

—

1-658228

2-140066

3-612 =

•2842680

•810930

1-704748

2-169053

3-929 = 1

•3684170

•916290

—

1-749199

—

2-197224

ici _

•5848U68

0^1

—

1-011600

—

1-791759

2-224623

IiT6y —

•o854i!05

—

1-098612

—

1-832581

—

2-251291

185 —

« 1 ~

•04-3030

1-178654

—

1-871802

—

2-277265

1-252762

—

1-909542

10*

2-302585

32
4

1-321755
1-386294

7'"

7:1

—

1-945910
1-981009

2-395049905

QUESTIONS.

1. Reduce 39° Fahrenheit to centigrade and 4°C. to F.

Ans. 3°f C. ;

2. Reduce - 12°F. to C., and - 12°C. to F. Ans. - 24°* C. ; 10°-|F.

3. Reduce 25° R. to F. and C. Ans. 88°£F. ; 31°|C.

4. Express 40°C. as P., and 40°F. as C. Ans. 104°F. ; 4°£C.

5. Convert 12°F. to C., and 40° R. to F. Ans. - 11°£C.; 122°F.

6. Express - 15°C. in the scale of Fahrenheit. Ans. 5°F.

7. In 55 circular inches how many square inches?

A circular inch is a circle having one inch for its diameter,
. *. 55 circular inches = 1 - x '7854 x 55— 43'197 square inches.

8. Convert 200 square inches to circular inches.

200 sq. in. =^1-254 '6 circular inches.
\'xx 7854 =200. '.etc.

RULES :

To reduce circular inches to'square inches, multiply by 7854.
To reduce square inches to circular, divide by 7854.

9. Convert 120 square inches to circular.

Ans. 1527 circular inches.

10. How many square inches are equivalent to 300 circular inches?

Ans. 235-6 sq. in.

11. A pound of water at 60° C. is mixed with a pound at 100°C.,
what is the resulting temperature ? Ans. 80° C.

12. A pound of ice at 0°C. is mixed with a pound of water at
100°C., what is the result? Ans. 2 Ibs. at 10°'3C.

To melt the ice will consume 79° '40., as this is the latent heat of
water. This will leave 100° -79° '4 = 20° '6. This residuum will be

2 Ibs. of water at a temperature of ?! ^=10°'3C., Ans.

13. 2 Ibs. of ice are mixed with 2 Ibs. of water at a temperature of
79° '4 C., what is the result ? Ans. 4 Ibs. of water at 0°C.

338 STEAM:.

* 14. 9 Ibs. of ice are mixed with 10 Ibs. of water at 100° C., what is
'the result? Ans. 19 Ibs. of water at 15°'02C.

15. What weight of ice at zero must be mixed with 12 Ibs. of
water at 25° C., in order to cool the water down to 10° C. ?

Each pound of ice in liquefaction will consume 79° '4, and as this has
to be raised 10°, . '. each pound of ice requires 89° '4 C. Each pound of
water will give up 25° - 10°=15°C.

.-. Total heat to be extracted from the water = 15° x 12-180°.

IQft0

. '. No. of Ibs. of ice required=^rr =2'013 Ibs., Ans.

16. 60 Ibs. of ice at 0°C. are mixed with 100 Ibs. of water at a tem-
perature of 45° C., will this melt the ice ?

Ans. No. It will require 264° C. more.

17. How many pounds of water at the above temperature would
have been just sufficient to melt the ice? Ans. 105^|- Ibs.

18. I mix 4 Ibs. of ice at 0°C. with 8 Ibs. of water at 95°C., what
is the resulting temperature?^ ^nSt 12 Ibs. of water at 36°'86C.

19. How many pounds of ice must I mix with 30 pounds of water
at 80° C., so that the result may be water at a temperature of 35° C. ?

Ans. 11-8 Ibs.

20. How many pounds of water at 27° C. must be mixed with 2 Ibs. of
steam at 100° C. to reduce the temperature of the steam to 45° C. ?

Latent heat of steam is 537 '2.

. •. Each pound of steam has to give up 637° '2 - 45°= 592° '20.

Each pound of water takes up 45° - 27°- 18°.

.-. No. of Ibs. of water to condense 1 Ib. of steam =! = 32*9 Ibs.

2 „ =32-9x2=65-8 Ibs.

21. How many pounds of water at 40° C. must be mixed with a
pound of steam at 100° C. to convert it into water at the boiling
point? Ans. 8 '95 Ibs.

22. How many pounds of water at 50° C. must be mixed with 21 Ibs.
of steam to condense it, so that the result shall be water at a tem-
perature of 80°C. ? Ans. 390-04 Ibs.

23. The temperature of steam is 100° C., and that of the condensing
y^ water 10° C., what will be the proportion of condensing water to

steam if the condenser is to be kept at a temperature of 38° C. ?

Ans. 21-4:1.

24. A pound of steam is converted into water by ice at 0°C., how
much ice will it just melt ? Am. 8 '02 Ibs.

25. How many pounds of steam at a temperature of 100° C. will be
required to melt 40 Ibs. of ice at -4°C. ?

Each pound of ice consumes 4 -f- 79 '4 = 83° '4 units of heat.
. \ 40 Ibs/ of ice will require 83° '4 x 40 = 3336° units of heat,

.-. No. of Ibs. of steam-^69=5.231bs.
037'^

QUESTIONS. 339

26. The temperature of steam is 105° C., and 5J Ibs. of steam
melted 42 Ibs. of ice, what was the temperature of the water remain-
ing? Aw. 4°-15C.

27. What weight of steam at 100° C. is necessary to raise the tem-
perature of 210 Ibs. of water from 15°C. to 33°C ? Ans. 6 '25 Ibs.

28. A pound of mercury at 40° C. is mixed with a pound of
water at 156° C., what is the resulting temperature?

The Specific heat of water is 1.
„ „ mercury '033.

Hence 1° from the water will raise the mercury = 30° '3,

'033

The difference of heat is 156° - 40°= 116°.
Evidently to find the number of degrees of heat to be added to the

40°, as mercury takes '033 and water 1, we shall get — — L = 112° '3.

A T" '(jOO

. *. The temperature of the mixture will be 40° 4- 112° '3= 152° '3.

Or we may reason thus : —

Every 30° *3 given to the water out of the 116° we must add 1° to
the mercury, which will raise it 30° '3.

. •. The increase of temperature above the 40°= 116x30'3= 112-3.

.'. Temperature = 152° '3, as before.

29. A pound of mercury at 10° C. was mixed with a pound of
water at 100° C., the result was found to have a temperature of
97°i C. ; find from this the capacity for heat of mercury.

The temperature of the water was lowered 2°jC.

,, ,, mercury was raised 87°£C. ;

and since the specific heat of water is 1, we have this proportion —
As 87°J : 2°5 : : 1 : -033, Ans.

30. A pound of mercury at 160° C. is placed with a pound of water
at 20° C.j what is the resulting temperature ?

Every 30*3 given up by the mercury will only heat the water one
degree, as it also requires 1° for itself, the difference (160° -20°)
divided by (30° "3+ 1°) will give what is required.

Hence gj = 4-47
Hence resulting temperature is 20° + 4° -47 =24° '47 C.

,31. A pound of mercury at 200° C. is placed with 5 Ibs, of water
*" C., what is the temperature of the mixture?

Ans. 21°-1S C.

How much mercury at a temperature of 120° C. will be required
to melt 10 Ibs. of ice? Ans. 200'48 Ibs.

33. A pound of iron at 200° C. is put into a pound of water at 10°,
both acquire a temperature of 28° '8 C., find the specific heat of iron.

- Ans. -1098.

340 STEAM.

34. A pound of iron at 500° C. is put into 10 Ibs. of water at 24° C.,
what is the temperature of the water? Arts. 29'' '34 C.

The specific heat of iron between 0° and 100° C. is '1098, between
0° C. and 300° C. it is '1218. In this question we have taken it as
•1138. (See Tyndall On Heat.)

35. 12 oz. of iron at 600° C. are placed in 8 oz. of water at 5f-
how much water is converted into steam, supposing no heat lost in
the process? Ans. '526 oz.

To leave iron at 100° C. it gives up 500 x 12 = 6000°.

To raise water to 100° C. it takes up 50 x 8 = 400°.

Specific heat of water is (.-rfos — ) 8787 times greater than that of
iron.

.-. These 400 units will take (8787x400) of those in the iron,
3514-8 units.

. •. There are left frwn the iron 6000-3514*8 = 2485*2 units of heat
to generate steam.

To find how many units of heat from the iron will convert an ounce
of water into steam, we have 537 '2 x 8787=4720*37 units.

248 5 '2

. •. Number of ounces converted into steam = - = '526 oz.

4720*37

If If5 oz. of iron at 500° C. are placed in 10 oz. of watf;r at
00° C., and the specific heat of iron is considered as '1138, how much
water will be converted into steam ? A //.*. -Oil <//..

37. Suppose 4 Ibs. of copper at 210° C. are placed in 2 Ibs. of
water at 60°, and that the temperature of the water is rai~

84° 0., what is the specific heat of copper? Ans.

38. I heat 40 cubic feet of air from 30° C. to 50°, what is the
increase of volume, and what is the present volume ?

1 cubic foot on being heated 1° expands -jj7 of its volume,

-'•40 ,, ,, ,, -j^j-

• '.40 „ „ 20° „ !£2LJ»

= 2*93 cubic feet, . •. Vol. "= 42*93 cubic feet.

39. 40 feet of gas lose 25° 0. of heat, what is the volume
remaining?

An approximate answer is obtained by the same method as aL
40x25

.'. Volume remaining = 40- 3'663 = 36*337 f

P>ut if the quantities are large the annexed is a UK
method.

Let x — volume remaining.

T* v.
If the 25° of heat be applied to x its increase ih

25 aj

•'• a +~273~ ~ 40
,-. x =86*61

QUESTK: 311

40. If 900 feet of air be heated through 753 of heat, what is the
increase of volume ? Atis. 247 '2 cubic feet.

Blanc is S3 '14 C., what is the height of the mountain? The boiling
point of water decreases 1° C. for every 1062 feet perpendicular height.

An$. 15,781 feet.

43. The summit of Monte Rosa is 15,000 feet above the level of the
what is the boiling point of water? An*. S5 -

44. Ou the 3rd August, 1858, the temperature of the boiling point
on the summit of the Finsteraarhorn was 187 °F., what may we infer
the height of the mountain to be from this fact ? -4»«.*14,750 ft.

The exact height is 14,100 feet; we may account for the dis-
crepancy by the reading of the barometer not being properly taken
into account.

The specific heat of air is *237
„ gravity „ yf,.
A cubic foot of water loses PC., how many cubic feet of air would

The specific heat of water is (^T=) 4'219 times greater than that

of air, . \ heat will do 4 -2 19 times the work on air it will on water.

But as the same weight of air will fill 770 times the same space as

r, .'. this cubic foot of water will heat

4219x770 = :VJ43'6 cubic feet of air.

40 cubic feet of water loses 10° of heat ; how much air will this
heat X Ans. 64972*6 cubic feet.

1.000.000 cubic feet of air has Us temperature depressed
. of how much water will this increase the temperature 3° if all the
.inunicated to the water? Atis. 1026*08 cubic feet.

- 1 Ibs. pressure is admitted into a cylinder above the
I in diameter ; find the total pressure on the piston
(1) when there is a vacuum below; (2) when the air is freely
Emitted below. An*. 47124 Ibs. : 17071 "5 Ibs.

of ;>0 Ibs. pressure is admitted below a piston SO inches
diameter, and the atmosphere admitted to the top ; find the
mber of ton? pressure to force the piston up. Aits. 33 '66 tons.

50. Steam of 30 Ibs. pressure is admitted (1) to one side ; (2) to
he other, the diameter is 45 inches, and diameter of piston-rod 5
-. find the difference between the pressures on the upper and
^n. AH*. 5S91bs.

M. Tfa li rare is 40 lb?. per circular inch, what is the

inch cylinder? Ans. 23f tons.

in the last question had been 40 Ibs. on the
-v inch, find the total pn a B 1 TlU tons.

If the pressure be CO Ibs. on the square inch, how much is that
i the circular inch ? AM. 47 '124 Ibs.

4. The pressure of air is 14'705S Ibs. on the square inch, the
f mercury is 135i)i> ; find the height of a column of

342 STEAM.

mercury, -whose "base is one square inch, to correspond with the
pressure of the atmosphere.

Let x - height of the column in inches.

Weight of 1 cubic inch of mercury =• • 96 ounces

1/28

. 13596xa; _
' ' 1728106
. „ 147058x16x1728 oniflA,0 • ,
••*' 13596 = 29'9<MS metes.

55. Answer the same question as above, but substitute pure water
for mercury, or assume a cubic foot of water to weigh 1000 ounces.

Ans. 33 '88 feet.

56. Answer the same question, but substitute salt water, the
specific gravity of which is 1'0267. Ans. 33 feet, nearly.

57. An air pump is 20 inches in diameter, and the length of the
stroke 2 feet 3 inches ; the engine makes 40 revolutions per minute,
and its piston is covered with water at each stroke to the depth of §
of the stroke ; find the number of tons of fresh water lifted in an
hour.

Capacity of pump = 202 x '7854x27. '

Quantity raised at each stroke -202 x '7854 x 27 x f .

Quantity raised in an hour=20a x 7854 x 27 x § x 40 x 60.

Number of cubic feet ™«»* r*r h-m-400 x '7854 x 27 x 2 x 40 x 60

3 x 1728

Weight of this in tons= ff° * *7854 * 27 * 2 * 4-^60 * 1000=
.3x1728x2240x16

58. You are required to answer the same question, but suppose
it to be a marine engine using salt * water. Ans. 224 '4 tons.

59. The air pump of a land engine is 24 inches in diameter, its
stroke is 20 inches, and it is £ full at every plunge ; find the weight
of water lifted in an hour when the engine is making 55 strokes per
minute. Ans. 289 '26 tons.

60. In question 59 we will suppose it to be a marine engine ; how
many more tons would it have lifted in the time ?

Ans. 6-9427 tons.

61. The air pump of a marine engine is 32 inches in diameter, and
is | full at each stroke ; find the weight of salt water lifted in 6
hours, when the strokes are 50 per minute, and the length of the
stroke 4 feet. Ans. 8616'96 tons.

62. What must be the diameter of an air pump with a stroke of
39 inches, f full at each stroke, and 45 revolutions per minute, to
lift 300 tons of salt water per hour ? Ans. 19 '12 inches.

* A cubic foot of salt water weighs 64 Ibs., or more exactly, as the specifle grarity
is 1-0267, it is 6416875 Ibs., but it ia customary to call it 64 Ibs.

QUESTIONS. 343

63. An air pump is 15 inches in diameter and 3i feet stroke, and
-| full at each stroke ; what must be the number of revolutions per
minute to lift 220 tons of salt water per hour ? Ans. 74'6,

64. The water level in a boiler is 12 feet below the surface of the
sea, (a) What is the pressure to force water into it ? (6) If the
pressure of steam is 5 Ibs. how high will the water rise ?

33 feet of water = 147058 Ibs. on the square inch.

It will be more convenient to say, in round numbers, that a
column of water 33 feet high, gives a pressure of 14f Ibs. on the
square inch. The usual rule is to allow 34 feet, but it is evident from
question 56 that the correct number is 33 feet when salt water is in
question.

(a) As 33 : 12 : : 1475 : 5'363 Ibs., Ans.

(I)} When the steam presses with 5 Ibs., there is left only '363 Ibs.
hydrostatic pressure to force in water —

.'. As 1475 : -363 : : 33 : '812 feet, Ans.

65. A boiler or water level in a boiler is 10 feet below the surface
of the sea, the pressure in the boiler is 8 Ibs. of steam, what is the
force acting against hydrostatic pressure in blowing out.

Ans. 3-53 Ibs.

66. The bottom of a boiler is 9 feet below the level of the sea,
suppose 2 feet of water have entered it, what is the pressure to still
force water into it ? Ans. 3 '128 Ibs.

67. Water enters a boiler by means of a pipe from a tank, the
surface being 35 feet high, what must be the pressure of steam to
exactly counteract the pressure of the water ? Ans. 15 '18 Ibs.

68. A boiler 5 feet in diameter is fed by an inch pipe, from a head 30
feet above the level of the top of the boiler ; find the hydrostatic pres-
sure on each circular inch on the bottom of the boiler when it is full.

Ans. 11 -92 Ibs.

69. A brine pump is 3 inches in diameter and 13 inch stroke >
it makes 15 strokes per minute, how much water will it extract
from the boiler in an hour, being % full at each stroke ?

Ans. 1837'831bSi

Capacity of pump, 32 x 7854x13.

Quantity brine pump lifts at each stroke, 3* x 7854 x 13 x -J.

Quantity per hour in Ibs. , ..3* x 7854 x 13 x | x 15 x 60 x 64

1728
= 1837 '836 Ibs.

70. Find the volume of water that will be lifted in 5 hours by a
orine pump under the following circumstances : 3f inches in diameter,
length of stroke 12 inches, and 10 strokes per minute, § full.

Ans. 153 '398 cubic feet.

71. The level of the water in a marine boiler is 10 feet below the
surface of the sea, the pressure of steam is 24 Ibs. , (a) What force
will the steam have to expel the brine ? (b) Can it drive out all the

K' 3r in boiler is 3 feet deep ?
Ans. (a) 478 Ibs. (b) Yes.

344 STEAM.

(a) At 10 feet deep pressure of water is —

As 33 ft. : 10 ft. : : 1475 Ibs. : 4-469 Ibs.
But pressure if column of air is 14*75 Ibs.

.'. Total pressure at 10 ft. is = 19*219.

. '. Force to expel brine, =24- 19 '219 = 4 781 Ibs.

(1) At 3 feet deeper or at 13 feet pressure of water is —
As 33 ft. : 13 : : 1475 : 5-81 Ibs.
.'. Total pressure at 13 ft., = 20*81.
. •. Force to expel brine is -24 - 20'81 = 3*19 Ibs.

72. The surface of the water in a marine boiler is 9 feet below the
sea, the steam pressure is 17^ Ibs. ; when the blow out cocks are
opened, will water enter or will the brine be expelled, and what is the
force to do this, (1) at the commencement of the action? (2) at the
end ? How long will it act ?

Ans. "Water will enter with a pressure of 1*27 Ibs., and will continue
till it rises 2 '84 feet.

73. The pressure in a boiler is 14 Ibs. above the atmosphere, what
is the force to blow out when the level of the water in the boiler is
8 feet below the surface of the sea? Ans. 10*42 Ibs.

74. The lever of a safety valve is 16 inches long, and the spindle
acts at 4 inches from the fulcrum, the diameter of the valve is
4 inches ; find the weight that will allow the valve to begin to act
when the steam pressure in the boiler is 45 Ibs.

Area of valve, = 42 x 7854.

Pressure to oppose the atmosphere, — 45 - 15 = 30 Ibs.

Pressure on the valve, =42 x 7854x30.

Moments of the pressure about the fulcrum = 42 x 7854 x 30 x 4.

,, ,, weight ,, ,, =^Wxl6.

By the condition of the question these two are equal —
.'. Wxl6=42 x 7854x30x4.
.-. W = 94 -248 Ibs.

75. The lever of a safety valve is 30 inches long, the spindle of the
valve acts at 3 inches from the fulcrum, while the diameter of the
valve is 3| inches the weight is 45 Ibs., find the pressure of steam
above the atmosphere when the valve begins to act.

Area of the valve, = 3*52 x 7854.

Moments, if pressure is x Ibs., = 3 *52 x 7854 x x x 3.

„ of weight =45x30.

.'. 3'52 x 7854x^x3 = 45x30.

.:x = 45 *30 =467 Ibs.
3*5a x 7854x3

76. Find what weight must be attached to the lever of a safety
valve 28 inches long, weighing 5 Ibs., when the valve is 1^ Ibs.
weight, with a diameter of 3 inches, and its spindle acting at 4 inches
from the fulcrum. Pressure of steam in the boiler being 55 Ibs.

QUESTIONS. 345

Moments of steam acting on valve, ............ = & x 7854 x 40 x 4.

,, valve, ................................... = 11x4.

, , lever acting at its centre of gravity, = 5 x 14.
,, the weight, ............................ = Wx28.

= 32 x 7854x40x4.

77. Find the diameter of a safety valve which acts at 3J inches from
the fulcrum, the arm is 24 inches long, and the weight 80 Ibs., and
pressure of steam 75 Ibs. Ans. 3*4 inches.

78. The lever of the safety valve is 26 inches long, the area of the
valve 16 square inches, the weight is 75 Ibs. ; at what distance should
the valve spindle act, so that the valve shall lift with a pressure of
55 Ibs. of steam ? Am. 3*047 inches.

79. The lever of a safety valve is 30 inches long, the diameter of
Vcalve 3^ inches, and spindle acts at 3 inches. The weight is 60 Ibs.,
what will be the pressure of steam when it begins to act ?

Ans. 77 '3 Ibs.

80. Find the weight that must be attached to a safety valve at 21
inches from the fulcrum, when the valve weighs 1^ Ibs. and acts at
3£ inches, while its diameter is 3£ inches, the lever of the safety valve
weighs 6 Ibs., and pressure above the atmosphere is 40 Ibs.

Ans. 52-05 Ibs.

81. A 3f inch valve weighs 2| Ibs., and acts at 4J inches from the
fulcrum, while the pressure is 5 atmospheres and the lever 21 inches
long, weighing 6^ Ibs. ; required the weight that shall just begin to
act under these circumstances. Ans. 130*35 Ibs.

82. The pressure in a boiler is 36 Ibs. above the atmosphere on the
circular inch, required the weight to be attached to the arm weighing
8 Ibs. and 30 inches long, when the 4 inch valve acts at 3| inches and
weighs 3£ Ibs. Ans. 6279 Ibs.

S3. Find the nominal horse-power of an engine of the following
dimensions : the diameter of the cylinder is 25 inches, the length of
the stroke 3 feet, and the number of revolutions 55. In calculating
the nominal horse-power of an engine the pressure is taken at 7 Ibs.

Area of piston, ...................... 252 x 7854

Pressure on the piston, ........... 252 x 7854 x 7

Number of units of work in one

revolution, ........................ = 252 x 7854x7x3x2

Number of Ibs. lifted 1 foot }

high per minute, I _ ~v v -7f^4

Or, number of units of work f ~ 25 x 7*54

done per minute, .

= 1133921-25

It is allowed that a horse can do 33000 units of work per minute/
or can lift 33000 Ibs. 1 foot high per minute,

1133921 -25j_
.', H.P. — -i 33QQQ - 34'36, Ana.

3iG STEAM.

84. The rule for finding the nominal horse-power of an engine is i
multiply the square of the diameter by the speed of the piston, and
divide the product by 6000. Prove this.

Let d = diameter of the piston,

I = the length of the stroke in feet,

n •=. the number of revolutions per minute.

The speed of the piston is = I x 2 x n.

Area of piston = rf2 x '7854!

. '. Units of work done per minute = d 2 x '7854 x7x(Zx2xfl)

d 2 x '7854 x 7 x speed of piston

33000
' d 2 x speed of piston

— ~ "

For 7854 x 7 will go into 33000 (very nearly) 6000 times.

Hence the rule.

85. Find the horse-power of a direct acting blowing engine, with 4
cylinders, diameters 4 feet, stroke 6 feet 6 inches, pressure CO Ibs.^
number of strokes per minute 15.

Area of pistons (4), ...... ; . . — 482 x *7854 x 4

Speed of piston per min., == 6J x 2 x 15
Total pressure on the pis-

tons,' ...................... :.. = 482 x '7854 x 4 x 60

. *. Units of work done per

minute, .................. ... = 482 x 7854x4x60x6ix2x 15

48? x -7854 x4x60x6|x2x!5

~ 33000

-2566'28, Am.

86. A portable engine has two cylinders, witji 9J inch diameters
and 14 inch stroke, the pressure of steam at which it is usually worked
is 42 Ibs., and the number of strokes per minute 60; find the horse-
power. Ans. 25-25 H.P.

87. A marine engine has four cylinders, each of 50 inches in dia-
meter and 4 feet stroke, the number of revolutions is 52 per minute,
and the engine is worked at a pressure of three atmospheres ; find
the horse-power. Ans. 4455*36 H.P.

88. , Ah engine with one cylinder of 3 feet diameter, 5 feet stroke;
and 25 revolutions per minute, is worked at a pressure of 30 Ibs. on
the circular inch ; find the horse-power. Ans. 294*54 H.P.

80. An engine with two 18 inch cylinders and 2 feet 6 inch stroke is;
required to do work equal to 150 horse-power, when the number of
revolutions is 40 per minute : what should bb the steam pressure ?

Ans. 48-6 Ibs.

90. What must be the diameter of a cylinder to develop 100 horse-
power with 4 feet stroke, 45 revolutions, and 80 Ibs. pressure ?

Ans. 12'07 inches,

QUESTIONS.

01. J?ine the nominal horse-power of a pair of engines, diameter of
cylinder 104 inches, stroke 1§ feet, number of revolutions 120.

Am. 14:7 H.P.

92. The diameters of the two cylinders of a marine engine are CO
inches each, the length of the stroke 4 feet 4 inches, and the number
of strokes per minute 40 ; fin4 the nominal horse-power.

Ans. 416 H.r.

93. If the cylinders of a locomotive are 12 inches in diameter, 18
inches stroke, and make 40 strokes per minute, while the pressure is
70 Ibs. per square inch; what is the horse-power? Ans. 57*57.

94. Steam at 60 Ibs. pressure is admitted into a cylinder 6 feet
long, and cut off after 2 feet of the stroke have been performed : (1)
find the terminal pressure ; (2) the average pressure throughout the
stroke.

We have always this proportion —

Initial pressure _ Whole stroke
Terminal pressure Part of stroke

•••?=! . •••-20

Or we may take the following rule for finding the terminal
pressure: The terminal pressure is always equal to the initial
pressure multiplied by the grade of expansion.
To find the average pressure —

1. Pressure during 1st foot of stroke /' =60
2; ,» „ 2nd =60

3. „ jf 3rd ,$ „ ==8x60=40

4. „ „ 4th ,; „ =1x60=30

5. j, „ 5th „ „ = £x 60=24

6. „ „ 6th „ » . =*x 60^20

6)234

39 Ibs;

The average pressure is therefore 39 Ibs.
„ total ,, „ ,, 234 Ibs.

,, terminal! ,, ,, as before 20 Ibs.
We may also1 find the steam pressure by Simpson's rule, which is &
nearer approximation.

Let A D represent the cylinder in this question, B D the length of
the stroke, 6 feet. Let A B represent 60 Ibs., then e 1 and/ 2 repre:
sent 60 Ibs. pressure of steam. When the piston gets to g 3, the
steam expanding from / to g will fill £ space half as large again,
.-. the pressure will be §x60=40 Ibs. So take n 3 = 40 it will
represent the pressure of steam. When the piston gets td li 4, it will
fill double the space, . '. the pressure will be £ of 60 = 30. Let
m 4 = 30. On the same principle o 5 and p 6 are respectively
24 and 20. Draw the curve through the points, it will repre-
sent the falling pressure of steam. The curve itself is an
hyperbola. We also see that by giving the steam a great initial
velocity, the actual pressure of which is only p 6 or p D, it has been

348

feTEAM.

made to do work equivalent to 39 Ibs. of steam, or, say, s (>. These
ordinates, then, now represent our steam pressures. To find their
sum we have —

Simpson's Rule: To the sum of the extreme ordinates add four
times the sum of the even ordinates and twice the sum of the odd
ordinates. This sum, multiplied by one-third the common distance
between the ordinates, will give the area (of the figure fp D2, and
therefore the total steam pressure).

Area= £ j 60 + 20 + 4 (40 + 24) +2x30 j =132.

"Work done before steam was cut off— 2 x 60 = 120.
. '. Total work done = 132 + 120 = 252.

951 1
. *. Average work done — - — ? = 42 Ibs.

In the chapter on De Pambour's theory we gave some rules for
finding the work done on a piston on one stroke. To show what a
near approximation Simpson's rule gives we work the same question
by those rules.

Units of work done on stroke of piston =± qp (l 4- log. g -)

= 2 x6o(l+log.f 3)

= 120 x 2-0986123
-251-833476

95. In a compound twin screw engine steam is admitted into the
smaller cylinder 44 inches in diameter, and cut off when 1^ feet of
the stroke are performed : the length of the stroke is 4 feet. The
steam then enters the larger cylinder, 50 inches in diameter, and
in which We will suppose the average pressure is 43 Ibs. Find the
horse-power when steam at 80 Ibs. initial pressure enters the first
cylinder. The revolutions are to be 40 per minute.

'. Grade of expansion =s Jl= |.
Terminal pressure = 80 x | - 30.

QUESTIONS.

349

To find average pressure in the smaller cylinder —

3rk do

ne in

the 1st half
2nd
3rd

foot o

f the s

Lbg.
troke =80
= 80
= 80(1)

4th

5th
Gth
7th
8th

= 1x80=60(2)
= % x 80=48 (3)
= f x 80 = 40 (4)
=f x80=34f(5)
= |x80 = 30(G)

By Simpson's rule the total pressure will be *

= SOx3 + J | 80 + 30+4 (60+40) + 2(48+34?-) j
=240 + 224^=446?.

.*. Average pressure = — r=55f Ibs.
8

Although half a foot is the common distance between the ordinates ,
the relative unit of distance is one, so we therefore multiply by ^ and
not £. Consider the stroke as 8 feet, and the reasoning is seen
perhaps better.

Secondly, we have the average pressure in the larger cylinder
given as 43 pounds. The reason why we assume it so high is, that
the vacuum is always exceedingly good in the larger cylinder, and
each cylinder is generally arranged so as to give the same horse-
power. Of course the steam will enter the second cylinder at about
30 pounds pressure, which, with the vacuum and not cut off, would
give something about the pressure we have assumed, namely, 43 Ibs.

Thirdly, to find the horse-power developed in each cylinder.

H.-P. of smaller cylinder =44° x ^54 x 2x 4 x 55f x 40 = 82

H.-P. of larger cylinder =

50* *

=81872

Total H. -P. =1642 -309.

98. A compound engine has two cylinders of 60 and 90 inches in
diameter, the stroke is 5 feet, and the number of revolutions 60 per
minute ; find the horse-power, pressure being 84 Ibs., cut off at one
foot in smaller cylinder, and allowing the average pressure to be 23
in the larger cylinder.

The average pressure (to be found by the student) is 44 '4 very
nearly. Ans. 2282*51 + 2660 '36 = 4942 '87 H.-P.

* This is not a case in which Simpson's rule should be applied, as there should
properly be an odd number of ordinates when the rule is used ; but we have
ventured to apply it here, as the error cannot possibly amount to more than a, very
small fraction,

350 STEAM,

97. Suppose we have a compound engine of the following dimen-
sions, ete., find the H.-P. : —

Diameter of cylinders, 40 in. and 70 in.

Length of stroke, 42 in.

Number of revolutions, 40

Initial pressure ofjsteam, 60 Ibs,

Steam is cut off in the smaller cylinder at 1J feet, and we will
allow the average pressure to be 20 Ibs. in the larger cylinder.

Ans. Pressure is 47|| Ibs., say 48 ; horse-power 51 179 + 653 '07 =
1164-86.

98. A stationary engine has a cylinder 24 inches in diameter, the
stroke of the piston is 3 feet, pressure 100 Ibs., and number of re-
volutions 80. Find the H.-P. when the grade of expansion is ^.

Ans. 463 or 4601 H.-P.

99. Find the nominal horse-power of a pair of engines 6 feet stroke,
36 inches in diameter, 46 revolutions. Ans. 119 '23.

100. In a locomotive engine the steam is cut off at ^ stroke, the
length of stroke is 24 inches, the diameter of each cylinder is 15
inches, number of revolutions of crank 50, and initial pressure of
steam 80 Ibs. ; find the horse-power.* Ans. 89J.

101. A blowing engine has 4 cylinders, diameter 40 inches, stroke
5 feet, grade of expansion ^th, number of strokes 18, and pressure of
steam 25 Ibs. ; find the horse-power. Ans. 359*47.

102. A cylindrical boiler with flat ends is 25 feet long, 5 feet in
diameter, and has two flues running through its whole length, each
2 feet in diameter ; find the whole pressure of steam on the internal
surface of the boiler when the steam gauge stands at 40 Ibs.

The surface of the shell is = 5 x 3*1416 x 25.

„ ,, two flues = 2x 3-1416x25x2.

,, ,, ,, ends = (52 -2 x22)x -7854x2.

% Whole internal surface =25x3-1416(5 + 4) + 17 x -7854x2.

=25 x 3-1416 x 9 + 34 x 7854.
. =733-5636 ft.

.-. Total pressure in tons, = ?33'5636 x 144 x 40= 1866-3064 tona,

2240

103. A cylindrical boiler of 3 feet in diameter, 14 feet long, has an
internal tube of 1^ feet diameter. If the steam pressure is 30 Ibs.,
find the whole internal pressure in tons.

Ans. 402-15 tons.

104. A cylindrical boiler is 40 feet long and 8 feet in diameter, it
has two internal flues running through its whole length each 2^ feet
in diameter. Suppose the water averages a pressure of 1| Ibs. over
the whole surface, and the steam 40 J Ibs., find the total internal
pressure in tons.

Ans. 4629:226 tons.

* Pressure is found as in Ex. 94. Simpson's rule does not apply.

QUESTIONS.

351

105. In a tubular boiler there are 144 tubes, each 2J inches in
diameter, and 10 feet long, find the amount of heating surface if the
heating surface around the fire box be 40 feet.

Heating surface of 1 tube —

2-25x31416x10
12

feet.

144

2-25x3-1416x10x144
12

= 848 -232 feet.

To this add surface around the fire box = 888*232 feet.

106. In a locomotive boiler there are 160 tubes 96 inches long and
H inches in diameter, find the total heating surface of the tubes.

Ans. 502 -656 ft.

107. Steam is used by an engine at 30 Ibs. pressure, and cut off
at ;}, find approximately the saving per cent, by working expansively.

Let us suppose stroke is 8 feet, we must find (1) terminal pressure,
(2) average pressure.

Terminal pressure = J x 30 = 7i Ibs.
foot . ....30"

, second ,

(1)

3.
4.

5.
G.

7. •
8.

third
fourth
fifth
sixth
seventh
eighth

§x30 ...
1x30 ...

|x30 .'.'.'
1x30.'.'

...=20
...=15
= 12
...'=10

(2)
(3)
(4)
(5)
(G)
(7)

Total pressure = 30 x 2 + J j 30 + 7^ + 4 (20 + 12 + 8^) + 2 (15 + 10) |
= 60 + 83H = 143J (nearly).

Average pressure =

= 17-J

Now had steam been admitted throughout the whole stroke, its
average would have been 30 Ibs.

. '. Out of 30 there is saved 30 - 17^3 = 12-^V
To find gain per cent— As 30 : 100 : : 12-& : 40-^, Ans.

There was no necessity to have found the average pressure, we
might have reasoned thus :

If steam had been continuously admitted, total pressure would have
been 30 x 8 = 240. But by expansive working, total pressure = 143J;.

. \ Out of 240 we gain 240 - 1^3^ = 96|.
As 240 : 100 : : 96^ : 40^, as 'before.

108. Steam at 50 Ibs. pressure is admitted into a cylinder 6 feet
long, and cut off at | stroke, find approximately the gain per cent, by
reason of expansive working. Ans. 30.

109. Steam at 45 Ibs. pressure is admitted into a cylinder 4 feet
long, and cut off at J stroke, find the gain per cent, by working
expansively. Ans. 15 -5.

3-53 STEAM,

1 10. The terminal pressure is 40 Ibs. , what was the initial pressure
if the stroke is 5 feet and steam is cut off at J stroke ?

Am. IGOlbs.

111. The stroke is 8 feet long, the initial pressure 120 Ibs., and
terminal pressure 50, at what point of the stroke was steam cut off?

An*. 3i ft.

112. What was the length of stroke when initial pressure was
80, terminal pressure 45, and steam cut off at 2 feet?

Ans. 3-J-.

113. The pitch of a screw propeller is 20 feet, and the diameter
18 feet, find the angle.

Tan. of angle = Circumference = 18x3.141G = 2872744
Log. 10 ............ = 1-000000

Log. 28-2744 ...... = 1-451393

Log. Tan. 19° 28' - 9 '548607

114. Find the angle of the screw propeller of the "Simoon," when
the diameter is 16 feet, and the pitch 20 feet. Ans. 21° 41'.

115. Find the angle of a screw when the pitch is 20 and the cir-
cumference 20V& Ans. 30°.

116. What angle has that screw whose pitch is equal to the circum-
ference? Ans. 45°.

117. The thread of a screw is to the pitch as 2 : 1, find the
inclination of the screw. Ans. 60°.

The circumference of a screw is to the pitch as

: : \/5-l. Find the angle. Ans. 18°.

119. The pitch of a screw is to the thread as \/5- 1 is to 4, find
the angle. Ans. 18°.

120. Find the pitch of a screw propeller when the angle is 20° and
the diameter 16 feet.

rpa OAO _ Pitch _ Pitch

Circumference 16 x 3 '1416

.-. Pitch = Tan. 20xl6x3'1416
Log. 16 ........... = 1-204120

Log. 3-1416 ..... = -497076

Log. Tan. 20*... ==9^661066
Log. 18-29 ....... = 1-262262

121. Find the pitch of a screw propeller, when the angle is 25° and
diameter 15 feet.

Ans. 21 -97 ft.

122. If the diameter of a propeller be 16 feet, and the angle 21° 10',
what is the pitch ?

Ans. 19-46 ft.

123. The pitch of a screw is 18 feet, and the number of revolutions
70, how many knots will the ship go per hour, making no allowance
for slip?

The length of a knot is 6080 feet,

QUESTIONS. 353

At each turn of the screw the ship advances 18 feet.
. '. The ship advances in one minute 18 x 70.

„ „ „ hour 18x70x60.

.-. Number of knots per hour = 18 x 7Q x 6Q = 12'43.

uUoU

124. A ship has a propeller making 55 revolutions per minute, the
pitch of the screw is 20 feet, the slip 15 per cent., find the speed of
the ship.

The speed of the screw per hour = 20 x 55 x 60 feet.

Taking off 15 per cent., leaves •££$•

.'. Speed of the ship per hour = 20x55x60x85 = 9'22 knots.

0080 x 100

125. A ship is required to steam 12 knots per hour when the screw
is making 75 revolutions, what must be the pitch of the screw?

Let x = pitch of the screw.
The velocity of the screw per hour — a; x 75 x 60 feet.

a; x 75 x 60 ,

6080
. •. x x 75 x 60 _ , 2

6080

126. Find the pitch of a screw to propel a vessel 10 knots per hour,
when the screw is making 72 revolutions per minute, after 12 per
cent, has been deducted for slip.

The slip is calculated on the speed of the screw.

To obtain these 10 knots, 12 per cent, or TV<7 = -fa have been

' :en off the speed of the screw.

This 10 is only f -§- of the speed of the screw.
. *. Speed of the screw = 10 x ff = 11^ knots.
Then as above

50 = 11T*T . •. x = 16 feet (nearly).

6080
Or we may reason thus :

a; x 72 x 60 12x100

6080 88

i. e., we take the 12 from 100, which leaves 88 or •$&.

127. Required the pitch of a screw propeller to drive a ship 14
knots per hour, when the engine crank is making 40 revolutions, and
the multiplying gear is 2 '3, and the slip is 20 per cent.

Ans. 19-27 feet.

128. What must be the pitch of a screw to drive a ship 13 knots

354 STEAM.

per hour, slip 15 per cent., number of revolutions of crank 42, when
in the multiplying gear the larger wheel has 120 teeth and smaller
55? Am. 16 -9 feet.

129. Eequired the speed of a ship when the pitch of the screw is
20, the number of revolutions C5, and the slip 25 per cent. ?

Ans. 9-63 knots.

130. The diameter of a paddle wheel should be four times the
length of the stroke ; find the diameter of the paddle wheels worked
by engines with 4 feet 3 inches, 5 feet 4 inches, and 3 feet 10 inches
stroke. Ans. 17 feet, 21 feet 4 inches, 15 feet 4 inches.

131. The crank of an engine is 3 feet 2 inches, find the velocity
of the ship in knots when the paddle wheel is properly proportioned
to the crank, the number of revolutions 15 per minute, and the
width of the paddle boards 2 feet 3 inches. The centre of pressure is
situated at one-third the width of the float from the outer edge.

Ft. In. Ft. In.

Diameter of effective working wheels 3 2x8-2x^x2 3

Ft. In. Ft. In. Ft. In.
= 25 4- 1 6 = 23 10
. •. Speed of ship per minute = 23% x 3 1416 x 15.

. •. Speed of ship per hour in knots =23^ x 3>1^ * 15 * G°.

OUoU

= 11-08, Ans.

132. The diameter of a paddle wheel is 24 feet, and the number of
revolutions 15 per minute; find the speed of the ship when the
width of the paddle boards is 2 feet 6 inches. Ans. 10*4 knots.

133. The crank of an engine is 4 feet, the paddle wheel is properly
proportioned to it, the revolutions are 12 per minute, and the width
of the paddle boards 2 feet; find the speed of the ship.

Ans. 11 '4 knots.

134. The diameter of a paddle wheel is 21 feet, the width of the
boards 1 foot 6 inches, number of revolutions 20; find the speed of
the ship when slip is 15 per cent. Ans. 10 '5 knots.

135. Suppose the diameter of a paddle wheel is 24 feet, the width
of the boards 4 feet, number of revolutions 16 ; find the speed of
the ship when slip is 12 per cent. Ans. 9 -31 knots.

136. A steamer is going up a river down which the tide is coming
at 3 miles an hour, how fast must she steam ?

Ans. The most economical speed is half as fast again as' the tide,

. '. Speed =3 x -} = 4^ miles, and progress IT? miles per hour.

137. A boat is steaming up a river down which a flood is coming 4
miles an hour, how fast must she steam ? Ans. 6 miles an hour.

138. The level of the water in a marine boiler is 9 feet below the

surface of the sea, the pressure of steam is 21 Ibs., the depth of
water in the boiler is 5 feet ; what depth of water will be driven
out by the force of steam if blow out cocks are left open ?

* Ans. There will be '58 feet left in.
139. The steam pipe leading to one of Hornblower's valves is 9

QUESTIONS, 355

inches in diameter ; find the lift to allow a free passage of steam if
the valve be 9 inches in diameter.

Here the area of steam pipe is 92 x 7854 ; and this volume of steam
must have free passage round the circumference of the valve.

. \ Circle for passage of steam =9 x 3 '1416.
Let h be the height, then

9 x 3-1416 x/i = 92x -7854

140. One of Hornblowers valves is 10 inches in diameter, and the
steam pipe leading to it is 11 inches in diameter, how high must the
valve be lifted to allow the steam to pass freely ?

Am. 3-jV inches.

141. Find the lift of a Hornblower's valve, the inner diameter of
steam pipe being 8 inches, to allow a free flow of steam.

Ans. 2 inches.

142. The feed water of a boiler was supplied at a temperature of
15° at the rate of 85 gallons per hour ; a feed water heater was
introduced, and then it was supplied at a temperature of 85° ; find
the units of heat saved in 24 hours.

To each gallon is supplied 85°- 15° ~ 70°.

A gallon of pure water weighs 10 Ibs (salt 10'27 Ibs. nearly).

. '. As each Ib. of water is raised in temperature 70°, the saving in

each gallon is .................. lOx 70 = 700 units.

. '. In 85 gallons, or in one hour,

the saving is .................. = 85x700 = 59500.

. '. In 24 hours the saving is 59500 x 24= 1,428,000 thermal units.

143. If the engine in the last question works 10 hours per day, six
days a week, how many pounds of coals are saved in a week ?

The combustion of a pound of coal produces 8000 thermal units
and as a thermal unit is the heat necessary to raise a pound of water
1° C., we have from above —

Heat saved in 1 hour ......... ................. = 59,500 units.

,, ,, 10 hours or 1 day ............. = 595,000

Gdays ............ =3570,000 ,,

.'. Ibs. of coals saved ................... = s-if-° = 446 '25 Ibs.

= 4 cwt. nearly.

144. The feed of a boiler was 15 cubic feet per hour, find the sav-
ing effected in a week of six days, 10 hours per day, by using a feed
water heater that raised the temperature of the water 00° C.

Ans. 421J Ibs.

145. A boiler evaporates 20 cubic faet of water per hour, the teed
water heater raises the feed through 75° of heat, find the saving in
100 days of 12 hours each. Ans. 14062 '5 Ibs.

146. To find the specific gravity of steam and weight of a cubic
foot of steam.

356 STEAM.

An inch of water produces 1669 cubic inches of steam at atmo-
spheric pressure.

Weight of an inch of water = ^_o|- = oz.
. *. Weight of 1669 cubic inches of steam =

_ _ \ ooo

— ~~~

• 1 79Q _ 100

,, 1/-0 ,, ,,

= -5991 oz.

Now, as water is 770 times heavier than air, and the specific gravity
of gases have air for their standard, . *. specific gravity of steam will
be found thus : —

A cubic foot of air weighs ^V = 1 '2987 oz.

If specific gravity of air weighing 1*2987 oz. is 1, what is tho
specific gravity of steam weighing *5991 oz. ?

As T2987 : '5991 : : 1 : -4613 specific gravity of steam.
Bourne gives specific gravity of steam as '481.

147. The diameter of a steam-pipe is 10 inches, the two equilibrium
valves measure 9 and 9i inches in diameter, find the lift when fully
open to steam.

Ans. 1 '35 inches.

148. Give a general proof of the rule for finding the weight to be
applied to a safety valve, — the length of the valve, the distance of the
spindle from the fulcrum, the weight of the valve, and the weight of
the lever being known.

A C

W F

Let A F be the lever of the valve, with its centre of gravity at C
and fulcrum at F.

Let 8, between C and F, be where the valve acts on the lever.

Taking the moments about F, and supposing d to be the diameter
of the valve, and p the pressure of steam above the atmosphere, we
have —

Letting W be the weight, and w that of the lever, and w' that of
the valve.

.-. WxAF + wxCF + w'xSF=d2x|xp xSF

(d* x~ x 2> - to') S F - u> C F

•'• W = AF

Or given the other elements, the quantities d or p may be found.

149. Show generally that the most economical speed to run in a
tide way, or against a stream, is. half as fast again as the stream.

Let x — the speed of the ship per hour.

,, v — the velocity of the tide or current per hour.
. '. x - v = the progress made by the ship per hour.

QUESTIONS. 357

Now tlie consumption of fuel varies as the cube of the speed, or
as x3.
Let the consumption be ex5.

. '. Consumption for each mile = ^L_; this is to be the most
economical consumption. x-v

Differentiating and equating to zero.

3 c x* (x - v) d x - c ccs d x _ Q

(x-v)*

. \ 3 c x* (x - v) - c xs = 0

.'. 3 (x-v)-x = Q

2x = 3v

•-v

150. Find approximately the surface of a screw blade.

In taking A B as the pitch, B C as the circumference, and A C as
the thread, it is very evident that if we consider the blade to be
made up of a very large number of A
triangles, placed side by side, and that
the part A B C is then taken away,
leaving AC to form the blade, that
if we could find the lengths of all
the lines corresponding to A C, their
sum divided by their number would
give an average length, which, mul-
tiplied by the radius, must be the

approximate area of the blade. In B
practice, it is usual to find only three of these lines, and then divid-
ing by three, and multiplying by the radius, gives the area of the
blade. A B may be considered as the length of the screw to obtain
the approximation.

In the above figure let us suppose B C is bisected in D, and A D
joined ; then A 0 represents the longest line on the surface of the
blade, A B the shortest, and A D an intermediate one.

151. The diameter of a propeller is 12 feet, the pitch 14 feet, and
the length 2 feet ; find the surface (1) of one blade, (2) of two
blades, (3) of a complete screw.

BC = 3-1416x12 = 37-6992.
A B = 14 and D B = £ of 37 '6992.
ACa = AB2 + BC2 = 196 + 1421-2296 = 1617'2296.

.-.AC = 40-214.

AD2 = AB2 + BD2 = 196 + i of 1421-2296.
.-. AD = 23 -479.

358 STEAM.

AB = 14
AD = 23-479
A C = 40-214
3)TT693
25-897
_ 6
Sq. ft. 155*38 = area of complete screw.

As the length is 2 feet, the area of one blade = T°T of the whole.

. '. Area of one blade = \ x 155 '38 — 22'19 sq. feet.
,, two blades = 44 '39 sq. feet.

152. Find the area of the two blades of a propeller of the follow-
ing dimensions : —

Diameter ^15 feet.
Pitch = 20 feet.
Length = 3 feet.

Ans. 76 '57 square feet.

153. Find the area of the two blades of a propeller and of the
complete screw, when diameter is 16 feet, pitch 20 feet, and length
2J feet. Ans. 70'S and 283*2472 square feet.

154. Find approximately the area of the blade of a propeller, 18
feet in diameter and 21 feet pitch, when the length is \ of the pitch.

Ans. 49*94 square feet.

155. Find the horse-power of an engine of the following dimen-
sions : —

Diameter of two cylinders, 70 inches.
,, trunks, 20 inches.
Length of stroke 6 feet, cut off at J.
Pressure 60 Ibs., number of revolutions 45.

Ans. 4241 -16 or 4854*68.

156. Obtain the usual expression for the locomotive performance

D^v2

of marine engines, viz., - 1

Show from your investigation with what limitations you may
apply it to measure the performance of different ships (1863).

Here v is the speed of the vessel.
,, D ,, displacement.
,, I ,, indicator horse-power.

When a steamer goes from place to place, she excavates, as it
were, a canal between the two places, the transrerse section of which
is the immersed midship section of the vessel. For similar vessels the
work done on a mile, or per hour, must bear a relation to this
immersed midship section. Let M be the midship section of the
vessel, and W the work done in foot pounds, and K the resistance
against M ; then R — M v2 ; and therefore the work done = M vs.

QUESTIONS. 359

This holds good for similar vessels only. The midship section
may be expressed in terms of the length /, breadth &, or height /£,
Z2, 62, 7t2, for the area of the midship section varies as the square of
these quantities.

It is evident that the whole displacement, depending upon the
length» breadth, and height of the vessel, will vary as the cubes of I, b,
or/?.

. •. M varies as I2 . '. I oc M* (a)

while D ,, Is .'. IK D* (b)

.*4 from (a) and (b) M* oc D* .'. M oc D^ (c)

so that now we can put Ds for M, where D is the displacement.
It is very evident that if a vessel go from one place to another at
double the usual speed, she goes in half the time, and therefore has
*our times the work to do in half the time, and hence there must be
eight times the power employed, or the horse-power varies as the
cube of the speed. If at three times the velocity, nine times the
work will be done in one-third the time, and therefore the power is
multiplied by 27. . *. a I — M v3 where I is the indicator horse-

power; but as M varies as D^, the measure of the locomotive per-
formance will be

In the latter part of this theorem we might have reasoned thus : —
The locomotive performance depends upon the fuel used, the fuel
used gives an approximation of the indicator horse-power (I).

. '. Work done by a unit of fuel = — =^-

:ore.

157. Reasoning as we have in this last question, we see that if C
and C' be the consumption of fuel, and K and K' the speed or
velocity.

.-. C:C': :K3 :K/S;
also H.P. : H.P.' : : K3 : K'3 ;

also, if n and nf be the number of boilers,
n :nr : :K3 :K/3;

also, if r and r' be the number of revolutions,

r : r' : : K8 : K's.

8. The degree of saltness of the water entering a boiler is
read of as -jV? an(i *na^ of the water in the boiler is kept at ^ the

360

STEAM.

temperature of the feed water is 100° F. (37°|C.), and that of the
water in the boiler is 248° F. (120°C.), what percentage of the total
heat given to the boiler is wasted by blowing off?

The total heat in steam at 248° is 1157° '64. See example 177.
Substitute in next formula. . A ns. 6 '5 per cent.

Formula for finding the loss of heat by blowing out and the loss
per cent.

Let x — the number of feet of water blown out every 3 hours.

Let y — „ ,, ,, evaporated ,,

.*. x+y~ „ ,, ,, entering „

Let t — the temperature of the feed water.

Let t' = ,, ,, „ boiler ,,

To turn y feet of water into steam will require (637 '2 - 1) y of heat.
To boil the x feet of water blown out will require (t' -t) x of heat.

. '. The total loss is (tr - 1) x.

* '. Total quantity of heat employed = (637° *2 -t}y+ (tf - 1} x.
Since out of (637° '2 -t)y+ (f -t)x there is lost (? - 1) x.

. *. Loss on 1 —

. \ Loss per cent. —

159. A marine boiler is blown out every 3 hours, in the proportion
of 1 gallon blown out to 3 evaporated. At each time 1000 gallons
are expelled, and the boiler evaporates 3000 gallons per hour. The
temperature of the feed water is 6°C. Find the loss per cent., if
temperature of water in boiler is 113°C.

Ans. 5*3 per cent.

160. A marine boiler is blown out every hour. On each
•occasion 33 gallons are expelled, while 132 gallons are evaporated in
the same time. Find the loss per cent, when the temperature of the
"water in the boiler is 115° C., and that of the feed 5°C.

Ans. 41 per cent.

161. If a be the number of cubic feet of feed water, b the quantity
folown out, e the quantity evaporated, supposing the water is to be

Hiamtained at ~ of saltness ; find the quantity blown out.
30

Since the feed water=e + & = a,
and also since the feed water has •£$ of saltness in it,

.'. e+b—sb

~s-l

(1)

QUESTIONS. 361

If the quantity evaporated is required e=b (s- 1)
Since a = e + b

i Oi

.*. a=sb .'. 6 = ~
s

162. The boiler water is to be kept at -5%, or 4 degrees of salt-
ness, how much must be blown out ?

From last example, b — ^- — ^
s 4

. •. Quantity blown out must be J the feed.

163. A marine boiler is to be kept at 3 degrees of saltness, how
much water must be blown out ? Ans. ^ feed.

164. If 900 gallons of water be converted into steam, what quan-
tity of brine must be blown out that the water in the boiler may be
maintained at -5% of saltness ? Ans. 300 gallons.

165. Prove that when a vessel is heeling over, the load on the
safety valve becomes L. Cos. h.

Let S be the safety valve. Let S A repre-
sent the load. Then when the vessel heels
over, the load AS will be resolved into the
two forces, AB acting horizontally and BS
perpendicularly ; the part B S only is effect-
ively acting to keep down the valve.

Angle B S A is the heel a S p. Let A S
= L or load.

Cos. heel = — .-. BS= AS Cos. heel.

= L. Cos. heel.

166. A boiler is loaded to 20 Ibs. on the square inch; the vessel
heels over 25° when the steam issues from the valve ; find the steam
pressure in the boiler.

When boiler begins to blow off, force of steam = Cos. heel x load
on the safety valve.

. •. Pressure = Cos. 25° x 20.
log Cos. 25° = 9-957276

log 20 - 1-301030

Ans. log 18-12 = 1-258306

167. A boiler is loaded at 50 Ibs. on the square inch ; the vessel
heels over 12°; what force will the steam have in blowing off?

Ans. 48'9 Ibs.

168. A ship heels over 15°, and the boiler blows off at 40 Ibs., what
is the load of the valve when the ship is on an even keel ?

Ans. 41-4 Ibs.

169. A marine safety valve is loaded to 35 Ibs., and blows off at
34, when the vessel inclines at a certain angle ; find the heel.

Ans. Cos. 13° 44'.

362

STEAM.

170. To investigate a formula for finding the position or angle of
the crank at any point of its stroke.

Let the length of the connecting rod R C = I
,, ,, crank CE~r

,, 6 be the angle H C E between the connecting rod and crank

,, h ,, height of the stroke made.
The length of the upstroke or down stroke ~ 2 r
If the piston were at the bottom of its stroke, E K would = r+l

QUESTIONS.

Since h is the portion of stroke made

.-. ER = r + l-li

Cos. 6 -

363
'$13

2RC.CE

2 r Z

(1)

(2)

From equations (1) or (2) we can find the angle at any point of th6
stroke.

Let h — r, or suppose the piston is halfway up or down, then
equation (2) becomes

.Cos. 6 =

21.

Let angle 6 = 90°, or let the crank be at right angles to the con-
necting rod.

2r I
And Cos. 90° = 0.

-0

= r+l-h

171. When the crank is at right angles to the piston rod, prove
that

172. The length of the crank is 2 feet, and the connecting rod
6 feet ; find the angle between the connecting rod and crank, when
the piston is in the centre of the cylinder. Ans. 80° 25'.

173. The crank is 2^ feet long, connecting rod 7| feet : find the
angle at half stroke. Am. 80° 43'.

174. The angle at half stroke is 78° 27', the piston has moved up
4 feet, find the length of the connecting rod.

Ans. 10 feet.

PARALLEL MOTION.

364 STEAM.

175. On page 62 it has been been proved that
If we divide C h in e so that

C e : c d : : do : oe
then by similar triangles gdo and o e C
.*. g d or he : C e : : do : oe
.'. he : C e : : C e : cd

, Cea

.-. cd= — -
/ie
which gives the length of the bridle rod c d.

To find o, the point where the air pump rod must be attached,
when the length of the bridle rod and back link are known.

C e : c d : : d o : o e

. '. ^— = °~ add one to each side
C e do

inverting, etc,

Ce do

e- de>

176. If 40 Ibs. of water are heated from 20° to 100°, how many
thermal units are required? Ans. 3200.

177. The steam in a boiler is at a temperature of 245° F., find the
total amount of heat in it, and the latent heat.

1082°+ -305 T = units of heat
1082°+ -305 x 245°= 1156°'525 F.

= 643° C. nearly.

.'. Latent heat = 1156°'525 - 180° = 976°'525, which is
(976° "525 -966° -6 =)10°in excess of the law as usually stated.

178. The temperature of steam in a boiler at a pressure of 6 '12
atmospheres is 320° F. ; find the total amount of heat in the steam
and the latent heat. A ( 1179° '6 F. = 655°^ C.

179. The pressure in a boiler is 10 atmospheres, and the tem-
perature 356° F. ; find the latent heat of the steam. Ans. 1010° F.

180. How many units of work are done in raising a cylinder
weighing two tons from the hold of a vessel 16 feet deep?

Ans. 71680.

181. An iron ship 300 feet long, when in water at a temperature
of 2°C., proceeds from Norway and meets the Gulf Stream off
C. Hatteras at a temperature of 27° C. ; find the increase in the
length of the ship, co-efficient of iron being '0000123.

Ans. 1'107 inches.

182. A locomotive boiler 16 feet long is increased in temperature
from 0°C. to 180° C., find the linear increase. Ans. '425088 inches.

QUESTIONS. 365

183. The stroke of the piston of an engine is 24 inches, and the
diameter of driving wheel is 8 feet ; what is the mean velocity of
the piston when the engine is running at 40 miles per hour ?

Am. Strokes 140; 560 '2 feet per minute.

184. A shaft in a marine engine was making 20 revolutions, and
the speed was 8 knots ; what will be the speed if the revolutions,
by means of the multiplying gear, be increased to 25 ?

The revolutions of the crank vary as the cube of the speed.
Let V be speed required.

"V? _ 2j>

8° ~ 2"0

/. V3 =-££ xS3 = 640.
.-. V,= 8-617. knots.

185. The revolutions of the crank of a marine engine are 24 per
minute, and the speed 10 knots. The multiplying gear was put into
action, and the revolutions increased to 30 ; find the increase of
speed. Am. "77 knots.

186. The revolutions of a crank are 30, and the speed 12 knots, to
what number of revolutions must the multiplying gear raise this 30
to increase the speed to 13 knots. Am. 38 '1 revolutions.

187. The horse-power of a pair of engines is 400, and the speed 10
knots ; it is required to give a speed of 12 knots to the ship, what
power engines must be put in ?

The rule " cube of speed " applies to this and all similar questions.
103 _ 400

188. A pair of engines of 850 horse-power, which give a speed of 9
knots, are replaced by others which give 11 knots, what is the
horse-power of the new engines ? Am. 1552 nearly.

189. If a pair of engines 1000 horse-power give 11 knots per hour,
what is the speed that will be given by 1200 horse-power ?

Am. 11 -68 knots.

190. A ship has 4 boilers. With 2 boilers the speed is 7 knots per
hour, what is the speed with 3 boilers ?

• x— — 2 • xs — 3 * ^

73 ~ 2 ' 2

.'. x - 8 -013 knots.
91. What will be the speed when all 4 boilers are used ?
Ana. 8 -819 knots.

192. To find the length of the pendulum and height of pendulum
governor.

The usual formula, as found in all works on mechanics, is that the
time of one oscillation in seconds is = * \/£, where g = 32 feet. I is
the length feet, and <v — 31416; and height of a pendulum governor

. 7 0 8

is h =. — J— — -

366 STEAM,

We have also this proportion deduced from the same equation :

n : 60 : : v/39'1393 : ^/T

where 39'1393 is the length in inches of a seconds pendulum in the
latitude of London.

193. Required the vertical height of a governor to revolve 80 times
per minute. Ans. nearly 5 '4 inches.

194. Required the height of a pendulum governor to revolve once
every half second. Ans. 2 '43 inches.

195. How often will a pendulum 2 feet long vibrate in a minute ?

Ans. 76-0.

196. To find the density of the air under the receiver of an air
pump after the piston has ascended any number of times.

Let A be the capacity of the receiver.
,, B ,, ,, ,, barrel.
,, d ,, density of atmospheric air.
,, dn ,, ,, after n ascents of the piston,

After one ascent the air which fills A fills A + B.

After two ascents we shall get by similar reasoning

cZ« (A + B) = dl A . '. cZ2 =

Substituting for d: =

A + B

A dA

A + B A + B

- dA'
(A + B)2

After the third ascent we have

eZA8

da (A + B) = dz A . \ ds=.

A + B (A + B)3
Generally after n ascents we have

Density of remaining air = — — _.

(A + B)"

197. To find the height through which the head of the piston-rod
has moved at any part of its stroke : —

Let the circle be that through which the crank pin moves.
Suppose the piston head to move from D to F,

QUESTIONS. 367

In triangle F E C

E F is the connecting rod = I

EC ,, crank = r

Let angle EOF -6

Now F E2 = E C2 + C F2 - 2 E C, C F, Cos. 6

Addino- E C2 Cos.2 6 to each side, and transposing

C F2 -2 E C. C F Cos. 6 4- E C2 Cos.2 6 = F E2 -E C2 + E C2 Cos.2*.

Extracting the square root

CF-ECCos. 6- ±_ yP E* - E C2 (1 - Cos. 2 6)
-. C F = E C Cos. 6 + VF E2-E C2(l-Cos.2 i)

orCF=rCos. l_f V^-^Sin.2^ (1)

Now GI> = r+l .-. DF+CF=r+Z

.'. CF = r + Z-DF (2)

Equating (1) and (2) _ _

The negative sign of which will give what is required.
If 6 - 90° then D F = r
\i6- 0° then D F = 0
If 6 = 180° then D F = 2 r }

198. Prove that if the crank pin move through the same angle 6
from A to H in the last figure, that the piston descends through a
space equal to D F.

199. Show fully that equation (3) in Example 197, will give the
correct height of the piston when aft the top, bottom, and middle of
its stroke.

200. Show how to construct an exact parallel motion (Honours).
This figure represents the parallel motion first suggested by Mr.

Scott Russell, and fitted by Mr. Seaward to the Gorgon engines.

The lever or bridle rod CD
turns about its fixed centre C,

and carries jointed to it at D
the link A D B, called the rocking

beam, and is so arranged that
AD=:DB = CD; if this be so,
we know by the third book of
Euclid that the angle ACB is
the right angle in a semi-circle.
If we compel B to move in a
straight line towards C, say from
E to B, as the three lines are
equal, we shall always have the
right angle at C, and therefore point A must move from F to A in
the straight line C A continued. Hence we have an exact parallel
motion, i.e., constrain point B to move in a straight line, point A will
do the same. In the Gorgon engines point B oscillates at the end of

368 STEAM.

another bar, called the rocking standard, which describes a small
arc nearly coinciding with a straight line.

C D is a mean proportion between A D and D B. This we see in a
moment. If a proof be necessary, consider that in one position C D
must be perpendicular to A B, and then by Eu. vi. 13, the fact is
established that it is a mean proportional. As the lengths of the
lines never vary, therefore in all other positions it is a mean propor-
tional. In fact, either AD, DB, or CD is a mean proportional
between the other two.

The distance through which the point B slides, or

BE = AB- ^AB2 - ~
4

where s is the length of the stroke of the engine, which may be
represented by A G.

CB2 = AB2 - AC2.

= AB2 - - (since AG = s,\ AC2=?!)

ButCB = AB - BE.

Consider A B to coincide with C B, then to rise gradually from it,
and we see C B= A B - B E.

The parallel motion of the side lever engine is not given, as such
engines are seldom or never constructed now. But if tiie reader
wishes to make himself acquainted with it, it is to be found in
Rankine's Applied Mechanics, Bourne on the Steam Engine, or
Goodeve's Mechanism.

INDEX.

MARINE AND LAND ENGINE.

ABSORPTION of Heat, 29.

Adhesion, 29.

Advantages of Screw, 105.

Affinity, 28.

Amount of Lap, to Find, 203.

Analysis of Coal, 192.

,, Sea Water, 162.
Angle of Screw, 101.
Angular Advance, 116.
Anthracite Coal, 195.
Appendages to Boiler, 152.
Atomic Force, 28.

BALANCED Slides, 124.
Balancing the Crank, 85.
Barclay's Ejector Condenser, 149,
Barometer Gauge, 154.
Beam Engine, 57.
Black, Dr., on Latent Heat, 13.
Blade of Screw, 101.
Blowing-out Boiler, 164.
Blow-through Valve, 124.
Boiler, 133-205.

Balloon, 133.

Blowing Out, 164.

Brining, 104.

Clothing, 143.

Copper, 143.

Cornish, 135-141.

Cylindrical, 134.

Elephant, 135.

Explosions, 197.

Evaporation, 328.

Field, 140.

Flue, 134-137.

Haystack, 133.

Internal Pressure, 137.

Lancashire, 135

Locomotive, 140.

Priming, 169.

Return Flue, 135.

Salt in, 161.

Scale, 135.

Testing, 144.

Tubular Marine, 137.

Vertical, 141.

Waggon, 134.
Boiler Explosions, 197.
Boiling Point, 13, 163, 167.
Bourdon's Gauge, 153.
Brine Pumps, 169.
Brining Boiler, 164.

mining .boner.

CAMBRIDGE'S Water Heater, 145.
Capacity for Heat, 38.
Cataract, 65.
Centre of Pressure, 100.
Chemical Affinity, 28.
Chest, Steam, 139.
Circulating Pumps, 147.
Clearance, 55.
Clothing Boilers, 143.
Coal, Analysis, 192.
Collapsing of Tubes, 200.
Combustion, 216.
Communication Valve, 124.
Comparison of Engines, 92.
Compound Engines, 82.
Condensation, Water for, 146.

„ Surface, 147.

Condensing Engine, 78.
Conduction, 30, 40.
Connecting Rod and Crank, 60.
Contraction by Cold, 24.
Co-efficient of Friction, 32.

,, Expansion, 26.

Cohesion, 28.

Continuous Expansion, 83.
„ Indicator, 218.

Convection, 40.
Copper Boilers, 143.
Cushioning, 55.
Cut off, 116.
Cycloidal Wheels, 98.
Cylinder, 52.

DANIELL'S Pyrometer, 35.
De Pambour's Theory, 316.
Diameter of Screw, 101.
Diagram, Indicator, 217.

,, Normal, 212.
Disc Valve, 124.
Disconnecting Paddles, 100.
Double Acting Engines, 54.

,, „ Pumps, 91.

,, Cylinder Engines, 89.
Duty of an Engine, 92.
Duties in Harbour, 203.

„ in Getting under Steam, 204,

,, under Steam, 205.

,, when in Port, 207 .
Dynamometer, 220.

EBULLITION, 11.
Eccentric, 68.

370

INDEX.

Ejector Condenser, 149.
Elasticity, 10.
Eugines, Land-
Air, 184.

Beam, 58, 177.

Caloric, 184.

Cornish Pumping, 187.

Fire, 186.

Gas, 183.

Horizontal, 177.

Hot Air, 184.

Intermedial, 182.

Portable, ISO.

Ramsbottom's, 182.

Regenerative, ISO.

Siemen's, 185.

Table, 180.

Vertical, 179.
Engines, Marine —

Beam and Geared, SO.

Compound, 82.

Hammer, 81.

Humphrey's, 83.

Launch, 92.

Maudslay's, 89.

Oscillating, 86.

Side Lever, 78.

Steeple, 88.
. Trunk, 90.

Twin Screw, 80.

Woolf's, 83.

Equivalent of Heat, 41.
Ericsson's Propeller, 104.
Escape Valve, 123.
Evaporation, 9.

of a Boiler, 328.
Exercises, 21, 44, 72, 94, 110, 128, 157,

175, 189, 195, 202, 208, 222, 334.
Expansion, Co-efficient of, 26.
„ by Heat, 24.
„ Continuous, 83.
„ Gear, 71.

,, of Superheated Steam, 20.
Expansive Working, 18.
Explosions of Boiler —

Accumulated Pressure, 198.

Airy's Theory, 201.

Bad Management, 201.

Colburn's Theory, 201.

Collapsing, 200.

Deficiency of Water, 200.

Hydrogen Theory, 198.

Incrustation, 199.

Spheroidal State of Water, 197

Water Purged from Air, 198.

FACING Slide Valves, 1 17.
Feathering Paddle, 98.
Feed Pump, 59, 173.

„ Locomotive, 174.
Field's Boiler, 141.
Fire Grate Surface, 172.
Flue Boiler, 137.

M Diameter of, 136.

Flue, Length of, 135.
Fly Wheel, 60.
Foot Pound, 191.
Friction, 31.

,, Dynamometer, 221.
Freezing Point of Water, 20.
Fusible Plug, 143.

GALLOWAY'S Water Tubes, 111.
Galvanic Action, 56.
Gauge —

Barometer, 154.

Bourdon's, 15-3.

Glass Water, 156.

Mercurial, 154.
Geared Engine, 89.
Giffard's Injector, 174.
Glands, 57.
Governor, 63, 64.

„ Marine, CO.
Guides, 62.

HAMMER Engine, 81. /j
Heat— <2i*fU3vvv*oav^, &ci

Absorption of, 29. *

Capacity for, 38.

Latent, 11, 13.

Radiation of, 29.

Specific, 38.

Unit of, 13.
Ileafc and Work, 41.
Heating Surface, 172.
Hodgson's Parabolic Propeller, 105.
Horse-power, 324.

,, from Indicator, 219.

Houldsworth's Pyrometer, 36.
Humphrey's Engine, 83.
Hydraulic Propulsion, 109.
Hydrometer, 168.

IMMERSION of Paddle, 99.
Incrustation, 199.
India Rubber Valve, 124.
Indicator, 209.

Continuous Diagram, 218.

Diagram, 211.

High Pressure Diagram, 217.

Horse-Power, 219.

Slide Diagram, 218.

Slide Rod Short, 214.
„ „ Long, L>14.

Stop Forward, i'1-l.

Throttling and Expansion, 2
Injector, 174.

KINGSTON'S Valves, 124.

LAMB'S Surface Blow Out, 1G5.
Lap and Lead, 118-208.
Latent Heat of Steam, 12.
Water, 11.

Launch Engines, 92.
Laws of Friction, 32.
Length of Flues, 135.

INDEX.

371

Length of Screw, 101.
Linear Advance, 116.
Link Motion, 70.
Liquefaction, 13.
Load, to Find the, 316.
Locomotive Boiler, 140.
Locomotive Slide, 104.

MARINE Engines, 78.

„ Governor, 66.

„ Tubular Boiler, 137.

„ Flue „ 137.

Maudslay's Engines, 89.
Maximum Useful Effect, 325.
Measure of Pressure of Steani, 14.

,, Temperature, 32.
Mechanical Equivalent of Heat, 41.
Molecular Force, 28.
Moreton's Ejector Condenser, 149.

NEWCOMEN'S Engine, 48.

OSCILLATING Engines, 85.
Oxidation of Metals, 56.

PADDLES,' Disconnecting, 100.
,, Immersion, 99.
„ Wheels, 97.
Parallel Motion, 61.
Piston, 55.
Pitch of Screw, 101.
Plates, Thickness, 136.
Plug, Fusible, 142.
Power of Expansion, 27.
Pressure, 317.

Pressure and Boiling Point, 13.
Prevention of Smoke, 193.
Priming, 170.
Propeller, 101.
Propulsion, 97.

„ Hydraulic, 109.
Pumps —

Brine, 164.

Circulating, 147.

Double-Acting, 91.

Feed, 59-173.

QUESTIONS, 337.

RADIAL Wheels, 98.
Radiation of Heat, 29.
Relative Volume, 18.
Remedy for Priming, 170.
Reverse the Engine, 69.
Reverse Valve, 156.
Rolling Circle, 100.
Rotatory Valve, 120.

SAFETY Valve, 152.
Salinometer, 169.
Salt in Boilers, 161.
Salter's Spring Balance, 152.
Saturation of Steam, 15.
Savary's Engine, 47.

Scale, 165.
Screw —

Advantages, 105.

Beatties, 105.

Disconnecting, 106.

Ericsson's, 104.

Feathering, 104.

Hodgson's, 105.

Raising, 106.

Slip, 102.

Thrust of, 107.

Twin, 104.

Woodcroft's, 104.
Scum Cocks, 105.
Sea Water, 162.
„ „ Specific Gravity, 163.

„ Boiling Point, 163-193.
Side Lever Engine, 78.
Silver's Governor, 66. •
Single-Acting Engine, 54.
Slide Diagram, 218.
Slides of Oscillating Engine, 85
Slide Valves, 104.

Balanced, 126.

Cylindrical, 115.

Lap and Lead of, 118.

Locomotive, 53, 104.

Long D, 105.

Motion of, 116.

Sea ward's, 114.

Short D, 105.

to Set, 208.
Smokeless Coal, 195.
Smoke Prevention, 193.
Snifting Valve, 124.
Special Pump, 119.
Specific Heat, 38.
Spheroidal State of Water, 197.
Starting the Engine, 204.

„ Gear (Steam), 205.
Steam-
Definition, 9.

Density, 14-15.

Elasticity, 10-15.

Expansive Working, 13.

Full Steam, 116.

High Pressure, 14.

Invisible, 9.

Latent Heat, 12.

Measure, 14.

Relative Volume, IS

„ „ and Temperature, 321.

Saturation 15.

Specific Volume, 14.

Superheated, 19.

Surcharged, 19.

Temperature of, 15.

„ and Pressure, 320.

Volume, etc., 17.
Steam Chest, 139.
Steam Starting Gear, 205.
Steeple Engine, 88.
Stephenson's Link Motion, 70.
Stufiing Box, 57.

372

INDEX.

Summary on Surface Condensation, 148.
Surface Blow Out, 165.
Surface Condensation, 147.
Surface of Fire Grate, 172.

TABLE of Temperature and Pressure, 16.

Table of Specific Heats, 39.

Temperature, Measure of, 32.

Testing Boilers, 144.

Thermal Unit, 191.

Thermometer, 32.

Thickness of Plates, 136.

Thread of Screw, 101.

Throttle Valve, 63.

Thrust of Screw, 107.

Trunk Engine, 90.

Tubes, Galloway's, 141.

Tubular Boiler, 137.

Twin Screw Engine, 80.

UNIT of Heat, 13.
Use of Pyrometer, 37.
Useful Load, 323.

VALVES—

Blow Through, 125.
Cornish, 123.
Communication, 124.
Crown, 123.
Double Beat, 123.
Drop, 123.
Equilibrium, 121.

Valves — Escape, 123.

Facing Slides, 127.

Gridiron, 115, 131.

Hornblower's, 122.

India Rubber Disc, 124.

Kingston's, 125.

Reverse, 156.

Rotatory, 120.

Safety, 152.

Self-Acting, 119.

Snifting, 124.

Stop, 124.

Tail, 124.

Vacuum, 156.
Vaporisation, 1, 13.
Vapour and Steam, 10.
Velocity of Maximum Useful Effect, 324.

WATER, 11.

Water at Freezing Point, 26.

„ Ebullition, 11.
Water for Condensation, 146.
Water's Gauge, 156.
Water, Latent Heat, 11.
Water Purged from Air, 198.
Water's Feed Water Heater, 145.
Water Heater, 144.
Watt's Engine, 51.
Wheels, Cycloidal, 98.
Wheels, Radial, 98.
Woolf's Engine, 83.
Work Done in One Stroke, 315.

THE LOCOMOTIVE.

ADHESION of Wheels, 227.
Ash Pan, 249.
Axle Boxes, 273.

BALLAST, 298.

Bars, Fire, 247.

Beattie's Coal Fire Box, 291.

Blast Pipe, 233.

Blow-off Cock, 265_

Blow Pipe, 291.

Bogies, 242.

Boiler of Rocket, 235.

Boiler, 243.

Brakes, 277.

Broad Gauge, 299.

Buffers and Buffer Springs, 276.

CARRIAGES on a Curve, 295.
Chair, 297.
Chimney, 252.
Clearance, 246, 281.
Coal Burning, 289.
Coke Burning, 288.
Combustion, 292.

Connecting Rod, 268.
Contrast, 237.
Counterweight, 272.
Coupling Rod, 269.
Cover of Slide, 281.
Crampton's Engine, 241.
Crane, Water, 259.
Crank, 268, 271.
Crossings, 301.
Curves, 295.
Cuttings, 298.
Cylinders, 266.
Cylider Pet Cocks, 267.

DAMPERS, 253.

Description of Locomotive, 238, 240.

Diagram of Great Britain, 307.

Dome, 253, 255.

Drain Cocks, 267.

Draw Bar, 276, 277.

Driving Wheel, 270.

ECCENTRIC, 280.
Embankments, 298.

INDEX.

373

Engine-
Bogie, 242.

Crampton's, 241.

Murray's, 229.

Rocket, 232, 234.

Sharp's, 239.

Stephenson's, 232.

Tank, 242.

Evaporation and Fuel, 251.
Expansion, 254.
Exercises, 308.

FASTENING of Tubes, 246.

Feed Pumps, 261.

Fell Railway, 299.

Fire Bars, 247.

Fire Box, 246, 269.

Fish Joint, 296.

Fuel and Evaporation, 251.

Furnace, 246, 269.

Furnace Gases, 285.

Furnace Stays, 247.

Fusible Plug, 258.

GAUGE Cocks, 264.

„ Pressure, 257.

,, Water, 264.
Glass Water Gauge, 264.
Gooch's Safety Valve, 252.
Gradients, 297.
Grease Cocks, 267.

HEATING Surface, 250.
Heat, Transmitting Power, 285.
Hedley's Engine, 230.
History of Locomotive, 225.

INDICATOR Diagram, 303.
JOINTING Rails, 297.

LAP of Slide, 281.
Laying of Rails, 298.
Lead of Slide, 281.
Link Motion, 279.
Locomotive Diagram, 306.

MAN Hole, 254.

Motion of Slide Valve, 281, 283.

Murray's Locomotive, 229.

NARROW Gauge, 299.

PET Cocks, 267.
Piston and Piston Rod, 26S.
Pressure Gauge, 257.
Prevention of Priming, 253.

Priming, 253.
Puffing Billey, 230.
Pumps, Feed, 261.

RAILROAD, 295.
Rails, 296.
Regulator, 254.
Relief Cocks, 267.
Richard's Indicator, 303.
Rocket, 232-4.

SAFETY Valve, 251.

Sand Cock, 273.

Screw Plugs, 265.

Scum Cock, 264.

Sector, 280.

Separator, 253.

Sharp Brothers & Co.'s. Engine, 239.

Single Eccentric, 281.

Sleeper, 297-299.

Slide Valve and Motion, 281.

Smoke Box, 249.

Springs, 274.

Staying of Furnace, 247.

Steam Dome, 253.

Steam Regulator, 254.

Steam Whistle, 255.

Stephenson's Driving Gear, 232.

„ Engine, 232.

Link Motion, 279.
Strap Gib and Cutter, 270.
Switches, 301.

TANK Locomotive, 242.
Tanks, 258.

Temperature of Furnace Gases, 285.
Through Tie Rods, 244.
Tire, 272.

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Tubes, 244.
Turn Table, 300.

VALVE, Safety, 251.

WARNING Cocks, 266.
Water Cocks, 267.

„ Crane, 259.

„ Gauge, 264.

„ Tanks, 258.
Wheels, Adhesion of, 227.
Whistle, 255.

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