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AN ELEMENTARY
STUDY OF CHEMISTRY
BY
WILLIAM McPHERSON, PH.D.
PROFESSOR OF CHEMISTRY, OHIO STATE UNIVERSITY
AND
WILLIAM EDWARDS HENDERSON, PH.D.
ASSOCIATE PROFESSOR OF CHEMISTRY, OHIO STATE UNIVERSITY
_REVISED EDITION_
GINN & COMPANY
BOSTON * NEW YORK * CHICAGO * LONDON
COPYRIGHT, 1905, 1906, BY
WILLIAM MCPHERSON AND WILLIAM E. HENDERSON
ALL RIGHTS RESERVED
The Athenæum Press
GINN & COMPANY * PROPRIETORS * BOSTON * U.S.A.
Transcriber's note:
For Text: A word surrounded by a cedilla such as ~this~ signifies that
the word is bolded in the text. A word surrounded by underscores like
_this_ signifies the word is italics in the text. The italic and bold
markup for single italized letters (such as variables in equations) and
"foreign" abbreviations are deleted for easier reading.
For numbers and equations: Parentheses have been added to clarify
fractions. Underscores before bracketed numbers in equations denote a
subscript. Superscripts are designated with a caret and brackets, e.g.
11.1^{3} is 11.1 to the third power.
Appendix A and B have been moved to the end of the book.
Minor typos have been corrected.
PREFACE
In offering this book to teachers of elementary chemistry the authors
lay no claim to any great originality. It has been their aim to prepare
a text-book constructed along lines which have become recognized as best
suited to an elementary treatment of the subject. At the same time they
have made a consistent effort to make the text clear in outline, simple
in style and language, conservatively modern in point of view, and
thoroughly teachable.
The question as to what shall be included in an elementary text on
chemistry is perhaps the most perplexing one which an author must
answer. While an enthusiastic chemist with a broad understanding of the
science is very apt to go beyond the capacity of the elementary student,
the authors of this text, after an experience of many years, cannot help
believing that the tendency has been rather in the other direction. In
many texts no mention at all is made of fundamental laws of chemical
action because their complete presentation is quite beyond the
comprehension of the student, whereas in many cases it is possible to
present the essential features of these laws in a way that will be of
real assistance in the understanding of the science. For example, it is
a difficult matter to deduce the law of mass action in any very simple
way; yet the elementary student can readily comprehend that reactions
are reversible, and that the point of equilibrium depends upon, rather
simple conditions. The authors believe that it is worth while to
present such principles in even an elementary and partial manner because
they are of great assistance to the general student, and because they
make a foundation upon which the student who continues his studies to
more advanced courses can securely build.
The authors have no apologies to make for the extent to which they have
made use of the theory of electrolytic dissociation. It is inevitable
that in any rapidly developing science there will be differences of
opinion in regard to the value of certain theories. There can be no
question, however, that the outline of the theory of dissociation here
presented is in accord with the views of the very great majority of the
chemists of the present time. Moreover, its introduction to the extent
to which the authors have presented it simplifies rather than increases
the difficulties with which the development of the principles of the
science is attended.
The oxygen standard for atomic weights has been adopted throughout the
text. The International Committee, to which is assigned the duty of
yearly reporting a revised list of the atomic weights of the elements,
has adopted this standard for their report, and there is no longer any
authority for the older hydrogen standard. The authors do not believe
that the adoption of the oxygen standard introduces any real
difficulties in making perfectly clear the methods by which atomic
weights are calculated.
The problems appended to the various chapters have been chosen with a
view not only of fixing the principles developed in the text in the mind
of the student, but also of enabling him to answer such questions as
arise in his laboratory work. They are, therefore, more or less
practical in character. It is not necessary that all of them should be
solved, though with few exceptions the lists are not long. The answers
to the questions are not directly given in the text as a rule, but can
be inferred from the statements made. They therefore require independent
thought on the part of the student.
With very few exceptions only such experiments are included in the text
as cannot be easily carried out by the student. It is expected that
these will be performed by the teacher at the lecture table. Directions
for laboratory work by the student are published in a separate volume.
While the authors believe that the most important function of the
elementary text is to develop the principles of the science, they
recognize the importance of some discussion of the practical application
of these principles to our everyday life. Considerable space is
therefore devoted to this phase of chemistry. The teacher should
supplement this discussion whenever possible by having the class visit
different factories where chemical processes are employed.
Although this text is now for the first time offered to teachers of
elementary chemistry, it has nevertheless been used by a number of
teachers during the past three years. The present edition has been
largely rewritten in the light of the criticisms offered, and we desire
to express our thanks to the many teachers who have helped us in this
respect, especially to Dr. William Lloyd Evans of this laboratory, a
teacher of wide experience, for his continued interest and helpfulness.
We also very cordially solicit correspondence with teachers who may find
difficulties or inaccuracies in the text.
The authors wish to make acknowledgments for the photographs and
engravings of eminent chemists from which the cuts included in the text
were taken; to Messrs. Elliott and Fry, London, England, for that of
Ramsay; to The Macmillan Company for those of Davy and Dalton, taken
from the Century Science Series; to the L. E. Knott Apparatus Company,
Boston, for that of Bunsen.
THE AUTHORS
OHIO STATE UNIVERSITY
COLUMBUS, OHIO
CONTENTS
CHAPTER PAGE
I. INTRODUCTION 1
II. OXYGEN 13
III. HYDROGEN 28
IV. WATER AND HYDROGEN DIOXIDE 40
V. THE ATOMIC THEORY 59
VI. CHEMICAL EQUATIONS AND CALCULATIONS 68
VII. NITROGEN AND THE RARE ELEMENTS IN THE ATMOSPHERE 78
VIII. THE ATMOSPHERE 83
IX. SOLUTIONS 94
X. ACIDS, BASES, AND SALTS; NEUTRALIZATION 106
XI. VALENCE 116
XII. COMPOUNDS OF NITROGEN 122
XIII. REVERSIBLE REACTIONS AND CHEMICAL EQUILIBRIUM 137
XIV. SULPHUR AND ITS COMPOUNDS 143
XV. PERIODIC LAW 165
XVI. THE CHLORINE FAMILY 174
XVII. CARBON AND SOME OF ITS SIMPLER COMPOUNDS 196
XVIII. FLAMES,--ILLUMINANTS 213
XIX. MOLECULAR WEIGHTS, ATOMIC WEIGHTS, FORMULAS 223
XX. THE PHOSPHORUS FAMILY 238
XXI. SILICON, TITANIUM, BORON 257
XXII. THE METALS 267
XXIII. THE ALKALI METALS 274
XXIV. THE ALKALINE-EARTH FAMILY 300
XXV. THE MAGNESIUM FAMILY 316
XXVI. THE ALUMINIUM FAMILY 327
XXVII. THE IRON FAMILY 338
XXVIII. COPPER, MERCURY, AND SILVER 356
XXIX. TIN AND LEAD 370
XXX. MANGANESE AND CHROMIUM 379
XXXI. GOLD AND THE PLATINUM FAMILY 390
XXXII. SOME SIMPLE ORGANIC COMPOUNDS 397
INDEX 421
APPENDIX A Facing back cover
APPENDIX B Inside back cover
LIST OF FULL-PAGE ILLUSTRATIONS
PAGE
ANTOINE LAURENT LAVOISIER _Frontispiece_
JOSEPH PRIESTLEY 14
JOHN DALTON 60
WILLIAM RAMSAY 82
DMITRI IVANOVITCH MENDELÉEFF 166
HENRI MOISSAN 176
SIR HUMPHRY DAVY 276
ROBERT WILHELM BUNSEN 298
AN ELEMENTARY STUDY OF CHEMISTRY
CHAPTER I
INTRODUCTION
~The natural sciences.~ Before we advance very far in the study of nature,
it becomes evident that the one large study must be divided into a
number of more limited ones for the convenience of the investigator as
well as of the student. These more limited studies are called the
_natural sciences_.
Since the study of nature is divided in this way for mere convenience,
and not because there is any division in nature itself, it often happens
that the different sciences are very intimately related, and a thorough
knowledge of any one of them involves a considerable acquaintance with
several others. Thus the botanist must know something about animals as
well as about plants; the student of human physiology must know
something about physics as well as about the parts of the body.
~Intimate relation of chemistry and physics.~ Physics and chemistry are
two sciences related in this close way, and it is not easy to make a
precise distinction between them. In a general way it may be said that
they are both concerned with inanimate matter rather than with living,
and more particularly with the changes which such matter may be made to
undergo. These changes must be considered more closely before a
definition of the two sciences can be given.
~Physical changes.~ One class of changes is not accompanied by an
alteration in the composition of matter. When a lump of coal is broken
the pieces do not differ from the original lump save in size. A rod of
iron may be broken into pieces; it may be magnetized; it may be heated
until it glows; it may be melted. In none of these changes has the
composition of the iron been affected. The pieces of iron, the
magnetized iron, the glowing iron, the melted iron, are just as truly
iron as was the original rod. Sugar may be dissolved in water, but
neither the sugar nor the water is changed in composition. The resulting
liquid has the sweet taste of sugar; moreover the water may be
evaporated by heating and the sugar recovered unchanged. Such changes
are called _physical changes_.
DEFINITION: _Physical changes are those which do not involve a change in
the composition of the matter._
~Chemical changes.~ Matter may undergo other changes in which its
composition is altered. When a lump of coal is burned ashes and
invisible gases are formed which are entirely different in composition
and properties from the original coal. A rod of iron when exposed to
moist air is gradually changed into rust, which is entirely different
from the original iron. When sugar is heated a black substance is formed
which is neither sweet nor soluble in water. Such changes are evidently
quite different from the physical changes just described, for in them
new substances are formed in place of the ones undergoing change.
Changes of this kind are called _chemical changes_.
DEFINITION: _Chemical changes are those which involve a change in the
composition of the matter._
~How to distinguish between physical and chemical changes.~ It is not
always easy to tell to which class a given change belongs, and many
cases will require careful thought on the part of the student. The test
question in all cases is, Has the composition of the substance been
changed? Usually this can be answered by a study of the properties of
the substance before and after the change, since a change in composition
is attended by a change in properties. In some cases, however, only a
trained observer can decide the question.
~Changes in physical state.~ One class of physical changes should be noted
with especial care, since it is likely to prove misleading. It is a
familiar fact that ice is changed into water, and water into steam, by
heating. Here we have three different substances,--the solid ice, the
liquid water, and the gaseous steam,--the properties of which differ
widely. The chemist can readily show, however, that these three bodies
have exactly the same composition, being composed of the same substances
in the same proportion. Hence the change from one of these substances
into another is a physical change. Many other substances may, under
suitable conditions, be changed from solids into liquids, or from
liquids into gases, without change in composition. Thus butter and wax
will melt when heated; alcohol and gasoline will evaporate when exposed
to the air. _The three states--solid, liquid, and gas--are called the
three physical states of matter._
~Physical and chemical properties.~ Many properties of a substance can be
noted without causing the substance to undergo chemical change, and are
therefore called its _physical properties_. Among these are its physical
state, color, odor, taste, size, shape, weight. Other properties are
only discovered when the substance undergoes chemical change. These are
called its _chemical properties_. Thus we find that coal burns in air,
gunpowder explodes when ignited, milk sours when exposed to air.
~Definition of physics and chemistry.~ It is now possible to make a
general distinction between physics and chemistry.
DEFINITION: _Physics is the science which deals with those changes in
matter which do not involve a change in composition._
DEFINITION: _Chemistry is the science which deals with those changes in
matter which do involve a change in composition._
~Two factors in all changes.~ In all the changes which matter can undergo,
whether physical or chemical, two factors must be taken into account,
namely, _energy_ and _matter_.
~Energy.~ It is a familiar fact that certain bodies have the power to do
work. Thus water falling from a height upon a water wheel turns the
wheel and in this way does the work of the mills. Magnetized iron
attracts iron to itself and the motion of the iron as it moves towards
the magnet can be made to do work. When coal is burned it causes the
engine to move and transports the loaded cars from place to place. When
a body has this power to do work it is said to possess energy.
~Law of conservation of energy.~ Careful experiments have shown that when
one body parts with its energy the energy is not destroyed but is
transferred to another body or system of bodies. Just as energy cannot
be destroyed, neither can it be created. If one body gains a certain
amount of energy, some other body has lost an equivalent amount. These
facts are summed up in the law of conservation of energy which may be
stated thus: _While energy can be changed from one form into another, it
cannot be created or destroyed._
~Transformations of energy.~ Although energy can neither be created nor
destroyed, it is evident that it may assume many different forms. Thus
the falling water may turn the electric generator and produce a current
of electricity. The energy lost by the falling water is thus transformed
into the energy of the electric current. This in turn may be changed
into the energy of motion, as when the current is used for propelling
the cars, or into the energy of heat and light, as when it is used for
heating and lighting the cars. Again, the energy of coal may be
converted into energy of heat and subsequently of motion, as when it is
used as a fuel in steam engines.
Since the energy possessed by coal only becomes available when the coal
is made to undergo a chemical change, it is sometimes called _chemical
energy_. It is this form of energy in which we are especially interested
in the study of chemistry.
~Matter.~ Matter may be defined as that which occupies space and possesses
weight. Like energy, matter may be changed oftentimes from one form into
another; and since in these transformations all the other physical
properties of a substance save weight are likely to change, the inquiry
arises, Does the weight also change? Much careful experimenting has
shown that it does not. The weight of the products formed in any change
in matter always equals the weight of the substances undergoing change.
~Law of conservation of matter.~ The important truth just stated is
frequently referred to as the law of conservation of matter, and this
law may be briefly stated thus: _Matter can neither be created nor
destroyed, though it can be changed from one form into another._
~Classification of matter.~ At first sight there appears to be no limit to
the varieties of matter of which the world is made. For convenience in
study we may classify all these varieties under three heads, namely,
_mechanical mixtures_, _chemical compounds_, and _elements_.
[Illustration: Fig. 1]
~Mechanical mixtures.~ If equal bulks of common salt and iron filings are
thoroughly mixed together, a product is obtained which, judging by its
appearance, is a new substance. If it is examined more closely, however,
it will be seen to be merely a mixture of the salt and iron, each of
which substances retains its own peculiar properties. The mixture tastes
just like salt; the iron particles can be seen and their gritty
character detected. A magnet rubbed in the mixture draws out the iron
just as if the salt were not there. On the other hand, the salt can be
separated from the iron quite easily. Thus, if several grams of the
mixture are placed in a test tube, and the tube half filled with water
and thoroughly shaken, the salt dissolves in the water. The iron
particles can then be filtered from the liquid by pouring the entire
mixture upon a piece of filter paper folded so as to fit into the
interior of a funnel (Fig. 1). The paper retains the solid but allows
the clear liquid, known as the _filtrate_, to drain through. The iron
particles left upon the filter paper will be found to be identical with
the original iron. The salt can be recovered from the filtrate by
evaporation of the water. To accomplish this the filtrate is poured into
a small evaporating dish and gently heated (Fig. 2) until the water has
disappeared, or _evaporated_. The solid left in the dish is identical in
every way with the original salt. Both the iron and the salt have thus
been recovered in their original condition. It is evident that no new
substance has been formed by rubbing the salt and iron together. The
product is called a _mechanical mixture_. Such mixtures are very common
in nature, almost all minerals, sands, and soils being examples of this
class of substances. It is at once apparent that there is no law
regulating the composition of a mechanical mixture, and no two mixtures
are likely to have exactly the same composition. The ingredients of a
mechanical mixture can usually be separated by mechanical means, such as
sifting, sorting, magnetic attraction, or by dissolving one constituent
and leaving the other unchanged.
[Illustration: Fig. 2]
DEFINITION: _A mechanical mixture is one in which the constituents
retain their original properties, no chemical action having taken place
when they were brought together._
~Chemical compounds.~ If iron filings and powdered sulphur are thoroughly
ground together in a mortar, a yellowish-green substance results. It
might easily be taken to be a new body; but as in the case of the iron
and salt, the ingredients can readily be separated. A magnet draws out
the iron. Water does not dissolve the sulphur, but other liquids do, as,
for example, the liquid called carbon disulphide. When the mixture is
treated with carbon disulphide the iron is left unchanged, and the
sulphur can be obtained again, after filtering off the iron, by
evaporating the liquid. The substance is, therefore, a mechanical
mixture.
If now a new portion of the mixture is placed in a dry test tube and
carefully heated in the flame of a Bunsen burner, as shown in Fig. 3, a
striking change takes place. The mixture begins to glow at some point,
the glow rapidly extending throughout the whole mass. If the test tube
is now broken and the product examined, it will be found to be a hard,
black, brittle substance, in no way recalling the iron or the sulphur.
The magnet no longer attracts it; carbon disulphide will not dissolve
sulphur from it. It is a new substance with new properties, resulting
from the chemical union of iron and sulphur, and is called iron
sulphide. Such substances are called _chemical compounds_, and differ
from mechanical mixtures in that the substances producing them lose
their own characteristic properties. We shall see later that the two
also differ in that the composition of a chemical compound never varies.
[Illustration: Fig. 3]
DEFINITION: _A chemical compound is a substance the constituents of
which have lost their own characteristic properties, and which cannot be
separated save by a chemical change._
~Elements.~ It has been seen that iron sulphide is composed of two
entirely different substances,--iron and sulphur. The question arises,
Do these substances in turn contain other substances, that is, are they
also chemical compounds? Chemists have tried in a great many ways to
decompose them, but all their efforts have failed. Substances which have
resisted all efforts to decompose them into other substances are called
_elements_. It is not always easy to prove that a given substance is
really an element. Some way as yet untried may be successful in
decomposing it into other simpler forms of matter, and the supposed
element will then prove to be a compound. Water, lime, and many other
familiar compounds were at one time thought to be elements.
DEFINITION: _An element is a substance which cannot be separated into
simpler substances by any known means._
~Kinds of matter.~ While matter has been grouped in three classes for the
purpose of study, it will be apparent that there are really but two
distinct kinds of matter, namely, compounds and elements. A mechanical
mixture is not a third distinct kind of matter, but is made up of
varying quantities of either compounds or elements or both.
~Alchemy.~ In olden times it was thought that some way could be found to
change one element into another, and a great many efforts were made to
accomplish this transformation. Most of these efforts were directed
toward changing the commoner metals into gold, and many fanciful ways
for doing this were described. The chemists of that time were called
_alchemists_, and the art which they practiced was called _alchemy_. The
alchemists gradually became convinced that the only way common metals
could be changed into gold was by the wonderful power of a magic
substance which they called the _philosopher's stone_, which would
accomplish this transformation by its mere touch and would in addition
give perpetual youth to its fortunate possessor. No one has ever found
such a stone, and no one has succeeded in changing one metal into
another.
~Number of elements.~ The number of substances now considered to be
elements is not large--about eighty in all. Many of these are rare, and
very few of them make any large fraction of the materials in the
earth's crust. Clarke gives the following estimate of the composition of
the earth's crust:
Oxygen 47.0% Calcium 3.5%
Silicon 27.9 Magnesium 2.5
Aluminium 8.1 Sodium 2.7
Iron 4.7 Potassium 2.4
Other elements 1.2%
A complete list of the elements is given in the Appendix. In this list
the more common of the elements are marked with an asterisk. It is not
necessary to study more than a third of the total number of elements to
gain a very good knowledge of chemistry.
~Physical state of the elements.~ About ten of the elements are gases at
ordinary temperatures. Two--mercury and bromine--are liquids. The others
are all solids, though their melting points vary through wide limits,
from cæsium which melts at 26° to elements which do not melt save in the
intense heat of the electric furnace.
~Occurrence of the elements.~ Comparatively few of the elements occur as
uncombined substances in nature, most of them being found in the form of
chemical compounds. When an element does occur by itself, as is the case
with gold, we say that it occurs in the _free state_ or _native_; when
it is combined with other substances in the form of compounds, we say
that it occurs in the _combined state_, or _in combination_. In the
latter case there is usually little about the compound to suggest that
the element is present in it; for we have seen that elements lose their
own peculiar properties when they enter into combination with other
elements. It would never be suspected, for example, that the reddish,
earthy-looking iron ore contains iron.
~Names of elements.~ The names given to the elements have been selected in
a great many different ways. (1) Some names are very old and their
original meaning is obscure. Such names are iron, gold, and copper. (2)
Many names indicate some striking physical property of the element. The
name bromine, for example, is derived from a Greek word meaning a
stench, referring to the extremely unpleasant odor of the substance. The
name iodine comes from a word meaning violet, alluding to the beautiful
color of iodine vapor. (3) Some names indicate prominent chemical
properties of the elements. Thus, nitrogen means the producer of niter,
nitrogen being a constituent of niter or saltpeter. Hydrogen means water
former, signifying its presence in water. Argon means lazy or inert, the
element being so named because of its inactivity. (4) Other elements are
named from countries or localities, as germanium and scandium.
~Symbols.~ In indicating the elements found in compounds it is
inconvenient to use such long names, and hence chemists have adopted a
system of abbreviations. These abbreviations are known as _symbols_,
each element having a distinctive symbol. (1) Sometimes the initial
letter of the name will suffice to indicate the element. Thus I stands
for iodine, C for carbon. (2) Usually it is necessary to add some other
characteristic letter to the symbol, since several names may begin with
the same letter. Thus C stands for carbon, Cl for chlorine, Cd for
cadmium, Ce for cerium, Cb for columbium. (3) Sometimes the symbol is an
abbreviation of the old Latin name. In this way Fe (ferrum) indicates
iron, Cu (cuprum), copper, Au (aurum), gold. The symbols are included in
the list of elements given in the Appendix. They will become familiar
through constant use.
~Chemical affinity the cause of chemical combination.~ The agency which
causes substances to combine and which holds them together when combined
is called _chemical affinity_. The experiments described in this
chapter, however, show that heat is often necessary to bring about
chemical action. The distinction between the cause producing chemical
action and the circumstances favoring it must be clearly made. Chemical
affinity is always the cause of chemical union. Many agencies may make
it possible for chemical affinity to act by overcoming circumstances
which stand in its way. Among these agencies are heat, light, and
electricity. As a rule, solution also promotes action between two
substances. Sometimes these agencies may overcome chemical attraction
and so occasion the decomposition of a compound.
EXERCISES
1. To what class of changes do the following belong? (a) The melting
of ice; (b) the souring of milk; (c) the burning of a candle; (d)
the explosion of gunpowder; (e) the corrosion of metals. What test
question must be applied in each of the above cases?
2. Give two additional examples (a) of chemical changes; (b) of
physical changes.
3. Is a chemical change always accompanied by a physical change? Is a
physical change always accompanied by a chemical change?
4. Give two or more characteristics of a chemical change.
5. (a) When a given weight of water freezes, does it absorb or evolve
heat? (b) When the resulting ice melts, is the total heat change the
same or different from that of freezing?
6. Give three examples of each of the following: (a) mechanical
mixtures; (b) chemical compounds; (c) elements.
7. Give the derivation of the names of the following elements: thorium,
gallium, selenium, uranium. (Consult dictionary.)
8. Give examples of chemical changes which are produced through the
agency of heat; of light; of electricity.