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ELEMENTARY LESSONS

IN THE

PHYSICS OF AGRICULTURE

BY

F. H. KING,

PROFESSOR OF AGRICULTURAL PHYSICS IN THE
UNIVERSITY OF WISCONSIN.

STATE JOURNAL PRINTING COMPANY,
PRINTERS AND STEREOTYPERS.
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PREEACE:

Because of the entire lack of literature relating to the
physics of agriculture, in any form available for class instruc-
tion, these elementary lessons have been undertaken to meet
the immediate needs of our Short Course students. They are
intended simply as a temporary expedient to be used until
time shall permit the preparation of a suitable text-book on
the Physics of Agriculture, this field being at present entirely
unoccupied.

Farm drainage ; the construction, ventilation and warming
of farm buildings; physical principles and care of farm ma-
chinery; water supply for farms; and the forecasting of
weather changes are among the topics presented to our classes,
but which could not be outlined in time to be included here.

INTRODUCTORY.

_1. Physical and Chemical Changes.— When trees are
cut into stove wood or cut into dust with the saw, the pieces
which remain are wood still and such changes are physical;
but when the wood is placed in the stove and burned changes
take place which destroy the wood, as such, and these are
chemical changes. When a lump of sugar is dissolved in water
the sugar is sugar still and may be recovered as such by
evaporating the water, and the change is a physical one; but
when yeast and “mother of vinegar” are added to the sweet-
ened water and allowed to stand the sugar is transformed,
alcohol and then vinegar appear in its stead, and the changes
are chemical ones. The fall of rain and snow to the ground,
the flowing of streams to the sea and the evaporation and
return of the water to the land again are all physical changes.
The operations of tillage, of drainage, the cutting and fea
ling of farm produce and the acne of butter are physical
processes. The running of farm iehiners, and the construc-
tion of farm buildings involve an understanding of physical
-rather than chemical laws.

Write a list of five physical and five chemical changes.

2. Matter and Force.— The physical universe, so far as
we are able to comprehend it at present, appears to be made
up of two classes of agencies, one of which is active and called
force, while the other is passive, or acted upon, and named
matter. Water is matter, and gravity is the unseen force or
agency which causes it to flow to the sea or to turn the water-
wheel; air is matter, but gravity is the force which moves it
in the wind when it drives the ship or turns the wind-mill.
Wood and oxygen are matter, but chemical affinity is the
force which drives their molecules into collision Bie y Getne. the
intense heat and light of the fire.

3. Kinds of Matter.— Chemistry at present distin guishes
about seventy kinds of matter which are known as aleriaeis
or elementary substances ; oxygen, hydrogen, nitrogen, carbon,

4

iron, sulphur and phosphorus are seven of these. Water is
not one of the elements, for it can be decomposed and shown
to consist of oxygen and hydrogen. Sugar is not an element,
but is made up of carbon, oxygen and hydrogen.

4. Constitution of Matter.— Each and every body or
mass of elementary substance, is composed of large numbers
of minute units or individuals named atoms, which various lines
of experiment, observation and reasoning show to be constant
in weight and properties, so far as we know them; and it is in
consequence of this constancy of weight and properties that
chemistry is able to analyze the various substances and tell us
their composition.

The atoms of which all bodies are composed rarely exist
alone; they are bound into tiny clusters called molecules.
Some of these molecules are made up of two atoms, like those
of common salt containing one of chlorine and one of sodium ;
other molecules contain three atoms, like those of water, two
of hydrogen and one of oxygen; molecules of cane sugar con-
tain forty-five atoms, twelve of carbon, twenty-two of hydro-
gen and eleven of oxygen. Commercial analine violet possesses
molecules of fifty-seven atoms of five different kinds, and there
are other atom clusters or molecules more complex than these.

5. The Size of Molecules.— The size of molecules is
almost inconceivably minute. Sir William Thompson com-
putes the number of molecules in a cubic inch of any perfect
gas having a temperature of 32° F. and under a pressure of
thirty inches of mercury, to be 10” or ten sextillions.

We have many strong proofs of the extremely minute size of
molecules. Ifa grain of strychnine be dissolved in one mill-
ion grains of water, and if we place one grain of the water
containing the strychnine in the mouth, its bitter taste is recog-
nizable, and yet the volume of a grain of strychnine is only
about st, of a cubic inch. A cubic inch of analine violet will
impart its purple color to more than eight million three hun-
dred and eighty-four thousand cubic feet of water. Nobert
succeeded in engraving parallel lines on glass at the rate of
more than one hundred thousand to the inch, and hence the
point of his diamond must have been much thinner than this,
and the diameters of the molecules which composed it smaller
still.

5

The fact that musk and other perfumes keep the air of large
apartments so charged with their molecules that we are able
to detect them in spite of the fact that the air is constantly
changing and the loss in weight of the perfume is extremely
small indeed, is still another striking proof of the minuteness
of molecules, and, at the same time, of our ability to recog-
nize them.

' 6. Properties of Atoms.— Atoms, so far as we know
them, and are able to deal with them, can neither be created
nor destroyed; they have magnitude and weight, but are in-
divisible and impenetrable.

7. Properties of Molecules.— Molecules possess all the
properties of atoms except that they can be both destroyed
and created and are divisible into atoms. Whenever a chem-
ical change takes place existing molecules are transformed
into new ones of a different kind, and chemistry, as a science,
deals with these changes, while physics deals with the mole-
cules and groups of them.

8. Structure of Bodies.— The bodies or masses of mat-
ter with which we are familiar are always composed of mol-
ecules, but these molecules are believed to be not in contact
with one another.

If a quantity of salt be placed in a vessel and then water
added so that the combined volume before solution fills the
vessel, when the salt dissolves the volume will be found to be
less.
The fact that bodies change their volume with changes of
pressure and of temperature also indicates that the molecules
which compose them are not in contact.

- The mercury in a thermometer, for example, fills the bulb
at 212° F. and a certain portion of the stem also, but as the
temperature falls the mercury in the stem withdraws into the
bulb and yet the capacity of the bulb diminishes by contrac-
tion at the same time, and this could not take place were there
not room in the bulb not occupied by the molecules of mer-
cury.

9. Molecules of Bodies Not at Rest.— Not only are the
molecules which constitute the various bodies around us not
in contact with one another, but a large number of facts and
observations indicate that they are not relatively at rest. It

6

a solution of sugar or salt be placed in the bottom of a vessel
and covered with water the molecules of sugar and salt travel
upward and those of the water downward until, finally, a uni-
form mixture of the two liquids. has resulted. The same fact
is also observed where two gases are brought in contact — diffu-
sion takes place. So, if a solid lump of sugar or of salt be
placed in water, the molecules travel away and disperse them-
selves through the whole mass. The molecules of fragrance
-from fruits and flowers are constantly traveling away from
their respective places of origin. Molecules of camphor leave
the solid lump and travel through the surrounding air, and
snow disappears into the atmosphere without melting on the
coldest of winter days.

The pressure which steam exerts upon the head of the piston
when driving the engine is regarded as due to the coltision of
the molecules against its face; and the pressure exerted by all
gases is explained in the same way. The temperature of
bodies is also an expression of the degree of molecular agita-
tion within them. When we place the fingers upon a warm
body the motion of its molecules is communicated to the
molecules of the cuticle, and this in turn to the nerve end-
ings, and onward through the nerves to the nerve centers in
the brain, giving rise to the sensations denominated hot, warm,
cool or cold.

The mean distance traveled without collision by a molecule
of hydrogen at ordinary temperature and pressure is computed
by Crooks at zg4o7 MM., Or y 57/559 IM., while the velocity is at
the rate of about six thousand feet per second. The heavier the
molecules are the slower they moye, the rates being inversely
as the square roots of their weights. Thus the oxygen mole-
cule, being sixteen times as heavy as the hydrogen molecule,
moves, under like conditions, only one-fourth as rapidly.

If it is difficult to think of a body like a horse-shoe or a ham-
mer maintaining its form when its molecules are neither in
contact nor relatively at rest, it may be helpful to turn to the
solar system, consisting of the sun, planets, satellites and as-
teroids, together with comets and meteors, all of which are
in constant and rapid motion, separated by immense distances,
and yet as a whole constituting one great body, maintaining
a definite form and size as it travels through space.

(

10. Kinds of Force.— The falling of leaves, of rain-drops
and of unsupported bodies generally, is a constant reminder
of an influence which the earth, as a whole, exerts upon bodies
at its surface. The strength and rigidity of solids as com-
pared with fluids; the union of two boards by means of glue;
the rise of oil in a lamp-wick, and its destruction by burning,
with the appearance of heat and light, all convince us of in-
fluences of some sort which the molecules of bodies exert upon
one another.

It has been customary to speak of these influences as due
to the action of different kinds of force, and they have re-
ceived distinctive names.

11. Gravitation is the action which any one molecule
exerts upon every other molecule, tending to draw them to-
gether no matter how great the distance may be between
them. The intensity of this attraction is directly propor-
tional to the mass and inversely proportional to the distance
between the molecules.

The weight of a load of hay or of a bushel of wheat is the
sum of the attractions of every molecule of the earth upon all
the molecules of the load of hay or bushel of wheat.

12. Molecular Forces.— When molecules are brought
very close to one another, so that the distances between them
become inappreciable, their tendency to come together or
their resistance to separation are spoken of as due to molec-
ular attraction, and three varieties are designated, viz., cohe-
sion, adhesion and chemical affinity.

18. Cohesion.— When water is cooled below 32° F. the
rate of molecular motion and the mean distance between the
molecules so diminishes that the force of cohesion begins to
bring them into new relations and to bind them more firmly
together, so that a solid body results. The same force comes
strongly into action when melted iron, copper or other metal
changes from a liquid to a solid state.

When finely ground graphite is subjected to extreme pres-
sure in moulds, after having been first thoroughly cleaned, the
molecules of the separate fragments are brought so closely to-
gether that they unite into solid cakes, from which the leads
of pencils are sawed. Where molecules of the same kind are
thus bound together the acting force is named cohesion.

8

14. Adhesion.— When the smooth, plane surfaces of two
pieces of wood are coated with a paste of glue and brought
firmly together they are held very securely when dry. In this
case the action between the molecules of glue and the mole-
cules of wood on either side serves to make a single body of
the three. The action seems to be essentially the same as that
of cohesion, but because it occurs between molecules of differ-
ent kinds the term adhesion is used to designate this distinc-
tion. The coating of walls with white-wash, paint, varnish,
and the like are other manifestations of the same force.

15. Chemical Affinity.— When the temperature of wood
is raised to a sufficiently high point in the presence of air an
action occurs between the molecules of wood and those of the
oxygen of the air, which results in the complete breaking
down of both sets of molecules and the formation of new ones
of entirely different kinds in their stead. This sort of molec-
ular action, as in the case of adhesion and cohesion, takes
place only across insensible distances, and the agency which
brings it about is named the force of chemical affinity. The
rusting of iron, the heating of a manure pile or of a silo, the
souring of milk and the processes of digestion are all phenom-
ena in which this force is operating to form new molecules
from old ones.

16. States of Substances.—It is common to speak of
substances as existing, under different conditions, in a solid,
liquid or gaseous state. A critical study of these states, how-
ever, shows that no absolute distinction exists between them,
and that, by insensible gradations, one state may shade into
another. The substance water we know as solid ice, liquid
water and gaseous steam. Iron at ordinary temperatures we
think of as a solid, but as its temperature is raised it gradually
becomes more and more soft until it passes by insensible shades
into the condition of a true liquid.

The ¢deal solid is a body which, if brought under a force
which tends to change its form, responds, if at all, to the
force, and then remains unchanged so long as that condition
of stress may exist. The steel spring, when loaded, changes
its form, and then remains constant until the load is removed,
or rather appears to when rough measurements only are ap-

9

plied as a test; but if more than a certain load is applied, the
form keeps changing so long as the load acts.

The zdeal liquid is the body which constantly changes its
form whenever a force is made to act more intensely upon
one portion of it than upon another. We think of water as a
perfect fluid, and yet a comparatively heavy load may be
placed upon a drop of water resting upon a dusty surface
without its changing form, except a definite amount at first.
On the other hand, we think of sealing-wax as a solid, and
yet if a bullet be placed upon it, it will, by its own weight,
gradually sink through it. But jelly, even when rather soft,
will keep its form under the same load which will sink through
the sealing-wax ; the sealing-wax conforms to the law of liquids
and the jelly to that of solids.

In the gaseous state the molecules of the substance have at-
tained so large a range of motion that the molecular attrac-
tions appear entirely overcome, and the molecules continually
separate from one another unless some confining surface or
wall prevents them. No vessel can be half filled with a gas
as it can with a solid or a liquid, for the molecules travel to
and fro from side to side or from top to bottom, thus occupy-
ing the whole space, no matter whether the number of mole-
cules be ten or ten millions.

17. Work.— When a force, like that exerted by a horse,
acts upon a quantity of matter and changes its position in any
direction, work is done, and the amount of it is measured by
the product of the force and the space through which the mass
has been moved.

Work=Force x Space.

If a horse exerts an average tension of twenty pounds
through the whippletree upon. the carriage and moves it
through ten thousand feet the work done is

20 Ibs. x 10,000=200,000 foot-pounds,
meaning the equivalent of two hundred thousand pounds lifted
one foot in opposition to gravity.

So if the horse exerts a tension of one hundred pounds in rais-
ing a forkful of hay and carries it through a height of forty
feet the work done is

100 lbs. x 40=400 ft.-lbs.

10

Simple pressure is not work. The load must move before
work is done. The man who stands still under a sack of grain
does no work on the load he holds.

The mean rate of doing work is the whole work done di-
vided by the time required to do it, and 550 foot-pounds per
second is called a Horse-power by Engineers. This, however,
is more work than the average horse can do, this being esti-
mated by General Morin at 26,150 foot-pounds per minute or
435.8 foot-pounds per second.

A laborer lifting dirt with a spade has been found able to
do 470 foot-pounds per minute, and on a tread power, raising
his own weight, 4,230 foot-pounds per minute; the first being
.018 of an animal horse-power and the latter .16 or a little less
than one-sixth.

18. Energy.— Energy is the ability of a moving body to do
work. If a twenty-pound weight, suspended by a cord, be
drawn to one side and then allowed to fall, it will rise on the
opposite side of the line of rest to a height nearly equal to
that from which it fell. This height would exactly equal that
from which it falls if the air and the suspending cord offered no
resistance. Here the moving weight, on reaching its lowest
level, has acquired an amount of energy equal to that which
has been expended in raising the weight to the point from
which it fell.

When a hammer is brought to rest on the head of a nail it
is the energy of the moving hammer which does the work of
forcing the nail into the wood.

The wind blowing through the wind-mill has its velocity re-
duced, and so much of its energy is transformed into motion
of revolution in the wheel. The same is true of water in flow-
ing through a water-wheel, the water loses energy by impart-
ing it to the wheel.

When the spring of a clock or watch is wound up its mole-
cules are drawn out of positions of rest, as with the weight re-
ferred to, and in falling back to their positions of rest again
their energy is imparted to the train of wheels to which the
spring is attached.

19. Energy and Matter Indestructible.— No discov-
ery of modern science is more fundamental and far-reaching

11

than that of the indestructibility of both matter and energy,
and equally fundamental is the other fact that neither of them
can be created.

One form of energy can be transformed into another form
and one kind of substance can be decomposed and others made
from the components, but in these transformations there is
never either annihilation or creation. The few bushels of
ashes left from the winter’s supply of coal or wood seem to
point to a destruction of matter, but their weight added to the
weight of the products which escaped through the chimney is
actually greater than that of the original fuel, for oxygen from
the air has united with it. So when the energy of eight or
ten horses is being expended in the threshing of grain it looks
as though energy were being annihilated, but it is simply
changed into heat, sound and energy of position, not lost.
We appear to realize in the waste products of domestic ani-
mals and the increase of their bodies a very much smaller
weight of matter than they have consumed, but this is because
so large a weight passes off in an invisible form through the
skin and lungs. Something is never, so far as we know, reduced
to nothing; neither is something created from nothing.

20. Machines Not Generators of Energy.— When,
through the aid of a machine, a man or a horse is able to move
a load which he could not otherwise handle, the machine is
not a source of energy, it is simply a device which enables
their energy to be transmitted and used more advantageously ;
but there is always some loss in the machine, no matter what
that machine may be. Some energy is required to overcome
the necessary friction of the moving parts of the machine so
that the useful work accomplished never quite equals the en-
ergy expended.

21. Inertia of Matter.— Newton’s first law of motion
may be stated as follows: Hvery body tends to persevere in its
state of rest or of uniform motion in a straight line unless acted
upon by some external force, or briefly, matter has inertia.
There are many unmistakable illustrations of this law. The
sudden starting of a wagon tends to throw a standing person
backward because his feet take on the motion first and are car-
ried out from under him. In beating a carpet the carpet is
driven forward away from the dust. In driving a nail the

12

suddenness of the blow forces the wood aside and in front of
the nail before the motion can spread to the surrounding wood.

When a horse, in rapid motion, suddenly turns a corner, the
rider must lean in the direction of turning until his tendency
to fall exactly balances his tendency to move on in a straight
line. It is the principle of inertia which enables the rider to
sit securely on the bicycle while it is in motion; the same prin-
ciple explains the standing of the top while in motion, and the
constant parallelism of the earth’s axis during its revolution
about the sun. The rider on the bicycle is moving rapidly in
one direction, and for him to fall either to the right or the left
would require him to change his direction of motion at a right
angle, which is the same thing as trying to turn a corner when
at full speed —a thing practicably impossible. It is this law of
inertia which makes it possible for the penman to make his
smooth curves only by rapid movements of the hand.

22. Centrifugal Force.— Centrifugal force, so called, is
another manifestation of the law of inertia. The stone twirled
about the head with a string, because of its tendency to move
always in a straight line, exerts a constant tension upon the
string, and if the rate of motion is great enough the string will
be broken.

It is this manifestation of inertia in circular motion which
lies at the foundation of all rotary forms of cream-separators
and extractors and of several forms of fat-tests for milk.

In the Babcock and Beimling “ milk-tests” the rapid revolu:
tion of the bottles which contain the fat to be separated from
the liquid with which it is mixed, throws the heavy liquid to
the bottom of the bottles, which reacts upon the fat, forcing
it toward the center of the circle, where the velocity is least.
The fat, like the heavier liquid, in consequence of its own in-
ertia, tends to go to the bottom of the bottles also and is
simply prevented from doing so by the greater inertia of the
heavier liquid.

23. The Gravity Method of Creaming.— To under-
stand the reason of the more rapid and perfect separation of
cream by the centrifugal methods over the simple gravity
methods we need to get first the principle of creaming by
gravity.

It is this: If a block whose weight is but one-half that of

13

an equal volume of water be immersed in water it will be
lifted by a force equal to the. difference between the weight
of the block and that of an equal volume of water, as shown
in Fig. 1.

fag. 1.

Regarding the water of the vessel divided into cubes exactly
equal in volume to the block of wood, and the block just half
as heavy as an equal volume of water, then the weight of

column A equals
24+2+41=5,

while the weight of column B is

24+24+2=6.
Now, as column B exerts a pressure upward on the column A
equal to its own weight, the block in column A must be pushed
upward by a force equal to the difference in the weight of the

two columns, or of
6—5=1,

A comparison of columns B and C will show that it makes
no difference where the block is placed in the liquid, the force
which tends to lift it to the surface is always the same. If
the attraction of the earth were just twice as strong as it is
then the cubes of water and the block in column A would

weigh
44+4+42—10,

and the cubes of water in column B would weigh
44+4+44=12,
and the lifting force on the block would be
12—10=2,
or just twice what it now is; so if the force of gravity were
made one hundred times what it now is, the lifting force act-

‘ 14

ing upon the immersed block would be increased one hundred
fold.

24. Centrifugal Creaming.— The centrifugal methods of
creaming are applications of the same principle as the gravity
methods, the only difference being in the substitution of a
stronger force in the place of gravity, and by so doing of
shortening the time and securing a more complete separation.
This is done by transforming the energy of an engine or of
some other form of motion into the energy of rapid rotation
in the milk, giving rise to a strong outward pressure, which
acts exactly as gravity does in the old method of creaming.

25. To Compute the Centrifugal Force.— The
strength of centrifugal force in a milk separator may be com-
puted as follows:

weight of milk x (velocity in feet per sec.)?

Centrifugal Force= eadinis Se 2202)

Suppose the mean diameter of the circle through which one
pound of milk is made to revolve is ten inches and that the
centrifuge is given seven thousand revolutions per minute.
In this case the ,

10 x 3.1416 x 7000_go5 4

Velocity = 13 x 60
iti __ Ib. x (805.4) 2 __
then centrifugal force= 3, x 822 = 6950,

and this means that the creaming force would be six thousand
nine hundred and fifty times as great as by the old gravity
method.

26. Strength of the Creaming Force.— Since the mean
specific gravity of milk fat at 85° to 90° F. is about .91 and
that of milk serum 1.034, the creaming force must be the dif-
ference between the two specific gravities, as shown in 28, or

1.034—.91=.124 ;
that is, if a ball of butter-fat weighing .91 pounds were placed
in milk serum, the lifting force of gravity upon it would be

.124 pounds, but if placed in milk serum in the centrifuge
under the conditions of 25 the creaming force would be

6950 x .124=861.8 Ibs.

This enormous creaming force seems unnecessarily large,
and so it would be if the fat globules were large enough to

15

weigh .91 of a pound each, as in the problem assumed, for
then creaming by the gravity method would be practically
instantaneous, whereas, under existing conditions, it requires
about twelve hours.

The actual diameter of the average fat globule in milk is not
far from sy'y9 Of an inch, while a sphere of butter-fat weighing
one pound would have a diameter of about 3.87 inches.

Now as the volumes of spheres are to each other as the
cubes of their diameters, the pound of fat should contain
about seven trillion two hundred and forty-five billion of fat
globules. But the surfaces of spheres are to each other as
the squares of their diameters, and hence the surface of the
| pound sphere will contain the surface of the fat globule about
three hundred and seventy-four million four hundred and
twenty-two thousand five hundred times; and this being true,
the aggregate surface of the seven trillion two hundred and
forty-five billion fat globules, whose aggregate volume equals
that of the pound sphere, must be

245000000000
q 374422500 =19,350

times the surface of the pound sphere; and when we remember
that the friction increases with the surface, and that more force
is required for rapid creaming than for slow, we can see that
a much stronger creaming force is really needed.

27. Storing Energy.—In many forms of machinery
where the work to be done, like that of sawing wood with a
buzz saw, is not a steady draught upon the source of power, a
fly-wheel, or its equivalent, is very useful in allowing the
power generator to store energy when work is not being done
and give it out again as needed. The wind-mill in pumping
water, with most pumps, does work only half the time, and
so there is often attached to the pump an air-chamber which
acts like a spring in which the mill stores energy by compress-
ing air which is given out during the reverse stroke. A con-
stant stream is thus maintained and the pump enabled to be
worked with lighter winds than would otherwise be possible.

In the animal mechanism the walls of the arteries are elastic
and act like springs. They are stretched by the powerful,
quick contractions of the heart, and then, while the heart is
resting, the blood is forced on by the steady return of the

16

stretched arterial walls, and continuous currents of blood are
thus moving through the tissues of the body.

28. Momentum.— When a body weighing ten is moving
with a velocity of ten, the quantity of motion is

10x 10=100,

and this is called its momentum. If the mass of the body is
one thousand and its velocity is five, then

1,000 x 5=5,000,

the quantity of motion, or momentum, of that body. Soa
body having a mass of five and a velocity of one hundred has

the same momentum as a body weighing ten, having a velocity

of fifty, for
5x 100=500 and 50x 10=500,

ELEMENTS OF MACHINES.

29. The Mechanical Powers. —The simple machines
known by the names lever, wheel and aale, inclined plane,
screw, wedge and knee find an explanation of their action in
the fact that they simply transmit motion with an altered
velocity or direction, the quantity remaining always the same,
except as it is diminished more or less by the friction and
weight of the parts of the machine itself.

30. The Lever.— The lever may be any bar sufficiently
rigid to retain its form when forces are applied to it. The
terms used in speaking of the action are the fulcrum, power-
arm and weight-arm, these are represented in Fig. 2.

Fulerum

There are three classes of levers, named First, Second and
Third, according to the relative positions of the fulcrum to the

17

points where the power and weight are applied; these are
represented in Fig. 3.

Wv
ep
su pt Class ae ant Class ai W 3rd Claks
= L903

The mechanical advantage of the crow-bar, in moving a heavy
object, lies in the fact that it enables the muscles to generate
energy at their usual relatively rapid rate, and transform it
into so slow a velocity in the load to be moved that a heavy
weight is required to balance the smaller, more rapidly acting
power. Suppose we have a crow-bar sixty inches long, and
the fulcrum is placed at two inches from one end when it is
being used as a lever of the first class. In this case, as shown
in Fig. 4,

FIg-4 rg z

both the power and the weight travel on the circumferences
of circles, the power circumference having a radius of fifty-
eight inches, and the weight circumference having a radius
of two inches.

Now the circumferences of these two circles have the same
relative lengths as their radii do, and since the lever does not
bend, the weight can have a velocity only 2; or 5 as great as
that of the power, and since the power is ten and its velocity
twenty-nine times that of the weight, its momentwm must be

10 x 29=290;
and this being true, the weight, in order to just balance the
power, must have mass enough so that, with a velocity of one

18

the amount of motion shall exactly equal that of the power,
and hence we have

1 x 290=290,
as the load which ten will balance on a lever acting as repre-
sented.

When the crow-bar is used as represented in Fig. 5, it be-
comes a lever of the second class, with the power-arm sixty
inches long, while the weight-arm is still two inches. In this
case a power of thirty pounds will balance a load of nine hun-
dred pounds.

When the power is applied to the lever between the weight
and the fulcrum, as represented in Fig. 6, the case becomes a
lever of the third class, and a power of nine hundred becomes
necessary to move a load of thirty.

The relation of power to weight in the case of any lever is
expressed by the equation below, where P. equals power, W.
equals weight, P. A. equals power-arm and W. A. equals
weight-arm :

: Peso, Aste Wee Wires

When any three terms in this equation are known the fourth

may readily be found.

19

How great a load may be moved by a power of thirty
pounds acting on a lever having a power-arm of twenty and a
weight-arm of three?

Pace lse Ae Vs ENV si Uy
30 x 20=W. x 3.

600=3 W.
W,=200 Ibs.

31. The Two-horse Evener.— This is a lever of the sec-
ond class where the whippletree clevis-pin acts as the fulcrum
for each horse, the weight or load being carried by the center
pin. As ordinarily constructed this instrument is designed to
divide the work of moving the load equally between the two
horses.. This, however, is not done at all times unless the
three holes lie in the same straight line.

When the holes are bored as shown in Fig. 7 the load is di-
vided equally only when one horse is not behind the other.

The figure shows that when the near horse falls behind the
other the effective length of his lever arm is diminished more
than is that of the off horse, and consequently he must pull a
larger share of the load.

When the holes are bored in the same straight line the pos-
sibility of this inequality is avoided, as shown in Fig. 8, be-
cause the changes in the effective lengths of the lever arms
are always equal no matter which horse falls behind. This
latter form, although the best so far as dividing the labor

‘

20

evenly between the two horses, is rarely adopted in practice,
owing chiefly to the possibility of more cheaply constructing
the evener the other way.

Where heavy loads are to be moved, like puting stones or
stumps, or hauling a load out of a rut or out of the mud, the
second type of evener will always allow a matched team to
pull a larger load, because the horse which happens to be
thrown behind, in attempting to start the load, is placed at
a disadvantage and the other horse can only pull enough to
hold his end against the one placed at a disadvantage. So,
too, in doing heavy work, where one horse is naturally a little
freer or stronger than the other, the tendency is always to
throw more than half the work upon the slower or weaker
horse.

32. “Giving One Horse the Advantage.” — The fre-
quent practice, where the two horses of a team are not equally
strong, of “giving one horse the advantage” is based upon -
the principle that the amount of work done by each horse is
inversely proportional to the length of the lever arm upon
which he works. Suppose it is desired to so modify an evener
that three-eighths of the work will fall upon one horse and five-
eighths upon the other. In this case the horse which is to do
five-eighths of the work must have his end of the evener
shortened until its length is just three-fifths as long a3 that
of the horse which is to do three-eighths of the work. If the
distance from 1 to 2 in Fig. 8 is forty-eight inches, then in

21

order to require the near horse to do five-eighths of the work
the power-arm of his lever will be

*3¢ in.=38.4 inches.
3

This is given by substituting the numerical values in the
general equation of the lever.
Pi PB. A= We xe WA.
By substituting, 2 x P. A.=1x 24 in,
Whence, P: A.=74 in. =38:4 in:
8

This length of 38.4 inches will be secured by setting the
clevis 9.6 in. nearer the center.

How far in must the clevis be set to give the other horse
an advantage of one-eighth? of one-sixteenth? of one-thirty-
second?

33. Platform Scales.— Levers are often used in combina-
tion when it is desired to balance a very heavy load by a small
weight, and such combinations are spoken of as compound
levers. The various forms of platform scales are examples of
such combinations. In the case of hay scales, four thousand
to six thousand pounds are balanced or lifted by a few pounds.

The principle by which such combinations of levers gives
these great mechanical advantages will be understood from
Fig. 9.

If F. F. F. F. are fulerums of the levers J, 11, III, IV, and
their power-arms are each ten while their weight-arms are
each one, then a power of two pounds at P. will balance a
load of twenty thousand pounds at W. This must be so, for
two pounds at P. will cause lever IV to exert a pressure of
twenty pounds upon the long arm of lever III; the twenty
pounds pressure of lever III will cause a pressure of two hun-
dred pounds on lever II; lever II transmits a pressure of two

22

thousand pounds to the end of lever I, and this pressure will
sustain a load of twenty thousand pounds placed at W.

For levers in combination the continued product of the
power and power-arms is equal to the weight into the contin-
ued product of the weight-arms.

P. x P. Arms=W. x W. Arms.
or, 2x10x10x10x10=20,000x1x1ix1x1.

In the platform scales the platform is supported at its four
corners by bearings which rest upon four levers, the ends of
which are joined by means of a vertical rod to the short end
of the graduated scale beam. The accuracy and sensitiveness
of such scales depend upon the exactness with which the lever
arms are constructed and the delicacy and durability of the
bearings and fulcrums which transmit the pressure to the
levers.

34. The Locomotion of Animals.— Most of the higher
animals which travel by means of appendages to their bodies
propel themselves with a system of levers which are operated
by sets of very powerful muscles.

The mechanism of muscles and their method of contraction
make it possible for them to move through only very small
distances, and hence where considerable movements are to be
executed the results are secured by attaching them to the
short arms of levers. In the forearm, for example, the biceps
muscle acts upon a lever whose power-arm is only one-sixth
as long as the weight-arm, and hence when a weight of fifty
pounds is held as represented in Fig. 10 the muscle must exert
a tension of three hundred pounds.

23

The triceps muscle which extends the forearm is a more
powerful one than the biceps, and in order to accomplish its
much more rapid movements it works upon a relatively much
shorter lever arm, the relative lengths of the two arms being
about as one to twenty or twenty-four. Now it is possible for
the triceps muscle to exert a force upon a spring-balance ex-
ceeding twenty-four pounds, and hence, since

. Phx PA Wis A.,

we have P. x 1=24 x 20,
and P.=480;
which proves that the triceps muscle can exert a tension of
four hundred and eighty pounds. It is this powerful muscle
acting upon the hammer which enables nails to be so readily
driven.

The great tension which some of the muscles of horses must
exert in pulling heavy loads, acting as they do at the short
ends of levers, is almost beyond belief.

35. The Wheel and Axle.— With the lever only a small
amount of motion can be communicated to a body at once,
further movements only being possible after reversing its ac-
tion. The wheel and axle, represented in Fig. 11, enables
power to be applied continuously in one direction to the load
or resistance to be overcome. |

24

The relation of power to weight in this element of machines
is expressed by the equation

Power x Power-Radius= Weight x Weight-Radius,

pounce: P.xP.R=W.x W.R
.xPR=W.x W.R,

and by substituting the numerical values given in Fig. 11 we

get
10 x 10=1 x 100.

The relation of power to weight may also be represented in
terms of the diameters or circumferences of the wheel and

axle, thus:
Paxg 2 aa —IVVieexaVV eats
Px Pp. Diam = We x W. Diam:
Pox Pines W.. Cir

This mechanical power has by far the most extended use of
any in machinery.

36. Trains of Wheels and Axles.— Wherever a great
rotary velocity is desired, as in the case of the wood saw, in
the cylinder of a threshing machine, in the fan of a fanning
mill, or in the much higher speed of centrifuges, several wheels
and axles are joined in a train by means of belts, gears, or
friction pulleys; such systems are analogous to compound
levers.

The relation of power to weight both in intensity of action
and in relative velocities is expressed by these equations :

1. For intensity of action:

Power x Continued product of P. R.=Weight x Continued product of W. R.
Pax (P. Radii= We x.oW., Radi:

2. For velocity :
P. x P. Velocity=W. x W. Velocity.

37. The Sweep Horse-Power.— This machine is an ex-
ample of a train of wheels and axles whereby the slow walk
of the horses is converted into the extremely rapid rotation
of the cylinder of the thresher, feed-cutter or feed-mill, the
sweeps to which the horses are attached constituting radii of
the first wheel in the train. Here the small amount of work
required of the machines at any one instant makes a high speed
of execution desirable.

25

38. The High Speed of Centrifuges.— This is secured
by a combination of wheels and axles connected with belts.
Suppose the diameter of the fly-wheel of the engine is twenty-
four inches and it makes two hundred and twenty revolutions
per minute. If this is belted to a six-inch axle or pulley on
the driving-shaft, then the number of revolutions made by the
wheel on the driving-shaft will be

: 220 x 4#=880.

If the shaft-pulley connecting with the axle of the interme-
diate pulley has a diameter of ten inches while the axle has a
diameter of five inches, then the wheel of the intermediate
pulley will make

880 x 1.2=1760
revolutions, and if the wheel of the intermediate pulley has a
diameter of twelve inches while the axle of the centrifuge is
three inches, then the centrifuge will make

1760 x 7=7040
revolutions per minute.

Change the diameter of a wheel or axle so as to give the
centrifuge four thousand revolutions; six thousand revolutions ;
five thousand revolutions.

39. Exertion of Great Power.— When the exertion of
a great lifting force is required at the expense of speed, this
may be done by reversing the action of a train of wheels such
as is considered in 88. In that case, if the power were ap-
plied at the Centrifuge and the work done at the other end
of the series, a load would be lifted very slowly indeed, but
its weight could be very great.

40. The Inclined Plane.— This mechanical power is a
rigid surface inclined to the line of the force or resistance
which it is to overcome, and is represented in Fig. 12.

26

When the power moves parallel with the length or face of
the plane, as in A, the relation of power to weight is given
by the equation

Power x Length of Plane=Weight x Height of Plane,
or 200 x 15=-600 x 5.
But when the power moves in a line parallel with the base of
the plane, as in B, then the relation of power to weight is
given by the equation,
Power x Length of Base=Weight x Height of Plane,
or 20x 10=40x5.

41. The Tread Power.— This method of transferring
energy is a practical application of the inclined plane, and the
amount which can be transmitted by it depends upon the
height of the plane as compared with its length.

If the length of the tread is eight feet and it is given a
slant of one foot in eight feet, then from the equation

P. x Length=W x Height
we get, with two thousand four hundred pounds as the weight
of two horses,

Pp. x 8=2400 x1,
whence P.=3800 lbs.,
as the intensity of the power exerted, diminished, of course,
by whatever friction there may be.

What would be the power if the slant were made one foot
in seven feet? one foot in six feet? one foot in five feet?

42. Traction on Common Roads.— The power required
to draw a wagon over common roads varies with the charac-
ter and condition of the road. Experiments in England with
a four-whecled wagon have given the following results for
level roads as indicated by a dynamometer:

Onicubicall blocks pavementty = rape sicpe se) siecle yiete aielatels 28 to 44 Ibs. per ton.
Oni Macadam road)... s0ctrete sie ss icle oye ct oleiore/erejeisis icles sie'sie 55 to 67 Ibs. per ton.
Ongeoravelenon decease walsh lets slalcieeiare.c slereleivesecisscieleetaniers 125 Ibs. per ton.
Ons planksTrOa ly. cia. s cysreovaie cielsiate sfarersts chelate w/a siete tole efelelonar 27 to 44 Ibs. per ton.
OMicomimon Girt TOMAS. caren cjeieiote icicle clea Wielsiaisicieieiciaiate 179 to 268 Ibs. per ton.

43. Traction Power of a Horse.— According to the
most reliable data available at present, which is certainly far
short of what could be desired, a horse in good condition, well
fed, and weighing not less than one thousand pounds, when
actually walking at the rate of two and one-half miles per
hour during ten hours per day, can exert a traction of one
hundred pounds on a level road or circular horse-path like that

SOO RRASRICRARDSMIL

thE I

Day aay

I

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Htc
AU

ih

wh

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im iti

prin Wii
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_ey
uf

27

of the sweep-powers. In order that a horse may exert his
force most advantageously on a sweep-power the track should
have a diameter of thirty to thirty-five feet,— never less than
twenty-five.

44. Increased Speed Diminishes the Traction
Power.— If the horse walks more rapidly than two and five-
tenths miles per hour, or at a slower pace, the force which he
can exert changes also and is less or greater than one hundred
pounds. Experience seems to indicate that at speeds between
three-quarters of a mile and four miles per hour, and con-
tinued ten hours per day, the traction will be given by the
following equation:

2.5 miles x 100=n miles x Traction.
Thus, at two miles per hour the traction would be:
2.5 x 100=2 x Traction;
whence, Traction=*5° or 125 lbs.

What would be the traction at one mile per hour? at three
miles? at four miles? .

45. Diminishing the Number of Hours of Work per
Day Increases the Traction.— When the speed remains
the same, experience has shown that, between five and ten
hours per day, diminishing the time increases the possible
traction in about the same ratio, or

10 hours x 100=n hours x Traction.
Thus if the horse is to be worked only five hours the trac-
tion he may exert will be
10 x 100=5 x Traction,
whence Traction=1222—200 Ibs.
- What may the traction be when the horse works six hours?
seven hours? eight hours? nine hours?

46. Traction Power Diminished by Up-Grades.—
When a horse is forced to draw a load up a hill his power of
traction is diminished by being forced to lift his own body at
the same time. If he is going up a hill which rises one in ten
he must expend a force of one hundred pounds per one thou-
sand pounds to overcome the force of gravity on his own body,
and if the load he was drawing weighed one thousand pounds
the force of gravity would require another one hundred pounds
to overcome the tendency of the load down the hill, leaving
all resistance out of consideration. Now if an empty wagon
weighs one ton, and the hauling of a ton on a level road of

28

the same character as the hill requires one hundred and fifty
pounds, then the force necessary to carry the load up the hill
rising one in ten would be, for a span of horses:

FOLIEW ON DOLSES's fd et ae nee ee tee I Ske, aR ae gE WHR, UR ued 2 200 Ibs.
| Xo) al Cay ha MRR L ReonE cTpe ces ZA I aie MONE Cac eats ps Wen li aS 200 <“
Ror rolling bricthtomst ose vera oe «see oasay oie aati eho attns 300 “
MO tba 8 cc ciotch cushy Glacteabe, rede cart vote| nome eter ee ohare oe eae OOM as
Hori One horse pase tae Sick oe ae eaes ICN Ci Gas Ohiete Soe 3850“

The rate at which the horses could move up the hill with
this load would be, by 44,

2.5 x 100=rate x 350;
whence, rate=22$=.7 miles per hour.

What would be the force required to move the same load
up a hill which rises one foot in twelve feet? one foot in thir-
teen feet? one foot in fourteen feet? one foot in fifteen feet?

47. Good Roads Make High Grades More Objection-
able.— It is evident that the better the road-bed is made,
thus reducing the traction on the level, the more objectionable
a hill becomes, because the force of gravity is just as strong
on a good road as on a bad one, and while a much larger load
may be hauled on the level, when the hill is reached it cannot
be drawn up. It was shown, in 46, that where the traction
was one hundred and fifty pounds per ton, a grade of one foot
in ten feet added to that traction one hundred pounds per one
thousand pounds of load, including the weight of the team.
Now if the road-bed were improved so as to reduce the trac-
tion to seventy-five pounds per ton, double the load could be
brought to the hill, but, unless the grade were also lessened,
it could not be moved over it.

48. Soft and Uneven Roads.— The reason why the
traction is so heavy on soft and uneven roads will be readily
seen from a study of Fig. 13.

4

29

At A, where the wheel is continually cutting into the ground,
it is, in effect, constantly tending to rise up a hill which is
steadily breaking down, and whose gradient varies with the
size of the wheel and the depth to which it sinks into the
ground. A wheel four feet in diameter which sinks two
inches into the ground is constantly tending to move up a
hill which rises about one inch in five and one-third inches.
If the wheel has a less diameter than four feet, not only does
it sink more deeply into the ground with the same load, but,
for the same depth, it is forced to tend to rise up a steeper
grade.

So, too, in raising the load over an obstruction, as shown at
B, there is, in a measure, the effect of rolling the load up an
inclined plane which is steeper in proportion as the height of
the obstruction is large and the diameter of the wheel small.
This case may, however, be more exactly compared to lifting
a load with a bent lever of the first class, where the obstruc-
tion is the fulcrum, the distance af the weight-arm and the
distance bf the power-arm. The higher the obstruction, and
the smaller the wheel, the more nearly equal are the lever
arms. It is this fact which explains, in part, why heavy loads
may be moved more easily over uneven roads on large wheels.
49. Wide and Narrow Wagon Tires.— The same fact
which makes a large wagon wheel more advantageous on soft
ground makes a wide wagon tire better than a narrow one,
under the same conditions. It presents more surface to bear
the load, and hence does not sink as deeply into the ground
as the narrow one does, and, this being true, the load is moved
with less traction. So far as lightness of draught is concerned,
broad tires are best adapted to field hauling, but, for hard
roads, there appears to be but little advantage in this particu-
lar. On soft roads the broad tires would be of advantage,
provided all wagons using the road were of this character, for
then the cutting of the roads would be less and the draught
lighter. There is, however, one serious disadvantage of wide
tires on an improperly drained road composed of sticky soil:
during wet times the wheels so fill with mud between the
spokes that the wagon becomes a load in itself.

50. The Telford System of Road Construction.— The
essential features of the system followed by this great English

‘

30)

road-engineer may be briefly stated to consist in first leveling
and thoroughly draining the road-bed, then to lay upon it a
solid pavement of large stones, these covered with a layer of
stones carefully broken, and the whole then covered with a
layer of gravel or other fine material. This was the system
he followed in the Highlands of Scotland.

But where much heavier traffic was to be provided for, the
middle of the road-bed was made as firm as possible by form-
ing a pavement of large stones which were carefully laid by
hand on a bed formed to the proper shape of the road and
previously well drained. All inequalities were broken off the
tops of these stones and the cavities filled in, the size of the
stone being 7x3 inches. Over this paving was placed a layer
of whinestone —a hard basaltic rock— seven inches in thick-
ness, the pieces being broken so that none should exceed six
ounces in weight and all be able to pass though a circular
opening two and one-half inches in diameter. This layer was
again covered with binding gravel sufficient to fill up all the
cavities. Great attention was paid to this road until it became
thoroughly settled and then it stood the heavy traffic between
Carlisle and Glasgow for six years, nothing being required
beyond cleaning the dirt off during that time.

51. The Macadam System of Road Construction.—
This differed from the Telford system in that it aimed to se-
cure, instead of the hard unyielding surface of that system, a
certain amount of elasticity. Macadam, after preparing his
road-bed essentially as described in the Telford system, laid
upon it several inches of angular fragments broken from the
hardest rock he could find, preference being given to granite,
' greenstone or basalt. This layer was carefully watched by
men, and as ruts appeared they were raked full and fresh ma-
terial added until a hard, even surface was secured.

52. Road Drainage.— Perfect drainage is one of the first
requisites of a good road, and in some places both surface and
under drainage may be required. If the contour of a road is
such that the water of rains may stand upon it in places, at
all such points the road-bed softens and ruts are cut more or
less deeply into it. In the construction of a road, therefore,
the aim should be to give the surface such a contour that all
rain is shed completely from it, and, at the same time, to de-

31

part as little from the horizontal section as possible. In Fig. 14
is given a profile of the Telford road-bed.

Read Bed

Gras Bae
Suface —— a
2 Ji

L179. 14

The section adopted by Telford is quite flat and more nearly
a portion of the side of a flat ellipse than the arc of a circle.
It will be seen that in a road-bed thirty feet wide the fall, in
the first four feet from the center, is only half an inch, in nine
feet two inches, and in fifteen feet six inches. The aim is to
have the road-bed as nearly flat as may be in the central
eighteen feet so as not to tilt the load and force the traffic to
follow one line. The tendency is to get the surface too
sloping, and when this is done the weight of high loads is
thrown more upon the lower set of wheels, which tends to de-
velop ruts on that side; there is also a tendency to slide, so
that the wear on the road-bed and upon the wagon-tire is in-
creased. The ridge, upon the two sides, is intended to keep
stones and dirt from being thrown into the side drainage
ditches. The road-bed is often made only eighteen feet wide
and the two level strips used, one as a foot-path and the other
as storage ground for crushed rock and gravel to be used in
repairing the road.

Where underdrainage is needed, two lines of tile are laid,
one on each side just outside of the road-bed but inside of the
sided ditches as shown in Fig. 15.

32

The two lines of tile are used to prevent water from run-
ning under the road-bed from either side to soften up the
ground, the surface, when properly made and kept in repair,
keeping water from entering from above.

53. Results of General Morin’s Experiments in
France.— General Morin, after a series of experiments car-
ried on at the expense of the French government, reached the
following general conclusions regarding roads and carriages:

1. The traction is directly proportional to the load, and in-
versely proportional to the diameter of the wheel.

2. Upon a paved or hard macadamized road the traction is
independent of the width of the tire when it exceeds three to
four inches.

3. At a walking pace the traction is the same for carriages
with springs as for those without springs.

4. Upon a macadamized or paved road the traction in-
creases with the speed above a velocity of two and one-quar-
ter miles per hour.

5. Upon soft roads of earth or sand the traction is inde-
pendent of the velocity.

6. The destruction of the road is in all cases greater as the
diameters of the wheels are less, and it is greater by the use
of carriages without springs than of those with them.

54. The Pulley.— This mechanical power consists of a
wheel, having a grooved circumference through which a cord
or chain may pass, and so mounted as to revolve freely about
an axis. Pulleys are spoken of as either jized or movable, ac-
cording as the axis of revolution is stationary or travels with °
the load it carries. The two types are represented in Fig. 16.

3)

At Ais represented a simple fixed pulley in which the power
must be equal to the weight, because, in this case, the pulley
may be regarded as a lever of the first class, where the axle of
the pulley becomes the fulcrum, and then the two arms are of
equal length, each being a radius of the pulley. At B the
lower pulley is movable, traveling upward with the load, and
here we have the equivalent of a lever of the second class,
with the fulcrum at the side of the pulley in contact with
rope 2. As the load hangs from the axis of the pulley the
power-arm is the diameter of the pulley and the weight-arm
is the radius, giving us the equation:

P.xP. A.=W.xW. A.
or 5x2=-10x1.

At C, D and E are combinations of several movable and
fixed pulleys. In-C we have a system with several separate
cords, and in this the relation of power to weight is expressed
by the equation

P.x22=W.,

where n equals the number of movable pulleys, or in C,

Pisx22=— We,
whence, 4x 2 x 2=16.

In D and E we have two systems of pulleys where a single
continuous cord is used. It makes no difference whether the
pulleys are arranged side by side, as in D, or one above the
other, as in E, the relation of power to weight is expressed by

the equation:
P. x No. cords supporting W.=W.,

whence for D, 4x4=16,
and for BK, 4x6=24,

These equations always suppose no loss due to friction or in
bending the ropes. There is, however, always a large and
variable loss, so the actual lifting power is less than the theo-
retical.

55. The Horse-fork and Pulley.— The horse-fork and
carrier are used in lifting hay, as represented in Fig.17. The
mechanical advantage is that of pulley B, Fig. 16, diminished,
of course, by the friction.

When no pulley is used next to the fork, the traction exerted
by the horse must always considerably exceed the weight of

‘

o4

hay lifted, so that a single horse is fully tasked in freeing from
the load and raising from two hundred to three hundred
pounds of hay.

56. Using the Pulley to Raise Heavy Stone Out of
the Ground.— The pulley. may frequently be used to ad-
vantage in raising heavy stone out of the ground, and in pull-
ing stumps, as shown in Fig. 18.

If a pulley is fixed to the chain in either of the above cases, |
and the team draws upon a rope passing through it to a fixed
attachment, as shown, two horses will exert the traction of
four upon the stump or stone, diminished by the friction of
the pulley. If the chain is attached to the stone, and so passed
over the top as to roll, instead of drag, it from its place, the
mechanical advantage will be still greater.

57. The Screw.— This mechanical power is practically a
combination of the inclined plane and the lever. The threads
of the screw, and of the nut also, represent inclined planes

35

free to slide one upon the other. One or the other of these
inclined planes is fixed while the other is moved by means of
a lever of some form, the movable one carrying the load.

When the distance between the threads of a screw is one-
fourth of an inch and the circumference described by the end
of the lever to which the power is applied is three feet, the
theoretical load lifted by a power of one hundred pounds is

; 100x3x4x 12=14,400.
But the friction is so variable, and so great with very heavy
loads, that it is practically impossible to calculate, from the-
ory, the load which may be thus moved. None of the me-
chanical powers can be so compactly constructed as this, and at
the same time allow so small a force to exert so great a pres-
sure. It is on this account that the screw is so much used in
the construction of vices, lifting-jacks and presses.

58. Friction Between Solids.— When one surface rests
upon another the roughness or inequalities of the one fit, to a
greater or less extent, into those of the other, so that in order
that one may be moved upon the other either the two bodies
must be, to some extent, separated, or else the interlocking
roughness must be broken away. We have seen that mole-
cules are not in contact in bodies, and also that they are very
small; from this it follows that no matter how smooth two
surfaces may appear there are always present inequalities of
surface and always a resistance which opposes sliding, and this
is called friction. |

59. The Friction of Rest or Static Friction Between
Solids.— When two surfaces have been at rest with reference
to each other for a time there is developed the maximum
amount of interlocking, and hence the greatest amount of
friction. This is analogous to a load standing upon a wagon
over night, causing the wheels to become depressed in the
surface upon which they rest. The load is started with greater
difficulty because the wheels must be rolled out of depressions,
and this illustrates the condition of static friction. On the
other hand, if the wagon moves rapidly with its load, espe-
cially if over soft ground, the wheels do not have time to form
deep depressions in the surface, and the resistance to forward
progress is smaller, and this is, in a measure, analogous to
friction of motion.

‘

56

60. The Friction of Motion or Kinetic Friction Be-
tween Solids.— When two surfaces are sliding rapidly one
over the other there is not time to change direction and de
velop the interlocking which is possible with a state of rest,
and consequently ee power is lost when one solid slides rap-
idly over another.

61. Influence of Presse on the Friction of Solids.
When other things remain the same, increasing the pressure
increases the friction, and the amount of friction is directly
proportional to the pressure. Thus if one hundred pounds
produce a friction of two pounds, one thousand pounds will
develop a friction of twenty pounds, and this is independent
of the amount of surface bearing the load provided the pres-
sure is not great enough to crush or tear the surfaces.

62. Friction Between Liquids and Solids.— In this
case the amount of friction follows a different law, for it in-
creases with the amount of surface and also with the square
of the velocity of sliding motion. It is, however, less than
that between solids and solids, and because of this fact the
oiling of the bearings of machinery diminishes very much the
loss of effective energy through friction.

Where the velocities of revolution are slow, thick oils, like
castor oil, develop but little friction, but as the speed is in-
creased the friction increases very rapidly, and this fact makes
a thick viscous oil inapplicable as a lubricant where high
velocities, like those of the bowls of centrifuges, are required.
On the other hand, when a very thin fluid is used as a lubri-
cant for slow motions there is time for such freely-flowing
fluids to be crowded out of inequalities and thus allow the in-
terlocking of solid surfaces to be partially set up and develop
a high friction for these low speeds which the thick slow-flow-
ing oils prevent; but for very high speeds the thin fluid is
able to maintain the depressions of the solid surfaces full, and
the much smaller internal friction of the thin oil gives rise to
a relatively lower friction for such speeds.

It is upon this same principle, in part, that a thick grease
serves so well the purpose of a lubricant to lessen friction in
the slow sliding which obtains in the axles of a wagon.

63. Bad Effects of Dirt in Journals.— When grit of any
kind becomes entangled in the lubricants of any journal or

37

friction surface these particles bridge across or cut the two
films of oil which closely adhere to the two sliding surfaces,
so that friction is set up between solids rather than between
liquids as it should be, and there results not only a great loss
of energy transmitted by the machine, but also an excessive
wear of the bearings, which quickly destroys the fit so es-
sential to steady, easy and economical motion. Scrupulous
cleanliness of the friction surface of farm machinery should
therefore be adhered to as well as ample lubrication.

64. Belting.—The transmission of power by means of belt-
ing is a useful application of the friction between solid sur-
faces. In order that power may be economically transmitted
by this means the belt must be so tight that little slipping
takes place, and for leather belts this is least when the pulley
is covered with leather, hair side out, and the belt runs upon
this, hair side in. When the belt is running at a high speed
the tension may be less in proportion to the power transmitted,
the activity of belting being expressed by the equation:

Activity =Tv,
where v is the velocity and T the effective tension. When the
velocity is very great the tension may evidently be small, and
yet the activity or horse-power remain large. It is on this ac-
count that small wire cables may be used at very high veloci-
ties in transmitting very large amounts of energy.

It is in consequence of this principle, too, that light ropes are
successfully used in transmitting energy to the centrifuge.

65. Sliding Friction in Machinery is Lost Energy.—
The sliding of the inequalities of friction surfaces over one
another sets the molecules constituting them into a state of
to-and-fro motion, and all such motions represent energy lost
either in the form of heat or of sound; and it is because no
machine can be so constructed as to run absolutely frictionless
that they, one and all, fail to transmit all the energy which is
imparted to them, and hence it is that perpetual motion is an
impossibility.

66. Friction in the Churn.— In all forms of churns the
agitation of the cream results in friction between the mole-
cules of milk and between the milk and the parts of the churn,
and this causes a transformation of the energy brought to the
churn from the source of power largely into heat in the milk,

‘

38

which causes its temperature either to actually rise or else
prevents it from cooling as rapidly as it would otherwise do.
Now, if churning is begun with the cream at too high a tem-
perature and the surrounding atmosphere is also too high, bad
results must necessarily follow.

STRENGTH OF MATERIALS.

67. A Stress.— When a post is placed upon a foundation
and a load of two thousand pounds is set upon it, the post is
undergoing or opposing a stress of two thousand pounds.
When a rope is supporting a load of one thousand pounds in
a condition of rest it is subject to a stress of one thousand
pounds. The joists under a mow of hay are subjected to a
stress measured by the tons of hay which they carry.

68. Kinds of Stress.— Solid bodies may be subjected to
three classes of stresses which tend to break them and will do
so if the stress is great enough. These are:

1. A crushing stress, where the load tends to crowd the
molecules closer together, as when kernels of corn are crushed
between the teeth of an animal.

2. A stretching stress, as where a cord is broken by a load
hung upon it.

3. A twisting stress, as where a screw is broken by trying
to force it into hard wood with a screw-driver.

69. Strength of Moderately Seasoned White and
Yellow Pine Pillars.— Mr. Chas. Shaler Smith has deduced,
from experiments conducted by himself, the following rule
for the strength of moderately seasoned white and yellow
pine pillars:

Rurr.— Divide the square of the length in inches by the
sqare of the least thickness in inches; multiply the quotient by
004 and to this product add 1; then divide 5,000 by this sum,
and the result is the strength in pounds per square inch of area
of the end of the post. Multiply this result by the area of the
end of the post in inches, and the answer is the strength of the
post in pounds.

In applying this rule in the construction of farm buildings
the timbers should not be trusted with more than one-sixth

39

to one-fourth of the theoretical load they are computed to
carry, because the theoretical results are based upon averages,
and there is a wide variation in the strength of individual
pieces.

TABLE OF BREAKING LOAD, IN TONS, OF RECTANGULAR PILLARS OF
HALF SEASONED WHITE OR YELLOW TINE FIRMLY FIXED AND
- EQUALLY LOADED, COMPUTED FRoM ©. 8. SmITH’s FORMULA:

@ : DIMENSIONS OF RECTANGULAR PINE PILLARS IN INCHES.
Bg ;

5 4x4 | 4x6 | 4x8 |4x10/4x12) 6x6 | 6x8 |6x10 6x12} 8x8 | 8x10} 8x12 |10x10)10x12
tons. |tons.|tons.|tons.|tons.|tons.|tons.|tons.|tons.| tons. | tons. | tons. | tons. | tons.
8/12 .1)18 1/24. 2!30.2 36.8 44.5 59 .3/74.1/88 .9]101 .. 7/126 .9)152 .3)/182. 7/219 .2
10} 8.7)13.0 17 .4/21.7)26.1 34.6)/46.2|57.7/69.2) 84.2/105.3/126.3)158.6/190.3
12] 6.5) 9.'7/12.9)16 1/19 .4.27.2/86.3/45.4/54.4) 69.7) 87.1)104.5)136.7/164.0
14) 5.0) 7.4) 9.9)12.4)14.9)/21.7/29.0/86.2/43.5}) 57.9) 72.3) 86.8/117.4/140.9
16) 3.9} 5.9) 7.8) 9.8)11.7|17.7/23.5)29.4/35.3) 48.4) 60.6) 72.'7)/101.0)121.2
Oe eee (eed stoke ...14.6/19.4 24.3)/29.1 40.8} 51.0) 61.2] 87.2)102.6
20 eer le wee aks .. .{12.2/16.2/20.3 24.3) 34.8} 43.4) 52.1) 75.7) 90.8
PAs el ioctl (ener itnckcerl ater 10.3/13.7/17.2)20.6) 29.9] 37.41 44.8] 65.8) 79.0
Alea aualllccatele [egeerellla o stella cet 8.8/11.7)14.7/17.6] 25.9} 32.3] 88.8) 57.9) 69.4
70. Tensile or Stretching Strength of Timber.— The

tensile strength of materials is measured by the least weight
which will break a vertical rod one inch square firmly and
squarely fixed at its upper end, the load hanging from the
lower end. Below are given the results of experiments with
different varieties of wood, but the strengths vary greatly
with the age of the trees, with the portion of the tree from
which the pine comes, the degree of seasoning, etc.

Bra teagan Me oa sles Ogee ons he Mole Meta ae et te fae ain a she 6,000 lbs. per sq. in.
(Atri ELL COTY rei Paice aisiereveistatel Mlayas aaimorti ities te atta everajete.¢ 1 O00 a a
IMIEIDLON sei atare, case sey. ops huncsin, a loleret hap onustchalicraate.e! a etitele, stelale OOOO) cor Neen ice) ice
Oaks white: and Ted. «icc... kote. skianeg Seis rai einiays eters ADOOD RS Creal
ROSA T eracte rad stata! \Bhene wt:csl she. « obatel etevese a avsseiel ene aba’ bach sir OOO; Sen BASS eines
RU VAEIPIET Ny ayn Sette ct ve oe ntab Sinlhl alaraalaliels elciavasniere erates aleve TO,000) er Seta sis
71. Tensile or Cohesive Strength of Other Materials.
ATAMCASATOU ccPeii (n!vin'o'<)< in Saeko supe Ne iA 16,000 to 28,000 Ibs. per sq. in.
Wrought iron wire, annealed .............. 30;000ito, GOOOOR See
Wrought iron! wire; hard... 05.025... + cece 00,000 to! 100,000) © 6
Wrought iron wire ropes, per sq. in. of rope........... SSO ee ase 1 FENCE
Leether belts, 1,500 to 5,000, good........2....8.00.06- SI DON GIs a PGS tt
Rope, manilla, best... ... a astesielet svar cleleuahacs vA eri ee ros temo T2200 ORES, ee Seianse

Ropes hemp alpest (y2's aiuto sce Mohaageawis ews ad ves TD O00; 67 —- Sra sepcs

40

72. Transverse Strength of Materials.— When a board
is placed upon edge and fixed at one end as represented at A,
Fig. 19, a load acting at W puts the upper edge under a
crushing stress.

We know from experience that in case the board breaks
under its load when so situated the fracture will occur some-
where near 5-6. Now in order that this may take place, there
must be, with white pine, according to 70, a tensile stress at
the upper edge of ten thousand pounds to the square inch, and
if the board is one inch thick the upper inch should resist a
stress of ten thousand pounds at any point from 5 to 1; but
we know that no such load will be carried at W. ‘The reason
for this, and also for its breaking at 5 rather than at any other
point, is found im the fact that the load acts upon a lever arm
whose length is the distance from the point of attachment of
the load to the breaking point, wherever that may be, and
this being true the greatest stress comes necessarily at 5.

If the board in question is forty-eight inches long and six
inches wide, it will, in breaking, tend to revolve about the
center of the line 5—6, and the upper three inches will be put
under a longitudinal strain, but according to 70, it is capable
of withstanding

3 x 10,000 Ibs. =80,000 Ibs.
without breaking; but in carrying the load at the end, as
shown, this cohesive power is acting at the short end of a bent
lever whose mean length of power-arm is one-half of 45 or
1.5 inches, while the weight-arm is forty-eight inches in length.
It should, therefore, only be able to hold at W. 937.5 pounds;

for
ase. x Py At Wexner
we have 3,000 x 1.5=W. x 48,
whence W,=+452.°°— 937.5 Ibs,

41

When a board, in every respect like the one in A, Fig. 19,
is placed under the conditions represented in either B or OC,
Fig. 19, it should require just four times the load to break it,
because the board is practically converted into two levers
whose power-arms remain the same, but whose weight-arms
are only one-half as long each.

73. The Transverse Strength of Timbers Propor-
tional to the Squares of their Vertical Thicknesses.—
Common experience demonstrates that a joist resting on edge
is able to carry a much greater load than when laying flat-
wise. If we place a 2x4and a 2x 8, which differ only in
thickness, on edge, their relative strengths are to each other as
the squares of 4 and 8, or as 16 to 64. That is, the 2 x 8, con-
taining only twice the amount of lumber as the 2 x 4, will,
under the conditions named, sustain four times the load. The
reason for this is as follows: In Fig. 20 let A represent a 2x 4
and Ba 2 x 8. i

In each of these cases the load draws lengthwise upon the
upper half of the joist, acting through a weight-arm F. W. ten
inches in length, to overcome the force of cohesion at the fixed
ends, whose strength, according to 70, is ten thousand pounds
per square inch, or a total

of 2 x 2 x 10,000 Ibs. =40,000 lbs. in the 2.x 4 joist,
and of 2x 4x 10,000 Ibs.=80,000 Ibs. in the 2x8 joist.
These two total strengths become powers acting through their
respective power-arms F. P., whose mean lengths are, in the
2x 4 joist, one inch, and in the 2x 8 joist, two inches.
Now we have, from 30,
PP AG We x Wer Al,

42

and substituting the numerical values, in the 2x4 joist, we
get
4x 10,000x1=W. x 10,
or 4 x 10,000=10 W.,
and W.=4,000.
Similarly, by substituting numerical values in the case of the
2x 8 joist, we get
8x 10,000 x 2=W. x 10,
or 16 x 10,000=10 W.,”
and W.=16,000.

It thus appears that the loads the two joists will carry are
to each other as four thousand is to sixteen thousand, or as
one is to four; but squaring the vertical thickness of the two
joists in question we get for the 2 x 4 joist

4x4—16,
and for the 2 x8 joist
8x8=64;
but sixteen is to sixty-four as one is to four, which shows that
the transverse strengths of similar timbers are proportional
to the squares of their vertical diameters.

74. The Transverse Strength of Materials Dimin-
ishes Directly as the Length Increases.— It will be
readily seen, from an inspection of Fig. 20, that lengthening
the pieces of joists, while the other proportions remain the
same, lengthens the long arm of the lever, while the short arm
remains unchanged; and since the force of cohesion remains un-
altered, the load necessary to overcome it must be less in pro-
portion as the lever arm upon which it acts is increased.
Thus, if the 2x8 in Fig. 20 is made twenty inches long, we
shall have, from 30,

Leos -@] bre Hen > aN Ye Ba
and by substituting the numerical values we get
80,000 x 2=W. x 20,

hence
W.=8,000,

instead of sixteen thousand, as found in 73.

75. The Constants of the Transverse Breaking
Strength of Wood.— Since the laws given in 72, 78 and
74 apply to all kinds of materials, it follows that the actual
breaking strength of different kinds of materials will depend
upon the cohesive power of the molecules as well as upon the

43

form and dimensions of the body which they constitute. The
breaking strength of a beam of any material is always in pro-
portion to its breadth, multiplied by the square of its depth,
divided by its length, or,
Breadth x the square of the depth
its length,

and if the breadth of a piece of white pine in inches is four,
its depth in inches ten, and its length in feet ten, we shall

have, taking the length in feet,
4x10x10 |

10 =40.
Now if we find by actual trial, by gradually adding weights
to the center of such a beam, that it breaks at eighteen thou-
sand pounds (including half its own weight), the ratio between
this and forty will be
18,000
40
and as this ratio is always found for white pine, when the
breadth and depth are taken in inches and the length in feet,
no matter what the dimensions of the timbers may be, four
hundred and fifty is called its breaking constant for a center
load. |
For other materials this constant is different, and has been
determined by experiment and given in tables in various works
relating to such subjects. The following are taken from Traut-
wine:
76. Breaking Constants of Transverse Strength of
Different Materials.—

=450,

WOODS.
AGN GTICAMMBVVELEC AS Weraererotertersterateretate tsjatarelelers (ereilinrelelcinlelelajetatals)sazelens, oi 650 Ibs.
aC ASI ire wis claiecvol te elalehe ceegereie tele otaltiavavetersials ajcrelee(areaehaiecReye winter ele 600
Mellow. -AMMericany BrCl’ se acieeisiscissieersic) se evoieteielereleislateteloleisiels oie 850 “
American ENckKory and: Bitter=nUternsricre sits « cle slere vie cleicle tie sis sic a aie/ole 800
Larch and Tamarack. ..... gu SO Cs AL ees 400 «
Sov JUIEEH 0) Re AAR eae Teen SGA Acer ic Riss CReRRAIG MOR EOIRE ORIG ti fae 750 “
INTINETICATMW LITO, INC is, «: sfaerayacteraeleraisltetoleisielsve’ sale bisle lelounaverpyecceiete@hai6 450 *“
PAIMIeniCgi, VelOW: E116... 7 kein eto eranel eet arebert elvan cise alesis! slefiehs cla evele we BOO!
OPM este eee es a's! «Sicily o wrals leheha deuteta’ tl atatahpe ts) oe alolaio aia, » id efeleisishs sha .ble 550
ENTHETIGAM AWHILE Oak, M12 dale eeretalaalerenteenereie wavete no's ia Graielale elavecetewereieye 600 “
PATIET CATIA GL OES fr:n's sree. old aroue te sep ete Mecloteel vw elceleeie wletare ove eveutisiels 800? “

METALS
(Ast OMe oe areata hice vata a oral da aca MARCA Se Tahe eeihe eave alereatere 1,500 to 2,700 Ibs,
Wrought iron bends at.............. atateh ee) essta tere wer cies at sini 1,900 to 2,600 Ibs,

1B ein Cio GO AICO IG EIGETS CDSS EES Goa e code aio elone cate 850 lbs,

44

77. To find the Quiescent Center Breaking Load of
Materials having Rectangular Cross-sections when
Placed Horizontally and Supported at Both Ends.—
In placing joists and beams in barhs it is important to know
the breaking load of the timbers used. This may be deter-
mined with the aid of the following rule and the table of con-
stants given in 76: |

Ruriy.— Multiply the square of the depth in inches by the
breadth in inches and this by the breaking constant given in 76;
divide the result by the clear length in feet, and the result is the
load in pounds.

But in the case of long, heavy timbers and iron beams one-
half of the clear weight of the beam must be deducted because
they must always carry their own weight.

Square of
_ depth |< Brena in inches x Constant
in inches
Breaking load=———_ —+— -
Length in feet.

What is the center breaking load of a white pine 2x 12 joist

twelve feet long?
Breaking load=12*12*® X 450_ 10,800 Ibs,

What is the breaking load for the same ten feet long?
fourteen feet long? sixteen feet long? eighteen feet long?

Solve the same problems for other woods.

78. General Statements Regarding the Quiescent
Breaking Loads of Uniform Horizontal Beams.— If
the center quiescent breaking load be taken as 1, then, when
all dimensions are the same, to find the breaking load:

(1) When the beam is fixed at both ends and evenly loaded
throughout its whole length, multiply the result found by 77
by two.

(2) When fixed at only one end and loaded at the other, di-
vide the result obtained by 77 by four.

(3) When fixed only at one end and the load evenly distrib-
uted, divide the result obtained by 77 by two.

(4) To find the breaking load of a cylindrical beam, first
find the breaking load of a square beam having a thickness
equal to the diameter of the log and multiply this result by
the decimal .559.

45

79. Breaking Load of Rafters.— In finding the break-
ing load of timbers placed in any oblique position as shown in
Fig. 21, take the length of the rafter equal to the horizontal

span ac and proceed as in 77 and 78.

Fig.2{

80. Table of Safe Quiescent Center Loads for Hor-
izontal Beams of White Pine Supported at Both

Ends.

In this table the safe load is taken at one-sixth of

the theoretical breaking load. This large reduction is made
necessary on account of the cross-grain of timbers and joists
and the large knots which weaken very materially the pieces.
Where a judicious selection is made in placing the joists, laying
the inherently weak pieces in places where little strain can
come upon them, much saving of lumber may be made.

4\Span 10 feet.;Span 12 feet.|Span 14 feet.|\Span 16 feet.
=
43 ———+— as
Si al BREADTH. BREADTH. BREADTH. BREADTH.
Be
A 2 in, |4in. |6 in. || 2 in. | din. | Gin. |} 2 in.| 4in. | Gin || 2 in. | 4 in. |6 in.
lbs.| lbs.| lbs. lbs.| Ubs.| lbs. || (lbs. lbs.| lbs. lbs.| lbs.| Ibs.
4| 240) 480) 720 200} 400) 600 172} 344) 516 150) 800) 450
6} 540} 1080} 1620]| 450) 900} 1350 386| 772) 1158]| 3836) 672) 1008
8) 960} 1920} 2880]} 800} 1600) 2400 686} 1372} 2058]] 600] 1200) 1800
10} 1500} 8000) 4500}| 1250} 2500} 3750|| 1072) 2144) 3216 936} 1872) 2808
12} 2160) 4320} 6480]; 1800] 8600] 5400]} 1544) 3088] 4632]! 1350! 2700) 4050
BREADTH. BREADTH. BREADTH. BREADTH.
8 in. | 10 in.| 12 in.|| 8 in. |10 in.| 12 in.|| 8 in. |10 in.|:2 in.|! 8 in. |10 in.}12 in.
lbs. lbs. lbs. Ibs. Ibs. lbs. lbs. lbs. lbs. lbs. lbs. lbs.
4) 960} 1200} 1440)| 800} 1000) 1200]| 688} 860] 1082]! 600} 750} 900
6) 2160) 2700} 8240]| 1800} 2250) 2700)| 1544! 1980] 2316]| 1344] 1680] 2016
8} 3840} 4800] 5760}| 8200) 4000} 4800|| 2744) 3480] 4116]} 2400} 3000) 3600
10} 6060) 7500} 9000)| 5000) 6250} 7500|| 4288) 5860) 64382!| 8744) 4680] 5616
12} 8640/10800|12960)| 7200) 9000|10800)| 6176) 7720} 9264|) 5400) 6750} 8100

——$—$$————— —t
—— CO TTT

46

FLUIDS.

81. Surface Tension of Liquids.— The molecules of
liquids exert an attractive force upon one another, but this is
most manifest at their surfaces because the interior molecules,
being pulled equally on all. sides by surrounding molecules,
have their tendency to move balanced in every direction.
The surface conditions, however, are different, as will be seen
from Fig. 22, where the arrows at
A and B show the direction of the
action of molecular forces on the in-
terior and surface molecules respect-
ively. The unbalanced condition of
forces between the surface molecules
of liquids causes them to act like a
thin elastic membrane or skin upon the liquid within. It is
the tension of these films which causes rain drops, and the
shot from the shot towers to assume the spherical form when
falling. The same action gives this form to the fat globules
of mill, to dew drops on cabbage leaves and to drops of water
on a dusty surface. It is this same surface tension which sus-
tains a fine needle on the surface of water and which enables
certain insects to walk upon water.

82. Strength of Surface Tension.— The strength of
the tension of fluid surfaces is different for different liquids,
and it varies with the surfaces which are in contact. The
following table gives the relative surface tensions in certain
cases : .

Between clear water and air.............ceceeeeees Ave, o tieuekeiae cys 82, nearly.
Between olive olllan drain seeks. xieiyn se euclsew ie fae a oes S heraivepemeravs 37, nearly.
Between chloroformmiyand arty See: oe cis Sales pis ere oe Bledsoe va otatse 31, nearly.
Between: water and olive ail... 5. ox «hak owned deeb ee cote 21, nearly.
Between water and chloroformin.. «1c y-miee teceicrd cee etaeiaeteieier 30, nearly,

These differences of tension give rise to a great variety of
phenomena. When oil is placed on water it tends to spread
out indefinitely in a thin sheet. On the other hand, if a little
water is placed upon chloroform it tends to draw it into a

47

sphere or drop. The reason for these facts will be understood
from Fig. 23:

In A, on the circumference, where the drop of oil, air and
water meet, the surface molecules are actuated by three sets
of forces represented in direction by the arrows and in inten-
sity by the numbers, and it is evident that the molecules so
affected must move in the direction of the stronger force, and
as the surface tension of the water-air surface is strongest,
the oil is drawn out indefinitely until an extremely thin film
results. It is on this account that so small a quantity of oil
put overboard by a vessel at sea, in times of storm, covers so
large an area as often to effectually protect the vessel from the
dangers of wave-action. It is in accordance with the same
principle that water and other fluids spread out over the sur-
faces of solids which they will wet.

In the case of B, where a drop of water is placed upon chlo-
roform, the conditions of A are reversed and the water at first
tends to draw up into a sphere. It is in the same manner also
that water on a dusty floor or on cabbage leaves is drawn up
into drops.

83. Capillary Action.— When slender glass and other
tubes, whose adhesive force for water is greater than the at-
traction of the molecules of water for one another, are placed
vertically in water, the water is seen to rise in them and come
to rest above the level of the water in the surrounding vessel.
It will also be observed that the hight attained by the water
in different tubes varies inversely as their inside diameters.
The rise of liquids in slender tubes is in accordance with the
principle illustrated in Fig. 23 A, the chief difference being
that the movement is in opposition to the force of gravitation
and that the rise is checked when the down-pulling forces
balance the surface tension.

The rise of water in soil and of oil in a lamp wick are other

48

instances apparently due to a closely allied, if not identical
action.

If, on the other hand, the attraction between the liquid and
the walls of the tube is less than the attraction among the
molecules themselves, so that the walls are not wet by it, the
surface of the liquid in the tube is depressed, the amount being
greater as the diameter of the tube is less. This depression
isin accordance with the principle explained under B, Fig. 23.

84. Influence of Surface Tension on Lactometer
Readings.— The rise of water on the sides of a tube floating
in it, as in the case of the lactometer, tends to draw it more
deeply into the liquid and thus gives a higher reading. On
the other hana, if the liquid has its surface tension weakened
by being overspread with oil, or if the stem of the lactome-
ter is made greasy by handling or otherwise, it will then be
lifted out of the liquid and too low a reading will be indi-
cated. It is important, therefore, in determining the specific
gravity of milk by this method to see that the lactometer is
thoroughly clean.

85. Solution of Solids in Liquids. When salt is placed
in water the adhesion between the molecules of water and
salt is at first stronger than the cohesion between the mole-
cules of salt, and successive layers of salt molecules are sepa-
rated and disseminated through the liquid. If the quantity
of salt placed in the water be large enough, there will come
a stage when the quantity of salt dissolved in the water has
so weakened its adhesive power that it ceases to be strong

enough to overcome the molecular cohesion of the salt and

at this stage further solution is stopped.

In the majority of cases where solids are being dissolved a
rise of temperature so weakens the cohesive force that solu-
tion may be carried still further. It is in part the greater
solubility of soil ingredients in water at high temperatures
than at low that makes a warm soil more conducive to plant
growth than a cold one.

86. Diffusion.— When a phial, nearly full of salt or sugar,
is placed in a vessel and the vessel carefully filled with water
so as to cover the phial, the salt or sugar will in time be dis-
persed through the whole water. The rate at which this dif
fusion takes place is different for different substances, and in

49

the table below, the numbers indicate the relative lengths of
time required for different substances to travel the same dis-
tance in water, under like conditions.

EL VGR OO GRTE ROCIO ea og OR cin tee cols siaeis et asi cik nara ois'Giaie ob cee on rere 1
Saltire bouts ca: Mcbelt acta ad Ptcea ea her s'clalaraterety o: tielal ais es <u atte teteaa ens 2.33
ROUULEN Set anit aru slave ets coat eee ela elect’ «EL, oa lel Moue nS shales ois'sie a atalioue ae 7
Na orics Ty SURAT to! fete stale einistevanjnce Satie mits aeaiwrei a a o'sle\ese dk svalevareeicare 7
PRED STO TI ate Aerts oie eM wee ala ccherels clalshaye aid st claelicte atefeteldine’ecie sled ct eaiere ars 49

All substances diffuse more rapidly at moderate tempera-
tures than at low ones, and here is another reason why a warm
soil is more conducive to plant growth than a cold one, for
the transfer of food from soil to plant is partly a process of
diffusion.

If two gases are placed in two vessels and an opening be
made connecting them, the molecules of each kind of gas will
travel from their respective vessels and enter the other until
a uniform mixture results. We have seen that the velocities
with which molecules travel are inversely proportional to their
densities, and it is found that the rate of diffusion of gases
obeys the same law, the lighter gas diffusing more rapidly.

Oxygen enters the air cells of our lungs and carbon dioxide
leaves them by this process of diffusion, and the same thing is
true of the intercellular air passages of leaves into which the
stomata lead.

87. Osmosis.— In case two liquids, which mix, are placed
on opposite sides of a porous membrane capable of being wet
by one or both of them, currents are established in one or both
directions. The membrane first becomes penetrated by the
liquid having the strongest attraction for it, and on reaching
the other side the liquid diffusing into it causes its attraction
for the walls to be lessened, and this allows this portion to be
crowded out into the liquid which has been approached and a
stream thus established. If the pores inthe membrane have a
diameter exceeding y35o0 inch, a return current of the sec-
ond liquid is established toward the first along the central
portion of the pores. It is by this process that the tissues of
plants and animals are nourished. Here again a warm tem-
perature makes the streams more rapid, and so still another
reason is found for having the soil in which the roots grow
sufficiently warm.

50 :

Osmose of gases as well as of liquids also takes place, and
it is by this process that animals get their supply of oxygen
and plants their supply of carbon dioxide.

88. Viscosity.— When the molecules constituting any
body are forced to move past one another their mutual molec-
ular attraction causes a dragging which sets the disturbed
molecules vibrating, and this. molecular vibration is at the ex-
pense of the energy which produced the movement. This
dragging effect of the molecules is called viscosity, and the
amount of energy transformed into heat in consequence of It
is a measure of the viscosity. The fat globules in rising
through milk serum encounter this viscosity, and a part of the
energy of the creaming force is transformed into heat, causing
the cream to rise more slowly than it would if there. were no
viscosity.

Liquids, in flowing through pipes or other channels, are re-
tarded by viscosity so much that in long and slender pipes the
amount of water discharged is very much diminished. This
fact makes it necessary, in tile draining and in conveying water
in pipes to pastures or other points, to use larger pipes than
would otherwise be necessary. In all those cases where t’ 2
liquid wets the surface past which it flows the friction is due
wholly to the viscosity of the fluid, for the layer in immediate
contact with the surface remains stationary while the other
molecules move past them. This is the case with oils used to
diminish friction in machinery.

When the inner surfaces of pipes are rough and uneven the
flow of liquids through them is further diminished by the di-
rection of the current being changed at these inequalities and
thrown toward the center of the pipes across the course of the
central current. It is important, therefore, in selecting tile to
avoid those having rough interiors, and also in laying them to
avoid making shoulders at the junctions of the many sections.

The viscosity of air and other gases is due to the promiscu-
ous traveling of the molecules, which causes those moving
transverse to the stream to be caught in it and thus retard the
onward movement, acting much as the eddy-currents set up
by inequalities in the surface of water pipes.

89. Pressure of Fluids.— The great freedom of motion
of molecules in masses of liquids and gases causes them to

51

exert an internal and to transmit an external pressure equal
and undiminished in all directions. The proof of this law, for
liquids, is found in the fact that when two vessels are so con-
nected that water can flow from one to the other the water
will have the same hight in both vessels, no matter what form
or direction the communicating passage may take. The
spherical form of a soap-bubble in mid-air proves the law true
for-air; for if the pressure from all sides were not equal the
form of the bubble would change from that of a sphere.

90. Pressure of Liquids in Vessels.— The pressure ex-
erted by liquids on the walls of vessels which contain them is
due to their weight, and, for a given liquid, is always propor-
tional to the depth. In the following table the weight of
water per cubic foot and pressure per square foot are given
for different temperatures :

PRESSURE IN LBS. PER SQ. FT. AT DIFFERENT DEPTHS.

At2 ft.| At4ft.| At 8 ft. At 10 ft.) At 20 ft. |At 40 ft.

Wee 62.417 | 124.83 | 249.67 | 499.34 | 624.70 | 1248.34 | 2476.68
59°.2| 62.425 | 124.85 | 249.70 | 499.40 | 624.25 | 1248.50 | 2497.00
40° 62.423 | 124.85 | 249.69 | 499.38 | 624.23 | 1248.46 | 2496.92
50° 62.409 | 124.82 | 248.64 | 499.27 | 624.09 | 1248.18 | 2496.36
60° 62.367 | 124.73 | 249.47 | 498.94 |. 623.67 | 1247.34 | 2494.68
70° 62.302 | 124.60 | 249.21 | 498.42 | 623.02 | 1246.04 | 2492.08
80° 62.218 | 124.44 | 248.87 | 497.74 | 622.18 | 1244.36 | 2488.72
90° 62.119 | 124.24 | 248.48; 496.95 | 621.19 | 1242.38 | 2484.76

212° 59.7 119.40 | 288.80 | 477.60 | 557.00 | 1194.00 | 2888.00

The pressure of the water on the bottom of a vessel can al-
ways be found by multiplying the area of the bottom in square
feet by the depth of the water, and this product by the weight
of a cubic foot of water, which is nearly 62.42.

P. on bottom=area x depth x 62,42.

The lateral or side pressure is proportional to the depth,
following exactly the same law as that for the pressure on
the bottom. Since the depth at the surface is zero, the lateral
pressure is also zero, and since the depth at the bottom of a
vessel is the greatest, the lateral pressure must there be at its
maximum; these being true, the mean pressure on the side of
a vessel would be the pressure at one-half the depth of the

52 aq

liquid, and hence, to find the total pressure on the side of a
vessel, we have

Area of sides x depth x 62.42,

Total lateral P.= 3

What is the total pressure on the bottom and on the sides
of a reservoir 6x 6x 6 feet filled with water at 39.2° F.? at
BOF Hes |

What is the lateral pressure on the lower six inches of a
cylindrical tank ten feet in diameter filled with water to a
depth of ten feet?

If this pressure is to be sustained by an iron hoop composed
of one-eighth inch band iron, how wide should the hoop be?

91. Pressure of Grain in Bins.— The downward pres-
sure of grain in bins follows the same law as that of liquids,
but the lateral pressure is always less on account of the fric-
tion between the kernels. When grain is heaped up on a level
surface it is found impossible to pile beyond a certain hight
without increasing the diameter of the pile at the base. A
certain angle of slope is maintained, which for wheat is about
31°, about 30° for shelled corn, and for oats about 34°.

The friction of the kernels upon one another is just great
enough to maintain this angle, but in filling a bin with wheat,
for example, introducing it at the center, after a certain quan-
tity has been added the base of the cone is extended until it
reaches the sides of the bin, and the addition of any further
quantity brings into existence an outward pressure on the
walls of the bin tending to spread them. The case is analogous
to the retaining walls which are often built to prevent sand or
earth from caving or sliding. The amount of this pressure
and the method of computing it will be understood from
Fig. 24.

| I

=

Fig. 24.

53

CMMC represents a section of a bin sixteen feet square and
eight feet deep filled with shelled corn. The cone MOM rep-
resents the cone of grain which exerts no pressure on the sides
of the bin. The remaining portion MOMCC has its weight
divided between the sides and the bottom, the sides prevent-
ing it from sliding down the inclines OM, OM. ‘The pressure
on the side CM, according to the theory of retaining walls, is
equal to the weight of tCM, acting as a wedge between the sur-
faces tM and CM. As the wedge is a movable inclined plane
where the force acts parallel to the base, the pressure may be
computed from the equation

Power x base=weight x hight.

The height, tC, is 4.5 feet, and the base CM, eight feet. The
weight is the weight of corn composing the wedge, and is
equal to

4.5 x 8 x 16 x 1728 x 56

2 x 2150.4

=12958.72 lbs.

Substituting the numerical values in the equation of the
wedge above we get
Power x 8=12958.72 x 4.5, whence, power =7289.28 lbs.
as the total pressure on the side of the bin, which is an average
of 56.9 pounds per square foot.

92. Pressure of Silage in Silos.— When silage is cut
into a silo the pressure against the sides conforms at first to
the same general law as that governing the pressure of grain
in bins, as given in 91; but it is always less than would be in-
dicated by calculation, because the weight of the silage, com-
bined with the fermenting processes, tends rapidly to compress
the cut pieces into flat disks, which pile up as one brick does
upon another, and the mass very soon becomes self-supporting,
as has been proven by the silage remaining standing when the
walls of large silos have been burned down within a few days
after the completion of filling. When in filling a silo the silage
is not evenly distributed, so that it settles unevenly, the firmer
portions may act as an inclined plane down which the silage
resting upon it tends to slide, and in this way give rise to a
side pressure which otherwise would not exist, and in my judg-
ment most of the disastrous pressures on the walls of silos
have resulted from this unnecessary cause.

~
b4

Such experiments as have been conducted to determine the
pressure of silage have given results ranging from fifty-three
pounds per square foot, at twelve feet deep, at the close of the
second day’s filling, to fifty-five pounds per square foot at
twenty-one feet below the surface four days after the filling
commenced.

93. The Principle of Flotation.— When a body is im-
mersed in a fluid it is pressed or lifted upward with a force
exactly equal to the weight of the fluid it displaces, and it is
because of this fact that stones can be moved so much more
readily under water than out of it. Thus, a stone containing
exactly one cubic foot will be lifted up, when in water, with a
force of 62.42 pounds, and hence appears that much lighter
when moved under those conditions. It is this principle which
makes possible water navigation and the ascension above the
earth’s surface in balloons.

94. Specific Gravity.— When the specific gravity of cast
iron is spoken of as 7.2 the meaning is that a cubic inch or
a cubic foot of that body weighs just 7.2 times as much as
the same volume of water, and when the specific gravity of
white pine is given as .4 the meaning is that a given volume
of that wood weighs only .4 as much as an equal volume of
water; hence, for liquids and solids, we have the equation

weight of body

iy SN weight of equal volume of water.

Air is taken as the standard of specific gravity for gases.

95. To Find the Specific Gravity of Solids.— The
principle of flotation affords a very simple means of nding
the specific gravity of solids. Since any body immersed in
water displaces its volume of water, and since it is also buoyed
up by a weight equal to that of the water displaced, it is only
necessary to weigh the body whose specific gravity is desired,
both in air and in water, the difference in weight giving always
the weight of a volume of water the size of the body whose spe-
cific gravity is sought. The weight of the body in air di-
vided by this difference gives the specific gravity, and hence
the rule

weight of solid in air
~ loss of weight in water

Specific gravity

Suppose a body weighs ten in air and when immersed in water

55

only eight. In this case the weight of a volume of water
equal in size to that of the body is
10—8=2
and hence, by the rule above, we have
Specific gravity =5=5

Find the specific gravity of a body weighing fifteen in air
and fourteen in water. What will be its specific gravity if it
weighs in water, three? one? four? six? ~even? ten? twelve?

96. Table of Specific Gravities and Weights per
Cubic Foot of Different Substances.

Sp. gr. Weight.

PASAT WNILG,, GEV,» 1.5 ad eyes Sexes 2 sete Sad aaa cso iene oye .61. 38 Ibs.
Anthracite coal, moderately shaken... ......2.000.200085 ie sen
Brick wcommen Ward. ccc. ccracte giels/s cece locale o/s oso yy 125 §
Carbonidioxade, referred @tovair a. 12565. bc cic bo ea cle oere ie eos 1.5 §
Sharcoal pines ‘and Oaks... 6... 6 2 cisccheeaate ls ed este ne piaiee Oa
Clay, dry, in lump, loose.: .....4.....-. DA SraRa Be Ho HERS e 63
CCEA) CC STE TETS YT ea RR REAR SR aa IB motes 9
Woal Wbitimaineus; broken, 1OOS6. :,5-2.-s\0<ce 2 ec er esos es a i AS
CICS STAN 59 Dy ia SB et Ae a So eodon aes
Earth; clay loam, dry, nat. condition... .............c00006 7 2
arth; clayaloamn (saburabedie «casei ciel sieels ontore oc ages ee osiec QSn ee
Karth, reddish clay, dry, nat. condition................... S8c jas
Bare meddishielavy, Saturabed <2). is 5! nije ne icatsicelsitiers one ers 6 OSes
arth: tinersand nab, Condition. .<.5 4046 ocsiec. « ce de.celces TOG 75
Hartieane same, saiiraed fs icc) 45 oi etaioie.cje2e sicve-w,s0ee wie elens <i 134-56
PRIME E tenet eta ee Ue Aah oe 2s als piste inlets: sudo b.e six, 6 ots 506: )- <8) -
May STUN, MOTOWN MOORS 12.0 ssc, ayia! ot vue eile a Htaje 0 sini piewe 0 w,s¥0 Oe
MGA CLL cieite fo tere,atocar nha ervae Pere nian sa hae Sas nee Wratten OG” <6
REST ePR Cate ATV IN se ohare tes 5 ois siti se ous OA le ha prepste lates 4 BO,
PSR MAINES ahs: 8 ld desde pcicbaate ele cing (als avelerehal # Malate! b oles! ociete 8b") SBE 4a
MRO 10g CAB eestor: | a's cee eas oe SEMEN she FID lo hetuiaave doy acle e450! , ©
LCE es tac Senn) Son aw asia T a ern SEE ee Ae tas eas 92), SIA ©
NSERC See Pee aS s, ocz S's yas aca da caraer austen eed ceaaey ante ats ic esi eiatoetts SOD; DOS) f°
THeAG so nase CIEE I Sone a sts STR A VTS ee 11-38 "709.6 ©
Lamedione,foroken |. ¢.5).4. i see ek tN AS er ROD at ee ee
Aes Cte Co fsie 5 c.0' oda teh ty Me eee Ses ec dds alerts dees e HID 49k ASS
RO ae weap AEN, © 5,5. 5s, <Monlaun me olalg ewe we onedeatey es Sie here hehe hin. nies {OMEN col el nes
Oakes me OG KSA CUsy. ic leue sels a,c chetetobee eee Sisal eet tin ole oinlesnia.eidls 39 =O
EAC aN PMMA, ALS, SS 2.5 us2, 5 = Meta a tae ele a Sie eich wistet oe! abel cis 4022p
Bane: syellowy, MOCuenN 2... .\3 onic desctts date tlie ola tine causa 0° 6843 66
penta NE "(ERNE SYS a OA A eS Aa Oe KO ra Boy ats
Sandstone ..... DRE REET So Bestia 3 ar Se nee eee Per GW (st Re
Snow, ireshpfalllen\c/.5 osn.<0000. TSE ete edel Rene See tes | ale 8.5“
SNOW ACOMMAGCHEH MOY AMAMM sis oreleiselte auiale areuharsere/oue ee cio dlacels! s 15.50 *
SU Ae ierar ees dais erste 2 kin balsa hla re alae cicchlt othe 4.8 490 | #*
VEG ET SEGS ener rir Eran anot. e+ cvaretaie Wart ieee ee waa Ses i 62.35 “

56

97. To Find the Specific Gravity of Liquids.— The
principle of flotation stated in 93 also furnishes an easy
method of finding the specific gravity of liquids, which is done
as follows: Find the difference in weight of any convenient
solid in air and in water and then in the liquid whose specific
gravity is desired. Suppose the solid selected loses a weight
of one in water and a weight of .75 in another liquid, then a
volume of water, the size of the body taken, weighs one, and
_ an equal volume of the second liquid weighs .75. Then by the
rule we have:

98. The Lactometer.— The use of the
lactometer in determining the specific grav-
ity of milk is also an application of the
principle of flotation, and is simply a mod-
ification of the method in 97. In this in-
strument, as shown in Fig. 25, the slender
and uniform stem is graduated so as to
give the specific gravity by direct read- ===
ing. Lig. 25.

99. Atmospheric Pressure.— The air which everywhere
envelops the earth to a depth probably exceeding five hun-
dred miles has weight and exerts a pressure in all directions
upon all bodies in it. This pressure, at the level of the sea, is
capable of sustaining a column of mercury 29.922 inches high
on the average when the temperature is at 32° F. and is equal
to a pressure of 14.73 pounds to the square inch. The amount
of this pressure depends always upon the total quantity of air
that exists at the time above the point where the pressure is
exerted. This being true, places situated above the level of
the sea have a less pressure because they are nearer the upper
limits of the air.

100. Variations in Atmospheric Pressure.— The
pressure exerted by the air at any place is almost con-
stantly changing, so that it is rarely the same at any two
consecutive moments; these changes are not as a rule very
large or very rapid. A change of one-half a pound to the
square inch in twenty-four hours is a large change, and a
change of one pound to the square inch never occurs during

57

short intervals, except when very violent storms are in prog-
ress. These changes in pressure are due to the fact that the
air is disturbed by currents and waves which owe their origin
to various causes.

101. Soil Breathing.— When the atmospheric pressure
is heavy over a given locality air is driven into the air passages
in the soil of that place, and then when the pressure changes
again, becoming lighter, the compressed air expands and es-
capes; thus there is maintained an irregular but constant
breathing of the soil in consequence of these changes in atmos-
pheric pressure. The soil breathing is further maintained,
especially during the growing season, by the daily changes in
temperature which occur in the upper two to five inches of
soil. During the day the expansion, due to heating, forces air
out and then at night the cooling causes the air left in the soil
to contract and the reverse action takes place. Just how im-
portant this soil breathing is in the operations of tillage we do
not know. Its amount will be increased or diminished as we
increase or diminish the porosity of the soil and as we modify
the conditions which affect the diurnal changes of tempera-
ture.

102. Effect of Atmospheric Pressure on Soil Water.
When soil is nearly saturated with water, air can neither
enter nor escape from it readily except where large openings
or passages exist. In consequence of these facts, when the air
pressure over a region becomes less the springs of such regions
often discharge more water and the water may stand higher
in the wells. The air confined in the soil and unable to escape
rapidly, expands when the pressure falls and forces the water
toward any openings which may exist. The reverse action
also takes place when the air pressure increases, causing the
water in the wells to be depressed and the same springs to
discharge more slowly. “ Blowing wells” owe their character
also to the changes in atmospheric pressure.

103. The Suction Pump.— The common pump is one
of the applications of atmospheric pressure. It should be un-
derstood, however, that the pressure of the air is in no way a
source of power; it originates no part of the energy expended
in pumping. Practically the only part the air plays in pump-
ing is that of crowding the water up into the cylinder of the

,

58

pump after the lifting of the piston has removed the pressure
from the water in the suction pipe. The hight to which the
atmosphere will sustain a column of water at sea level is
thirty-four feet ; but a pump producing a perfect vacuum could
not raise water to that hight on account of the downward
pressure exerted by the vapor of water and the air contained
in water rising into the vacuum formed by the pump and ex-
erting a pressure downward upon the column of water raised.
Common pumps are necessarily so imperfect in their action
that it is found impracticable to have the suction pipe longer
than sixteen to twenty feet above the water to be raised.
104. Size of the Piston.— The amount of water dis-
charged by a suction pump is determined by the length of the
stroke and the area of the piston; and these in turn are de-
termined by the strength of the pumping force and the depth
of the well. In working a common pump a man can exert a
pressure of only fifteen to twenty pounds comfortably upon
the pump handle, and as the power-arm of the lever is only
from five to seven times the length of the weight-arm the
weight of water which can be lifted at one stroke cannot much
exceed seventy-five to one hundred pounds. This being true,
it is evident that pumps to be placed in deep wells must have
smaller pistons than those placed in shallow ones. It was
shown in 89 that the pressure of water is proportional to its
depth, and in 90 that water forty feet deep exerts a pressure
of two thousand four hundred and ninety-six pounds per
square foot when at a temperature of 50° F., or at the rate of
seventeen and one-third pounds per square inch, and hence
the area of the piston for the pump to lift water forty feet
should not exceed
eas
aL ei
and this is given when the diameter of the piston is 2.7 inches.
On account of the friction of the piston and of the water in
the pipe and of the inertia of the water, a piston of that size
would work hard in a well of that depth. In a well where the
water is to be raised only twenty feet the area of the piston
could be twice, and for ten feet four times, as great respect-
ively; these would be given by diameters of 3.8 inches and
5.4 inches; but, as in the first case, they are too large for easy
action. Three inches would be large for twenty feet.

5.78 square inches,

59

105. Rate of Pumping.— The rate of discharge by a
pump will be governed by the area of the piston, the length
of the stroke and the number of strokes per minute. If the
area of the piston is five square inches, the length of stroke
five inches and the number of strokes per minute forty, then

5 x 5 x 40=1,000 cubic inches
or’4.3 gallons per minute.

106. Function of Air Chambers.— In all single-acting
pumps the power is able to do useful work on the piston only

1
i
cnt

ILEUM LLL AS A

SS
(LULLED Tt CLEP LEAL PELE
== ——— =

W=N >

Lap.

ey

G.*

YG,
yy

Yj

oF
a Hh

Bens

NORE

60

when it is moving in one direction. In deep wells, where a
long column of water must be quickly set in motion and then
allowed to come to rest again, the intermittent action of com:
mon pumps is a serious objection, and to avoid this, air cham-
bers are sometimes attached. The principle of their action
will be understood from a study of Fig. 26.

The air in the upper portion of the chamber, which cannot
escape, is compressed by the rapid action of the piston and
then, during the reverse movement, it gradually regains its
original volume, forcing the water. out in a nearly continuous
stream. The water, therefore, is obliged to flow with only
one-half the velocity of that which would be required with no
air chamber, and consequently a pump having an air chamber
properly placed can be worked by a wind-mill in a lighter
wind than one without the air chamber. The air chamber
attached commonly to pump stalks has no influence on the
pumping except when the pump is used to force water above
the level of the air chamber. To render the greatest service,
an air chamber should be placed at as low a point as practi-
cable in the well where there will be but a short column of
water between the piston and. the air chamber.

107. The Siphon.— The flow of water through the siphon
is maintained by a force
represented by the differ-
ence in pressure in the two
arms, the siphon being kept
full by atmospheric pres-
sure. The action of the
siphon is explained as fol-
lows:

When the siphon is filled
with water the downward
pressure in the short arm Fig. 27.
is due to the upward pres-
sure of the air at d, Fig. 27, and the downward pressure of.
the column of water @ 6, which, using the values in the figure,
gives a total of

2+2414.72=18.72.
The downward pressure in the long arm of the siphon 1s
equal to the downward pressure of the column of water a d

61

and the downward pressure of the air on the water in the
vessel, or
(6 x 2)+14.72=:26.72.
As the two air pressures are equal and in opposite directions
they balance each other, leaving the force which determines
the flow the difference in the pressure of the two columns of
water, or
12—4=8.

It is evident that the greater the difference in the length of
the siphon arms the greater will be the velocity of discharge.

108. The Flow of Water.— When liquids move in a
stream the molecules do not become separated from one an-
other to any appreciable extent. The stream moves as a
whole, the density of the liquid remaining the same in all its
parts.

The flow of fluids is caused by a difference of pressure
within the mass caused either by increasing it at some point
or by diminishing it at another. Small velocities are asso-
ciated with small differences of pressure and large velocities
with large differences.

109. “Head of Water.”— The velocity with which water
issues from an orifice in a vessel is due to the pressure of the
liquid above the center of figure of the orifice and this dis-
tance is called the head. If it were not for the viscosity of
the water, and the resistance offered by the orifice itself, the
velocity would be equal to that which a body falling in a
vacuum would acquire in falling through the distance equal to
the head. This is expressed by the equation

Velocity= /2¢H
where H is the head and g is the velocity the force of gravity
is able to produce in a falling body during a second of time
and is equal to 32.2 feet. Ifthe head is ten feet, then the
velocity of discharge, leaving resistance out of consideration,
would be
Velocity = /2 x 82.2 x 10=25.8,

What would be the velocity of discharge with a head of
two feet? four feet? six feet? eight feet? twelve feet?

110. Flow of Water in Pipes.— The quantity of water
discharged by pipes is very much modified by their diameters,

62

lengths, degree of roughness, and by the presence or absence
of curves or angles. Other things being the same, the greater
the head the greater the discharge; the greater the length
and the less the diameter the less the discharge; the greater
the number of bends or angles the less the discharge.

There is no simple rule for computing the amount of water
a pipe of a given length and diameter will discharge under a
given head. To compute the discharge exactly the velocity
of discharge at the mouth of the pipe and the area of its open-
ing are required. Where the pipes range from .75 inch to six
inches in diameter and their lengths lie between two hundred
and two thousand feet, the equations below give the velocity
in feet per second, but with only a rough degree of approxi-
mation.

y. diam. of pipe in feet x head in feet

CO ROR ae eu Der second ew i length in feet +54 x diam. in feet.

This may also be expressed as below, the dimensions all be-

ing in feet:

1600 x diam. pipe x head
(2) Square of velocity in feet per second= Jenpth << ad-tiies caeaet

In case the length of the pipe is twelve hundred to two
thousand times the diameter, the factor fifty-four times diam-
eter may be omitted without affecting the result very much.
In such cases if the diameter and head are expressed in inches
the velocities may be more readily determined by the follow-
ing:

1600 x diam. x head

12 x 12x length.

@6)v2=

If the diameter of a pipe is two inches, its length two hun-
dred feet and the head four feet, what is the velocity of dis-
charge?

By (1), v=404/ _ x4 49, / ts —9,950,
200 +54x 5% R08
1600 x 7 x4
200+54 x 75
whence, v=2.299 ft. per second.
1600 x 2 x 48
BY Oh Vode 0
whence, v=2.309 ft. per second.

By (2), v7= =5.1038 ;

The last formula gives a velocity of .05 feet per second too
large.

63

What is the velocity of discharge when the diameter of the
pipe is six inches, length two thousand feet, head four feet?

To find the discharge of water in cubic feet per second, mul-
tiply the velocity in feet by the area of a cross-section of the
pipe in feet.

Discharge = velocity x area of opening.

HEAT.

111. Nature of Heat.— Heat is a form of molecular en-
ergy. When a hot body is brought into contact with a cold
one, the molecules comprising the hot body have their veloci-
ties slowed down by collision with the slower-moving mole-
cules of the cold body and energy is transferred from the hot
body to the cold one; and, if the contact continues, the trans-
fer will go on until the molecular energy, per unit of weight,
is equal in the two bodies. If a hot ball of iron is allowed to
cool in the air, the cooling is the result of the ball doing work
on the air. The molecules of air which come in contact with
the surface of the ball are struck by the molecules of the ball
and made to move away with a higher velocity than they
had before, just as a ball approaching a bat is struck by it and
flies to field Jeaving the bat motionless, a nearly complete
transfer having taken place. When a cold iron is thrust into
the forge fire a part of the energy of the molecules of the
burning coal and of the products of combustions is transferred,
by collisions, to the molecules of iron, and the temperature of
the iron rapidly runs up.

112. Solar Energy.— When the sun rises the tempera-
ture of bodies upon which it shines becomes higher as a rule,
and when it sets the temperature again falls, and, as a rule,
continues to do so until the sun begins to shine on them again.
So too, as our days grow longer and longer with the approach
of summer, the mean daily temperature becomes higher, and
then falls away again as the nights become longer than the
days. Such, and many other facts, prove that the-sun is a
source of energy, and that in some manner this energy is being
transferred to the earth. Since the earth travels entirely

64

around the sun once each year, and yet each day receives en-
ergy from it, it follows also that solar energy is leaving the
sun continually in all the directions in the plane of the earth’s
orbit, and is in fact traveling away in every other direction.

1138. How Solar Energy Reaches the Earth.— When
one stands on the shore of a small lake and agitates its waters
in any manner, waves start out from the place of disturbance,
traveling in all directions toward the bottom and the distant
shore lines. When these waves reach the bottom, the shore
and the air resting upon the lake, they lose a part of their
energy, the lost portion being transferred to whatever foreign
medium is struck by them. The energy generated in the
muscles of the person agitating the water is thus conveyed
away from him in all directions, and, sooner or later, is changed
into the energy of molecular motion known as heat. The per-
son is therefore a source of energy, which is borne away from
him in the form of waves in the water and air, and this wave-
energy becomes changed to heat, and thus the person in a
small degree warms the pebbles lying on the distant margin
of the lake, not by the heat of his body, but by the waves he
set up in the water. It was not heat which traveled to the
distant shore, but water waves which, striking the sands and
pebbles, gave a part of their energy to be transformed into
energy of heat in them.

The sun is wholly immersed in a cold medium called ether
and the molecules of the sun’s surface beating against this
have their energy transformed into waves in it which travel

away in all directions just as waves of water spread away ;

from a disturbing body in it, but at a very much more rapid
rate, the velocity being one hundred and eighty-six thousand
six hundred and eighty miles per second, a speed which brings
them to us in about eight minutes after their origin at the
sun’s surface. Sir Wm. Thompson estimates that the sun is
constantly doing work upon the ether at its surface at the
rate of one hundred and thirty-three thousand horse power
for each square meter of its surface, and the “mechanical
value of a cubic mile of sunshine” near the earth is placed at
twelve thousand and fifty foot-pounds, and, as this energy is
approaching us at the rate of one hundred and eighty-six
thousand six hundred and eighty miles per second, the amount

65

which falls upon a square mile of the earth’s surface in that
time is

186680 x 12050 ft.-lbs. =2249494000 ft.-lbs,
and this is equivalent to about eighty foot-pounds per square
foot each second.

114. Kinds of Ether Waves.—The molecular oscillations
or vibrations at the sun’s surface are not all of them at the
same rate and hence they set up waves of different frequen-
cies of vibration in the ether, the slowest known being at the
rate of one hundred and seven billions of thrusts upon the
ether each second and the most rapid at about the rate of
forty thousand billions per second. When the wave frequen-
cies lie between three hundred and ninety-two billions and
seven hundred and fifty-seven billions per second, such waves,
falling in the eye, produce the sensation of light and we speak
of them as light waves. Waves slower than three hundred and
ninety-two billions per second produce no sensation of light in
the eye, but when absorbed by the skin they cause the sensa-
tion of warmth and are called dark heat waves. Waves more
rapid than seven hundred and fifty-seven billions per second,
when they fall upon the molecules of a photographer’s plate, or
upon a living green leaf, set up such intense vibrations in these
molecules as to break them down, producing chemical changes
and hence these are called chemical waves. It should, however,
be kept distinctly in mind that there is no light, no heat and no
chemical action until the ether waves have dashed against some
molecular shore and have been wrecked uponit. When any of
these waves fall upon what we call a dlack substance, like a
thick layer of lamp-black, they are nearly all absorbed and the
body becomes heated. On the other hand, when they fall
upon a pure white substance, like snow, the waves rebound
with nearly their full vigor and there is very little of either
heating or chemical effect. When the waves fall upon what:
we call green substances, like the chlorophyl of growing leaves,
most of the chemical waves and a portion of the light waves
are wrecked by it and the chemical changes natural to grow-
ing leaves are the result.

115. Work Done on the Earth by the Ether Waves.
It was stated in 118 that eighty foot-pounds of energy per
square foot reach the earth’s surface each second. This seems

66

like an enormous amount of work when it is figured in horse
power for a section of land, the amount being

een = 4089980 horse power,
and it is difficult at first to realize that it can be true. To
comprehend the situation we need to know that the earth is
traveling through a cold region having a temperature of abso-
lute zero or —273° C., with only the thin atmosphere to pro-
tect it from that cold. If the mean annual temperature of
Wisconsin is 45° F. or 7° C., its temperature is maintained by
the sun at
273° +'7°=280°-C.

higher than that of the space which surrounds it. The earth
is therefore rapidly sending ether waves back again into space,
and thus a large part of the energy which comes to us is lost.
The motions of the air, and of the water in the ocean and to
and from the land, represent other portions of this energy
transformed. Most of the chemical changes occurring in
growing vegetation represent other transformations of solar
energy, as do the activities of all forms of animal life; and
when to these are added the chemical and physical changes in
soils and rocks, due to it, it is plain that the amount needed
to maintain the earth in its present state of activity is really
very large.

116. Transfer of Heat.— When one portion of a body is
heated, as in the case of a poker thrust into the fire, the heat-
energy gradually spreads to the distant end. This sort of
transfer is known as conduction, and the rate at which it occurs
is very different with different materials. Metals and stone
are among the best conductors, while wood, glass, water and
woolen fabrics are among the poor conductors. The transfer
of heat through air, where currents are prevented, takes place
very slowly and it is on this account that several thin gar-
ments are warmer than the same weight of the same material
as a single garment. It is on this account also that sawdust,
in the walls of buildings and about ice, is so serviceable. Hollow
walls with dead air spaces utilize the same principle, as does
the practice of using one or more thicknesses of building paper
in the construction of buildings which are designed to keep
heat in or out.

67

When heat is applied to the lower portion of liquids or
gases the conduction of heat to portions of the mass causes it
to expand and become relatively lighter than that not affected,
and it is, in consequence, forced to rise, thus establishing up-
ward and downward currents. In such cases the heating is
by conduction, but the heated mass is then transported, that
not heated taking its place. The process is named convection.
The third method of transfer of heat is by radiation, and has
already been described in 118.

117. Draught in Chimneys.— The draught in ehimneys
is due to two principles, one that of convection, and the other
that of aspiration. In all properly constructed chimneys there
is a draught, usually, even when there is no
difference of temperature of air inside and 2 >
out, and such draughts are strongest when
the wind blows hardest. Why this is so will
be readily understood from Fig. 28. The
air, in its rapid motion across the top of the
chimney, encounters the air molecules in its
very top and forces them out and onward

iy |

with it; this diminishes the weight of air in 3
the chimney, and the pressure from below 3
forces a new quantity into the moving stream 3

which in turn is driven away. The rapid
forward motion of the outer air prevents it Fig. 28.
from descending into the space left by the

air forced forward. When the fire is kindled the air in the
chimney is made specifically hghter and is forced out on the
principle of flotation (93). When the temperature of the air
is raised one degree I’. its volume is increased ;1, of its orig-
inal volume, so that if air enters a stove at 70° F. and has its
temperature raised to 234° F. its volume would be increased
one-third and hence its weight diminished in the same propor-
tion, and the relative weights of air per cubic foot inside and
outside the chimney would be as two to three. When these
conditions exist, it is evident that the higher the chimney is
the greater will be the difference in the weight of the two
columns of air and the stronger the draught. When the
chimney has its top considerably extended above the surface
it is placed in a region of more rapidly moving air currents
and the draft is made stronger on this account also.

68

118. Transparency to Ether Waves.— When the hand
is placed near a pane of glass, through which the sun is shin-
ing, the ether waves falling upon the hand are absorbed and
so increase the molecular motion of the skin, raising its tem-
perature. The hand, in turn, sends out ether waves toward
the sun, but they are of the long sort and cannot pass through
the glass, but are reflected back again upon the hand and join
with those coming from the sun to raise the temperature to a
still higher point. The glass is transparent to the short waves
coming from the sun but opaque to the long ones into which
they have been transformed in the hand.

This is the principle upon which the hot-bed is constructed,
which is practically an energy trap, allowing it to enter from
the sun and then preventing its ready escape.

On the same principle, too, large windows in the south side
of dwelling-houses, especially if they are double, contribute a
very large amount of heat toward warming the room in win-
ter, and are really a great saving of fuel, besides contributing
so much to healthfulness. The amount of heat which may
enter a house in this manner during the winter is much larger
than can enter it in summer, because in winter the sun shines
more perpendicularly upon the windows, which has the effect
of making them larger, as explained in 167.

Our atmosphere acts practically in the same manner toward
the energy received from the sun and that radiated back again
by the earth. It is highly transparent to the first and very
opaque to the last. Clouds, fog and smoke are still more
opaque to terrestrial radiations, and this is why frosts on a cran- ¢
berry marsh or strawberry bed may sometimes be prevented
by producing a cloud of smoke over it.

119. Temperature.— The temperature of a molecule is
an expression of the amount of energy it contains, and all
molecules having the same temperatures are assumed to pos-
sess the same amounts of energy of motion. When the tem-
perature of a given body is doubled its energy of molecular
motion is doubled. Could the molecules of a body be brought
entirely to rest, its temperature would be absolute zero, but
this is a condition of things very difficult if not practically im-
possible to reach.

120. Measurement of Temperature.— The common
method of measuring temperature is by noting the changes in

69

volume of a body which are associated with changes in its
temperature. The material of a thermometer may be either
solid, liquid or gaseous, and all three types are in use. For
ordinary purposes the mercurial thermometers are the best.
The mercury expands more regularly than most other avail-
able liquids, thus making the graduation of the stem simple;
it boils at a high and freezes at a low temperature; it can be
readily seen and it responds quickly.

The sensitiveness of the thermometer depends upon tie
relative diameters of the bulb and tube; the finer the bore ox
the tube and the larger the bulb the longer will be each de-
gree. Too large a bulb is objectionable because a longer time
is required for it to acquire the temperature of the body
whose temperature is desired, and too fine a bore has the ob-
jection of not being readily seen. The long cylindrical bulbs
are better than the spherical ones because they present a
larger surface and therefore respond more quickly, reaching
a condition of rest sooner.

121. Testing a Thermometer.— The bulbs of most
thermometers shrink after they are made, and if the gradua-
tion has been done before the shrinkage has occurred the
reading of the thermometer will be found too high or will
ultimately become so. To see whether the thermometer is
correct, in this regard, it should be immersed in melting snow
or crushed ice, from which the water formed by melting may
readily drain away, and allowed to remain until the mercury
becomes stationary.

If the thermometer is one of the dairy types or has the bulb
exposed, its correctness at blood heat may be determined by
placing the bulb under the tongue and keeping the mouth
closed over it for about one minute, reading the temperature
while the bulb is yet in the mouth. Ifthe person is well the
thermometer should indicate about 98.8° F.

It is rarely true that the diameter of the tube of the ther-
mometer stem is uniform throughout, there being a general
tendency for the diameter to increase from one end to the
other. If the irregularity of the tube is large, it may be cor-
rect at the freezing and boiling points and yet incorrect at in-
termediate points. Ifthe tube grows larger from the bulb
the same amount of expansion in the bulb will cover a shorter

‘

70

distance on the scale, and vice versa. Large inequalities in
the tube may be detected by jarring the thermometer so as to
separate a short column of the mercury, say three-fourths of
an inch, and carefully measuring its length by divisions of the
scale in different portions of the stem; if there is a large vari-
ation the length of the column separated will vary as it is
moved from place to place.

122. Kinds of Thermometer Scales.— There are two
scales used in this country, the Fahrenheit and Centigrade.
The first places the freezing point of water at 32°, and the
boiling point at 212°, the second at 0° and 100° respectively.
The Fahrenheit scale, between 32° and 212°, is divided into
one hundred and eighty divisions called degrees, while for the
Centigrade scale the number of divisions is just one hundred.
This being true,

180° Fahr.=100° Centigrade

eee OO we Oy
a 80 208
and 1° C =i00-5 F,

To convert the readings of a Fahrenheit scale into Centigrade
degrees find the number of Fahrenheit degrees from the freez-
ing point and multiply this by 4.

No. of degrees F. from freezing x7=No. degrees C.
To convert Centigrade degrees into degrees Fahrenheit multi-
ply the number of degrees by $ and the result will be the
number of degrees F. above or below 32° F.

No. of degrees C. x==No, of degrees F. above or below 32° F.

123. The Heat Unit.— It requires sixteen times as much
heat to raise the temperature of a pound of hydrogen one de-
gree as it does a pound of oxygen, and other ratios are found
to exist when other substances are taken. This makes it nec-
essary to select a certain substance as a standard when a unit of
heat is desired. Water is taken as the standard and one heat
unit is the amount necessary to raise a pound of water from
32° F. to 33° F.

ve

124. Specific Heat.— When the amount of heat which
will raise. the temperature of a pound of water from 32° F. to
3° F. is applied to a pound of dry sand it will have its tem-
perature raised through about 10° F. (Oelmer), or the same
heat would raise the temperature of ten pounds of sand one
degree, and the specific heat of sand is said to be .1, that of
water being 1. With the exception of hydrogen, water pos-
sesses the highest specific heat known, and this means that it
warms more slowly than do other substances; but the reverse
is also true, and when once heated it cools more slowly or gives
out a larger amount of heat. This is why large bodies of
water make the winters of the lands adjacent to them warmer
and the summers cooler.

125. The Specific Heat of Soils.— Different soils, like
other substances, have different specific heats, and hence warm
at different rates under the same sunshine, and it is on account
of this fact, in part, that one soil is warmer than another. In
the following table are given the number of heat units neces-
sary to heat one hundred pounds of water and of varieties of
soils from 32° to 33° F., and the temperature each would have
after one hundred heat units had been applied to them ata
temperature of 32° F.

TABLE OF SPECIFIC HEAT OF Dry SOILs.

No. of heat units re- Temperature of 100
quired to raise 100 lbs. after the appli-

lbs. from 32° F. to cation of 100 heat
33° F. units.
Heat units. Degrees F.

VVaiGer th)" shad Bee -ckiets alee is 100.00 33.00
Moon ear tlays-1e-iecie see ate 22.15 36.51
ED TINTS eae, 6 cfesaveles spachatee a 20.86 36.79
SHO hy WME Gea Gapces 14.14 ‘ass 39.07
Loam rich in humus.... 16.62 . 38 .02
Clayey humus 5.2.7... \4.. 15.79 38.33
BOAR Is aie 515 doce sone 14.96 38.68
Prumberelatye a s/s sw has. 5 5h0 13.73 09.28
SAIC Mae are ai Mast ooo a clans 10.08 41.92
Pure Chalke es yoa6 3s eee 2 18.48 37.41

These figures do not, in themselves, indicate the actual dif-
ferences in temperature the several soils named would show
under natural conditions because they are not only never per-
fectly dry but they have different capacities for holding water,

‘

72

and they differ also in their specific gravities, so that one hun-
dred pounds of one soil covers more surface, at a given depth,
than another one does. We have not yet the data needed for
an exact comparison, by volume, of the specific heat of soils.
The higher the per cent. of water any soil contains the more
heat will be required to raise its temperature one degree; so,
too, the heavier the soil is per cubic foot the more heat will
be required to raise its temperature a given number of de-
grees. Sand has a less capacity for water than most other
soils and is, on this account, naturally warmer, yet its higher
specific gravity tends to make it colder than other soils. A
cubic foot of dry sand weighs about one hundred and six
pounds, while one of clay loam is only about seventy pounds.
Saturated sand will contain, in the field, only about eighteen
per cent. of water, while the clay loam may have as high as
thirty-three per cent. Below are given the number of degrees
one hundred heat units will raise the temperature of a cubic
foot of sand and of clay loam when each is saturated with
water, half saturated and dry.
Saturated. Half saturated. Dry.

SEO UN eh AERO Ge ab Cnr kc 34° FF, Bes aE. 9.92° F.
Gleng Kern coteman sae ontscdcEc Soon8 ables 18. 4,49° F, 6.02° F.
DUTELEN CE. | sajepreiiaie eiaicleialcis ste sate 42° F, 1° F, 3.9° F.

It is thus seen that the greater weight of the sand, per unit
volume, tends to offset the greater amount of water held by
the clay, giving the two a more nearly equal temperature than
they would otherwise possess. It will also be seen that the
difference in the per cent. of moisture a soil may contain
makes a relatively larger difference in the change in tempera-
ture a given amount of heat absorbed will produce. This is
one reason why a well-drained soil is warmer than a similar
one not so drained.

126. * Latent Heat.’”’— When heat is applied to ice at a
temperature of 32° F. its temperature does not rise until the
melting is completed, the whole energy applied being expended
upon the molecules in moving them into new relative positions
against the force of cohesion which binds them together in the
crystalline arrangement of the ice. The amount of heat re-
quired to melt a pound of ice whose temperature is 32° F. is,
in round numbers, one hundred and forty-two units, or enough

73

to raise the temperature of one hundred and forty-two pounds
of water from 32° to 33° F. This fact may be demonstrated
approximately as follows:

Take equal weights of water at 32° F. and at 212° F. and
mix them. The two weights of water will then be found to
possess a temperature nearly equal to

919° io
212°+82°_

If, on the other hand, equal weights of water at 212° F. and
dry ice at 32° are placed together and the ice allowed to melt,
the resulting water will be found to have a temperature of
51° F. The water has had its temperature lowered

212°—51°=161° F.
while the ice has had its temperature raised only
o1°—32°=19° F.
Now if one pound each of ice and water were taken for the
experiment it is evident that the number of heat units con-
sumed in melting the ice would be
161—19=142 heat units.

When water has been raised to the boiling point no further
increase of temperature can be effected so long as the pressure
upon it remains constant, the whole amount of heat energy
being now expended in converting the water into steam at the
same temperature. ;

If a pound of steam at 212° F. be condensed in 5.37 pounds
of water at 32° F. there will then be 6.37 pounds of water,
having a temperature of nearly 212° F. The pound of steam
in being converted into water has heated 5.37 pounds of water
through

212°—32°=180° F.
without having its temperature appreciably lowered. The
molecular energy of the one pound of steam which was ab-
sorbed by the 5.37 pounds of water was therefore
180 x 5.87=966.6 heat units.

This large amount of molecular energy in steam explains
why a scald from steam is so much more severe than one from
boiling water, and also why so small a quantity of steam, by
weight, is required to boil a barrel of potatoes or to cook a
barrel of other feed.

74

127. Evaporation Cools the Soil.— We have seen that
one pound of steam in condensing into water generates 966.6
heat units, and the reverse statement is also true, namely, to
convert a pound of water into the gaseous state, under the
mean atmospheric pressure, requires the absorption, by that
pound, of 966.6 heat units. When one pound of water disap-
pears from a cubic foot of soil by evaporation, it carries with
it heat enough to lower its temperature, if saturated sand,
32.8° F.; and if saturated clay loam, 28.8° F.

To dry saturated sandy soil until it contains one-half of its
maximum amount of water requires the evaporation of about
9.5 pounds to the square foot of soil surface when this drying
extends to a depth of one foot, while the similar drying of
clay loam requires the evaporation of 11.5 pounds, and

11.5—9.5=2 Ibs.

or the amount of evaporation which must take place in the
clay loam to bring it to the same degree of dryness as the
sandy soil. But to evaporate two pounds of water requires

966.6 x 2=1983.2 heat units,

and this, if withdrawn directly from a cubic foot of saturated
clay loam, would lower its temperature 57.6° F. Here is one
of the chief reasons why a wet soil is cold.

That the evaporation of water from a body does lower its
temperature may be easily proved by covering the bulb of a
thermometer with a close fitting layer of dry muslin, noting
the temperature. If the muslin be now wet, with water having
the temperature noted, and the thermometer rapidly whirled
in a drying atmosphere its temperature will rapidly fall, owing
to the withdrawal of heat from the bulb by the evaporation of
water from the muslin.

128. Regulation of Animal Temperatures.— All of
our domestic animals require the internal temperature of
their bodies to be maintained constantly at a point varying
only a little from 100° F., and this necessity requires provisions
both for heating the body and cooling it. The cooling of the
body is accomplished by the evaporation of perspiration from
the skin and the amount of perspiration is under the control
of the nervous system. When the temperature becomes too
high, because of increased action on the part of the animal, or

75

in consequence of a high external temperature, the sweat
glands are stimulated to greater action and water is poured
out upon the evaporating surfaces and the surplus heat is rap-
idly carried away; each pound evaporated by heat from the
animal withdrawing about 966.6 heat units.

129. Bad Effects of Cold Rains and Wet Snows on
Domestic Animals.— When cattle, horses and sheep are
left out in the cold rains of our climate the evaporation of the
large amount of water which lodges upon the bodies, and. es-
pecially in the long wool of sheep, creates a great demand
upon the animals to evaporate this water. The theoretical
fuel value of one pound of beef fat is 16,331 heat units, and
that of average milk is 1,148 heat units. A pound of beef fat
may therefore evaporate

16331
966.6 710° lbs. of water,

and a pound of average cow’s milk

1148
966.67 218 lbs. of water.

On this basis, if a cow evaporates from her body four pounds
of rain she must expend the equivalent of the solids of 3.39
pounds of milk.

A wet snow-storm is often worse for animals to be out in
than a rain-storm, because in this case, the snow requires melt-
ing as well as evaporating, and the number of heat units per
pound of snow is

142,65 + 966.6=1109,25 heat units,

and the heat value of a pound of milk is barely sufficient to
melt and evaporate a pound of snow.

130. Cooling Milk with Ice and with Cold Water.—
If it is desired to cool one hundred pounds of milk from 80° F.
down to 40° F. it is practically impossible to do so with water
in the summer season in Wisconsin. It is difficult even to
cool it as low as 48° F., for most of the well and spring water
has a temperature above 45° F. and much of it is above 50° F.
If lower temperatures than 48° F. are desired during the warm
season some other means must be resorted to. Since it re-

76
quires one hundred and forty-two heat units to melt a pound
of ice, one pound is capable of cooling from 80° F. to 40° F.

1424+8
40

=3.75 lbs. of milk,

supposing the specific heat of milk to be the same as that of
water, which is not quite true. To cool one hundred pounds
of milk from 80° F. to 40° F. will require, therefore, about

= 263 lbs. of ice,

supposing it to be used wholly in cooling the milk.

If the water has a temperature above 40° F., before the milk
and ice are placed in it, there will be required enough more
ice to cool the water down to the temperature desired for the
milk.

The greatest economy in the use of ice will be secured, there-
fore, when the creamer contains just as little water as will
cover the cans and give the needed space for the ice, and when
the walls of the creamer are made of so poor a conductor of
heat as to admit as little as possible from without.

131. Washing with Snow or Ice.— When ice or snow
are used in winter for washing purposes there is a large loss
of heat incurred in simply melting the ice and raising the tem-
perature of the water from 32° F. up to 45° F., the temper-
ature it may have in any well protected cistern. To melt a
pound of ice and raise its temperature to 45° F. will require

142 + 18=155 heat units.

If three hundred pounds of water are required for a washing
then the lost heat will be

800 x 155=46500 heat units.

The fuel value of one pound of water-free, non-resinous
wood, such as oak or maple, has been found to be 15,873 heat
units; that of ordinarily dry wood, not sheltered, containing 20.
per cent. of water, is 12,272 heat units. At this latter value
it will require, supposing 50 per cent. of the fuel value to be
utilized in melting the ice and heating the water,

2 x 46500

—jaa79 7 8 lbs. of wood

17

more than would be needed to do the same washing with
water at 45° F.; and if seventeen such washings are done dur-
ing the winter the total cost for fuel would be the value of

17 x 7.58=128 Ibs. of wood,

to say nothing of the expense of getting the snow or ice and
the unhealthfulness of handling it.

132. Burning Green or Wet Wood.— Whatever water
wood or other fuel may contain when it is placed in the stove,
so much of the fuel as is required to evaporate this water
must be so expended and is prevented from doing work out-
side of the stove. We have seen, 131, that when wood con-
tains 20 per cent. of water there is required

15873 —12272=3601 heat units

per pound of wood to evaporate the water contained, which is
22.7 per cent. of the total value. Wood, after being in a rain
of several days, contains more water than this, and green
wood much more, sometimes as high as 50 per cent., while
well-seasoned sheltered wood may contain less than half that
amount.

It is frequently urged that when some green or wet wood is
burned with that which is dry there is a saving of fuel. There
is some truth in this, especially in stoves having too strong a
draught and too direct a connection with the chimney and if
the radiating surface is small or poor. The evaporation of
the water prevents so high a temperature from occurring in
the stove, which makes the draught less strong, and this gives
more time for the heat to escape from the stove before reach-
ing the chimney, and hence less is lost in this way. Then as
the fire burns more slowly there is not the overheating of the
stove, at times, which may occur with lack of care when very
dry wood is used, and a considerable saving occurs in this way.
These statements apply more particularly to heating stoves
than to cooking stoves. Dry wood is best for the kitchen
stove under most circumstances, the slower fire being secured
when needed by using larger sticks and by controlling the
draft.

1383. High Winter Temperatures Associated with
Snow Storms.— “It is too cold to snow” is a common say-
ing, but the truth is it cannot snow and remain very cold.

78

Speaking in approximate terms, when a pound of water in the
form of aqueous vapor in the air is converted into snow there
is liberated

966.6 + 142=—1108.6 heat units,
and, as the specific heat of dry air is only .2875, one heat unit
will raise the temperature of one pound of air through

pea el ba Oe

and 4.21 pounds of air through 1° F. This being true, the
freezing of one pound of aqueous vapor will liberate heat
enough to warm through 1° F.

1108.6 x 4.21 pounds=4667.2 pounds of air,

and as water at 32° F. is 773.2 times heavier than air at the
same temperature, the number of cubic feet of air raised 1° F.
must be
4667.2
62.417

773.2

= 57815.6 cu. ft. of air,

which is equivalent to 5781.56 cubic feet raised 10° and to
1806 cubic feet raised from 0° F. to 82° F. When a snow fall
of four to six inches occurs, over a large area, there is, there-
fore, a very large volume of air heated by it.

PROTECTION AGAINST LIGHTNING.

134. Nature of Electricity.— No very clear statement
is yet possible in regard to the real nature of either electricity
or magnetism, but the strongest evidence points to the con-
clusion that they are manifestations due to some action of the
all-pervading ether which we have seen, 118, is the medium
through which energy generated at the sun’s surface reaches
the earth. In the battery, on the telegraph line, energy is
generated by the chemical action there taking place and, by
some action not yet clearly seen, the ether pervading the space
between and surrounding the molecules of the telegraph wire
conveys this energy to the distant stations, where it is ab-
sorbed by the receiving instruments and converted into me-

79

chanical motions which record or indicate the messages sont.
In some manner the molecules of a conducting wire prevent
the escape of energy to the outside ether as the walls of a
speaking tube confine the sound waves developed in them,
preventing them from being dissipated in the surrounding air
and allowing them to travel to the end only slightly enfeebled.

When a glass rod is rubbed with a piece of silk or fur the
mechanical action develops a state in the ether of the rod
which is shown by the ability of the rod, in this condition, to
attract light objects to it. When a person speaks in front of
a telephone the sound waves produced by the vibration of his
vocal cords set the metal plate, near the end of the telephone
magnet, swinging in unison with the vocal cords, and the
approaches and recessions of this plate so disturb the ether
of the magnet as to cause it to take up a part of the energy of
the vibrating plate and then to transmit it to the ether of the
wire wrapped about the magnet and leading to the receiving
station, where, by another of those wonderful yet universal
transformations of energy, the action is reversed and the me-
chanical swing of the plate in the receiving telephone gives
back the words which set up the action at the sending station.

135. Atmospheric Electricity.— What the origin is of
the intense electrical manifestations associated with thunder

Fig. 29.

80

storms as yet lacks positive demonstration, but the close re-
semblances of these manifestations to the electrical manifesta-
tions developed by friction, when combined with the fact that
the strongest atmospheric electrical displays are associated
with the most violent air movements where rain or hail is
present, has led to a general belief that this electricity owes
its origin to the friction of the air currents upon the con-
densed moisture they are carrying. Fig. 29 represents the
general character of an electrical discharge in the atmosphere.

136. Electrical Induction.— When a body, which has
become charged with electricity, is brought near another body
which has not been electrified it exerts an influence upon that
body inducing electricity in it, and if the charge is sufficiently
intense and the distance is not too great the electricity will
break across from one body to the other, and the act may be
accompanied by a flash of light and a report.

137. Positive and Negative Electricity.— It is impos-
sible to throw a stone into water, making a depression at any
point, without raising a ridge around it which is equal in mag-
nitude to the depression, but extending in the opposite direc-
tion. When these two opposite phases are developed they
tend to come together, and the tendency is stronger in propor-
tion as the waves are higher. Something analogous to this
state of things seems to occur whenever and wherever elec-
tricity is generated. There appears always to be engendered
two equal and opposite phases which tend to run together and
obliterate each other unless prevented from doing so. The
one phase is called positive and the other negative electricity.

188. Conductors and Non-conductors of Elec-
tricity.— There is a great difference in the ability of different
substances to convey electricity from one place to another;
those which convey electricity readily are called conductors,
and those which convey it poorly or not at all are called poor
conductors or non-conductors. The metals generally are
among the best conductors, and silver and copper are the best
of these. Glass, gutta percha and dry air are among the
poorest conductors.

139. Discharges from a Point.— When a body becomes
charged with electricity the charge manifests itself only on the
outside surface. If the body is a sphere the intensity of the

81

charge will be uniform at all portions of the surface. If, how-
ever, the body is conical or has points upon it the charge will
be most intense at the points, and if a discharge takes place it
will occur first from the points, and it is this fact which has
led to the placing of points on lightning-rods.

140. When an Object May be Struck by Lightning.
When a cloud becomes so heavily charged that the air between
it and an adjacent cloud or an object on the ground, in which
it has induced the opposite kind of electricity, is no longer
able to prevent the electricity from breaking through, a dis-
charge or stroke occurs. Usually the nearer the charged
cloud approaches an object the more intense will be the charge
induced by the cloud in the body approached and the greater
will be the chances of a stroke. The intensity of attraction
increases as the square of the distance decreases, and this is
why, when other conditions are the same, elevated objects,
like buildings, are more lable to a stroke than those which are
lower.

Buildings standing upon wet ground are more liable to a stroke
than buildings in other respects similar but standing upon dry
ground, the greater danger coming from the possibility of a
stronger charge being induced upon the house in consequence
of the better conduction of the wet soil. Large trees near
buildings have a tendency to prevent strokes.

141. The Function of a Lightning-rod.— Lightning-
rods have two functions to perform, the first and chief one
being to discharge quietly into the air above, the electricity
which may be induced upon a building as rapidly as it accu-
mulates, and thus prevent a stroke from occurring ; and second,
in case a stroke is inevitable, to diminish its intensity and
convey to the ground quietly as much of the discharge as pos-
sible, thus reducing the damage to a minimum.

142. Do Lightning-rods Afford Complete Protec-
tion?— There is now a general agreement among physicists
that properly constructed and mounted lightning rods furnish
a large protection to buildings; they are divided in opinion,
however, as to whether complete protection is possible. The
rod may be called upon to protect against discharges under
two conditions: first, where a heavily-charged cloud comes
slowly over the rod, giving it time to discharge the induced

4

82

electricity and thus prevent an accumulation ; and second, where
an uncharged cloud chances to be over a rod when it instan-
taneously becomes charged from some other cloud. When
this occurs it is claimed by some that the rod has insufficient
time to afford any material protection, and hence that it is
hopeless to think of protecting completely against this class of
cases. ,

143. Essential Features of a Lightning-rod.— For a
number of years past there has been a fairly unanimous agree-
ment in regard to the essential points of a lightning rod, but
some new discoveries in regard to the conduction of rapidly
alternating currents, and in regard to electrical inertia, has led
to a divergence again uponsome points. It may be said that
practically all are agreed that: ,

1. The rod should be of good conducting material, contin-
uous throughout, terminating in several points above, and well
connected with permanent moisture below the structure in
the ground.

2. The rod should be in good connection with the building,
especially with metal roof and gutters, and should be carried
as high as the highest point of the structure to be protected.

3. The points need not be very fine, but should be coated
with some metal which will not rust.

4, Aniron rod, everything considered, is better and cheaper
than one of copper, provided it is galvanized and of sufficient
size.

The fundamental point of disagreement at present is in re-
gard to the form of the rod; some claiming that if a sufficient —
area of cross-section is given the shape is immaterial so far as
conducting ability is concerned, the solid round rod being the
cheapest and most easily protected from rust; others maintain
that the larger the surface the rod presents the greater will
be its conducting power and that the flat ribbon is the cheap-
est and best.

The first view is founded on the fact that, for steady cur-
rents, the conducting power is directly proportional to the area
of the cross-section. The second view is founded upon what
now appears to be the fact that very rapidly alternating cur-
rents travel only through an extremely thin layer of the sur-
face of the conductor, and what also appears to be the fact, that

83

lightning discharges are a series of extremely rapid alternat-
ing currents. The settling of this point of dispute is likely to
require the testimony of actual and extended practical tests
with both forms of rods.

144. Danger to Stock from Wire Fences.— The in-
troduction of wire fences has to some extent increased the
danger from lightning to stock in pastures, owing to the tend-
ency of the wires to become charged, and then give off side
sparks to the animals standing near. The danger is less from
the barbed wire than from the plain, and the danger from both
may be lessened by connecting the several wires with the
ground by means of other wires tacked to the sides of the
posts, the lower end being turned under the point of the post
when set. The staples should be driven astride the two wires
so as to hold them in close contact. It is not possible to say
just how close together these discharging wires should be
placed, but probably not nearer than 15 to 20 rods,

SOIL PHYSICS.

145. Nature of Soil.— The basis of all soil consists of the
undissolved remnants of the underlying rocks. Associated
with these remnants there is always a varying per cent. of
organic matter, resulting from the decay of vegetable and
animal remains; a certain amount of dust particles brought
from varying distances by the winds, or washed down by rain-
drops and snowflakes which have formed about those floating

high above the earth’s surface; and a considerable amount of
saline substances brought constantly to the surface by the
upward movement of capillary water, and left deposited when
the water evaporates.

146. Origin of Soils.— All soils owe their origin to the
processes and agencies of rock destruction which have been
and still are taking place in three chief ways:

1. Many rocks have been mechanically broken into larger
or smaller fragments.

2. Other rocks have had their molecules separated by simple
solution as salt is dissolved by water, or the molecules have
first been changed chemically and then dissolved.

‘

84

3. Still other rocks have had some of their mineral constitu-
ents dissolved out, leaving the remainder as an incoherent mass
of fragments. In Fig. 30 are shown the stages of transition
from the underlying rock to the soil above as it occurs on lime-

SN eS es

Lig. 30.
stone hills, while Fig. 31 shows the same facts for a more level
limestone surface. On examining the rocks of almost any

Lig. $l.
quarry they are found to be divided into blocks of varying
sizes by fissures or breaks which owe their origin to a general
shrinkage of the rocks and to movements of the earth’s sur-
face layers. These are the first steps in soil formation, and
=re plainly shown in Figs. 82 and 33. They exert a great in-
fluence in rock destruction and soil formation by furnishing
easy access for water and the roots of trees to their interior,
where the first by freezing and the second by growth expand
and break the blocks into smaller fragments. Moving ice, in
the form of glaciers, has done a vast amount of rock grinding,
the present soil of all except the southwestern portion of our
own state being the altered surface of athick mantle of bould-
ers, gravel, sand and clay formed, transported and spread out
by glacial action and the waters from the melting ice. Then
there are many animals which have contributed largely to this
rock grinding and soil formation. Darwin, through a long
and careful study, reached the conclusion that in many parts

85

of England earth-worms pass more than 10 tons of dry earth

per acre through,their bodies annually, and that the grains of

Fig. 32.
Fort Danger, Wis. From a Photograph. Bee Bluff, Wis. FromaPhotograph. After
After Chamberlin. Chamberlin,

sand and bits of flint in these earths are partially worn to fine
silt by the muscular action of the gizzards of these animals;

Lig. 34.
A tower-like casting ejected by a species of earthworm, from the Botanic Garden,
Calcutta: é6f natural size, engraved from a photograph. After Darwin,

S6

this same work is going on in dur own soils, where the holes
bored by angle-worms represent the volume of dirt they have
passed through their bodies. All seed-eating birds take into
their gizzards and wear out annually large quantities of sand
and gravel, after the manner of our domestic fowls.

The other two methods of soil formation depend mainly,
though not wholly, upon chemical changes wrought in the rock
minerals. Pure water has the power to dissolve, without chem-
ical change, greater or less quantities of most rock minerals
which are brought to the surface by capillary action and be-
come fine grains in the surface soil; but the larger part of this
work is brought about by the action of water in conjunction
with oxygen, carbonic, nitric, sulphuric, humic and other acids
which it carries down into the rocks, where the work of solu-
tion goes on rapidly. Mr. 'T. M. Reade has estimated that the
Mississippi alone carries to the sea annually 150,000,000 tons
of rock in solution, and yet a large part of the water which
enters the soil is brought back again to the surface and evap-
orated, leaving the materials it has dissolved as a contribution
to agriculture.

147. Soil-convection.— On the surface of a lake the
water which is at the top one moment is at another below the
surface, the molecules changing position continually by con-
vection currents due to changes of temperature. There is a
movement somewhat analogous to this taking place in every
fertile soil, though the movements are less rapid and are due
to different causes. Earthworms, ants, crayfish, gophers anl
various other burrowing animals each season bring large
amounts of the finer portions of the lower soil and subsoil to
the surface, forming systems of galleries with openings lead-
‘ing out to the free air at various places. Each heavy rain, es-
pecially during the fall and spring, washes the finer surface
sou into these galleries, filling them up, and new excavations
are again made, thus keeping up a slow, but nevertheless a
certain circulation, which in some of its effects is like the fall
vid spring plowing, but much of it extending to far greater
de ths, the angleworms, ants and crayfish often going down
fcom three to five or more feet during dry seasons. Darwin’s
observations have shown that this rotation of soil, which he
attributes largely to the action of earthworms, tends to bury

87

coarse objects, like flints, lying on the surface, as time passes,
and in Fig. 85 is represented one of these cases as cited by

s

him.

Section reduced to half natural scale, of the vegetable mould in a field drained and reclaimed
15 years before. Showing turf, vegetable mould without stones, mould with fragments
of burnt marl, coal cinders and quartz pebbles; and subsoil of black peaty sand with
quartz pebbles. After Darwin. 3

148. Soil Removal.— Pitted against these processes of
growth there is a powerful and universal set of agencies con-
stantly operating everywhere to transport from higher to
lower levels and from the land to the sea the surface soils,
and the magnitude of this action has been estimated at not
far from one foot each 3,000 years as an average for the whole
land surface, and hence the superficial and exhausted soils are
being slowly removed and replaced by new soil originating
from the products of rock decay, and brought to the surface
by capillary action and that of burrowing animals generally.
The absolute amount of soil removal can be appreciated when
it is understood that the summits of the bluffs represented in
Figs. 36 and 37 show the general level of the surrounding
lower land at a former time and that, at times intervening

88

between the present and that earlier period, vegetation has
grown on soil occupying all the levels between the two shown
in the engravings.

Fig. 86. Fig. 87.

|Giant’s Castle, near Camp Douglas, Wis. Pillar Rock, Wis. From a Photegraph.
From a Photograph. After Chamberlin. After Chamberlin.

149. Surface Soil.—Soils proper comprise the surface
five to ten inches of fields and woodlands generally. Often-
times the depth of the true soil may be less than five inches,
and then again it may exceed a depth of ten inches by varying
amounts. It is the portion which has been longest and most
completely exposed to the disintegrating and solvent action of
rock-destroying agencies, and'as a eculk of this fact it con-
tains a smaller per cent. of the soluble minerals used by plants
than the less altered subsoil below. Its chief ingredients are:

1. Sand. } f

2. Clay. Composing about 90 to 95% of the dry weight;

3. Humus.
which are commingled in varying proportions, giving rise to
different varieties according as one or another of these ingredi-
ents predominates. The true soil, on account of its more
complete aeration and its higher temperature, is the chief lab-

89

oratory in which the nitrogen compounds for plant food are
elaborated.

150. Kinds of Surface Soil.— For practical purposes
soils are variously classified. When reference is had to the
ease or difficulty of working the soil it is spoken of as

1. Light, or

2. Heavy ;
but these terms have no significance as regards actual weights ;
for a sandy soil is spoken of as light, and yet it is the heaviest
of all soils, bulk for bulk. The greater weight of the sandy
soil is due more to the lack of large cavities which are found
in the clayey soils, than to the higher specific gravity of the
soil constituents. It is the greater adhesiveness of the clayey
soils which causes the plow, hoe or harrow to move with
greater difficulty through them.

When reference is made to the temperature of soils, at the
same season, they are spoken of as

1. Warm, or
2. Cold,

according as the temperature of the soil is relatively high or
low. In this case the soils containing the greatest amount of
water are, when other conditions are similar, the colder on ac-
count of the high specific heat, 125, of the water.

When the chief ingredients of soil are the basis of distinc-
tion they are frequently classified as

Sand. Clay. Humus.
Per cent. Percent. Per cent.

1:- Sandyjsoil, containing. 0... 2)..5 chee set. 80 to 90 8 to 10 1to3
ey Sandivgloama, FU GN ites ee raacakee cl sysjerels .. 60to 80 10 to 25 3 to 6
3. Loam, ne ieee ery 2 cae ae Be 25 to 60 ~—-60 to 25 3 to8
Ae Clayeyaloanny, (216 anv e's Wateicivets b sfaie ne 10 to 25 60 to80 =8 to8
5. Clayey soil, Puben net aioe cb Adel Pate Tee 2 os 8to15 70 to 80 3 to 6

In peaty soil, or those of our low marshes and swamps,
there is often as high as 22 to 30 per cent. of humus. It should
be kept in mind that the sand, clay and humus of soils are not
plant food proper except in a small degree; they are, except
apart of the humus, what is left after the plant food is re-
moved. They serve, however, an important purpose in fur-
nishing a proper feeding ground for the roots and a means of
supporting plants in their upright attitude.

‘

90

151. Subsoil.— The subsoil is the real source of the nat-
ural mineral constituents of plant food, while at the same time
it acts as a reservoir for water which is delivered at the sur-
face by capillary action or held within its mass until the pene-
trating roots remove it. The depth to which roots penetrate
the subsoil is really great, and I believe the depth is deter-
mined primarily by the water content of the soil, the roots
traveling farther when the supply is scanty. Wheat roots are
recorded as observed at a depth of seven feet in Rhenish subsoil
of a sandy loam. Corn roots with us commonly reach a depth
of three feet and often exceed four. It would appear, there-
fore, aside from the fact that the subsoil is the parent of the
true soil and that it acts as a water reservoir, that the chem-
ical composition and physical characters of the subsoil may
determine in a large measure the productiveness of land,
unless it should be determined by future investigations that
the deep-running roots are simply water-gatherers.

152. Variation in Composition of Subsoils.— There
is a marked difference in the composition of those subsoils of
Wisconsin which are simply the residuary products of the
decay of rocks in place, such as those represented in Figs. 30
and 31, and those which owe their origin to glacial grinding
and mixing. ‘This difference is clearly brought out in the
table given below, which is compiled from analyses of typical
samples of residuary subsoils from southwest Wisconsin and
of glacial subsoils from the vicinity of Milwaukee as given by
Chamberlin & Salisbury in the Sixth Annual Report of the
United States Geological Survey:

Residuary Glacial Difference.
Subsoils. Subsoils.

Per cent. Per cent. Per cent.
SUMICAas SIO Ss ciaiscveic 2 etstole oiele stot otaee Bicone tates te 55.7 44.52 —11.21
Athommina, Ali” Os .%.c/siclecicee st sta oiiels eh sae 18.16 8.01 —10.15
Mime 3CSaQO) elena Riches shears siaehaene tee ore .99 13.74 +12.75
Maomesia, MeO ii 2%. ices steele tenia ere sels! sysve iat 7.42 +6.31
PO tase Over steteitass. ccge crete athens ace 1.24 2.48 +1.24
Phosphorus sO), oc.) %.:</s/sertec ert etsr> 08 .09 + .06
Carbon Dioxide, CO, ......... Seite snun 35 17 +16.76
Rion; Was On eee hee nc ae ee waists he ae 10.57 2.68 —17,89
OrSaniCpMAPLOr, keer. ciacss yee fo(a'e alolserelele wile 9.86 2.33 —7.53
Other substances ........... Perso: tot il 1.95 + .58

91

It will be seen that the insoluble sand, clay and iron com-
pounds predominate in the residuary subsoils, while the lime,
magnesia, potash and phosphorus compounds are in excess in
the glacial subsoils, and this at first thought seems strange
when it is remembered that the resicuary soils are derived
directly from magnesium limestones and that two of the four
samples giving the average were taken in contact with the
limestone itself, but these soils are what is left after the solu-
ble carbonates are leached away.

The photo-engraving of a relief map of Wisconsin, Fig. 38,
showing the glaciated and non-glaciated areas of the state, also

Photo-engraving of a relief map of Wisconsin, showing the glaciated and non-glaciated
areas of the state.
shows, in general, the distribution of the glacial and residuary
subsoils. The area of rugged topography in the west and
southwest of the state is the region covered by the residuary
subsoils. It should not be inferred, however, that the compo-
sition of all of our glacial subsoils is fairly represented by
;

92

the samples from the vicinity of Milwaukee, for in the northern
portion of the state there were no large areas of limestone to
be ground down by the ice to contribute the large amounts of
lime and magnesia found in the locality cited.

1538. Size of Soil Particles.— The size of soil particles
has very much to do with the value of a soil, this quality de-
termining, in some measure, its water capacity, its retentive-
ness of fertilizers, its drainage, its aeration and the way in
which the soil works. In general the relative number of large
grains as compared with the smaller ones is greater at the sur-
face than at some depth below; this difference is due largely
to the tendency of rain to pick up and carry away or to carry
downward by percolation the finer particles.

Chamberlin and Salisbury, as a result of their studies bear-
ing upon the size of soil particles constituting residuary earths,
say: “Out of 158,522 measured particles from several repre-
sentative localities, only 929 exceeded .005 mm in diameter.
A fairly illustrative example from near the rock surface at
Mt. Horeb, Wis., gave, in a single miscroscopic field, the fol-
lowing showing:

Particles less than .00285 mm in diameter................00: aeceatne 15,152
Particles between .00285 mm and .005 mm in diameter.............. 208
Particles more tham.000' mm in diameter. .ie.0.5.02 cence ce cecleceme 54

None of the 54 particles reached so great a diameter as
.01 mm,” that is, the largest of the 54 large ones had a diam-
eter so small that 25,400 of them placed side by side would be
required to span a linear inch.

Many of the soils which tend so strongly to clog the plow
are of this extremely fine-grained type, and a partial explana-
tion may be found in the minute particles wedging into the
microscopic cavities due to the grain or texture of the material
of the mold-board.

154. Needs of Soil Aeration.— The necessity for a con-
siderable circulation of air in soil actively supporting veg-
etation is generally recognized, and the demand for this
circulation is three fold:

1. To supply free oxygen to be consumed in the soil.

2. To supply free nitrogen to be consumed in the soil.

3. To remove carbon dioxide liberated in the soil.

93

Prominent among the demands for oxygen in the soil may

be mentioned :

The respiration of germinating seeds.

The respiration of growing roots.

The respiration of nitric acid germs.

The respiration of free-nitrogen-fixing germs.
. The respiration of manure fermenting germs.

It has been abundantly demonstrated that when oxygen is
completely excluded from seeds, placed under otherwise nat-
ural conditions for germination, growth does not take place;
if the germination is allowed to commence and then oxygen is
withdrawn further development will cease. When the air
surrounding a sprouting seed contains only 3 of the normal
amount of oxygen the germination will go on, but the rate is
retarded and a sickly plant is likely to result. Experience
abundantly proves that when soil bearing other than swamp
vegetation is flooded with water, or even kept in an over-
saturated state, the plants soon sicken and die, and this, too,
when they may be in full leaf and abundantly supplied with
nourishment, sunshine and warmth. The difficulty is the lack
of root-breathing. Oxygen in sufficient quantity cannot reach
the roots to maintain life. The plants are suffocated. This
explanation is apparently disproved by the fact that seeds of
various kinds may be germinated in a float of cotton resting
on the surface of water, and may even be made to mature
seeds if thé water in which the roots are immersed is kept
supplied with the proper foods in solution. The floating gar-
dens of the Chinese, consisting of basket-work made strong
enough to carry a layer of soil in which crops are matured
with their roots immersed constantly in water, is another ap-
parent disproof that wet soils kill the plants by depriving
them of oxygen. The two classes of cases are, however, very
different. In the cases of water culture the free water is sub-
ject to strong convection and other currents which rapidly
bring the water exhausted of its free oxygen to the surface,
where it becomes charged again. In the water-soaked soil,
with a relatively much smaller quantity of water, all possibility
of convection currents is prevented by the cohesive power of
the soil, and the rate of diffusion in such cases must evidently

bo

He go

ot

9+

be extremely slow, so that, viewed in this light, the two sets
of cases stand in strong contrast.

The natural nitrates, so essential to fertile soils, owe their
origin to a minute germ closely related to the “mother of
vinegar” and called in olden times the “mother of petre.” This
ferment germ produces the nitric acid of soils which, after
uniting with some of the bases contained in the soil, is ab-
sorbed by the plants as food. When the production of salt-
petre was a considerable industry in Europe one of the condi-
tions necessary to rapid formation was to keep the rich soil
well aerated by frequent stirring and by the introduction of
gratings to increase the air spaces. Oxygen is one of the es-
sontials to the life of these important germs, and herein lies,
in part at least, the advantage of cultivation and of properly
drained soils.

While we have, as yet, less positive knowledge in regard to
the respiratory needs of the free-nitrogen-fixing germs, now
coming rapidly into recognition, there is no reason to doubt
the beneficial effects of a properly aerated soil upon them.

In regard to the manure fermenting germs we have abun-
dant proof of the need of ventilation from their action in the
strong heating of the well ventilated coarse horse manure
when contrasted with the absence of heating in close cow
dung free from coarse litter.

Not only must oxygen and nitrogen be introduced into the
soil, but the large amounts of carbon dioxide liberated by the
fermenting processes and by the decomposition of the bicar-
bonates contained in soil-waters must be passed out in order
to make room for the other gases to enter in a sufficiently
concentrated form to answer the conditions of life going on
there.

155. Methods of Soil Aeration.— Most field soils, when
in their natural undisturbed condition and nearly saturated
with water, are impervious to such air currents as the greatest
differences of atmospheric pressure and temperature in a given
locality can produce. It is on this account, in part, that earth-
worms come to the surface in such great numbers during and
after heavy rains. The many perforations made by earth worms
constitute so many chimneys in and out of which the air moves

95

with every change of atmospheric pressure and temperature.
Cultivation as soon as possible after rains aerates the soil at
the time when it contains an abundance of moisture at the
surface and is in the best possible condition for the rapid ac-
tion of the niter germs, which need plenty of air, moisture and
warmth.

. Harrowing winter grain in the spring tends to make the
aeration of the soil more perfect by breaking up the crust
formed by the deposit of saline substances brought up by cap-
illary action.

Drainage, by carrying off the water more rapidly and to a
greater depth, opens the pores of the soil, making its breath-
ing more perfect.

Strong-rooted crops, like the red clover, which send their
roots deeply into the subsoil, leave it so channeled by the de-
cay of those roots that a more perfect circulation of air is thus
secured.

156. Soil Moisture.— The moisture contained in soils is
of the utmost importance agriculturally, for without it all
growth is impossible. Some of its chief functions may be
stated as follows:

1. By its solvent power it facilitates and promotes chemical
changes in the soil.

2. By its expansive power when freezing it mechanically
divides the coarser soil particles into finer ones.

3. By its capillary movements it conveys food to the roots
of plants.

4. By its osmotic power it transports plant food to the
leaves for assimilation.

5. By the same power it conveys the assimilated food to the
tissues for growth.

6. By its osmotic power it swells the seed and ruptures the
seed coats preparatory to germination.

7. By the pressure it is under in the plant it gives succulent
tissues much of their rigidity.

8. By its high specific heat it prevents the soil temperatures
from becoming too high by day and too low during the night.

157. Amount of Water Consumed by Plants.— Hell-
riegel found, by experiments conducted in Prussia, that the

‘

96

amounts of water drawn from the soil and given to the air by
various plants under good condition of growth, for each pound
of dry matter produced by the crop in coming to maturity,
were as stated in the table below:

NUMBER OF POUNDS OF WATER TRANSPIRED BY PLANTS IN PRODUCING
ONE POUND OF DRY MATTER.

Water. Water.
Lbs. Lbs
Barley. i. 2.) 2 Seis oie ane a nie wrererate ar 310 HLOTSS DOGS sso. 0s sinem's 282
SUMMMEH TYG oy. cierto ecpererecte, ate 303 OAS irate a cuclersachebelesease a sponte 2738
Oataiercer nes cepaweld SAN ee 376 Red WlOVEL as Mes ee eee 310
Summer WHeAb Gs cess Seis tae 338 BS PGIEWNEAG Wis Bic teen Pie oS 363

This, it will be seen, is at an average rate of more than 325
tons of water for each ton of dry matter when growing under
the climatic conditions of Prussia. This amount seems enor-
mous and may perhaps be too high, but there can be no ques-
tion but that the quantity is very large, and necessarily so,
because practically all of the dry matter of the plant requires
to be in solution when in transit to the place where it is finally
deposited as a part of the structure.

The chemical analyses of nineteen natural spring and well
waters from different localities in Wisconsin show the saline
ingredients to constitute .0475 per cent. of their weight, or
.95 pounds of solids in solution per ton. The ash in a ton of
the dry matter contained in corn ensilage is about 152 pounds,
and for the average spring water to yield this would require
160 tons, supposing the total saline ingredients to be used by.
the plant. While it is probable that soil water as it comes in
contact with the roots of plants is much more highly charged
than the average spring water, it is also true that not all salts
held in solution contribute to the ash of plants, so that it still |
seems imperative to assume a large consumption of water per
pound of dry matter in plants.

If we take the average of Hellriegel’s results, given in the
table, as applying to corn in Wisconsin, and 8,400 pounds as
the average yield of dry matter per acre, about 12 inches of
rain must be drawn from our soils by this crop each year, and
yet this is a full third of our total mean annual rainfall. Not
all the water which evaporates from a corn field during the

97

growing season can pass through the corn, and there are eight
months each year when the corn is not in the ground but
evaporation goes on during all that time. To these losses
must be added the water carried out of the state by rivers.
Such facts should teach, in an emphatic manner, the need of
adopting such methods of tillage as will tend to conserve the
soil moisture.

158. Position and Attitude of the Water-Table.—
The water-table is the surfece of standing water in the soil.
The distance the water-table lies below the surface exerts a
marked influence upon the yield of crops per acre. If the
' water les too close to the surface, drainage is required to se-
cure the best yields; when the water-table lies too low, none

padave

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=;

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inom
Fig. 41.

Figs. 39, 40 and 41, showing the relations o. the water-table to the surface of the ground

on the Experiment Farm. Figs. 39 and 41 represent north and south profiles, and

Fig. 40. one extending across the other two. The vertical parallel lines represent wells,
Vertical scale,—1 in.—40 ft.; horizontal scale,—1 in.—about 380 ft,

98

of that water is available for plant growth. Permanent ponds
and lakes are continuations of the water-table above the sur-
face of the ground, and their levels lie at varying distances
below the level of the water in the ground, the water-table
rising usually as the distance from these bodies of water in-
creases and as the ground rises.

In Figs. 39 to 42 the position and attitude of the water-table
is shown as it occurs on the Experiment Farm. In these cases

(Bortrer*

Showing the relation of the water-table to the surface on Picnic Point. Vertical scale, for
the water-table 1 in.—4 ft., for the surface, 1 in.=8 ft.

the water stands highest under the highest ground, which ap-

pears to act simply as a reservoir in which the rains accumu-

late, the friction of the soil retarding the flow toward the

lake.

The common belief that wells are supplied with water from
adjoining lakes or rivers, the water simply filtering through
the soil into them, is not generally true though it may be
in some exceptional cases. Neither is it usually necessary to
dig to a depth of the level of adjoining lakes before water is
found. Here at Madison water is obtained in wells, in some
cases, 20 feet above the level of the lakes, and the wells may
not be more than 40 rods from the lake shore and sunk simply
inaridge of glacial sand and gravel lying between the two
lakes.

159. Fluctuations in the Level of the Water-Table.
The level of the water in the ground is not constant, but stands
higher after a series of wet years and falls again with a suc-
cession of dry seasons. There is also an annuai rise and fall
of the water-table, the water standing lowest toward the lat-
ter part of fall or early winter and highest in the spring. In
those cases where the water-table lies near the surface it is
frequently raised by single heavy rains. Even changes in at-

99

mospheric pressure affect slightly the level of water in wells,
causing it to rise with a falling barometer and fall with a ris-
ing barometer.

The growth of crops appears also to affect the hight of the
water-table when it les near enough the surface to come within
range of root action. This effect is shown in Fig. 43. The
same figure also shows to what extent the water-table fell
during a growing season.

Showing changes in the surface of the water-table under alternate fallow plats and plats
of growing corn. The straight lines connect the water-levels of wells 1 and 7 on the
dates specified at the right, and the broken line joins the water surfaces of wells 2,

3, 4, 5 and 6 on the same dates.

160. Best Hight of the Water-Table.— It is a matter
of great importance, as bearing upon all questions of land
drainage, to know at just what distance below the surface of
the ground the water-table should lie to interfere least, and at
the same time to contribute most, to plant growth. In Eu-
ropean cultivation it is held that the tillage of moors and bogs
can only be successful when the water-table is maintained at
least 3 feet below the surface in summer and 2 feet in winter.
For light and gravelly soils in good condition a depth of 4 to
8 feet is held to be best for the majority of crops. The prob-
lem is manifestly a complex one which cannot be simply stated.
The case must vary with the character of the soil, with the
season, and with the habit of the cultivated crop, as to whether
it is naturally a shallow or a deep-rooted one.

100

161. The Vertical Extent of Root-Feeding.— Just
how deeply root-feeding may extend below the general limit
of root growth must depend upon the vertical distance through
which capillary action is able to pass water upward into the
root zone. In the fall of 1889 it was found that clover and
timothy, growing upon a rise of ground some 28 to 30 feet
above the water-table, had reduced the water content of sand,
at a depth of 5 feet, to 4.92 per cent. of the dry weight, when
its normal capacity was about 18 per cent., and this seems to
be a case of strong root-feeding to a depth of more than 5
feet.

In the table below are given the percentages of water in the
soils of closely contiguous localities bearing different crops;
the distance between the two most distant localities not ex-
ceeding twelve rods and the ground nearly level:

SHOWING DEPTH OF ROOT-FEEDING AS INDICATED BY THE WATER CONTENT
OF THE SOIL AUGUST 24, 1889,

Clover in Timothy and Corn. Fallow

Depth of Sample. Pasture. Blue Grass. Ground,

Per cent. Per cent. Per cent. Per cent.
QEO MM sr cietensyorereyecsiete were 8.39 6.55 697 16.28
Ged 2 TaA sh haves edhe wisveie cto 8.48 7.62 7.80 17.74
APA TSN... 5 Sale < resin verte 12.42 11.49 11.60 19.88
ASH AS TM ais oo elSelee isos lors 13.27 13.58 11.98 19.84
PA=BONIN, .. <5. shucton resi > 13.52 13.26 10.84 18.56
AQTAS MN. 54s acide «bis ofa ore 9.53 18.51 4.17 15.90

Distance of lower sample :
above water-table..... 2.36 ft. 1.97 ft. 2.12 ft. 2.22 ft.

This table shows clearly that root-feeding, in the case of
both clover and corn, extended to a depth of at least four feet,-
and that the corn had fed deeper than the clover. It also
shows that the timothy and blue grass had exhausted the soil
moisture near the surface more than either of the other crops,
but that the depth of feeding was less.

The strong difference which is shown to exist between the
amount of water in the fallow ground and the ground bearing
crops shows in a marked manner the strong drying influence
of growing vegetation upon the soil.

101

162. Capacity of Soil to Store Water.— The rainfall
of our state during the summer season is rarely enough to
meet the demands of vegetation during the growing period,
but the soil acts as a reservoir, retaining considerable quanti-
ties of that which falls at other times. All soils, however,
have not the same storage capacities, and hence on fields re-
ceiving the same rainfall the water supply for crops may be
very unequal.

Klenze makes the following general statements in regard to
the water capacity of different soils:

1. The saturation capacity of a given kind of soil increases
as the size of the smallest particles decreases.

2. The capillary capacity of a given soil containing only
capillary spaces decreases as it is made more close and firm.

3. The saturation capacity of soils is decreased by increasing
the number of cavities which are larger than the capillary
spaces.

4, The saturation capacity of soil decreases as the tempera-
ture increases.

In the following table are given the percentage and abso-
lute capillary capacity of a section of soil 5 feet deep, as found
by experiment, the soil being in its natural condition:

Per cent. Pounds Inches
of Water. of Water. of Water.
Surface ft. of clay loam contained........ 32.2 23.9 4.59
Second ft. of reddish clay contained...... 23.8. 22.2 4.26
Third ft. of reddish clay contained........ 24.5 22.7 4.37
Fourth ft. of clay and sand contained.... 22.6 22.1 4.25
Fifth ft. of fine sand contained.......... 17.5 19.6 3.77
Do tally see coetct eeate tosreraten onstage oi etate 110.5 . 21.24

These figures show that the actual storage capacity of 5 feet
of soil is really very large, in the case in question, aggregating

43560 x 110.5

3000 =2406.69 tons per acre,

and this, at the rate of 325 tons of water per ton of dry mat-
ter, is sufficient, were it all available, to give a yield of

406.69
a = 1408 tons of dry matter.

102

Fig. 42 represents the proportions by vol-
ume, of soil, air and water in the above sec-
tion.

163. Proportion of Soil-Water Avail-
able to Plants.— Not all the water which
soils contain is available to plants, and con-
siderable must remain unused if large yields
are expected; we have also seen that soil
fully saturated is not in a suitable condition
to produce crops. Hellriegel concludes from
observations of his own that soils give the
best results when they contain from 50 to 60
per. cent. of their saturation amounts, but
this, I think, should be understood as apply-
ing strictly only to the upper 12 to 24 inches of
soil because, as the season advances and the
roots develop downward, the water of the
subsoil is drawn upon gradually as it is
needed, and the per cent. of saturation is re-
duced to the proper amount.

During the season of 1890 Litch Dent and
White Australian Flint corn grew side by
side at the Experiment Farm in a light clay
loam underlaid with sand, the soil contain-
ing at the time of planting 22.41 per cent.
of water, and at the time of cutting 15.45
per cent., the mean saturation capacity being
about 25 per cent. The Dent gave a yield
of 9,875 pounds of dry matter per acre and
the Flint 6,000 pounds. The amount of
water lost by transpiration, evaporation and
drainage was at the rate ot 456 pounds of
water per pound of dry matter for the Dent
corn, and of 610 pounds for the Flint.

Fig. 44.

Showing the relative
volumes of water,
air and soil in the
upper five feet of
cultivated ground.

An examination of the figures in 160 will show how com-
pletely crops may reduce the water-content of soil during dry
seasons; those given there, for corn, being from the same local-

ity as the above for the year 1889.

164. Kinds of Soils which Yield Their Moisture to
Plants Most Completely.— The sandy soils yield their
moisture to plants much more completely than do the clayey

108

and other soils having a greater water capacity. This is clearly
shown in 160, where sand, at the bottom under the corn,
contains only 4.17 per cent. while the clay with sand mixed,
in the second foot of the same section, contains an average of
11.79 per cent. The saturation capacity of the first is about
18 per cent., while that of the latter is about 26 per cent. The
sand had given up more than three-fourths of its water while
the clay still retained nearly one-half.

If we compare the absolute amounts of water given up by
each of the two soils in question we shall find that the sand
had yielded 15.83 pounds per cubic foot, while the clay had
yielded only 12.5 pounds. It thus becomes evident that while
the percentage capacity of the sand is much below that of clay
its greater weight per cubic foot and the greater freedom with
which it yields water to plants makes its practical storage ca-
pacity for water, so far as crops are concerned, nearly as great
as the loamy clays. It is thus very clear that a sandy soil
kept well fertilized has many advantages over the colder, less
perfectly aerated and more obstinate clayey ones, which crack
badly in excessively dry weather and become supersaturated
in wet seasons.

165. Movements of Soil Water.— The water in the
ground is subject to at least three classes of movements:

1. Those due to gravitation.

2. Those due to capillarity.

3. Those due to gaseous tension.

The direction of movement in each of these cases may be
either :

1. Downward.

2. Lateral.

3. Upward.

The gravitational movements are the most rapid, most ex-
tended and belong to two types:

1. Percolation movements.

2. Drainage or current movements.

The percolation movements are, as a rule, slower than the
drainage movements and are usually downward, being only
occasionally and locally upward; they consist of the slow fil-
tering of water through the smaller soil pores. It is chiefly
by percolation that all water finds its way into the ground.

104 :

The drainage currents consist of those portions of the per-
colation waters which could not be retained in the surface
soil by capillary action. They move like streams of water on
the surface or like currents through pipes, giving rise to springs
and flowing wells.

The capillary movements, 81 to 88, constitute the slow
creeping of water over the surface of soil particles and those
of root-hairs. In direction they are chiefly toward the sur-
face of the ground and toward the root-hairs, during the time
when these are in action; but after showers there may be
capillary movement downward provided there is unsaturated
soil below, but even under these conditions it will not always
occur.

The gaseous tension movements originate in the changes in
volume of the confined air due to changes of temperature and
of atmospheric pressure referred to in 101 and 158.

166. Rate of Percolation.— The rate at which water
percolates through soils varies with the character and phys-
ical condition of the soil. As a general rule the percolation is
more rapid through the coarse-grained soils than it is through
those of a finer texture, and it is on this account that sandy
soils leach so badly. Clayey subsoils, especially if they are
underlaid with sand, very often shrink and break into great
numbers of small cuboidal blocks leaving numerous fissures
between them which open down to the sand below; through
these a large amount of percolation may take place; and this
effect is greatly intensified when the surface of the ground
becomes cracked, as it often does when not prevented by cul-
tivation. When in this condition such soils may leach even
worse than sandy soil. The perforations made by earth-
worms and other burrowing animals also exert a considerable
effect upon the percolation of water and the leaching of soils.

In case a winter sets in with fall rains insufficient to sat-
urate the soil and close up the shrinkage cracks and the chan-
nels formed by burrowing animals, considerable water finds its
way into the ground after it has been deeply frozen. During
the winter rains and thaws which occurred in 1889, 1890 and
1891, there was a large amount of percolation on the Experi-
ment Farm made evident by the alternate starting and stop-
ping of the discharge of water in the tile drains. These facts

105

have a significance in their bearing upon the practice of winter
hauling and spreading of manure.

167. Rate of Capillary Movement.— The rate of cap-
illary movement in soils varies with the kind of soil, with
the physical conditions, and also with the amount of water it
contains. It appears to be more rapid in sand than it is in
clay, and more rapid. in clay containing humus than in that
without. It is more rapid in a well firmed soil than in one
possessing large pores. The degree of closeness may, how-
ever, be so great as to impede the rate of movement.

I have found that water may rise through 4 feet of fine
quartz sand at a rate exceeding 1.75 pounds per square foot in
24 hours, and in a light clay loam at a rate greater than 1.27
pounds per square foot. In these cases, however, the soil was
devoid of all spaces except those produced by the form and
size of the particles, and the rate was measured by the amount
of evaporation; but as the soil remained wet at the surface
throughout the experiment the possible capillary rates must
exceed those stated by undetermined amounts. I have found
changes in the water-content of the soils of fields which in-
dicate that, under these conditions, the rate of capillary move-
ment, when the soil is wet, may exceed 1.66 pounds per square
foot.

When the soil is perfectly dry the rate at which water
moves through it is relatively very slow, so slow that five
cylinders of soil, each 6 inches in diameter and 12 inches high,
standing in water one inch deep, and in a saturated atmos-
phere, required the intervals stated below for water to reach
the surface in sufficient quantity to make it appear wet.

In clay loam, time required to travel 11 inches................... 6 days.
In reddish clay, time required to travel 11 inches................. 22 days.
In reddish clay, time required to travel 11 inches................. 18 days.
In clay with sand, time required to travel 11 inches.............. 6 days.
In very fine sand, time required to travel 11 inches............... 2 days.

These are very fundamental facts in their bearing on the
control of evaporation by surface tillage.

168. Translocation of Soil-Water.— It frequently hap-
pens, in certain soils after rains and in most if not all soils after
rolling or firming, that water is brought up into the surface
stratum from the deeper layers; this change of position is

106

named translocation and has important bearings upon ques-
tions of tillage.

The translocation caused by rolling or otherwise firming the
soil is due to the fact that reducing the non-capillary pores in
soil increases its capacity for water andthe rate at which
water will move into it by capillarity, and this influence is
sometimes felt to a depth of three to four feet. The deeper
soil-waters may in this way, therefore, be brought to the sur-
face or within the zone of root growth.

The translocation caused by wetting the surface depends
upon the principle that when the per cent. of water in a soil has

~ fallen below a certain limit its ability to take water from another

soil is decreased, and that when it has risen above a certain
limit this ability is then diminished, that is, for each soil there
is a certain water-content at which the water enters it at the
most rapid rate. It theréfore frequently happens that the
water-content of the surface soil is below that at which water
enters it most rapidly, and when a rain comes which restores
its strongest action again, water is also taken into it from the
soil below so that the surface stratum may, in consequence of
a rain, receive more water than actually fell, while the soil be-
low is, by translocation, rendered actually drier than before
the rain. This fact has an important bearing upon surface
tillage immediately after showers, upon the transplanting and
watering of trees and upon questions of irrigation. If the sur-
face, after a rain, is allowed to remain undisturbed, the rapid
evaporation which occurs in such cases may take away in a
short time not only that which had fallen but also that which
was brought up by capillarity from below, whereas simply
stirring the surface, destroying the capillary connection below,
would allow the surface only to dry and act as a mulch, retain-
ing the balance in the ground for the use of the crop.

169. Influence of Topography on Percolation.— The
slope of the surface influences, sometimes in a marked man-
ner, the percolation of rain-water and the water-content of
the soil. Whenever rains occur which are sufficiently heavy
to cause water to flow along the surface, from the hill-tops
toward the lower and flatter areas, less water is left to perco-
late on the highest sloping ground, while the more nearly level
areas may have not only the water which falls as rain upon

107

them but a portion of that which has fallen upon other ground.
Nor is this all; as the water-table is generally higher under the
high ground, 157, there is a constant tendency for the water
in the soil itself to percolate from the high lands toward the
low lands, and so, when the water-table here lies within reach
of root action, to increase the water supply for the season,
sometimes to a disadvantageous extent, making drainage nec-
essary where in the absence of the high land it would not be
needed.

In those cases where the water-table under the high land
is below the level of the surface of the low lands, and the low
lands remain long over-saturated, there is a tendency for the
water to percolate toward the higher ground, but of course to
return again at a later season.

170. Influence of Topography upon Evaporation.
It is a matter of common observation that the south and
southwest slopes of steep hills are often simply grass-covered,
while the north and northeast slopes may be heavily wooded.
This difference of verdure is due largely to a difference in soil
moisture on the opposite slopes, which is determined chiefly
by the difference in the rate of evaporation upon the two
slopes.

Other things being the same, the rate of evaporation, in our
latitude, is greatest on hillsides sloping to the southwest and
least on those sloping to the northeast. Several conditions
work in conjunction to produce this effect:

1. More air comes in contact with windward than with lee-
ward slopes, and as rapid changes of air over a moist surface
increase the amount of water taken up, the evaporation is
greater on the windward slope.

2. Our prevailing winds, during the growing season, are
southwesterly, and hence more air comes in contact with
southwest slopes.

3. Westerly and northerly winds are, with us, almost al-
ways drier than easterly and southerly winds, and as evapora-
tion is more rapid under dry than under moist air the westerly
slopes are drier than easterly ones.

4, Other things being the same, surfaces which are nearest
vertical to the sun’s rays receive most heat, and for this reason
southward slopes, in the northern hemisphere, become most

108

heated, and as evaporation takes place more rapidly at high
than at low temperatures, southerly and southwesterly s'opes
lose most moisture from this cause. Fig. 45 shows how a surface

inclined toward the south must receive more heat per square
foot than either the level surface or the one inclined north-
ward. If A65B is a section of a cylinder of sunshine falling
upon the hill AEB, it is evident that A64E, the portion falling
on the south slope, is greater than E45B, the portion falling on
the north slope. It will also be evident that the 20-degree
slope receives more heat than does the 5-degree slope, and this
more than the level surface.

The effect of the wind upon the evaporation from the soil is
at its maximum at the summit of a hill, because at this place
the wind velocity is greatest, no matter from what direction
it may be blowing.

171. Effect of Woodlands on Evaporation.— A piece
of woodland which hes to the southwest and west of a field
exerts a considerable effect upon the humidity of the air which
traverses that field, the tendency being to make the air more
moist. Taking a specific illustration, the air on the leeward
side of a second growth black-oak grove was found, on one
occasion, to contain 3.8 per cent. more moisture than did that
on the windward side at the same time; and again, when the
wind was in the opposite direction, observations in the same
localities showed 3.8 per cent. more moisture on the leeward
side, the observations in the four cases being taken about 10
rods from the margin of the grove. There was observed at

109

the same time a difference of air temperature of 1.5° F., the
leeward air being this much cooler in the field 10 rods from
the grove, the width of the grove being about 30 rods and
the trees from 20 to 30 feet high.

TILLAGE.

172. The Objects of Tillage.— The chief objects of till-
age may be briefly stated as follows:

1. To destroy undesired vegetation.

2. To place organic matter of various kinds beneath the sur-
face where it will more readily ferment and decay and be
brought within reach of root action.

3. To develop a loose, mellow and uniform texture in certain
soils.

4. To control the water-content of soil.

5. To control the aeration of soil. 154 and 155.

6. To control the temperature of soil.

173. The Destruction of Undesired Vegetation.— In
securing this object of tillage we have two classes of vegeta-
tion to destroy, one, like the prairie grasses of a virgin soil or
like the cultivated meadow grasses, which must be destroyed
before there is root room for the desired crop, and the other
which is designated by the general term of weeds.

Plants spread out two broad surfaces, one in the air to ob-
tain carbon dioxide, oxygen and sunshine, and the other in the
soil to obtain water, nitrates and other food constituents. It
requires but little study to reveal the fact that plants usually
spread out their leaf surfaces in such a manner that each leaf
shall be forced as little as possible to breathe the air of an-
other leaf, and that one shall shade another as little as pos-
sible. In a dense forest or thicket no fact stands out more
prominently than the race each plant makes to outreach its
neighbor and get into bright sunshine and free air. <A study
of root development shows that the same law is followed be-
neath the surface. There are times of scarcity of food, and
each root and rootlet tends to develop away from its neighbor
into an unoccupied territory. Such facts teach, with abundant

110

evidence, that there is no room for weeds in any soil where an-
other crop is expected. |

When we remember that each pound of dry matter requires
more than 300 pounds of water taken from the soil, and that
in most soils there is usually a scant supply of moisture at
best, the importance of a weedless surface should be appre-
ciated. hae

The following definite case will serve to show how rapidly
weeds may consume the water of soil.

On May 13, 1889, the water-content in the soil, on adjoin-
ing margins of a field just planted to corn and one of clover
and timothy, was determined on the Experiment Farm, with
the results below:

Corn ground. Clover ground.
Per cent. of water. Per cent. of water.
Surface to 6 in. contained........ 23.38 9.59
12to 18" ino contammed... 5.00.02 5 19.13 14.79
18 to 24 in. contained: ......5<... 16.85 13.75

These figures illustrate m a very forcible manner the great
power vegetation has of withdrawing water from the soil,
how naked tillage conserves it, and the importance, in all ex-
cept the wettest seasons, of not allowing weeds to occupy
cultivated fields.

174. Plowing in Organic Matter.— The decomposition
of most animal and vegetable tissues is the result of a growth
in and upon them of micro-organisms which, like all other liv-
ing things, require a bountiful supply of moisture. Moisture
is usually found in abundance at the surface in the shade of
dense forests, but in open cultivated fields the stems of plants
and coarse manures are too dry, most of the time, to maintain
the life of micro-organisms unless they are buried a little dis-
tance below the surface where the rate of evaporation will be
checked and where there is a better capillary connection be-
tween them and the water of the soil. In this condition, if
the soil is sufficiently aerated so that the respiration of the
life going on there is ample, the organic tissues are rapidly
broken down and quickly become available as food for crops.

175. Circumstances which Modify the Time and
Depth of Plowing in of Manure.— We are yet a long way
from being in possession of the rigid knowledge which is

dit

needed to make specific and exact statements regarding mat-
ters like these. There are some general statements, however,
which may be helpful in practice if not followed too implicitly
and without judgment.

oarse manures, when plowed in, tend at first, to cut off the
capillary connection with the soil-water below, and where the
plowing occurs in the spring, certain crops are liable to suffer
from drought because of a lack of moisture in the surface soil:
this is especially liable to be the case if the spring is dry. If
heavy, soaking rains follow the plowing in of such manure,
the soil particles are washed in between the straws and other
litter and a good connection established between the surface
and the soil below. This is what does happen usually in the
case of fall plowing, and explains why on many, if not most,
soils, the fall plowing in of such manures is preferable. It is
evident that on soils naturally too wet, and especially in wet
seasons, the spring plowing, in such cases, might be prefer-
able.
If manure is plowed in too deeply, and especially if the soil
is close and fine, there is danger of too little air to permit of
rapid decay, and the effects of manure under such conditions
will be only partially felt the first season.

If the soil is a leachy one, plowing the manure in deeply
tends to increase the loss by underdrainage.

176. Effect of Manures on the Water Capacity of
Soils.— Humus stands foremost among the ingredients of soil
in its power to retain capillary water. The barnyard manures,
besides containing large quantities of saline fertilizers, contain
much undigested vegetable fiber, which, when plowed into the
soil, tends to decay into ordinary soil humus and thus to in-
crease the water capacity of the lands to which they are
applied; in this respect they have a superior value, when com-
pared with most commercial fertilizers, especially if it shall be
established that organic matter, in contact with dry earth, does
oxidize with a loss of free nitrogen.

177. The Importance of Good Tilth.— It is a gener-
ally recognized fact that one of the chief objects of tillage is
to produce a mellow seed-bed of uniform texture, and there are
several desirable ends which are met, wholly or in part, by
good tilth.

112

One of the strong recommendations of a rich sandy soil is
found in the evenness of its texture and the lack of adhesion
between its grains which permit of almost perfect symmetry in
the development of roots and allows the root hairs to occupy
most completely the soil interspaces. When this is true, not
only is all the soil laid under tribute, but each and every root-
let, with its numerous root hairs, is doing full duty. If, on the
other hand, the soil is uneven and filled with hard lumps, a
large portion of it is not only unavailable but it stands as a
positive hindrance to root development, checking rapid root-
growth and making a much greater actual length of roots nec-
essary in order to come in contact with a sufficient amount of
soil. Nor is this all; during the process of cultivation the
lumps tend to work to the surface and become very dry; in
this condition they absorb a large percentage of the summer
rains, and, as they are almost completely surrounded by free
air, they give back this moisture to the atmosphere and thus
prevent it from rendering any service.

On the principle of oxidation of nitrogenous compounds
with the liberation of free nitrogen the lumpy condition of
soil should be expected to be a large source of loss of that im-
portant element of plant food.

Mellow soil favors root-development in being easily crowded —
aside by the expanding roots, and this is a matter of some im-
portance in all the succulent root crops, like beets, parsnips,
turnips and carrots, for the actual soil displacement in an acre
of these crops is very great, and the conclusion seems irresist-
ible that a hard soil must mechanically impede root-growth in’
such crops to a large extent.

A mellow, even-textured soil is likely to be much better
aerated than one not in this condition and better supplied with ~
moisture also.

178. Control of the Water-Content of Soils.— The
operations of tillage aiming to control the water-content of
soils proceed along one of three lines of action:

1. To conserve the water contained in the soil.

(a) By surface tillage.
(b) By flat culture.
(c) By mulching.

1138

2. To reduce the quantity of water in the soil.
(a) By deep tillage.
(b) By decreasing the water capacity.
(c) By ridge culture.
(d) By surface drainage.
(e) By underdrainage.
(f) By tree planting.
3. To increase the quantity of water in ie soil.
(a) By increasing the water capacity.
(b) By irrigation.
(c) By firming the surface soil.

179. Conservation of Soil Water.— On the great ma-
jority of cultivated lands there is, as a rule, an insufficient
supply of moisture to give the largest possible yield when
other things are favorable, and hence it becomes a matter of
importance to check the evaporation from the soil surface and
divert the water currents through the growing crop.

180. Surface Tillage to Check Evaporation.— In one
of my experiments, where the rate of evaporation from the
undisturbed surface of clay loam had been going on at the
rate of .9 pounds per square foot in 24 hours, simply removing
the crust of salts brought to the surface and deposited there
by evaporation, increased the rate of evaporation to 1.27
pounds per square foot in the same time, and I found the same
fact true for fine sand. These facts have a bearing upon the
practice of harrowing winter grain in the spring, suggesting
that the practice may, in some cases, cause a waste of water.

In the case of the fine sand referred to, the evaporation had
been taking place at the rate of .91 pounds per square foot in
24 hours, just before the crust was removed; after its removal
the surface was cut in small squares with the blade of a sharp
knife held vertical to the surface, and then the rate of evapora-
tion rose from .91 pounds to 1.75 pounds per square foot per
day. On removing a thin layer of the sand, and replacing it
immediately, the rate of evaporation fell to less than .5 pounds
per square foot daily. It is thus shown that one form of sur-
face tillage may increase the rate of evaporation while another
form may check it in a very decided manner.

A tool working like the disc harrow when the discs are run-
ning at a small angle, simply slicing the surface as the knife

114

did, increases the surface exposed to the air without destroy-
ing the capillary connection with the soil below, and tends to
hasten rather than retard evaporation; but if the tool com-
pletely removes a surface layer, leaving the ground covered
with a layer of loose soil, a mulch is provided which excludes
the air, in a measure, and greatly retards evaporation.

181. Flat Cultivation.— When the surface of the ground
is thrown into ridges, as in hilling potatoes or corn, the
amount of surface exposed to the air is increased, and this,
other things being the same, tends to increase the rate of
evaporation from the surface and diminish the supply of
moisture for the crop. When three-foot rows are ridged to a
hight of six inches the surface is increased more than 5 per
cent., and when ridged to the hight of eight inches more
than 9 per cent.

182. Deep Tillage to Increase Evaporation.— When
the ground is stirred to a considerable depth repeatedly there
is a large and rapid evaporation from the soil stirred, and this
is one of the chief objects of discing and harrowing lands
that are to be planted early in the spring. The ground is cold
from the low temperature of winter and from tae large vol-
ume of contained water which requires a great ammount of heat
to warm it. Getting rid of this moisture by deep »:llage pro-
vides a warm and mellow seca-ved, well aerated, which also
-acts as a mulch to conserve the deeper water of the soil until
atime when itis needed. a aS

183. Firming the Ground to Control Moisture.—
Rolling or otherwise firming land, after it has been tilled, may
have two distinct objects as regards the control of soil water:
These are:

1. To dry the soil as a whole.

2. To increase the moisture of the seed-bed.

We have shown by two distinct lines of investigation con-
ducted in the fields of the Experiment Farm that rolling tilled
land tends to dry the soil, as a whole, the effect being meas-
urable at a depth of at least four feet. This drying effect is
brought about —

1. By increasing the capillary power of the surface.

2. By increasing the surface temperature.

3. By increasing the wind velocity at the surface.

115

These three important effects tending to dry the soil may
be employed to secure the most rapid evaporation when re-
peated deep tillage and rolling follow each other at short in-
tervals. Stirring the soil deeply, exposes a large surface of
moist earth to the air which dries quickly, and if this is rolled
as soon as dry enough, the soil again becomes wet at the ex-
pense of the deeper soil moisture, and this is soon lost if deep
tillage follows. Repetitions of these processes are an excel-
lent treatment for a seed-bed in too damp cold soil.

When the soil of the seed-bed is too dry for the proper ger-
mination of seeds, then firming the ground tends to increase
the moisture by bringing it from below to the place where it
is most needed, and the press-wheels used on various forms of
drills and planters have this to recommend them. They con-
centrate the moisture at the points where it is most needed,
leaving the remaining portion of the field covered with a loose
protecting mulch. In the case of broadcast seeding, rolling is
generally required, if the seed-bed is too dry, and if this roll-
ing is followed, in one or two days, with a light harrow to
develop a thin mulch, it will check the surface evaporation with-
out destroying the good capillary connections produced by
the rolling.

184. Puddled Soils.— All soils when completely or nearly
saturated with moisture become very plastic, and when they
are worked under these conditions the water and air are
crowded out of the larger interspaces and the soil becomes
much more compact. This is especially true of the adhesive
clayey soils whose particles, after such treatment, become so
firmly united as to develop into obstinate clods so injurious to
good tilth. Great care should always be taken not to work
soils when they are too wet. The roller should never be used
when the soil: will adhere to its surface.

185. Advantages of a Warm Soil.— The advantages of
a warm soil are several, and may be briefly stated as follows:

1. Soil ingredients are more soluble in warm than in cold
water.

2. Root absorption is more rapid at warm than at cold tem-
peratures.

3. Germination is more rapid at moderately high than at
low temperatures.

4. Nitrification takes place most rapidly at about 90° F.

116

It is a general law with all living beings that their vital
processes can go on normally only aiien certain limits of tem-
perature, and the range is usually a comparatively narrow one.

In our own case a change of a few degrees above or below

98° F. in the body, as a whole, produces very serious disturb-
ances; and while these ranges are larger with plants, yet they
are not so wide but that the bounds may frequently be
crossed.

186. Best Soil Temperature in Certain Cases.—
Haberlandt found that the germination of wheat, rye, oats and
flax is best at 77° to 87.8° F., and that corn and pumpkins
germinate best between 92° and 101° F. He found, for ex-
ample, that when corn germinated in three days at a soil tem-
perature of 65.3° F., it reruns 11 days to gerniinate at 51° F.,
and while oats comand in two days at a temperature of
65.8° F., 7 days were required when the temperature was
41° F.

Sachs found that tobacco and pumpkin plants wilted when
the soil temperature fell much below 55°. F. on account of a
too slow root absorption. It is found that the “mother of
petre ” develops niter at an appreciable rate only above a tem-
perature of 54° F., that its maximum power is manifested at
98° F., and that at 113° F. its power is less strong than at
59°. F.

187. Control of Soil Temperature.— The temperature
of soils may be increased in several ways as follows:

1. By diminishing the water capacity.

By diminishing the water content.

By diminishing the surface evaporation. 127.
By smoothing the surface.

By means of fermenting manures.

. By increasing percolation.

it has been semi 124 and 127, that diminishing the
water in soil and ieegantore the surface evaporation favors, in
a marked degree, the production of high soil temperatures,
while the reverse conditions tend in the opposite direction.

Smoothing the surface, as in the case of rolling, has a very
appreciable effect in raising the soil temperature. The results
observed in a special case are given in Fig. 46. It will be ob-
served that the air temperature over the unrolled ground is
higher than it is over the rolled, which shows that this soil

4 ot go to

117
must be losing heat faster; and since both surfaces must have
been receiving the same amounts from the sun, it is plain that
if the air is warmed more over the unrolled ground the soil
itself must be warmed less.

Lime. |5-6 Am |I-4PIn, | 72PM. | S-6 AM. J2-4Pln. | 1-12 PM.

i 7 fee
abive grown

Warm Air

XS
~
>

»*

o~

s
Ss

Fig 46

Showing differences of temperature of rolled and unrolled soil and associated air temper: -
tures.

The air receives more heat from the unrolled ground for two
reasons.

1. Its many lumps present a much greater contact surface.

2. The lumps being dry become warmer at the surface than
the more moist rolled soil.

Further than this, the lumps, being in poor connection with
the soil below, conduct their heat slowly downward while at
the sa’ .e time they shade the lower soil; and by exposing a
very large surface to the sky they cool rapidly by radiation.

The measured differences of soil temperature due to this
cause have been as great as 6.5° to 10° F., the lower figure
having been observed at a depth of three inches and the higher
at 1.5 inches. |

The heating effect of fermenting manures in the soil has
been observed to produce a rise in temperature of nearly 1° F.

In the case of well drained soil the percolation of warm
summer rains often carries rapidly and deeply into the soil
considerable heat and thus raises the temperature directly, and
as this water must evaporate more slowly from the drained
soil, if at all, than from the undrained, it is not cooled as much
as it might have been had percolation not occurred, thus leay-
ing all the water to evaporate in a short time.

118

IMPLEMENTS OF TILLAGE.

188. The Plow.— Foremost among the implements of
tillage unquestionably must be placed the plow. Historically,
it is probably one of the oldest of farm tools, and when viewed
from the standpoint of evolution no instrument has advanced
more slowly or has been changed more profoundly. It has
grown from a natural fork formed by the branches of a tree,
as depicted on an ancient monument in Asia Minor, with the
shorter limb simply sharpened and laboriously guided and
awkwardly drawn through the soil by the longer arm, to our
present almost self-guiding twisted wedge of hardened steel
susceptible of an extreme polish.

189. The Work Done by a Plow.— The mechanical
principles which do or should dictate the construction of a
plow can be most easily comprehended when a clear notion of
the work a plow is expected to perform is first in mind.
Speaking simply of the sod and stubble plows, the first has
two functions:

1. A cutting function.

2. An inverting function.

The stubble plow has three functions:

1. A cutting function.

2. A pulverizing function.

3. An inverting function.

With both plows the cutting is required in two planes, one
vertical and the other horizontal, to separate a furrow-slice of
the desired width and depth. The inversion of the furrow-
slice, required in both cases, necessitates first a lifting of the
slice and then a rolling of it to one side, bottom up. The
pulverizing of the furrow-slice is most simply done by bend-
ing the slice upon itself more or less abruptly and then drop-
ping it suddenly upon the ground.

190. The Mechanical Principles of Plows.— The
plows under consideration are sliding three-sided wedges hav-
ing one horizontal plane face, called the sole; one vertical
plane face, called the dand-side, and a third twisted and oblique
face, one portion of which is called the share and the other the
mold-board. The two lines formed by the meeting of the

119

twisted oblique face with the land-side and with the sole are
cutting edges. This wedge is simply shoved through the ground
by a force applied to the standard through the plow-beam,
and is guided in its course by a pair of levers. in the form of
handles. ;

A study of Figs. 47 to 52 will show that, in these types of
plows, the cutting edges are very oblique to the directions in
which they move, and that the obliquity is greatest in the
breaking type. It will also be seen that the strong difference
between the elevating and inverting surfaces or mold-boards,
in these plows, consists in the steepness of the inclined surface
and the abruptness of the twist in them, these being least
abrupt in the breaking plow, Fig. 52, and most abrupt in the
full stubble, Fig. 47.

191. Advantage of Oblique Cutting Edges.— There
are several conditions which have led to placing the cutting
edges of plows oblique to the direction in which they are
drawn. :

1. The shin, coulter and share free themselves from roots,
stubble and grass more perfectly.

2. The shin, coulter and share require less ‘power to cut
roots.

3. The plow enters the ground more easily and runs more
steadily.

4, There is less friction of the furrow slice on the inverting
surface.

When the coulter is placed with its cutting edge in a nearly
vertical attitude straw and roots tend to double around the
edge and clog under the beam, increasing the draft and tend-
ing to draw the plow out of the ground. If the coulter is dull
and the roots are long and tough, they fold over the edge
and thus increase the draft by making the edge in the soil
thicker. When the cutting edge is made to incline backward
the roots tend to slide upward and are severed by a partially
drawing cut, and this requires a less intense power than the
straight chisel thrust.

The obliquity of the share, particularly in the sod plow
where a large part of its work consists in cutting roots, ma-
terially lessens the draught by bringing a drawing cut upon
the roots by forcing them sidewise in its wedging action and

120

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120

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122
drawing the cutting edge across them while they are under
tension.

When hard spots in the furrow-slice are to be cut through
the more oblique the share is the greater distance will the
horses travel before it is cut off, and as the resistance is over-
come in a longer time less power is required per second. Of
course so much work must be done in plowing a given length
of furrow, but the oblique share tends to develop an even,
steady pull all the time, while the less oblique form allows the
inequalities of the soil to develop an irregular draft which is
more wasteful. It is, in effect, like the triangular sections in.
a mowing machine, which allow the horses to be cutting all
the time.

192. Function of the Land-side.— The land-side is made
necessary by the inequalities of the soil and the tendency of
the horses to vary their course from a straight line. When
the oblique share is brought against a more resisting spot of
soil, a root or a small pebble, were it not for the land-side the
plow would run too far to land and the furrow would become
crooked. This side pressure developed by the share produces
friction between the land-side and the edge of the furrow and
the land-side should, therefore, be of such a character as to
move most easily under this friction.

193. The Line of Draft.— There is a certain point, A,
Fig. 53, in the mold-board of the plow, to which if the horses
could be attached the plow would “swim free” in the soil;
and the attachment of the team to the bridle, B, of the plow ,
should be in such a position that the point of attachment, D,

123

of the traces to the harness, shall lie in the same plane with
A, as represented by the line ABD. If the attachment to the
bridle is made at C the draft of the team will draw the plow
more deeply into the ground; and should it be at some point
below B, or, what would amount to the same thing, should
the horses be hitched shorter, the draft would tend to run the
plow out of the ground. Not only is it important to adjust
the plow so that it will “swim free” vertically, but it should
likewise be adjusted to “swim free” from right to left. When
this is done, a properly constructed plow will almost hold itself
and will then move with the least possible draft.

If the plow requires any considerable power to be applied
to the handles in guiding it, no matter in what direction, not
only is the work harder for the man, but the draft is harder on
the team and at the same time the plow is wearing out more rap-
idly. So, too, the man who carelessly holds his plow, allowing
it to waver from side to side and run shallow and deep, is mak-
ing not only more work for himself and for his team, but is un-
necessarily wearing out his plow and at the same time produc-
ing a seed-bed which will necessarily yield a smaller crop.

194. Draft of the Plow.— The records we have, thus
far, bearing upon the draft of plows are, in many respects,
very unsatisfactory, owing partly to inherent difficulties in
making measurements which represent the actual resistance
of the soil to the plow, partially because of unreliable methods
of measurements, and again because the varying percentage
of water in soil greatly modifies its plasticity and its weight.

Mr. Pusey, in 1840, in England, made some extended trials
of the draft of plows in soils of different kinds, and the fig-
ures below show the average results of trials with ten plows,
the total mean draft being given and also the draft in pounds
per square inch of a cross-section of the furrows plowed:

No.of Sizeof Draft. Draft per

Plows. furrow. sq. in.
DASAMIA SATU 3 iaasi'a(s wie va emartnre Oe» 10 5x9 = ART Ibs. —5..04 Ibs.
Sam civ OAM ew ce) wis is)-ps)eloietseieleus, sinrove 10 5x9 200) “ 5.55 “
cote 2 i <forl |Aar a ee ions RIL etetess 10 5x9 280 “ 6.22.“
GEOM LOMUM ss cess ic,i0is 2 «melcinteiei dels 10 5x9 440 “ 9.78 <
Etats rok ts ls e.'s., aw alecelarn «ili ain 10 5x9 Obra Le Goes
Sandy loam (J.C. Morton)......... 5 6x9 O66) sy LOL SiS

Stiff clay loam (N, Y. 1850)...... an 14 fexlOny 407“ 5.81 “

4

124

Prof. J.W.Sanborn has made extended trials of plows re-
cently in Missouri and Utah. The average of all his trials,
reported in Bulletin No. 2 of Utah Experiment Station, is 5.98
pounds per square inch of furrow turned. If we separate
these trials historically we get, by leaving the clay out of the
English trials:

English trials, 1840, draft per sq. in. 7.41 Ibs.
American trials, 1850, draft per sq. in. 5.81 lbs.
American trials, 1890, draft per sq. in. 5.98 Ibs.

Both English and American experiments agree in showing a
decrease of power per square inch with increase of width of,
furrow when the depth remains the same; but this statement
should not be construed as saying that a wide furrow can be
plowed with less total draft than a narrow one.

The effect of depth on the draft is not so clearly shown by
the experiments on record, but they appear to indicate an in-
crease of power, per square inch, required with increase of
depth.

195. Effect of the Beam-wheel on the Draft of the
Plow.— If the wheel under the beam of the plow is so ad-
justed in hight as not to bring the attachment of the horses
to the plow-bridle above the line of draft there is found a ma-
terial lessening of the draft of the plow with its use. The re-
duction of the draft is occasioned by the more even running
of the plow, making it unnecessary for the plowman to be al-
ternately pressing down upon the handles, or raising them,
in order to maintain the desired depth of furrow. If the ,
wheel is so high as to bring the line of draft in the condition
represented by the line ABD, Fig. 53, a part of the power
of the team is expended in prcducing pressure downward upon
the wheel while the full resistance of the plow still remains to
be overcome. The proper adjustment of this wheel is secured
when it simply rolls on even ground without carrying weight ;
when in this condition it will prevent the plow from entering
too deeply into the less resisting soils, and will act to force it
deeper into the harder portions.

196. Draft of Sulky Plows.— It is generally claimed
by plow manufacturers that sulky plows are of lighter draft,
relatively, than the free-swinging types, the claim being based
‘upon the assumption that the friction of the sole and land-

125

side are transferred to the well oiled axles of the wheels and
a rolling resistance secured instead of a sliding one, which
ordinarily, on bare ground, is much less. The few records of
trials, we have seen, do not appear to show a material differ-

ence inthe draft. There seems to be no good reason, how-
ever, why a sulky plow, when properly hung and with the line
of draft so adjusted that the power of the horses is not con-
verted into a downward pressure upon the wheels, should not
lessen the draft, and especially in the gang types. If a plow
of the requisite strength could be made so light that the wp-

126

ward draft against the furrow-slice were sufficient to take the
weight entirely from the ground, and if the adjustment for
landing were perfect, there would remain only the friction of
the furrow-slice itself. In such a case the only work left for
wheels would be such as has been described for the beam-
wheel of the walking plow, but such a condition appears prac-
tically impossible.

197. Effect of Coulters on the Draft of Plows.— The
use of the coulter is chiefly confined to sod plowing, and in
this work it is simply indispensable in securing a proper fur-
row-slice where there is any considerable turf. The early
English trials, and those of Gould, in New York, indicate a
saving of power by their use, but Professor Sanborn, through
his Missouri and Utah experiments, comes to the conclusion
that they increase the draft from 10 to 15 per cent. and ad-
vises farmers to dispense with them. This position is surpris-
ing, in the face of general practice, and I believe untenable.
When the coulter is very thick, dull and set in an improper
place or attitude it will necessarily increase the draft.

If the coulter is thick and set ahead of the lifting action of
the plow-point, and especially if it is dull, it offers a large re-
sistance by being forced to compress the soil and cut the roots
at the greatest disadvantage; but if it is so placed, in the rear
of the point, as to do its cutting and side-wedging above the
place where the point and share are lifting and cutting, the
two wedging and cutting bodies mutually assist each other;
the roots in both cases are then severed while under strain
and to a greater extent, with a drawing cut and, I believe,
with an appreciable saving of power. So, too, when the wheel
coulter is dull and set far forward, it becomes necessary to
hitch to the plow-bridle at so high a point,in order to foree
the coulter into the ground, that there may be loss of power as
there may be with a beam-wheel; but when this form of coul-
ter is sharp and set well back where the beam of the plow acts
with leverage to force the coulter through the sod and where
the cutting occurs under the lifting strain of the point and
mold-board, there can but be a ne of draft in tough sod.

198. The Scouring of Plows.— There are certain soils
whose texture and composition are such that the most perfect
plow surfaces fail to shed them completely. The particles of

127

most such soils are extremely minute, 1538, and often contain
much silica. In Fig. 51 is represented a type of one of the
most successful plows for this class of soils. In form it resem-
bles the breaking-plow, and the surface of the mold-board is
very hard and susceptible of a high polish. The hard surface
in these plows appears to be demanded to prevent it from be-
coming roughened by the scratching of hard soil particles; the
less abrupt curvature of the mold-board diminishes the surface
pressure and thus the lability to scratching, while the fine
polish furnishes the fewest and shallowest depressions into
which the extremely minute particles can be wedged by the
pressure. It is a matter of great moment, in the care of such
plows, that they be kept from rusting, because this quickly
destroys the necessary polish.

199. Pulverizing Function of Plows.— The stubble
plows are constructed so as to pulverize the soil at the time it
is being overturned. This action of the plow can best be ap-
preciated by taking a thick bunch of paper, like the leaves of
a book, and bending it abruptly upon itself; when this is done
it will be observed that the leaves slide upon one another, and
through a greater distance the more abruptly the bending
takes place. The steep mold-board of the full-stubble plow
shown in Fig. 47 has this shearing action upon the soil as one
of its chief functions and this necessarily increases its draft.

In selecting plows for the naturally mellow soils where pul-
verizing is unessential, the type represented in Fig. 50 should
be taken, as, other conditions being the same, its draft will be
lighter.

200. Driving Three Horses Abreast.— Much time and
expense can be saved in plowing by driving three horses
abreast, using a larger plow or a gang of plows, and this
method is especially to be commended on all clear land where
there is any considerable acreage to be plowed. In Fig. 56 is

ci cn anno

Fig. 56.

128

represented a very compact type of three-horse evener, handled
by the 8. L. Sheldon Co., and Fig. 57 illustrates an approved
method of driving three horses abreast.

Lg. 57.

201. Care of Plows.— Next in importance to having
good tools to work with is the keeping of them in proper
working trim. It is extremely wasteful to purchase good tools
and convert them into poor ones by lack of care, and in no
case do these remarks apply with greater force than to plows.

The John Deere Co., in their catalogues, make some remarks
regarding the care of mone -shares, and through their kindness
Tam permitted to use some of their illustrations. Figs. 58
and 59 represent a proper and an improper form of point. A

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Fig. 58.
dull point may increase the draft of a plow six to eight per
cent. and more, besides necessitating poorer work. The tend-
ency of wear on the point is to change it from the sharp,
slightly dipping form represented in Fig. 58 to the blunt up-
turned form shown in Fig. 59.

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ii hill

Fig. 59.
The heel of the share, like the point, is especially subject to
wear, and soon comes into an improper shape. In case the
ground is hard and dry, as is often the case during fall plow-

129

ing, the share-heel requires a set shown in Fig. 60, dipping de-
cidediy downward, preventing it from lifting out of the ground
and tipping the plow to land. On the other hand, when the
soil is mellow and damp, the heel of the share should be given
a more nearly horizontal attitude, as shown in Fig. 61, to pre-
vent it from sucking too deeply into the ground, and necessi-

WA i} i I HHRSHVVATATYENOU TIA usd
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tating a steady pressure at the handles toward the land. It
should be remembered that, whenever the plow requires a
steady pressure at the handles in any direction in guiding it,
there is a defect somewhere that should be remedied; because
a pressure of only a few pounds on the long handles, working
as levers, is transformed into friction, increasing the draft on
the team and the wear on the plow.

In taking the share to the shop for setting or sharpening,
the land-side should accompany it, so the blacksmith may have
a guide in giving the proper set to it.

pa

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Fig. 61.

202. The Subsoil Plow.— One type of this instrument
is represented in Fig. 62. Its function is nominally to loosen
the ground to a greater depth than is practicable with the
ordinary plow, thus securing deeper tillage without burying
the humus-bearing soil too deeply below the surface. Its use
requires great discretion, otherwise more harm than good may
result from it. Better aeration, better drainage, deeper de-
velopment of roots and less suffering from drought are advan-
tages claimed for its use. [for large yields of root crops a
deep loose soil is indispensable, and one necessity for this is
found in the act that the thick roots require so much space

130

which can only be secured by forcing the soil aside. There is
great danger of puddling the soil in the use of the subsoil
plow, because the surface may appear dry enough to work
when the subsoil is too wet.

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203. The Harrow.

As implements of tillage, harrows
are used to secure several quite distinct ends:
1. To produce a shallow seed-bed.
To dry the soil preparatory to seeding.
To render the surface of the ground more even.
To pulverize the soil and secure a more even texture.
To cover seed.

To destroy young weeds.

To work manure into the surface soil.

To aerate the soil.

. To check evaporation by developing a soil mulch.

Ae sortling as one or another of these ends is to be secured,
the Phan of the harrow should be different. In Figs.
63, 64 and 65 are represented three of the strongly marked
types of harrows.

204. The Disc Harrow.— This harrow, Fig. 63, is dis-
tinctly a seed-bed-preparing and soil-drying tool and, in its
adjustable types, may be made to work to a remarkable depth
in fall plowing and in corn ground in the spring. An immense

Se Ne

131

amount of work can be done with it where there 1s the neces-
sary power to move it, which, although large when running
deep, is really small when compared with the amount of soil

moved. Its rolling, concave, thin discs, when set obliquely,
enable it to enter the soil and overturn it with less compression
and relatively less friction than almost any other tool. Asa
first tool to loosen the soil and dry it rapidly it does excellent
work. It is also very effective in pulverizing sod and may be
used to advantage in covering sowed peas. This is also an ex-
cellent tool to work in a surface dressing of manure.

205. The Acme Harrow.— This tool, so far as its effects
upon the soil are concerned, is like the disc harrow, but while
it slices the soil and turns it over it does so with more com-
pression, more friction and less movement. Like the disc har-

132

row it can be used to cut sod but has a greater tendency to
drag them out of place.

206. The Tooth Harrows.— These tools,in their great
variety of forms, are best adapted to secure the ends 3 to 9
named in 208. The heavier types are, however, fair drying
tools, especially on the more mellow soils, and in such situa-
tions, too, they give a sufficiently deep seed-bed for most of
the small grains., To kill weeds, when just emerging from the
ground, in potato and corn fields,and in developing a hght

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Lg. 66.

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mulch to retard evaporation from the soil, there is no tool
more effective or rapid in its execution than the light, many-
toothed harrows.

207. Cultivators.— We have much to learn yet in regard
to the real objects to be secured by summer tillage or cuilt-
vation. Three chief objects appear to control present practice ;
they are:

1. To kill weeds.

2. To lessen surface evaporation.

3. To cover the roots of plants more deeply.

I believe we shail find, however, that one of the most im-
portant functions is

4. To secure better soil aeration.

When we remember that good aeration, plenty of moisture,
and a warm temperature are among the essentials both to
soil nitrification and root-growth, and that nature’s ways of
soil aeration are decidedly interfered with by our methods
of tillage, it seems but natural that some equivalent should be
supplied by our manner of working soil.

If soil aeration is conducive to its fertility it would appear

133

to be rational practice with corn, potatoes and similar crops
to adopt deep tillage during the early portion of the season
before the roots have come to occupy the soil, to facilitate nitri-
fication, and then to adopt purely surface tillage, to check
evaporation and kill weeds, after the roots are well developed.

208. The Roller.— The firming of land with the roller,
if used on the soil in the proper condition, has several benefi-
cial effects :

1. It makes the soil warmer, 187.

2. It increases the capacity of the surface soil for water and
its capillary power, 183.

3. In cases of broadcast seeding, the germination of seeds is
more rapid and more complete on rolled than on unrolled
ground.

4. It is maintained by many that larger yields are secured
from rolling land.

In cases where the soil is too damp and cold the alternate
use of the harrow and the roller will hasten its drying very
much. Many farmers advocate the use of the roller on lands
sowed to small grains after the grain is up, especially if a
drought is threatened, the advantage claimed being the forma-
tion of a mulch by crushing the surface inequalities. It is one
of those practices, however, which demands careful study and
experiment to ascertain to what the advantage, if any, is due.

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ELEMENTARY LESSONS

IN THE

PHYSICS OF AGRICULTURE.

BY

2 FH KING

PROFES:

STATE JOURNAL PRINTING COMPANY,
PRINTERS AND STEREOTYPERS.
1891,

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