TEACHERS
John Swett
PRACTICAL
LESSONS IN SCIENCE
BY
JOSIAH T. SCOVELL, M.A., M.D.,
FOB TEN YEARS PROFESSOR OF NATURAL SCIENCE IN THE INDIANA STATE
NORMAL SCHOOL.
CHICAGO
THE WERNER COMPANY
1894 !
COPYBIGHT, 1894,
THE WERNER COMPANY,
CHICAGO.
EDUCATION DEFT.
PEEFAOE.
THE question before each one of us is how to use all our facul-
ties to the highest advantage of ourselves and others. This is
the great thing to learn, the great thing to teach. If we would
be strong in body and mind we must obey nature's laws. If
the farmer would succeed, he must work in accordance with the
laws that govern the phenomena of vegetable and animal life.
The miner and quarry man must recognize the laws of the min-
eral world; the machinist and mechanic the laws of mathematics
and physics, and the manufacturer the laws of chemistry ; while
the work of the artist, poet and musician must conform to and
interpret nature; so that from every economic standpoint the
study of science is of the widest importance. Nature is the field
of observation, the primary source of our ideas. Here we find
objects for comparison, material for the exercise of the memory
and data for the formation of judgments. The study of nature
promotes respect for law, developing honesty, self-reliance and
reverence, so that the careful study of nature's laws is of the
highest educational value.
It is the recognition of these truths that has given science a
prominent place in every university , college and high school, and
their wider appreciation has given rise to the demand for its
introduction into the common schools.
While admitting the great value of scientific training it did
not eeem desirable in this case to write a formal text-book, or an
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4 PREFACE.
exhaustive discussion of science, but rather to set forth in a clear
and concise manner the general principles of this important
branch of study. The plan has been to consider briefly the fun-
damental ideas of the different departments of science, illustrat-
ing them by examples of their practical application, and also to
consider the relation of these branches to each other as constitu-
ent parts of one great organic whole the earth, the home of
man. The writer has aimed to open up the fascinating field of
science in such a manner as to awaken and develop the spirit of
scientific inquiry, and the desire for scientific work. Such experi-
ments have been suggested as can easily be performed anywhere
without costly or complicated apparatus, and lines of work have
been mapped out in each division that may be pursued with
pleasure and profit in almost any locality.
It is hoped that the work will stimulate many to study nature
for themselves, to observe the phenomena of climate, to notice
the surface changes of the earth, to study plants and animals as
living things, to observe them in their homes, amid their natural
surroundings in fact, to study nature as the great fountain of
knowledge. Numbers may thus be encouraged to go beyond the
limits of these discussions, into special fields to which they may
have served as an introduction; yet if the book only helps to
bring our teachers and school children into closer sympathy with
nature, the purpose of the author will be well accomplished.
JOSIAH T. SCOVELL.
TERRE HAUTE, IXD., January 10, 1894.
CONTENTS.
CHAPTER I.
INTRODUCTION GENERAL PRINCIPLES OP SCIENCE, . : . 9
CHAPTER II.
PHYSICS: MATTER AND THE ATTRACTIVE FORCES, . . . 15
CHAPTER III.
HEAT : ITS SOURCES, EFFECTS AND MODE OF TRANSMISSION, . 24
CHAPTER IV.
PROPERTIES OF SOLIDS, LIQUIDS AND GASES, . . . . 32
CHAPTER V.
THE COMPOSITION AND RESOLUTION OF FORCES, .... 43
CHAPTER VI.
VIBRATIONS OF THE PENDULUM CORDS AND AIR, . " . . 50
CHAPTER VII.
FORCE, WORK AND ENERGY KINETIC AND POTENTIAL, ... . 58
CHAPTER VII Continued.
SIMPLE MACHINES, LEVER PULLEY, SCREW AND WHEEL, . . : 68
CHAPTER VIII.
LIGHT : ITS SOURCESINTENSITYREFLECTION AND REFRACTION, 70
CHAPTER IX.
OPTICAL INSTRUMENTS RAINBOW AND COLOR, .... 78
CHAPTER X.
FRICTIONAL ELECTRICITY, LIGHTNING AND MAGNETISM, . . 87
CHAPTER XI.
DYKAMICAL ELECTRICITY AND IT APPLICATIONS, . 93
(v)
Ti CONTENTS.
CHAPTER XII. PAOK
CHEMISTRY HISTORICAL, GENERAL AND THEORETICAL, , - r ; 101
CHAPTER XIII.
OXYGEN AND COMBUSTION, HYDROGEN AND WATER, . . . lOti
CHAPTER XIV.
NITROGEN, THE AIR, AMMONIA AND NITRIC ACID, . , . 116
CHAPTER XV.
CHLORINE, BROMINE, IODINE AND FLUORINE, . . .''. 120
CHAPTER XVI.
DIFFERENT FORMS OF CARBON, SILICON AND BORON, . . . 127
CHAPTER XVII.
SULPHUR, PHOSPHORUS, ARSENIC AND THEIR COMPOUNDS, . . 137
CHAPTER XVIII.
POTASSIUM, SODIUM, LITHIUM AND THEIR COMPOUNDS, . J . 146
CHAPTER XIX.
CALCIUM, BARIUM, STRONTIUM, MAGNESIUM AND ZINC, . . 156
CHAPTER XX.
COPPER, MERCURY, SILVER AND ALUMINIUM, . ... . 158
CHAPTER XXI.
IRON, NICKEL, COBALT, LEAD, TIN, GOLD AND PLATINUM, . . 168
CHAPTER XXII.
ILLUMINATING GAS, ANILINE DYES, RESINS AND GUMS, . . 169
CHAPTER XXIII.
STARCH, SUGAR, ALCOHOL, OILS AND VEGETABLE ACIDS, ... . 175
CHAPTER XXIV.
BOTANY GENERAL AND STRUCTURAL, . ... . . 182
CHAPTER XXV.
BACTERIA, ALGA, FUNGI, SEAWEEDS AND LICHXVI, . . . 190
CONTENTS. vii
CHAPTER XXVI. wo
BRYOPHYTA, Moss PLANTS AND PTERIDOPHYTA, FERN PLANTS, . 200
CHAPTER XXVII.
THE ANTHOPHYTA, LEAVES, REPRODUCTIVE ORGANS AND FBUIT, . 207
CHAPTER XXVIII.
THE GYMNOSPERM^E, AND A STUDY OF THE PINE, . . . . 215
CHAPTER XXIX.
THE MONOCOTYLEDONS, AND A STUDY OP THE OAT, .. ....-_.* 220
CHAPTER XXX.
THE DICOTYLEDONS, AS THE OAK, WALNUT AND MAGNOLIA. . . 227
CHAPTER XXXI.
THE DICOTYLEDONS, AS THE VINE, ROSE AND MINT, . . . 236
CHAPTER XXXII.
FORM, COLOR, ODOR AND RELATIONS OF PLANTS, . . . . 244
CHAPTER XXXIII.
ZOOLOGY GENERAL AND STRUCTURAL, . . . . . 251
CHAPTER XXXIV.
PROTOZOA, C<ELBNTBRATA, ECHINODERMATA AND VERMBS, . . 258
CHAPTER XXXV.
ARTHROPOD ACRUSTACEA, ARACHNIDA, AND MYRIAPODA, . . 267
CHAPTER XXXVI.
THE INSECTA, WITH A STUDY OF THE GRASSHOPPER, , . . 275
CHAPTER XXXVII.
MOLLUSCA, MOLLUSCOIDEA AND TUNICATA, . . _. . . 285
CHAPTER XXXVIII.
THI VERTEBRATA PISCES AND AMPHIBIA, . . . . . 290
CHAPTER XXXIX.
RKPTILIA AND Avis, AS SERPENTS, LIZARDS AND BIRDS, . . 298
riii CONTENTS.
CHAPTER XL.
THE MAMMALIA, AS HOESES, DEER, DOGS AND MONKEYS, . . 805
CHAPTER XLI.
GEOLOGY ASTRONOMICAL, SUN, STARS, PLANETS, ETC., . . 316
CHAPTER XLII.
MINERALS AND ROCKS, AS FELDSPAR AND GRANITE, . . , 320
CHAPTER XLIII.
EARTHQUAKES, VOLCANOES, GEYSERS AND HOT SPRINGS, . . 820
CHAPTER XLIV.
TEMPERATURE, WINDS, WAVES, TIDES AND CURRENTS, . . 331
CHAPTER XLV.
GEOLOGICAL ACTION OP AIR, WATER AND VARYING TEMPERATURE, 337
CHAPTER XLVI.
RIVER AND MARINE EROSION, COMPARED, . . . . 342
CHAPTER XLVII.
GEOLOGY THE ARCHAEAN AND ALGONKIAN ERAS, . . . 848
CHAPTER XLVIII.
GEOLOGY THE PALAEOZOIC ERA, . . . . 852
CHAPTER XLIX.
THE MESOZOIC OR SECONDARY ERA AND THE TERTIARY AGE, . 858
CHAPTER L.
THE QUATERNARY AGE AND THE GLACIAL PERIOD, . . 362
CHAPTER LI.
THE CHAMPLAIN, TERRACE AND RECENT PERIODS, . . . 369
CHAPTER LII.
THE THEORY OP ORGANIC DEVELOPMENT STATED, . . e 877
CHAPTER LIII.
SUGGESTIONS AS TO LINES OF STUDY, ... . t 384
PRACTICAL LESSONS IN SCIENCE.
CHAPTER I.
INTRODUCTION GENERAL PRINCIPLES OF SCIENCE.
SCIENCE is scarcely more than a century old. In fact the
investigations, discoveries and generalizations, which have
given science a standing before the intellectual world, were for
the most part made within the present century. The growth
and development of that great body of systematic knowledge,
which we call science, has been interesting from many points of
view. The scientific investigator, penetratiDg the hidden realms
of nature, has set forth new ideas. These ideas excited opposi-
tion, so that there has been a constant conflict between the new
and the old, between the conservative and the progressive.
Every advancement in science has been opposed by those who
thought its tendencies were atheistic, leading toward the sub-
version of religion and the church; by those who considered the
reasoning and conclusions of science unphilosophical ; by those
who considered the processes and results unpractical, and by
those who were willing to leave well enough alone, being hostile
to every change. Science has been looked upon with distrust by
the learned professions, has been sneered at by practical men,
and shunned as something uncanny by the illiterate.
The wide dissemination of information, the growth of intelli-
gence, the continued stability of the essentials of religion, the
immense economical value of many of the results of scientific
investigation and discovery, have happily dispelled nearly every
form of distrust and opposition. And the unanimity of opinion
among scientific men, on all the important conclusions and gen-
10 PRACTICAL LESSONS IN SCIENCE.
eralizations of science, and the wide application and continued
stability of these conclusions, is leading even philosophers and
metaphysicians to accord science some degree of respect.
While at the present time there is little active opposition to
science, there are still many people who, through lack of infor-
mation, think of science as something peculiar and difficult,
which only persons of superior ability and intelligence can under-
stand and appreciate. There are many people who have no
idea that scientific investigations are of any interest or value
to them, who have no idea that they suffer less pain, will live
longor, are surrounded on every hand by comforts and conven-
iences, and means for enjoying life, all as the direct results of
scientific work.
Science is neither strange nor peculiar. It deals in a business
way with those common facts and phenomena which are the
familiar events of our every-day experience. The earth on which
we live, the air we breathe, the water we drink, the food we eat,
the clothes we wear, the dwellings which afford us shelter, the
tools we use, the soil we cultivate, the sun that rules our day,
the moon and stars that cheer the night, and the myriad forms
of vegetable and animal life that swarm around us everywhere,
constitute the subject matter of science.
The discovery of facts, the arrangement of these facts in
accordance with their relations, and the formation of judgments
from these facts, which shall be free from personal feeling or bias,
is scientific work. Through this kind of work science attempts
to explain in a rational way the facts and phenomena of the
world. Such work results in the discovery of important laws
and principles, which lead the way to valuable inventions, and to
the development of new processes, that enable us more fully to
utilize the vast and varied resources of nature. Knowledge
gained in this way underlies the success of every industry, has
been potent in every wave of progress made by the human race.
The observations of Sir Isaac Newton on the relation between
the motions of a falling apple and the moon, gave the world
clearer ideas of the order that pervades the universe. The con-
LESSONS /A 7 PHYSICS. 11
vulsive movements of a frog's legs when in contact with iron and
copper, started in the mind of Galvani a train of thought which
grew and developed into the telegraph, telephone, ocean cables,
electric motors, electric light, etc. From other ideas, suggested
by the bobbing lid of a kettle partly filled with boiling water,
have resulted the steam engine and our modern steamship and
railway systems, which have revolutionized every form of in-
dustry.
But the chief value of science is not in its practical applica-
tions, valuable as they may be, but rather in the development of
the scientific method of thought and investigation. That train-
ing of the mind, which grows out of the nature of scientific work,
is of the highest educational value. The collection of facts, the
study of their varied relations, the testing of conclusions by
comparison and experiment, result in habits of thought that are
valuable in any field of human endeavor. Such work tends to
make man a self-reliant, independent thinker. The field of science
is the universe of matter. As more and more of this field was
opened by investigators, it was gradually divided into depart-
ments and sub-departments until there are as many as fifty
separate lines of scientific inquiry, either one of which would
furnish material enough to employ the life-time of an industrious
student.
The boundaries of these departments are, in many cases, not
sharply defined. The different parts of the universe are so inti-
mately related that any scheme of classification must be largely
artificial.
Of these departments, physics and chemistry seem to be funda-
mental. Physics deals with those phenomena of matter that do
not involve a change of substance, but simply change of position,
form or condition. Chemistry deals with those phenomena which
do involve a change of substance, as the various kinds of com-
bustion and decay. But the distinction between these branches
of science is not very exact. In fact there is a wide field of com-
mon ground between them.
Every body, whether mineral, vegetable or animal, whatever
12 PRACTICAL LESSONS IN SCIENCE.
its form, or substance, comes under the domain of physics and
chemistry. Some knowledge of these subjects is therefore neces-
sary to intelligent work in any other department of science.
Botany treats of the vegetable kingdom, including trees, flow-
ering plants, ferns, mosses, fungi, molds, alga?, etc., considering
their form and structure, the conditions of their growth, and
their relation on one side to minerals and on the other to ani-
mals. Zoology and its sub-departments deals with animal life,
including birds, fish, insects, reptiles, mammals, etc., in much the
same way that botany deals with vegetation.
Geology, drawing largely from other branches of science, con-
siders the earth as a working organism, giving special attention
to climate and those relations between the mineral, vegetable
and animal worlds which have so largely determined the past
and present conditions of our eartk. Geology covers much of
the field usually treated in physical geography, taking a general
view of the earth as a whole.
Yon Humboldt, at the beginning of the century, was able to
master the whole domain of science as known at that time. No
student of to-day could survey the whole field of science; in fact,
few can master the whole work of any one of its departments.
The growth of scientific knowledge during the present century
has been wonderful, not only as to quantity but as to quality.
It is as if workers from all parts of the world, bringing the pro-
ducts of their investigations, as bricks and stones, had laid them
somewhat haphazard into an edifice; these workers, following
the lead of a few master builders, have laid a structure of giant
proportions, rugged in form, incomplete in detail, but broad of
foundation, showing few lines of weakness and possessing a unity
and symmetry surpassing the work done by man in any other
field of human endeavor. The strength, unity and symmetry
of this body of knowledge depends mainly upon the scientific
method.
The great body of scientific knowledge may well discourage us
from attempting to master the whole, but should not turn us
aside from this important study. Careful scientific work in any
LESSONS IN PHTSrCS. 18
department of science, however limited, will be of greater educa-
tional value to the individual and will make him more helpful to
his fellows, than less careful work over a wider range of the sub-
ject. And so intimate are the relations of } the different parts of
the scientific field, that a thorough knowledge of one portion gives
one a better view of the whole than does the mere superficial
knowledge of even several branches.
Time is an important element in scientific investigations. It
takes time, often a long time, to gather sufficient facts, time to
arrange these facts according to their relations, time to draw
conclusions and form judgments. Many would-be scientific men
fail because they are over-anxious to reach conclusions. It was
a long time from Galvani's observations of the muscles of a frog
to the laying of the Atlantic cable, and yet they were related as
cause and effect. While time is necessary to reach scientific con-
clusions, some of the best scientific work the world has known
was done at odd moments, between the hours of regular employ-
ment.
The term law, as used in scientific discussions, means simply a
statement of the observed order, sequence or relation observed
among natural phenomena. The law of gravitation merely ex-
plains to us how every particle of matter in the universe is, or
appears to be, altering its motion with reference to every other
particle. It does not tell why the particles move as they do; it
does not tell why the moon moves in a certain curve about the
earth. It simply gives in a few brief words the relationships
observed between a vast range of phenomena. This is the nature
of all scientific law. Men gather facts, classify them, analyze
them, discover their relationships, and then describe in simple
terms the widest possible range of phenomena. A scientific law is
always liable to be replaced or reformed as knowledge increases.
Newton's law of gravitation has stood the test of human expe-
rience for over 200 years without necessity of change.
An hypothesis or theory is the supposition assumed to account
for that which is only partially known. Such suppositions have
been baaed on a larger or smaller knowledge of facts. They may
14 PRACTICAL LESSONS IN SCIENCE.
be more or less in harmony with natural phenomena, and they
may more or less fully agree with accepted ideas in science, but
they differ from natural laws, in that they attempt to explain
how a given order of phenomena might have been produced.
They are made by men who are fully acquainted with what is
known of the subject and whose gifts are often higher than
knowledge. Call it genius, call it intuition, or by whatever name,
there is an element which we all recognize in such creative minds
that enables them to apprehend truth in a manner and to an
extent which ordinary men cannot appreciate or understand.
Such theories are inductions and the whole history of science is
simply the story of verified inductions.
Many theories have failed when tested by experiment and ex-
perience, others have been verified and are permanent landmarks
in the field of science. The theories of Ptolemy and Aristotle
dominated the intellectual world for more than a thousand years.
Those theories were good working propositions, the best the
world then had, and it was hundreds of years before advancing
knowledge began to find out their weakness. To us they may
seem fanciful and crude, but considering the amount of knowledge
possessed by man those theories, for their time, were creditable.
If, without telescope, charts, or higher mathematics, one should
attempt to formulate some scheme to account for the motions
of the sun, moon, planets and stars, his respect for the old
Egyptian astronomers would be greatly enhanced.
At the present time, besides many lesser theories, there are
four great systems of science under whose guidance most of the
scientific work of to-day is being done. These are the theory of
universal gravity, the undulatory theory of light and heat, the
molecular theory of matter, and the theory of organic develop-
ment. These may or may not stand the test of progressive inves-
tigations, but they are good working theories and the best and
only ones we have regarding their subject-matter. Their value
and bearings will be developed in our treatment of the various
branches of science.
CHAPTER II.
PHYSICS MATTER AND THE ATTRACTIVE FORCES.
PHYSICS deals with matter and energy. It treats of the prop-
erties and phenomena of matter due to the action of the dif-
ferent forms of energy. We know many things about how
matter appears, and many things about how energy acts, but
we know very little about what matter really is and very little
about the true nature of energy.
A rod of iron may be heated, may be melted, may be molded
or worked into any form, it may be made a magnet, all without
change of substance. But if the rod of iron is exposed to- moist
air it soon begins to change into a reddish substance called rust,
or if we expose it to the action of strong acids other changes
occur and other products are formed. Experiments with other
substances show that matter is subject to two groups of changes
or phenomena, one resulting in change of substance, the other
resulting merely in change of form or structure without change
of substance.
Chemistry treats of those phenomena which result in change
of substance or composition, while physics treats of those phe-
nomena which do not result in change of substance. While this
is the distinction usually made between physics and chemistry it
scarcely exists in nature. There is a wide field of common ground
between these branches of science called chemical physics, which
considers heat, light and electricity in some of their phases, and
discusses some of the phenomena of gases and other subjects
which seem to involve both groups of changes.
The earth, air and water, plants and animals, are composed of
matter. Matter occupies space, it extends in three directions
that is, it has length, breadth and thickness, and as far as known
matter is indestructible.
(15)
16 PRACTICAL LESSONS IN SCIENCE.
The property of matter, by virtue of which it occupies space,
is called extension. Most arithmetics contain tables of the Eng-
lish and French systems of linear, square and cubical measures,
and they need not be given or discussed here.
Under ordinary circumstances, matter exists in three forms or
conditions : Solids, as wood and stone; liquids, as water and oil ;
gases, as air and illuminating gas.
Impenetrability is a property of matter which depends upon
extension, illustrating and emphasizing that property. By im-
penetrability is meant that property by which one body of mat-
ter occupies space to the exclusion of all other bodies of matter,
or that two bodies of matter cannot occupy the same space at
the same time.
The truth of the above statement may be shown by trying to
put two solids, as a stone and a block of wood , or two stones or
any other two solids, in the same place at the same time. The
nail in the board separates the particles of wood ; does not occupy
the same place with them. Take a cup or glass partly filled with
water, and put into it a piece of lead, a little stone, or thrust
into it a piece of wood, and in each case the rising of the water in
the glass shows that the solid does not occupy the same place
as the liquid water; and again, if we pour more water or some
other liquid into the glass, it is manifest that the two liquids
do not occupy the same space at the same time. Fill a deep pan,
holding four or five quarts, nearly full of water, and put a com-
mon tumbler into it; the water will force the air out of the tum-
bler and take its place. Invert the tumber and raise it partly
out of the water, being careful not to let any air enter it ; then
through a straw or some kind of a tube blow a little air under
the tumbler; the air rising drives out some of the water, showing
that air and water can not occupy the same place at the same
time. The diving bell, formerly much used for work under water,
illustrates this principle. If another portion of air is forced into
the tumbler more water is forced out, showing that two bodies of
air can not occupy the same space at the same time. When the
glefls is partly filled with air, if a piece of cork or light wood is
LESSONS IN PHYSICS. 17
pushed under the rim of the glass it rises to the surface of the
water inside the glass, pushing out a bubble of air, showing that
air and wood or cork can not occupy the same place at the same
time. These experiments may be varied in many ways with profit
and pleasure, and will fully satisfy the experimenter of the fact
that matter occupies space and possesses the properties of exten-
sion and impenetrability.
The property of matter, which allows it to be divided into small
particles, is called divisibility. We may crush a piece of common
salt to powder, and dissolve the powder in water, when the par-
ticles become so small as to escape the sense of sight, even when
aided by the most powerful microscope, and only the sense of
taste or the chemist's art can detect the salt. Again, take apiece
of aniline (magenta) about the size of a pin-head, dissolve in a
few drops of alcohol, then stir into a gallon of clear water, and
the little particles or divisions of aniline will tinge every drop of
the whole mass of water. Experiments with other substances
show that matter may be divided into particles that are exceed-
ingly small, without changing its composition.
When we have crushed and dissolved the salt the particles are
so small that we can divide them no further without changing
their nature. But the chemist can divide the smallest particle of
salt into two substances, one a silvery -white metal called sodium,
the other a greenish-yellow gas called chlorine, while the aniline
may be divided into the gases hydrogen and nitrogen, and
the solid, carbon. Those who have experimented with great
numbers of substances tell us that most bodies, mineral, vege-
table or animal, are compound bodies, like the salt or ani-
line, made up of two or more simpler bodies, which are called
elements.
The smallest division that can be made of a compound body,
without breaking it up into its component parts, is called a mole-
cule, and the particles that unite to form the molecule, whether
of the same or different kinds of matter, are called atoms. The
atom is the smallest division that we can make of matter. We
may in the future learn to divide atoms, but at present they seem
L. S. 2
18 PRACTICAL LESSONS IN SCIENCE.
to be indivisible, absolutely hard, inelastic, unchangeable as
bright, sharp-angled and perfect as when they left the creative
hand . They are the bricks of the material world . They have com-
bined with each other to form millions of compounds; these com
pounds have been broken up and new combinations formed over
and over again, and yet these particles of matter show no marks
of abrasion or signs of decay.
In general the molecules composing bodies are arranged in
some definite way, as the crystals so common among minerals,
and the various structural forms in plants and animals, leaving
many spaces unoccupied, which may be called structural spaces;
and it is supposed that the atoms and molecules which make up
even the most compact bodies, as the metals, do not touch each
other, so that even in a piece of gold there is more vacant than
occupied space. These spaces between the particles which make
up a body are called pores, and the property of matter depend-
ing upon the existence of pores is called porosity. Porosity sug-
gests the idea and possibility of the properties of compressibility
and expansibility. The porosity of water may be shown by filling
a glass with water and then sprinkling into the water fine salt or
sugar. The particles of salt seem to be smaller than the parti-
cles of water, and to run down among them as wheat may be
shaken into a barrel of apples or potatoes. Again, water pene-
trates the pores of wood, cloth, paper, some kinds of rock, etc.,
by a process called absorption, showing the existence of pores in
all such bodies.
Rest is that condition of a body when it is not changing its
position in regard to other bodies around it, while motion is that
condition of a body when it is changing its position in regard
to other bodies around it.
That which changes the condition of a body as regards rest
or motion is called force.
Bodies have no control over their conditions of rest or mo-
tion. They can not move themselves if at rest, and can not stop
themselves if in motion. It requires force to put a body, as a
wheel, in motion, and it requires force to stop the wheel when in
LESSONS IN PHYSICS. 19
motion. Inertia is the property of matter which does not allow
a body to change its condition of rest or motion.
Leaves and fruit fall to the earth ; force is necessary to lift a
body from the earth ; in short, all our experience seems to indi-
t-ate the existence of a force which draws or tends to draw all
things together into one mass. This force is called attraction.
It is known by different names from its different modes of action.
Gravitation is that form of attraction which acts on all
bodies and throughout all distances. Every body or particle of
matter in the universe attracts every other body or particle of
matter. The rain, the snow, the dead branch, or loosened rock,
falls under the action of gravitation; and it also holds the heav-
enly bodies in their accustomed orbits. The action of gravity, as
manifested on the earth, is to bring all bodies as near the center
of the earth as possible and hold them there.
The force of gravity is found to vary in accordance with two
laws.
If two bodies, one containing twice as much matter as the
other, are attracting a third body, equally distant from the
others, the force exerted by the larger one will be twice as great
as that exerted by the other. If one contained three times as
much matter as the other it would exert three times as muchforce,
etc., illustrating the first law of gravity, that the force of gravi-
tation varies directly as the quantity of matter exerting it; that
is, the greater the quantity of matter the greater the force of
attraction.
Suppose a body to be twice as far from a source of attraction
at one time as at another. In the first position the force of
attraction will be only one-fourth as strong as in the second.
If the distance be three times as great the attraction will be
one-ninth as strong, etc., illustrating the second law of gravity,
that the force of gravitation varies inversely as the square
of the distance through which it acts. In discussing gravity,
the center of gravity is considered as the center of the mass
of matter exerting the force, and the distances are estimated
from the center of gravity in each case. In the case of a sphere
20 PRACTICAL LESSONS IN SCIENCE.
or cube of uniform density the center of gravity is at the cen-
ter of the body, while in a pyramid or cone it is below the
center of the body. The lower the center of gravity the more
stable the body. A load of hay may be overturned more easily
than a load of stone, as the center of gravity is lower in the load
of stone. A body will stand up as long as a vertical line from its
center of gravity falls within the base of the body. It is easier
to stand on our feet than on a pair of stilts, because, in the
latter case, the slightest motion will throw the vertical line out-
side the supporting base.
It is difficult to illustrate the second law of gravity, but the
intensity of light and heat vary according to the same law, and
it can be more easily illustrated when treating of those subjects.
The weight of a body is the downward pressure which it can
exert, and this pressure or weight is due to the action of gravi-
tation exerted by the earth. Weight depends upon gravity,
measures gravity, and varies according to the laws of gravity.
On the surface of the earth the variations of gravity are so
slight that weight is usually considered as a good measure of the
mass or quantity of matter in a body as well as of the force of
gravitation. As the earth is eomewhat flattened at the poles,
the distance to the center of gravity of the earth is less at the
poles than at the equator, consequently the force of gravity is
-greater and a body will weigh more at or near the poles than at
or near the equator. Water, dirt or mud is thrown from a rap-
idly turning wheel; the earth as a rotating body tends to throw
off matter from the equatorial regions; this tendency also less-
ens the force of gravity and consequently the weight of bodies
at the equator. The combined effect of these two causes is to
make gravitation at the equator less by about 1-192 part of
its value at the poles. Conversely, the increase of the force of
gravity from the equator north and south, as shown by the
vibrations of the pendulum, indicates a flattening of the earth
toward the poles.
The quantity of space a body of matter occupies is its volume,
and is expressed in cubic inches or feet. The quantity of matter
LESSONS IN PHYSICS. 21
in a body is its mass, and is expressed in ounces, pounds, etc. If
you cut blocks of wood, cheese and lead of the same size you
will find their weights to be different; that is, bodies of the same
volume may contain unequal quantities of matter. Those bodies
which contain more matter in the same volume than others
are said to be more dense than the others. Density refers
to the quantity of matter in a given volume as compared
with some standard. Lead is more dense than iron, because
a cubic inch of lead contains more matter than a cubic inch
of iron.
Cohesion is that form of attraction which acts between the
molecules of a body, and which resists dividing, breaking, or
tearing forces, differing from gravity in that it only acts
through small distances and between molecules of the same
kind, making the diamond hard, copper tenacious, and iron
strong.
Cohesion varies with the kind of matter, being stronger in some
kinds than in others, and it varies on account of what seems to
be a different arrangement of molecules in the same kind of
matter, as in the case of tempered and untempered steel. In
welding iron the pieces must be heated, at least to the plastic
state, before the particles can be hammered together so that
cohesion will act.
Adhesion is that form of attraction which holds together
molecules of different kinds of matter. It is this form of attrac-
tion that makes glue, paint, mucilage and varnish valuable, and
is more m.arked between solids and liquids.
While adhesion is more marked between solids and liquids it
does exist between solids and solids, as in the case of dust adher-
ing to a wall, and between liquids and gases as well. This may
be shown by pouring water from one vessel into another; air
adhering to the descending stream is carried with it, as shown
by the bubbles of air formed in the water of the receiving vessel.
Gases sometimes adhere to solids. If a piece of glass be immersed
in water, bubbles will often appear on its surface. Dust, even
iron filings, gently spread over the surface of water, will float,
22 PRACTICAL LESSONS IN SCIENCE.
though much heavier than water. A layer of air adhering to the
particles of iron, serves as a boat in which the iron floats.
If a tumbler be placed on the surface of water and then lifted
slowly upward, ifc will draw up the water, forming a little hill.
After it has been raised from the water, the film of water on the
bottom of the tumbler shows that the force of adhesion between
the glass and the water was stronger than the force of cohesion
between the molecules of water. This can be measured by letting
one pan of a balance rest on the surface of water and then add-
ing weights to the other pan till the force of cohesion is overcome.
Capillary attraction is a kind of adhesion which causes some
liquids to rise along the sides of solids partly immersed in them
and to rise in narrow tubes, or between plates that are brought
near each other. By capillary attraction the blotter absorbs
ink, the oil rises in the lamp-wick, and doubtless, in the case of
paint and glue, these substances actually penetrate the solid by
capillary attraction, and when hardened, mechanical interlocking
of the particles aids the force of adhesion in making the union
firm. This form of attraction does not act the same in all cases.
If a glass tube be partly immersed in mercury, the mercury sinks
instead of rising in the tube; in general, those liquids which wet
the solid will rise, those that do not will be pushed down, and
the smaller the tube the higher the liquid will be raised or the
farther it will be pushed down. Experiments with two pieces of
glass three or four inches square, separated by different distances,
shows that capillary force is manifested between plates in the
same manner as within tubes.
The surface of a solid or liquid, is in a state of tension. It is
explained as follows : In the interior of bodies, each molecule is
attracted equally in all direction, and no tension exists, while
at the surface the molecules a re attracted laterally and inward ,
but not outward, so that there is strain on the surface molecules.
It is through this surface strain that cohesion causes small
bodies of liquids to assume a spherical form, as drops of water or
mercury. When a soap bubble is formed at the mouth of a pipe,
and the stem left open, the bubble soon shrinks and expels the
LESSONS IN PHYSICS. 23
air, which indicates tension in the surfaces of the bubble. Pure
water has the highest surface tension of any ordinary liquid
except mercury. It is the surface tension of water that causes oil,
dust, or any impurities that may settle on it, to spread out over
the whole surface. The interesting phenomena observed when
trying to spread a small quantity of water over an oily surface,
or when a drop of oil and a drop of alcohol are made to touch
each other on a plate of glass, or when small quantities of water
and alcohol or water and ether are brought together on a plate
or piece of glass, are all explained by the action of surf ace tension.
Surface tension explains capillarity. The force of adhesion be-
tween glass and water is stronger than the force of cohesion
between the molecules of water, and the water rises along the
sides of the tube, making the surface of the water inside the tube
concave like a cup. The effect of this action is to lessen the press-
ure on the water in the tube, and the air pressure on the outside
forces the water up in the tube until the weight of the column of
water equals the difference between the forces of adhesion and co-
hesion. In the case of an oiled tube and water, or a glass tube and
mercury, no cohesion is manifested, and surface tension causes
an increased pressure inside the tube, and the liquid is depressed.
Magnetic attraction is that form of attraction which acts
between a- lodestone or a magnet and iron, drawing the bodies
towards each other and causing them to assume some particular
position in reference to each other. The compass, so important
in navigation and in surveying, owes its value to this form of
attraction.
Electrical attraction is shown in lightning, and often results
from chemical action. Through the action of magnetic and elec-
trical forces we have the telegraph, telephone, dynamo, electric
motor, etc., which will be more fully discussed under the subjects
of magnetism and electricity.
Chemical attraction or affinity acts between the" atoms or
molecules of elementary bodies, binding them together into mole-
cules of compound bodies, whose molecules are held together by
the force of cohesion.
CHAPTER III.
HEAT: ITS SOURCES, EFFECTS AND MODES OF TRANS-
MISSION.
HEAT and the different forms of attraction are called physical
agents, forces, or forms of energy. They are known to us chiefly
by their effects.
Heat was once called an element ; later it was regarded as a
subtile form of matter contained in bodies, and manifesting itself
with more or less intensity. Now it is thought to be the vibra-
tory motion of the molecules of bodies, which may be increased
or diminished in various ways. When this motion is increased
the body becomes hot, the molecules are separated and the body
expands. When the motion is diminished the body grows cold,
the molecules approach each other and the body contracts.
Concerning the ultimate source of this motion which affects us as
heat, science as yet has no suggestions to make.
The process by which the blacksmith sets the tire of a wheel
shows that heat causes iron to expand and that when the heat
is removed or its intensity lessened, the iron contracts. Lay a
rod of iron or copper, ten or twelve inches long, on a board, and
drive a nail at each end so that the rod just touches the nails ;
then place the rod in the fire and when red-hot test its length
by the nails. A few experiments with different solids will show
that heat causes them to expand and that some expand more
than others. Purchase from the druggist an alcohol lamp,
some test tubes fitted with corks, and a few pieces of nar-
row glass tubing, and have holes cut in some of the corks of
such size that the glass tubing will fit them closely. If a lamp
seems too costly, one can be made with little trouble. Get a
bottle holding from two to four ounces, with a wide mouth, fit it
with a cork, bore the cork for a small tube made of tin, or the
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LESSONS IN PHYSICS. 25
ferrule of an old penholder ; then a little candle wicking and an
extinguisher, which may be made of cork, completes the lamp.
Take a piece of glass tubing, from eight to ten inches long, soften
it near the middle in the alcohol flame and bend it to an angle of
about 60 degrees, and, when cold, fit it in one of the perforated
corks. Fill a test tube with water and force in the cork, carry ing
the glass tube so that the water rises in the tube through the
cork ; then wipe dry, place the lower end of the test tube in the
alcohol flame, and notice the water in the smaller tube; with-
draw the heat and again observe the effect. The experiment
may be more interesting if colored water is used. If a vessel be
filled with cold water and heat applied, the water will expand and
overflow before it is hot enough to boil; this is a common oc-
currence in the cook room. Empty the water from the test tube,
used in showing the expansion of water, and when dry, close it
with the cork carrying the delivery tube ; then dip the free end
of the tube under water and apply the flame to the test tube.
The bubbles formed indicate that the air in the tube is expanding;
that some of it has been forced out. Remove the flame, keeping
the end of the delivery tube under the water, and soon the water
will be seen rising in the carrying tube; showing that the air
is contracting. These and other experiments indicate that heat
causes solids, liquids and gases to expand, and that when heat is
removed they contract, the attractive forces drawing the mole-
cules closer together.
The forces of heat and cohesive attraction, acting upon the
molecules of bodies, are called molecular forces, and from the
direction of their action are called attractive or repellant forces.
They are constantly struggling between the molecules of bodies,
and as the one or the other prevails the body is hot or cold,
is a solid, a liquid, or a gas. In a solid body the attractive
forces prevail, and its molecules are firmly bound together, so
that solid bodies tend to retain the form given them by nature
or art. In a liquid body the attractive and repellant forces are
nearly equal, and the molecules are free to move easily among
themselves, so that the form of liquids depends on the form of
26 PRACTICAL LESSONS IN SCIENCE.
some solid in which they are inclosed. In a gaseous body the
repellant forces prevail and the molecules are driven away from
each other to the greatest possible distance; consequently gases
have no independent form or volume. In the firmest solid the
repellant force is still active, and some degree of mobility still
exists, even in the hardest body. But in the case of gases the
particles seem to have been separated so far as to be beyond the
influence of cohesive attraction, so that if they ever become
liquids it must be through the action of some other force than
cohesion.
If we apply heat to a solid, as ice, it soon becomes a liquid;
and if the heat continues to increase, the liquid expands into a
gas. If heat is removed the pressure of the air and the force of
gravity bring the molecules together into a liquid form, and
finally the cohesive force draws them into the solid form again.
In common language, the gas cools and condenses into a liquid
and the liquid cools to a solid ; that is, cold is often spoken of as
an active force, while it is simply a condition of a body due to
the diminished action of heat ; as heat diminishes, the body be-
comes cooler, and the attractive forces prevail more and more
fully.
By temperature is meant the warmth or intensity of heat in a
body as compared with some standard. Temperature is not the
same as quantity of heat ; that is, a pond of water at a tempera-
ture of 40 degrees would contain more heat than a pail of water
at a temperature of 100 degrees.
We can tell by touch that one body is warmer than another if
the difference is considerable, but the touch does not give us an
accurate knowledge of the difference. In some substances there
is a definite amount of expansion or contraction for a definite
increase or diminution of the intensity of heat! This makes it
possible to construct an instrument called a thermometer, or
heat measurer, which, by the expansion or contraction of some
substance, enables us to get an accurate idea of the relative tem-
perature of bodies. In the thermometer for ordinary use the
temperature is indicated by the expansion or contraction of
LESSONS IX PHYSICS. 27
mercury which has been confined in a glass tube. A scale of
degrees is attached to the tube, of which the following are the
most important points : 212 degrees, which indicates the tem-
perature of boiling water; 32 degrees, which indicates the tem-
perature of freezing water; and zero, indicating a temperature
32 deegrees below that of freezing water. At 39 degrees below
zero mercury freezes, and to indicate lower temperatures alcohol
thermometers are commonly used.
The above are the figures on the Fahrenheit scale. On the
Centigrade scale, zero marks the freezing point, and 100 the boil-
ing point. Other scales are sometimes used.
To measure higher temperatures, an instrument called a pyrom-
eter is used, in which some metal or one of the permanent gases
serves to indicate the intensity of the heat. To measure delicate
changes in temperature an air thermometer is sometimes used.
In our experiments for showing the expansion of water and air
by heat, the tubes, with the water in one case and the air in the
other, formed a thermometer, needing only a scale for completion.
The principal sources of heat for the earth are the sun and
stars. Chemical action, as combustion, fermentation, and the
vital processes, is a source of heat; so is mechanical action, as
friction, percussion, etc. Illustrations of heat from these various
sources will be familiar to everyone.
Heat is assumed to be the motion of the molecules of bodies.
An imponderable but highly elastic substance, called ether, is
supposed to fill the spaces between the molecules of bodies and all
spaces throughout the universe not otherwise occupied. The
vibrating molecules of the heated body cause vibrations or waves
in this ether. These waves spreading out in all directions cause a
more rapid movement of the particles of bodies which they meet,
thus causing more intense heat. In fact, heat does not pass from
point to point as heat, but rather as energy which becomes heat
in the bodies acted upon by the waves of ether. This transfer-
ence of heat through waves of ether is called radiation. The
intensity of heat by radiation varies; first, as the intensity of
heat in the source; second, inversely, as the square ofthedistance
28 PRACTICAL LESSONS IN SCIENCE.
from the source. The first law needs no illustration, and our
experience leads us to believe that the other may be true also,
but its truth can be better illustrated in the discussion on the
subject of light, which varies according to the same law.
Radiant heat or energy moves in straight lines, as can be
shown by arranging screens about the source of heat. A body
with a rough surface will radiate heat more readily than a
similar body with a smooth surface. The teapot is given a
polished surface because such surfaces retain heat better than
rough ones do.
Suppose one end of an iron rod is held in the flame of a lamp,
the molecules in contact with the flame are made to vibrate
more rapidly. They swing against their neighbors and put them
also in more rapid motion ; they in turn give motion to the next,
and so on until those at the end of the rod are in more rapid
motion, and can put in more rapid motion molecules of other
bodies in contact with them, thereby increasing their tempera-
ture. This method of transferring heat from molecule to molecule,
through a body, is called conduction. The metals are, in general,
the best conductors of heat. Liquids and gases are poor con-
ductors of heat. If we take a test tube and put a piece of ice in
the bottom, weighted by a piece of iron or lead, and then fill the
tube with water, the water at the top of the test tube may be
boiled without melting the ice, showing that water does not
conduct heat as rapidly as some solids do.
The heat applied to a body is divided by it into two parts,
one part is used to increase the temperature of the body, an-
other part is used to expand the body. The first can be appre-
ciated by the touch, and is called sensible heat; the second
can not be appreciated by the touch or by the thermometer,
and is called latent heat. The latent heat has not been lost,
but it has simply been used up in doing the work of expansion.
Different substances do not divide heat in the same proportion.
Let equal parts of water and mercury be placed over the same
source of heat. Each divides the heat it receives into two parts
as above; but the heat devoted to temperature is more in the
LESSONS IN PHYSICS. 29
mercury thaD in the water, while that devoted to expansion is
less. We find that the temperature of mercury rises much faster
than that of water. It takes thirty times as long to raise water
to a given temperature as it does mercury, which means that
there must be thirty times as much heat in the water as in the
mercury when the same temperature is reached by both. We see,
then, that at the same temperature different substances may
have different quantities of heat in them. The relative quanti-
ties of heat in different bodies at the same temperature is called
specific heat. Water is the standard of specific heat. At a given
temperature water contains more heat than any other known
substance, its specific heat being 1, when the specific heat of
mercury is .03. By this is meant that when equal weights of
water and mercury are at the same temperature mercury will
contain only .03 as much heat as the water.
The expansion of a solid body continues nearly uniform until
its temperature has reached the melting point; the temperature
then stops rising while the expansion increases, and continues
until the solid is melted, the liquid resulting having the same
temperature as the melting point of the solid; that is, after the
body reaches the melting point all the heat applied is used in ex-
pansion, and none is used to increase temperature.
The melting points of different substances is uot the same.
Ice melts at 32 F., mercury at -39, iron at about 3,000, plat-
inum at about 5,000. Melting ice contracts while most other
bodies expand in melting. The expansion of a. liquid continues
gradually until the boiling point is reached ; at the boiling point
the temperature stops rising, while the expansion increases and
continues until the liquid is vaporized or becomes a gas. The
temperature at which a liquid begins to boil is called its boiling-
point. Liquids change to vapor slowly at all temperatures, the
change being called evaporation, but at the boiling point the
body changes rapidly into vapor, and the change is called vapor-
ization. The temperature of the boiling point depends upon the
purity of the liquid ; the presence of some impurities raises the
boiling point, while the presence of others lowers it. Salt water,
30 PRACTICAL LESSONS IN SCIENCE.
for example, boils at a higher temperature than pure water,
while that which contains air boils at a much lower temperature
than that which contains none. In the salt water the attract-
ive force is stronger than in the fresh water, and more heat
is necessary to overcome this force, while in the water contain-
ing air the attractive force is less, and less heat is necessary to
raise it to the boiling point. The temperature of the boiling
point also depends upon the nature of the vessel in which the
water is boiled. If the adhesion between the water and the vessel
is strong it requires more heat to overcome it, and vice versa.
Thus, water will boil at a lower temperature in an iron vessel
than in a glass vessel, because the force of adhesion is stronger
between water and glass than between water and iron. The tem-
perature of the boiling point of water also depends upon the
pressure. This pressure may be due to the atmosphere, or to
some force which may be brought to bear upon it by artificial
means. Whatever may be the cause of pressure the effect is to
raise the boiling point. Whatever serves to decrease the press-
ure lowers the temperature of the boiling point. It is well
known that water boils at a lower temperature on the top of a
mountain than at its base. It does so because the pressure of
the air upon it is less. At some high mountain stations the tem-
perature of boiling water is so low that it is of little value for
cooking purposes.
When heat falls upon a body a portion is thrown back, or
reflected, from the surface. Dense bodies, as the metals, with
smooth surfaces, are the best reflectors of heat as well as light.
About midday in summer, when the sun is shining, it is warmer
on the south side of a building than in an open field, showing
that even rough surfaces will reflect heat. Heat is reflected ac-
cording to the same laws observed in the reflection of light, but
they can be illustrated more easily in connection with the study
of light.
When heat falls on the surface of a body from any source, one
portion is reflected, while another portion penetrates the body,
passing from molecule to molecule, as in the case of conduction.
LESSONS IN PHYSICS. 31
While this process is called absorption, it is practically the same
as conduction.
Con vection is the process by which one body carries heat from
its source to another body. Air receives heat from the stove,
moves to other parts of the room and gives up the heat to other
bodies. Liquids and gases are good conveyers of heat.
Experiment: Take a test tube and fill it nearly full of dirty
water, and, inclining it slightly, apply heat to the bottom and
very soon currents will be observed in the tube, and if we test
with the finger the temperature of this water, we shall find that
there is a warm current on the upper side of the tube and a
cooler current on the lower side; now remove the heat and hold
the tube in a vertical position and it will be found that the
water at the top is warmer than the w r ater at the bottom of the
tube. The water has conveyed the heat from the bottom of the
tube to the top by the process of convection.
Heat from the sun will pass through the air and window glass,
and warm the window sill or the hand much more than it warms
the glass or the air. The property by which some bodies allow
heat to pass through them without themselves being much
warmed, is called diathermancy. Such bodies are called diather-
mic bodies. They are transparent to heat as some bodies are
transparent to light.
CHAPTER IV.
PROPERTIES OF SOLIDS, LIQUIDS AND GASES.
THE resistance which a substance offers to the separation of its
parts by pulling is called tenacity. This property varies greatly
in different substances, cast steel being the most tenacious sub-
stance known. Tenacity differs from toughness; the cast steel
will bear a pulling strain but will not bear much twisting or
bending backward and forward, while copper, which is not as
tenacious as the steel, will bear twisting and bending many
times before breaking, having the property of toughness in a
higher degree. Cast steel does not stretch. Other substances, as
copper, soft steel and iron, gold, silver, etc., yield to the pull-
ing force and may be drawn into wire, thus exhibiting the prop-
erty of ductility. This property varies greatly in different sub-
stances, and many substances which are but slightly ductile when
cold possess that property in a high degree when heated, as glass
and iron. The tenacity of a substance is increased by drawing it
out into wire. Thus the cables of suspension bridges are made
of fine wire twisted together, not only because such form makes
them flexible, but because the steel, in that form, possesses more
tenacity. Platinum is the most ductile of metals. Gold and
silver also possess this property in a high degree, while lead and
tin are only slightly ductile.
Malleability is a property similar to ductility, which allows a
body to be rolled or hammered into plates or thin sheets. Gold
is the most malleable substance known. Most of the metals
possess this group of properties in some degree.
Hardness is that property of solids which enables them to
resist any action which tends to abrade or scratch them. Hard-
ness does not mean strength, indeed hard substances usually
possess the property of brittleness as well, yielding easily to a
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LESSONS IN PHYSICS. 33
sudden blow, as glass or the diamond. The relative hardness of
two bodies is ascertained by trying which will scratch the other.
This test shows the diamond to be hardest of all substances and
the mineral, talc, to possess the property of hardness in the least
degree, or the property of softness in the highest degree. Many
substances after having been raised to a high temperature may
be tempered to almost any degree of hardness, and other sub-
stances, as glass, may be greatly toughened by the process of
annealing.
In many cases when substances pass from the liquid or gase-
ous state into the solid form, their molecules arrange themselves
in regular geometrical forms called crystals, as ice, common salt,
sugar and quartz. The greater portion of the older rocks are of
a crystalline structure, and most of the metallic ores and miner-
als have distinctive crystalline forms. Metals, by jarring, often
become crystalline, losing their ductility and tenacity. From this
cause, bells long rung change their tone; cannon, after long use,
lose their strength ; and the perpetual jar of bridges, shafts of ma-
chinery, car axles, etc., gradually changes the tough, fibrous iron
into the weaker crystalline form, which explains many accidents.
Most substances expand as they are heated, and contract as
they cool. In many cases the contraction and expansion is
somewhat uniform ; but those substances which crystallize when
cooling usually expand slightly as their temperature approaches
the point of solidification. Most crystalline structures occupy
more space than the same matter in a liquid form. Water con-
tracts as its temperature falls from the boiling point to 39 F.,
and then it expands, so that the volume at 32 F. is the same
as it was at 48 F. If water continued to contract to the freez-
ing point, it would be denser and heavier than the warmer water
below, and would sink. Lakes, rivers and other bodies of water
would begin to freeze at the bottom, and would soon become
solid ice. But as the surface stratum of water approaches the
freezing point, it expands, and, becoming lighter, floats, and thus
the cooler water and ice remain at the surface. Similar phe-
nomena occur in the cooling of some other substances. In freez-
L. s. s
84 PRACTICAL LESSONS IN SCIENCE.
ing, water expands with such force as to burst the strongest ves-
sels, and break up the most tenacious rocks. The molecular force
seems irresistible. The cohesive force is also very strong, and
is frequently made use of in mechanical operations, as in setting
the tires of wheels, in riveting the plates of boilers, etc. In the
building of iron bridges and similar structures provision must
be made for the expansion and contraction due to ordinary
changes of climate, or the structures would soon go to ruin from
the constantly recurring strains due to these forces.
Glass is a poor conductor of heat; so that if hot water is
poured into a thick glass bottle the inner part becomes hot and
expands before the outer part gets warm, and the glass is liable
to break from the sudden strain. Hence, glass vessels which are
to be subjected to extremes of temperature should be thin, so
that there may be less chance for unequal expansion.
Most solid bodies may be changed in form by compressing,
stretching, bending, or twisting forces, but when the forces cease
to act, in most cases, the body tends to resume its original form.
If the body has been compressed, the repellant force corrects the
form, while if the body has been stretched, it is the attractive
force that does the work of correction. After bending and twist-
ing, the same forces attempt to restore the original form. This
property of matter by which it assumes its original form after
distortion is called elasticity. Many bodies are elastic only
within certain limits that is, a body may be strained beyond the
limit of recovery the particles may be separated so far that
cohesion can not assert its power again. Vegetable and animal
substances decay, metals become crystalline and the properties
of tenacity, elasticity and strength are gradually lost.
Liquids are elastic and have other properties in common with
solids, but the characteristic property of liquids is mobility.
The attractive and repellant forces are so nearly balanced in
liquids, that the molecules are allowed to move freely among
themselves. Liquids under the action of gravity press down-
ward, but their mobility allows them to press sidewise as well as
downwards, so that water will pass out through holes in the sides
LESSONS IN PHYSICS. 35
of a pail or barrel filled with water, as well as through holes in
the bottom. And the fact that objects float on liquids, shows
that they press upward ; hence, it seems clear that liquids press in
all directions downward, sidewise and upward. Careful experi-
ments show that in a body of water, at rest, pressure is equal in
all these directions. The rigid mountain seeks its level as eagerly
as a body of water but the mobility of the water enables it to
find its level more easily and quickly than the mountain can.
Every body of liquid when at rest has a level surface, that is,
every part of the surface is equally distant from the center of the
earth, arid this is true however irregular the body of water may
be. If a tube or pipe, even miles in length, be connected with a
pond, lake, or other body of water, it becomes a part of the
pond or lake and the water rises to the same level in the pipe as
in the pond. This accounts for many springs and artesian wells,
and on this principal many cities and towns are supplied with
water from ponds or lakes, often miles away among the hills
above them, the main pipe being divided and subdivided into
thousands of service pipes in each of which the water rises to any
level not above the level of the reservoir. In practice it will not
rise quite as high as the source, on account of friction in pipes.
The liquid water weighs about 62% pounds or 1,000 ounces per
cubic foot, or about .577 of an ounce per cubic inch. Water is
heavy and when urged down a steep slope by the force of gravity
exhibits a terrific power; even when the slope is only moderately
steep its destructive power is immense, as shown in the case of
the disaster from the breaking of the dam at Johnstown, Penn-
sylvania, and as manifested everywhere in the work of torrents
and rivers. This force is sometimes utilized in placer mining, by
bringing the water down a steep slope in pipes, using it to move
soil, gravel and rocks, much as a garden hose is sometimes used
for cleaning walks, etc. It is also used for driving various kinds
of machinery.
The fact that liquids press upwards may be shown as follows :
Suspend a solid, as a stone, by a wire from one end of a scale
beam, so that it hangs near the bottom of a pail or tub. After
36 PRACTICAL LESSONS IN SCIENCE.
noting the weight, fill the pail with water, so that the stone
is covered, and again note the weight. The water seems to have
pushed upward against the stone, with a force equal to the
difference of weight in the two cases. Experiments show that
this difference between the weight of the stone in the air, and its
weight in water, is equal to the weight of a volume of water
which is equal to the volume of the stone. Now, if we divide the
weight of this volume of water by .577, the weight of a cubic inch
of water, in ounces, we get the volume of the water in cubic
inches, and the volume of the stone as well, however irregular the
stone may be. In this way the volume of any substance heavier
than water may be found.
Now, if we divide the weight of the stone, in air, by the weight
of an equal volume of water, which is equal to the difference
between the weight of the stone, in air, and its weight in water,
we find what is called the specific gravity of the stone.
Suppose a piece of marble weighs in the air 10 ounces ; in
water it weighs 6.3 ounces; the difference of weight in air and in
water, or the weight of an equal volume of water, is 3.7 ounces;
then 10 -r 3.7 = 2.7, the specific gravity of the piece of marble.
Now, if the specific gravity of all the more valuable substances be
carefully determined, we have at hand an easy method of testing
the purity of articles supposed to be made of gold or silver, of
jewels supposed to be diamonds or other precious stones, and for
determining the identity of many doubtful substances. The pro-
cess of finding the specific gravity of solids heavier than water
is simple, but in the case of solids lighter than water, the process
is more complicated, though not difficult.
In case we wish to find the specific gravity of a body lighter
than water, it will be necessary to attach some heavier substance,
as lead, to it, in order to make it sink in the water, and then we
need to consider the volume of water displaced by the lead. This
may be illustrated by the following experiment: A body lighter
than water weighs in air 200 grains. When attached to a piece
of lead weighing 1,736 grains, they both weigh in the air 1,936
grains; in water they together weighed 1,460, the loss in weight
LESSONS IN PHYSICS. 37
of the two being 476 grains, which is the weight of a volume of
water equal to the volume of both bodies. Then weighing the
lead by itself in water, it is found to lose 152 grains, and this
subtracted from 476, the loss of both, gives 324 grains as the
weight of the water displaced by the lighter body. Then dividing
the weight of the lighter body in air (200 gr.) by the weight of
an equal bulk of water (324 gr.) gives the specific gravity of the
lighter body. From this data the volume of the lighter body
may be found as before.
To do this kind of work accurately, delicate scales and pure
water of definite temperature, are necessary ; but with a home-
made balance, using bird-shot for weights, results of great accur-
acy may be obtained . Water is the standard in finding the specific
gravity of liquids as well as solids. We may find the specific
gravity of a liquid by weighing a given volume of the liquid and
dividing that weight by the weight of an equal volume of water.
To facilitate such operations specific gravity bottles are made,
holding 1,000 grains of pure water, so that one has only to fill
the bottle with the liquid he wishes to test, and weigh it and
divide the result by 1,000, to get the specific gravity. In this
way we compare the weight of a volume of the liquid to be tested
and the weight of an equal volume of the standard that is,
we compare weights of equal volumes but the same result
may be reached by comparing the volumes of equal weights,
which is the principle of the hydrometer, lactometer, alcohol-
meter, etc. These instruments are made so as to sink to a
given depth in pure water, milk, or alcohol. If the liquid tested
is lighter than the standard the instrument sinks deeper if
heavier it does not sink as far and the difference is read from
the scale. This principle may be illustrated by using a piece of
wood about an inch square by 6 or 8 inches long, into one end
of which a nail has been driven so that it will stand erect in a
liquid. Place the stick in a jar of water and note how far it sinks
then put it in a jar of milk, kerosene oil, or any other liquid,
and note how far it sinks, and the principle of the hydrometer is
easily understood.
38 PRACTICAL LESSONS IN SCIENCE.
Again, if a heavier body, as glass or iron, of known weight in
air, be weighed in water, the loss of weight shows the volume of
an equal weight of water. If the same body be weighed in alco-
hol or milk, the loss of weight shows the volume of an equal
weight of the milk or alcohol, which may be compared with that
of water and the specific gravity found. It is said that the prin-
ciple on which the whole subject of specific gravity is based was
accidentally discovered by Archimedes, an eminent philosopher,
who lived in the third century B. C., who used it to test the purity
of a crown, supposed to have been made of gold.
Liquids not only press in all directions, but they transmit
pressure in all directions. Fill a bottle with water, fit it with a
good cork, so that the cork touches the water in the bottle;
now pressure on the cork will be distributed to every part of the
bottle. Insert a pipe into the bottom of a cask and bend it so
that the free end is about as high as the cask, then fill the cask
with water, and the water will be found as high in the pipe as
in the cask. If you pour water into the tube, the water level
rises in the cask. If we fit a piston in the pipe and press down
upon the water, that force is transmitted to the whole mass in
the cask, as the whole mass rises to a higher level. The law
may be stated as follows : Pressure exerted on any given area
of a fluid, inclosed in a vessel, is transmitted without loss to
every equal area of the interior of that vessel. This principle
has been fully established by experiment and is utilized in the
construction of the hydraulic press. Presses have been made
that are capable of lifting as much as 3,000 tons.
Gases have weight and elasticity, and they surpass liquids in
mobility, but they are distinguished for their high degree of com-
pressibility and expansibility. Take a test tube fitted with a
cork and a delivery tube of about twelve inches in length. Insert
the free end of the delivery tube in water or some colored liquid,
and apply the flame of the lamp to the test tube until some of
the air is forced out; then remove the heat, keeping the delivery
tube under the liquid till about one-fourth of it is filled with
the liquid; then we have an air thermometer, with which can
LESSONS IN PHYSICS. 39
be illustrated the compressibility and expansibility of air. Blow
gently into the end of the delivery tube and the air will be com-
pressed ; apply the hand to the test tube and the air will expand
as shown by the movement of the fluid in the delivery tube.
The elasticity of the air may also be shown when illustrating
its compressibility. Experiments with other gases show that
they possess these properties in common with air.
Gases press in all directions. Fill a common tumbler with
water and cover it with a piece of paper a little larger than the
top of the glass; then, holding the paper in place with the fingers,
invert the glass, and the pressure of the air on the paper will
hold the water in the glass. It will do the same when the glass
is turned sidewiser This experiment shows that air presses up-
ward and side wise, and surely it must press downward, must
have weight. The specific gravity of gases is usually found by
comparing them with the weight of an equal bulk of hydrogen
or air. Objects floating in the air, as leaves, feathers, birds, bal-
loons, etc., show that air is buoyant, behaving much as liquids
do, and the destructive force of winds indicates that it must
have weight and other properties like liquids and solids.
Invert a tumbler under water, as in the experiment for im-
penetrability, and raising it partly out of the water, notice that
the water is higher inside the glass than on the outside. The air
can not press on the water inside the tumbler, but the pressure of
the air on the water outside keeps the water up on the inside.
This experiment shows the downward pressure of the air and
illustrates the principle of the common pump and the barometer.
Take a glass tube a little more than thirty inches long, closed
at one end, and fill it with mercury; then, closing the open end
with the finger, invert the tube, and place the end closed by the
finger in a cup of mercury; then withdraw the finger. The press-
ure of the air on the surface of the mercury in the cup will sus-
tain a column of mercury nearly thirty inches high in the tube.
Experiments of this kind show that the pressure of the air at the
level of the sea is about 15 pounds to the square inch, sustaining
a column of mercury about 30 inches high, or a column of water
40 PRACTICAL LESSONS IN SCIENCE.
about 33 feet high, varying somewhat with the condition of the
air, as to temperature, as to the presence of water vapor, etc.
At higher elevations some of the air is below the experimenter,
so that the pressure is less and the barometer column is shorter.
In this way elevations may be measured with considerable ac-
curacy. The mercurial barometer consists of a tube filled with
mercury inverted in an open cup of mercury, fitted with a scale,
an arrangement for making corrections, etc., the whole provided
with a case of wood or metal for protection. It is used for meas-
uring elevations, but its most important use is in connection
with navigation as a weather glass. It shows the varying press-
ure of the atmosphere, from which one may gain some idea of
what weather to expect. In general, a rising column, or increas-
ing pressure, indicates fair weather, while a falling column, or
diminishing pressure, indicates foul weather. An instrument
called an aneroid barometer is much used because of its porta-
bilitya good one need not be much larger than a watch.
Atmospheric pressure is indicated by its effect on an elastic box
containing slightly rarefied air. The aneroid is not as reliable
as the mercurial, and should be adjusted frequently by a stand-
ard mercurial, if one expects to get reliable indications. The
upward pressure or buoyancy of the air interferes somewhat
with the accuracy of weighing operations.
The molecules of gases are so far apart that one gas does not
hinder the expansibility of another. If a number of gases are
mixed in a limited space, each will be diffused throughout the
whole space, gases acting as vacuums to each other. In this way
poisonous gases, the products of respiration, combustion and
decay, and of various manufacturing operations, instead of
accumulating in one place are continually dissolved away and
dispersed in the great atmospheric ocean.
The siphon is an instrument by which liquids may be trans-
ferred from one vessel to another by atmospheric pressure. It
consists of a bent tube, one arm of which is longer than the
other. Take a piece of glass tubing about twelve inches long
and bend it into a U shape at five inches from one end. Fill the
LESSONS IN PHYSICS. 41
tube with water, then closing the end of the longer arm with the
finger, place the end of the short arm in a glass of water and
open the end of the long arm, when the water will flow from the
glass through the tube. If the water be allowed to run into
another glass it will flow until the water is at the same level in
the two glasses. If we take a glass in each hand, by changing
the level slightly the water may be made to run either way.
Almost any substance may be used for a tube. The first siphon
the writer ever saw was made of dandelion stems. In studying
the barometer we learned that the pressure of the air would sus-
tain a column of water that was over thirty feet high, in case the
air pressure was removed from the column. In the case of the
barometer the air pressure was removed by closing the end of
the tube. In the siphon the air pressure is removed by bending
the tube, so that both ends are under water. When both arms
are of the same length, that is when the water in each glass
is at the same level, the air pressure sustains equal columns of
water, and there is no motion ; but if we change the level of the
two glasses of water the pressure on the water in the lower glass
has a longer column of water to sustain than is sustained in the
upper glass, and water is pushed over into the lower glass to
establish an equilibrium. The long arm and short arm means
the perpendicular distance from the arch of the siphon to the
surface of the water on either side.
The common pump depends upon atmospheric pressure for its
usefulness. It consists of two barrels separated by a valve open-
ing upward. In the upper barrel there is a piston with a valve
opening upward. When the piston is raised the pressure of the
air is removed from the water in the lower barrel, and the press-
ure of the air on the water outside forces it up the barrel
through the lower valve. When the piston is pushed down the
lower valve closes and the valve in the piston opens so that the
water rises above the upper valve; as the piston is raised again
it lifts the water above the upper valve and allows water to be
forced through the lower, and so on. In the ordinary force pump
the piston is solid, and a valve, opening outward in the side of the
42 PRACTICAL LESSONS IN SCIENCE.
upper barrel, near its lower end, allows the downward stroke of
the piston to force the water into an air chamber, compressing
the air, and the elasticity of the air forces the water forward in a
steady stream.
The volume of a given weight of air or other gas varies in-
versely as the pressure upon it ; that is, the more pressure the
less the volume and vice versa. We have already learned that
air can be compressed, but careful experiments show that if we
double the pressure on a given body of air or other gas its vol-
ume will be reduced one-half, and if we lessen the pressure by
one-half the volume will be doubled. This is called Boyle's or
Mariotte's law, from the names of its discoverers. If the volume
of gas is decreased by pressure the density is increased, so that
the density of air or other gases varies directly as the pressure.
The density of the air is greatest at the sea level, while on high
mountains the density is much less.
We have already learned that gases expand and contract as
they are heated or cooled, but careful experiments show that this
expansion and contraction is somewhat uniform. If we have 491
cubic inches of air at the temperature of 32 F. it will have a
volume of 492 cubic inches when heated to a temperature of 33
F.; that is, it expands - 4 -i- T of the volume at 32 F. for each addi-
tional degree of heat. If the law holds good for lower tempera-
tures we should find absolute zero at about 495 F. below the
present Fahrenheit zero.
CHAPTER V.
FORCES AND MOTION.
THE forces which cause all the variety of motions in nature are
but different forms of attraction and repulsion. A constant force
is one that acts continually, as the force of gravity, while an
impulsive force is one that acts for a time, then ceases, as the
blow of a hammer, or the stroke of a bat that drives the ball.
A unit of time is a measured portion of time, as a second, a
minute, or an hour, and velocity is the distance passed over by
a body in a unit of time, as the train moves 40 miles an hour.
The velocity of a body may be uniform, increasing, decreasing,
or variable.
Space is the whole distance passed over by a body while in
motion. It equals velocity multiplied by the units of time, as
the velocity of a train is 40 miles an hour, units of time are 10
hours, then space equals 400 miles, the distance passed over by
the train. Motion will be uniform when the velocity of the body
is the same in successive units of time, and will be accelerated
when the velocity increases in successive units of time, and re-
tarded when the velocity decreases. Accelerated and retarded
motions may be uniform or variable.
The first law of motion is that a body at rest will remain at
rest, or if in motion, will continue in motion, unless acted upon
by some force to change its condition. This is practically the
law of inertia. The second law is that a given force will produce
the same amount of motion whether it acts upon a body at rest
or upon a body in motion. This law is illustrated by the motion
of a boat in crossing a river; the steam drives the boat across
the river while the current carries it down the river, and under
the action of both forces the boat moves across the stream in a
diagonal course.
(48)
44
PRACTICAL LESSONS IN SCIENCE.
The third law is that action and reaction are equal and in op-
posite directions. If the hand strikes the wall, the wall reacts on
the hand and the hand is bruised ; the bullet that shatters the
bone is itself bruised and flattened. The fact of reaction seems
evident, but careful experiments are necessary to show that
action and reaction are equal.
A constant force acting alone causes uniformly accelerated
motion, in a straight line, as the motion of a body falling by the
force of gravity. Experiments show that a falling body passes
over a space of about 16^ feet in the first second, over three
such spaces in the next second, over five the third, and so on.
The distance a body falls in a given number of seconds, equals
the square of the number of seconds multiplied by 16 T L feet.
The distance a body will fall in four seconds may be shown as
follows: 4 X 4 = 16 X 16^ = 257.25 feet. In the case of falling
bodies the motion is due to the action of the one force of gravity
retarded somewhat by the resistance of the air, but most of the
motions met with in nature are the result of the combined action
of several forces.
If we represent the intensity and direction of forces by lines, we
can more easily solve some of the problems of motion. Suppose
a body at A (see Fig. 1) is acted upon
by a force, whose intensity and direc-
tion is represented by the line AB,
sufficient to carry the body to B. At
B the body is acted upon by a force,
represented by the line BC, sufficient
to carry the body to C. The forces
AB and BC, acting separately, have
carried the body to C over the lines
AB and BC. But if the two forces
AB and AD, which equals BC, should act together on the body at
A, they would carry it to C, as before, but along the line AC, not
along the lines AB and BC, as in the former case. This illustrates
the truth of the second law of motion, and shows that one force
whose intensity and direction is represented by the line AC would
C
Fio.l
LESSONS IN PHYSICS. 45
carry the body to the same point as the two forces AB and BC,
acting separately or together. The separate forces, represented
by the lines AB and BC or AD, are called components and the
single force, represented by the line AC, their equivalent, is called
the resultant. The process of finding the resultant of two or
more forces is called the composition of forces. A resultant may
be made up of, and equivalent to, more than two forces. Suppose
that when the body is at C it is acted on by a force represented
by CF sufficient to carry the body to F. The forces AB, BC and
EF, acting successively, have carried the body to F. In the
former case we found that the force represented by AC equaled
the forces represented by the lines AB and BC ; now if we com-
plete the parallelogram on AC and CF we find that a force
represented by AF will carry the body to the same point as the
forces represented by AC and CF, acting separately, and conse-
quently to the same point as all three forces represented by AB,
BC and CF would carry it if acting separately, or as AB, AD,
which equals BC, and AE, which equals CF, would carry it if
acting together. In this way a resultant may be found for any
number of component forces.
If two or more parallel forces act on a body, at the same time,
and in the same direction, their resultant would be a force equal
to the sum of the component forces, and the motion would be
in the same direction. A span of horses drawing a wagon illus-
trates this principle. If two parallel forces act on a body at
different points, and in opposite directions, they will produce
rotary motion. No single force can replace two such forces.
If we have a force represented by AF ( Fig. 1 ) , we may find other
forces that would produce the same effect. AC and CF together
would equal AF. AB and BC would equal AC, and AB and BC
and CF together equaling AF, reversing the process of composi-
tion offerees. This process of finding two or more forces that
are equivalent to one force, is called the resolution of forces.
The study of motions in straight lines is interesting and im-
portant, but most of the motions in nature are along curved
lines ; so that the study of motion in curved lines will be as prac-
46 PRACTICAL LESSONS IN SCIENCE.
tical, and perhaps more interesting than the other. Every ripple
and wave, every swaying branch and rustling leaf, each nodding
flower, each bird and beast moves in ever varying curves.
Curved motion is produced by the action of at least two forces,
one of which must be a constant force. The motion of a ball, when
fastened to a string and whirled around the hand, is an example
of curved motion. The string represents a constant force, and
the muscles of the arm an impulsive force. An impulsive force,
acting alone, or any number of impulsive forces acting together,
tend to cause motion in a straight line, but one or more impul-
sive forces acting with a constant force, gives motion in a curved
line. The forces which cause circular motion are called central
forces ; one acts toward the center, from which the curve is de-
scribed, while the other acts in the direction of a tangent to the
curve. The one is called the centripetal force, and the other the
centrifugal force. The grandest examples of the actions of these
forces are found in the motions of the heavenly bodies, gravita-
tion acting as the centripetal force.
The centrifugal force varies as the quantity of matter in the
moving body ; that is, the more matter there is in the body the
greater will be the reaction against the centripetal force. It also
varies as the square of the velocity of the body in motion. These
laws are illustrated in a general way by the use of a sling ; the
heavier the stone the greater the reaction or pull, and the greater
the velocity the greater the pull. When a wagon moves slowly
along the road no mud is thrown from the wheels, but as the mo-
tion is increased the centrifugal force overcomes the force of ad-
hesion between the mud and the wheel, and the mud is thrown
off. This principle is made use of in the centrifugal machines
employed in laundries for drying clothes, in sugar refineries for
removing molasses from the sugar, and in apiaries for extract-
ing honey from the comb. It accounts for the action of the gov-
ernor on a steam engine; for bursting grindstones and balance
wheels; and the increased size of the earth at the equator was
undoubtedly caused by centrifugal force when the earth was cool-
ing from the liquid state. The effect of centrifugal forces may be
LESSONS IN PHYSICS. 47
illustrated by swinging a pail partly filled with water over the
head or in any direction; the centrifugal force so overcomes the
force of gravity that not a drop of water falls. Race tracks and
railroad tracks are raised on the outside of a curve to prevent
overturning from the centrifugal force exerted when -passing the
ciirve.
The ball from the bat, the arrow from the bow, the bullet from
the gun, are projectiles, and all move in curved lines. An impul-
sive force in each case gives the body motion, which would be in a
straight line but for the action of the constant force of gravity.
The range of a projectile is the horizontal distance through which
it moves. This distance depends upon the energy of the impulsive
force, the angle at which the body starts and on the resistance of
the air. Theoretically an angle of 45 degrees would give the
greatest range ; but in practice an angle of about 30 degrees is
found to be best for a bullet, and about 35 degrees for an arrow.
Motions in liquids may be waves caused by winds; may be
tidal waves caused by the attraction of the sun and moon; may
be currents caused by gravity, by winds or unequal heating; or
they may be vibrations arising from an endless variety of causes.
In either case the motions vary greatly, and are useful and in-
teresting in various ways. Examples of these motions and their
effects are so common and well known that they need only be
mentioned here. But wa,ter is often conveyed from reservoirs
through pipes for use in various ways, and it is interesting to
notice that the results in practice differ so widely from theoret-
ical deductions that most calculations are made from arbitrary
rules. If we examine a. jet of water flowing from an orifice in a
vessel we shall see that it grows rapidly smaller, so that at a
little distance its size is only about two-thirds as great as at the
orifice. Beyond this point the contraction of the jet is gradual . The
rapid contraction near the orifice is due to cross currents, caused
by the water flowing toward the orifice from different directions.
The effect of these cross currents can be diminished somewhat by
the use of short tubes; but when all is done scarcely more than
80 per cent, of theoretical flow can be secured. The flow of water
48 PRACTICAL LESSONS IN SCIENCE.
is greatly retarded by friction in the pipes, so that much larger
pipes should be used than might at first seem necessary.
Motions in the air and other gases are very common,
in fact the air is seldom or never at rest. The differences in
temperature between day and night, between the sea and
land, between forest and plain, all tend to cause inequalities
of pressure which result in more or less extensive motions,
which vary from gentle, almost imperceptible, breezes of two or
three miles per hour, to the fierce and destructive tornado in
which the velocity of the air is as great as 50, 75, or even 100
miles per hour. The difference of temperature between the equa-
torial and polar regions is perhaps the main cause of the general
system of winds of the globe, the rotation of the earth influ-
encing the direction of the air movement. If a fire is built, the
air near it is heated, and expanding becomes less dense than the
surrounding air. The heavier air crowding in from all directions
forces the lighter air upward, giving rise to currents of air from
all directions toward the fire, all of which unite in an upward
current from the fire. The great heat of the equatorial regions
causes the air of those regions to be less dense than that of regions
north or south. This gives rise to a movement of air from both
directions toward the equatorial regions, forming there an up-
ward current, which, spreading out, flows back toward the polar
regions as counter-currents, so that the air of the earth is in con-
stant circulation in a general way, besides the thousands of minor
movements due to local causes. If the earth did not rotate we
might expect these currents to move directly north and south ;
but the spherical form and rotary motion of the earth change the
directions somewhat. On account of the form and rotation of
the earth, those places near the equator move more rapidly than
those either north or south of the equator. Places on the equa-
tor have a motion of 1,042 miles per hour, while those at 20 N.
or S. have a motion of only 975 miles per hour. Air, moving
toward the equator, having the slower motion of places north
and south, falls behind places at the equator having the same
longitude as those from which it started, so that these currents
LESSONS IN PHYSICS. 49
instead of being north and south winds, are northeast winds
north of the equator, and southeast winds south of the equator.
Those currents going from the equator, having the more rapid
motion of places near the equator, are constantly getting in ad-
vance of places having the same longitude as those from which
they started, so that north of the equator they are southwest
winds instead of south winds, and south of the equator they are
northwest winds instead of north winds. Numerous observations
show that the winds between 32 N. and 25 S. have the direc-
tions given above.
As the land is a better absorber of heat than the water, in the
torrid zones and during summer in the temperate zones, it be-
comes hotter than the water during the day, and the air over the
land becomes hotter and lighter than that over the water, which
gives rise to a wind from the sea toward the land, called the sea
breeze. The land is also a better radiator than the water, so
that during the night the land becomes cooler than the water,
and the air over the land becomes heavier than that over the
water, which gives rise to a wind from the land toward the sea,
called the land breeze. The land and the sea breeze illustrate
how variations in the surface of the earth serve to promote mo-
tions in the air.
L. S. 4
CHAPTER VI.
VIBRATIONS.
VIBRATIONS are alternate movements backward and forward.
If with the finger we depress one scale-pan of a balance, it will
continue to move alternately up and down over the same path
for a long time after the finger is removed, or if we pull the scale-
pan to one side and then release it, it will swing backward and
forward for a time; or suppose a ball, hung by a fine wire, be
twirled by the finger so as to'twist the wire; let go of it, and,
speedily untwisting the wire, it will go on for a time twisting it
up the other way; these alternate motions are vibrations.
The pendulum is a body hanging from a fixed point upon
which it can swing freely. The fixed point is called the point of
suspension, and the point in the pendulum which vibrates as if
only under the influence of its own gravitation and inertia, is
called the center of oscillation, and the length of the pendulum
is the distance between the point of suspension and the center of
oscillation. The center of oscillation is generally a little below
the center of gravity of the pendulum ball.
The pendulum vibrates under the in-
fluence of gravitation and inertia. Sup-
pose a ball at M (see Fig. 2) to repre-
sent a pendulum hung from the fixed
point, C, by a cord MC. Now, if this
ball be lifted to the point A and for a
moment held there, the force of gravity
will act upon it in a vertical direction.
FIG. 2 \^ We will represent this force by the line
AB, and resolve it into two compo-
nents, shown by the lines AD and AE. The force, AD, acts length-
wise of the string without effect to move the ball ; the other force,
(50)
LESSONS IN PHYSICS. 51
AE, acting at right angles to AD, will pull the ball toward the
point M. If the ball is allowed to fall to M, its inertia will carry
it beyond that point; but when it passes the point M, gravita-
tion begins to pull backward, with just the same power it exerted
to pull the ball from A to M. The ball will rise from M to N, a
distance just as far beyond M as it has fallen to reach M. It will
there stop and gravitation will bring it back to M, while its
inertia will carry it up to A again. The resistance of the air and
friction of the cord will finally make it stop at M.
The time of one vibration at any given place varies as the
square root of the length of the pendulum, and varies inversely
as the square root of the force of gravity. In general, the am-
plitude or extent of vibration does not affect the time. The truth
of the first law may be shown by experiments with pendulums of
different lengths, when it will be found that a pendulum one foot
long vibrates twice, while a pendulum four feet long vibrates
once. The pendulum is used to measure time. If the wire sus-
pending the pendulum ball is of steel or any single substance, it
varies in length with the temperature during the year, so that the
pendulum will vibrate more rapidly in some seasons of the year
than in others; usually the movement will be more rapid in win-
ter and slower in summer. Compensation pendulums are some-
times made by using different metals, so that the contraction
of one balances the expansion of the other.
The pendulum? is also used to determine the figure of the earth.
The rate of the vibrations of the pendulum depends upon the force
of gravity. If at any place the pendulum vibrates more rapidly,
other conditions being the same, it shows an increase of the
force of gravity. If it vibrates more slowly, then the force of
gravitation must be less, indicating that in the one case the
pendulum was nearer the center of gravity of the earth than in
the other, which would indicate variations from a true spherical
form. The vibrations of the pendulum are more rapid toward
the poles, and vary somewhat in other directions.
Let a stone be thrown into the water of a lake or pond and
the tranquil surface will be carved into a series of circular ridges
52 PRACTICAL LESSONS IN SCIENCE.
and furrows called waves, which extend onward and onward,
finally breaking against the shore. The ridges and furrows
move outward from the point of disturbance, but the water only
moves upward and downward; that is, it vibrates. Another
stone dropped into the water a little distance from the first sets
up another series of waves. These waves interfere with the waves
caused by the first stone, breaking up the symmetry of each, cut-
ting the surface of the water into curious shaped elevations and
depressions having no semblance to uniformity. Sometimes the
elevation of one group of waves is piled upon the elevation of
the other group, making waves nearly twice as high as a single
wave of either group ; and sometimes the furrows of one group
correspond with the furrows of the other, making a much deeper
furrow than a single wave of either group; and again, a ridge of
one set will correspond with the furrow of another set, and a
level surface will result.
Waves may be caused in the air as in the water, but they differ
in form. The waves of water are circular, while the air waves are
like spherical shells, spreading out in every direction. The air
particles simply move backward and forward, as the water par-
ticles move upward and downward. Sometimes the vibrations of
the air are intense enough, so that, acting on the organs of hear-
ing, they give rise to sensation of sound. Single intense air
waves cause a sound called a report ; a series of such sounds in
irregular succession makes a noise, and when the waves succeed
each other so rapidly and regularly that there seems to be no in-
terval between them, the result is a musical sound or tone. In
general, less than from thirty -two to forty vibrations in a second
give rise to reports or noises, but vibrations, varying in number
from 40 to 40,000 per second, can ordinarily be appreciated as
musical tones.
The tones of the voice and of many musical instruments de-
pend upon the vibrations of chords that are subject to more or
less tension. Lay a brick or a piece of wood about the size of a
brick upon each end of a table. Tie a string to one leg of the
table, pass it over the bricks, and tie it to another brick as a
LESSONS IN PHYSICS. 53
weight; strike the cord near the center and notice the vibra-
tions. Add another brick as a weight and strike it again, and
compare the vibrations in the two cases. Stretch a heavier cord
and compare the vibrations of the two cords when stretched
with the same weight. Stretch a light wire and experiment with
it, and compare the vibrations of the wire with vibrations of
the cords. Shorten the strings, by putting a brick in the middle,
and then test the vibrations again; then shift the brick either
way, so that one end of the cord is longer than the other, and
again test the vibrations. Vary the weights, causing tension in
different ways, and notice and compare the vibrations in each
case. The result of these experiments will convince one that the
shorter the string, the cord or wire, the more rapid the vibra-
tions; and second, that the greater the weight or tension the
more rapid the vibrations; and that the heavier the cord or wire
the slower the vibrations. Experiments with more delicate appa-
ratus show that in the second case the vibrations vary as the
square root of the weight producing tension ; and in the third
case that they vary inversely as the square root of the weight of
the cord.
Musical sounds differ in pitch; the pitch of sounds is that
which distinguishes them as being high or low. It depends en-
tirely upon the rapidity of vibrations; the more rapid the vibra-
tions the higher the sound produced. Two sounds made by the
same number of vibrations per second, however they may differ
in other respects, will have the same pitch. With pitch as a guide,
test the laws of vibrating cords just given. When the num-
ber of vibrations which produce one sound is twice as great
as that which produces another, we do not say that the sound is
twice as high, but rather that it is an octave higher. The term
octave is used to designate the tone which is made by twice the
number of vibrations needed to produce the lower tone, called the
fundamental. The difference in pitch between a fundamental note
and its octave is very great. To fill up this interval sounds have
been chosen which blend and harmonize most perfectly with the
fundamental or with each other. These placed between the fun-
54 PRACTICAL LESSONS IN SCIENCE.
damental and its octave form a series of eight tones called the
natural or diatonic scale. Sounds resulting from the same num-
ber of vibrations are said to be in unison. When two notes differ
in pitch, but their combination is agreeable to the ear, they are
said to be consonant; when disagreeable, dissonant. This scale
repeated eleven times includes all sounds within the range of the
human ear. The capacity of the ear to appreciate vibrations
varies greatly. Some cannot appreciate one-half as many as
others can. Only about seven octaves are used in music. By the
English standard of pitch the note A of the treble clef is made
up of 400 vibrations in a second ; by the French standard the
rate for the same note is 435 vibrations per second. The tones
in the scale have definite relations to each other. If we represent
the number of vibrations for a fundamental note by one, then
the several notes of the scale will be made by the following
ratios: C 1, D 9-8, E 5-4, F 4-3, G 3-2, A 5-3, B 15-8, C 2. Now,
from this scale of fractions, and the fact that A is made up of
440 vibrations, the number for the others may be found; as.
for example, the number of vibrations to give the fundamental
C would be 3-5 of 440, equal to 264.
The intensity of sound is that which distinguishes it as being
loud or soft. It depends entirely upon the amplitude or width of
the vibrations which produce it. The greater the amplitude the
louder the sound will be.
Whenever a piano wire, or the cord of any stringed instrument
is struck, it vibrates as a whole and in segments at the same
time. The vibrations as a whole yield the fundamental note of
the cord; the vibrations in segments yield higher tones called
overtones or sometimes harmonics.
By quality we refer to that peculiarity of sound by which we
may distinguish notes of the same pitch and intensity made on
different instruments. The pitch or intensity of tones made on a
violin and on a piano may not differ and yet how easy to tell the
sounds apart. We recognize the voices of friends, not by their
pitch or intensity but by their quality. The various stringed
instruments, as the piano, harp, violin, depend for their value
LESSONS IN PHYSICS. 55
upon the vibrations of cords, in accordance with the laws already
discussed. Vibrations of the air, giving musical sounds, may arise
from the vibrations of strips of metal, wood, or other substances,
and on this principle the construction of organs, horns, trumpets,
and other reed and wind instruments depends. In an organ
sounds are made by vibrating columns of air in pipes, sometimes
aided by the vibrations of a slender and elastic tongue called a
reed. The pitch of sound in pipes depends upon the length of
the pipes, or in case of reed pipes on the length and weight of the
reed. The air in the pipes of an organ vibrates as a whole and
in segments as well, so that there are overtones or harmonics in
pipe instruments as well as in stringed instruments. In the case
of the horn the sounds are made by vibrating columns of air, the
lips aiding the vibrations, as the reed aids the vibrations in the
organ pipes.
The human voice is regarded by the best authorities as being
analogous to a reed-pipe, the vocal chords forming the reed,
and the cavity of the mouth the pipe; like the reed, it is rich in
harmonics, as many as sixteen having been detected in some
voices. But their number and relative intensities differ much in
different individuals, or even in the same person at different
times; and it is on this variety that the peculiarities depend by
which any one voice may be unmistakably distinguished from
every other. Voices in which overtones abound are sharp, and
even rough; those in which they are few or faint, are soft and
sweet.
Sound waves move through all elastic media, as wood, iron,
the earth, water, air, etc. The velocity of sound waves varies
inversely as the square root of the density of the substance, and
directly as the square root of its elasticity. These laws are
doubtless true for gases whose structure is uniform throughout,
but are not true for the air. Through the air at ordinary tem-
perature sound waves move with a velocity of about 1,118 ft.
per second, varying somewhat with temperature and with the
amounts of water vapor in the air, etc. One great danger to
commerce is the difficulty of locating rocks, shoals, and other
56 PRACTICAL LESSONS IN SCIENCE.
dangerous places during fogs and thick weather, which make the
sense of sight of no value. All the maritime nations have been
experimenting for years on various kinds of sound signals. These
experiments have resulted in some interesting facts about the air
and some of its peculiarities in transmitting sound waves. Prof.
Tyndall found the capacity of the air to transmit sound waves
vary so much that no laws could be discovered. He experimented
with guns, fog horns, steam whistles, and a steam syren. He
found that frequently, under a clear sky, when the air seemed
especially transparent to the sense of sight, it was especially
opaque to sound waves. These acoustic clouds so filled the
transparent air, that guns, fog horns, whistles and syrens which
had been heard from 10 to 13 miles, could not be heard at a dis-
tance of three miles. The interrupted sound waves seemed to be
wasted by repeated reflections from streams of air differently
heated or saturated in different degrees with water vapor.
Neither rain, hail, snow, or fog seem to have any power to ob-
struct sound waves. In fact, air that is filled with water vapor,
in some form, is in a highly favorable state for the transmission
of soundwaves. Sometimes the guns could be heard moreclearly,
sometiines the whistles, and sometimes the syrens; sometimes
low pitched, long-waved sounds could be heard more distinctly, and
again the high tones penetrated farthest. Prof. Tyndall thought
the steam syren the best instrument, considering it reliable for
two miles, and generally for three and three and one-half miles.
In general, when it could not be heard at least four miles, the
sky would be optically clear so that the sound signal would not
be as necessary as in thick weather. Other things being equal,
sound waves travel better with the wind than against it. The
velocity of sound in water is given by some authorities as about
4,700 ft. per second; in caoutchouc, as 197 ft. per second; in
lead, as 4,030 ft.; in copper, as 11,666 ft.; in oak timber, along
the grain or fiber, 12,622 ft.; in iron, as 16,800 ft. per second. *In
wet sand, as 825 ft. ; and in solid granite, as 1,664 ft. in a second.
Sound waves are often reflected from plane or curved surfaces,
causing echoes. At Woodstock, England, an echo returns 14
LESSONS IN PHYSICS. 57
syllables, and many other localities furnish interesting echoes.
Echoes are sometimes interesting; but sometimes they are
annoying, and the usefulness of many large halls or assembly
rooms is much diminished by conflicting echoes. Theceilings and
walls of such rooms should be so broken up by arches, balconies,
beveled angles, etc., that no large areas of plane surface appear;
drapery, furniture, etc., tend to break up and disperse the sound
waves so as to lessen the effect of reflections. People do not
intentionally build whispering galleries, but there are many
rooms in which at certain points the slightest noise is conveyed
with great intensity to certain other points, while it may not be
heard at all at intermediate points. The Mormon Tabernacle,
and the dome of St. Paul's Cathedral, London, are illustrations.
Sounds or vibrations are not only reflected, but are also re-
fracted. The laws of reflection and refraction of vibrations
causing sound are similar to those of vibrations causing light,
and may be considered in connection with the study of light.
CHAPTER VII.
FORCE AND ENERGY.
FORCE is that which causes motion or changes motion. While
this definition conveys no idea of what force is, it does give us
some idea of what force does. Force may be measured by an in-
strument called a dynamometer, of which the common draw
scale is an illustration. When a body is moved by the action of
force upon it, the force is said to do work on the body. For ex-
ample, steam exerts pressure on the piston of a cylinder of an
engine, causing it to move. The expansive force of the steam
does work on the piston in overcoming resistance and putting it
in motion. If there had been no motion of the piston no work
would have been done. In merely supporting a body no work is
done, since no motion is produced. The force of gravity does no
work on the stone resting on the ground, yet it causes a pressure
between the stone and the earth. Force and space are essential
elements of work. A force acting through a space of one foot in
raising a weight does a certain amount of work. The same force
acting through a space of two feet would do twice as much work.
That is, in general, force multiplied by the space through which
it acts equals the work done. Formula : Force, F. X Space, S.
work, W.
Every moving body can impart motion; can do work on any
other body, and is said to possess energy. The energy of a body
is its capacity to do work. For example, the moving bat in the
hands of a ball player imparts motion to the ball ; it does work
on the ball. The energy which a body, as the bat, possesses,
in consequence of its motion, is called kinetic energy. A stone
lying on the ground is devoid of energy. Do work upon the
stone by lifting it up to a shelf, or other support, and it seems as
devoid of energy as when lying on the earth. Attach one end of
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LESSONS IN PHYSICS. 59
a cord to the stone, pass the cord over a pulley and wind a por-
tion of it around a shaft connected with a sewing machine, coffee
mill, or other convenient machine. Suddenly withdraw the shelf
from beneath the stone, the stone falling communicates motion
to the machinery and you may sew, grind coffee, etc., with the
energy given to the machinery by the stone. The work done on
the stone in raising it was not lost. The stone gives it back
while descending to the earth. There is a very important differ-
ence between the stone lying on the ground and the stone lying
on the shelf. The former is powerless to do work, the latter can
do work. Both are alike motionless, and you can see no differ-
ence excepting the advantage which the latter has over the
former in having a position such that it can move. The work
done in raising it to its place on the shelf gave it this ad-
vantage. A body thus may possess energy due merely to the
advantage of its position derived always from work bestowed
upon it. Energy due to advantage of position is called potential
energy. We see, therefore, that energy may exist in either of two
widely different states. It may exist as actual motion in the
case of the bat, or it may exist in a stored-up condition, as in
the case of the stone lying on the shelf. The energy which the
stone on the shelf possesses is due to the fact that its position is
such that it can move, and that there is stress between it and the
earth which will cause it to move. The force of gravity is em-
ployed to do work as when mills are driven by falling water; but
the water must first be raised from the ocean bed to the hill side
by the work of the sun's heat. The elastic force of springs is
employed as a motive power; but this power is due to the ad-
vantage of position, which the molecules of the springs have
acquired by work done upon them. We are as much accustomed
to storing energy for future use as provisions for winter's con-
sumption. We store it when we wind up the spring or weight of
a clock to be doled out gradually in the movements of the ma-
chinery. We store it when we bend the bow, raise the hammer or
any body above the earth's surface.
The energy of a body is dependent wholly upon the work which
60 PRACTICAL LESSONS IN SCIENCE.
has been done upon it, so that both work and energy may be
measured by the same unit. The unit usually employed is the
work done, or energy imparted, in raising one pound to a ver-
tical height of one foot; it is called a foot-pound. With this unit
we may measure any species of work, and thereby compare work
of any kind with that of any other kind. For instance, let us
compare the work done by a man in sawing through a stick of
wood, whose saw must move 100 ft. against an average re-
sistance of 20 Ibs., with that done by a bullet in penetrating
a plank to a depth of two inches (1-6 ft.) against an average
resistance of 500 Ibs. Moving a saw 100 ft. against a resist-
ance of 20 Ibs. is equivalent to raising 20 Ibs. 100 ft., or doing
2,000 ft.-lbs. of work. A bullet moving 1-6 of a foot against
500 Ibs. resistance does the same amount of work as is required
to raise 500 Ibs. 1-6 of a foot high; that is, about 83 1-3 ft.-lbs.
of work ; hence the sawyer does about 24 times as much work as
is done by the bullet. The work done, the energy exerted by a
moving body, is equal to the weight of the body moved, multi-
plied by the number of feet it is raised. With a given velocity a
body will rise to a definite elevation, which is determined by
dividing the square of the velocity by twice the force of gravity ;
formula : -^-, the force of gravity being about 32 1-6. Hence, the
energy of a moving body, the work it may do, can be estimated,
if we know its weight and its velocity, by the following formula :
w * ya . Illustration: The energy of a cannon ball weighing
40 Ibs., and moving with the velocity of 800 ft. per second,
would be about 398,134 foot-pounds. The kinetic energy of two
bodies having the same velocity will vary as the weight of the
bodies; that is, if one body weighs 50 Ibs. and the other 100
Ibs., the energy in the one case will be twice as great as in
the other. The kinetic energy of two bodies having the same
weight varies as the square of the velocity; that is, doubling
the velocity multiplies the energy by 4, or tripling the velocity
multiplies the energy by 9. A railroad train, having a velocity
of 20 miles an hour, will, if the steam is shut off, run four
times as far as it would if its velocity were only 10 miles an
LESSONS IN PHYSICS. 61
hour. Thus, light substances, as the air, exhibit great energy
when their velocity is great. As a body is raised higher and
higher the work accumulates in the form of potential energy.
The accumulated work, or the potential energy, does not always
equal the work performed. Some of the work done is used in
overcoming friction, and is wasted. The work done by the saw-
yer and the bullet imparted no energy to the bodies upon which
they did work; it was entirely consumed in overcoming resist-
ance, disappearing as energy. Of the vast amount of work done
in propelling steam cars or vessels none accumulates, all is
wasted, and cannot be recovered or made available for doing
work. The available energy that a body possesses is the work
done upon the body, less the lost or wasted work. We may
calculate in foot-pounds the work performed on a body, and from
this deduct the number of foot-pounds wasted, and the remain-
der is the number of foot-pounds of energy that is imparted to
the body.
In estimating the total amount of work done, the time con-
sumed is not considered. The work done by a hod-carrier in
carrying 1,000 bricks -to the top of a building is the same
whether he does it in one day or a week. But in estimating the
power of any agent to do work, or the rate at which it is capable
of doing work, time is an important element. The unit in which
power or rate of doing work is estimated, is called a horse
power. A horse power represents the power to perform 33,000
foot-pounds of work in a minute.
Energy, like matter, is indestructible. It may be transmitted,
it may be changed into other forms, but not destroyed. The
quantity of energy cannot be increased or diminished. Whenever
a body in motion meets an obstacle energy is transmitted to it as
in the case of the bat and the ball.
Let a ball be shot vertically upwards. On starting, its energy
is kinetic, and it rises more and more slowly until it stops, and
then falls to the ground. At the moment it stops at the top of
its path its energy is potential. During its flight upwards kinetic
energy has been changing into potential energy, and again, dur-
62 PRACTICAL LESSONS IN SCIENCE.
ing its fall, potential energy is changed into kinetic energy. There
is no loss, but simply a change in the character of the energy.
The same thing is true in a swinging pendulum. The mechanical
energy of the hammer is not lost when the hammer stops. It
has been changed into molecular energy or heat. Whenever
energy disappears it has been changed into another form.
One of the most interesting discoveries of modern science is
that all forms of energy are so related to one another that
energy of any kind may be changed into energy of any other
kind. That a definite quantity of mechanical work when trans-
formed without waste will yield a definite quantity of heat ; and
that this heat, if there were no waste, could perform the original
mechanical work. That when one form of energy disappears an
exact equivalent of another form takes its place, so that the sum
total of energy is unchanged. This principle is known as the law
of conservation of energy.
CHAPTER VII Continued.
MACHINES.
A MACHINE is any contrivance which has for its object the
transferring or transforming of energy. In an electric-light plant
the energy of the steam is communicated to the moving parts of
the engine, to be transferred by belts to the armatures of the
dynamo, where it is transformed into electric energy. In me-
chanics it is customary to restrict the term " machine" to such
devices as merely transfer energy. This is clearly the case with
those known as simple machines. They are the lever, the wheel
and axle, the pully, inclined plane, wedge and screw; all other
machines, however complicated, are but combinations of two or
more of these simple machines.
No force is gained by the use of machines; indeed, much of the
force applied to the machine is wasted in overcoming friction
and other resistances, so that force is lost by the use of ma-
chines. But machines enable us to apply force advantageously;
enables us to employ the force of wind, water, steam or the
strength of animals. By the use of machines a small force mov-
ing rapidly may move a great body slowly, or a great force
moving slowly may put a small body in rapid motion. The force
applied to do work is called power, P. ; the resistance to be over-
come is called weight, W. Work consists of overcoming resist-
ance, 'and equals the product of the weight by the vertical height
to which it has been raised. Two forces, acting in opposite direc-
tions upon the same body, will be in equilibrium when they do
equal amounts of work.
With this principle as a test, we may study with interest the
simple machines mentioned, considering the parts as without
weight and moving without friction.
The lever is an inflexible bar, turning freely on a point called
(63)
64 PRACTICAL LESSONS IN SCIENCE.
the fulcrum. Levers are divided into three classes, on the relative
positions of the fulcrum and the points of application of the
power and weight. If the fulcrum is between the points of appli-
tion it is a lever of the first class, as in Fig. 3. The ordinary
steelyard and beam balances are illus-
p ?\ " trations of levers of this class. If the
weight is between the power and the
fulcrum, the lever is of the second class, as in Fig. 4. The
ordinary crowbar, when used for prying, is a lever of the first
class; when used for lifting, it is a lever of the second class. Two
persons carrying a weight hung from a pole are using a lever of
the second class, and a wheelbarrow is an illustration of a lever
of this class. If the power is between P p
the weight and fulcrum the lever is of Fio^
the third class, as in Fig. 5. The common fire tongs, sugar
tongs and sheep shears are pairs of levers of this class. When
we lift a weight with the hand the forearm is a lever of the third
class; the fulcrum is at the elbow and the power is applied
through the tendons which are inserted between the fulcrum and
weight. Levers may be combined in
p- ~ ~ w various ways. Fig. 6 shows a com-
bination of a lever of the first class
and one of the second class.
A lever consists of two arms along arm or power arm, which
is the distance from the fulcrum to the power, and a short arm
or weight arm which is the distance between the fulcrum and the
weight. Thus in Fig. 3, PF is the long arm and WF the short
arm, which is shorter than the power w * _*
arm, while in Fig. 5, the power arm, f""1 JTF
PT ~~w r
PF, is shorter than the weight arm A ' ^
WF. It may be shown by geometry
that the distances PF and WF in Fig. 3, have the same relations
to each other as the perpendicular distances through which the
power and weight, respectively, move, so that work will equal
the product of the power by its arm, and the product of the
weight by its arm, and the forces will be in equilibrium when
LESSONS IN PHYSICS. 65
P X PF = W X WF, in which case P : W :: WF : PF. That is the
power and weight will be in equilibrium when they are to each
other inversely as the lengths of their respective arms. The
greater the difference in the length of the arms, the more
effective is the lever in transferring power. If the arms of the
lever are equal, the power and weight will be equal, and in
case of motion the space moved by each will be equal. If the
weight arm is shortened by moving the fulcrum toward the right
a given power will overcome a greater resistance and do more
work. If the power arm is shortened by moving the fulcrum
toward the power, the power becomes less effective for overcom-
ing resistance, but more effective for producing motion, as in lift-
ing a weight with the hand the power acts through two or three
inches, while the weight moves through two or three feet.
In the case of the compound lever the power and weight will
be in equilibrium when the product of the power by the long arms
equals the product of the weight by the short arms, as in Fig. 6.
P X PF' X P'F = W X WF X W'F'.
The wheel and axle consists of a wheel and cylinder fitted
together so as to turn on the same axis. The power is applied to
the circumference of the wheel, and the weight, usually by means of
a rope is applied to the circumference
of the cylinder or axle. The power acts
through the circumference of the wheel
while the weight acts through the
circumference of the axle. And they
will be in equilibrium when P X cir. of
the wheel = W X cir. of the axle. An
end view of the wheel and axle shown
in Fig. 7, shows the wheel and axle to
be a lever of the first class and the FIG. 7.
equation may be P X PF the radius of the wheel =W X WF, the
radius of the axle. If power is applied to the axle there is gain
in velocity, as in the case of a circular saw. The common wind-
lass for drawing water from a well or raising weights is a familiar
illustration of this machine. The capstan used in moving build-
L. S. 5
66 PRACTICAL LESSONS IN SCIENCE.
ings, and on shipboard for raising the anchor or drawing the
ship to the dock, is a vertical wheel and axle.
Sometimes the wheel and axle appears in a modified form as
when they are on separate axes and connected by belts, cogs or
friction, in which case equilibrium is obtained by using the ratio
of the circumferences or the radii as above. In the case of a com-
pound wheel and axle there will be equilibrium when the power
multiplied by the product of the radii of the wheels equals the
weight multiplied by the product of the radii of the axles.
A pulley is a grooved wheel, turning freely on an axis, over
which runs a rope, to which the power and the weight are
attached. The frame of the pulley is the block and the pulley
may be fixed or movable. It is a lever of the first class having
equal arms. No force, or motion is gained by the use of a single
pulley, yet it is one of the most useful of the simple machines. By
its aid the sails of ships are adjusted, objects may be moved to
places otherwise inaccessible, and by the use of a horse or man
working on the ground, objects can be raised to the highest
elevations.
In the case of a single pulley or group of pulleys with a single
rope, power multiplied into the vertical distance it moves equals
the weight into the vertical distance it moves. If the weight
is supported by one branch of the rope, power and weight are
equal. If the weight is supported by two branches of the rope,
as the weight rises both branches shorten and the power moves
twice as far as the weight, in which case power would equal
weight divided by two, so in a general way power equals weight
divided by the number of ropes supporting it.
In the case of movable pulleys
with separate supporting ropes the
equation is: power equals weight,
divided by the power of two, whose
index is the number of pulleys.
A Fig. 8. C Any sloping surface may be used
as a simple machine called an incline plane (See Fig. 8.) AB
represents the incline plane; BC the height of the plane; AC the
LESSONS IN PHYSICS. 67
base of the plane. In case a weight is carried up this plane,
it rises only through the distance BC, while the power moves
through the distance AB, so that power multiplied by AB
equals weight multiplied by BC. That is, power is to weight
as the height of the plane is to the length of the plane. Casks,
etc., are frequently loaded into wagons by an inclined plane. It
was by means of the inclined plane that ancients raised the great
blocks of stone which we find in the ruins of the pyramids, tem-
ples, and other buildings. Common stairs are examples of an
inclined plane.
A wedge consists of two inclined planes joined by their base.
It is mostly used for cleaving timber. It is inserted in a crack,
and then driven home by blows from a hammer; but as we can-
not measure the energy of these blows, we cannot determine the
equilibrium of force in the case of a wedge.
A screw is a cylinder of wood or metal around which runs a
spiral ridge called a thread. This cylinder passes through a
block in which there is a corresponding groove to fit the ridge or
thread of the cylinder. When the cylinder makes one revolution
it rises in the nut to a distance equal to the distance between two
consecutive sections of the thread. The arm or bar through the
head of a screw increases the length of the power arm. The
equation of a screw is : power multiplied by the circumference of
the circle through which it moves, equals weight multiplied by
the distance between two contiguous threads of the screw. The
screw is used for raising buildings and for exerting pressure, as
in the pressing of hay or cotton; and when the thread is very
fine, it may be used to measure short distances, as in the case of
the micrometer screw.
The toggle joint, used commonly in adjusting the tops of car-
riages, is a very useful form of the lever, especially in exerting
pressure through a short distance.
In every class of machinery there is loss of power through
friction, rigidity of ropes, resistance of air, etc., so that power
must be furnished not only to do the work but to run the ma-
chine. Illustrations of the simple machines are common, and it
68 PRACTICAL LESSONS IN SCIENCE.
is interesting to notice how widespread their application is.
Every motion of the body, every tool, and nearly every article
we use, involves the action of some form of a simple machine.
Water wheels are simple machines, something like the wheel
and axle, designed for the utilization of the force of gravity
through running water. One of the most common forms is the
undershot wheel, which is driven by the current flowing under the
wheel against the floats. In the case of the breast wheel, the
water falls on the wheel near its center and more power is ex-
erted. In the case of the overshot wheel the water falls upon the
top of the wheel, and more force is exerted than in either of the
other cases. The undershot wheel, with plane floats, transmits
about 30% of the power of the water. With curved floats it
transmits from 50% to 60%. The breast wheel transmits from
40% to 50%, and the overshot wheel transmits from 70% to 80%.
The turbine wheel is the most valuable and economical of the
water wheels. While the other wheels are horizontal the axis of
the turbine wheel is vertical. In the center of the wheel is a sta-
tionary disk of cast-iron, circular in form and horizontal in posi-
tion. On the upper surface of this disk are fastened curved
guides. The wheel proper revolves outside of this disk. It con-
sists of two cast-iron plates, one above the other, the space
between them being divided into numerous channels by curved
partitions. The partitions in the wheel, and the guides on the
disk, curving in opposite directions. To the bottom of this
wheel is fastened a cast-iron plate which extends under the cen-
tral disk, and to the center of this plate is attached a vertical
shaft which comes up through the disk. The revolving part,
therefore, consists of an outside wheel, an iron plate underneath,
and the vertical shaft. This wheel is placed at the bottom of a
column of water. The weight of water upon the disk forces the
water between the curved guides on the disk against the curved
partitions of the wheel. The energy of these streams turns the
wheel and the shaft, and by means of cogs and belts this motion
is transferred to machinery. The turbine wheel transmits 80
per cent, or more of the computed energy of the falling water.
LESSONS IN PHYSICS. 69
While experimenting in the line of conservation of energy, Mr.
Joule of England discovered that a quantity of heat necessary
to raise one pound of water one degree Far. would raise 772 Ibs.
one foot high, or would do 772 foot-pounds of work, which is
called the mechanical equivalent of heat. A steam boiler and
engine constitutes a machine whose purpose is to transform heat
into mechanical motion or work. The essential parts are the
furnace, the boiler, the steam pipe, the steam chest and slide
valves, the cylinder, the piston, the exhaust pipe, piston rod,
crank and shaft. The fire in the furnace expands the water in
the boiler into steam. The steam pipe conveys this to the steam
chest from which it passes through the slide valves into the cylin-
der, where expanding now against one, then against the other end
of the piston, gives a forward and backward movement, which is
conveyed by the piston rod to the crank, where the backward and
forward movement is changed into a rotary movement. The
steam after expansion in the cylinder passes out through the
exhaust pipe. The shaft carries a heavy balance wheel which
serves as a reservoir of energy, which is needed to make the rota-
tion of the shaft and all machinery connected with it uniform, so
that the sudden changes connected with the driving power or
resistance are avoided by means of the inertia of this wheel.
Motion may be communicated from the shaft to any machinery
desirable. While this machine is for the purpose of transforming
heat into mechanical work, yet with all modern improvements
not more than 20 per cent, of the heat units can be utilized as
work.
CHAPTER VIII.
LIGHT: ITS SOURCES INTENSITY REFLECTION AND
REFRACTION.
IF we place the hand in the sunlight it soon becomes warm.
It also becomes illuminated so that it can be seen, and the skin
of the hand at length becomes tanned. Some force has been
transmitted to us causing the sensations of heat and of light,
and causing also chemical action. What we receive from the sun,
whether it affects the sense of touch, or the sense of sight, or
whether it promotes chemical action, must be energy.
These forms of energy are transmitted to us from the sun,
through waves of an exceedingly rare and tenuous medium, called
ether. This method of transmitting energy is called radiation.
All the ether waves from the sun, whatever their intensity, cause
an increase of heat in terrestrial objects, but only those of a par-
ticular intensity give us light. Probably all the ether waves
promote chemical action, but particular waves are more active.
Bodies hot enough to emit light waves are said to be incandes-
cent. The sun, the fixed stars, and other bodies which are
sources of light, are incandescent. Most artificial sources of
light depend for their light waves on the incandescence of car-
bon. There are some substances which, receiving light waves,
absorb their energy without becoming hot, and in turn emit
light waves in the dark for several hours after exposure to
the light. Such bodies are said to be phosphorescent. Some
forms of vegetable and animal life emit phosphorescent light, as
certain fungi among plants, and the glowworm and firefly among
animals.
Light waves move in straight lines, as may be seen by ar-
ranging screens before a source of light, or by examining a ray
of light through the dusty air of a room. A single line of light,
(70)
LESSONS IN PHYSICS. 71
or the path of a single point in the light wave, is called a ray of
light. The smallest portion of light which can be separated for
experiment is called a beam of light; a collection of rays which
diverge from a point or converge to a point is called a pencil of
light.
When light waves fall upon the surface of bodies some of them
are thrown back or reflected, and some of them are absorbed by
the bodies, so that they disappear as light waves, while in the
case of some bodies many of the light waves are allowed to pass
through them without much loss or change, the bodies being
called transparent, translucent, or opaque, as they allow differ-
ent quantities of light to pass. Transparent bodies allow so
much light to pass that objects can be seen through them dis-"
tinctly, as in the case of air, glass, water, etc. Translucent
bodies allow light to pass through them, but in such a scattered
condition that objects cannot be seen distinctly, as ground glass,
oiled paper, etc. Those objects are opaque which apparently ab-
sorb or cut off the .light waves so that nothing can be seen
through them. Transparent and opaque are relative terms, as
no body is wholly transparent or wholly opaque.
The Velocity of Light. For all distances upon the surface of
the earth the passage of light seems to be instantaneous, but in
observing the eclipse of one of the moons of Jupiter it was found
to occur earlier than the time indicated by calculation. On
investigation it was found that when the earth is in that part of
its orbit nearest to Jupiter, the eclipse begins 16 minutes 36 sec-
onds sooner than it appears to begin when the earth is in the oppo-
site part of its orbit. From this it was concluded that light must
take 16 minutes 36 seconds to go across the earth's orbit. This
distance being known and divided by the number of seconds,
the velocity of light is found. The result is about 186,000
miles a second. Other investigations have led to the same con-
clusions.
The intensity of light varies as the intensity of light in the
source. Again, the intensity of light varies inversely as the square
of the distance of the bodies emitting light, which is the same law
72
PRACTICAL LESSONS IN SCIENCE.
that applies to the intensity of heat and gravity, and in fact to
all forms of radiant energy. This law may be illustrated by the
following experiment: Take a piece of stiff cardboard, or tin,
about four inches square, and place it at a distance of four feet
from a wall or screen. Now, if a candle be placed in front of this
card, a shadow will be cast upon the wall which will be larger or
smaller as the candle is moved nearer or farther from the card.
If the candle is one foot in front of the card the shadow on the
wall will be about sixteen inches square, that is the light which is
intercepted by the card if allowed to pass on, would be spread out
over a surface sixteen times as large upon the wall, but if the
same amount of light is spread over sixteen times as much sur-
face in one case as in the other it can be only one-sixteenth as in-
A
FIG. 7'.
tense. At four times the distance from the luminous body in this
case the intensity of light is one-sixteenth as great; at three times
the distance the light would in the same way be found to be one-
ninth as intense. In other words, the intensity of light varies
inversely as the square of the distance from the luminous body.
These experiments may be varied in numerous ways with the
result of establishing the truth of this law.
It is often desirable to compare the illuminating power of dif-
ferent flames. The art of doing this is called photometry. The
simplest method employed is to place the two flames to be com-
pared at such distances from a screen that the intensity of light
each throws upon it shall be equal. Suppose, for example, we
want to know how many times more light one candle will give
than another candle of inferior quality. Let a slender rod be
placed just in front of a screen, and then move the flames to
LESSONS IN PHYSICS.
73
such a distance that the two shadows of the rod falling side by
side upon the screen shall appear to be of equal darkness, then
measure the distance from the flames to the screen, and the
amounts of light they give will be as squares of their distance;
that is, the one twice as far away gives four times as much light.
The angle formed in the eye by the rays of light coming from
the extremities of an object is called the visual angle, and its size
varies with the distance of the object. (See Fig.7 / .) The angle
ACB is greater than the angle AEB, and the object seen from
C appears larger and nearer than when seen from E. The dis-
tance and size of objects are so associated in our minds that we
judge of the distance of objects know-
ing their size, and knowing their dis-
tance we judge of their size.
The different kinds of vibrations, as
sound waves, heat waves, light waves,
etc., maybe reflected, but the laws of re-
flection which are the same in each case,
may be more easily illustrated in con-
nection with the study of light. More
or less light is reflected from bodies;
in fact, we see bodies by reflected light,
but some of the metals with smooth
surfaces throw back nearly all the light M FIG. 8'.
waves and are the best reflectors. In the case of ordinary
reflectors or mirrors, the reflecting surface is mercury. In fine
telescopic reflectors silver is considered the best material for a
reflecting surface. Reflecting surfaces may be plane, concave, or
convex. When a beam of light falls on a mirror so as to make a
right angle with the surface of the mirror, it is thrown back over
the incident path ; but when the beam falls upon the surface so as
to form an oblique angle with it, the beam is reflected in some other
direction. Suppose a beam of light falls upon a mirror MM at
the point A from the direction IA ; it will be reflected in the direc-
tion AR. (See Fig. 8'.) Now, if we measure the angles made
with the line AP perpendicular to the mirror at A, we find that the
74
PRACTICAL LESSONS IN SCIENCE.
angle IAP equals the angle PAR, that is the angle of reflection
PAR equals the angle of incidence IAP. IA is called the incident
beam, AR the reflected beam, and A the point of incidence.
Rays of light may be parallel, or converging or diverging.
They cannot have any other relation. As the angle of reflection
equals the angle of incidence in the case of plane mirrors, they do
not change the relations of rays of light falling upon them. The
reflected rays are parallel, converging or diverging after as
before reflection. In the case of concave mirrors the effect on the
pays of light is different and more interesting. Let MM in Fig.
F.c9
9 represent a concave mirror, C the center of curvature, G the
vertex of the mirror, and CG, its principal axis. The lines CA,
CB, and CG are radii, and perpendicular to the mirror. Light-
waves emanating from the point C would be reflected to their
source at C, but rays of light from E, as EA and EB, fall upon
the mirror at the points A and B, and as the angle of reflection
is equal to the angle of incidence, they would be reflected to
H; while if H were a source of light the rays HA and HB would
be reflected to E. The diverging rays in each case are by reflec-
tion made to converge to a point called a focus. As the light
waves which emanate from either of these points are brought
LESSONS IN PHYSICS. 75
by reflection to a focus at the other, they are nailed conjugate
foci. Parallel rays, as I A and KB falling on the mirror at
A and B are reflected to F, a point midway between C and G,
which is called the principal focus; while rays diverging from
the principal focus would be reflected as parallel rays, and the
converging rays LA and PB are reflected to S. This shows that
the general effect of the concave mirror is to converge the rays of
light they reflect, and they converge rays of heat as well, so that
a piece of paper or a chip of wood at the principal focus, may be
burned in the collected rays of the sun.
The reflector of a locomotive headlight is a parabolic mirror.
The light is placed at the principal focus, so that the reflected
rays are... parallel.
The general effect of convex mirrors is to separate rays of
light.
The image of an object made by a plane mirror appears to be
behind the mirror as far as the object is in front of it. It
appears to be of the same size as the object and is erect that is,
the plane mirror gives a perfect image of the object.
In the case of the concave mirror, if the object is beyond the
center of curvature the image will be between the center of curva-
ture and the principal focus, and will be inverted and smaller than
the object. If the object is between the center of curvature and
the principal focus, the image will be beyond the center of curva-
ture, inverted and larger than the object. The image of an object
between the principal focus and the mirror will be back of the
mirror, erect and larger than the object.
The images formed by the convex mirror are always erect,
behind the mirror and smaller than the object, and are generally
curiously distorted.
Many valuable and interesting experiments may be made with
cheap plane and curved mirrors, which will serve to verify these
laws. A bright silver spoon may serve both as a concave and a
convex mirror ; so of metal cups, bells and other articles of com-
mon use.
Light moves with different velocity, through different trans-
76
PRACTICAL LESSONS IN SCIENCE.
parent substances. This is shown by the bending or breaking
of a ray of light as it passes from one medium into another of
different density, if the ray is oblique to the surface separating
the two media. Thrust a pencil into the water so that it is per-
pendicular to the surface of the water and there is no apparent
change in the shape of the pencil, but if it be made oblique to the
surface of the water it appears to be bent or broken at the sur-
face, and the immersed portion seems elevated. Again, place a coin
on the bottom of an opaque dish as at B (Fig. 10), then standing
so that the coin is just hid from sight by the side of thedish,have
water poured slowly into the dish and the coin will rise into view
as the dish fills with
water. The difficulty
of putting a stick on a
given object in a body
of water is a familiar
illustration of the
same principle. Now, if
we remember that ob-
jects are seen by light
reflected from them,
we know that a ray of
light from the coin or
pencil point, is bent at the surface of the water at C toward A,
instead of going on to E, so that the ray appears to come from
D, and the coin seems to have been lifted from B to D, the pencil
appearing to be shorter and the water shallower than it is in
reality. If one looks at a pencil so that one part is seen through
glass oblique to the surface, and the other part through air, the
pencil appears broken at the surface of the glass, on account of
refraction of light.
The laws of refraction are that a ray of light, in passing from
a rarer into a denser medium, is bent toward the perpendicular
at the point of incidence, while in passing from a denser into a
rarer medium it is bent from the perpendicular at the point
of incidence. (See Fig. 10.) The angle ACF is the angle of
FIG 10
LESSONS IN PHYSICS.
77
incidence, BCG is the angle of refraction, and DCB is the angle of
deviation. The ray AC passing into the water at C is bent to-
ward the perpendicular FG, instead of going to D, while the ray
BC passing into the air at C, is bent from the perpendicular FG,
toward A, not going on to E.
The cause of refraction. In. the case of ether waves, the parti-
cles vibrate transversely to the direction in which the waves
move. Now, as the waves pass obliquely from one medium into
another that is more dense, the end that first enters the denser
medium seems to move more
slowly, while the end that is still
in the rare medium moving as be-
fore gets a little in advance, so
that there is a bending of the ray
at the surface separating the two
media; much as a column of sol-
diers changes direction by filing
right or left. The reverse is true
as the light passes into a rarer
medium. (See Fig. 11.)
FIG 1 1
\
From A as a center (see Fig. 10) describe the circumference of a
circle and draw the lines ab and df. The line ab is the sine of the
angle of incidence ACF, and the line df is the sine of the angle of
refraction BCG. Now if we divide the line ab by the line df the
quotient will be what is called the index of refraction, which is
constant with the same substance but varies with different sub-
stances, lead chromate having the highest index of refraction,
2.97; the diamond next, 2.5, and flint glass next, 1.61.
CHAPTER IX.
OPTICAL INSTRUMENTS RAINBOW AND COLOR.
LENSES are transparent bodies, usually glass, one or both of
whose surfaces are curved . The principal forms are the double
convex lens A, bounded by two convex surfaces; the piano con-
vex lens B, bounded by a plane surface and a convex surface;
the concavo convex lens C, in which one surface is convex and
the other concave, the concavity being less than the convexity ;
the double concave lens
D, which has two con-
cave surfaces ; the piano
concave lens E, with one
plane surface and the
other concave, and the
concavo convex lens F,
in which there is one
concave and one convex
surface, the convexity being less than the concavity. The con-
vex lenses diminish in width towards the edge, while the concave
lenses increase in width towards the edge. (See Fig. 12.)
The effect of convex lenses on rays of light may be shown by
tracing them through a lens according to the law of refraction.
Suppose MN, Fig. 13, represents a double convex lens, C and C'
representing the centers of curvature, and the line C C' the prin-
cipal axis of the lens. Now, if a ray of light from C fall upon the
lens at A it will be bent toward the perpendicular C'A at the
point A towards the point B, on emerging from the lens the ray
will be bent from the perpendicular CB at the point B towards
C'; and the ray of light from C' in the same way would be re-
fracted to the point C, so that C and C' are called the conjugate-
(78)
LESSONS IN PHYSICS.
79
foci of the lens, as light diverging from one point is converged
to the other.
Suppose that a ray of light from H parallel with the principal
axis, falls upon the lens at the point A, it will be bent toward
the perpendicular C' A to the point of G. At G it will be bent
from the perpendicular CG to F, which is called the principal
focus, while rays diverging from the principal focus become par-
allel on the other side of the lens. Thus the general effect of the
double convex lens is to collect the rays of light. Diverging rays
are made to diverge less, parallel rays are made to converge, and
1 - ^_ M
F.G 13
the converging rays will be made more convergent. Experiments
with the other convex lenses show the same effect. The point S
in the center of the lens on the principal axis is called the optical
center of the lens. Any line, as LSO, through the optical center
is called the secondary axis.
The effect of the concave lenses on rays of light may be shown
as follows: (See Fig. 14.) Let MN represent a double concave
lens, C and C' being the centers of curvature. Suppose the ray
of light S should fall upon the lens at A it will be bent toward
the perpendicular CB to D, on emerging from the lens it will be
bent from the perpendicular C' D to F, showing that the effect of
80
PRACTICAL LESSONS IN SCIENCE.
the double concave lens is to render rays parallel to the principal
axis divergent.
Experiments with diverging and converging rays show that
the general effect of the double concave lens is to disperse rays of
FIG 14
light. Experiments with the other concave lenses show the same
effect.
The double convex lens, or any of the convex lenses, not only
collect rays of light, but rays of heat as well, and are sometimes
called burning glasses. These lenses are also used as magnifying
glasses, or simple microscopes. The relations of images to ob-
jects in different cases are shown in the following figures (see
Fig. 15), in which the object is between the focus and the lens.
Let MN represent the lens whose focus is at C, and let the ob-
ject AB be placed between
s'
Fic.15.
point and the lens ; if we
trace the rays of light from
the object through the lens,
they are diverging after re-
fraction and cannot meet;
but if the eye receives these rays at E, they will have the same
effect as if they came from A' and B' ; hence the image will be
formed at A'B', which will be on the same side of the lens as
the object, erect and larger, than the object. In case the object
LESSONS IN PHYSICS.
81
be placed beyond the principal focus, and less than twice the dis-
tance of the principal focus, the image will be inverted and larger
than the object. (See Fig. 16.) Again, if it is twice the distance
of the principal focus the image will be inverted, but of the same
size. (See Fig. 17.) If the
object be placed more than
twice the distance of the
principal focus the image will
be inverted and smaller.
For the image in the case of the double concave lenses (see Fig.
18.) MN represents a double concave lens ; suppose the object at
AB, the rays of light are made to diverge in passing through
the lens, and if received by the eye at E, they appear to come
from a b, and the image is on the same side of the lens as the ob-
ject, erect and smaller.
The compound micro-
scope consists of two
double convex lenses, the
smaller called the object
glass and the larger the
' ' s ' '
eye-piece. If the object is placed just beyond the focus of the
object glass, an image will be formed on the other side which is
inverted and larger than the object; the eye-piece is so placed
that the image formed by the object glass falls just within its
focus, so that it is again enlarged by the eye-piece, as in Fig. 15.
The refracting tele-
scope consists of two
double convex lenses,
the larger called the
object glass, the
smaller the eye-piece.
Fie. 1 8.
The object is so far beyond the principal focus of the object glass
that the image is inverted and smaller, and the eye-piece is ad-
justed so that the image formed by the object glass falls just
within its principal focus, and is magnified by the eye-piece. In
a microscope an object is magnified both by the object glass and
L. S. <j
82 PRACTICAL LESSONS IN SCIENCE.
the eye-piece ; but in the case of the telescope the object is magni-
fied only by the eye-piece. . The object glass of the telescope serv-
ing as a light gatherer, an object glass of 20, 30 or 35 inches
collecting vastly more light than can the unaided eye.
The Galilean telescope consists of a double convex object
glass and a double concave eye-piece ; the object being more than
twice the focal distance of the lens, the image would be inverted
and smaller than the object; but between the object glass and
its focus the concave lens is inserted which separates or disperses
the converging rays, and the image is seen erect and enlarged.
The ordinary opera glass consists of two Galilean telescopes.
The terrestrial telescope used in surveying frequently consists
of four double convex lenses; the inverted image of the ordinary
telescope being confusing, two more lenses are added so as to give
an erect image of the object.
In the reflecting telescope light is gathered by a large concave
mirror, and the image formed is enlarged by a double convex
lens.
The magic lantern is an instrument by which the image of a
small object greatly magnified may be thrown upon a screen. It
consists of a dark box in which there is a strong light ; behind
this light there is a concave mirror, and in front of it an opening
from which projects a tube. At the entrance of the tube is
placed a double convex lens. or two piano convex lenses; inside
of this tube slides a smaller tube in which is fixed another
double convex lens. The picture or object is placed between the
lenses.
The first lens receiving light from the lamp, and by reflection
from the mirror, concentrates it upon the transparent object or
picture, strongly illuminating it. Light from the object goes on
through the second lens to a distant screen and there forms a
large and perfect image.
The camera consists of a dark box divided by a partition or
screen of ground glass. The box has openings in two opposite
sides, from one of which projects a tube in which slides a smaller
tube carrying a double convex lens. If the lens is properly
LESSONS IN PHYSICS.
88
adjusted a distinct image of objects in front of it may be seen
upon the screen by looking through the opening in the oppo-
site side of the box. When the image is properly focused the
photographer replaces the screen by a sensitized plate, and the
chemical powers of the sun's rays impress a true picture of the
object on this plate. (See Fig. 19.)
The human eye is a camera which differs from the common
form of that instrument only in its wonderful perfection.
A prism is a triangular transparent body that so refracts the
white light of the sun as to separate it into a band of colored
light called the solar spectrum. The solar spectrum is made up
of seven colors red, yellow, orange, blue, indigo, and violet, and
depends upon the fact that the waves of ether which give rise
to the different colors are bent at different angles by refraction
through the prism. This is explained by the fact that the vibra-
tions which give rise to red light are longer and less rapid than
those which give rise to the yellow light, and are less refrangible;
that is, are bent less than those which give rise to yellow light,
and so on through the spectrum the waves which give rise to
violet light being shorter, more rapid and more refrangible than
those which give rise to any other color. Experiments show that
there are waves outside those which give rise to the red light,
which are less refrangible than the red waves, and which we may
recognize as heat waves; and there are other waves, which are
more rapid, shorter and more refrangible than the violet rays,
which we may recognize by their chemical effects.
To the naked eye the colors of the spectrum seem continuous,
but when examined through a telescope the spectrum is found to
84 PRACTICAL LESSONS IN SCIENCE.
be crossed by great numbers of fine black lines, which for a long
time could not be explained.
Each of the elements which make up our earth gives its own
peculiar spectrum ; as sodium gives two yellow lines, potassium
two red lines and one purple line, nitrogen many lines of different
colors, hydrogen two lines, etc. The colors are as variable as
those of the solar spectrum, and vary in number through an im-
mense range. For instance: Iron shows as many as 450 lines,
while sodium shows only two. On comparing the spectrum
of iron with the solar spectrum, the bright lines of iron were
found to correspond with certain black lines in the solar spec-
trum, and similar results were obtained by experimenting with
other substances. This coincidence called for explanation. Ex-
perimenting with sodium vapor it was found that light passing
through sodium vapor gave a spectrum that was perfect, except-
ing that the place of the yellow light was occupied by a dark band.
Similar results were obtained from experimenting with the vapor
of other substances. These facts led to the conclusion that vapors
absorb the kind of light which they emit, letting the other kinds
pass through. And these facts led to the further conclusion that
the sun consists of a molten mass surrounded by an atmosphere
of metallic vapors, which absorb the light from the molten metals
within, thus giving rise to the dark lines in the solar spectrum.
An examination of the light of the fixed stars shows that
they are bodies like our sun, while the nebulae seem to be com-
posed entirely of gaseous matter. As the spectrum of the most
important terrestrial substances is known, the composition
of bodies may be determined by the spectroscope, and several
new substances have been discovered by its use. It has been
used to detect adulteration of liquids and diseased conditions
of the blood. By it iron, sodium, calcium, nickel, copper,
zinc, cobalt, manganese, aluminum, and other metals are shown
to exist in the sun. Hydrogen has been shown to exist in
hundreds of different stars. In the star Aldebaran, hydrogen,
iron, sodium, mercury, and five other elements common on the
earth are shown to exist, Some stars are so far from the earth
LESSONS IN PHYSICS. 85
that light traveling with the inconceivable velocity of 186,000
miles per second would be fifty years or more in traversing the
profound space, yet with the spectroscope we can analyze that
light and make it tell what substance sent it out.
The rainbow is a beautiful and gigantic solar spectrum, which
has been formed by the refracting power of thousands of rain-
drop prisms. The bow is seen when the sun is back of the ob-
server, and sometimes a second bow may be seen outside of the
primary one. The primary bow is formed by light that enters
the upper part of the drop, is refracted, reflected and refracted
again to the observer. The second bow is formed by the light
which enters the lower part of the drop, is refracted, reflected
twice, then refracted to the observer. (See Fig. 20.) R indicates
red ray, V violet ray and S" the sun.
The white light of the sun falls upon all bodies alike. This
light is decomposed in different ways by different bodies, some of
it being absorbed and some reflected. One body is red because it
reflects the red rays, absorbing the others; another is blue be-
cause it reflects only the blue rays, absorbing the others. The
foliage of plants receives the sun's white light, decomposes it,
reflecting only the green rays. The petals of the rose decompose
the sunlight, reflecting to us the colors peculiar to itself. A body
86 PRACTICAL LESSONS IN SCIENCE.
which reflects all the colors of the light it receives is white; when
it reflects none it is black. The clouds both refract and reflect
the sun-light, and all their varied colors are due to the decompo-
sition of light by the water vapor in the clouds of the morning
or evening sky.
The color of objects depends upon light. All objects are black
in the dark. When we paint our houses we apply to them a sub-
stance that has the property of reflecting the colors we desire
and absorbing the others. Thus bodies have no color of their
own. If a white body in a dark room be successively illuminated
by the colors of the spectrum, it appears red, yellow, orange,
green, etc., according to the light which illuminates it.
Red, green, and violet are called fundamental colors, since,
with these, all possible colors may be formed by mixture.
Two colors or tints which together give white are called com-
plementary colors. The following pairs of colors give white:
Red and bluish-green; orange and blue; yellow and indigo;
violet and yellowish-green.
Spectrum colors differ from pigment colors. Pigment yellow
and pigment blue produce green, not white.
CHAPTER X.
FRICTION AL ELECTRICITY AND MAGNETISM.
IF a dry glass tube, as a lamp chimney, is rubbed vigorously
with a piece of dry flannel for a moment or so, it will attract
small pieces of paper or pith, which, after remaining a short
time in contact, are repelled. After being rubbed, if the glass
tube is held near the cheek, a gentle breeze will seem to blow
against the cheek, and perhaps a pricking sensation may be felt
and crackling sounds be heard. Like phenomena sometimes occur
when stroking a cat or while combing the hair with a hard-rub-
ber comb. Sealing wax when rubbed in the same way exhibits
the same property. Bodies having this property are said to be
electrified.
When a glass tube is rubbed with a piece of flannel, only
the part rubbed will be electrified, and the same is true of sealing
wax. In these bodies electricity does not pass from one part to
another; that is, they do not conduct electricity, but when met-
als become electrified by friction or otherwise in any of their
parts the electricity immediately spreads out over the en-
tire surface, that is, metals do conduct electricity. Bodies
which resist the spread or passage of electricity through them
are called poor conductors, or non-conductors; while others
which resist the passage of electricity but slightly are called
good conductors. The difference between these two classes of
bodies is in the quantity of electricity they convey, as no body
is absolutely a non-conductor. Nearly all the metals are good
conductors of electricity, and so are graphite, water, charcoal,
animal and vegetable bodies and other substances, while lime,
India rubber, silk, diamond, wax, resin, air and other bodies are
poor conductors. A good conductor retains electricity only so
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88 PRACTICAL LESSONS IN SCIENCE.
long as it is surrounded by poor conductors, as glass or air,
which are sometimes called insulators.
It is often desirable to detect the presence of electricity, which
is done by the use of the electroscope. This, in the simplest
form, consists of a ball of pith from a cornstalk or elder, hung
by a silken thread from a glass support. Now, if a glass rod
which has been electrified by friction is brought near the ball of
pith it will attract the ball, but on coming into contact with
the rod the ball receiving electricity from the rod is instantly
repelled. Now, if an electrified stick of sealing wax and an elec-
trified rod of glass are alternately brought near the pith ball the
glass rod will repel and the wax attract the ball, which seems to
show that the glass and wax have different kinds of electricity,
and that the same kinds of electricity repel each other while un-
like kinds attract each other. The electricity produced on the
glass is called vitreous or positive electricity ; that developed in
the wax is called resinous or negative. They are developed to-
gether, positive in the glass and negative in the rubber, the nega-
tive in the wax and positive in the rubber. The supposition is
that each body is endowed with neutral electricity, and by fric-
tion this is decomposed, one body retaining the positive and the
other the negative. Another curious phenomenon which compli-
cates matters somewhat occurs when glass is rubbed with cat-
skin, in which case negative electricity is developed in the glass
instead of positive, as when rubbed with the flannel.
In all electrical experiments the air and the apparatus should
be dry, many delicate experiments fail by loss of electricity
through the conduction of moisture in the air.
Frictional electricity seems to rest only on the surface of bod-
ies. An insulated conductor charged with either kind of elec-
tricity decomposes the neutral electricity of bodies near it,
attracting the opposite and repelling the like kinds. The action
thus excited is called induction.
Machines are made for developing electricity by friction, and
with them are condensers of some kind for the accumulation of
the electricity developed ; sometimes the condenser is part of the
LESSONS' IN PHYSICS. 89
machine and sometimes separate. A common form of condenser
is the Ley den jar, which is a wide-mouthed jar covered inside and
out with tin foil for about two-thirds its height. Through the
wooden stopper passes a brass rod, terminating at the upper
extremity in a ball and at the other in a chain, which rests on
the bottom of the jar. The condenser in this case consists of two
good conductors separated by glass, a poor conductor, or insula-
tor. The jar is charged by connecting the inner coating with the
electrical machine, the other with the earth, the electricity inside
the jar holding or developing the opposite kind on the outside of
the jar by induction. The jar may be discharged by connecting
the two coatings of tin foil by holding the jar in one hand and
touching the ball with the other, which maybe done with safety if
the jar is a small one, or by connecting them by a wire attached
to a glass handle.
It has been found that smooth bodies without angles or
points retain electricity best. It is usually impossible to charge
the condenser of an electrical machine if it has points or angles,
as electricity passes away so quickly through them, but in
such cases it passes away very quietly, while in the case of
a smooth body the electricity is retained until the accumula-
tion is so great that disastrous results are liable to follow its
discharge.
The electricity of the atmosphere is of the same nature as
the frictional electricity. The air is usually positively elec-
trified, while the earth is negatively electrified. It is stronger
in summer than in winter, and during the day than in the
night. During cloudy weather, and on the approach of thun-
der storms the electrical condition of the air changes frequently
and rapidly. Clouds separated by dry air become Leyden jars
or condensers, and the electricity bursting across through the
non-conducting air causes lightning and thunder and often rain ;
again the clouds and the earth separated by dry air form a con-
denser, and while electricity is streaming toward the clouds
from every angle and point, from every tree and shrub, in some
places the accumulation becomes so great that it bursts through
90 PRACTICAL LESSONS IN SCIENCE.
the air and lightning and thunder follow, and sometimes with-
ered trees, burned buildings, and loss of life is the result.
As some protection from accidents from this cause lightning
rods have been devised. They consist of metal, usually of iron,
although copper is a better material. The lightning rod should
be of ample size, and attached securely and closely to the build-
ing and to all metallic pipes about the building. It should reach
downward to ground that is permanently moist, and it would
be better if it terminated in a broad plate of metal. It should
extend upward for some distance above the building and termi-
nate in bright, sharp points. When first invented it was thought
necessary to separate the lightning rod from the building, but it
was soon discovered that it was better to connect the whole
building with the rod, which discharges electricity so rapidly
that no accumulation occurs to cause dangerous results. The
effects of lightning, so well known to all, show that electricity
can do mechanical work, as in the tearing of trees, shattering of
walls, etc.
To Doctor Franklin belongs the immortal honor of provingthe
identity of electricity and lightning. A kite was the simple instru-
ment which he employed. Having made a kite by stretching a silk
handkerchief over two sticks in the form of a cross, he went out
into a field accompanied only by his son; raised his kite; fast-
ened a key to the lower end of its hempen string ; insulated it by
fastening it to a post by means of a silk cord, and anxiously
awaited the approaching storm. A dense cloud, apparently
charged with lightning, soon passed over the spot where he
stood, without causing his apparatus to give any sign of elec-
tricity. He was about to give up in despair, when he caught
sight of some loose fibers of the hempen cord bristling up as if
repelled. He immediately presented his knuckle to the key, and
received an electric spark. The string of his kite soon became
wet with the falling rain ; it was then a better conductor, and he
was able to obtain an abundance of sparks from the key. By
this experiment he furnished a decisive proof of the identity of
lightning and electricity.
LESSONS IN PHYSICS. 91
Magnetism. A magnet is a body which has the property of at-
tracting iron, and when suspended, so as to turn freely, of assum-
ing a north and south direction. The end toward the north is
called the north pole of the magnet, while the other end is called
the south pole. An ore of iron, called magnetite or lodestone, is
found in many localities. Lodestone was known to the ancients,
being found in Asia Minor, in Sweden, in the region of Lake Super-
ior, and in many other localities. The name lodestone or leadstone
seems to have been derived from the Saxon laedan,to lead. When
a steel bar or needle is rubbed by a natural magnet, it acquires
magnetic qualities and becomes an artificial magnet. Artificial
magnets are more powerful and convenient than lodestone mag-
nets, and are the only ones in ordinary use.
Magnets maybe straight, when they are bar magnets; or they
may be in the shape of a letter U, when they are called horseshoe
magnets. A bar of soft iron, called an armature, laid across the
poles of a magnet enables it to retain its magnetism for a longer
time. In the case of bar magnets they are laid in pairs, an arm-
ature connecting the north pole of one with the south pole of the
other.
If a magnet is rolled in a mass of fine iron filings, it will be
seen that the attractive force is stronger at the ends, gradually
diminishing to zero at the center. If a bar magnet, as an ordinary
knitting needle, is broken at the zero point, each end instantly
becomes a complete magnet, with strong poles and zero center
as before, and the same will be true however short the pieces be-
come. Either pole of the magnet attracts iron, but if we experi-
ment with two magnets, one of which is suspended, we find that
the north pole of one attracts the south pole of the other, but
repels the north pole, and vice versa; that is, poles of the same
name repel each other, while poles of different names attract
each other. The iron or steel attracted by a magnet becomes
itself a magnet, has a north and south pole, is polarized, and in
turn may polarize other pieces of iron or steel, as is shown by
the experiment of rolling the magnet in iron filings. If a piece
of writing paper is laid over a strong magnet, and then fine iron
92 PRACTICAL LESSONS IN SCIENCE.
filings be sprinkled over the paper, on tapping the paper gently
the filings will arrange themselves in beautiful curves about the
poles of the magnet, showing that a magnet makes magnets
without contact, and all these iron filings, as secondary magnets,
are arranged pole to pole in regular order according to the laws
mentioned above. The most important use of the magnet is in
the construction of the compass. A slender bar magnet bal-
anced on a pivot, is called a magnetic needle. The compass con-
sists of a circular box, usually of brass, with a glass cover, in
which a magnetic needle is balanced over a card on which the
different directions are marked. The mariner's compass is so
mounted that whatever the motion of the ship the compass is
always horizontal. With it the mariner, aided by observations
of the sun and stars, finds his way across the trackless sea.
In general, the needle varies more or less from the true
north. The line of no variation passes near Cape Lookout,
Cleveland, Ohio, thence across Hudson's Bay to the pole, enter-
ing Europe just east of the White Sea, thence across the Caspian
Sea, and through Western Australia to the south pole, thence
northward through eastern South America. West of this line the
needle varies west, east of it the needle varies east. This line itself
varies east and west. In 1580, the variation of the needle, at
Paris was 11 30' east, showing that the line of no variation was
west of Paris. In 1663 this line was at Paris, while in 1825 the
variation was 22 22' west, showing that the line of no variation
was far to the east. Besides this slow variation there are annual
and daily variations, and variations due to volcanic eruptions
and earthquakes, and variations attended upon marked displays
of the Aurora borealis, and disturbances in the sun as shown by
sun spots. These latter variations are said to be due to mag-
netic storms or disturbances.
The magnetic needle does not remain in a horizontal position,
but north of the equator the north end dips, while south of the
equator the south end dips, so that in practice one end must be
weighted to keep the needle horizontal. Here again we have no
rational explanation of the phenomena.
CHAPTER XI.
DYNAMICAL ELECTRICITY.
ABOUT the year 1786, Luigi Galvani, a professor of anatomy,
discovered that in the case of a recently killed frog, if one end of
a metal conductor, composed of zinc or copper, was placed in
contact with the nerves of the lumbar region and the other with
muscles of the thigh or leg, a prompt contraction of the muscles
ensued. He assumed that the electricity was inherent in the
animal substance; but Professor Volta from his experiments,
attributed to the metals the active part of the phenomena of
contraction. The investigations of these men and their suc-
cessors have led up to the dynamical electricity of to-day.
A little experiment will help us to understand how this form of
electricity is developed. Get a strip of sheet copper and two pieces
of zinc, each about five inches long and one and one-half inches
wide; and have a piece of No. 16 copper wire about ten inches
long soldered to one end of each. Fill a tumbler about two-thirds
full of water and add to it two tablespoonfuls of strong sulphuric
acid. Amalgamate one piece of zinc as follows: Dip it into the
acidulated water, and then pour a little mercury over the surface,
rubbing off any excess with a cloth. Put a piece of copper and a
piece of zinc that is not amalgamated into the liquid without
allowing them to touch each other, and vigorous action takes
place between the acid and the zinc, but none between it and
the copper. Now substitute amalgamated zinc for the other
and no action appears on either plate. Now, if the wires of the
two plates are brought in contact, gas is given off from the cop-
per but not from the zinc plate; and, if we separate the wires care-
fully, we may see a little spark of light, and the action in the fluid
ceases. There is no action between the liquid and the amalga-
mated zinc, unless it is connected with the copper. The wire
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94 PRACTICAL LESSORS IN SCIENCE.
conductors seem to be necessary to the action which takes
place. Do they acquire any new properties? Place a magnetic
needle near the tumbler and hold the connecting wires over
it, and the needle will be deflected from its north and south
direction, which indicates the presence of electricity in the wire.
This action is explained as follows : the zinc takes the place
of the hydrogen of the acid, forming zinc sulphate which re-
mains dissolved in the liquid, and the hydrogen is forced
along from molecule to molecule through the acid until it
reaches the copper plate where it escapes in bubbles. This action
is so rapid as to appear continuous, and it is believed to be the
cause of the electricity or electrical current in the wire, as the
result of the conversion of chemical energy into potential energy.
If this action continues the acid becomes weaker, and the zinc is
dissolved so that it must be renewed from time to time.
In order that water may flow from one place to another there
must be a difference of level ; so in the case of electricity, there
must be a difference in electrical conditions before there can be a
flow of electricity. When electricity at any place is greatly in
excess of that in the earth it is described as high potential, when
slightly in excess as low potential; when there is more electricity
in one body than in another again the terms high and low poten-
tial are used. Electricity moves from the place of high potential
to the place of low potential. Differences of potentials and elec-
tromotive force are commonly used in the same sense. The zinc
is positive, that is, has a higher potential than the copper, and
the electricity passes from the zinc through the liquid to the cop-
per in the attempt to restore the equilibrium of the potentials.
But as the chemical action is practically continuous the motion
toward the copper is continuous, and we have what is called an
electrical current. The current passes through the liquid between
the metal plates and through the wire connecting them, and to
this whole path or course of the current the term circuit is applied.
The wires are called the conductors, the end of the wire from the
copper plate is called the positive pole and the other the negative
pole. Separating the poles is called opening the circuit, bringing
LESSONS IN PHYSICS. 95
them together is called closing the circuit. Opening the circuit
and filling the gap with an instrument of any kind is called intro-
ducing the instrument into the circuit.
The tumbler of acid with the two metals is called a voltaic cell,
the metals are called elements. There are several different kinds
of cells, but all are constructed on the same general principle. A
number of cells working together form a battery. By enlarging
the plates of the cells batteries of low resistance are made, but
they furnish great quantities of electricity. By increasing the
number of cells, batteries of high resistance and great intensity
may be made. No conductor, whether liquid or solid, is perfect ;
each resists the passage of electricity more or less. The resist-
ance in a circuit is principally in the cells, when it is called
internal, or in the conductors, when it is called external.
The greatest difference between current electricity and fric-
tional electricity is this : Current electricity is remarkable for
its great quantity but feeble intensity, while frictional elec-
tricity is equally remarkable for its great intensity and small
quantity.
If a bar of soft iron be inclosed in coils of wire, and the ends
of the wire be attached to the poles of a battery, the current
passing through the wire makes the bar of iron a magnet. Break
the current and the magnetism is gone. The rapidity with which
an iron bar may receive and part with magnetism as the current
is made or broken is very great; it may occur as many as 8,000
or 10,000 times per minute. Such magnets are called electro
magnets, and may be made much stronger than permanent mag-
nets. The induction of magnetism by current electricity is the
principle on which depends the working of the electric telegraph.
The wire connecting the battery and the coil about the soft iron
may be very long, even miles in length ; so the battery may be in
one city or town and the coil in another, and still the magnet is
made and an armature may be attracted every time the circuit is
closed. For a long time two wires were thought necessary , but it
was discovered that if one pole of the battery was connected with
the coil by a wire, and both the battery and coil connected with
96 PRACTICAL LESSONS IN SCIENCE.
the earth, that the earth would complete the circuit. As the re-
sistance of the earth is practically nothing, less powerful batteries
were needed, as they had only to overcome the resistance of one
wire instead of two. The distance may be so great that the bat-
tery at one end cannot entirely overcome the resistance, in which
case relay batteries are introduced. In addition to the battery,
coil and line wire, an instrument called a key for opening and
closing the circuit is necessary, and a mechanical device for the
purpose of registering the action of the armature, which may be
by blows on a sounder or by marks on paper moved by clock
work. If the circuit is closed for an instant a dot is made on the
paper, or a short sound on the sounder; if for a longer time, a
line is made on the paper or a longer sound, and the differences
between the blows on a sounder, made by the dot or line closure
is easily distinguished by the ear, so that all first-class operators
work by sound. The telegraphic alphabet, consisting of dots
and dashes, is called the Morse alphabet, and the telegraph is
usually known as the Morse telegraph. But there is reason to
believe that while Morse introduced them to the world, they were
really invented by another man of whom the world has seldom
heard. Electric bells and electric clocks are based on the same
principle as the telegraph.
The magnetic needle whose deflection indicates electricity in the
connecting wires of the voltaic cell, is in fact a galvanoscope.
It may be made so that the needle hangs over a graduated circle
under which a coil of wire is placed, and so arranged that the
instrument may be introduced into a circuit.
Make two coils of wire, one containing a few feet of stout copper
wire, called the primary coil; and another containing a much
greater length of fine copper wire, called the secondary coil, and
make them so that the primary coil may be placed inside the
secondary, or removed at pleasure; connect the primary coil with
the battery and the secondary with the galvanometer. Now,
lower the primary coil into the secondary coil and the galvano-
meter shows the presence of a current in the secondary coil, but
the needle of the galvanometer soon settles to zero, showing that
LESSONS IN PHTSICS. 97
the current was temporary. Draw out the primary coil and again
the current is shown, but in the opposite direction, and again it
appears to be temporary. Again place the primary coil inside
the secondary, then break and close the circuit and in each case
we have a current in the secondary coil as before. When intro-
ducing the primary coil, and when closing the primary circuit, an
inverse induction current is formed in the secondary coil, while
on withdrawing the primary coil or breaking the primary circuit
a direct current is formed in the secondary coil.
Further, it has been discovered that the same results are
reached by using a magnet with the secondary coil, as are
reached by using a primary coil. That is, if a magnet be lowered
into the secondary coil, an inverse current is indicated in the
coil, and if the magnet is removed, a direct current is indicated.
Now, if a bar of soft iron be placed in the secondary coil, and the
pole of a permanent magnet be brought near it, the soft iron
becomes a magnet by induction and a current is manifested in
the secondary coil. Now, remove the permanent magnet and the
soft iron ceases to be a magnet, and a current is again indicated,
but in the opposite direction.
Again, a permanent magnet is placed within the secondary coil
and a bar of soft iron is moved toward it; the magnet causes the
soft iron to become a magnet by induction, and this seems to
increase or change the magnetism of the permanent magnet, and
a current is indicated in the secondary coil, and a current in the
opposite direction is shown on the removal of the soft iron.
The same effect maybe obtained if an electro-magnet be placed
within the secondary coil and a strong magnet rotate rapidly
in front of it, so that its pole acts inductively upon the branches
of electro-magnet in succession.
Similar results may be obtained by passing coiled wire around
the poles of a permanent horseshoe magnet, and revolving the
plate of soft iron in front of the poles of the magnet. The soft
iron becoming magnetized acts on the permanent magnet, and
alternate currents are induced in the coils of the wire.
On the principles just mentioned many different kinds of ma-
L. S. 7
98 PRACTICAL LESSONS IN SCIENCE.
chines or dynamos have been constructed by which electricity
may be transformed into work.
The dynamo electric machine, or the dynamo, consists of an
iron core wound with long coils of wire constituting the arma-
ture, which revolves between the poles or within the field of a
powerful electro-magnet, called a field magnet. The armature is
rotated by steam, and the currents induced are gathered up for
transmission by brushes of copper wire. These machines vary
greatly in detail, but all contain the above essentials. The
energy generated in the dynamo is transmitted through wires to
a similar machine called a motor, which transforms the electrical
energy into mechanical work.
The energy developed in the dynamo may be transmitted to
electric lamps where it is transformed into light. If the termi-
nals of the wires from a dynamo are connected with pencils of
carbon and these brought near each other, their tips are intensely
heated, some of the carbon being volatilized. This vapor, a con-
ductor of high resistance, attains a very high temperature,
emitting intense light. The light of the incandescent lamps is
produced by introducing some refractory substance of lower con-
ducting power into the circuit, which soon becomes heated to
incandescence. The substance commonly used is carbon, inclosed
in a glass bulb from which the air has been exhausted.
The value of the dynamo machines and the conducting wires
is not in gain of power, but in the distribution of power. The
heat energy which drives a great engine may through the dynamo
and conducting wires be distributed to hundreds of motors in
different parts of a city, to hundreds of arc lamps or thousands
of incandescents.
The power of falling water, as at Niagara Falls, may be trans-
formed through turbine wheels and dynamos into electric energy,
which may be transferred through long distances, even as far as
Buffalo, and then through motors be transformed to light or
mechanical work. In this way water power becomes as available
as steam power, and much cheaper.
The dynamo is also used in charging storage batteries, A
LESSONS IN PHYSICS. 99
storage battery consists of two lead plates, which have been
coated with the red oxide of lead, and these with a layer of paper
or cloth between them suspended in dilute sulphuric acid. When
these plates are connected with the terminals of a dynamo, a
portion of the water is decomposed, the lead oxide of the posi-
tive pole is peroxidized, and that of the negative pole reduced
to metallic lead of a spongy form. The electrical energy has been
transformed into chemical energy. The plates will remain in
this condition for several days if the circuit is left open, and may
be transported for long distances and used as ordinary voltaic
cells are used. They are used for moving cars, boats, wagons, etc.
The principles just given enable us to explain the action of the
Bell Telephone. It consists of a permanent bar magnet with a
coil of wire about one of its poles; a thin disk of sheet iron,
called a diaphragm, very near but not touching the pole of the
magnet ; two wires, one leading from the coil to the second in-
strument, the other to the earth. At the other end of the line is
a second instrument of the same kind. The speaker puts his lips
to the mouth of the instrument and speaks, while the listener at
the other end hears what is said. The air waves of the voices
vibrate the diaphragm of soft iron ; these motions to and from
the pole of the magnet strengthen or weaken the magnetism, and
this sends electric pulses through the wire to the distant station ;
the electric pulses from the transmitting telephone act through
the coil of the receiving telephone at the other end of the line,
and alternately strengthen and weaken its magnetism, and as
the strength of the magnet varies the thin disk springs back and
forth. These vibrations of the disk produce air waves, which
enter the ear of the listener. Vibrations in the disk of the re-
ceiving instrument are the same as those of the disk in the trans-
mitting instrument, and the air waves formed by the disk in the
receiving instrument are the same as those which caused the
vibrations of the disk in the transmitting instrument; and the
two sets of air waves will affect the ear in exactly the same way,
so that the voice at the transmitting instrument is reproduced in
the receiving instrument; hence by the telephone sound waves
100 PRACTICAL LESSONS IN SCIENCE.
are converted into electric pulses in the transmitter, and these
electric pulses reaching the receiver are converted back again
into sound waves.
The Telautograph is an electrical instrument by which writing
or drawing may be reproduced at a distant station. "A common
lead pencil is used to write the message; near its point are fast-
ened at right angles to each other, two silk cords, which, con-
necting with the instrument, follow the motion of the pencil and
control the receiving pencil at the other end."
"At the receiving station two aluminium arms hold the ca-
pillary glass tube which serves as a pen. This pen is guided by
the electrical impulse from the sender, and moves simultaneously
and in like direction and extent with every motion of the distant
pencil, so that the ink tracing which results must be a fac-simile
of whatever the sender writes or draws." It conveys a written
message, as the telephone conveys a spoken message.
A piece of No. 30 copper wire about 9.7 feet long has a resist-
ance of one ohm, and is used as a unit in measuring the resistance
of wires to the passage of electricity. The difference in potentials
is measured in volts, and the unit of current strength is the
ampere, but these units are not as definite as the ohm. Many
other interesting subjects might be discussed under the head of
physics, but the subjects considered seem to be sufficient for the
development of the general principles of this branch of science
and for the illustration of their more important applications.
CHAPTER XII.
CHEMISTRY HISTORICAL AND GENERAL.
CHEMISTRY is a branch of natural science which has always
been of great interest to mankind. There is ample evidence to
show that even before historic times men were able to extract
several of the useful metals from their ores, knew something of
the processes of tanning, dyeing, soap making and glass making;
could mix mortar and paints, and do many other things which
indicate considerable knowledge of practical chemistry.
But these ancient people do not seem to have had any knowl-
edge of the laws of chemical changes or any definite idea of the
chemical elements. In the time of Aristotle, 350 B.C., the four
elements were fire, hot and dry, air, hot and wet, earth, cold
and dry, and water, cold and wet. The qualities mentioned are
physical, not chemical. The elements, according to the Hindoos,
were earth, air, fire, water and ether. Among the Chinese they
were earth, fire, water, metal and wood; but in no case do the
ancients seem to have recognized chemical qualities.
The first mention of chemistry is found in a dictionary of the
llth century, where it is defined as the preparation of silver and
gold. In the 16th century Paracelsus says the true use of chem-
istry is not to make gold but to prepare medicines. In the works
of Glauber (1604-1668) he speaks of various compounds of iron
and copper, and of sulphuric, nitric, and hydrochloric acids, but
gives no idea of their composition. He also states that salt and
mercury are the principles of all metals, and that salt is the
origin of all things, and that water and earth have produced all
the minerals and metals.
Georg E. Stahl (1660-1734), whose researches gave rise to a
marked advance in chemistry, enumerated four elements, water,
acid, earth, and phlogiston. Phlogiston was supposed to be a
constituent of all combustible bodies, and it was believed that
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102 PRACTICAL LESSONS IN SCIENCE.
when bodies burned the phlogiston made its escape, and the resi-
due was regarded as the substance with which the phlogiston
had been combined. The British chemist, Black, about 1750,
began to use the balance as an aid in chemical investigation.
About 1774 Dr. Joseph Priestly discovered and isolated
oxygen, but called it dephlogistigated air. Scheele, a Swedish
chemist, discovered oxygen the next year, and the French chem-
ist, Lavoisier, claimed to have discovered the same gas independ-
ently of the others. He at least understood the nature of the
gas better than the others, and in 1781 gave it its present name,
oxygen, " acid-former," as he had recognized that it was an
essential ingredient in several important acids. Lavoisier pointed
out the fallacies of the phlogiston theory, and gave the received
explanation of combustion. He also introduced system into
chemistry and chemical research, and by many is called the
father of modern chemistry.
The discovery of oxygen has been called the capital discovery
of the last century, rivaling in importance the great discovery
of Newton in the previous one. It formed one of the great eras
in human progress. It resulted in gradually putting away old
and fanciful theories, the outgrowth of limited knowledge, and
laid the foundation of modern chemical science. It opened a
way to a knowledge of the composition of the air and of water,
of plants and animals. It may be said to have changed the
manners, customs and business habits of the world. More than
anything else it has explained the phenomena and opened up
the resources of the material universe.
The introduction of instruments for weighing has been of im-
mense value in chemical science, even rivaling the discovery of
oxygen. One of the greatest discoveries of modern times is the
truth that nature works with the same exactness on the small
scale as on the large. It is the glory of Newton to have proved
that the movements of all celestial and terrestrial bodies are
regulated by mathematical law. "It has been established by
chemists that the minutest particles of matter, in their actions
and reactions, obey law, and that every chemical compound has
LPJSSONS IN CHEMISTRY. 103
a mathematical constitution as fixed as that of the solar system
itself. The stones and soil beneath our feet, and the ponderous
mountains, are not mere confused masses of matter; they are
pervaded throughout their innermost constitution by the har-
mony of numbers, The fuel we burn wastes away before us, dis-
solves in air, and passes beyond the reach of sight ; but the in-
visible changes among the unseen particles are definite, exact,
and harmonious. And so it is with all chemical mutations." It
was found that, however often matter might change its form,
nothing was either gained or lost that its quantity always re-
mained the same ; and it was likewise discovered that the con-
stituents of chemical compounds are always combined in the
same definite proportions.
Chemistry deals with those phenomena of matter and energy
which involves some change in the composition of bodies. The
combination of two or more simple substances into one substance
possessing properties different from those of either of the compo-
nents is a chemical process. If we mix carefully powdered sulphur
and copper filings, they remain sulphur and copper and may be
separated ; but if they are heated strongly the sulphur combines
with the copper forming a compound which shows none of the
peculiar properties either of copper or sulphur. This illustrates
something of the difference between a physical mixture and a
chemical combination. The liquid, water, may be separated into
the gases oxygen and hydrogen. A piece of wood is composed
mainly of the gases, oxygen and hydrogen, and the solid, carbon.
When wood is burned, oxygen of the wood and of the air unites
with the hydrogen forming steam, which may be condensed into
water. Other portions of oxygen unite with some of the carbon
forming carbonic acid gas ; some of the carbon may be left as
charcoal; some, very finely divided, may be carried away with
the steam, making a black smoke from which the carbon may be
collected as soot; and in the ash are several mineral ingredients
which existed in small quantities in the wood. The various
reactions which take place in all kinds of combustion, whether
alow or rapid, are chemical changes.
104 PRACTICAL LESSONS IN SCIENCE.
Another difference between a physical mixture and a chemical
combination is that the former may consist of any possible
proportion of the ingredients, while in the case of chemical com-
binations the proportions are definite. Take the case of sulphur
and iron; they may be mixed in any proportion, but they com-
bine in the proportion of 56 parts of iron to 32 parts of sulphur.
If there is either too much sulphur or too much iron, the surplus
does not enter into the combination. In the case of oxygen and
sulphur the proportion of the chemical combination is 32 of oxy-
gen and 32 of sulphur. Experiments with many substances have
led chemists to the conclusion that chemical combinations always
occur between definite weights of substances. In some cases the
weight of a substance may vary in different combinations, but in
every such case some number can be found which shall express
the combining weight, or the weight will be some simple multiple
of that number.
Some of the ancients considered matter as made up of atoms,
but the idea was never more than a speculation. And when it
had been proved that chemical combinations were in definite
proportions, the old idea of atoms assumed a different position.
Dr. Dalton, who, early in this century, discovered and announced
the law of definite and multiple proportions, saw that the con-
ception that matter is made up of indivisible particles or atoms
might have some connection with this law. As a result of his
studies he conceived that the law might be explained by assum-
ing that all matter consists of indivisible, unchangeable par-
ticles, or atoms; that atoms of the same kind have the same
weight, while those of different kinds have different weights, and
that the combining weights of chemistry represent these atomic
weights. The supposition is that atoms of iron and atoms of
sulphur unite to form molecules of the compound substance,
sulphide of iron, so of the oxygen and sulphur, and other chem-
ical combinations. Atoms are considered the units of simple
substances or elements, and molecules, made up of atoms, are
the units of compound substances. The artomic theory, and the
law of definite and multiple proportions in chemical combinations
LESSONS IN CHEMISTRY. 105
may not be at once apprehended, but they underlie the whole
work of chemistry and will become clearer and more satisfactory
with every step of chemical investigation.
Chemists have discovered and isolated some seventy or more
elements which make up the earth as we know it. The composi-
tion by weight, of the crust of the earth is as follows : Oxygen
45 per cent., silicon 25 per cent., aluminium 9 per cent., iron
8 per cent., calcium 5 per cent., magnesium 2 per cent., so-
dium 2 per cent., potassium 2 per cent. If we add to these
elements hydrogen, nitrogen, carbon, chlorine, iodine, phos-
phorus and sulphur we not only have those that make up the
solid crust of the earth, but the constituents of the air, water,
plants and animals as well, fifteen elements which those must
study who pursue chemistry as a branch of general education,
since a knowledge of their properties is essential to the expla-
nation of those chemical changes which are common about us
everywhere. Several other elements are interesting and will re-
ceive brief consideration. It is the study of the laws in accord-
ance with which the elements combine with one another, and of
the properties of the elements and of the compounds formed by
them, which constitutes the science of chemistry.
The elements are divided into metallic elements, as iron, copper,
aluminium, sodium, mercury, etc., and non-metallic elements, as
oxygen, hydrogen, nitrogen, silicon, etc. The metals generally are
better reflectors of light and heat, better conductors of heat and
electricity, and as a rule have a higher specific gravity than the
non-metals. All these elements are designated by symbols, which
usually consist of the initial letter of the English or Latin name
of the element, as for oxygen, C for carbon, Si for silicon, Cl
for chlorine, Fe for iron, from its Latin name ferrum; Na for
sodium, from its Latin name natrium; K for potassium, from
its Latin name kalium ; Ca for lime, from calcium, its Latin
name. The symbols for other elements will be given as they are
described. The various sub-groups into which the elements seem
to be naturally divided can be more intelligently considered as
the elements are studied more in detail.
CHAPTER XIII.
OXYGEN, HYDROGEN AND WATER.
OXYGEN is a colorless, odorless, tasteless gas that constitutes
nearly one-half the weight of the solid crust of the earth, eight-
ninths of the water, one-fifth of the air, and enters largely into
the composition of all vegetable and animal bodies. Its symbol
is 0, and its combining weight 16. While it is so abundant, so
important in every way, it was not known, or isolated so that
its properties could be studied until the year 1774. Its discovery
marks an era not only in the growth of chemical science, but in
the progress of human affairs.
Oxygen may be prepared by heating crystals of potassium
chlorate in a test tube over a spirit flame; it soon melts into a
clear liquid which presently begins to boil from the escaping
bubbles of gas. That the gas is oxygen may be shown by
thrusting into the tube a stick whose end is a glowing coal, when
it will burst into flame, burning with great vigor. Any substance
that burns in air burns much more rapidly in oxygen. Take a
piece of wire and wind about one end of it a piece of twine
and soak the twine in melted sulphur, then ignite the sulphur
and thrust the wire into a jar of oxygen, the burning sulphur
ignites the iron, which burns brilliantly as long as the oxygen
lasts.
Another very common method of preparing oxygen in a small
way, is from the red oxide of mercury, which yields, when heated,
the liquid mercury and the gas oxygen. If the oxide be weighed
carefully, and after the decomposition the mercury and the
oxygen are weighed, their weight will be found to be equal to the
original weight of the oxide, which is thus shown to have con-
tained only oxygen and mercury in chemical combination. The
heat applied overcame the force of chemical attraction and the
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LESSONS IN CHEMISTRY. 107
compound was decomposed into its original elements. The red
oxide of mercury is represented in chemistry by the symbol
HgO, which signifies that it is a compound whose molecule con-
tains one atom of mercury and one atom of oxygen, and the
proportion of the components by weight is 200 parts of mercury
and 16 parts of oxygen.
The chemical formula of potassium chlorate from which
oxygen is usually prepared for laboratory purposes is KC10 3 ,
which indicates a compound body whose molecule is com-
posed of one atom of potassium, one atom of chlorine and
three atoms of oxygen; by weight there are 39 parts of
potassium, 35.5 parts of chlorine and 48 (16X3) parts of oxy-
gen. Potassium chlorate however made, wherever found al-
ways contains these substances, and in the proportions named.
The decomposition may be represented by an equation as
KC10 3 , after heating strongly equals KC1, potassium chloride,
+0 8 , the atoms of oxygen. The KC1 a solid, remains in the tube
or retort, and the oxygen is collected in jars over water.
The heat, strong enough to separate all the oxygen from the
original compound, was not sufficient to separate the chlorine
from the potassium. This shows that the attraction of the
potassium for the chlorine is stronger than the attraction of the
two, as combined, for the oxygen, which illustrates the general
fact that the elements differ widely in their attractions for each
other, which is a prominent feature in all chemical reactions.
In preparing oxygen in quantity a glass or metal flask of ap-
propriate size is used, and the gas is collected in jars over water,
or in regular gas receivers. The jars are immersed in water, then
inverted and placed on a perforated shelf so adjusted that the
mouth of the jar will be just below the surface of the water. The
delivery tube conducts the gas under the mouth of the jar, which,
rising through the water crowds it out, occupying its place in the
jar. When wanted for experiment, a piece of glass or board may
be slipped under the mouth of the jar, which may then be in-
verted. As the gas is heavier than air it can be retained in the
jar for some time, even though it be covered loosely.
108 PRACTICAL LESSONS IN SCIENCE.
The most marked characteristic of oxygen is its prompt and
vigorous support of combustion. But combustion, whether slow
or rapid, is a chemical process, and when we remember the wide
dispersion of oxygen, being found in chemical combination every-
where, we judge that it must be an extremely active chemical
agent, and yet at ordinary temperatures its action is by no
means vigorous. But if substances are heated to a greater or
less degree before being brought into contact with oxygen, it
unites promptly with most of the elements, making an endless
variety of compounds.
Sulphur burns in the air; it burns with greater vigor in oxy-
gen than in air. Sulphur has but a slight odor, oxygen has
none; and yet, after burning sulphur, whether in air or oxygen,
a pungent, suffocating odor is present, the odorless sulphur and
oxygen have disappeared and something with a pungent odor
remains. If a piece of charcoal, nearly pure carbon, be ignited
and thrust into a jar of oxygen it burns fiercely for a few moments,
then gradually ceases. Some of the charcoal has disappeared,
the oxygen is gone and in their place is a gas in which the char-
coal will not burn and which quickly extinguishes a lighted candle
thrust into it.
In the first case, the oxygen combined with the sulphur form-
ing a gas whose molecule contains one atom of sulphur and two
atoms of oxygen, its chemical symbol is S0 2 and it is called sul-
phur dioxide. The chemical equation is S + 2 = S0 2 . In the
other case, oxygen united with carbon forming a compound
whose molecule contains one atom of carbon and two atoms of
oxygen called carbon dioxide. The equation is C + 2 = C0 2 . If
we had used phosphorus, only a slight elevation of temperature
would have been necessary to start the chemical action. More
was needed in the case of sulphur, more still in the case of carbon ;
but when started in each case it continued vigorously till the
oxygen was all gone.
As soon as one atom of sulphur or carbon combined with
two atoms of oxygen their activity ceased, their attractive
powers had been satisfied. As these atoms rushed together
LESSONS IN CHEMISTRY. 109
under the action of chemical attraction, the collision gave rise
to the heat and light which attended the action. The heat
and light of chemical action being due in reality to atomic per-
cussion as the hammer and iron become warm from the blows
necessary to shape the iron. As the sulphur and carbon burn in
the air, forming the sulphur dioxide in one case and carbon
dioxide in the other, we have reason to suppose that oxygen
exists abundantly in the air.
Combustion means any chemical action attended by the evolu-
tion of heat, but is usually restricted to the union of oxygen with
other substances which results in the evolution of heat and light.
Substances which unite with oxygen are said to be combustible,
those that do not are incombustible. Most of the elements are
combustible, but the compounds resulting from combustion, as
the sulphur arid carbon dioxides, are incombustible. Chemical
action, or combustion, always produces the same amount of heat
whether the action be rapid or slow. When it is slow the heat
escapes by conduction or otherwise almost as rapidly as it is
formed, so that there is at no time any great intensity of heat and
no light, while if the combustion is rapid the heat becomes intense
and is accompanied with light as well.
. The amount of heat generated by chemical action may be
measured. This is done by causing the action to take place
in such a manner that the heat resulting may, without waste,
be applied to raising the temperature of water. The quantity
of heat is shown by the number of grams of water it will
raise one degree in temperature. From careful experiments in
this direction, it has been shown that the chemical combi-
nation not only contains definite unvarying proportions of
simples, but that in its formation a definite unvarying amount
of heat was generated. Chemical combination and the evolution
of heat represent work done. When the carbon united with the
oxygen forming carbon dioxide, a certain amount of heat was
given off, a definite amount of work was done, and the same
amount of work will be necessary to separate the oxygen from
the carbon as was developed in bringing them together. The law
110 PRACTICAL LESSONS IN SCIENCE.
of conservation of energy holds in chemical as well as in physical
phenomena.
Combustible substances are endowed with potential energy;
they can do work. The carbon of the coal, uniting with oxygen
generates heat which converts the water into steam, whose ex-
pansive force acting through machinery does manifold kinds of
work. The carbon dioxide formed by the respiration of animals
by many kinds of slow combustions has no potential energy,
but plants under the influence of sunlight can separate the carbon
from the oxygen and the carbon stored up in wood, coal, oil, or
gas, has acquired potential energy, can do work. Potential en-
ergy, derived from the sun, stored up in coal, oil and gas, millions
of years ago, is now doing a great part of the work of the world.
This is an interesting illustration of one of the wonderful econo-
mies of nature.
The compounds of oxygen with other elements are called ox-
ides. Thus the union of oxygen and mercury forms mercuric
oxide, composed of one part of mercury to one part of oxygen.
In some compounds, called dioxides, there are two atoms of oxy-
gen, as the carbon dioxide, and sometimes there are trioxides, as
in the case of sulphur. In the case of copper there are two oxides,
whose formula are Cu 2 0,the oxide of copper, or cupric oxide,
and CuO, suboxide of copper, or cuprous oxide.
HYDROGEN is a colorless invisible gas having neither odor nor
taste, and is the lightest substance known. Its symbol is H and
its combining weight I. Its weight is considered as the unit of
the system of combining weights. It has been found free in vol-
canic gases, but usually exists in combinations with other sub-
stances, making up one-ninth of the weight of water, and forming
a constituent part of all vegetable and animal bodies. Hydro-
gen is in many respects the most interesting of all the elements.
It unites with oxygen to form water, and by the decomposition
of water we may obtain both of these gases.
Water may be decomposed by the voltaic current, oxygen be-
ing given off at the positive pole and hydrogen at the negative.
LESSONS IN CHEMISTRY. Ill
Some of the metals decompose water. Throw a small piece
of the metal potassium on water ; it takes fire, burning with a
fine violet flame floating about as a melted globule on the sur-
face of the water. The potassium unites with the oxygen in the
water, and the heat generated is intense enough to ignite the
hydrogen which has been set free, and is also sufficient to
vaporize some of the potassium which gives the violet color to
the flame.
The metal sodium behaves much like potassium, only that the
heat is not quite sufficient to ignite the hydrogen. These experi-
ments are interesting, but for preparing hydrogen in quantity, a
simple process consists in passing steam over red-hot iron. The
iron combines with oxygen of the water, forming the black oxide
of iron (Fe 3 4 ) the hydrogen passes on and is collected in jars over
water. The equation is as follows : 4H 2 0, steam -f- Fe 3 = Fe 3 4 ,
oxide of iron -f H 8 . While the decomposition of water by po-
tassium and sodium at ordinary temperatures is prompt and
spontaneous, iron must be heated to a red heat before it can sep-
arate oxygen from hydrogen.
The most convenient method of preparing hydrogen for use
is by treating a metal, as zinc, with a strong acid. Put two
or three pieces of granulated zinc into a test tube and pour
upon them some dilute sulphuric acid. A brisk action takes
place immediately, gas being given off in abundance. After
the action has continued for a few moments, bring a lighted
match to the mouth of the tube and the gas takes fire with a
slight explosion, burning with a pale flame. In preparing the
gas in a larger way, use a wide-mouthed bottle with a cork hav-
ing two holes ; through one of these pass a glass funnel whose
stem is long enough to reach nearly to the bottom of the bottle;
through the other hole pass the delivery tube. Use zinc and acid
as before, being sure that the funnel tube extends below the sur-
face of the acid in the bottle. After the chemical action has con-
tinued long enough so that all of the air has been driven out of
the bottle, the gas may be collected over water as in the case of
oxygen. Acid may be added through the funnel if the action
112 PRACTICAL LESSONS IN SCIENCE.
becomes too weak. Care should be taken to see that the bottle
is closely corked so that the gas shall be free from air, as hy-
drogen with a little air makes an explosive mixture of great
vigor.
The chemical equation in the preparation of hydrogen by this
method is as follows : Zn, Zinc-f-H 2 S0 4 , sulphuric acid ZnS0 4 , zinc
sulphate +2H, that is one atom of zinc has taken the place of two
atoms of hydrogen, forming zinc sulphate and free hydrogen.
Hydrogen may be kept in an inverted jar for some time, but
quickly escapes from one that is upright. It can be poured up
but not down. Hydrogen or some of its compounds is used for
filling balloons. It is combustible, but must be heated up to the
kindling temperature when it unites vigorously with oxygen. The
temperature of the hydrogen flame is higher than that of any
other flame known. The oxyhydrogen flame, while giving very
intense heat gives but little light. But if a cylinder of lime be
put in the focus of this flame, it is soon heated to incandes-
cence and gives out a light second only to that developed by
electricity.
Oxygen and hydrogen combined form water, whose molecule
is composed of one atom of oxygen and two of hydrogen ; for-
mula H 2 0. Two volumes of hydrogen combined with one volume
of oxygen forming two volumes of water vapor or steam.
Water can be produced from a mixture of oxygen and hydro-
gen. If we introduce into a stout test tube a mixture of two
volumes of hydrogen and one of oxygen, on touching a lighted
match to the mixed gas it explodes, the hydrogen burning rap-
idly, so that a flash of flame fills the tube. After the explosion
water will be found deposited as dew on the sides of the tube. In
this experiment there is no attempt to measure the waterformed,
but careful experiments show that all the oxygen unites with all
of the hydrogen, forming the corresponding amount of water
vapor or steam.
In the decomposition of water by the voltaic current the
volume of the hydrogen is double that of the oxygen, and that
experiment seems to show that water contains only oxygen and
LESSONS IN CHEMISTRY. 113
hydrogen in its composition. Pure water has been decomposed
by the action of several different metals and by the electric
spark. It has been analyzed and found to contain only the gases
oxygen and hydrogen.
Pure water at ordinary temperature is a clear transparent
liquid, tasteless, odorless and neutral in its reactions. It is es-
sential to the life of plants and animals, forming the chief in-
gredient of all the liquids they contain. It is the standard for
obtaining the specific gravity of solids and liquids. It is the
standard for the measurement of specific heat. It is an abundant
ingredient of many rocks. Its presence or absence determines
whether a region shall be a barren waste or a teeming garden. As
a chemical compound, the combining tendencies of water extend
over a wider range than those of any other compound. Its com-
binations with other substances are usually called hydrates.
Water combines with the elements bromine and chlorine, forming
an exception to the general rule that combinations do not take
place between elementary and compound bodies. Water dis-
solves more substances than any other liquid known, so that in
nature pure water is seldom or never seen. But it may be easily
purified by filtration and distillation.
The purest water in nature is rain water, which falls after it has
rained for some time. During the first part of the storm the rain
washes dust and impurities out of the air, so that later the water
is nearly pure. Large quantities of natural waters contain car-
bonate of lime in solution, and are called hard waters, forming
deposits on the inside of boilers and kettles. Others contain iron,
salt, soda and other minerals, some of which are of medicinal value.
The solvent power of water is of great value in chemical operations,
as well as in the operations of nature. In some cases substances
which do not act upon one another when dry act promptly when
in solution, the particles come into more intimate contact and
chemical action seems to be facilitated. In solutions the particles
of the dissolving liquid seems to have some attraction for the
particles of the dissolved substances so that they are uniformly
distributed through the solution, but this attracting power may
L.S. 8
114 PRACTICAL LESSONS IN SCIENCE.
be saturated, and any amount added beyond this limit gradually
settles to the bottom of the solution.
Oxygen and hydrogen, whether free or combined as water, are
the most important and interesting substances within the do-
main of chemistry. They are alike in most of their physical
qualities, but differ widely in their chemical properties. Oxygen
combines with many substances with which hydrogen does not
combine, while hydrogen combines with some substances which
do not readily combine with oxygen, but under favorable condi-
tions they combine with each other. In fact, in this case and in
many others, unlike elements combine more freely than those
which have many properties in common.
CHAPTER XIV.
NITROGEN, THE AIR, AMMONIA AND NITRIC ACID.
THE air, an invisible, tasteless, odorless gas surrounds us every-
where. In motion it is wind, from which we may recognize not
only the existence of the air but something of its power as well.
It has weight, as shown by the action of the common pump and
mercurial barometer.
The air contains oxygen as shown by the fact that the same
products arise from burning sulphur, carbon and other sub-
stances in the air, that arise from burning those substances in
oxygen. But combustion in the air is not as prompt and vig-
orous as it is in oxygen, so that the oxygen of the air seems to be in
a sense diluted. On a broad piece of cork, or bit of board, fasten a
porcelain, crucible or a piece of earthenware; place it on the surface
of water; put on the porcelain a piece of phosphorus about the
size of a pea and set fire to it, then invert a jar over the burning
phosphorus, at first the heat of combustion may drive out a
few bubbles of air, but soon the water will rise in the jar, taking
the place of oxygen used in the combustion. The white clouds
which fill the jar at first is oxide of phosphorus, which the
water at length absorbs, and a transparent, tasteless, odorless
gas remains, but does not fill the jar. If we measure the jar
carefully it will be found that water occupies about one-fifth of
its capacity, the gas occupying the balance.
This gas is called Nitrogen, its symbol is N, and its combining
weight 14. If an experiment is carefully performed it will show
that the air is composed of about 21 per cent, of oxygen to 79
per cent, of nitrogen. Close the jar and invert it, then lower into
it a lighted candle and it is extinguished. Confine in it a mouse
or a bird and it dies ; the gas will not support combustion, it will
not support life. Nitrogen is prepared in quantity by passing
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116 PRACTICAL LESSONS IN SCIENCE.
air over red-hot copper, the oxygen combines with the copper
forming copper oxide, leaving the nitrogen free. Oxygen enters
into many combinations, and compounds of oxygen are gener-
ally stable, while nitrogen enters into comparatively few combi-
nations and they are generally unstable, breaking up under the
least provocation.
Besides occurring in the air nitrogen is an essential ingredient
of animal and vegetable substances, and is an important ingredi-
ent in many other interesting compounds. Besides the oxygen
and nitrogen the air always contains more or less water vapor,
carbon dioxide or carbonic acid, ammonia and small quantities
of other gases, and the lower portions are often loaded with
various kinds of dust. The air seems to be simply a mechanical
mixture of these various gases and not a chemical compound.
If the oxygen and nitrogen were in chemical combination we
would expect the proportions by weight to be as 14 of nitrogen
to 16 of oxygen, or in some multiple of those numbers, but the
proportion is as 23.10 of oxygen to 76.90 of nitrogen, and when
these gases are mixed in this proportion, under no circumstances
is there any generation of heat, light or electricity, as occurs in
chemical combinations. As far as known the gases of the air
exist everywhere in uniform proportions. The carbon dioxide
and ammonia are small but important ingredients of the air, as
it is from the air that plants get the greater part of the carbon
dioxide and ammonia necessary to their existence.
Ammonia is a colorless gas, formula NH 3 , composed of one
atom of nitrogen and three atoms of hydrogen. Formerly it
was made from the horns of harts, hence the name spirits of
hartshorn. The chief source of ammonia and ammonium com-
pounds is now the ammoniacal liquors of gas works derived as a
by-product in the distillation of coal. It is greedily absorbed by
water, and a solution of the gas in water is the ammonia of the
shops. This solution has a strong alkaline reaction, turning red
litmus to blue, neutralizing strong acids, forming salts of
ammonium.
In certain compounds a group of nitrogen and hydrogen
LESSONS IN CHEMISTRY. 117
atoms, represented by NH 4 , behave very much like some metals,
as potassium and sodium, and the name of ammonium has been
applied, but no such substance has ever been isolated. Ammo-
nia gas at a temperature of 40 F. becomes a liquid and at
103 it becomes a white crystalline solid. It can be reduced to
a solid by a pressure of about 10 atmospheres. When the pres-
sure is removed it expands into a gas by the action of heat de-
rived from surrounding objects. On this principle machines for
making ice are constructed.
Ammonia and hydrochloric acid, whether as gases or in
solution, unite to form ammonium chloride, a white solid.
If bottles containing the gases in solution be uncorked and
brought near each other, a cloud of the ammonium chloride
will be formed by the volatile gases. The chemical equation is
2NH 3 -f HC1=2NH 4 C1. This compound, called salammoniac, is
found in volcanic regions in considerable quantities.
Pure nitrogen may be prepared from the air, but the com-
pounds of nitrogen have never been prepared successfully from
the nitrogen of the air. It is difficult to cause nitrogen to
combine directly with either hydrogen or oxygen, but through
the action of myriads of minute organisms in some soils, atmos-
pheric nitrogen and decaying nitrogenous matters are trans-
formed into nitrates of lime or potassium.
One of the most important compounds of nitrogen is nitric
acid, whose molecule is composed of one atom of hydrogen with
one atom of nitrogen and three atoms of oxygen. Its symbol is
HN0 3 . It is prepared by the action of sulphuric acid on potas-
sium nitrate or sodium nitrate. The action is as follows:
KN0 3 +H 2 S0 4 =HN0 3 +KHS0 4 . Nitric acid is a colorless, cor-
rosive liquid whose applications in the arts and manufacturing
industries are very extensive.
Dilute nitric acid by adding an equal bulk of water, then add
ammonia water in small quantities from time to time, as long as
the mixture shows an acid reaction. If this mixture be evapo-
rated slowly, a solid substance with many transparent crystals,
called ammonium nitrate, will be formed. This experiment is a
118 PRACTICAL LESSONS IN SCIENCE.
good illustration of what is meant by chemical combinations.
Two liquids of strongly marked qualities, one an acid, one an
alkali, united forming a solid as unlike its constituents as could
well be imagined. Neither acid nor alkaline, neither sour nor
bitter, and with but slight odor. The chemical equation is
NH 3 +HN0 3 =NH 4 N0 3 .
If the ammonium nitrate obtained above be heated moder-
ately, it melts and a colorless gas is given off which supports
combustion almost as vigorously as oxygen. The equation is,
NH 4 N0 3 ==2H 2 0-f N 2 0. This gas, the sub-oxide of nitrogen or ni-
trous oxide, is the laughing gas used by dentists as an anaesthetic.
The several compounds of oxygen and nitrogen that occur are
of little value beyond illustrating the law of multiple propor-
tions. They are the nitrous oxide, N 2 0; nitric oxide, NO;
nitrous anhydride, N 2 3 ; nitrogen peroxide, N0 2 ; and nitric
anhydride, N 2 5 . An anhydride is an oxide which combined with
water, forms an acid, as nitrous anhydride N 2 3 fH 2 2HN0 2 ,
nitrous acid; and nitric anhydride N 2 5 4-H 2 O=2HN0 3 nitric
acid.
Acids are composed of hydrogen and some other non-metallic
element, and in most cases they contain oxygen, as hydrochloric
acid, composed of hydrogen and chlorine, formula HC1, nitric
acid, composed of hydrogen, nitrogen and three atoms of oxy-
gen, formula HN0 3 , and sulphuric acid composed of hydrogen,
sulphur and oxygen, formula H 2 S0 4 . Acids usually have a sour
taste, turn vegetable blue colors to red and are often poisonous.
The combination of a metal with hydrogen and oxygen, non-
metals, forms a compound called a base, as sodium hydroxide
composed of sodium, hydrogen and oxygen, formula NaHO, called
caustic soda, as potassium hydroxide, composed of potassium,
hydrogen and oxygen, formula KHO, called caustic potash, and
as calcium hydroxide, formula Ca0 2 H 2 , called caustic lime. The
bases are sometimes bitter corrosive poisons, turning red colors
to blue, but generally they are mild compounds.
The customary method of testing a substance for acid or
basic reaction is by the use of paper colored by the dye litmus.
LESSONS IN CHEMISTRY. 119
Acids change litmus blue to red, while a basic solution changes
the red to blue again.
When a base and an acid are mixed in solution they neutralize
or change the properties of each other, forming water and a com-
pound called 3, salt. If we mingle hydrochloric acid and sodium
hydroxide the salt, sodium chloride will be formed, together with
one molecule of water, according to the following equation, HC1
-j-NaHO=NaCl, common salt,-hH 2 0. The hydrogen of the acid
exchanges places with the metal of the base, as shown in the
equation. The following equation shows the same exchange.
Sulphuric acid, H 2 S0 4 -f-2NaHO, sodium hydroxide, Na 2 S0 4 ,
sodium sulphate, H-2H 2 0.
The names of the stronger acids end in ic, as nitric, sulphuric
and hydrochloric. If an acid containing the same elements has
a less proportion of oxygen the name ends in ous, as nitrous
acid, sulphurous acid. In the case of acids of which chlorine is
a distinguishing element we have a hypo or subchlorous acid
and a perchloric acid; the former contains less oxygen than
the ous acid, the latter more than the ic acid.
The bases are metallic hydroxides, and the metal of the com-
pound is the distinguishing part of the name, as sodium hydrox-
ide, potassium hydroxide and calcium hydroxide. Such com-
pounds are sometimes called hydrates, as they may have been
formed by the metal replacing one atom of hydrogen in water, as
H 2 0+K KOH-f-H, one atom of free hydrogen.
Salts are named from the acids forming them, as nitrates,
sulphates, chlorates, etc., and they are further distinguished by
the name of the metal of the base, as potassium nitrate, sodium
sulphate, etc. The salts formed by nitrous acid are called nitrites
and those by sulphurous acid are called sulphites, etc. If the
name of the acid ends in ic, the name of the salt ends in ate, if the
name of the acid ends in ous, the name of the salt ends in ite. The
reciprocal action of chemical agents, as in the case of an acid and
a base, or the action of some form of energy causing chemical
changes, is called a reaction, and a substance capable of producing
with another substance a chemical reaction is called a reagent.
CHAPTER XV.
CHLORINE, BROMINE AND IODINE.
CHLORINE is a greenish yellow gas, never found free in nature,
but existing in great quantities as an ingredient of common salt.
It also occurs in combination with potassium, magnesium and
silver. Its formula is Cl and combining weight 35.5. If common
salt be mixed with sulphuric acid and heated, a transparent in-
tensely acid gas will be given off, which must be collected over
mercury, as water absorbs it greedily. The sodium of the com-
mon salt and hydrogen of the sulphuric acid change places and
the acid is formed, which, dissolved in water, is the hydrochloric
acid of commerce. The equation is common salt, 2NaCl-KH 2 S0 4
=Na 2 S0 4 , sodium sulphate, -+-2HC1, hydrochloric acid.
This acid is one of the most useful agents in the chemical labor-
atory, and is extensively used in manufacturing industries. As
an acid it forms the class of salts called chlorides, as sodium chlo-
ride, or common salt. A mixture of hydrochloric and nitric acids,
called aqua regia, is the only solvent for gold, the acids decom-
pose each other, and the chlorine, when set free, attacks the gold.
If hydrochloric acid be well mixed with the binoxide of man-
ganese, and the mixture heated gradually, chlorine gas will be
set free. As it is heavier than air it may be collected in an open
jar by carrying a delivery tube to the bottom of the jar, its
color enabling one to see when it has filled the jar. The equa-
tion is, Mn0 2 +4HCl=MNCl 2 -f 2H 2 0+2C1. Chlorine is usually pre-
pared by heating a mixture of common salt, oxide of manganese
and sulphuric acid.
Chlorine combines readily with many elements and decom-
poses many compounds from its strong affinity for hydrogen.
If a piece of paper, soaked in oil of turpentine that has been
slightly warmed, be dropped into a jar of chlorine there will be
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LESSONS IN CHEMISTRY. 121
a flash of flame, followed by a dense black smoke; the turpen-
tine is composed mainly of hydrogen and carbon, the chlorine
uniting with the hydrogen leaves the carbon free, which helps to
form the dense black smoke.
Chlorine is a powerful bleaching agent. Pieces of calico or
other colored fabrics placed in chlorine gas, if dry, will remain
unchanged for some time, but when moistened the color will in
most cases disappear promptly. Some of the hydrogen is taken
from the coloring matter and oxygen set free, which doubtless
assists in decomposing the compounds which constitute the color,
but the action must not be allowed to continue long or the
fabric itself will be destroyed by the chlorine.
For bleaching purposes chlorine is usually prepared from cal-
cium chloride, which readily gives off chlorine when acted on by
dilute sulphuric acid. An interesting experiment illustrating
the difference in specific gravity between chlorine and air may be
shown with the chloride of lime. On the bottom of a glass jar or
wide-mouthed bottle place a much smaller bottle containing some
bleaching-powder, add a little sulphuric acid, diluted by an equal
bulk of water and partly cover the larger bottle with a piece of
glass or pasteboard. Chlorine gas will be set free, will gradually
fill the smaller bottle, and failing over the sides to the bottom of
the larger one will gradually crowd out the air till it fills the bottle.
With a small bottle as a dipper the gas may be dipped out and
poured into other jars. Care should be taken not to breathe
the gas.
Hydrogen is an important ingredient in many unpleasant, un-
healthful odors, and the strong affinity of chlorine for hydrogen
makes it a valuable disinfecting agent in such cases. It removes
the hydrogen, breaking up the compounds, and the oxygen set
free oxidizes or burns other parts into harmless compounds.
Chlorine combines with hydrogen even more promptly than oxy-
gen does. If hydrogen and oxygen be mixed in the proper pro-
portion for water, they will not combine except by the aid of heat,
as the electric spark. While if hydrogen and chlorine be mixed
in the same way the combination takes place with explosive vio-
122 PRACTICAL LESSONS IN SCIENCE.
lence under the influence of direct sunlight, taking place slowly
and quietly in moderately strong, diffused light. The action of
sunlight in this and other cases of chemical action, as in photog-
raphy, is not well understood. It does not seem to be the heat,
as even a higher degree of heat without light has no such effect.
Compounds of oxygen with elements are called oxides, the com-
pounds of chlorine with elements are called chlorides.
Chlorine combines energetically with bromine, iodine, sulphur,
phosphorus and arsenic, and with most of the metals also, mak-
ing it the rival of oxygen in the extent of its combinations. Chlo-
rine forms several interesting compounds with hydrogen and
oxygen. They are, hypochlorous acid, HC10; chlorous acid,
HC10 2 ; chloric acid, HC10 3 ; perchloric acid, HC10 4 .
The chloric and hypochlorous acid are the most important,
but the whole series is interesting as illustrating the law of mul-
tiple proportions. Chloric acid may be prepared by treating po-
tassium chlorate with sulphuric acid. The reactions are as
follows : 2KC10 3 +H 2 S0 4 =K 2 S0 4 +2HC10 3 . The potassium tak-
ing the place of the hydrogen in the sulphuric acid forms po-
tassium sulphate, and the hydrogen with the chlorine and
oxygen forms the chloric acid. The chloric and hypochloroun
acids form salts as the calcium hypochlorite, usually called
chloride of lime, or bleaching powder, and the potassium chlorate.
These compounds of hydrogen, chlorine and oxygen are not very
stable. The affinity with oxygen is not strong.
In considering the composition of hydrochloric acid it is found
that one volume of hydrogen unites with one volume of chlorine
to form two volumes of hydrochloric-acid gas. In the compo-
sition of water, two volumes of hydrogen combine with one
volume of oxygen forming two volumes of water-vapor. In the
case of ammonia, three volumes of hydrogen combined with one
of nitrogen to form two volumes of ammonia, and in marsh gas
we have four volumes of hydrogen combined with one of carbon
into two volumes of marsh gas.
These facts were discovered and have been abundantly verified
by experiment ; but how are they explained ? Dr. Dalton formu-
LESSONS IN CHEMISTRY. 123
lated the atomic theory. Avogadro, after a careful study of
gases, formulated this theory, that equal volumes of all gases,
whether simple or compound, under the same conditions of tem-
perature and pressure, contain the same number of molecules.
Elements differ in their chemical combinations, as HC1, hydro-
chloric acid, H 2 water, NH 3 ammonia, CH 4 marsh gas. The
atom of chlorine can hold one atom of hydrogen, the atom
of oxygen holds two, the atom of nitrogen three and the
atom of carbon four. On examination it is found that a sim-
ilar difference occurs among other elements. An element, whose
atom can hold only one other atom is called univalent, as
hydrogen and chlorine. An element whose atom can hold two
others in union is called a bivalent, as oxygen and mercury. An
element whose atom can hold three atoms in combination is
called trivalent, as nitrogen and antimony, and one that can
hold four is called quadrivalent, as carbon and tin. In the forma-
tion of salts elements of the same valence replace each other, as
in the formation of potassium, nitrate, the univalent potassium
replaces the hydrogen in HNO and the compound becomes KNO.
In the case of potassium sulphate two atoms of the univalent
metal replace the two atoms of hydrogen and H 2 S0 4 becomes
K 2 S0 4 . In zinc sulphate one atom of zinc, a bivalent metal, re-
places the two atoms of hydrogen and H 2 S0 4 becomes ZnSO 4
sulphate of zinc. From the foregoing data we may form a theory
for the peculiarities of combination by volume.
If we suppose our unit volume to contain 1,000 molecules then,
according to the law of Avogadro, one volume of hydrogen con-
taining 1,000 molecules unites with one volume of chlorine con-
taining 1,000 molecules forming two volumes of hydrochloric-acid
gas containing 2,000 molecules. But each molecule of the hydro-
chloric acid contains two atoms, and in the two volumes there
must be 4,000 atoms. From this we judge that the molecules of
hydrogen and chlorine are each made up of two atoms. In the
case of water we have two volumes of hydrogen containing 2, 000
molecules or 4,000 atoms, combining with one volume of oxygen
containing 1,000 molecules or two thousand atoms, forming
124 PRACTICAL LESSONS IN SCIENCE.
two volumes of water vapor, containing 2,000 molecules or 6, 000
atoms. The two-atom molecules of hydrogen and oxygen were
rearranged into three-atom molecules of water vapor, diminish-
ing the bulk by one-third. With ammonia the case is similar, one
volume of nitrogen containing 1,000 molecules or 2,000 atoms,
unites with three volumes of hydrogen containing 3,000 mole-
cules or 6,000 atoms, forming two volumes of ammonia, con-
taining 2,000 molecules with 8,000 atoms. The two-atom
molecules were broken up and rearranged into four-atom mole-
cules and the volume diminished by one-half. Thus the atomic
theory, Avogadro's principle, the theory of valence and the
phenomena of combination by volume, all seem to harmonize
with the facts of definite and multiple proportions in chemical
combinations, and to sustain and mutually verify each other.
The law of definite proportions has been demonstrated, the
others are still theories.
It has been found that elements at the instant they are set
free from compounds are much more active and can effect
changes which they cannot effect under other circumstances.
Hydrogen gas passed into nitric acid causes no change, but
hydrogen liberated in direct contact with nitric acid reduces the
acid and forms the lower oxides of nitrogen. Examples of simi-
lar action are of frequent occurrence. An element at the instant
of its liberation is said to be in the nascent state or atomic state
when it seems to be more active than after the atoms have com-
bined into molecules.
BROMINE (Br) is a dark brown liquid heavier than water having
an irritating disagreeable odor, hence the name, meaning a stench.
It is the only non-metal which is a liquid at ordinary tempera-
tures. It occurs in seawater and other natural brines, as
magnesium bromide, which is the main source of the bromine of
commerce. It is generally obtained from bittern, the residue
which remains after sodium chloride has been crystallized out
from the natural brines. Bromine forms compounds with hydro-
gen and oxygen, which are analogous to those of chlorine, and in
physical and chemical properties is somewhat similar to that
LESSONS IN CHEMISTRY. 125
element. Some compounds of bromine are used as bleaching and
disinfecting agents. Some are used in photography, and bromide
of potassium is used extensively in medicine.
IODINE (I) is also found in seawater. Certain varieties of sea-
weed separate the sodium iodide from the seawater and concen-
trate it in their tissues. The seaweed is collected, dried and
burned. The ashes and other residue are leached with water,
which dissolves out the sodium iodide, and this solution yields
the iodine of commerce. Iodine is a grayish black crystalline
solid of metallic luster. It melts at 225 F. and boils at 356,
forming a beautiful violet-colored vapor, which is the heaviest
known, being 872 times heavier than air. Drop a piece of iodine
as large as a grain of wheat into a test-tube and apply heat;
observe the vapor, notice the coating it forms on the tube; apply
heat to different parts of the tube and study the effects. Exam-
ine the coating for crystals.
Iodine is soluble in alcohol or ether and is sparingly soluble
in water. Iodine colors starch paste a deep blue ; this reaction
constitutes the most delicate test of its presence. Take a thin
solution of starch paste and add to it a few drops of an aqueous
solution of iodine and notice the color. Dip a piece of white pa-
per in the paste and suspend it while moist in a bottle or jar on
the bottom of which has been placed a small piece of iodine. In
a few moments the paper begins to show a blue color, indicating
that iodine is volatile at ordinary temperatures. Iodine stains
the skin yellow but is not as corrosive as either chlorine or bro-
mine. A solution of iodine in alcohol is familiarly known as
tincture of iodine and much used as a liniment. Iodide of mer-
cury is sometimes used in painting as a pure scarlet; the iodide
of lead has a bright golden color; the iodide of silver is yellow
and the iodide of potassium is white. The iodide of potassium
is extensively used in photography and in medicine.
Iodine combines with hydrogen forming hydriodic acid, a
colorless gas, with a suffocating odor. One part of hydrogen,
weight one, combines with one part of a highly colored iodine
vapor, weight 127, and the one part discharges the color and
126 PRACTICAL LESSONS IN SCIENCE.
changes the properties of the 127 parts forming a colorless
gas, formula HI.
Iodine forms an acid with hydrogen and oxygen called iodic
acid, formula HIO, analogous to chloric and bromic acid.
Chlorine, bromine and iodine constitute a well-defined natural
group of elements. They each unite with hydrogen in the same
proportions, forming acids of similar properties and each form-
ing similar salts. Each of these elements forms a powerful acid
containing three atoms of oxygen. With nitrogen they each form
explosive compounds. At ordinary temperatures chlorine is a
gas, bromine a liquid and iodine a solid. Chlorine is yellow,
bromine reddish-brown and iodine violet. In general chlorine is
more energetic and its compounds more stable, while iodine is
least energetic except in its combinations with oxygen.
FLUORINE is an element, known only in its compounds, of which
the most common is the mineral fluor spar. It occurs in vegetable
and animal substances and in several other minerals. Fluorine
forms an acid with hydrogen analogous to hydrochloric acid,
which is very corrosive, attacking glass vigorously, so that it
must be collected in lead, rubber, or platinum vessels. It is used
for etching glass. The glass is covered with a thin coat of wax,
and lines or figures are drawn with a pointed instrument so as
to cut through the wax. The glass is then exposed to the action
of the acid, and soon the figures drawn are corroded into the
glass. Fluorine seems to have affinities with the chlorine group
of elements, but so little is known of it that no extensive com-
parison can be made.
CHAPTER XVI.
CARBON, SILICON AND BORON
CARBON (C) is an essential constituent of all animal and vege-
table bodies. It is found in the air, in many kinds of rocks and
soils, and in many natural waters, but is especially the element of
organic bodies. Every living body from the microscopic animal-
cule up to the giant whale, from the tiniest vegetable to the lofty
red- wood contains carbon. It occurs in its purest form in the
crystalline transparent diamond, the hardest substance known.
Another form of nearly pure carbon is graphite, and another
still is common charcoal. Diamonds are found in South America,
South Africa, in the East Indies and in Australia, and to some
extent in other localities. They are usually found in alluvial de-
posits as water-worn pebbles whose crystalline form and trans-
parency have been obscured by abrasions. It is the most beauti-
ful and highly prized of all the gems. It is a powerful refractor of
light, and is sometimes employed in making the lenses of micro-
scopes. Small, dark stones are much used for cutting glass,
drilling gems and in making the cutting edges of core drills. If
heated to a very high temperature in oxygen gas it burns up, the
sole product of the combustion being carbon dioxide.
Graphite, another form of carbon, occurs in great quantities
among the older rocks of Canada and other localities, and is often
associated with iron ores. It sometimes occurs in six-sided plate-
like crystals, while the diamond usually has the form of an octa-
hedron. Graphite has a grayish black color with a metallic
luster ; has an oily feel, and is often used in place of oil to prevent
friction in machinery. Graphite resists a very high degree of
heat, and is used in manufacturing crucibles for melting steel and
other refractory substances. When subjected to a high degree of
heat in oxygen it burns, evolving intense heat nnd light, but the
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128 PRACTICAL LESSONS IN SCIENCE.
sole product, as in the case of the diamond, is carbon dioxide.
Graphite is insoluble and unaffected by moisture or air, and
forms a valuable coating for protecting iron from the effect of the
weather. Its chief use is, perhaps, the manufacture of pencils.
For this purpose it is reduced to a powder and subjected to great
pressure. It is then sawed into little bars which are cased with
wood. A mass of graphite seems soft and friable, but the par-
ticles are extremely hard, and soon wear out the steel saws used
in cutting it into shape.
We know nothing about the formation of diamonds, but
geologists consider graphite to be the residue of some of the
forms of life occupying the earth when the materials of the older
rocks were being deposited .
Another form of nearly pure carbon is charcoal. It is formed
when any organic substance, as wood, sugar, flesh, bone or blood
is burned in a limited supply of air. It is a black, brittle, tasteless,
solid. It is not easily affected by the action of air or water at
ordinary temperatures; charred cloths, grains, fruits, and other
remains of the Lake Dwellers of Switzerland, are as perfect to-day
as when entombed in the mud and waters of the lakes thousands
of years ago. The charcoal of commerce is formed from wood
by burning it in a limited supply of air. Wood is made up
mainly of carbon, oxygen and hydrogen, and when burned in the
open air the oxygen combines with the hydrogen forming water,
and with the carbon forming carbon dioxide until only a few
ashes are left ; but if the supply of oxygen is limited the hydrogen
and part of the carbon are driven off, but the main part of the
carbon remains as charcoal. Charcoal is used as a fuel, burning,
when dry, without flame, yielding a high degree of heat. Burned
in oxygen the sole product is carbon dioxide, as in the case of
diamond and graphite.
Charcoal is very porous, and possesses in a remarkable degree
the power of absorbing gases, some specimens absorbing 90
times their bulk of ammonia, 35 times their bulk of carbon diox-
ide. It is said that freshly burned charcoal will absorb moisture
from the air so as to increase at least 10 per cent, in weight.
LESSONS IN CHEMISTRY. 129
The absorbing properties of charcoal make it a good deodor-
izer and a powerful disinfectant, and it is much used in making
water filters. Charcoal from bones is much used in sugar refin-
eries to decolorize sirups. It destroys bad odors, and discharges
colors, not only by absorbing gases, but the absorbed oxygen
acting chemically on the noxious gases and other substances
changes them to harmless compounds.
Soot is another form of nearly pure carbon. It is carbon which
has been released by heat from its combinations, without being
burned, it helps to form the smoke of combustion. It may be
condensed from the smoke as a fine black powder. It is used for
making printers' ink, black paint, etc. .In the distillation of coal
for the manufacture of illuminating gas, there is deposited on the
inside of the retort a grayish coating called gas carbon. It is
quite as nearly pure carbon as any of the other forms, but
whether it is a variety of graphite, or a fourth form is not
settled. Gas carbon is a good conductor of electricity, and is.
used for electric-lamp carbons and other purposes. Coke and an-
thracite coal are nearly pure carbon. The different kinds of soft
coal and peat all have carbon as the basis of their composition
but associated with various impurities.
All these forms of carbon seem to be the result of the slow
decomposition of organic matter, mainly vegetation, usually
under water, so that the supply of oxygen was limited. This
mass of decomposing matter covered with sand or clay, sub-
jected to pressure and heat, gradually changed into various kinds
of coal and graphite. It seems hardly possible that the black,
brittle, porous charcoal, and the soft compact graphite are chem-
ically identical with the beautiful diamond. They are specimens
of the same element appearing in different or allotropic forms,
and notwithstanding their marked differences, they have well-
marked properties in common. The explanation of these differ-
ent forms of carbon is one of the unsolved problems of chemistry.
Carbon combines freely with oxygen in all forms of combus-
tion and combines also with hydrogen, nitrogen and other ele-
ments. When any of the forms of carbon is burned in oxygen
t S.-9
180 PRACTICAL LESSONS IN SCIENCE.
the product is carbon dioxide, formula C0 2 , one atom of car-
bon uniting with two of oxygen. It is ordinarily prepared by
treating calcium carbonate, limestone, with hydrochloric or some
other strong acid. It may be collected over water, or as it is
much heavier than air it can be collected in an open jar. The
chemical equation is CaC0 3 -f2HCl CaCl 2 -f H 2 0-fC0 2 . Calcium,
a bivalent element, replaces two atoms of hydrogen forming
calcium chloride, the two atoms of hydrogen taking one atom
of oxygen form water setting free (C0 2 ) carbon dioxide, which at
ordinary temperatures is a colorless, tasteless, odorless gas. If
a lighted stick or candle be put into a jar of this gas, it is extin-
guished as promptly as if thrust into water; if a bird or mouse
be confined in it, life is quickly destroyed.
Carbon dioxide will not support combustion, will not sup-
port animal life, and for the same reason that water does not,
they each contain plenty of oxygen, but it is so firmly bound
to the other members of the compound that it cannot be
utilized for the processes of life or combustion. Water and
the dioxide of carbon are cinders, the affinities of the oxygen,
hydrogen and carbon have been satisfied, their energy has been
expended, they are like rocks at the foot of a hill, work must
be done on them before they are in a condition to do any more
work ; and that work must be equal to the work they did as they
clashed together into molecules of water and carbon dioxide.
This gas sometimes accumulates in wells, abandoned mines and
caves. As a test of its presence a lighted candle is lowered into
places where its presence is suspected ; if the light is not extin-
guished or dimmed, the air does not contain a dangerous amount
of the dioxide. Carbon dioxide is a product of respiration. Im-
merse a jar in water and invert it so as to keep the mouth under
water; then through a tube fill the jar with air from the lungs,
displacing the water; cover the mouth of the jar with the hand
or piece of board and place it upright on the table and test the
contents with a lighted candle for carbon dioxide. If the air is
held in the lungs for a little time before being breathed into the
jar the effect will be more marked. This experiment will show
LESSONS IN CHEMISTRY. 181
that air that has been breathed once is not safe for breathing a
second time. But lesser quantities of the dioxide are harmful,
and a more delicate test of its presence is often desirable. Put a
small piece of quick lime into a tumbler or jar of water, after a
few minutes stir it well, and when the sediment settles pour off
the clear water for use. Fill a test-tube about two-thirds full of
lime water and force air from the lungs through the water by
means of a tube, and quickly the water becomes cloudy and
milky. This makes a delicate test for the dioxide. The lime of
the water combines with dioxide forming calcium carbonate
which is insoluble in water. If lime water is exposed to the air
in an open dish, the dioxide of the air uniting with the lime
soon forms a thin coating of calcium carbonate on the surface of
the water.
The dioxide of carbon accumulates so rapidly as the pro-
duct of combustion and respiration that the air of a room
occupied by a number of people soon becomes loaded with
this gas unless special arrangements have been made for free
ventilation. Tests of the* air of almost any school or assembly
room, especially when fires or lights are in use, will show dan-
gerous quantities of a gas which cannot support life, and which
by limiting the supply of oxygen becomes detrimental to health.
Under a pressure of 36 atmospheres (about 450 Ibs.) carbon
dioxide becomes a liquid; when the pressure is removed it begins
to evaporate rapidly, the evaporating portion absorbing so
much heat from the other that it freezes into a snow-like solid.
Carbon dioxide is absorbed freely by water and other liquids,
the sparkling appearance of wines and mineral waters, the foam
of beer and " soda water " are due to the presence of this gas. It
is also used in the manufacture of fire extinguishers. An English
coal mine that had been smouldering for years was extinguished
completely by the use of carbon dioxide. This gas combined
with water forms carbonic acid, formula H 2 C0 3 , and it is prob-
able that in the tests with lime water we find the carbonic acid
not the dioxide.
When coal is burned without a free supply of air, a gas is
132 PRACTICAL LESSONS IN SCIENCE.
formed called carbon monoxide. It is colorless, tasteless, odor-
less, but exceedingly poisonous when inhaled. We often hear of
deaths caused by coal gas, and the gas from a pan of smoulder-
ing charcoal is often the cause of suicidal death, especially in
France. In an open coal fire, before all the coal is fully ignited,
the pale blue flames flickering over the mass are burning moxideof
carbon. It is probably the cause of death in the cases mentioned.
All forms of artificial light, except the electric light, are flames
due to the combustion of some gas. In the case of illuminating
gas, the source of the light is made and stored as gas, in the case
of oil, the wick is ignited and as the oil comes up by capillary at-
traction it is expanded into gas and burns as a flame, and so
with the candle. At first a flame seems a simple thing and illumi-
nation seems as simple as the flame, but when one attempts to
explain the phenomena, the simplicity vanishes. We have already
learned that the hydrogen flame, while intensely hot yields but
little light. If we pulverize a little charcoal and dust it into a flame
of hydrogen it gives out an intense light; or if the hydrogen flame
be turned upon a piece of lime or other refractory substance it is
soon heated to incandescence giving out intense light, which leads
us to suspect that an illuminating flame must contain some solid
incandescent substance which is the cause of the illumination.
If we examine a flame, as of a candle, we find it conical in
shape, pale blue below, dark in the center and yellow at the sides
and at the apex. Put a piece of porcelain or any solid substance
into the flame and the coat of soot deposited indicates the pres-
ence of solids in the flame. Pass a piece of paper into the flame
just above the wick, hold it there a moment, then remove it, and
if skillfully done there will be a ring of burnt paper with a little
portion uncharred within it, which indicates that the outside of
the flame is hotter than the inside dark portion. The substances
used for illuminating flames, as gas, oils and fats are composed
largely of compounds of hydrogen and carbon. About the wick
of a lamp or candle or the opening of the gas jet the unburned
gas makes the cool dark center of the flame. The oxygen uniting
more readily with the hydrogen than with the carbon forms
LESSONS IN CHEMISTRY. 133
the hydrogen flame just outside the dark center and the
liberated carbon passing through the hydrogen flame is heated
to incandescence, and just outside this hydrogen flame it com-
bines with the oxygen forming the dioxide of carbon.
If air is admitted to the center of the flame, as in an Argand
burner, the dark center is lessened and the light increased. In
the case of the Bunsen burner air is allowed to mingle with the
gas so that the combustion is practically complete, yielding
a hot flame but very little light; for use in chemistry it is
better as it gives greater heat and leaves no deposit of soot.
The flame of alcohol yields but little light and deposits no
soot. Within certain limits the amount of light depends upon
the temperature of the flame. The temperature may be so low
as to hardly heat the carbon to incandescence when the light
must begin to fail. If by any means the temperature of the flame
falls below a certain limit it is extinguished.
A piece of fine wire gauze held across the flame of a lamp or
candle cools the combustible gases below the ignition point so
that they rise through the gauze in the form of smoke, the gauze
may become red hot and still not allow the flame to pass, so
rapidly does the wire conduct the heat away, and yet the gases
may be ignited above the gauze. On this principle the miner's
safety lamp is constructed. Light carbureted hydrogen or marsh
gas, abundant in some coal mines, forms with air an explosive
mixture of great power, but the mixture must be raised to the
igniting temperature before explosion takes place. As the gas
is odorless often the first intimation of danger was the fatal explo-
sion of fire damp, lighted from the miner's open lamp. Sir Hum-
phrey Davy studied the problem, and at last made a lamp in
which the flame was surrounded by a wire gauze which so con-
fined it that the explosive gases outside could not be ignited.
As the gauze restricted the light it soon became the custom to
explore the mine for dangerous gas with a safety lamp and if
none was found the men wnt to work with open lamps. Aflame
seems a little thing, but the full discussion of a candle flame would
make quite a complete treatise on chemistry.
134 PRACTICAL LESSONS IN SCIENCE.
Cyanogen, formula, C 2 N 2 , is a colorless poisonous gas composed
of carbon and nitrogen, which is best known in combination with
the metals potassium and iron, in connection with which it will
be more fully discussed.
No other two elements are capable of occurring in so many
different combinations as carbon and hydrogen. Compounds of
these elements are known as hydrocarbons, and include most of
the inflammable gases and a great many essential oils, naphthas
and other interesting substances. It is supposed that all these
compounds were originally derived from the vegetable kingdom,
and they may be considered under the head of organic chemistry.
Three members of this group of compounds may be mentioned
here for the purpose of affording a little insight into the mutual
relations of these important elements. When intensely heated,
as by the electric spark, carbon combines with hydrogen forming
a colorless gas called acetylene, formula C 2 H 2 . This gas is found
among the products of incomplete combustion, having a peculiar
odor something like that of geranium. It burns with a smoky
flame in the air, bursting spontaneously into flame when brought
into contact with chlorine. Olefiant gas, formula C 2 H 4 , is also a
product of the action of heat on coal, and is one of the illumi-
nating gases. This gas derives its name from its property of
uniting with chlorine and bromine, forming oily liquids.
If the mud and decaying vegetable matter at the bottom of
stagnant pools is stirred up, bubbles of gas rise more or less
abundantly to the surface. This gas has received the name of
methane, or marsh gas. It is abundant in coal mines, as the fire
damp of the miners ; it is a constituent of petroleum oil and is
the initial member of an interesting series of hydrocarbons. It
is a colorless, odorless, inflammable gas, burning with a lumi-
nous flame. When petroleum is brought up to the air several
gases are given off. The simplest of these is methane, formula
CH 4 , the next Ethane, C 2 H 6 , the next Propane, C 3 H 8 , the next
Butane, C 4 H 10 , the next Pentane, C 5 H 12 , and so on, each member
differing from the preceding one by CH 2 , altogether forming what
is called an homologous series. Such series are distinguishing
LESSONS IN CHEMISTRY. 135
marks of the hydrocarbons. The ordinary illuminating gas
consists of free hydrogen, marsh gas, olefiant gas, carbonic
oxide, acetylene and other substances.
SILICON (Si), next to oxygen, is the most abundant element in
nature. It has never been formed in an uncombined state, occur-
ring most abundantly as silicon dioxide or silica, formula, Si0 2 .
The dioxide uniting with water forms silicic acid, H 2 Si0 3 . This
acid forms silicates of sodium, potassium, aluminium, calcium
and other metals. These silicates are very abundant, silica and
the silicates make up the greater part of the crust of the earth.
The granite rocks, volcanic rocks, sand rocks, clay or slate rocks
everything except limestone and coal is composed largely of
the compounds of this element. Silica is not only abundant and
useful but is beautiful as well. The purest natural variety is the
transparent, colorless quartz crystal or rock crystal, occur-
ring in six-sided prisms terminated by six-sided pyramids. They
may be distinguished from most other crystals not only by their
form, but by their hardness, scratching glass almost as readily
as the diamond. With a little tinge of purple, the rock crystal
becomes the beautiful amethyst; when brown or smoky, Scotch
pebbles. Losing its transparency and crystalline form, we have
the translucent chalcedony, the brilliant carnelian, the banded
agate, the catseye, the onyx and the opal. Each of these forms
beautiful and enduring. Flint is a dark colored variety of silica
which is proverbial for its hardness. The percussion of flint and
steel for many years served our forefathers as a source of light
and heat in place of the lucifer match.
While silica is insoluble, some of its compounds are soluble,
and plants contain considerable quantities in their composition,
and animals as well. Many natural waters contain silica in solu-
tion, as in the Geysers of Iceland, and petrified wood indicates
that silica is soluble to some extent in water, but probably only
in hot water and under considerable pressure.
Hydrofluoric acid is the only substance that can decompose
silica at ordinary temperatures. Silicic acid does not appear to
be a very strong acid, seeming to be of about the same strength
136 PRACTICAL LESSONS IN SCIENCE.
as carbonic acid, and yet the silicates generally are quite stable
compounds. Glass is manufactured from the silicates of sodium,
potassium, calcium, etc., with other ingredients.
Silicon has been obtained as a brownish powder and in the
form of crystalline scales with metallic luster resembling graphite.
Carbon and silicon are similar in some respects, as both form
dioxides and weak acids, and the same hydrides and chlorides,
but differ in that most of the compounds of carbon are derived
from the hydrocarbons, while the compounds of silicon are derived
from silicic acid.
Boron (B)is an element which has not been found in vegetable
or animal bodies ; is never found free ; is not abundant ; is not es-
sential to life, and yet in many ways it is an interesting element,
similar in some respects to carbon and silicon. It forms with
oxygen boric trioxide, B 2 3 , which uniting with water forms
boracic, or boric acid, H 3 B0 3 .
This acid is found issuing from the earth as vapor, accom-
panied with steam in certain volcanic regions, as Northern Italy.
This steam is passed into water, which absorbs the acid yielding
boracic acid crystals on evaporation. Boracic acid is feeble like
silicic and carbonic acids. It fuses at high temperatures, when
it dissolves many of the metallic oxides forming glassy berates
which are of characteristic and often beautiful colors. On this
property depends the chief value of boron in the arts and in
chemistry. It forms a good test for detecting the presence of
metals, and is valuable in the manufacture of colored glass and
porcelains. It is used in hard soldering and in brass manu-
facture. The most important borate is the sodium borate called
borax, which is the form under which boron is best known.
Boron has been isolated as an olive-green powder; also in
copper-colored scales similar to graphite; also in transparent
octahedral crystals, rivaling diamonds in brilliancy and hardness.
Carbon, silicon and boron seem to form a natural group; each
has a crystalline, amorphous and graphite-like form. Neither
can be made a vapor, and each is practically insoluble.
CHAPTER XVII.
SULPHUR, PHOSPHORUS AND ARSENIC.
SULPHUR is an element that has been known from the earliest
times, as it is found in great quantities in volcanic regions,
especially in those of Southern Europe. It occurs as hydrogen
sulphide in mineral waters. It forms compounds with several
metals, as the bisulphide of iron, sulphide of iron and copper,
sulphide of lead, zinc, antimony and mercury. It also is a con-
stituent of numerous sulphates, as the sulphates of lime, baryta,
strontia, magnesia and soda. It is also found in small quanti-
ties in animals and some plants.
Sulphur is a yellow brittle solid. It melts at 239 F. to
a thin straw-colored liquid; when heated to a higher temper-
ature it becomes darker in color, and at 350 F. becomes a
dark viscid body. At this point the temperature remains
stationary for some time, although heat is applied continu-
ously, showing that heat is doing other work besides raising
temperature. As it begins to rise in temperature again it
becomes liquid at about 500 F., and at 836 F. it boils, form-
ing a brownish-yellow vapor, which burns in oxygen or in the
air with a bluish flame. When a liquid at about 500, if poured
into water, it becomes a dark plastic mass much like india rub-
ber, but this form is not permanent it soon changes back to the
yellow brittle form.
The plastic sulphur not only differs from brittle sulphur in
physical properties but it differs in chemical properties as well,
for brittle sulphur dissolves readily in bisulphide of carbon while
the plastic form is entirely insoluble ; and further, they differ in
their electrical relations, the plastic form is electro-positive while
the other is electro-negative.
The diamond crystallizes in the form of an octahedron and
(137)
138 PRACTICAL LESSONS IN SCIENCE. .
so does sulphur. Nearly all the compounds of sulphur as
well as most other substances of the mineral world have defi-
nite crystalline forms, and so constant and definite is this
form that it is one of the marks for the identification of min-
erals. The natural crystallization of sulphur is the octahedra,
and it takes this form when crystallizing from solutions, but
when crystallizing from the melted state it takes the form of
oblique prisms. The difference between these two crystalline
forms of sulphur extends to their specific gravities and the tem-
peratures of their melting points. Ordinary rolled sulphur con-
tains many prismatic crystals when first made which gradually
change to octahedra. This change in structure of the solid gives
rise to a state of tension which accounts for the extreme brittle-
ness of sulphur.
Sulphur is one of the most interesting of the non-metallic ele-
ments, and it may serve as the basis of many interesting and
instructive experiments . A large part of the sulphur of commerce
comes from Sicily. As the melting point and boiling point of
sulphur are low it is comparatively easy to separate it from im-
purities by the aid of heat. Large quantities of sulphur are also
obtained by decomposing iron pyrites or bisulphide of iron.
Sulphur is used in the manufacture of gunpowder and matches.
Sulphur unites with oxygen, forming many interesting com-
pounds. When sulphur is burned in the air, sulphur dioxide,
formula S0 2 , is formed with the evolution of light and heat. It
occurs among the products of volcanic action, is a transparent
colorless gas, having a pungent suffocating odor, such as arises
from a burning match. It may be prepared for examination
by treating copper with sulphuric acid. It is readily absorbed
by water but may be collected by displacement, as in the case of
chlorine or carbon dioxide, as it is heavier than air. It may
be condensed to a liquid by cold or pressure, and is a solid at
105 F. Sulphur dioxide S0 2 -hwater, H 2 forms sulphurous
acid, H 2 S0 3 . When neutralized by a base this acid forms a class
of salts called sulphites, as the sulphite of soda.
Sulphur dioxide is extensively used as a bleaching agent. Al-
LESSONS IN CHEMISTRY. 139
though less powerful than chlorine it is preferred in some cases,
because it is less liable to injure the fabric. The articles to be
bleached are moistened and hung in a chamber in which sulphur
dioxide is produced by burning sulphur. The coloring matters
seem to form colorless compounds with the acid and in some cases
the colors maybe restored by neutralizing the acid. Sulphur diox-
ide, like carbon dioxide, will not support combustion and is used
to stop combustion. This acid is an antiseptic promptly arrest-
ing fermentation. It is used as a disinfectant and as an insecti-
cide. The dioxide becomes an acid so readily by taking water
from the air that it is often difficult to decide whether a given
result is due to the dioxide or the acid.
While sulphurous acid is useful in many other ways its principal
use is in the manufacture of sulphuric acid, formula H 2 S0 4 . It
is a powerful acid which has very many practical uses. It is said
that more than 100,000 tons of it are used each year in England
alone. The steps involved in the manufacture of sulphuric acid are
the formation of the sulphur dioxide, and sulphurous acid H 2 S0 3 ,
which combined with one atom oxygen forms sulphuric acid. The
last step is the most difficult and most interesting. The sulphur-
ous acid cannot readily get the necessary oxygen from the air,
but nitric oxide, formula NO, takes oxygen from the air forming
nitrogen peroxide N0 2 . The peroxide gives off one atom of oxy-
gen to the sulphurous acid and sulphuric acid is formed, the nitric
oxide simply carrying oxygen from the air to the sulphurous acid.
Sulphurous acid is supplied from burning sulphur or decomposing
iron pyrites. Nitric acid, from which the nitric oxide is formed,
is supplied by the decomposition of niter by sulphuric acid.
A mixture of sulphurous and nitric acids, air and steam are
conveyed into a leaden chamber containing a layer of water.
The nitric acid by the action of the sulphurous acid is reduced to
nitric oxide, which takes oxygen from the air and gives it up to
the sulphurous acid, converting it into sulphuric acid. This is
absorbed by the water forming a weak acid which is concentrated
by evaporation, at first in leaden pans and then in glass retorts
or platinum stills.
140 PRACTICAL LESSONS IN SCIENCE.
This acid is a heavy corrosive liquid, colorless when pure, but
usually brownish from charred organic matter. It blackens
wood and cloth and almost every form of organic matter is ut-
terly destroyed by this powerful acid, even when much diluted.
If a few lumps of sugar be dissolved in a little water and mixed
with sulphuric acid, a violent action takes place and a black mass
of semi-solid substance results. Some varieties of shoeblacking
are made by the action of sulphuric acid on molasses or treacle.
Sulphuric acid has a strong affinity for water; if exposed to the
air in an open dish it soon absorbs water from the air so as to
greatly increase its bulk. It is frequently used in the laboratory
for drying substances without heat.
A high degree of heat is developed by the action of sulphuric
acid on water, when the two are mixed, which leads one to sus-
pect chemical action. The diluted acid has a smaller bulk
than that occupied by the acid and water before mixing. The
corrosive action of this acid seems largely due to its power of
absorbing water from the objects with which it conies in con-
tact.
Sulphuric acid acts on all the metals except gold and platinum,
and has a more powerful attraction for bases than any other
acid, displacing all other acids from their salts. Some bases
form two salts with sulphuric acid, as H 2 S0 4 +KOH KHS0 4 -f
H 2 0, acid potassium sulphate, and H 2 S0 4 +2KOK=K 2 S0 4 +2H 2
neutral potassium sulphate, while in the case of nitric acid only
one salt seems possible, as HN0 3 +KOH=KN0 3 +H 2 0. An acid
as sulphuric, which has the power to form two salts with one
metal, is called dibasic, while others that can form but one are
called monobasic.
Sulphuric acid is one of the most important substances used in
manufacturing. It is used in making sodium carbonate, citric,
tartaric, acetic and nitric acids, sodium and magnesium sul-
phates, and various paints. It is used in calico printing, in dye-
ing, in gold and silver refining, in purifying oil and tallow. It is
used in medicine and is invaluable about the chemical laboratory.
Hyposulphite of soda is a salt used extensively in photog-
LESSONS IN CHEMISTRY. 141
raphy. There are other hyposulphites, but no hyposulphurous
acids have ever been isolated.
When sulphur vapor is passed over red-hot charcoal the sul-
phur combines with carbon, forming carbon sulphide, formula
CS 2 . It is a volatile liquid of high refractive powers. It has never
been frozen and is used in making thermometers. It dissolves
crystalline sulphur, phosphorus, India rubber, fatty matters, and
is one of the most injurious impurities of illuminating gas.
When hydrogen passes over heated sulphur the two elements
combine forming hydrogen sulphide, a colorless gas of disgusting
odor, whose formula is H 2 S. It occurs in some natural waters,
and is formed in the decomposition of some organic substances,
as the albumen of eggs. It is soluble in water, and is usually
prepared by treating sulphide of iron with diluted sulphuric
acid. The chemical equation is FeS+H 2 S0 4 =FeO-fH 2 S. This
gas acts promptly on nearly all the metals forming sulphides.
Nearly every sulphide has a characteristic color, so that this
gas is an important reagent in chemical analysis. This gas
becomes a liquid under a pressure of 255 pounds, and a solid
at -122 F.
PHOSPHORUS combined with calcium exists in the older rocks
and the soils formed from them. Its compounds are abundant in
plants, especially in the seeds of the cereals which furnish such a
large portion of the food-supply of men and domestic animals.
Its compounds are abundant in all parts of the animal body,
especially in the bones, three-fifths of whose weight consists of
calcium phosphates. Formerly bones were the chief source of
phosphorus, but extensive deposits of phosphatic rocks have
been discovered in Florida and other localities, from which phos-
phorus and its compounds may be obtained. These deposits
are among the later rocks, and probably derive their phos-
phorus from decomposing animal matters, so that our supply
of phosphorus comes from the older rocks through the medium
of plants and animals.
In the preparation of phosphorus the animal matter is dis-
solved out of the bones by hot water at a high pressure, and
142 PRACTICAL LESSONS IN SCIENCE.
used in the manufacture of glue. The mineral matter of the bone
is then subjected to distillation, from which results ammonia
and bone charcoal. The charcoal is used by the sugar refineries
until its decolorizing power has been exhausted, when it is
strongly hearted, burning away the carbon, leaving the bone-ash,
consisting largely of calcium phosphate. This bone-ash is heated
with diluted sulphuric acid, which forms with the lime a nearly
insoluble calcium sulphate, leaving phosphoric oxide, P 2 5 , in
solution. This solution strained and evaporated to the consist-
ency of sirup is mixed with charcoal and strongly heated, when
the oxygen unites with the carbon, and the phosphorus rising as
vapor is condensed in water.
Phosphorus is a soft, yellowish, semi-transparent, waxy solid,
which exposed to the sunlight soon becomes darkened. It is
extremely inflammable, taking fire in the air by the heat arising
from the slightest friction. It is kept under water to protect it
from oxygen, and it should be kept and handled under water, as
the heat of the hand will cause it to burn. It not only burns in
oxygen and the air, but burns in chlorine, bromine, or iodine.
When exposed to the air it undergoes slow oxidation, giving off
a white vapor of a garlic odor. In the dark phosphorus gives
out light; hence its name, meaning bearer of light.
If phosphorus is heated without access of air a second variety
called red phosphorus is formed. Ordinary phosphorus is soluble
in the bisulphide of carbon, is poisonous and easily inflammable.
The red phosphorus is insoluble, not poisonous, not easily inflam-
mable. The allotropic forms of phosphorus are as well marked
as those of sulphur and carbon, and are as yet unexplained.
The principal use of phosphorus is the manufacture of
matches. Matches were invented early in the present century,
but the phosphorus friction match was first produced on a com-
mercial scale about 1832. A match consists of a splint of wood,
one end of which has been dipped in melted sulphur or wax, or
paraffine, and this substance covered with the " match composi-
tion," which is generally composed of chlorate of potash, phos-
phorus, red lead and glue. The match depends for its action
LESSONS IN CHEMISTRY. 143
on the easy ignition of phosphorus by friction, when mixed with
oxidizing agents, like chlorate of potash, the glue only servingto
bind the other parts together and attach them to the wood. The
phosphorus ignited by friction sets fire to the sulphur or paraf-
fine, which in turn ignites the wood. Several different " match
compounds" are made. When chlorate of potash is used there
is a slight explosion when the match is lighted. When potassium
nitrate is used a silent match is made. This form is most com-
mon in Germany, while the other is more common in this country
and in England.
A single match is a little thing, but the manufacture of matches
for the use of mankind is one of the great industries of the world.
More than 2,000 tons of phosphorus are used annually with cor-
responding amounts of the other ingredients, and thousands of
acres of forests are necessary to supply the splints used every year.
It is estimated that forty thousand millions of matches are used
annually in the United States alone. Matches made with red
phosphorus, called safety matches, are sometimes manufactured,
but for some reason they are not in general use. A match is
made in France, using red phosphorus, which is ignited by break-
ing the match and rubbing the ends together. In Mexico matches,
as generally made, are little wax tapers, tipped at both ends
with the " match compound."
Phosphorus forms several compounds with oxygen and hy-
drogen. When phosphorus burns in air or oxygen, the dense
white fumes formed are phosphoric oxide. This oxide com-
bines with water forming two acids as P 2 5 -j-H 2 0=H 3 P0 4 meta-
phosphoric acid and P 2 5 -h3H 2 0=2H 3 P0 4 orthophosphoric acid
commonly called phosphoric acid. It is the most important of
the compounds of phosphorus. It is tribasic, forming three
salts with the same metal, but the most common and important
salt is calcium phosphate, the chief mineral constituent of the
bones, and the form in which phosphorus usually occurs in
nature.
Phosphorus (P) is an indispensable ingredient in the food of
animals and plants. No other mineral substances can bear com-
144 PRACTICAL LESSONS IN SCIENCE.
parison with it as a measure of the capability of a country to
support life. Hence substances containing phosphate of lime are
of great value as fertilizers. The phosphate being practically
insoluble, is not easily distributed through the soil. But by
treating the phosphate with sulphuric acid it is transformed into
a soluble lime salt called superphosphate, which is easily distrib-
uted to the soil by water. It is said that in England alone more
than 500,000 tons of phosphate materials are used annually in
the manufacture of artificial manures. Phosphorus forms a
compound with hydrogen called phosphine, formula PH 3 . It is
somewhat analogous to ammonia. It has no economic value,
and is characterized as having the most villainous odor known.
ARSENIC (As) is often classed with the metals because of its
metallic luster, but it forms no base with oxygen, and in many
respects is similar to phosphorus. It is sometimes found pure
in nature and sometimes as an oxide, but more commonly in
combination with various metals, as the arsenides of nickel, co-
balt and iron. The principal source of arsenic and its compounds
is arsenical pyrites, formula, FeAsS. Arsenic is also obtained as
a by-product in working ores of tin, nickel and cobalt.
When arsenic is heated in the air it burns with a bluish flame,
giving off fumes which have the odor of garlic, and are very
poisonous. These fumes condense into a white solid called
arsenic trioxide, formula As 2 3 . It is the arsenic of the shops.
It is used in glass-making, in the manufacture of coloring mat-
ters; with water it forms a weak acid which forms salts, called
arsenites. An arsenical soap made of arsenite of potash, soap
and camphor is sometimes used by naturalists to preserve the
skins of birds and animals. Arsenite of copper, called Scheele's
green, is much used in coloring wall papers, feathers, muslin, etc.
In quantities less than poisonous doses arsenic trioxide has pe-
culiar effects on the animal body; it seems to favor the deposition
of fat ; grooms use it to improve the appearance of their horses,
and in some parts of Europe men and women take it for the
same purpose. A solution of arsenite of potash is much used
in medicine as Fowler's solutions. Arsenic pentoxide, formula
LESSONS IN CHEMISTRY. 145
As 2 5 , combined with water, forms arsenic acid, which forms
arseniates. Arsenic acid by its action upon aniline forms the
beautiful dye called magenta. It is also much used in calico
printing. There are three sulphides of arsenic. Kealgar, or red
orpiment, formula As 2 S 2 , is a beautiful mineral crystallizing in
orange red prisms. It is an important ingredient in compositions
used for fire-works and signal lights. Yellow orpiment, As 2 S 3 ,
is found native as yellow prismatic crystals. A fine yellow paint
is made from this substance. The other sulphide is not of special
interest.
Arsine is a compound of arsenic and hydrogen, formula,
AsH 3 , analogous to ammonia and phosphine. It is a color-
less, poisonous gas, having an unpleasant odor. Arrange an
apparatus as in preparing hydrogen, adding a little arsenic.
Arrange a delivery tube so that the gas formed may be burned.
When the gas is burning freely bring into the flame a piece of
porcelain, and a dark spot is formed by the condensed arsenic
called a mirror of arsenic. When carefully performed this is
a very delicate test for the presence of arsenic, and is exten-
sively used in examining the contents of the stomach of per-
sons in cases of suspected poisoning. It is known as Marsh's
test. Arsenic and its compounds are notable for their poisonous
properties, and for their bright and beautiful colors.
L. s. 10
CHAPTER XVIII.
SODIUM AND LITHIUM.
WE have discussed briefly the non-metal or acid-forming ele-
ments that seem of most importance, considering some of their
compounds, and we have developed and illustrated some of the
principles of chemical action. This work has, however, been
somewhat fragmentary and incomplete, because at every step it
was necessary to refer to and employ the aid of metallic or base-
forming elements, and of salts, that great class of compounds
resulting from the combinations of both acid and base-forming
elements. In the study of the more important metals, we must
at every step invoke the aid of the non-metallic elements in ex-
plaining the varied actions and other chemical phenomena that
occur. The work will consist, then, in taking new steps in re-
viewing and completing many steps already taken, and in the
practical application of chemical ideas and principles to the ordi-
nary affairs of life.
Potassium and sodium are typical representatives of the alka-
line metals, and from the number of times they have been men-
tioned while studying the non-metals we may form some idea of
their importance in all lines of chemical phenomena.
POTASSIUM (K), best known in its hydroxide called potash, is
a silver-white metal, lighter than water and so soft that it can be
cut and molded like wax. When thrown upon water it unites
rapidly with the oxygen, generating heat enough to ignite the
hydrogen set free and to vaporize some of the metal, which, burn-
ing with the hydrogen, gives the flame the beautiful violet color
characteristic of potassium. The oxide formed is dissolved in
the water, giving it a soapy feel which is a common property of
alkaline solutions.
Potassium compounds are components of many of the older
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LESSONS IN CHEMISTRY. 147
rocks, and these, broken down and pulverized, yield up a
portion of their potassium to growing vegetation. When
vegetable structures are burned, the potassium forms a por-
tion of the ash in the form of a carbonate, formula K 2 C0 3 .
When the wood ashes are leached with water the potassium car-
bonate is dissolved out and the solution evaporated yields an
impure salt, called potash, which is much used in the manufacture
of soft soap and of glass. It is also a valuable fertilizer. The
hydroxide or caustic potash is obtained from the solution of po-
tassium carbonate by treating it with slaked lime. The chemical
equation is K 2 C0 3 +CA0 2 H 2 , calcium hydroxide, =CaC0 3 , calcium
carbonate +2KOH, the potassium hydroxide. This compound
is a brittle, white solid , having a strong affinity for water, so that
it rapidly deliquesces in the air. It is the most powerful alkali
in use, and its activity as a chemical agent makes it of great
value to the chemist. It is used in medicine as a caustic. It re-
places the hydrogen of acids forming salts, as the carbonates,
nitrates and sulphates. It decomposes animal and vegetable
substances, whether living or dead. Potassium bicarbonate, for-
mula HKC0 3 ,is a salt much used in medicine for making efferves-
cent solutions by adding citric or tartaric acids.
Another very common and important salt of this metal is
potassium nitrate niter, or saltpeter, formula KN0 3 . It is a nat-
ural product of some parts of India and is produced in an artifi-
cial way, by heaping up organic matter with lime, ashes and
soil, keeping the mass well moistened with urine for two or three
years. In the mass nitrates are slowly formed and may be
leached out with water and purified for use. The potassium
nitrate may also be prepared from the sodium nitrate by treating
it with potassium chloride, according to the following equation :
NaN0 3 , sodium nitrate, +KCL, potassium chloride, KN0 3
niter, -hNaCl sodium chloride, all in solution together. In evap-
orating this solution the sodium chloride, being less soluble in
boiling water, crystallizes out, leaving the niter still in solu-
tion. When the solution is allowed to cool the niter crystallizes
out, as it is less soluble in cold water, leaving some chlorides
148 PRACTICAL LESSONS IN SCIENCE.
still in solution. In refining the niter it is dissolved in boiling
water, filtered, then allowed to cool and crystallize while kept in
constant motion, so that the salt may be deposited in smaller
crystals than if allowed to crystallize from a quiet liquid. The
crystals are thoroughly washed, then dried for use.
These operations illustrate some curious and interesting prop-
erties of the substances spoken of, and how these properties have
been studied out and made use of in preparing the substances for
use, and in most cases they were discovered and utilized by non-
scientific men, under pressure of business competition long before
they were even partially explained by a scientific man.
Potassium nitrate is a crystalline salt that readily dissolves
in water, having a cooling saline taste, and strong antiseptic
powers, so that it is often used in preserving meats. Potassium
forms an interesting compound with chlorine, called potassium
chloride, formula KC1, which occurs in great masses in the salt
mines in Saxony, and is an important source of potassium and
its compounds. It resembles rock salt in appearance. Another
important salt of potassium is potassium chlorate, formula
KC10 3 . It is prepared by passing chlorine gas through a solu-
tion of potassium carbonate. As this salt gives up its oxygen
freely to other bodies, it is called an oxidizing agent.
Pulverize carefully a small piece of potassium chlorate and mix
with it an equal bulk of sugar ; put the mixture on a brick in the
open air, then let a drop of sulphuric acid fall on it and a vivid
combustion will follow. Care should be taken both in pulverizing
and mixing not to use percussion or heavy pressure, and small
quantities should be used at least until one is familiar with the
explosive powers of this salt. Cream of tartar, much used in
cooking, is potassium tartrate, mainly obtained from fermenting
grape juice.
Potassium as a metal is of no economic value, but some of its
compounds are among the most important known. The use
of the carbonate as an alkali in making soap, the use of the
chlorate as an oxidizing agent in the manufacture of matches,
and the use of the nitrate as an oxidizing agent in the manufac-
LESSONS IN CHEMISTHY.
ture of gunpowder, puts potassium in the front rank of useful
metals.
Gunpowder is an intimate mixture of potassium nitrate, sul-
phur and powdered charcoal. The nitrate furnishes oxygen in
great abundance, charcoal, carbon in available form, and the
sulphur ignites at a low temperature, altogether tending to
rapid and intense combustion. The nitrate for the manufacture
of gunpowder should be free from the chlorides of potassium and
sodium, should be free from coloring matter and should show
neither acid nor alkaline reaction. The charcoal for gunpowder is
best made of some light wood, as alder or willow, as charcoal
from these woods is lighter and more easily combustible. The
wood is burned in a retort at a temperature of about 1,000 F.
which yields a charcoal of the most desirable density. The char-
coal is allowed to cool slowly, and is then exposed to the air for
several days, so that it may absorb moisture ; for if ground be-
fore it is liable to spontaneous combustion. It is then ground
and sifted to free it from dust. Distilled sulphur is used, as it is
soluble and free from sulphurous and sulphuric vapors. The pro-
portions of these ingredients varies among manufacturers. Eng-
lish government powder contains 75 per cent, of saltpeter, 15
per cent, charcoal and 10 per cent, sulphur. These substances
are first thoroughly mixed, and the mixture, in charges of about
50 pounds each, is subjected to the action of the incorporating
mill, which is something like the dry pan used in preparing clay
for brick making, consisting of heavy iron rollers with scrapers
and plows so as to keep the mass well mixed while it is being
pressed by the rollers. This process continues about three hours
for slow-burning cannon powder, and about five hours for rifle
powder. The mass is sprinkled with water during the time, so
that at the close of the process the grayish mass of mill cake
contains from 2 to 3 per cent, of water. The mill cake is broken
up and packed in layers about half an inch thick between copper
plates and subjected to great pressure under the hydraulic press.
This not only makes the powder compact, but it seems to have
less capacity for absorbing moisture. But this mass will not
150 PRACTICAL LESSONS IN SCIENCE.
burn rapidly enough. It must be broken up into grains, which
are separated by sieves, so that the grains of the same size go
together. These grains are polished by friction among them-
selves in revolving barrels, sifted from dust, dried and sifted
again, when the powder is ready for packing. For cannon powder
the grains are sometimes a half inch in diameter, and sometimes
they are made in molds, so that the form is definite.
Good powder should be composed of hard angular grains
which do not soil the fingers, and when fired on a sheet of paper
should burn without sparks and without scorching the paper or
soiling it to any great degree. The products of the combustion
of powder are chiefly potassium carbonates and sulphates, with
carbon dioxide, carbonic oxide, hydrogen and marsh gas. The
solid powder changing into these gases, which are expanded by
the great heat of the combustion, accounts for the mechanical
effects of the explosion.
It is estimated that the temperature resulting from the ex-
plosion of powder as ordinarily used is over 5,000 F., at which
temperature some of the gases might be separated into their
elements, which would increase the expansive force. It has been
estimated that the explosion of a cubic inch of good gunpowder
would exert a pressure of about fifteen tons to the square inch if
it could all be burned on the instant. It is at present impossible
to fully explain the phenomena of the combustion of powder, as
the products and conditions at the time of explosion must be
different from what they are afterward when the products may
be collected and studied. Gunpowder is of very great value.
Some have considered its influence on civilization as next in im-
portance to the discovery of the printing press and application
of steam to machinery. Besides its use in war it is of immense
value in all mining and quarrying industries and in many en-
gineering operations, although other explosives are supplanting
it in some directions. Gunpowder is superior to most other ex-
plosives in the uniformity of its action, in that its manufacture
and transportation are less dangerous, in that it is not liable to
change when stored, and for use in gunnery its slower action
LESSONS IN CHEMISTRY. 151
exerts less strain on the gun. The early history of powder is
obscure. Our first knowledge of its use as a military agent dates
from the seventh century, while its first use as a propelling agent
was in Spain in the 12th century. It was known and used in Eng-
land early in the 1.4th century.
Potassium and its compounds have been derived from the rocks
through the medium of plants, but sodium and its compounds
are derived from seawater, which derived them from the older
rocks by solution. While land plants gather up potassium com-
pounds along with some sodium compounds from the soils,
water takes up sodium compounds, with some potassium com-
pounds, and carries them down to the sea. These sodium com-
pounds are taken up to some extent by seaweeds, and we can
obtain sodium compounds from sea plants as we obtain po-
tassium compounds from land plants; but it is more profit-
able to take them directly from the seawater, or from beds of
rock salt which are supposed to have been deposited from sea-
water.
Rock salt is sometimes mined as other rock is mined ; some-
times water is let into the mine, then pumped out after it has dis-
solved its load of salt. Again in connection with these salt beds
natural brines are abundant, which flow out as springs or may
be pumped out for use. In some places seawater is pumped into
shallow ponds or lakes and allowed to evaporate in the sun until
it becomes strong enough to pay for artificial evaporation. In
Russia, sometimes a portion of the pure water is allowed to
freeze out of the brine. Seawater, rock salt, and natural brines,
besides the sodium chloride, contain also magnesium and potas-
sium chlorides, and sulphates of magnesia and lime. But as the
water is evaporated, most of the sodium chloride crystallizes out,
leaving the other substances in solution with iodine, bromine,
etc. From the sodium chloride, chlorine, hydrochloric acid and
the metal sodium with its various compounds are derived. So-
dium chloride, common salt, formula NaCl, is too well known to
need any description. Its usefulness in preserving meat, and as
an article of food for man and beast make it almost essential to
152 PRACTICAL LESSONS IN SCIENCE.
the existence of animal life. It is also used in glazing pottery
ware.
Previous to the war of the French Revolution most of the car-
bonate of soda came from Spain. As the supply became scanty
and the prices high, Napoleon offered a premium for the discov-
ery of a process by which the carbonate could be made in France.
The chemist LeBlanc discovered the process now in use for the
manufacture of sodium carbonate from sodium chloride, a case
in which science took the lead in an economic process. By this
process sodium chloride is mixed with an equal weight of sul-
phuric acid and strongly heated, which results in the formation
of the sodium sulphate, called salt cake and hydrochloric acid, as
follows: 2NaCH-H 2 S0 4 =Na 2 S0 4 -f2HCl. Arrangements are
usually made so that the acid passing off as a gas is absorbed
by water. The sodium sulphate is then mixed with about an
equal weight of limestone and about half its weight of fine coal,
and strongly heated, when the carbon takes up the oxygen of
the sulphate which reduces it to sodium sulphide, Na 2 S, and this
acted upon by the carbonic acid liberated from the limestone,
forms sodium carbonate Na 2 C0 3 and sulphide of calcium CaS,
according to the following equations : Na 2 S0 4 -f-4C=Na 2 S+4CO,
and Na 2 S+CaC0 3 limestone Na 2 C0 3 +CaS. The sodium car-
bonate is dissolved from the mass and crystallized from the
evaporating solution. Sodium bicarbonate HNaC0 3 is the sal-
eratus or soda used in bread making, etc.
The metal SODIUM (Na) is prepared from the carbonate by
heating it with coal when the carbon takes the carbon dioxide
from the sodium forming carbonic oxide, and the sodium passing
over as vapor is condensed under oil or naphtha. Equation,
Na2C0 3 +2C=2Na-h3CO. This metal is similar to potassium,
but does not decompose water as vigorously, and burns with a
yellow flame. It is used for the extraction of the metals alumi-
num, magnesium, gold and silver from their ores.
Sodium hydroxide, formula NaOH, is prepared by treating
sodium carbonate with calcium hydroxide, equation Na 2 C0 3 -f-Ca
O 2 H 2 =CaC0 8 +2NaOH. It is a white solid somewhat similar to
LESSONS IN CHEMISTRY. 153
caustic potash in appearance and quality. It is usually obtained
as a by-product in the manufacture of sodium carbonate. It is
used in the manufacture of hard soap. Sodium sulphate, Na 2 S0 4 ,
is a salt called Glauber's salt. It is produced as a by-product in
the manufacture of hydrochloric acid.
Nitrate of soda, or Chili saltpeter, is imported from Peru. It
is used as a fertilizer and in the manufacture of potassium ni-
trate. Fifteen parts of clean sand fused with eight parts of car-
bonate of soda form a silicate of soda, which is soluble in hot
water, forming a strongly alkaline solution called soluble glass.
It is sometimes used to lessen the inflammability of wood, and
sometimes as a matrix in forming some kinds of artificial
stone.
Ammonia, NH 3 , and the hypothetical metal ammonium, NH 4 ,
have been mentioned ; but several salts of ammonium are inter-
esting, and may be considered here as they are somewhat similar
to corresponding compounds of sodium and potassium. Am-
monium chloride is sometimes found in nature, but is usually
prepared from the ammoniacal liquors of gas works. These
liquors are treated with hydrochloric acid, the solution evapo-
rated and the residue heated, when the ammonium chloride vap-
orizes without melting, and is condensed on cold surfaces in a
crystalline form. It has a sharp salty taste, and is freely soluble
in water, lowering the temperature considerably, so that it is
frequently used in making freezing mixtures. From it ammonia
and carbonate of ammonia are prepared, and it is used in dye-
ing, in soldering copper and brass, and in galvanizing iron.
Ammonium sulphide (NH 4 ) 2 S,is prepared bypassing hydrogen
sulphide through aqua ammonia, 2NH 3 H-H 2 S=(NH 4 ) 2 S. This
compound is a colorless liquid of unpleasant odor, which soon
becomes yellowish from partial decomposition. It is a very use-
ful agent in the laboratory.
Bicarbonate of ammonia H(NH 4 )C0 3 , called "smelling salts,"
is frequently used in medicine, and it is also used by bakers and
confectioners. Ammonium sulphate, (NH 4 ) 2 S0 4 , is used in the
manufacture of artificial manures and ammonium alum.
154 PRACTICAL LESSONS IN SCIENCE.
LITHIUM, the lightest metal known, occurs in small quantities
in some kinds of mica and other minerals ; is found in the waters
of many springs; in tobacco, milk, blood, sea water, etc. It is
somewhat similar to potassium and sodium in its properties. It
gives a bright carmine color to flame. Lithia water is much used
in medicine. Potassium, sodium and lithium are alike in the
powerful alkalinity of their oxides and in the solubility of their
salts, and in that they give bright colors to flames, sodium
yellow, potassium violet or lilac, and lithium red.
CHAPTER XIX.
CALCIUM, BARIUM, STRONTIUM, MAGNESIUM AND ZINC.
CALCIUM (Ca) is a very abundant element, as calcium carbon-
ate it forms the limestones, the marbles and the chalk of the
earth. Calc spar, the marbles and many limestones are crystal-
line forms of this mineral. It occurs in bones, corals and the
shells of mollusks are nearly pure calcium carbonate.
Calcium oxide called lime or quick lime is formed by heating
the carbonate which drives off the carbon dioxide, leaving the
oxide as a white infusible solid, formula CaO. The oxide, com-
bines vigorously with water, forming the calcium hydroxide
Ca0 2 H 2 . In this process a high degree of heat is evolved, often
enough to ignite wood, the oxide swelling up and crumbling to a
white powder, called slacked lime, which is somewhat soluble in
water forming what is called lime water. If exposed to the air
the oxide taking water from the air slowly changes to the hydrox-
ide. The hydroxide is the most important of the bases, and is
used in almost every art or manufacture which involves chemical
changes. It is used in making mortar, glass and soap.
Calcium sulphate (CaS0 4 -|-H 2 0) occurs in nature as the trans-
parent selenite and the opaque gypsum, which is often beautifully
colored, sometimes it is pure white when it is called alabaster.
When heated to a temperature of 350 to 400 F. the water of the
gypsum is driven off and it becomes, what is called, plaster of
Paris. When this powder is mixed with water a combination
takes place forming a solid nearly as compact and strong as the
original gypsum. In the act of setting the plaster expands
slightly which makes it especially valuable for taking casts of
objects. It is much used in the reproduction of statues and other
sculptural forms. The walls and ornamentation of the Colum-
bian Fair buildings were made of light wood covered with
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156 PRACTICAL LESSONS IN SCIENCE.
plaster of Paris, and at a little distance they have the appearance
of stone. Stucco is plaster of Paris sometimes colored, and some
cements are made by mixing alum with the plaster. Its property
of quickly assuming a solid condition makes it an interesting
and very valuable substance. It is interesting to note that
plaster of Paris cannot be used a second time, indicating that it
is not the same as the gypsum.
Calcium chloride (CaCl 2 ) is a crystalline substance which has a
strong affinity for water and is much used as a drying agent in
chemical work. The bleaching powder, called chloride of lime, is
an impure hypochlorite of lime which depends for its action on
the chlorine it contains.
MORTAR is a compound of one part of freshly slacked lime
and two or three parts of clean sand mixed with water enough
to form a stiff paste. When this mixture is exposed to the air
the water evaporates, carbon dioxide from the air combines
with the calcium oxide forming the calcium carbonate. In this
way the mortar becomes very hard so that however massive the
structure the mortar can bear its share of the load.
COMMON GLASS is a silicate of calcium and sodium made by
melting together sand (silica) and the carbonates of sodium
and calcium. Bohemian glass, used in the manufacture of chem-
ical apparatus is a silicate of calcium and potassium. It is not
as easily fusible as common glass. Plate glass contains some
potassium silicate in addition to the silicate of calcium and so-
dium. Flint glass is a silicate of potassium and lead. It has a
high refractive power, is easily fusible and easily cut. It is much
used for optical instruments, and ornamental glassware. Glass
of various colors is produced by melting with it certain metallic
oxides, as the oxide of iron gives a green color, the suboxide of
copper a red color, the oxide of cobalt a blue, etc,
BARIUM (Ba), a yellowish malleable metal, is of little value
but some of its compounds are interesting. Barium sulphate,
called heavy spar, occurs abundantly as an associate of lead
ores in the mineral regions of Missouri. It is a white, heavy
mineral sometimes used to adulterate white lead paint, and for
LESSONS IN CHEMISTRY. 157
glazing cards, etc. Barium chloride, BaCl 2? is much used in lab-
oratory work as a test for the presence of sulphuric acid. Barium
compounds give a yellowish green flame.
STRONTIUM is less abundant than barium and is of little interest.
It occurs in nature chiefly as the mineral celestine which is the
strontium nitrate. This salt gives a bright red color to flames,
and is often used in the preparation of fire works.
MAGNESIUM (Mg) is a silver white metal. It burns at a low
temperature with a brilliant white light, which may be used to
illuminate objects for photographing. It is widely distributed
in nature as an ingredient of dolomite or magnesian limestone,
soapstone, asbestos, horenblend and talc. Most of these min-
erals have a soapy feel. Magnesium sulphate MgS0 4 H-7H 2 is
the epsom salts of the shops, and the oxide is the common mag-
nesia. When dolomite is burned it becomes what is called water
lime, which makes a mortar that will harden under water.
ZINC (Zn) is a bluish white metal of a crystalline structure,
light, easily fusible, but not easily corroded by atmospheric
influences. The strength of iron and durability of zinc are com-
bined in the so-called galvanized iron, which is made by dipping
well cleaned iron in melted zinc, much as tin plate is made. Zinc
is an ingredient of brass and German silver.
Zinc oxide is used in painting as zinc white, and zinc sulphate
(ZnS0 4 -h7H 2 0) is used in calico printing and to some extent in
medicine as white vitriol. Zinc is easily attacked by acids, and
the chemical action of acids on zinc is the most common source
of the galvanic current. Zinc precipitates lead, copper and silver
from solutions. A very interesting experiment is to place a strip
of zinc in a solution of acetate of lead. The lead quickly begins
to collect on the zinc forming what is called the lead tree. Zinc
occurs in nature most abundantly as the carbonate and as the
sulphide, which is the black jack of the lead miner.
CHAPTER XX. I
COPPER, MERCURY, SILVER AND ALUMINIUM.
COPPER (Cu) is a reddish, malleable, ducile metal found abund-
antly in nature as native copper, and as an ore combined with
sulphur and iron. Copper is used for coins in all parts of the
world, and is an ingredient of most of the gold and silver coins,
giving them additional hardness. Brass is an alloy of copper,
tin and zinc; bell metal and gun metal are alloys of copper and
tin, and aluminium bronze consists of 90 parts copper and 10
parts of aluminium. Hard solder contains equal parts of cop-
per and zinc. Copper is extensively used as a protection for
wooden ships; copper wire of different sizes is the substance gen-
erally used in transmitting electricity for power and lighting
purposes. As copper is found pure, or nearly so, in nature, it
was one of the earliest metals worked by man. The early inhab-
itants of America made cutting tools and ornaments of copper.
In Europe and the east brass or bronze was extensively used
for many purposes before the discovery of methods for working
iron. While iron has supplanted copper in many places, it still
remains one of the most useful and valuable of the metals.
Copper sulphate (CuS0 4 -f-5H 2 0), blue vitriol, is largely used by
the dyer and calico printer, and in the manufacture of pigments.
It is also used in electrotyping, in galvanic batteries, and in
medicine. When heated the crystals lose their water of crys-
tallization, crumbling down to a whitish powder, which again
becomes blue when allowed to combine with water.
Copper is precipitated from the solutions of its salts by the
metals zinc and iron and by the galvanic current. If a strip of
zinc is placed in a solution of copper sulphate it will soon become
covered with a layer of copper, the zinc displacing the copper in
the sulphate as follows : Zn-f-CuS0 4 =ZnS0 4 in solution -j-Cu as a
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LESSONS IN CHEMISTRY. 159
coating on the zinc. A knife blade placed in the solution is
quickly covered with copper. Objects are plated with copper by
placing them in a solution of copper sulphate and connecting
them with a galvanic current, when the sulphate is decomposed
and the copper deposited on the article. There are oxides,
sulphides, chlorides, carbonates and arsenites of copper, but
perhaps the most interesting are the blue and green malachites,
carbonates of copper which are highly prized for their beauty.
The metals generally are solids, but mercury is a liquid at
ordinary temperatures, having none of the properties usually
ascribed to metals except its brilliant luster and high specific
gravity. The pure mercury is sometimes found in nature, but it
more commonly occurs as a sulphide in the mineral cinnabar.
MERCURY (Hg) is obtained from cinnabar by the heat, which
burns out the sulphur, vaporizing the mercury, which is con-
densed in brick chambers or flues. It forms alloys, called amal-
gams, with most of the other metals, especially with gold and
silver. This property makes mercury a valuable agent in sepa-
rating gold and silver from their ores.
Mercury is used in making thermometers and barometers, but
its chief use is in silvering mirrors. The silvering of a mirror
consists of an amalgam of tin. A sheet of tin foil is laid on a
table and rubbed over with mercury, and then another thin
layer of mercury is poured over it. The glass is then carefully
slid over the foil so as to push off some of the superfluous mer-
cury, together with impurities; then heavy weights are laid on
the glass to squeeze out any excess of mercury, and in a short
time the amalgam adheres firmly to the glass.
The mercurous chloride is the calomel used in medicine, and the
mercuric chloride is the active poison, corrosive sublimate. An
oxide of mercury is an ingredient of red precipitate ointment, and
the pigment vermillion is the sulphide. The vapor of mercury, and
nearly all its compounds, are poisonous, and all those who work
with mercury in any of its forms suffer from its effects.
SILVER (Ag) is a white, malleable, ductile metal which is not
easily tarnished or corroded. Pure silver is often found in na-
160 PRACTICAL LESSONS IN SCIENCE.
ture, but it occurs most abundantly as the silver sulphide, com-
bined with lead sulphide and other substances. It also- occurs as
the chloride and bromide. The process of obtaining silver from
its ores is somewhat complicated and costly. In a general way
it is accomplished by heat aided by chlorine from common salt,
and by the dissolving power of mercury or lead, or both.
Silver is used for coin, for plate and for ornaments. Pure
silver is so soft that it is usually hardened by the addition of
from 7 per cent, to 10 per cent, of copper, so that coins and sil-
verware are in fact alloys of silver and copper. It is exten-
sively used in plating ware made of cheaper metals or alloys.
The chloride of silver, formula, AgCl, is one of the richest ores
of silver, and is the form into which silver is usually converted
in extracting it from ores. The chloride, bromide and oxide of
silver are insoluble in water and change color on exposure to
the light. There are many other compounds of silver of which
silver nitrate, AgN0 3 , called lunar caustic, is the most important.
It is used in surgery, and as it blackens on exposure to light is
made the basis of indellible inks. Silver may be precipitated
from solutions by zinc, copper, mercury and other metals.
The chemical changes which silver salts undergo on exposure to
light is the basis of the art of photography. To get a photograph
on glass pour over the glass a mixture of collodion and potas-
sium iodide, which forms a thin film over the glass, which is
then placed in a bath of silver nitrate, here a layer of silver
iodide is formed in the film. The plate is then exposed in the
camera to the action of light from some object to be photo-
graphed. When removed from the camera no image is percepti-
ble, but on treating the film with a "developer" as a solution
of gallic acid in alcohol and acetic acid, the illuminated por-
tions appear black while the shaded portions retain the yellow-
ish color of the iodide. When the details come out clearly, the
developer is washed off and the film treated with a solution of
sodium hyposulphite, which dissolves out the iodide that has not
been affected by the light, then the hyposulphite is washed away
and the plate dried and varnished to protect the film.
LESSONS IN CHEMISTRY. 161
After oxygen and silicon the most abundant element is the
metal ALUMINIUM (Al). It is a tin- white, malleable, ductile,
sonorous metal. It is lighter than most other metals and yet
it is very strong, approaching iron in this respect. It is never
found pure in nature, but is an abundant ingredient in many
minerals. The double silicate of aluminium and potassium
AlKSi 3 8 a constituent of feldspar, is abundant in trap rock,
basalt, mica, and porphyry. Aluminium silicate is the chief
ingredient of clay, shale and slate. Aluminium oxide, A1 2 3 ,
called alumina is nearly pure in the ruby, sapphire and emery.
This metal is an ingredient of several double sulphates called
alums, as AlK(SO- 4 ) 2 +12H 2 potassium alum, AlNa(S0 4 ) 2 4-
12H 2 sodium alum, A1NH 4 (S0 4 ) 2 -|-12H 2 ammonium alum.
Aluminium hydrate (A10 3 H 3 ) combines readily with many or-
ganic coloring matters, forming insoluble compounds. To a so-
lution of common alum add a solution of cochineal, and to the
mixture add a little ammonia when a colored precipitate of alu-
minium hydrate and cochineal will be formed, which is called
carmine lake. Similar precipitates may be formed with other or-
ganic coloring matters. Fiber of cotton that has been soaked in
a solution of alum will retain colors which the cotton alone can-
not hold. Soak a piece of cotton cloth in alum water and let it
dry a day or two, then treat it and a piece of ordinary cotton
with a solution of logwood an*d observe the difference in the
amount and permanence of the color taken by the two pieces.
Substances having this property are called mordants.
Clay, aluminium silicate, is the material of which all grades of
porcelain and pottery ware and all kinds of brick, tile and terra
cotta are made. Clay mixed with water may be moulded in any
required shape and after drying may be burned so as to become
firm and durable, but pure clay shrinks so much in burning that
articles made of it lose their shape and often crack, so that in
making bricks, pottery, etc., more or less sand is added to the
clay making a mixture which shrinks less and holds its form
better than pure clay.
Bricks are made of a great variety of material and vary in
I., s.-u
162 PRACTICAL LESSONS IN SCIENCE.
quality from the heavy compact vitrified brick that will absorb
not more than two or three per cent, of water to the light porous,
fragile brick that will absorb half of its weight of water. Bricks
are made by hand as they were in Egypt four thousand years
ago, and they are made by different kinds of machinery.
Pottery ware that is designed to hold water must be glazed,
which is done by dipping the ware in a mixture of fine sand and
water and heating it intensely, in a kiln into which a quantity of
wet salt has been thrown. The water, sand and sodium of the
salt from a sodium silicate glass, which fuses on the surface of
the ware, making it impervious to water.
In the manufacture of porcelain great care is used in the
selection and preparation of the material, definite proportions
are used and all the manipulations approach mathematical
exactness. One very fine ware is made as follows : The purest
materials are selected in the following proportions: Kaolin,
Al 4 (Si0 4 ) 3 +4H 2 0, 62 parts, chalk, CaC0 3 , 4 parts, sand Si0 2 , 17
parts and feldspar AlKSi 3 8 , 17 parts. These materials are
ground up with water and allowed to settle. The water is
drained away and the mass well kneaded, then stored away in
a damp place for some months, during which time any organic
matter is oxidized and the texture of the mass seems to be im-
proved. It is then moulded, dried in the air, and strongly heated
in a kiln with a wood fire. After burning, the ware must be
glazed, care being used to get a glaze that will expand and con-
tract with the ware so that it will not crack or craze. The glaze
employed at Sevres is a mixture of finely ground feldspar and
quartz. When the ware is dipped in this mixture some of it is
absorbed, a thin coating remaining on the surface. It is now
baked the second time when the glaze fuses, forming aglass var-
nish, which covers the surface penetrating the ware to someextent.
If the ware is to have a uniform color, some mineral pigment is
mixed with the glaze. If designs are to be painted, glasses
colored with metallic oxides ground up with the oil of turpentine
are used. After painting, the ware is again burned so that the
paint is fused upon the glaze.
CHAPTER XXI.
IRON, NICKEL, COBALT, GOLD AND PLATINUM.
IRON (Fe) is the most useful, the most widely diffused, and
next to aluminium, the most abundant of the metals. Meteoric
iron is nearly pure, but native iron is seldom found. Minerals in
great numbers contain iron; in fact there are few substances,
liquid or solid, that do not contain more or less of this element.
The most important ores of iron are the oxides and carbonates,
as the magnetic oxide, hematite, or sesquioxide, which consti-
tute the great bodies of ore found in the old rocks of New York,
Canada, Michigan and Missouri. Clay-ironstone, abundant in
the coal measures, is the carbonate of iron, FeC0 3 , mixed with
clay. It is the chief ore of England.
Iron is reduced from its ores by the action of heat and fluxes
in a blast furnace. The steps in the process are to expel the
water, sulphur, carbonic acid, etc., by heat reducing the ores to
oxides. Next reducing the oxides to the metallic state by heat-
ing them with carbon, and third, the separation of the earthy
impurities by fusion with limestone or clay into a glass or slag,
and lastly the carbonizing and melting of the iron. The blast
furnace is charged at the top with coal, ore and flux in alternate
layers. The air for the support of the combustion is forced in by
a powerful blast. The melted iron sinks to the bottom and is
drawn off into molds, forming the pig iron of commerce. The
lighter slag is also drawn off from time to time. The resulting
gases are collected and used in raising the temperature of the air
of the blast. This iron contains from two to five per cent, of
carbon, is hard, crystalline and easily fusible, being generally
contaminated with silicon, sulphur and phosphorus.
This pig iron is subjected to heat in the puddling furnace,
which oxidizes most of the impurities, finally reducing it to a
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164 PRACTICAL LESSONS IN SCIENCE.
pasty mass, when it is carried to a squeezer which drives out the
slag, welding the iron into a compact body called wrought iron.
Wrought iron may be obtained from some of the purer ores by
heating them with charcoal in an open forge. It is such ores that
are worked by the natives of Africa and Southern Asia.
The pig iron or cast iron is capable of bearing great pressure,
and is useful in the manufacture of articles which are not sub-
jected to heavy tension. Wrought iron is tough, and when
heated slightly may be drawn into wire or rolled into bars or
plates, and is extensively used, especially where toughness is a
quality desired. Steel, in composition, is intermediate between
cast iron and wrought iron. They are each compounds of iron
and carbon, the wrought iron containing very little carbon, one
or two parts in a thousand only, while steel contains from three
to ten parts and cast iron from fifteen to twenty-five parts. In
neither case does there seem to be a definite chemical combination.
Steel is made by heating wrought iron bars with charcoal to a
temperature of about 2,000 for several days, during which time
carbon penetrates the iron and the fibrous structure changes to
a fine granular form. This process is called cementation. These
bars broken up, heated and hammered become more uniform in
texture, more tenacious and ductile, forming what is often called
shear steel. Steel from the cementation furnace is melted in cru-
cibles and molded, forming cast steel, which is more dense, uniform
and hard than the shear steel.
Cast iron is converted into steel by melting it in a large vessel
called a converter, and then oxidizing the mass by currents of air
forced through it. When the oxidation is nearly complete cast
iron enough is added to furnish carbon for converting the whole
mass to steel, when it is cast into ingots. This is called the Bes-
semer process. Steel becomes very hard and brittle when heated
and suddenly cooled, but when allowed to cool slowly it can be
given almost any degree of hardness, with some degree of elas-
ticity. Pure iron is almost unknown, and of no value in the arts.
With all the care exercised in working iron and steel it is almost
impossible to secure uniform product.
LESSONS IN CHEMISTRY. 165
Ferrous sulphate (FeS0 4 -f7H 2 0) is commonly known as
green vitriol or copperas. It is manufactured from iron pyrites,
so common in the coal measures. It is used in the manufacture
of ink and black dyes. There are ferrous and ferric oxides and
chlorides, sulphates, nitrates and silicates, and many other in-
teresting compounds of iron, but they are of little value in the
arts and need not be discussed.
Iron oxides, hydrates and other compounds yield a large
variety of colors, and these compounds are so abundant every
where that iron has been called the pigment of nature.
There are ferrous and ferric cyanides of iron. Common Prus-
sian blue seems to be a mixture of these cyanides, formula
(Fe 7 C 18 N 18 ). It is largely used in dyeing and calico printing.
Potassium ferrocyanide is a mordant of great value.
NICKEL (Ni)is a metal sometimes found in meteoric iron, and is
found associated with cobalt arsenic and sulphur. It is chiefly
valuable from its property of imparting a white color to alloys
of copper and zinc, as German silver and the five-cent coins. The
salts of nickel form green solutions.
COBALT (Co) is a metal somewhat similar to iron, but is not
abundant enough to be of great value, but some of its com-
pounds are important on account of their brilliant and perma-
nent colors. The salts of the oxides have a fine red color in the
hydrated state, while they are blue in the anhydrous. Cobalt
blue is the more common color. Chloride of cobalt is used as a
sympathetic ink. It has a slight pink color when cold and turns
blue when heated.
MANGANESE (Mn) is a hard, grayish-white metal resembling iron
in some of its physical and chemical qualities, and is often asso-
ciated with iron in nature. The principal ore of Manganese is
the dioxide, Mn0 2 . The compounds of Manganese give up their
oxygen readily ; the use of the dioxide in preparing oxygen has
been noted. One of the most interesting and valuable com-
pounds of Manganese is potassium per manganate, KMn0 4 ; it
is soluble in water, forming a dark purple solution. It gives up
its oxygen easily, losing its color, and is much used in purifying
166 PRACTICAL LESSONS IN SCIENCE.
water, as well as in disinfecting or deodorizing decaying animal
and vegetable substances.
CHROMIUM (Cr) is found in nature chiefly as chrome iron ore,
Fe 2 Cr 2 4 . When this ore is heated with potassium carbonate and
potassium nitrate, potassium chromate is formed. And this salt
treated with nitric acid yields potassium dichromate, K 2 Cr. 2 O 7 ,
the most important form of chromium. It occurs as beautiful
red tabular crystals, which dissolve in about ten parts of water.
It is sometimes used in electrical batteries, and is a good oxidiz-
ing agent. Lead chromate is the chrome yellow used in painting
and calico printing.
BISMUTH (Bi) is a grayish brittle metal of crystalline form.
It is used in some alloys as type metal, giving them the property
of expanding slightly in the mold so that they are forced into
the finest lines. Two parts of bismuth, one of lead and one of
tin forms an alloy which melts below the temperature of boiling
water. The nitrate of bismuth is used in medicine.
LEAD (Pb) is a soft grayish metal which is useful in many
ways. Its most common form in nature is the sulphide which
occurs in connection with sulphides of copper, iron, zinc and
silver, with quartz, barium sulphate, calciun fluroide and some-
times with bismuth and antimony. Sulphide of lead or galena
crystallizes in cubes, having a bright metallic luster. Lead is
obtained from galena by heating it with iron, when the latter
combines with the sulphur and the lead is set free. Or the sul-
phide is roasted in the air until some of it is converted into lead
oxide and the lead sulphate, then heated without the access of
air when the lead and sulphur are set free as represented in the
following equations : PbS-f 2PbO=3Pb-f SO 2 and PbS+PbS0 4 =
2Pb-f-2S0 4 .
Lead is malleable, and in the form of sheets is used to line
tanks, cover roofs, make pipes, etc. Lead oxide, PbO is litharge
which heated in the air becomes red lead, Pb 3 4 . The red lead
is used in storage batteries, where it takes up oxygen becoming
lead peroxide Pb0 2 . The red oxide is used as a paint, and in the
manufacture of glass and matches and as a glaze for pottery.
LESSONS IN CHEMISTRY. 167
One part of litharge, and ten parts of brick dust with enough
linseed oil to form a paste makes a cement often used by build-
ers in repairing broken stone. Acetate of lead, or sugar of lead,
is formed by dissolving litharge in vinegar. Lead carbonate,
PbC0 3 is the well-known and much-used white lead.
Lead resists the action of most acids, but when exposed to the
air the surface is soon covered by the lead oxide, which with a
little moisture becomes lead hydrate, which, combined with car-
bon dioxide of the air, becomes lead carbonate. The salts of lead
are in general poisonous, and lead in all forms should be used with
care. Nearly all natural waters act on lead, forming dangerous
compounds. Lead is a constituent of several alloys, as type
metal, and solder; bird shot are an alloy of arsenic and lead, and
some bullets are an alloy of lead and antinfony, the alloys being
harder than lead.
TIN (Sn) is a soft, malleable white metal, having something of
the appearance of silver. The principal ore of tin is the stannic
oxide, Sn0 2 , from which the metal is obtained by heating it with
coal. Tin does not tarnish in the air at ordinary temperatures,
and is largely used as a coating for other metals, as copper and
iron. It is also an ingredient of several alloys, as bronze, solder,
pewter and type metal. The stannic oxide, when melted with
caustic soda, forms the sodium stannate, Na 2 Sn0 3 . This sub-
stance is largely used as a mordant by calico printers. Stannous
and stannic chlorides are also used in calico printing. Stannic
sulphide, SnS 2 , is known as mosaic gold, or bronze powder.
GOLD (Au) is a beautiful yellow metal, surpassing all others in
malleability and ductility. It may be beaten into sheets so thin
that 282,000 of them would make a pile only one inch high.
Gold is less affected by exposure to the air than any other metal,
and is used as a coating of other metals for their protection and
to increase their beauty. Gold is usually found free in the veins
of rocks, or in the sands resulting from the disintegration of the
rocks. It is sometimes so associated with iron, sulphur and cop-
per that it is very difficult of reduction. There are oxides and
chlorides of gold, but they are of little importance. Gold is so
168 PRACTICAL LESSONS IN SCIENCE.
soft that for coin and most other purposes it is alloyed with at
least 10 per cent, of copper.
PLATINUM (Pt) is a grayish-white metal, which is very malleable
and ductile. It resists the action of most non-metallic substances,
and is valuable to the chemist in many ways. It is used for cru-
cibles, forceps, tubes, stills, etc. It forms alloys readily, so that
it should not be used with easily fusible metals. It is much used
in connection with voltaic electricity. None of the platinum com-
pounds are of much value. It usually occurs as an alloy with
palladium, iridium and other metals.
CHAPTER XXII.
ILLUMINATING GAS, ANILINE DYES AND RESINS.
ILLUMINATING gas is one of the products of the destructive
distillation of coal. The coal is heated in earthenware retorts
without access of air till all the volatile matters are driven off,
leaving only gas carbon and coke in the retort. The volatile
products passing through water and coolers loses ammoniacal
liquids and tarry matters by condensation, then through beds of
lime or the ferric hydrate, which removes the sulphur and car-
bon dioxide, and thence to the gasometer. The gas in the
meter consists of marsh gas, hydrogen and carbon monox-
ide, with some vapor of benzole, olefiant gas and other hydro-
carbons.
The ammoniacal liquids are the main source of ammonia and
the ammonium salts. The coal tar contains, or is made up of
many substances which are volatilized at different temperatures.
The first to pass over is water with salts of ammonia in solution,
then a brown, oily liquid, lighter than water, containing benzole
toluole, etc., then a yellow oil heavier than water, containing
napthaline, aniline, carbolic acid, etc., and a black residue called
pitch remains, which is employed in making Brunswick black and
asphalt for paving. The benzole from the light oil is a colorless
liquid with the odor of coal gas. The fact of its dissolving
caoutchouc and gutta percha, and that it removes grease from
cloth and other objects, makes it a valuable substance.
The chief purpose to which benzole is devoted is the prepara-
tion of aniline, which may be converted into the brilliant dyes
now so extensively used. Benzole treated with nitric acid forms
a dark red liquid from which water precipitates a yellow oily
liquid called nitrobenzole. Benzole, C 6 H 6 +HN0 3 =C 6 H 5 (N0 2 ) ,
nitrobenzole. When nitrobenzole is treated with sulphuric acid
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170 PRACTICAL LESSONS IN SCIENCE.
and zinc the hydrogen set free from the acid replaces the oxygen
of the nitrobenzole as follows: C 6 H 5 (N0 2 )+6H=C 6 H 5 NH 2 or
C 6 H 7 N aniline, -j-2H 2 0. Aniline is colorless when pure, becom-
ing brown if exposed to the air. Aniline mixed with a little tolui-
dine derived from toluole, and treated with chloride of lime,
yields a beautiful violet dye. What share the toluidine has in
the production of the color is not known, and the chemical
changes are not understood, but it is known to be an oxida-
tion. Red, blue, green, black, yellow, etc., in varying shades
may be obtained from these substances by the action of various
chemical agents.
Carbolic acid (C 6 H 6 2 ) makes up the greater part of commer-
cial kreasote, which is extensively used as an antiseptic to pre-
vent the decay of wood. Carbolic acid is much used as a
disinfectant. The value of aniline dyes and other products from
coal tar manufactured in Europe amounts to about $30,000,-
000 annually. The recovery of the materials for aniline dyes,
carbolic acid and other substances from the waste products of
gas manufacture is a striking example of the utility of purely
scientific work.
While aniline dyes have superseded many of those formerly used,
yet a few are worthy of mention. Madder, furnishing beautiful
red and purples, is derived from the root of a plant much grown in
Europe. The essential ingredient of madder is alizarin, which
has been prepared artificially from coal-tar products, so that the
madder industry is fast passing away. Brazil wood and log-
wood, quercitron from oak bark, fustic and indigo are important
dyes. Indigo is prepared from various species of plants by al-
lowing them to ferment in water, and when a blue scum appears
on the surface of the water a little lime is added, when the indigo
is precipitated. Cochineal, a dye prepared from an insect, gives
a beautiful red.
The art of coloring fabrics of various kinds has been practiced
by man everywhere from the earliest times. The process varies
with different colors and different fibers. To obtain the finest
shades of mauve, magenta, purple and many other colors on
LESSONS IN CHEMISTRY. 171
silk or wool fiber the whole process consists in placing the ma-
terial in a solution of the desired color; it absorbs the color
becoming dyed. The color enters into such intimate combination
with the fiber that it cannot be washed out. There is probably
no chemical action between the fiber and the coloring matter,
although the union is very close and some have considered it a
chemical union.
In the case of the same kind of fibers, with cochineal, logwood
or madder, there would be no permanent color. In such cases
another class of bodies called mordants is necessary. They in
some way help to make the coloring matters adhere to the fiber.
The substances commonly used as mordants are the salts of
aluminum, iron, tin, chromium, copper and a few other metals.
Woolen goods, after boiling in salts of tin, will take on a brilliant
scarlet in a solution of cochineal. The process of dyeing calico
with logwood is first to pass the calico through a hot solution
of sulphate of iron, then through lime water, which decomposes
the iron salts, setting free the iron oxide, which remains in the
fiber ; the excess of lime is then washed away, preparing the calico
for the logwood. The calico, now of a buff color from the oxide,
when placed in the hot solution of logwood, speedily acquires a
dark hue, and in about half an hour has become dyed a dense
black color. The above will give some idea of the methods em-
ployed in one of the most important industries we have, and
that at every step from the preparation of the dye or mor-
dant it is mainly a chemical process. And a very large propor-
tion of all the chemical elements are in some way used in this
industry.
Some interesting products arise from the destructive distilla-
tion of wood. Wood and coal are both of vegetable origin, but
coal, having suffered partial decomposition, has lost much of its
original oxygen, so that the products of wood and coal differ
somewhat. The gases derived from wood are marsh gas, and
the carbon oxides. Among the liquids are toluole, kreasote,
acetic acid and wood spirit. Paraffin, a beautiful, semi-trans-
parent, waxy substance, is the most important solid. It is used
172 PRACTICAL LESSONS IN SCIENCE.
extensively as a lubricating oil. It burns with luminous flame,
and is used in the manufacture of candles.
Petroleum oil is a mixture of hydrocarbons of the marsh gas
and olefiant gas series, which makes it valuable for lubricating
and lighting purposes. Bitumen, or asphaltvm, is a hydrocar-
bon something like turpentine, which seems to be derived from
petroleum oil. It is soluble in turpentine, and is used as a water-
proof varnish and in making roadways, walks, etc.
When incisions are made in the bark and wood of the different
varieties of pine, spruce and allied trees, a viscous substance
flows out called pitch, gum, turpentine or balsam. It consists of
resin mixed with the essential oil of the plant. When this sub-
stance is distilled with water the oil passes over and the resin
remains, which is called rosin. Turpentine obtained from the
pine yields from 75 to 90 per cent, of rosin (C 20 H 30 2 ), and from
10 to 25 per cent, of essential oil commonly called spirits of tur-
pentine, C 10 H 16 .
Rosin burns with a smoky flame, and is used in the prepara-
tion of lampblack and varnish. The resins generally are in-
soluble in water, but dissolve in alcohol, naphtha and the oil of
turpentine. The solutions thus obtained are called varnishes.
When exposed to the air in a thin layer the solvent evaporates,
leaving a layer of resin over the substance which is impervious to
air and water. Gum copal, shellac, amber and the balsams are
resins similar to common rosin.
The oils of bergamot, cloves, lemons, tolu, valerian and
others are similar to the oil of turpentine, having about the
same composition.
Camphor, obtained from the camphor laurel of Japan, is
similar to the resins, having the formula C 10 H 16 0. It is a crys-
talline substance, melting at 175 F., burning with smoky flame,
and passing into vapor at ordinary temperatures. It is almost
insoluble in water, but is dissolved by alcohol and ether. The
alcoholic solution is known as spirits of camphor.
Asafoetida, aloes, gamboge, myrrh and others are gum-resins
which exude from plants in a milky state, gradually solidifying
LESSONS IN CHEMISTRY. 173
on exposure to the air. They consist of a mixture of gum, resin
and essential oil. They are partially soluble in alcohol, and are
used in medicine.
Caoutchouc is prepared from the milky juice of several varieties
of tropical plants. It is insoluble in water, but soluble in tur-
pentine and naphtha. It is elastic, and when warmed becomes
soft and pliable. It is not acted on by alkalies or dilute acids.
In time it oxidizes into a resin, losing its strength and water-
proof qualities. It is extensively used in the manufacture of
waterproof goods, water tubes, springs, elastic fabrics, gas
holders, etc. In many cases it is used in the manufacture of
waterproof cloth or felt, which is prepared by dissolving the
caoutchouc and spreading it over the cloth or felt, which is then
passed between rollers, which causes firm union, waterproofing
the cloth and strengthening the caoutchouc.
Caoutchouc placed in fused sulphur will absorb large quantities
of that element, and if heated to about 300 F. it becomes vul-
canized, and if heated to a higher degree it at length becomes
vulcanite, which is used in the manufacture of combs, etc. Vul-
canized caoutchouc is not soluble in turpentine or naphtha, and
is not sticky when warmed.
Gutta percha is similar to caoutchouc in many respects, but is
only slightly elastic at ordinary temperatures. It is insoluble in
water and a poor conductor of electricity, so that it is much
used for water pipes and as an insulator for electric wires, etc.
Gutta percha is a hydrocarbon, C 20 H 32 , often mixed with resins.
Caoutchouc, C 5 H 8 , has the same composition with the same pro-
portion of elements, but of different-sized molecules. Such bodies
are said to be isomeric (equal parts) . There are many instances
of isomerism among organic compounds.
Gums, as gum arabic, gum tragacanth appear like resins, but
unlike them are soluble in water, and contain oxygen, gum
arabic having the formula C 12 H 22 O n , and tragacanth C 15i H 20 10 ,
differing by only one molecule of water.
Wood, free from sap, consists of cellulose (C 6 H 10 5 ),lignine and
some mineral substances. The cellulose composes the wood cells,
174 PRACTICAL LESSONS IN SCIENCE.
and is the most abundant constituent; the lignine is the material
lining the cells, and is more abundant in the harder varieties of
woods. Woods differ widely in their physical properties, but are
quite similar in their chemical composition. Beech, birch, oak,
aspen and willow each contain about the same amount of car-
bon. Aspen 49.26 per cent., birch 50.29 percent., and the others
between these amounts varying less than 1 per cent. Of oxygen
willow contains 39.38 per cent., beech 42.36 per cent., the others
between, varying less than 4 per cent. The hydrogen, sulphur,
nitrogen and ash are also nearly the same in each. Cellulose is
nearly pure in cotton, linen and the best kinds of paper. If dry
white paper, pure cellulose, be drawn through a cooled mixture
of two parts of strong sulphuric acid and one part of water, and
then thoroughly washed, it is changed into a semi-transparent
substance called vegetable parchment; when dried it is found
that there has been no alteration in weight or composition, but
it is at least five times as strong as before, and is waterproof.
This change is supposed to be due to change in the molecule.
Cellulose treated with a mixture of nitric and sulphuric acids is
converted into nitrocellulose or gun cotton. Gun cotton dis-
solved in a mixture of alcohol and ether is the collodion much
used by photographers.
CHAPTER XXIII.
STARCH, SUGAR, ALCOHOL AND OILS.
STARCH, C 6 H 10 5 , is a product prepared by growing plants,
as food, for the nourishment of succeeding plants of their kind.
The starch of commerce is prepared from potatoes, rice and wheat.
Starch has the appearance of a white powder, but when examined
under the microscope it is found to consist of grains which vary
somewhat in size and appearance in different plants. The grains
of potato starch are about ^-^ of an inch in diameter, those of
wheat about y-oVo"' and of rice about 3-^^ of an inch.
Starch is insoluble in cold water but if heated with water to a
temperature of about 140 F. the grains swell up, burst and
yield the well-known paste used for stiffening linen and other
fabrics. A dry heat of 140 will also cause the grains to burst,
as in a roasted potato. A few drops of iodine added to a solu-
tion of starch gives a deep blue color, which disappears as the
solution is heated, reappearing as it cools.
When starch is heated to a temperature of about 400 F. it is
converted into a substance, called dextrine, which is soluble in
water. Dextrine has all the properties of gum, and is used by calico
printers for thickening their colors. It is also used as a muci-
lage, and for immovable surgical dressings. Dextrine (C 6 H 10 5 ),
i&isomerie with starch.
When starch is boiled with water containing a few per cent,
of sulphuric acid it is first converted into dextrine, and then into
glucose or grape sugar (C 6 H 12 6 ). These changes are usually
explained by supposing that in dextrine the starch molecule has
been changed in form, and in glucose has taken up one molecule
of water. Cellulose may be changed to grape sugar by the same
process.
SUGAR (C 12 H 22 O n ), occurs in the juices of several plants, as in
sugar-cane, sugar-maple, and sugar-beet. In this country most
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176 PRACTICAL LESSONS IN SCIENCE.
of the sugar is made from the juice of the sugar-cane, while in
Europe the juice of the sugar-beet is generally used. In the
manufacture of cane-sugar the canes are crushed between
grooved iron rollers and the juice mixed with the milk of lime is
boiled in open pans. The lime neutralizes the acids and hardens
some of the impurities; the albuminous matters, hardened by
heat, entangle these impurities and rise as a thick scum. The
scum is removed and the clear liquid remaining is evaporated to
such a consistency that on cooling it separates into two parts,
one crystalline, called brown sugar, the other unerywtalline,
called molasses. These products are purified, refined and con-
verted into the various grades of sugar and sirup of commerce.
Sugar melts to a colorless liquid which on cooling forms an
amber colored mass called barley sugar. When heated to about
400 F. sugar is changed to a dark brown substance called cara-
mel, which is soluble in water, being used for coloring sauces,
gravies, wines, brandies, etc.
The white of an egg is a typical form of an interesting and
important substance called albumen, which is found in all ani-
mals and vegetables. It is composed of carbon, hydrogen,
oxygen, nitrogen and sulphur, but the chemical formula is not
fully known. It seems to be about C 108 H 169 N 27 034S. It is found
in the blood and milk and in lean meat; it is associated with
starch in plants, as the gluten of wheat, and the legumin of
beans. The elements which compose albuminous compounds are
not firmly bound together; they break up and decompose very
readily, and in many cases promote change and decomposition
in other substances.
In addition to the starch, seeds and grains contain some form
of albumen. When placed in warm moist air the albumen
takes up oxygen forming carbon dioxide, and a substance, con-
taining carbon hydrogen, nitrogen and oxygen, called diastase.
Diastase has the power to set up changes by which the insoluble
starch is converted into the soluble glucose, which can be used
by the growing plant as food. If the seed is kept dry or cool it
will remain dormant for thousands of years, but expose it to air,
LESSONS IN CHEMISTRY. 177
warmth and moisture and at once the seed becomes a theater
of activity. Substances similar to diastase occur in the saliva
and other digestive fluids.
In the manufacture of ale and beer the barley is caused to
germinate for a short time and then it is dried at a high tem-
perature which stops the germination, forming what is called
malt. The malt is ground and heated with water for some
hours, during which time the diastase formed, has converted the
starch into glucose and the liquid is called the wort. Yeast is
then added to the wort, which by the process of fermentation
changes some of the glucose to alcohol.
YEAST is a fungoid plant, made up of minute cells, which con-
tain cellulose albuminoid matter and mineral salts. These cells
multiply rapidly in solutions of sugar containing albuminoid
and mineral substances, changing cane-sugar to grape-sugar,
and grape-sugar into alcohol and carbon dioxide. This decom-
position is called alcoholic fermentation. The changes may be
represented by the following equation: cane-sugar (G 12 H^flii^~
H 2 0=C 12 H 24 ]2 or 2(C 6 H 12 6 ) grape-sugar, and grape-sugar,
C 6 H 12 6 =2(C 2 H 6 0) alcohol, +2C0 2 .
ALCOHOL is the important ingredient in all fermented and dis-
tilled liquors, and is obtained from fermented liquors by distilla-
tion. Alcohol dissolves resins, oils and other vegetable substances,
and is much used in preparing medicines and varnishes. It is used
as a fuel and as a preservative fluid, preventing from decay ani-
mal or vegetable substances immersed in it. Wood spirit, or
methyl alcohol, is often used in place of ordinary alcohol.
When a mixture of strong sulphuric acid and alcohol is heated
in a retort there distills over with water a highly volatile inflam-
mable liquid called ether. When ether is inhaled for a few mo-
ments it produces insensibility, and is extensively used in surgical
operations.
When a fermented liquor is exposed to the air it gradually
becomes sour ; the alcohol taking up oxygen is converted into
acetic acid as follows : C 2 H 6 0-h0 2 =C 2 H 4 2 , acetic acid +H 2 0.
The chief source of this acid is the destructive distillation of
L. s. 12
178 PRACTICAL LESSONS IN SCIENCE.
wood. Vinegar is a dilute acetic acid which is prepared in various
ways. It is made from alcohol treated with yeast. It is made
from wine or cider by adding a ferment called the mother of
vinegar, and is prepared from dilute solutions of sugar. Acetate
of lead, or sugar of lead, is used in medicine, and aluminum ace-
tate is used in dyeing.
The process of fermentation is intimately related to bread-
making. Flour is composed of starch, an albuminoid substance
called gluten, with some mineral substances. The flour is mixed
up into a dough with water, yeast and salt, and allowed to stand
for some hours at a temperature of between 70 and 75 F.,
during which time some of the starch has been broken up by
fermentation into alcohol and carbon dioxide, which causes the
dough to swell up and become porous. The bread is then baked
at a temperature of about 500 F. The dioxide expanded some-
what by the heat increases the lightness of the bread, finally
escaping with the alcohol and some of the water. The internal
portions of the bread do not rise above the temperature of
boiling water, but the outside becomes much hotter and is
hardened into a crust, and some of the sugar is converted into
a caramel-like substance which gives the crust a sweetish taste.
Sometimes the fermentation is caused by leaven, being dough in
which fermentation has already commenced, and sometimes the
gas for making the bread light is formed from soda bicarbonate
and hydrochloric acid.
The various fats and oils, whether of vegetable or animal
origin, are mixtures of three well-defined bodies, stearin and
palmatin solids and olein, a liquid. Tallow is mainly stearin,
olive oil mainly olein, lard a mixture of olein and palmatin. They
are composed of carbon, hydrogen and oxygen of a complicated
formula, but are in effect salts of glyceryl. When stearin is boiled
with milk of lime, calcium stearate and glycerin are formed, and
when olein is boiled with litharge (PbO) lead oleate and glycerin
are formed. Glycerin (C 3 H 8 3 ) is a sweet, colorless, sirupy
liquid which dissolves in water or alcohol, but not in ether. It
is used in medicine and ag a preservative fluid.
LESSONS IN CHEMISTRY. 179
When glycerin is poured slowly into a mixture of sulphuric
and nitric acids a yellowish oil, called nitroglycerin, is formed.
It is insoluble in water, but very explosive. For use it is mixed
with some inert matter, as finely divided silica, when it is known
as dynamite.
One of the oldest industries involving chemical principles is
soap-making from natural fats and oils. Hard soap is made as
follows: A solution of carbonate of soda is boiled with lime,
forming an insoluble calcium carbonate and a soluble sodium
hydrate, called soda lye. Tallow is then boiled with a weak
lye, and as the process continues, stronger lyes are added until all
of the tallow has disappeared. In order to separate the soap
from the solution, a quantity of salt is thrown into the liquid,
when the soap rises to the surface, and is transferred to molds.
As tallow contains both stearin and olein the soap formed con-
sists of a mixture of sodium stearate and oleate, while glycerin
remains in solution. When a lye of potassium hydrate is used,
soft soap is formed. A great variety of soaps are made, but in
every case the essentials of the process are the same. Soaps con-
tain from 30 to 80 per cent, of water, which evaporates slowly,
so that in general soap that has been well dried is more econom-
ical than that which is freshly made.
Tallow is extensively used in the manufacture of stearine
candles. For this purpose the tallow is first converted into lime
soap, which is decomposed by sulphuric acid, causing the fatty
matters to separate from the other parts of the solution. They
are then strongly compressed to squeeze out tha olein, leaving
the solid elements for manufacture into candles.
Palm oil, cocoanut oil, olive oil, castor oil are common and
useful oils. Linseed oil has a tendency to become solid when ex-
posed to the air, and is called a drying oil. This tendency is
increased by heating the oil with litharge or the bin oxide of man-
ganese, when it is called boiled linseed oil. This oil is extensively
used by painters everywhere.
Several interesting acids of vegetable origin are used exten-
sively in the arts. Of these, perhaps the most interesting is
180 PRACTICAL LESSONS IN SCIENCE.
9
oxalic acid occurring in sorrel, rhubarb and other plants. It
is prepared by mixing sawdust into a paste with a strong solu-
tion of the potassium and sodium hydrates, and heating the
mixture on iron plates. The wood fiber is converted into oxalic
acid, which combines with the potassium and sodium forming
oxalates, from which the pure acid is obtained . Oxalic acid is
very poisonous ; the best antidote is chalk or magnesia. It is
much used in calico printing, in cleansing articles of brass and
copper, in removing stains of iron rust or ink and as a solvent
of Prussian blue in the manufacture of blue ink.
Wine during fermentation deposits on the inside of the cask a
crust called argol. It is a hydrogen potassium tartrate, and
when purified it is called cream of tartar. From argol, or cream
of tartar, tartaric acid (C 4 H 6 6 ) is prepared by the aid of lime
and sulphuric acid. It occurs in many fruits besides the grape
and is extensively used in dyeing and calico printing. It is also
used in medicine, as Eochelle salts and tartar emetic.
The acid of lemons, oranges and some other acidulous fruits,
called citric acid, is used in the preparation of acidulated drinks.
It is also used in medicine and in dyeing operations.
In the bark of the oak, pine, hemlock and other trees, in the
roots of many plants, in tea, coffee, and many other vegetables
is found an astringent substance called tannin or tannic acid.
Tannic acid may be extracted from its various sources by water,
and is chiefly valuable from the fact that it forms a black preci-
pitate with the salts of the peroxide of iron, and that it forms a
tough insoluble compound with gelatine, a form of albumen, and
with gelatinous membranes. The first characteristic makes it
useful in the manufacture of inks, and the second in the prepara-
tion of all kinds of leather.
In the process of tanning the skins are first soaked for three
or four weeks in strong lime water which removes the fat and
loosens the hair. They are then washed and treated with very
dilute sulphuric acid which removes any remaining lime and
opens the pores of the skin fitting it better for the action of the
tanning solution. They are then soaked in tannic acid solution
LESSONS IN CHEMISTRY.
181
for five or six weeks, then packed with alternate layers of coarsely
ground oak or hemlock bark and covered with water for six or
eight months, changing them occasionally so that all shall be
treated by a uniform strength of the tannic acid. By this time
the hide or skin has increased in weight from 30 to 40 per cent.,
has acquired a uniform brown color and is chemically leather,
ready for various mechanical operations which give it the de-
sired texture and finish. Special processes are used in preparing
kidskins, buckskins, etc. Tannic acid is used in medicine.
Morphine obtained from opium, quinine derived from Peruvian
bark, both used extensively in medicine, are vegetable alkaloids.
Strychnine from nux vomica, and nicotine from tobacco, two of
the most active poisons, are alkaloids, as are theine and caffeine,
the active elements of tea and coffee.
A list of the more important elements, with the symbol and
combining or atomic weight of each.
NON-METALLIC ELEMENTS.
Name. Symbol. Weight.
Oxygen O 15.96
Hydrogen H 1.00
Nitrogen N 14.00
Chlorine Cl 35.36
Bromine Br 79.75
Iodine I 126.53
Fluroine.... ...F 19.10
Name. Symbol.
Carbon C
Silicon Si
Boron B
Sulphur S
Phosphorus P
Arsenic... ...As
Weight.
12.00
28.00
11.00
31.98
30.96
74.90
METALLIC ELEMENTS.
Potassium (Kalium)...K 39.04
Sodium (Natrium) Na 23.00
Lithium Li 7.01
Calcium Ca 39.90
Barium Ba 136.80
Strontium Sr 87.20
Aluminium A! 27.30
Magnesium Mg 23.94
Zinc Zn 64.90
Silver (Argentum) Ag 107.66
Copper (Cuprum). .^....Cu 63.30
Mercury (Hydrargyrum) Hg
Iron (Ferrum) Fe
Nickel Ni
Cobalt Co
Manganese Mn
Chromium Cr
Bismuth Bi
Lead (Plumbum) Pb
Tin (Stannum) Sn
Gold (Aurum) Au
Platinum..., ...Pt
199.80
55.90
58.60
58.60
54.80
52.40
207.50
206.40
117.80
196.20
196.70
CHAPTER XXIV.
BOTANY GENERAL AND STRUCTURAL.
THE science of Botany includes everything relating to the
vegetable kingdom. It considers the external forms of plants,
their anatomical structure, however minute, their classification,
geographic distribution, and economic value. It treats of the
varied relations of plants among themselves, and of their rela-
tions to minerals on the one side, and to animals on the other.
It attempts to examine plants in their earliest form, as single
cells, and to follow them through all their stages of development
until they reach maturity; in short, endeavors to learn the life
history of plants.
Many plants are minute in size, and much of the structure of
all plants is microscopic, so that there is considerable botanical
work which can be done only in well equipped laboratories, with
microscopes, re-agents, and mechanical appliances beyond the
reach of most individuals; but wide and interesting fields, the
greater part of botany, lie easily within the range of the unaided
vision. A good pocket magnifying glass will, however, be found
useful in the study of plants, animals or minerals.
Plants are composed of carbon, hydrogen, oxygen, nitrogen,
sulphur, iron and potassium as essential elements, necessary to
their life and growth, and sometimes they contain phosphorus,
calcium, sodium, silicon, magnesium or chlorine, as elements of
secondary importance in the vegetable structure. While the plant
is made up of the elements mentioned, it cannot feed on them as
elements, they must be united into compounds as water, carbon
dioxide, ammonium nitrate, calcium phosphate, etc., before the
plant can utilize them for food. Oxygen seems to be the only
exception to this rule, being an elemental plant food.
The living portion of the plant, that which moves, appropri-
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LESSONS IN BOTANY. 183
ates food and grows, is a transparent, semi-fluid, albuminous
substance, called protoplasm. It is the protoplasm that takes
up these mineral compounds and transforms them into the struc-
tures and compounds of the vegetable kingdom. It is impossible
to distinguish the protoplasm of plants from that of animals.
We cannot say that they are the same for the precise nature of
living matter cannot be determined, but we know that the "physi-
cal basis of life "has in all cases some common characteristics of
structure and behavior, diverse as are the ways in which its
activity may be manifested.
Corn, beans, wheat or other grains growing by themselves or
in pots with other plants, are interesting objects for observation
and comparison, whether in the home or schoolroom. If the tip
of the root of a grain of corn or the bean be divided lengthwise
with a sharp knife, then moistened with a solution of iodine, it
will assume a yellowish or brownish color indicating the presence
of protoplasm. If the tip of the root is dipped in a solution of
sugar and then moistened with a dilute sulphuric acid, a reddish
color will show the presence of protoplasm.
Sometimes in the lower order of plants, as in slime-moulds, the
protoplasm is without form, but in general it occurs in somewhat
definite forms of minute size called cells, which are enclosed by a
wall of cellulose, secreted by the protoplasm. The protoplasm
contains carbon, oxygen, hydrogen, nitrogen, sulphur, and pos-
sibly iron ; and in addition the cellulose contains potassium and
possibly lime, so that the cell contains the essential elements of
the plant. The cell is the unit of all vegetable structures from
the simplest to the most complex. In some cases it performs all
the functions of a plant; it takes food, grows, reproduces its
kind, and dies.
Free cells are in general somewhat spherical in form, but when
grouped in masses they are more or less angular from pressure
upon each other, so that they may be cubical, tabular or many-
sided. It frequently happens that cells grow more in some direc-
tions than in others, and thus elongated cells are formed which
are sometimes cylindrical and sometimes angular. The walls of
184 PRACTICAL LESSONS IN SCIENCE.
cells are often thickened in various ways, forming wood cells,
spiral or banded cells, etc.
New cells are formed by the division of old cells, each division
soon growing to the size and form of the original, as in the
growth of some of the lower forms of plant life, and in the tips
of growing roots. And new cells are also formed by the union of
the contents of two cells, as in the reproduction processes of some
of the lower plants.
Besides the protoplasm within the cell wall there is often a
delicate green coloring matter called chlorophyll, which may be
dissolved out with alcohol. The chlorophyll gives the green
color to the leaves, stems and other parts of growing plants.
Another product of plant cells is starch, as in the potato, wheat,
corn and other grains. In addition to other substances many
cells contain solutions of various forms of sugar, as cane sugar,
grape sugaT, beet-root sugar, etc.; and the cells of some plants
secrete oils, as olive, castor, linseed and palm oil, the oils of tur-
pentine, lemon and thyme. Others secrete such substances as
camphor, essence of cinnamon, wintergreen, etc., and as the es-
sential oils of onions, mustard, asafcetida, etc. Others again
secrete gums, as gum tragacanth, gum arabic, and many others.
Several important acids are the product of vegetable cells, as
tartaric, citric and tannic acids. In addition to those mentioned,
opium, quinine, and other valuable medical substances, and many
valuable dyes are the products of cell action.
The embryos of all plants begin as single cells, and some of
the lower plants during their whole existence consist only of
single cells. In some cases cells at first distinct become united
more or less closely into a common mass, each cell to a great ex-
tent remaining a distinct individual. Sometimes the partitions
between contiguous cells are dissolved away, and the two cells
are merged into one. In this way long tubes or vessels are
formed. But in the great majority of plants the cells are com-
bined into tissues. They may be joined end to end, form-
ing threads, filaments or hairs, or they may be joined end-
wise and sidewise, forming cell surfaces, or they may be joined
LESSONS IN BOTANY.
in three directions forming masses of greater or less size and
solidity.
At the tips of young stems and roots there are groups of ac-
tive cells which, multiplying by division and growing rapidly,
form what is called the vegetative cone of the root or stem. This
mass of cells is sometimes called the primary meristem, the sec-
ondary meristem being a layer of cells between the bark and
wood of plants called the cambium layer. From the meristem
tissue all the other tissues of the higher plants are developed.
The next most important tissue is called parenchyma. It is
composed of cells whose walls are thin, nearly colorless and
transparent, and which vary greatly in form. This tissue makes
up the whole substance of many plants of the lower order, and
the essential portions of the green or assimilative, growing and
reproductive parts of the higher plants. Another tissue, perhaps
developed from parenchyma by thickening the walls of the cells
along their angles, is called collenchyma, or thick angled tissue.
It is found beneath the epidermis of many plants, for the pur-
pose, doubtless, of giving support and strength to it. Another,
in which the cell walls are somewhat uniformly thickened, is
called sclerenchyma. It occurs in the mosses, ferns and higher
plants.
The most abundant and important tissue after parenchyma is
the fibrous tissue. It is composed of long thick-walled cells,
which constitute the tough, flexible part of the bark, called bast,
and the hard woody parts of the stems of plants and the frame-
work of leaves. In some plants, as the milkweeds, there are nu-
merous vessels, containing a milky or colored fluid, which form
what is called the lactiferous or milk tissue. Another group of
vessels having numerous openings in their thin walls constitute
what is called the sieve tissue, which is abundant in the grape
vine, in ferns and other plants. Besides those mentioned, there
are in the higher orders of plants elongated cells whose thickened
walls are perforated at places where similar vessels touch each
other. They are called spiral, pitted or banded vessels, etc., and
together make up the tracheary tissue. While young these cells
186 PRACTICAL LESSONS IN SCIENCE.
contain protoplasm, but as they become older it disappears and
the tissue only contains air.
These various tissues are grouped into three systems : the epi-
dermal, the fibro-vascular, and the fundamental. Neither of
these systems occur in the lowest plants. The epidermal system
is the most simple, and appears earlier in the life of the individ-
ual, and earlier in passing from lower to higher forms than the
other systems. The first indications of this system is in smaller,
darker colored surface cells in some of the lower fungi and their
allies, while in some of the mosses a distinct epidermis occurs,
becoming well developed in the ferns and flowering plants. The
epidermis proper consists of modified parenchyma, the cells
changing form, thickening and hardening their walls and finally
losing their protoplasm.
From these epidermal cells hairs are produced, especially on
young roots, which vary somewhat in form and are active agents
m absorbing nutritive matters for the plant. And in the epider-
mis there are numerous stomata or breathing pores, which open
directly into intercellular spaces below. They are more numer-
ous on the under surface of leaves; on the lower surface of a
black walnut leaf there are nearly 300,000 stonmta in one square
inch of surface, with none on the upper side; while in the case of
a leaf of corn or maize, there are about 60,000 to the square
inch on the upper surface and about 100,000 on the lower sur-
face. In the case of the iris leaf and oat leaf there are more on
the upper surface.
In most of the higher orders of plants the fibrous, sieve and
tracheary tissues, with some parenchyma, form bundles of com-
pact tissue running through the plant from roots to leaves.
They are called the fibro-vascular or vascular bundles. The
young radish is crisp and brittle the vascular bundles are not
noticeable; but later, as they are more fully developed, the rad-
ish becomes stringy and woody. They constitute the framework
of leaves and may be separated from the more delicate tissues by
maceration, and they are easily found as threads in the pith of
the cornstalk. The components of the bundles vary in their pro-
LESSONS IN BOTANY. 187
portions in different plants ; but in every case they serve to
strengthen the plant structure and as a means for conducting
liquids from roots to leaves.
The fundamental system includes all the tissues not found in
the other systems, being made up mainly of parenchyma, thick
angled tissue, milk tissue, etc.
An examination of a green stem of Indian corn will give one a
good idea of the vascular bundles and the parenchyma surround-
ing them. An examination of the leaf stalk of the squash shows
whitish bands extending from end to end just beneath the epi-
dermis. They are masses of thick angled tissue, which may be
torn out, when the stalk becomes weak and flexible. The large
pores seen in cross sections of oak, ash and other woods are
pitted vessels.
Plants are made up of the various tissues and systems men-
tioned. The lower plants consist mainly of parenchyma, while
all three systems unite to form the bodies of the higher plants.
Such plants are made up of stem, leaves and roots.
The typical stem is illustrated in the trunk of a tree or the
body of an upright plant, bearing branches and leaves and sup-
ported by roots; but it also appears in many other forms : First,
as runners, which are slender and weak, creeping along the ground
and bearing stunted leaves or bracts, as in the case of straw-
berries. Second, rootstocks, scale-bearing underground stems,
as in the case of ferns. Third, tubers, scale-bearing, thickened
and subterranean, as the potato. Fourth, the cormb, a thick,
solid body with thin leaves, subterranean, as the Indian turnip.
Fifth, bulbs, small bodies covered by the thickened bases of
leaves, as the onion. Sixth, tendrils, slender branches usually
destitute of leaves. Seventh, thorns, short, thick, pointed
branches without leaves.
The leaves are broad, flat expansions of chlorophyll-bearing
tissue, supported by a framework of fibrous tissue. They may
be reduced to bracts, or scales, which have but little chlorophyll,
or, modified in form and color, they make up the different parts of
the flower, as the sepals, petals, stamens, pistils, and sometimes
188 PRACTICAL LESSONS IN SCIENCE.
they become tendrils, spines, and in some cases cups. Besides
these there are numerous outgrowths of the epidermal system,
known as bristles, prickles, scales, glands, root hairs, etc., which
are called trichomes.
The roots which fix the plants in the ground, or on some sup-
port, and absorb nutriment for the plant, show little variation
in form. The roots of parasites are usually short and thick, and
sometimes provided with sucker-like organs. And the aerial
roots of orchids, and similar plants, often have a thickened
epidermis containing more or less chlorophyll.
All parts of a growing plant are abundantly supplied with
water; it makes up about 75 per cent, of the weight of plants.
Water is constantly being taken up by the roots, and as con-
stantly being evaporated from the leaves. It has in solution,
materials from the soil and soluble products of plant action.
The tissues are constantly taking materials from this liquid for
their growth, and the various secretions, as oils, gums, acids,
etc., are formed from materials taken from the same source. The
cause of the movement of water or sap in plants is not fully
understood.
In the chlorophyll parts of plants during the daylight water
and carbon dioxide are broken up into materials for starch, cel-
lulose and other hydrocarbons, and oxygen is set free. This pro-
cess is called assimilation. These materials are then changed to
sugar, cellulose, protoplasm, etc., by a process called metastasis,
or metabolism. This process is not understood, but it seems to
go on more rapidly at night, and to be attended with the evolu-
tion of carbon dioxide, while assimilation is attended by the
evolution of oxygen.
In many plants starch or other material is stored up for the
future use of the plant in modified stems, as potatoes, onions,
etc. ; in seeds, as in the various grains, and in buds. In most
cases this material is used as a supply of food for the growth of
young branches or the young plant. Some plants are parasites,
taking materials already assimilated from other plants. Again,
they are partially parasitic, where some food is assimilated in the
LESSONS IN BOTANY. 189
plant. Many plants are saprophytes or partly so, deriving their
food wholly or partly from decaying matters.
The processes of assimilation and metabolism can only be car-
ried on within certain degrees of temperature; the limits vary with
different plants. In many plants these changes progress at tem-
peratures very little above freezing point, and in some plants
they are carried on freely at a temperature of from 110 to 120
F. Many of the subjects mentioned in this chapter will be more
fully discussed and illustrated in subsequent chapters.
CHAPTER XXV.
BACTERIA, ALG.E, FUNGI, AND LICHENS.
AMONG living things two processes must be maintained; first,
the nutritive, on which the life and vigor of the individual plant
or animal depends; second, the reproductive, on which the life of
the race, the perpetuation of the species, depends. The differences
in structure among plants, and the modifications of structure by
which the plant adapts itself to its surroundings, are important
items to consider in the study of plants. The structure of plants
and the processes of nutrition and reproduction comprise nearly
all the work of botany.
There are a great many kinds of plants, and it would be an
endless task to try and study each one ; but many plants are
similar to other plants in structure, in methods of reproduction,
etc., so that a careful study of one plant gives a good idea of
many similar plants. Plants are divided into species, genera ,
families, orders, divisions, etc. On the basis of structure we have
cellular plants, made up wholly of parenchyma, and vascular
plants in which the vascular bundles are prominent features of
the structure. These groups are separated into divisions mainly
on the basis of differences in the reproductive processes.
The division including the lowest plants is called PROTOPHYTA,
first plants. These are the lowest and simplest plants, usually of
minute size; the cells are poorly developed, and often there is no
cell wall. In many cases the plants consist of only one cell, and
when there is an aggregation of cells, the union is usually so
slight that each cell is practically an individual.
If we add a few drops of yeast to a solution of sugar and keep
it in a warm place, the mixture will soon become turbid and then
frothy, will lose its sweetness and acquire a spirituous odor, and
at length a scum of yeast will collect on the surface of the liquid.
(190)
LESSONS IN BOTANY. 191
If some of this scum be spread out on a piece of glass and exam-
ined with a pocket magnifier, fine grains may be seen scattered
through the mass. These grains, called torulse, are the active
part of the yeast. They are living bodies, as shown by the ra-
pidity with which they grow and multiply. Each torula is a cell
tvhich gives rise to minute buds, which grow rapidly and finally
become detached from the parent cell, though generally not till
they have themselves developed other buds. When yeast is dried
and burned it gives rise to an odor similar to that which arises
from burning meat. Dried yeast forms a fine powder which dif-
fuses itself rapidly through the air, so that a solution of sugar
open to the air, if kept warm, will soon begin to ferment from
yeast particles received from the air.
Infuse or steep some hay in warm water for an hour or so,
then filter it and set the filtrate in a warm place, and from time
to time notice the changes which take place in it. At first the
solution is clear, after 24 or 36 hours it becomes turbid, as did
the yeast solution, and at length a scum forms on the surface
and the solution acquires a putrid odor. These changes are due
to the growth and multiplication of Bacteria. All forms of putre-
faction are due to fermentation set up by bacteria of different
kinds. A living thing dies, other things still living attack the
dead body and speedily convert it into gases and liquids which
may be used for food by the same or other forms of life.
Bacteria may be developed in almost any vegetable infusion.
They are minute ; they cannot be studied in detail without pow-
erful instruments, but it is interesting to note the work of these
minute but numerous beings, which in some sense are the sub-
stratum of life. When dry the bacteria forms a dust of minute
grains which is diffused through the air everywhere, furnishing
the material for fermentation wherever the air can go freely.
They have size and form, for they may be filtered out of the air.
Take three test tubes and fill each about one-third full of
freshly made hay infusion; cause the solutions in two of the
tubes to boil for a few minutes, then while it is boiling cork one
of the tubes with a mass of cotton wool and let it boil for a min-
192 PRACTICAL LESSONS IN SCIENCE.
ute or so after closing; put the three tubes in a warm place and
note the results. Bacteria are developed promptly in the un-
boiled solution, and also appear in the boiled solution of the
unclosed tube, but not as promptly as in the first, while none ap-
pear in the other if the experiment was well performed. Experi-
ments show that every form of bacteria may be filtered out of
the air by a mass of cotton wool and in other ways; that they
may be filtered out of water by such material as porous pottery-
ware, and that if a body of air remains at rest for a few days
these germs of bacterial life will settle out of it so that it is as
pure as if filtered.
It is by excluding the germs of bacteria that vegetable and
animal substances are preserved from decay by the process of
canning. The discovery of bacteria and the recognition of their
importance in the economy of nature has been of great value to
man. It has promoted a more rational treatment of disease,
and has greatly extended the domain of surgery.
Another interesting one-celled plant, sometimes called a green
slime, is found as a green coating on the north side of old fences
or trees, especially after a few days of wet weather. Pieces of
wood or bark bearing this plant may be kept dry for a long time,
becoming fresh when moistened. Notice the color, and with the
pocket lens notice that it appears as if dusted over the surface.
Scrape off some of the slime and put it in a little alcohol, and after
an hour or so notice the color of the alcohol. The green color of
the plant and the color it imparts to the alcohol is due to the
delicate coloring matter called chlorophyll, which, in general, is
formed only in the sunshine. Potato stems growing in the sun-
light are bright green, but are nearly white when growing in the
dark. This slime is called Protococcus. It multiplies rapidly,
not by the process of budding, as did the torula, but by division,
one cell dividing into two and these dividing again, etc.
A dark blue-green scum is very common on stagnant water
about watering troughs, along street gutters and other places.
It can be kept for observation in water in an open dish. If a
small portion of this scum be allowed to remain for a few hours
LESSONS IN BOTANY. 193
in a saucer with a little water it will spread out in good shape
for study. Then notice the form and color of the hairlike fila-
ments and possibly careful observation will allow one to see the
slow vibratory movements which give this plant the name of
Oscillaria. The filaments are composed of cells attached end to
end in colonies, but each is an individual as fully as the cells of
protococcus.
These minute plants all live in water or in damp shady places,
yet all retain their vitality for a long time when dried so as to
form an impalpable dust. While these plants are minute in size
and simple in structure they constitute an important branch of
the vegetable kingdom.
On the surface of stagnant water and in quiet water along the
edges of streams, in the early spring, little patches of a frothy
substance appears, sometimes called frog spittle, later the sur-
face is covered with a bright green scum, and during June and
July great patches of a dirty brownish scum is present with the
green. When lifted from the water it has a slippery feel, and
strings out like wet hair. The plant is some species of Spirogyra
or Zygnema. It may be grown for observation in an open dish
of water, with some soil at the bottom, in which some water lov-
ing plant is growing.
The long hairlike filaments are colonies of cells attached end
to end as in oscillaria. The cells in spirogyra are marked by
spiral bands of chlorophyll, while in zygnema there is a central
starlike nucleus, with the chlorophyll in bands or plates. They
multiply by division as do protococcus and oscillaria, but in ad-
dition there is another form of reproduction. At the close of their
growth in the spring, the cells push out little processes from
their sides, which meet similar processes from other cells of par-
allel filaments. They flatten upon each other, the walls fuse and
are absorbed, leaving a connecting channel between the two cells,
through which the protoplasm of both cells become one mass.
This mass secretes a wall of cellulose forming a zygospore or
germ, which has much thicker walls than the ordinary cell, and
from which a colony of cells or plants may be developed.
L. S.-43
194 PRACTICAL LESSONS IN SCIENCE.
These bodies sink to the bottom of the water, when released
by the decay of the old cells, resting there till the next season.
With the warmth of spring, the zygospore becomes active, little
bubbles of gas are formed, which float it to the surface of the
water, the central portion lengthens, partitions are developed
forming cells, which multiplying by division extend intoahairlike
filament. Some idea of the cell markings and of the fruiting
stage can be gained by examination with the naked eye or with
the simple magnifier, but these plants are interesting if we can
do no more than observe the different stages of growth, the
changes in color, the rapid increase in bulk, their complete disap-
pearance at the end of the growing season and other phenomena
visible to the naked eye.
Another interesting plant colony common in ponds and sluggish
streams is the Water net. It is a tubular net composed of elon-
gated cells which, when full grown, are sometimes one-third of an
inch in length. The protoplasm of some of these cells breaks up
into a great number of daughter-cells which arrange themselves
into a miniature net inside the mother-cell which is set free by the
absorption of the enclosing walls. In other cells thousands of
little ciliated swarm spores are formed, which, after swimming
about for a time, thicken their walls and sink to the bottom of
the water, where they remain for a time in a resting stage, as in
the case of spirogyra.
The Fungi or Moulds are closely akin to the plants just consid-
ered. A common one forms a greenish coating upon bread, leather
and other substances left in damp places. When examined the
green color seems to be due to a fine powder which is apparently
the same as the torulae. Each of these grains or spores gives
rise to a long tubular filament called a hypha,, and a number of
these hyphae, make up the body of the fungus, which is called the
mycelium, hyphae projecting downward and upward like roots
and shoots from the mycelium. Some of the hyphae projecting
upward develop spores at their summit.
Moulds are easily grown for observation. A little moistened
horse dung placed in a, dish and covered with a glass will furnish
LESSONS IN BOTANY. 195
a vigorous growth of Mould. When these are full grown, some
of the spores may be sown on a piece of moistened bread,
which, under a glass will soon develop a fine crop of Mould.
The moulds do not contain chlorophyll and are saprophytes,
living upon decaying vegetable or animal matter, or they are
parasitic.
With the moulds, spirogyra and water net are associated des-
mids which are found abundantly in shallow fresh water, and
diatoms which occur in both salt and fresh water, often forming
a thin yellowish layer at the bottom of the water. These forms
of life are beautiful and interesting objects of study, but their
minute size makes their observation difficult. This group of
plants is called ZYGOPHYTA,from the fact of their forming a zygo-
spore or yoke spore. The plants of this group differ considerably
among themselves but are similar in their modes of reproduction,
but not alike, as in some cases the spores have organs of locomo-
tion while in others they do not have them. Yet in this respect
this class is clearly superior to the protophyta.
The next division of plants is called OOPHYTA, egg-spore-plants.
The distinguishing characteristic of the plants of this group
is that they develop special cells which contain one or more
rounded masses of protoplasm which are fertilized by the con-
tents of another special cell of smaller size, which results in the
production of an oospore from which a new plant may be de-
veloped.
In streams and ponds tufts of da,rk green plants may be seen
floating in the water from stones or sticks or other objects to
which they are attached. These masses of vegetable matter are
probably the simple or branching filaments of some species of
(Edogonium. These plants multiply by the sexual process of re-
production as above, and by an asexual process as well.
The Vaucheria is another member of this division of plants.
It forms dense felt-like masses in water, or on damp ground or
rocks. They do not have the slippery feel of spirogyra but
change to a dingy color at the fruiting stage and the filaments
are coarse enough so that many things can be learned about
196 PRACTICAL LESSONS IN SCIENCE.
them from observation with the naked eye. In studying the
vaucheria during the fruiting stage, it will be found interesting
to observe them carefully several times during the day, especially
late at night, and early in the morning.
Other members of this group are the seaweeds, Fucus and Sar-
gassum. They grow from just below low- tide to just above high-
tide, and often attain great size. They are washed ashore in
great quantities during storms, and are much used for manure,
and from their ashes Iodine and Bromine may be obtained.
The CARPOPHYTA or spore-fruit-plants are distinguished by the
formation of a sporocarp as the result of the fertilization of the
female element. The sporocarp usually consists of a fertile part
which produces spores, and a sterile part, so formed as to inclose
the fertile portion. The spores are not the direct but a secondary
result of the fertilization. The plant body usually has a more
perfect development than in the previous divisions.
To this division belong the large and interesting class of sea-
weeds called Florideae, which are noted for their delicate forms
and rich coloring. They are mostly of a red color, due to a pig-
ment soluble in cold fresh water. The color varies through every
shade of red from bright rose to purple. Irish moss used for
making blanc mange is one of the best known.
To this division also belong a great group of parasitic plants
or fungi, and while they are too minute for detailed study, yet
their presence in patches on plants and something of their effects,
their color, their changes when fruiting, etc., are interesting sub-
jects of study. A species occurs on the leaves of the apple and
cherry, another on the leaves of the willow; another on the
leaves of the grape, doing much injury, is called Oidium Tuckeri.
One occurs on the leaves of the maple and a very common spe-
cies is found on the leaves of the lilac. They occur on the leaves
of the oak, elder, mandrake, pea, and many other plants.
In the study of these fungi or mildews, or any other plant, it
is interesting to watch several plants of the same species through
the whole growing season, noting all changes, so as to get some
idea of the life history of the plant. By watching several plants,
LESSONS IN BOTANY. 197
mere accidental changes may be eliminated, so that at the end
of the season a clear and complete history can be given of the
particular species studied.
Lichens, a large and well-known group of plants, belong in this
division. These plants are common everywhere and have been
carefully studied, yet there has been much difference of opinion
about their true nature. The idea seems to prevail that they are
fungi which live in association with algse, which may be proto-
phytes or zygophytes, plants of a higher order as parasites on
those of lower orders. A lichen of Asia Minor is used for food,
and the so-called Reindeer moss is a lichen. They grow on the
bark of living trees, on rocks and decaying wood, and on the
ground ; they vary greatly in form and color, and are interesting
subjects for study. The ergot of rye, the rust of wheat, and the
smut of wheat, oats and barley and their allies, belong to this
division of plants.
The most valuable and best known group of this division are
the mushrooms. They are saprophytes, and the largest of the
Fungi, growing with great rapidity and decaying rapidly after
maturity is reached. Many species are poisonous, but many are
edible, and in France they are extensively cultivated for food ; in
one cave there are over six miles of mushroom beds.
The only chlorophyll-bearing plants in this division are the
Characese. They are submerged water plants, slim and delicate
in structure, sometimes attaining the height of two or three feet.
They grow in close patches at the bottom of fresh-water lakes,
ditches and streams ; in deep or shallow, stagnant or running
water. They are easily grown in an open dish, and associated
with spirogyra, or some other of the scums, make an attractive
and entertaining addition to a group of house plants.
The divisions already considered constitute the Thallophytes
of some authors, who generally divided them as follows : Algse,
aquatic chlorophyll-bearing plants; Fungi, terrestrial, sapro-
phytic, or parasitic plants destitute of chlorophyll; and Lichens,
terrestrial plants containing green gonidia. But the classifi-
cation already given, based mainly on the character of the
198 PRACTICAL LESSONS IN SCIENCE.
reproductive apparatus, has the sanction of the latest and best
authorities.
These plants show no indication of true roots, stems or leaves.
They are made up mainly of parenchyma cells showing no
wood cells, tubes or other characteristics of stems. Yet while
they are low in form and structure, and are of comparatively
small economic value, they are numerous, far exceeding the num-
ber of the higher plants. We cannot learn many things about
them by examination with the naked eye; but what we can learn
is of great interest, leading us into comparatively untrodden
fields of nature.
Among these cellular plants the nutritive processes go on in
all parts of the organism, there being little or no division of
labor, each cell acting a.s an individual. In the study of these
plants we have found three classes: the chlorophyll plants that
absorbed their nourishment, as carbon dioxide, water, etc., from
the mineral kingdom these in the sunlight were changed into
such compounds as the plant could build into tissue; others,
called parasites, absorbed compounds already prepared for use
from the juices of chlorophyll plants, and from them built up
their tissues; others called saprophytes absorbed compounds
from decaying vegetable substances, from which their tissues
could be nourished.
The members of this group of plants affect man in various
ways; directly, in causing such diseases as intermittent, typhoid,
yellow, scarlet and typhus fevers, cholera, smallpox, croup, con-
sumption, erysipelas, and many other diseases; and indirectly,
in causing diseases of domestic animals, as splenic fever, fowl
cholera, swine fever, rabies, glanders and others. And they are
the cause of the various kinds of fermentation, some of which
are valuable and some harmful. Some fungi are valuable for
food, but many of them are injurious. They cause skin diseases,
as ringworm. They infest almost every useful plant, lessening
the quantity of the food product, injuring its quality, as in the
case of the rust of wheat, the potato fungus and those which
infest the grape.
LESSONS IN BOTANY. 199
They attack many kinds of insects, as flies, wasps, beetles,
spiders, butterflies, etc., in some cases causing their death. Fish
are subject to attack from fungi. As saprophytes fungi are
doubtless in many cases beneficial; but they promote the decay of
timber, whether in the house, ship, bridge, furniture, or the piece
thrown aside as useless. Without going into further detail it
seems clear that Bacteria, Fungi and Algae are important mem-
bers of the vegetable kingdom , that they are present everywhere,
and that their general effect is to disintegrate and destroy the
more highly organized groups of plants and animals.
CHAPTER XXVI.
BRYOPHYTA, MOSS PLANTS AND PTERIDOPHYTA, FERN
PLANTS.
N
THE BRYOPHYTA are in some sense a transition group between
the cellular plants below and the well developed vascular plants
above. A plant called Marchantia polymorpba is a good repre-
sentative of a portion of this group. It is found in damp shady
places, growing on the rocks or on moist ground. It consists
of flat leaf-like stems, producing fine silky hairs from the lower
surface which serve to attach it to its resting place, and they
probably absorb nourishment as well, acting as true roots. The
dark green upper surface is covered with minute diamond-shaped
markings.
The reproductive organs occur on separate plants as disk-
crowned stems about an inch high. The antheridia or male ele-
ments have a scalloped disk, while the archegonia or female ele-
ments have the disk cut into finger-like rays. After fertilization
a sexual spore, called an oospore, is formed in the archegonium,
from which a sporogonium is developed. In the sporogonium
asexual spores are formed from which new plants grow. On the
upper surface of the plant little cups or cupules occur which con-
tain bright green scale-like bodies called gemmse. The gemmae
grow into new plants.
In studying this plant notice carefully the points already men-
tioned, note the difference in color between the upper and lower
sides of the plant, note the mode of branching, the indented
apex, the median line or midrib. Note also the pores on the
upper surface. Remove some of the gemma? and placing them
on a white surface, study their form. Examine carefully the
orchegomal and antheridial branches, and compare them with
(200)
LESSONS IN BOTANY. 201
each other. Write out an account of everything observed, with
a description of the locality in which the plant was found.
In the plants heretofore studied there was little differentiation
of parts, but in the marchantia the upper surface seems to have
been specialized for the purpose of assimilation and reproduc-
tion, and the under side for the absorption of nourishing liquids.
And there is some thickening of cell walls, and some indications
of the development of a vascular system. Marchantia grows
well in greenhouses and may be grown for observation on moist
earth anywhere about the house.
The true Mosses are common wherever moisture is abundant,
in swamps, on the ground, on trees, rocks and decaying vegeta-
tion. The stem, roots or root hairs and leaves in form and func-
tion are similar to those of the higher plants. The spore formed
by the sexual organs produces a branching body called the pro-
tonema, from which the moss plant proper grows, producing at
length the archegonia and antheridia. Mosses may be grown
for observation on moist decaying wood or earth under a glass.
In studying mosses, notice the following: the stem, its height,
shape and color, make a cross section of it and note different
tissues as shown by different colors. Note the shape, color and
arrangement of the leaves; study the flowering heads, the male
with its rosette of green leaves, and the female with the
leaves folded into a bud ; compare them in other respects ; note
the fruit which is a cylindrical pod or capsule, and the hood fit-
ting over the pod, remove the hood and note appearance and
contents of the pod. Make full notes of what you observe and
describe the locality in which the moss was found.
In the groups previously studied the sexually formed spore
produced a plant like the parent, but in this group it grows into
a fruit or sporogonium, which forms asexual spores that pro-
duce plants like the original. This process is known as an alter-
nation of generations.
In the economy of nature Mosses, with Lichens and other
plants of the lower orders, are precursors of higher plants; they
appear first on rocks and sterile places ; sand and dust collecting
202 PRACTICAL LESSONS IN SCIENCE.
around them with the decaying leaves and stems at length form
soil suitable for higher plants. Some species of Sphagnum grow-
ing in swamps enter largely into the formation of peat bogs, and
perhaps helped to form some varieties of coal. This moss is ex-
tensively used in packing trees and plants for shipment, and some
species are used for stuffing mattresses. Some species of mosses
and lichens are almost the only flora of the polar and high
mountain regions.
Pteridophytes or Ferns, produce no highly colored flowers, yield
no rich perfume, yet no group of plants attracts more notice, are
more sought for cultivation, or more enjoyed than the ferns,
whose sole charm consists in their delicate, graceful, feathery foli-
age. Ferns are abundant in all parts of the world, but exist in
greatest variety in the hot moist regions of the tropics. There
are said to be some 3,000 species ranging in size from less than
an inch to the gigantic tree ferns of Australia, some of which
reach an elevation of 75 feet, with leaves or fronds which exceed
in size those of any other plants. While in general they seem to
enjoy rich soil and warm, moist, shady localities, they do grow
on exposed hillsides, on rocky cliffs, and sometimes on trees
as air plants. They are not only abundant now, but they
have been a marked feature in the flora of the earth from very
early times. Their remains are found in the rocks of the Devo-
nian age, while the coal of the succeeding age is made up mainly
of the stems and leaves of ferns and allied plants.
Ferns consist of a stem, rootstock or rhizoma which is usually
horizontal and subterranean, but in some cases it creeps along
the surface ; and sometimes it is erect, as in the case of tree ferns.
From the rhizoma arises the leaf which consists of a stalk or
stipe and the blade or frond. The stipe may be green or black ;
may be smooth and polished or covered with scales or hairs;
the frond may have an even, uniform outline, like the leaf of an
apple tree, or it may be divided and subdivided into many dis-
tinct parts, as in the case of the maiden hair fern, so common
everywhere.
The continuation of the stipe through a simple frond is called
LESSONS IN BOTANY. 203
the mid vein, in a divided frond it is called the rachis. When a
frond is cut into lobes extending halfway or more toward the
mid vein, it ia pinnatified ; when the divisions extend to the mid-
vein the frond is simply pinnate, and the divisions are called pinnae.
When the pinnae are lobed the frond is bipinnatified and the lobes
are called segments. When these divisions extend to the mid vein
of the pinnae the frond is bipinnate and the divisions are called
pinnules, and the midvein of the pinnae becomes a secondary
rachis. The delicacy and extent to which this division is carried
is the chief beauty of many ferns.
Besides the leaves, the stem gives rise to roots, so that the
ferns and their allies are the first plants to show distinct stems,
roots and leaves; and in them the three tissue systems first make
their appearance. If the stipe of almost any fern be crushed or
broken, the vascular bundles, as yellowish bands, are easily found
and with a little care may be traced into the stem or rhizoma,
and also into the divisions and subdivisions of the frond. The
epidermal and'fundamental tissues can easily be made out at the
same time.
The reproductive process in the ferns is interesting and some-
what peculiar. On the under surface of the frond bodies called
sporangia are developed, in which spores are formed. The
spores, when mature, develop into a flat roundish body, deeply
notched on one side, so that it is sometimes heart-shaped, which
is called the prothalium. The prothalium develops the sexual
organs, archegonia and antheridia. After fertilization an ovum
is developed in each archegonium which produces a young fern.
The prothalia in most cases are small, and they escaped the eye
and investigation of the botanist until about 1848, when they
were discovered and the mystery of the reproduction of ferns
was cleared up.
Some variety of the maiden-hair fern may be found in almost
any locality. It may be recognized by its black polished stem,
which divides into two equal recurved branches, from these arise
secondary branches which support oblong leaflets. On the under
side of the leaflets, along their margins are the crescent-shaped
204 PRACTICAL LESSONS IN SCIENCE.
masses of sporangia called sori. The plant should be gathered
for study some time in August, and the fresh specimen may be
studied, or the stem and roots may be preserved in alcohol, and
the stipe and frond dried in a plant press or book, and the study
made at some other time.
With the complete plant in hand, notice the dark brown stem,
from which the slender branching roots arise, then the leaf with
its polished stipe and green leaflets, and lastly the hairs on the
roots, the scales on the rhizome, and the sori on the leaflets, which
together are called trichomes. Each of these parts is worthy of
study. Notice the shape, size and surface of the rhizome, its
growing apex and dying base. Those places on the rhizome from
which leaves grow are called nodes and the intervals between the
nodes are the internodes. Examine the buds at and near the
growing end of the rhizome; some show rudimentary leaves with
coiled stalks, and one or more are simply continuations of the
stem. Notice the arrangement of the buds and leaves on the
rhizome.
Crush a portion of the rhizome and then pick out the whit-
ish bands of vascular tissue, trace this tissue into buds, leaves
and branches of the stem. Make cross sections of the rhizome at
the nodes and between them and note the outer ring of brown
tissue, and the somewhat horseshoe-shaped whitish mass, the
vascular bundle; examine several sections so as to get a clear idea
of the position of this tissue in the internodes, at the nodes and
other places. Split a portion of the rhizome with a sharp knife
and examine the sections carefully. Notice the shape of the roots,
their mode of branching, the root hairs, the growing tip, make a
cross section and look for the vascular bundle.
Note the color, form and mode of branching of the stipe .or
rachis of the leaf, trace the vascular tissue into branches and
smaller divisions of the rachis. Make cross sections at different
places along the rachis, and compare with sections of the rhizome.
Study the shape of the leaflets and compare the one at the apex
with others on the seconday branches. Note the surface, texture,
color and framework or veins of the leaflet.
LESSONS IN BOTANY. 205
On the under side of some leaflets note the crescent-shaped sori,
find out if there is any law as to which leaflets carry sori. After
soaking in water open a sorus, and note what forms the cover,
called the indusium. The yellowish spheroidal bodies in the sorus
are the sporangia, notice that they are attached to the veins of
the leaflet. Study a sporangium noting its shape, stalk, and the
ridge, called the annulus, extending part way round it. Burst a
sporangium and note the minute bodies called spores. The spor-
angium is opened by the straightening of the annulus; place some
sporangia that have been soaked in water on a piece of glass,
watch them through a lens, noting the process of opening. Make
a diagram of the mode of branching, and write out a description
of what has been observed. A larger fern might be more interest-
ing and easier to examine in some respects. The same general
plan can be followed in examining any fern.
Such a study gives one some idea of the gross anatomy of the
fern and is full enough for purposes of classification. For classi-
fication the maiden-hair fern Adiantum pedatum is described as
follows by Prof. L. M. Underwood : Root, many delicate fibers
somewhat matted. Rhizome, scaly somewhat creeping. Stipe,
slender, polished, black, forked at base of frond forming two
recurved rachises. Frond, roundish in outline, formed of sev-
eral pinnse, which branch from the recurved rachises; pinnules
unequal sided, oblong or deltoid ; upper margins irregularly lobed,
surfaces smooth. Veins, free, several times forked. Sori, borne
at the end of the veins on the under side of the reflexed margins
of the lobes, which form somewhat kidney-shaped membranous
indusia. Sporangia, globose with a nearly complete vertical ring.
Spores, too minute for examination with an ordinary lens.
The germination of fern spores may be studied by sowing them
on closely pressed muck, or even on a piece of glass, and keeping
them warm and moist. In this way the prothalium may be ob-
tained for study.
The method of veining varies somewhat and often serves as an
aid in classification. In many cases the veins are free, that is
arising from either side of the midvein they do not unite with
206 PRACTICAL LESSONS IN SCIENCE.
any other vein. In other cases the branches of adjacent veins
unite forming a net work near the margin of the leaflet. The
sporangia in the true ferns are collected in clusters on the back of
the frond or are variously arranged in lines along the veins or
around the margins. The sporangia may be naked or covered
by an indusium. In the case of the ostrich fern, the sensitive and
cinnamon ferns there are sterile fronds, and fertile fronds, the
latter bearing large globose sporangia, appearing very little like
fronds; only a careful study of their life history would make one
sure of their origin.
Besides the ferns, the pteridophyta include the Equisetacese,
called horsetails or scouring rushes, and the Lycopodiacese called
lycopodium or club-moss. No member of the pteridophyta is of
great economic value, yet as the source of our coal supply they
have an honorable historical record.
CHAPTER XXVII.
THE ANTHOPHYTA, LEAVES, REPRODUCTIVE ORGANS AND
FRUIT.
THE anthophyta, or flowering plants, make up the greater
part of the vegetable kingdom. They include the common herbs,
shrubs and trees, the plants that are cultivated for pleasure and
profit, the plants that furnish materials for the food, clothing
and shelter of man.
Among these plants, the stem, roots and leaves are usually well
developed and the three tissue systems are clearly defined. And
there is a strict division of labor in all physiological functions,
indicating a more complex and highly developed organism than
among the plants already studied.
Leaves are organs of assimilation, and in a modified form
constitute the organs of reproduction for this group of plants,
so that they seem the most important parts of the plant. A
leaf consists of a vascular framework covered by a mass of par-
enchyma, whose cells are well supplied with chlorophyll, and the
whole covered with a delicate epidermis. The parts of a leaf are
the stalk or petiole, and the blade or expanded portion, and at
the base of the petiole there are sometimes leaf-like bodies called
stipules. The petiole continued through the leaf is the midrib,
and its branches and subdivisions are called ribs, veins and vein-
lets. The framework of the leaf is a branch from the vascular
system of the stem.
On the basis of the arrangement of the veins, leaves are
divided into two classes, namely netted- veined, as the leaves of
the apple and oak, the veins forming a conspicuous net work, and
the parallel- veined, as the leaves of corn and grass, in which
there are few branches, and no net work is formed.
Leaves vary greatly in form, some of the more common forms
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208 PRACTICAL LESSONS IN SCIENCE.
are: linear, when the leaf is several times longer than wide
and of the same width throughout; lanceolate, when sev-
eral times longer than wide and tapering upwards and down-
wards from the lower third of the leaf; oblong, when two or
three times as long as broad with rounded base and apex ;
elliptical and oval, much the same as oblong but taper-
ing more toward the ends of the leaf; ovate, when the out-
line is like the lengthwise section of a hen's egg, the broader end
downward; orbicular, when nearly circular in outline. When
the leaf tapers toward the base it may be oblanceolate, spatu-
late, obovate, or wedge-shaped.
If we consider the base of the leaf it may be cordate, or heart-
shaped, reniform or kidney-shaped, auriculate or eared, sagi-
tate or arrow-shaped, and hastate or halberd-shaped. The leaf
of the water-lily and mandrake are peltate or shield-shaped.
When the apex of the leaf is considered it may be acuminate
or pointed, acute or obtuse; truncate, when the end appears as if
cut off square ; retuse, when the rounded summit is slightly in-
dented; emarginate, when the summit is decidedly notched;
obcordate, when the apex is heart-shaped; cuspidate, when
tipped with a sharp rigid point ; aristate, when the apex is like
a bristle.
Leaves also vary in outline. When the margin is an even line
without teeth or notches the leaf is entire. It is serrate or saw-
toothed when the margin is cut into sharp teeth pointing to ward
the apex of the leaf. Dentate, when the teeth are wider and point
outward; crenate, when the teeth are rounded; repand or
wavy; sinuate, like repand with deeper waves; incisid, when
the margin is cut into sharp, deep and irregular teeth.
When the incisions do not extend more than halfway to the
midrib, dividing the leaf into a definite number of somewhat
rounded parts, it is said to be lobed, and the divisions are called
lobes, and their number is expressed by the phrase three-lobed,
five-lobed, etc. If the divisions extend more than halfway to the
midrib, the leaf is said to be cleft, and it may be three-cleft or five-
cleft, etc. If the incisions go nearly to the midrib or base of the
LESSONS IN BOTANY. 209
blade, the leaf is parted. If the divisions extend to the midrib,
or petiole, the leaf is said to be divided.
In studying leaves it will be noticed that the lobes, divisions,
etc., correspond to the veining of the leaf, the veins and divisions
in some cases radiating from the base of the leaf blade, when they
are said to be palmately veined, lobed, parted, etc., as in the
maple leaf; in other cases the branching, lobes and divisions are
related to the midrib rather than to the base of the leaf, when it
is said to be pinnately veined, lobed, parted, etc., as in the leaves
of the oak.
When a leaf consists of two or more parts, each part with a
distinct petiole, joined to the midrib or common petiole, it is a
compound leaf. It is often difficult to determine whether a leaf
is compound or simply divided. Leaves may be palma tely com-
pound, as in the case of the horsechestnut, or pinnately com-
pound, as in the case of the locust and pea.
A pinnately compound leaf may terminate with a single leaflet,
a pair of leaflets, or a tendril. The leaflets of compound leaves
may be divided and subdivided, and the leaf be bipinnate or tri-
pinnately compound, or twice palmate, etc.
Sometimes the stem grows through the base of the leaf, when
the leaf is called perfoliate. Sometimes two opposite leaves seem
to have grown together at the base, forming one roundish leaf
with the stem through the center. Such leaves are said to be
connate-perfoliate.
Many leaves are nearly horizontal with an upper and lower
side. Many others are nearly vertical, having inner and outer
surfaces, as the leaves of the iris. An examination of the leaves
of the iris shows the older straddling over the younger, as a man
straddles a horse, hence the leaves are called equitant leaves.
Equitant leaves, and many others, have no distinction of petiole
and blade, as the lea.ves of the pine, spruce and juniper. The
stipules are sometimes large and conspicuous, as in the case of
the pea and clover. Sometimes they form a sheath around the
stem, as in some grasses, where they serve as petioles.
Leaves sometimes take the form of cups, as in the pitcher
L. s.u
210 PRACTICAL LESSONS IN SCIENCE.
plants ; sometimes they are so formed as to serve as insect traps ;
sometimes they serve as storehouses for food and as foliage also,
and sometimes they appear as spines, tendrils or scales. Foliage
leaves are the most prominent parts of the plant, and are much
used in describing and classifying plants ; hence the necessity of
studying carefully the forms of leaves, and of naming them ac-
curately. Leaves differ in color. The under side differs from the
upper side. Sometimes they are smooth, sometimes hairy or
woolly, etc., all of which may be important details in the identi-
fication of a plant. To gather leaves, to study them in all their
details, to describe them accurately, is an interesting and valu-
able educational exercise.
Leaves usually arise from definite places on the stem called
nodes or joints. If two arise from the same joint, they are on op-
posite sides of the stem, the pair above stand at right angles
with the first pair and the third pair above are directly over the
first, so that there are four ranks or rows of leaves along the
stem. Another arrangement is when the second leaf is opposite
but on the joint above, the third being over the first, when there
are only two rows of leaves along the stem. Another is when the
second leaf is on the joint above, but only one-third the way
around the stem, so that the fourth above stands over the first
and there are three rows of leaves along the stem. Sometimes
there are several leaves on one joint when they are called whorled
leaves, and sometimes, as in the pine, they form a cluster or fas-
cicle which appear to be the leaves of a whole branch, which is so
short that the leaves seem to arise from one joint, but examina-
tion shows a spiral arrangement. Other arrangements occur,
any of which can easily be made out from the careful study of
young stems.
The buds from which branches grow are developed in the axils
of leaves, so that the branching of a plant or tree follows the
arrangement of the leaves and is always definite, although it is
often difficult to discover the law on the older parts of the stem
as many branches have been destroyed. This same arrangement
extends to the location of flowers on the stalk, so that while on
LESSONS IN BOTANY. 211
a hasty glance, one might think the top of a plant, shrub or tree
a mass of disorder, yet a careful investigation would show that
everything was in a definite place according to a plan.
The flower consists of parts or organs designed for the produc-
tion of seeds from which new plants may grow. The parts of a
complete flower are the calyx, the corolla, the stamens and pistil
or pistils. The flower is a short branch and the parts are com-
posed of more or less modified leaves arranged according to the
leaf plan of the plant.
The calyx is the lowest or outer whorl of leaves, they usually
have about the same color as the foliage leaves, and are called
sepals. Sometimes the sepals grow together forming a cup or
tube, when the calyx is called monosepalous. When the sepals
are distinct the calyx is polysepalous. The calyx may be regular
when all the sepals are alike, or they may vary in form when it
will be irregular.
The second whorl of leaves called petals make up the corolla.
They are usually of some attractive color differing widely from
that of the foliage leaf. The corolla may be monopetalous or
polypetalous, and it may be regular or irregular, and in some
cases it is wanting, when the flower is said to be apetalous, the
sepals sometimes having the appearance of petals.
The next whorl of leaves have been changed into stamens. A
stamen consists of a filament or stalk and the anther. The fila-
ment, usually slender, is sometimes broad and leaf-like. Some-
times the stamens are distinct, sometimes united into a tube,
when they are said to be monodelphous. Sometimes they stand
on the common receptacle of the flower, as an independent
group of organs, when they are said to be hypogynous, under
the pistil ; they maybe on the calyx around the pistils, when they
are perigynous ; they may be on the ovary, when they are epigy-
nous; they are sometimes united with the pistil, when they are
gynandrous; and again they may stand on the petals, when they
are epipetalous. Sometimes the anthers are united, when they are
syngenesious. The filaments may be of different length ; if there
are four stamens, two long and two short, they are didynamous.
212 PRACTICAL LESSONS IN SCIENCE.
When there are six, four long and two short, they are tetradyna-
movs. The variety of positions in which stamens are found has
led some authors to doubt whether they are changed leaves,
considering them as possibly outgrowths from the epidermal
system of the plant.
The anther consists of two lobes or cells in which pollen grains
are formed, that contain the fertilizing element of the plant.
When the anther is attached by its base to the apex of the fila-
ment, it is innate; when attached for its whole length to the side
of the filament, it is adnate, and when fixed near the middle to
the apex of the filament, it is versatile. When it faces inward, it
is introi'se; when outward, it is extrorse.
The upper or innermost whorl of the floral leaves form the
pistil or pistils. A pistil consists of a stigma, style and ovary.
The ovary is the enlarged hollow part of the pistil in which the
ovules are formed, the part from which the ovules arise being
called the placenta. Above the ovary the pistil narrows into the
style which bears the stigma, which is a moist, glandular body of
varying shape. There may be several pistils in one flower; or two
or more may unite, forming a compound pistil. If we think
of the ovary as formed from a leaf by bringing its edges to-
gether, the line of union is called the inner suture, and a line cor-
responding to the midrib of the leaf is called the outer suture.
The inner or ventral suture is the placenta. When two or more
ovaries unite to form a compound ovary, the union is usually
along their ventral sutures so that the ovules are attached to a
column in the center of the ovary; and sometimes the partitions
dissolve away and a one-celled compound ovary results with the
ovules on a stalk in the center.
In some compound ovaries the ovules are on the walls and not
in the center. We may imagine in such cases that the three
or four or more leaves forming the ovary united with each
other by their edges, thus forming ventral sutures at the junc-
tion of two leaves instead of at the junction of the edges of the
same leaf. In one case the placenta is central, in the other it is
said to be pariet&l.
LESSONS IN BOTANY. 213
Ordinarily the calyx is below the ovary, but sometimes the
calyx adheres to the ovary, so that the stamens and petals are
around or above the ovary, when the ovary is said to be inferior,
half inferior, or superior, as the case may be. Sometimes the
leaf forming the pistil is not closed, the pistil being a scale-like
leaf bearing the ovules on its upper or inner face near the base.
This form of pistil is peculiar to the pine family which is named
gymnospermous, or naked-seeded.
The ovule at first is a mass of parenchyma, a little later an
integument grows over the mass called the secundine coat, and
later another integument is formed called the primine coat. These
coats do not completely cover the ovule, a small opening called
the micropyle always remaining over its apex. Later an embryo
sac forms near the apex of the ovule.
In fertilization, the pollen grains are conveyed to the stigma
by the wind, by insects, or birds, or in some other way. The
grain resting on the moist surface of the stigma, absorbs mois-
ture and germinates, sending out a tube which penetrates the
soft tissues of the stigma and style, to the cavity of the ovary
where it enters the micropyle of an ovule, and through its tissues
to the embryo sac, where fertilization takes place.
As a result of the fertilization there is formed a proembryo,
from which is developed the embryo, which consists of one or two
leaves or cotyledons, the plumule and the root or radicle.
With the embryo in the embryo sac is formed the endosperm
which serves to nourish the embryo. The walls of the ovule
thicken and harden and the seed is formed.
Fruit usually consists of the seeds inclosed in a variously
modified ovary. Sometimes the wall of the ovary thickens and
becoming soft as it ripens, forms such a fruit as the currant,
gooseberry, grape and tomato. This softened wall may be cov-
ered with a thick skin as in the orange and lemon, or a hard rind
as in the melon and squash. While in the cherry and peach the
inner part of the ovary forms a stony wall about the seed while
the outer forms the delicious fruit. The blackberry consists of
the softened end of the stem on which the flower stood, covered
214 PRACTICAL LESSONS IN SCIENCE.
with little stone fruits. In the case of the apple, pear and quince
the thick fleshy part is not the wall of an ovary but a thickened
calyx.
Sometimes the wall of the ovary becomes thin like a mem-
brane, or hardens, or remains herbaceous, forming fruits, that
in some cases open at maturity for the escape of the seed, while
in other cases they remain closed, having the appearance of sim-
ple seeds, and are called akenes. The fleshy part of the straw-
berry is the softened end of the stem on which the flower stood
and the real fruits are ripened ovaries, usually called seeds,
scattered over its surface. The fruit of the sunflower, dandelion
and many others are akenes. In the case of wheat, corn and
other grains, the seed and ovary wall adhere so as to form one
body, so that a grain of wheat is a true fruit, called a caryopsis.
Capsule or pod is the name for dry seed vessels that split open
at maturity. The pea-pod is a good illustration. Fruits were
designed to help in some way toward the reproduction of species;
in many cases they serve as storehouses of food to aid in the
growth of the young plant. And they are the most valuable
sources of food for man and domestic animals.
CHAPTER XXVIII.
THE GYMNOSPERM.E.
THE Anthophyta are divided into two classes, the Gymno-
spermte, in which the ovules and seeds are not inclosed in an
ovary, and the Angiospermse, in which the ovules and often the
seeds are inclosed in an ovary.
The AngiospermaB are divided into two subclasses, the mono-
cotyledons, in which the embryo has one cotyledon, and the
plants generally have parallel veined leaves, and the numerical
plan of their flowers is three ; and the dicotyledons, in which the
embryo has two cotyledons, and the plants generally have netted
veined leaves, and the numerical plan of the flowers is five. This
subclass includes the greater part of plants and trees of the tem-
perate zones.
The gymnosperuise all have woody stems, and generally nar-
row, needle-shaped, parallel veined leaves. The members of this
class are mostly trees, including the redwood, pine, spruce, cedar,
fir and cypress. The male and female organs are in different
flowers, which are very simple, consisting of one or more stamens
in the one case, and naked ovules in the other. After fertilization
the embryo, consisting of root, stem and leaves, is soon formed.
The various parts of the reproductive organs are homologous
with those of the pteridophyta, the material from which the em-
bryo sac and embryo are developed corresponding with the
prothallium.
A careful study of the Scotch or the Austrian pine will give us
clearer ideas of the whole class than to spend the same amount
of time on several members of the group.
The Scotch pine is a species often planted for ornament. The
leaves, from two to four inches long, occur in pairs, and are cov-
ered with a whitish powder which gives a peculiar color to the
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216 PRACTICAL LESSONS IN SCIENCE.
tree. The cones are small, about two inches in length, the free
ends of the scales being produced into protuberances, which are
sometimes recurved. The Austrian pine has longer leaves of a
dark green color, without powder. The Cones are much larger,
but without the recurved protuberances.
As plants vary considerably during the growing season, a com-
plete study necessitates continuous observation during the inter-
val between fertilization and maturity, with a study of every
phase of growth ; or specimens of the different stages of develop-
ment may be collected and preserved in alcohol, so that the study
can be made at any time of the year.
The male flowers of the Scotch pine form a catkin or spike-like
cluster at the base of the young shoots, and should be gathered
for study in May or June. The female flowers form inconspicuous
clusters toward the end of the young branches. Specimens should
be gathered as above, and later in the season also. Leaves and
stems and young cones, found just below the new shoots, should
be gathered in July or August, and the terminal buds and mature
cones in late autumn. Fresh leaves and stems may be used at
any time, but the resin which abounds in fresh material often
makes it unpleasant to work with.
In studying the pine notice the central shaft or trunk of
the tree, extending without division to the very summit. Note
the whorls of branches at definite places on the stem, and
also the angle they make with the main stem, and compare the
pine with other kinds of trees in these respects. . In young trees
or branches of older trees note the difference in vigor between the
terminal and lateral shoots. Make cross sections of the smaller
stems and branches, then counting the rings of growth, notice if
there is any relation between the age of the stem and the number
of whorls of branches. Note the short branches bearing the pairs
of green leaves, pull out the leaves and then from the scars study
the numerical arrangement, also study the arrangement of the
scales on a mature cone and compare the two. Notice the surface
of the youngest shoots, then following the branch back to the
main stem note any changes as to bark, scales, etc.
LESSONS IN BOTANY. 217
Notice the position, shape and size of the buds; split a terminal
bud lengthwise and study carefully the relative position and the
form of the different parts; carefully take off some of the scales
with needles and note the character of their edges, and the differ-
ences between the apex arid base; note the secondary or new
buds, their form, position, etc. Compare the bud with a branch,
and observe whether the bud is a branch or not. Make a cross
section of a stem which is a half inch or so in diameter, and note
the central pith, the woody portion with its rings of growth, and
the bark outside the wood. Notice the fine lines radiating from
the pith to the bark, called medullary rays, and note that many of
them do not reach the pith. Notice also many scattered openings
from which resin exudes, they are resin ducts occurring both in
the wood and in the bark. Study the rings of growth noting the
difference between the inner and outer portions.
The bark may be divided into three layers an inner, whitish,
fibrous layer, the middle green layer and the outer brownish por-
tion. Note the relative thickness of these layers and the resin
ducts in the middle one. Split a portion of the stem and study
the appearance and relation of the various parts in the longitu-
dinal as well as in the cross section.
Notice the color, shape and texture of the leaves, note theapex,
edges, base and surface. Make cross sections and longitudinal
sections and notice the fibro-vascular bundles, resin ducts, the
green tissue and the epidermis.
Take a cluster of male flowers and note that it is made up of a
central axis on which are arranged the short-stalked bodies, called
stamens. Each stamen consists of a flat scale, bearing on its in-
ferior surface two enlargements, the pollen sacs. Find a pollen
sac that has burst and note the location and character of the
opening, burst a pollen sac and notice the yellowish grains of
pollen that escape. The flowers on a very short stalk are crowded
on an axis forming a cluster called a spike. Notice that the
flowers each replace a "branch on the young shoot.
Taking a spike of female flowers, notice the stalk or peduncle
by which it is attached to the stem, and that the spike is com-
218 PRACTICAL LESSONS IN SCIENCE.
posed of thin scales or bracts and thicker ones called carpellary
scales. Dissect out one of thicker scales and study its shape and
texture and compare it with the thinner bract. Note the promi-
nent ridge or keel on the upper surface and the two enlargements
near the base, the ovules. Notice the position of the ovules and
the opening at the free end called the micropyle. Note that the
cluster seems to take the place of a branch.
Split a one year old cone and examine carefully all the parts
in section, notice the ovules, the abortive ovules, the scales, and
make a diagram showing the relation of the parts to each other.
Dissect out an ovule and bisect it through the micropyle, and
notice the nucleus, and a large cavity called the embryo sac,
enclosing a soft substance called the endosperm.
In the mature cone notice the heavy carpellary scales, and the
smaller bracts, and along the inner surface of the scales will be
found a pair of thin wing-like scales, each bearing at its lower
end a seed or an abortive ovule.
In the case of the seed, note its form, character of surface,
micropyle, etc. Bisect the seed lengthwise, parallel with its nat-
ter faces, and notice the firm outer coat, the embryo and the
food for the embryo, the endosperm. Carefully pick out the
embryo with needles and note the short stem, and the young
leaves.
A study of the pine according to the foregoing scheme will give
one a good idea of the gross features of the pine family. The
careful study of one tree or plant is of great value even though
it may be far from complete. The scheme suggested may be va-
ried to suit individual ideas and opportunities. The idea has
been to encourage careful, systematic study, and to this end full
notes should be taken, and numerous drawings, diagrams and
sketches made and specimens gathered and preserved for reference
and study.
The wood of the pine is composed mainly of tracheides, while
the bark is made of sieve tissue and bast fibers. The tree grows
from the cambium layer or meristem tissue lying between the
wood and the bark. The cells of this tissue undergo division by
LESSONS IN BOTANY. 219
the formation of partitions, and the new cells develop into trach-
eides or wood cells on the one side and into sieve tissue and bast
fibers on the other. The new wood incloses the old, while the old
bark is outside the new, serving as a protective coating for it.
In the class Gymnospermse are included the Cycads, Conifers
and the Joint Firs. The conifers are the only ones common in
the United States, and the only ones of commercial value. The
order conifers includes the juniper, cypress, white cedar, arbor
vitce, the giant redwood, the silver fir, the tamarack or American
larch, the white pine, the sugar pine of California, the yellow pine
of Georgia, and many others. There are some 300 species of
pine, growing mostly in cool climates. In general, they are rapid
growers, furnishing strong and durable timber and lumber.
CHAPTER XXIX.
MONOCOTYLEDONS.
THE class Angiospermse includes the great mass of the flower-
ing plants. They differ from the gymnospermae in that they gen-
erally have the male and female organs in the same flower ; they
have the ovules in a closed ovary, and the flower differs more
widely from the other parts of the plant.
The subclass monocotyledons has one cotyledon, parallel
veined leaves, and parts of the flower in threes, and the structure
of the stem differs from that of the dicotyledons. A cross section
of a stalk of Indian corn, which belongs to this group of plants,
shows it to be composed of parenchymatous tissue traversed
by great numbers of fibro-vascular bundles. These bundles are
more numerous toward the surface of the stem, so that it in-
creases in density from the center outwards, the central portion
often disappearing leaving a hollow stem, as in the grasses.
These bundles are closed bundles; as they become permanent
tissue no cambium or meristem tissue remains and no further de-
velopment is possible, and such plants are usually short-lived.
The different stages of germination in these plants may be ob-
served by planting several grains of corn, and then by examining
a different grain every few hours the process may be followed
closely. The first leaf of the young plant has its dorsal surface
in contact with the endosperm or food supply, curving entirely
around the remainder of the embryo. As it begins to grow the
root pushes through the root sheath. The plumule, consisting
of a minute stem and a few rudimentary leaves, pushes out
through the curved cotyledon, which remains in contact with
the food supply, absorbing nourishment for the growing parts.
Make out these points from the study of the germinating grains,
making notes and sketches.
The monocotyledons include about fifty natural orders of
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LESSONS IN BOTANY. 221
plants. The most important of these is the order graminse, or
grass family. The members of this family are herbaceous, rarely
woody plants, with round stems, mostly jointed and hollow,
bearing alternate two-ranked leaves, each of which has a split
sheath or stalk. The flowers are arranged in spikelets, which
form a more or less compact cluster, which may be a spike or
panicle. The calyx consists of leaves called glumes, and the
parts of the corolla are called palets, which often bear bristles
called a-wns. There are rarely more than three stamens, and the
anthers are versatile. The ovary contains one ovule, which at
maturity forms a caryopsis, or grain. This is a large and widely
distributed group of plants, including the cultivated grains and
grasses, which furnish the major supply of food for man and
domestic animals.
The more important members of this order are wheat, rye,
barley, the oat, rice, Indian corn, and the grasses, timothy, red-
top, blue-grass, orchard grass, etc.; also the sugar cane, and
many others. We may gain some idea of the characteristics of
this interesting family by studying the cultivated grass known
as the oat. Specimens should be collected when some of the
flowers are expanded and others yet in the bud. They should not
be pulled up, but dug up with care and the dirt shaken gently
from the roots, which may be cleaned by washing. If possible
secure specimens with the empty grain from which the plant grew
still attached.
Notice first the parts of the plant, the roots, the stem with its nu-
merous branches to ward the top; the leaves, and possibly root hairs
may be seen as well as outgrowths from the stem and some parts
of the flower. Study carefully the different groups of roots, the
points from which they arise, their arrangement, relative size, etc.
The strongest root, from t he grain, is called the primary; those
from the nodes on the stem are secondary roots. Make a cross sec-
tion of a primary root and of a secondary root and notice the
parts shown and compare them. Strip off the bark from a root
and note its character, and that of the fibrous tissue which re-
mainsnote the position of the root hairs.
222 PRACTICAL LESSONS IN SCIENCE.
Remove the leaves and study the stem, noting its shape and
surface; make a section through a joint or node and note the
partition separating the cavities of the internodes. Make a
cross section and note the vascular bundles and the cortical or
bark layer with its clusters of chlorophyll cells. Make longitu-
dinal sections and find the parts shown in the cross sections.
In studying the leaves notice the split sheath with the thin
membraneous ligule, and compare the two as to texture, form
and use. Notice the shape of the blade, the veins, their direction,
and relations to each other; make a cross section and locate the
vascular bundles; the green tissue between is the mesophyll, or
parenchyma of the leaf.
The stem of the plant is the main axis of inflorescence; its
branches are secondary axes, and some of these are branched,
forming a flower cluster called a panicle. At the extremity of the
smaller branches there is a cluster of two or three flowers called
a spikelet. At the base of the spikelet notice two leaves which
enclose the flowers, called the glumes ; notice their position with
respect to each other, also note their shape, surface and veins.
The flattened axis on which the flowers stand is the rachis of the
spikelet; note the relative size of the flower inclosed by the
glumes and the tuft of hairs at the base of the lowest flower.
Take the lowest flower of the spikelet, and note the bract
called the lower palet which almost incloses the flower ; notice
carefully the size, shape, surface, texture, number of nerves, etc., of
the palet. It sometimes bears a bristle or awn ; if so, note its
position, length, texture, etc. Cut away the lower palet without
injuring the flower, and note another bract called the upper palet.
Study all its parts and compare it with the lower palet, also note
two little scales at the base of the upper palet. Notice the num-
ber of stamens, the character of the filament and anthers, and
the appearance of the pollen. Notice the top-shaped ovary, the
thread-like styles, and the feather-like stigmas. Compare the
lowest flower of the spikelet with the others.
In studying the ripe grain, strip off the chaff and note the
whitish hairs, especially at the upper end; the longitudinal
LESSONS IN BOTANY. 223
groove, and the scar at the base. Make a cross section and note
the white central portion and the darker shell or enclosing mem-
brane. After soaking in water for some time, remove the skin
and notice the embryo and try to make out the cotyledon, plu-
mule, and stem ; if this cannot be done, examine a grain that has
just begun to germinate. The process of germination maybe
followed step by step in oats germinating on a piece of wet blot-
ting paper. Any one of the grasses studied as indicated above
will give one some idea of this order of plants, and will enable
one to describe the plant examined accurately, so that it can be
identified.
The value of the hay crop of the United States is not far from
$300,000,000, and the cultivated grass eaten by domestic ani-
mals is worth as much more; and when we add the value of the
annual product of wheat, corn, oats, barley, rye, rice and sugar
cane, the total amounts to at least $1,500,000,000, as the an-
nual value of the grass crop of the United States. Grass is king.
Another extensive order is the Sedge Family, made up of her-
baceous, three-angled, solid-stemmed plants, growing in tufts,
generally in wet places. The members of this family are of little
economic value to man or beast. The papyrus, which the ancient
Egyptians used for paper, was made from the pith of sedges.
Ropes and mats are made from some species in India.
Order Liliacese or the Lily Family contains many interesting
and valuable plants. The members of this family are herbaceous,
rarely woody plants, with regular, and usually six parted flowers.
The different parts of the flower are distinct and free from the
chiefly three-celled ovary. Stamens six except in one case, anthers
two-celled. Cajyx and corolla colored alike except in trillium.
The plants usually rise from a bulb or short root stalk.
The trillium is a very common flower in the woods during
early spring and can easily be obtained for study. Secure
several complete plants, and notice the thick horizontal under
ground stem or root stalk. It is covered with broad scales, and
from it branch the roots, and it also sends up an aerial branch
which bears a whorl of three green leaves and a terminal flower.
224 PRACTICAL LESSONS IN SCIENCE.
Note the arrangement of the unbranched roots, their wrinkled
surface and the root hairs. Make transverse and longitudinal
sections of the larger roots, and notice the cortical, parenchyma
and fibro-vascular regions, and the thickness and peculiarities of
each. In the fibro-vascular region several large tracheary vessels
may be seen.
Notice the size and shapeof the root stalk, the number of nodes
and scars of former branches, and the number of roots from each
node. Make the two sections and note the vascular bundles amid
a mass of white material, which is probably reserved food. Crush
a bit of the white matter in a little water and add a drop or two
of iodine solution and note change in color indicating starch.
Compare the ends of the root stalk, studying especially the grow-
ing end as a whole and in longitudinal section, and note the form,
structure and veining of the scales or leaves of the root stalk.
Study the aerial stem with its whorl of leaves and flower, note
its form, size and the absence of nodes. Make the two sections
and note the three tissue systems, especially the two parts of the
vascular area, the light colored or cortical portion toward the out-
side, and the darker woody portion toward the center of the stem.
Notice the number, shape, arrangement and position of the foliage
leaves, especially the outline of the apex and base of each. Note
also the petiole and the venation or mode of veining of the leaves,
which is not usual in this order. Make a drawing of a leaf.
The flower is composed of four whorls of organs, the lower, of
three greenish sepals, the calyx, the next of three colored petals,
the corolla,, the next of six stamens, the andrcecium and the in-
nermost, of three partly united pistils, the gyncecium, and all
these parts stand on the broadened end of the stem called the re-
ceptacle. Note that the parts of a whorl alternate with those of
the whorl next to them. Notice the color, shape and venation of
both sepals and petals. In studying the anthers, notice the
pollen sacs, and the connection between them, which is a continu-
ation of the filament. In the filament notice the vascular
bundles, and the fundamental tissue. Note also the way the
anther opens and the character of the pollen.
LESSONS IN BOTANY. 225
The tapering, divergent styles, stigmatic along the inner sur-
face, unite below forming a compound ovary. Study the style,
noting its form, size, etc., find also the vascular bundles. Make
a cross section of the ovary and notice the form and position of
the ovules, especially notice the placenta on which they stand and
find out how it is formed. The fleshy pod incloses the seeds.
Where the ripe seed breaks away from the stalk a scar called the
hilum is formed. A cross section of a seed shows the thin brown
coat or testa, and the food material making up the main body
of the seed.
In these plants we have for the first time a complete flower.
The calyx and corolla serving in the bud and blossom as organs
of protection for the reproductive organs; the corolla in addition
serves to attract the attention of insects and birds, whose visits
are often beneficial to plants. Sometimes the calyx also becomes
colored and attractive. And here first we find the typical closed
ovary, the distinguishing characteristic of the Angiospermae. In
the oat the ovule and seed are adherent to the ovary, while in
trillium they are distinct. The trillium represents the lily
family very well except in the veining of the foliage leaves and
the color of the sepals.
Among the useful plants of this order may be mentioned as-
paragus and the onion, used for food; the aloe, green hellebore,
colchicum, sarsaparilla and others are used in medicine; and a
large number of lilies are cultivated as ornamental plants.
The Palm Family belongs to the monocotyledons, and for eco-
nomic value is second only to the grass family. The members of
this family furnish enormous quantities of food materials, of,
material for house-building, and for an endless variety of house-
hold goods and utensils. But nearly all the useful members of
the family are natives of the tropical regions.
The Orchid Family is an interesting member of this group of
plants. They are terrestrial plants in some cases, but generally
they are air plants, growing most abundantly and in greatest
variety in the tropical regions. They all have irregular flowers,
often having most grotesque forms, and sometimes simulating
L. S. 15
226 PRACTICAL LESSONS IN SCIENCE.
the forms of insects and birds. They are noted for the beautiful
color of their flowers and the varied forms of their foliage. They
are especially interesting for the many curious devices for cross
fertilization by insects and birds. They are very popular as or-
namental plants, and are represented in the United States by the
lady's slipper and a few other less showy flowers. The vanilla
plant is an orchid, and other members of the family are useful,
but in general they are of little economic value.
Another interesting member of this group is the Banana
Family. The genus Musa of this family contains the plaintain
and the banana of tropical regions. No other genus furnishes
food for as many people as does the genus musa. It is estimated
that about 25 tons of bananas can be grown upon an acre of
ground, furnishing more food per acre than any other plant.
There are many other interesting plants in this subclass, but
the ones mentioned are the most prominent, and will give a good
and comprehensive idea of the whole. This monocotyledon group
of plants is distinctively the foo d group of the vegetable kingdom.
CHAPTER XXX.
DICOTYLEDONS.
IN this group of plants the embryo has two cotyledons, the
leaves are netted-veined, and the plants grow in diameter by the
addition of new material each year between the bark and wood
of the previous year, as among the gymnosperms. This sub-
class contains nearly 200 natural orders or families, but only a
few of the more interesting and valuable can be noticed here.
The Willow Family consists of trees or shrubs, with bitter bark,
light, soft wood, and dioecious flowers that is, the male and fe-
male organs are in separate flowers on separate plants. Both
kinds of flowers are in clusters called catkins, which are much like
cones, only the scales are more leaf-like and the axis more slender.
The staminate or sterile flower consists of stamens only, the
pistilate or fertile flower of one pistil with a one-celled ovary. At
maturity the ovary contains numerous seeds each of which is fur-
nished with a tuft of cotton-like down at one end. This family
includes the willows, osiers, aspens, poplars, and the cotton-
wood. Some of these trees are grown for ornament; from the
aspen, pulp for coarse paper is made, and willow-ware is made
from the young shoots of the osier.
The Oak Family consists mainly of trees, with some shrubs,
bearing alternate leaves, which are sometimes entire and some-
times pinnately lobed or cleft. The flowers are monecious or di-
clinous, both on the same plant; the sterile in slender catkins,
the fertile, solitary or clustered. Among the oaks proper, the
sterile flowers have a four to seven lobed calyx, and from three to
twelve stamens clustered in pendant catkins, while the fertile
flower is one pistil in a bud-like involucre that becomes a scaly
cup, called the cupule, which partly covers the brown ovoid nut
or acorn.
(227)
228 PRACTICAL LESSONS IN SCIENCE.
Make a transverse and longitudinal section of an acorn, and
notice the pericarp or shell, the thin, brown membrane investing
the kernel, called the testa, and the whitish substance making up
the bulk of the seed which constitutes the cotyledons, with their
store of food for the young plant. Soak the seed of an acorn for
several hours in water and it can easily be separated into two
parts, but notice that they are united, study this bond of union,
and make out the radicle and plumule of the embryo.
Make a transverse section of an oak stem and note the rings
of growth, the medullary rays, the numerous very large openings
which are pitted vessels, and the smaller ones, some pitted ves-
sels and some tracheids, and wood fibers. Note that the rings of
growth are not of uniform thickness, and an individual ring is
not uniform throughout. Find out the reason. Make a longi-
tudinal section through the heart and notice the numerous shiny
plates, the silver grain, or medullary rays. Sometimes the oak
has a strong taproot with few spreading ones. Occasionally the
taproot is replaced by spreading multiple roots. Find out a
reason for the difference.
Oak timber is usually heavy, tough, durable and beautiful.
These qualities make it a valuable tree. It has a history; it is
famous in poetry and prose alike; it is especially interesting to
us as its history runs back through the early English and Anglo-
Saxon periods, and backward to our Aryan forefathers. The
tree has always been admired for its qualities, and it has often
been invested with superstition and romance.
The oak grows best in the cooler regions ; it is generally de-
ciduous, but many evergreen varieties exist. It varies in size
from a tiny shrub to the sturdy forest tree sometimes six to
eight feet in diameter. It grows in a great variety of soils, and
varies greatly in quality and appearance. There are some 250
species of oak which are found mainly north of the equator;
about 100 species are found in the United States. The White
Oak and its varieties furnish the best timber. The Live Oak of
our southern states is especially valuable for shipbuilding. But
nothing in North America quite equals the Quercus rohvr. the
LESSONS IN BOTANY. 229
British oak of England and Europe. The oak family not only
includes the oaks, but the beeches, chestnuts and others. The
nuts produced by members of this family are valuable food for
domestic animals, and the tannic acid of oak bark makes it valu-
able in leather making, and some varieties furnish a beautiful
yellow dye.
The Walnut Family includes the walnuts and the hickories.
They have alternate pinnately compound leaves and monecious
flowers, the sterile of numerous stamens in catkins, the fertile of
a single pistil, and but few in a cluster. The calyx is adherent to
the two-to-four-celled ovary which has only a single ovule. The
outer part of the nut is the thickened calyx, the stone part the
ovary walls, and the meat of the nut consists of the curiously
crumpled cotyledons of the embryo. The wood of the walnut is
highly prized for its beauty and durability. The bark and
young branches are aromatic and strong scented, and from the
bark a strong dye is made, and sometimes sugar is made from
the sap.
The hickories have a white, tough wood much used as handles
for tools, for parts of carriages, etc. Walnuts, butternuts, hick-
ory nuts and pecan nuts are highly prized for eating.
The Elm Family is made up of trees and shrubs, with alternate
two-ranked leaves which are usually rough entire and sharply
serrate. The fruit is a one-celled, one-seeded samara, or winged
fruit somewhat circular in form. Some of the elms are cultivated
for ornament and some of them furnish a tough timber that is
valuable when kept dry, or when kept continuously under water,
otherwise it deca}^s rapidly. The hackberry, the mulberry, and
the osage orange are interesting and valuable trees that are
closely allied to the elms.
The Buckwheat Family is represented in this country by a
large group of herbs, having entire leaves with stipules in the
form of scarious or membranous sheaths at the strongly marked
joints of the stem. The flowers have a green or colored calyx,
with the stamens on its base. The one-celled ovary ripens into
an akene or* nutlet, which is often triangular in form. Buck-
230 PRACTICAL LESSONS IN SCIENCE.
wheat is perhaps the most important member of the family, as
its seeds furnish excellent material for food, and its honey pro-
ducing flowers make it valuable to those who are raising bees.
The rhubarb used in medicine and the well-known pie-plant
are useful members of this family. Besides these there are
knot-grass, smartweeds, sorrels, water pepper, and several
kinds of Dock, belonging to this family, which are troublesome
weeds.
The Pink Family includes some beautiful and interesting
plants, but none that are of any great economic value. It is
made up of herbs with opposite entire leaves, and regular flow-
ers. The ovary is usually one-celled , with from two to five styles;
it ripens into a many-seeded pod which opens at the top and
contains a free central placenta. Stamens not more than ten,
usually standing on the calyx. The petals with slender stalks or
claws are also on the calyx. The calyx is composed of five sepals
which are united below into a cup or tube on which the stamens
and petals are inserted. Many varieties of pinks are cultivated
for ornament and are much prized for their beautiful colors and
sweet odor. The corn-cockle so injurious in the wheat fields is a
member of the pink family, and so are the different varieties of the
catchfly, which forms a sticky exudation on its stems and calyx
by which small insects are caught. The chickweeds, which belong
with the pinks, are mostly adapted to impoverished soils, sandy
and gravely wastes, etc. They are pioneers everywhere in
nature's attempts to renew worn out soils and to clothe barren
places with verdure.
The Crowfoot Family is made up mostly of herbs, growing
more abundantly in the cooler climates and in moist localities.
They have numerous stamens, usually more than one pistil, and
distinct carpels. Sepals usually five, deciduous, often petal
like; petals five, often wanting; plants usually with a watery
acrid juice; leaves sometimes simple and entire, but often much
divided ; flowers sometimes regular, but often irregular. Many
familiar plants belong to this family, as the clematis, hepatica,
anemone, buttercup, the cowslip, columbine, larkspur, aconite,
LESSONS IN BOTANY. 231
peony, and others. Several of these are cultivated for orna-
ment and some are used in medicine, as aconite, goldthread, etc.,
but no members of this family are of much economic value.
The Magnolia Family consists of trees and shrubs, with aro-
matic, bitter bark, alternate leaves mostly entire, and large,
showy, solitary flowers, stamens and pistils numerous on a long
receptacle, the pistils imbricated and cohering into a mass form-
ing a cone-like fruit. The most important member of this family
is the tulip tree or white wood, in some localities called poplar.
It is a handsome tree with greenish-yellow flowers and dark green
leaves. The leaves are broad, with two short side lobes and a
truncate apex. The timber is white, soft and durable. The nu-
merous species of magnolia are broad leaved evergreens noted
for the beauty of their leaves and flowers, the latter yielding a
rich perfume.
The Water Lily Family consists of numerous aquatic plants
having large roundish leaves, which float on the water. The
flower is large and showy, varying considerably among the dif-
ferent members of the family in color and arrangement of parts.
The water-shield, growing in quiet water, has an oval, centrally
peltate leaf, and a small purplish flower whose stem is coated
with a clear jelly-like substance.
The Nelumbium has large root-stalks, large leaves, and large
pale yellow flowers. The parts of the flower stand on a broad,
top-shaped receptacle in which at maturity there are a dozen or
more little pits, each containing an acorn-like seed. The seeds
and the tuberous root-stalk are edible. The sepals and petals
are numerous, passing gradually into each other so that onecan-
not tell where the calyx ends and the corolla begins. This plant
is sometimes called the lotus.
The white water lily is a beautiful and highly prized flower
with four sepals, but numerous petals, which pass gradually into
the numerous stamens, and is given as an illustration of the fact
that the stamens are changed leaves. The root-stalks are very
large, and the fruit ripens under water. The yellow pond lily is
a less showy flower than the others. It has six sepals and nu-
232 PRACTICAL LESSONS IN SCIENCE.
merous thick, yellow petals, the stigma forming a broad disk in
the center of the flower. The Egyptian lotus and the Victoria
Regia of the Amazon, with leaves three feet or more in diameter,
belong to this interesting family.
The Poppy Family is made up of herbs which have a milky or
colored juice. The calyx consitsof two sepals which are deciduous;
the petals and stamens are numerous, the ovary one-celled, rip-
ening into a many-seeded pod. Several members of the family
are cultivated for ornament. The juice of the opium poppy, fur-
nishing the opium and morphine so much used in medicine, makes
this one of the noted families of plants. The bloodroot, with its
reniform, palmate-lobed leaf, its white petals, and its blood-red
juice, is one of the most interesting flowers of early spring.
The Cruciferse, or Mustard Family, consist of a large group of
herbs having a pungent watery juice and four-parted cruciform
flowers. The cabbage, turnip, mustard, radish, water-cress
and horseradish are members of this family which are used as
food. Some are prized as ornamental plants, as candytuft and
sweet alyssum, and others are troublesome weeds, as the shep-
herd's purse. These plants are widely distributed throughout
the temperate regions, especially in southern Europe and south-
western Asia.
The flowers are much alike, having four sepals, four petals,
with long claws and spreading blade; the stamens are tetra-
dynarnous, four long and two shorter. They have a two-celled
ovary which forms a pod called a silique, or if short a silicle.
These pods are two-celled by a false partition between the two
parietal placenta?. It generally opens from the apex toward the
base by the sides splitting off, leaving the partition with the
placentae and seeds. The flower cluster is a raceme, often a com-
pound raceme. In this cluster each flower has a pedicel which is
a branch of a common axis, the lowest blossoms being the oldest,
so that often fruit may be found in the lower part of the cluster
with buds at the top and all stages between. The flowers of the
shepherd's purse are in a compound raceme, and the pod is a
silicle. The root leaves are pinnatified, and the stem leaves are
LESSONS IN BOTANY. 233
sagitate and partly clasping. The pod of the mustard is a
silique.
Many of these plants, as the radish, are biennials, that is, they
grow from the seed during one season, storing up in the roots
some nourishment for the next season. During the second sea-
son they produce flowers, mature seed and die. Many plants
live only one season, dying as soon as seed has been matured.
Such plants are called annuals, while trees arid many others live
on from year to year and are called perennials.
The Violacese or Violet Family. The members of this family
are well-known plants, highly prized for their beautiful flowers.
The flower is irregular, with five sepals and five petals, which are
more or less unequal, the lower one with a sack or spur at its
base. The stamens are five, the broad, flat filaments, slightly co-
hering around the pistil. The somewhat showy flowers are sel-
dom fertile. Another set of flowers, hidden under the leaves,
produce most of the fruitful pods. These flowers are of a green-
ish color, and are more nearly regular than the more conspicuous
ones above. The irregularity of the aerial flower is supposed to
have some relation to insect a,gency in fertilization. Some of the
violets send up flower stalks from underground stems, and some
have aerial stems. This is a very interesting flower from its
various irregularities, and a careful study of it according to the
plan followed with the trillium would be a valuable and inter-
esting work.
The members of the Droseracese or Sundew Family are inter-
esting chiefly from the fact that they are carniverous or insect
eating plants. They are bog plants with regular flowers, on the
plan of fives, having a tuft of glandular bristly leaves at the base
of the stem, which in the bud are rolled up from the apex, alter
the manner of ferns. The common sundew has small roots with
five or six root leaves spread out in a rosette around the base of
the stalk. The upper surface of each leaf is covered with gland
bearing filaments, each of which is crowned by a drop of a trans-
parent viscid secretion. Insects are attracted to these leaves,
and lighting on them are entangled by the secretion of the ten-
234 PRACTICAL LESSONS IN SCIENCE.
tacles or filaments, which by a curious waving movement trans-
fer the insect to the center of the leaf where it is soon drowned
in the liquid, and at length is digested and absorbed.
In the Venus fly-trap, the leaf with bristles on its edges and
filaments on its surface shuts up like a book thus capturing
insects, which are digested and absorbed. Neither of these plants
are sensitive to wind or rain. The most vigorous leaves rarely
digest more than twice, or at most three times. In these cases
we have illustrations of movements in plants due to some kind
of irritation that simulates very closely reflex action in animals.
The common pitcher plant, sarracenia, is carniverous. The
mouth of the trumpet-shaped leaves is protected by a lid, the
inner surface of which is smeared with nectar, and in some cases
a pathway, honey baited, lures the insect into the pitcher where
they are soon drowned in the liquid secreted wholly or in part by
the inner membrane of the leaf. This liquid does not digest the
insect, but seems to accelerate decomposition, and if the plant
gets any nourishment from the insect, it as a saprophyte, taking
nourishment from decaying matter. There are several other
pitcher plants which destroy insects, but their process is much
the same as given above. The most extensive studies in this
direction were made by Charles Darwin.
The Linden Family consists chiefly of tropical plants. It is
represented in this latitude by the lime tree or basswood. It
bears dull cream-colored flowers which are rich in honey. They
are arranged in a cluster called a cyme, which is united to a long
leaf-like bract ; the fruit is a woody globular two-celled nut. The
wood is soft, white, elastic, the inner bark rich in bast fibers.
The dark green leaves are roundish, serrate and somewhat heart
shaped at the base. It is a beautiful tree, much prized for its
timber and as an ornament.
The Mallow Family consists of herbs, shrubs and trees that
have alternate simple, palmately veined leaves, but are best
known by their monadelphous stamens, which are united into a
tube inclosing the pistil. The flowers are regular, sepals and
petals five, and there is often an involucre of several green bracts,
LESSONS IN BOTANY. 235
resembling an outer calyx. In the mallow family the calyx is
valvate and the corolla convolute in the bud. By valvate is
meant that the edges of the parts meet without overlapping or
infolding, while in the convolute arrangement one edge of each
leaf covers one edge of the next, so that each leaf has one cov-
ered and one free edge. A cross section of a bud of a mallow
blossom shows these arrangements nicely. Several members of
this family are cultivated for ornament, as the hollyhock, abu-
tilon, hibiscus and althea. But the family is best known from
the cotton plant, which furnishes more material for cloth and
other fabrics than all other plants. The cotton fiber consists of
hairs which are developed on the surface of the seed ; at first they
are cylindrical, but on drying they become flattened and twisted,
so that they are easily distinguished from other fibers. There are
several varieties of cotton, the sea island cotton of our southern
states being the finest in the world. The general superiority of
American cotton is supposed to be largely due to climate. Cot-
ton grows in all tropical countries, even as far north as Tennessee
and Arkansas. Cotton was extensively grown and manufactured
in India and Egypt centuries before the Christian era. The bast
fibers of some of the plants of this family are valuable, and are
much used in China, India and New Zealand. Besides the cotton
fiber, the cotton seed yields an oil that from its cheapness is be-
ing extensively used for many purposes, adding much to the
value of the cotton crop.
CHAPTER XXXI.
DICOTYLEDONS CONTINUED.
THE Linacese or Flax Family is composed of herbs, shrubs,
and a few trees, but is represented in this country by the one genus
of which the common flax is the only plant of economic value.
The flowers are regular, opening for only one day, and the decid-
uous petals are especially delicate in texture and color. This
plant rivals cotton in importance as a fiber producing plant. It
grows best on the borders of the tropical regions, having a much
wider range than cotton. The linen fiber consists of bast cells
from the stem of the plant, and has been used from the earliest
times. The oldest mummies of Egypt are wrapped in linen and
its remains are found in the ruins of the Lake Dwellers of Swit-
zerland and Italy.
The Rue Family includes the prickly ash, the hop-tree, the
orange, lemon, citron and lime trees. The chief characteristic of
the family is the transparent dots or glands in the leaves which
contain a pungent aromatic oil. In some cases the juices are very
bitter and in some cases acrid enough to blister the skin. The
orange, lemon and citron are the most important members of
the family.
TheAcerinese or Maple Family is made up of shrubs and trees
that are prized for their beauty and for their timber, and the sap
yields a sugar of a fine flavor. The flowers are sometimes per-
fect, sometimes dioecious; sometimes with petals, sometimes with-
out. They appear in early spring, with or before the leaves, in
drooping, umbel-like clusters. The fruit is a pair of samaras, or
winged fruits, united at the base. The leaves are palm ate- veined
and palmately lobed or parted, and sometimes serrate. There
are several varieties, as the sugar maple or hard maple, the soft
(236)
LESSONS IN BOTANY. 237
maple and the red maple. The hard and soft maples furnish ex-
cellent timber, much used in the manufacture of furniture.
The buckeye and the horse-chestnut, near relatives of the
maples, have white, somewhat irregular flowers arranged in a
conical cluster called a panicle, and large, palmately compound
leaves.
The Ampelideae or Vine Family consists mainly of woody
shrubs or vines climbing by tendrils. The leaves are simple,
rounded and heart shaped, sometimes lobed. In some cases the
leaves and young shoots are covered with a cotton-like down.
Flowers small and greenish forming a cluster called a panicle.
The calyx is short, and connected by a thick disk with the ovary.
On this disk the petals and stamens are inserted, five thick
glands or lobes of the disk alternating with the stamens. The
petals cohere slightly at the top and the corolla is thrown off
without expanding.
The vine has been cultivated and used by man from the earli-
est times. It is indigenous to southern Asia and North America.
There are many varieties. The best wine and raisin grapes grow
in southern Europe.
The Virginia Creeper climbing by tendrils and rootlets belongs
to this family. The flowers form a cymose cluster and the pal-
mately compound leaf with five lance oblong cut tooth leaflets
changing to crimson in autumn make it highly prized as an orna-
mental vine.
The Euphorbiaceze or Spurge Family is a vast group of more
than 3,000 species, distributed through a wide range of climate,
but growing most abundantly in tropical regions. They vary in
size and habit from a tiny creeping plant to a giant tree. They
usually have a milky, acrid, often poisonous juice, with flowers
varying widely in structure, but the ovary and fruit are usually
three-celled. Tapioca, castor and croton oil, caoutchouc and
several valuable woods are furnished by members of this family.
Many species, with thick succulent stems are cultivated for
ornament.
The Umbelliferse or Parsley Family is a large and widely dis-
238 PRACTICAL LESSONS IN SCIENCE.
tributed group of plants named from the fact that the small,
five-parted flowers are grouped in clusters called umbels. The
leaves are alternate, compound, and usually finely dissected.
Many of these plants contain a poisonous juice, and in general
the green parts are acrid and poisonous, while the seeds are aro-
matic and harmless. The parsnip, carrot, celery and parsley
are food products of this family. Coriander, caraway, fennel,
aniseed are aromatic and medical products, while gum asafoe-
tida, poison hemlock, sweet cicely and others indicate the great
variety of plants included in this interesting family.
The Saxifrage Family is made up of trees, shrubs and herbs,
which are not marked by any distinguishing character. The
leaves are opposite or alternate, pinnately or palmately veined.
There are usually five petals, with from five to ten stamens. The
calyx is generally monosepalous, and on it the petals and sta-
mens are inserted. To this family belong the currant and the
gooseberry, the syringia, hydrangea and the strawberry ger-
anium, and other interesting and beautiful flowers.
The Cactacete or Cactus Family consists of succulent herbs,
shrubs or trees, generally spiny and leafless. They grow mainly
in dry regions, and the surface for evaporation has been reduced
to the green rind of the stem, sometimes increased by a few
branches or thick leaves. These plants are illustrations of the
great changes in form which plants may undergo in adapting
themselves to varied circumstances. The scanty evaporating
surface and the protecting spines seem necessary to their exist-
ence. Many of these plants are cultivated as curiosities; some
furnish edible fruits; the leaves of others furnish a valuable fiber.
Some varieties instead of growing one year and maturing seed
the second, grow for eight or ten years, and then send up a flower
stalk from ten to twenty feet high, mature seed and die. In
Mexico as the flower stalk of the pulque plant begins to grow, it
is cut off and a bowl-shaped cavity made from which the juice,
designed for the growth of the flower stem, is gathered for use
by man. It is the Mexican pulque, and from it a distilled liquor,
called mescal, is made.
LESSONS IN BOTANY. 239
The Rosacese or Rose Family is divided into several tribes,
each of which contains interesting plants or shrubs. The Tribe
Pomse includes the apple, pear, crab apple, and quince, haw-
thornes, etc. They have simple leaves, two to five ovaries, which
in the fruit are covered by the thick walls of the calyx tube.
The Tribe Rosese includes the Roses, which exist in great va-
riety. They have pinnately compound leaves with entire serrate
leaflets. The calyx is five parted with a globose fleshy tube,
which incloses the pistil. The corolla consists of five petals,
which are greatly multiplied by cultivation, and the stamens are
numerous.
The Tribe Potentillese includes the potentillas and the straw-
berries. They have palmate or pinnately compound leaves.
Many of the potentillas are cultivated as ornaments, and the dif-
ferent varieties of strawberry furnish a delicious fruit, which is
the enlarged and softened receptacle covered with the seeds or
akenes which are the real fruit.
The Tribe Rubese includes the raspberries and the blackber-
ries. The raspberries are clusters of little stone fruits, while the
blackberry is a cluster of stone fruits with the receptacle on which
they stand. They are usually shrubs with prickly stems and
compound leaves.
The Tribe Prunese includes the almond, peach, apricot, plum,
and cherry. They have simple, usually serrate leaves, and their
stems and fruit yield a gum. The inner part of the ovary
wall hardens into a stone inclosing the kernel or seed ; the outer
part forms the edible portion of the fruit. The wild cherry of the
United States furnishes a timber much prized for its beauty and
durability. No other family of dicotyledons furnishes as large
quantities and as great a variety of fine fruit as does the rose
family, and it easily leads all others in the beauty and fragrance
of its flowers.
The Leguminsose or Pulse Family is made up of herbs, shrubs,
and trees, with alternate and usually compound leaves, and more
or less irregular flowers. The stamens are ten, generally mona-
delphous, forming a tube inclosing the pistil ; sometimes diadel-
240 PRACTICAL LESSONS IN SCIENCE.
phous, nine in one set and one in the other; and very rarely the
stamens are distinct. This great family, containing 1 some 6,000
species growing in all parts of the world, is divided into three
subfamilies.
The Papilionacese includes the pea, bean and peanut ; the lu-
pine and the clovers; the locust, rosewood and many other fine
trees; indigo, camwood and other dyes; the gums tragaeanth
and kino; the balsams of Peru and Tolu; and the plant that
yields the medicinal product, liquorice, and species that yield good
fiber, besides many species that are cultivated for ornament,
as the laburnum and wistaria. The name is derived from the
corolla, which is composed of five petals of such form and arrange-
ment as to resemble a butterfly. The petals of this corolla have
received special names. The upper and larger one, which is gener-
ally wrapped round the others in the bud, is called the banner ;
the two side petals are called the wings, and the two lower ones,
the blades of which usually stick together inclosing the stamens
and pistil, are called the keel.
The Csesalpmiese includes the honey locust, coffee tree, and
judas tree of the United States, and many valuable timber trees
from the tropical regions, as well as many dye-woods, and others
that produce valuable gums and balsams. The members of this
group have a somewhat irregular corolla, with usually ten dis-
tinct stamens, and often twice pinnately compound leaves.
The Mimosese have regular flowers, distinct stamens, and twice
pinnate leaves. The most important product from this group is
gum Arabic or acacia, and the different varieties of acacia fur-
nish very fine lumber highly prized for furniture, veneers, and
ornamental purposes generally. Some members of this group
are especially interesting on account of the movements executed
by their leaves, expanding in the light, closing in darkness, or
upon the slightest touch or jar, opening again in a few moments.
Mimosa pudica, is so prompt in its movements that it is called
the sensitive plant; numerous others are more or less sensitive.
As a whole the pulse family is interesting, important, and well
worthy of study. The common bean plant is a good specimen
LESSONS IN BOTANY. 241
from which to study the characteristics of the dicotyledons ; the
same general plan may be followed as in the study of the trillium
and oat. The bean plant can be grown easily at any time of the
year, and its whole life history can be studied easily by starting
a number of plants, and examining different individuals in the
various stages of germination, growth and maturity.
The Ericaceae or Heath Family is composed mainly of shrubby
plants which have monopetalous regular or irregular flowers,
and the calyx tube sometimes free and sometimes adherent to
the ovary. This family includes the huckleberry, cranberry and
blueberry; the wintergreen, trailing arbutus, laurel and other
beautiful flowering shrubs.
The Solonacese or Nightshade Family includes the potato,
tomato, and tobacco; red pepper, henbane, belladonna, bit-
ter-sweet, and other important plants. These plants have regu-
lar monopetalous flowers, a two-celled many seeded ovary, and
generally a colorless poisonous juice, with a strong unpleasant
odor; many of them are cultivated for their beautiful flowers.
While this family is important and interesting, it is peculiar,
presenting many sharp contrasts. The potato and tobacco,
natives of America, are now cultivated and used in all parts of
the earth.
The Figwort Family is made up mostly of herbs and shrubs,
with a more or less irregular monopetalous corolla and a two-
celled ovary. There is often an interesting irregularity among
the stamens, only a portion of them bearing anthers. In the
pentstemons and others there are four anther-bearing stamens,
the fifth represented by a barren filament or a scale. The family
includes many plants that are cultivated for ornament, as the
pentstemon, castilleia, veronica and others. Digitalis, used in
medicine, and many coarse weeds are also members of this family.
These plants are widely distributed from the tropics to the limits
of vegetation towards the poles. A castilleia and a mustard
were found at higher elevations on Mount Orizaba than any
other flowering plants.
The Labiatss or Mint Family consists of square-stemmed,
L. S. 16
242 PRACTICAL LESSONS IN SCIENCE.
opposite-leaved aromatic plants, with an irregular corolla and
didynamous stamens, and a deeply four-parted ovary. It in-
cludes lavender, hyssop, peppermint, sage, catnip and other
interesting plants, but none of great economic value.
The Oleacese or Olive Family is composed of trees and shrubs,
with simple or pinnate leaves, regular flowers, two stamens, and
two-celled ovaries. It includes the olive, which yields fruit, oil
and lumber, the different varieties of ash, which yield good tim-
ber, and some ornamental shrubs, as the lilac, jessamine and
others.
The Asclepiadacese or Milkweed Family. The members of this
family are woody or herbaceous plants with an abundant milky
juice. The flowers are regular, calyx and corolla five parted;
the two distinct ovaries have a common stigma; the five sta-
mens monadelphous, the anthers closely surrounding the stigma
and partly adhering to it. The pollen is in waxy masses which
are distributed by insects. The structure of the flower is peculiar
and difficult to describe, but exceedingly interesting to study, the
structure no doubt having reference to cross fertilization by the
aid of insects. The flowers are arranged in umbels; the fruit con-
sists of a pair of pods containing many flat seeds, which are fur-
nished with a tuft of soft, silky hairs, called a coma, at one end.
The milky juice contains caoutchouc, and some plants are culti-
vated for ornament, but the plants are chiefly interesting for the
peculiar structure of their flowers.
The Gourd Family is made up of tendril bearing herbs, with
watery juice, alternate palmately ribbed and lobed leaves, and
monopetalous flowers. It includes the gourd, pumpkin, squash,
watermelon, muskmelon and the cucumber.
The Composite or Sunflower Family. This immense family
including as many as 10,000 species has representatives in all
parts of the world. Many of the species are of great beauty and
are much admired as ornaments, but few are of any economic
value. The small monopetalous flowers with their syngenesious
anthers are gathered into compact heads or masses which often
resemble single flowers. The tube of the calyx is coherent with
LESSONS IN BOTANY. 243
the ovary, its margin, consisting of rigid or downy bristles, teeth
or scales is called the pappus. The end of the stalk on which the
simple flowers stand is the receptacle. The greater part of the
flower cluster is made np of tubular flowers, but often around
the margin of the cluster there are flowers whose corollas have
extended into a strap or leaf-like form called rays, which in many
cases seem to be the petals of ordinary flowers. Some well-known
members of this family are chickory, lettuce, dandelion, sun-
flower, golden-rod, chrysanthemum, thistle and burdock.
CHAPTER XXXII.
FORM, COLOR AND ODOR OF PLANTS.
PLANTS seem to differ widely in structure and in the processes
of nutrition and reproduction, but a careful investigation shows
that all plants are composed of essentially the same elements, so
that the processes of nutrition must be about the same among all.
And so with the process of reproduction, it is simply the formation
of new cells, whether in the humble protococcus or in the stately
oak. And the same is true in the matter of structure; every plant
structure, however complicated, is made up of modified paren-
chyma cells. We have thus far studied typical members of dif-
ferent groups of plants, from which the plant world might seem
to be composed of several distinct parts. When we try, however,
to find the dividing lines between the groups, they continually
evade us, one group seeming to merge into another by such in-
sensible degrees that the idea of distinct parts soon fades away,
and we are more impressed with the fact that the plant world is
essentially a unit.
The plant world, then, is practically a unit in its structure, in
its processes and in its relations. But why , in that case, the wide
differences in form, color, odor and habit of plants ? If we accept
the theory of special creation, nothing came by chance, each
peculiarity of form, each shade of color, each odor means some-
thing, nothing depends upon accident the form, color and odor
of each particular flower are, all things considered, the best pos-
sible, no others would do. Again, if we accept some form of the
theory of evolution or development the same thing is true.
Every peculiarity which distinguishes one group of plants from
others is supposed to be beneficial to that group. Such peculiar-
ities are not the result of caprice or chance, but of purpose.
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LESSONS IN BOTANY. 245
The air with its changing temperatures, the water with its
multiform impurities, the soil with its different qualities, the ex-
istence of other plants and animals, all constitute an endless
variety of conditions under which plants exist; and which plants
have been made to fit, either by their creation in special forms, or
in a form adaptable to all the different conditions that might
arise. And perhaps here lies the answer to our query the form,
color, fragrance and other peculiarities of plants are, or may be,
determined by their surroundings.
The lowest groups of plants, those which are supposed to have
appeared first on the earth, are water plants, or are active only
when surrounded by an abundance of moisture. The air and
water contain all the nutriment necessary to these, so that there
is no call for special organs of nutrition, each cell performing all
the functions of a plant, and as there is no division of labor the
whole body is an organ of nutrition, and of reproduction as
well. The ability to survive long periods of dessication, as in
the case of protococcus and many others, implies some modifi-
cation, some improvement over the organism of strictly aquatic
plants.
As the rocks were broken down and pulverized into soil, plant
life began to appear on the land. But water, one of the essen-
tials of plant life, was not now present on all sides; the supply
was in a sense limited, coming mainly from the soil below. It
was not necessary for the upper surface to be fitted to absorb
moisture, but it was necessary to so cover it as to prevent the
evaporation of moisture, and hence the plant is differentiated
into parts, consisting of a body from whose under surface roots
are developed to take up moisture and other nourishment, and
on the upper surface an epidermis is formed which protects the
body from excessive evaporation.
Another interesting modification arose when plants, as spiro-
gyra, in addition to reproduction by simple division became able
to form resting spores, which enabled the species to survive ex-
treme cold or drought, thus greatly extending the range of plant
life. These examples illustrate the first steps in the differentia-
246 PRACTICAL LESSONS IN SCIENCE.
tion of organs, and in the division of labor, which exist so fully
in the higher plants.
As the conditions became more favorable and plants increased
in size, a fibre-vascular system became necessary to strengthen
and support the plant, and to convey nutrient fluids to all its
parts. As plants grew more numerous the supply of light and
air became somewhat limited, the fibro-vascular system was
strengthened and an erect form was acquired, thus greatly in-
creasing their opportunity for these essentials of plant life.
The change in form and habit resulting from this struggle for
light and air, is often very marked. Trees growing singly in the
open field are shorter, thicker and have a relatively broader
foliage system than trees of the same species growing in a
crowded forest. The purslane, which is usually a prostrate creep-
ing plant, when crowded by other plants will assume an erect po-
sition, rising to seek the light.
Coincident with this growth of the stem, the leaves were devel-
oped from the vascular system, parenchyma, and epidermis, and
so arranged as to serve for digestive organs. As the work of
digestion or assimilation can only be carried on in the light, we
can easily understand that the struggle for light involves the life
or death of the plant. This struggle may account for many in-
teresting forms of plants; as vines climbing up the stems of stur-
dier plants, in whose shadow they could not live, to expand their
leaves in the life-giving light above. In some cases climbing
plants become air plants, able to derive nourishment from the
air, or parasites, living on the juices of the host plant, in either
case having no use for a stem connecting with the ground . In
this way plants become permanent residents amid the branches
of trees, so that a tree often appears to produce several kinds of
foliage. Thus the common ivy, sometimes becomes an air plant,
gathering nourishment from the air and from its support.
In some flowers the stamens and pistil or pistils are so ar-
ranged that self-fertilization is possible, but in general self-fertili-
zation is difficult or impossible, so that most flowers are fertil-
ized by pollen from other flowers. The pollen grains are carried
LESSONS IN BOTANY. 247
to the stigmatic surfaces by the wind, by insects, or in rare cases
by birds.
The grasses, sedges, pines, oaks and others, having small
uncolored flowers, produce great quantities of pollen. As this
floats easily in the air it is widely distributed by the wind, so that
while there may be instances of self-fertilization, cross-fertiliza-
tion is the rule. Other plants have highly colored flowers pro-
ducing nectar, which attracts such insects as bees, butterflies,
etc. The insects, in their excursions from flower to flower, carry
pollen from one blossom to the stigma of another. And this is
by no means a matter of accident or chance; in many cases the
flower and insect are so adapted to each other that only a par-
ticular insect can get nectar from a particular flower, and aid in
its fertilization. One case of many maybe mentioned; the yucca
in southern climates, ripens its seeds regularly, but while it thrives
well in the north it does not mature seed. In the south a little
moth called the yuccasella gathers up masses of yucca pollen,
and laying its eggs in them thrusts them down a stigmatic tube
and thus fertilization is accomplished. The yuccasella cannot or
does not live in the north and the yucca ripens no seed in that
region.
It is said that cats saved the clover crop in a certain district
in Australia. The cats caught the mice that destroyed the nests
of a long-billed bumble bee, which was the principal agent in the
fertilization of the clover blossoms. The orchids with their beau-
tiful flowers of grotesque forms afford many interesting illustra-
tions of mutual adaptation and dependence between flowers and
insects.
The flowers are fertilized, the seeds have ripened and are ready
for the soil; if they fall near the parent plant only one or two
could find room for growth, so that it seems necessary for seeds
to be scattered widely. This is accomplished in various ways;
the seeds of the maple and elm are furnished with wings, those of
the thistle, dandelion and milk-weed with plumes so that they
may be dispersed by the wind. The seeds of many plants are
furnished with hooks by which they may become attached to
248 PRACTICAL LESSONS IN SCIENCE.
animals and are distributed in their wanderings. The seeds of
other plants are inclosed in edible fruits and are scattered by
the animals using the fruit for food. In some cases the seed
pod at maturity opens with a jerk throwing the seeds some
distance.
Many plants, as the strawberry, multiply not by means of
seeds alone, but send out runners which, rooting at the tips, de-
velop into new plants. Again other plants send up new plants at
intervals along an underground stem; such plants aremore com-
monly found in sandy soils.
In general plants seem to spread out as much surface as possi-
ble for evaporation, but in the case of the cactaceae and some of the
spurges living in hot dry regions, this surface is much reduced,
seemingly as a protection against excessive evaporation. Many
plants living in cold climates are protected from cold by a thick
growth of hairs, which frequently disappear when such plants are
acclimatized to warm regions. Buds, the embryos of the next
season's branches and flowers, are often furnished with coats of
down or wool, and covered with thick varnished scales so that
they are protected from moisture and sudden changes of tem-
perature. Again, thorns, spines, prickles, stinging hairs, acid
and bitter juices, etc., seem to serve plants as a defense against
animals.
Some trees, as the red or soft maple, when cultivated will grow
vigorously on the highland, but when left to their own resources
other trees soon crowd them into the lowlands along the streams,
resulting in more or less change of form. This is an illustration
of the struggle going on between plants everywhere, by which
many seeds have no chance to grow, and many plants which begin
to grow are smothered out or stunted by stronger plants or are
crowded into undesirable localities.
Some spreading plants creep out over rocks or barren places,
dust collects along their stems, and mingling with the decaying
leaves forms a soil in which other plants may grow, as illustrated
by vegetation advancing over brick walks, and similar spaces.
Often soil is formed in this way that is deep enough to support
LESSONS IN BOTANY. 249
forest trees. Sometimes lichens or algae are the pioneers in
such invasions, which are often very rapid in tropical regions.
It is said that an island of lava, from the eruption of Kraka-
toa was covered from shore-line to summit with an abundant
vegetation of ferns and allied plants within six years after the
eruption.
The succession of plants on a tract of land that has been
cleared and then allowed to go to waste is interesting. In one
case a bit of pine forest had been cleared away and the land
abandoned. It was soon covered with weeds and grasses, then
quaking aspen and other woody plants began to smother out
the herbs, and it seemed as if the aspen was the natural occupant
of the soil. After a time, however, little pines began to grow;
these grew larger and others started; the aspens began to decay,
and in less than thirty years the pines were again in full posses-
sion of the ground.
The illustrations given may serve to suggest a possible
explanation of many peculiarities of form and structure, of color,
odor and other characteristic features, which exist among plants,
and to indicate interesting and profitable lines of study and
investigation, which may be pursued in almost any locality.
The collection and preservation of specimens is an important
part of botanical work. A specimen, to be of value, should show
roots, stem, leaves, buds, flowers, fruit, all with color and form
as perfect as possible. And the label should show the locality
and any peculiarity of position or surroundings that might in
any way modify the character of the plant, and any peculiarity
of the plant that cannot be preserved should be noted.
Most herbaceous plants may be preserved by drying them un-
der pressure. The plant, with its leaves and other parts, should
be carefully arranged in a fold of paper, and then subjected to
pressure in a discarded book or some kind of a press, which
may consist of two boards with a weight of stone. The plants
should be aired frequently until they are thoroughly dry. A
few trials will enable one to make good specimens of most
herbaceous plants. In the case of some succulent plants much
250 PRACTICAL LESSONS IN SCIENCE.
care is necessary to prevent them from decay or from becoming
mouldy.
Parts too thick or heavy for drying may be preserved in alco-
hol, or may be described in the label and not preserved. Lichens
may be dried and kept in boxes without pressing. Mosses, liver-
worts and algae, when it is desirable to preserve color, should be
immersed in glycerine or Miiller's solution.
When dry, the specimen may be transferred to a sheet of heavy
paper and fastened by strips of gummed paper, and the label
should be written on the paper or fastened to it in some way, so
that it may not be lost or separated from the specimen. The
size of the sheets commonly used for specimens is thirteen or
fourteen inches long by ten to eleven inches wide.
CHAPTER XXXIII.
ZOOLOGY GENERAL AND STRUCTURAL.
THE science of zoology treats of everything relating to ani-
mals. It considers their external form, anatomical structure and
physiological processes, their geographic distribution and eco-
nomic value. It attempts to trace out the life-history of animals
from the lowest to the highest forms; it considers also their re-
lations to one another, to the members of the vegetable kingdom,
and to other forms of environment.
The animal body is made up of about the same elements found
in the plant, but the proportions are different; in animals the
albuminous and calcium compounds predominate. From these
compounds the different tissues of the body are formed, and the
tissues variously modified and combined constitute the organs of
the animal body, which may be divided into the organs of the
mechanical system, the organs of digestion, circulation, respira-
tion and excretion, the organs of reproduction and of the nerv-
ous system with those of the special senses. To trace the devel-
opment of these different groups of organs and to follow out the
processes carried on by them is an important part of the work
of zoology.
The living portion of the animal, as of the plant that which
moves, assimilates food and grows is protoplasm, and an indi-
vidual portion of protoplasm, called a cell, is the unit of all ani-
mal structures. Thecell consists of a small portion of protoplasm
which is frequently surrounded by a structureless membrane. It
usually contains a nucleus, which may contain a nucleolus. The
nucleus may take different forms, but it always contains the nu-
clear fluid and the nuclear substance, each of which is of a proto-
plasmic nature.
Free, isolated cells exist in the blood, chyle and lymph. Those
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252 PRACTICAL LESSONS IN SCIENCE.
occurring in the blood of the invertebrates, or lower animals, and
some of those found in the blood of vertebrates, are colorless, ir-
regular in form, having the capacity of movement. They can
push out processes and draw them in again, by which means they
change position. They originate in the lymphatic glands, and
pass into the blood with the lymph. Others found abundantly
in the blood of vertebrates have a regular form usually coiitam-
inga reddish pigment, haemoglobin, which gives color to the blood
and is an important agent in the process of respiration. The ova
and spermatozoa, active agents in the process of reproduction, are
free cells differing widely in form and size.
The tissue covering the free surfaces of the body, whether ex-
ternal or internal, is called epithelium. Thecells forming thistissue
are cylindrical, ciliated, or flattened, making cylindrical, ciliated
or pavement epithelium. The cells of the lower layers of this
tissue have a semifluid consistency, and are active, continually
multiplying by division and growing, while those of the upper
layer are less active and more firm in substance, which, finally los-
ing their vitality, are thrown off, to be replaced by others from
the layers below.
On the outer surface of the body the upper cells of thistissue,
as thick horny layers form claws, nails and hoofs, they form
the leathery skin of insects, and with a little calcareous matter
they constitute the hard shell or outer covering of the craw-
fish and lobster. Feathers, hairs, bristles, scales and the horns
of some animals, are the outgrowths of the tissue covering the
body.
The epithelium covering the internal surfaces of the body se-
cretes a fluid which keeps the tissue moist, and facilitates the
movements of objects over its surface. Sometimes tubular, flask-
shaped or branching cavities called glands are formed in this
tissue, which secrete special fluids, as the saliva, gastric juice, etc.
The connective tissue, made up of cells separated by various
kinds of intercellular substance, is an important part of thebody.
In some cases the intercellular substance consists of white inelas-
tic fibers, forming a tissue from which the ligaments and tendons
LESSON& IN ZOOLOGY. 253
are made, and which invests the bones, muscles, nerves, etc.
Sometimes these fibers form a network which serves as the basis
of the skin and the fatty tissue.
Cartilage with spherical cells and a firm intercellular substance
is another variety of connective tissue. Sometimes the intercel-
lular substance contains a network of fibers, forming a fibro-car-
tilage, and there are numerous other intermediate forms.
When calcareous matters are deposited in the intercellular
substance of cartilage, it becomes osseous tissue. This bony sub-
stance is traversed by numerous canals, through which nutrient
fluids may pass to the cells. Sometimes the bones grow in thick-
ness by the deposition of calcareous matter in the inner layers
of their investing membranes.
The protoplasm of the cell has the power of contractility, but
some aggregations of cells possess this in a high degree, giving
rise to the muscular tissue, which is the chief agent in all the
movements of the body. When acting, these cells change their
form,becomingshorter and broader than when at rest, thus caus-
ing the muscle to contract. Two kinds of muscles are recognized,
the smooth and the striated. The smooth muscles are made
up of flat, spindle-shaped or band-shaped cells, and are somewhat
sluggish in their action. They are more common among the in-
vertebrata, but constitute the involuntary muscles of the verte-
brata. The striated muscles are made up of elongated cells or
fibers, across which there are minute lines giving them a striped
appearance. These muscles are more prompt and energetic in
their action than the smooth muscle, and are usually under the
conscious control of the animal.
The nervous tissue is made up of cells and fibers, which differ
not only in form, but in structure and chemical composition. The
cells usually contain a nucleus and nucleolus with a fine granular
substance, and have one or more branches, one of which is con-
tinued into a nerve fiber. The fibers consist of an axis cylinder
or thread of grayish matter, covered by a sheath of whitish
fatty matter, which in turn is covered by a sheath of connective
tissue ; such fibers are called medullated fibers. Sometimes the
254 PRACTICAL LESSONS IN SCIENCE.
axis cylinder is naked, having no sheath, and sometimes it has
only the sheath of connective tissue.
A group of nerve cells with their branches forms a ganglion.
The brain and the spinal cord are simply groups of ganglia.
Nerves are made up of nerve fibers; one set serves to connect va-
rious sense organs located in the outer surface of the body with
the brain and spinal cord, and another set connect the brain and
spinal cord with the muscles.
The lowest organisms consist of a single cell ; the body is the
protoplasm and the cell membrane is the skin. The skin absorbs
nutriment and removes waste, the protoplasm assimilates
material and grows. But as the organism grows, the body in-
creases in three directions, while the skin expands only in two di-
rections, so that, finally, the area of the skin is relatively too small
to furnish material for the growth of the body. Thus the size of
a cell or a one-celled animal is limited. If the organism increases
in size it does so by dividing into several cells which arrange
themselves so as to give the largest extent of surface, eventually
forming a cup-shaped organism with an outer and inner surface.
In the outer layers organs of motion and sensation, of respira-
tion and excretion are developed, carrying on the animal func-
tions and some of the vegetative ; while the inner layers or cavity
receives -and digests the food. Thus with an increase of size
comes a greater complexity of organism, and the essential char-
acteristics of the animal.
The more highly developed the organs, the more complete the
division of labor, the better the work done by each organ and the
higher and more perfect the life of the organism. The organs are
not only correlated in size but in form, so that from one organ a
good idea of the size and form of the organism maybe made out.
The digestive apparatus, at first a mere cavity, then a tube
which at length became separable into three parts, the fore part
for the reception of food, the middle part for its digestion, and
the hind part for the expulsion of the indigestible portions.
Then a mouth with masticatory or sucking organs and salivary
glands is developed at the fore end of the tube, and from the fore
LESSONS IN ZOOLOGY. 255
part of it the stomach with its glands and accessory organs is
formed. From the middle part, that portion of the intestine
in which digestion is completed, by the action of fluids from
the pancreas, liver, and intestinal glands, is derived, and from
the hind part that portion of the intestine concerned in the
collection and expulsion of undigested portions of food had its
origin.
The liver and pancreas appear to be outgrowths of the alimen-
tary canal which have become glands. The liver, distinguished
for its relatively great size and weight in the higher animals,
has been developed from a little patch of colored cells. The se-
cretion of the liver sometimes aids in digestion and sometimes it
does not.
Among the lowerformsof animals no circulatory system is nec-
essary, as the digestive cavity extends to all parts of the body ;
but in animals of a little higher grade the chyle or nutrient
fluid circulates in the space between the wall of the digestive cav-
ity and the body wall, doubtless due to the ordinary motions
of the organism; later a particular portion of this tract ac-
quires a muscular structure, which as a special organ maintains
the circulation. Between this and the double heart of the mam-
malia, with its systems of arteries and veins, all gradations may
be found.
The respiratory organs are appendages of the circulatory sys-
tem, arising from arches of the greater arteries, gradually devel-
oping from simple tubes, the gills of fish and the tracheae of insects,
to the capacious lungs of the warm-blooded mammalia.
The respiratory organs are to some extent excretory organs,
but the most important excretory organs are the kidneys. In
the lowest animals they are represented by contractile vacuoles;
in the worms they are known as water vascular vessels, and
sometimes they are mere appendages of the lower intestine, while
in the higher animals they are independent organs made up of a
great number of narrow coiled tubes with an abundance of blood
vessels. They separate from the blood broken down albuminous
matters. The skin is also in some sense an excretory organ, while
256 PRACTICAL LESSONS IN SCIENCE.
the sweat glands and sebaceous glands serve to equalize temper-
ature and keep the skin moist and supple.
The systems of organs already mentioned are all concerned in
the process of nutrition or the vegetative functions. The organs
of locomotion arid sensation, however, belong to the phenomena
of animal life. The organs of locomotion vary from the cilia of
some protozoa, and the muscular walls of worms to the compli-
cated mechanical apparatus of the vertebrata. The bones and
other hard parts which assist in locomotion frequently serve as
protecting organs for more delicate structures.
Among the higher animals the organs of sensation, in addition
to the brain and nerves, consist of certain peculiar-shaped bodies
of nervous tissue, which are called the end organs of certain nerves,
as the rods and cones of the eye, the auditory hairs, olfactory
cells, taste bulbs, and tactile corpuscles. Each of these has acces-
sory organs which serve to protect them and at the same time
aid them in gaming impressions of the outside world. These or-
gans appear in various forms among the lower animals, and
some of them are occasionally wanting.
Animals of the lower orders multiply by division and by bud-
ding, but some form of sexual reproduction is more common
among animals. Sexual reproduction depends on the formation
of two kinds of germinal cells, the combined action of which is
necessary to the development of a new organism.
One of these cells contains the material from which the new
individual grows and is called the ovum or egg cell ; the other
called the sperm cell contains the fertilizing material, which fuses
with the contents of the ovum and in some unexplained way
causes its development. The structure of the sexual organs
varies widely among the lower animals.
The simplest and most primitive case is where the ovum and
sperm cell are produced in the same individual; this is called
the hermaphrodite arrangement, and while it occurs in almost
every group of animals, the two cells are more commonly pro-
duced by different individuals. Sexual reproduction is in reality
a special form of growth, as the egg cell sometimes undergoes
LESSONS IN ZOOLOG Y. 257
spontaneous development without fertilization. This frequently
occurs among insects. Alternation of generations sometimes
occurs among animals as with plants.
The ovum is a cell composed of protoplasm and containing a
nucleus or germinal vesicle. In the ripe ovum a portion of the
vesicle with some of the protoplasm is forced out of the egg cell
forming the polar cells, the remaining portion as the female pro-
nucleus fuses with the spermatozoon or male pronucleus and the
resulting body is the nucleus of the fertilized ovum.
After fertilization the ovum divides into a great number of
cells, the mass for a time retaining a spherical form; but at
length, by invagination, one side is pushed or drawnin so thatthe
mass has a flask shape, with an outer layer of cells, ectoderm,
and an inner layer called endoderm, and between these layers a
third is formed called mesoderm. The skin, the nervous system,
and sense organs of the embryo are formed from the ectoderm.
The muscular system, the connective tissues, the corpuscles of the
lymph and blood, and the vessels carrying the fluids of the body,
all arise from the mesoderm. The lining membrane of the digest-
ive cavity and of the glands opening into it are derived from the
endoderm ; while the urinary and generative organs arise from
all three of the layers. The formation of the ovum and its devel-
opment is much the same among all classes of animals.
L. s. 17
CHAPTER XXXIV.
PROTOZOA, CCELENTERATA, ECHINODERMATA AND VERMES.
ANIMALS may be separated into nine groups or divisions, as
follows, beginning with the lowest:
(1) PROTOZOA. These are animals of minute size composed of
a nearly structureless substance called sarcode, having no cellular
organs, and usually asexual reproduction.
(2) CCELENTERATA. The coelenterata are radiate animals, on
the plan of two, four or six, having a central body cavity com-
mon to digestion and circulation.
(3) ECHINODERMATA. The echinodermata are radiating ani-
mals generally on the plan of five, with a calcareous dermal
skeleton or shell, often armed with spines, and having alimentary,
circulatory and nervous systems.
(4) VERMES. The vermes or worms are bilateral animals,
without limbs, and with paired excretory canals, sometimes called
the water vascular system.
(5) ARTHROPODA. The arthropoda are bilateral animals with
the body divided into segments, which carry jointed appendages
or limbs, and they have a well-developed nervous system, as in-
sects, spiders, crawfish, etc.
(6) MOLLUSCA. The mollusca are bilateral animals with a
soft unsegmented body inclosed in a single or bivalve shell, as the
oyster and mussel.
(7) MOLLUSCOIDEA. The molluscoidea are bilateral unseg-
mented animals with a ciliated circlet of tentacles. They usually
have a hard shell case and one or two nervous ganglia.
(8) TUNICATA. These are bilateral, unsegmented animals with
barrel-shaped bodies, having a simple nervous ganglion with a
heart and gills.
(258)
LESSONS IN ZOOLOGY. 259
The divisions mentioned are sometimes grouped together as
the invertebrata.
(9) VERTEBRATA. The vertebrata are bilateral animals with
an internal cartilaginous or bony skeleton, prominent in which is
the vertebral column, which serves as a protection for the highly
developed nervous system.
This scheme of classification is more or less incomplete and ar-
tificial. The knowledge of the animal kingdom is not sufficient
to enable zoologists to work out a natural system, if, indeed, such
a system exists in fact.
The Protozoa, the first or lowest animals, like the protophyta,
live in the water, and so much alike are these lowest plants and
animals that in many cases it is difficult to determine whether a
given organism is an animal or plant. One of the simplest forms
of animal life is the amoeba. This minute animal may be found
on the submerged leaves of plants or in the mud at the bottom of
stagnant water. It appears much like a piece of jelly, nearly col-
orless, often granular, and more fluid in its central portion.
When active, they are constantly changing form , thrusting out
rays or arms, called pseudopodia, from one part or another of
the mass. In the larger pseudopodia the granular matter passes
in a stream toward the extremity and back again, the circulation
probably caused by the contractility of the protoplasmic mass.
By means of the pseudopodia the animal creeps slowly along, but
in no definite direction. The amoeba has no mouth or stomach;
it flows around its food, digests and absorbs such parts as it can
use, then flows away from the undigested parts. Besides the
granular matter they often contain a rounded body called a nu-
cleus, and sometimes a contractile vesicle. The amoeba multiplies
by simple division as in the case of protococcus. The amoeba, a
little mass of protoplasm without organs of any kind lives,
moves, absorbs oxygen, expels carbon dioxide, eats, grows and
reproduces its kind in short, appears to be a complete organism.
The foraminiferae are much like the amoeba, except that they
secrete a calcareous shell. The earliest and oldest fossil known
IB supposed to be a member of this group. The shells of these
260 PRACTICAL LESSONS IN SCIENCE.
minute animals are the chief constituent of thick beds of lime-
stone rocks, as the chalk cliffs of England and nummulitic lime-
stone of France. They are exclusively marine animals, and good
specimens of their shells may be obtained by shaking a sponge
that has not been treated with acid.
The radiolaria are marine animals whose body contains a
capsule in which are oil globules, albuminous bodies, and some-
times concretions, with vacuoles and granules. They secrete a
silicious skeleton or shell. Their skeletons have given rise to ex-
tended rock formations.
If some vegetable or animal substance be soaked in water for
a few days, the water will be found to contain a large number of
different kinds of microscopic animals called infusoria. Among
them may be vorticella, paramoecium, stentor and others. One
group of the infusoria is especially interesting on account of their
close relationship to some of the alga3. They consist of a colony
of cells united by a gelatinous substance. In the inactive stage
they possess a cellulose membrane, exhale oxygen and have an
abundance of chlorophyll, and reproduce by simple division.
During the active stage the cells give rise to daughter colonies.
They are called volvocinidse, and the most common is volvox
globater. Some of the infusoria swim freely by means of their
cilia; others, fixed in one locality, create currents in the water by
the action of their cilia, thus bringing more food within their
reach. The usual mode of reproduction is by self-division, some-
times by budding and sometimes by conjugation, the nucleus
and nucleolus taking an important part in the process.
The Coslenterata. Among the coelenterata we find organs and
tissues composed of cells ; they have external and internal epithe-
lium, calcareous and silicious structures, with muscles, nerves and
sense organs. To this division belong the sponges, which are
composed of a contractile substance made up of amoeba-like cells
supported by a framework of horny fibers, or of calcareous or
silicious spicules. The sponge is traversed by numerous canals,
which open on the surface by larger or smaller openings. At
numerous places in the sponge there are little cavities or pas-
LESSONS IN ZOOLOGY. 261
sages which are occupied by ciliated cells, which, by the motion of
their cilia, keep up a circulation of water through the sponge.
Reproduction in the sponges takes place by division, by the
formation of gemmules, and by the formation of ova and germ
cells. The fertilized ova develop into embryos which are pro-
vided with cilia, by means of which they swim about until they
find some suitable resting place. Spongilla fluviatilis is common
in freshwater ponds; all other sponges are found in saltwater.
The sponges of commerce are the horny framework of the
sponge, and come mainly from the Mediterranean sea. These
sponge colonies vary greatly in form ; one can often find a half
dozen distinct forms in the display basket of one drug store.
The coral polyps, or actinozoa, belong to this division. They
consist of a cylindrical or club-shaped tube fixed at one end,
having a mouth surrounded by tentacles at the other. They
have internal generative organs and usually a calcareous skele-
ton. The sexes are usually separate, although hermaphrodite
individuals are sometimes seen. The embryos are frequently
born alive as ciliated larvae. They also multiply by budding.
The body has an ectoderm and endoderm and a mesoderna, which
in some cases becomes the seat of calcareous deposits. Corals
are radiate animals on the plan of four, five or six. They exist
in great variety in the shallow waters of the tropical ocean,
building extensive reefs ; there are corals having the form and
appearance of a human brain ; there are branching corals and
fan corals, etc. They are not only abundant in the seas of the
present time but their calcareous skeletons have been the most
abundant rock-forming material since the earliest geologic time.
The Medusse have a soft gelatinous semitransparent bell-shaped
body, the margin of which is fringed with stinging tentacles. Near
the margin are nerve rings and sense organs as auditory hairs,
and in some there is an appearance of eye-spots. The medusae
are the jelly-fish or sea-nettles so abundant in many parts of the
ocean. Many if not all the medusae are simply the free swimming
form of some of the fixed polyps. The polyp gives rise to a bud
which becomes a free swimming medusae, while the egg or genera-
262 PRACTICAL LESSONS IN SCIENCE.
tive bud of the medusae produces a polyp. The radiating parts
are on the plan of four.
The Echinodermata are popularly known as sea-urchins, star-
fish, feather-stars, etc. They are radiate animals on the plan of
five, and have a rough, often prickly skin, which has the power of
secreting calcareous matter. They have a distinct digestive canal
with mouth and vent, and a water vascular system, and a true
circulatory system are sometimes present. The nervous system
consists of nerves running down the five rays from a ring sur-
rounding the gullet. Sexual reproduction is the rule. These ani-
mals are inhabitants of the sea; are generally capable of a slow
creeping movement by means of suctorial tubes, feeding mainly
on mollusca and seaweeds. Many of them possess great repro-
ductive power, being able to replace lost parts with all their ap-
paratus of tubes, nerves, etc.
The Crinoids, during the whole or a portion of their existence,
are fixed by a jointed flexible stalk largely composed of calcare-
ous matter. The radiating feather-like arms give the organism
something of the appearance of a flower, hence the name, meaning
lily -form. The crinoids have been very abundant since early geo-
logical times, their stems and crowns contributing largely toward
building up great beds of limestone.
The Star-fish are characterized by their obviously star-shaped
body, the stomach, reproductive organs and the nervous system
all having the radiate arrangement. The color is yellow, orange
or red, the upper surface leathery, roughened by calcareous plates,
tubercles and spines. The mouth is below and the rays are fur-
rowed underneath, having numerous holes through which pass
the sucker-like tentacles or feet which serve as organs of locomo-
tion and prehension. They are voracious, and the most destruc-
tive enemies of the oyster.
The Brittle-stars are similar to the star-fish, but the long arms
are mere appendages of the body and do not contain any portion
of the digestive canal.
The Sea-urchin varies in form from a sphere to a disk. The
shell is composed of numerous calcareous plates, the whole cov-
LESSONS IN ZOOLOGY. 263
ered with numerous tubercles, to which spines of varying lengths
are jointed. The mouth on the underside is armed with a com-
plicated apparatus of calcareous teeth. From the stomach pro-
ceeds a long convoluted intestine, attached to the interior of the
shell by a delicate membrane or mesentery. The surface of the
mesentery and the lining membrane of the shell are furnished with
cilia, and by their motion the fluids of the body cavity are kept
in circulation, and in this way respiration is effected, and, in some
cases, they are provided with branched respiratory tubes. The
reproduction is sexual, the fertilized ova forming ciliated free
swimming embryos which pass through a complicated develop-
ment.
The Holothurians or sea-cucumbers are worm-shaped animals
with a leathery skin, endowed with longitudinal and transverse
muscles, by which, when irritated, some species can break their
bodies into several pieces. The mouth is surrounded by a circlet
of feathery tentacles. Locomotion is accomplished by the alter-
nate extension and contraction of their worm-like bodies. They
sometimes attain considerable size, a,nd are highly prized as food
by the Chinese.
Vermes or Worms. The worms are bilateral animals with a
much elongated, flat or cylindrical body without appendages.
Just beneath the skin there is a strongly developed muscular
system. The nervous system consists of a single ganglion, or a
pair of ganglia situated toward the anterior of the body above
the gullet, and sometimes of a nerve ring around the gullet. The
nerves given off are distributed symmetrically, supplying the sense
organs and forming two strong lateral nerves. The sense or-
gans are eyes or eye spots, auditory apparatus and tactile cor-
puscles. The function of respiration is performed through the
surface of the body. Sexual reproduction is common, but gem-
mation and fission often occur.
The Tubellaria are worms that have a small flattened body
covered with cilia. They occur in salt or fresh water, and lead
an independent life.
The Trematoda are suctorial worms or flukes, and are all in-
264 PRACTICAL LESSONS IN SCIENCE.
ternal parasites. The mouth is in the middle of a small sucker,
and frequently there are small hooks of chitin which may assist
the worm in attaching itself to desirable objects, and sometimes
there are several suckers. The best known is the liver-fluke,
which infests the ducts of the liver in sheep. The fertilized ova
produce ciliated embryos, which wander about till they die or
find a host, usually a snail, in which they are transformed into
sporocysts, which produce redise, that give rise to a generation
of tailed cercaria. In this form they leave the snail and encyst
on some foreign object, as a blade of grass ; in this state they
are swallowed by grazing sheep, and soon form mature flukes in
their livers.
The Cestoda are the tape worms. They have flattened bodies
without mouth or alimentary canal. They infest several different
animals, but Tssnia solium, which sometimes inhabits the intes-
tines of man, is perhaps the most interesting one to study. It
consists of a large number of flattened joints, each of which is a
complete hermaphrodite organism. At one extremity the organ-
ism is fixed to the mucous membrane of the intestine by means
of a crown of hooks and suckers. This part is called the head ;
the other parts are produced from the head by a process of bud-
ding. Each joint is well supplied with eggs. When mature the
joint breaks off and is expelled from the body. The eggs are
swallowed by the pig; the coat of the egg of the tape-worm is
dissolved and the embryo is set free. It soon passes through the
walls of the stomach to some of the internal organs of the pig,
where it forms a cyst, giving rise to the disease known as measles.
Meat containing these cysts is eaten, the worm is liberated from
the cyst and fixes itself to the intestine and develops into an
adult tape worm. The tape-worm of the cat is the mature cystic
worm of the mouse. The tape worm is nourished by absorbing
the nutrient fluids elaborated by its host.
The Nematoda are the round worms and thread worms which
are parasites in the lower part of the human intestine, and they
include about two hundred species that are not parasitic. The
so-called vinegar eel is a familiar member of this group. The
LESSONS IN ZOOLOGY. 265
4to
trichina is a parasite belonging to the nematoda. There are
other worms similar to the nematoda, but they need not be con-
sidered here.
The Annelida are worms whose bodies consist of definite seg-
ments. The segments are usually furnished with bristles or setae
which serve as organs of locomotion. The digestive system con-
sists of a mouth, of ten with a proboscis which may be protruded,
sometimes with horny jaws, a gullet, a stomach, intestine and
vent. The vascular system is sometimes distinct, and sometimes
in communication with the body cavity. When distinct the red-
dish blood in the vascular system and the fluid in the body cav-
ity both contain amoeboid cells. Branchia or gills are often
present as respiratory organs, but frequently respiration is car-
ried on through the general surface of the body. There are often
organs which seem to serve as kidneys, and there are sometimes
hepatic appendages. The nervous system consists of a cerebral
ganglion above the gullet and a ventral ganglionic chain. The
sense organs are paired eye spots, auditory vesicles, and tactile
organs. Sexual reproduction is common, but gemmation and
fission often occur. Frequently they develop with metamorpho-
sis. Sometimes there is a distinct head with tentacles and bran-
chia. They are terrestrial and aquatic animals, mostly marine,
living generally on animal food; sometimes they are parasitic.
The Tubicolse feed on vegetable matter and build tubes of
sticks, sand, etc., as a protection for their soft bodies. They
have external gills and red blood.
The Oligochseta include the ordinary earthworm or angle-
worm. It has but few locomotive bristles, but has well devel-
oped digestive organs. Some of this group are, parasitic, but
most of them lead an independent life.
The Hirudinea include the leeches inhabiting both salt and
fresh water. The body is ringed but has no appendages. The
common medicinal leech has a sucking-disk at each extremity, and
the mouth is armed with jaws strong enough to cut through the
human skin. When young it feeds on the blood of insects, then
of frogs, and not till maturity is a diet of warm blood necessary.
266 PRACTICAL LESSONS IN SCIENCE.
The Eotifera are worms with a ciliated apparatus at the ante-
rior end of the body which vibrates so rapidly as to produce the
impression of a rotating wheel; hence the name of wheel-animal-
cules. Some are free-swimming and some are fixed. In the free
forms the cilia are the organs of locomotion, and in all cases they
create currents in the water by which particles of food, as small
infusoria, algae and diatoms are brought within their reach. In
external appearance they are much like some infusoria, but they
are evidently of a higher order. The rotifer can be dried, then
brought to life by a little water, for many times in succession
without apparent injury.
CHAPTER XXXV.
ARTHROPODA CRUSTACEA, ARACHNIDA, AND MYRIAPODA.
THE Division Arthropods, includes a multitude of animal
forms which are distinguished from those already considered by
the possession of special organs of locomotion, by which they
may swim, creep, run, climb or fly. They are for the most part
terrestrial or aerial animals. With the organs of locomotion a
solid support was necessary for the attachment of the muscles,
hence the outer layer of the skin is hardened into a firm exo-
skeleton.
The body among the arthropoda is divided into three parts,
the head, thorax and abdomen, the appendages of each having
different structure and function. Each of these parts seems made
up of segments. The head is covered by a hard integument, in-
closes the brain and bears the sense organs and mouth parts.
The appendages of this region are changed so as to form antennae
and jaws. The thorax is a fusion of seven segments having a
hard integument. In some cases the head and thorax are fused
together forming the cephalothorax. The thorax bears the
appendages most important for purposes of locomotion. The
abdomen, composed of distinct rings or segments, seldom has
appendages, but when present they aid in locomotion, or in res-
piration, or may serve for carrying the eggs.
The skin is of two layers, a soft growing layer and an outer
one that has been hardened by the deposition of calcareous mat-
ter in the chitin base, so as to form a fi^m external skeleton. The
hairs, setae, spines, bristles and ot' -r appendages of the skin,
have their origin in the deeper layer. During the period of growth
this shell is cast off and renewed from time to time when the ani-
mal is said to moult. The muscles are all of the cross-striped
variety.
(267)
268 PRACTICAL LESSONS IN SCIENCE.
The nervous system consists of a brain, above the oesophagus,
the ventral chain of ganglia and the cesophagal ring connecting
the brain and the anterior ganglia of the ventral chain. The
sense nerves arise from the brain, while the ventral ganglia
send nerves to the muscles, organs of locomotion and skin. These
animals usually have eyes, organs of hearing, organs of smell
and tactile organs.
The digestive organs are well developed, with salivary glands,
hepatic appendages and excretory organs usually present. The
circulatory and respiratory organs exhibit the widest range of
form. Circulation is sometimes effected by a pulsating organ,
sometimes by the movements of the body, and again by regular
movements of certain organs, as the intestines. Respiration is
frequently effected by means of the surface of the body, sometimes
by branched appendages of thelimbs,and in other Cases by means
of internal tubes or tracheae. The reproduction is usually sexual,
but modified forms sometimes occur. The most of this group are
oviparous, some are viviparous, and in most a somewhat com-
plex embryonic development is followed by a complicated meta-
morphosis. The Division Arthropods includes four classes, the
Crustacea, as the crayfish and lobster, the Arachnida, as the
spiders, Myriapoda, as the centipede, and the Insecta.
The Crustacea are for the most part aquatic, breathing by
means of gills; some, however, breathe air and are terrestrial.
They vary greatly in size and form, but a study of the common
crayfish will give us a good idea of the whole class. Crayfish
may be found hidden among sticks and stones of shallow water,
and may be caught with a light dip net, which may be made of
stout wire and mosquito netting. Preserve a number in alcohol
for dissection and keep several in fresh water in a pan or glass
jar for observation.
Notice how the crayfish walks, how and which way he jumps
when frightened. Looking down upon the crayfish, notice the
cephalathorax, with its smooth horny covering called the cara-
pace, and the projection of the carapace forward between the
eyes, the rostrum. Count the segments in the abdomen, and,
LESSONS IN ZOOLOGY. 269
bending it backward and forward several times, notice bow tbe
segments are jointed together. With a pair of scissors or a
knife separate one of the segments of the abdomen from the
others, and notice the upper part or tergite, the lower part
or sternite, the side piece or pleurite, and the two appendages
or swimmerets. Compare the segment studied with other seg-
ments.
Observe the tail fin; the middle portion is the telson, the side
lobes belong to the sixth joint of the abdomen. The abdomen
of the female is relatively wider than that of the male, and the
genital openings of the male are on the first joints of the last pair
of thoracic appendages, while in the female they are on the first
joints of the last thoracic appendage but two. The eggs are
usually carried on the under side of the abdomen, glued to the
swimmerets.
Placing the crayfish on its back, count the legs and other
appendages of the cephalothorax and note if any of them appear
to arise from segments. How many joints in each leg, how do
the legs differ from each other, and how do the claws differ from
the legs. Notice also the three pairs of peculiar appendages an-
terior to the claws or chela? ; they are called foot jaws ; test them
carefully so as to learn how they work. Compare the foot jaws
with each other and with the legs and claws.
Now remove the legs, claws, and foot jaws from one side, using
care not to tear other parts. Then turn back or break away the
free edge of the carapace on that side, and the white feathery
organs brought to view are the gills, of which there are eighteen
pairs; six are attached to the second and third foot jaws, the
chela?, and the first, second, and third pairs of legs, the remain-
ing are fixed to the sides of the body. Each consists of a central
stem bearing a number of delicate filaments. Separate each
pair of gills and find out to what it is attached and how it is at-
tached. Study carefully the chamber containing the gills and
note the parts which compose it. With a probe explore for open-
ings from the branchial chamber. Projecting forward there is a
well-marked canal ; in this there is a flat oval plate, attached to
270 PRACTICAL LESSONS IN SCIENCE.
the second pair of jaws, and by its motion a circulation of water
is kept up through the gill chamber.
When the foot jaws are removed two pairs of soft leaf-like
appendages, called jaws or maxillse,come into view, and anterior
to these are the mandibles, short, hard, toothed organs which
seem more like jaws than the softer maxillae. Each mandible
bears an appendage, which curves around its anterior border in a
groove, and is known as the mandibular palpus. Fitting closely
against the posterior margin of each mandible is a soft plate-like
organ called the metastoma. Remove each of these organs, not-
ing carefully its mode of attachment and its relations, experi-
menting with each so as to gain a clear idea of how the mouth
parts are arranged, and what part each plays in the process of
mastication.
Just in front of the mandibles are the long feelers or antennae,
the antennulae, and lastly the eye stalks. Examine the an-
tennae; notice their mode of attachment, freedom of movement,
etc. In the basal segment of the antenna? there is an opening
leading to the green gland in the extreme front part of the body.
It serves the purpose of a kidney. In the basal joints of the
antennula? are the auditory organs; notice the auditory hairs
and the auditory sac. Examine the eye stalks and find the black
tip or cornea, and try if you can tell whether it is simple or com-
pound.
In the larger crayfish the digestive, circulatory, and nervous
systems may be studied, but the dissections are best made under
water. Wedge a thin board into the bottom of a shallow dish,
or cover the bottom with wax, then placing the ventral surface
downward, pin the body firmly through telson and claws. Then
with a pair of scissors cut from the posterior margin of the cara-
pace forward a little to one side of the median line to the cervical
groove, then break away the whole side of the carapace. Push
away the gills and cut them off at the point of attachment, Cut
away the other side of the carapace. With the forceps clear
away the lining membrane which discloses a small chamber con-
taining a little whitish polygonal sac which is the heart. Notice
LESSONS IN ZOOLOGY. 271
the tubes or blood vessels leading from the heart. In the heart
there are two holes above, two below and one on each side, each
hole guarded by a lip-like valve. From the gills the blood passes
into the pericardia! cavity; as the heart expands the blood flows
through the holes into it; as it contracts, the valves close and
the blood is forced into the different parts of the body, then to
the gills again. Under the heart are the reproductive organs,
the yellowish ovaries, and the oviducts leading to the genital
openings already mentioned, while in the male there are the
testes with long white coiled tubes leading to the genital opening
in the last thoracic leg.
Cut away the roof of the head. The space within the head is
quite fully occupied by the stomach. Pass a probe through the
mouth into the stomach. Note carefully the gullet, stomach and
intestine, and near the beginning of the intestine some reddish
masses, the hepatic glands or liver. Observe the white muscles
along each side the body cavity. Cut away the roof of the
abdomen, and trace the muscles through it to the telson, the
upper thinner layer straightens the abdomen while the thicker
lower layer below the intestine bends it.
Over the gullet there is a large ganglion, extending outward
and downward. Around the gullet are two masses of nervous mat-
ter connecting the ganglion above the gullet with the anterior
of twelve pairs of ganglia that lie along the ventral surface under-
neath the intestine and deeper muscles. Trace out the ganglia
and principal branches of this system. Try to have some cray-
fish for observation during their moulting season in the spring.
Those members of the Crustacea living in the sea, as the lob-
sters, shrimps and crabs are the most numerous, and individuals
among them sometimes attain great size. And these members
of the class furnish large quantities of food material.
The Barnacles belong to this class, as did the Trilobites, ani-
mals that were so abundant during the early geologic ages.
Besides the crayfish, there is a group of minute organisms called
Entomostraca that inhabit fresh water. They are an abundant
source of food for fish and other forms of aquatic life.
272 PRACTICAL LESSONS IN SCIENCE.
The Arachnida include the ticks, mites, scorpions and spiders,
animals similar to the Crustacea, but differing from them in some
particulars. The arachnid a are air-breathing animals, having
only four pairs of legs, and usually no antennae. Almost all the
arachnida live on animals, a few only living on vegetable juices,
and we may expect to find agility and intelligence as character-
istics of this class.
One group of this class are parasites in the nasal cavities of
dogs and wolves; the eggs find their way into the stomachs of
rabbits, penetrate to the liver and form a cyst ; after six months
or so they again become active for a time, and again encyst, in
which state they may reach the mouth of the original host.
Another group including the mites and ticks are called the
Acarina. Their mouth apparatus is adapted for biting, or for
piercing and sucking. There are no circulatory organs, and the
nervous and respiratory organs are of the lowest order, suggest-
ing the idea that the class is made up of degraded, depauperate
forms, sunk to their present low estate through indolence and
high living. Itch-mites, cheese-mites, ticks, water-mites and oth-
ers belong to this group of repulsive animals.
The Araneida, or true spiders, are distinguished by having a
much-swollen abdomen, four pairs of legs, an apparatus for spin-
ning webs, with from six to eight eyes, and generally poison
glands. In studying the spider make out the cephalothorax a.nd
abdomen, the mandibles, poison glands, maxillae, and the jointed
appendages of the maxillae, the maxillary palpi. Examine the
head for the eyes, usually from six to eight in number. Exam-
ine the posterior part of the abdomen for the spinnerets. Hold
a live spider by one leg with a pair of forceps and watch him
while spinning. The spinning glands secrete a viscid material
which, forced out through fine holes, hardens in the air to delicate
threads used by the spider for many purposes. Spiders differ
widely in form, color, and mode of life, but in any event they are
clean, active, intelligent and interesting.
The Mygalidse are large spiders thickly covered with hair, who
dig holes in the earth, or appropriate holes already made in
LESSONS IN ZOOLOGY. 273
wood or elsewhere. These they line with a soft silk web, some-
times arranging a cover that opens and closes like a trap door,
as the trap-door spider of Southern Europe and the bird spider of
South America.
The Saltigradse are springing spiders with eight eyes grouped
in a square; they do not construct webs. They have stout ante-
rior legs and a large arched cephalothorax.
The Lycosidse, or wolf spiders, pursue their prey by running
rather than by leaping. They build holes in the ground, often
building little walls around the opening.
The Laterigradse or crab-spiders have a rounded cephalotho-
rax and a flattened abdomen, and the two anterior pairs of legs
are longer than the others, so that they run sidewise or backward.
The Tubitelse or tube spinners, have six or eight eyes in two
transverse rows. The two middle pairs of legs are the shortest.
They weave horizontal webs, with tubes in which they lie in wait
for their food.
The Inaequitelae, or web spinners, have eight eyes of unequal size,
and long anterior legs. They construct irregular webs.
The Orbitelse, or wheel-spinners. Among these spiders the head
and thorax are separated by a groove and the abdomen is globu-
lar. The anterior legs are longest and the third pair shortest.
They spin a geometrical web, often of faultless symmetry.
Spiders are especially interesting as objects of study. Many
of them have fixed homes where they may be watched and studied
during the season. Nearly every group of spiders mentioned has
representatives in every part of the United States. If you wish
to study burrowing spiders, they are everywhere in the fields
along paths, about the yard, often between bricks in sidewalks.
A little stream of water will usually force them to the surface.
Study the spider; study his house, his family relations, his per-
sonal habits, his methods of catching food, etc.
Almost everybody thinks of the web-spinner as the typical
spider, and doubtless more will be interested to study the web-
weaving spiders. They are abundant everywhere, and at first may
be found more easily than the burrowing spiders. But it makes
L. S. 18
274 PRACTICAL LESSONS IN SCIENCE.
no difference about the kind ; locate a spider and commence ob-
servations on his habits and manners and customs at once, and
the work will afford you as much pleasure as any you ever did.
The Scorpions have jointed bodies, with a hooked telson and
poison gland; they have a bilobed brain, and four pairs of lungs,
evidently the most highly developed of the arachnida. They
are more common in the warmer countries. The results of the
bite of the largest spiders, and the sting of the scorpion have
doubtless been much exaggerated, but enough is known to make
it wise to avoid the bite or sting when possible.
The gossamer threads floating in great number in autumn
are the work of young spiders. Mounting some little elevation,
as a fence, in the warmer part of the day, they throw up the ab-
domen and allow the thread formed to float away on the ascend-
ing warm air until it becomes buoyant enough to carry the spi-
der away in the air. Spiders are oviparous, often carrying their
eggs on the abdomen until they are hatched. Spiders cast their
skin or moult several times before they attain full size.
The Myriopoda are animals whose bodies are divided into
many segments, but without division into thorax and abdomen.
They have a distinct head, three pairs of jaws and numerous
pairs of legs. The head is much like that of insects, while their
form resembles that of worms. The black cylindrical many-
legged worm that rolls up into a ball is a myriopod.
Some species of the centipede living in tropical countries at-
tain a large size, and the secretion from their poison gland is
dangerous even to man.
CHAPTER XXXVI.
INSECT A.
THE forms of life already studied have been for the most part
water animals of such low organism and retiring habits that
they have never forced themselves upon the notice of mankind.
But insects are air-breathing animals abounding everywhere,
in the air and soil, in our homes and workshops; they are para-
sites inside the human body, and often find an abiding place on
the outside; they bite and sting and irritate and annoy by night
and by day, and so persistent and aggressive are they in their
work that only occasionally can humanity turn aside from the
irrepressible conflict to notice that insects are intelligent, that
some are exceedingly beautiful, that some are useful, and that
insects as a class fill an important niche in the scheme of nature.
Insects are very numerous, outnumbering by far all other
forms of animal life; and while they differ widely in size, form
and mode of life, they are usually easily distinguished from
other kinds of life. Among the insecta there is a well-marked
division of the body into head, thorax and abdomen.
The head appears to be composed of but one mass, but many
think it really a consolidation of four segments. The appen-
dages of the head are the eyes, the antennae and the mouth
parts. The simple eye or ocellus consists of a convex cornea
resting on a crystalline lens, which in turn rests on a vitreous
humor, forming quite a complete eye; the compound eye is but
a collection of these simple eyes. Some think the ocelli are used
in the perception of nearer objects. The antennae are tubular
bodies well supplied with nerves, seeming to be organs of touch,
often appearing to be organs of hearing and smell. They differ
widely in form and size.
(275)
276 PRACTICAL LESSONS IN SCIENCE.
The mouth parts consist of the labrum or upper lip; the
mandibles or larger jaws; the maxillse or lesser jaws, to which
are attached little jointed bodies called maxillary palpi; and the
labium or lower lip, to which are attached a pair of jointed
bodies called labial palpi. These are the mouth parts of biting
insects, but some have the maxillae and labium more or less
modified so as to fit them for licking or sucking up liquids.
Sometimes the first maxillae are changed into a sucking tube, as
in butterflies and moths. Sometimes the labium forms a tube
and the maxillae forms cutting parts to open the way for the
sucking tube, so that the mouth appears in a great variety of
interesting forms.
The thorax consists of three segments, prothorax, meso-
thorax and metathorax. The appendages of the thorax are
the legs and wings. All true insects have a pair of legs jointed
to each segment of the thorax. Each leg consists of basal joint
or coxa, the femur, the tibia and the foot or tarsus, which may
be armed with a pair of claws. The legs vary widely in form and
size, depending mainly on their use. The wings arise from the
second and third parts of the thorax. They are considered by
many as simply expansions of the integument spread out over a
framework of horny tubes. The tubes are really double, consist-
ing of a central air tube inclosed in a larger tube which is filled
with blood , so that the wings serve the double purpose of organs
of locomotion and respiration. In some cases the anterior wings
are thickened and hardened by the deposition of horny matter
so as to form a protecting case for the other pair of wings and
for the abdomen.
The abdomen consists of nine or ten segments, each of which
is made up of a dorsal and a ventral plate. The segments are
joined together by soft connecting membranes, and the parts of
the segments are united in the same manner, so that the abdo-
men is capable of considerable expansion. At the extremity of
the abdomen there are terminal appendages, as stings, appa-
ratus for depositing eggs, and other organs pertaining to the re-
productive process.
LESSONS IN ZOOLOGY. 277
The digestive organs after the mouth are the (esophagus, into
which open the salivary glands; then a suctorial stomach in some
cases, and in others a crop or a straight or coiled intestine; but
whatever the name or form, one portion is adapted to digestion
of food and another concerned in the ejection of feces. There is
no liver, but certain glands in the walls of the stomach seem to
perform the office of such an organ, and there are also indica-
tions of pancreatic glands and urinary glands.
The circulatory apparatus of insects is a simple dorsal vessel
divided into eight chambers; as this vessel or heart expands
blood flows into it, and as it contracts the blood is driven into all
parts of the body without being conveyed by a distinct system of
tubes. The blood is usually colorless, and always contains
amoeboid blood cells.
Respiration by tracheae is one of the chief characteristics of an
insect. The tracheae are delicate tubes penetrating all portions
of the insect body, which receive their supply of air through
openings called stigmata situated in the membrane connecting
the dorsal and ventral plates of the abdomen. The number of
stigmata vary, but there are seldom more than nine or less than
two pairs present. The tracheae are kept open by a tough spiral
fiber of chitin, so that their structure is quite like that of the
tracheae of higher animals. Many insects seem to be able to de-
velop animal heat by increasing the vigor of respiratory move-
ments. The nervous system of insects is highly developed, all va-
riations between a common ganglionic mass in the thorax and a
ventral chain of ganglia occur. In some cases the brain attains
considerable size, which, according to one writer, " gives origin to
the sense nerves, and seems to be the seat of the will and of the
psychical activity." The ventral chain seems to correspond to the
spinal cord, and there seem to be instances of a true sympathetic
system. The muscular system lies just beneath the integument,
and seems to be continuous with it. The muscles are numerous,
especially about the head, some larva? having as many as 4,000
distinct muscles. They are generally of the cross-striped variety,
and give the insect great power and activity of movement. Some
278 PRACTICAL LESSONS IN SCIENCE.
insects are more powerful, all things considered, than &ny other
form of life.
Insects are supplied with glands somewhat analogous to the
cutaneous glands of higher animals, which secrete substances
often of the most intense and penetrating odor, which seeroe to
be used as a means of protection. Then there are glands that
secrete wax, and those that secrete a sebaceous liquid that serves
to lubricate the joints; and in some larvae there are spinning
glands which serve for the production of webs, pupa cases, etc.
And many insects have poison glands in connection with stinging
organs.
The sounds made by insects are produced by the friction of one
part of the external skeleton on another, as the legs against
wings, or wings against wings, etc., by the passage of air through
the thoracic stigmata, by the rapid movement of the wings, and
doubtless in other ways not understood. Insects emit odors and
doubtless have a sense of smell, but observers are by no means
agreed as to its nature or location. So it seems as if there must
be a sense of hearing. Among the grasshoppers and crickets
there seems to be an auditory apparatus in connection with the
anterior legs, but in reality little is known about the sense or-
gans among insects beyond what is known of the organs of sight.
Among insects reproduction is sexual. In some cases the egg
develops into a perfect insect without metamorphosis, but in
most cases the embryo passes through a well-marked metamor-
phosis, often requiring considerable time before the perfect stage
is reached.
After the egg is fertilized it gradually develops into a worm-like
form called the larva, known commonly as caterpillar, grub or
maggot. As soon as hatched the larva eats voraciously, grow
ing rapidly, moulting from time to time, storing up fat from which
to form the tissues of its future body. At length it stops eating,
makes a cocoon and, slowly changing form, loses its worm-like
body and develops the head, thorax and abdomen of the perfect
insect. Sometimes this resting or pupa stage is very brief ; some-
times it lasts for a considerable time.
LESSONS IN ZOOLOGY. 279
As soon as the insect is complete, the sexes meet, and soon
afterward the male, no longer useful, dies; the female lays her
eggs in or near some food supply, then dies. For most insects
this period occurs in the late summer or early antumn, so that
the species is represented during the winter by eggs alone. Some-
times the winter is passed in the pupal stage, and in some cases
in the larval stage. Insects may brood two, three or more times
in one season, but in general, insects are annuals. Sometimes
the larva live for many years, as in the case of the seventeen-year
cicadia.
The insect-fauna of a locality comprise all the insect forms
found in it. The limits of a fauna are usually determined by
temperature or some natural barrier, as the ocean or a high
range of mountains, etc. Insects may be distributed ,by the
wind, by the agency of birds, or other animals, or of man. The
life of an insect is short and active, and has but a single purpose,
and yet many insects are subject to disease, for the most part
diseases due to parasitic plants or animals. The honey bee, the
silkworm, and the house fly are each subject to fungoid diseases.
There are so many different kinds of insects that the names of
the principal groups with some distinguishing characteristics may
be helpful. The lowest group of insects are the Thysanura, includ-
ing wingless insects, with rudimentary mouth parts and setiform
anal filaments which of ten serve as springing organs, so that they
are sometimes known as spring-tails. They develop without
metamorphosis, and seem to be the most ancient insects as well
as the lowest.
The Orthoptersi. The insects of this order including the grass-
hoppers, crickets, etc., have biting jaws, and pass through an
incomplete metamorphosis. There is no resting stage ; the newly
hatched larva differs from the adult only in size, and the pupa is
characterized by rudimentary wings. As a rule they are vora-
cious eaters and make sounds of piercing shrillness.
Some of the largest insects are members of this group, and the
grasshopper is one of the best subjects for investigation. Have
several individuals in different stages of development confined
280 PRACTICAL LESSONS IN SCIENCE.
for observation, and have several large specimens preserved in
alcohol for dissection. In studying the grasshopper note the
general divisions of the body ; examine carefully the antennae and
eyes, using the lens in looking for the ocelli. Dissect out and
place by itself each one of the mouth parts. Notice the divisions
of the thorax, and compare them in size and form and as to the
appendages they bear. Note the position of the anterior wings
when folded, open these wings so that the anterior margin shall
be at right angles with the body, and then note the position of
the inner wing while folded; spread it out, noting carefully how it
was folded. Compare the framework of the two pairs of wings ;
also compare them as to size, shape, color, texture, position
and use. Study the legs; note their number, arrangement
and mode of attachment, and the parts of each. Notice the
different ways in which the grasshopper travels, and how he
makes sounds.
Note the number of segments in the abdomen and the two
longitudinal grooves on its under surface. That part of the ab-
domen between the grooves is the sternum, the side is the pleu rum
and the upper part the tergum; and the corresponding parts of a
segment are the sternite, pleurite and tergite. Note the spiracles
or breathing pores on the sides of the abdomen. On the sides of
the first segment find a pair of thin oval membranes called tym-
pana, which some think are an auditory apparatus. The four
short setae, which may be discovered at the end of the abdomen
of a female grasshopper, form an ovipositor by which she can
make a hole in the earth as deep as the abdomen is long, at the
bottom of which she deposits her eggs. Dissecting a large female
grasshopper under water, as in the case of the crayfish, one may
make out the air sacs and tubes, the egg masses and the alimen-
tary canal.
The Orthoptera include Forficulidse or earwigs, the Blattidse
or cockroaches, the Phasmidss or walking sticks, the Acridiidse or
grasshoppers, the Locustidse or locusts, the Gryllidse or crick-
ets, the TermitidsBor white ants, the Ephemeridae or the Mayflies,
the Libellulidse or dragon flies, and others. They are all inter-
LESSONS IN ZOOLOGY. 281
eating and many of them familiar insects, well worthy of study
and investigation.
The Neuroptera, includes insects that have biting mouth parts,
membranous wings, and that pass through a complete meta-
morphosis. They have something the appearance of the dragon
flies and May flies. One member of this order has long horns
and long delicate wings, and is called the Horned corydalis.
The Strepsiptera includes a few insects of minute size and no
special interest.
The Rhynchota are insects that have piercing mouth parts,
and pass through an incomplete metamorphosis. The Pediculidse
and other animal parasites, theAphida? and other plant-lice, and
the Cicadidse belong to this order, and so do the Hemiptera or
bugs, water bugs, etc. The bugs may be known by their anterior
wings which are horny toward the base and membranous toward
the tip. The Coccus cacti oi Mexico yields a coloring matter called
cochineal, which has considerable commercial value.
The Diptera. The members of this order are insects with
piercing and sucking mouth parts, passing a complete metamor-
phosis. The posterior wings are reduced to mere knobs, so that
they appear to have but one pair. This group includes insects
that are parasites on animals, and sometimes on other insects.
The common house fly, the bot fly, gad flies, gnats, fleas, mos-
quitoes and others are members of this order.
The Lepidoptera are insects having suctorial mouth parts,
two pairs of wings similar in form, which are covered with deli-
cate scales. This group includes the moths with feathery an-
tennae, that are active at night, and the butterflies with knobbed
antennae that are active during the day. Both moths and but-
terflies are noted for their beautiful colors and graceful forms.
They pass through a complete metamorphosis, and the cocoons
spun by some of the larvae of this group are the source of the
silk of commerce, making the silkworm chief among insects for
the economic value of its work.
The Coleoptera are insects with masticating mouth parts, and
hardened anterior wings, which are the chief 'characteristic of
282 PRACTICAL LESSONS IN SCIENCE.
this immense group of insects, numbering some 80,000 species.
They are properly called beetles, not bugs, which is the name ap-
plied to the Hemiptera.
The Hymenoptera. This group includes the bees, wasps and
ants. They have mouth parts adapted to biting and licking;
the head is large with three ocelli and large compound eyes.
There are two pairs of membranous wings fitted for prolonged
flight. The body is compact, of about average size, the nervous
system complicated and highly developed, so that in the matter
of intelligence and capacity for work we would expect this group
to stand easily at the head of the insect world. In the female
the abdomen ends in an ovipositor, or more commonly with a
sting and its associate poison glands. The leaf-wasps, wood-
wasps, gall wasps, ichneumen flies and others have ovipositors
and deposit their eggs in wood, leaves or other vegetable struct-
ures, some making quite deep excavations.
The Formicidae or Ants, live together in communities, which
contain winged males and females, but are composed mainly of
wingless individuals called workers. The female has a sting and
poison gland, and the workers, supposed to be aborted females,
also have poison glands. The dwellings of ant communities con-
sist of passages and cavities in rotten wood or in the earth.
Customs vary in different communities, but the following is per-
haps the history of an average colony : Some time during the
summer the males and females reach the adult size; soon after-
ward they take the marriage flight. The males soon die, and the
females attend to the matter of raising their brood or founding
new colonies. In general there seems to be a tendency among the
young females to form colonies by themselves or with a body of
workers, but usually females enough are forcibly retained by the
workers of the original colony to continue it as a strong commu-
nity. The fertilized eggs are exposed to the morning sun, covered
from its heat during midday and removed from the influence of
damp and cold at night. The grub is treated in the same way,
and besides is fed by the nurse or female with a liquid disgorged
from the stomach. After passing into the pupa state they are still
LESSONS IN ZOOLOGY. 288
under the constant care of the mother or nurse. It is supposed
that different care or different feeding develops the male, female,
soldier or worker from the same group of eggs, but this matter
seems to lack confirmation. Wonderful stories are told of the in-
telligence of ants. It is claimed that they carry on war; that
colonies are sometimes exterminated, sometimes enslaved, and
that some ants keep domestic animals, and that they sometimes
undertake migrations in great numbers.
The Vespidae or Wasps. The life history of a wasp is about as
follows : Males and females reach maturity in late summer, and
copulate in the air; soon afterward the males die, but many of
the females survive the winter. In the spring the wasp begins a
nest, making it of gnawed wood which resembles paper. During
the spring and summer she begets workers, which help to in-
crease the size of her nest, and to rear the perfect insects later in
the season.
The Apidse or Bees. The nest of the bumble bee is founded by
a single female which has survived the winter as in the case of
the wasp. Some bees excavate cavities in wood for the deposi-
tion of their eggs. The common honey-bee is, next to the ants,
the most interesting insect. Among them we have the commu-
nity of the queen, males and workers, the queen living for four or
five years no other perfect insect having as long tenure of life.
The wasp builds a cell of paper for its young, the bee builds one
of wax. The cells are of hexagonal form, and of a larger and
smaller size. In the smaller cells, provisions are stored, and in
them the worker brood is placed, while the larger ones are used
for the male brood and the reception of honey. On the edge of
the comb a few large irregular queen cells are formed. In early
spring the queen deposits eggs in the workers' cells, and later in
the drone cells, and later still she deposits an egg in each of sev-
eral queen cells. The larva in these cells receive richer food, and
reach maturity in about sixteen days, while the male requires
twenty-four days, and the worker twenty to reach maturity.
Just before the oldest of the young queens reaches maturity, the
queen mother leaves the hive or nest with a portion of the work-
284 PRACTICAL LESSONS IN SCIENCE.
ers as a first swarm. The young queen arrives at maturity, is
fertilized in marriage flight, returns to the colony, kills the queen
pupas in the remaining cells, and reigns undisputed; or, if prevented
from this she leads out another colony before the maturity of a
second queen. If the queen dies, the workers enlarge the cell of
some young worker grub, and feed it with royal jelly, so that it
develops into a queen, and the affairs of the colony go on as
usual ; but if there are no brood cells, a bee community soon goes
to pieces on the loss of the queen. Division of labor is well marked
among bees; the queen-mother and ruler, the fathers, gentlemen
of leisure, and the workers ; some collecting honey, some secreting
wax and building cells, some nursing the brood, some attending
to the ventilation of the hive, as their active respiration tends to
raise the temperature and foul the air. Bees, silk-worms and the
cochineal insects, are the only representatives of the great group
of insects that are of much economic value.
The collection of specimens is an interesting and valuable exer-
cise. A pint fruit jar two-thirds full of seventy-five per cent, alco-
hol will be a good receptacle for almost anything taken in the
field except moths and butterflies. They may be killed with
chloroform or cyanide. The cyanide bottle is perhaps the most
convenient, and may be made by placing several pieces of cyanide
over the bottom of a pint fruit jar, and just covering them with
plaster of paris. Insects shut up in the jar are soon killed ; after
which they can be transferred to folds of paper and packed in
boxes, or pinned in boxes. Great care is necessary in arranging
the legs and wings so that when dry the specimen shall look nat-
ural, be neat, and well preserved.
CHAPTER XXXVII.
MOLLUSCA, MOLLUSCOIDEA AND TUNICATA.
THE Mollusca are soft-bodied animals without internal skele-
ton, and without segments or joints. The body is covered loosely
with a soft contractile skin which usually secretes a calcareous
shell as a protective covering. Most of the mollusca are aquatic
animals or live in damp places, and many of them are perma-
nently fixed to solid bodies, having no organs of locomotion. A
mass of skin and muscular tissue called the foot is developed on
the ventral surface of many of this group, by means of which
slow movements may be accomplished.
The alimentary canal consists of the oesophagus, stomach
and intestine, and the rectum. Attached to the digesting por-
tion of the canal there is quite a complete liver, and kidneys are
always present. There is a vascular system with a heart driving
the blood through the body, but the system is not completely
closed from the body cavity. Respiration is carried on through
the general surface of the body, also by means of branchia or
gills, and occasionally by means of lungs.
The nervous system consists of a pair of dorsal ganglia lying
above the oesophagus, with pedal and visceral nerve cords; and
sometimes it would be better described as consisting of a cerebral
ganglion, a pedal ganglion and a ganglion supplying the walls of
the body. The cerebral ganglia supply the sense organs, which
usually consist of eyes, tactile and auditory organs. But no
general description can do justice to this large and interesting
group of animals; some notice must betaken of the more im-
portant subdivisions.
The Lamellibranchiata are mollusca without distinct head, that
breathe by means of plate-like branchia or gills, and have bivalve
shells. To this class belong the oyster, the salt water and the
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286 PRACTICAL LESSONS IN SCIENCE.
fresh water mussel. The fresh-water mussel is abundant in the
beds of most of the streams and ponds of the Mississippi valley,
and can easily be taken during the low water of the summer.
They may be kept for observation in a tub or bucket, in which
there are two or three inches of mud and sand covered by six or
eight inches of water. A few specimens should be preserved in
alcohol for dissection. With a live shell in the hand, notice the
two parts or valves of the shell : the edge along which the valves
are joined is the dorsal margin, and the other is the ventral mar-
gin of the shell. The concentric lines parallel to the ventral mar-
gin are lines of growth, the raised portion which forms the center
of these lines is the beak or umbo which is nearer the front or
anterior end of the mussel. Holding the shell with the dorsal
margin upward, and the anterior portion forward, notice the re-
lation of parts, the anterior and posterior regions, the right and
left valves, the ventral and dorsal margins, and the heavy hinge
ligament binding the valves together.
Drop two or three live mussels into water that is nearly boiling
hot. The hot water will kill the animal and loosen it from its shell.
When cool enough to handle open the shell by turning back the
left valve. Notice the white membrane, mantle, adhering to the in-
ner surface of the shell; it can easily be removed with the fingers;
then notice the glistening inner surface of the shell, and the rough
line parallel with the margin of the valve called the pallia! line t or
impression, as it marks the line along which the mantle was at-
tached to the shell. Notice that this line terminates in two oval
rough-bottomed pits near the extremities of the hinge ligament.
With the fingers or a thin piece of wood carefully separate the
mussel from the other valve, noting the pits near the dorsal
margin, and the bodies which occupied them. They are the ante-
rior and posterior adductor muscles' by which the mussel closes
his shell. Note their relative length and thickness, and their
structure. Notice that the shell does not remain closed, the
elasticity of the hinge ligament opens it as soon as the muscles
are cut or loosened. Notice that the mantle lobes are continuous
across the dorsal portion of the mussel. The hatchet-shaped,
LESSONS IN ZOOLOGY. 287
yellowish or whitish mass of flesh lying between the mantle lobes,
and forming the ventral portion of the animal is the foot. On
either side the foot find a pair of branchia or gills. Just in front
of the gills on each side are a pair of triangular processes called
the labial palpi, and between them just back of the anterior ad-
ductor muscle is the mouth. Toward the posterior of the ani-
mal notice that the mantle lobes coalesce so as to form two slit-
like openings called the ventral or inhalent siphon, and the dor-
sal or exhalent siphon. By the action of cilia in the ventral
siphon and gills, water is driven through the gill chamber, and
food materials pass with the water over the palpi to the mouth.
Commencing at the mouth with probe, blowpipe and scissors trace
out the alimentary canal. This can be done more easily with an
alcohol specimen.
Pry open the shell of a live mussel and insert a little block of
wood to keep it from closing; then cut the adductor muscles,
separate the mantle lobes from the shell, and on the dorsal
border of the animal, near the region of the umbo, notice a thin
space in the mantle covering a cavity filled with fluid. In this
cavity, called the pericardium, a yellowish transparent sac, called
the heart, may be seen pulsating in the pericardial fluid. This
dissection can be made more satisfactorily with a live clam, but
most of the work can be as well or better done with the alcohol
specimen, or one that has been killed with boiling water.'
Most mussel shells have hinge teeth with corresponding sockets
on the dorsal margin of the valves, near the ligament, by which
they are more firmly held together when the shell is shut. The
anterior is conical, sometimes sharp, the posterior narrow and
long. Notice a thin dark-colored membrane bordering the edge
of the shell, seemingly an extension of the outer covering or epi-
dermis of the shell. Burn some mussel shells in the open fire,
and note what properties they lost and what they gained from
burning. From the burned shells try to get some idea of how
the shell was built up. Test portions of the burnt shell with
acid and note results ; also test a fresh shell with acid and note
results. In observing the mussel note especially his methods of
288 PRACTICAL LESSONS IN SCIENCE.
locomotion, his position while lying in the mud, and the currents
of water when the siphons are in action. Water snails and land
snails having univalve shells are also interesting to keep for ob-
servation, as are also garden slugs or snails that have no shells,
or only little scales on the dorsal surface.
The nervous system of this group consists of three pairs of
ganglia, the cervical, pedal and visceral. The sense organs are
but slightly developed. Usually the sexes are separate, but
hermaphrodite individuals occur. They are generally oviparous,
but the fertilized eggs are often retained in the pouches of the
parent until the embryo is well advanced.
The Ostridse, or oysters, belong to this class. They have a fixed
left valve; the right valve closes upon the oyster held in position
by a strong ligament. They have no siphons, and only a rudi-
mentary foot. Oysters are either mainly hermaphrodite indi-
viduals or females. The fertilized ova, called spat, after escaping
from the organs of the parent, swim freely for several days, then
settle on some support as sticks, stones, old shells or other ob-
jects, and become fixed. The natural oyster beds of the Old
World and many of those of the United States have been ex-
hausted, and artificial beds have been made and cultivated and
protected to such an extent that oyster culture has become an
extensive and profitable industry.
The Gasteropoda, have a distinct head, often with tentacles
and stalked eyes, and simple mantle that secretes a plate-shaped
or coiled shell. The muscular foot forms the ventral side of the
body, hence the name signifying stomach foot. Eyes, olfactory,
tactile and auditory organs are fairly well developed. Sometimes
the mantle forms a long siphon. This family includes the uni-
valve land snails and the fresh water and salt water univalve
snails or mollusks, as well as some that do not secrete a shell.
The Cephalopoda have a circle of arms, bearing suckers round
the mouth, and they have a funnel-shaped perforated foot. The
water used for respiration, violently driven from the funnel, tends
to force the animal backward. This method of locomotion is
common among the animals of this class. The octopus, the
LESSONS IN ZOOLOGY. 289
nautilus, cuttlefish and other interesting mollusks belong to this
class. Some attain great size and strength, so that with their
long arms, supplied with powerful suckers, they sometimes de-
stroy men, and so fierce and destructive are they that one group
has received the name of devil fish.
The Molluscoidea. The bryozoa and brachiopoda, now
grouped as molluscoidea are interesting animals whose relations
are not well made out, and which do not appear much alike, but
a study of their developmental history seems to show them
closely related. The bryozoa are small animals usually united
together forming colonies so as to present the appearance of
sprigs of moss. There is no vascular system, and the nervous
system consists of a simple ganglion. The mouth, surrounded
by a crown of tentacles, leads to a capacious stomach, the intes-
tine terminating near the mouth. The brachiopoda are fixed ani-
mals of larger size, having a shell consisting of dorsal and ven-
tral valves. A vascular system is present, and the nervous
system is a ring about the oesophagus with two ganglia in it.
The mouth is provided with two long, coiled arms, which serve
as a respiratory apparatus, and aid in gathering food for the
animal. The oldest fossils belong to this group.
The Tunicata. These are saccular or barrel-shaped animals,
whose respiratory cavity has two wide openings, between which
is placed the simple ganglion which constitutes the nervous sys-
tem. Judging from the development of the different systems of
organs the ascidians would appear to take low rank in the scale
of being, but a study of their embryonic development seems to
show that they have close relations to the lower vertebrates.
They are nearly all marine animals of little or no economic
value, and of no special value for study by beginners in zoology.
L. S. 19
CHAPTER XXXVIII.
THE VERTEBRATA, PISCES, AND AMPHIBIA.
THE vertebrata are distinguished from other forms of animal
life by the possession of an internal skeleton. The principal part
of the skeleton is the vertebral column composed of several dis-
tinct bones called vertebrae. Each vertebra is made up of a body
and several processes or projections. Some of these processes en-
able the vertebrae to articulate with one another so as to form an
elongated, flexible, bony axis. Other processes jut out from each
vertebra so as to form a narrow bony tube, or canal on the dor-
sal side of the axis, and at least the framework of a much larger
cavity on the ventral. And perhaps we find here the chief differ-
ence between the two groups of animals : the in vertebrates consist
of onebody cavity and its contents; the vertebrates havethesame,
and in addition a second cavity, the vertebral canal and its con-
tents. While the Vertebrata are alike in many respects they differ
widely among themselves, forming five quite well-marked classes :
Pisces or Fishes, Amphibians, Reptiles, Aves or Birds, and Mam-
malia.
The class Pisces is made up of cold-blooded aquatic animals
that breathe by means of gills. As usually constituted, this class
includes several forms that are not regarded as true fishes. Of
these the lowest in the scale are the Leptocardii. They have a
membrane-cartilaginous skeleton, without a skull, the vertebral
column represented by an elastic substance called the notochord,
which in the higher vertebrates represents the column in the em-
bryo. The colorless blood circulates in pulsating vessels without
the aid of a heart; they have no nervous system or sense organs.
The mouth without jaws leads into the pharyngeal sac, whose
sides are pierced by numerous slits which serve for respiration.
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LESSONS IN ZOOLOGY. 291
The individuals of this group are small, and are found usually in
the sands of shallow water along the seashore.
The Marsipobranchia, are vermiform animals with a cartilagin-
ous skeleton, and persistent notochord. The mouth is suctorial ;
the alimentary canal a simple tube. The blood is red, and the
heart has two valves. The brain is distinct, with three sense
nerves: the optic, auditory and olfactory. They have dorsal
and caudal fins, but no scales. Respiration by means of five or
six pairs of gill sacs. They are all parasites, including the marine
hagfish, and the lampreys, living in both fresh and salt water.
They attach themselves to dead or living fish, and also eat worms
and other small aquatic animals.
The Selachii have a cartilaginous skeleton, pectoral and ven-
tral fins, transverse mouth, and a capacious stomach. Respira-
tion is accomplished by means of one or several gill openings.
There is no air bladder, and the arterial bulb has three series of
valves. The nervous system is well developed, but the optic
nerves do not decussate. This group includes the different kinds
of sharks, dog fishes, skates and rays. They are carnivorous,
and generally marine.
The Ganoidei and Teleostei are regarded as true fishes. The
Ganoidei have a bony or cartilaginous skeleton with enameled
scales or osseous plates. The arterial bulb is muscular with
numerous valves, and there is a partial decussation of the fibers
of the optic nerve. The sturgeons, gar-pikes and mud-fish are
the chief representatives of this group in the waters of the present
time, but earlier in the history of the earth they were the domi-
nant form of fish life.
The Teleostei are bony fish, and include the great bulk of the
fishes of the present time ; they are the typical fish, and perhaps
we can best learn something of them by a somewhat detailed
study of some common fish, as the yellow or ringed perch ; or a
bass or a croppie would serve as well.
Holding a fish in its natural position, notice that it is symmetri-
cal , has an anterior and posterior region, a dorsal and ventral sur-
face and a right and left side. A fish may be cylindrical, or flat-
292 PRACTICAL LESSONS IN SCIENCE.
tened from above downward, but they are usually "compressed,"
flattened from side to side ; as in the case of the bass or perch.
The fins are membranous organs, probably folds of skin, sup-
ported by spines or rays. The principal one is the caudal or tail
fin. Of these there are two kinds, the hoinocercal, when the back-
bone ends at the base of the fin and the fin is symmetrical, and the
heterocercal, when the backbone extends into the upper lobe of
the fin, making it unsymmetrical, as in the sturgeon and shark.
The fin along the center of the back is the dorsal; it is sometimes
single, sometimes double, and it may be supported by spines or
soft rays. Then there are the pectoral or breast fins, the ventral
fins and theana7fin. Count the spines in each of the fins, count the
soft rays, measure along the base to find the length of the fin,
and the length of the longest ray to get the height of the fin.
Compare the fins as to length, height, number of rays and spines,
and note their relative position. Close the mouth and measure
from the tip of the snout to the posterior margin of the bone
which covers the gill opening for the length of the head, and to
the base of the caudal fin for the length of the fish, and measure
from above downward at the widest place for the depth of the
fish. Compare the length of the head with the length of the body,
and the depth with the length and width, etc.
The bone that serves as an upper lip for the fish is the premax-
illary; note its form, size, and movements; notice also the fine
teeth on it, and their shape, size and arrangement. Back of the
premaxillary on each side are the oblong maxillary bones, and
abovethese in the median line are the nasal, prefrontal and frontal
bones, and on the sides of the lower jaw are the dentary bones.
In the front part of the roof of the mouth find a group of teeth
situated on a bone called the vomer. Extending backward on
each side of the roof of the mouth find rows of teeth located on
the palatine bones. Examine other parts of the mouth and the
tongue for teeth ; compare the different sets as to form , size and
arrangement. In front of the eye is the anteorbital and below it
are the suborbital bones.
The cavities in the sides of the fish which divide the head from
LESSONS IN ZOOLOGY. 293
the body are the #7*77 openings, and the bones covering them are
the g7*77 covers. The upper posterior part of the gill cover is the
opercle; below it is the subopercle; between the opercle and the
eye is the preopercle, which is sometimes serrate or toothed, and
below it is the interopercle. Below the gill cover find the bran-
chiostegal membrane, supported by curved bones called bran-
chiostegal rays. The narrow body in the median line separating
the right and left branchiostegal membranes is the isthmus.
Turn back or cut away the gill cover and examine the gills.
Notice the central bony arch, and the fringe of red filaments that
makeup each gill. On the front and inner border of each arch are
teeth-like bodies, called gill-rakers. The slits between the gills
are the gill clefts. A red spot on the inside of the gill cover is the
false gill. Below the four gill arches is a fifth arch, called the in-
ferior pharyngeal bone, and where the gill arches unite above is
the superior pharyngeal bone, each of which bears teeth.
Study a scale; notice its radiate and concentric markings. A
scale with an even posterior border is a cycloid scale, and one
with a toothed border is a ctenoid scale. Compare scales from
different parts of the fish. Notice a line called the lateral line
along the side of the fish. Compare a scale from the lateral line
with other scales and note the differences. Note that the arrange-
ment of the scales is regular and symmetrical. Count the scales
in the lateral line. Count the rows of scales above and below the
lateral line on the side of the fish. Remove a scale carefully and
notice a thin skin or epidermis covering it, and if we examine a
dark spot we find that the coloring-matter is in the epidermis
and not in the scale.
Open the fish by cutting from the anus forward in the median
line to the isthmus ; just back of the ventral fins, cut toward the
spinal column on each side, so as to open the body cavity fully.
Notice a silvery white membrane, the peritoneum, and in the front
part, a little to the left, a brownish mass, the liver, and under it
the hepatic vein.
Placing the fish on its right side ; turn down the liver, uncover-
ing the stomach. Pass a probe through the mouth and gullet
294 PRACTICAL LESSONS IN SCIENCE.
into the stomach; trace the intestine from the stomach to the
anus, and notice the delicate membrane called the mesentery.
Near the intestine find a reddish body, the spleen. Find the air
bladder', it sometimes communicates with the alimentary canal.
Does it in this case? Above the air bladder find two slender, dark
red bodies, the kidneys, and in the posterior part of the body
cavity find the urinary bladder and the reproductive organs;
the yellow single or double ovary with the oviduct in the female,
and the two white testes in the male.
In front of the liver, separated from it by the false diaphragm,
is the pericardial cavity. Examine the heart ; note the thin-walled
auricle and the thicker walled ventricle. The auricle receives
blood from the body through the venous sinus which passes to
the ventricle, then through the arterial bulb to the gills, thence
to the body ; the blood is usually red.
The pectoral fins represent the anterior limbs of other verte-
brates. They arise from the pectoral arch, which, in some cases,
is a simple cartilaginous arch, in others composed of the clavicle,
supraclavicle and post-temporal bones. The ventral tins repre-
sent posterior limbs.
Cut down to the ribs by the side of the dorsal fin and dissect
away the flesh, studying the relation of the fin to the vertebral
column. This, perhaps, can be done more easily in a fish that
has been cooked, and in this way the flesh may be removed from
the backbone so that it may be studied more satisfactorily.
Study a vertebra. Notice the form of the body, the dorsal spine
and neural arch and the haemal spine and arch below, and note
the neural canal with the spinal cord, and the haemal canal with
its contained blood vessels.
Open the cranial cavity and at least a portion of the spinal
canal, and, beginning at the front, notice the olfactory lobes giv-
ing rise to the olfactory nerves, then the cerebral hemispheres,
then the optic lobes, the widest part of the brain, then the cere-
bellum, and the medulla oblongata, merging gradually into the
spinal cord.
Cut away the lower jaw, and, working from the mouth, dissect
LESSONS IN ZOOLOGY. 295
out the muscles of the eye, and trace the optic nerve to the optic
lobes. Notice the form of the eye, its flat cornea and spherical
lens; its freedom of motion and the absence of eyelids.
Auditory organs are usually present, but it is said that fish
cannot hear well, and the senses of taste and touch do not seem
to be well developed. The olfactory sense is, perhaps, better
developed than any other except the sense of sight.
Open and shut the mouth and note the motion of the different
bones which make up that cavity. Cut away the gill cover on
one side and note the motion of the gills corresponding to the
motions of the jaws and tongue. Keep minnows or small fish in
jars for observation, and notice their movements and habits.
Fish, in general, are carnivorous; they are voracious eaters
and rapid growers. The flesh of most kinds is highly prized for
food. The fishing industry is one of the great industries of the
world .
Most fish are oviparous, producing vast quantities of spawn,
but their natural enemies are so numerous, and the number de-
stroyed by man so great, that many of the valuable fish began to
diminish in numbers. This fact led several nations to establish
departments looking toward the protection and culture of valu-
able food-fishes.
These departments have gathered an immense fund of informa-
tion relating^ to the habits and life history of the more valuable
food-fishes; to the habits and history of the various forms of life
used by them as food ; to the habits and history of those forms
of life that prey upon food-fishes, and to the various forms of
disease that attack valuable fish. This knowledge has led to the
adoption of rational methods of protection and culture, so that
waters formerly barren now yield an abundance of good fish, and
other waters are furnishing a largely increased product. The
more important food-fishes included in this group are the herring,
cod, mackerel, shad, salmon, hake, haddock, halibut, white fish,
trout, bass, pickerel, and many others.
The Dipnoi, are scaly animals breathing by means of gills and
lungs ; they have the form and appearance of fish, but their lungs
296 PRACTICAL LESSONS IN SCIENCE.
and the structure of the heart, make them appear as in some
sense a transitional group between the true fishes and the am-
phibians. They are not found in this country, and are of no
economic value, and are not numerous, although, during recent
geological periods, they were prominent forms of life.
The Amphibia are cold-blooded, usually naked-skinned animals
that are oviparous. The fertilized egg develops into a larva,
somewhat fish-like in form, that breathes by means of gills. The
larva eventually develops lungs and anterior and posteriorlimbs,
sometimes retaining the gills during life but usually losing them.
The lungs are not well organized and much of the respiration is
carried on through the skin. The medium of respiration whether
by gills, lungs or skin is supposed to be derived from the cutane-
ous surface.
The skeleton varies considerably, but the bones are usually
more compact and calcareous than those of fish, and, with the
development of the external limbs, the pectoral and pelvic arches
are more fully developed and the amphibian is fitted for crawl-
ing, swimming, climbing and walking.
The nervous system seems, on the whole, to be more highly de-
veloped than among fishes, although the sense organs do not
seem much superior to those of fish unless, perhaps, the senses
of touch and taste may be exceptions. Some of the amphibians
have a well-developed vocal apparatus in connection with the res-
piratory organs, which is a distinguishing mark of some impor-
tance.
The young, while breathing by means of gills, have the single
auricle and ventricle and the same arrangement of arterial trunks
as among fishes, but with the development of the lungs the auri-
cle is divided into two chambers, one receiving blood from the
body, the other from the lungs; but the ventricle remains single,
containing mixed blood. The lymphatic system is well developed ,
in some cases the lymph receptacles are contractile, having the
value of lymph hearts.
Some amphibia are terrestrial during the adult state, but usu-
ally live in damp localities since cutaneous respiration necessi-
LESSONS IN ZOOLOGY. 297
tates a moist atmosphere. In larval life they live mainly on
vegetable matters, in adult life on insects.
As a rule, their movements are sluggish, and the need of food
is relatively small, so that they live for months without food.
They also have the power of reproducing lost parts, as the limbs
or tail.
The Apoda are worm-like amphibia, without limbs, that were
for a long time thought to be snakes. They live in tropical
climates and are of no special interest beyond the question of
relationship.
The Caudata have four short limbs and a persistent tail, some-
times retaining external branchia through adult life.
This group includes the sirens, the mud puppies, which have
external gills, and the land and water salamanders which have
no gills.
The Batrachia are tailless amphibia with naked skin and well
developed extremities. This group includes water frogs, land
frogs, tree frogs, toad frogs and toads.
CHAPTER XXXIX.
REPTILIA AND AVES.
THE REPTILIA.
THE Reptilia are cold-blooded animals with a scaly or ar-
mored skin. In many cases there are no limbs, and when pres-
ent they are usually weak, scarcely raising the body from the
ground. In most cases the trunk, even when the limbs are pres-
ent, is an important agent inlocomotion, as the vertebral column
is adapted to serpentine movements. The internal skeleton is
always bony, and generally the ribs are numerous and well de-
veloped. Each half of the lower jaw is composed of several
pieces joined by sutures, and the two halves are usually only
loosely united. The lower jaw is jointed to the skull by means of
the " quadrate bone," which enables the mouth to be opened
much wider than would otherwise be possible. The jaws are
usually supplied with prehensile teeth, and salivary glands are
present. The stomach and intestines with pancreas and liver, are
well developed. The heart has distinct auricles, but the ventricle
is but imperfectly divided, so that mixed blood is distributed to
the organs. Respiration is by means of lungs, which often reach
considerable size, not being separated from the digestive organs
by a diaphragm, as in the higher vertebrates. The nervous sys-
tem is more highly developed than among the amphibians, the
cerebral hemispheres being relatively large, but the senses arenot
specially acute. The reptilia in general are oviparous, the eggs
having membranous shells. During the development a mem-
brane called the amnion grows out from the blastoderm around
the embryo so as to form a sac, which is filled with fluid. In ad-
dition the allantois, an extremely vascular organ, is formed,
which serves as an embryonic respiratory organ. The appear-
ance of the allantois corresponds with the disappearance of
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LESSONS IN ZOOLOGY. 299
branchial respiration, and every form of metamorphosis Rep-
tiles generally are tenacious of life ; can to some extent replace
lost parts ; can live- for long periods without food, and with but
limited respiration.
The Ophidm, or snakes, have elongated cylindrical bodies,
usually without limbs ; sometimes limbs are represented by small
spurs on the sides of the vent. They have an epidermal cover-
ing of scales, which are usually somewhat elongated, and may
be smooth or provided with a longitudinal ridge. The head is
covered with irregular-shaped plates, the abdomen with broad
band-like plates, while the subcaudal plates are in pairs. The
anal plate is sometimes entire and sometimes bifid. The number
of rows of scales, the number of ventral plates and the charac-
ter of the anal plates and body scales are important specific char-
acteristics. The ribs, of which they have great numbers, are the
chief locomotive organs of snakes. The free ends of the ribs are
attached to the abdominal plates by muscular fibers, so that the
ribs serve as legs and the plates as claws. The skin is shed and
replaced at somewhat regular intervals ; they have a forked pro-
trusible tongue and no eyelids.
The Colubrifonma, have both jaws armed with solid hooked
teeth, with no poison fangs, and no spur-like appendages near
the vent. This group includes the spreading vipers, watersnakes,
garter snakes, blacksnakes, the racers, milk snakes, and other
common snakes of our country. The harlequin, or bead snake,
which is much like the members of this group in general appear-
ance, has two grooved poison fangs in the upper jaw. It is jet
black, with seventeen broad crimson rings, spotted with black,
while the tail has yellow rings.
The Crotalidse have the upper jaw provided with an erectile
grooved poison fang on each of the relatively small upper jaws,
and the short tail is often provided with a rattle. This group
includes the rattlesnakes, massasaugas, .copperheads and moc-
casins.
The Lacertilia or Lizards, are sometimes snake-like in form,
but as a rule they have two pairs of limbs, and the body is usually
300 PRACTICAL LESSONS IN SCIENCE.
covered with scales ; the pectoral and pelvic arches are present,
and the bones of the head and jaws are more fully consolidated
than in the snakes. This group includes the tree swifts, horned
toads, glass snakes, which have hidden rudimentary limbs, lizards,
skinks, etc. Lizards are more abundant in the warmer parts of
the world, where they are common everywhere about walls, build-
ings, rocks, trees, etc.
The CrocodWaare not only larger than other reptiles, but they
seem in every way more highly developed. The alligators of our
Southern States are the only representatives of the class in this
country.
Lizards and crocodilian reptiles existed in great numbers and
variety and attained to an enormous size during middle geologic
times, so that one period is called the Age of Reptiles.
The Chelonia, are a well-marked group of animals. They have
a short stout body, with the dorsal and ventral surface covered
with osseous shields, which in turn are covered by horny plates
or a leathery skin. The neck and tail are flexible but the dorsal
and sacral vertebra? help to form the carapace, uniting with ribs
and overlying bony plates. The plastron or ventral plate seems
to consist of membrane bones. There are no teeth, but the jaws
are incased in horny sheaths which usually have sharp cutting
edges. The eye is furnished with eyelids, and respiration is ef-
fected by means of air that is swallowed . This group includes
the land tortoise, box turtles, terrapins, snapping turtles, soft-
shelled turtles, etc.
The Aves or Birds. The birds are warm-blooded oviparous
animals, clothed with feathers. They have four extremities, two
adapted for walking or swimming and two fitted for service as
organs of flight.
The bones of birds are more compact and lighter than those of
reptiles. The cranial bones are fused together into a light, firm
skull, which is articulated to the vertebral column by a single
condyle. The face bones unite to form projecting beaks, the mar-
gins of which are covered with a horny substance that supplies
the place of teeth. The vertebral column has a long, flexible,
LESSONS IN ZOOLOGY. 301
cervical region, a short, slightly flexible, caudal region and a
rigid dorsal lumbar and sacral region.
The ribs join the broad sternum forming a deep conical body
cavity, whose walls are an excellent foundation for a strong
shoulder joint. The clavicles unite so as to form an arch or fork,
then the scapula and coracoid wedged in between the rigid ver-
tebrae and the heavy sternum, making a socket for the broad
faced humerus that gives the bird one of the best of shoulder joints.
The wing is completed by the ulna and radius, and by the more
or less modified parts of the wrist and hand.
The foundation for the articulation of the legs consists of an
elongated pelvis made up of the lumbar and sacral vertebrae
fused with the long iliac bones and the shorter ischial and pubic
bones, The acetabular cavity is deep and the joint is firm. The
short, heavy femur is concealed within the body, the knee joint
usually being just at the surface of the body. The first free por-
tion of the leg is composed of the tibia, the fibula being rudimen-
tary; the second portion is a fusion of tarsal and metatarsal
bones, which lead to the phalanges.
The muscular system is well developed and especially adapted
to quick, vigorous movements. The skin is covered with feathers
which correspond to the hair of the mammalia. A feather has a
shaft and vane and the vane is made up of barbs and barbules.
Feathers from different parts of the body vary considerably in
appearance and use. Feathers are usually imbedded in the skin,
but the larger stiffer feathers of the wing, called quills, are inserted
in the bones of the wing.
The quills on the hand are the primaries, those on the forearm
are secondaries, and when found on the arm they are tertiaries.
The skin on the legs and toes is usually covered with horny scales
or plates.
The nervous system and the sense organs are well developed.
The alimentary canal consists of the mouth with the salivary
glands, the oesophagus, crop, pro-stomach, stomach or gizzard,
and the intestine with the pancreas and liver. The kidneys and
the ovaries evacuate through the intestine. The heart and the
302 PRACTICAL LESSONS IN SCIENCE.
circulatory organs are double. The lungs are capacious, but in-
stead of moving freely, as in the case of mammals, they are fixed
to the dorsal aspect of the body cavity. They communicate
freely with the cavities of the larger bones.
The matter of the adaptation of animals to their surroundings
is perhaps more easily shown in the study of birds than in the
study of any other group. The feet, the bill, the legs, the wings,
the neck, the plumage, the whole appearance and habit of the
bird depend on whether it is a wader, walker or swimmer; a
scratcher, climber or a bird of prey. The idea is common every-
where, but in some way it seems more prominent among the
the birds.
Birds are oviparous, the eggs having a large amount of yolk,
and requiring a high degree of heat for their development. In
the fertilized egg, the process of development begins before it is
laid ; the blastoderm is formed, the primitive groove and medul-
lary folds appear, then the cranial flexure, the digestive canal, the
amnion and allantois membranes, and soon the young bird is
ready to open the way to liberty from his stony cell.
Birds are intelligent; they have beautiful plumage and musical
voices, and are interesting to man in many ways. No group of
animals yet studied is as intimately related to man; none other
more available for study than the birds. Study birds; note the
migratory birds, the time they arrive and depart; note the ones
that remain during the whole year, and those that only remain
during the winter. Note also those birds that pass through your
locality in their spring and autumn migrations, stopping only
for a few days. Notice the birds that nest in your region ; the
kinds of nests they build ; when they build them ; how many eggs
are laid, and what was the period of incubation. Make a careful
study of the breeding and nesting habits of some particular pair
of birds, making full notes. Study the legs, feet, wings, bill and
other parts of birds and compare them. Study the bones and
skeletons of birds, and compare with those of other animals.
Notice that the claws of perching birds close automatically on
the perch. Examine the arrangement of tendons in the legs.
LESSONS IN ZOOLOGY. 303
Scald a bird and remove its feathers; notice if the feathers were
uniformly distributed over the body; notice if they are dis-
tributed in the same way on different kinds of birds. After
removing the feathers dissect the digestive, respiratory and cir-
culatory organs, and dissect the brain and the sense organs.
Study the development of the chick from day to day, breaking
the egg into blood-warm water for observation. Study birds in
every way.
The Natatores or Swimming Birds. These birds are clothed
with a thick compact plumage and a heavy coat of down, and
are supplied with a large oil gland. They are excellent swimmers
and divers, and usually strong flyers. The beak varies from the
strong cutting beak of the fish-eater to the soft yielding beak of
birds who live on infusoria. They are usually gregarious on the
seacoast or on large inland waters. Some species are valuable
for food and other purposes. To this group belong the penguins
with their fin-like wings, the auks, divers, swans, ducks, geese,
pelicans, gulls, the albatross and stormy petrel.
The Grallatores or Wading Birds. These birds have a long
beak, long neck and long legs, and are adapted for taking snails,
larvae, worms, frogs, fish and other materials for food from the
mud of shallow waters. They are mostly migratory birds, some
of them being highly prized for food. The plover, snipe, heron,
stork, rail and water hen belong to this group.
The GalHnacese. These are terrestrial birds, having stout
bodies and rounded wings not well adapted to flight. The legs
are strong, of medium length and well fitted for running and
scratching. To this group belong turkeys, domestic fowls,
grouse, quail and partridge.
The Columbinas or Pigeons. These birds are all of medium
size, small heads and short legs, with soft beaks swollen about
the nasal openings. They have long, pointed wings well fitted for
sustained flight. They live on grains and seeds, and their
plumage is often beautiful. To this group belong the pigeons and
doves, and the lately extinct dodo was a member of the group.
The Scansorial or Climbing Birds. These birds in general have
304 PRACTICAL LESSONS IN SCIENCE.
a powerful beak, sometimes especially fitted for chiseling and
hammering. They have strong climbing feet and a stiff plumage
that often aids in climbing. They generally inhabit forests, living
on insects, small birds, or on fruits and vegetable matters. The
toucans, trogans, cuckoos, woodpeckers, parrots, cockatoos,
etc., belong to this somewhat miscellaneous group.
The Passeres or Passerine Birds. The birds of this order are
generally of a small size, well fitted for flight, dwelling mainly
among the trees and bushes. They are sometimes divided into
singing birds or oscinesand shrieking birds or clamatores. They
are usually divided on the character of the beak into Levirostres,
light beaks, as the hornbills, king-fishers and bee-eaters. Tenui
rostres, slender-billed birds, as the humming-birds, honey-suckers
and tree creepers. Fissirostres or birds with a deeply-cleft beak,
and usually long-pointed wings, as the swallows, swifts, and
goat-suckers. Dentirostres, birds with the beak more or less
notched at the point, as the crow, starling, shrike, flycatcher,
titmouse, warblers and thrushes. And the Conirostres, birds
with conical beaks, that feed on seeds, etc., as the larks, spar-
rows, buntings and others.
The Raptores or Birds of Prey. These birds are of powerful
build, having strong hooked beak and claws, and they are usually
well adapted for vigorous long-sustained flight. Their sense
organs in most cases are highly developed, thus fitting them well
for their particular mode of life. They live mainly on warm-
blooded animals, and the food is softened in the crop before diges-
tion, the feathers and hair being rejected. To this group belong
the owls, vultures, eagles, hawks, buzzards, kites, etc.
The Cursores include the ostrich, rhea, cassowary, emu, etc.,
large birds that are incapable of flight. The sternum has no keel,
and the bones generally are massive and dense, more like those
of the mammalia. The apteryx sometimes called dwarf ostrich,
clothed with long hair-like feathers is also a member of this
group. The recently extinct moa, and the dinornis giganteus,
both enormous birds, were near relatives of the birds just men-
tioned.
CHAPTER XL.
THE MAMMALIA.
THE Mammalia are warm-blooded viviparous animals that
suckle their young with milk from the mammary glands. The
members of this class differ considerably among themselves in
matters of detail, but in general the structure is the same, and
the processes are carried on in the same way throughout the
group.
A good general idea of the class may be gained by the careful
study of some animal, as a rabbit, a cat, a puppy, or any other
that is convenient. A good knife and a saw are all the instru-
ments necessary, although a pair of forceps, and little hooks to
hold parts in position or out of the way are a great convenience.
First, go carefully over the external features of the animal, com-
paring it with others as far as possible. If not dead, kill it with
chloroform and open the body cavity for its whole length, cut-
ting a way the breast bone and a portion of the ribs. Notice the
diaphragm dividing the abdomen from the chest ; note the form
of the two cavities and the lining membrane of each. Study care-
fully the relative position of the organs in each cavity, turning
them over so as to find them all; do not hurry; try to see every
organ in its place, surrounded by its associated organs also in
place. Through a tube, inflate the lungs, trying to imitate the
breathing of the animal. Then study each organ and group of
organs somewhat in detail, so as to get, if possible, some idea of
how each organ performs its work. Study the heart carefully,
tracing out the distribution of the larger blood vessels. Open
the cranium ; notice the protective coverings of the brain, its di-
visions and external appearance. Find the origin of the nerves
of smell, sight, hearing and taste, and trace them to their respect-
L. S.-20 (305)
306 PRACTICAL LESSONS IN SCIENCE.
ive external organs, and make a special study of those organs.
Open the spinal canal and study the spinal cord; especially no-
tice the origin of the spinal nerves. Study the bones, ligaments,
muscles, tendons, joints, etc., in the legs, and in the spinal col-
umn. This study should be carried into detail as far as time
and circumstances will allow. If it is inconvenient to get animals
for dissection, material for an extended study may be obtained
at the slaughter-house or butcher shop.
The Mammalia in general have a skeleton composed of com-
pact bones filled with marrow, and the vertebral column is gen-
erally divided into five well-marked regions the cervical, dorsal,
lumbar, sacral and caudal. There are two pairs of limbs with
the pectoral and pelvic arches well developed. The feet are es-
pecially interesting from the variety of forms under which the
same group of bones appears. The digestive organs are well de-
veloped in all, but they vary widely with the nature of the food
used by the animal. In nearly all cases the jaws are armed with
bony teeth, differing in form, number and arrangement with the
kind of food. The heart has four chambers and the circulation
is double. The lungs are capacious and free to move in a special
cavity, and the skin is usually covered with hair. The brain is
relatively large and usually covered with convolutions, and the
special senses are all highly developed. They easily lead the ani-
mal kingdom in matters of intelligence, and for this reason they
are more useful and companionable to man.
There is considerable variation in the reproductive process,
but the young are always born alive, and need the mother's care
for considerable time afterward.
The Monotremata. This order includes the ornithorhyncus,
or duck-bill, and the echidna, or porcupine ant-eater, both living
in Australia. They have short legs armed with strong claws
well adapted for burrowing. The urinary and reproductive or-
gans open into the intestine, as with birds. The jaws are elon-
gated into toothless beaks. The duck-bill is clothed with fur,
has a smooth brain, a flattened body and swimming feet. The
echidna is covered with spines, has a protrusible tongue and
LESSONS IN ZOOLOGY. 307
folded brain; both have marsupial bones, but only the echidna
has a pouch, and both live on insects.
The Marsupialia. This order includes the kangaroo, wombat,
bandicoot and others of Australia, and the opossum of the
United States. The females of this order are furnished with an
abdominal pouch or marsupium, for the immature young after
birth. The marsupials form no placenta, so that the young
are born early in their embryonic life and transferred to the
pouch, where they attach themselves to the nipples of the mam-
mary gland and remain there during the remainder of their
helpless existence. Some of this order are carnivorous, some
herbivorous and others are omnivorous; some are specially
adapted for jumping, others for climbing, and others have a
naked prehensile tail; so that they are quite varied in form and
habits.
The Edentata. The members of this order are all sluggish,
stupid animals, with a small smooth brain; the teeth are fre-
quently absent, and when present are usually incomplete or im-
mature. To this group belong the ant-eaters, armadillos and
sloths. The ant-eaters have an elongated narrow snout, protru-
sible tongue and weak jaws; the legs are short and adapted for
digging. They live mainly on ants and termites. The armadil-
los are covered with bony plates, having legs and claws fitted for
digging. They can rapidly bury themselves in the ground when
pursued, and most of them can roll themselves into a ball that
is well protected by bony plates from the attacks of enemies.
The sloths are strictly arboreal, hanging by their curved claws
from the underside of branches. The sloth, armadillo and one
ant-eater live in South America, while the scaly ant-eater is
found in Asia and Africa. The remains of many gigantic edent-
ates are found in the later rocks of South America.
The Cetacea. The members of this order are aquatic mam-
malia, with fin-like anterior and no posterior extremities. The
body is fish-like in form, only that the caudal fin is horizontal,
not vertical as in the fishes. The surface is usually devoid of hair,
but a thick subcutaneous layer of fat serves to protect from cold,
308 PRACTICAL LESSONS IN SCIENCE.
and perhaps lessens specific gravity. This group includes the
Dolphins, Whales and Sirenia.
The dolphin is carnivorous, having both jaws armed with con-
ical teeth. They live on fish, and frequent the mouths of large
rivers. The narwhals have two upper teeth, which in the female
are small, but in the male the one on the left side usually be-
comes a spiral tusk, which sometimes attains a length of twenty
feet. The sperm whale has an enormous head, nearly one-third
the length of the body. The head is swollen by the accumulation
of fat spermaceti. They inhabit the colder regions, and live
mainly on cephalopoda. The whalebone whales have large
heads and wide mouths without teeth. From the palate and
upper jaw rows of whalebone plates project downward, forming
a kind of sieve which strains the small medusae and other forms
of life from the water as it flows out. The sirenia have a dis-
tinct neck and no canine teeth, they feed on fuci and seaweed
along the coast. They are known as sea cows, or manatees, on
the coasts of America, and as dugongs on the coasts of the In-
dian ocean. Stellar 's sea cow of the north Pacific has become
extinct within the last 200 years.
The Perissodactyla are large herbivorous animals having one
or three hoofs, and in all, the teeth are well developed. The teeth
are divided into incisors, canines, premolars and molars. In
this group the premolars and molars form a continuous series of
broad grinding teeth all much alike. The dorsal-lumbar verte-
brae are usually 23, never less than 22. The middle digit or toe
is always largest and symmetrical in form.
The Tapirs are short-haired animals of medium size, having
four hoofs on the anterior legs and three on the posterior. There
are 6 incisors, 2 canines and 6 molars in each jaw, while there are
8 premolars in the upper and 6 in the lower jaw. They have a
short proboscis, eat leaves and young twigs, and live in South
America and Southeastern Asia.
The Rhinocerotidse are large, unwieldy, thick skinned animals
bearing one or two epidermal horns on the nasal bones. In
each jaw there are 4 rudimentary incisors, 8 premolars and 6
LESSONS IN ZOOLOGY. 309
molars. They are natives of Africa and Southern Asia. They
have hoofs on the 2d, 3d and 4th toes of each foot.
The Equidse are as noted for their graceful, slender forms as the
other members of the order are for their bulky, clumsy bodies.
The dentition is 6 incisors, 2 canines, 8 premolars and 6 molars
in each jaw. Each of the incisors has a little pit near the sum-
mit, which, filled with foreign matter, seems like a black spot, that
wears away with age. This pit is peculiar to horses, and is not
found in the teeth of geological ancestors of the horse. The
canines are small, conical teeth and are usually present in both
jaws only in the male. The knee and hock joints of the horse
correspond to the wrist and ankle joints of man, the bones
below to the middle bone of the hand, and the bones of the mid-
dle finger are represented by the bones below the fetlock joint.
The hoof in all the ungulates corresponds with the nails or
claws of other animals. The slender form of the horse fits him
for harder ground and more open country than that occupied by
the tapir and rhinoceros, and his well developed incisors enable
him to take different kinds of food. The zebra, wild ass and
quaggas belong to the horse family. The present members of the
horse family are natives of the Old World, but in comparatively
recent geological times there were several species of horses in
America. Some of these ancient horses had three and some four
toes instead of one, as does the present species.
The Artiodactyla, are animals with paired hoofs, the third and
fourth digits on each foot supporting the body, the second and
fifth digits are generally present but are rudimentary and do not
help support the body.
The dorsal and lumbar vertebrae are 19 or 20 ; the premolars
are single, while the molars are two-lobed and the other teeth are
variable. This order contains several families.
The Suidse or swine family have an elongated mobile snout,
and the skin is clothed with coarse bristles. There are 6 incisors,
2 canines, 8 premolars and 6 molars in each jaw, sometimes an
upper incisor and a premolar are suppressed.
The canines in the male are developed into formidable tusks.
310 PRACTICAL LESSONS IN SCIENCE.
The wild boar of Europe, Africa and Asia was perhaps the progeni-
tor of all the varieties of the domestic pig, but they are so widely
distributed and vary so greatly that some have thought they
must have originated from several sources. Besides these, there
are the wart hogs of Africa, the peccaries of America, and the
babyroussa or hog deer of Southeastern Asia. The domestic
pig is one of the most important food-producing animals known
to man.
The Obesa, or Hippopotami, are large unwieldly amphibians,
vegetable eating animals, living in Southern Africa, that belong
in this order.
The other members of this order are ruminants, distinguished
by incomplete dentition and by the peculiarities of the digestive
organs. The animal crops the food, and without much mastica-
tion it passes from the oesophagus into the paunch, where it soaks
in the secretions for a time, then passes to the honeycomb bag,
or reticulum, where it is made up into little balls and returned to
the mouth by regugitation. After thorough mastication, the
food passes to the third stomach, called " many plies " or "psal-
teriunii" because its lining membrane lies in many folds. From
this cavity the food passes with little change into the rennet
stomach, where the food is really digested by the secretion of the
peptic glands.
The Tylopoda include the camel and dromedary of the Old
World and the llama, alpaca, etc., of the New. The soles of the
feet are covered with horny integument on which the animal
walks, and there is no separate psalterium.
The Arabian camel has numerous large cells in its paunch
which enable it to carry several days' supply of water. The gi-
raffes and musk-deer belong to this order.
The Cervidae, or deer, are characterized by a pair of solid dermal
horns attached to a bony process of the forehead ; they are cast
off and renewed from year to year, the weight and number of
parts usually increasing with each renewal. The red deer, the
stag, the elk, the reindeer, used as a beast of burden in Lapland,
and others, are members of this family. The deer and stag have
LESSONS IN ZOOLOGY. 311
pointed horns, while the horns of the elk and reindeer are broad
and flat at the extremities. The horns are borne only by the
males, except in the case of the reindeer. The cervidse have eight
incisors in the lower jaw working against a callous pad in the
upper jaw; occasionally canines occur in the upper jaw. There
are twelve grinders in each jaw, which are separated on the lower
by a little space from the incisors. The young of nearly all spe-
cies are spotted. The spines of the dorsal vertebrae are long, bet-
ter fitting them for the origin of the strong ligaments which
support the head with its load of horns.
The Cavicornia have hollow horns in both sexes, no canines,
but twelve grinders in each jaw with six incisors in the lower.
In this group belong the antelope, gnu, gazelle and chamois;
the sheep, goat, ibex, Rocky Mountain goat and others ; the
musk ox, the American bison, and the Indian buffalo and the do-
mestic ox the sheep and the ox, the horse and hog being the
most important and valuable domestic animals ol the temper-
ate and warm temperate zones.
The Proboscidea include the elephants and several extinct
animals, all of great size. They are characterized by a long flexi-
ble proboscis, which is an organ of touch and of prehension as
well. The skin is very thick and sparsely covered with hair,
though some of the extinct forms had an abundant coat of hair.
They have several toes on each foot furnished with hoofs, but
walk on thick pads of integument. The tusks are two upper in-
cisors; some extinct forms had lower tusks as well. The grind-
ers are seven on each side in each jaw, but they grow forward
gradually so that never more than one or parts of two are in
service at one time, the earlier ones dropping out and new ones
coming in. The grinders of the elephant are considerably longer
than wide, and are made up of thin alternate layers of enamel,
dentine and cement, showing a flat surface, while the teeth of the
mastodon show a tuberculatecl surface. The mammoth and mas-
todon seem to have been vegetarians, living in damp shady places,
much like the elephants of Africa and Asia of to-day. One extinct
form had tusks curving downward from the lower jaw.
312 PRACTICAL LESSONS IN SCIENCE.
The Eodentia are a numerous group of small animals charac-
terized by their chisel-shaped incisor teeth and the broad com-
pact skull furnishing attachment and leverage for the powerful
muscles used in their work of gnawing. The dental formula is
two incisors and six or eight grinders in each jaw. The hares and
rabbits having four incisors in the upper jaw, and some Aus-
tralian forms have only four grinders. The incisors are enameled
on the anterior surface with dentine on the posterior, and as the
dentine wears away faster the tooth is always sharp and chisel-
shaped. The teeth grow continuously during life about as fast
as they wear away, so that they are always the same length.
When one incisor is destroyed in any way its opposite unopposed
continuing to grow has been known to form a complete ring,
sometimes causing the death of the animal by preventing the use
of its other teeth. These animals are compactly built, very pro-
lific, and often showing great intelligence in the building of homes
and the storing of food. Some migrate at the beginning of win-
ter; some take a winter sleep. They are vegetarians, feeding on
roots, seeds, fruits, etc. The mammals already studied walked
on their toes, were in general digitigrada, but the rodentia walk
on the palm of the hand or sole of the foot, and are plan tigrada.
The digits are freely movable, having claws or nails. In this
order belong the hares and rabbits with long ears, powerful hind
legs and short tail; the guinea pig and agouti, the porcupine
with blunt nose and sharp quills ; the chinchillas and the jumping
mice; the true rats and mice and their allies; the voles with their
short hairy ears and tail, and the lemming, the beavers, dormice
and squirrels.
The Insectivora are small plantigrade animals whose feet are
furnished with strong claws ; the elongated head often ends in a
pointed snout and the jaws carry a full set of teeth; the den-
tition varies considerably, the most distinctive character being
the tubercles or points on the crowns of the grinders and that
the canines are not prominent. They feed on small animals,
insects and worms.
The Erinacidae or Hedgehogs with stiff bristles and spines.
LESSONS IN ZOOLOGY. 313
The Soricidss or Shrews, with a proboscis-like snout and a musty
smell. And the Talpidse or Moles with short, powerful digging
feet, soft fur and small eyes constitute this order of insect eaters.
The Pinnipedia are aquatic animals with a somewhat spindle-
shaped body, having two pairs of short legs ending in fin-like
feet. They are covered with a fine close fur and are carnivorous.
This order includes the Phocidse or Seals and the Trichechidae or
Walruses. The seals live on fish, have short canines and rough
molars. The walrus lives on crustaceae and molluscs, having
the upper canines developed into tusks.
The Carnivora are distinguished by their size, strength and
quickness ; by prominent canines and cutting molar teeth; by the
massive skull furnishing the attachment and leverage for the
powerful muscles moving the sturdy jaws, and they are all armed
with strong cutting claws. This order is made up of the Ursidae
or Bears. Stout unwieldly plantigrades including the polar
and grizzly bears, the black bear, the raccoon and others. Some
of the ursidge are omnivorous, eating roots, mast, honey, etc.
They have strong non-retractile claws, and some take a winter
sleep.
The Mustelidae or Martens, as the badger, marten, skunk, wea-
sel and otter. The Viverridae or Civet-cats. The Canidae or Dogs,
which are digitigrades with non-retractile claws, including the
dogs, wolves, jackals and foxes. The Hyaenidae or Hyenas ; and
lastly the Felidae, the typical family of carnivorous animals.
They are digitigrada, of slender but powerful build, with strong
retractile claws, with powerful canines and sharp cutting teeth.
This family includes the lion, tiger, leopard, panther, jaguar and
other cats.
The Cheiroptera or Bats are characterized by long anterior
limbs, with long digits, which are united by a delicate membrane
extending from the fore to the hind limbs, and, being attached to
the sides of the body, form true organs of flight. They are noc-
turnal animals; the eyes are small but the senses of hearing and
touch are very acute. Some of the bats live on fruits, some on
insects, and some on the blood of warm-blooded vertebrates.
314 PRACTICAL LESSONS IN SCIENCE.
The Prosimise or the Lemurs. These animals have hand& and
prehensile feet; live in trees and feed on insects and small animals,
and are generally nocturnal in their habits.
The Primates or Apes. The apes are vegetarians, generally
leading an arboreal life, for which their form, however varied,
seems adapted. They are usually of slender build, having hands,
prehensile feet and sometimes prehensile tails.
The jaws are much less prominent than with other animals,
which, with the obtuse ear and projecting eyebrow gives the face
something of a human appearance. They have two mammary
glands situated in the pectoral region, and are covered with a
complete coat of hair. The dentition is much like the human,
only that the canines are relatively larger and the grinders more
tuberculated. The clavicle is always present, and in general the
structure is very like the human, differing most widely in the size
and structure of the brain and cranium.
The Hapalidse are South American monkeys of small size with
long hairy, non-prehensile tails, and opposable great toes. The
Pithecidse have more teeth than the last but are otherwise much
the same.
The Cebidss are South American monkeys with prehensile tails
sometimes naked at the end.
The Cynocephalidse or Baboons. The baboons are of stout
build, semiterrestrial in their habits, with a dog-like face. Tail
sometimes long, sometimes short, never prehensile. The anterior
and posterior limbs sub-equal. The canine teeth are large and
the disposition is fierce. They sometimes eat eggs and small
birds; in captivity they are omnivorous. There a re several species,
but they are all inhabitants of Africa and Arabia.
The Cercopithecidse are of slender build, having a long tail,
with cheek pouches and a short muzzle. They are the common
apes of North Africa, Gibraltar, India, and adjacent islands.
The Semnopithecidse have longer pelvic limbs, no cheek pouches,
thumb small, sometimes absent. They are mainly Asiatic.
The Anthropomorphss have longer anterior limbs and without
tail or cheek pouches. In this family are the gibbons, having
LESSONS LV ZOOLOGY. 315
very long arms; the ourang-outang, a native of Borneo; the go-
rilla and chimpanzee of Africa.
Man. Man, in his physical structure, resembles the anthro-
poid apes in innumerable particulars. His hand may be more
perfect; his pelvis, legs and feet may fit him for a firm and erect
position, and he may differ in every particular detail of physical
structure from the apes, yet the difference is only in degree not in
kind. And not till we consider the size and development of the
brain and cranium and the correlative greater intellectual
capacity does the gap between man and other animals reveal
itself.
CHAPTER XLI.
GEOLOGY ASTRONOMICAL .
GEOLOGY is a general science which has the material world for
its subject. It attempts to give a history of the earth, to trace
its development from a mass of burning gases to a whirling
sphere clothed with verdure and teeming with life. From the
study of a manufactured article we may learn how it was made
and gain some idea of its history. The geologist studies the
earth as a planet in its relation to celestial bodies, he studies the
rocky pages of the earth's crust, and the data gathered from
these sources interpreted according to the principles of physics,
and chemistry, botany and zoology enable him to work out a
somewhat complete history of the development of the earth.
The Earth is a member of the solar system which consists of
the Sun, Planets, Planetoids or Asteroids, Moons or Satellites,
Comets and Meteors.
The Sun is the central and controlling member of the solar
system. It seems to consist of a central nucleus of molten mat-
ter bounded by the photosphere, outside of which is an atmos-
phere composed largely of the vapors of iron, nickel, manganese,
carbon, calcium, sodium, silicon, aluminium, potassium and sev-
eral other substances known upon the earth. This envelope is
called the chromosphere. Above this layer of vapors, rise flames
and prominences composed largely of hydrogen. And beyond
these is the solar corona. At times dark spots maybe seen upon
the sun that appear to be deep pits in the photosphere ; they vary
in size and in duration. The time of the minimum number of
spots occurs every eleven years and the time of the maximum
number occurs some four or five years afterwards. We know
little about the cause of the spots but they seem in some way to
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LESSONS IN GEOLOGY. 317
disturb the magnetic conditions of the earth, and possibly its
climatic conditions as well.
The gaseous envelopes of the sun are subject to violent dis-
turbances or storms, consisting largely of upward and down-
ward movements of the gases. It is thought by some that the
sun spots are in some way the result of these storms. The quan-
tity and intensity of the heat of the sun is beyond comprehension
and yet it must be diminishing as there seems to be no adequate
means of supplying the enormous and continuous loss of heat by
radiation. Others claim that while the sun is continuously send
ing out immense quantities of heat, it is actually increasing in
temperature through condensation of material due to gravity.
The sun is spherical in form and rotates once in about 25 or 26
days. Besides rotation, the sun with the whole solar system
has a progressive motion in space toward the constellation of
Hercules. Its diameter cannot be determined with accuracy, but
is given as about 866,000 miles.
The Planets are spherical bodies which revolve around the sun
from west to east in elliptical orbits. Named in their order from
the sun the planets are Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus and Neptune. Venus, Jupiter, Mars and Saturn
appear as brilliant stars. The planets differ in size, time of rev-
olution and in density. Mercury is more dense than the earth,
but the sun and all the other planets are less dense! Venus seems
to have an 'atmosphere, but Mercury is not known to have one.
No permanent marks or features have ever been discovered on
these planets so that it is not certainly known whether they ro-
tate or not. Mars and the earth each has a solid crust, and
somewhat similar atmospheric conditions and each rotates from
west to east. Jupiter and Saturn seem to be masses of molten
matter, each surrounded by a deep dense atmosphere, in which
extensive changes and disturbances are known to occur, and
somewhat permanent markings can be seen, from which it ap-
pears that each of these planets rotates from west to east. But
little is known of Uranus or Neptune beyond some idea of their
size, density and time of revolution.
31$ PRACTICAL LESSONS IN SCIENCE.
The Planetoids or asteroids are a group of smaller bodies re-
volving around the sun between the orbits of Mars and Jupiter.
The Moons or satellites are bodies which revolve around some
of the planets as these revolve around the sun. The Earth has
one moon, Mars two, Jupiter four, Saturn has eight moons and
in addition two rings, Uranus has four or more satellites, and
Neptune at least one. We can know but little about the moons
but they all seem to be spherical bodies and in general to revolve
in the same direction as their primaries. The satellite of the
Earth, one of the largest of the moons, is nearly a perfect sphere
having a diameter of 2,160 miles. It rotates on its axis and re-
volves around the earth in about twenty-seven and one-third
days, so that the same side is always toward the earth. Seen
through a telescope the surface of the moon appears to be very
rugged, not from mountain ranges but from great circular de-
pressions in which there are sometimes conical elevations. The
moon seems to be a great cinder-like body, devoid of air, water
and every form of life. It is supposed that the rocky mass may
have absorbed the air and water which were formerly abundant
on its surface.
The Comets are interesting, but little known, members of the
solar system. They are usually rather small bodies with an ex-
tensive atmosphere, revolving in much elongated orbits, moving
with great velocity when near the sun.
Meteors are bodies, which, falling toward the earth, are heated
to incandescence by friction in the air, and usually vaporized be-
fore reaching the earth. Sometimes they reach the earth as me-
teoric stones or meteorites. In general the meteorite is composed
mainly of iron, sometimes of a stony substance.
The Stars are supposed to be bodies like our Sun, many of
them, however, much larger than it. The spectroscope shows
that many of them contain substances found to exist in the sun
and well known on the earth. The stars vary in size, in distance
from the earth, in temperature, in color, and apparently in com-
position as well. Some appear to be double stars, some revolve
about others ; others are variable in appearance, often changing
LESSONS IN GEOLOGY. 310
rapidly. They are all supposed to be in motion in definite direc-
tions but whether they move together as one system or as many
distinct systems is not known.
The Nebulae are cloud-like masses, similar to the milky way,
which occur abundantly in different parts of the heavens. Many
of these, when examined with a telescope, are shown to consist of
distinct stars, others still appearing as clouds when viewed with
the most powerful telescopes. Some of these, when examined with
the spectroscope are shown to be star clusters, while others are
shown to be incandescent gaseous bodies. They differ in size and
in distance from the earth ; some are formless masses, some ring-
shaped and some spiral, as if the mass were beginning to rotate,
but our knowledge of them is very meager. The constitution
and conditions of the nebulae and stars ; the motions, conditions
and relations of the members of the solar system have given
rise to the Nebular Theory, which supposes that the sun was once
a mass of burning gases, which filled the orbit of Neptune. The
mass had a rotary motion which increased as it cooled and con-
tracted, becoming at length so rapid that portions were thrown
off, much as water and mud are thrown from rapidly turning
carriage wheels, this process continuing until all the planets were
formed, each assuming a spherical form, each revolving around
the parent mass, some and probably all rotating in the same
direction. Some of the planets rotated so rapidly that bodies
were thrown off from them and thus the satellites were formed.
This theory cannot be demonstrated but it harmonizes with most
of the facts known of the solar system.
The nebulae as burning gas, the sun and stars as molten
masses surrounded by intensely heated gases, Jupiter and Sat-
urn as molten bodies which have cooled below the point of incan-
descence, the Earth and Mars as bodies, over which at least a
solid crust has been formed, are each supposed to represent dif-
ferent stages through which the earth has passed in developing
from the primal fire mist, to its present condition. The moon
probably represents a farther stage toward which the earth is
approaching.
CHAPTER XLII.
MINERALS AND ROCKS.
THE greater part of geological work pertains to rocks. In
geology every thing that helps to make up the crust of the earth
is rock, whether it be hard and enduring, like the limestone and
granite, or loose earthy materials like sand, clay or dust. Rocks
are sometimes simple chemical compounds, but generally they
are composed of a mixture of several distinct compounds called
minerals. There are a great many different kinds of minerals ; all
of them are interesting and many are valuable, but only a few
are of much importance as rock-forming materials.
The most abundant and common of the minerals is silica,
composed of oxygen and silicon. It crystallizes in six-sided
prisms, appearing something like glass. It is hard enough to
scratch glass, and this quality distinguishes it from all other
minerals having a similar appearance. Silica is sometimes
called quartz. It is the chief ingredient of sand, gravel and
sandstone.
The Feldspars, often associated with silica, are a group of in-
teresting and abundant minerals. Orthoclase, the most common
feldspar, is a silicate of aluminium and potassium. It occurs in
all colors from white to a fleshy-red. It sometimes has the ap-
pearance of glass, but is readily distinguished from quartz by
its inferior hardness, as it will not scratch glass, and may be
scratched with a good knife. It crystallizes in rhombic prisms,
and splits easily and smoothly in two directions, but it some-
times has a massive or granular structure showing no signs of
crystallization. Moonstone and sunstone, often used as jewels,
are varieties of this feldspar. Sanadine, a glassy variety, is
common in many lavas.
Albite, another species of feldspar, is a silicate of aluminium
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LESSONS IN GEOLOGY. 321
and sodium, while Anorthite is a silicate of aluminium and cal-
cium. Several other feldspars are thought to be only mixtures
of the ones just mentioned. In general they are very much like
orthoclase in appearance, but on a fresh surface their crystals seem
like strips of glass on which fine lines may often be found that
do not occur in the orthoclase. These are usually called triclinic
feldspars. Broken down weathered feldspar is the basis of clays,
shales and slate rocks.
Mica is a silicate of aluminium and potassium or magnesium,
with iron and sometimes a little lime. It splits easily into thin
flexible leaves, which are nearly transparent, and are frequently
used in windows. It often occurs with silica and feldspar as an
ingredient of some kinds of granite rock. Sometimes from their
glistening appearance .scales of mica are mistaken for gold.
Hornblende and Pyroxene are silicates of magnesium and cal-
cium, containing oxides of iron and manganese. Some varieties
contain in addition a little aluminium. They vary in color from
white to black, but in general they are greenish-black or black.
In general the darker varieties are the ones containing alumin-
ium. The fibrous mineral asbestos is a variety of hornblende.
The darker varieties are more common, and are easily distin-
guished from mica by their hardness and crystalline form, and
are not liable to be mistaken for any other mineral. These are
common minerals in basalt and lava, in trap and syenite, and
sometimes the light-colored varieties occur in limestone.
Talc is a hydrated silicate of magnesium with a little oxide of
iron. It is the softest mineral known, separating easily into
thin scales. It has a light green color, a pearly luster and a
greasy feel. It is best known as steatite or soapstone.
Serpentine is much like talc in composition and qualities but
is a little harder and has a rich greenish color.
Chlorite contains more aluminium than talc and is harder
than that mineral. It has an olive green color and often a gran-
ular structure.
Calcite, carbonate of calcium, is a mineral that crystallizes in
several different forms. When pure it has a pearly luster and is
L. s. 21
322 PRACTICAL LESSONS IN SCIENCE.
nearly transparent. It is the basis of the different kinds of lime-
stone and marble, appearing in a great variety of forms. It is
easily scratched with a knife, and effervesces vigorously when
treated with any acid, even strong vinegar will decompose it.
Dolomite is a carbonate of calcium and magnesium. It is per-
haps a little harder than limestone, and is not as easily affected
by acids, but it is often difficult to distinguish between them.
Gypsum, the hydrated sulphate of calcium, often forms ex-
tensive beds of rock. It is easily cut with a knife, is white, some-
times variegated, in color and when burned to drive off water of
crystallization becomes plaster of Paris.
Pyrite, the disulphide of iron, is of a pale brassy yellow color,
crystallizing in cubes. It is very common in the neighborhood
of coal banks, and is the source of the sulphur in the coal. From
its color it is often mistaken for gold. Pyrite and the sulphides
of copper, lead, zinc, and other metals are often associated with
gold, and are abundant minerals.
Graphite, nearly pure carbon and the various ores of iron are
widely disseminated minerals of value and interest.
Chloride of sodium, common salt; corundum, nearly pure ox-
ide of aluminium; apatite, phosphate of lime, etc.; leucite, abun-
dant in some lavas ; olivine, a silicate of magnesium and iron, are
all important minerals.
The minerals mentioned, either singly or variously combined,
make up the greater part of the rocks which compose the earth's
crust.
Granite is a crystalline rock composed of thoroughly mixed
quartz, orthoclase feldspar and mica, the particles being of near-
ly uniform size. It is usually hard, light-colored and can gener-
ally be identified by the scales of mica. Sometimes the rock is
very fine grained, containing large crystals of feldspar scattered
through the mass when it is called porphyritic granite.
Quartz Felsite or Felsite. This rock consists of a fine granular
or homogeneous ground mass, through which are disseminated
crystals of quartz, feldspar, mica or hornblende. This rock va-
ries widely in structure without much modification in composi-
LESSONS IN GEOLOGY. 323
tion. Felsite consists of the ground mass without the crystals,
forming a tough compact rock.
Liparite has a similar composition but shows more evidence
of a former molten or glassy state in its structure.
Syenite, a rock often associated with granite, is composed of
orthoclase mixed with hornblende and occasionally some quartz
and mica, and sometimes triclinic feldspar occurs. There is sel-
dom any difficulty in identifying this rock after one learns to
recognize feldspar and hornblende.
Trachyte is a volcanic rock composed largely of sanidine, a
variety of orthoclase, with some triclinic feldspar, and usually
hornblende, mica and iron, and sometimes with pyroxene, apa-
tite, etc. It has much the same composition as syenite but has
not become fully crystallized.
Obsidian is a volcanic glass, varying considerably in its com-
position, but in general it is rather like trachyte. It shows no
trace of crystallization and may represent the first stage in the
development of crystalline rocks, trachyte and syenite represent-
ing others.
Diorite, or Green Stone, is composed of triclinic feldspar and
hornblende usually with apatite and iron.
Basalt is a dark-colored volcanic rock, composed of triclinic
feldspar, pyroxene, olivine, iron and apatite. It often has a
ground mass of glass through which crystals are scattered.
Schists are crystalline rocks of varied composition in which
the materials are arranged in nearly parallel layers. Schist rocks
may be composed of but one mineral, but they usually consist of
two or more minerals in alternate layers or mingled in the same
layer. They are usually named from the principal ingredient, as,
mica schist, chlorite schist, and talcose schist, usually containing
quartz, feldspar and other minerals besides the one naming the
rock.
Gniess. This rock is composed of quartz, feldspar and mica
but the proportions and the arrangements are different from
those in granite. It is schistose in structure but coarser than
schist. There is a larger proportion of mica than in granite. It
324 PRACTICAL LESSONS IN SCIENCE.
varies widely in appearance but is usually recognized without
difficulty.
Under the action of atmospheric influences the rocks are gradu-
ally pulverized, reduced to boulders, pebbles, gravel, sand and
clay. We may find all kinds of rocks represented among the
boulders and pebbles, while the gravel and sand are largely of
quartz. The clay, dust, etc., making up the soil are from the
feldspar, mica and other easily disintegrated materials. Much
of the clay, sand and dust are eventually spread out over the sea
bed as sediments. Great quantities of rocks are broken down
and pulverized by the action of the waves along the sea coast
and added to the sediments of the sea.
Pebbles or gravel, and sometimes boulders, may be cemented
together into conglomerate rock, and it is called quartz, lime-
stone or granite conglomerate, according to the nature of the
material. Conglomerates differ also in the nature of the cement
or paste, which may be of quartz, lime, clay or even iron.
The sand may be cemented into sandstone, which may vary
much as the conglomerate varies. The typical sandstone, how-
ever, is composed of quartz grains united by a paste of quartz.
The clays are compacted into shales. They are easily cut with
a knife, break into irregular blocks and vary greatly in purity.
The finer sands and coarser clays mingle in varying propor-
tions so as to form clayey sandstones or sandy shales.
In deeper water, away from the shore, calcareous sediments
are formed from materials furnished mainly by different forms of
life; these at length become limestone rocks. Peat and soft coal
are sediments.
The different kinds of sandstone, clay and limestone rocks are
formed from sediments, and are known as sedimentary rocks.
Metamorphic rocks are sedimentary rocks that have been
changed by heat, pressure and other agencies into a crystalline
form. The sandstones become quartzites ; the mixed sands and
clays become gneiss, granites, etc. Limestone becomes crystal-
line limestone and marble, and the clays and shales become slate,
which is but slightly crystalline. Peat and soft coal become
LESSONS IN GEOLOGY. 325
bituminous and anthracite. These rocks were formed from sedi-
ments that were deposited in layers or strata, and the rocks are
often called stratified rocks.
Obsidian, propylite, trachyte, basalt and other volcanic prod-
ucts are called igneous rocks, and are unstratified. Doubtless
many of the granites and gneisses had their origin in trachyte or
basalt, and are strictly igneous rocks.
Granite, syenite and other crystalline rocks are the last terms
in the series beginning with sediments, as well as in the series be-
ginning with obsidian or basalt.
All rocks are divided by cracks or joints into irregular blocks
of various sizes and shapes. In stratified rocks the bedding
planes bound the blocks on two sides, and divisions nearly per-
pendicular to these and to each other bound the other sides.
The last are called joints. In the case of igneous rocks the
blocks are bounded on all sides by joints. These blocks vary in
form in different rocks ; in limestones they are regular and cu-
bical; in basalt regular and columnar; in slate, small and indis-
tinct ; in sandstone, large and irregular, etc. The cause of joints
is probably the shrinkage of the strata in consolidating frojn
sediments. Similar joints or cracks may be seen in the dried mud
of ponds that have been drained of water. Joints are confined
to individual strata, but fissures are fractures passing through
several or many strata, probably caused by movements of the
earth's crust. Fissures 30 to 50 feet wide and many miles in
length are known. Sometimes the rock on one side of a fissure
is forced upward so as to change the relations of the strata,
causing what is called a fault. In some cases the displacement is
as great as 15,000 or 20,000 feet. Fissures in many cases have
been filled with some rock-forming material, when they are known
as veins. Much of the gold and silver of the world came origi-
nally from veins. In some cases these fissures were filled by an
injection of igneous material from below; others are filled by mat-
ters deposited from water circulating through them. Joints and
fissures are geologically interesting, as they facilitate erosion,
determine the course of rivers and the location of valleys.
CHAPTER XLIII.
EARTHQUAKES AND VOLCANOES.
IN the geological history of the earth, two sets of forces have
been active. Some which may be called plutonic, have been mak-
ing the surface of the earth uneven, through them the conti-
nents had their origin and the mountains were formed. The
others, which are eroding forces, mostly atmospheric, have been
equally busy in cutting down the elevations and filling up the
depressions, their action tending toward uniformity as the others
toward variety.
The internal condition of the earth is not well understood. As
we explore the crust by mines and wells, we find that heat in-
creases rapidly with the depth below the surface, so that at a
depth of thirty or forty miles, the heat must be intense enough
to melt any known substance, if it were only under atmospheric
pressure, but under the enormous pressures of such regions, sub-
stances would doubtless behave as solids, notwithstanding the
great heat.
In relation to other celestial bodies the earth behaves as a
solid, rigid as glass, so that while the interior of the earth is in-
tensely hot, it is probably not a liquid.
In general the irregularities of the surface of the earth are sup-
posed to be due to unequal contraction, the interior contracting
more rapidly than the crust. This results in enormous horizon-
tal pressures under which, along lines of weakness, the crust swells
up into wrinkles, folds or corrugations. The lines of weakness are
accounted for by supposing an irregular distribution of matter,
or that there was more radial contraction, or settling over the
area now occupied by the oceans. This idea is strengthened by
the fact that the matter underlying the oceans is more dense than
that underlying the continents. Whatever may have been the
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LESSONS IN GEOLOGY. 327
origin, when the irregularity was initiated, the pressures due to
unequal contraction would continue to intensify them.
Sometimes under this pressure the crust yields suddenly, is
fractured for a great distance, the rocks on one side of the frac-
ture being elevated or depressed with reference to the other. Thus
an earthquake is caused, a fissure vein is opened and a fault is
formed. The fault may be only a few feet at first, but it may in-
crease to hundreds of feet as it slowly yields to the continued
pressure. Other forces may cause earthquakes, as explosions of
superheated water or of gas, possibly in connection with volcanic
eruptions. These shocks cause vibrations of the crust, which
are often transmitted for immense distances. These waves may
be severe enough to overthrow buildings, produce avalanches
and land slips, sometimes changing springs and streams of water.
Again they cause great waves of the sea, which rush upon the
shore with great violence; in fact, the greatest destruction of life
by earthquakes has been from the ocean waves which they caused.
A wave that destroyed Lisbon in 1755 was nearly sixty feet
high. In 1868 an earthquake devastated the coast of Peru.
And less than half an hour after the earth wave came several
water waves from 50 to 60 feet high, adding greatly to the
destruction already begun. These waves reached the Sandwich
Islands, 5,580 miles, in 12 hours, and Japan, 10,000 miles dis-
tant, the next day. Such waves have been known to move at
the rate of 450 miles per hour. An earthquake which occurred
near Naples in 1857, by careful examination was shown to have
originated in a fissure about nine miles long, through about
three miles of rock, the center being about six miles below the
surface. The velocity of the earth wave in this case was between
nine and ten miles per minute.
No portion of the earth is free from earthquakes, but they are
more common in volcanic regions.
Again, a fissure is formed as noted above, and from it is poured
out vast quantities of molten matter or lava. Such fissure erup-
tions were frequent during Tertiary times in the Rocky Mountain
region and other localities. At the present time a volcano ia
328 PRACTICAL LESSONS IN SCIENCE.
usually an opening somewhere on the line of such a fissure, around
which a somewhat conical hill has been built up from the ma-
terials thrown out.
In a volcanic eruption gases and vapors are the first materials
to appear; they continue during the eruption of other material,
and often for centuries after all other evidence of subterranean
action has ceased. Aqueous vapor is probably most abundant;
it is sometimes given off in such quantities as to result in heavy
rainfall. Among the gases the most abundant are hydrochloric
acid, sulphuretted hydrogen, sulphurous acid, carbon dioxide,
free hydrogen and others. The typical volcanic material is mol-
ten rock called lava, which includes material varying considerably
in composition and specific gravity. The lighter varieties contain
a larger per cent, of silica, and are acid lavas, as trachyte and
pumice. Others are basic lavas containing less silica and more
iron and pyroxene, as basalt and leudte lava. Others again are
intermediate between these groups. Lavas also vary in structure ;
some are wholly crystalline, as some liparites ; some show a glassy
or stony ground mass, with imbedded crystals, which is, perhaps,
the most common structure. Again, others are pure volcanic
glass, as obsidian. Then some, as basalt, are dense and compact,
while others, as pumice, are vesicular.
Great quantities, a fine ash-like dust and coarser particles,
called sand, usually accompany eruptions. The dust and sand
are lava pulverized by escaping vapors and gases.
The quantity of dust formed and thrown out is sometimes
enormous. Dust from volcanoes in Iceland has fallen abundantly
in Sweden and Holland, and fell in such quantity at a distance of
600 miles as to destroy crops.
Large blocks of lava are frequently ejected. Water is some-
times a volcanic product, which, mingling with the dust and
sand, forms a mud stream, and mud itself is a product of some
volcanoes. A good idea of the flow of lava, and of the peculiar
forms it often assumes, may be obtained by watching the flow of
slag at a blast furnace.
Lavas differ in their fluidity ; those of Kilauea in Hawaii, are
LESSONS IN GEOLOGY. 329
very liquid, while those of Vesuvius are viscous. The fluidity
modifies the flow of the lava. That from Kilauea flows like mol-
ten iron; at first white hot, with a temperature of more than
2,000 F., it soon becomes red, growing darker till it assumes a
black, cinder-like appearance. The viscous lavas of Vesuvius
break in rough brown slags, which grind and grate over each
other with a metallic sound. Occasionally the lava flows over the
edge of the crater, but it often breaks through the side of the
mountain, sometimes 2,000 or 3,000 feet below the surface of the
lava in the crater, forming fountains of molten rock. Lava that
is completely fused when cooled quickly forms volcanic glass
obsidian; when cooled slowly crystals are formed and stony lavas
result. In most lavas the crystallization is quite complete before
the mass becomes solid.
A volcanic cone is, to a great extent, the work of the volcano,
and its composition and form depend on the materials thrown
out by eruptions. If the product is fluid lava, as in the case of the
Hawaiian volcanoes, the cone will be broad and flat. If the lava
is viscid the cone will be steeper and narrower. If the product is
chiefly ashes, scoriae and lava, the cone will be steep. The cones
formed by successive eruptions have somewhat the structure of
an exogenous tree. Sometimes the cone has been ruptured by
radiating fissures, and these filled with lava dikes. Secondary
cones are frequently formed inside the craters or on the sides of
the main cone; there are some 200 such cones on the slopes of
Mount Etna.
Volcanoes are mostly located in the mountain regions along
the shores of the Pacific ocean, and many of the islands of that
ocean are volcanic. Some are located about the Mediterranean
Sea, in the West India islands and elsewhere.
The causes of volcanic action are not understood, but many
theories have been advanced to account for the phenomena. It
is generally agreed that the expansive force of steam is the chief
force of eruption, but how the water reaches the molten rock is
not explained. The source of the volcanic product and of the
volcanic energy cannot be deep, as water could scarcely penetrate
330 PRACTICAL LESSONS IN SCIENCE.
to a depth of more than six or eight miles. Some think the crush-
ing of the rocks under the great horizontal pressure develops
heat enough to fuse the rocks and produce eruption. Others
ascribe the molten matter to chemical action between the unoxi-
dized interior and oxidizing agents, as air and water, from the
crust ; and again the action must be within reach of surface water.
The source must be local, as volcanoes near each other yield dif-
ferent kinds of material, and sometimes with lava standing in
their craters at widely different levels. And it frequently happens
that the same volcano yields different material at different times.
We know many things about the effects of earthquakes and vol-
canoes but very little about their causes.
Rocks and lava cool slowly, thick masses retaining high tem-
perature for many years. It is said that cigars and sticks might
be lighted at fissures in a lava stream from Jorullo, Mexico, 21
years after the out-flow. Water percolating through such ma-
terial appears again as hot springs, and often with dissolved
gases and minerals, as, sulphur springs, iron springs, etc., and
doubtless the geysers of Iceland and Yellowstone Park are in
a sense secondary volcanic phenomena.
A geyser appears to be a spring or pool of hot water, but when
its depth is measured it is found to be more like a funnel-shaped
well of hot water. At somewhat regular intervals eruptions of
water and steam occur. The phenomena of an eruption are about
as follows : Sounds like cannonading are heard below and bubbles
rise through the water, then the water rises a little, overflowing
the basin, and immediately afterward the water is thrown out as
from a fountain, followed by a great quantity of steam. It is
explained by supposing that water toward the bottom of the
tube is con verted into steam which throws out the water above it.
CHAPTER XLIV.
TEMPERATURE, WINDS, WAVES, TIDES AND CURRENTS.
THE forces active in early geological phenomena, had their
origin for the most part in the earth itself. But as the outer
portions cooled the initial heat became less effective, and the heat
of the sun, causing most of the phenomena of climate, became
an efficient geological agent, especially during the later stages of
the earth's history.
The earth revolves around the sun and rotates on its axis. If
the axis was perpendicular to the plane of revolution there would
be no change in the distribution of heat over the surface of the
earth during the year; there would be no zones; no changes of
seasons. But the axis is declined from a perpendicular to the
plane of revolution about 23 1-2, and to this fact we owe the
zones, the long cold winters in the polar regions, the winter and
summer of the temperate zones, and the wet season and dry sea>-
son of the tropics.
The crust of the earth is very uneven. The depressions filled
with water we call the sea; those portions above the sea we call
the land. The sea is divided into oceans and the land is divided
into continents, and these into grand divisions.
Water is not a good absorber nor a good radiator of heat,
hence does not gain heat rapidly during the day or the summer,
and does not lose heat rapidly during the night or the winter,
maintaining quite a uniform temperature during the year. The
rough, dense land is a much better absorber and radiator than
the water, so that it gets much hotter during the day and sum-
mer, and much colder during the night and winter than the water.
The water, with its uniform temperature, tends to equalize the
varying temperatures of the land, so that climates along the sea-
shore are markedly different from inland climates. For this rea-
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332 PRACTICAL LESSONS IN SCIENCE.
son the relative extent of land and water areas and the relative
positions of the bodies of land and water are important climatic
questions.
At first it seems as if there might have been more land ; but
on examination we find that only a portion of the present land
surface can get water enough to be productive of plant or animal
life. The land extends in two masses almost from pole to pole,
and with such general form and irregular outline that very large
portions come under the equalizing influence of the sea.
The land varies in elevation. There are low plains, plateaus
and mountains. The important facts to be learned about moun-
tains are their location, elevation and direction of extent ; and in
regard to plateaus their location, elevation and extent should be
known. In general the mountain systems of the Western conti-
nent trend north and south, and so do those of South Africa and
Australia, while in Europe and Asia the trend is more nearly
east and west. The greater mountain systems border closely on
the deeper oceans, as the Pacific and Indian.
The air is an invisible gas surrounding the earth, extending
upward some 400 or 500 miles. It is composed mainly of oxygen
and nitrogen, with varying quantities of water vapor, carbon
dioxide, ammonia, nitric acid, etc. Variation in the temperature
of the air is the principal cause of winds, rainfall, dew, frost and
other phenomena, which together make up what we call climate,
and which is generally discussed under the heads of temperature,
winds and rainfall.
The temperature of the air depends mainly on the temperature
of the earth's surface. The heat from the sun passes through the
air and warms the earth, and the earth in turn warms the air
mainly by convection, partly by radiation and reflection. It is
estimated that the air absorbs more than one-third of the heat
sent from the sun to the earth, the greater part being taken up
by the water-vapor and carbon dioxide, as pure air is nearly dia-
thermic. The air absorbs even a larger per cent, of the heat radi-
ated from the earth and prevents the surface from cooling as
rapidly as it would if the air were diathermic.
LESSONS IN GEOLOGY. 333
Thus the air serves the surface of the earth as a sun-shade by
day and as a blanket by night, tending to equalize its own tem-
perature. This effect is greatly increased by the presence of
clouds in the air. If it were not for this property of the air it
would be so hot in summer, and cold in winter as to destroy all
such life as exists on the earth at present.
As the surface of the earth is the main source of heat for the
air, the temperature of the air must decrease from the general
surface upward. Mountains and high plateaus usually have a
lower mean temperature than the general surface of the earth in
the same latitude.
The difference in temperature between the tropical and polar
regions is the chief cause of different pressures in the air, and the
unequal pressures cause currents of air or winds.
Along the equator there is a belt of light pressure ; at about
32 north and 25 south there are belts of heavier pressure, and
at about 64 north and 70 south there are areas of light pres-
sure. The movement of the air is from the heavy pressure toward
the light pressure. Currents blow from the belts of light pressure
at 32 north and 25 south toward the equator; these form an
upward current, which, after rising some distance, spreads out
toward the light pressures north and south.
Owing to the rotation of the earth these currents do not flow
directly north and south, but those going toward the equator
from 32 north, go southwest as northeast winds, and those
from 25 south go northwest as southeast winds. And those
toward the north pole go northeasterly as southwest winds;
and those toward the south pole, go southeast as northwest
winds. In general the winds of the tropics are easterly winds
and those of the temperate zones westerly winds. t
These winds represent the general movements of the air subject
to many local exceptions, occurring in each grand division, es-
pecially in the coast regions.
The air always contains water vapor, the amount depending
on the temperature of the air and on its distance from large bod-
ies of water. The air does not hold the water vapor as the
384 PRACTICAL LESSONS IN SCIENCE.
sponge holds water, but they are two gases mingled together,
each independent and sustained by the same force of heat. When
there is mingled with the air as much water vapor as the tem-
perature can sustain, the air is said to be saturated with mois-
ture, while if it might contain much more it is called dry air. As
the temperature of moist air is lowered the water-vapor at length
begins to condense into dew, fog or cloud.
Air in tropical regions, near the sea, contains the most water-
vapor. Nature's method of lowering the temperature of the air
is by sending it upward or toward the poles. The winds from the
equatorial regions are relatively warm and moist winds, and in
general are rain-bearing winds. As winds rise over mountain
chains their temperature is lowered and the water vapor falls as
rain, as they move toward the poles the same thing occurs. The
up ward current from the tropical regions rises so high that mois-
ture is condensed, forming the copious rains of those regions.
In South America the easterly winds of the torrid region com-
ing from the ocean, leave some moisture on the low mountains
near the eastern coast, but the greater part falls as they rise
over the giant Andes, giving that region an exceptionally heavy
rainfall and one of the most interesting river systems in the
world.
In North America the westerly winds furnish a heavy rainfall
for the region west of the mountains and north of San Francisco.
And southwesterly winds that come over the regions of Arizona,
as upper currents, are the main source of rainfall in the upper
Mississippi valley, and westerly winds give Europe an abundant
rainfall.
The eastern plateaus of Asia receive but little moisture on ac-
count of their high mountain borders ; their surfaces are barren,
and the air is nearly diathermic. During summer they become
excessively hot, and the air over them so light that exceptional
winds flow in from the east and south, which in rising over the
mountains lose their moisture as heavy rainfalls, forming an ex-
tensive system of great rivers.
Africa furnishes a region of exceptional rainfall. The regular
LESSONS IN GEOLOGY. 335
easterly winds from the Indian Ocean furnish abundance of mois-
ture, but during summer the central region becomes so hot
and the air so light that exceptional winds from the Atlantic
ocean flow into that portion of Africa. These winds both leave
abundant moisture on the slopes of the plateau, but the greater
part falls after the upward current is formed , condensed by cold
from elevation.
Thus the winds carry the water from the sea to the land, where
a portion becomes permanent in the rocks and soil, a portion
evaporates and a portion forms springs, brooks and rivers.
These inland waters are very efficient geological agents.
The sea, with waves, tides and currents, is also an important
force in geological work.
Waves are caused by the wind and are common on the sea every-
where varying in elevation with the force of the wind. The wave
has a forward movement, but the water only moves upward and
downward. When waves advancing toward the shore reach shal-
low water, the motion is retarded at the bottom by friction, and
the top moving on without support breaks over on the shore, thus
forming breakers. During storms waves break on the shore with
great force.
Tides are waves caused by the attraction of the sun and moon.
There are four tidal waves, two of equal size on opposite sides of
the earth caused by the moon, and two much smaller caused by
the sun. As the moon revolves around the earth once in about
27 days, the waves caused by the moon make the circuit of the
earth in the same time. Twice during this circuit the moon waves
coincide with the sun waves, making higher or spring tides, and
twice the lower part of one coincides with the higher part of the
other, and a lower or neap tide is formed. As the earth rotates
in the same direction that the moon revolves, a given place
passes through the crest of both moon waves once in 24 hours
and 52 minutes. In mid ocean the tide does not rise more than
three feet, but along some coasts and in narrow bays they rise
much higher. At the head of the Persian Gulf the tide rises
36 feet; at the Bay of St. Michael, France, 45 feet. In shoal
336 PRACTICAL LESSONS IN SCIENCE.
water and in narrow bodies of water these waves make strong to
and fro currents.
Ocean currents are as common as the waves, but are not quite
as manifest or as easily understood. They are caused mainly by
the winds and by the tides. Unequal heating and evaporation
would seem to be efficient causes of currents, but a little in-
vestigation shows that the effect of one tends to neutralize the
effect of the other. The rotation of the earth and the form and
arrangement of the land masses help to determine the direction
of the currents. In general the currents have the same direction
as the winds. The equatorial currents flow westerly with the
easterly winds, and the Japan current and the Gulf stream flow
northeasterly with the southwest winds, etc. Beside the surface
currents there are strong under currents toward the equator.
Thus the heat of the sun, the attraction of the earth, causes
winds and streams of water, waves and currents in the ocean,
and the attraction of the sun and moon cause the tides, all
efficient agents active in geological phenomena.
CHAPTEB XLV.
GEOLOGICAL ACTION OF AIR AND WATER.
AIR and water; winds, clouds and rain; frost, snow and ice;
springs, creeks and rivers ; waves, tides and currents, are the most
common objects and phenomena of the material world. They are
so common and familiar that most people fail to realize that they
are important, efficient, essential agents in nearly all geological
phenomena.
Quiet, dry air of uniform temperature is not an efficient agent,
but changes of temperature, which may be mentioned here, are
of great importance. The daily variation of temperature in
some dry regions is very great. On the southwestern plateaus of
North America the temperature varies from 90 F. at mid-day to
20 F. during the night, and the same is true of wide regions in
Africa and Asia, a variation of 90 F. between day and night be-
ing by no means uncommon. The expansion and contraction
due to such great and rapid change of temperature soon causes
rocks to crack and flake off and rapidly disintegrate into sand.
Dr. Livingstone, while in Africa, found that rocks heated up to
130 F. during the day, cooled so rapidly during the night that
they cracked and split, throwing off angular fragments of all
sizes up to those of a hundred pounds weight. In the dry regions
the rocks are broken up in this way almost as rapidly as in
regions where frost is the active agent.
The winds carry away the dust and sand formed, and the sur-
face of the region is gradually lowered by this dry erosion. The
sand carried in this way by the wind acts as a piece of sand-
paper, polishing and cutting down the rocks. These natural sand
blasts sometimes cut into the base of a cliff, and when under-
mined blocks fall, attack them in the same way, continuing the
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338 PRACTICAL LESSONS IN SCIENCE.
process till the cliff is reduced to sand and carried away by the
wind.
The combined action of wide and sudden variation of tem-
perature and the wind, has removed a thickness of more than ten
thousand feet of strata, from an area of thousands of square
miles, of the plateau through which the Colorado river flows.
The sand and dust eroded by the wind from one locality is de-
posited in another. The dust is widely disseminated, and settling
quietly is constantly adding to the growth of soil. In this way
dust from the high plateaus of Asia has built up a formation of
loess from 1,000 to 2,000 feet thick over regions between the
plateaus and the ocean. The loess is unstratified, fine yellow cal-
careous clay, containing abundance of land shells and remains of
vegetation. Other loess seems to have been formed with the aid
of water, and is called lake loess or river loess. It is said in some
places in Asia dust enough falls to serve as a fertilizer for the soil.
This dust, which pervades the air everywhere, is of interest in the
matter of rain-fall, for it seems that water-vapor condenses only
on free surfaces, and the cloud and mist is formed by the conden-
sation of moisture on the particles of cosmic dust.
The sand may be carried into rivers or lakes or into the sea, or
may form sand hills or dunes on the margin of the dessicated
region, as in northern Africa, Arabia and western United States.
But the most interesting sand dunes are those formed along the
margin of large bodies of water. When the prevailing winds are
from the water toward the land they carry sand from the beach
over the land till, meeting some obstruction, a dune is formed. It
may be ridge-like or somewhat conical in form; the seaward
slope is long and gentle, the other as steep as loose sand will
stand.
The wind not only carries or rolls sand from the beach, up the
gentle slope to the crest, but is continually carrying sand from
the slope itself to the crest and letting it fall on the landward
side, so that the dune travels inland, destroy ing forests and crops,
covering buildings, filling ponds, damming up streams, etc. In
time another dune forms between the first and the beach, which
LESSONS IN GEOLOGY. 339
follows the leader as waves follow each other. Where there is
abundance of moisture not much sand can be moved during the
year, and vegetation soon begins to grow on the dunes, and may
in time so cover them as to stop the action of the wind and the
dune becomes permanent. Sometimes these dunes interfere with
drainage forming lakes, ponds, and marshes, as alongthe eastern
shore of Lake Michigan and western coast of France. Dunes
sometimes serve as barriers against the sea and sometimes as
wind brakes. This action of the wind in moving sand can be
studied almost anywhere on windy days, even in the street or
schoolhouse yard.
Of the rain and snow that falls on the earth some is soon
evaporated, some is taken up by the soil, some by plants, some
sinks into the ground to reappear as springs, and some from
25 per cent, to 30 per cent. flows into the ponds, brooks and riv-
ers. Water acts on the soils and rocks chemically and mechanic-
ally. Water, when it reaches the soil, contains a little air and
carbon dioxide, dust, living germs, etc., so that one effect is to
fertilize the soil as well as to moisten it. Pure water usually pro-
tects the rock it covers, but water in conjunction with air is an
active oxidizing agent.
A thin pellicle of the oxide is formed on the surface, which if not
washed away thickens from the inside until a thick crust covers
the rock. The oxidation of iron and iron compounds is the most
interesting and important. Sulphide of iron is widely dissemi-
nated through nearly all kinds of rock, and under the influence of
air and water both the sulphur and iron are oxidized, sometimes
forming ferrous sulphate; and sometimes other bases take the
acid, leaving the iron free to become the ferric oxide. Thus
many kinds of rocks are entirely broken up, some parts passing
away in solution, allowing the whole to disintegrate rapidly.
Carbonate of iron is also acted on in much the same way, the iron
changing to the ferric oxide, allowing the rocks containing it to
decay rapidly.
Water dissolves salt, sodium chloride, without aid, but in
most cases of solution water is aided by carbon dioxide or
340 PRACTICAL LESSONS IN SCIENCE.
some other re-agent. In this way limestones, and feldspathic
rocks, carbonates and silicates of calcium, potassium, and sodium ,
are disintegrated, the calcium and alkalies, becoming carbonates,
are removed by solution and the rocks crumble down into sand
and clay.
In this connection may be mentioned the action of freezing
water. In northern latitudes the soils and rocks become satu-
rated with moisture during the autumn. During winter the water
in all the cracks, joints and interstices freezes, and by its expan-
sion increases all these spaces, and so on from year to year till
as the ice melts in the spring some of the outer particles becom-
ing loosened are washed away ; thus soils and rocks are broken
up and pulverized in some cases with great rapidity. The work
of water is somewhat increased by the mechanical action of fall-
ing rain.
The general effect of air and water aided by heat, frost, grav-
ity, and vegetable acids on rocks is called weathering. This ac-
tion varies with different rocks and in different climates ; by this
process nature transforms rocks into soil and carves out many
strange and interesting forms on the rocky surfaces of the earth.
Soil is formed in various ways, but on level or gently sloping
surfaces, much soil is formed by the decomposition of rock in situ
by the process of weathering. Perhaps most of the work is done
by carbonated water, but other agencies have more or less effect.
Nearly all rocks are more or less jointed or fissured, so that
water charged with carbon dioxide from the air or decaying veg-
etation, readily finds its way deep into the rocky strata, reappear-
ing at lower levels as springs. During its underground journey the
water dissolves more or less material from the rocks over which
it passes, so that the water of springs is seldom pure water.
Sometimes the water may have passed over insoluble rocks, and
issue from the earth as pure, soft water. Or it may have passed
over limestone rocks, and loaded with calcium carbonate form a
calcareous spring, supplying " hard " water. And according to
the nature of the rocks through which the water flows, a spring
will be ferruginous, sulphur, saline, alkaline, etc.
LESSONS IN GEOLOGY. 341
The effect on the rocks of this underground water is much the
same as the effect of air and water on the surface rocks. Solu-
tion and disintegration are usually more rapid in limestone rocks,
large channels and caves being common in such formations.
Sometimes the roof of the cave falls in and the cave or under-
ground channel becomes a gorge or narrow valley. The caves of
Southern Indiana, Kentucky and Tennessee are remarkable for
their size and the beauty of their stalactitic architecture. In
these caves there are often interesting examples of reparative
action. In cases where the bed of the stream has been lowered so
as to leave some rooms practically dry, the dripping from thereof
at length forms pillars, supporting the roof, and in time perhaps
fills the room. Again, where quantities of rock have fallen, the
drippings from above fill the spaces between the fallen rocks with
stalagmitic material and at length build supporting columns,
finally closing the cavity.
Sometimes the underground water, on sloping surfaces, dis-
solves away the union between large masses of rocks and the
mountain side, causing land slips, rock avalanches, etc.
CHAPTER XLVI.
RIVER AND MARINE EROSION.
THE rain falling upon the uneven surface of the earth, forms
little rivulets, which, uniting with others, form larger, and so on,
till the brooks and creeks are formed ; which together constitute
the river that receives all these little streamlets each with its
burden of sediment and conveys them, at length, to the great
and wide sea. Beside this surface water, the rivers receive the
water from thousands of springs, spring water, in many cases,
forming the greater part of the supply during the year. The re-
gion of country drained by a river is called the river valley, or
basin, and is usually considerably longer than wide. The char-
acter of a river will depend on the nature of the rocks of its val-
ley ; on the character of the climate of the valley and on the rap-
idity of its slope. Rivers vary in the amount of water and other
material they carry. Nearly all rivers have an annual flood, and
many are subject to change from exceptionally wet or dry seasons.
The Mississippi river, draining a wide valley embracing a va-
riety of climate, is somewhat uniform in its flow, subject to its
annual spring flood, and sometimes an exceptionally wet season
will give a summer flood.
The Nile river depends for its water supply on seasonal rains
in the upper part of its valley, and is very uniform in all its phe-
nomena from year to year. In regions subject to great irregu-
larities of rain-fall, the change from low water to flood is often
very great, as rivers in south-east Australia, or even in the south-
western part of the United States.
In general a river has three parts the mountain portion,
where formed by mountain torrents, it rushes noisily over its steep,
rocky bed to the lower ground that forms its middle or valley
course. In this part of its course the river flows through a more
varied country, lower mountains, wide valleys, narrow gorges,
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LESSONS IN GEOLOGY. 343
and sometimes spreading out into lakes, and in this region the
largest tributaries are received. From this undulating country
it passes into a broad alluvial plain, mostly deposited from its
own waters, and winds sluggishly onward, and finally, amid
marshes and banks of mud and sand, it empties into the sea.
The great rivers of the globe probably have an average slope of
less than 24 inches per mile. The Volga from source to sea has a
slope of less than 4 inches per mile, while the Missouri has a
slope of about 28 inches per mile. The water next the bottom
and sides of the river channel is retarded by friction, so that
water in the center and upper part of the river flows most rap-
idly. The fact that rivers flow more rapidly when in flood is
explained on the theory of less friction and increased slope from
high water in the upper courses.
Each little rivulet, each spring in the whole valley, brings to
the river products of terranean and subterranean weathering,
which the river carries out to sea with materials gathered up by
erosion along its course. The amount of material carried by riv-
ers in this way varies greatly; rivers flowing through cultivated
regions usually carry great quantities of sediments. The Mis-
souri river, flowing through recent, partially consolidated strata,
is loaded with sediment, and so are the rivers of China that flow
through the loess deposits; while the St. Lawrence system, with
its rocky valley and lake basins, is nearly always clear and free
from sediment. The water of rivers doubtless has some chemical
effect on the materials over which it flows, but the chief work of
flowing streams is mechanical. The matter carried by streams
is partly in solution and partly in suspension, and partly coarse
material pushed along the bottom. Of the substances in solu-
tion, calcium carbonate is most abundant, then calcium sul-
phate, sodium chloride, magnesium carbonate, and sulphate, etc.
It is estimated that the quantity of calcium carbonate removed
from the limestone areas of the Thames amounts to 140 tons
per square mile annually.
The power of a stream to transport suspended matter is said
to increase as the sixth power of the velocity of the current, so
344 PRACTICAL LESSONS IN SCIENCE.
that the power of the current is increased 64 times by doubling-
its velocity. A current of three inches per second will begin to
work on fine clay, one of six inches per second will lift fine sand,
and one of eight inches per second will move coarse sand, and one
of one foot per second will move fine gravel; while a current of
two feet per second, or a mile and a third per hour, will roll along
pebbles an inch in diameter, while a current of two miles per hour
will move stones the size of an egg. These figures are given for
the bottom velocity, and it should be remembered s'tones are not
more than two-thirds as heavy in the water as in the air, so that
they are more easily transported.
In the upper course of the stream large angular blocks of rock,
loosened by the frost, are urged down the steep slope by the
rushing torrent ; these, gradually abrading each other and the
bed of the stream, in time reach the sea as gravel, sand or mud.
Some fragments may have reached the sea within a year after
leaving their mountain bed, while the last particles of some of the
blocks may be thousands of years in reaching their final destina-
tion in the bed of the ocean.
The amount of solid matter conveyed by a large river to the
sea each year is almost beyond comprehension. Many investi-
gations have been made, but the most extensive and reliable are
those made by Humphrey and Abbott, on the Mississippi river.
They estimated that the amount pushed along the bottom of the
river into the Gulf, was 750,000,000 cubic feet annually, and the
amount in suspension was about 4,368,280,000 cubic feet, a to-
tal of 5,116,280,000 cubic feet per year, equal to a prism 268
feet high, with a base of one square mile. This means that the
Mississippi moves about one foot from the surface of its valley
in 6,000 years. Other rivers erode more rapidly, and some less
rapidly, but the above, as an average rate, would carry North
America into the sea within 4,000,000 years.
Rivers erode their channels, but clear water erodes very slowly,
as shown in the case of the Niagara and St. Lawrence rivers,
which have had very little effect on the glaciated rocks in their
beds, during the 3,000 or 4,000 years since glacial times. The
LESSONS IN GEOLOGY. 345
work of erosion seems to be done by sand and gravel carried or
pushed along the bed of the river. The rate of erosion will de-
pend on the strength of the current, the amount and kind of sed-
iment carried, and the nature of the rock through which the
channel was located. In the Missouri river, in many places,
there are from 40 to 50 feet of sand and mud between the bed
rock and the water. When the river is low, or at a medium stage,
this bed of mud and sand is quiet, and there is no erosion of the
rock-bed; but when the river is in flood, the whole mass is in
motion, sliding along like a rasp over the bottom of the rocky
channel. Limestone rocks erode more easily than some others,
and they are more easily soluble. Sometimes flint nodules in
limestone rocks hasten erosive action. The limestone eroding,
more rapidly, leaves the nodule as a projection; a piece of
floating ice or a log strikes the nodule, knocking it from its bed,
leaving a hollow. Sand and gravel collect in the hollow and, kept
in motion by the water, soon forma pot-hole, which is an interest-
ing and effective mode of erosion in rocks, where in any way little
cavities are formed.
Another special form of erosion, is by water-falls, which are
formed in various ways. The falling water splashing against the
foot of the cliff gradually undermines the upper portions, which
at length break down, and thus the falls recede and a gorge is
formed. If the lower portions are easily eroded, the action is
more rapid. At the Niagara Falls, the upper stratum is hard lime-
stone, the lower shale -which are favorable conditions for rapid
work. It is estimated that at the present time the falls are reced-
ing at the rate of about 2.4 feet per year. The Grand Canon of
the Colorado river about 300 miles long, and in some places
6,000 feet deep, is the work of the erosive forces of the river.
Sometimes a fissure determines the course of a river, and helps to
form its channel; but such cases are not as common as was for-
merly supposed. Ice in streams often adds considerably to their
erosive power. Land ice, or glaciers, are efficient geological
agents, which will be discussed in another place.
A stream of water carrying sediment begins to drop it when-
346 PRACTICAL LESSONS IN SCIENCE.
ever the current is checked. When a mountain torrent, with its
burden of sediment, flows out upon a plain, it drops the greater
part in a fan-shaped mass, the apex pointing up the stream ; lit-
tle streams flowing into ponds deposit sediments in the same
shape ; and the delta of the Mississippi is an enormous mass of
sediment of the same form, and deposited in the same way, the
current slackened by the waters of the Gulf.
A river seldom deposits any sediments along its mountain
course, but when it enters its middle course the current is lessened
and the sediments deposited sometimes raise the bed of the river
above the level of the adjacent land. The same thing occurs fre-
quently in rivers flowing through low plains or deltas. Some
rivers in Northern Italy illustrate the first and the Mississippi
river the second. During floods rivers often spread out over
adjacent low lands which are covered with vegetation ; the rough
ground and the vegetation check the current and a layer of sedi-
ment results. Turbid rivers flowing into lakes drop their sedi-
ments, the water at the outlet being clear. In this way lakes
are sometimes obliterated, entirely filled by the sediments of their
inlets. The course of a stream consists of a system of irregular
curves or bends, with occasional stretches of nearly straight
channel. On the convex side of a curve the current is strong
and erosive, while on the concave side it is weaker and depos-
iting sediments. In this way streams change their channels,
wandering about their valleys, eroding old sediments and depos-
iting new, so that a bit of gravel may form a portion of scores
of different gravel beds before it reaches the ocean. The whole
matter of the geological work of streams can be studied in almost
every phase along any little brook or creek in the country.
Marine erosion is very extensive, but is not as rapid or exten-
sive as river erosion. The waves with their burden of sand or
gravel gradually undermine the rocks so that they fall within
reach of the waves ; the smaller fragments are rolled backward
and forward by the waves, hurled against the larger ones till at
length they are broken up, and the fragments abrading each
other become pebbles that slide up and down the beach with
LESSONS IN GEOLOGY. 847
every wave, and are soon worn to sand and mud. In the river
the pieces of rock move forward, and are more nearly spherical
in form, while on the beach they move backward and forward
and soon become flattened, and are sometimes called shingle.
The sand resulting may form sand bars parallel with the shore,
or may be transported to other localities by ocean currents, or
may be built into dunes by the winds.
The different forms of life often are of great importance as
geological agents. Plants, as mosses and liverworts, by keeping
the surface of rocks moist, promote their decay, and in the decay
of their leaves and stems organic acids are formed which are
active oxidizing agents. These acids, for the most part, become
carbon dioxide, and in one form or the other are the great sol-
vents of the mineral world, often penetrating rocks to a great
depth. Plants and trees also aid erosion in a mechanical way,
as their growing roots open cracks and seams in the rocks.
Turf and trees protect from erosion. Forests protect hillsides
and sand dunes; the sand-grass and other plants also protect
the same from the wind. Mangrove swamps along the seashore
are especially effective in reclaiming and making land. While
live plants protect, dead and decaying plants often open the soil
to the erosive action of wind and rain. Decaying vegetation en-
riches soils, forms muck beds, peat bogs, etc., from which all the
coal and much of the rock oil and natural gas were formed.
Burrowing animals of all kinds, earth worms, cray-fish, open
the soil to the action of oxidizing agents, and often to the action
of erosive agents as well. Beavers build dams, making ponds
and swamps, while cray-fish, rats, etc., open holes through banks
which lead to destructive erosion. Some mollusca bore holes in
rocks and wood, thus promoting their disintegration. The shells
of the mollusca, the framework of corals and other animal
organisms have made up most of the calcareous or limestone
rocks. And the coral polype, in the tropical sea, is building
islands and reefs of coral limestone, while diatoms, and some
forms of animal life, are furnishing material for silicious deposits
of great extent.
CHAPTER XLVII.
THE ARCHAEAN AND ALGONKIAN ERAS.
ASTRONOMICAL studies lead us to suppose that our earth was
once a sphere of glowing gas, and that as it gradually cooled, por-
tions were condensed, forming a molten nucleus surrounded by
intensely heated gases. That as the cooling process continued,
the nucleus gradually increased in size and the temperature of the
surrounding gases diminished until the mass ceased to be lumi-
nous. At length a solid crust began to form over the heated in-
terior. It was doubtless broken up, remelted and reformed many
times, but at last a continuous slag-like crust became permanent.
From what we know of the composition of the rocks, this crust
was composed mainly of the silicates of aluminium, calcium,
potassium, sodium and magnesium, with iron manganese and
other substances.
All the water of the present oceans, lakes, and rivers, all the
mercury, sulphur, chlorine and other volatile matters with the
air formed an atmosphere of dense, poisonous vapors. In time,
portions of these vapors condensed, covering the crust with
broad, shallow oceans of hot, acid water. As the earth continued
to cool, the interior contracted more rapidly than the solid crust,
and as the crust settled down with the inner mass broad, low
swells and wide, shallow depressions were developed . These grad-
ually increased in elevation and depth until the continents ap-
peared, and the ocean boundaries were defined. Portions of
these ancient continents may have been submerged from time to
time for many hundreds of feet, but at no time have the conti-
nents and oceans changed places ; their relative positions have
probably always been substantially the same.
The reactions between the acid waters and the basic rocks re-
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LESSONS IN GEOLOGY. 349
suited in adding many soluble chlorides and sulphates to the
sea-water and in the formation of sediments as silica, silicates
of aluminium, potassium, calcium and sodium. These materials
with the original crust make up a system of granites, gneisses
and crystalline schists, which represent the oldest rocks of the
earth. These rocks are doubtless of a mixed origin partly igne-
ous, partly sedimentary, but they have been so completely
changed by metamorphic agencies that all trace of lava, slag,
and sediment has been obliterated.
These rocks, sometimes called the " Basement Complex," are
found in Arizona, Nevada, and Texas, in the regions of Lake
Superior and Hudson's Bay, including the greater part of theLau-
rentian rocks of Canada. These rocks were subjected to the
folding, crumpling and faulting incident to mountain formation
and to atmospheric erosion, and have been covered extensively
by later rocks so that we can know little of their original form
and extent. The time from the beginning of the crust to the time
when rocks that are distinctly sedimentary began to be formed
is called the Archaean or beginning era, and the rocks belong to
the Basement Complex, or Laurentian Age.
The AlgonkianEra. Under the action of erosive agencies large
portions of the Archaean rocks were broken down and distributed
over adjacent sea bottoms as sediments, which afterward were
changed into conglomerates, quartzites, quartz, mica and iron
schists and limestones. These rocks vary considerably, pass-
ing from quartzite to quartz-schist; from conglomerate to con-
glomerate schist ; from pure limestone almost like marble, to lime-
stone containing great quantities of chert; and with the iron
schists there are cherts and jaspers in abundance. These rocks are
called the Lower Huronian. At the end of Lower Huronian time
this region was raised above the sea, crumpled and folded, and
subjected to erosive agencies, which in some instances carried
away the whole series. After this period of erosion the surface
was depressed and sediments were deposited on the eroded sur-
faces that afterward were changed into the conglomerates, quartz-
ites, shales, schists, iron schists and slates, chert, jasper, etc.,
350 PRACTICAL LESSONS IN SCIENCE.
which make up a group of rocks known as the Upper Huronian.
The exposed area of these rocks is much greater than that of the
Lower Huronian, and they include the most of the rich iron ore
deposits of the Lake Superior region.
These rocks in some places are as much as 13,000 feet in thick-
ness. In general these rocks are not as highly metamorphic as
the Lower Huronian. At the close of Upper Huronian time
the surface was raised above the sea and exposed to erosive
agencies again. After some time great floods of volcanic mate-
rials were poured out over this region. Later the region was cov-
ered by the sea and sediments were deposited which afterwards
became conglomerates and sandstones. These volcanic and
sedimentary rocks make up the Keweenawan group or series. In
some cases the volcanic rocks are in terst ratified with the sediment-
ary rocks, which seems to indicate a subaqueous flow of lava. This
series is very extensive, and in some places is estimated to have
a thickness of 50,000 feet. These rocks include most of the rich
copper deposits of the Lake Superior region. Rocks to the east ot
Lake Superior belonging to this or an earlier series contain thick
beds of graphite as well as iron.
The reactions between the air, water, and land so purified the
air and water that low forms of aquatic life began to appear,
and soon became abundant, even acquiring new characters and
spreading out over the rocks. Great quantities of insoluble iron
ore were disseminated throughout the slag-like crust. Water
containing carbon dioxide derived from decaying organic matter
changed this insoluble peroxide into the soluble protoxide and
carried it down to the ponds, lakes and marshes, where taking
oxygen from the air, it again became insoluble, and settling to the
bottom helped to form sediments which afterward became thick
beds of iron ore. The immense beds of iron ore and graphite,
indicate that some forms of life must have been very abundant ;
but there is no positive evidence as to its character, as all
organic remains were destroyed when the sediments were changed
to rocks.
Granitic, gneissoid, schistose and slate rocks make up the
LESSONS IN GEOLOGY. 351
Laurentian tableland extending from Labrador southwestward
to the region of Lake Superior, thence north westerly to the Arctic
Ocean. They occur in the Adirondack and White mountain re-
gions, at many localities in the Western mountain regions
in the Alleghanies, in Arkansas and Missouri and in other
places, but only in the region of Lake Superior and some western
localities have the rocks of the two eras been clearly separated.
These rocks as exposed in the Laurentian tableland are from
40,000 to 50,000 feet in thickness. Their formation and their ele-
vation into mountains is explained as follows : The area now oc-
cupied by these rocks was a shallow sea, adjacent to an extensive
land surface, probably on the north in the region of Hudson's
Bay. The sediments derived from the land were spread out over
this sea bottom. For some reason this area of the crust was
weak, so that it settled gradually, as the sediments were depos-
ited, till they became more than 50,000 feet deep. At length the
settlement was so great that the rocky masses underneath be-
came softened by the internal heat, and the whole mass became
so weak that it yielded to the lateral pressure of the sinking
crust and the sediments were mashed together, the crumpled,
folded strata slowly swelling up into mountains.
Under this great pressure, through the agency of heat and
water, the organic matter of the sediments was destroyed and
they were changed into met amor phic rocks.
Originally the substances which make up the earth's crust
were widely disseminated, and the great bulk of the Archaean rocks
were formed from a mixture of a wide variety of substances ; but
the assorting tendency of nature's operations is manifest in the
beds of quartzite, slate, limestone, iron ore, and graphite.
The Laurentian tableland is the oldest portion of North Amer-
ica; it seems never to have been submerged. It has been subject
to eroding agencies for untold ages; it has furnished materials for
the rocks of all subsequent ages; yet rising by intervals or con-
tinuously, it has always kept pace with the degrading effects of
the eroding forces.
CHAPTER XLVIII.
THE PALCEOZOIC ERA.
THE next period of the earth's history is called the Palceozoic
, or era of old life. This era includes the Silurian age, the
Devonian age, and the Carboniferous age.
At the beginning of this era, besides the Lauren tian tableland,
there seems to have been a large body of land occupying the
region of the Atlantic coast plain ; and another in the region now
occupied by the Rocky Mountains. Between these bodies of land
there was a broad, shallow sea, called by some the Paloeozoic sea.
The earliest rocks of this era are sandstones and slates, composed
of materials that accumulated on the beach of this ancient sea,
over a region extending from Canada to Georgia. They are
known as the Cambrian rocks. In them we find the earliest re-
mains of life, representing protozoans, coelenterates,echinoderms,
worms, and crustaceans, nearly all the invertebrate forms of life,
besides several species of plants.
This abundance of the various forms of life, calls attention to
the nature of the geological record. We know nothing about how
much time elapsed between the formation of the primal crust and
the formation of the Algonkian rocks, with their evidences of
beginning life, and we know very little of what events transpired
during the period.
The life of the Algonkian era must have consisted mainly of low
forms of vegetation with some protozoans, as no other forms
could exist under the conditions of those times; and yet in the
next higher rocks that have been found there is evidence of an
abundance of life of well-advanced forms. The early rocks had
been strongly folded and deeply eroded before the later rocks were
deposited. Thus the relations of the rocks and the forms of life
show that after the formation of the Algonkian rocks there is an
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LESSONS IN GEOLOGY. 353
immense period of the earth's history, of which no record can be
found. Erosive forces were active; sediments inclosing remains
of various forms of life were deposited and changed to rocks, and
the whole submerged and covered from view by later rocks. The
rocks of that era which we can examine seem to be mere remnants
of great continents of rocks that have been cut away by erosion
and submerged. They stand between great unknown periods in
the history of the earth. Breaks in the geological record are
numerous, but perhaps no other is as well marked as this one.
During the balance of the Silurian age thick beds of rock were
deposited over a wide portion of the continent, as the Trenton,
Niagara and Galena limestones, the Utica and Niagara shales
and the Medina sandstones ; the limestone largely exceeding the
others in some regions, so that it is mentioned as the characteristic
rock of the age.
All classes of invertebrate life were abundantly represented, but
mollusks were most numerous and varied, so that this period is
often called the Age of Mollusks. Some fossil fishes have been
discovered in European rocks. More than 10,000 species of fos-
sils have been described from the Silurian rocks ; remains of sea-
weeds and of plants that were terrestrial, as ground pines and
others, some like the yew and pine.
The area of Silurian rocks extends from Newfoundland to Mis-
souri, from Lake Superior to Georgia, but they are thickest in the
Appalachian region. In the west the limestones are most abund-
ant, while in the Appalachians they only make up about one-half
of the beds. The limestones were formed in quiet waters, largely
from the shells of mollusks, the stems of crinoids, the framework
of corals, etc. The sandstones and shales were generally beach
deposits, sand bars, mud flats, etc. Some clayey iron ores and
salt deposits indicate the existence of marshes and shallow salt
lakes. The frequently alternating beds show many upward and
downward movements of the crust. It takes but a few moments
to make these statements of the events of this age, but they were
the work of millions on millions of years. And in this study we
need to keep constantly in mind that geological time units are
L. S. 23
354 PRACTICAL LESSONS IN SCIENCE.
very, very long. It is said that no group of strata has been
traced over a wider area of the earth's surf ace, and none are more
uniform and well marked in their composition and in the charac-
ter of their fossil remains than are the Silurian.
Following the Silurian age came the Devonian age, character-
ized by the " old red sandstone beds " of Great Britain. In North
America the lowest formation is the corniferous limestone, one of
the great limestones of the continent; the later strata were
mainly sandstones and shales in the east, with shales and
thin limestones in the west. The corniferous limestone is distin-
guished by seams of horns tone or flint and occurs in New York,
Ohio, Michigan, Iowa, Missouri, Kentucky and adjacent regions.
The Hamilton shales of New York and the black shales of Ohio
and neighboring regions belong to this age.
During the Devonian age the different classes of invertebrate
life were abundantly represented, but in general by different spe-
cies from those of the silurian age. Fishes, however, were the
characteristic and dominant life of the age. They were like the
sharks and skates, garfish and sturgeons of the present, repre-
senting the lower orders of vertebrate life. They existed in great
variety, and often attained a large size.
Plants were represented by seaweeds and other aquatic forms,
but terrestrial forms, as equisetaB, ferns, lycopods, and the lower
gymnosperms were abundant and characteristic, often attaining
the size of trees, forming forests. The corniferous limestone
indicates a quiet sea for a long time, but the later rocks were
largely the products of erosion deposited on the sea bottom near
the coasts. And the vegetation suggests extensive swamps and
marshes. The character and relations of the rocks indicate no
marked distinction or gap between the Silurian and Devonian
ages, but the marked difference between the life forms of the two
ages does suggest an interval of time not shown by the rocks.
The Devonian passed without violent changes into the carbon-
iferous age. The rocks in many localities show changes of level and
crumpling of strata indicating some difference of conditions be-
tween the Devonian and the following Carboniferous age; but the
LESSONS IN GEOLOGY. 355
difference is not very great. This age is divided into three parts,
the sub-carboniferous, carboniferous and permian. The sub-car-
boniferous rocks are mainly limestone, but in Ohio, Michigan and
Pennsylvania there are more sandstones and shales, all of marine
formation. The lowest strata of the Carboniferous is a coarse
sandstone called the Millstone grit. The other strata are thin
beds of coal, shale, limestone, sandstone, clay, iron, stone and
under clay. The permian rocks are an ill-defined group of sand-
stones, limestones, gypsum beds and shales, that mark a transi-
tion period from the palaeozoic to mesozoic eras.
Coal occurs in separate areas or basins, as the Appalachian
coal field, the greatest in the world, extending from Pennsylvania
to middle Alabama, with an area of about 60,000 square miles
of work able coal; the central field, covering the greater part of
Illinois, part of Indiana and Kentucky, about 47,000 square miles.
The western field includes southern Iowa, and portions of Missouri,
Kansas, Arkansas and Texas, about 80,000 square miles. Then
about 6,000 square miles in Michigan, about 500 in Rhode
Island and about 18,000 in the region of the Bay of Fundy.
The carboniferous and sub-carboniferous rocks have a much
more extended area than the coal proper, as given above.
As in the two previous ages, the invertebrates were well repre-
sented, and in addition to the marine forms there were many ter-
restrial and fresh- water mollusks, and some spiders and insects.
Fish were as large, abundant and varied as during the Devonian
age, and toward the close some amphibians appeared. But the
notable, the characteristic life of this age was its plants. Only
the cycads, a group of gymnosperms, were added to those known
in the Devonian age; but in general the plants of the carbonifer-
ous age were larger, more abundant and more varied in form; as
many as 500 species have been described from American rocks,
besides a large number of different ones from European rocks.
It is generally believed that coal is of vegetable origin, and
that coal and its associated rocks were, in general, deposited
under the following circumstances : A large, nearly level, some-
what basin-shaped area of land has been covered with a bed of
356 PRACTICAL LESSONS IN SCIENCE.
fine clay thick enough to hold water and support a growth of
vegetation ; a slight elevation makes shallow, stagnant or slow-
moving water, in which springs up a dense growth of mosses,
ferns, equisetse, lycopodia, sigillaria, calamites, etc., forming
a swamp. The stems and leaves of these plants, preserved from
complete decay by the water, accumulate as peat. After a time
the area is slightly depressed and currents of water flow over the
peat, depositing on it sediments of clay or sand, and perhaps the
depression may be enough to allow the sea to invade the region
and deposit lime sediments. Again the region is elevated, a de-
posit of fine clay is made and the cycle of deposits begins anew.
In Belgium, Nova Scotia and other localities there are more than
eighty seams of coal, and as at least two strata of other material
separate each seam from the next, we can form some idea of how
many upward and downward movements, how many changes of
condition have occurred in the for mat ion of a group of coal strata.
The layers of peat are changed by heat and pressure into bitu-
minous coal, and the pressure and heat maybe enough to change
the beds of peat to anthracite coal, or even to graphite.
Iron in some form always occurs with coal. Nearly all the iron
of England, and much of the iron of America, comes from the
coal measures. It often occurs as the sulphide, which is of no
value for iron, and is a damage to the coal ; but it occurs most
abundantly as clay iron stone, or kidney iron ore, which is a car-
bonate of iron. In some manner, not well understood, vegetation
gathers up the iron from adjacent rocks, and concentrates it into
these forms. Sand rocks and shales near coal seams are white or
gray, not red their coloring matter has become iron ore.
Besides coal, we find in the rocks of different ages, quantities
of asphalt and bitumen, petroleum oil and natural gas. They
are supposed to be of organic origin, as similar substances may
be derived from coal by distillation ; and while they might origi-
nate from any accumulation of organic matter, it is probable that,
for the most part, they were the products of the carboniferous
age, although they may have accumulated in cavities of rocks of
other ages.
LESSONS IN GEOLOGY. 357
During the Algonkian era, the Lauren tian tableland was raised
above the sea level, as a permanent feature of the continent.
During the Silurian age, the Green Mountains were formed; and
the paloeozoic era closed with the elevation of the Appalachians,
extending the land surface of the continent westward to the region
of the Missouri, and southward to the Tennessee. The elevation
was doubtless slow, and possibly there were oscillations, but this
area seems never to have been below the sea level since the car-
boniferous age.
The heat and pressure attending the elevation of the Appal-
achians, changed sediments to metamorphic rocks, as clays to
slates, sands to quartzite, limestones to marbles, peat beds to
anthracite coal, etc., the forces, the elevation and the metamor-
phism diminishing from the east toward the west. It is interest-
ing to note the similarity of events in North America and in
Europe ; the practical identity of the Algonkian rocks, the occur-
rence of evidences of a lost period, the similarity of the Silurian
and Devonian rocks, the identity of the millstone grit, the marshy
areas and other conditions for the formation of coal, with sim-
ilar forms of life, from beginning to end, including multitudes of
identical species ; and the eras of crumpling strata and mountain
formation seem to have been coincident.
CHAPTER XLIX.
THE MESOZOIC OR SECONDARY ERA, AND THE TERTIARY AGE.
THE Mesozoic Era in Europe'shows three well-marked divisions,
which are known as the Triassic, Jurassic, and Cretaceous periods.
The triassic and Jurassic are not as distinct in North America,
but the three periods are recognized. The triassic rocks are
mainly red sandstones, with some conglomerates, shales, and im-
pure limestones. They occur in Nova Scotia, Connecticut, enn-
sylvania, and North Carolina, and over wide areas in the Rocky
Mountain region, extending far north into the Canadian prov-
inces. Some quarries furnish a brown sandstone, much prized for
ornamental building ; but in general the rocks of this period are
not of much economic value. The rocks seem to have been
formed in shallow water, and the abundance of mud cracks, rain-
drop impressions, and tracks of animals show that the sediments
were often half-emerged sand flats.
Jurassic rocks are found near the Black Hills, and in the
Uintah, Wasatch and Sierra Nevada mountains, usually sand-
stones, sandy limestones, etc.
The cretaceous rocks are beds of sand, clay, shells, green sand,
limestone ; all these beds usually loose, easily crumbled, but occa-
sionally compact beds are found. They occur in detached areas
along the Atlantic and the Gulf coasts, and north along the
Mississippi almost to the Ohio river; along the slopes of the
Rocky Mountains from Texas into Canadian territory quite to
the Arctic ocean, the thickest beds being in Colorado, Utah, and
Wyoming, where the rocks are fully 9,000 feet thick. The life
forms were abundant. Among plants there were equisetae, ferns,
conifers, and others known during the coal period. The cycads,
having the appearance of palms, with leaves that unrolled like
ferns and wood like the pine, were characteristic and peculiar. In
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LESSONS IN GEOLOGY. 359
thecretaceous the first dicotyledons appeared, as the oak, willow,
maple, and sassafras, and became numerous, as many as 100
species having been discovered. And leaves of the redwood and
of the palm have also been discovered.
The characteristic life of the age was reptilian, so that it is
often called the Age of Reptiles. They practically appeared with
the age, reached their culmination and passed into a decline.
They were very large and very numerous, they dominated the
water and the land, and some were furnished with wings for ex-
cursions in the air. Invertebrate life was abundant, and so were
ganoid fishes and amphibians. In the cretaceous the teleosts, or
bony fishes, and birds of different kinds appeared, and remains
of mammals have been found in the triassic rocks.
The famous chalk cliffs of England, and the cretaceous beds of
eastern North America, were doubtless formed at the same time,
and were continuous. These localities were raised above the sea
level, while chalk is still being formed in the ocean between.
At the close of the Jurassic, there were some igneous eruptions
in the Connecticut Valley, and other slight disturbances on the
Atlantic coast; but the great revolution was the swelling up of
the then marginal sea bottoms into the Sierra Nevada and Coast
Range mountains, and doubtless theUintah and Wasatch ranges
began to rise about the same time.
At the close of the cretaceous, or soon afterward, the whole
western half of the continent was elevated, the interior cretaceous
sea disappeared, the Rocky Mountain region joined the tableland
and the Appalachian region, completing the continent.
The Cenozoic Era, or Age of Mammals, is divided into the Ter-
tiary and Quaternary Ages.
The Tertiary Age is divided into the Eocene, or lower, Miocene,
or middle, and Pliocene, or upper tertiary.
The tertiary deposits constitute the Atlantic and Gulf coast
plains, and extend from the Gulf up the Mississippi river to the
mouth of the Ohio river. These are marine deposits of a some-
what varied character. In the Rocky Mountain region there
are numerous basins of fresh-water deposits belonging to this
360 PRACTICAL LESSONS IN SCIENCE.
age, as the Green river and Uintah basins of the eocene ; basins
in Nebraska and Oregon belonging to the miocene; the Nio-
brara and White river basins and others containing pliocene
deposits.
The rocks of the tertiary consist of beds of sand and clay,
shell beds and marls, compact sandstones, calcareous sandstones
and limestones. On the Pacific slope some metamorphic rocks
are found, metamorphic agencies having been in force in that
region after some of the tertiary sediments had been deposited.
Some coal in the Western mountain system is referred to this
period .
Among plants, the genera of the dicotyledons, palms and
grasses were about the same as now, but most of the species were
different from those of the present. Magnolias, palms and other
sub-tropical plants grew in the extreme north of Europe and
North America, indicating a much warmer climate than now pre-
vails in those regions. Immense deposits of infusorial earth,
composed largely of diatom shells, indicate an abundance of
microscopic life.
Among animals, mollusks, insects, worms and fish were abun-
dant ; reptiles and birds were numerous, but mammals were the
characteristic and dominant form of life. Herbivorous animals,
like the rhinoceros, mastodon, elephant, camel, giraffe, tapir,
antelope, hog and horse were common. From the Green river
and adjacent basins more than 150 species of vertebrates have
been described. Carnivorous animals, like the tiger, panther,
wolf, fox and hyena were abundant, and remains of animals like
the beaver and porcupine have been found.
Quite a series of the ancestors of the modern horse have
been found in these rocks, beginning with one having four
toes, and gradually diminishing till the present form, with one
toe, is reached. The horse and camel seem to have originated on
this continent; and the number of old-world forms found in the
rocks of North America would indicate free communication be-
tween the continents through long periods of time. The nearly
common forest vegetation prevailing through the northern
LESSONS IN GEOLOGY. 361
parts of Asia, Europe, and North America, testifies in the same
direction.
The tertiary was the great mountain-forming period, and in
connection with this work the continents were elevated and
extended to their present limits ; in fact, the boundary lines be-
tween the land and the sea were laid during the tertiary period.
The whole western mountain system of North America was
elevated more or less, some of the eastern chains rising as much
as 10, 000 feet, and thecoast ranges were formed at this timealso.
Long cracks or fissures were opened and immense sheets of lava
poured out; one sheet, cut through by the Columbia river, is
over 3,000 feet thick and 150,000 square miles in extent. Eleva-
tions in the south-east exposed recent sediments and extended
the continent to its present limits, except a portion of the Penin-
sula of Florida. ' ; Throughout the old world, from the Pyrenees
to Japan, the bed of the early tertiary sea was upheaved into a
succession of giant mountains, some portions of that sea floor
now standing at a height of at least 16,500 feet above the level
of the sea" on the Himalayas. Along with these elevations of
the land, there were doubtless depressions in the ocean beds, of
which there are some indications in the Pacific ocean.
The movements of the crust of the earth during the tertiary,
are among the most extensive of which we have any record, yet
they were doubtless quiet and slow, in fact, rivers in the Rocky
Mountains and in the Himalayas have deepened their rocky
channels as rapidly as the mountains rose.
CHAPTER L.
GLACIAL PERIOD.
THE Quaternary Age is divided into the Glacial, the Champlain,
and the Terrace periods.
The glacial, or ice period, like other geological phenomena, seems
to have come on gradually. In the early part of the tertiary, the
climate of Central Europe and North America was sub-tropical,
and flowering plants and shrubs were growing within the Arctic
circle. During the extensive changes in the crust of the earth
which occurred in the tertiary, the northern parts of the conti-
nents seem to have been gradually elevated to a height of some
1,000 to 2,000 feet above the present level. With this elevation
the climate gradually became more severe, until the ice and snow
had crowded the shrubs and flowering plants far toward the
south, and were occupying the greater part of North America,
north of the Ohio river, and the northern and central portions of
Europe, and parts of Asia and the glacial period was in full
progress.
Then followed periods when the ice seems to have retreated
and advanced several times, as if the climate were alternately
warmer and colder. One retreat was so great, that many speak
of the next advance as a second glacier. But at length the ice
retreated to the confines of the polar zone, and temperate climates
prevailed over Central Europe and North America.
The glaciers of the Alps and the Pyrenees, those that linger in
Norway and cover Greenland, the glaciers of Alaska and the
Rocky Mountains, are but the remnants of the great ice sheet
that dominated the northern part of both continents for untold
centuries.
From a study of these existing remnants, and the work they
do, we may gain some idea of what were the conditions of our
(362)
LESSONS IN GEOLOGY. 363
country during the glacial period; and may find some rational
explanation of the interesting and peculiar surface features which
were determined wholly, or in part, by glacial ice.
The study of surface features is somewhat complicated by the
fact that coincident with the final retreat of the ice, the whole
region sank slowly down almost to sea level, and was cov-
ered with the broad, shallow lakes, or seas, of the Champlain
period, which greatly modified the surface left by the ice sheet.
Then the surface rose to about its present level, the lakes drained
away, still further modifying the old glacial surface, as the coun-
try gradually attained its present condition.
Ice seems to be a brittle solid, but as it accumulates in the
mountains of Switzerland, it flows down those valleys like rivers,
slowly but surely following every change in direction, every vari-
ation in slope, and every irregularity of surface almost as per-
fectly as water does.
As the ice moves down the valley loose fragments of rock are
pushed forward, abrading each other as they roll along; sharp
angles of rock are broken off, which, with rocks falling from cliffs
above, jostle along between the ice and the sides of the valley
abrading each other, till in time the whole mass of ice is filled
with sand, gravel, pebbles and fragments of rock. Those along
the bottom and sides, held firmly in the frozen grasp, make the ice
a gigantic rasp scratching, striating and grooving its rocky bed,
and smoothing out its sharper irregularities. Thus the ice river,
like the river of water, flows toward the sea with its burden of
mud, sand, pebbles, etc. At the end of the glacier the melting ice
forms a stream which carries away much of the fine dust from
the glacial mill ; but the pebbles, boulders and rocks, with much
of the finer materials accumulate, forming what is called a mo-
raine. A few hotter seasons cause the ice to retreat from the
moraine, covering the ground with clay, pebbles and boulders,
which otherwise would have been heaped on the moraine. A few
colder seasons and the ice advances again, pushing before it the
loose material it dropped on its retreat, until it again reaches
the moraine and perhaps crowds it forward.
364 PRACTICAL LESSONS IN SCIENCE.
As the continental ice sheet retreated, it left the whole country
covered with clay that was so filled with pebbles and boulders
that it has received the name of boulder clay, sometimes known
as bard pan ; it is so hard, and resists erosion so well that it is
often mistaken for rock. The margin of the ice sheet can be
traced across the United States with some degree of accuracy,
but in many cases the location is doubtful, as the original de-
posits, doubtless thin toward the margin, have been so washed
away and commingled with other material that the limit of the
ice cannot be denned.
The line that marks in a general way the southern limit of the
ice and drift, runs from Cape Cod along the south shore of Long
Island to New Jersey, then northwesterly to near the headwaters
of the Alleghany river, not far from Salamanca, thence south-
westerly through New Lisbon, Danville and Winchester, Ohio,
crossing the Ohio river near Cincinnati to Madison, Indiana,
thence northwesterly a little beyond Martinsville, thence south-
westerly through New Harmony to the Mississippi river near the
mouth of the Big Muddy, thence up the river crossing to the Mis-
souri below St. Louis, thence up the Missouri to the Osage, then
up the Osage for a short distance, then westerly and northwest-
erly in a course generally parallel with the Missouri river to the
Rocky Mountains, thence southerly nearly to the head waters of
the Red river, thence across the mountains and northerly to
about the Columbia river, thence southerly including most of
the Sierra Nevada Mountains and the northern part of the Coast
ranges. The mountain region was hardly covered by an ice
sheet, but was rather the seat of numerous local glaciers, much
as Alaska and Switzerland are to-day.
The greater part of this region had been above the sea and
subject to erosion since Devonian times, and was deeply scored
by drainage channels that in great measure determined the direc-
tion of the ice flow, tongues or lobes of ice flowing along the val-
leys in advance of the ice sheet ; and these are sometimes called
glaciers, as the Green Bay lobe or gla,cier, the Lake Michigan
glacier, the Saginaw glacier, the Maumee glacier and several les-
LESSONS IN GEOLOGY. 365
ser ones farther east. During the time of most extensive glacia-
tion these doubtless were all united into one broad sheet of ice
that extended nearly or quite to the line already traced across
the country ; but for the most part they were separate bodies of
ice. The moraines in many places are very distinct; they are
readily traced on Long Island, across Pennsylvania, Ohio and
Indiana. The moraine bounding the Lake Michigan glacier has
been traced, the common portion between the Lake Michigan and
the Saginaw glaciers being well marked, extending north and
south just west of the center of Michigan. And the one between
the Saginaw and Maumee glaciers is also well marked in the
eastern part of Michigan. And the peculiar relation of the St.
Mary's and St. Joseph rivers to the Maumee is due to a terminal
moraine of the Maumee glacier along which these rivers flow to
a common opening through the ridge. In Minnesota and Dakota
there are numerous moraines, forming two systems of lobes or
loops, the arrangement being more complicated than farther east.
At places over this area where bed rocks are exposed, they
show marks of glaciation, as at Put-in-Bay in Northern Ohio, Ni-
agara Falls, and other places, the striae indicating the direction
of ice flow ; sometimes two or more systems of striae occur on the
same surface, indicating two or -more invasions of ice flowing in
different directions.
Boulders from the hard pan are often glaciated ; sometimes
specimens are found that have been striated in a dozen different
directions, as they have turned in the loosening grasp of the ice.
Many of the boulders and much other glacial material came from
limestone and sandstone rocks whose original bed is not far
away, but for the most part glacial debris came from the Lauren-
tian tableland.
It is interesting to trace these boulders back to the native
quarry, selecting well-marked varieties, so that there shall be no
doubt as to the identity of specimen and quarry or ledge. In
this way it is shown that the "drift" material of Iowa, in
general, came from the northeast, of Indiana and Ohio from the
north, of New England from the northwest. In Indiana, Ohio
366 PRACTICAL LESSONS IN SCIENCE.
and Michigan nearly all the varieties of granitic rocks may be
found among the boulders of the hard pan. Large quantities of
drift have been transported from 300 to 500 miles, but for the
most part the transportation has seldom been more than 100
miles. But little is known about the thickness of the ice ; it seems
to have covered the mountains of New England, but was doubt-
less much thinner west and south, for in southwestern Wisconsin
and vicinity there is a large area over which no glacial ice ever
flowed; it is a "driftless area." The flow of ice over such low
gradients as seemed to prevail during the glacial period is not
well explained. It flows over similar gradients in Greenland, so
that it is not impossible, only difficult to understand. It is also
difficult to understand how the ice became so loaded through and
through with rocks, boulders, etc.
The Laurentian tableland includes the oldest mountains, and
the great lakes occupy the oldest valleys on the continent.
Their great depth, some of them reaching two or three hun-
dred feet below the level of the sea, is not only evidence of
great erosion, but of the fact that the whole region for ages stood
at least from 1,000 to 1,500 feet higher than now ; for those old
channels must have had outlets to the sea. The glacier smoothed
up these old channels, perhaps changing their form somewhat,
but not materially; and when it retreated, its load of clay and
rocks filled many of them, and parts of many more, result-
ing in the formation of thousands of lakes, great and small, over
some parts of the glaciated area.
The rocky bed of the Cuyahoga river, at Cleveland, is about
225 feet below the present level of Lake Erie. The beds of other
tributaries of Lake Erie are at about the same distance below its
level, which seems to indicate that the lake occupies an old valley,
which formerly had an outlet to the sea at a much lower level.
There is evidence of such a channel, now filled with glacial mate-
terial, extending from Lake Erie to the head of Lake Ontario.
The filling up of this old channel changed a portion of a river
valley into a lake, and the waters of this lake, finding an outlet
across the divide to Lake Ontario, formed the Niagara river, with
LESSONS IN GEOLOGY. 367
its famous rapids, gorge, and cataract. Some think the old out-
let of the Ontario valley was by the Mohawk and Hudson river
valleys, and that the St. Lawrence flows in a recent channel, at
least for a portion of its course. Lakes Huron and Superior are
supposed to have had their outlet by the Ontario valley, but
many suppose Lake Michigan flowed toward the Gulf.
The glacier as it advanced southward drove before it all the
plant and animal life of the region, carried away all the soil, and
in many respects changed and modified the surface features of the
country. Then retreating, it deposited material for a new soil,
obliterated many old channels and changed many others, formed
ridges, hills, and lakes, in fact changing the whole face of the
country.
The cause of the climate of the glacial period is one of the
questions which geologists have not satisfactorily answered.
The elevation of northern regions with the advance of the ice,
and their depression as the ice retreated, seems to connect the
events in the relation of cause and effect. Such elevation might
have closed Bering strait, and shut the Gulf stream from the
Arctic ocean, and yet it does not seem to geologists generally as
if such elevation was adequate to the effect. Some have at-
tempted to find a cause in the changes in the eccentricity of the
earth's orbit, combined with other astronomical causes, but this
idea does not appear satisfactory. Others have supposed a de-
pression of the Isthmus of Panama, allowing the Gulf stream to
pass into the Pacific ocean, as an adequate cause; but there is
no evidence of such depression during glacial times, and nothing
to show that it would have affected the climate if there had been.
Other theories have been advanced, but have not been received
with favor. At present it can only be said that most geologists
acknowledge elevation as a cause, but think that some other as
yet unexplained cause must have acted in connection with eleva-
tion to have produced the results.
When did the glacial period begin, how long did it continue,
and how many years has it been since the ice retreated? are
questions often asked of the geologist. No very definite answer
368 PRACTICAL LESSONS IN SCIENCE.
can be given to the first or the second questions, but many at-
tempts have been made to answer the third.
It is generally supposed that the gorge of the Niagara has
been formed since the retreat of the ice, and that if we knew the
age of the gorge we would know how long it has been since the
glacier. Early estimates of the age of the gorge varied from
35,000 to 100,000 years, but later ones vary from 4,000 to
10,000 years. The river at the present time is cutting back at
the rate of about 2.4 feet per year, or a mile in about 2,200 years,
and the gorge in about 15, 400 years. But there are evidences
that the river found considerable work already done on the
gorge when it began to flow, so that perhaps 7,000 years would
be a safe estimate for the age of the Niagara gorge, and for the
time that has elapsed since the ice retreated from the St. Law-
rence valley.
The glacier was a very effective erosive agent, but whether
more effective or rapid than air and water is very doubtful.
CHAPTER LI.
THE CHAMPLAIN AND TERRACE PERIODS.
AFTER a long period of elevation the northern portions of
Europe and North America were slowly depressed and the ice be-
gan to retreat. The floods from the melting glacier opened many
old drainage channels that had long been closed by glacial debris.
But as the depression continued, the streams became sluggish
and began to silt up their channels with clay, sand, gravel, etc.
At length over great areas drainage almost ceased, and wide,
shallow lakes and marshes and ponds were formed, their surplus
waters carried away by broad, sluggish streams. The waters and
waves of these shallow lakes dissolved and broke down much of
the hard pan and assorted it into beds of sand and clay. There
were several slight oscillations of the crust, giving rise to differ-
ent conditions, so that in some localities there are as many as
six or seven layers of different kinds of material lying over the
boulder clay.
The Orange sand or bluff gravel, a thick deposit of glacial
material along the Mississippi river as far south as Louisiana,
may have been transported by glacial floods early in this period.
Later the Erie, Champlain and other clays were deposited, and
later still, over much of the glaciated area, reaching far down the
Mississippi, thick beds of fine clay or loess were formed.
The ice seems to have retreated more rapidly in the west than
in the east, so that when the region now occupied by the great
lakes was free from ice, the natural outlet of the Ontario basin
was still closed by the glacier. These valleys, filled with water
from the melting ice, formed a great inland sea with shores of
ice on the east and north, discharging its surplus waters toward
the Gulf. An old beach ridge, nearly parallel with the shores of
Lake Erie, shows the level of this old lake to have been at one
L. 8.-5K
370 PRACTICAL LESSONS IN SCIENCE.
time at least 200 feet above the present level of Lake Erie. Other
beaches, at lower levels, seem to indicate that the barrier was cut
down at an irregular rate.
Icebergs were doubtless common on this inland sea, and per-
haps on other lakes of this period. It is thought by many that
they had much to do with distributing glacial material near the
margin of the drift area in the southwest, as there is often no evi-
dence of glacial ice having reached that region.
The Champlain period of Europe was much the same as in
North America, and is often called the era of fresh water for-
mations.
The glacial period merged gradually into the Champlain, and
the Champlain as gradually into the terrace period. The north-
ern regions began to rise again, sluggish rivers became narrower
and more rapid, other rivers were formed, lakes and inland seas
were drained away, carrying along great quantities of fine silts
and sands ; and at length the slender, rapid rivers began cutting
out channels in the sediments that filled the older, deeper,
wider valley. In this way bluffs and terraces were formed which
gave name to the period. Sometimes several terraces have been
formed, which are often known in common language as first bot-
tom, second bottom, etc.
Where the drainage was not complete, extensive marshes or
wet prairies and multitudes of little ponds or lakes are the only
remains of wider bodies of water.
The life of the quaternary was interesting as being the culmi-
nation of the mammalian type.
The plants and marine mollusca that during the glacial period
lived in what are now temperate regions, are represented at the
present time by species living in polar or sub-polar climates. As
the ice retreated both plants and mollusca migrated northward.
Very little is known about the birds, fishes and reptiles of the
period, but it is supposed that there was not much change, sim-
ply a migration southward as the ice advanced and a migration
northward as the ice retreated.
The mammalia of this period were abundant, varied in form
LESSONS IN GEOLOGY. 371
and often of enormous size. Their remains are found in caves, in
marshes, and sometimes in the drift and silt of streams. In Eu-
rope more have been found in caves, while in North America more
have been found in swamps and bogs.
The mastodon, two species of elephants, two great bisons, a
giant stag, large horses and beavers, the megalonyx and the tapir
were the most interesting among the herbivorous animals; there
were one lion and two bears to represent the carnivora. In South
America there were several large edentates, a mastodon, with
wolves, panthers and others. But Europe and Asia had the
richest variety of species, especially among the carnivora. In the
bone caves of Europe they have found remains of the cave bear,
cave hyena, cave lion and two tigers, all of remarkably large
size. Several elephants, a rhinoceros, a hippopotamus, horses,
oxen, the great Irish elk and others represent the herbivora. The
mammoth, a species of elephant, was over twice the bulk and
weight of modern elephants. Some have been found frozen in the
ice of Siberian swamps; they were covered with hair and wool,
and the flesh, preserved by cold, was eaten with relish by dogs.
In one cave the remains of 800 bears were found, and one con-
tained the remains of at least 300 cave hyenas.
The difference between the plant life of the quaternary and the
present was not great, neither was the difference between the
lower animals of that time and the recent period, and while, at
first, the difference between the mammalia seems great, yet the
type is still the same; many species of mammals, some birds
and others, have become extinct, but in general the change has
been slight. There is no definite event that marks the close of
the quaternary and the opening of the recent age, or age of
man. The country rose out of the waters of theChamplain
period, formed a soil, was clothed with vegetation, and entered
upon the various lines of activity now in progress.
The Mississippi river is silting up its channel, which indicates
that the region of its upper course is slowly settling. Old beach
lines along the shores of Lake Ontario, that, when made, were
level, have been raised considerably toward the east, so that the
372 PRACTICAL LESSONS IN SCIENCE.
two portions now differ in level. There are upward and down-
ward movements in Norway and Sweden and along the Mediter-
ranean sea. There are volcanoes and occasional earthquakes,
showing that one group of geological forces is still in operation.
The formation of sediments along river beds and at their
mouths, along the shores of lakes and of the sea, the formation
of sand dunes, of bog iron ore, and bog limestone, and the action
of rain and frost, etc., in furnishing the materials for the sedi-
ments, shows another set of forces at work also. The geological
agencies are doubtless working just as vigorously at the present
as ever in the history of the earth; but one set works so slowly
that we do not notice them, and the others are so common that
we do not think of them as geological.
The large and fierce animals that dominated the Quaternary
age passed away, and those of a smaller size and more tractable
disposition appeared in their stead. And the earth, with pure
air and water, with temperate climate, with useful plants and
animals, after ages of preparation at last became a fit place for
the home of man.
Man has doubtless lived on the earth for many centuries, was
contemporary with many of the large mammals, and with the
later events of the Glacial and Champlain periods, but does not
seem to have become the dominant type of life until quite recent
times. Remains of man are found in caverns, lake beds, peat
bogs and similar places, and we find the tools of bone, wood
and stone which he used ; and we may know something of how
he lived from finding fragments of bones and shells with tools,
etc., in caves, and at particular places along the shores of lakes
and seas. But the story told by these remains is very fragmen-
tary and not easily interpreted, but seems to indicate at least a
low stage of culture for primitive man.
Considered as an animal, man's appearance on the earth was
abrupt, as abrupt as the appearance of vertebrates in the Dev-
onian, and this idea is intensified when we consider man's intelli-
gence.
What is th ag of the earth? This is an interesting question,
LESSONS IN OEOLOOY. 373
often asked, but seldom answered with any degree of satisfaction.
The matter of geologic time bears on so many important ques-
tions that much time has been given to the investigation of all
available data on tl^ subject, and many estimates have been
made. The early estimates in general were large. Sir Charles
Lyell considered that the earth was at least 240,000,000 of years
old. Dr. Charles Darwin thought that 200,000,000 of years
could hardly be sufficient for the evolution of organic forms. Dr.
A. Winchell, 1883, estimates the time since the crust was formed
at 3,000,000 years. Mr. W. J. McGee, 1892, estimated the age
of the earth at 15,000,000, and Prof. Warren Upham, 1893.
thinks the time necessary for building up the stratified rocks and
developing the plant and animal life of the world must be about
100,000,000 of years. These results would seem to indicate that
the data were not satisfactory, or else that they were not cor-
rectly interpreted. Mr. Charles D. Waleott, Aug. 17, 1893, in an
elaborate paper reviews the whole question, working out an esti-
mate that seems conservative when compared with those given
by other investigators. Confining his investigations mainly to
the cordilleran region of North America, he shows that erosion
and deposition of mechanical and chemical sediments have al-
ways been going on at substantially the same rate. While one
foot in 3,000 years is usually considered an average rate of denu-
dation, he assumes a rate of one foot in 200 years for the region
under consideration. Then, carefully estimating the area of ero-
sion, the area of deposition, and the thickness of sediments, both
mechanical and chemical, he estimates the cenozoic, including gla-
cial or pleistocene, at 2,900,000 years; mesozoic at 7,240,000
years; paleozoic at 17,500,000 years; algonkian at 17,500,000
years and archsean at 10,000,000 years, a total of 55,140,000
years. He concludes that the time since the archaean age lies be-
tween 25,000,000 or 30,000,000 of years as a minimum and
60,000,000 or 70,000,000 as a maximum time.
The physicist, calculating on the time necessary for the earth
to cool to its present condition, limits the time to from 10,-
000,000 to 30,000,000 of years. These estimates may not be very
374
PRACTICAL LESSONS IN SCIENCE.
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7 PRACTICAL LESSONS IN SCIENCE,
satisfactory, but they give us some idea of how difficult it is to
say how old the earth is. Geological time is divided into eras,
ages, and periods, and the rocks into systems and groups. And
once there were primary, secondary, tertiary, and quaternary
systems or ages. The primary and secondary have been subdi-
vided, and the names dropped, while the terms tertiary and quat-
ernary have been retained.
Geological studies began in Europe, and the names were de-
rived from localities, as Devonian, from the town of Devon, and
Silurian from the town of Silures, in England, Jurassic from the
Jura mountains, etc. The first important geological work done
in this country was in New York. Some European names were
retained, but many local names were adopted, as Niagara, Ham-
ilton, Chemung, and other states have followed the same custom,
so that we have Knoxville, St. Louis, Keokuk, limestones, etc.
The period or group names for the Mesozoic and early Cenozoic
eras in this country are derived mainly from localities in the
western mountain region, where those rocks are most abundant.
With increasing investigation and knowledge the nomenclature
and classification will change, but the diagram on two preceding
pages represents in a general way the present condition of the
subject.
CHAPTER LII.
THE THEORY OF ORGANIC DEVELOPMENT.
WE have learned something about the different kinds of matter,
and of the forms under which they appear; and we have studied
the forces acting upon matter, and the laws in accordance with
which they are supposed to act. In this study we have learned
that the molecular or atomic theory of matter, the law of defi-
nite proportions in chemical combinations, the undulatory the-
ory of light and heat, the conservation of energy, and the theory
of universal gravitation, are the great propositions or theories
which determine the lines of scientific thought, and around which
all the varied phenomena of the material world cluster for corre-
lation and explanation. These theories may not stand the test
of future investigation; they may prove inadequate, may be
modified, may give place to others; but at present they are the
best the only working theories we have and through them
most of the activities of nature around us may be explained ;
hence, some knowledge of them is valuable in any system of
education.
We have studied the different forms of life which occur on the
earth. In them we found matter under the influence of a new
force, displaying quite a different cycle of events. A group of
molecules, endowed with life, comes into existence, is developed to
maturity , reproduces its kind, and dies. The history of life forms,
as individuals, is simply this and nothing more all their en-
ergies are directed toward growth and reproduction. Primarily,
their relations are to parents on the one side, and to offspring on
the other; incidentally, they have a wide range of relations with
other forms of life, and with the inorganic world. Living beings
differ widely in form, structure, and intelligence, and in many re-
spects the phenomena of life are more interesting than those of
(877)
78 PRACTICAL LESSONS IN SCIENCE.
the inorganic world; and the question is often asked, how do
you account for, and explain this bewildering variety of life
forms and the complex phenomena incident to their existence?
Until quite recent times, most people believed that the sun,
moon and stars, the earth, with all its varied forms of life, and
all material things, were created out of nothing. No one could
comprehend the idea, but few doubted its truth. But as man be-
came more intelligent, the idea of the creation of matter from
nothing began to be questioned, not irreverently, but simply
from a desire for the truth. This inquiry brought out the fact
that the word creation, as used, had different meanings, and the
idea began to grow that perhaps matter in its essence is eternal,
was not created from nothing, but was moulded or shaped over
into its present forms, something as the potter moulds the clay,
or the workman makes a watch. And it was believed that every
particular form of life was the result of a special act of creation.
But a careful study of the phenomena of life has led students of
botany, zoology and geology to the conclusion that special crea-
tion was not God's method in nature, but that some form of
evolution or development was most probably the method
employed. Organic development, then, is the great proposi-
tion or theory around which the facts and phenomena of the
vegetable and animal kingdoms gather for correlation and
explanation.
This theory may prove inadequate ; may not stand the test of
future investigation; but it is the only one now recognized by
scientific men. No other theory ever promulgated has been as
prolific of good results. It has stimulated thought in every de-
partment of human endeavor, not only in all lines of scientific
work, but in all lines of social and historical work. Thus, whether
true or false, every intelligent person should know at least some-
thing of the grounds for its existence. Evolution in its present
form is a modern theory which required for its elaboration an
amount of knowledge whick could only be acquired gradually
through years of scientific research. But the idea of evolution is
by no means recent; some of its problems have been considered
LESSONS IN QEOLOGI. 379
in almost every system of philosophy. They were matters of
speculation among the East Indians, the Arabs, the Jews, the
Greeks and the Schoolmen, and they have been discussed by later
philosophers, as Hobbs, Descartes, Locke, Kant, Hegel and
others. But the honor of bringing the doctrine before the world
in such a clear and forcible way as to command universal atten-
tion belongs to Charles Darwin and Russel Wallace, whose first
publications were in 1858 and 1859.
One of the first steps toward this theory is the observed unity
of all forms of life, as shown by the fact that plants and animals
have about the same chemical composition; that plant and ani-
mal protoplasm appear to be identical; that the germinal vesicle
and sexual reproduction are similar in each; the difficulty in dis-
tinguishing between the lower forms of animals and plants; that
plants and animals are cellular in structure; that plants and an-
imals, as individuals, develop from a bit of structureless proto-
plasm to a complicated organism, each growing by the simple
multiplication of cells; and the fact that animals and plants are
affected in much the same way by physical environment all of
which with many other things point toward the unity, the con-
tinuity of life on the earth; plants and animals possibly develop-
ing from a common germinal stock, plants through fixed forms,
animals through motile forms.
Another is the fact that offspring inherit some of the charac-
teristics of the parents, but not all. A number of children may
be similar to their parents and to each other in many respects,
the family features and traits may be well marked, yet each has
his pecmliarities, differing from all the others in some particulars.
This fact is expressed in the phrase, " heredity, or descent with
variation." Variation in size and activity is common among
men and domestic animals, and among wild animals as well, va-
riations in size sometimes amounting to as much as one fourth
of the average size of the species. There may be variations in
the length of legs, breadth of wings, size of fins and in other respects.
Then the fact that a pair of the slowest breeding animals, or
plants if unchecked, would stock the earth to repletion within
S80 PRACTICAL LESSONS IN SCIENCE.
1,200 or 1,500 years. Thus with the great numbers of different
kinds of animals and plants there must be a continued struggle
for existence, animals of the same kind struggling with each
other, and with other kinds of animals and with plants, and
plants struggling with each other and with animals, and all per-
haps struggling against unfavorable climatic conditions. In
this conflict many in fact, most perish, the few only survive.
The strongest, the most active, the most intelligent, those that
are in some way superior, survive and produce offspring. This
process Darwin called " natural selection," Spencer calls" survival
of the fittest." In this way Mr. Darwin believed new species were
formed instead of by special creation, and that animals were de-
scendants from at most only four or five progenitors, and plants
from an equal or lesser number. Thus, he says, "From the war of
nature, from famine and death, the most exalted object which we
are capable of conceiving, namely, the production of the higher
animals, directly follows." " There is grandeur in this view of life
with its several powers, breathed by the Creator into a few forms,
or into one; and that from so simple a beginning endless forms
most beautiful and most wonderful, have been and are being
evolved."
Many things seem to point toward the probable truth of the
theory. There is no doubt about the fact of individual develop-
ment; we are all descended from Adam by natural processes;
each individual a complex organism, developed from structureless
protoplasm. If evolution is God's method with the individual,
there seems to be no reason why it may not be His method with
the species, genus, etc.
In horses, the bone above the fetlock joint corresponds to the
middle bone of the hand. On each side of this bone there is a
little bone called a splint bone. These splint bones seem to be
of no use 01 value to the horse, and on the theory of special crea-
tion they cannot be explained, but on the theory of descent they
represent the second and fourth digits of some three or five-toed
ancestor, and thegeological record shows that thehorsehad such
ancestors. Many similar cases might be mentioned. Most ani-
LESSONS IN GEOLOGY. 381
raals are able to move their ears freely and many can move por-
tions of the skin ; in general, man can move neither the ears nor skin
and yet muscles for moving the ears and scalp exist in an aborted
form, and occasionally individuals can use them. The presence
of these muscles is not explained by special creation, but on the
theory of descent with variation they indicate that some ances-
tor of man had use for such muscles.
The embryos of the higher animals in their development simu-
late the forms of lower animals; the embryo of the chick shows
the gill slit of fishes and the teeth of reptiles, and it is not till
quite late in its embryonic life that the human embryo takes on
or begins to develop human characteristics. These phenomena,
utterly unexplained on one theory, are at least partially elucidated
under the other. According to the theory of evolution, the devel-
opmental history of the individual appears to be a short recapitu-
lation of the course of development of the species. There seems
to be a correspondence between the individual development of the
higher animals and the progressive advance of organization
in the whole animal series. The geological record gives interest-
ing evidence in the case; it is necessarily an imperfect record, for,
as a rule, only the hard parts of aquatic life would regularly be
preserved, and only a small part of the record has been or can be
examined. When the crust was first formed, no life of any kind
could exist; but as the earth cooled water and other substances
were condensed from the atmosphere, and the inter-actions be-
tween the atmosphere, water and crust removed impurities from
the air and water, and put them away in permanent form, leav-
ing the water and air in a. condition favorable for the lower forms
of life. And such forms of life appeared in great abundance, as
the thick beds of iron ore and graphite in the older rocks are
supposed to show. The life must have been of low form, as none
other could have existed under the conditions which probably
prevailed. As these chemical reactions continued, the plant and
animal life also removing impurities, the air and water gradually
became fitted for higher and higher types of life. The early forms
of life seem to have been flexible and abundant, so that they
382 PRACTICAL LESSONS IN SCIENCE.
adapted themselves to changing conditions and crowded into
every new addition to the domain of life. As conditions changed
some forms could not adapt themselves, and, overcome in the
struggle, passed away and others took their places. It is esti-
mated that there were more than thirty complete changes of
species during the paleozoic time. So that the principle of the
" survival of the fittest " seems to have prevailed from the very
beginning of life on the earth.
The graphite of the early ages, the limestones of the Silurian
and later ages, the coal of the carboniferous, all represent impuri-
ties removed from air and water by different forms of life. It is
interesting to note that each form of life has helped to prepare
the way for other and higher forms, generally lessening the op-
portunities for their own existence. The coal plants not only ren-
dered the air more pure, but so changed it as to allow the sunshine
to reach the surface of the earth with vigor enough to promote
the growth of flowering plants.
Every step in the history of the earth prior to the advent of life
was in preparation for life, and every step afterward was in prep-
aration for higher forms of life.
But the geological record at present is by no means contin-
uous; the Wank between the archaean and the Cambrian equals
nearly one third of the whole record, leaving the origin of the
protozoa, coelenterata, arthropoda, echinodermata, mollusca,
molluscoida and tunicata without record. Some of the rocks of
this period have been found, and some fossils have been discov-
ered, but the rocks are so highly metamorphic that there is little
hope of ever finding anything like a complete record of the period.
In this period the protophyta, zygophyta, oophyta, and carpo-
phyta had their origin, of which no trace has been found in the
rocks.
Fishes, the first of the vertebrates, appeared somewhat ab-
ruptly in the later part of the Silurian age. It is claimed that
the first so-called fiiJies were of a comprehensive type, from which
both fishes and reptiles were derived, but transitional forms are
not numerous. And so on, the geological record inageneral way
LESSONS IN GEOLOGY. 383
sustaining the development theory, new discoveries as a rule
being favorable to that idea.
While the testimony is fragmentary, and the evidence incom-
plete, yet there is scarcely a botanist, zoologist or geologist of
note, who does not believe that some form of development was
God's method of creation. Progress means the laying aside of
ideas which are the result of limited knowledge, and the accept-
ance of other ideas, the result of wider information. The world
had to give up the Ptolemaic theory, had to accept the theory of
universal attraction, had to give up the idea that the earth was
not more than 8,000 or 10,000 years old, had to give up the
corpuscular theory of light, had to accept the theory of conserva-
tion of energy, had to change its theory as to the treatment of
the insane. These and many other changes hare been ma^e, as
the result of wider knowledge, and these changes were made with-
out detriment to any, but rather resulted in benefit to all. So if
we have to give up the idea of special creations, and accept the
idea of development, no damage will be done.
Some persons object to the theory of evolution as atheistical.
Dr. Asa Gray, a strict Presbyterian, Prof. Joseph Le Conte, an
earnest Christian, Dr. Alexander Winchell, a Methodist, and hosts
of others equally prominent as believers in God, would unite with
Prof. John Fiske in saying, " The doctrine of evolution asserts as
the widest and deepest truth, which the study of nature can dis-
close to us, that there exists a Power to which no limit in time or
space is conceivable, and that all the phenomena of the universe,
whether what we call material, or what we call spiritual, are
manifestations of this infinite and eternal Power."
CHAPTER Lin.
SUGGESTIONS AS TO LINES OF STUDY.
THE first and perhaps the most important work to do in be-
ginning the study of the geology of any locality is topographic.
The topography of a place includes its actual location, its rela-
tive position as to mountains, hills, valleys and plains; as to
lakes, ponds, swamps, marshes, rivers and other streams. It
also includes a study of the soil and vegetation, and as these and
other topographic features depend largely on climatic conditions,
temperature, winds and rainfall need to be considered in topo-
graphic work.
This work is not only an important introduction to geological
investigation, but the items considered in topography constitute
the environment of the various forms of life, and need to be un-
derstood and considered in any good botanical or zoological
work. Topographic work is not only important, but easy and
interesting.
Actual location is readily ascertained in all those states where
the rectangular system of survey was used. Under this system
principal meridians were located with great accuracy, and the
country on each side was divided into ranges six miles wide by
secondary meridians, as nearly parallel with the primary merid-
ian as the spherical form of the earth would permit. The first
principal meridian is the boundary between Ohio and Indiana in
longitude 84 51' west; the second runs through Indiana in
longitnde 86 28' west; the third through Illinois in longitude
89 10' 30" west; the fourth is in longitude 90 29' 56" west,-
the fifth is in longitude 90 58' west; the sixth in longitude 97
22' west, and the Michigan meridian in longitude 84 19' 9 //
west. Others were located as occasion required. A base line
(384)
LESSONS IN GEOLOGY.
385
was also run with great care perpendicular to the principal me-
ridian, and then lines were run parallel to the base line at inter-
vals of six miles on either side, dividing the ranges into townships
about six miles square.
On account of the form of the earth it was necessary to estab-
lish correction, or secondary base lines at certain intervals. The
base line for Indiana and Illinois is in 38 58' 12" north latitude.
N
1
(3)
(2)
(1)
3
w
13
(4)
(5)
(6)
E
Base.
Line.
i
1
2
(9) I
(8)
(7)
s
fl) Township 2 north of range 2 east.
(2) Township 2 north of range 1 east.
(3) Township 2 north of range 1 west.
(4) Township 1 north of range 1 west.
(5) Township 1 north of range 1 east.
(6) Township 1 north of range 2 east.
(7) Township 1 south of range 2 east.
(8) Township 1 south of range 1 east.
(9) Township 1 south of range 1 west.
The ranges are designated by number east or west of the
principal meridian and the townships by number north or south
of the base line; as shown in the above diagram.
A township is six miles square and is divided into thirty-six
L. S. 25
386
PRACTICAL LESSONS IN SCIENCE.
square miles, or sections, which are numbered from 1 to 36,
inclusive; as shown in the diagram below.
The township is not perfect in form, neither is the section, but
the township is so divided as to throw most of the irregularity
into the north and west tiers of sections which are often frac-
tional, and there are fractional sections along lakes and large
streams of water.
6
5
4
3
2
1
7
8
9
10
11
12
18
17
16
15
14
13
19
20
21
22
23
24
30
29
28
27 .
26
25
31
32
33
34
35
36
A section contains about 640 acres. It is divided by lines
through the center, parallel to its sides, into quarter sections of
160 acres each, and these into quarter quarters of 40 acres each,
and so on as far as desirable.
A section is one mile, 80 chains, 320 rods, or 5,280 ft. square,
the quarter section is one-half mile, 40 chains, 160 rods or 2,640
ft. square, and the quarter quarter is 80 rods or 1,320 ft.
LESSONS IN GEOLOGY. 387
square. The system is simply the application of latitude and
longitude to land measurement, and was first used in Ohio.
The following sample description will show the practical work-
ing of the system : Five acres being the south half of the north-
west quarter of the northeast quarter of the southeast quarter
of section twelve (12), township ten (10), north of range nine (9),
west of the second principal meridian. From the foregoing one
can easily interpret the description of an ordinary deed. If you
wish to locate a certain tract of land, hill, stream, or ledge of
rock, borrow a deed of the land or of some in the immediate
neighborhood; make a diagram of a township and locate the
land described in the deed on the diagram. Sometimes the one
description solves the whole question of location; sometimes one
may have to consult several deeds, and may need to ask some one
to point out a few section lines and corners before a given locality
is fixed satisfactorily.
After locating a few prominent points, find out by measure-
ment where the streams you wish to locate cross the section lines,
and if very crooked, where they cross the quarter-section lines
also, then map in the stream across the section as accurately as
possible. In this work a pocket compass is useful. For measur-
ing use the surveyor's chain or tape measure, if possible, but for
much of such work many people can learn to step off the distance
with sufficient accuracy. A little practice in walking over a meas-
ured distance, as 100 feet will enable one to walk with 2-foot
step. The field work for some of the finest geological maps I ever
saw was done with a pocket compass and step measurement. The
elevations were taken with an aneroid barometer. But the eleva-
tion of a moderately steep hill can be determined quite closely
without instruments. Measure accurately the height of the eye
from the ground, then practice in "standing straight" and
''looking level " will soon enable one to stand at the foot of a hill
and note on its side a point on the level of his eye, then advanc-
ing to that point, note another, and so on until the summit is
reached, when the product of the number of stations by the
elevation of the eye gives the approximate elevation of the hill.
388 PRACTICAL LESSONS IN SCIENCE.
Locate and map the streams, hills, outcrops of rock, and other
prominent physical features, also the roads, farm lines, and
houses of the neighborhood or district you are intending to
study. In this work school children and their parents can ren-
der material aid. The children should make maps for themselves;
in no way can map drawing be made more interesting and prac-
tical than when familiar ground is made the subject of study.
While the map is in process of construction other work may be in
progress. Perhaps the most important group of material phe-
nomena affecting man is the one called the weather or climate.
Many of these phenomena and their relations can be observed,
and some idea of future manifestations can be derived, from an
intelligent knowledge of the present. It is one of the latest deduc-
tions of science that it pays to collect and study " weather saws,'*
to observe and note the relations of sunshine and cloud, wind,
rain, etc. We have in the barometer an artificial weather glass,
but among plants and animals there are many natural barome-
ters or weather indicators. Cultivate the powers of observation
by noting the aspects of the weather, and requiring the children to
do the same; observe which way the wind blows, morning, noon
and night; whether the day was clear, cloudy or rainy; any
marked changes of temperature during the day or night should
be noted, and the observations of each day should be made a
matter of record. Collect " weather saws " and study them, some
may be fanciful, but many will be found to stand on a scientific
basis. In connection with this work note the habits of plants
and animals that appear to relate to climate, also study the
weather predictions from Washington and compare them with
your own observations.
In winter corn and beans may be grown and each studied in dif-
ferent stages, gaining ideas of the seed embryo, cotyledons, ordi-
nary leaves, etc., and noting the distinctions between the great
classes of exogenous and endogenous plants. Much also may be
learned from the study of the various house plants so common
everywhere. Make a list of the different trees and shrubs of the
neighborhood, studying carefully the peculiarities that distin-
LESSONS TN GEOLOGY. 389
guish them in winter. Get specimens of the wood of different
trees and learn to distinguish them by the character of the wood.
Most insects die in autumn, being represented during the winter
by eggs, larvae, or some imperfect form, but a large number live
through the winter, usually in a torpid state. They are perhaps
more commonly found under decaying logs, in rotten wood, or
between the bark and wood and similar places. A collection of
such insects with notes of the circumstances under which they
were found would be interesting and valuable. Whilelooking for
insects one may find salamanders, mice, snail shells and other
things of interest. In every locality a number of birds, as owls,
hawks, woodpeckers, shrikes, chickadees, blue jays and others are
found during the winter; make a list of these winter birds, and
note their habits, the food they eat, and the places in which they
are found.
As spring approaches watch for signs of life in the trees and
plants; note which trees and shrubs blossom before putting out
their leaves, and the plants that send up the first flowers; study
the trees and shrubs in their spring and summer vegetation, and
note the colors the leaves of different plants and trees assume in
autumn. Note the soil and surroundings in which the different
plants and trees seem to thrive best; some will be found to have
a wide range, others will be confined to narrow limits.
Observe, also, the returning summer birds, which come first, and
when they come, and how soon after the first one is seen do the
birds of its kind become common. Study the feeding and nesting
habits of the birds, and note the localities the different kinds
seem to prefer. Notice how completely the opening flowers and
returning birds depend on the weather. At certain times in the
spring birds visit us for a few days on their journey to more
northern regions, and again in autumn on their return to the
warmer regions. Make notes of these dates and of the birds
passing.
The study of the smaller mammals, as mice, moles, shrews,
ground squirrels, etc., is an interesting and neglected field of ob-
servation. The study of reptiles, batraehians, crustaceans, mol-
390 PRACTICAL LESSONS IN SCIENCE.
lusks and other forms of life well repays the time spent in making
the investigations.
In connection with the topographic work make notes of geo-
logical features, the kinds of rock, thickness of beds, the effects
of weathering upon them, and their relations to each other.
Study water sheds and divides; you can find as typical examples
of each in every township as you could find in the Rocky moun-
tains. Study the valleys of the streams, the upper, middle and
lower course. Notice the work done by the streams, eroding
here, building up there busy everywhere. Observe in how many
different ways during the year material is removed from an
eroding bank. Where the stream is making ground note the
order in which different forms of vegetation occupy the new-made
land. The study of fish and other life of the streams is interest-
ing and profitable. Much of this study should be general, en-
gaged in by the whole school, and a little time should be set
apart each day for report of observations. Other work may be
delegated to certain pupils according to their liking or aptitude.
Do as much work as you can and do it as well as you can, and
you will be astonished at the amount accomplished during a
season.
INDEX.
PAGE
Abdomen of Grasshopper 280
Abdomen of Insects 276
Absolute Zero 42
Acids defined 118
Acids named 119
Acetylene, how formed 134
Acetic Acid, composition 177
Acid of Lemons, etc 180
Acorn, the parts of 228
Acarina, Mites and Ticks 272
Adhesion defined 21
Adaptation illustrated 246, 302
Adductor Muscles 286
Age of the Earth 372
Air, properties of 115
Air, composition of 116
Air, pressure of 39
Air Plants described 246
Aluminium described 161
Aluminium, compounds of 161
Alumus, different kinds 161
Albumen, composition of 176
Alcohol, composition of 177
Alternation of generations 201
Allantois, purpose of 298
Algonkian Era described 349
Ammonia, composition of 116
Ammonium , a compound 117, 153
Ammonium, chloride 117, 153
Ammon mm, nitrate 118
Ammonium sulphide 153
Amphibia described 296
Amoeba, description of 259
Amnion, a membrane 298
Aniline and Aniline Colors 169
Antheridia described 200
Anthophyta defined 207
Andro2cium defined 224
Annuals defined 233
Annelida described 265
Autenuse defined (crayfish) 270
Antennulse defined 270
Ants, communities of 282
Anthropomorphse 314
Annuals as geological agents 347
Aphidse, Plant Lice 281
Apidse or Bees described 283
Apoda, description of 297
Aristotle, theories of 14
Arsenic and its compounds 144
Arsenical Colors 145
Arsenic, tests for 145
Archegonia described 200
Arthropoda described 258, 267
Arachnida described 272
Araneida, true spiders 272
Artiodactyla described
Archsean Era described
Archaean Rocks, kinds of
Assimilation defined
Astronomical Geology
Atoms and Atomic Theory. .
Attraction defined...
PAGE
...348
...349
...188
... 316
.17,104
. 19
Attractive Forces, effect of 25
Auditory hairs and sac 270
Avogadro's Law stated 123
Aves or Birds described 300
Avalanches of Rock, etc 341
40
95
99
118
156
Barometer, principle of
Batteries, Electrical, described
Batteries, Storage, described
Base, definition and composition.
Barium and its compounds ..... ..
Bacteria, description of ............. 191
Bark, manner of growth ............. 217
Banana Family described ........... 226
Barnacles described ................ 271
Batrachia described ................ 297
Basalt, composition of .............. 323
Base lines and correction lines ... .384
Benzole, composition of ............ 169
Bees or Apidse described ........... 288
Bismuth and its compounds ....... 166
Biennials defined .................... 233
Bivalve Shells described ............ 286
Birds, description and study of ..... 301
Birds, development of ............... 302
Botany, treats of what ............... 12
Boiling Point explained ............. 29
Boron and its compounds ........... 136
Botany, general statement .......... 182
Botany in winter ..................... 388
Bony Tissue described .............. 253
Boulders, from the drift ............. 364
Boulder Clay or Till ................. 364
Brittleness defined .......... ........ 32
Breezes, Land and Sea ............... 49
Bromine described ............ ...... 124
Brick, made of what ................. 161
Bread making explained ............ 178
Bryophyta described ................ 200
Brittle Stars described ............. 262
Bryozoa described ................... 289
Brachioppda described .............. 289
Bunsen Burner described ........... 133
Butterflies, description of ........... 281
Buckwheat Family described ....... 229
Capil lary Attraction denned ........ 22
Capstan described ................... 66
392
INDEX.
Camera described
Carbon, different forms of
Carbon, Oxides of
Calcium and its compounds . . .
Carbolic Acid, source of
Camphor described
Caoutchouc, properties of
Cambium Layer described
Canning, process explained
Carpophyta described
Calyx and Sepals defined
Catkin, description of
Cactus Family described
Cartilage described
Carapace, formed how
Cavicornia described
Carnivora, description of
Canidse or Dogs described
Calcite, composition of
Carbon Dioxide and Water
Caves, how formed
Cambrian Rocks, kinds
Cambrian Life, nature of
Carboniferous Age and Life
Cellulose, composition of
Cells of Plants described . . . . \
Cells of Animals described
Cells, Products of
Celery described
Cestoda described
Cephalothorax described
Centipede, description of
Cephalopoda described
Cetacea or Whales described . .
Cervidae or Deer described
Cenozoic Era described
Chemistry, deals with what
Chemical Attraction denned. .
Chemistry, history of
Chemical Combinations
Chlorine Properties, etc
Chlorine Disenfectant, etc
Chloric and other Acids
Charcoal, properties of
Chromium described
Chlorophyll described
Characese described
Chickweeds, universal
Chelonia or Turtles described
Cheiroptera or Bats described.
Champlain Period, cause
Circulatory System, general . .
Circulatory Organs, Insects
Cicadidse or Cicadia
Clay, composition and use
Clover Crop, depends on
Classification of Animals
Cohesion defined
Cold, what is it
Conduction defined
Conductors, good and poor
Colors, what the cause
Coil, primary and secondary. .
Combustion explained
Composition by volume
Coal and Cake described
Copper and its compounds
Copper and its alloys
Corolla and Petals defined ....
Cotyledons described
Cones, Bracts, Scales, etc
PAGE
.... 127
.130, 132
.... 155
.... 170
.... 172
.... 173
.... 185
..... 192
.... 196
.... 211
.... 227
.... 238
.... 253
.... 268
.... 311
.... 313
.. 313
.... 321
.... 339
.... 341
.... 352
.... 352
.... 355
.... 173
.... 183
.... 251
.. 184
.... 267
.... 274
.... 288
.... 308
.... 310
.... 359
.... 11
.... 23
.... 102
.. .103
.... 120
.... 121
.... 122
128
.... 166
.184, 192
197
.... 230
300
.. 313
255
277
281
161
247
258
21
85
96
.103, 109
.122, 124
129
158
..... 159
211
.213, 215
.. 218
PAGE
Coniferae Family 219
Cotton Plant described 235
Collection of Plants 249
Connective Tissue described 232
Correlation of Organs 254
Coelenterata described 260
Coral Polyps described 261
Cockroaches described 2Hi
Coccus Cacti described 281
Coleoptera, number and description 281
Collection of Specimens 284
Colubriformia described 299
Compositae Family described 242
Columbines or Pigeons 303
Comets described 318
Conglomerate Rocks :'>2i
Colorado Canon, The 345
Continents, permanence of 348
Coal, how found 355
Coal Strata, number of 356
Comprehensive Type 382
Crystals, what and how found 88
Crowfoot Family described 230
Cruciferae Family described 232
Crotalidse, description of 300
Crinoids, description of 262
Crustacea, description of 268
Crayfish, a study of 268
Crickets, description of 280
Crocodilia, description of 300
Crush of the Earth 348
Cretaceous Rocks, kinds 358
Cuttle Fish described 289
Cursores, description of 304
Cyanogen described 134, 165
Cyanide Bottle, how made 284
Cynocephalidse or Baboons 314
Development, Theory of
Density defined and "illustrated. . . .
Dextrine, composition of
Desmids and Diatoms
Development of Insects
Dentirostres, Fissirostres, etc
Devonian Age, Rocks
Devonian Age, Life
Descent, with variation
Divisibility defined
Diathermancy illustrated
Diamond, description of
Diastase, how formed
Diseases caused by plants
Dicotyledons described
Dioecious explained
Digestive Apparatus, general
Dissection under water
Digestive Organs, crayfish
Digestive Organs, insects
Diptera (flies) described
Division of Labor, Bees
Dipnoi, description of
Digitigrada and Plantigrada
Diorite or Greenstone described. . .
Dolomite, composition of
Dragon Flies described
Drift, sources of
Driftless Area, cause
Ductility defined and illustrated. .
Dynamo, Electric Machine
Dynamo, extensive use of
14
21
175
195
278
304
354
854
379
17
31
127
176
198
227
227
254
270
271
277
295
312
JNUEX.
393
Dyeing, the process of 170, 171
Dynamite, how made 179
Earwigs (Forficulidae) described ... 280
Earth, internal condition of 326
Earthquakes, causes of 327
Earthquakes, effects of ^ . . 327
Earth Surface, irregular 326
Echo, cause of, in rooms 56
Echinodermata described 262
Edentata, description of 307
Elements defined 17
Electrical Attraction defined 23
Elasticity defined 34
Electricity, kinds of 87
Electricity, how shown 87
Electricity, frictional 88
Electrical Conductors, good and
poor : 95, 98
Electricity, dynamical 93
Electrical Circuit 94
Electrical Current 94
Electrical Batteries described 95
Electro Magnets described 95
Electric Telegraph 95
Electric Lightning 98
Electrical Units 100
Elements, most important 105
Elements, symbols of, etc 105
Elm Family described 229
Embryo of the Plant, etc 213
Embryonic Life (animals) 381
Energy defined and illustrated 58
Energy, kinetic and potential 58
Energy, changes form 62
Entomastracea described 271
Epidermal System (plants) 186
Epithelial Tissue 252
Equi'setaceae, described. . , 206
Equidse or Horses , 309
Ergot of Rye, what is it ? 197
Erinacidae or Hedgehogs 312
Evaporation, explained 29
Events of the Silurial Age 353
Evolution, history of 378
Evolution and Geology 381
Evolution not atheistic 383
Extension, definition of 16
Expansion of Bodies explained 29
Excretory Organs, general 255
Experiments showing :
Impenetrability of solids and
liquids 16
Impenetrability of liquids and
gases, etc 16
Divisibility of Matter, etc 17
Adhesive Attraction , etc ; . . 22
Capillary Attraction 22
Conduction of Heat 28
Convection of Heat 31
Specific Gravity of Solids, etc 37
Specific Gravity and Elasticity of
Gases 39
The Laws of Vibrating Cords 53
Frictional Electricity, etc 87
Physical Mixture and Chemical
Combination 103
The Composition of the Air 115
Bleaching by Chloride of Lime ... 121
Blue Color with Iodine and Starch 125
Experiments showing : PAGE
Carbon Dioxide to be non-combus-
tible 130
A flame to consist of parts 132
Combustion, Potassium, Chlorate
and Sugar 148
Decomposition of Sugar Solution. 190
Bacteria in Infusions 191
Falls of Niagara described 345
Falling Bodies, Laws of 44
Feldspars, different kinds 161, 320
Ferns, description and study of 202
Feathers and Quills described 301
Felidae or Cats described 313
Fibrous Tissue described 185
Fibro Vascular System 186
Figwort Family described 241
Fibro Cartilage described 253
Field work, how done 387
Fish, dissection of 292, 293
Fish, economic value of 285
Fish, preservation of 295
Fish, first appearance of 382
Fissures and Faults 325
Fluorine, preparation of 126
Flame, parts of, shown 132
Flint, composition and use 135
Floridese (seaweeds) described 196
Flax Family described 236
Force defined and illustrated 18
Force constant and impulsive 43
Forces, composition of 45
Forces, resolution of 45
Force, Centripetal and Centrifugal. 46
Fog horns, their value, etc 56
Foot Pounds defined 60
Food Group of Plants 226
Foraminiferse described 259
Formicidse or Ants described 282
Foot of Mollusca described 287
Forces, Plutonic, effect of 326
Forces, Erosive, effect of 326
Friction, cause and use 61
Franklin Dr., a Discoverer 90
Frond and Stipe described 202
Fruit of Different Kinds 213
Fundamental System in Plants 187
Fungi or Moulds described 194
Fucus, Seaweeds, described 196
Galvani and the Telephone 11, 93
Galvanometer described 96
Gas, relation of forces in 25
Gas, properties of, etc 39
Gases, diffusion of 40
Gases, volume of, varies how 41
Gas Carbon, where formed 129
Gas, Illuminating, how made 169
Ganglion, formed of what 254
Gasteropoda described 288
Ganoidei (fishes) described 291
Gallinacese described 303
Germs, removed by filtering 191
Gemmae, purpose of 200
Geyser explained 330
Geological Agents 337
Geological Record Imperfect 353
Geological Work of the Present 371
Geological Diagram 374, 375
394
INDEX.
FAGE
Geological Names 876
Geological Periods 876
Geological Studies 889
Gills of Crayfish described 269
Gills of Fish described 298
Glass, composition of 156
Glucose or Grape Sugar 175
Glyoerine, how made 178
Glumes described 221
Glands, how formed 252
Glacial Period : . 862
Glacial Climate 362, 367
Glacier, effect on plants 362
Glacier, the work of 363
Glacial Striae, direction 365
Gneiss, structure of 323
Gold, properties of, and uses 167
Golden Rod described 243
Gourd Family described 242
Gravitation or Gravity defined 19
Gravity, laws of, shown 19
Gravity, center of, how found 20
Graphite, where found 127, 350
Grass Family, extent 221
Grass Crop, value of 223
Grasshopper, study of 280
Grallatores or Wading Birds 303
Granite, composition of 322
Gunpowder, manufacture of 149
Gunpowder, expansive force of 152
Gunpowder, gases of explosion 150
Gum Resins described 172
Gutta Perch a, properties of 173
Gun Cotton, composition of 174
Gum Acacia, description of 240
Gypsum, composition of 155
Gyncecium defined 224
Hardness defined 32
Harmonics or Overtones 54
Haemoglobin described 252
Hairs and Scales of Animals 252
Hapalidse (monkeys) described 314
Heart uf a Crayfish 270
Heart of Mussel 287
Heat and Light, Theory of 14, 27
Heat, effects of 25
Heat, Sensible and Latent 28
Heat, specific standard of 29
Heat, absorption and reflection of . . 30
Heat, convection and radiation of, 27, 31
Heat, conduction and conductors . . 28
Heat, mechanical equivalent of 69
Heat, sources of 27
Heaih Fainilv described 241
Hermaphrodite Animals 256
Hemiptera described 281
Hilum described 225
Hinge Ligament 286
Hibiscus, description of 235
Horse Power denned 61
Holothurians described 263
Hornblende and Pyroxene 321
Honey Locust described 240
Huronian, Lower Rocks of 849
Huronian, Upper Rocks of 350
Hydrometer, principle of 87
Hydraulic Press, principle of 38
Hydrogen, how prepared Ill
Hydroxides denned , 119
PAGE
Hydrochloric Acid 120
Hydrocarbons defined 134
Hydrogen Sulphide 141
Hymenoptera, Bees, etc 282
Hysenidse or Hysenas 313
Ice, why it floats 33
Ice Lobes or Glaciers 364
Ice Sheet, extent of 864
Igneous Rocks 825
Illuminating Gas 185
Images in a Convex Lens 80
Images in a Curved Mirror 75
Images in a Plane Mirror 75
Impenetrability defined 16
Inclined Plane, equation of 66
Indig9 described 170, 240
Individual, development of 880
Indusium described 205
Inertia defined and illustrated 19
Infusions, how made 191
Infusoria described 260
Insect, fauna of 279
Tnsecta, description of 275
Insectivora described 312
Insectivorous Plants 234
Insects, diseases of 279
Insects in winter 389
Iodides of Mercury 125
Iodine, properties and use 125
Iron and Decay of Rocks 889
Iron, Cast and Wrought 164
Iron, compounds of 165
Iron, distribution of 168
Iron, reduction of 163
Iron in Algoukian Rocks 350
Jelly Fish described 261
Joints in Rocks, cause of 825
Jurassic Period, etc 358, 859
Kinetic Energy 58
Keweenawan Rocks 350
Lamellibranchiata described 285
Laughing Gas described 118
Law as used in Science 13
Law of Falling Bodies 44
Laws of Radiant Heat 27
Lava, different kinds 829
Land, surface uneven 382
Lakes, settling basins 846
Laurentian Tableland 351
Lake Erie, how formed 366
Lever defined and illustrated 64
Lever, principle and equation of 64
Lever, compound equation of 65
Lens, different kinds of 78
Lenses, convex effect of 79
Lenses, concave effect of 79
Leyden Jar described 89
Lead and its compounds 166
Leaves, different forms of 187, 208
Leaf, the parts of 207
Leaves, mode of veining 207
Leaves, form of base and apex 208
Leaves, lobed and cleft 208
Leaves, simple and compound 209
INDEX.
395
PAGE
Leaves, arrangement of, on stem. . . 210
Leech (medical) described 265
Lepidoptera described 281
Leptocj.rdii described 290
Liquids, properties of 34
Light, the sources of, etc 70
Light, phosphorescent 70
Light, velocity and intensity of . . . . 71
Light, reflected and absorbed 71, 73
Light, refraction of 76
Lightning explained 89
Lightning rods described 90
Litmus paper, use of 118
Lithium, where found 154
Linseed oil, properties of 179
Lichens described 197
Lily Family described 223
Linden Family described 234
Liuen Fiber, value of 236
Lizards described 299
Limestone rocks described 324
Life of the early eras 350
Life of Silurian Age 353
Location, how found 387
Loess, of different origin 338
Lost Period in Geology 352
Lycopodium or club-moss 206
Lycosedse (spiders) described 273
Matter, some properties of 15
Mass defined and illustrated 21
Magnetic attraction defined 23
Malleability defined 82
Mariotte's Law stated 42
Machines, principle of 63
Magic Lantern defined 82
Magnetism and Magnets 91
Magnetic needle and poles 91, 92
Mariners' compass 92
Magnetic variation 92
Matches, how made 142
Magnesium and its compounds 157
Manganese and its compounds 165
Malt, how formed 177
Marchantia described 200
Magnolia Family described 231
Mallow Family described 234
Maple Family described 236
Maxilla and Mandibles 270
Mav Flies described 280
Mantle of a Mussel 286
Mammalia, description of 805
Margipobranchia 291
Mammal, skeleton and organs 306
Marsupialia described 307
Man and animals 315
Marine erosion 346
Man's appearance on earth 372
Map drawing, etc 388
Melting points explained 29
Methane or Marsh Gas 134
Metastasis or Metabolism 188
Mercury, chlorides of 159
Mercury-amalgams 159
Medullary rays 217
Meteors described 318
Metamorphic Rocks 324
Mesozoic Era and Life 358
Method of the Creation 878
Mirrors, plane, effect of 73
PAGE
Mirrors, concave, effect of 74
Mirrors, convex, effect of 75
Microscope, simple, compound. . .80, 81
Mirrors, how made 159
Mimosa, or sensitive plant 240
Mint Family described 241
Milkweed Family 242
Minerals defined 820
Mica, composition of 321
Mississippi Rivej 344
Mixture and Combinations 104
Molecular theory of Matter 14
Molecules defined 17
Molecular Forces 25, 34
Mobility explained 35
Motion, varying or uniform 43
Motion, Laws of 43
Motion in Curved Lines 46
Mortar, how made 156
Mordants, use of 161, 165
Mosses described 201
Monocotyledons described 220
Mono3cious Flowers 227
Monadelphous Stamens 239
Mouth Parts of Insects 276
Mollusca, description of 285
Molluscoidea 258, 289
Moon, condition of 318
Monotremata described 806
Mountains 332, 351, 357
Mountains of the Tertiary 361
Moraines explained 365
Musical Tones and Scale 52, 54
Musical Pitch Standard 64
Musical Instruments 55
Multiple Proportions 104
Mushrooms described 197
Muscular Tissue 253
Muscular System of Insects 277
Mussel, study of 286
Mustelidse or Martens 813
Mycelium described 194
Mygalidse, Spiders 272
Myriopoda described 274
Nascent state explained 124
Nails, Hoofs, and Claws 252
Natochord described 290
Natatores or Swimming Birdg 303
Natural Gas. source of 356
Natural Selection 380
Newton , Sir Isaac 10
Nelumbium (water lily) 231
Nervous Tissue 253
Nerve Cells described 253
Nerve Fibers, different kinds 253
Nerves, their structure and use. ... 254
Nematoda described 264
Nervous System of Crayfish 271
Nervous System of Insects . . 277
Nebulae described 319
Nebular Theory 819
Neuroptera described 281
Niagara River Gorge 368
Nickel, alloys of 165
Nitrogen, properties of 116
Nitric Acid described 117
Nitroglycerin, properties of 179
Nitrobenzole described . 160
Nodes and Internodes 2*4
396
JNDEX.
Oak Family described
Oak, different kinds
Oak Timber, value of
Obesa or Hippopotami
Obsidian, volcanic glass
Ocellus, Ocelli, eyes
Octopus, Devilfish
Ocean Currents, causes
CEdogonium described
Oils, composition of
Oil of Bergamot, etc
Oidium Tucheri (fungi)
Olefiant Gas Composition
Olive Family described
Olfactory cells, etc
Oligocb.se ta (worms) ?
Oldest laud in America
One-celled organisms
Oophyta, characteristic of
Oospore, a spore case
Opaque bodies defined
Opera Glass described
Opium, source and use
Opercle, Subapercle, etc
Ophidia or Snakes
Orchid Family described
Orange, Lemon, etc
Organs, systems of
Organs of Locomotion
Organisms, Complex
Organs, developed from
Organic Development
Orbitelse (wheel-spinners)
Orthoptera described
Oscillaria, blue-green scum . . .
Osseous or Bony Tissues
Ostridse or Oysters
Oscillations of the Crust
Overtones or Harmonics
Ovule described
Ovum or Egg-cell
Ovum, development of
Oxygen, discovery of
Oxygen, preparation of
Oxygen, properties of
Oxides defined
Oxides of nitrogen
Oxyhydrogen flame
Oxalic and other acids
Oysters, development of
Palets and awns
Palm Family described
Paloeozoic Era and Sea
Panicle described
Pancreas described
Parsley Family described
Pappus described
Parasites, plants
Passeres or Passerine buds . . .
Pendulum, use of
Petroleum, gases of
Petroleum oil, source of
Perennials defined
Pediculidse or lice
Perissodactvla described
Physics deals with what 1
Physics and chemistry distin-
guished
Photometry explained
PAGE
.. 227
228
310
275
.... 195
.... 178
.... 172
. ..196
.... 134
.... 242
.... 256
.... 265
.... 351
.... 254
.... 195
.... 195
.... 71
.... 82
.... 232
.... 293
... 299
.... 225
.... 235
.... 251
.. . 256
.... 254
.... 257
.... 377
273
279
.... 193
.... 253
....288
.356, 369
54
... 213
256
.... 257
.102, 106
.... 106
108
110
.... 118
112
.. 180
.... 221
.... 225
.... 352
222, 237
... 255
... 237
.... 243
.188, 198
304
50
134
.172, 356
.... 233
.. 281
..11, 15
. 15
.... 72
PAGE
Phosphorus, source of 141
Phosphorus, different forms of 142
Phosphorus, uses of 144
Photography, principle of 160
Phocidse or seals 313
Pistil, stigma, style, and ovary.... 212
Pine, a study of 215
Pine, the growth of 218
Pink Family described 230
Pitcher plant described 2;>4
Pisces or fishes described 290
Pithecidse described 314
Plants fertilized by insects 242
Plaster of Paris, how made 155
Platinum, properties of 168
Plants, composition of 182
Plants as geological agents 347
Placenta, purpose of 212
Plumule described 213
Pleurite, sternite, etc., 269
Planets named in their order 317
Planetoids or asteroids 318
Porosity explained 18
Potential energy 58
Power, loss of, in use 67
Potential, high and low 94
Potential energy in coal HO
Poles, positive and negative 94
Potassium, properties of 146
Potassium, compounds of 147, 148
Pottery ware, how made 162
Porcelain ware, how made 162
Potassium per mangauate 165
Pot holes, how formed 345
Poppy Family descri bed 232
Proboscidea described 311
Prisms described 83
Projectiles, trajectory, etc 47
Prosimioe or Lemurs 314
Primates or apes 314
Principal meridians 384
Progress means what 383
Processes of life 190
Protoplasm described 183
Protophyta described 190
Protococcus, green scum 102
Protonema in Mosses 201
Prothalium in Ferns 203
Proembryo, embryo, etc 213
Protection, means of, in plants 248
Preservation specimens of plants.. 249
Pronucleus, male and female 257
Protozoa described 258
Pseudopodia described 259
Ptolemy, theories of 14
Pump, principles of 41
Pulley, equation of 66
Pulque plant and pulque 238
Pulse or Pea Family 239
Pyrometer, made of what ? 27
Pyroxene and Hornblende 321
Pyrites of iron described 322
Quartz or Silica 135, 320
Quaternary Age 362
Quaternary plants and animals 370
Radiation explained 27
Radiators, good and poor 30
Rainbow explained 85
INDEX.
397
PAGE
Rachis, midvein and stipe 203
Raspberries described 239
Radiolaria described 260
Raptores, birds of prey 304
Rain, explanation of :-i34, 338
Rainfall, exceptional 334
Rainwater, where does it go ? 339
Rest and motion defined 18
Reflection defined 30
Reflectors, good and poor 30
Refraction, laws of 76
Refraction, cause of 77
Refraction, index of 77
Reactions and Reagents 119
Reindeer Moss 197
Resin ducts 217
Receptacle defined 224
Respiratory organs 255
Reproductive process 250
Respiration in insects 277
Reptilia, description of 298
Recent Geological Period 372
Reproduction, rapidity of 379
Relations of life forms 382
Rectangular system of survey 384
Rhizoma or rootstock 202
Rhubarb, uses of 230
Rhinocerotidse described 308
Rivers, how formed 342
Rivers vary how 342
River valley, parts of 342
River, carrying power 344
Rivers, eroding agents 344
Rivers deposit sediments 346
Rosin and resins 172
Roots, uses of 188
Rose Family described 239
Rotifera described 266
Rodentia described 312
Rocks, composition of 320
Rocks, disintegration of 324
Rocks, first formed 349
Rocks of Silurian Age 353
Rocky Mountains formed 359
Rue Family described 236
Ruminants, stomach of 310
Salt, composition and definition 119
Salts, how named 119
Safety lamp, principle of 133
Saltpeter, how made 147
Samara or wing fruit 229, 236
Sargassum, seaweed 196
Saxifrage Family 238
Saprophytes 189, 198
Saltigradse (spiders) 273
Satellites or moons 318
Sandstone rocks 324
Sand dunes formed 338
Sand bars in rivers 346
Sand bars in the sea 347
Sample descriptions 387
Science age and growth 9
Science considers what 10
Science, opposed by whom 9
Science attempts what 10
Scientific work 10
Scientific meti^d 11
Science, educational value 12
Screw described 67
Scorpions described
Scales of a fish
Scansorial or Climbing Birds.
Schists, structure of
Sepals and calyx
Sedge Family described
Sensitive plant
Seeds, dispersal of
PAGE
.. 274
303
323
211
223
240
247
Sea urchins ........................... 262
Sense organs, insects ................ 278
Selachii described ................... 291
Semnopithecidse, monkeys .......... 314
Serpentine, composition of ........ 321
Sediments deposited ................ 346
Section, size, divisions .............. 386
Siphon explained .................... 40
Silicon, properties of ................ 135
Silica, forms of ........... ^ .......... 135
Silicates, abundance of ............. 135
Silver, properties of .................. 159
Silver nitrate ......................... 160
Silver chloride and bromide ........ 160
Silique and silicle (pods) ............ 232
Siphons of a mussel .................. 287
Skin of the insect ..................... 267
Slime moulds ........................ 183
Snails and slugs ...................... 288
Snakes described ..................... 299
Solids described ...................... 25
Sounds, how caused .................. 52
Sound, report, noise ................. 52
Sound, transmission of .............. 55
Solar spectrum ....................... 83
Sodium, source of .................... 157
Sodium compounds .................. 152
Sodium silicate ...................... 153
Soap, how made ...................... 179
Solonacese (potato) .................. 241
Soricidse or shrews ................... 313
Soil, composition of. ................. 324
Soil, how formed .................... 340
Specific gravity defined .............. 36
Specific gravity, how found ......... 36
Specific gravity, uses of .............. 36
Spectrum of iron
Spectrum of stars
Space and motion
Spirogyra (green scum)
Sporocarp described
Sporogonium described
Sphagnum, Moss
Sporangia
84
84
43
193
196
200
202
203, 205
Spike and spikelet ............... 217, 222
Spurge Family ........................ 237
Sperm cell and egg cell .............. 256
Sponge described. ................... 260
Spider, study of ..................... 272
Spiders ballooning .................. 274
Springs, how formed. . . ............ 340
Springs, soft and hard water ....... 340
Springs, mineral, etc ................ 340
Spring studies ...................... 389
Study of nature, importance of .... 3
Steam engine, parts of .............. 69
Strontium, properties of ............. 157
Steel, composition of ................ 164
Steel , how made ...................... 164
Strawberry, what is it? .............. 239
Starch, source, use .......... . ........ 175
Stearin, properties of ................ 178
Stomato described ................... 186
898
PAGE
Stems, forms of 187
Stamens, filament and anther 211
Struggle among plants 248
Star fish described 262
Stigmata insects 277
Stars described 318
Streams, study of 390
Struggle for existence 380
Study of Marchautia 200
Study of Mosses 201
Study of Ferns 204
Study of the Pine 217
Study of growing corn
Study of the Oat
Study of the Trillium
Study of the Oak
Study of the Bean
Study of the Crayfish
Study of a Spider
Study of the Giasshopper
Study of a Mussel
Study of a Fish
Study of a Bird
Study of a Mammal
Surface Tension
Sunlight, its effects
Sulphur, forms of
Sulphur, compounds of
Sulphuric acid, how made.. . .
Sulphuric acid, its uses jay
Sugar from cane and beet 175
Sugar, manufactured 176
Sundew Family 233
Succession of plants 249
Sun, description of 316
Sun spots, effect 816
Sun, size and motions 317
Suidse or Swine Family 309
Survival of the fittest 380
Swimmerets, crayfish 269
Syenite composition 323
Syngenesious 211, 242
.. 221
.. 223
,.228
.. 240
.. 268
... 272
.. 280
.. 286
.. 292
.. 301
.. 305
.. 21
. .. 70
.. 137
.. 138
Tallow, source and use
Tannic acid
Tanning, process of
Tape Worms described
Tapirs described
Talpidse, or Moles
Talc, composition of
Temperature defined
Tenacity and toughness
Telescope, refracting
Telescope, reflecting
Telescope, terrestrial and Galilean
Telephone bells
Telautograph, Gray's
Temperature for plants
Tergite, sternite, pleurite
Telson, the parts of
Termites, or white ants
Teleostei described
Temperature modified by land
Temperatmre modified by water . . .
Temperature. great variation of
Tertiary Age, divisions of
Tertiary deposits, where ?
Tertiary Rocks and Life
Tertiary Lava flows
Tertiary Mountains formed
178
180
180
264
308
313
321
26
32
81
82
82
99
100
280
331
337
359
359
360
861
861
Terrace Period defined
Thermometer, principle of
Thallophytes mentioned ......
Thorax of Arthropoda
Thysanura, or Spring Tails
The Earth, motions of
The Air, how warmed
The Air modifies temperature.
The Air varies in density
The Air and winds *
Theories of Matter
Theories of Heat and Light . . .
The Sea first formed
Time, importance of
Time, an element in work
Tin, properties and use
Tissues of plants
Tissue systems
Tides, how formed
Torulse described
Tobacco, its relations
Topographic work
Townships and Ranges
Townships, how divided
Transparent bodies
Trematoda described
Tragacanth, a germ
Trichina described
Trichomes named
Trilobites, abundant when ? .
Trap-door spider
Tracheae of insects
Trichechidse, or Walruses
Trachyte Rock described
Turbine wheels :
Turpentine, etc
Tubellaria described
Tulip Tree mentioned
Tubicolse described
Tubitelse, spiders
Tunicata described
Turtles, description of
Turf and trees, protect
PAGE
.. 370
.. 26
.. 197
.. 267
.. 279
.. 331
.. 332
.. 333
.. 333
.. 333
.. 377
.. 877
.. 348
.. 13
.. 61
.. 167
.. 184
Umbels described
Umbo of a shell
Undulatory, theory of heat. . .
Unit of Time
Unity in Plant Structure
Univalve Shells
Unity of Plants and Animals.
Ursidse or Bears
191
241
384
384
886
71
263
240
265
188
271
272
277
68
172
263
231
265
273
289
300
347
238
286
14
43
244
288
379
313
Vaporization explained 29
Valence explained 128
Vascular Plants 190
Vaucheria described 195
Valvate explained 235
Variation in Form 244
Valleys, Preglacial 366
Velocity defined 43
Vegetable Parchment 174
Venus Fly Trap 234
Vermes or Worms 2G3
Vespidse or Wasps 283
Vertebrata, characteristics of 290
Vertebral column 290
Veins and Fissures 826
Vibrations of the Pendulum 50
INDEX.
399
PAGE
Vibrations of the Air 52
Vibrations of Cords 53
Vibrations, vary how 53
Vibrations, velocity of 56
Vinegar, how made 177
Victoria Regia 232
Violet Family 237
Violet, hidden flowers 2:33
Vine Family 237
Virginia Creeper 237
Viverridse or Civet cats 313
Von Humboldt 12
Volume defined 20
Volume of irregular bodies 36
Voices, peculiarities of 65
Volta, Professor 93
Volvox globater 260
Volcano, description of 328
Volcano, products of 329
Volcano, causes of 329
Volcanic Action, depth of 829
Water, weight of 35
Waves caused by Wind 47
Waves or Vibrations in Air 52
Water Wheels 68
Waves of Light 83
Water, composition of 110
Water, decomposition of Ill
Water, properties of 113
Water a cinder 130
\Vater in plants 188
Water Net described 194
Walnut Family 227
Water Lily Family 231
Watermelon, gourd, etc 242
Walking Sticks, insects 280
Water Vapor in the Air 333
PAGE
Water and Frost 840
Waves, how formed 335
Weight defined 20
Weight, modified how 20
Wedge defined 67
Weathering explained . 340
Weather, observation of 888
" Weather saws," collect 388
W T heel and Axle 65
White Water Lily 231
Whales, different kinds 308
Winds, cause of 48
Winds, direction of 48
Winds explained 333
Willow Family 227
Wings of Insects 276
Wind and Sand, action of 337
Winter Birds, study of 889
Work defined 58
Work, formula of 58
Work, how measured 60
Work wasted 61
Woods, differ how 174
Wood, distillation of 171
Worms or Vermes 268
Yeast, what is it 177
Yucca, fertilized how 247
Yuccasella, the insect 247
Zero, absolute 42
Zinc, properties of 157
Zinc, compounds of 157
Zoology, treats of what 12, 251
Zygnema, green scum 193
Zygospore described 193
Zygophyta described 195
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