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PRINCIPLES AND CONSTRUCTION
OP
MACHINERY :
A PRACTICAL TEEATI8E
OK
THE LAWS OF THE TRANSMISSION OF POWER, AND OF
THE STRENGTH AND PROPORTIONS OF THE VARIOUS
ELEMENTS OF PRIME MOVERS, MILL- WORK,
AND MACHINERY GENERALLY;
RRANGED FOR THE USE OF
(Ettginrm',
BY FRANCIS CAMPIN, C.E.,
PHESIT)ENT CIVIL AN'i) MEi'hA.flfA f. hXCINEFK^' S')'r:TV
LONDON:
ATCHLEY & CO., 106, GEEAT RUSSELL STREET,
publishers of (Engtnttnng & ^rtbitcttur;U wlorhs.
[The right of Translation is Reserved.]
LONDON :
PRINTED BY P. GRANT, 3 & 4, Ivr LANE, PATERNOSTER Row, E. C.
C 15
f
REV. JOHN FREDERICK HARDY, M.A.,
fefe i
IS RESPECTFULLY DEDICATED,
As A MARK OF ESTEEM, AND IN GRATEFUL REMEMBRANCE,
BY
HIS FORMER PUPIL,
(Tbe ^ulbor.
a
379384
PEEFACE.
IN issuing the present Treatise, a few words ex-
plaining the motives of its production, addressed to
those classes for whose use it is designed, seem not
only appropriate but necessary, in order to account
for the arrangement which has been adopted.
The contents of the work are in substance a care-
fully-revised digest of the author's oral instructions,
which for some years past he has found successful
in training pupils to a knowledge of that portion
of Civil Engineering which takes cognizance of
Machinery and Mill- work. The great bulk of treatises
on Mechanics are cumbrous to the last degree, loaded
with varieties of rules and overwhelming numbers
of examples of their application, to determine the
modification of forces and ratio velocities of gearing ;
but in none of them has the Author found the laws
of construction in reference to strength of parts set
forth at all fully ; hence the Lectures given by him
were specially arranged to show, not only the prin-
ciples by which forces and velocities are modified,
but also the mode of determining the least dimen-
sions of all descriptions of mill- work and machinery,
so that the reader may understand not only why a
given machine produces a certain effect, but also //on-
to make it practically. Sufficient examples are given
in the first portions of the book to show the method
of using symbolical formulae, wherefore in the latter
parts the formulae are not all illustrated by arith-
metical examples, as to have followed such a course
would have inconveniently extended the bulk of the
volume.
The Author's aim throughout has been, in the first
place, to explain the Fundamental Theoiies of Me-
chanism in the clearest and briefest manner, so as to
impress upon the mind general principle*, not special
cases, and then to show the practical development of
such theories, care being taken so to arrange the
matter as to try the facidties of the mind as little
as possible.
FKANCIS CAMPIN.
CONTENTS.
PAGE
INTRODUCTION 1
CHAPTER 1. FORCE OR PRESSURE 5
2. WORK, POWER, AND MOTION 11
3. GENERAL LAW FOR ALL MACHINES MODIFYING
FORCE 17
4. CENTRE OF GRAVITY. MECHANICAL POWERS . . 22
o. ELEMENTS FOR CHANGING THE NATURE OF MOVE-
MENTS 31
6. FRICTION 34
7. ON THE CONSTRUCTION OF MACHINERY AND
MILL-WORK 36
8. STEAM AND HoT-Am ENGINES 56
9. BOILERS AND FURNACES 81
10. WATER-WHEELS AND TURBINES 112
11. PUMPS AND HYDRAULIC MACHINES 128
12. MARINE ENGINEERING 141
13. MATERIALS USED IN CONSTRUCTION 143
14. MANIPULATION OF TIMBER AND THE METALS . . 174
15. ON THE WORKING OF METALS COLD 187
16. JOINTS, BEARINGS, AND PACKINGS. 197
17. FOUNDATIONS AND FRAMING 210
18. ADAPTATION OF MACHINERY TO SPECIAL PURPOSES 220
19. PHYSICAL SCIENCE CONSIDERED IN RELATION TO
MECHANICS 232
20. ELECTRICAL AND CHEMICAL MACHINERY . . . 261
21. MISCELLANEOUS 271
22. ESTIMATION OF QUANTITIES 277
CONCLUSION 280
PEINCIPLES
AND
CONSTRUCTION OF MACHINERY.
INTEODUCTION.
IN the majority of treatises on Mechanics, and perhaps
more especially in those which are professedly of an
elementary character, a great number of unnecessary
divisions and classifications have been introduced, tend-
ing to complicate rather than elucidate the questions
discussed, and taxing the memory of the student by
imposing upon it the duty of retaining a number of
purely arbitrary systems of formulae or rules, instead of
impressing upon the mind of the learner the main
principles upon which all such formulae are based.
Every kind of machine or structure met with in engi-
neering practice is of necessity based upon some
fundamental principle or principles which should be
thoroughly comprehended by those who undertake to
construct, modify, or improve upon, these machines or
structures. It is very insufficient merely, as it were, to
learn the action of one particular machine, without
ascertaining the principle of such action and the extent
of its application, for without this latter knowledge a
thorough comprehension of the machine cannot be
attained. Similarly in regard to structures, say lattice
bridges, the student who merely learns by rote the rules
for calculating the trussing of all (at present) known
descriptions of lattice girders will find himself at a loss
2 PRINCIPLES AND CONSTRUCTION
and incompetent to fulfil the duties he assumes should
a new method of trussing be invented, according to
which he may be called upon to design a bridge ;
whereas had he mastered the principles which rule the
arrangement of trussed girders, the matter would be
one of no difficulty whatever.
The intention of this work is to instil into the minds
of engineering students and mechanics, in the simplest
way, what may be termed the alphabet of engineering
practice, and in order to render it available to as large a
class of readers as possible, everything approaching to
high mathematics will be carefully avoided, and all
calculations restricted to the simplest language.
It is, however, impossible to deal with the subject
before us in a sufficiently lucid manner without employ-
ing simple equations, upon which, therefore, a few
words in this place may be appropriate. Suppose x to
represent the quantity proposed to be found from an
ordinary "proportion" or "rule of three" statement,
such as the subjoined :
12: 45 :: 13 : x,
then, according to the rule,
_ 45 x 13
12
This is simply the same thing, but stated as an equa-
tion. It is, however, convenient to have a general
formula, for there may be many similar cases where the
values of the first three terms are not as above ; hence
replace 12, 45, and 13 respectively by the letters a, b,
and c, then the general equation becomes
' -~ ">
The value of an equation, or rather its equality, is not
altered by either multiplying or dividing both its sides
OF MACHINEBY.
by the same multiplier or dividend, for " things which
are double of the same are equal to one another," and
" things which are halves of the same are equal to one
another." (Euc., Axioms vi. and vii.) Hence
Let the general equation (1) be multiplied by a,
I X c = x x a
but usually the multiplication symbol x is substituted
by a period, thus
a . x =. b . c
The object of such an equation as this is evidently that
three terms out of four being known, we may be able
to find the unknown quantity : according to the terms
represented by the letters, any one of the latter may
present the unknown quantity ; therefore let an equa-
tion be found for each :
T
Divide by x, then a = -
Divide by c, then b = -
Divide by , then c = -
Divide by a, then x =
In this case there are only multiplications and divisions
to be performed ; but very commonly, as well as these,
additions and subtractions will be found to occur, as in
the equation following :
+ y=8*+$_*. . . (2)
D
We can, without vitiating the truth of the equation,
subtract from or add a like quantity to both sides, for
4 PEIXCIPLES AND CONSTRtrCTIOX
" if equals be added to equals the wholes are equal,"
and ' ' if equals be taken from equals the remainders are
equal." (Euc., Axioms ii. and iii.)
In equation (2) add m to both sides of the equation,
z + y + m=3al + m + m = 3al + (3)
6 6
Or subtract y,
x + y y = x = 3al + - m y . (4)
D
Both are true equations.
From observation of the above process the following
rule is drawn : If it is required to change a quantity from
one side of an equation to the other, in so doing alter the sign
of the quantity moved.
Thus m in eq. (2) on the right becomes + m in eq.
(3) on the left, and + y in eq. (2) on the left becomes
y in eq. (4) on the right.
These few brief remarks will probably be sufficient
to explain the nature of a simple equation, so far as may
be requisite to the comprehension of the formulae and
analyses with which we shall subsequently have to
deal.
In concluding this Introduction it seems desirable to
point out the general object of every machine or
structure. This object, then, is to render some natural
law or set of natural laws subservient to human pur-
poses, to subjugate and guide the energies of the
physical forces, either in motion or at rest, so that they
may be expended at the places convenient and in
manner suitable to our requirements. Thus, from coal
dug out of the earth energy is developed to propel
vessels on the ocean ; and by a skilful arrangement of
materials vast loads are supported over chasms, and
their weight transmitted to the piers or abutments on
either side.
OF MACHINERY. 5
Tlie main distinction in principle between a machine
and a structure may be thus stated : A machine is
used to apply physical force in motion ; a structure
depends upon the laws of physical force at rest. The
former is termed dynamic, the latter static force (from
the Greek cvvapi, I move, and rnj/, I stand).
CHAPTEE I.
FORCE OR PRESSURE.
FORCE or pressure acting upon any body indicates that
such body is under some control which for the time
being regulates the circumstances of its existence and
condition ; but of forces there are several which, although
capable of reproducing each other mutually, neverthe-
less may be regarded as of different characters from
the different phenomena to which they give rise. The
natures of these forces will now receive our attention.
According to the most generally received theory all
matter is composed of minute bodies called atoms (from
the Greek a privative, and TC/II/.S, I cut), which are
indivisible, and by the building up of which molecules
of matter are formed, by the aggregation of which again
masses of matter are formed. The character of a
molecule is that it consists of a number of atoms either
similar or dissimilar chemically attracted towards each
other ; but a mass of matter consists of molecules
mechanically attracting each other : thus the mass of
matter may be broken or crushed by mechanical means,
but the molecules can only be disintegrated by chemical
action.
The atoms of matter, which Newton describes as
being hard, impenetrable, and incapable of wear, form-
6 PBINCIPLES AND CONSTRUCTION
ing a mass, are not in actual contact, as is evident from
the compressibility of matter ; hence they must be
balanced in certain positions, allowing greater or less
intervals between them according to the nature of the
body of which they are the component parts ; and to
occupy such a position, two forces must be acting upon
them, the one tending to bring them together, the other
exerting a repelling force which unopposed would drive
them asunder.
The force tending to bring the molecules together
is called the attraction of cohesion, and that which
repels them is heat, and the molecules occupy positions
dependent on the relative intensities of these two
opposing forces. The intensity of the attractive force
remains constant amongst the molecules of any given
body, but that of the heat may be varied by external
agencies; thus we can add heat to a mass of matter or
deprive it of a portion of that which it already pos-
sesses. In the former case the additional heat further
opposing the cohesive force drives the molecules further
apart, and the body expands ; but in the latter case the
repulsive force being diminished, the molecules are
drawn by the predominant cohesive attraction into
closer contiguity, and the body contracts. It would be
foreign to the purpose of the present treatise to dilate
more fully upon these forces, as by so doing we should
be trenching too much upon the sphere of physics.
The next force to which we must allude is the attrac-
tion of gravitation, by virtue of which all heavy bodies
tend to approach one another. It is this force which
holds the planets in their orbits, and to it is due the
weight of matter. By gravitation ponderable substances
fall to the earth, and by gravitation ships and balloons
are supported in the aqueous and aerial oceans ; but in
OF MACHINERY. 7
the last two instances the vessels are floated upwards
because they are displaced by the superior gravitative
force of the media by which they are sustained : they
are forced up as a light weight is drawn up by a heavier
one.
Gravitation furnishes the measure for force, work,
and power, as all forces, in whatever direction they may
act, are always stated according to the weight of a mass
which by reason of its tendency to fall to the earth
would produce the same effect in a vertical direction.
Thus, if a man push a carriage, exerting on it with his
hand the same energy he would have to exhibit to sup-
port a weight of thirty pounds, he is said to be pressing
the carriage with a force of thirty pounds.
The actual weight of a body does not affect the
intensity of the earth's attraction for its parts, as a mass
weighing ten pounds will fall no quicker to the earth
than one weighing five pounds, nor any slower than
twenty pounds' weight, as the effect of gravitation is
manifest on each molecule of the mass independently of
the neighbouring molecules, and were they all separate
they would fall with the same velocity as they have
when aggregated together in a solid mass. Not only
do bodies gravitate towards the centre of the earth,
however, but also towards irregularities on its surface
and towards each other. The pendulum which in level
country points when hanging freely to the centre of the
earth, will when placed in the neighbourhood of moun-
tains deviate from that position, being attracted in some
degree by the masses of earth in its vicinity.
Matter in general possesses a property termed inertia,
by reason of which it will, if unacted Tipon by external
agencies, continue in any state in which it may happen
to be left by the last force that acted upon it ; that is to
8 PRINCIPLES AND CONSTRUCTION
say, if a body is at rest it will remain so until some
exterior force moves it, and if it be in motion it will con-
tinue to move until some external resistance stops it.
A body acted on by one force alone cannot be in a
state of rest ; there must be at least two in operation,
and these two must be equal in intensity and opposite
in direction : in the language of statics these forces are
termed action and re-action, hence the law of equilibrium
of forces.
To satisfy the conditions of equilibrium, Hie action and
re-action must be EQUAL and OPPOSITE.
If two forces only are acting, as a matter of course
they must act in one and the same straight line, but in
opposite directions.
It not unfrequently happens that two forces act at a
point so as to produce a combined effect ; it is necessary
in that case to find what single force would produce the
same effect as these two forces, which latter are sup-
posed to be inclined at an angle to each other.
Let two forces act at the point a, Fig. 1.
Fig. 1, respectively in the directions
of the lines a b, a c, and let their inten-
sities be represented by the lengths
of the lines a b and a c ; complete the
parallelogram, abed, and join a d,
then will the diagonal a d represent
in direction and intensity the force equivalent to the
two forces a b and a c. This is obvious at sight, for
if we suppose the two forces acting to move a body from
a, and each acts singly, first the body will be drawn to
c ; and then c d, being equal and parallel to a c, will
represent it and draw the body to d; but if both forces,
maintaining parallelism to their initial directions, act
continuously and at the same time, the body would
really be moved along the diagonal a d.
OF MACHINERY.
If there be more than two forces acting at a given
point, they may be solved by pairs by the ' ' Theory of
the Parallelogram of Forces," until at last one force is
found equivalent in intensity and direction to all of them
together.
All solid bodies are to some greater or less degree
elastic, although in some, such as lead for instance, the
elasticity is not easily perceptible ; elasticity being that
property by which bodies when compressed, extended,
or otherwise altered in form by external force, endea-
vour to recover their former shape and size. If a
weight be placed upon a spring balance, the spring is
shortened in proportion to the weight placed upon it,
and similarly if a weight is placed upon a solid mass
there is induced a compression of the solid, and its ten-
dency to expand to its original bulk produces the force
sustaining the weight ; in short, the weight is the action,
and the elasticity of the material supplies the re-action.
Hence, when force is brought into action upon a fixed
body, compression (or extension, as the case may be)
takes place until the elastic resistance of the material
supplies a re-action equal to the external force which
has called it into operation ; provided always that the
external force has not sufficient intensity to overcome
the molecular attraction, and so rupture the body upon
which it is acting.
The reaction to every action which occurs on the earth
might be reasoned out ; but to do so would be merely
occupying a large quantity of space for no useful pur-
pose, and the argument would be merely a series of
repetitions of the example just given.
Force may be transmitted from the first point of its
application through either a solid, liquid, or gas, to
operate at some distant point ; but if through a solid
10 PRINCIPLES AJTD COXSTEUCTION
no mechanical appliance intervening the force can only
ultimately act in the same direction as that in which it
is first applied, or in one parallel to it.
If, however, the force be transmitted through a liquid
or gaseous medium confined in a vessel, the force may
be received from such medium in any direction, regard-
less of that in which the force was applied in the first
instance. This difference is due to the distinctive cha-
racteristics of solids and fluids, which are as follows :
The weight of a solid body presses vertically towards
the centre of the earth, but
The weight of a fluid body presses equally in all
directions.
We must now pass on to describe "potential," or stored
force. Perhaps as good an illustration as can be cited
on this point is that supplied by a clock-spring when
wound up ; a certain amount of force is communicated
to the spring, and there remains stored up ready for
use at pleasure ; while the spring is at rest this force is
regarded as potential force, because although its pre-
sence is not evidenced by any phenomena, yet it exists
and is capable of being brought into action at any time.
The same may be said of any weight raised and sus-
pended over a body on which it may subsequently be
required to exert pressure, or of steam or gas compressed
in a close vessel, whether it be by actual forcing into
the vessel more than it normally holds, or by increasing
the tension of its normal contents by the effects of exter-
nally applied heat. In conclusion, the forces which act
upon all terrestrial matter may be arranged in two
classes : Internal forces and forces acting externally.
The internal forces are those upon which the form,
properties, and constitution of various bodies depend in
a normal state.
OF MACHINERY. 11
The external forces are those which, proceeding from
without the body, tend to move it from its position, alter
its shape or bulk, or to destroy the cohesion of its
parts.
CHAPTEE H.
WORK, POWER, AND MOTION.
IN the previous chapter forces at rest have been treated
of principally, but now we have to consider the results
which accrue from forces accompanied by motion, that
is from dynamic forces.
When a force is exerted through a space, then WORK
is said to be done ; if a resistance is overcome through-
out the space passed through by the force, then uniform
work is being done ; but if the resistance is all at the
end of the space, then the work accumulated in passing
through the space overcomes it. Work is usually ex-
pressed in pounds lifted through feet as foot-pounds ;
thus, if a resistance of 45 Ibs. is overcome through a
distance of 50 feet, then the amount of work done is
= 45 Ibs. X 50 ft. = 2250 ft. : Ibs.
It matters not what direction the force is exerted in,
whether to push a truck or lift a weight.
By introducing a third element, time, comparative
measurements of POWER are obtained. A horse, accord-
ing to Watt, can lift 33,000 Ibs. one foot per minute ;
hence, if a steam-engine be lifting 1,848,000 Ibs. one
foot per minute, its power is
1,848,000
= =56 horse-power.
33,000
12 PEIXCIPLES AOT) CONSTRUCTION
Hence, to find the horse-power exerted by any machine
the following rule may be used :
Multiply the weight or resistance by tlie speed per minute
at which it is overcome, and divide the product by 33,000.
Example : Let the resistance be equal to 503,089 Ibs.
Speed per minute . . . 100 ft.
503,089 x 100
Horse-power = -- ---
If a body fall freely, then the work, not being expended
as it falls, is accumulated in it ; thus, if a weight of
15 Ibs. drops 10 feet, the work^accumulated in it will be
15 X 10 = 150ft.: Ibs.
But supposing such a mass as a railway train in motion,
then the accumulated work must be ascertained from
the velocity ; it is equal to the weight of the train
multiplied by the height through which it would have
to fall to acquire a velocity equal to that at which it
is moving ; but in order to find a rule to determine what
this would be, we must ascertain the laws which govern
the motion of bodies falling freely.
From experiment it is found that a heavy body during
the first second of its fall passes through 16'1 feet;
hence its velocity at the end of the first second must be
32-2 feet per second, as at the commencement the
velocity is and
= 16-1 ft.
the average velocity as found from the initial and final
velocities. During the next second the body will pass
through 32-2 feet, due to the velocity already acquired,
and 16-1 feet, due to the continued attraction of gravita-
tion, in all 48-3 feet ; and in the two seconds 64-4 feet ;
OF MACHINERY. 13
it will also acquire another 32-2 feet per second, making
a final velocity of 64-4 per second. Following this up,
the distances and velocities corresponding to different
durations of time will be found as follows :
Let h = total distance fallen through, and v corre-
sponding final velocity per second :
Duration of fall in seconds.
h
V
1
16-1
32-2
2
64-4
64-4
3
144-9
96-6
4
257-6
128-8
5
402-5
161-0
From this table it is evident that the distance fallen
through varies as the square of the time occupied by
the fall, and the velocity varies simply as the time.
Let t = time of fall in seconds, and g = 32-2 feet per
second, then the following formula will serve to solve
all cases relating to falling bodies :
Let the time be 5 seconds,
h = I X 32-2 x 25 = 402-5 feet fall in 5 seconds.
Let the velocity per second be 100 feet, the fall to
acquire such a velocity will be
10,000
= 155-3 feet nearly.
2 X 32-2
Again, to find the velocity, we have, by transposing the
above equations,
14 PKINCIPLES AND CONSTRUCTION
Let the time of fall be 5 seconds,
v = 32-2 x 5 = 161 feet per second.
Let the height of fall be 100 feet,
v = -v/2 X 32-2 x 100 = 80-25 feet per sec. nearly.
The weight of a body being = 7F", the work accumu-
lated in it in falling through a distance = h, will be =
W7i, and, also, replacing h by its value in the foregoing
formulee equation (5).
Accumulated work = -
2<7
Let a weight of 5 Ibs. be moving at a velocity of 20 feet
per second, the accumulated work is
_ 5 X 400 _ foot ndg
2 X 32-2
Taking the example of a train weighing 80 tons
(I79,200lbs.), and moving at a speed of 20 miles per
hour (29-3 per second), we find the accumulated work
40
= 2,388,840 foot-pound*.
Again, let a cannon ball weighing 60 Ibs. leave the
mouth of a gun at a velocity of 2,000 feet per second,
the work accumulated in it will be
= 6 X 4 ' 000 ' 000 = 3,726,708 foot-pounds.
2 x 32-2
This well illustrates the immense destructive power
which may be concentrated in comparatively small
weights by causing them to move at high velocities ;
for whereas the accumulated work varies simply as the
weight, it varies as the square of the velocity.
If the velocity of a moving body, such as a train, after
attaining a certain point becomes constant, then the
body is said to have a uniform motion, and the pro-
pelling power is just sufficient to overcome the frictional
OF MACHINERY. 15
resistances opposed to the motion of the body at the
velocity acquired. Let the propelling force cease to
act, and the body will gradually come to rest, the work
accumulated in it being expended in overcoming the
frictional resistances to the gradually 'deer easing motion
of the mass.
Any mass set in motion will, if unoperated upon by
any fresh force, move continually in a right line having
the direction in which the force imparting motion to the
body originally acted, but through the intervention of
another force the body may be caused to move in a
curve instead of in a right line. Let a body in motion
be compelled, by a cord of constant length attached to
it at one end and to a fixed point at the other, to
revolve about a centre describing a circle at each revo-
lution. A rule is required to determine the tension on
the cord, or the centrifugal force.
In order to state the amount of force necessary to draw
a body through any given space, we must consider the
case in comparison with the earth's attraction, which
produces an effect of g, or 32-2 feet velocity, in one second
of time. The attractive for ce varies as the bulk of the
body, hence the mass of a body is expressed by
W
9
The normal direction of the moving body will be a
tangent to a circle, and according to the laws of the
circle (Cape's Mathematics, vol. ii., p. 233,) the distance
which it will be drawn out of this direction by the ten-
sion of the cord will be expressed for one second by
_^_ 2 ; hence the centrifugal force will be,
r
if r = radius of gyration,
Wv*
= iorce in pounds.
16
AND CONSTRUCTION
In order to make more clear the mode of comparing
centrifugal force with gravitative attraction, a special
case may be taken. Let a force be capable of imparting
a velocity of 64-4 feet to a mass of matter in one second,
then will this force have twice the intensity of the
attraction of gravitation, and a body requiring 5 Ibs.
pressure to sustain it against the latter will require
10 Ibs. to sustain it against the former. Let it be
required to determine the centrifugal force of a mass
weighing 15 Ibs., revolving in a circle 4 feet in diameter
at a velocity of 20 feet per second, the centrifugal force
will be
= 15 X 4 = 46-58 Ibs.
4 X 32-2
Bodies may be caused to move in a great variety of
curves, dependent upon the composition of the forces
acting upon them; thus the planets in their courses
describe elliptical orbits, the path being determined by
the initial velocity and direction of movement combined
with the attraction of the sun.
Let the ellipse Fig. 2.
shown in Fig. 2
represent the path
of a planet moving
round the sun S
placed in one of the
foci of the ellipse.
The rationale of its
movement is as fol-
lows : If the body
first have a motion impressed upon it acting in the
direction a b, by the time the body would have
reached e the attraction of the sun has drawn it
out of the right line as far as e d, when it may
UF MACHINERY. 17
be considered as again moving in a tangent to the
curve; and again, when it would have reached e,
the sun's attraction has drawn it to /, and so forth.
It will be observed that during the passage through
this part of the orbit, the sun's attraction is retarding
the moving body, until at k its course is turned round
and it approaches the sun, the attraction of which
is now accelerating its speed, as is evident from the
direction in which it is acting, as shown at i j ; thus the
loss of velocity due to the sun's attraction in one half of
the orbit is restored in the other half, so that when the
body again arrives at the point a it is moving with its
initial velocity.
It would very rarely occur that a planet, moving
under the influence of its initial velocity and the sun's
attraction, would adopt a circular orbit, as, for such to
be the case, the latter must first come into action when
the planet is in such a position that a line drawn from
the sun to it would be perpendicular to its motion, and
in addition to this there would be required a certain
definite relation between the velocity of the body and
the attractive force of the sun.
CHAPTEE III.
GENERAL LAW FOB ALL MACHINES MODIFYING FORCE.
WHEN a force acts about a fixed Fig. 3.
point as a centre, the effort of this
force reduced to the centre is termed
the moment of the force. In Fig.
3 let a b show the direction in
which a force p is acting ; its mo-
ment about the point c is required
18 PRINCIPLES AND CONSTRUCTION
to be determined. From the point c let fall a perpen-
dicular c d upon a b, and let the length of this perpendicu-
lar be represented by I, then the moment of the force p
about the point c will be
= P X I
Thus, if the force have an intensity of 20 Ibs., and its
distance be 3-5 feet, the moment of the force about the
point c will be
= 20 x 3-5 = 70 foot-pounds.
In all appliances for increasing or diminishing the
intensity of force there are two main points requiring
primary attention the point of application of the force
and the point at whiclwt is given off. In every case
there is a tendency to produce motion, and whether it
actually is produced or not, the proportions of the
machine to secure equilibrium between force and resis-
tance, whether at rest or in uniform motion, will be the
It is one of the fundamental laws of natural science
that force can neither be created nor destroyed ; hence,
if a force is increased, as by means of a lever, something
else is diminished, as the space through which the force
acts. Let work be done on one end of a machine equal
to 10 Ibs. acting through 20 feet, that will equal
200 feet-pounds ; and this may be given off at the other
end of the machine in a variety of different ways, but
only the same amount of work can be given off. (At pre-
sent friction is disregarded.)
If the part of the machine at which the work is given
off moves 2 feet while the point of application moves
10 feet, then dividing the work done by the space
through which the force passes, it is found that the
intensity of the force will be
*200 *
- 100 Ibs. pressure
OF MACHINERY. 19
thus the intensity of the force is increased by means of
the machine five times, but the space through which it
acts is diminished in like ratio.
Again, if two forces act about a centre so as to pre-
serve equilibrium, acting, of course, in opposite direc-
tions, their moments must be equal. Let a force of
30 Ibs. act about a centre at a distance of 3 feet from it,
the moment of force will be
= 30 X 3 = 90 ft. : Ibs.
at what distance from the same centre must a force of
12 Ibs. act in the opposite direction to balance this
moment ? Let x equal the required distance, the
moment of this last force will be
12 x x = 12 x
but to satisfy the conditions of equilibrium the moments
must be equal ; hence
12 x = 90 ft. : Ibs.
wherefore,
x = ^ = 7'5 feet.
In this case, if the forces were rotating, the spaces
passed through would be inversely as the forces acting,
because the circumferences of circles vary as their radii,
and the distances of the forces from the point about
which they act are the radii of the circles of gyration of
such forces, and from the above it is observed that
these distances are inversely as the forces to which they
refer; the force of which the intensity is 30 Ibs., having
a distance of 3 feet, and that of 12 Ibs. a distance of
7-5 feet.
The generallaw formachines formodifying or increasin g
pressure (irrespective of friction) may now be stated :
The pressure is to the resistance as the space through which
the resistance is overcome in a given time is to the tpace
through which the force acts in the same time.
c 2
20 PBDTCIPLES ASD CONSTRUCTION
By this law may be solved questions referring to every
description of lever, pulley, toggle, train of wheels,
hydrostatic press, or other similar contrivance.
Let p = pressure or force in pounds, R =. resistance
in pounds.
s = distance traversed by force in a given time.
S = ,, ,, by resistance in the same
time.
From the following four equations any one of these
qiiantities may be found, the other three being given:
S-
- P ' 8
A few examples will serve to show the application of
these formulae :
A b is a lever supported Fig. 4.
on a fulcrum at c, the points
of resistance and force being ,
respectively at a and b, the ^
distance a c = 10 inches, and p R.
b c 56 inches, a c, b c being radii of gyration of the
points a and b, the spaces passed through in a given
time would be a, 10 inches, and b, 56 inches ; hence,
if it is required to equal a resistance of 114 Ibs., the
force applied must be
p = 1I4 X 10 = 20-36 Ibs. nearly.
56
Let a weight of half a ton be required to be lifted by a
force of 80 Ibs., the distance a e being equal to 2 inches,
then the distance b c will be
1120 x 2
s = - = 28 inches.
80
In these cases it must be understood that the distances
a c, be, are employed instead of the spaces actually
OF MACHINERY.
passed through by a and b, because the ratios are the
same, that is
Fig. 5.
8 ac
The principle of the hydro-
static press is illustrated in
the section shown in Fig. 5.
a and b are small and large
cylinders fitted with water-
tight pistons or plungers, one
Qp) being the point of appli-
cation of force, the other (jK)
that of resistance ; the cy-
linders communicate with each other by means of
the pipe c. The water flowing out of a into b evi-
dently has to cover a much larger surface in the latter
than in the former, and consequently the depth of a
given quantity of water would be much greater in a than
in b ; or, in other words, if the piston in a be forced
down, that in b will be raised to a height less than that
through which p descended, in proportion as the area of
b is greater than that of a ; but the areas of circles vary
as the squares of their diameters (Eire., Bk. xii., Prop.
ii.) ; hence the distances ( and $) passed through in a
given time by the points of force and resistance, in
the present case, are inversely as the squares of the
diameters of the respective cylinders to which they are
applied. Let the diameter of the cylinder a be 1-5
inches, and that of the cylinder b 10 inches, then the
spaces passed through by p and R respectively in a
given time will be
2
s = 10 = 100
2
8 = 1-5 = 2-25
22 PRINCIPLES AND CONSTRUCTION
hence a force being applied at p = 25 Ibs., the resist-
ance it will be capable of balancing is,
= 25xl00 =llll.ilb.
2*25
or nearly half a ton.
CHAPTEE IY.
CENTRE OF GRAVITY. MECHANICAL POWERS.
IT has hitherto been customary, when treating on the
attraction of gravitation, to explain the use of the term
" centre of gravity ; " but in this treatise its considera-
tion has been advisedly postponed to this chapter, in
order that the reader might first be made acquainted with
the principle of moments of force, as by pursuing this
course we are enabled the more clearly to deal with our
subject now.
That point in any body at which the whole weight
may be supposed to be aggregated together is called the
"centre of gravity" of such body, and if suspended
from this point it will remain at rest in any position in
which it may be placed. A mass of matter may be re-
garded as an assemblage of small particles or molecules,
each and all exerting moments of force about a certain
point, about which all such moments are in equilibrio ;
this point will be the centre of gravity of the mass.
It is required to find the Fig. 6.
centre of gravity of two
forces, p, / Fig. 6, distant
from each other a b. Let c
be the centre of gravity of
OF MACH1NEBY, 23
the forces, then the moments of the forces about c must
be equal, or
hence,
p _ cb
p ae
let p 24 and p' = 7, then the ratio will be
P _ cb _ 24
y ~~ aTc ~ T
or c will be of b c ; or as there are 24 parts in b ,
and 7 parts in a c (24 -f 7 = 31) of a b
31
Let a b = 27 inches, then
and
= - x 27 = 6-09 inches,
31
I c = x 27 = 20-91 inches.
31
The centre of gravity of any number of forces may be
thus finally found by solving it first for one pair, then
considering the two forces as acting at their centre of
gravity, and determining the point for this and another
of the forces, and so forth,
In all symmetrical bodies the centre of gravity is
evidently coincident with the centre of figure or mass.
The simplest machine for modifying pressure or resist-
ance is the lever, and after what has already been said
the solution of all questions connected with it will be
sufficiently easy.
Let p = the force, d = its distance perpendicularly
from the fulcrum ; R == resistance, D = its distance from
the fulcrum, then
PRINCIPLES AXD CONSTRUCTION
These four equations will serve Fig. 7.
for any kind of lever ; the wheel
and axle shown in Fig. 7 is
identical in principle with the
lever. The radius of the wheel
equals d, one arm of the lever,
and the radius of the axle equals
D, the other arm of the lever.
The circular movement of any
point in the periphery of the
wheel is called its angular velo-
city, of which the proper definition is as follows :
The angular velocity of a, wheel is equal to the velocity of
any point in the periphery divided ly the radius of the wheel.
The inclined plane, wedge, and screw are all but differ-
ent forms of one and the same mechanical element.
Fig. 8 is an inclined plane ; it
is required to determine what force
will be necessary to support the
weight TFupon it. Let p = this
force, I = length of the inclined
plane, and h = its height. It is
evident that in order to raise the
weight W vertically through the
height 7, it must be moved through
the distance I, hence the force
moves through the distance I,
while the resistance of gravitation only acts through the
distance h ; hence
p= TFx A, W =
Fig. 9.
A wedge consists of two inclined planes placed base to
base ; the formulae are the same as above, but replacing
OF MACHINERY. 25
I by L and h by 2h, which would be the thickness of the
back of the wedge, supposing it to consist of two equal
and similar inclined planes.
If an inclined plane, a b (Fig. 9), be wrapped round
a cylinder, c d, it will describe a screw about it, as shown
by the dotted lines. At each revolution of the screw
any body on which it acts will be moved through a space
equal to the distance from centre to centre between two
successive convolutions of the thread ; this distance is
called the pitch of the screw. The screw is usually
turned by a bar or lever, e f. Let the distance from the
axis of the screw at which the force acts = Z, the pitch
6f the screw = p, the force == P, and resistance = R
in one revolution the force will describe a circle of wliich
the radius = Z, or will pass through a space equal to
6-2832 L;
hence the formulae for solving questions connected with
the screw will be as follows :
p - R x P R = p x 6 ' 2832 L
6-2832 L ' J
The toggle, Fig. 10, forms a Fig. 10.
very powerful mechanical element.
A B are two blocks, one fixed,
the other capable of sliding in
the direction a b, but offering a resistance, R, to
motion ; a c, c I are two links jointed together at
c, the force being applied in the direction of the
26 PEIXCIPLES AXD CONSTRUCTION
arrow p, or at riglit angles to the direction of the
resistance. While the force is moving through the
space c d, the resistance will evidently be overcome
through a distance equal to twice the difference between
a e and a d. But (Era., Bk. i., Prop. 47),
, / 2 1
= V <** ~ ^
hence the space through which the resistance is over-
come is
Let I = length of one link (a c), d = distance traversed
by force (c d), R =. resistance, p =. force, then
This gives the relation of force to resistance when the
former is acting in the position shown, but as the re-
sisting block moves so the force becomes more and more
intensified, until, just as the links a c, b c, fall into the
same right line, the ratio becomes infinite.
We next have to consider the effects Fig. \ 1 .
produced by arrangements of pulleys
intervening between the weight or
resistance and the force opposed to it.
If but one pulley is used, and that
one is fixed as at a, Fig. 11, it merely
serves to change the direction of the
force, and does not alter its intensity ;
hence, in this case,
OF MACHINERY. 27
When, however, move- Fig. 12. Fig. 13.
able pulleys are used,
the case is altered, and
the force becomes inten-
sified. In Fig. 12 it is
evident that half the
weight, W, is carried
on each of the portions,
a and b, of the cord;
hence the tension on the
cord is
W
2
In Fig. 13 the weight is carried on the four parts,
0, b, e, d, of the cord, hence the tension on it in this
case is
W
4
So, in these two instances, the ratio of force to weight is,
Fig. 12 : f =
Fig. 13 : p =
The following formula will apply to all combinations of
this class where only one cord runs through the whole
system of pulleys :
Let p = force, W = resistance, n number of
tnoveable pulleys,
PRINCIPLES AND CONSTRUCTION
In Fig. 14 are shown
four moveable pulleys and
four separate cords. It is a
combination of systems of
which each reduces the
resistance by one half,
hence the tensions are on
W . W W , W
'T'*'T'' T>* 16.
Hence the following for-
mulae will serve to solve
cases of this sort. Let n
= the number of times
one system alone will re-
duce the weight or resist-
ance, and x =. the number
of systems combined, then
Fig. 14.
W
In the case illustrated, the number of times one system
will reduce the resistance is 2, the number of systems
combined 4, hence
W _ W
p ~ 2 4th ~~ TG
Of course in all cases of pulleys what is gained in
intensity of force is lost in space passed through ; thus,
in Fig. 12, the parts a and b of the cord have both to be
shortened as much as the weight is raised ; hence the
cord at p has to be drawn through a distance twice as
great as that through which the weight is lifted or the
resistance overcome.
In machines which act by percussion, such as ham-
mers, pile engines, &c., the effect is produced by
OF MACHINERY.
expending work, accumulated through a certain dis-
tance, in a comparatively very short space. For instance,
let the "monkey" of a pile-driving engine weigh
300 Ibs., and have a fall of 10 feet, then in each fall the
work accumulated in the monkey will be
300 Ibs. X 10 ft. = 3000 ft.-lbs.
If this work be expended in driving the pile % inch into
the ground, then ( inch = -^ foot) the mean force
exerted will be
2^2 = 72,000 Ibs.
In order to vary the speed Fig. 15.
obtained from a prime mover,
wheels having teeth on their
peripheries, called cog, toothed
or spur wheels, are very com-
monly used ; the general forms
of some of these are shown in
Fig. 15. A and H are two pa-
rallel shafts carrying the spur
wheels c and d. which, by
gearing together, ensure a cer-
tain ratio of velocity between
the shafts ; and also the hold
afforded by the teeth allows of
power being transmitted from
one shaft to the other. The
dotted circles show the effective size of the wheels,
that is, the size they would be if the motion were trans-
mitted by mere rubbing contact without teeth ; they are
called pitch circles, because the pitch, or distance from
centre to centre of the teeth, is measured on them.
When the shafts are inclined at an angle to each other,
SO PRINCIPLES AND CONSTRUCTION
" bevil wheels," as shown at e and/, are used. In this
case the periphery of each wheel is conical, the apices
of the cones being where the inclined shafts would meet
if produced, as shown by the dotted lines. In both
these cases the wheels revolve in opposite directions.
If, however, the large wheel has the teeth inside the
rim, as shown at A, and the small spur-wheel or pinion
g works within the large wheel, then both wheel and
pinion revolve in the same direction.
The ratio of the angular velocities, or number of re-
volutions made by the shafts, will be dependent upon
the radii of the wheels, as the peripheral velocity will of
necessity be the same for both wheels. Let the radii of
of A and BberandE, and the number of revolutions made
by them be respectively n and N, in a given time, then
n = N X ,N=n X y ~H = nX ~r = N x
v ./. 7V n
Let the radius of A =. r 4 inches, its number of
revolutions per minute = n = 30. The wheel is
required to make 7 revolutions per minute ; its radius
will be
^ = 30 x y = 17-1 inches at the pitch circle.
As the teeth on both wheels are pitched at the same
distance apart, it follows that the number of teeth on
the wheels will vary also as the radii of the wheels. If
both wheels are required to move in the same direction,
an intermediate wheel is sometimes interposed between
the driving wheel and that driven; this, which is called
an idle wheel, has no other effect beyond reversing the
direction of the motion. The shape of the teeth of
wheels will be treated of in a subsequent chapter.
Very commonly, instead of using toothed gearing
(especially where the shafts are far apart and noise is
OF MACHINERY.
o!
objectionable), pulleys or riggers, connected by belts or
straps running round them, are employed ; in this case
the ratio of the angular velocities of the shafts is deter-
mined in the same manner as in the last, presuming, of
course, that the belt does not slip.
For some especial purposes toothed gearing of unusual
forms is applied, the wheels assuming the appearance
of ellipses, squares and lobed figures ; but it is unneces-
sary here to describe them, though it may be advisable
to observe that in setting out such work care must be
taken that in every position the sum of the radii of the
pitch lines, at the point between the centres of the
wheels, is, equal to the distance between such centres.
CHAPTER Y.
ELEMENTS FOB CHANGING THE NATURE OF MOVEMENTS.
The simplest modes of
changing continuous
rotary motion into reci-
procal, or vice versa, are
shown in Fig. 16. a is a
shaft carrying a crank ab,
to which is jointed a I, a
connecting rod, b c; c, the
end of the connecting-
rod, is jointed to a block
sliding between guides,
e /, so the revolution of
the crank will impart the
required motion to the
rod d.
If we imagine the
crank pin b enlarged
PBINCIPIiES AXD COXSTllUCTIOX
until its periphery extends beyond the main shaft
a, the principle of the crank is maintained; but
in the altered form the element is termed an eccentric
wheel, or, for brevity, an eccentric. One is shown
at C. C is the eccentric, j the main-shaft, i the
geometrical centre of the eccentric, g a band surrounding
it, sufficiently free to allow the eccentric to revolve
within it, h a connecting rod by which motion is trans-
mitted from the eccentric.
Instead of the connecting-rod and guides a slotted
link k may be used. This link is carried by two rods
working in guides 1 1; to keep its motion rectilineal the
lateral motion of the crank pin m is allowed for by the
slot in the link. By making the slot sufficiently broad,
an eccentric may also be used with this arrangement.
Fig. 17 exhibits types of three
descriptions of cams in most
general use. A is a heart-
shaped cam carried on a revol-
ving axis b, the end of a rod c
rests upon the edge of the cam,
the rod passing between guides
d. As the cam revolves it lifts
the rod through a distance equal
to the difference of the radii b c
and b e, the mode in which it is
lifted depending on the forma-
tion of the periphery of the cam
between c and e; the rod falls
again by its own weight or by a
spring or another cam.
J? is a face-cam on an axis //,.
the rod k working in guides I is pressed against its face
by a spring or otherwise. The part g pushes the rod
OF MACHINERY. 33
back as the cam revolves through a distance equal to the
difference between h g and i j.
The third cam C has a groove in its face w, t, in
which works a pin n, carried at the end of a bar 0,
capable of oscillating on a centre p. As the cam
revolves the bar o will vibrate by reason of the irregu-
larity of the groove m m.
Cams are very much used in machines where varying
movements and those of an intermittent character are
required. An intermittent movement is any movement
of which whilst one part is always in motion the next
has alternate intervals of motion and rest ; such as
would be the case if the cam A were circular all round
except at one place, as then the rod c would be at rest
except when the one irregular part of the cam was
passing under it, when for a short space it would move.
The cam C is an intermittent movement, as part of the
groove in its face is circular, and therefore does not
move the pin n.
In Fig. 1 8 is shown a spur Fig. 18.
pinion working into a rack ;
by the revolution of the'
pinion the rack is caused
to travel in a rectilineal
direction. A similar change
of motion is effected by a
screw which works in a block or nut. This nut is
prevented from turning by a guide or other restraint ;
hence when the screw is turned the nut progresses in a
straight line parallel to its axis.
In like manner a screw may be caused to act on the
teeth of a segmental rack or on those of a wheel, thus
converting rotatory motion in one direction into the
same but at right angles to its original direction ; this
34 PRINCIPIES AND CONSTRUCTION
last combination is called a worm-wheel and tangent-
screw.
To enumerate one tithe of all the various cams and
elements for changing motion would probably be impos-
sible ; nor does it seem desirable in a work such as the
present to occupy space by enlarging further on the
subject, as sufficient examples have already been shown
to make clear the principles upon which such mechanical
contrivances are based, and these once thoroughly
understood the mechanician will have but little trouble
in setting out details suitable for the attainment of any
special object which he may have in view.
CHAPTER VI.
FRICTION is that kind of resistance which is opposed to
one body sliding upon another, or to a part of a machine
moving when rubbing against another part, as the
journal of a shaft against its bearings, a sliding block
between its guides, &c. The law of the friction of solids
is that the amount of friction varies simply as the
weight or pressure acting upon the surfaces in contact ;
nor is it in any way whatever affected by the extent of
the rubbing surfaces, so long as they are sufficiently
large to withstand the crushing effect of the pressure
acting upon them.
Let A B represent a slab having Fig. 1 9.
a horizontal top surface, upon
which is a weight W, or body,
which is pressed against A by
a force equal to W; from W let
a cord be passed (parallel to A }
OF MACHINERY. 35
over a guide pulley, </, and at the loose end place a
weight, /, of such intensity that if W be set in motion
towards g it will continue to move, but, if stopped, it
will remain at rest ; then/ will be the force equal to the
friction between W and A B, and -^ will be the rela-
tion of this force to the weight or pressure creating the
friction. This is called the co-efficient of friction for the
materials under consideration, and is useful to deter-
mine the friction of any other mass of the same material.
The following table gives the co-efficients of friction for
most of the substances met with in the construction of
machinery :
CO-EFFICIENTS OF FRICTION.
Timber on Stone . . . . 0-4
Iron . . . 0-3 to 0-7
Iron on Metal . ... . 0-15 to 0'25
Timber 0-2 to 0-5
Timber on Metal . . . . 0-2 to 0'6
Lard and Oil .... 0-07 to 0*08
Wrought-iron on Brass . . 0*16
Cast-iron 0-144
CHAPTEE VH.
ON THE CONSTRUCTION OF MACHINERY AND MTLL-WORK.
HAVING: in previous chapters set forth the various
manners in which mechanical forces are altered in
intensity, velocity, and direction, it now becomes neces-
sary to show how the elements by which such effects are
produced may be combined and applied practically as
machines, each part being duly proportioned according
to the stress to which it will be subjected when in use.
36 PKINCIPLES AND CONSTRUCTION
In designing machinery of all descriptions there are
numerous details which are proportioned according to
experience only, but these will generally be found to be
such as from the circumstances of the case are neces-
sarily made much stronger than is absolutely necessary
to resist the strain ; thus, for instance, if one part of a
casting have a great strain upon it, and another part
have scarcely any, the latter must not be made exces-
sively thin in proportion, else from the unequal rapidity
in cooling of the different parts of the casting it may be
rendered weak and unreliable.
The principal elements, however, of machinery may
be calculated in order to ascertain the proper dimensions
to assign to them ; but, before commencing to explain
the processes by which this is done, a few general re-
marks on the action of strains on machinery are
requisite.
In comparison with structures, such as bridges,
mechanism requires to be made proportionately very
much stronger, by reason of its having to undergo stress
while in a state of more or less rapid movement, which
induces a certain amount of vibration and concussion,
whereas in the former the same fibres or portions of
material are always subject to the same description of
stress. The strains to which the parts of machines are
liable are four in number : tension, compression, trans-
verse strain, and shearing strain. Of these, transverse
strain may be resolved into tension and compression ;
thus, if a bar be supported at both ends and loaded in
the centre, then the fibres at the top of the bar will be
in compression, and those on its lower side in tension,
there being somewhere near the centre a layer of fibres
having no strain upon them (this is called the neutral
axis of the bar), on each side of which, upwards and
OF MACHINERY. 37
downwards, the compressive and tensile strains gradu-
ally increase to their maximum intensities at the sur-
faces of the bar. Now, while the bar is at rest, it is
certain that some fibres are always in, tension, and
others are always in compression ; but if the bar be
revolving 1 , as the shafting of machinery, then will every
fibre of which it is composed be subjected to tensile
and compressive strain alternately, the rapidity of the
changes from one to the other being regulated by the
velocity of the moving part. This constant change in
the nature of the strain produces vibration, which, in
order that the apparatus may have a maximum dura-
bility, should be reduced to a minimum.
Also in those elements which reciprocate, or move to
and fro, the strain very generally changes from tension
to compression, or vice versd, at each reciprocation also
causing vibration in such elements.
The revolving parts, such as heavy wheels, cams, &c.,
are also liable to be ruptured by centrifugal force. For
instance, it may occur that a fly-wheel is moving at so
great a velocity that the strength of the rim and arms
is overcome by the centrifugal force generated in the rim,
in which case the wheel will come to pieces, the frag-
ments being thrown considerable distances. Very
serious accidents have arisen through the breakage of
large grindstones from this cause ; hence it is very
necessary carefully to proportion revolving elements to
resist the effects of centrifugal force.
As the vibration of a machine increases with the
weight of its moving parts and with the velocity of their
motion, it evidently is economical to reduce the speed
of such parts as admit of it, and to make all the moving
elements as light as is consistent with the possession
of due strength. The framework, however, should be
7;>,'{S4
38 PRINCIPLES AND CONSTRUCTION
massive and rigid, and so designed as to resist without
sensible yielding all the thrusts and pulls brought
upon it by the various parts of the machinery, for if the
framework be not strong enough the machine will soon
be useless. The following table gives the ultimate
strength of materials per square inch of sectional
TENSION.
Swedish bar-iron
Russian ,,
English ,,
Cast-iron
,, brass .
copper .
Wrought-copper
Wire-rope .
Ibs.
65,000
59,470
56,000
17,628
17,968
19,072
33,892
90,000
COMPRESSION.
Cast-iron .
Wrought-iron
Brick .
Portland stone
Craigleith stone .
Bromley Fall stone
Purbeck stone
York paving
Granite.
Ibs.
120,000
36,000
800
4,550
5,460
5,915
8,000
5,460
9,000
Having made these general remarks, we can now pro-
ceed to consider the laws which rule the proportions of
the different elements of machines. In the first place,
it will be necessary to analyse the resistance of mate-
rials to transverse strain.
OF MACHINERY. 39
If two imaginary sections be
taken infinitely close together
in a rectangular beam when
unloaded, and then a stress be
put upon it, so as to bend it,
as shown at A B, Fig. 20, then
the sections may be considered to have crossed each
other, as exhibited at a b, e d ; all the fibres above the
neutral axis, which is supposed to be in the centre of
the depth of the beam, as shown by the dotted line, will
be compressed, and those below extended.
It is evident that each fibre will be strained exactly
in proportion to its distance from the neutral axis or
point of intersection of the lines a b, and its reaction
tending to resist the load will be equal to this strain. If
S =. strain per square inch on the outer fibre a e, then
that on any other fibre, e f, distant x from the neutral
axis will be, if D depth of beam,
and if the width be unity, the sum of all the strains wil
be represented by the area of the triangle age,
But all these forces or reactions may be regarded as
collected at the centre of gravity of the triangle a g c,
and acting about the point g at a distance equal to that
of the said centre of gravity, which is
_ 2 D
6
hence the total moment of force for the two sets of
fibres, age and d g b, will be
40 PRINCIPLES AND CONSTRUCTION
but the resistance also varies as the breadth, let the
breadth equal b, then the general expression of
moment of resistance for a rectangular beam the maxi-
mum stress per square inch of section on which = S is
if the stress be in pounds and the dimensions in inches,
the moment will be given in inch-pounds (instead of
foot-pounds).
Action and reaction being equal and opposite when
equilibrium is maintained, the moment of resistance will
equal the moment of force.
If a bar is fixed at one end and loaded at the other
with a weight, W, the length being I inches, the
moment of strain will be
M = Wl
hence, Wl =
S b
The safe working depth would therefore be,
For cast-iron D = \/ -
For wrought-iron D =
'V 900 b
the first being a tenth, and the second an eighth of the
breaking strain. If the bar be uniformly loaded, the
moment of strain will be one half of that due to the
concentrated load ; hence the formulae for a bar fixed at
one end and uniformly loaded with a weight, W, will
be
For cast-iron D
= / Wl
V 1600 I
OF MACHINERY. 41
For wrought-iron D = \/-
W I
1800 b
If the bar be supported at both ends and loaded in the
centre, the moment of stress will be
hence the formulae in this case are
For cast-iron D = A / W l
V 3200 I
For wrought-iron D = /
W I
3600 b
Or if the load be distributed uniformly
For cast-iron D A / W l
V 6400 I
For wrought-iron D = A /
V 7200 b
If a weight be placed upon the bar not centrally, then
the length, I, must be substituted as follows :
Let x and y respectively equal the distances of the
points of support from the weight, then
By a process similar to that pursued in reference to
rectangular beams, the moment of resistance of a
cylindrical bar may be found. The following formulae
give safe working results for a cylinder supported at each
end and loaded in the centre (if not so loaded replace / as
above) : let I = length in feet, d = diameter in inches,
W equal weight in pounds
For cast-iron d = 3 A / 1_
V 120
For wrought-iron d = 3 J " *
42 PRINCIPLES AND CONSTRUCTION
Large girders and bearers may be calcu- Fig. 21.
lated in a simpler way. Let Fig. 21
represent a wrought-iron flanged bearer
supported at both. ends. D =. depth in feet,
I = length in feet, a = area of one flange,
plate and angle irons in square inches, s =
safe strain per square inch, W = load in tons at centre,
then for the resistance of both flanges
M~ s x a x d
for the moment of strain,
*=
4
hence 3 tons per square inch being taken as a safe
strain,
__ Wl
~vn>
or if the load be equally distributed,
_ Wl
~24Z>
These general rules for estimating transverse strength
apply to all kinds of machines ; hence require no special
illustration here, as their application will appear here-
after, as progress is made in the analysis of the laws
which govern the proportions of prime-movers, machines
and gearing.
CYLINDERS HAVING PISTONS WORKING IN THEM. Two
points have here to be considered : first, the bursting
pressure ; second, the wear and vibration. The first is
very simple. The pressures in the two halves Fig. 22.
of the cylinder may be considered as acting
and reacting against each other at any
diameter, as shown in Fig. 22 by the arrows,
tending to tear the two sections a and b ;
hence if p = pressure per square inch, and
OF MACHINERY. 43
r = radius of cylinder in inches, the strain on one part
of the shell is
pr
but the question of vibration is not so easily solved, and,
in fact, must be determined by experience. Taking the
two strains together the following formula is found to
give good practical results :
d = diameter of cylinder in inches, p = internal
pressure per square inch, t =. thickness of cylinder in
inches
-ii-+
CYLINDRICAL PIPES. These are cylinders (cast-iron)
having only to withstand pressure with a certain allow-
ance for wear, hence the same notation as above being
used,
t = ^L + 0-66
6000
BOLTS AND NUTS. Let the number of bolts holding
a cover on a cylinder or other vessel having internal
pressure = n, the pressure = p, D diameter of cover
in inches, and d diameter of bolts, then from the
tensile resistance of iron it is found
d =r,
In order that the nut may have a sufficient hold on the
bolt, its thickness should not be less than half the
diameter of the bolt, but it is usual to make the thick-
ness equal to the diameter of the bolt. In some cases,
such as in bearings, check nuts are used, which are thin
nuts screwed down upon the main nuts to prevent their
turning, and so becoming loose.
COVERS AND LIDS. Covers and lids, under pressure,
are subject to transverse strain, and from its laws, aided
44 PRINCIPLES AND CONSTRUCTION
by practical observation, the following formulae are
drawn:
t thickness of cover in inches, p pressure on it
per square inch, D = diameter of cover, C = height of
curve of cover, both in inches
f==
14400 x C
For fiat covers let I = diameter, or if oblong, length
of shortest side :
" RODS UNDER TENSION ONLY. Allowing one tenth of
the breaking strength as safe for working, the following
formulae are found : Let W = the weight in pounds, d
= diameter in inches
. / -irr
For cast-iron d =
GO
t/ W
For wrought-iron d
36
HODS UNDER COMPRESSION. Let the rods be mode-
rately short, so as not to yield by bending, then,
For wrought-iron d =
48
\/~w~
For cast-iron d =
88
If these rods, either in tension or compression, are
placed horizontally or at an angle, so that they are sub-
jected to transverse strain, care must be taken to ascer-
tain that they are sufficiently strong to bear such stress
as may be due to their weights.
HOLLOW CAST-IRON PILLARS. The following formula)
are derived from experiments, and refer to columns of
OF MACHINERY. 45
which the length does not exceed thirty times the
diameter : Let d and d' = the external and internal
diameters in inches, I = length in feet, and W = safe
working load,
It will be observed that the powers to which the
quantities are to be raised are fractional, hence this
formula can only be solved by the aid of logarithms ;
but the following approximate rule is accurate enough
for practical purposes :
w = 4-4 H 3 x J**\_- i^x y^>
V i x V i 3
CAST-IRON BOOKING BEAMS. Let W = weight in
pounds at the end of beam, I = length in feet from
weight to axis of beam, t = thickness in inches, and d
depth in inches ; then from the laws of transverse
strain,
t = Wl
60 d 2
This rule is very suitable to determine the dimensions
of main beams and side levers of engines, and other
like elements.
CRANKS. Let W = the weight in pounds acting on
the crank, D = the outer diameter of its boss, and d =
the diameter of the aperture made to receive the shaft ;
/ = length of the crank in inches from the centre of the
crank pin to the centre of the shaft ; b = the depth of
the crank boss :
W I
For cast-iron b = ----
720 |2> 2 - d*\
W I
For wrought-iron I = -----
800 D* -d*
46 PBINCIPLES AND CONSTRUCTION
REVOLVING SHAFTS. For transverse strain, load in
the centre, let d = diameter in inches, W = load in
pounds, I = length in inches
For cast-iron d =
For wrought-iron d =
Tredgold's rule for water-wheel journals :
d = diameter in inches, I length in inches, W =
load in pounds :
d =1 v~nv
Revolving shafts, through which power is transmitted,
are subject to a twisting force or torsional strain, hence
the shafts must have sufficient strength in this respect.
Long shafts are mostly determined for transverse, but
short ones for torsional strain. Many years back cast-
iron shafts were in vogue, but now they are almost
entirely displaced by wrought-iron. The following for-
mula is convenient for determining the diameters of
main-shafts for prime-movers : Let HP = horse-power
of prime-mover, It = number of revolutions of main-
shaft per minute, d = diameter in inches
=v
320 IIP
R
A very general formula for finding the diameter of
secondary running shafting is
*~\/LSL
v R
The proportions most suitable for the journals of
revolving shafts as determined by experience are, if
OF MACHINERY. 47
d = diameter and I length of journal inches (the
journal being the part in contact with the bearings),
For cast-iron I = 1-5 d
For wrought-iron I = l'7o d
If the weight, such for instance as a fly-wheel carried
upon a shaft, be placed close to the bearing, then the
transverse strain becomes insensible, and the shearing
force has to be considered ; that is, the tendency of the
weight to shear or cut the shaft close to the bearing.
The ultimate resistance of wrought-iron to shearing
force is about 54,000 Ibs. per square inch of sectional
area ; hence the proper diameter being = d inches
W = weight, will be
d= V~W~
65
FLY-WHEELS AND PLAE* PTJLLEYS. In proportioning
wheels of all descriptions sufficient strength must be
provided to resist the tendency to rupture through the
tension caused by the centrifugal force of the mass in
motion. First, in regard to the rim, let v = velocity in
feet per second at the periphery, n = number of revolu-
tions per minute, d = diameter in feet, w = weight
per foot of the rim of the wheel, a = sectional area of
rim in square inches, c centrifugal force. Then c for
one foot of the rim of the wheel will be
w x # 2
Treating this simply as a radial force tending to burst
the ring, we find for the strain ( = $) on any section of
the rim,
48 PRINCIPLES AND CONSTRUCTION
Then, allowing 1,800 Ibs. per square inch as the tensile
working strength of cast-iron, the sectional area should
be
57,960
but, from the specific weight of cast-iron, it is found
that
Also,
19 v
wherefore the limit to the velocity of wheels will be
2546
For cast-iron n = =
4427
For wrought-iron n = ^
The arms of the wheels should be strong enough to
resist the centrifugal force of the whole rim, so that if
it should be broken or flawed between every pair of
arms, yet it will not come to pieces. Cast-iron wheels
very frequently have arms of the form Fig. 23.
shown in Fig 23, though sometimes
they are made round or oval in section, v
The section a I c d must be sufficiently <- -
strong to resist the centrifugal effort of
its portion of the periphery. Let a = the sectional area
of the rim in square inches, d = diameter of wheel in
feet, v = velocity in feet per second, and A = area of
one arm, and JV = number of arms in the wheel, then
the weight of rim
W = a x 3-2 x 3-1416 d = . a . 10 d
OF MACHINERY. 49
hence the centrifugal force on all the arms may be
Wv* av*
~ 16-1 X d ** 1-6
but, n x d
V
19
hence, _ a (n d
_
~
577-6
The safe resistance of all the arms will be
= A x N X 1800
1800 .4 JV. =
A
577-6
a (n d) 2
1,039,680 N
The strength of arms necessary to transmit power must
next be ascertained. In this case the part a b alone
will be taken as carrying the whole strain, the feathers
c and </, on either side of it, being left to give lateral
rigidity, and, in point of fact, being near the neutral
axis, they afford but little towards the resistance of the
transverse strain.
Let D = diameter of wheel-boss in feet, I = length
of arms in inches, n = number of revolutions per
minute, HP = horse-power transmitted, b = width in
inches of a b, t = thickness in inches, V = velocity of
outer edge of wheel-boss in feet per minute, L = strain
at same place, If = number of arms :
HP x 33000
~V~
but, V 3-1416 X D x n
hence _ HP x 10504
D X
50 PRINCIPLES AND CONSTRUCTION
hence, from the formula for rectangular beams of cast-
iron (there being n arms)
/ HP x I x 13
i X n x N x t
TEETH OF WHEELS. The strength of the arms of the
wheels being determined, it is necessary to show the
method of proportioning the teeth to the power to be
transmitted.
Let S = the stress on a tooth, V velocity of pitch
circle in feet per minute, then
HP x 33000
o =
let t = thickness of tooth in inches, I = length in inches,
I = breadth in inches, a = safe resistance of a bar
one inch every way fixed at one end and loaded at the
other, then
t _ / S x I
if we assume b = 2 /,
where c is a constant, which
For cast-iron - = 0-025
,, brass - - = 0*035
,, hard wood = 0-038
Tredgold's formula is as follows :
Let v = velocity of pitch circle in feet per second,
Where # is a constant, which
For cast-iron - = 0*587
brass - - = 0-821
, hard wood = 0-891
OF MACHINEKY. 51
In calculating the stress on teeth of wheels driven by
steam-engines, the maximum power transmitted through
the teeth should always be assumed as 25 per cent,
greater than the mean power of the engine.
FORM OF THE TEETH OF WHEELS. The strength of
the teeth of wheels being calculated, the next step con-
sists in setting out the shape of them, and this is a
point requiring great attention, for if the teeth be not
of the correct form the wheels will not work well
together, whereas, if they be carefully set out and
made properly, the wheels will work noiselessly. The
following are the best relative proportions of the teeth
as determined by practical experience :
Let the Pitch of teeth . = 100
Then - Depth = 75
Working depth . = 70
Clearance = 5
Thickness = 45
Width of space = 55
Play = 10
Lengthbeyond pitch line = 35
The form of the faces of the teeth should be that of the
epicycloid, which is a curve formed by one circle rolling
upon the periphery of another ; if outside the curve is
an epicycloid, if inside it is a hypocycloid. The moving
circle is called the generating circle, and should not
exceed one half the diameter of the spur wheels.
The mode of setting out templates from which to form
the teeth is shown in Fig. 24. Let a 5 be a portion of
the pitch circle of the wheel,
properly marked to show where
the faces of the teeth cross it;
make two templates, A and JJ,
with edges to fit the said pitch
circle. Place template A so as
52 PRINCIPLES AND CONSTRUCTION
to coincide with, the pitch, circle and against cause the
segment c of the generating circle to roll, then a
pencil fixed in its edge will draw the upper part of one
face of a tooth at e f. Remove A and make template B
coincide with the pitch circle, then place the segment of
the generating circle as shown at d, and by it draw the
part e g of the tooth within the pitch circle, and so forth
for as many teeth as are required on the template.
Other curves, such as the involute, &c., have been
proposed for the teeth of wheels, but it is unnecessary
here to enter into a discussion of them.
Not unfrequently, instead of casting wheels with the
teeth on, they are cast with mortices in, and wooden
teeth or cogs are inserted ; a wheel of this description,
working with one having iron teeth, gives very satisfac-
tory results, and is very durable.
ENGAGING AND DISENGAGING GEAR. Various me-
chanical arrangements are employed in workshops and
mills, and other places where machinery is used, to
afford means of starting and stopping any one machine
independently of the others and of the prime mover.
The simplest method is by the use of " fast and loose "
pulleys when the machine is driven by a belt. Two
belt pulleys or riggers are fixed on the driving- shaft of
the machine, one of which is firmly keyed to the shaft,
the other being left free to revolve upon the shaft. A
forked guide leads the belt from one pulley to the other,
both being close together, side by side. When the band
from the driving shafting is guided on to the firmly
fixed pulley the machine is set in motion, but when it is
running upon the loose pulley the machine is at rest.
Another method of disengaging is by clutches, of
which one kind is shown in Fig. 25. c and d are two
shafts, of which the extremities meet but do not touch
OF MACHINERY.
Fig. 25.
-*, J
at m. The clutch is shown in
section, b is keyed firmly on
to the shaft d, but a, al-
though having a sliding key j
which compels it to revolve
with the shaft c, is capable
of sliding endways upon it,
being moved by the forked-
lever e, the ends of which
work in the annular grove
/. Each part of the clutch
has two recesses, li and ', and two projections, k and I,
shown at g. When a is slided up to b, the projections on
each part of the clutch fall into the recesses in the other
part, and thus the motion is transmitted to the other so
long as the clutch is closed ; but this transmission of
power ceases as soon as it is again opened. Most of the
clutches in common use are but variations of this one.
Spur-gearing may be engaged and disengaged by
making one of the shafts so that it will slide longitudi-
nally upon its axis, then by sliding it thus the teeth of
the wheels can be thrown into or out of gear very
readily.
Fig. 26 shows an arrange-
ment of bevil wheels by
means of which a shaft
may be driven in either
direction or left- at rest at '
pleasure, a is the driving c i .
wheel, which is constantly
moving in one direction and
in gear with the two bevil
wheels b and c, which revolve freely on the shaft <?, one
of them in each direction ; d is a double clutch capable
Fig. 26.
f -t
54 PRINCIPLES AND CONSTRUCTION
of gearing into recesses in either b or c, or of standing
clear between them ; it is regulated by the forked lever
/, and is firmly keyed to the shaft e. In the position
shown the shaft e is at rest, but by moving the clutch
in one direction or the other, according to the motion
required to be imparted to e, that shaft immediately is
started. This movement is very useful in some machine
tools, such as screwing machines, where it is necessary
to be able to stop and reverse the machine instantly.
Clutches of this form, however, are not suitable for
high speeds, as the sudden shock of bringing the clutch
pieces together may cause breakage either in them or
in the machinery to which they are applied ; hence, in
such cases it is better to use friction clutches, of which
one is shown in Fig. 27 : a and b .
are the two shafts to which the
clutch is attached; the cone c is ijj$4c
firmly keyed to the shaft a, but d, nJj| m
although compelled to revolve with
b, may slide upon it when acted on
by the forked lever e. When this
clutch is closed the cone d grasps
the cone c and by its friction turns
it round. In this case, the strain being more gradually
brought on to the shaft that was at rest, there is not
much liability to breakage. Having alluded to sliding
pieces it will be desirable to show how they are fitted
to the shafts upon which they are intended to move.
In Fig. 28 a is a plan of a sliding
piece; it is compelled to revolve
with the shaft B B by a key
which slides with it in the pro-
longed groove c d in the side of
the shaft ; or, on the other hand,
OF MACHINERY. 55
there may be a long feather fixed into the shaft upon
which the piece a slides freely, but which compels it to
revolve with the shaft ; e shows a cross section of the
shaft with the sliding piece upon it.
"\Vhere the shafting but seldom requires to be discon-
nected the two shafts may carry discs at their extremities
fixed on and with their faces close together. These
discs being drilled in suitable holes, are connected
together by ordinary screw-bolts and nuts. Short
coupling-boxes keyed on to both shafts may also be
used to connect different lengths of shafting.
The various forms of plummer-blocks, brackets, and
hangers for carrying the bearings of shafting are too
well known to need any special description, and, of
course, the strengths will be determined according to
the weight of the shafting to be supported, and the
strains produced by the power transmitted through it ;
the length of the bearings will be fixed by that of the
journals which has already been given. It is always
well, especially where there is much vibration, to have
the bearings of ample length, as otherwise the shafts
soon become shaky, and the general deterioration of the
machine progresses at a greatly increased rate. We
have seen steam-engines soon rendered comparatively
useless from this cause alone.
In concluding this chapter, we would impress the
necessity in designing machinery of always assuming
maximum strains and minimum strengths ; let no
chance of increased strain pass unnoticed, and be care-
ful to have good sound castings, or, if the machine is
not to be constructed under the supervision of the
designer, extra allowances of strength must be given
to provide against possible inferiorities of material or
workmanship. In designing framing and foundation
56 PRINCIPLES AND CONSTRUCTION
plates for heavy machinery, cross strains should be
avoided as much as possible, more especially when
accompanied by jerking or jarring action ; and wher-
ever such action occurs the framework should be
strengthened to resist such special stress by ties or
struts, as the nature of the strain may indicate.
CHAPTEE Vni.
STEAM AND HOT-AIR ENGINES.
AMONGST prime-movers, in England at all events, the
steam-engine occupies the first place : water-wheels are
scarce, and air and gas engines are seldom heard of,
whilst windmills are becoming obsolete ; our attention
will, therefore, in the first instance, be turned to the
principles of the steam-engine.
The action of this motor is proximately due to the
expansive force of steam, and it may easily be shown
that the greater the extent to which the principle of
expanding the steam when acting is carried, the greater
will be the economy attained. Notwithstanding the
simplicity of this axiom, and the fact that it is and has
been for a very long time generally admitted, strange to
say, at the present time, a great majority of the engines
constructed give nothing like the economical results
which would accrue from a more careful attention to
the means by which the principle of expansion can most
conveniently be applied in practice ; in short, many of
the steam-engines now constructed are a discredit to
their manufacturers.
Before entering upon special details connected with
steam machinery, it is necessary to consider the general
OF MACHINERY. 57
principles upon which its action is based, and the
nature of the expansive fluid by which it is propelled.
Steam is the vapour of water, generated from the
latter by the addition of nearly 1,000 degrees of heat
by Fahrenheit's thermometer. The total heat of steam
is nearly constant for all pressures used in ordinary
practice, ranging from 1178-9 degrees at atmospheric
pressure to 1230-3 degrees at 200 Ibs. absolute pressure
per square inch, which is equal to 185 Ibs. pressure
above the atmosphere. This total heat of the steam is
considered as divided into two portions ; one the
sensible heat affecting the thermometer, the other
latent heat, not affecting it.
The valuation in the total heat of steam being com-
paratively small within the ordinary limits of working,
may, with sufficient accuracy for all practical purposes,
be regarded as constant ; then, if = sensible heat 7 =
S v
latent heat, and T = total heat,
and taking T = 1,179 degrees,
*, = 1179 - t s
The sensible heat is increased and the latent pressure
correspondingly reduced by increase of pressure ; thus,
at 1 5 Ibs pressure per square inch, the sensible heat is
213-1 degrees, whereas at 50 Ibs. pressure it is 281
degrees
In order to arrive at some approximate rule to show
the relation of pressure to temperature or sensible heat,
we must use empirical means, as by pure reasoning we
cannot deduce a formula. It may be assumed that the
pressure varies as some power of the temperature, and
it is necessary to ascertain the index of that power.
58 PRINCIPLES AND CONSTRUCTION
Let t and t' represent a pair of temperatures cor-
responding to the pressures p and p', then
p_ _ /-t\n^
in order to ascertain the value of n recourse must be had
to logarithms ; the logarithmic equation will be
log. p log. p' = n | log. t log. t' |
therefore,
log. p log. p'
= log. t - log. H
this being solved for a number of pairs of temperatures
and pressures taken from Eegnault's experiments, gives
the following values for , the pressures being
a -
140)
200) ~ n = 45
200 ! - w = 4 ' 4
hence, for practical purposes, we may assume n = 4'4,
without being sensibly inaccurate, then the formulae for
temperature and pressure will become
Boyle and Marriot's law concerning the pressure and
density of gases and vapours shows the pressure to be
inversely as the volumes of a given weight ; but this
will not hold quite good with steam, because the tern-
OF MACHIICERY. 59
peratures are different at different pressures. Thus,
from one volume of water, 1,669 volumes of steam being
evolved at 15 Ibs. per square inch, the theoretical quan-
tity at 30 Ibs. pressure should be 834-5 volumes, but it
is 881 volumes really.
No practical rule can conveniently be laid down to
determine the addition or diminution necessary as cor-
rection to the volume determined by this law, as at
different temperatures the steam holds in suspension
different quantities of water finely divided, the steam in
contact with water not being dry.
According to the views of J. Grill, of Palermo, the
conversion of sensible steam into latent heat is the con-
comitant of work done, and the contrary that of work
absorbed by or stored up in the steam ; and it is a
certain fact that as steam in doing its work expands, so
sensible heat is rendered latent, and when steam is
forcibly compressed the latent heat is rendered sensible.
The effect of heat or caloric has been supposed to
consist in causing the molecules of matter to gyrate in
greater or smaller spheres, according to the intensity of
the heat; this is the " theory of molecular vortices," and
by its aid some explanation may be given of the differ-
ence between sensible and latent heat. There being a
certain addition of heat to a body of water, its molecules,
or some of them, take the form of steam and gyrate in
larger spheres than before, but so long as they have
room for their enlarged gyrations, the caloric is by them
taken up and remains latent; but if the molecules be
crowded together by increased pressure, then the
molecules being confined to spheres of gyration smaller
than those they would naturally assume, they press
against the neighbouring molecules, and give rise to
the phenomena of sensible heat.
60 PKIKCIPLES AXD CONSTRUCTION
Mr. Charles Wye "Williams elucidated a doctrine
concerning steam and water of a very ingenious cha-
racter, and deserving of much attention ; it is as
follows : There is no such thing as warm water in the
abstract meaning of the term ; that is to say, a molecule
of water cannot be warmed so as to remain water, but
each certain increment of heat causes a molecule of
water to assume the proportions of a molecule of steam,
although it may not escape from the water, by reason
of the aqueous and atmospheric pressure. That steam
formed in water is retained there is well known, as if
steam be generated under pressure in a close vessel and
in contact with water, and the steam accumulated in the
space above the water be suddenly removed by con-
densation, or by letting it suddenly escape, a dense
mass of steam will at once arise from the water, which
steam up to that time had been as it were dissolved in
or mixed with the water in the boiler or generating
vessel : in point of fact, practically, the rush of steam
would be so great from all parts of the mass of water,
that the latter would, if the pressure were at all con-
siderable, be carried up bodily with it.
If one ounce of steam be passed into 6-35 ounces of
water at 60 degrees Fahrenheit, placed in a vessel
wrapped round with some non-conductor so that no
heat can be abstracted by the atmosphere, the whole
will be raised to the boiling point, 212 degrees. Now,
let this body o water be poured into a shallow pan,
also protected from atmospheric chills, a cloud of steam
will rise from it, and when it has reached the tempera-
ture of 60 degrees, it will have its original weight of
6-35 ounces. This experiment, published "by Mr.
Williams, has been repeatedly verified by the author of
the present work ; but let us see to what conclusion
OF MACHINERY. 61
it points. According to the old doctrine, the one
ounce of steam would be said to be condensed; but, if
actually converted into water, why should it again
resume the form of steam without any external agency
being brought to bear upon it ? It seems far more in
accordance with common sense to regard the steam
as dissolved in the water, and held there by the attrac-
tion of the water, aided by the pressure due to its depth,'
the steam escaping when by pouring the water so as to
form a thin layer its pressure is reduced to a minimum.
From this view it would appear that heat is incapable
of being transmitted from one aqueous molecule to
another, although it will freely pass between molecules
of steam and certain solid bodies ; for instance, if warm
water (so called) be added to cold, the steam in the
former will diffuse itself through the whole mass, which
takes a mean temperature (being as it were a weaker
solution of steam) ; but, if the two waters are separated
by a metal plate, the steam on one side partly condenses,
giving its heat to the metal, whence it generates steam
in the water on the other side of the metallic plate.
We will now take some examples to give some idea
of the amount of economy attained by carrying out the
principle of expansion as far as can conveniently be
done. The economy will be measured by the quantity
of work done by the steam generated from a cubic foot
of water, as under all pressures the same amount of
coal will practically evaporate the same quantity of
water.
In both cases let the steam be generated at a pressure
of 50 Ibs. per square inch, that will be equal to 7,200 Ibs.
per square foot supposed to act upon a piston of which
the area is one square foot. In the first case let the
steam act with its full pressure for half the stroke,
62 PRINCIPLES AND CONSTRUCTION
which half will be completed when one cubic foot of
water is converted into steam (the pressure is absolute,
not above the atmosphere), the distance will be 552 feet,
because one cubic foot of water will supply 552 cubic feet
of steam at 50 Ibs. per square inch, hence the work done
during this part of the stroke will be
= 552 x 7200 = 3,974,400 ft. Ibs.
during the other half it will be expanded to a volume
of 1,104 cubic feet, corresponding to 26 Ibs. pressure
per square inch ; for the present purpose we may take
the mean pressure during the second half of the stroke
at 38 Ibs. per square inch, or 5,472 Ibs. per square
foot ; this is exerted through 552 feet, doing work
= 552 x 5472 = 3,020,544 ft. Ibs.
the total work done being
= 3,974,400 + 3,020,544 '= 6,994,944 ft. Ibs.
If, however, after the steam was all generated at 50 Ibs.
per square inch it were to be expanded to three times
its bulk, much more work would be done by it. Its
final volume would then be 1,656, corresponding to a
pressure of 14 Ibs. per square inch, and to a 'mean
pressure for the last two-thirds of the stroke of 32 Ibs.
per square inch, or 4,608 Ibs. per square foot, which
would be exerted through a distance of 1,104 feet, doing
work
= 1604 x 4608 = 5,087,232
making the whole work during the stroke
= 3,974,400 -j- 5,087,232 = 9,061,632 ft. Ibs.
or more than half as much work again without any
extra consumption of fuel.
It may be interesting to show the theoretical duty
which might be attained by cutting off at one-tenth of
the stroke. Assume the coal to be of such quality that
one pound will evaporate 7 '5 Ibs. of water, the steam
OF MACHINERY. 63
acting against a vacuum, i.e., in a condensing engine
and with an initial absolute pressure of 60 Ibs. per inch,
The work done by one cubic foot will be, before
expansion,
= 467 x 64 x 144 = 4,034,880 ft. Ibs.
during expansion
= 4203 x 32-3 x 144 = 19,549,008 ft. Ibs.
the whole work done being
= 4,034,880 + 19,549,008 = 23,583,888 ft. Ibs.
But if 1 Ib. of coal evaporates 7-5 Ibs. of water it will re-
quire, to evaporate one cubic foot (62-5 Ibs.) of water,
8-33 Ibs. of coal; hence the duty done by 112 Ibs. of
coal would theoretically be
= 317,094,244 ft. Ibs.
however, the highest nett duty yet recorded is
= 109,000,000 ft. Ibs.
It is true that considerably higher duties (146 millions)
have been reported from Cornwall, but examination
showed that sufficient allowance was not made for loss
of water in the pumps through the inefficiency of the
valves. This statement is made on the authority of the
late Thomas Wicksteed, Esq., M.I.C.E., through whose
means principally the Cornish engine was first intro-
duced into London.
Some years back a marine-engine in which the ex-
pansion was carried to twelve times, the consumption
reported on the trial trip was only 1-08 Ibs. coal per
horse-power per hour, corresponding to a duty
= 205,333,333ft. Ibs.
but statements based upon the results of short trials
must always be received with caution, as many circum-
stances may occur, some accidental, to render the duty
much higher on short trials than in ordinary working.
64 PRINCIPLES AND CONSTRUCTION
On the other hand, there may be urged against
extreme degrees of expansion the larger size of engine
required for a given power ; but where the work is such
as mine-pumping this is not of so much consequence ;
and besides this the difficulty may, to a great degree,
be obviated by using steam of a very high initial
pressure. Engines largely using expansion require
heavier fly-wheels than others, as, from the great
difference in the initial and final pressures, the pro-
pelling force of the piston varies in a greater degree
than in those engines in which but a low degree of
expansion is used.
Much was at one time expected from the employment
of heated air, instead of steam, as a propelling power,
but the hopes entertained of it were doomed to speedy
disappointment. It is true that some air-engines of
small power are at work in the United States of
America and elsewhere, but there seems to be no pre-
sent likelihood of their employment becoming at all
general ; some of the best we have seen owe their
economy of working, not to the principles of the engine,
but to the fact that the fuel has been consumed under
pressure, a method which secures a great saving of fuel,
as was abundantly proved some years back in the trials
of the apparatus patented by Messrs. Moor and Shil-
litoe, by which something like 46 per cent, of fuel was
saved.
One great objection to hot-air engines is the high
temperature required to be maintained in them, which
rapidly injures the machinery, and renders the applica-
tion of ordinary lubricants almost useless. Jn order to
obtain a pressure of 15 Ibs. per square inch above that
of the atmosphere, it is necessary to raise the tem-
perature of the air by 480 degrees, a temperature which,
OF MACHINERY. 65
applied to steam, would give a pressure of 43 Ibs. per
square inch above the atmosphere. It must also be
remembered that with air-engines no vacuum can be
created to give the benefit of the ordinary atmospheric
pressure, which in a very large class of steam-engines
forms a very considerable item in the working pressure ;
thus we find marine-engines commonly working with a
steam pressure of 20 Ibs. per square inch above the atmo-
sphere, and with a vacuum of 13 or 13-5 Ibs. per square
inch, making a total effective pressure of 33 '5 Ibs. per
square inch.
Mr. J. Gill, of Palermo, proposed an engine in which
air and steam mixed were to be used to propel the
piston, and according to his preliminary experiments,
as published a few years since, this system promised
great results, but from some cause or other the project
seems to have been allowed to drop.
When a steain-engine is required of any considerable
power, the purchaser should remember that his greatest
economy is not to be attained by keeping the first cost
down to the lowest possible price, for with steam-
engines as with other articles of merchandise, the terms
cheapness and badness are interchangeable, and in all
cases it will be the best policy to engage the services of
a competent mechanical engineer to design the engine,
as his professional fees and the extra cost for patterns
and the engine, involved in special designs, will be more
than returned by the saving in fuel effected. Of course
where a firm of contractors make an engine, and
guarantee its duty, the same end is gained, the extra
charges being all included in the price of the engine.
As regards the strength of the different parts of
steam-engines, that may be determined from the rules
set forth in Chapter vii. on construction, as the formula,'
F
66 PEINCIPLES AND CONSTRUCTION
there given apply to the steam-engine as well as to
other descriptions of machinery; but in the present
part of this work the proportions generally will be
treated of, efficiency, not strength, at present occupying
our attention.
One of James Watt's improvements in the steam-
engine was the jacket or steam-casing round the
cylinder ; this being filled with steam, and in commu-
nication with the boiler, supplied, as it were, a reservoir
of heat which would, by raising the temperature of the
expanding steam in the cylinder, retard the condensa-
tion therein due to the loss of heat consequent on ex-
pansion ; but in parting with heat thus to the steam
within the cylinder a portion of that in the steam-
jacket is condensed, hence it is very questionable if any
economy of fuel ultimately results from the adoption of
the steam-jacket. In all cases, however, the cylinder,
whether jacketted or not, should be surrounded by
" lagging," that is, by a layer of some material which
is a very slow conductor of heat, in order to prevent
loss by radiation.
The amount of work which is termed one-horse
power is 33,000 ft.-lbs. per minute, and according to
this standard the value of engines is estimated. The
calculation of the power of a steam-engine is exceedingly
simple. Let HP = the horse-power, V = speed of
piston in feet per minute, p = pressure of steam (pro-
ducing effect) on the piston per square inch, A =
diameter of cylinder in inches
Hp _ -785 x d* x p x V _ d 2 . p . V
33,000 42,038
omitting the decimals.
For engines having peculiar movements, such as the
"disc-engine," and the " semi-cylinder engine," where
OF MACHINERY. 67
it is not so easy to compute the velocity of the piston as
in the common engine (in which V = the length of
stroke multiplied by the number of strokes per minute),
the following rule will be found convenient :
Let c = cubic contents of steam-chamber in feet,
n = number of strokes per minute, p = pressure of
steam per square inch, then
229
To determine the effective pressure in the cylinder of
a non-condensing engine, we must subtract from the
absolute mean pressure that of the atmosphere and the
resistance offered by the steam exhausting out of the
cylinder through the exhaust passages ; this last is
called "back pressure," and varies widely according
to the construction of the engine and the velocity of the
piston ; let it = a Ibs. per square inch, A absolute
pressure of steam
p = A - (a + 15)
For a condensing engine, let u the vacuum in
pounds per square inch in the condenser, then
p = A - (15 - )
The nominal horse-power of an engine is a term used
chiefly in commerce in buying and selling engines, and
is not to be taken as a criterion of the real power of the
engine, which may work up to three, four, or even six
times its nominal horse-power. Many manufacturers
determine the nominal power of their engines simply by
the area of the piston, allowing a certain number of
square inches to each horse-power. In the old rule, for
nominal horse-power for condensing engines, seven
pounds per square inch is assumed as the effective
F 2
68 PRINCIPLES A2TD CONSTRUCTION
pressure per square inch on the piston, thus making the
formula for nominal horse-power
--
42,038 6006
if we assume the velocity of the piston at 240 feet per
minute, then this formula becomes
N HP = - = omitting decimals.
6006 25
Let us compare this with what is actually done in
practice. Assume the pressure at the commencement of
the stroke to be 20 Ibs. per square inch, and the supply
to be cut off at one-third of the stroke this pressure
being above the atmosphere, the absolute pressure will
be 35 Ibs. per square inch which at the end of the
stroke has expanded down to 10*5 Ibs. per square inch.
The mean absolute pressure on the piston per square
inch will therefore be 26-8 Ibs. Let the vacuum in the
condenser be 13 Ibs. per square inch, then the mean
effective pressure will be
= A - (15 - ) = 26-8 - (15 - 13) = 24'8lbs.
hence the rule for horse-power will be
HP = 24 ' 8 X 240 X d* = d*
42,038 " = 7-63
or more than three times the nominal power found by
the foregoing rule. These proportions, being tolerably
common, we may adopt as an approximate rule for the
type of marine-engines served by square boilers
d 2
HP = = working power.
8
To determine accurately the power exerted by the
steam in an engine, that is, the gross or indicated horse-
OF MACHINEBY. 69
power, an instrument called an indicator is fitted on to
the cylinder to register the pressure at every part of the
stroke of the piston. The indicator comprises a small
cylinder fitted with a steam-tight piston, carrying on its
rod a pencil ; this piston is held in a certain position by
a spiral spring. When in communication with the engine
cylinder, the indicator piston rises and falls with the
pressure in the cylinder, the spring being more or less
compressed or extended, according to the variations of
pressure and vacuum. The pencil rising and falling
with the piston draws a figure upon a card or piece of
paper, moved (by being attached to some part of the
engine) backward and forward once in every revolution
of the engine : the kind
of figure drawn is shown
at Fig. 29. alls called
the atmospheric line,
being drawn by moving
the paper when the in-
dicator is not in com-
munication with the
cylinder. As soon as the
engine is started, the indicator being fixed and open to
the cylinder, the pencil starts up to c ; but when the
pressure has overcome the friction of rest and the engine
begins to move a little, the pressure falls slightly, then
remains uniform, or nearly so, till the steam is cut off
at d, and expansion continues to the end of the stroke
at b ; then the exhaust opening, the pencil descends below
the atmosphere line to e, showing vacuum, and remains
steady to /, where the valve begins to close the exhaust,
when the pencil gradually rises to the starting point a.
To ascertain the mean pressure from an indicator card
the following method must be pursued : Divide the
70 PRINCIPLES AND CONSTRUCTION
figure into any number of equal parts, say 10, as shown
by the lines x x, &., then mean absolute pressure
_ 2 (2 + 3 + 4 + 9 + 10 + 1 + 11)
20
or if it be divided into n parts, the formula
2 (2 + 3 + n) + 1 + (n + 1)
2 n
The value of the lines 1, 2, &c., are found from a scale
of pressures corresponding to the tension of the spring
in the indicator.
The indicator diagram forms a key to the construc-
tion of the apparatus for regulating the admission and
emission of steam through the cylinder ports. That
shown above shows a well-constructed engine ; but
that shown below, in Fig. 30, is illustrative of the
contrary : a b is the
atmospheric line. It is Fi 9' 30 ' ^ ^ f
evident from the great
excess of pressure c d
to start the engine over
that to keep it moving
that the engine in this
case works stiff; next,
the pressure, instead of remaining steady to the point of
cut-off e, falls, showing that the steam passages are too
small and wire-draw the steam ; thirdly, on the back
stroke, instead of the vacuum being got at once it is
not got till g is reached, showing too small an exhaust
passage into the condenser.
In such an engine as would give this diagram there
is evidently a great loss of power due to the resistance
of the steam passages and ports, or the defective
vacuum may be partly due to insufficient injection
water, or other defects in the condensing apparatus.
OF MACHINERY. 71
The horse-power found from the indicator diagram
shows the gross amount of work done by the steam in
the cylinder, tut this is not all used in the work for
which the engine is designed, a portion being absorbed
in friction and in working feed and air pumps, &c. ; hence
other means must be adopted to show the actual amount
of work given off by the engine to be expended usefully.
The apparatus used for this purpose is termed a
friction dynamometer, and is of the general form
shown in Fig. 31.
a is the main-shaft Fig. 31.
of the engine, bed
is the dynamometer,
which is somewhat
similar to a friction
brake; between the
adjustable belt I e
and the shaft a are
interposed blocks of wood to prevent any biting that
would injure the main-shaft of the engine; these are.
tightened up by the screw-bolt e until the friction is
sufficient to keep the arm d horizontal, the engine
moving at a uniform rate (the shaft revolving within
the belt b c) and the scale / being suitably loaded.
Now, in sustaining this weight by friction on the shaft,
the engine is virtually giving off as much work as if at
every revolution the weight W on the scale / were
moved through a distance equal to the circumference of
a circle having x for a radius. Hence, to find the useful
power of the engine, we have the following rule :
x being in feet and W in pounds, n = number of
revolutions per minute
jrp 3-1416 X 2 a; X W X n _ x . W .n
33,000 5252
omitting decimals.
12 PRINCIPLES AND CONSTEt'CTION
The useful effect of Cornish and other pumping
engines is easily computed from the quantity of water
raised in a given time. Thus let Q = gallons of water
raised in twelve hours, h = the height in feet to which
the water is pumped above the surface of the well,
reservoir, or river from which the supply is taken, then
(1 gallon of water weighs lOlbs.)
HP = Q x h x 10 o A
12 x 60 x 33,000 2,376,000
If the valves of a pump (such as Harvey and West's
double-beat) close exactly at the end of the stroke, the
following rule will give the delivery in gallons per
stroke for a single-acting pump, such as is commonly
used with a Cornish engine. Let g = gallons per
stroke, d diameter of plunger in inches, S = stroke
of pump in feet
s.d*
ff =~2^4
For the power to work a pump: Let g = gallons
per stroke, h = height of lift in feet, n = number of
strokes per minute, HP = horse-power (exclusive of
friction) absorbed by pump
HP= V- h -?L
3300
To determine the useful effect that is, the tractive
force of a locomotive engine a spring dynamometer is
introduced as a coupling between it and the train,
which registers the traction on a paper moved by
clockwork if the horse-power is required. By means of
a similar dynamometer, the dragging power of steam-
tugs may be ascertained.
In former times it used to be the practice to allow
one-third of the total power of an engine as absorbed in
OF MACHINERY. 73
its own friction ; but if it be well designed, and of good
workmanship, there is no necessity for the friction of
its parts to absorb more than from 6 to 8 per cent, of its
total power
In discussing the points connected with the apparatus
for regulating the admission and egress of the steam to
and from the cylinder, let it be particularly understood
that we do not pretend to give examples of the different
forms of valves, &c., used for that purpose at length,
but rather to explain the principles which should guide
the designer in his endeavours to produce an efficient
machine ; those who desire to study the different forms
of valves are referred to the author's PRACTICAL
TREATISE ON MECHANICAL ENGINEERING.
The steam which is left in the steam passages at the
end of each stroke is evidently so much waste, hence the
passages between the valves and the cylinders should
be made as short as possible in order to reduce this
waste; also the room allowed above and below the
piston to prevent its coming in contact with the
cylinder covers should be small : this is called clearance,
and in our opinion a quarter of an inch is sufficient
clearance for ordinary engines.
The area of the ports and steam passages must be
determined according to the velocity at which the piston
is intended to travel and the difference between the
pressures in the boiler and the steam cylinder, this
difference representing the pressure by which the steam
is caused to flow through the passages and ports from
the boiler into the cylinder.
Let D = diameter of cylinder in inches, S = speed
of piston in feet per minute, p = absolute pressure
per square inch in cylinder, P = absolute pressure per
square inch in boiler, a = area of port in square inches.
74 PRINCIPLES AND CONSTRUCTION
Then, according to the laws which regulate the flow
of gases, the minimum area of the steam-ports will be
If we assume the difference between the pressures in the
cylinder and boiler (Pp) to be always equal to four
pounds per square inch, the formula will become
30,000 '
For example, let the diameter be 10 inches, the speed
of piston in feet per minute 250, and the pressure 40 Ibs.
per square inch
a ~^TF^^ x 25 A / 40 = 5 ' 26 square inches.
oO,OUO Y'
the exhaust-port is commonly made not less than twice
the area of the steam-ports.
In Fig. 32 a is an ordinary Fig. 32.
short slide-valve acting on the
ports communicating with the
ends of the cylinder through
the passages I and c, d is the
exhaust passage. The edges of the valves must be at
least th of an inch wider than the steam-ports to ensure
the closing of one port before the other is opened. The
full and dotted lines show the two extreme positions of
the valve. In the former the steam is passing from the
slide-jacket / into the end c of the cylinder, whilst
it is exhausting from the end b through d. If the
edges are made as above stated, as soon as one port
begins to open to the exhaust the other opens to the
steam, and they close together in the same way.
In order to ensure that the engine shall move in a
specified direction, it is necessary that the valve shall be
OF MACHINERY. 75
somewhat ahead of the piston, so that when the piston
arrives at the top of the cylinder the top port shall be
partly open, so that the piston gets steam early in the
stroke. The reason that this arrangement controls the
direction of the engine's revolution is as follows : Let
the piston be on the up-stroke, then, on reaching the
top of the cylinder, the steam-port will be (say) half-way
open, and if the engine continues in the right direction
the valve will continue to open till the middle of the
down-stroke, but if the piston on the down-stroke pulls
the crank back on the wrong side of the centre, the
valve which was half open will close again and open
the bottom port. This advance which is given to the
valve is called its "lead." The number of degrees
which the eccentric driving the valve should be put in
advance of the crank is called the " angular lead," and,
with the aid of a table of natural cosines, may be found
from the following formula : Let a = the angular
lead, d = distance in inches over which the valve has
passed when the piston is at the end of its stroke, t =
travel (or stroke) of valve in inches, then
As an example, let the travel of a valve be 3 inches, and
d =. 2 inches, then
Cos = 1 - ^~- = - 0-33
hence, from a table of natural cosines,
a = 70 degrees, 30 minutes.
The effect of the angular position of the eccentric rod
driving the valve is too slight to require any practical
notice.
7b PRINCIPLES AXD CONSTRUCTION
Sometimes the edges of the slide-valve are extended
outwards, the effect of which is to give a cut-off at a
certain definite portion of the stroke; but of course,
when the engine is once made, this cut-off and the cor-
responding degree of expansion cannot be altered : this
is called giving the valve "lap." If, however, the ex-
pansion frequently requires altering, a separate valve,
which controls the supply of the steam entering the
slide-valve jacket, is used, working independently of the
slide-valve ; by this means, or by using a link motion
with the slide-valve, the degree of expansion may be
varied at pleasure.
The exhaust is usually closed some short space before
the piston reaches the end of the stroke, thus confining
a portion of vapour which acts as a " cushion," and
obviates part of the jarring consequent upon the sudden
reversal of the motion of the reciprocal parts of the
machine. Nothing is lost by this, as, although some
work is done in compressing the " cushion" of vapour,
yet in the return stroke this is given up again.
The various parts of a steam-engine when moving
have of necessity a certain amount of work accumulated
in them, which must be absorbed at the end of each
stroke from such parts as change the direction of their
motion, and this work must be expended in friction,
concussion, and compressing the cushion of steam ;
hence it is advisable to avoid high velocities in recipro-
cating parts. Heavy cranks also produce vibration, as
on one side of the centre they aid, but on the other
hinder, the revolution of the main-shaft ; these, there-
fore, work smoother where counterbalanced, or they
may, in some cases, be replaced by crank wheels, which
are discs carrying crank pins near the periphery.
There are many causes which interfere with uni-
OF MACHINERY. 77
formity in the motion of the steam-engine, such as
sudden variations in the work to be done, by the throw-
ing into or out of gear any machine in a factory or
workshop ; but we will first deal with the irregularities
which arise in the engine itself ; these are due to the
varying angle of the crank, and also to the varying
pressure of steam in the cylinder due to expansion.
These latter imperfections are met, and to a great
extent remedied, by the use of a heavy fly-wheel, which
serves as a reservoir of force, absorbing work, and
storing it as accumulated work, when the engine is
imparting the maximum power to the main-shaft, and
again yielding it up when the engine is exerting little
or no power, as is the case at and near the dead points,
and thus by giving and taking, according to whether
there is a deficiency or excess of power, something
approaching to a mean velocity is attained.
It is not, however, only the fly-wheel that serves thus
to regulate the speed of the engine, for the momentum
of the whole mass of shafting and running gear also
assists ; hence, when an engine is working a factory,
we cannot calculate the fly-wheel as absorbing all the
excess of power and storing it until it is wanted. If
we suppose a six-horse high-pressure engine to be
running alone and merely overcoming its own friction,
having a 4-foot fly-wheel moving at 30 revolutions per
minute, the accumulated work would be in the rim of
the fly-wheel weighing 600 Ibs.
_ 600 x y 2
64 T 4
but the velocity per second is
= 30 x 4 X 3-1416
60
78 PRINCIPLES AND CONSTRUCTION
therefore the accumulated work
600 x 39-47
64-4
= 367-73 ft.-lbs.
The work required to overcome the friction of the engine
being taken at 5 per cent, of its full power, that done
in each revolution would be about 330 ft.-lbs. ; hence
the excess of work to be taken up and stored would be
probably about 45 ft.-lbs. ; hence the total accumulated
work when this is taken up would be
367-73 + 45 = 412-73 ft.-lbs.
from which we find,
600 x fl 2
64-4
= 412-73
but the mean velocity is 6*2832 feet per second, hence
the variation in velocity is
6-655 - 6-2832 = 0-3718
which is equal to
0-3718 X 100
6-2832
= 5-91 per cent, of mean velocity.
When the variations of power are considerable, as
from the varying amount of work to be done or number
of machines to be driven, an apparatus called a
governor is attached to the engine. A great number
of different descriptions of governors have been in-
vented, but that most generally in use is the conical
OF MACHINERY.
pendulum applied by James Watt, which is shown
in Fig. 33. a b is a vertical
shaft driven by bevil gearing c, d t
or other suitable means, so as to
revolve at a rate proportioned to
the speed of the engine; at the
top of the shaft are two joints,
g, g, carrying the arms g, e,
having heavy balls e, e, at their
lower extremities ; there is also
on a b a sliding collar connected
by links /, /, with the arms g, e.
The quicker the engine goes the
faster will this governor revolve,
and the centrifugal force will
cause the arms to fly outwards
about the centres g, g, thereby
raising the sliding collar, which lifts the end of a forked
lever moving on a centre at i and through a link j,
controlling the steam supply either by partially closing
a valve in the steam-pipe from the boiler, or by causing
the flow of steam into the cylinder to be cut off at an
earlier period than when there was more work upon the
engine. To determine the height of the points g, g,
above the plane of revolution of the balls is sufficiently
simple : it is equal to the length of a pendulum which
would make two beats while the governor makes one
revolution. Let h = height in inches, n = number of
revolutions per minute, then
, ( 187-7 ) 2 , 187-7
n = I - } , and n =
I I / h
Engines are almost always fitted with feed-pumps for
supplying water to the boiler from which to generate
80 PRINCIPLES AST) CONSTRUCTION
steam to work the engine, and, as a matter of pre-
caution, these pumps are made large enough to supply
at least twice the minimum quantity of water required
for use in the form of steam. From the relations of
pressure and comparative volumes already referred to,
the following rule for the size of a feed-pump is
deduced :
Let p = pressure of steam in pounds per square inch
above the atmosphere,
s = stroke of piston in feet,
D = diameter of steam cylinder in inches,
c = contents of feed-pump in cubic inches, then
40 (15
According to the quantity of steam used must the water
for condensation also be regulated ; the temperature at
which the water is desired to leave the condenser being
determined, the quantity of injection water required
will be found from the following formula :
C = cubic feet of condensation water required per
cubic foot of water used as steam in the engine, t' =
temperature of water entering the condenser, t = tem-
perature of water leaving the condenser, then
Having made these practical observations on the
designing of steam-engines, we shall now conclude this
chapter by stating that examples of different kinds of
engines and their details may be found in the work on
" Mechanical Engineering " already alluded to.
OF MACHINERY. 81
CHAPTER IX.
BOILERS AND FURNACES.
IN arranging the proportions of boilers and furnaces an
amount of care and experience equal to that exercised
in preparing the plans of the engine is demanded, for a
well-designed engine will not work economically if the
boiler be badly constructed, without due regard being
had to the principles which regulate combustion and the
transmission of heat.
The heat obtained from combustion is due to. the
oxidation of the carbon and hydrogen of the fuel used,
which oxidation consists in the decomposition of those
elements from each other and their recombination with
oxygen gas from the atmosphere or from some other
source. Thus the carbon becomes converted into car-
bonic acid, and the hydrogen into steam ; the chemical,
change is shown in the following diagram :
T-, T (Carbon (Hydrogen)
Fuel 1 Hydrogen ^7 1 Oxygen j water "
X^-^ (Carbon | carbonic
.. I Oxygen ~~/ " (Oxygen j acid.
(Nitrogen . . nitrogen.
In this case the fuel is supposed, for simplicity, to con-
sist of hydrogen and carbon only ; in fact, to be a pure
hydro-carbon.
The heating value of fuel may be given in pounds of
water evaporated per pounds of fuel used, or units of heat,
one unit of heat being that quantity which is required to
raise the temperature of one pound of water one degree
Fahrenheit. The theoretical calorific value of fuel may
be determined from the following formula, in which the
constants are, of course, obtained from experiment,
a
82 PRINCIPLES AND CONSTRUCTION
Let C = weight of carbon in one pound of fuel, H ==.
ditto of hydrogen, = ditto of oxygen, and L =
pounds of water evaporated from 212 degrees by one
pound of fuel :
P = 15 | C x 4-28 (H - \\
Practically, however, it may be taken that one pound
of good average coal will evaporate about 7 -5 Ibs. of water
from a temperature of 212 degrees, and this is a more
reliable datum than that calculated from the chemical
analysis.
We have now to consider the quantity of air required
for combustion, and the mode of bringing it into con-
tact with the fuel. According to the doctrine of
chemical equivalents, every pound of carbon in being
converted into carbonic acid will require 2-66 Ibs. of
oxygen, and every pound of hydrogen will require
8 Ibs. of oxygen. Assuming a fuel to be of the follow-
ing composition :
Carbon . . 0-855 Ibs.
Hydrogen . . 0-053
Oxygen . . 0-092
the quantity of air required for combustion will be found
as follows : for the carbon the oxygen required
0-855 x 2-66 = 2-274 Ibs.
and the quantity for the hydrogen
0-053 X 8 = 0-424 Ibs.
but in the composition of the fuel there is 0-092 oxygen ;
hence this must be deducted from the total quantity
required, which will then be
2-274 -f 0-424 0-092 = 2-606 Ibs. oxygen ;
but oxygen exists in the atmosphere to the amount of
OF MACHINERY. 83
20 per cent, of the whole mass of air, hence the quantity
of air required per pound of fuel will be
2-606 x 5 = 13-03 Ibs.
and as air is 773 times lighter than water, the volume
of air required will be
13-03 x 12-37 = 49-85 cubic feet of air per Ib. of fuel ;
this would be required for actual combustion; but, in
reality, a much greater quantity of air would require to
be passed in when ordinary furnaces are used, as nothing
near the whole quantity of oxygen is taken from the
atmospheric air passing through the fuel.
It may be assumed that the quantity of air required
on the average will be 150 cubic feet per pound of
coal consumed, and this, after combining with the
gaseous and solid portions of the fuel, will produce
about 164 cubic feet of heated air and gases. The
heat of a furnace in a boiler may be taken as 1,000
degrees, and this will expand the air and gases to
about three times their previous bulk, making the
above
= 164 x 3 = 492 cubic feet,
the velocity of which, according to Dr. Ure, would be
36 feet per second, requiring a minimum area of flue
of 0-516 inch per pound of coal consumed per hour.
In practice, however, about 2 inches is the allowance in
the narrowest part of the flue, and 1*5 inches at the top
of the chimney per pound of coal per hour.
If a high-pressure engine requires the consumption of
6 Ibs. of coal per horse-power per hour, and is 10-horse
power, the total consumption per hour will be
6 x 10 = 60 Ibs. coal;
G 2
84 PRINCIPLES AND CONSTRUCTION
hence the least area of flue (that over the fire-bridge at
the back of the furnace) will be
60 x 2 = 120 square inches;
ditto area at the top of the chimney,
60 x 1 '5 = 90 square inches.
To ascertain the quantity of hot air which will be
evolved at any special temperature per hour, the fol-
lowing formula will serve : Let Q = Ibs. of coal con-
sumed per hour, n = volume of cold air required in
cubic feet per Ib. of coal, V = volume of heated gases
per hour, t = temperature in chimney
V = Q . n . (1 + 0-00365 t)
or, taking n as generally equal to 150
V = Q jl + 0-5475 *J
The comparative evaporative values of different kinds
of fuel may be found from the following table, which
has been compiled from the most reliable experiments ;
it shows the quantity of water in each case evaporated
from a temperature of 212 degrees by the combustion
of 1 Ib. of the fuel under experiment :
Name of Fuel. Water evaporated.
Oak seasoned 4-95
,, dried 5-53
Nut-wood . . . . . . 5-41
White-pine 5-41
Yellow-pine . . . . . 5*74
Coal, Welsh 12-24
Newcastle . . . .12-20
,, Wigan 10-15
,, Belgium 11-36
Durham . 12-49
OF MACHINERY. 85
Name of Fuel. Water evaporated.
Coke, good . ... 10-24
,, common 7-62
Anthracite, French . . . .11-36
Pennsylvania . . . 9-88
Peat 4-09
Such high results as these, however, are not obtained
in the actual working of steam-boilers in practice, be-
cause the circumstances under which the combustion
takes place necessarily are different from those attending
on an experiment.
There is a very noticeable difference between the
evaporative values of wood and coal ; it may, there-
fore, be interesting to ascertain whether this may be
accounted for by the difference in chemical composition.
As is well known, coal is a species of fossilized wood,
the most striking difference being in the loss of hydro-
gen and oxygen wood sustains in the transition from
the ligneous to the carbonaceous state ; these two
analyses indicate the difference in composition :
Constituents. Wood. Coal.
Carbon 49-1 . 82-6
Hydrogen . 6*3 .. 5-6
Oxygen . . 44-6 . . 11-8
100-0 100-0
In the wood all the hydrogen is combined with oxygen,
or nearly so, or, otherwise, with carbon in such manner
that its liberation requires as much heat as its subse-
quent oxidation will yield ; hence the theoretical evapo-
rative values would be per pound of fuel :
Wood = 0-491 x 15 = 7-36 Ibs. water.
86 PRINCIPLES AND CONSTRUCTION
Coal= 15 {82-6 + 4-28 (5-6 - 11-8)) = 15 Ibs. water,
the ratio being
15 =2-038
7-36
Taking the averages of wood and coal from the experi-
ments as recorded in the above table, the ratio is
5-408
= 2-104
which does not differ widely from that found theoreti-
cally.
From a comparison of practical with theoretical
values, a factor may be found to correct the latter so
as to more nearly approximate to the former, thus :
Theoretical number - - 15
=r* - = -- n - 1 - 1-, oo ^ = 1*817 divisor.
Experimental number - 11 '383
It is now necessary to consider the relations of the
dimensions of boilers to the proposed power. In the
first place, the proportion of heating surface to grate
surface and fuel consumed may be determined. This is
a subject which has been very fully investigated by
Mr. D. K. Clarke, with the following results. To
secure equal evaporative efficiency :
1. If the grate surface is constant, the quantity of
fuel consumed per hour should vary as the square of the
heating surface.
2. If the heating surface is constant, the quantity of
fuel should, vary inversely as the grate surface.
3. If the consumption of fuel is constant, the quantity
of fuel should vary as the square of the heating surface.
If C represent a constant depending on the type of
OF MACHINERY. 87
boiler used, then these three laws -will be embodied in
the formula :
Where Q = pounds of fuel per hour, h = area of heat-
ing surface, and a = grate surface, a Cornish boiler
will burn from 6 to 10 Ibs. of fuel per square foot of
grate surface per hour ; hence, taking the average duty
of Cornish engines at 80,000,000 ft. -Ibs. per 112 Ibs.
of coal, the rule for grate surface will be as follows :
Let the average consumption of coal be 8 Ibs. per
square foot of grate per hour, HP = horse-power,
G area of grate in square feet
HP
G = - nearly
3
the heating surface required for the proper absorption
of caloric would be, if S = heating surface in square feet,
all taken as horizontal
8 = 8-5 X HP
Vertical heating surface has only half the efficiency of
horizontal ; hence, all vertical surface taken from the
area found by this rule must be doubled; comparing
the two formulfe, the ratio of heating surface to grate
surface in the Cornish boiler is found to be
-^ = 8-5x3 = 25-5
Cr
or it will be accurate enough for practice to make the
heating surface 26 times the area of the grate surface
The value of C for Cornish boilers will be
88 PRINCIPLES A>T) CONSTRUCTION
An ordinary factory boiler will burn about 1 5 Ibs. of coal
per square foot per hour ; hence, if the engine is work-
ing with a consumption of about 5 Ibs. of coal per horse-
power per hour, the grate surface will be in the same
proportion as above, and also the heating surface ; but,
if an engine (condensing, for instance) be working at a
consumption of 3 Ibs. of coal
and
S = 8-5 x HP
Cr
= 8-5x5 = 42-5 (say 43)
Gr
hence the value of C for such boilers will be
'=*-' = --'
In locomotive furnaces the greatest quantity of fuel
is consumed per square foot of grate surface per hour,
varying, in fact, from 40 Ibs. to upwards of 100 Ibs.; but
this is, of course, due to the strong draught created by
the blast. The range being so wide, it would be useless
to give a special formula for grate surface, but the
following general rule may be found useful : Let F =
equal consumption per square foot per hour, / = con-
sumption per horse-power per hour
With some high-pressure engines the consumption
of fuel per horse- power per hour is very heavy, amount-
ing to 9, 10, or 12 Ibs. of coal, and this would give a
ratio of grate surface to heating surface as 1 to 1 1 ; but
OF MACHINERY. 89
past experience indicates that a mean between this and
the ratio for a Cornish boiler will give most satisfactory
results as regards evaporative efficiency ; the mean ratio
will be
As to the proper capacity for steam-boilers per horse-
power, there has been much conflict of opinion. Mr.
Fairbairn, after many years' experience, fixed upon
15 to 20 cubic feet as the proper allowance, after de-
ducting the space taken up by the flues ; but the late
Mr. Armstrong always maintained that 27 cubic feet
per horse-power should be allowed, one-half of this
space being for water, and the other half for steam.
No rule, however, can be laid down in regard to the
capacity of boilers which shall apply generally to all
types, for much depends upon the construction of the
boiler, the arrangement of the steam dome or chest,
and other incidental matters too numerous to mention.
The object in having plenty of steam space is to prevent
great fluctuation from occurring in the boiler pressure
every time steam is taken into the cylinder ; and also the
steam, if drawn off close to the surface of the water,
would be loaded with aqueous particles, which, being
deposited as water at the bottom of the cylinder,
cause much inconvenience, and even, in some cases,
accident. This passing of water over into the cylinder
along with the steam is called priming. When super-
heating arrangements are applied, this suspended
water is converted into steam, and the steam is then
called dry ; in this state it is much less liable to
condense in the cylinder, but it has the disadvantage,
if highly super-heated, of drying and rendering
inefficient the packings of the engine.
90 PEINCIPLES AND CONSTRUCTION
The super-heating of steam does not largely increase
its pressure, as so soon as all the suspended aqueous
particles are converted into steam, and it becomes dry,
it follows the law of permanent gases, and its expansion
is slow.
A very quick draught is not economical, as the
quicker the draught the greater the quantity of heated
air passing off, and the less time is allowed for the fuel
to abstract the oxygen from the atmospheric air ; hence,
any means which will so far cool the gases in the chim-
ney, after they have passed over all the heating surface
of the boiler, as to check the excessive velocity of the
current, and at the same time apply the heat abstracted
to some useful purpose, will effect some considerable
economy in fuel.
The waste gases from boiler furnaces commonly escape
at a temperature of from 400 to 600 degrees ; but a
considerable portion of this heat may be utilized, for,
by causing the products of combustion to pass through
tubes surrounded with the water intended to be supplied
to the boiler, they will yield up as much as 225 degrees
of heat to such feed- water. A fair allowance of feed-
water-heating surface is 10 square feet per horse-power.
A little reflection will show that it is easy to abstract
heat from the escaping gases by the feed-water when
none will any longer be yielded up to the water in the
boiler. The transmission of heat from one body to
another varies in rapidity as the difference of the
temperature of the two bodies ; hence the water in
the boiler takes up the heat quickest at the furnace
end of the flue, after which, the rate of transmission
gradually decreases as the temperature of the heat, air,
and gases more nearly approaches that of the water
and steam in the boiler, until, if the process is con-
OF MACHINERY. 91
tinued long enough, the difference will not be sufficient
to cause the heat to pass through the metal by which
the water is separated from the heated gases in the
flues.
If steam is being generated in a boiler at a pressure
of 60 Ibs. per square inch, the corresponding temperature
of the water and steam will be 293 degrees ; hence, if
the temperature in the furnace is 1,000 degrees, and
that at the end of the flues 400 degrees, the differences
of temperature will be for each place respectively,
1000 293 = 707 degrees
400 - 293 = 107
the ratio of the two differences being
ft
hence the rate of transmission of heat at the commence-
ment of the flues is nearly seven times that at the end
of the same ; or, in other words, one foot of heating sur-
face at the furnace end is equivalent in evaporative
power to seven feet at the chimney end of the flues.
The thickness of the metal of which the boiler is made
also affects the passage of caloric, hence the parts
which are heating surfaces should not be made unne-
cessarily thick. To return to the question of abstracting
heat by the feed- water from the gases leaving the boiler
flues, we find the difference of temperatures, if the feed-
water be at 60 degrees, to be
400 60 = 340 degrees
hence the feed- water surface will commence absorbing
heat half as fast as the most efficient portion of the
heating surface of the boiler, and this abstraction may
be continued until the water is heated up to 200 degrees,
or in some cases more.
92 PRINCIPLES AND CONSTRUCTION
The rapidity of the conduction of heat also varies
according to the metal through which it has to pass ;
thus the relative conducting powers of copper, brass,
and iron are as under :
Wrought-copper . . . . 100-0
Wrought-brass . . . . 96-6
Sheet-iron 41-5
While treating of furnaces, the subject of smoke con-
sumption may properly be dealt with. To consume
coal-smoke has been, and often is, said to be a matter
of ease, only requiring care to effect the object sought ;
yet it is remarkable that generally the smoke is not
consumed, although it is manifestly to the advantage of
the users of steam-power to utilise it as much as
possible, for smoke, properly so called, consists of a
great number of very minute and finely-divided
particles of carbon, which are carried up by the
ascending draught, only ultimately to fall again as soot
or " blacks " as soon as they come into cold or damp
air. This carbon of course has a certain calorific value,
and would serve to assist in evaporating the water in
the boiler. In order to ensure the combustion of the
smoke and gases not previously oxidised, a sufficient
supply of air must be furnished for their thorough
oxidation, the fire-bridge being a very good place to
supply it ; but its temperature must not be so low as
to cool down the unconsumed products of combustion to
a temperature below that at which they will burn, other-
wise the introduction of the extra quantity of air will
be worse than useless, as its sole effect will consist in
cooling the heated air and gases before they pass over
the heating surface of the boiler, thus lessening the
OF MACHINERY. 93
rapidity of the transmission of the heat, and in addition
to this, increasing the bulk of waste air, which, leaving
the chimney at a temperature higher or lower, accord-
ing to circumstances, . carries away a quantity of heat
proportional to the volume of air escaping into the
atmosphere.
It is very evident that, if the air could be kept in
contact with the fuel until all its oxygen was taken up
by the carbon and hydrogen of the same, a great in-
crease of economy would ensue, as was shown by expe-
riments with a plan patented by Moor and Shillitoe.
According to Moor and Shillitoe' s method of working,
instead of there being a free outlet from the flues into
the atmosphere, the combustion was carried on under
pressure, and the results obtained from some experi-
ments conducted at Manchester were in the highest
degree satisfactory.
The up-take from a portable engine-boiler was closed
by a valve lightly weighted, and the air required for
combustion was forced into the fire-box ; a very vivid
combustion was thus produced, accompanied by a great
saving of fuel. By using this mode of working, the air
is held in contact with the fuel until the latter has
absorbed nearly all its oxygen, hence a much smaller
quantity of air is required than that consumed in an
ordinary furnace, and the quantity of waste gases is
correspondingly reduced ; hence, also, the quantity of
heat escaping through the chimney. If, instead of
150 cubic feet of air, 50 per Ib. of fuel will suffice, the
quantity of heat carried off by the waste gases will be
greatly reduced. In combining with the gaseous and
solid parts of the coal the products of combustion
formed will be in amount about 64 cubic feet, whereas
in the ordinary way of managing the furnace it would
94 PRINCIPLES AND CONSTRUCTION
never be less than 164 cubic feet per Ib. of coal, and
very often amount to considerably more. Thus, by the
use of the patent furnace, the loss of heat by waste
gases is always reduced by about 60 per cent., and
generally by a much larger per-centage. Also, the air
being kept in contact with the fuel under pressure, the
oxygen in contact with the fuel is a much larger
quantity per cubic foot of air than when the draught is
free, hence the combustion is far more rapid, and of
necessity more vivid, than under ordinary circum-
stances, and being more vivid the furnace is heated to
a higher temperature, which favours the absorption of
heat by the water in the boiler. The combustion being
more rapid, the grate surface may be reduced to about
one quarter of that used with a free draught ; and as
the difference of temperature between the gases in the
furnace and the water in the boiler is increased, the
amount of heating surface may be proportionately
reduced ; in short, for a given amount of steam evapo-
rated per hour, the whole proportions of the boiler may
be very materially reduced, and a saving of upwards of
40 per cent, of coal will be effected and all the smoke
consumed.
It may be interesting here to give some idea
of the saving effected by letting into the furnace only
sufficient air to maintain the combustion. In the
ordinary case, 150 cubic feet of air are required per Ib.
of coal, of which 50 feet are sufficient to supply the
oxygen actually required for combustion. Of this air
there will be 100 cubic feet over and above that actually
required, and the specific heat of air, according to the
experiments of Delaroche and Bernard, is 0-267, that of
water being TOGO. Supposing the gases and products
of combustion to leave the chimney at a temperature of
OF MACHINERY. 95
400 degrees, the normal temperature of the air being
60 degrees, then the 100 cubic feet of air will have been
heated
400 60 = 340 degrees.
The weight of the air will be equal to about 8 Ibs.,
hence the number of degrees of heat lost, which might
otherwise have been transmitted to the water to be
evaporated, would be sufficient to raise the temperature
of one pound of water 213-6 degrees. There is good
reason, however, to believe that practically a much
larger quantity of air than that above mentioned passes
through ordinary furnaces.
It may at first seem unaccountable that a system
affording such beneficial results should not be generally
adopted, but this is attributable to the fact that circum-
stances prevented the inventors from introducing their
plan at the time when it was first brought before the
public, and since that the patent has been allowed to
Although the principle of combustion under pressure
has not been adopted in connection with the steam-
engine, yet it is practically in use in some classes of hot-
air engines Messer's, for instance, in which the piston
in the working cylinder is driven by the pressure of the
products of combustion issuing from a closed furnace.
The air requisite for combustion and to propel the ma-
chinery is forced into the furnace by an air-pump
worked by the engine ; after yielding sufficient oxygen
to the fuel the spare air and the heated gases are
passed through suitable valves into the working
cylinder. Some years back, when we examined one of
these engines, it was reported to be working very
economically, a result which is immediately referable to
the mode of working the furnace. In this case the coal
96 PEDfCIPLES AND CONSTRUCTION
was manifestly burned under a pressure somewhat in
excess of that driving the engine. The conclusions
then arrived at are that for the greatest economy of fuel
there should be
1 . A slow draught current,
2. A rapid and vivid combustion,
3. A minimum quantity of waste gases at a minimum
temperature ;
and, by means of the above method of working, these
conditions, impossible in the ordinary apparatus, may
be easily satisfied. If this process be carried to per-
fection, the escaping gases would consist simply of
nitrogen, carbonic acid, and probably a little sulphurous
acid ; and in the case of steam-ships, it might be dis-
charged into tjie water. Thus, also, is a means afforded
of raising steam of a very high pressure, as the in-
creased temperature of the furnace will allow of the
equally rapid transmission of heat to the water when
steam is being generated under a higher pressure, and
of course higher temperature.
During the last few years very strenuous efforts have
been adopted to introduce liquid fuels into use in steam-
boilers, and there has been much controversy upon the
merits and demerits of such a system. Undoubtedly
the evaporative value of such fuel, when properly
applied, is high, and it is compact for stowage (as in
sea-going vessels) ; but, on the other hand, in hot
climates there is a danger to be apprehended from the
accumulation in the tanks of quantities of inflammable
gases which may by some accident become ignited,
when, of course, all efforts at extinction would be
futile, and that such inflammable vapours would be
formed is certain ; for instance, if a vessel were to
start on a voyage with tanks full of hydro-carbon oils,
OF MACHINERY. 97
although there would be no danger so long as the tanks
remained full, but as soon as space was formed above
the surface of the oil inflammable vapours would begin
to accumulate, and more especially in tropical climates.
We are informed, however, that under the directions of
the Admiralty this subject is now being investigated, in
order to determine some means by which this appre-
hended danger may be obviated.
Where tried liquid fuel has given very good results,
both with stationary and marine boilers, the system
which appears to give the best practical results being
that invented' by Mr. E. H. Aydon. By this pro-
cess the liquid fuel is carried into the furnace by a jet
of steam acting through an appliance similar to the
Giflard Injector, now commonly used for supplying
steam-boilers with water.
In considering the circumstances under which the
combustion occurs, it is very desirable not to be misled
as to the chemical re-actions which take place, as some
people have thought that some decomposition of the
super-heated steam associated with the dead oil takes
place, which, if even it did occur, could not ultimately
affect the results, as the decomposed steam would yet, by
combustion, resume the condition of steam. In apply-
ing the "Aydon" system, steam is first got up in the
boiler by a coal fire, after which a thin layer is kept
merely to ensure the ignition of the oil spray scattered
into the fire-box by the steam jet. In the early part
of 1867 an experiment was tried at Lambeth on this
system, applied to a Cornish boiler of the ordinary con-
struction, of which the following is an account : The oil
was allowed to fall through a narrow orifice in a con-
tinuous stream (the worst kind of creosote refuse being
used) about one-eighth of an inch in diameter, at a
98 PRINCIPLES AST) CONSTRUCTION
rate of about three gallons per hour. With this con-
sumption the steam was maintained at a pressure of
from 32 Ibs. to 35 Ibs. pressure per square inch. The
amount of water evaporated was 10 cubic feet per 100
square feet of heating surface in the boiler. The cost
of creosote refuse was from 1 10s. to 2 per ton;
hence, taking the creosote used at Id. per gallon, the
cost of fuel burned per hour would be 3d., and the
work done was equivalent to that which would be
given by 56 Ibs. of the best Aberdare coals at 1 2s.
per ton, the value of which would be rather more than
6d. The evaporation of water, so far as it could be
determined from the experiments, amounted to 19-5 Ibs.
of water per Ib. of fuel consumed.
The composition of creosote is as follows : in lib. of
creosote there is
Carbon .... 0-775 Ibs.
Hydrogen . . . 0-080 ,,
Oxygen .... 0-145 ,,
hence the theoretical evaporative value of this creosote
will be
= 15 JO-775 + 4-28 (-08 - '^ 45 )| = 15-6 Ibs.
water per Ib. of fuel.
This, however, is the general analysis of creosote;
hence it must be concluded that the quality used in
trying the " Aydon " method must have been superior
to that of which the analysis is given, for, even if it
were admitted that the super-heated steam which enters
with the oil is decomposed, yet, for reasons given above,
this action could not ultimately affect the amount of
water evaporated.
OF MACHINERY. 99
The theoretical calorific value of petroleum may be
found from the following analysis :
Hydrogen . 12-5 = -125 Ibs. per Ibs. of oil.
Carbon . . 87-5 = -875
hence the evaporative value
= 15 j-875 + 4-28 x -125 j = 21-15 Ibs. water per
Ib. of oil.
The great economy of liquid fuel over coal is quite
evident from the above statements ; but it has been
further shown that a steamer making a round from
London to Rio Janeiro, Monte Video, and Buenos Ayres,
out and home, would actually effect a saving of 1,230
out of 2,235 by burning oil instead of coal.
We will now pass from the furnace and fuel to the
proportions of the various descriptions of boilers.
General rule for horse-power of toilers. Let HP=
horse-power, a = horizontal heating surface in square
feet, A = vertical heating surface in square feet, then
or let A = , then
8-5 . n
if, for instance, a = 100 feet and n = 4, then
Hp= 4X100 +100 = 14 . 7 horse . power .
8-5 X 4
TUBULAR BOILERS. For tubes having half their sur-
faces exposed to the heat (as in the Cornish and
H 2
100 PEDfCIPLES AIO) COKSTEUCTION
Manchester boilers), let I = length in feet, d = diameter
in inches, then
for tubes having their entire surface exposed to the
heat, it will be
30
To find the proper thickness for the outer shell of the
boiler to resist safely the internal pressure, the following
formula will serve : Let t = the thickness in inches,
p = internal pressure in pounds per square inch
above the atmosphere, r = radius of tube in inches,
8,000 Ibs. = the safe working tension per square inch,
allowing for wear for solid work, and 6,000 Ibs. for
rivetted work, then
Solid work
.
8000
Eivetted work . t = 2-^-
6000
The resistance of wrought-iron tubes to external or
crushing pressure has been experimentally determined
by Mr. Fairbairn, and the following formula, deduced
from the experiments, will give the proper thickness of
metal. Let t = thickness of metal in inches, I length
of the tube in feet; d = diameter of tube in inches, or,
if it be elliptical, the diameter corresponding to the
flattest part of the tube, p = the pressure in pounds
per square inch on the exterior of the tube, above the
atmosphere, then
161,200
If the tubes be very long they may be virtually
OF MACHINERY. 101
divided into shorter tubes by fixing in or round them
stout angle-iron or tee-iron rings.
Let there be a tube 30 feet long divided into three
parts by two rings, then the virtual length of the tube
will be 10 feet; let the diameter be 24 inches, and the
pressure of steam 30 Ibs., then the thickness of the tube
should be
In boilers having flat sides, such as the common
square marine-boiler, and the water space outside the
fire-box of a locomotive engine, it is necessary to use
stays, in order to prevent the sides from being bulged
out. In this case it is evident that the plates are under
the influence of transferable pressure ; hence the rule to
determine the thickness of such plates is found from the
general laws of the resistance of materials to that
description of strain.
Let ^7 = the pressure in pounds per square inch,
d =. the greatest distance between stays in inches,
t thickness of stayed plate in inches, then
t = 0-008 d \f~p
Let d = 10 inches, p = 25 Ibs.,
t = 0-008 x 10 /25 = 0-4 inch.
The stays supporting the plate are, of course, subject
to tensile strain.
Let a = vertical distance between stays in inches,
b = horizontal distance between stays in inches, p =
pressure in pounds per square inch on the stayed surface,
p = diameter of stays in inches, then
\/a b p
'*= -70-
102 PRINCIPLES AND CONSTRUCTION
Let a = 10, b 8, p = 25, as in the last case, then
If the vertical and horizontal distances are equal, the
formula will then become
The designs or types of boilers that have from time
to time been brought forward are almost innumerable ;
hence but a few of the leading forms will be noticed here.
The old waggon-shaped boiler, fired underneath, has
long been out of date, although a few of them may now
be seen in some parts of the country utilized as tanks.
These boilers were not intended to raise steam at higher
pressure than 4 Ibs. to 6 Ibs. per square inch, the steam
being then used only as a means of getting a vacuum, so
that the effect of the atmospheric pressure upon the
piston should propel the engine. The Cornish boilers
are now very generally used for large engines where
very high pressures are not required to be employed.
These boilers consist simply of a cylindrical shell with
flat ends, and a tube running from end to end through
the boiler. The ends require to be stiffened by means
of stays connecting them either with the shell of the
boiler or with the tube. These boilers may have the
furnace either placed inside the tube, or under the
bottom of the boiler, in which case the tube is used as
one of the return flues. Egg-ended boilers have a cylin-
drical shell, terminated at each end by a hemispherical
dome : they have nothing particular to recommend them,
and appear somewhat more liable to explosion than other
classes of boilers.
Multitubular boilers are those which have in them a
OF MACHINERY. 103
considerable number of small tubes through which the
flame and heated air pass from the furnace. The object
gained by this arrangement is that a large amount of
heating surface is obtained with a comparatively small
area "of flue, for whilst the sectional area of the tubes
decreases as the square of their diameter, the heating
surface diminishes as the diameter only ; hence, if the
total area of the tubes be constant, the amount of heat-
ing surface will vary as the number of tubes used to
make up such total.
In determining the number of tubes to be put into a
boiler, it requires care to be taken to follow a middle
course, for by putting in too many tubes they crowd
each other so that the steam cannot get away quick
enough from between them to allow the water to circu-
late round them as rapidly as is desirable, in which case
the evaporative value of the boiler is deteriorated, and
the tubes are liable to be very soon burnt out, because the
waterfails to take away from them the heat absorbed from
the products of combustion with sufficient promptitude.
About the worst case of crowding the tubes which has
come under our notice occurred in a French locomotive,
in which the space between the tubes was little more
than three-eighths of an inch ; but we have known of
cases in England where the evaporative efficiency of loco-
motive boilers which had been over filled with tubes was
actually increased by plugging up some of the tubes.
Vertical tubes in multitubular boilers may, however,
be put closer together than those which are fixed in a
horizontal or inclined position, as they do not so much
tend to retard the ascending and descending currents of
water as the latter, as these currents rise and fall
between the tubes instead of having to go round them.
Although almost all multitubular boilers use the tubes
104 PRINCIPLES AND CONSTRUCTION
as flues or passages for the heated air and products of
combustion, yet this is not the most advantageous mode
of construction ; it is better to have the water in the
tubes and the fire outside them ; but for a long time
makers were deterred from adopting this arrangement
on account of certain practical difficulties connected with
the circulation of the water. The superior strength of
boilers having water tubes highly recommends their use
in cases where very great pressures are required, for as
the strength of a boiler varies inversely as its diameter,
the relative strength of two boilers of the diameters D
and d, for the same thickness of metal, will be
.D
d
but as the larger boilers must be made of separate
plates rivetted together, this will practically become
1-5 .D
For actual strength let Craddock's boiler be considered ;
n this the water tubes are three inches in diameter, and
the metal is about one-eighth of an inch thick. From
one of the formulae for thickness we have for solid work
8000
8000 t
p = -
hence, in this case, the safe pressure per square inch on
the tubes will be
8000 x 0-125
p = = 666-66 Ibs. per square inch,
1*5
and the metal being thin will also favour evaporation
by offering a comparatively small resistance to the
OF MACHINERY.
105
transmission of heat from the products of combustion to
the water in the tubes.
Compare this with a cylindrical boiler, the shell of
which is 4 feet 6 inches in diameter and f ths of an inch
in thickness, being of rivetted work ; the safe pressure
in this case will be
p = 6000 2 X 7 - 375 = 83-3 Ibs. per square inch.
In the construction of tubular boilers care must be
taken to make the joints of the tubes perfectly sound,
for if a leakage occurs the metal will rapidly corrode
and the leak become worse ; a good and rapid circula-
tion of the water must also be ensured to prevent the
tubes from being burnt out.
Of tubular boilers, having water inside the tubes, pro-
bably the best is that invented by Mr. Edward Field,
and generally known as the " Field " boiler. The
tubes used hang
down into the
furnace, and may
be applied to va-
rious kinds of
boilers. A very
usual form of
this boiler is
shown in Fig.
34 : a is the fur-
nace, b the chim-
ney, c, c, water
and steam space,
d, d, the tubes
j
?ig. 34
I
a,
C
c
c
c
11
il
a
a
Jl
jl
tube-plate i, i, and hanging down into the furnace.
The detail shows a section of the upper part of one of
106
PRINCIPLES AND CONSTRUCTION
these tubes. Into the outer tube y, and reaching nearly
to the bottom of it, is dropped a smaller tube /, suppoited
at the top by a metal feather and funnel-
shaped deflector h. When the boiler is in
action a very rapid current circulates down
the interior tube and up outside of it, that
is, in the annular space between the interior
and exterior tubes. Without the deflector
h, Mr. Field found he could get no circula-
tion at all, and the result was that the water
was blown out of the tubes and the tubes 9
burnt accordingly, but with it the circulation
is perfect. The tubes are usually about
3 feet 6 inches long and 2J inches or 3J
inches diameter and th of an inch thick,
though, in special cases, they vary from
these dimensions. One of these boilers was
tried in comparison with a Cornish boiler, the particulars
being as under, both doing exactly the same work,
working at the same pressure, and with the same
evaporation of water per hour.
Cornish boiler, well set, with a good draught, and gene-
rally economical ; 4 feet diameter, 14 feet long, flue
2 feet 8 inches diameter, fire-bars 2 feet long, dura-
tion of trial 1 16 hours, consumption of coal 4 tons at
20s. per ton=8'24d. per hour.
"Field" boiler. Vertical, with descending flue 3 feet
7 inches diameter, 9 feet high, duration of trial
69 hours, consumption of coke 2 chaldrons at 16s.=
5'56d. per hour.
This gives for the evaporation per Ib. of coal in Cornish
boiler 5-79 Ibs. water, and for the same per Ib. coke
(the coke weighed 3,584 Ibs.) in "Field's" boiler
8-57,
OF MACHINERY. 107
which is greatly in favour of the latter, as the evapora-
tive value of coke is less than that of coal generally.
The saving in cost of fuel by the " Field" boiler was
39 per cent.
The heating surface of the Cornish boiler was 124 square
feet,
whereas that of the " Field" boiler was only 100 feet.
The usual proportions for the "Field" boiler are
10 square feet of heating surface, and 0'5 square foot
grate surface per horse-power.
A 15 horse-power "Field" boiler was tested to
ascertain its evaporative efficiency; it had then been
two years at work. It was an upright boiler, 4 feet
diameter and 10 feet high ; duration of trial 5 hours.
1,344 Ibs. of coke evaporated 11,022 Ibs. of water, or
8-2 Ibs. per Ib. coke. This, reduced to Ibs. water per
Ib. of coke evaporated from 212 degrees, would be
9-8 Ibs. The tubes were 2J inches in diameter.
In 1867 a Manchester boiler, 20 feet long, 6 feet
6 inches diameter, having two flues, each 2 feet in
diameter, was fitted with 270 tubes 1 foot long,
2 inches diameter, radially fixed in the flues. The
results of its trial were as follow :
Duration of experiment 46 hours, consumption of
Aberdare coals, at 20s. 6d. per ton, 3 tons, content of
feed- water cistern 99 gallons, quantity of feed-water
used 80 cistern-Ms, total quantity of water used
7,920 gallons, or 79,200 Ibs., =10-1 Ibs. of water evapo-
rated per Ib. coal from atmospheric temperature, which,
reduced to the boiling point, gives an evaporation of
12-3 Ibs. of Abater evaporated per Ib. of coal.
The results obtained from a "Field" boiler fitted
to a steam fire-engine show very strikingly the capacity
given by this mode of construction. The water and
108 PRINCIPLES AJtD CONSTRUCTION
steam space is entirely above the furnace, there being
no water space round it. The diameter is 3 feet 6 inches,
and the depth 2 feet 4 inches. The total height of
furnace and boiler 5 feet 2 inches. The length of the
tubes varies from 2 feet 3J inches to 1 foot 7 inches ;
they are 1 inch in internal diameter, 1-16 inch thick;
total length of tubes 797 feet ; heating surface
235 square feet (corresponding to a nominal horse-
power of 23 h.-p.) ; steam pressure 160 Ibs. per square
inch.
The engines which work without expansion have two
cylinders each 8f inches diameter, with 2-foot stroke,
making 100 revolutions per minute. Total weight of
machine 2 tons 18 cwt. The engine on trial sent a jet
210 feet high, discharging 1,200 gallons per minute;
allowing nothing as lost by friction and disturbances of
the atmosphere, this gives 76 horse-power as the useful
effect, yielding 1 horse-power for every 3 feet of heating
surface, which, be it remembered is vertical, and in
the old-fashioned boilers 17 square feet of vertical
heating surface would be allowed per horse-power.
The thinness of the tubes seems remarkable at first
sight, but they are amply strong, as shown by the
annexed calculation.
Let 8 = strain in pounds per sectional square inch of
metal, then
= '"
Showing ample strength. We have seen a portion of
one of these tubes which has for a considerable time
been in use, but it is not in the slightest degree worn
or deteriorated. The metal being thin, of course en-
hances the rapid transmission of heat.
Before concluding the present chapter it is desirable
OF MACHDfEEY. 109
to offer a few brief observations on the subject of boiler
explosions.
The theories which have been put forward to account
for the explosion of steam boilers are numerous, and
many of them extremely far-fetched, such as the elec-
trical theory and the theory which presumes that the
steam is first decomposed into its constituent gases,
oxygen and hydrogen, which subsequently recombined
with sudden and destructive violence. Instead of wan-
dering so far into the field of speculation, a brief con-
sideration of the plain facts under immediate observation
will occupy our attention.
In the first place, a great proportion of the boiler
explosions which occur are due to weakness in the
boiler, and such weakness may gradually be increasing
and insidiously rendering it unfit for the duty it has to
perform, unless a rigorous system of periodical examina-
tion be adopted. As was the case with the boiler of a
steam-tug which exploded on the Thames a short time
since, stays in the interior of the boiler may yield or
break and pass unnoticed until some catastrophe occurs,
and perhaps even then the original cause of the accident
may not be discovered, as all damage found in the boiler
may be attributed to the final explosion. Other kinds
of injuries may proceed unnoticed, such as corrosion
from the exterior through dampness of the boiler setting,
or the lodgment of water on the rivetted joints. Also
the joints of the boiler, where angle-irons are used, may
suffer burning from the heat not being taken up quick
enough by the water to keep the joint rings or angle-
irons at a sufficiently low temperature. If any part of
the furnace crown be left uncovered by water it will
become heated, and then being softened, will be forced
out of its normal shape by the steam pressure. Danger
110 PBINCIPLES AND CONSTRUCTION
is not to be anticipated by the sudden formation of
steam through contact with red-hot metal which has
been left uncovered, for, from the low specific heat of
iron, that quantity of caloric which will raise one pound
of water a given number of degrees will increase the
temperature of eight pounds of iron by the same amount ;
hence every pound of red-hot iron possesses but heat
enough in cooling down to 300 degrees to evaporate
one-tenth of a pound of water into steam ; hence,
assuming in a ten-horse boiler 150 cubic feet of steam
space, then, if the plate became red-hot to such an
extent that 50 Ibs. of the iron is so heated, only 5 Ibs. of
water would be evaporated ; and supposing the normal
pressure to be from 60 to 70 Ibs. per square inch, even
this comparatively large surface of iron becoming red-
hot would only increase the pressure by about one-fifth,
causing it to rise so as to range from 70 to 84 Ibs., cer-
tainly not enough to explode a boiler having a safe
working pressure of 60 to 70 Ibs. per square inch.
One of the causes of boiler explosions (which we
believe was first pointed out by Mr. Z. Colburn) rests
in the body of steam interspersed throughout the mass
of water, which, upon the pressure being removed from
the surface of the water, will in escaping tend to carry
up the whole body of water, and cause it to strike a
violent blow on the crown of the boiler. The pressure
of steam may easily be accidentally suddenly reduced,
as by the introduction of cold water, the sudden escape
of steam from the safety valve, or by starting the
engine, &c.
Over-pressure being put upon boilers, through the
carelessness or ignorance of those in charge, may also
be added to the causes of boiler explosions, but the
means of preventing this are obvious.
OF MACHINERY. Ill
The accumulation of scale in boilers is a source of
danger, inasmuch as, by obstructing the passage of heat
from the plates to the water (the calcareous matter of
which it consists being a very slow conductor), it allows
of the plates getting heated or burnt, in either case
weakening them ; and although many things have
been patented, and more proposed, to prevent scaling
in boilers, yet none of them appear to be satisfactory
enough to be generally adopted.
The precautions to be taken against boiler explosions
may be stated thus :
1. Always keep plenty of water in the boiler.
2. Never open the steam valve or safety valve sud-
denly.
3. Have one of the safety valves properly weighted
under lock and key, so that the attendant cannot over-
press the boiler.
4. If tolerably pure water cannot be obtained, have
the scale removed sufficiently often from the boiler.
5. Do not overstrain the boiler in the testing prior to
use (twice the maximum working pressure is quite high
enough for the test to be carried).
6. Have the boiler periodically examined by a com-
petent boiler-engineer.
If these precautions be borne in mind and taken,
there will be no danger of boiler explosions.
As regards the inspection of boilers, some years back
an attempt was made to organise a boiler association in
London, similar to that established some years since in
Manchester, but it did not succeed, and the undertaking
had to be abandoned almost before its existence was
made generally known ; this was in 1862, and it does
not appear that any attempts have been made since to
revive the plan in the metropolis, a matter to be
112 PEIXCIPLES AND CONSTEUCTION
regretted, because such an association, besides saving
manufacturers heavy losses, is also instrumental in
preventing accidents which but too often end fatally.
CHAPTER X.
WATEE-WHEELS.
WATER- WHEELS, although occurring of great number of
different designs, may be classified in four general
divisions, as follows :
Undershot wheels, overshot wheels, breast (or pitch-
back) wheels, and turbines. The motion of the first
class is obtained from the velocity of a running stream
of water which impinges against the floats of the water-
wheel. The second and third classes are actuated by
the weight of the water falling upon them; and the
fourth by reaction.
In this first place it is necessary to explain the laws
of liquid pressure and motion. Let h = the height in
feet of a column of water, p = pressure in Ibs. per
square inch at the base of the column, then, since one
cubic foot of water weighs 62*5 Ibs.,
p = 0-434 h
the pressure of a column of water 45 feet in height will
therefore be
p = 0-434 x 45 = 19-53 Ibs. per square inch.
FLOW OF WATEE THEOUGH OELFICES. If in a vessel
of water an opening be made at a distance, x, below the
level of the water surface in the vessel, then the velocity
of the water flowing therefrom will be the same as
OF MACHINERY. 113
would be acquired by a solid body falling through, the
distance x. This at first sight may appear somewhat
incomprehensible, but the following remarks may serve
to set the matter in a clearer light :
If any perfectly elastic body be dropped and unacted
upon by friction, it will, upon coming into contact with
another solid body, be compressed (by the accumulated
work within it) and rebound to the height from which
it descended, the accumulated work contained in the
body at the moment of contact being equal to the
weight multiplied by the height of the fall. If the
body be so controlled that it cannot rebound, but is
retained in its most compressed state, then, if it be sub-
sequently released, it will spring up to the height from
which it originally fell, by virtue of the accumulated
work within it. If the body be released by the removal
of the lower or supporting surface, the accumulated
work would be expended downwards ; and if the atoms
of the body be separate, it may be all expended in pro-
jecting one atom. If a quantity of water be poured
into a vessel, it will be compressed by its own weight to
some extent, although the amount may not be sensible,
and this compression will represent a certain amount
of accumulated work ; if this accumulated work can be
expended on one atom, it may produce motion propor-
tionate to the weight of the mass above such atom. Let
us suppose that an aperture is made in the vessel so
that the bottom layer of atoms of water may escape,
then will the whole mass above descend through a dis-
tance equal to the thickness of such a layer, and in
so doing will do work the same as would have been
done by the descent of one layer of atoms through a
distance equal to the height of the entire mass of water ;
hence the velocity of efflux of water under pressure will
114 PRINCIPLES AND CONSTRUCTION
be equal to that attained by a body falling the height
of the head-water producing such efflux.
Theoretically, if S = area of orifice in square feet,
h = head of water in feet, and Q = cubic feet of water
discharged per minute
Q = c. S V~h
c being a constant determined by experiment, replacing
it we have
Q = 297-6 S \/~h
and by transposition,
S = Q _
297-6 J h
h- <2 2
~~ 88565 7 76"7">S'
FLOW OF WATER OVER WEIRS. Applying the same
laws to the flow of water over weirs and notch -boards,
we have, if I = length of weir in feet, the other nota-
tions remaining the same as above
Q = 192-6 I \/H?
FLOW OF WATER IN CANALS, TROUGHS, &c. Let * =
sectional area in square feet, I = length of channel in
feet, c = wetted perimeter in feet, Y = velocity in feet
per minute
V = 774-6 A/-
and for the quantity discharged
FLOW OF WATER THROUGH PIPES. The gravitating
force which causes the flow of water in pipes evidently
varies as the head of water divided by the length of
OF MACHINERY. 115
pipe through which the water has to flow ; hence, if
h = head or height of water in feet, and I = length of
pipes in feet, the accelerating force will vary as
h
~J
The resistances are of a frictional character, and are re-
presented by the following formula : Let v =. velocity
in feet per second, C = circumference of the pipe, 8 =.
sectional area of the pipe, and c = a constant to be deter-
mined by experiment, then the resistances
= V* X ~ X C
o
and as action and reaction are equal and opposite, the
accelerating force must be equal to the resistances ;
hence, if d = diameter of pipe in feet,
hence,
- = 4x|x,
Let Q = the discharge in cubic feet per minute, then
Q = v X 0-7854 d 2 X 60
ff = $ x 60
0-7854 . d* . 60
From Smeaton's experiments the constant c was found
to be = -^^ ; hence the above formula becomes
Q = 2356 y1. x
or if D = diameter of pipe in inches,
I 2
116 PRINCIPLES AND CONSTRUCTION
The following coefficients may be found useful in
practice :
To reduce cubic feet to gallons multiply by 6 '25
,, ,, pounds ,, 62-50
,, gallons to cubic feet ,, 0-16
pounds 0-016
There are two methods of action by which water
impresses motion and imparts power to water-wheels,
either by its weight pressing on the wheel, or by impact
of flowing water against float-boards, the work done
being due to the vis vivd of the moving water ; some-
times water acts in both ways at once, the work done
being partly due to the weight, and partly to the
vis vivd of the water. In any case, if the water is
acting by weight, and h = difference of level of water
at its point of supply to the wheel and at its point of
discharge, and Q = quantity in pounds of water falling
per minute, the power theoretically is
33000
or if v velocity of water per second,
2,125,200
but of course the actual work done is much less than
this, being diminished by friction and loss of water.
UNDERSHOT WATER-WHEHL. The undershot water-
wheel is usually made with floats placed radially, or
curved slightly backward, so as to get free of the water
in leaving the tail-race. These floats may be so curved
OF MACHINE Y.
117
that the water does not act by direct impact, but by
pressure, as shown in
the arrangement of Fig. 36.
Fig. 36 : a is the shaft
carrying the wheel of
which c d is the peri-
phery carrying the
curved floats e e; a b
is the bottom of the
wheel-race, and it will
be observed that the
water comes tangenti-
ally and without shock
upon the wheel; the
sides of the race should fit tolerably close to the wheel
to prevent loss of water. A clearance of about one inch
is sufficient.
If the wheel were moving at the same velocity as the
water it would receive no pressure from the latter, and
if it were held still it would receive the greatest amount
of pressure; but being at rest would give off no work or
power, hence there is some relation intermediate between
these two conditions existing between the velocities of
the wheel and water which will produce a maximum
effect. The less velocity that the water leaving the
wheel has the more work is being done, as if H and h
represent the virtual heads to produce the velocities
V and v before and after the water acts on the wheel,
the work done will vary, as
Q [If -h\
64-4 64-4
varies as J v 2
118 PRINCIPLES AND CONSTRUCTION
and it is evident the smaller v is the greater will be the
amount of work done.
It has been found that undershot water-wheels give
as good a coefficient of useful effect as can be obtained
when running at half to one third the speed of the
water propelling them.
Let V = velocity of water in feet per second before
acting on the wheel,
v = velocity of water in feet per second after
acting on the wheel,
Q = quantity of water passing wheel in pounds
per minute,
the other notations remaining as above, then the horse-
power will be
where c = the coefficient of efficiency, hence
_ Q.e
33000 I 64-4
2.
2,125,200
F 2 - v-
but for falls under 6 feet c = from 0-33 to 0'4, hence
the rule becomes practically,
HP ( F 2 v 2 }
6,440,000 I j
but the wheel be so designed that v = o, as should be
the case to obtain the greatest economy, we have
Q. F 2
HP =
6,440,000
OF MACHINERY.
119
These are for radial floats, but if curved floats be used
the value of c = 50 to 60, hence the above formulae
become
TTTt ** ( TTZ ..2 I
and if v = o
4,000,000 I
Q
4,000,000
Fig, 37.
OVERSHOT WATER-WHEELS. Overshot wheels are
principally worked by the weight of the water in the
buckets of the wheel, which weight being always on
one side of the wheel causes it to revolve ; if, how-
ever, the water has any velocity, which by impact
assists in moving the wheel, the virtual head corre-
sponding to such velocity must be added to the distance
through which the water passes in acting on the wheel.
A, Fig. 37, is
the axis of an
overshot water-
wheel b, b, the
buckets to catch
the water from
the pen-trough
c, which sub-
sequently flows
out as at e into
the tail-race d.
Let h = the
height of the
water in the
pen-trough above that in the tail-race, and Q = the
120 PKINCIPLES AND CONSTKUCTION
quantity of water discharged in pounds per minute, then
the horse-power will be
Q.h.e
33000
but for overshot wheels c = 0*6, hence
Q.k
SP-
55000
The duty done by overshot wheels will to some consi-
derable extent depend upon the form and size of the
buckets, which should be arranged so as to avoid as
much as possible the too early discharge of water from
the descending buckets at e. When the buckets have
openings, as shown at /, they are termed ventilating
buckets. This form has come much into use of late. The
buckets should be designed of ample size, so that they
may not be more than two-thirds filled with water. If
Q, = quantity of water in Ibs. per minute, N = number
of revolutions per minute, n = number of buckets on
wheel, then practically the content of each bucket
should be
Q
C =
62-5 . N .n
the result being given in cubic feet. In the case of the
undershot wheel, the force acting on the wheel might
be considered as acting upon the shaft with a leverage
equal to the mean radius, that is, the radius to the
centre of the float-board, but such is not the case with
the overshot wheel. Supposing all the buckets to be
full, the whole weight of water may be regarded as
acting at its centre of gravity, which is distant from the
centre
0-636 r
OF MACHINERY. 121
r being equal to the mean radius at which the buckets
are placed.
To find the force or pressure exerted at the periphery
of a spur-wheel of which D = diameter, and fixed on
the water-wheel shaft, we have W = weight of water
in buckets in Ibs., p = pressure
1-272 . r
- W
1)
If Q = quantity in Ibs. discharged per minute, the
other notations being as above
for c being a constant to allow for loss by the spilling of
water out of the buckets, hence the practical formula
will be, neglecting the friction of the shaft, which is
about 5 per cent. Q.^g Q
~N~
whence, 0-572 . Q . r
* = N.D.
As regards the speed of overshot wheels, it may be
observed that from 4 to 6 feet per second is very good in
the results yielded, this velocity being at the periphery
of the wheel.
Let D diameter of wheel in feet,
S velocity of periphery in feet per second,
JV = number of revolutions per minute
8 = JV. D . 188-5
*=?
188-5. .AT
jr= s -
188-5 . D
122
PRINCIPLES AND CONSTRUCTION
hence, if S _ 5 feet,
D-
1
37-7 N
N r=
37-7 . D
BREAST OR PITCH-BACK WHEELS. These wheels are
somewhat similar in their action to overshot wheels,
only the supply, instead of coming over the top of the
wheel, is poured at some point lower down, as at g,
Fig. 37. These wheels give a very good result. They
are divided into two classes, high and low breast
wheels, according to whether the water comes upon the
wheel above or below the centre. The power of the
wheel may be determined by the formula
HP-
Q.h
44,000
Fig. 38.
TURBINES. Fig. 38
shows a horizontal
section of a turbine
of modern construc-
tion. This wheel is
fixed horizontally ;
that is to say, with
the axis vertical. A
is the centre of the
wheel where the
supply of water is
brought to it, b, b.
fixed guides which
lead the inflowing
water into the most
suitable direction to impinge upon the vanes c, c, in the
moving rim D. Not only is this wheel driven by the
impact of the water against the floats or vanes, but also
by the pressure or reaction of effluent water on such
OF MACHINERY. 123
vanes. If the wheel be properly constructed the water
as it leaves should have been deprived of all motion,
having given up its vis vivd to the turbine, hence the
peripheral velocity of the wheel should be equal to that
due to the head of the water under which it is working.
Let D = diameter of wheel in feet,
h = head of water in feet,
JW = number of revolutions per minute,
v = peripheral velocity per second, then
= / 64-4 h
but
3-1416 . D . N
60
hence,
153-2 1
N =.
D
For example : Let h = 20 feet, D = 2-5 feet.
N = = 684-8 revolutions per minute.
2i'O
If Q, = Ibs. of water passing through turbine per minute
then the power is
33,000
For turbines c varies from 0-6 to 0-8, so for the better
class of wheels taking the last constant,
4,125
These wheels are exceedingly valuable for neighbour-
hoods where there are high sources of supply; they
will work well either in or out of water.
124 PRINCIPLES AND CONSTRUCTION
Fig. 39 illustrates Whitelaw's turbine or reaction
wheel viewed in plan. This wheel has two arms a, a,
revolving about a centre -p- g Q
A, the water being sup-
plied through this centre.
As in the last case, the best
peripheral space is
v \/ 64-4 h
the water leaving the tur-
bine without motion. The
arms are formed in the shape of an Archimedean spiral.
The proportions of the machine may be determined by
the following formula using the same notation as
above
33,000
but c = 0-74 to 0-78, hence, assuming its value as 0-76,
we have
Let w = width of each discharging orifice, and D =
diameter of machine, N = number of revolutions per
minute
135 . HP
1000 h </~h
Width of each arm . . . = 4 w
Diameter of machine . . = 50 w
,, central opening . = 10 w
149-43 i/T
OF MACHINERY. 125
VOKTEX WHEEL. A vortex wheel is in construction
similar to a turbine, but instead of the water being sup-
plied at the centre and flowing outward towards the
periphery of the wheel, it is supplied at the outer edge
of the wheel and flows inward towards its centre.
Professor Thompson's vortex wheel gave an efiiciency
equal to 75 per cent, of the theoretical quantity of
work, hence the formula for power will be
HP=
44,000
It seems desirable, before leaving the subject of tur-
bines, to explain the principles upon which the opera-
tion of reaction machines in general depends.
Let A, Jl, Fig. 40, be a horizontal section of a hollow
arm capable of revolving about an axis at A through
which water or other
liquid is supplied to the ,
arm. So long as the
arm is perfectly closed
no motion will ensue,
because the pressure of
the liquid acts equally
on each side of the hollow arm, hence has no tendency
to cause it to revolve in either direction about the axis A.
If, however, an aperture be made near the end of the
arm as shown at a, then the pressure on the other
side of the arm at c is unbalanced over an area equal
to that of the opening a, and there is a tendency to cause
the arm to revolve in the direction of the arrow ; the
force theoretically would be found as follows : Let =
area of orifice in square inches, I = length of arm from
centre of orifice to centre A in feet, p = pressure of
126 FBDTCIPLES AJTD CONSTKTICTIOW
liquid in pounds per square inch, M = moment of force
about A
M = p x 8 x I
If the machine be moving at the most economical
velocity, the water will simply fall from the orifice a,
being, as it were, left behind by the revolving arm by
virtue of its inertia. The disadvantages of this ma-
chine when used with light fluids, such as gas, air, or
steam, are so great as to quite preclude its application
in connection with such sources of power, but it answers
admirably when used with non-elastic fluids. That a
very high result is got is evident from the fact that
turbines have actually yielded as much as 78 per cent,
of the total work theoretically to be got from the water
used in driving, which is very good considering what
has to be deducted on the score of friction of the bear-
ings and friction of the water in the pipes and guide
curves of the machine.
Another action of the water has, however, to be con-
sidered that is, its angular pressure on the vanes of
the turbine.
Let a, Fig. 41, represent one of
the guide channels of a turbine, b
being one of the cells comprised
between two vanes of the turbine
ring, of which c is the outer and
d the inner ring. It is evident
the water is delivered on the
vane tangentially to d. But when the guides are
radial its mean velocity will be
= i / 64-4 h = 4-01 |/ A
and the velocity of the periphery of the wheel
= 8-02 t/T
OF MACHINERY. 127
hence the relation between x and y will be
x = 2y
in order that the water may reach the periphery de-
prived of all vis vivd and leave the wheel radially.
In the case, however, of curved guides, the direction
of the water being tangential to d, it will travel in a
direction mid-way between radial and tangential in
giving up its energy :=
KEGULATION OF POWER OF WATER-WHEELS TO SUIT
VARYING AMOUNTS OF EESISTANCE. The amount of
power given off by a water-wheel of any description
can of course be regulated by adjustment of the quantity
of water supplied to it, which may be determined either
by valves or by sliding sluices in the pen-trough, and
such valves may be under the control of any ordinary
conical governor, which will regulate the supply of water
in the same way that it does the supply of steam to the
steam-engine.
Other kinds of governors may of course be used if
thought desirable, but the simplicity and durability of
the apparatus commonly used greatly recommend its
adoption, and although, under different loads, the speed
will not be mathematically uniform, yet the variations
of velocity are not sufficiently great to affect practically
the working of the machine.
One great advantage possessed by water-wheels over
steam-engines may here be mentioned : it exists in the
constancy of the dynamic effort which causes the revo-
lution of the shaft. As is well known in a single-
cylinder engine, the moment of force about the main-
128 PELNCIPLES AND CONSTRUCTION
shaft varies from the maximum when the piston (work-
ing without expansion) is at half-stroke to at the dead
points, and when expansion is used there are more
variations of force, all of which have to be equalised as
much as possible by the use of a heavy wheel.
If, however, a water-wheel be the prime mover, these
irregularities do not occur, and so long as the supply of
water is maintained the moment of pressure about the
main-shaft of the wheel is regular and uniform through-
out each revolution, a matter of some considerable im-
portance where delicate processes are being effected.
The dimensions of the arms, &c., of the wheels may
be determined from the general formulee for strengths
already given.
CHAPTEE XI.
PUMPS AND OTHER HYDRAULIC MACHINES.
THE ordinary form of pump is too well known to
require any special description, but those used for pur-
poses dealing with large quantities of water require
particular attention paid to their details.
To find the quantity of water discharged by any given
single-acting pump :
Let Q = quantity of water discharged in gallons per
minute,
d = diameter of piston in inches,
s = stroke of pump in feet,
n = number of strokes per minute, then
29-4
OF MACHINERY. 129
Thus a plunger pump attached to a Cornish engine in
London has a diameter of 50 inches, stroke 11 feet,
number of strokes per minute 6
Q, = 29 = 5612-2 gallons per minute.
The following formula will give the power required to
work a pump, exclusive of the friction of the parts :
Let h = height of lift in feet, the other notations
being as above. The work done in one minute is
evidently (as 1 gallon weighs 10 Ibs.)
10 x n . s . d z . h
29-4
hence the horse-power to work a pump (excluding
friction, which may be taken at 5 to 10 per cent.,
according to the description of pump,) will be
n . s . d z . h
97,020
with the pump referred to in the last case the lift is
100 feet, hence
In very large pumps, such as the one just referred to,
common butterfly or clack valves could not be used, as,
from their not closing until the column of water begins
to return, there is a great concussion in shutting; at
some times as much as from 10 to 15 per cent, of the
water is lost through the delay in the valves closing,
hence, amongst others, the double-beat valves applied
130
PRINCIPLES AND CONSTRUCTION
by Harvey and West have been much used. One of
these valves is shown in
section in Fig. 42. A is
a pipe guarded by a valve
at the top, a, a, and b, b,
are the seatings which
carry the valve c c. When
this valve lifts the water
flows out over both seat-
ings in the direction of
the arrows.
Now it is evident in this arrangement that this valve
is heavier in proportion to its annular area than is the
common valve in proportion to its whole area, hence the
former, at the termination of the stroke of the pump,
falls through the column of water at once instead of
waiting to fall with the water. The pressure requisite
to open such a valve may be found in the following
manner :
Let p = pounds pressure per square inch requisite to
open the valve,
w = weight of valve in pounds,
a = area of valve in square inches against which
the water acts, then
w
* = ^
let w = 100 and a = 80,
i on
p = = 1-25 Ibs. per square inch.
In large pumps the work done in lifting the valves
becomes an item worthy of notice in estimating the
power lost by friction, &c.
OF MACHINERY. 131
Let / = lift of the valve in inches,
w = weight in pounds of both valves,
n = number of strokes per minute,
P = power absorbed by two valves (suction and
discharge)
v.l
P =
396000
Let each valve weigh 1,800 Ibs., and have a lift of
7 inches, then the number of strokes being 6 per
minute,
6 x 3600 X 7
P = 396000 = ' 38 hor8e -P wei> >
which would probably amount to about 3-5 per cent, of
the whole frictional resistances.
In the construction of such pumps as those referred
to, the suction and outlet pipes should, where practicable,
have a diameter equal to that of the pump plunger or
piston, in order to reduce the friction to the lowest
possible amount.
HYDRATOIC KAM. An ingenious apparatus known as
the hydraulic ram is shown in Fig. 43 ; its object is,
where there is a great supply of water with a moderately
high fall, to cause a
certain part of the Fi 9- 43 -
supply to be forced
up into a cistern by
the flowing away of
the greater bulk of
the supply: a is an gasg^^^
air-vessel, from which
a delivery-pipe e pro-
ceeds to the cistern. 4 is the supply-pipe leading into a
K 2
132 PRINCIPLES AKD CONSTKUCTION
chamber e, whence the water flows away through a
valve d until it acquires momentum enough to shut the
valve d; the sudden check thus put upon the flowing
water causes it, by virtue of the work accumulated in
it, to open the valve / and force a portion of water
into the air-chamber a, whence it passes away through
the delivery -pipe e, after which the valve d again opens
by its weight.
The velocity to be acquired by the water in order that
it may close the valve d, must be somewhat in excess
of that which it would receive from a head that would
give a pressure equal per square inch to the weight of
the valve d.
Let w = weight of valve d per square inch multiplied
by 1-05,
I = length in feet of supply-pipe,
a = area in square feet of supply -pipe,
v = velocity of water in feet per second,
h = corresponding head of water,
Q = water raised in foot-pounds, then
h-
"
v = 12-15 yV
the quantity of water in the conduit-pipe in pounds,
I X a x 62-5 = q
and the accumulated work in this will be
hence,
Q = 144 . I. a . w .
Let the weight of the valve d per square inch be
0-25 Ibs., then
w = 0-25 X 1-05 = 0-262 Ibs.
OF MACHINERY. 133
Let a = 0-3 square foot, and I = 50 feet, then
Q = 144 X 50 X 0-3 X 0-262 = 565'9 ft.-lbs.
but this has to be reduced by a coefficient, as there
exists a loss due to the shock of the water and the cur-
rents created thereby.
A general coefficient cannot with confidence be given,
as so much will depend upon the design of a ram, for if
the passages are properly curved much better results
are obtained than if they be left square. It is evident
that by means of this machine a proportionately small
quantity of water can be raised to a level above that
whence it is supplied. Amongst other similar things
for raising water may be mentioned the application of
water-wheels working pumps.
HYDROSTATIC PRESS. The general arrangement of
the hydrostatic press has been described in Chapter iii.,
but the mode of calculating the power of the complete
machine is not there given. Usually the hydrostatic
press is fitted with two plunger pumps, one of larger
diameter than the other. The largest one is first used
to bring the ram of the press up to its work, when the
smaller one is employed to get the highest pressure.
Let P = the greatest pressure in tons,
D = diameter of ram in inches,
d == diameter of small pump in inches,
I = length of pump-handle or lever from point
of application of power to the fulcrum,
L = distance between fulcrum and axis of small
pump,
/ = force in pounds applied to pump lever, then
P = 2240 . d* L
134 PRINCIPLES AND CONSTRUCTION
Let D = 10 inches, / = 50 Ibs., I = 40 inches, d =
1 inch, L = 3 inches, then
The thicknesses of the pumps and cylinders, &c., may
be calculated from the general rules already given, but
great care should be exercised in order to ensure the
supply of good castings, as a cylinder cast with bad metal,
eyen if strong enough to sustain the pressure, will
allow the water to sweat out through its pores, thus
causing the pressure to be lost, an important difference
in some trades where goods are left in the presses
all night.
The tables of presses are calculated as beams to resist
cross strain, and ample strength should be allowed them,
as it not unfrequently happens that they get unfairly
strained through twisting or unequal stress coming
accidentally upon them.
HYDRAULIC LIFTS are in principle similar to the
hydrostatic press, but, being used for raising weights,
they have a greater stroke, and are usually worked by
a head of water supplied from an elevated tank or other
convenient reservoir.
Let W = greatest weight in pounds to be lifted,
D = diameter of lift-ram in inches,
h = height in feet of water supply above the
highest point to which the lift is designed
to work
Let W = 2000, h = 30
/
D = 1-71 A/ = 13-88 inches.
OF MACHINERY. 135
WATER-PRESSURE ENGINES. In some places engines
somewhat similar in general construction to steam-
engines, but worked by the pressure of water, are used.
The great difference in the two kinds of engines con-
sists in the fact that, whilst the steam-engine is worked
by a very compressible and elastic fluid, the one now
under consideration receives its motion from a liquid
practically incompressible, a quality which very mate-
rially modifies the arrangement of the valve-gear.
The water being incompressible, it follows that the
exhaust or outlet valve should remain open until the
completion of the stroke, as otherwise the piston would
be stopped by the confined water, or the machine
strained or broken, The most convenient valves for
these engines will be either equilibrium puppet-valves
or piston- valves, opened and closed by means of tappets
or cams. The speed of these engines is necessarily slow,
the usual velocity of the piston being from 3 to 6 feet
per second. The available pressure will be that pro-
duced by the head of water minus the head due to the
speed of the piston.
Let h = head of water in feet, H = ditto due to
velocity of engine,
V = velocity of piston ,in feet per second, p =
pressure in pounds per square inch on
piston
p = 0-434 JA - H\
H = ^l
H = ~^>
but if V = 6 feet per second,
p = 0-434 h 0-242
136 PRINCIPLES AND CONSTRUCTION
hence, if the total head were 30 feet, the effective pres-
sure would be
p = 12-778 Ibs. per square inch.
If the valves be balanced the friction of the machinery
may be taken at 6 per cent, of the effective power;
hence, if P = pressure per square inch available for
useful work,
P = 0-94 j 0-434 A 0-242 \
= 0-408 h 0-227
This, of course, only applies to the best-constructed
engines having but little friction in the water passages
leading into the working cylinder. The thicknesses of
the cylinder and pipes may be found from the rules
given in Chapter vii.
The horse-power of a water-engine may be deter-
mined as follows :
Let d = diameter of piston in inches, v = velocity of
piston in feet per minute
nrp _ h v '785 d 2 . Q-434 . e
33,000
taking c the constant as 0'8,
h . v . d* .
HP =
122,222
ARRANGEMENT AND PROPORTIONS or YALVES AND
WATER PASSAGES. Pig. 44 represents a piston-valve
arrangement, the principle of which is that the pressure
of the water acts between two pistons of equal area
fixed on the same stem or piston-rod, hence it has no
OF MACHINERY.
137
Fig. 44.
tendency to move them in either direction, the pres-
sure on one piston
being balanced by
that on the other,
so that the two to-
gether form a per-
fect equilibrium
valve, which re-
quires no force to
move it except that
necessary to over-
come its friction.
The pistons may
have metallic pack-
ing.
a a is the supply
or pressure pipe
leading from the
reservoir to the
engine, and discharing the supply of water into the
valve-case I; c, c, are the two pistons fixed on the
rod b to constitute the valve ; d, d, are exhaust
passages leading into the waste-pipe e e, into which
the water flows after doing its duty in the work-
ing cylinder, which is in this case supposed to be
double-acting ; f and g are passages leading to opposite
ends of the cylinder ; i is a fixed pin or stud, on which
a lever moves connected with the valve-rod h ; II is a
tappet-rod carrying two tappets, one of which is shown
at k, and these, acting on the horns j, move the valve
at each end of the stroke. In the position of valve
shown by the full lines the water is flowing into the
cylinder through g and out through /; but, if the
pistons be moved to the position shown by the dotted
138 PRINCIPLES AND CONSTRUCTION
lines, the reverse occurs. In some cases an auxiliary
valve-case and pistons are used to move the main
valves, but this, of course, incurs an extra consumption
of water.
It is now necessary to determine the area of the
water passages, which will be done assuming that they
are curved so as to offer the least possible resistance to
the passage of the water. From the formulae for flow
of water through pipes, in the preceding chapter, we
have
h o C
T = ** X ^ x .
Let Q = cubic feet discharged per minute, and D =
diameter of working cylinder in feet, = speed of
piston in feet per second
Q = 60 . a . 0-7854 D z
but
Q = 60 . v . S
s . 0-7854 D 2
but
\/ f X X
hence
*. 0-7854 .
0-617. <s 2 .D 4 h S
- - = * - X C
therefore
3
16200 h 25-3
_ 3 /s*.v*.T7c _ i 3 /s 2 .z> 4 . iTc
V 16200 h = 25-3 V h
OF MACHINERY. 139
But the speed of the piston should for economy be
= 3 feet per second,
and h will be the head corresponding to the difference
of pressure in the pressure-pipe and cylinder :
or,
hence this quantity is constant, and may be replaced
in the formula making it, with sufficient accuracy for
practice,
S = 0-16 V-D 4 ^- C
if the passages be square, however,
C = 4 \/~S
hence, in this case,
S = 0-19 \/~Wl
Let the length of the water passage be 5 feet, and the
diameter of the working cylinder 9 inches, or 0'75 feet,
then
= 0-225 square feet = 32 -4 square inches,
hence the inside length of one side of the water passage
should be
= 5-7 inches nearly ;
the areas of the valves will of course be not less than
that of the water passages, and the area of the exhaust
passages and waste-pipe should be larger.
140 PRINCIPLES AND CONSTRUCTION
If the above speed of piston and square passages be
adopted as a general practice, the following formula will
give the breadth of the passage :
Let b = breadth in inches, and D = diameter of
working cylinder in inches,
I = 0-714
which, with the above figures, will become
\/ 9 x 5 = 5-7 inches,
the same as in the last formula.
WATER METERS. In some instances water is supplied
to consumers by quantity instead of on the principle of
rating, and in such cases it is evidently necessary to
have some convenient means of measuring the quantity
so supplied.
This has been most commonly effected by small ma-
chines on the principle of the turbine or reaction wheel,
the number of revolutions of which registers the qantity
of water transmitted. Some forms have been made like
water-pressure engines, the number of strokes of the
engine registering the amount of water passed through
the meter. If well constructed the latter class are most
certain as to accurate measurement, but the former
possess the advantage of allowing an uninterrupted cur-
rent of water to pass through, which of course the latter
cannot do, as the inlet and outlet valves must alter-
nately be opened and closed to allow each meterful to
be discharged and the registering vessel to be refilled.
We have, however, seen and tried meters on the turbine
system through which water was obtained without so
much as one quarter of it being registered.
OF MACHINERY. 141
CHAPTEE XII.
MARINE ENGINEERING.
ALTHOUGH the subject of marine propulsion may pro-
perly be regarded as one requiring separate treatment,
yet, so far as proportioning the power to the resistances
to be overcome, and correctly arranging the dimensions
of the propelling machinery, it may be dealt with in
this chapter it being understood that the question of
the form of lines will not be discussed, it being assumed
in formulae for ascertaining the power requisite to pro-
pel a given vessel that its lines are trochoidal.
The resistance to the motion of a vessel passing
through the water is caused by the friction of the water
against the sides of such vessel, the same as in a pipe
the resistance to the flow of water is due to friction. In
the case of a vessel the distance through which the
resistance is overcome varies, as
v for a given time, v being = to velocity of motion in
feet per second.
Also the number of atoms moved in a given time varies
as v, and the velocity with which they are displaced
varies as v also, hence the sum of the frictional resist-
ance varies as
' c s
Filling in the constants found by experiment, we
have the following formula for indicated horse -power :
Let L = length of ship in feet at water-line,
Cr = mean girth under water,
v = velocity in feet per second,
142 PRINCIPLES AND CONSTRUCTION
Let L = sum of lengths of bow and stern in feet,
B = greatest breadth in feet
HP = L ' & ' 9 * l ' 9 ' 87 ' Z}
95500 ( L , 2 )
or if L ; = Z,
*-&[*?*]
For example: Let L = 160 feet, G 15 feet, B
16 feet, Z, = 160 feet, v = 25 feet per second
horse-power.
COMPARATIVE EFFICIENCY. To find the comparative
efficiencies of two or more vessels, criterion numbers
may be obtained from the following formula, based upon
the laws of fluid resistance :
Let C = the criterion number,
P = indicated horse-power of engine,
D = displacement,
S = speed
THICKNESS OF IRON SKINS. The nature of the strain
to which the iron skins of ships are subjected by the
pressure of the surrounding water is evidently of a
transverse nature, and to determine the thickness to
withstand this pressure, the following formula, based on
the laws of resistance to transverse strain, and the inten-
sity of liquid pressure under given heads, may be used.
The wrenching strain due to the yielding of the ship is
supposed to be carried by the framing.
OF MACHINERY.
143
Let t = thickness of the plate in inches,
I = distance between ribs in feet,
d = depth of immersion in feet
CHAPTEE
MATERIALS USED IN CONSTRUCTION.
ALTHOUGH, in some parts of this treatise, we have had
occasion to allude to some of the properties of certain
materials, yet, in order to render the treatment of our
subject complete, it is necessary to dilate more generally
upon those substances used for the purposes of con-
struction, which we now proceed to do.
The strength of metals having been given already,
will not again be inserted here.
TENSILE EESISTANCE OF WOOD PER SECTIONAL
SQUARE INCH.
Oak
Ibs.
17,300
Mahogany .
Ibs.
. . 8,000
Do
13,950
Walnut . .
. . 8 130
/ 8 000
Teak .
15 000
Do., English dry
Beech
j 12,000
17 709
Poplar
t 6,641
' ' } 4 596
Do
11,500
i 13,448
Alder .
14 186
Fir-
( 11,000
Chestnut, Spanish .
Ash, very dry
Do
13,300
j 17,850
I 15,784
12000
Do. ...
Scotch Pine .
Norway Pine
Larch . . .
. . 8,506
. . 7,818
. . 7,287
. . 10,224
Elm
13 489
Cedar . . .
. . 4,973
20,582
144 PRINCIPLES AND CONSTRUCTION
CoMPRESsrvE EESISTANCE OF WOOD IN CUBES OF
ONE INCH.
Ibs.
Elm 1,284
American Pine . . 1,606
Ibs.
White Deal . . . 1,928
English Oak . . . 3,860
Before the art of working in metal was to any
considerable degree developed, timber was an almost
universal material for the construction of various kinds
of machinery, and at the present time in such localities
as abound in timber it is very largely employed for
those purposes, to which in countries possessed of pre-
dominating mineral resources the metals are applied.
In the felling and subsequent preservation of woods
considerable care must be exercised, as if timber be not
properly seasoned it soon becomes a prey to decay, and
in consequence worthless. The usual time for felling
timber is during the cold months, when the vegetative
powers of the tree are almost dormant, and when they
are also most free from sap. None of the woods, how-
ever, are fit for use in the state in which they are cut
down, for although no distinct circulation is going on
within the heart-wood, yet the capillary vessels which
permeate the tissue keep the tree moist throughout its
substance, and therefore in an unfit state for use. If
green or wet woods are placed in confined situations
they become stained, and speedily yield to decay, a
result which is avoided by careful drying with free
access of air.
On this account the timbers for ships should be cut
out to their shapes and dimensions about a year before
they are framed together, after which they should be
left a year longer in the skeleton state to complete the
seasoning, as in that state they become better qualified
OF MACHINERY. 145
to resist the effects of exposure than if they were imme-
diately covered in with planking.
Other mischiefs almost as serious as decay also occur
to improperly-seasoned woods ; round blocks cut out of
the stem of green wood, or the same pieces divided into
quarterings, split radially, and sometimes, but more
rarely, in annular directions. Eound blocks cut from
the entire section contract pretty equally, and nearly
retain their circular form, but those from the quarter-
ings become oval from their unequal shrinking.
SEASONING AND PREPARING OF WOODS. The woods
immediately after being felled are in some cases im-
mersed in running water for a few days, weeks, or
months, according to circumstances ; otherwise they are
boiled or steamed. The object of thus treating the
timber appears to be the dilution of the sap, after which
the process of drying is carried on quicker and better,
and the colours of the white woods are improved. The
ordinary course, however, is merely to subject the mate-
rial to a process of air-drying simply, but then the
timber is usually reduced to sizes more nearly approach-
ing those required for use, such as square logs and
beams, planks or boards of various thicknesses, short
lengths or quarterings, &c.
The stems and branches of such trees as alder, birch,
and beech, used largely by turners, frequently require
no reduction in size ; if they do, they are split into
quarterings ; but in either case they are stacked in
heaps to dry.
The smaller hard woods are much more wasteful than
the timber woods, as, independently of their thick bark,
their sections are frequently very irregular, indented,
and ill-defined. Others are almost constantly unsound
146 PRINCIPLES A*T> CONSTRUCTION
in their growth, and either exhibit central hollows or
cavities, or cracks and radial divisions, which part the
section into three or four pieces.
All the harder woods require extra care in their
seasoning, the difficulty of satisfactorily effecting which
is often increased by exposure to the sun and hot winds
in their native climates. The closeness of their texture
also renders them less easily penetrable by the air, thus
increasing the liability to crack, while their scarcity and
expense also render their preservation a matter of great
importance. It is therefore advisable to prepare them
for their passage from the yard or store to the turning
shop by removing those portions which must be neces-
sarily wasted, so as the more thoroughly to dry them by
more complete exposure to the air, before they are taken
into a house, and care should be taken not to place
them near a fire, or at first in a hot room.
Many of the timber woods are divided in the saw-pit
into planks, in order to increase the number of surfaces
upon which the air can act in the process of drying, and
also to leave less distance for its penetration ; after
sawing they should never be allowed to remain in con-
tact, and the partial admission of air often causes stain-
ing and other mischief to arise. They should therefore
be placed either horizontally or vertically in racks, or
stacked in a pile with slips of wood in between
them.
Thin pieces will be about sufficiently seasoned in one
vear's time, but thick wood requires two or three years'
preparation before it is fit to be removed into hot rooms
to complete the drying. Mahogany, cedar, rosewood, and
other large foreign woods, require to be very carefully
dried when they are cut into planks, as, notwithstand-
ing the great length of time which elapses between their
OF MACHINERY. 147
being felled and brought into use, they retain a great
proportion of moisture as long as they remain in logs.
The drying of woods, technically speaking, cannot be
said to be completed until the wood ceases to lose
weight by evaporation on the continued application of
heat ; but to arrive at this degree of dessication would
require two or three times as long as is usually allowed
for the seasoning of timber. A good and expeditious
method of completing the seasoning of wood consists in
placing it in hot rooms having a free circulation of air,
which enters at the lower part heated and dry, and
therefore in an excellent condition to absorb moisture,
and it leaves the upper part of the room charged with
aqueous vapour taken from the wood which is under-
going the process of dessication. This mode of pro-
cedure is so expeditious that by its adoption two-
thirds of the time required for common air-drying is
saved.
As a general rule, the specific gravities of woods will
give a very fair idea of their comparative degrees of
hardness.
In order to render timber more durable than it is
when merely air-dried various special processes have
been invented, such as injecting its pores with corrosive
sublimate, sulphate of copper, or creosote, the latter
being practised to a very great extent for railway
sleepers and other timbers placed in very exposed
situations, liable to the combined action of moisture
and air.
GENERAL CHARACTERISTICS OF WOOD. Timber, on
account of its great flexibility, comparatively speaking,
is but little adapted for the manufacture of parts of
machinery which reciprocate at high velocities, but its
cheapness, toughness, and facility of being wrought
L 2
148 PRINCIPLES AXD COXSTKUCTIOX
render it useful for framework and parts of machines
at rest or always moving in one direction.
Although the specific gravity of timber is very low,
yet in its use there is seldom any saving in weight, as
from its correspondingly slight resistance to strains a
much larger sectional area is required to resist a given
strain where it is used than if metal be the material
applied.
The liability of wood to twist and warp, especially
when exposed to damp and to alternations of tempera-
ture, as well as its liability to combustion, are also dis-
advantages weighing heavily against its use if other
materials are available at a moderate cost. Some of
the toughest kinds of wood are, however, used to a
considerable extent for the teeth of wheels, and for
this purpose are found to wear as well as iron ; in fact,
in some cases, wheels with wood teeth will outlast the
iron-toothed wheels in gear with which they work.
Wood is also very useful as a packing material to place
under portions of machines subject to concussion, so as
to deaden the shock which would otherwise be trans-
mitted to the parts below with almost its normal force.
IBOX. The various descriptions of cast and wrought
irons and steels used in commerce for the multifarious
purposes of the manufacturer are obtained by suitable
processes from certain minerals containing more or less
iron, and which are known as iron ores. In these ores
the iron exists chiefly in the form of oxides and
carbonates. The oxides of iron are two in number :
the protoxide and peroxide, or sesquioxide of iron.
The first contains one atom or chemical equivalent of
oxygen to each atom of iron, its chemical symbol being Fe.
0. (Fe. representing Ferrum, Lat., Iron, and 0. Oxygen).
But the chemical equivalents, or atomic weights, are,
149
Iron 28, Oxygen = 8* ; hence the composition of
protoxide of iron is,
Parts. Parts.
Iron .... 28 .. 77-78
Oxygen 8 . 22-22
100-00
The sesquioxide of iron contains two equivalents of
iron to three of oxygen ; hence its formula is Fe2 0$, and
its composition
Parts. Parts.
Iron . 28 x 2 . = 56 . . 70-00
Oxygen 8 x 3 . = 24 . . 30-00
100-00
There exist also in the ores containing the iron other
substances, such as silica, graphite, alumina, &c., from
association with which the iron must be removed ; but
with many of these the iron is not chemically combined,
and may, therefore, be readily freed. Carbonate of iron
is a salt consisting of protoxide of iron combined with
carbonic acid, the latter being composed of one atom of
carbon and two atoms of oxygen, and, therefore, being
represented by the formula C. 2 . Carbonate of iron
will have the formula Fe. 0. C. 2 , or Fe. C. 3 . It
occurs in many countries in the form of a light grey or
buff massive stone in large quantities. The celebrated
Styrian steel is prepared from this ore, which is com-
monly termed Spathic Iron Ore, or Spherosiderite, and
from this most of the English iron is prepared. The
composition of carbonate of iron is
Parts. Parts.
Iron ... 28 48-27
Carbon ... 6 10-34
Oxygen . 8 X 3 = 24 41-39
100-00
* In the use of chemical nomenclature throughout this treat i-r,
the old or Daltonian system of equivalents and formulae will be used.
150
PRINCIPLES AND CONSTRUCTION
I
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S 5 3 O O
o s s
-g ,0 ,Q g
lifii
o <o o ^-i r^ o co oo i
| | 1 1 1||:
o
t^- us --i >c -* ^
IIIH I!
Wl:l !
S g
fill
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111
rAiifii.!rt
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OF MACHINERY. 151
The iron is separated from the oxygen with which
it is combined by the action of substances which, aided
by heat, have fi greater attraction or affinity for oxygen
than the iron has, and, therefore, deprive it of that
element. Thus, if finely divided oxide of iron be sub-
jected at a red heat to the action of hydrogen gas, the
latter combines with the oxygen of the former to form
water (H. 0.), and pure iron is left. In commercial
processes, however, carbon in the form of coal or char-
coal is the principal deoxodizer employed to free iron
from its oxygen.
The conditions of the iron in combination with the
most important ores from which it is manufactured are
as under :
In Magnetic iron ore . . Fe. 0. + Fe2 3
Spathic or clay ironstone Fe. 0. C. 2
Eed hematite . . Fe 2 3
Brown iron ore (yellow j HQ
ironstone, ochre, &c.) )
METALLTJRGY OF IKON. The metallurgy of iron, or
practical extraction of the metal from the masses of
matter in which it naturally occurs, is, as has already
been shown, a process of a chemical nature in the first
instance, although the subsequent treatment is chiefly
mechanical.
The first process with those ores which contain car-
bonic acid, water, and sulphur, consists in roasting them
in a suitable furnace, in order to expel those ingredients,
after which the calcined ores will be ready for smelting.
The operation of SMELTING depends, first, upon the
tendency of most earthy and metallic substances to
melt by heat ; next, upon the affinities of the substances
put into the furnace together as causing them to decom-
152
PKEs'CrPLES A10) CONSTRUCTION
pose each, other in fusion, and form new compounds by
recombination of the different elements, and then upon
the excessive gravity of the metallic iron, which causes
it to sink through the mass to the bottom of the furnace.
As regards this last point, it may be observed the specific
gravity of all the other solid materials likely to come
together in smelting (even in a coal or coke furnace) is
not much more than twice that of water, whereas iron
is seven times as heavy as water, bulk for bulk, and its
gravitating tendency is, therefore, more than three times
as great as that of the materials by which it is sur-
rounded. In charcoal furnaces the gravitating tendency
is considerably greater.
The following diagram shows the materials which are
usually brought to act upon each other in smelting
furnaces, and the products which result from their
mutual decomposition and recombination.
PRODUCTS.
Gaseous
Atmospheric air.
Solid.
OF MACHINERY. 153
From this it will be seen that the fuel in combustion
takes oxygen from the substances surrounding it, and
its hydrogen passes away as water, its carbon as carbonic
acid and carbonic oxide ( 0. 0.), whilst the flux dissolves
the siliceous matrix, and so frees the iron, which, melting
by the heat, descends to the bottom of the furnace,
leaving the slag and cinder floating above in a nearly
fluid state.
The success of the process, of course, depends upon
the means employed to carry it out ; if there be plenty
of air and plenty of fuel, heat can be generated sufficient
to fuse the most refractory and voluminous materials.
As, however, both air and fuel are costly in their supply,
it behoves the smelter so to mix and proportion the
quantities of his ores and fluxes that fusion 'of both shall
take place at the lowest possible temperatures, that it
shall be the most perfect, and that it shall afford the
greatest facilities for the separation and descent of the
metal. Also, that by the presence of suitable substances
all, or as many as possible of accidental impurities, may
be neutralised or taken up, so that after its first separa-
tion the iron shall not in its passage through the furnace
enter into new and injurious combinations.
This was very tersely but accurately expressed a very
long time since by Rogw, the Welsh founder, who said,
"In order to make iron you must first make glass."
To cause all the substances which do not pass away from
the furnace in the gaseous condition, of course excepting
the iron, to assume the condition of a glassy cinder is
the aim of the smelter, and it is from the quality of the
cinder coming from the furnace that its working is
practically judged of. In early times, and even now
with some, the determining of the proportions of the
different materials involved a tentative process, and the
154
PRINCIPLES AXD CONSTRUCTION
rules laid down were the results of experience; but,
with the development of chemical science and the exten-
sion of theoretical knowledge, methods of calculating
those proportions and the dimensions of the furnaces
have arisen.
In Fig. 45 a general outline of a blast furnace for
iron-smelting is shown in vertical section, a represents
the mouth of the furnace at which the fuel, fluxes, and
ores to be treated are
thrown into the fur-
nace ; the part b b re-
presents the shaft or
cuvette of the furnace ;
c the boshes, d the
crucible, and e the
hearth where the metal
after reduction accu-
mulates, being re-
tarded by the dam /;
g is termed the stack,
and h the lining.
Above the hearth the
air necessary for com-
bustion of the fuel is
forced in through pipes called tuyeres (pronounced
tweers), or, more commonly amongst workmen, " tue-
irons." It would be exceeding our intentions to
describe the mode of constructing the furnace, as its
form is only introduced as necessary to make clear the
explanation of the method of extracting iron from the
ores in which it naturally exists, but it is important to
give some idea of its average proportions according to
the fuel intended to be used in it. They are contained
in the following table :
OF MACHINERY.
155
High Furnaces
Anthracite
Dimensions.
Charcoal.
using Coke.
Coal.
Stack height from foun-
dation . .
25 feet.
50 feet.
35 feet.
width at bottom . .
28
50
40
width at top . . . .
16J
25
33
Cuvette diameter at top
4
8
6
height of conical in-
walls
25
33
11
height of cylindrical
in-walls ....
...
...
8
width of boshes. . .
9|
15
12
angle of boshes . . .
55 deg.
65 deg.
75 deg.
height of boshes . .
4J feet.
10| feet.
11 feet
Crucible height of
hearth
5 >?
fM
5 n
mean of length and
breadth at top . .
2i
5
6
mean of length and
breadth at bottom .
2
4
4
height of tuyere above
hearth
1
2
1|
Approximate capacity .
1000 cubic ft
4200 cubic ft.
Time of descent of
20 hours.
40 hours.
The form of cuvette used with anthracite coal is shown
by the dotted lines in Fig. 45. The action of the fur-
nace upon the ingredients placed in it as they pass
downwards, is as follows :
In the upper portion of the shaft the ore is heated to
redness that is to say, it is roasted; the water, carbonic
acid, and sulphur being expelled, and also the carbonic
acid of the limestone in the flux escapes here. Further
down, under the influence of more intense heat, the
carbon of the fuel reacts upon the oxide of iron, carry-
ing off its oxygen in the form of carbonic oxide, which
on coming in contact with the atmosphere at the mouth
of the furnace is consumed and converted into carbonic
acid, occasioning in its combustion the bright flame
156 PRINCIPLES AND CONSTRUCTION
which is seen to issue from the mouths of blast
furnaces.
In the boshes, where the greatest temperature is
maintained, the reduced iron melts and falls in drops
upon the hearth, together with the silica, lime, and clay ;
these latter form a slag which floats upon the top of the
iron, whence it can be drawn off when necessary. After
having heated to 200 degrees or more the air requisite
for combustion, it is forced by suitable blowing machi-
nery into the crucible part of the furnace, where a heat
of from 2,200 degrees to 2,550 degrees Fahrenheit may
be produced.
In proportion as the melted iron and slag are drawn
off from the hearth, fresh charges of ore flux and fuel
are fed into the mouth of the furnace, and thus the
smelting may be continuously carried on for five or six
years, according to how the furnace holds out.
Fuel is one of the most important materials in smelt-
ing both as regards quality and cost. The object in
the use of fuel is principally to obtain the requisite heat,
but it also acts as a reducing agent in separating the
metallic iron ; hence its value will be proportionate to
the amount of carbon it contains.
Wood, which may generally be taken as half carbon,
and half oxygen and hydrogen, in the proportions to
form water, is too poor in carbon to be serviceable, and
compared with coke, bulk for bulk, its capacity to
generate heat is but one-fifth of that of the latter. The
presence of hydrogen in fuel, although it promotes in-
flammability, does not in blast furnaces act as a reducing
agent on the ore, hence it is a disadvantage in fuels for
smelting purposes. Therefore, raw coal, turf, lignite,
and brown coal are unsuitable ; but pressed and charred
turf is extensively used on the Continent, and is said to
produce a charcoal of peculiar value.
OF MACHINERY. 157
The general fuels used are wood in the form of char-
coal, coal, and coke. Charcoal is prepared by charring
wood either in stacks or ovens, and coke may be obtained
from coal charred in gas retorts or in ovens constructed
on purpose, the latter producing a much harder and
better material than the former.
The yield of charcoal in proportion to the wood from
which it is made, is found to be
Charcoal prepared in kilns . . 18 to 22 per cent.
ovens . . 20 25
The quantities of coke yielded by coal are very
variable; but ovens give a yield about 10 per cent,
greater than that obtained from gas retorts. Gas-coke
is cheap, but unsuitable for furnace use.
Coal in coking yields . . 45 to 90 per cent.
Average of all qualities . 63 ,,
In regard to VOLUME, most coals expand in coking ;
some, however, do not alter in bulk materially, and
those of which the earthy matters are principally of an
aluminous character sometimes shrink.
The average composition of good coke may be thus
represented :
Parts.
Carbon 82
Earthy matters 15
Volatile 3
100
If coke contains more than 15 per cent, of earthy
matters it is not suited for smelting, for, in all cases,
these earthy matters can serve no useful purpose, and
merely act as absorbents of heat.
Good coke may be inferred from its not having
undergone great change in volume or shape, its colour
158
PRINCIPLES AND CONSTRUCTION
being iron grey, or nearly that of graphite, from its
having a lustre more silky than metallic from much
hardness, elasticity, and resistance to impact, from a
texture more fibrous than compact, imparting sonorous-
ness when struck, and its specific gravity should some-
what exceed that of water.
The following table shows the probable consumption
of fuel per cent, of crude iron from ores of different
degrees of richness :
Per-centage
of Metal
Per-centage of Fuel Consumed .
in Ore.
Charcoal.
Coke.
Fusible Ores .
25 to 30
66 to 90
110 to 150
30 ,
, 35
90
110
150
180
35 ,
, 40
110
130
180
220
Ores of mean fusibility
30
40
110
140
180
240
40
50
140
180
240
300
50
60
180
210
300
360
Refractory Ores
30
40
160
200
275
350
40
50
200 ,
, 250
350 ,
, 400
50 ,
, 60
250 ,
, 300
400 ,
, 500
Anthracite coal may be regarded as very similar to
hard-coked coals, whose constitution its own much resem-
bles, as is shown by the subjoined analysis :
Parts.
Carbon 88-7
Earthy matters 7-4
Volatile matters . . . . . 3 '9
100-0
FLUXES. It is but very seldom that ores of iron can
be smelted by the fuel without the use of fluxes, which
are matters containing no metal, or but very little, the
object of their use being to promote fusion. Although
the earthy bases most easily accessible, silica, lime,
OF MACHINERY. 159
alumina, and magnesia, are, when taken singly, almost
infusible, yet when combined, two and two, three and
three, &c., they become fusible at readily attainable
temperatures, and their addition to the ferruginous ores
in the furnace materially assists in bringing the latter
into a state of fusion. It may here be observed, as a
practical maxim, that, in addition to the silica, alumina,
&c., constantly present in the ores and fuel, the positive
flux most commonly used is lime, in the form of shells,
limestone or chalk, and the proportions in which it is
supplied, on the average, are :
In charcoal furnaces l-14th the weight of the other
solid ingredients ;
In coke furnaces l-8th the weight of the other solid
ingredients.
In general, the whole of the solid material (except the
metallic iron) may be taken as of the following compo-
sition :
Parts. Parts.
Silica 45 to 60
Lime 20 30
Alumina . . . . 10 ,, 15
Magnesia . . . . . 10 ,, 25
Oxide of Manganese . . . 15 ,, 20
100
If all the four first mentioned are together present at
one time, the most fusible proportions in which they can
exist are
Parts.
Silica 35-2
Alumina . . . . .31*7
Lime .19-1
Magnesia 14-0
100-0
The atmospheric air now remains to be considered as
160
PRINCIPLES AND CONSTRUCTION
the only material used in smelting not yet treated of,
and which must be regularly blown into the furnace to
keep up the combustion. It is, therefore, of very great
importance that its supply should be properly managed,
and when the enormous quantities of it that are required
are taken into consideration, its influence and effect can
be better appreciated. The following is an average
statement derived from practice :
Charcoal
Solid.
Furnaces
Gaseous.
Coke.
Solid.
Furnaces.
Gaseous.
Volume of materials in cub. ft.
0-295
900-0
1-06
3000-0
Volume of do. proportionate
1-000
3050-0
1-00
2830-0
Weight of do. inlbs. permin.
do. proportionate
26-82
1-00
75-0
3-022
102-12
1-00
269-0
2-634
In round numbers the volume of the air injected into
the furnace in a given time is 3,000 times that of the
other materials supplied, and its weight three times as
great. The elements used above would also show that
about nineteen tons of air are required for the manu-
facture of one ton of iron.
Iron is manufactured both with cold and hot blasts,
and there has been a great deal of discussion as to the
relative strengths of the products, a strong prejudice
having existed against hot-blast iron ; but this opinion
is exaggerated beyond what is warranted by actual
experiments. The following statement shows the rela-
tive resistances of metals prepared with hot and cold
blasts to resist strains of different descriptions :
Stretching. Crushing. Transverse. Impact.
Cold-blast iron 1000 1000 1000 1000 1000
Hot-blast . 913 1033 963 1005 935
The hot-blast method works easier, and produces a
greater yield than the cold-blast, and by it more refrac-
OF MACHINERY. 161
tory materials may be reduced than by the latter, and it
is also accompanied by a notable economy of flux and
fuel ; the saving in fuel on the average may be stated for
Coke furnaces at 32 per cent, from temperature of 330 F.
Charcoal do. at 20 " " 390 F.
Moreover, the use of hot blast allows of the adoption
of certain raw coals, which could not otherwise be
employed. As regards the general quality of the metal
produced, it is a grey foundry iron with a more uni-
formly cubic crystalline form than is observed in the iron
yielded by cold blast.
We must now speak of other products of the blast-
furnace. The following analysis shows the composition
of cinder averages when the furnace is doing good
work :
Charcoal Cinder. Coke Cinder.
Silica 53 43
Lime 22 35
Alumina .... 16 14
Magnesia .... 5 4
Protoxide of Iron 4 4
Too" 100
The gaseous products of the furnace may be taken to
consist on an average of
Parts.
Nitrogen 56
Carbonic acid 19
Carbonic oxide . . . .16
Carburetted hydrogen ... 2
Steam 7
100
The physical properties of iron now require our care-
ful attention. The colour varies according to the pro-
portion and mode of combination of the crude iron with
162 PRINCIPLES AND CONSTRUCTION
its chief foreign ingredient, carbon, from dark grey to
silvery white. Dark grey crystalline iron, with its
small facets, is considered suitable for foundry purposes
for making castings ; as its colour brightens and becomes
more silvery it is considered more suitable for conver-
sion into wrought-iron.
In order to produce malleable or wrought-iron from
crude iron it is necessary to eliminate the carbon con-
tained in the latter, which is done by subjecting it to
the action of atmospheric air while in a state of fusion,
thereby oxidizing the carbon and carrying it off as car-
bonic acid or carbonic oxide. This process may be
accomplished by stirring the molten metal about in a
refinery, or in a puddling furnace, or by forcing air
through the liquid mass, as in Bessemer' s process.
Steel in composition is between cast and wrought
iron, as it contains a certain proportion of carbon, that
element existing in combination with the metal in the
proportion of about 2 per cent. Steel may be made
from malleable bars by keeping them for a length of
time at a red heat in contact with powdered charcoal,
then the iron, taking up a suitable portion of carbon,
becomes converted into steel. This process is termed
cementation, and the furnace in which it is carried out a
cementing furnace.
Steel may also be produced from crude iron by Bes-
semer' s process, by forcing air through the melted cast-
iron until all the carbon except that required to consti-
tute steel is eliminated from the mass under treatment.
The average specific gravities of different irons are
(water being 1-00)
Crude iron foundry or grey iron . . 7*0
Crude iron forge-pig or white iron . 7-5
Malleable iron 7'6
OF MACHINERY. 163
The effects produced by various foreign ingredients
upon the quality of iron are worthy of careful study :
Sulphur renders iron exceedingly fusible and brittle
at all temperatures, especially when hot, thus
giving rise to a quality which is known as red-
short-ness.
Phosphorus imparts cold-short-ness to iron, making it
brittle at low temperatures, though not to the same
extent that sulphur does. Occurring in quantities
not exceeding per cent., it increases the hardness
without injuring the tenacity of bar iron, but in
larger proportions it exerts a deleterious effect on
the metal.
Antimony has a great affinity for iron, and, combined
with it in the proportion of J per cent., renders it
very brittle when hot. When the metals are in
proportion of their chemical equivalents iron
28 parts to antimony 129 the elements are inse-
parable by the highest degree of heat.
Arsenic in the proportion of 1-6 per cent, has been
noticed to entirely destroy the tenacity of iron.
Chrome united with iron produces alloys hard, brittle,
and crystalline. When the chrome is present to
the amount of 60 per cent, the alloy is hard enough
to scratch glass as deeply as a diamond. 1 to 2
per cent, hardens cast steel without diminishing its
malleability.
Copper in the proportion of 1 to 2 per cent, increases the
tenacity of crude iron, but its presence in malleable
iron injures its property of welding, and in large
proportions makes it red-short.
M 2
164 PRINCIPLES AND CONSTRUCTION
Manganese is most commonly found associated with iron
in small quantities ; up to If per cent, it hardens
the metal without impairing its tenacity ; it also
diminishes the fusibility of iron. The tendency of
ores containing manganese is to yield a metal
easily convertible into steel.
Nickel renders iron whiter, less oxidizable, and less
ductile than it is when unalloyed, otherwise the
iron is of good quality.
Palladium, Rhodium, Iridium, and Osmium cause iron to
become hard and brittle ; the presence of any of
these to the extent of 3 per cent, enables the iron
to be tempered like steel.
The following table is interesting as showing how the
quality of iron is affected by different proportions of
carbon associated or combined with it :
Iron half-converted into steel contains one 150th of
carbon.
Soft cast-steel capable of welding contains one 120th
of carbon.
Cast-steel for common purposes contains one 100th of
carbon.
Cast-steel requiring more hardness contains one 90th
of carbon.
Steel bearing a few blows, but unfit for drawing, con-
tains one 50th of carbon.
First approach to steely-granulated fracture contains
one 30th to one 40th of carbon.
White cast-iron contains one 25th of carbon.
Mottled cast-iron contains one 20th of carbon.
Carbonated cast-iron contains one 15th of carbon.
Super-carbonated crude iron contains one 12th of
carbon.
OF MACHINERY. 165
Cast-iron and steel admit of being prepared in hard
or soft state. Thus, if a casting is required to have a
portion of its surface hard, that side of the mould con-
sists of some substance (as iron) which will rapidly cool
the metal which is run in contact with it, thus producing
a very hard surface. Castings thus made are called,
from the method employed, chitted castings.
Steel is hardened by raising it to a red heat and
plunging it into salt water ; but this process renders it
absolutely hard and brittle, hence, for most purposes,
this must be lowered by tempering, which consists in
heating the hard steel to a temperature depending upon
the purpose for which it is intended to be used; the
right temperature is commonly recognised by the work-
man from the colour of the film of oxide which forms on
the steel, as shown by the following table :
Colour of Film.
Ten
ip.
Use.
Very pale straw yellow
430 deg.-v
A shade of darker straw
C Tools for metaL
yellow
440
)
Darker straw yellow
470
> Tools
tat
wood and screw
taps,
Dark yellow ....
490
S &c.
Brown yellow . . .
500
^
Yellow tinged slightly
(.Hatchets,
chipping chisels,
and
with purple ....
520
1 othe
T percussive tools, saws, &c.
Light purple ....
530
Dark purple ....
Dark blue
550
570
| Spring
JS.
Pale blue
590
M
\
Paler blue
Paler blue tinged with
610
' ) Too soft for the above purposes.
green
630
J
Iron castings are rendered soft by abstracting a por-
tion of their carbon, whereby they are partially (or, if
thin, entirely) changed to the condition of malleable iron.
In order to effect this decarbonization the castings are
Ibb PRINCIPLES A]S T D CONSTRUCTION
put into boxes or cases surrounded with pounded iron-
stone and submitted to heat, or metallic oxides may be
used. Thus the carbon is oxidized out of the metal to
a certain depth from the surface. After being heated
for a sufficient length of time the castings are allowed
to cool very gradually.
Wrought-iron may be case-hardened by a very sim-
ple process, which converts the outside of the forg-
ing or casting for a certain limited depth into steel,
which is hardened in the usual way by sudden cooling.
The articles to be case-hardened are placed in a case
and surrounded on every side by powdered bones, hoofs,
skins, or leather, with which the case is filled up, being
then securely fastened air-tight, and put in a furnace
raised to a red heat, and maintained at that temperature
for a period of from one to five hours, according to the
depth to which it is desired that the case-hardening
may penetrate. On removal of the partially-converted
articles, while still hot, they are hardened by sudden
immersion in cold water.
A very thin, or even perhaps discontinuous, coating
of steel may be produced on iron by burying the latter
at a red heat for two or three minutes in powdered
ferrocyanide of potassium (the common yellow prussiate
of potash of commerce), a salt which is prepared from
various animal matters.
The steely surface thus obtained is not nearly so good
and durable as steel made in the usual way and ham-
mered, and generally the cementation does not pene-
trate to a depth of more than one- sixteenth of an inch;
nor is it necessary that it should do so, as the object of
case-hardening is to increase the durability of the
surface without impairing the general strength and
toughness of the article operated upon.
OF MACHINERY. 167
The introduction of cheap steel has done much to
decrease the practice of case-hardening certain small
articles of manufacture. According to Dr. Thompson's
analysis of some cast-steel from a manufactory near
Glasgow, it contains a very slight proportion of silicon,
but this does not appear to be essential. The composi-
tion of the sample was
Parts.
Iron 99
Carbon with some silicon . . 1
100
This very nearly corresponds to the formula, Fe2o C.,
which would give
Parts. Parts.
Iron . . 28 X 20 = 560 . . 98-94
Carbon ... 6 . 1-Q6
100-00
COPPER is the next material demanding attention.
The ore from which the copper of commerce is prin-
cipally obtained contains the metal in combination with
sulphur, as a sulphuret or sulphide of copper, generally
accompanied by sulphide of iron, as in copper pyrites ;
thus, in addition to the sulphur, there is the iron to be
eliminated. The process of extracting copper from its
ores is exceedingly lengthy and tedious, and requires
great care on the part of those conducting it ; and it
consists of a considerable number of separate operations,
through all of which the material must pass before it is
fit for the market. In the first place, the ores must be
roasted or calcined, in order to convert the copper into
oxide of copper and the iron into protoxide of iron, the
sulphur being expelled in the form of sulphurous acid.
Secondly, the roasted ore must be melted with charcoal
168 PEINCIPLES AND COIs'STKUCTION
and some siliceous substance in a suitable furnace, by
which means metallic copper and carbonic oxide are
formed from the oxide of copper and charcoal, and sili-
cate of protoxide of iron (or iron slag) from the pro-
toxide of iron and quartz. This appears simple enough
as thus stated, but the actual establishment of the reac-
tions to bring about the desired end in practice is in
reality so difficult that the roasting and melting have to
be repeated from ten to twenty times alternately in some
cases, in order to get rid entirely of the sulphur and
iron with which the copper is associated. The melted
mass, which is obtained when about half the sulphur
and iron is removed, is called matt, or crude copper, and
black copper when it contains only about 5 per cent, of
these two substances.
The ultimate refining of black copper is effected by
remelting the metal, exposing it at the same time to the
action of the air, whereby the remaining iron, sulphur,
and foreign metals, such as lead and antimony, which
may be present, are oxidized before the copper (which
has a less affinity for oxygen), and thus are separated
from it. During the various processes some of the slags
which are rich in copper may be reworked with fresh
ore. In some stages the removal of the sulphur may be
facilitated by stirring the molten metal with a stick of
green wood, which probably acts by the moisture sup-
plied by it decomposing the sulphide of iron, and form-
ing oxide of iron and sulphuretted hydrogen.
The species of furnace chiefly used in the reduction
of copper is that known as the reverberatory furnace,
of which a vertical section is shown at Fig. 46 ; it
admits of the regulation of the chemical reactions to a
very great nicety, a is the fire-grate, and I b the bed or
sole of the furnace, whereon the materials to be treated,
OF MACHINERY.
together with any re-agents which may be requisite, are
placed ; c is an outlet which can be opened at pleasure
for the withdrawal of slag, &c. ; e and / are doors to
allow of the observation of the state of the furnace; d is
the chimney-shaft. The charges of metal are drawn
through a door in the side of the furnace.
Fig. 46.
Now, it is evident in this arrangement that, by regu-
lating the quantity of fuel and air admitted to the fur-
nace, there may be either excess of air passing over the
sole, producing an oxidizing effect, or, on the other hand,
by reducing the quantity of air below that requisite for
the complete combustion of the fuel, there will be car-
bonic oxide passing over the materials tending to de-
oxidize them.
When the ores are combined with oxygen instead of
sulphur, the operation of working them is much easier,
as they yield metallic copper by merely treating them
with charcoal, which abstracts the oxygen ; but such
ores are unfortunately too rare to afford anything
approaching to a sufficient supply of copper to meet the
demand.
Copper possesses certain physical characteristics which
render it especially suitable to particular purposes. It
is slow to oxidize when compared with iron ; is tough
170 PRINCIPLES AND CONSTRUCTION
and extremely ductile, the latter property allowing
wrought copper to be drawn into exceedingly fine wire
and beaten into almost any conceivable shape. Thus
copper pans, kettles, and parabolic reflector-backs may
be beaten up out of flat sheets of copper. It is useful
for lining air-pumps, and as a material for other pumps
when alloyed with some other metals, and more espe-
cially in such machinery as is subject to sea water or
foul water, which would rapidly corrode iron. Copper
may be to some extent hardened by hammering, and
the tenacity of cast copper may be greatly increased
by the addition of about 3 per cent, of phosphorus,
which is introduced into molten copper without great
loss by first coating it with a layer of copper for pro-
tection.
LEAD, the next of the useful metals upon which we
shall dilate, is largely used in the arts. The following
ores of lead are the most important :
Gralena, or sulphide of lead, has metallic lustre and a
crystalline structure distinctly derived from the cube.
It is a compound of lead and sulphur in atomic propor-
tions, consisting of
Parts.
Lead 86-67
Sulphur 13-33
100-00
and has a specific gravity of 7*6. Its colour is blackish
grey.
Native minium, or red lead, is of a lively red colour,
but sometimes inclining to orange ; it has an earthy
aspect, and specific gravity from 4-6 to 8-9 : it is rare.
Carbonate of lead (white lead), when pure, is colour-
less, and transparent like glass ; its specific gravity is
from 6 to 6 7.
OF MACHINERY. 171
Galena, or sulphide of lead, is, however, the only ore
which is sufficiently abundant to become the object of
mining and metallurgy, and in its treatment, after the
due sorting, cleaning, and grinding, is usually reduced
in reverberatory furnaces. The sulphur, in combina-
tion with the metals as sulphides, is so firmly asso-
ciated with them by chemical affinity that it cannot
easily be expelled, hence it is necessary to have recourse
to a circuitous method ; first, the sulphide must be con-
verted into an oxide of the metal, and the oxygen must
then be expelled to free the metal. The galena is
heated or roasted with free access of atmospheric air, the
result being that the lead becomes oxide of lead, the
sulphur escaping as sulphurous acid, but there is also a
small portion of sulphate of lead formed during the
process.
After roasting, then, the galena leaves a mixture of
oxide of lead with some sulphate of lead, which may be
reduced by heating in a blast or' reverberatory furnace
with charcoal.
Another method of freeing lead from sulphur consists
in heating the galena with a metal which has a greater
affinity for the sulphur, and therefore replaces the lead :
such a metal is iron. Thus iron and sulphide of lead,
heated together, will yield lead and sulphide of iron. In
the reaction one atom of iron replaces one atom of lead :
hence 28 Ibs. of iron will suffice to throw down 104 Ibs.
of metallic lead.
Physically the characteristics of lead are distinctive ;
it has little or no elasticity, is very ductile and flexible,
possesses but little strength in any direction, and is
fusible at a low temperature (600 P.), and has a very
high specific gravity 11-5.
TIN is a white metal possessing considerable lustre,
172 PRINCIPLES AND CONSTRUCTION
in bars ; it makes a peculiar cracking noise when bent ;
its specific gravity is 7-2, and melting point 446 F.
Tin is prepared in the smelting houses in a simple
manner from tin stone, which consists of peroxide of tin
with some arsenic and iron. The ore is first finely
stamped, after which it is roasted, whereby the arsenic
is volatilized and the iron oxidized. It is then washed
with water, whereby the lighter particles of stone, and
to a great extent the oxide of iron, are carried away.
Finally, it is fused with charcoal in a blast furnace, and
a reaction taking place, carbonic acid and metallic tin
result, the latter flowing from the bottom of the furnace.
In the mechanical arts tin is almost entirely used in
connection with other metals.
ZINC has a specific gravity of 6-8, is a white metal,
and will show a certain amount of ductility at a mode-
rate heat. It is prepared from carbonate of zinc, which
by the miners is called calamine, in order to convert
which into metallic zinc the carbonic acid and oxygen
must be expelled.
The first is effected by calcination in furnaces, the
latter in the same way as is applied to iron ores, by
heating to redness with charcoal; but this cannot be
done in open furnaces, as the reduced zinc would evapo-
rate and burn, again becoming converted into oxide of
zinc. The vessels used in which to treat the zinc ores
are called muffles, and are, in fact, a species of retorts
made of clay ; into these retorts the calamine and char-
coal are put and raised to a red heat, then the carbonic
acid and evaporated zinc pass away through the neck,
the former to escape, the latter condenses and falls in
drops into a vessel of water.
The zinc of commerce always contains a small
quantity of iron and lead, but if the amount of the latter
OF MACHINERY. 173
is more than 1| P er cent., the zinc becomes brittle and
cannot be rolled into sheets even when heated.
There are several alloys which are largely used in the
construction of machines, and which must therefore not
be overlooked. An alloy is a mixture or a mechanical
combination of two or more metals, in contradistinction
to a compound which is a chemical union ; but although
the combination of the different components is mecha-
nical, yet the physical properties of the alloy are not to
be deduced from those of the metals entering into its
composition.
Brass, much used for bearings for the revolving shafts
of machinery, and for bushes, and various minor details,
consists of copper and zinc. Gun-metal or bell-metal is
a very hard alloy, useful for small cams, valves, pumps,
&c. ; it is composed of copper and tin. There are also
other alloys of copper, such as Muntz's yellow metal, Ger-
man silver, &c., which are applied to specific purposes.
The following is a list of the most useful alloys, and
the proportions in which their component metals are
associated :
Bismuth 1, tin 2 Cowper's alloy, for rose-engine and
eccentric-turned patterns to be printed from.
Bismuth 2, lead 4, tin 3)
Bismuth 1 , lead 1 , tin 2 j Coilstitute pewterers' soft solders.
Copper 5, zinc 1 red sheet brass, made at Hegermiihl.
Copper 2, zinc 1 brass that bears soldering well.
Copper 2, zinc 1 ordinary brass.
Copper 16, zinc 9 )
Copper 16, zinc lOf j The two extremes of Muntz's metal.
Copper 4, zinc 3 spelter solder for copper and iron.
Copper 1, zinc 1 spelter for brass.
Copper 1, zinc 8 metal used for lap and polishing discs.
Copper 16, tin Isoft gun-metal.
174 PRINCIPLES AND CONSTRUCTION
Copper 12, tin 1 gun-metal for mathematical instru-
ments.
Copper 10, tin 1 wheel metal for small-toothed wheels.
Copper 8, tin 1 Brass ordnance or hard bearings for
machinery.
Copper 6, tin 1 very hard bearing metal, too brittle for
general use.
Copper 2, tin 1 speculum metal.
Copper 2, lead 1 pot metal.
Copper 32, tin 3, zinc 1 pump metal ; has great tenacity.
Copper 32, tin 5, zinc 1 bearing metal for very heavy
weights.
Lead 3, tin 1 coarse plumbers' solder.
Lead 1, tin 2 fine solder.
There are a variety of other alloys made, but they
are used for purposes which do not come within the
compass of the present work, being applied to the manu-
facture of articles of ornament rather than utility, or as
substitutes for the precious metals.
CHAPTEE XIV.
THE MANIPULATION OF TIMBER AND THE METALS.
IT is most essential that anyone designing machinery
shall be thoroughly acquainted not only with the in-
trinsic properties of materials, but also with the methods
of manipulation by which they are converted to such
purposes as they may suit. Otherwise it is not only
possible but probable that details of machines may be
drawn and specified to be made of materials which are
highly insuitable, or which can be wrought into the
required form only at great expense, or in some oases
not at all.
OF MACHINERY.
TIMBER. Although, timber is but little used in the
construction of machinery in" localities where iron is
plentiful and cheap, yet in some places it is applied for
framework or even for some of the moving parts ; hence
it is necessary to explain the proper method of making
the connections between different parts so as to secure
the requisite strength and rigidity.
In Fig. 47 A represents an inclined timber liable
to a thrust ; it is jointed to the tie as shown, the
end resting in a notch,
., Fiq. 47.
and having a rib or fea-
ther on it, shown by the
dotted line c, to maintain
its lateral position ; it is
held in its place by a bolt
and nut, or by an iron
strap passing the end of A and bolted through B.
A trussed frame is illustrated at c, Fig. 48 ; it consists
of three top pieces in compression, one horizontal tie
at the bottom, two
upright struts e, e,
and two iron tie-
bars d d, by the
tightening up of
which the whole
frame is brought
firmly together and
the different parts
are prevented from
slipping out of their
proper positions.
By an addition
to this arrange-
ment a rectangular
Fig. 48.
176 PRINCIPLES AND CONSTRUCTION
frame is produced as shown at D ; it is in construction
similar to the last.
The parts of frames are in many instances joined by
means of tenons and mortises, and in making these
particular care should be taken. E is a section of a
bad or slovenly joint, F of a good one ; in the former
the mortise is cut true on the surface, but somewhat
undercut towards e e, hence the tenon /, being par-
allel, will not fit firmly, and there will therefore be
a tendency to wriggle or shake about, which, if the
joint be subject to vibration, will soon render it defective.
In F, on the contrary, the mortise is cut to a pattern or
template, and is tapered slightly so as to be smaller at
the bottom than at the surface where it commences ; the
tenon is cut paralled and forced or driven into the mor-
tise, where it is secured by an iron strap, as shown by
the dotted lines passing round the joint and secured by
bolts to the timber carrying the tenon ; this strap may
rise above the surface of the timber, or a recess may be
cut to allow of its lying flush where necessary, but of
course to a certain extent the framework is weakened
by cutting away any portion of its substance to form
such recesses.
For purposes requiring more rigidity than can con-
veniently be obtained with timbers of a reasonable size,
a piece of bar iron is frequently placed in the centre
between two layers of wood, the three being secured to-
gether by bolts, as shown by the elevation G and the
transverse section H. In the latter * i is the piece of
iron, which is commonly termed a flitch plate. It is
always placed so that the bending strain upon the timber
acts in the direction of i, as, if it acted in the direction indi-
cated by the arrow, the flitch plate would not materially
add either to the strength or rigidity of the element.
OF MACHINERY. 177
When timbers require to be joined in the direction of
their length, it is effected by a process termed scarfing,
which may be either lateral or transverse. Three
methods are
49 ; in the two ^ j >^ ^Pli
lateral methods ~ <& ^ dli ui
the ends of the
pieces to be
joined are ta-
pered off and
notched accord-
ing to the di-
rection in which the strain will act ; the extremities
thus prepared are placed in contact, and retained so by
bolts and nuts, as shown, a I represents a suitable
scarf to resist a tensile strain, and e f the mode of
notching when the timber is subject to a compressive
strain ; c, d, are the ends of two timbers prepared for
transverse scarfing ; the tenon-like projections^,^, on the
piece d enter the recesses shown by the dotted lines at
h, h, on the piece e, and are there secured by a bolt and
nut. This style of scarfing is chiefly suitable for com-
pressive strains, such as come upon uprights, &c.
When timber is used for the manufacture of spring
beams to receive accidental impact, as in the spring
beams of Cornish pumping-engines, &c., they are made
of a number of thin layers of timber put together some-
what after the fashion of carriage springs, the ends
being carried in iron boxes or straps which, while hold-
ing them laterally in position, will yet allow them in
bending to slide slightly one upon another ; similar
beams may be used to quicken the strokes of tilt-
hammers, &c.
N
I
178 PKIXCIPLES AXD CONSTRUCTION
We will conclude our remarks upon timber by show-
ing the different purposes to which the various species
are specially adapted, together with their weights, the
latter being given for them both in the green or wet
state and in the dry or seasoned condition ; the first
will be marked g, the second d, and the weights given in
pounds per cubic foot :
Acacia For sills, wall-plates, posts, fences, and tree-
nails, harder, tougher, and more elastic than the
best oak weight, g 63-2, d 48-5.
Alder Valuable for piles and other subaqueous work
weight, g 62-3, d 39-5.
Ash Useful for beams, joists, and wheels weight,
g 65-0, d 50-0.
Beech Useful for piles and for teeth of wheels weight,
g 66-0, d 50-0.
Elm Used for planking, piles, and wheels weight,
g 70-0, <Z48-5.
Fir Is much valued for its timber, which is used for a
great variety of purposes. Its quality varies
according to the soil on which it is grown weight,
g 54 to 74, d 31 to 41.
Pine Of this there are several varieties, much used for
planking, &c. ; it is of the same family with fir.
Hornbeam Used for the teeth of spur-wheels very
tenacious and durable, hard and heavy weight,
g64, db\.
Laburnum Valued for making pulleys and blocks
weight, do3.
Larch A wood useful for all kinds of carpenters' work,
and for -beams and principals of frames.
OF MACHINERY. 179
Lignum Vita A very dense, hard wood, used by mill-
wrights weight, d 83-3.
Mahogany Used in various parts of machinery weight,
from 35 to 53.
Oak Very useful where rigidity is wanted weight,
g 74, d 53.
Poplar For flooring and boards generally weight,
g 58, d 38.
Poplar (Black poplar) Used by turners and wheel-
wrights weight, g 60-5, d 29.
Walnut A solid compact wood which will not warp
or crack, but bends under ordinary weights, and,
therefore, is not suited for machinery.
Willow (Eed willow) Is light, pliable, elastic, and
tough. Before wheels were rung with iron this
kind of willow was much employed by wheelwrights
for making the fellies, as it will endure under
friction and exposure a much longer time than most
other woods.
Iron Wood The hardest wood known ; it is durable, but
not much used on account of the great difficulty of
working it.
We shall now proceed to consider the manipulation of
cast-iron in forming it into the various shapes required
in the construction of machinery.
PATTERN-MAKING. In the ordinary method of making
castings, such as are of moderate size, green sand, or
rather a mixture of green sand, loam, &c., is used, the
impression of the body to be cast being imprinted upon
it by a representation or model in wood or other material
of the object to be produced.
N 2
180 PRINCIPLES AJO) CONSTRUCTION
The model or "pattern," as it is technically called,
must be made somewhat larger than the proposed cast-
ing is intended to be, in
order to allow for the con- *' 50 '
traction of the metal in
cooling down from the
molten state. The amount i<
of contraction commonly
allowed is,
For cast-iron one-tenth
of an inch per lineal foot.
For brass one-eighth of
an inch per lineal foot.
A simple example will render the mode of making
patterns and thence forming the mould and casting
easily comprehensible. Let it be supposed that a dis-
tance piece of cast-iron is required in the form of a pipe
with slight flanges.
The pattern will appear as shown at c in Fig. 50,
being made of the shape of the required casting, with
the proper allowance for contraction. Instead, however,
of being made hollow, there is attached to each end of
the, pattern a projection d, corresponding in shape and
size to the hollow through the distance piece ; these
projections are called " core prints," and their use will
presently be explained. In preparing patterns great
care is to be taken that they may be accurate and of
sound, well- seasoned wood, in order that when put into
contact with the damp sand they may not warp, or
twist, or split. A certain amount of protection against
damp is afforded by the use of a good varnish, which
also materially affects the readiness with which the
pattern leaves or parts from the sand. Large patterns
are usually painted, but for small ones the following
OF MACHINERY. 181
varnish will be found very useful : Take a convenient
quantity of good shellac and dissolve it by means of a
gentle heat in a sufficient amount of methylated spirit ;
this may be then coloured with " vegetable black ;" the
varnish will then be fit for use ; it should be applied
coat after coat as each one dries, rubbing down each
coat with glass paper until the grain of the wood ceases
to be discernible and the pattern presents an uniformly
smooth surface. This varnish is perfectly waterproof
and very durable.
In forming the pattern care must also be used that
there be no sharp or well-defined internal angles left, as
at such the casting will be weak from the shrinking of
the metal ; hence, where these arise they should be filled
in with rounded fillets, as shown at F, Fig. 50. Jf the
fillets are large they may be made of wood, but if small,
of some composition such as Burgundy pitch, rosin, &c.
(Hueing should be avoided as much as possible in
pattern-making, the connection of the different parts
being made by means of nails and screws wherever
practicable, but where glue must be used it should be
properly prepared. The best glue should be taken and
broken into small pieces and then allowed to soak in
cold water for from 24 hours to 48 hours, after which
it is put in a glue-pot and dissolved by heat in the usual
manner, the heat not being allowed to exceed 212 de-
grees. The glue may be strained through coarse muslin
if there be many impurities in it. The pattern being
completed, it is ready for the foundry. The hollow
within the casting is formed by a " core " of sand
running through the mould, and in cases where the
cores are of special shapes the pattern-maker must
supply core-boxes in which they may be pressed into
form. These, however, are not required when the cores
182 PRINCIPLES AND CONSTRUCTION
are cylindrical, as such cores are roughly turned, of
different diameters, and in lengths from which portions
may be cut off as required. The pattern and core boxes
being finished pass into the hands of the moulder.
MOULDING AND FOUNDING. The apparatus used to
hold and support the sand in "which the impressions are
made from patterns to give form to the castings are
called flasks, and consist of boxes without either top or
bottom, made so as to fit accurately together.
A and B in Fig. 50 represent two flasks fitted
together, and kept in their proper position by pins or
pegs, a, b, fixed in legs on the top flask, and passing into
holes in legs on the bottom flask. In the first place, one
flask is taken and rammed full of sand, which is made
smooth and level on the surface, then in the centre of it
is scooped out a cavity, in which the pattern is buried
to half its depth, or to some other distance, according to
its shape, but always so that it may, when required, be
removed from the sand without adhesion, which tends
to cause breakage of the mould. Then on the surface
of the sand is sprinkled coal-dust or other material,
which will prevent other sand from adhering to that
already rammed down ; this is called " parting" sand,
because it ensures the parting of the mould when
required. The flask A being undermost, the flask B is
fitted on to it, and filled up with sand, which is care-
fully rammed down so as to lie close all round the
pattern and form an exact matrix to it. The flasks are
then turned over ; A being now on the top, is removed,
emptied, and refitted on , then filled and rammed down
with sand, certain pegs, e, f, being placed in it to allow
of the metal being poured into the mould and to let the
steam and gas evolved by the heat escape. The flask
A is now again lifted off from , and the pattern, after
OF MACHINERY. 183
being lightly tapped with a hammer, is taken out of the
sand ; the mould is then, if broken anywhere, mended
and smoothed by the moulder with suitable trowels,
after which the core is placed in its proper position,
being supported at the ends by the indentations made
by the core prints.
The cores, if heavy, are made on iron rods, and if
very long are supported at intervals by broad-headed
nails, which, of course, remain in the casting ; they are
made of sand, with straw or cow-dung to bind them,
after which they are dried in a core-stove to render them
firm.
The core replaced, the top flask is again put on the
lower one and firmly fixed to it, and the pieces e and /
having been removed, the molten metal is poured in,
and, spreading round the core, it fills the mould,
assuming the required shape. When the casting is
sufficiently set the mould is opened, and the "heads"
filling the places of e and f knocked off, and on cooling
the rough skin of sand which, under the influence of the
heat of the iron, vitrifies on to the casting, is, when
necessary, rubbed down with a piece of hard coke.
Precaution must be taken that the sand be not too
damp, else there is danger of the liquid metal being
blown about the foundry by the steam formed, and
ample room should be allowed for the escape of gases
and vapours. On the other hand, if the sand be too dry,
or having too much baked sand amongst it, the surface
of the mould will be apt to peel off, and the casting will
accordingly be scaly.
Moulding in loam is effected without a pattern, and
is the method generally used for large castings of bodies
symmetrically described by the revolution of surfaces,
such as cylinders, &c.
184
PRINCIPLES AND CONSTRUCTION
Fig. 51.
Let it be required to mould a large cylinder in loam.
Upon a cast-iron ring of suitable size build a well of
loose bricks A A, around which place a layer of kneaded
loam; then, at a proper
distance from the centre,
with a scraper d, carried on
a central revolving spindle,
strike the surface of the
loam to correspond with the
inside of the cylinder. Then |
thoroughly paint the sur- ^ ph:
face of the loam in order to ~
ensure its parting. Next put on another layer of loam
and strike it to the radius of the outside of the cylinder.
Outside the cast-iron ring above-mentioned place
another, and adjust it to the former by set screws.
Having painted the second layer of loam, which repre-
sents the thickness of the metal in the cylinder, sur-
round it by loam supported by brickwork where ne-
cessary. Now lift up the outer ring clear of the
inner ring, and break away the layer B , represent-
ing the thickness of metal ; mend and complete the
mould, and dry with a fire in the centre. The cylinder
being cast, the metal runs into the space previously
occupied by the layer of loam d. The casting is done as
usual, but as soon as it has sufficiently set to bear its
own weight the brickwork within it should be loosened
to allow of the free contraction of the metal.
Large cylinders, columns, and long castings generally
are much stronger if cast in a vertical position than in a
horizontal, but all small castings should be run with a
good head to consolidate the metal of the casting, and
so to prevent its being honeycombed.
Before leaving the foundry castings are trimmed or
OF MACHINERY. 185
dressed, by having any ribs, seams, or feathers chipped
off ; but it is not advisable to take off more of the sand-
skin than is requisite for rough castings intended for
purposes where they will be subject to exposure.
It is well for those inspecting castings from the
foundry, if any blow-holes are suspected, to put them
over a forge fire for some minutes, as it may sometimes
occur that such holes are filled up by the founder with
lead, which, while concealing the fault, does not obviate
its injurious character.
For hardening and softening of iron see chapter
" On Materials."
FORGING AND WELDING. Wrought-iron is reduced
to the shapes required for the purposes of manufacture
by beating or rolling it when hot; thus masses are
passed through heavy rollers to form plates and bars, or
wrought under tilt and sledge hammers, either alone or
with moulds to shape them. These moulds are called
"swages" and "swage-blocks." Malleable iron at
nearly a white heat, and steel at a low red heat, may be
shaped into almost any required form by the smith, but
by a process which is more tedious and costly than that
of founding cast-iron ; hence the wrought metal is not
used for usually- formed elements unless great strength
or tenacity is more an object than economy. To render
forgings thoroughly good, elastic, and homogeneous, the
hammering should be continued lightly until they are
nearly cold ; thus will the density of the iron be in-
creased, and its toughness proportionately so.
In working cast-steel under the hammer, it must
always be borne in mind that a low, cherry-red heat is
sufficient, as, if the steel be made too hot, it will
literally crumble under the blows and be useless ; but
186 PRINCIPLES AND CONSTRUCTION
some of the inferior steels will bear a much higher tem-
perature without injury.
The process of welding pieces of iron together is suffi-
ciently simple. The two portions to be welded together
are raised to a bright white heat, and then, having
been dipped in a flux consisting of white sand, or white
sand and salt, or borax calcined with some essential
hydrocarbon oil, they are laid together and hammered
until they become firmly united. The hammering
should begin in the centre of the sections to be united,
and gradually proceed outwards, so as to drive out any
particles of scale or slag instead of closing it in the
weld or " shut," as it is commonly termed.
The best flux is that which will the most readily dissolve
the iron scale, which is sure to form even from momen-
tary contact with the atmospheric air, and reduce it to
the most liquid condition. Until lately no method was
known of detecting the presence of a flaw or imper-
fection in a weld lying deep in the metal, but it has
been discovered that by passing a magnetic needle,
under certain circumstances, over a weld in a piece of
iron, it will indicate the soundness or otherwise of the
shut, and, if any defect exists, show the position and
extent of such defect. The welding of iron into steel
has always been regarded as a work of some difficulty,
on account of the different temperatures at which the
metals are worked, as the welding heat of iron is suffi-
cient to burn steel, and the heat of steel is not high
enough to allow of the welding of iron.
In addition to forming iron by rolling, hammering,
and pressing, the only other manipulations commonly
performed on hot iron are cutting and punching, but
even this latter is but seldom done. Iron railway bars
are cut to suitable lengths, while hot, by circular saws.
OF MACHINERY. 187
CHAPTEE XV.
ON THE WORKING OF METALS COLD.
IN the last chapter the mode of forming iron when hot
has been explained, both for cast and wrought or mal-
leable iron, and now we shall proceed to describe those
processes which are resorted to in finishing the metal
when cold, such processes comprising turning, planing,
shaping, slotting, filing, chipping, &c.
THE TOOLS generally used are shown in Fig. 52.
a represents side and top view of a point tool for turn-
ing, planing, or shaping metal. This tool is used for
taking the first cuts ; it may be regarded as forming a
superficies geometrically, as it makes a number of cuts
in straight lines side by side, being moved at right
angles to the line of cut after every stroke when planing.
This tool turns out true work, but, from being rigid and
unyielding, will not give way to any hard places, hence
sometimes leaves a somewhat rough surface. In cutting
cast-iron the metal, being brittle, falls away in chips or
as dust, and no lubricant is required to cool the tool ;
but when wrought-iron is being operated upon, the
shavings, longer or shorter, according to circumstances,
by rubbing on the tool soon heat it ; hence it is usual
188 PRINCIPLES AND CONSTRUCTION
to keep wrought-iron or steel moist by the constant
dripping from a suitable can of a ley of soft-soap and
water on to it at the point where the tool is acting.
When this tool is used in a lathe the line cut by it is a
very fine screw, or helix,
b is a point tool for inside work, such as for boring
out small cylinders and hollow work generally.
c shows a plan and side view of a spring tool, which is
used to finish work off with a smooth surface ; its edge
is broad, and slightly rounded at the corners, in order
to prevent its digging into the work at those points.
From the thinness of its extremity and its bowed form,
it will spring and yield to any hard spot, instead of
tearing it out, hence this tool leaves a smoother surface
than the point tool, though not such an accurate one.
d is a parting tool, used for dividing pieces of metal,
for cutting grooves in them, and for cutting the threads
of large square-threaded screws ; from the cutting edge
the metal is tapered down in thickness, both downward
and backward, in order that it may clear the cut, and
not become jammed in the metal on which it is used.
e is a side tool, for taking heavy cuts when the di-
mensions are to be much reduced ; its action is shown
reducing a cylindrical piece sup-
posed to be in a lathe at Fig. 53.
a is the reduced part, and b
the part being reduced by the
tool c.
To return to Fig. 52, / shows screw tools for cutting
small screws, both external and internal ; the cutting
edges are inclined so as to give the proper angle to the
thread of the screw.
g is a machine drill, for use in the lathe or drilling
machine ; the half of the cutting edge A is facing and
OF MACHINERY. 189
that B on the other side. Hand drills, which do not
continuously revolve in one direction, are ground alike
on both sides, and act rather by scraping the metal
away than by cutting it ; but the edges turning, first
one, then the other way, must be thus ground.
h is another form of drill, on which the edge is
formed by cutting away half of the conical extremity,
as shown.
i is a drill formed of a cylindrical bar, having the
end of it cut up into edges, so as to cut away the ma-
terial against which it is pressed ; but this kind of tool
is best suited for enlarging holes already drilled, as
otherwise there is some difficulty in clearing out the
chips.
k shows a small cutter, or loring bit, fixed in a slot in
a bar ; this bar passes through a hole already made,
and the cutter either "trues" it or enlarges it, as the
case may be.
I shows a loring head carried on a shaft called a
loring bar ; it is furnished with two or more cutters, or
boring bits, o, o. m is a screw working in a nut in the
head, and laying in a slot or groove in the bar n, and by
it the head is caused to move along the bar, so as to
carry the tool forward as the work progresses. This
head and bar are used for boring large cylinders.
p and q respectively show a chipping chisel with a broad
edge, and one with a point of a diamond shape, r is a
centre punch, used for marking centres and other guide
points in setting out work.
The edges of cutting tools require to be carefully
formed, according to the nature of the work for which
they are intended, and, as a general rule, it may be
taken that the harder and rougher the work the more
obtuse should be the angle of the cutting edge. Thus,
190 PRINCIPLES AM) CONSTRUCTION
we see, in heavy shears for cutting thick iron the edge
of the shears is, very nearly, bounded by a right angle.
Most machine tools, after being hardened, are tem-
pered down to a pale straw yellow colour ; but drills and
chisels require a lower temperature.
External screws are sometimes made in dies, and
internal with taps or hols, but in this method the threads
are formed partly by cutting and partly by squeezing up
the metal into shape hence the screws thus produced
are inferior to those which are cut by screwed tools.
In addition to those tools already mentioned may be
named punches, which are merely hardened steel cylinders,
that are driven by force through metal which is required
to be perforated. Soic-saws, for metal ; rotary-cutters,
which are made of all descriptions and sections, having
cutting-teeth both on their peripheries and sides,
according to the purposes for which they are designed ;
hammers, of various descriptions; and
Files. These are numerous in form and size, and also
vary widely in their coarseness of cut. Those on which
the cutting edges are continuous from side to side,
without intersections, are termed floats, and those which
have small points cut upon them over their surfaces are
rasps. The commonest descriptions of files have their
teeth cut by first making a number of serrations from
side to side, and parallel with each other, at an angle of
somewhat less than 90 to the side of the file, close
together, and from end to end, and subsequently
crossing these with similar cuts in an opposite direction,
so as to form a number of fine cutting or scratching
points all over the surface of the file. The hardening of
files must be conducted with care, in order to prevent
their warping or twisting in the process. File-making
is a special manufacture, and used to be done entirely by
OF MACHINERY. 191
liand ; but of late years file-cutting machinery has been
introduced. The coarseness of files is indicated by dis-
tinctive names, as rough, second-cut, bastard, smooth, and
dead-smooth. If any of the sides of the file be left uncut,
in order to prevent it from injuring any work on which
it may be used, that is called a safe-edge.
The different shapes of files are divided first, accord-
ing to their plan view, into parallel and taper files ; then,
according to their sections, into fiat, square, round,
crossing, three-square, half-round, &c.
To become an adept in the use of the file requires
considerable practice, and there are some men who
never will make good fitters. As the file is passed to and
fro over the work, the constantly varying leverage of
the two hands tends to cause the file to rock, and so
round off the edges of the work, thus producing a sur-
face which, instead of being a true plane, approaches
the form of a cylinder or spheroid. In order to avoid
this defect the pressure of the hands must be accommo-
dated to the motion of the file. In order also that the
files may not wear out unnecessarily quickly there should
be no pressure upon them during the back stroke, when
it would be liable to break the points off the teeth.
To get a surface as true as it can be made the final
tool used is the scraper. The surface is applied to a true
plane, called a surface-plate, which has been previously
smeared over with ruddle or other colouring matter ; this,
of course, marks the highest points on the surface to be
made true, and those points are scraped down, and the
process repeated until the marking becomes uniform all
over the surface under treatment.
In this brief description of the tools it must not be
supposed that we intend to present anything approaching
to an exhaustive account of those to be found in the work-
192 PRINCIPLES AND CONSTRUCTION
shop, as such a course would not only occupy an incon-
venient amount of space, but would also be of no
practical use, as the workman knowing the general types
described above, can readily modify their forms to suit
any particular purpose which may arise. In like manner
we shall omit detailed descriptions of the machinery used
in the shop descriptions which, to those unaccustomed
to such apparatus, are tedious, and often unsatisfactory,
and merely set forth some of the modes of applying them,
illustrating our remarks with a few necessary details.
FIXING on CHUCKING WORK. On every machine used
in the manipulation of masses of matter to be operated
upon by cutting tools there -p- c.
must be fitted apparatus
supplying the means of
firmly fixing the work,
and holding it while it is
being operated upon ; and
although this part has
different names in different classes of machines, yet, in
all of them its action depends upon similar, or almost
identical, principles. This part, in the lathe, and in
boring and screwing machines, is termed the chuck ; in
drilling, slotting, and shaping machines, the table ; and in
planing machines, sometimes the bed. A portion of one
of these chucks or tables is shown in Fig. 54, a being
a plan and b a section, or end view. It will be seen
that it is made with a number of undercut grooves, so
arranged that the heads of bolts may be slipped into
the grooves at the ends, and slid along to any required
position, to hold the work firmly against the table by
clips or by brackets called " dogs;" c shows an enlarged
section of one groove having in it a bolt d, which is
OF MACHINERY. 193
retained by the head ; on this bolt is a nut /, which
firmly holds down the bracket or dog e.
When work is brought into the machine shop the
first thing to be done is, with great care, to mark the
centres of those parts that have to be turned, and to
line out with accuracy all other guiding marks, so that
there may be no difficulty in the chucking, which must
be done so as to hold the piece of metal immoveable,
except in obedience to the movements of the chuck or
table, as the slightest yielding will most likely spoil the
work and break the cutting tool as well, the latter being,
of course, of no consequence compared with the former.
Where the action of the machine is reciprocating, and
the cutting tool is intermittent in its operation on the
work, the lateral movement is generally given to it
after the stroke, this movement being called the feed.
The back motion should be quick, in order to prevent
the waste of time as much as possible. In machines
where the action of the tool is continuous, as in the
lathe, and drilling and boring machines, the feed should
also be continuous.
In self-acting machines of the first class the feed is
commonly given by a reciprocating pall or detent, which
passes over a ratchet or spur wheel freely in one di-
rection, but moves it when driven the opposite way;
this latter motion is given to it during the return stroke,
after taking a cut. The amount or rapidity of feed can
be varied by means of altering the effective leverage of
the arms by which the detent is moved, and the direc-
tion of the feed can be controlled by causing the detent
(which is usually double, or of a T shape) to act above
or below the arm that carries it, as may be required.
In machines where the cutting action is continuous
the feed may be given by an arrangement of tangent-
o
194 PRINCIPLES AND CONSTRUCTION
screw and worm-wheel, or by a screw acting on a nut,
which, by opening and shutting, engages and disen-
gages with the screw, or by spur-wheels or rack and
pinion, or by all combined.
In cutting large screws the pitch is regulated by
introducing spur-wheels of suitable sizes between the
mandril of the lathe carrying the cylinder on which the
screw is to be cut and the screw which gives the feed to
the tool; the wheels are called change-wheels, and the
screw, the leading screw. These should be constructed
with the greatest care, as the accuracy of the screws
made is dependent upon the correctness of their forms
and excellence of construction.
The velocities at which the various machines are
driven is regulated by means of speed pulleys and spur-
wheels, so as, without interfering with the prime mover,
to adjust the rate of cut eo as to suit the size of the
work and the hardness of the material wrought. A
surface velocity of from twelve to twenty feet per minute
is thought by many mechanics to suit the different kinds
of metal ; of course, the cut being slower for the hard
substances than for the soft.
POLISHING. Some elements, after being finished as
far as can be done by the machinist and the fitter, re-
quire a finer surface, which can only be imparted by
processes of grinding and polishing.
Grinding, as for tools and cutlery generally, is effected
by revolving grindstones, followed, if necessary, by
polishing, and in nearly all cases requiring the final
adjustment of the cutting edge on an oil-stone, more
especially for cutting soft materials. In polishing a
variety of materials are used, such as powdered emery,
finely- ground glass, diamond powder, crocus martis
OF MACHINERY. 195
(sesquioxide of iron), putty powder (peroxide of tin),
bath brick, &c. A very good indeed, the best crocus
martis may be made as follows : Taking equivalent
weights of sulphate of iron and carbonate of soda, and
having dissolved them in distilled water separately, and
filtered the solutions through bibulous or white blotting
paper, Tm'y them and stir together; let the mixture
stand for an hour, after which decant the supernatant
liquor, and place the deposited precipitate upon filter
paper, and thoroughly wash it until the water which
passes through the filter is clear, and gives no precipi-
tate with solution of acetate of lead; then put the
precipitate into a crucible with a loosely-fitting lid, and
raise it to a low red heat to drive off the carbonic acid ;
the resulting substance, being freely exposed to the air,
will become pure sesquioxide of iron in an impalpable
powder. Crocus prepared thus, and carefully preserved,
can have no grit in it, and, therefore, cannot scratch the
work upon which it is used.
A revolving wheel, or moving table of some sort, must
be used in the application of polishing powders, and
the material may be either wood or metal, but it must
be remembered always that the " lap," or wheel, must
be softer than the body to be ground or polished. The
reason of this is, that the particles of grinding or
polishing powder may be able to imbed themselves in
the softer material, and being there held, will act upon
the harder.
Where metal is used for the substance of the lap we
have found a mixture of one part antimony to nine and
a half parts of lead give very good results, especially
in working on hard steel, where not even a microscopical
fault would be tolerated.
Such nicety in working may seem, at first sight, to
o 2
196 PRINCIPLES AND CONSTRUCTION
be unnecessary, but there are purposes for which it is
requisite, one of which presents itself in the flattening
by steel rollers of the gold-covered silver-wire which is
used for the manufacture of gold-lace embroidery. This
wire is thus prepared : First, a layer of one ounce of
gold is laid on to an ingot of silver, weighing nineteen
ounces ; the ingot thus plated is beaten and drawn out
to a fine wire, the gold coating drawing out uniformly
with the silver core, and when the wire has been drawn
down sufficiently fine, it is pressed flat between hard
polished steel rollers ; the flattened wire only measures
about one-thirty-second of an inch in width, and, in the
course of further manufacture, is wound round silk,
from which the embroidery above alluded to is made.
Before concluding our remarks upon the working of
metals cold, a few observations on the perforating of
sheet metals must be offered. In the ordinary practice,
the greater portion of metal intended for rivetting is
perforated by punching, a process that unduly weakens
the plates operated upon, as they are stretched on the
under surface by the sudden and violent action of the
punches, and the pieces forced out of them also are not
cylindrical, thus showing an unequal straining of the
material. This, of course, does not occur when the
metal is cut away as it is in drilling, hence, wherever
feasible, the latter process should be adopted ; but in
many cases it is too tedious and too costly to be adopted
for purposes of an ordinary character.
OF MACHINERY 19?
CHAPTER XVI.
ON JOINTS, BEARINGS, AND PACKINGS.
IN any structure or machine its strength is measured
by the weakest part, for it is evident that a machine will
not be capable of sustaining a greater effort than the
greatest which am be borne by its weakest part, hence
it is important, in order to use all the strength of a
machine, to make it as nearly as possible equally strong
throughout. Where weakness is most likely to occur is
in the joints, if they be not very carefully proportioned.
JOINTS. In ordinary rivetted joints the number of
rivets used must present sufficient sectional area to carry
the strain from one element to
the other, and the same remark
applies to bolts. The nature of
the strain on the rivet or bolt is
shearing force,because the plates
tending to slide one upon the
other would rupture the bolts
by cutting or shearing them asunder. In rigid joints
the friction of the plates upon each other, due to the
force with which they are pressed together by the ri\tets,
has been shown in some experiments to take up all the
strain, but this is not calculated upon in practice. The
safe shearing stress which may be put upon wrought -
iron is estimated at from three to four tons per square
inch of sectional area.
Let A represent the end of a link to be sustained by
a bolt passing through the hole in its extremity, the
198 PBDfCIPLES AND COSTSTBITCTION
weakest part of the body of this link will be represented
by the sectional area at b, I ; the head should be so pro-
portioned that the sum of the two sectional areas a and a
on each side of the bolt-hole shall be equal to the sec-
tional area b, b, and this area a must be continued round
the hole from one side to the other.
Let the diameter of the KnTr be d at b, b, and the
thickness of the head t, D being the diameter of the
bolt, all in inches. If the head be forked, as in some
steam-engine connecting-rods, t = the sum of the thick-
ness of the two arms, w = thickness of metal at a, and
B = total breadth of the head of the link, the area of
the section at I, b,
= 0-785 d*
and the area of the two sections at a and a
= 2 . t .w
but as these must be equal, it is evident
2 t . w = 0-785 . d*
0-392 d*
--T-
The total breadth, , however, equals 2 w + D, where-
fore,
t
D, however, has yet to be determined. The bolt may be
supported at one end or at both ; in the former case it
will have to carry the whole strain on one section, in the
latter on two sections.
Let the strain be carried by one section only, then if
S = the strain, and 3 tons be the safe shearing strength
of the metal
8 = 0-785 . D* . x 3
~8
OF XACHIXERY. 199
but if the strain be carried by two sections, then we
shall have
S = 0-785 . Z> 3 x 2 x 3
4-71
As an example let us take the forked connecting-rod of
a steam-engine ; in this case the bolt will evidently carry
the strain upon two sections. Let the strain on the link
be 14 tons, then the diameter of the bolt or pin will be
D A/ = 1-73 inches (say), If inches.
The minimum diameter of the body of the link will be
about 2^ inches ; hence, if 2 inches be the sum of the
thickness of the two arms of the forked end of the con-
necting-rod, then
inches.
In the classes of rigid joints shown at e d and ef, a
number of rivets or bolts are used. In the former case
the joint is lapped, as the strain is transmitted direct
from one part to the other. Let S = strain in tons,
d = diameter of rivets in inches, n = number of rivets,
and 4 tons safe strain per square inch, then
S = 0-785 . d 2 x n X 4
hence,
S S
0-785 d 2 x 4 3-14 d*
In the second joint, which is butted, the strain is trans-
200 PRINCIPLES AND CONSTRUCTION
mitted first from e to the cover g, and thence to /, there-
fore the above number of rivets must be put in on each
side of the line of juncture, the total number of rivets
in this case being,
8_ _ 8
~ 0-392 d z x 4 ~ 1-57 d*
If there be two cover plates, one on each side of the
plates to be joined, then will the rivets carry the strain
on two sections, hence half the number of rivets will be
required.
It has been determined experimentally that the relative
strengths for solid and rivetted work of boiler plate is,
Solid plate . . . .100
Single-ri vetted joint . . . 56
Double ,,,,.. 70
The bolts and nuts must be also so proportioned that
the head shall not strip off, nor the nut under a less
strain than that which will tear the bolt asunder.
The strain, in passing from the body of a bolt to its
head, tends to shear off the annular portion of metal by
which the overhanging part of the head is formed ; the
surface to be sheared will be, if h = height of head,
= d X 3-1416 x h
and the area of the bolt is
= d 2 x 0-785
taking the relative resistances of the metals to tensile
and shearing strain as 5 to 4, we have,
d x 3' 1416 x h x 4 = d* x 0-785 x 5
h- 5d
"W
but the heads are very seldom made less than one half
OF MACHINERY. 201
the diameter, and most commonly equal to the dia-
meter.
In the case of nuts it is to he considered that there is
not the same continuity of hold that there is in the
solid metal, hence they are made with a minimum length
equal to twice that given by the above formula, hence
for nuts we have,
-.-
Sometimes joints are made by joint tubes having
right and left handed threads cut in them, so that by
turning the joint tubes, the bars are tightened up or
slackened as circumstances may require.
When joints are made by means of keys, wedges,
or cotters, the area of the cotter must be determined
similarly to that of the bolt, which is done by replacing
0-785 d 2 in the foregoing formula?, by E x W, where li
is the breadth, and W the thickness of the cotter in
inches.
In joints where the pressure is entirely compressive,
the bearing area must be made sufficiently large to
prevent any spreading, or great and unnecessary wear
on the surfaces in contact. These connections often occur
in the toggle joints of Stanhope and certain other
presses.
In bars, such as long pump rods, which require to be
occasionally disconnected, a species of scarf joint is
much used, as shown in Fig. 55.
The scarfed ends a, 4, being Fig. ^
placed together, the box c is
slid over them to hold them in
position. The strength of the necks of the rods must
be duly proportioned.
The proper diameters of rivets to join two plates of
PRINCIPLES AOT) CONSTRUCTION
given thicknesses together, as determined by long ex-
perience, are stated in the following table :
Thickness of Plate.
Inches.
Diameter of Rivets.
Inches.
Thickness of Plate.
Inches.
Diameter of Rivets.
Inches.
1/4
1/2
5/8
3/4
5/16
5/8
11/16
7/8
3/8
5/8
3/4
7/8
7/16
5/8
13/16
7/8
1/2
3/4
7/8
1
9/16
3/4
15/16
1
1
1
The diameter of the nut may be made about 1-75
diameters of the bolt, or in extreme cases twice the
diameter of the bolt.
In making the joints of pipes under pressure and
cylinder covers, &c., the first step is to arrange to have
a sufficient number of bolts to carry the strain. A bolt
of good sound malleable iron, one inch in diameter,
should safely support a tensile strain equal to 10,000 Ibs. ;
hence if p = total pressure on joint in pounds, d =.
diameter of bolt in inches, w =. number of bolts,
then
- P
10000 X d*
10000 x n
thus if there be a joint in a steam pipe, of which the
diameter is four inches, and the pressure per inch is 80
Ibs., then the total pressure on the joint will be
= 0-785 x 16 x 80 = 1004-8 Ibs.
OF MACIimEKY. 203
hence the minimum diameter of bolts to secure this joint
must be
d = A / 1004 ' 8 = o-025 inch, or 3-16 bolts.
V 10000 X 4
Bolts so small as this, however, would not be used in
practice.
To take another example, let the joints of an air
vessel be under a pressure due to a head of water equal
to 200 feet, and let the diameter of the air vessel be 7
feet, there being 44 bolts in the joint, giving a distance
of about 6 inches between the bolts :
The pressure per square inch will be
= 200 x 0-434 = 86-8 Ibs. per square inch ;
the area of the vessel at the joint in square
inches
= 49 x 0-785 x 144 = 5541 square inches ;
hence the load on the bolts
= 5541 x 86-8 = 480,958-8 Ibs.
For simplicity, this maybe called 481,000 Ibs., then the
diameter of the bolts required will be
=v;
4810 = 1-09 inch (say), 1J inch
10000 X 44
diameter.
In respect to bolts, as in all other matters of construc-
tion, it is found that when we have to deal with small
quantities and light strains, it is not practicable to keep
204 PRINCIPLES AND CONSTRUCTION
the dimensions down nearly so low as is shown to be
safe by calculation, and, moreover, all elements must be
sufficiently massive to withstand accidental blows and
concussions.
In all descriptions of joints, the parts to be joined
together should be made true so as to fit, otherwise an
undue strain, will be thrown upon the bolts, or perhaps
a side or twisting stress. Of course in steam and water
joints it is necessary, generally, to interpose some
material to render the joint tight, for this purpose
canvas covered with a mixture of red and white lead
together in about equal parts may be used, the lead
being moistened, if necessary, with boiled oil to make
it spread.
In all cases where the main nuts of a joint cannot be
jammed down hard upon the parts which they hold, as
with the nuts on bearing caps, cross-heads of piston and
connecting rods, a second thinner nut is used which is
called a guide or check nut ; by screwing the latter tight
upon the main nut both are effectually secured from
moving. In some instances also, guards made of thin
iron to fit the nuts are used, which, by closely encircling
them, prevent their turning.
BEARINGS. The bearings of machinery being those
parts in which naturally the greatest amount of wear
takes place, it is very important that much care should
be given to proportioning their dimensions, and to the
selection of materials from which to manufacture them.
The requirements to be satisfied are to have the greatest
steadiness of working, with a minimum wear and mini-
mum friction, so as to require the least quantity of
unguent for lubrication.
OF MACHINERY. 205
Fig. 57 shows a side elevation of the ordinary kind
of bearing for revolving shafts and elements having an
oscillating motion, and a
vertical section of the same
taken on the dotted line
x a is the lower /
part, which is called the
plummer-block, usually of
cast-iron ; b indicates the
bearings or brasses, made each in the form of a semi-
cylinder, of gun-metal or bearing metal ; c is the cap of
the plummer-block, by which the brasses are kept in
position, the cap being secured by the bolts and nuts
d, d. In light work sometimes the whole bearing is
made of brass. For wrought-iron shafts the length of
bearing should be T75 times the diameter of the journal
of the shaft, which is that part which lies in the brasses.
If a sufficient length of bearing be not given, especially
in machines that are liable to much vibration, the journals
will work about in the bearings, and the whole machine
soon becomes shaky. This may frequently be noticed
with some ill-contrived marine-engines, where, apparently
in order to save room, the bearings have been made
much too short.
In the construction of bearings and journals, the
former should be bored and the latter turned as truly
as possible, after which the fitting of them accurately
together may be completed by scraping. In this pro-
cess ruddle or other colouring matter is rubbed on the
shaft, which is then slightly worked on the bearings
to show the most prominent parts; the operator then
reduces these parts with a scraper, and the process is
repeated until a satisfactory result is obtained.
As the bearings wear away they are brought together
206 PRINCIPLES AST) COXSTBUCTIOir
by tightening the nuts d, d, and where there is a de-
cided tendency to wear oval, as in the bearings of
a steam-engine, the plummer-blocks should be so
arranged that the thrust and pull act relatively in the
direction of the dotted line x , that is to say, at
right angles to the diameter on which the brasses are
separated.
A great variety of metals and alloys have been tried
for bearings in order to obtain the most durable com-
bination available ; brass, gun-metal, hard white metal,
steel and glass, have each had their trial, but almost
universally brass and gun-metal are used for the bear-
ings for wrought-iron shafts, and if kept well lubricated
the results are tolerably satisfactory.
If an unguent could be found sufficiently permanent
not to be squeezed out of the bearings, then the nature
of the material would not much affect the friction, as the
rubbing surfaces would in fact be of the unguent, and not
of the metals upon which it is spread, then the hardest
material would be the best that could be used for the
bearings, as that would wear the slowest.
There is some trouble about the efficient lubrication
of bearings, both in regard to the kind of unguent used
and the mode of applying it so as always to keep the
bearing sufficiently oiled or greased and yet not waste the
substance used for that purpose. The unguent should be
sufficiently cohesive not to be readily forced out from
between the shaft and bearing, yet it should not be of a
gummy or clogging nature, in which case it would cause
the bearing to become hot. In every case vegetable oil
is far preferable to mineral, no matter how pure the
latter, for it is apt to decompose into certain compounds
injurious to the surfaces of the metals with which it is
in contact.
OF MACHINERY.
207
A great variety of contrivances have been applied for
the regulation of the supply of oil to machine bearings,
some being on the same principle as a common lamp,
sucking up the oil by a cotton wick, and allowing it to
fall drop by drop through a hole in the plummer-block
on to the journal of the shaft, while others have acted
as pumps, making one stroke for every revolution of the
shaft. This latter is an improvement, inasmuch as the
oil is not supplied to the shaft when at rest, during which
time it would be merely running away to waste. To at-
tempt to describe the varieties of these apparatus would
occupy more space than they are worth, notwithstanding
the importance of the subject, but we may mention that
an oil vessel has been introduced, and in use for some
time, which seems to work satisfactorily. It is called the
needle lubricator.
PACKINGS. The object of packing is to allow moving
parts to work in contact without permitting the passage
between them of certain liquids and gases. In Tig. 58
different methods of packing are illustrated, a I repre-
sents a cylindrical rod, such as a piston or slide rod,
which is required to work steam and air tight through
a plate. Upon this plate is formed a box or gland
208 PRINCIPLES AND CONSTRUCTION
called a stuffing-box, e. This box, which is cylindrical,
is somewhat larger in its internal diameter than the rod
which works through it. d is a flanged cylinder bored
out to fit the rod closely but yet not tightly, as the rod
has to slide to and fro within it ; the outer surface of
this cylindrical piece is accurately turned to fit into the
box c, which is bored out to receive it. The mode of
using the stuffing-box is thus : Into the cavity e around
the rod is pretty tightly packed a plait of untwisted
rope or gaskin, which has previously been been well
saturated with Eussia tallow, or some other unguent of
equal efficiency; then the part d is placed upon this
packing and tightened down upon it by means of the
screws and nuts shown ; by this pressure the packing is
caused to lay close against the rod, so as to prevent the
passage of air or steam by it, whilst, being freely lubri-
cated, it allows the rod to move with but little friction.
As the packing wears away, the nuts are screwed down
so as to keep the Joint air-tight until there is not suffi-
cient of the material left in the box, when it must be
opened, emptied, and re-filled. In small glands the
bolts are frequently dispensed with, the part d of the
gland having a thread cut on it so as to screw down
into the stuffing-box. Various materials besides hemp
may be used for stuffing, metal rings of a conical
form, shown at JT, have been applied, also india-rubber,
but for steam joints we certainly give the preference
to gaskin. The object of introducing other packing
material is to obviate the inconvenience of frequent re-
packing. In using india-rubber packing we have found
a great liability to cut longitudinal grooves in the piston
rod. The length of the glands is regulated by the
circumstances of the particular case, according to the
amount of pressure to be resisted and the nature of the
OF MACHINERY. 209
material used for stuffing ; if it be made longer than is
necessary undue friction is created.
For hydraulic machinery, leather packing is commonly
used. / is the ram of a hydrostatic press working in
the cylinder/. In the upper part of the cylinder is
turned a recess in which is placed a leather collar of an
inverted U section, having between its sides a copper
ring to prevent its collapse ; this collar, shown in place
at (/, is illustrated in section more clearly at <k ; upon it
is placed a thin annulus of metal, and over that some
hemp or tow, as seen at h, the whole being kept in
position by the plate i, which is fastened down by
screws. From the form of the leather collar, it follows
that, upon pressure being put upon it, water entering
between its arms or sides will press them asunder and
keep them firmly against the cylinder on the one side
and the ram on the other, thus making a water-tight
joint ; these leathers, if of good quality, will wear for
a considerable time without renewal, according to the
work done by the press.
In the early steam-engines the pistons were univer-
sally packed with gaskin, but now metallic packing
rings or segments are in general use. I shows the body
of a piston in section ; it has a groove around it in
which the packing-rings o o, of cast-iron, are fitted,
being held in position by a junk-ring, m, fastened to
the piston by bolts, n. These rings are sometimes kept
in contact with the surface of the steam cylinder by their
own elasticity, being turned somewhat larger than it,
and cut so as to admit of their being forced into it,
otherwise they are made in segments and forced out by
springs placed behind them or by the action of steam
from the cylinder upon them. When one cut ring alone
is used, the line through which it is cut should be inter-
210 PRINCIPLES AND CONSTRUCTION
rupted by a tongue-piece, shown in the partial eleva-
tion, q. In some instances pistons running at high
speed have been fitted with numerous small rings put
each into a separate groove, as shown in the part
section; r.
Pistons for pumps and hydraulic engines are packed
by having cup leathers on them, as shown in section at
s, s, held between two plates, t, t, bolted together on the
rod w. The pressure of the water or other liquids on the
edges of these cup leathers also assists in keeping them
close against the pump-barrel or cylinder.
CHAPTEE XYII.
FOUNDATIONS AND FRAMING.
HOWEVER well and carefully the proportions and rela-
tive strengths of the working parts of a machine may
be calculated and set out, yet it is evident that if the
parts supporting these elements be not sufficiently strong
and rigid to resist the vibration produced by motion, the
combination will not be durable ; hence a rigid frame-
work and firm foundation should in all cases be
secured.
The nature of the strains upon framing, and the vibra-
tions occurring, will necessarily depend upon the con-
struction of the machine and the object which it effects ;
thus while some engines produce scarcely any extraneous
vibration at all, others will tend to wrench and twist
their frames in every direction ; and again, another class
of apparatus may tend to tear up its foundations bodily.
The characters of the various vibrations which arise in
OF MACHINERY 211
machinery do not seem to have received consideration in
any systematic treatise, hence we propose in the present
to enter somewhat at length into the matter.
Eevolving masses, if perfectly balanced and moving
on true centres at unvarying velocities, would produce no
vibration whatever; but these are conditions which cannot,
in practice, be satisfied, and the result is that tremors
are produced by revolving bodies on account of unavoid-
able inequalities in balance or bearing. If an element
in rotation be not balanced about its centre of motion,
it is evident that the centrifugal force of the unbalanced
portion will be ever tending to draw the bearings into
an oval or elongated form ; but the direction in which
this force acts will be constantly varying as the element
revolves, hence a general tremor will be created. The
only way in which to meet this is by a general rigidity
and massiveness of the bearings and framework to which
they are fixed ; but when the masses in revolution are
very large, they should be counterbalanced in all cases
where it is practicable.
Oscillating and reciprocating masses cause a vibratory
impulse every time a change in the direction of the
motion occurs, the effects of which may be modified in
some instances by the use of springs, or equivalent
means, as, for example, in the ordinary steam-engines,
in "cushioning " the steam.
In addition to these two descriptions of vibration
common to all kinds of machinery, there are others of
various kinds peculiar to special machines, and, if
occurring with much violence, productive of very dele-
terious effects. To discuss every sort of shock and vibra-
tion that presents itself would be beyond our scope,
hence some examples of engines and machines will be
selected, from the consideration of the strains on which
p 2
212 PRINCIPLES AND CONSTRUCTION
a general knowledge of the practical way of dealing
with shocks and vibrations may be gained.
CORNISH PUMPING-ENGINES. These engines are single-
acting, the general principle on which they work being
the lifting of a weight, called the preponderating weight,
by steam, which, in its descent, forces the water to the
place where it is required. It is evident that the steam
acting to press the piston downwards, must exert an
equal pressure upwards, tending to lift the cylinder
instead of the preponderating weight ; therefore, the
former must be securely held or " anchored " down to
the foundation upon which it is placed, and this founda-
tion must be sufficiently heavy to resist the tendency to
raise the cylinder. To give some idea of the quantity of
masonry necessary for the " cylinder load" of a large
engine, the following example will suffice : Let the
diameter of the pump be 50 inches, the height to which
the water has to be raised being 100 feet, then the total
pressure on the pump-plunger will be
= 0-7854 X 2500 X 0'434 X 100 = 85,216 Ibs.
adding to this 5 per cent, for friction, we get for the
preponderating weight, approximately,
85,216 + 4260 = 89,476 Ibs.
This, then, will be the upward pull upon the foundations
of the cylinder, and if we presume that for safety the
load is made double of this amount, it will practically
become equal to 180,000 Ibs. If this mass of matter be
made of masonry equal in specific weight to flint or
granite, the bulk of it required will be
= 1200 cubic feet,
150
OF MACHINERY. 213
which will be equal to a mass 10 feet square and 12 feet
high.
Another matter to be considered is the making provi-
sion to receive the blow of the preponderating weight if
it should fall or "run out" suddenly, through the pump
losing its water from injury to the valves or a main-pipe
bursting. For this purpose the box holding the weights
is cast with brackets or snugs on it, which come upon
spring-beams made of laminae of timber somewhat after
the fashion of a coach-spring, or they may be received
by buffers of india-rubber or other elastic material.
The valves of the Cornish engine
are actuated by tappets striking on Fig. 59.
handles or horns connected with
them, and to prevent concussion the
handles must be of such form that
the tappets will first touch them in
a tangential direction, as shown in
the elevation of an equilibrium valve-
handle in Fig. 59. a b is the curved
handle which moves upon an axis c ; the tappet d is just
coming in contact with the handle to depress it. If the
curves of these handles be properly set out, and the
tappets suited to them, the valve-gear of the engine
will work almost without sound, so slight will be the
actual blow on the handles. In the earlier engines pro-
vision had to be made against the concussions produced
by the main pump-valves, but improvements in those
elements have obviated this necessity.
EOTATIVE BEAM-ENGIXES. In the Cornish engine, to-
wards the end of each stroke the speed slackens, so as
gradually to bring the parts of the machine to rest ; but
in the rotative beam-engine the change of direction of
motion is more sudden, and, therefore, gives rise to more
214 PRINCIPLES AND CONSTRUCTION
continuous, OT, rather, more repeated vibrations, though
not comparatively so intense. Yery commonly these
vibrations are sustained by a sole or foundation plate of
cast or wrought iron, resting upon a solid mass of
masonry or concrete. The centre frame or columns sup-
porting the main-beam have evidently to bear twice the
total pressure on the piston, acting alternately in tension
and compression, hence care must be taken that the
holding-down bolts be strong enough, and that the nuts
on them be screwed down tightly, as, if any play is
allowed, the whole engine will be violently shaken at
each change of motion, and ultimately the bolts broken.
It is worth remembering that wrought-iron and steel,
under the influence of repeated concussions, change their
texture and from fibrous become crystalline, losing their
tenacity and exhibiting much brittleness.
Concussions of this sort also occur in the main-bear-
ings and connecting-rod heads when their brasses wear
loose, if they be not kept properly tightened up to
counteract the effects of such wear.
The effect of the alternate tensile and compressive
strain on the centre frame or columns of the engine,
will be to produce a transverse strain on the sole or bed
plate, putting it under the conditions of a girder sup-
ported at both ends and loaded in the centre, but differ-
ing from that inasmuch as an ordinary girder always has
the description of strain on any particular part constant ;
thus, generally, the top flange is compressed and the
bottom one extended, but in the case under considera-
tion each flange suffers alternately extension and com-
pression. The load put upon the sole-plate by the action
of the engine may be thus determined : Let p = the
maximum effective pressure of steam per square inch in
the cylinder, a = the area of the steam-piston, I =
OF MACHINERY 215
length of the working-beam in feet, D distance of
centre pin of connecting-rod from main gudgeon of
beam, W = load, then
w ^ p X a X I
D
and if the piston-rod and connecting-rod are at equal
distances from the main gudgeon, I =. 2 J), hence,
Jl r =<pxax2 = 2 p . a .
If d = depth of frame or sole in feet, the strain in
pounds on either flange will be
_ 2 . p . a . I _ p . a . I
Td ; ~2 . d
For example, let the diameter of the cylinder be 25
inches, then its area is
a = 0-7854 x 625 = 490-8 square inches ;
let the initial pressure be 40 Ibs. per square inch in the
cylinder^ then the direct strain on either flange of the
beam will be, the length of the beam being = 9 feet,
and depth of frame 9 inches
if the frame be of cast-iron, then taking the working
strength at 3000 Ibs. the area of each flange should be
= 39-26 square inches;
or if of wrought-iron, having a safe resistance of 8000
Ibs. per square inch,
117,792
= 14-72 square inches ;
oUUU
The reason of the much greater area required in the
cast-iron frame is accounted for by the low tensile
216 PRINCIPLES AND CONSTRUCTION
strength of that metal, and as the strains on the flanges
alternate, the section with unequal flanges is not suit-
able. If the sole-plate be bolted down to a bed of con-
crete it will be very materially strengthened.
In referring to these foundations a convenient oppor-
tunity occurs to mention the mortars and cements used
in making them.
Hydraulic Mortars are composed of silica and
caustic lime in general, and their peculiar property of
hardening under water may be attributed to their form-
ing hydrated silicate of lime ; when clay and magnesia
are added double silicates of greater consistency and
strength are produced. The silica should always be in
such a state that it is easily converted into a gelatinous
paste by the addition of an acid, and it should be pre-
pared by calcining it at a bright red heat with an alka-
line earth, after which it will dissolve in acids. Sand of
the quartzose kind, when mixed with lime in the 9rdinary
way, will not make a hydraulic mortar, but, after being
burnt with lime, becomes suitable for building under
water.
Those limestones which contain about 10 per cent, of
clay, when strongly burnt form good hydraulic mortars ;
but if the proportion of clay be double or treble of this
quantity it requires to be well ground before it will set.
Marls containing 30 per cent, of clay make excellent
mortar without the addition of any other ingredient ;
when the proportion of clay is greater it must not be
subjected to any great or prolonged heat.
As a general rule, all those limestones which burn to
a buff colour make hydraulic mortars.
Parker's Cement contains 45 per cent, of clay and
55 per cent, of carbonate of lime ; it is manufactured
from reniform limestones found in nodules in beds of
OF MACHINERY. 217
clay ; the analysis of the cement shows 55 parts of lime,
38 of alumina, and 7 of oxide of iron.
Concrete. A very good and durable concrete is
made of six parts gravel and well- sifted sand to one
part of chalk lime, or barrow lime. Neither sand nor
gravel alone will make a good concrete. In putting
concrete down it should be shot from as great a height
as possible in order to consolidate it ; and, where it has
heavy weights to bear, the stratum should not be less
than five or six feet deep.
Puzzolana. Artificial puzzolana may thus be pre-
pared : Eeduce coarse red bricks to powder, and mix
them with lime which has been slaked for some time,
in the proportion of two measures of brickdust to one
of lime paste, with the addition of as much water as is
necessary to incorporate them throughly.
Common lime, sand, and brickdust, in equal propor-
tions, have been found to make a good hydraulic mortar.
The Roman and Portland cements are also much
used, the latter being, when properly prepared, probably
the strongest cement there is.
If the strains on a foundation are all compressive or
of a downward tendency, the sole-plate only requires to
take sufficient hold of it to obviate the general tremor
of the machine ; but if the strains are of a lifting or
upward nature then the holding-down bolts must be
carried completely through the concrete or masonry
forming the foundation, and fastened to anchor-plates
at the bottom of it, in order that the weight of the mass
may act in steadying the superstructure. In some
cases it may be found convenient to make the bed-plate
in the form of a trough or box, and weight it by filling
it with concrete, in order to give steadiness to the engine
the steadiness increasing as the weight of the base.
218 PRINCIPLES AND CONSTRUCTION
In the GRASS-HOPPER, or half-beam engine, the maxi-
mum load on the sole-plate will be at a point under the
main-shaft, which in these engines is between the
cylinder and rocking post which supports the end of
the beam. Let P = total pressure on piston, / =: length
of beam in feet, and d = distance of connecting-rod pin
from main gudgeon of beam, then the maximum weight
on the sole
The case is very similar to that of the beam-engine.
VERTICAL, INCLINED, AND HORIZONTAL ENGINES. In
these engines the vibration and shocks caused by the
reciprocating nature of the movement are taken as direct
tensile and compressive strain by the framing to which
the main-shaft plummer-blocks are attached, hence the
calculation of the area of such framework become simple.
In a vertical engine let the steam cylinder be 16
inches in diameter and the initial .effective pressure of
the steam 40 pounds per square inch, then the total
pressure will be
= 0-785 x 256 x 40 = 8040 Ibs.
If the framework be of cast-iron it will be weakest in
tension, hence the least area to withstand this strain
would be
8040 . ,
- = 4'0 square inches.
2000
Very frequently, instead of using a common crank
with engines of these classes, solid discs or crank- wheels
are used, carrying crank-pins, and these certainly work
very smoothly and uniformly.
A horizontal engine, well arranged, and placed on a
OF MACHINERY. 219
sound foundation, will work as equably as any kind
ordinarily made, and the reason is obvious ; in the first
place, there is no massive beam to cause vibration by
its oscillations, and, in addition to this, the parts of the
horizontal engine are usually lighter than those of a
beam- engine.
MARINE ENGINES. Marine engines are, from the
peculiar circumstances under which they are placed,
much more liable than land engines to vibration and
concussions. It is, of course, impossible to get a solid
foundation for the machinery, as the ribs of the vessels
are in themselves yielding ; hence, all that can be done
is to make the engine framing as rigid and solid as
possible ; then almost all the vibration which passes to
the ships' frames will be due to the concussion of the
paddle-floats or propeller and to the " way" on the
ship. Feathering paddle-wheels, of which the floats
enter the water edgewise, cause less concussion than
those with radial boards.
LOCOMOTIVE ENGINES. The vibratory movements of
the locomotive engine, although due to causes similar
to those producing the tremors of other horizontal
engines, are yet peculiar to the former class, on account
of its high velocity and the want of a solid foundation.
The action of the steam on the cylinder covers causes
the frame of the engine to vibrate laterally and longi-
tudinally, and the unbalanced revolving masses give
rise to vertical vibrations, producing a galloping move-
ment of the engine frame. Some years back an engine
was slung in chains, and a pencil being attached to the
buffer-beam, the machinery was started ; upon a piece
of paper being placed under the pencil an ellipse was
220 PRINCIPLES AND CONSTRUCTION
drawn upon it by the vibratory, or rather, compound
oscillatory movement of the suspended engine.
MACHINES GENERALLY. In machines generally are
found the same kinds of vibrations as those already
referred to as belonging to steam-engines, but that
class, having percussive movements, are, of course,
liable to more violent concussions than others. In such,
cases materials vrhich, from their inelasticity, will
deaden vibration, should be interposed in the joints
through which the percussive action passes. Felt is
useful, also lead, if laterally prevented from spreading
under the force of the blows. In such machines as
steam-hammers the momentum of the blow, or that
portion which is not expended on the work, should be,
in great measure, taken up by the inertia of the anvil
block, which block may be bedded upon ashes kept
together by well made ground or piling. In some
peculiar cases vibrations may be taken up by springs,
and in others caused to counteract each other.
CHAPTEE XVULL.
THE ADAPTATION OF MACHINERY TO SPECIAL PURPOSES.
HAVING examined the laws by which the action of
the various mechanical elements are controlled and their
parts proportioned to the strains they are intended to
sustain, the mode of combining them for special pur-
poses requires careful and studious consideration. In
all machinery in ordinary use the engineer who desires
to construct more of a similar character may derive some
assistance from examining that already made ; but
OF MACHINERY. 221
when a new machine is required differing in its
details and purpose from any to which reference can
be made, the ingenuity of the constructor is called into
action.
Those whose practice lies amongst inventors soon
ascertain that, in the majority of cases, the inventor
knows what he wants to do, but the consulting engineer
has the task of showing how to do it ; it is, therefore,
evident that he should have a thorough knowledge of
combinations of mechanical elements and of the limits
of their application.
To define these limits is not a very easy task, so wide
is the sphere of those purposes to which mechanical
arrangements are readily applicable ; but, although it
is possible to contrive machinery capable of superseding
hand labour in almost every branch of manufacture,
yet, in many cases, the results are not financially satis-
factory, wherefore it is necessary not only to contrive a
machine which shall accomplish the desired end, but to
construct it in the simplest form and at the least cost,
both in first expenditure and subsequent working.
In the practical application of a new machine there is
almost invariably some more or less considerable time
expended in trials, and more especially when new modes
of manufacture are attempted ; as an instance, we may
refer to P. H. Devignes' flax and hemp machinery. This
was originally designed to supply, in a compact form, a
machine to clear the fibrous portions of flax, hemp, and
other similar substances, of the accompanying pithy and
siliceous matters. After many tentative experiments a
satisfactory result was attained, the machinery being
constructed at Messrs. Ledger & Co.'s factory, at Dept-
ford. Before describing the apparatus it is desirable
to consider the operations to be effected. As supplied,
222
PRINCIPLES AND CONSTRUCTION
the fibrous substance is surrounded externally by a
siliceous coating, while internally it is in contact with
pith, or "boom;" hence, both these materials must be
removed in order to obtain the fibre in a clean condi-
tion. The pith is of a short, non-fibrous nature, but
soft and yielding, and the siliceous coating of the stems
is hard, brittle, and adherent. The first, evidently,
would be removable by crushing and rubbing, the
latter by attrition and beating.
In Fig. 60 are shown the details of the machine.
The lower series of rollers revolve in fixed bearings,
but the upper series is fitted with bearings which are
Fig. 60.
capable of sliding in vertical slots, and they are kept in
contact with the lower rollers or materials operated
upon by spiral springs pressing upon the bearings of
the upper rollers, and contained in the vertical slots.
The first operation the hemp undergoes is a flattening
or crushing, by the simple pressure of the plain cj'lin-
drical rollers a a, the raw material being fed in at the
end A of the machine. The next pair of rollers b b is
grooved in a vandyked form, as shown in the section,
and serves to break the boom into short pieces ; the
OF MACHINERY. 223
pair c c carry undulations, the effect of which crushes
the boom, and causes the greater portion of it to fall
out at the bottom of the machine. The last pair of
rollers d D are formed with surfaces like rasps, as
shown in the plan view g. The upper roller, besides
revolving, has a longitudinal motion, so that the one
roller rubbing upon the other breaks up the siliceous
coating of the flax and hemp, whilst the revolution of
the rollers passes the fibre onwards towards the exit
from the machine. The axis of the roller d carries a
grooved pulley h, in which gears a vibrating piece k
actuated by a cam i, having on its periphery a spiral
groove, and being fixed on the axis of the upper roller
of the pair c c. The fibre, after passing through the
four pairs of rollers above mentioned, falls upon the
step-roller e, on which it is beaten by the revolving
blades f t thus clearing it of the remaining siliceous
coating.
The first point to be determined in this machine was
the relative sizes of the rollers, to ensure the fibre pass-
ing through without being broken or entangled. The
material stretched as the woody and siliceous matters
were removed from it, hence the rollers evidently
require to be of a progressively-increasing perimeter.
The first pair a a being three inches in diameter, the
following pairs require to be one-twentieth of an inch
greater in perimeter each than the previous pair. If the
increase be less than this the material does not clear the
machine, if greater the fibre is broken.
In the first machines made some difficulty was caused
by the fibres wrapping round the beaters/, which drew
them up by creating a draught; this was at first
attempted to be counteracted by a supplementary fan,
which, however, proved a failure ; the addition, how-
224 PRINCIPLES AND CONSTRUCTION
ever, of the guards I I prevented the wrapping of the
fibres, as the beaters giving back on coming in contact
with the steps of the wheel e, as soon as they pass those
steps are brought back by their springs into a radial
position, at the same time causing a slight draught of air
in closing against the guards 1 1, which is sufficient to
blow the fibrous material off the beaters.
The rollers were made of cast-iron, hollow, and with
wrought-iron axles, and the V and semicircular grooves
cut by rotary cutters, the work being fixed on the
bed of a planing machine, through which the feed was
given. The vibrating piece Ic was made of hard gun-
metal, and showed itself rather liable to rapid wear.
This cam arrangement was not so well designed as it
might have been ; thus, the cam h might have had a
spiral groove cut in its periphery, and a roller on a
fixed stud or " dead centre " working in such groove
would have produced the required movement, and with
fewer parts and less wear than was entailed by the plan
adopted.
This contrivance serves to illustrate the nature of the
obstacles to be dealt with in the treatment of textile
fabrics, of which the elasticity is altered as it passes
through the machine, this variation requiring adjust-
ments which can only be determined by actual experi-
ment, occupying considerable time and requiring careful
attention. The machine, in its completed state, weighs
about 7 cwt., whereas the old machines each weighed
about 1 tons.
As another example of special machinery we may cite
the pin-making machines designed by Mr. Thomas
Ruler. The wire of which the pins is made is coiled on
a reel, from which it is drawn into the different parts of
the apparatus.
OF MACHINERY. 225
In Fig 61 the principal details of the apparatus are
shown. The wire a I is first taken by the pincers C and
drawn forward a slight distance, when it is grasped by
the dies d e actuated by face cams, then a blow from the
snap g, which is carried on a spring, half forms the
head of the pin ; the dies d e then release the pin wire,
and the pincers C bring it a little farther forward, and
a second blow from the snap g finishes the head of the
Fig. 61.
pin, which is then cut off by the shears h. The pin
then falls into a groove formed by two rectangular bars,
shown in section at i; these bars are inclined at an
angle of about 45 degrees to the horizon, and the pins
slide down thm to the pointing-mill shown at m. In
order to give the pins points of a conoidal form, the
mill is placed upon vertical rocking-posts moving on an
axis n, and caused to vibrate by links I actuated by
eccentrics o. The different motions in these machines
for moving, heading, and cutting the wire are actuated
by cams. The pins are turned out at a rate of about
226
PRINCIPLES AND COXSTPvUCTIOX
400 per minute, and of lengths from one-eighth of an
inch upwards.
Calculating and registering machines have presented
and still present problems of which the solution is often
exceedingly difficult hence calculating apparatus have
not come much into use, and are now chiefly used in the
preparation of tables.
We will now explain the laws by which variable
kinds of motion for any purpose whatever within the
scope of mechanics are ruled, and from the knowledge
of which elements may be designed to produce them.
Let it be required to produce a varying rectilineal
reciprocating motion from an edge cam, the nature of
the movement
being shown in Fi 3- 62 -
the diagram,
Fig. 62. Make
a b a right line
equal in length
to the circum-
ference of a cir-
cle e, on which it
is proposed to set
out the required
cam; draw the
ordinates a b, d c, &c. of such a length as to repre-
sent at c the position of the element in contact with
the cam ; that is to say, the various distances of the
point of contact from the centre on which the cam
revolves, corresponding to proportional angular dis-
tances travelled. Thus the line a b being divided into
sixteen equal parts, the periphery of the circle e must
also be divided into a like number of equal parts, and
radii drawn from these divisions to the centre, then any
OF MACHINERY. 227
convenient radius being taken, the length a c is marked
off on it, and on the following ones the lengths d c, until
the first one is again reached, the length of which will
correspond with b c. The actual distance traversed by
the element actuated by the cam at any point in the
revolution will be found by deducting the radial length
for such point from the length a c. If it be desired to
use a cam such as that shown at/, the groove is set out
by dividing the periphery as in e, and marking off the
lengths d c on the surface parallel to the axis of re-
volution of/, and from a line/y passing round the cam,
&c. at right angles to its axis. A very brief consider-
ation will suffice to show that the varieties of cams which
can be thus set out are infinite, hence elements of this
description are very largely used in machinery having
peculiar movements.
In order to understand the nature of movements pro-
duced by any mechanical element, it is convenient to
conceive another movement combined with that due to
the element itself. Thus if a card be supposed to move
at right angles to the direction in which the action of
the cam is exerted upon a piece carrying a pencil, then
will a line be drawn on such card, the proportions of
which and its conformation will be determined by the
shape of the cam and its velocity in relation to that of
the card. In the above case the lines c, c, c, &c. would
be drawn. If, however, the card revolved instead of
moving rectilineally, the form of the curved line would
be compounded of that shown and the circle described
by the paper or card under the pencil.
If the student of engineering science desires to be
able at any time without delay to determine what class
of element is most suitable for any particular purpose,
he will find that a previous knowledge of the diagrams
Q 2
228 PRINCIPLES AND CONSTRUCTION
drawn by the elements most commonly used in machinery
will materially assist him, and frequently save long and
vexatious delays in arriving at a satisfactory result.
The cam as shown above has no distinctive diagram,
but with some of the elements the diagrams, however
varied, are ruled by fixed laws. If in an ordinary crank
movement a pencil be attached to the sliding block at
the end of the connecting rod, and a piece of paper travel
under it at right angles to the direction of the motion of
the block, and at such a velocity that during one revolu-
tion of the crank the paper will have passed through a
space equal to the circumference of the circle described
by the centre of the crank pin, then will the curve
described be almost a true cycloid, the irregularities in it
being due to the varying angle of the connecting rod ;
this, however, being slight, and the more so where long
connecting rods are used, may be neglected.
The ordinate corresponding to any angular position of
the crank will be for the first quadrant from one end of
the stroke
where r = radius of crank and v = versed sine of the angle
described by the crank since the commencement of the
stroke ; for the second quadrant the ordinate becomes
= r|a-,|
If a pencil is attached to the connecting rod at any
point between the crank pin and sliding block, and a
paper be held at rest under it, then in one revolution
of the crank an egg-shaped oval will be described on
the paper, having its longest diameter in the direction
of and equal to the stroke or throw of the crank. This
figure becomes a circle at the point of junction with the
<-rank pin, and a right line where the connecting rod
OF MACHINERY.
joins the sliding block, and is flatter as it is nearer to
the latter, its length being constant, and its narrow end
presented towards the sliding block- If motion be im-
parted to the paper as before, the result will be a some-
what similar curve developed upon the oval.
As the eccentric is identical in principle with the
crank, the diagrams described by it will of course be
the same as those above referred to.
There are many contrivances of which the object is
to restrain the movement of some particular element of
the machine in a right line. These combinations are
called parallel motions. The simplest method of obtaiiv-
ing the required end is by the use of guide bars placed
parallel to each other, and having between them a guide
block, or roller, to which the part of the machinery to
be kept moving in a right line is connected ; this is
very commonly used for horizontal, inclined, and verti-
cal steam-engines.
In beam-engines, and some other machinery, the
parallel motions are usually formed by a combination
of jointed rods, of such
proportions that a cer-
tain point shall move
in a right line, or so
nearly so as to be
practically satisfactory.
Let A, , Fig. 63, re-
present half the beam
of an engine, A being
one end-pin, the
main pin, or gudgeon,
by which the beam is
carried, and c a pin mid-way between A and ; let
the bars A e, c d, be equal and parallel, and e d,
230 PRINCIPLES A17D CONSTHUCTIOX
equal A c. There is also another bar, d g, shown
in the second view, in which the beam is in the position
it attains when the piston is at the top of its stroke, but
in the first hidden by the bar d e, to which it is equal,
and consequently also to c B. The end g works on a
dead-centre fixed to the framing of the engine.
In this arrangement there are two points which will
preserve a rectilineal movement ; first, the point e, to
which the head of the piston rod is usually attached.
The rod d g, in revolving about the centre g, describes
the arc h d, causing the position of the point d to shift
laterally through a distance, h i, and carry with it the
end d of the bar e d ; but, at the same time, the latter
bar has revolved about d in such a manner as to cause
the end e to describe (in respect to d} an arc equal to
h d, shifting the end e as much towards the centre, B,
as the motion of d g shifted it in the opposite direction ;
hence the motion of the end e of the rod e f is
restricted to a right line.
B c being equal to d g, and having the same angular
velocity, it is evident that by its movement the end c of
c d will be moved in an opposite direction to, but in an
equal degree with the end d, hence the centre of the bar
c d will move in a right line. If the distances d g, c B,
were not equal, then would the rectilineally-moving
point be situated away from the centre of c d. This
point, marked /, is the second one above referred to,
and to it the head of the air-pump rod is usually
attached.
By similar arrangements parallel motions may be
made for any kind of engine, but those consisting of
links are much more expensive than those formed with
guide-bars, and they are also apt to be not quite so
accurate.
OF MACHINERY. 231
In Fig. 64 is shown an element termed a snail. This
is a species of earn revolving on the axis a ; its peri-
phery is a curve of gradually increasing radius, being
smallest at b, and greatest at c. d is a bar held against
the periphery of the snail by
suitable means and guided ^'
so as only to be capable of
moving in a right-line, as
indicated by the arrow.
As the snail revolves the
bar d will be forced farther
from the centre a, the distance through which it moves
for a given angular movement of the snail being
determined by the form of the curve bounding the
latter, which may be set out in a manner similar to
that described for setting out cams.
In arranging the different parts of a machine those
elements should be selected which consist of the fewest
parts, and will occupy the least room the former, for
economy of prime cost and subsequent repairs, the latter
for compactness. Where the velocity-ratios of shafts
are required to be exact and perfectly constant, belts
should not be relied upon, although they are good enough
for transmitting power to workshop machinery, but
toothed gearing, or some other of an equally positive
and certain character, should be used, such as the
worm-wheel and tangent- screw, or helical wheel, accord-
ing to the relative positions of the driving and driven
shafts.
In setting out spur-gearing for purposes requiring
nicety of movement, great care should be observed in
the formation of the teeth, as, without properly-shaped
teeth, wheels will not run well together; and, on the
other hand, where the form of tooth is correctly set out
232 PRINCIPLES AND CONSTRUCTION
and accurately cut, there need be no shaking or jarring
at all. In France for many years spur-gearing has been
used for the transmission of motion in some delicate
machinery employed in the manufacture of textile
labrics, and the only noise to be heard from them is the
"whirring" due to the currents of air set in motion
by the revolution of the wheels moving at a high
velocity.
As has been already stated, the teeth of wheels running
together should be of an epicycloidal form, but in a
wheel and rack arrangement the teeth should be of a
cycloidal shape, and those of chain wheels involute on
the faces.
CHAPTEE XIX.
PHYSICAL SCIENCE CONSIDERED IN RELATION TO MECHANICS.
IN the construction of machinery for ordinary purposes,
the mechanical engineer does not require the aid of a
knowledge of physical science, except in those branches
to which we have already referred; but in general
practice it very frequently happens that the engineer is
called upon to design or report on apparatus in which
chemical and electrical forces are applied, hence it is
necessary that he should possess some knowledge of
these forces, otherwise he will be liable to grave mis-
takes. In the present chapter, therefore, we propose
giving a sketch of physical science, necessarily brief, but
sufficient to impart a general idea of the action of the
cosmical forces.
OF MACHINERY. 233
CHEMISTEY. Chemical affinity is that force by which
bodies of dissimilar natures attract each other so as to
form compounds, and by the overcoming of which com-
binations are separated again into their constituent
elements. The building up of a compound substance
from, its elements is termed synthesis, separating it into
its component parts analysis, and when the presence of
a body causes certain chemical effects to be produced
upon other substances while itself is unaffected, the
action thus produced is called catalysis. Animal mem-
branes have a property by which, when in contact with
certain substances, they will allow some to pass through
them but not others, hence thus is a method afforded
for the separation of matters which has been named
dialysis,
The mode of combination is ruled by certain fixed
laws ; that is to say, bodies do not combine in uncertain
or chance quantities, but in ascertained definite propor-
tions which are invariable. Thus water consists of
oxygen and hydrogen ; it being assumed (according to
the old notation, which will be adhered to herein) that
one equivalent of water contains one atom of oxygen
and one atom of hydrogen, water will be represented by
the equation
Water = H + HO
the numbers which represent the combining proportions
of these gases are H = 1 and = 8, hence the equi-
valent of water becomes = 9. It does not always
happen that the number of the different atoms are equal,
but the relative proportions of the different elements
always give either the equivalent numbers or multiples
of them ; these numbers are called the atomic weights.
The red rust of iron consists of two atoms of iron and
234 PRINCIPLES AND CONSTKUCTION
three of oxygen, the composition being thus written
(Fe being the symbol for iron)
Oxide of Iron Fe
- 2 3
the small figures representing the number of atoms.
The atomic weight of iron is 28, hence oxygen being 8,
that of rust or sesquioxide of iron will be
28x2 +
Hydrogen gas, the lightest of all the elements, is usually
taken as unity, the atomic weights of the other ele-
ments being given in relation to that of hydrogen.
Some modern writers have adopted a view that atomic
volumes should be equal, and consequently have doubled
the equivalents of certain bodies, but, as stated above,
we intend to use the old notation.
The elements are divided into two principal classes,
metalloids and metals, and these again are subdivided
into other classes according to their different properties,
but upon these secondary divisions it is not necessary
here to dilate.
The following table shows the atomic weight of the
metalloids and their symbols :
At Wt. 8ym.
Hydrogen. . . 1 H
Oxygen ... 8 O
Nitrogen . . . 14 N
Carbon. ... 6 C
Sulphur . . . 16 S
Selenium . . 79 Se
At Wt. Sym.
Chlorine . . . 36 Cl
Iodine . . . .127 1
Bromine . . . 80 Br
Fluorine . . . 19 Fl
Boron . . . . 11 Bo
Silicon . . . . 21 Si
Phosphorus . . 32 P
The second class, the metals, comprises a great num-
ber of elements, but many of them are rare and costly,
hence are not used to any extent in the arts ; the equiva-
OF MACHINERY.
235
lents and symbols of such as occur more commonly
are given below :
At Wt. Sym.
At Wt. Sym.
Potassium .
. 40 K
Aluminum
. 13-7 Al
Sodium . .
. 23 Na
Manganese .
. 27-6 Mn
Lithium . .
. 6-5 Li
Iron . . .
. 28-0 Fe
Barium . .
. 68-5 Ba
Chromium .
. 26-7 Cr
Strontium .
. 43-8 Sr
Nickel . .
. 29-6 Ni
Calcium . .
. 20 Ca
Cobalt . .
. 29-5 Co
Magnesium .
. 12 Mg
Zinc . . .
. 32-6 Zn
Bismuth . .
. 213 Bi
Copper . .
. 31-7 Cu
Lead . . .
. 103-7 Pb
Tin . . .
58 Sn
Antimony .
. 129 Sb
Silver . . .
. 108 Ag
Gold . . .
. 197 Au
Mercury . .
. 100 Hg
Platinum
. 98-7 Pt
Arsenic . .
. 75 As
Oxygen in combining with other elements forms
either oxides or acids ; the former acting as bases to the
latter, the two kinds of bodies uniting to form salts,
thus one atom of oxygen with one of potassium forms
oxide of potassium, or potash (potassa), which is a power-
ful alkali or antacid. Three atoms of oxygen with one
of sulphur forms sulphuric acid, which will combine
readily with the potash and form the salt known as sul-
phate of potash, the composition of which is
K o + s o d = jr. s <9 4
This is a typical salt of one class, being that formed
from oxyacids, or acids in which oxygen is the ascescent
principle.
Hydrogen also in combination with certain bodies
forms acids ; thus one atom of this element with one of
chlorine forms hydrochloric or muriatic acid, and this
acid may be combined with potash, forming a salt
typical of another class.
KO + K . Cl = K. Cl + HO
236 PRINCIPLES AND CONSTRUCTION
here the chlorine and potassium combine to form chlo-
ride of potassium, and the oxygen and hydrogen unite
as water. Salts of this class are called haloid salts, from
the similarity of their constitution to that of sea salt.
Unfortunately the rapid development of chemical
science has been attended with an evil which is great
to beginners ; this is a constant tendency on the part of
experimentalists and theoretical chemists to alter the
nomenclature to suit the results of their researches or
the requirements of the theories built thereon, and thus
an amount of confusion is unnecessarily imported into the
matter which might well be avoided, for although the
professional chemist is of course always informed of
alterations and acquainted with the systems adopted by
different physicists, yet others whose profession requires
a knowledge of the science cannot afford time to study
every new proposition or doctrine put forth, hence
cannot conveniently avail themselves of the discoveries
of certain experimentalists because the language adopted
by them is unusual.
A few examples may here be inserted to illustrate the
terminations and prefixes used in the nomenclature of
chemical compounds.
Different terminations and prefixes in some cases
show the quantities of oxygen in a body ; nitrogen is
capable of combining with oxygen in five different pro-
portions, which are named as follows :
Nitrous oxide . . = JV. 0.
Nitric oxide . . = N. 2
Hyponitrous acid = N. 3
Nitrous acid . . = N.
Nitric acid . . . = N. Os
Thus the termination " CMS" indicates the presence of
OF MACHDTEBY. 237
less oxygen than the terminal " ic," and prefix " hypo "
also shows a still lower proportion of the acidified, but
" hyper" would indicate more oxygen.
Salts formed from acids ending in "ie" have names
ending in " ate," those from acids having the terminal
"ous" end in " ite"
Thus sulphuric acid and oxide of iron form sulphate
of iron, the composition being,
Fe. + 8 . 3 + aqua,
the last (aqua) indicating water, which is incidentally
present in the proportion of seven equivalents. Sul-
phurous acid and soda form sulphite of soda,
Na. + S 2 + aqua.
The water present is termed water of crystallization,
being necessary for the substance to retain its cha-
racteristic crystalline form. The prefixes to the acids
remain the same when applied to the salts.
The acids of hydrogen give terminations " ide" or
" uret " to their salts ; thus from hydrochloric acid and
oxide of zinc we get chloride of zinc, and from hydro-
sulphuric acid and oxide of iron we have the sulphide or
sulphuret of iron.
The oxides have prefixes according to the qualities of
oxygen in them ; thus, " proto " signifies atom, to atom ;
"bis," two oxygen ; " sesqui" two metal to three oxygen ;
"per," the highest oxide. These prefixes also attach to
the salts of the bases to which they refer ; thus we have
protosulphate of iron from protoxide of iron, and sesqui-
sulphate or persulphate from sesquioxide or peroxide.
When Greek prefixes are used, they signify that the
number of atoms of metal predominates over that of the
oxygen, thus deutoxide would indicate two atoms of
oxygen to one of metal.
238 PRINCIPLES AND CONSTRUCTION
Bodies may be separated from each other according
to their solubilities, and in mineral chemistry it is by
this method principally that analyses are conducted.
If to a solution of acetate of lead some sulphate of soda
be added, the two bases will change places with each
other, sulphate of lead will form and fall to the bottom
of the solution, while the acetate of soda will remain in
solution, and may be filtered off from the precipitate.
If a body is to be analysed, the first step is to dissolve
it in water, or if necessary in acid, then the elements
must be precipitated in various forms, according to cir-
cumstances, and from the weights of such precipitates
and their known constitution, the amounts of the various
elements present may be readily computed.
In organic chemistry a different course has to be
pursued, as it is not so much the ultimate elements as
the proximate constituents which serve as a means of
judging of the nature of any given substance ; thus
nearly all organic matters are mainly composed of two,
three, or all of the elements, oxygen, hydrogen, carbon,
and nitrogen, hence it is more frequently the relative
amounts of the gluten, sugar, starch, &c., which are re-
quired to be determined than those of the ultimate
elements. These may be separated by using different
solvents, or menstrua, such as water, a cohol, ether, &c.,
to dissolve out the various components. The following
catalogue shows the behaviour of some of the commonly
occurring substances with re-agents, and may serve as a
guide in qualitative analyses, that is to say, in analyses
where the nature only, not the quantity, of substances
present is to be determined :
Potassa with bichloride of platinum yields on evapora-
tion yellow crystals.
OF MACHINERY. 239
Potassa with tartaric acid, a granular crystalline pre-
cipitate.
Soda with antimoniate of potash yields a crystalline pre-
cipitate.
Lithia boiled with phosphate of soda and ammonia gives
a slightly soluble precipitate.
Baryta with carbonates of alkalies gives white pre-
cipitate, also with sulphates and oxalic acid, and a
yellow precipitate with chromate of potash.
Lime with sulphuric acid and water, no precipitate, but
with alcohol a precipitate.
Magnesia with potash a flocculent precipitate dissolved
by adding chloride of ammonium.
with oxalate of ammonia yields white pre-
cipitate.
Alumina with potash or ammonia yields a bulky white
precipitate.
Zinc with potash and ammonia, a white gelatinous
precipitate, with sulphuretted hydrogen, a white
precipitate, except in acid solutions.
Iron Protoxide with potash or ammonia, flocculent pre-
cipitate turning brown.
with phosphate of soda, white precipitate
turning green.
with ferrocyanide and ferricyanide of
potassium, a blue precipitate.
with alcaline carbonates, white preci-
pitate.
Iron Peroxide with potash and ammonia, reddish brown
precipitate.
240 PEIXCIPLES A2O) CONSTRUCTION
Iron Peroxide with alkaline carbonates, light brown
precipitate.
with ferrocyanide of potassium, blue
precipitate.
Lead with iodide of potassium, or chromate of potash,
a yellow precipitate.
with sulphuric acid, a white one.
Silver with phosphate of soda, a yellow precipitate
ferrocyanide of potass, white ferricyanide of
potass, brown, persulphate of iron, white.
Mercury with potash, a yellow precipitate, iodide of
potassium, red, and with chloride of tin, grey.
Copper with carbonate of potash, greenish-blue pre-
cipitate, ferrocyanide of potassium, brown, and
ferricyanide of potassium, yellowish-green.
Amongst the proximate constituents of organic
matter
JEther dissolves fatty matters, caoutchouc and sulphur.
Alcohol dissolves many organic crystalline matters, such
as vegetable alkalies, &c.
Water dissolves sugar, gum, starch, and other bodies
insoluble in alcohol and sether.
Benzole and Chloroform resemble aether in their action.
"We have not space, nor indeed is it necessary for our
present purpose, to give a more detailed account of the
methods of detecting and extracting bodies, but we
shall now set forth the general properties of some
elementary substances and their compounds.
OF MACHINERY. 241
Hydrogen has the least atomic weight, and is also
specifically the lightest of the elements, the weight
of a given bulk of atmospheric air being 1000, that
of the same bulk of hydrogen would be 68. Its heat-
ing power during combustion is very great, but its
flame is colourless, and gives no light of any intensity.
In combination with certain of the metalloids it forms
acids. The distinctive test of an acid is that it will turn
infusion of litmus red, and when thus changed an
alkali will restore the original blue color ; but there are
certain substances which will combine with bases after
the manner of acids, which do not exhibit this property.
With sulphur, selenium, and phosphorus hydrogen
forms sulphuretted seleniuretted, and phosphuretted
hydrogen, the latter burning on exposure to the air.
The first is a very valuable analytical test for classify-
ing the metals. With chlorine, iodine, bromine, and
fluorine the hydracids are formed, which, in conjunction
with bases, yield haloid salts. Hydrogen combines
with oxygen in two proportions, protoxide or water,
and binoxide of hydrogen, which latter does not occur
in nature.
With nitrogen hydrogen combines in proportion of
three atoms to one, producing that well known body
ammonia. This product is formed in many ways, as by
the decomposition of animal matter by heat or putres-
cence, and by the action of powerful alkaline sub-
stances on its salts. If ammonia and hydrochloric
acid are brought together chloride of ammonium is
formed (ammonium is a hypothetical metal having the
formula N HI ) thus,
+ H . Cl = NJT 4 Cl.
if this body be acted upon by caustic lime there results
242 PRINCIPLES AND CONSTRUCTION
ammonia, chloride of calcium (lime is oxide of calcium),
and -water,
NH Cl + Ca. = NH 3 + Ca Cl. + HO
the ammonia escapes in a gaseous state, and the water
remains in mechanical combination with the chloride
of calcium, which is a powerful absorbent, and when
dried by a strong heat is used to dry gases in various
chemical processes.
We may here cite one practical effect of this re-
action ; when it occurs through the addition of lime
as a deodorizer to sewage matter, the latter is rendered
of no value as manure, because the ammonia in it is
expelled, and therefore its constituent nitrogen, which is
one of the most valuable elements of manure.
Ammonia is strongly alkaline ; it affects some of the
metals, dissolving oxide of copper pretty freely, and
combining rapidly with the acids ; its salts are mostly
volatile under the influence of heat. One volume of
water will absorb 600 volumes of ammoniacal gas.
Hydrogen will not support combustion or animal
life, and it is rapidly condensed by contact with spongy
platinum, spontaneously burning, the product of its
combustion is water.
Hydrogen is easily obtained by the decomposition of
water by some substance which takes away its oxygen,
leaving the hydrogen free. Metallic zinc is commonly
used for the purpose, but as the coating of oxide of zinc
covering its metallic surface soon stops its action, it is
necessary to add sulphuric acid to dissolve it. The
action is represented by the equation,
Hydrogen, in combination with carbon, forms a great
OF MACHINERY. 243
variety of bodies known as hydro-carbons, which are
much used for lighting and heating purposes ; coal gas,
paraffine, and naphtha are familiar examples. The
hydrogen greatly increases the heating power, and
carbon that of illumination. A unit of heat being that
amount which will raise one pound of water in tem-
perature one degree Fahr., the theoretical heating
powers of hydrogen and carbon are
Calorific value of hydrogen per pound, 62,081 units
carbon 14,505
OXYGEN is incombustible, but a supporter of com-
bustion and animal life. It combines with all the
metalloids to form acids, and with the metals to form
oxides; its specific gravity (air being 1,000) is 1,100.
Oxides combine with acids and form salts, and there are
two modes of regarding such combination : the first
merely assumes the simple combination of the two
bodies, thus
Zn . + S 3 = Zn . . S . 3 sulphate of zinc ;
the second is somewhat more complex, but yet inge-
nious, as explanatory of the changes occurring both in
mineral and organic chemistry. It is based on the
assumption that the salts of the oxygen acids are
similar in structure to those of the hydrogen acids.
Instead of considering, say, sulphuric acid as existing
as S #3 the elements of a molecule of water are intro-
duced, creating a salt radical combined with hydrogen,
thus,
S0 3 + HO = SO*H
which may be termed sulphate of hydrogen ; then
E 2
244 PRINCIPLES AND CONSTRUCTION
other sulphates are produced by the substitution of
metals for the hydrogen
S 4 + H becomes, by substituting, Zn, S 4 Zn
or sulphate of zinc, and similarly other salts are
obtained ; thus the combination of the acid or radical
with the base is shown fully by the equation,
8 Oiir + ZnO = S O^Zn + HO
the displaced hydrogen combining with the oxygen
of the base and forming water. The ordinary atmo-
spheric air consists mainly of oxygen largely diluted
with nitrogen gas, the composition of 100 measures of
air being
79 measures of nitrogen,
21 oxygen.
There is usually a little carbonic acid present, and also
aqueous vapour in variable proportions ; thus, at a tem-
perature of 42 degrees, it is O'O.l, and at 80 degrees,
0-035 of the bulk of air. Air is about 800 times lighter
than water. Oxygen may be obtained by heating chlo-
rate of potash, when it will freely be given off, leaving
chloride of potassium behind, thus
K . Cl #5 = K . Cl + G
The gas is evolved at a much lower temperature if
oxide of manganese be added, which acts catalytically,
its own composition being unaltered.
Combustion, putrefaction, rusting, &c., are processes
of oxidation, and reduction is a process of deoxidation.
(See Chap, xiii.)
NITROGEN, in a pure state, is an inert gas, incapable of
supporting life or combustion, although, at a very high
OF MACHINERY. 245
temperature, it may be burnt ; but its combustion does
not generate sufficient caloric to maintain the tem-
perature at which it burns. Its specific gravity is 970,
and it may readily be obtained by depriving atmo-
spheric air of its oxygen by burning phosphorus in it,
or by passing it slowly over spongy iron at a red heat.
This latter method is used for commercially obtaining
nitrogen, when required for preserving perishable mat-
ters, a purpose to which it is admirably adapted from
its perfect inertness.
Nitrogen, in combination with other elements, forms
substances capable of producing violent and sudden
chemical action ; thus nitric acid, JV 0^ is a most
powerful re-agent, and exerts an instant destructive
action on organic matter, and there i's scarcely any
explosive material which does not contain this ele-
mentary gas ; it is found in gunpowder, gun-cotton,
nitro-glycerine, &c.
The nitrates have a very great power of oxidation,
and have been employed to oxidize the carbon in cast-
iron in the process of manufacturing steel.
CARBON is the only solid amongst the four elements
which mainly constitute organic matter. It possesses
the property of absorbing gases so as probably to bring
them by catalytic action into combination, hence it is
useful to destroy the foul gases from putrescent matter,
or rather to reconibine them in an innocuous form, and
also as a filter for purifying and decolorising water and
other liquids. It exists in many different forms, such
as soot, charcoal, coke, bone-black, plumbago, and
diamond. Charcoal may also be prepared from sugar,
which consists of carbon, with hydrogen and oxygen in
the proportions of water ; by removing this water the
carbon is left. Sulphuric acid has a stronger affinity
246 PRINCIPLES AND CONSTRUCTION
for water than has the carbon, hence if it be added to a
saturated solution of sugar, the latter will be decom-
posed and the carbon eliminated, thus
c.n.o+so 3 = so 3 iro+ c= s OIH+ c
by washing and drying, pure carbon will thus be ob-
tained in a finely divided (atomic) state.
Carbon combines with oxygen in burning, producing
carbonic oxide and carbonic acid gases, having the for-
mula CO and C0 2 ; the latter unites readily with bases,
but is displaced with effervescence by the stronger
acids.
SULPHUR, SELENIUM, and PHOSPHORUS are three
elements which may be classed together as pyrogens,
from the readiness with which they ignite, forming
sulphuric, selenic, and phosphoric acids. Selenium
bears a great resemblance to sulphur, but it is of very
rare occurrence, hence is not used in the arts.
Sulphuric and phosphoric acids act as oxidizers, the
former being a powerful and stable acid ; it may be dis-
tilled from sulphate of iron, or prepared by the combus-
tion of sulphur, which produces sulphurous acid S0 2 ,
that may be oxidized into sulphuric acid by the subse-
quent action of nitric acid. Phosphoric acid may be
similarly produced ; but either of the more highly
oxidized acids may be obtained direct by combustion in
pure oxygen.
CHLORINE, IODINE, BROMINE, and FLUORINE are four
bodies of similar character; between the three first,
which have been more studied than the last, there are
very striking analogies.
These bodies combine with hydrogen to form hydracids
OF MACHINERY. 247
of the type x ft, where x represents any of the above
elements ; they also combine with oxygen to form oxy-
acids in different proportions. Chlorine, which is
gaseous, will support combustion to a certain extent ; it
has a very pungent odour, and is destructive to life.
It is a powerful bleaching agent, acting indirectly by
combining with the hydrogen of aqueous molecules
present, thus producing nascent oxygen, which removes
colouring matter ; its specific gravity is 2,500. Chlorine
is obtained by the action of hydrochloric acid on black
oxide of manganese, assisted by heat, thus
Mn. 6> 2 + 2 #. Cl = 2 H + Mn . Cl+ Cl
Iodine is a solid, having a specific gravity 5,000
(water being 1,000), and bromine is a liquid of specific
gravity, 3,000. Both these elements are very volatile,
and are found in company with chlorine.
BORON and SILICON occur in nature in combination
with oxygen, as boracic and silicic acids, and with many
bases they form amorphous salts, as glass, slag, glaze,
&c., wherefore they maybe called hyalogens.
The foregoing thirteen bodies are termed non-metallic
elements or metalloids, in contradistinction to the metals.
They are bad conductors of heat and electricity. When
substances are decomposed by galvanism, they always
separate at the positive (zinc) pole, hence are called
electro-negative bodies; almost all of these combine
with hydrogen, forming acids, and with oxygen, forming
oxy-acids. The conditions in which they exist are
7 Metalloids, solid : C. 8. P. 8e. L S. Sv
1 ,, liquid : Br.
5 gaseous: 0. H. N. CL Fl.
248 PRINCIPLES AND CONSTRUCTION
They form four families, or groups, founded on their
resemblance to each other
1st Group Organogens, animal andplant producers,
0. H. N. C.
2nd ,, Pyrogens, fire producers, S. Se. P.
3rd ,, Halogens, salt producers, Cl.I. Br. Fl.
4th ,, Hyalogens, glass producers, Bo. Si.
Having briefly shown the behaviour of metalloids
with metals, it will not be necessary to treat of the
latter individually, we shall, therefore, merely consider
them generally.
METALS. The following are the general properties of
the metals in contradistinction to the metalloids. All
the metals have a peculiar lustre, are opaque, and are the
best conductors of heat and electricity. Most of themetal s
will crystallize on being slowly cooled from a molten
state ; generally the crystals are cubical. All the metals
axe fusible, and some may be volatilized.
All metals will combine with oxygen, sulphur, and
chlorine, and with each other they form alloys. Most
of the metals form basic oxides with oxygen, and which
are usually insoluble in water. The sulphurets of the
light metals are soluble in water, and those of the heavy
metals insoluble. Most of the chlorides may be crystal-
lized, and are soluble in water. Generally the oxy-salts
of metals may be crystallized, sometimes with, and
sometimes without, the accession of water, but they have
different degrees of solubility in water.
The metals principally occur native in five forms,
1st, Pure Gold, Platinum, Silver, Bismuth, Mercury,
Arsenic. 2nd, as Sulphurets Lead, Antimony, Copper,
OF MACHINERY.
249
Silver, Mercury, Arsenic, Iron, Zinc. 3rd, as Arseniurets
Cobalt, Nickel, Silver, Iron. 4th, as Oxides Manga-
nese, Tin, Iron, Chromium, Zinc, Uranium, Copper.
5th, as Salts Potassium, Sodium, Barium, Strontium,
Calcium, Magnesium, Aluminum, Zinc, Iron, Lead,
Copper. The following arrangement shows the order
of affinities of elements, commencing with the most
negative and finishing with the most positive :
Oxygen
Fluorine
Chlorine
Bromine
Iodine
Sulphur
Selenium
Phosphorus
Nitrogen
Carbon
Boron
Silicon
Arsenic
Antimony
Tin
Hydrogen
The negative elements, forming preferably acids, are
the first, as far as carbon. The next to nickel are
undecided, and the remainder are positive, forming pre-
ferably bases. In chemistry generally the law holds
good that the more dissimilar bodies are to each other
the more eagerly will they combine with each other ;
thus in the above series potassium and oxygen have
a much stronger affinity for each other than manganese
has for sulphur, but there are many circumstances under
which bodies are brought together that tend to cause
the scale of affinities to fluctuate.
If any two solutions be mixed together and they con-
Platinum and Gold
Silver
Mercury
Copper
Lead and Bismuth
Nickel and Cobalt
Zinc
Iron
Manganese
Chromium
Aluminum
Calcium and Mag-
nesium
Barium and Strontium
Sodium
Potassium
250 PRINCIPLES AND CONSTRUCTION
tain elements that by exchanging places will form an
insoluble compound, such a reaction will almost in-
variably occur ; thus if to a solution of acetate of lead
another containing sulphate of soda be added, a reaction
shown by the following equation will take place,
_ Na. S & + PI. O.A = Na. 0. A + Pb S 4
(A is the symbol of acetic acid). The sulphate of lead
being insoluble falls to the bottom of the solution as a
dense white precipitate and may be separated by pouring
the solution on to a filter of bibulous or blotting paper ;
the acetate of soda will pass through in the solution,
leaving the sulphate of lead on the filter. By elective
affinity also bodies may frequently be displaced from
their compounds. Chemical changes are wrought in
some instances by invisible means ; thus the actinic or
chemical rays emanating from the sun and other sources
will produce certain reactions, such as are exhibited in
photography. These rays act independently of those
that are luminous, and in fact the most vigorous of them
when refracted by a prism fall outside of the luminous
spectrum.
The next series of physical phenomena which requires
our attention is that due to ELECRICITY. The word
electricity is derived from the Greek eXcKrpov (amber),
from its effects first being noticed as arising from fric-
tion on amber. It has been very common to speak of
electricity as a fluid, and even two kinds, positive and
negative, have by some physicists been assumed to exist,
others considering the negatively electrical state of a
body to be due to a deficiency of electricity, that is to
say, caused by the body being less electrical than it is in
its normal condition.
Electricity has been classed as static and dynamic,
OF MACHINERY. 251
the former being obtained by friction of vitreous matters,
the latter by chemical action ; also the first has great
intensity, whereas in the latter quantity predominates.
It is necessary to explain these terms as a correct under-
standing of their application is indispensable to a know-
ledge of electricity. Intensity refers to the quantity
accumulated on a given surface, whereas the quantity
is shown by the chemical effects it is capable of pro-
ducing ; the former is capable of giving violent shocks,
and shattering non-conducting bodies, biit the latter,
although the quantity passing may be much greater,
will not produce effects so evident to the senses. It is
not to be supposed, however, that intense effects can-
not be produced by electricity chemically developed, for
the intensity can be regulated, as will presently be
shown.
It appears to us that the doctrine of the existence of
an electric fluid is not satisfactory, and that the
phenomena arising from it are more conveniently con-
sidered as resulting from vibratory motions, somewhat
akin to those supposed to cause the phenomena of heat.
Frictional electricity is usually obtained from a
machine consisting of a glass plate or cylinder mounted
on insulators (non-conductors), and caused to revolve in
contact with a rubber of wash-leather, on which is
smeared an amalgam or alloy of mercury, to increase
the friction ; the electricity is collected by metal points
connected with a metallic ball, cylinder, or other prime
conductor, which is insulated, and from which the elec-
tricity may be led by suitable conductors, and applied
to any required purpose, or it may pass off, if any body
be brought within striking distance of the prime con-
ductor, when the force will bridge over the intervening
space, exhibiting a flash or spark, as the case may be.
252 PRINCIPLES AND CONSTRUCTION
Dynamic, or galvanic, or voltaic electricity is formed
by the action of acids, &c., upon metals ; thus, if two
plates, one of copper and the other of zinc, be immersed,
but not in contact with each other, in an acid solution,
then upon making a connection between them by a con-
ductor outside the liquid, a current of electricity will
pass along the conductor, and at the same time the zinc
will be attacked and partially dissolved by the acid,
whereas the copper will remain intact. The latter will
form the positive, and the former the negative pole of the
battery or cell. The course taken by the electrical
current is from the zinc through the acid solution to the
copper, whence it passes back through the conductor
from the copper to the zinc.
In the frictional machine the electricity is lowered in
the cushion or rubber, and increased in the prime con-
ductor, hence the positive pole is on the latter, the
negative on the former part in this case.
In the battery, although the zinc is the negative pole,
the metal is positive, compared with copper, as the cur-
rent passes first from it through the acid solution to
the copper. The quantity of electricity generated by
the same materials will vary as the size of the plates of
metal, but the intensity as the number of cells which are
used. In combining a number of cells to form a battery,
the zinc of one cell is connected to the copper of the
next, and so forth, the poles being located in the terminal
cells. It is evident that by enlarging the plates the
surface for the chemical action is increased, so that
more electricity is developed, but as it is developed
on a larger surface, the intensity remains constant ; but
if the number of cells be increased, the electricity
passes from one plate on to the next, where more is
developed, thus causing more electricity to exist on the
OF MACHINERY. 253
same surface, hence the intensity is increased, but not
the quantity.
We will now direct our attention, in the first place
specially, to frictional electricity. Insulated bodies
oppositely electrified attract, but those similarly electri-
fied repel each other. The insulation of bodies is accom-
plished by supporting them on glass, or some other
material which, being a non-conductor, will not allow
the electricity to pass so as to restore equilibrium.
When two bodies by friction become electrified, such
as glass and leather, then one body becomes positively
charged, the other negatively ; and if both are in elec-
trical communication with the earth, the surcharge will
pass to the earth from the positive body, and return to
the negative : the earth may be regarded as the reservoir
of electricity. The behaviour of electrified substances
towards each other is ruled by the following laws :
1 . The attractive and repellent forces vary inversely
as the squares of the distances.
2. At equal distances these forces vary as the quantities
of electricity contained by the two bodies.
The intensity of charge is in some cases the same all
over the surface of an electrified body, but this is not al-
ways the case, depending upon the form of the body ; it
will be uniform, for instance, on a sphere, but if an ellip-
soid, with one end elongated into a point, be charged, the
greatest intensity will be found at the point, naturally by
its repulsion seeking the most distant parts. The elec-
tricity will also pass off into the air from a point, showing
a light in the dark. The electrical equilibrium may also
be disturbed by induction; thus, if a body, such as a
cylinder, have one end presented to a positively electri-
fied mass, that end will be negatively electrified, and
the more distant one positively. In all these cases the
254 PRINCIPLES AND CONSTRUCTION
bodies experimented upon are supposed to be insulated.
On the removal of the cylinder from the positively elec-
trified body its electrical equilibrium is restored, provided
it has not been held near enough for any portion of
electricity to pass into it. If a wheel, carrying on its
periphery points placed tangentially, and suspended so
as to admit of rotation, be electrified, it will revolve
rapidly, as if driven by a reaction current ; and similarly
a charged point being applied to a flame, will deflect it.
In order to produce greater effects than can conveniently
be obtained from the sparks passing from prime con-
ductors, it is accumulated on a metallic surface, commonly
consisting of metallic foil lining a glass jar, or bottle,
which is also coated externally with metallic foil, the
two coatings being separated by the glass of which the
jar is made. On positively charging the internal lining
from a frictional machine, the external coating becomes
negatively charged, and the jar may then be discharged
by making electrical connection between the two coat-
ings, and any substances placed in the circuit of such
connection will be subjected to the electric shock. If
necessary, a number of these jars may be combined into
a battery, by connecting all the internal linings together,
and also all the external, then the whole series of jars
may be discharged simultaneously through one conduc-
tor. By means of an electrical spark non-conducting
bodies may be perforated, and also chemical effects may
be produced; thus, by its means, the combination of
gases may be brought about ; hydrogen and oxygen,
when a spark is passed through them, combine with
violently explosive effects.
Frictional electricity is not used in the arts to any
extent, as it is inconvenient to procure it, whilst that de-
rived from chemical means is always obtained with great
OF MACHINERY. 255
facility, being, of course, of the same character. Dynamic
electricity will, therefore, now be more fully considered.
The forms of galvanic batteries are multifarious, but
the fundamental principle being the same throughout,
it is not necessary to catalogue them all, though some
are worthy of a special notice. In the ordinary cell one
surface of the plate of copper and one of the zinc are in
action ; but in Wollaston's battery the copper plate is
curved into a U shape, so as to surround the zinc, then
both the surfaces of the latter will be brought into
action. The batteries may be charged with water
acidulated with nitric acid. As the zinc of commerce
is never pure, it will always occur that local currents are
set up in it, causing rapid destruction ; hence the zinc
should be amalgamated, then it will only be consumed
when the battery is in action and the circuit complete.
Amalgamation consists in rubbing mercury on the zinc,
which absorbs it, thus forming a protective coating.
The theory of the action of the galvanic battery is as
foUows :
1. In the combination of oxygen with an oxidizable
body, the former takes the positive and the latter the
negative electricity.
2. When an acid combines with a base, the former
takes the positive, the latter the negative electricity.
3. When an acid acts chemically on a metal, the
former is electrified positively and the latter negatively.
4. In decompositions the electrical effects are the in-
verse of those above mentioned.
5. In double decompositions the electrical equilibrium
is not disturbed.
The quantity of electricity disengaged by chemical
action is something enormous ; in fact M. Becquerel
256 PRINCIPLES AND CONSTRUCTION
found that the oxidation of sufficient hydrogen to yield
one millegramnie of water evolved sufficient electricity
to charge a metallic surface of one square metre so
highly as to discharge a spark through a distance of one
centimetre, and similar results have been arrived at by
Faraday, Pelletier, and Buff. Grove's battery consists
of an external vessel of glass or earthenware, partly
filled with water acidulated with sulphuric acid, con-
taining a zinc cylinder open at both ends and all down
one side ; inside this is a porous vessel of pipe-clay, con-
taining ordinary nitric acid, in which is immersed a piece
of platinum.
Bunsen's battery is similar in form to the last, but in
the porous tube, instead of the platinum, solid carbon is
used.
The calorific effects of dynamic electricity are con-
trolled by the following laws :
1. The quantity of heat varies as the square of the
quantity of electricity passing in a given time.
2. This quantity of heat varies as the resistance of the
conductor to the passage of the electricity.
3. Whatever be the length of the conductor, if its
diameter is constant, and will pass the same quantity of
electricity, the elevation of temperature will be the same
throughout its length.
4. For a given quantity of electricity, the elevation of
temperature at different points of the conductor varies
inversely as the fourth power of the diameter.
In chemical actions Faraday has found that if the
same quantity of electricity acts successively on a series
of solutions, the weights of the elements separated are
in proportion to their chemical equivalents.
If a piece of wire be insulated by covering it with silk
OF MACHINEBY. 257
or other non-conducting material, and then coiled round
a bar of soft iron, the latter will become magnetic
whenever an electric current is passing through the coil
of wire, but the magnetism ceases directly the current
is discontinued. The effect of a current on a permanent
magnet freely suspended, such as a mariner's compass
needle, if the current be caused to travel through a wire
laying north and south, is to make the needle for the
time being point east and west, returning to its normal
position on the cessation of the current. On this effect
is based the construction of the electric telegraph now
most commonly used.
If two conducting circuits are in proximity to each
other, but not in electrical contact, on passing a current
of electricity through one, an induced current flows
through the other, but is only momentary, occurring
only on the completing and at the breaking of the
primary circuit. The following are the laws of
induction :
1. The distance being the same, a continuous constant
current does not induce a current in a neighbouring
circuit.
2. An inducing current creates an induced current in
a direction opposite to its own when the current com-
mences.
3. Both currents are in the same direction when the
inducing current is ending.
4. A diminishing current gives rise to a direct induced
current.
5. An increasing current induces a current in an
inverse direction.
By means of passing a current through a short
primary insulated coil in the vicinity (say on the same
258 PRINCIPLES AND CONSTRUCTION
reel) of a long secondary coil, arrangements being made
for incessantly breaking the contact, a secondary current
of greatly-increased intensity is obtained, from which
very remarkable effects may be obtained. An apparatus
of this description is known as Kuhmkorff's Coil, or
more commonly as an induction coil.
Currents of electricity are also induced by causing the
armature of a permanent magnet to revolve rapidly in
proximity to the magnet, and these currents may be
collected by suitable coils of insulated wire surrounding
the armatures.
Electricity may be evolved by variations of tempera-
ture under some circumstances.
It would be inappropriate to conclude this brief notice
of the physical forces without considering the very im-
portant doctrines referring to the correlation and mutual
convertibility of the physical forces.
It hasbeen experimentally ascertained that the various
physical forces are mutually convertible ; that is to say,
the force producing one particular set of phenomena
may be changed into a force exhibiting a different class
of phenomena ; the following example will suffice to
indicate the nature of this correlation :
The combustion of fuel in the furnace of a steam-
boiler is an instance of chemical action which produces
heat, which heat, by expanding the aqueous molecules
in the boiler, gives rise to stored or potential force, and
this force may, through the intervention of a steam-
engine, be converted into mechanical power and over-
come the force of gravity, or, being expended in creating
friction, may be reconverted into heat. The same
work may be employed to develop electricity from a
frictional machine or from a magneto-electrical machine,
and this electricity may be caused to incite chemical
OF MACHINEEY. 259
action ; thus, commencing with chemical force, after a
variety of changes, it is finally again reached.
Similar transformations may be accomplished in other
ways ; thus, electricity may be used, through the agency
of electro-magnets, to do mechanical work of any descrip-
tion, or to generate heat direct by its action on certain
substances, or to incite chemical action.
Commencing with heat, it may be converted into
mechanical effect, or will incite electricity or chemical
action.
It is now desirable to point out generally in what
ways a knowledge of physical science is requisite or
advantageous to the mechanical engineer. It will be
admitted that it is expedient for any one engaged in
designing machinery for a manufacturer to be acquainted
with not only the nature of the work to be done, but
also with the nature of the materials and character of
the processes employed in connection with the apparatus.
Where acids are present the apparatus must be of such
materials as will resist their action ; thus, sulphuric and
nitric acid, with some others, rapidly corrode the common
metals, and require platinum or glass to resist their
deteriorating tendency, while, for fluoric acid, silver or
lead is requisite, glass being destroyed by it.
To conduct successfully novel metallurgical operations,
and for the comprehending of existing methods, a
knowledge of chemistry is required.
The sciences of electricity and magnetism involve
those principles on which depends the action of
telegraphic instruments and of electro- magnetic prime-
movers, and, in addition, affords us the means of
measuring and recording the efficiency of all kinds of
machinery.
While strongly urging the desirability of the me-
s 2
260 PRINCIPLES AN1> CONSTRUCTION
chanical engineer acquainting himself with the gene-
ral principles and fundamental laws of all branches of
natural philosophy, it is not to be imagined that we
wish him to be a thorough practical chemist and elec-
trician, as this would be almost beyond his reach, as the
time that can be spared to obtain a comprehension of
such laws is not sufficient to master the details of the
sciences to which they refer, nor is it necessary that he
should be able actually to practise the various manipu-
lations, although he may know how they are done by
seeing and reading, without having the manual dexterity
necessary for their performance, and which can only be
acquired after continued practice during a long period
of time. But even where there is no actual chemical
process to be carried on in the machinery, as with
sewerage works, &c., it is desirable to be conversant
with the nature of the materials passing through, and
of the changes to which they are liable ; and very fre-
quently, in all kinds of manufactures, an engineer who
is also a scientific man may be able to see and suggest
improvements which would not present themselves to
any one who did not combine the two kinds of know-
In concluding this chapter it cannot be too forcibly
impressed upon the mind of the student that there are
many intervals of time actually wasted which would
serve well, if properly applied, for obtaining scraps of
knowledge on subjects near the boundaries of strictly
engineering science which subsequently may prove of
immeasurable value. By seizing these opportunities,
and gathering together, one by one, certain physical
facts, they are each more enduringly marked in the
memory, so as to be more distinctly remembered indi-
vidually, than when a great number of facts are taken
OF MACHINERY. 261
in quick succession, as in this case it not unfrequently
happens that before one matter is well appreciated
another is commenced upon, and thus, in the mental
effort to retain the two, both are confused together. It
is a notable fact that " a little well learnt is much
better than a great deal half learnt," as the former
use is useful, as far as it goes, and the latter is no
at all.
By storing the mind with information little by little,
and at times when the facts which come under notice
may be considered and digested, it is found that, after
a time, these elements coalesce into a complete know-
ledge of the science to which they refer, and the student
becomes acquainted with it in a manner almost unknown
to himself.
CHAPTEE XX.
ELECTRICAL AND CHEMICAL MACHINERY.
FOR many years different designs for electro-motive
engines have from time to time been brought out, but
hitherto this class of machinery has not come much into
use, for although the actual efficiency of an electrical
engine may be made to approach more nearly to that
determined by theory than is the case with the useful
effect of an ordinary steam-engine, yet from the greater
expense of the materials used in the electrical than in
the steam engine, the amount of work obtained for a
given price is greater, when the latter is employed, than
when the former motor is used.
262 PBINCIPLES AND CONSTRUCTION
A current of electricity of unit strength -will decom-
pose 0-02 grains of water per second, or 0*0103 pounds
per hour, and to produce a current of this strength re-
quires the consumption in each cell of
0-0728 grains zinc per second,
0-0374 pounds zinc per hour.
The quantity of zinc necessary to decompose one
pound of water per hour would be, according to the
above figures,
. Q1Q3 = 3-63 pounds of zinc,
and the quantity of water which would be evaporated
into steam by oxidizing the hydrogen thus set free
would be, the quantity of hydrogen being 0-111 Ibs.,
= 64-2 x 0-1 1 = 7-13 Ibs.
or the units of heat developed by one pound of zinc will
be in this way,
which is equal to less than two pounds of water evapo-
rated per pound of zinc consumed. Although the force
obtained by electrical influence is not thus applied, this
calculation will yet serve to give some idea of the
quantity of heat evolved from the zinc in the process of
oxidation.
A simple form of electro-motive engine is shown in
Fig. 65 ; it may be found useful where a small power is
required to be occasionally at work, and where, there-
OF MACHINERY.
fore, a steam-engine would not be required, and
constant attention to it would be inconvenient. A
and B are two electro-magnets, made of soft iron,
and surrounded
by coils of insu- Fig. 65.
la ted wire,
through which
currents of elec-
tricity may be
passed at plea-
sure, c d is a
vibratingpiece,
moving on a fixed
centre c. To the
end d is attached a
connecting-rod d e,
of which the upper
end is connected
with a crank e f,
fixed to a shaft /,
carrying a fly-wheel ff, from which motion and power may
be transmitted to the machinery to be worked by the
engine.
When either magnet is in action, that is to say, whilst
a current is flowing round either, that one will attract
the vibrating link c d, and cause the shaft / to revolve,
one magnet acting to produce an up-stroke, and the
other a down-stroke. In order that the strokes may be
successively and regularly made, there is fixed on the
shaft / a small wheel called a rheo-motor, which changes
the current from one magnet to the other as may be re-
quired ; thus, when the top of the stroke is reached, the
conductor to the magnet A passes on to the non-con-
ducting part a b of the rheo-motor, and the conductor to
\- __ ^
264 PRINCIPLES AND CONSTRUCTION
S falls on the conducting part, the contrary change oc-
curring at the bottom of the stroke.
The electro-magnets must be placed near the fixed
centre c, as, although the magnetic force may be intense,
its power rapidly diminishes as the distance between the
magnet and 66
armature in-
r
creases, varying
inversely as the
square of the dis-
tance. Fig. 66 CZ
shows another
form of electro-
magnetic en-
V
gine. A is the electro-magnet, B the wheel to be caused
to revolve. The latter carries on its periphery a number
of armatures, e c, &c , which are successively attracted
by the magnet ; in this machine the electrical contact is
broken as each armature comes opposite the magnet,
and made again shortly before the next armature comes
before it, and so forth. A number of magnets may be
arranged if required round the wheel S. This kind of
engine works more uniformly than that last described.
The mode of constructing the rheo-motor is self-evident,
and this engine may be commended for its general
simplicity, there being but one moving part in it.
By far the most extensive application of electricity to
useful purposes is to be seen in the all-encircling system
of telegraphs, which has now been improved almost to
perfection ; in the laying of the Atlantic Cable, the
greatest question yet raised in connection with electrical
intercommunication, found its solution ; the difficulties
peculiar to the special undertaking had but to be
thoroughly understood, and once surmounted, to render
OF MACHINERY. 265
the future establishment of ocean telegraphs an ordinary
matter of business, and great honour is due to those
who, undaunted by repeated misadventure, boldly per-
sisted in their undertaking, and persevered until re-
warded with success in a matter which many thought
impossible of achievement.
Electrical telegraphs may be divided into two principal
classes : 1 , those which communicate by signs indi-
cated by the oscillation of a needle or magnetised bar ;
2, those in which the signs are made by electro-
magnets; but very frequently the two methods are
combined.
The action of telegraphs of the first class depends upon
the behaviour of magnetised needles when currents of
electricity are passing through wires in their vicinity.
The common magnetic needle points north and south,
its position being induced by an earth current of
electricity running east and west. The properties of a
freely-suspended magnetic needle are, first, they will
assume a position according to neighbouring currents ;
second, they may be affected by magnets or pieces of
iron. Similar poles repel each other, and opposite poles
exert mutual attraction ; if the north pole of a permanent
magnet be brought near a magnetic needle, it will repel
the north pole of the latter, and attract the south.
If a current of electricity be passed through a wire
lying parallel to a needle, the latter will deflect to a
position more or less at right angles to the course of the
current. The direction in which the needle will vibrate
is determined by the course of the current and the
position of the conductor through which the electrical
current is passing ; the distance through which the oscil-
lation takes place will depend upon the relative strengths
of the artificial and the earth currents, hence in any
266 PBINCIPLES AND CONSTBUCTIOX
given apparatus the direction of oscillation may be con-
trolled at pleasure, by causing the current to flow in
the course corresponding to the vibration required. On
breaking the circuit so as to stop the current, the mag-
netic needle resumes its normal position.
If two magnetic needles of exactly the same magnetic
power be attached together, so as to be suspended on
the same axis, parallel to each other, but with their poles
in reverse positions, then the directive effort of the earth
current on one will be exactly counteracted by the effort
on the other, and the system will be indifferent to the
earth current, which, be it remembered, passes under
them. If a current be passed through a wire lying
between the needles, they will obey it, as one needle being
above, and the other below, the current, the directive effort
on both will be the same. Any position once taken up
by the two needles will be retained until another current
comes into action, or some other force is applied.
This arrangement of needles, on account of its in-
difference to the natural currents which regulate the
normal positions of single magnetised bars placed under
their influence, is termed an astatic system, and is ex-
ceedingly delicate in its action, being affected by very
slight currents.
As a galvanometer, two needles may be similarly fixed,
but not exactly of equal power, then the earth current
will affect them, but the resistance to motion from the
normal position will be very feeble, and easily overcome
by weak artificial currents.
Usually in telegraphs the electricity is conducted
through wires, which, of course, oppose a certain resis-
tance to the passage of the current, hence it is necessary
to indicate the laws which regulate such resistance.
. A current of electricity of unit strength will decompose
OF MACHINERY. 267
0'0103 pounds of water per hour, and requires for its
maintenance a consumption of 0'03744 pounds of zinc
per hour. Hence, to find the strength of a current,
divide the pounds of zinc consumed per hour by 0'03744,
or,
Let S = strength of current
w = weight in pounds of zinc consumed per hour :
let the consumption of zinc be half a pound per hour,
then the strength of the current caused by its oxi-
dation is
8 = 26-7 x 0-5 = 13-35 units.
The strength of the current varies directly as the elec-
tro-motive force of one cell and the number of cells, and
inversely as the resistance of the circuit.
Let E = electro-motive force of one cell,
n = number of cells,
It = resistance of circuit, then
En
The resistance of a conductor, however, is equal to
its length divided by its sectional area and multiplied
by a factor depending on the material.
Let I = length in feet of conductor,
a = sectional area in inches,
c factor of resistance, then
a-,.!
a
or, if W weight of conductor in pounds,
R=f. I W*
For copper wire, at 50 Fahrenheit,
/ = 128 to 176
268 PRINCIPLES AND CONSTRUCTION
Let 10 feet of copper wire weigh one quarter of a pound,
then
= 128 X = 3200
0-25
replacing R by its value in the formula, for strength of
current we have
The second class of telegraphs indicates signals by
means of mechanical action brought into play through
electro-magnets ; of this kind are printing and writing
telegraphs, and also electrical bell-signals The action
of the magnet may be merely to release a stop and so
allow of the movement of clockwork driven by a spring
or weight, or the attractive force of the magnet may
produce the required effect. Generally on railways bell-
signals are used in conjunction with the needle instru-
ments.
In all cases the conducting wires of telegraphs must
be insulated, as otherwise the current proceeding from
the positive pole of the battery would return to the
negative pole by the shortest route, and without passing
through the instruments it is desired to actuate. Rail-
way and similar wires are supported by earthen carriers
attached to the posts, but subterranean and submarine
cables consist of conductors insulated by coatings of
caoutchouc or gutta percha, or some analogous com-
pound, the perfect insulation being a matter of the
greatest importance, as defect in this matter must be
attended with certain failure.
Electricity has been successfully applied in weaving,
to obviate the necessity of making costly new cards for
every pattern to be produced in the Jacquard loom. A
number of electro-magnets are employed, being regulated
OF MACHINEEY. 269
in their action by a band having the required pattern
painted on it, thus producing a surface partly conduct-
ing and partly insulating, which acts as a rheo-motor.
Several kinds of prime-movers have at different times
been brought forward, somewhat similar to the steam-
engine, but the elastic force of steam as the propelling
agent is replaced by that of some other gas.
Oxygen and hydrogen gases will explode very forcibly
when mixed in due proportion and ignited, hence by
thus combining the gases in a cylinder fitted with a
moveable piston, motion may be imparted to the latter.
The modes of ignition adopted have been various. In
the earlier engines an electric-spark was the agent, but
in those more recently constructed, gas jets have been
employed. Generally the ordinary carburetted hydro-
gen used for purposes of illumination is also employed
for the propulsion of these engines.
In the Hugon engine, manufactured by Messrs.
Vallance, of Greenwich, the gas, after being mixed with
a due proportion of atmospheric air, is ignited by a gas
jet at the end of the slide ; in this method there is neces-
sarily a communication between the interior of the
cylinder and the outer air at the moment of explosion,
hence a part of its expansive force must be lost. There
are two igniting jets, one at each end of the cylinder,
to cause the explosions to occur alternately above and
below the piston. The cylinders of gas-engines are in
proportion very much larger than those of steam-engines,
hence this class of machine would not be admissible in
situations where economy of space is an object, but they
are not used for heavy work, rarely being made of more
than about three-horse power.
Gas-engines have advantages which adapt them to
light work, where they are not required to be constantly
270 PRINCIPLES AND CONSTRUCTION
running, as when still they require no attention, and
also there is no toiler to be looked to, and consequently
no danger of destructive explosions occurring. As to
their economy of working, we are not in a position to
give any particulars.
Other gases have been proposed to be used in motive-
power engines, such, for instance, as carbonic acid,
which may be generated under pressure in a close vessel,
and used similarly to steam. Carbonic acid for this pur-
pose may be generated readily from an alkaline earthy
carbonate, such as chalk or limestone, by the addition
of a strong mineral acid, and, if it were required, the
carbonic acid gas, after doing its work in the cylinder of
the prime-mover, may again be taken up by an alkali.
Such contrivances, however, must for the present be
regarded rather as scientific curiosities than as of prac-
tical utility.
There are other numerous apparatus, any of which may
occasionally be brought under the notice of the mechanical
engineer in the course of practice ; but to describe these
in detail would occupy too much of our space, and would
fail to be of sufficient general interest, and any of these
contrivances may be readily understood when a know-
ledge of the general laws of chemistry and electricity is
obtained.
Electric lights obtained from galvanic currents, and
also from magneto-electric currents, have been applied
for the illumination of lighthouses, but there is nothing
in the arrangements which here require any particular
notice ; the light produced, although possessing much
intensity, is, like all others, obscured by mists, aqueous
vapour intercepting light rays as effectually as a solid
body, as may be observed by noticing the depth of shadow
thrown by the exhaust steam from a locomotive chimney.
OF MACHINERY. 271
CHAPTER XXI.
MISCELLANEOUS.
IN the present chapter it is proposed to notice certain
miscellaneous matters which, although worthy of notice,
could not with propriety have been included under any
of the foregoing heads.
CAST-IRON FLOOR PLATES. The following rule will
serve to determine the proper thickness of cast-iron floor
plates to sustain a given load ; it is based upon the laws
of resistance to transverse strain already set forth :
Let t = thickness of plate in inches,
I = length of plate in inches,
w = load in pounds per square foot :
I V^
380
Let I = 30 inches, and 10 =. 64 pounds :
= 0.63 inches
say five-eighths of an inch.
DOCK GATES. To find the thrust in pounds on the
ribs of dock gates,
Let D = depth of water in feet,
If = length of one gate in feet,
d = distance between point at which gates meet
and a right line joining their hinges,
P = thrust in pounds, then
p _ D 2 X Z^ x 31-2
272 PRINCIPLES AND CONSTRUCTION
Let the depth of water be 20 feet, the length of one
gate 30 feet, and the distance d 3 feet, then
P = 400X90 3 X3 '- 2 = 3,744,000 pounds.
Supposing the ribs to be of a rigid form, and of
wrought-iron, and assuming 8,000 Ibs. as the safe resis-
tance to compression per square inch, the total area of
the ribs in one gate in square inches will be
3,744,000
8QOO = 468 square inches.
To find the normal pressure on the surface of the gate
we have
P= 32. Z. 7)2.
TRACTIVE POWER OF LOCOMOTIVES.
Let T = tractive force in pounds of a locomotive,
p= mean pressure in pounds per square inch on
piston,
I =. length of stroke in inches,
d = diameter of cylinder in inches,
D = ,, driving-wheel in inches,
then, T _ p .1 .d z
D
Suppose a train weighing 110 tons requires to be pro-
pelled, the friction being on the average 1 1 pounds per
ton, what will be the mean pressure, the dimensions of
the locomotive being as follows :
I =. 24 inches, d = 16 inches D, = 60 inches ?
Transposing the above equation we have to find the
value of p,
T . D
From the weight of train and relative frictional resis-
OF MACHINERY. 273
tance given above, we have, for the total traction
required,
110 X 11 = 1210 Ibs.
hence the pressure will be
1210 X 60
= -- =11-8 Ibs. per square inch.
24 x 256
This would apply to the train running on a level ; if it
be ascending an inclined plane higher tractive power
will be required ; thus the additional tractive force to
take the train up an incline of 1 in 100 will be
the total tractive force in this case will be
2464 + 1210 = 3674 Ibs.
and the mean pressure per square inch,
3674 x 60
24 X 256
= 35-8 Ibs. per square inch.
SUPER-ELEVATION OF OUTER KAIL ON CURVES. Kail-
way trains in passing round curves, have a tendency, by
virtue of the centrifugal force, to leave the metals ; but
to obviate this the outer rail is laid at a higher level
than the inner. From the laws of centrifugal force, and
of the inclined plane, we find a formula to show what
super-elevation is necessary :
Let S = super-elevation in inches,
G = gauge of rails in feet,
v = speed of train in miles per hour,
r = radius of curve in chains, then
G . v 2
S =
397-5 . r
1>74 PRINCIPLES AND CONSTRUCTION
Let the gauge be 7 feet, speed 50 miles per hour, and
radius 10 chains,
7 X 2500
Of course the highest speed is taken in calculation, but
from the super-elevation may be deducted that due to
the conicality of the wheels' tires.
EQUILIBRATION CHAINS TO GAS-HOLDERS. As a gas-
holder rises out of the water in its tank, its pressure on
the gas increases because the metal weighs heavier in air
than in water ; hence the chains carrying the equilibra-
ting weights, when such are used, should be constructed
to counterbalance this difference. The following formula
gives the required weight of the chain :
Let w = weight of one foot vertical of gas-holder
in pounds,
G = specific gravity of the iron in gas-holder,
W = weight of one foot of chain in pounds,
n = number of chains :
For example, let to = 2000, G = 7-8, n = 4, then
9000
W= = 32-05 pounds per foot of chain.
2x7.8x4
PRESSURE DUE TO GAS-HOLDER. Let p = pressure in
inches of water, w = weight of gas-holder in pounds,
d = diameter in feet, then
4-1 d*
To find the weight of counterbalance to holder to pro-
duce a given pressure, let W = counterbalance in
pounds, P = required pressure in inches of water :
OF MACHINERY. 275
WEIGHT OF GAS. To find the weight of gas the fol-
lowing formula will suffice :
Let G = specific gravity (air = 1), v = volume in
cubic feet, w = weight required :
w = 0-0766 v . G .
STEAM CBANES. It is required to ascertain what
weight a given steam-crane is capable of lifting. In the
first place, the velocity ratio of the main drum to the
steam piston must be determined. The piston velocity
will, of course, be determined by multiplying the stroke
in feet by the number of strokes per minute, there being
two strokes of the piston to each revolution of the crank
shaft.
Let n = revolutions of crank shaft per minute,
I = length of stroke in feet,
S = speed of piston in feet per minute :
S = 2n.l.
Let JV = number of revolutions of main drum per
minute (found from n by calculating from
the diameters of wheels in the gearing),
d = diameter of main drum in feet,
s =. speed of main drum in feet :
* = 3-1416 .N.d
The velocity ratio will be
- 3 ' 1416 N ' - d
2 .n.l.
The total pressure on the pistons, there being two of
them, will be
= 2 x 0-785 x D*~ X p
where D = diameter of piston in inches,
p = pressure of steam in pounds per square inch.
T 2
276 PRINCIPLES AND CONSTRUCTION
If W =. the load the crane is capable of lifting,
Fig. 67.
Let n = 100, Z = 1-5 feet, D = 5 inches, p = (mean
pressure) 30 Ibs., 1? = 5, d = 2 feet, then
W = 100 x !***& X 30 = llj25Q lbg = 5 tons>
1 qr., 22 Ibs.
PNEUMATIC HAMMER. A hammer in which the power
is transmitted through air is now considerably used ; it
has been introduced by Mr. F. H. Roberts, and seems
admirably
adapted for light
work, such as
stamping, plan-
ishing, copper- i,
smiths' work,
light forgings,
ri vetting, &c.
This hammer con-
sists of two cylin-
ders of different
diameters, ar-
ranged one over
the other, and
communicating
with each other
internally, as
shown in Fig.
67 at j and k.
The larger and
uppermost cylin-
der has a piston or trunk-plunger h, worked by a
OF MACHINERY. 277
slotted crank-plate /. In the smaller cylinder is a
piston /, attached to which by the rod m is the
hammer-head n. On the up-stroke of the piston h a
partial vacuum is formed in the cylinder k, causing the
piston, I, and hammer, n, to rise, being again driven
down on the descent of the larger piston. The relative
strokes of the two pistons are usually made so as to be
nearly in inverse proportion to their areas.
a shows the fast and loose pulleys for driving the
hammer, being on the shaft b, carrying the cone or
speed-pulleys c, whence the power is transmitted to the
speed-pulleys d on the driving shaft e. In order to
control the force of the blow, or stop the hammer
altogether, a stop-cock is fitted to the large cylinder, by
opening which the air flows in and out, as the piston h
moves, without causing any movement of the hammer-
head. A slide-valve t is also attached to the lower end
of the small cylinder, to afford additional command over
the force of the blow. These hammers, having heads
weighing about 25 Ibs., will give 250 blows per minute,
and at that speed do their work very efficiently.
CHAPTEE XXII.
ESTIMATION OF QUANTITIES.
WHEN any machine has been designed it may be neces-
sary to calculate the weight of material which will be
required for its construction, hence it is advisable here to
insert rules whereby such weights may be readily ascer-
tained from the dimensions of the different parts.
Wroguht-iron Work. The weight of a mass of
wrought-iron is equal to its content in cubic inches mul-
278 PRINCIPLES AND CONSTRUCTION
tiplied by 0-278 pounds or 0*000124 tons, or to its con-
tent in cubic feet multiplied by 490 pounds or 0-2143 tons.
Round Ears. Multiply the square of the diameter in
inches by the length in feet, and by 2'618 pounds or
0-00117 tons.
Elliptical Bars. Multiply the conjugate diameter in
inches by the transverse diameter in inches, by the
length in feet, and by 2-618 pounds or 0-00117 tons.
Rectangular Bars. Multiply the width in inches by
thickness in inches and length in feet, and by 3-33
pounds or 0-00149 tons.
Plate-iron. Multiply the surface in square feet by the
thickness in inches, and by 40 pounds or 0-0178 tons.
Angle-iron. Add together the breadths in inches,
measured on the outside, from the sum subtract the
thickness of the metal in inches, multiply the remainder
by the thickness in inches and length in feet, and by 3-33
pounds or 0-00149 tons.
Bars of irregular section. Multiply the sectional ar a
in square inches by the length in feet, and by 3-33
pounds or 0-00149 tons.
Sphere. Multiply the cube of the diameter in inches
by 0-1454 pounds or 0-000065 tons.
Rivetted Work. Allow 5 per cent, additional weight
for heads of rivets.
Steel, Cast-iron, fyc. To ascertain the weights for other
metals proceed as directed above, and then multiply the
results by one of the following factors, corresponding to
the metal to be used :
If the material is steel . multiply by 1 -008
cast-iron ,, 0-915
brass . 1-084
copper . ,, 1-150
lead 1-477
OF MACHINERY. 279
If the pattern for a casting be made of dry pine the
weight of the casting will be equal to that of the pattern
multiplied by 1 1 .
Timber Flooring. Multiply the length in feet by the
breadth in feet and thickness in inches, and by one of
the following factors, according to the material :
Elm . . 3-50 Ibs. or 0-00156 tons.
Yellow Fir . 3-42 0-00153
White Fir . 2-97 0-00132
Dry Oak . . 4-85 0-00216
Timber fleams, Posts, $c. Multiply the length 'in feet
by the breadth and depth in inches, and by one of the
following factors :
Elm . . 0-292 Ibs. or 0-000130 tons.
Yellow Fir . 0-285 0-000127
White Fir . 0-247 0-000110
Dry Oak . 0-404 0-000180
In the estimation of quantities and measuring of work
the following numbers may also be frequently found
serviceable :
1 centimetre . . . .0-3937 inches
1 metre 39-37
1 8-2808 feet
1 gramme .... 15*436 grains
1 kilogramme .... 2-2048 Ibs.
1 link 7-92 inches
1 foot 1-5151 links
36cubic ins.of wrought-iron weigh 10 Ibs.
1 inch square bar 1 yard long weighs 10 , ,
inch plate 1 foot square ,, 10
1 cubic inch wrought-iron ,, 0-278 Ibs.
36 cubic inches of cast-iron ,, 9*96 ,,
PRINCIPLES AND CONSTRUCTION
1 inch square bar I yard long
9-96 Ibs.
inch plate 1 foot square
9-96
cubic inch of cast-iron .
0-262
lead .
,, 0-41
brass .
0-283
copper
0-317
,, ,, steel
0-283
cubic foot of elm .
,, 42
yellow fir .
41-1
1 white fir .
35-6
1 ,, ,, dry oak
58-2
80 chains ....
1 mile
69-121 chains .
. 1 geog. degree
10 square chains
1 acre
640 acres ....
1 square mile
Circumference of a circle .
. 3- 141 6 x diameter
Area . ,,
0-7854 X sq. diam.
Surface of a sphere .
. 3-1416 x sq. diam.
Solidity of a sphere .
. 0-5236 xcubediam
1 cubic foot pure water
. 62-321 Ibs.
1 imperial gallon
. 277-274 cubic ins.
1 ton of water .
. 35-84 cubic feet
1 mile
. 5280 feet
1 mile per hour
. 1-466 feet per send.
CONCLUSION.
IN concluding this Treatise, which has been written with
the view of supplying a work which shall furnish at once
the data upon which the practice of mechanical engi-
neering is based, and to serve as a convenient book of
reference, it may not be unadvisable to offer a few re-
marks upon the conducting of such practice.
OF MACHINERY. 281
The first thing which the young engineer has to do is
to use every endeavour and seize every opportunity to
gain a thorough knowledge, practically and theoretically,
of the materials and processes with which in after life
he will be called upon to deal. Having such a know-
ledge (and this cannot be acquired except by years of
patient, untiring, study and observation) he will be
guarded from falling into such mistakes as that wide-
spread one on which so many fortunes, and lives have
been wasted, " perpetual motion." Although this is the
notable fallacy, the ignis fatuis which has led so many
uneducated mechanicians astray, yet there are many
others which, though not so important in their results,
are sufficiently vexing, and cause a considerable waste
of both time and money, besides bringing discredit upon
those who are misled by them ; but these smaller mis-
takes will not be committed by such as thoroughly
understand their business and take sufficient care.
In order to carry out any work in the most satisfac-
tory and, at the same time, most expeditious manner, the
folio wing course should be pursued : First Thoroughly
examine and become acquainted with all that is required
to be done, the mechanical forces to be brought into
action, and the nature of the materials to be dealt with.
Second, Give a full consideration to all the details of the
work and the mode of combining them. Third Having
planned the work, do not readily alter such plans ; that is
to say, do not alter the plans unless some evident benefit
is to be gained by so doing ; and Fourth Take means
to ensure that the work shall be rigorously in accordance
with the designs both as to form and materials used in
manufacture.
THE END.
EEEATUM.
At p. 81, the diagram, showing the chemical changes
during combustion, has been accidentally reversed.
The reactions are as follows :
The hydrogen of the fuel combines with oxygen of
the air, forming water, the carbon of the fuel com-
bines with oxygen of the air, forming carbonic acid gas,
and the nitrogen of the air remains free as shown by
the equation, where a hydro-carbon fuel is assumed :
FueL Air. Products of Combustion.
C 10 H + On + Nn = ffO + W.C0 2 + 79N
INDEX
A PAGE
Atoms . ..... 6
Accumulated work . . . . . .11
Axle, wheel and . . 24
Area of chimneys .....
Air-engine, Messer's ... .95
Aydon's liquid-fuel system . .97
Alloys of metals . . .173
Atomic weights . ... 234
B
Bodies, falling .... . . 12
Bevil wheels . . 29
Beams, strength of rocking . 45
Boilers, grate surface in . .86
heating surface in . .86
horse-power of
Craddock's patent . 104
Field's patent . 105
Explosions
Breast wheel . .122
Blast furnace . . . . .164
Bearings ..... 204
Battery, galvanic . . . . .255
Cohesion .... . . 6
Centrifugal force ... . . 15
Centre of gravity . . . . .22
284 INDEX.
PAGE
Cogwheels . . . . . 29
Cranks ...... 3145
Cams ........ 32
Co-efficients of friction . . . . .35
Cylinders, strength of . . . . .42
Covers ....... 43
Cast-iron pillars, strength of . . . . .44
Clutches. . . . . . . .53
Condensation water . . . . . .81
Craddock's boiler . . . . . .104
Canals, flow of water in . . . . .114
Comparative efficiency of vessels . . .142
Characteristics of wood . . . . .147
Copper . . . . . . . 167
Chucking work . . . . . .192
Cement, Parker's . . . . . .216
Concrete . . . . . . .217
Cast-iron floor-plates, strength of . . . .271
Chemical nomenclature ..... 236
Cranes, steam . . . . . . . 275
D
Diagram, indicator . . . . .69
Dynamometer, friction . . . . .71
Delivery of water, through orifices . . . .112
over weirs . . . . .114
,, through canals . . . .114
,, ,, through pipes .... 114
Dock gates, thrust on . . . . . .271
E
Equations, simple ...... 2
Elasticity , . .9
Eccentric . . . . . . .31
Engaging and disengaging gear . . . .52
Engines, horse-power of steam . 67
Explosions, boiler . . 108
Efficiency of vessels, comparative . . . .142
Electro -motive engines . ... 263
Electric telegraphs. . . . . . .265
INDEX. 285
PAGB
Electrical loom . . . . . . .268
induction . . . 253
Electricity, fractional . . . . . .251
Electric battery . . . . . .255
Equilibration chains ... ... 274
Force of cohesion . . . . .6
gravitation . . .6
parallelogram of . . . . .8
potential . . . . . .10
centrifugal . .... 15
moment of . . . .17
Friction, co-efficients of ..... 35
Friction dynamometer . . . . .71
Fuel, evaporative value of . . . .83
Fuel, liquid, Aydon's system . . 97
Field's boiler 105
Flow of water through orifices . . . .112
over weirs . . . . .114
in canals . . . . .114
through pipes . .114
Fluxes .... . 158
Forging and welding . . . . . .185
Files . . 190
Foundations ....... 210
Framing ....... 210
Flax machinery (Devignes') ..... 221
Frictional electricity . . . . . .251
G
Gravitation .... .6
Gravity, centre of . . . . .22
Girders, strength of . . . . .42
Gear, disengaging . . . . . .52
Gill's theory of steam ...... 59
Governors ..... .79
Grate surface in boilers. . . . . .86
Galvanic battery, theory of . . 255
Gas-holders, equilibration chains for .... 274
286 INDEX.
H PAGE
Hydrostatic press . . . 21,133
Horse-power of engines . .67
Heating surface in boilers . . 86
Horse-power of boilers . 99
Hydraulic ram .... .131
lift .134
mortars . . 216
Hammer, pneumatic ...... 276
I
Inertia . .7
Iron pillars, strength of cast . . 44
Indicator diagram . . . . . .69
Iron . .148
metallurgy of . . 151
Induction, laws of electrical . . . . .257
Iron floor-plates, strength of cast . . 271
L
Lever ..... . 20,23
Liquid fuel, Aydon's system . . 97
Lead . . . . 1 . 170
Locomotives, tractive power of .... 272
M
Machine, definition of ... .5
Moment of force . . . . . .17
Moor and Shillitoe's furnace ..... 64,93
Muntz's metal . . . . . . .173
Metals, alloys of . . .173
Moulding and founding . .182
Motions, variable . . . . . .226
parallel ....... 229
N
Nominal horse-power . . 67
O
Overshot water-wheels . .119
Parallelogram of force
INDEX. 287
PAGE
Potential force 10
Power .... . 11
Planetary motion . . . < . .16
Pulleys 26
Pipes, strength of . .43
Pillars, strength of cast-iron . . 44
Pipes, flow of water through . .114
Pump valves . . . . . . .129
Pattern-making ... .179
Polishing ... .194
Packings ..... .207
Parker's cement ...... 216
Puzzolana . . . 217
Pin-making machinery . . 224
Parallel motions ...... 229
Pneumatic hammer ... . . 276
R
Rack and pinion . . .33
Rocking beams, strength of . . . .45
Ram, hydraulic . . . . . .131
Rivets, size of . . . . . . . 202
S
Simple equations ...... 2
Screw ........ 24
Spur wheels ....... 29
Slotted link 31
Strength of iron, &c 38, 160
girders . . . . . .42
cylinders . . . . . .42
pipes . . 43
covers . . . . . .43
cast-iron pillars . 44
rocking-beams . . . . .45
cranks . . .45
shafts . . . . . .46
fly-wheels . . .47
teeth of wheels . . . . .50
timber . .143
288
. PAOB
Slide-valve ....
. 74
Skins of iron ships
. 142
Seasoning timber
. 145
Steel, tempering of
. 165
Snail .....
. 231
Super-elevation of outer rail
. 273
Steam cranes
. 275
T
Toggle .
. 25
Teeth of wheels, strength of .
. 50
form of
. 61
Turbines
. 122
Timber, seasoning
. 145
Tin
. 171
Tools for working metal
. 187
U
Undershot water wheel
. 116
V
Variable motions
. 226
Vortex wheel ....
. 125
W
Wheel and axle
. 24'
Wedge
. 24
Williams' s theory of steam
. 60
Water wheels ....
. 112
Whitelaw's turbine . . .
. 124
Z
Zinc .....
. 172
t
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